A composite catalytic thermal reactor suitable for RDF with low ash melting point and a segmented oxygen supply steam gasification method thereof

Abstract

The present application relates to the technical field of solid waste thermochemical conversion, and discloses a composite catalytic thermal reactor suitable for RDF with low ash melting point and a segmented oxygen supply steam gasification method thereof. The reactor comprises a lower chain grate or reciprocating grate moving bed reaction zone, an ascending reaction chamber located above the moving bed reaction zone, a catalyst particle fluidized catalytic layer located at the upper part of the middle and rear section of the hearth, a bottom oxygen steam distribution system, and a high-temperature cyclone fly ash return unit. The upper catalyst particle fluidized catalytic layer is not provided with an independent oxygen steam direct injection branch, and the fluidization power comes from the high-temperature raw synthesis gas generated by the lower moving bed reaction zone; the high-temperature cyclone separated particles are returned to the upper reaction area of the moving bed. With the structure, the main high-temperature cracking and tar conversion area can be moved upward, the risk of grate slagging and sticking can be reduced, and the tar can be reduced, the carbon conversion rate can be improved, and the quality of the raw synthesis gas can be stabilized.

Description

[0001] This invention belongs to the technical field of solid waste resource utilization and thermochemical conversion equipment, specifically relating to a composite catalytic thermal reactor suitable for low ash melting point RDF fuel and its segmented oxygen supply steam gasification method.

[0002] Solid alternative fuels such as RDF typically exhibit characteristics such as large compositional fluctuations, low ash melting points, a pronounced tendency to form tar, and high levels of dust and chlorine impurities. Existing gasification devices for this type of fuel mostly employ fixed-bed, single-fluidized-bed, or structures where the high-temperature oxidation zone is directly arranged on the grate surface.

[0003] The aforementioned existing technologies, when processing low-ash-melting-point RDF, are prone to problems such as localized overheating of the grate surface, ash adhesion and agglomeration, slag discharge blockage, high tar content, and insufficient operational flexibility. Furthermore, in systems that need to balance subsequent purification, power generation and gas supply, and comprehensive steam utilization, they also commonly suffer from drawbacks such as inefficient oxygen and steam distribution, insufficient fluidization stability in the upper reaction zone, and ineffective recovery and utilization of high-temperature particulate heat.

[0004] Therefore, it is necessary to provide a new composite catalytic thermal reactor and its gasification method to simultaneously suppress slagging and jamming, reduce tar, improve carbon conversion rate, and stabilize the quality of crude syngas at the outlet under low ash melting point RDF conditions.

[0005] To address the aforementioned technical problems, this invention provides a composite catalytic thermal reactor and its segmented oxygen supply steam gasification method. The reactor employs a structure combining a lower chain grate or reciprocating grate moving bed reaction zone with an upper fluidized catalyst particle catalytic layer, and achieves coupled operation through segmented oxygen steam supply from the bottom and high-temperature particle return from the outlet.

[0006] According to one aspect of the invention, the reactor includes a furnace body, a moving bed reaction zone disposed at the lower part of the furnace body, an ascending reaction chamber located above the moving bed reaction zone, a catalyst particle fluidized catalytic layer located in the upper part of the middle and rear section of the furnace, a bottom oxygen steam distribution system connected to a segmented wind box, and a high-temperature cyclone ash return unit connected to the furnace body outlet; the catalyst particle fluidized catalytic layer does not have an independent oxygen steam direct injection branch, and its fluidization power comes from the high-temperature crude syngas generated in the lower moving bed reaction zone.

[0007] According to another aspect of the present invention, a method for RDF gasification using the above-mentioned composite catalytic thermal reactor is provided. By implementing segmented oxygen steam supply to the lower moving bed reaction zone, high-temperature crude syngas enters the upper catalyst particle fluidized catalytic layer to complete tar cracking and secondary gasification, and high-temperature cyclone-separated particles are returned to the upper part of the moving bed to achieve continuous and stable gasification.

[0008] Compared with the prior art, the present invention has at least the following beneficial effects: Moving the main high-temperature pyrolysis zone upwards to the fluidized catalyst layer can significantly reduce the risk of high-temperature residence and slag adhesion on the grate surface.

[0009] The upper catalyst particle layer does not have an independent oxygen vapor direct injection branch. Instead, it uses the high-temperature crude syngas generated in the lower bed as the main fluidization force, which can reduce local over-oxidation in the upper part, simplify the upper piping, and stabilize the tar cracking zone.

[0010] Independent oxygen supply to each section is achieved by using a bottom loop pipe and a short-range mixing manifold, which facilitates fine-tuning according to the bed condition.

[0011] By directing the hot ash back to the top of sections B and C through a high-temperature cyclone, the waste heat of the hot ash can be utilized, fine particles can be remixed, and local reaction can be enhanced.

[0012] The three-level control strategy, which includes fuel quantity feedforward, segmented bed temperature feedback, and outlet gas quality correction, can adapt to RDF composition fluctuations and maintain the stability of the outlet crude syngas boundary.

[0013] Figure 1 This is a schematic diagram of the overall structure of the composite catalytic thermal reactor of the present invention.

[0014] Figure 2 This is a cross-sectional schematic diagram of the lower moving bed reaction zone and the upper catalyst particle fluidized catalytic layer of the present invention.

[0015] Figure 3 This is a schematic diagram of the bottom oxygen vapor distribution system of the present invention.

[0016] Figure 4 This is a schematic diagram of the structure of the air distribution component at the bottom of the fluidized catalyst layer of the present invention.

[0017] Figure 5 This is a schematic diagram of the high-temperature cyclone ash return unit and the return path of the present invention.

[0018] Figure 6 This is a schematic diagram of the three-level control structure of the present invention.

[0019] The present invention will be further described below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the following embodiments.

[0020] In some embodiments, a single catalytic thermal reactor can be configured with an RDF processing capacity on the order of approximately 2500 kg / h. A moving bed reaction zone formed by a chain grate or reciprocating grate is located at the bottom of the furnace. Multiple independent wind boxes, preferably four, are arranged below the grate, corresponding to the drying and preheating zone, the pyrolysis ignition zone, the main oxidation and gasification zone, and the reduction and burnout zone, respectively. A refractory-lined rising reaction chamber is located above the grate, and a fluidized bed of catalyst particles is arranged in the upper part of the middle and rear section of the furnace.

[0021] In a preferred embodiment, the effective width and effective length of the moving bed reaction zone can be determined according to the throughput, residence time, and furnace flow field requirements. For example, a structural dimension of approximately 3.00 m in width and approximately 6.00 m in length can be adopted. The catalyst particles can be selected from particulate materials suitable for tar cracking and secondary gasification, with a particle size of, for example, 1.5 to 3.0 mm, and a stationary bed thickness of, for example, 250 to 300 mm. The above dimensions and parameters are used to illustrate preferred embodiments that can be achieved by the present invention and do not constitute a limitation on the scope of protection.

[0022] When a chain grate is used in the lower moving bed reaction zone, the fuel can be continuously propelled along the grate's running direction; when a reciprocating grate is used in the lower moving bed reaction zone, the fuel can be stratified, propelled, and its reaction residence time adjusted during the alternating reciprocating pushing process. Both grate types can work in conjunction with the segmented wind box, the upper catalyst particle fluidized bed, and the high-temperature cyclone ash return system.

[0023] Oxygen and steam are introduced laterally from the lower part of the furnace body into the bottom annular main pipe, and then fed into the respective short-path mixing manifolds before entering the nozzle system. Each reaction section performs different functions: the front section is mainly used for preheating and initial pyrolysis, the middle section is mainly used for oxidation and steam vaporization, and the rear section is mainly used for reduction, burnout, and synergistically with the upper catalyst particle layer to complete tar polishing and cracking. The nozzle outlet velocity, number of nozzles, and arrangement can be adjusted according to bed resistance, target penetration depth, and local agitation requirements.

[0024] The upper catalyst granular fluidized bed does not have a separate oxygen steam direct injection branch. Instead, the high-temperature crude syngas generated in the lower bed is accelerated by the constriction and air distribution components to serve as the fluidization power. Since the main high-temperature pyrolysis zone is located in the upper catalyst granular bed, the metal surface of the grate is prevented from being in a high-temperature oxidation state for a long time, thereby reducing the risk of slagging and jamming.

[0025] A high-temperature cyclone separator can be installed at the furnace outlet. The separated high-temperature particles can be returned to the return port at the top of the moving bed reaction zone via an airlock device and a conveying device, preferably to the area above the middle reaction section, so that the high-temperature particles can come into contact with the fresh RDF and catalyst particle layer again, thereby improving heat utilization efficiency and the degree of secondary reaction. The bottom slag can be continuously discharged to the water seal device via a chain grate or reciprocating grate, and then discharged externally via a wet conveying device.

[0026] The control system preferably adopts a three-level control strategy of fuel quantity feedforward, segmented bed temperature feedback, and outlet gas quality correction. First, the feed rate can be used as the feedforward reference for total oxygen and total steam. Second, the oxygen and steam branches of each section are dynamically adjusted according to the bed temperature, catalyst particle temperature, and wind box temperature. Finally, the upstream distribution strategy is corrected according to the outlet tar, crude syngas composition, and system pressure to maintain low tar and stable gas quality.

[0027] In one exemplary embodiment, the total oxygen flow rate, total steam flow rate, and the oxygen-steam distribution ratio in each section can be set according to fuel properties, throughput, and target gas composition. For example, by increasing the oxidation and steam gasification load in the middle reaction section, the main high-temperature zone can be concentrated in the upper catalyst particle fluidized bed, thereby suppressing the grate surface temperature and reducing the outlet tar content. These operating parameters are adjustable process conditions in the implementation of this invention, and are not necessary limitations on the scope of protection.

Claims

1. Claim 1. A composite catalytic thermal reactor, characterized in that, The furnace includes a furnace body, a moving bed reaction zone consisting of a chain grate or reciprocating grate located at the bottom of the furnace body, an ascending reaction chamber located above the moving bed reaction zone, a catalyst particle fluidized bed catalytic layer located in the upper part of the middle and rear section of the furnace and connected to the ascending reaction chamber, a bottom oxygen steam distribution system connected to the segmented wind box of the moving bed reaction zone, and a high-temperature cyclone ash return unit connected to the furnace body outlet; the return port of the high-temperature cyclone ash return unit is located in the upper part of the moving bed reaction zone; the catalyst particle fluidized bed catalytic layer does not have an independent oxygen steam direct injection branch, and its fluidization power comes from the high-temperature crude syngas generated in the moving bed reaction zone and entering the catalyst particle fluidized bed catalytic layer upward.

2. The composite catalytic thermal reactor according to claim 1, characterized in that, The lower moving bed reaction zone adopts a chain grate structure.

3. The composite catalytic thermal reactor according to claim 1, characterized in that, The lower moving bed reaction zone adopts a reciprocating grate structure.

4. The composite catalytic thermal reactor according to any one of claims 1 to 3, characterized in that, The lower chain grate or reciprocating grate moving bed reaction zone is supported by at least four independent air boxes, each corresponding to the drying and preheating section, the pyrolysis ignition section, the main oxidation and main gasification section, and the reduction and burnout section.

5. The composite catalytic thermal reactor according to any one of claims 1 to 4, characterized in that, The bottom oxygen and steam distribution system includes an oxygen branch, a steam branch, a bottom annular main pipe, and a short-range mixing manifold connected to each section of the air box, all located at the lateral inlet of the lower part of the furnace body. The oxygen and steam are not premixed in the long-distance main pipe, but are mixed in the short-range mixing section near the nozzle before entering the bed.

6. The composite catalytic thermal reactor according to any one of claims 1 to 5, characterized in that, The high-temperature crude syngas is accelerated by the constriction and air distribution components before entering the fluidized catalytic layer of catalyst particles.

7. The composite catalytic thermal reactor according to any one of claims 1 to 6, characterized in that, The catalyst particle fluidized bed is arranged above the middle and rear section of the grate, covering the upper areas corresponding to zones B, C and D. The catalyst particle size is 1.5 to 3.0 mm, and the static bed thickness is 250 to 300 mm.

8. The composite catalytic thermal reactor according to any one of claims 1 to 7, characterized in that, The high-temperature particles separated by the outlet high-temperature cyclone ash return unit are returned to the return port in the area above the junction of section B and section C via a lock valve and a screw conveyor, so that the ash can fully contact the preheated fuel and the fluidized catalyst layer of catalyst particles.

9. The composite catalytic thermal reactor according to any one of claims 1 to 8, characterized in that, The bottom slag is continuously discharged to the overall water seal pool via a chain grate or reciprocating grate, and then continuously discharged externally via a wet screw conveyor.

10. The composite catalytic thermal reactor according to any one of claims 1 to 9, characterized in that, The reactor is equipped with segmented bed temperature measuring points, catalyst particle layer temperature measuring points, windbox temperature measuring points, and outlet gas quality analysis measuring points, forming a three-level control structure of fuel quantity feedforward, segmented bed temperature feedback, and outlet gas quality correction.

11. A method for RDF gasification using the composite catalytic thermal reactor according to any one of claims 1 to 10, characterized in that, The process includes the following steps: continuously feeding RDF fuel into the lower chain grate or reciprocating grate moving bed reaction zone; supplying oxygen and steam to each section of the wind box in stages, so that the fuel completes drying, pyrolysis, partial oxidation and reduction reactions in the lower moving bed reaction zone; and allowing the high-temperature crude syngas generated in the moving bed reaction zone to enter the upper catalyst particle fluidized catalytic layer, so as to complete tar cracking and secondary gasification in the catalyst particle fluidized catalytic layer. The high-temperature particles separated by the high-temperature cyclone at the outlet are returned to the upper return port of the grate; the oxygen and steam distribution in each section is dynamically adjusted according to the bed temperature, outlet gas quality and fuel quantity.

12. The method according to claim 11, characterized in that, The distribution of oxygen and steam in each section adopts a total feedforward plus segmented proportional regulation method. Section A mainly undertakes preheating and initial pyrolysis, sections B and C undertake the main oxidation and steam gasification loads, and section D undertakes the reduction, burnout and tar polishing and cracking loads in coordination with the upper catalyst particle layer.

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