Evaluation of the Aqua Pure Mechanical Vapor ...

 

 

 

Extensively used by the food, chemical, and pharmaceutical industries, the mechanical vapor recompression (MVR) process is viewed by a number of shale gas companies as one of the most reliable methods of recovering demineralized water from concentrated brines. For this reason, Devon Energy has supported the demonstration of three modular NOMAD units that are manufactured by Aqua-Pure Ventures and operated in the field by Fountain Quail Water Management. This report presents process data on a commercial-scale (6,000-6,800 bbl/day) mechanical vapor recompression distillation (MVR) processing plant treating shale gas hydro-fracture flowback and produced water in North Central Texas (Barnett shale region). Process data were collected during a 60 day period during summer 2011. The pretreatment at this plant included caustic addition and clarification for total suspended solids and iron control. Pretreated water was distilled with three Aqua Pure MVR units, each rated at 2,000-2500 bbl/day. Distilled water recovery averaged 72.5% of the influent to the MVR’s The influent total dissolved solids (TDS) fed to the MVR’s averaged just under 50,000 mg/l. More than 99% of the TDS was captured in the concentrate stream. The distillate averaged about 171 mg/l TDS. The fate of multivalent cations, total petroleum hydrocarbons (TPH), and benzene, toluene, ethylbenzene and xylenes (BTEX) throughout the treatment system was determined. Most of the iron (90%) and TPH removal (84%) occurred in the clarification step. The removal of iron, magnesium, calcium, barium, and boron from the distillate exceeded 99%. BTEX removal from the distillate exceeded 95%. The power at the facility was provided by two natural gas generators, plus the three generators on the MVR units, making isolation of the MVR energy requirements problematic. Best-fit correlations between treated water and distillate production versus total plant utilization of natural gas indicated that there was a base power load throughout the facility of about 120-140 thousand standard cubic feet of gas per day. Approximately 48 SCF per barrel influent water treated (or 60.5 SCF per barrel distillate produced) was required; this represents an energy cost of less than 25 cents per barrel treated and about 30 cents per barrel of distillate product generated (assuming a natural gas cost of $5/mmBtu). Performance in terms of water recovery and product water quality was stable throughout the 60-day test. The treatment process is available throughout the shale gas industry; Fountain Quail Water Management provides the complete equipment package and operation of the integrated MVR treatment facility on a price per barrel basis. Cost factors and approximate pricing for example applications are included in the report.