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Plate heat exchanger and loss of flow
Loss of flow of plate heat exchanger: the pressure in the steam space of plate heat exchanger is less than or equal to the total back pressure behind the steam trap, which leads to the phenomenon that the condensate cannot be discharged in time.
Jul 5th,2021
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Loss of flow of plate heat exchanger: the pressure in the steam space of plate heat exchanger is less than or equal to the total back pressure behind the steam trap, which leads to the phenomenon that the condensate cannot be discharged in time.
There are three main situations that can cause the pressure in the heat exchanger to be lower than the back pressure behind the steam trap:
The increase of the inlet temperature of the secondary fluid results in the decrease of the load.
Due to the decrease of the flow rate of the secondary side fluid, the load is reduced.
Due to the decrease of the set temperature, the outlet temperature of the secondary fluid decreases.
When the load is reduced, the control valve will be turned down to reduce the steam pressure, resulting in insufficient pressure difference between the front and back of the steam trap, so that the condensed water is discharged through the steam trap, resulting in water accumulation in the steam space.
What are the signs of loss of flow and what are the effects of loss of flow?
In brief, when loss of current occurs, one or more of the following phenomena may occur:
1. The steam trap temperature is very low or even cold.
2. The control valve oscillates continuously.
3. Temperature fluctuation at the outlet of the product.
4. Stratification of heater temperature.
5. Water hammer.
6. Lower heat output.
7. The quality of the product has declined.
8. The heat exchanger is easy to corrode.
9. The heat exchanger is easy to leak.
10. Failure of heat exchanger.
The specific performance is as follows
The steam trap temperature is very low or obviously lower than the steam inlet pipe of the heat exchanger.
The control valve will keep oscillating, for example, the control valve will keep on and off.
The outlet temperature of the secondary side of the heat exchanger is usually lower than the set value.
The secondary side temperature at the outlet of the heat exchanger is stratified, especially in the air heater group or heating unit.
The heat exchanger will produce continuous or intermittent vibration, knock or impact noise. Sometimes accompanied by water hammer phenomenon, resulting in heat exchanger or its connection equipment damage. The condensation of steam in the accumulated condensate causes water hammer and noise,
This phenomenon is more serious when the load changes and the condensate level changes.
In the process application, the above phenomena will harm the product quality, cause quality instability and increase the possibility of corrosion.
The temperature of the accumulated condensate will be much lower than that of the steam. Carbon dioxide and oxygen dissolve more easily in cold water. Due to improper boiler water treatment, when the boiler generates steam, carbon dioxide will be continuously generated, and carbon dioxide is usually carried to the heat exchanger by steam. When carbon dioxide dissolves into water, it forms carbonic acid, causing corrosion. If oxygen in raw water cannot be completely removed by water treatment process, it will also be carried by steam. Dissolved in water, it is also highly corrosive. When the above two gases are present, the corrosivity will be stronger.
The properly designed plate heat exchanger with gasket seal can overcome the stress and is more suitable for steam application.
Loss of flow will eventually lead to the increase of maintenance, reduce the service life of heat exchanger and its ancillary equipment, thus increasing the overall operating costs.
