A sludge pyrolysis method and system

Abstract

The invention discloses a sludge pyrolysis method and system, the method comprises the following steps: controlling the water content of sludge; pyrolysis of sludge produces sludge charcoal and pyrolysis gas, the pyrolysis gas is burned to obtain high-temperature flue gas, the high-temperature flue gas pyrolyzes the sludge, saturated steam obtained by heat exchange of the generated flue gas is used for pretreatment of circulating heating sludge, the flue gas after heat exchange can enter step 2 for combustion and temperature adjustment, and is used for preheating air for combustion assistance; the system comprises a pretreatment unit, a pyrolysis unit and a discharging unit which are connected in sequence, the pretreatment unit is connected to a steam heat exchanger; the pyrolysis unit comprises a combustion chamber, a rotary drum and a flue gas interlayer, the rotary drum is connected to the combustion chamber, the combustion chamber is connected to the flue gas interlayer, the flue gas interlayer is connected to the steam heat exchanger, and the rotary drum is connected to the discharging unit; the flue gas passing through the steam heat exchanger enters the combustion chamber for combustion and temperature adjustment, the preheated air is used for combustion assistance in the combustion chamber, and the flue gas is discharged after being purified by tail gas; the invention makes efficient use of heat, operates stably for a long time, and does not produce secondary pollution.

Description

Technical Field

[0001] The present invention relates to the technical field of sludge treatment, and in particular to a sludge pyrolysis method and system. Background Art

[0002] With the improvement of modernization and industrialization, the discharge of domestic and industrial sewage is increasing, and sludge has become an inevitable product in the process of treating these wastewaters. Sludge treatment technology is an extremely important part of modern environmental protection projects and has great social value.

[0003] Since the sludge has a high moisture content, mechanical dehydration + direct contact drying with heat medium is generally used, such as plate and frame filter press + rotary drum dryer, etc. However, direct contact will cause a large amount of odor and other volatiles in the sludge to enter the flue gas, increasing the flue gas volume and subsequent flue gas purification treatment costs.

[0004] In addition, sludge also contains a large number of harmful substances such as pathogens, antibiotics and heavy metals. At present, aerobic composting and anaerobic fermentation are difficult to treat them thoroughly, which has a certain impact on subsequent resource utilization. Incineration technology can eliminate these harmful substances, but the heavy metals escape with the exhaust gas during the treatment process, and the dioxins produced by incineration have a great impact on environmental pollution.

[0005] Chinese patent CN214693826U discloses a pyrolysis process system for reducing and recycling industrial and municipal sludge. The system includes: a dehydrated sludge receiving and supplying device, a dehydrated sludge drying device, a sludge pyrolysis combination device, and a sludge charcoal conveying and storage device. The sludge pyrolysis process system undergoes a series of processes such as dehydrated sludge receiving, conveying, drying, pyrolysis, storage, packaging, dust collection, and flue gas treatment, and solidifies harmful heavy metal ions in the sludge in pyrolytic charcoal. The sludge drying process of this application uses a method in which hot flue gas directly contacts and heats the sludge, which will cause a large amount of odor and other volatiles in the sludge to enter the flue gas, increasing the flue gas volume and subsequent flue gas purification treatment costs. The sludge pyrolysis heating furnace is a vertical multi-stage spiral conveying tube heating furnace. This type of furnace is convenient for controlling material transportation, but the metal spiral structure is in a high temperature environment for a long time, which easily causes the spiral shell to deform and jam the spiral, resulting in a high system operation failure rate.

[0006] Chinese patent CN214747157U discloses a three-stage rotary furnace, including a drum, a furnace head device, a furnace tail device, a solid phase conveying device, a follower jacket and an exhaust box in the furnace; the drum rotates continuously in the same direction, and its interior is divided into independent pre-drying section, drying section and carbonization section from the feeding end to the discharging end, and the pre-drying section is connected to the furnace head device; the two ends of the solid phase conveying device are connected to the two adjacent process sections; the follower jacket is fixed to the drum wall, the drying section and the carbonization section are indirect heating sections, and the pre-drying section is an indirect heating section and / or a direct heating section. The sludge in this application is pre-dried, dried, and pyrolyzed in the furnace in turn, and the material is completely sealed in the furnace. The control of the moisture content of the material and the pyrolysis end point is relatively slow, and the pre-drying, drying, and pyrolysis process sections are arranged in the furnace in turn, which will cause a single device to occupy a long area, which is not conducive to site layout.

[0007] Chinese patent 202210295195.1 discloses a sludge drying and pyrolysis system. The drying temperature of the sludge dryer reaches 500℃-600℃ when working, and the moisture content is 60%. The sludge cake is crushed and then enters the sludge dryer through the conveying equipment for drying, the sludge pyrolysis furnace for pyrolysis, and the cooling bin for cooling, and finally obtains sludge charcoal with a temperature of 60-80℃ and a moisture content of 1%-5%. The temperature of the sludge dryer is 500℃-600℃, which will not only take away moisture but also volatilize more low-boiling organic volatiles in the sludge with the flue gas. The calorific value of the sludge after drying by the sludge dryer is reduced; at the same time, it may cause partial combustion of the sludge, generate dust, and there is a risk of dust explosion. Summary of the invention

[0008] The purpose of the invention is to provide a sludge pyrolysis method and system, which solves the problem of how to fully utilize the heat of flue gas coming out of the flue gas interlayer in the prior art, reduce the energy consumption of sludge treatment, and reduce the cost of tail gas treatment.

[0009] The present invention is achieved by a sludge pyrolysis method, the method comprising the following steps:

[0010] Step 1: Pretreatment: The pretreatment includes dehydration and drying. The dehydrated sludge is dried under the action of circulating gas at 70℃-100℃, so that the moisture content of the sludge is controlled at 15%-30%;

[0011] Step 2, pyrolysis: the sludge treated in step 1 is fed into the rotary drum of the double-layer pyrolysis furnace to undergo pyrolysis reaction to produce sludge charcoal and pyrolysis gas. The pyrolysis gas is burned to obtain high-temperature flue gas, which is returned to the flue gas interlayer of the double-layer pyrolysis furnace to pyrolyze the sludge;

[0012] Step 3, flue gas utilization: the flue gas at the outlet of the flue gas interlayer exchanges heat with the steam heat exchanger to generate saturated steam of 135℃-150℃, the saturated steam exchanges heat with the circulating gas, the circulating gas temperature after heat exchange is controlled at 70℃-100℃, the saturated steam after heat exchange generates liquid water and returns to the steam heat exchanger; a part of the low-temperature flue gas after heat exchange between the flue gas at the outlet of the flue gas interlayer and the steam heat exchanger enters step 2 for combustion and temperature adjustment, and the other part is used for preheating air, the preheated air is used for combustion and combustion-supporting in step 2, and the flue gas after preheating the air is discharged after exhaust gas purification.

[0013] The flue gas coming out of the flue gas interlayer contains a relatively high amount of heat, and drying requires heat. The heat of the flue gas coming out of the flue gas interlayer can be used for drying, but the prior art does not disclose how to use this part of the heat for drying, because the heat of the flue gas coming out of the flue gas interlayer is not easy to be used directly or indirectly for drying. The reasons are as follows: If it is used directly for drying, the flue gas temperature at the outlet of the flue gas interlayer is relatively high and it contains a small amount of oxygen, which may cause partial combustion of the sludge, and when the temperature is high, more low-boiling organic volatiles in the sludge evaporate with the flue gas, and the calorific value of the sludge after drying is reduced; if heat exchange is performed first and then used, the heat after heat exchange cannot be directly used for sludge drying, because sludge drying has a temperature range requirement, the drying temperature is 70-100°C, and the flue gas temperature coming out of the flue gas interlayer is in the range of 300-500°C, which is obviously The temperature range of flue gas coming out of the flue gas interlayer is large, and the heat after heat exchange cannot be guaranteed, while the temperature range of hot air for drying is small, so it is difficult to ensure that the flue gas coming out of the flue gas interlayer enters the sludge drying temperature at 70-100℃; if the flue gas at the outlet of the flue gas interlayer is supplemented with other media to cool down and then used for sludge drying, the flue gas temperature may be lower than the dew point, and the flue gas air volume will increase, and some sludge dust will escape with the flue gas, affecting the sludge drying effect; it can be seen that the heat of the flue gas coming out of the flue gas interlayer is not good for drying directly or indirectly.

[0014] The present invention is aimed at how to apply the flue gas coming out of the flue gas interlayer to drying. First, the flue gas coming out of the flue gas interlayer is heat-exchanged by a steam heat exchanger, and the heat is exchanged with liquid water to form saturated steam; 135℃-150℃ steam is generated to supply heat to the front-end sludge drying or other work sections, making full use of the flue gas waste heat. The reason why the steam heat exchanger is used for heat exchange is that, first, the heat exchange efficiency between gas and liquid is higher than that between gas and gas, and the utilization of flue gas waste heat is more efficient; second, the latent heat of saturated steam is large, and the same volume of saturated steam and air can take away more heat. In other words, to transport the same amount of heat, the saturated steam uses a smaller delivery pipeline, which reduces consumables and is easy to control the heat exchange between saturated steam and the drying circulating gas, which is convenient for subsequent drying temperature regulation. Moreover, the temperature of saturated steam is controlled at 135°C-150°C, which can effectively ensure the drying efficiency; when the temperature of steam is higher than 150°C, the same amount of water produces less saturated steam, so the drying efficiency of the sludge in step one is low; when the temperature of steam is lower than 135°C, part of the saturated steam is easily condensed into water during transportation, so the drying efficiency of the sludge in step one is low.

[0015] Secondly, saturated steam exchanges heat with circulating gas to ensure that the circulating heating temperature after heat exchange is 70°C-100°C. This is because the temperature during drying is higher than 100°C, which is easy to take away low-boiling point substances in the sludge. When the sludge enters the pyrolysis furnace, the low-boiling point substances are reduced, resulting in a low calorific value when the sludge enters the subsequent pyrolysis furnace. At the same time, a temperature higher than 100°C may cause the sludge to burn and there is a risk of dust explosion; when the temperature is lower than 70°C, it takes a long time to dry the sludge to a moisture content of 15%-30%, and the drying efficiency of the moisture in the sludge is low; if the same time is taken, the moisture content of the sludge after drying is high, which also affects the calorific value of the sludge after entering the pyrolysis furnace; therefore, the sludge drying temperature is controlled at 70°C-100°C in the present invention.

[0016] Finally, it is possible to obtain 70℃-100℃ circulating hot air for sludge drying by exchanging heat between saturated steam at 135℃-150℃ and circulating gas.

[0017] The sludge is first dried at 70℃-100℃ to remove the moisture in the sludge without causing the sludge to burn, ensuring the calorific value of the sludge in the double-layer pyrolysis furnace, while avoiding the risk of dust explosion caused by sludge combustion; after the sludge is dried, it enters the double-layer pyrolysis furnace for pyrolysis. The double-layer pyrolysis furnace includes a rotary drum and a flue gas interlayer. The flue gas interlayer is used to remove high-temperature flue gas, and the rotary drum is used to pyrolyze the sludge. The sludge is not in direct contact with the high-temperature flue gas, thereby avoiding a large amount of odor and other volatile substances in the sludge from entering the flue gas, reducing the cost of tail gas treatment; the pyrolysis gas after pyrolysis enters step 2 for combustion, and the heat in the pyrolysis gas is By utilizing, the amount of fuel used for combustion is reduced, and the high-temperature flue gas generated by the combustion provides heat for sludge pyrolysis; after the high-temperature flue gas after the sludge pyrolysis is completed comes out of the flue gas interlayer, the temperature drops to below 500°C, the flue gas coming out of the flue gas interlayer is first heat exchanged and then part of it enters step two for combustion, and the other part can be preheated air, and the preheated air enters step two as combustion-supporting air to form high-temperature flue gas, and the oxygen concentration entering the combustion is adjusted by flue gas distribution, which can reduce the generation of nitrogen oxides, reduce the exhaust gas treatment cost and environmental pollution; the flue gas after preheating the air is discharged after exhaust purification; the saturated steam of the flue gas after heat exchange is used for heat exchange with the circulating gas for drying.

[0018] It should be emphasized that: the flue gas coming out of the flue gas interlayer in the present invention exchanges heat with the steam heat exchanger, and the generated saturated steam exchanges heat with the circulating gas. The saturated steam after heat exchange generates liquid water and returns to the steam heat exchanger. This is the process of cyclic heat exchange between saturated steam and circulating gas; in addition, the circulating gas absorbs heat from the saturated steam and heats up and returns to the pretreatment to dry the sludge, and the circulating gas forms a cyclic drying process. There are two circulation processes between the pretreatment and the steam heat exchanger to ensure that the heat of the flue gas coming out of the flue gas interlayer can be fully utilized for the pretreatment, while ensuring the pretreatment temperature.

[0019] A further technical solution of the present invention is: the circulating gas dried in step 1 is dehumidified and then heat exchanged with saturated steam.

[0020] The dried circulating gas is dehumidified and then heat-exchanged with saturated steam to prevent the water-containing circulating gas from entering the pretreatment process and affecting the drying effect.

[0021] The dried circulating gas is dehumidified and then exchanges heat with saturated steam to form hot air with a temperature of 70℃-100℃, which returns to the pretreatment unit to continue drying the sludge. The moisture in the sludge evaporates with the circulating gas, is dehumidified again, and exchanges heat with saturated steam to form circulating hot air drying sludge.

[0022] A further technical solution of the present invention is that part of the circulating gas dried in step one can enter step two for combustion treatment.

[0023] The hot flue gas coming up from the flue gas interlayer can generate saturated steam and flue gas after heat exchange after heat exchange; the saturated steam is used for circulating heat supply to the drying process for sludge drying. Specifically, saturated steam is used for heating the sludge, and sludge drying produces water vapor and low-boiling volatiles. After dehumidification, circulating hot air is generated through saturated steam heat exchange, and the circulating hot air returns to the drying process to cool the saturated steam after heat exchange in the drying process to form liquid water and return to the steam heat exchanger. The saturated steam is recycled with high energy utilization rate. The low-boiling organic volatiles entrained in the circulating gas during drying are sent to the combustion chamber for combustion, and enter the subsequent flue gas purification process with the flue gas, which is environmentally friendly; and the flow rate of the circulating gas for heat exchange with the saturated steam can be controlled to ensure the temperature range of the circulating hot air.

[0024] A further technical solution of the present invention is: a first sensor is provided at the flue gas interlayer outlet, a second sensor for detecting steam temperature is provided in the steam heat exchanger, the first sensor and the second sensor are both connected to a controller, and the controller is connected to a pump body for controlling the water amount in the steam heat exchanger.

[0025] The steam generated by the steam heat exchanger is controlled at 135-150°C. The first sensor is used to detect the flue gas temperature at the outlet of the flue gas interlayer, and the second sensor is used to detect the temperature of the saturated steam generated by the steam heat exchanger. The controller controls the speed range of the pump body according to the temperature of the first sensor, and the specific speed is accurately controlled according to the temperature of the second sensor. The speed of the pump body determines the amount of water entering the steam heat exchanger, thereby controlling the temperature of the generated steam; when the temperature of the flue gas coming out of the flue gas interlayer is low, the pump body controls the amount of water entering the steam heat exchanger to decrease, reduce the generation of saturated steam, and ensure the temperature range of saturated steam; conversely, when the temperature of the flue gas coming out of the flue gas interlayer is high, the pump body controls the amount of water entering the steam heat exchanger to increase, increase the generation of saturated steam, thereby achieving temperature control of saturated steam.

[0026] A further technical solution of the present invention is: the temperature of the low-temperature flue gas after heat exchange is 180°C-250°C, a third sensor for detecting the temperature of the low-temperature flue gas after heat exchange is provided at the outlet of the steam heat exchanger, and the third sensor is connected to the controller.

[0027] The flue gas after heat exchange contains a certain amount of sulfur dioxide. When the flue gas temperature is lower than 150℃, it is easy to reach the dew point, form acidic droplets with water vapor, and corrode the steam heat exchanger. When the flue gas temperature after heat exchange is higher than 250℃, the effect of entering step 2 of combustion temperature adjustment is not obvious, and the amount of steam generated is reduced, so the flue gas temperature at the outlet of the steam heat exchanger is maintained at 180℃~250℃. The specific temperature control is as follows: the third sensor detects the temperature of the flue gas after heat exchange, and then the controller controls the amount of water in the steam heat exchanger according to the temperature of the third sensor combined with the temperature of the second sensor; when the temperature of the flue gas coming out of the flue gas interlayer is high, the amount of water in the steam heat exchanger is increased, and more water exchanges heat with the flue gas, ensuring that the flue gas temperature after heat exchange is 180℃~250℃, and the temperature of saturated steam can be achieved at 135℃-150℃.

[0028] The temperature of the high-temperature flue gas after the combustion in step 2 is about 1000℃. In order to utilize the heat of the flue gas coming out of the flue gas interlayer, slow down the damage of the high-temperature flue gas to the rotary drum under the premise of ensuring pyrolysis, and extend the service life, the temperature of the high-temperature flue gas entering the flue gas interlayer is controlled at 700℃-800℃, so the temperature of the flue gas entering the combustion in step 2 cannot be too high. Specifically, the flue gas at the outlet of the flue gas interlayer is cooled by a steam heat exchanger to obtain low-temperature flue gas. The low-temperature flue gas has more advantages than the flue gas that has not been heat exchanged by a steam heat exchanger. The reasons are as follows: the flue gas with a higher temperature is used for the air distribution and temperature adjustment in step 2 combustion, and more flue gas is required. The pipes and equipment used to transport this part of the flue gas need to be resistant to high temperatures. In addition, the diameter of the pipe is large, the consumables are serious and the adjustment is complicated, which is not suitable for industrial production; and the air volume is too large, the wind speed in the flue gas interlayer increases, which affects the use of the insulation layer. Specifically, the temperature of the low-temperature flue gas after heat exchange in the steam heat exchanger of the present invention is controlled at 180-250°C. Because the flue gas contains a certain amount of sulfur dioxide, when the flue gas temperature is lower than 150°C, it is easy to reach the dew point and form acidic droplets with water vapor to corrode the steam heat exchanger. Therefore, the flue gas temperature at the steam heat exchanger outlet is maintained at 180-250°C.

[0029] A further technical solution of the present invention is: the low-temperature flue gas after heat exchange enters step two for combustion and temperature adjustment through a second fan, and the temperature of the high-temperature flue gas generated entering the flue gas interlayer is 700°C-800°C, the second fan is connected to a controller, and the controller is connected to a fourth sensor for detecting the temperature of the high-temperature flue gas in the flue gas interlayer.

[0030] The fourth sensor is used to detect the flue gas temperature in the flue gas interlayer, and controls the mixing amount of the low-temperature flue gas after heat exchange in the steam heat exchanger and the high-temperature flue gas generated by combustion according to the detected temperature. Specifically, the mixing amount is controlled by controlling the second fan; thereby ensuring that the temperature of the flue gas interlayer is 700℃-800℃.

[0031] A further technical solution of the present invention is: in step three, the flow rates of saturated steam and circulating gas are both controllable.

[0032] The temperature of saturated steam used for drying heat exchange is controlled within the range of 135°C-150°C and the flow rate can be controlled within a certain range. At the same time, the flow rate of circulating gas for heat exchange with saturated steam can be controlled within a certain range. Therefore, the temperature of circulating gas after heat exchange with saturated steam can be controlled within a certain range, which can ensure that the drying circulating heating temperature is 70°C-100°C.

[0033] A further technical solution of the present invention is: a flow meter and a solenoid valve are provided on the saturated steam delivery pipeline and the circulating gas delivery pipeline, the flow meter and the solenoid valve are connected to a controller, and the controller is connected to a fifth temperature sensor for detecting the circulating gas temperature.

[0034] The flow meter is used to detect the gas flow in the delivery pipeline. The solenoid valve, the flow meter and the fifth temperature sensor are all connected to the controller. The fifth temperature sensor sends the detected circulating gas temperature signal to the controller. The controller controls the opening and closing degree of the solenoid valve according to the temperature of the circulating gas, thereby controlling the flow in the delivery pipeline. When the flow reaches stability, the temperature and flow of the saturated steam are within the set range, and the flow of the circulating gas is also within the set range, so that the temperature of the circulating gas can be controlled within a certain range.

[0035] In order to make better use of the excess heat of saturated steam and low-boiling-point volatile organic compounds in the circulating gas, the excess heat generated by the steam heat exchanger can be used for heating in other directions, such as domestic heating and heating for other processes; the dried circulating gas will carry some low-boiling-point volatile organic compounds during drying, and some of the excess gas will be regularly sent into the combustion chamber for combustion support.

[0036] A further technical solution of the present invention is that the temperature of the low-temperature flue gas after heat exchange with the steam heat exchanger is 180°C-250°C, and the temperature of the tail gas after purification drops to below 100°C.

[0037] The flue gas after tail gas purification is heated by the flue gas heat exchanger to eliminate white smoke.

[0038] A further technical solution of the present invention is: the temperature of the low-temperature flue gas after heat exchange with the steam heat exchanger is 180°C-250°C, and preheated air is obtained after heat exchange with air, and the preheated air is used for combustion and combustion support in step two.

[0039] A further technical solution of the present invention is: the low-temperature flue gas after heat exchange has a temperature of 180°C-250°C and directly enters step 2 for combustion and temperature adjustment, and the generated high-temperature flue gas enters the flue gas interlayer with a temperature of 700°C-800°C.

[0040] The temperature of the low-temperature flue gas after heat exchange is 180°C-250°C, and the temperature of the high-temperature flue gas burned in step 2 is about 1000°C. After the flue gas after heat exchange at 180°C-250°C is mixed with the high-temperature flue gas at about 1000°C, the temperature of the high-temperature flue gas entering the flue gas interlayer is 700°C-800°C, which reduces the damage of the high-temperature flue gas to the rotary drum while ensuring pyrolysis, thereby extending the service life of the double-layer pyrolysis furnace.

[0041] A further technical solution of the present invention is: in the step 1, the sludge has a water content of more than 90%, which is reduced to 60%-70% by dehydration, and then dried at 70°C-100°C to reduce the water content to 15%-30%.

[0042] A further technical solution of the present invention is: in the step 1, the temperature of the high-temperature flue gas after pyrolysis and heat supply in the flue gas interlayer is 300-500°C.

[0043] The present invention also provides a sludge pyrolysis system, comprising a pretreatment unit, a pyrolysis unit and a discharging unit connected in sequence.

[0044] The pretreatment unit is connected to the steam heat exchanger through a double circulation pipeline. The steam heat exchanger generates saturated steam at 135°C-150°C for heat exchange with the circulating gas in the double circulation pipeline. The circulating gas temperature after heat exchange is controlled at 70°C-100°C for circulating heat supply to dry the sludge. The water content of the sludge is controlled at 15%-30%. The saturated steam after heat exchange generates liquid water and returns to the steam heat exchanger.

[0045] The pyrolysis unit comprises a double-layer pyrolysis furnace and a combustion chamber. The double-layer pyrolysis furnace comprises a rotary drum and a smoke interlayer. The gas outlet of the rotary drum is connected to the combustion chamber. The gas outlet of the combustion chamber is connected to the gas inlet of the smoke interlayer. The output end of the smoke interlayer is connected to the steam heat exchanger. The discharge end of the rotary drum is connected to the discharge unit.

[0046] Part of the low-temperature flue gas after heat exchange in the steam heat exchanger enters the combustion chamber for combustion and temperature adjustment, and the other part of the low-temperature flue gas after heat exchange is used to preheat the air. The preheated air enters the combustion chamber to assist combustion, and the flue gas after preheating the air is discharged after passing through the exhaust gas treatment unit.

[0047] The double-layer pyrolysis furnace includes a rotary drum and a flue gas interlayer. The flue gas interlayer is used for conveying high-temperature flue gas, and the rotary drum is used for pyrolyzing sludge. The sludge is not in direct contact with the high-temperature flue gas, thereby preventing a large amount of odor and other volatile substances in the sludge from entering the flue gas, thereby reducing the cost of tail gas treatment. The temperature of the high-temperature flue gas burned in step 2 is about 1000°C, and is mixed with a part of the hot flue gas after heat exchange in the combustion chamber. The temperature of the flue gas entering the flue gas interlayer is controlled to be 700°C-800°C, thereby ensuring that the damage of the high-temperature flue gas to the rotary drum is slowed down under the premise of pyrolysis, and the service life is extended. Moreover, the low-temperature flue gas after heat exchange can preheat the air, and the preheated air enters the combustion chamber as combustion-supporting air to form high-temperature flue gas. The oxygen concentration entering the combustion is adjusted by flue gas distribution, which can reduce the generation of nitrogen oxides, reduce the cost of tail gas treatment and environmental pollution; the flue gas after preheating the air is discharged after tail gas purification.

[0048] A further technical solution of the present invention is: the discharging unit comprises a two-stage water-cooling spiral, and the hot water end of the water-cooling spiral is connected to the steam heat exchanger for replenishing water to the steam heat exchanger or preheating air.

[0049] The sludge charcoal comes out from the output end of the rotary drum and enters the discharging unit; part of the primary cooling return water of the water-cooled spiral is sent to the steam heat exchanger to make up water or preheat air, thereby increasing the steam generation amount or the temperature of the preheated air.

[0050] Beneficial effects of the present invention: The heat of the flue gas coming out of the flue gas interlayer cannot be used directly or indirectly for drying. The present invention is aimed at how to apply the flue gas coming out of the flue gas interlayer to drying. First, the flue gas coming out of the flue gas interlayer is heat-exchanged by a steam heat exchanger, and the heat is exchanged with liquid water to form saturated steam; 135℃-150℃ steam is generated to supply heat to the front-end sludge drying or other work sections, making full use of the waste heat of the flue gas. The reason why a steam heat exchanger is used for heat exchange is that, first, the heat exchange efficiency between gas and liquid is higher than that between gas and gas, and the utilization of the waste heat of flue gas is more efficient; second, the latent heat of saturated steam is large, and the same volume of saturated steam and air can take away more heat. In other words, to transport the same amount of heat, the saturated steam uses a smaller delivery pipeline, which reduces consumables and is easy to control the heat exchange between saturated steam and the drying circulating gas, which is convenient for subsequent drying temperature regulation. Moreover, the temperature of saturated steam is controlled at 135°C-150°C, which can effectively ensure the drying efficiency; when the temperature of steam is higher than 150°C, the same amount of water produces less saturated steam, so the drying efficiency of the sludge in step one is low; when the temperature of steam is lower than 135°C, part of the saturated steam is easily condensed into water during transportation, so the drying efficiency of the sludge in step one is low.

[0051] Secondly, saturated steam exchanges heat with circulating gas to ensure that the circulating heating temperature after heat exchange is 70°C-100°C. This is because the temperature during drying is higher than 100°C, which is easy to take away low-boiling point substances in the sludge. When the sludge enters the pyrolysis furnace, the low-boiling point substances are reduced, resulting in a low calorific value when the sludge enters the subsequent pyrolysis furnace. At the same time, a temperature higher than 100°C may cause the sludge to burn and there is a risk of dust explosion; when the temperature is lower than 70°C, it takes a long time to dry the sludge to a moisture content of 15%-30%, and the drying efficiency of the moisture in the sludge is low; if the same time is taken, the moisture content of the sludge after drying is high, which also affects the calorific value of the sludge after entering the pyrolysis furnace; therefore, the sludge drying temperature is controlled at 70°C-100°C in the present invention.

[0052] Finally, it is possible to obtain 70℃-100℃ circulating hot air for sludge drying by exchanging heat between saturated steam at 135℃-150℃ and circulating gas.

[0053] In the present invention, the flue gas coming out of the flue gas interlayer exchanges heat with the steam heat exchanger, and the generated saturated steam exchanges heat with the circulating gas. The saturated steam after heat exchange generates liquid water and returns to the steam heat exchanger. This is the process of cyclic heat exchange between saturated steam and circulating gas. In addition, the circulating gas absorbs heat from the saturated steam and heats up and returns to the pretreatment to dry the sludge, and the circulating gas forms a cyclic drying process. There are two circulation processes between the pretreatment and the steam heat exchanger, which ensure that the heat of the flue gas coming out of the flue gas interlayer can be fully utilized in the pretreatment, while ensuring the pretreatment temperature.

[0054] In the present invention, the drying and pyrolysis of sludge are processed in different units respectively. Through different equipment processing, the control of the moisture content of the material and the pyrolysis end point is more sensitive. The pyrolysis system is divided into multiple parts, which is convenient for transportation and assembly. Compared with an integral structure, the pyrolysis system of the present invention is more conducive to site layout.

[0055] The heat source for low-temperature drying in the pretreatment unit is the saturated steam generated by the steam heat exchanger, which exchanges heat with the drying circulating gas to form circulating hot air, which is used for circulating heat supply when drying sludge. The energy utilization rate is high. The low-boiling point organic volatiles entrained in the circulating gas during drying can be sent to the combustion chamber for combustion and enter the subsequent flue gas purification process with the flue gas, which is environmentally friendly.

[0056] The low-temperature flue gas after heat exchange in the steam heat exchanger passes through the preheated air of the exhaust gas treatment unit. The preheated air is used as combustion-supporting air and burns directly with the pyrolysis gas in the combustion chamber. At the same time, a part of the flue gas from the steam heat exchanger is added to the air distribution, and the temperature of the high-temperature flue gas entering the double-layer pyrolysis furnace from the combustion chamber and the oxygen concentration in the combustion chamber are flexibly adjusted. The high-temperature flue gas and the double-layer pyrolysis furnace indirectly transfer heat to make full use of the waste heat of the flue gas. At the same time, the temperature of the high-temperature flue gas is within the tolerable range of the furnace body, which reduces the thermal damage of the furnace and prolongs its service life. In addition, reducing the oxygen concentration of combustion can reduce the generation of nitrogen oxides, reduce the cost of exhaust gas treatment and environmental pollution.

[0057] The present invention can effectively control the residence time of solid materials, realize efficient utilization of energy generated in the sludge pyrolysis system, has strong controllability of the treatment process, low cost, long-term stable operation, and does not generate secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] Figure 1 It is a structural schematic diagram of a sludge pyrolysis system provided by the present invention;

[0059] Figure 2 This is a process flow chart of a sludge pyrolysis method provided by the present invention;

[0060] Figure 3 It is a structural schematic diagram of the pyrolysis unit provided by the present invention;

[0061] Figure 4 It is a structural schematic diagram of a discharging unit provided by the present invention;

[0062] Figure 5 It is a structural schematic diagram of the tail gas purification unit provided by the present invention.

[0063] Reference numerals: 1. pretreatment unit, 2. pyrolysis unit, 3. discharging unit, 4. tail gas purification unit, 11. mechanical dehydration device, 12. first screw conveyor, 13. low temperature drying device, 14. second screw conveyor, 15. dehumidification heat exchange equipment, 21. feed hopper, 22. first star valve, 23. furnace tail cover, 24. rotary drum, 25. flue gas interlayer, 26. furnace head cover, 27. ash bucket, 28. Second star valve, 29. Cyclone dust collector, 210. First fan, 211. Burner, 212. Combustion chamber, 213. Second fan, 31. First water-cooling spiral, 32. Second water-cooling spiral, 33. Coal storage bin, 41. Steam heat exchanger, 42. Air heat exchanger, 43. Flue gas heat exchanger, 44. Spray tower, 45. Defogger, 46. Adsorption box, 47. Third fan, 48. Chimney. DETAILED DESCRIPTION

[0064] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0065] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present invention, so they have no substantial technical significance. Any modification of the structure, change of the proportion relationship or adjustment of the size should still fall within the scope of the technical content disclosed by the present invention without affecting the effects and purposes that can be achieved by the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle" and "one" quoted in this specification are only for the convenience of description, and are not used to limit the scope of the implementation of the present invention. The change or adjustment of their relative relationship should also be regarded as the scope of the implementation of the present invention without substantially changing the technical content.

[0066] Embodiment 1:

[0067] like Figure 1-5 A sludge pyrolysis method is shown, the method comprising the following steps:

[0068] Step 1: Pretreatment: The pretreatment includes dehydration and drying. The dehydrated sludge is dried under the action of circulating gas at 70℃-100℃, so that the moisture content of the sludge is controlled at 15%-30%;

[0069] Step 2, pyrolysis: the sludge treated in step 1 is fed into the rotary drum of the double-layer pyrolysis furnace to undergo pyrolysis reaction to produce sludge charcoal and pyrolysis gas. The pyrolysis gas is burned to obtain high-temperature flue gas, which is returned to the flue gas interlayer of the double-layer pyrolysis furnace to pyrolyze the sludge;

[0070] Step 3, flue gas utilization: the flue gas at the outlet of the flue gas interlayer exchanges heat with the steam heat exchanger to generate saturated steam of 135℃-150℃, the saturated steam exchanges heat with the circulating gas, the circulating gas temperature after heat exchange is controlled at 70℃-100℃, the saturated steam after heat exchange generates liquid water and returns to the steam heat exchanger; a part of the low-temperature flue gas after heat exchange between the flue gas at the outlet of the flue gas interlayer and the steam heat exchanger enters step 2 for combustion and temperature adjustment, and the other part is used for preheating air, the preheated air is used for combustion and combustion-supporting in step 2, and the flue gas after preheating the air is discharged after exhaust gas purification.

[0071] In this embodiment, the circulating gas dried in step 1 is dehumidified and then heat-exchanged with saturated steam to form circulating hot air with a temperature of 70° C.-100° C. and returns to step 1 for drying.

[0072] In this embodiment, part of the circulating gas dried in step 1 can enter step 2 for combustion treatment.

[0073] In this embodiment, a first sensor is provided at the flue gas interlayer outlet, and a second sensor for detecting steam temperature is provided in the steam heat exchanger. Both the first sensor and the second sensor are connected to a controller, and the controller is connected to a pump body for controlling the water amount in the steam heat exchanger.

[0074] The steam generated by the steam heat exchanger is controlled at 135-150°C. The first sensor is used to detect the flue gas temperature at the outlet of the flue gas interlayer, and the second sensor is used to detect the temperature of the saturated steam generated by the steam heat exchanger. The controller controls the speed range of the pump body according to the temperature of the first sensor, and the specific speed is accurately controlled according to the temperature of the second sensor. The speed of the pump body determines the amount of water entering the steam heat exchanger, thereby controlling the temperature of the generated steam; when the temperature of the flue gas coming out of the flue gas interlayer is low, the pump body controls the amount of water entering the steam heat exchanger to decrease, reduce the generation of saturated steam, and ensure the temperature range of saturated steam; conversely, when the temperature of the flue gas coming out of the flue gas interlayer is high, the pump body controls the amount of water entering the steam heat exchanger to increase, increase the generation of saturated steam, thereby achieving temperature control of saturated steam.

[0075] In this embodiment, the temperature of the low-temperature flue gas after heat exchange is 180°C-250°C, and a third sensor for detecting the temperature of the low-temperature flue gas after heat exchange is provided at the outlet of the steam heat exchanger, and the third sensor is connected to the controller.

[0076] The flue gas after heat exchange contains a certain amount of sulfur dioxide. When the flue gas temperature is lower than 150℃, it is easy to reach the dew point, form acidic droplets with water vapor, and corrode the steam heat exchanger. When the flue gas temperature after heat exchange is higher than 250℃, the effect of entering step 2 of combustion temperature adjustment is not obvious, and the amount of steam generated is reduced, so the flue gas temperature at the outlet of the steam heat exchanger is maintained at 180℃~250℃. The specific temperature control is as follows: the third sensor detects the temperature of the flue gas after heat exchange, and then the controller controls the amount of water in the steam heat exchanger according to the temperature of the third sensor combined with the temperature of the second sensor; when the temperature of the flue gas coming out of the flue gas interlayer is high, the amount of water in the steam heat exchanger is increased, and more water exchanges heat with the flue gas, ensuring that the flue gas temperature after heat exchange is 180℃~250℃, and the temperature of saturated steam can be achieved at 135℃-150℃. In this embodiment, the low-temperature flue gas after heat exchange enters step two for combustion temperature adjustment through the second fan, and the temperature of the high-temperature flue gas generated entering the flue gas interlayer is 700°C-800°C. The second fan is connected to the controller, and the controller is connected to the fourth sensor for detecting the temperature of the high-temperature flue gas in the flue gas interlayer.

[0077] The fourth sensor is used to detect the flue gas temperature in the flue gas interlayer, and controls the mixing amount of the low-temperature flue gas after heat exchange in the steam heat exchanger and the high-temperature flue gas generated by combustion according to the detected temperature. Specifically, the mixing amount is controlled by controlling the second fan; thereby ensuring that the temperature of the flue gas interlayer is 700℃-800℃.

[0078] The theoretical correspondence between the flue gas interlayer temperature, saturated steam temperature and the temperature after heat exchange in the steam heat exchanger is as follows: 1 kg of sludge dried to a moisture content of 15% has a calorific value of 1500 kcal and enters the pyrolysis furnace. The pyrolysis furnace produces pyrolysis gas, which burns in the combustion chamber to produce high-temperature flue gas with air conditioning and then enters the flue gas interlayer for heat exchange. The flue gas at the flue gas interlayer outlet is 300°C, which can be controlled by the steam generator to produce 0.24 kg of 135°C steam, and at the same time, the flue gas temperature after heat exchange in the steam generator is 180°C. The theoretical value provides a basis for actual regulation. The air supply volume of the second fan is calculated as follows: the flue gas temperature after heat exchange in the steam generator is 180°C. For every kg of absolutely dry sludge, pyrolysis produces pyrolysis gas that enters the combustion chamber to produce flue gas of about 900°C, which is 1.5 m3 of 180°C flue gas delivered by the second fan. 3 The high-temperature flue gas with a temperature adjustment of 750°C is mixed and enters the interlayer of the double-layer pyrolysis furnace. The theoretical value provides a basis for actually regulating the delivery volume of the second fan.

[0079] In the present embodiment, in the step 3, the flow rates of saturated steam and circulating gas are both controllable, and the circulating heating temperature for drying is 70° C.-100° C. In the present embodiment, flow meters and solenoid valves are provided on the saturated steam delivery pipeline and the circulating gas delivery pipeline, and the flow meters and solenoid valves are connected to a controller, and the controller is connected to a fifth temperature sensor for detecting the temperature of the circulating gas.

[0080] The flow meter is used to detect the gas flow in the delivery pipeline. The solenoid valve, the flow meter and the fifth temperature sensor are all connected to the controller. The fifth temperature sensor sends the detected circulating gas temperature signal to the controller. The controller controls the opening and closing degree of the solenoid valve according to the temperature of the circulating gas, thereby controlling the flow in the delivery pipeline. When the flow reaches stability, the temperature and flow of the saturated steam are within the set range, and the flow of the circulating gas is also within the set range, so that the temperature of the circulating gas can be controlled within a certain range.

[0081] The saturated steam temperature is 135-150℃, how to ensure that the drying hot air temperature is 70-100℃? The flow rate of the generated saturated steam entering the dehumidification heat exchange equipment is controlled within a certain range, specifically through the solenoid valve installed on the pipeline between the steam heat exchanger and the dehumidification heat exchange equipment; the flow rate of the dried circulating gas entering the dehumidification heat exchange equipment is also controlled within a certain range, specifically through the solenoid valve installed on the pipeline between the dehumidification heat exchange equipment and the drying, so that the saturated steam at 135-150℃ exchanges heat with the dried circulating gas, the temperature and flow rate of the saturated steam are constant, and the flow rate of the circulating gas is constant, thereby ensuring that the temperature of the dried gas after heat exchange is 70-100℃.

[0082] In order to better utilize the excess heat of saturated steam and low-boiling organic volatiles in the circulating gas, the excess heat generated by the steam heat exchanger can be used for heating in other directions. The drying circulating gas will carry some low-boiling organic volatiles during drying, and some excess gas will be regularly sent to the combustion chamber for combustion support. In special cases, when the calorific value of the sludge is so low that it cannot produce enough saturated steam, the sludge drying needs to use external heating to ensure the drying temperature is 70℃-100℃.

[0083] In this embodiment, the temperature of the low-temperature flue gas after heat exchange with the steam heat exchanger is 180°C-250°C, and the temperature of the exhaust gas after purification drops to below 100°C.

[0084] In this embodiment, the temperature of the low-temperature flue gas after heat exchange with the steam heat exchanger is 180°C 250°C, and preheated air is obtained after heat exchange with air. The preheated air is used for combustion and combustion support in step two.

[0085] In this embodiment, the exhaust gas purification process is carried out in an exhaust gas purification unit. The exhaust gas purification unit 4 includes an air heat exchanger 42, a flue gas heat exchanger 43 and a spray tower 44 connected in sequence. The air heat exchanger 42 preheats air for combustion support in step two.

[0086] In this embodiment, the low-temperature flue gas after heat exchange has a temperature of 180°C-250°C and directly enters step 2 for combustion and temperature adjustment. The generated high-temperature flue gas enters the flue gas interlayer with a temperature of 700°C-800°C.

[0087] In this embodiment, in step 1, the sludge has a water content of more than 90%, which is reduced to 60%-70% by dehydration, and then reduced to 15%-30% by low-temperature drying.

[0088] In this embodiment, the temperature of the rotary drum 24 in the double-layer pyrolysis furnace gradually increases from the feed end to the discharge end, with the highest temperature being 650°C, and the temperature of the flue gas interlayer 25 gradually decreases from the feed end to the discharge end, with the temperature range of the flue gas interlayer 25 being 300°C-750°C.

[0089] In this embodiment, the material movement direction of the rotary drum 24 is opposite to the smoke movement direction of the smoke interlayer 25 .

[0090] In this embodiment, a sludge pyrolysis method, S1: mechanical dehydration: sludge with a moisture content of more than 90% in the sewage treatment plant is fully conditioned by adding a conditioning agent, and the conditioned sludge is sent to a mechanical dehydration to complete liquid-solid two-phase separation. After the sludge is dehydrated, the moisture content is reduced to 60-70%, and the sludge is sent to a low-temperature drying device 13, and the filtrate is sent to the sewage treatment plant for treatment;

[0091] S2: Low temperature drying: Using heat pump low temperature drying technology, using condensation to remove water, heat exchange between cold and hot media, the sludge is in direct contact with hot air to evaporate the sludge water and reduce the sludge moisture content to 15-30%;

[0092] S3: Pyrolysis unit 2: The dried sludge is transported to the double-layer pyrolysis furnace for pyrolysis reaction. The sludge undergoes further drying, heating, pyrolysis and other processes in the double-layer pyrolysis furnace to produce sludge charcoal and pyrolysis gas containing carbon monoxide, methane and tar. After high-temperature dust removal, the pyrolysis gas is sent to the combustion chamber 212 by the first fan 210 for combustion. The high-temperature flue gas generated returns to the flue gas interlayer 25 of the double-layer pyrolysis furnace for indirect heating;

[0093] S4: Discharging unit 3: The sludge charcoal is discharged through the furnace cover 26, enters the water-cooled spiral cooling, the temperature drops to below 100°C, and is transported to the sludge charcoal storage bin 33;

[0094] S5: tail gas purification unit 4: the flue gas at the outlet of the double-layer pyrolysis furnace is heat exchanged through the steam heat exchanger, and the generated saturated steam is sent to the low-temperature drying device 13 to participate in sludge drying. The flue gas at the outlet of the steam heat exchanger is purified and discharged through the chimney 48.

[0095] In this embodiment, after water is removed from the humid hot air at the outlet of the low-temperature drying device 13, a portion is sent to the combustion chamber 212 for combustion, and a portion is re-exchanged with steam to circulate and dry the sludge. The condensed water generated by the steam heat exchange is returned to the steam heat exchanger as part of its water replenishment.

[0096] In this embodiment, the double-layer pyrolysis furnace is a continuous rotary furnace, and intermittent lifting plates are arranged in the rotary drum 24. On the basis of realizing controllable material transportation, the contact area between the material and the furnace wall is increased, and the material is lifted up and falls and broken with the lifting plates, which is beneficial to the heat transfer of the material.

[0097] In this embodiment, there is a flue gas interlayer 25 between the furnace wall and the furnace body of the double-layer pyrolysis furnace; the flue gas coming out of the combustion chamber 212 indirectly exchanges heat with the material in the flue gas interlayer 25, and a guide plate is arranged in the flue gas interlayer 25 to improve the heat exchange efficiency.

[0098] In this embodiment, a cyclone dust collector 29 is used before the pyrolysis gas enters the combustion chamber 212 to reduce the amount of sludge dust entering the subsequent flue gas.

[0099] In this embodiment, the pipes and equipment between the hot gas generated in the double-layer pyrolysis furnace and the combustion chamber 212 need to be well insulated to reduce heat dissipation and prevent condensation of pyrolysis oil. The pyrolysis gas uses a cyclone dust collector 29 and the pipe is insulated to maintain the temperature of the pyrolysis gas as much as possible to prevent large particles from entering the subsequent pipes and prevent condensation of pyrolysis oil in the pipes.

[0100] In this embodiment, in the discharge unit 3, the sludge charcoal discharge cooling adopts a multi-stage water-cooling spiral structure, and part of the hot water generated by cooling is sent to the steam heat exchanger for water replenishment, and part is recycled through the cooling tower.

[0101] In this embodiment, a spray nozzle is added to the inner cylinder of the water-cooling spiral to flexibly control the real-time temperature of the sludge charcoal at the outlet of the device.

[0102] In this embodiment, the flue gas at the steam heat exchanger outlet is divided into two paths, one path of the flue gas returns to the pyrolysis gas combustion chamber 212 for air distribution to adjust the flue gas temperature, and the other path of the flue gas is sent to the two-stage heat exchanger of the tail gas treatment unit.

[0103] In this embodiment, the first stage of the two-stage heat exchanger of the exhaust gas treatment unit is an air heat exchanger 42, which is used to exchange heat between the flue gas coming out of the steam heat exchanger 41 and the air. The preheated air enters the combustion chamber 212 to participate in the combustion of the pyrolysis gas and to assist combustion. The second stage is a flue gas heat exchanger 43, which is used to exchange heat between the flue gas coming out of the air heat exchanger 42 and the exhaust flue gas, thereby increasing the temperature of the exhaust flue gas, achieving flue gas whitening, and meeting emission requirements.

[0104] In this embodiment, the flue gas at the outlet of the flue gas heat exchanger 43 enters the spray tower 44 + demister 45 + adsorption box 46, is led out by the fan and returns to the flue gas heat exchanger for heat exchange, and is finally discharged through the chimney 48.

[0105] Embodiment 2:

[0106] Figure 1-5 A sludge pyrolysis system is shown, comprising a pretreatment unit 1, a pyrolysis unit 2 and a discharge unit 3 connected in sequence.

[0107] The pretreatment unit 1 is connected to the steam heat exchanger 41 through a double circulation pipeline. The steam heat exchanger generates saturated steam at 135°C-150°C for heat exchange with the circulating gas in the double circulation pipeline. The circulating gas temperature after heat exchange is controlled at 70°C-100°C for circulating heat supply to dry the sludge. The water content of the sludge is controlled at 15%-30%. The saturated steam after heat exchange generates liquid water and returns to the steam heat exchanger.

[0108] The pyrolysis unit 2 includes a double-layer pyrolysis furnace and a combustion chamber 212. The double-layer pyrolysis furnace includes a rotary drum 24 and a smoke interlayer 25. The gas outlet end of the rotary drum 24 is connected to the combustion chamber 212. The gas outlet end of the combustion chamber 212 is connected to the gas inlet end of the smoke interlayer 25. The output end of the smoke interlayer 25 is connected to the steam heat exchanger 41. The discharge end of the rotary drum 24 is connected to the discharge unit 3.

[0109] A part of the low-temperature flue gas after heat exchange in the steam heat exchanger 41 directly enters the combustion chamber 212 for combustion, air distribution and temperature adjustment, and another part of the flue gas after heat exchange is used for preheating air, and the preheated air enters the combustion chamber 212 for combustion assistance, and the flue gas after preheating air is discharged after passing through the exhaust gas treatment unit.

[0110] In this embodiment, the dual circulation pipeline includes a saturated steam circulation pipeline and a circulation gas circulation pipeline.

[0111] The double-layer pyrolysis furnace in the pyrolysis unit 2 includes a rotary drum 24 and a flue gas interlayer 25. The flue gas interlayer 25 is used to carry high-temperature flue gas, and the rotary drum 24 is used to pyrolyze sludge. The sludge is not in direct contact with the high-temperature flue gas, thereby avoiding a large amount of odor and other volatile substances in the sludge from entering the flue gas, reducing the cost of exhaust gas treatment; the temperature of the pyrolysis gas entering the combustion chamber 212 is as high as about 1000°C after combustion. After a part of the flue gas passes through the steam heat exchanger 41 and enters the combustion chamber 212 for mixing, the temperature entering the double-layer pyrolysis furnace is reduced. The temperature entering the double-layer pyrolysis furnace is controlled at 700°C-800°C, which reduces the damage of the high-temperature flue gas to the rotary drum and extends its service life. Another part of the flue gas passing through the steam heat exchanger 41 preheats the air to generate preheated air. The preheated air enters the combustion chamber 212 and forms high-temperature flue gas through combustion, which adjusts the oxygen concentration entering the combustion, extends the service life and reduces the oxygen concentration at the same time, which can reduce the generation of nitrogen oxides, reduce the exhaust gas treatment cost and environmental pollution; the low-temperature flue gas after preheating the air is discharged after exhaust gas purification.

[0112] In the present invention, the drying and pyrolysis of sludge are processed in different units respectively. Through the processing of different equipment, the control of the moisture content of the material and the pyrolysis end point is more sensitive. The pyrolysis system is divided into multiple parts, which is convenient for transportation and assembly. Compared with an integral structure, the pyrolysis system of the present invention is more conducive to site layout.

[0113] The saturated steam generated by the steam heat exchanger 41 exchanges heat with the dehumidification heat exchange equipment 15 in the pretreatment unit 1, and the saturated steam after cooling returns to the steam heat exchanger 41 for recycling; the dehumidification heat exchange equipment 15 generates hot air to control the water content of the sludge, and the water vapor and low-boiling organic volatiles evaporated in the sludge escape with the circulating gas, and a part of them returns to the dehumidification heat exchange equipment 15 to exchange heat with the saturated steam to form circulating hot air, thereby circulating and drying the sludge; the other part enters the combustion chamber 212 for combustion, and enters the subsequent flue gas purification process with the flue gas, which is environmentally friendly.

[0114] The pyrolysis gas and the combustion-supporting air are directly burned in the combustion chamber 212, and a portion of the flue gas from the steam heat exchanger 41 is added to the air distribution, so as to flexibly adjust the temperature of the flue gas entering the double-layer pyrolysis furnace from the combustion chamber 212 and the oxygen concentration of the combustion, so as to make full use of the waste heat of the flue gas; at the same time, the high-temperature flue gas temperature is within the tolerable range of the furnace body, so as to reduce the thermal damage of the double-layer pyrolysis furnace and extend its service life; and reducing the oxygen concentration of the combustion can reduce the generation of nitrogen oxides, reduce the cost of exhaust gas treatment and environmental pollution.

[0115] The present invention can effectively control the residence time of solid materials, realize efficient utilization of energy generated in the sludge pyrolysis system, has strong controllability of the treatment process, low cost, long-term stable operation, and does not generate secondary pollution.

[0116] The temperature of the rotary drum 24 gradually increases from the feed end to the discharge end, with a maximum temperature of 650°C. The temperature of the flue gas interlayer 25 gradually decreases from the air inlet end to the air outlet end. Limited by the furnace body material, the maximum flue gas temperature is controlled at 700°C-800°C, and the temperature of the flue gas interlayer 25 is 300-500°C. The temperature range is relatively large, which is determined by the sludge raw material. The sludge has a high organic matter content, and a lot of pyrolysis gas is produced. The amount of flue gas after combustion is large, and the outlet temperature of the flue gas interlayer 25 is relatively high. If the sludge has a low organic matter content, less pyrolysis gas is produced, and the amount of flue gas after combustion is small, the outlet temperature of the flue gas interlayer 25 is relatively low; the temperature of the combustion chamber is controlled at about 1000°C, and after being matched with a part of the flue gas at the outlet of the steam heat exchanger 41, the temperature of the flue gas after combustion is reduced to no more than 800°C to prevent the temperature from being too high to damage the furnace body of the double-layer pyrolysis furnace; at the same time, reducing the oxygen concentration of combustion can reduce the generation of nitrogen oxides, reduce the cost of tail gas treatment and environmental pollution.

[0117] In this embodiment, the exhaust gas purification unit 4 includes a steam heat exchanger 41 and an exhaust gas treatment unit connected to the output end of the steam heat exchanger 41 .

[0118] In this embodiment, the exhaust gas purification unit 4 includes an air heat exchanger 42, a flue gas heat exchanger 43 and a spray tower 44 connected in sequence. The air heat exchanger 42 is connected to the steam heat exchanger 41, and the outlet end of the spray tower 44 is connected to the flue gas heat exchanger 43 through a demister 45 and an adsorption box 46. The air heat exchanger 42 preheats the air for combustion in the combustion chamber 212.

[0119] The low-temperature flue gas after heat exchange in the steam heat exchanger 41 enters the air heat exchanger 42 to generate preheated air and flue gas after heat exchange, wherein the preheated air enters the combustion chamber 212 for combustion assistance, and the flue gas after heat exchange enters the flue gas heat exchanger 43 for subsequent treatment.

[0120] When the flue gas after spraying, demisting and adsorption is discharged, it exchanges heat with the medium and low temperature flue gas in the flue gas heat exchanger 43 to achieve the whitening emission of the flue gas.

[0121] In this embodiment, the discharging unit 3 includes a two-stage water-cooling spiral, and the hot water end of the water-cooling spiral is connected to the steam heat exchanger 41 for steam water replenishment or preheating air.

[0122] The sludge charcoal comes out from the output end of the rotary drum 24 and enters the discharging unit 3; a part of the primary cooling return water of the water-cooling spiral is sent to the steam heat exchanger 41 for water replenishment, thereby increasing the steam generation amount or the temperature of the preheated air.

[0123] In this embodiment, the two-stage water-cooling spirals respectively include a first water-cooling spiral 31 and a second water-cooling spiral 32 connected to the first water-cooling spiral 31 , and a carbon storage bin 33 is provided at the discharge end of the second water-cooling spiral 32 .

[0124] In this embodiment, the pretreatment unit 1 includes a mechanical dehydration device 11 , a first screw conveyor 12 , a low-temperature drying device 13 and a second screw conveyor 14 which are connected in sequence, and the low-temperature drying device 13 is connected to the steam heat exchanger 41 .

[0125] The sludge from the sewage treatment plant has a moisture content of more than 90%. It passes through the mechanical dehydration device 11 to reduce the moisture content to 60-70%, and is sent to the low-temperature drying device 13 through the first screw conveyor 12. Under the action of circulating hot air, the moisture content of the sludge is reduced to 15-30%.

[0126] In this embodiment, the low-temperature drying device 13 is connected to the steam heat exchanger 41 through the dehumidification heat exchange equipment 15 .

[0127] The circulating hot air is the hot air generated by the circulation between the dehumidification heat exchange device 15 and the low-temperature drying device 13. The dehumidification heat exchange device 15 is divided into a dehumidification section and a heat exchange section. The circulating hot air passes through the dehumidification heat exchange device 15. The dehumidification section removes the water vapor content in the hot air. The dehumidified gas exchanges heat with the steam heat exchanger 41 in the heat exchange section to generate hot air, and then re-enters the low-temperature drying device 13 to dry the sludge.

[0128] In this embodiment, a cyclone dust collector 29 is provided between the rotary drum 24 and the combustion chamber 212 .

[0129] The discharge end of the rotary drum 24 is connected to the discharge unit 3 and the cyclone dust collector 29 through the furnace cover 26. In this embodiment, the cyclone dust collector 29 is connected to an ash bucket 27 through a second star valve 28; a first fan 210 is provided on the pipeline between the cyclone dust collector 29 and the combustion chamber 212.

[0130] In this embodiment, a burner 211 is provided on the combustion chamber 212 ; and a second fan 213 is provided on the pipeline between the combustion chamber 212 and the steam heat exchanger 41 .

[0131] In this embodiment, the feeding end of the rotary drum 24 is connected to the feeding hopper 21 through the furnace tail cover 23, and the output end of the feeding hopper 21 is provided with a first star valve 22.

[0132] In this embodiment, a lifting plate is provided in the rotary drum 24 to increase the contact area between the material and the double-layer pyrolysis furnace wall, and a guide plate is provided in the flue gas interlayer 25 to improve the heat exchange efficiency.

[0133] In this embodiment, a shaftless screw is provided in the pipe between the rotary drum 24 and the combustion chamber 212 for regularly cleaning dirt on the pipe wall.

[0134] A shaftless screw is installed in the pipeline to regularly clear blockages during operation, allowing the equipment to operate for a long time.

[0135] The working principle of this embodiment: the sludge from the sewage treatment plant has a moisture content of more than 90%. After passing through the mechanical dehydration device 11, the moisture content is reduced to 60-70%, and then sent to the low-temperature drying device 13 through the first screw conveyor 12. Under the action of circulating hot air, the moisture content of the sludge is reduced to 15-30%. The circulating hot air is the hot air generated by the circulation of gas between the dehumidification heat exchange device 15 and the low-temperature drying device 13. The circulating hot air passes through the dehumidification heat exchange device 15, exchanges heat with the saturated steam from the steam heat exchanger 41 to generate dry hot air, and re-enters the low-temperature drying device 13 to dry the sludge. After drying, the sludge enters the drying silo from the outlet of the low-temperature drying device 13. The sludge in the drying silo is sent to the feed hopper 21 of the pyrolysis unit 2 through the second screw conveyor 14 to complete the treatment of the sludge pretreatment unit 1.

[0136] The dried sludge passes through the first star valve 22, and then enters the rotary drum 24 in the double-layer pyrolysis furnace through the furnace tail cover 23, and at the same time, the rotary drum 24 is sealed with the outside world. Intermittent lifting plates are arranged in the rotary drum 24, which increases the contact area between the material and the furnace wall on the basis of realizing controllable material transportation. The material is lifted, dropped, and crushed with the lifting plates, which is beneficial to the heat transfer of the material. The outer periphery of the rotary drum 24 is a high-temperature flue gas interlayer 25 with a temperature of 700℃-800℃. The hot flue gas in the flue gas interlayer 25 is all supplied by natural gas or other heat sources in the combustion chamber 212 at the initial stage of the furnace opening. The hot flue gas indirectly exchanges heat with the material in the rotary drum 24 in the flue gas interlayer 25. The flue gas interlayer 25 is arranged with a guide plate to improve the heat exchange efficiency. Under the conveyance of the rotary drum 24, the sludge is sent from the tail end to the head end of the furnace, and the pyrolysis gas generated by the pyrolysis of the sludge is drained by the first fan 210, enters the cyclone dust collector 29 from the head cover 26, removes large particles of dust in the pyrolysis gas, enters the combustion chamber 212, and burns with natural gas, gradually reducing the supply of natural gas; the combustion air is preheated and supplied by the air heat exchanger 42, and in order to efficiently utilize the waste heat of the flue gas, a part of the hot flue gas at the outlet of the steam heat exchanger 41 is introduced into the combustion chamber 212, reducing the oxygen concentration in the combustion chamber 212, thereby reducing the generation of nitrogen oxides, and at the same time, the flue gas temperature can be controlled at 700℃-800℃, ensuring pyrolysis while reducing the damage of the high-temperature flue gas to the rotary drum 24; after the high-temperature flue gas completes pyrolysis and heat supply in the flue gas interlayer 25, the temperature drops to below 500℃, enters the steam heat exchanger 41 and can be used in other links, and the sludge charcoal enters the discharge unit 3 from the head cover 26.

[0137] The high-temperature sludge charcoal enters the two-stage water-cooling spiral from the furnace head cover 26 , and after cooling, the temperature drops to below 80° C. and enters the charcoal storage bin 33 for temporary storage. A part of the hot water from the water-cooling spiral is used as water for the steam heat exchanger 41 .

[0138] The flue gas at the outlet of the flue gas interlayer 25 enters the steam heat exchanger 41 for heat exchange to produce saturated steam. The saturated steam exchanges heat with the circulating hot air of the low-temperature drying device 13. After cooling, it returns to the steam heat exchanger 41 for re-heating. In this embodiment, the flue gas temperature at the outlet of the steam heat exchanger 41 is controlled at 180°C 250°C. The outlet flue gas passes through the two-stage heat exchanger of the exhaust gas treatment unit, and the two-stage heat exchangers are an air heat exchanger and a flue gas heat exchanger. The flue gas temperature after heat exchange drops to below 100°C, enters the spray tower 44 for desulfurization, the demister 45 for demisting, and the adsorption box 46 for purification. Then, it returns to the flue gas heat exchanger 43 for heat exchange and de-whitening with the flue gas, and is discharged through the chimney 48 through the third fan 47.

[0139] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A sludge pyrolysis method, characterized in that: The method comprises the following steps: Step 1: Pretreatment: The pretreatment includes dehydration and drying. The dehydrated sludge is dried under the action of circulating gas at 70℃-100℃, so that the moisture content of the sludge is controlled at 15%-30%; Step 2, pyrolysis: the sludge treated in step 1 is fed into the rotary drum of the double-layer pyrolysis furnace to undergo pyrolysis reaction to produce sludge charcoal and pyrolysis gas. The pyrolysis gas is burned to obtain high-temperature flue gas, which is returned to the flue gas interlayer of the double-layer pyrolysis furnace to pyrolyze the sludge; Step 3, flue gas utilization: the flue gas at the outlet of the flue gas interlayer exchanges heat with the steam heat exchanger to generate saturated steam of 135°C-150°C, the saturated steam exchanges heat with the circulating gas, the circulating gas temperature after heat exchange is controlled at 70°C-100°C, the saturated steam after heat exchange generates liquid water and returns to the steam heat exchanger; a part of the low-temperature flue gas after heat exchange between the flue gas at the outlet of the flue gas interlayer and the steam heat exchanger enters step 2 for combustion and temperature adjustment, and the other part is used for preheating air, the preheated air is used for combustion and combustion support in step 2, and the flue gas after preheating air is discharged after exhaust gas purification; The temperature of the low-temperature flue gas after heat exchange is 180°C-250°C. The low-temperature flue gas after heat exchange enters step 2 for combustion and temperature adjustment through the second fan. The temperature of the generated high-temperature flue gas entering the flue gas interlayer is 700°C-800°C.

2. A sludge pyrolysis method according to claim 1, characterized in that: The circulating gas dried in step 1 is dehumidified and then exchanges heat with saturated steam.

3. A sludge pyrolysis method according to claim 2, characterized in that: Part of the circulating gas dried in step 1 can enter step 2 for combustion treatment.

4. A sludge pyrolysis method according to claim 1, characterized in that: The flue gas interlayer outlet is provided with a first sensor, the steam heat exchanger is provided with a second sensor for detecting steam temperature, the first sensor and the second sensor are both connected to a controller, and the controller is connected to a pump body for controlling the water volume in the steam heat exchanger.

5. A sludge pyrolysis method according to claim 4, characterized in that: The outlet of the steam heat exchanger is provided with a third sensor for detecting the temperature of the low-temperature flue gas after heat exchange, and the third sensor is connected to the controller.

6. A sludge pyrolysis method according to claim 5, characterized in that: The second fan is connected to a controller, and the controller is connected to a fourth sensor for detecting the temperature of high-temperature smoke in the smoke layer.

7. A sludge pyrolysis method according to claim 1, characterized in that: In step three, the flow rates of saturated steam and circulating gas are both controllable.

8. A sludge pyrolysis method according to claim 7, characterized in that: The saturated steam delivery pipeline and the circulating gas delivery pipeline are both provided with a flow meter and a solenoid valve, the flow meter and the solenoid valve are both connected to a controller, and the controller is connected to a fifth temperature sensor for detecting the temperature of the circulating gas.

9. A sludge pyrolysis method according to claim 1, characterized in that: The flue gas temperature at the flue gas interlayer outlet is 300-500°C.

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