Technical

Paper

Integrated Approach to Water/

Wastewater Treatment at Zero Liquid
Discharge, Combined Cycle Power Plants
Author: Dave Ciszewski, Resource Conservation (demineralizer regeneration wastes, ash pile run-off,
Company (RCC) scrubber blowdown, plant drain, and site contain-
ment). Most of the early installations were at exist-
Note: GE’s Water & Process Technologies purchased ing operating power plants. Substantial engineering
RCC in 2005. studies were performed in many cases at these
plants in an attempt to minimize overall water
Abstract usage and maximize overall water recycling. These
efforts helped to minimize the size of the required
This paper discusses the design process and ex- ZLD system, but little or nothing was done to inte-
periences of selected integrated zero liquid dis- grate the water and wastewater treatment system
charge, water/wastewater treatment systems at involving the cooling tower, demineralizer and the
power plants. Typically, the cooling tower treat- ZLD equipment.
ment, demineralizer, and zero liquid discharge (ZLD)
equipment are specified and designed independ- The recent combined-cycle plants have been pre-
ently for new plants. Two case studies with inte- dominantly greenfield sites. With the proper plan-
grated treatment systems will be presented and ning, this allowed for engineering evaluations to be
reviewed. performed up-front on the overall plant water bal-
ances. These efforts led to better optimization of the
Introduction water/wastewater treatment systems resulting in
an integrated approach. The approach links
Environmental regulations and lengthy permitting together the cooling tower, demineralizer system,
processes pushed many of the recently installed and the ZLD equipment. Two case studies involving
(1999-2002) wave of natural gas-fired combined- ZLD combined-cycle power plants from different
cycle, power plants to use zero liquid discharge regions of the United States have been evaluated.
(ZLD). In some cases this significantly eased and The design considerations, process parameters, unit
speeded along the permit cycle. In other cases, no capacity requirement, and overall performance of
other viable discharge options existed. ZLD is more the treatment systems were reviewed along
“politically correct” in today’s world and helps win with the expected plant make-up water sources
local community acceptance of new facilities. ZLD and composition. Most importantly, the advantages
also conserves water resources by reducing con- and benefits of integrated water/waste-water treat-
sumption by up to 10% to 20%, which can be sig- ment systems to the power plants are summarized.
nificant in water-short areas around the world.
ZLD has been used at coal-fired power plants since
the mid-1970’s for the treatment of cooling tower
blowdown and other power plant wastewaters

Find a contact near you by visiting www.ge.com/water and clicking on “Contact Us”.
* Trademark of General Electric Company; may be registered in one or more countries.
©2011, General Electric Company. All rights reserved.

TP1043EN.doc Feb-11
Case One: tion after a preliminary evaluation. EPC and plant
Southwest Power Plant representatives visited operating ZLD plants to
assess the overall reliability and operating histories,
The Texas Independent Energy (TIE) Guadalupe then selected a system which included a raw
Power Plant in Marion, Texas is a 1000 MW com- water softener/clarifier unit (SCU), brine concentra-
bined-cycle plant with two power blocks (2 x 1 con- tor (BC), calandria crystallizer, and an electrodeioni-
figuration, 500 MW each) using General Electric 7F zation (EDI) unit with a mixed bed ion exchange (MB
gas turbines. The plant was designed with supple- IX) polisher. The overall plant water balance and
mental duct firing during peak power demand peri- treatment subsystems are depicted in Figure 1.
ods. The plant started up in 2000 and went
commercial in 2001.
The nearby Guadalupe River supplies the make-up
water to the plant. The design make-up water
chemistry is given in Table 1. The design range
specified is a function of seasonal variations. A raw
water clarifier was required to accommodate
increased suspended solids (TSS) loads during
the rainy season.

Table 1: Make-up Water Composition (ppm [mg/L] as

ion) TIE Guadaloupe Power Plant

Figure 1: Overall Guadaloupe Plant Water Balance

(Normal Case)

The raw water softener/clarifier (SCU) reduces the

calcium and silica in the make-up water to allow up
to 12 cycles of concentration in the cooling tower.
Hydrated lime is added to accomplish the required
reduction. The clarifier also removes the silty sus-
pended solids during the river water upset periods.
The softener sludge is thickened, dewatered in a
filter press, and disposed of off-site.
The initial ZLD water treatment design included a
raw water clarifier, a cooling tower sidestream sof- The cooling tower blowdown is sent directly to a
tener/clarifier unit (SCU), a wastewater reverse mechanical vapor recompression (MVR) evaporator
osmosis (RO) unit, a brine concentrator, and a crys- (commonly referred to as a Brine Concentrator
tallizer. This type of system demanded a high (BC) - Figure 2) where 99% of the wastewater is re-
chemical consumption, plus it created a large waste covered as high-quality distillate (5 to 10 ppm
sludge stream requiring off-site disposal. [mg/L] TDS).
The plant engineering, procurement, and construc- The blowdown from the BC goes to the steam-
tion (EPC) company wanted single-source responsi- driven calandria crystallizer (Figure 3), which cou-
bility and a turnkey supply for the water and pled with a dewatering pressure filter, reduces the
wastewater treatment. The system specifications waste stream to solids suitable for off-site disposal.
allowed for alternate design approaches to allow
for optimization of the overall water treatment
scheme. Multiple suppliers proposed varying alter-
nate schemes, allowing the initial treatment
approach to be eliminated from further considera-

Page 2 TP1043EN
 after the contract was awarded. Typically, similar
systems require 18 to 24 months from award to
mechanical completion.

Figure 4: Electrodeionization Process (EDI)

Most of the difficulties during the start-up were

associated with the softener/clarifier, which was
hard to operate with the frequent cycles and down-
Figure 2: Mechanical Vapor Recompression Brine Con-
time associated with the plant commissioning
centrator
period. The calandria crystallizer foaming was prob-
lematic until the optimal anti-foam program was
developed. This was the first successful power
plant installation coupling brine concentrator distil-
late with an EDI. After some initial problems with
feed temperature excursions and membrane foul-
ing (due to the improper feed pump seal water),
the EDI system has worked very well, consistently
averaging product quality of 15 to 16 megohm-cm.
The excellent performance of the EDI has rendered
the mixed-bed ion exchange redundant, but it does
provide an inexpensive back-up system.

Conclusions

The integrated approach at TIE Guadalupe yielded

the customer the following benefits:
• Significant reduction in the sludge produced
Figure 3: Calandria Crystallizer compared with the original design concept,
reducing landfill disposal costs up to 25%.
A portion of the distillate from the BC is directed to
• A simplified process design with more operating
the EDI (Figure 4), which provides the plant’s demin-
flexibility for feed chemistry fluctuations and
eralized water and the remaining distillate is
flow rates.
recycled back to the cooling tower. The off-site
regenerated mixed-bed IX is provided as a back up • A single-source supplier dramatically reducing
to the EDI. the overall schedule and providing single-point
accountability and more efficient supplier
In addition to reducing the treatment chemical management.
usage and waste disposal requirements, another • Common integrated control system for monitor-
advantage of this integrated approach is a stream- ing the entire water and wastewater
lined project schedule. The entire ZLD water treat- treatment plant, which allowed for reduced
ment plant was supplied and installed 13 months operator requirements.

TP1043EN Page 3
Case Two: for the overall plant water balance and selected
Northeast Power Plant subsystems.
The AES Ironwood facility in Lebanon, Pennsylvania This integrated system utilized a more aggressive
is a 700 MW combined cycle plant with a 2 x 1 con- cooling tower chemical program to increase the
figuration using Siemens Westinghouse 501G gas cycles (about 15x at peak design conditions) with
turbines. The plant is primarily designed to operate the blowdown going directly to a BC. The selected
on natural gas, but originally had provisions to cooling tower chemical program required a scale
accommodate oil firing, if required. The plant inhibitor, corrosion inhibitor, dispersant, and bio-
started up in 2001 and went commercial in 2002. cide. This eliminated the need for a lime sof-
tener/clarifier and wastewater RO, thereby
The Ironwood plant has two sources of make-up minimizing the number of unit operations required.
water; secondary treated effluent from the nearby The MVR BC operating at 97% recovery, blows
publicly owned treatment works (POTW) and quarry down to a small steam driven crystallizer (Figure 6).
water from the adjacent quarry. The design The solids produced in the crystallizer are dewa-
make-up feed to the power plant is a 60% quarry - tered in a pressure filter and are sent to a landfill for
40% POTW blend. See Table 2 for compositions. disposal.
Table 2: Make-up Water Composition (mg/l as ion) AES
Ironwood Power Plant

The original design concept for the plant was for

the cooling tower to operate at low cycles of con-
centration (about 8x). The tower blowdown was to
be sent to a lime softener/clarifier and wastewater
Figure 5: Overall Ironwood Plant Water Balance (Nor-
reverse osmosis (RO) system for preconcentration,
mal Mode)
then to a brine concentrator (BC), and finally to a
crystallizer. With this approach, the preferred
chemical supplier had determined the optimum
cooling tower cycles, the wastewater treatment
was designed by the ZLD system supplier, and the
demineralizer system had not yet been fully devel-
oped. The plant EPC hired an independent consult-
ant to take a look at the overall water balance. The
consultant came up with the innovative idea of
requesting one supplier to develop the optimum
overall water/wastewater treatment system and
supply all the required equipment and a one-year
supply of the specialized cooling tower chemicals
on a turnkey basis.
This total water management idea resulted in a fully
integrated system for the plant. Refer to Figure 5

Page 4 TP1043EN
 with polyaluminum chloride (PAC) addition was ret-
rofitted to the water treatment plant. The primary
cause of the high SDI was traced back to a sand
filter installed at the POTW that wasn’t performing
as expected. The other main issue discovered dur-
ing start-up was higher than expected total organic
carbon (TOC) in the demineralized water. The com-
bination of treatment additives and high cycles in
the cooling tower produced a build up of volatile
inorganic components, which resulted in a higher
TOC level in the BC distillate, above a level that
could be effectively removed in the EDI. Granular
activated carbon (GAC) canisters were installed on
the BC distillate, which removed enough of the TOC
to meet the plant demineralized water specification
(< 300 ppb).

Figure 6: Steam-Driven Crystallizer Conclusions

The distillate is fed to the electrodeionization (EDI) The integrated system installed at the Ironwood
units to produce the required 10 megaohm-cm power plant provided the following benefits:
boiler feedwater. During the normal, gas-fired • Optimized recirculating cooling tower treatment
mode, the distillate flow is sufficient to meet the program.
EDI/demineralizer feedwater demand. The original
• Elimination of the lime softener/clarifier mini-
design allowed for operation in an oil fired mode,
mized addition of bulk chemicals and reduced
during which time the demineralized water
off-site sludge disposal requirements by up
demand for the plant was designed to be nearly ten
to 40%.
times higher due to the NOx reduction
requirements in the combustion turbines. Because • Simplified treatment system with fewer unit
there was not sufficient BC distillate to satisfy the operations, yet flexible enough to accommodate
EDI/demin demand under all conditions, another chemistry variations in the make-up water.
source of EDI feed was required. A two-stage, two- • Shorter contract schedule and more efficient
pass RO unit (Figure 7) was included to supple- supplier management by utilization of a single-
ment the BC distillate. The RO is only required dur- source supplier for the entire plant
ing periods of high demineralized water demand. water/wastewater treatment system.
• Common, integrated control system interface
for all the plant water and wastewater treat-
ment functions allowing for streamlined opera-
tion and fewer operators.

Summary
An integrated approach to water and wastewater
treatment can yield a number of advantages to ZLD
power plants when compared to conventional, seg-
regated methods. The unit operations for the cool-
Figure 7: Reverse Osmosis ing tower, ZLD system, and demineralizer are based
on fundamentally similar principles and combining
During start-up of the plant, it was discovered that the responsibility for the design makes good engi-
the make-up water blend silt-density index (SDI) neering and contracting sense. The performance of
was out-of-spec high. To reduce the SDI to an each operation is often dependent on the other, so
acceptable level, a multi-media filter (MMF) system having one supplier responsible for all the water
TP1043EN Page 5
treatment is the preferred solution to eliminate con-
flicts. When designed properly, the plant benefits
with streamlined processes and simpler, easier-to-
operate treatment systems.
Other recently commissioned power plants such as
La Paloma Generating near Bakersfield, California
and Hays Energy near San Marcos, Texas have used
the same integrated approach. Both installations
included reverse osmosis pre-concentration stages
in the ZLD train to reduce the system’s overall
power consumption.

References
Prato, T., Muller, R., Alvarez, F., “EDI Application:
Evaporator Product Polishing”, Ultrapure Water,
April 2001.
Heimbigner, B., “Integrated Water and Wastewater
treatment including ZLD”, PowerGen Latin America,
August 2002.
Solomon, R., Schooley, K., Griffin, S., “The Advan-
tages of Mixed Salt Crystallizers in ZLD Wastewater
Treatment Systems”, International Water Confer-
ence, October 1998.
Bostjancic, J., Ludlum, R., “Getting to Zero Discharge:
How to Recycle that Last Bit of Really Bad Waste-
water”, International Water Conference,
October 1997.

Page 6 TP1043EN