Both multi-stage and MVR evaporators are capable of producing distilled quality water from produced water. Distilled water quality ranges from 100 to 500 ppm TDS depending upon the initial TDS of the produced water and the level of concentration of bottoms (waste) obtained. Typical systems are capable of attaining final concentrations ranging from 270,000 ppm to 350,000 ppm TDS.
The limiting factor is the actual concentrations of the ionic contaminates -- usually sodium chloride, calcium sulfate, calcium carbonate, barium sulfate and strontium sulfate and other similar salts -- and the solubility’s of these salts. Without additional technologies such as crystallizers or other methods of solids extraction the ability of both types of evaporators to concentrate produced water/produce distillate are limited by precipitation.
The selection of one technology over the other is primarily based upon economics. The key drivers are the cost and availability of the prime energy source, the initial capital investment and the non-energy operating costs such as labor, maintenance and spare parts inventory.