Design diagram of a biogas digester for a pig farm: how big does it need to be for 500 pigs?
Biogas digesters are very common in rural areas. Besides household biogas digesters, the most common type in rural areas is the pig farm biogas digester. This kind of digester can protect the environment and has many benefits. Many people now want to build biogas digesters, and before building one, most people probably want to know exactly what its specific design method is.
Pig farm biogas digester design (diagram)
1. Setting out lines. Setting out lines and digging the pit is the first key step to ensuring the quality of the digester, and construction must be carried out according to the specified dimensions. Mark out the overall plan. Mark out the area of the greenhouse and the pig house, with the pig house on the east side or the west side. Mark out the center line of the “model” width. Taking O as the starting point, find the center point O of the digester on the inner side of the pig house, draw a circle with O as the center and the digester radius plus 6 cm as the radius, and determine the position of the digester. Determine the positions of the inlet and outlet. On the center line of the “model” width, determine the center point of the inlet and the center point of the outlet located inside the solar greenhouse, and mark them with white lime.
2. Pit excavation. Biogas digesters built within the “model” all adopt the underground buried type, and the earthwork for the biogas digester adopts the construction technique of large-scale excavation. First, the positive and negative zero elevation should be determined. The depth of the pit is determined according to the design drawing, that is, the top of the biogas digester and the outlet are kept on the same horizontal plane, and are 10 cm higher than the pig house floor. The inlet is 2 cm above the ground. If it is dug too deep, the biogas digester will be lower than the ground level, affecting its supporting use; if it is dug too shallow, the biogas digester will protrude above the ground, causing difficulties for pig raising and fertilizing the solar greenhouse.
3. Masonry of the outlet passage. The outlet passage is built with red bricks and mortar, with cement:sand = 1:2.5. To facilitate construction and discharge, the passage opening is 50 cm wide and 70 cm high, with an arched top, but the upper opening must not be less than 35 cm from the arch corner of the digester top, to prevent gas from escaping when the water surface drops back during high gas production.
4. The pouring of the digester wall and the lower part of the hydraulic chamber adopts the general brick-form masonry method: first soak the bricks in water to prevent difficulty in removing the formwork. Each brick is laid horizontally, and the brick joints of each layer are staggered, without mud joints or mortar joints, so that after laying one layer of bricks, one layer of concrete is poured, and after vibrating it dense, the second layer is laid. The concrete mix ratio by weight is cement:sand:crushed stone = 1:3:3. The digester wall is 1 m high and 0.05 m thick.
5. Construction of the digester arch cover. At present, the arch cover of the biogas digester in the “model” is built with bricks, and the biogas digester in the “model” generally uses straight-pipe feeding. Before building the digester arch cover, the feed pipe must be installed. Generally, a ceramic pipe with a diameter of 200 mm and a length of about 600 mm is used. A rope is passed through the pipe and tied to a wooden stake on the ground. The bell mouth of the feed pipe faces upward, vertically up and down, and is fixed tightly against the digester wall. The depth of insertion into the digester should preferably be 250-300 mm at the arch corner. When building the arch cover, iron hooks or the hanging-rope method can be used to fix the bricks. Start building from the feed pipe, and the area around the feed pipe must be reinforced with cement. The bricks used for building the arch cover should be of good quality; first soak them in water to keep them wet outside and dry inside, and build with 1:2 cement mortar. The mortar should have good workability and full joints, and the bricks should be pressed tightly against each other. After each ring is built, it should be secured with small stone pieces, and attention should be paid to the curvature of the arch cover while building. After every 3-5 rings are built, the outer wall of the arch cover should be plastered tightly and solidly with 1:3 cement mortar. When plastering the upper layer of the first ring of bricks at the arch corner, the thickness should reach 30-50 mm to replace the ring beam. Plaster as you build, and then backfill soil evenly from the outside to the inside. Before backfilling, several layers of bricks should also be built on the upper part of the feed pipe to prevent backfill soil from entering the digester through the feed pipe. The inlet width should preferably be 240 mm, and the length varies by household. Note that about 60% of the first backfill is sufficient to prevent collapse, and part of the remaining soil should be backfilled the next day before sealing the digester. After the entire digester is completed for 10 days, all backfilling can be completed.
How big a biogas digester is needed for 500 pigs
For 500 pigs, if the biogas slurry is flushed back into the pig house and all pig manure enters the biogas digester, a true 100 cubic meter biogas digester with automatic biogas slurry separation is sufficient.
Design principles of a pig farm biogas digester
To build the biogas digester in the “model”, design work must first be done well. Summarizing years of experience in scientific experiments and production practice, the design of a biogas digester matching the model must adhere to the following principles:
1. The principle of “four combinations” must be adhered to. The “four combinations” means that the biogas digester is connected to the livestock pen, toilet, and solar greenhouse, so that human and livestock manure continuously enters the biogas digester, ensuring normal and continuous gas production, and facilitating manure management, improving environmental sanitation, and allowing biogas slurry to be conveniently transported to the solar greenhouse vegetable field for use as fertilizer.
2. Adhere to the principle of “round, small, shallow”. According to geometric principles, for biogas digesters of the same volume, a round shape has a smaller surface area than a square or rectangular one, saving more material. It has good airtightness and is relatively sturdy. The internal structure of a round digester is reasonable, and the digester wall has no right angles, making it easy to solve the sealing problem, and the surrounding forces are uniform, making the digester body relatively sturdy. The temperature in northern China is relatively low, and placing a round digester underground is conducive to heat preservation in winter and safe overwintering.
What materials need to be prepared for building a biogas digester
Material preparation is the first step in biogas fermentation. Before building a new biogas digester and before a major material change in the biogas digester, sufficient fermentation raw materials must be prepared. According to the fermentation concentration requirement of 6%-10%, maintain 6%-8% in summer and 10% in winter. As for the biogas built in Qingfeng County, a 10 m3 household biogas digester requires 2.7 m3 of human and livestock manure in spring and summer, and 4.4 m3 of human and livestock manure in autumn and winter.
When building a pig-raising biogas digester, site selection must be done well, and then setting out lines, pit excavation, and so on all need to be very precise. The selection of cement and sand is also very important. For 500 pigs, the biogas digester to be built will also be relatively larger.