Method for preparing natural gas from coal gas

Abstract

The invention provides a method for preparing natural gas from coal gas, which comprises the following steps of: preparing mixed gas of H2 and CO: carrying out partial shift hydrogen production reaction on the coal gas, and separating N2 from a system by a pressure swing adsorption separation method before or after the partial shift hydrogen production reaction step; wherein when N2 is separated from a system through the pressure swing adsorption separation method, natural gas is used as flushing gas, and obtained gas containing CO and the natural gas is subjected to the partial shift hydrogen production reaction; during flushing with the flushing gas, CO and natural gas are desorbed in a desorption mode of combining at least one of high-pressure flushing desorption, low-pressure flushing and vacuumizing; the high-pressure washing desorption refers to high-pressure gas of which the feeding washing gas pressure is 0.3-10 MPa; and carrying out methanation reaction on the H2 and CO mixed gas to prepare the natural gas. According to the invention, N2 is separated from the system before methanation, a cryogenic method is avoided, and the method has the advantages of simple process flow, low equipment investment and low compression power consumption.

Description

[0001] This application is a divisional application of the invention patent application filed on November 7, 2018, with application number 201811317512.5 and entitled "A Method and Apparatus for Converting Coal Gas into Natural Gas". Technical Field

[0002] This invention relates to the field of natural gas production technology, and more specifically to a process for producing natural gas from coke oven gas, blast furnace gas, and converter gas. Background Technology

[0003] These industrial production processes generate large amounts of coke oven gas (coking), blast furnace gas (ironmaking), and converter gas (steelmaking), collectively known as the "three gases." Other ferrous and non-ferrous metal smelting processes also produce blast furnace gas, converter gas, and tail gases with similar gas compositions to blast furnace gas and converter gas.

[0004] Among the three types of gases emitted by steel plants, blast furnace gas has the lowest effective gas content, but its emissions are the largest.

[0005] The main components of blast furnace gas are CO, CO2, N2, H2, and CH4, with CO accounting for approximately 25%, CO2 and N2 accounting for 15% and 55% respectively, and H2 and CH4 present in very small amounts. Blast furnace gas has a low calorific value, only 3300–3800 kJ / Nm³. 3 Because CO2 and N2 in blast furnace gas neither participate in combustion to generate heat nor support combustion, but instead absorb a large amount of heat generated during combustion, the theoretical combustion temperature of blast furnace gas is relatively low, only around 1300℃. The combustion of blast furnace gas at room temperature is unstable. Generally, industrial furnaces cannot use blast furnace gas as a single fuel; it must be blended with high-calorific-value gases such as coke oven gas or converter gas. However, the calorific value of blast furnace gas fluctuates greatly when blended with coke oven gas or converter gas, which not only places higher demands on combustion equipment but also affects product quality to varying degrees. Since most enterprises have surplus blast furnace gas but a shortage of high-calorific-value gases, there is varying degrees of blast furnace gas venting, which not only pollutes the environment but also wastes energy.

[0006] How to effectively utilize blast furnace gas, which is characterized by low calorific value, high impurity content, huge production volume, difficulty in purification, and severe environmental pollution, is a problem that needs to be solved both domestically and internationally. Currently, blast furnace gas is generally used for combustion, but due to its low calorific value, high content of non-combustible components, poor combustion efficiency and utilization rate, and the waste of a large amount of valuable CO that could be used as a high-value-added chemical raw material, it is also wasted. Converter gas is generally used for combustion or power generation, but due to its low calorific value, poor combustion efficiency and utilization rate, and the fact that the revenue generated from power generation is far lower than the revenue from processing it and using it as a chemical raw material to produce high-value-added chemical products, this is a challenge that needs to be addressed both domestically and internationally.

[0007] Furthermore, the basic principle of Pressure Swing Adsorption (PSA) is to utilize the differences in the adsorption characteristics of gaseous components on solid materials, achieving gas separation or purification through a periodic pressure change process. For any adsorbate (adsorbate), under adsorption equilibrium conditions, the lower the temperature and the higher the pressure, the greater the adsorption capacity. Conversely, the higher the temperature and the lower the pressure, the smaller the adsorption capacity. If the temperature remains relatively constant, adsorption under pressure, using methods such as decompression (vacuuming), purging with a weakly adsorbed gas, or low-pressure desorption, is called pressure swing adsorption. Pressure swing adsorption generally includes adsorption, desorption (vacuuming, purging, or vacuuming and purging), and possible processes such as pressure equalization, pressurization, convex release, reverse release, and displacement. It is evident that pressure swing adsorption achieves adsorption and desorption by changing pressure. Pressure changes result in energy loss, and current pressure swing adsorption methods do not recover this energy, leading to wasted energy and reduced economic efficiency. This results in situations where pressure swing adsorption is necessary at excessively high pressures, but its cost becomes prohibitively high.

[0008] With industrial development, gas separation under high-pressure conditions has become increasingly common. The higher the operating pressure, the higher the energy consumption. On the other hand, due to the frequent pressurization and depressurization changes between numerous devices during the industrial operation of pressure swing adsorption (PSA), it is difficult to effectively recover its energy. Summary of the Invention

[0009] The purpose of this invention is to provide a process for preparing natural gas that meets standard requirements from blast furnace gas and converter gas through multiple processing steps, which is simple in process flow, requires less equipment investment and has low power consumption. This process can not only alleviate the current situation of energy shortage in China and serious waste of gas, especially blast furnace gas, but also further increase the economic and environmental benefits of gas, especially blast furnace gas. It does not require the use of cryogenic nitrogen separation method, which is uneconomical.

[0010] The technical solution is:

[0011] A method for producing natural gas from coal gas, comprising:

[0012] (1) Preparation of H2 and CO mixture gas, the preparation process includes: partial conversion of coal gas to produce hydrogen, and separation of N2 from the system by pressure swing adsorption separation method before or after the partial conversion hydrogen production step;

[0013] In the process of separating N2 from the system by pressure swing adsorption separation, natural gas is used as the flushing gas to obtain a gas containing CO and natural gas for the partial conversion hydrogen production reaction.

[0014] During flushing with flushing gas, a combination of high-pressure flushing and desorption, along with at least one of low-pressure flushing and vacuuming, is used to desorb CO and natural gas. The high-pressure flushing and desorption refers to a high-pressure gas with a feed flushing gas pressure of 0.3~10MPa.

[0015] (2) The H2 and CO mixture undergoes a methanation reaction to produce natural gas.

[0016] As an optional implementation, the gas mainly includes blast furnace gas or converter gas; the gas may also contain one or a mixture of two or more of the following: coke oven gas, other tail gas, or purge gas.

[0017] As an optional implementation, before separating CO and N2, the pressure swing adsorption separation method also performs a first impurity removal pretreatment, which includes one or a combination of steps such as dust removal, phosphorus removal, arsenic removal, dehydration, dehydrogenation and deoxygenation, desulfurization, CO2 removal, or CH4 removal.

[0018] As an optional implementation, the first impurity removal pretreatment includes: desulfurization and CO2 removal, wherein CO2 removal is performed simultaneously with desulfurization or CO2 removal is performed after the desulfurization step.

[0019] As an optional implementation, the CO2 removal in the first impurity removal pretreatment adopts the absorption method and / or pressure swing adsorption method.

[0020] As an optional implementation, the first impurity removal pretreatment includes: the first impurity removal pretreatment further includes: CH4 removal and / or dehydrogenation and deoxygenation; CH4 removal is performed after the desulfurization step; dehydrogenation and deoxygenation are performed after the CH4 removal step.

[0021] As an optional implementation, after the partial conversion hydrogen production reaction, the gas is decarbonized to obtain the H2 and CO mixture for methanation, or the methanation reaction is carried out directly, and the CO2 produced by the conversion reaction is removed after the methanation reaction.

[0022] As an optional implementation method, the coal gas is subjected to a partial conversion hydrogen production reaction to obtain a gas containing CO, N2 and H2. The CO is separated by pressure swing adsorption separation method, and then the N2 and H2 are separated. The separated H2 and CO are mixed and then subjected to a methanation reaction.

[0023] As an optional implementation, the coal gas undergoes desulfurization and / or dehydrogenation and deoxygenation before the partial shift hydrogen production reaction; the dehydrogenation and deoxygenation occur after the desulfurization step; and carbon dioxide is removed after the partial shift hydrogen production reaction and before pressure swing adsorption separation of CO.

[0024] An apparatus for converting coal gas into natural gas, comprising:

[0025] The first shift reactor is used to partially shift CO in coal gas to produce hydrogen.

[0026] A first pressure swing adsorption device is installed upstream or downstream of the first shift reactor to separate N2 from the gas system by pressure swing adsorption separation method;

[0027] A methanation reactor is used to perform a methanation reaction on a mixture of H2 and CO to produce natural gas.

[0028] In the first embodiment, a first pressure swing adsorption (PSA) device is located upstream of a first shift reactor. The purge gas inlet of the PSA device is connected to a CH4 input pipe or an H2 input pipe, wherein the CH4 input pipe is connected to the gas outlet of the methanation reactor. A first impurity removal pretreatment device is connected upstream of the PSA device. This pretreatment device includes one or a combination of several of the following: a dust removal device, a phosphorus removal device, an arsenic removal device, a dehydration device, a dehydrogenation and deoxygenation device, a desulfurization device, a CO2 removal device, a CO removal device, or a CH4 removal device. The CH4 input pipe or the H2 input pipe is used to input CH4 purge gas or H2 purge gas into the first PSA device, respectively. The first impurity removal pretreatment device is used to remove impurities from the coal gas, corresponding to dust removal, phosphorus removal, arsenic removal, dehydration, dehydrogenation and deoxygenation, desulfurization, CO2 removal, CO removal, or CH4 removal.

[0029] Furthermore, the first impurity removal pretreatment device includes a desulfurization device and a CO2 removal device, wherein the CO2 removal device is integrated with the desulfurization device or the CO2 removal device is located downstream of the desulfurization device.

[0030] Furthermore, the first impurity removal pretreatment device also includes a CH4 removal device and / or a dehydrogenation and deoxygenation device; the CH4 removal device is located downstream of the desulfurization device; the dehydrogenation and deoxygenation device is located downstream of the CH4 removal device. That is, when a CH4 removal device is included, it is located downstream of the desulfurization device; when the desulfurization device and the CO2 removal device are separate, the CH4 removal device is located downstream of the desulfurization device and upstream of the CO2 removal device. When a dehydrogenation and deoxygenation device is included, it is located downstream of the desulfurization device; when the desulfurization device and the CO2 removal device are separate, the dehydrogenation and deoxygenation device is located downstream of the desulfurization device and upstream of the CO2 removal device. If a CH4 removal device is also included, it is located downstream of the CH4 removal device. For different combinations, obviously, the first pressure swing adsorption device is connected to the tail end of the first impurity removal pretreatment device (i.e., after the last unit of the first pretreatment device is completed).

[0031] The gas-to-natural-gas apparatus further includes a first diversion device connected to the first shift reactor, used to divide the gas after partial shift hydrogen production into two parts; the first diversion device is connected to the first pressure swing adsorption device through a first pipeline and to the methanation reactor through a second pipeline.

[0032] Furthermore, the first pipeline is equipped with a hydrogen purification device, and / or the second pipeline is equipped with a carbon dioxide removal device. One end of the H2 input pipe is connected to the hydrogen purification device on the first pipeline, and the other end is connected to a first pressure swing adsorption (PSA) device. A second shift reactor is also provided upstream of the hydrogen purification device on the first pipeline, used to further process the gas passing through the first pipeline after partial shift hydrogen production through the shift reactor. The hydrogen purification device on the first pipeline primarily removes carbon dioxide and purifies hydrogen, and can employ either pressure swing adsorption or absorption methods.

[0033] The first pressure swing adsorption (PSA) unit is located upstream of the first shift reactor. In another embodiment, the pipeline of the first impurity removal pretreatment device or the gas source is also connected to a second branch, which is connected to a third shift reactor. Downstream of the third shift reactor, a third PSA unit for hydrogen extraction is located, and the third PSA unit is connected to the first PSA unit via an H2 input pipe. After a portion of the gas is completely converted to hydrogen in the third shift reactor, hydrogen is extracted by the third PSA unit, and the hydrogen is supplied as flushing gas to the first PSA unit via the H2 input pipe. The extracted hydrogen can be directly purified hydrogen or / and the outflow gas from the third PSA unit, providing flushing gas at different pressures. The first shift reactor is connected to a methanation reactor, and the output gas undergoes a methanation reaction; or the first shift reactor and the methanation reactor are implemented by the same device, such as a wide hydrogen-to-carbon ratio methanation device.

[0034] In the second embodiment, the first pressure swing adsorption (PSA) device is located downstream of the first shift reactor. The first PSA device includes a connected PSA CO extraction unit and a PSA N2 and H2 separation unit. The PSA CO extraction unit is connected to the methanation reactor, and the PSA N2 and H2 separation unit is connected to the flushing gas inlet of the PSA CO extraction unit via an H2 output pipe. After partial shifting in the first shift reactor, the coal gas enters the PSA CO extraction unit, where CO is extracted and mixed with H2 (used as flushing gas) before entering the methanation reactor for methanation. Gases not adsorbed by the PSA CO extraction unit (mainly containing N2 and H2) are separated by the PSA N2 and H2 separation unit to extract H2, which is then used as flushing gas.

[0035] Furthermore, the pipeline connecting the pressure swing adsorption CO extraction device to the first shift reactor is equipped with a CO2 removal device for removing carbon dioxide.

[0036] The first and third pressure swing adsorption devices mentioned above are merely numbered and named for clarity, and the same applies to the changeover reactor. There are no structural limitations. In addition, the pressure swing adsorption devices mentioned in this invention are also named for their functions, such as pressure swing adsorption hydrogen extraction device, pressure swing adsorption CO and N2 separation device, and pressure swing adsorption CO extraction device. These are all for the purpose of clearly describing this invention, rather than for making major structural limitations.

[0037] Furthermore, the aforementioned separation process requires numerous pressure swing adsorption (PSA) purification unit operations. The high operating pressure during PSA results in high energy consumption and frequent pressure changes. When pressure and energy fluctuations are significant, and impact loads are substantial, exceeding the allowable fluctuation range of conventional energy recovery equipment, it can lead to shortened equipment lifespan, safety hazards, and even equipment malfunction, ultimately hindering energy recovery. This invention couples the normal adsorption separation process with the energy recovery process and a gas or liquid pressurization process, recovering energy with high energy utilization and a simple process, reducing the operating costs of PSA and expanding its market reach from a cost perspective. The energy recovery operation is primarily achieved through a coaxially driven energy recovery system composed of an expander, motor, compressor, or pump. This equipment also features a compact structure, high overall efficiency, and low overall equipment and operating costs, resulting in good economic benefits.

[0038] In the pressure swing adsorption process described above, the following methods can also be used:

[0039] An energy recovery method using pressure swing adsorption (PSA) includes the following steps: recovering energy from the gas during the pressure reduction process in PSA using an expander; smoothing out gas pressure fluctuations at the gas inlet and / or gas outlet of the expander using a fluid buffer device; or, suppressing rotational speed fluctuations by using a rotational resistance device on the expander shaft.

[0040] The fluid buffer device is selected from one or more of the following: a regulating valve or a buffer tank; the rotational resistance device refers to a flywheel.

[0041] The pressure reduction process refers to processes involving pressure changes, such as equalization, pressurization, displacement, pressurized flushing, and forward or reverse release.

[0042] In one embodiment, the expander drives a generator to generate electricity, which is then used for other equipment that requires power. Alternatively, the electricity generated by the generator is used by a compressor to compress the gas or liquid that needs to be pressurized during the pressure swing adsorption process.

[0043] The required electrical energy can be supplemented by controlling the input current of the motor connected to the compressor; fluctuations in the electrical energy input to the motor can be smoothed out by using battery packs or capacitor packs.

[0044] In one embodiment, the electrical energy generated by the generator is fed into the power grid, which uses its capacity to smooth out fluctuations in the electrical energy generated by the expander. The electrical energy obtained from the power grid is used for other equipment that requires power, or for compressing the gas that needs to be pressurized during the pressure swing adsorption process using a compressor.

[0045] In one embodiment, the expander shaft and the motor shaft are coaxially connected, and the expander and the motor work together to drive the compressor.

[0046] Based on the above method, the following apparatus can also be used:

[0047] A pressure swing adsorption device includes:

[0048] 1) At least one high-pressure adsorption tower;

[0049] 2) At least one energy recovery device, wherein the energy recovery device includes an expander for recovering the energy of the high-pressure gas discharged from the high-pressure adsorption tower;

[0050] A fluid buffer device is connected to the gas inlet and / or gas outlet of the expander;

[0051] Alternatively, a rotational resistance device can be installed on the expander's shaft.

[0052] The fluid buffer device is selected from one or more of the following: a regulating valve or a buffer tank; the rotational resistance device refers to a flywheel.

[0053] In one embodiment, the high-pressure adsorption tower is connected to the low-pressure adsorption tower via an energy recovery device.

[0054] In one embodiment, the pressure swing adsorption device further includes a generator, and the expander is connected to the generator.

[0055] The generator is connected to other equipment that requires electricity, or the generator drives a compressor to compress the gas or liquid that needs to be pressurized during the pressure swing adsorption process.

[0056] The generator is connected to the power grid, and the role of the power grid is to use its capacity to smooth out the fluctuations in electrical energy generated by the generator.

[0057] In one embodiment, the pressure swing adsorption device further includes a compressor and an electric motor, and the shaft of the expander and the shaft of the electric motor are coaxially connected, with the expander and the electric motor jointly driving the compressor to work.

[0058] Battery packs or capacitor packs are also installed on the electric motor.

[0059] A buffer tank is also provided at the gas inlet and / or gas outlet of the compressor.

[0060] Compared with conventional pressure swing adsorption (PSA) methods, the method and apparatus of this invention add an energy recovery process to the PSA process, coupling the normal adsorption separation process, the energy recovery process, and the pressurization process of a certain gas or liquid together. This recovers energy, improves the energy utilization rate of the system, reduces the operating cost of PSA, expands the market for PSA from a cost perspective, and features a simple process, high safety factor, high degree of automation, easy operation, small equipment footprint, guaranteed product purity, guaranteed recovery rate, flexible operation, and reduced number and size of tower equipment.

[0061] Beneficial effects:

[0062] The process concept of this invention is as follows: National standards require a low calorific value for natural gas, necessitating low levels of non-combustible components such as nitrogen and CO2. However, for blast furnace gas and converter gas, which have high nitrogen content, the conventional approach is to first synthesize natural gas and then cryogenically separate methane and nitrogen. Cryogenic separation is an uneconomical method due to high reinvestment and operating costs. This method separates nitrogen before synthesizing natural gas, thus avoiding cryogenic separation and saving costs. Furthermore, the presence of nitrogen in the natural gas synthesis reaction, along with the methanation catalyst, can lead to ammonia synthesis, which is detrimental to the methanation reaction, resulting in raw material waste. The presence of ammonia and water after the reaction is corrosive to equipment, requiring subsequent ammonia removal steps, significantly increasing investment and operating costs. Pre-removing nitrogen also avoids ammonia synthesis during the conversion reaction using iron-based catalysts, which is also detrimental to the conversion reaction, leading to raw material waste, equipment corrosion, and the need for additional equipment to remove ammonia, further increasing investment and operating costs.

[0063] Compared with existing technologies, this invention has substantial features and significant progress in the following aspects: This invention proposes a method for preparing natural gas from blast furnace gas and converter gas through multiple processing steps, which not only provides a new technical route for the comprehensive utilization of gas, especially blast furnace gas, but also further improves the economic value of gas, especially blast furnace gas. The process for preparing natural gas from blast furnace gas and converter gas (meeting GB17820-2012 and its updated versions) disclosed in this invention can also co-produce industrial nitrogen, with nitrogen concentration reaching industrial-grade requirements and capable of being recycled and reused. The integrated process for preparing natural gas from blast furnace gas and converter gas disclosed in this invention was derived through extensive experiments, simulation calculations, on-site surveys of steel plants, and years of engineering design experience. Material matching and energy utilization are considered from the perspective of the overall process, optimizing the process flow and reducing equipment investment and overall energy consumption. Attached Figure Description

[0064] Figure 1 This is a flow chart of the process for producing natural gas from coal gas;

[0065] Figure 2 This is a process flow diagram of the method for producing natural gas from coal gas in Example 1;

[0066] Figure 3 This is a process flow diagram of the method for producing natural gas from coal gas in Example 2;

[0067] Figure 4 This is a process flow diagram of the method for producing natural gas from coal gas in Example 3;

[0068] Figure 5 This is a process flow diagram of the method for producing natural gas from coal gas in Example 4;

[0069] Figure 6 This is a structural diagram of a coal gas to natural gas production unit;

[0070] Figure 7 This is a structural diagram of an energy recovery device used in the pressure swing adsorption process.

[0071] Figure 8 This is a structural diagram of another energy recovery device used in the pressure swing adsorption process;

[0072] Figure 9 It is a two-tower pressure swing adsorption purification H2 device that integrates an energy recovery unit;

[0073] Figure 10 It is a three-tower pressure swing adsorption purification H2 device that integrates an energy recovery unit;

[0074] 1 is the adsorption tower, 2 is the first stage of the turbine expander, 3 is the compressor, 4 is the electric motor, 5 is the air evacuation buffer tank, 6 is the vacuum pump, 7 is the reverse venting buffer tank, 8 is the reverse venting compressor, 9 is the flywheel, 10 is the capacitor bank, 11 is the compressed gas inlet buffer tank, 12 is the compressed gas outlet buffer tank, 13 is the turbine inlet high-pressure buffer tank, 14 is the turbine outlet high-pressure buffer tank, 15 is the turbine inlet low-pressure buffer tank, 16 is the turbine outlet low-pressure buffer tank, 17 is the second stage of the turbine expander, 18 is the feed gas buffer tank, 19 is the tower top product gas buffer tank, 20 is the first stage turbine outlet heat exchanger, and 21 is the second stage turbine outlet heat exchanger. Detailed Implementation

[0075] The natural gas production method provided by this invention mainly utilizes blast furnace gas and converter gas as raw materials or primary raw materials. The primary raw materials constitute the vast majority of the composition, for example, 85%, 90%, or 95% by volume or higher. The gas may also contain one or a mixture of two or more of the following: coke oven gas, other tail gases, or purge gases. The natural gas described in this invention is characterized by or is primarily composed of methane.

[0076] The gas composition of the aforementioned coal gas mainly includes: N2, H2, CO, CO2, O2, CH4, H2S, COS, etc. In some typical blast furnace gas, its composition includes, by volume percentage: N2 40-65%, H2 0.5-5%, O2 0.2-5%, CO2 10-30%, CO 10-30%, CH4 0.1-2.0%, H2S 5-400ppm, COS 0.1-100ppm.

[0077] Before the above-mentioned raw materials, such as coal gas, enter the process and equipment described in this patent, they can also undergo corresponding pretreatment processes such as impurity removal using conventional methods; there are no particular restrictions on these pretreatment processes.

[0078] A method for producing natural gas from coal gas includes:

[0079] (1) Preparation of H2 and CO mixture gas, the preparation process includes: partial conversion of coal gas to produce hydrogen, and separation of N2 from the system by pressure swing adsorption separation method before or after the partial conversion hydrogen production step;

[0080] (2) The H2 and CO mixture undergoes a methanation reaction to produce natural gas.

[0081] Partial shift reaction of coal gas for hydrogen production refers to the shift reaction of a portion of the CO in the incoming coal gas to produce hydrogen. After partial shift hydrogen production, a mixture of CO and H2 can be obtained through separation methods, rather than purifying CO and H2 separately. This mixture can then be subjected to methanation to produce natural gas. Unlike conventional technologies, this invention separates N2 before the methanation reaction, avoiding the use of cryogenic methods. The basic principle of CO shift is:

[0082] ;

[0083] This is a reversible, exothermic, and isotropic chemical reaction. From the perspective of chemical equilibrium, increasing the pressure has no effect on the chemical equilibrium. However, decreasing the reaction temperature and increasing the amount of water vapor in the reactants both favor the reaction in the direction of producing CO2 and H2. The reactor used is a pseudo-isothermal shift reactor, with a reaction pressure of 0.1–10 MPa (0.2–3 MPa in some embodiments) and a reaction temperature of 160–550 °C (170–400 °C in some embodiments). The conversion reaction can employ catalysts commonly used in the art, such as copper-based and / or iron-based and / or cobalt-molybdenum catalysts. The catalysts contain oxides of copper and / or iron and / or zinc and / or aluminum and / or manganese and / or cobalt and / or molybdenum and / or cerium and / or magnesium and / or chromium and / or potassium and / or vanadium and / or nickel and / or titanium and / or palladium and / or platinum and / or ruthenium and / or rhodium and / or sodium and / or rubidium and / or cesium and / or niobium and / or zirconium and / or rare earth elements and / or alkali metals and / or their sulfides and / or their soluble salts and / or complex metal oxides formed therebetween. The carriers include activated carbon, alumina, silicon dioxide, magnesium oxide, titanium dioxide, silica gel, molecular sieves, hydrotalcite, spinel, honeycomb ceramics, monazite, honeycomb metal, metal plates, corrugated fillers, corrugated plates, fiber (cloth) materials and structures, woven fabrics, metal foams, ceramic foams, graphite-based foams, copper and / or iron and / or zinc and / or aluminum and / or manganese and / or cobalt and / or molybdenum and / or cerium and / or magnesium and / or chromium and / or potassium and / or vanadium and / or nickel and / or titanium and / or palladium and / or platinum and / or ruthenium and / or rhodium and / or sodium and / or rubidium and / or cesium and / or niobium and / or zirconium and / or oxides of rare earth elements and / or alkali metals and / or their sulfides and / or their soluble salts and / or composite metal oxides formed therebetween. In one embodiment, when the required pressure of the synthetic natural gas is high, excessively high pressure may require higher temperatures to prevent the gas from becoming liquid and to ensure a certain margin. Excessively high reaction temperatures may also have an adverse effect on the shift reaction catalyst. Therefore, the shift reaction can be carried out with appropriate pressure and temperature, and the pressure can be further increased after the subsequent decarbonization and hydrogenation process to achieve the required pressure for the synthetic natural gas.

[0084] As a first embodiment, the method for preparing a mixture of H2 and CO includes: separating CO and N2 from coal gas by pressure swing adsorption separation, and then using the gas after N2 separation to produce a mixture of CO and H2 through a partial shift hydrogen production reaction.

[0085] Before separating CO and N2 using the pressure swing adsorption (PSA) method, a first impurity removal pretreatment is performed. This first impurity removal pretreatment includes one or a combination of steps such as dust removal, phosphorus removal, arsenic removal, dehydration, dehydrogenation and deoxygenation, desulfurization, CO2 removal, or CH4 removal. The content of harmful impurities in the purified gas is controlled to be sulfides ≤1.15ppm, NH3 ≤200ppm, O2 ≤0.4%, H2O ≤100ppm, and Cl... + ≤0.03ppm, arsenic ≤0.1ppm, tar + dust ≤1mg / Nm 3 Naphthalene ≤ 1 mg / Nm3. Furthermore, the content of harmful impurities is controlled at sulfides ≤ 0.1 ppm, Cl+ ≤ 0.01 ppm, and O2 ≤ 0.2%.

[0086] The further described first impurity removal pretreatment includes desulfurization and CO2 removal, with CO2 removal occurring simultaneously with desulfurization or after the desulfurization step. This is because blast furnace gas and / or converter gas contain trace amounts of sulfur, which can adversely affect various catalysts (dehydrogenation and deoxygenation, conversion, methane synthesis, and even demethanization catalysts) and adsorbents (CO and nitrogen separation) in subsequent steps, even causing them to deactivate or shorten their service life. Furthermore, the sulfur content in these gases is lower than the minimum sulfur content required by some sulfur-resistant catalysts, so it must be removed first. Additionally, since the incoming blast furnace gas and / or converter gas have a relatively high initial temperature, this is beneficial for the reaction rate and desulfurization effect of desulfurizing agents based on metal oxides.

[0087] Various methods can be used to remove sulfur or sulfur-containing impurities, including adsorption, membrane separation, solid desulfurizing agents containing oxides or hydroxides of iron, manganese, zinc, copper, nickel, calcium, or tin, or complex metal oxides formed therein, low-temperature methanol washing, propylene carbonate method, N-methylpyrrolidone method, polyethylene glycol dimethyl ether method, polyethylene glycol methyl propyl ether method, tributyl phosphate method, hot potassium alkali method, activated hot potassium alkali method, MEA method, DEA method, MDEA method, DIPA method, propylene carbonate method + DIPA, propylene carbonate method + glycolamine, sulfolane method, sulfolane + DIPA method, sulfolane + MDEA method, methanol + secondary amine method, alkyl alcoholamine solution method, and MEA method, DEA method, MDEA method with added activators, and ammonia water. The desulfurization process includes various methods such as washing, caustic soda process, ADA process (Strettford process), tannin process, LO-CAT process, Sulferox process, Sulfint process, Konox process, Bio-SR process, naphthoquinone process (Takahax process), metal phthalocyanine process (PDS process), GV (modified arsenic-alkali process), arsenic-alkali process, MSQ process, Sulfolin process, EDTA process, wet oxidation process, alkaline absorption process, limestone-gypsum process, ammonia process, magnesium process, phosphate fertilizer process, sodium organic acid-gypsum process, lime-magnesium process, calcium process, dry circulating fluidized bed process, zinc oxide process, urea process, complexation absorption process, charged dry absorbent injection process, plasma process, electron beam process, dual alkali process, sulfide process, and combinations thereof. The removed sulfur is sent to a sulfur recovery system, and the sulfur in the feed gas is reduced to 0.01–0.1 ppm after desulfurization. When using the absorption method, the absorbent has the ability to absorb both sulfur and carbon dioxide, thus removing both simultaneously. For better desulfurization results, it is best to follow up with a fine desulfurization step (e.g., using a solid desulfurizing agent). Desulfurization is carried out at 0.2~10 MPa and 20~700℃, or in some embodiments (0.2~3 MPa, 20~400℃, such as 400~280℃ for some metal oxide solid desulfurizing agents, and 20~70℃ for the absorbent liquid).

[0088] When the sulfur content of the incoming gas is too high, the organic sulfur can be converted into H2S through catalytic hydrogenation or catalytic hydrolysis, and then desulfurized so that the sulfur content of the treated gas meets the requirements. When the sulfur content of the incoming gas is mainly SO2 and the content is too high, SO2 can be converted into H2S through catalytic hydrogenation, and then desulfurized so that the sulfur content of the treated gas meets the requirements. The catalyst for the catalytic hydrogenation reaction here can be a commonly used catalyst in the art, such as one containing iron and / or copper and / or cobalt and / or manganese and / or molybdenum and / or zinc and / or aluminum and / or nickel and / or titanium and / or zirconium and / or tungsten and / or cerium metals and / or their oxides and / or their sulfides and / or their soluble salts and / or complex metal oxides formed therebetween as the active component, and one or more of the following metals and / or oxides of titanium, zirconium, manganese, iron, nickel, cobalt, copper, molybdenum, tungsten, zinc, cobalt, and cerium, as well as oxides and / or sulfides of silicon, rare earth, alkali metals, alkaline earth metals, and transition metals as auxiliary agents. The support can be activated carbon, alumina, silicon dioxide, magnesium oxide, titanium dioxide, silica gel, molecular sieves, honeycomb ceramics, monazite, honeycomb metals, metal plates, corrugated fillers, corrugated plates, fiber (cloth) materials and structures, woven fabrics, metal foams, ceramic foams, graphite-based foams, etc. The catalyst for the catalytic hydrolysis reaction here uses magnesium and / or lanthanum and / or barium and / or aluminum and / or titanium and / or zirconium and / or cerium and / or potassium and / or calcium and / or cobalt and / or molybdenum and / or iron and / or copper and / or manganese and / or zinc and / or nickel and / or tungsten metals and / or their oxides and / or their sulfides and / or complex metal oxides formed therebetween as active components, and titanium, zirconium, nickel, cobalt, molybdenum, cobalt, cerium metals and / or their oxides, as well as silicon, rare earth, alkali metals, alkaline earth metals, transition metal oxides and / or their sulfides as auxiliary agents. The support can be activated carbon, alumina, silicon oxide, magnesium oxide, titanium oxide, silica gel, molecular sieves, honeycomb ceramics, monazite, honeycomb metals, metal plates, corrugated fillers, corrugated plates, fiber (cloth) materials and structures, woven fabrics, metal foams, ceramic foams, graphite-based foams, etc.

[0089] If industrial nitrogen that does not meet standards is not required, CH4 removal may not be necessary. The resulting nitrogen will contain a slight excess of CH4. Furthermore, the first impurity removal pretreatment also includes CH4 removal, which can be achieved through catalytic oxidation to ensure the purity of the obtained nitrogen meets industrial nitrogen standards (GB3864-2008 and its updates). Since the reaction requires a high temperature, CH4 removal is performed first, i.e., after the desulfurization step. If desulfurization and carbon dioxide removal are separated, CH4 removal is performed after desulfurization and before carbon dioxide removal, which helps save energy and heat exchange equipment, reducing equipment investment and operating costs. In one embodiment, CH4 removal is mainly achieved by catalytic combustion of methane at a specific temperature (200–1000°C, e.g., 250–350°C) and pressure (0.1–10 MPa, e.g., 0.3–1.6 MPa) to remove methane, preventing the catalyst from losing activity. The catalyst used can be a commonly used catalyst in the art, such as an active component containing iron and / or copper and / or cobalt and / or manganese and / or molybdenum and / or zinc and / or aluminum and / or nickel and / or chromium and / or bismuth and / or magnesium and / or titanium and / or barium and / or ruthenium and / or zirconium and / or cerium and / or lanthanides and / or platinum and / or palladium and / or gold and / or rhodium and / or calcium, or their oxides and / or their soluble salts and / or complex metal oxides formed therebetween. One or more of the following metals and / or their oxides and / or their soluble salts and / or complex metal oxides formed therebetween, such as titanium, zirconium, manganese, iron, nickel, cobalt, copper, molybdenum, tungsten, zinc, cobalt, cerium, aluminum, chromium, bismuth, magnesium, titanium, barium, ruthenium, zirconium, cerium, lanthanum, platinum, palladium, gold, rhodium, and calcium, and / or their oxides and / or their soluble salts and / or complex metal oxides formed therebetween, as well as oxides of silicon, rare earth, alkali metals, alkaline earth metals, and transition metals, are used as promoters. The carriers include activated carbon, alumina, silicon dioxide, magnesium oxide, titanium dioxide, silica gel, molecular sieves, honeycomb ceramics, monazite, honeycomb metal, metal plates, corrugated packing, corrugated plates, fiber (cloth) materials and structures, woven fabrics, metal foams, ceramic foams, graphite-based foams, etc. The content of CH4 in the feed gas is ≤0.5%, and further ≤0.1%.

[0090] If the oxygen content in the blast furnace gas and / or converter gas is high (approximately >0.1%, further >0.04%, typically higher than this value in most gases), it will adversely affect the subsequent shift catalyst, CO and nitrogen separation adsorbent, and even the catalyst in the methanation step, potentially causing deactivation or shortening their lifespan. Therefore, pre-deoxygenation is necessary to ensure that the O2 concentration before entering the pressure swing adsorption (PSA) separation unit for CO and nitrogen is ≤0.4%, further ≤0.2%. Catalytic deoxygenation of pure CO in the subsequent process leads to more CO and O2 reaction, resulting in CO waste. Furthermore, additional impurity removal steps and equipment are required to remove impurities generated during the catalytic reaction. Excessive oxygen content also degrades the shift catalyst, leading to increasingly poor shift reaction efficiency, lower hydrogen purity after shift reaction, and higher CO content in the purified tail gas, resulting in unnecessary waste of raw materials and environmental degradation. Moreover, excessive oxygen content degrades the adsorbent, eventually rendering it unable to meet separation requirements over time. Therefore, in the first pre-removal process, dehydrogenation and deoxygenation are performed first (since deoxygenation also removes hydrogen, although the primary purpose is not to remove hydrogen, but to remove H2, resulting in higher nitrogen purity in subsequent steps). This protects the adsorbents and catalysts in subsequent steps, reduces CO waste, and minimizes the need for impurity removal steps after catalytic dehydrogenation and deoxygenation, shortening the process and reducing investment and operating costs. Furthermore, the higher gas temperature at the beginning meets the reaction temperature requirements for catalytic dehydrogenation and deoxygenation, avoiding the investment and operating costs of heat exchange equipment required for later heating. Therefore, dehydrogenation and deoxygenation are performed after desulfurization. If desulfurization and CO2 removal are performed sequentially, dehydrogenation and deoxygenation are performed after desulfurization and before CO2 removal. If a CH4 removal step is involved, dehydrogenation and deoxygenation are performed after CH4 removal and before CO2 removal. Dehydrogenation and deoxygenation help increase nitrogen purity, obtaining industrial nitrogen that meets standards. This sequence also conforms to the principle of progressively lower reaction temperatures, reducing investment and operating costs for heat exchange equipment.

[0091] Dehydrogenation and deoxygenation can be performed at pressures of 0.1–10 MPa (0.2–3 MPa in some embodiments) and temperatures of 50–1000 °C (80–250 °C in some embodiments) using a selective dehydrogenation catalyst to remove H2 and O2 from blast furnace gas. When the dehydrogenation and deoxygenation step is added before the carbon dioxide removal step, the CO concentration in the gas is lower, which is beneficial for improving the selectivity of catalytic oxidation dehydrogenation, reducing the reaction between CO and oxygen, thus reducing CO waste, making the reaction conditions less stringent, and facilitating catalyst selection. The temperature for removing H2 and O2 using catalytic oxidation is ≥100 °C. The catalyst can be a commonly used catalyst in the field, for example, it can be an active component containing palladium and / or platinum and / or cobalt and / or manganese and / or copper metals and / or their oxides and / or sulfides, and one or more of sodium, potassium, magnesium, titanium, zirconium, vanadium, manganese, iron, nickel, cobalt, copper, molybdenum, tungsten, lanthanum, zinc, silver, palladium, cobalt, or cerium metals and / or their oxides and / or sulfides and / or complexes formed therefrom as auxiliaries. The support can be activated carbon, alumina, silica, magnesium oxide, titanium oxide, silica gel, molecular sieves, honeycomb ceramics, monazite, honeycomb metal, metal plates, corrugated packings, corrugated plates, fiber (cloth) materials and structures, woven fabrics, metal foams, ceramic foams, graphite-based foams, etc. As an option, since the O2 content in the feed gas is very low, O2 removal can be omitted, so that the O2 concentration is ≤0.4% before entering the pressure swing adsorption separation unit for CO and nitrogen. This will not cause rapid deactivation of the adsorbent and catalyst, but it will shorten the service life of the adsorbent and catalyst and increase operating costs.

[0092] CO2 affects the separation efficiency of the CO and nitrogen separation step in pressure swing adsorption (PSA). Because CO2 has a certain adsorption capacity on the adsorbent used in the CO and nitrogen separation step, the separation coefficients for CO2 and CO, and CO2 and nitrogen, are not high. The presence of CO2 leads to incomplete separation of CO and nitrogen, resulting in CO and nitrogen gases containing a relatively high amount of CO2. Therefore, CO2 removal must be performed before the CO and nitrogen separation step to ensure complete separation of CO and nitrogen, yielding high-purity CO and nitrogen respectively. Furthermore, if CO2 is removed again in a later step, an intermediate stage pressurization is required, along with process losses, costs, and additional equipment. Pressure swing adsorption, absorption, and combinations thereof can be used for CO2 removal from coal gas. The absorption methods include: water washing, low-temperature methanol washing, propylene carbonate method, N-methylpyrrolidone method, polyethylene glycol dimethyl ether method, polyethylene glycol methyl propyl ether method, Catacarb method (catalytic hot alkali method), hot potassium alkali method, activated hot potassium alkali method, modified hot alkali method, hot carbonate method, amino acid salt method, ammonia washing method, combined urine (alkali) method, GV (modified arsenic alkali method), MEA method, DEA method, MDEA method, DIPA method, TEA method, sulfolane method, sulfolane + DIPA method, sulfolane + MDEA method, methanol + secondary amine method, alkyl alcoholamine solution method, and MEA and DEA methods with added surfactants. Methods such as MDEA and TEA remove CO2 from the feed gas to 0.01–0.8 vol% after decarbonization. CO2 removal is carried out at 0.2–10 MPa and 20–120°C. In some implementations (0.2–3 MPa and 20–40°C), the removed carbon dioxide can be sold as a carbon dioxide product, used as feed gas in other processes, or vented after meeting venting standards. When absorption is used as the separation unit for decarbonization, a trace amount of absorbent is usually carried out in the gas. A temperature swing adsorption separation unit needs to be added after this unit to remove water and some heavy components contained in the gas. Temperature swing adsorption removes water and heavy components; the adsorbent is molecular sieve, activated carbon, alumina, silica gel, or a composite bed of these. The tail gas containing a large amount of carbon dioxide, when the pressure is greater than 0.15 MPa, can enter a residual pressure recovery device to recover energy. After the first impurity removal pretreatment, the coal gas is separated into CO and N2 by pressure swing adsorption separation. By using pressure swing adsorption (PSA) to separate CO and nitrogen, commonly used catalysts in the field can be employed, such as copper-based or silver-based adsorbents, metal-organic framework adsorbents (MOFs, ZIFs), or metal-organic polyhedra (MOPs).The carrier can be activated carbon, alumina, silica gel, molecular sieve, honeycomb ceramics, monazite, honeycomb metal, metal plate, corrugated packing, corrugated plate, fiber (cloth) materials and structures, woven fabric, metal foam, ceramic foam, graphite-based foam, etc. CO and nitrogen are separated using pressure swing adsorption (PSA). The adsorption pressure of PSA is approximately 0.02–10 MPa (0.2–1.8 MPa in some embodiments), and the operating temperature is 0–150℃ (20–80℃ in some embodiments). PSA extracts 99.2% of industrial-grade nitrogen by volume, which can be directly used or sold as a product. When separating CO and nitrogen using PSA, a temperature swing adsorption method needs to be added before the PSA unit to separate and remove water and heavy components. When more than one pressure swing adsorption (PSA) unit is connected in series, the temperature swing adsorption (TSA) separation unit is added before the first PSA separation unit. In the PSA separation process, CO and nitrogen are separated, and nitrogen that does not meet industrial standards is obtained. When the nitrogen pressure is greater than 0.15 MPa, it can enter the residual pressure recovery system to recover the pressure energy carried by the nitrogen. When using PSA, an energy recovery device can be added to the PSA unit to recover the pressure energy wasted in the PSA process while completing the PSA separation process.

[0093] In the CO desorption process of the pressure swing adsorption (PSA) separation of CO and N2, this invention uses natural gas or H2 as the flushing gas to obtain a gas containing CO and natural gas, or a gas containing CO and H2, for the partial shift hydrogen production reaction. The reaction depth of the partial shift hydrogen production is generally controlled to have a CO / H2 molar ratio of about 1 / 3, such as 1 / 3 to 4.

[0094] The H2 produced by the shift reaction and the CH4 produced by the methanation reaction of natural gas are used as flushing gases. Multiple (≥1) high-pressure flushing and low-pressure flushing, or a combination of high-pressure flushing and low-pressure flushing with vacuum, or a combination of high-pressure flushing and vacuum, can be used to desorb a mixed gas containing CO and H2 or CH4. High-pressure flushing generally refers to a pressure greater than atmospheric pressure, typically 0.2~10 MPa, and in some embodiments 0.3~3 MPa. The purified H2 or CH4 is generally within this pressure range. Low-pressure flushing generally refers to atmospheric pressure, where some of the purified H2 or CH4 can be used to reduce the pressure, or the vent gas (mainly composed of H2 or CH4) from the H2 or CH4 purification unit can be used.

[0095] In one implementation method using H2 as the flushing gas, after a partial shift reaction for hydrogen production, the gas is divided into two parts. One part (volume fraction 5-80%) undergoes a further shift reaction to completely convert CO to H2. After removing carbon dioxide, the extracted H2 is used as the flushing gas. A portion of the extracted H2 can be used as a conditioning gas to adjust the C-H ratio of the methanation reaction. The other part (20-95%) undergoes carbon dioxide removal to obtain the H2 and CO mixture, or it can directly undergo a methanation reaction. Subsequently, the CO2 generated by the shift reaction needs to be removed. This method is preferred because CO2 can reduce the concentration of the reactants CO and H2, which helps to reduce the intensity of the reaction, lower the reaction temperature, and extend the catalyst life. The ratio of the two parts is determined by the subsequent process requirements and the quantity and ratio of CO and / or H2 in the feed gas used as a supplementary external gas source. This allows for the adjustment of the CO and H2 ratio to meet the requirements of subsequent processes.

[0096] In another implementation method using H2 as the flushing gas, the coal gas is separated into CO and N2 via pressure swing adsorption (PSA). The gas after N2 separation is directly divided into two parts. One part, containing 5-80% CO by volume, undergoes a shift reaction to produce hydrogen, which is then used as the flushing gas. The remaining gas, containing 20-95% CO by volume, undergoes a partial shift reaction to produce a mixture of CO and H2, which is then used for methanation to produce natural gas. The ratio of the two parts is determined by the subsequent process requirements and the quantity and ratio of CO and / or H2 in the feed gas, which serves as a supplementary external gas source. The CO and H2 ratio is thus adjusted to meet the requirements of subsequent processes (generally, the CO / H2 ratio in methanation is 1 / 3, but this limitation does not apply to wide hydrogen-to-carbon ratio methanation because it includes a shift function).

[0097] In another embodiment where H2 is used as the flushing gas, before the partial shift hydrogen production reaction, a portion of the coal gas is subjected to the shift hydrogen production reaction, and then H2 is extracted as the flushing gas. The extracted gas undergoes a second impurity removal pretreatment process before the shift hydrogen production reaction. This second impurity removal pretreatment process includes the first impurity removal pretreatment step performed when mixed with other gases, as well as separate pretreatment steps. The second impurity removal pretreatment process includes one or a combination of several steps selected from dust removal, phosphorus removal, arsenic removal, dehydration, dehydrogenation and deoxygenation, desulfurization, CO2 removal, CH4 removal, and heavy component removal. After purification by the second pretreatment process, the harmful impurity content of this gas is controlled as follows: sulfides ≤ 1.15 ppm in H2, NH3 ≤ 200 ppm, O2 ≤ 0.4%, H2O ≤ 100 ppm, and Cl... + ≤0.03ppm, arsenic ≤0.1ppm, tar + dust ≤1mg / Nm 3 Naphthalene ≤1mg / Nm 3Furthermore, the content of harmful impurities should be controlled to sulfides ≤ 0.1 ppm and Cl... + ≤0.01ppm, O2≤0.2%.

[0098] The separation of some coal gas can be carried out at the source of the coal gas, during or after the first impurity removal pretreatment. For example: the incoming gas can be separated directly, after desulfurization, after CH4 removal, after dehydrogenation and deoxygenation, after CO2 removal, or after CO and nitrogen separation. However, since some treatment and impurity removal processes are required for both gas components, such as desulfurization, deoxygenation (when oxygen content is high), and CH4 removal (when industrial nitrogen or environmental protection requirements are needed), some processes can be shared (or separate, functionally similar devices can be used separately). This leads to different separation points in the process flow and slightly different subsequent treatment processes. The location of the separation point is affected by the different composition of the feed gas and the different product requirements. For example, if both gas components need desulfurization, they can be separated after desulfurization. If the oxygen content in the incoming gas is relatively low, the branch gas for producing pure H2 gas can be directly subjected to a conversion reaction. If both gas components need to be deoxygenated for industrial nitrogen or environmental requirements, they can be separated after deoxygenation. If the oxygen content in the feed gas is low, the branch gas for producing pure H2 can directly undergo the shift reaction. If the oxygen content in the feed gas is high, the branch gas for producing high-purity H2 can be deoxygenated separately before undergoing the shift reaction. This deoxygenation step only considers oxygen content, without considering hydrogen content, requiring no trace oxygen addition, or adjusting the hydrogen-oxygen ratio, thus reducing the amount of hydrogen reacting with oxygen and increasing hydrogen production. If the oxygen content in the feed gas is high, both gas components need to be deoxygenated. They can be separated after dehydrogenation and deoxygenation. Although performing dehydrogenation and deoxygenation in one step slightly increases hydrogen loss, it reduces the number of units, floor space, investment, and operating costs. Separating after CO2 removal allows the high concentration of unwanted CO2 in the gas to be separated, increasing the content of useful gas, facilitating subsequent pressurization operations, and reducing pressurization energy consumption. However, the subsequent shift reaction will still generate CO2, requiring further CO2 removal. Separating CO and nitrogen after separation maximizes the content of useful gases, facilitates pressurization operation, and reduces pressurization energy consumption. Since the required high-purity H2 gas has a high pressure, increasing the operating pressure of the conversion reaction and its subsequent steps will only slightly increase costs, but can reduce equipment volume, improve equipment utilization, reduce floor space, and reduce investment costs.

[0099] When natural gas is used as the flushing gas, the natural gas originates from the final produced natural gas. During pressure swing adsorption (PSA) of CO and N2, after separating N2, a gas containing CO and natural gas is obtained, which is then directly subjected to a partial shift reaction for hydrogen production. The appropriate C-H ratio is adjusted by controlling the shift depth. This method eliminates the need for deep shift hydrogen production followed by high-pressure flushing and desorption of CO using H2 as the flushing gas. Instead, a portion of the produced CH4 is used as the flushing gas for high-pressure flushing and desorption of CO. This method may result in some CH4 loss, but it shortens the process, reduces equipment requirements, and the use of CH4 as a circulating gas reduces the concentrations of reactants CO and H2, thus reducing reaction intensity, lowering the reaction temperature, and extending catalyst life.

[0100] In a second embodiment, the method for preparing the H2 and CO mixture includes: subjecting coal gas to a partial shift reaction to produce hydrogen, obtaining a gas containing CO, N2, and H2; separating the CO using a pressure swing adsorption (PSA) separation method; then separating the N2 and H2; and using the separated hydrogen as a flushing gas for CO separation. Before the partial shift reaction, the coal gas undergoes desulfurization and / or dehydrogenation and deoxygenation; the dehydrogenation and deoxygenation occur after the desulfurization step. In this method, the incoming gas undergoes preliminary impurity removal, desulfurization, and deoxygenation treatments, followed by a partial shift reaction to adjust the CO / H2 ratio to approximately 1 / 3. After the reaction, the gas is cooled and first undergoes coarse dehydration in a separatory tank, followed by fine dehydration and recombinant removal via temperature swing adsorption (TSA). The gas then needs to have CO2 removed before being sent to a pressure swing adsorption (PSA) CO, H2, and nitrogen separation unit for separation of CO, H2, and nitrogen. The gas exiting from the top of the PSA adsorption tower primarily contains H2 and nitrogen, which are then further separated by PSA. The nitrogen removed from the bottom of the adsorption tower is treated to meet emission standards before being released into the atmosphere.

[0101] The gas after methanation is purified (dehydrated, or dehydrated and decarbonylated sequentially) to extract natural gas.

[0102] Figure 1 A preferred process flow is shown. Coal gas, such as blast furnace gas, is sequentially desulfurized, demethanated, dehydrogenated, deoxygenated, and deCO2 removed. Then, CO and N2 are separated by pressure swing adsorption (PSA). During PSA, H2 is used as the flushing gas to separate N2, resulting in a mixed gas containing CO and H2. This mixed gas then undergoes a partial shift reaction to produce hydrogen. The gas is then split into two streams: one stream undergoes a methanation reaction to remove carbon dioxide and obtain natural gas; the other stream undergoes a further shift reaction. After the reaction is completed, hydrogen is extracted and used as the flushing gas.

[0103] The corresponding equipment provided for producing H2 / CO feedstock gas from coal gas, such as Figure 6 ,include:

[0104] The first impurity removal pretreatment device is used to perform a first impurity removal pretreatment on the coal gas feedstock. The first impurity removal pretreatment device includes a desulfurization device, a CH4 removal device, a dehydrogenation and deoxygenation device and a CO2 removal device connected in sequence.

[0105] The first pressure swing adsorption (PSA) device is connected to the gas outlet of the CO2 removal device. Preferably, a temperature swing adsorption (TSA) device (not shown in the figure) is provided between the first PSA device and the CO2 removal device. The first PSA device separates N2 from the gas system to obtain a mixture containing H2 and CO.

[0106] A first shift reactor, connected upstream to a first pressure swing adsorption (PSA) unit, is used to partially shift CO in the gas exiting the PSA unit to produce H2. The gas outlet of the first shift reactor is connected to a first splitter 301, which divides the partially shifted gas into two parts. The splitter is connected to the PSA unit via a first pipeline and to a methanation reactor via a second pipeline. A hydrogen purification device is installed on the first pipeline. One end of the H2 input pipe is connected to the hydrogen purification device on the first pipeline 303, and the other end is connected to the PSA unit. Upstream of the hydrogen purification device on the first pipeline is a second shift reactor, used to further completely shift the split gas. The completely shifted gas is then purified of carbon dioxide by the hydrogen purification device to obtain hydrogen. The hydrogen is then fed into the PSA unit as flushing gas via the H2 input pipe 304. The other gas enters the methanation reactor via the second pipeline 302 for methanation.

[0107] The gas outlet of the methanation reactor is connected to a CO2 removal and CH4 extraction unit, and natural gas is obtained after removing carbon dioxide and supplied externally.

[0108] In the above methods, some separation steps require the use of pressure swing adsorption (PSA). The purpose of this invention is to address the significant pressure changes that occur in ambient temperature PSA and non-ambient temperature PSA processes where the incoming gas pressure is relatively high or requires pressurization to achieve the desired separation effect. During frequent pressure increases and decreases, the high-pressure gas discharged from the equipment carries a high pressure energy, resulting in substantial energy loss. Therefore, an energy recovery device is added to recover energy during these processes with large pressure changes. The recovered energy is then used to provide mechanical energy to pressurize the gas or liquid.

[0109] The equipment used to discharge high-pressure gas in industrial pressure swing adsorption (PSA) systems includes various types, the most common being adsorption towers, but other types such as pressure stabilizing tanks and buffer tanks can also be used. These devices contain high-pressure gas, and the depressurization process may involve equalization, pressurization, and forward or reverse release with another low-pressure adsorption tower, pressure stabilizing tank, or buffer tank. During these processes, the high-pressure gas in the saturated adsorption tower recovers recoverable gas energy through an energy recovery device before flowing back to the low-pressure adsorption tower, pressure stabilizing tank, or buffer tank. This simultaneously completes energy recovery and the normal depressurization process of PSA. When an expander is used, the energy recovery device can convert the pressure energy of the high-pressure gas into mechanical energy, which can be used to drive compressor rotation, generate electricity, supplement the output of electric motors, and so on. In the PSA process, the flow rate, pressure, and pressure drop of the depressurized gas connected to the energy recovery device are unstable, exhibiting periodicity and significant fluctuations. This often leads to the energy recovery device being unable to operate stably, thus requiring corresponding improvements.

[0110] The main design concept of this invention is to enable the expander to work normally by smoothing the periodic rapid fluctuations of the gas discharged from the high-pressure device. This is mainly achieved by smoothing the gas pressure fluctuations through a fluid buffer device at the gas inlet and / or gas outlet of the expander. Another solution is to achieve smooth operation by suppressing the fluctuations in the rotational speed of the expander's shaft, which can be achieved by installing a rotational resistance device on its shaft.

[0111] Based on the above concept, the following implementation methods are possible:

[0112] A buffer tank of a certain volume is added to the gas that needs energy recovery before it enters the turbine expander in the energy recovery device or after it leaves the energy recovery device. The buffer tank can be used to smooth out the pressure and flow fluctuations of the pressurized gas and make it basically stable. This allows the expander to recover the energy of the gas in the pressure swing adsorption and convert it into the mechanical energy of the shaft.

[0113] In another embodiment, a regulating valve is installed on the gas pipeline in the energy recovery device. By adjusting the opening of the regulating valve according to the frequency and magnitude of the pressure change during the pressure change process, the pressure and flow fluctuations of the high-pressure gas entering the expander are suppressed.

[0114] For designs that require increased rotational resistance of the expander shaft, in another embodiment, a flywheel of a certain size and mass distribution is installed on the expander shaft to increase the shaft's moment of inertia. The flywheel can be installed on the upstream or downstream side of the expander shaft.

[0115] As can be seen from the above, when a buffer device or resistance device is used, the pressure energy fluctuations can be better suppressed during the process of the expander converting gas pressure energy into mechanical energy, so that the expander can work normally and stably. This makes it suitable for applying mechanical energy to other processes that require energy consumption.

[0116] In order to make better use of the mechanical energy generated by the expander, the mechanical energy can be used to drive other equipment to rotate and work, or the mechanical energy can be converted into electrical energy and then used.

[0117] In one embodiment, the expander drives the electric motor to generate electricity. Since the rotation of the expander has a certain periodic fluctuation, the generated electrical energy is fed into the power grid. The power grid needs to have a large electrical load capacity. By utilizing the large capacity of the power grid to accommodate periodically changing current, the periodically fluctuating electrical energy can be smoothed out for utilization. The electrical energy in the power grid can be transmitted to other electrical equipment, or it can drive the compressor in the pressure swing adsorption device to compress gas or liquid, so that the electrical energy can be reused.

[0118] In the pressure swing adsorption (PSA) process, there is a periodic pressurization of the gas. Therefore, in another embodiment, the electrical energy generated by the expander-driven motor can be used to drive the compressor to pressurize the gas or liquid, thereby enabling the recovery and reuse of electrical energy.

[0119] Since overload during the operation of the motor connected to the compressor can adversely affect the equipment's reliability, stability, lifespan, and safety, in one embodiment, the motor can be connected to a capacitor bank or a battery bank. When the current fluctuates significantly, the capacitor bank or battery bank can quickly smooth out the rapid changes in current, thereby enhancing the motor system's response to the rapidly changing rotational energy required by the shaft.

[0120] The above describes an implementation method that converts the mechanical energy generated by an expander into electrical energy. Alternatively, the mechanical energy generated by the expander can also be utilized directly. In this implementation, the expander, motor, compressor, or pump form an energy recovery device that can be a coaxial drive system or a non-coaxial drive system. A coaxial drive system directly supplements the shaft of the compressor or pump with the mechanical energy converted from the expander, while the insufficient portion is supplemented by the motor. For example, the motor can be connected to a large power grid, where it is driven by electricity, and the motor's shaft is also linked to the expander's shaft, achieving the effect of the expander simultaneously supplementing the motor with mechanical energy. This method directly utilizes the mechanical energy obtained from the expander and, through the combined action of the expander and motor, smooths out fluctuations in mechanical energy. Coaxial drive systems are compact, highly efficient, and have relatively low overall equipment and operating costs, resulting in good economic benefits.

[0121] In the pressure swing adsorption (PSA) process, a high-pressure unit (e.g., a higher-pressure adsorption tower) typically supplies high-pressure gas to a low-pressure unit (e.g., a lower-pressure adsorption tower) to reduce the pressure in the high-pressure tower and increase the pressure in the low-pressure tower. Alternatively, the pressures can fluctuate between two gas buffer tanks or between the adsorption tower and a buffer tank. When the fluid buffer device and expander described in this invention are used as the main energy recovery device, a temperature drop occurs as the gas flows from the high-pressure side to the low-pressure side after passing through the expander. This is because the energy recovery process is an expansion process that reduces pressure and outputs work. The temperature of the gas at the expander outlet decreases. When this low-temperature gas enters another tower requiring pressurization, the adsorption temperature decreases, causing the adsorption temperature of the adsorption tower to be lower than the desorption / regeneration temperature. A lower adsorption temperature increases the adsorption capacity per unit of adsorbent, while a higher desorption / regeneration temperature ensures more thorough desorption, increasing the dynamic adsorption capacity of the adsorbent. Alternatively, the gas at the expander outlet can be cooled by a heat exchanger and supplied to other devices.

[0122] In addition, by adding fluid buffer devices before and after the expander, rapid periodic changes in gas pressure can be effectively prevented. Since excessive and frequent impact loads can easily cause the adsorbent to pulverize, reducing its lifespan, and also adversely affecting the safety and fatigue life of the adsorption tower, devices with control valves and buffer tanks are used in the pressure swing adsorption unit to suppress rapid fluctuations in high-pressure gas, thereby extending the lifespan of the adsorbent and also benefiting the safety and fatigue life of the adsorption tower.

[0123] Based on the operation of the energy recovery device described above, a typical pressure swing adsorption process in this invention is as follows:

[0124] A common industrial process of pressure swing adsorption is as follows:

[0125] Step 1: The mixed gas from the upstream feed enters the adsorption tower in the adsorption stage. Most of the easily adsorbed components are adsorbed by the adsorbent in the adsorption tower, while most of the unadsorbable components pass through the adsorption tower bed. This is the adsorption stage.

[0126] Step 2 involves depressurizing the adsorption tower that is saturated from Step 1. This depressurization process may involve equalizing pressure with another adsorption tower, pressure stabilizing tank, or buffer tank that is already at a low pressure, or performing forward or reverse release. During these processes, the high-pressure gas in the saturated adsorption tower recovers the recoverable energy through an energy recovery device and then flows back to the adsorption tower, pressure stabilizing tank, or buffer tank that is already at a low pressure. This simultaneously completes the energy recovery and the normal depressurization process of pressure swing adsorption.

[0127] Step 3 may require further depressurization of the gas obtained in Step 2, which is currently in the adsorption tower, pressure stabilizing tank, or buffer tank. Alternatively, the depressurized gas may undergo certain treatments (such as displacement or re-adsorption, pressurized flushing, or pressurization) before further depressurization. This process may require similar treatment methods to Step 2. This process may involve pressure equalization, forward or reverse release, or other procedures with another adsorption tower, pressure stabilizing tank, or buffer tank operating at low pressure. During these processes, the high-pressure gas in the saturated adsorption tower recovers energy through an energy recovery device and then flows back to the low-pressure adsorption tower, pressure stabilizing tank, or buffer tank. This simultaneously completes energy recovery and the normal depressurization process of pressure swing adsorption.

[0128] Step 4 may involve repeating a similar process to step 2 or 3 until the adsorption tower is reduced to a sufficiently low pressure.

[0129] Step 5: The adsorption tower, which was reduced to a low-pressure state in Step 4, undergoes a desorption and regeneration process under low-pressure conditions. In this process, methods such as vacuuming, purging, vacuuming plus purging, or low-pressure desorption may be adopted.

[0130] Step 6: It may be necessary to pressurize the adsorption tower that has undergone low-pressure desorption by other adsorption towers, pressure stabilizing tanks, or buffer tanks in Step 3. During this process, it may receive the high-pressure gas that has been depressurized after energy recovery in Step 2 or Step 3.

[0131] Step 7: It may be necessary to repressurize the gas obtained in Step 6, which is in an adsorption tower, pressure stabilizing tank, buffer tank, etc., or to repressurize the gas after it has been treated (such as displacement or re-adsorption, pressurized flushing, pressurization, etc.). In these possible pressurization processes, the high-pressure gas that has been depressurized after energy recovery in Step 2 or Step 3 may be received.

[0132] Step 8: It may be necessary to pressurize the adsorption tower, which has been pressurized in step 7, again with raw material gas or non-adsorbed gas after adsorption in the adsorption tower to a pressure close to that of the adsorption step.

[0133] Step 9, the process of the first 8 steps, involves continuous cyclical operation for a single tower, and continuous cyclical operation between towers in coordination and alternation.

[0134] Its high-pressure adsorption, depressurization energy recovery, depressurization, and low-pressure desorption processes are continuously cyclical for a single tower, and are also continuously cyclical for towers to cooperate and alternate.

[0135] By recovering the periodic, rapid pressure changes during the pressure swing adsorption (PSA) separation process and converting them into usable mechanical energy to power the gas pressurization process, the electrical energy consumed in gas pressurization is saved. Compared to PSA systems without energy recovery devices, this method can recover 50% of the energy lost due to pressure differences in conventional PSA systems.

[0136] In addition, the non-adsorbed gas after adsorption in the adsorption tower during the adsorption process may have a relatively high pressure. It may be used as venting gas or gas that does not require such a high pressure at the demand end. The high-pressure gas can be connected to a quantity recovery and pressurization coupling device for energy recovery. The gas with reduced pressure after energy recovery can then be connected to the demand end or vented again.

[0137] In this invention, the adsorbent used in the adsorption process can be any type of adsorbent that performs adsorption, without any particular limitation. It can be molecular sieve, activated carbon, carbon molecular sieve, activated alumina, carbon fiber, etc., as well as their mixed packing and layered packing.

[0138] This invention provides a method for preparing a supported metal-organic framework CO adsorbent, comprising:

[0139] (1) Dissolve 0.6 to 1 mmol of divalent copper compound and cerium nitrate in 15 to 20 mL of deionized water at a molar ratio of 100:1 to 1:100 to obtain a divalent copper compound-cerium nitrate mixture;

[0140] (2) Dissolve 0.3~0.5 mmol of 1,3,5-pyromellitic acid in a mixed solution of 8~10 mL of ethanol and dimethylformamide with a volume ratio of 10:1~1:10, and add commercially available NaY molecular sieve to it. The molar ratio of NaY molecular sieve to divalent copper compound - cerium nitrate is 1:40~50.

[0141] (3) After mixing and stirring the solutions from steps (1) and (2) at room temperature for 5-8 minutes, sonicate at 150-200W for 8-10 minutes, then heat to 230-250°C at a heating rate of 3-5°C / min, hold at that temperature for 20-22 hours, and then cool to room temperature at a cooling rate of 2-5°C / min to form a precipitate. Centrifuge and filter the precipitate. Wash the crystals obtained with anhydrous ethanol.

[0142] (4) Add 3.0 mL of 0.1-0.2 mmol / L AgNO3 ethanol solution to the obtained crystals, irradiate with ultrasound at 80-100W for 1-2 h, soak in the dark for 10-12 h, centrifuge, and filter; wash the obtained crystals three times with anhydrous ethanol, and irradiate with a 100-150W ultraviolet lamp for 10-13 h (so that AgNO3 is absorbed by the light). + Oxidize to Ag), centrifuge and wash with anhydrous ethanol, dry at 100-110℃, and oxidize with a mixture of O2 / He gas (2-3% O2 ​​volume fraction) at 250-260℃ for 1-2 h (so that Ag and Cu are oxidized). 2+ The reaction produces Ag + and Cu + ), to obtain powder;

[0143] (5) Dissolve CuCl, AgCl and rare earth powders with a molar ratio of 10:1~2:0.25~0.5 and molar amounts of 1mmol / 0.1~0.2mmol / 0.025~0.05mmol in 30~40mL of 0.4~0.5 mol / L hydrochloric acid solution, then add 0.225~0.3g of the powder obtained in step (4), irradiate with ultrasound at 100~150W for 20~30min, stir at room temperature for 2~3h, evaporate the solvent with a rotary evaporator, put it into a vacuum drying oven, dry for 10~12h, and then activate at 200~220℃ in H2 atmosphere for 4~5h to obtain powder material.

[0144] (6) Weigh a certain amount of the powder material obtained in step (5) above, methylcellulose and citric acid aqueous solution (the mass ratio of the three is 0.5:0.3~0.4:0.1~0.2), put them in a kneader and stir evenly. Then place the mixture in a centrifugal shot blasting machine to form it. Dry the formed product at 200~250℃ to obtain round particles with a diameter of about 2~3 mm, which is the supported metal-organic framework CO adsorbent molded body.

[0145] The preparation concept of this adsorbent is as follows: a metal-organic framework (Cu / Ce-BTC) is jointly prepared by Cu and rare earth element (cerium). The rare earth element (cerium) plays a role in stabilizing the structure, while also providing sulfur and oxidation resistance. Since the methods for preparing metal-organic frameworks (MOFs) are generally immature and have certain defects, this invention incorporates commercially available NaY-type molecular sieves to fill these defects, increasing the adsorption capacity. Ag is loaded onto the metal-organic framework. + and Cu + It can improve the adsorption capacity and selectivity of the adsorbent for CO.

[0146] In step (1), the divalent copper compound is selected from copper nitrate trihydrate, copper sulfate pentahydrate, copper chloride dihydrate and copper acetate tetrahydrate, with copper nitrate trihydrate being preferred.

[0147] In step (5), the rare earth powder is one or more of scandium, yttrium, lanthanum, cerium, praseodymium, neodymium, promethium, samarium, europium, or gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium.

[0148] The present invention will be further illustrated below with reference to specific embodiments. Unless otherwise specified, the methods, adsorbents or catalysts used in the embodiments can be obtained by conventional means in the art.

[0149] Example 1

[0150] The incoming converter gas (0.2 MPa, 350℃) first undergoes dust removal, and then catalytic hydrogenation to convert the sulfur in the gas into easily removable hydrogen sulfide (0.2 MPa, 300℃). After treatment, the gas is pressurized to 0.4 MPa and cooled to 40℃ before entering the carbon dioxide absorption tower. This carbon dioxide absorption tower uses the DEA absorption method, which simultaneously removes most of the sulfur contained in the gas. The unsaturated DEA absorbent after decarbonization (i.e., absorption of carbon dioxide) is pressurized and sent to the absorption tower of the decarbonization and hydrogen extraction unit, where it is used as absorbent for further decarbonization. Then, the absorbent is passed back into the secondary decarbonization absorption tower using the DEA absorption method, where it mainly removes the carbon dioxide generated by the pseudo-isothermal shift reaction. After the DEA solution is saturated, it undergoes depressurization regeneration to release the contained carbon dioxide. Most of the activated and regenerated DEA solution is sent to the absorption tower as a semi-lean solution to remove carbon dioxide. The remaining DEA solution is regenerated in a thermal regeneration tower by heating to release the contained sulfur and a small amount of remaining carbon dioxide, and then activated and regenerated until it is completely activated and regenerated into a lean solution. The removed carbon dioxide is treated to meet emission standards and then vented. The gas after carbon dioxide removal is sent to a temperature-switched adsorption unit, where it undergoes temperature-switched adsorption separation under conditions of adsorption pressure of 0.2 MPa and operating temperature of 32°C to remove water and other heavy components. After further desulfurization in a fine desulfurization adsorption tower composed of activated carbon, molecular sieves, and alumina, the gas composition at this point mainly contains CO and nitrogen.

[0151] This portion of the gas is fed into a pressure swing adsorption (PSA) CO and nitrogen separation unit for CO and nitrogen separation. Under similar adsorption pressure (0.2 MPa) and adsorption temperature (32°C), CO and nitrogen are separated by PSA. The gas containing a large amount of nitrogen separated at the top of the column passes through a residual pressure recovery device to recover its pressure energy, and after treatment to meet emission standards, it is released into the atmosphere. The PSA CO and nitrogen separation unit uses a combination of multiple (≥1) high-pressure rinsing and low-pressure rinsing to desorb the mixed gas containing CO and H2. The rinsing gas comes from hydrogen obtained from a DEA absorption decarbonization and hydrogen extraction unit. This utilizes the hydrogen obtained from the decarbonization and hydrogen extraction unit to desorb CO from the CO and nitrogen separation unit. This method couples two units, resulting in the lowest cost. Generally, the rinsing pressure of PSA is selected near atmospheric pressure, as low pressure is beneficial for desorption. However, the method used here is to use the hydrogen at the top of the tower to perform two flushing and desorption processes on the adsorption device that separates CO and nitrogen at its hydrogen extraction pressure and at a pressure slightly higher than atmospheric pressure; then the resulting mixed gas with different components after flushing at different pressures is fed to the compressor step by step according to the pressure and then carried out the next isothermal conversion. The advantages of this method are as follows: First, since the pressure of the hydrogen obtained from the decarbonization and hydrogen extraction unit is higher than that of the CO and nitrogen separation units, although high-pressure flushing and desorption of the CO and nitrogen separation units may result in incomplete adsorbent desorption, it still allows most of the gas to be desorbed. Simultaneously, the resulting gas is high-pressure, reducing the energy consumed in further pressurizing them. Second, the low-pressure flushing process ensures more thorough adsorbent desorption. Third, this desorption method allows the gas depressurization process to be gradually reduced in stages, decreasing the impact load on the adsorbent, increasing its lifespan, and also reducing the desorption time under low pressure, thus reducing the amount of oxygen infiltration from the air, reducing the explosion hazard of combustible gases (CO, H2, and CH4), and increasing safety. Finally, because this method produces a mixed gas containing CO and H2, the CO concentration in the gas is reduced, resulting in a lower conversion depth when adjusting the CO / H2 ratio subsequently. This reduces the exothermic temperature rise of the reaction, lowers the maximum operating temperature of the catalyst, reduces the severity of the conversion conditions, and increases the catalyst's lifespan. In summary, this method comprehensively balances the cyclic adsorption capacity and energy consumption per unit adsorbent, as well as the adsorbent loading capacity, adsorbent lifespan, and catalyst lifespan.

[0152] The desorbed CO and H2 mixed gas is then pressurized to 1.2 MPa and mixed with water vapor before entering a pseudo-isothermal shift reactor for the shift reaction. The pseudo-isothermal shift reactor uses water cooling to remove the exothermic reaction, with a reaction temperature of 180–450°C. The cooling water is heated to generate 1.2 MPa steam for use in this unit or other units. After the molar ratio CO / H2 = 1 / 3 is achieved, the mixed gas is divided into two parts: one-third continues deep shift hydrogen production; the other, after complete CO conversion, is further cooled to 40°C and enters a gas-liquid separator at 1.2 MPa to remove excess water. Then, it is fed into a DEA absorption decarbonization and hydrogen extraction unit, which primarily removes the carbon dioxide generated in the shift reaction. The absorbent mainly comes from the DEA absorbent that has completed the decarbonization absorption process in the carbon dioxide absorption tower of the previous step. The decarbonization and hydrogen extraction unit also uses absorbent from lean liquid that has undergone thermal regeneration and semi-lean liquid that has undergone vacuum regeneration. The ratio of lean and semi-lean liquid is set according to actual conditions. Then, the gas is removed by a temperature swing adsorption (TSA) device (not shown in the figure). During the decarbonization and hydrogen extraction process of the DEA absorption method, trace amounts of moisture and heavy components are carried away from the gas. Finally, the purified hydrogen is divided into three parts (the first part is used as conditioning gas, with a small volume; the second and third parts are used as flushing gas, with a volume ratio of 3:1 between high-pressure flushing and low-pressure flushing): the second part of the purified hydrogen is used as high-pressure flushing gas (1.2 MPa) to perform high-pressure flushing and desorption on the pressure swing adsorption (PSA) device for separating CO and nitrogen; and the third part of the hydrogen is depressurized to atmospheric pressure and used as low-pressure flushing gas to perform low-pressure flushing and desorption on the PSA device for separating CO and nitrogen. Another portion of the gas, after undergoing partial isothermal transformation, is further cooled to 40°C and enters a gas-liquid separator at a pressure of 1.2 MPa to remove excess water. It is then fed into a secondary decarbonization absorption tower using the DEA absorption method, which mainly removes carbon dioxide generated by the pseudo-isothermal transformation reaction. The absorbent mainly comes from the DEA absorbent that has completed the decarbonization absorption process in the previous decarbonization and hydrogen extraction unit. The secondary decarbonization absorption tower also has some absorbent from lean liquor that has undergone thermal regeneration and semi-lean liquor that has undergone vacuum regeneration (the ratio of lean liquor to semi-lean liquor is determined according to the actual situation). After being decarbonized in the secondary decarbonization absorption tower, the mixed gas is then passed through a temperature-switching adsorption device to remove trace amounts of moisture and heavy components contained in the gas during the secondary decarbonization absorption tower of the DEA absorption method. After this process, it is mixed with the hydrogen gas used as the CO / H2 regulating gas in the first part, adjusting the molar ratio of CO / H2 to about 1 / 3. Then, it enters the pseudo-isothermal methanation reactor to synthesize methane. The reactor uses water cooling to remove the exothermic reaction. The reaction temperature is 250-700℃, the pressure is 1MPa, and the cooling water is heated to generate 1.2MPa steam for use in this device or other devices.Finally, after cooling and removing moisture in a gas-liquid separator (1MPa, 32℃), and removing trace amounts of moisture and heavy components from the gas after the methanation reaction, the purified synthetic natural gas (meeting GB17820-2012 and its updated versions) is sent to an intermediate gas storage tank for external transportation.

[0153] In this embodiment, the process and reaction flow for natural gas synthesis primarily considers the DEA absorption method to remove CO2 in three stages at two different CO2 concentrations and two different pressures. All three CO2 removal methods employ absorption, and the same absorbent is used in all three stages. In the first CO2 removal process, the absorbent absorbs a certain amount of CO2 in a carbon dioxide absorption tower at a lower pressure. After being pressurized, it undergoes a second CO2 removal process in a decarbonization and hydrogen extraction absorption tower at a higher pressure to continue absorbing CO2. Then, in the third CO2 removal process, a secondary decarbonization absorption tower at a higher CO2 concentration continues to absorb CO2. After absorption is complete, it enters a regeneration tower to complete the activation and regeneration process. Because the first CO2 removal operation is carried out at a lower pressure, the absorbent generally does not achieve saturation adsorption. However, the CO2 obtained after CO conversion has a higher pressure, allowing the absorbent to further absorb CO2. Finally, taking advantage of the absorbent's higher absorption capacity at higher CO2 concentrations, the absorbent is used again at a higher CO2 concentration to further absorb CO2, thus reaching saturation. This method helps reduce the circulation volume of the absorbent, thereby reducing the circulation volume of the regenerated liquid and thus simplifying the regeneration process. In this example, the steps are simplified, the process is shortened, and costs are saved, while the pressure recovery system recovers the pressure energy contained in the vented gas.

[0154] For the detailed process flow of Example 1, please refer to [link / reference]. Figure 2 The gas components in each step of the process are shown in Table 1.

[0155] Table 1

[0156] composition% Converter gas <![CDATA[First CO2 removal]]> After fine desulfurization After CO and nitrogen are separated After the transformation reaction After the third carbon dioxide removal After methanation reaction <![CDATA[N2]]> 22.8 26.67 26.67 0.29 0.19 0.29 1.11 <![CDATA[H2]]> 1.6 1.87 1.87 24.88 49.92 74.9 3.98 <![CDATA[O2]]> -- -- -- -- -- -- -- <![CDATA[CO2]]> 14.6 0.1 0.1 0.13 33.42 0.1 0.38 CO 61 71.36 71.36 74.7 16.47 24.71 0.34 <![CDATA[CH4]]> -- -- -- -- -- -- 94.19 sulfur 41ppm 2 ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm

[0157] Example 2

[0158] The blast furnace gas feedstock first undergoes dust removal, then desulfurization using a desulfurizing agent composed of manganese oxides and ZnO at 350℃ and 0.3MPa. As the temperature decreases, a catalytic reaction is carried out at 220℃ and pressurized to 1MPa to remove trace amounts of hydrogen and oxygen. The gas is then mixed with water vapor and enters a multi-stage quench shift reactor for a shift reaction, producing H2. The reaction depth is adjusted to maintain a CO / H2 molar ratio of approximately 1 / 3. The shift reactor uses intermediate-stage water quenching to remove the exothermic reaction, with a reaction temperature of 180–450℃. The gas phase is further cooled to 32℃ and then enters a gas-liquid separator at 1MPa to remove excess water. It then enters a temperature swing adsorption unit (1MPa, 32℃) to remove trace amounts of moisture and heavy components before entering a pressure swing adsorption decarbonization unit (1MPa, 32℃) to remove carbon dioxide. The removed carbon dioxide is treated to meet emission standards before being released into the atmosphere. At this time, the gas components mainly contain CO, H2 and nitrogen.

[0159] This portion of the gas is fed into a pressure swing adsorption (PSA) CO, H2, and nitrogen separation unit for the separation of CO, H2, and nitrogen. The adsorption pressure is 1 MPa, and the operating temperature is 32°C. The PSA CO, H2, and nitrogen separation unit uses a combination of multiple (≥1) high-pressure and low-pressure rinsing processes to desorb the mixed gas containing CO and H2. The rinsing gas comes from the hydrogen obtained from the PSA hydrogen extraction unit and the outflow gas (mainly H2, with trace amounts of CO) from multiple towers within that unit. This method utilizes the hydrogen obtained from the PSA hydrogen extraction unit to desorb CO from the CO and H2 / nitrogen separation unit. This coupling of two units allows both units to jointly determine the outflow pressure of the outflow gas and the rinsing pressure range of the PSA adsorption unit separating CO, H2, and nitrogen, thus minimizing costs. Generally, the rinsing pressure for PSA is chosen near atmospheric pressure, as low pressure is beneficial for desorption. However, the method used here is to use the hydrogen from the top of the tower and the outflow gas to perform two flushing and desorption processes on the adsorption device that separates CO, H2, and nitrogen at the hydrogen extraction pressure and slightly above atmospheric pressure; then the resulting mixed gas with different components after flushing at different pressures is fed to the compressor for pressurization in stages according to the pressure.

[0160] The gas exiting from the top of the pressure swing adsorption (PSA) CO, H2, and nitrogen separation unit mainly contains H2 and nitrogen. It then enters the PSA hydrogen extraction unit to separate H2 and nitrogen. The nitrogen removed from the bottom of the PSA hydrogen extraction unit is treated to meet emission standards before being vented. The H2 exiting from the top is used as high-pressure purging gas to perform high-pressure purging and desorption (1 MPa) on the PSA CO, H2, and nitrogen separation unit. The outflow gas from the PSA hydrogen extraction unit is used as low-pressure purging gas (at atmospheric pressure) to perform low-pressure purging and desorption on the PSA CO, H2, and nitrogen separation unit.

[0161] The CO and H2 mixture is then pressurized to 1.6 MPa and fed into a pseudo-isothermal methanation reactor for methane synthesis. The reactor employs water cooling to remove exothermic reactions, with a reaction temperature of 280–700 °C. Cooling water is heated to generate 1.6 MPa steam for use in this unit or other equipment. The resulting gas is then further cooled to 32 °C and, under 1.6 MPa pressure, first enters a gas-liquid separator to remove most of the excess water. It then passes through a temperature-switching adsorption unit (1.6 MPa, 32 °C) to remove trace amounts of moisture and heavy components. Finally, the purified synthetic natural gas (meeting GB17820-2012 and its updates) is sent to an intermediate storage tank for external transportation.

[0162] The process and reaction flow in this embodiment not only yielded synthetic natural gas, but also comprehensively balanced the lifetime of the shift catalyst. At the same time, it combined and utilized a large amount of high-pressure hydrogen and some low-pressure process gases such as outgassing gas generated at the top of another unit for desorption, so that the useful gas could be fully utilized and the gas pressurization energy was reduced.

[0163] For the detailed process flow of Example 2, please refer to [link / reference]. Figure 3 The gas components in each step of the process are shown in Table 2.

[0164] Table 2

[0165] composition% Blast furnace gas After desulfurization After deoxygenation After the transformation reaction After carbon dioxide removal After CO and nitrogen are separated After methanation reaction <![CDATA[N2]]> 53.86 53.86 54.23 46.73 68.33 0.49 1.8 <![CDATA[H2]]> 2.15 2.15 2.16 15.53 22.71 73.47 2.64 <![CDATA[O2]]> 0.7 0.7 0.02 0.02 0.03 0.08 0.29 <![CDATA[CO2]]> 20.75 20.75 20.89 31.83 0.32 0.39 1.43 CO 21.69 21.69 21.84 5.15 7.53 24.34 0.33 <![CDATA[CH4]]> 0.85 0.85 0.86 0.74 1.08 1.23 93.51 sulfur 34ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm

[0166] Example 3

[0167] The blast furnace gas (350℃, 0.4MPa) first undergoes dust removal, then desulfurization with a desulfurizing agent composed of manganese oxides and ZnO at 350℃ and 0.4MPa. As the temperature decreases, it undergoes a methane catalytic combustion reaction at 290℃ and 0.4MPa to remove trace amounts of methane. Further catalytic reaction is carried out at a lower temperature of 220℃ and a constant pressure of 0.4MPa to remove trace amounts of hydrogen and oxygen. The gas then enters a temperature swing adsorption unit (0.4MPa, 32℃) to remove trace amounts of moisture and heavy components, before proceeding to a pressure swing adsorption decarbonization unit (0.4MPa, 32℃) to remove carbon dioxide. The removed carbon dioxide is treated to meet emission standards before being released into the atmosphere. At this point, the gas composition mainly contains CO and nitrogen. This portion of the gas is fed into a pressure swing adsorption (PSA) CO and nitrogen separation unit for CO and nitrogen separation. Under adsorption pressure of 0.4 MPa and operating temperature of 32°C, a portion of industrial-grade nitrogen with a volume composition ≥99.2% is extracted and sent as a product to the nitrogen recovery system. The PSA tower desorbs the mixed gas containing CO and synthetic natural gas using a combination of multiple (≥1) high-pressure rinsing and low-pressure rinsing with vacuum. The rinsing gas originates from the final product, synthetic natural gas, and the outflow gas (mainly methane) from multiple towers in the PSA decarbonization and methane extraction unit. This method couples two units, with both units jointly determining the outflow pressure and the rinsing pressure of the PSA adsorption unit separating CO and nitrogen, thus minimizing costs. Typically, the rinsing pressure for PSA is chosen near atmospheric pressure, which is beneficial for desorption under low pressure. However, the method used here is to use the hydrogen gas at the top of the tower and the outflow gas at its hydrogen extraction pressure and slightly higher than atmospheric pressure to perform high-pressure rinsing and desorption on the adsorption device that separates CO and nitrogen, and low-pressure rinsing and vacuum desorption; then the resulting mixed gas with different components after rinsing at different pressures is fed to the compressor for pressurization in stages according to the pressure. The advantages of this method are as follows: First, although flushing with purging gases at different pressures may result in incomplete adsorbent desorption, it still allows most of the gas to be desorbed, and the resulting gas is high-pressure, reducing the energy required for further pressurization. Second, the process of simultaneously evacuating and purging with venting gas reduces the vacuum level of the vacuum pump, saves energy, and ensures more thorough adsorbent desorption. Third, this desorption method allows for a step-by-step decompression process, reducing the impact load on the adsorbent and increasing its lifespan. Finally, the desorbed gas mixture containing CO and synthetic natural gas, obtained through this method, is considered inert since synthetic natural gas does not participate in the shift reaction, thus lowering the CO concentration and the depth of shift reaction. This reduces the exothermic temperature rise, lowers the maximum operating temperature of the catalyst, reduces the severity of the shift reaction conditions, and increases the lifespan of the shift catalyst.Similar situations and effects occur during methane synthesis. Reducing the CO concentration in the gas decreases the depth of the methanation reaction, reduces the exothermic temperature rise, lowers the maximum operating temperature of the catalyst, reduces the severity of the methanation reaction conditions, and increases the lifespan of the methanation catalyst. In summary, this method comprehensively balances the cyclic adsorption capacity and energy consumption per unit adsorbent, as well as the adsorbent loading, adsorbent lifespan, shift catalyst, and the lifespan of the methane synthesis catalyst. It also connects with and recovers the outgassing gas from another unit, reducing the waste of effective gases such as CO. The mixed gas (a mixture of CO and methane) is then slightly pressurized to 1 MPa and mixed with water vapor before entering a pseudo-isothermal shift reactor for partial shift reaction. The isothermal shift reactor uses water cooling to remove the exothermic reaction, with a reaction temperature of 180–450 °C. The cooling water is heated to generate 1 MPa steam for use in this unit or other units. By adjusting the depth of the shift reaction to maintain a CO / H2 molar ratio of approximately 1 / 3, the gas enters a pseudo-isothermal methanation reactor for methane synthesis. The reactor employs water cooling to remove the exothermic reaction, with a reaction temperature of 250–700°C. Cooling water is heated to generate 1 MPa of steam for use in this unit or other equipment. The resulting gas is then further cooled to 32°C and, under 1 MPa pressure, first enters a gas-liquid separator to remove excess water. It then passes through a temperature swing adsorption unit (1 MPa, 32°C) to remove trace amounts of moisture and heavy components. Finally, it enters a pressure swing adsorption (PSA) unit for decarbonization and methane extraction, primarily processing the carbon dioxide generated during the shift reaction. The purified synthetic natural gas (meeting GB17820-2012 and its updates) is then sent to an intermediate storage tank for external transportation.

[0168] In this embodiment, the process and reaction flow not only yielded synthetic natural gas but also recovered industrial-grade nitrogen. Furthermore, the final produced natural gas was used as the high-pressure flushing gas and a portion of the outflow gas from the adsorption-decarbonization-methane extraction unit as low-pressure desorption gas, ensuring full utilization of the useful gas and reducing gas pressurization energy. Alternatively, in another embodiment, the process is essentially the same as this embodiment, but instead of using natural gas as the high-pressure flushing gas and a portion of the outflow gas from the adsorption-decarbonization-methane extraction unit as low-pressure desorption gas, conventional vacuum desorption is used. While this also produces natural gas, it increases energy consumption and is detrimental to the lifespan of the catalyst and adsorbent.

[0169] For the detailed process flow of Example 3, please refer to [link / reference]. Figure 4 The gas components in each step of the process are shown in Table 3.

[0170] Table 3

[0171] composition% Blast furnace gas After desulfurization After demethanization After dehydrogenation and deoxygenation After carbon dioxide removal After CO and nitrogen are separated After the transformation reaction After methanation reaction After decarbonization and methane extraction <![CDATA[N2]]> 52.67 52.67 52.81 54.26 68.7 0.1 0. 06 0.1 0.22 <![CDATA[H2]]> 2.16 2.16 2.16 0.01 0.01 0.02 35.97 0.23 0.52 <![CDATA[O2]]> 0.54 0.54 0.55 0.03 0.03 0.02 0.01 0.02 0.04 <![CDATA[CO2]]> 20.56 20.56 20.62 21.19 0.22 0.08 36.02 56.03 1.28 CO 23.76 23.76 23..83 24.48 31 74.88 11.99 0.08 0.17 <![CDATA[CH4]]> 0.3 0.3 0.03 0.03 0.04 24.9 15.94 43.54 97.75 sulfur 37ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm

[0172] Example 4

[0173] The blast furnace gas (350℃, 0.4MPa) is first treated with dust removal, then desulfurized by a desulfurizing agent composed of manganese oxides and ZnO at 350℃ and 0.4MPa. As the temperature decreases, it undergoes a methane catalytic combustion reaction at 290℃ and 0.4MPa to remove trace amounts of methane. Further catalytic reaction is carried out at a lower temperature of 220℃ and a constant pressure of 0.4MPa to remove trace amounts of hydrogen and oxygen from the blast furnace gas. The gas is then divided into two parts: one part is pressurized to 1MPa and mixed with steam before entering a pseudo-isothermal shift reactor for a shift reaction. The pseudo-isothermal shift reactor uses water cooling to remove the exothermic reaction. The reaction temperature is 180–450℃, and the cooling water is heated to generate 1MPa steam for use by other equipment. The gas phase is then further cooled to 32°C and enters a gas-liquid separator at 1 MPa to remove excess water. Afterward, it enters a temperature swing adsorption (TSA) unit (1 MPa, 32°C) to remove trace amounts of moisture and heavy components. Finally, it enters a pressure swing adsorption (PSA) unit (1 MPa, 32°C) to remove impurities such as carbon dioxide and nitrogen, yielding H2. The removed carbon dioxide and nitrogen are treated to meet emission standards and then vented. The resulting H2 is used as high-pressure purging gas (1 MPa) to perform high-pressure purging and desorption on the PSA CO and nitrogen separation units. The outflow gas from the PSA hydrogen extraction unit is used as low-pressure purging gas (at atmospheric pressure) to perform low-pressure purging and desorption on the PSA CO and nitrogen separation units.

[0174] Another portion of the gas after dehydrogenation and deoxygenation enters a temperature swing adsorption (TSA) unit (0.4 MPa, 32℃) to remove trace amounts of moisture and heavy components. It then enters a pressure swing adsorption (PSA) decarbonization unit (0.4 MPa, 32℃) to remove carbon dioxide. The removed carbon dioxide is treated to meet emission standards before being released into the atmosphere. At this point, the gas composition mainly contains CO and nitrogen. This portion of the gas is then sent to a PSA CO and nitrogen separation unit for CO and nitrogen separation. Industrial-grade nitrogen (volume composition ≥99.2%) is extracted under adsorption pressure of 0.4 MPa and operating temperature of 32℃ and sent as a product to the nitrogen recovery system. The PSA tower uses a combination of multiple (≥1) high-pressure rinsing and low-pressure rinsing with vacuum to desorb the mixed gas containing CO and H2. The rinsing gas comes from the hydrogen obtained from the PSA hydrogen extraction unit and the outflow gas (mainly hydrogen) from multiple towers within that unit. This method couples two sets of equipment, with both sets jointly determining the venting pressure of the outgassing gas and the purging pressure of the pressure swing adsorption (PSA) unit separating CO and nitrogen, thus minimizing costs. Typically, PSA purging pressures are chosen near atmospheric pressure, which is beneficial for desorption at low pressure. However, the method used here utilizes top-of-the-column hydrogen and outgassing gas at their hydrogen extraction pressure and slightly above atmospheric pressure to perform high-pressure purging and desorption on the CO and nitrogen separation unit, followed by low-pressure purging and vacuum desorption. The resulting multi-stream mixed gases with different compositions and pressures are then fed stepwise to a compressor for pressurization. The mixed gas (a mixture of CO and H2) is mixed with steam at 1 MPa and then enters a wide-hydrogen-to-carbon ratio methanation reactor, where shift reaction and methanation reactions occur sequentially. The reactor employs multi-stage heat exchange to remove exothermic reactions, with reaction temperatures ranging from 250 to 700°C. The resulting gas is then further cooled to 32°C and fed into a gas-liquid separator at 1 MPa to remove most of the water. Next, it passes through a temperature swing adsorption unit (1 MPa, 32°C) to remove trace amounts of moisture and heavy components. Finally, it enters a pressure swing adsorption (PSA) unit for decarbonization and methane extraction, primarily to remove carbon dioxide generated in the broad hydrogen-to-carbon ratio methanation reaction. The purified synthetic natural gas (meeting GB17820-2012 and its updates) is then sent to an intermediate storage tank for external transportation.

[0175] The process and reaction flow in this embodiment not only yields synthetic natural gas but also recovers industrial-grade nitrogen. Furthermore, it employs a wide hydrogen-to-carbon ratio methanation reactor, shortening the process, saving energy and investment. Simultaneously, it utilizes a large amount of high-pressure hydrogen and some low-pressure process gases, such as outgassing gas, generated at the top of another unit for desorption, ensuring full utilization of useful gases and reducing gas pressurization energy. This wide hydrogen-to-carbon ratio methanation reactor essentially combines a shift reactor and a methanation reactor. Under suitable CO and H2 ratio conditions, it can replace both shift reactors and methanation reactors. This wide hydrogen-to-carbon ratio methanation reactor can be used in the various methods described above.

[0176] For the detailed process flow of Example 4, please refer to [link / reference]. Figure 5 The gas components in each step of the process are shown in Table 4.

[0177] Table 4

[0178] composition% Blast furnace gas After desulfurization After demethanization After dehydrogenation and deoxygenation After carbon dioxide removal After CO and nitrogen are separated After methanation reaction After decarbonization and methane extraction <![CDATA[N2]]> 53.86 53.86 54.27 55.85 71.01 0.01 0.02 0.06 <![CDATA[H2]]> 2.15 2.15 2.17 0.02 0.03 24.5 1 2.93 <![CDATA[O2]]> 0.7 0.7 0.7 0.02 0.03 0.01 0.02 0.06 <![CDATA[CO2]]> 20.75 20.75 20.91 21.52 0.21 0.07 65.9 0.23 CO 21.69 21.69 21.85 22.49 28.59 74.5 0.1 0.29 <![CDATA[CH4]]> 0.85 0.85 0.1 0.1 0.13 0.01 32.96 96.43 sulfur 41ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm 0.1ppm

[0179] Comparative Example 1

[0180] The difference from Example 4 is that the catalytic H2 and O2 removal steps preceding the blast furnace gas purification process in Example 4 are moved to after the pressure swing adsorption (PSA) decarbonization and methane extraction unit. Only the O2 content is controlled, and the pure methane obtained after the PSA decarbonization and methane extraction unit undergoes catalytic O2 removal. All other parts are the same as in Example 4. Since the O2 content of the synthesized natural gas should not be too high, otherwise it will be explosive and have a significant impact on the safety of natural gas, it needs to be removed.

[0181] The results showed that in the pressure swing adsorption (PSA) CO and nitrogen separation unit, the extracted nitrogen volume composition was ≤99.2% under adsorption pressure of 0.4 MPa and operating temperature of 32°C, which could not meet the requirements for industrial-grade nitrogen. Therefore, it had to be sent to the energy recovery system to recover the nitrogen pressure energy before being vented. Furthermore, the adsorbent began to degrade over time. After about a month, the purity of the purified CO began to decrease; after about two months, the CO purity decreased significantly (nitrogen concentration greater than 10%, compared to ≤1% in Example 4). Increasing the displacement gas flow rate was used to try to improve the CO purity; however, after about four months, even increasing the displacement gas flow rate could not prevent the decrease in CO purity, and the adsorbent could no longer meet the separation requirements.

[0182] A portion of the gas is pressurized to 1 MPa and mixed with water vapor before entering a pseudo-isothermal shift reactor for the shift reaction. The isothermal shift reactor uses water cooling to remove the exothermic reaction, and the reaction temperature is 180–450 °C. As time goes on, the shift catalyst begins to deteriorate. After 6 months, the shift effect of the pseudo-isothermal shift reactor becomes increasingly worse. It can be seen that after adopting the comparative scheme, the purity of the hydrogen after shifting decreases over time, and the CO conversion rate is less than 90% (in Example 4, the CO conversion rate is ≥99.6%). After passing through the pressure swing adsorption decarbonization and hydrogen extraction device, the CO content in the purified tail gas becomes increasingly higher, causing unnecessary waste of raw materials and being detrimental to the environment.

[0183] A mixture of CO and H2 gas is mixed with water vapor at 1 MPa and then enters a wide H / C ratio methanation reactor. The reactor undergoes a shift reaction and a methanation reaction sequentially. Multi-stage heat exchange is used to remove exothermic reactions, and the reaction temperature ranges from 250 to 700°C. Over time, the shift catalyst in the wide H / C ratio methanation reactor begins to deteriorate. After six months, the shift effect becomes increasingly worse, and the methanation catalyst also begins to deteriorate, resulting in a lower methane content and higher CO and H2 content in the methane (although the example still maintains shift quality with a conversion rate close to 100%). In the pressure swing adsorption (PSA) decarbonization and methane extraction unit, the CO content in the purified tail gas increases, causing unnecessary waste of raw materials and being detrimental to environmental protection. Furthermore, after 12 months, the calorific value of the obtained synthetic natural gas decreases, even failing to meet the requirements of the GB17820-2012 standard.

[0184] Catalytic removal of O2 from CH4 at higher concentrations would result in more CH4 reacting with O2, leading to a waste of CH4. Furthermore, the reaction requires higher temperatures, necessitating gas heating, and the reaction products, as impurities, need to be removed, requiring additional impurity removal steps and equipment.

[0185] The process and reaction flow in this embodiment result in synthetic natural gas with a calorific value that fails to meet standard requirements and also fails to meet the requirements for industrial-grade nitrogen. Furthermore, it poisons the adsorbent, shift catalyst, and the shift catalyst and methanation catalyst in the wide hydrogen-to-carbon ratio methanation reactor. Over time, the adsorbent and catalyst begin to deteriorate until they become unusable. The calorific value of the obtained synthetic natural gas decreases further, even failing to meet standard requirements. Catalytic deoxygenation in pure CH4 leads to more CH4 reacting with O2, resulting in CH4 waste. Moreover, the reaction products after deoxygenation in the catalytic reaction are impurities that need to be removed, necessitating additional impurity removal steps and equipment.

[0186] Example 5 This example illustrates the energy recovery process in a two-tower pressure swing adsorption system.

[0187] The exhaust gas contains trace amounts of impurities such as N2, CO, CO2, CH4, and Ar. To meet the hydrogen requirements of the product, a hydrogen separation unit needs to be installed for separation and purification. Due to the high operating pressure of the upstream unit, the feed gas pressure entering the pressure swing adsorption separator for H2 is also high. At the same time, the H2 after separation needs to be pressurized to 4.2 MPa (G).

[0188] Raw material gas conditions:

[0189] Components (dry basis) CO <![CDATA[H2]]> <![CDATA[CO2]]> <![CDATA[N2]]> Ar <![CDATA[CH4]]> <![CDATA[H2S+COS]]> Vol, % 11.179 68.28 10.004 10.227 0.003 0.308 0.1ppm

[0190] Flow rate: 2000 Nm 3 / h (dry basis)

[0191] Pressure: 2.2 MPa (G)

[0192] Temperature: ≈32℃

[0193] Total H2O, O2, NH3, CH3OH, chlorine, phosphorus, arsenic, fluorine, HCN: ≤0.1ppm

[0194] The H2 was separated and purified using a pressure swing adsorption (PSA) purification device equipped with a specialized adsorbent for H2 separation. The separation steps included: adsorption, pressure equalization and depressurization, reverse depressurization, vacuuming, pressure equalization and pressurization, and final pressurization. Energy recovery and pressurization coupling devices were used in the pressure-changing steps—pressure equalization, reverse depressurization, and final pressurization—to recover energy while simultaneously achieving the specialized separation and purification of H2.

[0195] The energy recovery and pressurization coupling device is a system consisting of a screw expander, a compressor, and an electric motor, along with auxiliary components such as a capacitor bank, regulating valve group, flywheel, multiple buffer tanks, and a complex system including a speed change mechanism and a control system. A buffer tank of a certain volume is added before the pressurized H2 enters the energy recovery device and after it leaves the device to smooth out fluctuations in the pressure and flow rate of the pressurized H2, thus stabilizing it.

[0196] The device provided in this embodiment is as follows: Figure 7 and Figure 8 , Figure 9As shown, the exhaust pipe of adsorption tower 1A is connected to the first stage 2 of expander, and the exhaust direction of the first stage 2 of expander is connected to adsorption tower 1B. Buffer tanks 13 and 14 are connected to the inlet and outlet pipes of the first stage 2 of expander, respectively. The rotating shaft of the first stage 2 of expander is connected to motor 4, and motor 4 is connected to compressor 3 for pressurizing the gas. Compressed gas inlet buffer tank 11 and compressed gas outlet buffer tank 12 are also provided on the inlet and outlet of compressor 3, respectively. A capacitor bank 10 is also connected to motor 2.

[0197] The following section provides a further explanation of the device's operation, taking into account its operational process:

[0198] During the 0-3 minute time period, adsorption tower 1A (hereinafter referred to as Tower A) undergoes adsorption. Valves A5 and A1 are opened, and the raw material gas enters Tower A, which is in the adsorption state, through the raw material gas pressure stabilizing tank (18) and regulating valve E4. The unadsorbed gas at the top of the tower is used as product gas for other devices through the product gas pressure stabilizing tank (19) and regulating valve E3. During the vacuuming process of adsorption tower 1B (hereinafter referred to as Tower B), valve B6 is opened, and Tower B is evacuated by the reciprocating pump (6) through the air evacuation buffer tank (5). No gas passes through the energy recovery device, and no energy is recovered to supply the compressor (3) for gas compression.

[0199] During the 3-4 minute time period, the pressure equalization process of tower A and tower B is carried out. Valve A2B3E2 is opened, and the high-pressure gas in tower A is used to pressurize tower B. First, at the moment valve A2B3E2 is opened, the pressure in the pipeline, the pressure difference between the inlet and outlet of the expander (3), and the flow rate change are all very large, which will cause a relatively large impact load. Excessive impact load will affect the stable and safe operation of the equipment and will affect the service life of the equipment. Therefore, by adjusting valve E5E10, the pressure difference and flow rate between the inlet and outlet of expander 3 are adjusted. At the moment valve A2B3E2 is opened, the opening degree of adjusting valve E5E10 is reduced to pressurize the corresponding adsorption tower, so as to reduce the impact load on the expander. Buffering is also achieved through buffer tanks (13) and (14) connected to the inlet and outlet pipelines of the expander. When the pressure in the pipeline connected to the buffer tank is higher than the pressure set by valve E6E7, valve E6E7 is opened, the buffer tank is connected to the pipeline, and the gas is diverted into the buffer tank, reducing the amount of gas entering the expander and reducing the impact of the impact load. This provides the necessary time for the expander adjustment mechanism to operate, so that the adjustment control mechanism operates the slide valve of the screw expander and adjusts the flow rate, internal pressure ratio, and internal volume ratio through the expander to be suitable for the external pressure ratio and flow rate of the expander inlet and outlet after the valve is opened. At the same time, the pressure energy acting on the expander drives the shaft to rotate and is converted into the mechanical energy of the shaft. Since the impact load formed when the valve is opened is easy to make the shaft speed exceed the set required speed, the change in shaft speed is not conducive to forming a combined force with the motor to jointly drive the compressor to complete the compression process of another gas. By adding a flywheel of a certain size and a certain mass distribution on the shaft, the rotational inertia of the shaft is increased, so that the acceleration obtained by the shaft is reduced under the same torque, which is conducive to stabilizing the shaft speed at the set required speed. The expander shaft is connected to the motor (4), which can drive the motor to rotate. However, the speed of the mechanical energy output by the expander will change periodically due to the frequent changes in the pressure swing adsorption process, which will cause the motor to run unstablely. Therefore, the current required by the motor needs to be connected to the overall power grid. The large power grid can accommodate the periodically rapid changes in current, and a control device is used to drive the motor smoothly. Under the action of impact load, the current flow of the power grid to the motor may decrease rapidly, or even cause the current transmission direction to change. Therefore, by connecting the motor and the capacitor bank (10), the rapid change in the current flow caused by the impact load can be suppressed, which can enhance the motor system's response to the rapidly changing rotational energy required by the shaft and reduce the impact on the power grid. As the running time increases, the gas in tower A gradually flows to tower B, the pressure in tower A gradually decreases, the pressure in tower B gradually increases, the pressure difference between the two towers gradually decreases, the pressure difference between the gas inlet and outlet of the expander gradually decreases, and the flow rate also gradually decreases. This process changes gradually. Increase the opening of the regulating valve E5E10 to reduce the resistance loss at the valve.As the pressure in the pipelines at the expander's inlet and outlet gradually changes, the gas flows from the buffer tank to the outlet. When the pressure in the pipeline connected to the buffer tank falls below the pressure set by valves E6 and E7, valves E6 and E7 close, and the buffer tank is no longer connected to the pipeline. Since the compressed gas requires relatively stable pressure and flow rate, this means the shaft power required for the compressed gas also needs to be relatively stable. Therefore, buffer tanks are connected to both the compressor inlet and outlet to handle potential pressure and flow rate fluctuations. Over time, the pressure difference between the expander's inlet and outlet gradually decreases, and the flow rate also gradually decreases. Consequently, the shaft power output by the expander gradually decreases, requiring the shaft power output by the motor to gradually increase. This necessitates a gradual increase in the current input from the power grid, which needs to be adjusted by the control system to compensate for the shaft power required by the compressed gas. The current required by the motor needs to be connected to the overall power grid. Utilizing the large grid's capacity to accommodate periodically and rapidly changing current, a control device is used to ensure smooth motor drive. Simultaneously, by adjusting the control mechanism and regulating the screw expander's slide valve, the flow rate, internal pressure ratio, and internal volume ratio of the expander are adjusted to maintain high efficiency.

[0200] Since the energy recovery process is an expansion process that reduces pressure and outputs work to the outside, the temperature of the gas at the expander outlet will decrease. The temperature drop is determined by the pressure difference between the expander inlet and outlet. The gas at the expander outlet is sent to the outside via heat exchangers (20) and (21) to provide a certain temperature of cooling energy for use by other devices. The gas at the expander outlet enters tower B, which undergoes a process of equalizing and pressurizing. After recovering a certain amount of cooling energy through heat exchange, the gas temperature is lower than the gas temperature at the expander inlet. The entry of the low-temperature gas causes the temperature of tower B to decrease. For tower B, a similar process of low-temperature gas entering and causing the temperature of tower B to decrease also occurs in the next pressurization process. This will cause the adsorption temperature of tower B to decrease in the next adsorption step, making the adsorption temperature of the adsorption tower lower than the desorption and regeneration temperature. The lower temperature during adsorption is beneficial to increasing the adsorption capacity per unit of adsorbent, while the higher temperature during desorption and regeneration is beneficial to making the desorption of the adsorbent more thorough and increasing the dynamic adsorption capacity of the adsorbent. Meanwhile, because the gas recovers energy through the expander, the pressure increase or decrease process in the adsorption tower becomes slower. Compared to pressure swing adsorption (PSA) units without energy recovery, this reduces the impact load on the adsorption tower during the pressure equalization process. Excessive and frequent impact loads can easily cause the adsorbent to pulverize, reducing its lifespan and negatively impacting the safety and fatigue life of the adsorption tower. Therefore, using an energy recovery device in a PSA unit extends the adsorbent's lifespan and also benefits the safety and fatigue life of the adsorption tower.

[0201] During the 4-5 minute time period, tower A undergoes reverse venting, while tower B undergoes pressurization. Valve A4E13 is opened, and the high-pressure gas in tower A, after recovering pressure energy and cold energy through the energy recovery system, passes through the reverse venting buffer tank (7) and the reverse venting compressor (8) before being sent to other combustion devices. Similar to the operation of the energy recovery system during the equalization process, the impact load formed at the moment of valve opening is buffered and alleviated by the regulating valve group E6E8E9, buffer tanks (13)(15)(16), flywheel, and capacitor group (10). The connection of a large power grid and the adjustment of the expander slide valve can also play a certain role in buffering the impact load. Similarly, similar to the operation of the energy recovery system during the equalization process, as the running time increases, the pressure of the gas in tower A gradually decreases, the pressure difference between the gas inlet and outlet of the expander gradually decreases, and the flow rate also gradually decreases. Therefore, the shaft power output by the expander gradually decreases, and the shaft power output by the motor needs to gradually increase. Thus, the current input by the power grid needs to be gradually increased through the control system to make up for the shaft power required by the compressed gas. The current required by the motor needs to be connected to the overall power grid. By utilizing the large power grid's capacity to accommodate periodically and rapidly changing currents, a control device is applied to drive the motor smoothly. The capacitor bank also contributes to the smooth drive of the motor through the input and output of current. At the same time, by adjusting the control mechanism to adjust the slide valve of the screw expander, the flow rate, internal pressure ratio, and internal volume ratio of the expander are made suitable for the external pressure ratio and flow rate of the expander inlet and outlet after the valve is opened, so that the expander maintains a high efficiency. Similarly, a certain temperature of cold energy is output to the outside through the heat exchanger at the outlet of the expander for use by other devices. Similar to the operation of the energy recovery system during the pressure equalization process, the addition of the energy recovery system during the process of excessive pressure change extends the service life of the adsorbent and is also beneficial to the safety and fatigue service life of the adsorption tower. When valves E1, E2, and B3 are opened, the high-pressure gas in the product gas pressure stabilizing tank (19) recovers pressure energy and cold energy through the energy recovery system and then pressurizes tower B, raising the pressure of tower B to close to the pressure of the adsorption step. In this process, the energy recovery system's response to the impact load of valve opening, the smooth drive effect of changes in input current from the power grid, the provision of cooling capacity through the heat exchanger, and the adjustment of the expander's flow rate, internal pressure ratio, and internal volume ratio by the slide valve are similar to the forward discharge process of tower A. After recovering a certain amount of cooling capacity through heat exchange, the gas temperature is lower than the gas temperature at the expander inlet, and the entry of the low-temperature gas causes the temperature of tower B to decrease.

[0202] During the 5-8 minute time period, tower B undergoes a vacuuming process. Valve A6 is opened, and reciprocating pump (6) evacuates tower A. Tower B is in an adsorption state. The raw material gas enters the adsorption tower B in the adsorption state through the raw material gas pressure stabilizing tank (18) and regulating valve E4. The unadsorbed gas at the top of the tower passes through the product gas pressure stabilizing tank (19) and regulating valve E3 as product gas for use by other devices. Because the temperature of the gas received by tower B after energy recovery during the previous equalization, pressurization and pressurization process is lower than the gas temperature at the inlet of the expander, the adsorption temperature of tower B will decrease. During the adsorption step of tower B, the adsorption temperature of the adsorption tower will be lower than the temperature of vacuum desorption and regeneration. The lower temperature during adsorption is beneficial to increase the adsorption amount per unit adsorbent, while the higher temperature during desorption and regeneration is beneficial to make the desorption of the adsorbent more thorough, thus increasing the dynamic adsorption amount of the adsorbent. During this period, no gas passes through the energy recovery device, and no energy is recovered to supply the compressor (3) for gas compression.

[0203] During the 8-9 minute time period, pressure equalization is performed between towers B and A. Valve B2A3 is opened, and the high-pressure gas in tower B is used to pressurize tower A. This process is similar to the pressure equalization process during the 3-4 minute time period. Towers A and B cooperate with each other and alternate in a continuous cycle.

[0204] During the 9-10 minute time period, tower A undergoes a pressurization process, while tower B undergoes a reverse release process. Valve E1, E2, and B3 allow the high-pressure gas in the product gas pressure stabilizing tank (19) to recover pressure energy and cold energy through the energy recovery system, pressurizing tower A until its pressure approaches that of the adsorption step. Valve B4 and E13 open, allowing the high-pressure gas in tower A to recover pressure energy and cold energy through the energy recovery system before passing through the reverse release buffer tank (7) and the reverse release compressor (8) to other combustion devices. This process is similar to the reverse release process in tower A and the pressurization process in tower B during the 4-5 minute time period. Towers A and B cooperate and alternate in a continuous, cyclical operation.

[0205] At this point, the adsorption tower has completed a full adsorption-regeneration cycle and is ready for the next cycle. The operation of tower B is the same as that of tower A. Each adsorption tower alternates between the various steps, and for a single tower, the cycle is repeated continuously. The towers cooperate with each other and alternate in a continuous cycle.

[0206] By recovering the periodic, rapid pressure changes during the pressure swing adsorption (PSA) separation of H2, the energy is converted into conventionally usable mechanical energy to power the H2 pressurization process and the output cooling capacity, thus saving the electrical energy consumed in pressurizing H2. Compared to a PSA system without an energy recovery device, this system can recover 46% of the energy lost due to pressure difference in a conventional PSA system.

[0207] Table 5. Sequence Table of Operation Steps for H2 Purification by Two-Tower Pressure Swing Adsorption

[0208]

[0209] Example 6 This example illustrates the energy recovery process in a three-tower pressure swing adsorption system.

[0210] The exhaust gas contains trace amounts of impurities such as N2, CO, CO2, CH4, and Ar. To meet the hydrogen requirements of the product, a hydrogen separation unit needs to be installed for separation and purification. Due to the high operating pressure of the upstream unit, the feed gas pressure entering the pressure swing adsorption separator for H2 is also high. At the same time, the H2 after separation needs to be pressurized to 4.2 MPa (G).

[0211] Raw material gas conditions:

[0212] Components (dry basis) CO <![CDATA[H2]]> <![CDATA[CO2]]> <![CDATA[N2]]> Ar <![CDATA[CH4]]> <![CDATA[H2S+COS]]> Vol, % 11.179 68.28 10.004 10.227 0.003 0.308 0.1ppm

[0213] Flow rate: 2000 Nm 3 / h (dry basis)

[0214] Pressure: 2.2 MPa (G)

[0215] Temperature: ≈32℃

[0216] Total H2O, O2, NH3, CH3OH, chlorine, phosphorus, arsenic, fluorine, HCN: ≤0.1ppm

[0217] The H2 is separated and purified using a pressure swing adsorption (PSA) purification device equipped with a specialized adsorbent for H2 separation. The separation steps include: adsorption, pressure equalization and depressurization, reverse depressurization, vacuuming, pressure equalization and pressurization, and final pressurization. In the pressure-changing steps—pressure equalization, reverse depressurization, and final pressurization—an energy recovery and pressurization coupling device is used to recover energy while simultaneously completing the specialized separation and purification of H2. The energy recovery and pressurization coupling device is a system consisting of a turboexpander, a compressor, an electric compressor, and auxiliary components such as capacitor banks, regulating valve banks, a flywheel, multiple buffer tanks, a gearbox, and a complex control system. Buffer tanks of a certain volume are added before the compressor enters the energy recovery device and after it leaves the energy recovery device to smooth out pressure and flow fluctuations in the pressurized H2, stabilizing it.

[0218] like Figure 10 As shown.

[0219] The energy recovery process in each operational step of this pressure swing adsorption (PSA) and energy recovery coupled with pressurization exhibits similar characteristics. During operational transitions, the pressure changes in the pipeline and the pressure difference between the inlet and outlet of the expander are significant at the instant the valves are opened, resulting in substantial impact loads. Excessive impact loads can affect the stable and safe operation of the equipment and shorten its lifespan. Therefore, regulating valves E2 and E5 adjusts the pressure difference and flow rate at the expander's inlet and outlet. At the moment the valves open, the opening degree of valve E2 and E5 is reduced to pressurize the corresponding adsorption tower, thereby minimizing the impact load on the expander. Buffering is also achieved through buffer tanks (13)(14)(15)(16) connected to the inlet and outlet pipelines of the expander. When the pressure in the pipeline connected to the buffer tank is higher than the pressure set by valves E6E7E8E9, valves E6E7E8E9 open, connecting the buffer tank to the pipeline, allowing gas to be diverted into the buffer tank, reducing the amount of gas entering the expander and reducing the impact of the impact load. This provides the necessary time for the expander adjustment mechanism to operate, allowing the adjustment control mechanism to adjust the deflection angle of the inlet guide vanes of the turbine expander or the opening of the adjustable nozzle, adjusting the flow rate and pressure difference through the expander to be suitable for the pressure difference and flow rate at the inlet and outlet of the expander after the valve is opened. At the same time, the pressure energy acting on the expander drives the shaft to rotate, which is converted into the mechanical energy of the shaft. Since the impact load formed when the valve is opened easily drives the shaft speed to accelerate, the change in shaft speed is not conducive to forming a combined force with the motor to jointly drive the compressor to complete the compression process of another gas. By adding a flywheel of a certain size and mass distribution to the shaft, the moment of inertia of the shaft is increased, so that the acceleration obtained by the shaft is reduced under the same torque. The electric motor requires current connected to the overall power grid. Utilizing the grid's capacity to accommodate periodically changing, rapidly varying currents, a control device is used to ensure smooth motor operation. Under impact loads, the current flow from the grid to the motor may decrease rapidly, even causing a change in the current's direction. Therefore, connecting the motor to a capacitor bank helps mitigate these rapid current changes caused by impact loads, enhancing the motor system's response to rapidly changing shaft rotational energy requirements and reducing the impact on the power grid. As operating time increases, the gas in the high-pressure tower gradually flows to the low-pressure tower or pressure vessel, causing the high-pressure tower pressure to gradually decrease and the low-pressure tower pressure to gradually increase. This reduces the pressure difference between the two towers, and consequently, the pressure difference between the expander inlet and outlet, leading to a gradual decrease in flow rate. This process is gradual. Increasing the opening of regulating valves E2 and E5 reduces resistance losses at the valves. As the pressure in the pipelines at the inlet and outlet of the expander gradually changes, the gas gradually changes from flowing into the buffer tank to flowing out of the buffer tank. When the pressure in the pipeline connected to the buffer tank is lower than the pressure set by valves E6E7E8E9, valves E6E7E8E9 close, and the buffer tank is no longer connected to the pipeline.Because the compressed gas requires relatively stable pressure and flow rate, the shaft power required for compression also needs to be relatively stable. Therefore, buffer tanks are connected to both the inlet and outlet of the compressor to handle potential pressure and flow rate fluctuations. Over time, the pressure difference between the inlet and outlet of the expander gradually decreases, and the flow rate also gradually decreases. Consequently, the shaft power output by the expander gradually decreases, requiring the shaft power output by the motor to gradually increase. This necessitates a gradual increase in the current input from the power grid, regulated by the control system, to compensate for the required shaft power. The current required by the motor needs to be connected to the overall power grid, utilizing the grid's capacity to accommodate periodically changing currents. A control device is then used to ensure smooth motor drive. Simultaneously, the deflection angle of the inlet guide vanes or the opening of the adjustable nozzles of the turbine expander are adjusted by regulating the flow rate and pressure difference through the expander, maintaining its high efficiency. Since the energy recovery process involves pressure reduction and power output during expansion, the temperature of the gas at the expander outlet decreases. The degree of temperature reduction is determined by the pressure difference between the inlet and outlet of the expander. The gas at the expander outlet is then cooled by a heat exchanger and supplied to other devices. The gas exiting the expander enters the low-pressure tower, undergoing a pressurization process. After heat exchange and recovery of a certain amount of cold energy, the gas temperature is lower than the gas temperature at the expander inlet. The introduction of this low-temperature gas lowers the temperature of the low-pressure tower. Similarly, in the subsequent pressurization process, the low-pressure tower experiences a similar temperature drop due to the introduction of this low-temperature gas. This results in a lower adsorption temperature during the adsorption phase after pressurization, placing it below the desorption / regeneration temperature. Lower adsorption temperatures increase the adsorption capacity per unit of adsorbent, while higher desorption / regeneration temperatures ensure more thorough desorption, increasing the dynamic adsorption capacity. Furthermore, because the gas recovers energy through the expander, the pressurization and depressurization processes in the adsorption tower are slower. Compared to pressure swing adsorption (PSA) devices without energy recovery, this reduces the impact load on the adsorption tower during the pressure equalization process. Excessive and frequent impact loads can easily cause adsorbent pulverization, reducing its lifespan and negatively impacting the safety and fatigue life of the adsorption tower. Therefore, using an energy recovery device in a pressure swing adsorption unit can extend the service life of the adsorbent, and also improve the safety and fatigue life of the adsorption tower.

[0220] In simple terms, by adding a buffer tank and regulating valve group of a certain volume to the pressure swing adsorption (PSA) and energy recovery and pressurization coupling device, fluctuations in the pressure or flow rate of the gas in the pipeline are smoothed out. First, a turboexpander recovers the energy of the gas from the PSA, converting it into mechanical energy of the shaft. A flywheel of a certain size and mass distribution is added to the energy recovery device to increase the shaft's moment of inertia, thus smoothing out the periodically rapidly changing rotational energy of the shaft. Then, the control system determines the required output of the electric compressor based on the total energy needed by the system, controls the motor output, and the electric compressor or electric pump provides energy to supplement the remaining energy needed to complete the pressurization process of H2. The motor and capacitor bank are connected; when the current fluctuation is large, the battery bank can quickly smooth out rapid current changes, enhancing the motor system's response to rapidly changing rotational energy required by the shaft. The current required by the motor needs to be connected to the overall power grid. Utilizing the large grid's capacity to accommodate periodically rapidly changing current, the control device ensures smooth motor drive. This allows for the recovery of the periodic, rapid pressure changes during the pressure swing adsorption (PSA) separation of H2, converting them into usable mechanical energy to power the H2 pressurization process, thus saving the electrical energy consumed in pressurizing H2. Compared to a PSA system without an energy recovery device, it can recover 46% of the energy lost due to pressure difference in a conventional PSA system. Furthermore, according to the three-tower PSA purification H2 cycle operation sequence table (Appendix 1), each adsorption tower alternately performs the above steps, with each tower operating continuously in a cyclical manner, and the towers cooperating and alternating in a continuous cyclical operation.

[0221] The reverse venting and air extraction systems, used as waste gas flare networks, lead to the plant's waste gas flare network. The H2 adsorption and separation unit yields H2 with a purity ≥99.9% at a concentration of 1300 Nm³. 3 / h, with the remaining CO approximately 0.03%, CO2 approximately 0.03%, N2 approximately 0.03%, and Ar+CH4 approximately 0.01%; reverse venting and air extraction 700 Nm 3 / h, of which CO is approximately 31.94%, CO2 is approximately 28.59%, N2 is approximately 29.22%, H2 is approximately 9.37%, and CH4 is approximately 0.88%.

[0222] The process of separating H2 by pressure swing adsorption (PSA) is illustrated using column A as an example:

[0223] (a) Adsorption (0~2min): Under a pressure of 2.2MPa, valve A4 is opened and the feed gas enters the fixed bed for adsorption. Adsorption stops before the adsorption front reaches one end of the bed outlet, leaving a fresh bed between the adsorption front and the bed outlet. The H2 obtained at the top of the column is discharged as the product gas through the open valve A1 at the top of the column. The adsorption pressure is close to the feed gas inlet pressure.

[0224] (b) Adsorption (2~3min): While adsorbing, the top outlet of tower A is connected to tower B after homogenization. The H2 obtained from the top of tower A is used to pressurize tower B. This step requires energy recovery and pressurization coupling device to recover energy. Valves A1 and A4 are opened, and valves A2 at the top of tower A, B3 at the bottom of tower B, and E3, E6, and E7 are opened. When the pressure of the gas in the tank connected to E6 is lower than 1.9MPa, E6 is closed. When the pressure of the gas in the tank connected to E7 is lower than 1.4MPa, E7 is closed. The regulating valve group E2 and E5 are used to adjust the pressure and gas flow in the pipeline to gradually increase or decrease, which can reduce the fluctuation of the turbine expander (2) operation. The buffer tank connected to valves E6 and E7 and the regulating valve group E2 and E5 can buffer the flow and pressure difference of the gas passing through the turbine expander at the moment the valve is opened, which can reduce the instantaneous output of the turbine expander.

[0225] (c) Pressure Equalization (3-4 min): Tower A is connected to Tower C, which is under vacuum, for pressure equalization. Energy is recovered through an energy recovery and pressurization coupling device. Valve A2 at the top of Tower A, valve C3 at the bottom of Tower C, and valves E3, E6, and E9 are opened. When the gas pressure in the tank connected to E6 drops below 1.9 MPa, E6 closes; when the gas pressure in the tank connected to E9 drops below 0.4 MPa, E7 closes. Control valve groups E2 and E5 are used to gradually increase or decrease the pressure and gas flow in the pipeline, reducing fluctuations in the turbine expander's operation. The buffer tanks connected to valves E6 and E9, and control valve groups E2 and E5, buffer the gas flow and pressure difference passing through the turbine expander at the moment the valves open, reducing the instantaneous output of the turbine expander. For Tower A, this is a pressure reduction process; for Tower C, it is a pressure increase process. After equalization, the pressure in column A is slightly higher than half of the original pressure (1.1 MPa), and the purity of the equalized gas is basically the same as the purity of the product gas flowing out from the top of the column.

[0226] (d) Reverse Release (4-5 min): Connect tower A to a buffer tank containing reverse release gas at near-atmospheric pressure for the reverse release step. The reverse release loop simultaneously recovers energy through an energy recovery and pressurization coupling device. Valve A3, E1, E4, E8, and E9 at the bottom of tower A are opened. When the gas pressure in the tank connected to E8 is below 0.9 MPa, E8 closes; when the gas pressure in the tank connected to E9 is below 0.4 MPa, E9 closes. Regulating valve groups E2 and E5 are used to gradually increase or decrease the pressure and gas flow in the pipeline, reducing fluctuations in the turbine expander's operation. The buffer tank connected to valves E8 and E9, and regulating valve groups E2 and E5, buffer the gas flow and pressure difference passing through the turbine expander at the moment the valves open, reducing the instantaneous output of the turbine expander. After the pressure equalization and reduction process, the impurity front in the adsorption bed has reached the outlet position of the adsorption tower. At this point, the pressure of the adsorption tower is reduced to near-atmospheric pressure (0.11 MPa) in the opposite direction of adsorption. During this process, the impurities adsorbed in the adsorption tower begin to desorb in large quantities from the adsorbent. The reverse pressure gas is then sent to other combustion devices after passing through the reverse pressure gas buffer tank (7) and the reverse pressure gas compressor (8).

[0227] (e) Vacuuming (5~6 min): After the reverse release step, in order to regenerate the adsorbent more thoroughly, the adsorption tower is evacuated to allow the adsorbent to be completely desorbed. Open valve A5 at the bottom of tower A and use vacuum pump (6) to evacuate the bed in reverse until the pressure inside the tower is -0.09 MPa.

[0228] (f) Equalization (6-7 min): Connect tower A, which is under vacuum, to tower B, which has finished adsorption, for an equalization step. This is a pressurization process for tower A and a depressurization process for tower B. Valve A3 at the bottom of tower A and valves B2, E3, E6, and E9 at the top of tower B are opened. Energy is recovered through an energy recovery and pressurization coupling device. The process is similar to (c) equalization, except that tower A becomes a low-pressure tower receiving gas and being equalized and pressurized. After equalization, the pressure in tower A is slightly lower than half of the adsorption step pressure (0.9 MPa), and the purity of the equalized gas is basically the same as the purity of the product gas flowing out from the top of tower B.

[0229] (g) Idle (7~8min): The valves at the top and bottom of column A are closed, and there is no gas entering or leaving column A. Column A is in a waiting state.

[0230] (h) Pressurization (8~9min): After homogenization, the connection between the top outlets of tower A and tower C is used to pressurize tower A with a portion of H2, increasing the internal pressure of tower A to close to the adsorption pressure (2.1MPa). Valve A3 at the bottom of tower A, valve C2 at the top of tower C, and valves E3, E6, and E7 are opened. This step, which requires energy recovery and pressurization coupling, is similar to the adsorption process in (b), except that tower A becomes a pressurized low-pressure tower that receives the gas.

[0231] At this point, the adsorption tower has completed a full adsorption-regeneration cycle and is ready for the next cycle. The operation of the other three towers is the same as that of tower A. Each adsorption tower alternates in performing the above steps, with each tower operating continuously in a cyclical manner, and the towers cooperating and alternating in a cyclical manner.

[0232] The specific operation steps, timing, and sequence are shown in Table 6, while the control and operation of the opening status of each valve in each tower are shown in Table 7. According to the timing table (Table 6) and valve opening control table (Table 7), the energy recovery system is in a continuous working state, with alternating equalization, reverse release, and pressurization processes, continuously and repeatedly. The continuous operation of the energy recovery system recovers energy from these three operation steps, preventing the energy recovery system from being idle, which is conducive to the safe and stable operation of the machine and avoids adverse effects on the machine and energy loss.

[0233] Table 6. Sequence Table of Operation Steps for Three-Tower Pressure Swing Adsorption Purification of H2 Circulation

[0234]

[0235] Table 7 Valve Opening Control Table for Each Tower

[0236] t / min Tower A Tower B Tower C Energy recovery circuit 0~1 A1A4 adsorption B3 all rose C2 both decreased E3E6E9 1~2 A1A4 adsorption Vacant C3 Reverse Playback E1E4E8E9 2~3 A1A4A2 adsorption B3 charging C5 empty E3E6E7 3~4 A2 both decreased B1B4 adsorption C3 all rose E3E6E9 4~5 A3 Reverse Playback B1B4 adsorption Vacant E1E4E8E9 5~6 A5 empty B1B4B2 adsorption C3 charging E3E6E7 6~7 A3 average rise B2 both decreased C1C4 adsorption E3E6E9 7~8 Vacant B3 reverse release C1C4 adsorption E1E4E8E9 8~9 A3 charging B5 empty C1C4C2 adsorption E3E6E7

[0237] Example 7

[0238] A method for preparing a supported metal-organic framework CO adsorbent is as follows:

[0239] (1) Co-dissolve 0.6 mmol of copper nitrate trihydrate and cerium nitrate hexahydrate in 15 mL of deionized water at a molar ratio of 19:1 to obtain a clear blue copper nitrate-cerium nitrate mixture.

[0240] (2) Dissolve 0.3 mmol of 1,3,5-pyromellitic acid (H3BTC) in a mixed solution of ethanol and dimethylformamide (DMF) in a volume ratio of 1:1 in 8 mL, add commercially available NaY molecular sieve, and the molar ratio of NaY molecular sieve to copper nitrate-cerium nitrate is 1:50.

[0241] (3) After mixing and stirring the solutions from steps (1) and (2) at room temperature for 5 min, sonicate at 150 W for 8 min, then heat to 250 °C at a heating rate of 3~5 °C / min, keep warm for 20 h, and then cool to room temperature at a cooling rate of 2 °C / min to generate a precipitate. Centrifuge and filter; wash the obtained crystals three times with anhydrous ethanol.

[0242] (4) Add 3.0 mL of 0.1 mmol / L AgNO3 ethanol solution to the obtained crystals, irradiate with ultrasound at 80 W for 1 h, soak in the dark for 12 h, centrifuge, and filter; wash the obtained crystals three times with anhydrous ethanol, and irradiate with a 100 W ultraviolet lamp for 10-13 h (so that AgNO3 is absorbed into the crystals). + Oxidized to Ag), centrifuged and washed with anhydrous ethanol, dried at 110°C, and oxidized at 250°C for 1 hour with a 2% (v / v) O2 / He mixture (so that Ag and Cu are oxidized). 2+ The reaction produces Ag + and Cu + ), flow rate 50 ml·min −1 , to obtain powder;

[0243] (5) CuCl, AgCl and rare earth powder (a mixture of yttrium, lanthanum and cerium in a mass ratio of 1:1:0.25, with molar amounts of 1 mmol / 0.1 mmol / 0.025 mmol respectively) were dissolved in 30 mL of 0.4 mol / L hydrochloric acid solution, and then 0.225 g of the powder obtained in step (4) was added. The mixture was irradiated with 100 W ultrasound for 20 min, stirred at room temperature for 2 h, and the solvent was evaporated by rotary evaporator. The mixture was then placed in a vacuum drying oven and dried for 12 h. After drying, the mixture was activated at 220 °C in H2 atmosphere for 5 h to obtain the powder material.

[0244] (6) Weigh a certain amount of the powder material obtained in step (5) above, methylcellulose and 5% citric acid aqueous solution (the mass ratio of the three added except water is 10:0.3:0.2), put them in a kneader and stir evenly, then put the mixture in a centrifugal shot blasting machine for molding, and dry the molded product at 200 ℃ to obtain round particles with a diameter of about 2 mm, which is the molded body of the supported metal-organic framework CO adsorbent.

[0245] Comparative Example 7-1

[0246] The solution in step (1) uses only copper nitrate and does not contain cerium nitrate or rare earth powders (yttrium, lanthanum, cerium), otherwise it is the same as in Example 1.

[0247] Comparative Example 7-2

[0248] In step (2), there is no NaY type molecular sieve, and everything else is the same as in Example 1.

[0249] Comparative Example 7-3

[0250] In step (5), no AgCl is added, only Cu is used. + CO adsorption, otherwise the same as in Example 1.

[0251] result:

[0252] The adsorption capacity of each adsorbent for carbon monoxide was tested using an ASAP 2020 physicochemical adsorption analyzer. The adsorbent in Example 7, used at 25°C and 0.1 MPa, had an adsorption capacity of 72 L / g for carbon monoxide. The adsorption capacities of Comparative Examples 7-1 to 7-3 were 67 mL / g, 64 mL / g, and 59 mL / g, respectively. In contrast, the adsorption capacities of conventional commercially available adsorbents range from 20 to 50 mL / g. This invention represents a significant improvement in adsorption capacity compared to existing commercially available adsorbents.

[0253] When the sulfides accumulated to 0.2% of the sulfur by weight of the adsorbent, the adsorption capacity of Example 7 decreased by 4%, the adsorption capacity of Comparative Example 7-1 decreased by 21%, and the adsorption capacity of Comparative Examples 7-2 to 7-3 decreased by 5% respectively. The adsorbent of Example 7 has good sulfur resistance.

Claims

1. A method for producing natural gas from coal gas, characterized in that, include: (1) Preparation of H2 and CO mixture gas, the preparation process includes: partial conversion of coal gas to produce hydrogen, and separation of N2 from the system by pressure swing adsorption separation method before or after the partial conversion hydrogen production step; In the process of separating N2 from the system by pressure swing adsorption separation, natural gas is used as the flushing gas to obtain a gas containing CO and natural gas for the partial conversion hydrogen production reaction. During flushing with flushing gas, a combination of high-pressure flushing and desorption, along with at least one of low-pressure flushing and vacuuming, is used to desorb CO and natural gas. The high-pressure flushing and desorption refers to a high-pressure gas with a feed flushing gas pressure of 0.3~10MPa. (2) The H2 and CO mixture undergoes a methanation reaction to produce natural gas.

2. The method for producing natural gas from coal gas according to claim 1, characterized in that, The gas mainly includes blast furnace gas or converter gas; the gas may also contain one or a mixture of two or more of the following: coke oven gas, other tail gas, or purge gas.

3. The method for producing natural gas from coal gas according to claim 1, characterized in that, Before separating CO and N2 by pressure swing adsorption, a first impurity removal pretreatment is performed, which includes one or a combination of steps such as dust removal, phosphorus removal, arsenic removal, dehydration, dehydrogenation and deoxygenation, desulfurization, CO2 removal, or CH4 removal.

4. The method for producing natural gas from coal gas according to claim 3, characterized in that, The first impurity removal pretreatment includes desulfurization and CO2 removal, wherein CO2 removal is carried out simultaneously with desulfurization or after the desulfurization step.

5. The method for producing natural gas from coal gas according to claim 4, characterized in that, The CO2 removal in the first impurity removal pretreatment is performed using absorption and / or pressure swing adsorption.

6. The method for producing natural gas from coal gas according to claim 4, characterized in that, The first impurity removal pretreatment includes: CH4 removal and / or dehydrogenation and deoxygenation; CH4 removal is performed after the desulfurization step; dehydrogenation and deoxygenation are performed after the CH4 removal step.

7. The method for producing natural gas from coal gas according to claim 1 or 3, characterized in that, After a partial shift reaction to produce hydrogen, the gas is decarbonized to obtain a mixture of H2 and CO, which is then subjected to a methanation reaction. Alternatively, the gas can be directly subjected to a methanation reaction, and the CO2 produced by the shift reaction is removed after the methanation reaction.

8. The method for producing natural gas from coal gas according to claim 1, characterized in that, Coal gas is partially converted to produce hydrogen, yielding a gas containing CO, N2, and H2. CO is then separated using pressure swing adsorption (PSA), followed by N2 and H2 separation. The separated H2 and CO are then mixed and subjected to a methanation reaction.

9. The method for producing natural gas from coal gas according to claim 8, characterized in that, Before the partial shift hydrogen production reaction, the coal gas undergoes desulfurization and / or dehydrogenation and deoxygenation; dehydrogenation and deoxygenation occur after the desulfurization step; after the partial shift hydrogen production reaction is completed, carbon dioxide is removed before pressure swing adsorption separation of CO.

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