A sludge drying and carbonization treatment system and method based on thermal hydrolysis pretreatment

Abstract

The present invention discloses a sludge drying and carbonization treatment system and method based on thermal hydrolysis pretreatment, comprising: a wet sludge silo is connected to a thermal hydrolysis reactor, a sludge outlet of the thermal hydrolysis reactor is connected to a mechanical dehydration device, the mechanical dehydration device is connected to a mixing screw feeder, and the mixing screw feeder is connected to a carbonization device; a biomass feed port is also provided on the mixing screw feeder; the pyrolysis gas outlet of the carbonization device is connected to the combustion inlet of a hot blast furnace; the gas outlet of the mechanical dehydration device is connected to a condenser; the condenser is connected to a hot blast furnace; the smoke outlet of the hot blast furnace is connected to the heat source inlet of the carbonization device; and the heat source outlet of the carbonization device is connected to a waste heat recovery system. The present invention has no requirements on the moisture content of the sludge and does not require the addition of drugs for conditioning, effectively improves the output of pyrolysis gas, realizes the self-sustaining supply of energy for the coupled carbonization process of sludge and biomass, and thus realizes the continuous operation of the sludge thermal hydrolysis and carbonization process.

Description

Technical Field

[0001] The invention belongs to the technical field of sludge treatment and disposal, and specifically relates to a sludge drying and carbonization treatment system and method based on thermal hydrolysis pretreatment. Background Art

[0002] Sludge is a semi-solid or solid substance produced during the sewage treatment process, excluding screens, scum and grit. Sludge from urban sewage treatment plants is a product of sewage treatment, mainly from process links such as primary sedimentation tanks and secondary sedimentation tanks. With the increase in environmental protection policies, the harmless treatment and disposal of sludge has been continuously valued. In recent years, the national sludge production has continued to rise. According to statistics, the total amount of urban sludge (80% water content) in 2020 has reached 51.3 million tons per day, and the pressure for harmless treatment and disposal of sludge is enormous.

[0003] Sludge drying is an important part of the harmless treatment and disposal of sludge. Its reliability and economy directly affect the reliability and economy of the subsequent disposal process. Sludge dehydration and drying can be divided into: natural drying, mechanical dehydration and thermal drying. Natural drying is restricted by factors such as climate and site, and is basically unable to adapt to the increasing amount of sludge today. Traditional sludge mechanical dehydration cannot meet the requirements of moisture content in the subsequent sludge disposal process. Due to the high moisture content of the sludge, it cannot meet the moisture requirements of the current sludge terminal treatment and can only be used as a pretreatment before sludge thermal drying. Thermal drying, with its own advantages, such as high efficiency, large processing capacity, and high degree of automation, is the main development direction of sludge drying and dehydration technology in the future.

[0004] However, existing sludge thermal hydrolysis technology is mainly used for sludge with high moisture content (>80%). At this time, the moisture content of the sludge is too high, and most of the heat required for high-temperature thermal hydrolysis of the sludge is used to increase the water temperature, resulting in high energy consumption, long time, low processing efficiency, large equipment size and other problems.

[0005] Patent document CN112094004A discloses a novel sludge thermal hydrolysis treatment system and method with a recyclable carbon source, which increases the dissolution rate of COD through thermal hydrolysis, and reduces the content of ammonia nitrogen and phosphorus in the waste liquid by adding magnesium salts and struvite precipitation without adding phosphate salts, providing a carbon source for the sewage treatment plant, and recycling the heat generated by the incineration of the sludge itself into the thermal hydrolysis process, reducing the consumption of heat and energy, and obtaining struvite fertilizer. However, this method still requires the addition of chemical drugs such as strong alkali, CaO and magnesium-containing compounds, which not only increases the cost of the agent, but also increases the cost of the back-end sewage treatment and the operating risk of the workers.

[0006] Patent document CN109626783A discloses a sludge treatment process of ultra-high temperature biological drying coupled with fluidized bed incineration, which includes mechanical dewatering sludge with a moisture content of 75%-80%; pretreatment of the dewatered sludge, including sludge thermal hydrolysis and sediment separation; ultra-high temperature biological drying of the pretreated sludge; and finally, transfer the biologically dried sludge to a cyclonic fluidized bed incinerator for incineration, and the high-temperature flue gas generated by the combustion enters the steam waste heat boiler, and the slag is solidified and landfilled. However, the biological ultra-high temperature fermentation and sludge ultra-high temperature drying cycle of this method is 17-26 days, which takes a long time and requires the addition of fermentation bacteria, and the production process is complicated and the cost is high. Summary of the invention

[0007] The technical problem to be solved by the present invention is to provide a sludge drying and carbonization treatment system and method based on thermal hydrolysis pretreatment, so as to expand the application schemes and approaches for safe treatment and disposal of sludge.

[0008] The purpose of the present invention is achieved through the following technical solutions:

[0009] The present invention discloses a sludge drying and carbonization treatment system based on thermal hydrolysis pretreatment, characterized in that it comprises: a wet sludge silo, which is connected to the sludge inlet of a thermal hydrolysis reactor, and the sludge outlet of the thermal hydrolysis reactor is connected to the sludge inlet of a mechanical dehydration device, characterized in that the sludge outlet of the mechanical dehydration device is connected to the inlet of a mixing screw feeder, and the mixing screw feeder is also provided with a biomass feed inlet; the outlet of the mixing screw feeder is connected to the inlet of a carbonization device; the pyrolysis gas outlet of the carbonization device is connected to the combustion inlet of a hot blast furnace; the gas outlet of the mechanical dehydration device is connected to the gas phase inlet of a condenser; the gas phase outlet of the condenser is connected to the combustion inlet of a hot blast furnace; the smoke exhaust port of the hot blast furnace is connected to the heat source inlet of the carbonization device; the heat source outlet of the carbonization device is connected to a waste heat recovery system.

[0010] A sludge drying and carbonization treatment method based on thermal hydrolysis pretreatment of the present invention is characterized by comprising the following steps:

[0011] (1) Put a certain amount of wet sludge into the thermal hydrolysis reactor at one time and close the sludge inlet; slowly introduce saturated water vapor and continuously stir the sludge until the thermal hydrolysis reactor reaches the specified pressure and temperature; maintain constant temperature and pressure for thermal hydrolysis reaction for a period of time (the specific time varies according to the water content and organic matter content of the sludge);

[0012] (2) Stop supplying the saturated water vapor, then release the high-temperature, moist odor in the thermal hydrolysis reactor, and slowly adjust the reactor to normal temperature and pressure; send the hydrolyzed sludge to a mechanical dehydration device, and obtain dry sludge with a moisture content of no more than 40% through dehydration; send the high-temperature, moist odor to a condenser for cooling and dehumidification to obtain low-humidity odor and wastewater; send the low-humidity odor to a hot air furnace for incineration, and discharge the wastewater through a sewage pipe for separate treatment;

[0013] (3) The dry sludge is fed into a mixing screw feeder, mixed with biomass in a certain proportion, and then fed into a carbonization device for carbonization reaction to generate pyrolysis gas, tar and carbonized products; the pyrolysis gas carries tar into a hot air furnace and burns with the low-humidity odor to generate high-temperature flue gas;

[0014] (4) The high-temperature flue gas enters the carbonization device as a heat source to maintain the reaction temperature. The outlet flue gas is sent to the waste heat recovery system to exchange heat with fresh desalted water to generate saturated water vapor, which serves as the heat source of the thermal hydrolysis reactor.

[0015] Preferably, the saturated water vapor in step (1) is saturated water vapor generated from a waste heat recovery system, with a pressure of 1.5 to 2.0 MPa and a temperature of 180 to 220°C.

[0016] Preferably, the pressure of the thermal hydrolysis reaction in step (1) is 1.5-2.0 MPa, the temperature is 180-215° C., and the reaction time is not less than 20 min.

[0017] Preferably, the carbonization device in step (3) operates at a slightly negative pressure, with a pressure of -0.03 to 0 MPa and a temperature of 400 to 500°C.

[0018] Compared with the prior art, the advantages of the present invention are:

[0019] Compared with mechanical dehydration of sludge, the sludge of the present invention does not need to be conditioned with water or chemical agents, thus reducing the cost of sewage treatment and the cost of agents at the back end. Compared with traditional steam thermal drying, the water in the sludge thermal hydrolysis reaction of the present invention does not undergo phase change, greatly reducing the energy consumption of steam; moreover, the amount of odor generated is very small, the condenser is small in size, the concentration is high, and it can be directly burned. Compared with ordinary thermal hydrolysis, the thermal hydrolysis technology of the present invention is similar to the principle of a pressure cooker. There is no need to dilute the incoming sludge to more than 90% before adding chemicals for conditioning, and there is no strict requirement for the moisture content of the sludge; the yield of pyrolysis gas can be effectively increased, and the energy self-sustaining supply of the sludge and biomass coupled carbonization process can be achieved by adjusting the amount of biomass added, thereby achieving continuous operation of the sludge thermal hydrolysis and carbonization process. The present invention can achieve the coordinated treatment of sludge and conventional agricultural and forestry wastes, and the carbonization process is conducive to carbon sinks and promotes carbon emission reduction. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of an embodiment of the device of the present invention;

[0021] In the figure, 1-wet sludge silo, 2-thermal hydrolysis reactor, 3-mechanical dehydration equipment, 4-mixing screw feeder, 5-carbonization device, 6-condenser, 7-hot air furnace, 8-waste heat recovery system, 9-spiral water cooler.

[0022] The attached drawings are not drawn to scale, but are intended to illustrate the basic principles and basic structure of the present invention. The structural features and components in the drawings are simplified. The implementation methods covered by the technical solution of the present invention are not limited to the implementation methods and examples listed in the attached drawings. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. 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.

[0024] like Figure 1 A sludge drying and carbonization treatment system based on thermal hydrolysis pretreatment comprises: a wet sludge silo 1, the wet sludge silo 1 is connected to the sludge inlet of the thermal hydrolysis reactor 2, the sludge outlet of the thermal hydrolysis reactor 2 is connected to the sludge inlet of the mechanical dehydration device 3, characterized in that the sludge outlet of the mechanical dehydration device 3 is connected to the inlet of the mixing screw feeder 4, and the mixing screw feeder 4 is also provided with a biomass feed inlet; the outlet of the mixing screw feeder 4 is connected to the inlet of the carbonization device 5; the pyrolysis gas outlet of the carbonization device 5 is connected to the combustion inlet of the hot blast furnace 7; the gas outlet of the mechanical dehydration device 3 is connected to the gas phase inlet of the condenser 6; the gas phase outlet of the condenser 6 is connected to the combustion inlet of the hot blast furnace 7; the smoke exhaust port of the hot blast furnace 7 is connected to the heat source inlet of the carbonization device 5; the heat source outlet of the carbonization device 5 is connected to the waste heat recovery system 8.

[0025] Furthermore, the wet sludge silo 1 is connected to the thermal hydrolysis reactor 2 via a screw pump or a plunger pump; the thermal hydrolysis reactor 2 and the mechanical dehydration equipment 3 are connected via a fluid pump that meets the requirements.

[0026] Furthermore, the carbide outlet of the carbonization device 5 is externally provided with a spiral water cooler for cooling the carbide.

[0027] Furthermore, since the thermal hydrolysis reactor (2) is operated intermittently, the thermal hydrolysis reactor (2) is preferably composed of two or more thermal hydrolysis reactors connected in parallel to ensure continuous operation of subsequent equipment.

[0028] Example 1

[0029] A certain place produces 90 tons of sludge with a moisture content of 80% per day. The sludge drying and carbonization treatment method based on thermal hydrolysis pretreatment of the present invention is used to safely treat and dispose of the sludge. The process is as follows:

[0030] (1) First, put the sludge into the wet sludge silo 1 for temporary storage, and transport 5 tons of sludge into a thermal hydrolysis reactor 2 (3 thermal hydrolysis reactors are connected in parallel, and the processing capacity of a single reactor is 5 tons / time) through a plunger pump or a screw pump, and close the sludge inlet; when starting the furnace, first add auxiliary fuel through the hot blast furnace 7, and directly enter the waste heat recovery system 8 to generate saturated water vapor with a pressure of 1.7MPa and a temperature of 205℃; slowly pass the saturated water vapor into the thermal hydrolysis reactor 2 to directly contact and exchange heat with the sludge. The thermal hydrolysis reactor 2 is equipped with a stirring device to continuously stir the sludge until the pressure in the reactor reaches 1.6MPa and the temperature reaches 200℃; maintain constant temperature and pressure for thermal hydrolysis reaction for about 30 minutes to promote the decomposition of high molecular organic matter in the sludge into small molecules;

[0031] (2) Stop supplying saturated water vapor, then open the exhaust valve to slowly release the high-temperature, moist odor inside, and slowly adjust the temperature and pressure inside the thermal hydrolysis reactor 2; send the high-temperature, moist odor into the condenser 6 for cooling and dehumidification to obtain low-humidity odor and wastewater; send the low-humidity odor to the hot air furnace 7 for incineration, and the wastewater is discharged through the sewage pipe for separate treatment;

[0032] The entire thermal hydrolysis reaction, from feeding, heating, maintaining temperature, pressure relief, to discharging, takes a total of 3 hours for one batch; after the pressure release of the thermal hydrolysis reactor 2 is completed, the remaining hydrolyzed sludge in it is sent to the mechanical continuous high-drying dehydration equipment 3, and the dry sludge with a moisture content of about 35% is obtained by dehydration;

[0033] (3) The dry sludge is fed into the mixing screw feeder 4, mixed with the biomass in a certain proportion, and then fed evenly into the carbonization device 5; the mixed fuel of the dry sludge and biomass undergoes a carbonization reaction at a pressure of -0.02MPa and a temperature of 425°C to generate pyrolysis gas, tar and carbide; the carbide is cooled by the water-cooling screw 8 and then sent to the carbide storage bin for storage and further treatment; the pyrolysis gas carries the tar into the hot air furnace 7 and burns with the low-humidity odor from the condenser 6 to generate high-temperature flue gas;

[0034] (4) The high-temperature flue gas enters the carbonization device 5, providing a high-temperature environment to maintain the bed temperature of the carbonization device 5; the outlet flue gas of the carbonization device 5 is sent to the waste heat recovery system 9, and exchanges heat with fresh desalted water to generate saturated steam of 1.5-2.0 MPa, which serves as the heat source of the thermal hydrolysis reactor 2; the flue gas after waste heat recovery is sent to the exhaust gas treatment system for purification and then meets the emission standards.

[0035] Since the water in the sludge does not undergo a gasification process during the heating process, less steam is used, approximately 300 kg steam / ton of water, which is much lower than the steam consumption of conventional sludge steam thermal drying processes (approximately 1.2 tons of steam / ton of water).

Claims

1. A sludge drying and carbonization treatment system based on thermal hydrolysis pretreatment, comprising: A wet sludge silo (1), wherein the wet sludge silo (1) is connected to the sludge inlet of a thermal hydrolysis reactor (2), and the sludge outlet of the thermal hydrolysis reactor (2) is connected to the sludge inlet of a mechanical dehydration device (3), characterized in that the sludge outlet of the mechanical dehydration device (3) is connected to the inlet of a mixing screw feeder (4), and the mixing screw feeder (4) is also provided with a biomass feed inlet; the outlet of the mixing screw feeder (4) is connected to the inlet of a carbonization device (5); the pyrolysis gas outlet of the carbonization device (5) is connected to the combustion inlet of a hot blast furnace (7); the gas outlet of the thermal hydrolysis reactor (2) is connected to the gas phase inlet of a condenser (6); the gas phase outlet of the condenser (6) is connected to the combustion inlet of a hot blast furnace (7); the smoke outlet of the hot blast furnace (7) is connected to the heat source inlet of the carbonization device (5); and the heat source outlet of the carbonization device (5) is connected to a waste heat recovery system (9); The thermal hydrolysis reactor (2) is operated intermittently, and is composed of two or more thermal hydrolysis reactors connected in parallel. The saturated water vapor required is the saturated water vapor generated by the waste heat recovery system (9), and the pressure is 1.5-2.0 MPa and the temperature is 180-220° C. The pressure of the thermal hydrolysis reaction is 1.5-2.0 MPa, the temperature is 180-215° C., and the reaction time is not less than 20 minutes. The carbonization device operates at a slightly negative pressure, the pressure is -0.03-0 MPa, and the temperature is 400-425° C.

2. The sludge drying and carbonization treatment system according to claim 1, characterized in that: The wet sludge silo (1) is connected to the thermal hydrolysis reactor (2) via a screw pump or a plunger pump; the thermal hydrolysis reactor (2) and the mechanical dehydration equipment (3) are connected via a fluid pump that meets the requirements.

3. The sludge drying and carbonization treatment system according to claim 1, characterized in that: The carbide outlet of the carbonization device (5) is externally provided with a spiral water cooler (8).

4. A sludge drying and carbonization treatment method based on thermal hydrolysis pretreatment, characterized in that: The following steps are involved: (1) Put a certain amount of wet sludge into the thermal hydrolysis reactor at one time, and close the sludge inlet; slowly introduce saturated water vapor and continuously stir the sludge until the thermal hydrolysis reactor reaches the specified pressure and temperature; maintain the thermal hydrolysis reaction at a constant temperature and pressure for a period of time; the saturated water vapor is the saturated water vapor generated by the waste heat recovery system; (2) Stop supplying the saturated water vapor, then release the high-temperature, moist odor in the thermal hydrolysis reactor, and slowly adjust the reactor to normal temperature and pressure; send the hydrolyzed sludge to a mechanical dehydration device, and obtain dry sludge with a moisture content of no more than 40% through dehydration; send the high-temperature, moist odor to a condenser for cooling and dehumidification to obtain low-humidity odor and wastewater; send the low-humidity odor to a hot air furnace for incineration, and discharge the wastewater through a sewage pipe for separate treatment; (3) The dry sludge is fed into a mixing screw feeder, mixed with biomass in a certain proportion, and then fed into a carbonization device for carbonization reaction to generate pyrolysis gas, tar and carbonized products; the pyrolysis gas carries tar into a hot air furnace and burns with the low-humidity odor to generate high-temperature flue gas; the carbonization device operates at a slightly negative pressure, with a pressure of -0.03 to 0 MPa and a temperature of 400 to 500°C; (4) The high-temperature flue gas enters the carbonization device as a heat source to maintain the reaction temperature. The outlet flue gas is sent to the waste heat recovery system to exchange heat with fresh desalted water to generate saturated water vapor, which serves as the heat source of the thermal hydrolysis reactor.

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