Agricultural waste comprehensive treatment system

Abstract

The application discloses a kind of agricultural waste comprehensive treatment system, it is related to solid waste treatment field, including pretreatment module, anaerobic fermentation module, marsh gas utilization module and aerobic composting module;The pretreatment module includes sorting device, crushing device and homogenization conditioning pool connected in sequence, for agricultural waste is sorted, crushing and homogenization treatment;The anaerobic fermentation module includes anaerobic fermentation tank, and the feed inlet of the anaerobic fermentation tank is connected with the discharge port of the pretreatment module, for the waste after pretreatment is anaerobic fermentation to produce marsh gas and fermentation residue;This agricultural waste comprehensive treatment system, through the dynamic distribution strategy of three-way regulating valve based on the real-time temperature feedback of anaerobic fermentation tank (all supply anaerobic when anaerobic tank <37.0 ℃, PID regulation when 37.0-38.0 ℃, ≥38.0 ℃ all supply composting), the precise matching of surplus heat supply and actual heat required period of each module is realized.

Description

Technical Field

[0001] This invention relates to solid waste treatment technology, specifically to an integrated agricultural waste treatment system. Background Technology

[0002] With the continuous expansion of agricultural planting and livestock breeding scale in my country, the annual output of agricultural waste such as crop straw, vegetable waste, and livestock manure has continued to increase. According to statistics, my country produces about 3.8 billion tons of livestock manure and about 900 million tons of crop straw every year. If not properly treated, this will not only waste resources but also cause serious pollution to the soil, water bodies, and atmospheric environment.

[0003] Currently, agricultural waste resource utilization technologies mainly fall into two categories: anaerobic fermentation for biogas production and aerobic composting for organic fertilizer production. Anaerobic fermentation technology can convert organic waste into clean energy biogas, and the fermentation residue can be made into organic fertilizer through aerobic composting. However, in existing coupled systems of anaerobic fermentation and aerobic composting, the following specific engineering contradictions still urgently need to be resolved:

[0004] Leachate produced during aerobic composting is typically weakly acidic to acidic (pH 5.5-6.5) and contains soluble organic acids. Direct recirculation of this leachate to the anaerobic digester can easily cause the pH level to drop below the optimal range for methanogens (6.8-7.4), inhibiting methanogen activity and reducing gas production. Existing systems lack a coordinated control scheme for the amount of leachate reused, the reuse point, and the feed buffer capacity, limiting the safe and efficient recycling of leachate. Summary of the Invention

[0005] To address the risk of acidity in aerobic compost leachate inhibiting the activity of methanogenic bacteria in anaerobic fermentation, the present invention provides an integrated agricultural waste treatment system. Through a system integration design that incorporates dynamic energy cascade distribution, precise coupled re-spraying of biogas slurry, and safe leachate reflux buffering, the system achieves efficient resource utilization of agricultural waste.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an agricultural waste comprehensive treatment system, comprising a pretreatment module, an anaerobic fermentation module, a biogas utilization module, and an aerobic composting module;

[0007] The pretreatment module includes a sorting device, a crushing device, and a homogenization and conditioning tank connected in sequence, used for sorting, crushing, and homogenizing agricultural waste.

[0008] The anaerobic fermentation module includes an anaerobic fermentation tank, the inlet of which is connected to the outlet of the pretreatment module, for anaerobic fermentation of pretreated waste to produce biogas and fermentation residue.

[0009] The biogas utilization module includes a biogas purification device and a biogas power generation device. The inlet of the biogas purification device is connected to the biogas outlet of the anaerobic digester, and the outlet of the biogas purification device is connected to the biogas power generation device.

[0010] The aerobic composting module includes an aerobic composting chamber, the inlet of which is connected to the slag outlet of the anaerobic fermentation tank, for aerobic composting of fermentation residues into organic fertilizer.

[0011] The waste heat recovery pipeline of the biogas power generation device is connected to the heating and insulation jacket of the anaerobic fermentation tank and the auxiliary heating pipeline of the aerobic composting bin. The waste heat recovery pipeline is equipped with a three-way regulating valve. The opening of the three-way regulating valve is controlled according to the temperature sensor signal in the anaerobic fermentation tank to prioritize meeting the heat insulation requirements of the anaerobic fermentation tank. The remaining waste heat is then supplied to the aerobic composting bin for auxiliary heating.

[0012] The aerobic composting bin is equipped with a leachate collection pipeline, which is connected to the homogenization and conditioning tank to return the leachate generated during the aerobic composting process to the homogenization and conditioning tank to adjust the moisture content of the material.

[0013] The anaerobic fermentation tank's biogas slurry outlet is connected to the aerobic composting bin's spraying device via a biogas slurry return pipeline. This device sprays the biogas slurry produced by anaerobic fermentation into the aerobic compost material to adjust the moisture content and supplement the nitrogen source.

[0014] Furthermore, the sorting device is a drum screen with a screen hole diameter of 20-50mm; the crushing device is a twin-shaft shear crusher with a crushed material particle size ≤20mm; the homogenization and conditioning tank is equipped with a stirring device and a moisture content monitoring sensor to adjust the material moisture content to 75%-85% and the carbon-nitrogen ratio to 20:1-30:1.

[0015] Furthermore, the anaerobic fermenter is a completely mixed anaerobic fermenter with a heating and insulation jacket on the inner wall of the tank. The tank is equipped with a stirring device and a temperature sensor. The heat exchange medium inlet of the heating and insulation jacket is connected to the waste heat recovery pipeline of the biogas power generation device. The fermentation temperature of the anaerobic fermenter is 35-38℃, the hydraulic retention time is 20-25 days, and the total solids concentration of the material is 8%-12%.

[0016] Furthermore, the three-way regulating valve is an electric three-way regulating valve. The temperature sensors are installed at three different heights (upper, middle, and lower) inside the anaerobic fermenter. The opening of the three-way regulating valve is controlled according to the average temperature measured by the three temperature sensors. When the average temperature is below 37.0℃, the three-way regulating valve is fully closed to the auxiliary heating pipeline of the aerobic composting chamber, and all the waste heat is supplied to the heating and insulation jacket of the anaerobic fermenter. When the average temperature is higher than or equal to 38.0℃, the three-way regulating valve is fully open to the auxiliary heating pipeline of the aerobic composting chamber. When the average temperature is between 37.0℃ and 38.0℃, the opening of the three-way regulating valve is adjusted according to the PID ratio.

[0017] Furthermore, the aerobic composting bin is a trough-type aerobic composting bin, with a ventilation and aeration device at the bottom, an auxiliary heating pipeline on the bin wall, and a spraying device and exhaust gas collection pipeline on the top. The heat exchange medium inlet of the auxiliary heating pipeline is connected to the waste heat recovery pipeline of the biogas power generation device, and a solenoid valve is installed on the auxiliary heating pipeline. The solenoid valve only opens when the temperature at the center of the compost pile inside the aerobic composting bin is below 50°C.

[0018] Furthermore, the biogas slurry return pipeline is equipped with a biogas slurry storage tank, a delivery pump, and a flow regulating valve. The spraying device is a rotary spray head installed on the top of the aerobic composting bin. The main pipeline of the ventilation and aeration device of the aerobic composting bin is equipped with a gas flow meter and a temperature and humidity sensor. The system also includes a central controller. The central controller calculates the cumulative moisture evaporation of the compost pile based on the detection signals of the gas flow meter and the temperature and humidity sensor, and uses 75%-85% of the cumulative moisture evaporation as the target value of the biogas slurry return spray volume for the next day to control the opening of the flow regulating valve.

[0019] Furthermore, the aerobic composting bin is equipped with a turning machine, and the spraying device is turned on synchronously during the operation of the turning machine, with the spraying direction aimed at the cross-section of the material turned up by the turning machine; after the spraying is completed, the turning machine continues to move forward and turn the material for at least two more strokes.

[0020] Furthermore, the leachate collection pipeline includes a slope guide plate and an outlet located at the bottom of the aerobic composting bin. The outlet is connected to the homogenization and conditioning tank via a pipeline, which is equipped with a filter device and a reflux pump. An online pH meter is installed at the outlet of the homogenization and conditioning tank, and the online pH meter is signal-connected to the reflux pump. When the pH value of the material at the outlet of the homogenization and conditioning tank is lower than 6.7, the reflux pump operates at 30% of its rated speed. When the pH value is lower than 6.3, the reflux pump stops.

[0021] Furthermore, it also includes an intelligent control system, which includes a central controller and material metering sensors, temperature sensors, pH sensors, methane concentration sensors, moisture content sensors, and gas flow meters that are respectively connected to the central controller via signals; the central controller controls the feeding rate of the pretreatment module, the fermentation temperature of the anaerobic fermentation module, the power generation load of the biogas utilization module, and the ventilation and spraying volume of the aerobic composting module based on the feedback signals from each sensor.

[0022] Furthermore, the intelligent control system also includes a remote monitoring terminal and a data storage module. The remote monitoring terminal is wirelessly connected to the central controller and is used to display system operating parameters and issue remote control commands in real time. The data storage module is used to store historical system operating data and optimize the operating parameters of each module based on the historical data.

[0023] The agricultural waste includes crop straw, vegetable waste, and livestock and poultry manure.

[0024] Compared with existing technologies, the agricultural waste comprehensive treatment system provided by the present invention has the following beneficial effects:

[0025] (1) This invention achieves precise matching between waste heat supply and the actual heat demand periods of each module through a dynamic distribution strategy of a three-way regulating valve based on real-time temperature feedback from the anaerobic digester (full anaerobic supply when anaerobic digester temperature <37.0℃, PID regulation when 37.0-38.0℃, and full composting supply when ≥38.0℃). Calculations show that, based on a daily processing capacity of 50 tons, the waste heat recovery from power generation is approximately 180-220 GJ / day (based on a biogas production of 1400 m³). 3 Based on a daily output of 55% methane, a power generation efficiency of 40%, and a waste heat recovery efficiency of 47%, the heat demand for heating and insulation of the anaerobic digester accounts for approximately 75% (calculated based on a material specific heat capacity of approximately 4.2 kJ / (kg·℃), a feed temperature of 15℃, a fermentation temperature of 38℃, and a heat loss of approximately 5.5 kW / ℃ from the digester). After cascaded heat utilization, the system's external heating energy consumption is reduced by approximately 60%, the annual external heating time for the anaerobic digester is reduced to less than 5 days, and the comprehensive utilization rate of waste heat from power generation is increased to 52%-58%.

[0026] (2) This invention recycles the leachate produced by aerobic composting to a homogenization equalization tank, utilizing the large-capacity buffering effect of the equalization equalization tank (effective volume ≥ 2 days' treatment capacity, approximately 100-150 m³). 3 The system neutralizes acidic leachate and sets up dual-limit safety controls based on pH (frequency reduction when pH < 6.7, shutdown and dilution with water when pH < 6.3), preventing the acidic leachate from inhibiting anaerobic methanogens. The pH in the anaerobic tank is stabilized at 6.8-7.2, eliminating the need for additional acid-base regulators.

[0027] (3) This invention achieves dynamic matching between the amount of biogas slurry returned and the actual moisture evaporation demand of compost by using a feedforward spraying strategy based on the real-time calculation of the cumulative moisture evaporation of the compost pile, combined with the interlocking control of spraying and turning actions. The compost moisture content is stabilized at 50%-60%, and the total nitrogen content of the final product is increased to 2.0%-2.5%, while avoiding secondary pollution caused by the discharge of biogas slurry.

[0028] (4) Through system integration design, the present invention organically integrates four modules: pretreatment, anaerobic fermentation, biogas utilization and aerobic composting, forming a closed loop of waste pretreatment - anaerobic fermentation to produce biogas - biogas power generation - waste heat recovery - aerobic composting of residues - leachate / biogas liquid return, realizing the full-scale and resource-based utilization of agricultural waste. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this invention. For those skilled in the art, other drawings can be obtained based on these drawings.

[0030] Figure 1 This is a schematic diagram of the agricultural waste comprehensive treatment system of the present invention;

[0031] Figure 2 This is a control logic block diagram of the intelligent control system of the present invention;

[0032] Figure 3 This is a flowchart of the three-level control logic for dynamic waste heat distribution in this invention.

[0033] Explanation of reference numerals in the attached figures:

[0034] 1. Sorting device; 2. Crushing device; 3. Homogenizing tank; 4. Anaerobic fermentation tank; 5. Heating and insulation jacket; 6. Temperature sensor; 7. Biogas purification device; 8. Biogas power generation device; 9. Aerobic composting bin; 10. Ventilation and aeration device; 11. Auxiliary heating pipeline; 12. Spraying device; 13. Tail gas collection pipeline; 14. Three-way regulating valve; 15. Leachate collection pipeline; 16. Biogas slurry return pipeline. Detailed Implementation

[0035] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0036] As attached Figure 1 To be continued Figure 3 As shown:

[0037] Example 1: (Daily processing capacity 50 tons, corn stalks + cow manure, mesophilic anaerobic digestion + waste heat utilization)

[0038] This embodiment provides an integrated agricultural waste treatment system that uses corn stalks and cow manure as the treatment objects, with a daily processing capacity of 50 tons (the stalks and cow manure are mixed at a dry matter mass ratio of approximately 3:7) and an annual processing capacity of approximately 18,000 tons.

[0039] Pre-treatment module: Sorting device 1 uses a drum screen with a screen aperture diameter of 30mm to remove stones, metal, and other impurities; crushing device 2 uses a twin-shaft shear crusher to crush the straw to a particle size ≤20mm; the crushed material enters the homogenization and equalization tank 3, where the moisture content is adjusted to 80%±2% and the carbon-to-nitrogen ratio (C / N) is adjusted to 25:1 by a stirring device and a moisture content monitoring sensor. The effective volume of the homogenization and equalization tank is 120m³. 3 (Approximately 2.4 days' worth of processing capacity).

[0040] Anaerobic fermentation module: Anaerobic fermenter 4 adopts a completely mixed (CSTR) anaerobic fermenter with an effective volume of 800m³. 3 The tank is equipped with a heating and insulation jacket 5 on its inner wall, and a stirring device and temperature sensors 6 (located at three different heights inside the tank). The fermentation temperature is maintained at 37.5±0.5℃ (mesothermal fermentation), the hydraulic retention time (HRT) is 22 days, and the total solids concentration (TS) of the fermentation material is 10%. The biogas production from anaerobic fermentation is approximately 1400 m³. 3 / day (methane content approximately 55%), biogas enters biogas power generation unit 8 after passing through purification device 7 (alkali desulfurization + condensation dehydration).

[0041] Biogas Utilization Module: Biogas Power Generation Unit 8 uses a biogas internal combustion generator set (500kW), with a power generation efficiency of approximately 40% and a waste heat recovery efficiency of approximately 47%. The waste heat recovery amount is approximately 198 GJ / day (based on a 1400m³ / day). 3 / day × 55% CH4 × 35.9 MJ / m 3 (Calculated as ×40%×47%), of which the heat requirement for heating and insulation of the anaerobic fermenter is approximately 148 GJ / day (accounting for 75%), and the remaining approximately 50 GJ / day is supplied to the aerobic composting silo for auxiliary heating. The waste heat recovery pipeline is equipped with an electric three-way regulating valve (14), which dynamically allocates heat according to a three-level logic: "anaerobic tank <37.0℃, all anaerobic heat is supplied; 37.0-38.0℃, PID adjustment, to ≥38.0℃, all composting heat is supplied".

[0042] Aerobic composting module: After solid-liquid separation by a screw extruder, the fermentation residue discharged from the anaerobic digester, with a moisture content of approximately 70%, enters the aerobic composting bin 9. The aerobic composting bin is a trough-type aerobic composting bin (length × width × height = 30m × 6m × 2.5m), and the bottom of the bin is equipped with a ventilation and aeration device 10 (ventilation capacity 0.2m³ / h).3 air / m 3 The composting time is 18 days. The silo walls are equipped with auxiliary heating pipes 11, and the silo roof is equipped with rotating spray heads 12 and exhaust gas collection pipes 13. The composting cycle is 18 days. For the first 5 days, forced ventilation is used to maintain the temperature of the compost pile at ≥55℃, and the pile is allowed to cool down and mature naturally for the next 13 days.

[0043] The biogas slurry return spray is controlled according to the formula "spraying volume = previous day's cumulative evaporation volume × 80%", and the spraying device is turned on synchronously during the operation of the compost turner. The leachate at the bottom of the aerobic compost bin (pH about 6.0) is collected by the slope guide plate, and then returned to the feed end of the homogenization equalization tank after three-stage sedimentation + 50-mesh filtration. The return pump is controlled by the pH signal at the outlet of the homogenization equalization tank (frequency is reduced to 30% when pH < 6.7, and stops when pH < 6.3).

[0044] Treatment results: After 6 months of stable operation, the system produced an average of 1420 m³ of biogas per day. 3 Daily power generation 568kWh (based on 1m³) 3 The biogas power generation capacity is 0.4 kWh, and the annual production of organic fertilizer is approximately 6,500 tons (moisture content 28%). The organic fertilizer product, after testing, has the following characteristics: total nutrients (N+P2O5+K2O) 6.2%, organic matter 52%, pH 7.1, seed germination index (GI) 82%, meeting the NY / T 525-2021 standard. The pH inside the anaerobic digester is stable at 6.9-7.2. The system's external heating energy consumption is reduced by approximately 62% compared to traditional independent operation, requiring only 3 days of external heating per year (during extreme cold waves). The comprehensive utilization rate of waste heat from power generation reaches 56%.

[0045] Example 2: (Daily processing capacity 30 tons, vegetable waste + pig manure, high temperature anaerobic digestion + different raw material ratios)

[0046] This embodiment provides an integrated agricultural waste treatment system that treats vegetable waste (cabbage leaves, tomato vines, etc.) and pig manure, with a daily processing capacity of 30 tons (vegetable waste and pig manure are mixed at a dry matter mass ratio of approximately 4:6) and an annual processing capacity of approximately 11,000 tons. This embodiment is used to verify the adaptability of the invention to different types of raw materials and its operational effectiveness under high-temperature anaerobic fermentation conditions.

[0047] Pre-treatment module: The sorting device has a 25mm diameter screen to remove lightweight impurities such as plastic film and rope ends; the crushing device crushes vegetable waste to a particle size ≤15mm (vegetable waste has low fiber content, allowing for finer crushing); the homogenization and equalization tank has an effective volume of 80m³. 3 The moisture content of the material is adjusted to 82%±2%, and the C / N ratio is adjusted to 22:1 (the C / N ratio of vegetable waste is relatively low, so straw-based conditioners need to be added appropriately).

[0048] Anaerobic fermentation module: anaerobic fermenter with an effective volume of 500m³. 3The fermentation temperature was maintained at 53±1℃ (high-temperature fermentation), with a HRT of 18 days (high-temperature fermentation results in a faster reaction rate) and a TS of 9%. High-temperature anaerobic fermentation produces a higher biogas rate, with a biogas yield of approximately 1100 m³. 3 / day (methane content approximately 58%). High-temperature fermentation yields greater waste heat recovery (waste heat recovery from power generation approximately 165 GJ / day). However, due to the high fermentation temperature, the anaerobic digester's own heat insulation requirement is lower than that of the mesophilic condition (the temperature difference with the environment is greater, but the heat dissipation area is the same, and the heat insulation requirement accounts for approximately 65% ​​of the total waste heat). Therefore, the proportion of waste heat available for aerobic composting is higher (approximately 35%, or 58 GJ / day).

[0049] Waste heat distribution adjustment: Since the tank of high-temperature anaerobic fermentation has a higher insulation temperature, the control threshold of the three-way regulating valve is adjusted accordingly: when the average temperature inside the tank is below 52.0℃, the entire tank is supplied for anaerobic digestion; between 52.0℃ and 53.0℃, the temperature is adjusted by PID; and when the temperature is ≥53.0℃, the entire tank is supplied for composting.

[0050] Aerobic composting module: Biogas residue enters the aerobic composting bin, with a composting cycle of 15 days (high-temperature anaerobic slag discharge results in more thorough degradation of organic matter, shortening the composting time). The auxiliary heating pipeline activates the solenoid valve when the temperature at the center of the compost pile is below 50°C. In winter, the frequency of auxiliary heating activation is lower than in Example 1 (because a higher proportion of high-temperature anaerobic waste heat is supplied to the compost).

[0051] Biogas slurry and leachate recirculation: The biogas slurry recirculation ratio is controlled according to "spraying volume = previous day's cumulative evaporation volume × 78%" (the water content of biogas slurry from vegetable waste is slightly higher, so the recirculation ratio should be appropriately reduced). The leachate recirculation control logic is the same as in Example 1.

[0052] Treatment effect: After the system is running stably, the average daily biogas production is 1080 m³. 3 The system generates 432 kWh of electricity per day and produces approximately 3,800 tons of organic fertilizer annually (27% moisture content). The organic fertilizer product has a total nutrient content of 5.8%, organic matter of 48%, pH of 6.9, and a GI of 79%, meeting the NY / T 525-2021 standard. Under high-temperature fermentation conditions, the system's external heating energy consumption is reduced by approximately 58%, and the comprehensive utilization rate of waste heat from power generation reaches 59%. The system requires approximately 5 days of external heating per year.

[0053] Comparative Example 1 and Example 2: High-temperature fermentation (53°C) gas production rate (approximately 36m³) 3 / ton of raw materials) is higher than that of mesophilic fermentation (approximately 28m). 3 While high-temperature fermentation consumes more energy and is more complex to operate and control, mesophilic fermentation (37.5℃) offers more stable operation and longer equipment lifespan. This invention is well-adaptable to both temperature modes, allowing users to choose based on raw material characteristics and local climate conditions.

[0054] Example 3: (Daily processing capacity 100 tons, mixed raw materials, verification under winter conditions in northern China)

[0055] This embodiment provides an integrated agricultural waste treatment system that uses a mixture of corn stalks, wheat stalks, cow manure, and chicken manure (mixed in a dry matter ratio of 2:2:3:3) as the treatment material, with a daily processing capacity of 100 tons and an annual processing capacity of approximately 36,000 tons. This embodiment is set up in a northern region (winter ambient temperature -15℃ to -5℃) to verify the operational effectiveness of the invention under extreme low-temperature conditions.

[0056] Pre-treatment module: The sorting device has a screen aperture diameter of 40mm (the screen aperture can be appropriately enlarged as the processing capacity increases); the crushing device uses two twin-shaft shear crushers operating in parallel to crush particles to ≤25mm; the homogenization and equalization tank has an effective volume of 250m³. 3 The moisture content of the material was adjusted to 78%±2%, and the C / N ratio was adjusted to 26:1.

[0057] Anaerobic fermentation module: Anaerobic fermenter with an effective volume of 1600m³ 3 (Two 800m) 3 (Parallel operation), fermentation temperature maintained at 37.5±0.5℃, HRT=22 days, TS=11%. Biogas production is approximately 3000 m³. 3 The plant generates electricity daily through two 500kW biogas generator sets.

[0058] Waste heat utilization: Approximately 425 GJ / day of waste heat is recovered from power generation. Under northern winter conditions, the heat demand for insulation in the anaerobic digester increases (due to low ambient temperature and increased heat loss), accounting for approximately 82% of the total waste heat (approximately 348 GJ / day), while the proportion of waste heat available for aerobic composting decreases to approximately 18% (approximately 77 GJ / day). To cope with extreme winter conditions, the system is additionally equipped with an electric heating auxiliary device (150kW) to automatically supplement heat when waste heat is insufficient, ensuring that the anaerobic digester temperature does not fall below 37.0℃.

[0059] Aerobic composting module: The aerobic composting silo uses two parallel trough-type composting production lines (each 30m×6m×2.5m). Auxiliary heating pipes on the silo walls are activated when the center temperature of the compost pile is below 50℃. In winter, the frequency of auxiliary heating activation increases significantly (approximately 65% ​​of total operating time), but thanks to the continuous supply of waste heat from power generation, no additional fossil fuel consumption is required. The top of the aerobic composting silo is equipped with an insulation layer (50mm thick, polyurethane insulation board) to reduce heat loss.

[0060] Treatment results: During three months of continuous operation in winter, the average daily biogas production was 2950 m³. 3The system generates 1180 kWh of electricity per day and produces approximately 13,500 tons of organic fertilizer annually (29% moisture content). The organic fertilizer product has a total nutrient content of 5.9%, organic matter of 50%, pH 7.0, and GI of 80%, meeting the NY / T 525-2021 standard. Although lower ambient temperatures in winter lead to increased heat loss, the system maintains stable operation through a strategy of prioritizing waste heat in the anaerobic digester and supplementing with auxiliary electric heating. The annual external energy consumption, calculated using external electrical energy supplementation, is approximately 55% lower than in a system without waste heat recovery. The comprehensive utilization rate of waste heat from power generation is approximately 51% (slightly lower in winter due to increased heat loss compared to other seasons).

[0061] Comparative Example 1: (Traditional independent operation mode, without waste heat cascade distribution and biogas slurry leachate recirculation)

[0062] This comparative example provides a traditional agricultural waste treatment system, which also includes a pretreatment module, an anaerobic fermentation module, a biogas utilization module, and an aerobic composting module. However, each module operates independently and does not employ the waste heat cascade dynamic distribution, precise biogas slurry reinjection, and leachate safe return control of this invention. This comparative example is used to verify the superiority of the technical solution of this invention compared to traditional solutions.

[0063] System configuration: The processing objects are the same as in Example 1 (corn stalks + cow manure, daily processing capacity 50 tons). The pretreatment modules (sorting, crushing, homogenization) are the same as in Example 1. The anaerobic digester is also a CSTR tank with an effective volume of 800 m³. 3 Fermentation temperature 37.5±0.5℃, HRT=22 days, TS=10%.

[0064] Differences:

[0065] (1) Waste heat utilization method: The waste heat from biogas power generation is simply used for the insulation of the anaerobic fermentation tank (heating the jacket through the heat exchanger), without dynamic distribution by a three-way regulating valve, and the waste heat is not supplied to the aerobic composting bin. The aerobic composting bin relies on electric heating or coal-fired boilers for auxiliary heating in winter, and there is no waste heat utilization.

[0066] (2) Treatment of biogas slurry: The biogas slurry produced by anaerobic fermentation is not returned to aerobic composting, but enters a biogas slurry temporary storage tank, and is discharged after flocculation sedimentation + aerobic treatment to meet the standards. The water required for aerobic composting is supplied by tap water.

[0067] (3) Leachate treatment method: The leachate (pH about 5.8-6.2) generated by aerobic composting is collected and directly discharged into the municipal sewage network or enters a separate treatment facility, and is not returned to the equalization tank.

[0068] (4) Water replenishment method for composting: Aerobic composting uses tap water spraying and turning, without precise control based on evaporation. The spraying amount is a fixed value (about 6% / day), which can easily lead to excessive moisture or dryness.

[0069] Running result:

[0070] (1) Energy consumption: The anaerobic fermentation tank requires additional electricity (electric heating) or natural gas for insulation, with an average annual external energy consumption equivalent to about 85 tons of standard coal (without waste heat recovery), which is about 60 times higher than Example 1 (with only 3 days of external heat supplementation per year and extremely low energy consumption). The aerobic composting bin requires additional electricity or coal for winter auxiliary heating, with an average annual external energy consumption equivalent to about 32 tons of standard coal.

[0071] (2) Biogas slurry treatment: The annual biogas slurry production is about 12,000 tons, the cost of treatment to meet the standards is about RMB 18 / ton, and the annual treatment cost is about RMB 216,000. The annual cost of tap water replenishment for aerobic composting is about RMB 45,000 (based on an annual replenishment of 18,000 tons of water).

[0072] (3) Leachate treatment: The annual production of leachate is about 1,500 tons, the treatment cost is about 12 yuan / ton, and the annual treatment cost is about 18,000 yuan.

[0073] (4) Biogas production and power generation: Due to the lack of waste heat utilization, the temperature of the anaerobic digester fluctuates greatly in winter (it can drop as low as 34°C), and the biogas production rate is about 12%-15% lower than that of Example 1, with an average daily biogas production of about 1220 m³ / year. 3 (Compared to 1420m in Example 1) 3 (14% lower), with an annual power generation loss of approximately 80,000 kWh.

[0074] (5) Organic fertilizer quality: Due to the lack of biogas slurry to replenish nitrogen source, the total nitrogen content of the final compost product is only about 1.6%-1.8% (2.0%-2.5% in Example 1), the organic matter content is about 44%-46% (lower than 52% in Example 1), and the seed germination index is about 72% (lower than 82% in Example 1).

[0075] (6) System stability: Because the leachate is directly discharged and the biogas slurry is not returned, the system materials do not form a closed loop. Under the low temperature conditions in winter, it is difficult for the aerobic composting bin to heat up (the central temperature is difficult to reach 55℃), and the harmlessness effect is unstable.

[0076] Summary of comparisons between the examples and comparative examples:

[0077]

[0078]

[0079] Comparative effect analysis

[0080] From the above comparison, we can see that:

[0081] (1) Effect of waste heat utilization: In Comparative Example 1, the waste heat from biogas power generation is only used for anaerobic tank insulation, and aerobic composting still requires external heating, with 365 days of external heating throughout the year; while in Example 1, through the dynamic priority allocation of the three-way regulating valve, the excess waste heat is supplied to aerobic composting, and the number of days of external heating is reduced to only 3 days per year (during extreme cold wave period), and the comprehensive utilization rate of waste heat is increased from less than 30% in the traditional mode to 56%.

[0082] (2) Effect of precise re-spraying of biogas slurry: In Comparative Example 1, biogas slurry was treated as wastewater (annual cost of RMB 216,000), and additional tap water was required for composting (annual cost of RMB 45,000); In Example 1, biogas slurry was used to replace tap water and nitrogen source additives and re-sprayed into compost, saving a total of RMB 260,000 in water and biogas slurry treatment costs per year. At the same time, the total nitrogen content of organic fertilizer increased from 1.7% to 2.2% (an increase of 29%), and the seed germination index increased from 72% to 82% (an increase of 14%).

[0083] (3) Effect of safe return of leachate: In Comparative Example 1, the leachate was treated as wastewater and discharged externally (annual cost of RMB 18,000); In Example 1, the leachate was returned to the homogenization and equalization tank, and the acidity was neutralized by the large-capacity buffer. At the same time, the pH of the anaerobic tank was stabilized at 6.9-7.2 (compared to 6.5-7.4 in Comparative Example 1, with large fluctuations), without the need to add additional acid-base regulators, thus achieving zero discharge and zero treatment cost of leachate.

[0084] The foregoing has only described certain exemplary embodiments of the present invention by way of illustration. Undoubtedly, those skilled in the art can modify the described embodiments in various ways without departing from the spirit and scope of the present invention. Therefore, the foregoing drawings and descriptions are illustrative in nature and should not be construed as limiting the scope of protection of the claims of the present invention.

Claims

1. An integrated agricultural waste treatment system, comprising a pretreatment module, an anaerobic fermentation module, a biogas utilization module, and an aerobic composting module; The pretreatment module includes a sorting device (1), a crushing device (2), and a homogenization regulating tank (3) connected in sequence, for sorting, crushing, and homogenizing agricultural waste; The anaerobic fermentation module includes an anaerobic fermentation tank (4), the inlet of which is connected to the outlet of the pretreatment module, for anaerobic fermentation of the pretreated waste to produce biogas and fermentation residue. The biogas utilization module includes a biogas purification device (7) and a biogas power generation device (8). The inlet of the biogas purification device (7) is connected to the biogas outlet of the anaerobic fermentation tank (4), and the outlet of the biogas purification device (7) is connected to the biogas power generation device (8). The aerobic composting module includes an aerobic composting chamber (9), the inlet of which is connected to the slag outlet of the anaerobic fermentation tank (4), for aerobic composting of fermentation residues into organic fertilizer. Its features are: The waste heat recovery pipeline of the biogas power generation device (8) is connected to the heating and insulation jacket (5) of the anaerobic fermentation tank (4) and the auxiliary heating pipeline (11) of the aerobic composting bin (9). A three-way regulating valve (14) is provided on the waste heat recovery pipeline. The three-way regulating valve (14) controls the opening degree according to the temperature sensor (6) signal in the anaerobic fermentation tank (4) to prioritize meeting the heat insulation requirements of the anaerobic fermentation tank (4). The remaining waste heat is then supplied to the aerobic composting bin (9) for auxiliary heating. The aerobic composting bin (9) is equipped with a leachate collection pipeline (15), which is connected to the homogenization regulating tank (3) to return the leachate generated during the aerobic composting process to the homogenization regulating tank (3) to adjust the moisture content of the material. The biogas slurry outlet of the anaerobic fermentation tank (4) is connected to the spraying device (12) of the aerobic composting bin (9) via the biogas slurry return pipeline (16) to spray the biogas slurry produced by anaerobic fermentation into the aerobic composting material to adjust the moisture content and supplement the nitrogen source.

2. The agricultural waste comprehensive treatment system according to claim 1, characterized in that, The sorting device (1) is a drum screen with a screen hole diameter of 20-50mm; the crushing device (2) is a twin-shaft shear crusher with a crushed material particle size ≤20mm; the homogenization regulating tank (3) is equipped with a stirring device and a moisture content monitoring sensor to adjust the material moisture content to 75%-85% and the carbon-nitrogen ratio (C / N) to 20:1-30:

1.

3. The agricultural waste comprehensive treatment system according to claim 1, characterized in that, The anaerobic fermenter (4) is a completely mixed anaerobic fermenter (4). The inner wall of the tank is provided with a heating and insulation jacket (5). The tank is equipped with a stirring device and a temperature sensor (6). The heat exchange medium inlet of the heating and insulation jacket (5) is connected to the waste heat recovery pipeline of the biogas power generation device (8). The fermentation temperature of the anaerobic fermenter (4) is 35-38℃, the hydraulic retention time is 20-25 days, and the total solids concentration of the material is 8%-12%.

4. The agricultural waste comprehensive treatment system according to claim 1, characterized in that, The three-way regulating valve (14) is an electric three-way regulating valve (14). The temperature sensor (6) is set at three different height positions (upper, middle, and lower) inside the anaerobic fermenter (4). The three-way regulating valve (14) controls the opening degree according to the average temperature measured by the three temperature sensors (6). When the average temperature is lower than 37.0℃, the three-way regulating valve (14) fully closes the auxiliary heating pipeline (11) of the aerobic composting chamber (9), and all the waste heat is supplied to the heating and insulation jacket (5) of the anaerobic fermenter (4). When the average temperature is higher than or equal to 38.0℃, the three-way regulating valve (14) fully opens the auxiliary heating pipeline (11) of the aerobic composting chamber (9). When the average temperature is between 37.0℃ and 38.0℃, the three-way regulating valve (14) adjusts the opening degree according to the PID ratio.

5. The agricultural waste comprehensive treatment system according to claim 1, characterized in that, The aerobic composting bin (9) is a trough-type aerobic composting bin (9). The bottom of the bin is equipped with a ventilation and aeration device (10), the bin wall is equipped with the auxiliary heating pipeline (11), and the top of the bin is equipped with the spray device (12) and the exhaust gas collection pipeline (13). The heat exchange medium inlet of the auxiliary heating pipeline (11) is connected to the waste heat recovery pipeline of the biogas power generation device (8), and the auxiliary heating pipeline (11) is equipped with a solenoid valve. The solenoid valve is only opened when the temperature at the center of the compost pile inside the aerobic composting bin (9) is lower than 50°C.

6. The agricultural waste comprehensive treatment system according to claim 1, characterized in that, The biogas slurry return pipeline (16) is equipped with a biogas slurry storage tank, a delivery pump and a flow regulating valve. The spraying device (12) is a rotary spray head installed on the top of the aerobic composting bin (9). The main pipeline of the ventilation and aeration device (10) of the aerobic composting bin (9) is equipped with a gas flow meter and a temperature and humidity sensor. The system also includes a central controller. The central controller calculates the cumulative water evaporation of the compost pile based on the detection signals of the gas flow meter and the temperature and humidity sensor, and uses 75%-85% of the cumulative water evaporation as the target value of the biogas slurry return spray volume for the next day to control the opening of the flow regulating valve.

7. The agricultural waste comprehensive treatment system according to claim 6, characterized in that, The aerobic composting bin (9) is equipped with a turning machine. The spraying device (12) is turned on synchronously during the operation of the turning machine, and the spraying direction is aimed at the cross section of the material turned up by the turning machine. After the spraying is completed, the turning machine continues to move forward and turn the material for at least two more strokes.

8. The agricultural waste comprehensive treatment system according to claim 1, characterized in that, The leachate collection pipeline (15) includes a slope guide plate and an outlet at the bottom of the aerobic composting bin (9). The outlet is connected to the homogenization tank (3) via a pipeline. The pipeline is equipped with a filter device and a reflux pump. An online pH meter is installed at the outlet of the homogenization tank (3). The online pH meter is connected to the reflux pump. When the pH value of the material at the outlet of the homogenization tank (3) is lower than 6.7, the reflux pump operates at 30% of its rated speed. When the pH value is lower than 6.3, the reflux pump stops.

9. The agricultural waste integrated treatment system according to any one of claims 1 to 8, characterized in that, It also includes an intelligent control system, which includes a central controller and a material metering sensor, a temperature sensor (6), a pH sensor, a methane concentration sensor, a moisture content sensor and a gas flow meter that are respectively connected to the central controller; the central controller controls the feeding rate of the pretreatment module, the fermentation temperature of the anaerobic fermentation module, the power generation load of the biogas utilization module and the ventilation and spraying volume of the aerobic composting module according to the feedback signals of each sensor.

10. The agricultural waste comprehensive treatment system according to claim 9, characterized in that, The intelligent control system also includes a remote monitoring terminal and a data storage module. The remote monitoring terminal is wirelessly connected to the central controller and is used to display system operating parameters and issue remote control commands in real time. The data storage module is used to store historical system operating data and optimize the operating parameters of each module based on the historical data.

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