Heat Recovery Steam Generators (HRSGs) in combined-cycle and cogeneration plants lose significant heat through bare casings, superheater headers, and outlet flanges. Removable insulation cuts those losses by up to 96%, reaching touch-safe surface temps, with payback often under 18 months on high-temperature equipment.
A large HRSG's hot headers, casing, valves and expansion joints can radiate on the order of 100+ kW uninsulated. Cutting that surface loss about 90% recovers roughly 800–900 MWh/year — about €60,000/year and ~200 t CO₂/year on gas firing.
Verified estimate (ASTM C680 / ISO 12241). Conservative still-air basis; figures scale with size, temperature and operating hours. Estimate your exact case with the free calculator →
An HRSG is a high-efficiency, high-temperature heat exchanger designed to extract waste heat from a gas turbine exhaust and produce steam for a steam turbine, boiler feed, or process use. Yet if the casing and key header sections run uninsulated—or with deteriorated insulation—the plant loses significant heat continuously across hundreds of square metres of bare surface. For a 100 MW combined-cycle unit, the total uninsulated loss can be verified with the calculator based on your specific geometry and operating conditions.
HRSG insulation losses concentrate in three areas:
An uninsulated HRSG insulation at 200–300 °C exposes 50–100 m² of surface to ambient. At 0.5 m/s air velocity and 25 °C ambient, this alone radiates 200–400 kW continuously. Industrial sites rarely insulate casing fully after installation due to access and equipment layout constraints.
Bare high-pressure steam headers on the outlet side run at 250–350 °C and often lack covers. A 300 mm diameter, 5 m header at 300 °C radiates ~150 kW. Operators avoid permanent lagging because turbine inlet controls and safety valve testing require frequent access.
Lower-temperature piping and manifolds, while losing less per square metre, run continuously; uninsulated 50 m of DN50 feedwater line at 120 °C costs €15,000+/year in lost fuel.
| Component | Bare surface (°C) | Heat loss (kW) | Insulated (kW) | Cut (%) |
|---|---|---|---|---|
| Casing + ductwork (50 m²) | 250 | 320 | 18 | 94% |
| Superheater headers (5 m) | 300 | 150 | 8 | 95% |
| Flanges & feed connections (12 pcs) | 200–280 | 85 | 4 | 95% |
| Total (typical 100 MW HRSG) | ~555 kW | ~30 kW |
Figures indicative (ASTM C680, 0.5 m/s, ambient 25 °C, emissivity 0.9); confirm with a short plant survey.
HRSG insulation payback is calculated as annual fuel saved ÷ installed capital cost. For a typical large HRSG with bare casing, headers, and piping, the annual savings are substantial—often €100,000+/year. Payback typically ranges from 6–18 months depending on your fuel cost, operating hours, and HRSG size. Use the calculator to size your specific unit and see exact savings and payback for your fuel price and duty cycle.
HRSG operators need regular access to:
Rigid hard lagging blocks all of this; removing it takes 2–4 hours and often leaves the flange or header bare thereafter. Removable modular covers unclip in 30 seconds, stay intact, and are refitted immediately—so the high-temperature, high-cost equipment never runs uninsulated.
Bare outlet headers at 300 °C create a serious burn hazard. OSHA 1910.269 (electric power generation) and EN ISO 13732-1 place the safe-touch threshold around 60 °C for brief incidental contact. Removable insulation typically lowers HRSG header surfaces to ≤45°C, meeting touch-safe personnel-protection limits while eliminating the need for exclusion zones.
Inzonex removable HRSG insulation is engineered for up to +600°C continuous and available in multiple thicknesses (50–100 mm depending on target surface temp and ambient). Fabric outer covers are inherently fire-safe (non-flammable), and quick-release systems use stainless-steel fasteners rated for thermal cycling.
HRSGs operate at the boundary between extreme temperatures (gas turbine exhaust >400 °C, steam generation at 200–300 °C) and ambient cooling. This creates steep thermal gradients that drive both conduction through the metal structure and radiation/convection to ambient. Insulation breaks this radiation path; on bare casings and headers, the exposed metal reaches temperatures that create visible shimmer and heat hazard zones around the unit.
Combined-cycle operators report that insulating HRSG insulations and outlet headers also stabilizes turbine inlet temperature by reducing fluctuations in ambient heat loss—a control benefit that improves steam generation consistency and extends turbine blade life.
Standard fiberglass or mineral-wool insulation can embrittle or sag at 250–300 °C continuous. Inzonex removable covers use high-performance aerogel or vacuum-panel cores rated to +600°C, with stainless-steel hardware and high-temperature silicone-impregnated fabric. This ensures minimal maintenance and full performance over the 20–30 year HRSG design life.
Modern HRSGs carry dozens of sensors: outlet thermocouples, pressure transmitters, level gauges, and drain valve pressure taps. Removable modular covers have custom cutouts for these instruments, allowing technicians to access, replace, or recalibrate sensors without removing the insulation. This is critical for units running advanced process-control algorithms that depend on rapid, accurate feedback.
HRSG heat loss is direct Scope 1 emissions: fuel burned on-site to replace waste heat radiated from bare casing and headers. Insulating an HRSG is a low-capex lever for Scope 1 reduction and ISO 50001 energy-management plans, with payback under 2 years—making it a high-priority project in net-zero roadmaps and EU ETS cost-avoidance strategies.
Typically 400–600 kW depending on size, design, and ambient. A 100 MW combined-cycle HRSG with bare casing, headers, and piping loses roughly 555 kW (94% reducible via insulation).
Often 6–12 months on headers and high-temp fittings, up to 18 months on lower-temp piping. The calculator shows exact numbers for your HRSG geometry and fuel cost.
Removable covers can be installed on a live plant during normal operation; rigid lagging typically requires shutdown. Modular snap-on approach means no welding or extended hot-work permits.
No — external insulation only reduces convective & radiative losses. Internal flow dynamics, heat-exchange efficiency, and steam purity are unaffected.
Removable fabric covers last 10+ years with routine inspection. If a section deteriorates, individual modules replace without removing neighbours—no downtime for the whole unit.
