CN113460963A

CN113460963A - Method for producing hydrogen from biogas

Info

Publication number: CN113460963A
Application number: CN202110885429.3A
Authority: CN
Inventors: 许慎启; 潘晓峰; 佩特拉·佩霍瓦; 阿兰·布里格利亚
Original assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2021-08-03
Filing date: 2021-08-03
Publication date: 2021-10-01

Abstract

The invention discloses a method for preparing hydrogen from biogas, which comprises the following steps: providing pretreated crude biogas, and providing a first raw material gas and a second raw material gas into at least part of the crude biogas under the condition of not separating carbon dioxide in advance to form a mixed gas, so that the volume ratio of the carbon dioxide in the mixed gas is lower than 30%; carrying out steam reforming reaction on the mixed gas in the presence of a catalyst to obtain synthesis gas containing hydrogen and carbon monoxide; oxidizing carbon monoxide in the synthesis gas to carbon dioxide by a carbon monoxide shift reaction, while correspondingly producing hydrogen; and then obtaining a substantially pure hydrogen product by pressure regulation in an adsorption unit, wherein the first raw material gas is water vapor, and the second raw material gas is methane and/or hydrogen. The method not only adjusts the hydrogen-carbon ratio in the reaction process, but also improves the utilization rate of carbon dioxide in the biogas and reduces the carbon deposition of the catalyst in the carbon dioxide reforming process.

Description

Method for producing hydrogen from biogas

Technical Field

The invention belongs to the field of hydrogen production, and relates to a method for preparing hydrogen from biogas.

Background

Hydrogen is an ideal secondary energy source, and has the advantages of various sources, storage, reproducibility and the like. There are a number of known hydrogen production processes in the art, such as steam reforming of natural gas (methane), catalytic reforming of hydrocarbons, and the like. The deactivation of catalyst carbon deposition is a common problem in the process of preparing hydrogen from natural gas.

Biogas (also known as "biogas") is a gas produced during the decomposition of organic matter in the absence of oxygen (anaerobic fermentation). Biogas contains mainly methane and carbon dioxide, the proportions of which vary according to the source and manner of obtaining the biogas, and also smaller proportions of water, nitrogen, hydrogen sulfide, oxygen or other organic compounds in trace form. Typically, biogas comprises from 30 to 75% volume fraction methane and from 15 to 60% volume fraction carbon dioxide, calculated on a dry basis, e.g. the carbon dioxide content in biogas formed from agricultural waste can reach 30 to 50% by volume. The biogas biomass energy has the characteristics of abundant resources, renewability and environmental friendliness, and can realize zero emission of pure carbon dioxide. The development and utilization of the biogas biomass for hydrogen production have important significance for establishing a sustainable energy system, economic development and ecological environment.

One disadvantage and challenge of using biogas-like bio-energy is the need to upgrade the biogas to bio-methane, and the carbon dioxide removal during the upgrading process consumes significant energy, greatly increasing the cost of the overall system. There are several methods of purifying biogas in the prior art, and sufficient purification of biogas can produce biogas (i.e., biomethane) that has been purified to standard natural gas specifications and can replace standard natural gas.

Chinese patent publication No. CN103332650B discloses a system for producing hydrogen by catalytic decomposition of methane by a dry method and simultaneously separating carbon dioxide. In the process of catalytic decomposition of methane, the catalyst is easy to deposit carbon and lose the catalytic performance. The system extracts hydrogen by a combination of gas phase hydrogen membrane separation and carbon deposit elimination. According to the method, methane is decomposed into carbon and hydrogen under the action of a catalyst, the obtained gas is separated through a filter membrane, the generated hydrogen is recovered, the generated carbon deposit enters a reduction reactor, the carbon is subjected to gasification reaction under the action of a gasification medium, a gasification product is generated to react with an oxide to generate carbon dioxide and water vapor, the water vapor is condensed to obtain high-purity carbon dioxide, the reacted oxide enters an oxidation reactor to perform oxidation reaction with air, and the oxide is regenerated and releases heat to provide heat for catalytic decomposition. But this method is suitable for use in cases where the carbon dioxide content of the raw biogas is low (typically below 15% volume fraction). If the carbon dioxide content in the raw biogas is high, a catalyst regeneration reduction reactor and an oxide oxidation reactor need to be introduced, and carbon deposition and regeneration circulating on the catalyst can damage the structure of the catalyst and influence the service life of the catalyst.

The Chinese patent application with the publication number of CN107986578A discloses a methane hydrogen production circulating system and a process for PTA sewage treatment. Because the components of the biogas after PTA (terephthalic acid) sewage treatment are relatively close to those of the raw material natural gas in the natural gas hydrogen production process, the components mainly comprise methane, carbon dioxide, water, steam and a small amount of hydrogen sulfide, wherein the content of the methane is more than or equal to 65 volume percent, after the carbon dioxide, the water, the steam and the hydrogen sulfide in the biogas are subjected to impurity separation, the concentration of the methane can reach more than 90 volume percent or even higher, and the index of the natural gas is reached. The carbon dioxide content of this biomethane is very low, even lower than 2%. Then the 90 volume percent of methane and water vapor are converted into CO and hydrogen under the action of high temperature and catalyst, and high-purity hydrogen is obtained through pressure swing adsorption, so that the cyclic recycle of the internal resources of the PTA device can be realized. The method for preparing hydrogen by the system is still based on steam reforming of biomethane, and the carbon dioxide is still required to be separated in advance.

In view of the extremely high difficulty in developing and researching the catalyst capable of resisting carbon deposition, the applicant wants to find a method for reducing the carbon deposition of the catalyst used in the process of directly converting the methane rich in carbon dioxide, overcomes the defects and shortcomings that the prior methane needs to be subjected to carbon dioxide separation in advance, and the like, and realizes that the hydrogen meeting the requirements is directly prepared from the methane without separating the carbon dioxide in advance.

Disclosure of Invention

In order to solve the technical problems, the invention provides a method for directly preparing hydrogen from biogas without separating carbon dioxide in advance, so that the risk of carbon deposition inactivation of a catalyst is greatly reduced.

In a first aspect, the present invention provides a method for producing hydrogen from biogas, comprising the steps of:

(1) providing a raw biogas after pretreatment (e.g., after drying and desulfurization treatment);

(2) without prior separation of CO₂Providing a first raw material gas and a second raw material gas into at least part of the crude biogas to form a mixed gas, wherein the volume ratio of carbon dioxide in the mixed gas is lower than 30%;

(3) carrying out steam reforming reaction on the mixed gas in the presence of a catalyst to obtain synthesis gas containing hydrogen and carbon monoxide;

(4) oxidizing carbon monoxide in the synthesis gas to carbon dioxide by a Shift reaction of carbon monoxide (CO Shift) while correspondingly producing hydrogen,

(5) obtaining a substantially pure hydrogen product by pressure regulation in an adsorption unit;

wherein the first raw material gas is water vapor, and the second raw material gas is methane and/or hydrogen.

Further, the pretreated raw biogas comprises, in volume fraction, 30% to 60% methane and 30% to 60% carbon dioxide. In particular, the raw biogas comprises, on a dry basis, a volume fraction of 30% to 60% methane, 30% to 60% carbon dioxide, 0 to 15% nitrogen, 0 to 5% oxygen and other minor impurities.

Further, the ratio of the carbon deposition equilibrium constant K of the catalyst to the reaction entropy Q in the steam reforming reaction is less than 1.

Further, the steam reforming reaction is carried out in a reforming reactor, the reforming reactor is provided with a carbon deposit prediction and flow control module, each K value and each Q value in the reforming reactor under different working conditions are stored in the carbon deposit prediction and flow control module in advance, and the steam reforming reaction is adjusted by monitoring the K/Q value.

Further, the second raw material gas is methane until the volume ratio of the carbon dioxide to the total methane in the mixed gas is less than 1: 2.3.

further, the second raw material gas is methane until the volume ratio of the water vapor to the total methane in the mixed gas is in a range of 1.4: 1 to 5: 1. The water vapor is introduced to react with the pretreated crude biogas, so that the incomplete reaction of methane in the crude biogas can be avoided to pollute the environment and reduce the energy utilization rate, and the generation of carbon deposition in the reaction can be inhibited.

Further, the second raw material gas is hydrogen until the hydrogen in the mixed gas accounts for 15-32% of the volume of the mixed gas, preferably 17-32%, more preferably 25-32%. The separate introduction of additional hydrogen may allow the following reactions to proceed in a direction that reduces carbon production:

C_nH_m→nC+0.5_m H₂；C_nH_m→ olefins (olefins) → coke (coke).

Further, the second feed gas is derived from the substantially pure hydrogen product.

Further, 10% to 30% by volume of the substantially pure hydrogen product is used as the second feed gas.

Further, the methane provided by the second feed gas is derived from substantially pure natural gas or biomethane.

Further, the crude biogas is divided into a first part of crude biogas and a second part of crude biogas, the first raw material gas and the second raw material gas form a mixed gas, wherein the second raw material gas is biomethane obtained after the second part of crude biogas is separated from carbon dioxide.

Compared with the prior art, the technical scheme provided by the invention has the following advantages:

the invention provides a novel method for directly preparing hydrogen from biogas, which adjusts the hydrogen-carbon ratio in the reaction process, improves the utilization rate of carbon dioxide in the biogas and reduces carbon deposition of a catalyst in the carbon dioxide reforming process by adjusting components such as water vapor, methane, carbon dioxide, hydrogen and the like. Wherein the methane can be from pipeline natural gas or biomethane, and the hydrogen can be partially recovered from the final hydrogen product or can be from an independent hydrogen source. Moreover, the technology for producing hydrogen from biogas can be used for generating green power and supplying power for a biogas reforming system or PSA and the like.

Drawings

The advantages and spirit of the present invention can be further understood by the following detailed description of the invention and the accompanying drawings.

Fig. 1 shows a schematic flow chart of hydrogen production from biogas according to a first embodiment of the present invention.

FIG. 2 shows a schematic flow chart of the process for producing hydrogen from biogas according to the second embodiment of the present invention.

Detailed Description

Specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. However, the present invention should be understood not to be limited to such an embodiment described below, and the technical idea of the present invention may be implemented in combination with other known techniques or other techniques having the same functions as those of the known techniques.

In the following description of the embodiments, for purposes of clearly illustrating the structure and operation of the present invention, directional terms are used, but the terms "front", "rear", "left", "right", "outer", "inner", "outward", "inward", "axial", "radial", and the like are to be construed as words of convenience and are not to be construed as limiting terms.

In the following description of the specific embodiments, it is to be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like are used in an orientation or positional relationship indicated in the drawings for convenience in describing the invention and to simplify the description, but are not intended to indicate or imply that the referenced device or element must have a particular orientation, be constructed and operated in a particular orientation, and are not to be construed as limiting the invention.

Furthermore, the terms "first" and "second" are used for descriptive purposes only and are not intended to limit the temporal order, quantity, or importance, but are not intended to indicate or imply relative importance or implicitly indicate the number of technical features indicated, but merely to distinguish one technical feature from another technical feature in the present disclosure. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically stated otherwise. Similarly, the appearances of the phrases "a" or "an" in various places herein are not necessarily all referring to the same quantity, but rather to the same quantity, and are intended to cover all technical features not previously described. Similarly, unless a specific number of a claim recitation is intended to cover both the singular and the plural, and also that claim may include a single feature or a plurality of features. Similarly, modifiers similar to "about", "approximately" or "approximately" that occur before a numerical term herein typically include the same number, and their specific meaning should be read in conjunction with the context.

It should be understood that in the present application, "at least one" means one or more, "a plurality" means two or more. "and/or" is used to describe the association relationship of the associated objects, meaning that there may be three relationships, for example, "a and/or B" may mean: only A, only B and both A and B are present, wherein A and B may be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single item(s) or plural items. For example, at least one (one) of a, b, or c, may represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", wherein a, b and c may be single or plural.

As used herein, "biogas" (also referred to as "biogas") refers to a gas produced by anaerobic fermentation of animal or plant organic material in the absence of oxygen. Biogas typically contains 30% to 75% methane and 15% to 60% carbon dioxide, and may also contain nitrogen and trace amounts of other components of the sulfide, siloxane or volatile organic compound type. Biogas can be used in various ways, such as supplying heat, electricity, or a mixture of both, near the production site after light treatment. If the carbon dioxide content of the biogas is too high, the calorific value thereof is reduced, and the compression and transportation costs are increased, and therefore, the biogas is purified in various ways, for example, the biogas which can be sufficiently purified to produce natural gas which can replace fossil sources has been produced, and thus the purified biogas is called "biomethane", and the biomethane can be put to the same use as natural gas of fossil sources, can be supplied to natural gas pipelines, vehicle gas stations, and the like.

As used herein, "raw biogas" may be understood as biogas that has been dried and desulfurized, as opposed to purified biogas that is substantially pure methane (also referred to as "biomethane").

"substantially pure hydrogen or methane" refers to a gas having a purity of greater than 80% volume fraction, preferably a purity of greater than 90% volume fraction, and more preferably a purity of greater than 95% volume fraction.

One of the main limitations of using raw biogas Steam Reforming (Steam Reforming) without removing carbon dioxide is that the catalyst used in the reaction, such as the nickel-based catalyst commonly used in industry, is liable to carbon deposition during the reaction to reduce the activity of the catalyst, and even to block the reactor or system piping in severe cases, and the reaction is a strong endothermic reaction and consumes a lot of energy.

One of the main limitations of optimal operation is related to the formation of carbon. Carbon deposition can lead to catalyst damage, increased pressure drop, and uneven flow distribution, resulting in overheating of the tubes. This will limit the life of the catalyst tubes. Generally, carbon deposits can be formed by three different mechanisms:

the first is filamentous Carbon (Whisser Carbon), which grows on the crystallites on the catalyst surface at temperatures above 720K, and the main formation mechanism includes several reactions, the first of which is the most predominant reaction of filamentous Carbon formation.

C_nH_m→nC+0.5mH₂

The second is Gum (Gum), the main formation mechanism is C_nH_m→ ose → olefinis → make the catalyst pore blocking, leading to catalyst deactivation.

The third one is Pyrolytic Carbon (Pyrolytic Carbon) which is formed by thermal cracking of hydrocarbon compounds at the temperature higher than 873K, and the main forming mechanism is C_nH_m→(CH₂)_nSuch char also deactivates the catalyst → gum.

Therefore, reforming of carbon dioxide rich gas requires investigation of how to adjust the H/C molar ratio in the feed gas to reduce the strength of the gas used to form carbon and convert any higher hydrocarbons.

In actual industrial production, reaction equilibrium constants K under corresponding temperature and pressure can be obtained for different chemical reaction equations of catalyst carbon deposition, and the reaction direction of the carbon deposition reaction is estimated by calculating a reaction quotient Q in a reforming reactor. The reforming reactor is provided with a carbon deposit prediction and flow control module. For example, for

Wherein the balance constant K may be a pressure balance constant and Q ═ P_H2^²/P_CH4. If Q is>K, the reaction proceeds in the carbon deposition direction, and vice versa. In practice, the K and Q values in the reforming reactor under different conditions (such as different feed compositions, feed temperatures and feed pressures) can be pre-stored in the database, and the process parameters such as feed compositions and the like can be adjusted according to the K/Q value to avoid carbon deposition. And a polynomial fitting method can also be adopted to correlate the carbon deposition data with the feeding temperature, the feeding pressure and the water vapor feeding amount, and predict and evaluate the carbon deposition reaction, so that the process parameters are controlled and adjusted, and the carbon deposition risk is reduced.

Unless clearly indicated to the contrary, each aspect or embodiment defined herein may be combined with any other aspect or embodiments. In particular, any feature indicated as being preferred or advantageous may be combined with any other feature indicated as being preferred or advantageous.

Specific embodiments of the present invention will be described in detail below with reference to fig. 1 to 2.

Example 1

As shown in fig. 1, raw material Biomass 11(Biomass) based on sewage, sludge, household organic waste, animal or agricultural waste is fed into an anaerobic digester 12, and the produced biogas is desulfurized by a pretreatment 13 to produce a raw biogas, and the desulfurized raw biogas is then divided into two parts, wherein the raw biogas is rich in methane and carbon dioxide. After the first part of the crude biogas 13a is subjected to the carbon dioxide removal and purification process 14, the methane content is increased to be biomethane 15, and the composition of the biomethane is equivalent to that of a substantially pure natural gas and can be used as a substitute of the natural gas. Then 208Nm³H the above biomethane 15 and 416Nm³The/h second biogas fraction 13b is fed to a steam reformer 18 together with 1404kg/h steam 16 as a mixture 17 for wet reforming of carbon dioxide, methane and water, the main reactions being as follows:

3CH₄+2H₂O+CO₂→4CO+8H₂

CO₂+CH₄→2CO+2H₂

CH₄+H₂O→CO+3H₂

wherein the first portion of the raw biogas comprises about 33% by volume of the total raw biogas and the second portion of the raw biogas comprises about 67% by volume of the total raw biogas. The volume of carbon dioxide in the mixed gas is reduced to below 30 volume percent, and the volume ratio of methane to carbon dioxide is 2.35: 1.

Of course, in the route of this embodiment, it is also possible to mix essentially pure natural gas from fossil origin directly with all of the crude biomass and steam and to feed it as a mixture gas to the steam reformer.

The mixed gas is used as a reforming reaction gas and is pressurized to 2.7MPa to enter a reforming operation unit. In order to adjust the water-carbon ratio during the reforming reaction, the reforming operation unit is provided with a carbon deposit prediction and flow control module 22 for the delivery and metering of steam and methane required to complete the reforming reaction. In this reforming process, a nickel-based catalyst is used at 573 ℃ to 807 ℃ to produce a syngas having a hydrogen to CO molar ratio of about 5: 1.

The reformed synthesis gas is subjected to carbon monoxide shift reaction 19 and pressure swing adsorption separation 20 to produce a substantially pure hydrogen product 21.

It should be noted that the steps of crude biogas desulfurization, removal of carbon dioxide after desulfurization, and upgrading of the crude biogas to biomethane, carbon monoxide shift reaction are not described in detail herein, and depending on the complexity of the actual production scenario, some of the flow schemes are not shown in the schematic diagram of fig. 1 and can be performed using known suitable methods. The whole process needs a plurality of necessary modules such as heat supply, power supply, cooling water, power equipment and the like.

Example 2

The same reference numerals as in embodiment 1 are given to the same reference numerals in this embodiment.

As shown in FIG. 2, sewage, sludge, household organic waste, animals based on waste water, sludge, and the like are added to the anaerobic digester 12Or raw material Biomass 11(Biomass) of agricultural waste, the biogas produced is desulfurized in a pretreatment 13 to produce a raw biogas, which is then desulfurized (rich in methane and carbon dioxide) 843Nm ³16, 176 Nm/h of water vapour and 1544kg/h of water vapour³The mixed gas 17 composed of hydrogen gas 21a is fed into the steam reformer 18 together to perform wet reforming, and the main reaction is as follows:

3CH₄+2H₂O+CO₂→4CO+8H₂

CO₂+CH₄→2CO+2H₂

CH₄+H₂O→CO+3H₂

the hydrogen added above may be part of the final hydrogen product 21 until the volume fraction of hydrogen in the mixed gas 17 reaches 17%.

As the volume fraction of hydrogen added to the mixture increased, the inventors simulated three sets of data for carbon deposition to obtain the data shown in table 1 below. The pressure in the reforming reactor in the simulated case was 14bar and the outlet temperature of the reforming reactor was substantially around 860 c. It can be seen that as the volume fraction of hydrogen added to the mixture increases, the K/Q value of the soot reaction changes accordingly. At the inlet of the reforming reactor, there is a small section of space in which carbon is very prone to deposit because of the relatively high methane content and the lack of mixing of hydrogen. The hydrogen content gradually increases with increasing distance from the inlet to react with the main carbon deposit

For example, it will go in the opposite direction of the soot reaction, and at this point the K/Q value is calculated at intervals, it can be seen that when the volume fraction of hydrogen in the mixture is below a certain value, the maximum value of K/Q for the soot reaction will still be greater than 1, which means that some of the catalyst will still have soot thereon. And when the volume fraction of the hydrogen in the mixed gas is higher than a certain value, the maximum value of K/Q of the carbon deposition reaction is less than 1, which means that the carbon deposition reaction is carried out towards the opposite direction of the carbon deposition, and the carbon deposition is effectively inhibited.

TABLE 1 simulation data for carbon deposition

	First group	Second group	Third group
				Volume fraction of hydrogen in the gas mixture	0％	13.38％	25.08％
Steam/methane molar ratio	3	3	3
				Outlet temperature/. degree.C.of reforming reactor	857	857	860
Maximum value of K/Q	1.11	1.02	0.86
				Whether carbon is deposited or not	Is that	Is that	Whether or not

The embodiments described in the specification are only preferred embodiments of the present invention, and the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the present invention. Those skilled in the art can obtain technical solutions through logical analysis, reasoning or limited experiments according to the concepts of the present invention, and all such technical solutions are within the scope of the present invention.

Claims

1. A method for producing hydrogen from biogas, comprising the steps of:

(1) providing pretreated crude biogas;

(4) oxidizing carbon monoxide in the synthesis gas to carbon dioxide by a carbon monoxide shift reaction while correspondingly producing hydrogen;

2. The method of claim 1, wherein the pretreated raw biogas comprises 30% to 60% methane and 30% to 60% carbon dioxide by volume fraction.

3. The process according to claim 1, wherein the ratio of the carbon deposit equilibrium constant K of the catalyst to the entropy of reaction Q in the steam reforming reaction is < 1.

4. The method as claimed in claim 3, wherein the steam reforming reaction is performed in a reforming reactor provided with a soot prediction and flow control module in which respective K and Q values in the reforming reactor under different operating conditions are previously stored, and the steam reforming reaction is adjusted by monitoring the K/Q value.

5. The method of claim 1, wherein the second feed gas is methane until the volume ratio of carbon dioxide to total methane in the mixed gas is in the range of less than 1: 2.3.

6. the method of claim 1, wherein the second feed gas is methane until the volume ratio of the steam to the total methane in the mixed gas is in the range of 1.4: 1 to 5: 1.

7. The method of claim 1, wherein the second raw material gas is hydrogen gas, and the hydrogen gas in the mixed gas accounts for 15-32% of the volume of the mixed gas, preferably 17-32%, and more preferably 25-32%.

8. The method of claim 7, wherein the second feed gas is derived from the substantially pure hydrogen product.

9. The method of claim 8, wherein 10% to 30% by volume of the substantially pure hydrogen product is used as the second feed gas.

10. The method of claim 1, wherein the methane provided by the second feed gas is derived from substantially pure natural gas or biomethane.