Biomass is the residue of organic matter that comes from living things and is composed of elements such as Carbon, Hydrogen, Nitrogen, Phosphorus, Oxygen, etc. It is a widely available renewable source of energy, which can be converted into useful biofuels, biopower, producer gas and chemicals through the process of gasification, pyrolysis, combustion which involves heat, steam, and oxygen.
Biomass feedstocks includes:
- Forestry wood and residues of wood such as chips, pellets, sawdust, firewood
- Agricultural energy crops and residues: corn stalk, rice hulls and stalks, wheat straw, nutshells, soybeans, bamboo, straws of various pulses and cereals
- MSW: paper, cotton, food, wood wastes
- Animal manure
Biomass gasification (BG) is the thermochemical conversion of organic materials in closed, pressurized vessels at high temperatures. It is a simple, reliable, and low-cost process, useful in producing biofuel, hydrogen, syngas, and electricity. Biomass gasification does not add significantly to the carbon levels as the biomass used for feedstock has already absorbed carbon dioxide from the atmosphere. Besides being carbon neutral, biomass gasification can result in carbon negative by capturing carbon dioxide.
- Based on the moisture content, it is divided into low moisture biomass and high moisture biomass. Low moisture biomass can be used in gasification, combustion, and other thermochemical conversion process while high moisture biomass can be used in biochemical conversion processes such as fermentation and anaerobic digestion, involving microbes.
- Gasification: In this process, the wet biomass is dehydrated by exposing to a low temperature of 150 degrees Celsius and then heated to a high temperature of 800 to 900 degrees Celsius, along with an oxidising agent in a gasifier. The dry waste residue first undergoes degradation with increased heat and then goes through the volatilization and break down of solid complex hydrocarbons into combustible gas like syngas, hydrogen, tar, etc. Syngas can be treated to produce more hydrogen and impurities can be removed by adsorption shift or membrane separation to get hydrogen with 99.9% purity.
Advantages:
- Conversion of Waste to Useful Energy: Biomass gasification can effectively convert various types of waste into valuable energy vectors, including electricity, hydrogen gas, and biofuels. This supports the creation of a circular economy by repurposing waste into useful resources.
- Reduced Landfill Dependence: In countries like India, where a significant portion of waste ends up in landfills, biomass gasification offers an alternative that reduces the need for landfill space. This, in turn, can help mitigate groundwater pollution and decrease waterborne diseases associated with traditional landfill practices.
- Mitigation of Stubble Burning: Biomass gasification technology can be deployed in areas where stubble burning is a common practice. By providing an alternative use for agricultural residues, it helps address environmental concerns associated with stubble burning.
Challenges:
- Feedstock Characteristics: Biomass feedstock for gasification often has high moisture content and lower heating value compared to coal. This variability in feedstock composition can affect the energy output and efficiency of the gasification process.
- Local Feedstock Availability: The operational barrier of ensuring a consistent and locally accessible supply of biomass feedstock remains a challenge. Aggregating and transporting feedstock to the processing unit can be logistically complex.
- Technical Challenges: Gasification may lead to the formation of solid tar during the cracking of pyrolysis volatiles. This poses technical challenges such as equipment and pipeline clogging, potentially reducing the overall system efficiency.
