Method for producing carbon monoxide by using industrial calcium-containing tail gas

Abstract

The present application belongs to the technical field of industrial waste gas resource utilization and synthesis gas preparation, and particularly relates to a method for preparing carbon monoxide by using industrial calcium-containing tail gas. The present application comprises: conveying the hot state dust-containing tail gas discharged from the calcium carbonate calcination section to a mixing zone through an insulation pipeline, wherein the hot state dust-containing tail gas carries calcium-containing dust; introducing the hot state dust-containing tail gas and oxygen-containing oxidizing agent into the mixing zone for mixing to obtain a gas-solid suspended gasification agent flow; feeding the gasification agent flow into a fluidized bed gasification reactor from bottom to top to contact with carbon-rich substrates filled in the reactor and added steel slag powder to perform a gasification reaction; and cooling and dust removal purification of the generated crude synthesis gas to obtain product gas. The present application realizes efficient co-digestion of industrial tail gas physical sensible heat and solid waste, greatly improves the one-way conversion rate of carbon dioxide, and avoids the sticking and blocking of high-temperature dust-containing pipelines.

Description

Technical Field

[0001] This invention belongs to the field of industrial waste gas resource utilization and syngas preparation technology, specifically relating to a method for producing carbon monoxide from industrial calcium-containing tail gas. Background Technology

[0002] In the metallurgical, chemical, and building materials industries, limestone (calcium carbonate) calcination is an extremely common process. Large and medium-sized steel and building materials enterprises in my country have built large-scale limestone production facilities. This calcination process generates a large amount of high-temperature exhaust gas, which is typically characterized by temperatures above 500°C, carbon dioxide volume fractions exceeding 70%, and the exhaust gas carrying large amounts of calcium oxide and calcium carbonate fine dust.

[0003] Traditionally, the treatment of the aforementioned exhaust gases typically involves first subjecting them to physical cooling (such as mixing with cold air or using a water-cooled casing), followed by deep dust removal (such as bag filters or electrostatic precipitators), after which they are either directly discharged or used solely as a low-grade heat source. This process of separating waste gas from solid waste suffers from the following insurmountable drawbacks:

[0004] (1) Serious waste of sensible heat: The high-temperature physical sensible heat carried by the exhaust gas is lost in large quantities during the cooling process and fails to be effectively converted into chemical energy or high-grade heat energy.

[0005] (2) Low carbon source conversion efficiency: High concentration of CO2 is a very valuable carbon source. Direct emission not only increases the carbon tax and environmental pressure on enterprises, but also misses the opportunity for in-situ resource utilization.

[0006] (3) The system is prone to blockage: Because the exhaust gas dust contains a large number of alkaline CaO particles, during the traditional cooling and speed reduction process, CaO is very easy to react with CO2 and trace moisture in the exhaust gas to undergo reverse carbonation and hydration reactions, generating highly adhesive CaCO3 scale, which leads to frequent blockage of the dust collector and conveying pipeline, resulting in extremely poor system operation continuity.

[0007] For the recovery and utilization of CO2 exhaust gas, existing technologies typically require the removal of impurities such as dust before purification, resulting in extremely high investment and operating costs. It is known that CO2 and elemental carbon can react to produce carbon monoxide, but this reaction is strongly endothermic, and its kinetics are greatly affected by temperature and catalytic activity. Currently, there is a lack of a process that can directly utilize high-temperature, dust-laden lime kiln exhaust gas, maintaining dust activity in situ under harsh operating conditions without pre-cooling or pre-dust removal, and efficiently autothermal catalytic gasification using the sensible heat of the exhaust gas and solid components.

[0008] Therefore, developing a method that can directly utilize industrial calcium-containing exhaust gas, avoid system blockage, and efficiently produce carbon monoxide has significant industrial application value and environmental significance. Summary of the Invention

[0009] The purpose of this invention is to provide a method for producing carbon monoxide from industrial calcium-containing exhaust gas. This method uses the high-temperature calcium-containing exhaust gas and the dust it carries as a whole reaction medium with specific thermal state, chemical composition and physical form for in-situ collection and transportation. It is directly introduced into the fluidized bed gasification reactor without pre-dust removal, which completely avoids the cooling and clogging problems of traditional processes and achieves a double leap in energy efficiency and carbon efficiency.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] S1: The hot dust-laden exhaust gas discharged from the calcium carbonate calcination section is transported to the mixing zone through an insulated pipeline. The hot dust-laden exhaust gas carries calcium-containing dust.

[0012] S2: The hot dust-laden exhaust gas and the oxygen-containing oxidant are introduced into the mixing zone for mixing to obtain a gas-solid suspended gasifying agent stream;

[0013] S3: The gasifying agent is fed into the fluidized bed gasification reactor from bottom to top, and comes into contact with the carbon-rich matrix and added steel slag powder packed in the fluidized bed gasification reactor to carry out the gasification reaction.

[0014] S4: Cool and purify the crude syngas generated by the reaction to obtain the product gas.

[0015] Specifically, in step S1, the temperature of the hot dust-laden exhaust gas is 550~850℃, and the volume fraction of CO2 is ≥70%; the calcium-containing dust contains CaO and / or CaCO3; the hot dust-laden exhaust gas is directly sent into the mixing zone without pre-dust removal.

[0016] Specifically, in step S2, the volume fraction of O2 in the oxygen-containing oxidant is ≥85%.

[0017] Specifically, in step S2, the mixing zone is equipped with a Venturi mixer. The hot dust-laden exhaust gas and the oxygen-containing oxidant are mixed at the throat of the Venturi mixer and then mixed in the post-mixing tube, where the residence time is 0.5~2s. At the inlet of the Venturi mixer, the flow velocity of the hot dust-laden exhaust gas is 12~25m / s, and the concentration of calcium dust in the hot dust-laden exhaust gas is 15~40g / Nm³. 3 .

[0018] Specifically, in step S3, the temperature of the reaction zone of the fluidized bed gasification reactor is 880~1100℃, the operating pressure is 0.1~0.5MPaG, and the apparent gas velocity is 0.8~2.5m / s.

[0019] Specifically, the carbon-rich matrix is ​​metallurgical coke and / or semi-coke, the fixed carbon content of the carbon-rich matrix is ​​≥82wt%, and the particle size is 0.5~5mm; and the carbon-rich matrix contains iron-based components calculated as Fe2O3, the mass percentage of the iron-based components is 0.3~1.2wt%.

[0020] Specifically, in step S3, the amount of steel slag powder added is 3-8% of the weight of the carbon-rich matrix; the particle size of the steel slag powder is <150μm, and the specific surface area is ≥200m² / kg; the steel slag powder comprises, by mass percentage: 35-50% CaO, 15-30% FeO+Fe2O3, 10-20% SiO2, 5-10% MgO, and 0-4% MnO.

[0021] Specifically, in step S3, the catalytic component of the gasification reactor is composed of CaO in the calcium-containing dust, CaO in the steel slag powder, and iron-based reduction products in the carbon-rich matrix and the steel slag powder.

[0022] Specifically, the fluidized bed gasification reactor adopts a staged oxygen supply method: 50-100% of the oxygen-containing oxidant is fed from the bottom of the fluidized bed gasification reactor, and the remainder is introduced from the lower to middle height range of the fluidized bed gasification reactor.

[0023] Specifically, in step S1, when the temperature of the hot dust-laden exhaust gas is below 650°C, the temperature of the hot dust-laden exhaust gas is raised to 650~750°C by electric heating and / or supplementary combustion; in step S4, the crude syngas is cooled to 200~250°C and then sent to a high-temperature bag filter for purification, and the solid particles separated by dust removal and purification are returned to the fluidized bed gasification reactor.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. This invention directly utilizes the high-temperature dusty exhaust gas discharged from the calcium carbonate calcination section without pre-cooling or pre-dust removal, thus avoiding the problem of CaO reverse carbonation scaling and blockage caused by cooling. At the same time, it maximizes the retention of the physical sensible heat of the exhaust gas, realizing the efficient conversion of thermal energy into chemical energy.

[0026] 2. This invention uses high-concentration CO2 in exhaust gas as a carbon source for gasification, which reacts with a carbon-rich matrix to generate high-value-added carbon monoxide, significantly reducing carbon emissions and carbon tax pressure, and realizing in-situ resource utilization of carbon dioxide.

[0027] 3. This invention utilizes a Venturi mixer to achieve rapid and uniform mixing of hot dusty exhaust gas and high-purity oxygen-containing oxidant, and adopts a bottom-up gas-solid contact method in the fluidized bed gasification reactor, combined with staged oxygen supply, which effectively suppresses local overheating and improves gasification reaction efficiency and syngas quality.

[0028] 4. This invention synergistically utilizes industrial solid waste steel slag powder, whose rich CaO, FeO, Fe2O3 and other components, together with CaO in calcium-containing dust and iron-based components in carbon-rich matrix, form a composite catalytic system, which significantly reduces the activation energy of the reaction and increases the reaction rate. At the same time, the alkaline components in steel slag powder help to fix trace amounts of sulfides in the exhaust gas, reducing the burden of subsequent purification.

[0029] 5. This invention returns the solid particles separated from the crude syngas after cooling and dust removal to the fluidized bed gasification reactor, realizing the recycling of unreacted carbon and catalytic components, and further improving the utilization rate of raw materials and the economic efficiency of the process. Detailed Implementation

[0030] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these embodiments. Those skilled in the art should recognize that the present invention covers all possible alternatives, improvements, and equivalents included within the scope of the claims.

[0031] Example 1

[0032] a. Raw materials and feeding conditions:

[0033] Hot, dust-laden exhaust gas: taken from the smoke chamber outlet and led out through a high-silica, oxygen-insulated pipe. Temperature: 700℃; dry basis volume composition: CO2 85%, N2 15%; concentration of calcium-containing dust carried: 27.5 g / Nm³. 3 Median particle size d of dust 50 The particle size is 35 μm, and this calcium-containing dust contains both CaO and CaCO3.

[0034] Assisted oxidant: Oxygen-enriched air containing 92.5% oxygen by volume.

[0035] Carbon-rich matrix: metallurgical coke powder with a fixed carbon content of 86 wt% and iron-based components (calculated as Fe2O3) in its ash content, with a mass content of 0.75 wt% and a particle size distribution of 2~4 mm.

[0036] Additional catalyst: Steel slag powder (derived from converter steel slag, obtained through crushing, magnetic separation for iron removal, and grinding), added at 5.5% of the weight of the carbon-rich matrix. The steel slag powder has a particle size of less than 150 μm, specifically 100 μm, and a specific surface area of ​​220 m². 2 / kg; its chemical composition by mass percentage is: CaO 42.5%, FeO+Fe2O3 22.5%, SiO2 15%, MgO 7.5%, MnO 2%.

[0037] b. Process Operation:

[0038] Hot, dust-laden exhaust gas is introduced into the inlet of the Venturi mixer at a flow rate of 18.5 m / s, where it undergoes high-speed shear mixing with oxygen-enriched air at the throat. The mixing residence time is maintained at 1.25 s in the post-mixing tube to obtain a uniformly distributed gas-solid suspension gasification agent flow.

[0039] The gasifying agent is introduced into the fluidized bed gasification reactor from the bottom, and the operating pressure is controlled at 0.3 MPaG. The temperature in the reactor reaction zone is stably controlled at 990℃ by adjusting the oxygen-enriched air intake. The apparent gas velocity in the fluidized bed is controlled at 1.65 m / s to keep the bed in a turbulent fluidized state.

[0040] This embodiment adopts a staged oxygen supply method: 75% of the oxygen-enriched air is introduced from the bottom of the fluidized bed, and the remaining 25% is introduced from the lower to middle height range of the fluidized bed, so as to maintain a reducing atmosphere at the reactor outlet.

[0041] The crude syngas produced in the reaction has an outlet temperature of approximately 930℃. After being cooled to 230℃ by a waste heat boiler, it is sent to a high-temperature bag filter for solid-gas separation and purification. The separated solid particles are returned to the fluidized bed reactor. The composition of the purified product gas is shown in Table 1.

[0042] c. Execution results:

[0043] Because all process parameters are in optimal equilibrium, the fluidization state and phase distribution are optimally matched. The volumetric space velocity (based on the volume of the carbon-rich matrix in the fluidized bed reactor) is 1300 h⁻¹. -1 The single-pass CO2 conversion rate reached 95.5%. The system operated stably for a long period of time, with no adhesion or blockage in the pipeline.

[0044] Product gas composition (dry basis)

[0045] Components CO <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[H2]]> Volume fraction / % 91.5 4.2 4.3 0.0

[0046] Table 1

[0047] Example 2

[0048] a. Raw materials and feeding conditions

[0049] Hot dust-laden exhaust gas: temperature 850℃; dry basis volume composition: CO2 95%, N2 5%; carrying calcium-containing dust concentration 40g / Nm³ 3 Median particle size d of dust 50The particle size is 50 μm, and this calcium-containing dust contains both CaO and CaCO3.

[0050] Auxiliary oxidant: Industrial oxygen with a purity of 99.6%.

[0051] Carbon-rich matrix: semi-coke is used, with a fixed carbon content of 82wt%, containing iron-based components calculated as Fe2O3, with a mass percentage of 1.2wt%, and a particle size distribution of 1-5mm.

[0052] Additional catalyst: The amount of steel slag powder added is 8% of the weight of the carbon-rich matrix. This steel slag powder has a particle size of less than 150 μm and a specific surface area of ​​210 m². 2 / kg. By mass percentage, this steel slag powder comprises: CaO 50%, FeO+Fe2O3 30%, SiO2 10%, MgO 5%, MnO 4%.

[0053] b. Process Operation

[0054] The exhaust gas velocity at the inlet of the Venturi mixer is controlled at 25 m / s, and the residence time in the Venturi post-mixing tube is controlled at 0.5 s. The operating pressure of the fluidized bed gasification reactor is controlled at 0.5 MPaG, the reaction temperature is controlled at 1100℃, and the apparent gas velocity is controlled at 2.5 m / s.

[0055] A staged oxygen supply method is adopted: 50% of the oxygen is introduced from the bottom of the reactor, and the remaining 50% is introduced from the lower to middle height range of the reactor.

[0056] The crude syngas generated by the reaction is first cooled to 220°C and then sent to a high-temperature bag filter for solid-gas separation and purification. The separated solid particles are then returned to the fluidized bed reactor.

[0057] c. Execution Results

[0058] Both the reaction flow rate and gas velocity were high, the gas phase residence time was short, and at extremely high temperatures, slight physical coking occurred on some dust surfaces, resulting in a slight reduction in the catalytic area. The volume hourly space velocity (based on the volume of the carbon-rich matrix in the fluidized bed reactor) was 2000 h⁻¹. -1 The composition of the product gas is shown in Table 2. The single-pass conversion rate of CO2 is 90.5%. The system operates stably, and no significant pipeline blockage has occurred.

[0059] Product gas composition (dry basis)

[0060] Components CO <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[H2]]> Volume fraction / % 85.2 8.1 6.7 0.0

[0061] Table 2

[0062] Example 3

[0063] a. Raw materials and feeding conditions:

[0064] Hot dust-laden exhaust gas: temperature 550℃; dry basis volume composition: CO2 70%, N2 30%; concentration of calcium-containing dust carried: 15g / Nm³ 3 This calcium-containing dust contains both CaO and CaCO3.

[0065] Assisted oxidant: Oxygen-enriched air containing 85% oxygen by volume.

[0066] Carbon-rich matrix: metallurgical coke with a fixed carbon content of 82 wt% and iron-based components (calculated as Fe2O3) of 0.3 wt% by mass, with a particle size distribution of 0.5–2 mm.

[0067] Additional catalyst: The amount of steel slag powder added is 3% of the weight of the carbon-rich matrix. The particle size of this steel slag powder is <150μm, and the specific surface area is 200 m². 2 / kg, the steel slag powder comprises, by mass percentage: CaO 35%, FeO+Fe2O3 15%, SiO2 20%, MgO 10%, MnO 0%.

[0068] b. Process Operation:

[0069] The exhaust gas velocity is controlled at 12 m / s, and the residence time in the mixing tube is controlled at 2.0 s.

[0070] Because the initial temperature of the exhaust gas was low, the electric heating and afterburning system was activated on the delivery pipeline to raise the temperature of the exhaust gas to 700°C.

[0071] The operating pressure of the gasification reactor was controlled at 0.1 MPaG, and the reaction temperature was controlled at 880℃. To compensate for the slowdown in chemical kinetics caused by the low temperature, the apparent gas velocity in the fluidized bed was reduced to 0.8 m / s to prolong the contact time. A single-stage bottom oxygen supply was used (100% of the oxygen was introduced from the bottom in a staged manner).

[0072] c. Execution results:

[0073] The volume hourly space velocity (based on the volume of the carbon-rich substrate in the fluidized bed reactor) was reduced to 800 h⁻¹. -1 The product gas composition is shown in Table 3. Due to the decrease in apparent gas velocity and the increase in reaction time, the single-pass conversion rate of CO2 can still reach 81.3% under the lower limit of process parameters.

[0074] Product gas composition (dry basis)

[0075] Components CO <![CDATA[CO2]]> <![CDATA[N2]]> <![CDATA[H2]]> Volume fraction / % 78.5 13.5 8.0 0.0

[0076] Table 3

[0077] Comparative Example 1

[0078] The process conditions in this comparative example are the same as in Example 1, except that: the introduced hot dust-laden exhaust gas was subjected to deep dust removal (removing more than 99% of the CaO dust), and the carbon-rich matrix selected in the fluidized bed is ultra-low ash high-purity coke (its iron-based component content as Fe2O3 is <0.1wt%).

[0079] Results: Under the same reaction conditions, the reaction rate decreased significantly due to the lack of in-situ multiphase synergistic catalysis of active CaO catalyst and low-valent iron components. The CO concentration in the product gas was only 62%, while the CO2 concentration was as high as 33%.

[0080] Comparative Example 2

[0081] The process conditions for this comparative example are the same as those for Example 1, except that the hot dust-laden exhaust gas discharged from the lime kiln is first cooled to 40°C by indirect water cooling and then subjected to wet deep dust removal and purification. The purified CO2 is then reheated to 990°C, the same as in Example 1, and sent into the gasification reactor.

[0082] Results: Due to the complete loss of the physical sensible heat of the exhaust gas, the consumption of auxiliary oxygen increased by 42% compared to Example 1 in order to maintain the same reaction temperature in the reactor. The energy consumption for the preparation of CO gas per unit was 36% higher. In addition, the traditional wet dust removal system experienced frequent pipe scaling and adhesion blockage.

[0083] Comparative Example 3

[0084] The process conditions for this comparative example are the same as those for Example 1, except that the steel slag powder is not added and the staged oxygen supply is not used (all the oxygen-enriched air is introduced into the bottom of the self-fluidized bed reactor at one time).

[0085] Results: Due to the lack of a high specific surface area composite catalytic phase provided by steel slag powder, and the absence of staged oxygen supply leading to partial secondary oxidation of carbon monoxide at the fluidized bed outlet, the final product gas contained only 70.8% CO by volume, and the single-pass CO2 conversion rate decreased to 72.2%. This comparative experiment demonstrates that steel slag powder and staged oxygen supply make irreplaceable technical contributions to improving the preparation efficiency and carbon monoxide purity of this invention.

[0086] The results show that:

[0087] (1) This invention directly utilizes the hot dusty tail gas discharged from the calcium carbonate calcination section without pre-cooling and pre-dust removal. This not only completely avoids the pipe and equipment blockage problem caused by CaO reverse carbonation in the traditional process, but also makes full use of the high temperature physical sensible heat of the tail gas to drive the Boudouard endothermic reaction, which significantly reduces external energy consumption.

[0088] (2) The hot dusty tail gas and high-purity oxygen-containing oxidant are rapidly and uniformly mixed by the Venturi mixer, and the bottom-up gas-solid contact method and staged oxygen supply strategy are adopted in the fluidized bed gasification reactor to effectively suppress local overheating and improve the gasification reaction efficiency and syngas quality.

[0089] (3) The calcium-containing dust carried by the exhaust gas itself, the added steel slag powder and the iron-based components inherent in the carbon-rich matrix constitute a multiphase synergistic catalytic system, which significantly improves the reaction rate and can achieve a high CO2 single-pass conversion rate under a wide operating window.

[0090] (4) Comparative examples 1 to 3 further verified that the in-situ retention of calcium-containing dust in the exhaust gas, the presence of natural iron-based components in the carbon-rich matrix, the addition of steel slag powder, and the graded oxygen supply method have a synergistic effect on improving the reaction rate and the purity of the product gas.

[0091] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing carbon monoxide from industrial calcium-containing tail gas, characterized in that, Includes the following steps: S1: The hot dust-laden exhaust gas discharged from the calcium carbonate calcination section is transported to the mixing zone through an insulated pipeline. The hot dust-laden exhaust gas carries calcium-containing dust. S2: The hot dust-laden exhaust gas and the oxygen-containing oxidant are introduced into the mixing zone for mixing to obtain a gas-solid suspended gasifying agent stream; S3: The gasifying agent is fed into the fluidized bed gasification reactor from bottom to top, and comes into contact with the carbon-rich matrix and added steel slag powder packed in the fluidized bed gasification reactor to carry out the gasification reaction. S4: Cool and purify the crude syngas generated by the reaction to obtain the product gas.

2. The method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, In step S1, the temperature of the hot dust-laden exhaust gas is 550~850℃, the volume fraction of CO2 is ≥70%, the calcium-containing dust includes CaO and CaCO3, and the hot dust-laden exhaust gas is directly sent into the mixing zone without pre-dust removal.

3. The method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, In step S2, the volume fraction of O2 in the oxygen-containing oxidant is ≥85%.

4. The method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, In step S2, the mixing zone is equipped with a Venturi mixer. The hot dust-laden exhaust gas and the oxygen-containing oxidant are mixed at the throat of the Venturi mixer and then mixed in the post-mixing tube, where the residence time is 0.5-2 seconds. At the inlet of the Venturi mixer, the flow velocity of the hot dust-laden exhaust gas is 12-25 m / s, and the concentration of calcium dust in the hot dust-laden exhaust gas is 15-40 g / Nm³. 3 .

5. The method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, In step S3, the temperature of the reaction zone of the fluidized bed gasification reactor is 880~1100℃, the operating pressure is 0.1−0.5MPaG, and the apparent gas velocity is 0.8−2.5m / s.

6. The method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, The carbon-rich matrix is ​​metallurgical coke and / or semi-coke, the fixed carbon content of the carbon-rich matrix is ​​≥82wt%, and the particle size is 0.5−5mm; and the carbon-rich matrix contains iron-based components calculated as Fe2O3, the mass percentage of the iron-based components is 0.3−1.2wt%.

7. The method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, In step S3, the amount of steel slag powder added is 3-8% of the weight of the carbon-rich matrix; The steel slag powder has a particle size of <150μm and a specific surface area of ​​≥200m². 2 / kg; the steel slag powder comprises, by mass percentage: 35-50% CaO, 15-30% FeO+Fe2O3, 10-20% SiO2, 5-10% MgO, and 0-4% MnO.

8. The method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, In step S3, the catalytic component of the gasification reactor is composed of CaO in the calcium-containing dust, CaO in the steel slag powder, and iron-based reduction products in the carbon-rich matrix and the steel slag powder.

9. The method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, The fluidized bed gasification reactor adopts a staged oxygen supply method: 50-100% of the oxygen-containing oxidant is fed from the bottom of the fluidized bed gasification reactor, and the remainder is introduced from the lower to middle height range of the fluidized bed gasification reactor.

10. A method for producing carbon monoxide from industrial calcium-containing tail gas according to claim 1, characterized in that, In step S1, when the temperature of the hot dust-laden exhaust gas is below 650°C, the temperature of the hot dust-laden exhaust gas is raised to 650-750°C by electric heating and / or supplementary combustion. In step S4, the crude syngas is cooled to 200-250°C and then sent to a high-temperature bag filter for purification. The solid particles separated by the dust removal and purification are returned to the fluidized bed gasification reactor.