Bioenergy is a renewable source of energy that is produced from materials derived from biological sources. Materials that can store sunlight in the form of chemical energy like wood, wood waste, straw, crop residue, manure, sugarcane, and many other by-products from a variety of agricultural processes form biomass; the fuel used in the production of bioenergy.
Biomass plants can protect forests, boost the rural economy, and make use of various natural resources. Bioenergy, in turn, can bridge the gap left by large thermal power plants, such as coal-fired stations, and ensure constant generation that is independent of weather conditions.
Biomass is a carbon-neutral energy source as the amount of CO2 generated by combustion is the same as that absorbed by the biomass-producing plants as they grow. The slag and ash that are left behind after combustion are reused in the production of fertilizers and aggregates that helps maintain a circular economy that will help with rural development as well.
Biomass Harvesting is the process of turning living plants into bioenergy through biomass power plants. This transformation into bioelectricity (biomass used to produce electricity) or bioheat (biomass used for heating applications) first begins with the collection and compaction of plant material.
Three main types of biomass are used for the conversion process.
- Herbaceous Biomass:
This is made up of cereal straw (wheat, barley, oats, corn, etc.) It is easy to pack and usually has a very low uniform moisture content that ensures high calorific value (the energy contained in the fuel that is determined by measuring the heat produced by the complete combustion of it) The only drawback of this fuel is that it produces a high amount of ash (6%), which leads to various corrosion problems.
- Woody Biomass:
This comes from agrarian pruning (vine shoots, olive trees, etc.) and forest biomass (pine, eucalyptus, oak, etc.) Once it is collected from crops and forests, it is then shredded or chipped. It produces little ash (less than 2%), but it has a lower calorific value.
- Industrial Biomass:
This is usually used as supplementary material and it comes from processes like oil extraction, paper production, and from the food industry (dried fruit peels, rice, etc.)
HOW IT WORKS
Once the feedstock (the raw material used to fuel a machine) is collected, it is stored in a storage facility that keeps track of it to prevent any supply shortages. Conveyor belts transport the feedstock from the storage facility to the boiler.
Once inside the boiler, combustion turns the water flowing through the boiler’s walls into steam. A system of tubes carries the steam back inside the boiler until it reaches a desired temperature and pressure (520° and 90 bar) The air needed to facilitate this process is heated by the combustion gases which also pre-heat the water headed into the boiler.
Once the steam has reached the desired temperature and pressure, it exits the boiler and is fed into a turbine that consists of a rotor and blades that spin at 5,400 revolutions per minute. The turbine is connected to a generator, to which it transfers its rotary motion from kinetic energy into electrical power.
The steam exiting the turbine is then cooled in a condenser and it returns to its liquid state. It then returns to the boiler to begin the process all over again. The gases leaving the boiler contain particles that are captured in a large fabric filter to prevent their emission into the atmosphere. The slag and ash that are produced during combustion are collected from the bottom of the boiler and are reused for the rehabilitation of degraded land.
THE CURRENT SCENARIO OF BIOENERGY IN INDIA
In India, about 32% of the total primary energy used is derived from biomass and more than 70% of the country’s population depends on it for their energy needs. The Ministry of New and Renewable Energy (MNRE) has recognised the potential of biomass and has set a target of achieving 10 GW of installed biomass power by 2022. They are now working towards enhancing the viability of biomass plants by providing financial incentives and subsidies for biomass projects in the country. State governments have also instituted their incentives and subsidies which have led to states like Maharashtra, Uttar Pradesh, and Karnataka each having more than 1 GW of grid interacted biomass power.
Yet, there are still major challenges that have to be overcome to ensure that the target is met. At the moment, barriers in the supply chain have hindered the growth of biomass. Mainly the fluctuations in availability due to yearly cropping patterns, (harvesting for only 2-3 months in a year) and the cost of biomass storage and transportation have hindered its use. Biomass plants will need design and engineering improvements, performance monitoring and management systems, and focused research and development to ensure that states with high biomass power potential are using their resources efficiently.