Application of activated deacidification agent to wet deacidification in field of hazardous waste incineration

Abstract

The invention discloses an application of an activated deacidification agent in wet deacidification in the field of hazardous waste incineration, which is characterized in that the activated deacidification agent is prepared by grinding and activating a calcium-magnesium deacidification agent, so that the median particle size D50 of the calcium-magnesium deacidification agent is not greater than 19 microns; wherein the calcium-magnesium deacidification agent is one or more of calcium oxide MgO, calcium hydroxide Ca (OH) 2, calcium carbonate CaCO3, magnesium oxide MgO, magnesium hydroxide Ca (OH) 2 and magnesium carbonate MgCO3. According to the method, the hazardous waste deacidification tower adopts calcium-magnesium alkali for deacidification, so that the deacidification efficiency which is comparable to that of sodium alkali is achieved, the problem of system scaling is solved, the circulating slurry in the deacidification tower is prevented from being sticky, bubbling and overflowing, the problems of newly increased equipment and newly increased operation cost caused by aeration oxidation of the slurry are solved, and the method is suitable for industrial production. And the technical prejudice that only sodium alkali can be used in hazardous waste incineration wet deacidification is overcome.

Description

Technical Field

[0001] The invention relates to the application of an activated deacidifying agent in wet deacidification in the field of hazardous waste incineration, and belongs to the technical field of hazardous waste treatment. Background Art

[0002] With the increasingly stringent environmental protection supervision requirements in China, most coal-fired power plants in China have completed ultra-low emission transformation. After the transformation, the emission concentrations of smoke, sulfur dioxide and nitrogen oxides are no more than 10mg / m 3 , 35mg / m 3 , 50mg / m 3 , typical processes are as follows Figure 1 After the coal-fired flue gas is heated by the boiler to generate steam, it passes through the denitration reaction device, electrostatic precipitator / bag filter, limestone / gypsum wet desulfurization oxidation tower, and wet electrostatic precipitator in sequence before reaching the emission standards.

[0003] The calcium-based wet desulfurization process with calcium hydroxide as the representative desulfurizer has a history of more than 50 years in my country. More than 90% of China's thermal power plants and steel mills use calcium-based desulfurization processes such as lime / limestone-gypsum method. It has been widely used in flue gas desulfurization in coal-fired power generation, steel metallurgy, chemical industry and other fields.

[0004] The calcium desulfurization technology uses calcium hydroxide, limestone, etc. as desulfurizers. The flue gas is fully in contact with the lime and other calcium-alkali slurry sprayed from the deacidification tower, and a chemical reaction occurs. The SO2 in the flue gas is removed, and the deacidification tower always maintains a weakly acidic environment. The slurry after absorbing SO2 further reacts with air oxidation to generate calcium sulfate dihydrate (gypsum), which is pumped out of the deacidification oxidation tower through a gypsum discharge pump and transported to the dehydration system for filtration and dehydration. Finally, the byproduct gypsum (such as attached) with a calcium sulfate dihydrate content of more than 90% is obtained. Figure 2 shown).

[0005] The reaction mechanism of the calcium desulfurization process represented by limestone or lime is as follows, and its absorption process can be expressed as:

[0006] CaCO3+SO2+1 / 2H2O→CaSO3·1 / 2H20+CO2↑

[0007] Ca(OH)2+SO2→CaSO3·1 / 2H20+1 / 2H2O

[0008] Oxidation process:

[0009] 2CaSO3·1 / 2H20+O2+3H2O→2CaS04·2H20

[0010] The process and equipment of magnesium-based wet desulfurization are similar to those of calcium-based desulfurization. Using magnesium oxide as a desulfurizer, the desulfurization process is that the slurry made of magnesium oxide absorbs SO2 in the flue gas to generate magnesium sulfite, and the air is introduced to oxidize the magnesium sulfite into magnesium sulfate with higher solubility. The reaction process of the magnesium-based desulfurization process represented by magnesium oxide can be expressed as:

[0011] Absorption process:

[0012] Mg(OH)2+SO2+6H2O→MgSO3·6H20

[0013] Oxidation process:

[0014] 2MgS03·6H20+02+2H2O→2MgS04·7H20

[0015] The above-mentioned slurry absorption deacidification methods such as "limestone-gypsum desulfurization", "slaked lime-gypsum desulfurization" or "magnesium desulfurization" are characterized by gas-liquid-solid heterogeneous reactions, that is, the deacidification tower always maintains a weak acidic environment, so that SO2 in the flue gas is adsorbed and dissolved and migrates from the gas phase to the liquid phase, and at the same time, the desulfurizer and solvent water are activated and hydrated, dissolving and migrating from the solid state to the liquid state to form hydroxides, and promoting the precipitation of calcium / magnesium metal cations in the liquid phase from the liquid state to the solid state (calcium sulfite, magnesium sulfite). In order to ensure the stable reaction and prevent the desulfurization products from covering the desulfurizer and causing the desulfurization efficiency to decrease, it is also necessary to oxidize the generated unstable calcium sulfite and magnesium sulfite to convert them into relatively stable calcium sulfate dihydrate (gypsum) or magnesium sulfate, so that the desulfurization products can be promptly migrated out of the desulfurization system for recycling.

[0016] In order to ensure the continuous absorption of SO2, improve the desulfurization efficiency, improve the quality of the desulfurization byproduct gypsum, and prevent calcium sulfite from scaling in the absorption tower and gypsum slurry tank, it is advisable to control the chloride ion content in the deacidification slurry to a lower level. According to the Technical Supervision Guidelines for Desulfurization Devices in Thermal Power Plants (DL / T1477-2015), the Cl ion content in the gypsum slurry is - The content should be controlled within 10000mg / L.

[0017] The raw material used for coal-fired power generation is thermal coal, which usually contains about 0.5-2.5% sulfur and very low chlorine and fluorine content. The deacidification tower uses limestone slurry with a content of more than 20% for absorption to obtain a slurry with a high content of calcium sulfite, which needs to be further oxidized by air and converted into calcium sulfate. Finally, it is dehydrated to produce by-product gypsum for sale. A complete set of wet flue gas desulfurization equipment, taking the limestone-gypsum method as an example, as shown in the attached figure Figure 3As shown in the figure, it consists of process water system, limestone slurry preparation system, flue gas circulation absorption system, circulating slurry oxidation system, gypsum dehydration system, slurry discharge and accident slurry system, etc. Its system is complex and the equipment investment cost is high, but the flue gas treatment capacity is large, the operating cost is low, the by-products are recyclable, and the commercial value is high.

[0018] Hazardous waste usually contains a large amount of harmful factors such as fluorine, chlorine, sulfur, nitrogen, heavy metals, etc. During the process of incineration reduction and harmlessness, the main pollutants produced are hydrogen chloride, nitrogen oxides, smoke particles, heavy metals, dioxins, etc. After more than 20 years of development, typical hazardous waste incineration flue gas treatment devices such as Figure 4 As shown in the figure, the process is: "hazardous waste pit + elevator + rotary kiln + secondary combustion chamber + waste heat boiler (including SNCR device) + semi-dry quenching tower + dry deacidification tower + bag filter + two-stage deacidification tower + flue gas reheater + fan + chimney". A few newly built devices have further added wet electrostatic demisters to eliminate flue gas whitening, or added SCR reactors to achieve ultra-low emissions of nitrogen oxides. Compared with the ultra-low emission treatment process of coal-fired flue gas, the outstanding feature of the treatment of hazardous waste incineration flue gas is the addition of a flue gas quenching process, which reduces the flue gas temperature at the outlet of the waste heat boiler from more than 500°C to 200°C in about 1 second in the quenching tower to avoid the re-generation of dioxins.

[0019] In the field of hazardous waste incineration, hazardous waste is incinerated to achieve the purpose of harmlessness and reduction. Usually, harmful elements such as fluorine, chlorine and sulfur in hazardous waste need to be matched with raw materials to make the chlorine, sulfur and fluorine content appropriate (for example, the chlorine content is controlled at 5%, the sulfur content is 1%, and the fluorine content is controlled within 0.2%). The corresponding harmful flue gas is mainly hydrogen chloride, and there are acid gases such as sulfur dioxide and hydrogen fluoride. After the flue gas is deacidified by alkaline solutions such as sodium hydroxide, it is finally discharged from the chimney as required (Hazardous Waste Incineration Pollution Control Standard GB 18484-2020).

[0020] Wet scrubbing plays a very important role in the treatment process of hazardous waste incineration flue gas. Acidic gases such as hydrogen chloride and sulfur dioxide in the incineration flue gas are mainly washed and removed in the deacidification tower. In order to facilitate the deacidification operation and ensure that the flue gas is stably discharged and meets the standards, the hourly average index of the flue gas pollutant emission concentration limit is strictly controlled. The deacidification absorption liquid generally uses a water-soluble sodium-based alkali solution, that is, 32% industrial liquid alkali (NaOH) or industrial soda (NaCO3) is diluted with water to keep the absorption liquid in the deacidification tower alkaline (generally PH value is 7-10), and then spray cycle deacidification is carried out. In order to further improve the washing and deacidification effect, wet scrubbing has generally developed from primary washing to secondary washing. After the sodium-based alkali solution in the washing and deacidification tower reacts with the incineration flue gas, it is finally converted into high-salt wastewater containing sodium chloride, sodium sulfite, sodium sulfate, and sodium fluoride. The whole process requires intermittent replenishment of fresh alkali solution and intermittent discharge of high-sodium salt wastewater. This wastewater is discharged into the wastewater system for treatment, usually using the steam generated by the waste heat boiler. After evaporation, concentration and crystallization in a triple-effect evaporator, it becomes solid sodium-based waste salt hazardous waste for further disposal.

[0021] In the field of hazardous waste incineration, the National Energy Administration has issued the industry standard "Technical Specifications for Hazardous Waste Incineration Flue Gas Purification Systems" (DL / T 2428-2021). In Part 7 "Deacidification Process" of the industry standard, it is mentioned:

[0022] "7.2.2 The neutralizing agent for semi-dry deacidification (i.e., quench tower deacidification) should be slaked lime, sodium bicarbonate or sodium alkali"

[0023] "7.3.4 Dry powder spraying for dry deacidification should use slaked lime and sodium bicarbonate as neutralizers"

[0024] "7.4.3 The spray liquid of the wet deacidification system should be prepared with sodium hydroxide flakes or high-concentration sodium hydroxide solution."

[0025] Usually, in the use of standards, the word "should" means recommendation, suggestion, and is a recommended description, indicating that the clause is the first choice but not a mandatory requirement. From the above industry standards, it can be seen that calcium alkali such as slaked lime is recommended for semi-dry deacidification and dry deacidification, but not recommended for wet deacidification. It is understood that the spray liquid of the wet deacidification system of the hazardous waste incineration production lines that have been built in the country all uses sodium alkali, among which the vast majority of projects choose sodium hydroxide, and very few choose sodium carbonate. And no incineration line uses calcium hydroxide slurry for wet deacidification.

[0026] For this reason, there has always been a prominent problem in the process of hazardous waste incineration production and operation: in order to dispose of worthless hazardous waste, the wet deacidification tower uses high-quality and high-value liquid alkali (sodium hydroxide solution) obtained by electrolysis. At present, in the process of hazardous waste incineration, chlorine-containing hazardous waste is converted from solid or liquid organic chlorine or inorganic chlorine into gaseous hydrogen chloride flue gas in the first combustion chamber or the second combustion chamber, and then neutralized with liquid alkali in the deacidification tower to become high-salt wastewater containing sodium chloride, and finally evaporated and crystallized into waste salt (hazardous waste) containing sodium chloride in the multiple-effect evaporator, or sprayed back into fly ash (hazardous waste) containing sodium chloride waste salt through the quenching tower. In this process, people put in high-value sodium hydroxide liquid alkali, but finally get worthless hazardous waste salt, which eventually needs to be landfilled or recycled by incineration, dissolution, crystallization, and salt separation at a higher cost. Analyzing from the most basic material elements, in essence, in order to remove harmful chlorine elements, expensive and ineffective sodium elements are introduced, which in turn causes high costs for incineration deacidification disposal.

[0027] The 32% sodium hydroxide liquid alkali on the market is obtained by electrolysis of refined sodium chloride, and its price is usually in the range of 600 to 1,500 yuan per ton, while the current unit price of incineration disposal is only in the range of 1,000 to 2,000 yuan per ton. Alkali consumption has become a major cost item for hazardous waste incineration disposal companies.

[0028] Especially when the fluorine, chlorine and sulfur content in the hazardous waste materials to be disposed is high, the above problems are more prominent. Usually, the consumption of liquid caustic soda is generally between 100 and 200 kg for the incineration of 1 ton of hazardous waste. According to the data of an incineration disposal company in northern Jiangsu, it processes 28,000 tons of hazardous waste annually, consumes 5,000 tons of 32% liquid caustic soda annually, and the cost of liquid caustic soda is about 4.5 million yuan, which is one of the main components of its production cost.

[0029] Industrial salt (sodium chloride) is obtained by refining seawater after sun exposure, or extracting underground brine and distilling it. The price is usually between 200 and 400 yuan per ton. The supply of industrial salt from sea salt or rock brine is extremely sufficient, accompanied by medium and large salt chemical bases. Compared with this, hazardous waste regeneration salt has low output, complex process and no competitive advantage.

[0030] In order to reduce the cost of using liquid alkali for incineration deacidification, Chinese patent CN114832518A discloses a wastewater resource utilization system and method for a hazardous waste incineration tail gas deacidification tower, wherein the water outlet of the sodium-alkali deacidification tower is connected to a lime slurry stirring tank, and the discharge end of the lime slurry stirring tank is connected to the semi-dry quenching tower. This invention proposes to prepare lime milk with high-salt wastewater containing NaCl and Na2SO4 produced by the deacidification tower and calcium hydroxide. The lime milk is ground in a stirring tank with vertical stirring and then used for deacidification in a semi-dry quenching tower. The grinding rate is 60 to 200 rpm, and the particle size of the ground lime milk is controlled at 200 to 400 meshes. This invention solves the problem that the use of deacidification tower wastewater to prepare lime milk easily produces coating film agglomeration, affects the effective utilization rate of lime milk, and blocks the pipeline. However, the above patent only solves the problem of zero discharge of high-salt wastewater generated by sodium-alkali wet deacidification. Its incineration deacidification process still uses sodium hydroxide solution as the deacidification spray liquid in the wet deacidification system, and calcium hydroxide as a semi-dry deacidification neutralizer in the quenching tower. In essence, it is still within the guidance scope of the "Technical Specifications for Hazardous Waste Incineration Flue Gas Purification Systems" (DL / T 2428-2021).

[0031] Chinese patent CN114570189 A discloses a device and method for deacidification of flue gas in hazardous waste incineration system. The device involved in the invention is mainly a deacidification tower, a spray structure is arranged on the upper part of the deacidification tower, a solid-liquid separation zone is arranged on the lower part of the deacidification tower, and an aeration zone is arranged above the solid-liquid separation zone. The method involved in the invention is to pass the flue gas into the deacidification tower, the spray liquid containing magnesium oxide reacts with the flue gas, and the deacidification spray liquid after spraying is contacted with aeration in the aeration zone to obtain an oxidized spray liquid; the oxidized spray liquid is subjected to solid-liquid separation in the solid-liquid separation zone to obtain a concentrated slurry and a clarified liquid; the concentrated slurry is contacted with the flue gas in the quenching tower, and the magnesium chloride, magnesium sulfate, and magnesium fluoride in the concentrated slurry become magnesium salt solids under the high temperature of the flue gas. The patented method retains the complex aeration oxidation and solid-liquid separation processes, and is still a classic magnesium desulfurization process. It has high equipment investment and site requirements, and is difficult to transform at the hazardous waste incineration site. In addition, the solid content of the concentrated slurry after solid-liquid separation of the oxidizing spray liquid of the invention is not disclosed. Generally, the solid content of the classic magnesium desulfurization method is relatively high, and the efficiency of semi-dry pre-deacidification with acidic flue gas in the quenching tower is low, and the waste of deacidifying agent is relatively large. In the embodiment of the invention, an ultra-fine ceramic membrane filter is specially added to intercept insoluble matter, and the clarified liquid is then sprayed into the quenching tower to contact the high-temperature flue gas, indicating that the slurry cannot be directly sprayed back to the quenching tower. In particular, the magnesium sulfate obtained after oxidation of the deacidification spray liquid is soluble in water, so the magnesium salt solid obtained after quenching contains water-soluble magnesium chloride and magnesium sulfate, and the subsequent separation process is complicated and cumbersome, and the utilization value is low. Therefore, this invention also has various shortcomings and is difficult to further promote.

[0032] The "Technical Specifications for Hazardous Waste Incineration Flue Gas Purification Systems" (DL / T 2428-2021) states in clause "7.4.3" that "the spray liquid of the wet deacidification system should be prepared with sodium hydroxide flakes or high-concentration sodium hydroxide solution." This does not completely deny the possibility of using calcium-based slurry or magnesium-based slurry in the wet deacidification system. It is only that it is not recommended first under the current situation of the industry. The inventors also recognize that if the various problems caused by the calcium-magnesium slurry alkali spray liquid can be solved, it will not only achieve a technological breakthrough in the field of hazardous waste incineration, but also create significant environmental and economic benefits.

[0033] Calcium hydroxide with a content of 90% is mostly obtained by thermal decomposition and hydration of common limestone, and its price is in the range of 500-800 yuan / ton. The price of magnesium oxide with a content of 90% is in the range of 800-1000 yuan / ton. According to the alkali equivalent balance, 1 ton of calcium hydroxide with a content of 90% is equivalent to 3 tons of 32% sodium hydroxide liquid alkali. 1 ton of magnesium oxide with a content of 90% is equivalent to 5 tons of 32% sodium hydroxide liquid alkali. Based on the estimation of 750,000 tons of liquid alkali, solving the above problems can reduce costs by more than 300 million yuan. If fly ash is further utilized as a resource, the amount of fly ash landfill disposal can be reduced by about 150,000 tons, which has huge environmental and economic benefits.

[0034] However, in the field of hazardous waste incineration, it is not appropriate to directly apply calcium alkali or magnesium alkali wet deacidification, and the use of sodium alkali wet deacidification is currently recognized by the industry. The calcium alkali wet deacidification process is not used in the hazardous waste deacidification process, which is mainly due to the particularity of hazardous waste incineration itself.

[0035] The following table lists the main differences between the calcium / magnesium wet desulfurization process in power plants and the sodium-alkali wet deacidification process for hazardous waste incineration:

[0036]

[0037] The incineration flue gas load fluctuates greatly. Sodium alkali has the advantages of good water solubility, fast deacidification reaction, convenient operation, and high equipment reliability. It can relatively better ensure that the flue gas deacidification is stable and meets the standards, and prevent the hourly emission average of flue gas pollutants such as hydrogen chloride and sulfur dioxide from exceeding the standard. Therefore, sodium alkali is mostly used for deacidification in hazardous waste incineration deacidification towers. If calcium magnesium slurry alkali is used for direct replacement, the following problems will occur:

[0038] (1) How to solve the problem of decreased efficiency of slurry deacidification relative to sodium alkali?

[0039] (2) How to solve the problem of slurry scaling and blockage?

[0040] (3) How to solve the problem of slurry stickiness and overflow?

[0041] (4) How to solve the problem of additional equipment and additional operating costs caused by aeration and oxidation of slurry?

[0042] (5) How to solve the problem of reasonable disposal and utilization of by-product mixture after slurry separation?

[0043] These problems affect each other and are difficult to solve. We know that the alkaline wet deacidification of calcium magnesium slurry needs to be carried out under acidic conditions. This can avoid the production of a large amount of insoluble calcium sulfite hemihydrate and calcium sulfate dihydrate under alkaline conditions, which will precipitate on the surface of the equipment to form scale. However, the deacidification efficiency is greatly affected by the pH value. Under other identical working conditions, the deacidification rate and deacidification efficiency of calcium magnesium slurry alkali under acidic conditions must be lower than the deacidification rate and deacidification efficiency of sodium alkali under alkaline conditions. In this way, the above problems (1) and (2) are difficult to solve at the same time. Moreover, calcium magnesium slurry is not well soluble in alkaline water and has a high slurry concentration. If the hazardous waste incineration flue gas contains some carbon particles or tar organic matter, or the dust concentration exceeds the standard, or the COD and BOD content in the desulfurization process water is too high, or the gypsum dehydration system or the desulfurization wastewater treatment system cannot be put into operation normally, or the oxidation fan fails, causing the oxidation rate of calcium sulfite to fall in the range of 15% to 95%, it is easy to cause the deacidification slurry to foam and overflow, seriously affecting the normal deacidification operation. Due to the large changes in hazardous waste operating conditions and the frequent temporary parking, the above problems (3) are very likely to occur.

[0044] In addition, conventional slurry alkaline deacidification has the step of sulfite aeration oxidation, which means that its application in hazardous waste incineration systems must add a series of auxiliary systems, such as limestone slurry preparation system, circulating slurry oxidation system, gypsum dehydration system, slurry discharge and accident slurry system, etc. These new devices and facilities are difficult to design and arrange on site for most hazardous waste incineration production lines.

[0045] In particular, the composition of hazardous waste incineration flue gas is complex. If slurry alkali deacidification is used, it is impossible to obtain high-content gypsum or magnesium sulfate byproducts by oxidation separation like coal-fired power generation desulfurization. Instead, it can only obtain solids mixed with mixed waste salts such as calcium chloride, calcium sulfate, and calcium fluoride. It is still classified as hazardous waste rather than a byproduct and has no utilization value. The above problem (5) has no good solution in terms of economic efficiency.

[0046] Since the above-mentioned problems cannot be solved at the same time, although calcium or magnesium wet desulfurization technologies have been widely used in flue gas deacidification in coal-fired power generation, municipal solid waste incineration power generation, steel metallurgy, chemical industry and other fields, they have never been used in the field of hazardous waste incineration. Summary of the invention

[0047] The invention discloses an application of an activated deacidification agent for wet deacidification in the field of hazardous waste incineration. Through a grinding activation method, the crystal structure of particles is relaxed, the lattice is distorted, and there are many defects. A certain number of groups with different polarities are adsorbed on the surface, the surface energy is increased, and the activity of slurry alkali is increased, so that the activated deacidification agent can replace sodium alkali for wet deacidification in the field of hazardous waste incineration.

[0048] The technical solution adopted by the present invention is:

[0049] The application of activated deacidifier for wet deacidification in the field of hazardous waste incineration, wherein the activated deacidifier is a calcium magnesium deacidifier added to water and ground and activated so that the median particle size D50 is not greater than 19 microns, wherein the calcium magnesium deacidifier refers to one or more of calcium oxide MgO, calcium hydroxide Ca(OH)2, calcium carbonate, magnesium oxide MgO, magnesium hydroxide Ca(OH)2, magnesium carbonate MgCO3, and magnesium calcium carbonate CaMg(CO3)2. Specifically, it includes but is not limited to a single component or a mixture of quicklime, slaked lime, limestone powder, carbide slag, alkali slag white mud, magnesia powder, magnesia powder, and dolomite powder.

[0050] Preferably, the activated deacidifying agent is slurried with water and then wet-grinded to obtain the activated deacidifying agent, and the pH value of the activated deacidifying agent at a solid content concentration of 1% by mass is greater than 8.0.

[0051] Through grinding and activation, the solid particles of quicklime, slaked lime, limestone powder, carbide slag, alkali slag white mud, magnesia powder, magnesia powder, dolomite powder and other low-cost calcium-based or magnesium-based alkalis collide, squeeze and rub against each other, so that they are broken, dispersed and surface activated, so that the deacidification agent quickly increases its reaction activity in the deacidification slurry, so that the deacidification agent can be hydrated and matured more quickly, thereby improving the mass transfer coefficient, mass transfer rate and deacidification reaction rate. At the same time, grinding and activation rapidly reduces the particle size of the deacidification agent, rapidly increases the specific surface area, and exponentially increases the contact area between the liquid and solid phases, thereby increasing the mass transfer rate between the liquid and solid phases. . After the deacidification agent is ground and activated, the finer the particle size, the narrower the distribution. However, the required equipment, energy consumption investment and operating costs are also higher. In the field of hazardous waste incineration, the present invention has been experimentally tested, and its characteristics are that the median particle size D50 of the deacidifier detected by a laser particle size analyzer is not greater than 19 microns, and the "median particle size D50" containing the meaning of particle size distribution can better characterize the grinding and activation characteristics of the deacidifier than the "mesh number", and the pH value of the slurry with a characteristic 1% solid content is greater than 8.0. This has a good practical guiding significance. Grinding activation can be prepared on site at the incineration project or in advance at other places. Obviously, after on-site wet grinding, water is used as a dispersant and it is ready for use, which can better prevent the activated particles from re-aggregating and inactivating, and the effect is better. With this as a guide, it is very convenient to prepare and screen out calcium magnesium slurry alkali with high deacidification efficiency, so that the deacidification efficiency of calcium magnesium slurry alkali can be comparable to that of sodium alkali.

[0052] Grinding activation can be performed using a ball mill, air flow mill, stirred mill, stirred tank, reactor, pipeline shear pump, wet Raymond mill, colloid mill, wet tower mill, vertical sand mill, ball mill (horizontal or vertical), etc. Preferably, wet grinding is performed using a vertical sand mill, and the grinding balls are made of zirconium oxide or stainless steel with a diameter of 1 to 5 mm. The grinding time is 10 to 60 minutes.

[0053] The invention also discloses the application of the activated deacidification agent in the field of hazardous waste incineration for wet deacidification.

[0054] Power plant desulfurization uses calcium magnesium alkali wet desulfurization, and in order to prevent scaling, desulfurization has always been carried out under weak acidic conditions. In order to pursue higher deacidification efficiency, hazardous waste incineration uses sodium alkali wet deacidification under alkaline conditions. The present invention uses activated calcium magnesium alkali wet deacidification, mainly through the adjustment and innovation of process technology conditions, so that it can treat the flue gas in the field of hazardous waste incineration under acidic or alkaline conditions.

[0055] Preferably, during the reaction process of the deacidification tower, the mass percentage concentration of the second deacidification slurry in the control tower is controlled to be below 15%, and the density is 1.15 g / cm 3 the following.

[0056] Preferably, the steps include:

[0057] (1) Prepare the above-mentioned activated deacidification agent. The grinding activation can be prepared on-site at the incineration project or in advance at other places. More preferably, the grinding activation adopts a wet grinding method to prepare the activated deacidification agent on-site;

[0058] (2) The activated deacidifying agent is put into the wet deacidifying tower for hazardous waste incineration, and the deacidifying agent is continuously absorbed and deacidified with the incineration flue gas in the deacidifying tower through an absorption circulation pump to obtain a second deacidified slurry; the wet deacidifying tower can be deacidified by means of power wave reverse jet washing, cyclone plate tower washing, pneumatic emulsification washing, multi-layer spray washing, etc.

[0059] A spare slurry nozzle can also be set in the wet deacidification tower or in the connecting flue. When the flue gas pollutant emission index exceeds the standard instantaneously, the spare nozzle can be opened to enhance the spray washing effect of the deacidification tower.

[0060] (3) The second deacidified slurry is sent to a quenching tower without aeration and oxidation. The slurry in the quenching tower is atomized and then quenched and dried on the high-temperature incineration flue gas to form incineration fly ash containing calcium chloride or magnesium chloride.

[0061] The rapid cooling of slurry into ash realizes the following functions:

[0062] The first is to achieve the optimization of flue gas rapid cooling and flue gas deacidification. Secondly, there are still a small amount of solid deacidifier particles in the deacidification slurry that have not reacted with the flue gas, and they can further react with the high-temperature flue gas during the rapid cooling and drying process to deacidify, thereby improving the deacidification efficiency of the slurry alkali and reducing the amount of deacidifier. Compared with the conventional calcium-based semi-dry desulfurization in power plants, the amount of deacidifier used has been significantly reduced. Moreover, compared with the conventional sodium-alkali high-salt wastewater rapid cooling tower back-spray process, the calcium-magnesium slurry alkali rapid cooling deacidification has been significantly improved, which is equivalent to adding a pre-deacidification tower, reducing the load of the subsequent wet deacidification tower, and is more conducive to the stable and standard emission of incineration flue gas. Especially when the second deacidification slurry is sent to the quenching tower indirectly, that is, it is more optimal. Since the concentration of the second deacidification slurry is lower than 15%, it can be used as part of the pulping water. Returning to step 1), during the wet grinding activation process, calcium bisulfite can react with the alkaline deacidification agent to undergo acid-base neutralization reaction, which is equivalent to further increasing the deacidification step and time, and can reduce the coverage and shielding of the deacidification agent surface by insoluble sulfite, forming a highly active activated deacidification agent. At this time, the activated deacidification agent is strongly alkaline and contains a large amount of calcium chloride or magnesium chloride, which has a better pre-deacidification effect in the quenching tower. At the same time, such an activated deacidification agent contains a large amount of calcium sulfite / magnesium and calcium sulfate particles that can be used as crystal seeds. When the activated deacidification agent is pumped to the deacidification tower for use, the scaling problem of the deacidification tower can be improved.

[0063] The second is to obtain solid fly ash containing calcium chloride or magnesium chloride. The clever thing is that calcium chloride / magnesium is water-soluble, while calcium sulfite / magnesium, calcium sulfate, and calcium fluoride / magnesium are all insoluble in water. In this way, the fly ash containing calcium chloride / magnesium can be separated by simple filtration to obtain pure calcium chloride / magnesium solution. This characteristic provides great convenience for the utilization of fly ash in the subsequent steps of the present invention and the purification and preparation of calcium chloride products or magnesium chloride products. However, the wet deacidification using sodium alkali and the back-spraying process of the high-salt wastewater quenching tower can only obtain water-soluble mixed sodium salts containing sodium chloride, sodium sulfate, etc., which lack utilization value. The wet desulfurization of calcium magnesium alkali in power plants requires huge investment, complex equipment, and complicated operation in order to obtain by-product gypsum or magnesium sulfate, which is obviously not suitable for hazardous waste incineration. Compared with each other, the ingenuity of the present invention is more evident.

[0064] The third is to achieve low-cost disposal of deacidification wastewater. In the quenching tower, a large amount of water in the slurry is heated and flashed by the high-temperature flue gas from the waste heat boiler, which fully utilizes the thermal enthalpy of the flue gas from 500°C to 200°C, avoiding the use of additional steam for evaporation, dehydration and desalination on the multi-effect evaporator. Reduce the energy consumption cost of subsequent fly ash utilization. Therefore, in step 3) of the present invention, the second deacidification slurry containing calcium and magnesium is directly or indirectly quenched and sprayed back, which can make full use of the process characteristics and existing technical equipment of hazardous waste incineration. There is no need to build a complex circulating slurry oxidation system, gypsum dehydration system, slurry discharge and accident slurry system inside or beside the wet deacidification tower, as in limestone-gypsum wet desulfurization. This simplifies the process, the device occupies a small area, saves a lot of equipment investment, and is also easy to transform the existing sodium-alkali wet deacidification system. Similar to the process of sodium alkali incineration and deacidification of hazardous waste, the process of spraying high-salt wastewater back into the quenching tower also solves the "zero emission" problem of deacidification wastewater at the incineration site in a simple and efficient way.

[0065] Through the above-mentioned technical improvements, the present invention solves the problem of reasonable disposal and utilization of by-product mixtures after slurry separation. After rapid cooling and back spraying, incineration fly ash is obtained. Such fly ash can be separated by simple water washing, filtration and separation to obtain a relatively pure chloride salt solution. This characteristic provides favorable conditions for the subsequent purification and preparation of high-value calcium chloride or magnesium chloride products. As for the sulfur element and the fluorine element, the insoluble residues such as calcium sulfite / magnesium, calcium fluoride / magnesium in the fly ash are landfilled or disposed of in a cement kiln or other high-temperature kiln in a coordinated manner, thereby achieving reduction and improving the disposal and utilization benefits. The fly ash produced by the present invention also avoids the drawbacks that the sodium-based incineration fly ash can only be washed with water to obtain a low-concentration sodium chloride mixed salt solution, and then the evaporation crystallization has high energy consumption and is difficult to separate and purify. And this is precisely the result of the present invention's transformation of ideas, thereby achieving a breakthrough in technical engineering.

[0066] The various steps of the present invention support each other, forming an integral technical solution, which is inseparable, overcoming the technical prejudice that only sodium alkali can be used in a hazardous waste wet deacidification tower, and obtaining unexpected technical effects:

[0067] Step 1) grinding and activation provides technical support for step 2) deacidification and washing, solving the problem of decreased deacidification efficiency of calcium and magnesium deacidification slurry under acidic conditions and easy scaling under weak alkaline conditions;

[0068] Step 3) slurry quenching provides technical support for step 2) deacidification and washing, so that the second deacidification slurry containing calcium chloride / magnesium does not need to be separated from calcium sulfate / magnesium by complex means such as aeration oxidation and solid-liquid separation, but is directly or indirectly sprayed back to the quenching tower, solving the problem of treating the wastewater from the deacidification tower in the calcium deacidification of hazardous waste incineration;

[0069] Step 1) grinding and activation provides technical support for step 3) slurry rapid cooling, reduces the load of the deacidification tower, and improves the process stability of the device.

[0070] Step 3) indirect quenching of the slurry also provides technical support for step 1) grinding and activation. The second deacidified slurry forms a highly active activated deacidifying agent with the deacidifying agent during the grinding and activation process, which not only has a better pre-deacidification effect in the quenching tower, but also contains a large number of seed crystals, which can improve the scaling problem of the deacidifying tower.

[0071] The various steps of the present invention work together, and the overall technical effect is to use low-cost calcium-magnesium slurry alkali to replace high-cost sodium alkali, solving the problem of high cost of sodium alkali in the field of hazardous waste incineration. At the same time, it can also make the chlorine, sulfur, fluorine and other elements in hazardous waste be well treated and utilized. The present invention is particularly suitable for the treatment of high chlorine characteristics of hazardous waste.

[0072] The following table lists the main differences between the power plant calcium alkali wet desulfurization process, the hazardous waste incineration sodium alkali wet deacidification process and the hazardous waste incineration calcium alkali wet deacidification process of the present invention:

[0073]

[0074]

[0075] Preferably, the incineration fly ash is washed with water, the washing water is concentrated to form calcium chloride or magnesium chloride, and the insoluble part is transferred to a cement kiln or other high-temperature kiln for co-treatment.

[0076] Preferably, in step (3), a portion of the second deacidification slurry is sent to a quenching tower to form fly ash, and another portion of the second deacidification slurry is recycled as water for preparing an activated deacidification agent.

[0077] Preferably, in step (2), a portion of the activated deacidification agent is fed into a wet deacidification tower for hazardous waste incineration to undergo absorption and deacidification reaction, and another portion of the activated deacidification agent is directly fed into a quenching tower for quenching and drying.

[0078] Preferably, in step (1), a hydrocyclone or a rotary vibrating screen can be used to screen and separate the activated deacidifying agent to obtain two coarse and fine slurries with a volume ratio of 5:5 to 1:9. The coarse slurry is subjected to cyclic wet grinding, and the fine slurry is fed into a wet deacidification tower for hazardous waste incineration for absorption and deacidification reaction, or the fine slurry is directly sent to a quenching tower for quenching and drying.

[0079] Preferably, in step (2), the mass concentration of the second deacidified slurry is controlled to be below 15% and the density is controlled to be 1.15 g / cm 3 Below, the pH value in the wet deacidification tower is controlled above 5.5.

[0080] The present invention reduces the mass percentage concentration of the second deacidified slurry to less than 15%, or the density is less than 1.15 g / cm 3 , the concentration of limestone slurry is significantly reduced compared to the limestone-gypsum flue gas desulfurization of more than 20% in the power plant. And after the second deacidified slurry in step 2) of the present invention absorbs the hydrogen chloride gas generated by the hazardous waste incineration flue gas, it contains a large amount of soluble calcium chloride or magnesium chloride, and the chloride solution has a good electrolyte demulsification effect, which can well avoid the stickiness, bubbling and overflow of the circulating slurry. In order to inhibit the oxidation of calcium sulfite or magnesium sulfite, the inventor controls the pH value of the deacidified slurry to be above 5.5, abandons the aeration oxidation process, and uses the small amount of oxygen of about 6% in the hazardous waste incineration flue gas to keep the natural oxidation degree of the deacidified slurry less than 15%. In this way, calcium chloride and calcium sulfite are easily separated, or magnesium chloride and magnesium sulfite are easily separated, and the corresponding aeration oxidation equipment investment in the desulfurization process of the power plant can be omitted.

[0081] More preferably, under acidic conditions, the pH value is controlled between 5.5 and 6.5. At this time, the deacidification slurry contains a large amount of calcium bisulfite or magnesium bisulfite, and the insoluble soft scale calcium sulfite salt is easily converted into soluble bisulfite, while the process of further oxidation into insoluble hard scale calcium sulfate is inhibited, and scaling is not easy to form in the deacidification tower. For the problem of reducing the absorption activity of sulfur dioxide due to the common ion effect of chloride in the slurry, the deacidification agent is ground and activated to make the particle size D50 of the deacidification slurry less than 19 microns, increase the reaction activity and reaction area of ​​the deacidification agent, and thus improve the method of increasing the deacidification reaction rate. In addition, by spraying the deacidification tower slurry back to the quenching tower for semi-dry pre-deacidification, a three-stage deacidification system of "semi-dry deacidification + dry deacidification + wet deacidification" for hazardous waste incineration flue gas is formed, which can meet the requirements of hazardous waste incineration deacidification efficiency and achieve a deacidification effect comparable to sodium alkali deacidification.

[0082] When the working conditions of the hazardous waste incineration site change greatly, resulting in a corresponding change in the flue gas load, the flue gas pollutants change quickly, and the hourly average index of the emission concentration limit, especially the sulfur dioxide index, exceeds the standard, the present invention can also improve the deacidification effect by further appropriately increasing the pH value of the deacidification tower. The pH value is controlled between 7 and 8, which is weakly alkaline. Since the solid deacidification agent used in the present invention is activated by grinding, the activated slurry particle size is fine and the distribution is narrow, especially the wet grinding activation method is adopted, so that the slurry generated by the reaction in the deacidification tower contains a large number of microcrystals, which can form a large number of crystal seeds, so that the insoluble calcium salt or magnesium salt precipitated in the solution preferentially grows on the crystal seeds of the same structure, rather than gradually crystallizing and growing on the inner wall of the flow surface of the deacidification tower, pipeline, pump valve, etc., which can effectively prevent scaling. And the deacidification slurry with fine particle size can also reduce the viscosity of the slurry, increase the flow rate of the slurry relative to the inner wall of the container, thereby inhibiting the generation of scaling.

[0083] Preferably, the liquid-to-gas ratio of the second deacidified slurry to the flue gas in step (2) is not greater than 10 L / NM 3 .

[0084] Preferably, a deacidification synergist is added to the activated deacidification agent or the second deacidification slurry, and the components and proportions of the deacidification synergist are:

[0085]

[0086] Deacidification enhancers can increase the solubility and activity of slurry alkali in water, improve the atomization and dispersion ability of slurry, and improve the gas-liquid contact mass transfer ability of flue gas and slurry. The chelating ligand and dispersant cooperate with each other to strengthen the hydration and maturation ability of calcium-based alkalis such as calcium hydroxide, calcium carbonate, and calcium oxide, improve the solid-liquid mass transfer coefficient of calcium alkali in water, and increase the solubilization and dispersion ability of insoluble calcium in water, increase the supersaturation of insoluble calcium, and reduce the scaling tendency on the inner wall of containers and pipes. Surfactants can reduce the surface tension of deacidification slurry, improve the atomization ability of absorption liquid in deacidification tower, and improve the contact condition between flue gas and deacidification slurry. Therefore, deacidification enhancers can better improve the absorption efficiency of flue gas in hazardous waste deacidification tower, and can also improve the absorption efficiency of flue gas in quenching tower, and at the same time make the calcium chloride-containing slurry crystallize finely and evenly during the flash drying process to avoid the formation of large scale.

[0087] Preferably, the amount of the deacidification enhancer added is 0.1% to 3% by mass.

[0088] The present invention also discloses a hazardous waste incineration deacidification device, comprising a slurry tank, a wet deacidification tower pool, and a quenching tower. The slurry tank is filled with an activated deacidifying agent. The slurry tank is connected to the inlets of the wet deacidification tower pool and the quenching tower through pipelines, respectively. The wet deacidification tower pool is connected to the inlet of the quenching tower through a pipeline. The quenching tower is provided with 1 to 2 layers of double-fluid atomizing nozzles for atomizing the slurry flowing in from the inlet of the quenching tower.

[0089] Preferably, it also includes an electrical control system, which controls the flow rate or flow velocity of the activated deacidifying agent entering the wet deacidifying tower pool according to the pH value of the deacidifying slurry in the deacidifying tower; controls the flow rate or flow velocity of the second deacidifying slurry leaving the wet deacidifying tower pool according to the liquid level of the second deacidifying slurry; and controls the atomization flow rate of the activated deacidifying agent or the second deacidifying slurry entering the quenching tower according to the outlet temperature in the quenching tower.

[0090] The present invention is guided by economy, starting from the problem of disposal and utilization of deacidification by-product mixture, analyzing the material composition at the bottom level, studying the physical changes and corresponding value differences of various elements such as fluorine, chlorine, sulfur and sodium in the whole process from generation to disposal of flue gas in the field of hazardous waste incineration, changing the idea, treating harmful chlorine in flue gas as usable hydrogen chloride gas for collection and utilization, and innovatively transforming the calcium magnesium wet desulfurization method. By grinding and activating the deacidification agent and optimizing the particle size, the high cost problem caused by the use of sodium alkali in incineration deacidification disposal is solved, and combined with reducing the concentration of deacidification slurry and controlling the pH value of deacidification slurry, the problems of decreased deacidification efficiency, slurry scaling and blockage, and slurry stickiness and overflow are solved. At the same time, a new process of direct rapid cooling and back-spraying of deacidification slurry without aeration oxidation is adopted to solve the problems of additional equipment and additional operating costs caused by aeration oxidation of slurry, as well as the reasonable disposal and utilization of by-product mixture after slurry separation.

[0091] First of all, the flue gas from hazardous waste incineration is mainly composed of hydrogen chloride, a lot of sulfur dioxide, and relatively little hydrogen fluoride. If traditional calcium alkali or magnesium alkali is used for wet deacidification in the field of hazardous waste incineration, the by-product obtained after aeration oxidation is a complex mixed salt, which is very unfriendly to its subsequent use, and separation and purification will cost a lot of money. If the calcium salt is obtained by calcium deacidification, calcium chloride is soluble in water, calcium sulfate is slightly soluble in water, and calcium fluoride is insoluble in water. If the magnesium salt is obtained by magnesium deacidification, magnesium chloride is soluble in water, magnesium sulfate is also soluble in water, and magnesium fluoride is insoluble in water. Since both magnesium chloride and magnesium sulfate are soluble in water, separation requires more complex processes such as evaporation, cooling, crystallization, and recrystallization, and separation and purification will cost a lot of money.

[0092] At the same time, since the disposal scale of a single hazardous waste incineration line usually does not exceed 100 tons / day, the corresponding flue gas volume is only a few dozenths of the flue gas volume of a single coal-fired boiler in a power plant, and there is more chlorine and less sulfur in the flue gas. If the calcium method is used for deacidification, the amount of calcium sulfate produced is very small, and the price of desulfurized gypsum powder is low, usually only one or two hundred yuan per ton. Therefore, it makes no economic sense to prepare desulfurized gypsum powder from the deacidification products produced by hazardous waste incineration.

[0093] However, the value of industrial calcium chloride or magnesium chloride is much higher. The price of calcium chloride dihydrate or magnesium chloride hexahydrate is usually in the range of 400 to 800 yuan per ton, and the price of anhydrous calcium chloride is even higher, about 600 to 2,000 yuan per ton. It is usually a by-product of the brine industry after salt separation, or it is obtained by distillation and refining after the reaction of hydrochloric acid with limestone, magnesite, etc. The chlorine element in the flue gas of hazardous waste incineration is converted into hydrogen chloride gas after incineration. If calcium alkali or magnesium alkali is used for wet deacidification, a large amount of calcium chloride or magnesium chloride will naturally be obtained.

[0094] In this process, if the chlorine element in the hazardous waste can be converted into water-soluble calcium chloride or magnesium chloride, and the sulfur element is only converted into the precipitated insoluble matter of calcium sulfite or magnesium sulfite without further oxidation into calcium sulfate or magnesium sulfate, the fluorine element is converted into the precipitated insoluble matter of calcium fluoride or magnesium fluoride. The clever thing is that by utilizing the different solubilities of calcium and magnesium ions and compounds of chloride ions, sulfite, sulfate, and fluoride ions, it is easy to obtain a high-concentration calcium chloride or magnesium chloride solution through a low-cost process of dissolving and filtering and separating, which can be further concentrated and crystallized to obtain the corresponding high-value chloride product, which is obviously more economically feasible.

[0095] If calcium alkali or magnesium alkali is to obtain high concentration of chloride, it is necessary to reduce the production of magnesium sulfate or calcium sulfate, so the oxidation process of sulfite needs to be suppressed during the wet deacidification of hazardous waste incineration. This is very different from the current common calcium alkali or magnesium alkali flue gas wet desulfurization process in power plants.

[0096] Conventional power plant flue gas wet desulfurization processes require aeration forced oxidation steps. This is mainly due to the large amount of coal-fired flue gas in power plants, which contains more sulfur and less chlorine in the elemental composition, making it suitable for making by-product desulfurization gypsum powder. In this way, the hemihydrate calcium sulfite produced by wet desulfurization needs to be further oxidized. In addition, during the wet desulfurization process of power plants, since the hemihydrate calcium sulfite produced is a viscous substance, it will reduce the desulfurization efficiency and easily cause the desulfurization slurry to foam and overflow. Therefore, it is usually necessary to control the calcium sulfite content within 0.5% of the desulfurization slurry and control the calcium sulfite oxidation rate to >95%. This can ensure the continuous absorption of SO2, improve the desulfurization efficiency, and improve the quality of the desulfurization by-product gypsum. On the other hand, it can prevent calcium sulfite from forming a large amount of soft scale in the absorption tower and gypsum slurry tank. At the same time, it can also produce enough gypsum seeds to make the gypsum crystals grow rapidly and prevent the gypsum from forming a large amount of hard scale in the desulfurization equipment. During the deacidification process, it is necessary to use sulfuric acid to adjust the deacidified slurry to the most suitable condition of weak acidity of 4 to 4.5, and use a Rhodes blower to blow in a large amount of fresh air for forced aeration oxidation.

[0097] Su Daxiong pointed out in his paper "Study on Scaling and Scaling Prevention of Wet Lime Flue Gas Desulfurization" that the most important factor affecting the oxidation of calcium sulfite to calcium sulfate is pH value, followed by oxygen content, and temperature has a smaller impact. He also believes that the pH value of wet lime flue gas desulfurization slurry should be controlled at 5.0-5.5.

[0098] The present invention believes that under the above-mentioned acidic conditions, the essence of calcium sulfite oxidation is that insoluble CaS03 continues to react with S02 in the flue gas to generate a large amount of soluble Ca(HSO3)2. Correspondingly, under acidic conditions, Ca(HSO3)2 undergoes an oxidation reaction with air in the liquid phase and is converted into crystals of CaS04·2H20. The conversion process of (CaS03) solid-Ca(HSO3)2 liquid-(CaS04·2H20) solid is realized, and the generation and conversion of Ca(HSO3)2 in the liquid phase is a key step. Therefore, the present invention believes that controlling the pH value of the deacidified slurry above 5.5 can better reduce HSO3 - concentration, that is, inhibiting the formation of Ca(HSO3)2 in the liquid phase, thereby inhibiting the oxidation process of calcium sulfite. In addition, the flue gas from hazardous waste incineration contains only a small amount of oxygen, about 6%, and the small amount of CaS04·2H20 generated by its natural oxidation is not the main influencing factor. This can better meet the requirements of obtaining chloride products after wet deacidification of hazardous waste incineration with calcium alkali or magnesium alkali, and can omit the corresponding aeration oxidation equipment investment in the desulfurization process of power plants.

[0099] However, the oxidation of sodium sulfite in the deacidification slurry is inhibited, which will cause the accumulation of sodium sulfite in the slurry. Since hemihydrate sodium sulfite contains crystal water and has high viscosity, it is easy to adhere to the surface of the deacidification agent solid, reducing the deacidification efficiency. Therefore, the slurry deacidification process is adopted for hazardous waste incineration. It is necessary to control the content of calcium sulfite within 0.5% of the desulfurization slurry and discharge the sodium sulfite from the deacidification tower in time. The wet desulfurization process of the power plant uses a vacuum belt filter to separate the solid and liquid of the oxidized gypsum slurry. The whole set of equipment occupies a large area, requires large investment, and has high requirements for continuous operation. It is obviously not suitable for specific use scenarios such as hazardous waste incineration production lines with small flue gas volume and cramped and limited sites.

[0100] The clever thing is that the hazardous waste incineration device must be designed with a quenching tower. Generally, the water used in the quenching tower is designed to be tap water. At present, some companies use the high-salt wastewater produced by sodium alkali wet deacidification instead of tap water for the quenching tower. Zuo Xun mentioned in the document "Selection of Flue Gas Quenching Tower and Feasibility Study of Simultaneous Deacidification in Hazardous Waste Incineration System" that the flue gas temperature of the hazardous waste incineration system must drop to 200°C in about 1 second in the quenching tower. Sodium hydroxide solution can be used for pre-deacidification. The key is that the atomized particle size of sodium hydroxide must be less than 200μm, and the smaller the droplet atomization particle size, the shorter the cooling time, and the deacidification efficiency can reach 30-70%. The present invention believes that the slurry discharged from the deacidification tower contains sodium sulfite and a small amount of solid deacidifier that has not been completely reacted. Usually, the initial calcium-sulfur ratio of calcium desulfurization itself is often around 1.05:1, and the deacidifier is slightly excessive. If the slurry discharged from the hazardous waste incineration deacidification tower is used as quenching water in the quenching tower, the unreacted solid deacidifying agent particles can further react with the high-temperature flue gas during the quenching and drying process, thereby improving the overall deacidification efficiency of the incineration flue gas and reducing the final calcium-sulfur ratio to 1:1, thereby reducing the amount of deacidifying agent. The deacidified slurry is used for pre-deacidification and back-spraying in the hazardous waste incineration quenching tower, which can be regarded as the application of semi-dry deacidification in the hazardous waste incineration process. At the same time, the deacidified slurry is also quenched and spray-dried, and finally converted into flue gas fly ash containing chloride. As mentioned above, this fly ash can be easily washed and separated to obtain calcium chloride or magnesium chloride.

[0101] Therefore, the calcium desulfurization process is improved, the calcium sulfite oxidation process is omitted, and it is applied to the field of hazardous waste incineration. The method of pre-deacidification and quenching by back-spraying the quenching tower is adopted, which not only omits the circulating slurry oxidation system in the original desulfurization process, but also omits the gypsum dehydration system, slurry discharge and accident slurry system. This saves equipment investment and improves the flue gas deacidification efficiency.

[0102] However, there are new problems in the application of calcium-magnesium slurry for deacidification in the field of hazardous waste incineration. Since there is more chlorine and less sulfur in the flue gas of hazardous waste incineration, a large amount of chloride ions and calcium-magnesium ions will eventually be formed in the deacidification slurry. The effects of these anions and cations on the wet deacidification reaction are manifested in the following aspects:

[0103] (1) If the oxidation of calcium sulfite is inhibited only by increasing the pH value of the slurry, a large amount of CaSO3·1 / 2H20 and a small amount of CaS04·2H20 will be generated in the deacidification tower due to the increase in pH value, which will easily cause scaling.

[0104] (2) The solubility of solid deacidifier is relatively low. The deacidifier mainly exists in the slurry as solid particles. Therefore, the dissolution of the deacidifier is a factor that needs to be considered during the desulfurization process. The presence of a large number of anions and cations will affect the ionic strength of the solution. Due to the common ion effect, the presence of some ions in the slurry will affect the dissolution of the deacidifier and the migration and diffusion speed of sulfur dioxide after dissolving in water, thereby affecting the desulfurization efficiency.

[0105] (3) The ionic strength of the desulfurization slurry directly affects the surface tension of water, and changes in solution viscosity and surface tension are two important factors in slurry foaming. Slurry overflow caused by slurry foaming in the absorption tower is a common problem in system operation. In severe cases, it will cause the desulfurization tower to malfunction or even shut down.

[0106] Among these problems, the problem of slurry foaming and overflow is relatively easier to solve. Since the main components of flue gas are the increase in the content of organic matter and heavy metal ions in the flue gas, some unburned materials in the fly ash enter the absorption tower with the flue gas, which increases the content of organic matter or heavy metal ions in the slurry of the absorption tower, and a saponification reaction occurs to form an oil film on the surface of the slurry. Under the action of the high temperature and high pressure inside the absorption tower, the oil film will cause the liquid level of the absorption tower to rise sharply, resulting in foaming and overflow. Since the hazardous waste incineration system is set in the secondary combustion chamber, the flue gas stays at 1100℃ in the secondary combustion chamber for more than 2 seconds, so there are very few organic matters in the flue gas of hazardous waste incineration. Even if the desulfurization slurry contains more chloride ions and calcium and magnesium ions, saponification reaction is not easy to occur.

[0107] In addition, the present invention abandons the oxidation process of the deacidified slurry, thus eliminating the problem of overflow of the absorption tower due to excessive air volume of aeration oxidation, which causes excess air to overflow to the slurry surface in the form of bubbles. In addition, the presence of high-concentration calcium chloride or magnesium chloride in the deacidified slurry after incineration will form a good electrolyte demulsification effect and inhibit the occurrence of foam.

[0108] On the basis of the above, the present invention further proposes to reduce the slurry concentration, so that the water quality of the absorber water supply can be better controlled, the filtration and pretreatment can be improved, the COD and BOD content in the water supply can be reduced, the deacidification wastewater can be discharged, and the content of heavy metal ions, chlorides and organic matter in the absorber slurry can be reduced to ensure the slurry quality and reduce the formation of foam. The flue gas volume of power plant desulfurization is large and the slurry concentration is high. Taking the most commonly used limestone method as an example, the mass concentration of 20-25% can usually meet the process requirements. In contrast, the flue gas volume of hazardous waste incineration is small, and the use of 10% sodium hydroxide solution can meet the production requirements. Therefore, comprehensive consideration can not only improve the slurry foaming overflow problem, but also meet the needs of deacidification efficiency, and can also reduce the quenching back spray slurry in the spray gun and pipeline transportation and wear. The present invention further proposes that on the basis of the slurry back spraying to the quenching tower, the slurry concentration is reduced, and it is more reasonable to choose to control the concentration of the deacidification slurry within 15%. Since there is a strong correlation between slurry concentration and density, the slurry density can also be controlled at 1.15 g / cm for the convenience of on-site operation and analysis. 3 The following will do.

[0109] On the basis of reducing the slurry concentration to less than 15% and adjusting the pH value to greater than 5.5 to inhibit sulfite oxidation, if calcium alkali or magnesium alkali is used for wet deacidification in hazardous waste incineration, it is necessary to achieve a deacidification efficiency similar to that of sodium alkali, which puts higher requirements on the activity of the slurry.

[0110] Activity refers to the ability of solid deacidifier to participate in chemical or physicochemical processes. The essence of activity is the unsaturation of the bond on the surface of the crystal. The distortion and defects of the lattice aggravate the unsaturation of this bond. Therefore, activity is an instinctive attribute of solid deacidifier, and the difference in activity mainly comes from factors such as the size of the solid deacidifier crystal and the incomplete structure. Activity is greatly affected by grinding. Through grinding, the crystal structure of the particles can be relaxed, the lattice can be distorted, and there are more defects. Then a certain number of groups with different polarities are adsorbed on the surface, the surface energy is increased, and the activity of the slurry alkali is increased. It should be emphasized that if the solid deacidifier has high activity, it must have a fine particle size and a narrow distribution. Conversely, it is not necessarily the case. A fine particle size may not be highly active. For example, after dry Raymond grinding, the solid particles will heat up and agglomerate, and the surface will be passivated, and its activity is far from that of wet grinding. Therefore, wet grinding of solid deacidifier is a better choice than dry grinding. After wet grinding, the solid deacidifying agent can effectively improve the reaction activity of the slurry, so that the slurry alkali can be hydrated and matured more quickly, thereby improving the mass transfer coefficient, mass transfer rate and deacidification reaction rate.

[0111] Wet grinding can also rapidly reduce the particle size of slurry alkali, rapidly increase the specific surface area, and exponentially increase the contact area between the liquid and solid phases, thereby increasing the mass transfer rate between the liquid and solid phases, and rapidly migrating the generated hydroxide into the liquid phase. It makes it easier for acidic gases such as hydrogen chloride, sulfur dioxide, and hydrogen fluoride to enter the absorption liquid phase from the gas phase, thereby increasing the deacidification reaction rate in the semi-dry quench tower and the wet deacidification tower.

[0112] The inventors of the present invention believe that for hazardous waste incineration flue gas, since the solubility and ionization degree of hydrogen chloride and hydrogen fluoride gases in water are much greater than those of SO2 gas, the deacidification efficiency can be mainly analyzed by the desulfurization efficiency, which is closely related to the pH value of the system and the morphology of ions and compounds in the liquid phase.

[0113] Under alkaline conditions, i.e., pH>7, the sulfur anions in the liquid phase are mainly SO3 2- The system has no buffering capacity. During the desulfurization process, CaSO3·1 / 2H20 or CaS04·2H20 with very low solubility is mainly generated. Scaling is easy to occur at this time. Flue gas deacidification is mainly the following two processes that interact and influence each other:

[0114] Step 1, gas-liquid mass transfer, hydration and dissociation process, that is, when SO2 molecules in flue gas come into contact with water, they dissolve in water, hydrate with water molecules to form H2SO3, and dissociate:

[0115]

[0116] Step 2: Ca(OH)2 in the liquid phase dissociates into OH - A neutralization reaction occurs to generate H2O molecules, and at the same time, Ca(OH)2 dissociates to generate Ca 2+ With SO3 2- Under the participation of water molecules, it combines into CaSO3·1 / 2H20, and CO3 2- Combined as CaCO3:

[0117]

[0118] In the above process, the contact, dissolution, ionization, and diffusion of SO2 molecules from the gas phase to the liquid phase in step 1 are the controlling steps, and the dissolution and migration of the solid deacidifying agent from the solid phase to the liquid phase in step 2 is the controlling step. Usually, to improve step 1, people choose a relatively high deacidification liquid-gas ratio, adopt multi-layer spraying, and increase the spray coverage intensity, all of which aim to increase the gas-liquid contact and improve the gas-liquid migration and ionization of SO2 molecules. To improve step 2, under cost constraints, power plant flue gas desulfurization mostly uses 200-300 mesh limestone powder to increase the slurry concentration to more than 25% to generate more OH - , thereby promoting the improvement of deacidification efficiency.

[0119] The present invention believes that in the process of deacidification of hazardous waste incineration flue gas, there are a large number of chloride ions and calcium and magnesium metal ions, which will inhibit the rightward occurrence of the above-mentioned step 2 reaction (6) due to the common ion effect. And as mentioned above, choosing a lower concentration below 15% can better ensure the slurry quality and reduce the formation of foam. Therefore, in order to ensure the deacidification efficiency, it is necessary to expand the solid-liquid contact area and improve the activity of the solid deacidifier, which requires a method of further reducing the particle size of the deacidifier to achieve this.

[0120] Calcium desulfurization usually chooses mesh number as the particle size characterization. Particle size, as an important parameter of the screen, is also directly related to the size of the screened material. It represents the number of holes per square inch on the screen. According to the general standard particle size and mesh number comparison table, the maximum sieve hole corresponding to 200 mesh is 75μm, and the maximum sieve hole corresponding to 300 mesh is 48μm. It does not represent all the particle sizes of the screened material and their particle size distribution. However, flue gas deacidification is obviously more related to the particle size distribution of the deacidifier, that is, the proportion of small particle size. From the perspective of grinding effectiveness, the deacidifier with a smaller particle size occupies more surface area and has better reaction activity. In addition, after the powder or slurry is ground, its particle size distribution is closer to the normal distribution. The method of using the median particle size, that is, the particle size value when the cumulative distribution percentage reaches 50%, to characterize the particle size of the deacidifier required for incineration deacidification by D50 is more instructive. Therefore, the inventors have finally determined through experiments that the particle size D50 of the deacidifying agent is no more than 19 microns. The deacidifying agent with such a particle size distribution can better meet the needs of incineration wet deacidification.

[0121] In addition, it is particularly noteworthy that when the flue gas from hazardous waste incineration is under alkaline conditions, that is, when pH>7, if calcium magnesium slurry alkali is used for wet deacidification, even if the oxidation inhibition process is adopted, sulfite with very low solubility will still be the main product during the desulfurization process, and scaling is likely to occur at this time.

[0122] The present invention believes that the fundamental cause of scaling is that the supersaturated solution of scaling ions crystallizes near the inner wall of the container, adheres to the wall, and finally covers the wall to form a scaling layer. In order to prevent scaling, from a mechanistic point of view, there are mainly three methods: method ① is to prevent the generation of crystal nuclei or critical crystal nuclei; method ② is to control crystal growth; method ③ is to disperse crystals.

[0123] Since there are a large number of calcium ions or magnesium ions in the incineration deacidification slurry, under alkaline conditions, the saturation index of calcium sulfite or magnesium sulfite is greater than 0, which is in an oversaturated state and has a tendency to precipitate and scale. Therefore, it is more difficult to adopt method ①, but it is obviously more advantageous to choose a lower pH value. It is feasible to control the pH value between 7 and 8 and adopt method ② seed growth control technology. This method is to produce a large number of seeds in the slurry, and use the same structure of the seeds as the scale. The affinity of the crystal surface to the scale is greater than that of the wall of the pipeline material, so that the molecules of calcium sulfite (magnesium) and calcium carbonate (magnesium) precipitated in the salt solution are preferentially attached to the suspended crystals, and the insoluble calcium salt precipitated in the solution is preferentially grown on the seeds of the same structure, rather than gradually crystallizing and growing on the inner wall of the flow surface of the deacidification tower, pipeline, pump and valve, which can effectively prevent scaling. A sufficient number of seeds provide a large crystal surface, so that the supersaturation of calcium sulfite in the solution is eliminated in time, thereby avoiding the nucleation and growth of molecules such as calcium sulfite (magnesium) and calcium carbonate (magnesium) on the wall. The activated slurry obtained by wet grinding has a fine particle size and a narrow distribution. The slurry generated by the reaction in the deacidification tower contains a large number of microcrystals, which can form a large number of seed crystals. The deacidification slurry with fine particle size can also reduce the viscosity of the slurry and increase the flow rate of the slurry relative to the inner wall of the container, thereby inhibiting the formation of scale. In addition, due to the presence of a large number of CaSO3·1 / 2H20 microcrystals in the slurry, it can co-precipitate with a small amount of CaS04·2H20 generated by natural oxidation during the deacidification of incineration flue gas to form a solid solution containing 22.5% CaS04·2H2O. Therefore, scaling of CaS04·2H2O in the tower can be avoided.

[0124] Therefore, when the magnesium alkali is used for wet deacidification of hazardous waste incineration flue gas, the concentration of the deacidification slurry is reduced to less than 15%, and a large number of seed crystals are produced through grinding activation, so that the particle size D50 of the deacidification slurry is less than 19 microns, and the pH value in the deacidification tower is controlled to be above weak acidity, usually above 5.5, and preferably between 5.5 and 6.5 or 7 and 8. This can not only ensure good deacidification efficiency, but also inhibit the problems of slurry scaling and bubbling overflow. More preferably, by adding a deacidification enhancer, the solubilization and dispersion ability of the generated insoluble calcium salt or magnesium salt in water is increased, the supersaturation of the insoluble calcium salt or magnesium salt is increased, and the scaling tendency on the inner wall of the container and the pipeline is reduced.

[0125] We know that the flue gas from hazardous waste incineration contains a large amount of hydrogen chloride and hydrogen fluoride gases, and the flue gas load changes frequently. When the deacidification tower has a poor washing effect, it is easy to cause the hourly average index of the flue gas pollutant emission concentration limit to exceed the standard, especially the hourly average index of SO2 to exceed the standard. When this happens, the general on-site measures are to add liquid alkali to increase the pH value of the washing absorption liquid in the deacidification tower. Therefore, the flue gas from hazardous waste incineration generally uses a 10% liquid alkali solution for wet washing and deacidification. In this way, when the flue gas changes, the deacidification tower can respond quickly by utilizing the high alkalinity and high activity of the liquid alkali. In addition, the deacidification liquid needs to control the pH value above 7. If the pH value is less than 7, since the deacidification liquid contains sodium chloride, sodium sulfite, and sodium fluoride solutions, the pH buffering capacity is small, which can easily cause the hourly average index of SO2 to rise rapidly and exceed the standard.

[0126] We know that the pH value of the slurry in the deacidification washing tower of the conventional power plant wet desulfurization process is often controlled between 5 and 6. Therefore, if the above-mentioned process conditions of calcium magnesium slurry deacidification under alkaline conditions are adopted, that is, the concentration of the deacidification slurry is controlled to be below 15%, and the particle size D50 of the deacidification slurry is made less than 19 microns through grinding activation, whether it is still applicable under acidic conditions, that is, when the pH of the deacidification tower slurry is less than 7, whether it meets the requirements of incineration flue gas washing and deacidification, further analysis is needed.

[0127] It is noted from the literature that under acidic conditions, within this pH range, the sulfur anions in the liquid phase of the calcium desulfurization slurry are almost all in the form of HSO3 - In the first step of the above analysis, the gas-liquid mass transfer, hydration and dissociation process basically only proceeds to reaction (1), reaction (2) and reaction (3), while the further ionization of sulfite in reaction (4) can be ignored. The second step only proceeds to reaction (5), reaction (6) and reaction (7), and Ca(OH)2 in the liquid phase dissociates into OH - A neutralization reaction occurs to generate H2O molecules, and at the same time, Ca(OH)2 dissociates to generate Ca 2+ Then with HSO3 - Under the participation of water molecules, they combine to form Ca(HSO3)2 with great solubility. However, CO2 gas is basically insoluble, reaction (3) is also suppressed, and no CaCO3 is produced, so scaling is difficult to occur at this time.

[0128] In the tower, a small amount of original scaling CaSO3 dissociates into SO3 2- The dissociated H + According to reaction (12), HSO3 is generated - . CaSO3 dissociates into Ca 2+ Then the HSO3 generated by reaction (3) and reaction (12) -Ca(HSO3)2 is generated according to reaction (13). The desulfurization process mainly generates Ca(HSO3)2 with high solubility. The main scaling CaSO3·1 / 2H20 is gradually dissolved and descaled according to the following reaction.

[0129]

[0130] If the hazardous waste incineration flue gas is deacidified under acidic conditions using the magnesium slurry alkali, due to the common ion effect of chloride ions, according to the gas-liquid double membrane theory, SO2 molecules contact, dissolve, ionize and diffuse into the water film, which is more affected than under alkaline conditions, especially reaction (3) is more inhibited, which will affect the deacidification efficiency. Cui Gaofeng pointed out in the literature "Factors Affecting SO2 Absorption Rate in Flue Gas" that the alkalinity of the absorption liquid and the gas-liquid contact conditions are the two key factors that determine the SO2 absorption rate of flue gas. When the alkalinity of the absorption liquid has dropped to 147 mg / L and the pH is 5.04, the SO2 absorption rate is still above 97%. When the alkalinity of the absorption liquid has dropped to 0 (pH ≥ 3.8), the SO2 absorption rate will drop sharply. When the pH of the absorption liquid is 2.7, the SO2 absorption rate is only 10%. In addition, under the condition that other conditions remain unchanged, as long as the alkalinity of the absorption liquid is greater than 0 (pH ≥ 3.8) during the absorption process, the SO2 absorption rate is not affected by the pH of the absorption liquid. Therefore, the absorption rate of SO2 gas can be improved by increasing the alkalinity of the absorption liquid and improving the gas-liquid contact condition. According to the characteristics of large instantaneous changes in the flue gas load of hazardous waste incineration, the present invention selects a process requirement of a pH value greater than 5.5 in combination with experimental results. More preferably, the pH value is controlled between 5.5 and 6.5. In this way, in conjunction with other process conditions, the concentration of the deacidification slurry in the deacidification tower is controlled to be below 15%, and the particle size D50 of the deacidification slurry is made less than 19 microns by grinding and activation, especially grinding to reduce the particle size of the slurry, increase the reaction area of ​​the deacidification agent, and increase the reaction speed of the deacidification agent, so that the alkalinity of the absorption liquid and the gas-liquid contact condition can be quickly improved to respond to the needs of changes in the hazardous waste flue gas load, so that the requirements of deacidification efficiency can be met, and a deacidification effect comparable to that of sodium alkali under alkaline conditions can be achieved. At the same time, the occurrence of the problem of slurry scaling and foaming can also be better suppressed.

[0131] Through the above technical innovation, the present invention overcomes the technical prejudice that the wet deacidification tower for hazardous waste has always used sodium alkali. The present invention has little modification to the existing equipment of the incineration system. It does not need to build a complex circulating slurry oxidation system, gypsum dehydration system, slurry discharge and accident slurry system like the wet desulfurization of limestone-gypsum. It only needs to add a set of slurry wet grinding device and corresponding control pipelines, and the original equipment and facilities of the quenching tower and deacidification tower of hazardous waste incineration can be used, so the system can be transformed from sodium alkali to calcium magnesium alkali. The investment in technical transformation and upgrading is not large, and the effect is significant. The present invention can convert the chlorine element in the hazardous waste into calcium chloride or magnesium chloride, and the fly ash generated by sulfur, fluorine and other elements can be well disposed of through cement kiln synergy and other methods. Analyzing from the most basic material composition, the present invention essentially utilizes the harmful chlorine element in the hazardous waste, introduces low-priced and effective calcium or magnesium elements, and abandons the high-priced sodium element, thereby reducing the cost of incineration deacidification disposal. And the incineration fly ash obtained by the wet deacidification of calcium-magnesium slurry alkali is different from the sodium-alkali method, which lays a good foundation for the resource utilization path of incineration fly ash to prepare calcium chloride or magnesium chloride. The present invention realizes the deacidification of hazardous waste using calcium-magnesium alkali, which not only achieves a deacidification efficiency comparable to that of sodium alkali, but also solves the problem of system scaling, avoids the stickiness, bubbling and overflow of the circulating slurry in the deacidification tower, solves the problem of additional equipment and additional operating costs caused by aeration and oxidation of the slurry, and overcomes the technical prejudice that only sodium alkali can be used for wet deacidification of hazardous waste incineration. Therefore, the present invention has good economic and environmental benefits and has strong market value. BRIEF DESCRIPTION OF THE DRAWINGS

[0132] Figure 1 The present invention is a process flow chart of ultra-low emission treatment of coal-fired flue gas in power plants using existing technology.

[0133] Figure 2 This is a simplified diagram of the limestone (lime) / gypsum wet process for flue gas desulfurization in the prior art.

[0134] Figure 3 This is a typical integrated desulfurization oxidation tower structure diagram in the prior art.

[0135] Figure 4 The present invention is a process flow chart of a hazardous waste incineration flue gas treatment device in the prior art.

[0136] Figure 5 The schematic diagram of the test experimental device of the present invention is shown in the figure. In the figure, the markings are: 1-deacidifying slurry inlet, 2-deacidifying slurry outlet, 3-SO2 inlet, and 4-SO2 gas outlet.

[0137] Figure 6 The present invention is a process flow chart of the alkaline wet deacidification of calcium and magnesium slurry from hazardous waste incineration, wherein the deacidified slurry is directly reused.

[0138] Figure 7 The present invention is a process flow chart of the alkaline wet deacidification of calcium and magnesium slurry from hazardous waste incineration, wherein the deacidified slurry is indirectly reused. DETAILED DESCRIPTION

[0139] The present invention is further described below in conjunction with embodiments, but the description of the embodiments does not impose any limitation on the protection scope of the present invention.

[0140] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention, and the terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. In addition, although demonstrations of parameters containing specific values ​​may be provided herein, it should be understood that the parameters do not need to be exactly equal to the corresponding values, but can be approximated to the corresponding values ​​within an acceptable error tolerance or design constraint. The directional terms mentioned in the embodiments, such as "up", "down", "front", "back", "left", "right", etc., are only directions with reference to the accompanying drawings. Therefore, the directional terms used are used to illustrate rather than to limit the scope of protection of the present invention.

[0141] Unless otherwise specified, the materials and instruments used in the following examples can be obtained from conventional commercial channels.

[0142] Example 1

[0143] Select 120 mesh limestone powder, and then use QM-15 laboratory horizontal drum ball mill, select 3mm and 5mm zirconium oxide grinding balls, and perform dry grinding at a fixed speed. Samples were taken at 0 minutes, 10 minutes, 20 minutes, 30 minutes, and 60 minutes, respectively, and marked as 0#, 1#, 2#, 3#, and 4# samples. The particle size distribution of these samples was analyzed using the Malvern Mastersizer 2000 laser particle size analyzer to obtain D10, D50, and D90 data. At the same time, for these samples, according to the method of "Rapid Determination of Limestone Powder Reaction Rate in Wet Flue Gas Desulfurization" (DB44 / T1373-2014), at room temperature, the limestone powder was reacted with 1.2 mol / L hydrochloric acid at pH = 4.0 for 5 minutes, and the mass percentage of the conversion of the limestone powder was calculated based on the hydrochloric acid consumed in the neutralization reaction, which was characterized as the deacidification chemical reaction activity of the limestone powder. The experimental results are as follows:

[0144]

[0145] We know that the essence of wet grinding is to use water as the dispersion medium, which is more conducive to the surface reaction of the activated deacidification agent particles and improve the deacidification reaction activity. Take 120-mesh limestone powder, prepare it into a 10% slurry, and grind it with a QM-15 laboratory horizontal drum ball mill under the same conditions as before for 10 minutes, 20 minutes, 30 minutes, and 60 minutes. The samples are still numbered 1#, 2#, 3#, and 4#, and 10g of each sample is stirred evenly to replace the 1g dry powder sample to be tested in the "Rapid Determination of the Reaction Rate of Limestone Powder in Wet Flue Gas Desulfurization" (DB44 / T1373-2014), and the deacidification chemical reaction activity is tested again. The reaction activity comparison between dry grinding and wet grinding is as follows:

[0146]

[0147] It can be seen from the above table that the range of change in the activity of limestone powder is greater than the range of change in its particle size. This shows that grinding activation not only reduces the particle size and increases the reaction area of ​​the solid surface, but also relaxes the crystal structure of the particles, causing lattice distortion and more defects. A certain number of groups with different polarities are adsorbed on the surface, increasing the surface energy and increasing the activity of the solid.

[0148] As the grinding time increases, D50 will gradually decrease, but the reduction will also gradually decrease. When the total amount of material to be ground is fixed, the grinding speed is inversely proportional to the grinding time. The longer the grinding time, the smaller the grinding amount of the same grinding equipment. Therefore, considering the comprehensive grinding effect and the economy of grinding time, it is better to choose a median particle size D50 of no more than 19 microns after grinding and a grinding time of more than 10 minutes. Even better, choose wet grinding.

[0149] Example 2

[0150] The commercially available 325-mesh desulfurization calcium hydroxide powder ground by dry tower mill was selected, and then a small 30L vertical ball mill was used. Two stainless steel grinding balls of 1mm and 3mm were selected, and a calcium hydroxide slurry with a solid content of 10% was configured. Wet cycle grinding was performed at a fixed speed. Samples were taken at 0 minutes, 10 minutes, 20 minutes, 30 minutes, and 60 minutes, respectively, and marked as 5#, 6#, 7#, 8#, and 9# samples. The samples were analyzed for particle size distribution using a Malvern Mastersizer 2000 laser particle size analyzer to obtain D10, D50, and D90 data. At the same time, these samples were poured into 50mL measuring cylinders, and the slurry gradually separated into layers. The top layer was a clear saturated solution of calcium hydroxide, and the middle layer was a stable colloid formed by calcium hydroxide and water after activation. This colloid is fine and uniform, has good fluidity, and reacts quickly with acid. It can achieve a reaction effect similar to that of sodium hydroxide, and can replace the use of sodium hydroxide in the deacidification reaction of hazardous waste incineration flue gas. The lower layer is a flocculent sediment of a mixture of calcium hydroxide and mechanical impurities. The suspension performance of calcium hydroxide after standing for 48 hours was observed, and the suspension performance was expressed as a volume percentage.

[0151] Solid content ratio = middle layer colloid volume / total volume

[0152] The data is organized as follows:

[0153]

[0154]

[0155] The suspension performance is actually a manifestation of the ability of calcium hydroxide samples to bind water, and can also be regarded as another simple and convenient way to characterize the activity of the deacidification reaction. As can be seen from the above table, for conventional calcium hydroxide desulfurization powder, if it is directly mixed with water to make pulp, its activity is relatively low, indicating that the surface of the calcium hydroxide powder has few surface defects on the basis of dry Raymond milling, and the activation ability of reacting with water is not strong. However, after a short period of 10 to 30 minutes of wet grinding, although the particle size D90 does not change much, the average particle size D50 has significantly decreased, indicating that grinding relaxes the crystal structure of the particles, lattice distortion, and more defects, then a certain number of groups with different polarities are adsorbed on the surface, the surface energy increases, and the activity of calcium hydroxide increases. After a long period of 60 minutes of wet grinding, D90 and the average particle size D50 have significantly decreased. Considering the comprehensive grinding effect and the economic efficiency of grinding time, the grinding time is selected to be 10 to 60 minutes. The equipment selected is a wet vertical ball mill. Preferably, the grinding time is 20 to 30 minutes.

[0156] Example 3

[0157] For the 5 samples 0#, 1#, 2#, 3#, and 4# obtained in Example 1, a 5% slurry was prepared with deionized water and a laboratory smoke simulation generating device (its structure is as follows) was used. Figure 5 As shown in the figure, the deacidification absorption effect of different alkaline absorption liquids was detected. Since the solubility of HCl and HF in water is very high, the deacidification efficiency is less affected by the pH value and the difference is small in different alkaline absorption liquids. For simplicity, only SO2 gas was simulated in this embodiment.

[0158] In the slurry tank, the prepared 5% slurry is pumped into the first-stage reaction device by the deacidified liquid metering pump. After it is filled, the slurry enters the second-stage reaction device through overflow, and finally enters the third-stage reaction device. The deacidified slurry is collected and then returned to the first-stage reaction device for repeated circulation. The pH value is maintained at 4.0 during the whole process. The sulfur dioxide gas first enters from the third-stage reaction device, and the tail gas after the reaction enters the second-stage reaction device to continue the reaction. Finally, the tail gas after the reaction in the first-stage reaction device is discharged.

[0159] During the experiment, the sulfur dioxide inlet and outlet concentrations of each reactor were mainly recorded.

[0160] Data processing

[0161] 1) Calculation of sulfur dioxide removal rate. The formula is:

[0162] Where: C1---3-stage reaction unit inlet sulfur dioxide concentration, mg / m 3 ;

[0163] C2---1st stage reaction device outlet sulfur dioxide concentration, mg / m 3 .

[0164] The experimental results are summarized as follows:

[0165]

[0166] As can be seen from the table above, as the particle size D50 gradually decreases, the deacidification effect of the slurry on the flue gas will first be significantly improved, but the particle size D50 is not greater than 19 microns, and the absorption efficiency tends to be stable. Considering the investment cost and operation cost of the grinding equipment and the absorption effect, the particle size D50 after grinding and activation is selected to be no greater than 19 microns.

[0167] Example 4

[0168] On the basis of Example 3, different samples were selected, and the removal efficiency of sulfur dioxide (SO2) was tested according to the experimental device and method in Example 2. The 5# sample obtained in Example 2, i.e., 10% Ca(OH)2 slurry, was selected without further wet grinding activation; the 7# sample, i.e., 10% Ca(OH)2 slurry, was selected to obtain a better particle size, particle size distribution and reaction activity through wet grinding; the 10# sample, i.e., 10% NaOH solution, was selected; and a deacidification enhancer was prepared at the same time. The specific formula is as follows:

[0169]

[0170] Then the prepared deacidification enhancer was mixed with the 7# sample according to the following different mass concentration ratios of 0.5%, 1.5%, and 3%, respectively, and recorded as 11# sample (7# sample + 0.5% deacidification enhancer), 12# sample (7# sample + 1.5% deacidification enhancer), and 13# sample (7# sample + 3% deacidification enhancer). Several groups of samples were tested under the same conditions, and the experimental results are summarized as follows:

[0171]

[0172] As can be seen from the table above, the calcium-magnesium slurry alkali of calcium hydroxide that has been ground, sized and activated can basically replace liquid alkali as the alkali absorption liquid for the wet process. Especially after adding the deacidification enhancer, the removal efficiency of sulfur dioxide (SO2) can be effectively improved. Considering the comprehensive deacidification effect and the addition cost, it is appropriate to choose an addition ratio of 1.5%.

[0173] Example 5

[0174] Prepare sample 14#, that is, select sample 7# obtained in Example 3, that is, 10% Ca(OH)2 slurry, further dilute it 5 times with distilled water, and prepare it into 2% slurry. According to the experimental device in Example 2, first use dilute hydrochloric acid to adjust the pH value of the slurry in the circulation tank of the device to 4.0, and then slowly add the 2% slurry configured by the above sample 7# to control the pH value to rise slowly, and test the removal efficiency of sulfur dioxide (SO2) under different pH conditions. The experimental results are summarized as follows:

[0175]

[0176]

[0177] From the table above, we can see that the deacidification efficiency of the deacidified slurry changes significantly from acidic to alkaline. Under neutral conditions, that is, pH is around 7, the deacidification efficiency is the lowest. This is because a large amount of CaSO3 is generated at this time, resulting in precipitation and scaling.- and H + The concentration of SO2 is also the lowest, and the effect of promoting the dissolution and ionization of SO2 gas in the slurry is also the smallest. When the acidity gradually increases to about pH = 4, the H + The increase in concentration contributes to the HSO3 - The formation of HSO3 - It exists in the form of, under acidic conditions, it helps dissolve CaSO3. Considering the inhibitory effect of pH on CaSO3 and the requirement to reduce the corrosion of the deacidification tower and pipelines in the incineration system, the appropriate pH value is selected to be 5.5-6.5. When the pH of the deacidification slurry is greater than 7, the deacidification efficiency will gradually increase, but at this time there will be obvious scaling problems. Therefore, at this time, the appropriate pH value is selected to be 7-8, and the grinding and activation of the slurry containing seed crystals is selected to inhibit scaling. Even better, 1.5% deacidification enhancer can be added to inhibit scaling.

[0178] Comparative Example 1

[0179] In a 100t / d hazardous waste rotary kiln incineration production line, the flue gas adopts the post-process of "secondary combustion chamber + SNCR + rapid cooling semi-dry deacidification + activated carbon slaked lime dry deacidification + bag + secondary liquid alkali absorption deacidification + wet electrostatic precipitator + chimney high-altitude emission". The original wet secondary deacidification uses 32% ion membrane alkali,

[0180] 1) Pump the purchased 32% liquid alkali into the wet deacidification tower, add tap water, circulate and absorb the incineration flue gas in the deacidification tower, and control the pH value in the deacidification tower to 9.5-7.5 and the liquid-gas ratio to 5.

[0181] 2) When the pH value in the deacidification tower is close to neutral and the inorganic salt content in the deacidification tower rises to 10%, a part of the deacidification high-salt wastewater is discharged to the quenching water tank. In addition, 32% liquid alkali and part of tap water are added to restart the deacidification cycle.

[0182] 3) The high-salt wastewater from the deacidification tower is pumped into the semi-dry quenching tower for atomization deacidification and drying, and finally forms fly ash and bag dust removal ash at the bottom of the quenching tower. The compressed air pressure of the atomization of the quenching tower reaction tower is 0.3-0.6MPa, and the pH value of the fly ash at the bottom of the quenching tower is 4-5.

[0183] Example 6

[0184] On the basis of Comparative Example 1, the calcium hydroxide slurry alkali method of the present invention is now used for deacidification: the wet deacidification process after technical modification is as shown in the attached Figure 6 .

[0185] 1) The purchased slaked lime is evenly sent to the grinding tank through a feeder for wet pulping and grinding. The particle size D50 after grinding is 5 to 15 microns and the slurry concentration is 15%;

[0186] 2) The activated slaked lime slurry is sent to the wet deacidification tower to replace 32% of the liquid caustic soda for absorption. The deacidification slurry is circulated in the deacidification tower to absorb the incineration flue gas through a circulation pump to obtain a second deacidification slurry. The solid content of the second deacidification slurry is controlled to be 10-15%, the pH value is 5.5-6.5, and the liquid-gas ratio is controlled to be less than 10;

[0187] 3) A portion of the second deacidified slurry is pumped into a semi-dry quenching tower for atomization deacidification and drying according to the temperature control requirements of the quenching process, and finally forms fly ash and bag dust removal ash at the bottom of the quenching tower. The compressed air pressure for controlling the atomization of the quenching tower reaction tower is 0.3-0.6MPa, and the pH value of the fly ash at the bottom of the quenching tower is 5-7.

[0188] During the deacidification process, the tap water supplementary water of the deacidification tower is adjusted to keep the liquid level in the deacidification tower stable, without overflow and lack of liquid. At the same time, the solid content of the second deacidification slurry is controlled at 10-15% and the density is 1.15g / cm 3 the following.

[0189] When the liquid alkali wet deacidification method was used, the online monitoring system of the chimney detected that the monthly average value of the flue gas pollutant emission concentration limit was 5-10 mg / Nm 3 , SO2 is 20~30mg / Nm 3 ,HF is 3~5mg / Nm 3 After calcium alkali wet deacidification, the monthly average index is HCl 5-11 mg / Nm 3 , SO2 is 20~35mg / Nm 3 ,HF is 3~5mg / Nm 3 There was no significant fluctuation in the hourly and daily average values, and the emissions in the flue gas met the standards throughout the entire process.

[0190] Example 7

[0191] On the basis of Example 6, the slaked lime powder was replaced with magnesium oxide powder and wet grinding was adopted; the wet deacidification process after technical modification is as shown in the attached Figure 7 .

[0192] 1) The purchased magnesium oxide powder is evenly sent to the pulping stirring tank through a feeder for mixing and aging. After wet grinding, the particle size D50 is 5 to 15 microns, the solid content of the magnesium oxide slurry is less than 10%, and 0.5% of the deacidification synergist is added to obtain an activated deacidification agent.

[0193] 2) A portion of the above activated deacidification agent is used to replace 32% of the liquid caustic soda and is pumped into a wet deacidification tower. The combustion flue gas is circulated and absorbed in the deacidification tower by a circulating pump to obtain a second deacidification slurry. The pH value of the second deacidification slurry in the deacidification tower is controlled to be 5.5-6.5. When the instantaneous index of the flue gas pollutant SO2 exceeds the standard, the pH value of the second deacidification slurry is increased to run between 7.0 and 8.0, and the liquid-gas ratio is controlled to be less than 10.

[0194] 3) The other part of the first activated deacidifying agent is pumped into a semi-dry quenching tower for atomization deacidification and drying, and finally forms fly ash at the bottom of the quenching tower and bag dust removal ash. The compressed air pressure of the atomization of the quenching tower reaction tower is controlled to be 0.3-0.6MPa, and the pH value of the fly ash at the bottom of the quenching tower is 5-7.

[0195] 4) a portion of the second deacidified pulp is pumped into a pulping stirring tank as pulping water, mixed with the newly added deacidifying agent magnesium oxide, and then ground again for activation pulping;

[0196] During the deacidification process, the tap water supplementary water of the deacidification tower is adjusted to keep the liquid level in the deacidification tower stable, without overflow and lack of liquid. At the same time, the solid content of the second deacidification slurry is controlled at 10-15% and the density is 1.15g / cm 3 the following.

[0197] When the liquid alkali wet deacidification method was used, the online monitoring system of the chimney detected that the monthly average value of the flue gas pollutant emission concentration limit was 5-10 mg / Nm 3 , SO2 is 20~30mg / Nm 3 ,HF is 3~5mg / Nm 3 After calcium alkali wet deacidification, the monthly average index is HCl 5-11 mg / Nm 3 , SO2 is 20~30mg / Nm 3 ,HF is 3~5mg / Nm 3 There was no significant fluctuation in the hourly and daily average values, and the emissions in the flue gas met the standards throughout the entire process.

[0198] Example 8

[0199] A hazardous waste incineration deacidification device is designed to match the above-mentioned method of wet deacidification using calcium magnesium slurry alkali in the field of hazardous waste incineration. The device consists of a slurry grinder, a wet deacidification tower pool, a quenching tower and an electrical control system, a slurry delivery pump and a pipeline. The electrical control system adopts a PLC programmable control system, which automatically or manually controls the flow rate or flow velocity of the activated deacidifying agent entering the wet deacidification tower pool according to the pH value of the deacidification slurry in the deacidification tower pool; the electrical control system controls the flow rate or flow velocity of the second deacidification slurry leaving the wet deacidification tower pool according to the liquid level of the second deacidification slurry; the electrical control system controls the atomization flow rate of the activated deacidifying agent entering the quenching tower according to the outlet temperature in the quenching tower. The above-mentioned slurry delivery pumps all adopt variable frequency screw pumps and are interlocked with the PLC programmable control system.

[0200] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. The application of activated deacidification agent for wet deacidification in the field of hazardous waste incineration is characterized by: The activated deacidifying agent is a calcium-magnesium deacidifying agent that is ground and activated so that its median particle size D50 is not greater than 19 microns. The calcium-magnesium deacidifying agent refers to one or more of calcium oxide MgO, calcium hydroxide Ca(OH)2, calcium carbonate CaCO3, magnesium oxide MgO, magnesium hydroxide Ca(OH)2, and magnesium carbonate MgCO3.

2. The use according to claim 1, characterized in that: The activated deacidifying agent is obtained by adding water to make pulp and then wet grinding and activation. When the solid content is 1% by mass, the pH value of the activated deacidifying agent is greater than 8.

0.

3. The use according to claim 1, characterized in that: The steps include: (1) preparing an activated deacidifying agent; (2) adding the activated deacidification agent into a wet deacidification tower for hazardous waste incineration, and continuously performing absorption and deacidification reaction with the incineration flue gas in the deacidification tower to obtain a second deacidification slurry; (3) The second deacidified slurry is sent to a quenching tower. The second deacidified slurry in the quenching tower is atomized and then used to quench and dry the high-temperature incineration flue gas to form incineration fly ash containing calcium chloride or magnesium chloride.

4. The use according to claim 3, characterized in that: In step (2), a portion of the activated deacidification agent is put into the wet deacidification tower for hazardous waste incineration to carry out absorption and deacidification reaction, and the other portion of the activated deacidification agent is directly sent to the quenching tower for quenching and drying to form incineration fly ash containing calcium chloride or magnesium chloride.

5. The use according to claims 3-4, characterized in that: In step (1), a pulping tank is provided to prepare the activated deacidifying agent, and in step (3), a portion of the second deacidifying pulp is recycled to the pulping tank as water for preparing the activated deacidifying agent.

6. The use according to claim 3, characterized in that: The pH value of the second deacidification slurry in the wet deacidification tower in step (2) is controlled to be above 5.5, the mass percentage concentration is controlled to be below 15%, and the density is controlled to be 1.15 g / cm 3 the following.

7. The use according to any one of claims 2 to 6, characterized in that: The liquid-to-gas ratio of the second deacidified slurry to the flue gas in step (2) is not greater than 10 L / NM 3 .

8. The use according to any one of claims 2 to 6, characterized in that: A deacidification synergist is added to the activated deacidification agent or the second deacidification slurry, wherein the components and proportions of the deacidification synergist are as follows:

9. The use according to claim 8, characterized in that: The added amount of the deacidification enhancer is 0.1% to 3% by mass.

10. The use according to any one of claims 2 to 6, characterized in that: Incineration fly ash is washed with water, and the washing water is concentrated to produce calcium chloride or magnesium chloride. The insoluble matter after washing is transferred to a landfill for disposal or sent to a high-temperature kiln for coordinated disposal.

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