Utilization of mill rejects with biomass pellets in the existing coal power plants- a novel approach towards sustainability & fuel security

Abstract

ABSTRACT The present work is focused on the possible utilization of mill rejects blended with the biomass non-torrefied pellets (made of paddy straw, dry grasses and fallen sal leaves) in the existing tangential coal-fired boiler through the gasification process. The physio-chemical analysis and combustion behavior study of the materials is done based on thermo-gravimetric analysis (TGA) and differential thermal analysis (DTA). The result shows that the gross calorific value (GCV) of the developed bio-mass pellet is about 3900–4300 kCal/kg with the mass percentage of fixed carbon (FC) and volatile matter (VM) of about 15% and 70%, respectively. From the TGA and DTG study, it is observed that about 7% weight loss was found in all pellets at a temperature range of about 85–110°C but for the mill rejects, it is about 5–6%. At the peak temperature, the maximum weight loss of pellets and mill rejects is about 0.90 gm/min and 0.16 gm/min, respectively. The combined use of mill rejects and pellets (1:1) in the updraft gasifier generates combustible syngas with mole fractions of CO and H2 of about 0.29 and 0.30, respectively with a lower heating value of about 159 kJ/mole. The direct use of generated combustible syngas into the coal-fired boiler of a 500 MW power plant increases the net energetic and exergetic performance by about 0.09 and 0.07% points, respectively and resulting in a reduction of annual CO2 emissions by about 9452 tons. Cost-benefit analysis is used to determine the feasibility of the system.