Boiler Biomass Gasification
Gasification of Biomass Boilers
Biomass Definition
Biomass is a form of renewable energy derived from recently deceased organisms, in contrast to fossil fuels. Common biomass sources include wood fuel, waste, and alcohol. This energy form is considered renewable because plants can regenerate on the same land. Currently, wood is the predominant biomass source, accounting for almost 90% of biomass fuel in the United States. Biomass is deemed carbon-neutral, absorbing carbon from the atmosphere during plant growth and releasing it when burned. This closed carbon cycle theoretically prevents an increase in atmospheric carbon dioxide (CO2) levels. Biomass encompasses various organic materials such as wood, agricultural waste, alcohol, and refuse.
Sources of Biomass
In Indonesia, firewood, twigs, agricultural and plantation waste, as well as household, municipal, and industrial waste, hold substantial potential as biomass energy sources. These sources can be utilized for electricity generation through direct energy conversion processes and intermediary energy conversion.
Biomass, originating from photosynthesis, includes materials left over from plants or animals, like wood from forests, agricultural waste, and organic human and animal waste. The sun's energy is stored in biomass through photosynthesis, converting carbon dioxide into carbon molecules (such as sugar and cellulose) in plants. Different types of biomass have varying energy content, for instance, green wood has 8 MJ/kg (equivalent to 2.22 kWh), oven-dried material has 20 MJ/kg (equivalent to 5.56 kWh), and methane gas has 55 MJ/kg (equivalent to 15,277 kWh).
Biomass Conversion
Historically, our ancestors used biomass boilers to produce heat, burning biomass directly. In modern applications, combustion heat is converted into electricity through turbines and generators. The combustion of biomass produces steam in the boiler, which, in turn, drives the turbine connected to a generator. To enhance the benefits of biomass as fuel, various technologies are employed.
Carbonization is the process of converting organic materials into charcoal. This process releases combustible substances like CO, CH4, H2, formaldehyde, methane, formic, and acetic acid, along with non-combustible substances like CO2, H2O, and liquid tar. The gases released have a high heating value and can be used to meet the heat requirements of the carbonization process.
Anaerobic Digestion is a process involving microorganisms without oxygen in a digester. It produces product gas in the form of methane (CH4) and carbon dioxide (CO2), along with small amounts of gases like H2, N2, and H2S. This process can be dry or wet anaerobic digestion, with dry anaerobic digestion having a biomass content of 25-30%, while wet types have a biomass content of less than 15% (Sing and Misra, 2005).
In simple terms, biomass gasification is the process of converting cellulose material into fuel in a gasification reactor (gasifier). The resulting gas is utilized as a motor fuel to power a generator. Gasification serves as an alternative for energy conservation and diversification. It addresses the handling and utilization of agricultural, plantation, and forestry waste. The gasification device comprises three main parts: (a) the unit to convert raw material (feed) into gas, known as a gasification reactor or gasifier; (b) gas purification unit; (c) gas utilization unit.
Another application of biomass boiler energy involves biochemical processes such as hydrolysis, fermentation, and anaerobic digestion. Anaerobic digestion decomposes organic matter or cellulose into CH4 and other gases through biochemical processes. The stages of the anaerobic digestion process are shown in the figure. Ethanol production from biomass is also considered biochemical conversion. Biomass rich in carbohydrates or glucose can be fermented to break down into ethanol and CO2. However, carbohydrates must undergo hydrolysis first to convert into glucose. The fermented ethanol typically has a high water content and needs distillation to achieve ethanol levels above 99.5%.