Waste salt treatment process based on spiral kiln

Abstract

The invention discloses a waste salt treatment process based on a spiral kiln, and belongs to the technical field of waste salt high-temperature treatment.The waste salt treatment process comprises the following steps that atmosphere establishment is conducted, specifically, high-temperature inert gas is introduced into the spiral kiln for purging, gas purging is stopped, and the gas flow is kept; gradient temperature rise control: starting a spiral kiln, starting heating, raising the temperature according to a set temperature, and starting feeding after the temperature is raised to the set temperature; dynamic feeding treatment: the waste salt gradually moves from a feeding end to a discharging end along with rotation of a screw, and the waste salt stays at a high-temperature section by adjusting the conveying rotation speed of the screw; and rapidly cooling and outputting: cooling the waste salt through a cooling section and discharging. The method is used for solving the problems of equipment corrosion and non-uniform heat transfer caused by high-viscosity waste salt adhering to the wall, TOC residue standard exceeding caused by incomplete decomposition of organic matters in a single temperature area, out-of-control oxygen content and potential safety hazards caused by low inert gas purging efficiency, overhigh discharge temperature and subsequent equipment damage caused by insufficient cooling rate and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of high-temperature treatment of waste salt, and specifically relates to a waste salt treatment process based on a spiral kiln. Background Art

[0002] With the development of industries such as chemical engineering and pharmaceuticals, the problem of treating waste salt containing organic pollutants has become increasingly prominent. Traditional waste salt treatment processes mainly use heat treatment methods such as rotary kiln incineration and fluidized bed pyrolysis, but there are significant defects in treating waste salt with high viscosity and high organic matter content.

[0003] Current technical status and defects:

[0004] 1. Material sticking to the wall and uneven heat transfer: When traditional rotary kilns treat viscous waste salt, the material is prone to sticking to the inner wall of the kiln, resulting in a decrease in heat transfer efficiency, local overheating or underburning. For example, when using a tubular rotary kiln, the viscous material melts and adheres to the tube wall at high temperatures, not only causing fluctuations in product quality (such as a difference in salt crystal particle size distribution > 50%), but also leading to equipment wear due to mechanical scraping; when using a metal furnace tube, the corrosion is very large and it is easy to corrode the screw rod.

[0005] 2. Incomplete decomposition of organic matter: Existing processes mostly use a single high-temperature zone (usually 600 - 800°C) for treatment, and the decomposition efficiency of multi-component complex organic matter is insufficient.

[0006] 3. Defects in oxygen content control: The conventional nitrogen protection process uses constant pressure purging (usually > 20000 Pa), resulting in high energy consumption and the inability to effectively remove residual oxygen in the equipment dead corners. During actual operation, the oxygen content in the kiln fluctuates within a range of ±500 ppm, and the oxygen concentration in local areas exceeds 2000 ppm, triggering oxidation reactions of waste salt and generating harmful gases such as Cl2 and SOx, while accelerating the oxidation corrosion of metal components.

[0007] 4. Low cooling efficiency: Traditional discharge cooling mostly uses natural cooling or single-stage water cooling, with a cooling rate < 30°C / min, resulting in an outlet temperature higher than 150°C; high-temperature salt particles are prone to moisture absorption and caking during subsequent packaging or storage, and cause thermal damage to the conveying equipment, increasing the equipment failure rate by more than 40%.

[0008] 5. Imperfect waste gas treatment: The tail gas treatment systems of existing processes mostly use single alkali washing or activated carbon adsorption, with a removal rate of dioxin-like substances re-synthesized during the quenching process < 70%, and the VOCs emission concentration generally higher than 50 mg / m³, making it difficult to meet the requirements of the "Pollution Control Standard for Hazardous Waste Incineration" (GB 18484 - 2020).

[0009] The above defects lead to prominent problems in traditional waste salt treatment processes, such as low organic matter removal rate, short equipment life (<6 months), high energy consumption, and high environmental protection risks. Especially for waste salts with a viscosity >5000 cP, the existing technologies cannot achieve continuous and stable operation, seriously restricting the process of resource utilization of industrial waste salts. Summary of the Invention

[0010] In view of the above problems, the present invention provides a waste salt treatment process based on a spiral kiln to solve problems such as equipment corrosion and uneven heat transfer caused by high-viscosity waste salt sticking to the wall, excessive TOC (total organic carbon) residue caused by incomplete decomposition of organic matter in a single temperature zone, out-of-control oxygen content and safety hazards caused by low inert gas purging efficiency, excessive discharge temperature and damage to subsequent equipment caused by insufficient cooling rate, and re-synthesis of dioxins and excessive VOCs emissions caused by imperfect waste gas treatment.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A waste salt treatment process based on a spiral kiln includes the following steps:

[0013] (a) Atmosphere establishment: Purge the spiral kiln with high-temperature inert gas until the oxygen content ≤ 1000 ppm, stop gas purging and maintain the gas flow rate at 5 - 20 L / min to maintain the stability of the atmosphere in the kiln;

[0014] (b) Gradient temperature rise control: Start the spiral kiln, set the temperature at 600 - 900 °C, start heating and raise the temperature according to the set temperature. After the temperature reaches the set temperature, start feeding.

[0015] (c) Dynamic feeding treatment: Continuously input waste salt at a feeding speed of 3 - 25 kg / h. As the spiral rotates, the waste salt gradually moves from the feeding end to the discharging end, and the residence time of the waste salt in the high-temperature section is adjusted to 1 - 10 h by adjusting the rotational speed of the screw conveyor.

[0016] (d) Rapid cooling and output: The waste salt after temperature rise and heat preservation is cooled in the cooling section and discharged at a temperature of 20 - 200 °C within 5 - 100 min.

[0017] In a preferred embodiment, the high-temperature inert gas includes nitrogen or argon.

[0018] In a preferred embodiment, the spiral kiln uses a carbon-based spiral material.

[0019] In the preferred embodiment, the high-temperature inert gas purge in step (a) is carried out by staged pressure reduction purge: in the first stage, purge at a pressure of 8000 - 10000 Pa for 5 - 10 min; in the second stage, purge at a pressure of 5000 - 8000 Pa for 10 - 15 min; in the third stage, maintain the purge at a pressure of 2000 - 5000 Pa until the oxygen meets the standard.

[0020] In the preferred embodiment, the heating process in step (b) is implemented with segmented acceleration control: in the stage below 200 °C, the heating rate is 8 - 10 °C / min; in the stage of 200 - 500 °C, the heating rate is 5 - 8 °C / min; in the stage above 500 °C, the heating rate is 2 - 5 °C / min.

[0021] In the preferred embodiment, three-stage temperature gradients are set in the high-temperature section of step (c): the temperature in the material inlet area is 600 - 700 °C; the temperature in the core treatment area is 700 - 800 °C; the temperature in the material outlet area is 800 - 900 °C; the temperature difference between adjacent temperature zones is ≥ 50 °C and the temperature fluctuation is ≤ ± 15 °C.

[0022] In the preferred embodiment, the cooling process of step (d) includes: first, initial cooling by inert gas counterflow: using nitrogen or argon for gas-solid heat exchange at a flow rate of 5 - 10 m / s; then, enhanced indirect water cooling: reducing the material temperature below 150 °C through a jacket cooling water system; finally, final cooling by cyclone separation: using a gas-solid separation device to complete the final cooling to 20 - 200 °C.

[0023] In the preferred embodiment, when treating in the high-temperature section of step (c), sodium carbonate powder accounting for 0.1 - 0.5 wt% of the total material amount is periodically injected into the kiln as a flux, and the injection frequency is once every 30 min.

[0024] In the preferred embodiment, during the treatment process of step (c), waste gas samples are collected every 15 - 30 min for FTIR detection. When the intensity of the characteristic peak of organic matter detected is > 1000 a.u., the temperature of the high-temperature section is automatically increased by 50 - 100 °C and the residence time is extended by 20 - 30 min.

[0025] In the preferred embodiment, the waste gas discharged from the cooling section is treated in three stages: the first stage: the quench tower quickly cools the waste gas from 800 °C to below 200 °C; the second stage: alkaline solution spray is used to absorb acidic gases; the third stage: activated carbon is used to adsorb residual organic matter, and the concentration of VOCs (volatile organic compounds) in the finally discharged gas is ≤ 20 mg / m³.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) By purging with high-temperature inert gas and maintaining a continuous flow rate, the oxygen content in the kiln is stably controlled below 1000 ppm, effectively preventing the oxidation of organic substances and equipment corrosion at high temperatures, improving the safety of the heating process. The coordinated control of gradient heating and dynamic feeding ensures that the viscous waste salt is evenly heated, avoiding material sticking to the wall and coking. The combination of the residence time in the high-temperature section and the rapid cooling in the cooling section enables the TOC degradation rate to be > 99.9%, while avoiding thermal damage to downstream equipment by high-temperature materials. The spiral structure is adopted to solve the problem of high energy consumption, and carbon-based spiral materials are used to avoid serious equipment corrosion;

[0027] (2) The staged pressure reduction purging of the present invention saves 30 - 40% of the consumption of high-temperature inert gas compared with the traditional constant-pressure purging. The stepped pressure change effectively removes the residual oxygen in the dead corners of the kiln body, and the oxygen content reaching the standard time is shortened by 50%, avoiding material splashing and dust entrainment caused by high-pressure purging;

[0028] (3) The staged accelerated heating of the present invention reduces equipment deformation caused by thermal stress, extends the service life of the spiral kiln. The rapid heating in the low-temperature zone shortens the process cycle, and the slow heating in the high-temperature zone ensures uniform heating of the material, with high heating efficiency. The overall heating time is shortened by 20 - 25% compared with the traditional linear heating;

[0029] (4) The three-stage temperature gradient of the present invention forms a directional heat flow, promoting the gradual decomposition of organic components in the material. The highest temperature in the outlet area reaches 1100 °C, ensuring the complete mineralization of high-boiling-point organic substances. The temperature gradient with a temperature difference ≥ 50 °C inhibits the resynthesis of harmful substances such as dioxins;

[0030] (5) The three-stage cooling method of the present invention quenches and solidifies the material, controlling the salt crystal particle size within 50 - 200 μm. The initial cooling with inert gas avoids the oxidation of high-temperature materials, the water-cooled jacket prevents equipment overheating, and the final cooling by cyclone separation realizes efficient gas-solid separation, with the dust entrainment rate < 0.1%;

[0031] (6) The present invention uses sodium carbonate flux to reduce the melting point of the salt by 50 - 100 °C, significantly improving the fluidity of the material. The periodic injection avoids the accumulation of impurities caused by continuous addition, and the purity retention rate > 99.5%. Sodium ions and chloride ions form a eutectic mixture, inhibiting the generation of HCl gas;

[0032] (7) The on-line detection by FTIR (Fourier Transform Infrared Spectroscopy) of the present invention realizes closed-loop control of the process. The fluctuation range of the organic matter removal rate is < ±5%. The dynamic adjustment of temperature and residence time responds to raw material fluctuations, ensuring the stability of the treatment effect. When the characteristic peak intensity > 1000 a.u., the enhanced treatment mode is automatically triggered to avoid the production of unqualified products;

[0033] (8) The three - stage waste gas treatment system of the present invention enables the VOCs emission concentration to be lower than 20 mg / m³, meeting the GB31571 - 2015 standard. The quench tower inhibits the formation of dioxins, the caustic scrubbing sprays to neutralize acidic gases such as HCl and SOx, and the activated carbon adsorption device removes refractory organic compounds such as residual benzene series. Specific Embodiments

[0034] To enable those skilled in the art to better understand the technical solution, the present invention will be described in detail below in combination with embodiments. The description in this part is only exemplary and explanatory, and should not have any restrictive effect on the protection scope of the present invention.

[0035] Example 1:

[0036] A waste salt treatment process based on a spiral kiln includes the following steps:

[0037] (a) Atmosphere establishment: High - purity nitrogen is introduced into the spiral kiln for purging until the oxygen content ≤ 1000 ppm. Then, the nitrogen purging is stopped and the nitrogen flow rate is maintained at 20 L / min to maintain the stability of the atmosphere in the kiln. The spiral kiln uses a carbon - based spiral material. The nitrogen purging adopts staged pressure reduction purging: In the first stage, it purges at a pressure of 8000 Pa for 10 min; in the second stage, it purges at a pressure of 5000 Pa for 15 min; in the third stage, it maintains purging at a pressure of 3000 Pa until the oxygen meets the standard;

[0038] (b) Gradient temperature rise control: The spiral kiln is started, and the set temperature is 600 °C. The heating is started and the temperature is raised according to the set temperature. After the temperature reaches the set temperature, feeding starts. The temperature rise process implements segmented acceleration control: In the stage below 200 °C, the heating rate is 10 °C / min; in the stage of 200 - 500 °C, the heating rate is 6 °C / min; in the stage above 500 °C, the heating rate is 2 °C / min;

[0039] (c) Dynamic feeding treatment: The waste salt is continuously input at a feeding speed of 25 kg / h. As the spiral rotates, the waste salt gradually moves from the feeding end to the discharging end. By adjusting the rotational speed of the screw conveyor, the waste salt stays in the high - temperature section for 10 h. The high - temperature section is set with a three - stage temperature gradient: The temperature in the material inlet area is 600 °C; the temperature in the core treatment area is 800 °C; the temperature in the material outlet area is 850 °C; the temperature difference between adjacent temperature zones is ≥ 50 °C and the temperature fluctuation is ≤ ± 15 °C. During the treatment in the high - temperature section, sodium carbonate powder accounting for 0.5 wt% of the total amount of the material is periodically injected into the kiln as a flux, and the injection frequency is once every 30 min. During the treatment process, waste gas samples are collected every 15 min for FTIR detection. When the intensity of the organic compound characteristic peak detected is > 1000 a.u., the temperature of the high - temperature section is automatically increased by 50 °C and the residence time is extended by 30 min;

[0040] (d)Rapid cooling output: The waste salt after heating up and heat preservation is cooled to 80°C for discharging within 10 minutes through the cooling section. The cooling process includes: First, initial cooling by inert gas counterflow: Using nitrogen or argon at a flow rate of 10 m / s for gas-solid heat exchange; then, enhanced indirect water cooling: Cooling the material below 150°C through the jacket cooling water system; finally, final cooling by cyclone separation: Completing the final cooling to 80°C using the gas-solid separation device; The exhaust gas discharged from the cooling section is treated in three stages: The first stage: The quench tower quickly cools the exhaust gas from 800°C to below 200°C; The second stage: Alkaline solution spraying to absorb acidic gases; The third stage: Activated carbon adsorption of residual organic matter, and the VOCs concentration of the finally discharged gas ≤ 20 mg / m³.

[0041] Example 2:

[0042] A waste salt treatment process based on a spiral kiln, comprising the following steps:

[0043] (a)Atmosphere establishment: Purge the spiral kiln with high-purity nitrogen until the oxygen content ≤ 1000 ppm, stop nitrogen purging and maintain a nitrogen flow rate of 5 L / min to maintain the stability of the atmosphere inside the kiln. The spiral kiln uses a carbon-based spiral material. The nitrogen purging adopts staged pressure reduction purging: The first stage purges at a pressure of 10000 Pa for 5 minutes; The second stage purges at a pressure of 8000 Pa for 10 minutes; The third stage maintains purging at a pressure of 5000 Pa until the oxygen meets the standard;

[0044] (b)Gradient heating control: Start the spiral kiln, set the temperature to 900°C, start heating and raise the temperature according to the set temperature. After the temperature reaches the set temperature, start feeding. The heating process implements segmented acceleration control: The heating rate in the stage below 200°C is 8°C / min; The heating rate in the stage of 200 - 500°C is 5°C / min; The heating rate in the stage above 500°C is 4°C / min;

[0045] (c)Dynamic feeding treatment: Continuously input waste salt at a feeding speed of 5 kg / h. The waste salt moves gradually from the feeding end to the discharging end as the spiral rotates. By adjusting the rotation speed of the screw conveyor, the waste salt stays in the high-temperature section for 1 h. The high-temperature section is set with a three-stage temperature gradient: The temperature in the material inlet area is 700°C; The temperature in the core treatment area is 750°C; The temperature in the material outlet area is 900°C; The temperature difference between adjacent temperature zones ≥ 50°C and the temperature fluctuation ≤ ±15°C. During the treatment in the high-temperature section, inject sodium carbonate powder accounting for 0.1 wt% of the total material amount into the kiln periodically as a flux, and the injection frequency is once every 30 minutes. During the treatment process, collect exhaust gas samples every 30 minutes for FTIR detection. When the intensity of the organic matter characteristic peak detected > 1000 a.u., automatically raise the temperature of the high-temperature section by 100°C and extend the residence time by 20 minutes;

[0046] (d)Quick cooling output: The waste salt after heating up and heat preservation is cooled down to 180 °C within 5 minutes through the cooling section for discharging. The cooling process includes: First, inert gas countercurrent initial cooling: Nitrogen or argon is used for gas-solid heat exchange at a flow rate of 5 m / s; Then, indirect water cooling enhancement: The material is cooled down to below 150 °C through the jacket cooling water system; Finally, cyclone separation final cooling: The final cooling to 180 °C is completed by using the gas-solid separation device; The waste gas discharged from the cooling section is treated in three stages: The first stage: The quench tower quickly cools the waste gas from 800 °C to below 200 °C; The second stage: Alkaline solution spraying is used to absorb acidic gases; The third stage: Activated carbon is used to adsorb residual organic matters, and the VOCs concentration of the finally discharged gas ≤ 20 mg / m³.

[0047] Example 3:

[0048] A waste salt treatment process based on a spiral kiln, comprising the following steps:

[0049] (a)Atmosphere establishment: High-purity argon is introduced into the spiral kiln for purging until the oxygen content ≤ 1000 ppm. Stop argon purging and maintain the argon flow rate at 15 L / min to maintain the stability of the atmosphere in the kiln. The spiral kiln uses a carbon-based spiral material. The argon purging adopts staged pressure reduction purging: The first stage purges at a pressure of 9000 Pa for 8 minutes; The second stage purges at a pressure of 6000 Pa for 13 minutes; The third stage maintains purging at a pressure of 2000 Pa until the oxygen reaches the standard;

[0050] (b)Gradient heating control: Start the spiral kiln, set the temperature to 800 °C, start heating and raise the temperature according to the set temperature. After the temperature reaches the set temperature, start feeding. The heating process implements segmented acceleration control: The heating rate in the stage below 200 °C is 9 °C / min; The heating rate in the stage of 200 - 500 °C is 8 °C / min; The heating rate in the stage above 500 °C is 5 °C / min;

[0051] (c)Dynamic feeding treatment: Continuously input waste salt at a feeding speed of 15 kg / h. The waste salt moves gradually from the feeding end to the discharging end as the spiral rotates. By adjusting the rotation speed of the screw conveyor, the waste salt stays in the high-temperature section for 4 hours. The high-temperature section is set with a three-stage temperature gradient: The temperature in the material inlet area is 650 °C; The temperature in the core treatment area is 700 °C; The temperature in the material outlet area is 800 °C; The temperature difference between adjacent temperature zones ≥ 50 °C and the temperature fluctuation ≤ ±15 °C. During the treatment in the high-temperature section, sodium carbonate powder accounting for 0.3 wt% of the total amount of the material is periodically injected into the kiln as a flux, and the injection frequency is once every 30 minutes. During the treatment process, waste gas samples are collected every 20 minutes for FTIR detection. When the intensity of the organic matter characteristic peak detected > 1000 a.u., the temperature of the high-temperature section is automatically raised by 60 °C and the residence time is extended by 25 minutes;

[0052] (d) Quick cooling output: The waste salt after heating and heat preservation is cooled to 20 °C within 100 min in the cooling section and discharged. The cooling process includes: First, initial cooling by inert gas counterflush: Using nitrogen or argon for gas-solid heat exchange at a flow rate of 7 m / s; then, enhanced indirect water cooling: Cooling the material below 150 °C through the jacket cooling water system; finally, final cooling by cyclone separation: Completing the final cooling to 20 °C using a gas-solid separation device. The waste gas discharged from the cooling section is treated in three stages: The first stage: The quench tower quickly cools the waste gas from 800 °C to below 200 °C; the second stage: Alkaline solution spray is used to absorb acidic gases; the third stage: Activated carbon adsorbs residual organic matter, and the VOCs concentration in the finally discharged gas ≤ 20 mg / m³.

[0053] Comparative Example 1:

[0054] In this comparative example, a traditional tubular rotary kiln is used to replace the spiral kiln, and the metal furnace tube is made of 310S stainless steel. The rest is the same as in Example 1.

[0055] Compare the various indicators of the process treatments in the above Example 1 and Comparative Example 1. The comparison results are shown in the following table.

[0056] Table 1

[0057] Comparative Example 2:

[0058] In this comparative example, a constant high pressure of 10000 Pa is used for purging until the oxygen reaches the standard, without stepwise pressure reduction. The rest is the same as in Example 2.

[0059] Compare the process effects of the above Example 2 and Comparative Example 2. The comparison results are shown in the following table.

[0060] Table 2

[0061] Comparative Example 3:

[0062] In this comparative example, in step (b), the temperature is raised to 800 °C at a constant rate of 6 °C / min without segmented control. The rest is the same as in Example 3.

[0063] Compare the quality parameters of the above Example 3 and Comparative Example 3. The comparison results are shown in the following table.

[0064] Table 3

[0065] Comparative Example 4:

[0066] In this comparative example, in step (c), the high-temperature section is kept at a constant temperature of 1000 °C without gradient. The rest is the same as in Example 1.

[0067] Compare the indicators obtained by the different process treatments in the above Example 1 and Comparative Example 4. The comparison results are shown in the following table.

[0068] Table 4

[0069] It should be noted that in this article, the terms: including, containing and any other variants are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such a process, method, article or device. Specific examples are used in this article to elaborate on the principles and implementation methods of the technical solutions of the present invention. The description of the above examples is only used to help understand the method of the present invention and its core idea. The above is only the preferred implementation mode of the present invention. It should be pointed out that due to the limited nature of written expression and the objectively infinite specific structures, for those of ordinary skill in the art in this technical field, without departing from the principle of the present invention, several improvements, refinements or changes can be made, and the above technical features can also be combined in an appropriate manner; these improvements, refinements, changes or combinations, or directly applying the concept and technical solution of the present invention to other occasions without improvement, should all be regarded as the protection scope of the present invention.

Claims

1. A waste salt treatment process based on a spiral kiln, characterized in that, It includes the following steps: (a)Atmosphere establishment: Introduce high-temperature inert gas into the spiral kiln for purging until the oxygen content ≤ 1000 ppm, then stop the gas purging and maintain the gas flow rate at 5 - 20 L / min to maintain the stability of the atmosphere inside the kiln; (b)Gradient temperature rise control: Start the spiral kiln, set the temperature at 600 - 900 °C, start heating and raise the temperature according to the set temperature. After the temperature reaches the set temperature, start feeding; (c)Dynamic feeding treatment: Continuously input waste salt at a feeding rate of 3 - 25 kg / h. As the spiral rotates, the waste salt gradually moves from the feeding end to the discharging end, and the residence time of the waste salt in the high-temperature section is adjusted to be 1 - 10 h by adjusting the rotation speed of the screw conveyor; (d)Fast cooling and output: The waste salt after heating and heat preservation is cooled in the cooling section and discharged at a temperature of 20 - 200 °C within 5 - 100 min.

2. The waste salt treatment process based on a spiral kiln according to claim 1, wherein, The high-temperature inert gas includes nitrogen or argon.

3. A waste salt treatment process based on a spiral kiln according to claim 1, characterized in that, The spiral kiln uses carbon-based spiral materials.

4. A waste salt treatment process based on a spiral kiln according to claim 1, characterized in that, In the step (a), the high-temperature inert gas purging adopts staged pressure reduction purging: In the first stage, purge at a pressure of 8000 - 10000 Pa for 5 - 10 min; in the second stage, purge at a pressure of 5000 - 8000 Pa for 10 - 15 min; in the third stage, maintain purging at a pressure of 2000 - 5000 Pa until the oxygen meets the standard.

5. A waste salt treatment process based on a spiral kiln according to claim 1, characterized in that, In the step (b), the temperature rise process implements staged acceleration control: In the stage below 200 °C, the temperature rise rate is 8 - 10 °C / min; in the stage of 200 - 500 °C, the temperature rise rate is 5 - 8 °C / min; in the stage above 500 °C, the temperature rise rate is 2 - 5 °C / min.

6. The waste salt treatment process based on a spiral kiln according to claim 1, characterized in that, In the step (c), a three-stage temperature gradient is set in the high-temperature section: The temperature in the material inlet area is 600 - 700 °C; the temperature in the core treatment area is 700 - 800 °C; the temperature in the material outlet area is 800 - 900 °C; the temperature difference between adjacent temperature zones is ≥ 50 °C and the temperature fluctuation is ≤ ± 15 °C.

7. A waste salt treatment process based on a spiral kiln according to claim 1, characterized in that, The cooling process in the step (d) includes: First, inert gas counterflush for initial cooling: Use nitrogen or argon to conduct gas-solid heat exchange at a flow rate of 5 - 10 m / s; then indirect water cooling for strengthening: Cool the material to below 150 °C through the jacket cooling water system; finally, cyclone separation for final cooling: Use the gas-solid separation device to complete the final cooling to 20 - 200 °C.

8. A waste salt treatment process based on a spiral kiln according to claim 1, characterized in that, During the high-temperature section treatment in the step (c), sodium carbonate powder accounting for 0.1 - 0.5 wt% of the total material amount is periodically injected into the kiln as a flux, and the injection frequency is once every 30 min.

9. A waste salt treatment process based on a spiral kiln according to claim 1, characterized in that, During the treatment process in the step (c), exhaust gas samples are collected every 15 - 30 min for FTIR detection. When the intensity of the characteristic peak of organic matter detected > 1000 a.u., the temperature of the high-temperature section is automatically increased by 50 - 100 °C and the residence time is extended by 20 - 30 min.

10. A waste salt treatment process based on a spiral kiln according to claim 1, characterized in that, The exhaust gas discharged from the cooling section is treated in three stages: The first stage: The quench tower quickly cools the exhaust gas from 800 °C to below 200 °C; The second stage: Alkaline solution spray is used to absorb acidic gases; The third stage: Activated carbon adsorbs residual organic matter, and the VOCs concentration of the finally discharged gas ≤ 20 mg / m³.

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