Power plants are isolating turbine lube-oil coolers on ultra-clean, closed water loops and dumping the heat through a dedicated exchanger into the main cooling circuit. The result: near-zero fouling, >99% availability, and massive water savings backed by industry sources.
In a sector obsessed with reliability, the lube-oil cooler is suddenly the star of the balance-of-plant. The setup sounds simple: a sealed, closed-loop water circuit (a recirculating, non-vented cooling system) that keeps turbine bearings happy, and a dedicated heat exchanger that offloads the heat to the main plant cooling water. But the gains are outsized. With high-purity water and isolation from tower water, plants are reporting virtually zero scale and drastic corrosion cuts, according to the Veolia Water Handbook and industry analyses (watertechnologies.com; esmagazine.com).
Numbers sharpen the picture. One large steam turbine lube system needed ~576 kW of heat removal using a 91.5 m² plate cooler at ~78 m³/h water flow (chemxperts.com). Designers typically expect a closed-water flow of ~10–20 m³/h per MW of turbine capacity (depending on ΔT, the temperature rise of the fluid) across applications; duplex pumps and twin oil coolers (duty+standby) with three-way bypass valves push availability past 99% (chemxperts.com).
The isolation heat exchanger that bridges to the tower loop is the unsung hero here. Evapco’s field notes say plate exchangers are “most frequently used” to buffer process and tower loops, ensuring only heat—never fluids—crosses that boundary (esmagazine.com). It’s a simple architectural shift with big operational consequences.
Closed-loop architecture and components
A typical configuration recirculates a dedicated water inventory through a buffer tank, pump(s), filters or a strainer, and the primary oil–water heat exchanger (the lube oil cooler); the warmed coolant then passes to a dedicated secondary heat exchanger that rejects heat to the main plant cooling water before returning to the tank (watertechnologies.com; esmagazine.com).
Component sizing starts with the lube oil heat load. The ~576 kW/91.5 m²/78 m³/h data point provides a realistic anchor (chemxperts.com). In general, ~10–20 m³/h per MW of turbine capacity (depending on ΔT) might be expected on the closed side. Pumps are sized to maintain flow and head; duplex duty+standby pumps and twin coolers enable maintenance without losing function, delivering >99% availability (chemxperts.com).
Plate-and-frame heat exchangers (compact gasketed plates) are common thanks to high heat transfer coefficients and ease of inspection; they’re typically much smaller than shell-and-tube for the same duty (generalcargoship.com). Shell-and-tube units (steel tubes in a carbon-steel shell) remain a robust alternative, especially for vertical installs; either way, provide vents and drains to purge air and condensate and consider vertical orientation (generalcargoship.com).
Crucially, the secondary exchanger is dedicated to isolating the closed loop from the main cooling water. That prevents cross-contamination between tower water and the lube circuit; valving allows bypass for maintenance without interrupting turbine lube cooling (esmagazine.com).
Water quality, corrosion, and monitoring
Because the loop is sealed and makeup is minimal, it can—and should—run on very high-purity water (deionized water free of scaling ions). Closed recirculating systems allow use of demineralized water, virtually eliminating scale deposits (watertechnologies.com; powermag.com). Typical specs: conductivity <10 µS/cm (microsiemens per centimeter), TDS <5 mg/L (milligrams per liter), hardness <10 µg/L (micrograms per liter), chlorides <5 mg/L, iron <1 mg/L, and turbidity <1 NTU (nephelometric turbidity unit)—essentially twin-bed demineralized quality (scribd.com; watertechnologies.com).
Makeup water should come from a demineralizer or condensate recovery; zeolite-softened or condensate makeup helps avoid long-term scaling (watertechnologies.com). Plants sourcing DI makeup often rely on a demineralizer or, for polishing, a mixed-bed deionizer.
Even with pure water, corrosion control matters. Common practice doses the closed loop with nitrite/azoles or molybdate/azoles and maintains pH around 8.5–9.0 for carbon steel systems; oxygen ingress is minimized by eliminating air contact (powermag.com). Inhibitor levels (e.g., >200 ppm) and weekly pH/conductivity checks are typical; additions may be infrequent (weeks to months) if the loop is tight (powermag.com). A small dosing pump supports controlled addition of closed-loop treatment blends or targeted corrosion inhibitors.
“Closed recirculating systems…have many advantages. They provide better control of temperatures… and their small makeup water requirements greatly simplify potential waterside problems. …High-quality water can usually be used for makeup, and as a result, scale deposits are not a problem.” (watertechnologies.com)
The payoff is tangible: “Closed systems reduce corrosion drastically, because the recirculating water is not continuously saturated with oxygen, as in an open system” (watertechnologies.com). Conductivity and hardness trends act as early warnings; ΔT across the oil cooler and pressure drop trending catch the rare particulate or scale event.
Dedicated exchanger to main cooling loop
The closed-loop water rejects heat through a dedicated water-to-water exchanger connected to the main plant cooling circuit (often an open recirculating cooling tower or condenser loop). The secondary HX is sized for the lube loop’s duty plus margin and often built in corrosion-resistant stainless. For the earlier case (~576 kW at 78 m³/h), designers note a plate exchanger surface area on the order of 1.5–2 m² can be sufficient depending on approach temperature, whereas a shell-and-tube may need larger area (chemxperts.com).
From the oil side, heat to remove is roughly pump power plus bearing friction. A rule-of-thumb is ~3–6% of turbine electrical output must be rejected through lube cooling; a 100 MW unit might shed ~300–600 kW. Using the ChemXperts data point (575.7 kW for a large unit) suggests ~6 kW/MW of turbine. With ΔT≈5–10°C on the closed-loop water, that implies ~6–12 m³/h per 100 kW—consistent with ~78 m³/h for ~576 kW (chemxperts.com).
Interface details matter. Ensure the cooling tower capacity and approach support the plate exchanger selection; secondary exchangers and towers are often CTI– or AHRI-certified for performance. The isolation benefits are material: no mineral-laden tower water ever touches the lube loop, and no loop chemistry crosses into the plant circuit (esmagazine.com).
Performance, water use, and maintenance
Closed loops reuse over 95% of coolant per pass—compared with open towers that essentially consume 100% of their water each cycle via evaporation and blowdown. That cuts makeup roughly 20×–30×; in the earlier example, instead of ~78 m³/h continuously, a closed loop may only need a few liters per hour to replace leakage (czjsim.com).
Fouling and corrosion drop sharply with ultra-pure coolant. The fouling factor for the oil cooler is essentially zero; plants report cooling performance staying within <1% of design over long periods, with no algae or slime growth in the sealed circuit (watertechnologies.com). Planned maintenance typically involves periodic inspection and inhibitor top-ups.
Operationally, oil sump temperature control tightens to within 1–3°C of setpoint; plants report stable bearing temperatures and fewer trips or derates. N+1 redundancy (duty+spare) yields >99% availability, allowing maintenance on a standby cooler without shutting down the turbine (chemxperts.com).
Economically, lower water and treatment consumption shrink operating expense, reinforcing adoption amid rising water-conservation pressures (esmagazine.com).
Indonesian climate and compliance
In Indonesia’s tropical climate, high ambient wet-bulb temperatures and variable water quality make closed circuits attractive. Using demineralized makeup (potentially from condensate) avoids the scale issues common with fresh surface water. Moreover, strict local environmental standards (e.g., Peraturan Pemerintah on industrial wastewater) favor minimizing thermal and chemical discharges. A sealed demineralized loop discharges virtually no effluent (only minimal sample or renewal flows), easing regulatory compliance.
Key quantified benefits
- Water makeup reduction: from ~100% in open loops to <5% (95% reuse) (czjsim.com).
- Corrosion reduction: nearly 100% elimination of oxygen pitting when properly treated (watertechnologies.com).
- Scale/fouling: virtually zero fouling factor compared to 0.0001–0.001 in open systems.
- Thermal performance: Oil sump temperature control to within 1–3°C of setpoint due to stable heat rejection.
- Operational uptime: N+1 redundancy yields >99% availability of cooling function; with one cooler on standby, maintenance can proceed without turbine shutdown (chemxperts.com).
Sources and design references
Sources: Authoritative industry and technical references were used to inform this design. These include the Veolia Water Handbook on closed-loop cooling (watertechnologies.com; watertechnologies.com), power‑industry trade publications on closed system chemistry (powermag.com; powermag.com), and practical design data from turbine OEMs (chemxperts.com). Where possible, the figures above are drawn from real system specifications and published analyses (chemxperts.com; czjsim.com).
