Design and construction of farm biogas digester
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The application of farm biogas digester can prevent environmental pollution, protect the rural environment, and promote the development of the breeding industry. After generating biogas, the power generation benefits are greater, and the comprehensive benefits are relatively significant.
The farm biogas digester can use a black HDPE membrane to seal the bottom and top of the pool into one body, and it is a super-large sewage anaerobic bioreactor with the functions of fermentation and gas storage.
Taking advantage of the anti-seepage and anti-leakage advantages of hdpe impermeable membrane, a layer of hdpe impermeable membrane is laid in the dug pit. According to the requirements of the anaerobic fermentation process, water inlets, slag extraction pipes and biogas collection pipes are installed in the tank. The mouth is sealed with an hdpe impermeable membrane, and the surrounding anchor grooves are fixed to form an overall anaerobic fermentation space. "Less investment, good results."
(1)Its characteristics are as follows:
1. The anaerobic fermentation volume of the biogas pool is large, the sewage retention time can reach about 180 days, and the effluent is clean and usable; organic matter can be fully anaerobically fermented;
2. The service life of the geomembrane farm biogas pool can be more than 10 years, without polluting groundwater and soil, and because of the solid-liquid separation, the odor is improved and does not affect the surrounding farmers;
3. The black film biogas tank can store 10 to 20 times more biogas than the conventional biogas tank.
(2)farm biogas digester slope and anchor trench profile：
(3) farm biogas digester Pipeline laying
After the farm biogas digester is excavated, blind trenches are excavated according to the actual conditions on site, and water inlet pipes, water outlet pipes, slag pipes, biogas outlet pipes, etc. are laid. The bottom of the slag pipe is close to the bottom membrane. The biogas tank gas pipeline uses a ?110mm pipe that can withstand a pressure of more than 10kpa. Before installing the gas pipeline, check whether the gas pipeline is leaking, especially the buried gas pipeline must be checked. Inspection method: Place the pipe in water, block one end of the pipe mouth, use an air pump to inflate or blow air to the other end, and observe whether there are bubbles around the pipe. If there are no bubbles, the gas pipeline is not leaking. Otherwise, it is leaking.
The slag discharge pipe is in contact with the bottom membrane as shown above and can be laid flat on the bottom geomembrane.
Pipeline layout diagram
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The nodes of the water inlet and outlet pipes are sealed and fixed by extrusion welding.
(4) Selection and welding process of HDPE biogas pool black geomembrane，
The biogas tank anti-seepage film plays a decisive role in determining the environmental protection effect of the biogas pool. Once the biogas tank geomembrane leaks, the consequences are relatively serious. The entire project will be wasted. The biogas tank black film is made of high-quality polyethylene virgin resin, about 2.5% carbon black, anti-aging agent, antioxidant, ultraviolet absorber, stabilizer and other auxiliary materials, using blow molding technology, and is produced according to the US GRI standard and ASTM test standard. So how to choose the top film and bottom film? First of all, the top film of the biogas digester geomembrane is exposed to the outside for a long time, and it is easy to age due to wind and sun exposure. Therefore, ASTM geomembrane with better aging resistance should be selected, and the recommended thickness is 1.5mm or above; 1.5mm or 2mm American standard blown geomembrane is generally used in engineering. This geomembrane is produced by blowing film technology, and its strength and other indicators are far superior to the black film produced by ordinary laminating film; Generally speaking, for the bottom film, it is recommended to use 1.0mm American standard geomembrane or national standard 1.2mm geomembrane for sewage coverage and protection of the top film. 1.5mm can also be used;
For the welding of HDPE anti-seepage membrane, hot melt welding machines, also known as double-track welding machines and extrusion fusion welding machines, are now mostly used. For large-area welding of anti-seepage membranes, double-track hot melt welding machines are used to form double welds and an inflatable cavity. For parts that cannot be welded by double-track welding machines, extrusion fusion welding machines should be used, equipped with welding rods of the same material as the raw materials, to form a single weld of surfacing. The temperature of the welding machine is 280-350℃. Before welding, do sample welding first. After the test welding is qualified, start formal welding. When welding, check the overlap width of the anti-seepage black film again, and ensure that the overlap range is clean, without foreign matter or anything else that may affect welding. There are two welds within the seam width (double insurance), and the width of each weld is not less than 10cm. The HDPE anti-seepage membrane at the weld is melted into a whole, and there must be no false welding or over-welding. The two layers of the connected membrane should overlap flat and smooth.
Estimated investment for construction of black film biogas pool
1. 1500m3 (25mx20mx5m): 85,000 RMB;
2. 2000m3 (30mx20mx5m): 105,000 RMB;
3. 3000m3 (35mx25mx5m): 135,000 RMB;
4. 5000m3 (50mx30mx5m): 180,000 RMB;
5. 10000m3 (60mx45mx5m): 255,000 RMB;
6. 20000m3 (100mx50mx5m): 380,000 RMB.
A black geomembrane biogas digester of 20,000 to 30,000 cubic meters can be built for a stock of 10,000 heads;
The cost of using black geomembrane to build a biogas digester in a farm is low: the cost per cubic meter is only 30-40 RMB (excluding civil engineering); the operating cost of the black film biogas digester after completion is almost negligible.