Biogas slurry fertilizer preparation device based on double-membrane coupling

Abstract

The utility model discloses a biogas slurry fertilizer making device based on double-membrane coupling. The device comprises a preheating unit, a feeding side membrane contactor, an absorption side membrane contactor, a gas circulation pipeline, a negative pressure gas pump and a rear end crystallization fertilizer making system. Hydrophobic microporous membrane components are respectively arranged in the feeding side membrane contactor and the absorption side membrane contactor; the gas circulation pipeline is communicated with the gas cavities on the two sides to form a closed loop, and gas circulation is driven by the negative pressure gas pump. And the rear-end crystallization fertilizer preparation system is communicated with the acid liquid cavity of the absorption side membrane contactor and is used for preparing the extracted nutrients into a solid fertilizer. According to the utility model, the closed circulating air flow is used as an intermediate medium, so that the direct contact between the biogas slurry and the acid absorbent is thoroughly avoided, the efficient separation of high-concentration ammonia nitrogen in the biogas slurry and the conversion of high-added-value fertilizer are realized on the premise of not additionally adding chemicals to adjust the pH value, and the system has excellent thermodynamic energy efficiency and energy self-sufficiency characteristic.

Description

Technical Field

[0001] This utility model relates to the field of agricultural waste resource utilization and fertilizer production technology, specifically to a biogas slurry fertilizer production device based on dual-membrane coupling. Background Technology

[0002] Livestock and poultry breeding wastewater contains high concentrations of ammonia nitrogen. After multi-stage integrated treatment and anaerobic digestion, the resulting biogas slurry accounts for over 80% of the total biogas fertilizer. Limited by farmland carrying capacity and high physical transportation costs, the massive amount of biogas slurry cannot be fully utilized through traditional methods of returning it to nearby fields. Therefore, extracting the high-concentration ammonia nitrogen from the biogas slurry and converting it into high-value-added solid fertilizer has become a key engineering step in the resource utilization of agricultural waste. However, currently available nutrient salt recovery and fertilizer production technologies suffer from several significant engineering defects and energy consumption bottlenecks:

[0003] Air stripping method: It requires heating the material to a high temperature of 80-95℃ and performing high-intensity aeration, resulting in extremely high heat and electricity consumption of the system, and is prone to problems such as equipment blockage and foaming, making it less economical for fertilizer production.

[0004] Chemical precipitation method: It is highly dependent on expensive chemical reagents such as magnesium chloride and phosphate, and requires strict control of pH value at around 9-10. The operating cost is high, and the precipitation process is easily affected by calcium, heavy metal ions, etc., which affects the purity of fertilizer.

[0005] Traditional single-membrane separation technology typically requires the addition of large amounts of alkaline agents on the biogas slurry side to adjust the pH value and promote the conversion of ammonium nitrogen into free ammonia. Furthermore, in single-membrane mode, the liquid directly contacts both sides of the membrane, easily leading to wetting of the membrane pores or blockage by complex organic matter, severely affecting the membrane's lifespan and the long-term stability of the fertilizer production system.

[0006] Therefore, there is an urgent need for a new type of hardware system that can efficiently separate and recover ammonia nitrogen to prepare fertilizer without the need for additional chemicals to adjust the pH value, effectively avoid membrane fouling, and possess excellent thermodynamic efficiency. Utility Model Content

[0007] In view of the shortcomings of the existing technology, the purpose of this utility model is to provide a biogas slurry fertilizer production device based on dual-membrane coupling, so as to solve the problems of high energy consumption of traditional fertilizer production systems, easy membrane wetting and pollution of traditional single-membrane separation, and the need for a large amount of chemical agents to adjust the pH value, so as to realize the efficient and low-cost conversion of agricultural waste into solid fertilizer.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] A biogas slurry fertilizer production device based on dual-membrane coupling includes a preheating unit, a feed-side membrane contactor, an absorption-side membrane contactor, a gas circulation pipeline, a negative pressure air pump, and a rear-end crystallization fertilizer production system.

[0010] The preheating unit is used to preheat the biogas slurry entering through the biogas slurry inlet and to transport the preheated biogas slurry from the biogas slurry outlet to the feed-side membrane contactor.

[0011] The feed-side membrane contactor is vertically equipped with a first hydrophobic microporous membrane assembly, which divides the feed-side membrane contactor into a biogas chamber and a first gas chamber. The biogas outlet of the preheating unit is connected to the inlet of the biogas chamber.

[0012] The absorber-side membrane contactor is vertically provided with a second hydrophobic microporous membrane assembly, which divides the absorber-side membrane contactor into a second gas chamber and an acid chamber.

[0013] The gas circulation pipeline connects the first gas chamber and the second gas chamber to form a closed gas circulation loop; the gas circulation pipeline is used to connect the gas discharged from the first gas chamber to the absorption side air inlet at the top of the absorption side membrane contactor, enter the second gas chamber and flow from top to bottom; the second gas chamber is used to transport the discharged gas to the feeding side air inlet at the bottom of the feeding side membrane contactor, enter the first gas chamber and flow from bottom to top.

[0014] The back-end crystallization fertilizer production system is connected to the acid chamber of the absorption-side membrane contactor and is used to crystallize the concentrated acid to produce fertilizer.

[0015] Furthermore, the back-end crystallization fertilizer production system includes an evaporator, a crystallizer, and a centrifuge connected in sequence by pipelines. The evaporator is used to heat and evaporate biogas and then transport it to the crystallizer. The crystallizer is used to crystallize the biogas and then transport the crystals to the centrifuge. The centrifuge is used to centrifuge the crystals to obtain solid fertilizer.

[0016] Furthermore, the feed-side membrane contactor is provided with a liquid inlet at the top of the biogas slurry chamber, a liquid outlet at the bottom of the biogas slurry chamber, a feed-side air inlet at the bottom of the first air chamber, and a feed-side exhaust port at the top of the first air chamber. The liquid inlet is connected to the biogas slurry outlet of the preheating unit, and the liquid outlet is connected to the biogas slurry tank. The feed-side exhaust port at the upper end of the first air chamber is connected to the absorption-side air inlet of the absorption-side membrane contactor through a gas circulation pipeline, and the feed-side air inlet at the lower end of the first air chamber is connected to the absorption-side exhaust port of the absorption-side membrane contactor through a gas circulation pipeline.

[0017] The absorber-side membrane contactor is provided with an acid inlet at the bottom of the acid chamber, an acid outlet at the top of the acid chamber, an absorber-side air inlet at the top of the second air chamber, and an absorber-side exhaust outlet at the bottom of the second air chamber. The absorber-side air inlet is connected to the feed-side exhaust outlet of the first air chamber, and the absorber-side exhaust outlet is connected to the feed-side air inlet of the first air chamber. The acid inlet is connected to the first outlet of the acid tank via a pump, and the absorber-side exhaust outlet is connected to the feed-side air inlet of the feeder-side membrane contactor via a gas circulation pipeline. The second outlet of the acid tank is connected to the downstream crystallization fertilizer production system.

[0018] Furthermore, both the first hydrophobic microporous membrane module and the second hydrophobic microporous membrane module are hollow fiber polytetrafluoroethylene, polypropylene, or polyvinylidene fluoride membrane modules.

[0019] Furthermore, the device also includes a front-end pretreatment system, which includes a sedimentation tank and an anaerobic fermentation tank connected in sequence; the sedimentation tank is used to settle the biogas slurry, and the bottom of the anaerobic fermentation tank is provided with a discharge port, which is connected to the biogas slurry inlet of the preheating unit and the evaporator inlet through a solid-liquid separator.

[0020] Furthermore, the biogas outlet at the top of the anaerobic digester is connected to a gas purification device via a biogas collection pipeline. The gas purification device is used to purify the biogas, and its outlet is connected to an external biogas storage tank.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] Enhanced mass transfer dynamics for zero-pesticide extraction: This device employs a liquid-gas-liquid dual-membrane coupling structure, establishing an extremely low ammonia partial pressure within the intermediate gas circulation pipeline via a negative pressure gas pump. Even without additional alkali to adjust the pH of the biogas slurry, the mass transfer dynamics can be maintained at a consistently high level, significantly reducing the cost of chemical reagents in the fertilizer production process.

[0023] Blocking liquid-phase contact and extending equipment lifespan: This device uses a closed-loop circulating airflow as the intermediate medium between two stages of hydrophobic microporous membrane modules, completely preventing direct contact between the biogas slurry and the acidic absorbent on both sides of the membrane. This physical structure significantly reduces the probability of membrane pore wetting and effectively blocks the migration of heavy metals and other impurities in the biogas slurry to the absorption side (fertilizer end), not only extending the life of the membrane modules but also improving the purity of the final fertilizer.

[0024] The system features a closed-loop energy system with extremely high thermodynamic efficiency: the device cleverly channels biogas resources generated by the front-end anaerobic digester to the back-end crystallization fertilizer production system via pipelines, serving as a heat source for the evaporator. This design eliminates the need for additional external fossil fuel consumption, achieving energy self-sufficiency and a perfect closed loop for the entire system. Combined with the gas-liquid counter-flow piping design, the overall energy consumption of the fertilizer production system is significantly reduced. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the overall structure of the dual-membrane coupled biogas slurry ammonia recovery system in this embodiment of the present invention.

[0026] Figure 2 This is a connection principle diagram of the dual-membrane coupled ammonia recovery device (core membrane module part) in the embodiment of this utility model;

[0027] Figure 3 This is a cross-sectional view of the internal mass transfer structure of the dual-membrane coupling contactor in an embodiment of this utility model.

[0028] The following is a list of components represented by the numbers in the attached diagram:

[0029] 100. Front-end pretreatment system; 110. Sedimentation tank; 120. Anaerobic digester; 130. Solid-liquid separator; 140. Biogas slurry tank. 200. Core ammonia recovery system; 210. Preheating unit; 220. Feed-side membrane contactor; 221. Biogas slurry chamber; 222. First gas chamber; 223. First hydrophobic microporous membrane module; 230. Gas circulation pipeline; 240. Negative pressure air pump; 250. Absorption-side membrane contactor; 251. Second gas chamber; 252. Acid chamber; 253. Second hydrophobic microporous membrane module; 260. Acid tank. 300. Back-end crystallization fertilizer production system; 310. Evaporator; 320. Crystallizer; 330. Centrifuge; 340. Biogas collection pipeline; 350. Gas purification device. Detailed Implementation

[0030] The principles and features of this utility model are described below with reference to the accompanying drawings. The examples given are only for explaining this utility model and are not intended to limit the scope of this utility model.

[0031] like Figures 1 to 3 As shown in the figure, this embodiment provides a biogas slurry fertilizer production device based on dual-membrane coupling. The overall structure of the device mainly includes a front-end pretreatment system 100, a core ammonia recovery system 200, and a back-end crystallization fertilizer production system 300.

[0032] Pre-treatment and biogas collection structure: Wastewater from the livestock farm first collects in a sedimentation tank 110, where suspended impurities are separated by gravity settling. The settled wastewater is then pumped through corrosion-resistant pipes into a fully mixed anaerobic digester 120 with a volumetric load suitable for anaerobic fermentation. A biogas collection pipeline 340 connects to the top of the anaerobic digester 120, and the biogas produced during fermentation enters a gas purification device 350 for collection and purification. The purified biogas is then led out to an external gas storage device, which can be used for other energy-consuming processes in the livestock farm or for centralized grid-connected power generation, realizing the recovery and utilization of biomass energy. Simultaneously, the remaining fermentation products enter a solid-liquid separator 130 through a discharge port at the bottom, and the separated biogas slurry is stored in a biogas slurry tank 140 with an anti-corrosion layer. The outlet pipe of the biogas slurry tank 140 is connected to the inlet of the preheating unit 210.

[0033] Biogas slurry preheating and liquid-gas mass transfer structure: The preheating unit 210 is preferably a plate heat exchanger or a water bath device. The biogas slurry outlet of the preheating unit 210 is connected to the liquid inlet at the top of the feed-side membrane contactor 220 via a pipe. The feed-side membrane contactor 220 is internally equipped with a first hydrophobic microporous membrane assembly 223, which divides its interior into a biogas slurry chamber 221 and a first gas chamber 222. The biogas slurry enters from the top, flows downward along the biogas slurry chamber 221, and is discharged from the bottom drain port. The biogas slurry discharged from this drain port is returned to the biogas slurry tank 140 through a return pipeline, forming a multiple circulation extraction loop for the biogas slurry to fully remove ammonia nitrogen components. At the same time, the first gas chamber 222 is connected to the gas circulation pipeline 230 through the lower air inlet and the upper exhaust port. The gas circulation pipeline 230 is equipped with a negative pressure air pump 240, which provides power to maintain a negative pressure environment and drive gas circulation within the pipeline.

[0034] Gas-phase circulation and gas-liquid mass transfer structure: The gas circulation pipeline 230 connects the ammonia-rich gas discharged from the first gas chamber 222 to the air inlet at the top of the absorber-side membrane contactor 250, enters the second gas chamber 251, and flows from top to bottom. The absorber-side membrane contactor 250 is internally equipped with a second hydrophobic microporous membrane assembly 253, which divides its interior into the second gas chamber 251 and the acid chamber 252. The acid tank 260 is connected to the acid inlet at the bottom of the absorber-side membrane contactor 250 via a pump. The acidic absorbent is pumped into the acid chamber 252 and flows from bottom to top, then flows out from the acid outlet at the top, thus forming a highly efficient counter-current contact mass transfer structure with the gas flowing from top to bottom. During this contact process, free ammonia in the gas phase passes through the second hydrophobic microporous membrane assembly 253, is absorbed by the acid, and undergoes a chemical reaction to form ammonium salts. The acid solution continuously circulates between the acid tank 260 and the absorber-side membrane contactor 250. As the circulation time increases, the acid solution continuously accumulates ammonia nitrogen, eventually forming a high-concentration ammonium salt solution.

[0035] Back-end crystallization fertilizer production structure: Initially, the second outlet of the acid tank is closed. After a period of time, the ammonium salt solution in the acid tank 260 circulates and accumulates to near saturation concentration. Then, the second outlet of the acid tank is opened, and the ammonium salt solution in the acid tank is drawn out and pumped into the back-end crystallization fertilizer production system 300. The back-end crystallization fertilizer production system 300 includes an evaporator 310, a crystallizer 320, and a centrifuge 330 connected in sequence by pipelines. After the solution sequentially passes through the evaporator for concentration, the crystallizer for crystallization, and the centrifuge for dehydration and solid-liquid separation, a high-value-added solid fertilizer product is finally produced.

[0036] The above description is only a preferred embodiment of the present utility model and is not intended to limit the present utility model. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present utility model should be included within the protection scope of the present utility model.

Claims

1. A biogas slurry fertilizer production device based on dual-membrane coupling, characterized in that, It includes a preheating unit (210), a feed-side membrane contactor (220), an absorption-side membrane contactor (250), a gas circulation pipeline (230), a negative pressure air pump (240), and a back-end crystallization fertilizer production system (300). The preheating unit (210) is used to preheat the biogas slurry entering through the biogas slurry inlet and to transport the preheated biogas slurry from the biogas slurry outlet to the feed-side membrane contactor (220). The feed-side membrane contactor (220) is vertically provided with a first hydrophobic microporous membrane assembly (223), which divides the feed-side membrane contactor (220) into a biogas chamber (221) and a first gas chamber (222). The biogas outlet of the preheating unit (210) is connected to the inlet of the biogas chamber (221). The absorber-side membrane contactor (250) is vertically provided with a second hydrophobic microporous membrane assembly (253), which divides the absorber-side membrane contactor (250) into a second gas chamber (251) and an acid chamber (252). The gas circulation pipeline (230) connects the first gas chamber (222) and the second gas chamber (251) to form a closed gas circulation loop; the gas circulation pipeline (230) is used to connect the gas discharged from the first gas chamber (222) to the absorption side air inlet at the top of the absorption side membrane contactor (250), enter the second gas chamber (251) and flow from top to bottom, and the second gas chamber (251) is used to transport the discharged gas to the feed side air inlet at the bottom of the feed side membrane contactor (220), enter the first gas chamber (222) and flow from bottom to top; The back-end crystallization fertilizer production system (300) is connected to the acid chamber (252) of the absorption-side membrane contactor (250) and is used to crystallize the concentrated acid to produce fertilizer.

2. The biogas slurry fertilizer production device based on dual-membrane coupling according to claim 1, characterized in that, The back-end crystallization fertilizer production system (300) includes an evaporator (310), a crystallizer (320) and a centrifuge (330) connected in sequence by pipelines. The evaporator (310) is used to heat and evaporate biogas and then transport it to the crystallizer (320). The crystallizer (320) is used to crystallize biogas and then transport the crystals to the centrifuge (330). The centrifuge (330) is used to centrifuge the crystals to obtain solid fertilizer.

3. The biogas slurry fertilizer production device based on dual-membrane coupling according to claim 1, characterized in that, The feed-side membrane contactor (220) is provided with a liquid inlet at the top of the biogas slurry chamber (221), a liquid outlet at the bottom of the biogas slurry chamber (221), a feed-side air inlet at the bottom of the first air chamber (222), and a feed-side exhaust outlet at the top of the first air chamber (222). The liquid inlet is connected to the biogas slurry outlet of the preheating unit (210), and the liquid outlet is connected to the biogas slurry tank (140). The feed-side exhaust outlet at the upper end of the first air chamber (222) is connected to the absorption-side air inlet of the absorber-side membrane contactor (250) through a gas circulation pipeline (230), and the feed-side air inlet at the lower end of the first air chamber (222) is connected to the absorption-side exhaust outlet of the absorber-side membrane contactor (250) through a gas circulation pipeline (230). The absorber-side membrane contactor (250) is provided with an acid inlet at the bottom of the acid chamber (252), an acid outlet at the top of the acid chamber (252), an absorber-side air inlet at the top of the second air chamber (251), and an absorber-side exhaust outlet at the bottom of the second air chamber (251). The absorber-side air inlet is connected to the feed-side exhaust outlet of the first air chamber (222), and the absorber-side exhaust outlet is connected to the feed-side air inlet of the first air chamber (222). The acid inlet is connected to the first outlet of the acid tank (260) via a pump. The absorber-side exhaust outlet is connected to the feed-side air inlet of the feeder-side membrane contactor (220) via a gas circulation pipeline (230). The second outlet of the acid tank (260) is connected to the downstream crystallization fertilizer system (300).

4. The biogas slurry fertilizer production device based on dual-membrane coupling according to claim 1, characterized in that, Both the first hydrophobic microporous membrane module (223) and the second hydrophobic microporous membrane module (253) are hollow fiber polytetrafluoroethylene, polypropylene or polyvinylidene fluoride membrane modules.

5. The biogas slurry fertilizer production device based on dual-membrane coupling according to claim 1, characterized in that, The device also includes a front-end pretreatment system (100), which includes a sedimentation tank (110) and an anaerobic fermenter (120) connected in sequence. The sedimentation tank (110) is used to settle the biogas slurry. The bottom of the anaerobic fermenter (120) is provided with a discharge port, which is connected to the inlet of the evaporator (310) of the preheating unit (210) through a solid-liquid separator (130).

6. The biogas slurry fertilizer production device based on dual-membrane coupling according to claim 5, characterized in that, The biogas outlet at the top of the anaerobic digester (120) is connected to a gas purification device (350) via a biogas collection pipeline (340). The gas purification device (350) is used to purify the biogas, and its outlet is connected to an external biogas storage tank.

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