A new methodology for the optimal design of batch fermentation plants

In the design of batch and fed-batch fermentation plants, the problem of determining the adequate combination of number and size of the fermentors to be used, so to accomplish the desired production schedule must be faced. The problem has infinite solutions, as for any fermentor size, a number of units of that size will do the work, but not all solutions are equal from an economical standpoint. The problem of determining the optimum number of pieces of equipment and the optimum operation schedule has been addressed by several authors in the process engineering field. The optimal combination of size and number of fermentors will be the one that maximizes the net present value. The objective of this work was to develop a methodology for the optimal design of batch fermentation plants based in the maximum net present value criterion and to compare it with the more restricted criterion of minimum investment in production fermentors. Results show that considering only the investment in production fermentors underestimates the optimum number of fermentation units, probably because it only considers the investment in production fermentors and its assumptions of equal preparation and discharge times. On the other hand, the method proposed in this work, although somewhat more complex, gives a more accurate result.