Ro, MSF and VTE/VC desalination: a comparative evaluation

Abstract

The two main processes currently in vogue, for sea -water desalination 3̄-- multistage flash. (MSF) and reverse osmosis (R.O.) -- are compared, on the basis of cost economics. Cost data are reported for unit sizes up to 10 million (U.S.) gallons per day. Both single-pass and double-pass systems are considered for the R. 0. unit, while the cost of water from MSF plants is calculated for different performance ratios. Controlling factors such. as fuel prices, pretreatment costs, membrane life, energy recovery and terms of financing, are discussed. On the basis of present technology, notwithstanding new developments, it is concluded that R. 0. is the more economical of the two for small unit sizes and regions of high fuel costs. There is a break-even point, depending on these two parameters, beyond which the MSF process yields lower water costs. Attention is focussed on a third process —- Vertical Tube Evaporation/Vapor Compression (VTE/VC), a self-contained, low-energy consuming system which is particularly suitable for barge-mounted or land-based single- purpose (water only) installations. The process, -which, is in an advanced stage of development under Envirogenics Systems Company's R and D program, is potentially competitive with R.O , even for small unit sizes. Future improvements and operational experience could make this the process of choice for single-purpose sea water desalination plants.