Biomass utilization is becoming a subject of increasing interest as an alternative to clean fuel. A novel gasification process using highly preheated air gasifier using agricultural residue such as sugar bagasse, rice husks, and palm stem widely available in Tanzania is presented. The study examines, irreversibilities making the gasifier the least efficient unit in the gasification process employing a thermodynamic equilibrium model allowing predicting the main product gas composition CO, CO2, H2, and CH4. The derived model equations are computed using the MAPLE process simulation code in MATLAB. The gasification regime is investigated at temperatures ranging from 800？K to 1400？K and at equivalence ratio (ER) values between 0.3 and 0.4. The results obtained conform to the second law efficiency based on chemical exergy yielding maximum values for the types of biomass materials used. These results indicate that the application of preheated air has an effect on the increase of the chemical exergy efficiency of the product gas, hence reducing the level of irreversibility. Similarly, these results show that the combined efficiency based on physical and chemical exergy is low, suggesting that higher irreversibilities are encountered, since the exergy present in the form of physical exergy is utilized to heat the reactants. Such exergy losses can be minimized by altering the ratio of physical and chemical exergy in the syngas production. 1. Introduction The need for sustainable energy sources is growing as fossil energy sources are diminishing. Moreover, stringent environmental laws about the greenhouse gas emissions and increase in oil prices are prompting for the need to invest in the area of renewable energy sources. Biomass referring to all the forms of plant-based material that can be converted into usable energy is a renewable source of energy. In Tanzania, biomass is in abundance and is a nonconventional source of energy. The main biomass sources available are in the form of wood sawdust and agricultural residues. The utilization of biomass in an efficient and sustainable manner will provide sufficient energy which can be utilized for electricity generation, engine applications, and so forth, through the deployment of gasification technology. Gasification is the process in which biomass is converted into clean and combustible gas in the presence of limited amount of air. Thermoconversion process of biomass based on the gasification technology is the most convenient way for the utilization of biomass and is believed to be an efficient method for
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