System for co-production of ammonia and lng by calcium carbide furnace gas for methanol synthesis

Abstract

The utility model discloses a calcium carbide furnace gas methanol co-production synthetic ammonia and LNG's system, including shift device, decarburization device, depth purification device, methanol synthesis rectification device, methanation device, TSA device, PSA device, cryogenic separation device, synthetic ammonia device, shift device, decarburization device, depth purification device, methanol synthesis rectification device, methanation device, TSA device, PSA device are connected in proper order, and the PSA device is connected in proper order in synthetic ammonia device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper order in the PSA device and is connected in proper.

Description

Technical Field

[0001] This utility model relates to the field of resource utilization of calcium carbide furnace gas, and in particular to a system for producing methanol, synthetic ammonia and LNG from calcium carbide furnace gas. Background Technology

[0002] Calcium carbide furnace gas contains CO and H2, so a good approach to its resource utilization is to use it for methanol synthesis. However, because the gas composition of calcium carbide furnace gas differs significantly from that of gasified coal gas and coke oven gas, its hydrogen-to-carbon ratio is too low to fully utilize the raw material. Therefore, unlike traditional coal-to-methanol processes, calcium carbide furnace gas requires significant conversion and decarbonization processes to adjust the hydrogen-to-carbon ratio before methanol synthesis. Similar to methanol production from other feedstock gases, the calcium carbide furnace gas-to-methanol process also generates a large amount of methanol purge gas, at a rate of 800 Nm³ / ton for every ton of methanol produced. 3 ~900Nm 3 The methanol purge gas has the following volume ratios for its various gas components: H2 – 70%~75%; N2 – 20%~25%; CO + CO2 — 3%~8%; The methanol off-gas contains the highest amount of H2. Previous treatment methods typically involved purifying the H2 using conventional adsorption and pressure swing adsorption, followed by direct combustion of the resulting exhaust gas. However, this exhaust gas contains a large amount of carbon compounds, and direct combustion would inevitably exacerbate carbon emissions and energy waste. Therefore, the reuse of methanol off-gas is also essential.

[0003] Chinese patent CN208617726U discloses a system for the combined production of methanol, liquefied natural gas (LNG), and synthetic ammonia from semi-coke tail gas. The system includes a gas pretreatment unit, a conversion unit, a decarbonization unit, a methanol synthesis and distillation unit, a methanation unit, a cryogenic separation unit, and a synthetic ammonia unit, all connected sequentially by pipelines. It uses semi-coke tail gas, which has a high nitrogen content and low calorific value, as raw material, and processes H2, CO, CO2, and N2 within it. The system converts the gas into methanol, liquefied natural gas (LNG), and synthetic ammonia. While the unit's structure and production process are simple and easy to operate and control, several issues exist: 1. The lack of a dehydration unit and a PSA unit after the methanation unit means that the converted methane gas carries a large amount of moisture after methanation. This moisture can cause severe icing and blockage of pipelines and equipment during subsequent cryogenic separation. PSA separation and desorption concentrates the methane gas, improving cryogenic separation efficiency. The absence of a PSA unit hinders this process. 2. Due to the low CO content (approximately 10%) in the semi-coke tail gas, the conversion unit uses a sulfur-intolerant catalytic isothermal conversion method. This method is sensitive to sulfides in the feed gas, requires careful temperature control, and has a limited conversion capacity. The high CO content in the calcium carbide furnace gas necessitates a large conversion capacity, resulting in more exothermic reactions and making precise temperature control difficult. Therefore, the conversion process used in this unit is unsuitable for calcium carbide furnace gas conversion applications. Summary of the Invention

[0004] Based on the problems existing in the prior art, the purpose of this utility model is to provide a system for producing methanol from calcium carbide furnace gas and co-producing synthetic ammonia and LNG. While using calcium carbide furnace gas to produce methanol, the system uses the H2, N2, CO, and CO2 contained in the methanol off-gas to produce liquid ammonia and LNG products. The aim is to achieve high-value comprehensive utilization of calcium carbide furnace gas and reduce carbon emissions and energy waste.

[0005] This utility model is implemented using the following solution: A system for producing methanol, synthetic ammonia, and LNG from calcium carbide furnace gas includes a shift converter, a decarbonization unit, a deep purification unit, a methanol synthesis distillation unit, a methanation unit, a TSA unit, a PSA unit, a cryogenic separation unit, and a synthetic ammonia unit. The inlet of the shift converter is connected to the calcium carbide furnace gas inlet pipeline. The shift converter, decarbonization unit, deep purification unit, methanol synthesis distillation unit, methanation unit, TSA unit, and PSA unit are connected in sequence. The outflow gas outlet of the PSA unit is connected to the synthetic ammonia unit. The desorbed gas outlet of the PSA unit is connected to the cryogenic separation unit. The non-condensable gas outlet of the cryogenic separation unit is connected to the inlet of the PSA unit.

[0006] Furthermore, the acid gas release pipeline of the decarbonization device is connected to the sulfur recovery and carbon dioxide recovery system.

[0007] Furthermore, the ammonia synthesis unit's tail gas venting pipeline is connected to the flare.

[0008] Furthermore, the methanol product delivery pipeline of the methanol synthesis distillation unit is connected to the methanol product storage tank.

[0009] Furthermore, the liquid ammonia product delivery pipeline of the ammonia synthesis unit is connected to the liquid ammonia product storage tank.

[0010] Furthermore, the LNG product delivery pipeline of the cryogenic separation unit is connected to the LNG product storage tank. Beneficial effects

[0011] The advantages of this utility model are as follows: (1) The system of this utility model has a reasonable structure and a relatively simple and uncomplicated process flow. It can realize the simultaneous production of methanol, liquid ammonia and LNG products using calcium carbide furnace gas, turning waste into treasure, realizing the high-value resource utilization of waste, and generating significant economic and social benefits; (2) The system of this utility model can realize the "one head and multiple tails" production mode, realize product diversification, and make enterprises more adaptable to the market; (3) This utility model uses the temperature-switching adsorption method of the TSA device to remove moisture from the gas. Compared with other dehydration methods, the removal is more thorough, which can effectively extend the service life of the adsorbent in the subsequent PSA device and reduce production costs; (4) The entire system generates very little waste during production and it is easy to handle, resulting in significant environmental benefits. Attached Figure Description

[0012] The accompanying drawings are provided to further understand the present invention and form part of the specification. They are used together with the embodiments of the present invention to explain the present invention and do not constitute a limitation thereof.

[0013] Figure 1 This is a schematic diagram of the system structure of this utility model. Detailed Implementation

[0014] The technical solutions in the embodiments of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only typical embodiments of this utility model, and not all embodiments. Example 1

[0015] See attached document Figure 1This embodiment provides a system for producing methanol from calcium carbide furnace gas, co-producing ammonia and LNG, including a shift converter, a decarbonization unit, a deep purification unit, a methanol synthesis distillation unit, a methanation unit, a TSA unit, a PSA unit, a cryogenic separation unit, and a synthesis ammonia unit. The inlet of the shift converter is connected to the calcium carbide furnace gas inlet pipeline. The shift converter, decarbonization unit, deep purification unit, methanol synthesis distillation unit, methanation unit, TSA unit, and PSA unit are connected sequentially. The outflow gas outlet of the PSA unit is connected to the synthesis ammonia unit, the desorbed gas outlet of the PSA unit is connected to the cryogenic separation unit, and the non-condensable gas outlet of the cryogenic separation unit is connected to the inlet of the PSA unit. The acid gas venting pipeline of the decarbonization unit is connected to the sulfur recovery and carbon dioxide recovery system. The synthesis tail gas venting pipeline of the synthesis ammonia unit is connected to the flare combustion system. The methanol product delivery pipeline of the methanol synthesis distillation unit is connected to the methanol product storage tank. The liquid ammonia product delivery pipeline of the synthesis ammonia unit is connected to the liquid ammonia product storage tank. The LNG product delivery pipeline of the cryogenic separation unit is connected to the LNG product storage tank.

[0016] In this embodiment, the main components of the raw material calcium carbide furnace gas are: CO: 70.32% H2: 10.38% N2: 15.40% CO2: 3.48% The process operation steps are as follows: S01 Conversion: After dust removal and compression, the pressure of the calcium carbide furnace gas is increased to 1.5MPa and then sent to the conversion unit. The conversion temperature is controlled within 220℃~280℃ by a waste heat boiler. Sulfur is added to the calcium carbide furnace gas to make its H2S content 75mg / m³. 3 Under conditions of a sulfur-resistant catalyst and a water-to-gas ratio of 0.15, some CO is converted into CO2 and H2. The main components of the converted gas are... CO: 15.16% H2: 37.81% N2: 15.34% CO2: 31.18% After the reaction, the ratio of H2 to CO is 2.49. A value greater than 2 can ensure that the appropriate hydrogen-carbon ratio is achieved during the subsequent methanol synthesis, resulting in a high CO conversion rate. The shift gas is then cooled, dehydrated, and separated before being sent to the decarbonization unit. SO2 decarbonization and desulfurization: Using a 40% N-methyldiethanolamine solution as the absorbent, the shifted gas undergoes a decarbonization process involving absorption, depressurization, heating, and desorption to separate CO2 and H2S, producing acidic gas. The main components of the acidic gas are... CO2: 98.85% H2S: 0.97% The acidic gas is transported to the sulfur recovery and carbon dioxide recovery system. Through the Claus sulfur recovery process and carbon dioxide purification process, the CO2 and H2S in the acidic gas are reused as resources. The main components of the decarbonized gas are... CO: 21.97% H2: 55.24% N2: 22.58% The decarbonized gas is then transported to a deep purification unit after gas-liquid separation. S03 Deep Purification: The decarbonized gas first uses various adsorbents to remove trace amounts of harmful impurities such as sulfur, phosphorus, and halogens. Then, under the action of a hydrogenation catalyst, the hydrogen in the gas is used to convert the trace amounts of unsaturated bonds into saturated bonds, achieving further purification. The purified gas is then transported to the methanol synthesis distillation unit. S04 Methanol Synthesis and Distillation: The purified gas is compressed and heat-exchanged to increase its pressure to 5.0 MPa and temperature to 200℃. The reaction temperature is controlled within 220℃±5℃ using a waste heat boiler, and the space velocity is carefully controlled to ensure a good conversion rate (over 90%). An isothermal low-pressure synthesis process is used to react the H2 and CO contained within the gas with a synthesis catalyst to produce crude methanol and methanol purge gas as a byproduct. The main components of the methanol purge gas are... CO+CO2: 4.12% H2: 72.37% N2: 23.12% The crude methanol is then subjected to multi-stage distillation to remove impurities such as water, light fractions, and heavy fractions to obtain methanol product, which is then transported to the methanol product storage tank, and the methanol purge gas is transported to the methanation unit. S05 Methanation Reaction: Methanol purge gas is heated to 230℃ via heat exchange and enters the methane reactor. The CO and CO2 in the gas are converted to CH4 using the H2 contained within the gas under the action of a catalyst. The catalyst bed temperature is controlled within 255±5℃, and the space velocity is carefully controlled to ensure a good conversion rate. The CO+CO2 content in the resulting methane conversion gas can be reduced to ≤10μmol / mol. The main components of the methane conversion gas are... CH4: 4.08% H2: 71.99% N2: 23.40% After heat exchange and water cooling to below 40°C, the water produced in the reaction is separated and removed, and the separated methane conversion gas is transported to the TSA unit. S06 Dehydration and De-alcoholization: The methane conversion gas is removed by the TSA temperature-switching adsorption process to remove trace amounts of water and high-boiling-point impurities such as methanol. The dew point of the dehydration and de-alcoholization methane conversion gas is ≤-70℃ and it is then transported to the PSA unit. S07 Pressure Swing Adsorption: The purified methane conversion gas undergoes a PSA pressure swing adsorption process to separate CH4 from H2 and N2. The main components of the outgas and desorbed gas are respectively... Release gas in the direction of air release—H2: 75.42% N2: 24.51% Desorption – CH4: 74.75% H2: 18.82% N2: 6.23% The outgassing gas (a mixture of H2 and N2) is fed to the ammonia synthesis unit, and the desorbed gas (methane-rich gas) is fed to the cryogenic separation unit. S08 Ammonia Synthesis: The ratio of H2 to N2 in the H2 and N2 mixture is 3.08. A ratio of H2 to N2 of around 3 in the H2 and N2 mixture can achieve the stoichiometric ratio of the reaction, so that the utilization rate of the raw material gas reaches the optimal level. After pressurization and preheating, the pressure of the mixture is increased to 14.5MPa and the temperature is increased to 220℃. Liquid ammonia product is obtained through ammonia synthesis and ammonia cold separation process, and synthesis tail gas is generated. During this process, the heat of the circulating gas is removed by the waste heat boiler to control the reaction temperature within 450℃±10℃. The liquid ammonia product is transported to the liquid ammonia product storage tank, and the synthesis tail gas is transported to the flare for incineration. S09 Cryogenic Separation: Methane-rich gas undergoes a cryogenic separation and liquefaction process to obtain LNG products and non-condensable gases containing H2, N2, and a small amount of CH4. The LNG products are transported to the LNG product storage tank, and the non-condensable gases are returned to the PSA unit for further separation and utilization after the cold energy is recovered. Example 2

[0017] As another embodiment, the difference from Embodiment 1 is that the main component of the raw material calcium carbide furnace gas in this embodiment is... CO: 78.05% H2: 11.66% N2: 7.60% CO2: 2.39% As another embodiment, the difference from Embodiment 1 lies in the following process operation steps: S01 Conversion: After dust removal and compression, the pressure of the calcium carbide furnace gas is increased to 2.0 MPa, the water-to-gas ratio is 0.2, and the H2S content after sulfur supplementation is 97 mg / m³. 3 The main components of the transformed gas are CO: 19.58% H2: 40.81% N2: 7.44% CO2: 31.95% After the reaction, the ratio of H2 to CO was 2.08; SO2 decarbonization and desulfurization: The main components of the acid gas and decarbonized gas after treatment are as follows: Acidic gases – CO2: 98.94% H2S: 1.52% Decarbonization gas: CO: 25.85%, H2: 53.78%, N2: 19.96% S04 Methanol Synthesis and Distillation: The purified gas is compressed and heat-exchanged to increase its pressure to 5.5 MPa and temperature to 250℃. The main components of the methanol purge gas are... CO+CO2: 4.96% H2: 69.18% N2: 25.61% S05 methanation reaction: The main components of the converted methane gas after treatment are... CH4: 4.93% H2: 69.14% N2: 25.74% S07 Pressure Swing Adsorption: The main components of the treated outgas and desorbed gas are respectively... Release gas in the correct direction—H2: 72.93% N2: 27.04% Desorption – CH4: 86.78% H2: 9.62% N2: 3.57% S08 ammonia synthesis: The ratio of H2 to N2 in the H2 and N2 mixture is 2.70. An appropriate amount of H2 is added to maintain the ratio of H2 to N2 at around 3. After pressurization and preheating, the pressure is increased to 15MPa and the temperature is increased to 240℃. Example 3

[0018] As another embodiment, the difference from Embodiment 1 is that the main component of the raw material calcium carbide furnace gas in this embodiment is... CO: 65.05% H2: 12.82% N2: 18.34% CO2: 3.47%.

[0019] As another embodiment, the difference from Embodiment 1 lies in the following process operation steps: S01 Conversion: After dust removal and compression, the pressure of the calcium carbide furnace gas is increased to 1.2 MPa, the water-to-gas ratio is 0.1, and the H2S content after sulfur supplementation is 65 mg / m³. 3 The main components of the transformed gas are CO: 15.78% H2: 36.21% N2: 17.07% CO2: 32.65% After the reaction, the ratio of H2 to CO was 2.30; SO2 decarbonization and desulfurization: The main components of the acid gas and decarbonized gas after treatment are as follows: Acidic gases – CO2: 98.45% H2S: 0.68% Decarbonization gas: CO: 22.75%, H2: 52.43%, N2: 24.68% S04 Methanol Synthesis and Distillation: The purified gas is compressed and heat-exchanged to increase its pressure to 4.5 MPa and temperature to 180℃. The main components of the methanol purge gas are... CO+CO2: 6.34% H2: 74.88% N2: 18.23% S05 methanation reaction: The main components of the converted methane gas after treatment are... CH4: 6.29% H2: 74.81% N2: 18.28% S07 Pressure Swing Adsorption: The main components of the treated outgas and desorbed gas are respectively... Release gas in the direction of air release—H2: 80.36% N2: 19.59% Desorption – CH4: 92.17% H2: 6.17% N2: 1.50% S08 ammonia synthesis: The ratio of H2 to N2 in the H2 and N2 mixture is 4.10. An appropriate amount of N2 is added to maintain the ratio of H2 to N2 at around 3. After pressurization and preheating, the pressure is increased to 15.5 MPa and the temperature is increased to 250℃.

Claims

1. A system for producing methanol from calcium carbide furnace gas and co-producing synthetic ammonia and LNG, characterized in that: It includes a conversion unit, a decarbonization unit, a deep purification unit, a methanol synthesis distillation unit, a methanation unit, a TSA unit, a PSA unit, a cryogenic separation unit, and a synthetic ammonia unit; the inlet of the conversion unit is connected to the calcium carbide furnace gas inlet pipeline, and the conversion unit, decarbonization unit, deep purification unit, methanol synthesis distillation unit, methanation unit, TSA unit, and PSA unit are connected in sequence, the outgassing outlet of the PSA unit is connected to the synthetic ammonia unit, the desorbed gas outlet of the PSA unit is connected to the cryogenic separation unit, and the non-condensable gas outlet of the cryogenic separation unit is connected to the inlet of the PSA unit.

2. The system for producing methanol from calcium carbide furnace gas and co-producing synthetic ammonia and LNG according to claim 1, characterized in that: The acid gas release pipeline of the decarbonization device is connected to the sulfur recovery and carbon dioxide recovery system.

3. The system for producing methanol from calcium carbide furnace gas and co-producing synthetic ammonia and LNG according to claim 1, characterized in that: The ammonia synthesis unit's tail gas venting pipeline is connected to the flare.

4. The system for producing methanol from calcium carbide furnace gas and co-producing synthetic ammonia and LNG according to claim 1, characterized in that: The methanol product delivery pipeline of the methanol synthesis distillation unit is connected to the methanol product storage tank.

5. The system for producing methanol from calcium carbide furnace gas and co-producing synthetic ammonia and LNG according to claim 1, characterized in that: The liquid ammonia product delivery pipeline of the ammonia synthesis unit is connected to the liquid ammonia product storage tank.

6. The system for producing methanol from calcium carbide furnace gas and co-producing synthetic ammonia and LNG according to claim 1, characterized in that: The LNG product delivery pipeline of the cryogenic separation unit is connected to the LNG product storage tank.

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