We focus on cellulase production by Trichoderma reesei. Cellulases are needed in the conversion of lignocellulosic waste to bioethanol, and the enzyme cost is critical for the establishment of a competitive process. As stoichiometry and reaction kinetics are assumed equal for all technologies, the power consumption including aeration, cooling, and agitation is therefore the key performance indicator. In the literature, this factor is defined as the energy efficiency of oxygen transfer, EEO2, measured in kg/kWh.
We have collected literature data for a range of different fermentation technologies and applied a fed-batch fermentation model developed for stirred tank reactors1 in up-scaling the process to industrial scale. The up-scaling criteria were oxygen transfer and geometrical symmetry. In this way the required reactor sizes were determined.
For each technology, simulations were performed providing an objective basis for the comparison. It has not been possible to consider mixing, which is however assumed to be impaired at large scale compared to most literature data obtained at laboratory scale.
The most energy efficient systems are low-productivity technologies. This implies that larger fermentor volumes are required; in turn investment costs may be lower if the reactor design is “simple”. The process is run with variable filling, an important consideration often overlooked in the past.
- Albaek, Gernaey, Hansen, Stocks. 2011. Evaluation of the energy efficiency of enzyme fermentation by mechanistic modeling. Biotech. Bioeng. (submitted)
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