Optimal Design of Grain Sorghum Based Ethanol Plant

The increasing interest in supplement or substitute products such as fuels, chemicals, plastics, etc. derived from fossil resources has driven the study and development of different processes that could use a wide variety of renewable raw materials. In particular, bioethanol production can improve energy security, reduce carbon dioxide emissions, and decrease urban air pollution.

In the present work, we carry out a study for an ethanol production plant based on grain sorghum. This cereal has a low water requirement making it suitable for cultivation in drier areas and it is not use for human consumption. The produced ethanol could be used to produce ethanol-blended fuels or as raw material for ethylene production. We formulate mass and energy balances for the dry milling process, which is the most widely used for grain-based ethanol production. Byproducts are carbon dioxide and DDGS, distilled dried grains with solubles Carbon dioxide can be used, after ethanol removal, in soft drinks plants, as supercritical solvent in many extraction processes, as raw material in algal-based biorefineries, etc. DDGS are used for animal feed due to their high nutritional value. We perform heat integration and optimization of water consumption on the proposed ethanol process. An economic evaluation is also carried out for the two scenarios (optimized and non-optimized (base case) plant).

In this work we consider a grain sorghum based ethanol plant production of 310 ton ethanol/day. Water consumption is a key issue in this type of plants, being an acceptable value 3 l water/l ethanol. In our case study, numerical results show that water consumption could decrease from 4 l water/l ethanol for the base case to 1.3 l water/l ethanol for the optimized case. On the other hand, a reduction of 24% on energy consumption is achieved in the optimized plant with respect to the base case. The economic analysis reveals an increase of 23% in the net present value for the optimized plant for a project useful life of 10 years. Another important result obtained from the costs evaluation is that raw material cost constitutes about 75% of ethanol production cost, which emphasizes the advantages of grain sorghum against corn, due its lower price with respect to corn.