According to the different sources of biomass energy, biomass suitable for energy use can be divided into five categories: forestry resources, agricultural resources, domestic sewage and industrial organic wastewater, municipal solid waste, and livestock and poultry manure.
1. Forest Energy
Forestry biomass resources refer to some residues in the process of forest growth and forestry production. The collection and utilization of these residues can provide biomass energy, including firewood, scattered wood in forest tending and thinning operations, and residues. Branches, leaves and sawdust, etc.; branches, sawdust, sawdust, tips, slabs and truncations in the process of timber harvesting and processing; wastes from forestry by-products, such as shells and cores.
Forest energy occupies an important position in China’s rural energy. Around 1980, the country’s rural energy consumption of forest energy was about 100 million tons of standard coal, accounting for more than 30% of the total rural energy consumption. In the hills, mountainous areas, and forest areas, rural life energy is used. More than 50% of these are provided by forest energy.
Fuelwood comes from the pruned branches during the growth of trees, leftover materials from wood processing, and firewood forests that provide fuelwood. In 1979, the country reasonably provided 8.85 million tons of fuelwood, and the actual consumption was 181 million tons; in 1995, the reasonable provision of forest energy was 14.322.9 million tons, of which the fuelwood forest could provide more than 20 million tons of fuelwood, and the country’s rural areas consumed 21.39 million tons. The gap is about 70 million tons. According to incomplete statistics, China can obtain about 40 million cubic meters of surplus from forest logging and wood processing every year.
2. Agricultural Resources
Agricultural biomass energy resources refer to agricultural crops (including energy crops); wastes in the agricultural production process, such as crop stalks (corn stalks, sorghum stalks, wheat straws, rice straws, bean straws, and cotton stalks) left in the farmland when crops are harvested Etc.); waste from the agricultural processing industry, such as the remaining rice husks in the agricultural production process. Agricultural crops, or energy plants, generally refer to various plants used to provide energy, usually including herbaceous energy crops, oil crops, hydrocarbon-producing plants, and aquatic plants.
Crop straw is a by-product of agricultural production and a traditional fuel in rural China. Straw resources are closely related to planting production. According to statistical data in 1995, China’s annual output of crop straw is 604 million tons, of which about 15% are lost from fertilization and collection, and 513.4 million tons remain. The available crop straw is 513.4 million tons. In addition to being used as feed and industrial raw materials, most of the rest can also be used as fuel for cooking and heating of farmers. At present, the consumption of straw as energy in rural areas in the country is about 286.2 million tons, but most of them are in inefficient use, that is, directly burned on wood stoves, and the conversion efficiency is only about 10%-20%.
With the development of the rural economy and the increase of farmers' income, regional differences are gradually expanding, and the proportion of commercial energy used in rural life is increasing at a relatively rapid rate. In fact, the increase in farmers' income and the difficulty in obtaining commercial energy can both become an opportunity and motivation for them to switch to commercial energy. In rural areas closer to commercial energy production areas or rich rural areas, commercial energy (such as coal, liquefied petroleum gas, etc.) has become its main cooking energy. The straw used in the traditional way is the first object to be replaced, causing the amount of straw discarded for direct burning in the field to increase year by year. In many areas, the amount of discarded straw has accounted for more than 60% of the total amount of straw, which harms the environment and wastes resources. Therefore, it is imperative to accelerate the conversion and utilization of high-quality straw.
In recent years, energy crops that mainly provide energy, including herb energy crops, oil crops, hydrocarbon plants and aquatic plants, have gradually become a major resource of agricultural biomass energy. Taking into account the characteristics of the availability of crop straw, it is estimated that the amount of crop straw resources that can be converted into energy from China's agricultural biomass resources is about 300 million tons, which is equivalent to 150 million tons of standard coal. In addition, the development and utilization of energy crops in China has also begun. Relevant Chinese departments and scientific research units are organizing a large number of experts to select, cultivate and test energy crops under the principle of "not competing for food or land with people." The development and research of energy conversion technology and equipment, and has achieved phased results.
3. Domestic sewage and industrial organic wastewater
Domestic sewage is mainly composed of various drainages from urban residents' life, commerce and service industries, such as cooling water, bathing drainage, toilet drainage, laundry drainage, kitchen drainage, fecal sewage, etc. Industrial organic wastewater is mainly wastewater discharged from the production process of alcohol, wine, sugar, food, pharmaceutical, papermaking and slaughtering industries, which are rich in organic matter.
After surveys and statistics on the national statistical yearbook and publicly published data of more than 20 major industrial industries, it is known that China's major industrial enterprises discharge approximately 850 million tons of organic wastewater and 25 million tons of waste residues each year.
4. Municipal solid waste
Municipal solid waste is mainly composed of solid wastes such as urban household garbage, commercial and service industry garbage and a small amount of construction industry garbage. Its composition is relatively complex, and is affected by factors such as the average living standard of local people, energy consumption structure, urban construction, natural conditions, traditional habits, and seasonal changes.
With the expansion of the scale of cities and the acceleration of urbanization, the amount of garbage generated and accumulated in China's cities and towns has increased year by year. In 1991 and 1995, the amount of industrial solid waste generated nationwide was 588 million tons and 645 million tons, respectively. During the same period, the amount of urban domestic waste increased at a rate of about 10% per year. In 1995, the total number of cities in China reached 640, and the garbage removal volume was 107.5 million tons.
The composition of waste in China’s large cities has shown a trend of transition to a modern city, with the following characteristics: First, the organic content in the waste is close to 1/3 or even higher; second, food waste is the main component of organic matter; third, High content of easily degradable organic matter. At present, the calorific value of urban waste in China is about 4.18 MJ/kg (1000 kcal/kg).
According to the analysis of relevant experts, in 2008, China's urban waste removal and transportation volume was nearly 200 million tons. Considering that the current collection rate of urban waste is less than 50%, the amount of resources available as biomass energy conversion is about 100 million tons.
5. Livestock and poultry manure
Livestock manure is the general term for livestock and poultry excrement. It is the conversion form of other forms of biomass (mainly grain, crop straw and pasture, etc.), including feces and urine discharged by livestock and poultry, and their mixture with bedding. Livestock manure is a very good and important biomass resource. Except for a small amount of direct combustion in pastoral areas, livestock manure is mainly used as a raw material for biogas fermentation. Biogas is a kind of combustible gas converted from biomass energy, which can usually be used by farmers for cooking, lighting, etc.
The main livestock in China are chickens, pigs, and cattle. Based on such factors as breeds, weight, and excretion of manure, the amount of manure resources can be estimated. According to calculations, the current total amount of livestock manure resources in China is about 850 million tons, which is equivalent to more than 78.4 million tons of standard coal, of which 578 million tons of cow manure, which is equivalent to more than 48.9 million tons of standard coal; and 259 million tons of pig manure, which is equivalent to more than 22.3 million tons. Standard coal, 14 million tons of chicken manure, equivalent to more than 7.17 million tons of standard coal. Among the manure resources, manure from large and medium-sized farms is more convenient for centralized development and large-scale utilization. There are currently more than 6,000 large and medium-sized cattle, pig, and chicken farms in China, which discharge more than 800,000 tons of waste water and flush sewage every day. The country's annual waste water resources are 160 million tons, equivalent to 11.575 million tons of standard coal.
According to the calculation of the stock of live pigs, chickens and cattle in China in 2008, the manure emissions of major livestock and poultry nationwide are more than 3 billion tons, and their dry matter weighs more than 500 million tons. According to predictions by relevant experts, the potential for biogas production from livestock manure in China in 2008 is about 220 billion cubic meters. According to the analysis of experts from relevant departments, the current potential of China's main biomass resources that can be transformed into energy is about 800 million to 1 billion standard coal per year.