Flowsheeting, combined with estimates of the production cost, is a valuable
tool for the comparison of process alternatives and to determine bottlenecks
that require further improvement. It is, however, difficult to compare production
costs from different studies due to the many assumptions made in
the simulations, such as ethanol yield, productivity and concentration, as no
commercial-scale plants are in existence. Also, differences in capacity and
cost of raw material, as well as currency exchange rates, add to the uncertainty.
This is clearly illustrated by the large variation in the estimated ethanol
production cost, from 0.13 to 0.81 US$ L–1 ethanol.