The function of the unit is to catalytically crack hydrotreated long resid to lower boiling, high value products, primarily propylene and other C3-C4 LPG products, high octane gasoline, and light cycle oil. Using vapor phase chemical reactions in the presence of specialized cracking catalyst, the long molecular chain feedstock is cracked to shorter chain molecules. Heat for the cracking process is supplied by the hot regenerated catalyst which vaporizes the finely atomized oil feed and sets the stage for the rapid, but selective cracking process. The vaporization and cracking reactions occur partially in the reactor-riser in roughly two seconds and are finalized in a bed of catalyst in the reactor. As byproducts of the reaction, ethylene-rich fuel gas, slurry oil, and coke are also generated. The converter equipment handles catalyst / vapor product separation and catalyst regeneration by burning coke from the catalyst and recovers heat efficiently from the flue gas.