The walking-beam reheating furnace is the core high-temperature equipment of a hot rolling mill. The furnace bottom water beams and skid rails are subjected to high-temperature oxidation and heavy loads inside a 1250 ℃ furnace chamber, and must be forcibly cooled. Traditional open-circuit cooling water is prone to scaling, which can cause water beam rupture accidents. This project uses SAMIT fully-welded plate heat exchangers to build a closed-circuit cooling system, eliminating scaling risk at the source.
I. Project Background
Customer
A large steel group's hot rolling mill in North China, building a new 1880 mm hot rolling line equipped with two walking-beam reheating furnaces.
Furnace Specifications
Single-furnace output 380 t/h (steel slabs), furnace chamber temperature 1250 ℃, total weight of furnace bottom water beams + skid rails 280 t.
Cooling Requirements
- Closed-circuit cooling water outlet ≤ 55 ℃
- System pressure 0.6 MPa
- Water supply availability 99.9%
II. Technical Solution
SAMIT WB30 fully-welded plate heat exchangers are adopted, with a single-unit heat transfer area of 180 m². The closed-circuit cooling water side uses demineralized deaerated soft water (permanently closed circulation), while the open-circuit cooling water side uses conventional industrial water (open circuit). The two water streams are completely isolated by the fully-welded plate heat exchanger, allowing the closed-circuit water to operate long-term without replenishment, fundamentally preventing water beam scaling.
| Parameter | Closed-Circuit Water Side (Hot Side) | Open-Circuit Water Side (Cold Side) |
|---|---|---|
| Medium | Demineralized deaerated water | Industrial water (open cooling tower) |
| Inlet/outlet temperature | 55 / 43 ℃ | 30 / 41 ℃ |
| Flow rate | 900 m³/h | 1150 m³/h |
| Pressure rating | PN10 | PN10 |
| Pressure drop | 38 kPa | 42 kPa |
| Heat load | 12 MW (per unit) | |
| Plates | 316L fully-welded, gasket-free | |
III. Process Flow
IV. Implementation Process
- Solution design: Based on a maximum heat load of 24 MW for the 380 t/h furnace, two SAMIT WB30 fully-welded plate heat exchangers are configured in parallel (no standby; in case of single-unit failure, the system runs at reduced load).
- Closed-circuit water treatment: External deaeration + nitrogen blanket pressurization ensures closed-circuit water dissolved oxygen ≤ 0.1 mg/L and conductivity ≤ 10 μS/cm.
- Commissioning and acceptance: 168-hour full-load operation, closed-circuit water inlet/outlet temperature difference stably at 12 ℃, system pressure drop 80 kPa (including piping), K value 4800 W/(m²·K).
Core advantages: The fully-welded structure has no gaskets and can withstand thermal shock and pressure fluctuations; 316L plates resist industrial water corrosion; the plate heat exchanger is only 1/5 the volume of a shell-and-tube unit, allowing it to fit in a compact equipment room beside the furnace. The gasket-free design means no consumables need replacement for 5–8 years; CIP (clean-in-place) online cleaning alone maintains performance.
V. Operating Results
Equipment Reliability
3 years of operation with zero leakage and zero water beam scaling incidents, K value stable at 4800 W/(m²·K).
Footprint and Investment
Footprint reduced by 80% compared with shell-and-tube solution, equipment room only 35 m², total investment down 22%.
O&M Cost
No gasket replacement needed; annual O&M cost only 30% of shell-and-tube.
VI. Lessons Learned
The first principle of steel reheating furnace cooling is "absolutely no scaling," because once the water beams scale, heat transfer deterioration will cause slab deformation or even damage to the furnace bottom structure. The SAMIT fully-welded plate heat exchanger + closed-circuit circulation solution eliminates the possibility of impurities entering the water beams at the source, and the fully-welded structure handles temperature and pressure fluctuations far better than gasketed plate heat exchangers. It is recommended to uniformly adopt fully-welded plate heat exchangers for high-temperature cooling scenarios in the metallurgical industry.