Typical values quoted are in the range of 2-6%, depending on the source of information and the process plant type. For the sake of simplicity, other fixed costs such as insurance, property taxes, rent of land etc., have not been specifically accounted for, however in the present study O&M costs are fixed to 3% of the total CAPEX. In the present study, two approaches are taken, the first is using DACE (Design and Analyis of Computer Experiments) via a Box-Behnken 3-factor design and applying Response Surface Methodology (RSM). An exhaustive presentation of the methods of DoE and RSM will not be given here. Instead the reader is referred to relevant textbooks and literature. The general second order response surface model can be expressed as