LP condensate flash vessel 1

[USR]

I am currently working on the design of a LP condensate flash vessel.This vessel receives lp condensate from various users and lp condensate from a MP condensate flash vessel.This lp condensate flash vessel will be kept floating with the atmosphere.please guide me on the following things:
1.What should be the correct location for the u loop seal for maintaining the level of condensate?
2.What should be the method for venting the vessel to the atmosphere?

 

[sshep]

Hey USR,

I thought surely you would get some response to this, and I was interested because my plants have several such systems, all struggling.

Our vents to the atmosphere off of these drums are via an exchanger to act as a flash steam condenser, the drain is back to the drum. The drum is horizontal. We have both cooling water and air coolers as vent condensers, but cooling water was a foolish choice due to high scaling. The final vent was just a pipe, but now we are putting in an exhaust head to address to address drift from a substantial steam vent plume (cause by inadequate flash steam condensing).

The overflow lines in most cases come off the condensate pump suction and have significantly less than 1 meter between the bottom inside elevation of the pipe and the liquid level. The siphon break is to atmosphere. Due to high back pressure on the drum from inadequate flash condenser performance, the seal is in some cases inadequate. I think this under estimate of possible drum pressure is a common problem (we are talking like 12" to 24" of water), compounded by the fact that chemical engineers often don't do gravity flow piping very well.

I have previously posted to ask how others do this, most recently thread124-278398. I never saw such problems at other sites where I worked, and consequently never really looked at it before. Is direct contact condensing via a pump around used, do people cool some steams before the flash drum, etc. Things that might really help you are to do heat recovery from liquid from your MP drum before flashing down to the LP drum, or better yet, pump it back to your steam plant deaerator hot from the MP drum.

I can only tell you what I have seen as inadequacies and speculate as to what would be better. I hope for guidence to best practices also.

best wishes,
sshep

 

[steamdog]

I work with flash tanks a lot. If this is really an atmospheric tank, it means that there should be no pressure in it and a loop seal should not be necessary, unless to establish a level in the tank.

That being said, if the size of the vent is not correct, the tank will develop a positive pressure. Every 1 psig pressure will be 2.3 feet of loop seal required. MANY of these tanks have undersized vents. Yes, they may be sized correctly for the flashing condensate, but maybe no one has taken into account any failed open steam traps blowing live steam into the line.

My recommendation, if possible, is either try to find and fix all of the failed traps or to increase the size of the vent - or put an additional vent on the tank.

 

[sshep]

The loop seal is for over-fill protection in the event of pump or level control failure. The take-off is below the liquid surface as a seal to avoid being a vent for flash steam. The overflow has nothing to do with designing for pressure.