Fixed bed gasifier and method based on retorting gas internal circulation

Abstract

The invention provides a fixed bed gasifier and method based on retorting gas internal circulation, and belongs to the technical field of solid waste resource utilization. The gasification furnace comprises a furnace body, and a drying layer, a dry distillation layer, a gasification layer, a combustion layer and a slag pool are formed in the furnace body from top to bottom. The improvement lies in that a retorting gas collecting and gas back-spraying system is arranged. After being collected and preheated in the junction area, the retorting gas is re-sprayed into the high-temperature area in the furnace through the back-spraying nozzles distributed at the lower part. The gas sprayed back to the gasification layer is cracked and reformed to generate hydrogen-rich synthesis gas; and the gas sprayed back to the combustion layer combusts to supplement heat for the process. And in-situ removal of tar is realized. And the lower part of the furnace body adopts a conical furnace bottom structure, so that residual carbon combustion and slag discharge are facilitated. The invention fundamentally solves the tar problem of the fixed bed gasifier, has the advantages of high carbon conversion rate, stable operation, wide raw material adaptability, good economical efficiency and the like, and is especially suitable for gasification treatment of high volatile materials such as municipal solid waste, mixed materials of garden waste and sludge and the like.

Description

Technical Field

[0001] This invention belongs to the field of solid waste resource utilization and renewable energy manufacturing technology, specifically relating to an apparatus and process for producing hydrogen-rich syngas using high-volatile materials as raw materials and a gasification process. It is particularly suitable for the efficient conversion of high-volatile materials such as municipal solid waste, garden waste, sludge, and agricultural waste into syngas containing CO and H2, using a gasifier and gasification method. Background Technology

[0002] Currently, there are numerous technical problems in the resource utilization process of materials such as waste and biomass. For example, waste incineration power generation results in significant energy waste and low resource utilization efficiency. Incineration only recovers heat energy, while a large amount of gas resources are wasted and carbon emissions are generated.

[0003] Fixed-bed gasifiers are simple in structure and have low investment costs. However, when processing materials with high volatile content and complex composition (such as municipal solid waste), a large amount of tar and vapor generated in the pyrolysis layer is carried out with the syngas, easily clogging and contaminating downstream pipelines and equipment. To solve this problem, existing technologies typically require complex tar purification, cracking, or scrubbing systems to be installed outside the gasifier. This not only increases system investment and operating costs but also reduces overall energy efficiency.

[0004] While fluidized bed gasification technology can effectively reduce tar, it presents challenges related to raw material pretreatment and energy consumption. Fluidized bed gasification requires materials to be pretreated to micron-level powder or slurry, which results in extremely high energy consumption and costs for complex municipal solid waste. Furthermore, its operating temperature, exceeding 1300℃, also leads to high energy consumption and stringent requirements for refractory materials.

[0005] Circulating fluidized bed gasifiers are widely used, but they have stringent requirements for material uniformity and operational stability, making them difficult to adapt to the drastic fluctuations in the composition and calorific value of municipal solid waste. The large amount of tar in the furnace is also a significant problem affecting the normal production of circulating fluidized beds. Furthermore, the carbon conversion rate is usually low, and the fly ash has a high carbon content.

[0006] Therefore, there is an urgent need for a new type of gasifier and method that can solve the tar problem in situ from within the gasification process, improve carbon conversion rate, and enhance system economy. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a fixed-bed gasifier and method that can realize internal circulation of distillation gas, thereby achieving in-situ efficient removal of tar, high carbon conversion rate, stable operation and wide adaptability of raw materials.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A fixed-bed gasifier based on internal circulation of pyrolysis gas includes a furnace body, wherein a drying layer, a pyrolysis layer, a gasification layer, a combustion layer, and a slag pool are formed sequentially from top to bottom within the furnace body. The gasifier is characterized by further comprising: a pyrolysis gas collector, which is a separation system composed of multiple sleeves, disposed within the drying layer and the pyrolysis layer, for separating the syngas generated in the gasification layer from the steam and pyrolysis mixed gas generated in the drying and pyrolysis layers, respectively collecting and exporting the mixed gas rich in steam, volatiles, and tar, and the syngas generated in the gasification layer; a gas return injection system, the inlet of which is connected to the outlet of the pyrolysis gas collection and export system via a pipeline; the gas return injection system includes a preheating device, a gas conveying device, and at least one return injection nozzle disposed at the lower part of the gasifier; the preheating device is used to preheat the collected gas to above the tar condensation temperature and below the pyrolysis temperature; and a conical furnace bottom, wherein the lower part of the furnace body forms a conical structure with a gradually decreasing cross-sectional area from top to bottom. Preferably, there are multiple return spray nozzles, distributed at different heights in the lower part of the gasification layer and the combustion layer, forming a multi-layer return spray structure. Preferably, the preheating device is a heat exchanger, and its heat source can be selected from high-temperature syngas drawn from the syngas outlet of the gasifier, an external heat source, or a combination of both. Preferably, the gas conveying device is a high-temperature resistant fan. Preferably, the cone angle of the conical furnace bottom is 35° to 60°.

[0009] A gasification method based on the above-mentioned gasifier is characterized by the following steps: Pre-treated high-volatile feedstock is added from the top of the furnace; the feedstock sequentially undergoes drying, pyrolysis, gasification, and combustion-melting processes within the furnace; steam and a mixed gas rich in volatiles and tar are collected in the area from the drying layer to the boundary between the pyrolysis layer and the gasification layer; the collected mixed gas is preheated to 350°C~600°C; the preheated gas is injected back through a return nozzle into the lower part of the gasifier where the temperature is above 1000°C; the gas injected back into the oxygen-deficient zone at the bottom of the gasification layer undergoes cracking and reforming reactions to generate syngas mainly composed of H2 and CO; the gas injected back into the oxygen-rich zone of the combustion layer undergoes combustion reactions to supplement heat for the melting and gasification processes; the temperature of each bed is stably controlled by adjusting the gas flow rate distributed to return nozzles at different heights; the final syngas is discharged from the syngas outlet at the top of the gasification layer. The ash from the material passes through the combustion layer to form a molten liquid ash slag containing solid substances such as heavy metals. The ash slag is eventually discharged from the furnace through the slag outlet at the bottom of the gasifier and condenses to form a glassy solid substance.

[0010] The gasifier processes high-volatile materials such as mixtures of municipal solid waste, garden waste, and sludge. Industrial parameters such as calorific value, moisture content, volatile matter, fixed carbon, and ash content are adjusted by modifying and proportioning different materials. Based on the adjusted material composition, the gasifier's operating parameters are determined to maintain its heat balance and the necessary conditions for the gasification reaction, thereby ensuring stable operation.

[0011] Compared with existing technologies, the beneficial effects of this invention are as follows: Highly efficient in-situ tar removal: By directly introducing the dry distillation gas into the highest temperature zone of the furnace for cracking and reforming, the tar problem is fundamentally solved from within the reactor, resulting in extremely low tar content in the outlet gas and eliminating or significantly simplifying the external purification system. High carbon conversion rate and energy efficiency: Tar and hydrocarbons in the dry distillation gas are converted into effective syngas (H2 and CO), allowing for the recycling of energy and materials; the conical furnace bottom structure ensures complete combustion of residual carbon, with a slag residual carbon rate of less than 1%. Stable operation and strong raw material adaptability: Through a multi-level back-spray system, the furnace temperature field and reaction process can be flexibly adjusted, effectively addressing fluctuations in operating conditions caused by different raw materials. Significant environmental benefits: The slag forms a glassy inert substance, effectively solidifying heavy metals and other harmful substances; the high-temperature environment inhibits the generation of harmful gases such as dioxins from the source. Good economic efficiency: The equipment structure is relatively simple, the system integration is high, and the investment and operating costs are significantly lower than gasification technologies that require complex external purification systems. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the gasification furnace of the present invention.

[0013] Figure 2 This is a schematic diagram of the gasifier structure of the present invention.

[0014] (In the diagram: 1. Furnace body; 2. Drying layer; 3. Drying layer; 4. Gasification layer; 5. Combustion layer; 6. Raw material inlet; 7. Drying gas duct; 8. Drying gas collector; 9. Syngas outlet; 10. Return spray nozzle; 11. Gasifying agent nozzle; 12. Slag inlet; 13. Heat exchanger; 14. High-temperature fan; 15. Slag pool; 16. Insulation layer.) Detailed Implementation

[0015] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0016] The lower part of the gasifier furnace body 1 of the present invention adopts a conical furnace bottom structure with a cone angle of 43°. Raw materials (such as pretreated municipal solid waste) are added from the top raw material inlet (6), slowly moving downwards within the furnace, sequentially passing through the drying layer (2) (~200°C), the pyrolysis layer (3) (~600°C), and the gasification layer (4) (~800°C), finally burning and melting in the combustion layer (5) (~1300°C) and the slag pool (15). The resulting liquid slag is periodically discharged from the slag outlet (12). An annular pyrolysis gas collector (8) is provided at the junction of the bottom of the pyrolysis layer (3) and the top of the gasification layer (4) to efficiently collect gases rich in H2, CH4, CO, and tar vapor in this area. The gas is led out through the pyrolysis gas conduit (7). (Refer to...) Figure 2 Gas (approximately 500°C) drawn from the pyrolysis gas duct (7) is introduced into a heat exchanger (13). A portion of the high-temperature syngas (approximately 800°C) drawn from the syngas outlet (9) is used as a heat source to indirectly heat the gas, raising its temperature to 600°C. The preheated gas is pressurized by a high-temperature fan (14) and transported through pipelines to multiple return nozzles (10) evenly distributed in the lower part of the furnace body. A portion of the return nozzles (10) are located below the gasification layer (4), injecting this portion of high-temperature pyrolysis gas into an oxygen-deficient environment at approximately 1000°C. The tar and long-chain hydrocarbons carried in the gas undergo violent cracking and reforming reactions here, ultimately transforming into small-molecule effective gases such as H2 and CO. Another portion of the return nozzles (10) are located in the middle of the combustion layer (5), injecting this portion of gas into an oxygen-rich region with a temperature higher than 1100°C. The combustible components in the gas burn instantaneously, releasing a large amount of heat to maintain the fluidity of the slag and provide a heat source for the upper gasification layer. The main syngas is discharged from the syngas outlet (9) located at the top of the gasification layer. The tar content in the outlet syngas is found to be less than 50 mg / Nm³, and the residual carbon after condensation of the liquid slag discharged from the slag outlet (12) is less than 1%.

Claims

1. A fixed bed gasifier based on internal circulation of dry distillation gas, comprising a furnace body (1), a drying layer (2), a dry distillation layer (3), a gasification layer (4), a combustion layer (5) and a molten slag pool (15) are formed in the furnace body (1) from top to bottom in sequence; characterized in that, The gasifier further comprises a dry distillation gas collector (8) arranged in the dry layer (2) and dry distillation layer (3) range, for separating the synthesis gas generated by the gasification layer (4) from the steam and dry distillation mixed gas generated by the dry layer (2) and dry distillation layer (3), and collecting and discharging the steam, volatile and tar-rich gas in this area and the synthesis gas generated by the gasification layer (4) respectively; a dry distillation gas back spraying system, the inlet of which is communicated with the gas outlet of the dry distillation gas collector (8); the gas back spraying system comprises a preheating device (13), a gas conveying device (14) and a back spraying nozzle (10) arranged at the lower part of the gasifier; the lower part of the furnace body (1) forms a conical structure with gradually reduced cross-sectional area from top to bottom. The conical bottom is internally provided with a partial gasification layer (4), a combustion layer (5) and a molten slag pool (15).

2. The gasifier of claim 1, wherein The back spraying nozzle (10) is multiple and arranged at different heights of the lower part of the gasification layer (4) and the combustion layer (5).

3. The gasifier of claim 1, wherein The preheating device (13) is a heat exchanger, and the heat source can be selected from the high-temperature synthesis gas led out from the synthesis gas outlet (9), an external heat source or a combination of the two.

4. The gasifier of claim 1, wherein The gas conveying device (14) is a high-temperature resistant fan.

5. The gasifier of claim 1, wherein The taper angle of the conical bottom is 35° to 70°.

6. A gasification method employing the gasifier according to any one of claims 1 to 5, characterized by, The method comprises the following steps: S1: feeding raw materials from the top of the furnace, so that they undergo drying, dry distillation, gasification and combustion melting in the furnace in sequence; S2: collecting steam and volatile and tar-rich gas in the junction area of the dry distillation layer (3) and the gasification layer (4); S3: preheating the gas collected in step S2 to 350°C~620°C; S4: back spraying the preheated gas to the lower part of the gasifier where the temperature is higher than 1000°C through the back spraying nozzle (10); S5: discharging synthesis gas from the synthesis gas outlet (9) at the upper part of the gasification layer.

7. The gasification method of claim 6, wherein, In step S4, the back sprayed gas is distributed and simultaneously sprayed into the oxygen-poor area of the lower part of the gasification layer (4) and the oxygen-rich area of the combustion layer (5).

8. The gasification method of claim 7, wherein, According to the temperature feedback of the dry layer (2), dry distillation layer (3), gasification layer (4) and combustion layer (5), the flow ratio of the gas distributed to the oxygen-poor area and the oxygen-rich area is automatically adjusted.

9. The gasification method of claim 6, wherein, The raw materials include one or more mixed materials of municipal solid waste, garden waste, sludge or agricultural waste and high-volatile materials such as biomass.

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