Biogas is a combustible gas, so it is called biogas because it was first found in swamps.
Definition: Biogas is a kind of combustible gas produced by organic matter under the action of biogas bacteria under the conditions of air isolation and certain temperature, humidity and pH value.
Biogas is a mixed gas, its main components are 55%-70% methane, 25%-40% CO2 and a small amount of H2, H2 sulfur, carbon monoxide, nitrogen and so on.
Physical and chemical properties of biogas The main component of biogas is methane. Methane is a colorless and odorless gas with molecular formula of CH4 and molecular weight of 16.04, and molecular weight of 0? In the standard state of C 10 1325Pa, the relative density of methane to air is 0.5548, and that of biogas is about 0.94. The calorific value of methane is 35.9MJ/m3, and the low calorific value of biogas is 2025MJ/m3.
Application of biogas
For a family of 4-5 people, if three large pig manure enters the biogas digester every day, it can meet the energy demand for cooking and lighting.
Burning biogas can keep chickens and piglets warm, and can also be used to store grain for killing insects or keeping fruits fresh.
Biogas slurry and biogas residue are high-quality fertilizers and bait. Feeding pigs with biogas slurry can reduce the feed-meat ratio and shorten the feeding cycle.
After running biogas in rural areas, human and animal feces were fermented in time, which inhibited the breeding of mosquitoes and flies. The killing rate of some bacteria in parasite eggs, schistosomiasis eggs and feces reached 98%, and the rural sanitation situation was improved, ensuring the health of farmers. Biogas fermentation microbial biogas fermentation
Definition of biogas fermentation:
Under anaerobic conditions, organic substances (such as human and animal manure, sludge, etc. ) is decomposed and metabolized by various microorganisms with different functions, and finally produces biogas. Biogas fermentation
trait
1) Biogas microorganisms consume less energy.
2) Biogas fermentation can treat high concentration organic waste.
3) Biogas microorganisms have low nutritional requirements and can treat various wastes.
4) Biogas fermentation is greatly influenced by temperature.
5) Methane and CO2, the main end products of fermentation, can be easily separated from the fermentation broth.
Distinguished by feeding operation mode
1) continuous fermentation, suitable for treating urban sewage, industrial wastewater and feces of large and medium-sized livestock and poultry farms, with stable sources;
2) Semi-continuous fermentation is mainly used in rural areas of China because of the characteristics of raw materials and the concentration of fertilizer used in rural areas;
3) Fed-batch fermentation is mainly used to study the law of organic biogas fermentation and the relationship between fermentation and gas production.
Distinguish by fermentation temperature
1) High-temperature fermentation, especially active microorganisms, has fast decomposition and digestion of organic matter and high gas production rate, and is mainly suitable for treating high-temperature organic wastewater, such as waste liquid from wineries;
2) Medium temperature fermentation, which is widely used in large and medium-sized biogas projects all over the world;
3) Normal temperature fermentation, simple biogas structure and low cost. Under the current economic conditions in rural areas, this fermentation process is as follows.
Suitable.
Distinguish by the difference of fermentation grade
1) single-stage fermentation, which is characterized in that the fermentation tank is carried out in one fermentation tank. The tank has simple structure, convenient operation and low cost. Most rural biogas digesters in China belong to this type.
2) Two-stage and multi-stage fermentation have long residence time and complete decomposition of organic matter, but the investment is high. Biogas fermentation raw materials
Almost all organic substances in nature can be used as raw materials for biogas fermentation, such as human, livestock, poultry manure, domestic sewage and so on.
Classification:
1) Nitrogen-rich raw materials (human, livestock and poultry manure)
2) Carbon-rich raw materials (crop straws)
3) Others: urban organic garbage, aquatic plants, etc.
Biogas fermentation process types
Proportion of biogas fermentation raw materials
1) C/N ratio, 20-30: 1 is more suitable;
2) concentration, the concentration of fermentation broth is generally 6%;
3) dung-grass ratio: In production and application, dung-grass ratio should be above 2: 1 and not less than 1.
Biogas fermentation conditions
Inoculation * *
1) Function: There must be a large number of strains (inoculum) in biogas fermentation, and the inoculation amount is directly related to biogas production;
2) Source: The urban underground sewage and the sediment at the bottom of the sewage pit at the lake pond contain a large number of biogas microorganisms, and the most direct inoculum in rural areas is the sludge sediment of the biogas digester itself;
3) Inoculation amount: generally, it is 10~ 15% of the fermentation broth. When old biogas fermentation broth is used as inoculum, it is fermentation broth.
Over 30%.
Biogas bacteria
At the beginning of biogas fermentation, there should be enough inoculum containing excellent biogas strains.
Sufficient fermentation raw materials
Material basis of biogas production. When biogas is fermented, the raw materials should be sufficient and properly matched, and a certain ratio of carbon to nitrogen should be maintained.
For example.
Fermentation raw material concentration
6% is more appropriate
Suitable pH value
PH6.8-7.8, alkalinity 3000-8000 mg/L.
Strict anaerobic environment
The biogas digester must be strictly closed except for the inlet and outlet.
comfort temperature
Normal temperature fermentation 10~26? C
Medium temperature fermentation 28~38? C
High temperature fermentation 46~60? C
Biogas fermentation in rural areas generally adopts normal temperature fermentation (biogas digester has simple structure and low cost).
Fermentation start of biogas digester
definition
The process from feeding to normal and stable gas production in newly-built or re-fueled biogas digesters.
Requirements:
(1) Add rich inoculum.
Add 10~30% inoculum, that is, various anaerobic activated sludge containing a large number of biogas fermentation microorganisms.
Suspended sludge, organic wastewater from fermentation and bubbling, pit mud, etc. Can be used as an inoculation.
(2) raw material pretreatment
Inoculation dose
Composting outside the pool
(3) selecting high-quality fermentation raw materials
Cow manure, pig manure, sheep manure or horse manure with suitable organic nutrition has a C/N ratio.
(4) Grasp the concentration of fermentation broth and the amount of water added.
The concentration of fermentation broth refers to the percentage of the total solid (or dry matter) weight of raw materials to the weight of fermentation broth.
The first feeding amount should be 80% of the pool volume, at most 85%, and feeding should be continued every day after operation.
The feeding and water adding amount of 6m ~ 3 pond is 4.8 ~ 5. 1 m3, and that of 8m ~ 3 pond is 6.4 ~ 6.8m ~ 3.
The feed concentration should be controlled at 3 ~ 6%. If the concentration is too high, the feed liquid will be acidified.
The water content of fermentation raw materials is 90 ~ 94%.
(5) adjusting the pH value of fermentation raw materials.
The pH value is preferably 6.8 ~ 7.5. Normally-started biogas digesters will automatically adjust the pH value to achieve balance.
When ph
Normal gas production.
(6) Start the combustion test and deflate.
Choose sunny days to mix the pretreated raw materials with the prepared inoculum and put them in the pool. Add water to seal the activity according to the above requirements.
Guy. The biogas digester has started.
When the water column of the pressure gauge reaches 30 ~ 40 cm * m, it is necessary to deflate and test the fire, and generally it will not ignite. The water column rose to 20 cm again.
When the water is above the water column, deflate and test the fire for the second time. If it can be ignited, it means that fermentation has started normally.
Generally, the pool can be ignited in 3 days.
Daily management of biogas digesters
Diligent in and out.
The three-in-one biogas digester can flush human and animal feces into the pool every day, and the biogas digester without the three-in-one biogas digester is replenished every 3 ~ 5 days.
In order to ensure the normal water level in the biogas digester, the materials should be discharged from the slag extractor or water pressure room in time, but the amount of materials in and out should be kept roughly.
Balance.
Frequently stir the fermentation raw materials in the biogas digester.
Controlling fermentation concentration
Check the pH value regularly.
Strengthen overwintering management
Before winter, the biogas digester should be fully filled with oil, and the entrance and exit of the biogas digester should be covered with plastic, which is larger than the pool area.
Cover, used for cold protection.
Do a good job of safe fermentation
1. Pesticides, heavy metal compounds and other harmful substances cannot be put into the biogas digester to kill biogas bacteria and stop the operation of the biogas digester.
Natural gas production.
If biogas bacterial poisoning is found, half of the fermentation broth in the pool should be taken out and half of the new material should be put in to produce gas normally.
2. Lime, ammonia water for adjusting the pH value of fermentation broth, adding ammonium carbonate and urea to stimulate the production of fermentation gas, etc.
safety measure
1. The fire test at the initial stage of biogas fermentation should be carried out on the lamp furnace, and it is strictly prohibited to test the fire at the gas passage of biogas digester.
2. The import and export of biogas digesters should be stamped to prevent people and animals from falling into it and causing harm.
3. When maintaining the inside of the biogas digester, first open all the covers, take out the feed liquid in the biogas digester, open it for 1 ~ 2 days, blow air into the biogas digester, and discharge the remaining biogas. Then use small animals such as chickens to test. If there is no abnormal phenomenon, you can enter the pool under the full supervision of the guardian outside the pool. Personnel entering the swimming pool must wear safety ropes. If they feel dizzy or stuffy, they should be rescued from the pool immediately. It is forbidden for workers in the pool to use open flames and smoke in the pool.
4, often check whether the gas pipeline, switch, joint leakage, if leakage should be replaced or repaired immediately, so as to avoid fire. Please turn off the switch when the gas is not used. If you smell rotten eggs in the kitchen, you should open the door, open the window, cut off the air supply and people should leave. When the room is tasteless, repair the leaking parts.
5, each biogas digester to install water pressure gauge, often check the pressure change of biogas digester. When the pressure in the tank is too high, use gas and deflate it immediately to prevent the tank cover from bursting and causing accidents. If the pool cover has been washed away, the fireworks nearby must be put out immediately to avoid fire.
6. Under the condition that the movable cover of the biogas digester is sealed, the feeding and discharging speed should not be too fast, so as to ensure that the biogas digester can slowly boost or depressurize. When discharging in large quantities, the biogas conveying pipe should be unplugged at the airway to prevent negative pressure from damaging the biogas digester.
7, in case of abnormal situation, should ask the local rural energy departments to assist in handling.