Micro-Scale Multi-Effect Distillation System for Low Steam Inputs

Distillation can remove all types of contaminants at any concentration level. In this phase change method the feed water is evaporated into steam using a heat source. The vapor formed leaves behind all contaminants in the feed water. The steam led to a condenser gives premium quality water with Total Dissolve Solids (TDS) less than 10 ppm. Generation of 1 kg of steam takes about 1kWh of energy making it energy and cost intensive. Recycling of latent heat of vaporization by Multi-Effect Distillation (MED) makes the process economical. The challenge is to develop small scale MED units for applications in rural areas. The paper describes a Micro Scale MED (MSMED) designed specifically for a low heat source where amount of steam generated is low as with small solar energy collectors. An earlier MED design by some of the present authors, comprising vertical tube evaporators, condenser and water reservoir was optimized for MSMED to work with about 3 kg input of steam at 1.5 bar, which can be generated by a solar concentrator of area 6 m2. Using 3 effects and a condenser the MSMED was able to produce 11 to 12 liters of water per hour. The Gained Output Ratio (GOR) was 3.6 and the heat recovery at every effect was high. The TDS of the distilled water was reduced from an initial value of 748 to less than 10 ppm.