9-1 A multiple-effect evaporator is to be used for evaporating 200,000 kg of water per day from a salt solution. The total initial cost for the first effect is $18,000, and each additional effect costs $15,000. The service life of the evaporator is estimated to be 10 years, and the salvage or scrap value at the end of the life period may be assumed to be zero. The straight-line depreciation method is used. Fixed charges minus depreciation are 15 percent yearly, based on the first cost of the equipment. Steam costs $0.0033/kg. Annual maintenance charges are 5 percent of the initial equipment cost. All other costs are independent of the number of effects. The unit will operate 300 days/yr. If the kilograms of water evaporated per kilogram of steam equals 0.85(number of effects), determine the optimum number of effects for mini- mum annual cost