A sludge anti-wall-sticking continuous pyrolysis method and system based on in-situ coating and granulation of pyrolysis carbon powder

Abstract

The present application relates to a kind of sludge anti-wall sticking continuous pyrolysis method and system based on pyrolysis carbon powder in-situ coating granulation, the method includes the following steps: dry sludge is pyrolyzed under anaerobic or low-oxygen condition, oil gas and high-temperature pyrolysis carbon powder are generated, high-temperature pyrolysis carbon powder is carried out online screening, small particle size high-temperature pyrolysis carbon powder is separated, and small particle size high-temperature pyrolysis carbon powder is backflowed to premixing modification bin, small particle size high-temperature pyrolysis carbon powder is formed with wet sludge in premixing modification bin and bulk granule;Bulk granule is continuously sent into pyrolysis reactor, and pyrolysis is carried out under anaerobic or low-oxygen condition, oil gas and high-temperature pyrolysis carbon powder are generated, and high-temperature pyrolysis carbon powder is continuously carried out online screening.The method of the present application recovers and utilizes the sensible heat effect of high-temperature pyrolysis carbon, modifies wet sludge in-situ before pyrolysis, makes it cross the plasticity stage, and directly converts into bulk granule with self-lubricating characteristics, so that continuous and stable pyrolysis under no drying process is realized.

Description

Technical Field

[0001] This invention belongs to the field of sludge treatment technology, specifically relating to a continuous pyrolysis method and system for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder. Background Technology

[0002] Pyrolysis technology, as a thermochemical treatment method that converts organic matter into bio-oil, combustible gas, and biochar under anaerobic or hypoxic conditions, has become a research hotspot in sludge treatment due to its thorough volume reduction, high heavy metal solidification rate, and high energy recovery efficiency.

[0003] Despite the promising prospects of pyrolysis technology, in practical engineering applications, especially in the continuous pyrolysis process of viscous sludge with high water content, the following technical bottlenecks remain difficult to overcome: (1) Coking and clogging problems caused by the viscous zone: Municipal sludge is a non-Newtonian fluid with special rheological properties. During the pyrolysis heating process, especially when the water content is in the range of 40%-60%, the sludge will experience a "plastic viscous phase" stage. In this stage, the sludge is very easy to adhere to the feed screw, stirring blades and reactor inner wall. As the temperature further increases, the adhesion layer carbonizes and condenses, forming a hard "coking layer". This will not only cause the reactor heat transfer efficiency to drop sharply and increase the thermal resistance, but in severe cases, it may even seize the conveyor shaft, forcing the system to stop for cleaning, which greatly limits the stable operation of the continuous pyrolysis device. (2) Pre-drying consumes a lot of energy and has low thermal efficiency: The moisture content of wet sludge is usually as high as 80%, making direct pyrolysis difficult. Existing processes usually adopt the method of "drying first and then pyrolyzing", that is, using equipment such as paddle dryers to dry the sludge to a moisture content of less than 20% before pyrolysis. The drying process requires a lot of fossil energy or electrical energy, and the latent heat loss during the drying process is huge. In addition, the high-temperature solid products (pyrolytic carbon) produced by pyrolysis are usually discharged directly by water cooling or air cooling, and the large amount of high-grade sensible heat they carry is not effectively utilized, resulting in energy waste. (3) Heat and mass transfer is limited and the reaction is uneven: Sludge is a poor conductor of heat. Under the traditional block feeding mode, the phenomenon of external carbonization and internal carbonization is very likely to occur, that is, the surface of the particles has been overheated and carbonized, while the internal moisture has not been evaporated. This results in the underdeveloped pore structure of the produced biochar and large fluctuations in the quality of oil and gas products.

[0004] Therefore, there is an urgent need to develop a new continuous pyrolysis process that does not require separate high-energy-consuming drying equipment and can effectively overcome the problem of sludge coking. This invention addresses these needs by utilizing high-temperature pyrolysis carbon powder produced by the pyrolysis system itself as a heat carrier and coating agent, proposing an innovative solution. Summary of the Invention

[0005] To address the technical problems in existing municipal sludge pyrolysis treatment technologies, such as severe coking and sticking of feed sludge, high energy consumption for raw material drying, and difficulties in continuous feeding and conveying, this invention provides a continuous pyrolysis method and system for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder. By recycling the sensible heat of high-temperature pyrolytic carbon, the wet sludge is in-situ coated and modified before pyrolysis, allowing it to bypass the viscoplastic stage and directly transform into granular particles with self-lubricating properties, thereby achieving continuous and stable pyrolysis without a drying process.

[0006] The technical solution of the present invention is as follows:

[0007] This invention provides a continuous pyrolysis method for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder, comprising the following steps:

[0008] S1. Pyrolysis of dried sludge;

[0009] After drying, the sludge is fed into the pyrolysis reactor through a premixed modification chamber and pyrolyzed under anaerobic or low-oxygen conditions to produce oil and gas and high-temperature pyrolysis carbon powder. The oil and gas are then recovered as bio-oil and non-condensable gases through an oil and gas condensation and recovery device.

[0010] S2, pyrolytic carbon screening and reflux;

[0011] The high-temperature pyrolysis carbon powder obtained in step S1 is screened online to separate small-particle-size high-temperature pyrolysis carbon powder. The small-particle-size high-temperature pyrolysis carbon powder is returned to the premixed modification chamber through a heat-insulated conveying device. At the same time, wet sludge is sent into the premixed modification chamber, and the remaining high-temperature pyrolysis carbon is collected as a product.

[0012] S3, in-situ coating granulation;

[0013] Under the mechanical stirring action in the premixed modification chamber, the residual heat and hydrophobic properties of the small-particle-size high-temperature pyrolysis carbon powder are used to break up the wet sludge and form a dried carbon powder coating layer on the surface, finally obtaining granular particles with an outer dry and inner wet structure.

[0014] S4. Prevents wall-sticking pyrolysis;

[0015] The granular particles obtained in step S3 are continuously fed into the pyrolysis reactor. When the granular particles come into contact with the wall of the pyrolysis reactor, they rely on the dried carbon powder coating layer on the surface to achieve self-lubrication and anti-sticking, and pyrolyze under oxygen-free or low-oxygen conditions to produce oil and gas and high-temperature pyrolysis carbon powder.

[0016] S5. Product separation and recycling;

[0017] The oil and gas obtained in step S4 are processed by an oil and gas condensation and recovery device to recover bio-oil and non-condensable gas; at the same time, the high-temperature pyrolysis carbon powder obtained in step S4 is further processed in step S2.

[0018] According to a preferred embodiment of the present invention, in step S1, the moisture content of the dried sludge is 30% to 40%.

[0019] According to a preferred embodiment of the present invention, in step S2, the aperture of the sieve for online screening is set to 0.5 mm to 2 mm.

[0020] According to a preferred embodiment of the present invention, in step S2, the temperature of the small-particle-size high-temperature pyrolysis carbon powder is maintained between 400°C and 600°C when it is returned through the heat-insulating conveying device, so as to facilitate the subsequent use of sensible heat to instantly evaporate the surface moisture of the wet sludge and destroy the colloidal viscous structure of the wet sludge.

[0021] According to a preferred embodiment of the present invention, in step S2, the mass ratio of the small-particle-size high-temperature pyrolysis carbon powder to the wet sludge is (0.5~1.5):1; more preferably, the mass ratio of the small-particle-size high-temperature pyrolysis carbon powder to the wet sludge is (0.8~1.2):1.

[0022] According to a preferred embodiment of the present invention, in step S2, the moisture content of the wet sludge is 60% to 80%.

[0023] According to a preferred embodiment of the present invention, in step S3, the overall moisture content of the mixed granules is 30% to 40%.

[0024] According to a preferred embodiment of the present invention, in step S3, a stirring device is provided in the premixed modification chamber, and the stirring device is a dual-shaft differential speed stirring paddle or a plow-type stirrer; more preferably, the stirring device is a dual-shaft differential speed stirring paddle, and the end linear velocity of the dual-shaft differential speed stirring paddle is controlled in the range of 2~5m / s, so as to ensure that the small-particle-size high-temperature pyrolysis carbon powder can be uniformly embedded and coated on the surface of the wet sludge clumps, rather than simple macroscopic mixing.

[0025] According to a preferred embodiment of the present invention, in steps S1 and S4, the pyrolysis temperature is 500~800℃.

[0026] According to a preferred embodiment of the present invention, in step S5, the non-condensable gas, after purification, is introduced into the heating jacket or combustion chamber of the pyrolysis reactor for combustion, providing a heat source for the pyrolysis reaction and achieving energy self-sustainability of the system.

[0027] The present invention also provides a system for the above-mentioned continuous pyrolysis method for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder.

[0028] A continuous pyrolysis system for preventing sludge from sticking to the wall, based on in-situ coating and granulation of pyrolytic carbon powder, includes a premixing and modification chamber. The inlet of the premixing and modification chamber is connected to a sludge hopper. The outlet of the premixing and modification chamber is connected to a pyrolysis reactor. The oil and gas outlet of the pyrolysis reactor is connected to an oil and gas condensation and recovery device. The carbon powder outlet of the pyrolysis reactor is connected to a carbon powder screen. The carbon powder screen is connected to the premixing and modification chamber via a heat-insulated conveying device. The outlet of the carbon powder screen is connected to a carbon powder storage device.

[0029] According to a preferred embodiment of the present invention, the pyrolysis reactor is an externally heated screw propulsion reactor or a rotary kiln reactor.

[0030] The technical features and beneficial effects of this invention are as follows:

[0031] 1. The method of the present invention forms a dried carbon powder coating layer on the surface of wet sludge through a hot carbon coating process, forming granular particles with an outer dry and inner wet structure. After entering the pyrolysis reactor, the dry hydrophobic carbon powder is in contact with the wall, realizing the self-lubricating conveying of materials. There is no need to install a complicated mechanical scraper descaling device in the pyrolysis reactor, which significantly improves the stability of equipment operation.

[0032] 2. The method of the present invention cleverly utilizes the sensible heat properties of high-temperature pyrolytic carbon itself, which can be directly used for preheating and surface drying of wet sludge, realizing the cascade utilization of thermal energy, significantly reducing energy consumption, and eliminating the expensive pre-drying process and equipment investment.

[0033] 3. The method of the present invention uses small-particle-size high-temperature pyrolysis carbon powder to reflux and mix with wet sludge, which greatly increases the specific surface area and porosity of wet sludge. In addition, the carbon powder, as a good heat-conducting medium, improves the heat transfer performance inside the sludge and avoids the phenomenon of burnt outside and raw inside when pyrolyzing large sludge blocks in the traditional method. This makes the pyrolysis reaction more thorough and the produced carbon powder more uniform in quality.

[0034] 4. The method of the present invention utilizes the solid waste (pyrolytic carbon) generated by itself to assist in the treatment of raw materials (wet sludge), without the need for external chemical conditioners or physical fillers (such as lime, sawdust), thus reducing operating costs; at the same time, the granular material can form a material blockage effect, which helps to prevent pyrolysis gas from leaking out of the feed inlet compared with blocky wet sludge, thereby improving the oil and gas yield and simplifying the sealing system of the pyrolysis reactor. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a continuous pyrolysis device for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolysis carbon powder according to Embodiment 1 of the present invention; wherein, 1, sludge hopper, 2, premixed modification bin, 3, pyrolysis reactor, 4, carbon powder screener, 5, carbon powder storage device, 6, heat-insulated conveying device, 7, oil and gas condensation and recovery device.

[0036] Figure 2 This is a schematic diagram of in-situ coating granulation in the premixed modified chamber according to Embodiment 1 of the present invention. Detailed Implementation

[0037] The present invention will be further described below with reference to embodiments, but is not limited thereto. The described embodiments are some embodiments of the present invention. Based on these embodiments, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0038] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other. Unless otherwise specified in the embodiments of the present invention, all techniques existing in the art can be used.

[0039] Example 1

[0040] like Figures 1-2 As shown, this embodiment provides a continuous pyrolysis method for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder, including the following steps:

[0041] S1. Pyrolysis of wet sludge;

[0042] The dried sludge with a moisture content of 30% is added to the sludge hopper 1, and then sent to the pyrolysis reactor 3 through the premixed modification bin 2. It is then pyrolyzed under anaerobic or low-oxygen conditions at a temperature of 700℃ to produce oil gas and high-temperature pyrolysis carbon powder. The oil gas is then recovered by the oil gas condensation and recovery device 7 to recover bio-oil and non-condensable gases.

[0043] S2, pyrolytic carbon screening and reflux;

[0044] The high-temperature pyrolysis carbon powder obtained in step S1 is conveyed to the carbon powder sieve 4 for online sieving. The sieve aperture is set to 1 mm to separate the high-temperature pyrolysis carbon powder with a particle size of less than or equal to 1 mm. The high-temperature pyrolysis carbon powder with a particle size of less than or equal to 1 mm is then returned to the premixed modification bin through the 500°C heat preservation conveying device 6. At the same time, wet sludge is sent into the premixed modification bin 2. The water content of the wet sludge is 70%. The high-temperature pyrolysis carbon powder with a particle size of less than or equal to 1 mm is mixed with the wet sludge at a mass ratio of 1:1. The remaining high-temperature pyrolysis carbon powder is collected as a product in the carbon powder storage device 5.

[0045] S3, in-situ coating granulation;

[0046] Under the mechanical stirring action in the premixed modification chamber, the residual heat and hydrophobic properties of the small-particle-size high-temperature pyrolysis carbon powder are used to break up the wet sludge and form a dried carbon powder coating layer on the surface, finally obtaining granular particles with an outer dry and inner wet structure. The overall moisture content of the granular particles is 35%, and the surface wettability is hydrophobic.

[0047] S4. Prevents wall-sticking pyrolysis;

[0048] The granules obtained in step S3 are continuously fed into the pyrolysis reactor 3. The premixed modification chamber is equipped with a dual-shaft differential speed stirring paddle with the end linear velocity controlled within the range of 3 m / s. When the granules come into contact with the wall of the pyrolysis reactor 3, they rely on the dry carbon powder coating layer on the surface to achieve self-lubrication and anti-sticking, and are pyrolyzed under oxygen-free or low-oxygen conditions. The pyrolysis temperature is 700℃, producing oil and gas and high-temperature pyrolysis carbon powder.

[0049] S5. Product separation and recycling;

[0050] The oil and gas obtained in step S4 are processed by the oil and gas condensation and recovery device 7 to recover bio-oil and non-condensable gas. After purification, the non-condensable gas is introduced into the heating jacket or combustion chamber of the pyrolysis reactor 3 for combustion, providing a heat source for the pyrolysis reaction and realizing the energy self-sustaining of the system. At the same time, the high-temperature pyrolysis carbon powder obtained in step S4 is used to continue the operation in step S2.

[0051] The system used for the above-mentioned continuous pyrolysis method for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder includes a premixing and modification chamber 2, which is equipped with a dual-shaft differential speed stirring paddle. The inlet of the premixing and modification chamber 2 is connected to a sludge hopper 1, and the outlet of the premixing and modification chamber 2 is connected to a pyrolysis reactor 3. The pyrolysis reactor 3 is an externally heated screw propulsion reactor with a screw motor torque of 150 N·m. The oil and gas outlet of the pyrolysis reactor 3 is connected to an oil and gas condensation and recovery device 7, and the carbon powder outlet of the pyrolysis reactor 3 is connected to a carbon powder screen 4. The carbon powder screen 4 is connected to the premixing and modification chamber 2 through a heat-insulated conveying device 6, and the outlet of the carbon powder screen 4 is connected to a carbon powder storage device 5.

[0052] Comparative Example 1

[0053] A method for pyrolysis of wet sludge includes the following steps:

[0054] S1. Wet sludge is continuously fed into a pyrolysis reactor and pyrolyzed under anaerobic or low-oxygen conditions to produce oil and gas and high-temperature pyrolysis carbon powder.

[0055] S2. The oil and gas obtained in step S1 are processed through an oil and gas condensation and recovery device to recover bio-oil and non-condensable gases; at the same time, the high-temperature pyrolysis carbon powder obtained in step S1 is collected as a product.

[0056] The system for the above-mentioned pyrolysis method of wet sludge includes a pyrolysis reactor, the inlet of which is connected to a sludge hopper, the oil and gas outlet of which is connected to an oil and gas condensation and recovery device, and the carbon powder outlet of which is connected to a carbon powder storage device.

[0057] The difference between this comparative example and Example 1 is that the wet sludge was not mixed with small-particle-size high-temperature pyrolysis carbon powder, but directly entered the pyrolysis reactor for pyrolysis. The high-temperature pyrolysis carbon powder produced by pyrolysis was not screened online, but directly collected as a product. Other steps and conditions are the same as in Example 1.

[0058] Test case

[0059] To verify the technical effectiveness of the pyrolysis method of the present invention in improving the thoroughness of the pyrolysis reaction and the uniformity of product quality, the torque changes of the reactor screw motor in Example 1 and Comparative Example 1 were recorded during operation to observe whether there was any wall-sticking or jamming phenomenon. Samples were taken from Example 1 and Comparative Example 1 one hour after system startup and stable operation. High-temperature pyrolysis carbon powder samples were collected every 30 minutes at the pyrolysis reactor outlet, for a total of 10 sets of samples. The appearance of the products in Example 1 and Comparative Example 1 was observed. The moisture content, residual volatile matter, and fixed carbon content of the samples in Example 1 and Comparative Example 1 were tested, and the absolute deviation of moisture content and the standard deviation of residual volatile matter for the 10 sets of samples were calculated. The results are shown in Table 1.

[0060] Table 1: Parameter Comparison of Example 1 and Comparative Example 1

[0061]

[0062] Table 1 shows that the moisture content of the sample in Example 1 is lower than that in Comparative Example 1, and the absolute deviation of the moisture content of the sample in Example 1 is also lower than that in Comparative Example 1, indicating better product consistency and more stable pyrolysis reaction in Example 1. The average residual volatile matter content of the sample in Example 1 is lower than that in Comparative Example 1, and the average fixed carbon content of the sample in Example 1 is higher than that in Comparative Example 1, indicating a more thorough pyrolysis reaction in Example 1. The standard deviation of the residual volatile matter content of the sample in Example 1 is lower than that in Comparative Example 1. Furthermore, the sample in Example 1 is a uniform black granular material without agglomeration, while the sample in Comparative Example 1 consists of coke lumps of varying sizes with uncarbonized clay cores, indicating better uniformity in the sample in Example 1. The torque setting of the screw motor in the pyrolysis reactor in both Example 1 and Comparative Example 1 is 150 N·m. The average torque of the screw motor in the pyrolysis reactor in Example 1 is 45 N·m, while the average torque of the screw motor in the pyrolysis reactor in Comparative Example 1 is 120 N·m. N·m, and the running time of the pyrolysis reactor in Example 1 is significantly longer than that in Comparative Example 1. In the Comparative Example, the pyrolysis reactor is forced to shut down due to sludge sticking to the wall and clogging. The operation in Example 1 is more stable.

[0063] In summary, the method of the present invention makes the pyrolysis reaction more stable and thorough, and improves the uniformity of high-temperature pyrolysis carbon powder and the operational stability of the pyrolysis reactor.

Claims

1. A continuous pyrolysis method for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder, characterized in that, Includes the following steps: S1. Pyrolysis of dried sludge; After drying, the sludge is fed into the pyrolysis reactor through a premixed modification chamber and pyrolyzed under anaerobic or low-oxygen conditions to produce oil and gas and high-temperature pyrolysis carbon powder. The oil and gas are then recovered as bio-oil and non-condensable gases through an oil and gas condensation and recovery device. S2, pyrolytic carbon screening and reflux; The high-temperature pyrolysis carbon powder obtained in step S1 is screened online. The screen aperture is set to 0.5mm~2mm to separate small-particle-size high-temperature pyrolysis carbon powder. The small-particle-size high-temperature pyrolysis carbon powder is returned to the premixing and modification chamber through a heat-insulated conveying device. The temperature is maintained between 400℃ and 600℃ during the return. At the same time, wet sludge is sent into the premixing and modification chamber. The water content of the wet sludge is 60%~80%. The mass ratio of small-particle-size high-temperature pyrolysis carbon powder to wet sludge is (0.5~1.5):

1. The remaining high-temperature pyrolysis carbon is collected as product. S3, in-situ coating granulation; Under the mechanical stirring action in the premixed modification chamber, the residual heat and hydrophobic properties of the small-particle-size high-temperature pyrolysis carbon powder are utilized to break up the wet sludge and form a dried carbon powder coating layer on the surface, ultimately obtaining granular particles with an outer dry and inner wet structure. The overall moisture content of the mixed granular particles is 30%~40%. S4. Prevents wall-sticking pyrolysis; The granular particles obtained in step S3 are continuously fed into the pyrolysis reactor. When the granular particles come into contact with the wall of the pyrolysis reactor, they rely on the dried carbon powder coating layer on the surface to achieve self-lubrication and anti-sticking, and pyrolyze under oxygen-free or low-oxygen conditions to produce oil and gas and high-temperature pyrolysis carbon powder. S5. Product separation and recycling; The oil and gas obtained in step S4 are processed by an oil and gas condensation and recovery device to recover bio-oil and non-condensable gas; at the same time, the high-temperature pyrolysis carbon powder obtained in step S4 is further processed in step S2.

2. The continuous pyrolysis method for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder according to claim 1, characterized in that, In step S3, a stirring device is provided in the premixed modification chamber. The stirring device is a dual-shaft differential speed stirring paddle, and the end linear velocity of the dual-shaft differential speed stirring paddle is controlled within the range of 2~5m / s.

3. The continuous pyrolysis method for preventing sludge from sticking to the wall based on in-situ coating and granulation of pyrolytic carbon powder according to claim 1, characterized in that, In steps S1 and S4, the pyrolysis temperature is 500~800℃.

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