Knock Out Drum or KO drum, this equipment is very important through oil and gas system. KO drum used to place before flare system. Slightly this package look like pressure vessel that lay on horizontal position. Main idea on KO drum is gravitation on each fluid into it. Using wall inside as border but not fully close area (like a weir). Let me introduce first regarding KO Drum system. Oil that may contain water, heavy oil, condensate,and gas. Oil will flow into KO Drum to segregate them. Inside KO drum needs heater, and it was provided by hot water form Heating Medium Header. Generally, on FPSO layout, HMH are placed on alone module, but it isn’t far away from Waste Heat Recovery Unit (WHRU). To imaging WHRU, we can look turbocharge on engine, but it will replaced with heat exchanger through outlet gas which output combustion system. Like shell and tube on that connection, but tube is line of exhaust engine. And shell is small tubes that contain water. After get the heat, water will be used with another packages that need low temperature. Some of them will flow into Heating Medium Heater (HMH). Why we have to use normal water? Actually, we can use water whose normal temperature, but to reach high efficiency, we must use water after absorb heat from WHRU. One of user of those heating water is KO Drum. Actually, if we ignore temperature on line which contain crude oil, it will be big problem for engineer. Since the pipe will block due to wax happen. I already involved on Production Drilling Quarter, in the project indicate that crude oil through KO Drum will be maintain around 40 deg C, even when it is heavy weather. Bellow pic is sample of wax on pipe, please look up bellow link to deeply understand and I got the pic on the link. Let me mention the listening about it, Oil depends on temperature, temperature will effect on viscosity, it means if oil flow with heat tracing on boundary, it will velocity constant. but if it decrease temperature, so average velocity on cross section of pipe will decrease too, and as we know that on edge profile velocity has zero value, so wax layer tend happen on closest of pipe. (WAX LINK)
Oke, back to KO Drum, bellow visualization of KO Drum. Let me try explain bellow figure. After oil inlet in KO Drum, since gravitation, it will separate each others. water will flow on close drain system, oil out after reach a weir inside KO Drum. and gas will out in above nozzle whose Pressure Control Valve to hinder gas entrainment on bellow nozzle (water, oil or both). Some of model use electrostatic on it to coalesce droplet of water into bottom of vessel.
On gas section, before kick from KO Drum, they will allow on mist eliminator. Gas will be routed on many edge to exit from it. The mechanism has many momentum to tend separate water contain. After droplet happened, they will marge and with gravitation,it will drain into vessel again. Mesh parameter can enhance quality of separation.
Sometimes, it will be ambigou if we meet with Slug Cather. Maybe, in my understanding it has same fundamental, but another purpose. Slug Cather is provide on system (generally on riser system), to hinder slug flow conducted on line. Since it can be big impact if it happen. Slug flow related with water hammer impact. gas expedite velocity above water, and wives continuously can reach top of pipe whose have momentum if impact with elbow, Tee, and so on.