where i is the interest rate and n is the number of annuities over project lifetime. In this study, the interest is set to 8% (i = 0.08) and the project lifetime is set to 20 years (n = 20). The fixed O&M cost is often expressed as a fraction of the overnight costs. Typical values quoted are in the range 2-6%, depending on the source of information and the process plant type . For 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 4%.