Like you when I heard about this , it was strange for me to install control valve on condensate line after heat exchanger. in all application I have seen control valve on steam supply line to heat exchanger.
one of the supplier introduced this system that a control valve is installed on condensate before steam trap.
his argue wasthat, a control valve on the steam supply has disadvantage for condensate return, especially when the pressure within the shell of the exchanger provides the driving force for the condensate to flow back to the boiler feed-water makeup equipment.
control valve on condensate will control the level of condensate within the exchanger, which affects the effective heat transfer area, which affects the heat transfer rate.
With regard to condensate return, the pressure within the shell always is the steam supply pressure that this pressure is adequate to return the condensate to the boiler feed-water makeup.
just wanted to know if anyone has seen this system in any project and if it works fine. We don't want to experience something new especially when it comes to steam.
As mentioned by katmar, in common practice of temperature control of HE fed with steam you can have two configurations:
1) Control valve on the steam supply side and a steam trap at the HE’s outlet
2) Control valve in the condensate return line
The two methods listed above imply a different approach in HE design process.
To go deeper on this subject I’ve taken the liberty of suggesting a couple of interesting links.
Thanks, just one more question. what if control valve fails. In first method (control valve on the steam supply side) control valve fails closed. what about second method?
I am familiar with the concept of a control valve on the condensate outlet, but that is not the question that was asked in the OP. Adding a trap in series after the valve makes it into a completely different situation.
On the second method mentioned above, if the control valve fails shut, assuming continued flow on the tube side, the Hx would eventually flood as it continues to condense steam and then after flooding covers the tubes, stop transferring heat altogegher.
I think it has been repeated several times throughout this thread that it is NOT the right thing to do to have a control and valve in series after a heat exchanger. To do so is a poor design. Are you trying to justify the design?
If the question is whether or not it is a "proper design" to install a control valve on the condensate line (WITHOUT a trap and without any controls on the steam supply), as a means to control the duty of a steam-heated exchanger when heating a fluid to temperatures below 100 C, the answer is YES. This is BETTER than trying to ontrol the steam flow to the exchanger by means of a control valve, as it prevents the shell from pulling a VACUUM and hence making condensate removal impossible.
I meant to say "...in series with a trap.." in my earlier post.
To add to moltenmetal's comment above, it also allows full steam pressure (which has a temperature relationship) in the Hx rather than a reduced pressure across a control valve at the inlet, and for some Hx's or processes, that is important. But I have seen it done on steam pressure/temperatures much higher than 100C.
