Dr. S. S. Verma, Department of Physics, S.L.I.E.T., Longowal, Distt.-Sangrur (Punjab)-148106.
Biomass residues from agro-forest production activities, such as rice husk, sawdust, coffee hull, corncob, sugarcane dregs, coconut fiber and rice straw, etc., is existing from the day of starting of agriculture by mankind and have been made to their (residues) cost effective and environmental friendly use on need basis of human life style which was in full coordination with such agro-forest inputs. But things start changing with the changing life style of civilization which is more inclined towards the complacent nature and is dependent on easily available life sustaining inputs and this dependency is increasing day by day and such agro-forest residues are presently being termed as waste. At present, most of this waste is either discharged to ponds, lakes, creeks and rivers or is burnt; causing serious environmental pollution and only a small percentage is used as burning fuel, animal feed, and fertilizer in rural areas.
When the heaps of such residues are seen scattered/unused or being burnt without use, then environment conscious people start thinking to put such agro-forest residues to some suitable use for the society. Teetering on brink of energy exhaustion, people have to look for new sources of energy, and one of them is found in agro-forest waste. Agricultural waste does not produce much more electricity than hydroelectricity or thermo-electricity plants, but it does not pollute the environment. In addition, it can provide on the spot electricity for the rural areas, especially remote regions. Therefore, the use of agro-forest waste to generate energy serving processing industry is necessary. The threat of increased global warming has subjected the usage of fossil to be further researched for better alternatives. As a result, the utilization of renewable and sustainable energy resources, such as biomass, for electricity production has become increasingly attractive.
Co-firing biomass with low percentages in coal fired power plants will enable the use of sustainable fuels for power production without large investments. Co-firing can be seen as a method to mitigate the emissions of CO2 as the amount of CO2 released from combustion is equal to the amount consumed during plant growth. The use of rice husk as a source of renewable and sustainable energy source for co-firing in coal power plants have been extensively studied by scientists and engineers showing the feasibility of the rice husk as a fuel. In order to achieve the research area, modelling of the combustion of both coal and a blend of coal and rice husk was done. It was found that the rice husk and coal blend was able to produce the same temperature needed to produce the steam quality as specified by a coal power plant.
The suitable methods to burn agro-forest waste are fluidized bed combustion (FBC) providing heat for drying and processing of rice, maize, coffee, wood/timber, fruits ad vegetables, and fluidized bed combustion co-generation of heat and power. In FBC, maximum temperature is approximately 8000C when rice husk’s moisture is less than 14 percent. Rice husk at moisture of 30-40 percent with mould can still be burnt in FBC, but temperature reaches only 7300C due to some energy is used for evaporating water from fuel, and there is much black smoke. Rice husk with moisture higher than 40 percent is hard to be burnt. As shown in a flow chart of technology for producing heat and power from rice husk FBC – CHP is the wise way to get both heat and electricity. Primary steam is used to rotate a turbine for producing power, and secondary steam is used for supplying heat for other purposes.
Two Virginia University (USA) students have started a project with an India-based partner to supply electricity to villages in Bihar by burning rice husks. So far, two pilot rice husk generators are providing power to about 10,000 rural Indians, which will save 200 tonnes of emissions annually for each village if compared to generation of power from diesel or coal. The project may help turn the huge piles of husks that accumulate in many “rice belt” villages into two valuable products: electricity and ash that can be sold as an ingredient for cement. This technology provides off-grid power to rural Indian villages of 200 to 500 households. Using the husk-powered mini power plant, the team plans to offset close to 200 tons of carbon emissions per village, per year in India. There are 480 million Indians with no power and 350 million of them live in rural villages, concentrated in eastern India’s “Rice Belt,” where the villagers are “rice rich and power poor. It is expected such miniature power plants making use of all types of agro-forest residues will be developed and set up in hundreds more villages within a few years thereby assisting local farmers, supplementing huge demand for energy, and preserving the environment.