Capstone: Diagnosing a Heat Rate Deviation
The Scenario
You come on shift on Unit 2 and notice generator output is running about 1% below what it normally holds for these steam conditions and valve positions. It's a small enough deviation that it would be easy to dismiss — nothing has alarmed, nothing has tripped, and the unit is otherwise running smoothly. But the Shift Data tab shows a five-shift heat rate trend that's been climbing steadily. This module walks through the same diagnostic reasoning a performance engineer or experienced operator would apply, using the concepts from Modules 1.1 through 1.5.
Step 1 — Read the Trend Before the Snapshot
A single reading out of range could mean almost anything — instrument drift, a transient condition, or a real problem. The five-shift heat rate trend is what turns this from "maybe nothing" into "worth investigating": a steady, gradual climb with no discrete alarm event is exactly the signature Module 1.4 described for slow-developing losses like fouling, as opposed to a sudden mechanical failure. That shape alone should point your attention toward a gradual degradation mechanism, not a trip-worthy event.
Step 2 — Rule Out the Known Governing and Regenerative Losses
Module 1.4 identified four common field heat rate drivers: condenser vacuum, valve-point throttling, feedwater heater status, and blade fouling. Two of them are quickly ruled out by the shift log: governor valves are confirmed wide open (eliminating valve-point throttling as a cause), and all feedwater heaters are confirmed in service with normal terminal temperature differences (eliminating a regenerative-cycle loss). That narrows the field to two remaining candidates: condenser vacuum and blade fouling.
Good troubleshooting works by elimination as much as by pattern-matching. Confirming what's normal is just as valuable as spotting what's abnormal — it narrows the search space so you're not chasing every possible cause at once.
Step 3 — Follow the Condenser Vacuum Signature
Condenser vacuum is reading 2.8" HgA against a normal of 1.5" HgA — a significant degradation. Per Module 1.4, this directly reduces the pressure drop available across the whole turbine, which alone can account for both the output shortfall and the climbing heat rate. But a good diagnosis doesn't stop at "vacuum is bad" — it asks why. The circulating water ΔT across the condenser is reading 14°F against a normal of 18°F, meaning the cooling water isn't picking up as much heat as it should.
A reduced circ water ΔT alongside degraded vacuum, with no indication of a flow problem, points specifically toward reduced heat transfer effectiveness at the condenser tubes themselves — most commonly, tube fouling or scaling that insulates the tube surface from effective heat exchange, even though water is still flowing through at a normal rate.
Condenser tube fouling → reduced heat transfer → reduced circ water ΔT → degraded condenser vacuum → reduced turbine pressure drop → lower output and higher heat rate for the same steam conditions. Every link in that chain is directly traceable to a concept from Modules 1.1–1.4: expansion pressure drop, condenser role in the Rankine cycle, and vacuum as a heat rate driver.
Step 4 — What This Diagnosis Points Toward
The combination of readings — degraded vacuum, reduced circ water ΔT, governing and feedwater heaters both confirmed normal, and a gradual multi-shift trend with no discrete event — builds a consistent case for condenser tube fouling as the most likely root cause, rather than a mechanical turbine problem. The appropriate next step would typically be flagging condenser performance for the next available cleaning opportunity (mechanical tube cleaning or backwashing, depending on plant equipment) rather than any turbine-side maintenance action. This is the kind of conclusion that comes directly from correctly reading and cross-referencing the field indicators covered throughout this track — not from any single reading in isolation.