Ideally there should be no heating or cooling at any stage in a fermentation process, but because this is virtually impossible, heat should be conserved and cooling minimized by careful process design. A fermentation may include the following heating or cooling stages:
1. Sterilization or boiling of the medium to 100° or above followed by cooling to 35° or below.
2. Heating the fermenter and ancillary equipment to sterilize it, followed by cooling.
3. Heat may be generated during the fermentation. This heat output has to be removed by cooling to maintain the growth temperature of the microorganism within prescribed limits.
4. After harvesting, heat may be required to remove water from the product.
Cooling requirements will be influenced by the size and type of an individual process (Chapter 7). British petroleum Ltd. estimated that the cooling requirements for a 100,000 tonnes annum single-cell protein plant to be 110 X 106 kcal h 1 using n-alkanes or gas-oil as the primary substrate (Litchfield, 1977). To reduce cooling requirements, the specific energy input may be minimized through the use of air-lift fermenters (Schugerl et al, 1978). Cooling equipment has been estimated at 10 to 15% of the investment cost for single-cell protein (Moo-Young, 1977; Schugerl et al, 1978). Another way to minimize cooling costs is to use micro-organisms with higher optimum growth temperatures, if it is feasible. The selection and use of ther-mophiles and thermotolerant organisms would have obvious advantages to reduce cooling demands (Chapter 3).
Was this article helpful?