---
title: "Heat Recovery Steam Generator (HRSG)"
description: "A Heat Recovery Steam Generator (HRSG) recovers heat from the exhaust of a gas turbine to generate steam — the second cycle of a combined-cycle gas turbine (CCGT) power plant. HRSGs raise overall plant efficiency from the ~38% of a simple-cycle gas turbine to 55–62% of a modern combined-cycle plant."
canonical_url: "https://sylio.co/glossary/heat-recovery-steam-generator"
last_updated: "2026-06-28T02:29:33.807Z"
---

A **Heat Recovery Steam Generator (HRSG)** recovers heat from the exhaust of a gas turbine to generate steam — the second cycle of a [combined-cycle gas turbine (CCGT)](/glossary/combined-cycle-gas-turbine) power plant. HRSGs raise overall plant efficiency from the ~38% of a simple-cycle gas turbine to 55–62% of a modern combined-cycle plant.

## HRSG layout

A typical HRSG contains multiple [finned-tube](/glossary/finned-tube-harp-tube) tube banks arranged in series along the gas-path direction: superheaters, evaporators, economisers, and (on units with SCR) the catalyst layers. Modern HRSGs operate at three pressure levels (HP, IP, LP) to maximise energy recovery from the cooling exhaust gas.

## Fouling

HRSG fouling is generally lighter than coal-fired boiler fouling because gas-turbine exhaust contains far less particulate. The dominant fouling mechanisms are:

- **Ammonium bisulphate (ABS)** on units with SCR — slipped ammonia + SO₃ from fuel sulphur condenses on finned tubes
- **Fine ash deposition** on finned-tube banks reducing heat transfer
- **Duct-burner-driven** particulate on units with supplementary firing
- **Cold-end corrosion** below the acid dew point on sulphur-bearing fuels

## Cleaning

[Sonic horns](/glossary/sonic-horn) installed across the gas path are increasingly common on HRSG maintenance plans, particularly for keeping SCR catalyst layers and cold-end finned tubes clear of ABS without the need for offline water-wash campaigns.

## Related terms

- [Combined-cycle gas turbine (CCGT)](/glossary/combined-cycle-gas-turbine)
- [Finned tube / harp tube](/glossary/finned-tube-harp-tube)
- [Duct burner](/glossary/duct-burner)
- [Ammonium bisulphate](/glossary/ammonium-bisulphate)
- [Sonic horn](/glossary/sonic-horn)