Volume 12: Low Carbon Cities and Urban Energy Systems: Part I

Process and Equipment Modelling and Design of a Coffee Husks Gasifier for Drying Operation Grafilo, Laumar Alan Dave R., Berana, Menandro S., Alamani, Bryan G.

Abstract

This study was conducted to test the viability of coffee husks as a potential feedstock in a gasifier-dryer system. The projection of the total amount of waste produced is necessary in determining the input for the process modelling, together with the proximate and ultimate analyses that were conducted thru standard testing. In the tests, the proximate analysis gave 12.30% moisture content, 64% volatile matter, 23.30% fixed carbon and 12.70% ash content. On the other hand, the ultimate analysis gave 38.50% carbon, 5.89% hydrogen and 42.91% oxygen. No traces of nitrogen and sulfur were found. Aspen Plus Version 11, a package that can be used for modelling reactors for biomass gasification was used to produce a model and determine the producer gas composition. To dry 2 tons of coffee fruits in a gasifier-dryer system, it requires 50 kg/hr of the biomass feedstock. By feeding 50 kg/hr of coffee husks and 0.578 kg/hr of air in the model, it produced simulation results of 925.85 °C gasification temperature in the reactor to gasify the coffee husks and air mixture to produce the producer gas composed of 84.2851 carbon monoxide (CO), 4.7104 carbon dioxide (CO2), 0.1063 methane (CH4), 6.9086 hydrogen (H2), 1.0164 nitrogen (N), and 2.9726 water (H2O) in mass percentages. Finally, the energy efficiency of the gasifier with respect to temperature and air to biomass ratio was computed. All the inputs are based on the actual elemental analysis of coffee husks feedstock. A valid point at 704 °C was established, indicating the realistic limit of the gasifier based on the simulations. The trend of the results was found to be consistent with the experimentally validated analysis of other biomass feedstocks in published investigations. The model developed in this study is intended to be validated through experimental verification in our future studies, and the results of the modelling and validation will be used in prototyping the specific gasifier.

Keywords Waste to energy, gasifier-dryer system, proximate and ultimate analysis, producer gas