High pressure change-membrane reactor coupled water gas shift hydrogen production process comprehensively considering heat energy utilization

Abstract

The invention belongs to the field of petrochemical engineering, discloses a high-temperature change-membrane reactor coupled water gas shift hydrogen production process comprehensively considering heat energy utilization, and provides a set of two-stage series water gas shift process of a high-temperature reactor and a membrane reactor. And the reaction temperature of the second-stage conversion is matched with the high-temperature conversion, so that the reduction of the energy grade is avoided, and the yield of high-quality steam is increased. And meanwhile, the selective separation of hydrogen also promotes the liquefaction latent heat of water to be fully utilized on the reaction side, and the quality of the produced steam is further improved. Compared with the traditional process, the hydrogen production system provided by the invention has the advantages that under the condition of a certain raw material conversion rate, the hydrogen recovery rate reaches 93.8%, the steam output value is increased by 16.2% on year-on-year basis every year, the total equipment investment of the whole system process is saved by 42.1% on year-on-year basis, the operation cost is saved by 12.1% on year-on-year basis every year, and remarkable economic advantages are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of petrochemical industry and relates to a water-gas shift hydrogen production process coupling high-temperature shift and membrane reactor with comprehensive consideration of heat energy utilization. Background Art

[0002] The water-gas shift process is a key step in the processing of coal-derived syngas and also a key link for the sustainable hydrogen production of a plant. At the same time, it is widely used in other industries to produce important chemical raw materials such as hydrocarbons like ethylene, alcohols like methanol, and ammonia. It plays an important role in the chemical industry.

[0003] The water-gas shift reaction is an exothermic and reversible process. To ensure a high raw material utilization rate, the industrial water-gas shift process often adopts a multi-stage series mode, and the two-stage series mode is the most common. It uses a high-temperature reaction (HTS, 300 - 500 °C) to make the reaction occur quickly and rapidly reduce the CO content. Then, it uses a low-temperature reaction (LTS, 180 - 250 °C) to further promote the reaction, maximizing the CO conversion rate (≥95%) and increasing the hydrogen production. The reaction heat of the water-gas shift process is usually used to produce steam and hot water of different qualities. However, in the traditional conversion process, due to the temperature difference between the high-temperature reaction and the low-temperature reaction itself, a cooling treatment is required between the two. Some of the energy released by the reaction is converted into low-temperature heat energy, and this part of the reaction heat accounts for about 10% of the total reaction heat. The decrease in energy grade results in the heat used to produce low-quality steam and hot water accounting for more than 55%, and the heat recovery benefit is low. At the same time, the low-temperature conversion process also requires a large amount of highly active catalysts under low-temperature conditions, resulting in high equipment investment.

[0004] The fundamental reason for the above problems is that the accumulation of hydrogen at a higher temperature limits the reaction progress, while the membrane reactor can solve this problem. It breaks the limitation of the thermodynamic equilibrium by separating the product H2, realizes a high-conversion reaction process at high temperature, converts the original low-temperature conversion reaction heat into the high-temperature reaction heat in the membrane reactor, and can produce more high-quality steam. An inorganic membrane made of palladium and its alloys is used to separate hydrogen, and its selectivity for hydrogen can reach infinity, which is very beneficial for the separation and purification of hydrogen. The produced hydrogen can meet the use of fuel cells. The membrane reaction process realizes a high degree of integration of the reaction process and the separation process, simplifies the entire hydrogen production process, removes the pressure swing adsorption process for hydrogen purification compared with the traditional process, and the CO2 fixation process is also transformed from a complex absorption process to a simple low-temperature liquefaction process. In addition, the selective separation of hydrogen will cause the water vapor partial pressure in the main stream to rise. When heat energy is utilized, gaseous water will be liquefied in advance, and the released latent heat is more concentrated at a higher temperature, further improving the heat grade and increasing the proportion of high-quality steam output.

[0005] This study proposes a membrane reactor and heat exchange system hydrogen production process that improves the quality of by-product steam in the water-gas shift process. In view of the problems in the traditional water-gas shift process where the thermal energy utilization value caused by the low-temperature shift is low and the output of low-quality steam accounts for a large proportion, a two-stage series water-gas shift process of a high-temperature reactor and a membrane reactor is proposed. The means of improving the conversion rate is changed from lowering the reaction temperature to removing the product hydrogen, so that the reaction temperature of the second-stage conversion matches the high-temperature shift, avoiding the decline in energy grade and increasing the output of high-quality steam. At the same time, the selective separation of hydrogen also promotes more full utilization of the latent heat of liquefaction of water on the reaction side, further improving the quality of the output steam. The two-stage series water-gas shift process of the high-temperature reactor and the membrane reactor described in the present invention can realize a water-gas shift process with high conversion rate at high temperature, increase the proportion of high-quality by-product steam products, and improve the economic advantages of the by-products of the water-gas shift process.

[0006] Table 1 Composition of raw coal gas for water gas shift in a coal-to-hydrogenation plant

[0007] Summary of the Invention

[0008] The purpose of the present invention is to provide a membrane reactor and heat exchange system hydrogen production process that improves the quality of by-product steam in the water-gas shift process. This process uses a palladium membrane reactor instead of a low-temperature shift reactor, changes the means of improving the conversion rate from lowering the reaction temperature to removing the product hydrogen, and constructs a two-stage series water-gas shift process of a high-temperature shift process and a palladium membrane reactor to achieve a high-conversion hydrogen production process at high temperature. The purity of the produced hydrogen meets the standards for use in fuel cells, and the hydrogen yield exceeds 93%. The increase in the reaction temperature of the second stage conversion and the full utilization of the latent heat of the stream increase the output of by-product steam and the proportion of high-quality steam output, thereby improving the economic benefits of the water-gas shift process.

[0009] The technical solution of the present invention:

[0010] A water gas shift hydrogen production process coupling high temperature shift and membrane reactor with comprehensive consideration of heat energy utilization. The pretreated raw coal gas S1 enters the high temperature shift reactor unit 1 for reaction to obtain the high temperature shift treated gas S2; the high temperature shift treated gas S2 enters the membrane reaction unit 2 for further reaction. On the reaction side of the membrane reaction unit 2, the reaction retentate gas S5 is obtained, and on the permeation side of the membrane reaction unit 2, the reaction permeate gas S3 with a hydrogen purity reaching 99.99% is obtained; after being treated by the membrane reaction unit 2, the temperatures of both the reaction permeate gas S3 and the reaction retentate gas S5 exceed 450 °C. Then, heat recovery is carried out on the reaction permeate gas S3 and the reaction retentate gas S5 respectively. The reaction permeate gas S3 is cooled to 40 °C by the first multi-stage heat exchanger 3 to obtain the hydrogen product S4; the reaction retentate gas S5 is cooled to 40 °C by the second multi-stage heat exchanger 4 to obtain the retentate cooling gas S6; the retentate cooling gas S6 enters the first liquid separation tank 5, and the first mixture aqueous solution S7 is obtained at the bottom of the first liquid separation tank 5; the first non-condensable gas S8 is obtained at the top of the first liquid separation tank 5, and the remaining moisture in the first non-condensable gas S8 is removed by the drying tower 6. The second mixture aqueous solution S9 is obtained at the bottom of the drying tower 6, and the dried gas S10 is obtained at the top of the drying tower 6; the dried gas S10 recovers the cold energy of the low-pressure non-condensable gas S15 treated by the expander 10 through the third heat exchanger 7 to obtain the second dried gas S11. The second dried gas S11 passes through the fourth heat exchanger 8 to obtain the third dried gas S12. The third dried gas S12 is cooled to -40 °C under the action of the refrigerant and then enters the second liquid separation tank 9; the second non-condensable gas S14 at the top of the second liquid separation tank 9 is depressurized by the expander 10 to obtain the low-pressure non-condensable gas S15; the low-pressure non-condensable gas S15 recovers the cold energy through the third heat exchanger 7 and is heated to 35 °C to obtain the fuel gas S16 for combustion heating; the CO2 rich liquid S13 is withdrawn from the bottom of the second liquid separation tank 9 for oil displacement.

[0011] Advantages of the present invention: By using a palladium membrane reactor to replace the low-temperature shift reactor, the means of increasing the conversion rate is changed from lowering the reaction temperature to removing the product hydrogen. A two-stage series water-gas shift process of a high-temperature shift process and a palladium membrane reactor is constructed to achieve a hydrogen production process with high conversion rate at high temperature. The purity of the produced hydrogen meets the fuel cell usage standard, and the hydrogen yield reaches 93.8%. The membrane reactor replaces the traditional low-temperature water-gas shift process. On the one hand, the reaction stream after high-temperature shift treatment does not need to be cooled and can directly enter the membrane reactor to continue. The reaction temperature increases by about 250K. On the other hand, the membrane reactor realizes the separation and purification of hydrogen, resulting in an increase in the partial pressure of water vapor in the reaction-side stream. When heat is utilized, the vaporous water will liquefy earlier. Compared with the traditional shift process, the latent heat release temperature of the improved process is higher and more concentrated at a higher quality. Compared with the traditional hydrogen production process, the increase in reaction temperature and the early release of latent heat improve the energy grade, facilitate heat recovery, and ultimately increase the income from by-product steam and hot water by 16.2%. In addition, the membrane reaction process realizes a high degree of integration of the reaction process and the separation process, simplifies the process, and compared with the traditional hydrogen production process, the investment cost is saved by 42.1% and the operating cost is reduced by 18.5%. Brief Description of the Drawings

[0012] Figure 1 It is a principle process flow of a hydrogen production process using a membrane reactor and a heat exchange system to improve the quality of by-product steam in the water-gas shift process.

[0013] In the figure: 1 high-temperature water-gas shift unit; 2 membrane reactor unit; 3 first multi-stage heat exchanger; 4 second multi-stage heat exchanger; 5 first liquid separation tank; 6 drying tower; 7 third heat exchanger; 8 fourth heat exchanger; 9 second liquid separation tank; 10 expander; S1 raw coal gas; S2 high-temperature shift treated gas; S3 reaction permeate gas; S4 hydrogen product gas; S5 reaction retentate gas; S6 retentate cooling gas; S7 first mixture aqueous solution; S8 first non-condensable gas; S9 second mixture aqueous solution; S10 dried gas; S11 second dried gas; S12 third dried gas; S13 CO2-rich liquid; S14 second non-condensable gas; S15 low-pressure non-condensable gas; S16 fuel gas. Detailed Embodiments

[0014] The following further describes the detailed embodiments of the present invention in conjunction with the drawings and technical solutions.

[0015] Example 1

[0016] For the raw coal gas after pretreatment in the purification unit of a certain coal-to-hydrogen plant, the raw material is 380,000 Nm 3The raw coal gas at [X] Nm³ / h, with the composition shown in Table 1, adopts the hydrogen production process of the membrane reactor and heat exchange system for improving the quality of by-product steam in the water gas shift process of the present invention, reducing the investment and operation costs, and increasing the benefits such as by-product steam products. The flow rate of the pretreated raw coal gas feedstock is 380,000 Nm³ / h, the pressure is 4.30 MPaG, and the temperature is 244 °C, and this feed stream consists of 22.56 mol% of CO, 50.95 mol% of H₂O, 4.34 mol% of CO₂, 17.52 mol% of H₂, and 4.63 mol% of N₂. 3 The raw coal gas (S1) after sufficient pretreatment first enters the high-temperature water gas shift unit (1) for reaction, with the CO conversion rate reaching 89.42%, and the temperature (S2) rises to 440 °C. Then it enters the membrane reactor unit (2) to continue the reaction. The reaction permeate gas S3 and the reaction retentate gas S5 have their temperatures rise to 475 °C, and the total CO conversion rate reaches 98.32%. The reaction permeate gas S3 is processed by the multi-stage heat exchanger 3, and after cascade heat exchange, the temperature drops to 40 °C, obtaining a hydrogen product gas S4 with a hydrogen purity of 99.999 mol%, and respectively producing steam at 4.1 MPaG, 1.0 MPaG, 0.5 MPaG and 95 °C hot water; at the same time, the reaction retentate gas S5 is processed by the multi-stage heat exchanger 4, and after cascade heat exchange, the retentate cooling gas S6 has its temperature drop to 40 °C and the pressure drop to 4.24 MPaG, respectively producing steam at 4.1 MPaG, 1.0 MPaG, 0.5 MPaG and 95 °C hot water. The retentate cooling gas S6 enters the first liquid separation tank 5 to remove most of the water in the retentate cooling gas S6 (the water content drops from 45.62 mol% to 0.31 mol%). In order to prevent freezing blockage in the shallow cooling process, it is necessary to deeply remove water. The first non-condensable gas S8 enters the drying tower 6, and dry gas S10 without water is obtained at the top of the tower, with a CO₂ content of 77.83 mol%; after the dry gas S10 is heat exchanged by the third heat exchanger 7 and the fourth heat exchanger 8, the temperature drops to -40 °C and the pressure is 4.12 MPaG. Subsequently, it enters the second liquid separation tank 9, and the second non-condensable gas S14 is obtained at the top of the tower. After that, S14 is depressurized and expanded and the cold energy is recovered to obtain the fuel gas S16; at the same time, the CO₂ product gas S13 is obtained at the bottom of the second liquid separation tank 9, with the CO₂ content reaching 96.03 mol%. The actual key material composition and operation parameters in the example are shown in Table 2.

[0017]

[0018] Table 2 List of Composition and Operation Parameters of Key Materials in the Example

[0019]

[0020] ​The process simulation optimization results show that by using the hydrogen production process of the membrane reactor and heat exchange system for improving the quality of by-product steam in the water-gas shift process described in the present invention, the following products can be produced: high-quality hydrogen directly used in the fuel cell / synthesis ammonia reaction process, where the purity of hydrogen exceeds 99.999 mol% and the carbon monoxide content is less than 20 ppmv, and the production is 142445 Nm 3 / h, and the hydrogen recovery rate reaches 93.79%; 99197 Nm of 4.1 MPaG steam 3 / h, 71748 Nm of 1.0 MPaG steam 3 / h, 39874 Nm of 0.5 MPaG steam 3 / h, and 496 t / h of 95 °C hot water; 92874 Nm of CO2 product gas (purity 96.03 mol%) that can be used for oil displacement 3 / h.

[0021] In the hydrogen production process of the membrane reactor and heat exchange system for improving the quality of by-product steam in the water-gas shift process described in the present invention, a palladium membrane reactor is used to replace the low-temperature shift reactor, and the means of increasing the conversion rate is changed from reducing the reaction temperature to removing the product hydrogen. A two-stage series water-gas shift process of high-temperature shift process and palladium membrane reactor is constructed to realize a high-conversion hydrogen production process at high temperature. Compared with the traditional process, the total value of the by-product steam of the improved process reaches 39.2 MW, an increase of 11.1% year-on-year, and the efficiency is increased from 79.1% to 81.5%. The total equipment investment in the whole system process can be reduced by 94 million yuan, a year-on-year savings of 42.1%, the operating cost can be reduced by 16 million yuan per year, a year-on-year savings of 12.1%, and the steam output value can be increased by 41 million yuan per year, a year-on-year increase of 16.2%.

[0022] In summary, in the hydrogen production process of the membrane reactor and heat exchange system for improving the quality of by-product steam in the water-gas shift process described in the present invention, under the same CO conversion rate as the traditional shift, the reaction heat is fully utilized, the proportion of high-quality steam output increases significantly, the steam output value increases by 41 million yuan per year, a year-on-year increase of 16.2%. At the same time, the shift process of this study realizes the selective separation of hydrogen, simplifies the subsequent separation and purification process, and the total equipment investment and operating cost of the whole system process are greatly reduced, with significant economic benefits.

Claims

1. A water gas shift hydrogen production process coupling high temperature shift membrane reactor with comprehensive consideration of heat energy utilization, characterized in that: The pretreated raw coal gas (S1) enters the high-temperature shift reactor unit (1) for reaction to obtain the high-temperature shift treated gas (S2); the high-temperature shift treated gas (S2) enters the membrane reaction unit (2) for further reaction. On the reaction side of the membrane reaction unit (2), the reaction retentate gas (S5) is obtained, and on the permeate side of the membrane reaction unit (2), the reaction permeate gas (S3) with a hydrogen purity reaching 99.99% is obtained; after being treated by the membrane reaction unit (2), the temperatures of both the reaction permeate gas (S3) and the reaction retentate gas (S5) exceed 450°C. Then, heat recovery is carried out on the reaction permeate gas (S3) and the reaction retentate gas (S5) respectively. The reaction permeate gas (S3) is cooled to 40°C by the first multi-stage heat exchanger (3) to obtain the hydrogen product (S4); the reaction retentate gas (S5) is cooled to 40°C by the second multi-stage heat exchanger (4) to obtain the retentate cooling gas (S6); the retentate cooling gas (S6) enters the first liquid separation tank (5), and the first aqueous mixture solution (S7) is obtained at the bottom of the first liquid separation tank (5); the first non-condensable gas (S8) is obtained at the top of the first liquid separation tank (5). The remaining moisture in the first non-condensable gas (S8) is removed by the drying tower (6). The second aqueous mixture solution (S9) is obtained at the bottom of the drying tower (6), and the dried gas (S10) is obtained at the top of the drying tower (6); the dried gas (S10) recovers the cold energy of the low-pressure non-condensable gas (S15) treated by the expander (10) through the third heat exchanger (7) to obtain the second dried gas (S11). The second dried gas (S11) passes through the fourth heat exchanger (8) to obtain the third dried gas (S12). The third dried gas (S12) is cooled to -40°C under the action of the refrigerant and then enters the second liquid separation tank (9); the second non-condensable gas (S14) at the top of the second liquid separation tank (9) is depressurized by the expander (10) to obtain the low-pressure non-condensable gas (S15); the low-pressure non-condensable gas (S15) recovers the cold energy through the third heat exchanger (7) and is heated to 35°C to obtain the fuel gas (S16) for combustion heating; the CO2-rich liquid (S13) is withdrawn from the bottom of the second liquid separation tank (9) for oil displacement.

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