Gas Turbines CHP for Bioethanol and Biodiesel Production Without Waste Streams

Abstract

In the context of the recent decision of the European Commission to incorporate a minimum of 10% biofuel by 2020 in total transport fuel use, the production of bioethanol and biodiesel will be boosted. When compared to fossil fuels this two biofuels have numerous advantages i.e. they are renewable, they run in conventional vehicles, they are not toxic, they are biodegradable, they show low particulate emissions and they are CO2 neutral. However they show some disadvantages such as the high energy demand of their production and the high yield of byproducts (i.e. glycerin for biodiesel and distiller’s waste for bioethanol), that require a dedicated marketing effort and supply chain. The energy demand required for the production of both biodiesel, through transesterification of vegetal oils, and bioethanol, through fermentation followed by distillation, is thermal and mechanical and can be satisfied by means of a CHP plant integrated in the production line fueled by its own byproducts. The paper analyzes the energy balances of two CHP plants fed with the above mentioned wastes (glycerin and wheat straw residues) and integrated in the biofuels (respectively biodiesel and bioethanol) production plants. The CHP plant considered are based on the IPRP (Integrated Pyrolysis Regenerated Plant) technology, meaning a gas turbine fed with syngas obtained from slow pyrolysis of the residues. Results show that in the case of biodiesel the production of glycerine is sufficient to satisfy the electricity demand of the plant that is lower than the heat demand, while the last cannot be completely covered because glycerine production is reduced respect to the input mass of vegetable oil and equal to 10% w/w. Concerning bioethanol, wheat straw residues are enough to cover heat demand that is the most important energy input of the process but they are not able to cover electricity input that is linked with the milling of the raw material. This is because of the reduced syngas yields and its lower energy content if compared with that obtained using glycerine.