The short answer
A WHRB is the boiler itself; a WHRS is the whole power island around it. In a cement plant the WHRS almost always contains two boilers — an AQC boiler on clinker cooler exhaust and a PH boiler on preheater exhaust — feeding one steam turbine.
The two acronyms get used interchangeably in tender documents, and it causes real scope confusion at bid stage. They are not the same thing, and the difference decides how much work is actually in the package.
The distinction in one line
WHRB — Waste Heat Recovery Boiler — is a single pressure vessel that turns hot exhaust gas into steam. WHRS — Waste Heat Recovery System — is the complete power island: boilers, steam turbine, condenser, cooling tower, feed water system, ducting, piping and controls. Awarding "WHRB erection" and awarding "WHRS erection" are very different quantities of steel.
The two boilers in a cement WHRS
A cement kiln line rejects heat at two points, at two very different temperatures. That is why a cement WHRS normally has two boilers rather than one.
| AQC boiler | PH boiler | |
|---|---|---|
| Heat source | Air quenching cooler exhaust | Preheater / precalciner exhaust |
| Typical gas inlet | ~250–400 °C | ~280–380 °C |
| Dust loading | Low to moderate | High, abrasive |
| Typical arrangement | Horizontal, multiple modules | Vertical, hanging coils |
| Erection concern | Module alignment, casing seal | Dust hopper access, wear protection |
The PH boiler is the harder erection. It sits high, it handles dust-laden gas, and its coils hang rather than sit — so support settings, expansion allowance and hanger adjustment all matter more than they do on the AQC side.
What is actually in the erection scope
On the packages we execute, a complete WHRS erection scope typically contains:
- Structural steel for both boiler support structures, platforms and staircases
- Site fabrication of casing, ducting, hoppers and expansion joints where not supplied pre-made
- Pressure part erection — headers, coils, drums, downcomers and risers
- IBR steam and feed water piping between boilers, turbine and deaerator
- Dust handling below the PH boiler hoppers
- Insulation and cladding across boilers, ducting and steam lines
- Hydro testing, steam blowing, box-up and commissioning support
Capacity, and what it tells you about the job
Cement WHRS packages in India commonly land between 5 MW and 35 MW depending on kiln line size. As a rough guide, a 3,000–4,000 TPD line supports roughly 6–9 MW; a 10,000 TPD line can support 30 MW or more. Larger does not simply mean more of the same — above roughly 20 MW the pressure parts, structure heights and crane requirements step up together.
Why the erection contractor matters more than it looks
The boiler OEM designs and supplies. The plant owner runs the asset for thirty years. In between sits an erection contractor whose weld quality, alignment discipline and documentation determine whether the asset performs to the design curve or becomes a maintenance problem. Tube leaks in the first operating year almost always trace back to erection, not design.
That is why OEMs tend to re-award the same erection partners rather than shop each package. Consistency of crew, qualification records and hold-point discipline is worth more to them than a marginal rate difference.
Topics