Metal oxide semiconductor heat generating material and preparation thereof, semiconductor heat generating element, and sludge solid waste dewatering and drying reduction system and method

Abstract

The present application belongs to the technical field of sludge solid waste deep dewatering and reduction, and particularly relates to a metal oxide semiconductor heating material, a preparation method thereof, a semiconductor heating element, and a sludge solid waste dewatering, drying and reduction system and method. The metal oxide semiconductor heating material comprises 75-85% of main phase semiconductor powder, 5-12% of ion doping modifier, 3-8% of low-temperature sintering aid, and 2-5% of inorganic bonding carrier; the main phase semiconductor powder comprises titanium dioxide, zinc oxide and gallium oxide; and the ion doping modifier comprises antimony trioxide, manganese dioxide and yttrium oxide. The semiconductor heating element made of the metal oxide semiconductor heating material has the characteristics of high electric-thermal conversion efficiency, stable low-temperature self-limiting temperature, acid and alkali corrosion resistance, and small long-term power attenuation, and is suitable for low-temperature closed drying and reduction disposal of various high-moisture sludge such as municipal sewage plant biochemical sludge, chemical sludge, printing and dyeing sludge, electroplating sludge, etc.

Description

Technical Field

[0001] This invention belongs to the field of deep dewatering and volume reduction technology of sludge and solid waste, specifically involving metal oxide semiconductor heating materials and their preparation, semiconductor heating elements, and sludge and solid waste dewatering, drying, and volume reduction systems and methods. Background Technology

[0002] Mechanically dewatered sludge produced by wastewater treatment plants typically has a moisture content of 78% to 82%. It is large in volume, high in organic matter, and prone to putrefaction and foul odor. Direct landfilling occupies a large amount of land, while incineration is energy-intensive and poses a high risk of dioxin emissions. Therefore, deep drying and volume reduction of sludge is an essential need in the industry. Existing sludge drying technologies are mainly divided into three categories: hot air steam drying, heat pump low-temperature drying, and resistance heating drying.

[0003] Hot air steam drying relies on high-temperature flue gas heat exchange, resulting in heat losses of 35% to 45%. The sludge surface rapidly loses water and forms a crust, making it difficult for internal moisture to escape, leading to poor drying uniformity. Drying temperatures generally exceed 100℃, causing the organic matter in the sludge to decompose, producing large amounts of hydrogen sulfide, volatile organic acids, and other malodorous gases, severely corroding equipment. The investment and operating costs for exhaust gas treatment are high. It also relies on natural gas and coal-fired heat sources, resulting in high carbon emission intensity. Heat pump low-temperature drying relies on air convection heat exchange, but hot air has difficulty penetrating highly viscous sludge, resulting in a long drying cycle. The system's fan circulation energy consumption accounts for more than 40% of the overall energy consumption. The circulating hot air carries fine dust from the sludge, posing a dust explosion hazard. The heat exchanger is in long-term contact with chlorine- and sulfur-containing volatile gases, making it prone to scaling and corrosion, requiring frequent equipment maintenance. Traditional resistance wires and ordinary ceramic heating tubes lack self-limiting temperature function, and local heat accumulation can easily cause overheating and ignite the organic matter in the sludge, posing a high safety risk; the electrothermal conversion efficiency is only 70%~78%, resulting in low energy utilization; the metal heating substrate has poor corrosion resistance, and the heating power decays rapidly under long-term sludge conditions, leading to high replacement costs.

[0004] In summary, current sludge drying technologies suffer from drawbacks such as high energy consumption, uneven drying, significant safety hazards, short lifespan of heating elements, and high exhaust gas treatment load, making them unsuitable for widespread application in deep sludge reduction. Summary of the Invention

[0005] The purpose of this invention is to provide metal oxide semiconductor heating materials and their preparation, semiconductor heating elements, and a system and method for dewatering, drying, and reducing the volume of sludge and solid waste. The invention uses metal oxide semiconductor heating materials to make semiconductor heating elements, which have the characteristics of high electrothermal conversion efficiency, stable low temperature self-limiting temperature, resistance to acid and alkali corrosion, low long-term power attenuation, and safety and environmental protection. It is suitable for low-temperature closed drying and volume reduction treatment of various high water content sludges such as biochemical sludge, chemical sludge, printing and dyeing sludge, and electroplating sludge from municipal sewage treatment plants.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a metal oxide semiconductor heating material, comprising the following components by mass percentage: The composition comprises 75-85% main phase semiconductor powder, 5-12% ion doping modifier, 3-8% low-temperature sintering aid, and 2-5% inorganic binder; the main phase semiconductor powder includes titanium dioxide (TiO2), zinc oxide (ZnO), and gallium oxide (Ga2O3); the ion doping modifier includes antimony trioxide (Sb2O3), manganese dioxide (MnO2), and yttrium oxide (Y2O3); the low-temperature sintering aid includes silicon dioxide and borate glass powder; and the inorganic binder includes kaolin and alumina.

[0007] Preferably, the mass ratio of titanium dioxide, zinc oxide and gallium oxide is (5~7):(2~4):1; the mass ratio of antimony trioxide, manganese dioxide and yttrium oxide is (1~3):(0.5~1.5):(0.3~1); the mass ratio of silicon dioxide to borate glass powder is 1:(2~4); and the mass ratio of kaolin to alumina is (1~3):1.

[0008] This invention provides a method for preparing the metal oxide semiconductor heating material described in the above technical solution, comprising the following steps: The main phase semiconductor powder, ion doping modifier, low-temperature sintering aid and inorganic binder are ball-milled and mixed to obtain a mixed precursor powder; The mixed precursor powder and the water-based inorganic binder are kneaded to obtain a mixture; The mixture is molded to obtain a heating blank; The heating blank is sintered to obtain the metal oxide semiconductor heating material.

[0009] Preferably, the ball milling is a planetary ball milling process, and the conditions for planetary ball milling include: the dispersion medium is ethanol, and the ball milling time is 4-6 hours; the wet ball-milled material is obtained directly after ball milling, and the wet ball-milled material is further subjected to drying, crushing, and sieving in sequence to obtain the mixed precursor powder, wherein the sieving screen is preferably 150-250 mesh; the aqueous inorganic binder is silica sol, and the solid content of the aqueous inorganic binder is 30±2%; the dry basis solids of the aqueous inorganic binder account for 3-7 wt% of the mass of the mixed precursor powder.

[0010] Preferably, the molding pressure is 12~16MPa; the morphology of the heated blank includes one or more of flat plate, tubular and arc-shaped; the sintering includes sequentially performing a first stage of heat preservation sintering, a second stage of heat preservation sintering and a third stage of heat preservation sintering, wherein the temperature of the first stage of heat preservation sintering is 220~280℃ and the holding time is 1~2h, the temperature of the second stage of heat preservation sintering is 580~630℃ and the holding time is 2~3h, and the temperature of the third stage of heat preservation sintering is 880~930℃ and the holding time is 3~4h.

[0011] This invention provides a semiconductor heating element, comprising a semiconductor heating substrate, electrode layers disposed on both sides of the semiconductor heating substrate, and a corrosion-resistant protective layer covering the remaining surface of the semiconductor heating substrate and the electrode layers; the semiconductor heating substrate is a metal oxide semiconductor heating material as described in the above technical solution or a metal oxide semiconductor heating material prepared by the preparation method described in the above technical solution.

[0012] This invention provides the application of the semiconductor heating element described in the above technical solution in the dewatering, drying and volume reduction of sludge and solid waste.

[0013] This invention provides a sludge solid waste dewatering, drying, and volume reduction system, comprising a sludge feeding unit, a drying treatment unit connected to the sludge feeding unit, a condensate tail gas treatment unit connected to the gas outlet of the drying treatment unit, and a temperature controller; the drying treatment unit includes a drying chamber, a stirring mechanism, and multiple semiconductor heating elements as described in the above technical solutions; the stirring mechanism includes a stirring shaft and stirring blades connected to the stirring shaft; the stirring blades are disposed within the drying chamber; the semiconductor heating elements are disposed on the inner sidewall of the drying chamber and on the stirring blades; the temperature controller is electrically connected to the semiconductor heating elements.

[0014] Preferably, the sludge feeding unit includes a sludge silo and a screw feeder, the screw feeder being connected to the sludge silo and the drying chamber; the condensate tail gas treatment unit includes a condensation tower connected to the gas outlet of the drying chamber, a condensation tank connected to the liquid outlet of the condensation tower, and a gas adsorption purification box connected to the gas outlet of the condensation tower; the temperature controller is a PID temperature controller.

[0015] This invention provides a method for dewatering, drying, and reducing the volume of sludge solid waste, which uses the sludge dewatering, drying, and volume reduction system described in the above technical solution to treat the sludge.

[0016] This invention provides a metal oxide semiconductor heating material, comprising the following components by mass percentage: 75-85% main phase semiconductor powder, 5-12% ion-doping modifier, 3-8% low-temperature sintering aid, and 2-5% inorganic binder; the main phase semiconductor powder includes titanium dioxide (TiO2), zinc oxide (ZnO), and gallium oxide (Ga2O3); the ion-doping modifier includes antimony trioxide (Sb2O3), manganese dioxide (MnO2), and yttrium oxide (Y2O3); the low-temperature sintering aid includes silicon dioxide and borate glass powder; and the inorganic binder includes kaolin and alumina. This invention uses a ternary composite metal oxide as the main phase semiconductor powder, combined with ion-doping modifier, low-temperature sintering aid, and inorganic binder, to obtain a metal oxide semiconductor heating material with excellent electrothermal conversion performance. The electrothermal conversion efficiency of the metal oxide semiconductor heating material is ≥92%, the self-limiting isothermal range is 55-75℃, and the volume resistivity is 10⁻⁶. 3 ~10 5 The temperature rises at a rate of ≥3℃ / min at low temperatures (Ω·cm), and the power attenuation is ≤6% after a 2000-hour acidic sludge volatile gas corrosion test. This invention achieves near-efficient conversion of electrical energy into heat energy with low energy wastage. The semiconductor heating element, made from the aforementioned metal oxide semiconductor heating material, possesses high electrothermal conversion efficiency, stable low-temperature self-limiting temperature, resistance to acid and alkali corrosion, and low long-term power attenuation. It is suitable for low-temperature, closed-loop drying and volume reduction treatment of various high-moisture sludge types, including biochemical sludge, chemical sludge, dyeing and printing sludge, and electroplating sludge from municipal wastewater treatment plants.

[0017] This invention provides a method for preparing the metal oxide semiconductor heating material described in the above technical solution. The preparation method provided by this invention has a simple process, low raw material cost, and is suitable for industrial mass production. This invention provides a sludge solid waste dewatering, drying, and volume reduction system. Compared with existing technologies, this invention has the following advantages: The system provided by this invention has significant energy-saving effects. The semiconductor heating element used in this invention has an electrothermal conversion efficiency of ≥92%, eliminating the fan circulation energy consumption of traditional hot air drying and heat pump drying. The power consumption per unit of sludge treatment is reduced to 70~85kW·h / t, which is 30~40% more energy-efficient than conventional heat pump drying. Furthermore, the semiconductor heating element has self-limiting temperature characteristics, eliminating the need for continuous full-power heating. Intermittent operation can further reduce electricity costs.

[0018] The system provided by this invention is safe to operate and produces no secondary pollution. This invention employs a fully enclosed, low-temperature drying unit, with a maximum temperature not exceeding 75℃, below the pyrolysis temperature of sludge organic matter, eliminating the risk of dust explosions and sludge spontaneous combustion; there is no high-speed hot air circulation, completely eliminating drying dust pollution; under low-temperature conditions, the generation of malodorous substances such as hydrogen sulfide and volatile organic acids is reduced by more than 60%, the size of the exhaust gas treatment equipment is significantly reduced, and investment and maintenance costs are lowered.

[0019] The semiconductor heating element used in the system provided by this invention is corrosion-resistant and has a long service life. The semiconductor heating element used in this invention adopts a ternary composite metal oxide lattice with an outer corrosion-resistant protective layer, which can withstand long-term corrosion from hydrogen sulfide, organic acids, and chloride ions released by sludge. The heating element has a continuous and stable operating life of ≥8000h, which is far superior to ordinary metal heating tubes and single oxide heating elements.

[0020] The system equipment provided by this invention has strong adaptability and is easy to operate and maintain. The semiconductor heating element in this invention can be processed into various specifications such as flat plate, arc shape, tubular shape, and blade embedded, and can be newly matched with blade, disc and belt sludge dryers, or can be used to upgrade existing traditional drying equipment; it adopts a modular design, and a single heating element can be disassembled and replaced individually if it fails, without the need for the whole machine to be shut down, and the equipment utilization rate is high.

[0021] The system provided by this invention is purely electrically heated, does not consume fossil fuels such as gas or coal, and has no carbon emissions from combustion; after deep reduction of sludge, the carbon footprint of landfill, incineration, and transportation processes is greatly reduced, making it green, environmentally friendly, and highly safe.

[0022] In summary, the sludge solid waste dewatering, drying, and volume reduction system provided by this invention achieves closed-loop, low-temperature surface contact drying of sludge, significantly reducing energy consumption, eliminating dust and explosion risks, reducing the generation of odorous pollutants, and completing deep sludge volume reduction. It is suitable for the low-temperature, closed-loop drying and volume reduction treatment of various high-moisture sludge types, such as biochemical sludge from municipal wastewater treatment plants, chemical sludge, dyeing and printing sludge, and electroplating sludge. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the sludge solid waste dewatering, drying and volume reduction system in this invention; Figure 2 This is a schematic diagram of the drying chamber in this invention; Figure 3 This is a partial structural schematic diagram of the semiconductor heating element in this invention; In the figure: 1-Drying chamber, 2-Semiconductor heating element, 3-Stirring shaft, 4-Stirring blade, 5-Gas outlet, 6-Semiconductor heating substrate, 7-Electrode layer. Detailed Implementation

[0024] This invention provides a metal oxide semiconductor heating material, comprising the following components by mass percentage: The composition comprises 75-85% main phase semiconductor powder, 5-12% ion doping modifier, 3-8% low-temperature sintering aid, and 2-5% inorganic binder; the main phase semiconductor powder includes titanium dioxide (TiO2), zinc oxide (ZnO), and gallium oxide (Ga2O3); the ion doping modifier includes antimony trioxide (Sb2O3), manganese dioxide (MnO2), and yttrium oxide (Y2O3); the low-temperature sintering aid includes silicon dioxide and borate glass powder; and the inorganic binder includes kaolin and alumina.

[0025] In this invention, unless otherwise specified, all raw materials / components used in the preparation are commercially available products well known to those skilled in the art.

[0026] The metal oxide semiconductor heating material provided by the present invention comprises, by mass percentage, 75-85% of the main phase semiconductor powder, more preferably 80-85%, further preferably 82-85%, and in the embodiments, 84.4%. In the present invention, the main phase semiconductor powder comprises titanium dioxide (TiO2), zinc oxide (ZnO), and gallium oxide (Ga2O3). The preferred mass ratio of titanium dioxide, zinc oxide, and gallium oxide is (5-7):(2-4):1, more preferably 6:3:1.

[0027] The metal oxide semiconductor heating material provided by this invention comprises, by mass percentage, 5-12% ion-doped modifier, more preferably 6-10%, further preferably 7-9%, and in the embodiments, 8.85%. In this invention, the ion-doped modifier comprises antimony trioxide (Sb₂O₃), manganese dioxide (MnO₂), and yttrium oxide (Y₂O₃). The preferred mass ratio of antimony trioxide, manganese dioxide, and yttrium oxide is (1-3):(0.5-1.5):(0.3-1), and in the embodiments, it can be 2:1:0.5.

[0028] The metal oxide semiconductor heating material provided by this invention comprises 3-8% by mass percentage, more preferably 3.5-6%, and even more preferably 4-5%, with 4.22% in the embodiments. In this invention, the low-temperature sintering aid comprises silicon dioxide and borate glass powder. The mass ratio of silicon dioxide to borate glass powder is preferably 1:(2-4), with 1:3 in the embodiments.

[0029] The metal oxide semiconductor heating material provided by this invention comprises, by mass percentage, 2-5% inorganic binder, preferably 2.1-4%, more preferably 2.3-3%, and in the embodiments, 2.53%. In this invention, the inorganic binder comprises kaolin and alumina. The mass ratio of kaolin to alumina is preferably (1-3):1, more preferably 2:1. The alumina can be alumina micropowder, specifically α-alumina micropowder. In this invention, the median particle size D of the alumina micropowder... 50 The preferred size is 1.0~3.0μm.

[0030] In this invention, the metal oxide semiconductor heating material has an electrothermal conversion efficiency ≥92%, a self-regulating temperature range of 55~75℃, and a volume resistivity of 10. 3 ~10 5 Ω·cm, low temperature heating rate ≥3℃ / min, power attenuation ≤6% after 2000h acidic sludge volatile gas corrosion test.

[0031] In this invention, the morphology of the metal oxide semiconductor heating material includes one or more of the following: flat plate, tubular, and arc-shaped.

[0032] This invention provides a method for preparing the metal oxide semiconductor heating material described in the above technical solution, comprising the following steps: The main phase semiconductor powder, ion doping modifier, low-temperature sintering aid and inorganic binder are ball-milled and mixed to obtain a mixed precursor powder; The mixed precursor powder and the water-based inorganic binder are kneaded to obtain a mixture. The mixture is molded to obtain a heating blank; The heating blank is sintered to obtain the metal oxide semiconductor heating material.

[0033] This invention involves ball milling a main phase semiconductor powder, an ion-doped modifier, a low-temperature sintering aid, and an inorganic binder to obtain a mixed precursor powder. In this invention, the ball milling is preferably performed using a planetary ball mill. The ball milling is carried out in a planetary ball mill. The preferred conditions for the planetary ball milling include: the dispersion medium can be ethanol, specifically anhydrous ethanol. The mass percentage of the dispersion medium relative to the total mass of the main phase semiconductor powder, ion-doped modifier, low-temperature sintering aid, and inorganic binder is preferably 100-120%. The grinding beads are preferably zirconia beads. The ball-to-powder ratio is preferably 4:1. The grinding beads preferably include a first-stage grinding bead and a second-stage grinding bead, with the first-stage grinding bead preferably having a particle size of 10 mm and the second-stage grinding bead preferably having a particle size of 3 mm. The mass ratio of the first-stage grinding bead to the second-stage grinding bead is 1:1. The ball milling time is preferably 4-6 hours, and in this example, it can be 5 hours. The ball milling speed is preferably 300-400 r / min. The ball milling process directly yields wet ball-milled material. Preferably, the invention further includes sequentially drying, crushing, and sieving the wet ball-milled material to obtain the mixed precursor powder. The drying is preferably carried out in an electrically heated forced-air drying oven, with a drying temperature preferably of 100-105°C and a drying time preferably of 12-15 hours. The sieving screen is preferably 150-250 mesh, but in this embodiment, it can be 200 mesh.

[0034] After obtaining the mixed precursor powder, the present invention mixes the mixed precursor powder with an aqueous inorganic binder to obtain a mixture. In the present invention, the aqueous inorganic binder is preferably silica sol. The solid content of the aqueous inorganic binder is preferably 30±2%. The percentage of the dry basis solids of the aqueous inorganic binder to the mass of the mixed precursor powder is preferably 3~7wt%, and in the examples, it can be 5wt%. In the present invention, the mixing is preferably carried out in a double planetary vacuum kneader. In the present invention, the mixing conditions preferably include: a vacuum degree preferably of -0.06MPa and a mixing time preferably of 25~30min.

[0035] In this invention, the mud is obtained directly after the mixing is completed; the moisture content of the mud is preferably 8-10%. This invention preferably also includes aging the mud to obtain the mixture. The aging temperature is room temperature, and the aging time is preferably 10-12 hours.

[0036] After obtaining the mixture, the present invention performs compression molding to obtain a heating blank. In the present invention, the mold used for compression molding is a steel flat mold. The inner surface of the mold is preferably sprayed with a water-based release agent before compression molding. The compression molding pressure is preferably 12~16MPa, and in the embodiment it can be 14MPa. Before compression molding, a pre-compression treatment is preferably included, the pressure of which is preferably 2~3MPa, the pre-compression is vented for 30s, and then the pressure is increased to the compression molding pressure for compression molding. The compression molding time is preferably 100~120s. After compression molding, the present invention removes the blank from the mold and performs air-drying and drying treatments on the blank in sequence to obtain a heating blank. The air-drying treatment is performed at room temperature for 12~15h. The drying temperature is preferably 100~110℃ for 3~4h. In the present invention, the morphology of the heating blank preferably includes one or more of the following: flat, tubular, and arc-shaped. After obtaining the heating blank, the present invention sintersects the heating blank to obtain the metal oxide semiconductor heating material. Preferably, the heating blank is placed in a single layer on an alumina sintering pad and pushed into a box-type atmosphere sintering furnace for sintering. The sintering atmosphere is air. The heating rate during the sintering process is preferably 2~5℃ / min. The sintering preferably includes sequentially performing a first-stage holding sintering, a second-stage holding sintering, and a third-stage holding sintering. The temperature of the first-stage holding sintering is preferably 220~280℃, and the holding time is preferably 1~2h. The first-stage holding sintering removes the binder, eliminating organic binder components within the blank. The temperature of the second-stage holding sintering is preferably 580~630℃, and the holding time is preferably 2~3h. The second-stage holding sintering activates the metal oxide semiconductor crystal structure. The temperature of the third-stage holding sintering is preferably 880~930℃, and the holding time is preferably 3~4h. The third-stage holding sintering completes the dense sintering. After sintering, the material is naturally cooled in the furnace to obtain the metal oxide semiconductor heating material.

[0037] like Figure 3 As shown, the present invention provides a semiconductor heating element, including a semiconductor heating substrate 6, electrode layers 7 disposed on both sides of the semiconductor heating substrate 6, and a corrosion-resistant protective layer covering the remaining surface of the semiconductor heating substrate 6 and the electrode layers 7; the semiconductor heating substrate 6 is a metal oxide semiconductor heating material as described in the above technical solution or a metal oxide semiconductor heating material prepared by the preparation method described in the above technical solution.

[0038] In this invention, the electrode layer 7 is preferably a silver-palladium alloy electrode layer. The corrosion-resistant protective layer is preferably a silicon-aluminum composite corrosion-resistant protective layer.

[0039] This invention provides a method for preparing the semiconductor heating element described in the above technical solution, preferably comprising the following steps: printing electrode layers 7 on both sides of the semiconductor heating substrate 6 using a screen printing method, and then drying them to obtain a substrate after electrode printing; subjecting the substrate after electrode printing to heat treatment to obtain a semi-finished product; coating the outer surface of the semi-finished product with a silicon-aluminum composite corrosion-resistant coating (the silicon-aluminum composite corrosion-resistant coating is purchased from Beijing Zhisheng Weihua Chemical Co., Ltd., product model ZS-1041), and then curing it to obtain the semiconductor heating element. The screen printing conditions include: a screen mesh count of 200 mesh, and a printing thickness preferably of 25~30 μm. The drying temperature is preferably 110~120℃, and the drying time is preferably 30~40 min. The heat treatment temperature is preferably 500~550℃, and the heat treatment time is preferably 1~1.5 h. The coating is preferably spraying. The coating thickness is preferably 40~50 μm. The curing temperature is preferably 80~85℃, and the curing time is preferably 1~2 h.

[0040] This invention provides the application of the semiconductor heating element described in the above technical solution in the dewatering, drying and volume reduction of sludge and solid waste.

[0041] like Figures 1-2 As shown, this invention provides a sludge solid waste dewatering, drying, and volume reduction system, including a sludge feeding unit, a drying treatment unit connected to the sludge feeding unit, a condensate tail gas treatment unit connected to the gas outlet of the drying treatment unit, and a temperature controller. The drying treatment unit includes a drying chamber 1, a stirring mechanism, and multiple semiconductor heating elements 2 as described in the above-mentioned technical solutions. The stirring mechanism includes a stirring shaft 3 and stirring blades 4 connected to the stirring shaft 3. The stirring blades 4 are disposed within the drying chamber 1, and the semiconductor heating elements 2 are disposed on the inner wall of the drying chamber 1 and on the stirring blades 4. The temperature controller is electrically connected to the semiconductor heating elements 2. The sludge solid waste dewatering, drying, and volume reduction system provided by this invention does not have a hot air circulation heat exchange structure. The sludge solid waste dewatering, drying, and volume reduction system provided by this invention utilizes the self-limiting temperature characteristic of the semiconductor heating elements 2 (55~75℃) in conjunction with the temperature controller to maintain a constant temperature of 55~75℃ inside the drying chamber.

[0042] In this invention, the sludge feeding unit enables continuous, closed-loop conveying of sludge with high water content. The sludge feeding unit includes a sludge silo and a screw feeder, the screw feeder being connected to the sludge silo and the drying chamber 1.

[0043] In this invention, the drying chamber 1 is a sealed drying chamber. The drying chamber 1 is a fully sealed pressure-bearing structure. The stirring shaft 3 and the stirring blade 4 are disposed inside the drying chamber 1. In this invention, a gas outlet 5 is provided at the top of the drying chamber 1.

[0044] In this invention, the condensate exhaust gas treatment unit includes a condensation tower connected to the gas outlet 5 of the drying chamber 1, a condensation tank connected to the liquid outlet of the condensation tower, and a gas adsorption purification box connected to the gas outlet of the condensation tower. This invention uses the condensation tower to perform condensation and liquid separation on the gas components obtained in the drying chamber 1, and the resulting liquefied water is stored in the condensation tank. The resulting non-condensable gas is an odorous gas, which is treated in the gas adsorption purification box to meet emission standards.

[0045] In this invention, a fitted semiconductor heating element is disposed on the inner wall of the drying chamber 1. An embedded semiconductor heating element is disposed on the stirring blade 4. Preferably, the semiconductor heating element is disposed on the stirring blade 4 in an embedded manner.

[0046] In this invention, the temperature controller is a PID temperature controller. The controlled load of the temperature controller is all the semiconductor heating elements within the cavity, including heating elements attached to the inner wall of the cavity and heating elements embedded inside the stirring blades. A conductive slip ring on the stirring shaft 3 ensures continuous electrical connection between the rotating blade heating elements and the PID temperature controller output. All heating elements are connected in parallel to the output of the PID temperature controller. The PID temperature controller collects ambient temperature in real time through multiple temperature sensors within the cavity and coordinates with the inherent self-limiting temperature characteristic of the semiconductor heating material (55~75℃) for coordinated control: under normal conditions, it uses a pulse duty cycle power adjustment method to regulate the output power of the heating elements, stably maintaining a constant temperature range within the cavity; it only cuts off the power supply to the heating elements when the temperature exceeds the limit and triggers safety protection, rather than relying solely on a two-position switch for power on / off control. The sludge feeding unit, the sealed drying chamber shell, the stirring shaft blade base, the condensation recovery tank, and the tail gas adsorption purification box are all common and mature components in the sludge drying industry. This invention integrates the metal oxide semiconductor heating element on the inner wall of the chamber and the stirring blade, eliminating the hot air circulation heat exchange structure. It is combined with the material's self-limiting temperature and the PID temperature controller to form a sealed low-temperature surface contact drying complete set of equipment.

[0047] This invention provides a method for dewatering, drying, and reducing the volume of sludge solid waste, employing the sludge dewatering, drying, and volume reduction system described above to treat the sludge. The preferred method for dewatering, drying, and reducing the volume of sludge solid waste provided by this invention includes the following steps: sludge is conveyed from a sludge feeding unit to a drying chamber; a temperature controller controls the energization of a semiconductor heating element to maintain the temperature in the drying chamber at 55-75°C; the sludge in the drying chamber is dewatered and dried under stirring conditions; the gas components obtained in the drying chamber enter a condensate tail gas treatment unit through a gas outlet; gas-liquid separation is performed in a condensation tower; the liquefied water obtained from the condensation tower is transported to a condensation tank for storage. The non-condensable gas generated in the condensation tower is an odorous gas, which is treated in a gas adsorption purification box to meet emission standards before being discharged. In this invention, the sludge is mechanically dewatered sludge, and the moisture content of the sludge is preferably 78-82%. The sludge is continuously conveyed to the drying chamber by the sludge feeding unit. In this invention, the sludge product obtained by the dehydration and drying treatment has a moisture content of ≤28% and a sludge volume reduction of ≥65%.

[0048] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0049] The raw materials used in the following examples include: titanium dioxide, Yunnan Nano Electronic New Materials Co., Ltd., NA-ET03; zinc oxide, Changzhou Kenada New Materials Technology Co., Ltd., KN-Z04; gallium oxide, Hefei Kejing Materials Technology Co., Ltd., Ga2O3-4N; antimony trioxide, Yiyang Huachang Antimony Industry Co., Ltd., HC-SB02; manganese dioxide, Tim (Beijing) New Materials Technology Co., Ltd., MN-4N01; yttrium oxide, Shandong Desheng New Materials Co., Ltd., DS-Y-04; silicon dioxide, Nanjing Baoket New Materials Co., Ltd., BK-S03; borate glass powder, Jiangsu Qiuzheng New Materials Technology Co., Ltd., Zn-3039; alumina micro powder, Zibo Baida New Materials Technology Co., Ltd., BN-A02; and kaolin, China Kaolin Co., Ltd., JS-1000.

[0050] Example 1 This embodiment provides a metal oxide semiconductor heating material, comprising the following components in parts by weight: 60 parts TiO2, 30 parts ZnO, 10 parts Ga2O3; 6 parts Sb2O3, 3 parts MnO2, 1.5 parts Y2O3; 5 parts SiO2 and borate glass powder; and kaolin and α-alumina micropowder (the median particle size D of the α-alumina micropowder is...). 50 Three portions (1.0~3.0 μm) were prepared. The mass ratio of silica to borate glass powder was 1:3. The mass ratio of kaolin to alumina powder was 2:1. The specific preparation method of the metal oxide semiconductor heating material provided in this embodiment includes: (1) Accurately weigh all 118.5 parts by weight of the solid powder and put them into a vertical planetary ball mill jar. Add anhydrous ethanol as a dispersion medium at 120% of the total powder mass, and match it with zirconia grinding balls (the mass ratio of balls to powder is 4:1, and the mass ratio of large balls Φ10mm and small balls Φ3mm is 1:1). Seal the ball mill jar, set the planetary ball mill speed to 300r / min, and continuously wet ball mill for 5h to ensure that the powder is fully dispersed and there are no agglomerated particles. After ball milling, transfer all the suspension slurry to a stainless steel tray and put it into an electric heating forced-air drying oven. Dry it at a constant temperature of 105℃ for 12h to completely remove the ethanol solvent. After drying, the agglomerated powder is pre-crushed with an agate mortar and passed through a 200-mesh standard sieve. The fine powder that passes through the sieve is the mixed precursor powder. Store it in a sealed, moisture-proof container for later use.

[0051] (2) The mixed precursor powder is put into a double planetary vacuum kneader and sprayed with 19.75 parts of water-based inorganic binder (the water-based inorganic binder is silica sol and the solid content of the water-based inorganic binder is 30%) at a low speed stirring state; the kneader is sealed and kneaded for 25 minutes under a vacuum of -0.06MPa to ensure that the binder evenly coats each powder particle; after the kneading is completed, the moisture content of the mud is tested and controlled at 10%; if the moisture content is too high, the lid is opened and the kneading is carried out at a low speed for 5~10 minutes for fine adjustment; if the moisture content is too low, a small amount of deionized water is added; after conditioning, the mud is sealed and left to stand for 10 hours to release internal stress, improve molding plasticity, and avoid delamination and cracking of the pressed blank, so as to obtain the mixed material.

[0052] (3) Select a 300mm×400mm steel flat mold, and spray a small amount of water-based release agent evenly into the inner cavity of the mold; fill the aged mixture into the mold evenly, scrape the surface smooth, and place it on the worktable of the four-column hydraulic molding machine; pressurize in two stages: first, pre-press at a low pressure of 3MPa for 30s to exhaust air, then increase the pressure to 14MPa and hold for 120s, and slowly and evenly release the pressure. Remove the green blank from the mold and air dry it in a ventilated place at room temperature for 12 hours to remove free water from the surface. Then, put it into an oven at 110℃ and dry it for 4 hours to obtain a dry and dense green blank. The green blank is free from warping, delamination, and edge defects, which is the heating green body, specifically a 300mm×400mm flat green body. (4) Place the dried heating blanks in a single layer on the alumina sintering pad, push them into the box-type atmosphere sintering furnace, maintain an air atmosphere throughout the process, and keep the temperature at a uniform rate of 2℃ / min. The process is divided into three stages of heat preservation: Stage 1: The room temperature is raised to 250℃ and kept at 250℃ for 2 hours (binding removal process). The purpose is to slowly remove residual moisture and low molecular weight components of water-based binders from the blanks to prevent rapid bubbling and cracking of the blanks; Stage 2: The temperature is raised from 250℃ to 600℃ and kept at 600℃ for 3 hours (pre-sintering lattice activation). The purpose is to activate the TiO2 / ZnO / Ga2O3 semiconductor composite lattice and dope the metal. Ions are uniformly dissolved and enter the main phase lattice, initially forming a conductive path; the third stage: the temperature is raised from 600℃ to 900℃ and held at 900℃ for 4 hours (dense sintering), which allows the borate glass powder to melt and form a liquid phase, promoting the dense sintering of the powder particles, and the silicon-aluminum phase fills the internal pores, improving the strength and corrosion resistance of the matrix; after sintering, the heating power is turned off, the furnace door is kept sealed, and the furnace is allowed to cool naturally to room temperature (total cooling time is about 16 hours), and the metal oxide semiconductor heating material is obtained, which serves as the semiconductor heating substrate for semiconductor heating elements, with a morphology of a 300mm×400mm plate.

[0053] This embodiment provides a method for preparing a semiconductor heating element, specifically including the following steps: Screen-printed electrodes: A 200-mesh screen is used to uniformly print silver-palladium alloy electrode layers on the upper and lower surfaces of the semiconductor heating substrate, with a printing thickness of 25μm; after printing, dry at 120℃ for 30min. Low-temperature electrode curing: The substrate after printing the electrode is placed in an oven at 550℃ for 1 hour to ensure that the silver-palladium electrode is firmly bonded to the substrate surface and to ensure stable conductivity. Anti-corrosion coating: Spray a silicon-aluminum composite corrosion-resistant coating material (Beijing Zhisheng Weihua Chemical Co., Ltd., ZS-1041) on the outer surface of the heating substrate and the entire electrode. The coating thickness is 40μm; dry at 80℃ for 2h to fully cure. The final product is a semiconductor heating element with a size of 300mm×400mm, namely a semiconductor heating plate.

[0054] The performance test results of the semiconductor heating element prepared in this embodiment are as follows: the electrothermal conversion efficiency is 93.5%, the self-limiting temperature is stable at 68℃, the heating power decreases by 4.2% after 2000h acid corrosion test, and the heating rate is 3.6℃ / min. The specific test methods are as follows: The test conditions and results of various performance tests of the semiconductor heating element prepared in this embodiment are as follows: (1) The electrothermal conversion efficiency is 93.5%: The test refers to the heat flow meter method of GB / T 7287-2008 "Test Method for Infrared Radiation Heaters". The test environment is 25±2℃, and a 50mm thick aluminum silicate thermal insulation layer is laid on the back of the element; a high-precision power analyzer is used to collect the active power input of the element; multiple heat flow sensors are arranged on the heating surface, and the total effective output heat power is collected after the element is thermally balanced (temperature fluctuation ≤±1℃ / 10min); the electrothermal conversion efficiency η = (effective output heat power ÷ input active power) × 100%.

[0055] (2) Self-limiting stable temperature of 68℃: The test method for the highest maintenance temperature in GB / T 29470-2012 "Self-limiting heating element" was used. The sample was unloaded and without forced convection, and the rated voltage was applied. Five K-type thermocouples were evenly arranged on the surface of the heating element. After the temperature reached thermal equilibrium, the arithmetic mean of all temperature measurement points was taken as the self-limiting steady-state temperature, and the steady-state limit temperature was measured to be 68℃.

[0056] (3) Heating rate 3.6℃ / min: The test environment is 25±2℃. The sample is pre-stationary until it is in equilibrium with the ambient temperature. The rated voltage is turned on, and the thermocouple continuously collects the surface temperature. The temperature data is recorded once every 10s. The average heating slope from 25℃ to the near steady-state temperature range is taken to calculate the heating rate 3.6℃ / min.

[0057] (4) 4.2% decrease in heating power after 2000h acidic sludge volatile gas corrosion test: The corrosion test was conducted in accordance with GB / T2423.51-2020 "Environmental Testing Part 2-51: Test Ke: Corrosion Test of Flowing Mixed Gases", simulating the sludge drying process under a combined corrosive atmosphere of hydrogen sulfide, organic acid, and water vapor. Test chamber conditions: temperature 65±2℃, relative humidity 90±3% RH; mixed corrosive atmosphere: H2S 25ppm, acetic acid 15ppm; the element was continuously powered on for 2000h under rated operating voltage. Before the test and after cooling to room temperature at the end of the test, the active heating power of the element was tested under rated voltage; power attenuation rate = (initial power - power after corrosion) ÷ initial power × 100%; the measured power attenuation was 4.2%.

[0058] Example 2: Sludge drying and volume reduction test The semiconductor heating plate prepared in Example 1 was assembled into a closed paddle drying device, specifically on the inner wall of the drying chamber and embedded in the stirring paddle, to treat mechanically dewatered sludge from a municipal wastewater treatment plant. The initial moisture content of the sludge was 81.2%, and the chamber temperature was kept constant at 68°C. Figure 1The sludge solid waste dewatering, drying, and volume reduction system shown in the diagram operates continuously. Operating data: sludge residence time in the drying chamber is 4.5 hours; the output sludge moisture content is 26.7%; sludge volume reduction is 68.3%; power consumption per unit sludge is 76 kW·h / t; the odor concentration in the exhaust gas is reduced by 62% compared to commercial heat pump drying equipment; and there is no dust emission throughout the process.

[0059] Comparative Example 1: Single Titanium Dioxide Semiconductor Heating Material This comparative metal oxide semiconductor heating material differs from Example 1 only in that the main phase semiconductor powder is replaced with a single titanium dioxide. The composition and proportions of the ion-doping modifier, low-temperature sintering aid, and inorganic binder are completely identical. The mass fractions of each component are as follows: Main phase semiconductor powder: TiO2 100 parts; Ion-doping modifier: Sb2O3 6 parts, MnO2 3 parts, Y2O3 1.5 parts; Low-temperature sintering aid: SiO2 and borate glass powder combined 5 parts, with a mass ratio of 1:3; Inorganic binder: Kaolin and α-alumina micropowder (median particle size D...). 50 Three portions (1.0~3.0μm) were prepared, with a mass ratio of 2:1.

[0060] The selection of powder raw materials, ball milling and mixing, vacuum mixing, molding, segmented sintering, electrode printing of semiconductor heating elements, and preparation of anti-corrosion coating are all exactly the same as in Example 1, except that ZnO and Ga2O3 powders are no longer added in the batching stage.

[0061] Performance testing of the semiconductor heating element prepared in this comparative example (testing method is the same as in Example 1): The electrothermal conversion efficiency is 77%, and there is no stable self-limiting temperature range of 55-75℃. After 800 hours of operation under simulated corrosion conditions, the heating power decreases by 20.3%. Local hot spots appear on the surface of the component, with the highest local temperature exceeding 112℃. Local scorching of sludge occurs after contact with sludge material.

[0062] As shown in the above embodiments, this invention provides a metal oxide semiconductor heating material specifically for sludge drying. The heating material is based on a ternary oxide of TiO2 / ZnO / Ga2O3, with antimony, manganese, and yttrium oxides as composite ion doping. It is formed through segmented solid-state sintering with a low-temperature sintering aid, exhibiting advantages such as an electrothermal conversion efficiency of over 92%, stable self-limiting temperature of 55-75℃, resistance to acid and alkali corrosion from sludge, and low long-term power attenuation. This invention is paired with a closed sludge drying system that integrates the semiconductor heating element with the cavity and stirring blades, employing solid-surface contact for low-temperature heat conduction. This eliminates the need for hot air circulation, thus eliminating dust and dust explosion hazards. The low drying temperature significantly reduces the production of odorous pollutants, and the water vapor condensation and separation simplify tail gas treatment. Compared to traditional heat pumps and hot air drying, the power consumption per unit of sludge is reduced by more than 30%, the sludge volume is reduced by more than 65%, the heating element has a long service life, and maintenance costs are low. It is suitable for deep reduction and treatment of various high-moisture sludge types in municipal, chemical, and dyeing industries, offering broad prospects for low-carbon, environmentally friendly, and industrial applications.

[0063] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, not all embodiments. Other embodiments can be obtained based on these embodiments without creative intent, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A metal oxide semiconductor heating material, characterized in that, Includes the following components by mass percentage: The composition comprises 75-85% main phase semiconductor powder, 5-12% ion doping modifier, 3-8% low-temperature sintering aid, and 2-5% inorganic binder; the main phase semiconductor powder includes titanium dioxide, zinc oxide, and gallium oxide; the ion doping modifier includes antimony trioxide, manganese dioxide, and yttrium oxide; the low-temperature sintering aid includes silicon dioxide and borate glass powder; and the inorganic binder includes kaolin and alumina.

2. The metal oxide semiconductor heating material according to claim 1, characterized in that, The mass ratio of titanium dioxide, zinc oxide and gallium oxide is (5~7):(2~4):1; the mass ratio of antimony trioxide, manganese dioxide and yttrium oxide is (1~3):(0.5~1.5):(0.3~1); the mass ratio of silicon dioxide to borate glass powder is 1:(2~4); and the mass ratio of kaolin to alumina is (1~3):

1.

3. The method for preparing the metal oxide semiconductor heating material according to claim 1 or 2, characterized in that, Includes the following steps: The main phase semiconductor powder, ion doping modifier, low-temperature sintering aid and inorganic binder are ball-milled and mixed to obtain a mixed precursor powder; The mixed precursor powder and the water-based inorganic binder are kneaded to obtain a mixture. The mixture is molded to obtain a heating blank; The heating blank is sintered to obtain the metal oxide semiconductor heating material.

4. The preparation method according to claim 3, characterized in that, The ball milling mixing is planetary ball milling mixing, and the conditions for planetary ball milling mixing include: the dispersion medium is ethanol, and the ball milling time is 4-6 hours; the ball milling mixing directly yields wet ball milled material, and further includes drying, crushing, and sieving the wet ball milled material in sequence to obtain the mixing precursor powder, wherein the sieve screen is preferably 150-250 mesh; the aqueous inorganic binder is silica sol, and the solid content of the aqueous inorganic binder is 30±2%; the dry basis solids of the aqueous inorganic binder account for 3-7 wt% of the mass of the mixing precursor powder.

5. The preparation method according to claim 3 or 4, characterized in that, The molding pressure is 12~16MPa; the morphology of the heated blank includes one or more of flat, tubular and arc-shaped; the sintering includes sequentially performing a first stage of heat preservation sintering, a second stage of heat preservation sintering and a third stage of heat preservation sintering, wherein the temperature of the first stage of heat preservation sintering is 220~280℃ and the holding time is 1~2h, the temperature of the second stage of heat preservation sintering is 580~630℃ and the holding time is 2~3h, and the temperature of the third stage of heat preservation sintering is 880~930℃ and the holding time is 3~4h.

6. A semiconductor heating element, characterized in that, It includes a semiconductor heating substrate, electrode layers disposed on both sides of the semiconductor heating substrate, and a corrosion-resistant protective layer covering the remaining surface of the semiconductor heating substrate and the electrode layers; the semiconductor heating substrate is the metal oxide semiconductor heating material according to claim 1 or 2 or the metal oxide semiconductor heating material prepared by the preparation method according to any one of claims 3 to 5.

7. The application of the semiconductor heating element according to claim 6 in the dewatering, drying and volume reduction of sludge solid waste.

8. A sludge solid waste dewatering, drying, and volume reduction system, characterized in that, The device includes a sludge feeding unit, a drying unit connected to the sludge feeding unit, a condensate tail gas treatment unit connected to the gas outlet of the drying unit, and a temperature controller; the drying unit includes a drying chamber, a stirring mechanism, and a plurality of semiconductor heating elements as described in claim 6; the stirring mechanism includes a stirring shaft and stirring blades connected to the stirring shaft; the stirring blades are disposed within the drying chamber; the semiconductor heating elements are disposed on the inner wall of the drying chamber and on the stirring blades; the temperature controller is electrically connected to the semiconductor heating elements.

9. The sludge solid waste dewatering, drying, and volume reduction system according to claim 8, characterized in that, The sludge feeding unit includes a sludge silo and a screw feeder, the screw feeder being connected to the sludge silo and the drying chamber; the condensate tail gas treatment unit includes a condensation tower connected to the gas outlet of the drying chamber, a condensation tank connected to the liquid outlet of the condensation tower, and a gas adsorption purification box connected to the gas outlet of the condensation tower; the temperature controller is a PID temperature controller.

10. A method for dewatering, drying, and reducing the volume of sludge solid waste, characterized in that, The sludge is treated using the sludge dewatering, drying, and volume reduction system described in claim 8 or 9.

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