Harmless and reduction treatment process for sludge

Abstract

The invention relates to the technical field of solid waste treatment, and discloses a sludge harmless and reduction treatment process which comprises a central control system, and a hydrolysis unit, an anaerobic reaction unit, a digestive juice temporary storage unit, a centrifugal dewatering unit, a sunlight drying unit and a sludge temporary storage and packaging unit which are sequentially connected in series. Marsh gas generated by the anaerobic reaction unit is purified and then enters the marsh gas utilization unit, and a heat energy recovery device configured in the marsh gas utilization unit conveys waste heat to the hydrolysis unit, the anaerobic reaction unit and the sunshine drying unit through a heat medium water circulation pipe network to form a heat circulation loop. The central control system is used for blending feeding based on a dry matter mass balance principle, controlling anaerobic temperature by utilizing cascade feedforward logic, and adjusting drying ventilation according to an indoor and outdoor absolute moisture content difference value. The energy self-sufficiency rate and the operation stability of sludge treatment are improved by constructing a closed-loop system for material conveying and energy recovery and combining a multi-parameter coupling control strategy.

Description

Technical Field

[0001] This invention relates to the field of solid waste treatment technology, specifically to a process for the harmless and volume-reduced treatment of sludge. Background Technology

[0002] With the continuous expansion of urban wastewater treatment scale, sludge production is increasing accordingly. Sludge contains a large amount of organic matter, pathogens, and heavy metals, and improper treatment can cause secondary pollution to the environment. Currently, the main technical routes for sludge treatment include anaerobic digestion, aerobic fermentation, and thermal drying, among which anaerobic digestion is widely used because it can produce biomass energy (biogas) and has a significant volume reduction effect. However, in existing sludge treatment engineering practices, the integration of process systems and operation control strategies still have certain limitations.

[0003] In terms of energy utilization, traditional sludge anaerobic digestion systems typically operate independently. Although the biogas produced can be used for power generation or boiler combustion, the utilization of internal thermal energy is often insufficient or lacks overall planning. For example, anaerobic digestion requires maintaining a constant mesophilic environment, while the subsequent sludge drying process consumes a large amount of heat. In existing technologies, the supply and demand of thermal energy in these two stages are often disconnected, resulting in the direct discharge of waste heat from the generator set's cylinder liners or flue gas, while the drying workshop needs to consume additional natural gas or electricity for heating. This mismatch between energy supply and demand increases the system's operating costs.

[0004] Regarding process control stability, the raw sludge entering the treatment system typically originates from diverse sources, with significant fluctuations in its solids content. Existing feed control methods often employ simple constant flow or volume conveying, lacking a dynamic adjustment mechanism based on dry matter mass. This leads to drastic changes in the organic load within the anaerobic reactor as the feed concentration fluctuates, easily causing system acidification or unstable gas production. Furthermore, as a large-volume container, the anaerobic reactor exhibits considerable thermal inertia, and conventional temperature feedback control often suffers from severe hysteresis, making it difficult to cope with disturbances caused by sudden changes in feed temperature or a sharp drop in ambient temperature.

[0005] In the sludge drying process, sun-drying chambers are common low-energy-consumption treatment facilities, but their operational efficiency is greatly affected by environmental climate. Existing ventilation control logic for drying chambers is rather crude, relying heavily on manual experience or simple timed start-stop systems, without fully considering the difference in absolute moisture content between indoor and outdoor air. In high-humidity outdoor environments or rainy weather, indiscriminate ventilation can actually cause external moisture to enter the chamber and be absorbed by the sludge, resulting in low drying efficiency or even sludge re-soaking. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a process for the harmless and volume-reduced treatment of sludge, which solves the problem that traditional anaerobic digestion systems for sludge usually operate independently. Although the biogas produced can be used for power generation or boiler combustion, the utilization of thermal energy within the system is often insufficient or lacks overall planning.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a sludge harmlessness and volume reduction treatment process, comprising a central control system and, in series via pipelines and conveying equipment, a hydrolysis unit, an anaerobic reaction unit, a digestate storage unit, a centrifugal dewatering unit, a solar drying unit, and a sludge storage and packaging unit. The gas phase outlet of the anaerobic reaction unit is also connected in series to a desulfurization unit and a biogas utilization unit. The biogas utilization unit is equipped with a heat recovery device, which is connected to the heating interfaces of the hydrolysis unit, the anaerobic reaction unit, and the solar drying unit via a heat transfer medium water circulation network, forming a heat circulation loop capable of supplying heat to the aforementioned units. The central control system is connected to the field control components of each unit via a communication network for collecting operational data and sending control commands.

[0008] In the hydrolysis unit, an online solids content detector and flow meter are installed on the feed pipeline of the hydrolysis tank, and an electric regulating valve is installed on the dispensing water pipeline. The central control system executes the feed dispensing logic based on the dry matter mass balance principle to eliminate the impact of fluctuations in the solids content of the raw sludge on subsequent processes. Specifically, the control logic is as follows: the system collects the solids content and feed flow rate of the raw sludge in real time, calculates the amount of dilution water required to maintain a constant dry matter mass based on the preset target solids content, and uses this as the control target value. The opening of the electric regulating valve is adjusted using a ratio control algorithm to maintain a constant ratio between the amount of dilution water added and the dry matter mass flow rate of the raw sludge.

[0009] The anaerobic reactor unit employs a combined anaerobic digester, which features a vertical cylindrical tank structure integrating an anaerobic digestion zone, a biogas storage zone, and a heat exchange assembly. The biogas storage zone, located at the top of the tank, consists of a double-membrane gas holder, enabling in-situ collection and pressurized storage of biogas. The heat exchange assembly includes a spiral coil attached to the inner wall of the tank, connected to a heat transfer medium water circulation network. An internal three-dimensional stirring system comprises a lift-type mixer located in the central guide tube and a submersible jet mixer located on the lower side wall. The jet direction of the submersible jet mixer is tangential to the inner wall of the tank, working in conjunction with the vertical flow field generated by the lift-type mixer to create a composite circulating flow field within the tank, eliminating dead zones and breaking up surface scum.

[0010] To address the high inertia thermodynamic characteristics of the anaerobic reactor, temperature control employs cascaded PID control logic with feedforward compensation. The internal temperature sensor of the anaerobic tank serves as the measurement input to the main controller, while the supply and return temperatures of the heating medium water serve as the measurement input to the secondary controller. When the feed flow sensor detects a sudden increase in flow or the ambient temperature sensor detects a sharp drop in outdoor temperature, the control system uses these disturbance variables as feedforward signals. Before a deviation occurs in the main loop, a correction is directly added to the setpoint of the secondary loop, proactively adjusting the opening of the heating medium water branch valves to increase heating power.

[0011] The biogas utilization unit includes a biogas generator set, a biogas boiler, and a safety flare. The heat recovery device includes a flue gas-water heat exchanger connected in series on the biogas generator set's exhaust pipe and a plate heat exchanger coupled to the generator set's cylinder liner water circulation loop. The heat transfer medium water circulation network delivers the recovered heat energy to each heat-using unit through a main supply pipe and a main return pipe. The main supply pipe has independent thermal branch pipes and regulating valves at the hydrolysis unit and the anaerobic reaction unit. The central control system is equipped with a heat distribution strategy; when the total heat of the heat transfer medium water is insufficient, priority is given to maintaining the heat supply flow of the anaerobic reaction unit's thermal branch pipes to ensure the temperature stability of the anaerobic fermentation system.

[0012] A receiving hopper is located below the solids outlet of the centrifugal dewatering unit, and a hydraulically driven high-pressure plunger pump is connected to its bottom. An annular water-lubricating device is installed between the outlet flange of the high-pressure plunger pump and the conveying pipe connected to the solar drying unit. This annular water-lubricating device is connected to a high-pressure water pump, which injects a lubricating water film between the inner wall of the conveying pipe and the high-concentration sludge to reduce friction resistance during long-distance pipeline transport.

[0013] The solar drying unit includes a solar drying chamber with an electric skylight on the roof and electric air inlet louvers and negative pressure exhaust fans on the side walls. The interior floor is a hardened concrete floor with pre-embedded underfloor heating pipes connected to the heat transfer fluid circulation network, utilizing waste heat to assist in moisture evaporation. The solar drying chamber is equipped with an integrated machine for spreading, collecting, and turning sludge. This machine, through the coordination of a main beam spanning the workshop, a longitudinal traveling mechanism, a lifting trolley, and a rotary tiller, achieves automatic spreading, turning, and transport of sludge.

[0014] The central control system incorporates a ventilation control logic module based on enthalpy-humidity chart calculations for environmental control of the solar drying unit. This module uses temperature and relative humidity data collected from weather stations and indoor sensors to calculate the absolute humidity of outdoor and indoor air in real time using the humid air state equation. The control logic is set to ensure effective ventilation only when the absolute humidity of indoor air is greater than that of outdoor air and the difference exceeds a preset dead zone threshold. In this case, the system instructs the opening of the electric skylight, air inlet louvers, and negative pressure exhaust fan. The exhaust fan's operating frequency is positively correlated with the difference in absolute humidity between indoor and outdoor air to improve dehumidification efficiency. When outdoor rainfall is detected or the difference falls below the threshold, the system automatically switches to internal circulation mode.

[0015] The sludge temporary storage and baling unit includes a dry material temporary storage bin and an automatic quantitative baling machine. An arch-breaking device is installed on the outer wall of the lower conical hopper of the dry material temporary storage bin. This device is electrically interlocked with the flow switch at the discharge port and automatically operates to restore fluidity when a material flow interruption is detected. Negative pressure dust collection hoods are installed at the top of the temporary storage bin and at the discharge port of the baling machine, and are connected to an explosion-proof pulse bag filter to suppress dust diffusion.

[0016] The process also includes the following steps: the hydrolysis unit receives the material and dynamically distributes and conditions the water based on the real-time solids content; the slurry enters the anaerobic reaction unit for mesophilic digestion, and the biogas produced is desulfurized and purified to generate electricity and heat, with the heat energy being recycled for front-end heating and insulation; after centrifugation and dewatering, the dewatered sludge is pumped to a solar drying room, where it is dried using solar energy and waste heat floor heating, with ventilation controlled according to the absolute moisture content difference and the sludge turned over periodically; finally, the dried sludge is automatically packaged and transported off-site.

[0017] This invention provides a process for the harmless and volume-reduced treatment of sludge. It has the following beneficial effects: 1. This invention constructs a heat energy recycling network, which returns the waste heat generated by the biogas utilization unit to the hydrolysis unit for material preheating, the anaerobic reaction unit for insulation, and the terminal solar drying room for auxiliary ground heating via a heat transfer medium water pipeline network. This fully exploits the associated energy value in the sludge treatment process, using waste heat from biogas power generation to replace the external heat source required in traditional processes, reducing the system's dependence on external electricity and natural gas, and achieving low-cost operation.

[0018] 2. This invention eliminates the impact of raw material fluctuations on the anaerobic system through a feed and water distribution logic based on dry matter mass balance; and avoids ineffective ventilation and excessive energy consumption through a ventilation control logic based on absolute moisture content differences, ensuring drying efficiency. This guarantees that each unit operates under its design conditions, improving process stability.

[0019] 3. This invention employs a combined anaerobic digestion reactor, integrating reaction, gas storage, and heat exchange, thus reducing the floor space required. It combines hydrolysis pretreatment with a dual drying process utilizing solar radiation and waste heat from underfloor heating, overcoming the bottleneck of conventional dehydration methods' inability to achieve deep dehumidification. Simultaneously, the use of a high-pressure plunger pump coupled with water injection lubrication technology enables the closed-loop transport of high-concentration sludge, solving the problems of odor overflow and material transfer within the plant area, and achieving deep sludge reduction and harmless treatment. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the process flow of the present invention; Figure 2 This is a schematic diagram of the overall device connection structure of the present invention; Figure 3 This is a diagram showing the hardware topology and network connection of the present invention.

[0021] The system includes: 1. Hydrolysis unit; 2. Anaerobic reaction unit; 3. Desulfurization unit; 4. Biogas utilization unit; 5. Digester liquid temporary storage unit; 6. Centrifugal dewatering unit; 7. Sun drying unit; 8. Sludge temporary storage and packaging unit; and 9. Central control system. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example: Please see the appendix Figure 1 -Appendix Figure 3 This invention provides a sludge harmless and volume reduction treatment process, including a hydrolysis unit 1, an anaerobic reaction unit 2, a desulfurization unit 3, a biogas utilization unit 4, a digestate temporary storage unit 5, a centrifugal dewatering unit 6, a solar drying unit 7, a sludge temporary storage and packaging unit 8, and a central control system 9. The units are connected via fluid transport pipelines, heat pipelines, and communication lines to form a complete closed-loop treatment system.

[0024] Hydrolysis unit 1 is the raw material receiving and pretreatment end of the closed-loop treatment system. Hydrolysis unit 1 is equipped with a receiving tank and a conveying pump set. The input end of hydrolysis unit 1 is connected to an external material source and is specifically used to receive food waste slurry, kitchen waste slurry, and sludge from sewage treatment.

[0025] The function of hydrolysis unit 1 is to homogenize the various input materials. Hydrolysis unit 1 is equipped with water distribution pipelines and heating pipelines, and adjusts the moisture content and temperature of the mixture according to the set process parameters to bring the materials to a suitable state for anaerobic fermentation.

[0026] The output of hydrolysis unit 1 is connected to anaerobic reaction unit 2 via a pipeline. Anaerobic reaction unit 2 is a combined anaerobic digestion reactor and is the core reaction site of this process.

[0027] Anaerobic reactor unit 2 is equipped with a stirring device for mixing and flow control of materials. The pre-treated hydrolyzed materials undergo anaerobic digestion here, converting organic matter into biogas and producing digestate. A gas collection structure is located at the top of anaerobic reactor unit 2 to collect the generated biogas.

[0028] The gas outlet of anaerobic reactor 2 is connected to desulfurization unit 3 via a pipeline. Desulfurization unit 3 is used to remove hydrogen sulfide impurities from biogas, thereby improving biogas purity.

[0029] The output of desulfurization unit 3 is connected to biogas utilization unit 4. Biogas utilization unit 4 includes a biogas boiler, a biogas generator set, and a safety flare. Clean biogas is converted into electrical or thermal energy here.

[0030] The heat energy generated by the biogas utilization unit 4 is connected in reverse to the heat exchange interface of the hydrolysis unit 1 and the anaerobic reaction unit 2 through the heating pipeline loop, providing the necessary heat source for the hydrolysis unit 1 and the anaerobic reaction unit 2 and realizing the internal heat circulation.

[0031] The liquid outlet of anaerobic reaction unit 2 is connected to digestion liquid storage unit 5. Digestion liquid storage unit 5 acts as a buffer and regulator, and its output is connected to centrifugal dehydration unit 6.

[0032] Centrifugal dewatering unit 6 is equipped with a high-efficiency centrifugal dewatering machine. Centrifugal dewatering unit 6 uses centrifugal force to separate the input digestate into solid and liquid components. The separated supernatant is returned or discharged through pipelines, while the separated dewatered sludge enters the next process.

[0033] The solid outlet of the centrifugal dehydration unit 6 is connected to the solar drying unit 7 via a high-pressure plunger pump and a delivery pipeline.

[0034] The solar drying unit 7 consists of several independently set up solar drying chambers. Inside the solar drying unit 7, there is an integrated machine for material handling, including a spreading, collecting, and turning machine, as well as a ventilation system for environmental control. Within the solar drying unit 7, the dewatered sludge undergoes further reduction of moisture content through solar radiation and controlled airflow.

[0035] The end of the sun drying unit 7 is connected to the sludge temporary storage and packaging unit 8. The dried sludge that has reached the target moisture content is transported to the sludge temporary storage and packaging unit 8 for bagging, weighing and packaging operations, and finally formed into finished products for shipment.

[0036] The central control system 9 adopts a distributed control architecture. It establishes communication connections via industrial Ethernet with field control stations distributed across the hydrolysis unit 1, anaerobic reaction unit 2, biogas utilization unit 4, centrifugal dehydration unit 6, and solar drying unit 7. The central control system 9 collects operational data from each unit and, based on preset control logic, issues commands to actuators such as pumps, valves, fans, and agitators.

[0037] Hydrolysis unit 1, serving as a transitional node connecting the front-end raw material receiving and the back-end anaerobic digestion, is a closed hydrolysis tank. The tank has a material receiving interface on its top or side wall, which is connected via pipelines to a food waste slurry conveying pipe, a kitchen waste slurry conveying pipe, and a wastewater treatment plant dewatered sludge conveying pipe. Flow meters and online solids content analyzers (or online moisture analyzers) are connected in series on the conveying pipelines to collect real-time instantaneous flow rate and initial solids content data of the input materials. The signal output of the online solids content analyzer group is electrically connected to the signal input of the central control system 9, forming the data acquisition basis for feed matching control.

[0038] Hydrolysis unit 1 is also connected to a water distribution pipeline, which is equipped with a controlled electric regulating valve or a variable frequency water pump. To address the significant differences in moisture content between materials from different sources, hydrolysis unit 1 implements a feeding and distribution logic based on real-time monitoring data: the central control system 9 compares the real-time values ​​fed back by the online solids content detector with the preset process target value (solids content 8%-10%); when the detected value exceeds the upper limit of the target value, it automatically calculates the required amount of dilution water according to the material balance principle and outputs a corresponding opening signal to the electric regulating valve or a frequency signal to the variable frequency water pump to inject process water or recycled water into the hydrolysis tank. By controlling the solids content of the mixture within the range of 8%-10%, it ensures that the material viscosity is suitable for subsequent pumping and stirring, while maintaining a high reactor volume utilization rate.

[0039] Hydrolysis unit 1 is equipped with a low-speed, high-torque mechanical agitator, whose blades extend into the lower part of the hydrolysis tank. During operation, the agitator continuously shears and mixes the materials inside the tank, ensuring thorough contact and mixing of high-viscosity slurries from different sources with the added water, thus eliminating local concentration gradients within the hydrolysis tank. This mechanical action also physically breaks down the flocculent structure of the sludge, promoting the transfer of organic matter from the solid phase to the liquid phase, completing the initial hydrolysis and acidification process.

[0040] In terms of temperature control, the hydrolysis unit 1 is equipped with a temperature regulating mechanism, including a temperature sensor installed inside the hydrolysis tank and a jacketed or built-in spiral plate heat exchanger attached to the outer wall of the hydrolysis tank. The heat source interface of the spiral plate heat exchanger is connected to the waste heat recovery circuit of the biogas utilization unit 4. When the temperature sensor detects that the temperature of the material inside the tank is lower than the lower limit of the set range of 37℃±1℃, the central control system 9 controls the valve on the heat medium pipeline to open, introducing hot water from the waste heat of biogas power generation or the biogas boiler. The hot water exchanges heat with the material inside the tank through the heat exchanger wall, heating the material and maintaining it at the temperature level required for mesophilic fermentation. The specific selection and installation method of the heat exchanger and sensor are well known to those skilled in the art and will not be described in detail here.

[0041] After homogenization, conditioning and temperature control, the material is kept in the hydrolysis unit 1 for a preset time, and then transported to the subsequent anaerobic reaction unit 2 at a constant flow rate by a discharge screw pump or plunger pump located at the bottom of the hydrolysis tank.

[0042] The core equipment of anaerobic reaction unit 2 is a combined anaerobic digester. The combined anaerobic digester adopts a vertical cylindrical tank structure, and its main body is made of enamel-coated steel plates or reinforced concrete, and is installed on a reinforced concrete foundation. The combined anaerobic digester integrates the anaerobic digestion reaction zone, biogas storage zone, heat exchange components, and sedimentation and sand removal zone into a single physically enclosed space.

[0043] The vertical cylindrical tank of the combined anaerobic digester is sealed at the top with a double-membrane gas holder as a flexible gas storage cover via flanges or pressure plates. The double-membrane gas holder consists of a corrosion-resistant inner membrane and a UV-resistant outer membrane. A variable-volume gas storage chamber is formed between the inner membrane and the liquid surface inside the tank to collect and store biogas produced during anaerobic fermentation. A pressure regulating chamber is formed between the outer and inner membranes, connected to a matching pressure-stabilizing blower and a pressure relief valve. The pressure-stabilizing blower introduces air into the pressure regulating chamber, maintaining the gas holder's external rigidity and generating a constant compressive force on the inner membrane, thus maintaining the output biogas at a preset pressure value. The gas-bag-type gas storage structure directly covers the reaction liquid surface, achieving in-situ collection and storage of biogas.

[0044] To achieve constant temperature control inside the reactor, a heat exchange assembly is installed on the inner wall of the vertical cylindrical tank. Specifically, the heat exchange assembly consists of spiral coils arranged circumferentially along the inner wall of the vertical cylindrical tank, or multiple sets of parallel heat dissipation pipes fixed inside the vertical cylindrical tank. The inlet and outlet of the heat exchange assembly pass through the tank wall and are connected to the hot water circulation loop of biogas utilization unit 4 via pipelines. The outer wall of the vertical cylindrical tank is fully covered with an insulation layer, which uses polyurethane foam material or rock wool board, and is externally covered with a color steel plate protective layer.

[0045] In terms of the feed and discharge structure, the feed inlet of the combined anaerobic digester is located in the lower middle part of the side wall of the vertical cylindrical tank, and is connected to the discharge pump of the hydrolysis unit 1 via a pipeline. The discharge outlet of the combined anaerobic digester is designed as a gravity overflow structure, specifically, an overflow weir or overflow pipe is installed at the designed liquid level height on the side wall of the vertical cylindrical tank. A U-shaped water seal pipe or an anti-gas water seal box is installed on the overflow pipe to block the flow of gas phase using the liquid level difference, preventing biogas in the tank from leaking through the discharge pipe, and at the same time preventing external air from entering the tank. The outlet end of the overflow pipe is connected to the digestate temporary storage unit 5. Through this physical structure, the combined anaerobic digester maintains a constant effective volume, relying on hydrostatic pressure and the principle of communicating vessels to maintain the liquid level height, without relying on a liquid level sensor for closed-loop control.

[0046] To address the issue of inorganic grit deposition during sludge fermentation, the bottom of the combined anaerobic digester is designed as a conical structure sloping towards the center, or it is equipped with a sand collection pit. A sand discharge port is located at the lowest point of the conical bottom, and the sand discharge port is connected to a sand discharge pipe and a sand discharge valve.

[0047] To support the three-dimensional mixing process, the combined anaerobic digester is equipped with a specific mechanical mounting structure. A guide tube is vertically installed at the central axis of the vertical cylindrical tank. The guide tube is fixed to the tank top ring beam or tank wall by a bracket. The upper end of the guide tube is below the design liquid level, and the lower end extends to the lower part of the reaction zone. A lifting agitator is installed inside the guide tube. Simultaneously, several submersible propeller agitators are installed on the lower part of the side wall of the vertical cylindrical tank. The installation angle of these propeller agitators is adjustable, causing the direction of their generated jets to deflect tangentially to the tank wall, thereby creating a swirling flow field within the tank.

[0048] Material mixing inside the reactor is achieved through a three-dimensional stirring mechanism, which utilizes a central guiding stirring component and a peripheral propulsion stirring component located within the reactor to work in tandem. By generating a composite flow field of vertical circulating flow and horizontal circumferential flow, the stirring mechanism avoids the stirring dead zones and material stratification problems that are prone to occur in single stirring modes.

[0049] The central guiding and stirring assembly is operated by a lift-type mixer located inside the guide tube. When the lift-type mixer is running, its impeller rotates, drawing the material from the upper part of the guide tube axially downwards, forming a forced vertical flow from top to bottom due to the constraint of the guide tube. After being ejected from the lower end of the guide tube, the vertical flow impacts the bottom of the tank and spreads outwards, subsequently forming an upward backflow near the side wall of the vertical cylindrical tank. This process constitutes a complete vertical circulation loop in the central region of the vertical cylindrical tank.

[0050] For the common problem of surface scum in anaerobic sludge fermentation, the operation of the central guide flow mixing component achieves physical removal of the scum. Because the upper port of the guide flow tube is located below the reactor liquid surface, the operating lift-type mixer can generate a local negative pressure zone, drawing the scum layer, composed of low-density organic matter or grease, floating near the liquid surface along with the surface liquid into the guide flow tube. Once inside the guide flow tube, the scum is broken up and dispersed under strong turbulence and shear force, and is then forcibly transported with the main fluid to the bottom of the vertical cylindrical tank, where it mixes with the activated sludge and high-density slurry at the bottom.

[0051] The peripheral agitation assembly is performed by several submersible agitators installed on the lower sidewall of the vertical cylindrical tank. These agitators do not direct their jets towards the center of the tank, but rather arrange them tangentially to the inner wall of the vertical cylindrical tank. When the agitators are running, the high-speed jets they generate propel the surrounding material, creating a unified horizontal circumferential vortex within the vertical cylindrical tank. This circumferential flow field ensures that the material in the peripheral area of ​​the vertical cylindrical tank does not stagnate and enhances the heat transfer efficiency between the material and the tank wall heat exchange components.

[0052] The synergistic working principle of the three-dimensional mixing mechanism lies in the fact that the material inside the tank is simultaneously subjected to the combined effects of vertical circulating flow and horizontal circumferential flow. While the material undergoes vertical tumbling (center down, sides up) and horizontal rotational motion, this combined motion mode ensures that newly introduced material from hydrolysis unit 1 can be quickly dispersed and thoroughly mixed with the existing activated sludge in the tank, avoiding short-circuiting. At the same time, scum and debris dispersed to the bottom of the tank are carried away from the central area of ​​the bottom by the horizontal circumferential flow, preventing them from re-aggregating or settling, and ultimately overflowing as part of the mixed slurry.

[0053] The central control system 9 controls the two types of agitators according to a preset program. Specifically, the submersible jet mixer is set to operate continuously or for extended periods to maintain the basic mixing state and heat transfer effect within the reactor; simultaneously, the center lift mixer is set to a time-programmed intermittent operation mode (e.g., starting and running for 15 minutes every 2 hours) to periodically break up the scum layer and enhance vertical mixing. The start and stop times of the two agitators can overlap or stagger to achieve a balance between mixing efficiency and operating energy consumption.

[0054] The raw biogas collected from the double-membrane gas holder at the top of anaerobic reactor 2 contains hydrogen sulfide (H2S) and saturated water vapor, which are corrosive to subsequent utilization equipment, and therefore requires purification. The biogas treatment process is as follows: the gas is drawn from the storage chamber of the double-membrane gas holder, undergoes preliminary dehydration in a gas-water separator, then enters desulfurization unit 3, and finally the purified dry biogas is delivered to biogas utilization unit 4.

[0055] To prevent water vapor from causing the desulfurizing agent to become damp and ineffective, the biogas passes through a gas-water separator or condenser before entering desulfurization unit 3. This process uses temperature reduction or physical barriers to separate and remove water mist and some condensate entrained in the biogas.

[0056] Desulfurization unit 3 employs a dry desulfurization tower filled with a desulfurizing agent whose main active ingredient is iron oxide. When dehydrated biogas passes through the desulfurizing agent bed from bottom to top, a chemical reaction occurs: hydrogen sulfide reacts with iron oxide to form solid iron sulfide, thus removing hydrogen sulfide from the gas phase. The goal of desulfurization is to reduce the hydrogen sulfide content in the biogas to below 25 ppm to meet the cleanliness requirements of biogas generator sets for fuel gas. Desulfurization unit 3 typically consists of two or more desulfurization towers, operating in a one-in-one-backup or series configuration to allow for online replacement of expired desulfurizing agents without interrupting operation.

[0057] The buffer storage of biogas is achieved using a double-membrane gas holder at the top of anaerobic reactor unit 2. A storage chamber for raw biogas is formed between the inner membrane of the gas holder and the liquid surface of the reactor. Its storage principle is based on a constant pressure design: a pressure regulating chamber between the outer and inner membranes is connected to a pressure-stabilizing fan via a duct. The fan injects air into the regulating chamber, causing the outer membrane to expand and applying a uniform and constant pressure to the inner membrane.

[0058] When the anaerobic digester produces more biogas than it consumes at the downstream end, the newly produced biogas enters the storage chamber, pushing the inner membrane upwards and increasing the chamber's volume. Conversely, when the downstream biogas consumption rate exceeds the production rate, the biogas in the storage chamber is consumed, and the inner membrane moves downwards under the pressure of the pressure regulating chamber, decreasing the chamber's volume. The pressure-stabilizing blower monitors pressure changes in the pressure regulating chamber, automatically starting, stopping, or adjusting the airflow to maintain a constant pressure difference between the inner and outer membranes, thus ensuring a stable biogas supply pressure within the storage chamber.

[0059] To ensure safety and coordinated control, the dual-membrane gas holder is equipped with an ultrasonic level gauge to monitor the height of the inner membrane in real time and calculate the gas storage volume. When the gas storage volume reaches the set high value (e.g., 80%), the central control system 9 sends a start signal to the biogas utilization unit 4 (e.g., starting the generator); when the gas storage volume reaches the set over-high alarm value (e.g., 95%), the central control system 9 activates the safety flare. When the gas storage volume falls below the set low value (e.g., 30%), the central control system 9 sends a stop signal to the biogas utilization unit 4; when the gas storage volume falls below the set under-low alarm value (e.g., 10%), the central control system 9 issues an alarm.

[0060] The biogas generator set in biogas utilization unit 4 is equipped with a waste heat recovery mechanism while burning biogas to output electricity. The waste heat recovery mechanism mainly consists of two heat exchange devices: a flue gas-water heat exchanger (using shell-and-tube or finned tube structure) connected in series on the generator set's exhaust pipe to recover sensible heat from the high-temperature flue gas; and a plate heat exchanger coupled to the generator set's cylinder liner cooling water circulation loop to remove heat from the high-temperature cylinder liner water.

[0061] These two stages of heat exchange devices transfer the recovered heat energy to a shared heat transfer medium water circulation network. The network is constructed as a closed-loop pressurized water pipeline, connecting the main circulation pump, an expansion pressure tank located on the return water pipeline, and main supply and return water pipes laid to each heat-using unit. In the heat transfer medium water circulation network, softened water or antifreeze serves as the heat transfer medium. After flowing through plate heat exchangers and flue gas / water heat exchangers, it absorbs heat (typically raising the temperature to 80°C to 90°C) and is then transported by the main circulation pump to hydrolysis unit 1 and anaerobic reaction unit 2.

[0062] In terms of heat distribution and transmission, the main water supply pipe has independent thermal branch pipes at both the hydrolysis unit 1 and the anaerobic reaction unit 2. Each thermal branch pipe is equipped with an electric regulating valve (specifically an electric three-way valve or an electric two-way regulating valve) and a flow meter. The heated water flows through the jacket of the hydrolysis unit 1 or the spiral coil inside the anaerobic reaction unit 2, releasing heat to the sludge material through heat conduction via the pipe wall. The cooled heated water then flows back to the waste heat recovery end of the biogas utilization unit 4 via the return water main pipe for reheating. If an electric two-way regulating valve is used, a differential pressure bypass valve or a frequency converter-controlled circulating main pump is also installed between the main water supply pipe and the return water main pipe to maintain stable network pressure.

[0063] The central control system 9 executes closed-loop temperature control logic based on the principle of thermal balance. It collects real-time temperature data from the sensors inside the hydrolysis unit 1 and the anaerobic reaction unit 2, comparing it with the preset process temperature (e.g., 35℃±1℃ for mesophilic digestion). When the real-time temperature of a unit falls below the set lower limit, the central control system 9 outputs a control signal to increase the opening of the electric regulating valve on the corresponding thermal branch pipe of that unit, thereby increasing the flow rate of the heating medium and enhancing the heating power.

[0064] The central control system 9 is set with a control strategy that prioritizes meeting the heat demand of the anaerobic reaction unit 2: when the temperature of the main heat medium water pipe is lower than the set threshold and cannot meet the heating demand of both at the same time, the central control system 9 automatically reduces or closes the electric regulating valve on the branch pipe of the hydrolysis unit 1, and forces the heat medium water to be preferentially allocated to the anaerobic reaction unit 2 to ensure the constant temperature of the anaerobic fermentation environment.

[0065] To address insufficient biogas production or extreme low temperatures during initial startup, an auxiliary heat source (specifically a biogas boiler or electric heating compensation device) is connected in parallel within biogas utilization unit 4. The central control system 9 monitors the temperature of the main heat transfer water supply pipe. When the temperature of the main supply pipe remains below the minimum heating temperature threshold (e.g., 70°C), the auxiliary heat source is automatically activated to supplement heat to the network. Conversely, when the summer heat load is low, causing the generator set's cooling water return temperature to be too high, a three-way switching valve installed in the cooling water circuit switches the cooling water to outdoor radiators or cooling towers, discharging excess heat to the atmosphere and maintaining the generator set's thermal balance.

[0066] The digestate overflowing from anaerobic reactor 2 enters the digestate storage tank in digestate storage unit 5. The storage tank acts as a flow buffer, its effective volume designed to meet the continuous output for a preset time (e.g., 12 hours). To prevent suspended solids in the digestate from settling due to gravity, a low-speed submersible mixer is installed inside the storage tank to continuously agitate and maintain the material in a homogeneous suspended state. The storage tank is equipped with an ultrasonic level gauge, the signal output of which is electrically connected to the frequency converter of the feed screw pump, used to automatically adjust the feed flow rate or control the pump's start / stop based on changes in the liquid level.

[0067] The homogenized digestate is pumped to centrifugal dewatering unit 6 via a feed screw pump. Centrifugal dewatering unit 6 includes a centrifugal dewatering machine. A flocculant injection point is installed on the conveying pipeline before the homogenized digestate enters the dewatering machine, and this injection point is connected to an automatic dosing device. Based on feedback signals from the feed flow meter, the automatic dosing device injects a pre-prepared polymeric flocculant (such as polyacrylamide, PAM) solution into the pipeline in a specific ratio. The mixture then passes through a tubular static mixer or coagulation reactor, where, through compression of the electric double layer and adsorption bridging, fine particles aggregate into larger flocs.

[0068] The conditioned material enters a horizontal screw sedimentation centrifuge for mechanical dewatering. The core structure of the centrifuge includes a high-speed rotating drum and a screw feeder rotating in the same direction at a differential speed. During operation, the drum rotates at high speed driven by the main motor, generating a high-intensity centrifugal force field. Its separation factor (Fr) is set between 3000g and 5000g (belonging to the high separation factor model). Under the action of the high centrifugal force field, the heavier solid particles settle rapidly and adhere to the inner wall of the drum, forming a solid ring layer; the lighter liquid phase forms a liquid ring layer in the inner layer.

[0069] The screw feeder is driven by a cycloidal pinwheel differential or a hydraulic motor, rotating at a speed slightly lower or slightly higher than that of the drum, generating relative motion. This relative motion pushes the sludge deposited on the inner wall of the drum towards the conical end (drying zone). During this process, the sludge is subjected to both centrifugal compression and screw shearing, further dewatering it to form a low-moisture cake that is discharged. The separated supernatant is discharged from the overflow port at the large end of the drum and flows back to the hydrolysis unit 1 through a pipeline. The central control system 9 monitors the main motor current and vibration value of the centrifuge in real time, automatically adjusting the differential ratio according to torque changes to adapt to fluctuations in feed concentration using a constant torque control mode.

[0070] The dewatered cake discharged from the centrifuge falls into the receiving hopper. A high-pressure plunger pump is connected to the bottom of the hopper for long-distance pipeline transportation. It adopts a hydraulically driven double-cylinder or single-cylinder reciprocating structure, mainly composed of a hydraulic power station, a main oil cylinder, a material cylinder, and a distribution valve box.

[0071] The distribution valve box is equipped with an intake cone valve and a delivery cone valve (POPPET valve). These two sets of valves are opened and closed by material pressure or a hydraulic linkage mechanism. The working logic is as follows: high-pressure oil generated by the hydraulic station drives the main cylinder to reciprocate, which in turn drives the plunger in the material cylinder. When the plunger retracts to suck in material, the intake cone valve opens and the delivery cone valve closes, drawing the sludge cake into the cylinder. When the plunger advances to push material, the intake cone valve closes and the delivery cone valve opens, pushing the sludge cake into the fully enclosed delivery pipeline at high pressure (5-10 MPa).

[0072] To reduce the transport resistance of high-solids-content mud cake in long-distance pipelines, an annular water-injection lubricator (or drag-reducing ring) is installed at the connection between the plunger pump outlet flange and the transport pipeline. A high-pressure water injection pump injects a polymer solution or water into the annular gap of the lubricator, forming a low-viscosity lubricating film between the inner wall of the pipeline and the mud cake. The plunger pump control is interlocked with the hopper level gauge; when the material level reaches the set height, the pumping cycle is automatically triggered. The reciprocating frequency of the plunger is precisely controlled by adjusting the displacement of the hydraulic oil pump, ensuring that the transport flow rate matches the mud output of the upstream centrifuge in real time.

[0073] The main structure of the solar drying unit 7 consists of one or more large-span solar drying rooms. The main structure of the solar drying room adopts a portal steel frame structure system, with its framework treated with hot-dip galvanizing for corrosion protection to withstand the high humidity and corrosive environment. The roof and side walls are covered with high-transmittance polycarbonate (PC) hollow panels or tempered glass, utilizing the greenhouse effect for heat collection. To control indoor humidity and accelerate moisture evaporation, the drying room roof is equipped with an automatically opening skylight controlled by an electric actuator, and the side walls are fitted with forced dehumidification fans and air inlet louvers. The interior floor is paved with wear-resistant and corrosion-resistant reinforced concrete, with underfloor heating pipes embedded within the concrete layer. The inlet of the underfloor heating pipes is connected to the heat medium water circulation network of the biogas utilization unit 4 via pipes, utilizing waste heat return water as an auxiliary heat source to improve drying efficiency in winter.

[0074] Inside the sun-drying room, there is a single integrated machine that spans the entire width of the floor, handling material placement, collection, and turning. This integrated machine is a bridge-type automated machine, mainly composed of a truss-style main beam spanning the workshop, longitudinal traveling mechanisms installed at both ends of the main beam, a lifting trolley suspended below the main beam, a rotary tiller roller installed below the lifting trolley, and a leveling scraper assembly located on one side of the roller. The longitudinal traveling mechanism is equipped with a variable frequency drive motor and steel wheels, reciprocating along heavy-duty steel rails laid on the low walls on both sides of the drying room.

[0075] The core working component of the integrated machine is the rotary tiller. The drum is a horizontally positioned rotating shaft with several sets of wear-resistant alloy steel turning blades welded to its surface in a specific spiral pattern. The rotary tiller's vertical position is adjusted via a hydraulic cylinder or screw jack on a lifting trolley, allowing for precise control of the depth of penetration into the sludge layer. Simultaneously, the drum is driven by a high-power motor, enabling high-speed rotation in both forward and reverse directions.

[0076] The integrated machine achieves three functions—closing, turning, and collecting—through different combinations of motion logic: During the material distribution stage, the outlet of the plunger pump delivery pipeline is located in the feeding area at the front of the drying chamber, transporting the wet sludge to the ground for accumulation. The integrated machine moves to the feeding area, and the central control system instructs the lifting trolley to adjust its height, using the leveling scraper assembly or setting the rotary tiller to rotate in the opposite direction at a low speed. In conjunction with the longitudinal movement of the trolley, the accumulated wet sludge is leveled along the width and length directions, spreading it on the ground of the feeding area to form an initial sludge layer of uniform thickness (e.g., 20-30cm).

[0077] During the turning and drying stage, the integrated machine performs periodic sludge turning operations. It travels longitudinally along the track while the rotary tiller rotates at high speed. The turning blades cut into the sludge layer, turning up the bottom layer of wet sludge and throwing it backwards, while simultaneously breaking up the dried crust formed on the surface. This increases the surface area of ​​the sludge in contact with air, enhancing moisture transfer. By controlling the matching relationship between the longitudinal travel speed of the integrated machine and the rotation speed of the drum, the sludge is displaced towards the discharge end during its throwing and falling process, thus achieving a gradual movement of material from the feeding area to the discharge area through repeated turning.

[0078] During the receiving stage, the dried sludge (with a moisture content reduced to below 40%), after being repeatedly turned and moved to the discharge area at the end of the drying chamber, is centrally pushed to the central control system 9 by the integrated machine. The central control system 9 adjusts the roller to its extreme position close to the ground and, in conjunction with high speed, throws the dried sludge into the discharge pit or onto the horizontal belt conveyor located at the end of the drying chamber. The integrated machine is equipped with a laser rangefinder (for locating the trolley coordinates) and an ultrasonic sludge layer thickness gauge mounted on the lifting trolley. Based on the sludge layer thickness and position data fed back by the sensors, the central control system 9 automatically plans the turning path and adjusts the roller lifting height, achieving fully automated operation without human intervention.

[0079] To optimize energy efficiency in the solar drying process, the solar drying unit 7 is equipped with an environmentally responsive intelligent ventilation system. Based on real-time meteorological data and indoor microenvironment parameters, the ventilation system dynamically adjusts the ventilation equipment in the drying chamber via a central control system 9. The hardware of the ventilation system mainly consists of environmental monitoring components and ventilation execution components.

[0080] The environmental monitoring components include a weather station located outside the drying chamber and a sensor array distributed inside the drying chamber. The external weather station integrates a solar radiation sensor (total radiation meter), an ultrasonic anemometer, a rain and snow sensor, and an outdoor temperature and humidity transmitter. The internal sensor array includes multiple sets of temperature and humidity sensors arranged above the sludge surface, in the middle of the chamber, and on the roof, as well as ammonia (NH3) or hydrogen sulfide (H2S) concentration sensors. All sensor data is transmitted to the central control system in real time via a fieldbus.

[0081] The ventilation system mainly includes an electrically operated skylight installed at the ridge, electrically operated air inlet louvers at the bottom of the side walls, a negative pressure exhaust fan at the top of the side walls, and an internal circulation fan suspended from the top of the drying room. Both the electric skylight and louvers are equipped with adjustable electric actuators, allowing for continuous angle adjustment from 0 to 90 degrees according to control commands. Both the negative pressure exhaust fan and the internal circulation fan are driven by variable frequency motors, enabling stepless speed regulation.

[0082] The central control system 9 performs coordinated control of the aforementioned actuators based on a preset PID control algorithm. Its core control strategy is to maximize the vapor pressure deficit on the sludge surface.

[0083] When the weather station detects that the outdoor solar radiation intensity is higher than a set threshold (e.g., 400W / m²), 2 When there is no rain or snow, the environmentally responsive intelligent ventilation system enters natural ventilation mode. At this time, the central control system commands the electric skylight to open to its maximum angle, simultaneously opening the side wall air intake louvers. Utilizing the thermal pressure difference (chimney effect) generated by solar radiation heating the indoor air, combined with outdoor wind pressure, a bottom-up natural convection is formed within the drying chamber. Dry outdoor air enters through the side wall louvers, sweeping across the surface of the sludge and carrying away moisture, while the hot, humid air is exhausted through the roof skylight.

[0084] When the indoor relative humidity is detected to be consistently higher than the set value (e.g., 60%) and the outdoor air humidity is lower than the indoor air humidity, the environmentally responsive intelligent ventilation system switches to forced ventilation and dehumidification mode. The central control system 9 calculates the required air exchange rate based on the difference in indoor and outdoor humidity and adjusts the operating frequency of the negative pressure exhaust fan. The exhaust fan forcibly extracts the humid air from the room, creating a slight negative pressure that forces drier outdoor air to quickly enter through the air inlet louvers. During dehumidification, the airflow reduces the thickness of the air boundary layer on the sludge surface, decreasing mass transfer resistance and thus accelerating moisture evaporation.

[0085] When outdoor humidity is too high for ventilation, or to eliminate localized temperature and humidity dead zones indoors, the central control system 9 activates the internal circulation fan. The internal circulation fan generates turbulent airflow, stirring the indoor air to ensure even distribution of heat and moisture, preventing condensation from forming in corners or deep within sludge piles.

[0086] The environmentally responsive intelligent ventilation system prioritizes safety protection. When the rain and snow sensor detects precipitation, or the anemometer detects that the instantaneous outdoor wind speed exceeds the safety threshold (e.g., level 8 wind), the central control system prioritizes the execution of protection procedures, immediately instructing the motorized skylights and air intake louvers to close forcibly, preventing rainwater from backflowing and wetting the sludge or strong winds from damaging the building structure. In this closed state, the environmentally responsive intelligent ventilation system automatically operates the internal circulation fan to maintain indoor air circulation and continues the closed-loop drying process using heat provided by the underfloor heating.

[0087] The dried sludge (with a moisture content reduced to below 40%) processed by the sun drying unit 7 is discharged into the feed port of the sludge temporary storage and packaging unit 8 via a discharge conveying device. The vertical conveying link of the sludge temporary storage and packaging unit 8 adopts a fully enclosed plate chain bucket elevator (or Z-type bucket conveyor). The elevator vertically lifts the dried sludge to a set height and discharges it into the dry material temporary storage bin through the top discharge port.

[0088] The main body of the dry material storage silo is a steel cylindrical structure, with the lower part designed as a conical funnel with a cone angle greater than 60 degrees to utilize the gravity flow of the material. Given the hygroscopic and adhesive properties of dried sludge particles, which easily form arches or central holes at the conical hopper to obstruct material flow, an arch-breaking device consisting of a pneumatic hammer or a high-frequency silo wall vibrator is installed on the outer wall of the hopper. This arch-breaking device is electrically connected to the flow switch at the discharge port. When a material flow interruption is detected, the central control system automatically triggers the arch-breaking device to intermittently vibrate at high frequency, disrupting the internal stress structure of the material and restoring its fluidity.

[0089] A radar level gauge is installed on the top of the temporary storage silo for non-contact measurement of the material accumulation height inside the silo. The central control system 9 executes interlock control based on the analog signal fed back from the level gauge: when the material level reaches the high threshold (e.g., 90%), the central control system 9 automatically interlocks and stops the bucket elevator at the front end and the discharge equipment in the drying room; when the material level is lower than the low threshold (e.g., 20%), the central control system 9 issues a material shortage signal and suspends the packing operation below.

[0090] The conical bottom outlet flange of the temporary storage bin is connected to an electric rotary feed valve (star-shaped unloader). The electric rotary feed valve is driven by a variable frequency motor. Its internal rotating impeller maintains a small gap with the housing, which not only achieves quantitative material dispensing but also acts as an airlock to isolate the temporary storage bin from the external environment.

[0091] The rotary feeding valve is directly connected to a gravity-type automatic quantitative packaging machine. The gravity-type automatic quantitative packaging machine mainly includes an automatic bag-loading robot, a pneumatic bag-clamping mechanism, a weighing hopper, and a belt conveyor. During the packaging cycle, the automatic bag-loading robot uses a vacuum suction cup to pick up the packaging bag and open its opening, and the pneumatic bag-clamping mechanism then clamps it. The central control system 9 executes a dual-speed feeding logic based on real-time feedback from the weighing sensor: first, it instructs the rotary feeding valve to operate at a high frequency for rapid, high-flow feeding (coarse feeding); when the weight reaches 90% of the preset value, the frequency converter switches to a low-frequency operation for trickle feeding (fine feeding); when the target weight (e.g., 50kg) is reached, the feeding valve quickly closes and brakes, the bag-clamping mechanism releases, and the full packaging bag falls onto the conveyor below. Subsequently, the packaging bag is sealed by an automatic sewing machine or heat sealing machine and transported to the finished product stacking area.

[0092] To address the flammable and explosive nature of dry sludge dust, negative pressure dust collection hoods are installed on the top of the temporary storage silo and at the baling machine's discharge port, connected to a pulse-jet baghouse dust collector via anti-static conductive ducts. The dust collector uses anti-static membrane-coated filter bags and is equipped with explosion-proof pressure relief vents. The induced draft fan generates continuous negative pressure to draw in and intercept the fine dust particles. After being backflushed by compressed air pulses, the collected dust falls into the dust collector's ash hopper and flows back to the baling process through the ash discharge valve, thus achieving clean production while eliminating the safety hazards caused by dust accumulation.

[0093] The central control system 9 adopts a hierarchical distributed control architecture (DCS or SCADA architecture), logically and physically divided into an information management layer, a process control layer, and a field device layer. The information management layer, located in the central control room, serves as the core of the plant's scheduling. Its hardware configuration includes two data servers with RAID redundant disk arrays, one engineering workstation, multiple operator workstations, and a large-screen display wall. The data server runs industrial monitoring configuration software, responsible for centralized data acquisition of process parameters across the plant, historical trend archiving based on an SQL relational database, alarm management, and production report generation. The engineering workstation is used for PLC program writing, debugging, and configuration screen modification. The operator workstation provides a human-machine interface for remote monitoring and operation by management personnel. All core equipment in the control room is powered by an online uninterruptible power supply, ensuring at least 30 minutes of real-time data retention and safe shutdown after a mains power outage.

[0094] The process control layer consists of independent PLC control stations distributed across various processes (including anaerobic reaction unit 2, biogas utilization unit 4, centrifugal dehydration unit 6, and solar drying unit 7). Each PLC control station adopts a modular rack design, integrating a central processing unit (CPU) module, power supply module, communication module, and several analog input / output (AI / AO) and digital input / output (DI / DO) modules. For critical process steps, the PLC employs a dual-CPU hot standby redundancy configuration. The two CPUs are synchronously linked via fiber optics to mirror memory data in real time. When the primary CPU fails, the backup CPU performs a bumpless transfer within one scan cycle, automatically taking over control. Each PLC control station independently executes local data acquisition, PID closed-loop calculation, and logic interlock control according to a preset logic program, ensuring that even if the upper-level communication network is interrupted, the lower-level equipment can still maintain a safe operating state.

[0095] The field equipment layer encompasses various sensors and actuators installed at the process site. Sensors (such as electromagnetic flowmeters, pressure transmitters, and ultrasonic level gauges) convert physical quantities into 4-20mA standard analog current signals (with HART protocol) or transmit them to the PLC's input module via RS485 communication. Actuators include electric valves, pneumatic solenoid valves, and motor drive circuits. For high-power loads or loads requiring speed regulation, such as feed screw pumps and centrifuge main motors, their electrical control circuits are equipped with frequency converters or soft starters. The frequency converter communicates with the PLC via a fieldbus (such as Modbus-RTU or Profibus-DP) to achieve real-time interaction of frequency setting, current feedback, and fault codes. A local control box is installed next to key pumps and machines, equipped with a remote / local switching knob and an emergency stop button. The emergency stop button is directly connected in series with the contactor coil of the motor control circuit via hardwiring, physically cutting off the power supply and simultaneously connecting its status signal to the PLC's DI input terminal, ensuring the highest priority physical shutdown authority in emergency situations.

[0096] In terms of network communication architecture, a gigabit industrial Ethernet ring network based on fiber optic media was constructed as the backbone communication link. Each PLC control station and the network cabinet in the central control room are equipped with industrial-grade managed Ethernet switches, and all switches are cascaded using single-mode fiber to form a closed physical ring topology. The network communication architecture is configured with a media redundancy protocol (MRP or RSTP). When any segment of the fiber optic cable in the ring network physically breaks or a switch node fails, the network management logic can automatically block the fault point and activate a backup path within milliseconds (less than 50ms), achieving network self-healing. High-speed data exchange between the information management layer and the process control layer is achieved through the OPCUA protocol or industrial Ethernet protocol (EtherNet / IP or PROFINET).

[0097] To achieve visualized management, the industrial video surveillance network is logically integrated with the production control network. Explosion-proof high-definition network cameras or thermal imaging cameras with pan-tilt units are installed in key locations such as the centrifuge room, the sun-drying room, the perimeter of the biogas tank, and the discharge packaging area. Video signals are aggregated to a hard disk recorder via an independent transmission network. The SCADA software of the central control system 9 embeds the video playback window using ActiveX controls or HTML5 Web components, and establishes a mapping relationship between alarm tags and video channels. When SCADA detects abnormal parameters in a certain process area (such as a biogas leak alarm or equipment shutdown), the script automatically triggers and displays a pop-up window showing the real-time video monitoring screen associated with that area, overlaying key process parameters onto the video screen to assist operators in fault diagnosis and emergency handling.

[0098] The central control system 9 has built-in dedicated control algorithm modules for different process sections. It interacts with the PLCs of each unit through the fieldbus to achieve coordinated and optimized operation of the entire system.

[0099] In the feed conditioning stage of hydrolysis unit 1, a feed moisture content and water distribution coupling control strategy based on the dry matter mass balance principle is implemented. This control strategy aims to compensate for the impact of fluctuations in the solids content of the raw sludge on the efficiency of subsequent hydrolysis and anaerobic fermentation. The specific control logic is as follows: an online sludge concentration meter installed on the feed pipeline collects real-time solids content data of the raw sludge, while an electromagnetic flow meter collects the instantaneous feed flow rate. The PLC's internal calculation unit dynamically sets the setpoint for the dilution water flow rate based on a preset target solids content (e.g., 8%-10%) and the real-time collected feed parameters, following the calculation logic: dilution water flow rate = sludge flow rate × (measured solids content / target solids content - 1). A ratio control algorithm is used, with the calculated value serving as the target for the secondary loop. The PID loop adjusts the opening of the electric regulating valve on the dilution water pipeline or the output frequency of the dilution water pump inverter to maintain a constant ratio between the dilution water addition and the raw sludge dry matter mass flow rate, ensuring that the material concentration entering the hydrolysis tank remains within the optimal process range.

[0100] For anaerobic reactor unit 2, temperature control employs cascaded PID control logic with feedforward compensation. In the logic loop, the temperature sensor inside the anaerobic tank serves as the measurement input to the main controller, and its output signal is transmitted as the setpoint to the secondary controller of the heating medium water jacket or coil. Based on the instructions from the main loop and real-time feedback of the heating medium water supply and return temperatures, the secondary controller rapidly adjusts the opening of the three-way regulating valve on the heating medium water branch pipe. When the feed flow sensor detects a sudden increase in flow or the ambient temperature sensor detects a sudden drop in outdoor temperature, the central control system 9 directly adds a correction to the setpoint of the secondary loop, increasing the heating power in advance. Furthermore, to prevent sludge coking and a reduction in heat transfer coefficient due to excessive temperature difference on the heating coil surface, a maximum temperature difference limit logic is set in the control algorithm, forcibly constraining the difference between the heating medium water temperature and the sludge temperature to not exceed a set threshold (e.g., 60℃).

[0101] In the operation and control of the sunlight drying unit 7, to overcome the limitations of relying solely on relative humidity to control ventilation, an absolute moisture content comparison logic based on enthalpy-humidity chart calculation is adopted. The central control system 9 calculates the absolute moisture content of outdoor air and indoor humid air in real time using the built-in humid air state equation, based on temperature and relative humidity data collected from the weather station and indoor sensors. Only when the absolute moisture content of indoor humid air is greater than that of outdoor air and the difference exceeds a preset dead zone threshold, the central control system 9 determines that ventilation and dehumidification conditions are met, and then starts the exhaust fan and opens the air intake louvers. The operating frequency of the fan is not fixed, but rather establishes a functional relationship with the difference in absolute moisture content between indoors and outdoors using a proportional-integral (PI) algorithm: when the difference in absolute moisture content is large, the inverter outputs a high frequency, and the fan runs at full speed to utilize the higher mass transfer potential energy for rapid moisture removal; as the difference in absolute moisture content decreases, the fan speed automatically and linearly decreases to reduce energy consumption; when the difference in absolute moisture content falls below the dead zone threshold or a rainfall signal appears outdoors, the central control system automatically shuts off the exhaust fan and interlocks to close the air inlet louvers, while simultaneously starting the internal circulation fan. This control strategy effectively avoids the phenomenon of sludge absorbing moisture and becoming damp again due to ineffective ventilation during the rainy season or in high humidity weather, achieving a dynamic balance between energy consumption and drying efficiency.

Claims

1. A process for harmless and volume-reduced treatment of sludge, characterized in that, The following processing steps are included: The hydrolysis unit (1) receives external materials, and through online detection of solid content and automatic water distribution, conditions the materials into a slurry with constant solid content and temperature; The slurry enters the anaerobic reaction unit (2) for mesophilic anaerobic digestion. The biogas produced is purified by the desulfurization unit (3) and then enters the biogas utilization unit (4) to generate heat and electricity. The generated heat is recycled for heating the hydrolysis unit (1) and for heat preservation of the slurry entering the anaerobic reaction unit (2). After anaerobic digestion, the digestive liquid is buffered by the digestive liquid storage unit (5) and then enters the centrifugal dewatering unit (6) to be separated into supernatant and dewatered sludge; The dewatered sludge is pumped to the solar drying unit (7) by a high-pressure pump and dried in the solar drying room using solar radiation and the waste heat recovered by the biogas utilization unit (4); The central control system (9) calculates the absolute moisture content difference between the inside and outside of the sun drying room in real time, dynamically adjusts the operation status of the ventilation equipment, and uses the integrated machine for spreading, collecting and turning the sludge periodically for turning and transporting. The dried sludge is transported to the sludge temporary storage and packaging unit (8) for automatic weighing and packaging.

2. The sludge harmlessness and volume reduction treatment process according to claim 1, characterized in that, The hydrolysis unit (1) includes a hydrolysis tank, and an online solids content detector and a flow meter are installed on the feed pipe of the hydrolysis tank. The hydrolysis tank is connected to a water distribution pipeline, and an electric regulating valve is installed on the water distribution pipeline.

3. The sludge harmlessness and volume reduction treatment process according to claim 1, characterized in that, The anaerobic reaction unit (2) adopts a combined anaerobic digestion reactor. The combined anaerobic digestion reactor includes a vertical cylindrical tank that integrates an anaerobic digestion zone, a biogas storage zone, and a heat exchange component. The biogas storage zone is located at the top of the vertical cylindrical tank and is composed of a double-membrane gas holder. The heat exchange component includes a spiral coil attached to the inner wall of the vertical cylindrical tank. The spiral coil is connected to the heat medium water circulation network. The combined anaerobic digestion reactor is equipped with a three-dimensional stirring system. The three-dimensional stirring system includes a lifting stirrer located in the central guide tube of the vertical cylindrical tank and a submersible jet stirrer located at the lower part of the side wall of the vertical cylindrical tank. The jet direction of the submersible jet stirrer is arranged along the tangential direction of the inner wall of the vertical cylindrical tank.

4. The sludge harmlessness and volume reduction treatment process according to claim 1, characterized in that, The biogas utilization unit (4) includes a biogas generator set, a biogas boiler and a safety flare. The heat recovery device includes a flue gas and water heat exchanger connected in series on the exhaust pipe of the biogas generator set and a plate heat exchanger coupled in the cylinder liner water circulation loop of the generator set. The heat medium water circulation network includes a circulating main pump, a water supply main pipe and a return main pipe. The water supply main pipe is provided with independent thermal branch pipes at the hydrolysis unit (1) and the anaerobic reaction unit (2). Each thermal branch pipe is equipped with a controlled regulating valve.

5. The sludge harmlessness and volume reduction treatment process according to claim 1, characterized in that, A receiving hopper is provided below the solid outlet of the centrifugal dehydration unit (6). A hydraulically driven high-pressure plunger pump is connected to the bottom of the receiving hopper. An annular water lubricator is provided between the outlet flange of the high-pressure plunger pump and the conveying pipe connected to the sun drying unit (7). The annular water lubricator is connected to a high-pressure water pump.

6. The sludge harmlessness and volume reduction treatment process according to claim 1, characterized in that, The solar drying unit (7) includes a solar drying room. The roof of the solar drying room is equipped with an electric skylight, and the side walls are equipped with electric air inlet louvers and negative pressure exhaust fans. The indoor floor is paved with hardened concrete flooring. Underfloor heating coils are pre-embedded in the hardened concrete flooring. The water inlet end of the underfloor heating coils is connected to the heat medium water circulation network of the biogas utilization unit (4) as a heating interface. An internal circulation fan is also suspended above the interior of the solar drying room.

7. The sludge harmlessness and volume reduction treatment process according to claim 6, characterized in that, The sun drying room is equipped with an integrated machine for spreading, collecting, and turning materials. The integrated machine includes a main beam spanning the workshop, a longitudinal traveling mechanism, a lifting trolley, and a rotary tiller installed under the lifting trolley. The surface of the rotary tiller is welded with spirally arranged turning blades, and a flat scraper assembly is provided on one side of the rotary tiller.

8. The sludge harmlessness and volume reduction treatment process according to claim 6, characterized in that, The central control system (9) is connected to a sensor group for detecting indoor and outdoor environmental parameters of the sun drying room. The sensor group has a built-in ventilation control logic module based on enthalpy-humidity diagram.

9. The sludge harmlessness and volume reduction treatment process according to claim 1, characterized in that, The sludge temporary storage and packaging unit (8) includes a dry material temporary storage bin and an automatic quantitative packaging machine. The lower cone of the dry material temporary storage bin is equipped with an arch-breaking device. The arch-breaking device is electrically interlocked with the flow switch of the discharge port. The bottom outlet of the dry material temporary storage bin is connected to the automatic quantitative packaging machine through an electric rotary feeding valve. Negative pressure dust collection hoods are provided at the top of the dry material temporary storage bin and at the discharge port of the packaging machine. The negative pressure dust collection hoods are connected to an explosion-proof pulse bag dust collector through an anti-static air duct.

10. The sludge harmlessness and volume reduction treatment process according to claim 1, characterized in that, The desulfurization unit (3) includes at least two sets of dry desulfurization towers arranged in parallel. The dry desulfurization towers are filled with iron oxide desulfurizing agent. Each set of dry desulfurization towers is equipped with a pneumatic shut-off valve on the inlet and outlet pipes.

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