Thermodynamic Analysis and Mathematical Equilibrium Modelling of the Downdraft Gasifier

Abstract

Indian electricity demands in day to day life are increasing but at a same time, carbon emission is also increasing. Major fossil fuel to generate electricity in Indian power sector is usually coal. Worldwide researchers are focusing more to move on renewable energy for generating electricity to reduce global warming and carbon emissions. Source of lignite coal is very large in World but it has limited applications due to high ash and moisture content. Gasification is incomplete combustion process in which combustible produce as is generated. It can be used to generate electricity by applications of I.C. engine, gas turbine etc. This process produces less carbon emission as compared to other electricity generation system and one of the suitable ways in rural electrification and waste to energy. Purpose of this study is to optimize the performance of lignite in a 10 kWe downdraft gasifier. Thermodynamic analysis such as energy, exergy, mass balance, heat loss analysis has been carried out for lignite gasification. The performance of gasification has been investigated by varying different particle size of lignite. Six different particle size of lignite had selected (13-16 mm, 16-19 mm, 19-22 mm, 22-25mm, 25-28mm, 28-31mm). 22-25 mm particle size of lignite was found optimum and had highest exergy efficiency 29.64 % among selected particle size of lignite. The performance of lignite and steam gasification was carried out with different steam flow rate (0.48, 1.08, 1.38, 1.76, 1.92, 2.76 kg/hr). Maximum exergy efficiency 34.91 % was found at 1.6 kg/hr steam flow rate. Thermo-equilibrium model was prepared to predict gas composition of producer gas and heating value of gas. The performance of gasifier has been analysed by varying equivalence ratio (ER). The effect of equivalence ratio (0.24-0.386) on gas composition and heating value has been investigated. These results compared and found reasonably well with experimental results. The optimum results were found at ER of 0.376. The heating value of producer gas increases (4.07-4.91 MJ/Nm3) as equivalence ratio (ER) increase and temperature increases as ER increases in the range of 1009-1147 K. The hydrogen and carbon dioxide decrease and carbon monoxide increase with increase in equivalence ratio.