Turning industrial aerobic fermentation plants into thermal power stations

Abstract

The industrial aerobic bioprocess of baker's yeast production requires large amounts of water to cool down large bubble column bioreactors. As result, an appreciable quantity of low-grade heat is generated. Because of the low temperature level of the water (~25°C) exiting the bioreactors cooling system, very little attention has been dedicated to heat recovery and conversion from this stream, which is usually released in rivers, streams, and canals. In this work, we simulated the generation of low-grade heat (up to 14.4 MW) from an industrial baker's yeast production plant consisting of seven 150-m3 bioreactors. Subsequently, a dedicated transcritical carbon dioxide heat pump system for the conversion of this low-grade heat into fourth generation district heat (~16.2 MW) was successfully designed. Fourth generation district heat employs low-temperature water (30-70°C) as heat carrier and is expected to play a major role in future sustainable energy system. Finally, an economic study confirmed the feasibility and the applicability of our approach and a concept for long-term energy storage including state-of-the-art phase change material (PCM)–units was discussed.