The ethylene production process begins with unprocessed material, or feedstock. Feedstock enters the plant and goes through the ethylene furnaces, in a process known as pyrolysis. Once it is cracked into a variety of hydrocarbons and hydrogen, it immediately begins to recombine into larger molecules. To prevent these reactions and stop the recombination, the cracked vapor goes through a quench tower to cool using oil or water. The largest hydrocarbons are carried with the water into the quench settler or the quench water separation drum (QWSD). As feedstock is increased, more cooling fluids are required.
Magnetrol® has produced a brochure detailing different applications throughout the ethylene industry and discussing measurement challenges and solutions for each one. This blog post is part of an occasional series exploring each application in detail.
Challenges for Quench Tower Level Measurement
Level measurement is crucial to increase the efficiency of the quench towers and settlers. The residence time in the settlers needs to be minimal to maintain composition and prevent secondary reactions (including larger chains or heavier hydrocarbons). A quench settler or QWSD that catches the hydrocarbon liquids and water from the quench tower creates an interface in the QWSD, and possibly an emulsion layer if too much caustic is added. Knowing the interface level is important in order to properly recirculate the quench water from the settler to the tower and not recirculate the hydrocarbons. When hydrocarbons are recirculated, it reduces productivity and can potentially cause fouling of equipment. If the quench water or oil is not recycled correctly from the quench settler, it can also cause fouling problems with equipment and degrade the fluid composition from the furnaces. If too much fouling occurs or the fluid composition changes for the worse in the quench tower, less ethylene is eventually produced from the feedstock. Regulating an interface level with reliable instrumentation can help keep the fluid composition at the proper level and also aid in using less caustic if quench water is used.
Level Solutions for Quench Towers and Settlers
MAGNETROL has produced level instrumentation solutions for regulating interface level in quench towers and settlers:
- Eclipse® Model 706 Guided Wave Radar Transmitter
- Jupiter® Model JM4 Magnetostrictive Level Transmitter