intensive. Existing harvesters involve costs
upwards of 20 cents/gallon, which has been
the deal breaker for industrial-scale AWH.
‘Free’ excess gas can power large-scale
AWH systems to supply freshwater to
oilfields. This is especially attractive for
places where three factors converge:
availability of excess gas, local water needs,
and high humidity. The Eagle Ford, in
particular, meets these criteria very well.
Condensing water releases 2260 kilojoules
of heat per kilogram of water condensed;
this has to be absorbed by the refrigeration
system. While vapor compression cycles
(household refrigerator) can be used,
analyses indicate that vapor absorption
cycles will offer better water yields. Water-lithium bromide vapor absorption systems
are used for large-scale air-conditioning, and
could be adapted for this application.
In a flared gas-based vapor absorption
system, natural gas from the wellhead is
fed to a boiler after treatment in a gas-conditioning module. Steam generation
in this boiler essentially powers the cycle.
Cooling is generated in the evaporator
by dissolving a refrigerant (water). The
evaporator is a tube bundle with refrigerant
evaporating inside and atmospheric
moisture condensing outside. The
evaporated refrigerant is next absorbed by
a secondary liquid (lithium bromide) in the
absorber. This refrigerant saturated solution
is then heated in the vapor generator (using
the boiler steam) to release refrigerant
as high pressure vapor. This vapor then
compresses in the air-cooled condenser,
thereby rejecting the condensation heat
release back to the ambient.
Vapor absorption systems offer distinct
advantages compared to other refrigeration
systems. Firstly, analyses indicate that vapor
absorption systems will generate higher
cooling capacity per unit of gas burnt, as
compared to vapor compression systems.
Secondly, absorption systems do not need
Flaring is a big environmental and resource- waste issue in energy-rich, but other wise poor Nigeria. Unfortunately, flares now
dot the U.S. Shale oil patch. (Photo credit: Bahadur Group, UT Austin)
Daily water harvest from the gas flared per well in the Eagle Ford and Bakken Shales. The total harvest from the 1000’s
of currently flared wells can meet 10 percent and 65 percent water requirements of these Shale fields, respectively.