CN117903855A - Multistage hydrogen returning cold shock methanation production method and system - Google Patents
Multistage hydrogen returning cold shock methanation production method and system Download PDFInfo
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Abstract
The invention provides a multi-section hydrogen returning cold shock methanation production method and system. The method comprises the following steps: allowing the purified coke oven gas to enter a high-temperature methanation reactor for reaction; dividing the gas after the high-temperature methanation reaction into two parts, wherein one part is used as circulating gas, and the other part enters a medium-temperature methanation reactor to continuously react; after the waste heat recovery of the gas after the medium-temperature methanation reaction, the gas enters a gas-water separation tank for separation to obtain synthesis gas; enabling the synthesis gas to enter a membrane separator for separation to obtain hydrogen and product gas; and enabling the hydrogen obtained through the membrane separator to enter a high-temperature methanation reactor for cold shock. The system comprises a high-temperature methanation reactor, a first waste heat recovery device, a medium-temperature methanation reactor, a second waste heat recovery device, a gas-water separation tank and a membrane separator. The invention can improve the methanation reaction efficiency of coke oven gas, reduce the content of carbon oxide in methane product gas and increase the yield of methane product gas.
Description
Technical Field
The invention relates to a multi-section hydrogen returning cold shock methanation production method and system, and belongs to the technical field of coke oven gas methanation.
Background
Natural gas is a clean energy source, has higher added value and has very wide application. In the coal industry, a large amount of coke oven gas is produced. The coke oven gas mainly comprises H 2(53％～59％)、CH4(22％～30％)、CO(6％～9％)、CO2 (2% -3%), N 2 (2% -5%) and other small components, and is an ideal raw material for preparing natural gas. The core technology for synthesizing natural gas is methanation catalyst and methanation process technology. Wherein, the development of methanation catalyst is mature, and the research universities grasping the production process of methanation catalyst are not more than counted. However, the methanation technology of the existing coal natural gasification plants is not mature enough. The key of methanation technology is to solve the problems of large heat release amount, difficult heat extraction and the like in the reaction process, maintain the constant temperature of a reactor bed layer, and prevent the deactivation and sintering of a catalyst under the high temperature condition.
After being purified, the coke oven gas mainly contains H 2、CH4、CO、N2, CO 2 and the like. The principle of the methanation process is that under the condition of proper temperature and pressure, CO 2 and H 2 react under the action of a catalyst:
CO+3H2＝CH4+H2O△H0298＝-206.2kJ/mol；
CO2+4H2＝CH4+2H2O△H0298＝-165.0kJ/mol；
CO+H2O＝CO2+H2△H0298＝-41.16kJ/mol。
As can be seen from the above equation, methanation is a strongly exothermic reaction with reduced volume. The adiabatic temperature rise that can occur per conversion of 1% of the CO and CO 2 is about 72℃and 60℃respectively. From the thermodynamic analysis, the reaction pressure is increased, the reaction temperature is reduced, and the reaction equilibrium is facilitated to be carried out in the forward direction. The development of the reactor and the optimal utilization of the process energy are the difficulties and keys of the methanation unit.
CN204385149U discloses a coke oven gas cold shock methanation reaction device. The coke oven gas methanation reaction adopts a cold shock type reactor, and is characterized in that the catalyst is filled in sections, a cold shock area is arranged between two sections of catalyst beds, and at least one cold shock area is arranged in the reactor. The coke oven gas containing a proper amount of circulating gas enters from the upper part of the reactor, and after entering the first section of catalyst bed layer, methanation reaction occurs, and the temperature rises. The gas flowing out of the first stage of bed layer enters a cold shock zone to be mixed with a certain amount of low-temperature coke oven gas, and enters the second stage of catalyst bed layer to undergo methanation reaction, and the temperature is increased. The gas flowing out of the second section of bed layer enters a cold shock zone to be mixed with a certain amount of low-temperature coke oven gas, and enters a third section of catalyst bed layer to undergo methanation reaction, and the temperature is increased. The device only carries out circulating dilution on the coke oven gas entering the first section bed layer of the cold shock reactor.
However, the coke oven gas cold shock methanation reaction device adopts a mode of connecting adiabatic fixed beds in series, so that the methanation reaction is gradually reacted in each adiabatic reactor. In order to avoid the situation of over-high hot spot temperature, coke oven gas is supplemented, and each cooling zone can only simply reduce the reaction temperature. The addition of coke oven gas does not increase the conversion rate and increases the reactor length. These not only increase the equipment investment, but also waste energy.
CN206109337U discloses a multistage cold shock type coke oven gas methanation device, which comprises a methanation reactor, an electric heater, an air cooler, a boiler feed water preheater, a medium pressure steam drum and a gas-liquid separator; the methanation reactor is formed by sequentially connecting an adiabatic reaction section I, a quenching chamber I, an adiabatic reaction section II, a quenching chamber II, an adiabatic reaction section III, a quenching chamber III and an isothermal reaction section, wherein a carbon dioxide inlet is arranged at the inlet of the quenching chamber III, the isothermal reaction section is in a tubular form, and the shell side of the isothermal reaction section is connected with a medium-pressure steam drum. The device reduces the temperature of the reaction gas through multistage cold shock, so that the temperature of the reaction bed layer of the methanation reactor is kept in a controllable range, and the sintering deactivation of the catalyst caused by overhigh temperature of the bed layer is avoided.
However, the device adopts coke oven gas to cool the reaction, only can control the temperature of a bed layer, prevents the catalyst from being sintered and deactivated, and can not make the catalyst better utilized. Meanwhile, the problem of higher carbon oxides in the product cannot be solved. In addition, the device has the waste of energy, and the gas carries out the flow of cooling and heating, so that the energy consumption is high, and the process flow is unreasonable.
CN103820183a discloses a method for preparing synthetic natural gas by directly supplementing carbon dioxide into coke oven gas, the main working procedures of the method comprise coke oven gas compression, purification, CO 2 gasification, methanation and membrane separation, and the coke oven gas methanation working procedure is three-stage methanation reaction. Supplementing CO 2 in the methanation reaction process, and fully utilizing CO 2 and H 2 in the mixed gas to the maximum extent; and distributing methanation synthesis gas into a reactor before the final stage methanation reactor and partial internal circulation of gas among methanation reactors before the final stage methanation reactor according to a certain proportion to realize effective control of reaction balance, reaction pressure and reaction heat release of methanation reaction.
Although this method can increase the yield of CH 4 in synthetic natural gas, the process sends the product from the outlet of the second stage reactor as a diluent gas to the inlet of the first stage reactor, which only reduces the temperature at the inlet of the reactor and does not increase the reaction rate. The investment, failure rate and safety risk of the process are all high. In addition, the temperature of the first reactor of the process is higher, and the catalyst has the problems of higher heat inactivation speed and higher carbon deposition rate.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a multi-stage hydrogen returning cold shock methanation production method and system. The invention can improve the methanation reaction efficiency of coke oven gas, reduce the content of carbon oxide in methane product gas and increase the yield of methane product gas.
In order to achieve the above object, the first aspect of the present invention provides a multi-stage hydrogen returning cold shock methanation production method, which comprises the following steps:
enabling the purified coke oven gas to enter a high-temperature methanation reactor from the top of the high-temperature methanation reactor to react to obtain high-temperature methanation reacted gas, and enabling the gas to flow out from the bottom of the high-temperature methanation reactor;
Dividing the high-temperature methanation reaction gas into two parts, mixing one part of the high-temperature methanation reaction gas serving as circulating gas with the purified coke oven gas, returning the mixture to the high-temperature methanation reactor, enabling the other part of the high-temperature methanation reaction gas to enter the medium-temperature methanation reactor from the top of the medium-temperature methanation reactor for continuous reaction, obtaining medium-temperature methanation reaction gas, and enabling the medium-temperature methanation reaction gas to flow out from the bottom of the medium-temperature methanation reactor;
after the waste heat recovery is carried out on the gas after the medium-temperature methanation reaction, the gas enters a gas-water separation tank for separation, and synthesis gas is obtained;
Allowing the synthesis gas to enter a membrane separator for separation to obtain hydrogen and product gas;
Enabling the hydrogen obtained through the membrane separator to enter the high-temperature methanation reactor for cold shock;
The high-temperature methanation reactor comprises a plurality of sections of catalyst beds in the vertical direction, a heat transfer coil pipe arranged between every two sections of adjacent catalyst beds, and a hydrogen returning device arranged in each section of catalyst beds; the hydrogen obtained by the membrane separator enters each section of catalyst bed layer from the hydrogen returning device for cold shock; introducing a liquid-phase cooling medium into the heat-transfer coil pipe to transfer heat; and (5) recovering waste heat of the heat transfer coil.
In the above-described method, preferably, the catalyst bed in the high-temperature methanation reactor is a fixed bed.
In the above method, preferably, the hydrogen returning device is arranged at 1/2-2/3 of the top to bottom of each section of catalyst bed.
In the invention, the hydrogen returning device is arranged in each section of catalyst bed, compared with the hydrogen returning device arranged between the catalyst beds, the design of the invention can more directly finely adjust the reaction temperature, can control the reaction temperature to fly up, reduce the temperature gradient in the reactor, reduce the local reaction rate fluctuation caused by hot spots and temperature difference, improve the stability of the reactor and reduce carbon deposition for the adiabatic reactor. Meanwhile, the hydrogen returning device is arranged at 1/2-2/3 of the initial position of each section of catalyst bed (namely from the top to the bottom of the bed), the temperature of the later section of the reaction is higher, the reaction speed is faster, the reaction is easy to run away, the temperature is easy to rise, and cold hydrogen is fed into the later section of the catalyst bed, so that the reaction rate can be adjusted, and the reaction is milder.
In the above method, preferably, the hydrogen returning device includes a hydrogen returning main pipe and a plurality of hydrogen returning branch pipes connected to the hydrogen returning main pipe, the hydrogen returning main pipe is perpendicular to an axial direction of the high-temperature methanation reactor, the plurality of hydrogen returning branch pipes are perpendicular to the hydrogen returning main pipe and are on the same plane, and the plurality of hydrogen returning branch pipes are provided with a plurality of gas distribution holes. The hydrogen returning device can efficiently and uniformly supplement hydrogen into the catalyst bed, accurately control the temperature of the catalyst bed, and ensure the yield of target products and the long-period stable operation of the catalyst.
In the above method, preferably, the high-temperature methanation reactor comprises two-four sections of catalyst beds, a heat transfer coil arranged between every two adjacent sections of catalyst beds, and a hydrogen returning device arranged in each section of catalyst beds. More preferably, the high temperature methanation reactor comprises two sections of catalyst beds, a heat transfer coil disposed between the two sections of catalyst beds, and a hydrogen return device disposed in each section of catalyst bed.
According to the invention, two-section to four-section catalyst beds can be arranged according to the scale of the reactor, 2 to 4 hydrogen gas are correspondingly introduced into the high-temperature methanation reactor, the temperature of the high-temperature methanation reactor is controlled, the reaction temperature is prevented from rising, the carbon formation and the deactivation of the catalyst are prevented, and the service life of the catalyst is further prolonged.
In the above method, preferably, in the high-temperature methanation reactor, a temperature measuring device is arranged on each section of catalyst bed layer so as to monitor the temperature of the bed layer in real time. The specific setting positions and the number of the temperature measuring devices can be adjusted conventionally by those skilled in the art, and the present invention is not particularly limited.
According to the invention, through the arrangement of the hydrogen returning device and the arrangement of the heat transfer coil between the catalyst beds, the temperature of the reactor can be controlled more stably, so that the traditional three-stage methanation reactor is reduced to be a two-stage methanation reactor (namely the high-temperature methanation reactor and the medium-temperature methanation reactor) and the two-stage methanation reactor is combined into a whole.
In the high-temperature methanation reactor, carbon oxides in purified coke oven gas are adsorbed on the surface of a catalyst, carbon-oxygen bonds are broken under the action of the catalyst, carbon atoms and oxygen atoms are separated, the carbon atoms in an adsorption state collide with hydrogen molecules on the surface of the catalyst to form methane, and the oxygen atoms are combined with the hydrogen molecules in the reactor to generate water vapor molecules to enter a gas phase, so that gas after the high-temperature methanation reaction is obtained.
In the above method, preferably, the pressure of the purified coke oven gas is 3.0MPa to 3.5MPa and the temperature is 230 ℃ to 250 ℃. The reaction pressure in the high-temperature methanation reactor is 3.0-3.5 MPa, the reaction rate is ideal under the condition of the reaction pressure, and the reaction rate is not obviously increased when the reaction pressure is continuously increased.
In the above method, preferably, the temperature of the purified coke oven gas after mixing with the recycle gas is 280 ℃ to 320 ℃. According to the invention, a part of the gas after the high-temperature methanation reaction is used as the circulating gas and returned to the high-temperature methanation reactor, so that not only can water vapor be supplemented, the conversion rate can be improved, but also the circulating ratio can be adjusted to control the temperature of the reactor and improve the inlet temperature of the reactor.
In the above-described method, the circulation ratio of the high-temperature methanation reactor is preferably 0.25 to 0.35. The higher the reactor hot spot temperature, the greater the design is to control the temperature rise cycle. The invention can maximize the methane flow by controlling the ratio of the circulating gas to the purified coke oven gas (namely the circulating ratio) to be 0.25-0.35, and reduces the reactor volume by reducing the circulating ratio of the reactor.
In the above method, preferably, the hydrogen is introduced into the first-stage catalyst bed layer of the high-temperature methanation reactor from top to bottom by the hydrogen returning device, so that the gas temperature in the first-stage catalyst bed layer is controlled at 400-450 ℃.
In the above method, preferably, the heat transfer coil is a tube bundle formed by spirally winding a plurality of lines, and the tube bundle is spiral. According to the invention, through the spiral winding design of the heat transfer coil, the problems of pipeline deformation and tearing caused by thermal stress shrinkage due to the temperature difference between the liquid-phase cooling medium in the heat transfer coil and the high-temperature environment inside the reactor are solved, and the continuous and stable feeding of the liquid-phase cooling medium in the heat transfer coil is ensured.
In the above method, preferably, a liquid-phase cooling medium is introduced into the heat transfer coil, so that the gas temperature in the high-temperature methanation reactor after passing through the heat transfer coil is controlled to be 280-350 ℃. More preferably, the liquid-phase cooling medium comprises cooling water.
In the invention, the heat transfer quantity of the heat transfer coil is controlled by temperature, and the difference between the heat transfer devices arranged between the multi-stage methanation reactors in the prior art is that the two-stage methanation reactor is integrated, and the heat transfer coil is arranged between every two adjacent catalyst beds, so that heat exchange is carried out in the high-temperature adiabatic reactor, parameters such as temperature, pressure and the like in the reaction process can be monitored and adjusted in real time, the reaction temperature gradient can be effectively controlled, and the optimal control of the reaction process is realized.
In the above method, preferably, the hydrogen is introduced into the second-stage catalyst bed layer of the high-temperature methanation reactor from top to bottom by the hydrogen returning device, so that the gas temperature in the second-stage catalyst bed layer is controlled at 380-430 ℃.
In the above method, preferably, the hydrogen is introduced into the nth stage catalyst bed of the high temperature methanation reactor from top to bottom by the hydrogen returning device, n is an integer not less than 3, more preferably, n is 3 or 4, and the gas temperature in the nth stage catalyst bed is reduced by 20 ℃ to 60 ℃ compared with the gas temperature in the nth-1 stage catalyst bed.
In the above method, the reaction temperature in the medium-temperature methanation reactor is preferably 280 to 300 ℃ and the reaction pressure is preferably 3.0 to 3.2MPa.
In the above method, preferably, the separation membrane used in the membrane separator includes a separation membrane having a H 2/CH4 selectivity of greater than 35.
According to a specific embodiment of the present invention, preferably, the method further comprises: and mixing carbon dioxide with the purified coke oven gas, and then enabling the mixture to enter a high-temperature methanation reactor from the top of the high-temperature methanation reactor for reaction. The method of the invention can further supplement CO 2 to increase methane production.
The second aspect of the invention provides a multi-stage hydrogen returning cold shock methanation production system for realizing the multi-stage hydrogen returning cold shock methanation production method, which comprises the following steps: the device comprises a high-temperature methanation reactor, a purified coke oven gas inlet main pipe, a first waste heat recovery device, a high-temperature methanation reactor outlet main pipe, a high-temperature methanation reactor circulating gas pipe, a medium-temperature methanation reactor outlet main pipe, a second waste heat recovery device, a gas-water separation tank, a membrane separator and a hydrogen conveying main pipe;
The high-temperature methanation reactor comprises a plurality of sections of catalyst beds in the vertical direction, a heat transfer coil arranged between every two sections of adjacent catalyst beds and a hydrogen returning device arranged in each section of catalyst beds, wherein the top of the high-temperature methanation reactor is provided with a raw material gas inlet, and the bottom of the high-temperature methanation reactor is provided with a reacted gas outlet; the top of the medium-temperature methanation reactor is provided with a reaction gas inlet, and the bottom of the medium-temperature methanation reactor is provided with a reacted gas outlet; the gas-water separation tank is provided with an air inlet and a synthesis gas outlet; the membrane separator is provided with an air inlet, a hydrogen outlet and a product gas outlet;
the raw material gas inlet at the top of the high-temperature methanation reactor is communicated with the purified coke oven gas inlet main pipe, the reacted gas outlet at the bottom of the high-temperature methanation reactor is communicated with the reaction gas inlet at the top of the medium-temperature methanation reactor through the high-temperature methanation reactor outlet main pipe, the high-temperature methanation reactor circulating gas pipe is communicated with the purified coke oven gas inlet main pipe and the high-temperature methanation reactor outlet main pipe, and the heat transfer coil of the high-temperature methanation reactor is communicated with the first waste heat recovery device;
The reacted gas outlet at the bottom of the medium temperature methanation reactor is communicated with the gas inlet of the gas-water separation tank through the gas outlet main pipe of the medium temperature methanation reactor, and the gas outlet main pipe of the medium temperature methanation reactor is provided with the second waste heat recovery device;
The synthesis gas outlet of the gas-water separation tank is communicated with the gas inlet of the membrane separator, and the hydrogen outlet of the gas-water separation tank is communicated with the hydrogen returning device through the hydrogen conveying main pipe.
In the above system, preferably, the catalyst bed in the high temperature methanation reactor is a fixed bed.
In the above system, preferably, the hydrogen returning device is arranged at 1/2-2/3 of the top to bottom of each section of catalyst bed.
In the above system, preferably, the hydrogen returning device includes a hydrogen returning main pipe and a plurality of hydrogen returning branch pipes connected to the hydrogen returning main pipe, the hydrogen returning main pipe is perpendicular to an axial direction of the high-temperature methanation reactor, the plurality of hydrogen returning branch pipes are perpendicular to the hydrogen returning main pipe and are on the same plane, and the plurality of hydrogen returning branch pipes are provided with a plurality of gas distribution holes.
In the above system, preferably, in the high-temperature methanation reactor, a hydrogen return main pipe of the hydrogen return device in each section of catalyst bed layer is respectively communicated with the hydrogen delivery main pipe through a hydrogen delivery branch pipe, and each hydrogen delivery branch pipe is provided with a hydrogen return regulating valve.
In the above system, preferably, the high-temperature methanation reactor comprises two-four sections of catalyst beds, a heat transfer coil arranged between every two adjacent sections of catalyst beds, and a hydrogen returning device arranged in each section of catalyst beds. More preferably, the high temperature methanation reactor comprises two sections of catalyst beds, a heat transfer coil disposed between the two sections of catalyst beds, and a hydrogen return device disposed in each section of catalyst bed.
In the above system, preferably, in the high temperature methanation reactor, a temperature measurement device is provided for each section of catalyst bed.
In the above system, preferably, the heat transfer coil is a tube bundle formed by spirally winding a plurality of lines, and the tube bundle is in a spiral shape.
In the system, preferably, a circulating gas regulating valve is arranged on a circulating gas pipe of the high-temperature methanation reactor.
In the above system, preferably, the separation membrane used in the membrane separator comprises a separation membrane having a H 2/CH4 selectivity of greater than 35.
According to a specific embodiment of the present invention, preferably, the system further comprises: the carbon dioxide gas inlet main pipe is communicated with the purified coke oven gas inlet main pipe and the feed gas inlet at the top of the high-temperature methanation reactor, and a carbon dioxide supplementing regulating valve is arranged on the carbon dioxide gas inlet main pipe.
The invention provides a multi-section hydrogen returning cold shock methanation production method and system, optimizes a coke oven gas methanation process and is a technology for saving energy and increasing yield of methane by utilizing coke oven gas hydrogen returning. The natural gas prepared by methanation of coke oven gas in the prior art has the defects of long flow, high preparation cost and the like. In addition, after methanation of coke oven gas in the prior art, the methane product gas has high content of carbon oxides, incomplete reaction, large circulation amount and residual hydrogen. Moreover, the energy consumption for separating methane from hydrogen is high. Meanwhile, the reaction temperature of the methanation reactor rises, and the catalyst cannot be effectively utilized. The inventor optimizes the existing coke oven gas methanation process and provides the multi-section hydrogen returning cold shock methanation production method and system. The method and the system can improve the methanation reaction efficiency of the coke oven gas, reduce the content of the carbon-oxygen compound in the methane product gas and increase the yield of the methane product gas. In addition, the method and the system of the invention have convenient operation, high catalytic reaction efficiency and better stable production. Meanwhile, the method and the system of the invention can also increase the service life of the catalyst, reduce the size of the reactor and reduce the equipment investment, thereby saving the production cost.
The invention uses the hydrogen obtained by separation after reaction as a cold shock source, supplements the hydrogen into the catalyst bed layer of the high-temperature methanation reactor through the hydrogen returning device, realizes the full utilization of coke oven gas hydrogen and simultaneously effectively controls the hot spot temperature of the reactor. And the temperature of the reactor can be controlled more stably by matching with the arrangement of the heat transfer coil pipes between the catalyst beds, the temperature gradient inside the reactor is reduced, the local reaction rate fluctuation caused by hot spots and temperature difference is reduced, the stability of the reactor is improved, and carbon deposition is reduced. Meanwhile, the traditional three-stage methanation reactor is reduced to be a two-stage methanation reactor, and the two-stage high-temperature methanation reactor is combined into a whole. In addition, the invention uses the gas after the high-temperature methanation reaction as the circulating gas, increases the circulating ratio in the high-temperature methanation reactor, can supplement water vapor, can effectively inhibit the temperature of the reactor from flying, can improve the conversion rate, can also adjust the circulating ratio to control the temperature of the reactor, and can improve the inlet temperature of the reactor. And, by supplementing CO 2, methane production can be improved. The temperature of the high-temperature methanation reactor can be controlled by adjusting the hydrogen return flow rate and the circulating gas circulation ratio of different positions. The hydrogen-carbon ratio of the raw material gas in the high-temperature methanation reactor can be controlled by adjusting the flow of the returned hydrogen and the carbon dioxide, so that the volume of the reactor is obviously reduced.
The technical scheme of the invention has at least the following beneficial effects:
1. the invention fully utilizes the rich hydrogen of the coke oven gas, carries out cold shock on the high-temperature methanation reactor, controls the temperature of the reactor, prevents carbonization and catalytic deactivation, further improves the service life of the catalyst, better plays the catalytic role and can better stabilize the production.
2. The invention utilizes the multistage hydrogen returning cold shock methanation reaction, increases the hydrogen partial pressure, accelerates the reaction efficiency, can effectively reduce the size of the reactor, reduces the high preparation cost and further saves the production cost.
3. The invention adopts the multi-stage hydrogen returning mode of the product gas to ensure that the temperature of the reactor is more stable.
4. The invention has simple process flow, reasonable system overall configuration and energy conservation.
5. The invention improves the conversion rate of carbon dioxide and carbon monoxide, improves the methanation reaction efficiency of coke oven gas, ensures that the conversion rate of carbon monoxide can reach 100%, ensures that the conversion rate of carbon dioxide can reach more than 95%, increases the yield of methane product gas, and effectively solves the problem of high content of carbon-oxygen compounds in the prepared methane product gas.
Drawings
FIG. 1 is a schematic diagram of the flow and system configuration of a multi-stage hydrogen returning cold shock methanation production process according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of the structure of a high temperature methanation reactor in an embodiment of the invention.
Reference numerals illustrate:
1-a high temperature methanation reactor; 2-a purified coke oven gas inlet main pipe; 3-a first waste heat recovery device; 4-a main gas outlet pipe of the high-temperature methanation reactor; a circulating gas pipe of the 5-high temperature methanation reactor; 6-a medium temperature methanation reactor; 7-a main gas outlet pipe of the medium-temperature methanation reactor; 8-a second waste heat recovery device; 9-a gas-water separation tank; 10-a membrane separator; 11-a hydrogen delivery main pipe; 12-hydrogen delivery branch pipes; 13-a carbon dioxide air inlet main pipe;
101-a catalyst bed; 102-heat transfer coil; 103-a hydrogen return device;
120-a hydrogen return regulating valve;
501-a circulating gas regulating valve;
130-a supplemental carbon dioxide regulator valve;
701-butterfly valve.
Detailed Description
The technical solution of the present invention will be described in detail below for a clearer understanding of technical features, objects and advantageous effects of the present invention, but should not be construed as limiting the scope of the present invention.
According to a specific embodiment of the invention, the invention provides a multi-stage hydrogen returning cold shock methanation production method, which comprises the following steps as shown in fig. 1:
The purified coke oven gas enters a high-temperature methanation reactor 1 from the top of the high-temperature methanation reactor 1 through a purified coke oven gas inlet main pipe 2 to react to obtain high-temperature methanation reacted gas, and the high-temperature methanation reacted gas flows out from the bottom of the high-temperature methanation reactor 1 and enters an outlet main pipe 4 of the high-temperature methanation reactor;
The gas after the high-temperature methanation reaction is divided into two parts, one part is taken as circulating gas, the circulating gas is mixed with the purified coke oven gas through a circulating gas pipe 5 of the high-temperature methanation reactor and then returned to the high-temperature methanation reactor 1, the other part enters the medium-temperature methanation reactor 6 from the top of the medium-temperature methanation reactor 6 for continuous reaction, the gas after the medium-temperature methanation reaction is obtained, and the gas flows out from the bottom of the medium-temperature methanation reactor 6 and enters a gas outlet main pipe 7 of the medium-temperature methanation reactor;
after the gas subjected to the intermediate-temperature methanation reaction is subjected to waste heat recovery by the second waste heat recovery device 8, the gas enters the gas-water separation tank 9 for separation, and synthesis gas is obtained;
allowing the synthesis gas to enter a membrane separator 10 for separation to obtain hydrogen and product gas;
The hydrogen obtained by the membrane separator 10 enters the high-temperature methanation reactor 1 through the hydrogen conveying main pipe 11 for cold shock;
As shown in fig. 2, the high-temperature methanation reactor 1 includes a plurality of catalyst beds 101 (two catalyst beds 101 shown in fig. 2) in a vertical direction, a heat transfer coil 102 disposed between each two adjacent catalyst beds 101, and a hydrogen returning device 103 disposed in each catalyst bed 101; the hydrogen obtained by the membrane separator 10 enters each section of catalyst bed 101 through the hydrogen conveying main pipe 11 by the hydrogen returning device 103 for cold shock; introducing a liquid-phase cooling medium into the heat-transfer coil 102 for heat transfer; the heat of the heat transfer coil 102 is subjected to waste heat recovery by the first waste heat recovery device 3.
According to an embodiment of the present invention, the present invention further provides a multi-stage hydrogen-returning cold shock methanation production system for implementing the multi-stage hydrogen-returning cold shock methanation production method, as shown in fig. 1 and 2, where the system includes: the device comprises a high-temperature methanation reactor 1, a purified coke oven gas inlet main pipe 2, a first waste heat recovery device 3, a high-temperature methanation reactor outlet main pipe 4, a high-temperature methanation reactor circulating gas pipe 5, a medium-temperature methanation reactor 6, a medium-temperature methanation reactor outlet main pipe 7, a second waste heat recovery device 8, a gas-water separation tank 9, a membrane separator 10 and a hydrogen conveying main pipe 11;
The high-temperature methanation reactor 1 comprises a plurality of sections of catalyst beds 101 in the vertical direction, a heat transfer coil 102 arranged between every two sections of adjacent catalyst beds 101 and a hydrogen returning device 103 arranged in each section of catalyst beds 101, wherein the top of the high-temperature methanation reactor 1 is provided with a raw material gas inlet, and the bottom is provided with a reacted gas outlet; the top of the medium-temperature methanation reactor 6 is provided with a reaction gas inlet, and the bottom is provided with a reacted gas outlet; the gas-water separation tank 9 is provided with an air inlet and a synthesis gas outlet; the membrane separator 10 is provided with an air inlet, a hydrogen outlet and a product gas outlet;
The method comprises the steps that a raw material gas inlet at the top of a high-temperature methanation reactor 1 is communicated with a purified coke oven gas inlet main pipe 2, a reacted gas outlet at the bottom of the high-temperature methanation reactor 1 is communicated with a reaction gas inlet at the top of a medium-temperature methanation reactor 6 through a high-temperature methanation reactor outlet main pipe 4, a high-temperature methanation reactor circulating gas pipe 5 is communicated with the purified coke oven gas inlet main pipe 2 and the high-temperature methanation reactor outlet main pipe 4, and a heat transfer coil 102 of the high-temperature methanation reactor 1 is communicated with a first waste heat recovery device 3;
the reacted gas outlet at the bottom of the intermediate temperature methanation reactor 6 is communicated with the gas inlet of the gas-water separation tank 9 through an intermediate temperature methanation reactor gas outlet main pipe 7, and a second waste heat recovery device 8 is arranged on the intermediate temperature methanation reactor gas outlet main pipe 7;
The synthesis gas outlet of the gas-water separation tank 9 is communicated with the gas inlet of the membrane separator 10, and the hydrogen outlet of the gas-water separation tank 9 is communicated with the hydrogen returning device 103 through the hydrogen conveying main pipe 11.
In some embodiments, the catalyst bed 101 in the high temperature methanation reactor 1 is a fixed bed.
In some embodiments, the hydrogen return device 103 is disposed at 1/2 to 2/3 of each section of the catalyst bed 101 from the top to the bottom of the bed.
In some embodiments, the hydrogen returning device 103 includes a hydrogen returning main pipe and a plurality of hydrogen returning branch pipes connected with the hydrogen returning main pipe, the hydrogen returning main pipe is perpendicular to the axial direction of the high-temperature methanation reactor 1, the plurality of hydrogen returning branch pipes are perpendicular to the hydrogen returning main pipe and are on the same plane, and a plurality of gas distribution holes are arranged on the plurality of hydrogen returning branch pipes.
In some embodiments, in the high-temperature methanation reactor 1, the hydrogen return main pipe of the hydrogen return device 103 in each section of catalyst bed 101 is respectively communicated with the hydrogen conveying main pipe 11 through the hydrogen conveying branch pipes 12, and each hydrogen conveying branch pipe 12 is provided with a hydrogen return regulating valve 120.
In some embodiments, the high temperature methanation reactor 1 includes two to four catalyst beds 101, a heat transfer coil 102 disposed between each two adjacent catalyst beds 101, and a hydrogen return device 103 disposed in each catalyst bed 101. Preferably, as shown in FIG. 2, the high temperature methanation reactor 1 comprises two catalyst beds 101, a heat transfer coil 102 disposed between the two catalyst beds 101, and a hydrogen return device 103 disposed in each catalyst bed 101.
In some embodiments, in the high temperature methanation reactor 1, each section of catalyst bed 101 is provided with a temperature measurement device to facilitate real-time monitoring of the bed temperature. The specific arrangement positions and the number of the temperature measuring devices can be routinely adjusted by those skilled in the art, and the present invention is not particularly limited thereto.
In some embodiments, the purified coke oven gas has a pressure of 3.0MPa to 3.5MPa and a temperature of 230 ℃ to 250 ℃.
In some embodiments, the temperature of the purified coke oven gas after mixing with the recycle gas is 280 ℃ to 320 ℃.
In some embodiments, the recycle ratio of the high temperature methanation reactor 1 is from 0.25 to 0.35.
In some embodiments, a recycle gas regulating valve 501 is provided on the high temperature methanation reactor recycle gas pipe 5.
In some embodiments, the hydrogen is introduced into the first catalyst bed of the high temperature methanation reactor 1 from top to bottom by the hydrogen returning device 103, so that the gas temperature in the first catalyst bed is controlled between 400 ℃ and 450 ℃.
In some embodiments, the heat removal coil 102 is a tube bundle formed by a plurality of tubes in a spiral wound manner, the tube bundle being serpentine.
In some embodiments, the liquid phase cooling medium is passed into the heat transfer coil 102 such that the temperature of the gas in the high temperature methanation reactor 1 after passing through the heat transfer coil 102 is controlled between 280 ℃ and 350 ℃. Preferably, the liquid-phase cooling medium comprises cooling water.
In some embodiments, the hydrogen is introduced into the second catalyst bed of the high temperature methanation reactor 1 from top to bottom by the hydrogen returning device 103, so that the gas temperature in the second catalyst bed is controlled to be 380 ℃ to 430 ℃, preferably 380 ℃ to 390 ℃.
In some embodiments, a hydrogen return device 103 is used to introduce hydrogen into the nth stage catalyst bed of the high temperature methanation reactor from top to bottom, where n is an integer greater than or equal to 3, preferably where n is 3 or 4, such that the temperature of the gas in the nth stage catalyst bed is reduced by 20 ℃ to 60 ℃ compared to the temperature of the gas in the nth-1 stage catalyst bed. For example: the gas temperature in the third catalyst bed is controlled to be 360-410 ℃, preferably 360-370 ℃. For another example: the gas temperature in the fourth stage catalyst bed is controlled to be 340-390 ℃, preferably 340-350 ℃.
In some embodiments, the reaction temperature in the medium temperature methanation reactor 6 is 280 ℃ to 300 ℃ and the reaction pressure is 3.0MPa to 3.2MPa.
In some embodiments, the separation membrane employed in the membrane separator 10 comprises a separation membrane having an H 2/CH4 selectivity greater than 35. In particular, the separation membranes employed may be existing commercial polymer membranes, such as those having a H 2 permeation rate of about 5.0 x 10 -8mol·m-2·s-1·Pa-1 (about 150 GPU) and a H 2/CH4 selectivity of 38-42.
In some embodiments, the method further comprises: carbon dioxide is mixed with the purified coke oven gas through a carbon dioxide inlet main pipe 13, and then enters the high-temperature methanation reactor 1 from the top of the high-temperature methanation reactor 1 for reaction.
In some embodiments, the system further comprises: the carbon dioxide gas inlet main pipe 13, the carbon dioxide gas inlet main pipe 13 is communicated with the purified coke oven gas inlet main pipe 2 and the feed gas inlet at the top of the high-temperature methanation reactor 1, and a supplementary carbon dioxide regulating valve 130 is arranged on the carbon dioxide gas inlet main pipe 13.
Example 1
The embodiment provides a multistage hydrogen returning cold shock methanation production system, as shown in fig. 1 and 2, comprising: the high-temperature methanation reactor 1, a purified coke oven gas inlet main pipe 2, a first waste heat recovery device 3, a high-temperature methanation reactor outlet main pipe 4, a high-temperature methanation reactor circulating gas pipe 5, a medium-temperature methanation reactor 6, a medium-temperature methanation reactor outlet main pipe 7, a second waste heat recovery device 8, a gas-water separation tank 9, a membrane separator 10, a hydrogen conveying main pipe 11, a hydrogen conveying branch pipe 12 and a carbon dioxide inlet main pipe 13;
The high-temperature methanation reactor 1 comprises two sections of catalyst beds 101 in the vertical direction, a heat transfer coil 102 arranged between the two sections of catalyst beds 101 and a hydrogen returning device 103 arranged in each section of catalyst beds 101, wherein the top of the high-temperature methanation reactor 1 is provided with a raw material gas inlet, and the bottom of the high-temperature methanation reactor 1 is provided with a reacted gas outlet; the top of the medium-temperature methanation reactor 6 is provided with a reaction gas inlet, and the bottom is provided with a reacted gas outlet; the gas-water separation tank 9 is provided with an air inlet and a synthesis gas outlet; the membrane separator 10 is provided with an air inlet, a hydrogen outlet and a product gas outlet;
The method comprises the steps that a raw material gas inlet at the top of a high-temperature methanation reactor 1 is communicated with a purified coke oven gas inlet main pipe 2, a reacted gas outlet at the bottom of the high-temperature methanation reactor 1 is communicated with a reaction gas inlet at the top of a medium-temperature methanation reactor 6 through a high-temperature methanation reactor outlet main pipe 4, a high-temperature methanation reactor circulating gas pipe 5 is communicated with the purified coke oven gas inlet main pipe 2 and the high-temperature methanation reactor outlet main pipe 4, a circulating gas regulating valve 501 is arranged on the high-temperature methanation reactor circulating gas pipe 5, and a heat transfer coil 102 of the high-temperature methanation reactor 1 is communicated with a first waste heat recovery device 3;
The reacted gas outlet at the bottom of the intermediate temperature methanation reactor 6 is communicated with the gas inlet of the gas-water separation tank 9 through an intermediate temperature methanation reactor gas outlet main pipe 7, and a butterfly valve 701 and a second waste heat recovery device 8 are arranged on the intermediate temperature methanation reactor gas outlet main pipe 7;
The synthesis gas outlet of the gas-water separation tank 9 is communicated with the gas inlet of the membrane separator 10, the hydrogen outlet of the gas-water separation tank 9 is communicated with the hydrogen returning device 103 through a hydrogen conveying main pipe 11 and a hydrogen conveying branch pipe 12, and each hydrogen conveying branch pipe 12 is provided with a hydrogen returning regulating valve 120;
The carbon dioxide gas inlet main pipe 13 is communicated with the purified coke oven gas inlet main pipe 2 and a raw gas inlet at the top of the high-temperature methanation reactor 1, and a carbon dioxide supplementing regulating valve 130 is arranged on the carbon dioxide gas inlet main pipe 13.
In the present embodiment, the catalyst bed 101 in the high temperature methanation reactor 1 is a fixed bed.
In this example, the inner diameter of the high-temperature methanation reactor 1 is Φ2800mm, the filling height of the first-stage catalyst bed from top to bottom in the high-temperature methanation reactor 1 is 3.5m, and the filling height of the second-stage catalyst bed is 3.0m.
In this embodiment, the hydrogen return device 103 is disposed at 2/3 of the top to bottom of each section of the catalyst bed 101.
In this embodiment, the hydrogen returning device 103 includes a hydrogen returning main pipe and a plurality of hydrogen returning branch pipes connected to the hydrogen returning main pipe, the hydrogen returning main pipe is perpendicular to the axial direction of the high-temperature methanation reactor 1, the plurality of hydrogen returning branch pipes are perpendicular to the hydrogen returning main pipe and are on the same plane, and a plurality of gas distribution holes are arranged on the plurality of hydrogen returning branch pipes.
In the present embodiment, in the high temperature methanation reactor 1, each section of catalyst bed 101 is provided with a temperature measuring device so as to monitor the bed temperature in real time.
In this embodiment, the heat transfer coil 102 is a tube bundle formed by spirally winding a plurality of tubes, and the tube bundle is spiral.
In this embodiment, the separation membrane employed in the membrane separator 10 comprises a separation membrane having an H 2/CH4 selectivity of greater than 35. In particular, the separation membranes employed may be existing commercial polymer membranes, such as those having a H 2 permeation rate of about 5.0 x10 -8mol·m-2·s-1·Pa-1 (about 150 GPU) and a H 2/CH4 selectivity of 38-42.
The embodiment also provides a multi-stage hydrogen returning cold shock methanation production method, which adopts the system, as shown in fig. 1, and comprises the following steps:
Purified coke oven gas from a desulfurization section is 100000Nm 3/h, the components are shown in table 1, the pressure is 3.0MPa to 3.5MPa, and the temperature is 230 ℃ to 250 ℃;
Table 1 composition of purified coke oven gas
| Composition of the composition | CH4 | H2 | CO | CO2 | N2 | O2 | CmHn |
| V％ | 23.64 | 48.99 | 9.31 | 3.95 | 9.08 | 0.02 | 2.61 |
After the purified coke oven gas in the purified coke oven gas inlet main pipe 2 is mixed with the circulating gas passing through the circulating gas pipe 5 of the high-temperature methanation reactor, the temperature is raised to 300 ℃, and the mixture enters a first-stage catalyst bed layer in the high-temperature methanation reactor 1 from the top of the high-temperature methanation reactor 1 for reaction; along with the progress of the reaction, the pressure is reduced, the temperature flies up, the hydrogen obtained by the membrane separator 10 enters a first-stage catalyst bed layer through a hydrogen conveying main pipe 11 and a hydrogen conveying branch pipe 12 from a hydrogen returning device 103 for cold shock, the flow rate of the introduced hydrogen is 4000-5000 Nm 3/h, and the gas temperature in the first-stage catalyst bed layer is controlled at 430-450 ℃; cooling water is introduced into the heat transfer coil 102 between the two sections of catalyst beds 101, so that the temperature of the gas passing through the heat transfer coil 102 in the high-temperature methanation reactor 1 is controlled at 300-320 ℃; the first waste heat recovery device 3 is utilized to carry out waste heat recovery on the heat of the heat transfer coil 102, namely, the waste heat recovery is carried out on the steam formed in the heat transfer coil 102; the gas with the temperature of 300-320 ℃ continuously enters a second section of catalyst bed layer for reaction, the temperature is increased again, the hydrogen obtained by the membrane separator 10 enters the second section of catalyst bed layer for cold shock through the hydrogen conveying main pipe 11 and the hydrogen conveying branch pipe 12 by the hydrogen returning device 103, the flow rate of the introduced hydrogen is 4000Nm 3/h, the gas temperature in the second section of catalyst bed layer is controlled at 380-390 ℃ to obtain gas after the high-temperature methanation reaction, and the gas flows out from the bottom of the high-temperature methanation reactor 1 and enters the gas outlet main pipe 4 of the high-temperature methanation reactor;
The gas after the high-temperature methanation reaction is divided into two parts, one part is taken as circulating gas, the circulating gas is mixed with purified coke oven gas through a circulating gas pipe 5 of the high-temperature methanation reactor and then returned to the high-temperature methanation reactor 1, the circulating ratio of the high-temperature methanation reactor 1 is controlled to be 0.25, the methane flow can reach 36000Nm 3/h, the circulating ratio is controlled to be 0.35, the methane flow can reach 37000Nm 3/h, and the volume of the high-temperature methanation reactor 1 is effectively reduced by adjusting the circulating ratio of the high-temperature methanation reactor 1;
The other part enters the medium temperature methanation reactor 6 from the top of the medium temperature methanation reactor 6 to continuously react, the reaction temperature in the medium temperature methanation reactor 6 is 300 ℃, the reaction pressure is 3.0MPa, the gas after the medium temperature methanation reaction is obtained, and flows out from the bottom of the medium temperature methanation reactor 6 and enters an air outlet main pipe 7 of the medium temperature methanation reactor;
Carbon dioxide is mixed with purified coke oven gas through a carbon dioxide inlet main pipe 13, and enters the high-temperature methanation reactor 1 from the top of the high-temperature methanation reactor 1 for reaction, and raw material gas of the high-temperature methanation reactor 1 consists of three parts, namely purified coke oven gas, circulating gas after the high-temperature methanation reaction and adjustable supplementary external CO 2, so that the methane yield requirement can be adjusted;
The gas after the medium-temperature methanation reaction is subjected to waste heat recovery by utilizing the second waste heat recovery device 8, the waste heat can be used for a power generation system without energy waste, and then the gas after the waste heat recovery enters the gas-water separation tank 9 for separation, and water is separated out to obtain synthesis gas;
The synthesis gas enters the membrane separator 10 for separation to obtain hydrogen and product gas, the methane gas (namely the product gas) is separated to 37000Nm 3/h, the hydrogen is returned to the high-temperature methanation reactor 1 for cold shock, and the product gas can be output.
The carbon monoxide conversion rate of the embodiment can reach 100%, the carbon dioxide conversion rate reaches more than 95%, the methane content of the reacted gas outlet at the bottom of the high-temperature methanation reactor 1 is 73 mol%, and the carbon conversion rate is superior to other existing production processes. The carbon-oxygen compound content in the methane product gas is 0.2 mol%.
Comparative example 1
The present comparative example employs a conventional three stage methanation reaction system. The reaction temperature and the reaction pressure of the tertiary methanation reaction are respectively as follows: first-stage inlet: the reaction pressure is controlled to be 3.0-3.3 MPa in the whole course, the temperature is 300 ℃, the primary outlet is 540 ℃, the secondary inlet is 300 ℃, the secondary outlet is 370 ℃, the tertiary inlet is 270 ℃, and the tertiary outlet is 300 ℃. The traditional three-stage methanation reaction system does not set a hydrogen return point, and the circulation ratio is controlled to be 1.8.
The comparison of the results of this comparative example and example 1 is shown in Table 2.
TABLE 2
| Circulation ratio | CO conversion rate | CO 2 conversion | CO content (mol.) | CO 2 content (mol.) | |
| Example 1 | ～0.35 | ～100％ | ～85％ | 0 | 0.6 |
| Comparative example 1 | ～1.8 | ～99％ | ～70％ | 0.1 | 1.2 |
In table 2, the CO conversion and the CO 2 conversion refer to the CO conversion and the CO 2 conversion in the first stage methanation reactor (high temperature methanation reactor 1 in example 1), and the CO content and the CO 2 content refer to the CO content and the CO 2 content in the gas detected at the gas outlet after the reaction in the first stage methanation reactor (high temperature methanation reactor 1 in example 1).
As can be seen from table 2, example 1 achieves temperature control of the methanation reactor by a specially designed hydrogen return chilling process with reduced recycle ratio (i.e., reduced reactor volume) as compared to comparative example 1, while also achieving higher conversion than comparative example 1.
Claims (15)
1. A multi-stage hydrogen returning cold shock methanation production method comprises the following steps:
enabling the purified coke oven gas to enter a high-temperature methanation reactor from the top of the high-temperature methanation reactor to react to obtain high-temperature methanation reacted gas, and enabling the gas to flow out from the bottom of the high-temperature methanation reactor;
Dividing the high-temperature methanation reaction gas into two parts, mixing one part of the high-temperature methanation reaction gas serving as circulating gas with the purified coke oven gas, returning the mixture to the high-temperature methanation reactor, enabling the other part of the high-temperature methanation reaction gas to enter the medium-temperature methanation reactor from the top of the medium-temperature methanation reactor for continuous reaction, obtaining medium-temperature methanation reaction gas, and enabling the medium-temperature methanation reaction gas to flow out from the bottom of the medium-temperature methanation reactor;
after the waste heat recovery is carried out on the gas after the medium-temperature methanation reaction, the gas enters a gas-water separation tank for separation, and synthesis gas is obtained;
Allowing the synthesis gas to enter a membrane separator for separation to obtain hydrogen and product gas;
Enabling the hydrogen obtained through the membrane separator to enter the high-temperature methanation reactor for cold shock;
The high-temperature methanation reactor comprises a plurality of sections of catalyst beds in the vertical direction, a heat transfer coil pipe arranged between every two sections of adjacent catalyst beds, and a hydrogen returning device arranged in each section of catalyst beds; the hydrogen obtained by the membrane separator enters each section of catalyst bed layer from the hydrogen returning device for cold shock; introducing a liquid-phase cooling medium into the heat-transfer coil pipe to transfer heat; and (5) recovering waste heat of the heat transfer coil.
2. The multistage hydrogen returning cold shock methanation production method according to claim 1, wherein a catalyst bed layer in the high-temperature methanation reactor is a fixed bed;
Preferably, the hydrogen returning device is arranged at 1/2-2/3 of the position from the top to the bottom of each section of catalyst bed.
3. The multistage hydrogen return cold shock methanation production method according to claim 1, wherein the high-temperature methanation reactor comprises two-four stages of catalyst beds, a heat transfer coil arranged between every two adjacent stages of catalyst beds, and a hydrogen return device arranged in each stage of catalyst beds;
Preferably, the high temperature methanation reactor comprises two sections of catalyst beds, a heat transfer coil arranged between the two sections of catalyst beds and a hydrogen return device arranged in each section of catalyst bed.
4. The multi-stage hydrogen returning cold shock methanation production method according to claim 1, wherein the pressure of the purified coke oven gas is 3.0-3.5 MPa and the temperature is 230-250 ℃.
5. The multi-stage hydrogen-returning cold shock methanation production method according to claim 1, wherein the temperature of the purified coke oven gas after being mixed with the circulating gas is 280-320 ℃;
Preferably, the circulation ratio of the high temperature methanation reactor is 0.25-0.35.
6. The multistage hydrogen returning cold shock methanation production method according to claim 1, wherein the hydrogen returning device is adopted to introduce hydrogen into the first-stage catalyst bed layer from top to bottom of the high-temperature methanation reactor, so that the gas temperature in the first-stage catalyst bed layer is controlled at 400-450 ℃.
7. The multistage hydrogen returning cold shock methanation production method according to claim 1, wherein a liquid-phase cooling medium is introduced into the heat transfer coil, so that the gas temperature in the high-temperature methanation reactor after passing through the heat transfer coil is controlled to be 280-350 ℃.
8. The multistage hydrogen returning cold shock methanation production method according to claim 1, wherein the hydrogen returning device is adopted to introduce hydrogen into a second-stage catalyst bed layer from top to bottom of the high-temperature methanation reactor, so that the gas temperature in the second-stage catalyst bed layer is controlled at 380-430 ℃;
preferably, the hydrogen is introduced into the nth stage catalyst bed of the high temperature methanation reactor from top to bottom by the hydrogen returning device, n is an integer more than or equal to 3, more preferably, n is 3 or 4, so that the gas temperature in the nth stage catalyst bed is reduced by 20-60 ℃ compared with the gas temperature in the nth-1 stage catalyst bed.
9. The multistage hydrogen returning cold shock methanation production method according to claim 1, wherein the reaction temperature in the medium temperature methanation reactor is 280-300 ℃ and the reaction pressure is 3.0-3.2 MPa.
10. The multistage hydrogen-returning cold shock methanation production method according to claim 1, wherein the separation membrane adopted by the membrane separator comprises a separation membrane with H 2/CH4 selectivity of more than 35.
11. The multi-stage hydrogen-returning cold shock methanation production process according to claim 1, wherein the process further comprises: and mixing carbon dioxide with the purified coke oven gas, and then enabling the mixture to enter a high-temperature methanation reactor from the top of the high-temperature methanation reactor for reaction.
12. A multi-stage return hydrogen cold shock methanation production system for implementing a multi-stage return hydrogen cold shock methanation production process according to any one of claims 1-11, the system comprising: the device comprises a high-temperature methanation reactor, a purified coke oven gas inlet main pipe, a first waste heat recovery device, a high-temperature methanation reactor outlet main pipe, a high-temperature methanation reactor circulating gas pipe, a medium-temperature methanation reactor outlet main pipe, a second waste heat recovery device, a gas-water separation tank, a membrane separator and a hydrogen conveying main pipe;
The high-temperature methanation reactor comprises a plurality of sections of catalyst beds in the vertical direction, a heat transfer coil arranged between every two sections of adjacent catalyst beds and a hydrogen returning device arranged in each section of catalyst beds, wherein the top of the high-temperature methanation reactor is provided with a raw material gas inlet, and the bottom of the high-temperature methanation reactor is provided with a reacted gas outlet; the top of the medium-temperature methanation reactor is provided with a reaction gas inlet, and the bottom of the medium-temperature methanation reactor is provided with a reacted gas outlet; the gas-water separation tank is provided with an air inlet and a synthesis gas outlet; the membrane separator is provided with an air inlet, a hydrogen outlet and a product gas outlet;
the raw material gas inlet at the top of the high-temperature methanation reactor is communicated with the purified coke oven gas inlet main pipe, the reacted gas outlet at the bottom of the high-temperature methanation reactor is communicated with the reaction gas inlet at the top of the medium-temperature methanation reactor through the high-temperature methanation reactor outlet main pipe, the high-temperature methanation reactor circulating gas pipe is communicated with the purified coke oven gas inlet main pipe and the high-temperature methanation reactor outlet main pipe, and the heat transfer coil of the high-temperature methanation reactor is communicated with the first waste heat recovery device;
The reacted gas outlet at the bottom of the medium temperature methanation reactor is communicated with the gas inlet of the gas-water separation tank through the gas outlet main pipe of the medium temperature methanation reactor, and the gas outlet main pipe of the medium temperature methanation reactor is provided with the second waste heat recovery device;
The synthesis gas outlet of the gas-water separation tank is communicated with the gas inlet of the membrane separator, and the hydrogen outlet of the gas-water separation tank is communicated with the hydrogen returning device through the hydrogen conveying main pipe.
13. The multistage hydrogen returning cold shock methanation production system according to claim 12, wherein the hydrogen returning device comprises a hydrogen returning main pipe and a plurality of hydrogen returning branch pipes connected with the hydrogen returning main pipe, the hydrogen returning main pipe is perpendicular to the axial direction of the high-temperature methanation reactor, the hydrogen returning branch pipes are perpendicular to the hydrogen returning main pipe and are on the same plane, and a plurality of gas distribution holes are arranged on the hydrogen returning branch pipes.
14. The multistage hydrogen-returning cold shock methanation production system according to claim 12, wherein in the high-temperature methanation reactor, a temperature measuring device is provided for each stage of catalyst bed.
15. The multi-stage hydrogen-returning cold shock methanation production system according to claim 12, wherein the heat-transfer coil is a tube bundle formed by a plurality of pipelines in a spiral winding manner, and the tube bundle is in a spiral shape.
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