Hydrogen Production Using Cashew Nutshells via gasification for electricity generation in Guinea-Bissau

Abstract

Global development has made energy more vital across many sectors, including agriculture, industries, health, transportation, and communications, among others. Governments around the world are hoping to attain emissions reductions by converting power generation away from fossil fuels towards cleaner options such as biomass and hydroelectric power, supported by leading conversion technologies. This study characterizes biomass as a substitute for fossil fuels through the use of the gasification process in the production of hydrogen. Cashew nutshells are explored as a potential biomass feedstock. Guinea-Bissau is one of the world's largest producers of cashews, where production is increasing and the government actively supports local processing to add value and create jobs. Cashew nutshells are a good, renewable biobased material, providing a profitable byproduct for energy or chemical production. It refers to the hard outer shell encasing the cashew seed, commonly known as the cashew nut. This shell is considered waste and is a non-edible part of the nut, containing various compounds, including cashew shell liquid, which is toxic if ingested and potentially harmful to the environment if it is not managed correctly. This study aims to evaluate the hydrogen potential in Guinea-Bissau and to reduce the environmental hazards posed by cashew nutshell waste. Aspen Plus was utilised to predict the yields of hydrogen and other compounds through simulation based on kinetic modelling, employing a multi-stage gasification system comprising drying, pyrolysis, gasification, and gas separation. The simulation also assessed the influence of pressure and temperature on gas yields in the Rplug reactor. Cashew nutshells were evaluated based on two criteria: theoretical potential and mobilizable potential, with the latter reaching over 60% annually, corresponding to 1,215 tonnes. The conducted simulation indicated that introducing 1,000 kg/h of cashew nutshells into the system could generate approximately 221.922 kg/h of hydrogen without using catalytic agents. Based on this hydrogen mass flow rate and its energy content, expressed as LHV, the theoretical energy output of the fuel cell system would be around 26,630.64 MJ/h. For effective waste management, stakeholder engagement, education, and planning have been suggested as key strategies. This study concludes that cashew nutshells with cold gas efficiency and carbon conversion efficiency, which were respectively 84% and 93.6%, represent a promising and sustainable biomass resource for hydrogen production via gasification, with results demonstrating that high-temperature conditions can facilitate effective hydrogen generation without catalysts.