Preparation method of high-calorific-value biomass gas

Abstract

The present application belongs to the technical field of biomass gasification, and particularly relates to a preparation method of high-calorific-value biomass gas. The preparation method comprises: (1) pyrolysis of modified biomass raw materials in a pyrolysis reactor to obtain pyrolysis gas and solid biochar; (2) co-currently passing the pyrolysis gas and water vapor into a fixed bed reactor filled with a catalyst layer from bottom to top to perform a methanation reaction to obtain product gas, the product gas flowing out from the top of the fixed bed reactor, the product gas being divided into three streams, denoted as product gas A, product gas B and product gas C, the product gas A being cooled to 40-50 DEG C and then returned to the fixed bed reactor, the product gas B being directly returned to the fixed bed reactor, and the reaction gas C being cooled and then collected as biomass gas. The preparation method can significantly increase the content of methane in the gas and the calorific value of the gas.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of biomass gasification, and particularly relates to a preparation method of high-calorific-value biomass fuel gas. BACKGROUND

[0002] Thermochemical gasification technology is one of the most effective ways to convert biomass into combustible gas (synthesis gas), which can be used for power generation, heating, chemical raw material production or natural gas substitution. However, the traditional biomass gasification technology, especially the atmospheric air gasification, has the defects of low calorific value and poor quality of the produced fuel gas. In order to overcome these problems, oxygen gasification, steam gasification and other routes are used in the existing process. Among them, oxygen gasification avoids nitrogen dilution, which can increase the calorific value of the fuel gas to 10-12 MJ / Nm 3 .

[0003] CN115873636A uses steam and oxygen as gasification agents to carry out gasification reaction at a high temperature of 700-900℃, and through adjusting the gasification temperature, steam flow and oxygen ratio, bamboo chips are converted into high-calorific-value biomass fuel gas by using a small fixed bed gasification furnace, but the methane content in the finally prepared fuel gas is low, and the carbon dioxide content is low; CN115851298A uses high-temperature pyrolysis technology and a secondary pyrolysis zone, carries out pyrolysis reaction on bamboo chips at 600-900℃ by using a small fixed bed pyrolysis reactor, and carries out high-temperature cracking on the fuel gas and tar in the secondary pyrolysis zone at 800℃, to generate high-calorific-value combustible gas, which is removed of water by a condensation purification device to increase the volume fraction of CH4 in the fuel gas, but the methane content in the finally prepared fuel gas is low, and the carbon dioxide content is low; CN105542861A increases the oxygen concentration in air by adding an oxygen control device on the basis of using air as a biomass pyrolysis gasification agent, generates oxygen-rich gas, increases the reaction temperature of the fixed bed pyrolysis furnace, accelerates the gasification reaction, increases the H2 content and CO generation in the fuel gas, promotes tar cracking, and improves the fuel gas calorific value and gasification efficiency. However, the cost of oxygen production is high, which seriously restricts its economic feasibility. Steam gasification can produce medium-calorific-value fuel gas rich in H2 and CO, but the methane content in the finally prepared fuel gas is limited, and the calorific value is not high.

[0004] Therefore, there is an urgent need for a preparation method of high-calorific-value biomass fuel gas which can realize high calorific value, high methane content and long-period stable operation. SUMMARY

[0005] The purpose of the present application is to provide a preparation method of high-calorific-value biomass fuel gas. The biomass fuel gas prepared by the preparation method can solve the defects of low calorific value and low methane content in the existing biomass fuel gas preparation.

[0006] The present application provides a preparation method of high-calorific-value biomass fuel gas, which comprises:

[0007] (1) the modified biomass raw material is pyrolyzed in a pyrolysis reactor to obtain pyrolysis gas and solid biochar;

[0008] (2) the pyrolysis gas and steam are passed into a fixed bed reactor filled with a catalyst layer from bottom to top in parallel to perform a methanation reaction to obtain product gas, the product gas flows out from the top of the fixed bed reactor, the product gas is divided into three streams, denoted as product gas A, product gas B and product gas C, the product gas A is cooled to 40-50℃ and then returned to the fixed bed reactor, the product gas B is directly returned to the fixed bed reactor, and the product gas C is cooled and collected as biomass fuel gas.

[0009] As a preferred technical solution of the present application, the preparation method of the modified biomass raw material comprises: mixing N-octyl-N-methyl piperidine bis (trifluoromethyl sulfonate) imidazolium salt (CAS number: 887607-28-5), glycerol, sodium dodecyl benzene sulfonate and water to obtain a mixed solution, then performing a contact reaction between the biomass raw material and the mixed solution, and finally performing filtration and drying to obtain the modified biomass raw material.

[0010] The prior art generally uses dolomite as a catalyst during pyrolysis. Although dolomite has a certain ability to catalyze the cracking of tar, the inventors of the present application have found that the content of tar, CO and H2 in the product is high, and the amount of CH4 precursors (such as olefins and oxygen-containing substances) is small when the biomass raw material is subjected to the action of dolomite, which results in poor quality of the feed gas for the subsequent methanation reaction, and finally leads to low CH4 content and high unreacted CO and H2 content in the final fuel gas. Further research has found that the modified biomass raw material obtained by pretreating the biomass raw material with a mixed solution of N-octyl-N-methyl piperidine bis (trifluoromethyl sulfonate) imidazolium salt, glycerol and sodium dodecyl benzene sulfonate in the present application can effectively destroy the structure of cellulose and other structures in the biomass raw material during pyrolysis, thereby greatly increasing the internal porosity and active sites of the biomass raw material. Meanwhile, N-octyl-N-methyl piperidine bis (trifluoromethyl sulfonate) imidazolium salt has better permeability and stability under the action of glycerol, which can further prevent the re-aggregation of biomass raw material particles, promote the generation of olefins and other substances that are easy to produce methane precursors, and thereby increase the content of methane in the final fuel gas.

[0011] As a preferred technical solution of the present application, the mass ratio of N-octyl-N-methyl piperidine bis (trifluoromethyl sulfonate) imidazolium salt, glycerol, sodium dodecyl benzene sulfonate and water is 1: (2-3): (0.05-0.1): 10.

[0012] As a preferred technical solution of the present application, the mass ratio of the mixed solution to the biomass raw material is (10-15): 1.

[0013] In this invention, when preparing modified biomass raw materials, the contact reaction is preferably dynamic contact, that is, it is carried out under stirring conditions.

[0014] As a preferred technical solution of the present invention, the conditions for the contact reaction are: temperature of 70℃-80℃ and time of 3h-4h.

[0015] As a preferred technical solution of the present invention, the drying method can be a conventional drying method in the art, and the drying endpoint is that the moisture content of the modified biomass raw material is less than 1 wt%, for example, drying at 105℃-120℃ until the moisture content is less than 1 wt% to obtain the modified biomass raw material.

[0016] In a preferred embodiment of the present invention, the biomass raw material is selected from at least one of sawdust, straw, wood waste, corn cobs, and rice husks. The sawdust can be from different trees, such as poplar sawdust, pine sawdust, birch sawdust, etc.; the straw can be from different plants, such as wheat straw, corn straw, etc. In the following embodiments of the present invention, wood waste and corn straw are used as biomass raw materials in a 1:1 mass ratio, but this does not constitute a limitation of the present invention.

[0017] As a preferred embodiment of the present invention, the biomass raw material has a particle size of 5mm-20mm. To obtain biomass raw materials with the above-mentioned particle size, conventional crushing and screening methods in the art can be used.

[0018] As a preferred technical solution of the present invention, in step (1), the temperature of the pyrolysis reaction is 600℃-800℃, for example 600℃, 620℃, 650℃, 680℃, 700℃, 620℃, 750℃, 780℃, 800℃, preferably 700℃-750℃.

[0019] As a preferred technical solution of the present invention, in step (1), the pyrolysis reaction time is 30 minutes to 60 minutes, for example, 30 minutes, 40 minutes, 50 minutes or 60 minutes.

[0020] As a preferred embodiment of the present invention, in step (1), the pyrolysis reaction is carried out in a mixed atmosphere of inert gas and air, preferably with a volume ratio of inert gas to air of (10-20):1, more preferably (15-18):1. The inert gas can be nitrogen or argon, preferably nitrogen.

[0021] The mixed atmosphere in this invention can provide oxygen for some of the oxidation reactions, which on the one hand provides some energy for pyrolysis and enables self-heating; on the other hand, trace amounts of oxygen can vaporize some tar precursors, further reducing tar formation.

[0022] In the present application, the pyrolysis reactor in step (1) can be a rotary kiln pyrolysis furnace or a fluidized bed reactor, and the present application has no special limitation on this.

[0023] As a preferred technical solution of the present application, the step in step (1) can be: mixing N-octyl-N-methyl piperidine bis (trifluoromethyl sulfonate) imidazolium salt, glycerol, sodium dodecylbenzenesulfonate and water with a mass ratio of 1: (2-3): (0.05-0.1): 10 to obtain a mixed solution, then stirring the biomass raw material (wood waste and corn stalks with a particle size of 5mm-20mm after crushing and screening, with a mass ratio of 1:1) with a mass ratio of 1: (10-15) and the mixed solution at 70-80℃ for 3h-4h, and finally filtering and drying at 105-120℃ until the water content is less than 1wt% to obtain a modified biomass raw material.

[0024] The modified biomass raw material is added to the rotary kiln pyrolysis furnace and pyrolyzed at a temperature of 600℃-800℃ for 30min-60min in a mixed gas atmosphere of nitrogen and air with a volume ratio of (15-18):1 to obtain pyrolysis gas and solid biochar.

[0025] As a preferred technical solution of the present application, the catalyst layer contains the solid biochar in step (1).

[0026] The present application adds solid biochar to the catalyst layer, which can better increase the calorific value of the final prepared fuel gas, presumably because the addition of solid biochar can avoid local overheating phenomenon, reduce the pressure drop of the catalyst bed, and also effectively avoid the generation of tar.

[0027] As a preferred technical solution of the present application, the catalyst layer comprises, from bottom to top, a catalyst layer A formed by loading the mixture of platinum-based catalyst and solid biochar, and a catalyst layer B formed by loading the mixture of nickel-based catalyst and solid biochar.

[0028] In the present application, the above specific catalyst layer is provided, which can better increase the content of methane in the fuel gas and the calorific value of the fuel gas, presumably because in the catalyst layer A, the complex macromolecular tar compounds in the pyrolysis gas are first catalytically cracked into small molecule gases, promoting the water vapor shift reaction, so that the components in the small molecule gases are closer to the stoichiometric ratio required for methanation reaction, and then entering the catalyst layer B for methanation, thereby increasing the content of methane in the final fuel gas.

[0029] As a preferred technical solution of the present application, in the catalyst layer A, the mass ratio of the platinum-based catalyst to the solid biochar is 100: (0.5-2), for example, 100:0.5, 100:0.8, 100:1, 100:1.5, 100:2, preferably 100: (0.8-1).

[0030] As a preferred technical solution of the present application, in the catalyst bed B, the mass ratio of the nickel-based catalyst to the solid biochar is 100:(1-3), for example, 100:1, 100:1.3, 100:1.5, 100:1.8, 100:2, 100:2.5, 100:3, preferably 100:(1.5-1.8).

[0031] As a preferred technical solution of the present application, the volume ratio of the catalyst layer A to the catalyst layer B is 1:(1.5-3), for example, 1:1.5, 1:1.8, 1:2, 1:2.3, 1:2.5, 1:2.8 or 1:3, preferably 1:(2-2.5).

[0032] As a preferred technical solution of the present application, the platinum-based catalyst is a platinum-rhenium catalyst.

[0033] The platinum-rhenium catalyst in the present application can be obtained from the market, for example, its model is Shike Institute PRT-C, the mass content of platinum is 0.25%, the mass content of rhenium is 0.26%, and the carrier is pseudo-boehmite (SB).

[0034] As a preferred technical solution of the present application, the nickel-based catalyst is a nickel / alumina catalyst.

[0035] The nickel / alumina catalyst in the present application can be obtained from the market, for example, it is purchased from Zhuoran Environmental Protection Technology (Dalian) Co., Ltd., and the model is RS-204.

[0036] As a preferred technical solution of the present application, in step (2), the conditions of the methanation reaction include: the space velocity of the pyrolysis gas is 1200h -1 -2000h -1 , the space velocity of the water vapor is 500h -1 -1000h -1 , and the inlet temperature of the fixed bed reactor is 800-900℃. Preferably, the space velocity of the pyrolysis gas is 1500h -1 -1800h -1 , the space velocity of the water vapor is 600h -1 -700h -1 , and the inlet temperature of the fixed bed reactor is 800-900℃.

[0037] As a preferred technical solution of the present application, the volume flow rate ratio of the product gas A, the product gas B and the product gas C is 1:(1-3):(5-10), preferably 1:(1.5-2):(6-7).

[0038] As a preferred technical scheme of the present application, the product gas A is returned to the fixed bed reactor from the middle position of the fixed bed reactor to continue the methanation reaction along the height direction of the fixed bed reactor.

[0039] As a preferred technical scheme of the present application, the product gas B is returned to the fixed bed reactor from the position of 2 / 3 height of the fixed bed reactor to continue the methanation reaction along the height direction of the fixed bed reactor.

[0040] In the present application, two product gases A and B are returned to the fixed bed reactor respectively, which can better increase the content of methane in the fuel gas and increase the calorific value of the fuel gas, presumably because the methanation is a strong exothermic reaction. The product gas A is returned after cooling and injected into the hot spot area (middle part) of the reactor, which can effectively take away the reaction heat and prevent the catalyst from sintering and deactivation due to high temperature. Meanwhile, the product gas B is directly returned to the fixed bed reactor without cooling, which can increase the residence time of the reactants and make them have more opportunities to contact with the catalyst, thereby improving the overall conversion of CO and H2. Moreover, the positions of the product gases A and B returned to the fixed bed reactor can avoid affecting the gas flow distribution from the bottom, so that most of the reaction gas (pyrolysis gas) cannot fully contact with the catalyst.

[0041] In the present application, the product gas A can pass through a steam generator to recover high-temperature heat energy to make water into water vapor, which can be used in step (2) of the present application.

[0042] As a preferred technical scheme of the present application, the step in step (2) can be: taking part of the solid biochar obtained in step (1) as standby, mixing platinum-rhenium catalyst with mass ratio of 100:(0.8-1) and the solid biochar to obtain mixture A; mixing nickel / alumina catalyst with mass ratio of 100:(1.5-1.8) and the solid biochar to obtain mixture B, sequentially loading the mixture A and the mixture B into the fixed bed reactor from bottom to top to form catalyst layer A and catalyst layer B with corresponding volume ratio of 1:(2-2.5); passing the pyrolysis gas and water vapor into the fixed bed reactor loaded with the catalyst layer A and the catalyst layer B from bottom to top to perform the methanation reaction to obtain product gas, the product gas flows out from the top of the fixed bed reactor, the product gas is divided into three streams with volume flow ratio of 1:(1.5-2):(6-7), which are denoted as product gas A, product gas B and product gas C, the product gas A is returned to the fixed bed reactor from the middle height position of the fixed bed reactor to continue the methanation reaction after being cooled to 40-50℃ by a steam generator, the product gas B is directly returned to the fixed bed reactor from the position of 2 / 3 height of the fixed bed reactor to continue the methanation reaction, and the reaction gas C is cooled and collected as biomass fuel gas; wherein the space velocity of the pyrolysis gas is 1500h -1 -1800h -1, the space velocity of water vapor is 600h -1 -700h -1 , the inlet temperature of the fixed bed reactor is 800℃-900℃.

[0043] Compared with the prior art, the present application has at least the following beneficial effects:

[0044] The preparation method of the present application can significantly increase the content of methane in the fuel gas and the calorific value of the fuel gas, and the quality of the fuel gas is close to that of natural gas, so that the fuel gas can be directly used as high-quality civil fuel gas or industrial fuel, and the high-value conversion of biomass energy is realized. DETAILED DESCRIPTION

[0045] The technical solutions in the embodiments of the present application will be described below in a clear and complete manner. Obviously, the described embodiments are only some of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0046] In the following examples and comparative examples:

[0047] The platinum-rhenium catalyst is PRT-C from the Institute of Coal Chemistry, with a platinum mass content of 0.25% and a rhenium mass content of 0.26%, and the carrier is pseudo-boehmite (SB).

[0048] The nickel / alumina catalyst is RS-204 from Zhuo Ran Environmental Protection Technology (Dalian) Co., Ltd.

[0049] The dolomite is purchased from Tianjin Yandong Haotian Mineral Products Co., Ltd., and the particle size range is 1mm-3mm. Example 1

[0050] Preparation of biomass fuel gas:

[0051] N-octyl-N-methyl piperidine bis(trifluoromethylsulfonyl) imidazoline salt, glycerol, sodium dodecylbenzenesulfonate and water with a mass ratio of 1:2.5:0.08:10 are mixed to obtain a mixed solution, then biomass raw materials (wood waste and corn stalks with a particle size of 12mm and a mass ratio of 1:1 after crushing and sieving) with a mass ratio of 1:12.5 are mixed with the mixed solution and stirred at 72℃ for 3.5h, and finally filtered, dried at 105 to obtain a modified biomass raw material with a water content of less than 1wt%;

[0052] The modified biomass raw material is added to a rotary kiln pyrolysis furnace and pyrolyzed at a temperature of 750℃ for 40 minutes in a mixed gas atmosphere of nitrogen and air with a volume ratio of 16.2:1 to obtain pyrolysis gas and solid biochar;

[0053] Part of the solid biochar obtained in step (1) was reserved, platinum-rhenium catalyst with mass ratio of 100:0.85 was mixed with the solid biochar to obtain mixture A; nickel / alumina catalyst with mass ratio of 100:1.63 was mixed with the solid biochar to obtain mixture B, mixture A and mixture B were sequentially loaded into a fixed bed reactor from bottom to top to form catalyst layer A and catalyst layer B with corresponding volume ratio of 1:2.25; pyrolysis gas and steam were passed into the fixed bed reactor loaded with catalyst layer A and catalyst layer B from bottom to top in parallel flow to carry out methanation reaction to obtain product gas, the product gas flowed out from the top of the fixed bed reactor, the product gas was divided into three streams with volume flow ratio of 1:1.85:6.5, denoted as product gas A, product gas B and product gas C, product gas A was cooled to 42℃ by a steam generator and then returned to the fixed bed reactor from the middle height position of the fixed bed reactor to continue the methanation reaction, product gas B was directly returned to the fixed bed reactor from the position of 2 / 3 height of the fixed bed reactor to continue the methanation reaction, and reaction gas C was cooled and collected as biomass fuel gas; wherein the space velocity of the pyrolysis gas was 1650h -1 -1, the space velocity of the steam was 580h -1 -1, and the inlet temperature of the fixed bed reactor was 835℃. Example 2

[0054] Preparation of biomass fuel gas:

[0055] N-octyl-N-methyl piperidinium bis(trifluoromethanesulfonyl)imide salt, glycerol, sodium dodecylbenzenesulfonate and water with mass ratio of 1:3:0.05:10 were mixed to obtain a mixed solution, then biomass raw material (wood waste and corn stalk with particle size of 20 mm and mass ratio of 1:1 after crushing and sieving) with mass ratio of 1:10 was stirred with the mixed solution at 80℃ for 3h, and finally filtered and dried at 105℃ to a water content of less than 1wt% to obtain modified biomass raw material;

[0056] The modified biomass raw material was added into a rotary kiln pyrolysis furnace and pyrolyzed at a temperature of 800℃ for 30 minutes under a mixed gas atmosphere of nitrogen and air with volume ratio of 15:1 to obtain pyrolysis gas and solid biochar;

[0057] Part of the solid biochar obtained in step (1) was reserved, platinum-rhenium catalyst with mass ratio of 100:0.8 was mixed with the solid biochar to obtain mixture A; nickel / alumina catalyst with mass ratio of 100:1.8 was mixed with the solid biochar to obtain mixture B, mixture A and mixture B were sequentially loaded into a fixed bed reactor from bottom to top to form catalyst layer A and catalyst layer B with volume ratio of 1:2; pyrolysis gas and steam were passed into the fixed bed reactor loaded with catalyst layer A and catalyst layer B from bottom to top to carry out methanation reaction to obtain product gas, the product gas flowed out from the top of the fixed bed reactor, the product gas was divided into three streams with volume flow ratio of 1:2:6, and was recorded as product gas A, product gas B and product gas C, product gas A was cooled to 40℃ by a steam generator and then returned to the fixed bed reactor from the middle height position of the fixed bed reactor to continue the methanation reaction, product gas B was directly returned to the fixed bed reactor from the position of 2 / 3 height of the fixed bed reactor to continue the methanation reaction, and reaction gas C was collected after cooling as biomass fuel gas; wherein the space velocity of the pyrolysis gas was 1800h -1 -1, the space velocity of the steam was 700h -1 -1, and the inlet temperature of the fixed bed reactor was 800℃.

[0058] Comparative Example 1

[0059] Preparation of biomass fuel gas:

[0060] According to the method of Example 1, the difference is that:

[0061] The modified biomass raw material was replaced by biomass raw material (wood waste and corn stalks with particle size of 12 mm and mass ratio of 1:1 after crushing and screening); the biomass raw material and dolomite with mass ratio of 100:1 were added into a rotary kiln pyrolysis furnace to pyrolyze at a temperature of 750℃ for 40 minutes under a mixed gas atmosphere of nitrogen and air with volume ratio of 16.2:1 to obtain pyrolysis gas and solid biochar.

[0062] The rest was similar to Example 1, and finally the biomass fuel gas was prepared.

[0063] Comparative Example 2

[0064] According to the method of Example 1, the difference is that:

[0065] Potassium hydroxide, glycerol, sodium dodecylbenzenesulfonate and water with mass ratio of 1:2.5:0.08:10 were mixed to obtain a mixed solution.

[0066] The rest was similar to Example 1, and finally the biomass fuel gas was prepared.

[0067] Comparative Example 3

[0068] According to the method of Example 1, the difference is that:

[0069] N-octyl-N-methylpiperidinium bis(trifluoromethylsulfonyl)imide salt, glycerol, sodium dodecylbenzenesulfonate and water were mixed to obtain a mixture solution with a mass ratio of 2.5:1:0.08:10.

[0070] The rest was similar to Example 1, and finally a biomass gas was prepared.

[0071] Comparative Example 4

[0072] According to the method of Example 1, except that:

[0073] N-octyl-N-methylpiperidinium bis(trifluoromethylsulfonyl)imide salt, sodium dodecylbenzenesulfonate and water were mixed to obtain a mixture solution with a mass ratio of 1:0.08:10.

[0074] The rest was similar to Example 1, and finally a biomass gas was prepared.

[0075] Comparative Example 5

[0076] According to the method of Example 1, except that:

[0077] The modified biomass raw material was added to the rotary kiln pyrolysis furnace and pyrolyzed at a temperature of 750°C for 40 minutes in a mixed atmosphere of air.

[0078] The rest was similar to Example 1, and finally a biomass gas was prepared.

[0079] Comparative Example 6

[0080] According to the method of Example 1, except that:

[0081] The platinum-rhenium catalyst and the nickel / alumina catalyst were loaded in the fixed bed reactor to form catalyst layer A and catalyst layer B from bottom to top with a corresponding volume ratio of 1:2.25.

[0082] The rest was similar to Example 1, and finally a biomass gas was prepared.

[0083] Comparative Example 7

[0084] According to the method of Example 1, except that:

[0085] Mixing A was loaded alone in the fixed bed reactor to form a catalyst bed.

[0086] The rest was similar to Example 1, and finally a biomass gas was prepared.

[0087] Comparative Example 8

[0088] According to the method of Example 1, except that:

[0089] Mixing B was charged into the fixed bed reactor alone to form a catalyst bed.

[0090] The rest was similar to Example 1, and finally a biomass gas was prepared.

[0091] Comparative Example 9

[0092] The method of Example 1 was followed, except that:

[0093] The product gas was divided into two streams in a volume flow ratio of 2.85:6.5, and was recorded as product gas A and product gas B. Product gas A was cooled to 42°C by a steam generator and returned to the fixed bed reactor from the middle height of the fixed bed reactor to continue the methanation reaction, and product gas B was cooled and collected as a biomass gas.

[0094] The rest was similar to Example 1, and finally a biomass gas was prepared.

[0095] Comparative Example 10

[0096] The method of Example 1 was followed, except that:

[0097] Product gas A was cooled to 42°C by a steam generator and returned to the fixed bed reactor from the bottom of the fixed bed reactor to continue the methanation reaction, and product gas B was directly returned to the fixed bed reactor from the bottom of the fixed bed reactor to continue the methanation reaction.

[0098] The rest was similar to Example 1, and finally a biomass gas was prepared.

[0099] Performance test

[0100] The main components and contents of the biomass gas in each example and comparative example were tested using a gas chromatograph.

[0101] The high heat value of the biomass gas in each example and comparative example was tested using a volumetric split-flow calorimeter.

[0102] The test results are shown in Table 1.

[0103] Table 1 Test results

[0104]

[0105] Comparative Example 1 did not use modified biomass raw materials, but directly co-pyrolyzed with dolomite. Although the combustible gas did not decrease significantly compared with Example 1, the hydrogen content in the final gas increased and the methane decreased, resulting in a significant decrease in the heat value of the gas.

[0106] In the preparation of the modified biomass raw material, the modifier is changed, resulting in a decrease in the heat value of the final fuel gas. Specifically, in Comparative Example 2, KOH is used instead of N-octyl-N-methyl piperidinium bis(trifluoromethylsulfonyl) imide salt. Although KOH can also react with the biomass raw material, it can cause the biomass raw material to be more easily carbonized during pyrolysis due to its excessive alkalinity, or it can not be able to react with glycerol as well, resulting in a decrease in the catalytic effect. In Comparative Example 3, the ratio of N-octyl-N-methyl piperidinium bis(trifluoromethylsulfonyl) imide salt and glycerol is changed, which cannot well play a catalytic role, resulting in a decrease in the heat value of the final fuel gas. In Comparative Example 4, glycerol is not added, resulting in a significant reduction in the modification effect, thereby reducing the catalytic effect and the heat value of the final fuel gas. In Comparative Example 5, the pyrolysis atmosphere is air, and the heat value of the final fuel gas is significantly reduced. This can be because most of the carbon elements are oxidized to carbon dioxide, resulting in a decrease in the content of combustible gas. In Comparative Example 6, there is no solid biochar in the catalyst layer, and the heat value of the fuel gas is reduced. The absence of solid biochar can cause an increase in the pressure drop of the bed, which cannot effectively utilize the active components of the catalyst and is more prone to coking. In Comparative Examples 7-8, the catalyst bed of each only uses a mixture of platinum-rhenium catalyst and solid biochar, a mixture of nickel / alumina catalyst and solid biochar, and the heat value of the final fuel gas is reduced. This can be because it reduces the occurrence of methanation reaction. In Comparative Example 9, the product gas is returned to the fixed bed reactor in a conventional group, and the heat value of the fuel gas is reduced. This can be because the return of a single stream can cause the local temperature in the fixed bed reactor to deviate from the optimal reaction interval, thereby affecting the methanation efficiency and reducing the catalyst life. In Comparative Example 10, two streams of circulating gas are returned from the bottom of the fixed bed reactor, and the heat value of the fuel gas is reduced. This can be because the return from the bottom can dilute the concentration of the inlet reactants, causing the efficiency of the entire reactor to decrease.

[0107] The above experimental results further demonstrate the importance of the technical solutions defined in the present application to its technical effects.

[0108] The above is a preferred embodiment of the present application. It should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application. These improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method for producing a high-calorific-value biomass gas, characterized by, The preparation method comprises: (1) pyrolysis reaction of modified biomass raw material in a pyrolysis reactor to obtain pyrolysis gas and solid biochar; (2) the pyrolysis gas and water vapor are passed into a fixed bed reactor filled with a catalyst layer from bottom to top for methanation reaction to obtain product gas, the product gas flows out from the top of the fixed bed reactor, the product gas is divided into three streams, denoted as product gas A, product gas B and product gas C, the product gas A is cooled to 40-50 DEG C and then returned to the fixed bed reactor, the product gas B is directly returned to the fixed bed reactor, and the reaction gas C is cooled and collected as biomass fuel gas; The preparation method of the modified biomass raw material comprises: mixing N-octyl-N-methyl piperidine bis (trifluoromethyl sulfonate) imidate, glycerol, sodium dodecyl benzene sulfonate and water to obtain a mixed solution, then carrying out contact reaction of the biomass raw material and the mixed solution, and finally carrying out filtration and drying to obtain the modified biomass raw material; The catalyst layer contains the solid biochar in step (1); the catalyst layer comprises, from bottom to top, catalyst layer A formed by mixing and packing a platinum-based catalyst and solid biochar, and catalyst layer B formed by mixing and packing a nickel-based catalyst and solid biochar.

2. The method of claim 1, wherein the high-calorific-value biomass gas is prepared by the steps of: The mass ratio of the N-octyl-N-methyl piperidine bis (trifluoromethyl sulfonate) imidate, glycerol, sodium dodecyl benzene sulfonate and water is 1: (2-3): (0.05-0.1): 10; the mass ratio of the mixed solution to the biomass raw material is (10-15): 1; and the contact reaction is carried out at a temperature of 70-80 DEG C for 3-4 hours.

3. The method of claim 1, wherein the high-calorific-value biomass gas is prepared by the steps of: The biomass raw material is selected from at least one of wood chips, straw, wood waste, corn cob and rice husk; and the particle size of the biomass raw material is 5-20 mm. ​ 4. The method of claim 1, wherein the high-calorific-value biomass gas is prepared by the steps of: In step (1), the pyrolysis reaction is carried out at a temperature of 600-800 DEG C for 30-60 minutes in a mixed atmosphere of inert gas and air. ​ 5. The method of claim 1, wherein the high-calorific-value biomass gas is prepared by the steps of: In the catalyst layer A, the mass ratio of the platinum-based catalyst to the solid biochar is 100: (0.5-2); in the catalyst layer B, the mass ratio of the nickel-based catalyst to the solid biochar is 100: (1-3); and the volume ratio of the catalyst layer A to the catalyst layer B is 1: (1.5-3). ​ 6. The method of claim 1, wherein the high-calorific-value biomass gas is prepared by the steps of: In step (2), the conditions for the methanation reaction include: the space velocity of the pyrolysis gas is 1200 h⁻¹. -1 -2000h -1 The space velocity of the water vapor is 500 h⁻¹. -1 -1000h -1 The inlet temperature of the fixed-bed reactor is 800℃-900℃. ​ 7. The method of claim 1, wherein the high-calorific-value biomass gas is produced by the steps of: The volume flow rate ratio of the product gas A, the product gas B and the product gas C is 1: (1-3): (5-10). ​

Images