A drying process and system suitable for materials containing high content of volatile VOC

Abstract

The invention discloses a drying process and system suitable for materials containing high volatile VOC content. The raw material balls are first sent to a first-stage indirect dryer for indirect drying to a moisture content of 10%, and then sent to a second-stage direct dryer for direct drying to a moisture content of less than 2%, and then sent to a rotary kiln for calcination; the drying medium of the first-stage indirect dryer is heat transfer oil, and the drying heat source comes from the flue gas at the kiln tail. After dust removal, the flue gas at the kiln tail is heat exchanged by a heat transfer oil heat exchanger, and the heat transfer oil introduces the residual heat at the kiln tail into the first-stage indirect dryer; the drying heat source of the second-stage direct dryer is the hot air after dust removal from the grate cooler; the drying waste gas containing a higher concentration of VOC generated in the first-stage indirect dryer and the drying waste gas containing a lower concentration of VOC generated in the second-stage direct dryer are sent to a condensation system for cooling after dust removal, and the cooled waste gas is sent to a rotary kiln or a grate cooler. The invention solves a series of problems caused by the presence of a large amount of VOC components in the material, and realizes low-carbon green production.

Description

Technical Field

[0001] The invention relates to the technical field of environmental protection engineering, and in particular to a drying process and system suitable for materials containing high content of volatile organic compounds (VOCs). Background Art

[0002] At present, both solid waste and hazardous waste are environmental pollutants that are generated in large quantities, have huge historical stockpiles, and are difficult to treat. In particular, coal gangue, ground oil sludge, chemical sludge, etc. contain high levels of volatile substances (VOCs), petroleum hydrocarbons, dioxins and other harmful substances. The VOC content of volatile substances is as high as over 40%.

[0003] Generally, when using solid waste and hazardous waste to prepare ceramsite, the ceramsite raw material balls need to be dried at 200-300℃ before calcination before entering the kiln for calcination, and only one conventional equipment is used for drying. In view of the fact that the drying process will produce a large amount of volatile VOC components and flammable and explosive volatile substances such as petroleum hydrocarbons, the existing technology (for example, Chinese patent publication number CN114370759A discloses a low-energy consumption system and process for preparing ceramsite using solid waste) is difficult to remove such flammable and explosive volatile organic compounds through flue gas treatment methods such as desulfurization, denitrification and dust removal, and it is necessary to further set up a secondary combustion chamber for burnout treatment, resulting in a relatively large flue gas treatment volume and high energy consumption.

[0004] The heat source for the ceramsite drying process is generally provided by the flue gas out of the kiln and the hot air out of the grate cooler. However, when the comprehensive moisture content in the raw material balls is high, it is often necessary to add a hot air furnace to provide the heat source required for drying.

[0005] In summary, the prior art has at least the following technical problems:

[0006] (1) When solid waste and hazardous waste are used as raw materials to prepare expanded clay, the flue gas from the rotary kiln and dryer contains a large amount of volatile organic compounds. During the drying process, volatile VOCs and petroleum hydrocarbons encounter oxygen-containing gases, which will cause flammability and explosion risks. However, there are currently no protective measures in the existing technology against volatile organic compounds that are prone to explosion. In addition, waste gas containing high concentrations of VOCs is difficult to treat through conventional tail gas treatment methods. According to national environmental protection emission requirements, a secondary combustion chamber is generally required for burnout treatment. However, since the secondary combustion chamber needs to be maintained at above 850°C to burn out the VOCs, when the VOC concentration is relatively high, the flue gas treatment volume is relatively large, and the energy consumption of the secondary combustion chamber is relatively high.

[0007] (2) When the volatile VOC in hazardous waste or solid waste has a volatilization temperature higher than 300°C, the breakage rate of ceramsite raw balls will increase when the drying temperature is increased. This is because the ceramsite raw balls containing moisture will release moisture rapidly due to the high temperature during drying, causing the ceramsite to crack. When the comprehensive moisture content of the raw balls is higher than 18%, the breakage rate of the ceramsite raw balls cannot be guaranteed in this case.

[0008] (3) Currently, a one-stage dryer is used in the drying system. As the moisture content of the ceramsite raw material balls decreases, the breakage rate increases significantly, and the product yield decreases, resulting in a sharp increase in the amount of dust in the flue gas, flying sand in the kiln, and an increase in the cost of the dust collection system.

[0009] (4) Among the kiln tail waste heat utilization technologies, the currently commonly used air-to-air heat exchange efficiency is relatively low and the heat exchange time is long. It is impossible to rapidly reduce the kiln tail flue gas from 850°C to 350°C to avoid the re-generation of dioxins. Summary of the invention

[0010] One of the purposes of the present invention is to provide a drying process suitable for materials containing high volatile VOC content. While using hazardous waste and solid waste containing high concentrations of VOC and petroleum hydrocarbons as raw materials to prepare ceramsite, it fully utilizes the waste heat in the calcination system for combustion-supporting, ball drying, etc., to improve the system thermal efficiency, reduce system energy consumption and the breakage rate of raw balls, etc.; in particular, the use of a two-stage drying process (one stage of indirect drying, two stages of direct drying) solves the problem of flue gas treatment caused by a large amount of VOC components and petroleum hydrocarbons in ceramsite raw balls, the problem of VOC and other components causing deflagration when encountering oxygen-containing gases during the drying stage, and the technical problems of protective measures such as introducing a certain amount of explosion-proof protective gas during concentrated condensation. The low-carbon green production of ceramsite and coal gangue-based active mixed materials prepared by calcining solid waste and hazardous waste has been realized, which has important practical significance.

[0011] Another object of the present invention is to provide a drying system suitable for materials containing high content of volatile VOCs.

[0012] The present invention is achieved by a drying process suitable for materials containing high content of volatile VOCs, the process comprising:

[0013] The shaped raw material balls are first sent to the first stage indirect dryer for indirect drying until the moisture content is 10%, and then sent to the second stage direct dryer for direct drying until the moisture content is less than 2%. After that, the raw material balls are sent to the rotary kiln for high-temperature calcination. The calcined clinker balls are cooled by the grate cooler and then screened and stored.

[0014] The drying medium of the first-stage indirect dryer is heat transfer oil, and the drying heat source comes from the flue gas at the kiln tail of the rotary kiln. After dust removal, the flue gas at the kiln tail passes through the heat transfer oil heat exchanger and then enters the flue gas treatment system for treatment and then meets the emission standards. The heat transfer oil introduces the residual heat at the kiln tail into the first-stage indirect dryer to dry the raw material balls; the drying heat source of the second-stage direct dryer is the hot air from the grate cooler after dust removal;

[0015] The drying waste gas containing higher concentration of VOC generated in the first-stage indirect dryer and the drying waste gas containing lower concentration of VOC generated in the second-stage direct dryer are sent to the condensation system for cooling after dust removal, and the condensed water generated by the condensation system enters the water treatment system. The cooled waste gas is sent to the rotary kiln or the grate cooler.

[0016] Preferably, the condensation system contains two condensers, and the drying waste gas containing a higher concentration of VOC generated in the first-stage indirect dryer is sent to a condenser for cooling after dust removal, and the condensed water generated by this condenser enters the water treatment system. The cooled waste gas is directly sent to the kiln head of the rotary kiln as combustion-supporting air, so that the small amount of VOC contained therein is burned at high temperature in the kiln; the drying waste gas containing a lower concentration of VOC generated in the second-stage direct dryer is sent to another condenser for cooling after dust removal, and the condensed water generated by this condenser enters the water treatment system, and the cooled waste gas is sent to the grate cooler as cooling gas.

[0017] Preferably, the condensation system contains a condenser, and the drying waste gas containing a higher concentration of VOC generated in the first-stage indirect dryer and the drying waste gas containing a lower concentration of VOC generated in the second-stage direct dryer are mixed together after dust removal and enter a condenser, and explosion-proof protective gas is introduced into the condenser. The explosion-proof protective gas comes from the kiln tail flue gas after heat exchange in the heat transfer oil heat exchanger, and the kiln tail flue gas contains 5-20% carbon dioxide. The condensed water generated by the condenser enters the water treatment system, and the cooled waste gas is sent to the grate cooler as cooling gas.

[0018] Further preferably, part of the gas fed into the grate cooler is blown into the rotary kiln by a blower to assist combustion and burn off VOCs at high temperature, and the other part is fed into the second-stage direct dryer for recycling after carrying heat in the grate cooler.

[0019] Preferably, the drying temperature and drying efficiency of the first-stage indirect dryer and the second-stage direct dryer are adjusted by automatically adjusting the air intake ratio in the grate cooler according to the concentration of volatile VOCs in the raw material balls and the volatilization temperature range.

[0020] Preferably, the drying heat source of the two-stage direct dryer can also come from a natural gas hot air furnace.

[0021] A drying system suitable for materials containing high content of volatile VOC, comprising a rotary kiln, a grate cooler, a first stage indirect dryer, a second stage direct dryer, a heat transfer oil heat exchanger, a condensation system, a water treatment system and a flue gas treatment system;

[0022] The kiln tail of the rotary kiln is connected to the gas inlet of the first dust collector, the gas outlet of the first dust collector is connected to the gas inlet of the thermal oil heat exchanger, the gas outlet of the thermal oil heat exchanger is connected to the flue gas treatment system, the thermal oil outlet of the thermal oil heat exchanger is connected to the drying medium inlet of the first stage indirect dryer, and the drying medium outlet of the first stage indirect dryer is connected to the thermal oil inlet of the thermal oil heat exchanger;

[0023] The tertiary air gas outlet of the grate cooler is connected to the gas inlet of the second dust collector, and the gas outlet of the second dust collector is connected to the drying medium inlet of the second-stage direct dryer; the material outlet of the first-stage indirect dryer is connected to the material inlet of the second-stage direct dryer, and the material outlet of the second-stage direct dryer is connected to the kiln tail of the rotary kiln;

[0024] The drying waste gas outlet of the first-stage indirect dryer is connected to the gas inlet of the third dust collector, the gas outlet of the third dust collector is connected to the gas inlet of the condensation system, the drying waste gas outlet of the second-stage direct dryer is connected to the gas inlet of the fourth dust collector, the gas outlet of the fourth dust collector is connected to the gas inlet of the condensation system, the gas outlet of the condensation system is connected to a rotary kiln or a grate cooler, and the condensed water outlet of the condensation system is connected to a water treatment system.

[0025] Preferably, the condensation system contains two condensers, the gas outlet of the third dust collector is connected to the gas inlet of the first condenser, and the gas outlet of the first condenser is connected to the kiln head of the rotary kiln; the gas outlet of the fourth dust collector is connected to the gas inlet of the second condenser, and the gas outlet of the second condenser is connected to the grate cooler; the condensate outlet of the first condenser and the condensate outlet of the second condenser are both connected to the water treatment system.

[0026] Preferably, the condensation system contains a condenser, the gas outlet of the third dust collector is connected to the gas inlet of the condenser, the gas outlet of the fourth dust collector is connected to the gas inlet of the condenser, the condenser is also provided with a protective gas inlet, the gas outlet of the condenser is connected to a grate cooler; the condensed water outlet of the condenser is connected to a water treatment system.

[0027] Preferably, it also includes a natural gas hot air furnace, which is connected to the drying medium inlet of the two-stage direct dryer.

[0028] The present invention has the following advantages and beneficial effects:

[0029] The present invention utilizes hazardous waste or solid waste raw materials containing relatively high concentrations of VOC to prepare ceramsite, and fully utilizes the waste heat in the calcination system for combustion-supporting, ball drying, etc., thereby improving the system thermal efficiency and reducing the system energy consumption; in particular, the two-stage drying process using a first stage of indirect drying and a second stage of direct drying solves the problems of flue gas treatment caused by high content of volatile VOC components and petroleum hydrocarbons in ceramsite raw balls, the risk of deflagration caused by VOC and other components encountering oxygen-containing gases in the direct drying stage, and the technical difficulties of introducing a certain amount of explosion-proof protective gas protection measures during centralized condensation. The low-carbon green production of ceramsite and coal gangue-based active mixed materials prepared by calcining solid waste and hazardous waste has been realized, which has important practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is a schematic structural diagram of a drying system using separate condensation provided in an embodiment of the present invention;

[0031] Figure 2 It is a schematic diagram of the structure of a drying system using centralized condensation provided in an embodiment of the present invention.

[0032] In the figure: the double-dotted line with an arrow is the air flow direction; the solid dashed line with an arrow is the material flow direction. DETAILED DESCRIPTION

[0033] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] The embodiment of the present invention provides a drying process suitable for materials containing high content of volatile VOCs, the process is as follows: the shaped raw material balls (water content is generally about 20%) are first sent to a first-stage indirect dryer for indirect drying to a water content of 10%, and then sent to a second-stage direct dryer for direct drying to a water content of less than 2%, and then the raw material balls are sent to a rotary kiln for high-temperature calcination, and the calcined clinker balls are cooled by a grate cooler and then screened and stored;

[0036] The drying medium of the one-stage indirect dryer is heat transfer oil, and the drying heat source comes from the flue gas at the tail of the rotary kiln. The flue gas at the tail of the kiln is dedusted by a dust collector and then indirectly heat-exchanged by a heat transfer oil heat exchanger before entering the flue gas treatment system for treatment and meeting the emission standards. The heat transfer oil introduces the residual heat at the tail of the kiln into the one-stage indirect dryer to dry the raw material balls; the drying heat source of the two-stage direct dryer is the hot air from the grate cooler after dedusting by a dust collector, and the drying heat source of the two-stage direct dryer can also come from a natural gas hot air furnace.

[0037] See also Figure 1 When the condensation system contains two condensers, separate condensation is performed. The drying waste gas with a higher concentration of VOC generated in the first-stage indirect dryer is sent to a condenser for cooling after dust removal by a dust collector. The condensed water generated by this condenser enters the water treatment system. The cooled waste gas is directly sent to the kiln head of the rotary kiln as combustion air, so that part of the VOC contained therein is burned at high temperature in the kiln; the drying waste gas with a lower concentration of VOC generated in the second-stage direct dryer is sent to another condenser for cooling after dust removal by a dust collector. The condensed water generated by this condenser enters the water treatment system, and the cooled waste gas is sent to the grate cooler as cooling gas.

[0038] The flue gas from the rotary kiln is dedusted by the dust collector and then indirectly heat-exchanged by the heat transfer oil heat exchanger. The exhaust gas from the kiln enters the flue gas treatment system for treatment and then meets the emission standards. The heat transfer oil enters an indirect dryer to dry the ceramsite raw material balls. During the high-temperature drying process, most of the VOC and moisture in the ceramsite raw material balls begin to evaporate at high temperatures to form drying exhaust gas. After sufficient indirect heat exchange, the drying exhaust gas containing a high concentration of VOC is dedusted by the dust collector and then sent to a separate condenser for cooling. The condensed water produced by the condenser enters the water treatment system. The condensed exhaust gas is directly sent to the kiln head of the rotary kiln as combustion-supporting air, so that some of the VOC contained therein is burned at high temperature in the kiln.

[0039] The waste heat from the grate cooler is sent to the second-stage direct dryer after dust removal by the dust collector to continue drying the expanded clay raw material balls from the first-stage indirect dryer. The heat generated by the natural gas hot air furnace enters the second-stage direct dryer for heat energy supplement. The drying waste gas containing a small amount of VOC generated by the second-stage direct dryer also enters a separate condenser for cooling. The generated condensed water enters the water treatment system, and the cooled waste gas is sent to the grate cooler as cooling gas.

[0040] See also Figure 2When the condensation system contains a condenser, integrated condensation is performed, and the drying waste gas containing a higher concentration of VOC generated in the first-stage indirect dryer and the drying waste gas containing a lower concentration of VOC generated in the second-stage direct dryer are respectively dedusted by a dust collector and mixed together to enter a condenser. Explosion-proof protective gas is introduced into this condenser. The explosion-proof protective gas comes from a small part of the kiln tail flue gas after heat exchange in a thermal oil heat exchanger. The kiln tail flue gas contains 5-20% carbon dioxide. The condensed water generated by the condenser enters the water treatment system, and the cooled waste gas is sent to the grate cooler as cooling gas.

[0041] Part of the gas sent to the grate cooler is blown into the rotary kiln by the blower to assist combustion and burn off VOCs at high temperature, and the other part is sent to the second-stage direct dryer for recycling after carrying heat in the grate cooler.

[0042] The drying temperature and drying efficiency of the first-stage indirect dryer and the second-stage direct dryer are adjusted by automatically adjusting the air intake ratio in the grate cooler according to the concentration of volatile VOC in the raw material balls and the volatilization temperature range.

[0043] A drying system suitable for materials containing high volatile VOC content, wherein the raw material balls contain high volatile VOC components, and the volatile VOC components are introduced by solid waste or hazardous waste raw materials during the batching process. The drying system includes a rotary kiln, a grate cooler, a first-stage indirect dryer, a second-stage direct dryer, a heat transfer oil heat exchanger, a natural gas hot air furnace, a condensation system, a water treatment system, and a flue gas treatment system.

[0044] The kiln tail of the rotary kiln is connected to the gas inlet of the first dust collector, the gas outlet of the first dust collector is connected to the gas inlet of the thermal oil heat exchanger, the gas outlet of the thermal oil heat exchanger is connected to the flue gas treatment system, the thermal oil outlet of the thermal oil heat exchanger is connected to the drying medium inlet of the first indirect dryer, and the drying medium outlet of the first indirect dryer is connected to the thermal oil inlet of the thermal oil heat exchanger.

[0045] The tertiary air gas outlet of the grate cooler is connected to the gas inlet of the second dust collector, the gas outlet of the second dust collector is connected to the drying medium inlet of the two-stage direct dryer, and the natural gas hot air furnace is connected to the drying medium inlet of the two-stage direct dryer; the material outlet of the one-stage indirect dryer is connected to the material inlet of the two-stage direct dryer, and the material outlet of the two-stage direct dryer is connected to the kiln tail of the rotary kiln.

[0046] When the condensation system contains two condensers, the drying waste gas outlet of the first-stage indirect dryer is connected to the gas inlet of the third dust collector, the gas outlet of the third dust collector is connected to the gas inlet of the first condenser, and the gas outlet of the first condenser is connected to the kiln head of the rotary kiln; the drying waste gas outlet of the second-stage direct dryer is connected to the gas inlet of the fourth dust collector, the gas outlet of the fourth dust collector is connected to the gas inlet of the second condenser, and the gas outlet of the second condenser is connected to the grate cooler; the condensate outlet of the first condenser and the condensate outlet of the second condenser are both connected to the water treatment system.

[0047] When the condensation system contains a condenser, the drying exhaust gas outlet of the first-stage indirect dryer is connected to the gas inlet of the third dust collector, the gas outlet of the third dust collector is connected to the gas inlet of the condenser, the drying exhaust gas outlet of the second-stage direct dryer is connected to the gas inlet of the fourth dust collector, the gas outlet of the fourth dust collector is connected to the gas inlet of the condenser, the condenser is also provided with a protective gas inlet, and the gas outlet of the condenser is connected to a grate cooler; the condensed water outlet of the condenser is connected to a water treatment system.

[0048] The present invention is further described in detail below.

[0049] Example 1

[0050] Preparation of ceramsite from hazardous waste oil sludge. The volatile temperature range of VOC in oil sludge is 243-326℃. This example is introduced by drying oil sludge ceramsite. Please refer to Figure 1 and Figure 2 The wind entering the system from the burner is the primary air, the wind entering the rotary kiln from the grate cooler is the secondary air, the wind entering the two-stage direct dryer from the grate cooler is the tertiary air, and the wind entering the natural gas hot air furnace is also the tertiary air.

[0051] The order of material flow is as follows: the wet ceramsite raw material balls enter the first stage indirect dryer to be dried to a certain moisture content and then enter the second stage direct dryer. The dry material balls coming out of the second stage direct dryer enter the rotary kiln for high-temperature calcination. The calcined ceramsite clinker enters the screening and storage section.

[0052] The order of air flow in the first stage of indirect drying is as follows: the flue gas from the tail of the rotary kiln enters the dust collector and then enters the heat transfer oil heat exchanger for sufficient heat exchange. The heat transfer oil enters the first stage of indirect drying machine to dry the wet material balls with a moisture content of 20% to a moisture content of 10%. More than 90% of the VOC in the wet material balls evaporates in the first stage of indirect drying machine at 300-330℃, and the high-concentration VOC and water vapor enter a separate condenser to be cooled into water and waste gas containing VOC. The waste gas containing VOC is sent to the head of the rotary kiln as combustion air to burn VOC, and the cooling water enters the water treatment system for treatment before being discharged in compliance with the standards.

[0053] The order of air flow in the second-stage direct drying is as follows: the tertiary air coming out of the grate cooler enters the second-stage direct dryer with waste heat (200-250℃) to directly dry the semi-dry raw balls with a moisture content of 10% from the first-stage indirect dryer, and the remaining VOC in the raw balls evaporates. The small amount of VOC and water vapor generated in the second-stage direct dryer enters a separate condenser to be cooled into water and waste gas containing VOC. The cooling water enters the water treatment system for treatment, and the waste gas containing VOC is sent to the grate cooler as cooling air, a part of which (60%) enters the rotary kiln as high-temperature secondary air as combustion-supporting air, and the low-concentration VOC (<10%) contained in it is burned out in the kiln, and the remaining part (40%) is heated in the grate cooler and then enters the second-stage direct dryer again for recycling and drying the balls. When the moisture content of the raw material balls after shaping is ≥18%, the waste heat generated by the ceramsite firing system is not enough to meet the drying heat demand. At this time, a natural gas hot air furnace is used to supplement the heat source to meet the thermal balance of the entire drying system.

[0054] This embodiment sets up a two-stage drying process according to the volatilization temperature range of VOCs in hazardous solid wastes, so that more than 90% of the VOCs are volatilized in the indirect drying stage, and are sent to the kiln head for burning after entering a separate condensation system for treatment along with supersaturated water vapor, thereby avoiding the risk of explosive combustion of volatile VOCs encountering air during the one-stage direct drying process.

[0055] Example 2

[0056] Set the drying temperature based on the VOC volatilization temperature range and content obtained during testing.

[0057] When the volatile VOC content of the sludge is relatively high and the volatilization temperature range is relatively wide during the implementation of Example 1, it is first detected and judged to select a suitable drying temperature range and drying medium.

[0058] When the VOC content is greater than 3.5%, it is more economical to use a two-stage drying method and a separate condensation system to condense and dehydrate the dried exhaust gas. The advantage of this treatment is that it avoids the explosion of high-concentration volatile VOCs from indirect drying encountering oxygen-containing exhaust gas from direct drying, and can greatly reduce the amount of drying exhaust gas, saving flue gas treatment.

[0059] When the VOC content is ≤3.5%, the CO2 gas with a concentration of 10-15% can be used as the protective gas after centralized condensation and heat exchange at the kiln tail while mixing the exhaust gases of the two dryers (see the specific process). Figure 2 ), to avoid the problem of explosion caused by the exhaust gas from the first stage of indirect drying encountering the exhaust gas from the second stage of direct drying with an oxygen concentration close to that of air. This treatment method reduces the complex system of condensation equipment and exhaust gas entering the kiln after indirect drying, and it is economically feasible to use the exhaust gas from the kiln tail as an inert protective gas.

[0060] When the volatile VOC volatilization temperature range is ≤350℃, using heat transfer oil as the heat exchange medium has low energy consumption and high efficiency; when the volatile VOC volatilization temperature range is greater than 350℃, air or flue gas is used as the cooling medium.

[0061] In order to solve the problem of the change of VOC volatilization temperature range in solid waste and hazardous waste, the volatilization temperature range of VOC can be detected by thermal analysis and other technical means, and then the two-stage drying capacity can be adjusted according to the test results, so that most VOCs can be volatilized by indirect drying. The advantage of this treatment is that the VOCs from indirect drying can be sent to the kiln for burning, and the VOC concentration in the direct drying exhaust gas is reduced, which is conducive to the emission of flue gas meeting the standards.

[0062] Example 3

[0063] Adjust the air volume ratio of the grate cooler to adjust the drying temperature of the two-stage drying.

[0064] In order to better deal with the small amount of VOC contained in the second stage direct drying process, this waste gas is introduced into the grate cooler, wherein the proportion of waste gas blown into the kiln by the grate cooler as high-temperature secondary air to burn VOC is adjusted to 0-60%, which correspondingly increases the temperature of the flue gas at the end of the kiln, and then the drying temperature in the first stage indirect dryer is increased, so that most of the VOC in the sludge is volatilized, thereby also improving the drying capacity of the first stage, and the remaining part (0-40%) is heated and continues to enter the second stage direct dryer for recycling and continues to dry the expanded clay.

[0065] The advantage of this is that the grate cooler air volume configuration can be set to adjust the drying temperature range of the two-stage drying according to the VOC volatilization temperature in different hazardous wastes and solid wastes to adapt to the VOC characteristics of the drying material, which has very good flexibility.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents, and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A drying process suitable for materials containing high content of volatile VOC, characterized in that: The process is: The shaped raw material balls are first sent to the first stage indirect dryer for indirect drying to a moisture content of 10%, and then sent to the second stage direct dryer for direct drying to a moisture content of <2%. After that, the raw material balls are sent to the rotary kiln for high-temperature calcination. The calcined clinker balls are cooled by the grate cooler to obtain ceramsite and coal gangue-based active mixed materials, which are screened and stored; When the volatile VOC volatilization temperature range is ≤350°C, the drying medium of the first indirect dryer is heat transfer oil; when the volatile VOC volatilization temperature range is >350°C, the drying medium of the first indirect dryer is air or flue gas; the drying heat source comes from the kiln tail flue gas of the rotary kiln, which is dedusted and indirectly heat-exchanged by the heat transfer oil heat exchanger before entering the flue gas treatment system for treatment and meeting the emission standards. The heat transfer oil introduces the residual heat from the kiln tail into the first indirect dryer to dry the raw material balls; the drying heat source of the second direct dryer is the hot air from the grate cooler after dedusting; The drying waste gas with a higher concentration of VOC generated in the first-stage indirect dryer and the drying waste gas with a lower concentration of VOC generated in the second-stage direct dryer are sent to the condensation system for cooling after dust removal, and the condensed water generated by the condensation system enters the water treatment system, and the cooled waste gas is sent to the rotary kiln or the grate cooler; Part of the gas sent to the grate cooler is blown into the rotary kiln by the blower to assist combustion and burn off VOC at high temperature, and the other part is sent to the second-stage direct dryer for recycling after carrying heat in the grate cooler; The condensation system comprises two condensers. The drying waste gas with a relatively high concentration of VOC generated in the first-stage indirect dryer is sent to a condenser for cooling after dust removal. The condensed water generated by this condenser enters the water treatment system. The cooled waste gas is directly sent to the kiln head of the rotary kiln as combustion air, so that the small amount of VOC contained therein is burned off at high temperature in the kiln; the drying waste gas with a relatively low concentration of VOC generated in the second-stage direct dryer is sent to another condenser for cooling after dust removal. The condensed water generated by this condenser enters the water treatment system. The cooled waste gas is sent to the grate cooler as cooling gas; Alternatively, the condensation system includes a condenser, and the drying waste gas containing a higher concentration of VOC generated in the first-stage indirect dryer and the drying waste gas containing a lower concentration of VOC generated in the second-stage direct dryer are mixed together after dust removal and enter a condenser, and explosion-proof protective gas is introduced into the condenser. The explosion-proof protective gas comes from the kiln tail flue gas after heat exchange in a heat transfer oil heat exchanger, and the kiln tail flue gas contains 5-20% carbon dioxide. The condensed water generated by the condenser enters the water treatment system, and the cooled waste gas is sent to the grate cooler as cooling gas.

2. The drying process for materials containing high volatile VOC content as claimed in claim 1, characterized in that: The drying temperature and drying efficiency of the first-stage indirect dryer and the second-stage direct dryer are adjusted by automatically adjusting the air intake ratio in the grate cooler according to the concentration of volatile VOC in the raw material balls and the volatilization temperature range.

3. The drying process for materials containing high volatile VOC content as claimed in claim 1, characterized in that: The drying heat source of the two-stage direct drying machine can also come from a natural gas hot air furnace.

4. A drying system suitable for materials containing high content of volatile VOC, characterized in that: It includes rotary kiln, grate cooler, one-stage indirect dryer, two-stage direct dryer, thermal oil heat exchanger, condensation system, water treatment system and flue gas treatment system; The kiln tail of the rotary kiln is connected to the gas inlet of the first dust collector, the gas outlet of the first dust collector is connected to the gas inlet of the thermal oil heat exchanger, the gas outlet of the thermal oil heat exchanger is connected to the flue gas treatment system, the thermal oil outlet of the thermal oil heat exchanger is connected to the drying medium inlet of the first stage indirect dryer, and the drying medium outlet of the first stage indirect dryer is connected to the thermal oil inlet of the thermal oil heat exchanger; The tertiary air gas outlet of the grate cooler is connected to the gas inlet of the second dust collector, and the gas outlet of the second dust collector is connected to the drying medium inlet of the second-stage direct dryer; the material outlet of the first-stage indirect dryer is connected to the material inlet of the second-stage direct dryer, and the material outlet of the second-stage direct dryer is connected to the kiln tail of the rotary kiln; The drying exhaust gas outlet of the one-stage indirect dryer is connected to the gas inlet of the third dust collector, the gas outlet of the third dust collector is connected to the gas inlet of the condensation system, the drying exhaust gas outlet of the two-stage direct dryer is connected to the gas inlet of the fourth dust collector, the gas outlet of the fourth dust collector is connected to the gas inlet of the condensation system, the gas outlet of the condensation system is connected to the rotary kiln or the grate cooler, and the condensate outlet of the condensation system is connected to the water treatment system; The condensation system comprises two condensers, the gas outlet of the third dust collector is connected to the gas inlet of the first condenser, and the gas outlet of the first condenser is connected to the kiln head of the rotary kiln; the gas outlet of the fourth dust collector is connected to the gas inlet of the second condenser, and the gas outlet of the second condenser is connected to the grate cooler; the condensate outlet of the first condenser and the condensate outlet of the second condenser are both connected to the water treatment system; Alternatively, the condensation system contains a condenser, the gas outlet of the third dust collector is connected to the gas inlet of the condenser, the gas outlet of the fourth dust collector is connected to the gas inlet of the condenser, the condenser is also provided with a protective gas inlet, the gas outlet of the condenser is connected to a grate cooler; the condensed water outlet of the condenser is connected to a water treatment system.

5. The drying system for materials containing high volatile VOC content as claimed in claim 4, characterized in that: It also includes a natural gas hot air furnace, which is connected to the drying medium inlet of the two-stage direct dryer.

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