After a district heating system had been in operation for two years, the secondary-side outlet temperature of the plate-shell heat exchanger was about 3°C lower than the design value, while the primary-side pressure drop increased by approximately 15%. Inspection after disassembly revealed aging indentations on some inter-plate sealing gaskets and slight fouling in the inter-plate flow channels. Such problems are often related to gasket selection, medium compatibility, and flow-pass arrangement verification, rather than insufficient performance of the equipment itself.
Compared with shell-and-tube heat exchangers, plate-shell heat exchangers have a larger heat transfer area per unit volume, a more compact structure, and a smaller footprint; compared with fully welded plate heat exchangers, plate-shell units use detachable gasket sealing, making core removal, cleaning, and maintenance easier, but the gasket material must match the medium temperature and chemical properties. Shell-and-tube heat exchangers have a wide pressure and temperature resistance range, but a smaller heat transfer area per unit volume and a larger footprint; fully welded plate heat exchangers have no gaskets and are suitable for high-temperature, high-pressure applications where leakage is unlikely, but they cannot be dismantled for inspection and are difficult to clean. Plate-shell heat exchangers fall between the two and are suitable for working conditions requiring periodic cleaning and moderate parameters.
Gasket material directly affects sealing life and operational safety. Nitrile gaskets are suitable for oil and water conditions below 80°C; EPDM gaskets are suitable for hot water and steam conditions below 120°C and have good aging resistance; fluororubber gaskets can be used for weakly corrosive media below 180°C. During selection, the gasket material should be determined according to the medium composition, maximum working temperature, and chemical properties, avoiding use beyond the temperature or medium range that could cause gasket failure.
When purchasing, please provide the medium composition, inlet and outlet temperatures, design pressure, and flow rate so that the required number of plates and flow-pass arrangement can be calculated, matching the heat transfer area and pressure drop to the actual working conditions. The number of plates and the flow-pass arrangement must be considered together with the pressure drop limit; increasing the number of passes can raise the flow velocity and heat transfer coefficient, but the pressure drop will also increase accordingly. It is recommended to specify the allowable pressure drop range in the parameter table to facilitate comparison of multiple options.
Regularly check the gasket compression and aging degree, and record the trends of the secondary-side outlet temperature and primary-side pressure drop. If the pressure drop continues to rise, cleaning can be scheduled according to water quality conditions; if the outlet temperature drops while the pressure drop remains normal, priority should be given to checking gasket sealing and plate fouling. During maintenance, tighten the clamping bolts evenly in a diagonal sequence to avoid deformation of the plates caused by over-tightening on one side.
