A case study of an existing DPPW production plant in Qatar was used in the analysis. The basic configuration of the case study plant is shown in Fig. 46.1. The power production side consists of a compressor (CP), combustion chamber (CC) and a gas turbine (GT), while the water production side is based on the multistage flash (MSF) distillation process.
The compressor compresses incoming air to a high pressure which is then mixed with natural gas and burnt in the combustion chamber to produce high pressure and high velocity gas which in turn is used as mechanical energy to drive the compressor and the electrical generator. The hot exhaust gases from the power generation gas turbine section is used in the waste heat boiler section as a heat source to generate the steam required for the distillers. The case study plant operates with 14 gas turbines, 12 waste heat recovery boilers and 10 auxiliary boilers.
The simplified structure of the MSF desalination plant is shown in Fig. 46.2. The plant consists of the following principal sections: (i) heat input section-which consists of the brine heater, where thermal energy is supplied; (ii) heat recovery
Fig. 46.2 Simplified structure of the MSF desalination plant
section-where heat of condensation is transferred to the brine, and thus pre-heats the recirculated brine in stages 1 through 14; and (iii) heat rejection section-where heat of condensation is partly transferred to the make-up stream and mostly to sea water cooling stream, through stages 15 and 16.
The distillation unit has two operating modes: mode 1, 85-100 % of 18,000 m3/ day at a top brine temperature of 91 °C; and mode 2, 70-100 % of 22,500 m3/day at a top brine temperature of 112 °C.