Steam Trap after Desuperheater 1

[Keef]

I have been asked to select a steam trap for installation after a desuperheater. I have been led to believe that it is usual to install a collecting pocket with a trap in such circumstances. I believe the desuperheater will be a spray type.
What load do you base the sizing of the trap on? The steam flow rate is 150 ton/hour and the pressure is 1 bar g

 

[Joesteam]

I have seen some engineers specify the steam trap after a desuperheater to the maximum water flow rate through the desuperheater valve - in case of an upset condition.
In this case, we have recommended two parallel steam steam traps attached to an oversized drip leg so that the steam trap will not be too oversized on normal loads.

 

[gmorin]

If it's a big line or if you're trying to get close to saturation, you may want to consider a drain pot with level switches and an air operated valve instead of traps.

You also have very little differential pressure across the trap, so if you go with a trap, it's likely going to be quite large.

Using an operated valve allows you to make a conservative assumption as to how much water you might overspray. The most conservative thing to do is to assume that you need to remove all the water that the desuperheater can introduce into the pipe. That approach is often not practical and you'll need to develop a logical overspray scenario to size your trap or valve.

I can't give a simple answer, but factors to consider are whether the line is in continuous or intermittent operation, the turndown requirements/capabilities of the desuperheater, the location of the temperature feedback probe, whether the desuperheater control valve has a tight shutoff isolation etc.

Our normal practice is to size a drain pot for no less than 2 pipe sizes smaller than the line size, minimum 4".

http://www.armintl.com

is a manufacturer's website with some decent info regarding trap placement, etc

Good luck

Greg

 

[rmw]

I would like to know that the turndown is on your steam header. If it is a constant 150TPH flow, that is one answer, and if it is significantly reduced at times (other than start up) that is another answer. Also, how much superheat do you have in this steam.

I normally use Steam atomized DSH's in this steam service because of the potential for high turndown, and because the atomizing steam will 'blast' the cooling water, minimizing potential for free water in the steam header.

rmw