Causes of Excessive Pressure Drop in Plate Heat Exchangers

Reasons for Excessive Pressure Drop

1. Inadequate Heat Transfer Area During Initial Selection
When the plate heat exchanger is first selected, an undersized heat transfer area causes excessively high flow velocity between plates, leading to a large pressure drop.

2. Lack of Proper Pipeline Flushing in the Operating System
The pipeline of the operating system, especially in newly installed systems, is not properly flushed. Many contaminants (such as welding slag) enter the interior of the plate heat exchanger. Due to the narrow cross-sectional area of the heat exchanger’s flow channels, sediments and suspended matter accumulate in the corner holes and flow guide areas, significantly reducing the flow channel area and causing most of the pressure loss in these locations.

3. Scaling on Plate Surfaces After Extended Operation
After the plate heat exchanger operates for a period, scaling on the plate surfaces increases flow resistance, leading to excessive pressure drop.

Treatment Methods

1. Remove dirt in the heat exchanger channels or scale on the plates: For newly - operated systems, clean it once a week according to the actual situation. When cleaning the scale (mainly CaCO₃) on the plate surface, select a cleaning solution containing 0.3% sulfamic acid or a 0.8% nitric acid solution containing 0.3% urotropine, 0.2% aniline, and 0.1% potassium thiocyanate. The cleaning temperature should be between 40 - 60°C. When performing chemical immersion cleaning without disassembling the equipment, open the inlets and outlets of the cold medium of the heat exchanger. Or, when installing the equipment, install a DN25 cleaning port on the medium inlet and outlet nozzles. Inject the prepared cleaning solution into the equipment. After soaking, rinse the residual acid solution with clean water to make the pH ≥ 7. When disassembling for cleaning, soak the plates in the cleaning solution for 30 minutes, then gently brush the scale with a soft brush, and finally rinse it clean with clean water. Avoid damaging the plates and rubber gaskets during the cleaning process. If the non - disassembling mechanical back - flushing method is adopted, connect a nozzle to the medium inlet and outlet pipelines in advance, connect the equipment to the mechanical cleaning vehicle, inject the cleaning solution into the equipment in the opposite direction of the medium flow, and the circulating cleaning time is 10 - 15 minutes. Control the medium flow rate at 0.05 - 0.15 m/s. Finally, circulate with clean water several times to control the mass concentration of Cl in the clean water below 25 mg/L.

2. Use softened water for the secondary circulating water: It is best to use softened water for the secondary circulating water. Generally, it is required that the mass concentration of suspended solids in the water is not more than 5 mg/L, the diameter of impurities is not more than 3 mm, and the pH ≥ 7. When the water temperature is not more than 95°C, the concentrations of Ca and Mg should not be more than 2 mmol/L; when the water temperature is higher than 95°C, the concentrations of Ca and Mg should not be more than 0.3 mmol/L, and the mass concentration of dissolved oxygen should not be more than 0.1 mg/L.

3. Adopt the method of supplying water from the primary circuit to the secondary circuit for the district heating system: For the district heating system, the method of supplying water from the primary circuit to the secondary circuit can be adopted.