Click each stage to see how heater type and function change across the feedwater train's full journey.

LP, HP & Deaerating Heaters

Track 3: Feedwater Heaters — Module 4 of 5

The Full Journey, Not Just One Heater

Modules 1-3 focused on individual closed feedwater heater construction and performance monitoring. This module zooms out to cover the complete feedwater heating train from condenser to boiler, including a fundamentally different heater design — the deaerator — positioned at a specific, important point in that journey.

Low-Pressure Heaters — Where the Journey Begins

LP heaters are positioned between the condenser and the deaerator, drawing extraction steam from the turbine's lower-pressure stages. These are the closed, shell-and-tube heaters covered throughout Modules 1-3 — the design and monitoring concepts already discussed (TTD, DCA, drain cascading) apply directly to this portion of the train.

The Deaerator — A Fundamentally Different Design

Positioned between the LP and HP heater sections sits the deaerator, which breaks from the closed-heater pattern entirely: extraction steam and feedwater mix together directly in an open design, rather than remaining separated by a tube wall. This direct contact serves a purpose beyond heating alone — it provides highly effective removal of dissolved oxygen and other gases from feedwater, a critical water chemistry function preventing corrosion in downstream high-pressure feedwater piping and the boiler itself.

Why direct contact removes gas so effectively: unlike closed heaters where feedwater and steam never touch, the deaerator's direct mixing allows dissolved gases within feedwater to escape directly into the steam space and be vented, a mechanism simply unavailable in a closed, tube-wall-separated design. This is precisely why deaeration specifically requires this different, open heater approach rather than being accomplished within an ordinary closed heater.

A Storage Function Too

Beyond heating and deaeration, the deaerator typically also serves as the plant's primary feedwater storage point — holding several minutes of feedwater inventory that boiler feed pumps draw from continuously. This storage buffer provides operational flexibility and a stable suction source for the pumps covered next, a function distinct from, though physically co-located with, the deaerator's heating and gas-removal roles.

The Boiler Feed Pump — A Major Pressure Step

Immediately following the deaerator, boiler feed pumps take suction from the deaerator's storage volume and dramatically increase feedwater pressure — from the deaerator's relatively modest operating pressure up to whatever pressure is needed to actually enter the boiler against its operating pressure. This specific positioning takes advantage of the deaerator's storage volume and slightly elevated pressure to provide favorable, reliable pump suction conditions.

High-Pressure Heaters — The Final Stage

After the boiler feed pump, HP heaters provide final feedwater heating using extraction steam from the turbine's higher-pressure stages, before feedwater finally enters the boiler. Because HP heaters operate at substantially higher pressure on both the shell and tube sides compared to LP heaters, their construction is generally more robust to handle this more demanding pressure environment.

Watch for: HP heaters are the last heating stage before the boiler — there's no further opportunity to compensate for underperformance downstream. HP heater degradation therefore has a particularly direct impact on the actual feedwater temperature reaching the boiler, and correspondingly, on boiler fuel consumption — this makes HP heater performance monitoring especially significant compared to earlier stages in the train.

What's Ahead

Module 5 applies this entire track's concepts — heater construction, drain cascading, TTD/DCA monitoring, and this module's full-train overview — to a feedwater heating train diagnostic capstone.

Module Quiz

6 questions • 80% (5 of 6) required to pass