TIAC’s hidden bottleneck: water purity and chemistry decide CCGT megawatts

Inlet air cooling (TIAC, turbine inlet air cooling) can be a quiet profit center for gas turbines: inlet‑fogging typically adds roughly 0.6–0.8% more power for each 1°C drop in inlet temperature (Ikeuchi), so a 2–4°C drop yields ≈1.2–3.2% extra output. It’s why fogging is now deployed on over 1,300 turbines globally (MeeFog) and prized for low parasitic cost.

The catch: water quality. For fogging systems, even trace minerals in droplets can bake onto compressor blades as they evaporate, degrading airflow, reducing mass flow and pressure ratio, and even corroding hot parts (MDPI; Efficient Plant; Turbomachinery Magazine). The industry’s answer is uncompromising: fogging water must be ultra‑pure, demineralized.

Inlet fogging: ultra‑pure demineralized water

OEMs and experts specify demineralized water—[reverse osmosis (RO) or deionized (DI)](https://beta.co.id/en/blog/the-hidden-contaminant-in-paint-booths-why-ro-di-water-and-biocides-now-decide-firstpass)—with essentially zero hardness or conductivity for direct fogging. Guidance cited in the field: <1 ppm total dissolved solids (TDS) with conductivity ≲2 μS/cm to “prevent mineral build‑up on compressor blades” (Efficient Plant). Review articles corroborate that demineralized water is required to avoid high‑temperature corrosion when water is injected anywhere into the turbine path (MDPI).

Practitioners often write specs as zero measurable hardness, with resistivity >1 MΩ·cm (≈1 μS/cm) (Efficient Plant). Anything less invites mineral salts—CaCO₃, Mg compounds, iron, silicates—to plate out during droplet evaporation and accumulate cycle over cycle (MDPI). One veteran likens using impure fog water to “pouring tap water into a car battery” (Eng‑Tips).

In practice, the treatment train is straightforward: a filter + RO skid produces the [demineralized feed](https://beta.co.id/en/blog/the-hidden-power-plant-bottleneck-demin-plants-decide-hrsg-uptime). Power‑plant grade units such as brackish‑water RO are commonly applied, often with upstream pretreatment like ultrafiltration for colloids and a final polish using mixed‑bed DI (for example, a mixed‑bed deionizer) to keep conductivity tight during hot seasons. Precision fogging nozzles demand clean feed; sub‑micron filtration with robust housings, such as 316L stainless cartridge housings paired with fine cartridge filters, helps keep particulate under control (Efficient Plant).

Fogging hardware and maintenance standards

Fogging today uses high‑pressure pumps with precision nozzles generating ~10–30 μm droplets, designed so >95% evaporates in the inlet path (Ikeuchi). Well‑designed systems consume 40–80% less water than older spray approaches (Ikeuchi), but the remaining volume still must meet the purity spec.

Materials and upkeep matter. All wetted metals should be stainless or plastic; carbon‑steel fittings can rust and foul filters (Efficient Plant). Automatic drains and frequent line flushes limit microbial growth in stagnant sections (Efficient Plant). Intake ducts and silencers should be kept clean; after any shutdown, dust or algae on duct walls must be washed off before restart to avoid spalling debris into the compressor (Efficient Plant).

Why the rigor? Fouling is a major source of compressor degradation and lost output (Turbomachinery Magazine). Field data show online washing with demineralized water typically recovers ~0.2–1% power each cycle (Turbomachinery Magazine)—an indication of what accumulates between washes if fog water isn’t pure.

Evaporative coolers: scaling and biofouling control

Media‑type evaporative coolers pass inlet air over wetted pads, cooling via evaporation. Because recirculating water repeatedly contacts the air, dissolved minerals concentrate and biological growth can proliferate. Without treatment, salts precipitate on the cellulose media, blocking airflow and reducing cooling effectiveness (GE O&M via pdfcoffee).

General cooling‑tower‑style limits apply: hardness, alkalinity, silica, and total dissolved solids must be managed by blowdown (purging concentrated water) plus targeted chemical control (GE O&M via pdfcoffee). Where makeup water is hard, pretreatment such as a sodium‑cycle softener (softener) or RO (membrane systems) raises allowable cycles.

Scaling indices and blowdown control

GE’s guideline is to keep recirculating water slightly scale‑dissolving, tracking indices like Langelier Saturation Index (LSI), Ryznar Stability Index (RSI), and Puckorius (PSI). Typical targets are LSI ≈0.5 (±0.25), RSI ≈6.0 (±0.5), and PSI ≈6.5 (±0.5) (GE O&M via pdfcoffee). In practice, this often means keeping alkalinity and calcium around 100–200 ppm and pH ~7.5–8.0, and limiting cycles so the sump hardness stays controlled—for typical groundwater ≈100–200 mg/L as CaCO₃, cycles are often 3–6× (GE O&M via pdfcoffee).

Because intermittent wetting limits the efficacy of inhibitors, the emphasis is water balance rather than heavy dosing: instrument the TIAC controls with site‑specific blowdown constants and perform quarterly water analyses to optimize concentration (GE O&M via pdfcoffee). In many plants, a regular sump purge—e.g., 10–20% daily bleed—keeps TDS in check with minimal chemical use (GE O&M via pdfcoffee).

Crucially, “conventional cooling” recipes don’t map cleanly: scale inhibitors “will have little or no positive effect” in this media and can become part of the precipitate (GE O&M via pdfcoffee). Treatment focuses on preventing build‑up via blowdown and keeping LSI slightly negative (slightly corrosive) so old scale tends to re‑dissolve (GE O&M via pdfcoffee).

Biological control program design

Unchecked microbes can plug media, deteriorate metals, and cause odors; even with filtered inlets (a “clean air path”), identified growth must be controlled (GE O&M via pdfcoffee). Typical practice pairs oxidizing biocides (chlorine, bromine) with occasional non‑oxidizers (isothiazolinones, glutaraldehyde), dosing to maintain residuals between drains and ensuring material compatibility. For delivery accuracy, plants often rely on a dosing pump; generating chlorine on‑site via electrochlorination is a common oxidant source in utilities. Ancillary tasks include cleaning screens, weirs, and sumps; if the system will stand idle, a flush with dilute bleach at end of season is recommended.

Constituent limits and materials

GE’s O&M manual (2005) lists recirculation limits such as chloride ≤250 mg/L, sulfate ≤400 mg/L, silica ≤100 ppm, and hardness ≤250 ppm (as CaCO₃), with makeup/recirc specifics depending on unit (GE O&M via pdfcoffee). When salts concentrate excessively—especially during idling—uneven deposition on cellulose media causes bypass and large pressure drop (GE O&M via pdfcoffee). Where chemicals are used (e.g., for closed‑loop segments), utilities draw from standard cooling‑tower chemicals and biocides, noting the caveat above on inhibitor efficacy. For any solids management in blowdown, gravity separation using a clarifier is a common first step in industrial water work.

Performance and compliance outcomes

Done correctly, evaporative TIACs run for years without major fouling, delivering full design cooling with negligible efficiency loss. In contrast, poor treatment quickly bites: even a 1 mm calcium deposit can drop evaporative efficiency by many percent, and one combined‑cycle case study found that improving cooling‑water quality extended media life by 50% and prevented a 2°F drift in outlet temperature.

Beyond performance, blowdown from TIAC systems in Indonesia must comply with local discharge rules, including Government Regulation 82/2001 (water discharge). Spent water should meet the relevant Ministry of Environment standards (*Permen LH*) or be recycled; facilities typically achieve this by neutralizing pH and capturing suspended solids before disposal.

Bottom line for operators

For fogging: ultra‑pure demineralized water or accept measurable losses. Jane Alexander notes that using demineralized water for fogging avoids mineral “build‑up on compressor blades” (Efficient Plant). A compact filter + RO train—think RO‑based membrane systems with tight polishing—pays back in sustained output. For evaporative coolers: disciplined blowdown and a balanced chemical program trump brute‑force inhibitors; track LSI/RSI/PSI, maintain gentle biocide residuals, and stick to OEM constituent limits. Observing these basics is what converts hot‑day TIAC promises into bankable megawatts at, say, 35°C ambient (Ikeuchi).

Sources: Engineering guides and manufacturer O&M manuals provide the detailed water specs above (pdfcoffee.com; pdfcoffee.com; pdfcoffee.com). Peer‑reviewed reviews and trade press corroborate that any soluble mineral in inlet water is detrimental to turbine blades (MDPI; Efficient Plant). Empirical and OEM data quantify power gains per °C cooled (Ikeuchi) and warn of multi‑ton contaminant ingress if air and water hygiene are ignored (Turbomachinery Magazine).

References: As cited above (Ikeuchi; MDPI; Efficient Plant; pdfcoffee.com; pdfcoffee.com; MeeFog; Turbomachinery Magazine), plus specific maintenance notes on nozzle plugging, drains, and duct cleanliness from the same Efficient Plant article (nozzle/filter fouling; filters and drains; duct cleaning) and droplet size/water‑use deltas from Ikeuchi (10–30 μm droplets; 40–80% less water).