What Is a Methane Digester?

Biogas: It is a kind of combustible gas produced by organic matter in anaerobic environment under certain temperature, humidity, and pH conditions through microbial fermentation. Because this gas was originally found in swamps, lakes, and ponds, people call it biogas.

Biogas digester

Biogas and its production process

With the development of China's economy and social progress, the lives of urban residents have been further improved, but there are still many problems in the lives of rural residents. In order to build a well-off society in an all-round way, the construction of a new socialist countryside appears very necessary. This requires the grand goal of developing rural ecological agricultural production methods, improving the rural environment, and increasing farmers' income. Of which comprehensive utilization

(1) Provide low-cost and high-quality fuel for rural families. A family of 3 ~ 5 mouths will build a 6³ ~ 10³ biogas digester. As long as the raw materials are sufficient, it can provide 9 ~ 11 months of cooking and lighting a year

Removal of traditional septic tanks

The following factors must be taken into consideration when designing the biogas tank matching the "model" and formulating the construction plan of the tank:

Soil quality should be considered when selecting pond foundation

For the construction of a biogas digester, it is important to choose the foundation. This is a question that affects the quality of the pond and the life of the pond, and must be taken seriously. Since the biogas digester is a buried building, it has a lot to do with the quality of the soil. Different soils have different densities and firmness, and the allowable bearing capacity varies. And the same place, the soil layer is not the same. If the soil layer is soft or sandy soil or rotten soil with a high groundwater level, the bearing capacity of the pool foundation is not large. If the pool is built here, it cannot bear it, which will inevitably cause the pool body to settle or unevenly settle, causing the pool body to rupture and leak. gas. Generally, the permissible bearing capacity of natural soil layers exceeds 10 tons per square meter. There is no problem in constructing biogas digesters on such natural soil layers. Therefore, the foundation of the pond should be selected with solid soil and low groundwater level, and there are no hidden dangers such as tunnels, cellars, seepage wells, spring holes, virtual soil at the bottom of the soil layer; and the pond must be at a distance from trees, bamboo forests or ponds to avoid trees When roots and bamboo roots enter the pond or the pond rises, the pond body will be affected, causing the pool to leak water and air. In arid regions of the north, the pond should be closer to the water source and the user. If the pond is far away from the user, not only the management (such as adding water) , Feeding, etc.) is inconvenient, and the pipeline for transporting biogas should also be very long, which will affect the pressure of the biogas and the combustion effect is not good. In addition, as far as possible, the leeward direction of the sun should be chosen to build a pool.

Design ponds should take into account loads

Make sure the load is

(1) Use of additives to improve gas production rate

In order to stabilize gas production in winter, in addition to heat preservation of the biogas digester, various biogas additives must be used to provide the fermentation bacteria with various trace elements required for growth and reproduction. Pulverized coal, hydrogen carbonate, silkworm sand, drum skin, and lees waste liquid can be used as additives. Only scientific use can accelerate the decomposition of organic matter and increase gas production. This is an important technical measure.

(2) Winter management of biogas digesters in use

In use, the biogas digester is mainly used to make the biogas liquid flow directionally by using the biogas pressure difference. In addition to the self-guided stirring in the winter, it is mainly managed by manual stirring methods, that is, a 3-meter long wooden stick (tree stick) is often stirred up and down the inlet and outlet to make the fermentation liquid agitate and destroy The material liquid in the tank crusts to ensure the normal gas production of the biogas digester. In colder places, plastic can be used to increase the temperature in the biogas digester.

(3) Winter management of new biogas digesters

For the new biogas digester built in winter, it can not keep up with the feed, nor can it be empty for winter. Filling with straw (rice, wheat straw) or weeds, etc., can have the dual effects of heat preservation, anti-freezing and stacking fermentation.

(IV) Winter management measures for biogas digesters in areas above 2000 meters above sea level

1. Build a pool. Areas above 200 () meters above sea level should choose leeward and sunny locations to build pools. Farmers with conditions can build solar warming greenhouses in the courtyard, build a biogas tank underground at one end of the greenhouse, build livestock pens and toilets above the biogas tank, and plant vegetables or fruit trees in the greenhouse to allow solar energy to provide a safe and effective wintering environment for the biogas tank.

2. Heating measures. Add thermal raw materials such as lees and horse dung. Insist on frequent mixing and do it once or twice a day. Cover the bare pool with high-quality plastic film. Rinse the enclosure with hot water, and the temperature should be relatively high.

To build a biogas digester, the volume of the pond must be calculated in advance, which means that it is better to build a larger pond. The size of the calculated volume should, in principle, be determined based on the use and amount. The pond is too small, and there is less gas production, which can not guarantee the needs of production and living; the pond is too large, often due to insufficient fermentation raw materials or management failure to keep up, etc., resulting in low gas production rate. The gas production rate in China's rural biogas digesters is generally not stable. In the summer and night, the volume of gas produced per cubic meter can produce about 0.15 cubic meters of gas, and in winter it can produce about 0.1 cubic meters of gas. Generally, a family of five people in rural areas cooks rice every day, It takes about 1.5 cubic meters of gas to boil water (the actual gas consumption required by each person for daily life is about 0.2 cubic meters, and the maximum does not exceed 0.3 cubic meters). At the same time, production fertilizers should be considered. Therefore, it is more suitable to build a pool in rural areas on the average of 1.5 to 2 cubic meters per person (effective volume generally refers to the total volume of the fermentation room and the gas storage tank). According to this standard, a family with a large population has a smaller average effective volume, and a family with a small population has a larger average effective volume. In northern regions, the temperature is generally lower and can be a little more.

Prepare

To build an 8-cubic-meter biogas digester requires 1 ton of cement, 2 cubic meters of sand, 0.6 cubic meters of crushed stone (size 1 to 3 cm), 600 red bricks, 1 to 2 ceramic tubes (20 to 30 cm in diameter), Rebar (14 mm diameter) 1.2 meters. If a 10-cubic-meter biogas digester is built, its cement, bricks, and sand will increase by 10%. If a 6-cubic-meter biogas digester is built, the amount of cement, brick, and sand will be reduced by 10% compared to an 8-cubic-meter biogas digester.

Pay off

Line digging is the first step to ensure the quality of the pool, and it must be constructed in accordance with the specified size. Points for putting out the line: Draw out the overall plane. Delineate the area of the greenhouse and pigsty, with the pigsty on the east or west side. Draw the center line of "pattern" width. Take O as the starting point, find the center point O of the pond on the inside of the piggery, use O as the center of the circle, and draw a circle with the radius of the pool plus 6 cm to determine the position of the pool. Determine the position of the inlet and outlet. To determine the center point of the inlet on the center line of the "pattern" width and the center point of the outlet in the solar greenhouse, mark with white ash.

Pool pit excavation

The built-in biogas digesters in the "model" are all underground, and the earthmoving works of the biogas digesters adopt large excavation construction techniques. First, determine the height of the positive and negative zero. The depth of the pond pit is determined according to the design drawing, that is, the top of the biogas digester and the discharge opening are kept on a horizontal plane and 10 cm higher than the ground of the piggery. The feed inlet is 2 cm above the ground. If it is dug too deep, the biogas digester will be lower than the ground level, which will affect the supporting use. If it is dug too shallow, the biogas digester will protrude from the ground, which will make it difficult for pigs and sunlight greenhouse fertilization. The specific dimensions are shown in Table 2.1.

In order to facilitate the installation of the pool mold or the use of brick mold to pour the pool body and reduce material loss, the pool pit should be rounded and vertical. For areas with good soil quality, the pit wall can be dug straight, and excavated from the middle to the surrounding area when taking the soil, leaving a certain margin when digging to the pit wall. Then locate the center point according to the positioning pile, and nail a fixed wooden pile. One end of a rope is fixed to a wooden pole at the center point, and a small handle is tied to the other end of the rope so that the length of the trowel to the center point is equal to the radius of the pool plus the wall thickness of 6 cm. Digging and trimming the pond pit until the design depth. Immediately after the pit is dug, the bottom of the pool is repaired to the shape of the bottom of the pot; a U-shaped shallow groove is dug from the center of the bottom of the pot to the bottom of the water pressure chamber, and the slope is 5%. For places with loose soil, 80 cm below the ground should be placed on slopes for soil extraction. The slope depends on the degree of soil looseness. The principle is that the walls of the pits do not collapse, and the inlet and outlet pits are dug at the same time. If groundwater appears, a sinkhole should be dug at the bottom of the pond for drainage.

When groundwater is encountered during the construction of the pool, the method of "avoiding, diverting, and blocking" can be adopted to solve the problem. "Avoid" means to avoid groundwater and try not to carry out construction in rainy seasons. Choose places with low groundwater levels and high terrain to build pools. Spherical pools or raised bodies can be built in water network areas to form semi-underground pools. "Diversion" means to divert groundwater. Dig a drainage ditch before construction to divert water as much as possible. The wall of the pool seeps water. You can insert a bamboo pipe into the seepage or cut a small star-shaped ("Y") trench on the pool wall to concentrate the water from the trench to the bottom of the pool. For water seepage at the bottom of the pool, a cross ditch or annular ditch can be used to collect water, and a deeper small well is dug in the center of the bottom of the pool to allow the water to flow into the well and drain away. This well will be filled when there is no seepage from the project. "Blocking" is to block the groundwater. To individual Koizumi eyes in the pond, you can use bricks and small stones to plug them. If the water seeps in a large area, water glass medicinal liquid impermeant can be mixed with cement for painting, solidifying quickly, and the blockage is effective. At the same time, the pool is built at a poor soil and high groundwater level. Sand pebble cushion must be set under the bottom of the pond. The construction of the cushion can be paved with pebble, and then the sand will be used to fill the gap between the pebble to ensure the construction of the pool. The role of quality. If there is no groundwater in the pool construction site, cushioning and drainage measures may not be added below the pool bottom.

Pouring from concrete

The biogas digester in the four-in-one ecological greenhouse model is generally built in combination. The so-called combined building pool means that the bottom of the pool, the wall of the pool, and the lower part of the water pressure room are concrete cast-in-place, and the pool arch cover and the upper part of the water pressure room are made of brick. When mixing cast-in-place concrete, it is necessary to control the water-cement ratio 0.65, the soil content in the sand 3%, the mica content 0.5%, the maximum particle size in the crushed stone 3 cm, and the soil content 2%. The concrete pouring process must be carried out continuously, the interruption time must not exceed 1 hour, and the concrete must be vibrated and compacted during pouring to prevent the phenomenon of honeycomb hemp. The construction sequence is as follows:

Masonry Outlet Passage

The discharge channel is built with red brick and sand ash, cement: sand = 1: 2.5. In order to facilitate the construction and discharge, the passage opening is 50 cm wide and 70 cm high, and the top is arched, but the upper opening angle from the upper part of the pool should not be less than 35 cm, to prevent gas from returning to the surface and running out of gas.

Pond wall and water pressure pouring

The pouring of the pool wall and the lower part of the water pressure chamber can use steel molds, wooden molds and brick molds. Generally, the above molds are internal molds, and the pool walls are external molds. Due to the high cost of steel molds, they are rarely used, while wood molds and brick molds are more commonly used. If multiple biogas digesters are built in a village, it is more convenient to use wooden molds. If only one is built, brick molds are appropriate. The general method of laying bricks is to soak the bricks with water first to prevent difficult removal of the molds. Each brick is laid horizontally, and the bricks of each layer are staggered. No mud or ash is required, so that one layer of bricks can be placed in one layer with concrete, and the second layer can be built after compaction. The concrete weight ratio is cement: sand: gravel = 1: 3: 3, the pool wall is 1 meter high and 0.05 meter thick.

Construction of pool arch cover

The biogas digester in the "model" is made of bricks. The biogas digester in the "model" is generally fed with straight pipes. The feed pipe must be installed before the masonry pond arch cover. Generally, the diameter is 200 mm and the length is 600 mm. The left and right ceramic pipes are hung on wooden stakes on the ground through ropes, the bell mouth of the feeding pipe is facing upward, vertical up and down, and is fixed close to the wall of the pool. It is appropriate to insert the arch depth 250-300 mm into the pool. The masonry arch cover can be fixed with iron hooks or lanyards. The masonry is started from the feed pipe, and the surrounding of the feed pipe should be reinforced with cement. The bricks of the masonry arch cover should be of good quality. They should be soaked with water, kept wet and dry inside, and built with 1: 2 cement sand ash. The sand ash is easy to work, and the ash mouth is full. Tight, use small pieces of stone for every circle of masonry, pay attention to the arc of the arch cover while masonry, every 3 to 5 circles, the outer wall of the arch cover is cemented with 1: 3 cement sand, and the corner of the arch When plastering the upper layer of the first circle of bricks, the thickness must reach 30-50 mm to replace the circle beam. Plaster as you go, and then backfill the soil evenly from outside to inside. Before backfilling, several layers of bricks should be laid on the upper part of the feeding tube to prevent the backfilling soil from entering the tank from the feeding tube. The width of the feeding opening should be 240mm, and the length varies from household to household. Note that about 60% of the soil can be backfilled for the first time to prevent landslides. The remaining amount of soil can be backfilled before being sealed in the pond the next day. The entire pond can be backfilled 10 days after completion. The construction drawing of the pool arch cover is shown in Figure 2.13. At the same time as the masonry pool arch cover, the upper part of the water pressure chamber should be erected. The upper half of the water pressure room is erected with 1/4 bricks and 1: 3 cement sand ash.

When the arch cover of the masonry pool is to be sealed, a copper air duct with a diameter of 9-10 mm is placed in the center of the vault, and the insertion depth is about 10 mm exposed after the sealing layer in the tank is completed. 700 mm long iron bars are placed in the shape of #. Plastering must be thickened and strengthened to prevent the gas tank from being damaged by excessive pressure during the operation of the biogas digester. Around the air duct, a square enclosure wall with a depth of 200 to 300 mm and a side length of 180 to 200 mm is laid, and a gap is reserved in the direction of the gas pipe. Below the ground of the pigsty, a ditch can be built or an iron pipe or plastic pipe with an inner diameter of 20-50 mm can be placed in order to lead the gas pipeline. Cover the air tube with a movable cover to prevent the gas tube from being damaged by pigs. The size of the movable cover plate is 240 mm × 240 mm, and the thickness is 50-60 mm. It can be replaced by 2 red bricks, as shown in Figure 2.14.

Pool bottom construction

A layer of crushed stone is laid on the bottom of the pool, and the cracks of the crushed stone are filled with 1: 4 cement mortar, and then the bottom of the pool is poured with 1: 3: 3 concrete with cement, sand, and crushed stone, and the thickness must be 8 to 12 cm.

Internal sealing of biogas tank

The biogas digester constructed by the combination of brick and concrete cannot meet the anti-leakage requirements only by the structural layer. The pond body must be sealed to prevent air leakage and water leakage. The sealing layer of the biogas digester adopts a 7-layer approach and a 3-layer approach. The 7-layer approach is adopted for the gas storage chamber and the feed pipe part in the tank; the 3-layer approach is adopted for the bottom of the pool, the pool wall, the water pressure chamber, and the discharge channel. The first layer consists of 450 # cement sand ash, ash: water = 0.3: 1; the second layer is cement ash with cement: sand = 1: 2.5, the thickness is 0.8 1 cm; Apply 0.1 cm thick plain ash; the fourth layer is covered with cement: sand = 1: 2 cement sand ash with a thickness of 0.4 cm; the fifth layer is covered with 0.1 cm thick plain ash; the sixth layer is covered with 1: 1 fine sand ash Apply 0.3 to 0.4 cm; brush the mortar for the third layer three times. The three-layer approach is to do the first layer with the second layer in the seven-layer approach; the second layer is done with the sixth layer in the seven-layer approach; the third layer is done with the seventh layer in the seven-layer approach.

Conservation

Every part poured with concrete must be cured. It is required to be naturally cured under the condition that the average temperature is greater than 5 ° C. The exposed concrete should be covered with a straw curtain and watered. The curing time is 7 to 10 days. Spring and autumn should pay attention to antifreeze sooner or later. In order to achieve the purpose of conservation, after the biogas digester is sealed, the outlet, feed inlet and top of the pond shall be covered with a film. After the natural curing period is reached, it can be put into use after checking the pressure test. If it rains 24 hours after the completion of the construction of the pool, water should be added to the pool in a timely manner, and the amount of water added should be half of the loading volume in the pool to prevent the groundwater level from rising and damaging the pool.

Inspection and acceptance

Newly built biogas digesters and old tanks maintained after large material replacements must be checked and accepted before they can be put into use. There are two types of inspection methods:

The direct inspection method can only be performed if the strength of the entire pool is over 70%. Use your fingers or a small wooden stick to hit the non-warped shell. The inner wall of the entire pool has no traces of water seepage, no visible defects such as cracks, trachoma, pores, etc. The supporting facilities such as gas pipelines and switches outside the pool are fully installed.

The pressure test method is based on the direct inspection, and it is recommended to use the air pressure test as the main method, and the water pressure method as the auxiliary method. It can also be used in combination. The general method is to fill the water to the upper end of the inlet and outlet pipes with a height of 20 cm. After 12 hours of observation, there is no significant change in the water level, which is considered to be no water leakage; 50% of the design pressure, observe for 24 hours. If the pressure does not decrease, continue to inflate to the design pressure, and then observe for another 24 hours. The pressure reduction value is within 3% of the design pressure, which is regarded as no air leakage. It can also adopt the method of closing the inlet and outlet of the empty pool and directly inflating and testing the pressure. The requirements are the same as above. During the pressure test, it is better to connect all the gas pipelines and check whether there is leakage. If there are leaks or leaks during the inspection, the location and cause must be identified. After repairing to achieve the required strength, it can pass the re-inspection before being put into use. However, before use, excess water must be removed. Those who have not passed the re-inspection shall not be used reluctantly. What is written above is the construction method of the hydraulic pressure biogas digester, which is mainly adapted to the construction of rural biogas digesters. The national inspection is 5 years in rural areas and 5 years in cities.

Daily safety operation management of biogas digester

Daily operation management technology:

1. The new pond starts with pure cattle and horse dung. 8m & sup3; biogas digester requires 2m & sup3 of cattle and horse dung. Before entering the pond, stack hoe outside the pond for 5-7 days to enrich the bacteria and speed up the startup. ^[1]

2. When the new pool starts, use warm water to start. Water temperature of 30 -50 is appropriate. It is forbidden to start with cold water and prolong the startup time.

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

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

5. Before using the lamp or cooker, read the instructions carefully and standardize the operation. Daily attention to timely clean up the sundries and stoves, keep clean.

6. Inbound and outbound. The 8m3 biogas digester should be filled with 20kg of fresh livestock and poultry manure per day. How much to enter and how much to output, prohibit large discharge, so as not to affect gas production.

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

8. Observe pressure changes frequently. When the biogas pressure reaches 9 or more, gas should be used or deflated in time to avoid damage to the pressure gauge and the tank due to excessive pressure.

9, often check the interfaces, pipelines, appliances are sealed, damaged, aging, blocked, if problems are found, timely repair.

10. Strengthen the management of overwintering. Before entering the winter, a suitable amount of thermal raw materials such as cow and horse dung should be added, and the pool should be covered with thermal insulation film to ensure normal gas production in winter.