Plate heat exchanger is a kind of heat exchange equipment, which has advantages that other heat exchange equipment cannot match: it has high heat transfer coefficient, low heat loss, small footprint, compact and light structure, easy maintenance and cleaning,Plate heat exchangers have a wide range of applications and a long service life. However, they also have some disadvantages, such as pressure cannot exceed 2.5Mpa, temperature cannot exceed 250 degrees Celsius, cannot exchange heat for larger particles and long fibers, cannot be used in extremely corrosive working conditions, and are prone to clogging. The following is an analysis of some common abnormal phenomena of heat exchangers:
Core reasons:
Scaling/clogging of heat exchange plates: Calcium and magnesium ions and impurities in the fluid are deposited on the surface of the plates, forming a scale layer with extremely low thermal conductivity; fluid short circuit: plate sealing gaskets are aging or misaligned,This causes some cold and hot fluids to mix directly without undergoing heat exchange; plate channel blockage: solid particles and fibers (such as sewage and slurry) in the fluid are stuck in the plate guide area or flow channel, reducing the effective heat exchange area.
Solution:
01
Chemical descaling (for scaling):
Stop the equipment, drain the fluid, and flush with a weak acidic cleaning agent (such as 5%-8% citric acid solution to avoid corrosion of stainless steel plates) for 2-4 hours,
02
then rinse with clean water until neutral;If the scale layer is hard (such as calcium carbonate hard scale), soak it for 1 hour before recirculating.
03
Do not use highly corrosive solutions such as hydrochloric acid (which can easily damage the plate passivation film).
04
Physical cleaning (for blockage):
Disassemble the heat exchanger, remove the plates, and flush the flow channel with a high-pressure water gun (pressure ≤ 0.8MPa to avoid deformation of the plates);
Core reasons:Gasket aging/damage: Long-term high temperature and pressure fluctuations cause the gasket to lose elasticity, or fluid corrosion (such as acidic fluid) causes the gasket to swell and crack; Plate deformation/misalignment: Uneven tightening of bolts during assembly Or long-term overpressure operation causes plate warping and loose sealing surfaces; flange seal failure: inlet and outlet flange gaskets age, or bolts become loose (alternating hot and cold causes bolts to expand and contract). Shutdown leakage is mainly caused by frequent start-up and shutdown of the heat exchanger, and restoration of normal working conditions is possible; internal leakage is mainly caused by damaged gaskets and plate corrosion and perforation;The main reasons for external leakage are misalignment, extrusion, damage of the sealing gasket, corrosion and deformation of the plate, and failure to tighten to the specified clamping size; the main reason for leakage between the blind plate and the clamping plate is that the blind plate is pierced by hard objects.
Solution:Emergency treatment: immediately reduce the system pressure, close the heat exchanger inlet and outlet valves (close the hot side first, then the cold side), drain the fluid and shut down; replace the seals: disassemble the heat exchanger, remove all the gaskets,Check the plate sealing groove for scratches (if any, smooth it with fine sandpaper); replace the sealing gasket with the same type (it is recommended to use heat-resistant and corrosion-resistant materials, such as nitrile rubber for oil and EPDM for water/weak alkali);Reassemble and tighten: stack the plates in the original order (plate numbers must be aligned to avoid reverse installation), and tighten the bolts evenly (tighten diagonally in steps to avoid excessive local pressure);
The difference between the inlet and outlet pressure gauges of the heat exchanger exceeds the design value (for example, the design pressure drops by 0.1MPa, but the actual pressure drops to 0.3MPa); the pump outlet pressure increases, but the heat exchanger inlet flow rate decreases (the pump is overloaded and the noise increases).
Core reasons:Flow channel blockage: impurities in the fluid (such as sand and rust) are deposited in the plate flow channel, reducing the flow cross-sectional area;Wrong number or type of plates: The actual flow rate far exceeds the design value, or the plate flow channel is too narrow (for example, a small channel plate is used to process a large flow rate fluid);Abnormal fluid viscosity: The fluid temperature is too low (for example, the viscosity of oil increases at low temperatures), or the fluid contains a large amount of suspended matter (such as slurry), resulting in increased flow resistance.
Solution：Clean the flow channel: After shutting down, disassemble the heat exchanger and flush the plate flow channel with a high-pressure water gun, or use a special ball (with a diameter slightly smaller than the flow channel width) to clear the blockage; adjust the operating parameters: if the flow rate is too large, appropriately reduce the pump frequency (control it within the range of ±10% of the design flow rate); if the fluid viscosity is high, increase the fluid inlet temperature (such as heating the oil to the appropriate viscosity range), or install a preheater at the inlet.
a:The hot side outlet temperature is higher than the design value. The main reasons are: the selection problem, the hot side flow rate is greater than the design value, the plate is blocked or the cold side flow rate is small;
b:The cold side outlet temperature is too low. The main reasons are small hot side flow or temperature lower than the design value, plate blockage, etc.