In a system for thermal cracking gaseous feedstocks, the system including a gas cracker for producing an effluent comprising olefins, at least one transfer line exchanger for the recovery of process energy from the effluent and a water quench tower system, a process for extending the range of system feedstocks to include liquid feedstocks that yield tar is provided. The process includes the steps of injecting a first quench fluid downstream of a primary transfer line exchanger to quench the process effluent comprising olefins, separating in a first separation vessel a cracked product and a first byproduct stream comprising tar from the quenched effluent, directing the separated cracked product to a water quench tower system and quenching the separated cracked product with a second quench fluid to produce a cracked gas effluent for recovery and a second byproduct stream comprising tar. An apparatus for carrying out such process is also provided.