Vapor compression distillation with maximum use of waste heat

Abstract The vapor compression distillation process can be designed as a low capital cost and corresponding low performance ratio (about 7 lbs product per KBtu) or as a higher capital cost and higher PR (about 31) plant. The low PR plant is designed with a maximum brine temperature of about 130°F requiring only a polyelectrolyte scale inhibitor. This design would employ a centrifugal compressor that has a pressure ratio of about 1.2. The high PR plant design, which is the subject of this paper, operates at maximum brine temperature of 250°F and uses a higher pressure ratio of 1.58 use of waste heat will be stressed. Either the high or low PR VC process is extremely versatile in application, since it is well adapted to either a dual purpose (power and water) or a single purpose (water only) plant. The high PR that is easily attainable in this design is becoming increasingly more attractive, from an economic view, as the price of fuel continues to escalate. For example, at $5.0/MBTU the fuel contribution to the total cost of water is $5.20/Kgal at a PR of 8 and is reduced to about $1.34/Kgal at a PR of 31. The design and process descriptions for a 2.35 mgd plant will be presented. This plant employes a 65,000 CFM centrifugal compressor. The compressor is driven by a diesel engine and operates across a 4 effect vertical tube foam evaporator. The design employs an exhaust gas and water jacket waste heat recovery scheme. An updated plant cost estimate will be presented and cost of product water.