How do we produce biogas?

Biogas and its production process Biogas is a combustible gas produced by microbial fermentation of organic matter in anaerobic environment under certain conditions of temperature, humidity and pH value. Because this gas was originally found in swamps, lakes and ponds, people call it biogas. Biogas contains a variety of gases, the main component of which is methane (CH4). Biogas bacteria decompose organic matter and produce biogas, which is called biogas fermentation. According to the function of various bacteria in biogas fermentation, biogas bacteria can be divided into two categories. The first kind of bacteria is called decomposing bacteria, and its function is to decompose complex organic matter into simple organic matter and carbon dioxide (CO2). Some of them specialize in decomposing cellulose, called cellulolytic bacteria; There are bacteria specialized in decomposing protein, called proteolytic enzymes; Specializing in decomposing fat is called lipolytic bacteria; The second kind of bacteria is called methanogenic bacteria, usually methanogenic bacteria. Its function is to oxidize or reduce simple organic matter and carbon dioxide into methane. Therefore, the process of turning organic matter into biogas is like two processes of producing a product in a factory: one is to decompose bacteria and process complex organic matter such as feces, straws and weeds into semi-finished products-compounds with simple structure; Then under the action of methanogens, simple compounds are processed into products-that is, methane is generated. 2. 1.2 Biogas is a mixed gas, and its main component is methane, followed by carbon dioxide, hydrogen sulfide (H2S), nitrogen and other components. Among the components of biogas, combustible components include methane, hydrogen sulfide, carbon monoxide and heavy hydrocarbons. Noncombustible components include gases such as carbon dioxide, nitrogen and ammonia. The content of methane is 55% ~ 70%, the content of carbon dioxide is 28% ~ 44%, and the average content of hydrogen sulfide is 0.034%. 2. 1.3 Physical and chemical properties of biogas Biogas is a colorless, odorless, toxic and smelly gas, and its main component methane is a colorless, odorless and nontoxic gas at room temperature. The molecular formula of methane is CH4, which is a simple hydrocarbon with one carbon atom combined with four hydrogen atoms. The weight ratio of methane to air is 0.54, which is about half lighter than air. Methane has little solubility. At 20℃ and 0. 1 kPa, 100 unit of water can only dissolve 3 units of methane. Methane is a simple organic compound and a high-quality gas fuel. It burns in a blue flame, and the highest temperature can reach 1? 400? It's about 30 degrees Celsius. The calorific value of pure methane per cubic meter is 36.8 kilojoules. The calorific value of biogas per cubic meter is about 23.4 kilojoules, which is equivalent to the heat released after 0.55 kg of diesel oil or 0.8 kg of coal is completely burned. From the analysis of thermal efficiency, the heat available per cubic meter of biogas is equivalent to the heat available by burning 3.03 kilograms of coal. 2.2 Types of household biogas digesters With the development of biogas science and technology in China and the popularization of rural household biogas, household biogas digesters have hydraulic tanks with fixed arch cover, hydraulic tanks with large open cover, hydraulic tanks with hanging pipes, hydraulic tanks with meandering water distribution, hydraulic tanks with backwater, tanks with independent floating covers, semi-plastic tanks, all-plastic tanks and tank tanks. Although there are various forms, they are generally composed of four basic types of biogas digesters: hydraulic biogas digesters, floating hood biogas digesters, semi-plastic biogas digesters and tank biogas digesters. The biogas digesters supporting the four-in-one ecological greenhouse model are generally hydraulic biogas digesters, which have several different forms. 2.2. 1 There are three types of hydraulic biogas digesters with fixed arch covers: cylindrical (see Figure 2. 1), spherical (see Figure 2.2) and ellipsoid (see Figure 2.3). The upper air chamber of the tank body is completely closed, and with the continuous production of biogas, the biogas pressure increases accordingly. This increased air pressure forces part of the feed liquid in the biogas digester to enter the hydraulic chamber communicated with the tank body, so that the liquid level in the hydraulic chamber rises. In this way, there is a water level difference between the water pressure room and the biogas digester. This water level difference is called "water pressure" (that is, the value displayed by the U-tube biogas pressure gauge). When using gas, turn on the biogas switch, and the biogas will be discharged under water pressure; When the biogas decreases, the feed liquid in the water pressure chamber flows back to the tank, which makes the water level difference decrease continuously, resulting in a corresponding decrease in biogas pressure. This kind of biogas digester, which uses part of the feed liquid to reciprocate in series, causes repeated changes in water pressure to store and discharge biogas, is called hydraulic biogas digester There are generally two kinds of biogas digesters, one is ordinary cement and the other is glass fiber reinforced plastic, which are divided into ordinary and patent. I specialize in FRP biogas digesters in Xinjiang, which is a patented product. The price of cement is slightly lower, but the construction time is long, so gas cannot be produced in winter, and groundwater level is needed. First, the product features 1, and the molded product is easy to install. This product belongs to industrial molding products, and the installation time is only a few hours. After installation, it can be used as a filler the next day. 2. Lightweight and convenient transportation. The total weight of a pool is only one or two hundred kilograms, which is made separately and convenient for transportation. 3. Advanced technology and reasonable design. Adopt ellipsoid volume, buried depth, large fermentation bottom, convenient for special circulation of feces, no fermentation blind area, automatic slag discharge and high gas production. 4. The tank has good sealing performance and high strength. Determined by the performance of FRP, combined with the use of special composite materials, its strength, sealing, pressure resistance, aging resistance, wear resistance and heat insulation are stronger than those of concrete biogas digesters. 5, the pool body does not crack and has a long service life. The pool body will never crack, and there is no need for maintenance during use, and the service life can be as long as 20 years. 6. The swimming pool is low in cost and price. The product price is at a low price among similar products in the same industry. Although the price is higher than building a concrete biogas digester, its gas production is high, it does not need maintenance, its service life is long, and it is cost-effective to calculate the general ledger. Second, the installation procedure (a) the site selection and installation location should first consider the combination with the toilet, pigsty and kitchen. It is necessary to facilitate the excrement from toilets and pigsty to flow into the inlet of biogas digester, and biogas residue and biogas slurry to flow into vegetable fields from the outlet. The gas outlet of biogas digester is introduced into the kitchen, and the length of gas transmission pipeline is controlled within 30m to avoid too long pipeline and insufficient air pressure. In addition, we should also pay attention to avoid areas where roots and gravel gather. (2) Dig a pit 1. Dig a hole at the selected location (please dig the hole according to the size shown in the attached figure). The diameter of the upper hemisphere of the pit is larger, and the bottom of the pit should be dug into the shape of the bottom of the FRP biogas digester. The entrance and exit should be dug according to their shapes and sizes, so that the tank can be properly placed in the into the pit for bonding operation. 2. When digging a pit, there are stones, cavities or landslides at the bottom, which should be handled or filled in time to avoid the tank being broken or cracked by stones after heavy charging. When digging a hole, you must cut off a few roots, and paint some expensive diesel oil or lime on the incision to stop it from growing or even rotting, so as to prevent the growth of roots from damaging the pool body. 4. After digging a hole, check the size with a tape measure and trim it to the required standard. (3) Before assembling 1 and installing, glue the inlet and outlet to the corresponding opening position of the upper half pool. 2. Before installation, carefully check whether the biogas digester is damaged, and repair it in time if there is any damage. 3, before putting the pool, check whether the bottom is flat, and put a layer of fine loose soil, can not have water, stones and other hard objects. 4. When placing the pond, place the upper hemisphere in into the pit according to the marked direction, flatten it and backfill it. After tamping the lower half along the bottom, fasten the upper hemisphere to the lower hemisphere according to the marked direction. 5. When entering the pool, clean up the sundries and sludge at the junction of the upper and lower pools, polish the new crop with sandpaper, and fill up the junction of the upper and lower pools with glass fiber reinforced plastic putty. Outside the pool, the joint between the upper and lower pools outside the pool body will be drilled with glass fiber reinforced plastic putty, which can be filled after it is cured. 6. Drill a hole in the movable cover or pool top, stick on the air outlet pipe, install the switch, and you can cut the door. 7, the use of glass fiber reinforced plastic flange cover. After the raw materials, inoculum and water are added, the flange of glass fiber reinforced plastic (FRP) is wiped clean, and then the gasket-free sealant is squeezed on the plane of the inner edge of the flange and left to air for about one hour. When the sealant solidifies into an elastic apron, cover the FRP cover plate on the flange (the screw hole of the cover plate should be aligned with the screw hole of the flange), screw on eight screws with the diameter of 10MM×50MM, and seal the pool. 8. Use concrete movable cover. After feeding, inoculating and water, clay and lime powder with high viscosity are selected. First, dry clay without sand is hammered, coarse particles and sundries are screened out, and dry mixed with lime powder according to the ratio of 3-5:1,and then mixed with backwater to knead into dough. Before sealing, use a broom to clean the mud and sand impurities stuck on the water storage ring, the bottom of the movable cover and the surrounding edges, then rinse them with water, spread the kneaded lime mortar evenly on the movable cover, and then sit the movable cover on the mortar. Pay attention to the uniform gap between the movable cover and the water storage ring, and tighten it with your feet to make it closely combined. After sealing the movable cover with lime cement, tighten the reverse bolt, turn on the biogas switch, pour water into the water storage ring, keep it for 1~2 days, and turn off the switch for later use. It is best to keep the top cover from dehydration for a long time. 9. Stick the gas pipeline to the partition door, install the water controller and desulfurizer, introduce the pipeline indoors, and connect the biogas appliances such as stoves and lamps. (4) After the installation of pressure test biogas digesters and biogas appliances is completed, close all shut-off doors, inject water into the pool for pressure test until the water surface rises to the edge of the import and export, and then wipe the joint between the pool body and the pipeline with a soap brush to observe whether there are bubbles. If there are bubbles, it means that there is air leakage here, so it should be sealed in time. (5) backfill soil 1. After the tank is sealed with the pipeline, backfill the gap with fine loose soil or sand, water it while filling, and then tamp it with a wooden stick. Be careful not to puncture the pool wall or water it too much to avoid the biogas digester floating up. 2. In areas with high groundwater level, water should be added to the pool to half the volume at the same time before water injection. When backfilling rammed earth, don't hit the biogas digester with wooden sticks or other tools to avoid damaging the biogas digester. 3. After the backfill is padded to the upper edge of the water inlet and outlet and the height of the flange ring, the wall with the radian of the water inlet and outlet is bricked, and the ground is leveled. The water outlet leaking out of the ground and the flange retaining wall should be covered with wooden covers to prevent people and animals from falling into it. 4. After the backfill soil is compacted, assemble the ground pool shed, straighten out the gas pipeline, adjust the cooker, and close all the cutting doors for standby after gas production. (6) Fire test When the barometer shows that there is air pressure, you can deflate and test the fire. At the initial stage of biogas fermentation, the gas produced is mainly carbon dioxide produced by acidification. When the pool is closed, there is still a lot of air in the gas box, so the methane content in the gas is low and usually non-combustible. Therefore, when the small water column of the biogas pressure gauge reaches more than 3kpa, the gas of 1~2 times should be released first, and ignition can only be started when the methane content of the gas in the pool reaches more than 30%.