CCGT cooling towers are thirsty. Two moves are cutting that bill fast

Combined‑cycle gas turbine (CCGT) plants use a lot of freshwater — on the order of 0.5–1.0 L/kWh in wet cooling towers (mdpi.com). One documented case reports ~0.74 L/kWh, or roughly 2.8×10^6 m^3/year for a large unit (mdpi.com).

The backdrop is tightening. Industry is the largest water user globally (~45% of total abstraction), and ~80% of that is for cooling (sciencedirect.com). The IPCC estimates ~50% of people could be water‑stressed by 2025 (mdpi.com). In cooling towers, operators are zeroing in on two levers: maximize cycles of concentration and use non‑traditional makeup.

Cooling tower cycles of concentration

Cycles of concentration (COC — the ratio of dissolved solids in recirculating water versus makeup) quantify how intensively cooling water is reused. From a water‑efficiency standpoint, the aim is to push COC as high as possible without triggering scale, corrosion, or biofouling (energy.gov). Many towers run at 2–4 COC, but with proper treatment “6 cycles or more may be possible.” Doubling from 3 to 6 COC can cut makeup roughly ~20% and blowdown by ~50% (energy.gov).

The savings are direct. One detailed case showed that softening makeup and running at 10 COC (versus hard water at ~2.2 COC) reduced annual makeup water from 17.77 to 10.77 million gallons (≈26.5×10^6 L) — a ~37% cut — while saving ~$78.8K/year in water, sewer, and chemicals (prochemtech.com). Plants frequently deploy a dedicated softener to remove hardness before the tower to make those higher cycles feasible.

Scaling is the cap. As evaporation concentrates Ca, Mg, silica, and salts, precipitates form unless pH, inhibitors, and solids are controlled. Acid dosing (e.g., sulfuric acid) can convert carbonate alkalinity to more soluble bicarbonate, allowing higher COC (energy.gov), but it adds EH&S hazards and cost. Accurate metering via a dosing pump is standard when acid is used.

More often, operators rely on [tailored chemistry](https://beta.co.id/en/blog/inside-the-chemistry-race-keeping-ccgt-cooling-towers-clean-and-saving-millions-of-gallons) and higher‑quality feedwater. One patented program (Aqua Ionic) combines polymers (polyplex and silicates) with softened makeup to achieve ≥10 COC with corrosion rates <0.5 mil/yr (prochemtech.com). Removing hardness via ion exchange enabled 10× COC without scaling; by contrast, using hard water required 50% more acid and chemicals to reach even 4 COC, at higher cost (prochemtech.com). Where ion exchange is part of the train, sites often specify a full ion‑exchange system upstream of the cooling circuit.

Continuous monitoring matters. Conductivity controllers and indices such as LSI (Langelier Saturation Index — a shorthand for scale potential) help operators hold setpoints; an LSI near zero (slightly corrosive) indicates minimal deposition risk. Side‑stream filtration is a common assist to control suspended solids; facilities frequently use dual‑media beds such as sand/silica filtration to keep fines out of heat exchangers.

Data from arid operations underline the chemistry point. In a Saudi Aramco pilot, secondary‑treated sewage effluent (TDS≈1500 mg/L, Ca≈106 mg/L) had low LSI (~0–0.5), so scale risk was low and the tower could safely run at 3.5 COC — nearly double the prior 2 COC (watertechonline.com). By contrast, the local groundwater (TDS≈3040, Ca≈233 mg/L) caused severe condenser scaling at 2 COC (watertechonline.com).

Operational results and control targets

At full scale with softened makeup and 10 COC, reported steel corrosion was only 0.1–0.5 mil/yr (prochemtech.com) (prochemtech.com), and zinc oxide (galvanized) corrosion was controlled using a proprietary “white rust” inhibitor. In freshwater systems, blowdown conductivity (a proxy for COC) often stays below ~4500 µS/cm (sciencedirect.com).

The operating principle is simple: target the maximum COC recommended by cooling‑water engineers for the site’s water quality, and use automated conductivity/blowdown controls alongside biological fouling inhibitors (energy.gov). Chemistry programs typically couple a scale inhibitor with a corrosion inhibitor to hold the line at higher cycles.

Reclaimed water as tower makeup

Beyond higher COC, replacing potable feeds with alternate sources slashes a plant’s water footprint. DOE guidance points to air‑handler condensate, once‑through cooling drains, industrial rinse/process water, stormwater, and — crucially — treated municipal or industrial wastewater (energy.gov). High‑quality municipal effluent is expressly cited as acceptable makeup (energy.gov). Dechlorination is often necessary ahead of the tower to protect metallurgy and bio‑programs; plants commonly dose a dechlorination agent in that role.

Globally, many power stations in arid regions (Southwest U.S., Florida, Middle East) already use secondary‑ or tertiary‑treated wastewater for cooling (powermag.com) (mdpi.com). Singapore’s “NEWater” program (>5 million people) supplies industries and feeds back into cooling systems (mdpi.com), typically via membrane trains that resemble membrane bioreactors followed by RO. In Indonesia, regulations exist but enforcement is weak (mdpi.com), making global best practices and robust membrane systems an adoption pathway where a municipal plant is nearby.

Case in point: A Saudi Aramco facility piloted using secondary‑treated sewage effluent (TSE) as cooling makeup (watertechonline.com). The TSE (TDS ~1500 mg/L, moderate hardness and nutrients) showed lower scale potential (Langelier index ~0–0.5) than the previous groundwater (TDS 3040 mg/L), enabling 3.5 COC vs. 2.0 and cutting water demand by 27% (watertechonline.com) (watertechonline.com). The 1,200‑ton pilot saved ~16,500 m^3/year; scaling to 5,000–6,000 tons could save ~82,500 m^3/year (plus ~82,505 kWh energy) (watertechonline.com).

Public‑health controls were central: continuous chlorination and biocides kept Legionella, coliforms, and viruses undetected (watertechonline.com), a role often filled by a tailored biocide program. Condenser surfaces remained clean (no mineral deposits) (watertechonline.com), leading to a clear conclusion: “TSE is a viable and sustainable alternative” for makeup (watertechonline.com).

Elsewhere, a GE–Power Magazine case described an 1,800 MW CCGT using 100% secondary‑treated municipal effluent (13 ppm phosphate) as tower makeup (powermag.com). By switching to a specialized polymeric treatment, the plant eliminated a [side‑stream lime softening unit](https://beta.co.id/en/blog/ccgts-wastewater-reckoning-lime-for-phosphate-highph-for-zinc) — avoiding a $5–10 million capital expense — and achieved net O&M savings of ~$0.75–1.0M/year (powermag.com). These conditions demand robust chemistry (phosphate, silica, chloride, ammonia, organics), but the report noted performance matched or improved without scaling (powermag.com). Where phosphate drives calcium‑phosphate scale risk, plants typically lean harder on a scale‑inhibitor package.

Pretreatment for reclaimed water tends to include solids capture and chlorine removal. Plants commonly deploy pressure membranes such as ultrafiltration to intercept fine particulates before dose‑controlled entry to the tower.

Blowdown recycling and membrane trains

Another lever is reusing cooling tower blowdown. One study found that treating and recycling blowdown (via RO/UF/activated carbon) reduced overall system water usage by ~13% and was more cost‑effective than upgrading makeup (sciencedirect.com). A typical train pairs UF for solids control with activated carbon for organics, ahead of brackish‑water RO for salt removal.

At larger scale, a Chilean 750 MW CCGT piloted an RO–crystallizer on blowdown and attained 96% recovery (watertechonline.com). The demonstration ran continuously for 30 days and pointed to nearly zero liquid discharge, allowing extremely high COC limited mainly by inlet quality (watertechonline.com) (watertechonline.com). Capital is significant, but the technical feasibility of near‑complete water conservation is proven.

Cost–benefit signals for CCGT operators

Local tariffs set the stakes. Indonesian industrial users pay roughly US$0.60–0.80/m^3 for high‑volume supply (123dok.com), while Jakarta domestic rates will reach ~Rp5,550/m^3 (~$0.36) for consumption >20 m^3 (megapolitan.kompas.com). Each thousand m^3 saved is worth ~$600–800 in avoided water charges. If a 500 MW CCGT uses ~3.7×10^6 m^3/year, a 20% cut in makeup (~0.74×10^6 m^3) saves ~$444–592k/year at those tariffs; at $1/m^3, ~$740k/year. Blowdown disposal (if charged) and chemical savings add value. DOE notes water savings should be balanced against chemical costs — acid treatment adds labor and H₂SO₄, and higher COC can increase inhibitor demand (energy.gov).

Case studies show fast payback. In the Phoenix example, installing a softener (CAPEX ~$26.3k, ~40 gpm) to reach 10 COC cut annual water/chemical costs by ~$78.8k, for a ~4‑month ROI (prochemtech.com) (prochemtech.com). The Saudi pilot’s ~16,500 m^3/year savings at $0.6/m^3 is ~$9.9k/year (plus ~<$span>8k in energy) (watertechonline.com), enough to justify modest pretreatment over a few years. At the largest scales, eliminating side‑stream softening by adopting reclaimed water and specialized polymers avoided $5–10M in capital and delivered ~$0.75–1.0M/year in O&M savings (powermag.com) (powermag.com).

Capex depends on the strategy. Upgrades range from pipelines/pumps for alternate sources and side‑stream filtration to membrane plants for blowdown reuse. Advanced RO/evaporation trains can cost millions but recover 90%+ of water (watertechonline.com). Chemistry programs may need upgrading when switching to tertiary effluent; in the 1,800 MW case, a proprietary terpolymer effectively substituted for $5–10M of calcium/biological treatment (powermag.com). When membranes are added, utilities typically plan for spares and consumables as part of lifecycle O&M.

Operations don’t always get more expensive at higher cycles. In the Phoenix data, hard‑water treatment at 2.2 COC used 6,739 lb/year of inhibitor ($24.9k), while softened water at 10 COC needed 3,370 lb/year ($11.5k) (prochemtech.com) (prochemtech.com). By contrast, acid dosing at 4 COC cost $44.5k/year in sulfuric acid (prochemtech.com). In the Saudi pilot, maintaining 1.5–2.5 mg/L chlorine reduced illness risk with negligible added chemical expense (biocides were already dosed continuously) (watertechonline.com).

Stacking measures multiplies benefits. Using reclaimed water and raising COC pushes potable demand toward zero. Hypothetically, saving 1×10^6 m^3/year at $0.6/m^3 yields ~$600k/year; if pipes plus treatment cost $2M, simple payback is ~3–4 years. Even partial recycling (say 50% of blowdown) can cut over half of water intake. Data‑backed evidence consistently shows that higher cycles and non‑traditional makeup minimize freshwater intake and are cost‑effective under scarcity; reported projects often pay back in under 1–2 years (sciencedirect.com) (powermag.com).