A method of sintering a sludge-based water-retaining clay

Abstract

The application discloses a sintering method of sludge-based water storage pottery, which comprises the following steps: controlling the temperature of sludge-based water storage pottery, then carrying out incomplete combustion treatment in a low-oxygen environment, and carrying out combustion and sintering treatment in an oxygen-rich environment, so that two types of combustible components in the sludge undergo controlled incomplete combustion and residual carbon combustion, the problem of sintering over-temperature loss of control of high-organic material is solved from the chemical reaction source, precise temperature control in all working conditions is realized, all fixed carbon is completely combusted by 100%, safety risks are completely avoided, the content of CO in tail gas is greatly reduced, the CO in the tail gas does not need to be disposed of, the prepared water storage pottery is free of residual carbon, has stable structure and adjustable performance, and can be widely applied to ecological restoration, sponge cities, mine treatment and the like, and has environmental protection, economic and social benefits.

Description

Technical Field

[0001] This invention belongs to the technical field of harmless treatment and high-value resource utilization of solid waste and preparation of environmentally friendly functional materials, specifically involving a sintering method for sludge-based water-retaining clay. Background Technology

[0002] Water-retaining clay is a porous material with a honeycomb structure, made from agricultural solid waste, clay, and other raw materials, with the addition of straw, through mixing, granulation, and high-temperature sintering. It possesses water absorption, purification, storage, and slow-release functions, and can be used to support sponge city construction and agricultural water conservation. With the continuous expansion of my country's sponge city construction, mine ecological restoration, polluted water body sediment barrier, arid agricultural water conservation, desertification control, and saline-alkali land management, the market demand for porous water-retaining materials continues to grow. Traditional water-retaining clay, due to its high clay content, experiences liquefaction of the inorganic phases during sintering, forming a shell-like coating. Then, the internal organic matter and foaming gas-producing components decompose and produce gas, causing the ceramsite to expand in volume, resulting in a low-density, high-closed-cell water-retaining clay (fire-expanded type). Therefore, its water absorption is poor, making it only suitable as a lightweight building filler, and it is gradually failing to meet market demands. Therefore, a low-clay-content, loss-of-ignition water-retaining clay has been developed. Its interconnected pore structure is formed in situ through the combustion and decomposition of organic matter and the escape of gases. Pore shaping relies entirely on the high-temperature vitrification reaction of clay minerals, i.e., the loss of organic matter to form pores. The higher the organic matter content, the greater the volume lost during ignition, resulting in more pores and better water absorption. Simultaneously, the product must achieve complete combustion of all combustible components, leaving no residual carbon, to avoid inorganic phase liquefaction encapsulating organic matter or residual carbon. Otherwise, it will lead to unstable batch performance, pulverization after long-term use, and a decrease in water absorption rate. Therefore, strict temperature control is necessary during the sintering process. Existing conventional water-retaining clay sintering processes generally adopt a four-stage process: heating-centralized combustion-sintering-cooling. The kiln maintains an oxygen-rich atmosphere throughout the process, where combustible organic compounds in the sludge and fixed carbon undergo simultaneous, oxygen-sufficient, and complete combustion. The core reactions are as follows: (1) Complete combustion of combustible organic compounds (mainly organic matter in sludge): C x H y O z N w +O2→CO2+H2O(g)+NO x (Oxygen-enriched complete combustion) This reaction is a strongly exothermic reaction. Taking typical organic matter in sludge as an example, the heat released by the complete combustion of glucose components reaches 2803 kJ / mol, and the heat released by the complete combustion of protein and lipid components is also huge. Moreover, volatile organic components can be rapidly pyrolyzed and burned at temperatures above 300°C.

[0003] (2) Incomplete combustion of combustible organic compounds (mainly organic matter in sludge): Cx H y O z N w →C + H₂O(g) + N₂ (Oxygen-deficient pyrolysis) C x H y O z N w +O2→CO+H2O(g)+N2 (incomplete combustion in the absence of oxygen). During combustion, some organic matter may undergo incomplete combustion or pyrolysis and carbonization into elemental carbon due to localized oxygen deficiency. (3) Complete combustion of pyrolytic carbon: C + CO2 → CO2, ΔH = -393.5 kJ / mol (complete combustion).

[0004] For example, Chinese patent CN109776064B discloses a dry method for preparing water-retaining clay. The method involves mixing an appropriate amount of natural soil and a mixture of silica-alumina ratio modifiers, a foaming agent, and an air-retaining agent, then forming spherical blanks and drying them. The dehydrated spherical blanks are then placed in a vertical gradient low-temperature sintering machine for continuous production of water-retaining clay, and sintered at 800°C under negative pressure. The material is fired at 850℃ to produce semi-clinker; then, the semi-clinker is placed in an oxygen-rich environment and fired at 800℃. The clinker is fired at 850℃; finally, it is placed in an oxygen-rich environment, and the temperature is gradually reduced from 800℃ to 400℃ to obtain the finished product. This method improves the drying speed of spherical blanks, has significant energy-saving effects, and is conducive to the continuous production of water-retaining clay.

[0005] However, this four-stage sintering process cannot simultaneously address the core contradiction of "temperature control during sintering of high-organic raw material pellets to prevent overheating" and "complete combustion of all residual carbon." It lacks a staged temperature control and step-by-step combustion mechanism tailored to the combustion characteristics of the two types of combustible materials, resulting in two major pain points: First, under full oxygen-enriched conditions, combustible organic compounds and fixed carbon burn simultaneously and instantaneously, leading to a concentrated burst of heat release. This easily causes localized overheating within the kiln, pellet melting and collapse, and damage to the pore structure, making it impossible to form a stable, interconnected open structure. Second, when low-oxygen temperature control is used to avoid overheating, it results in incomplete combustion of fixed carbon, leaving a large amount of residual carbon in the product. This leads to unstable product performance and long-term failure. Furthermore, there are no control measures for unburned carbon monoxide and small-molecule hydrocarbons, posing both the risk of excessive exhaust gas and the safety hazard of combustible gas accumulation and explosion. To avoid this, secondary combustion treatment of the flue gas is necessary to ensure that combustible hydrocarbons and carbon monoxide do not exceed standards.

[0006] Meanwhile, the existing process does not consider the explosion limits of carbon monoxide and small molecule hydrocarbons in air, nor does it design an oxygen content control strategy to match the reaction conditions for complete combustion of combustible components. There is no zoned control of oxygen content in the kiln. Either combustible gas accumulates into an explosive mixture under low oxygen conditions, posing a major safety hazard, or the concentrated combustion temperature runs out of control under oxygen-rich conditions, and unburned combustible components are emitted with the exhaust gas, posing a high risk to environmental compliance.

[0007] Therefore, the existing sintering process for water-retaining clay adopts a single-stage oxygen-enriched complete combustion mode, which cannot simultaneously address the core contradictions of "temperature control and overheating prevention" and "complete combustion of residual carbon." It does not match the combustion characteristics of the two types of combustible substances in sludge—combustible organic compounds and fixed carbon—and does not consider the explosion limits of combustible gases and the constraints of complete combustion. The reaction heat release is concentrated, the temperature is uncontrollable, the residual carbon is not fully burned, the safety risks are high, and the environmental performance is poor. It cannot solve the core contradictions of "combustion controllability, residual carbon burnout rate, precise control of oxygen content, environmental compliance, and production safety" in the sintering process of high organic matter sludge-based raw material balls. There is an urgent need to develop a special sintering process adapted to high organic matter water-retaining clay raw material balls. Summary of the Invention

[0008] To address the aforementioned technical issues, this invention provides a sintering method for sludge-based water-retaining clay. Through precise and controllable pyrolysis and stepwise combustion reaction regulation of two types of combustible components, the method achieves controllable cultivation of the open-pore structure of the water-retaining clay, ensuring a balance between high water absorption and sufficient cylinder compressive strength. Simultaneously, all residual carbon is completely burned off, resulting in a carbon-free product with stable performance, meeting the functional requirements of ecological restoration, sponge city, and other scenarios.

[0009] To achieve the above objectives, the present invention provides a sintering method for sludge-based water-retaining clay, comprising the following steps: (1) Heating and pyrolysis section: The raw material balls of sludge-based water storage clay are heated to 350-600℃ for preliminary pyrolysis to obtain pyrolysis balls; (2) Incomplete combustion section: The pyrolysis balls are heated to 500-800℃ at a heating rate of 1-15℃ / min to undergo incomplete combustion treatment to obtain combustion balls; (3) Combustion burnout section: The combustion ball is heated to 700~900℃ at a rate of 1~15℃ / min to obtain the burnout ball; (4) Sintering section: The burnt-out balls are heated to 900-1000℃ at a rate of 1-10℃ / min to obtain sintered balls; (5) Cooling section: The sintered balls are cooled in two stages to obtain sludge-based water-retaining clay.

[0010] Preferably, the heating rate of the pyrolysis section in step (1) is 10~50℃ / min, and the residence time is 5-50min.

[0011] Preferably, the oxygen content of the heating pyrolysis section in step (1) and the incomplete combustion section in step (2) is 0.5% to 2%.

[0012] Preferably, the oxygen content of the combustion burnout section in step (3) and the sintering section in step (4) is 6% to 12%.

[0013] Preferably, the two-stage cooling in step (5) consists of a high-temperature cooling stage and a low-temperature cooling stage.

[0014] More preferably, the high-temperature cooling section cools the temperature from 900-1000℃ to 500-700℃ at a rate of 10-50℃ / min; the low-temperature cooling section cools the temperature from 500-700℃ to 50-80℃ at a rate of 30-70℃ / min.

[0015] More preferably, the air in the low-temperature cooling section is refluxed to the high-temperature cooling section, and 5-15% (by volume) of the low-temperature air in the high-temperature cooling section is refluxed to the heating pyrolysis section, 30-50% (by volume) is refluxed to the incomplete combustion section, 30-40% (by volume) is refluxed to the combustion burnout section, and 10-20% (by volume) is refluxed to the sintering section.

[0016] Preferably, the raw material balls of the sludge-based water-retaining clay in step (1) contain 50% to 80% combustibles by dry weight, have a moisture content of 10% to 40%, and a particle size of 1 to 30 mm.

[0017] More preferably, the combustible material is composed of sludge and straw in any mass ratio; the raw material pellets also contain 20-50% clay by dry weight.

[0018] Preferably, the pressure of the heating pyrolysis section in step (1) is -200Pa to -400Pa; and the pressure of the combustion and burnout section in step (3) is -100Pa to -300Pa.

[0019] Preferably, the incomplete combustion treatment time in step (2) is 10~60 min; the combustion treatment time in step (3) is 10~60 min; and the sintering treatment time in step (4) is 10~30 min.

[0020] Preferably, 60-80% (by volume) of the incomplete combustion exhaust gas generated in the incomplete combustion section in step (2) is returned to the combustion burnout section, and 20-40% (by volume) is returned to the sintering section.

[0021] Preferably, 5-15% (by volume) of the high-temperature exhaust gas in the sintering section described in step (4) is recycled to the heating pyrolysis section, and 10-20% (by volume) is recycled to the incomplete combustion section.

[0022] Preferably, the sintering temperature in step (4) is 900-1000℃.

[0023] Preferably, the discharge pressure of the sludge-based water-retaining clay in step (5) is -100Pa to -400Pa.

[0024] The beneficial effects of this invention are as follows: 1. Before firing, the raw pellets of sludge-based water-retaining clay contain combustible residual sludge (sludge produced from wastewater biochemical treatment), accounting for 50% to 80% of the total dry weight of the raw pellets. The combustibles in this clay mainly consist of volatile organic matter such as proteins, polysaccharides, lipids, and humic substances from the residual sludge, which are the core components of the pyrolysis reaction. Pyrolysis begins at 300℃, with 350-600℃ being the main anaerobic pyrolysis range. Under low-oxygen conditions, pyrolysis generates volatile combustible gases (CO, H2, small molecule hydrocarbons) and elemental fixed carbon. Under oxygen-rich conditions, these gases are directly and completely combusted, releasing a large amount of heat instantaneously. Fixed carbon is a product of the pyrolysis of combustible organic compounds, which begins to burn above 500℃. Under low-oxygen conditions, incomplete combustion occurs to generate CO, while under oxygen-rich high-temperature conditions, complete combustion generates CO2. This is the core component that this process must ensure complete combustion of. This invention divides the core reaction of the sintering process into four core stages: controllable pyrolysis, incomplete combustion, temperature-controlled endothermic reaction, and complete combustion. This enables all combustible components to burn in stages and ultimately achieve 100% complete combustion.

[0025] 2. In the controlled pyrolysis stage, combustible organic compounds are the core components. Controlled pyrolysis occurs in a low-oxygen environment, releasing volatile combustible gases step by step and simultaneously generating elemental fixed carbon, achieving "gas-solid separation" of combustible components. This lays the foundation for subsequent stepwise combustion and gradient heat release, avoiding concentrated flashover. Nitrogen is released directly in the form of N2, significantly suppressing the formation of fuel-type NOx. This provides raw materials for subsequent incomplete combustion and complete combustion reactions, forming a closed-loop process of "pyrolysis-stepwise combustion-complete combustion".

[0026] C x H y O z N w C (elemental fixed carbon) + CO↑ + H2↑ + C m H n (Small molecule hydrocarbons)↑+N2↑+H2O(g)↑.

[0027] 3. In the incomplete combustion stage, with combustible organic compounds and fixed carbon as the core, the remaining organic components and fixed carbon after the controlled pyrolysis stage undergo controlled incomplete combustion in a low-oxygen environment, gently releasing some heat and avoiding concentrated heat release and overheating; generating combustible intermediate products such as CO and H2, further reducing the total calorific value; simultaneously forming a through-pore structure inside the raw material ball through gas escape; and continuously suppressing NOx formation in a low-oxygen environment. C x H y O z N w +O2 CO↑ + H2O(g)↑ + N2↑ C+O2 CO↑ ΔH=-221.0kJ / mol.

[0028] 4. During the combustion and burnout stage, the final combustion and burnout of carbon in the solid phase forms the final porous structure and generates heat. In the gas phase, combustible gas burns and burns in the gas phase space, generating heat to maintain the ambient temperature. The main reactions are as follows: C+O2 CO2↑, Gas-phase reaction: CO + O2 CO2↑, H2+O2 H2O↑, C m H n +O2 CO2↑ + H2O↑, The combustible intermediate products generated in the first stage are completely burned in an oxygen-rich and high-temperature environment, releasing all remaining calorific value and stabilizing the ceramicizing temperature in the kiln; all fixed carbon in the material balls is 100% completely burned in a high-temperature and oxygen-rich environment, leaving no residual carbon; at the same time, pollutants such as CO and hydrocarbons are completely eliminated, avoiding the risk of explosion; the gas escape during the combustion process further optimizes the pore structure, and together with high-temperature ceramicizing, the pores are shaped.

[0029] 5. This invention pioneers a controllable pyrolysis-complete combustion reaction system for combustible organic compounds, addressing the core industry contradictions of "temperature control and overheating prevention" and "complete combustion of residual carbon" at the source of chemical reaction. Targeting the characteristics of combustible organic compounds and fixed carbon in sludge, it innovatively incorporates a pre-processed, temperature-controlled pyrolysis step at 350-600℃. This allows macromolecular organic matter to decompose into volatile combustible gases and elemental fixed carbon under low-oxygen conditions, achieving "gas-solid separation" of combustible components. Then, through a two-step reaction mechanism of low-oxygen incomplete combustion and oxygen-rich complete combustion, combined with endothermic reduction reactions for synergistic temperature control, the total calorific value of organic matter is broken down, achieving a stable, step-by-step release of heat. This completely eliminates the problems of flash fire, overheating, and collapse of high-organic-matter raw material pellets, while ensuring 100% complete combustion of all combustible components and fixed carbon, leaving no residual carbon. The product yield is ≥95%, an improvement of over 25% compared to traditional processes.

[0030] 6. This invention adopts gradient micro-negative pressure control, which completely solves the problems of backflow, crossflow and overflow of flue gas in traditional processes, and ensures the stability of oxygen content and temperature field in the kiln throughout the process. It provides stable working conditions for controllable pyrolysis of organic matter, stepwise combustion and complete combustion of residual carbon, and improves the temperature control accuracy to within ±15℃.

[0031] 7. Based on the explosion limits of CO and small molecule hydrocarbons and the reaction stoichiometry for complete combustion of fixed carbon, this invention pioneers a dual-loop oxygen content interlocking control logic. The low-oxygen zone ensures the stable and controllable pyrolysis and incomplete combustion of organic matter, while completely avoiding the safety risks of gas accumulation and explosion, and significantly reducing CO generation. The oxygen-rich zone ensures the complete combustion of combustible intermediate products and fixed carbon, recovering the calorific value of secondary combustion and achieving 100% burnout of residual carbon, completely eliminating the hidden dangers of combustible pollutant emissions, and achieving a five-fold improvement in the safety, stability, energy saving, environmental protection, and burnout rate of the sintering process.

[0032] 8. This invention precisely controls the sintering process within the vitrification temperature range by matching gradient heating with staged oxygen content. This avoids pore blockage and excessive residual carbon caused by premature sintering and encapsulation of residual carbon, while also preventing the loss of water retention function due to over-firing. It can stably produce qualified products with "low residual carbon, strong water retention, qualified strength, and high pelletizing rate" within a wide range of organic feed materials, and its performance can be gradient-adjusted to adapt to different scenarios. Simultaneously, through a staged combustion mode of "oxygen-deficient energy release + oxygen-enriched combustion," it effectively controls the residual carbon in the finished product and reduces CO and hydrocarbons in the flue gas at the source, achieving low emissions without end-of-pipe secondary combustion treatment, significantly reducing environmental governance costs and operation and maintenance difficulties. Furthermore, the gradient temperature control throughout the process avoids common industry problems such as flash fire, pellet explosion, temperature runaway, and over-firing, and the cascaded waste heat recirculation also improves energy utilization efficiency, making it suitable for continuous industrial production. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the process of the present invention; the black lines in the diagram represent the specific method flow, and the dashed and gray lines represent the flue gas recirculation direction. Detailed Implementation

[0034] The technical solution of the present invention will be further explained and described below with reference to the accompanying drawings and specific embodiments. It is worth noting that the following embodiments are only preferred embodiments of the present invention and should not be construed as limiting the present invention. The scope of protection of the present invention should be determined by the contents of the claims. Modifications and substitutions made by those skilled in the art to the technical solution of the present invention without creative effort all fall within the scope of protection of the present invention.

[0035] Sludge-based water-retaining clay raw material balls: Municipal sludge from a wastewater treatment plant (dried to a moisture content of 15-50%) is mixed with rice straw and clay and granulated to obtain raw material balls; the combustible material in the raw material balls accounts for 50-80% of the dry basis, the clay accounts for 20-50% of the dry basis, the particle size of the raw material balls is 1-30mm, and the moisture content of the raw material balls is 10-40%.

[0036] Example 1 A sintering method for sludge-based water-retaining clay includes the following steps, wherein the parameters of the sludge-based water-retaining clay raw material balls are: particle size of 20-30 mm, moisture content of 37%, combustible content of 54% of the dry weight of the raw material balls, and clay content of 46% of the dry weight of the raw material balls; (1) Heating and pyrolysis section: The sludge-based water-storage clay raw material balls are evenly and uniformly spread with a thickness of 150 mm; then the pressure is controlled to be stable at -375±25 Pa, and the temperature is raised from 25℃ to 370℃ at a heating rate of 46℃ / min, with a residence time of about 7.5 min, to obtain pyrolysis balls; the amount of high-temperature tail gas refluxed from the sintering section is controlled to be 2520 Nm³ throughout the entire process. 3 / h (accounting for 11.8% of the reflux exhaust gas in the sintering section), 1200 Nm of low-temperature air refluxed from the high-temperature cooling section. 3 / h (accounting for 9.23% of the low-temperature air recirculated in the high-temperature cooling section), the oxygen content in the section is 1.8%±0.1%; (2) Incomplete combustion section: The pyrolysis pellets are heated from 370℃ to 545℃ at a heating rate of 12℃ / min and held for 14.6 min at an oxygen content of 1.5%±0.1% to obtain combustion pellets; the pressure in the section is -350±25Pa, and the amount of high-temperature tail gas refluxed from the sintering section is 3300 Nm³. 3 / h (accounting for 15.4% of the reflux exhaust gas in the sintering section), and 5200 Nm³ of low-temperature exhaust gas refluxed from the high-temperature cooling section. 3 / h (accounting for 40.00% of the high-temperature cooling section recirculated exhaust gas), extracting 9000 Nm³ of incomplete combustion exhaust gas. 3 / h; (3) Combustion burnout section: The combustion ball is heated from 545℃ to 710℃ at a heating rate of 12℃ / min and held for 13.8min with an oxygen content of 6.8%±0.1% to obtain the burnout ball; the pressure in the section is -275Pa±25Pa, and the incomplete combustion exhaust gas recirculated from the incomplete combustion section is 6300 Nm³. 3 / h (accounting for 70% of the incomplete combustion exhaust gas), the low-temperature air returning from the high-temperature cooling section is 4600 Nm 3 / h (accounting for 35.38% of the low-temperature air recirculated in the high-temperature cooling section); (4) Sintering section: The burnt-out balls are heated from 710℃ to 980℃ at a heating rate of 9.6℃ / min and held for 28.1min at an oxygen content of 7.2%±0.1% to obtain sintered balls; the pressure in the section is -250±25Pa, and the incomplete combustion exhaust gas recirculated from the incomplete combustion section is 2700 Nm³. 3 / h (accounting for 30% of the incomplete combustion exhaust gas), 2000 Nm of low-temperature air returning from the high-temperature cooling section. 3 / h (accounting for 15.38% of the low-temperature air refluxed in the high-temperature cooling section), extracting 21420 Nm of high-temperature exhaust gas from sintering. 3 / h; (5) Cooling section: The sintered balls are cooled from 980℃ to 690℃ at a rate of 16℃ / min (high temperature cooling section), during which 13000 Nm of low temperature air is extracted. 3 / h; then the temperature is reduced from 690℃ to 78℃ at a rate of 33℃ / min (low temperature cooling section) to obtain sludge-based water-retaining clay; the pressure in the section is -250±25Pa, the discharge pressure is -225±25Pa, and all the air in the low temperature cooling section is returned to the high temperature cooling section.

[0037] Example 2 A sintering method for sludge-based water-retaining clay includes the following steps, wherein the parameters of the sludge-based water-retaining clay raw material balls are: particle size of 10~20mm, moisture content of 21%, combustible material accounting for 69% of the dry weight of the raw material balls, and clay accounting for 31% of the dry weight of the raw material balls; (1) Heating and pyrolysis section: The sludge-based water-storage clay raw material balls are evenly and uniformly spread with a thickness of 80 mm; then the pressure is controlled to be stable at -275±25 Pa, and the temperature is raised from 25℃ to 535℃ at a heating rate of 21℃ / min, with a total residence time of about 24.3 min, to obtain pyrolysis balls; the amount of high-temperature tail gas refluxed from the sintering section is controlled to be 3270 Nm³ throughout the process. 3 / h (accounting for 11.7% of the reflux exhaust gas in the sintering section), the low-temperature air recirculated from the high-temperature cooling section is 1910 Nm 3 / h (accounting for 11.2% of the low-temperature air recirculated in the high-temperature cooling section), the oxygen content in the section is 1.2%±0.1%; (2) Incomplete combustion section: The pyrolysis pellets are heated from 535℃ to 690℃ at a heating rate of 4℃ / min and held for 38.8min with an oxygen content of 0.9%±0.1% in the section to obtain combustion pellets; the pressure in the section is -250±25Pa, and the amount of high-temperature tail gas refluxed from the sintering section is 4180 Nm³. 3 / h (accounting for 15.0% of the reflux exhaust gas in the sintering section), the low-temperature air recirculated from the high-temperature cooling section is 6650 Nm³. 3 / h (accounting for 39.1% of the low-temperature air recirculated in the high-temperature cooling section), extracting 11000 Nm3 / h of incomplete combustion exhaust gas; (3) Combustion burnout section: The combustion ball is heated from 690℃ to 835℃ at a heating rate of 4℃ / min, and held for 36.3min at an oxygen content of 9.6%±0.1% to obtain the burnout ball; the pressure in the section is -225Pa±25Pa, and the incomplete combustion exhaust gas recirculated from the incomplete combustion section is 7800 Nm³. 3 / h (accounting for 71% of the incomplete combustion exhaust gas), the low-temperature air returning from the high-temperature cooling section is 5720 Nm 3 / h (accounting for 33.7% of the low-temperature air recirculated in the high-temperature cooling section); (4) Sintering section: The burnt-out balls are heated from 835℃ to 940℃ at a heating rate of 4.5℃ / min and held for 23.3 min at an oxygen content of 10.0%±0.1% to obtain sintered balls; the pressure in the section is -200±25Pa, and the incomplete combustion exhaust gas recirculated from the incomplete combustion section is 3200 Nm³. 3 / h (accounting for 29% of the incomplete combustion exhaust gas), the low-temperature air returning from the high-temperature cooling section is 2720 Nm 3 / h (accounting for 16.0% of the low-temperature air recirculated in the high-temperature cooling section), extracting 27850 Nm of high-temperature exhaust gas from sintering. 3 / h; (5) Cooling section: The sintered balls are cooled from 940℃ to 570℃ at a rate of 34℃ / min and held for 10.9 min (high temperature cooling section), during which 17000 Nm of low temperature air is extracted. 3 / h; then the temperature is reduced from 570℃ to 61℃ at a rate of 59℃ / min (low temperature cooling section) to obtain sludge-based water-retaining clay; the pressure in the section is -200±25Pa, the discharge pressure is -175±25Pa, and all the air in the low temperature cooling section is returned to the high temperature cooling section.

[0038] Example 3 A sintering method for sludge-based water-retaining clay includes the following steps, wherein the parameters of the sludge-based water-retaining clay raw material balls are: particle size of 5~15mm, moisture content of 13%, combustible material accounting for 76% of the dry weight of the raw material balls, and clay accounting for 24% of the dry weight of the raw material balls; (1) Heating and pyrolysis section: The sludge-based water-storage clay raw material balls are evenly and uniformly spread with a thickness of 50 mm; then the pressure is controlled to be stable at -225±25 Pa, and the temperature is raised from about 25 °C to 585 °C at a heating rate of 12 °C / min to obtain pyrolysis balls; the amount of high-temperature tail gas refluxed from the sintering section is controlled to be 3750 Nm³ throughout the process. 3 / h (accounting for 11.9% of the reflux exhaust gas in the sintering section), the low-temperature air recirculated from the high-temperature cooling section is 2150 Nm³. 3 / h (accounting for 11.3% of the low-temperature air recirculated in the high-temperature cooling section), with an oxygen content of 0.9%±0.1% in the section; (2) Incomplete combustion section: The pyrolysis pellets were heated from 585℃ to 770℃ at a heating rate of 3.4℃ / min and held for 54.4min at an oxygen content of 0.6%±0.1% to obtain combustion pellets; the pressure in the section was -200±25Pa, and the amount of high-temperature tail gas refluxed from the sintering section was 4870 Nm³. 3 / h (accounting for 15.5% of the reflux exhaust gas in the sintering section), the low-temperature air recirculated from the high-temperature cooling section is 7480 Nm 3 / h (accounting for 39.4% of the low-temperature air recirculated in the high-temperature cooling section), extracting 12000 Nm³ of incomplete combustion exhaust gas. 3 / h; (3) Combustion burnout section: The combustion ball is heated from 770℃ to 885℃ at a heating rate of 2.1℃ / min and held for 54.8min at an oxygen content of 11.2%±0.1% to obtain the burnout ball; the pressure in the section is -175Pa±25Pa, and the incomplete combustion exhaust gas recirculated from the incomplete combustion section is 8350 Nm³. 3 / h (accounting for 70% of the incomplete combustion exhaust gas), the low-temperature air returning from the high-temperature cooling section is 6380 Nm 3 / h (accounting for 33.6% of the low-temperature air recirculated in the high-temperature cooling section); (4) Sintering section: The burnt-out balls are heated from 885℃ to 910℃ at a heating rate of 2℃ / min, and held for 12.5min at an oxygen content of 11.6%±0.1% to obtain sintered balls; the pressure in the section is -150±25Pa, and the incomplete combustion exhaust gas recirculated from the incomplete combustion section is 3650 Nm³. 3 / h (accounting for 30% of the incomplete combustion exhaust gas), the low-temperature air returning from the high-temperature cooling section is 2990 Nm 3 / h (accounting for 15.7% of the low-temperature air refluxed in the high-temperature cooling section), extracting 31420 Nm³ of high-temperature exhaust gas from sintering. 3 / h; (5) Cooling section: The sintered balls are cooled from 910℃ to 520℃ at a rate of 48℃ / min (high temperature cooling section), during which 19000 Nm of low temperature air is extracted. 3 / h; then cool from 520℃ to 52℃ at a rate of 68℃ / min (low temperature cooling section) to obtain sludge-based water-retaining clay; the pressure in the section is -150±25Pa, the discharge pressure is -125±25Pa, and all the air in the low temperature cooling section is returned to the high temperature cooling section.

[0039] Example 4 A sintering method for sludge-based water-retaining clay includes the following steps, wherein the parameters of the sludge-based water-retaining clay raw material balls are: particle size of 15~25mm, moisture content of 29%, combustible material accounting for 62% of the dry weight of the raw material balls, and clay accounting for 38% of the dry weight of the raw material balls; (1) Heating and pyrolysis section: The sludge-based water-storage clay raw material balls are evenly and uniformly spread with a thickness of 110 mm; then the pressure is controlled to be stable at -325±25 Pa, and the temperature is raised from about 25 °C to 445 °C at a heating rate of 38 °C / min to obtain pyrolysis balls; the amount of high-temperature tail gas refluxed from the sintering section is controlled to be 2760 Nm³ throughout the process. 3 / h (accounting for 11.3% of the reflux exhaust gas in the sintering section), 1550 Nm of low-temperature air refluxed from the high-temperature cooling section. 3 / h (accounting for 10.3% of the low-temperature air recirculated in the high-temperature cooling section), with an oxygen content of 1.5% ± 0.1% in the section; (2) Incomplete combustion section: The pyrolysis pellets are heated from 445℃ to 620℃ at a heating rate of 8℃ / min and held for 21.9min at an oxygen content of 1.2%±0.1% to obtain combustion pellets; the pressure in the section is -300±25Pa, and the amount of high-temperature tail gas refluxed from the sintering section is 3620 Nm³. 3 / h (accounting for 14.9% of the reflux exhaust gas in the sintering section), the low-temperature air recirculated from the high-temperature cooling section is 5970 Nm 3 / h (accounting for 39.8% of the low-temperature air recirculated in the high-temperature cooling section), extracting 10,000 Nm³ of incomplete combustion exhaust gas. 3 / h; (3) Combustion burnout section: The combustion ball is heated from 620℃ to 770℃ at a heating rate of 6℃ / min and held for 25min at an oxygen content of 8.2%±0.1% to obtain the burnout ball; the pressure in the section is -250Pa±25Pa, and the incomplete combustion exhaust gas recirculated from the incomplete combustion section is 6900 Nm³. 3 / h (accounting for 69% of the incomplete combustion exhaust gas), low-temperature air returning from the high-temperature cooling section 5100 Nm 3 / h (accounting for 34.0% of the low-temperature air recirculated in the high-temperature cooling section); (4) Sintering section: The burnt-out balls are heated from 770℃ to 965℃ at a heating rate of 6℃ / min and held for 32.5min at an oxygen content of 8.6%±0.1% to obtain sintered balls; the pressure in the section is -225±25Pa, and the incomplete combustion exhaust gas recirculated from the incomplete combustion section is 3100 Nm³. 3 / h (accounting for 31% of the incomplete combustion exhaust gas), the low-temperature air returning from the high-temperature cooling section is 2380 Nm 3 / h (accounting for 15.9% of the low-temperature air refluxed in the high-temperature cooling section), extracting 24380 Nm of high-temperature exhaust gas from sintering. 3 / h; (5) Cooling section: The sintered balls are cooled from 965℃ to 630℃ at a rate of 26℃ / min (high temperature cooling section), during which 15000 Nm of low temperature air is extracted. 3 / h; then the temperature is reduced from 630℃ to 69℃ at a rate of 48℃ / min (low temperature cooling section) to obtain sludge-based water-retaining clay; the pressure in the section is -225±25Pa, the discharge pressure is -200±25Pa, and all the air in the low temperature cooling section is returned to the high temperature cooling section.

[0040] Comparative Example 1 A sintering method for sludge-based water-retaining clay includes the following steps, wherein the parameters of the sludge-based water-retaining clay raw material balls are: particle size of 20~30mm, moisture content of 37%, combustible material accounting for 54% of the dry weight of the raw material balls, and clay accounting for 46% of the dry weight of the raw material balls; (1) Spread the sludge-based water storage clay raw material balls evenly without any deviation, with a thickness of 150mm; (2) The pressure was kept stable at -375±25Pa, and the temperature was increased from 25℃ to 980℃ at 14.9℃ / min, and the oxygen content was kept at 7.2%±0.1% for a total residence time of 64min to obtain sintered balls; (3) The sintered balls are cooled from 980℃ to 78℃ at a rate of 24.6℃ / min to obtain sludge-based water storage clay, wherein the cooling pressure is -250±25Pa and the discharge pressure is -225±25Pa.

[0041] Comparative Example 2 The method and steps are the same as in Example 1, except that step (1) is omitted. The raw material balls of sludge-based water-retaining clay are heated from room temperature to 545°C at a heating rate of 23.5°C / min for incomplete combustion, followed by combustion burnout, sintering and cooling treatment to finally obtain sludge-based water-retaining clay.

[0042] Comparative Example 3 The method and steps are the same as in Example 1, except that step (2) is omitted. The pyrolysis balls are directly burned to obtain sludge-based water-retaining clay.

[0043] Comparative Example 4 The method and steps are the same as in Example 1, except that step (3) is omitted. The burning ball is directly sintered to finally obtain sludge-based water-retaining clay.

[0044] Comparative Example 5 The method and steps are the same as in Example 1, except that step (4) is omitted. The burnt balls obtained in step (3) are directly subjected to two-stage cooling to finally obtain sludge-based water-retaining clay.

[0045] Comparative Example 6 The method and steps are the same as in Example 1, except that the two-stage cooling in step (5) is changed to directly cooling from 980°C to 78°C at a rate of 24.6°C / min to obtain sludge-based water-retaining clay, while the pressure in the middle stage and the discharge pressure remain unchanged.

[0046] Comparative Example 7 The method and steps are the same as in Example 1, except that the step of extracting the generated flue gas in step (2) is omitted, and finally sludge-based water storage clay is obtained.

[0047] Comparative Example 8 The method and steps are the same as in Example 1, except that the oxygen content in all steps is changed to 7.2%±0.1%, and sludge-based water-retaining clay is finally prepared.

[0048] Comparative Example 9 The method and steps are the same as in Example 1, except that the high-temperature tail gas recirculated from the sintering section in steps (2) and (3) is omitted, and sludge-based water storage clay is finally prepared.

[0049] Result detection: The sludge-based water-retaining clay prepared in the above examples and comparative examples was tested using the industrial analytical differential weight method (referring to GB / T 212-2008 "Industrial Analysis Methods for Coal") to determine the residual carbon rate; the bulk density was tested using the standard volumetric weighing method (according to GB / T 17431.2-2010 "Lightweight Aggregates and Their Test Methods Part 2: Test Methods") to determine the bulk density; the saturated water absorption rate was tested using the atmospheric pressure immersion weighing method (according to GB / T 17431.2-2010 "Lightweight Aggregates and Their Test Methods Part 2: Test Methods") to determine the saturated water absorption rate; the cylinder compressive strength was tested using the pressure cylinder pressurization method (according to GB / T 17431.2-2010 "Lightweight Aggregates and Their Test Methods Part 2: Test Methods") to determine the cylinder compressive strength; the porosity was tested using the density difference method (according to GB / T 17431.2-2010 "Lightweight Aggregates and Their Test Methods Part 2: Test Methods"); and the sieve weighing statistical method (according to GB / T The pelletizing rate was determined according to 17431.2-2010 "Lightweight aggregates and their test methods - Part 2: Test methods"; the results are shown in Table 1: Table 1 Performance parameters of sludge-based water storage clay

[0050] Note: Qualified product indicators should meet the following requirements: residual char rate <1%, bulk density <500 kg / m³. 3Saturated water absorption rate >30%, cylinder compressive strength >0.3MPa, porosity >20%, pelletizing rate >90%.

[0051] Table 2 Other Indicators

[0052] The results showed that Examples 1-4, through gradient temperature control, graded oxygen content matching, and a five-stage sintering process, ensured the complete combustion of organic matter in the inorganic components, resulting in a residual carbon rate of less than 0.1% in the finished product, far exceeding the acceptable threshold of ≤1%. Furthermore, the inorganic components had already completed internal pore formation upon entering the ceramicization zone, ensuring unobstructed pore channels. Consequently, the water storage performance exhibited a regular gradient change: as the proportion of dry combustible material in the raw material increased from 54% to 76%, the porosity gradually increased from 40% to 69%, the saturated water absorption rate simultaneously increased from 58% to 74%, and the bulk density increased from 480 kg / m³. 3 Gradually reduced to 310 kg / m 3 All indicators met the qualification requirements, achieving precise and controllable regulation of water storage performance.

[0053] Comparative Example 1 uses a one-step heating process without gradient upgrades, resulting in a char rate as high as 11%. Comparative Example 3 lacks the incomplete combustion stage, resulting in a char rate as high as 22%. Comparative Example 4 lacks the burnout stage, resulting in a char rate as high as 15%. All three examples show high char rates, and there is a corresponding relationship between higher char rates and lower porosity and water absorption. This fully demonstrates the mechanism of action of "pre-sintering to encapsulate char → filling and sealing pores → deterioration of water storage performance," further proving the superiority of the five-stage sintering process in this application.

[0054] In Comparative Example 7, the incomplete combustion flue gas was not promptly removed; in Comparative Example 8, the oxygen content remained constant throughout the process; and in Comparative Example 9, there was no high-temperature flue gas recirculation for temperature control. Although all three examples ensured a char residue rate of less than 0.1%, concentrated deflagration of organic matter or concentrated deflagration of combustible flue gas led to uncontrolled sintering temperature, exceeding the vitrification temperature range. This resulted in large-area melting and vitrification of inorganic components, with internal pores being filled and closed by the liquid phase. Ultimately, the saturated water absorption rate was only 8%~9%, and the porosity was only 6%~7%, essentially losing the water retention function of the product. This is a typical case of over-fired vitrification failure. In addition, Comparative Examples 7-9, which lacked tail gas recirculation, also showed a significant decline in pelletizing rate due to localized temperature loss and uneven combustion.

[0055] Comparative Examples 2 and 6 retained complete staged combustion and temperature control, with the char residue rate controlled below 0.1%, and the porosity and water absorption rate also maintained within a suitable range. However, since Comparative Example 2 omitted the heating and pyrolysis stage, and Comparative Example 6 only underwent one cooling process, there was a situation where the temperature change was too large and the pellets exploded, resulting in a significant decrease in the pelletizing rate.

[0056] In Examples 1-4, the sintering temperature was controlled within the vitrification range, allowing the inorganic components to undergo moderate vitrification and bonding to form a stable framework, thus achieving a cylinder compressive strength of 0.4-1.1 MPa. This maintained good mechanical load-bearing capacity despite high porosity, overcoming the industry pain point of "high porosity inevitably leading to low strength" and achieving a performance balance of "lightweight, high water retention, and reasonable strength." Comparative Examples 1, 3, and 4, due to uneven sintering of the inorganic components and the formation of numerous structural defects from internal residual carbon, had cylinder compressive strengths of only 0.1-0.3 MPa, far below the acceptable level, following a degradation path of "temperature runaway → premature carbonization → structural defects → decreased strength." In Comparative Examples 8 and 9, due to the complete melting and vitrification of the inorganic components and the densification of the structure, the cylinder compressive strength increased to 1.7-1.9 MPa, a significant improvement in strength. However, this was accompanied by complete pore closure and loss of water absorption function, following a degradation path of "excessively high temperature → vitrification and densification → increased strength → functional failure." Neither of the two degradation paths can simultaneously meet the dual requirements of strength and water retention, fully demonstrating that the design of precisely controlling the sintering temperature within the ceramic range is the key to balancing product functionality and mechanical properties.

[0057] Examples 1-4, through staged combustion and precise temperature control, ensure that combustible components are fully oxidized and decomposed in the oxygen-rich combustion zone, and that CO emission concentrations are stabilized at 50-80 mg / m³. 3 Hydrocarbon emission concentrations remained stable at 5–20 mg / m³ 3 The emissions are extremely low, eliminating the need for additional flue gas treatment facilities such as secondary combustion chambers and VOCs treatment. Simple dust removal is sufficient to meet the environmental control requirements of the domestic building materials industry and industrial kilns, significantly reducing the project's environmental investment and operating costs. Comparative examples 1, 3, 4, and 7-9 lacked staged combustion or burnout sections, resulting in temperature runaway and chaotic combustion, with CO emission concentrations rising to 600-1200 mg / m³. 3 Hydrocarbon emission concentrations rose to 80-120 mg / m³ 3 The emissions were more than 10 times higher than in the previous embodiment, which is a typical example of incomplete combustion pollution emissions. This indicates that the previous embodiment released combustible components through anoxic pyrolysis-incomplete combustion stage, followed by full oxidation and decomposition in an oxygen-enriched combustion stage. This not only effectively controlled the residual carbon in the finished product, but also reduced the incomplete combustion products in the flue gas from the source, making the emission reduction path more economical and stable.

Claims

1. A sintering method for sludge-based water-retaining clay, characterized in that: Includes the following steps: (1) Heating and pyrolysis section: The raw material balls of sludge-based water storage clay are heated to 350~600℃ and pyrolyzed to obtain pyrolysis balls; (2) Incomplete combustion section: The pyrolysis balls are heated to 500-800℃ at a heating rate of 1-15℃ / min to undergo incomplete combustion treatment to obtain combustion balls; (3) Combustion burnout section: The combustion ball is heated to 700~900℃ at a rate of 1~15℃ / min to obtain the burnout ball; (4) Sintering section: The burnt-out balls are heated to 900~1000℃ for sintering treatment to obtain sintered balls; (5) Cooling section: The sintered balls are cooled in two stages to obtain sludge-based water-retaining clay.

2. The sintering method for sludge-based water-retaining clay according to claim 1, characterized in that: The heating rate of the pyrolysis section is 10~50℃; the residence time of the pyrolysis section is 5-50min.

3. The sintering method of sludge-based water-retaining clay according to claim 1, characterized in that: The oxygen content of the heating pyrolysis section in step (1) and the incomplete combustion section in step (2) is 0.5%~2%.

4. The sintering method of sludge-based water-retaining clay according to claim 1, characterized in that: The oxygen content of the combustion burnout section in step (3) and the sintering section in step (4) is 6%~12%.

5. The sintering method of sludge-based water-retaining clay according to claim 1, characterized in that: The two-stage cooling described in step (5) consists of a high-temperature cooling section and a low-temperature cooling section.

6. The sintering method of sludge-based water-retaining clay according to claim 5, characterized in that: The high-temperature cooling section cools the temperature to 500-700℃ at a rate of 10-50℃ / min; the low-temperature cooling section cools the temperature to 50-80℃ at a rate of 30-70℃ / min.

7. The sintering method of sludge-based water-retaining clay according to claim 1, characterized in that: In step (1), the raw material balls of the sludge-based water-retaining clay contain 50% to 80% combustible material by dry weight, 10% to 40% moisture content, and 1 to 30 mm particle size.

8. The sintering method of sludge-based water-retaining clay according to claim 7, characterized in that: The combustible material consists of sludge and straw.

9. The sintering method of sludge-based water-retaining clay according to claim 1, characterized in that: The pressure of the heating pyrolysis section in step (1) is -200Pa to -400Pa; the pressure of the combustion and burnout section in step (3) is -100Pa to -300Pa.

10. The sintering method of sludge-based water-retaining clay according to claim 1, characterized in that: The incomplete combustion treatment time in step (2) is 10~60 min; the combustion treatment time in step (3) is 10~60 min; the sintering treatment time in step (4) is 10~30 min.

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