Method for recycling PSA (Pressure Swing Adsorption) desorption gas in natural gas hydrogen production process and natural gas hydrogen production system
By using sodium hydroxide solution to absorb CO2 in the natural gas-to-hydrogen system, the greenhouse gas emissions caused by the combustion of PSA desorbed gas were solved, hydrogen production was increased and costs were reduced, achieving system decarbonization and energy conservation and emission reduction.
Patent Information
- Application Number
- CN202410755126.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-06-12
- Publication Date
- 2025-12-12
AI Technical Summary
In existing natural gas-to-hydrogen methods, the combustion of PSA stripped gas at distributed hydrogen refueling stations results in high greenhouse gas emissions, low hydrogen yield, and additional treatment of flue gas generated during combustion, increasing costs.
The CO2 in the PSA annealed gas is absorbed by sodium hydroxide solution absorbent, and the annealed gas after CO2 removal is recycled back to the natural gas reforming process to prepare soda and sodium bicarbonate, thereby realizing the recovery and utilization of CO2 and avoiding combustion treatment.
It achieves zero emissions in the natural gas-to-hydrogen system, improves hydrogen production rate and utilization rate of raw natural gas, reduces hydrogen production costs, and simplifies the operation process.
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Figure CN121107356A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of hydrogen production, in particular to a method for recycling PSA desorption gas in a natural gas hydrogen production process and a natural gas hydrogen production system. BACKGROUND
[0002] At present, energy transformation characterized by diversification, cleanization and low carbonization is imminent. Hydrogen energy is an important carrier for green and low-carbon transformation of energy terminal. Hydrogen filling station is an important infrastructure for hydrogen energy transportation, which is an important hub linking upstream hydrogen production and transportation and downstream fuel cell vehicle application. The hydrogen supply mode of hydrogen filling station (hydrogen filling station) includes centralized hydrogen supply mode and distributed hydrogen supply mode, among which distributed hydrogen supply mode is increasingly concerned because it can minimize the high cost and safety risk brought by hydrogen storage and transportation. Distributed hydrogen production is divided into methanol hydrogen production, natural gas hydrogen production, alkaline water electrolysis hydrogen production, PEM water electrolysis hydrogen production and ammonia decomposition hydrogen production.
[0003] The distributed natural gas hydrogen filling station uses the product gas after reforming and shifting of raw natural gas as fuel, in addition to hydrogen, the product gas also contains unreacted methane, CO and CO2. In order to obtain product hydrogen with a purity of 99.99%, a pressure swing adsorption (PSA) device is needed to purify the product. High-purity hydrogen flows out from the outlet through the adsorption layer, and after reaching the required purity (more than 99.9%), it is used as product hydrogen. Other gases are adsorbed by the adsorbent of the PSA device. The adsorption tower after adsorbing impurities is desorbed by decompression, reverse release and pressure flushing operation to complete regeneration and realize the adsorption and regeneration cycle of the adsorbent. The released PSA desorption gas contains about 48% CO2, about 5% CO, about 20% CH4 and about 27% H2 in volume.
[0004] The current distributed natural gas hydrogen filling station sets a burner inside the reforming converter that can meet the simultaneous combustion of natural gas and PSA desorption gas. The PSA desorption gas is sent back to the natural gas reforming section and burned with the supplemented natural gas in the burner of the reforming converter to provide the heat required for the strong endothermic natural gas reforming reaction. The PSA desorption gas treatment method used in this distributed natural gas hydrogen filling station is to send it to the natural gas reforming section as fuel, and the hydrogen in it is also burned as fuel, which is not conducive to improving hydrogen yield and reducing production cost. In addition, the flue gas produced by combustion contains a large amount of greenhouse gases such as carbon dioxide, sulfur dioxide, nitrogen oxides and smoke dust, which must be recovered and treated.
[0005] Therefore, there is an urgent need for a distributed natural gas hydrogen production hydrogen filling station coupled with a carbon dioxide capture system to improve hydrogen yield and reduce carbon dioxide emissions. SUMMARY
[0006] The present application aims to overcome the problems of high greenhouse gas emissions and low hydrogen yield in the prior art distributed natural gas hydrogen production hydrogenation station, and provides a PSA resolved gas recycling method in a natural gas hydrogen production process and a natural gas hydrogen production system. The method uses sodium hydroxide solution absorbent to absorb CO2 in the PSA resolved gas, and the resolved gas after CO2 removal is sent to the natural gas reforming process for recycling, increasing the yield of product hydrogen and improving the utilization rate of raw material natural gas. The sodium hydroxide solution absorbing CO2 can be prepared into soda and / or baking soda for recycling, achieving zero greenhouse gas emissions.
[0007] To achieve the above-mentioned purpose, the first aspect of the present application provides a PSA resolved gas recycling method in a natural gas hydrogen production process, which comprises the following steps:
[0008] (1) Contacting raw material natural gas, water vapor and resolved gas after CO2 removal to occur a reforming reaction, and performing a shift reaction on the obtained reforming gas to obtain a crude hydrogen product, and separating the high-purity hydrogen product and the resolved gas by PSA pressure swing adsorption;
[0009] (2) Contacting the resolved gas with sodium hydroxide solution for CO2 absorption, and recycling the resolved gas after CO2 removal to step (1); and recycling the sodium hydroxide solution after absorbing CO2 to prepare edible soda and / or baking soda.
[0010] The second aspect of the present application provides a natural gas hydrogen production system, which comprises a reforming unit, a shift unit, a PSA pressure swing adsorption unit, a CO2 absorption unit, an alkali solution collecting unit and a resolved gas booster;
[0011] The reforming unit is used for reforming raw material natural gas and water vapor to produce reforming gas;
[0012] The shift unit is used for shifting water vapor and CO in the reforming gas into H2 and CO2 to obtain shift gas;
[0013] The PSA pressure swing adsorption unit is used for separating the shift gas to obtain hydrogen product and resolved gas;
[0014] The CO2 absorption unit is used for removing CO2 in the resolved gas to obtain resolved gas after CO2 removal;
[0015] The alkali solution collecting unit is used for collecting sodium hydroxide solution after absorbing CO2;
[0016] The resolved gas booster is used for introducing the resolved gas after CO2 removal into the reforming unit.
[0017] The PSA desorption gas (CO2 volume content is about 48%, CO volume content is about 5%, CH4 volume content is about 20%, and volume content is about 27%) contains CO2 gas, the heat value of the desorption gas is low, as a fuel for the natural gas reforming reaction, not only a large amount of combustion value is lost, but also the amount of flue gas and the load of the induced draft fan are increased, the H2 product and the intermediate product CO are wasted, and the CO2 gas generated by combustion still needs to be recovered and treated, which is not conducive to improving the yield of the product hydrogen and has a high production cost. However, the additional CO2 removal treatment of the PSA desorption gas before entering the natural gas reforming reaction process is not found in the traditional natural gas hydrogen production process, on the one hand, because the existing CO2 removal treatment process is complex, the equipment is more, the distributed natural gas hydrogen production station has a small area, the hydrogen production amount is small, the amount of PSA desorption gas to be treated is small, and the input-output ratio is too low; on the other hand, the existing CO2 removal technology, such as the low-temperature methanol washing technology, needs to regenerate the absorbent after removing CO2 for recycling, and the CO2 gas is desorbed, and the CO2 gas discharged by fuel heating, so that the carbon zero emission of the hydrogenation station cannot be achieved, and thus the CO2 in the desorption gas does not need to be removed.
[0018] Through the above technical scheme, the present application has the following beneficial effects:
[0019] (1) The natural gas hydrogen production process and the PSA desorption gas recycling method provided by the present application, by absorbing CO2 in the desorption gas with a sodium hydroxide solution absorbent, the desorption gas after removing CO2 is introduced into the natural gas reforming reaction process for recycling, compared with the prior art, the desorption gas does not need to be burned as a fuel, greenhouse gas zero emission of the distributed natural gas reforming hydrogenation station is achieved; and the hydrogen, CO and methane contents in the desorption gas after removing CO2 are high, the desorption gas is recycled back to the reforming section, the yield of the product hydrogen is improved, and the utilization rate of the raw material natural gas is improved.
[0020] (2) The natural gas hydrogen production process and the PSA desorption gas recycling method provided by the present application, the desorption gas obtained by PSA pressure swing adsorption separation is contacted with a sodium hydroxide solution for CO2 absorption, the sodium hydroxide solution after absorbing CO2 is recycled and used to directly prepare edible baking soda and / or soda, CO2 zero emission is achieved in the entire natural gas hydrogen production system, compared with the traditional natural gas hydrogen production process, the natural gas conversion rate reaches 100%, low carbonization of the natural gas hydrogen production process and energy saving and emission reduction of the system are achieved, the operation is simple, and the cost is low.
[0021] (3) The natural gas hydrogen production process and the PSA desorption gas recycling method provided by the present application, preferably, the heat of the natural gas reforming reaction is fully recycled, heat loss is reduced, energy saving is achieved, system energy consumption and hydrogen production cost are reduced, and energy utilization efficiency is improved. Attached Figure Description
[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof.
[0023] Figure 1 This is a process flow diagram of the present invention.
[0024] Explanation of reference numerals in the attached figures
[0025] 1. Raw material natural gas; 2. Desulfurized natural gas; 3. Mixed gas for reforming.
[0026] 4. Reformed gas 5. Raw water 6. Steam
[0027] 7. Crude hydrogen product 8. High-purity hydrogen product 9. Desorption gas
[0028] 10. CO2-removed stripped gas 11. Alkali solution after CO2 absorption 12. NaHCO3 solution I. Natural gas desulfurization unit II. Reforming unit III. Steam generation unit IV. Shift converter V. PSA pressure swing adsorption unit VI. Hydrogen buffer tank VII. Desorbed gas buffer tank VII. CO2 absorption unit IX. Desorbed gas booster X. Alkali solution collection unit XI. Alkali solution pump Detailed Implementation
[0029] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0030] The first aspect of this invention provides a method for recovering and utilizing PSA stripping gas in a natural gas-to-hydrogen process, the method comprising the following steps:
[0031] (1) The raw material natural gas, steam and CO2-removed desorbed gas are contacted to undergo a reforming reaction. The resulting reformed gas is subjected to a shift reaction to obtain crude hydrogen product. High-purity hydrogen product and desorbed gas are obtained by PSA pressure swing adsorption separation.
[0032] (2) The desorbed gas is contacted with sodium hydroxide solution to absorb CO2, and the desorbed gas after CO2 removal is recycled to step (1); the sodium hydroxide solution after CO2 absorption is recovered to prepare edible baking soda and / or sodium bicarbonate.
[0033] In the traditional hydrogen production method from natural gas, the PSA desorption gas (containing CO2, H2, CO and CH4) is used as fuel to be sent into the natural gas reforming process for combustion to provide the required heat for the reforming reaction, which wastes H2 product and intermediate product CO, and the flue gas generated by combustion contains a large amount of greenhouse gas. The inventors of the present application found in the research process that, after removing CO2 in the PSA desorption gas with a sodium hydroxide solution as the absorbent, the desorption gas is introduced into the natural gas reforming process, combustion is not needed in the natural gas reforming process, methane gas participates in the reforming reaction again, and hydrogen and carbon monoxide can be recycled and utilized, which greatly increases the yield of product hydrogen and improves the utilization rate of raw material natural gas; and the removed CO2 is prepared into soda and / or baking soda for recycling and utilization, achieving zero emission of greenhouse gas. The method is simple and easy to implement, has low cost, and has wide application prospect.
[0034] In the present application, the source and form of the raw material natural gas are not particularly limited. For example, the natural gas can be at least one natural gas body with methane as the main component selected from oil and gas wellhead natural gas, long-distance pipeline natural gas, domestic pipeline natural gas, CNG and LNG.
[0035] In the present application, the content of sulfur in the raw material natural gas is not particularly limited. Preferably, the content of sulfur in the desulfurized natural gas is not higher than 0.1 ppm. Controlling the content of sulfur in the desulfurized natural gas in the above range is beneficial to making the desorption gas obtained by subsequent PSA (pressure swing adsorption) not containing impurities such as sulfur dioxide, nitrogen oxides and smoke dust, thereby being beneficial to recycling the absorbent for absorbing CO2 to prepare edible soda and baking soda products.
[0036] In the present application, when the content of sulfur in the raw material natural gas is higher than 0.1 ppm, preferably, the method further comprises desulfurizing the raw material natural gas. The method of desulfurization is not particularly limited and can be a method of desulfurizing raw material natural gas commonly used in the art. Preferably, the method of desulfurization comprises contacting the raw material natural gas with a desulfurization adsorbent to obtain desulfurized natural gas. The type of adsorbent used in the desulfurization process is not particularly limited and can be various adsorbents commonly used in the art for desulfurization, as long as the content of sulfur in the obtained desulfurized natural gas is not higher than 0.1 ppm. In the present application, the conditions of desulfurization are not particularly limited and can be the conditions of desulfurizing raw material natural gas commonly used in the art.
[0037] In the present application, the content of sulfur in the desulfurized natural gas is tested by a gas chromatograph without particular specification.
[0038] In the present application, preferably, step (1) further comprises heating and vaporizing raw water to obtain water vapor.
[0039] In the present application, the source of the raw water is not particularly limited, for example, the raw water can be selected from at least one of deionized water, urban and rural tap water, underground water and industrial circulating water.
[0040] In the present application, the method of heating and vaporizing the raw water is not particularly limited, and the method of heating and vaporizing water commonly used in the art can be used. For example, at least one of electric heating, heat transfer oil furnace heating, steam heating and heat exchange with other materials can be used. Preferably, the heat released by the natural gas reforming reaction provides the process of vaporizing the raw water to obtain water vapor. The method of the present application uses H2, CH4, CO, CO2 obtained by the reforming reaction to provide heat for the generation of water vapor, saving the energy consumption of water heating and vaporization, and saving cost.
[0041] In the present application, the temperature and pressure of the water vapor obtained by heating and vaporizing the raw water are not particularly limited, for example, the temperature of the water vapor is 158-300℃, and the pressure of the water vapor is 0.5-3.3 MPa.
[0042] In the present application, part of the water vapor can enter the reforming reaction process, and the other part can enter the shift reaction process, or all of the water vapor can enter the reforming reaction process. Preferably, all of the water vapor enters the reforming reaction process.
[0043] In the present application, preferably, in step (1), the raw gas for the reforming reaction includes raw natural gas, water vapor and desorbed gas after removal of CO2. The reforming reaction refers to the process of reacting methane and water vapor in the raw gas to generate hydrogen and carbon dioxide to form reforming gas. Preferably, the reforming gas includes methane, water vapor, hydrogen, carbon monoxide and carbon dioxide.
[0044] In the present application, the conditions of the reforming reaction are not particularly limited, and the conditions of the natural gas reforming reaction commonly used in the art can be used. Preferably, the conditions of the reforming reaction include: in the presence of a catalyst, the reforming reaction pressure is 1.5-3 MPa, and the reforming reaction temperature is 800-900℃; the gas space velocity is 1000-1350 h -1 .
[0045] In the present application, the ratio of the raw gas has a wide selection range. Preferably, the molar ratio of carbon to hydrogen in the raw gas for the reforming reaction is 0.5-3, more preferably 1.5-3. In the present application, unless otherwise specified, the molar ratio of carbon to hydrogen refers to the molar ratio of methane to water vapor. The raw gas refers to the raw natural gas and water vapor in step (1).
[0046] In the present application, the source of heat required for the reforming reaction is not particularly limited. For example, the heat required for the reforming reaction can be provided by at least one of electric heating, heating by a heat conducting oil furnace, heating by steam, and heat exchange with other materials. Preferably, the heat required for the reforming reaction is provided by an external electric heating system.
[0047] In the conventional natural gas reforming method in the art, a burner is provided in the natural gas reforming process, and the natural gas, steam, and PSA desorbed gas (containing CO2, H2, and CO) are combusted simultaneously to provide the heat required for the natural gas reforming reaction. In the present application, the desorbed gas after removal of CO2 from the raw material gas does not contain CO2, and the reforming reaction does not need to be subjected to a combustion process, and the heat required for the reforming reaction is provided by electric heating, which not only improves the hydrogen yield and the raw material utilization rate, but also eliminates the emission of CO2 gas.
[0048] In the present application, the type of catalyst used in the reforming reaction is not particularly limited, and can be any catalyst for natural gas reforming reaction commonly used in the art. For example, the catalyst for the reforming reaction can be a nickel oxide catalyst.
[0049] In the present application, in step (1), the shift reaction refers to a process in which carbon monoxide and steam in the reforming gas are reacted to generate hydrogen and carbon dioxide, thereby forming a crude hydrogen product. Preferably, the crude hydrogen product comprises hydrogen, carbon monoxide, steam, methane, and carbon dioxide.
[0050] In the present application, the conditions for the shift reaction are not particularly limited, and can be any conditions for CO shift reaction commonly used in the art. Preferably, the conditions for the shift reaction comprise: in the presence of a catalyst, the shift reaction temperature is 180°C-260°C, the shift reaction pressure is 2.5 MPa-3.5 MPa, the gas hourly space velocity is 2000 h-3000 h, and the hydrogen content in the crude hydrogen product is 70% or more. -1 -3000 h -1 .
[0051] In the present application, the type of catalyst used in the CO shift reaction is not particularly limited, and can be any catalyst for CO shift reaction commonly used in the art. Preferably, the catalyst for the shift reaction is selected from a copper-zinc-chromium-based catalyst and / or a copper-zinc-aluminum-based catalyst.
[0052] In the present application, in step (1), the crude hydrogen product enters the PSA pressure swing adsorption process for hydrogen purification, releases a high-purity hydrogen product, and the remaining gas is adsorbed by the adsorbent of the PSA pressure swing adsorption process, and the impurities are desorbed by pressure reduction, reverse release, and stamping operation, and the adsorbent is regenerated, thereby realizing the adsorption and regeneration cycle of the adsorbent and releasing the desorbed gas.
[0053] In the present application, preferably, the method further comprises introducing the high-purity hydrogen product into a hydrogen buffer tank, and then storing and filling after pressurization. The purity of the hydrogen product reaches 99.99%, meeting the requirements of high-purity hydrogen. In the present application, the purity of the hydrogen product is tested by a gas chromatograph unless otherwise specified.
[0054] In the present application, the desorption gas obtained by the PSA comprises hydrogen, carbon monoxide, methane and carbon dioxide. The content of each gas in the desorption gas is not particularly limited, and preferably, the content of hydrogen in the desorption gas is 25% to 28% by volume, the content of methane is 18% to 22% by volume, the content of carbon monoxide is 4% to 6% by volume, and the content of carbon dioxide is 46% to 52% by volume.
[0055] In the present application, the conditions of the PSA are not particularly limited, and the conditions of the PSA commonly used in the art can be used. Preferably, the conditions of the PSA include a temperature of 40-80℃ and a pressure of 1.2-3.1 MPa.
[0056] In the present application, the adsorbent for the PSA is not particularly limited, and the adsorbent commonly used in the art can be used. For example, the adsorbent for the PSA can be selected from activated alumina and / or activated carbon.
[0057] In the present application, preferably, in step (2), the method further comprises introducing the desorption gas obtained by the PSA into a desorption gas buffer tank for buffering before CO2 absorption.
[0058] In the present application, in step (2), the CO2 absorption is a neutralization reaction between the desorption gas and a sodium hydroxide solution to remove CO2 in the desorption gas.
[0059] In the conventional method, the PSA desorption gas is not treated for removing CO2 before entering the natural gas reforming reaction process. On the one hand, the existing CO2 removal process is complex and requires many devices. The distributed natural gas hydrogen station has a small area and produces a small amount of hydrogen, and the amount of PSA desorption gas to be treated is also small, and the input-output ratio is too low. On the other hand, using the existing CO2 removal technology, such as the low-temperature methanol washing technology, the absorbent after removing CO2 needs to be regenerated for recycling, and CO2 gas is also desorbed. In addition, the CO2 gas discharged by fuel heating is difficult to achieve zero carbon emission of the hydrogen station, so the CO2 in the desorption gas is not removed.
[0060] The inventors of the present application found in the research process that the hydrogen and carbon monoxide in the resolved gas are difficult to dissolve in water, the solubility of methane in water is extremely low (3.5 mg / 100 mL) at 17℃, only CO2 is slightly soluble in water, and part of CO2 forms carbonic acid in water, which is a weak acid. In order to improve the solubility of CO2 in water, the present application uses sodium hydroxide solution as an absorbent to absorb CO2, and hydrogen, carbon monoxide and methane do not react with the base in the sodium hydroxide solution. The separation of CO2 gas in the resolved gas can be realized at room temperature (25℃), and the resolved gas after removing CO2 is obtained. Then, the resolved gas after removing CO2 is introduced into the reforming reaction process of step (1) as raw gas for recycling; and the sodium hydroxide solution (sodium bicarbonate solution) absorbing CO2 can be recycled. This method does not need to remove CO2 by adsorption at high or low temperature, and the whole process does not emit CO2 gas.
[0061] In the present application, the sodium hydroxide solution refers to a liquid caustic soda with a solubility of 30-32wt% unless otherwise specified. The sodium hydroxide solution of the present application can be commercially available or prepared by the prior art. The sodium hydroxide solution is used as a CO2 absorbent to absorb CO2 in the resolved gas. Sodium hydroxide reacts with a large amount of CO2 to generate sodium bicarbonate. The sodium bicarbonate solution is recycled to obtain edible soda and baking soda, avoiding the problem of recycling the CO2 released by the absorbent after absorbing CO2 in the regeneration process. The CO2 generated in the whole natural gas hydrogen production process is completely recycled, and the sodium hydroxide solution adsorbent is cheap and easy to obtain.
[0062] In the present application, the method for preparing soda and / or baking soda from the recovered sodium hydroxide solution absorbing CO2 is not particularly limited, and the conventional method for preparing sodium bicarbonate solution into soda and / or baking soda in the art can be used, for example, the method of evaporation crystallization can be used. Preferably, the recovered sodium hydroxide solution absorbing CO2 is transported to the alkali liquid centralized treatment point in the city by tank car, and evaporated to produce edible baking soda and soda needed for urban residents, completely solving the problem of greenhouse gas emission in hydrogenation station.
[0063] In the present application, the content of hydrogen, carbon monoxide and methane in the desorption gas after removal of CO2 is not particularly limited. Preferably, the content of hydrogen in the desorption gas after removal of CO2 is 45% to 55% by volume, the content of methane is 30% to 40% by volume, and the content of carbon monoxide is 5% to 15% by volume. More preferably, the content of hydrogen in the desorption gas after removal of CO2 is 48% to 53% by volume, the content of methane is 36% to 39% by volume, and the content of carbon monoxide is 8.5% to 10% by volume. The content of high-calorific-value components in the desorption gas after removal of CO2 is greatly increased, which is recycled to the natural gas reforming section, thereby increasing the yield of product hydrogen and improving the utilization rate of raw material natural gas.
[0064] In the present application, the components in the desorption gas after removal of CO2 and their contents are tested by a gas chromatograph.
[0065] The second aspect of the present application provides a natural gas hydrogen production system, which comprises a reforming unit, a shift unit, a PSA unit, a CO2 absorption unit, a caustic solution collecting unit and a desorption gas booster;
[0066] The reforming unit is used for carrying out a reforming reaction on raw material natural gas and steam to produce a reforming gas;
[0067] The shift unit is used for shifting steam and CO in the reforming gas into H2 and CO2 to obtain a shift gas;
[0068] The PSA unit is used for separating the shift gas to obtain a hydrogen product and a desorption gas;
[0069] The CO2 absorption unit is used for removing CO2 from the desorption gas to obtain a desorption gas after removal of CO2;
[0070] The caustic solution collecting unit is used for collecting sodium hydroxide solution after absorption of CO2;
[0071] The desorption gas booster is used for introducing the desorption gas after removal of CO2 into the reforming unit.
[0072] In the present application, the reforming unit can be various natural gas reforming reaction devices commonly used in the art, for example, it can be a natural gas reforming reactor; the shift unit can be various CO shift reaction devices commonly used in the art, for example, it can be a CO shift tower.
[0073] In some embodiments of the present application, preferably, the system further comprises a natural gas desulfurization unit for removing sulfur compounds in the raw material natural gas to obtain desulfurized natural gas. In the present application, the natural gas desulfurization unit can be various natural gas desulfurization devices commonly used in the art, for example, it can be a desulfurization tower.
[0074] In some embodiments of the present application, preferably, the system further comprises a water vapor generating unit for heating water to generate water vapor. In the present application, the water vapor generating unit can be any device for generating water vapor commonly used in the art, for example, it can be a water vapor generator.
[0075] In some embodiments of the present application, preferably, the system further comprises an alkali liquor pump for introducing the alkali liquor after absorbing CO2 into the CO2 absorption unit to circulate and absorb CO2. In the present application, the CO2 absorption unit can be any device for absorbing CO2 commonly used in the art, for example, it can be a CO2 absorption tower.
[0076] In some embodiments of the present application, preferably, the reforming unit is in communication with the water vapor generating unit, and the heat generated by the reforming unit is supplied to the water vapor generating unit for heating water to generate water vapor. In the present application, the H2, CH4, CO, CO2 obtained by the reforming reaction provide heat for the generation of water vapor, saving the energy consumption of water heating vaporization and saving costs.
[0077] The method and system of the present application are described below in combination with Figure 1 and preferred embodiments of the present application:
[0078] a) subjecting the raw natural gas 1 to desulfurization treatment by the natural gas desulfurization unit I to obtain desulfurized natural gas 2, wherein the content of sulfur in the desulfurized natural gas is not higher than 0.1 ppm; and subjecting the raw water 5 to vaporization by the water vapor generating unit III to obtain water vapor 6;
[0079] d) subjecting the mixed gas 3 composed of the desulfurized natural gas 2, the water vapor 6 and the resolved gas 10 after removing CO2 to reforming reaction by the reforming unit II in the presence of a catalyst to obtain the reforming gas 4, wherein the heat required by the reforming reaction is provided by an external electric heating system; and using the heat released by the natural gas reforming reaction to provide the process of vaporizing the raw water to obtain water vapor;
[0080] c) using the heat of the reforming gas 4 to provide the process of heating and vaporizing the raw water 5 to obtain water vapor 6, after cooling by the water vapor generating unit III, introducing the water vapor 6 into the reforming unit II to participate in the reforming reaction, introducing the reforming gas 4 into the shift conversion unit IV to perform shift conversion reaction, and separating the obtained crude hydrogen product 7 by the PSA pressure swing adsorption unit V to obtain high-purity hydrogen product 8 and resolved gas 9; and buffering the high-purity hydrogen product 8 by the hydrogen buffer tank VI, and storing and refueling after pressurization;
[0081] d) the desorption gas 9 is buffered by the desorption gas buffer tank VII and then sent to the CO2 absorption unit VIII, the desorption gas 9 is contacted with the alkali liquor absorbent to absorb CO2, the desorption gas 10 after removing CO2 is introduced into the reforming unit II by the desorption gas booster IX for recycling; the alkali liquor 11 after absorbing CO2 is introduced into the alkali liquor collecting unit X and then sent to the CO2 absorption unit VIII by the alkali liquor pump XI for recycling, when the PH value of the alkali liquor in the alkali liquor collecting unit X reaches about 8, the NaHCO3 solution 12 is recovered to prepare edible baking soda and soda;
[0082] In the desorption gas 10 after removing CO2, the content of hydrogen is 45% to 55% by volume, the content of methane is 30% to 40% by volume, and the content of carbon monoxide is 5% to 15% by volume.
[0083] The application will be described in detail below by way of examples.
[0084] In the following examples, the experimental methods used are conventional methods unless otherwise specified. In the following examples, the raw materials, reagents, etc. used are commercially available unless otherwise specified.
[0085] Example 1
[0086] (1) The raw material natural gas is sent to a desulfurization process to contact with a desulfurizer (coarse desulfurization and fine desulfurization) to perform natural gas desulfurization treatment, and 360℃, 3MPa, 450Nm 3 / h desulfurized natural gas with a sulfur content of 0.1ppm is obtained; the raw material water is heated and vaporized in a water vapor generation unit to obtain 300℃, 3.3MPa, 1350Nm 3 / h water vapor;
[0087] (2) The desulfurized natural gas, water vapor and the desorption gas after removing CO2 are sent together to a reforming reactor to perform reforming reaction, the gas space velocity is 1000h -1 , the carbon-hydrogen molar ratio is 3, and 800℃, 3MPa, 2700Nm 3 / h reforming gas is obtained, and the required heat is provided by an electric heating system;
[0088] (3) The reforming gas enters a water vapor generation unit to exchange heat with the raw material water, the raw material water absorbs heat to generate water vapor, and the water vapor enters the reforming unit; the reforming gas enters a shift conversion unit to perform CO shift conversion, and 250℃, 3MPa, 2700Nm 3 / h crude hydrogen gas product is obtained, the crude hydrogen gas product is cooled after heat exchange and then enters a PSA pressure swing adsorption unit to perform purification, and 40℃, 2.1MPa, 1500Nm 3 / h hydrogen gas product (with a purity of 99.99%) and 40℃, 0.05MPa, 750Nm3 / h of the resolved gas;
[0089] (4) The hydrogen product is buffered by a hydrogen buffer tank, then sent to a hydrogen filling section for pressurization and storage, and filling; the resolved gas is buffered by a resolved gas buffer tank, then sent to a CO2 absorption unit, and contacted with a sodium hydroxide solution (concentration of 32wt%) countercurrently at normal temperature (about 25℃) and normal pressure, so that the CO2 in the resolved gas is absorbed, and 20℃, 0.05MPa, 390Nm 3 / h of the resolved gas after removal of CO2. The resolved gas after removal of CO2 is introduced into a reforming reaction process by a desorbed gas booster for recycling; the alkali solution after absorption of CO2 is recycled back to the CO2 absorption unit to continue to react with CO2 in the resolved gas until the pH is 8. The recovered Na2CO3 solution and NaHCO3 solution are prepared into soda and baking soda, wherein the H2 content in the resolved gas after removal of CO2 is 51.92vol%, the CO content is 9.62vol%, and the CH4 content is 38.46vol%.
[0090] The hydrogen production capacity of the natural gas hydrogen production system described in the embodiment is 1700Nm 3 / h, the entire system has zero CO2 emission, the hydrogen production rate is increased by 11.9% compared with the traditional process, and the CO2 emission is zero.
[0091] The preferred embodiments of the application are described in detail above, but the application is not limited thereto. Within the technical concept of the application, various simple modifications can be made to the technical solutions of the application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the application, and all fall within the protection scope of the application.
Claims
1. A method for recovering and utilizing PSA stripping gas in a natural gas-to-hydrogen process, characterized in that, The method includes the following steps: (1) The raw material natural gas, steam and CO2-removed desorbed gas are contacted to undergo a reforming reaction. The resulting reformed gas is subjected to a shift reaction to obtain crude hydrogen product. High-purity hydrogen product and desorbed gas are obtained by PSA pressure swing adsorption separation. (2) The desorbed gas is contacted with sodium hydroxide solution to absorb CO2, and the desorbed gas after CO2 removal is recycled to step (1); the sodium hydroxide solution after CO2 absorption is recovered to prepare edible baking soda and / or sodium bicarbonate.
2. The method according to claim 1, wherein, The desorbed gas after CO2 removal contains 45% to 55% hydrogen, 30% to 40% methane, and 5% to 15% carbon monoxide. Preferably, the hydrogen content in the desorbed gas after CO2 removal is 48% to 53% by volume, the methane content is 36% to 39% by volume, and the carbon monoxide content is 8.5% to 10% by volume.
3. The method according to claim 1 or 2, wherein, The conditions for the reforming reaction include: in the presence of a catalyst, a reforming reaction pressure of 1.5-3 MPa, a reforming reaction temperature of 800-900 °C, and a gas hourly space velocity of 1000-1350 h⁻¹. -1 ; Preferably, the carbon-hydrogen molar ratio in the reforming reaction feed gas is 0.5-3, and more preferably 1.5-3.
4. The method according to any one of claims 1-3, wherein, The conditions for the shift reaction include: in the presence of a catalyst, a shift reaction temperature of 180-260℃, a shift reaction pressure of 2.5-3.5 MPa, and a gas hourly space velocity of 2000-3000 h⁻¹. -1 .
5. The method according to any one of claims 1-4, wherein, The conditions for PSA pressure swing adsorption include: a pressure swing adsorption temperature of 40-80℃ and a pressure swing adsorption of 1.2-3.1 MPa. Preferably, the adsorbent for the PSA pressure swing adsorption is selected from activated alumina and / or activated carbon.
6. The method according to any one of claims 1-5, wherein, The heat required for the reforming reaction is provided by an external electric heating system.
7. The method according to any one of claims 1-6, wherein, Step (1) also includes heating and vaporizing the raw water to obtain water vapor; Preferably, the heat released from the natural gas reforming reaction is used in the process of vaporizing the raw material water to obtain water vapor.
8. A natural gas-to-hydrogen system, characterized in that, It includes a reforming unit, a conversion unit, a PSA pressure swing adsorption unit, a CO2 absorption unit, an alkaline liquid collection unit, and a desorbed gas booster; The reforming unit is used to reform the raw material natural gas and steam to produce reformed gas. The conversion unit is used to convert water vapor and CO in the reformed gas into H2 and CO2 to obtain the reformed gas. The PSA pressure swing adsorption unit is used to separate the shift gas to obtain hydrogen product and desorption gas; The CO2 absorption unit is used to remove CO2 from the desorption gas to obtain desorption gas after CO2 removal; The alkaline solution collection unit is used to collect the sodium hydroxide solution after absorbing CO2. The desorbed gas booster is used to introduce the desorbed gas after CO2 removal into the reforming unit.
9. The system according to claim 8, wherein, The system also includes a natural gas desulfurization unit for removing sulfur compounds from the raw natural gas to obtain desulfurized natural gas; Preferably, the system further includes a steam generating unit for heating water to vaporize it and obtain steam; Preferably, the system further includes an alkaline solution pump for introducing the alkaline solution after CO2 absorption into the CO2 absorption unit for cyclic absorption of CO2.
10. The system according to claim 9, wherein, The reforming unit is connected to the steam generating unit and is used to supply the heat generated by the reforming unit to the steam generating unit for water heating and vaporization.