Sludge low-temperature drying and fertilizer preparation method and system

Abstract

The invention discloses a sludge low-temperature drying and fertilizer preparation method and system.The sludge low-temperature drying and fertilizer preparation system comprises a pretreatment mechanism, a low-temperature drying mechanism, a biological fermentation mechanism and a heat energy recovery mechanism, and the pretreatment mechanism comprises a sludge storage tank and a stirring and conveying mechanism; the low-temperature drying mechanism comprises a drum-type drying machine and a sludge disperser, the drum-type drying machine comprises an inner drum body and an outer drum body, the biological fermentation mechanism comprises a multi-stage fermentation tank, a stirring piece and a temperature control device, and partition plates are arranged in the multi-stage fermentation tank to divide the interior of the multi-stage fermentation tank into a plurality of independent fermentation chambers. The temperature control device is arranged on the side wall and the bottom of the fermentation chamber, and the heat energy recovery mechanism comprises a heat exchange unit and a gas circulation unit. The sludge low-temperature drying and fertilizer preparation method and system provided by the invention have the advantages of low energy consumption, and stable and controllable fermentation process and product.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sludge resource utilization, and in particular to a sludge low-temperature drying and fertilizer preparation method and system. BACKGROUND

[0002] At present, the sludge treatment has high energy consumption and cost, the energy consumption of high-temperature drying accounts for 60%-70%, the waste heat utilization rate of low-temperature drying is less than 30%, and the pretreatment reagent and auxiliary environmental protection equipment further increase the cost; the quality of the resource product is unstable, the temperature control of single-chamber fermentation is uneven, and the dried sludge is agglomerated, which leads to large fluctuations of the fertilizer nutrient and safety index, and restricts the landing of sludge resource utilization. SUMMARY

[0003] The present application aims to at least solve one of the technical problems in the related art. To this end, the embodiments of the present application provide a sludge low-temperature drying and fertilizer preparation method and system, which has the advantages of low energy consumption, stable and controllable fermentation process and product.

[0004] The sludge low-temperature drying and fertilizer preparation system according to the embodiments of the present application comprises a pretreatment mechanism, a low-temperature drying mechanism, a biological fermentation mechanism and a heat energy recovery mechanism, the pretreatment mechanism comprises a sludge storage tank and a stirring and conveying mechanism, the stirring and conveying mechanism is arranged at the outlet of the sludge storage tank, the low-temperature drying mechanism comprises a roller dryer and a sludge disperser, the roller dryer comprises an inner cylinder and an outer cylinder, a closed interlayer is formed between the inner cylinder and the outer cylinder, a heating medium can be introduced into the closed interlayer, the sludge disperser is arranged at the feeding end of the inner cylinder, a medium inlet and a medium outlet are arranged on the outer cylinder, a humidity sensor is arranged at the outlet of the inner cylinder, spiral guide plates are arranged on the surface of the inner cylinder, the biological fermentation mechanism comprises a multi-stage fermentation tank, a stirring part and a temperature control device, a partition plate is arranged in the multi-stage fermentation tank to divide the multi-stage fermentation tank into a plurality of independent fermentation chambers, one stirring part and temperature control device are arranged in each fermentation chamber, the temperature control device is arranged on the side wall and the bottom of the fermentation chamber, a feeding port is arranged at the top of the multi-stage fermentation tank and is connected with the discharging end of the inner cylinder, a discharging port is arranged at the bottom of the multi-stage fermentation tank, and the heat energy recovery mechanism comprises a heat exchange unit and a gas circulation unit, the hot side of the heat exchange unit is connected with the medium outlet of the outer cylinder for heat exchange, the cold side of the heat exchange unit is connected with the outside air, and the gas circulation unit is connected with the heat exchange unit to send the outside air after heat exchange into the multi-stage fermentation tank.

[0005] The sludge low-temperature drying and fertilizer preparation method and system according to the embodiments of the present application have the advantages of low energy consumption, stable and controllable fermentation process and product. The present application has the following advantages: the system integrates the functions of pretreatment, low-temperature drying, biological fermentation, heat energy recovery and tail gas purification, which not only improves the system integration degree of the whole link, but also reduces the installation space of the whole system. The higher the system integration degree of the whole link, the higher the work efficiency of sludge treatment and fertilizer preparation. The inclined design of the sludge storage tank and the setting of the filter screen effectively improve the preliminary dewatering efficiency of the sludge; the double-layer cylinder structure and the spiral guide plate design of the roller dryer significantly improve the heat transfer efficiency; the partition plate and the temperature control device of the multi-stage fermentation tank ensure the stability and controllability of the fermentation process; the heat energy recovery device realizes the energy reuse of the wet hot gas, and reduces the overall energy consumption. In addition, the cyclone separator and the activated carbon filter of the tail gas purification device work together to effectively reduce the pollutant emissions and meet the environmental protection requirements.

[0006] In some embodiments, the heat side of the heat exchange unit is connected to the medium outlet of the outer cylinder for heat exchange, the cold side of the heat exchange unit is connected to the ambient air, and the gas circulation unit is connected to the heat exchange unit to send the ambient air after heat exchange into the multi-stage fermentation tank.

[0007] In some embodiments, the tail gas purification mechanism is further included, the tail gas purification mechanism includes a cyclone separator and an activated carbon filter, the inlet of the cyclone separator is connected to the heat side of the heat exchange unit, the activated carbon filter is connected to the outlet of the cyclone separator, and the outlet of the activated carbon filter is connected to the ambient air.

[0008] In some embodiments, the heat exchange unit is a plate heat exchanger, the hot side inlet of the plate heat exchanger is connected to the exhaust port of the roller dryer through a pipeline, the cold side inlet of the plate heat exchanger is connected to the ambient air inlet, the hot side outlet of the plate heat exchanger is connected to the inlet of the cyclone separator through a pipeline, and the cold side outlet of the plate heat exchanger is connected to the multi-stage fermentation tank.

[0009] In some embodiments, the bottom of the sludge storage tank is provided with a drain hole, the drain hole is provided with a filter screen, and the bottom of the sludge storage tank is inclined by 1-3°.

[0010] In some embodiments, the stirring and conveying mechanism includes a conveying cylinder and a screw stirrer, at least part of the screw shaft of the screw stirrer is located in the conveying cylinder, one end of the screw shaft is connected to a driving motor, the other end of the screw shaft extends to the outlet of the sludge storage tank along with the conveying cylinder, a plurality of blades are uniformly distributed on the screw shaft, and a gate valve is arranged at one end of the conveying cylinder adjacent to the outlet of the sludge storage tank.

[0011] In some embodiments, the sludge disperser includes a rotary motor, a gear set, and multiple rotating blades, wherein the output end of the rotary motor is connected to the multiple rotating blades via the gear set.

[0012] In some embodiments, the stirring element is a stirring paddle with four layers of blades, the blades being rotatable relative to the stirring element.

[0013] In some embodiments, the temperature control device includes a heating element and a cooling coil, the heating element being disposed on the side wall of the fermentation chamber and the cooling coil being disposed at the bottom of the fermentation chamber.

[0014] In some embodiments, the multi-stage fermenter has four independent fermentation chambers, the temperatures of which are 50°C to 60°C, 40°C to 50°C, 30°C to 40°C, and 20°C to 30°C, respectively.

[0015] The sludge low-temperature drying and fertilizer preparation method according to an embodiment of the present invention includes the following steps: The sludge is unloaded into the sludge storage tank, and the stirring and conveying mechanism is started. The drive motor drives the screw shaft and blades to rotate, and the sludge is evenly distributed and initially dewatered in the sludge storage tank. Adjust the opening of the gate valve to control the speed of sludge input into the drum dryer of the low-temperature drying mechanism; Start the sludge disperser. The rotating blades break the sludge into blocks and distribute them on the surface of the inner cylinder. The heating medium is introduced into the sealed jacket. The drum speed is adjusted to control the residence time of the sludge in the inner cylinder for 30-60 minutes. The humidity sensor detects the moisture content of the sludge. When the moisture content drops to 20%-30%, the sludge is discharged. The dried sludge enters a multi-stage fermentation tank and passes through multiple fermentation chambers in sequence for fermentation. The rotation speed of the agitator in each fermentation chamber decreases sequentially, and the temperature in each fermentation chamber is adjusted by a temperature control device, resulting in a sequential decrease in temperature. Fermentation lasts for 7 to 10 days, and the sludge is discharged after fermentation is completed. Heat recovery: The hot and humid air discharged from the drum dryer enters the hot side channel of the plate heat exchanger and exchanges heat with the outside air in the cold side channel. After heat exchange, the air enters the fermentation tank to supply oxygen for fermentation, and the cooled hot and humid air enters the cyclone separator for dust removal. After being processed by the cyclone separator, the gas enters the activated carbon filter to filter out organic matter and adsorb odors. The purified gas is then discharged into the outside atmosphere. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the sludge low-temperature drying and fertilizer preparation system according to an embodiment of the present invention.

[0017] Figure 2This is a schematic diagram of the structure of the drum dryer in the sludge low-temperature drying and fertilizer preparation system according to an embodiment of the present invention.

[0018] Figure 3 This is a schematic diagram of the multi-stage fermenter structure of the sludge low-temperature drying and fertilizer preparation system according to an embodiment of the present invention.

[0019] Reference numerals: 1. Pretreatment unit; 2. Sludge storage tank; 3. Mixing and conveying unit; 4. Low-temperature drying unit; 5. Drum dryer; 6. Sludge disperser; 7. Heat recovery unit; 8. Exhaust gas purification unit; 9. Biological fermentation unit; 10. Fermentation chamber; 11. Partition plate; 12. Stirring paddle; 13. Temperature control device. Detailed Implementation

[0020] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0021] According to an embodiment of the present invention, a sludge low-temperature drying and fertilizer preparation system includes a pretreatment unit 1, a low-temperature drying unit 4, a biological fermentation unit 9, and a heat recovery unit 7. The pretreatment unit includes a sludge storage tank 2 and a stirring and conveying unit 3, with the stirring and conveying unit 3 located at the outlet of the sludge storage tank 2. The low-temperature drying unit 4 includes a drum dryer 5 and a sludge disperser 6. The drum dryer 5 includes an inner cylinder and an outer cylinder, with a closed interlayer formed between the inner and outer cylinders. A heating medium can be introduced into the closed interlayer. The sludge disperser 6 is located at the feed end of the inner cylinder. A medium inlet and a medium outlet are provided on the outer cylinder. A humidity sensor is provided at the outlet of the inner cylinder. A spiral guide is provided on the surface of the inner cylinder. The flow plate and biological fermentation mechanism 9 include a multi-stage fermenter, a stirring component, and a temperature control device. A partition plate 11 is installed inside the multi-stage fermenter to divide the interior of the multi-stage fermenter into multiple independent fermentation chambers 10. Each fermentation chamber 10 is equipped with a stirring component and a temperature control device. The temperature control device is arranged on the side wall and bottom of the fermentation chamber 10. The top of the multi-stage fermenter is provided with a feed inlet that is connected to the discharge end of the inner cylinder, and the bottom of the multi-stage fermenter is provided with a discharge outlet. The heat recovery mechanism 7 includes a heat exchange unit and a gas circulation unit. The hot side of the heat exchange unit is connected to the medium outlet of the outer cylinder for heat exchange, and the cold side of the heat exchange unit is connected to the outside air. The gas circulation unit is connected to the heat exchange unit to send the heat-exchanged outside air into the multi-stage fermenter. The sludge storage tank 2 of the pretreatment unit 1, in conjunction with the stirring and conveying mechanism 3, pre-treats the sludge. After uniform distribution, the sludge undergoes initial dewatering. The stirring and conveying mechanism 3 then transports the sludge to the low-temperature drying unit 4. The low-temperature drying unit 4 uses a drum-type desiccant to heat and dry the sludge. The double-layered cylinder improves heat transfer and avoids heat energy waste. The spiral guide plate on the surface of the inner cylinder allows the sludge to move slowly along the guide plate after entering, and it can also evenly adhere to the inner cylinder wall, extending the sludge's flow time in the inner cylinder and ensuring thorough dewatering and drying. The sludge disperser 6 disperses the sludge, increasing the contact area between the sludge and the inner cylinder and preventing clumping and blockage. The moisture content of the sludge is judged by humidity to avoid insufficient drying affecting subsequent fermentation or excessive drying wasting energy. The multi-stage fermentation tank forms multiple independent fermentation chambers 10 through dividing plates, enabling staged fermentation. In the early stage, microorganisms multiply and decompose organic matter rapidly at a higher temperature, while in the later stage, fermentation is stable at a lower temperature to avoid nutrient loss and ensure stable fertilizer nutrients. The heat recovery mechanism 7 reduces energy consumption by recovering the preheat of the heating medium on the one hand, and preheating the air to meet the fermentation requirements on the other hand, thereby reducing the heat consumption for temperature control.

[0022] In some embodiments, the hot side of the heat exchange unit is connected to the medium outlet of the outer cylinder for heat exchange, the cold side of the heat exchange unit is connected to the outside air, and the gas circulation unit is connected to the heat exchange unit to send the heat-exchanged outside air into the multi-stage fermenter.

[0023] Specifically, the hot-side channel is connected to the medium outlet of the outer cylinder, introducing the medium from the sealed interlayer between the outer and inner cylinders for preheating. The heating medium can be clean hot air, hot water, heat transfer oil, etc. The cold-side channel is connected to the outside atmosphere, introducing ambient air at room temperature. During the heat exchange process, the waste heat medium on the hot side and the ambient air on the cold side flow counter-currently on both sides of the plates. The hot-side medium cools down, while the cold-side air heats up. The heated air is then sent into the fermentation chamber 10 of the multi-stage fermenter to supply oxygen, ensuring smooth fermentation and reducing the energy consumption of the temperature control device. The gas circulation unit includes a fan and pipes. The fan sends the heated air into the fermenter. Optionally, a check valve can be installed on the pipes to prevent the fermentation exhaust gas containing volatile organic compounds from flowing back into the heat exchange unit. The heating medium temperature of the drum dryer 5 is 60℃ to 80℃, and the residence time of the sludge in the drum is 30 minutes to 60 minutes. In some embodiments, the system further includes an exhaust gas purification mechanism 8, which includes a cyclone separator and an activated carbon filter. The inlet of the cyclone separator is connected to the hot side of the heat exchange unit, the activated carbon filter is connected to the outlet of the cyclone separator, and the outlet of the activated carbon filter is connected to the outside.

[0024] Specifically, the exhaust gas purification unit 8 removes dust through a cyclone separator and removes odors from the air by adsorbing organic matter through an activated carbon filter. In the cyclone separator, under centrifugal force, fine dust particles in the exhaust gas are thrown against the inner wall of the separator, slide down the wall to the conical dust collection section, and are finally discharged through the ash hopper discharge valve. The porous structure of the activated carbon in the activated carbon filter captures VOCs (such as formic acid and acetic acid) and malodorous gases (such as ammonia and hydrogen sulfide) in the exhaust gas through physical adsorption, achieving the removal of organic matter and odors. Removing fine dust particles from the exhaust gas first prevents dust from clogging the porous structure of the activated carbon, extends the activated carbon replacement cycle, and reduces costs. The activated carbon particle size is 2 to 5 millimeters. Optionally, a thermal regeneration mechanism is installed at the activated carbon filter. The thermal regeneration mechanism includes an electric heating tube, a fan, and a desorption gas outlet. After the activated carbon in the activated carbon filter is saturated with adsorption, the electric heating tube of the hot air regeneration module is activated to introduce clean hot air at 120~150℃. Through thermal desorption, the VOCs adsorbed by the activated carbon are desorbed from the odorous gas. The desorbed gas can be returned to the heating medium inlet of the drum dryer 5 as an auxiliary heat source.

[0025] In some embodiments, the heat exchange unit is a plate heat exchanger. The hot side inlet of the plate heat exchanger is connected to the exhaust port of the drum dryer 5 through a pipe. The cold side inlet of the plate heat exchanger is connected to the outside air inlet. The hot side outlet of the plate heat exchanger is connected to the inlet of the cyclone separator through a pipe. The cold side outlet of the plate heat exchanger is connected to the multi-stage fermenter.

[0026] Specifically, the plates of the plate heat exchanger are made of corrosion-resistant alloys such as stainless steel, and a drain valve is installed at the bottom of the heat exchanger to regularly drain the condensate on the hot side to prevent plate corrosion.

[0027] In some embodiments, a drainage hole is provided at the bottom of the sludge storage tank 2, a filter screen is provided at the drainage hole, and the bottom of the sludge storage tank 2 is inclined at 1-3°.

[0028] Specifically, the mixing and conveying mechanism 3 is located at the lowest point of the inclined bottom, ensuring that the sludge flows slowly towards the outlet under gravity. If the bottom inclination angle of the sludge storage tank 2 is too large, the sludge will easily accumulate excessively at the outlet due to gravity, resulting in uneven feeding of the mixing and conveying mechanism 3. Drainage holes are located at the lowest point of the bottom of the sludge storage tank 2, with the number of drainage holes set according to the volume of the sludge storage tank 2 to ensure that the drainage load of a single drainage hole is within the expected range. The filter screen has a mesh size of 200 to 300 mesh, and the filter screen can be detachably fixed to the sludge storage tank 2 with bolts for easy disassembly and cleaning. Preferably, the bottom inclination angle of the sludge storage tank 2 is 2°, and the filter screen mesh size is 250 mesh.

[0029] In some embodiments, the mixing and conveying mechanism 3 includes a conveying cylinder and a screw agitator. At least part of the screw shaft of the screw agitator is located inside the conveying cylinder. One end of the screw shaft is connected to a drive motor, and the other end of the screw shaft extends along the conveying cylinder to the outlet of the sludge storage tank 2. Multiple blades are evenly distributed on the screw shaft, and a gate valve is provided at one end of the conveying cylinder near the outlet of the sludge storage tank 2.

[0030] Specifically, the feed end of the conveyor cylinder can be a flared funnel shape, with blades continuously spirally distributed on the screw shaft. The gate valve is an electrically adjustable gate valve, which can be remotely controlled, and a rubber sealing gasket is installed on the gate to ensure that sludge does not leak when closed. The screw agitator and the conveyor cylinder work together to achieve integrated mixing and conveying, improving processing efficiency. The mixing action also promotes the release of residual free water in the sludge.

[0031] Optionally, a polytetrafluoroethylene (PTFE) anti-stick coating can be sprayed onto the blades to reduce sludge adhesion.

[0032] In some embodiments, the sludge disperser 6 includes a rotary motor, a gear set, and multiple rotating blades, with the output end of the rotary motor being connected to the multiple rotating blades via the gear set.

[0033] Specifically, the number of rotating blades is 3 to 6, arranged radially along the axis of rotation, with a certain spacing between them. The spacing is controlled to be between half and a quarter of the blade size to avoid sludge entanglement due to too small a spacing or blind spots due to too large a spacing. Preferably, there are 4 rotating blades, evenly distributed around the circumference to ensure balanced dispersing force. In some embodiments, the agitator is a stirring paddle 12 with four layers of blades, the blades being rotatable relative to the agitator.

[0034] Specifically, each layer of the agitator 12 has 3 to 4 blades, evenly distributed around the circumference to ensure thorough mixing without dead zones. The four layers of blades are spaced a certain distance apart along the axial direction of the agitator shaft, forming a three-dimensional mixing system to prevent the deposition of sludge at the bottom layer, which can easily lead to localized anaerobic conditions. The angle of each layer of blades is adjustable, with an adjustment range of 0° to 45°.

[0035] In some embodiments, the temperature control device includes a heating element and a cooling coil, with the heating element arranged on the side wall of the fermentation chamber 10 and the cooling coil arranged at the bottom of the fermentation chamber 10.

[0036] Specifically, heating pipes are arranged on the side walls, and cooling coils are arranged at the bottom to achieve bidirectional temperature control. This allows for precise temperature regulation of the fermentation chamber 10, ensuring high temperature control accuracy and maintaining microbial activity and fermentation stability. The side wall heating covers the upper material, while the bottom cooling targets the lower material that is prone to sedimentation, avoiding localized temperature differences.

[0037] In some embodiments, the multi-stage fermenter has four independent fermentation chambers 10, with temperatures of 50°C to 60°C, 40°C to 50°C, 30°C to 40°C, and 20°C to 30°C, respectively.

[0038] Specifically, the stirring paddles 12 in the four fermentation chambers 10 rotate at different speeds: 10-20 rpm for the first fermentation chamber 10, 5-10 rpm for the second, 3-5 rpm for the third, and 1-3 rpm for the fourth. This decreasing temperature gradient in the four fermentation chambers 10 matches the full-cycle characteristics of sludge biological fermentation. The four-stage temperature gradient ensures that microorganisms at each stage are within their optimal temperature range, enhancing the overall activity of the microbial community. The initial temperature helps kill pathogens. The decreasing temperature helps stabilize fertilizer nutrients. The fermenter has an inlet and an outlet at the top, and an outlet at the bottom, with a screen at the outlet having a mesh size of 5 to 10 mm.

[0039] The sludge low-temperature drying and fertilizer preparation method according to an embodiment of the present invention includes the following steps: The sludge is unloaded into the sludge storage tank 2. The stirring and conveying mechanism 3 is started, and the drive motor drives the screw shaft and blades to rotate. The sludge is evenly distributed in the sludge storage tank 2 and initially dewatered. Adjust the opening of the gate valve to control the speed of the drum dryer 5 of the low-temperature drying mechanism 4 for sludge input; Start the sludge disperser 6. The rotating blades break the sludge into blocks and distribute them on the surface of the inner cylinder. The heating medium is introduced into the sealed jacket. The drum speed is adjusted to control the residence time of the sludge in the inner cylinder for 30-60 minutes. The humidity sensor detects the moisture content of the sludge. When the moisture content drops to 20%-30%, the sludge is discharged. The dried sludge enters a multi-stage fermentation tank and passes through multiple fermentation chambers 10 for fermentation. The rotation speed of the agitator in the fermentation chamber 10 decreases sequentially. The temperature in the fermentation chamber 10 is adjusted by a temperature control device, and the temperature in the fermentation chamber 10 decreases sequentially. Fermentation takes 7 to 10 days. After fermentation is completed, the sludge is discharged. Heat recovery: The hot and humid air discharged from the drum dryer 5 enters the hot side channel of the plate heat exchanger and exchanges heat with the outside air in the cold side channel. After heat exchange, the air enters the fermentation tank to supply oxygen for fermentation. The cooled hot and humid air enters the cyclone separator for dust removal. After being processed by the cyclone separator, the gas enters the activated carbon filter to filter out organic matter and adsorb odors. The purified gas is then discharged into the outside atmosphere.

[0040] The heating medium temperature of the drum dryer 5 is 70℃, the residence time of the sludge in the drum is about 45 minutes, and the moisture content of the dried sludge is 25%.

[0041] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0042] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0043] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0044] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0045] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0046] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A sludge low-temperature drying and fertilizer preparation system, characterized in that, include: A pretreatment unit, comprising a sludge storage tank and a mixing and conveying mechanism, wherein the mixing and conveying mechanism is arranged at the outlet of the sludge storage tank; A low-temperature drying mechanism includes a drum dryer and a sludge disperser. The drum dryer includes an inner cylinder and an outer cylinder, with a closed interlayer formed between the inner and outer cylinders. A heating medium can be introduced into the closed interlayer. The sludge disperser is arranged at the feed end of the inner cylinder. A medium inlet and a medium outlet are provided on the outer cylinder. A humidity sensor is provided at the outlet of the inner cylinder. A spiral guide plate is provided on the surface of the inner cylinder. A biological fermentation mechanism includes a multi-stage fermenter, a stirring component, and a temperature control device. The multi-stage fermenter is divided into multiple independent fermentation chambers by a partition plate. Each fermentation chamber is equipped with a stirring component and a temperature control device. The temperature control device is arranged on the side wall and bottom of the fermentation chamber. The top of the multi-stage fermenter has a feed inlet connected to the discharge end of the inner cylinder, and the bottom of the multi-stage fermenter has a discharge outlet. The heat recovery mechanism includes a heat exchange unit and a gas circulation unit. The hot side of the heat exchange unit is connected to the medium outlet of the outer cylinder for heat exchange, and the cold side of the heat exchange unit is connected to the outside air. The gas circulation unit is connected to the heat exchange unit to send the heat-exchanged outside air into the multi-stage fermenter.

2. The sludge low-temperature drying and fertilizer preparation system according to claim 1, characterized in that, It also includes an exhaust gas purification mechanism, which includes a cyclone separator and an activated carbon filter. The inlet of the cyclone separator is connected to the hot side of the heat exchange unit, the activated carbon filter is connected to the outlet of the cyclone separator, and the outlet of the activated carbon filter is connected to the outside.

3. The sludge low-temperature drying and fertilizer preparation system according to claim 2, characterized in that, The heat exchange unit is a plate heat exchanger. The hot side inlet of the plate heat exchanger is connected to the exhaust port of the drum dryer through a pipe. The cold side inlet of the plate heat exchanger is connected to the outside air inlet. The hot side outlet of the plate heat exchanger is connected to the inlet of the cyclone separator through a pipe. The cold side outlet of the plate heat exchanger is connected to the multi-stage fermenter.

4. The sludge low-temperature drying and fertilizer preparation system according to claim 1, characterized in that, The bottom of the sludge storage tank is provided with a drainage hole, and a filter screen is installed at the drainage hole. The bottom of the sludge storage tank is inclined at 1-3°.

5. The sludge low-temperature drying and fertilizer preparation system according to claim 1, characterized in that, The mixing and conveying mechanism includes a conveying cylinder and a screw agitator. At least part of the screw shaft of the screw agitator is located inside the conveying cylinder. One end of the screw shaft is connected to a drive motor, and the other end of the screw shaft extends along the conveying cylinder to the outlet of the sludge storage tank. Multiple blades are evenly distributed on the screw shaft, and a gate valve is provided at one end of the conveying cylinder adjacent to the outlet of the sludge storage tank.

6. The sludge low-temperature drying and fertilizer preparation system according to claim 1, characterized in that, The sludge disperser includes a rotary motor, a gear set, and multiple rotating blades. The output end of the rotary motor is connected to the multiple rotating blades via the gear set.

7. The sludge low-temperature drying and fertilizer preparation system according to claim 1, characterized in that, The stirring element is a stirring paddle with four layers of blades, and the blades can rotate relative to the stirring element.

8. The sludge low-temperature drying and fertilizer preparation system according to claim 1, characterized in that, The temperature control device includes a heating element and a cooling coil. The heating element is arranged on the side wall of the fermentation chamber, and the cooling coil is arranged at the bottom of the fermentation chamber.

9. The sludge low-temperature drying and fertilizer preparation system according to claim 1, characterized in that, The multi-stage fermenter has four independent fermentation chambers, with temperatures of 50°C to 60°C, 40°C to 50°C, 30°C to 40°C, and 20°C to 30°C, respectively.

10. A method for low-temperature drying of sludge and preparation of fertilizer, utilizing the low-temperature drying of sludge and preparation of fertilizer system as described in any one of claims 1-9, characterized in that, Includes the following steps: The sludge is unloaded into the sludge storage tank, and the stirring and conveying mechanism is started. The drive motor drives the screw shaft and blades to rotate, and the sludge is evenly distributed and initially dewatered in the sludge storage tank. Adjust the opening of the gate valve to control the speed of sludge input into the drum dryer of the low-temperature drying mechanism; Start the sludge disperser. The rotating blades break the sludge into blocks and distribute them on the surface of the inner cylinder. The heating medium is introduced into the sealed jacket. The drum speed is adjusted to control the residence time of the sludge in the inner cylinder for 30-60 minutes. The humidity sensor detects the moisture content of the sludge. When the moisture content drops to 20%-30%, the sludge is discharged. The dried sludge enters a multi-stage fermentation tank and passes through multiple fermentation chambers in sequence for fermentation. The rotation speed of the agitator in each fermentation chamber decreases sequentially, and the temperature in each fermentation chamber is adjusted by a temperature control device, resulting in a sequential decrease in temperature. Fermentation lasts for 7 to 10 days, and the sludge is discharged after fermentation is completed. Heat recovery: The hot and humid air discharged from the drum dryer enters the hot side channel of the plate heat exchanger and exchanges heat with the outside air in the cold side channel. After heat exchange, the air enters the fermentation tank to supply oxygen for fermentation, and the cooled hot and humid air enters the cyclone separator for dust removal. After being processed by the cyclone separator, the gas enters the activated carbon filter to filter out organic matter and adsorb odors. The purified gas is then discharged into the outside atmosphere.

Images