Biogas is a renewable and clean energy source. Because this gas was first discovered in swamps, it is called biogas. Biogas is a kind of combustible gas produced by the action of biogas bacteria under the condition of the isolation of air and certain temperature, humidity and pH. Biogas is a mixed gas, the main component is methane, the rest is carbon dioxide, oxygen, nitrogen and hydrogen sulfide, of which methane content is about 55% - 70%, carbon dioxide content is about 30% - 45%. The calorific value of methane is 35.9 MJ/m3, and the low calorific value of methane is 20-25 MJ/m3. When mixed with air, it has a blue flame and a temperature of up to 1400°C. It can generate a large amount of heat, and the calorific value per m3 of methane is comparable. In 5500 kcal raw coal 3.3 kg. Rural household biogas digesters use 450m3 of gas per household per year, which saves 5,500 kcal of raw coal by 1.5 tons a year. China's existing 252 million rural households can replace 5,500 kcal of raw coal by 112.5 million tons per year based on 30% penetration rate. . The methane automation plant established in the United Kingdom can replace 25% of UK gas consumption. The United States currently has 24 methane production plants, of which a US farm has built a 30 meter wide, 213 meter long plant that can handle 1,650 tons per day. Manure, which can provide 113,000 cubic meters of methane per day for ranching, enough for 10,000 families.
Zhang Baowen, Vice Minister of Agriculture of the National Agricultural Ecological Environment and Renewable Energy Construction Working Conference, proposed: According to the “National Rural Biogas Development Plan 2003-2010â€, actively promote all types of energy based on rural households and household biogas digesters. The ecological model promotes the construction of ecological homes and achieves the goal of home warmth and cleanliness, high efficiency of garden (park) economy and harmlessness of agricultural production.
The “2003-2010 National Rural Biogas Development Plan†issued by the Ministry of Agriculture proposes that the total number of biogas digesters in the country by the end of 2002 is 11 million households. By 2010, the total number of biogas digesters in the country will reach 50 million or more, and 20% of the country’s farmers can use biogas. From 2003 to 2010, the total investment was 61 billion yuan, and the central government had invested 44.9 billion yuan. The central government's subsidy standards for investors are: 1,200 yuan per household in the northwest and northeast regions, 1,000 yuan per household in the southwest region, and 800 yuan per household in other regions. Since 2005, the universal biogas project has been accelerated from the central policy level to the implementation stage of all provinces and municipalities. It is an important measure taken by the country to resolve poverty and prosperity in the middle and western regions and improve the ecological environment. For biogas construction, various provinces and cities have introduced a series of supporting systems to ensure the smooth progress of biogas projects. Take Henan Province as an example: In 2004, Henan Province explicitly proposed to take biogas project construction as one of the focuses of rural work. There are 30 counties (cities) and 306 villages. 41110 households have undertaken rural biogas projects, and the project approval plan has a total investment of 10.405 million yuan. Yuan, including 32.788 million yuan of central government bond funds. Rural biogas construction has been highly valued by the Party Central Committee, the State Council, and governments at all levels.
China's household biogas utilization technology has been at the leading level in the world. From the domestic point of view, traditional biogas plants are mainly made of concrete. Although the structure and construction technology of the biogas plant have been improved over the years, they are still improving. However, there are still problems such as long construction period, complicated construction process, inconvenient daily management, and high maintenance costs.
Rural household biogas digesters have great potential in domestic and international markets, and are suitable for rural areas in Southeast Asia, South America, and African countries. China has organized technical personnel to provide technical assistance to more than 10 developing countries in the construction of rural methane tanks. They have received great attention and welcome from all recipient countries. In 2005, 30 demonstration sets of rural household biogas digesters in Cambodia were completed. It was highly praised by the Cambodian government.
The mobile solar biogas generator is the latest patented product (patent application number .5) developed by the research group of the solar biogas project of the Beijing Qingda Huamei Environmental Protection and Energy Technology Research Institute. It is composed of two parts: a solar heat collector and a biogas generator. The dry fermentation technology has the advantages of fast gas production, large gas production, and easy maintenance.
First, solar heat collector
Mainly consists of solar collectors and heat pipes. The solar collector is a heat collector, which can be assembled and assembled into different heat collection areas according to the needs. Its main purpose is to collect heat and exchange heat with its associated device. The heat collector is the main heat sink. Components, through a lot of lighting, the absorption of solar energy into heat, through the heat pipe to the biogas tank, increase the temperature inside the tank, so as to achieve the best results can be used throughout the year.
Second, biogas generator
The biogas generator is made of organic fiber cloth and inorganic composite material. It is equipped with air outlet, inlet and outlet, etc., wall thickness is 2-6cm, tensile strength is 93.5pg, bending strength is 100mpg, and there is strong mechanical strength and The elongation rate greatly exceeds the strength of conventional underground methane tanks. The models are available in sizes of 4m3, 6m3, 8m3, 10m3, 12m3 and so on, which can meet the needs of different regions and families. Dry fermentation technology, fast gas production and large gas production completely change the cost of conventional underground methane tank construction. High, large area, long construction period, no gas production in winter and many other problems, can be installed once the material can be continuous gas production 150-180 days, as easy as liquefied petroleum gas, clean and environmentally friendly, life expectancy of up to 20 years.
三ã€Equipment of biogas fermentation raw materials and principle of gas production
1. Raw materials and equipment can be used as raw materials for biogas fermentation. The most commonly used are manure (pig, cattle, sheep, horses, chickens, ducks) manure and various crop straws (straw, wheat straw, corn stalks, rapeseed, soybeans, peanut stalks). ), all kinds of green weeds, rotten vegetables, water hyacinth, waste residue, waste water (distillers grains, tofu waste water) and so on.
2. The type and characteristics of biogas fermentation raw materials can be divided into the following categories according to the chemical properties and sources of biogas fermentation raw materials:
A. nitrogen-rich raw materials; nitrogen-rich raw materials mainly refers to human and animal feces, these raw materials contain more low-molecular compounds, nitrogen content is also high, the carbon, nitrogen ratio is generally less than 25:1, so no pretreatment The fermentation cycle is short, decomposition and gas production rate is relatively fast, is the main raw material of rural biogas.
B. Other types of raw materials: organic wastes, including waste water of various wastes, such as lees, tofu, domestic sewage, and organic waste, various types of straw, grass, weeds, and aquatic plants, and their soft tissues are easily susceptible to microorganisms. Decomposition and utilization.
C. The characteristics of natural gas production from biogas and the influence of temperature: The gas production characteristics of raw materials are an important technical parameter of biogas fermentation. There are many kinds of raw materials for biogas fermentation. Due to their different chemical compositions, the characteristics of each raw material have different gas production characteristics, including the gas production rate and gas production rate of raw materials. The gas production rates at different temperatures for different raw materials are shown in the following table:
Material name medium temperature 15-25°C normal temperature 6-15°C
Pig manure 0.45-0.76 0.25-0.30
Cow dung 0.30-0.68 0.20-0.25
Human feces 0.43-0.71 0.25-0.30
Green weeds 0.44-0.73 0.20-0.25
3. The first phase of the gas production principle, the hydrolysis phase: the insoluble organic compounds and polymers are converted into soluble organics by enzymatic methods;
In the second stage, the acidification stage: fermenting the first stage organics into organic acids;
The third stage, the methanation stage: the production of methane by organic acid fermentation.
IV. Rate of production of biogas feedstock
The rate of gas production refers to the rate at which biogas is generated from raw materials under suitable fermentation conditions. The percentage of biogas produced in a given period of time is expressed as a percentage of the total production. The rate of gas production is related to internal factors such as the nature of raw materials, and is also affected by fermentation. Conditions and effects of inoculum biogas generators and other external factors. Correctly grasping the gas production rate of raw materials is of great significance to reasonable ingredients and daily management.
Gas production rate of commonly used fermentation raw materials (% of total gas production)
Raw material name fermentation time
10 20-30 40-50 60-70 80-90
Human feces 40.7 81.5 94.1 98.2 98.7-100
Pig manure 46.0 78.1 93.9 97.5 99.1-100
Cow dung 34.4 74.6 86.2 92.7 97.3-100
All kinds of weeds ---- 30.3-47.7 78.3-88.7 93.2-96.7 98.9-100
Wheat straw 18.8 30.8-53.7 78.3-88.7 93.2-96.7 98.9-100
Organic waste of all types 10.08 29.4-45.7 77.5-85.3 94.7-97.9 98.8-100
V. The conditions of biogas fermentation and the effect of inoculum on the gas production of similar raw materials
Biogas fermentation is a biochemical process and if it does not have the appropriate conditions, it will not get biogas or get very little.
A. Strict anaerobic conditions: Biogas fermentation microorganisms include two major categories of acid-producing bacteria and methanogens. Acid-producing bacteria (non-producing methanogens) in the acid production stage are mostly anaerobic bacteria, and some are aerobic and facultative anaerobic bacteria. The methanogens in the gas production stage are obligate anaerobic bacteria. Oxygen is needed. Oxygen is poisonous to methanogens. Therefore, good anaerobic conditions must be created. The two major types of biogas constitute a complex ecosystem. When the biogas fermentation is started or a new material is introduced into the generator, a part of the oxygen is brought in, but due to the activity of aerobic bacteria and facultative anaerobes in the sealed generator, this part of oxygen is rapidly consumed, thereby creating a good Anaerobic conditions.
B. Inoculum: Organic wastes are produced by various biogas microorganisms during the anaerobic decomposition of methane. Therefore, in the biogas fermentation, it is extremely important to add enough microorganisms as inoculants (commonly known as strains). The effect of biogas inoculants on the gas production of similar raw materials is detailed in the following table:
Raw material inoculation % Biogas production (ml) Methane content %
Human feces 50 grams 10 1435 48.3
Human feces 50 g 20 3085 55.2
Human feces 50g 50 10093 69.3
Human feces 50 g 150 16030 87.2
Ten advantages of mobile solar biogas generators
1. Advanced technology: dry fermentation technology, gas production speed, large gas production;
2. Design Science: Spherical design, composed of two hemispheres, heat insulation, heat preservation effect, small footprint, convenient loading and slag removal;
3. Good sealing performance: good airtightness, no seepage, no leakage, corrosion resistance, aging resistance, easy maintenance;
4. Good mechanical properties: Earthquake, pressure, ground freezing may damage the underground concrete digester, while FRP products have a certain degree of flexibility and tensile resistance, will not be cracked by frozen soil, suitable for use in northern cold regions;
5. High gas production rate: the thermal conductivity of FRP materials is 1.42KJ (m/h), and the thermal conductivity of concrete is 5.44KJ (m/h), which ensures a high gas production rate, and gas production rate and gas storage capacity increase by 30%. about;
6. Automatic desulfurization: The automatic desulfurizer and gas-water separator can automatically remove sulfur dioxide and water vapor during the reaction to maximize the purity of methane and increase the calorific value (about 8,000 kcal/m3, pure methane 8600-9500). Kcal/m3);
7. Anti-crust technology: Traditional underground methane tanks must rely on artificial mixing to prevent crusting of liquid materials due to design reasons, and biogas generators are scientifically designed to solve this problem.
8. High safety factor: automatic voltage regulation, safety valve, barometer, automatic pressure reducing valve, automatic exhaust valve, safe and reliable;
9. High strength, light weight, simple installation: stackable, easy to transport, install on the ground, that is, safe use, not limited by geographical conditions, easy to move;
10. Low cost and long service life: Each set of production costs between 350 yuan and 400 yuan, the service life of up to 20 years.
Product technology maturity and holding attributes
In 2005, the "biogas generator" demonstration project was established in Hainan Province and north and south of Hebei Province. Both of them achieved good results and were well received by the local government and farmers.
As of December 2006, biogas generators have been widely used in Beijing, Hebei, Shanxi, Sichuan, Yunnan, Hainan, and Jiangxi, and have achieved good results. They are highly praised by local government authorities and farmers.
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