At utility scale, every 10°F of cooling range flashes off roughly 1% of circulating water, concentrating salts and biofilm risk. Plants are countering with tightly monitored blends of scale and corrosion inhibitors plus a robust biocide program — and the payoff is measurable.
Modern power stations push vast volumes of warm, oxygenated water through condensers and towers — ideal conditions for mineral scale, metal corrosion, and biological growth. The fix is not a single silver-bullet chemical but a coordinated program: concentration control (blowdown), scale inhibitors, corrosion inhibitors, and a biocide regimen tuned to both heat load and water chemistry, then verified in real time with sensors and coupons. As Veolia’s industry handbook underscores, open recirculating systems save orders of magnitude of fresh water versus once‑through — but only if fouling is held in check (watertechnologies.com).
For every 10°F (≈5.5°C) of cooling range, roughly 1% of circulating water evaporates; a 20°F approach can consume ~2% of tower water, demanding disciplined makeup and blowdown (intentional discharge to control dissolved solids) (watertechnologies.com). Many plants run at moderate cycles of concentration (COC — the ratio of dissolved solids in the system to the makeup) of 3–6× by polishing blowdown and feeding inhibitors, rather than relying on blowdown‑heavy, low‑cycle operation (watertechnologies.com). Chemical feed is typically automated with metering systems such as dosing pumps to keep residuals steady under variable load.
System scale and water balance
Evaporation concentrates hardness (Ca²⁺, Mg²⁺) and anions (HCO₃⁻, SO₄²⁻, silica, phosphates), pushing sparingly soluble salts toward deposition on hot surfaces. The first defense is concentration control via blowdown. But water loss is costly, so plants pair cycles control with chemistry designed for high heat loads, keeping the system in balance between water savings and fouling risk (watertechnologies.com).
Scale‑control strategies and pH management
Conventional scale inhibitors — phosphonates and polymeric dispersants — interrupt crystal growth and keep precipitates mobile. Sulfuric or hydrochloric acid dosing trims pH to reduce carbonate alkalinity where needed. Industry guidance cited by Veolia shows why chemistry matters as hardness rises: at ~125 ppm Ca as CaCO₃, blowdown alone can be “B” (sufficient), but at 250–375 ppm Ca (≈5–8× cycles) blowdown plus inhibitor (“B/S”) is required; at 750 ppm Ca as CaCO₃ (~15× cycles), acid + inhibitor (“B/A/S”) are needed to prevent CaCO₃ deposition (watertechnologies.com). In practice, moderately hard makeup (100–200 ppm as CaCO₃) often calls for a few ppm of phosphonate or polycarboxylate; with higher hardness and alkalinity, doses can run 5–10 mg/L, with acid feed holding pH in the 7–8 range.
Programs target a near‑zero or negative Langelier Saturation Index (LSI — a calcium carbonate scaling tendency index) in the basin by watching Ca²⁺, alkalinity, and conductivity in blowdown and adjusting inhibitor feed or blowdown to keep LSI ≤ 0. Silica and sulfate scaling are corralled by holding dissolved silica below ~150–200 ppm, or by using specialized silicate inhibitors if required. Plants typically combine antiscalants with polymeric dispersants; in cooling service, these align with scale inhibitor and dispersant packages designed for high‑cycle operation. Recent R&D emphasizes biodegradable formulations that reduce toxicity while maintaining efficacy; a 2016 review calls out “a new generation: environmentally friendly biodegradable scale inhibitors” (researchgate.net).
Corrosion‑inhibitor program and metallurgy
Warm, aerated water accelerates attack on steel and copper alloys; a single inhibitor is generally inadequate (watertechnologies.com). Effective programs blend pH control (circulating pH 8–9 with soda ash or caustic), film‑formers where appropriate (volatile amines such as cyclohexylamine to passivate low‑flow zones), and inorganic/organic inhibitors that passivate metal surfaces. Historically, “zinc dianodic” formulations (phosphate plus 15–25 ppm Zn) replaced chromate; zinc precipitates as mixed Zn/Fe or Zn/Ca phosphates to protect steel. Molybdate (200–300 ppm as MoO₄²⁻) is a lower‑toxicity alternative stabilizing oxide films, while nitrite (400–1000 ppm NO₂⁻) protects steel, though typically not used alone in high‑hardness systems without copper (watertechnologies.com).
Organic inhibitors such as tolyltriazole or benzotriazole (~10–50 ppb) protect copper alloys, and modern polymers buffer local pH. Chromates, once common, are now largely banned; per EPA norms, open recirculating cooling avoids chromate. In practice, plants may feed 5–15 mg/L of a mixed Zn/phosphate or molybdate blend plus a copper inhibitor, while monitoring pH and dissolved oxygen; continuous oxygen control (deaeration or oxygen scavenger) is often included. These formulations map to commercial corrosion inhibitor programs formulated for all‑metal coverage and biofilm resilience.
Biological control: oxidizing and non‑oxidizing biocides
Open towers are prime microbiological habitats; slime and biofilms drive under‑deposit corrosion and foul heat exchangers. Robust programs combine oxidizers with non‑oxidizers (watertechnologies.com). Oxidizing biocides — chlorine, chlorine dioxide, bromine, ozone, hydrogen peroxide — are fed continuously at low residual (e.g., 0.2–0.5 mg/L free chlorine) with periodic shocks. One industrial study showed that shock plus continuous chlorination cut Legionella by ~1.8 logs and heterotrophs (HPC, heterotrophic plate count) by ~2 logs (mdpi.com), and “chlorination has been accepted as the most widely used biocide for biofouling control” (mdpi.com). In practice, continuous low‑level halogenation is often delivered via onsite systems like electrochlorination, with non‑oxidizers such as glutaraldehyde, isothiazolinones, or DBNPA rotated per CTI/CDC guidance to suppress resistant populations. The chemical families here align with integrated biocide programs for cooling towers.
Dosing is controlled by ORP (oxidation‑reduction potential, a disinfecting‑power proxy) or direct chlorine residual. Indonesia’s Ministerial Regulation 8/2009 limits condenser blowdown to 0.5 mg/L free chlorine (text-id.123dok.com), so field targets are set accordingly (≈0.1–0.3 mg/L free Cl₂ during operation, with short spikes to 1–2 mg/L during shock). Excess oxidant drives corrosion and trihalomethanes; high Cl₂ can pit copper or steel. To reduce chemical load, some facilities supplement halogens with ozone (a non‑residual oxidant) or physical barriers like UV, and, when necessary, neutralize residual oxidant to meet limits using dechlorination agents.
Monitoring, control, and performance metrics
Integrated programs rely on online instrumentation (conductivity probes, pH meters, ORP sensors) and routine lab tests to tighten control. Cycles of concentration are calculated from makeup and blowdown conductivity (or a tracer ion like chloride): cycles = (system solids)/(makeup solids). For example, with 500 ppm TDS makeup and a 5× COC target, operators hold ≈2500 ppm in the basin.
Deposit‑control residuals are checked with colorimetric or titrimetric tests; “squeeze” checks, such as silica titration, confirm availability. Alkalinity is tracked weekly to spot drift; pH informs LSI, and acid or CO₂ feed is adjusted to hold LSI near zero. Corrosion coupon racks (steel, copper, aluminum) provide long‑term rates, while galvanic/polarization instruments give real‑time feedback. Microbial load is trended via HPC counts and tower film swabs; ORP is often kept above a setpoint (e.g., +650 mV in a chlorine program) to ensure kill. Ancillary instrumentation and spares are typically bundled as water‑treatment ancillaries, with site teams keeping parts and consumables on hand for continuous service.
Performance shows up in plant KPIs: condenser pressure (vacuum) and approach temperature. As fouling accumulates, vacuum degrades; one engineering source attributes a 5 mmHg degradation to ~0.5% turbine heat‑rate loss (≈3 MW for a ~600 MW unit) (researchgate.net). Keeping surfaces clean preserves design approach (typically 7–15°F).
Measurable outcomes and plant economics
Done well, treatment programs deliver low deposit loading, higher cycles (water savings), and stable metal surfaces. In the short term, optimized pH/cycles and feed rates minimize chemical consumption and blowdown waste (watertechnologies.com). Over time, “cleaner heat exchanger surfaces, less frequent equipment replacement, and reduced downtime” drive efficiency gains (watertechnologies.com). With disciplined chemistry — the realm of integrated cooling‑tower chemical programs — plants commonly achieve 5–7 cycles of concentration versus 3–4 untreated, halving blowdown and saving millions of liters per day.
Biological control results are similarly stark. One case reported a ~98% Legionella drop (1.95‑log reduction) with combined shock plus continuous oxidizers and near‑elimination of heterotrophic bacteria (mdpi.com). Eliminating thin mineral films matters, too: a 250 μm deposit can raise condenser pressure substantially, and removing it can recover megawatts of output. Historically, fouling at a 500 MW station was pegged at £15,000/day in lost generation (researchgate.net). By analogy, operators quantify the upside today: each 0.1% heat‑rate improvement (via cleaner condensers) yields ~1 MW on a 1000 MW unit, worth ~$0.5–1.5 million per year in fuel savings.
Regulatory and environmental constraints
Chemistry choices are shaped by discharge limits. Indonesia’s Ministerial Regulation 8/2009 sets thermal‑power wastewater standards; for condenser discharge (air‑bahang), it caps outlet temperature at +40°C and free chlorine at 0.5 mg/L (text-id.123dok.com). By contrast, clean seawater’s natural temperature rise should not exceed 2°C (mongabay.co.id). Practically, chlorine feeds must not exceed 0.5 ppm in effluent; higher doses are removed or neutralized before blowdown (e.g., via dechlorination or lagooning). Limits on alkalinity, oil & grease, and heavy metals further steer formulations toward minimal toxic byproducts.
Globally, chromates are banned and regulators limit ammonia, nitrate, and THM byproducts, steering plants toward low‑phosphorus polymers and organics. Phasing out phosphonate antiscalants reduces total‑P discharge, and worldwide research (2016 and later) emphasizes phosphorus‑free, biodegradable inhibitors (researchgate.net). Similar caution guides corrosion inhibitors. Biocide choices reflect ecotoxicity, too: for example, Germany’s drinking‑water rules (THM <0.1 mg/L) have driven some European towers to use UV or peracetic acid where makeup is tied to potable systems. In Indonesia, while BOD/COD limits for cooling blowdown may be moderately relaxed, best practice is to minimize COD using high‑residual oxidants (like ozone) and biodegradable organics.
Integrated program design and ROI
The playbook is three coordinated pillars: (1) scale inhibitors plus pH/blowdown control, (2) corrosion inhibitors plus pH maintenance, and (3) biocides (oxidizing + non‑oxidizing). Each reinforces the others — biocides keep surfaces clean so inhibitors work, while dispersants hold fines mobile — and all are governed by automated blowdown and online analytics (watertechnologies.com). The return is tangible: run 5× cycles instead of 3× and fresh‑water use drops ~40% with negligible scaling; EPRI/EPA pilot work consistently shows well‑treated towers use ~2–5% less makeup water and save on maintenance.
In practice, a modern blend might comprise a phosphonate‑based scale inhibitor (2–5 mg/L), a polyacrylate dispersant (1–3 mg/L), a zinc‑phosphate corrosion package (10 mg/L PO₄³⁻ + 2 mg/L Zn²⁺), and dual biocides (continuous 0.2 mg/L Cl₂ plus weekly 20 mg/L DBNPA shocks). These doses are illustrative; actual setpoints come from lab evaluation of site makeup and the loop. The key is balance: for example, a steady pH ≈8.5 with ~10 ppm total inhibitor and ~0.3 ppm Cl₂ has yielded corrosion rates <0.05 mpy (mils per year, a corrosion‑rate unit) and scaling held to <10% of the untreated fouling rate, using EHS‑compliant choices (biodegradable polymers, low‑chloride inhibitors) that meet Indonesia’s 0.5 ppm free‑chlorine discharge cap and international norms. Chemistry is delivered and trimmed with automated dosing equipment and verified against field data.
The scoreboard is operational: condenser approach within design, tower range stable, COC targets hit, and routine lab data showing negligible calcium or biofilm accumulation. Those translate into higher net generation, lower fuel burn, and extended asset life — exactly the metrics that justify the program. Source materials include Veolia Water Technologies’ Water Handbook for open recirculating systems (watertechnologies.com; watertechnologies.com), the Indonesian effluent standards (Permen LH 8/2009) (text-id.123dok.com; mongabay.co.id), peer‑reviewed work on biodegradable inhibitors (researchgate.net), and cooling‑tower disinfection outcomes (mdpi.com).
