Abstract

The objective of the work is to utilize waste heat from power stations’ flue gases in desalination of seawater by humidificationdehumidification. Two power station fuels namely fuel oil and natural gas are considered. The two fuels differ in composition, calorific value, and usage of percent excess air requirements. In order to achieve the same electric power production, the composition (moisture content and specific heat) and amount of flue gases ensuing from combustion of the above two fuels will be different. One humidificationdehumidification desalination scheme is generated and results are compared with respect to the anticipated cost of produced water versus
the source of flue gases. Cost is calculated on the basis of energy balance and design equations. The scheme includes: preheating of seawater using hot flue gas, humidification of an air stream by direct contact with seawater, and dehumidification of the same stream by indirect cooling in a condenser. In case of fuel oil combustion, desulphurization of the flue gas by seawater is also included. The cost of produced fresh water includes the fixed cost of heat exchangers, condensers, humidifiers, packing, pumps and fans based on the cost index of 2018, and the operating cost is based on the current electricity cost. The results show that the total cost of the produced water is much less in the case of using flue gases ensuing from natural gas fueled power stations. This happens because the flue gases in this case have a very high humidity ratio which will result in the condensation of a significant amount of water on cooling. As a result, the total amount of fresh water produced is greater than in the case of fuel oil flue gases.