AN MSF EVAPORATOR FOR THE UANW-9 AND UANW-10 POWER-STATION - DESIGN CONSIDERATIONS BASED ON ENERGY AND EXERGY

A thermoeconomic study was conducted to obtain the optimum design parameters of an MSF seawater evaporation plant to be associated with the UANW 9 and 10 steam power plants which can provide turbine extraction steam for the evaporator. The study used both energy (enthalpy) and exergy in cost accounting in order to compare the optimum design parameters which are obtained for each case. Cost accounting was based on realistic capital and fuel cost figures as obtained from recent bids. Based on current capital cost estimates for MSF evaporators and auxiliary boilers, as well as cost estimates for electricity and steam obtained from the thermoeconomic study, it was found that the optimum performance ratio and number of stages of the proposed MSF evaporator were slightly larger for the case of energy accounting compared to exergy accounting. For an evaporator having a capacity of 2600 m(3)/h, the optimum performance ratio was found to be 10.3 for energy accounting compared to 10.1 for exergy accounting. The optimum number of stages was estimated to be 27 for energy accounting and 25 for exergy accounting. The optimum top brine temperature for both accounting methods was found to be close to the upper constraint value of 120 degrees C. The optimum cost of distilled water was found to be slightly (about 7%) higher for the case of energy accounting compared to exergy accounting.