Design of a 1.4 mgd desalination plant based on MSF and RO processes for an arid area in India

Abstract

Although India receives an average rainfall of 100 cm, some parts of the country get only scanty rains and are subject to chronic water shortages. Due to the occasional failure of the monsoons, a drinking water problem in these areas becomes quite acute. Water has to be brought in tankers and railway wagons to meet the drinking water needs of the people. With the advent of desalination technology based on both thermal and membrane processes, it is being considered as an alternate source to provide/augment the drinking water sources in the coastal water scarce areas. R & D work carried out at the Bhabha Atomic Research Centre (BARC) on desalination in the last 10–15 y has resulted in the development of technology for brackish water and seawater desalination in the country. Operation of pilot plants based on both membrane and thermal desalination has provided useful data for the design of large-scale desalination plants. This paper gives the details of a 1.4 mgd (6300 m 3 /d) desalination plant to be installed in a coastal area for augmenting the drinking water supply. This consists of a 1.0 mgd multi-stage flash (MSF) and a 0.4 mgd two-stage reverse osmosis (RO) plant based on an indigenously available cellulosic membrane. A two-stage RO process is required in view of moderate salt rejection of cellulose acetate membranes for seawater feed. These membranes, however, possess better chlorine tolerance and fouling resistance compared to TFC membranes. As such this system is more appropriate under Indian conditions. The steam for the MSF plant will be available from a thermal power station where the plant is to be set up. Part of the product water obtained from the MSF plant will be used for entire boiler feed make up of the power station (in lieu of obtaining steam and power for the desalination plant). The remaining product water from the MSF plant (around 0.6 mgd) and RO plant (0.4 mgd) will be blended to get potable water of 250 ppm TDS. The MSF and RO plants are based on indigenous technology using most of the materials and equipment made locally. The detail design aspects and the cost estimates are presented in the paper.