Controversial projections about natural gas reserves depletion by the 1980s and 1990s, the oil embargo of 1973, and more restrictive and stringent environmental standards provided incentive to explore and promote the commercialization of new sources of fuel, such as biomass. The term biomass covers a broad range of materials that have been derived from recently living organisms. Recycling, composting, incineration, and land filling constitute four acceptable biomass handling options. Recently, gasification of biomass materials has also been introduced as a thermochemical conversion; a process to convert carbonaceous materials to a synthetic gas (syngas), mainly comprised of CO and H2. A combustion process needs stoichiometric feed of air/oxygen, while gasification process is performed at sub-stoichiometric conditions. The fuel gas produced has a relatively low calorific value in comparison with that of natural gas; however, it can be combusted at a relatively high efficiency and with good degree of control without emitting smoke. In this paper, a biomass gasification process is modeled using thermochemical equilibrium with equilibrium constants. The residence time of the reactants is supposed to be high enough to reach chemical equilibrium and all gases are assumed to be ideal. The composition of produced syngas is approximated to be comprised of H2, CO, CO2, H2O, and CH4. Validation of the numerical model is the first issue, which is done via comparison between calculated results and experimental data. In order to compare various biomass sources of energy, gasification of five different samples of five major families are simulated under the same conditions. Olive pits are found to produce the highest calorific value (5.9 MJ/m3) and therefore, were selected as the biomass material for the rest of this study. The influence of oxygen enrichment and pressure on gasification characteristics is then studied for olive pits. These characteristics are the syngas composition, gasification temperature, calorific value and the cold gas efficiency. An increase of oxygen enrichment from 21% (oxygen ratio in atmospheric air) to 100% results in a 50% increase of gasification temperature. Also syngas calorific value is increased considerably from 5.23 MJ/m3 to 11.42 MJ/m3. The gasification under pressure has no significant effects on gasification characteristics. However, this technique is economically preferred over pressurizing the syngas downstream. The developed model can be used to simulate/optimize gasification of different types of biomass materials and predict the effect of processing parameters.

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