CN115215293A - Method and system for producing hydrogen from synthesis gas - Google Patents
Method and system for producing hydrogen from synthesis gas Download PDFInfo
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Abstract
The invention relates to the field of hydrogen production from synthesis gas, and discloses a method and a system for improving hydrogen recovery rate and reducing carbon dioxide emission. The method comprises the following steps: separating hydrogen in the purified synthesis gas to obtain low-hydrogen synthesis gas and hydrogen-rich synthesis gas, absorbing carbon dioxide in the low-hydrogen synthesis gas to obtain converted synthesis gas, carrying out water-gas shift reaction on the converted synthesis gas and water vapor in the presence of a catalyst to form hydrogen-rich mixed gas, and converging the hydrogen-rich synthesis gas and the hydrogen-rich mixed gas for purification to obtain high-purity hydrogen. The invention can improve the yield of hydrogen and the conversion rate of carbon monoxide, prolong the service life of the catalyst and the hydrogen separation membrane component and reduce the cost.
Description
Technical Field
The invention relates to the field of hydrogen production by synthesis gas, in particular to a method and a system for producing hydrogen by synthesis gas, which can improve the recovery rate of hydrogen and reduce the emission of carbon dioxide.
Background
Hydrogen is widely used in industrial processes such as petroleum, chemical industry, metallurgy, medicine, aerospace, etc., and in recent years, fuel cell vehicles using hydrogen as fuel have become one of the important directions for the development of the automotive industry. Therefore, how to obtain high-purity hydrogen becomes a research hotspot. At present, the hydrogen production technology is mature and is two technologies of hydrogen production by electrolyzing water and hydrogen production by fossil fuel. The hydrogen production by water electrolysis is high in cost and high in energy consumption, and although research for many years is carried out, hydrogen with extremely high demand cannot be provided; fossil fuel hydrogen production remains the primary method of hydrogen production. In China, coal resources are abundant in reserve and low in cost, and the method becomes an important way for preparing hydrogen at one time.
The traditional coal gasification hydrogen production technology mainly comprises three processes, namely a coal gas production process, a water gas shift reaction and hydrogen purification and compression. Namely, coal is firstly prepared into synthesis gas by a coal gasification technology, and after washing and purification and hydrogen concentration improvement by water gas shift reaction, high-concentration hydrogen is obtained by purification and compression.
However, the content of hydrogen in the synthesis gas is high, generally between 20 and 30 vol%, the water gas shift reaction is easy to reach balance, high-concentration hydrogen cannot be generated, a large amount of carbon monoxide resources in the purification process are wasted, and the efficiency of producing hydrogen from coal is directly low. Meanwhile, the hydrogen content is high, and the heat generated by the water gas shift reaction cannot be reasonably used, so that the temperature of the primary water gas shift reactor is increased, and the activity of the catalyst is reduced or inactivated, so that the conversion rate of the water gas shift reaction is low. To facilitate the conversion of carbon monoxide, it is now common to carry out the water gas shift reaction using a two-stage water gas shift reactor. In order to overcome the problem of catalyst deactivation caused by temperature rise, the prior art generally uses a wide-temperature catalyst or a catalyst containing noble metal to improve the temperature tolerance range of the catalyst, but the catalyst greatly increases the hydrogen production cost.
CN110093174A discloses a method for producing hydrogen from low-rank coal, which comprises the steps of drying the low-rank coal, carrying out parallel gasification reduction and water gas gasification process treatment, carrying out conversion and separation on the obtained synthesis gas, and finally obtaining hydrogen. The scheme makes full use of the composition characteristics of the low-rank coal, realizes cascade utilization, and finally causes the problems of low efficiency of produced hydrogen, waste of carbon monoxide and the like because the obtained synthesis gas is still directly converted. And the method is not suitable for the process of producing hydrogen by gasifying common fossil fuel.
CN103359688B uses semi coke oven gas as raw material to prepare hydrogen, and uses membrane separation and temperature swing adsorption separation technology based on metal hydride to obtain hydrogen products with different purity grades. In the scheme, products of a methane catalytic stroke enter a water gas shift membrane reactor and are subjected to water gas shift reaction in the presence of catalysts (Fe-Cr, co-Mo, pt-CeO) 2 ) While reacting in the presence of (A) and (B) and separating. However, the method still has the problems of high carbon dioxide emission, incapability of capturing carbon dioxide with higher concentration, expensive catalyst/toxic to human body and environmental pollution/complicated flow before use, higher water gas shift reaction temperature, energy waste, reduced service life of the membrane and the like.
Disclosure of Invention
The invention aims to overcome the problems in the prior art and provides a method and a system for producing hydrogen by coal gasification with high-efficiency and low-carbon emission. The method only uses a first-stage water gas shift reactor, improves the conversion rate of the water gas shift reaction, saves energy consumption, reduces carbon emission and prolongs the service life of a separation membrane and a catalyst.
In order to achieve the above object, a first aspect of the present invention provides a method for producing hydrogen from syngas, comprising the steps of:
(1) Separating hydrogen in the purified synthesis gas to obtain low-hydrogen synthesis gas and hydrogen-rich synthesis gas;
(2) Absorbing carbon dioxide in the low-hydrogen synthesis gas to obtain a conversion synthesis gas;
(3) Carrying out water gas shift reaction on the shift synthesis gas and steam in the presence of a catalyst to form a hydrogen-rich mixed gas;
(4) And merging the hydrogen-rich synthesis gas and the hydrogen-rich mixed gas for purification to obtain the high-purity hydrogen.
In a second aspect, the present invention provides a system for producing hydrogen from syngas, the system comprising: the device comprises a hydrogen separation membrane component, a carbon dioxide absorption tower, a water gas shift unit and a hydrogen purification unit;
the hydrogen separation membrane component is used for separating hydrogen in the purified synthesis gas to form hydrogen-rich synthesis gas and low-hydrogen synthesis gas;
the carbon dioxide absorption tower is used for absorbing carbon dioxide in the low-hydrogen synthesis gas to form a conversion synthesis gas;
the water gas shift unit is used for reacting the shifted synthesis gas with steam to generate hydrogen and carbon dioxide, and finally forming a hydrogen-rich mixed gas.
Compared with the prior art, the method for preparing hydrogen from synthesis gas has the advantages that the converted synthesis gas is obtained by separating hydrogen and absorbing carbon dioxide, the synthesis gas is high in carbon monoxide concentration and low in hydrogen and carbon dioxide concentrations, so that the yield of hydrogen in the water gas shift reaction is increased, the hydrogen recovery rate is improved, the carbon emission is reduced, and meanwhile, the heat released by the water gas shift reaction is fully utilized. Specifically, the method comprises the following steps:
1. according to the method, the hydrogen separation membrane component and the carbon dioxide chemical absorption tower are arranged in front of the water gas shift device, so that the shift synthesis gas with high carbon monoxide concentration and low hydrogen and carbon dioxide concentration can be obtained, a low-cost catalyst can be used in the water gas shift reaction, high carbon monoxide conversion rate can be obtained under the low-temperature condition, a large amount of hydrogen is generated, and the hydrogen yield is improved. Meanwhile, the hydrogen separation membrane component and the water gas shift unit are arranged separately, so that the hydrogen separation membrane component is not influenced by high temperature, and the service life of the hydrogen separation membrane component is prolonged.
2. The carbon dioxide can be absorbed by the chemical absorbent and then is resolved from the chemical absorbent by the carbon dioxide resolving tower, the chemical absorbent can be recycled, the resolved carbon dioxide can be sealed or used in other ways without being discharged, and the carbon emission is reduced. Meanwhile, low-quality heat generated by the water gas shift reaction can be supplied to the carbon dioxide analysis tower for analysis, so that the heat required by the carbon dioxide analysis tower is solved, the energy consumption is saved, the catalyst is prevented from being deactivated due to the fact that the temperature of a reactor of the water gas shift reaction exceeds a reaction temperature range, and the water gas shift reaction can be promoted to move towards the hydrogen generation direction. Therefore, compared with the prior art, the catalyst used in the invention can be a catalyst with lower activity temperature, narrower activation temperature range and lower cost, and the service life of the catalyst can be ensured.
3. In the traditional water gas shift reaction for producing hydrogen by coal gasification, because a two-stage water gas shift reactor is required in the process, the requirements on a catalyst and the reaction temperature are high. In the practice of the process of the present invention, the reaction can be carried out with low cost catalyst and at low temperatures and with only one water gas shift reactor to achieve the hydrogen yields achieved in the two-stage water gas shift reactor of the conventional process.
Drawings
Fig. 1 is a schematic flow diagram of synthesis gas hydrogen production according to a preferred embodiment of the present invention.
Description of the reference numerals
1. Water-cooled wall gasifier 2, synthetic gas purification unit 3 and hydrogen separation membrane component
4. Carbon dioxide absorption tower 5, carbon dioxide analysis tower 6 and water gas shift reaction unit
7. Hydrogen purification unit
Detailed Description
The endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
In a first aspect, the present invention provides a method for producing hydrogen from synthesis gas, as shown in fig. 1, the method comprising the steps of:
(1) Separating hydrogen in the purified synthesis gas to obtain low-hydrogen synthesis gas and hydrogen-rich synthesis gas;
(2) Absorbing carbon dioxide in the low-hydrogen synthesis gas to obtain a conversion synthesis gas;
(3) Carrying out water gas shift reaction on the shift synthesis gas and water vapor in the presence of a catalyst to form a hydrogen-rich mixed gas;
(4) And merging the hydrogen-rich synthesis gas and the hydrogen-rich mixed gas for purification to obtain the high-purity hydrogen.
In some embodiments of the present invention, preferably, the separating is performed by separating the purified synthesis gas by a hydrogen separation membrane module. In the present invention, the hydrogen separation membrane module may be a hydrogen separation membrane device commonly used in the art, such as a Prism hollow fiber membrane separator, a polyimide membrane separator, and the like.
In the present invention the hydrogen-rich synthesis gas (based on the total amount of hydrogen-rich synthesis gas) has a hydrogen content of 85-95 vol%, a carbon monoxide content of 2-8 vol% and a carbon dioxide content of 2-8 vol%, preferably a hydrogen content of 93-95 vol%, a carbon monoxide content of 2-4 vol% and a carbon dioxide content of 2-4 vol%.
In the present invention, the low hydrogen synthesis gas (based on the total amount of the low hydrogen synthesis gas) has a hydrogen content of 1 to 8 vol%, a carbon monoxide content of 57 to 73 vol%, and a carbon dioxide content of 26 to 35 vol%, and preferably, the hydrogen content is 1 to 5 vol%, the carbon monoxide content is 62 to 70 vol%, and the carbon dioxide content is 25 to 33 vol%.
In the present invention, the shifted synthesis gas (based on the total amount of shifted synthesis gas) has a hydrogen content of 5 to 17 vol%, a carbon monoxide content of 80 to 95 vol%, and a carbon dioxide content of 0 to 3 vol%, and preferably, a hydrogen content of 5 to 9 vol%, a carbon monoxide content of 90 to 95 vol%, and a carbon dioxide content of 0 to 1 vol%.
In the present invention, the hydrogen-rich mixture (based on the total amount of the hydrogen-rich mixture) has a hydrogen content of 45 to 55 vol%, a carbon monoxide content of 0 to 8 vol%, and a carbon dioxide content of 40 to 50 vol%, and preferably, the hydrogen content is 50 to 55 vol%, the carbon monoxide content is 0 to 4 vol%, and the carbon dioxide content is 45 to 48 vol%.
In the invention, the impurity content in the purified synthesis gas, the hydrogen-rich synthesis gas, the low-hydrogen synthesis gas, the shift synthesis gas and the hydrogen-rich mixed gas is negligible.
In some embodiments of the present invention, preferably, the absorption is performed by contacting the low hydrogen syngas with a chemical absorbent for carbon dioxide absorption.
In some embodiments of the invention, preferably the reaction temperature of the water gas shift reaction is in the range of 200 to 250 ℃, preferably 225 to 235 ℃.
In processes conventional in the art, the high temperature of the water gas shift reaction is typically in the range of 300 ℃ to 420 ℃ and the low temperature is typically in the range of 160 ℃ to 300 ℃. In the present invention, the low temperature conditions for the water gas shift reaction refer to 200 to 250 ℃, preferably 225 to 235 ℃.
The catalyst used in the present invention may be a water gas shift reaction catalyst, which is conventional in the art, and is preferably a low temperature catalyst. In some embodiments of the inventionPreferably, the catalyst is selected from the group consisting of Cu or Ni as a main active component, zrO 2 、ZnO、Al 2 O 3 、MgO、SiO 2 And TiO 2 At least one of them is a supported metal catalyst. Preferably, the content of the main active ingredient in the above catalyst is 1 to 20 mass%, and the content of the carrier is 80 to 99 mass%.
The activation temperature of the above catalyst is usually 160 to 260 ℃.
In the invention, the low-temperature catalyst is a water gas shift reaction catalyst with the activity temperature of 160-260 ℃, the high-temperature catalyst is a water gas shift reaction catalyst with the activity temperature of 300-420 ℃, and the wide-temperature catalyst is a water gas shift reaction catalyst with the activity temperature of 200-400 ℃. In some embodiments of the present invention, preferably, the method further comprises resolving the absorbed carbon dioxide. Preferably, the heat required for desorption is derived from the heat released by the water gas shift reaction.
In the invention, the purified synthesis gas can be obtained by purifying raw synthesis gas generated by gasification reaction of conventional raw materials in the field, such as coal dry powder, coal water slurry, natural gas and the like. Preferably, the raw material is coal water slurry or coal dry powder. Preferably, the method further comprises: carrying out gasification reaction on the coal water slurry or coal dry powder to generate the crude synthesis gas; and purifying the crude synthesis gas to obtain purified synthesis gas.
In the invention, the gasification reaction refers to a process of generating crude synthesis gas by carrying out gasification reaction on coal water slurry or coal dry powder through an entrained flow bed.
In the present invention, the purification refers to a process of removing impurities such as hydrogen sulfide and fly ash in the synthesis gas.
In some embodiments of the present invention, preferably, the gasifying agent used in the process of the gasification reaction is selected from O 2 、O 2 /H 2 Mixed gas of O or O 2 /CO 2 At least one of the mixed gas.
Preferably, the gasification reaction is carried out in a waterwall gasifier.
Preferably, the water-cooled wall gasifier produces superheated steam of 2MPa to 5 MPa.
Preferably, the temperature of the gasification reaction is 1400 ℃ or higher.
Preferably, the superheated steam is used for the water gas shift reaction.
In the present invention, preferably, the purification process is passing the raw synthesis gas through a synthesis gas purification unit.
In the conventional method, the water gas shift reactor is gradually deactivated with the progress of the water gas shift reaction due to the heat release of the water gas shift reaction, in which the temperature is gradually increased, and has a short service life and a low carbon monoxide conversion rate. Therefore, in the conventional method, a two-stage water gas shift reactor is usually provided, the reaction temperature of the one-stage water gas shift reactor is 360 ℃, a high-temperature catalyst (usually an iron-based catalyst, the activity temperature is 260-420 ℃) is used, the reaction temperature of the two-stage water gas shift reactor is 220 ℃, and a low-temperature catalyst (usually a copper-based catalyst or a supported gold ultramicro-ionic catalyst, the activity temperature is 160-240 ℃) is used. However, the cost of providing a two-stage water gas shift reactor is high, and high temperature catalysts, which typically contain chromium or gold, can cause environmental pollution, harm to the human body, or be costly. CN103359688B uses only a first water gas shift reactor, i.e., a water gas shift membrane reactor, and the reaction and separation are carried out in the presence of a catalyst. However, as the reactor temperature continues to rise, high or wide temperature catalysts (Fe-Cr, co-Mo, pt-CeO) are required 2 ) The conversion of carbon monoxide and the yield of hydrogen in the reaction can be continuously ensured. However, these catalysts have low activity at low temperatures and are harmful to human bodies and pollute the environment, or the procedures before use are complicated, or they are expensive. In addition, the hydrogen separation membrane is also required to be high in temperature, and the continuous high temperature causes the life of the hydrogen separation membrane to be reduced.
In the invention, most of hydrogen and carbon dioxide in the purified synthesis gas are separated by the hydrogen separation membrane component and absorbed by the carbon dioxide absorption tower respectively, so that the concentration of carbon monoxide in the obtained converted synthesis gas is increased, the concentration of hydrogen and carbon dioxide is reduced, and the reaction is promoted to move towards the direction of hydrogen generation. In the present invention, the shifted synthesis gas after passing through the hydrogen separation membrane module and the carbon dioxide absorption tower (based on the total amount of the shifted synthesis gas) has a carbon monoxide content of 80 to 95 vol%, a hydrogen content of 5 to 17 vol%, and a carbon dioxide content of 0 to 3 vol%. In addition, the heat generated by the water gas shift reaction is led out to be used for the carbon dioxide analysis of the carbon dioxide analysis tower, so that the temperature in the water gas shift unit is controlled not to exceed the active temperature of the catalyst, the service life of the catalyst is prolonged, and the energy consumption of carbon dioxide analysis is saved. In the present invention, the conversion of carbon monoxide is more than 95% in the water gas shift reaction using a low temperature catalyst at a reaction temperature of 200 to 250 ℃, whereas in the conventional method using a two-stage water gas shift reactor, since the gas introduced into the second water gas shift reactor is the first-stage synthesis gas generated from the first-stage water gas shift reactor, the conversion of carbon monoxide in the second water gas shift reactor can only reach 75% at the same temperature and catalyst. Furthermore, the inventors have surprisingly found that the heat required for carbon dioxide desorption using the system of the present invention is significantly reduced compared to the heat required in conventional processes. On the other hand, due to the separation of the hydrogen separation membrane component and the water gas shift reactor, the hydrogen separation membrane component does not need to resist high temperature, the selection range of the hydrogen separation membrane component is widened, and the service life of the hydrogen separation membrane component is prolonged.
In a preferred embodiment of the present invention, the purified synthesis gas is obtained by purifying a coal water slurry or a coal dry powder after gasification in a water-cooled wall gasifier, and the water vapor generated by the water-cooled wall gasifier is used for the subsequent water gas shift reaction without separately producing water vapor.
Compared with the traditional method, the method greatly reduces the hydrogen production cost and the cost for obtaining high-concentration carbon dioxide. In a preferred embodiment of the invention, the hydrogen production cost of the invention is reduced by more than 2%, the production and operation cost of the reactor is reduced by more than 40%, and the cost for obtaining high-concentration carbon dioxide is reduced by more than 30% compared with the traditional method for producing hydrogen by using a two-stage water gas shift reactor.
In a second aspect, the present invention provides a system for producing hydrogen from syngas, the system comprising: the device comprises a hydrogen separation membrane component, a carbon dioxide absorption tower, a water gas shift unit and a hydrogen purification unit;
the hydrogen separation membrane component is used for separating hydrogen in the purified synthesis gas to form hydrogen-rich synthesis gas and low-hydrogen synthesis gas;
the carbon dioxide absorption tower is used for absorbing carbon dioxide in the low-hydrogen synthesis gas to form a conversion synthesis gas;
the water gas shift unit is used for reacting the shift synthesis gas with steam to generate hydrogen and carbon dioxide, and finally forming a hydrogen-rich mixed gas;
the hydrogen purification unit is used for purifying the hydrogen-rich synthesis gas and the hydrogen-rich mixed gas to obtain high-purity hydrogen.
In some embodiments of the present invention, it is preferable that the system further comprises a carbon dioxide desorption tower for desorbing carbon dioxide absorbed in the carbon dioxide absorption tower. Further preferably, the water gas shift unit is communicated with the carbon dioxide desorption tower and is used for providing heat generated by the water gas shift unit to the carbon dioxide desorption tower for desorption.
Preferably, the system further comprises: the water-cooled wall gasifier is used for generating crude synthesis gas by taking coal water slurry or coal dry powder as a raw material; and the synthesis gas purification unit is used for purifying the purified crude synthesis gas to obtain purified synthesis gas.
In the present invention, the syngas purification unit can be various purification devices commonly used in the art, such as a carbon scrubber.
In some embodiments of the invention, preferably, the water gas shift unit is provided with a primary water gas shift reactor. That is, in the present invention, the water gas shift reaction is performed only once, and the shift effect can be achieved without performing multiple water gas shift reactions as in the prior art.
The method and system of the present invention are described below in conjunction with FIG. 1 and a preferred embodiment of the present invention:
(1) And (2) carrying out gasification reaction on the coal water slurry or the dry powder through a water-cooled wall gasifier 1 to generate crude synthesis gas, wherein the content of hydrogen in the crude synthesis gas is 20-40% by volume. Wherein, the water-cooled wall structure in the combustion chamber of the gasification furnace can generate superheated steam of 2MPa-5 MPa. The gasifying agent adopts O 2 、O 2 /H 2 Mixed gas of O or O 2 /CO 2 The gasification temperature of the mixed gas is above 1400 ℃.
(2) The raw synthesis gas passes through the synthesis gas purification unit 2, and impurities such as hydrogen sulfide and fly ash are removed to obtain purified synthesis gas.
(3) And (3) introducing the purified synthesis gas into a hydrogen separation membrane component 3 for hydrogen separation, and separating the purified synthesis gas into hydrogen-rich synthesis gas and low-hydrogen synthesis gas, wherein the hydrogen content in the hydrogen-rich synthesis gas is more than 85 volume percent.
(4) The low-hydrogen synthetic gas enters a carbon dioxide absorption tower 4, carbon dioxide in the low-hydrogen synthetic gas is absorbed by using a chemical absorbent, enriched liquid rich in carbon dioxide and converted synthetic gas with carbon dioxide removed are obtained, and the absorption rate of the carbon dioxide is higher than 99%. The shift synthesis gas is composed primarily of carbon monoxide.
(5) And (3) sending the enriched liquid into a carbon dioxide desorption tower 5 for desorption, releasing carbon dioxide, obtaining a chemical absorbent, returning the chemical absorbent to a carbon dioxide absorption tower 4 for recycling, and sealing the released carbon dioxide for further utilization in the industries of chemical engineering, food and the like.
(6) The converted synthesis gas enters a water gas conversion unit 6 (only a first-stage water gas conversion reactor is arranged), the water gas conversion reaction is carried out under the action of a catalyst, and meanwhile, superheated steam generated by the water-cooled wall gasification furnace 1 is added into the unit, so that the concentration of reactants is increased, and the generation of hydrogen is promoted. The carbon monoxide concentration in the hydrogen-rich gas mixture obtained at the outlet of the water gas shift unit 6 is less than 8% by volume. Meanwhile, heat generated in the reaction process is transferred to the temperature rise of the carbon dioxide desorption tower 5 in the step (5) for the desorption of the carbon dioxide absorption liquid, so that the energy consumption for desorbing the carbon dioxide absorption liquid is saved, and the catalyst is prevented from being invalid due to the temperature rise of the reactor.
The present invention will be described in detail below by way of examples.
The experimental procedures used in the following examples are all conventional procedures unless otherwise specified. The raw materials, reagents and the like used in the following examples are commercially available unless otherwise specified.
Catalyst 1 is Cu/ZrO 2 A catalyst having an activation temperature of 200 to 250 ℃ and a composition of mainly about 5 mass% of Cu and about 95 mass% of ZrO 2 。
Catalyst 3 is Cu/ZnO/Al 2 O 3 A catalyst having an active temperature of 230 to 270 ℃ and a composition consisting essentially of about 9 mass% of Cu, about 34 mass% of ZnO and about 56 mass% of Al 2 O 3 。
Catalyst 5 is Au/CuO/Al 2 O 3 A catalyst having an active temperature of 120 to 240 ℃ and a composition consisting essentially of about 8 mass% of Au, about 28 mass% of CuO and about 64 mass% of Al 2 O 3
Example 1
(1) The synthesis gas generated in the gasification process of the 500t/d coal water slurry entrained flow bed is purified to generate purified synthesis gas, and the flow rate is 40000Nm 3 H, composition (by volume) 20% by volume carbon dioxide, 35% by volume hydrogen and 45% by volume carbon monoxide.
(2) Separating hydrogen from the purified synthesis gas by a hydrogen separation membrane component, wherein the recovery rate of the hydrogen is 90%, the concentration of the hydrogen in the hydrogen-rich synthesis gas is 95% by volume, and the flow of the hydrogen-rich synthesis gas is as follows:
40000*35％*0.9/0.95＝13263Nm 3 h, wherein the hydrogen content is:
40000*35％*0.9＝12600Nm 3 h, the remainder being small amounts of carbon monoxide andcarbon dioxide;
(3) The low-hydrogen synthetic gas enters a carbon dioxide absorption tower, the absorption rate of the carbon dioxide is 99%, and the absorbed carbon dioxide flow is as follows:
[40000*0.2-(13263-12600)*0.2/(0.2+0.45)]*0.99＝7718Nm 3 h, the flow of the shift synthesis gas is:
40000-13263-7718＝19019Nm 3 h, containing 78Nm of carbon dioxide 3 Hydrogen gas 1400Nm 3 H, the remainder is carbon monoxide;
(4) The shift synthesis gas enters a water-gas shift reactor, and reacts with sufficient steam generated in the gasification process at the low temperature of 230 ℃ and under the condition of a catalyst 1, the conversion rate of carbon monoxide is 96%, and heat generated in the process is transferred to a carbon dioxide desorption tower, so that the reactor is not over-temperature. Thus, after the water gas shift reaction, the amount of hydrogen at the reactor outlet is:
(19019-78-1400)*0.96+40000*0.35*0.1＝18240Nm 3 h, the amount of carbon dioxide at the outlet is:
(19019-78-1400)*0.96+78＝16917Nm 3 /h。
(5) The hydrogen-rich gas passing through the water gas shift unit and the hydrogen-rich synthetic gas generated by the hydrogen separation membrane component pass through the hydrogen purification unit together, so that high-purity hydrogen can be obtained, the recovery rate of the hydrogen is 96%, and the finally generated high-purity hydrogen is as follows: (12600 + 18240) + 0.96=29607Nm 3 /h；
The hydrogen yield per ton coal of the technology can reach 1422Nm 3 The hydrogen production cost is 5513 yuan/t calculated according to 700 yuan per ton of coal. Compared with the conventional coal hydrogen production technology, the hydrogen production cost can be reduced on a large scale.
In the embodiment, the catalyst has low cost, can be used for half a year without regeneration, the separation membrane in the hydrogen separation membrane component does not need to be used in a high-temperature environment, the cost of the separation membrane is only 30% of that of the high-temperature resistant separation membrane component, and the service life of the separation membrane is 2 times that of the high-temperature resistant membrane component.
Example 2
Hydrogen was prepared according to the procedure of example 1, except that the water gas shift reaction temperature was 200 ℃ and the catalyst used was catalyst 2.
And (4) after the shift synthesis gas enters the water gas shift reactor, the conversion rate of the carbon monoxide is 95%. Thus, after the water gas shift reaction, the amount of hydrogen at the reactor outlet is:
(19019-78-1400)*0.95+40000*0.35*0.1＝18064Nm 3 h, the amount of carbon dioxide at the outlet is:
(19019-78-1400)*0.95+78＝16742Nm 3 /h。
the recovery rate of hydrogen in the step (5) is 96%, and the finally generated high-purity hydrogen is as follows: (12600 + 18064) + 0.96=29437Nm 3 /h；
The hydrogen yield per ton of coal by the technology can reach 1413Nm 3 The hydrogen production cost is 5548 yuan/t calculated according to 700 yuan per ton of coal.
Example 3
Hydrogen was prepared according to the procedure of example 1, except that the water gas shift reaction temperature was 250 ℃ and the catalyst used was catalyst 3.
And (5) after the shift synthesis gas enters the water gas shift reactor in the step (4), the conversion rate of the carbon monoxide is 95%. Thus, after the water gas shift reaction, the amount of hydrogen at the reactor outlet is:
(19019-78-1400)*0.95+40000*0.35*0.1＝18064Nm 3 h, the amount of carbon dioxide at the outlet is:
(19019-78-1400)*0.95+78＝16742Nm 3 /h。
the recovery rate of hydrogen in the step (5) is 96%, and the finally generated high-purity hydrogen is as follows: (12600 + 18064) 0.96=29437Nm 3 /h；
The hydrogen yield per ton of coal by the technology can reach 1413Nm 3 The hydrogen production cost is 5548 yuan/t according to 700 yuan per ton of coal.
Comparative example 1
(1) The synthesis gas generated in the 500t/d coal water slurry entrained flow bed gasification process is purified to generate purified synthesis gas with the flow rate of 40000Nm 3 Composition (by volume) 20% by volume carbon dioxide, 35% by volume hydrogen and 45% by volume carbon monoxide.
(2) The purified synthesis gas enters a first-stage water gas shift reactor, the reaction temperature is 360 ℃, the catalyst is catalyst 4, the conversion rate of carbon monoxide is 75%, and after the reaction is finished, the content of hydrogen in the first-stage synthesis gas out of the first-stage water gas shift reactor is as follows:
40000*0.35+40000*0.45*0.75＝27500Nm 3 /h。
(3) The first-stage synthesis gas is cooled to 220 ℃ after heat exchange, enters a second-stage water gas shift reactor, the catalyst is catalyst 5, the water gas shift reaction continues to occur, the content of carbon monoxide in the synthesis gas is little at the moment, the conversion rate of the carbon monoxide is 60%, and after the reaction is finished, the content of hydrogen in the second-stage synthesis gas which is discharged from the second-stage water gas shift reactor is as follows:
27500+40000*0.45*(1-0.75)*0.55＝29975Nm 3 /h。
(4) The hydrogen-rich gas passing through the water gas shift unit and the hydrogen-rich synthetic gas generated by the hydrogen separation membrane component pass through the hydrogen purification unit together, so that high-purity hydrogen can be obtained, the recovery rate of the hydrogen is 96%, and the finally generated high-purity hydrogen is as follows: 29975 × 0.96=28776nm 3 /h；
(5) The hydrogen yield per ton of coal can reach 1381Nm 3 And h, the hydrogen production cost is 5677 yuan/t calculated according to 700 yuan per ton of coal.
In this comparative example, a two-stage reactor was required, and similarly, a high-temperature catalyst was purchased. During the construction of the gasification plant, the design, installation and operation cost of the prepared water gas shift device is about 1000 ten thousand yuan. The more one reactor is used, the more the overall cost can be reduced by 40%.
Comparative example 2
According to the method in CN103359688B, the synthesis gas generated in the 500t/d coal water slurry entrained-flow bed gasification process is purified to generate purified synthesis gas, and the flow rate is 40000Nm 3 H, a purified synthesis gas having a composition (by volume) of 20% by volume of carbon dioxide, 35% by volume of hydrogen and 45% by volume of carbon monoxide is subjected to a water gas shift reaction using catalyst 1 at a reaction temperature of 230 ℃.
As a result, it was found that the conversion of carbon monoxide was only 80%, the catalyst was deactivated after 3 months of use, and the separation membrane in the hydrogen separation membrane module was replaced after 3 months.
It can be seen from examples 1-3 and comparative example 1 that the process and system of the present invention has higher co conversion, higher hydrogen production per ton of coal, lower hydrogen production cost, lower equipment cost, significantly lower catalyst cost, longer catalyst life, and longer continuous service life than the conventional process and system using two-stage water gas shift reactors.
It can be seen from examples 1-3 and comparative example 2 that, with the method and system of the present invention, the conversion rate of carbon monoxide is increased, the service life of the catalyst and hydrogen separation membrane module is prolonged, and the system can be continuously used for a long time.
The preferred embodiments of the present invention have been described above in detail, but the present invention is not limited thereto. Within the scope of the technical idea of the invention, many simple modifications can be made to the technical solution of the invention, including combinations of various technical features in any other suitable way, and these simple modifications and combinations should also be regarded as the disclosure of the invention, and all fall within the scope of the invention.
Claims (10)
1. A method for producing hydrogen from synthesis gas, the method comprising the steps of:
(1) Separating hydrogen in the purified synthesis gas to obtain low-hydrogen synthesis gas and hydrogen-rich synthesis gas;
(2) Absorbing carbon dioxide in the low-hydrogen synthesis gas to obtain a conversion synthesis gas;
(3) Carrying out water gas shift reaction on the shift synthesis gas and water vapor in the presence of a catalyst to form a hydrogen-rich mixed gas;
(4) And merging the hydrogen-rich synthesis gas and the hydrogen-rich mixed gas for purification to obtain the high-purity hydrogen.
2. The method of claim 1, wherein the separating is by passing the purified syngas through a hydrogen separation membrane module;
and/or the absorption process is to contact the low-hydrogen synthesis gas with a chemical absorbent to absorb carbon dioxide.
3. A process according to claim 1 or 2, wherein the water gas shift reaction has a reaction temperature of 200-250 ℃; preferably, the reaction temperature is 225-235 ℃;
and/or the catalyst is selected from the group consisting of Cu or Ni as the main active component and ZrO 2 、ZnO、Al 2 O 3 、MgO、SiO 2 And TiO 2 At least one of which is a supported metal catalyst.
4. The method according to any one of claims 1 to 3, further comprising resolving the carbon dioxide-absorbing absorbent obtained in step (2);
preferably, the heat released by the water gas shift reaction provides the process of desorption.
5. The method according to any one of claims 1-4, wherein the method further comprises: carrying out gasification reaction on the coal water slurry or coal dry powder to generate crude synthesis gas;
purifying the crude synthesis gas to obtain purified synthesis gas;
preferably, the gasifying agent used in the process of the gasification reaction is selected from O 2 、O 2 /H 2 Mixed gas of O or O 2 /CO 2 At least one of the mixed gases;
preferably, the gasification reaction is carried out in a water-cooled wall gasifier;
preferably, the water-cooled wall gasification furnace generates superheated steam of 2MPa-5 MPa;
preferably, the temperature of the gasification reaction is above 1400 ℃;
preferably, the superheated steam is used for the water gas shift reaction;
preferably, the purification process is passing the raw synthesis gas through a synthesis gas purification unit.
6. A system for producing hydrogen from syngas, the system comprising: the device comprises a hydrogen separation membrane component, a carbon dioxide absorption tower, a water gas shift unit and a hydrogen purification unit;
the hydrogen separation membrane component is used for separating hydrogen in the purified synthesis gas to form hydrogen-rich synthesis gas and low-hydrogen synthesis gas;
the carbon dioxide absorption tower is used for absorbing carbon dioxide in the low-hydrogen synthesis gas to form conversion synthesis gas;
the water gas shift unit is used for reacting the shifted synthesis gas with steam to generate hydrogen and carbon dioxide, and finally forming a hydrogen-rich mixed gas;
the hydrogen purification unit is used for purifying the hydrogen-rich synthesis gas and the hydrogen-rich mixed gas to obtain high-purity hydrogen.
7. The system of claim 6, further comprising a carbon dioxide desorption tower for desorbing carbon dioxide absorbed in the carbon dioxide absorption tower.
8. The system of claim 7, wherein the water gas shift unit is in communication with the carbon dioxide stripper for providing heat generated by the water gas shift unit to the carbon dioxide stripper for carbon dioxide stripping.
9. The system of any one of claims 6-8, wherein the system further comprises:
the water-cooled wall gasifier is used for generating crude synthesis gas by taking coal water slurry or coal dry powder as a raw material;
and the synthesis gas purification unit is used for purifying the crude synthesis gas to obtain purified synthesis gas.
10. The system of claim 9, wherein the water gas shift unit provides a primary water gas shift reactor.
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