Produced Water Treatment Using Direct Contact Membrane Distillation

De-oiled produced water in current produced water treatment facilities for water reclamation from steam-flooded oil exploration activities is available at temperatures between 160-200⁰F (71-93⁰C). Desalination of this de-oiled produced water is accomplished currently by reverse osmosis after a number of steps including cooling. Membrane distillation processes can utilize this sensible heat to achieve desalination. Direct contact membrane distillation studies using a hollow fiber membrane module with the brine in cross-flow have been successfully conducted using a variety of produced waters such as Chevron A (Pre-RO, Post WEMCO), Chevron B1 and Chevron B2 having total dissolved solids (TDS) respectively of 7622, 12040 and 35000 mg/l. The brine feed temperature was varied between 50 and 85⁰C. The effect of brine feed flow rate variation was also studied. At 80⁰C, the highest observed water vapor flux at a higher feed brine velocity was 15 kg/m²-hr. The permeated waters were substantially pure with very low TDS value in each case indicating very high salt rejections. These conclusions held even when the feed de-oiled produced water was concentrated via batch recirculation to recover as much as 80% of the feed produced water in the distillate stream.