A device suitable for ethylene cracking furnace flue gas SCR catalytic denitration reaction

Abstract

The utility model discloses a kind of be applicable to ethylene cracking furnace flue gas SCR catalytic denitration reaction device, including ammonia gas metering control system, ammonia air mixing system, dilute ammonia gas conveying system, AIG ammonia injection grid, SCR reaction system, ammonia air mixing system is communicated in furnace by bypass flue, AIG ammonia injection grid and SCR reaction system are sequentially arranged from below to top in flue gas flow direction in furnace, AIG ammonia injection grid is connected dilute ammonia gas conveying system by ammonia injection grid feed pipe, dilute ammonia gas conveying system is connected ammonia air mixing system by pipeline, ammonia air mixing system is connected ammonia gas metering control system by pipeline.The utility model uses small volume, low density corrugated plate type catalyst, space is extremely small, and need not change cracking furnace original design, even if cracking furnace does not reserve denitration space still can be installed.The utility model can contact with catalyst surface in ascending process, catalytic reaction is complete, rapid, without other pollution product generation, and ammonia escape is lower.

Description

Technical Field

[0001] This utility model relates to the field of flue gas denitrification technology, and in particular to an SCR catalytic denitrification reaction device suitable for flue gas from an ethylene cracking furnace. Background Technology

[0002] Ethylene cracking furnaces are the core equipment of ethylene plants. With the rapid development of ethylene cracking furnaces and the continuous increase in their total capacity, the emission of nitrogen oxides (NOx) from ethylene cracking furnace flue gas has gradually attracted attention. NOx is one of the most harmful and difficult-to-treat air pollutants, and major ethylene companies worldwide attach great importance to NOx emissions from cracking furnaces. The main NOx removal processes for ethylene cracking furnaces generally adopt low-NOx burner technology. However, with increasingly stringent environmental protection requirements, this technology can no longer meet current needs, and it is necessary to consider achieving even lower NOx emission standards in cracking furnace flue gas.

[0003] In response to this situation, current research both domestically and internationally mainly focuses on low-temperature denitrification processes for flue gas at the tail end of pyrolysis furnaces, resulting in various SCR catalytic denitrification reaction devices for ethylene pyrolysis furnace flue gas. Existing structured denitrification catalysts employ a honeycomb structure, where flue gas rises through straight channels formed by the denitrification catalyst and contacts the catalyst surface. Due to the high flow velocity of the flue gas through these channels, a large catalyst volume is required. Furthermore, many pyrolysis furnaces lack pre-reserved space for denitrification, making it impossible to install large-volume catalysts. Modifying the original design of the pyrolysis furnace inevitably leads to adverse effects on the denitrification device, resulting in high costs for flue gas denitrification retrofitting. How to effectively remove NOx from ethylene pyrolysis furnace flue gas with low cost and minimal impact remains a significant technical challenge. Utility Model Content

[0004] To solve the above-mentioned technical problems, this utility model designs an SCR catalytic denitrification reaction device suitable for flue gas from ethylene cracking furnaces.

[0005] The present invention adopts the following technical solution:

[0006] A catalytic denitrification (SCR) reactor for ethylene cracking furnace flue gas includes an ammonia metering and control system, an ammonia-air mixing system, a dilute ammonia conveying system, an AIG ammonia injection grid, and an SCR reaction system. The ammonia-air mixing system is connected to the furnace via a bypass flue. The AIG ammonia injection grid and the SCR reaction system are arranged sequentially from bottom to top in the flue gas flow direction within the furnace. The AIG ammonia injection grid is connected to the dilute ammonia conveying system via an ammonia injection grid feed pipe. The dilute ammonia conveying system is connected to the ammonia-air mixing system via a pipeline. The ammonia-air mixing system is connected to the ammonia metering and control system via a pipeline.

[0007] Preferably, the ammonia injection grid is made of 304SS material.

[0008] Preferably, the ammonia injection grid feed pipe is arranged to correspond to the position of the steel structure in the convection section inside the furnace.

[0009] Preferably, an ammonia regulating valve is provided at the outlet end of the ammonia injection grid feed pipe.

[0010] Preferably, the SCR reaction system includes an SCR catalyst module with a rectangular cross-section, in which denitrification catalyst layers are arranged, and the catalyst layers are supported by support beams.

[0011] Preferably, the catalyst in the SCR catalyst module is a corrugated catalyst, with high-temperature resistant inorganic fiber as the substrate and a highly active catalyst coating on the surface.

[0012] This invention controls the specific parameters of the ammonia-air mixing system through an ammonia metering and control system. A certain concentration of ammonia (or ammonia water), dilution air, and high-temperature flue gas from the pyrolysis furnace bypass are thoroughly mixed and diluted to the corresponding safe concentration in the air-ammonia mixer. Then, the mixture is transported to the AIG ammonia injection grid area via a dilute ammonia gas delivery system. The ammonia-air mixture is then injected into the flue gas upstream of the SCR reaction system by the ammonia injection grid nozzles, further mixing it into flue gas containing a certain concentration of NH3. Finally, the mixed flue gas flows downstream through the SCR reactor. Under the action of a catalyst, the reducing agent NH3 reacts with NOx in the flue gas to produce N2 and water, thereby removing NOx from the flue gas and ensuring that the NOx emissions from the final pyrolysis furnace flue gas meet the standards.

[0013] The beneficial effects of this invention are as follows: This invention uses a small-volume, low-density corrugated plate catalyst, which occupies very little space and does not require changes to the original design of the pyrolysis furnace. It can still be installed even if the pyrolysis furnace does not have reserved space for denitrification. The arrangement of this invention allows the flue gas to come into contact with the catalyst surface during its ascent through the straight channel formed by the catalyst, resulting in a complete and rapid catalytic reaction with no other polluting products generated and low ammonia slip. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the structure of this utility model;

[0015] In the diagram: 1. Ammonia metering and control system; 2. Ammonia-air mixing system; 3. Dilute ammonia conveying system; 4. AIG ammonia injection grid; 5. SCR reaction system. Detailed Implementation

[0016] The technical solution of this utility model will be further described in detail below through specific embodiments and with reference to the accompanying drawings:

[0017] Example: Figure 1As shown, an SCR catalytic denitrification reactor for ethylene cracking furnace flue gas includes an ammonia metering and control system 1, an ammonia-air mixing system 2, a dilute ammonia conveying system 3, an AIG ammonia injection grid 4, and an SCR reaction system 5. Ammonia (0.35 MPa, 50°C) and dilution air (0.6 MPa, AMB) are supplied outside the boundary area. The ammonia-air mixing system, controlled by the ammonia metering and control system, thoroughly mixes ammonia or ammonia-containing air with the high-temperature flue gas from the cracking furnace bypass. The mixture is diluted to a safe concentration below 5% in the air-ammonia mixer, and then transported to the AIG ammonia injection grid area via the dilute ammonia conveying system. The ammonia-air mixture is then injected into the flue gas upstream of the SCR reaction system through the injection grid nozzles, further mixing it into flue gas containing a certain concentration of NH3. Finally, the mixed flue gas flows downstream through the SCR reactor, where, under the action of a catalyst, it undergoes a reduction reaction with NOx in the flue gas to generate N2 and water, thereby removing NOx from the flue gas and ensuring that the final NOx emission from the cracking furnace flue gas meets the standards.

[0018] The ammonia injection grid in this reactor is located between convection section modules BFW-1 and BFW-2. Its main function is to thoroughly mix ammonia or ammonia-containing air with the high-temperature flue gas. This mixing is a crucial step in the selective catalytic reduction (SCR) denitrification process, directly affecting the concentration distribution of nitrogen oxides (NOx) and ammonia slip at the denitrification reactor outlet, thus impacting the overall denitrification efficiency and preventing clogging of downstream equipment. The ammonia injection grid is made of 304SS. The arrangement of the ammonia injection grid feed pipe takes into full account the position of the steel structure in the convection section. The ammonia flow rate is controlled in real time by adjusting the opening of the ammonia regulating valve based on the NOx emission concentration at the cracking furnace outlet, ensuring a complete reaction between the ammonia injected from the grid and the NOx in the flue gas.

[0019] The SCR catalyst module of this reactor is arranged in the flue gas duct of the cracking furnace. It has a rectangular cross-section and contains denitrification catalyst modules. Flue gas flows in from the bottom of the reactor and passes vertically through the catalyst layer, which is supported by support beams. The encapsulation material of the catalyst module can meet various flue gas temperature conditions, and the catalyst design meets the installation space requirements and pressure drop loss requirements of the ethylene cracking furnace. According to the information on the ethylene cracking furnace, the catalyst module support and ammonia injection grid support should be designed to withstand a flue gas temperature of up to 450℃. The catalyst layer is supported by support beams and arranged between two sets of heat exchange tube bundles corresponding to the SCR denitrification reactor temperature. The catalyst module support and ammonia injection grid support are designed to withstand a flue gas temperature of up to 450℃. The SCR catalyst module mainly consists of reactor wall panels and reinforcing ribs, catalyst support beams, catalyst installation doors and rails, manhole doors, and catalyst modules.

[0020] The catalyst in this reactor is a corrugated catalyst, based on high-temperature resistant inorganic fibers and coated with a highly active catalyst coating. It is lightweight, highly efficient, and has strong thermal shock resistance, capable of withstanding temperature shocks of up to 150℃ / min. Its bulk density is 60% that of honeycomb catalysts, significantly reducing weight and reactor load. The catalyst is housed in a modular design, encapsulated in a stainless steel shell, providing sufficient rigidity to ensure stability during handling and commissioning.

[0021] Compared to traditional SCR catalytic denitrification reactors for ethylene cracking furnace flue gas, this invention utilizes a small-volume, low-density corrugated plate catalyst, which can be installed even if the cracking furnace lacks dedicated space for denitrification. As the flue gas flows through the catalyst-constructed straight channel, it comes into contact with the catalyst surface during its ascent, resulting in a complete and rapid catalytic reaction with no other polluting products and low ammonia slip. This invention's reactor requires no alteration to the original cracking furnace design, effectively removing NOx from the ethylene cracking furnace flue gas with minimal impact on furnace operation. It significantly reduces the cost of denitrification retrofitting for ethylene cracking furnaces, and the retrofit does not occupy excessive furnace space, allowing for substantial future modifications. Its denitrification effect not only meets current emission standards but also provides room for future upgrades to more stringent standards.

[0022] The embodiments described above are merely preferred solutions of this utility model and are not intended to limit this utility model in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A SCR catalytic denitrification reactor for ethylene cracking furnace flue gas, characterized in that, It includes an ammonia metering and control system, an ammonia-air mixing system, a dilute ammonia conveying system, an AIG ammonia injection grid, and an SCR reaction system. The ammonia-air mixing system is connected to the furnace through a bypass flue. The AIG ammonia injection grid and the SCR reaction system are arranged sequentially from bottom to top in the flue gas flow direction inside the furnace. The AIG ammonia injection grid is connected to the dilute ammonia conveying system through an ammonia injection grid feed pipe. The dilute ammonia conveying system is connected to the ammonia-air mixing system through a pipeline. The ammonia-air mixing system is connected to the ammonia metering and control system through a pipeline.

2. The SCR catalytic denitrification reactor for ethylene cracking furnace flue gas according to claim 1, characterized in that, The ammonia injection grille is made of 304SS.

3. The SCR catalytic denitrification reactor for ethylene cracking furnace flue gas according to claim 1, characterized in that, The arrangement of the ammonia injection grid feed pipe corresponds to the position of the steel structure in the convection section inside the furnace.

4. The SCR catalytic denitrification reactor for ethylene cracking furnace flue gas according to claim 1, characterized in that, An ammonia regulating valve is installed at the outlet end of the ammonia injection grid feed pipe.

5. The SCR catalytic denitrification reactor for ethylene cracking furnace flue gas according to claim 1, characterized in that, The SCR reaction system includes an SCR catalyst module with a rectangular cross-section, inside which are arranged layers of denitrification catalyst, which are supported by support beams.

6. The SCR catalytic denitrification reactor for ethylene cracking furnace flue gas according to claim 5, characterized in that, The catalyst in the SCR catalyst module is a corrugated catalyst, with high-temperature resistant inorganic fiber as the substrate and a highly active catalyst coating on the surface.

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