Prasun Barua
CHAPTER-4: HOW TO GENERATE ELECTRICITY FROM BIOMASS?
Generating heat energy by burning biomass is one of the most familiar method since long time. This biomass fired heat can produce steam power for generating electricity. Burning biomass in conventional boilers provides environmental and air-quality benefits over burning fossil fuels.
Recent researches by researchers indicate that biomass can be converted more cleanly into liquid fuels. For example, producing combustible gases from gaseous process. It decreases different kinds of emissions from biomass combustion.
Technologies which can convert renewable biomass fuels into heat and electricity is called biopower technologies. It follows same process wherein fossil fuels are used to generate electricity. The energy is stored in biomass. It can be released to produce biopower by using three methods. They are – Direct Combustion, Decomposing by Anaerobic Bacteria and conversion to gas/liquid fuel.
Direct combustion
Direct combustion is one of the most used methods for generating electricity from biomass. In this method, high-pressure steam is produced by burning biomass. This steam flows over a series of turbine blades and help them to rotate. The rotation of the turbine drives a generator for generating electricity. In an existing power plant furnace wherein a portion of coals are used for generating electricity, there biomass can be used as substitute by co-firing process. Co-firing is combusting two different types of materials at the same time.
Decomposing by anaerobic bacteria
Organic waste material animal dung or human sewage, is collected in oxygen-free tanks called digesters. Some organic waste materials like cow dung, human sewage etc. are reserved in oxygen-free tanks called digesters and decomposed by anaerobic bacteria. It produces methane and other byproducts to form a renewable natural gas. After purifying, it is used for generating electricity.
Converting biomass into to a gas or liquid fuel
By using gasification and pyrolysis process, biomass can be converted to a gaseous or liquid fuel. In the gasification process, synthesis gas or syngas is produced by exposing solid biomass material to high temperatures with very small amount of oxygen present. Synthesis gas or syngas is a mixture that consists mostly of carbon monoxide and hydrogen. This gas is burnt in a conventional boiler for generating electricity. In a combined-cycle gas turbine, it can also be used as a replacement of natural gas.
In the process of pyrolysis, crude bio-oil can be produced by heating biomass in the complete absence of oxygen at a lower temperature range. This bio-oil can be used in the power plant as a substitute wherein diesel or fuel oil is used for generating electricity.