Zero
liquid discharge (ZLD) systems installed at power facilities
with the primary purpose of meeting water discharge regulations have
the added benefit of providing high quality effluent that can be reused
in the facility. This paper provides a review of water use in power
sector recirculating cooling towers and a baseline assessment of on-site
water reuse at natural gas combined cycle (NGCC) power facilities.
Two NGCC facilities with reverse-osmosis (RO) or brine-concentrator
processes followed by evaporation ponds were selected as case studies;
data from these facilities were used to quantify the water, energy,
and cost implications of implementing conventional and emerging ZLD
technologies. At one case study facility, model results show that
implementation of ZLD would reduce water withdrawals by 18%, which
is less than savings associated with implementation of dry cooling
but comparable to current efforts to reduce water withdrawals by increasing
cycles of concentration. Implementation of ZLD using high-recovery
RO resulted in a doubling of the levelized cost of water (LCOW). LCOW
increased more when a brine concentrator was used. For both case studies,
the ZLD system using high-recovery RO required less than 0.1% of a
facilitiy's annual electricity generation and the ZLD system
using
a brine concentrator process required less than 0.8%. Additionally,
increasing the evaporation pond area to minimize required ZLD system
recovery rates and reduce system electricity costs does not reduce
the LCOW. Instead, the LCOW increases because less water is recovered
and more water is lost to evaporation. However, if water availability
decreases or water competition/cost increases, facilities may be incentivized
to maximize water recovery from ZLD systems.