A method and device for preparing high-quality fuel gas from biomass

Abstract

The present invention relates to the technical field of biomass energy utilization, and provides a method and device for preparing high-quality fuel gas from biomass. The present invention performs tar cracking while pyrolyzing biomass, converting tar into small-molecule permanent gas, thereby greatly reducing the tar content in the fuel gas, avoiding the hot and cold disease problem of the pyrolysis gaseous material first cooling down and then heating up from a high-temperature state when it exits the gasification reactor, making the temperature distribution of the process more reasonable, reducing the cost of reactor equipment, and improving energy efficiency. The present invention couples the water-gas shift and methanation reaction into a one-step reaction, so that the two reactions assist each other, which is beneficial to promoting the equilibrium conversion rate of the reaction, and the water-gas shift can directly utilize the product H2O of CO methanation, reducing the consumption of external steam and lowering the cost. The device structure provided by the present invention includes an upstream moving bed reactor and a downstream fixed bed reactor, which has a simple structure and is easy to operate, and can achieve efficient preparation of high-quality fuel gas.

Description

Technical Field

[0001] The present invention relates to the technical field of biomass energy utilization, and in particular to a method and device for preparing high-quality fuel gas from biomass. Background Art

[0002] Biomass is the earliest and most widely used clean energy source in history, and it accounts for a significant proportion of current global energy consumption. With clean energy sources like wind and solar facing development bottlenecks and nuclear energy safety being questioned, the development and utilization of biomass resources will undoubtedly play a vital role in energy upgrading and structural adjustment.

[0003] Biomass gasification is an important method for utilizing biomass resources. It involves the thermochemical conversion of solid biomass into a combustible gas containing components such as CH₄, CO, and H₂ under high-temperature conditions. The combustible gas obtained from biomass gasification has numerous applications, including centralized gas supply, power generation using internal combustion engines or gas turbines, and chemical product synthesis.

[0004] Biomass gas is a mixture, usually containing components such as CH4, CO, H2, CO2, and H2O. However, due to the differences in raw material types (including rice husks, straw, sawdust, etc.), gasification media (water vapor, oxygen, air, etc.), and operating conditions (temperature, pressure, reactor type, etc.), biomass gasification gas has different compositions and calorific values. The CO content is generally 15-40%, and the low calorific value is generally less than 10MJ / Nm 3 According to the current national standard for manufactured gas, the lower calorific value is used as the evaluation index, and it is stipulated that urban gas must meet the following conditions: the lower calorific value of a type of gas must be greater than 14MJ / Nm 3 The lower calorific value of Class II gas must exceed 10MJ / Nm 3 For centralized gas supply in cities and towns, referring to relevant standards, it can be seen that the calorific value of the above-mentioned biomass combustible gas is too low to guarantee the normal use of urban residents. Therefore, it is necessary to adopt technical means to improve the quality of biomass combustible gas, that is, to increase the calorific value of biomass combustible gas.

[0005] The commonly used technical approach currently is to further methanize the biomass crude gas obtained from pyrolysis and gasification to reduce its CO content, increase its CH4 content, and thus improve the gas quality. Since the methanation reaction requires the synthesis gas to have a high hydrogen-to-carbon ratio, a water-gas shift reaction is required to adjust the hydrogen-to-carbon ratio (H2 / CO). Currently, most processes use a water-gas shift unit and a CO methanation unit in series, that is, the biomass combustible gas first passes through the water-gas shift unit to adjust the hydrogen-to-carbon ratio before entering the methanation unit to synthesize methane. However, the addition of a water-gas shift reaction process upstream of the methanation reactor not only increases system energy consumption, but also increases equipment costs, operation, and maintenance costs.

[0006] Furthermore, the difficulty in removing tar is a technical obstacle in current commercial coal / biomass-to-natural gas or high-quality fuel gas processes. Current practices involve using low-temperature purification methods to remove some tar before the methanation reaction. Specifically, the high-temperature raw syngas is cooled and scrubbed, then purified for tar separation. The resulting low-temperature syngas is then heated again and conditioned with water vapor before participating in the methanation reaction. This high-temperature cooling and then heating process reduces the overall system's thermal efficiency and increases heat exchange investment, often referred to as the "cold-hot syndrome." Furthermore, because the tar is removed through low-temperature purification and scrubbing, the tar removal effect is suboptimal, threatening the stable and efficient operation of downstream pipeline equipment and lowering the quality of the resulting natural gas or fuel gas. Summary of the Invention

[0007] The present invention aims to provide a method and apparatus for producing high-quality fuel gas from biomass. This method simultaneously pyrolyzes biomass and cracks tar, avoiding the problem of thermal shock. Furthermore, by coupling the water-gas shift reaction with the methanation reaction, the method eliminates the need for an additional water-gas shift step, omitting the consumption of external steam and reducing costs.

[0008] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0009] A method for producing high-quality fuel gas from biomass, comprising the following steps:

[0010] mixing a biomass raw material and a tar cracking catalyst to perform a biomass pyrolysis-tar cracking reaction to obtain a gaseous mixture;

[0011] Under the action of a water-gas shift-methanation dual-function catalyst, the gaseous mixture undergoes a water-gas shift coupled methanation reaction to obtain high-quality fuel gas; the calorific value of the high-quality fuel gas is 14MJ / Nm 3 above.

[0012] Preferably, the temperature of the biomass pyrolysis-tar cracking reaction is 500-800°C; the temperature of the water-gas shift coupled methanation reaction is 300-500°C.

[0013] Preferably, the water gas shift-methanation bifunctional catalyst comprises a ZSM-5 molecular sieve carrier and metal Ni particles coated inside the ZSM-5 molecular sieve carrier.

[0014] Preferably, the preparation method of the water gas shift-methanation bifunctional catalyst comprises the following steps:

[0015] The ZSM-5 molecular sieve is immersed in a nickel salt aqueous solution and then dried and calcined in sequence to obtain an intermediate product;

[0016] mixing the intermediate product and tetrapropylammonium hydroxide solution and performing a hydrothermal reaction to obtain a catalyst precursor;

[0017] The catalyst precursor is reduced under a hydrogen atmosphere to obtain the water gas shift-methanation bifunctional catalyst.

[0018] Preferably, after the water-gas shift coupled methanation reaction is completed, the obtained gas is condensed and then dried.

[0019] The present invention also provides a device for preparing high-quality fuel gas from biomass, comprising:

[0020] Inert gas storage tank 1;

[0021] An upstream heating furnace 4, wherein the interior of the upstream heating furnace 4 is a moving bed reactor 16; a silo 6 is provided on the top of the upper moving bed reactor 16, and an ash hopper 7 is provided on the bottom; a gaseous mixture outlet 8 and a carrier gas inlet 18 are provided on the side wall of the upper moving bed reactor 16, and the carrier gas inlet 18 is connected to the outlet of the inert gas storage tank 1;

[0022] Downstream heating furnace 10; the interior of the downstream heating furnace 10 is a fixed bed reactor 17, wherein the fixed bed reactor 17 is provided with a porous bed layer 9; the gas inlet of the fixed bed reactor 17 is connected to the gaseous mixture outlet 8;

[0023] The inlet of the cold trap 12 is connected to the outlet of the fixed bed reactor 17;

[0024] The gas storage tank 15 has an inlet connected to the outlet of the cold trap 12 , and a dryer 13 is provided on the pipeline connecting the gas storage tank 15 and the cold trap 12 .

[0025] Preferably, the upstream heating furnace 4 is connected to the first programmable temperature controller 3 via an electrical signal; the downstream heating furnace is connected to the second programmable temperature controller 11 via an electrical signal;

[0026] A first throttle valve 2 is provided on the pipeline connecting the inert gas storage tank 1 and the carrier gas inlet 18, and a blower 5 is provided at one end close to the carrier gas inlet;

[0027] The outlet of the fuel gas storage tank 15 is connected to the carrier gas inlet 18 , and a second throttle valve 14 is provided on the connecting pipeline.

[0028] Preferably, the cold trap 12 is a three-stage cold trap.

[0029] The present invention also provides a method for producing high-quality gas using the device described in the above solution, comprising the following steps:

[0030] The water gas shift-methanation dual-function catalyst is loaded into the porous bed 9; an inert gas is introduced from the carrier gas inlet 18;

[0031] Biomass and tar cracking catalyst are mixed and the resulting mixture is placed in a silo 6. After the upstream heating furnace 4 is heated to the temperature of the biomass pyrolysis-tar cracking reaction and the downstream heating furnace 10 is heated to the temperature of the water-gas shift coupled methanation reaction, the mixture is fed into the moving bed reactor 16 for biomass pyrolysis-tar cracking reaction. The generated gaseous mixture enters the fixed bed reactor 17 from the gaseous mixture outlet 8 under the action of an inert gas, and undergoes a water-gas shift coupled methanation reaction. The resulting gas product enters the cold trap 12 for condensation, and then is dried by the dryer 13 before entering the fuel gas storage tank 15.

[0032] Preferably, after the device has been running for 20 to 40 minutes, the first throttle valve 2 and the second throttle valve 14 are switched to use the gas in the gas storage tank as the carrier gas instead of the inert gas.

[0033] The present invention provides a method for preparing high-quality fuel gas from biomass, comprising the following steps: mixing a biomass raw material and a tar cracking catalyst to carry out a biomass pyrolysis-tar cracking reaction to obtain a gaseous mixture; subjecting the gaseous mixture to a water-gas shift-methanation dual-function catalyst to a water-gas shift coupled methanation reaction to obtain high-quality fuel gas; the calorific value of the high-quality fuel gas is 14MJ / Nm 3 The above. The present invention mixes the biomass raw material and the tar cracking catalyst, and cracks the tar while the biomass is being pyrolyzed. That is, compared with the low-temperature purification means in the prior art, the present invention adopts medium- and high-temperature purification means to remove the tar produced in the process of biomass pyrolysis and gasification by cracking, and converts the tar molecules into small-molecule permanent gases, so that the tar content of the final obtained fuel gas is greatly reduced, while the carbon conversion rate, gas production and energy efficiency are improved, the harm of tar to the downstream reaction system is reduced, and the quality of the fuel gas is improved. The method of the present invention simplifies the process flow of traditional biomass to gas, avoids the hot and cold disease problem of pyrolysis gaseous materials cooling down and then heating up from a high-temperature state when coming out of the gasification reactor outlet, makes the temperature distribution of the process flow more reasonable, reduces the cost of reactor equipment, and improves energy efficiency.

[0034] This invention couples the water-gas shift (WGS) and methanation reactions into a single-step reaction. The H₂ product of the WGS reaction serves as a methanation reactant, while the H₂O product of the methanation reaction serves as a WGS reactant. These two reactions occur simultaneously and mutually promote each other, thereby reducing the CO content and increasing the CH₄ content in the crude biomass fuel gas, thereby producing higher-quality fuel gas. This coupling of the WGS and methanation reactions allows them to complement each other, promoting the equilibrium conversion rate. Furthermore, the WGS process directly utilizes the H₂O product of the CO methanation reaction, reducing external steam consumption and resulting in lower costs.

[0035] The present invention also provides a device for preparing high-quality gas from biomass. The device provided by the present invention includes an upstream heating furnace and a downstream heating furnace, and the interior of the upstream heating furnace is a moving bed reactor, and the interior of the downstream heating furnace is a fixed bed reactor, which can be filled with a water gas shift-methanation dual-function catalyst. Using the device of the present invention and preparing high-quality gas according to the above method can achieve efficient preparation of high-quality gas.

[0036] Furthermore, when the present invention uses the above-mentioned device to prepare high-quality fuel gas, an inert gas is used as a carrier gas at the beginning of the reaction. After the device is running stably, the fuel gas in the fuel gas storage tank is used instead of the inert gas as a carrier gas to continue the reaction, which can reduce the concentration of the inert gas in the product and further improve the calorific value and quality of the fuel gas. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the apparatus for producing high-quality fuel gas from biomass (moving bed-fixed bed continuous reactor) according to the present invention; wherein: 1 - inert gas storage tank; 2 - first throttle valve; 3 - first programmable temperature controller; 4 - upstream heating furnace; 5 - blower; 6 - silo; 7 - ash hopper; 8 - pyrolysis gas outlet; 9 - porous bed; 10 - downstream heating furnace; 11 - second programmable temperature controller; 12 - cold trap; 13 - dryer; 14 - second throttle valve; 15 - fuel gas storage tank; 16 - moving bed reactor; 17 - fixed bed reactor; 18 - carrier gas inlet;

[0038] Figure 2 This is a process flow chart for producing high-quality fuel gas from biomass according to the present invention;

[0039] Figure 3 The XRD pattern of the water gas shift-methanation bifunctional catalyst prepared in the present invention;

[0040] Figure 4 This is a transmission electron microscope image of the catalyst before the hydrothermal reaction (i.e., the calcined product);

[0041] Figure 5 This is a transmission electron micrograph of the water gas shift-methanation bifunctional catalyst obtained after the hydrothermal reaction. DETAILED DESCRIPTION

[0042] The present invention provides a method for preparing high-quality fuel gas from biomass, comprising the following steps:

[0043] mixing a biomass raw material and a tar cracking catalyst to perform a biomass pyrolysis-tar cracking reaction to obtain a gaseous mixture;

[0044] Under the action of a water-gas shift-methanation dual-function catalyst, the gaseous mixture undergoes a water-gas shift coupled methanation reaction to obtain high-quality fuel gas; the calorific value of the high-quality fuel gas is 14MJ / Nm 3 above.

[0045] The present invention mixes a biomass raw material and a tar cracking catalyst to carry out a biomass pyrolysis-tar cracking reaction to obtain a gaseous mixture. The present invention has no special requirements for the type of the biomass raw material, and a biomass raw material familiar to those skilled in the art can be used. In a specific embodiment of the present invention, the biomass raw material used is rice husk. In a specific embodiment of the present invention, it is preferred that the biomass raw material is first subjected to impurity removal, grinding, screening and drying in sequence, and then subjected to a biomass pyrolysis-tar cracking reaction; the grinding and screening are specifically based on obtaining a biomass raw material with a particle size of 0.1 to 0.3 mm; the drying temperature is preferably 105°C, and the drying time is preferably 12 hours.

[0046] The present invention has no particular requirements for the specific type of tar cracking catalyst; any tar cracking catalyst known to those skilled in the art can be used. Specifically, the tar cracking catalyst comprises a carrier and an active component supported on the carrier. The carrier preferably comprises one or more of a molecular sieve, alumina, or a carbon-based material, preferably rice husk coke. The active component is preferably nickel metal, and the mass fraction of nickel metal in the tar cracking catalyst is preferably 2-6%. In the present invention, the mass ratio of the biomass feedstock to the tar cracking catalyst is preferably 1:(0.5-3), more preferably 1:1.

[0047] In the present invention, the temperature of the biomass pyrolysis-tar cracking reaction is preferably 500-800°C, more preferably 500°C, 600°C, 650°C, 700°C, 750°C or 800°C; in the biomass pyrolysis-tar cracking reaction, the biomass undergoes pyrolysis, and the tar produced by the pyrolysis undergoes cracking. The main components of the gaseous mixture produced by the reaction include permanent small molecule gases such as CO, CH4, H2, CO2 and gaseous organic matter such as acetic acid and phenols.

[0048] After obtaining the gaseous mixture, the present invention conducts a water-gas shift coupled methanation reaction on the gaseous mixture over a water-gas shift / methanation dual-function catalyst to produce high-quality fuel gas. In the present invention, the water-gas shift / methanation dual-function catalyst comprises a ZSM-5 molecular sieve support and metallic Ni particles coated within the ZSM-5 molecular sieve support. The mass fraction of the Ni particles in the water-gas shift / methanation dual-function catalyst is preferably 5-10%.

[0049] In the present invention, the preparation method of the water gas shift-methanation bifunctional catalyst comprises the following steps:

[0050] The ZSM-5 molecular sieve is immersed in a nickel salt aqueous solution and then dried and calcined in sequence to obtain an intermediate product;

[0051] mixing the intermediate product and tetrapropylammonium hydroxide solution and performing a hydrothermal reaction to obtain a catalyst precursor;

[0052] The catalyst precursor is reduced under a hydrogen atmosphere to obtain the water gas shift-methanation bifunctional catalyst.

[0053] In the present invention, the silicon-aluminum ratio of the ZSM-5 molecular sieve is preferably 21 to 60, preferably 38; the present invention preferably first dries the ZSM-5 molecular sieve and then impregnates it; the drying temperature is preferably 100 to 150°C, preferably 105°C, and the time is preferably 12 to 24 hours; the nickel salt is preferably nickel nitrate hexahydrate; the mass of the nickel element in the nickel salt is 5% to 10% of the mass of the ZSM-5 molecular sieve; the impregnation is preferably isovolumetric impregnation, and the amount of water in the nickel salt aqueous solution can be determined according to the standard of isovolumetric impregnation. The water is deionized water, and the amount is specifically the mass of water that the ZSM-5 molecular sieve can adsorb at most. The present invention preferably adds ZSM-5 molecular sieve to a nickel salt aqueous solution, then stirs for 0.5 hours, and then stands for 12 hours in a vacuum environment. After standing, the resulting mixture is dried; the drying temperature is preferably 100-150°C, preferably 105°C, and the time is preferably 12-24 hours; the calcination temperature is preferably 550-650°C, the calcination time is preferably 4-5 hours, the calcination is preferably carried out in an air atmosphere, and the device used for calcination is preferably a muffle furnace.

[0054] In the present invention, the mass fraction of the tetrapropylammonium hydroxide solution is preferably 20-30%, preferably 25%, and the amount ratio of the intermediate product to the tetrapropylammonium hydroxide solution is preferably 1g:10-20mL, more preferably 1g:15mL; the temperature of the hydrothermal reaction is preferably 160-180°C, more preferably 170°C, and the reaction time is preferably 48-72h, preferably 72h. After the hydrothermal reaction is completed, the present invention preferably centrifuges, washes, and dries the resulting reaction solution in sequence; the washing reagent is preferably deionized water, which is washed to neutrality; the drying temperature is preferably 100-150°C, and the drying time is preferably 12-24h.

[0055] In the present invention, the reduction temperature is preferably 500° C. to 800° C., and the reduction time is preferably 1 to 2 hours; and the hydrogen flow rate during the reduction process is preferably 50 to 200 mL / min.

[0056] In the present invention, tetrapropylammonium hydroxide can selectively etch out the silicon oxide component inside the ZSM-5 molecular sieve under hydrothermal conditions and crystallize it on the surface for secondary crystallization. At the same time, since the metal component Ni has already entered the internal pore size of the molecular sieve by impregnation, when silicon dioxide re-crystallizes on the surface of the molecular sieve and forms a cavity inside, the metal particles are coated therein. The bifunctional catalyst prepared by the present invention is observed by transmission electron microscopy and scanning electron microscopy, and it is found that an internal cavity structure is formed. At the same time, the surface still maintains the same morphology as before. XRD diffraction analysis finds that it still has all the typical MFI type topological structures of the ZSM5 molecular sieve, and the crystallinity does not change significantly, which proves the changes that occur in the preparation process of the above-mentioned hollow catalyst. The present invention forms a cavity inside the ZSM-5 molecular sieve and coats the metal Ni particles therein, thereby forming a hollow structure, which can prevent the sintering of the Ni component at high temperatures.

[0057] In the present invention, the temperature of the water-gas shift-coupled methanation reaction is preferably 300-500°C, specifically 300°C, 350°C, 400°C, 450°C, or 500°C. The reaction temperatures required for the water-gas shift and methanation units are relatively close (around 300°C), and the product of the water-gas shift reaction, H2, is a reactant for the methanation, while the product of the methanation reaction, H2O, is a reactant for the water-gas shift reaction. These two reactions occur simultaneously and promote each other, thereby reducing the CO content and increasing the CH4 content in the crude biomass gas, thereby producing higher-quality gas.

[0058] In the present invention, after the water-gas shift coupled methanation reaction is completed, the obtained gas is further condensed and then dried; the condensation is preferably performed by condensing the gas through a cold trap filled with an ice-water mixture, and the remaining tar in the gas is removed by condensation, thereby further improving the quality and calorific value of the gas; the drying is preferably performed by using calcium chloride to remove water vapor in the gas.

[0059] The present invention also provides a device for preparing high-quality fuel gas from biomass (also known as a moving bed-fixed bed continuous reactor), the structural diagram of which is shown in FIG. Figure 1 As shown below, combined Figure 1 Provide detailed explanation.

[0060] The device provided by the present invention includes an inert gas storage tank 1. The present invention has no special requirements for the inert gas storage tank 1, and any inert gas storage tank well known to those skilled in the art can be used, such as a nitrogen storage tank.

[0061] The device provided by the present invention includes an upstream heating furnace 4. In the present invention, the interior of the upstream heating furnace 4 is a moving bed reactor 16; the moving bed reactor 16 is divided into a drying zone and a pyrolysis-gasification zone from top to bottom; in a specific embodiment of the present invention, the pyrolysis-gasification zone is the central area of the furnace. During actual operation, the temperature of the pyrolysis-gasification zone is controlled at a constant temperature (a temperature between 500 and 800°C) by the heating furnace. When the biomass raw material falls to the pyrolysis-gasification zone by gravity, rapid pyrolysis and gasification occur. The generated pyrolysis gas is blown upward by the carrier gas and continuously exchanges heat with the falling biomass raw material during the upward process. On the one hand, the temperature of the falling biomass raw material continues to rise, while the temperature of the pyrolysis gas itself continues to decrease. When it reaches the drying zone, the temperature drops to a temperature between 200 and 400°C.

[0062] In the present invention, a silo 6 is provided on the top of the moving bed reactor 16 and an ash hopper 7 is provided on the bottom; the raw materials in the silo 6 are continuously fed into the moving bed reactor 16 through a screw feeder.

[0063] In the present invention, a gaseous mixture outlet 8 and a carrier gas inlet 18 are provided on the side wall of the moving bed reactor 16, and the carrier gas inlet 18 is connected to the outlet of the inert gas storage tank 1; specifically, the gaseous mixture outlet 8 is provided at a position between the drying zone and the pyrolysis-gasification zone, and the carrier gas inlet 18 is provided at the bottom of the side wall of the moving bed reactor; a first throttle valve 2 is preferably provided on the pipeline connecting the inert gas storage tank 1 and the carrier gas inlet 18, and a blower 5 is preferably provided at one end close to the carrier gas inlet; in the present invention, the upstream heating furnace 4 is also connected to the first programmable temperature controller 3 through an electrical signal, and the first programmable temperature controller 3 controls the heating temperature of the upstream heating furnace.

[0064] The apparatus provided by the present invention also includes a downstream heating furnace 10. In the present invention, the interior of the downstream heating furnace 10 is a fixed-bed reactor 17, which is provided with a porous bed layer 9. The gas inlet of the fixed-bed reactor 17 is connected to the gaseous mixture outlet 8, and the gas inlet and gas outlet of the fixed-bed reactor are preferably located at the top. The downstream heating furnace 10 is connected to a second programmable temperature controller 11 via an electrical signal, and the second programmable temperature controller 11 controls the heating temperature of the downstream heating furnace.

[0065] The device provided by the present invention includes a cold trap 12. In the present invention, the inlet of the cold trap 12 is connected to the outlet of the fixed bed reactor 17; the cold trap 12 is preferably a three-stage cold trap; and the cooling medium in the cold trap is preferably an ice-water mixture.

[0066] The device provided herein includes a gas storage tank 15; the inlet of the gas storage tank 15 is connected to the outlet of the cold trap 12, and a dryer 13 is provided on the pipeline connecting the gas storage tank 15 and the cold trap 12. The present invention has no particular requirements for the type of dryer 13; any dryer familiar to those skilled in the art, such as a dryer for calcium chloride, can be used. In the present invention, the outlet of the gas storage tank 15 is preferably connected to the carrier gas inlet 18, and a second throttle valve 14 is provided on the connecting pipeline.

[0067] The present invention also provides a method for producing high-quality gas using the device described in the above solution, comprising the following steps:

[0068] The water gas shift-methanation dual-function catalyst is loaded into the porous bed 9; an inert gas is introduced from the carrier gas inlet 18;

[0069] The biomass and tar cracking catalyst are mixed and the resulting mixture is placed in a silo 6. After the upstream heating furnace is heated to the temperature of the biomass pyrolysis-tar cracking reaction and the downstream heating furnace is heated to the temperature of the water-gas shift coupled methanation reaction, the mixture is fed into the moving bed reactor 16 for biomass pyrolysis-tar cracking reaction. The generated gaseous mixture enters the fixed bed reactor 17 from the gaseous mixture outlet 8 under the action of an inert gas, and undergoes a water-gas shift coupled methanation reaction. The resulting gas product enters the cold trap 12 for condensation, and then is dried by the dryer 13 before entering the fuel gas storage tank 15.

[0070] In the present invention, the type of the tar cracking catalyst and the ratio of the tar cracking catalyst to the biomass are the same as those in the above-mentioned scheme, and will not be repeated here; the type of the biomass and the treatment method before use are the same as those in the above-mentioned scheme, and will not be repeated here; the temperature of the biomass pyrolysis-tar cracking reaction and the temperature of the steam shift coupled methanation reaction are preferably the same as those in the above-mentioned scheme, and will not be repeated here.

[0071] In the present invention, after the mixed material is fed, it passes through the drying zone and the pyrolysis-gasification zone in sequence under the action of gravity, and is rapidly gasified in the pyrolysis-gasification zone. Finally, the residue is temporarily accumulated and stored in the ash hopper at the bottom. The feeding method of the present invention is continuous feeding.

[0072] In the present invention, the inert gas is preferably nitrogen. The inert gas initially serves to remove the air inside the device and then serves as a carrier gas after the reaction proceeds. The gaseous mixture generated in the moving bed reactor flows into the fixed bed reactor under the action of the carrier gas (inert gas in the early stage and gas in the gas storage tank in the later stage). The space velocity of the gaseous mixture is preferably 2000 to 5000 h -1 .

[0073] In the present invention, after the device has been running for 20 to 40 minutes, the first throttle valve 2 and the second throttle valve 14 are switched, and the gas in the gas storage tank is used as a carrier gas instead of the inert gas to continue the above reaction, thereby reducing the concentration of the inert gas in the obtained gas and improving the calorific value and quality of the gas until high-quality gas that meets the national first-level urban gas standards is obtained.

[0074] The solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be understood as limiting the scope of protection of the present invention.

[0075] The device structure used in the embodiment is as follows Figure 1 As shown, the process flow is as follows Figure 2 shown.

[0076] The tar cracking catalyst used in this example is a rice husk coke-supported Ni-based catalyst, with a Ni content of 5% by mass. The rice husk coke is obtained by pyrolyzing raw rice husks at 700°C for 1 hour. The resulting rice husk coke is then impregnated with nickel nitrate hexahydrate to produce the desired tar cracking catalyst.

[0077] The preparation method of the water gas shift-methanation dual-function catalyst used in the embodiment is as follows:

[0078] Powdered ZSM-5 molecular sieve with a silicon-aluminum ratio of 38 was dried in a drying oven at 105°C overnight;

[0079] Nickel nitrate hexahydrate is dissolved in deionized water to obtain a nickel nitrate solution, wherein the weight of the nickel metal accounts for 5% of the weight of the ZSM-5 molecular sieve, and the weight of the deionized water is the maximum weight of water that the ZSM-5 molecular sieve can adsorb, that is, the amount of water used in the equal volume impregnation method;

[0080] An equal volume of ZSM-5 molecular sieve was immersed in a nickel nitrate solution, stirred for 0.5 h, and then allowed to stand under vacuum for 12 h. The resulting mixture was dried in a drying oven for 12 h to obtain a powder product. The powder product was then calcined at 550°C in an air atmosphere in a muffle furnace for 4 h. The calcined product was mixed with a 25% tetrapropylammonium hydroxide solution at a ratio of 1 g:15 mL and stirred thoroughly. The resulting turbid solution was then placed in a hydrothermal reactor and hydrothermally reacted at 170°C for 72 h. After the hydrothermal reaction, the resulting weakly alkaline turbid solution was repeatedly centrifuged and rinsed with deionized water until neutral. The resulting solid was dried in a drying oven for 12 h and then reduced at 500°C under a 50 mL / min hydrogen atmosphere for 1 h. The resulting sample is a hollow-structured water gas shift-methanation bifunctional catalyst.

[0081] Figure 3 The XRD pattern of the water gas shift-methanation bifunctional catalyst prepared in the present invention; Figure 3 The θ range is 7°~9°, and 22°~25° is the typical MFI structure of ZSM-5, indicating that the basic skeleton structure framework of ZSM-5 is still maintained.

[0082] Figure 4 This is a transmission electron microscope image of the catalyst before the hydrothermal reaction (i.e., the calcined product); Figure 5 This is a transmission electron microscope image of the water gas shift-methanation bifunctional catalyst obtained after the hydrothermal reaction. Figures 4-5 It can be seen that the catalyst forms a hollow structure after the hydrothermal reaction.

[0083] Example 1

[0084] Take some rice husks, remove impurities, grind, sieve to 0.1-0.3 mm, and dry at 105°C for 12 hours. Mix the rice husks and tar cracking catalyst in a 1:1 mass ratio to ensure a uniform mixture, and place the mixed raw materials in silo 6;

[0085] The water gas shift-methanation catalyst is pre-loaded into the porous bed 9 at the center of the downstream heating furnace 10, and the carrier gas storage bottle is opened to introduce inert protective gas nitrogen to purge the air inside the device.

[0086] After the upstream heating furnace reaches 550°C and the downstream heating furnace reaches 350°C, the tar cracking catalyst and rice husk mixture is placed in silo 6 and fed into a moving bed reactor 16 via a screw feeder for rapid pyrolysis and tar cracking. The resulting gaseous mixture, under the influence of a carrier gas, enters the downstream fixed bed reactor 17 for a water-gas shift coupled methanation reaction. The gaseous product produced in the fixed bed reactor 17 is condensed in a cold trap 12, dried in a dryer 13, and collected in a gas storage tank 15.

[0087] After the device is stabilized for 20 minutes, the biomass gas collected in the gas storage tank 15 is used as a carrier gas to replace the original inert gas by cutting the valve, and the pyrolysis / tar cracking and direct methanation processes are continued. After continuing to operate for 20 minutes, high-quality gas that meets the national first-level urban gas standards is obtained.

[0088] Example 2

[0089] Take some rice husks, remove impurities, grind, sieve to 0.1-0.3 mm, and dry at 105°C for 12 hours. Mix the rice husks and tar cracking catalyst in a 1:1 mass ratio to ensure a uniform mixture, and place the mixed raw materials in silo 6;

[0090] The water gas shift-methanation catalyst is pre-loaded into the porous bed 9 at the center of the downstream heating furnace 10, and the carrier gas storage bottle is opened to introduce inert protective gas nitrogen to purge the air inside the device.

[0091] After the upstream heating furnace reaches 550°C and the downstream heating furnace reaches 300°C, the tar cracking catalyst and rice husk mixture is placed in silo 6 and fed via a screw feeder into a moving bed reactor 16 for rapid pyrolysis and tar cracking. The resulting gaseous mixture, under the influence of a carrier gas, enters the downstream fixed bed reactor 17 for a water-gas shift-coupled methanation reaction. The gaseous product produced in the fixed bed reactor 17 is condensed in a cold trap 12, dried in a dryer 13, and collected in a gas storage tank 15.

[0092] After the device is stabilized for 20 minutes, the biomass gas collected in the gas storage tank 15 is used as a carrier gas to replace the original inert gas by cutting the valve, and the pyrolysis / tar cracking and direct methanation processes are continued. After continuing to operate for 20 minutes, high-quality gas that meets the national first-level urban gas standards is obtained.

[0093] Comparative Example

[0094] Other conditions were the same as those in Example 1, except that the water gas shift-methanation dual-function catalyst was not placed in the downstream fixed-bed reactor, and the temperature at the bed of the fixed-bed reactor was controlled at 550° C. (this temperature is not suitable for methanation reaction).

[0095] The test results of the composition and calorific value of the fuel gas obtained in Examples 1-2 and the comparative example are shown in Table 1.

[0096] Table 1 Composition and calorific value test results of the fuel gas obtained in Examples 1 to 2 and the comparative example

[0097]

[0098] According to the results in Table 1, it can be seen that the gas prepared by the present invention has a high methane content and a high gas calorific value, which meets the national standard for first-class town gas, while the gas prepared in the comparative example has a low methane content and a low gas calorific value, which does not meet the national standard for first-class town gas.

[0099] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for producing high-quality fuel gas from biomass, characterized in that: The following steps are involved: A biomass feedstock and a tar cracking catalyst are mixed to perform a biomass pyrolysis-tar cracking reaction to obtain a gaseous mixture; the tar cracking catalyst comprises a carrier and an active component supported on the carrier, the carrier comprising one or more of a molecular sieve, alumina, or a carbon-based material; the active component is Ni metal, and the mass fraction of Ni metal in the tar cracking catalyst is 2-6%; the mass ratio of the biomass feedstock to the tar cracking catalyst is 1:(0.5-3); and the temperature of the biomass pyrolysis-tar cracking reaction is 500-800°C; Under the action of a water-gas shift-methanation dual-function catalyst, the gaseous mixture undergoes a water-gas shift coupled methanation reaction to obtain high-quality fuel gas; the calorific value of the high-quality fuel gas is 14MJ / Nm 3 The water gas shift-methanation bifunctional catalyst comprises a ZSM-5 molecular sieve support and metal Ni particles coated inside the ZSM-5 molecular sieve support; a cavity is formed inside the ZSM-5 molecular sieve, and the metal Ni particles are coated therein; The mass fraction of Ni particles in the water gas shift-methanation dual-function catalyst is 5-10%; The preparation method of the water gas shift-methanation bifunctional catalyst comprises the following steps: impregnating a ZSM-5 molecular sieve in a nickel salt aqueous solution, followed by drying and calcining to obtain an intermediate product; mixing the intermediate product with a tetrapropylammonium hydroxide solution, followed by a hydrothermal reaction to obtain a catalyst precursor; and reducing the catalyst precursor under a hydrogen atmosphere to obtain the water gas shift-methanation bifunctional catalyst; The temperature of the water-gas shift coupled methanation reaction is 300-500°C.

2. The method according to claim 1, characterized in that After the water-gas shift coupled methanation reaction is completed, the obtained gas is condensed and then dried.

3. The method according to claim 1, characterized in that The device used in the method for preparing high-quality fuel gas from biomass includes: Inert gas storage tank (1); An upstream heating furnace (4), wherein a moving bed reactor (16) is provided inside the upstream heating furnace (4); a silo (6) is provided on the top of the moving bed reactor (16), and an ash hopper (7) is provided on the bottom; a gaseous mixture outlet (8) and a carrier gas inlet (18) are provided on the side wall of the moving bed reactor (16), and the carrier gas inlet (18) is connected to the outlet of the inert gas storage tank (1); A downstream heating furnace (10); a fixed bed reactor (17) is provided inside the downstream heating furnace (10), and a porous bed layer (9) is provided inside the fixed bed reactor (17); a gas inlet of the fixed bed reactor (17) is connected to the gaseous mixture outlet (8); A cold trap (12); the inlet of the cold trap (12) is connected to the outlet of the fixed bed reactor (17); A gas storage tank (15); the inlet of the gas storage tank (15) is connected to the outlet of the cold trap (12), and a dryer (13) is provided on the pipeline connecting the gas storage tank (15) and the cold trap (12).

4. The method according to claim 3, characterized in that The upstream heating furnace (4) is connected to the first programmable temperature controller (3) via an electrical signal; the downstream heating furnace is connected to the second programmable temperature controller (11) via an electrical signal; A first throttle valve (2) is provided on the pipeline connecting the inert gas storage tank (1) and the carrier gas inlet (18), and a blower (5) is provided at one end close to the carrier gas inlet; The outlet of the gas storage tank (15) is connected to the carrier gas inlet (18), and a second throttle valve (14) is provided on the connected pipeline.

5. The method according to claim 3, characterized in that The cold trap (12) is a three-stage cold trap.

6. The method according to claim 3, characterized in that The production of high-quality fuel gas using the device comprises the following steps: The water gas shift-methanation dual-function catalyst is loaded into the porous bed (9); an inert gas is introduced from the carrier gas inlet (18); Biomass and a tar cracking catalyst are mixed, and the resulting mixture is placed in a silo (6). After the upstream heating furnace (4) is heated to a temperature for a biomass pyrolysis-tar cracking reaction and the downstream heating furnace (10) is heated to a temperature for a water-gas shift coupled methanation reaction, the mixture is fed into a moving bed reactor (16) for a biomass pyrolysis-tar cracking reaction. The generated gaseous mixture enters a fixed bed reactor (17) from a gaseous mixture outlet (8) under the action of an inert gas, and undergoes a water-gas shift coupled methanation reaction. The resulting gas product enters a cold trap (12) for condensation, and then is dried by a dryer (13) before entering a gas storage tank (15).

7. The method according to claim 6, characterized in that After the device has been running for 20 to 40 minutes, the first throttle valve (2) and the second throttle valve (14) are switched to use the fuel gas in the fuel gas storage tank as a carrier gas instead of the inert gas.

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