Mechanical Vapor Recompression for the Treatment of Shale-Gas Flowback Water

Abstract

Used extensively by the food, chemical, and pharmaceutical industries, the mechanical-vapor-recompression (MVR) process is viewed as a reliable method for recovering demineralized water from concentrated brines. Devon Energy has supported the operation of an advanced MVR system at a north-central Texas (Barnett shale region) treatment facility. At this facility, pretreatment included caustic addition and clarification for total-suspended-solids and iron control. Pretreated shale-gas flowback water was then sent to three MVR units, each rated at 2,000-2,500 B/D (318-398 m 3 /d). Data were collected during a 60-day period in the summer of 2010. Distilled-water recovery volume averaged 72.5% of the influent water to the MVR units. The influent total dissolved solids (TDS) fed to the MVR units averaged just under 50 000 mg/L. More than 99% of the TDS were captured in the concentrate stream. 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 and TPH removal (90 and 84%, respectively) occurred during pretreatment. The total removal of iron, magnesium, calcium, barium, and boron from the distillate exceeded 99%. BTEX removal from the distillate exceeded 95%. Electric power at the facility was provided by two natural-gas generators, and compressors associated with the MVR units were driven by natural-gas-fueled internal-combustion engines. Energy requirements at the entire treatment facility were tracked daily by total natural-gas use. Best-fit correlations between treated water and distillate production vs. total plant use of natural gas indicated that there was a base power load throughout the facility of approximately 120 to 140 Mscf/D (3400 to 3960 m 3 /d) of gas. Approximately 48 scf natural gas/bbl influent water treated (270 m 3 /m 3 influent) or 60.5 scf/bbl distillate produced (340 m 3 /m 3 distillate) was required; this represents an energy cost of less than USD 0.25/bbl treated (USD 0.04/m 3 treated) and approximately USD 0.30/bbl of distillate product generated (USD 0.048/m 3 distillate), assuming a natural-gas cost of USD 5/million Btu (USD 4.72/GJ). Performance in terms of water recovery and product-water quality was stable throughout the 60-day test.

Organic Pollutants in Shale Gas Flowback and Produced Waters: Identification, Potential Ecological Impact, and Implications for Treatment Strategies

“…17,38 The reports cover sampling of 19 wells of Marcellus shale (Pennsylvania and West Virginia, USA) and 5 wells of the Barnett Shale (Texas, U.S.) (Table 1). Fifteen volatile organic compounds (VOCs) and 17 semivolatile organic compounds (sVOCs) were detected by the authors in more than one FPW sample.…”

“…To date, the largest sources of information on quantitative determination of particular organic compounds in shale gas FPW are the reports of Hayes (2009) and Hayes and Severin (2012). 17 , 38 The reports cover sampling of 19 wells of Marcellus shale (Pennsylvania and West Virginia, USA) and 5 wells of the Barnett Shale (Texas, U.S.) ( Table 1 ). Fifteen volatile organic compounds (VOCs) and 17 semivolatile organic compounds (sVOCs) were detected by the authors in more than one FPW sample.…”

An Inventory and Engineering Assessment of Flared Gas and Liquid Waste Streams From Hydraulic Fracturing in the USA

“…This analysis incorporates a model of an on-site reciprocating engine generator with a thermal efficiency of η = 35% to produce the electricity for driving the compressor. An energy intensity of 148 MJ/m 3 (530 BTU/gal) of TW is used as an estimation for the MVR process based on available data from literature and interviews with existing operators of MVR units [27,30]. Additional parasitic losses, such as pressure drop in system pipelines, were not included in this analysis.…”

“…However, there are many technologies under development and so it is likely that in the coming decades, new treatment approaches will be implemented. While MVR and other distillation techniques are often preceded by primary treatment steps such as chemical precipitation and coarse filtration, the energy intensity of these steps are not included in this analysis as they are often much lower by comparison [25][26][27]. As such, the energy intensity of MVR serves as a benchmark in this study to assess the amount of energy that would be required to treat the volume of WW in each region Figure 3.…”

“…The Marcellus/Utica region also has few SWD sites, which means WW requiring disposal must be trucked long distances, resulting in a logistical scenario that might favor on-site treatment of WW. The WW in Marcellus/Utica averages approximately 130,000 mg/L TDS, low enough that technologies like MVR are effective in treating the water [25,27]. In fact, some operators are already treating their WW on-site [30].…”