Performance Research On Small Scale Marine Desalination System Using Waste Heat

As water is essential for life, the21st century will be a water’s century. Though the earth storages rich moisture capacity, salt water holds a part of97.5%, while99%of the rest of moisture capacity is storage in the two poles of the earth, which cannot be used by humans. Though conventional seawater desalination technology has partly solved the problems around the world, some areas where are dispersed and lesser demand for fresh water, has limit space or lack of fossil fuel, will not be applicable to use conventional seawater desalination technology to produce fresh water. However, small-scale desalination, a technology using new energy, self-sufficient, is suitable to support the areas.In ocean, ships consume a large amount of fresh water every day. Distillation, an important part of small-scale desalination technology, can help ships to improve the cargo capacity, endurance and safety of navigation under the large amounts of waste heat produced by ships. As a part of distillation system, plate evaporator has been replacing the traditional shell and tube evaporator in the field.In this paper, the desalination system using waste heat, working with plate rising film evaporator is studied on the basis of conservation of mass and energy, the mathematical model and economic calculation model of the two effect desalination system using plate rising film evaporator using waste heat of flue gas and cooling water output by marine power plant, which includes a heat recovery steam generator, rising film evaporator and plate condenser, are established under MATLAB programming, considering the boiling point elevation of brine and the temperature loss while steam flows through the demister and the boards in the evaporators. According to the results, freshwater production, the heating steam temperature of the first effect and the temperature between effects are given to study the marine desalination systems’ thermal performance at different processes, and a reference for the thermal performance of marine desalination system using waste heat is provided.The calculation results shows, under the conditions setting in this paper, as water production increasing, GOR of the marine desalination system had no change, while the areas of the heat recovery steam generator, evaporators and condenser were proportionally increased. As heating steam temperature of first effect increasing, the area of heat recovery steam generator increased, while GOR, the area of evaporators and condenser decreased. As temperature between effects increasing, GOR and the area of evaporators decreased while the area of the heat recovery steam generator and condenser increased. Under the same operating conditions, GOR of forward feed was always smaller than parallel feed’s, while the heat transfer area was larger than it. Therefore, under the prerequisite for safe operation, workflow process should work in parallel feed to achieve maximum system thermal performance.This paper also researches the constitute of the system cost and analysis the change of fresh water cost under the calculation conditions while freshwater production, heating temperature of first effect, temperature between effects, ship tariffs and the material prices of recovery steam generator and fabricating cost of evaporators and condenser changed. The conclusions are helpful to the design and operation of marine desalination plant using waste heat.