Thin films of silica and copper can quietly strip several percent of a steam turbine’s output — and the fix ranges from disciplined chemistry and cleaning to reblading with 3‑D aerodynamics. Case studies show multi‑MW recoveries and rapid paybacks.
Blade cleanliness and output loss
Steam-turbine efficiency hinges on clean blades and high-quality steam. Even thin deposits on nozzles or blades “distort the original shape” and roughen the flow path, boosting flow resistance and pressure drop — a direct aerodynamic penalty that cuts available power (watertechnologies.com). A 30 MW turbine that ingested contaminated water (silica and oxides) lost over 5% of output due to blade deposits (watertechnologies.com).
Industry experience is blunt: copper plating on HP (high‑pressure) blades can lop off ~2–3 MW per month, roughly 1 MW of output lost for every 1–2 lb of deposit accumulated (powermag.com). Deposits can also unbalance the rotor or force unplanned shutdowns — one unit tripped just three months after startup (watertechnologies.com).
Steam purity and silica control
In HRSG (heat recovery steam generator) and cogeneration units, silica vaporization is a notorious contaminant: silica can carry into steam at pressures as low as 400 psig, then re‑deposit as the steam cools, especially in low‑pressure stages (watertechnologies.com). Industry practice is to hold steam silica below 0.02 ppm (parts per million) to avoid blading deposits (watertechnologies.com). Attemperation water (spray used to control steam temperature) must be purified and free of volatile contaminants to prevent scaling of turbomachinery (watertechnologies.com) (watertechnologies.com).
Condensate/feedwater chemistry is the first line of defense. Well‑kept plants prefer all‑volatile treatment and oxygenated treatment (OT — maintaining a small, controlled oxygen level to stabilize oxide layers) for HRSGs with no copper in the system, rather than legacy phosphate or oxygen‑scavenger programs; this reduces iron corrosion products that feed the turbine (powermag.com) (powermag.com). Copper corrosion must be minimized because dissolved copper and other oxides plate onto HP blades, “significantly [reducing] unit generating capability” while raising heat rate (powermag.com).
On the hardware side, plants lean on condensate polishing to strip particulates and ions; an inline condensate polisher is standard after heat exchange cooling. For final silica and TDS (total dissolved solids) control, a mixed-bed polisher can deliver less than 20 ppb silica with very low TDS.
Makeup-water systems matter as much as drum internals. Where hardness or organics are present, pretreatment with ultrafiltration stabilizes RO feed quality; for saline or brackish sources, baseloaded plants deploy brackish-water RO or sea-water RO for reliable, low-silica makeup. Some facilities opt for continuous ultra‑pure production via EDI (electrodeionization) to eliminate chemical regenerations.
Precise dosing supports stable pH and film formation in the cycle; operators commonly pair a metering dosing pump with a neutralizing amine program to control condensate/feedwater pH.
Monitoring and deposit detection
Well‑kept plants use continuous monitors — steam flow/pressure, exhaust temperature, and lube‑oil contamination — to catch early fouling (powermag.com) (massengineers.com). Trending specific steam consumption, stage pressures, and isentropic efficiency (a standard thermodynamic efficiency metric) can spotlight wedge accumulations in HP sections (watertechnologies.com) (powermag.com). Inline deposit sensors or periodic borescope inspections localize build‑up quickly.
Offline and chemical cleaning methods
Routine inspections collect and analyze deposits each outage. Cleaning is executed as needed: water washes or dilute condensate jets remove soluble salts, while mechanical methods (blasting, brushes) tackle insoluble scale (massengineers.com) (powermag.com).
Chemical foam cleaning has emerged as a fast, surgical option: specialized “CuSol” foams dissolve copper and iron oxides on blades without disassembly (powermag.com) (powermag.com). One 4–5 day foam job fully restored lost capacity; performance tests immediately after cleaning confirmed full recovery (powermag.com).
As policy, plants schedule off‑line washing or foam cleaning at each major outage (every 1–3 years). Simple steam blow‑throughs clear soluble salts (massengineers.com), but stubborn copper/iron films often require chemical foam treatment (powermag.com). Mechanical removal (abrasive blasting or brushing) is reserved for disassembly when heavy scale is present. In practice, many sites perform a full HP‑path foam clean during major inspections to “restore the lost capacity” and halt progressive efficiency drop (powermag.com).
Rules‑of‑thumb from field repairs are stark: each pound of deposit can cost ~1 MW of capacity; one plant’s data showed a 7 MW drift over seven years of copper build‑up, with an immediate jump back after cleaning (powermag.com).
Performance erosion and downtime costs
Published case studies quantify the stakes. One analysis estimated that as little as 1% of blade‑path flow blockage can shave ~1% off unit output. Constant fouling drove several‑percent heat‑rate penalties: a capital‑era plant consumed over 10% more fuel (heat input) than its original design until targeted fixes were made (mdpi.com). Targeted overhauls (condenser leak repairs, heater cleaning) recouped about 5 MW on a 120 MW unit (mdpi.com).
Conversely, failure to clean can force repeated downtime. US fossil units plagued by magnetite carryover needed major rebuilds every 5–6 years because HP/IP (high/intermediate‑pressure) efficiencies fell by up to 5% within 3–4 years from particulate erosion (modernpowersystems.com). In short, an incremental capacity loss of ~1–3 MW per year per 100 MW of turbine due to fouling is common, equating to yearly efficiency hits of several percent (watertechnologies.com) (powermag.com).
Steam‑path upgrade technologies
Clean blades are necessary but not sufficient. Efficiency is capped by steam‑path design, which is why major overhauls are the moment to repower with modern components. State‑of‑the‑art turbines use advanced aerodynamics and seals — narrower chords, 3D‑curved blades, increased reaction, tip‑shrouds, and dense packing — to extract more energy from the same steam (power-eng.com) (researchgate.net). Typical scopes: reblading with optimized profiles; adding or reconfiguring stages (often 1–4 new stages with higher RPM rotors); full‑arc HP admission; larger LP (low‑pressure) exhaust area and better moisture removal.
A recent simulation study underscores the impact of modern 3D blades: replacing an older 2‑D design in a 210 MW turbine with 3‑D‑optimized stages raised sectional design efficiency — HP from ~83% to 90%, LP from ~82% to 94% — for a 14 MW net power increase at fixed steam or a −6.6% heat‑rate change (researchgate.net). In brief, “3‑D optimized” reblading typically yields 5–10%+ improvement in turbine‑generator efficiency versus obsolete blades (researchgate.net) (powermag.com).
Efficiency and capacity gains
Field retrofits deliver single‑digit efficiency jumps and double‑digit MW gains. One 390 MW coal‑steam unit retrofit raised HP‑turbine isentropic efficiency by ~5%, IP by ~4%, and LP by ~2.5%, boosting gross output from 360 to 371 MW — an ~11 MW gain (3% net capacity) with an equivalent heat‑rate improvement of ~1.5% (power-eng.com) (power-eng.com). Engineers report larger gains on older machines: a ~500 MW subcritical retrofit achieved HP +8–10% and IP +2–4% efficiency, translating to a 20–27 MW output increase (powermag.com).
On very large USC (ultra‑supercritical) turbines (800–1,300 MW), comprehensive HP upgrades have clawed back 8–11% efficiency in the HP section, corresponding to a 2–2.5% unit heat‑rate drop and 30+ MW output lifts; HP sections can approach the mid‑90% efficiency range after retrofit (vs. mid‑80s in older designs) (modernpowersystems.com) (power-eng.com).
Economics and utility outcomes
The 390 MW case’s 1.5% steam‑use reduction cut fuel heat input by ~54 MMBtu/hr, saving ≈$162/hr (~$1.4 million/year) (power-eng.com). Because the same steam flow produced 11 MW more power, additional revenue of ≈$3.3 million/year was realized, with payback often in 1–3 years on retrofit costs of a few $M–$10M (power-eng.com). A back‑of‑envelope benchmark: improving a baseloaded 500 MW unit’s heat rate by 100 Btu/kWh can save on the order of $5–15 million per year in fuel (powermag.com).
Major utilities have institutionalized these programs. TVA and peers routinely reblade and upgrade rotors to “keep boiler ratings unchanged” while increasing MW output (modernpowersystems.com). After upgrading two 700 MW units, TVA reported HP‑cylinder efficiencies near the mid‑90s (with only ∼1% loss over a decade) and sustained ~2% heat‑rate gains for the overall unit (modernpowersystems.com). Designs with integral shrouds and single‑flow paths also reduce solid‑particle erosion and extend overhaul intervals (modernpowersystems.com) (modernpowersystems.com).
HRSG operations and planning
A practical playbook emerges. Keep steam‑water chemistry tight (monitor silica, alkalinity, and contaminants; use blowdown as needed), and combine drum demisters with anti‑foaming control to keep droplets out of the steam (watertechnologies.com). Filter particulates and ions ahead of the boiler with polishing and filtration; high‑purity demin makeup from RO or deionization complements the in‑cycle condensate polisher.
Schedule and document regular cleanings: off‑line washes, foam cleans, and mechanical removal during overhauls as needed, with inspection‑guided intervals of 1–3 years. Data trending and borescope checks ensure deposits are localized early and cleared before rotor balance or capacity are compromised (massengineers.com) (powermag.com).
Finally, plan to modernize the steam path at major overhauls. Multiple studies show ≥5% net cycle efficiency gain (heat‑rate drop) and double‑digit MW capacity from new blade geometries and seals, with clean‑blade baselines preserving those gains. Operators, including those in Indonesia’s fleet of HRSG‑combined‑cycle plants, treat blade maintenance as essential preventive care and budget for turbine retrofits to capture the multi‑MW and multi‑percent efficiency benefits of modern turbine technology (watertechnologies.com) (power-eng.com) (modernpowersystems.com) (researchgate.net).
Sources and further reading
Sources include recent industry studies and case reports with measured performance, heat‑rate, and financial outcomes: watertechnologies.com; powermag.com; power-eng.com; modernpowersystems.com; researchgate.net; mdpi.com; massengineers.com. Additional anchors cited in‑text include performance‑monitoring and foam‑cleaning details (powermag.com) (powermag.com) (powermag.com) and maintenance economics (power-eng.com) (powermag.com).
