Condensate in low pressure superheated steam line

[AdamEngineer]

At the power station there is a steam pipe + 100 metres long , 250 mm Diameter , the pipe contains superheated steam at 3.5 barg and 215'C ..... when on load there is no steam demand an no flow (this is auxiliary steam). Historically this pipe has become flooded with condensate due to incorrect size or malfunctioned trap therefore a 50 mm drain valve is left permanently open.

I would like the close this drain valve to a position so that it prevents condensate build up in the line but does not waste excessive steam.....

my thoughts are that as long as drain valve is opened sufficiently so that the steam flow is turbulent then any condensate will get entrained within the flow and thus be removed.

Is my approach correct ? are there better ways of removing the condensate ?

 

[MFJewell]

Why not correct the trap? That seems like the most logical answer.

Another option would be to put a timed solenoid valve on the drain to allow intermittent blowdown.

 

[KoachCSR]

Agreed with MFJewell - the proper fix is to correct the trap.

 

[crshears]

Might not be an issue, but it seems to me timed blowdown isn't optimal as steam line would be thermally cycled on a continuously repeating basis; better to fix the trap & hold temperature constant.

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Ehzin]

Is it an incorrect size or malfunctioned trap or both? It doesn't sound like the actual problem has ever been diagnosed. If you're trying to avoid wasting steam look into a trap that is actually designed for superheat conditions. Some traps such as inverted bucket can have problems in superheat systems where they can lose their prime and go into blowthru bringing you back to just wasting excess steam.

This is a +100 meter long 250 mm diameter line that apparently has a single drain valve to remove condensate. Does this have line expansion loops and are they all at the same elevation or do they have any elevation change along the expansion loops or in any sections of the piping?

Thanks,
Ehzin

 

[georgeverghese]

A steam trap should have a upstream condensate cooling leg.

 

[MJCronin]

It sounds like this 100m steam pipe should have been designed with a couple of condensate drain lines

Spirax Sarco has good clear guidelines detailing how steam and condensate systems should be designed.

As I recall, there should be a drain leg everytime that the steam pipe changes elevation.

Large amounts of condensate left in steam piping causes watterhammer and can be dangerous.... Piping systems have failed and people have died.

Is the system properly sloped toward the steam destination location ? Proper slope is also important

MJCronin
Sr. Process Engineer

 

[mk3223]

It could be okay that you crack open the drain valve to dump out condensate with some steam, but not too much as you hope. The question is how to control it, and how much different in saving steam will be. And then, if any saving really occurred, you may use it to fix the the broken steam traps.

 

[Dhurjati Sen]

AdamEngineer
The pipe is on a rack, I guess. You cannot change the traps as you need a shutdown which is not even in the horizon. You also have to cut on steam losses, what do you do?
Think of a scenario where you have pinched the drain valve and saving on a lot of steam. Now, you need to take the steam line back. What could happen? MJCronin has already cautioned you. The pipe might fall off from the rack!
Better procure correct traps, maybe thermodynamic ones and make sure all the traps are replaced in the next shutdown.
In the meantime, cut down on steam losses elsewhere!