Biomass sources are converted into other forms of energy such as electricity, heat, steam, and fuel through two main technologies: thermochemical and biochemical.

1. Forms of biomass energy

Biomass energy is divided into two basic levels:

  • Primary: Biomass energy is generated from the accumulation of solar energy through the natural photosynthesis process of green plants.
  • Secondary: Biomass energy is generated from the decomposition and conversion of all organic waste in human daily activities and the natural activities of organisms.

Biomass energy exists in three forms: solid, liquid, and gas.

- Solid biomass (biomass feedstock): These are organic materials in solid, powdered, or compressed pellet form that release energy through combustion.

  • Examples: Straw, bagasse, wood chips, wood pellets, compressed straw pellets.

- Liquid biomass (biofuels): This is the form of biomass that is processed and converted into liquid mixtures in water or other solvents, used to produce biofuels, or in other industrial chemical production processes.

  • Examples: Vegetable oil, methanol fuel, ethanol, biodiesel.

- Gaseous biomass (biogas): This type of gas is naturally formed at landfill sites, household waste, animal manure, manure sludge, or produced through gasification methods from organic materials, which can be recycled and used as fuel.

  • Examples: Methane gas, biogas, hydrogen.


2. The purpose of converting energy from biomass

Biomass can be converted into various useful forms of energy using several different processes. Factors influencing the choice of conversion technology include the type and quantity of biomass feedstock, technical requirements of the product, economic conditions, and other factors specific to each project. Biomass can be converted into three main types of products, of which two are related to energy: electricity, heat, and biofuels, while the other type is chemical feedstock.


There are three generations of biofuels:

- First-generation biofuels are fuels derived from food crops: sugarcane, wheat, barley, corn, potatoes, soybeans, sunflower, coconut, etc.

- Second-generation biofuels are produced from materials containing lignocellulose and residual biomass waste from agriculture, forestry, industrial production, and municipal solid waste (MSW). This promising solution aims to minimize environmental issues related to emissions by converting waste into useful bioenergy.

- Another type of biomass called algae is used as feedstock for third-generation biofuels. This rapidly growing source of raw material has a high potential for producing a large amount of suitable fats for the production of biodiesel and various other biofuels.

The conversion of biomass into energy is carried out using two main technologies: thermochemical and biochemical. Conversion by thermochemical methods involves the decomposition of organic components in biomass using heat, while biochemical methods use microorganisms or enzymes to convert biomass into useful energy.

3. Methods of biomass energy conversion

3.1 Thermochemical Conversion

Conversion through thermochemical technology involves high-temperature chemical conversion processes that require breaking down and restructuring organic matter into solid biochar, synthetic gas (syngas), and oxygen-enriched liquid bio-oil.

  • Combustion

Combustion is a common method of converting biomass energy by burning organic materials. It is widely used to convert the chemical energy stored in biomass into heat, steam, mechanical power, or electricity. While all biomass can be directly combusted, in reality, combustion occurs most effectively with biomass containing less than 50% moisture. Biomass with higher moisture content is more suitable for other biochemical conversion methods. During combustion, biomass is heated to about 200 - 320°C, causing it to dry completely, losing about 20% of its initial weight while retaining 90% of its energy. Biomass utilization for combustion ranges from small-scale residential heating to industrial plants with capacities ranging from 100-3000 MW.


  • Gasification

Biomass gasification technology involves thermochemical reactions at high temperatures (500 - 1,400°C) in oxygen-deficient conditions (primary combustion), producing a gas mixture (CO, H2, CH4). This gas mixture is combusted in the secondary stage upon contact with oxygen at sufficiently high temperatures (secondary combustion), resulting in two products: syngas and biochar. Syngas are burned to generate heat for industrial applications, and households, and are used in the production of synthetic compounds such as ammonia, methanol, and dimethyl ether. Biochar is used as a soil conditioner, fertilizer, water filtration medium, and other environmental remediation applications. Gasification is considered an energy-independent, energy-balanced process and is ideal for converting various biomass feedstocks from agricultural and industrial waste to food waste and farm waste.


  • Pyrolysis

Pyrolysis is the thermal decomposition of biomass in the absence of oxygen, with temperatures ranging from 350 to 550°C, reaching up to 700°C. Pyrolysis decomposes organic matter into a mixture of solids, liquids, and gases. The difference between gasification and pyrolysis is that gasification produces combustible fuel gas, while pyrolysis produces liquid fuel called bio-oil (biofuel) that can replace fossil fuels for heating or electricity generation. The produced bio-oil can be stored directly and transported easily. Currently, liquid production from the pyrolysis process is gaining more attention due to its energy efficiency, high fuel yield of up to 75% by weight, cost optimization, and environmental friendliness.


  • Liquefaction

Liquefaction is the conversion of biomass into stable liquid hydrocarbons using low-temperature and high-pressure hydro conditions. Liquefaction and biomass pyrolysis are two techniques for producing liquid products such as bio-oil or crude bio-oil. There are two liquefaction methods:

- Thermochemical liquefaction involves producing bio-oil at low temperatures and high pressures with the presence of hydrogen (with or without a catalyst).

- Hydrothermal liquefaction (hydro-pyrolysis) uses water at moderate temperatures ranging from 250 - 374°C and operating pressures from 40 - 220 bar to convert biomass into bio-oil. This method is often applied to high-moisture biomass to minimize costs for drying or water separation. Various feedstocks, such as woody biomass, waste, and algae biomass, are suitable for producing bio-oil through hydrothermal liquefaction.


3.2 Biochemical Conversion

Biochemical conversion involves the use of specialized enzymes/microorganisms to convert biomass into useful energy.

  • Anaerobic Digestion

Anaerobic digestion directly converts organic matter into biogas. This is primarily a mixture of methane (CH4) and carbon dioxide (CO2) with a small amount of hydrogen sulfide (H2S). Biogas contains energy content ranging from 20 - 40%, with lower heat values compared to biomass. Anaerobic digestion can handle wet biomass with a moisture content of up to 90%. It is widely used in livestock waste treatment, where high organic matter content is present. The biogas produced is used for cooking, electricity generation, and heating and has become an effective solution in many agricultural countries worldwide. Biogas can also be used directly for engines and gas turbines. However, to upgrade its quality closer to natural gas, CO2 needs to be removed.


  • Fermentation

Fermentation is widely used to produce bioethanol from high-sugar crops such as sugarcane, sugar beets, or starchy crops like corn, wheat, and barley, using yeast or bacteria. The cellulose, hemicellulose, and starch components in biomass are converted by enzymes into sugars, which are then fermented into ethanol. It is estimated that every ton of dry corn can produce about 450 liters of ethanol. By-products from the fermentation process are used as animal feed. In the case of converting sugarcane, bagasse can be used as fuel for boilers or subsequent gasification processes. Fermentation of biomass such as wood and grasses is more complex due to longer polysaccharide chain molecules and may require acid or enzyme hydrolysis before fermentation. However, this hydrolysis technique is still in the experimental stage. The most common hydrolysis methods use acid/alkali and enzymes. Acid treatment is cheap and fast but may convert sugars into unwanted forms. In contrast, enzymatic treatment is efficient and does not produce unwanted by-products, but enzymes are expensive and slower. Crude alcohol (10 - 15% ethanol) produced needs to undergo distillation to concentrate. The remaining solid residue can still be processed into valuable products using liquefaction, gasification, or pyrolysis methods with microwave assistance.


  • Transesterification

Using potential biomass, such as those containing a lot of cellulose, to produce biofuels is more complex because the properties and efficiency of extracted oil need to be adjusted to match the hydrocarbon-based fuel properties. Biofuels derived from biomass such as lignocellulosic materials often face issues of high viscosity, low stability, and unsaturation. These issues can be addressed through various pre-treatment methods, with esterification being the most feasible method. Transesterification is the exchange reaction between alcohol and ester, where fats and oils are converted to form esters and glycerol, with the presence of a catalyst. The physical properties of fatty acid methyl esters (FAME) produced thereafter will be equivalent to commercial petroleum diesel fuels, and the by-product glycerol also holds commercial value.



There are various biomass conversion technologies, and the choice of technology depends on the feedstock and desired end products. Further research has shown that while all technically feasible processes can produce suitable fuels, gasification is the only commercially viable process. This finding is based on considering the overall conversion efficiency of gas production through the gasification process and has been demonstrated using gasification products for biomass fuel development. Pyrolysis is a rapidly developing technology with great potential, but it is more suitable for producing feedstocks for diesel engines and gas turbines. Anaerobic digestion also has its position as a conversion process to provide gas fuel and is a treatment method for high-moisture industrial organic waste, such as wet biomass waste or sludge...


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