6 replies to this topic

[TS1979]

Hi all,

 

Please see attached file for your understanding.

 

This is a about 100% oversized naphtha heater. Naphtha is on tube side and 50# steam is on shell side. Naphtha outlet temperature is controlled by adjusting the liquid level inside the heat exchanger. Since the heat exchanger is greatly oversized, only controlling the condensate level can not meet the requirement for naphtha outlet temperature control and steam inlet block valve is used for throttling steam as well.

 

Since the heater was installed, Water hammering has been observed inside the heat exchanger. Operators opened the drain valve to sewer the condensate to eliminate the water hammer. It seems to me that the system has difficulty to get the condensate back to condensate drum mainly due to low pressure inside the heat exchanger (high pressure drop through the stream inlet gate valve). Another reason may be the interference of condensate control valve and steam trap or pressure drop through the steam trap.

 

My questions is:

Is the steam trap down stream of the control valve necessary or the steam trap can be removed?

 

Thanks advance for your comments.

 

 

[Bobby Strain]

Remove the steam trap. But doing so won't necessarily eliminate the hammering.

 

Bobby

[PKS]

As per understanding your question, I have found a very good explanation.

 

When the load to the heat exchanger drops (due to factors such as a reduction in the amount of product to be heated or an increase in the product's temperature), the pressure differential between the trap inlet and outlet pressures disappears, and condensate starts to pool inside the shell. This phenomenon is known as 'stall.'

 

When steam is supplied to an area that has a high level of condensate, it instantly condenses and water hammer occurs. 

 

To identify and correctly prevent the accumulation of condensate, it is necessary to thoroughly determine its cause(s), and apply preventative measures accordingly.

 

So, when the shell is fully filled with condensate and steam enters the shell, hammering occurs inside the shell. As you said, there is difficulty to drain the condensate, it may be only when the shell is fully filled and it does not get any ventilation to get drained (as due to full filling of shell, pressure inside the shell is not sufficient to drain the liquid). This means you have to avoid full filling of the shell with condensate. Open the bypass of the control valve or open the Control Valve manually to some extent that the condensate should continuously drain out of the system. 

 

I hope it helps!!

 

regards

 

PKS

 

 

Please follow the below link.

 

http://www.tlv.com/g...-equipment.html

 

[katmar]

The oversized area means that you need a lower temperature on the shell side to drive the heat, and as pointed out above the hot steam collapses as it hits the cold condensate.  I see 2 possible solutions.  Block off some of the tubes so  that you need a higher condensate temperature, or lower the steam temperature by installing a thermo-compressor and sucking in some of the flash steam from the condensate drum to mix with the 50# steam and lower the pressure and temperature of the steam feed to the heater.

[Bobby Strain]

You should take a look at your exchanger design. The baffling may be trapping condensate and causing the hammering. Cutting away baffles can solve your problem, but this requires that you take the exchanger out of service. And Katmar's suggestion to plug tubes will work, too. Plug the upper tubes first. Of course, you will experience higher pressure drop with plugged tubes. To stop the hammering now, you can flow a bit of nitrogen into the steam side, but not too much. Another thing you should do is connect the tempreature controller directly to the condensate valve and forget about the level control. This, too, might help to eliminate the hammering.

 

Bobby

[TS1979]

Thanks all of you for your valuable contributions. I have proposed to plug 40% tubes to reduce the heat transfer area. Wait and see what will be the result of the modification.

[PKS]

We all will wait, for your result of modification.

 

Thanks

 

PKS