Environmental Engineering Reference
In-Depth Information
such as bag iltration, settling tanks, and mobile treatment systems have been used, while
offsite treatment tends to focus on primary and secondary clariication, precipitation, and
iltration. Major challenges include reducing TDS (which can reach 205,000 mg/l), calcium
(which can reach 31,000 mg/l), and hardness (which can reach 55,000 mg/l as CaCO 3 ) of
the lowback or produced water as they contribute to scale development in wells, which
can cause reductions in well production [30]. In areas where TSS is low enough (e.g., in
areas of the Marcellus shale, approximately 160 ppm) the produced water can be iltered
to remove the suspended solids [42]. In order to place the TSS numbers in context, for
seawater based RO plants TSS content usually varies between 1 and 15 ppm as a function
of temperature (e.g., higher in summer) and geographical location. The produced water is
also tested for calcium, magnesium, and other common ionic species to determine the cor-
rect amount of freshwater to blend back into the recovered water and reinject into the wells
[42]. Given the lack of standards and available data for frac luids, the approach driving the
reblending for reuse of lowback water is “dilution is the solution.”
28.3.3 Refining
Water resources are also consumed in the production and processing of many energy
sources, including coal, natural gas, oil, uranium, and hydrogen, as summarized in Table
28.6. In the coal mining process, whether surface or underground, water is used for coal
cutting, dust suppression, and coal washing. The inal process is performed to remove
some sulfur and increase the heat content by removing non-combustibles, and is per-
formed on approximately 80% of the coal mined in the United States. Water consump-
tion for mining ranges from 10 to 100 gal/ton (3.4-20.5 gal/MWh) of coal mined, while
washing requires an additional 20-40 gal/ton (3.4-6.8 gal/MWh), totaling approximately
70-260 million gallons per day of water withdrawal. In addition, after water is used,
treatment is required to remove coal sludge and other particulates [5]. Uranium mining
and processing requires 27.3-47.8 gal/MWh, generating about 3-5 million gallons per
day at a mine that has to treated for trace metals before release back into the water cycle
[5]. Typical onshore oil extraction requires 5-13 gal of water per barrel of oil equivalent
(boe) (2.7-7.5  gal/MWh), while enhanced recovery wells that inject water or steam to
extract oil require between 81 and 14,000 gal/boe (47.8-8532 gal/MWh) [5]. In addition
to water required for extraction, a typical reinery will withdraw 3-4 million gallons per
day, returning only 30%-40% as wastewater while the rest is evaporated. The remaining
water must be treated for residual petroleum products left from the reining process as
well as increased TDS [5]. Approximately 95% of the hydrogen made in the United States
is produced from steam reforming of natural gas and is used in ammonia production
facilities, oil reineries, and methanol production plants. Hydrogen production by this
TABLE 28.6
Comparative Summary for Water Consumption toward Fuel Reining
Fuel
Gal Water/MWh
Coal mining and washing
6.8-27.3
Uranium mining
27.3-47.8
Onshore oil extraction
2.7-7.5
Enhanced oil recovery wells
47.8-8532.4
Hydrogen
146.8
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