Reduction of wet flue gas desulphurisation water consumption through heat recovery
Stephen, Candice Leandra
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The Power Station X is expected to be retrofitted with a Wet Flue Gas Desulphurisation (WFGD) plant to comply with new stringent environmental legislation prescribed for SO2 emissions. Once retrofitted the WFGD is expected to be the largest consumer of water in the power plant, responsible for nearly 60 % of the stations total raw water consumption. This is of particular importance as South Africa is considered to be a water scarce country and the Power Station X is also located in the water stressed region of Lephalale. Research has shown that cooling of the flue gas upstream of the WFGD plant can result in water savings. A techno-economic assessment of options for flue gas cooling with heat integration with existing power plant systems was conducted to evaluate the feasibility of the options for the application at Power Station X. The flue gas cooling through heat recovery options evaluated include: flue gas reheat and boiler feed water (FW) heating. A WFGD process model (WPDM) was developed to evaluate the options and the outputs of the technical assessment were used to obtain vendor information, and develop the capital and operating cost estimates. The implementation of any of the flue gas cooling options would result in WFGD water savings of 28 % to 30 % (that is, from 0.21 l/kWh to approximately 0.15 l/kWh for WFGD) making the WFGD water consumption comparable to that of conventional semi-dry FGD systems. The implementation of any of the flue gas cooling options would incur significant capital and operating costs. The flue gas cooling through FW heating option was found to have the least life-cycle cost however the life cycle assessment of the options was found to be extremely sensitive to the outage time requirements for the modification and the cost of water.
- Engineering