The short answer
The PH boiler is consistently the harder erection. It sits higher, handles abrasive dust-laden preheater gas, and its coils hang rather than sit — so support setting, expansion allowance and hanger adjustment govern the outcome.
Both boilers arrive on the same purchase order and are often priced as one line. On site they are two different jobs.
Side by side
| AQC boiler | PH boiler | |
|---|---|---|
| Gas source | Clinker cooler exhaust | Preheater / precalciner exhaust |
| Dust loading | Low to moderate | High and abrasive |
| Orientation | Usually horizontal | Usually vertical |
| Coil support | Supported from below | Hung from top structure |
| Access | Reasonable | High level, congested |
| Main erection risk | Casing seal and module fit | Hanger setting and expansion |
Why hanging coils change everything
A supported coil sits on steel and grows upward as it heats. A hung coil grows downward from a fixed top. Get the cold setting wrong and the coil either fouls something below it at temperature, or stays in tension and cracks a support lug.
- Record cold hanger positions before insulation goes on
- Verify travel direction against the design expansion drawing
- Leave hanger locking pins in until the procedure says otherwise
- Re-check after first heat-up and record the hot position
Dust is an erection issue, not only an operating one
Preheater gas carries abrasive dust. Hoppers, wear liners and rapping gear below the PH boiler need real maintenance access — and that has to be designed into the erection sequence, because once the surrounding steel is up it cannot be added.
What this means for planning
Do not assume the two boilers take similar durations. On the packages we execute the PH side typically drives the critical path, and crane access to the high level is the constraint that decides the sequence.
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