We currently run a steam ejector to evacuate an evaporator system.  The exhaust for the ejector is vented out the wall horizontally, and sprays steam and condensate all over.

I am going to turn the vent vertically up, and leave a drain leg on the vent.  I am wondering if there are rules of thumb for running a vent of this type.  Is it better to just run the steam pipe into the center of a reducing tee, with the large end pointed up and the small end run to the ground?

We are in Ohio, so we get cold weather, is heat trace/insulation necessary for the drain leg?

Running the steam directly into the branch of a tee with the run in the vertical would probably work.  Keeping the bottom run full size for a few feet before reducing to a smaller drain line would provide a small reservoir to help keep any slugs of liquid from overloading the drain line and blowing drops out of the top vent.

If steam clouds at ground level will be a problem, a p-trap in the drain line would force all vapor to exit out the top.  The trap would probably require freeze protection.

I'll second ETG01:  An exhaust head like the Hayward collects the droplets and routes them to a drain.  Most of your major reputable steam trap suppliers offer something similar: A centrifugal separator that knocks out the droplets before the dry steam discharges to atmosphere.  It's a direct solution to the problem you described.  AND it would not have to go through the roof: just elbow up a few feet from your current discharge, and install the exhaust head and drain line.  

Normally, only the hogging ejectors used on start-up discharge to atmosphere. Once most of the air is removed, then the system is switched over to a smaller air ejector which is much cheaper to operate. Is there a reason you aren't using a condenser to collapse this steam?

I've seen a diary operation where they were actively considering tearing out a perfectly good ejector system, and replacing it with mechanical vacuum pumps. The only thing I could see wrong with the existing system was that the control valve for the cooling water to the condenser was seized in an almost fully closed position. Of course, the engineer for the vacuum pump company insisted that the steam condenser was a restriction in the exhaust. The idea that steam collapsing into 1 / 1700th of it's volume when it condenses was apparently not relevent - at least to his being able to close the sale for his product.

The best solution would be to exhaust into a hotwell, below the liquid level.  Just make sure you don't submerge the exhaust pipe too deep or you will get excessive back-pressure.

If there is no sump/hotwell, you are best off pointing the discharge upwards, and then have a drain off the bottom.  Make sure the drain is always opened in case of rain.  Pointing the ejector upwards is also best for lowering the noise level.

I don't see any advantage to using a reducing tee, but heat tracing the drain may be a good idea because the flows will be very low and could freeze.  But I have no experience with freezing there.

MORE NEWS