A sludge treatment method

Abstract

This invention discloses a sludge treatment method, comprising: unloading wet sludge into a sludge tank; conveying the wet sludge to a storage silo via a shaftless spiral cutter; temporarily storing the wet sludge in the storage silo while simultaneously introducing it into a deodorization system for treatment; conveying the wet sludge to a chute, allowing it to enter the interior of a vertical mill, the chute being positioned below the mill's inlet impeller; in the vertical mill, the wet sludge is dried and vaporized, simultaneously mixed with raw material powder and ground; the ground material enters a preheater system for preheating via the mill outlet; the preheated material enters a decomposition furnace for calcination; the calcined material enters a rotary kiln for final calcination to form clinker. This invention can effectively treat municipal sludge, is less likely to cause secondary pollution, and enables resource utilization.

Description

Technical Field

[0001] This invention relates to the field of sludge treatment technology, and more specifically to a sludge treatment method. Background Technology

[0002] Currently, the main methods for treating and disposing of municipal sewage sludge include landfill, composting, thermal drying, and separate incineration. Landfilling consumes a large amount of land resources, and heavy metals and pathogens in the sludge can easily seep into the soil and groundwater, causing secondary pollution. Composting has a long treatment cycle, and the organic matter remaining in the sludge may not be completely degraded during the composting process, resulting in continued decay and odor after application, and it is difficult to remove heavy metals. Thermal drying only reduces the water content of the sludge without changing its chemical properties, and the dried sludge still requires further treatment. The investment and operating costs of building a separate sludge incineration plant are high, and the fly ash and bottom ash from incineration still need to be landfilled or treated as hazardous waste or general solid waste, failing to achieve true resource utilization.

[0003] Therefore, there is an urgent need for a sludge treatment method that can effectively treat municipal sludge, avoid causing secondary pollution, and enable resource utilization. Summary of the Invention

[0004] In view of the above-mentioned shortcomings of the existing technology, the present invention provides a sludge treatment method that can effectively treat municipal sludge, is not prone to causing secondary pollution, and can realize resource utilization.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A sludge treatment method includes the following steps:

[0007] The wet sludge is unloaded into the sludge tank;

[0008] Wet sludge is transported from the sludge tank to the storage silo by a shaftless spiral cutter installed inside a closed conveying pipeline;

[0009] The wet sludge is temporarily stored in the storage silo, and the gas in the storage silo is introduced into the deodorization system for treatment.

[0010] Wet sludge is transported from the storage silo to the chute via a closed conveying pipeline, so that the wet sludge enters the vertical mill through the chute, which is located below the inlet impeller of the vertical mill.

[0011] In the vertical mill, wet sludge is dried and vaporized, and at the same time, the wet sludge is mixed with raw material powder and ground. The ground material enters the preheater system through the outlet of the vertical mill for preheating.

[0012] The preheated material is then fed into a decomposition furnace for calcination.

[0013] The material calcined in the decomposition furnace enters the rotary kiln for final calcination to form clinker.

[0014] The working principle of this invention is as follows: Since wet sludge has a moisture content of approximately 80%, directly feeding it into high-temperature equipment would cause the moisture to rapidly vaporize and absorb heat, disrupting the thermal balance. Therefore, in this invention, the wet sludge is first dried in a vertical mill using high-temperature exhaust gas from the preheater, causing the moisture to evaporate. Simultaneously, raw material powder is ground to a certain fineness in the vertical mill and thoroughly mixed with the dried sludge. The raw material powder has a large specific surface area, enabling it to adsorb water vapor and some volatile organic compounds, reducing the load on subsequent exhaust gas treatment. The dried and mixed material enters the preheater, where it exchanges heat with the hot flue gas, gradually increasing the material temperature and causing partial decomposition of the organic matter. Subsequently, the material enters the decomposition furnace, where, in a high-temperature oxidizing atmosphere, most of the organic matter is oxidized and decomposed into carbon dioxide and water vapor. Finally, the material enters the rotary kiln, where the residual organic matter is completely mineralized at high temperature. The inorganic matter in the material undergoes solid-phase and liquid-phase reactions with calcium oxide, silicon dioxide, aluminum oxide, iron oxide, etc. in the raw material to generate cement clinker mineral phases such as calcium silicate and calcium aluminate, thereby completely transforming the sludge into components of cement clinker.

[0015] In summary, this solution utilizes closed-loop pipelines and facilities throughout the entire process. Odors generated during sludge transportation and temporary storage are collected and treated. The vertical mill and preheater are kept under negative pressure, ensuring no odor leaks into the workshop environment, thus solving the odor pollution problem of traditional sludge treatment plants. Furthermore, by utilizing existing equipment in the cement production line (vertical mill, preheater, decomposition furnace, rotary kiln) and waste heat, there is no need to construct a separate sludge incinerator, significantly reducing investment and operating costs. The organic matter in the sludge burns and releases heat in the decomposition furnace and rotary kiln, which can replace part of the pulverized coal, achieving energy recovery and reducing energy consumption in cement production. Therefore, this invention completely ablates the organic matter in the sludge, while the inorganic matter becomes part of the cement clinker, with no solid waste discharged externally, achieving the effects of harmless discharge and resource utilization.

[0016] Preferably, a mass flow meter is provided at the inlet of the vertical mill, and the shaftless spiral reamer is connected to the power output end of the motor. The mass flow meter is used to detect the instantaneous flow rate of wet sludge entering the vertical mill in real time and transmit the signal to the controller. The controller compares the instantaneous flow rate of wet sludge with the amount of raw material fed into the vertical mill in the same period to obtain the actual mass ratio of wet sludge and raw material, and compares the actual mass ratio with the preset mass ratio range.

[0017] When the actual mass ratio is greater than the upper limit of the preset mass ratio range, the controller outputs a control signal to the motor to reduce the rotation speed, and the motor drives the conveying speed of the shaftless spiral reamer to decrease; when the actual mass ratio is less than the lower limit of the preset mass ratio range, the controller outputs a control signal to the motor to increase the rotation speed, and the motor drives the conveying speed of the shaftless spiral reamer to increase.

[0018] Preferably, the deodorization system includes an activated carbon adsorption device and a biological filter. The inlet of the activated carbon adsorption device is connected to the gas outlet at the top of the storage silo via an exhaust pipe. The outlet of the activated carbon adsorption device is connected to the inlet of the biological filter. The biological filter is filled with microbial carrier packing material. The outlet of the biological filter is connected to the atmosphere. The gas in the storage silo flows sequentially through the activated carbon adsorption device and the biological filter under the action of the exhaust fan.

[0019] Preferably, the chute is an inclined pipe with a rectangular or circular cross-section. The inclination angle of the chute is a preset acute angle. The upper inlet of the chute is connected to the outlet pipe of the storage silo. The lower outlet of the chute extends into the feed inlet below the grinding impeller of the vertical mill. There is a preset expansion gap between the edge of the lower outlet of the chute and the inner wall of the feed inlet of the vertical mill. The inner surface of the chute is provided with multiple ceramic plates along the material flow direction. The ceramic plates are fixed to the inner wall of the chute, and there is a set distance of expansion joint between adjacent ceramic plates.

[0020] Preferably, in the vertical mill, the wet sludge is dried and vaporized, and simultaneously mixed with raw material powder and ground. The ground material then enters the preheater system through the outlet of the vertical mill for preheating.

[0021] During the drying and vaporization process of the wet sludge in the vertical mill, the hot gas inside the vertical mill comes from the preheater exhaust gas of the cement clinker production line. After being drawn out from the preheater, the exhaust gas is transported to the hot air inlet at the bottom of the vertical mill. The exhaust gas flows from bottom to top inside the vertical mill. The wet sludge and raw meal powder are crushed by the grinding rollers on the grinding disc of the vertical mill and then blown upward by the exhaust gas, so that the exhaust gas forms a counter-current contact with the wet sludge and raw meal powder. During this contact process, the liquid water in the wet sludge is converted into water vapor. Part of the water vapor is adsorbed on the surface of the raw meal powder dispersed in the exhaust gas. The raw meal powder with adsorbed water vapor, together with the remaining water vapor that is not adsorbed and the dried sludge, constitute the material carried by the exhaust gas. This material is discharged from the outlet of the vertical mill with the exhaust gas and enters the preheater system for preheating.

[0022] Preferably, the method for calcining the preheated material in the decomposition furnace is as follows: the interior of the decomposition furnace is divided into a lower reduction zone and an upper oxidation zone. Tertiary air is sent from the middle of the decomposition furnace to form an oxidizing atmosphere in the upper oxidation zone. The material is sent from the middle and lower part of the decomposition furnace. The organic matter in the material undergoes an oxidative decomposition reaction with oxygen under this oxidizing atmosphere to generate carbon dioxide and water vapor. The inorganic matter in the material is suspended in the airflow in the form of solid particles and enters the rotary kiln from the top outlet of the decomposition furnace with the airflow.

[0023] Preferably, during the calcination process of the preheated material entering the decomposition furnace, the calcination temperature in the decomposition furnace is controlled by adjusting the tertiary air volume and the coal powder feed rate. The tertiary air is fed into the decomposition furnace from the middle, and the coal powder is fed into the decomposition furnace from multiple points at the bottom and side walls. The pressure inside the decomposition furnace is under negative pressure. The residence time of the material in the decomposition furnace is determined by the effective volume of the decomposition furnace, the gas flow rate, and the suspension state of the material particles.

[0024] Preferably, the method for the material calcined in the decomposition furnace to enter the rotary kiln for final calcination is as follows: the material from the decomposition furnace enters the kiln tail end of the rotary kiln and moves towards the kiln head end as the rotary kiln rotates. The internal temperature of the rotary kiln gradually increases along the material movement direction. During the movement, the material successively passes through the solid phase reaction zone, the liquid phase reaction zone, and the cooling zone. The inorganic matter in the material begins to undergo a solid phase reaction in the solid phase reaction zone and generates a liquid phase and forms the cement clinker mineral phase in the liquid phase reaction zone. The cement clinker mineral phase includes calcium silicate and calcium aluminate.

[0025] Preferably, during the final calcination of the material after decomposition furnace into the rotary kiln to form clinker, the final calcination temperature in the rotary kiln is controlled by adjusting the amount of pulverized coal and the primary air volume fed into the rotary kiln. The primary air carries the pulverized coal into the rotary kiln. The gas temperature distribution in the rotary kiln is as follows: the temperature in the kiln tail area is within a first preset temperature range, the temperature in the kiln middle area is within a second preset temperature range, and the temperature in the kiln head area is within a third preset temperature range. The third preset temperature range is higher than the second preset temperature range, and the second preset temperature range is higher than the first preset temperature range.

[0026] Preferably, the method further includes a step of cooling the clinker after calcination in the rotary kiln: after the clinker is discharged from the kiln head outlet of the rotary kiln, it enters a cooling device. The cooling device is provided with a channel for cooling air to pass through. The cooling air enters from the bottom of the cooling device, passes through the clinker layer, and becomes hot air. The temperature of the clinker gradually decreases during its movement in the cooling device, and the temperature of the clinker discharged from the outlet of the cooling device drops below a preset maximum temperature value. Part of the hot air discharged from the cooling device is sent into the rotary kiln and the decomposition furnace.

[0027] Compared with the prior art, the present invention has the following advantages:

[0028] 1. This invention achieves complete mineralization and resource utilization of sludge. The sludge is successively dried in a vertical mill, preheated in a preheater, and calcined at high temperature in a decomposition furnace and rotary kiln. All organic matter is oxidized and decomposed into carbon dioxide and water, while inorganic matter reacts with cement raw materials at high temperature to form cement clinker mineral phases such as calcium silicate and calcium aluminate. There is no residue discharge and no risk of secondary pollution.

[0029] 2. This invention operates in a completely closed system, with no odor leakage. It employs a shaftless spiral cutter, sealed flanges, a sealed storage silo, and a deodorization system. The sludge is transported through closed pipelines and facilities from its entry into the plant to its entry into the vertical mill. Odors generated in the storage silo are treated by activated carbon adsorption and biological filters before being discharged, completely solving the odor problem in the sludge treatment workshop.

[0030] 3. This invention fully utilizes the waste heat from the cement production line, resulting in significant energy savings. The hot gas required for drying sludge in the vertical mill is directly taken from the preheater exhaust gas, eliminating the need for an additional heat source; the organic matter in the sludge itself burns and releases heat in the decomposition furnace, which can partially replace fuel and reduce coal consumption. Attached Figure Description

[0031] Appendix Figure 1 This is a flowchart of the sludge treatment method of the present invention. Detailed Implementation

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0033] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0034] Furthermore, in describing representative embodiments, the specification may have presented methods and / or processes as a specific sequence of steps. However, the method or process should not be limited to the specific order of steps described herein, to the extent that it does not depend on such a specific order. As will be understood by those skilled in the art, other sequences of steps are also possible. Therefore, the specific order of steps set forth in the specification should not be construed as a limitation on the embodiments. Moreover, the method and / or process should not be limited to the steps performed in the written order; those skilled in the art will readily understand that these orders can be varied and still remain within the spirit and scope of the embodiments of this application.

[0035] This specific embodiment provides a sludge treatment method, which includes the following steps:

[0036] Step S1) Unload the wet sludge into a sludge tank. The wet sludge has a moisture content of approximately 80%, is paste-like, and is characterized by high viscosity, easy spoilage, and foul odor. A dedicated sludge tank is set up as a receiving and temporary storage container. The tank body is made of concrete and has anti-seepage treatment, which can centrally collect the sludge and prevent leakage and pollution of surface and groundwater. The sludge tank is usually designed underground or semi-underground to facilitate gravity flow or mechanical grab unloading. A sealed cover can be installed on top of the tank to reduce odor escape. This step avoids environmental pollution caused by indiscriminate sludge dumping and provides a stable material source for subsequent transportation.

[0037] Step S2) Wet sludge is transported from the sludge tank to the storage silo via a shaftless spiral reamer installed inside the closed conveying pipeline. Wet sludge is highly viscous and often contains entangled materials such as plastic bags, cloth strips, and fibers. If a conventional shafted screw conveyor is used, these entangled materials will wrap around the central shaft, causing motor overload, shaft breakage, or even jamming. This solution uses a shaftless spiral reamer, whose spiral blades have no central shaft; the blades directly contact the material, preventing entangled materials from wrapping around the shaft during the spiral's push. Simultaneously, the entire conveying pipeline is a fully enclosed structure, connected to the sludge tank outlet and the storage silo inlet using sealed flanges, ensuring the sludge does not come into contact with the outside environment during transport. Therefore, the shaftless design completely solves the problem of entangled materials jamming the shaft, greatly improving conveying reliability and requiring almost no maintenance; the fully enclosed pipeline prevents sludge leakage and odor escape, improving the workshop working environment; and the sealed conveying system prevents external rainwater and debris from entering the sludge, ensuring the stability of the sludge properties.

[0038] Specifically, a mass flow meter is installed at the inlet of the vertical mill. The shaftless spiral cutter is connected to the power output end of the motor. The mass flow meter is used to detect the instantaneous flow rate of wet sludge entering the vertical mill in real time and transmit the signal to the controller. The controller compares the instantaneous flow rate of wet sludge with the amount of raw material fed into the vertical mill in the same period to obtain the actual mass ratio of wet sludge and raw material, and compares the actual mass ratio with the preset mass ratio range.

[0039] When the actual mass ratio is greater than the upper limit of the preset mass ratio range, the controller outputs a control signal to the motor to reduce the rotation speed, and the motor drives the shaftless spiral reamer to reduce its conveying speed; when the actual mass ratio is less than the lower limit of the preset mass ratio range, the controller outputs a control signal to the motor to increase the rotation speed, and the motor drives the shaftless spiral reamer to increase its conveying speed.

[0040] In cement production, the chemical composition and calorific value of raw materials need to be strictly stabilized. The addition of sludge introduces a certain amount of moisture, organic matter, and ash. Excessive fluctuations in the sludge content can alter the moisture content, calorific value, and composition of the materials fed into the kiln, thus affecting the thermal regime of the decomposer and rotary kiln, ultimately impacting clinker quality (such as excessive free calcium oxide and reduced strength). Therefore, the proportion of sludge added must be precisely controlled.

[0041] A mass flow meter is installed at the inlet of the vertical mill to directly measure the mass of wet sludge entering the mill through the chute per unit time. The controller simultaneously receives the raw material flow signal from the raw material feeding system. Dividing the two yields the actual mass ratio. The preset mass ratio range is pre-calibrated based on the cement kiln's tolerance and sludge characteristics, for example, sludge accounting for 3%-8% (mass percentage) of the raw material. When the actual ratio is higher than the upper limit, indicating excessive sludge, the controller sends a signal to the motor to reduce its speed. The reduced motor speed decreases the conveying speed of the shaftless spiral cutter, thus reducing the amount of sludge entering the mill, and the ratio returns to normal. Conversely, when the actual ratio is lower than the lower limit, the controller increases the motor speed, increasing the sludge feed rate.

[0042] This achieves automatic adjustment of sludge quantity without manual intervention, with a rapid response speed, timely correction of feeding deviations, and long-term stability of the sludge blending ratio. Simultaneously, the stable sludge feed rate ensures constant drying load in the vertical mill, heat exchange load in the preheater, and combustion load in the decomposition furnace, which is beneficial for the stable operation of the cement kiln and avoids temperature fluctuations or blockage accidents caused by sudden changes in sludge quantity. Furthermore, by precisely controlling the ratio, sludge treatment capacity can be maximized while ensuring cement quality, meeting environmental protection requirements without affecting the cement product qualification rate.

[0043] Step S3) The wet sludge is temporarily stored in a storage silo, while the gas inside the silo is introduced into the deodorization system for treatment. The wet sludge needs to be temporarily stored in the storage silo while waiting to enter the vertical mill (e.g., buffering for 0.5-2 hours). During this period, the microorganisms in the sludge will continuously undergo anaerobic or aerobic metabolism, releasing malodorous gases such as hydrogen sulfide, ammonia, mercaptans, and volatile organic compounds. If not treated, the odor will escape from the top of the storage silo, polluting the factory air. This solution introduces the odorous gas into the deodorization system using an exhaust fan. On the one hand, negative pressure suction maintains a slight negative pressure inside the storage silo, preventing odor leakage; on the other hand, the collected odorous gas is treated to meet environmental standards before being discharged; the temporary storage function of the storage silo also acts as a buffer, smoothing production fluctuations and ensuring continuous operation when the upstream sludge transportation and downstream vertical mill processing rhythms are mismatched.

[0044] Specifically, the deodorization system includes an activated carbon adsorption device and a biological filter. The inlet of the activated carbon adsorption device is connected to the gas outlet at the top of the storage silo via an exhaust pipe. The outlet of the activated carbon adsorption device is connected to the inlet of the biological filter. The biological filter is filled with microbial carrier packing material. The outlet of the biological filter is connected to the atmosphere. The gas in the storage silo flows through the activated carbon adsorption device and the biological filter in sequence under the action of the exhaust fan.

[0045] The deodorization system employs a two-stage process: activated carbon adsorption and a biological filter. First, an exhaust fan draws gas from the top of the storage silo and sends it to the activated carbon adsorption unit. Activated carbon, with its extremely large specific surface area (typically 500-1500 m² / g) and abundant microporous structure, can efficiently capture polar molecules such as hydrogen sulfide, ammonia, and organic sulfides in odorous gases through physical and chemical adsorption. After activated carbon adsorption, most of the high-concentration odorous substances are removed, and the remaining low-concentration, easily biodegradable organic matter in the gas enters the biological filter. The biological filter is filled with specially designed microbial carrier packing materials (such as bark, sawdust, porous ceramic granules, polyurethane sponge, etc.), and the surface of the packing materials is covered with a large number of odor-loving bacteria, nitrifying bacteria, denitrifying bacteria, and other microbial communities. When the gas passes through the packing layer, the biodegradable organic matter is absorbed and decomposed by the microorganisms as a carbon and energy source, ultimately converting into carbon dioxide, water, and microbial cell matter. After this two-stage treatment, the gas is essentially odorless and can be directly discharged into the atmosphere.

[0046] Therefore, the activated carbon adsorption device in the deodorization system, acting as a pretreatment, can quickly remove high concentrations of impactful odors, protecting the subsequent biological filter from high-load impacts. Simultaneously, the activated carbon can be periodically regenerated or replaced to ensure adsorption efficiency. The biological filter has low operating costs, requires no chemical additives, and only needs appropriate humidity and pH levels for microorganisms to reproduce and sustain themselves, with no secondary pollution. The two-stage series treatment of the activated carbon adsorption device and biological filter achieves high efficiency, removing over 95% of typical odorous substances such as hydrogen sulfide, ammonia, and VOCs, while ensuring that the emitted gas meets relevant requirements.

[0047] Step S4) The wet sludge is transported from the storage silo to the chute through a closed conveying pipeline, so that the wet sludge enters the vertical mill through the chute. The chute is located below the inlet impeller of the vertical mill.

[0048] The conventional feeding method for vertical mills involves feeding material into the mill through the inlet impeller. However, wet sludge is highly viscous and easily adheres to the impeller blades when passed directly, gradually accumulating and causing impeller blockage, jamming, and even motor damage. This design places the outlet of the chute below the inlet impeller, bypassing the impeller. The sludge slides directly into the vertical mill feed inlet without passing through the impeller blades. The chute is angled, utilizing gravity to allow the sludge to slide down automatically. This completely avoids contact between the sludge and the impeller, fundamentally eliminating the risk of impeller blockage and jamming, and significantly improving the system's operational reliability. Furthermore, the chute structure is simple, has no moving parts, and is virtually fault-free.

[0049] Specifically, the chute is an inclined pipe with a rectangular or circular cross-section. The inclination angle of the chute is a preset acute angle. The upper inlet of the chute is connected to the outlet pipe of the storage silo. The lower outlet of the chute extends into the feed inlet below the mill impeller of the vertical mill. There is a preset expansion gap between the edge of the lower outlet of the chute and the inner wall of the feed inlet of the vertical mill. Multiple ceramic plates are provided on the inner surface of the chute along the material flow direction. The ceramic plates are fixed to the inner wall of the chute, and there is a set distance of expansion joint between adjacent ceramic plates.

[0050] This design uses an inclined chute (e.g., 45°-60°) to allow sludge to slide down automatically under gravity, eliminating the need for external power. The inclination angle needs to be pre-set based on the sludge's angle of repose and flowability (i.e., a preset acute angle). An angle that is too small will cause sludge accumulation, while an angle that is too large will increase the installation height. The lower end of the chute extends into the feed inlet of the vertical mill, with an expansion gap between the edge and the inner wall. This is to absorb the high-temperature thermal expansion during mill operation and prevent stress damage from rigid contact between the chute and the mill shell. Multiple wear-resistant ceramic plates are laid along the material flow direction on the inner wall of the chute. These ceramic plates have extremely high hardness (Mohs hardness 9) and an extremely low coefficient of friction, preventing sludge from adhering to their surface and resisting abrasion from sand, gravel, and metal fragments within the sludge. The ceramic plates are fixed with high-temperature adhesive and embedded pins, with expansion joints between adjacent plates to prevent them from cracking due to thermal expansion.

[0051] Step S5) In the vertical mill, the wet sludge is dried and vaporized. At the same time, the wet sludge is mixed with raw material powder and ground. The ground material enters the preheater system through the outlet of the vertical mill for preheating.

[0052] Specifically, during the drying and vaporization process of wet sludge in the vertical mill, the hot gas inside the mill comes from the preheater exhaust gas of the cement clinker production line. This exhaust gas is drawn out from the preheater and transported to the hot air inlet at the bottom of the vertical mill. The exhaust gas flows from bottom to top inside the vertical mill. The wet sludge and raw meal powder are crushed by the grinding rollers on the mill's grinding disc and then blown upward by the exhaust gas, causing the exhaust gas to form a counter-current contact with the wet sludge and raw meal powder. During this contact process, the liquid water in the wet sludge is converted into water vapor. Part of this water vapor is adsorbed on the surface of the raw meal powder dispersed in the exhaust gas. The raw meal powder with adsorbed water vapor, the remaining water vapor that is not adsorbed, and the dried sludge together constitute the material carried by the exhaust gas. This material is discharged from the outlet of the vertical mill with the exhaust gas and enters the preheater system for preheating.

[0053] Vertical mills are commonly used in cement production for grinding raw meal and can also utilize kiln tail gas for drying. This solution introduces wet sludge into the vertical mill, fully utilizing this function. Preheater exhaust gas (approximately 180°C) enters from the hot air inlet at the bottom of the vertical mill and flows upward at high speed. Wet sludge and raw meal powder are fed from the middle of the vertical mill, falling onto the rotating grinding disc and being crushed by the grinding rollers. The crushed fine particles are blown up by the upward hot air flow, forming a gas-solid two-phase flow. In this reverse contact process, firstly, the hot exhaust gas comes into direct contact with the wet sludge, and heat is rapidly transferred to the liquid water in the sludge, causing it to vaporize into water vapor. Due to the sufficient flow rate and temperature of the exhaust gas, almost all the moisture in the sludge can be evaporated, reducing the sludge's moisture content from 80% to near zero, turning it into a dry solid. Secondly, as the water vapor rises with the exhaust gas, it encounters the raw meal powder particles dispersed in the exhaust gas. The surface of the raw meal powder particles has a large number of micropores and polar groups, which can physically adsorb water vapor molecules. This adsorption process reduces the water vapor content in the exhaust gas, lowering the risk of condensation in subsequent dust collectors. Furthermore, the adsorption of water vapor on the surface of the raw material powder facilitates the uniform mixing of the sludge solids and the raw material powder. Additionally, the exhaust gas, carrying the dried sludge solids and raw material powder, exits from the top outlet of the vertical mill and enters the preheater system. At this point, the material has completed the drying, mixing, and grinding processes and is in a suspended state, which is conducive to efficient heat exchange in the preheater.

[0054] Therefore, this step utilizes the waste heat from the cement production line for drying, eliminating the need for additional energy consumption and significantly reducing the energy costs of sludge treatment. Simultaneously, the moisture in the wet sludge is absorbed by the raw meal powder, effectively performing dry dehumidification of the waste gas, reducing the burden on subsequent dust collectors and preventing heat loss caused by directly feeding wet sludge into the kiln. Furthermore, the vertical mill achieves microscopic mixing of sludge and raw meal powder, ensuring that the inorganic matter in the sludge can be uniformly dissolved into the clinker minerals during subsequent high-temperature calcination, preventing localized enrichment from affecting cement quality. Finally, the entire vertical mill system operates under negative pressure, with waste gas returning to and from the preheater, forming a closed loop with no waste gas leakage.

[0055] Step S6) The preheated material enters the decomposition furnace for calcination.

[0056] Specifically, the interior of the decomposition furnace is divided into a lower reduction zone and an upper oxidation zone. Tertiary air is introduced from the middle of the decomposition furnace to create an oxidizing atmosphere in the upper oxidation zone. The material is introduced from the middle and lower parts of the decomposition furnace. The organic matter in the material undergoes an oxidative decomposition reaction with oxygen under this oxidizing atmosphere to generate carbon dioxide and water vapor. The inorganic matter in the material is suspended in the airflow in the form of solid particles and enters the rotary kiln from the top outlet of the decomposition furnace with the airflow.

[0057] The decomposition furnace is the core equipment in a cement precalciner kiln system. Its function is to decompose the carbonates in the raw materials (CaCO3→CaO+CO2) at a high temperature of around 900℃, while simultaneously burning fuel. This scheme introduces sludge into the decomposition furnace, utilizing its high-temperature oxidation environment to decompose the organic matter in the sludge.

[0058] The decomposition furnace is typically divided into two zones: a lower reduction zone and an upper oxidation zone. The lower zone, near the pulverized coal injection inlet, has a localized reducing atmosphere due to incomplete combustion of the pulverized coal; the upper zone, with the introduction of tertiary air (hot air drawn from the kiln head cooler, containing 21% oxygen), forms a strongly oxidizing atmosphere. This design feeds the material from the lower middle section of the decomposition furnace, so the material first passes through the lower reduction zone, but the main reaction occurs in the upper oxidation zone. In the oxidizing atmosphere, the organic matter in the sludge (mainly composed of proteins, fats, polysaccharides, etc. from microbial remains) undergoes a vigorous oxidative decomposition reaction with oxygen: C x HᵧO2 + O2 → CO2 + H2O + heat. Because the temperature inside the decomposition furnace is uniform (around 900℃) and there is sufficient oxygen, the oxidation reaction of organic matter proceeds very thoroughly. The only gaseous products generated are carbon dioxide and water vapor, and no incomplete combustion products such as tar, carbon monoxide, or carbon black are produced.

[0059] Meanwhile, the inorganic matter in the sludge (mainly oxides or salts of silicon, aluminum, iron, and calcium) does not melt at 900℃ (most minerals have melting points above 1200℃), but instead remains suspended in the gas flow as solid particles. These solid particles have a large specific surface area and can undergo preliminary solid-phase reactions with CaO, CO2, and other substances in the gas flow. Since the outlet of the decomposition furnace is directly connected to the inlet of the rotary kiln, these suspended solid particles, along with the waste gas, are sent into the rotary kiln for final calcination.

[0060] Therefore, under an oxidizing atmosphere of 900℃, the organic matter in the sludge is completely oxidized and decomposed, leaving no organic substances that could cause secondary pollution, thus achieving harmlessness. Secondly, the heat released by the oxidation of organic matter can assist the combustion of pulverized coal in the decomposition furnace, reducing the amount of external fuel used and achieving energy recovery. Furthermore, inorganic matter enters the rotary kiln in a suspended state of solid particles, providing good contact conditions for subsequent solid-phase and liquid-phase reactions, which is conducive to the formation of high-quality cement clinker. Fourthly, the temperature inside the decomposition furnace is stable, without the generation of local high-temperature or low-temperature zones, avoiding the volatilization of harmful heavy metals in the sludge.

[0061] For example, the calcination temperature in the decomposition furnace is controlled by adjusting the tertiary air volume and the coal powder feed rate. The tertiary air is fed into the decomposition furnace from the middle, and the coal powder is fed into the decomposition furnace from multiple points at the bottom and side walls. The pressure inside the decomposition furnace is under negative pressure. The residence time of the material in the decomposition furnace is determined by the effective volume of the decomposition furnace, the gas flow rate, and the suspension state of the material particles.

[0062] The temperature inside the decomposition furnace must be strictly controlled at around 900℃: if the temperature is too low, the organic matter will not decompose completely and the carbonate decomposition rate will be low; if the temperature is too high, it may cause the material to crust, become blocked, or even cause some low-melting-point heavy metals to volatilize. Therefore, a reliable control mechanism needs to be established.

[0063] Temperature control is primarily achieved by adjusting two variables: tertiary air volume and pulverized coal feed rate. Tertiary air, sourced from the kiln head cooler, has a temperature of approximately 800-1000℃ and an oxygen content of 21%. Increasing the tertiary air volume introduces more oxygen and heat, promoting the combustion of pulverized coal and organic matter, thus raising the temperature; conversely, decreasing the tertiary air volume lowers the temperature. The pulverized coal feed rate directly provides heat; increasing the pulverized coal feed rate raises the temperature. In this invention, pulverized coal is fed from multiple points at the bottom and side walls of the decomposition furnace. This aims to ensure a more uniform distribution of pulverized coal within the furnace, avoiding localized over-concentration or under-concentration, thereby guaranteeing a uniform temperature field. The pressure within the decomposition furnace is controlled by an induced draft fan to maintain a negative pressure state (e.g., -500 to -1000 Pa). This negative pressure prevents high-temperature flue gas from escaping through gaps such as the feed inlet, and also promotes stable airflow.

[0064] The residence time of materials in the decomposition furnace is a key parameter affecting the decomposition rates of organic matter and carbonates. Too short a residence time results in incomplete reactions; too long a residence time increases the equipment size. Residence time is determined by three factors: the effective volume of the decomposition furnace (V), the gas flow rate (v), and the suspension state of the material particles (characterized by circulation ratio or separation efficiency). Specifically, residence time τ ≈ V / (v × A) multiplied by a correction factor. This scheme, through the design of a reasonable decomposition furnace structure and operating parameters, achieves an average residence time of 3-6 seconds, sufficient to complete the oxidation of organic matter and the decomposition of carbonates.

[0065] Therefore, in this step, by adjusting the tertiary air volume and pulverized coal quantity, precise closed-loop control of the decomposition furnace temperature can be achieved, ensuring that the temperature remains stable within the range of 900℃±50℃, thereby ensuring the complete decomposition of organic matter. Secondly, multi-point pulverized coal feeding avoids localized high-temperature zones, reducing the risk of scaling and blockage, and improving the reliability of system operation. Furthermore, negative pressure operation ensures no flue gas leakage, meeting environmental protection requirements. Finally, the rationally designed residence time makes the decomposition furnace of moderate size, ensuring complete reaction without being excessively large.

[0066] Step S7) The material calcined in the decomposition furnace enters the rotary kiln for final calcination to form clinker.

[0067] Specifically, the material from the decomposition furnace enters the tail end of the rotary kiln and moves towards the head end as the rotary kiln rotates. The internal temperature of the rotary kiln gradually increases along the direction of material movement. During the movement, the material successively passes through the solid-phase reaction zone, the liquid-phase reaction zone, and the cooling zone. The inorganic matter in the material begins to undergo a solid-phase reaction in the solid-phase reaction zone and generates a liquid phase in the liquid-phase reaction zone, forming the cement clinker mineral phase, which includes calcium silicate and calcium aluminate.

[0068] The rotary kiln is the final piece of equipment for cement clinker calcination, with an internal temperature reaching up to 1500℃. Material from the preheater (temperature approximately 900℃, mainly containing CaO, SiO2, Al2O3, Fe2O3, and sludge ash) enters from the kiln tail (the higher end) and slowly moves towards the kiln head (the lower end) as the rotary kiln rotates. Simultaneously, pulverized coal and primary air are injected into the kiln head burner, generating a high-temperature flame. The gas temperature inside the kiln gradually decreases from over 1500℃ at the kiln head to around 900℃ at the kiln tail, while the material temperature rises in the opposite direction, gradually increasing from 900℃ at the kiln tail to around 1450℃ at the kiln head.

[0069] The material sequentially passes through three reaction zones during its movement:

[0070] Solid-phase reaction zone (approximately 900-1200℃): In this range, CaO undergoes solid-phase diffusion reactions with SiO2, Al2O3, Fe2O3, etc., to generate intermediate products such as C2S (dicalcium silicate), C3A (tricalcium aluminate), and C4AF (tetracalcium aluminoferrite). These reactions do not require the participation of a liquid phase and rely on contact and diffusion between solid particles.

[0071] Liquid phase reaction zone (approximately 1200-1450℃): When the temperature exceeds approximately 1250℃, low-melting-point minerals such as C3A and C4AF in the material begin to melt, forming a liquid phase. The appearance of the liquid phase greatly accelerates the reaction between C2S and CaO, generating C3S (tricalcium silicate, the main component of calcium silicate). Simultaneously, Al2O3 reacts with CaO to generate C3A (calcium aluminate). These mineral phases are the main source of strength in cement clinker.

[0072] Cooling zone (near the kiln head outlet): After the clinker leaves the rotary kiln, it is rapidly cooled, the liquid phase solidifies to form a glassy body and crystalline minerals, and prevents C3S decomposition.

[0073] The inorganic substances in sludge (mainly SiO2, Al2O3, Fe2O3, CaO, MgO, etc.) participate in the reaction in the solid-phase reaction zone and become part of the clinker minerals. Since the chemical composition of sludge ash is similar to that of cement raw materials, it can completely replace part of the natural raw materials without negatively affecting the quality of clinker.

[0074] Thus, the high temperature of 1500℃ completely killed all pathogens in the sludge and thoroughly decomposed all organic matter, achieving complete harmlessness. Heavy metals in the sludge were solidified in the crystal lattice of minerals such as calcium silicate and calcium aluminate at the high temperature, forming stable solid solutions that would not leach into the environment, achieving stabilization. All sludge ash was converted into cement clinker, leaving no solid waste residue, achieving resource recovery. The formed calcium silicate and calcium aluminate mineral phases endowed the cement with excellent mechanical properties, and product quality remained unaffected.

[0075] For example, during the process of the material calcined in the decomposition furnace entering the rotary kiln for final calcination to form clinker, the final calcination temperature in the rotary kiln is controlled by adjusting the amount of pulverized coal and the primary air volume fed into the rotary kiln. The primary air carries the pulverized coal and is injected into the rotary kiln. The gas temperature distribution in the rotary kiln is as follows: the temperature in the kiln tail area is within the first preset temperature range, the temperature in the kiln middle area is within the second preset temperature range, and the temperature in the kiln head area is within the third preset temperature range. The third preset temperature range is higher than the second preset temperature range, and the second preset temperature range is higher than the first preset temperature range.

[0076] The temperature distribution within a rotary kiln is crucial to clinker quality. The kiln head has the highest flame temperature (reaching over 1600℃) and the kiln tail has the lowest temperature (around 900℃), and this gradient distribution is necessary for cement clinker firing. To achieve and stabilize this temperature distribution, the input of fuel and combustion air must be precisely controlled.

[0077] In this scheme, pulverized coal and primary air (approximately 10-15% of the total air volume) are injected into the rotary kiln through the kiln head burner. The pulverized coal burns rapidly at the kiln head, forming a high-temperature flame, bringing the kiln head region to the third preset temperature range (e.g., 1450-1550℃). The primary air's main function is to transport the pulverized coal and provide the oxygen required for initial combustion. The temperature in the kiln region (second preset temperature range, e.g., 1300-1450℃) is determined by the radiation and convection heat transfer of the flame, as well as material movement, and generally falls between the kiln head and kiln tail. The temperature in the kiln tail region (first preset temperature range, e.g., 900-1100℃) is mainly affected by the material temperature and exhaust gas volume from the preheater, and also by the flame length within the kiln. By adjusting the total amount of pulverized coal and the ratio of primary air, the flame length and temperature distribution can be altered: increasing the pulverized coal amount raises the overall temperature, while increasing the primary air ratio shortens the flame, increases the kiln head temperature, but may decrease the kiln tail temperature.

[0078] The technical advantages of this temperature distribution are: First, the high temperature at the kiln head causes the material to rapidly generate a liquid phase, promoting C3S formation; second, the moderate temperature inside the kiln is conducive to the growth and maturation of C3S crystals; third, the lower temperature at the kiln tail prevents the material from prematurely forming a liquid phase and thus forming rings. Without this gradient distribution, for example, if the kiln tail temperature is too high, the material will form a liquid phase at the kiln tail, adhering to the kiln tail lining plate and forming rings, hindering material flow; if the kiln head temperature is too low, insufficient C3S formation will occur, leading to a decrease in clinker strength. This scheme, by adjusting the amount of pulverized coal and the primary air volume, can flexibly adjust the temperature gradient to adapt to thermal changes with different sludge incorporation amounts, ensuring consistently stable clinker quality.

[0079] Step S8) Cooling the clinker after calcination in the rotary kiln: After the clinker is discharged from the kiln head outlet of the rotary kiln, it enters the cooling device. The cooling device is equipped with a channel for cooling air to pass through. The cooling air enters from the bottom of the cooling device, passes through the clinker layer and becomes hot air. The temperature of the clinker gradually decreases during its movement in the cooling device. The temperature of the clinker discharged from the outlet of the cooling device drops below the preset maximum temperature value. Part of the hot air discharged from the cooling device is sent into the rotary kiln and the decomposition furnace.

[0080] The clinker exiting the rotary kiln reaches temperatures as high as 1300-1400℃ and must be rapidly cooled to below 100℃ before subsequent storage and grinding. The purpose of cooling is threefold: first, to recover heat from the clinker and reduce heat loss; second, to prevent C3S from decomposing into C2S and CaO during slow cooling, which would lead to a decrease in cement strength; and third, to facilitate clinker transportation and grinding.

[0081] In this step, high-temperature clinker falls onto the cooling device from the rotary kiln head outlet. The cooling device reciprocates, pushing the clinker forward. Cooling air is blown in from the air chamber below the cooling device, passing through the clinker layer. Due to the high clinker temperature, the air and clinker undergo intense heat exchange. The air is heated to 800-1000℃, becoming hot air, while the clinker is cooled to below 100℃ (a preset maximum temperature value, such as ambient temperature + 65℃). The hot air is discharged from the top of the cooling device. A portion (approximately 50-60%) is drawn into the rotary kiln head hood to participate in the combustion of pulverized coal; another portion (approximately 30-40%) is sent to the decomposition furnace as tertiary air through the tertiary air duct to provide oxygen for the combustion of pulverized coal and organic matter in the decomposition furnace; the remaining portion (approximately 10%) can be used for waste heat power generation or directly discharged.

[0082] In this step, the heat from the high-temperature clinker is recovered by cooling air and returned to the kiln system as secondary and tertiary air, significantly improving the thermal efficiency of cement production (reducing heat consumption by approximately 100-150 kcal / kg clinker). Rapid cooling (quenching) maintains the high-temperature crystal form of C3S in the clinker, preventing its decomposition and thus ensuring the early strength of the cement. The low temperature of the cooled clinker facilitates transportation by belt conveyors and bucket elevators, and also reduces the heat load and dust explosion risk in the subsequent cement grinding workshop. Sending some of the hot air into the rotary kiln and decomposition furnace directly utilizes the recovered heat, reducing coal powder consumption and achieving energy conservation and emission reduction.

[0083] The working principle of this invention is as follows: Since wet sludge has a moisture content of approximately 80%, directly feeding it into high-temperature equipment would cause the moisture to rapidly vaporize and absorb heat, disrupting the thermal balance. Therefore, in this invention, the wet sludge is first dried in a vertical mill using high-temperature exhaust gas from the preheater, causing the moisture to evaporate. Simultaneously, raw material powder is ground to a certain fineness in the vertical mill and thoroughly mixed with the dried sludge. The raw material powder has a large specific surface area, enabling it to adsorb water vapor and some volatile organic compounds, reducing the load on subsequent exhaust gas treatment. The dried and mixed material enters the preheater, where it exchanges heat with the hot flue gas, gradually increasing the material temperature and causing partial decomposition of the organic matter. Subsequently, the material enters the decomposition furnace, where, in a high-temperature oxidizing atmosphere, most of the organic matter is oxidized and decomposed into carbon dioxide and water vapor. Finally, the material enters the rotary kiln, where the residual organic matter is completely mineralized at high temperature. The inorganic matter in the material undergoes solid-phase and liquid-phase reactions with calcium oxide, silicon dioxide, aluminum oxide, iron oxide, etc. in the raw material to generate cement clinker mineral phases such as calcium silicate and calcium aluminate, thereby completely transforming the sludge into components of cement clinker.

[0084] In summary, this solution utilizes closed-loop pipelines and facilities throughout the entire process. Odors generated during sludge transportation and temporary storage are collected and treated. The vertical mill and preheater are kept under negative pressure, ensuring no odor leaks into the workshop environment, thus solving the odor pollution problem of traditional sludge treatment plants. Furthermore, by utilizing existing equipment in the cement production line (vertical mill, preheater, decomposition furnace, rotary kiln) and waste heat, there is no need to construct a separate sludge incinerator, significantly reducing investment and operating costs. The organic matter in the sludge burns and releases heat in the decomposition furnace and rotary kiln, which can replace part of the pulverized coal, achieving energy recovery and reducing energy consumption in cement production. Therefore, this invention completely ablates the organic matter in the sludge, while the inorganic matter becomes part of the cement clinker, with no solid waste discharged externally, achieving the effects of harmless discharge and resource utilization.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A sludge treatment method, characterized in that, Includes the following steps: The wet sludge is unloaded into the sludge tank; Wet sludge is transported from the sludge tank to the storage silo by a shaftless spiral cutter installed inside a closed conveying pipeline; The wet sludge is temporarily stored in the storage silo, and the gas in the storage silo is introduced into the deodorization system for treatment. Wet sludge is transported from the storage silo to the chute via a closed conveying pipeline, so that the wet sludge enters the vertical mill through the chute, which is located below the inlet impeller of the vertical mill. In the vertical mill, wet sludge is dried and vaporized, and at the same time, the wet sludge is mixed with raw material powder and ground. The ground material enters the preheater system through the outlet of the vertical mill for preheating. The preheated material is then fed into a decomposition furnace for calcination. The material calcined in the decomposition furnace enters the rotary kiln for final calcination to form clinker.

2. The sludge treatment method according to claim 1, characterized in that, A mass flow meter is installed at the inlet of the vertical mill. The shaftless spiral cutter is connected to the power output end of the motor. The mass flow meter is used to detect the instantaneous flow rate of wet sludge entering the vertical mill in real time and transmit the signal to the controller. The controller compares the instantaneous flow rate of wet sludge with the amount of raw material fed into the vertical mill in the same period to obtain the actual mass ratio of wet sludge and raw material, and compares the actual mass ratio with the preset mass ratio range. When the actual mass ratio is greater than the upper limit of the preset mass ratio range, the controller outputs a control signal to the motor to reduce the rotation speed, and the motor drives the conveying speed of the shaftless spiral reamer to decrease; when the actual mass ratio is less than the lower limit of the preset mass ratio range, the controller outputs a control signal to the motor to increase the rotation speed, and the motor drives the conveying speed of the shaftless spiral reamer to increase.

3. The sludge treatment method according to claim 1, characterized in that, The deodorization system includes an activated carbon adsorption device and a biological filter. The inlet of the activated carbon adsorption device is connected to the gas outlet at the top of the storage silo via an exhaust pipe. The outlet of the activated carbon adsorption device is connected to the inlet of the biological filter. The biological filter is filled with microbial carrier packing material. The outlet of the biological filter is connected to the atmosphere. The gas in the storage silo flows sequentially through the activated carbon adsorption device and the biological filter under the action of the exhaust fan.

4. The sludge treatment method according to claim 1, characterized in that, The chute is an inclined pipe with a rectangular or circular cross-section. The inclination angle of the chute is a preset acute angle. The upper inlet of the chute is connected to the outlet pipe of the storage silo. The lower outlet of the chute extends into the feed inlet below the grinding impeller of the vertical mill. There is a preset expansion gap between the edge of the lower outlet of the chute and the inner wall of the feed inlet of the vertical mill. The inner surface of the chute is provided with multiple ceramic plates along the material flow direction. The ceramic plates are fixed to the inner wall of the chute, and there is a set distance of expansion joint between adjacent ceramic plates.

5. The sludge treatment method according to claim 1, characterized in that, In the vertical mill, wet sludge is dried and vaporized, and simultaneously mixed with raw material powder and ground. The ground material then enters the preheater system through the outlet of the vertical mill for preheating. During the drying and vaporization process of the wet sludge in the vertical mill, the hot gas inside the vertical mill comes from the preheater exhaust gas of the cement clinker production line. After being drawn out from the preheater, the exhaust gas is transported to the hot air inlet at the bottom of the vertical mill. The exhaust gas flows from bottom to top inside the vertical mill. The wet sludge and raw meal powder are crushed by the grinding rollers on the grinding disc of the vertical mill and then blown upward by the exhaust gas, so that the exhaust gas forms a counter-current contact with the wet sludge and raw meal powder. During this contact process, the liquid water in the wet sludge is converted into water vapor. Part of the water vapor is adsorbed on the surface of the raw meal powder dispersed in the exhaust gas. The raw meal powder with adsorbed water vapor, together with the remaining water vapor that is not adsorbed and the dried sludge, constitute the material carried by the exhaust gas. This material is discharged from the outlet of the vertical mill with the exhaust gas and enters the preheater system for preheating.

6. The sludge treatment method according to claim 1, characterized in that, The method for calcining the preheated material in the decomposition furnace is as follows: The interior of the decomposition furnace is divided into a lower reduction zone and an upper oxidation zone. Tertiary air is sent from the middle of the decomposition furnace to form an oxidizing atmosphere in the upper oxidation zone. The material is sent from the middle and lower part of the decomposition furnace. The organic matter in the material undergoes an oxidative decomposition reaction with oxygen under this oxidizing atmosphere to generate carbon dioxide and water vapor. The inorganic matter in the material is suspended in the airflow in the form of solid particles and enters the rotary kiln from the top outlet of the decomposition furnace with the airflow.

7. The sludge treatment method according to claim 6, characterized in that, During the calcination process of the preheated material entering the decomposition furnace, the calcination temperature in the decomposition furnace is controlled by adjusting the tertiary air volume and the coal powder feed rate. The tertiary air is fed into the decomposition furnace from the middle, and the coal powder is fed into the decomposition furnace from multiple points at the bottom and side walls. The pressure inside the decomposition furnace is under negative pressure. The residence time of the material in the decomposition furnace is determined by the effective volume of the decomposition furnace, the gas flow rate, and the suspension state of the material particles.

8. The sludge treatment method according to claim 1, characterized in that, The method for the final calcination of the material after decomposition furnace calcination into the rotary kiln is as follows: the material from the decomposition furnace enters the kiln tail end of the rotary kiln and moves towards the kiln head end as the rotary kiln rotates. The internal temperature of the rotary kiln gradually increases along the material movement direction. During the movement, the material successively passes through the solid phase reaction zone, the liquid phase reaction zone, and the cooling zone. The inorganic matter in the material begins to undergo a solid phase reaction in the solid phase reaction zone, and generates a liquid phase and forms the cement clinker mineral phase in the liquid phase reaction zone. The cement clinker mineral phase includes calcium silicate and calcium aluminate.

9. The sludge treatment method according to claim 8, characterized in that, During the final calcination process of the material after calcination in the decomposition furnace into the rotary kiln to form clinker, the final calcination temperature in the rotary kiln is controlled by adjusting the amount of pulverized coal and the primary air volume fed into the rotary kiln. The primary air carries the pulverized coal into the rotary kiln. The gas temperature distribution in the rotary kiln is as follows: the temperature in the kiln tail area is within a first preset temperature range, the temperature in the kiln middle area is within a second preset temperature range, and the temperature in the kiln head area is within a third preset temperature range. The third preset temperature range is higher than the second preset temperature range, and the second preset temperature range is higher than the first preset temperature range.

10. The sludge treatment method according to claim 1, characterized in that, The method also includes a step of cooling the clinker after calcination in the rotary kiln: after the clinker is discharged from the kiln head outlet of the rotary kiln, it enters a cooling device. The cooling device is provided with a channel for cooling air to pass through. The cooling air enters from the bottom of the cooling device, passes through the clinker layer and becomes hot air. The temperature of the clinker gradually decreases during its movement in the cooling device, and the temperature of the clinker discharged from the outlet of the cooling device drops below the preset maximum temperature value. A portion of the hot air discharged from the cooling device is fed into the rotary kiln and the decomposition furnace.

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