Energy consumption in equivalent work by different desalting methods: case study for Kuwait

Kuwait needs to add more desalting units to its present installed capacity to satisfy the growing need of potable water. The energy consumed by different desalting system is one of the main parameters affecting the choice of new desalting system. Every desalting system consumed either thermal, or mechanical energy or both. This paper presents a method to compare these energies on one scale that the equivalent work consumed. Based on this analysis, the energy consumed by the multi stage flash MSF system, the only system presently used in Kuwait to desalt seawater, was calculated and found equal to 25 kWh/m3. This is much higher than the energy consumed by the other two reliable systems, namely reverse osmosis (RO) and multi-effect boiling (MEB) extensively used now in many of the Arabian Gulf Countries, AGC. The average energy consumed by the RO system is 5 kWh/m3, and by the MEB is in the range of 12 kWh/m3 when steam is extracted from steam turbines at low availability.

More desalting units are urgently needed for Kuwait to satisfy the growing consumption of potable water. The only used system to desalt seawater is MSF desalting system. The energy consumed by the MSF system in Kuwait, based on operation records, reached more than 25 kWh/m3. It was noticed that in the year 2000, 19.6% of desalted water was produced by steam supplied directly from boilers with consumed equivalent work of 40 kWh/m3, while for the balance 83.4% production, the steam was extracted from turbines with consumed work equivalent of 22.26 kWh/m3. The RO and MEB with conventional or TVC operations are much more efficient, energy-wise than the presently used MSF system. The new developments in RO membranes and brine staging can bring the consumed work to 5 kWh/m3. The steam supplied to the MEB has lower availability, and its pumping work is half that consumed by the MSF system. Moreover, the capital cost and delivery time of both RO and MEB are less than those of the MSF system. The delivery time may be crucial to Kuwait where the present installed desalting capacity is almost equal the consumption and the demand continues to increase. The RO and MEB systems should be considered seriously by the Ministry of Electricity and Water in their decision to install new units.