Method and system for efficiently removing refractory organic matters in near-zero-emission evaporative crystallization mixed salt

Abstract

The invention discloses a method for efficiently removing refractory organic matters in near-zero-emission evaporative crystallization mixed salts, which comprises the following steps of: taking a plurality of types of mixed salts, setting an expected target value of a TOC (total organic carbon) removal rate for each type of mixed salts under the conditions of pyrolysis temperature, pyrolysis duration and temperature rise amplitude, and carrying out response surface optimization design to obtain a target value of the TOC removal rate; the suitable pyrolysis condition range of the mixed salt is obtained; and taking an intersection of suitable pyrolysis condition ranges of various mixed salts as an optimal pyrolysis condition, and removing the refractory organic matters in the various mixed salts at one time. The invention also provides a system for realizing the method. The system comprises a pretreatment unit, a pyrolysis main body unit, a carrier gas supply unit, a tail gas collection and treatment unit, a heat energy recovery unit and a waste salt recovery unit, according to the method, refractory organics in the mixed salt can be reduced to the maximum extent, and the removal rate of the organics is close to 100%. The heat treatment process is simple, operation is easy and controllable, and near-zero-emission dangerous solid waste can be converted into available and valuable resources.

Description

Technical Field

[0001] The present invention belongs to the technical field of sewage treatment, relates to the near-zero discharge of sewage and wastewater, and in particular to a method and system for efficiently removing refractory organic matter in near-zero discharge evaporative crystallization mixed salt. Background Art

[0002] Zero liquid discharge means that after industrial water is reused, the salt and pollutants contained in it are highly concentrated and recycled, and no waste liquid is discharged from the factory. Zero liquid discharge can minimize the amount of waste liquid discharged, improve water resource recovery efficiency, the purity of the end product, and the long-term operation stability of the system, which is of great significance to the current situation of freshwater resource shortage and urgent water resource reuse.

[0003] The industrial processes of fine chemicals, petroleum refining, leather and food processing industries inevitably discharge a large amount of saline wastewater with an inorganic salt content of between 3.5% and 20%, and contain a large amount of organic matter that is difficult to degrade by conventional sewage treatment processes such as biological treatment. Direct discharge of such saline wastewater without treatment will cause serious environmental and ecological problems. Currently, the widely used industrial wastewater treatment technologies mainly include reverse osmosis membrane (RO) and electrodialysis reversal (EDR) technology, but the system recovery rate of pure water of RO technology is low, and the treatment of the remaining wastewater containing high concentrations of harmful substances is still a problem, and there is a serious membrane pollution problem, which leads to high treatment costs. Evaporation crystallization technology is a commonly used separation technology that generates mixed solid salts by evaporating high-salt wastewater. At present, most typical high-salt wastewater treatment projects use evaporation crystallization technology, which produces a large amount of industrial mixed salts. The industrial mixed salts themselves contain high concentrations of salt, and the excessive osmotic pressure makes it difficult for organisms to grow. It also contains difficult-to-degrade organic matter such as benzene ring compounds and hydrocarbons. The most common method of treating industrial waste salt is landfilling. However, hazardous waste buried underground not only damages the land, but also may produce flammable, explosive or toxic gases through decomposition, which poses a series of risks. In addition, the high cost of treatment and the difficulty of resource recovery are also the main challenges faced by mixed salt treatment.

[0004] The pyrolysis treatment technology of solid waste is to cause the organic matter in the solid waste to undergo thermal cracking reaction in the absence of oxygen or in the absence of oxygen, so that the macromolecular organic matter is cracked into small molecular liquid and gas, and solid waste residue is produced. The pyrolysis treatment technology is applied to the treatment and recovery of industrial mixed salts, which can well solve the problems of insufficient purity of mixed salts, difficulty in recovery, and difficulty in handling a large number of refractory toxic organic matter. However, the pyrolysis reaction is usually affected by many factors, mainly including pyrolysis temperature, pyrolysis temperature rise, pyrolysis duration, humidity and particle size. Among them, the most critical factor affecting the pyrolysis process is the pyrolysis temperature. The high or low pyrolysis temperature greatly affects the properties and yield of the pyrolysis products; the optimal pyrolysis conditions of different industrial mixed salts also vary depending on the different components they contain. In actual industrial production, it is difficult to use a single fixed pyrolysis condition to achieve the best pyrolysis of all mixed salts. In view of the current problem of high organic matter in the mixed salts at the end of near-zero discharge of wastewater, an efficient treatment method is needed to achieve the resource recycling of zero-discharge end products. Summary of the invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art and solve the problems faced by near-zero discharge of wastewater, the purpose of the present invention is to provide a method and system for efficiently removing refractory organic matter in near-zero discharge evaporation and crystallization mixed salt, combining evaporation and crystallization to achieve zero discharge of wastewater and the advantages of pyrolysis treatment technology for mixed salt treatment, and using pyrolysis treatment technology to treat mixed salts obtained by evaporation and crystallization of various real industrial wastewaters. The pyrolysis conditions are analyzed, optimized, summarized and verified, which can achieve high removal of refractory organic matter in industrial mixed salts and recovery of pure salt, and has the characteristics of being economical, easy to operate, simple and controllable.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A method for efficiently removing refractory organic matter in near-zero emission evaporative crystallization mixed salt comprises the following steps:

[0008] Step 1, taking several kinds of mixed salts, for each kind of mixed salt, taking pyrolysis temperature, pyrolysis duration and temperature rise as conditions, setting the expected target value of TOC removal rate, performing response surface optimization design, and obtaining the suitable pyrolysis condition range of the mixed salt; the mixed salt refers to a salt in which hydrogen atoms in two or more acid molecules are replaced by the same metal atom or a salt composed of a metal cation and two acid anions;

[0009] Step 2, taking the intersection of the suitable pyrolysis condition ranges of various types of mixed salts as the optimal pyrolysis condition;

[0010] Step 3, according to the optimal pyrolysis conditions, the refractory organic matter in various mixed salts is removed at one time, wherein the refractory organic matter is a long-chain hydrocarbon or aliphatic compound.

[0011] In one embodiment, the suitable pyrolysis condition range refers to a TOC removal rate of a type of mixed salt of not less than 80%.

[0012] In one embodiment, in step 1, three kinds of mixed salts are taken, namely, the aged mother liquor mixed salt from vacuum conversion of coal chemical zero emission project, the four-effect evaporation mixed salt, and the single-effect evaporation mixed salt, and the suitable pyrolysis condition ranges of each are obtained by the following formula:

[0013] DH1=96.88-0.0813A1-0.8312B1-1.25C1-2.6A1B1-1.96A1C1-2.38B1C1-1.19A1 2 +0.0588B1 2 -1.21C1 2 ;

[0014] DH2=74.61-1.11A2+2.45B2+1.43C2+2.81A2B2+2.64A2C2-4.97B2C2+3.48A2 2 +3.39B2 2 +2.43C2 2 ;

[0015] DH3=70.05+8.10A3-1.95B3-2.04C3-8.65A3B3+6.05A3C3+13.59B3C3-4.41A3 2 +4.8B3 2 -12.67C3 2 -23.46A3B3 2 ;

[0016] Among them, DH1, DH2 and DH3 represent the TOC removal rates of the three industrial waste salts, A1, A2 and A3 represent the pyrolysis temperatures of the three industrial waste salts, B1, B2 and B3 represent the pyrolysis durations of the three industrial waste salts, and C1, C2 and C3 represent the pyrolysis temperature rises of the three industrial waste salts.

[0017] The values ​​of DH1, DH2 and DH3 were set within the appropriate range of pyrolysis conditions, and the optimal pyrolysis conditions were obtained through response surface optimization.

[0018] In one embodiment, the optimal pyrolysis conditions are:

[0019] The temperature rise range is 10-15℃ / min, the pyrolysis temperature is 500-550℃, and the pyrolysis maintenance time is 50-80min.

[0020] The present invention also provides a system for realizing the highly efficient removal method of refractory organic matter in the near-zero emission evaporative crystallization mixed salt, comprising a pretreatment unit, a pyrolysis main unit, a carrier gas supply unit, an exhaust gas collection and treatment unit, a heat energy recovery unit and a waste salt recovery unit;

[0021] The pretreatment unit performs drying and crushing pretreatment on the mixed salt to be treated;

[0022] The pyrolysis main unit is connected to the pretreatment unit, and operates under the pyrolysis conditions of the mixed salt to perform pyrolysis treatment on the evaporated crystallized mixed salt;

[0023] The carrier gas supply unit is connected to the pyrolysis main unit to deliver nitrogen or air thereto;

[0024] The tail gas collection and processing unit is connected to the pyrolysis main unit, and performs closed collection and processing on the generated pyrolysis gas and discharges it after it reaches the standard;

[0025] The heat energy recovery unit is connected to the pyrolysis main unit to recover and utilize the heat energy contained in the tail gas after pyrolysis;

[0026] The waste salt recovery unit is connected to the pyrolysis main unit to realize resource recycling and reuse after secondary purification of the mixed salt after pyrolysis treatment.

[0027] In one embodiment, the drying and crushing pretreatment of the pretreatment unit is implemented as follows:

[0028] For wet and agglomerated mixed salt, the heat of the high-temperature tail gas after pyrolysis is transmitted by the heat recovery unit to remove the residual moisture in the mixed salt, and then it is mechanically crushed to increase the contact area;

[0029] The mixed salt from the evaporation crystallization unit is directly transported to the pyrolysis main unit.

[0030] In one embodiment, the pyrolysis main unit adopts a closed quartz tube furnace, a rotary quartz tube furnace or an intermittent atmosphere rotary electric furnace, which can continuously input the mixed salt to be treated and continuously output the mixed salt after pyrolysis.

[0031] In one embodiment, the flow rate of the air or nitrogen output by the carrier gas supply unit is 60-200 sccm and is stably regulated by a flow meter.

[0032] In one embodiment, the exhaust gas collection and treatment unit treats and absorbs harmful gases in the exhaust gas and discharges them after the treatment meets the standards. The harmful gases include CO, VOC, formaldehyde and SO2.

[0033] In one embodiment, the heat recovery unit preheats the un-decomposed mixed salt by heat exchange to reduce the consumption of preheating energy.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. It can reduce the hard-to-degrade organic matter in mixed salt to the maximum extent and achieve an organic matter removal rate close to 100%.

[0036] 2. The heat treatment process is simple, easy to operate and controllable, and can transform near-zero emission hazardous solid waste into usable valuable resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the process of the present invention.

[0038] Figure 2 It is the removal rate of organic matter under different pyrolysis conditions corresponding to Example 2 of the present invention.

[0039] Figure 3 It is the removal rate of organic matter under different pyrolysis conditions corresponding to Example 3 of the present invention. DETAILED DESCRIPTION

[0040] The embodiments of the present invention are described in detail below with reference to the accompanying drawings and examples.

[0041] The mixed salt of the present invention refers to a salt formed by replacing the hydrogen atoms in two or more acid molecules with the same metal atom or a salt composed of a metal cation and two acid anions; typical examples are: calcium nitrate chloride [Ca(NO3)2Cl], calcium hypochlorite chloride CaOCl2, etc.

[0042] The organic components in the mixed salt of the present invention mainly refer to long-chain hydrocarbons or fatty compounds and other difficult-to-degrade organic substances, which are usually difficult to effectively degrade by biological and chemical methods.

[0043] The method for efficiently removing refractory organic matter in the near-zero emission evaporation crystallization mixed salt of the present invention comprises the following steps:

[0044] Step 1: Take several types of common mixed salts. For each type of mixed salt, set the expected target value of TOC removal rate based on pyrolysis temperature, pyrolysis duration and temperature rise amplitude, perform response surface optimization design, and obtain the appropriate pyrolysis condition range for this type of mixed salt.

[0045] The traditional response surface method optimizes a class of objects and gives a set of solutions, that is, a set of solutions that are predicted to achieve the best pyrolysis effect. In this set of solutions, each condition is a fixed value. The present invention sets an expected target value (TOC removal rate), for example, a TOC removal rate of 80% or 90% or more, and then the value is expanded into a range, that is, the range of suitable pyrolysis conditions for this type of mixed salt.

[0046] Step 2, taking the intersection of the suitable pyrolysis condition ranges of various types of mixed salts as the optimal pyrolysis condition.

[0047] In this step, the intersection of the ranges of suitable pyrolysis conditions for various types of mixed salts obtained in step 1 is taken, and the obtained range is the optimal pyrolysis condition. It is worth noting that for a certain type of mixed salt, the optimal pyrolysis condition is not the condition that can achieve the maximum TOC removal rate, but only means that its TOC removal rate can meet the set expected target value. The contribution of the present invention is that through the optimal pyrolysis condition, it can be generalized to various common mixed salts. In subsequent applications, there is no need to conduct separate experiments for a certain type of mixed salt, and several types of mixed salts can also be mixed together and treated to remove TOC at the same time.

[0048] Step 3: According to the optimal pyrolysis conditions, the refractory organic matter in various mixed salts is removed at one time.

[0049] The following are several specific embodiments of the present invention.

[0050] Example 1

[0051] like Figure 1 As shown, this embodiment provides a method for efficiently removing refractory organic matter in near-zero emission evaporation crystallization mixed salt, and the main steps include:

[0052] The mixed salt at the outlet of the evaporation crystallization unit or other sources is pretreated by a drying pretreatment unit and a mechanical crushing pretreatment unit; the pyrolysis main unit is connected to the pretreatment unit through a transportation device, and the waste salt is pyrolyzed after the pyrolysis temperature rise amplitude, pyrolysis temperature and temperature maintenance time of the pyrolysis main unit are set; the carrier gas supply unit transports nitrogen or air to the pyrolysis main unit at a low flow rate; the tail gas collection and treatment unit collects and treats the pyrolysis gas in a closed manner and discharges it after meeting the standards; the heat energy recovery unit recycles the heat energy contained in the tail gas after pyrolysis; the waste salt recovery unit purifies the high-purity mixed salt after pyrolysis treatment for secondary resource recycling.

[0053] In the present invention, the selection and setting of the drying pretreatment unit and the mechanical crushing pretreatment unit for the mixed salt pyrolysis are based on the following: for wet and agglomerated mixed salt, the heat of the high-temperature exhaust gas after pyrolysis is transmitted by the heat energy recovery unit to remove the residual moisture in the mixed salt, and then it passes through the mechanical crushing pretreatment unit to crush it to increase the contact area; for the mixed salt at the outlet of the evaporation crystallization unit, it can be directly transported to the subsequent pyrolysis main unit.

[0054] In the present invention, the pyrolysis main unit can be a device with pyrolysis function such as a closed quartz tube furnace, a rotary quartz tube furnace or an intermittent atmosphere rotary electric furnace; among them, a rotary quartz tube furnace and an intermittent atmosphere rotary electric furnace are preferred.

[0055] In the present invention, the pyrolysis main unit can set the temperature rise amplitude, the maximum pyrolysis temperature and the temperature maintenance time, and can continuously input the mixed salt to be treated and continuously output the mixed salt after pyrolysis; wherein, the temperature rise amplitude is preferably 10-15°C / min, the pyrolysis temperature is preferably 500-550°C, and the pyrolysis maintenance time is preferably 50-80min.

[0056] In the present invention, the carrier gas supply unit can output air or nitrogen at a low flow rate, the corresponding gas flow rate is 60-200 sccm, and is stably regulated by a flow meter; among them, nitrogen is preferably used as the carrier gas.

[0057] In the present invention, the exhaust gas collection and treatment unit treats and absorbs harmful gases in the exhaust gas and discharges them after the treatment meets the standards. The exhaust gas treatment device mainly treats harmful gases such as CO, VOC, formaldehyde, SO2, etc.

[0058] In the present invention, the waste salt recovery unit and the pyrolysis removal method can achieve effective removal of more than 95% of organic matter. The waste salt recovery unit can re-purify the high-purity mixed salt obtained after the pyrolysis treatment and then realize resource recycling.

[0059] In the present invention, the heat recovery unit mainly refers to the tail gas after pyrolysis still containing a large amount of waste heat, which can preheat the unpyrolyzed mixed salt through heat energy exchange to further reduce the consumption of preheating energy.

[0060] Embodiment 2:

[0061] According to the optimal pyrolysis condition range, three groups of pyrolysis condition combinations were selected to carry out pyrolysis treatment on the actual industrial wastewater zero-discharge terminal mixed salt. The inorganic components of the mixed salt are: 72%-73% sodium sulfate, 23%-24% sodium chloride, 0.1%-0.3% silicate, 0.4%-0.6% sodium carbonate, 0.02%-0.04% sodium bicarbonate, 0.01%-0.03% nitrate, 25%-3.5% water, and the organic components are: 0.5-0.6 mg / kg N,N-dimethylformamide, 6.0-7.0 mg / kg long-chain alkanes, 0.01-0.02 mg / kg 1,2-diphenoxyethane, and 1.0-2.0 mg / kg alkylbenzene.

[0062] Condition 1 is: pyrolysis temperature 500°C, pyrolysis duration 75.81 min, temperature rise 9.74°C / min, and TOC removal rate under this pyrolysis condition is 99.75%.

[0063] Condition 2 is: pyrolysis temperature 578°C, pyrolysis duration 34.19 min, temperature rise 14.72°C / min, and TOC removal rate under this pyrolysis condition is 99.93%.

[0064] Condition 3 is: pyrolysis temperature 540°C, pyrolysis duration 75 min, temperature rise 10.5°C / min, and the TOC removal rate under this pyrolysis condition is 99.5%.

[0065] Condition 4 is as follows: pyrolysis temperature 649°C, pyrolysis duration 58.3 min, temperature rise 6.04°C / min, and TOC removal efficiency under this pyrolysis condition is 98.92%.

[0066] like Figure 2 As shown, the method of the present invention can achieve efficient removal of refractory organic matter in near-zero emission evaporation and crystallization mixed salt, and the corresponding organic matter removal rate is above 98.5%.

[0067] It can be seen that in this embodiment, although the removal rate corresponding to the optimal pyrolysis conditions is the highest, it is not much different from the result of condition 2. This may be because the pyrolysis conditions of condition 2 are relatively close to the optimized pyrolysis conditions of the mixed salt but do not enter the intersection range.

[0068] Embodiment 3:

[0069] According to the optimal pyrolysis condition range, three groups of pyrolysis condition combinations were selected to carry out pyrolysis treatment on the zero-discharge terminal mixed salt of a certain actual coal chemical wastewater, such as Figure 3 As shown:

[0070] Condition 1 is: pyrolysis temperature 500°C, pyrolysis duration 75.81 min, temperature rise 9.74°C / min, and the TOC removal rate under this pyrolysis condition is 92.51%.

[0071] Condition 2 is: pyrolysis temperature 578°C, pyrolysis duration 34.19 min, temperature rise 14.72°C / min, and the TOC removal rate under this pyrolysis condition is 97.55%.

[0072] Condition 3 is as follows: pyrolysis temperature of 540°C, pyrolysis duration of 75 min, and temperature rise of 10.5°C / min. The TOC removal rate under this pyrolysis condition is 96.46%.

[0073] Condition 4 is as follows: pyrolysis temperature 649°C, pyrolysis duration 58.3 min, temperature rise 6.04°C / min, and the TOC removal rate under this pyrolysis condition is 94.85%.

[0074] Similarly, in this embodiment, although the removal rate corresponding to the optimal pyrolysis conditions is the highest, it is not much different from the result of condition 3. This may be because the pyrolysis conditions of condition 3 are close to the optimized pyrolysis conditions of the mixed salt but do not enter the intersection range.

[0075] In general, each salt will have an optimal value after optimization. In order to make the results universal, the present invention expands this value to a range. Therefore, using one condition to pyrolyze multiple different salts may not achieve an organic matter removal rate of 99.9% for each mixed salt, but it can reach more than 95%. In other words, the present invention uses a part of the removal effect in exchange for the universality of the method. Therefore, the present invention can be used for the simultaneous and efficient treatment of difficult-to-degrade organic matter in one or more mixed salts.

Claims

1. A method for efficiently removing refractory organic matter from mixed salt by near-zero emission evaporation and crystallization, characterized in that: The steps include: Step 1, taking several kinds of mixed salts, for each kind of mixed salt, taking pyrolysis temperature, pyrolysis duration and temperature rise as conditions, setting the expected target value of TOC removal rate, performing response surface optimization design, and obtaining the suitable pyrolysis condition range of the mixed salt; the mixed salt refers to a salt in which hydrogen atoms in two or more acid molecules are replaced by the same metal atom or a salt composed of a metal cation and two acid anions; Step 2, taking the intersection of the suitable pyrolysis condition ranges of various types of mixed salts as the optimal pyrolysis condition; Step 3, according to the optimal pyrolysis conditions, the refractory organic matter in various mixed salts is removed at one time, wherein the refractory organic matter is a long-chain hydrocarbon or aliphatic compound.

2. The method for efficiently removing refractory organic matter in near-zero emission evaporative crystallization mixed salt according to claim 1, characterized in that: The setting of the expected target value of TOC removal rate refers to setting the TOC removal rate of a type of mixed salt to be no less than 80%.

3. The method for efficiently removing refractory organic matter in near-zero emission evaporation crystallization mixed salt according to claim 1, characterized in that: In the step 1, three types of mixed salts are taken, namely, the aged mother liquor mixed salt from vacuum conversion of zero-emission coal chemical projects, the four-effect evaporation mixed salt, and the single-effect evaporation mixed salt. The suitable pyrolysis condition ranges of each type are obtained by the following formula: DH1=96.88-0.0813A1-0.8312B1-1.25C1-2.6A1B1-1.96A1C1-2.38B1C1 -1.19A1 2 +0.0588B1 2 -1.21C1 2 ; DH2=74.61-1.11A2+2.45B2+1.43C2+2.81A2B2+2.64A2C2-4.97B2C2+ <h2 style=";text-align:left;direction:ltr">3.48A2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +3.39B2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +2.43C2<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> ; DH3=70.05+8.10A3-1.95B3-2.04C3-8.65A3B3+6.05A3C3+13.59B3C3- <h2 style=";text-align:left;direction:ltr">4.41A3<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +4.8B3<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -12.67C3<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -23.46A3B3<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> ; Among them, DH1, DH2 and DH3 represent the TOC removal rates of the three industrial waste salts, A1, A2 and A3 represent the pyrolysis temperatures of the three industrial waste salts, B1, B2 and B3 represent the pyrolysis durations of the three industrial waste salts, and C1, C2 and C3 represent the pyrolysis temperature rises of the three industrial waste salts. The values ​​of DH1, DH2 and DH3 were set within the appropriate range of pyrolysis conditions, and the optimal pyrolysis conditions were obtained through response surface optimization.

4. The method for efficiently removing refractory organic matter in near-zero emission evaporative crystallization mixed salt according to claim 1 or 3, characterized in that: The optimal pyrolysis conditions are: The temperature rise range is 10-15℃ / min, the pyrolysis temperature is 500-550℃, and the pyrolysis maintenance time is 50-80min.

5. A system for realizing the highly efficient removal method of refractory organic matter in the near-zero emission evaporation crystallization mixed salt as described in claim 1, characterized in that: It includes a pretreatment unit, a pyrolysis main unit, a carrier gas supply unit, a tail gas collection and treatment unit, a heat energy recovery unit and a waste salt recovery unit; The pretreatment unit performs drying and crushing pretreatment on the mixed salt to be treated; The pyrolysis main unit is connected to the pretreatment unit, and operates under the pyrolysis conditions of the mixed salt to perform pyrolysis treatment on the evaporated crystallized mixed salt; The carrier gas supply unit is connected to the pyrolysis main unit to deliver nitrogen or air thereto; The tail gas collection and processing unit is connected to the pyrolysis main unit, and performs closed collection and processing on the generated pyrolysis gas and discharges it after it reaches the standard; The heat energy recovery unit is connected to the pyrolysis main unit to recover and utilize the heat energy contained in the tail gas after pyrolysis; The waste salt recovery unit is connected to the pyrolysis main unit to realize resource recycling and reuse after secondary purification of the mixed salt after pyrolysis treatment.

6. The system according to claim 5, characterized in that The drying and crushing pretreatment of the pretreatment unit is achieved as follows: For wet and agglomerated mixed salt, the heat of the high-temperature tail gas after pyrolysis is transmitted by the heat recovery unit to remove the residual moisture in the mixed salt, and then it is mechanically crushed to increase the contact area; The mixed salt from the evaporation crystallization unit is directly transported to the pyrolysis main unit.

7. The system according to claim 5, characterized in that The pyrolysis main unit adopts a closed quartz tube furnace, a rotary quartz tube furnace or an intermittent atmosphere rotary electric furnace, which can continuously input the mixed salt to be treated and continuously output the mixed salt after pyrolysis.

8. The system according to claim 5, characterized in that The flow rate of air or nitrogen output by the carrier gas supply unit is 60-200 sccm and is stably regulated by a flow meter.

9. The system according to claim 5, characterized in that The tail gas collection and treatment unit treats and absorbs harmful gases in the tail gas and discharges them after the treatment meets the standards. The harmful gases include CO, VOC, formaldehyde and SO2.

10. The system according to claim 5, characterized in that The heat energy recovery unit preheats the un-pyrolyzed mixed salt by heat energy exchange to reduce the consumption of preheating energy.

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