Research on the combined extraction process of CO2 and H2 in dry gas hydrogen production (reprinted)

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Research on the process of joint extraction of CO2 and H2 in dry gas hydrogen production. Source: China Chemical Information Network. December 5, 2006. The No. 1 hydrogen production unit of Wuhan Branch uses catalytic dry gas as raw material and uses the steam reforming method to produce hydrogen. The 1.3-1.5MPa medium-change gas contains 12%-18% carbon dioxide and a small amount of nitrogen, methane, carbon monoxide, etc. PSA technology is then used to absorb impurities such as carbon dioxide, nitrogen, methane, and carbon monoxide to obtain pure hydrogen. 0.03MPa analytical gas (35% hydrogen, 40% carbon dioxide) is used as low-pressure gas and then discharged into the atmosphere. As a result, about 30,000 tons of carbon dioxide are emitted into the atmosphere every year. Recovering carbon dioxide from analytical gas has economic problems due to its low pressure. On the other hand, the hydrogen recovery rate of PSA is closely related to the carbon dioxide content. The lower the content of impurities such as carbon dioxide, the greater the processing capacity of PSA and the higher the hydrogen recovery rate. The current hydrogen recovery rate is only 75-80%. Therefore, we are developing a mid-range gas decarbonization-PSA series extraction process of hydrogen and carbon dioxide, which can not only recover carbon dioxide, but also improve the hydrogen recovery rate of PSA. Wet decarburization is divided into chemical absorption method and physical absorption method. The chemical absorption method uses a weak alkaline solution as the absorbent, reacts with CO2 to form a compound, has a high degree of purification and is less affected by operating pressure. When the temperature of the rich liquid that has absorbed CO2 gas increases and the pressure decreases, the compound decomposes and releases the CO2 gas components again, and the absorbent is regenerated. Representative methods of this type are the alkyl alcohol amine (the most typical is MDEA) method and the alkaline salt solution (including hot potassium alkali, amino acid salt) method. The physical solvent (including cold methanol method, Flour and Selexol, etc.) absorption method uses organic compounds as the absorption solvent and is suitable for gas purification with high partial pressure of CO2 gas and low heavy hydrocarbon content. Among the chemical absorption methods, the alcoholamine method is widely used because of its wide adaptability, high purification, and low operating costs. Among them, the activated MDEA process developed based on the MDEA method has gradually become the best process for acid gas purification due to its advantages of low energy consumption, weak corrosiveness, low vapor pressure, low losses, and small impact on the environment. The self-developed activated MDEA decarburization agent is used to remove CO2 from the medium swing gas through a one-stage absorption regeneration decarburization process, and then H2 is extracted through an improved pressure swing adsorption (PSA) system, achieving obvious results. When the desorption pressure reaches 0.15MPa, the purity of the desorbed CO2 reaches more than 99%, and the sulfur content is less than 1 μg/g, which is beneficial to the production of food-grade carbon dioxide. ； The H2 recovery rate reaches more than 90%. 2 Test principle 2.1 MDEA decarburization mechanism MDEA (N-Methyldiethanolamine) is N-methyldiethanolamine, with a boiling point of 246-248°C, a flash point of 260°C, and a freezing point of -21°C. Under certain conditions, it has a strong ability to absorb acidic gases such as CO2, has small reaction heat, low desorption temperature, stable chemical properties, and is non-toxic. The 40% MDEA aqueous solution used in industry has a boiling point of 110-120°C and a freezing point of -5°C. MDEA is a tertiary amine. Unlike primary amines and secondary amines, MDEA does not easily react with CO2 to form stable aminoformates in aqueous solutions, but to form unstable bicarbonates. Its aqueous solution and CO2 can react as follows:: CO2 +H2O=H+ +HCO3- (1) H+ +R2NCH3 =R2NCH3H+ (2) Formula (1) is controlled by the liquid film and the reaction is extremely slow. Formula (2) is an instant reversible reaction. Therefore, formula (1) is the control step for MDEA to absorb CO2. In order to speed up the absorption speed, after adding an appropriate amount of activator (R2/NH) to the MDEA solution, the reaction proceeds as follows: R2/NH + CO2 = R2/NCOOH (3) R2/NCOOH+R2NCH3 +H2O= R2/NH+ R2CH3NH+ +HCO3- (4) (3)+(4): R2NCH3 + CO2 + H2O=R2CH3NH+ +HCO3- (5) It can be seen from (3)-(5) that the activator absorbs CO2 and then transfers CO2 to the liquid phase MDEA, * * Speeded up reaction speed. The absorption of CO2 by MDEA solution is a typical physical-chemical absorption. The MDEA solution can be regarded as an absorbent. The absorbed CO2 can be desorbed through flash evaporation, which can not only meet the requirements of purification degree, but also save regeneration energy consumption. Moreover, MDEA contains a tertiary amine as an active group, which absorbs CO2 to generate bicarbonate. When heated and regenerated, the heat required to generate a more stable carbamate is much lower than that of primary and secondary amines and CO2. Since the absorption and desorption processes in the industrial production of MDEA decarburization are linked together, the traditional research method is to separate absorption and desorption and study them in isolation. Therefore, it is difficult to reflect the comprehensive performance of the decarburization solvent. This study established a pilot plant to simulate the industrial decarburization process, which can comprehensively evaluate the absorption and desorption performance of the decarburization solution under different desorption pressures to determine the feasibility and optimal process conditions of the process. 2.2 Principle of pressure swing adsorption process PSA is mainly physical adsorption. It refers to the adsorption that relies on the molecular forces (including van der Waals forces and electromagnetic forces) between the adsorbent and adsorbate molecules. The adsorption process proceeds extremely quickly, and the dynamic balance between the various phases involved in the adsorption can be completed in an instant, and this adsorption is completely reversible. In physical adsorption, the ability of various adsorbents to adsorb gas molecules is due to the special shape of the gas molecules at the interface between the gas and solid phases. Generally speaking, gas molecules that are only in the gas phase experience the same molecular attraction from all directions, and the gas molecules are in a state of free movement. ； When gas molecules move to the interface between the gas and solid phases (i.e., when they hit the surface of the adsorbent), the gas molecules will be subject to the gravitational pull of molecules in the solid phase and the gas phase at the same time. The gravitational pull from the solid phase molecules is greater. When the molecular kinetic energy of the gas molecules is not enough to overcome this molecular gravitational pull, the gas molecules will be adsorbed on the surface of the solid adsorbent. Gas molecules are adsorbed on the solid surface to form an adsorption phase, whose density is much greater than that of the gas phase, and is generally close to the density of the liquid. The attraction of solid adsorbent surface molecules to gas molecules in the adsorbed phase can be described by the following formula: F=C1/rm -C2/rn (m>n) where, F-molecular gravity ； C1-gravitational constant, related to the size and structure of the molecule ； C2-Electromagnetic force constant, mainly related to the polarity and instantaneous dipole moment of the molecule ； r- represents the intermolecular distance. Therefore, for different gas components, due to the different size, structure, polarity and other properties of their molecules, the adsorbent's ability to adsorb them and their adsorption capacity are also different. The hydrogen production device takes advantage of this characteristic of the adsorbent. Since the adsorbent has a weak adsorption capacity for the hydrogen component in the mixed gas but a strong adsorption capacity for other components, various impurities can be adsorbed through a mixed adsorption bed equipped with different adsorbents to achieve the purpose of purifying hydrogen. The adsorption capacity of the pressure swing adsorption (PSA) system has a great relationship with the adsorption process conditions. Specifically manifested in: (1) Raw gas composition: The processing capacity of the adsorption tower is closely related to the composition of the feed gas. The higher the hydrogen content in the feed gas, the greater the processing capacity of the adsorption tower. ； The higher the impurity content of the raw gas, especially the higher the content of harmful impurities with high purification requirements, the smaller the processing capacity of the adsorption tower will be. (2) Raw gas temperature: The higher the temperature of the raw gas, the smaller the adsorption capacity of the adsorbent, and the lower the processing capacity of the adsorption tower. (3)Adsorption pressure: The higher the pressure of the raw gas, the greater the adsorption capacity of the adsorbent, and the higher the processing capacity of the adsorption tower. (4)Desorption pressure: The lower the desorption pressure, the more complete the adsorbent regeneration, the greater the dynamic adsorption capacity of the adsorbent, and the higher the processing capacity of the adsorption tower. (5) Product purity: The higher the required product purity, the lower the effective utilization rate of the adsorbent and the lower the processing capacity of the adsorption tower. (6) Hydrogen recovery rate: Since the hydrogen loss of the PSA unit comes from the regeneration stage of the adsorbent, the higher the processing capacity of the adsorption tower, the longer the regeneration cycle, the fewer the number of regenerations per unit time, the less hydrogen loss, and the higher the hydrogen recovery rate. 3 Test process and analysis method 3.1 Test process The test was carried out with a side line installed on site in the hydrogen production workshop. It consists of a decarbonization part and a pressure swing adsorption system connected in series. The processing capacity of the pilot plant is 2-3Nm3/h. The decarbonization process flow is shown in Figure 1 (omitted): The medium-change gas enters the bottom of the collection tower after passing through the buffer tank, pressure stabilizing valve, and flow meter, and contacts with the absorption liquid (lean liquid) flowing countercurrently from the top of the absorption tower to realize the absorption process. The medium-change gas (hereinafter referred to as purified gas) after absorbing CO2 enters the PSA from the top of the absorption tower after being stabilized by the pressure-stabilizing valve. After absorption, the rich liquid enters the flash tower for flashing from the bottom of the absorption tower through the liquid level regulating valve. The flash vapor is released from the top of the flash tower through the pressure stabilizing valve. The rich liquid at the bottom of the flash tower enters the top of the solvent regeneration tower through the liquid level regulating valve, flows downward through the packing section, and undergoes mass transfer and heat transfer with the gas rising from the lower tower before being further regenerated in the reboiler. The heat required for regeneration is provided by an electric heater. The regeneration lean liquid enters the lean liquid cooler from the bottom of the regeneration tower and is cooled to 60°C, and then is sent to the upper part of the absorption tower by the lean liquid pump. The desorbed gas from the top of the solvent regeneration tower is cooled to 40°C by the CO2 cooler and released after passing through the regulating valve. After the entire device has been running stably for a period of time, the carbonization degrees of the lean liquid and the rich liquid no longer change with time. Using the analysis results of the purified gas, desorbed gas, lean liquid, and rich liquid, the comprehensive performance of the process and the decarburization solution can be comprehensively evaluated. At this time, the absorption rate is equal to the desorption rate and the system decarbonization rate. The pressure swing adsorption process flow is shown in Figure 2 (omitted): The decarbonized purified gas with a pressure of 1.1-1.3MPa (C) and a temperature of 40°C first passes through the T101 water washing tower to remove the decarburized liquid in the purified gas. After passing through the T102 gas-water separator and flow meter (F1), it enters two adsorption towers in the adsorption tower (T103A-F) that are in adsorption mode. , under the sequential selective adsorption of a composite adsorption bed composed of multiple adsorbents, all impurities except hydrogen are removed at one time, and the product hydrogen with a purity greater than 99.8% is directly obtained and discharged from the top of the tower, and then sent out of the boundary area through the T104 buffer tank, adsorption pressure regulating valve PV01 and flow meter (F2). In addition to sending out product hydrogen, the PSA device also produces reverse release and desorption gas. The reverse release desorbed gas comes from the reverse release step of the adsorption bed, and all desorbed gas is sent to the desorbed gas buffer tank T105. The reverse release desorption gas is mixed in the desorption buffer tank and then sent out of the boundary area through the flow meter (F3). The PSA adsorption tower is made of Φ57×3.5×550 carbon steel material, the adsorbent filling capacity is 1L, the program-controlled valve is a solenoid valve, and the PSA device is programmed by a computer. 3.2 In the test analysis method, the composition of the variable gas, purified gas, and desorbed gas is analyzed with the 672 gas analyzer, and the CO2 content of the lean liquid and rich liquid is analyzed by the acidolysis method. 4 Test and discussion 4.1 Selection of decarburization process conditions The main process conditions for decarburization include: Absorption pressure, absorption temperature, desorption pressure, desorption temperature and gas-liquid ratio of decarburization liquid. Due to the chemical and physical absorption properties of MDEA solution. Low absorption temperature is conducive to physical absorption, while MDEA is mainly chemical absorption. The absorption of CO2 by MDEA is an exothermic reaction. From a thermodynamic point of view, a low absorption temperature is conducive to the reaction equilibrium shifting to the right, that is, it is conducive to absorption. ； From a kinetic perspective, high absorption temperature is conducive to increasing the absorption rate. In the absorption tower, the gas-liquid contact time is limited, so both the absorption balance and the absorption rate must be considered. Based on the performance of MDEA and the operation results of existing industrial devices, the absorption temperature is fixed at 60℃ ； The pressure of the shift gas in this test was 1.2MPa, so the absorption pressure was fixed at 1.2MPa. Under this condition, the effects of desorption temperature, desorption pressure and gas-liquid ratio of the decarburization liquid on the decarburization effect were investigated. 4.1.1 Desorption temperature test The desorption process of MDEA rich liquid that has absorbed carbon dioxide is a reversible process of absorption and an endothermic reaction. From a thermodynamic point of view or a kinetic point of view, the higher the desorption temperature, the more conducive it is to desorption of CO2. However, if the desorption temperature is too high, it will cause equipment corrosion and degradation of the activator and MDEA. At present, the normal pressure desorption temperature of industrial equipment is generally controlled at about 108°C, the desorption temperature of MDEA desulfurization is generally controlled at about 118°C, and the desorption temperature of hot Benfield decarburization is generally controlled at about 120°C. Therefore, the test temperature was selected in the range of 108℃-128℃. Tests show that the desorption temperature has little effect on the CO2 content of the desorbed gas, but has a significant impact on the CO2 content of the purified gas and lean liquid. The CO2 content in the lean liquid decreased from 26.5 g/L at 108°C to 6.7g/L at 128°C. ； The CO2 content in the purified gas also decreases significantly with the increase of desorption temperature, so that the CO2 yield increases with the increase of desorption temperature (Table 1). Taking into account equipment corrosion, degradation of activator and MDEA, CO2 yield, and the production and energy consumption of PSA and food-grade CO2 in the subsequent sections of the process, the desorption temperature was selected as 118°C. Table 1 Experimental data on the effect of desorption temperature on decarburization Desorption temperature/°C Purified gas CO2, V% Desorbed gas CO2, V% Lean liquid CO2/g/L CO2 yield, % 108 2.8 99.1 26.5 84.4 118 1.4 98.9 15.1 93.6 128 0.2 99.0 6.7 99.1 Test conditions: Medium variable air flow 2.1m3/h ； The CO2 content of medium variable gas is 18.2% ； Absorption pressure 1.2MPa ； Desorption pressure 0.15MPa ； Absorption liquid circulation volume 9.6L/h ； Absorption temperature is 60℃. 4.1.2 Desorption pressure test From the perspective of chemical equilibrium, low desorption pressure is conducive to the balance moving to the right, that is, it is conducive to the desorption of CO2 in MDEA. However, from the perspective of CO2 recovery, appropriately increasing the desorption pressure will significantly reduce the compression ratio of the CO2 compressor, thereby reducing energy consumption. To this end, the desorption pressure was adjusted from 0.03 MPa to 0.35 MPa while other conditions remained unchanged, and the changing trends of CO2 content in the purified gas, desorbed gas, lean liquid, and rich liquid were examined. The test results are shown in Table 2. From the data in the table, the CO2 content in the desorbed gas basically does not change with the change of desorption pressure, and its content remains above 98.5%. ； The CO2 content in the purified gas changes as the desorption pressure increases, and the change trend is obvious. When the pressure increases from 0.03MPa to 0.15MPa, the CO2 content in the purified gas increases gently from 0.1 V% to 1.6V%. The desorption pressure continues to increase, and the CO2 content in the purified gas rapidly increases to 10.1 V%. ； The CO2 yield decreases as the desorption pressure increases, and its trend is opposite to that of the purified gas. It can also be seen from the data in Table 2 that the CO2 content in the lean liquid increases with the increase of desorption pressure, but the increase is gentle in the range of 0.03MPa-0.12MPa. When the desorption pressure continues to increase from 0.12MPa, the CO2 content in the lean liquid increases rapidly. This is because as the desorption pressure increases, the partial pressure of CO2 in the desorption tower continues to increase, which is not conducive to CO2 desorption. ； The change in CO2 content in the rich liquid has its own characteristics. When the desorption pressure increases from 0.03MPa to 0.15MPa, the CO2 content in the rich liquid increases slowly. When the desorption pressure continues to increase, the CO2 content in the rich liquid remains basically unchanged. This is because a large amount of CO2 in the lean liquid is not desorbed, which easily makes the decarburization liquid basically approach the saturated absorption state in the absorption tower. The most obvious thing from Figure 4 (omitted) is the total amount of CO2 absorbed by the decarburization liquid. Before the desorption pressure is 0.15MPa, the absorption amount decreases slowly. After the desorption pressure is greater than 0.15MPa, the absorption amount decreases rapidly. Table 2 Experimental data on the influence of desorption pressure on decarbonization Desorption pressure/MPa Purified gas CO2, V% Desorbed gas CO2, V% Lean liquid CO2/L·L-1 Rich liquid CO2/L·L-1 CO2 absorption/L·L-1 CO2 yield/% 0.03 0.1 98.8 1.12 39.18 38.06 99.5 0.08 0.5 99.1 1.68 38.87 37.19 97.2 0.12 1.0 98.7 4.68 40.77 36.09 94.4 0.15 1.6 98.6 7.69 42.93 35.21 92.1 0.25 6.0 98.8 18.6 43.70 25.10 66.2 0.35 10.1 98.7 27.2 43.65 16.41 43.2 Test conditions: Medium variable air flow 2.1m3/h ； The CO2 content of medium variable gas is 17.8% ； Absorption pressure 1.2MPa ； Absorption liquid circulation volume 9.6L/h ； Absorption temperature 60℃ ； Desorption temperature is 118°C. According to the desorption pressure test, combined with the CO2 yield and the production and energy consumption of PSA and food-grade CO2 in the subsequent sections of the process, the medium variable gas processing capacity is 25000Nm3/h, the medium variable gas CO2 content is 15.5%, and the CO2 yield is 90%. The results are as follows: Table 3 Relationship between desorption pressure and energy consumption of decarbonization system and CO2 compressor Desorption pressure/MPa Lean liquid CO2 content/L·L-1 Lean liquid CO2 absorption/L·L-1 Semi-lean liquid CO2 absorption/L·L-1 Decarbonization system energy consumption/KW·h-1 CO2 compressor energy consumption/KW·h-1 Total energy consumption/KW·h-1 0.03 1.12 38.06 15 230 517 747 0.08 1.68 37.19 14 245 452 697 0.12 4.68 36.09 13 256 414 670 0.15 7.69 35.21 10 283 389 672 0.25 18.6 25.10 8 349 326 685 0.35 27.2 16.41 5 510 280 790 It can be seen from Table 3 and Figure 3 (omitted)-4 that the total energy consumption of the decarbonization system and CO2 compressor has a lowest point as the desorption pressure increases, and the lowest point is the desorption pressure 0.15-0.18MPa. 4.1.3 Gas-liquid ratio test The gas-liquid ratio is one of the important parameters in the design and operation of the absorption tower, and is also an important reference for determining the absorbent circulation amount. The gas-liquid ratio test is to conduct analysis of purified gas and desorbed gas under the conditions of certain absorption and desorption pressures and absorption liquid circulation volume for different medium-variable gas flow rates after the device has been running stably for 3 hours to observe the impact of the gas-liquid ratio on the decarbonization effect (Figure 5-6 omitted)] ). From Figure 5, the CO2 content in the desorbed gas has little to do with the gas-liquid ratio, and is basically maintained above 98%. ； The CO2 content in the purified gas increases with the increase of the gas-liquid ratio, and the CO2 recovery rate decreases with the increase of the gas-liquid ratio. The intersection point of the two curves is: The CO2 content in the purified gas is about 2%, the CO2 recovery rate is about 88%, and the gas-to-liquid ratio is about 240. Obviously, under this gas-to-liquid ratio condition, both the CO2 content and CO2 recovery rate in the purified gas meet the test target values. From Figure 6, the CO2 content in the lean liquid basically does not change with the gas-liquid ratio. This is because the CO2 content in the lean liquid is mainly controlled by the desorption temperature and desorption pressure. ； The CO2 content in the rich liquid increases with the increase of the gas-liquid ratio, but the trend becomes flat after it reaches a certain level (about 44 L/L). The total CO2 absorption in the decarburization liquid is similar to the change trend of the CO2 content in the rich liquid. This is because as the gas-liquid ratio increases, the total CO2 content in the gas phase increases, and the amount of CO2 absorbed by the decarburization liquid also increases, but after it increases to a certain level, the CO2 content in the rich liquid increases. * * balance and then remained essentially unchanged. By examining the impact of changes in conditions such as desorption temperature, desorption pressure and gas-liquid ratio during the decarbonization process on decarbonization performance, combined with comprehensive considerations of carbon dioxide recovery energy consumption and subsequent pressure swing adsorption systems, CO2 in medium swing gas can be effectively removed under experimental conditions such as absorption pressure 1.2MPa, desorption pressure 0.15MPa, decarbonization liquid gas-liquid ratio 220-240, absorption temperature 60°C and desorption temperature 118°C. (Table 4), after decarbonization, the CO2 content in the purified gas is reduced from 18.2v% to 1.8v%, the decarbonization rate reaches 90%, and the impurity content in the medium-change gas is reduced from 25% to less than 12% ； The CO2 content of the desorbed gas reaches 99.1%, providing a high-quality gas source for subsequent CO2 recovery. Table 4 Changes in gas composition before and after decarbonization of intermediate gas V% Composition CO2 CO H2 N2 CH4 Raw gas 18.2 1.1 74.5 4.5 1.7 Purified gas 1.8 1.2 88.2 6.9 1.9 Desorption gas 99.1 0.3 0.2 0.2 0.1 4.2 Decarbonization device and PSA device in series Table 6 Average data of decarbonization and ISA serial continuous tests V% project CO2 CO H2 N2 CH4 Variable gas in decarbonization unit 15.5 0.9 77.5 4.4 1.7 Purified gas 1.9 0.8 90.2 5.1 2.0 Desorbed gas 99.06 0.3 0.2 0.2 0.2 Yield 88.7 — — — — ISA purified gas — — 99.8 0.2 — Desorption gas 10.7 4.5 44.7 28.8 11.3 Yield — — 91.3 — — The series process of ISA and wet decarbonization is based on the principle that the lower the impurities in the raw material gas, the higher the hydrogen recovery rate. The hydrogen recovery rate is increased through combination. Adjust the decarbonization device test conditions to: The absorption pressure is 1.25MPa, the desorption pressure is 0.15MPa, the absorption liquid circulation volume is 9.6L/h, the medium variable air flow rate is 2.3Nm3/h, the absorption temperature is 60℃ and the desorption temperature is 118℃ ； The PSA device test conditions are controlled at: The adsorption pressure is 1.2MPa, the desorption pressure is 0.03MPa, the temperature is 40°C, and the hydrogen purity is 99.8%. Carry out a series test of medium-variable gas moisture decarbonization and PSA. After the test ran for 50 hours, the hydrogen recovery rate stabilized at around 91%, which was 10 percentage points higher than the hydrogen recovery rate of the factory’s current equipment. ； The carbon dioxide recovery rate is around 88% (Figure 7 omitted)] ), the average data of the test are shown in Table 6. It can be seen from Table 6 that the CO2 content of the desorbed gas reaches 99.1%. 4.3 Economic Benefit Analysis Based on the research and test results of this project and the actual production situation of the hydrogen production unit of Wuhan Branch, the economic benefit evaluation was carried out. Wuhan Branch's current hydrogen production unit PSA system design capacity is 18,000Nm3/h, the actual production capacity is 15,000Nm3/h, and the CO2 content in the medium variable gas is between 15% and 18%. Using the technology of this research, the intermediate gas is decarbonized to reduce the CO2 content to less than 2%. At the same time, only the adsorbent in the PSA system is adjusted. Other equipment and instruments in the PSA system are not significantly modified. The processing capacity of the existing ISA system can be increased from 15,000 Nm3/h to 25,000 Nm3/h. ； Hydrogen recovery rate increased from about 80% to more than 90% ； In addition, the CO2 content in the decarbonization and desorption gas reaches 99%, and the purity is high. The CO2 pressure is 0.15 MPa, which is about 0.1 MPa higher than the CO2 pressure (0.03 MPa) in the traditional decarbonization device, which is beneficial to CO2 purification and liquefaction recovery. The H2 yield of the existing ISA is calculated as 80%. After changing to the decarburization and PSA series process, the H2 yield of the new process is calculated as 90%. The increased H2 production of the new process is: 25000×0.754×0.1=1885Nm3/h ； The production cost of H2 is calculated as 4,900 yuan/t, and the annual benefit of producing more H2 is 8,000×1,885/22.4×2/1,000×4,900=6,597,500 yuan. Based on the medium variable gas flow rate of 25,000 Nm3/h and the CO2 content of 16%, the annual output of CO2 is 52.5kt, the selling price of each ton of CO2 is 500 yuan, and the production and sales cost of each ton of CO2 is 220 yuan, then the profit of the annual output of 52.5kt of CO2 is 5.25×(500-220)=14.7 million yuan. 5 Conclusion (1) It is feasible to connect the pressurized desorption MDEA decarbonization with the pressure swing adsorption (ISA) system and the food-grade CO2 production device in series to produce pure hydrogen and food-grade CO2 from the medium gas. (2) Pilot plant data shows that using this process, the preferred process conditions for decarburization are:: Desorption temperature 118℃, absorption temperature 60℃, desorption pressure 0.15MPa, gas-liquid ratio 220-240L/L ； The improved PSA process conditions are: The adsorption pressure is 1.2MPa, the adsorption temperature is 40°C, and the desorption pressure is 0.03MPa. Under these process conditions, the hydrogen yield is >90% and the CO2 yield is >85%. (3) This process to recover CO2 from secondary gas is waste utilization, which is beneficial to environmental protection and has good social benefits. The CO2 content of the desorbed gas is as high as about 99%, with few impurities and high pressure. The cost of recovering and purifying food-grade CO2 is low. (4) The process is technically feasible and has good economic benefits. According to preliminary estimates, the annual benefits from decarbonization and PSA transformation alone are nearly 6.6 million yuan. The annual economic benefit of producing 50kt of food-grade CO2 is about 15 million yuan, with an investment of only about 8 million yuan. This post was last edited by Pastoral Poet on 2008-7-4 16:59 ]