Synthesis gas preparation method based on double-circulation gasifier

Abstract

The invention provides a synthesis gas preparation method based on a double-circulation gasifier. The synthesis gas preparation method based on the double-circulation gasification furnace comprises the following steps: S1, feeding a biomass raw material and a gasification agent into the double-circulation gasification furnace for gasification; s2, performing primary separation on the synthesis gas generated by gasification, returning a solid material generated by the primary separation to the double-circulation gasification furnace, and performing secondary separation on the synthesis gas after the primary separation; and S3, returning the solid material generated by the second-stage separation to the double-circulation gasification furnace. According to the preparation method of the synthesis gas, the carbon conversion rate and the gasification efficiency can be effectively improved, the total concentration of carbon monoxide and hydrogen in the synthesis gas is greater than 65%, and the quality of the biomass gasification synthesis gas is greatly improved.

Description

Technical Field

[0001] The present invention relates to the field of gasification technology, and in particular to a method for preparing synthesis gas based on a double-circulation gasifier. Background Art

[0002] Biomass raw materials primarily include various types of urban and rural organic waste, such as crop straw, livestock farm waste, domestic garbage, and industrial organic wastewater. Biogas, a combustible gas primarily containing methane, is produced through thermochemical or biochemical conversion of biomass as a raw material. There are two main types of biogas: one is produced by incomplete combustion and pyrolysis of biomass under high-temperature, oxygen-deficient conditions, producing combustible gases primarily composed of carbon monoxide, hydrogen, and nitrogen, known as gasification gas; the other is produced by anaerobic decomposition of biomass by anaerobic bacteria under anaerobic conditions, producing combustible gases primarily composed of methane and carbon dioxide, known as biogas.

[0003] Biomass pyrolysis and gasification produces biogas, which can be used to replace coal in industrial furnaces such as cement kilns, lime kilns, heating furnaces, and boilers. This has significant carbon reduction potential and is currently the lowest-cost alternative to fossil fuels. Every ton of biomass used reduces CO2 emissions by approximately 1 ton. Biogas can be further synthesized into methanol, jet fuel, and hydrogen for use in shipping, aviation, and land transportation, achieving carbon reductions exceeding 65% compared to traditional fuels. However, existing biomass gasification technologies suffer from low carbon conversion rates and gasification efficiency, resulting in low-quality syngas with a combined carbon monoxide and hydrogen concentration below 30%.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The object of the present invention is to provide a method for preparing syngas based on a dual-circulation gasifier, which can effectively improve the carbon conversion rate and gasification efficiency, and greatly improve the quality of biomass gasification syngas.

[0006] The present invention provides a method for preparing synthesis gas based on a double-circulation gasifier, comprising the following steps:

[0007] S1: sending biomass raw materials and gasifying agent into the double circulation gasifier for gasification;

[0008] S2: Perform primary separation on the synthesis gas produced by gasification, return the solid materials produced by the primary separation to the dual-circulation gasifier, and perform secondary separation on the synthesis gas after the primary separation;

[0009] S3: Return the solid materials produced by the secondary separation to the dual-circulation gasifier.

[0010] In step S1, the dual-circulation gasifier includes a gasifier, a primary separator and a secondary separator. The synthesis gas outlet of the gasifier is connected to the inlet of the primary separator, the gas outlet of the primary separator is connected to the inlet of the secondary separator, and the solid material outlets of the primary separator and the secondary separator are respectively connected to the gasifier.

[0011] The gasifier is equipped with a quartz sand fluidized bed with a particle size of 0.3-0.8mm. The sand with a particle size of 0.3mm ≤ < 0.5mm accounts for 8-12%, 0.5mm ≤ < 0.6mm accounts for 45-55%, and 0.6mm ≤ ≤ 0.8mm accounts for 35-45%. The volume of quartz sand used is 2-4% of the gasifier's volume. This quartz sand fluidized bed with this particle size distribution effectively maintains thermal balance within the dual-circulation gasifier, improving gasification efficiency and syngas quality.

[0012] The present invention does not impose strict restrictions on the biomass raw materials used. For example, crop straw, forestry waste, organic municipal waste and combustible industrial solid waste can be used. In addition, the biomass raw materials can be crushed to a particle size of ≤100mm and then fed into the dual-circulation gasifier.

[0013] The gasifying agent of the present invention includes pure oxygen and water vapor. The pure oxygen equivalent ratio is 0.2-0.3, which refers to the ratio of the amount of oxygen provided during the gasification process to the theoretical amount of oxygen required for complete combustion of the biomass raw material; the water vapor ratio is 0.3-0.5, which refers to the mass ratio of the water vapor provided during the gasification process to the biomass raw material.

[0014] The gasification temperature during gasification is 750-800° C., and the gasification time is 6-20 seconds, for example, 6-15 seconds.

[0015] In step S2, a cyclone separator can be used to perform primary separation and secondary separation; the primary cyclone separator and the secondary cyclone separator can use water vapor as the power for returning the material and blowing off the soot. The mass ratio of water vapor to biomass raw material used in the primary cyclone separator can be (0.01-0.03):1, and the mass ratio of water vapor to biomass raw material used in the secondary cyclone separator can be (0.07-0.09):1.

[0016] The CO content in the synthesis gas after secondary separation is ≥35%, the H2 content is ≥30%, the water content is 16-25%, and the tar content is 800-1200 mg / Nm 3 The total concentration of carbon monoxide and hydrogen in the synthesis gas prepared by the above preparation method is greater than 65%, and the quality of the biomass gasification synthesis gas is greatly improved.

[0017] Step S3 also includes: performing tar cracking on the synthesis gas after the secondary separation.

[0018] In one embodiment, tar cracking includes feeding the secondary separated syngas and pure oxygen into a closed cracking furnace for tar cracking. The tar cracking temperature is 1000-1200°C, and the amount of pure oxygen used is 8-10% of the mass of the biomass feedstock. Introducing pure oxygen during tar cracking not only solves the problem of cracking tar with high moisture content but also improves tar conversion.

[0019] In another embodiment, tar cracking is carried out in the presence of a tar cracking catalyst; wherein the tar cracking temperature is 450-600°C, the tar cracking catalyst comprises a multi-stage pore molecular sieve, a transition metal oxide and a rare earth element, the loading amount of the active component is 5-20wt%, and the addition amount of the rare earth element is 1-5wt%.

[0020] More specifically, the multi-level pore molecular sieve is selected from at least one of multi-level pore ZSM-5 molecular sieve, multi-level pore MCM-41 molecular sieve and multi-level pore SBA-15 molecular sieve; the transition metal oxide is selected from at least one of nickel oxide, cobalt oxide and iron oxide; and the rare earth element is selected from one of cerium, lanthanum and neodymium.

[0021] Furthermore, the specific surface area of the multi-stage pore molecular sieve is 500-700m 2 / g, pore volume is 0.4-0.6cm 3 / g, with an external surface area of 150-300m 2 / g, and the total acid content is 5.0-7.0mmol / g. In particular, the multi-level pore molecular sieve contains micropores with a pore size of 0.5-1nm and mesopores with a pore size of 2-10nm, with the mesopores accounting for 40-60%.

[0022] These multi-level molecular sieves possess high surface area and large pore volume, enhancing reactant adsorption and mass transfer efficiency. Furthermore, their bimodal pore size distribution balances shape-selective catalysis with diffusion performance, while their hierarchical connectivity addresses the diffusion bottleneck of macromolecular reactions. Their strong acid sites and high thermal stability enhance reactivity and lifespan. Using these tar cracking catalysts for tar cracking not only increases the conversion rate of high-water-content tar but also significantly reduces the tar cracking temperature.

[0023] Furthermore, the preparation method of the tar cracking catalyst comprises the following steps:

[0024] A) impregnating the multi-level pore molecular sieve into a mixed solution containing a transition metal salt and a rare earth metal salt, and stirring uniformly to prepare a precursor solution;

[0025] B) Drying and calcining the precursor solution.

[0026] Specifically, the transition metal salt is selected from at least one of nickel nitrate, cobalt nitrate and iron nitrate, and the rare earth metal salt is selected from at least one of cerium nitrate, lanthanum nitrate and neodymium nitrate; the mass content of the transition metal salt in the mixed solution is 0.1-0.15 g / mL, and the mass content of the rare earth metal salt is 0.02-0.03 g / mL; the mass ratio between the multi-level pore molecular sieve, the transition metal salt and the rare earth metal salt is 10:(2-3):(0.3-0.7); the drying temperature is 80-120°C, and the drying time is 2-6 hours; the roasting temperature is 400-600°C, and the roasting time is 2-4 hours.

[0027] The moisture content of the syngas after tar cracking is 5-8%, and the tar content is less than 80mg / Nm 3 .

[0028] The synthesis gas preparation method of the present invention can effectively improve the carbon conversion rate and gasification efficiency. The carbon conversion rate is greater than 92%, the gasification efficiency is greater than 80%, and the total concentration of carbon monoxide and hydrogen in the synthesis gas is greater than 65%, which greatly improves the quality of biomass gasification synthesis gas. In addition, by carrying out tar cracking in a specific manner, problems such as the difficulty in cracking tar with high water content are solved, thereby improving the tar conversion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0030] Figure 1 It is a structural diagram of a double-circulation gasifier;

[0031] Figure 2 This is a schematic diagram of the structure of the synthesis gas preparation system based on a dual-circulation gasifier.

[0032] Description of reference numerals:

[0033] 1: Gasifier; 2: Primary separator; 3: Secondary separator; 4: Gasifying agent inlet; 5: Quartz sand feeding device; 6: Biomass feeding device; 7: Slag discharge device; 8: Primary return device; 9: Secondary return device; 10: Sand hopper; 11: Silo; 12: Feeding belt; 13: Crushing device; 14: Forklift; 15: Electric steam boiler; 16: Closed cracking furnace; 17: Spray tower; 18: Dehydration tower; 19: Desulfurization tower; 20: Filter; 21: Burner; 22: Chemical synthesis utilization branch pipe. DETAILED DESCRIPTION

[0034] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present application belongs.

[0035] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular also includes the plural. In addition, it should be understood that when the terms "comprise" and / or "include" are used in this specification, they indicate the presence of features, steps, operations, devices, components and / or combinations thereof.

[0036] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the embodiments. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0037] Example 1

[0038] The synthesis gas preparation method based on the dual-circulation gasifier of this embodiment comprises the following steps:

[0039] 1. Gasification

[0040] Quartz sand is fed into a double-circulation gasifier to form a fluidized bed. The particle size of the quartz sand is 0.3-0.8 mm. Among them, the component with a particle size of 0.3 mm ≤ < 0.5 mm accounts for 10%, the component with a particle size of 0.5 mm ≤ < 0.6 mm accounts for 50%, and the component with a particle size of 0.6 mm ≤ ≤ 0.8 mm accounts for 40%. The volume of the quartz sand is 3% of the volume of the gasifier.

[0041] The crop straw is crushed to a particle size of ≤100 mm and then fed into a dual-circulation gasifier. Pure oxygen and water vapor are introduced into the dual-circulation gasifier as gasifying agents to gasify the biomass raw materials. The pure oxygen equivalent ratio is 0.2, the water vapor ratio is 0.3, the gasification temperature is 750°C, and the gasification time is 10 s.

[0042] 2. Primary separation

[0043] The gasified synthesis gas is sent to the first-stage cyclone separator for primary separation, and the separated solid materials (including sand and ungasified residues) are returned to the dual-circulation gasifier; the first-stage cyclone separator uses water vapor as the return material soot blowing power, and the mass ratio of water vapor to biomass raw material is 0.02:1.

[0044] 3. Secondary separation

[0045] The synthesis gas at the top of the first-stage cyclone separator then enters the second-stage cyclone separator for secondary separation, and the separated solid materials are returned to the dual-circulation gasifier; the second-stage cyclone separator uses water vapor as the return material soot blowing power, and the mass ratio of water vapor to biomass raw material is 0.08:1.

[0046] The carbon conversion rate of this embodiment is 93.45%, and the gasification efficiency is 81.50%. The main composition of the synthesis gas after the secondary separation is shown in Table 1.

[0047] Example 2

[0048] 1. Gasification

[0049] Quartz sand is fed into a double-circulation gasifier to form a fluidized bed. The particle size of the quartz sand is 0.3-0.8 mm. Among them, the component with a particle size of 0.3 mm ≤ < 0.5 mm accounts for 10%, the component with a particle size of 0.5 mm ≤ < 0.6 mm accounts for 55%, and the component with a particle size of 0.6 mm ≤ ≤ 0.8 mm accounts for 35%. The volume of the quartz sand is 3% of the volume of the gasifier.

[0050] The forestry waste pruning is crushed to a particle size of ≤100mm and then sent to a double-circulation gasifier. Pure oxygen and water vapor are introduced into the double-circulation gasifier as gasifying agents to gasify the biomass raw materials. The pure oxygen equivalent ratio is 0.3, the water vapor ratio is 0.5, the gasification temperature is 800℃, and the gasification time is 6s.

[0051] 2. Primary separation

[0052] The gasified synthesis gas is sent to the first-stage cyclone separator for primary separation, and the separated solid materials (including sand and ungasified residues) are returned to the dual-circulation gasifier; the first-stage cyclone separator uses water vapor as the return material soot blowing power, and the mass ratio of water vapor to biomass raw material is 0.02:1.

[0053] 3. Secondary separation

[0054] The synthesis gas at the top of the first-stage cyclone separator then enters the second-stage cyclone separator for secondary separation, and the separated solid materials are returned to the dual-circulation gasifier; the second-stage cyclone separator uses water vapor as the return material soot blowing power, and the mass ratio of water vapor to biomass raw material is 0.08:1.

[0055] The main composition of the synthesis gas after secondary separation is shown in Table 1.

[0056] Example 3

[0057] 1. Gasification

[0058] Quartz sand is fed into a double-circulation gasifier to form a fluidized bed. The particle size of the quartz sand is 0.3-0.8 mm. Among them, the component with a particle size of 0.3 mm ≤ < 0.5 mm accounts for 10%, the component with a particle size of 0.5 mm ≤ < 0.6 mm accounts for 45%, and the component with a particle size of 0.6 mm ≤ ≤ 0.8 mm accounts for 45%. The volume of the quartz sand is 3% of the volume of the gasifier.

[0059] The organic waste is crushed to a particle size of ≤100mm and then sent to a dual-circulation gasifier. Pure oxygen and water vapor are introduced into the dual-circulation gasifier as gasifying agents to gasify the biomass raw materials. The pure oxygen equivalent ratio is 0.2, the water vapor ratio is 0.4, the gasification temperature is 750℃, and the gasification time is 15s.

[0060] 2. Primary separation

[0061] The gasified synthesis gas is sent to the first-stage cyclone separator for primary separation, and the separated solid materials (including sand and ungasified residues) are returned to the dual-circulation gasifier; the first-stage cyclone separator uses water vapor as the return material soot blowing power, and the mass ratio of water vapor to biomass raw material is 0.02:1.

[0062] 3. Secondary separation

[0063] The synthesis gas at the top of the first-stage cyclone separator then enters the second-stage cyclone separator for secondary separation, and the separated solid materials are returned to the dual-circulation gasifier; the second-stage cyclone separator uses water vapor as the return material soot blowing power, and the mass ratio of water vapor to biomass raw material is 0.08:1.

[0064] The main composition of the synthesis gas after secondary separation is shown in Table 1.

[0065] Comparative Example 1

[0066] Except that air was used to replace pure oxygen in the gasification step (the air equivalence ratio was 0.2), the rest was the same as Example 3; the main composition of the synthesis gas after the secondary separation is shown in Table 1.

[0067] Comparative Example 2

[0068] Except that the particle size of the quartz sand in the gasification step is 0.5-0.6 mm (i.e., the component with a particle size of 0.5 mm ≤ < 0.6 mm accounts for 100%), the rest is the same as Example 3; the main composition of the synthesis gas after the secondary separation is shown in Table 1.

[0069] Table 1 Main components of synthesis gas

[0070] <![CDATA[H2(%)]]> CO (%) Example 1 30.22 36.01 Example 2 31.50 37.52 Example 3 32.45 37.64 Comparative Example 1 14.90 12.80 Comparative Example 2 29.15 33.25

[0071] Example 4

[0072] The synthesis gas after the secondary separation in Example 1 (water content 20%, tar content 1000 mg / Nm 3 ) tar cracking; specifically as follows:

[0073] The synthesis gas and pure oxygen after secondary separation were sent to a closed cracking furnace for tar cracking. The tar cracking temperature was 1000°C, the tar cracking time was 5 seconds, and the amount of pure oxygen used was 10% of the mass of the biomass feedstock. The tar cracking results are shown in Table 3.

[0074] Example 5

[0075] The synthesis gas after the secondary separation in Example 1 was subjected to tar cracking; the details are as follows:

[0076] 1. Preparation of tar cracking catalyst

[0077] 10 g of hierarchical ZSM-5 molecular sieve was immersed in 25 mL of a mixed solution containing 2.5 g of nickel nitrate and 0.5 g of cerium nitrate, and stirred evenly to prepare a precursor solution;

[0078] 2) drying the precursor solution at 100° C. for 4 h;

[0079] 3) The dried product was calcined at 500° C. for 3 h under a nitrogen atmosphere to obtain a high-efficiency catalyst for catalytic cracking of biomass gasification tar.

[0080] The multi-level pore ZSM-5 molecular sieve used in this example was purchased from Luoyang Jianlong Micro-Nano New Materials Co., Ltd., and its quality parameters are shown in Table 2.

[0081] Table 2 Quality parameters of multi-level pore ZSM-5 molecular sieve

[0082] The synthesis gas after secondary separation was subjected to tar cracking in the presence of the above tar cracking catalyst. The tar cracking temperature was 600 ° C and the hourly space velocity (GHSV) was 1000h -1 ; Tar cracking results are shown in Table 3.

[0083] Comparative Example 3

[0084] The same procedure as in Example 4 was employed except that only the synthesis gas after the secondary separation in Example 1 was fed to a closed cracking furnace for tar cracking (i.e., pure oxygen was not introduced during tar cracking). The tar cracking results are shown in Table 3.

[0085] Comparative Example 4

[0086] The process was the same as in Example 5 except that ordinary ZSM-5 molecular sieve (containing only micropores with a pore size of 0.5-1 nm, with a micropore ratio of 100% and a mesopore ratio of 0%) was used instead of the multi-level pore ZSM-5 molecular sieve. The tar cracking results are shown in Table 3.

[0087] Table 3 Tar cracking results

[0088] Tar conversion rate (%) <![CDATA[H2 Selectivity (%)]]> <![CDATA[Tar content (mg / Nm 3 )]]> Example 4 92.45 75.8 75.5 Example 5 93.68 78.2 63.2 Comparative Example 3 86.82 60.8 131.8 Comparative Example 4 84.46 65.2 155.4

[0089] Example 6

[0090] Combine Figure 1 、 Figure 2 As shown, the dual-circulation gasifier used in Examples 1-3 includes a gasifier 1, a primary separator 2, and a secondary separator 3. The gasifier 1 is provided with a quartz sand inlet, a biomass inlet, a gasifying agent inlet 4, a syngas outlet, and a slag outlet. The quartz sand inlet, the biomass inlet, and the slag outlet are respectively connected to a quartz sand feeding device 5, a biomass feeding device 6, and a slag discharge device 7. The syngas outlet of the gasifier 1 is connected to the inlet of the primary separator 2, the gas outlet of the primary separator 2 is connected to the inlet of the secondary separator 3, and the solid material outlets of the primary separator 2 and the secondary separator 3 are respectively connected to a primary return material 8 and a secondary return material 9. The primary return material 8 is connected to the gasifier 1, and the secondary return material 9 is connected to the gasifier 1 through the primary return material 8.

[0091] The synthesis gas production system based on the dual-circulation gasifier 1 includes the aforementioned dual-circulation gasifier, a quartz sand feeder 5 connected to a sand hopper 10, a biomass feeder 6 connected to a silo 11, and a silo 11 connected to a crushing device 13 via a feeding belt 12. An electric steam boiler 15 is installed outside the dual-circulation gasifier 1. The steam outlet of the electric steam boiler 15 is connected to the steam inlets of the gasifier 1, the primary separator 2, and the secondary separator 3, respectively. The gas outlet of the secondary separator 3 is connected to a sealed cracking furnace 16. A spray tower 17, a dehydration tower 18, a desulfurization tower 19, a filter 20, and a burner 21 are sequentially arranged at the downstream end of the sealed cracking furnace 16. A chemical synthesis utilization branch pipe 22 is provided on the connecting pipe between the filter 20 and the burner 21.

[0092] The working process of the above-mentioned synthesis gas preparation system based on the dual-circulation gasifier is as follows:

[0093] Biomass feedstock is fed into a crushing device 13 using a forklift 14. After being crushed to a particle size of less than 100 mm, it is conveyed to a silo 11 via a feeding conveyor 12. The biomass feedstock in silo 11 then enters the furnace of the gasifier 1 via a biomass feeder 6. Quartz sand is then buffered in a sand hopper 10. During filling, a screw feeder at the bottom of the sand hopper 10 delivers the quartz sand into the gasifier 1. Using quartz sand as bed material maintains thermal equilibrium within the gasifier 1. The gasification process uses pure oxygen and water vapor as gasifying agents, with an oxygen equivalence ratio of 0.2-0.3 and a water vapor ratio of 0.3-0.5. After the biomass is gasified at 750-800°C, the resulting syngas is separated in a primary separator 2 and a secondary separator 3. The separated solid material is returned to the gasifier 1 via a primary returner 8 and a secondary returner 9. The resulting ash is discharged by a slag discharger 7. The separated synthesis gas enters the closed cracking furnace 16 for tar cracking. After the tar cracking, it passes through the spray tower 17, dehydration tower 18, desulfurization tower 19, and filter 20 for spraying, dehydration, desulfurization, and filtration. The filtered synthesis gas enters the burner 21 for combustion. In addition, it can also be sent to chemical synthesis utilization through the chemical synthesis utilization branch pipe 22.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing synthesis gas based on a double-circulation gasifier, characterized in that: The steps include: S1: sending biomass raw materials and gasifying agent into the double circulation gasifier for gasification; S2: Perform primary separation on the synthesis gas produced by gasification, return the solid materials produced by the primary separation to the dual-circulation gasifier, and perform secondary separation on the synthesis gas after the primary separation; S3: Return the solid materials produced by the secondary separation to the dual-circulation gasifier.

2. The method for preparing synthesis gas according to claim 1, wherein: A quartz sand fluidized bed is provided in the dual-circulation gasifier. The quartz sand particle size used in the quartz sand fluidized bed is 0.3-0.8 mm; among them, the component with a particle size of 0.3 mm ≤ < 0.5 mm accounts for 8-12%, the component with a particle size of 0.5 mm ≤ < 0.6 mm accounts for 45-55%, and the component with a particle size of 0.6 mm ≤ ≤ 0.8 mm accounts for 35-45%.

3. The method for preparing synthesis gas according to claim 1, wherein: The biomass raw materials are crushed to a particle size of ≤100mm and then fed into the double-circulation gasifier.

4. The method for preparing synthesis gas according to claim 1, wherein: The gasifying agent includes pure oxygen and water vapor, the pure oxygen equivalent ratio is 0.2-0.3, and the water vapor ratio is 0.3-0.

5.

5. The method for preparing synthesis gas according to claim 1, wherein: The gasification temperature during gasification is 750-800°C.

6. The method for preparing synthesis gas according to claim 1, wherein: The CO content in the synthesis gas after the secondary separation is ≥35%, and the H2 content is ≥30%.

7. The method for producing synthesis gas according to claim 1, wherein: Step S3 also includes: performing tar cracking on the synthesis gas after the secondary separation.

8. The method for preparing synthesis gas according to claim 7, characterized in that: Tar cracking includes: sending the synthesis gas and pure oxygen after secondary separation to a closed cracking furnace for tar cracking; wherein, the tar cracking temperature is 1000-1200℃, and the amount of pure oxygen used is 8-10% of the mass of the biomass raw material.

9. The method for preparing synthesis gas according to claim 7, characterized in that: Tar cracking is carried out in the presence of a tar cracking catalyst; wherein the tar cracking temperature is 450-600°C, the tar cracking catalyst comprises a multi-stage pore molecular sieve, a transition metal oxide and a rare earth element, the loading amount of the active component is 5-20wt%, and the addition amount of the rare earth element is 1-5wt%.

10. The method for producing synthesis gas according to claim 9, characterized in that: The multi-level pore molecular sieve is selected from at least one of multi-level pore ZSM-5 molecular sieve, multi-level pore MCM-41 molecular sieve and multi-level pore SBA-15 molecular sieve; the transition metal oxide is selected from at least one of nickel oxide, cobalt oxide and iron oxide; and the rare earth element is selected from one of cerium, lanthanum and neodymium.

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