A well‑tuned condensate polisher can be a profit center in disguise. Evidence from EPRI and industry case reports shows online analyzers and counter‑current regeneration extend resin life, cut acid/caustic, and protect turbines from costly upsets.
In heat recovery steam generator (HRSG) service, the condensate polishing unit is the quiet insurance policy against corrosion, carryover, and forced outages. The financial swing is stark: an Electric Power Research Institute analysis of a 440 MW unit tallied first‑year benefits of about $780,000 (1994 dollars) from an effective polish program—reduced blowdown, fewer turbine losses, and fewer chemical cleanings with higher availability (www.scribd.com) (www.scribd.com).
The flip side is documented too: one combined‑cycle condenser leak triggered three weeks of acid corrosion and a full boiler re‑tube when polish control failed (www.power-eng.com). In practice, plants minimize operating costs by stretching resin run length and throughput, curbing fouling, and trimming regenerant usage.
That optimization spans equipment choices, chemistry discipline, and data. It also leans on well‑specified condensate polishers and targeted pretreatment to keep resin doing what it should: polishing steam condensate after heat exchange cooling.
Mixed‑bed design and pretreatment
Most systems are deep‑bed mixed‑resin units (mixed‑bed: a blend of cation and anion ion‑exchange beads) with external regeneration to achieve very low ionic leakage. Modern external‑regen units have sodium (Na⁺) leakages ≤3 µg/L, versus ~10 µg/L for in‑situ regeneration (www.powermag.com), which is why many operators specify a mixed bed for ultra‑low TDS and silica.
Deep beds have limited filtration capacity: suspended solids can plug the bed and foul resin, raising pressure drop (www.powermag.com). To protect the main resin and extend run length, plants install pre‑filters or pre‑coat filters upstream; powdered‑resin candle filters remove particulates before the mixed bed (www.powermag.com).
There is a trade‑off: precoat or fiber filters carry a small resin inventory and must be recoated or changed when fouled, but they shield the deep bed. Where high pressure dictates rugged housings, operators often place upstream steel filter housings to host fine pre‑filters without compromising pressure integrity.
Resin separation and regeneration design
Hardware layouts commonly use multiple vessels—two or three in service plus one standby—so resin can be sluiced out and regenerated without interrupting flow (www.power-eng.com). Efficient separation of cation and anion resin during regeneration is critical to avoid cross‑contamination and excess chemical use.
Modern systems create an interface layer or use gravity separation—sometimes with an inert resin bed—to keep resins clean for full regeneration (www.hungerfordterry.com) (www.hungerfordterry.com). Operators may follow regeneration with weak ammonium or lime washes to strip residual sodium from fines so it does not return with service resin (www.hungerfordterry.com).
Any boost in regeneration quality—lower residual sodium on cation resin—directly reduces breakthrough in the next run, delaying the next regen and saving chemicals. Specifying the right ion‑exchange resin inventory and separation protocol is part of that equation.
Off‑site regeneration and logistics
On‑site regeneration brings storage of large volumes of sulfuric acid and caustic plus wastewater neutralization, with handling cost and safety risk. Many plants contract off‑site regeneration, eliminating on‑site regeneration capital and chemical handling at the expense of transport logistics (www.power-eng.com) (www.powermag.com).
Off‑site service typically guarantees resin purity—often <3 µg/L sodium leakage—on a flat service cost. Analyses show lower net costs when chemical prices are high or staffing is limited, though distant sites pay more to ship resin (www.powermag.com).
Another capital‑saving option during commissioning is rented polisher skids with pre‑loaded resin; spent units are swapped instead of regenerated. Rentals avoid on‑site regen altogether but trade off limited flow/pressure ratings and higher rental fees (www.power-eng.com).
Operating chemistry and run length
Cycle chemistry sets the load profile. Many combined‑cycle plants use AVT(O) chemistry (all‑volatile treatment oxidizing; ammonia‑based pH control), and high ammonia feed loads the cation resin because ammonium (NH₄⁺) is treated as an impurity. An Indonesian case study quantified a cation resin exhaustion time of ~6.6 hours under such conditions, while the anion resin could have run over 500 hours (www.researchgate.net).
In that plant the cation resin was the limiting factor, pointing to adjustments such as adding cation volume or operating part of the cycle in ammonium form. When condensate is very clean, running to the first sign of leakage rather than a fixed time extracts maximum capacity; tolerance for short sodium/silica bleed (especially with NH₄⁺‑form operation) may be acceptable when it cuts regeneration frequency. Each avoided regeneration saves hundreds of dollars in chemicals and downtime.
Tailoring the resin ratio and operating mode (H⁺‑OH⁻ vs NH₄⁺‑OH⁻) to the actual load profile is a core optimization tactic, supported by precise chemical feeds through an accurate chemical dosing pump during regeneration.
Online analyzers and regen timing
Real‑time monitoring of condensate/feedwater chemistry maximizes resin utilization and avoids unscheduled outages. Plants deploy continuous analyzers for sodium, silica, and conductivity at strategic points—condensate pump discharge, polisher inlet/outlet, and feedwater—for early warning of resin exhaustion or leaks.
On measurement fidelity, Hungerford & Terry note that sodium and silica leakage are “generally determined by means of continuous inline analyzers,” whereas grab samples “are very susceptible to contamination” at ppb levels (www.hungerfordterry.com). WJF Instrumentation adds that an on‑line Na⁺ analyzer at the polisher outlet provides earlier warning of breakthrough than effluent conductivity (www.wjf.ca).
OEMs typically limit steam and feed conductivity stringently—often <0.2 µS/cm (microSiemens per centimeter) or a few ppb of Na⁺ and silica. As one guideline notes, ultrapure makeup water should have Na⁺ ≤2 ppb and silica ≤10 ppb (www.chemengonline.com); any excursion should trigger regeneration or a walk‑through.
Conductivity, CACE, and alarms
The first indication of an “NH₃ break” (ammonia slip through cation resin) is often a gradual rise in polisher effluent conductance and pH, followed by Na⁺ and SiO₂ increases (www.hungerfordterry.com). Many plants use cation conductivity (CACE: conductivity after cation exchange) downstream to catch the earliest signs.
A useful diagnostic is to pump the standby polisher to waste and compare inlet vs outlet conductivities to separate feed effects from resin exhaustion. In practice, operators set regen alarms on these signals—e.g., Na⁺ at the outlet >1–2 ppb, or a step up in effluent conductivity—so a shutdown, flushing, and resin exchange occur just before breakthrough. For a 50 mgd polisher (million gallons per day), one extra day of run length can save 100–200 kg of H₂SO₄ and NaOH.
Other online monitors include dissolved oxygen (DO) for condenser air leaks and differential pressure across the bed for particulate loading. A sudden DO spike or conductivity rise at condensate pump discharge suggests a condenser tube leak; a slow DP drift points to resin “crud” fouling, indicating the need to backwash or change a powdered precoat. Some plants add automated Larson‑Lane columns or a second CACE. Data logging and trend analysis—via DCS or specialized systems—help set the next target (if runs lasted 5 days last month, aim for 6 when demand allows) and hold steam cation conductivity near <0.15 µS/cm (www.powermag.com).
Counter‑current regeneration techniques
Traditional co‑current (same‑direction) regeneration leaves a contamination gradient and needs large chemical excesses. True counter‑current (reverse‑flow) regeneration introduces regenerant opposite service flow, contacting the most exhausted resin layer first (dardel.info).
SUEZ summarizes the payoff: counter‑current regeneration “improves both quality of the treated water and the performance of regeneration, therefore lower[ing] operating costs” (www.suezwaterhandbook.com). As François de Dardel notes, “less regenerant is required, as the contaminating ions don’t have to be pushed through the whole bed” (dardel.info).
In practice, this can mean 20–50% savings in acid and caustic versus standard upflow methods. Supplier data (not quoted here) indicate acid doses under counterflow protocols can be 30–50% lower for equivalent final conductivity. Maintaining a compact bed (no backwash) keeps the cleanest resin at the effluent end during rinse (dardel.info), as implemented in commercial processes like Conesep™ and Amberpack™.
The breakthrough curve also tightens—near‑zero leakage until late in the run, then a sharp rise—whereas co‑flow often shows a long leakage tail. Bench tests and field practice show reverse regeneration can make final ionic leakage essentially independent of regenerant dosage—even a minimal dose can yield near‑optimum results (dardel.info).
In dollar terms, if a single co‑flow regeneration consumes 200 kg of acid and caustic, an optimized counter‑flow might use ~120 kg, saving ~$50–100 per cycle depending on market prices. Over dozens of cycles a year, precise counter‑flow dosing—delivered via an accurate dosing pump—quickly offsets added complexity and trims neutralization waste.
Published guidance and case evidence
Authoritative industry literature and guidelines underlie these points. Buecker (2019) and POWER magazine emphasize how polishers enable ultra‑low conductivity (<0.15 µS/cm) and reliable operation (www.powermag.com) (www.chemengonline.com), and EPRI cost studies quantify multi‑hundred‑thousand‑dollar annual benefits from effective systems (www.scribd.com) (www.scribd.com). Technical guides detail the monitoring and regeneration methods cited above (www.hungerfordterry.com) (www.suezwaterhandbook.com) (dardel.info), and the Indonesian case study confirms cation resin life can be extremely short under typical HRSG conditions (www.researchgate.net).
Procurement anchors for reliability
Specifying the right equipment supports the chemistry and monitoring discipline described above. Plants lean on a serviceable condensate polisher design, rigorous ion‑exchange resin selection, and upstream fine solids capture with an industrial cartridge filter to keep resin clean.
