Method for synergistically removing sintering flue gas pollutants and recycling energy

Abstract

The invention provides a sintering flue gas pollutant collaborative removal and energy recycling method, which comprises the following steps that coal and a desulfurizing agent are introduced into a hearth of a circulating fluidized bed boiler, primary air and secondary air are introduced, the source of the primary air is air, the source of the secondary air is sintering flue gas, and the temperature of the hearth is 800-900 DEG C; smoke dust formed after combustion in the hearth is subjected to afterburning and SNCR denitration and then is introduced into a cyclone separator to be separated, separated smoke gas enters a tail flue, and separated bed materials return to the hearth; flue gas in the tail flue is discharged to the atmosphere after being subjected to wet desulphurization, SCR denitration, heat exchange and dust removal. The sintering flue gas is introduced into the hearth for combustion, boiler fuel consumption is reduced through sensible heat and chemical energy of the sintering flue gas, and waste heat recovery of the sintering flue gas and cooperative treatment of pollutants are achieved.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment and energy recovery technology, and in particular to a method for the synergistic removal of pollutants and energy recovery and utilization from sintering flue gas. Background Technology

[0002] Under normal circumstances, producing one ton of sintered ore generates 4000-6000 Nm³ of nitrogen oxides. 3 Sintering flue gas is characterized by its complex composition, wide temperature range (120-180℃), high oxygen content (above 13%), and high moisture content. It contains various pollutants such as SO2, NOx, PM, and dioxins. Notably, it also contains approximately 5000 ppm CO, which can be used as a low-concentration fuel to recover its combustion heat. Simple calculations show that for every ton of sinter produced, the sintering flue gas carries away 0.72 GJ of waste heat, accounting for about 50% of the total energy input of the sintering process. In particular, the waste heat from the sintering flue gas accounts for as much as 19%-35% of the total energy consumption. Therefore, simultaneously treating multiple pollutants in the sintering flue gas and recovering and utilizing the aforementioned waste heat and a certain concentration of combustible components' combustion heat is of great significance for reducing the total energy consumption of the steel production process.

[0003] Existing end-of-pipe treatment technologies for sintering flue gas mostly employ a series connection of devices such as SCR denitrification, SNCR denitrification, semi-dry desulfurization, wet desulfurization, bag filter dust collection, and activated carbon adsorption to remove pollutants from the sintering flue gas. If an additional step is added to remove CO from the sintering flue gas and recover waste heat, additional heat input is often required. Some existing technologies combine sintering flue gas pollutant treatment with power generation, using boiler combustion to treat the sintering flue gas. However, these technologies do not consider problems such as equipment blockage and pipe wear caused by the complex composition of pollutants in sintering flue gas, nor do they pay attention to the setting of boiler operating parameters, resulting in insufficient removal of pollutants from the sintering flue gas. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, embodiments of this invention provide a method for the synergistic removal of pollutants from sintering flue gas and the recovery and utilization of energy, which can efficiently remove pollutants from sintering flue gas and then recycle them, reducing the cost of synergistic pollutant treatment.

[0005] This invention proposes a method for the synergistic removal of pollutants and energy recovery from sintering flue gas, comprising the following steps: coal and desulfurizing agent are introduced into the furnace of a circulating fluidized bed boiler, along with primary air and secondary air, wherein the primary air is sourced from air and the secondary air is sourced from sintering flue gas, and the furnace temperature is 800–900°C; the flue gas formed after combustion in the furnace is separated in a cyclone separator after supplementary combustion and SNCR denitrification, and the separated flue gas enters the tail flue, while the separated bed material is returned to the furnace; the flue gas in the tail flue is discharged into the atmosphere after wet desulfurization, SCR denitrification, heat exchange, and dust removal.

[0006] In some embodiments, when the sintering machine is under maintenance or the source of sintering flue gas is cut off, the source of secondary air is switched to air.

[0007] In some embodiments, both the primary air inlet pipe and the secondary air inlet pipe pass through the tail flue. The primary air and the secondary air exchange heat with the flue gas in the tail flue before being introduced into the furnace.

[0008] In some embodiments, a superheater and an economizer are connected in the tail flue to absorb the heat of the flue gas after cyclone separation for power generation or heating.

[0009] In some embodiments, a portion of the primary air is drawn into the return valve of the cyclone separator to facilitate the discharge of bed material at the return valve into the furnace.

[0010] In some embodiments, the upper limit of the particle size of the coal fed into the furnace is determined by formula d. max =min(e 7.5Vdaf 70e -6Aar )Sure.

[0011] In some embodiments, the desulfurizing agent is limestone particles.

[0012] In some embodiments, the limestone particles have a particle size of less than 100 μm.

[0013] In some embodiments, the temperature of the furnace is 850°C.

[0014] In some embodiments, the sintering flue gas is dedusted before being introduced into the furnace. Attached Figure Description

[0015] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0016] in:

[0017] Figure 1 This is a flowchart of the method for synergistic removal of pollutants and energy recovery and utilization in sintering flue gas according to an embodiment of the present invention;

[0018] Figure 2 for Figure 1 A schematic diagram of the system structure used in the method described above;

[0019] Figure label:

[0020] 1. Circulating fluidized bed boiler; 2. Dust collector; 3. Desulfurization tower; 4. Chimney; 5. Furnace; 6. Cyclone separator; 7. Return valve; 8. Tail flue; 9. Superheater; 10. Economizer; 11. SCR reactor; 12. Secondary air preheater; 13. Primary air preheater; 14. Air fan; 15. Sintering machine head flue gas inlet device; 16. Secondary air inlet; 17. Primary air inlet; 18. Return air outlet; 19. Coal feed inlet; 20. Desulfurizing agent inlet; 21. Combustion air inlet; 22. SNCR ammonia injection port; 23. Induced draft fan; 24. Sintering flue gas dust removal device. Detailed Implementation

[0021] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0022] The following describes a method for synergistic removal of pollutants and energy recovery and utilization from sintering flue gas according to an embodiment of the present invention, with reference to the accompanying drawings.

[0023] like Figure 1 , 2 As shown in the embodiment of the present invention, a method for synergistic removal of pollutants and energy recovery and utilization of sintering flue gas is proposed, comprising the following steps: coal and desulfurizing agent are introduced into the furnace 5 of the circulating fluidized bed boiler 1, and primary air and secondary air are introduced, wherein the primary air is sourced from air and the secondary air is sourced from sintering flue gas, and the temperature of the furnace 5 is 800-900℃; the flue gas formed after combustion in the furnace 5 is separated into cyclone separator 6 after supplementary combustion and SNCR denitrification, and the separated flue gas enters the tail flue 8, and the separated bed material is returned to the furnace 5; the flue gas in the tail flue 8 is discharged into the atmosphere after wet desulfurization, SCR denitrification, heat exchange and dust removal.

[0024] In this embodiment of the invention, sintering flue gas is introduced into the furnace 5 for combustion. The sensible heat and chemical energy (CO combustion heat release) of the sintering flue gas are used to reduce boiler fuel consumption, thereby achieving waste heat recovery and synergistic treatment of pollutants from the sintering flue gas.

[0025] It should be noted that CO in sintering flue gas is a combustible gas that reacts with oxygen in the circulating fluidized bed. Since the temperature of the fluidized bed reactor is high enough for CO oxidation and the gas residence time is long, the reaction of CO with O2 releases heat to the boiler, which also saves some of the boiler's heat input and further saves fuel. This achieves the removal of pollutant CO from sintering flue gas and the utilization of combustion heat.

[0026] In this embodiment of the invention, the temperature of the furnace 5 is set to 800–900°C. Within this temperature range, and under sufficient oxygen conditions, the stability of dioxin molecules in the sintering flue gas decreases, the chlorinated aromatic ring structure is destroyed, and C-Cl and C-C bonds begin to break, forming chlorine atom free radicals and other organic molecular free radicals. Then, under high temperature and sufficient oxygen conditions, chlorine atoms are oxidized to chlorine gas, C in organic matter is oxidized to carbon dioxide, and H is oxidized to water. Because the gas residence time in the circulating fluidized bed is long, it can meet the temperature and residence time requirements for dioxin decomposition. Combined with flue gas dechlorination technology, dioxin pollutants in the sintering flue gas can be removed without generating secondary pollution. Simultaneously, CO in the sintering flue gas, as a combustible gas, reacts with oxygen in the circulating fluidized bed boiler 1. Since the temperature of the fluidized bed reactor is sufficiently high for CO oxidation, and the gas residence time is long, the heat released by the reaction of CO and O2 is provided to the boiler, saving some of the boiler's heat input and further saving fuel. This achieves the removal of pollutant CO from the sintering flue gas and the utilization of combustion heat.

[0027] The temperature of the furnace chamber 5 is preferably set at 850°C, at which temperature the above effects are optimal.

[0028] This invention, through the addition of a desulfurizing agent within the furnace 5, achieves in-furnace desulfurization, improving desulfurization efficiency and saving costs associated with subsequent tail gas desulfurization. Combined with tail gas desulfurization (wet desulfurization), it achieves highly efficient removal of sulfides.

[0029] In this embodiment of the invention, particulate matter in the flue gas is removed by passing it through a dust collector 2 before it is discharged into the atmosphere from the tail flue 8. Because the flue gas undergoes combustion, desulfurization, low-NOx combustion, SNCR denitrification, and SCR denitrification in the furnace 5, most of the dioxins, nitrogen oxides, and sulfides in the flue gas are removed, reducing its chemical composition and significantly improving problems such as dust collector corrosion and reduced dust removal efficiency. Since the sintering flue gas remains in the high-temperature furnace 5 for a sufficiently long time, the dust formed after combustion in the furnace 5 is further combusted, ensuring complete combustion and decomposition of CO and dioxins in the sintering flue gas.

[0030] Furthermore, the primary air inlet 17 and the secondary air inlet 16 are located at different positions. The primary air inlet 17 is located at the bottom of the furnace 5, and the secondary air inlet 16 is located on the side of the furnace 5 and above the primary air inlet 17. This separation of primary and secondary air allows the use of air for primary air and sintering flue gas for secondary air to avoid the problem of primary air duct blockage caused by sintering flue gas completely replacing air entering the furnace 5, which would prevent both primary and secondary air from entering the furnace 5 smoothly. It should be noted that sintering flue gas contains alkali metals (K / Na) and particulate matter, which can easily clog the duct area.

[0031] It should be noted that blast furnace combustion can also be used as an alternative for end-of-pipe treatment of sintering flue gas. Specifically, sintering flue gas is introduced into the blast furnace as primary air. The high-temperature environment provided by blast furnace combustion can effectively reduce emissions of sulfur dioxide and nitrogen oxides in the flue gas, and may even allow dioxins to decompose thermally, while utilizing waste heat. However, because the oxygen content of sintering flue gas is low (usually below 15%), directly replacing primary air with it may lead to incomplete combustion of coke in the furnace, a drop in hearth temperature, and additional fuel consumption. Furthermore, sulfides (SO2), alkali metals (K / Na), and dust carried in the sintering flue gas can contaminate the quality of molten iron. Compared to blast furnace combustion, the circulating fluidized bed combustion method used in this embodiment of the invention has advantages such as wide fuel adaptability, low cost of pollutant emission control, high combustion efficiency, and outstanding load regulation capability. Therefore, using a circulating fluidized bed boiler 1 to treat sintering flue gas has high economic and environmental benefits.

[0032] Furthermore, the flue gas from tail flue 8 undergoes desulfurization again after dust removal before being discharged into the atmosphere. This ensures ultra-low SO2 emissions from the outlet flue gas.

[0033] Furthermore, the proportion of sintering flue gas in furnace 5 is 40%-60%. The remainder is air, ensuring complete combustion of fuel in furnace 5.

[0034] In some embodiments, when the sintering machine is under maintenance or the source of sintering flue gas is cut off, the source of secondary air is switched to air. This ensures the continuity and reliability of the system.

[0035] Furthermore, the gas source can be switched by installing a reversing valve on the pipeline upstream of the induced draft fan 23. The two inlets of the reversing valve are for air and sintering flue gas, respectively. The switching method is simple and quick, further improving the continuity and reliability of the system.

[0036] In some embodiments, both the primary air inlet pipe and the secondary air inlet pipe pass through the tail flue 8. The primary air and the secondary air exchange heat with the flue gas in the tail flue 8 before being introduced into the furnace 5.

[0037] Because the temperature of sintering flue gas is higher than that of cold air, within the range of 120 to 180°C, less heat is required to preheat the sintering flue gas to the same temperature, saving boiler fuel consumption and realizing the recovery and utilization of waste heat from sintering flue gas.

[0038] In some embodiments, a superheater 9 and an economizer 10 are connected inside the tail flue 8 to absorb the heat of the flue gas after cyclone separation and use it for power generation or heating, which is of great significance for optimizing the overall system energy structure and reducing the total energy consumption of the steel production process.

[0039] In some embodiments, a portion of the primary air is drawn into the return valve 7 of the cyclone separator 6 to facilitate the discharge of bed material at the return valve 7 into the furnace 5, thereby preventing the bed material at the return valve 7 from accumulating and clogging.

[0040] In some embodiments, the upper limit of the particle size of the coal fed into the furnace 5 is determined by formula d. max =min(e 7.5Vdaf 70e -6Aar This is confirmed. This reduces coal particle size, thereby achieving low-NOx combustion in the furnace. Combining SNCR denitrification with SCR denitrification in the tail flue 8 forms a three-stage denitrification process, achieving highly efficient removal of nitrogen oxides.

[0041] By appropriately reducing the particle size of coal, the average bed material particle size is reduced, the bed quality is improved, and the circulation volume is increased. This can change the local gas-solid flow state in furnace 5, thereby affecting the spatial distribution, mass transfer, and heat transfer of active particles, changing the atmosphere and temperature distribution, and spontaneously creating local reducing conditions. At the same time, the low concentration of CO in the sintering flue gas also has reducing properties, which can reduce the initial formation of NOx or promote NOx reduction, thus achieving low-NOx combustion in furnace 5.

[0042] In some embodiments, the desulfurizing agent is limestone particles.

[0043] In some embodiments, the limestone particles have a diameter of less than 100 μm. Using ultrafine limestone can improve the desulfurization effect.

[0044] In some embodiments, the sintering flue gas is dusted before entering the furnace 5.

[0045] Since the sintering flue gas is sent into the furnace 5 through the induced draft fan 23, a sintering flue gas dust removal device 24 is installed in front of the induced draft fan 23 to remove dust, which can alleviate the problem of severe wear of the induced draft fan 23 caused by excessive particulate matter content in the sintering flue gas.

[0046] The method of this invention can be implemented using the following system.

[0047] like Figure 2 As shown, a system for the synergistic removal of pollutants and energy recovery from sintering flue gas includes: a furnace 5, a cyclone separator 6, and a tail flue 8. The furnace 5 is an insulated furnace 5, and the cyclone separator 6 is an insulated cyclone separator 6. The furnace 5 has a primary air inlet 17, a secondary air inlet 16, a coal feed inlet 19, a desulfurizing agent feed inlet 20, a discharge outlet, and a return material inlet. The primary air inlet 17 of the furnace 5 is connected to an air fan 14 through a primary air inlet pipe. An air distribution plate is provided above the primary air inlet 17 of the furnace 5, and multiple air outlets are evenly distributed on the air distribution plate. Each air outlet is connected to an air cap. The secondary air inlet 16 of the furnace 5 is connected to the flue gas feed device 15 at the head of the sintering machine through a secondary air inlet pipe. The secondary air inlet 16 is located above the air distribution plate.

[0048] Cyclone separator 6 has a feed inlet, an air outlet, a return outlet, and a return air inlet 18. The feed inlet of cyclone separator 6 is connected to the outlet of furnace 5 through a discharge pipe. The discharge pipe has a burnout air inlet 21 and an SNCR ammonia injection port 22, which are used for flue gas re-combustion and SNCR denitrification. The return outlet of cyclone separator 6 is connected to the return inlet of furnace 5 through a return pipe. The return air inlet 18 of cyclone separator 6 is connected to air fan 14 through a primary air inlet pipe.

[0049] The tail flue 8 has an air inlet and an air outlet. The air inlet of the tail flue 8 is connected to the air outlet of the cyclone separator 6, and the air outlet of the tail flue 8 is connected in sequence to the dust collector 2, the desulfurization tower 3 and the chimney 4.

[0050] The interior of the tail flue 8 is equipped with a superheater 9, an economizer 10, an SCR reactor 11, a secondary air preheater 12, and a primary air preheater 13, arranged sequentially from the air inlet to the air outlet. The secondary air inlet pipe passes through the secondary air preheater 12 to preheat the secondary air, and the primary air inlet pipe passes through the primary air preheater 13 to preheat the primary air.

[0051] The secondary air inlet duct is connected to an air bypass. When the sintering machine is under maintenance or the source of sintering flue gas is cut off, the source of secondary air is switched to air.

[0052] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0053] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0054] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0055] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0056] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0057] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for synergistic removal of pollutants and energy recovery from sintering flue gas, characterized in that, Includes the following steps: Coal and desulfurizing agent are introduced into the furnace of the circulating fluidized bed boiler, along with primary air and secondary air. The primary air is sourced from air, and the secondary air is sourced from sintering flue gas. The temperature of the furnace is 800–900°C. The smoke and dust generated after combustion in the furnace are separated by a cyclone separator after supplementary combustion and SNCR denitrification. The separated flue gas enters the tail flue, and the separated bed material is returned to the furnace. The flue gas from the tail flue undergoes wet desulfurization, SCR denitrification, heat exchange, and dust removal before being discharged into the atmosphere.

2. The method for synergistic removal of pollutants and energy recovery from sintering flue gas according to claim 1, characterized in that, When the sintering machine is under maintenance or the source of sintering flue gas is cut off, the source of secondary air is switched to air.

3. The method for synergistic removal of pollutants and energy recovery from sintering flue gas according to claim 2, characterized in that, Both the primary air inlet pipe and the secondary air inlet pipe pass through the tail flue. The primary air and the secondary air exchange heat with the flue gas in the tail flue before being introduced into the furnace.

4. The method for synergistic removal of pollutants and energy recovery and utilization from sintering flue gas according to claim 3, characterized in that, The tail flue is connected to a superheater and an economizer, which absorb the heat of the flue gas after cyclone separation and use it for power generation or heating.

5. The method for synergistic removal of pollutants and energy recovery and utilization from sintering flue gas according to claim 3, characterized in that, A portion of the material is drawn from the primary airflow and introduced into the return valve of the cyclone separator to facilitate the discharge of the bed material at the return valve into the furnace.

6. The method for synergistic removal of pollutants and energy recovery and utilization from sintering flue gas according to claim 5, characterized in that, The upper limit of the particle size of the coal fed into the furnace is given by formula d. max =min(e 7.5Vdaf 70e -6Aar )Sure.

7. The method for synergistic removal of pollutants and energy recovery and utilization from sintering flue gas according to claim 1, characterized in that, The desulfurizing agent is limestone particles.

8. The method for synergistic removal of pollutants and energy recovery and utilization from sintering flue gas according to claim 7, characterized in that, The limestone particles have a particle size of less than 100 μm.

9. The method for synergistic removal of pollutants and energy recovery from sintering flue gas according to any one of claims 1-7, characterized in that, The temperature of the furnace chamber is 850°C.

10. The method for synergistic removal of pollutants and energy recovery and utilization from sintering flue gas according to claim 1, characterized in that, Dust removal is performed on the sintering flue gas before it enters the furnace.

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