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A mathematical simulation of the largely graphical pro- ~, N cedures outlined by the U. S. Department of the Interior (1972).' 00 is summarized for a MSF desalting plant (including pretreatmen'f' ~ and post~treatment) in Table 1. In estimating capital costs for ~ construction, steam, site development, and land, the functions are based on product water capacity, C. The same is true for annual expenditures for labor and matePials, chemicals, fuel, steam, and electricity. Interest during construction is deter- mined by multiplying an estimate of construction time by one- half of the interest rate and applying this result to the sum of capital costs for construction, steam and site development. Start-up costs are assumed to be equal to one month of the sum of annuaL costs, whereas working capital is assumed to be twice the start-up costs. Costs for "owner's general expenses" are based on the level of investment in construction, steam facili- ties, and site development. It should be noted that the equations in Table 1 are expressed in terms of English units in order to be congruent with the ~rocedures in the source. Since this work is presented in metric. units, the interested users of these models should lllu~tiply product water capacity expressed in m3/day by 2.6417 x lO 4 to convert to million gallons per day (mgd). In addition, land prices in $ mi11ion/ha need to be multiplied by 0.4047 to get $ million/acre; fuel rates in $/m:illion joules (MJoules) need to bl= multiplied by 9.4787 x 10 -4 to get $/million BTU's (MBTU) and electrical rates in $/MJoules need to be multiplied by 2.7778 x 1Q ,-4 to get $/1000 kilowatt-hours (kwh). Vertical Tube Evaporation - MSF Another distillation process designed to maximize heat transfer efficiencies is the vertical tube evaporator (VTE) which has been by itself an alternative to MSF systems. However, hybrid VTE-MSF processes have been shown to improve thermo- dynamic efficiency, reduce brine pumping costs, and lower structural costs due to several common elements (U. S. Department of the Interior, 1972). Consequently, VTE by itself will not be included in this costing analysis although it is helpful to review its operation. Like MSF systems, VTE processes make use of the principle that water will vaporize at a progressively lower temperature if associated also with progressively lower pressures. Unlike the MSF process, vapor produced in any stage is condensed in the succeeding stage to aid vapor formation therein (Figure 5). In the VTE-MSF process, feedwater is pumped alternately from MSF stageS to VTE effects. The desalting system is best applied to the conditions noted earlier for the MSF process. 33 ,,-. 'l'1 " , , -:j 'j -, '.0 '. . , .