Plate heat exchanger and loss of flow

Plate heat exchanger and loss of flow

Loss of flow of plate heat exchanger: the pressure of the steam space of plate heat exchanger is less than or equal to the total back pressure after the trap, leading to the phenomenon of condensed water cannot be discharged in time.

There are three main situations that will lead to the pressure in the heat exchanger is lower than the pressure behind the trap:

The load is reduced due to the increase of fluid inlet temperature on the secondary side.

The load is reduced due to a decrease in the flow of the secondary fluid.

Due to the decrease of the set temperature, the fluid outlet temperature on the secondary side decreases.

When the load is reduced, the control valve will turn down the pressure to reduce the steam, resulting in not enough pressure difference between the front and rear of the trap to allow condensate to discharge through the trap, resulting in water accumulation in the steam space.

What are the signs of loss and what are the effects of loss?

Briefly speaking, when loss of flow occurs, one or more of the following phenomena may occur:

1. The trap temperature is very low or even cold.

2. Control valve oscillates continuously.

3. Temperature fluctuation at product exit.

4. The temperature of heater is stratified.

5. Water hammer phenomenon.

6. Reduced heat output.

7. Decline in product quality.

Heat exchangers are easy to corrode.

Heat exchanger is easy to leak.

10. Heat exchanger failure.

Specific manifestations are as follows:

The trap temperature is very low, or significantly lower than the steam inlet pipe of the heat exchanger.

The control valve will continue to oscillate, for example: the phenomenon of the control valve constantly on and off.

The fluid outlet temperature on the secondary side of the heat exchanger is usually lower than the set value.

The secondary side temperature at the outlet of heat exchanger appears stratification phenomenon, especially on the air heater group or heating unit.

The heat exchanger will continuously or intermittently emit vibration, knock or impact noise. Sometimes accompanied by water hammer phenomenon, resulting in heat exchanger or its connected equipment damage. The steam condenses in the accumulated condensate, causing water hammering and making noise,

This phenomenon is more serious especially when the change of load causes the change of condensate water level.

In the process of application, the above series of phenomena will harm the quality of the product, resulting in quality instability, increase the possibility of corrosion.

The temperature of the accumulated condensate will be much lower than the steam temperature. Carbon dioxide and oxygen dissolve more easily in cold water. Because of improper boiler water treatment, when the boiler produces steam, carbon dioxide will also be continuously produced, and carbon dioxide will usually be carried to the heat exchanger by steam. When carbon dioxide dissolves into water, it forms carbonic acid, which causes corrosion. The oxygen present in the raw water, if not completely removed by the water treatment process, will also be carried by steam. Dissolved in water, it is also highly corrosive. When both of these gases are present, the corrosion will be stronger.

Properly designed plate heat exchangers with gasket seals can overcome stress and are more suitable for steam applications.

Loss of flow will ultimately lead to increased maintenance, reducing the service life of the heat exchanger and its ancillary equipment, and thus increasing the overall operating costs.

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