High-water-content feeds, minimization

Reverse osmosis is a cross-flow membrane separation process which separates a feed stream into a product stream and a reject stream. The recovery of a reverse osmosis plant is defined as a percentage of feedwater that is recovered as product water. As all of the feedwater must be pretreated and pressurized, it is economically prudent to maximize the recovery in order to minimize power consumption and the size of the pretreatment equipment. Since most of the salts remain in the reject stream, the concentration of salts increases in that stream with increased recovery. For instance, at 50% recovery, the salt concentration in the reject is about double that of the feed and at 90% recovery, the salt concentration in the reject is nearly 10 times that of the feed. In cases of sparingly soluble salts, such as calcium sulfate, the solubility limits may be exceeded at a high recovery. This could result in precipitation of the salt on the membrane surface resulting in decreased flux and/or increased salt passage. In addition, an increase in recovery will increase the average salt concentration in the feed/reject stream and this produces a product water with increased salt content. Consequently, the recovery of a reverse osmosis plant is established after careful consideration of the desired product quality, the solubility limits of the feed constituents, feedwater availability and reject disposal requirements. 

The factors affecting the hydrogen sulfide removal from Elkton field gas were evaluated in the extensive optimization study [70]. It was carried out to apply activated carbon based adsorption/oxidation to the industrial environment. In order to make the process as simple and economical as possible the temperature, pressure, O/H2S ratio, water vapor content in the feed gas, minimizing production of SO2 and time achieving high conversion of H2S to sulfur and water were varied [70], Moreover, the efficiency of using thermally regenerated carbon was evaluated. 

Beside the highest possible cobalt and copper recoveries, the auto-thermal operation of those fluid bed roasters, were of prime importance in order to avoid the extra operating cost of auxiliary fuel consumption. In order to limit any fuel (coal) addition, the feed slurry was maintained at 75 wt% solids to minimize the energy loss to water vaporization. This resulted in a slurry that presented a significant challenge in the roaster feed system design due to its high viscosity and solid content. 

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