This:
To this:
The link from #19 is a nice summary.
What is a Cracker and Why Should I Care?
http://education.afpm.org/petrochemicals/what-is-a-cracker-and-why-should-i-care/
Once the ethane is separated it is shipped by pipeline to a cracker facility, which is a very sophisticated series of processes that convert the ethane to ethylene. The first process is using steam to transport a mixture of ethane and a small amount of propane to a series of industrial furnaces and heating it to approximately 1500 degrees Fahrenheit, which requires a lot of energy. At that temperature single bond of the ethane molecule is loosened to the point that it loses two of the hydrogen atoms. The two hydrogen atoms combine and form a stable hydrogen molecule known as H2. In addition to ethylene, a number of other molecules are formed, but ethylene is in much greater abundance (about 80 percent) than the other substances.
The next step is sending the mixture of very hot gases – liquids also become gases at that temperature – to a series of heat exchangers that use steam to cool the gaseous mixture. Once cooled, the mixture of steam and gases go to a tower where cold water is poured onto it from above to force all the different liquids to the bottom. These liquids are usually hydrocarbons with more than five carbon atoms. This process is also called quenching and the tower is referred to as a quenching tower.
Two separate product streams come out of the quenching tower. One product stream is water and a mixture of heavier hydrocarbons commonly referred to as pyrolysis gasoline. The water is cleaned and recycled back into the quench tower. The pyrolysis gasoline is sent to a separation unit that extracts the petrochemical aromatics (benzene, toluene and xylenes) for use in making plastics and other chemicals. The remaining liquid hydrocarbon mixture is used to blend in automotive fuels or sent to a refinery for further processing.