Heat Recovery Steam Generators (HRSGs) for Data Center Power: An Engineering Guide

A heat recovery steam generator (HRSG) captures the hot exhaust from a gas turbine and turns it into steam. That recovered steam is what lifts a gas turbine from roughly 38% efficiency on its own to about 60% in combined cycle. For decades this was a power-industry concern. Now it is a data center concern.

Data centers facing multi-year grid interconnect queues are building their own natural gas power on site, and combined cycle is the efficient way to do it. The HRSG is the component that decides how efficient and how reliable that plant will be, and it is the part a turbine-focused project most often gets wrong.

This guide brings together our technical articles on HRSGs for behind-the-meter and data center power. Each section is a short overview with a link to the full piece. FIS has engineered fired heat-transfer equipment since 1996 for refining, petrochemical, hydrogen, and power clients, and brings that independent, heat-transfer-first perspective to HRSG sizing, specification, and revamp work.

Start here: how combined-cycle power works

A gas turbine on its own rejects about 60% of its fuel energy as hot exhaust. An HRSG recovers that heat as steam, and a steam turbine converts it to additional power with no extra fuel, which is what raises plant efficiency from around 38% to about 60%. This article walks through the whole chain in plain terms, with the heat-balance and efficiency math, and shows why the HRSG is the piece that makes combined cycle worth building for a data center power island.

Read the full article: Combined-Cycle Power for Data Centers: How the HRSG Fits

Duct burners and supplementary firing

When steam demand exceeds what turbine exhaust alone can produce, a duct burner fires supplementary fuel directly into the exhaust duct, using the residual oxygen in the exhaust as combustion air. It is the most flexible way to add steam on demand. This article covers how supplementary firing works, the heat-balance and oxygen-margin calculations that size it, the main burner types, and the design factors that decide whether a duct burner performs over the life of the plant.

Read the full article: Duct Burners in HRSGs: A Practical Introduction

Dampers and draft control

Behind-the-meter plants cycle harder than baseload utility plants, and every start, stop, and standby runs through the plant's dampers and draft system. This article explains the diverter, isolation, and stack dampers in a combined-cycle plant, why gas-side pressure drop quietly costs turbine output, and how engineering the draft and damper scheme against the real duty cycle protects restart speed, output, and thermal life.

Read the full article: Dampers and Draft Control in Cycling HRSG Plants

Gas turbine upgrades and HRSG revamps

Load growth is driving a wave of gas turbine uprates, and an upgrade is rarely just a turbine change. More exhaust flow, hotter gas, and more steam all land on the HRSG downstream. This article shows, with worked numbers, how a modest uprate raises HRSG duty and turbine backpressure, walks through the downstream failure modes, and makes the case for re-rating the HRSG before the upgrade scope is locked.

Read the full article: Gas Turbine Upgrades and the HRSG: What Changes Downstream

How an HRSG compares with a fired heater

Both machines are tube-based heat-transfer equipment sized with the same fundamentals; the difference is where the heat comes from. This article walks through what is the same (duty, flux, fins, fouling, flow distribution) and what is different (radiation versus convection, draft versus backpressure, process fluid versus steam, API versus ASME), and why fired heater engineering transfers directly to HRSG work.

Read the full article: HRSGs and Fired Heaters: What Is the Same, What Is Different

The same comparison, with model output

A follow-up with numbers: we simulated an HRSG and a crude heater convection section with the same software and methods. The hot ends are nearly identical, one is pulled by a stack and the other pushed by a turbine, the HRSG's pressure drop costs real turbine output, and the HRSG's tubes run hotter.

Read the full article: We Simulated an HRSG and a Fired Heater Convection Section

Stack dampers and draft: the physics

Where draft comes from, with the equation, why the arch is the control point, and why most stack dampers are oversized, non-linear, leaky, and parked open. The fired heater companion to the HRSG dampers article, with real results from damper conversions.

Read the full article: Stack Dampers and Draft Control: A Practical Guide

Finned tubes and fin selection

Fins multiply convection surface about nine times but duty only four to six, and the gap is where fin engineering lives. Fin density, height, thickness, and material against tip temperature and pressure drop, with an interactive calculator built on the ESCOA correlations.

Read the full article: Finned Tubes: A Practical Guide to Fin Selection

When the duct burner flame reaches the tubes

Why duct burner flames impinge on superheater tubes (uneven inlet flow, insufficient mixing length, turbine uprates), what the hidden overheating costs in creep life, and the engineering sequence that fixes it.

Read the full article: When the Duct Burner Flame Touches the Tubes

Working with FIS on HRSGs

FIS provides independent HRSG and fired heat-transfer engineering for EPCs, IPPs, and data center energy teams. We rate and revamp heat-transfer equipment for a living, so we evaluate an HRSG on its own merits, independent of the turbine OEM's scope. Typical work includes HRSG sizing and specification review, duct burner design, draft and damper engineering, re-rates ahead of gas turbine upgrades, CFD modeling, and independent audits.

If you are scoping a data center power island or evaluating an existing HRSG, we can help. Contact info@heatflux.com to scope a study or review.