Treatment method of epichlorohydrin production waste gas

Abstract

The invention belongs to the technical field of industrial organic waste gas treatment, and particularly discloses an epoxy chloropropane production waste gas treatment method which comprises the following steps: (1) waste gas collection; (2) waste gas combustion, wherein an incinerator is adopted for high-temperature treatment; (3) heat recovery, wherein a waste heat boiler is adopted for heat recovery; (4) acid liquor recovery, including quenching treatment, preliminary deacidification and deep deacidification, to remove hydrogen chloride; (5) flue gas purification: adopting a denitration device, and adding a modified vanadium-titanium catalyst, an SCR (Selective Catalytic Reduction) catalyst and a reducing agent to remove nitrogen oxides; and (6) harmless discharge. The graphite tower is used for rapidly cooling, and the modified vanadium-titanium composite catalyst system and the activated carbon adsorption tower process are matched to greatly reduce the generation of a harmful product dioxin; the incinerator, the waste heat boiler and the like are subjected to corrosion-resistant treatment, so that the damage of acidic components of hydrogen chloride to equipment is reduced; and meanwhile, the waste heat boiler is adopted for heat recovery, energy consumption can be reduced, and green development is met.

Description

Technical Field

[0001] This application relates to the technical field of industrial organic waste gas treatment, and in particular to a method for treating waste gas from epichlorohydrin production. Background Technology

[0002] Epichlorohydrin (ECH), an important organic chemical raw material and petrochemical intermediate, is mainly used to produce epoxy resins, synthetic glycerol, and chlorohydrin rubber. ECH is also widely used in the manufacture of ion exchange resins, adhesives, plasticizers, surfactants, coatings, and pharmaceutical products.

[0003] Existing epichlorohydrin synthesis technologies mainly include the high-temperature chlorination of propylene, the propylene acetate method, the glycerol method, and the direct epoxidation of allyl chloride. However, regardless of the synthesis method used, the management of byproducts and waste disposal involved in epichlorohydrin preparation significantly restricts the industry's development. In particular, the treatment of industrial waste gas and residue is crucial. The organic waste gas generated during epichlorohydrin preparation is primarily composed of chlorine-containing organic compounds, and existing waste gas treatment technologies include activated carbon adsorption, catalytic combustion with precious metal catalysts, and biological treatment using polyurethane foam as filler in biofilters. When high-temperature combustion is used to treat industrial waste gas, the generation of harmful intermediates (such as dioxins) is difficult to avoid, and the equipment is susceptible to corrosion from acidic gases (such as hydrogen chloride). Furthermore, combustion-based treatment systems often lack heat recovery mechanisms.

[0004] Regarding the aforementioned technologies, the applicant believes that existing methods for treating organic waste gas during epichlorohydrin preparation not only consume enormous amounts of energy but also fail to meet the requirements for harmless treatment of waste gas. Summary of the Invention

[0005] In order to ensure that the organic waste gas produced during the epichlorohydrin preparation process can meet the requirements for harmless treatment while reducing energy consumption during combustion, this application provides a method for treating the waste gas produced during epichlorohydrin production.

[0006] This application provides a method for treating waste gas from epichlorohydrin production, comprising the following steps: S1, Waste gas collection; S2. Waste gas combustion: The waste gas is heated to 900-1200℃ in an incinerator and the residence time is 3-5 seconds for high-temperature treatment. S3. Heat recovery: The waste heat boiler is used to recover heat from the exhaust gas at the outlet of the incinerator in step S2, and then the temperature is reduced to 500-600℃, with a residence time of 0.6-1.8s. S4. Acid recovery, including (1) rapid cooling, (2) preliminary deacidification and (3) deep deacidification, to remove hydrogen chloride from the waste gas in step S3; S5. Flue gas purification: A denitrification device is used, and modified vanadium-titanium catalyst, SCR catalyst and reducing agent are added to remove nitrogen oxides from the exhaust gas in step S4. S6. Harmless emissions.

[0007] By adopting the above technical solution, the organic chlorine-containing waste gas is collected under pressure and then fed into an incinerator. Under high temperature and sufficient oxygen conditions, it is converted into inorganic substances such as carbon dioxide, hydrogen chloride, and water, ensuring that toxic substances (such as unreacted epichlorohydrin, dichloropropane, and dioxin precursors) are completely oxidized and decomposed. Simultaneously, limiting the heating temperature and residence time in this step ensures that the organic chlorine-containing waste gas has sufficient conditions to complete high-temperature degradation, and at this temperature range, dioxin synthesis is also inhibited. The high-temperature flue gas from the incinerator outlet is then efficiently recovered through a waste heat boiler to recover the sensible heat released during combustion, converting the heat energy into steam or hot water. This, combined with a heat energy circulation device, significantly reduces energy consumption and costs. Simultaneously, the high-temperature flue gas undergoes preliminary cooling to suit the acceptable temperature range of the subsequent acid recovery unit, and is quickly passed to the next process to avoid prolonged residence in this temperature range, which could lead to dioxin resynthesis. It is then passed into the acid recovery process to efficiently remove and recover the main acidic pollutant, hydrogen chloride (and a small amount of sulfur dioxide), and combines rapid cooling, preliminary deacidification, and deep deacidification to ensure that the concentrations of hydrogen chloride and other pollutants are far below emission limits. Finally, it is passed into the flue gas purification process, where a composite catalyst system constructed by loading modified vanadium-titanium catalysts and SCR catalysts into the denitrification unit removes residual trace pollutants such as nitrogen oxides, dioxins, and harmful dust, thereby ensuring that the final emissions fully meet standards.

[0008] Preferably, the incinerator undergoes a corrosion-resistant pretreatment; the corrosion-resistant pretreatment includes constructing the combustion chamber sidewall of the incinerator using a corrosion-resistant composite material, the corrosion-resistant composite material including silicon carbide, boron nitride, chromium corundum, ceramic microspheres, polymethyl silicone, and ultra-low temperature cement. The silicon carbide accounts for 55-65% of the total amount of the corrosion-resistant composite material, and the average particle size of the ceramic microspheres is 100-400 μm.

[0009] By adopting the above technical solution, since high-temperature treatment of organic chlorine-containing waste gas will generate a large amount of hydrogen chloride, the combustion chamber inside the incinerator is pretreated with a corrosion-resistant and high-temperature-resistant composite material. This reduces the corrosive effect of acidic substances on the equipment (resistance to hydrogen chloride corrosion rate) while ensuring high-temperature decomposition. The corrosion-resistant composite material uses silicon carbide composite castable, with silicon carbide as the main body. Silicon carbide forms a dense silica protective layer (inert barrier) under a hydrogen chloride atmosphere. This silica layer can also act as a self-healing material to fill cracks, thereby significantly improving the chlorine penetration resistance of the incinerator's internal structure. Silicon carbide particles have high hardness and poor flowability. If the content exceeds 65%, it will be difficult for the material to be fully coated and filled by the binder during molding, easily forming pores or microcracks. This reduces the chlorine penetration resistance. Furthermore, silicon carbide material is brittle. When the content exceeds 65%, it is prone to cracking due to thermal stress concentration during temperature fluctuations in the incinerator (such as during start-up and shutdown), disrupting the continuity of the silica protective layer. The core of chlorine corrosion resistance lies in the dense silica layer formed by the reaction of silicon carbide and HCl. The thickness and continuity of this layer are directly related to the silicon carbide content. If the silicon carbide content is less than 55%, the amount of silica generated is insufficient, making it difficult to form a complete and dense inert barrier. HCl can then easily penetrate directly into the material, reducing its lifespan. Boron nitride is used as a toughening phase, chromium corundum as a matrix material, and an appropriate amount of polymethyl silicone as a binder (to adjust the compatibility of the various solid materials) to significantly improve the density and compressive strength of the furnace structure. Simultaneously, the filling with blended small-diameter ceramic microspheres can block the penetration of acidic condensate, preventing chloride ions from diffusing into the insulation layer and adjusting the thermal expansion coefficient of the corrosion-resistant composite material within the furnace, thereby significantly extending the incinerator's service life. Ultra-low-temperature cement provides initial hydration strength.

[0010] Preferably, the waste heat boiler in step S3 is selected from either a heat pipe boiler or a water pipe boiler; the waste heat boiler undergoes corrosion-resistant pretreatment, and the heat exchange component material of the waste heat boiler includes either C-276 Hastelloy or C-22 Hastelloy.

[0011] By adopting the above technical solution, heat pipe boilers and / or water pipe boilers are selected as waste heat boilers according to the heat load and steam parameter requirements to recover the sensible heat of the high-temperature flue gas from the incinerator outlet in the previous process. Simultaneously, combined with the hot surface design of the waste heat boiler, the recovered waste gas is rapidly introduced into the acid recovery process through active / passive cooling measures within a short time. This significantly reduces energy consumption while preventing the waste gas from remaining in the low-temperature zone for too long and thus preventing dioxin synthesis. Furthermore, since the waste gas after high-temperature treatment contains a large amount of hydrogen chloride, C-276 and / or C-22 Hastelloy alloy materials are used for corrosion resistance on the heating surfaces of the waste heat boiler (especially in the low-temperature zone). Utilizing the material properties of Hastelloy, not only can the high thermal conductivity requirements of the heat exchange device be met, improving waste heat recovery efficiency, but it can also enhance the device's resistance to chloride ion corrosion and oxidation, thereby extending the device's service life.

[0012] Preferably, the rapid cooling treatment in step S4 includes using a graphite tower to rapidly cool the waste gas from step S3 to 60–80°C for 0.2–0.8 seconds. The rapid cooling treatment can be performed through direct contact, where the waste gas and the falling film circulating liquid are in full contact within the downcomer. The surface temperature of the circulating liquid rises until it vaporizes, carrying away heat and lowering the waste gas temperature, thus preventing high-temperature waste gas from damaging the spray tower.

[0013] Preferably, supercritical water is sprayed inside the graphite tower to rapidly cool the waste gas in step S3, with a spray pressure of 25-30 MPa and a water-to-gas ratio of 0.7-1.4 L / Nm3.

[0014] By adopting the above technical solution, since the previous process has already pre-cooled the high-temperature treated waste gas, the waste gas is now in a low-temperature zone (around 200-500℃). If the residence time in this stage is too long (more than 2 seconds), the concentration of dioxins will increase exponentially. The supercritical water jetting technology inside the graphite tower uses supercritical water (374℃, 22.1MPa) as a medium, atomized and sprayed through a fan-shaped nozzle. Utilizing its extremely high latent heat of vaporization and strong heat transfer capacity, millisecond-level (0.2-0.8s) temperature control of the waste gas is achieved, rapidly cooling it to near saturation temperature (60-80℃), preventing the synthesis of dioxins in a short time and significantly reducing the risk of harmful intermediate product formation. Furthermore, by controlling the jetting pressure of the supercritical water to 25-30MPa, the supercritical state is ensured, and the droplet size is controlled within a suitable range. Furthermore, by controlling the water-to-air ratio to 0.7–1.4 L / Nm3, the cooling rate and subsequent humidity load can be balanced, thus serving as an important transitional stage to prevent dioxin formation.

[0015] Preferably, the preliminary deacidification in step S4 includes water washing and circulating absorption; the water washing and circulating absorption includes using a spray tower to circulate water to flush the waste gas; the spray tower undergoes corrosion-resistant pretreatment, and the internal material of the spray tower includes one or more of C-276 Hastelloy, C-22 Hastelloy, silicon carbide, and polytetrafluoroethylene.

[0016] By adopting the above technical solution, a spray tower is used to wash and circulate the waste gas to efficiently absorb hydrogen chloride. Water's good solubility for hydrogen chloride gas at lower temperatures allows for the absorption of most of the hydrogen chloride in the waste gas, forming dilute hydrochloric acid, which is then discharged as a byproduct for recycling. A circulating pump continuously pumps the dilute acid solution from the bottom of the tower to the top for spraying, and continuously replenishes the spray water. This not only allows for real-time control of the dilute hydrochloric acid concentration but also further reduces the waste gas temperature and washes away any remaining traces of harmful dust. Simultaneously, the interior of the spray tower uses C-276 Hastelloy, C-22 Hastelloy, silicon carbide, and polytetrafluoroethylene for corrosion resistance treatment to enhance the device's resistance to chloride ion corrosion and oxidation, thereby extending its service life.

[0017] Preferably, the deep deacidification in step S4 includes neutralizing the residual acidic gas in the waste gas using an alkaline scrubbing tower, wherein the alkaline solution in the alkaline scrubbing tower is selected from either a sodium hydroxide solution with a concentration of 10-30% or a sodium carbonate solution with a concentration of 10-40%.

[0018] By adopting the above technical solution, an alkaline scrubbing tower is used to neutralize the residual acidic hydrogen chloride and the trace amount of sulfur dioxide produced by combustion. Specifically, a sodium hydroxide solution with a concentration of 10-30% and / or a sodium carbonate solution with a concentration of 10-40% are selected as cost-effective alkaline solutions for final neutralization and washing, so as to ensure that the concentrations of hydrogen chloride and sulfur dioxide in the exhaust gas are far below the emission limits.

[0019] Preferably, step S5 further includes heat exchange pretreatment, which raises the temperature of the exhaust gas after step S4 to 220-280°C before it is introduced into the denitrification device.

[0020] By adopting the above technical solution, a heat exchange pretreatment is added before the flue gas purification process to heat the waste gas before it enters the denitrification unit to the required reaction temperature, i.e., 220-280℃, which meets the optimal activity reaction temperature of the modified vanadium-titanium catalyst and the SCR catalyst. It should be noted that since the chlorine-containing components in the waste gas have been largely absorbed and treated in the previous process, there is no need to worry excessively about the risk of dioxin synthesis in the low-temperature zone. Simultaneously, the heat source used in this heat exchange pretreatment step can be reused from the waste heat boiler in step S3 through industrial-scale circuit design for reheating, thereby ensuring the quality of waste gas treatment while reducing the energy consumption required by the original circuit through heat recycling.

[0021] Preferably, the modified vanadium-titanium catalyst in step S5 is a cerium-doped vanadium-titanium catalyst. The SCR catalyst includes any one or more of Cu-based molecular sieve catalysts and Fe-based molecular sieve catalysts; The mass ratio of the modified vanadium-titanium catalyst to the SCR catalyst is 1:(0.7-0.9). The reducing agent is selected from any one or more of ammonia water and urea solution.

[0022] By employing the above technical solution, under the action of a composite catalyst system composed of modified vanadium-titanium catalyst and SCR catalyst, a reducing agent is also injected into the waste gas, thereby efficiently removing nitrogen oxides from the waste gas and reducing them to harmless nitrogen and water. On the one hand, the modified vanadium-titanium catalyst is selected as a cerium-based doped vanadium-titanium catalyst. By doping the vanadium-titanium catalyst with a cerium source as a basic support, it obtains a high specific surface area, good thermal stability, and high dispersion of active components. Furthermore, the various acid sites on the surface of the modified vanadium-titanium catalyst can adsorb chlorinated hydrocarbons, promoting the breaking of carbon-chlorine bonds and thus preventing the chlorination reaction of dioxin precursors. Therefore, while vanadium-titanium catalysts possess industrial denitrification capabilities, they can also catalytically decompose potentially residual dioxins and other chlorine-containing harmful substances. The combination of cerium-doped vanadium-titanium catalysts and low-temperature denitrification SCR catalysts achieves simultaneous removal of nitrogen oxides and dioxins. Furthermore, using Cu-based and / or Fe-based molecular sieve catalysts for the SCR catalyst ensures good denitrification performance in the low-to-medium temperature range. Controlling the mass ratio of modified vanadium-titanium catalyst to SCR catalyst within a specific range balances the removal of nitrogen oxides and chlorinated organic compounds, achieving the deepest purification of the waste gas in step S5. The nitrogen-containing compounds, such as ammonia and / or urea solution, used as reducing agents also act as inhibitors of dioxin synthesis, competitively consuming active chlorine free radicals and reducing the formation of chlorine precursors.

[0023] Preferably, step S5 further includes using an activated carbon adsorption tower to adsorb and filter the denitrified waste gas, wherein the adsorbent used in the activated carbon adsorption tower is selected from any one or more of sulfur-impregnated activated carbon and halogen-impregnated activated carbon.

[0024] By adopting the above technical solution, activated carbon adsorption towers are used as an effective physical adsorption method, and sulfur-impregnated activated carbon and / or halogen-impregnated activated carbon are selected as adsorbents to deeply remove trace pollutants (including possible residual dioxins, heavy metals, sulfides and other harmful dust) from the waste gas, thereby ensuring that the gas emitted into the atmosphere by subsequent processes meets various emission indicators and achieves harmless emissions.

[0025] In summary, this application has the following beneficial effects: 1. This application involves collecting pressurized organic chlorine-containing waste gas and then incinerating it in a furnace under high temperature and sufficient oxygen conditions to convert it into inorganic substances such as carbon dioxide, hydrogen chloride, and water. This ensures that toxic substances (such as unreacted epichlorohydrin, dichloropropane, and dioxin precursors) are completely oxidized and decomposed. Simultaneously, limiting the heating temperature and residence time in this step ensures that the organic chlorine-containing waste gas has sufficient conditions to complete high-temperature degradation, and also inhibits dioxin synthesis within this temperature range. The high-temperature flue gas from the incinerator outlet is then efficiently recycled through a waste heat boiler to recover the sensible heat released during combustion, converting the heat energy into steam or hot water. This, combined with a heat energy circulation device, significantly reduces energy consumption and costs. Simultaneously, the high-temperature flue gas undergoes preliminary cooling to suit the acceptable temperature range of the subsequent acid recovery unit, and is quickly passed to the next process to avoid prolonged residence in this temperature range, which could lead to the resynthesis of dioxins. It is then passed into the acid recovery process to efficiently remove and recover the main acidic pollutant, hydrogen chloride (and a small amount of sulfur dioxide), and combines rapid cooling, preliminary deacidification, and deep deacidification to ensure that the concentrations of hydrogen chloride and other pollutants are far below emission limits. Finally, it is passed into the flue gas purification process, where a composite catalyst system constructed by loading modified vanadium-titanium catalysts and SCR catalysts into the denitrification unit removes residual trace pollutants such as nitrogen oxides, dioxins, and harmful dust, thereby ensuring that the final emissions fully meet standards. 2. This application pre-treats the combustion chamber inside the incinerator with a corrosion-resistant and high-temperature-resistant composite material to reduce the corrosive effect of acidic substances on the equipment (resistance to hydrogen chloride corrosion rate) while ensuring high-temperature decomposition. The corrosion-resistant composite material uses silicon carbide composite castable, with silicon carbide as the main component. Silicon carbide forms a dense silica protective layer (inert barrier) under a hydrogen chloride atmosphere. This silica layer acts as a self-healing material to fill cracks, significantly improving the chloride penetration resistance of the incinerator's internal structure. Boron nitride is used as a toughening phase, chromium corundum as the matrix material, and an appropriate amount of polymethyl silicone as a binder (to adjust the compatibility of the solid materials), greatly enhancing the density and compressive strength of the furnace structure. Simultaneously, the filling with blended small-diameter ceramic microspheres can block the penetration of acidic condensate, preventing chloride ions from diffusing into the insulation layer and adjusting the thermal expansion coefficient of the corrosion-resistant composite material inside the furnace, thereby significantly extending the service life of the incinerator. 3. This application utilizes a composite catalyst system consisting of a modified vanadium-titanium catalyst and an SCR catalyst, and further injects a reducing agent into the waste gas to efficiently remove nitrogen oxides from the waste gas and reduce them to harmless nitrogen and water. On one hand, the modified vanadium-titanium catalyst is selected as a cerium-doped vanadium-titanium catalyst. By doping the vanadium-titanium catalyst with a cerium source as a basic support, it achieves high specific surface area, good thermal stability, and high dispersion of active components. Furthermore, the various acid sites on the surface of the modified vanadium-titanium catalyst can adsorb chlorinated hydrocarbons, promoting the breaking of carbon-chlorine bonds and thus preventing the chlorination reaction of dioxin precursors. Therefore, while vanadium-titanium catalysts possess industrial denitrification capabilities, they can also catalytically decompose potentially residual dioxins and other chlorine-containing harmful substances. The combination of cerium-doped vanadium-titanium catalysts and low-temperature denitrification SCR catalysts achieves simultaneous removal of nitrogen oxides and dioxins. Furthermore, using Cu-based and / or Fe-based molecular sieve catalysts for the SCR catalyst ensures good denitrification performance in the low-to-medium temperature range. Controlling the mass ratio of modified vanadium-titanium catalyst to SCR catalyst within a specific range balances the removal of nitrogen oxides and chlorinated organic compounds, achieving the deepest purification of the waste gas in step S5. The nitrogen-containing compounds, such as ammonia and / or urea solution, used as reducing agents also act as inhibitors of dioxin synthesis, competitively consuming active chlorine free radicals and reducing the formation of chlorine precursors. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this application clearer and to provide a more thorough and comprehensive understanding of the disclosure of this application, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments. The described embodiments are only a part of the embodiments of this application, and not all of them.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0028] In this application, terms such as "further," "even more," "particularly," "for example," "like," "example," and "exemplary" are used for descriptive purposes to indicate that different technical solutions preceding and following each other are related in terms of their coverage, but should not be construed as limiting the preceding technical solution or restricting the scope of protection of this application. In this application, unless otherwise specified, A (e.g., B) indicates that B is a non-limiting example of A, and it can be understood that A is not limited to B.

[0029] In this application, the technical features or solutions described in open-ended language include both closed-ended technical features or solutions consisting of the listed contents and open-ended technical features or solutions that include the listed contents.

[0030] In this application, the exemplary descriptions such as "in some implementations (or embodiments)" and "in one implementation (or embodiment)" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0031] In this application, where the method flow involves multiple steps, unless otherwise explicitly stated herein, there is no strict order restriction on the execution of these steps; they can be executed in any order other than those described. Moreover, any step may include multiple sub-steps or multiple stages, which are not necessarily completed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be performed alternately or simultaneously with other steps or parts of the sub-steps or stages of other steps.

[0032] This application specifically discloses a method for treating waste gas from epichlorohydrin production, which is actually an industrial treatment line for by-product management and waste treatment in the epichlorohydrin industry. According to existing epichlorohydrin synthesis methods, the main methods include high-temperature chlorination of propylene, propylene acetate method, glycerol method and direct epoxidation of chloropropylene. The by-products and wastes obtained by different preparation methods are different. However, in industrial applications, the key to the technical solution provided by this application is to treat acidic tail gas (mainly hydrogen chloride, which may contain a small amount of sulfur dioxide), prevent the synthesis of harmful intermediate products dioxins (including their precursors) by organic chlorides in a suitable temperature range during the treatment process, and recover the heat generated by incineration. This ensures that the final emission gas meets national or local environmental standards (such as GB 31571-2015). This application mainly includes the following treatment steps: (1) waste gas collection; (2) waste gas combustion; (3) heat recovery; (4) acid recovery; (5) flue gas purification; (6) harmless emission.

[0033] For (1) the waste gas collection process, the waste gas generated during the epichlorohydrin production process is introduced into the waste gas collection tank and pressurized to increase the concentration of chloride per unit volume in the waste gas; and the pressurization range can be adjusted according to the actual distance to the next process. For example, 3-6 kPa can be used for short-distance pipeline transportation, while 8-12 kPa can be used for long-distance pipeline transportation (>200m). Therefore, the overall pressure range can be controlled as 3-12 kPa. The power unit used or integrated in the pressurization process can be a negative pressure fan, liquid ring compressor, etc. The collection tank and the transportation pipeline can be treated with corrosion resistance, such as using FRP (fiberglass) material, etc. At the same time, relevant protective measures can be arranged for this process, such as installing a buffer tank and safety valve at the compressor outlet.

[0034] For (2) the waste gas combustion process, an incinerator is used to completely oxidize and decompose the organic pollutants (especially chlorinated organics) in the waste gas transported from the previous process to the incinerator under high temperature and sufficient oxygen conditions, so as to convert them into inorganic substances such as carbon dioxide, water and hydrogen chloride, and ensure that toxic substances such as unreacted epichlorohydrin, dichloropropane, and dioxin precursors are completely destroyed. For the incinerator, a regenerative thermal oxidizer (RTO) or a thermal oxidizer (TO) can be selected, and the combustion temperature is set to 900-1200℃, preferably 1050-1200℃. Chlorinated organics usually require a temperature of more than 1100℃ to ensure complete decomposition. The residence time is set to 3-5s to ensure that the residence time of the waste gas in the high-temperature incinerator is not too long, but sufficient time is required to complete the oxidation reaction. At the same time, in order to meet the above combustion conditions, the incinerator can be preheated before the waste gas is introduced, and an excess of oxygen (≥3%) is maintained to ensure complete combustion of the waste gas. The choice of fuel for incinerators usually requires the supplementation of auxiliary fuels such as natural gas or fuel oil to maintain stable furnace temperature.

[0035] When pressurized, high-concentration chlorine-containing waste gas is burned at high temperatures, it produces a large amount of acidic hydrogen chloride gas. The interior of the incinerator requires corrosion-resistant pretreatment, meaning that the internal structure of the incinerator, such as the combustion chamber sidewalls and pipelines, can be constructed using corrosion-resistant composite materials. These corrosion-resistant composite materials also need to possess high-temperature resistance and thermal shock resistance to meet the processing conditions of high-temperature incineration. Corrosion-resistant composite materials include silicon carbide, boron nitride, chromium corundum, ceramic microspheres, polymethyl silicone, and a small amount of ultra-low-carbon cement (calcium oxide < 2.5%) as a base filler. These materials are prepared through physical blending to obtain a castable, which can be used to form incinerator components of various shapes.

[0036] This corrosion-resistant composite castable, by percentage content, specifically includes 55-65% silicon carbide, 15-20% chromium corundum (Al2O3·Cr2O3), 3-5% boron nitride, 8-10% ceramic microspheres, 6-8% polymethyl silicone resin, 4-8% ultra-low-temperature cement (optional CA-70), and 1-2% other additives. Other additives include water-reducing agents and retarders. The water-reducing agent can be a polycarboxylate-based water-reducing agent, such as BASF ADVA 109; the retarder can be sodium citrate to control the hydration rate of the castable. Silicon carbide, as the main aggregate, not only provides high-temperature strength, wear resistance, and acid corrosion resistance, but also forms silica under a high-temperature hydrogen chloride atmosphere to self-repair cracks in the furnace cavity, continuously ensuring high resistance to chloride penetration. Chromium corundum, as the main matrix, has a high melting point and good thermal stability, making it resistant to deformation or damage under high-temperature conditions, ensuring the structural integrity of the incinerator's internal structure. Furthermore, it exhibits strong resistance to corrosive substances such as acids, alkalis, and salts, and possesses extremely high chemical stability, enabling it to resist the erosion of various acids, alkalis, and oxidants. Boron nitride serves as a toughening phase to improve thermal shock stability and reduce the high-temperature friction coefficient. Ceramic microspheres, preferably with a small particle size (100–400 μm, more preferably 100–200 μm), act as fillers to buffer thermal stress within the combustion chamber and, in conjunction with the dense silica layer formed by silicon carbide, adjust and repair defects within the furnace. Polymethyl silicone resin, as an organic binder, not only provides compatibility with various solid materials and enhances toughness but also undergoes high-temperature pyrolysis to generate an amorphous silica reinforcing network, synergistically participating in the repair process of silicon carbide and ceramic microspheres. Ultra-low hydration cement (CaO·Al2O3) provides initial hydration strength, but care must be taken to ensure that the calcium oxide content is not too high to avoid the reaction of calcium oxide with hydrogen chloride, which could lead to pulverization of the structure.

[0037] This application provides a specific method for preparing a corrosion-resistant composite castable, comprising, by percentage content, 60% silicon carbide, 15% chromium corundum, 5% boron nitride, 8% ceramic microspheres, 6% polymethyl silicone resin, and 1% other additives (including 0.5% water-reducing agent and 0.5% retarder), with the balance being ultra-low temperature cement. The specific preparation steps include: 1. Pretreatment of raw materials: Silicon carbide, chromium corundum, and boron nitride are dried continuously at 110℃ for 24 hours to ensure that the moisture content of each solid material is <0.1%; ceramic microspheres are pretreated by soaking in silane coupling agent (KH-550) and ethanol solution to improve their bonding performance with the system. 2. Dry mixing: First, add silicon carbide and chromium corundum to a high-speed mixer and stir continuously at 200 rpm for 10 minutes; then add boron nitride and surface-treated ceramic microspheres and stir continuously at 300 rpm for 20 minutes until uniform to obtain a dry mixture. 3. Wet mixing: Premix polymethyl silicone resin, water-reducing agent and retarder into liquid components, and then slowly add them to the dry mixture, controlling the stirring speed at 200 rpm for 10 minutes to form a uniform slurry; in the last 2 minutes, mix in ultra-low cement and continue stirring until the system is uniformly mixed to avoid premature hydration and heat generation, and obtain the mixture. 4. Casting and molding: The mixture is poured into the mold and compacted using a vibrating table (frequency 50Hz, amplitude 0.5mm, time 2min); then vacuum degassing is performed, and a vacuum (-0.095MPa) is drawn immediately after vibration to eliminate air bubbles; 5. Curing and sintering: Depending on the application (such as bricks in the combustion chamber of an incinerator), after curing, high-temperature sintering is carried out under nitrogen protection to obtain corrosion-resistant composite castable.

[0038] For the heat recovery process (3), it can be divided into two steps: the preceding heat recovery and the subsequent waste gas cooling. Among them, heat recovery mainly involves using a waste heat boiler to efficiently recover the sensible heat of the high-temperature waste gas from the incinerator outlet in step (2), converting the heat energy into steam or hot water, which can then be reused in subsequent heating processes, thereby reducing energy consumption and better conforming to the trend of green industrial development. Depending on the actual production / processing scale, heat pipe boilers and water pipe boilers can be selected. Among them, in the heat pipe waste heat boiler, the working medium (water / ammonia) inside the heat pipe absorbs heat and vaporizes in the evaporation section, and the steam rises to the condensation section to release heat and condense, relying on capillary recirculation to achieve efficient heat transfer; in the water pipe waste heat boiler, water flows inside the header and pipes, while the outside of the pipes is flushed by high-temperature waste gas to achieve efficient heat transfer of the water medium inside the pipes.

[0039] During heat recovery, the temperature of the exhaust gas is significantly lower than that inside the incinerator, posing a risk of localized condensation and corrosion by acidic substances within the waste heat boiler. Therefore, the internal structure of the waste heat boiler requires corrosion-resistant pretreatment. Specifically, corrosion-resistant materials can be applied to the heat exchange surfaces prone to localized condensation. Either Hastelloy C-276 or Hastelloy C-22 can be used. Hastelloy alloys exhibit good corrosion resistance and high-temperature stability. For example, Hastelloy C-276 is a nickel-based alloy (Ni-Mo-Cr), predominantly nickel (approximately 57%), with molybdenum (15-17%) and chromium (14.5-16.5%). Using this material in the waste heat boiler can mitigate its susceptibility to HCl corrosion, allowing for long-term operating temperatures of 400-600℃ and short-term tolerance above 100℃. It also possesses a high thermal conductivity (approximately 10 W / m·K), thus improving the waste heat recovery efficiency of the waste heat boiler. From the perspective of industrialization cost, Hastelloy alloys can be used to replace the high heat exchange frequency parts in the waste heat boiler, while low-cost steels with certain corrosion resistance, such as ND steel and 2205 duplex steel, can be used for other parts.

[0040] The subsequent steps of exhaust gas cooling are mainly to rapidly reduce the exhaust gas temperature to the acceptable range of the subsequent step (4) acid recovery (graphite cooling tower), that is, to reduce the exhaust gas temperature to 500-600℃ and the residence time to 0.6-1.8s. This step requires the cooling / residence time to be controlled as short as possible to avoid prolonged residence in the medium and low temperature zone (200-500℃) leading to dioxin synthesis. After multiple tests, it was found that the residence time generally cannot exceed 2s. It is speculated that the continuous free radical chain reaction causes the accumulation rate of chlorine free radicals to increase nonlinearly, thereby accelerating the condensation reaction of polychlorinated aromatic hydrocarbons and causing dioxins to grow exponentially.

[0041] For (4) acid recovery process, it specifically includes three steps in sequence: 1. quenching treatment; 2. preliminary deacidification; and 3. deep deacidification to efficiently remove and recover the main acidic pollutant hydrogen chloride in the waste gas, generating commercially valuable hydrochloric acid byproduct. Among them, the quenching treatment process is to use a graphite tower to rapidly cool the waste gas that has already undergone the previous cooling process to 60-80°C, with a cooling time of 0.2-0.8s. This step is a key step to effectively inhibit the resynthesis of harmful intermediate dioxins, so as to avoid entering the dioxin synthesis temperature zone (the mechanism is the same as above). The graphite tower can be either a graphite falling film absorption tower or a graphite quenching tower, and the graphite has good thermal conductivity and strong acid corrosion resistance. Usually, the graphite tower equipment uses cooling water sprayed into the top of the tower to form countercurrent contact with the high-temperature waste gas to achieve cooling, but this method still does not have timeliness (millisecond-level heat absorption requirement). In graphite falling film absorption towers, waste gas and falling film circulating liquid come into full contact in the downcomer. The surface temperature of the circulating liquid rises until it vaporizes, carrying away heat and reducing the waste gas temperature, thus preventing high-temperature waste gas from damaging the spray tower. However, this method cannot control the film thickness in real time under load fluctuations, resulting in unsatisfactory cooling effects. Therefore, this application specifically uses supercritical water injection inside the graphite tower to rapidly cool the waste gas, controlling the injection pressure at 25–30 MPa, the cooling water droplet size at <50 μm, and the water-to-air ratio at 0.7–1.4 L / Nm3 to balance the cooling rate with the subsequent humidity load. Specifically, supercritical water (374℃, 22.1 MPa) is atomized and injected through a fan-shaped nozzle, utilizing its high latent heat of vaporization (>2000 kJ / kg) and heat transfer capacity (heat transfer coefficient up to 105 W / m2·K) to rapidly reduce the waste gas temperature to 60–80℃ within 0.2–0.8 s. For the design of supercritical water injection parameters, especially the nozzle layout, a dual-tangential swirl array can be adopted to achieve a coverage of >95% of the tower interface, thus providing a more uniform cooling effect on the entire exhaust gas. Simultaneously, the injected or returned supercritical water can also wash away some of the harmful dust within the exhaust gas.

[0042] The preliminary acid removal process involves using a spray tower to wash and circulate the quenched waste gas from the previous step. Water's high solubility for hydrogen chloride at lower temperatures allows for the absorption of most of the hydrogen chloride in the waste gas, converting it into economically valuable dilute hydrochloric acid as a byproduct. The dilute acid solution from the bottom of the spray tower is continuously pumped to the top for spraying via circulation components (circulation pumps and pipelines), with water continuously added. When the hydrogen chloride concentration in the circulating liquid reaches the target recovery value (typically 15-20%), it is discharged from the tower as the dilute hydrochloric acid byproduct for recovery. This step requires real-time monitoring of the HCl concentration and pH value in the circulating liquid to control the water replenishment and the amount of dilute hydrochloric acid extracted. Since the spray tower requires long-term monitoring and recycling of HCl, it also needs corrosion-resistant pretreatment. Specifically, core components such as the circulating absorption system and spraying devices can be constructed using one or more of the following materials: C-276 Hastelloy, C-22 Hastelloy, silicon carbide, and polytetrafluoroethylene (PTFE) (based on the same principle). This improves the spray tower's corrosion resistance and extends its service life. Simultaneously, the water circulation system in the spray tower further reduces the exhaust gas temperature and effectively removes any remaining harmful dust.

[0043] The deep acid removal process involves neutralizing residual acidic gases in the exhaust gas using an alkaline scrubbing tower. This neutralization process removes any small amounts of unabsorbed hydrogen chloride and sulfur dioxide produced by high-temperature combustion. Specifically, a spray tower similar to or the one used in the previous step can be employed to circulate an alkaline solution for neutralization and washing, ensuring that the concentrations of hydrogen chloride and sulfur dioxide in the exhaust gas are well below emission limits. From an industrial cost perspective, the alkaline solution can be either a 10-30% sodium hydroxide solution or a 10-40% sodium carbonate solution to absorb and wash the acidic gases. As the final step in the acid recovery process, this step also requires the installation of a high-efficiency demister (such as a wire mesh, blade type, or fiber bed) at the top of the spray tower to remove alkaline mist and entrained droplets, protecting equipment in subsequent stages, especially the SCR catalytic denitrification unit and the activated carbon adsorption unit.

[0044] For (5) flue gas purification process, it specifically includes three steps in sequence: 1. heat exchange pretreatment; 2. denitrification device treatment; 3. activated carbon adsorption treatment to efficiently remove nitrogen oxides, as well as harmful intermediate products such as dioxins, VOCs, and harmful dust particles from the waste gas. Among them, the heat exchange pretreatment process involves using a heat exchanger to raise the temperature of the waste gas to 220-280°C before passing it into the subsequent denitrification device. On the one hand, preheating can meet the reaction activity of the subsequent modified vanadium-titanium catalyst and SCR catalyst. At the same time, there is no need to worry too much about the resynthesis of dioxins in this step. Although it is within its suitable temperature window, since most (≥98%) of the hydrogen chloride has been removed in the previous step, there is no chlorine source for dioxin synthesis in this step. On the other hand, the heat source for heating the waste gas in this step can be obtained from the heat recovery process in step (3) of the previous step. Through the design of the heat source transmission pipeline, the heat recovered by the waste heat boiler in step (3) can be recycled back to the preheating process in step (5) in the form of steam / hot water, which can significantly reduce the energy consumed in the entire process route. The heat exchanger can be a conventional device type such as rotary or tubular.

[0045] The denitrification process involves using a denitrification device in conjunction with a modified vanadium-titanium catalyst, an SCR catalyst, and a reducing agent to remove nitrogen oxides from the waste gas. Specifically, the modified vanadium-titanium catalyst is a cerium-doped vanadium-titanium catalyst, while the SCR catalyst is any one or more of a Cu-based molecular sieve catalyst and an Fe-based molecular sieve catalyst, with the mass ratio of the modified vanadium-titanium catalyst to the SCR catalyst controlled at 1:(0.7–0.9). The reducing agent can be any one or more of ammonia water and urea solution. The denitrification device used in the denitrification process is an SCR reactor, with the composite catalyst system constructed from the modified vanadium-titanium catalyst and the SCR catalyst modularly arranged within the SCR reactor. Simultaneously, an ammonia injection system is required to inject the reducing agent, ammonia water / urea solution, into the waste gas after pyrolysis or hydrolysis, thereby reducing the nitrogen oxides in the waste gas to harmless ammonia and water. The selected ammonia injection system can use an ammonia injection grid (AIG) to ensure thorough and uniform mixing of the reducing agent and the waste gas.

[0046] For modified vanadium-titanium catalysts, cerium-doped vanadium-titanium catalysts are used. Since vanadium-titanium catalysts (V₂O₅ / TiO₂) have both denitrification and good dioxin removal effects, they are combined with conventionally used SCR catalysts at medium and low temperatures to achieve simultaneous removal of nitrogen oxides and dioxins. By modifying traditional vanadium-titanium catalysts with cerium, they can efficiently and stably catalyze the decomposition of gaseous dioxin precursors and already formed dioxins. This application also provides a method for preparing a cerium-doped vanadium-titanium catalyst, the specific preparation steps of which include: 1. Solution preparation: Dissolve ammonium metavanadate, oxalic acid dihydrate and cerium dioxide in deionized water, mix and stir thoroughly at room temperature for 10 min, then add titanium chloride and mix and stir thoroughly for 2 h to obtain a mixed metal salt solution. 2. Precipitation: Ammonium carbonate solution was slowly added to the mixed metal salt solution, heated to 60°C, pH controlled at 9, and stirred for 30 min to induce precipitation. After aging under precipitation conditions for 20 h, the solution was filtered and washed to obtain the catalyst precursor precipitate. 3. Calcination and molding: The catalyst precursor is dried in an oven at 120°C for 24 hours. The dried powder is then placed in a muffle furnace and calcined at 500°C for 6 hours. The calcined powder is then pressed into tablets to form modified vanadium-titanium catalyst blocks that conform to the modular arrangement in the SCR reactor.

[0047] Regarding the selection of SCR catalysts, both Cu-based and Fe-based molecular sieve catalysts are chosen from conventional molecular sieve catalysts within their suitable activity temperature range (the topology and pore size of the molecular sieve can be further selected based on the actual process conditions). Specifically, Cu-based molecular sieve catalysts can be one or more of the following types: Cu-ZSM-5, Cu-SAPO-44, Cu-SAPO-34, Ce-Cu-SAPO-18, Cu-Mn-UZM-9, Cu-OFF-CHA, Cu-LTA, and Cu-UZM-35; Fe-based molecular sieve catalysts can be one or more of the following types: Fe-SSZ-13, Fe-Cu-ZSM-5, Fe-ZSM-5, Zr / Fe-SSZ-13, and Fe-LTA. Simultaneously, ammonia and / or urea solutions can be used as reducing agents, which can also act as inhibitors of dioxin synthesis, competitively consuming active chlorine free radicals.

[0048] The activated carbon adsorption treatment process involves using an activated carbon adsorption tower to adsorb and filter the denitrified waste gas. This step serves as a final safety measure, performing deep physical adsorption on the waste gas after the preceding steps to remove any remaining dioxins, heavy metal particles, residual VOCs, sulfides, and harmful dust particles. The internal structure of the activated carbon adsorption tower can employ a fixed-bed and / or moving-bed structure, but a fixed-bed structure is preferred to ensure the adsorbent is packed within the tower and easily replaced after saturation. The adsorbent used in the activated carbon adsorption tower is impregnated activated carbon, specifically any one or more of conventional sulfur-impregnated and halogen-impregnated activated carbon. Additionally, a filter can be installed at the outlet of the activated carbon adsorption tower to remove activated carbon dust.

[0049] For (6) the harmless emission process, clean flue gas that has undergone all the above treatment processes and whose various pollutant indicators meet the national or local emission standards will be discharged into the atmosphere through a chimney. At the same time, an online monitoring system can be set up in this step to monitor the concentration of key pollutants in the emitted flue gas (such as dioxins, hydrogen chloride and nitrogen oxides) and flue gas parameters (such as flow rate, temperature, pressure and oxygen content) in real time to ensure that the emission meets the standards.

[0050] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for treating waste gas from epichlorohydrin production, characterized in that, Includes the following steps: S1, Waste gas collection; S2. Waste gas combustion: The waste gas is heated to 900-1200℃ in an incinerator and the residence time is 3-5 seconds for high-temperature treatment. S3. Heat recovery: The waste heat boiler is used to recover heat from the exhaust gas at the outlet of the incinerator in step S2, and then the temperature is reduced to 500-600℃, with a residence time of 0.6-1.8s. S4. Acid recovery, including (1) rapid cooling, (2) preliminary deacidification and (3) deep deacidification, to remove hydrogen chloride from the waste gas in step S3; S5. Flue gas purification: A denitrification device is used, and modified vanadium-titanium catalyst, SCR catalyst and reducing agent are added to remove nitrogen oxides from the exhaust gas in step S4. S6. Harmless emissions.

2. The method for treating epichlorohydrin production waste gas according to claim 1, characterized in that, The incinerator undergoes a corrosion-resistant pretreatment; the corrosion-resistant pretreatment includes constructing the combustion chamber sidewall of the incinerator using a corrosion-resistant composite material, the corrosion-resistant composite material including silicon carbide, boron nitride, chromium corundum, ceramic microspheres, polymethyl silicone and cement; The silicon carbide accounts for 55-65% of the total amount of the corrosion-resistant composite material, and the average particle size of the ceramic microspheres is 100-400 μm.

3. The method for treating epichlorohydrin production waste gas according to claim 1, characterized in that, The waste heat boiler in step S3 is selected from either a heat pipe boiler or a water pipe boiler; the waste heat boiler undergoes corrosion-resistant pretreatment, and the heat exchange component material of the waste heat boiler includes either C-276 Hastelloy or C-22 Hastelloy.

4. The method for treating epichlorohydrin production waste gas according to claim 1, characterized in that, The rapid cooling process in step S4 includes using a graphite tower to rapidly cool the waste gas from step S3 to 60-80°C for a time of 0.2-0.8 seconds.

5. The method for treating epichlorohydrin production waste gas according to claim 4, characterized in that, The graphite tower employs supercritical water injection to rapidly cool the waste gas in step S3. The injection pressure is 25–30 MPa, and the water-to-gas ratio is 0.7–1.4 L / Nm3.

6. The method for treating epichlorohydrin production waste gas according to claim 1, characterized in that, The preliminary deacidification in step S4 includes water washing and circulating absorption; the water washing and circulating absorption includes using a spray tower to circulate water to flush the waste gas; the spray tower undergoes corrosion-resistant pretreatment, and the internal material of the spray tower includes any one or more of C-276 Hastelloy, C-22 Hastelloy, silicon carbide, and polytetrafluoroethylene.

7. The method for treating epichlorohydrin production waste gas according to claim 1, characterized in that, The deep deacidification in step S4 includes neutralizing the residual acidic gas in the waste gas using an alkaline scrubbing tower. The alkaline solution in the alkaline scrubbing tower is selected from either a sodium hydroxide solution with a concentration of 10-30% or a sodium carbonate solution with a concentration of 10-40%.

8. The method for treating epichlorohydrin production waste gas according to claim 1, characterized in that, Step S5 also includes heat exchange pretreatment, which raises the temperature of the exhaust gas after step S4 to 220-280°C before it is introduced into the denitrification device.

9. The method for treating epichlorohydrin production waste gas according to claim 1, characterized in that, The modified vanadium-titanium catalyst in step S5 is selected as a cerium-based doped vanadium-titanium catalyst. The SCR catalyst includes any one or more of Cu-based molecular sieve catalysts and Fe-based molecular sieve catalysts; The mass ratio of the modified vanadium-titanium catalyst to the SCR catalyst is 1:(0.7-0.9). The reducing agent is selected from any one or more of ammonia water and urea solution.

10. A method for treating epichlorohydrin production waste gas according to claim 1, characterized in that, Step S5 further includes using an activated carbon adsorption tower to adsorb and filter the denitrified waste gas. The adsorbent used in the activated carbon adsorption tower is selected from any one or more of sulfur-impregnated activated carbon and halogen-impregnated activated carbon.