Gasification of coffee bean husks : analysis and model development for energy generation using ASPEN Plus simulation software

This paper develops a model and evaluates the viability of producing a gaseous fuel (syngas) from the coffee bean husks using ASPEN Plus simulation software. The paper examined the formation of syngas from agricultural waste, to make it less vague and to give it a consistent focus, the study was carried out in the context that the syngas is to be utilised to power an Internal Combustion (IC) engine that is being utilised to drive a generator to produce electricity in a remote village in the Highlands of Papua New Guinea. Despite the preciseness of the setting and scenario, it has only been utilised where direction was required, and it is purely the formation of the syngas that has been considered in depth. This study found that the air/fuel (A/F) ratio and moisture contents are inversely proportional to potential enthalpy of combustion (PEC) of syngas produced, and reduction zone temperature is proportional to PEC asymptotic to a maximum value based on A/F ratio and moisture content of feedstock. Based on these findings it can be clearly seen that the air feed into the gasifier needs to be controlled by the temperature of the syngas as it is being produced. The other key finding is that 171 tonnes of coffee bean need to be produced to generate 5 kW continuously for a year. It seems unlike that a village would produce such a quantity; however a centralised processing plant may be able to work with the community to supply electricity for a common need, such as electricity for a school or health post. This technology was investigated due to its simplicity lending itself to being suitable for a developing country. Any proposed improvements need to also be examined in this same context if they are to be widely embraced.