SALIENT FEATURES AND OPERATING EXPERIENCE WITH WORLD'S FIRST RICE STRAW FIRED FLUIDISED BED BOILER IN A 10 MW POWER PLANT

摘要

India has a vast resource of biomass, a renewable source of fuel, which if used effectively would reduce the rate of depletion of fossil energy resources. Rice straw is one such biomass which is available abundantly in the state of Punjab in India. Bharat Heavy Electricals Ltd (BHEL), Tiruchirapalli established the Fluidised Bed Combustion of rice straw in their test facilities and engineered a 10 MW rice straw fired power plant. The plant has been installed in the state of Punjab. This is the world's first power plant using 100% rice straw as fuel in baled form in a fluidised bed. The plant is in successful operation now after overcoming the teething problems. The steam generator is a bi-drum, bottom supported, bubbling fluidised bed bed unit, with a pendant superheater and boiler bank. In-bed surfaces have been provided to limit the temperature of the fluidised bed well below that of the straw ash softening temperature. Rice straw bales weighing 15-20 kg are fed through unique overbed feeding system. The bed is segmented in the wind box below the air distributor to enable part load operation. The system generator is provided with heat recovery surfaces like economiser and air heater in the convection pass. An elelectrostatic precipitator limits the dust emission to the stack. During shakedown trials, it was noticed that combustion of straw was extending upto the freeboard exit. This caused temperature peaks and ash agglomeration on superheater tubes. The straw ash is not free flowing in the convection pass hoppers due to its fluffiness, hence accumulates, sinters making ash evacuation difficult. These problems have been resolved by adopting an improved overfire air arrangement and by use of additives. The salient features and operational experience are elaborated in this paper.