Ethylene is a crucial component of industrial chemicals and plastics. The ethylene production process starts with hydrocracking. Feedstock comes into the ethylene plant and goes through the furnaces (pyrolysis). Then it is broken down into a variety of hydrocarbons and hydrogen in a process known as “cracking.”
Once the feedstock is cracked, it immediately begins to recombine into larger molecules. To prevent these reactions, the cracked vapor goes through the quench towers to cool using oil or water. The heaviest hydrocarbons are carried with the water into the quench settler or the quench water separation drum (QWSD). An interface is created in the quench settler, and an emulsion layer can develop.
This blog post, part of a Magnetrol® series on interface level measurement based on our new white paper, discusses the challenges that can arise when interface is not properly controlled in the quench settler and how better level instrumentation can improve interface measurement.
The Cost of Improper Interface Control
Keeping control of the interface is important in the quench settler for multiple reasons:
- Proper water recirculation back into the quench tower is important, as carrying over hydrocarbons reduces productivity and causes potential fouling of equipment.
- As feedstock is increased, more cooling fluids are required which also increases the importance of water recirculation.
- Loss of interface control will ultimately reduce efficiency of the quench tower operation, leading to reduced productivity.
- If fluid composition negatively changes in the quench tower, less ethylene is produced from the feedstock.
- Regulating interface can also aid in using less caustic, keeping costs down.
Depending on the size of the emulsion layer, guided wave radar (GWR) or magnetostrictive technologies are recommended options to keep tighter control of the liquid separation in the quench settler. GWR is typically recommended when the emulsion layer has a tighter window, but if the emulsion layer is thick, then it may be best to utilize a magnetostrictive device with a float designed to follow the bottom of the emulsion.
For more information on measurement solutions for petrochemical interface applications, download our interface white paper.