Heat integration of biochemical ethanol production from straw – A case study

Ethanol produced from lignocellulosic biomass is a desired, renewable fuel that can help to reduce our dependence on oil. In order to achieve the commercial deployment of this fuel good economic and environmental performance are mandatory. Both these targets are tackled by the efficient use of process heat. This work deals with the heat integration of the biochemical production of ethanol from straw. Process simulation and pinch analysis are applied to investigate a base case design of the production process. The energy intensive unit operations distillation and evaporation are in the focus of this pinch analysis. Pressure and heat load modifications of these sections are applied to improve the process design. For this improved process design a heat exchanger network is synthesized. Energy stream and pinch analysis revealed that process residues easily suffice to provide the investigated process with heat. The design modifications of the distillation and evaporation sections lead to increased heat integration. Consequently, a 15% reduction of the utility targets compared to the base case is obtained in the improved design. The heat exchanger network for the improved design is simple, yet the increase in utility consumption compared to the utility targets is quite modest. As a result, in the network only 51% of waste biomass suffice to provide the process with heat. The exceeding biomass can be used for the recovery of energy or material by-products, which highlights the need for efficient polygeneration concepts.