Utilisation of heat and organic wastes for energy recovery in the industry

Abstract

Food and drink processing industries are extremely large consumers of thermal energy as well as bio waste producer. There are huge opportunities to utilise the bio wastes for energy generation. In this project two cases were studied. Fermented grains and hops are used for the beer production and at the end the used materials are disposed with the yeast as organic wastes, in a similar way rice spirit is produced from a mixture of grains which are discarded at the end as spent grains. The feasibility of using the waste individually or in a mixture as feed for Anaerobic Digestion (AD) was evaluated. This project has considered the concepts of generating a more environmentally friendly thermal energy using solely the bio wastes from the industry and if applicable the low grade waste heat available to integrate a waste to energy system. In order to assess the viability of the use of the bio wastes, experimental work in the laboratory for the characterisation of the waste streams as well as an energy audit was performed. Continuous Stirred Tank Reactors (CSTR) were run for a period of time at mesophilic and thermophilic conditions, using the waste grains individually and in a mix. Once the bio methane potential was determined, simulations of the process were executed using engineering software and compared with the data gathered from the site visit. It is found that the figures of final composition of the product as well as the mass and energy balance were similar to the data obtained. The results showed the potential to use the spent grains as feed for the AD plant to produce biogas is positive, covering up to 70% of the total fuel required for production in the case of the brewery and 100 % in a spirit plant. It was also noticed that running the system at thermophilic temperature had a better performance in terms of methane content. The biogas could be used instead of the fossil fuel being used at the moment. Replacing the current use of fossil fuel will be a positive impact in CO2 emissions reduction as well as economic performance for the brewery, since these bio wastes are often given away to farmers free of charge or more expenses would be incurred in discarding them from the site. This will lead to self-sustained production process and improve the waste management.