I'm looking for some help from someone more knowledgeable than me. This past weekend my
plant finished installing a scrubber system to scrub the exhaust from a rotary salt dryer.
The scrubber tank would not drain properly, building up past the cone of the tank into the
air duct. When we would turn off the supply, the water would eventually start to flow. In
the interest of time, they eventually plumbed the scrubber into the old scrubber gravity
drain with success. This same size line empties to a different (not preferred) place and
does not have a below ground portion as the new one does (you'll see in the sketch - it
basically forms a trap). I studied Art's gravity flow excel file a few times and it is
helpful, but I am not confident in how to apply it to my problem.
It was suggested that the line was airlocked and the behavior seems to support this, so a
vent was installed, but it looks to me like the wrong place (it was a convenient place).
Based on my friction loss tables, there is more than adequate vertical head to move the
required flow rate of water. I think that what is happening is that water drains into the
open top tank, leaving water standing in the vertical line on that end and water flowing
until water in the upstream vertical leg reaches that same equilibrium elevation. This
leaves air in the line from that point all the way to the scrubber. I suspect that when
water is added it flows until is passes the first vent (allowing that amount of air to
escape), but then due to a small (6") step up with two elbows, the air from that point
forward cannot escape, airlocking the system until some air manages to burp out of the
system somewhere (they were manually cracking a joint below to relieve it).
I believe that the elbow where the pipe turns vertical should be replaced with a tee and a
vent stack and that should allow the system to flow. Can someone familiar with these sort
of systems give me some advice? Alternately it has been suggested we add a pump. Some
other advice that has been given doesn't make sense to me - it was suggested this could be
solved by adding a dip pipe at the discharge end, ending at least 16" below the surface of
the water. I am not certain that the engineer that gave that advice had a full description
of the system. I will send them the same sketch as it attached. Any help would be
appreciated before we start modifying.
Thanks!
Nathan