Abstract: A process for operating a thermal or catalytic cracking unit is described. The process entails generating a product that includes cracked hydrocarbon vapor and solid coke-particles from a heavy hydrocarbon input. The product is communicated towards a fractionator and a quench liquid is introduced into the product for creating a two-phase flow of cracked hydrocarbon vapor and the quench liquid with solid coke-particles entrained in the quench liquid. The two-phase flow is introduced into the fractionator and the cracked hydrocarbon vapor are separated from the quench liquid and the solid coke-particles entrained therein by gravity separation. The two-phase flow can reduce or remove the requirement of a wash zone within the fractionator. A recirculation loop is included in a wash-zone circulation system. The recirculation loop bypasses one or more spray headers of the wash zone and returns to a first end of the wash-zone circulation system.