Parametric analyses of energy consumption and losses in SWCC SWRO plants utilizing energy recovery devices

The reduction of energy consumption constitutes one of the major thrust areas of research in SWRO desalination process industries. The cost of energy in the SWRO process is usually about 30 to 50% of the total production cost of water and can be as much as 75% of the operating cost, depending on the cost of electricity. Thus, energy forms the major contributing factor in determining the water production cost. Hence reducing the energy consumption, which is mainly due to wastage of energy in high-pressure brine, is a major goal of desalination industries. Excepting Jeddah and Al-Birk, all the SWCC SWRO plants are equipped with several types of energy recovery devices, which are utilized to recover otherwise wasted energy in the reject. These energy recovery devices (ERD) are of varying efficiencies and their ability to recover the wasted energy is different in each case. ERD performance is very much dependant on the operating parameters such as flow as well as pressure, which of course is influenced by the feed water temperature. This paper describes in detail the performance of several ERD systems used in various SWCC SWRO plants and compares their efficiencies with regard to operating conditions for a period of one year and its effect on total energy saving and total power consumption by the high pressure pump in addition to the energy loss occurring in the process stream of SWRO plants. The average overall efficiency of the ERDs ranged from 3.2% to 65% which enabled savings of about 1.5% to 27% of total energy consumed by the high pressure pump. The average power consumed by the high pressure pump was in the range of 5.56–7.93 kWh/m3. However, it was observed that a substantial amount of energy is lost by throttling that ranged from 6.4% to 21.8% of the total energy input to the high pressure pump. It was found that only at Al-Jubail plant, the performance of ERD was affected by the seasonal variation in operation parameters and for the rest of the plants the variation was not large enough to cause any significant change in the ERD performance.