Biomass energy is a kind of new energy that stands out. It not only has energy function, but also can be engaged in the material production of biochemical products; it can not only relieve energy and environmental pressure, but also a renewable energy, and it is also the only one. Renewable carbon source.
Biomass energy is the most extensive renewable energy source in the world. The current use of biomass energy by humans includes crop stalks and firewood that are directly used as fuel; agricultural and forestry waste, animal manure, garbage, and algae are indirectly used as fuel. They produce biogas through the action of microorganisms, or use pyrolysis to produce liquid and gas fuels, or produce biochar.
Biomass energy includes biodiesel, bioethanol, bio-particle fuel, bio-based chemical products, etc. Biodiesel is a liquid fuel made from seed oils, such as soybeans and rapeseeds and other oil crops, oil palm and pistacia tree fruits, and engineering microalgae and other oily aquatic plants. Biodiesel is an environmentally friendly fuel oil that can replace diesel and is a typical "green energy". Bioethanol is produced by the hydrolysis and fermentation of starch. It can be blended into gasoline or directly used for driving. It is currently a kind of bioenergy that can be produced on a large scale and widely used. Bio-particle fuel is the use of shrubs, forestry wastes and other compression molding to replace coal and petroleum combustion to generate electricity.
It is estimated that the total amount of biomass produced on the earth through photosynthesis alone amounts to 144 to 180 billion tons (dry weight) each year, and its energy is approximately 3 to 8 times the total energy consumption of the world in the early 1990s. However, it has not been used rationally by people, and most of it is directly used as fuelwood, which is inefficient and affects the ecological environment. The utilization of modern biomass energy is the production of methane through anaerobic fermentation of biomass, the use of pyrolysis to generate fuel gas, bio-oil and biochar, the use of biomass to produce ethanol and methanol fuel, and the use of bioengineering technology to cultivate energy plants. Develop energy farms.
Relevant experts estimate that biomass energy is very likely to become a component of the future sustainable energy system. By the middle of the next century, various biomass alternative fuels produced by new technologies will account for more than 40% of the world's total energy consumption.
Biomass energy can be converted into conventional solid, liquid and gaseous fuels in the process of utilization.
1. Solid biomass fuel
Currently, solid biomass fuels mainly include:
① Biomass directly burned;
②Compression molding fuel;
③The fuel used for mixed combustion of biomass and coal.
(1) Directly burned biomass
The direct combustion of biomass is a very old way of energy utilization. Using organic matter such as firewood, stalks and animal manure as fuel, and then through the transformation of the structure and combustion methods of traditional stoves, the thermal efficiency of rural household stoves/Kangs can be improved. The key to the design of a firewood-saving stove is to let the firewood burn as much as possible and to make the most of the heat generated. For example, in rural Shaanxi, the original large-mouth stove consumes a lot of firewood and has a low heat utilization rate. Experiments have shown that if it is changed to a small-mouth stove, it can save 30% of firewood, and if the wind box is added, it can save 60% of firewood than a large-mouth stove. The thermal efficiency of firewood-saving stoves is generally 1-2 times higher than that of old stoves, saving fuel by 1/3~1/2, and saving time.
In areas where firewood-saving stoves have been popularized, the problem of fuel shortage has basically been solved, which has greatly reduced the phenomenon of cutting trees and shoveling turf uphill, protecting forests and vegetation, and restoring the virtuous cycle of natural ecology.
(2) Compression molding fuel
Biomass compression and compaction molding technology is a technology that presses various types of biomass into dense rods, blocks, or pellets, such as shaped feeds or shaped fuels, under certain temperature and pressure. Molded fuels can replace coal and gas as civil fuels for cooking and heating, and can also be used for industrial heating and power generation.
The promotion of compression and compaction molding technology can solve the problem of waste and incineration of straw resources; it can improve the efficiency of straw resource utilization and expand the scope of application; it can improve the rural living environment, improve the quality of life of farmers, increase farmers' income, and provide more employment opportunities; it can alleviate China's fossils The energy supply is tight, and the pollution of fossil energy to the environment is reduced. However, this kind of compression molding fuel is burned with slightly improved traditional equipment after solidification of biomass. It can increase the energy density. However, due to the problem of compression technology, the compression cost of the molding fuel is relatively high.
(3) Fuel for mixed combustion of biomass and coal
The mixed combustion of biomass and coal is mainly used to generate electricity. There are two main methods for this mixed combustion of fuel to generate electricity: one is to directly burn biomass raw materials with coal in a coal-fired boiler to generate steam, and the steam drives a steam turbine to generate electricity; The other is that biomass raw materials are first gasified to generate combustible gas, which is then mixed with coal and burned to generate electricity.
At present, the original boiler equipment can be used for the mixed combustion of coal and biomass with a biomass ratio of less than 8%; while the biomass ratio is higher than 15%, the original technical equipment needs to be modified. The key point of the coal and biomass combustible gas mixed combustion technology lies in the biomass gasification device. The quality of the gasification equipment determines the quality of the mixed combustion.
2. Liquid biomass fuel
Liquid biomass fuel refers to the use of biomass resources to produce fuel ethanol and biodiesel, etc., to replace gasoline and diesel produced from petroleum resources, and is one of the important directions for the development and utilization of renewable energy.
(1) Fuel ethanol technology
Fuel ethanol is the ethanol used as engine fuel. Compared with ordinary edible alcohol, its water content is lower, not more than 0.5%, and its purity requirements are also lower. Under the impact of the oil crisis, fuel ethanol, as an efficient and clean renewable energy source, has become a focus of attention and research by scientific and technological workers and business circles in various countries.
The production of ethanol mainly adopts the biological fermentation method. The raw materials for ethanol production by fermentation are mainly starchy crops (corn, wheat, sorghum, cassava, etc.), sugary crops (sugar cane, sweet sorghum, sugar beet, etc.) and fibrous raw materials (straw, wood chips, crop hulls, etc.). These raw materials are processed and processed into sugars that can be used by microorganisms. After fermentation, the alcohol in the fermented mash is extracted. The characteristic of this process is that the product purity is relatively high, and the raw materials are renewable.
(2) Biodiesel technology
Biodiesel is another liquid biomass fuel besides fuel ethanol. It refers to the methyl ester or ethyl ester fuel made from oil crops (such as jatropha, pistacia, etc.), wild oil crops and other vegetable fats, as well as animal fats, waste catering oil, etc. through the transesterification process. Biodiesel can replace some fossil resources such as petroleum, and has the characteristics of low greenhouse gas emissions and easy biodegradation of emissions.
After years of research and development, biodiesel production technology has formed a relatively complete technical system and method, covering chemical catalyst method, biological enzyme catalyst method, catalyst-free method (under high temperature and high pressure), normal pressure method and pressurized method. French production technology. The early pyrolysis method was the simplest, and ordinary households could carry out small workshop production.
At present, in the research and development and utilization of biodiesel, it is necessary to improve the conversion process of biodiesel to biodiesel, and to seek cheap sources of biodiesel. Woody oil plants (such as Camellia oleifera, Jatropha, etc.) are highly resistant, easy to manage, and have high oil yield. They have huge development potential and broad development prospects. They are irreplaceable for the development of the edible oil industry and energy oil in the future The role of.
3. Gaseous biomass fuel
Gaseous biomass fuels include biogas, biomass gasification, etc.