In-furnace low-cost high-efficiency desulfurization operation method of sintering flue gas collaborative purification device

Abstract

The invention discloses an in-furnace low-cost and high-efficiency desulfurization operation method of a sintering flue gas collaborative purification device, explores a desulfurization method for creating an oxygen-deficient atmosphere in a hearth, and realizes stable combustion and high-efficiency and stable operation of a boiler at the same time. The oxygen content of tail smoke is adjusted to 3%-4%, the carbon content of furnace bottom slag is adjusted to 2% or below, and the carbon content of fly ash is adjusted to 6% or below; the supply amount of sintering flue gas input into a hearth is gradually reduced, the excess air coefficient of the boiler is adjusted to be 1.1 or below according to the ratio of the supply amount of the solid waste fuel of the boiler to the supply amount of the sintering flue gas, and the boiler is made to work in the state that the oxygen content of tail flue gas is 3%-4%, the carbon content of furnace bottom slag is 2% or below, and the carbon content of fly ash is adjusted to be 6% or below; and gradually reducing the injection of the CaCO3 desulfurizer into the hearth, and determining the flow of the CaCO3 desulfurizer injected into the hearth on the premise of meeting the environmental protection index of the sulfur content in the tail flue gas of the boiler.

Description

Technical Field

[0001] This invention relates to a sintering flue gas co-purification device, and more particularly to an operation method of a low-cost, high-desulfurization-efficiency sintering flue gas co-purification device 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 Toxic and harmful gases such as HCl and dioxins are present in sintering flue gas. Current technologies treat these gases by adding environmental protection equipment, which has drawbacks such as high investment, high operating and maintenance costs, and limited elimination of harmful gases. To address these issues, existing technologies have developed a circulating fluidized bed (CFB) boiler for treating sintering flue gas. This special CFB boiler is also known as a multi-pollutant synergistic purification device for sintering flue gas. The main principle of the multi-pollutant synergistic purification device for sintering flue gas is to replace air with the sintering flue gas generated in the sintering machine as the combustion air for the CFB boiler. Through the high-temperature environment inside the CFB boiler furnace and the unique environmental advantages of the CFB boiler, harmful gases in the sintering flue gas are burned off. The steam or hot water generated by the CFB boiler is then supplied to other processes in the ironmaking plant, achieving a dual benefit.

[0003] Conventional circulating fluidized bed boilers use air for combustion, with oxygen comprising approximately 21% of the air. Desulfurization within the boiler occurs under a strong oxidizing atmosphere, where SO2 reacts with the desulfurizing agent (CaCO3) to form the stable desulfurization product CaSO4. However, in a strong oxygen atmosphere, NO... x Correspondingly, the amount of excess air will also increase. Therefore, traditional in-furnace dry desulfurization needs to balance the contradiction between desulfurization and denitrification. Generally, the excess air coefficient of the boiler is designed to be 1.2-1.25. The sintering flue gas co-purification device is derived from circulating fluidized bed boiler technology. The desulfurization technology in the device is also derived from the traditional circulating fluidized bed boiler. However, the oxygen content in the sintering flue gas is about 10%, which is half that of the oxygen content in the traditional circulating fluidized bed boiler that uses air for combustion. For the sintering flue gas co-purification device, the dry desulfurization in the furnace requires more sintering flue gas to achieve in-furnace desulfurization. Therefore, those skilled in the art design the excess air coefficient in the device to be 1.25-1.34. In the field operation, new problems have emerged, such as a large increase in the amount of desulfurizing agent input and low desulfurization efficiency. How to reduce the desulfurization cost and improve the in-furnace desulfurization efficiency has become a prominent problem in the operation of the sintering flue gas co-purification device.

[0004] Before formal operation, the sintering flue gas co-purification device needs to be commissioned. The specific commissioning process involves adjusting the fuel-to-air ratio and testing the oxygen content of the tail gas and the carbon content of the bottom slag and fly ash to determine if the boiler is operating at its optimal state. During boiler commissioning, current technology typically adjusts the oxygen content of the tail gas to 3%-4%, the carbon content of the bottom slag to below 2%, and the carbon content of the fly ash to below 6%, thereby determining the appropriate air supply to the boiler. Since the oxygen content of sintering flue gas is lower than that of air, the excess air coefficient is generally designed to be 1.25. Within the -1.3 range, it is higher than that of conventional coal-fired circulating fluidized bed boilers; the increased excess air coefficient means an increase in the oxygen supply in the furnace. Although this is beneficial to boiler combustion, it is not conducive to low-cost in-furnace desulfurization. The reason is that the existing in-furnace desulfurization is to spray calcium carbonate powder into the furnace. Calcium carbonate decomposes into calcium oxide and carbon dioxide at high temperature. After the calcium oxide reacts with sulfur dioxide and oxygen in the furnace, it generates calcium sulfate. This desulfurization process is carried out under oxygen-rich conditions in the furnace, which requires the input of more calcium carbonate desulfurizing agent, directly leading to a significant increase in desulfurization costs and low in-furnace desulfurization efficiency. Summary of the Invention

[0005] This invention provides a low-cost, high-efficiency desulfurization operation method for a sintering flue gas co-purification device, exploring a desulfurization method that creates an oxygen-deficient atmosphere in the furnace, while simultaneously achieving stable combustion and efficient and stable operation of the boiler.

[0006] The present invention solves the above technical problems through the following technical solutions: The overall concept of this invention is as follows: By adjusting the excess air coefficient of the boiler to 1.1 or below, a hypoxic, strongly reducing atmosphere is created in the dense phase region of the furnace. Under these conditions, limestone desulfurizing agent is uniformly sprayed into the furnace, where it decomposes upon heating into calcium oxide and sulfur dioxide. The sulfur dioxide in the flue gas, catalyzed by the carbon elements in the fuel particles, generates calcium sulfide and carbon dioxide, thus achieving low-cost, high-efficiency desulfurization. This invention explores a pre-operation commissioning method for a sintering flue gas synergistic purification device that creates a hypoxic environment in the furnace, achieving both efficient combustion operation and stable combustion of the boiler. Furthermore, considering the characteristics of the boiler using sintering flue gas for combustion assistance, the invention modifies… The existing structure of the pre-air chamber with uniform pressure intake is modified to create a primary air with more uniform pressure. A uniform injection area of ​​CaCO3 desulfurizing agent is created in the dense phase zone of the boiler. Through the single-layer arrangement of secondary air and the uniform supply of desulfurizing agent, the uniform pressure of the primary air and secondary air, under the low resistance, high momentum and strong penetration of the secondary air, greatly improves the gas-solid mixing effect of desulfurization in the furnace. By maximizing the length of the separator inlet acceleration section, increasing the separator cylinder diameter and the contraction angle of the cone, the upward flow velocity of flue gas in the separator cylinder is reduced, thereby increasing the separator efficiency to 99.999%. The boiler structure ensures the synergistic purification of solid waste fuel and sintering flue gas.

[0007] A low-cost, high-efficiency desulfurization operation method for a sintering flue gas co-purification device includes a furnace and a cyclone separator. Solid waste fuel is added to the furnace. A cyclone separator inlet acceleration section is set 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 in the furnace, and secondary air branch ducts are evenly distributed on the rear wall of the dense phase zone in the furnace. An air distribution plate is set below the dense phase zone in the furnace, and a primary air chamber is set 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 input pipe is connected to the first pre-air chamber, and a second hot air input pipe is connected to the second pre-air chamber. Sintering flue gas is input into both the first and second hot air input pipes. The excess air coefficient of the boiler is 1.1. This device operates for desulfurization using the following method. Perform boiler commissioning according to 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 the above conditions, the amount of sintering flue gas input through the first hot air input pipe and the second hot air input pipe is initially 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, and the boiler is operated with the oxygen content of the tail flue gas at 3%-4%, the carbon content of the bottom ash at 2% or below, and the carbon content of the fly ash at 6% or below. The third step is to inject CaCO3 desulfurizing agent into the furnace through the secondary air branch pipes on the front wall and the secondary air branch pipes on the rear wall, and monitor the sulfur content index in the tail flue gas discharged from the boiler. Gradually reduce the injection of CaCO3 desulfurizing agent into the furnace, and determine the flow rate of CaCO3 desulfurizing agent injected into the furnace under the premise of meeting the environmental protection index of sulfur content in the tail flue gas of the boiler. After the boiler is put into operation and commissioning, the boiler is put into normal operation according to the supply flow rate of solid waste fuel, the supply flow rate of sintering flue gas and the flow rate of CaCO3 desulfurizing agent injected into the furnace obtained by commissioning; so that the dense phase zone of the furnace can carry out desulfurization in an oxygen-deficient atmosphere.

[0008] 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 5 meters per second.

[0009] The ratio of the air inlet area of ​​the rectangular air inlet of the secondary air branch duct on the front wall to the desulfurizing agent injection pipe area is 92.5:7.5.

[0010] This invention, based on a circulating fluidized bed flue gas co-purification device, creatively proposes an operation method under low oxygen or strong reducing atmosphere, which realizes multiple cycles of materials and desulfurizing agents and full reaction 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 chamber 1 and the cyclone separator 2 of the present 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 unreacted SO2 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 low-cost, high-efficiency desulfurization operation method for a sintering flue gas co-purification device 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. A [further details about the method are missing]. An air distribution plate 4 is provided, 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 inlet pipe 11 is connected to the first pre-air chamber 10, and a second hot air inlet pipe 13 is connected to the second pre-air chamber 12. Sintering flue gas is introduced into both the first hot air inlet pipe 11 and the second hot air inlet pipe 13. The excess air coefficient of the boiler is 1.1. The boiler is debugged before operation according to 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 the above 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 initially 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, and the boiler is operated with the oxygen content of the tail flue gas at 3%-4%, the carbon content of the bottom ash at 2% or below, and the carbon content of the fly ash at 6% or below. The third step is to inject 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 monitor the sulfur content index in the tail flue gas discharged from the boiler. Gradually reduce the injection of CaCO3 desulfurizing agent into the furnace, and determine the flow rate of CaCO3 desulfurizing agent injected into the furnace under the premise of meeting the environmental protection index of sulfur content in the tail flue gas of the boiler. After the boiler is put into operation and commissioning, the boiler is put into normal operation according to the supply flow rate of solid waste fuel, the supply flow rate of sintering flue gas and the flow rate of CaCO3 desulfurizing agent injected into the furnace obtained from the commissioning; so that the dense phase zone of the furnace can carry out desulfurization in an oxygen-deficient atmosphere; and achieve 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 low-cost, high-efficiency desulfurization operation method for a sintering flue gas co-purification device, 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 ducts (6) are evenly distributed on the front wall of the dense phase zone (5) in the furnace (1), and rear wall secondary air branch ducts (7) are evenly distributed on the rear wall of the dense phase zone (5) in the furnace (1). (5) An air distribution plate (4) is provided below the air distribution plate (4), 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 excess air coefficient of the boiler is 1.1; characterized in that, Perform boiler commissioning according to the following steps: Step 1: 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 the above 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 initially 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, and the boiler is operated with the oxygen content of the tail flue gas at 3%-4%, the carbon content of the bottom ash at 2% or below, and the carbon content of the fly ash at 6% or below. The third step is to inject 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 monitor the sulfur content index in the tail flue gas discharged from the boiler. Gradually reduce the injection of CaCO3 desulfurizing agent into the furnace. Under the premise of meeting the environmental protection index of sulfur content in the tail flue gas of the boiler, determine the flow rate of CaCO3 desulfurizing agent injected into the furnace. After the boiler is put into operation and commissioning, the boiler is put into normal operation according to the supply flow rate of solid waste fuel, the supply flow rate of sintering flue gas and the flow rate of CaCO3 desulfurizing agent injected into the furnace obtained by commissioning; so that the dense phase zone of the furnace can carry out desulfurization in an oxygen-deficient atmosphere.

2. The method for low-cost, high-efficiency desulfurization operation of a sintering flue gas co-purification device according to 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 5 meters per second.

3. The method for low-cost, high-efficiency desulfurization operation of a sintering flue gas co-purification device according to claim 1 or 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 desulfurizing agent inlet area of ​​the desulfurizing agent injection pipe (9) is 92.5:7.5.

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