A soft-fill high-salt leachate-based flue gas deacidifier and its application

Abstract

The invention discloses a soft filling high-salt leachate-based flue gas deacidification agent and its application, belonging to the field of energy-saving and environmental protection technology. The soft filling high-salt leachate-based flue gas deacidification agent is made of the following raw materials in parts by weight: 50 to 90 parts of leachate concentrated mother liquor, 5 to 15 parts of lime or slaked lime, and 0 to 40 parts of water; wherein the leachate concentrated mother liquor is prepared by the following method: the soft filling high-salt leachate is subjected to preliminary precipitation treatment, and the obtained supernatant is filtered to remove the solid suspended matter therein; after the filtered feed liquid is evaporated and concentrated, the concentrated feed liquid is collected, crystallized, and the crystallized salt is separated, and the leachate concentrated mother liquor is collected. The leachate concentrated mother liquor can improve the solubility and dispersibility of lime or slaked lime in the solution, improve the adsorption performance and deacidification efficiency of the deacidification agent, and save the amount of lime. The invention realizes the reuse, reduction and harmlessness of the soft filling high-salt leachate, treats waste with waste, and saves energy and is environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of energy conservation and environmental protection, and specifically relates to a soft-fill high-salt leachate-based flue gas deacidification agent and application thereof. Background Art

[0002] Flexible hazardous waste landfill is a common hazardous waste disposal facility currently in use. Unlike domestic waste landfills, the wastes treated in flexible hazardous waste landfills are mostly incineration fly ash, solid slag, waste containing heavy metals, etc., which are characterized by containing more salt and a small amount of organic matter. In addition, a large amount of lime, cement, chelating agents and other substances are added during the stabilization process of hazardous waste pre-treatment in the landfill. Due to the moisture contained in the waste itself and environmental factors, leachate will be produced. The leachate contains more salt and toxic and harmful substances. The leachate must be treated to meet the emission standards before it can be discharged.

[0003] The treatment of leachate from flexible landfills is difficult, and there is currently no perfect treatment process in the industry. The commonly used existing technologies include: (1) the leachate is mixed with other wastewater and then subjected to physical, chemical and / or biochemical treatment; (2) the leachate is first subjected to salt separation treatment, and then subjected to physical, chemical and / or biochemical treatment.

[0004] The Chinese patent document with publication number CN109665676A discloses a zero-discharge system process for wastewater from a hazardous waste disposal center. The method is to treat various external wastewater from the hazardous waste disposal center, various plant wastewater and domestic sewage generated by the disposal of hazardous wastes by incineration and physical and chemical treatment in a three-stage treatment process and reuse process in sequence, including quality pretreatment, biochemical treatment, and deep treatment, into reusable clean water and reuse them all. However, the above method may have problems such as low efficiency of the evaporation system, high energy consumption, and easy clogging.

[0005] A Chinese patent document with publication number CN104986906A discloses a method for treating hazardous waste leachate, which first uses a flocculation method after alkali adjustment to remove particulate matter, some organic matter and some heavy metals in the leachate, then removes high-concentration ammonia nitrogen in the leachate through a stripping process under certain conditions, and finally uses alkaline evaporation concentration to reduce the amount of leachate, and the concentrated liquid and flocculated sludge are solidified and then landfilled again. This method is suitable for high-salt, high-ammonia nitrogen leachate, but the amount of concentrated liquid is large, solidification is difficult, the amount of medicine required is large, and the cost is high.

[0006] In the treatment of leachate from flexible landfills, efficient treatment technologies and processes are developed in order to achieve safer and more reasonable treatment and utilization of leachate from flexible landfills and overcome the difficulty in treating leachate from flexible landfills.

[0007] The incineration flue gas generated after waste incineration contains a large amount of acidic gases, including HCl and SO2, and the incineration flue gas needs to be deacidified to meet the emission indicators. The existing flue gas deacidification methods mainly include: dry, semi-dry, and wet deacidification. Different processes have different scopes of application and advantages and disadvantages. Among them, semi-dry deacidification is to spray the deacidifier (slaked lime, limestone, etc.) into the flue gas in the form of slurry. While absorbing and neutralizing, the water in the slurry droplets evaporates completely to obtain a dry product. Semi-dry deacidification can play the role of preliminary deacidification and protection of bag dust removal. When used in conjunction with subsequent bag dust removal, the deacidification efficiency can reach more than 90%.

[0008] The development of deacidifying agents is a research hotspot in the prior art. For example, Chinese patent document with publication number CN117695834A discloses a flue gas deacidification method for a waste incineration power plant based on alkali-making white mud. The invention uses alkali-making white mud and wet deacidification waste liquid to mix and stir into a slurry, sieve to remove large particles, and obtain a deacidifying agent slurry, which can achieve "waste treatment with waste"; Chinese patent document with publication number CN117205735A discloses a deacidifying agent for waste incineration flue gas purification, which includes 30-50% baking soda, 30-50% slaked lime and 5-10% rare earth slag, wherein the rare earth slag is the slag of a weathering crust leaching type rare earth ore after being leached with an ammonium salt leaching solution, thereby achieving the rational utilization of the rare earth slag and the improvement of the acid gas removal rate.

[0009] In order to alleviate environmental pollution problems, realize the resource utilization of waste and the reduction and harmless treatment of waste, it is of great application value to develop a low-cost and efficient semi-dry deacidifier for removing acidic components in flue gas. Summary of the invention

[0010] In order to solve the problem of difficulty in treating leachate from flexible landfills and realize "waste treatment with waste" of leachate from flexible landfills, the present invention provides a flexible landfill high-salt leachate-based flue gas deacidifier, which has high deacidification efficiency and realizes the reuse of leachate from flexible landfills.

[0011] The specific technical solutions adopted are as follows:

[0012] A soft-fill high-salt leachate-based flue gas deacidifier is made from the following raw materials in parts by weight: 50 to 90 parts of leachate concentrated mother liquor, 5 to 15 parts of lime or slaked lime, and 0 to 40 parts of water;

[0013] The concentrated leachate mother liquor is prepared by the following method:

[0014] (1) performing preliminary precipitation treatment on the soft fill high-salinity leachate, filtering the obtained supernatant to remove suspended solids therein; the pH value of the soft fill high-salinity leachate is 7-10, the total dissolved solids TDS concentration is 10-200 g / L (further, 50-200 g / L), the sodium ion concentration is 5-50 g / L, the calcium ion concentration is 5-80 g / L, the sulfate concentration is 0-2 g / L, the chloride ion concentration is 5-100 g / L, the nitrate ion concentration is 0-1 g / L, and the organic matter concentration is 5-30 g / L in terms of chemical oxygen demand (COD);

[0015] (2) After the filtered liquid in step (1) is evaporated and concentrated, the concentrated liquid is collected, and the evaporation and condensation wastewater is treated to meet the standards and then discharged or reused;

[0016] (3) crystallizing the liquid obtained in step (2), separating the crystallized salt, collecting the concentrated mother liquor of the leachate, and transporting the separated crystallized salt for comprehensive utilization or disposing of it by rigid landfill.

[0017] The present invention performs precipitation-evaporation concentration-crystallization treatment on the soft filling high-salt leachate to obtain a leachate concentrated mother liquor, which includes calcium ions, organic components including chelating agents, salt inhibitors, surfactants, etc. dissolved by the leachate of hazardous waste, and the mother liquor is compounded with lime or slaked lime and water to prepare a flue gas deacidifier. On the one hand, the leachate concentrated mother liquor can improve the solubility and dispersibility of lime or slaked lime in the solution, improve the adsorption performance and deacidification efficiency of the deacidifier, and save the amount of lime. On the other hand, the disposal and reuse of the soft filling high-salt leachate is realized, and the production cost of the deacidifier is reduced.

[0018] Preferably, the solid suspended matter concentration of the slurry after filtering in step (1) is less than 10 mg / L. A low concentration of solid suspended matter can reduce the blockage of the evaporation equipment and improve the evaporation efficiency.

[0019] Specifically, in step (1), the preliminary precipitation treatment method is static precipitation or flocculation precipitation with drug addition, depending on the condition of the high-salt leachate of the soft fill.

[0020] Preferably, in step (2), a single-effect or multi-effect steam evaporator is used for evaporation concentration, the evaporation temperature is 50 to 90° C., and the vacuum degree is -50 kPa to -90 kPa.

[0021] Preferably, in step (3), the temperature is lowered to 45-70° C. to allow the liquid obtained in step (2) to crystallize, retaining the calcium salt. The main component of the separated crystalline salt is sodium chloride, which is beneficial to the subsequent comprehensive utilization of the crystalline salt. The salt content of the concentrated leachate mother liquor is 20-40wt%, the calcium ion concentration in the concentrated leachate mother liquor is 50-150g / L, and the organic matter content is 50-200g / L in terms of COD.

[0022] Specifically, in step (3), the method for separating the crystalline salt is centrifugal separation, filtration separation, or gravity sedimentation separation.

[0023] Preferably, the particle size of the lime or slaked lime is maintained at a screening rate of >90% through a 200-mesh standard sieve.

[0024] The present invention also provides a method for preparing the soft-fill high-salt leachate-based flue gas deacidifier, comprising: taking the leachate concentrated mother liquor, lime or slaked lime, and water in selected weight portions, mixing them, stirring at 10 to 40° C. for 20 to 40 minutes, and obtaining a uniformly dispersed suspension, which is the soft-fill high-salt leachate-based flue gas deacidifier.

[0025] The present invention also provides an incineration flue gas purification method, which utilizes the soft-fill high-salt leachate-based flue gas deacidification agent.

[0026] The semi-dry deacidification reaction involves three phases: gas, solid and liquid. It is a comprehensive process including mass transfer, heat transfer and chemical reaction. In water, lime or slaked lime cannot be completely dissolved, and the undissolved ions react slowly, which will cause the loss of alkali once discharged. The use of the soft-fill high-salt leachate-based flue gas deacidification agent of the present invention can increase the content of effective ingredients in the liquid phase, improve the adsorption performance of the deacidification agent and the deacidification efficiency.

[0027] The incineration flue gas includes but is not limited to garbage incineration flue gas, hazardous waste incineration flue gas, medical waste incineration flue gas, etc.

[0028] The incineration flue gas purification method specifically comprises the following steps:

[0029] The incineration flue gas is passed into a semi-dry deacidification tower, and the rotary sprayer is started to atomize the soft fill high-salt leachate-based flue gas deacidification agent, and the incineration flue gas is deacidified to remove acidic gases including SO2 and HCl. The deacidified flue gas is separated by bag dust removal, and the solid matter (calcium sulfate, calcium sulfite, calcium chloride, other smoke, etc.) formed by the deacidification treatment and unreacted raw materials are regularly discharged and transported to the stabilization landfill workshop for landfill disposal.

[0030] Preferably, the incineration flue gas flow rate is 4.0×10 4 ~4.5×10 4 m 3 / h, the temperature during deacidification treatment is 150-200℃.

[0031] Compared with the prior art, the present invention has the following beneficial effects:

[0032] (1) Traditional flue gas semi-dry deacidifiers generally use lime slurry (lime or slaked lime dissolved in water) as a deacidifier. The present invention improves the composition of the flue gas deacidifier, and uses a leachate concentrated mother liquor obtained by precipitation-evaporation concentration-crystallization treatment of a soft-fill high-salt leachate, lime or slaked lime, and water to prepare a soft-fill high-salt leachate-based flue gas deacidifier. The leachate concentrated mother liquor can improve the solubility and dispersibility of lime or slaked lime in the solution, accelerate the reaction with acidic gases such as sulfur dioxide and hydrofluoric acid, improve the adsorption performance and deacidification efficiency of the deacidifier, and save the amount of lime.

[0033] (2) The treatment of high-salt leachate from the soft fill is difficult. The present invention first performs a precipitation-evaporation concentration-crystallization treatment on the leachate to reduce the salt content and the boiling point of the liquid. Furthermore, the obtained leachate concentrated mother liquor is used to prepare a flue gas semi-dry deacidification agent, thereby realizing the reuse, reduction and harmlessness of the high-salt leachate from the soft fill, treating waste with waste, and saving energy and protecting the environment.

[0034] (3) The composition of waste landfilled in hazardous waste landfills is very complex, containing high salt, various organic matter, fly ash salt inhibitors, anti-caking agents, etc. When the leachate from a flexible landfill is treated by evaporation, the salt content therein is difficult to crystallize, resulting in a large amount of mother liquor. In order to reduce the amount, a cyclic continuous evaporation method is conventionally used for treatment, which consumes extremely high energy. The present invention collects the evaporated mother liquor from the evaporation system, which can reduce the circulation amount of the evaporated material. Compared with conventional methods, the salt content of the material in the evaporator is reduced, which is beneficial to maintaining the evaporation efficiency of the system and can significantly reduce energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 The present invention is a preparation flow chart of the soft-fill high-salt leachate-based flue gas deacidification agent.

[0036] Figure 2 The process flow chart of Examples 1-3. DETAILED DESCRIPTION

[0037] The present invention is further illustrated below in conjunction with the examples and accompanying drawings. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturer.

[0038] Example 1

[0039] This embodiment treats high-salinity leachate from a certain hazardous waste flexible landfill. The wastes treated in the hazardous waste flexible landfill include chemical hazardous waste, pharmaceutical hazardous waste, incineration slag, fly ash, stabilized hazardous waste, etc. The corresponding indicators of the high-salinity leachate are: pH value 8.3, chemical oxygen demand COD concentration 10.3g / L, sodium ion concentration 16g / L, calcium ion concentration 7.2g / L, sulfate concentration 0.22g / L, chloride ion concentration 39.5g / L, total dissolved solids TDS concentration 78.5g / L, suspended matter concentration 0.65g / L;

[0040] like Figure 1 and Figure 2 As shown, the method for preparing the soft-fill high-salt leachate-based flue gas deacidification agent comprises the following steps:

[0041] (1) The high-salt leachate from the soft fill is discharged into the regulating tank through the collection system to uniform the water quality, and the regulating tank does not change the material composition and concentration;

[0042] (2) The soft fill high-salinity leachate discharged from the regulating tank is pumped into the sedimentation tank by a lifting pump, and initially allowed to settle by gravity to remove some of the larger suspended particles. The supernatant is filtered through a filter to further remove the suspended solids, so that the effluent suspended solids concentration SS is less than 10 mg / L;

[0043] (3) The filtered feed liquid is pumped into a triple-effect evaporator system for evaporation and concentration, the evaporation temperature is 50-90°C, the vacuum degree is -50kPa--90kPa, the steam tail gas generated by evaporation is condensed by a condenser and transferred to a collection tank for collection, further transferred to a hydrolysis tank for hydrolysis, and then transferred to an AO tank for biochemical anaerobic aerobic process treatment, and finally passed through a secondary sedimentation tank, a final sedimentation tank, and a sand filter tank, and then processed by an ultrafiltration (UF) and reverse osmosis (RO) system process, so that the effluent index is pH 7.5, COD 20mg / L, TDS 100mg / L, and total hardness 10mg / L, meeting the cooling water quality requirements of "Water Quality for Industrial Water Use in Urban Wastewater Recycling" (GB / T19923-2005), and used as circulating cooling water. The concentrated water generated by the RO system is returned to the regulating tank;

[0044] (4) the concentrated evaporation liquid is cooled and crystallized in a thickening kettle, and after cooling to 45-50° C., the crystallized salt is separated by a centrifuge, and the concentrated mother liquor of the leachate obtained after centrifugation is collected, and the concentrated mother liquor of the leachate is transferred to a mother liquor collection tank, and the processing capacity of the evaporation system and the reflux circulation capacity of the mother liquor are controlled to obtain a mother liquor concentration of 20 wt %, a calcium ion concentration of 60 g / L, and an organic matter content of 80 g / L in terms of COD;

[0045] (5) Pump the concentrated mother liquor of the leachate into a pulping tank, add slaked lime into the pulping tank, in parts by weight, the concentrated mother liquor of the leachate is 85 parts, the slaked lime is 15 parts, the particle size of the slaked lime is maintained at a screening rate of >90% on a 200-mesh standard sieve, stir continuously during the addition of slaked lime, react at 35° C. for 30 minutes, and the resulting uniformly dispersed suspension is the soft-fill high-salt leachate-based flue gas deacidifier.

[0046] Furthermore, the soft fill high-salt leachate-based flue gas deacidifier is used to treat the flue gas from a hazardous waste incineration plant. The hazardous waste incineration flue gas is passed into a semi-dry deacidification tower with an inlet temperature of (~190°C). The rotary sprayer is started to atomize the soft fill high-salt leachate-based flue gas deacidifier to deacidify the incineration flue gas. The outlet temperature of the deacidification tower is 150°C to remove acidic gases such as SO2, SO3, HCl, and HF in the incineration flue gas. The rotation speed of the rotary sprayer and the amount of the soft fill high-salt leachate-based flue gas deacidifier are controlled so that the high-temperature flue gas completely dries the deacidifier. The deacidified flue gas is separated by bag dust removal. The solid matter (calcium sulfate, calcium sulfite, calcium chloride, other smoke, etc.) formed by the deacidification treatment and the unreacted raw materials are regularly discharged and transported to a stabilized landfill workshop for landfill disposal.

[0047] Example 2

[0048] The process parameters for preparing the soft-fill high-salt leachate-based flue gas deacidification agent in this embodiment are the same as those in Embodiment 1, with the only difference being that in step (4), the evaporation-concentrated liquid is cooled and crystallized in a thickening kettle, and after cooling to 50-60°C, the crystallized salt is separated by a centrifuge; at the same time, the processing capacity of the evaporation system and the reflux circulation capacity of the mother liquor are controlled to obtain a mother liquor concentration with a salt content of 40 wt%, a calcium ion concentration of 100 g / L in the leachate concentrated mother liquor, and an organic matter content of 100 g / L in terms of COD.

[0049] The method for treating hazardous waste incineration flue gas using the soft fill high-salt leachate-based flue gas deacidification agent prepared in this example is the same as that in Example 1.

[0050] Example 3

[0051] The process parameters for preparing the soft-fill high-salt leachate-based flue gas deacidification agent in this embodiment are the same as those in Example 1, with the only difference being that in step (4), the processing capacity of the evaporation system and the reflux circulation capacity of the mother liquor are controlled to obtain a mother liquor concentration with a salt content of 30%, a calcium ion concentration of 80 g / L in the leachate concentrated mother liquor, and an organic matter content of 90 g / L in terms of COD.

[0052] The method for treating hazardous waste incineration flue gas using the soft fill high-salt leachate-based flue gas deacidification agent prepared in this example is the same as that in Example 1.

[0053] Comparative Example 1

[0054] In this comparative example, water and slaked lime are used to prepare a deacidifying agent. In parts by weight, water is 85 parts and slaked lime is 15 parts. The particle size of the slaked lime is maintained at a 200-mesh standard sieve screening rate of >90%. Stirring is continued during the addition of slaked lime. The reaction is stirred at 35°C for 30 minutes. The uniformly dispersed suspension obtained is the deacidifying agent.

[0055] The method for treating hazardous waste incineration flue gas using the deacidifying agent prepared in this comparative example is the same as that in Example 1.

[0056] Sample analysis

[0057] (1) Analysis of deacidification ability of deacidifier

[0058] The deacidification agents prepared in Examples 1, 2, 3 and Comparative Example 1 were filtered through precision filter paper, 500 ml of the filtrate was taken, and titrated with 0.1 mol / L HCl standard solution. The pH of the titration endpoint was 5.5. The consumption of HCl solution was recorded. The results are shown in Table 1:

[0059] Table 1 Statistical results of HCl standard solution consumption

[0060]

[0061] (2) Semi-dry flue gas deacidification effect

[0062] In Examples 1 and 2 and Comparative Example 1, the incineration flue gas is from the same batch. After semi-dry deacidification, the flue gas inlet and outlet flow rates are the same, and the exhaust flue gas monitoring data are shown in Table 2;

[0063] Table 2 Statistics of flue gas monitoring data after deacidification

[0064]

[0065] From the results of Table 1 and Table 2, it can be seen that compounding the concentrated mother liquor of leachate with lime or slaked lime can increase the solubility of lime or slaked lime. After the slaked lime is dissolved, it may react with certain components in the concentrated mother liquor of leachate to form a complex, thereby increasing the deacidification rate.

[0066] The embodiments described above provide a detailed description of the technical solutions of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, supplements or similar substitutions made within the scope of the principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A soft-fill high-salt leachate-based flue gas deacidifier, characterized in that: The method is prepared from the following raw materials in parts by weight: 50-90 parts of concentrated leachate, 5-15 parts of lime or slaked lime, and 0-40 parts of water; the particle size of the lime or slaked lime is maintained at a 200-mesh standard sieve screening rate of >90%; The concentrated leachate mother liquor is prepared by the following method: (1) performing preliminary precipitation treatment on the soft fill high-salinity leachate, filtering the obtained supernatant to remove suspended solids; the pH value of the soft fill high-salinity leachate is 7-10, the total dissolved solids TDS concentration is 10-200 g / L, the sodium ion concentration is 5-50 g / L, the calcium ion concentration is 5-80 g / L, the sulfate concentration is 0-2 g / L, the chloride ion concentration is 5-100 g / L, the nitrate ion concentration is 0-1 g / L, and the organic matter concentration is 5-30 g / L in terms of chemical oxygen demand (COD); (2) evaporating and concentrating the filtered liquid in step (1), and collecting the concentrated liquid; (3) cooling the solution obtained in step (2) to 45-70° C. to crystallize the solution, separating the crystallized salt, and collecting the concentrated leachate mother liquor; the concentrated leachate mother liquor has a salt content of 20-40 wt %, a calcium ion concentration of 50-150 g / L, and an organic matter content of 50-200 g / L in terms of COD.

2. The flexible filling high-salt leachate-based flue gas deacidification agent according to claim 1, characterized in that: The solid suspended matter concentration of the filtered feed solution in step (1) is less than 10 mg / L.

3. The soft-fill high-salt leachate-based flue gas deacidification agent according to claim 1, characterized in that: In step (2), a single-effect or multi-effect steam evaporator is used for evaporation concentration, the evaporation temperature is 50 to 90° C., and the vacuum degree is -50 kPa to -90 kPa.

4. The method for preparing the soft-fill high-salt leachate-based flue gas deacidification agent according to any one of claims 1 to 3, characterized in that: include: The concentrated mother liquor of leachate, lime or slaked lime and water are mixed according to the selected weight parts, and stirred at 10-40° C. for 20-40 minutes to obtain a uniformly dispersed suspension, which is the soft-fill high-salt leachate-based flue gas deacidifier.

5. A method for purifying incineration flue gas, characterized in that: Utilize the soft-fill high-salt leachate-based flue gas deacidification agent described in any one of claims 1-3.

6. The incineration flue gas purification method according to claim 5, characterized in that: The incineration flue gas is garbage incineration flue gas.

7. The incineration flue gas purification method according to claim 5, characterized in that: The incineration flue gas is hazardous waste incineration flue gas.

8. The incineration flue gas purification method according to claim 5, characterized in that: The incineration flue gas is medical waste incineration flue gas.

9. The incineration flue gas purification method according to claim 5, characterized in that: include: The incineration flue gas is passed into a semi-dry deacidification tower, and the rotary sprayer is started to atomize the soft-fill high-salt leachate-based flue gas deacidification agent, and the incineration flue gas is deacidified to remove acidic gases including SO2 and HCl. The deacidified flue gas is separated by bag dust removal.

10. The incineration flue gas purification method according to claim 9, characterized in that: The incineration flue gas flow rate is 4.0×10 4 ~4.5×10 4 m 3 / h, the temperature during deacidification treatment is 150-200℃.

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