costs required by the whole methanol production process. For
the material costs, it is assumed that feed cost (FCOST) only
accounts for methane, and income (INCOME) is obtained from
the selling of methanol. As a matter of fact, to sell methanol as
a product, a high purity should be attained. Therefore, it is
enforced that the methanol should be at least as pure as 99.5%
(mass basis) in order to sell it at a full price of $0.8/kg. Otherwise,
it does not have any selling value. A comparison between
the utility costs before and after heat integration with
the different objective functions is shown in Fig. 14. After heat
integration, the utility cost has been decreased by 78.4% using
the objective function of minimizing utility cost and by 43.8%
minimizing capital cost. Also, if estimating the profits on an
annual basis, the estimated net profit for the methanol