Research progress of biomass conversion and utilization technology

1. Characteristics of biomass energy

Biomass is a complex material consisting mainly of cellulose, hemicellulose and lignin, with small amounts of tannins, fatty acids, resins and inorganic salts. This renewable raw material has great potential for power generation and the production of high value-added chemicals. As a new renewable energy, biomass energy has many advantages compared with other fossil energy sources:

1) Renewable. Biomass energy can be regenerated through the photosynthesis of plants, compared with coal, oil, natural gas and other fossil energy, is a renewable energy, and rich resources, can ensure the permanent use of energy.

2) Low pollution. The non-metallic content of sulfur and nitrogen in biomass is low, and the sulfur compounds and nitrogen oxides produced by combustion are less. Since the amount of carbon dioxide absorbed by biomass during growth is the same as the amount of carbon dioxide emitted, the net emissions of carbon dioxide to the atmosphere are almost zero when used as fuel, which can effectively reduce carbon dioxide emissions and the production of acid rain phenomenon.

3) The total quantity is very abundant. Biomass is the world's fourth-largest carbon-containing energy source after coal, oil and natural gas. Biomass energy plants (referred to as "biomass resources") distribution area is very wide, with the continuous development of agriculture and forestry, biomass resources will be more and more. Biomass resources can increase rapidly through large-scale planting, which can ensure its yield.

4) Security. The use of biomass energy is quite safe, and there will be no major safety accidents such as explosions and leaks.

5) Wide application. It is used in many fields of national economy such as biogas, solid fuel compression molding, pyrolysis gasification to produce gas, power generation, fuel alcohol production, biodiesel and so on.

In terms of the current international situation, there is an urgent need to adopt unconventional sustainable energy sources to meet the growing demand for liquid fuels. The use of biomass for the production of biodiesel, biofuels and ethanol is approaching commercialization. The development of biomass energy will play a positive role in ensuring energy supply, reducing dependence on oil market and stabilizing economic development, and is an effective new way to solve future energy problems. Many experts point out that the 21st century will be the era of biomass energy.

2. Utilization technology of biomass energy

The biggest advantage of biomass is that it is the only renewable resource containing carbon, and liquid and gas fuels can be produced by thermochemical conversion, biochemical conversion and photochemical conversion, involving pyrolysis, gasification, liquefaction, molding and direct combustion technologies. Clean fuels that are easy to store, transport and use are available in physical forms of liquids, solids and gases. Figure 1 lists the various biomass energy utilization technologies.

2.1 Biomass direct combustion technology

2.1.1 Biomass direct combustion fluidized bed technology

Biomass direct combustion technology is mainly divided into stove combustion, boiler combustion and dense forming technology. The technologies involved are biomass direct combustion fluidized bed technology and biomass direct combustion layer combustion technology.

Many foreign companies such as the United States Idaho Energy Products Company, the United States B&W, the United States CE company and so on the use of fluidized bed technology to develop fluidized bed power generation boilers to treat biomass has a considerable scale and certain operating experience. In Sweden, branches and leaves are used as fuel for large fluidized bed boilers, and the thermal efficiency of the boilers has reached 80%. In Denmark, hay and coal are burned according to a mass ratio of 6:4 using a high-rate circulating fluidized bed boiler, with a thermal power of 80MW and a boiler output of 100t/h. Liu Hao, Lin Zhijie et al. improved the traditional fluidized bed combustion boiler according to the physical and chemical properties of rice husk and considering its combustion characteristics. With a unique combustion and air distribution method, a boiler with good fluidization performance, stable combustion and easy coking has been developed.

Chen Guanyi et al. cooperated with Wuxi Boiler Factory to design and develop a pneumatic conveying device for transporting rice husks, which not only has large throughput but also delivers safety, for 35t/h rice husk fired fluidized bed boiler. The unique design of the conveying device not only avoids the phenomenon of feed interruption, but also reduces the wear of the buried pipe in the bed and the ash accumulation on the heating surface. At the same time, the fuel application range of the boiler is expanded. The future development of biomass boilers depends on the fossil fuel market and decisions about the biomass market.

2.1.2 Direct combustion layer combustion technology

2.1.2.1 Development and utilization technology of agricultural and forestry wastes