Sintering flue gas collaborative purification device capable of realizing low-cost and high-efficiency desulfurization in furnace

Abstract

The invention discloses a sintering flue gas collaborative purification device capable of realizing low-cost and high-efficiency desulfurization in a furnace. The low-cost and high-efficiency desulfurization in the furnace is realized. A front air chamber communicating pressure-equalizing pipeline (14) is communicated between the first front air chamber (10) and the second front air chamber (12), and a hot air pipe communicating pressure-equalizing pipeline (15) is communicated between the first hot air input pipe (11) and the second hot air input pipe (13); the structure of each front wall secondary air branch pipe (6) is completely the same as that of each rear wall secondary air branch pipe (7), a desulfurizing agent injection pipe (9) is arranged in each front wall secondary air branch pipe (6), and a CaCO3 desulfurizing agent is conveyed in each desulfurizing agent injection pipe (9); the inertial thought that SO2 should be converted into CaSO4 in an oxygen-rich hearth environment in traditional in-furnace dry desulfurization is changed, an oxygen-deficient reaction environment is created in a hearth, and SO2 is converted into CaS; the desulfurization cost is greatly reduced, and the in-furnace desulfurization efficiency is greatly improved.

Description

Technical Field

[0001] This invention relates to a sintering flue gas co-purification device, and more particularly to a sintering flue gas co-purification device that enables low-cost and high-efficiency dry desulfurization in the furnace. Background Technology

[0002] The ironmaking process in an ironworks involves first crushing iron ore into iron ore powder, then uniformly mixing it with coke, limestone powder, and other materials. This mixture is then sintered in a sintering machine to form hot briquettes, which are subsequently used in ironmaking. During the sintering process, a large amount of sintering flue gas is generated, containing CO, SO2, and NO. x The flue gas contains toxic and harmful gases such as HCl and dioxins. Current technologies treat these gases by adding environmental protection equipment, which suffers from high investment costs, high operating and maintenance costs, and limited effectiveness in eliminating harmful gases. To address these issues, a technology using circulating fluidized bed (CFB) boilers to treat sintering flue gas has emerged. This flue gas treatment system, centered on a CFB boiler, is also known as a multi-pollutant synergistic purification device for sintering flue gas. The main principle of this device is to use the sintering flue gas generated in the sintering machine to replace air as the combustion air for the CFB boiler. Leveraging the high-temperature environment within the CFB boiler furnace and its unique environmental advantages, harmful gases in the sintering flue gas are synergistically removed through combustion decomposition, desulfurization reactions, and denitrification reactions. Incidentally, the steam or hot water generated by the CFB boiler is supplied to other processes in the ironmaking plant, achieving a dual benefit.

[0003] The existing sintering flue gas co-purification device has the following defects in operation: (1) On the water-cooled air chamber below the air distribution plate in the furnace of the existing sintering flue gas co-purification device, there are two isolated front air chambers connected to each other. Each front air chamber is connected to the corresponding air preheater through its own primary hot air duct. The inlet of each air preheater is connected to its own primary air fan through its own cold air duct. The inlet of each primary air fan is connected to the sintering flue gas conveying pipe. In the operation of this existing independent primary air supply structure, the air pressure of the two front air chambers is often different, which directly leads to uneven air pressure in the water-cooled air chamber and affects the uniform fluidization effect of the air distribution plate; (2) Secondary air branch pipes are evenly distributed on the front and rear walls of the dense phase zone of the furnace of the existing sintering flue gas co-purification device. The layout of the existing secondary branch pipes is mainly based on the furnace secondary phase zone. The demand for secondary air is generally determined by the fact that large-diameter limestone desulfurizing agent injection pipes are installed in 2-4 secondary branch air pipes on the front wall, while limestone desulfurizing agent injection pipes are not installed in other branch air pipes and secondary branch air pipes on the rear wall, resulting in uneven limestone desulfurizing agent injection during operation; (3) The separator inlet section of the existing sintering flue gas co-purification device is generally 3.5-4 meters long, the cone contraction angle is generally 72°, the flue gas rising velocity in the separator cylinder is 5.5 meters / second, and the cylinder diameter is about 8 meters. How to upgrade and optimize the separator is also a problem that needs to be considered on site; (4) In the commissioning stage before the sintering flue gas co-purification device is put into operation, according to the existing technical specifications, the system operating conditions usually need to be adjusted to the target range: that is, the oxygen content of the tail flue gas is stabilized at 3%-4%, and the carbon content of the bottom ash of the furnace is controlled at 2%. The carbon content of fly ash is controlled below 6%. After the above key parameters meet the set requirements and the operation is stable, the optimal air supply parameters of the unit will be determined based on this operating condition. From the perspective of process design logic, the oxygen content of sintering flue gas is naturally lower than that of air (the oxygen content of conventional air is about 21%, while the oxygen content of sintering flue gas is usually 10%-15%). In order to ensure the full combustion of fuel in the furnace and avoid heat loss and pollutant emissions caused by incomplete combustion, its excess air coefficient is usually designed to be 1.25-1.3, which is significantly higher than that of conventional coal-fired boilers (the excess air coefficient of conventional boilers is generally 1.2-1).25) While this design can maintain fuel combustion efficiency above 90% by increasing oxygen supply and meeting boiler heat output requirements, it also imposes a double constraint on low-cost desulfurization and denitrification processes within the furnace from a synergistic purification perspective. In the desulfurization stage, the industry currently widely adopts furnace calcium injection desulfurization technology. Its core reaction mechanism is as follows: calcium carbonate particles are injected into the high-temperature zone (800-1000℃) of the furnace. At high temperatures, calcium carbonate rapidly decomposes into calcium oxide (CaCO3→CaO+CO2↑) and carbon dioxide. Subsequently, calcium oxide acts as a desulfurizing agent, reacting with sulfur dioxide in the furnace to generate calcium sulfate (2CaO+2SO2). +O2→2CaSO4); however, this reaction has a significant "passivation effect". Since the molar volume of calcium sulfate (about 52.2 cm³ / mol) is much larger than that of calcium oxide (about 16.9 cm³ / mol), the calcium sulfate produced in the reaction will form a dense "coating layer" on the surface of calcium oxide particles. This coating layer will block the micropore channels (pore size is usually 0.1-1 μm) on the surface of calcium oxide, so that sulfur dioxide gas cannot come into contact with the calcium oxide inside the particles. The utilization rate of desulfurizer is usually only 30%-50%. The aforementioned high excess air coefficient design creates an oxygen-rich environment within the furnace. This oxygen-rich environment accelerates the formation rate of the calcium sulfate coating, further shortening the effective reaction time of the desulfurizing agent and leading to a 20%-30% increase in reagent consumption, directly increasing desulfurization operating costs. In the denitrification stage, the oxygen-rich environment also adversely affects the selective non-catalytic reduction (SNCR) denitrification reaction within the furnace. SNCR denitrification requires the reductant (such as ammonia or urea) to react with nitrogen oxides within a temperature window of 850-920℃. However, oxygen-rich conditions promote side reactions between the reductant and oxygen (such as NH3 + O2 → NO + H2O), reducing the reductant utilization rate (by 15%-25%) and generating additional nitrogen oxides, resulting in a 5%-10% decrease in denitrification efficiency. Furthermore, it necessitates increasing the reductant dosage to compensate for the losses from side reactions, further exacerbating the overall operating cost pressure of the entire unit. Summary of the Invention

[0004] This invention provides a sintering flue gas co-purification device that can achieve low-cost and high-efficiency desulfurization in the furnace, thus realizing low-cost and high-efficiency desulfurization in the furnace.

[0005] The present invention solves the above technical problems through the following technical solutions: The overall concept of this invention is to change the conventional thinking that in-furnace dry desulfurization should convert SO2 into CaSO4 in an oxygen-rich furnace environment, and instead create an oxygen-deficient reaction environment in the furnace to convert SO2 into CaS. The invention also modifies the pressure-equalizing air intake structure of the pre-flush air chamber to create a more uniform primary air pressure. A uniform injection zone for CaCO3 desulfurizing agent is constructed in the dense phase zone of the boiler. Through a single-layer arrangement of secondary air and a uniformly distributed supply of desulfurizing agent, the pressure-equalizing primary air, combined with the secondary air, under the low resistance, high momentum, and strong penetration of the secondary air, significantly improves the gas-solid mixing effect of in-furnace desulfurization. This allows the combustion material particles and desulfurizing agent to fully react in a strong reducing atmosphere to generate stable desulfurization product CaS. By maximizing the length of the separator inlet acceleration section and increasing the separator cylinder diameter and cone contraction angle, the upward flow velocity of flue gas inside the separator cylinder is reduced, thereby increasing the separator efficiency to 99.999% and achieving higher-efficiency desulfurization.

[0006] A sintering flue gas co-purification device capable of low-cost, high-efficiency in-furnace desulfurization includes a furnace and a cyclone separator. Solid waste fuel is added to the furnace. A cyclone separator inlet acceleration section is located between the upper part of the furnace and the top of the cyclone separator. Secondary air branch ducts are evenly distributed on the front wall of the dense phase zone within the furnace, and secondary air branch ducts are evenly distributed on the rear wall of the dense phase zone within the furnace. An air distribution plate is located below the dense phase zone within the furnace, and a primary air chamber is located below the air distribution plate. A first pre-air chamber and a second pre-air chamber are connected to the primary air chamber. A first hot air inlet pipe is connected to the top, and a second hot air inlet pipe is connected to the second pre-air chamber. Sintering flue gas is introduced into both the first and second hot air inlet pipes. A pre-air chamber connecting pressure equalization pipeline is connected between the first and second pre-air chambers, and a hot air pipe connecting pressure equalization pipeline is connected between the first and second hot air inlet pipes. The structure of each front wall secondary air branch pipe is exactly the same as that of each rear wall secondary air branch pipe. A desulfurizing agent injection pipe is installed in the front wall secondary air branch pipe, and CaCO3 desulfurizing agent is transported in the desulfurizing agent injection pipe.

[0007] The length of the inlet acceleration section of the cyclone separator is 6 meters, the diameter of the cylindrical section of the cyclone separator is 9 meters, the contraction angle of the cone contraction section of the cyclone separator is 80 degrees, and the upward flow velocity of the flue gas inside the separator cylinder is less than or equal to 5 meters per second.

[0008] The ratio of the air inlet area of ​​the rectangular air inlet of the secondary air branch duct on the front wall to the inlet area of ​​the desulfurizing agent injection pipe is 92.5:7.5.

[0009] The boiler has an excess air coefficient of 1.1, which creates an oxygen-deficient reaction environment in the furnace.

[0010] This invention, based on a circulating fluidized bed flue gas co-purification device, creatively proposes operation under low-oxygen or strong reducing atmosphere. Through a highly efficient adiabatic cyclone separator, a unique single-layer arrangement of secondary air, a desulfurizing agent feeding structure, and a pre-air chamber pressure equalization air intake structure, the device ensures safe, stable, and efficient combustion. It realizes multiple cycles of materials and desulfurizing agents and fully reacts to generate stable desulfurization product CaS, greatly reducing desulfurization costs and significantly improving in-furnace desulfurization efficiency. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the structure of the present invention; Figure 2 This is a diagram showing the relationship between the furnace 1 and the cyclone separator 2 in this invention. Figure 3 This is a schematic diagram of the secondary air branch duct in the dense phase zone 5 of the present invention in the main view direction; Figure 4 This is a schematic diagram of the secondary air branch duct in the dense phase zone 5 of the present invention from a top view. Figure 5 This is a schematic diagram of the structure of the two front air chambers connected on the primary air chamber 3 of the present invention; Figure 6 yes Figure 5 Sectional view along direction AA. Detailed Implementation

[0012] The present invention will now be described in detail with reference to the accompanying drawings: A sintering flue gas co-purification device capable of low-cost and high-efficiency in-furnace desulfurization includes a furnace 1 and a cyclone separator 2. Solid waste fuel is added to the furnace 1. A cyclone separator inlet acceleration section 16 is provided between the upper part of the furnace 1 and the top of the cyclone separator 2. Secondary air branch ducts 6 are evenly distributed on the front wall of the dense phase zone 5 in the furnace 1, and secondary air branch ducts 7 are evenly distributed on the rear wall of the dense phase zone 5 in the furnace 1. An air distribution plate 4 is provided below the dense phase zone 5 in the furnace 1, and a primary air chamber 3 is provided below the air distribution plate 4. A first pre-air chamber 10 and a second pre-air chamber 12 are respectively connected to the primary air chamber 3. A first hot air input pipe 11 is connected to the first pre-air chamber 10, and a second hot air input pipe 13 is connected to the second pre-air chamber 12. Sintering flue gas is input into both the first hot air input pipe 11 and the second hot air input pipe 13. The system includes a pressure equalization pipeline 14 connecting the first pre-air chamber 10 and the second pre-air chamber 12, and a hot air pipe pressure equalization pipeline 15 connecting the first hot air input pipe 11 and the second hot air input pipe 13. By connecting and equalizing pressure twice, the uneven air pressure in the primary air chamber 3 is avoided, and the primary air blown into the furnace through the air distribution plate in the primary air chamber is uniformly used to fluidize the fuel in the furnace. The structure of each secondary air branch pipe 6 on the front wall is exactly the same as that of each secondary air branch pipe 7 on the rear wall. A desulfurizing agent injection pipe 9 is installed in the secondary air branch pipe 6 on the front wall, and CaCO3 desulfurizing agent is transported in the desulfurizing agent injection pipe 9. The desulfurizing agent injection pipe 9 is evenly distributed in the secondary air branch pipes, which realizes the uniform spraying of desulfurizing agent in the dense phase zone of the furnace, so that the uniform desulfurizing agent and fluidized fuel are uniformly combined and reacted, achieving high-efficiency and low-cost desulfurization.

[0013] The inlet acceleration section 16 of the cyclone separator is 6 meters long, the cylindrical section 17 of the cyclone separator 2 has a diameter of 9 meters, and the conical contraction section 18 of the cyclone separator 2 has a contraction angle of 80 degrees. This structure of the cyclone separator improves the separation efficiency of circulating ash and reduces the upward flow velocity of flue gas in the separator, allowing the unreacted desulfurizing agent to circulate repeatedly between the furnace and the cyclone separator, achieving the effect of repeated desulfurization. The upward flow velocity of flue gas in the separator cylinder is less than or equal to 5 meters per second, which also improves the separation of ash particles by the separator.

[0014] The ratio of the air inlet area of ​​the rectangular air inlet 8 of the secondary air branch duct 6 on the front wall to the inlet area of ​​the desulfurizing agent injection pipe 9 is 92.5:7.5; this ratio is to achieve complete combustion and effective desulfurization in the furnace, and is data obtained through on-site commissioning.

[0015] The boiler has an excess air coefficient of 1.1, which creates an oxygen-deficient reaction environment in the furnace. Under the premise of ensuring the full combustion of solid waste in the furnace, oxygen-deficient combustion also reduces the formation of nitrogen oxides in the furnace.

[0016] A sintering flue gas co-purification device that can achieve low-cost and high-efficiency in-furnace desulfurization is tested and commissioned before operation through the following steps: The first step is to adjust the oxygen content of the tail flue gas to 3%-4%, the carbon content of the bottom ash to below 2%, and the carbon content of the fly ash to below 6%. Under these conditions, the amount of sintering flue gas input through the first hot air input pipe 11 and the second hot air input pipe 13 is preliminarily determined. The second step is to gradually reduce the amount of sintering flue gas supplied into the furnace. Based on the ratio of the amount of solid waste fuel supplied to the amount of sintering flue gas supplied, the excess air coefficient of the boiler is adjusted to below 1.1 to ensure that the system is stably maintained at the optimal operating conditions of "oxygen content of tail flue gas of 1%-2%, carbon content of bottom ash of less than 2%, and carbon content of fly ash of less than 6%". The third step involves injecting CaCO3 desulfurizing agent into the furnace through the secondary air branch pipe (6) on the front wall and the secondary air branch pipe (7) on the rear wall, and monitoring the sulfur content index in the tail flue gas discharged from the boiler. The amount of CaCO3 desulfurizing agent injected into the furnace is gradually reduced. Under the premise of meeting the environmental protection index of sulfur content in the tail flue gas of the boiler, the total amount of CaCO3 desulfurizing agent injected into the furnace is determined; thus achieving a balance between the dual goals of desulfurization cost and environmental compliance.

[0017] Traditional dry desulfurization technologies in furnaces generally follow the conventional design concept of "converting SO2 into CaSO4 in an oxygen-rich furnace environment." This technology, however, overturns this core understanding by innovatively creating a relatively oxygen-deficient reaction atmosphere within the furnace, allowing SO2 to preferentially convert into CaS. From the perspective of reaction product characteristics, the molar volume of CaS is significantly smaller than that of CaSO4, effectively avoiding the problem of CaSO4 deposition clogging the micropores of calcium oxide in traditional processes. This significantly improves the reactivity and utilization rate of the limestone desulfurizing agent, laying the foundation for subsequent desulfurization efficiency improvements. This technology constructs a synergistically adapted desulfurization reaction system through technical improvements to the following subsystems: (1) Primary air system: Optimize fluidization and reducing atmosphere control. The core function of primary air is to "ensure stable fluidization of the bed material at the bottom of the boiler" and "provide basic oxygen for initial combustion of fuel". This technical solution improves the pressure equalization air intake structure of the front air chamber, breaks the limitation of uneven air pressure distribution in the traditional air intake, and realizes uniform air distribution of primary air in the bed. This improvement brings dual technical advantages: (a) Improved fluidization efficiency. Under the premise of reducing the total amount of primary air, it can still maintain stable fluidization of the bed material and reduce ineffective air consumption; (b) Enhanced reducing atmosphere. Combined with the characteristic of low oxygen content in sintering flue gas, under the condition of ensuring the amount of primary air required for bed material fluidization, the concentration of reducing atmosphere in the furnace is significantly higher than that of conventional boilers, providing a suitable reaction environment for the conversion of SO2 to CaS in the dense phase zone. (2) Secondary air and desulfurizing agent supply system, optimize gas-solid mixing and reaction conditions. The function of secondary air focuses on "burning and combustion assistance of material particles in dilute phase zone and suspended section", and at the same time, it works in conjunction with the desulfurizing agent supply system to form a synergistic effect: (a) Secondary air structure optimization, adopting a single-layer front and rear wall layout design, utilizing the airflow characteristics of secondary air of "low resistance, large momentum and strong penetration" to enhance the ability to disturb the airflow in the furnace; (b) Desulfurizing agent uniform supply, accurately constructing a uniform injection area of ​​CaCO3 desulfurizing agent in the dense phase zone of the boiler, through the airflow synergy of "uniform pressure primary air + strong penetration secondary air", on the one hand, it realizes the full combustion of fuel under lower total oxygen content (avoiding the destruction of the reducing atmosphere due to excessive oxygen), on the other hand, it greatly improves the gas-solid mixing effect in the furnace, ensuring that sulfur dioxide and desulfurizing agent fully contact and react in a relatively oxygen-deficient reducing atmosphere, and ensuring the stable generation of CaS; (3) Separator System: Enhance material circulation and desulfurization efficiency. The core technical goal of the separator is to "optimize material circulation, ensure fuel burnout, stabilize in-bed heat storage, and improve desulfurization efficiency." Its performance directly affects the reaction conditions and desulfurization effect in the furnace: (a) Key structural improvements: By maximizing the length of the separator inlet acceleration section, increasing the separator cylinder diameter, and optimizing the cone contraction angle, the rising velocity of flue gas in the separator cylinder is significantly reduced, reducing the escape loss of fine particulate materials; (b) Core performance improvement: The separator efficiency is increased to 99.999%, achieving high-ratio material circulation; on the one hand, the uniformity of gas-solid mixing in the furnace is increased, reducing the amount of oxygen required for material combustion, ensuring that the boiler maintains high combustion efficiency in a relatively oxygen-deficient environment; on the other hand, the residence time and mixing of the desulfurizing agent in the furnace are extended, further enhancing the conversion reaction of SO2 to CaS, improving desulfurization efficiency from the dual dimensions of "reaction time" and "mixing effect"; through the primary air system (fluidization and reducing atmosphere control), secondary air- Through the coordinated improvement of the entire desulfurizing agent system (gas-solid mixing and reaction condition optimization) and separator system (material circulation and efficiency improvement), the sintering flue gas purification device has achieved a technological breakthrough: under a relatively oxygen-deficient reducing atmosphere, it not only ensures the stable and complete combustion of fuel, but also continuously and stably generates CaS, a highly efficient desulfurization product. Ultimately, it achieves the dual technical goals of "significantly improving in-furnace desulfurization efficiency" and "significantly reducing the cost of desulfurizing agent use," solving the industry pain point of "difficulty in balancing efficiency and cost" in traditional in-furnace desulfurization.

Claims

1. A sintering flue gas co-purification device that enables low-cost and high-efficiency desulfurization in a furnace, comprising a furnace (1) and a cyclone separator (2), wherein solid waste fuel is added to the furnace (1), and a cyclone separator inlet acceleration section (16) is provided between the upper part of the furnace (1) and the top of the cyclone separator (2), and front wall secondary air branch pipes (6) are evenly distributed on the front wall of the dense phase zone (5) in the furnace (1), and rear wall secondary air branch pipes (7) are evenly distributed on the rear wall of the dense phase zone (5) in the furnace (1). 1) An air distribution plate (4) is provided below the dense phase zone (5) within the 1) and a primary air chamber (3) is provided below the air distribution plate (4). A first pre-air chamber (10) and a second pre-air chamber (12) are respectively connected to the primary air chamber (3). A first hot air input pipe (11) is connected to the first pre-air chamber (10) and a second hot air input pipe (13) is connected to the second pre-air chamber (12). Sintering flue gas is input into both the first hot air input pipe (11) and the second hot air input pipe (13); characterized in that, Between the first pre-air chamber (10) and the second pre-air chamber (12), there is a pre-air chamber connecting pressure equalization pipeline (14), and between the first hot air input pipe (11) and the second hot air input pipe (13), there is a hot air pipe connecting pressure equalization pipeline (15); the structure of each front wall secondary air branch pipe (6) is exactly the same as the structure of each rear wall secondary air branch pipe (7), and a desulfurizing agent injection pipe (9) is provided in the front wall secondary air branch pipe (6), and CaCO3 desulfurizing agent is transported in the desulfurizing agent injection pipe (9).

2. The sintering flue gas co-purification device for low-cost and high-efficiency in-furnace desulfurization as described in claim 1, characterized in that, The length of the inlet acceleration section (16) of the cyclone separator is 6 meters, the diameter of the cylindrical section (17) of the cyclone separator (2) is 9 meters, the contraction angle of the conical contraction section (18) of the cyclone separator (2) is 80 degrees, and the upward flow velocity of the flue gas inside the separator cylinder is less than or equal to 5 meters per second.

3. The sintering flue gas co-purification device for low-cost and high-efficiency in-furnace desulfurization as described in claim 2, characterized in that, The ratio of the air inlet area of ​​the rectangular air inlet (8) of the secondary air branch duct (6) on the front wall to the inlet area of ​​the desulfurizing agent injection pipe (9) is 92.5:7.

5.

4. The sintering flue gas co-purification device for low-cost and high-efficiency in-furnace desulfurization as described in claim 3, characterized in that, The boiler has an excess air coefficient of 1.1, which creates an oxygen-deficient reaction environment in the furnace.

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