What is Bagasse? How is it used as a Renewable Energy source?
Bagasse is the fibrous matter that remains after sugarcane or sorghum stalks are crushed to extract their juice. It is a by-product generated in the process of manufacturing sugar. It can either be sold or be captively consumed for generation of steam. It is currently used as a biofuel and manufacturing of pulp and paper products and building materials. The bagasse produced in a sugar factory is used for generating steam. This steam is used as a fuel source. The surplus generation is exported to the power grids of state governments.
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| Sugarcane Bagasse |
According to the Indian Sugar Mills Association(ISMA), as of 31st January 2022, 507 sugar mills in the country were in operation and had produced 187.08 lac tons of sugar, as compared to 177.06 lac tons produced by 491 mills last season which operated on the corresponding date. This is 10.02 lac tons higher as compared to the last season’s production for the corresponding period.
India emerges as the world’s largest producer and consumer of sugar and the world’s 2nd largest exporter of sugar, records over 5000 LMT of sugarcane produced in sugar season 2021-22; 35 LMT of sugar used for ethanol production and 359 LMT sugar produced by sugar mills in the season, and records the highest sugar exports of 109.8 LMT.
What is Cogeneration?
When two forms of energy (where one must always be heat and the other can either be mechanical or electrical) are produced from one fuel, it is called Cogeneration. In a cogeneration plant, very high-efficiency levels can be reached in the range of 75%–90%. This is so because the low-pressure exhaust steam coming from the turbine is not condensed but used for heating purposes in factories or houses.
The Technology of Electricity Generation & Transmission:
The prime technology for sugar mill cogeneration is the conventional steam-Rankine cycle design for converting fuel into electricity. A combination of stored and fresh bagasse is usually fed to a specially designed furnace to generate steam in a boiler at typical pressures and temperatures of usually more than 40 bars and 440°C respectively. The high-pressure steam is then expanded either in back pressure or single extraction back pressure or single extraction condensing or double extraction cum condensing type turbo generator operating at similar inlet steam conditions.
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| Rankine Cycle |
Bagasse (when burned in quantity) produces sufficient heat energy to supply all the needs of a typical sugar mill with enough energy to spare. To this end, a secondary use for this waste product is in cogeneration, the use of a fuel source to provide both heat energy, used in the mill, and the electricity typically sold to the consumer through power grids. The power produced through co-generation substitutes for the conventional thermal alternative and reduces greenhouse gas emissions. In India, interest in high-efficiency bagasse-based cogeneration started in the 1980s when the electricity supply started falling short of demand. High-efficiency bagasse cogeneration was perceived as an attractive technology both in terms of its potential to produce carbon-neutral electricity as well as its economic benefits to the sugar sector. In the present scenario, where fossil fuel prices are shooting up and there is a shortage and non-availability of coal, co-generation appears to be a promising development.
Due to the high pressure and temperature, as well as the extraction and condensing modes of the turbine, a higher quantum of power gets generated in the turbine–generator set, over and above the power required for the sugar process, other by-products, and cogeneration plant auxiliaries. The excess power generated in the turbine generator set is then stepped up to an extra-high voltage of 66/110/220 kV, depending on the nearby substation configuration, and fed into the nearby utility grid. As the sugar industry operates seasonally, the boilers are normally designed for multi-fuel operations to utilize mill bagasse, procured bagasse or biomass, coal, and fossil fuel to ensure year-round operation of the power plant for export to the grid.