Modeling of Coffee Husks Degradation Process under High Temperature Gasification (HTAG) Regime

Abstract

The prevailing global warming resulting from climate change is exacerbated by increasing environmental pollution due to high consumption levels of fossil sources of energy including petroleum oils and coal. Effects of climate change would thus provide adverse conditions for possible multiplication of diseases, lowering agricultural productivity, reduction in the availability of safe and clean water, and multiplication of extreme climatic events. Biomass utilization is becoming a subject of increasing interest as one of the attractive alternative solutions to clean fuel production. In order to achieve a sustainable harnessing of the biomass energy potential and to increase its contribution to the world’s primary energy consumption, there is therefore a need to develop and sustain contemporary technologies that increase the biomass-to-energy conversion. This paper investigates a novel gasification process employing high temperature air/steam gasification (HTAG) of biomass that will result in the production of syngas having an improved range of heating values as a direct result of both the gasifier design used and the reactants chosen. In addition to syngas, other products including char and tars produced at varying levels are examined. The technique makes use of highly preheated air to provide additional energy into the gasification process that enhances the thermal decomposition of the gasified solid feedstock materials. The gasification studies conducted are based on the use of coffee husks as feedstock materials under three gasification temperature regimes of 700°C, 800°C, and 900°C, whicht shows an increase in syngas production under high temperature. The results show an increase of the amount of CO yield and N2 under 2% O2 concentrations. The recorded amounts of chars left while gasifying at 700°Cand 800°Care respectively 2.4 and 1.5 times than that for the case of 900°C. The estimated kinetic parameter values for the coffee husks derived from thermal degradation analysis exhibits a reaction mechanism of zero order with apparent activation energy of 161 kJ/mol and frequency factor of 3.89104/min. When steam is injected as the oxidation agent, CO evolution yielded is in the tune of 13.1 to 19.5 Vol. %, compared to 20.8 and 23.8 Vol. %,by comparisonwith the case when steam is injected,which gives negative effects on CO evolution obtained when air is used as an oxidation agent. On the other hand H2 evolution is also seen to be favored when steam is used as an oxidation agent.