Natural gas plants must burn off the flammable gases released by pressure relief valves throughout the facility. If these gases are not burned off, dangerous amounts of pressure can build up in the processing equipment, potentially causing shutdowns and accidents. Waste gas that cannot be transported is also burned in order to avoid releasing it into the atmosphere. The process of burning waste or excess gas is known as flaring.
Before being flared, it is very important to ensure the gas is free of any liquids. Liquid in the vent stream can extinguish the flame or cause irregular combustion and smoking. In addition, flaring liquids can generate a spray of burning chemicals—a “rain of fire”—that create a severe safety hazard. Knockout drums collect these liquids prior to entering the flare system. Vertical separators are used when there is small liquid load, limited plot space, or where ease of level control is desired. When a large liquid storage vessel is required and the vapor flow is high, a horizontal drum is usually more economical.
This blog post, part of the Magnetrol® series on natural gas processing applications, explores the measurement technology that can help remove hazardous liquids from flare gas in the knockout drum.
Level Measurement Challenges and Considerations
Level gauges and drain connections are built into knockout drums. Knockout drums are also equipped with instrumentation to monitor liquid level with pump out or drain facilities. High and low level alarms are frequently installed in knockout drums. This level instrumentation must be able to accurately and precisely detect high and low level in order to prevent leaks and keep hazardous liquids from re-entering the gas.
In addition, the intermixing of liquids in the knockout drum can create an interface. Level measurement technology with the capability to detect interface level should be selected for this application.
Level Measurement Solutions
MAGNETROL has produced level measurement solutions for flare knockout drums:
- For point level:
Echotel® Model 961/962 ultrasonic switch; external float level switch; or Thermatel® TD1/TD2 thermal dispersion switch
- For continuous level:
Eclipse® Model 706 guided wave radar transmitter or E3 Modulevel® displacer transmitter
- For visual indication:
Atlas or Aurora® magnetic level indicators
For more information on level measurement solutions for flare knockout drums and other natural gas processing applications, download the natural gas processing brochure.