Waste incineration plant flue gas treatment method

Abstract

The invention relates to the technical field of flue gas treatment, in particular to a method for treating flue gas of a waste incineration plant. The problem of low flue gas treatment efficiency in the prior art is solved. The method comprises the following steps: firstly, simultaneously spraying a nitrogen oxide reducing agent and a micronized calcium-based deacidification agent into a high-temperature section of flue gas, and carrying out non-catalytic denitration and pre-deacidification treatment; then, the flue gas enters a medium-temperature composite catalytic reactor, and efficient denitration, elemental mercury oxidation and catalytic decomposition of dioxin are achieved through cooperation of a composite catalyst; then, the flue gas enters a graded circulating fluidized bed system, acid gas is efficiently removed through a first-stage circulating fluidized bed, then the flue gas enters a second-stage circulating fluidized bed after being cooled, and mercury and heavy metal are efficiently adsorbed through modified active coke; finally, the flue gas passes through a composite filter bag, and residual CO and VOCs are catalytically degraded while dust is removed. According to the invention, deep purification of various pollutants in the flue gas is realized through quality-divided cooperation and temperature-divided and zoned treatment, the treatment efficiency is high, and the operation is stable.

Description

Technical Field

[0001] This invention relates to the field of flue gas treatment technology, specifically a method for treating flue gas from a waste incineration plant. Background Technology

[0002] In industrial waste gas treatment, particularly in the field of air pollution control, flue gas originating from municipal solid waste incineration is one of the most complex and difficult-to-purify gas mixtures. This type of flue gas is characterized by the coexistence of multiple pollutants, including not only particulate matter but also various harmful gaseous components such as acidic gases (SO2, HCl), nitrogen oxides (NOx), volatile heavy metals (especially mercury, cadmium, and lead), and persistent organic pollutants (such as dioxins, PCDD / Fs). To meet increasingly stringent air pollutant emission standards, developing purification technologies and separation methods that can simultaneously and efficiently separate, transform, and remove these multiple harmful gaseous components is a pressing technical challenge in this field.

[0003] Currently, the mainstream technical approach for purifying such complex pollutants in the industry involves a combination of multi-unit operations, typically including: SNCR + semi-dry / dry method (injection of calcium-based absorbent) + activated carbon injection (using adsorption to separate heavy metals and dioxins) + bag filter (solid-gas separation) + SCR (selective catalytic reduction, further converting NOx). However, this technical combination faces serious challenges in terms of separation efficiency and economics. First, SNCR has limited chemical conversion efficiency for NOx, making it difficult to meet low emission requirements; second, excessive injection of calcium-based absorbent for acid removal leads to high absorbent consumption, high operating costs, and the generation of a large amount of solid waste to be treated; more critically, for mercury (especially gaseous elemental mercury Hg)... 0 The removal of dioxins and other pollutants relies excessively on the physical or chemical adsorption of activated carbon. This is essentially a form of pollution transfer rather than a complete in-situ chemical transformation and removal. Furthermore, it consumes a large amount of adsorbent, has low synergistic treatment efficiency, and makes it difficult to achieve stable compliance.

[0004] Therefore, a method for treating flue gas from waste incineration plants is proposed. Summary of the Invention

[0005] The purpose of this invention is to design a method for treating flue gas from a waste incineration plant. This method first involves simultaneously injecting a nitrogen oxide reducing agent and a micronized calcium-based deacidifying agent into the high-temperature section of the flue gas for non-catalytic denitrification and pre-deacidification treatment. Subsequently, the flue gas enters a medium-temperature composite catalytic reactor, where the composite catalyst synergistically achieves efficient denitrification, elemental mercury oxidation, and catalytic decomposition of dioxins. Next, the flue gas enters a staged circulating fluidized bed system, first undergoing efficient removal of acidic gases in the primary circulating fluidized bed, then cooling before entering the secondary circulating fluidized bed, where modified activated carbon efficiently adsorbs mercury and heavy metals. Finally, the flue gas passes through composite filter bags, where dust removal is achieved while catalytically degrading residual CO and VOCs. This invention, through differentiated treatment based on quality and temperature, achieves deep purification of multiple pollutants in the flue gas, resulting in high treatment efficiency and stable operation.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for treating flue gas from a waste incineration plant, comprising the following steps: The flue gas is treated by non-catalytic denitrification and pre-acidification to obtain primary treated flue gas; the primary treated flue gas is treated by composite catalytic treatment to obtain secondary treated flue gas; the secondary treated flue gas is treated by circulating fluidization to obtain tertiary treated flue gas; the tertiary treated flue gas is treated by composite filter bag dust removal to obtain fly ash and treated flue gas.

[0007] The preferred non-catalytic denitrification and pre-deacidification process is as follows: Flue gas is held in the incinerator at 850-950℃ for >2 seconds to ensure basic decomposition of dioxins, control the O2 content at 6%, and maintain stable combustion; urea solution and micronized (D50<10μm) Ca(OH)2 dry powder are simultaneously injected from their respective spray guns at the same furnace window, controlling the SNCR ammonia-nitrogen molar ratio to 1.2-1.8 (the urea injection rate is automatically adjusted according to the NOx concentration at the furnace outlet and the flue gas volume), resulting in pretreated flue gas; the pretreated flue gas is then passed through a water-cooled wall, superheater, and evaporator to lower the temperature to 300℃, resulting in primary treated flue gas; steam is generated for power generation, and the boiler heating surfaces must be regularly and effectively blew soot to prevent ash accumulation from causing a decrease in heat exchange efficiency and temperature fluctuations.

[0008] Preferably, the specific process of composite catalytic treatment is as follows: the primary treated flue gas is fed into a fixed-bed catalytic reactor (filled with composite catalyst), the reaction temperature is 300℃, and the space velocity is 3000-5000 h⁻¹. -1 Catalytic flue gas is obtained; the volume of the composite catalyst (composite catalyst volume (m³)) is calculated based on the flue gas treatment rate and space velocity. 3 = Flue gas treatment capacity (Nm³) 3 / h) / Airspeed (h) -1Based on the measured NOx value at the chimney outlet, the ammonia injection rate of the ammonia injection grid (AIG) is adjusted to ensure that the total ammonia-nitrogen molar ratio (NSR) is sufficient to achieve a denitrification rate of >90%, while controlling the final ammonia slip to <2.5ppm; the composite catalyst is VW-Ti based + RuO2 / CeO2; the catalytic flue gas passes through the economizer (heating boiler feedwater), and the temperature is controlled at 170-190℃ to obtain secondary treated flue gas.

[0009] Preferably, the composite catalyst is prepared by means of 80-90 parts by weight of anatase TiO2 powder (specific surface area > 80 m²). 2 / g) was dried in an oven at 120℃ for 4h to obtain pretreated TiO2; 1-3 parts of ammonium metavanadate and 9 parts of ammonium paratungstate were added to 50 parts of deionized water, and oxalic acid was added as a complexing agent (the molar ratio of oxalic acid to vanadium was 2:1). The mixture was stirred and heated in a water bath at 60℃ until completely dissolved, and then cooled to room temperature to obtain solution A; solution A was slowly and dropwise added to the pretreated TiO2 under vigorous stirring, and aged at room temperature for 2h. The aged material was dried at 110℃ for 12h, and the dried material was transferred to a muffle furnace and dried in air. Under an atmospheric atmosphere, the temperature was increased to 500℃ at a rate of 5℃ / min and held for 4 hours to obtain an intermediate powder. 12.5 parts of cerium nitrate hexahydrate and 1.2 parts of trinitronitrosylruthenium were dissolved in 50 parts of deionized water, and 0.1 parts of dilute nitric acid (1M) were added to obtain solution B. Solution B was slowly and dropwise added to the intermediate powder under vigorous stirring, aged at room temperature for 2 hours, dried at 110℃ for 12 hours, and then heated to 450℃ at a rate of 5℃ / min under an air atmosphere and held for 3 hours to obtain a composite catalyst.

[0010] Preferably, the specific process of circulating fluidized bed treatment is as follows: the secondary treated flue gas passes through the primary circulating fluidized bed, where it undergoes high-speed turbulent mixing. The solids after the reaction are captured by a cyclone separator, with most returning to the reactor and a small portion being discharged. The reaction temperature is 180℃, and the circulation ratio is 50-100, controlled by adjusting the aeration rate of the return valve. Based on the measured values ​​of SO2 and HCl concentrations at the chimney outlet, the rotational speed of the lime feed screw conveyor is adjusted via a PID controller, maintaining the fluidization velocity at 3-5 m / s. After leaving the primary circulating fluidized bed, the secondary treated flue gas enters a water spray quench tower, where the temperature is controlled at 140℃. It then enters the secondary circulating fluidized bed, where the circulating material is modified activated coke, the adsorption temperature is 140℃, and the circulation ratio is 50-100, resulting in tertiary treated flue gas. Based on the online mercury monitoring data at the chimney outlet, the rate of the adsorbent feeder is adjusted. For dioxins, a basic feed rate is set based on periodic sampling results and boiler operating conditions, and is corrected online using mercury data.

[0011] Preferably, the modified activated carbon is prepared by means of: 90-100 parts by weight of activated carbon (specific surface area > 300 m²). 2 Pretreated activated carbon (with an average particle size of 100-200 mesh) was dried in an oven at 110℃ for 4 hours. The pretreated activated carbon and 18-22 parts of sulfur powder were transferred to a mixer and mixed at 30 rpm for 30 minutes at room temperature to obtain a mixture. The mixture was placed in a reactor, and N2 was first introduced to purge all the air in the system. The N2 atmosphere was maintained, and the temperature was increased from room temperature to 450℃ at a rate of 10℃ / min for 2 hours. The product was allowed to cool naturally. After cooling, the N2 was turned off, and the product was removed. The product was placed in hot water at 80℃ and stirred and washed for 1 hour. It was then filtered and dried at 110℃ for 4 hours to obtain modified activated carbon.

[0012] Preferably, the specific process of composite filter bag dust collection is as follows: the tertiary flue gas is passed into a catalytic composite filter bag dust collector. The filter bags are made of PTFE / P84 membrane and coated with an oxidation catalyst (Hogarat catalyst) on the surface. The filtration velocity is controlled at 0.8-1.2 m / min and the operating temperature is 140℃, resulting in fly ash and treated flue gas. The dust removal adopts a dual control of "differential pressure + timing", mainly relying on the set differential pressure (1200Pa) to start pulse dust removal, avoiding excessive dust removal that damages the filter cake layer, and preventing the differential pressure from being too high. The collected fly ash (mixed with deacidification products and adsorbent) is sent to the fly ash stabilization system for treatment. The treated flue gas is discharged after passing real-time detection.

[0013] Preferably, the overall online real-time monitoring consists of a final continuous emission monitoring system for flue gas (providing feedback on key pollutants) and process control sensors along the route (providing operating parameters such as temperature, pressure, and flow rate); all these signals are ultimately fed into the plant's control system, where the control system automatically executes the PID feedback regulation and feedforward control in the scheme.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This method, by synergistically injecting urea and micronized calcium-based materials in the high-temperature zone of the furnace, pre-removes some acidic gases (HCl, SO2) while performing SNCR denitrification. This significantly reduces the overall load on the subsequent flue gas purification system, particularly drastically reducing the total lime consumption of the subsequent primary CFB desulfurization tower, directly lowering operating costs. Simultaneously, the pre-removal of acidic gases effectively mitigates the risk of corrosion and blockage of the waste heat boiler's heating surfaces and the subsequent medium-temperature SCR catalyst, improving the operational stability and service life of key equipment (such as the boiler and SCR).

[0015] 2. Utilizing a composite catalyst, four core tasks—denitrification, dioxin decomposition, elemental mercury oxidation, and CO oxidation—are synergistically completed within a single unit, demonstrating extremely high system integration. More importantly, it transforms the traditional adsorption-transfer mode of dioxin decomposition into a catalytic decomposition mode, achieving in-situ harmless treatment of pollutants; it also efficiently removes elemental mercury (Hg), which is difficult to remove from flue gas. 0 It is oxidized into ionic mercury, which is easily soluble in water and easily adsorbed, laying a key chemical foundation for the efficient mercury capture of the subsequent secondary CFB.

[0016] 3. Circulating fluidized bed (CFB) technology utilizes its strong solid-gas turbulent mixing and extremely high material internal circulation ratio to make the reaction residence time of the deacidifying agent (lime) much longer than that of traditional dry or semi-dry systems. This allows for a stable increase in lime utilization, thereby significantly reducing lime consumption and operating costs, significantly reducing the total amount of fly ash generated, and greatly alleviating the pressure and cost of subsequent fly ash stabilization and landfill disposal.

[0017] 4. This solution completely separates high-temperature deacidification from low-temperature adsorption, allowing the secondary CFB to operate independently within the optimal low-temperature window for heavy metal and dioxin adsorption. This perfectly resolves the conflicting operating conditions between deacidification (requiring higher temperatures) and adsorption (requiring lower temperatures) in traditional mixed-use processes. Furthermore, the use of modified activated carbon, which exhibits extremely strong chemical adsorption of ionized mercury, achieves ultra-high efficiency targeted removal of mercury (Hg), with results far superior to conventional activated carbon.

[0018] 5. PTFE membrane filter media can ensure that particulate matter emission concentration is reduced and meets emission standards; secondly, the catalytic coating on the surface of the filter bag, as the last line of defense, can effectively treat trace amounts of CO and VOCs that escape momentarily due to fluctuations in incineration conditions, greatly improving the stability and operational safety of the entire flue gas system in response to changes in operating conditions, and ensuring that all pollutants fully and stably meet the standards. Attached Figure Description

[0019] Figure 1 This is a flowchart illustrating the process of treating flue gas from a waste incineration plant according to the present invention. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] For details, please refer to [link / reference]. Figure 1 This invention provides a method for treating flue gas from a waste incineration plant, the technical solution of which is as follows: The levels of various pollutants in the flue gas from a waste incineration plant in Zhejiang Province are as follows: Particulate matter: 1000-5000 mg / m³ 3 CO: 150-200 mg / m³ 3 NOx: 200-750 mg / m³ 3 SO2: 150-900 mg / m³ 3 HCl: 500-2000 mg / m³ 3 Hg and its compounds: 0.1-0.5 mg / m³ 3 Cadmium, thallium and their compounds: 0.5-1 mg / m³ 3 Antimony, arsenic, lead, chromium, cobalt, copper, manganese, nickel and their compounds: 3-7 mg / m³ 3 Dioxins: 1-10 ng TEQ / m³ 3 .

[0022] Example 1 85 parts of anatase TiO2 powder (specific surface area > 80 m²) were used. 2 / g) was dried in an oven at 120℃ for 4h to obtain pretreated TiO2; 2 parts ammonium metavanadate and 9 parts ammonium paratungstate were added to 50 parts deionized water, and oxalic acid was added as a complexing agent (the molar ratio of oxalic acid to vanadium was 2:1). The mixture was stirred and heated in a water bath at 60℃ until completely dissolved, and then cooled to room temperature to obtain solution A; solution A was slowly and dropwise added to the pretreated TiO2 under vigorous stirring, and aged at room temperature for 2h. The aged material was then dried at 110℃ for 12h. The dried material was then transferred to a muffle furnace and dried in air. Under an atmosphere, the temperature was increased to 500℃ at a rate of 5℃ / min and held for 4 hours to obtain intermediate powder. 12.5 parts of cerium nitrate hexahydrate and 1.2 parts of trinitronitrosylruthenium were dissolved in 50 parts of deionized water, and 0.1 parts of dilute nitric acid (1M) were added to obtain solution B. Solution B was slowly and dropwise added to the intermediate powder under vigorous stirring, aged at room temperature for 2 hours, dried at 110℃ for 12 hours, and then heated to 450℃ at a rate of 5℃ / min under an air atmosphere and held for 3 hours to obtain the composite catalyst.

[0023] 95 portions of activated coke (specific surface area > 300 m²) were used. 2Pretreated activated carbon (with an average particle size of 100-200 mesh) was dried in an oven at 110℃ for 4 hours. The pretreated activated carbon and 20 parts of sulfur powder were transferred to a mixer and mixed at 30 rpm for 30 minutes at room temperature to obtain a mixture. The mixture was placed in a reactor, and N2 was first introduced to purge all the air in the system. The N2 atmosphere was maintained, and the temperature was increased from room temperature to 450℃ at a rate of 10℃ / min for 2 hours. The product was allowed to cool naturally. After cooling, the N2 was turned off, and the product was removed. The product was placed in hot water at 80℃ and stirred and washed for 1 hour. It was then filtered and dried at 110℃ for 4 hours to obtain modified activated carbon.

[0024] The flue gas is held at 900℃ for >2 seconds in the incinerator to ensure basic decomposition of dioxins and control the O2 content at 6% to maintain stable combustion. In the same furnace window, urea solution and micronized (D50<10μm) Ca(OH)2 dry powder are jointly injected from their respective spray guns, controlling the SNCR ammonia-nitrogen molar ratio to be 1.5 to obtain pretreated flue gas. The pretreated flue gas is then passed through a water-cooled wall, a superheater, and an evaporator to lower the temperature to 300℃ to obtain primary treated flue gas. The primary treated flue gas is fed into a fixed-bed catalytic reactor (filled with composite catalyst), and the reaction temperature is 300℃ with a space velocity of 4000 h⁻¹. -1 The catalytic flue gas is obtained; the catalytic flue gas passes through an economizer (heating boiler feedwater), and the temperature is controlled at 180℃ to obtain secondary treated flue gas; The secondary treated flue gas passes through a primary circulating fluidized bed, where it undergoes high-speed turbulent mixing. The solids after the reaction are captured by a cyclone separator, with most returning to the reactor and a small portion being discharged. The reaction temperature is 180℃, and the circulation ratio is 75, controlled by adjusting the aeration rate of the return valve. Based on the measured SO2 and HCl concentrations at the chimney outlet, the rotational speed of the lime feed screw conveyor is adjusted via a PID controller, maintaining the fluidizing air velocity at 4 m / s. After leaving the primary circulating fluidized bed, the secondary treated flue gas enters a water spray quench tower, where the temperature is controlled at 140℃. It then enters the secondary circulating fluidized bed, where the circulating material is modified activated coke, with an adsorption temperature of 140℃ and a circulation ratio of 75, resulting in tertiary treated flue gas. The tertiary-stage flue gas is passed into a catalytic composite filter bag dust collector, with the filtration velocity controlled at 1 m / min and the operating temperature at 140℃, to obtain fly ash and treated flue gas. The collected fly ash is sent to a fly ash stabilization system for treatment. The treated flue gas is discharged after passing real-time monitoring.

[0025] Examples 2-5 refer to the parameter conditions in Example 1, with specific differences shown in Table 1.

[0026] Table 1 Parameters and conditions for Examples 1-5 Comparative Example 1 follows the same parameters and conditions as in Example 1, except that it does not remain at high temperature in the furnace.

[0027] Comparative Example 2 follows the same parameters and conditions as in Example 1, except that no pre-deacidification treatment is performed, i.e., no urea solution and Ca(OH)2 dry powder are sprayed in.

[0028] Comparative Example 3 follows the same parameters and conditions as in Example 1, except that no composite catalytic treatment is performed.

[0029] Comparative Example 4 uses the same parameters and conditions as in Example 1, except that the composite catalyst used in the composite catalytic treatment is a commercially available V2O5-WO3 / TiO2 denitration catalyst.

[0030] Comparative Example 5 follows the same parameters and conditions as in Example 1, except that the temperature is not lowered before the composite catalytic treatment.

[0031] Experiment Example 1: Flue Gas Treatment and Detection The treated flue gas was tested and compared with GB 18485-2014 "Standard for Pollution Control of Municipal Solid Waste Incineration". The test results were all 24-hour averages, and the results are shown in Table 2.

[0032] Table 2. Flue gas performance indicators of Examples 1-5 and Comparative Examples 1-5 Table 2 shows that in Comparative Example 1, where the waste was not kept at high temperatures in the furnace, CO and dioxin emissions significantly exceeded standards. This is because incomplete combustion products and raw dioxins from waste incineration could not be fully decomposed within the furnace. This forced the subsequent purification system (composite catalysis and adsorption) to handle CO and dioxins far exceeding the design load, leading to rapid penetration of the catalyst and adsorbent and ultimately failing to meet emission standards. Comparative Example 2 showed excessive NOx, HCl, and SO2 emissions. This was because the SNCR (urea injection) step in the furnace was eliminated, causing all raw NOx, HCl, and SO2 to directly enter the subsequent composite catalytic unit. The catalyst volume and ammonia injection volume were insufficient to independently handle the full pollutant load, resulting in a significant reduction in denitrification efficiency. In Comparative Example 3, which did not undergo composite catalytic treatment, all four key indicators—NOx, CO, Hg (mercury), and dioxins—significantly exceeded standards. This was because the entire composite catalytic unit was removed, lacking catalytic function. NOx from non-catalytic denitrification and pre-deacidification treatment was directly emitted, and the crucial Hg was missing. 0The oxidation function of elemental mercury prevents the modified activated coke in the subsequent secondary circulating fluidized bed from capturing the highly toxic elemental mercury; it also lacks the function of catalytically decomposing dioxins and CO, causing these two pollutants to penetrate the system. Comparative Example 4 used a standard denitrification catalyst, which met NOx emission standards, but CO, Hg (mercury), and dioxins significantly exceeded standards. This demonstrates that commercial catalysts only have a single denitrification function and do not possess the unique ability to oxidize elemental mercury (Hg) as described in this invention. 0 The synergistic function of Hg and its efficient dioxin decomposition further proves that without Hg 0 The oxidation of mercury and the near-ineffective capture of mercury by subsequent circulating fluidization highlight the necessity of the composite catalyst in this invention. Comparative Example 5, which did not cool down before composite catalysis, showed a complete system collapse. High-temperature flue gas from the waste heat boiler was directly injected into subsequent treatment stages without cooling. This not only caused the deacidification reaction to occur in a non-optimal temperature range, resulting in low efficiency, but more critically, the high-temperature flue gas completely burned the subsequent modified activated coke and composite filter bags. This demonstrates that the temperature and zone control in this invention is a prerequisite for achieving stable operation of the entire process.

[0033] Examples 6-9 refer to the parameter conditions in Example 1, with specific differences shown in Table 3.

[0034] Table 3 Parameter conditions for Examples 1 and 6-9 Comparative Example 6 uses the same parameters and conditions as in Example 1, except that the flue gas does not pass through a primary circulating fluidized bed.

[0035] Comparative Example 7 uses the same parameters and conditions as in Example 1, except that the flue gas does not pass through a secondary circulating fluidized bed.

[0036] Comparative Example 8 uses the same parameters and conditions as in Example 1, except that the modified activated carbon in the secondary circulating fluidized bed is not modified and is used directly.

[0037] Comparative Example 9 follows the same parameters and conditions as in Example 1, except that the flue gas does not undergo dust removal treatment via composite filter bags.

[0038] Comparative Example 10 follows the same parameters and conditions as in Example 1, except that the filter bag surface is not coated with an oxidation catalyst.

[0039] Experiment Example 2: Flue Gas Treatment and Detection The treated flue gas was tested according to the test method and comparison method of Experiment Example 1, and the results are shown in Table 4.

[0040] Table 4. Flue gas treatment indicators for Examples 1, 6-9 and Comparative Examples 6-10 Table 4 shows that Comparative Example 6, without a primary circulating fluidized bed, exhibited severely excessive SO2 and HCl emissions. Although the in-furnace pre-desulfurization step could remove some acidic gases, its load and efficiency were limited. Lacking the primary circulating fluidized bed's main desulfurization function, the vast majority of SO2 and HCl in the flue gas were emitted directly without treatment, resulting in severe emissions non-compliance. This demonstrates that a primary circulating fluidized bed is indispensable for efficient and deep removal of acidic gases. Comparative Example 7, without a secondary circulating fluidized bed, showed severely excessive emissions of heavy metals such as mercury (Hg), cadmium, and thallium, as well as dioxins. The reason for this is that the upstream composite catalytic unit had successfully removed the highly toxic element mercury (Hg)... 0 The mercury ions are oxidized to ionic mercury. However, this invention relies on a two-stage circulating fluidized bed (filled with modified activated carbon) to ultimately capture these ionic mercury, heavy metals, and residual dioxins. Without the two-stage circulating fluidized bed, these pollutants lose their adsorption units and directly penetrate the subsequent dust collector, leading to excessive pollutant emissions. In Comparative Example 8, the two-stage circulating fluidized bed used unmodified activated carbon, resulting in severely excessive mercury (Hg) emissions. This clearly demonstrates the necessity of modification in this invention. Ordinary activated carbon has physical adsorption capacity for dioxins and certain heavy metals, but its chemical adsorption capacity for ionic mercury from upstream conversion is very weak. The modified activated carbon used in Example 1 of this invention, however, has sulfur functional groups on its surface that can strongly chemically adsorb ionic mercury (forming stable HgS), which is key to achieving ultra-low mercury emissions. Comparative Example 9, without composite filter bag dust removal, exhibited extremely high particulate matter (PM) emissions, along with severely excessive levels of all heavy metals and dioxins. This is because the bag filter is the final solid-gas separation step in the entire process. Eliminating this step not only prevents the capture of the deacidification products from the primary circulating fluidized bed and the adsorbents from the secondary circulating fluidized bed (which are already enriched with mercury, heavy metals, and dioxins), but also results in the complete discharge with the flue gas, causing severe particulate matter and secondary pollution emissions. Comparative Example 10, with its filter bags uncoated with a catalyst, showed only slight CO exceedances, demonstrating the role of the catalytic coating in this invention. In Example 1, the upstream composite catalytic unit treated most of the CO, while the catalytic coating (Hogarat catalyst) on the filter bags was used to treat trace amounts of CO escaping due to fluctuations in operating conditions. In Comparative Example 10, the filter bags only had a filtration function, leading to direct penetration and emission of trace amounts of CO.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for treating waste incineration plant flue gas, characterized in that, The method comprises the following steps: The flue gas is subjected to non-catalytic denitration and pre-acid removal treatment to obtain first-stage treated flue gas; The first-stage treated flue gas is subjected to composite catalytic treatment to obtain second-stage treated flue gas; The second-stage treated flue gas is subjected to circulating fluidized treatment to obtain third-stage treated flue gas; The third-stage treated flue gas is subjected to composite filter bag dedusting treatment to obtain fly ash and treated flue gas; The circulating fluidized treatment comprises first-stage and second-stage circulating fluidized beds.

2. A method of treating flue gas from a waste incineration plant according to claim 1, characterized in that, The specific process of the non-catalytic denitration and pre-acid removal treatment is that urea solution and Ca(OH)2 dry powder are simultaneously sprayed into a furnace window where the flue gas is located to obtain pretreated flue gas; and the pretreated flue gas flow is subjected to cooling to obtain the first-stage treated flue gas.

3. A method of treating flue gas from a waste incineration plant according to claim 1, characterized in that, The specific process of the composite catalytic treatment is that the first-stage treated flue gas is subjected to catalysis by a composite catalyst to obtain catalytic flue gas; and the catalytic flue gas is subjected to cooling to obtain the second-stage treated flue gas.

4. A method of treating flue gas from a waste incineration plant according to claim 3, characterized in that, The preparation method of the composite catalyst is that TiO2 powder is dried to obtain pretreated TiO2; ammonium metavanadate and ammonium paratungstate are added into deionized water, and oxalic acid is added, and the mixture is stirred in a water bath until dissolved to obtain solution A; The solution A is added into the pretreated TiO2, and the mixture is aged at room temperature, and then dried and transferred into a muffle furnace for calcination to obtain an intermediate powder; cerium nitrate hexahydrate and ruthenium nitrosyl nitrate are dissolved in deionized water to obtain solution B; the solution B is added into the intermediate powder, and the mixture is aged at room temperature, and then dried and calcined to obtain the composite catalyst.

5. A method of treating flue gas from a waste incineration plant according to claim 1, characterized in that, The specific process of the circulating fluidized treatment is that the second-stage treated flue gas is subjected to mixing reaction circulation in the first-stage circulating fluidized bed, and after the second-stage treated flue gas leaves the first-stage circulating fluidized bed, the flue gas is subjected to cooling and enters the second-stage circulating fluidized bed, and the circulating material is modified activated coke, and the third-stage treated flue gas is obtained after treatment.

6. A method of treating flue gas from a waste incineration plant according to claim 5, characterized in that, The preparation method of the modified activated coke is that activated coke is dried to obtain pretreated activated coke; the pretreated activated coke is mixed with sulfur powder to obtain a mixture; and the mixture is calcined in a N2 atmosphere, and the product is naturally cooled, washed and filtered in deionized water, and dried to obtain the modified activated coke.

7. A method of treating flue gas from a waste incineration plant according to claim 1, characterized in that, The specific process of the composite filter bag dedusting treatment is that the third-stage treated flue gas is introduced into a catalytic functional composite filter bag deduster, the filter bag adopts PTFE / P84 film coating, and an oxidation catalyst is coated on the surface layer to obtain the fly ash and the treated flue gas; The fly ash is sent to a fly ash stabilization system for treatment; and the treated flue gas is discharged after real-time detection.

Images