Ultra-low emission purification method for the whole process of hazardous waste incineration flue gas

Abstract

The present invention discloses a method for ultra-low emission purification of hazardous waste incineration flue gas throughout the entire process. It includes the following steps: step one: semi-dry deacidification; step two: dry deacidification; spraying slaked lime to remove part of the acidic gas; step three: bag filter dust removal; step four: wet deacidification; step five: wet electrostatic precipitator dust removal; step six: determine whether the nitrogen oxide front end meets the emission standard; if it meets the emission standard, the flue gas after demisting by the wet electrostatic precipitator is directly heated to 130°C through the GGH flue gas heat exchanger and then discharged to the chimney; if it does not meet the emission standard, SCR medium and low temperature denitrification is adopted, and the purified flue gas is cooled to 130°C through the GGH flue gas heat exchanger and then discharged to the chimney. The present invention has the characteristics of efficient removal of pollutants, low investment, and low operating cost. At the same time as the ultra-low emission of flue gas, only fly ash is output for safe landfill, there is no wet desulfurization wastewater discharge, and no secondary pollution will be caused.

Description

Technical Field

[0001] The invention relates to a full-process ultra-low emission purification method for hazardous waste incineration flue gas. Background Art

[0002] The impact of hazardous waste on human health and pollution to the natural environment has received widespread attention. Toxic and harmful substances in hazardous wastes not only cause direct harm to human health, but also migrate and transform in the natural environment, thereby polluting the ecological environment such as soil, water and atmosphere. The general principle of my country's hazardous waste pollution prevention and control technology policy is to reduce, recycle and harmlessly treat hazardous wastes. First, prevent or reduce the generation of hazardous wastes at the source; for hazardous wastes that have been generated, consider whether they can be recycled and utilized in a comprehensive resource manner according to their nature to reduce the subsequent disposal load. For hazardous wastes that cannot or cannot be recycled temporarily, they must be properly disposed of harmlessly by methods such as incineration and safe landfill. At present, hazardous waste disposal technologies mainly include physical methods, chemical methods, solidification / stabilization, incineration disposal technology, non-incineration disposal technology and safe landfill disposal technology. Incineration disposal technology refers to the technology of using heat to oxidize and decompose organic toxic and harmful substances in hazardous wastes at high temperatures, mainly including incineration and pyrolysis gasification technologies, which are suitable for the disposal of hazardous wastes with high organic components and high calorific value. Among them, the incineration method can effectively reduce the volume of waste by 85% to 95% and the weight by 60% to 70%. While destroying and decomposing dangerous and harmful substances, it can recover the energy generated by incineration. It has become one of the most widely used hazardous waste disposal technologies in my country.

[0003] Incineration of hazardous waste can reduce the amount of hazardous waste, recycle it into resources and render it harmless. However, the incineration process will produce a large amount of flue gas and incineration ash, which usually contains CO, SO2, NO x , HF, HCl and other conventional pollutants as well as heavy metals, dioxins / furans, etc. These pollutants discharged into the atmosphere will cause harm to human health and the environment, so the country has formulated strict emission standards for pollution control of hazardous waste incineration. In November 2019, the Ministry of Ecology and Environment issued the "Hazardous Waste Incineration Pollution Control Standards (Second Draft for Comments)", which raised the emission control requirements for particulate matter, hydrogen fluoride, hydrogen chloride, heavy metals and their compounds in the flue gas. In order to achieve more stringent pollutant emission standards, effectively control SO2, NO in the flue gas of hazardous waste (hazardous waste) incineration x In order to solve the secondary pollution problems of Hazardous Waste Incineration, such as HF, HCl, dioxins and heavy metals, it is necessary to study the flue gas purification technology of hazardous waste incineration in order to cope with the increasingly stringent environmental protection policies.

[0004] Most of the flue gas treatment of hazardous waste incineration projects that meet the limit requirements of GB18484-2020 adopts the "SNCR + quench tower + dry deacidification + activated carbon + bag dust removal + wet deacidification + flue gas heating" process. Some regions such as Shandong have implemented more stringent local standards. x The requirements in this regard are more stringent, and new denitrification process technologies have been added to the original process, including ozone denitrification and low-temperature SCR denitrification. However, for the existing process, it is difficult to achieve ultra-low emissions when incinerating hazardous wastes containing high sulfur, high chlorine, high fluorine, and high heavy metals. If the post-treatment purification device is added to barely meet the standards, the amount of wet desulfurization wastewater will be large, causing secondary pollution, and the cost will be higher and the system will be more complicated.

[0005] Therefore, it is necessary to develop a full-process ultra-low emission purification method for hazardous waste incineration flue gas with high efficiency in removing pollutants, low investment, low operating cost, no wet desulfurization wastewater discharge, and no secondary pollution. Summary of the invention

[0006] The purpose of the present invention is to provide a full-process ultra-low emission purification method for hazardous waste incineration flue gas. It is a full-process ultra-low emission method for hazardous waste incineration flue gas, which has the characteristics of efficient removal of pollutants, low investment and low operating cost. While the flue gas has ultra-low emissions, the entire purification process only has fly ash output for safe landfill, and there is no wet desulfurization wastewater discharge, which will not cause secondary pollution. It overcomes the problem that the existing technology is difficult to achieve ultra-low emissions for the incineration disposal of hazardous wastes containing high sulfur, high chlorine, high fluorine, high heavy metals, etc.

[0007] In order to achieve the above-mentioned purpose, the technical solution of the present invention is: a full-process ultra-low emission purification method for hazardous waste incineration flue gas, characterized in that it comprises the following steps:

[0008] Step 1: semi-dry deacidification (desulfurization wastewater quenching tower back spray);

[0009] The flue gas from hazardous waste incineration passes through the waste heat boiler and its temperature drops to 500-600℃. It then enters the quenching tower system and the outlet flue gas temperature is 180-200℃. The cooling time is less than 1 second, which can avoid dioxin regeneration to the greatest extent.

[0010] A dual-fluid atomizing spray gun is arranged above the quenching tower, and a dual-fluid nozzle is adopted. The nozzle material is Hastelloy C276, and the gun body material is S316L. The quenching water tank is made of 304 stainless steel, and the water consumption is not less than 2 hours. Meanwhile, considering the safeguard measures in case of failure of the water supply system, the present invention arranges a multi-source water replenishment method. Casting materials with good thermal shock stability, good chemical stability, and wear resistance should be used in the quenching tower, and they should also have acid corrosion resistance. Safeguard measures in case of failure of the quenching water supply system should be considered. In the quenching tower, the spray system can automatically track and adjust the water spraying amount of the quenching spray gun according to the changes in the flue gas temperature at the outlet of the quenching tower, to ensure that the outlet temperature of the quenching tower is maintained within the appropriate temperature range, and to ensure that overspray or underspray does not occur;

[0011] Taking into account the high content of S and Cl in the waste, the present invention adds a semi-dry deacidification function in the quenching link to improve the operational flexibility of the system. The main purpose of the quenching tower is to spray water for cooling. However, when treating flue gas with high pollutant concentration, there is a lot of wet desulfurization wastewater. The present invention sprays the wet desulfurization wastewater back to the quenching tower to absorb the wastewater while cooling it down, and can remove some pollutants at the same time. The deacidification efficiency is greater than 80%, and it can be specifically set according to actual working conditions. The salt concentration of the back-sprayed wet desulfurization wastewater is generally 5%-15%. The present invention needs to add a scale inhibitor when back-spraying the desulfurization wastewater to avoid salt crystallization and scaling, which affects the stable operation of the system;

[0012] Step 2: dry deacidification;

[0013] Spray slaked lime to remove part of the acidic gas. The specific method is:

[0014] The flue gas from the quench tower enters the dry deacidification tower from the bottom of the dry deacidification tower with dry deacidification structure. The activated carbon is transferred at a very high mass transfer rate (generally, the conveying air is set, and the pressure of the activated carbon conveying air is 39kpa; 50Nm per kilogram of material is required for injection). 3 The amount of air is sufficient to completely disperse the material and make it mix better with the flue gas. It mixes with the flue gas and absorbs pollutants such as dioxins and heavy metals in the flue gas. The slaked lime powder is sprayed at a very high mass transfer rate (generally, the conveying air is set, and the slaked lime conveying air pressure is 39kpa; 35Nm is required for each kilogram of material sprayed 3 The air volume is sufficient to completely disperse the materials and make them mix better with the flue gas) and react with acidic substances such as SO2 in the flue gas to generate reactants such as CaSO4, CaSO3 and CaCl2, which are quickly dried into a solid state in the high-temperature flue gas; a small part of these solid reactants are discharged from the bottom ash outlet of the dry deacidification tower of the dry deacidification structure, and most of them enter the bag filter with the flue gas;

[0015] The amount of activated carbon injected into the dry tower of hazardous waste industry is 1.5kg / t hazardous waste; the amount of slaked lime injected is based on the deacidification efficiency of the dry tower, which is generally 10-40%. At the same time, slaked lime plays a role in protecting the filter bags of the subsequent bag filter;

[0016] Step 3: Bag dust collector dust removal;

[0017] The equipment for removing solid particles in flue gas in the present invention is a bag filter, which has a dust removal efficiency of up to 99.99%, especially for effectively capturing submicron particles. This feature is conducive to the removal of aerosol particles of heavy metals; and the effect on removing dioxins is more prominent. Most of the dioxins in the incineration flue gas can be decomposed through good combustion control, but there is a possibility of resynthesis under certain conditions. The present invention controls the flue gas temperature between 500 and 200°C through a quenching tower to urgently cool the flue gas, thereby reducing and avoiding the dangerous temperature area for the resynthesis of dioxins. A dry reaction is carried out in the flue, and trace dioxin particles in the flue gas are adsorbed by tiny particles of slaked lime. In addition, activated carbon is added before the bag filter to adsorb dioxins, heavy metals and other substances in the flue gas. In the bag filter, the dioxins adsorbed on the submicron particles are captured; most of the dioxins and heavy metals are present in solid particles. Finally, the dust concentration at the outlet of the bag filter is controlled to control the emission of dioxins to the greatest extent.

[0018] The cleaning system of the bag filter uses an offline pulse cleaning method, and the cleaning system is automatically controlled by PLC. The control method uses both timing and constant pressure, and the timing control time is adjustable.

[0019] Hazardous waste flue gas has a high moisture content, and the temperature inside the dust collector must be maintained at 10 to 30°C higher than the flue gas dew point temperature to prevent internal dust from sticking to the wall and scaling and clogging; the bag filter is designed with a filtration wind speed of 0.6m / min or less to enhance the removal efficiency of dioxins and heavy metals. Bag filters not only capture general particulate matter, but also remove volatile heavy metals or their chlorides, sulfates or oxides that condense into aerosols with a diameter of ≤0.5μm, and can also remove organic pollutants such as dioxins adsorbed on ash or activated carbon particles. The bag material in the bag dust removal system: PTFE + PTFE coating, which filters the exhaust gas to achieve the purpose of dust removal and dioxin adsorption. The smoke particles accumulate on the surface of the filter cloth to form a dense thin layer, so the bag dust collector of the present invention generally has a high dust removal rate;

[0020] Step 4: wet deacidification;

[0021] The present invention uses sodium hydroxide as an absorbent and as the main deacidification means;

[0022] In the present invention, the wet deacidification tower of the wet deacidification structure undertakes the main deacidification function, and at least a secondary wet deacidification tower is set to ensure that the deacidification efficiency is above 99% and improve the anti-fluctuation performance; the deacidification liquid (sodium hydroxide) in the alkali liquid pool is sent to the wet deacidification tower through a circulation pump, and the tower spray system in the wet deacidification tower 7 is atomized into 1-3 mm droplets through the primary nozzle and the secondary nozzle, which fully covers the entire wet deacidification tower body cross-section (coverage rate is about 300%), forming a good atomization area, and fully contacts with the flue gas from bottom to top in reverse convection to complete the mass transfer process and achieve the purpose of purifying the flue gas.

[0023] Three layers of nozzles are arranged in the washing tower (wet deacidification tower), and the distance between each layer is about 1.4 to 1.7 meters; that is, three layers of first-level nozzles are arranged in the first-level spray deacidification tower, and the distance between adjacent second-level nozzles is 1.4 to 1.7 meters; three layers of second-level nozzles are arranged in the second-level spray deacidification tower, and the distance between adjacent second-level nozzles 17 is 1.4 to 1.7 meters;

[0024] Sodium hydroxide lye is added to the inlet pipe of the circulating pump through the lye pump. The amount of lye added is controlled by the pH value of the circulating lye. The pH meter monitors the alkali concentration of the washing water online and controls the amount of added liquid to ensure that the circulating liquid meets the alkali concentration requirements, that is, the acid gas does not corrode the system equipment after neutralization with the liquid.

[0025] The salt concentration of desulfurization wastewater is controlled at 5%-10%. In order to ensure zero discharge of desulfurization wastewater, all of it needs to be sent to the quenching tower for spraying. In the flue gas of hazardous waste incineration with high sulfur (>5%) and chlorine (>2%) content, the amount of wet desulfurization wastewater is very large. Even if the three deacidification methods are reasonably adjusted, dry and semi-dry deacidification are responsible for the maximum deacidification capacity. The amount of wastewater in the wet deacidification tower is still greater than the amount required for rapid cooling of the quenching tower. In this case, the sodium-calcium double alkali method can be selected to add lime slurry to the circulating water pool. The lime slurry reacts with sodium sulfite and sodium sulfate in the circulating water to form calcium sulfite and calcium sulfate precipitates. The precipitates in the circulating water are then filtered out by a filter press. This can reduce the salt concentration in the circulating water, while replacing sodium hydroxide, reducing the consumption of alkali solution, and reducing the amount of wastewater to meet the requirements of full back spraying.

[0026] Step 5: Wet electrostatic precipitator dust removal;

[0027] The flue gas at the outlet of the wet deacidification tower of the wet deacidification structure enters the wet electrostatic precipitator. The wet electrostatic precipitator is a high-efficiency gas-liquid separation equipment, especially for the capture of fine / viscous / high resistivity dust, aerosol, fine metal particles and dioxins, etc. It captures and deeply purifies the micron and submicron particles in the flue gas after washing, so that the droplets in the exhaust gas reach the pollutant emission standard value, ensuring ultra-low exhaust emissions;

[0028] Step 6: Determine whether the NOx front end meets emission standards;

[0029] When the nitrogen oxide front end meets the emission standards (i.e. the flue gas output by the wet electrostatic precipitator meets the emission standards), the flue gas after wet tower desulfurization and wet electrostatic demisting is directly heated to 130°C by the GGH flue gas heat exchanger and then discharged to the chimney;

[0030] When nitrogen oxides do not meet the emission standards (i.e. the flue gas output by the wet electrostatic precipitator does not meet the emission standards), SCR medium and low temperature denitrification is required. The specific method is as follows: the flue gas temperature after wet electrostatic removal of water mist is 60-70°C, and the temperature is raised to about 150°C through heat exchange with the SCR outlet flue gas through the GGH heat exchanger, and then the flue gas is heated to about 220°C through natural gas or steam. When it reaches the appropriate temperature for the SCR, it enters the SCR denitrification tower with denitrification structure for further denitrification and purification treatment. The purified flue gas is cooled to about 130°C through the GGH heat exchanger and then discharged to the chimney.

[0031] The method for purifying the flue gas from hazardous waste incineration in the present invention with ultra-low emission in the whole process adopts an ultra-low emission purification system for the flue gas from hazardous waste incineration to purify the flue gas from hazardous waste incineration in the whole process with ultra-low emission; wherein the ultra-low emission purification system for the flue gas from hazardous waste incineration in the whole process includes a deacidification structure, a dust removal structure, a burner, a denitrification structure, and a GGH flue gas heat exchanger;

[0032] The deacidification structure, dust removal structure, and GGH flue gas heat exchanger are connected in sequence;

[0033] The natural gas system, burner, denitrification structure, and GGH flue gas heat exchanger are connected in sequence;

[0034] The deacidification structure includes a semi-dry deacidification structure, a dry deacidification structure, and a wet deacidification structure;

[0035] The dust removal structure includes bag filter and wet electrostatic precipitator;

[0036] The semi-dry deacidification structure, the dry deacidification structure, the bag dust collector, the wet deacidification structure, and the alkali liquid pool sewage discharge system are connected in sequence to form a circulation loop.

[0037] In the above technical scheme, the GGH flue gas heat exchanger includes a flue gas heat exchanger tube layer and a flue gas heat exchanger shell layer; the flue gas heat exchanger tube layer is connected to the burner through the induced draft fan; the flue gas heat exchanger shell layer is connected to the wet electrostatic precipitator; the flue gas inlet of the denitrification structure is connected to the burner, and the flue gas outlet of the denitrification structure is connected to the flue gas inlet located at the upper end of the GGH flue gas heat exchanger; the GGH temperature rising section (the flue gas temperature after wet deacidification rises from 70°C to 150°C, and goes through the shell layer) and the GGH temperature falling section (the flue gas temperature after SCR denitration drops from 210°C to 130°C, and goes through the tube layer) are both in the GGH flue gas heat exchanger.

[0038] The flue gas at the outlet of the deacidification tower enters the GGH heating section and rises from 70℃ to 150℃, which still does not reach the denitrification temperature. It is then heated to 220℃ by burning natural gas in a burner and then enters the SCR reactor. The flue gas at the outlet of the SCR reactor is 210℃ and enters the GGH to heat the flue gas at the outlet of the deacidification.

[0039] In the above technical scheme, the alkali liquid pool sewage discharge system includes an alkali liquid pool, a desulfurization wastewater pump, an alkali liquid pool sewage pump, a regenerator, a filter press and a clear liquid tank; the alkali liquid pool, the desulfurization wastewater pump, the regenerator, the filter press, the clear liquid tank, and the alkali liquid pool sewage pump are connected in sequence, and / or the alkali liquid pool, the desulfurization wastewater pump, the regenerator, the clear liquid tank, and the alkali liquid pool sewage pump are connected in sequence.

[0040] In the above technical solution, the wet deacidification structure is provided with at least two wet deacidification towers, namely, a first-level spray deacidification tower and a second-level spray deacidification tower; the wet tower undertakes the main deacidification function, and at least a second-level wet deacidification tower is provided to ensure that the deacidification efficiency of the present invention is above 99% and improve the anti-fluctuation performance;

[0041] The first-stage spray deacidification tower adopts an empty tower structure, and the second-stage spray deacidification tower is equipped with a second-stage demister.

[0042] In the above technical solution, the lower ends of the first-stage spray deacidification tower and the second-stage spray deacidification tower are connected to the alkali solution pool;

[0043] The first-stage nozzle is located in the first-stage spray deacidification tower; the first-stage nozzle has multiple layers; the first-stage spray pump is connected to the first-stage nozzle;

[0044] The alkali liquid pool, the first-stage spray pump, and the first-stage spray deacidification tower are connected in sequence to form a circulation loop;

[0045] The secondary nozzle is located in the secondary spray deacidification tower and below the secondary demister. The secondary nozzle has multiple layers. The secondary spray pump is connected to the secondary nozzle.

[0046] The alkali liquid pool, the secondary spray pump, and the secondary spray deacidification tower are connected in sequence to form a circulation loop;

[0047] The above connection structure constitutes the wet deacidification tower double alkali process system of the present invention (such as Figure 1 , Figure 2 shown).

[0048] In the above technical solution, the semi-dry deacidification structure is a quenching tower system, including a quenching tower, a dual-fluid atomizing spray gun arranged above the quenching tower, a quenching pump, and a quenching water tank; the quenching water tank, the quenching pump, and the dual-fluid atomizing spray gun are connected in sequence.

[0049] In the above technical solution, the alkali liquid pool is connected to the quenching water tank; the connecting pipeline between the alkali liquid pool and the quenching water tank is sequentially provided with a desulfurization wastewater pump, an alkali liquid pool sewage pump, a filter, and a salt inhibitor dosing device;

[0050] The tap water system is connected to the quenching water tank.

[0051] In the above technical solution, the dry deacidification structure is a dry reaction device; the quenching tower is connected to the dry deacidification structure;

[0052] A plurality of activated carbon injection points are arranged on the dry deacidification structure.

[0053] In the above technical solution, a ash outlet is provided at the lower end of the dry deacidification tower of the quenching tower and the dry deacidification structure;

[0054] A dust discharger is arranged below the bag dust collector.

[0055] The present invention is a full-process ultra-low emission purification method for hazardous waste incineration flue gas, which has the characteristics of efficient removal of pollutants, low investment, and low operating cost, and has the following advantages:

[0056] (1) The present invention organically combines the three deacidification technologies of semi-dry, dry and wet methods, and allocates the deacidification efficiency according to the pollutant concentration, the water-soluble salt content of fly ash <10%, the treatment of wet desulfurization wastewater and other issues, ensuring zero discharge of desulfurization wastewater, and only transporting fly ash for safe landfill;

[0057] (2) The present invention is suitable for the treatment of flue gas with high concentration of pollutants. It is difficult to achieve ultra-low emission due to the high concentration of pollutants. The present invention adopts the method of changing the sodium hydroxide desulfurization and deacidification to double alkali desulfurization and deacidification (i.e., setting up a secondary wet deacidification tower and an alkali liquid pool sewage discharge system), and the lime slurry reacts with the sodium sulfite and sodium sulfate in the circulating water to generate calcium sulfite and calcium sulfate precipitates, and then the precipitates in the circulating water are filtered out by a filter press, which can reduce the salt concentration in the circulating water and is conducive to the stable operation of the system; at the same time, sodium hydroxide can be replaced to reduce the consumption of alkali liquid; the desulfurization slag is safely landfilled;

[0058] (3) The present invention combines multiple methods such as rapid cooling, dry activated carbon adsorption, bag dust removal, SCR catalytic decomposition, etc., step by step, to achieve the purpose of removing dioxins and heavy metals, and control the concentration of dioxins and heavy metals to the greatest extent;

[0059] (4) The design temperature of the bag filter in the present invention is 10-30°C higher than the flue gas dew point temperature, which can effectively prevent internal dust from sticking to the wall and scaling and clogging; the bag filter is designed with a filtration wind speed of 0.6m / min or less, which greatly enhances the removal efficiency of dioxins and heavy metals and achieves ultra-low emissions of the entire system; the bag material is suitable for PTFE+PTFE (polytetrafluoroethylene) coating to filter the exhaust gas to achieve the purpose of dust removal and adsorption of dioxins and heavy metals;

[0060] (5) The wet electrostatic precipitator in the present invention can realize the combined removal of multiple pollutants, effectively remove acid mist, fine dust, fine droplets, etc., alleviate working conditions, slow down the corrosion of subsequent equipment, and extend the life of subsequent equipment;

[0061] (6) The present invention utilizes the waste heat of flue gas. When the temperature needs to be raised for subsequent SCR denitrification, the waste heat of the high-temperature flue gas after SCR denitrification is used to heat the low-temperature flue gas coming out of the wet process tower. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a structural diagram of the full-process ultra-low emission purification system for hazardous waste incineration flue gas adopted in the present invention.

[0063] Figure 2 This is a system diagram of the wet deacidification tower double alkali method adopted in the present invention.

[0064] Figure 3 It is a process flow chart of the present invention.

[0065] exist Figure 1 In the figure, D represents the flue gas from the waste heat boiler; E represents activated carbon; F represents slaked lime; G represents ammonia water; I represents chimney; and J represents induced draft fan.

[0066] exist Figure 2 In the figure, X represents the flue gas from the bag filter; Y represents the clean flue gas to the wet electrostatic precipitator; Z represents the desulfurization slag sent to the landfill; and R represents the alkali solution used for replenishment.

[0067] In the figure, 1-deacidification structure, 1A-semi-dry deacidification structure, 1B-dry deacidification structure, 1C-wet deacidification structure, 2-dust removal structure, 2A-bag dust collector, 2B-wet electrostatic precipitator, 3-natural gas system, 4-burner, 5-denitrification structure, 6-GGH flue gas heat exchanger, 6A-flue gas heat exchanger tube layer, 6B-flue gas heat exchanger shell layer, 7-wet deacidification tower, 7A-first-stage spray deacidification tower, 7B-second-stage spray deacidification tower, 8-demister, 9-quenching tower, 10-dual-fluid atomizing spray gun, 11- Quick cooling pump, 12-Quick cooling water tank, 13-Injection point, 13A-Slaked lime injection point, 13B-Activated carbon injection point, 14-Alkali pool, 15-First-stage spray pump, 16-First-stage nozzle, 17-Second-stage nozzle, 18-Second-stage spray pump, 19-Desulfurization wastewater pump, 20-Alkali pool sewage pump, 21-Filter, 22-Salt inhibitor dosing device, 23-Tap water system, 24-Regenerator, 25-Filter press, 26-Clear liquid tank, 27-Ash discharger, 28-Alkali pool sewage system. DETAILED DESCRIPTION

[0068] The following is a detailed description of the implementation of the present invention in conjunction with the accompanying drawings, but they do not constitute a limitation of the present invention and are only used as examples. At the same time, the advantages of the present invention are made clearer and easier to understand through the description.

[0069] The present invention optimizes and upgrades the flue gas purification technology for hazardous waste incineration in view of the problems that the existing technology is difficult to achieve ultra-low emissions, the amount of wet desulfurization wastewater is large, causing secondary pollution, and the cost is also high. The system is complex, and the whole process ultra-low emission purification system is developed. While the flue gas is ultra-low emission, the entire system only outputs fly ash for safe landfill, and there is no wet desulfurization wastewater discharge. In the present invention, the flue gas after incineration passes through the waste heat boiler and enters the flue gas quenching tower (wet desulfurization wastewater back spray) + dry deacidification (activated carbon and slaked lime injection) + bag dust removal + wet deacidification tower + wet electrostatic precipitator + GGH (flue gas heat exchanger) heating section + burner + SCR (selective catalytic reduction technology) denitrification + GGH (flue gas heat exchanger) cooling section. If nitrogen oxides do not meet the emission standards, SCR medium and low temperature denitrification is required. The flue gas temperature after wet electrostatic removal of water mist is 60-70℃. It is heated to about 150℃ through GGH heat exchanger and SCR outlet flue gas heat exchange, and then heated to about 220℃ by natural gas or steam. When it reaches the appropriate temperature for SCR, it enters the SCR denitrification tower for further denitrification and purification. The purified flue gas is cooled to about 130℃ through GGH heat exchanger and discharged to the chimney.

[0070] Example

[0071] The present invention is now described in detail by taking the application of the present invention to a hazardous waste incineration disposal project as an example, which also has a guiding role in the application of the present invention to other hazardous waste incineration disposals.

[0072] The hazardous waste incineration treatment scale of this embodiment is 3000kg / h. The average element composition analysis of the hazardous waste after the formulation in this embodiment is shown in Table 1 below:

[0073] Table 1 Analysis of average element composition of hazardous waste after compatibility

[0074]

[0075] This embodiment adopts the technical route of the present invention: flue gas quenching (desulfurization wastewater back spray, because the desulfurization wastewater uses sodium salt, it is necessary to add antiscalant) + dry deacidification + activated carbon injection + bag dust removal + wet primary tower + wet secondary tower (alkali solution spray + filler + demister) + wet electrostatic precipitator + GGH heating section + burner + SCR denitrification + GGH cooling section;

[0076] like Figure 3 As shown, the specific method includes the following steps:

[0077] Step 1: semi-dry deacidification;

[0078] The flue gas from hazardous waste incineration passes through the waste heat boiler and its temperature drops to 500-600°C. It enters the quenching tower 9 of the semi-dry deacidification structure 1A, and the outlet flue gas temperature is 180-200°C. The cooling time is less than 1 second, which can avoid dioxin regeneration to the greatest extent.

[0079] Step 2: dry deacidification;

[0080] Inject slaked lime to remove some of the acidic gases, specifically:

[0081] The flue gas from the quenching tower 9 enters the dry deacidification tower from the lower part of the dry deacidification tower of the dry deacidification structure 1B, and the activated carbon is mixed with the flue gas to absorb the pollutants in the flue gas; the slaked lime powder is mixed with the acidic substances in the flue gas to react to generate reactants CaSO4, CaSO3 and CaCl2, and the reactants are quickly dried into a solid state in the high-temperature flue gas; a part of these solid reactants is discharged from the ash discharge port at the bottom of the dry deacidification tower of the dry deacidification structure 1B, and the other part enters the bag filter 2A with the flue gas;

[0082] Step 3: Bag dust collector dust removal;

[0083] The cleaning system of bag filter 2A adopts offline pulse cleaning method, and the cleaning system adopts PLC automatic control; the control method adopts both timing and constant pressure methods, and the timing control time is adjustable;

[0084] Step 4: wet deacidification;

[0085] The sodium hydroxide in the alkali liquid pool 14 is sent to the wet deacidification tower 7 through a circulation pump. The spray system in the wet deacidification tower 7 is atomized into 1-3 mm droplets through the primary nozzle 16 and the secondary nozzle 17, which fully covers the entire cross section of the wet deacidification tower 7, forming a good atomization area, and fully contacts with the flue gas from bottom to top in reverse convection, completing the mass transfer process and achieving the purpose of purifying the flue gas.

[0086] Three layers of nozzles are arranged in the wet deacidification tower 7, and the interval between each layer of nozzles is 1.4 to 1.7 meters;

[0087] Step 4: Wet electrostatic precipitator dust removal;

[0088] Flue gas from the outlet of wet deacidification tower 7 enters wet electrostatic precipitator 2B for demisting;

[0089] Step 5: Determine whether the NOx front end meets emission standards;

[0090] When the flue gas output by the wet electrostatic precipitator 2B meets the emission standards, the flue gas after demisting by the wet electrostatic precipitator 2B is directly heated to 130°C by the GGH flue gas heat exchanger 6 and then discharged to the chimney;

[0091] When the flue gas output by the wet electrostatic precipitator 2B does not meet the emission standards, SCR medium and low temperature denitrification is adopted. The specific method is as follows: the flue gas temperature after the water mist is removed by the wet electrostatic precipitator 2B is 60-70°C, and the flue gas outlet temperature is raised to about 150°C through heat exchange between the GGH flue gas heat exchanger 6 and the SCR denitrification structure 5, and then the flue gas is heated to about 220°C by natural gas or steam. After reaching the suitable temperature of SCR, it enters the SCR denitrification tower of the denitrification structure 5 for further denitrification and purification treatment. The purified flue gas is cooled to 130°C through the GGH flue gas heat exchanger 6 and then discharged to the chimney.

[0092] To rapidly cool the flue gas from 55°C to 180°C, about 5 tons of water needs to be sprayed.

[0093] The quench tower of the semi-dry deacidification structure 1A sprays back the desulfurization wastewater solution, which bears 40% of the desulfurization efficiency and 60% of the deacidification efficiency; the dry tower of the dry deacidification structure 1B bears 15% of the desulfurization efficiency and 30% of the deacidification efficiency; the wet tower of the wet deacidification structure 1C (i.e., the wet deacidification tower 7) bears 55% of the desulfurization efficiency and 10% of the deacidification efficiency; the semi-dry, dry, and wet deacidification technical means are organically combined, and the deacidification efficiency is allocated according to the pollutant concentration content, the water-soluble salt content of fly ash <10%, the treatment of wet desulfurization wastewater, etc., to ensure zero discharge of desulfurization wastewater, and only fly ash is transported out for safe landfill. The salt concentration of the wet tower of the wet deacidification structure 1C (i.e., the wet deacidification tower 7) is set to 5%, and sodium hydroxide is used for deacidification, then the deacidification wastewater is 6.4t / h, which is much larger than the amount of water spray required for rapid cooling. Therefore, the secondary deacidification tower is changed to double alkali deacidification, lime slurry is added to the circulating water pool, and the lime slurry reacts with sodium sulfite and sodium sulfate in the circulating water to form calcium sulfite and calcium sulfate precipitates, and then the precipitates in the circulating water are filtered out by a filter press, which can reduce the salt concentration in the circulating water and replace sodium hydroxide, thereby reducing the consumption of alkali solution. The desulfurization wastewater volume of the wet tower (i.e., wet deacidification tower 7) of wet deacidification structure 1C can be reduced from 6.4t / h to 2.5t / h, which is only half of the water volume required for the flue gas quenching tower, and zero wastewater discharge of the entire system can be achieved.

[0094] After testing, it was found that after the system of the present invention was adopted in this embodiment, the flue gas could meet the emission standards, among which: the dust concentration was ≤10mg / Nm 3 ; Sulfur dioxide ≤ 35mg / Nm 3 ; Nitrogen oxides ≤ 50mg / Nm 3 , dioxins ≤0.1TEQ ng / Nm 3 ; Heavy metals chromium, tin, antimony, copper, manganese and their compounds (calculated as Cr+Sn+Sb+Cu+Mn) ≤ 2mg / Nm 3, which are all lower than the emission standards required by the "Hazardous Waste Incineration Pollution Control Standard". In addition, this embodiment adopts the optimized design of the system described in the present invention, the wastewater system self-digests, and the three deacidification processes of dry, semi-dry and wet are organically combined and the deacidification efficiency is designed, which can achieve the purpose of energy saving and consumption reduction.

[0095] The smoke components and contents before and after treatment by the present invention in this embodiment are shown in Table 2 below:

[0096] Table 2 The components and contents of flue gas before and after treatment by the present invention in this embodiment

[0097]

[0098] From Table 2 above, it can be seen that the content of pollutants to be treated in this embodiment is quite high. This embodiment adopts the present invention to achieve ultra-clean emission standards, and at the same time, no wastewater is discharged, and no additional wastewater treatment is required, which is a technical solution with low energy consumption and low cost. And from Table 2 above, it can be seen that the removal rate of sulfur oxides is 99.8%; the removal rate of nitrogen oxides is 85.7%; and the removal rate of dust is 99.8%.

[0099] Other parts not described belong to the prior art.

Claims

1. A full-process ultra-low emission purification method for hazardous waste incineration flue gas, characterized by: The following steps are included: Step 1: semi-dry deacidification; After the hazardous waste incineration flue gas passes through the waste heat boiler, the flue gas temperature drops to 500-600°C and enters the quenching tower (9) of the semi-dry deacidification structure (1A). The outlet flue gas temperature is 180-200°C and the cooling time is less than 1 second, thereby avoiding dioxin regeneration to the greatest extent. The semi-dry deacidification structure (1A) is a quenching tower system, comprising a quenching tower (9), a dual-fluid atomizing spray gun (10) arranged above the quenching tower, a quenching pump (11), and a quenching water tank (12); the quenching water tank (12), the quenching pump (11), and the dual-fluid atomizing spray gun (10) are connected in sequence; Step 2: dry deacidification; Inject slaked lime to remove some of the acidic gases, specifically: The flue gas from the quenching tower (9) enters the dry deacidification tower from the bottom of the dry deacidification tower of the dry deacidification structure (1B), and the activated carbon is mixed with the flue gas to absorb the pollutants in the flue gas; the slaked lime powder is mixed with the acidic substances in the flue gas to react to generate reactants CaSO4, CaSO3 and CaCl2, and the reactants are quickly dried into a solid state in the high-temperature flue gas; a part of these solid reactants is discharged from the ash discharge port at the bottom of the dry deacidification tower of the dry deacidification structure (1B), and the other part enters the bag filter (2A) along with the flue gas; Step 3: Bag dust collector dust removal; The cleaning system of the bag filter (2A) adopts offline pulse cleaning method, and the cleaning system adopts PLC automatic control; the control method adopts both timing and constant pressure methods, and the timing control time is adjustable; Step 4: wet deacidification; The sodium hydroxide in the alkali liquid pool (14) is transported to the wet deacidification tower (7) of the wet deacidification structure (1C) through a circulation pump. The spray system in the wet deacidification tower (7) atomizes the sodium hydroxide into 1-3 mm droplets through the primary nozzle (16) and the secondary nozzle (17), which fully cover the entire cross section of the wet deacidification tower (7) to form a good atomization area, and fully contact with the flue gas from bottom to top in countercurrent convection, completing the mass transfer process and achieving the purpose of purifying the flue gas. Three layers of nozzles are arranged in the wet deacidification tower (7), and the interval between the nozzles in each layer is 1.4 to 1.7 meters; The wet deacidification structure (1C) is provided with at least two wet deacidification towers (7), namely a first-stage spray deacidification tower (7A) and a second-stage spray deacidification tower (7B); The first-stage spray deacidification tower (7A) adopts an empty tower structure, and the second-stage spray deacidification tower (7B) is provided with a second-stage demister (8); The lower ends of the primary spray deacidification tower (7A) and the secondary spray deacidification tower (7B) are both connected to the alkali solution pool (14); The primary nozzle (16) is located in the primary spray deacidification tower (7A); the primary nozzle (16) has multiple layers; the primary spray pump (15) is connected to the primary nozzle (16); The alkali liquid pool (14), the primary spray pump (15), and the primary spray deacidification tower (7A) are connected in sequence to form a circulation loop; The secondary nozzle (17) is located in the secondary spray deacidification tower (7B) and below the secondary demister (8), and the secondary nozzle (17) has multiple layers; the secondary spray pump (18) is connected to the secondary nozzle (17); The alkali liquid pool (14), the secondary spray pump (18), and the secondary spray deacidification tower (7B) are connected in sequence to form a circulation loop; The alkali liquid pool (14) is connected to the quenching water tank (12); a desulfurization wastewater pump (19), an alkali liquid pool sewage pump (20), a filter (21), and a salt blocking agent dosing device (22) are sequentially arranged on the connecting pipeline between the alkali liquid pool (14) and the quenching water tank (12); The tap water system (23) is connected to the quenching water tank (12); Step 5: Wet electrostatic precipitator dust removal; The flue gas at the outlet of the wet deacidification tower (7) enters the wet electrostatic precipitator (2B) for demisting; Step 6: Determine whether the NOx front end meets emission standards; When the flue gas outputted by the wet electrostatic precipitator (2B) meets the emission standards, the flue gas after being defogged by the wet electrostatic precipitator (2B) is directly heated to 130° C. by the GGH flue gas heat exchanger (6) and then discharged to the chimney; When the flue gas output by the wet electrostatic precipitator (2B) does not meet the emission standards, SCR medium and low temperature denitrification is adopted. The specific method is as follows: the flue gas temperature after the water mist is removed by the wet electrostatic precipitator (2B) is 60-70°C, and the flue gas outlet is heated to 150°C through the GGH flue gas heat exchanger (6) and the SCR denitrification structure (5). The flue gas is then heated to about 220°C by natural gas or steam. After reaching the temperature suitable for the SCR, it enters the SCR denitrification tower of the denitrification structure (5) for further denitrification and purification treatment. The purified flue gas is cooled to 130°C through the GGH flue gas heat exchanger (6) and then discharged to the chimney; The GGH flue gas heat exchanger (6) comprises a flue gas heat exchanger tube layer (6A) and a flue gas heat exchanger shell layer (6B); the flue gas heat exchanger tube layer (6A) is connected to the burner (4) via an induced draft fan; the flue gas heat exchanger shell layer (6B) is connected to the wet electrostatic precipitator (2B); the flue gas inlet of the denitration structure (5) is connected to the burner (4), and the flue gas outlet of the denitration structure (5) is connected to the flue gas inlet located at the upper end of the GGH flue gas heat exchanger (6); In the purification method, the quenching tower of the semi-dry deacidification structure (1A) sprays back the desulfurization wastewater solution to bear 30% of the desulfurization efficiency and 60% of the deacidification efficiency; the dry tower of the dry deacidification structure (1B) bears 15% of the desulfurization efficiency and 30% of the deacidification efficiency; the wet deacidification tower (7) of the wet deacidification structure (1C) bears 55% of the desulfurization efficiency and 10% of the deacidification efficiency; the purification method organically combines the three deacidification technologies of semi-dry deacidification, dry deacidification and wet deacidification, and allocates the deacidification efficiency according to the pollutant concentration content, the fly ash water-soluble salt content <10%, and the treatment problem of wet desulfurization wastewater, ensuring zero discharge of desulfurization wastewater, and only the fly ash is transported out for safe landfill.

2. The method for ultra-low emission purification of hazardous waste incineration flue gas in the whole process according to claim 1 is characterized by: The deacidification structure (1) includes a semi-dry deacidification structure (1A), a dry deacidification structure (1B), and a wet deacidification structure (1C); The dust removal structure (2) includes a bag dust collector (2A) and a wet electrostatic precipitator (2B); The semi-dry deacidification structure (1A), the dry deacidification structure (1B), the bag filter (2A), the wet deacidification structure (1C), and the alkali liquid pool sewage discharge system (28) are sequentially connected to form a circulation loop; The deacidification structure (1), the dust removal structure (2), and the GGH flue gas heat exchanger (6) are connected in sequence; The natural gas system (3), the burner (4), the denitration structure (5), and the GGH flue gas heat exchanger (6) are connected in sequence.

3. The method for ultra-low emission purification of hazardous waste incineration flue gas in the whole process according to claim 1 is characterized by: The alkali liquid pool sewage discharge system (28) comprises an alkali liquid pool (14), a desulfurization wastewater pump (19), an alkali liquid pool sewage discharge pump (20), a regenerator (24), a filter press (25) and a clear liquid tank (26); the alkali liquid pool (14), the desulfurization wastewater pump (19), the regenerator (24), the filter press (25), the clear liquid tank (26) and the alkali liquid pool sewage discharge pump (20) are connected in sequence, and / or the alkali liquid pool (14), the desulfurization wastewater pump (19), the regenerator (24), the clear liquid tank (26) and the alkali liquid pool sewage discharge pump (20) are connected in sequence.

4. The method for ultra-low emission purification of hazardous waste incineration flue gas in the whole process according to claim 1 is characterized by: The dry deacidification structure (1B) is a dry reaction device; the quenching tower (9) is connected to the dry deacidification structure (1B); A plurality of injection points (13) are arranged on the dry deacidification structure (1B); The injection points (13) include a slaked lime injection point (13A) and an activated carbon injection point (13B).

5. The method for ultra-low emission purification of hazardous waste incineration flue gas in the whole process according to claim 4 is characterized in that: A dust discharger (27) is arranged below the bag filter (2A).

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