Semicontinuous diffusion fermentation of fodder beets for fuel ethanol and cubed protein feed production

A novel, semicontinuous diffusion fermentation system was used to produce fuel ethanol and a cubed protein feed (CPF) from fodder beets at an intermediate scale. In the process, fodder beet cubes were augered diagonally upward against a flow of 0.26N H(2)SO(4) and yeast in a tubular fermentor. Exiting one end of the fermentor was CPF, while fermented beer 6-9% (v/v) ethanol] exited the other end. Retention times for beer and CPF were 264 and 72 h, respectively. Contamination was controlled by maintaining the fermentation pH between 2.1 and 2.6 using H(2)SO(4). Production costs for a greatly scaled-up (times 1400) conceptual version of this system (using a continuous rather than a semicontinuous processing mode) were projected by calculation to be $0.529/L for 95% ethanol (net of a $0.112/L credit for CPF). The calculated energy balance (energy output-energy input ratio) was estimated to be 3.04. In calculating the energy balance, the output energy of the CPF and input energy for growing the fodder beets were not included. A design for the scaled-up plant is provided.