Raw materials from nature and waste products from wood, agriculture, and industry undergo the process of locking to create biomass energy. Biomass energy has solved many agricultural, industrial and environmental problems. One of the most popular methods to convert biomass energy is thermal-chemical technology. So what are the methods to convert biomass energy? How to convert biomass energy by thermal-chemical technology? Let’s find out about it in this article.
Methods to convert biomass energy
The conversion of biomass to energy includes several different methods depending on the source of raw materials, conversion technologies, application forms of biomass energy, and national economic conditions.
Biomass raw materials can be produced from specialized energy crops, short-term fuel crops, forest products, and agricultural residues such as tree trunks, firewood, and straw. It can also derive from industrial and organic waste or animal manure. In all cases, biomass feedstocks are collected, transported, and stored before being processed into a form suitable for processing. Accordingly, biomass energy is a form of renewable energy. When used, will help reduce the harmful effects of the current exploitation and use of fossil fuels. However, as with any other energy source, biomass energy also has certain limitations. Besides, it must compete not only with fossil fuels but also with other renewable energy sources from wind, solar and tidal power.
Biomass can be converted into useful forms of energy using a variety of different processes. Various factors affect the choice of conversion technology. These elements are the type and quantity of biomass raw materials, technical requirements of products, economic conditions as well as other factors for the implementation of each project.
Biomass can be converted into three main types of products. Two of them are related to energy, electricity/heat, and transport fuels, and another is chemical feedstocks.
Biomass to energy conversion uses two main technologies: thermochemistry and biochemistry. In addition, there is another way to convert it into energy that is biofuel production. However, biofuel is not yet popular at present. Nonetheless, with increasing pressure on emission reduction and environmental pollution reduction, especially in big cities, biofuel might be a potential alternative shortly.
Currently, there are four forms of thermal-chemical conversion: combustion, pyrolysis, gasification, and liquefaction. Biochemical conversion includes two main forms: digestion and fermentation.
Biomass energy conversion using thermal-chemical technology
Combustion
Biomass incineration is widely used to convert chemical energy stored in biomass into heat, mechanical or electrical energy, by using equipment such as stoves, furnaces, boilers, steam turbines, and generators. The combustion of biomass can produce hot gas at a temperature of about 800-1000°C. It is possible to burn any kind of biomass fuel. However, in practice, combustion only occurs with biomass with moisture content less than 50%. Biomass with high moisture content is more suitable for biological conversion processes.
The usage scale of burning biomass is very diverse, from residential heating to industrial plants with a capacity of 100-3000 MW. Combining biomass combustion with coal combustion in power plants is an attractive option because of its high energy conversion efficiency. Meanwhile, the biomass energy conversion efficiency of power plants that only burn biomass is only 20% to 40%. This form also does not convert biomass into fuel suitable for use in internal combustion engines or gas turbines.
Gasification
Gasification is the conversion of biomass into a combustible gas mixture by partial oxidation of the biomass at high temperatures, usually in the range of 800-900°C. This gas can be burned directly or used as a fuel for internal combustion engines and gas turbines. Products from this gas can also be used as a syngas feedstock in the production of chemicals such as methanol.
Biomass-integrated gasification combined cycle (BIG/CC) enables gas turbines to convert gaseous fuels into electricity with higher conversion efficiency. Another advantage of the BIG/CC system is that the gas is cleaned before burned, resulting in less use of expensive gas cleaning equipment, and the reduction of gas volume to be cleaned. The integration of gasification and utilization of combustion heat will ensure a high conversion efficiency of 40-50% for a plant with a capacity of 30-60 MW. Currently, BIG/CC technology is only at the testing stage. In the future, the production of syngas from biomass will allow producing methanol and hydrogen to be used as fuel for transportation.
Pyrolysis
Pyrolysis is the conversion of biomass into a liquid, solid, or gas by heating the anaerobic biomass to a temperature of about 500°C.
It is mainly used to produce bio-oil. Using flash pyrolysis enables the conversion of biomass to raw biofuels with an efficiency of up to 80%. Bio-oil can be used in engines and turbines. The use of bio-oil as feedstock for refineries is also being considered. However, the problems of conversion and the use of bio-oil products still need to be studied further, such as low thermal stability or engine corrosion. Currently, biodiesel can be used for certain applications by reducing the amount of oxygen and removing alkalis by hydrogen.
Other transitions
Other processes for bio-oil production can be accomplished by hydro-thermal upgrading (HTU) and liquefaction.
HTU is converting biomass in a humid environment at high pressure to partially oxidize hydrocarbons. However, this process is still in the experimental phase.
Liquefaction is the conversion of biomass into stable liquid hydrocarbons using low temperature and high hydrogen pressure. Consequently, interest in liquefaction is low because reactors and fuel supply systems are much more complex and expensive than pyrolysis.
