World Energy Resources | 2016

WORLD ENERGY COUNCIL | CARBON CAPTURE & STO RAGE
Water use in capture systems
Many commodity production processes (e.g. thermoelectric power production, cement
manufacturing, steel production, oil refining, and others) require reliable, abundant, and
predictable sources of water. Coal-fired power plants, for example, use significant quantities
of water for electricity generation - a 500-MW power plant uses more than 45.4 million
liters/hour. The largest demand for this water is process cooling. Adding a CO2 capture
system to an existing power station or industrial process has the potential to increase the
water demand at the site where it is applied.
There are basically two types of cooling water system designs – once-through (open loop) or
recirculating (closed loop). In once-through systems, the cooling water is withdrawn from a
local water body such as a lake, river, or ocean and heat is transferred to the cooling water.
The warm cooling water is subsequently discharged back to the same water body. In wet
recirculating systems, warm cooling water is typically pumped to a cooling tower where the
heat is dissipated directly to ambient air by evaporation of the water and heating the air. For
a wet recirculating system, only makeup water needs to be withdrawn from the local water
body to replace water lost through evaporation.
The two commonly used metrics to measure water use are withdrawal and consumption.
Water consumption is used to describe the loss of withdrawn water, typically through
evaporation into the air, which is not returned to the source. When evaluated in terms of the
two types of cooling water system designs described above, once-through systems have
high withdrawal but low consumption, whereas plants equipped with wet recirculating
systems have relatively low water withdrawal, but high water consumption, compared to
once-through systems.
The water requirements for CO2 capture systems are widely known and acknowledged, and
as such a number of studies have been conducted in which estimates of water use for
different types of capture systems and power plants have been calculated. Table 2 provides
an overview of relevant studies. A wide variety of capture systems are included in the
studies. The Zhai et al. and US DOE studies used wet recirculating cooling systems to
develop their water consumption estimates, whereas the other studies were based on oncethrough
cooling systems. The results presented here focus on post-combustion capture
systems, which are consistent with the results for pre-combustion and oxy-combustion
systems as well.
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