Thermo Economic Analysis of Co-Firing Based Thermal Power Plant

Abstract

Co-firing option for utilizing biomass fuels is gaining popularity in developing countries like India. Fluidized bed combustion (FBC) system is widely used to effectively utilize co-firing option. In the present study, combustion and kinetic characteristics of a coal, biomass co-fired thermal power plant is studied. The biomass used is rice husk and blends of rice husk with coal varying in proportions of 20%, 30%, and 40% by weight of rice husk were prepared. TG and DTG analysis was then carried out on both samples and their combustion and kinetic parameters were analyzed. It was found that co-combustion of coal and rice husk blends consisted of mainly three stages i.e. moisture evaporation, volatile release and char combustion. Further, the kinetic parameters obtained by using Coats-Redferns method provided the best suitable solid state mechanism that could be used for kinetic analysis. The results obtained are in agreement with TG and DTG data. Further exergy analysis of co-fired boiler is carried out and results show 55.46 MW of exergy destruction in boiler along with 35.1% of exergy efficiency. Co-firing with biomass fuel is not an easy task; there are some issues of slagging, fouling and bed agglomeration. These problems greatly affect the economics of plant. In this present study, bed agglomeration and economic analysis is also done of 20MW FBC boiler based thermal power plant. Bed agglomeration is also depicted from free swelling index (FSI). FSI provides the measure of sticky nature of particles in FBC boilers. Along with samples collected from plant (Rice husk and coal (S-III)), one bagasse sample and two Indian coal samples (S-I from Bathinda thermal power plant, S-II from Yamuna nagar thermal power plant) were used and their blends with each biomass fuel were prepared. Experimental results have shown no signs of bed agglomeration for all the samples. Bagasse and iv S-I, S-II shows sticky nature when tested for FSI and can form large agglomerates. Economic analysis shows the huge effect of sale rate on the profit share of plant. Break-even point in terms of operating hours has been calculated and various means of enhancing the profit has been suggested.