The closed-cooling-water system in a power plant is the core subsystem that supplies constant-temperature cooling water to key auxiliary equipment such as the main-engine lube-oil cooler, generator hydrogen cooler, and feed-water-pump lube-oil cooler. This project addressed the severe scaling and 35% capacity loss of the original shell-and-tube closed-cooling-water heat exchangers at a 2×600 MW supercritical coal-fired unit in Northwest China, replacing them entirely with SAMIT large plate heat exchangers.
1. Project Background
Customer
A state-owned power company in Northwest China; 2×600 MW supercritical coal-fired units, commissioned in 2012.
Original Equipment
2 shell-and-tube closed-cooling-water coolers (one per unit), cooling area 850 m².
Original Issues
- Sediment deposition on the open-water (reservoir) side
- 1.5 mm scaling on tube walls
- Heat-transfer capacity down 35%
- Required 2 shutdown cleanings per year
2. Technical Solution
SAMIT BR0.8 large plate heat exchangers replaced the original shell-and-tube units; each unit is equipped with 2 PHEs (one duty, one standby), with a heat-transfer area of 320 m² each. The open-water-side plates use a thickened corrugation design to handle sediment-laden water, with a 3.5 mm plate gap to prevent clogging.
| Parameter | Closed-Cooling-Water Side (Hot) | Open-Cooling-Water Side (Cold) |
|---|---|---|
| Medium | Demineralized deaerated water (closed) | Reservoir once-through water (trace sediment) |
| Inlet/outlet temp. | 45 / 33 ℃ | 25 / 36 ℃ |
| Flow rate | 1200 m³/h | 1500 m³/h |
| Pressure rating | PN10 | PN10 |
| Pressure drop | 45 kPa | 50 kPa |
| Heat load | 18 MW (per unit) | |
| Plate material | 316L | 316L (thickened corrugation) |
3. Process Flow
4. Implementation
- Original equipment removal: Used a 45-day unit overhaul window to remove the 2 shell-and-tube units (32 t each).
- New equipment installation: 4 SAMIT BR0.8 PHEs (8 t each), single-person hoisting into place, no heavy machinery required.
- Commissioning: 168-hour full-load trial run; closed-cooling-water outlet stable at 33 ± 0.5 ℃, K value 5200 W/(m²·K).
Key technology: To address the sediment in the reservoir water, the plates use a thickened corrugation (3.5 mm depth) + 316L stainless steel. A 20% wider corrugation maintains turbulence while lowering the per-channel pressure drop, so sediment is less likely to deposit. With the CIP back-flush connection, a 30-minute in-line cleaning each quarter restores initial performance.
5. Operating Results
Heat Transfer Capacity
K value raised from 3200 to 5200 W/(m²·K), up 62%.
Footprint & Weight
Equipment weight down 75%, plant-room footprint saved 60%.
O&M Cycle
Shutdown-cleaning cycle extended from half a year to 5 years (in-line back-flush suffices).
6. Lessons Learned
The core of a power-plant closed-cooling-water retrofit is "handling the water quality." The original shell-and-tube equipment is extremely sensitive to sediment-laden water; just 1.5 mm of scaling can cut heat-transfer capacity by 35%. The SAMIT thickened-corrugation PHE + in-line CIP back-flush solution fundamentally resolves this, with a footprint only 1/4 that of a shell-and-tube unit — especially suited to the tight retrofit conditions of a power-plant room.