Urban district heating in northern China generally uses a four-tier system of "combined heat and power plant → primary network → heating station → secondary network → end users." The primary network runs at water temperatures up to 130 ℃, while the secondary network only reaches 85 ℃; in between, heating stations are required for energy transfer and pressure isolation. This project designed and built four parallel large plate heat exchanger units in one pass for the 2-million-m² heating area of a new district in a Northeast China city.
1. Project Background
Customer
Thermal utility company of a new district in a Northeast China city, responsible for heating operations for 2 million m² of commercial and residential space in the district.
Heat Source
Upstream combined heat and power (CHP) plant, primary network design temperature 130/70 ℃, pressure rating PN25.
Design Parameters
- Total heating area: 2 million m²
- Design heat index: 45 W/m²
- Total heat load: 90 MW
- Divided into 4 stations, 25 MW per station
2. Technical Solution
Uses SAMIT BR1.0 large plate heat exchangers with a heat transfer area of 240 m² per unit, configured as 1 duty + 1 standby per station (mutual standby). The primary side (130/70 ℃) and secondary side (85/60 ℃) are completely isolated by the plate heat exchanger, preventing primary-network high pressure from directly entering the residential end-loop piping.
| Parameter | Primary side (high-temperature side) | Secondary side (low-temperature side) |
|---|---|---|
| Medium | Power plant demineralized water | Softened circulating water |
| Inlet/Outlet temperature | 130 / 70 ℃ | 60 / 85 ℃ |
| Flow rate | 860 m³/h | 1550 m³/h |
| Pressure rating | PN25 | PN16 |
| Pressure drop | 52 kPa | 48 kPa |
| Heat duty | 25 MW (per unit) | |
3. Process Flow
4. Implementation Process
- Design: Back-calculated the heat index from the local outdoor design temperature of -19 ℃; sized each station at 25 MW and distributed the 4 stations close to loads to reduce network losses
- Equipment supply: 8 SAMIT BR1.0 plate heat exchangers (2 per station, 1 duty + 1 standby), paired with VFD circulating pumps, pressurization make-up units, and automation cabinets
- Commissioning: During the extreme cold period at -22 ℃, the measured return temperature was stable; the end-of-secondary-network temperature difference was only ±1.5 ℃; main plant room noise ≤ 75 dB(A)
Design highlights: The primary-network pressure PN25 and secondary-network PN16 are fully isolated by the plate heat exchanger, so even if the secondary-network end loops introduce impurities during renovation, there is no backflow contamination of the primary network (CHP plant side). At the same time, the high K value of the plate heat exchanger (5500 W/(m²·K)) means it requires only 1/4 the footprint of a shell-and-tube unit for the same heat duty.
5. Operating Results
Heat Exchange Capacity
Each station operated stably at the full 25 MW load, with the K value maintained at 5500 W/(m²·K).
Footprint
Saves 75% of footprint compared with a traditional shell-and-tube scheme; each station's plant room is only 80 m².
O&M Cost
Zero failures over 3 heating seasons; annual O&M cost down 40% versus shell-and-tube.
6. Lessons Learned
The key to selecting large district heating stations is "high temperature difference + large temperature drop." A primary-network temperature difference of 60 ℃ (130/70 ℃) plus a secondary-network difference of 25 ℃ (85/60 ℃) lets SAMIT plate heat exchangers transfer the maximum heat in the smallest footprint. For projects above 2 million m², we recommend a multi-station parallel + plate heat exchanger unit layout to avoid the O&M risk of a single oversized station.