Design basis of biogas digester

The following factors must be considered when designing biogas digesters matching the "model" and formulating the construction scheme of biogas digesters: all biogas digesters built in the "model" are buried underground, and the earthwork of biogas digesters adopts the construction technology of large excavation. First, we must determine the height of plus or minus zero. The depth of the pit is determined according to the design drawings, that is, the top of the biogas digester and the discharge port are kept on a horizontal plane, which is 10 cm higher than the pigsty ground. The feed inlet is 2 cm from the ground. If you dig too deep, the biogas digester will be lower than the ground, which will affect the supporting use. If you dig too shallow, the biogas digester will protrude from the ground, which will make it difficult to fertilize pigs in solar greenhouse. See table 2. 1 for specific dimensions.

In order to facilitate the placement of pool-building molds or the use of brick molds to pour the pool body and reduce material loss, the pool pit should be round and vertical. For areas with good soil quality, the pit wall can be dug straight, digging around from the middle, leaving room when digging to the pit wall. Then find the center point through the positioning pile and nail the fixed pile. One end of a rope is fixed on the stake at the center point, and the other end of the rope is tied with a small hoe, so that the length from the hoe to the center point is equal to the radius of the pool plus the wall thickness of 6 cm, so that the sand blocking the passage can be scraped off, and the pit can be repaired while digging. After the pit is dug, immediately repair the bottom of the pool into the shape of the bottom of the pot; Dig a U-shaped shallow groove from the center of the bottom of the pot to the bottom of the hydraulic chamber, with a downward slope of 5%. Where the soil is loose, the slope of 80cm below the ground should be used to borrow soil. The slope depends on the degree of loose soil, and the pit wall should not collapse. At the same time, the entrance and exit pits should be dug. If there is groundwater, a sump should be dug at the bottom of the pool for drainage.

When groundwater is encountered in the construction of the pool, the method of "avoiding, leading and blocking" can be adopted to solve it. "Avoid" means to avoid groundwater, try not to construct in rainy season, choose places with low groundwater level and high terrain to build ponds, build spherical ponds or improve ponds in water network areas, and build semi-underground ponds. "Diversion" means drawing groundwater, digging drainage ditches before construction and pumping water away as much as possible. If the pool wall leaks, you can insert a bamboo tube in the seepage place or open a small Y-shaped ditch on the pool wall to let the water flow from the ditch to the bottom of the pool. For water seepage at the bottom of the pool, cross ditch or annular ditch can be used to collect water, and a deep small well can be dug in the center of the pool bottom to make the water flow into the well and be taken away, and then the well can be filled when there is no water seepage discharged after the project is completed. "Blocking" means blocking groundwater. For individual Koizumi eyes in the pool, bricks and pebbles can be used to block them. If there is water seepage in a large area, the water glass liquid impervious agent can be mixed with cement for brushing, which can be quickly solidified and effectively blocked. At the same time, when building a pool in a place with poor soil quality and high groundwater level, a sandy pebble cushion must be set below the bottom of the pool. The construction of cushion layer can be paved with pebbles first, and then filled with pebbles by submerged method to ensure the quality of pool construction. If there is no groundwater at the pool site, there is no need for padding and drainage measures below the pool bottom. The arch cover of "mode" biogas digester is made of brick, and the "mode" biogas digester generally adopts straight pipe feeding. Before the arch cover of biogas digester is laid, a ceramic tube with a diameter of 200mm and a length of about 600mm is generally used, and the tube is hung on a stake on the ground with a rope. The bell mouth of the feed pipe is upward and vertical, and it is fixed close to the biogas digester wall. It is advisable to insert the arch angle of 250 ~ 300mm into the pool. Masonry arch cover can be fixed by iron hook or hanging rope. Masonry starts from the water supply pipe, and the periphery of the water supply pipe should be reinforced with cement. Bricks with good quality should be selected for arch cover construction. They should be soaked in water first, keeping the outside moist and the inside dry. 1∶2 cement mortar should be used for masonry, with good workability of mortar and full mortar mouth. Bricks should be compacted with bricks. Every time you build it, you should embed pebbles. Pay attention to the radian of the arch cover when laying. Every 3 ~ 5 times, the outer wall of the arch cover should be built with 1. With build by laying bricks or stones with plaster, and then evenly backfill soil from outside to inside. Before backfilling, several layers of bricks should be laid on the upper part of the feed pipe to prevent backfill from entering the pool from the feed pipe. The width of the feed inlet should be 240 mm, and the length varies from household to household. Pay attention to backfill about 60% for the first time to prevent landslide, and backfill a part of the remaining soil before closing the pool the next day, which can be completely backfilled after 10. The construction drawing of the pool arch cover is shown in Figure 2. 13. When laying the arch cover of the pool, the upper part of the water pressure room should be built. The upper part of the hydraulic chamber is built with 1/4 bricks and poured with 1: 3 cement mortar.

When the arch cover of the masonry pool is sealed, a copper airway with a diameter of 9 ~ 10 mm should be placed in the center of the vault, and the insertion depth is about 10 mm after the sealing layer in the pool is completed. Four iron bars with a length of 500 ~ 700 mm should be placed in the center of the vault in a # shape, and reinforced and plastered to prevent the gas box from being damaged due to excessive pressure during the operation of the biogas digester. Around the air duct, build a square fence with a depth of 200 ~ 300m and a side length of180 ~ 200mm, leaving a gap in the leading-out direction of the air duct. Underneath the pigsty floor, an underground ditch can be built or an iron pipe or plastic protective pipe with an inner diameter of 20 ~ 50 mm can be placed to lead out the gas pipeline. The air duct is covered with a movable cover to prevent the air duct from being bitten by pigs. The size of the movable cover plate is 240mm× 240mm, and the thickness is 50 ~ 60mm. You can use two red bricks instead, as shown in Figure 2. 14. Newly-built biogas digesters and old biogas digesters maintained after aeration must be accepted before they can be put into use. There are two inspection methods:

(1) The direct inspection method must be carried out when the strength maintenance of the whole pool reaches more than 70%, and it shall be knocked with fingers or small sticks, and the shell shall not become warped. There is no trace of water seepage on the inner wall of the whole pond, and there are no visible defects such as cracks, sand holes and air holes; Gas pipelines, switches and other supporting facilities outside the pool are installed completely and firmly.

(2) On the basis of direct inspection, it is suggested that the pressure test should be given priority to, supplemented by water pressure test, or mixed use. The general practice is to fill the upper end of the inlet and outlet pipes with water to a height of 20 cm and observe for 12 hours. If the water level does not change obviously, it is considered impervious; Then use a pump (machine) to inflate (or pressurize with water) to make the pressure gauge reach 50% of the design pressure, and observe for 2 ~ 4 hours. If the pressure does not drop, continue to inflate to the design pressure and observe for 24 hours. If the pressure drop is less than 3% of the design pressure, it is considered that there is no air leakage. You can also use the method of closing the inlet and outlet of the empty pool and directly inflating it for pressure test. The requirements are the same as above. During pressure test, it is best to connect all gas pipelines and check whether there is any leakage. If there is water leakage or air leakage in the inspection, find out the location and reason. After repair, the strength can meet the requirements, and it can only be put into use after re-inspection. But before use, the excess water must be pumped away. If the re-inspection is unqualified, it shall not be compulsory. What is written above is the construction method of hydraulic biogas digester, which is mainly suitable for the construction of rural biogas digesters. The national examination is five years in rural areas and five years in cities.

Daily safe operation management of biogas digester

Daily operation management technology:

1. It is best to start the new pond with pure cow and horse manure. 8m&sup 3 biogas digester needs 2 m cow and horse manure &; Sup3 is piled outside the pool for 5-7 days before entering the pool to enrich the strains and speed up the start-up.

2. When the new pool is started, it should be started with warm water first. When the water temperature is 30℃-50℃, it is forbidden to start with cold water and extend the start time.

3. After feeding, seal the movable cover as required, and pay special attention to sealing the skylight to prevent air leakage.

4. The gas generated in the initial stage of startup is waste gas, which cannot be burned. Exhaust gas should be discharged for 7 days, and it should be discharged for more than 30 minutes every day.

5. Before using lamps and cookers, read the instructions carefully and standardize the operation. Daily attention should be paid to cleaning up the sundries on lamps and cookers in time to keep them clean.

6. Regular feeding and discharging. The 8m3 biogas digester needs to feed 20kg of fresh livestock manure every day. It is forbidden to put as much as possible, so as not to affect gas production.

7. Strengthen daily stirring, and stir the feed liquid for more than ten minutes every day with a slag extraction piston or a wooden stick to promote fermentation and improve gas production rate.

8, often observe the pressure change, when the biogas pressure reaches more than 9, should be timely deflated or deflated, so as to avoid excessive pressure damage to the pressure gauge and tank.

9. Always check whether the interfaces, pipes and appliances are sealed, damaged, aged and blocked. If problems are found, maintain them in time.

10. Strengthen overwintering management. Before winter, some hot raw materials such as cow manure and horse manure are added, and the tank body is covered with insulation film to ensure normal gas production in winter.