Potential for thermal conversion of brewer’s spent grain into biocoal via hydrothermal carbonization in Africa

Abstract

Abstract Brewer’s spent grain (BSG) has the potential to contribute to the supply of energy in Africa, as concern for clean and sustainable energy grows. The synthesis of biocoal from BSG via an artificial coalification process, hydrothermal carbonization (HTC), is preferred amongst other thermal conversion techniques as HTC is capable of handling high moisture feed. BSG which consists of insoluble cereal residue that is separated from the mash before fermentation has been a major disposal problem in the brewing industry for decades. Considering the energy crises experienced in Africa, its use for energy is a more useful option. In this study, an estimate of BSG production, expected yield of biocoal and energy potential for African countries is given. Due to temporal variation and data uncertainty, a stochastic model supported by 50,000 Monte Carlo simulations was developed to carry out the assessment. The method involved the development of a mathematical model for estimating the yield of BSG-derived hydrochar. Probability distributions were applied to each independent variable based on historical datasets and published scientific literature. Monte Carlo simulations were conducted using commercially available software, Palisade’s @RISK, to give a probabilistic representation of the expected yield of hydrochar for each country. The total quantity of BSG generated in Africa has been estimated at 627,050 Mg/yr (514,177 - 739,914 Mg/yr at a 90% confidence level) since 2013 and the potential for biocoal production via hydrothermal carbonization annually is 309,140 Mg/yr (9.43 million GJ/yr) on average. Estimates at a country level are given and based on the evaluation, BSG-derived biocoal alone cannot make a significant contribution to meeting Africa’s demand for energy.