CN107987907B

CN107987907B - Method for preparing methane-rich gas from synthesis gas

Info

Publication number: CN107987907B
Application number: CN201610950692.5A
Authority: CN
Inventors: 任文坡; 宋倩倩; 翟绪丽; 丁文娟; 师晓玉; 乔明; 王红秋; 周笑洋; 李振宇; 李雪静; 杨延翔
Original assignee: Petrochina Co Ltd
Current assignee: Petrochina Co Ltd
Priority date: 2016-10-26
Filing date: 2016-10-26
Publication date: 2020-07-10
Anticipated expiration: 2036-10-26
Also published as: CN107987907A

Abstract

The invention provides a method for preparing methane-rich gas from synthesis gas, which comprises the following steps: carrying out contact reaction on the clean synthesis gas and a first methanation catalyst in a first methanation reactor to obtain methanation raw gas; carrying out contact reaction on the methanation raw gas and a second methanation catalyst in a second methanation reactor to obtain a gas material flow I; the first methanation catalyst is led out from the first methanation reactor and is divided into three parts; and the first gas flow is in contact reaction with the third part of catalyst and/or the regenerated first methanation catalyst in a third methanation reactor to obtain a gas product rich in methane. The methanation catalyst provided by the invention has the function of a heat carrier in the moving bed, can be regenerated and recycled on line, and can effectively recycle reaction heat.

Description

Method for preparing methane-rich gas from synthesis gas

Technical Field

The invention relates to a method for preparing methane-rich gas from synthesis gas, in particular to a method for preparing methane-rich gas by converting carbonaceous materials into synthesis gas and carrying out methanation combined process on the synthesis gas.

Background

With the rapid growth of Chinese economy, the traditional natural gas and petroleum resources can not meet the requirements of social production and people's life. It is expected that the natural gas gap in china will exceed 1000 billions of cubic meters (standard) per year by 2020. Based on the consideration of energy resource endowment and energy safety in China, coal, biomass and the like are required to be converted into civil gas, transportation fuel, basic chemical raw materials and the like. The technology for preparing the natural gas from the coal is a process of preparing synthesis gas by gasifying low-order lignite, and then converting the synthesis gas into methane which is used as a gas fuel. The process of preparing natural gas from coal has high energy efficiency, low water consumption and relatively mature technology, and has important significance for developing coal in remote areas in the western China, improving the living standard of people and reducing the emission of polluted gas. In addition, the utilization of coke oven gas for methane production is also a new technical and industrial growth point.

The methanation device is one of the core devices of the process for preparing natural gas from coal and the process for preparing methane from coke oven gas. Fixed bed reactors (CN200810099464, CN200910054761, CN2010800399242, CN2011102686680, CN2011104182734, CN201210121649, CN201210150228, CN2012102193086 and the like) are mostly adopted in the conventional methanation process, and a small number of patents disclose that fluidized bed reactors (CN101817716A, CN2011100236913, CN2012102545935, CN 2013107159, CN 2011360 201010123120.2) and slurry bed reactors (CN 201110498) are adopted. In practical application, in combination with the characteristic that the methanation process is a strong heat release process and the principle of heat energy recycling, one or two high-temperature methanation reactors are generally arranged at first to convert a larger part of CO into CH₄Recovering reaction heat release to generate high-pressure steam, and arranging one or two low-temperature methanation reactors (also called supplementary methanation reactors) to convert all residual CO into CH₄。

Unlike fixed bed or fluidized bed reactors, moving bed reactors are another type of reactor conventionally employed. When a moving bed reactor is adopted, granular or pellet catalysts are continuously added from the top of the reactor, gradually move downwards under the action of gravity, and are continuously discharged from the bottom of the reactor. The reaction material is contacted with the catalyst for reaction in a counter-current, cocurrent or cross-current mode. Since there is substantially no relative motion between the solid particles, but the solid particle layer moves downward continuously, the catalyst can move in the reactor and continuously move in and out of the reactor, so it can be regarded as a moving fixed bed reactor. The operation performance and the requirement on the catalyst of the moving bed are between those of the fixed bed and the fluidized bed, and the moving bed is suitable for the reaction with moderate catalyst deactivation speed but still needing cyclic regeneration. Until now, no patent disclosure or research report of the moving bed methanation reactor is found.

Disclosure of Invention

The invention aims to provide a combined process method for preparing methane-rich gas from synthesis gas, which combines a fixed bed process and a moving bed process, has the advantages of cyclic regeneration of a moving bed catalyst, high heat recovery efficiency and convenient operation.

The inventor of the invention researches and analyzes and finds that in the moving bed reactor, a catalyst bed layer continuously moves at a certain speed, and can be regenerated or not regenerated after being discharged from the bottom of the reactor, and then recycled. The moving bed reactor is suitable for the reaction process with moderate catalyst deactivation rate but still needing cyclic regeneration. Therefore, when the catalyst is matched with a moving bed reactor for use, the catalyst is required to have higher catalytic activity and target product selectivity, and a certain reversible deactivation rate of the catalyst is also allowed. And the moving bed reactor can also be used as a heat exchanger to realize the direct contact heat exchange of gas phase and solid phase, and has the characteristics of high heat transfer efficiency, simple operation and the like.

Based on the above findings, to achieve the aforementioned object of the present invention, the present invention provides a process for producing a methane-rich gas from a synthesis gas, comprising the steps of:

(1) carrying out contact reaction on the clean synthesis gas and a first methanation catalyst in a first methanation reactor to obtain methanation raw gas;

(2) carrying out contact reaction on the methanation raw material gas obtained in the step (1) and a second methanation catalyst in a second methanation reactor, and carrying out heat exchange and cooling on a high-temperature gas stream obtained by the reaction to obtain a gas stream I; the heat exchange and temperature reduction is indirect heat exchange, a heat exchanger known to persons in the field is adopted to carry out heat exchange and temperature reduction on the high-temperature gas stream after the contact reaction, the adopted heat exchange media are water, low-pressure steam and the like, and the low-pressure steam is preferably used as the heat exchange medium to generate high-grade steam;

the second methanation catalyst is a methanation catalyst of commercial brand G1-86HT, CRG-L H or MCR-2X, or other catalysts of the same type as described above.

(3) Leading out the first methanation catalyst in the step (1) from the first methanation reactor, and dividing the first methanation catalyst into three parts: feeding the first part of catalyst into a regeneration reactor for regeneration treatment to obtain a regenerated first methanation catalyst, and feeding the regenerated first methanation catalyst into a third methanation reactor for recycling; a second portion of the catalyst is discharged from the reaction system as spent catalyst; and the third part of catalyst is directly sent to a third alkylation reactor for recycling.

(4) Carrying out contact reaction on the gas stream I obtained in the step (2) and a fresh first methanation catalyst, a third part of catalyst and/or a regenerated first methanation catalyst in a third methanation reactor, and cooling a gas product obtained after the reaction to obtain a gas product rich in methane; the first methanation reactor and the third methanation reactor are both moving bed reactors, and the second methanation reactor is a fixed bed reactor. The cooling mode is indirect heat exchange, and the heat exchanger known to persons in the art is adopted to exchange heat with the gas after the contact reaction, so that the gas product is cooled, and moisture is separated out to obtain the gas product rich in methane. The heat exchange medium is preferably water and low-pressure steam, and the steam with improved grade obtained after heat exchange is further sent to the outlet of the first methanation reactor to exchange heat with the high-temperature gas material flow, so that high-grade steam is generated.

In the method for preparing the methane-rich gas from the synthesis gas according to the present invention, in step (1), the contact reaction conditions are preferably: 5-100 absolute atmospheric pressure, 40-400 ℃ and gas space velocity of 50-80000h^-1The residence time of the catalyst is 24h-10 days; the conditions of the contact reaction are further preferably: 10-70 absolute atmospheric pressure, 100-350 ℃, and the gas space velocity of 1000-50000h^-1The residence time of the catalyst is 72h-5 days; in the step (2), the conditions of the contact reaction are preferably: 15-100 absolute atmospheric pressure, 330-^-1(ii) a In the step (4), the conditions of the contact reaction are preferably: 2-100 absolute atmospheric pressure, 250-700 ℃ and gas space velocity of 50-80000h^-1The residence time of the catalyst is 24h-100 days; the conditions of the contact reaction are further preferably: 10-70 absolute atmospheric pressure, 310-620 ℃ and gas space velocity of 1000-50000h^-1The residence time of the catalyst is 72h-30 days.

In the method for preparing a methane-rich gas from a synthesis gas according to the present invention, in the step (1), preferably, the clean synthesis gas is obtained by pre-treating at least one of the group consisting of a coal-to-synthesis gas, a biomass-to-synthesis gas, and a coke oven gas to remove impurities and/or by water-gas shift.

The method for preparing the methane-rich gas from the synthesis gas is characterized in that the moving bed reactor is preferably at least one type selected from the group consisting of a vertical type, an inclined type, a horizontal type, a vertical sleeve type and a vertical reducing type.

The method for preparing the methane-rich gas from the synthesis gas is characterized in that the number of the third alkylation reactors is preferably 2-4, and the third alkylation reactors are preferably connected in series, in parallel, in series-parallel or in parallel-series.

In the method for preparing a methane-rich gas from a synthesis gas according to the present invention, in step (1), the contacting process is preferably performed by passing the clean synthesis gas through the catalyst bed of the first methanation reactor once in a counter-current, cross-current or co-current manner.

Hair brushThe method for preparing the methane-rich gas from the synthesis gas comprises the step (1) of methanation raw material gas (H)₂-CO₂)/(CO+CO₂) The molar ratio is preferably 2.8 to 3.5, more preferably 2.9 to 3.3.

In the method for preparing the methane-rich gas from the synthesis gas, in the step (4), the first gas stream and the third part of the catalyst are preferably contacted in a counter-current, cross-current or co-current manner.

The method for preparing the methane-rich gas from the synthesis gas is characterized in that the first methanation catalyst is preferably a pellet catalyst, and the particle size range of the pellet catalyst is preferably 0.1-200 mm; further preferably 0.4 to 100 mm; more preferably 0.7-30 mm.

In the method for preparing the methane-rich gas from the synthesis gas, the first methanation catalyst preferably comprises an active component, a carrier, a binder and a modification auxiliary agent, wherein the active component, the carrier, the binder and the modification auxiliary agent respectively account for 5-90 wt%, 6-64 wt%, 3-45 wt% and 10 wt%^-6～2％。

In the method for preparing a methane-rich gas from a synthesis gas according to the present invention, the active component is preferably at least one selected from the group consisting of Ni, Mo, Fe, Co, Ru, Pt, Pd, and Rh.

The method for preparing the methane-rich gas from the synthesis gas is characterized in that the modification auxiliary agent is preferably at least one selected from the group consisting of rare earth elements, transition metal elements and main group elements.

The method for preparing the methane-rich gas from the synthesis gas is characterized in that the rare earth elements are L a, Ce, Pr, Nd and Sm, the transition metal elements are Zr, Y, Nb, Cr, Ti, Zn, Cu, Mn, Os and Ir, and the main group elements are Si, Al, Mg, K and Rb.

In the method for preparing the methane-rich gas from the synthesis gas, in the step (3), the weight percentages of the first part of catalyst, the second part of catalyst and the third part of catalyst in the total amount are preferably 20-60%, 0-20% and 30-80% in sequence.

In the method for preparing the methane-rich gas from the synthesis gas, in the step (3), the regeneration treatment preferably comprises three steps of carbon deposit elimination, chemical modification and reduction treatment.

In the method for preparing the methane-rich gas from the synthesis gas, the carbon deposit elimination process is preferably to contact and react a carbon elimination gas with the first part of the catalyst, wherein the carbon elimination gas is selected from O₂Water vapor mixed gas, O₂/N₂Mixed gas, air, O₂/CO₂Mixed gas and H₂At least one of the group consisting of water vapor mixed gas, the reaction conditions of the carbon deposit eliminating process are as follows: 180 ℃ at 450 ℃, 1.0-50 absolute atmospheric pressures and 50-100000h space velocity of the decarburized gas^-1。

In the method for preparing the methane-rich gas from the synthesis gas, the chemical modification process is preferably a contact reaction of a chemical modifier and a first part of catalyst for eliminating carbon deposition, and the chemical modifier is selected from HNO₃、HCl、HBr、HI、Cl₂、Br₂、I₂HClO and NO₂At least one of the group consisting of: 120-DEG C, 600 ℃, 1.0-20 absolute atmospheric pressures and gas volume space velocity of 50-50000h^-1。

In the method for producing a methane-rich gas from a synthesis gas according to the present invention, it is preferable that the reduction treatment employs H₂Reducing the first part of the catalyst which is chemically modified as a reducing gas, wherein the reaction conditions of the reduction treatment are as follows: 300 ℃ at 650 ℃, 1.0-20 absolute atmospheric pressures and a gas volume space velocity of 50-50000h^-1。

In the method for preparing a methane-rich gas from a synthesis gas according to the present invention, in the step (3), preferably, the regeneration reactor is at least one selected from the group consisting of a fixed bed reactor, a moving bed reactor, a fluidized bed reactor and a entrained flow reactor, and the regeneration reactors are connected in series.

Because the methanation reaction is a heat release process, in order to control the temperature of the catalyst bed layer in the reaction process, a heat extraction pipeline can be arranged in the middle of the bed layer of the moving bed reactor or on the inner wall of the reactor, measures such as process gas preheating, water vaporization heat extraction, water vapor heat exchange and the like are adopted, and the catalyst bed layer is prevented from generating local hot spots, so that the catalyst structure is damaged to generate permanent inactivation, and the reaction efficiency of the process is influenced.

In the present invention, the third alkylation reactor may also be operated in an adiabatic mode to control the single pass conversion of CO based on factors such as the composition of the reactor inlet gas, the nature of the catalyst, etc., thereby controlling the temperature of the reaction process, with the heat of reaction being carried out of the reactor by the circulating catalyst and gas streams. When controlling the per pass conversion of CO, a certain amount of unconverted synthesis gas is contained in the gas stream at the reactor outlet. At the moment, the gas stream at the outlet of all the reactors is subjected to heat exchange and cooling, then is compressed and sent to the gas inlet of the next methanation reactor to participate in the reaction again, and finally all CO is converted into CH₄。

The preparation method of the first methanation catalyst comprises the steps of preparing an active component, a carrier component and a modified element component into solid powder, then combining the solid powder with a binder, and preparing the solid powder into a globular catalyst by a rolling ball method. The method for preparing the solid powder can be impregnation method, coprecipitation method, hot melting method, sol-gel method, mixed grinding method, etc., and then the solid powder is obtained after drying, roasting and crushing treatment. In addition, the preparation method of the pellet catalyst can also comprise the steps of preparing the active component and the carrier component into solid powder, combining the solid powder with the binder, preparing the pellet catalyst by a rolling ball method, modifying the pellet catalyst by the aid of modification auxiliary elements through methods such as impregnation and chemical precipitation, drying, roasting and the like, and finally obtaining the pellet first methanation catalyst.

The process according to the invention enables the production of a methane-rich gas product from a carbonaceous material via synthesis gas. Because the moving bed catalyst circulates in the reactor, the catalyst particles can play the double functions of the methanation catalyst and the heat carrier, and the exothermic heat of the reaction is effectively recovered. And, the moving bed catalyst can be recycled through on-line regeneration, thus reducing the requirement for the single service life of the catalyst.

More specifically, compared with the prior art, the beneficial effects of the invention are mainly reflected in the following three aspects:

firstly, the method provided by the invention adopts a methanation method of optimally combining a fixed bed high-temperature reactor and a moving bed supplementary reactor, selects proper gas residence time, can flexibly adjust the gas residence time, and can control the 'hot spot' of a fixed bed reactor while maximally recovering the reaction heat of the high-temperature methanation reactor, so that the temperature of the reactor and the conversion rate in the reaction process are easier to control compared with a fixed bed series process.

Secondly, the method provided by the invention adopts a mode that two moving bed reactors are connected in series to supplement the methanation reactor, the methanation catalyst adopted by the method is circularly used in the two moving bed reactors, and simultaneously has two functions of catalyst and heat carrier, and the methanation raw material gas is directly subjected to contact type heat exchange, so that the initial reaction temperature of the fixed bed reactor is improved, and the gas from the outlet of the fixed bed reactor is not circulated back to the inlet of the reactor, so that the production capacity of the whole fixed bed reaction system is increased.

Thirdly, the method provided by the invention adopts the moving bed reactor as a supplementary methanation reactor, can realize the on-line regeneration and the recycling of the adopted methanation catalyst, and can greatly shorten the active life cycle of the catalyst to days or months, thereby obviously reducing the development difficulty of the catalyst and improving the development efficiency of the methanation catalyst.

Drawings

FIG. 1 is a process flow diagram of the process of the present invention for producing a methane-rich gas from synthesis gas.

Detailed Description

The following examples further illustrate the invention but are not intended to limit the invention thereto.

The invention provides a method for preparing methane-rich gas from synthesis gas, which comprises the following steps: carrying out continuous pretreatment on a raw synthesis gas obtained by converting a carbon-containing material to remove impurities in the raw synthesis gas so as to obtain a clean synthesis gas 1; the clean synthesis gas 1 is in countercurrent contact with a first methanation catalyst 6 in a first methanation reactor 9 to obtain a methanation gas raw material 8; the method comprises the following steps of (1) carrying out contact reaction on a methanation gas raw material 8 and a second methanation catalyst in a second methanation reactor 2, and carrying out heat exchange and cooling on a product obtained after the contact through a first heat exchanger 3 to obtain a first gas stream 4 rich in methane; the first methanation catalyst 6 in the first methanation reactor 9 is led out and divided into two parts: the first part of catalyst 11 is continuously divided into two parts, wherein one part of the catalyst is sent into a regeneration reactor for regeneration treatment, the obtained regenerated methanation catalyst is sent into a third methanation reactor 5 for recycling, and the other part of catalyst is taken as waste catalyst and discharged out of the reaction system; the second part of the catalyst 10 is directly sent to the third alkylation reactor 5 for recycling. The gas stream I4 and the first methanation catalyst are subjected to contact reaction in a third methanation reactor 5, and a product obtained after the contact is cooled through a second heat exchanger 7 to obtain a methane-rich gas stream 12.

Example 1

The brown coal fragments (chemical composition shown in table 1) with the particle size of 5-50mm are gasified into crude synthesis gas by using oxygen/steam as a gasifying agent, and the obtained crude synthesis gas is sequentially subjected to cooling, tar removal, water-gas shift and crude desulfurization to obtain the pure synthesis gas (composition shown in table 2), wherein (CO + H) is₂) The content was 74.59 vol%, H₂The mol ratio of/CO is 3.07, H₂The S content was 5 ppm.

TABLE 1

TABLE 2

Main component	(mol%)
		H₂	56.26
CO	18.33
		CO₂	2.20
CH₄	20.87
		N₂	1.14
Ar	0.57
		C2+ hydrocarbons	0.63
H₂S	5ppm

The first methanation reactor is a moving bed reactor, and the catalyst is a spherule A with the average diameter of 2.6mmAlkylation catalyst (composition: 20.3 wt% NiO, 78.9 wt% Al)₂O₃0.6 wt.% Fe₂O₃0.2% by weight of K₂O) catalyst inventory in the bed is 0.8L, the clean syngas at normal temperature enters the reactor through the gas distributor at the bottom of the first methanation reactor, directly contacts with the hot catalyst moving downwards, carries out countercurrent heat exchange, the temperature of the catalyst is reduced from 500 ℃ when entering the reactor at the top of the reactor to 312 ℃, the temperature of the gas stream coming out at the top of the reactor is 305 ℃, and then the gas stream is sent to the second methanation reactor.

The second methanation reactor is a fixed bed reactor, the catalyst is a complete methanation catalyst (commercial brand CRG), the loading amount is 0.2L, and the methanation reaction conditions are that the inlet temperature is 303 ℃, the inlet pressure is 3.35MPa, and the gas space velocity is 20000h^-1. The highest temperature point in the reactor was detected to be 618 ℃ and no downward shift of the "hot spot" occurred within 96h of the detection time. And the temperature of the gas material flow is reduced to 310 ℃ after heat exchange, and the gas material flow is sent to a third methanation reactor after gas-liquid separation.

The spherule methanation catalyst moving to the outlet at the bottom end of the first methanation reactor leaves the first methanation reactor and is divided into two parts with equal weight, wherein 0.4L catalyst is directly sent back to a hopper at the top end of the third methanation reactor and then enters the reactor to continuously participate in methanation reaction, and in addition, 0.4L catalyst is sent into the fixed bed reactor to be regenerated, and O is sequentially introduced into the regenerated fixed bed reactor₂Water vapor mixed gas (O)₂Volume fraction of 2%) is subjected to decarbonization, and HCl/water vapor mixed gas (HCl content of 200 mg/Nm) is introduced³) Carrying out chemical regeneration by introducing H₂/N₂(H₂Volume fraction 5%) of the mixed gas was subjected to reduction treatment. And (3) carbon elimination treatment conditions: the temperature is 285 ℃, the pressure is 0.4MPa, and the gas space velocity is 2400h^-1And the treatment time is 0.8 h. Chemical regeneration treatment conditions: the temperature is 500 ℃, the pressure is 0.4MPa, and the gas space velocity is 2400h^-1And the treatment time is 6 h. Reduction treatment conditions: the temperature is 575 ℃, the pressure is 0.4MPa, and the gas space velocity is 2400h^-1And the treatment time is 20 h.

The catalyst after regeneration treatment leaves the fixed bed regenerator, is cooled to 310 ℃ through indirect heat exchange, is also sent to a hopper at the top end of a third methanation reactor, and then enters the reactor to continuously participate in methanation reaction.

And gas material flows from the second reactor enter the reactor through the top of the third reactor and are in parallel-flow contact reaction with the spherical catalyst, and the spherical catalyst continuously moves downwards by means of gravity. The methanation reaction conditions are as follows: the inlet temperature is 310 ℃, the inlet pressure is 3.30MPa, and the gas space velocity is 20000h^-1. The maximum temperature of the bed in the reactor was detected to be 501 ℃. Cooling the gas stream from the bottom outlet of the reactor to near 0 deg.C by heat exchange via a cold well, adsorbing residual water by molecular sieve bed, detecting the composition of the gas by gas chromatography, and calculating CO conversion rate X_CO(see Table 3). The residence time of the catalyst in the moving bed was 144 h.

0.5g of the catalyst sample leaving the third alkylation reactor and cooled, and 0.5g of the catalyst sample after the catalyst regeneration treatment and cooled were taken, and the CO conversion rates thereof were evaluated on a constant temperature micro fixed bed apparatus (using a gas chromatograph, a TCD detector, see Table 4). Evaluation of reaction conditions: reaction temperature 305 ℃ and gas H₂The mol ratio of/CO is 3.0, the inlet pressure is 3.0MPa, and the gas space velocity is 35000h^-1。

Comparative example 1

The preparation and composition of the neat syngas was the same as in the examples. The clean synthesis gas firstly enters a first methanation reactor to contact with a catalyst for heat exchange and react, then enters a second methanation reactor to contact with the catalyst for reaction, and enters a third methanation reactor to contact with the catalyst for reaction after heat exchange and temperature reduction. Gas composition (dry basis) and CO conversion rate X from the bottom outlet of the third alkylation reactor are timely detected by adopting gas chromatography_CO(see Table 3).

Wherein, the three reactors are filled by adopting fixed beds, and the catalyst does not move.

The first methanation reactor and the third methanation reactor are both filled with 0.8L spherule methanation catalyst with average diameter of 2.6mm (composition: 20.3 weight portions)% NiO, 78.9 wt.% Al₂O₃0.6 wt.% Fe₂O₃0.2% by weight of K₂O). In the first methanation reactor, the reaction conditions are as follows: the gas inlet temperature is 307 ℃, the inlet pressure is 3.36MPa, and the gas space velocity is 20000h^-1. In the third alkylation reactor, the reaction conditions are as follows: the inlet temperature is 302 ℃, the inlet pressure is 3.31MPa, and the gas space velocity is 20000h^-1。

The second reaction was packed with 0.2L of complete methanation catalyst (commercial designation CRG). The reaction conditions were 305 ℃ inlet temperature, 3.33MPa inlet pressure and 20000h gas space velocity^-1。

The catalyst in the three reactors, which was spaced apart from the top 1/3 at the bed height, was sampled at the appropriate time for 0.5g and evaluated for CO conversion (using gas chromatography, TCD detector, see Table 4) in accordance with the same thermostatted mini-fixed bed apparatus as the examples and the same evaluation of the reaction conditions.

TABLE 3

Note:

wherein:

TABLE 4

Note:

is the ratio of the areas of CO and Ar peaks in the original TCD standard gas

From the results of example 1 and comparative example 1, it can be seen that, compared with comparative example 1, the synthesis gas can be effectively converted into methane by the method provided by the present invention, and a fine desulfurization tower is not required to be arranged before the methanation reactor, so that the equipment investment and the desulfurizer consumption can be reduced. The third moving bed reactor simultaneously plays a role in desulfurization, protects the catalyst in the first reaction from being poisoned, and the methanation catalyst with reduced activity caused by sulfur poisoning and other factors in the third methanation reactor can recover the initial activity of the catalyst after being treated by the catalyst regeneration treatment method provided by the invention, thereby ensuring that the catalyst in the second methanation reactor always maintains higher activity and improving the production efficiency of the reactor. Moreover, because the second methanation catalyst can be continuously regenerated, the method provided by the invention can avoid the harsh requirement that the catalyst has long service life because of adopting a fixed bed reactor, and embodies the advantage of adopting a moving bed reactor.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore intended that all such changes and modifications as fall within the true spirit and scope of the invention be considered as within the following claims.

Claims

1. A process for producing a methane-rich gas from synthesis gas, comprising the steps of:

(1) carrying out contact reaction on the clean synthesis gas and a first methanation catalyst in a first methanation reactor to obtain methanation raw gas (H)₂-CO₂）/（CO+CO₂) The mol ratio is 2.8-3.5, the first methanation catalyst consists of an active component, a carrier, a binder and a modification auxiliary agent, wherein the active component, the carrier and the binderThe weight percentages of the agent and the modifying auxiliary agent are respectively 5-90%, 6-64%, 3-45% and 10^-6~2%；

(2) Carrying out contact reaction on the methanation raw material gas obtained in the step (1) and a second methanation catalyst in a second methanation reactor, and carrying out heat exchange and cooling on a high-temperature gas stream obtained by the reaction to obtain a gas stream I;

(3) leading out the first methanation catalyst in the step (1) from the first methanation reactor, and dividing the first methanation catalyst into three parts: feeding the first part of catalyst into a regeneration reactor for regeneration treatment to obtain a regenerated first methanation catalyst, and feeding the regenerated first methanation catalyst into a third methanation reactor for recycling; a second portion of the catalyst is discharged from the reaction system as spent catalyst; the third part of catalyst is directly sent to a third alkylation reactor for recycling;

(4) carrying out contact reaction on the first gas stream obtained in the step (2), the third part of catalyst and the regenerated first methanation catalyst in a third methanation reactor, and cooling a gas product obtained after the reaction to obtain a gas product rich in methane;

the first methanation reactor and the third methanation reactor are both moving bed reactors, and the second methanation reactor is a fixed bed reactor;

in the step (1), the contact reaction conditions are as follows: 5-100 absolute atmospheric pressure, 40-400 ℃ and gas space velocity of 50-80000h^-1The residence time of the catalyst is 24h-10 days; in the step (2), the contact reaction conditions are as follows: 15-100 absolute atmospheric pressure, 330-^-1(ii) a In the step (4), the contact reaction conditions are as follows: 2-100 absolute atmospheric pressure, 250-700 ℃ and gas space velocity of 50-80000h^-1The residence time of the catalyst is 24h-100 days.

2. The method according to claim 1, wherein in step (1), the clean syngas is obtained by pre-treating at least one of the group consisting of coal-based syngas, biomass-based syngas, and coke oven gas to remove impurities and/or water-gas shift.

3. The process of claim 1, wherein the moving bed reactor is of a type selected from at least one of the group consisting of vertical, inclined, and horizontal.

4. The process of claim 3, wherein the vertical moving bed reactor is at least one selected from the group consisting of a vertical sleeve and a vertical variable diameter.

5. The process for producing a methane-rich gas from a synthesis gas according to claim 1, wherein the number of the third alkylation reactors is 2 to 4, and the third alkylation reactors are connected in series, in parallel, in series-parallel or in parallel-series with each other.

6. The process for preparing a methane-rich gas from a synthesis gas according to claim 1, wherein in step (1), the contacting process is that the net synthesis gas passes through the catalyst bed of the first methanation reactor once in a counter-current, cross-current or co-current manner.

7. The process for producing a methane-rich gas from a synthesis gas according to claim 1, wherein in step (4), the contacting of the first gas stream with the third portion of the catalyst is performed in a counter-current, cross-current or co-current manner.

8. The method for preparing a methane-rich gas from synthesis gas according to claim 1, wherein the first methanation catalyst is a pellet catalyst, and the particle size of the pellet catalyst is in the range of 0.1-200 mm.

9. The method of claim 1, wherein the active component is at least one selected from the group consisting of Ni, Mo, Fe, Co, Ru, Pt, Pd, and Rh.

10. The process for producing a methane-rich gas from a synthesis gas according to claim 1, wherein the modification promoter is at least one selected from the group consisting of rare earth elements, transition metal elements, and main group elements.

11. The process for producing a methane-rich gas from a syngas according to claim 10, characterized in that the rare earth elements are L a, Ce, Pr, Nd and Sm, the transition metal elements are Zr, Y, Nb, Cr, Ti, Zn, Cu, Mn, Os and Ir, and the main group elements are Si, Al, Mg, K and Rb.

12. The method for preparing a methane-rich gas from synthesis gas according to claim 1, wherein in step (3), the weight percentages of the first portion of catalyst, the second portion of catalyst and the third portion of catalyst in the total amount are 20-60%, 0-20% and 30-80% in sequence.

13. The process for producing a methane-rich gas from a synthesis gas according to claim 1, wherein in the step (3), the regeneration reactors are at least one selected from the group consisting of fixed bed reactors, moving bed reactors, fluidized bed reactors and entrained flow reactors, and the regeneration reactors are connected in series with each other.