Naphtha steam-cracking quench

Claim 1

IN A PROCESS OF STEAM-CRACKING HYDROCARBONS AT AN ELEVATED TEMPERATURE AND LOW HYDROCARBON PARTIAL PRESSURE TO FORM UNSATURATED C2 TO C6 HYDROCARBONS, THE IMPROVEMENT WHICH COMPRISES MIXING WITH CRACKED PRODUCTS LEAVING A CRACKING ZONE A QUENCH OIL IN A SUFFICIENT AMOUNT TO RAPIDLY LOWER THE TEMPERATURE OF THE RESULTING MIXTURE FROM ABOVE ABOUT 1350*F. TO BELOW ABOUT 650*F. AS THE MIXTURE IS PASSED TO A QUENCHING AND FRACTIONATING ZONE, SEPARATING FROM THE QUENCH CRACKED PRODUCTS IN SAID QUENCHING AND FRACTIONATING ZONE A RESIDUSAL FRACTION BOILING ABOVE ABOUT 430*F. AND LOWER BOILING VAPORS WHICH PASS RAPIDLY UPWARDLY THROUGH THE QUENCHING AND FRACTIONATING ZONE COUNTERCURRENT TO RELATIVELY COOLER QUENCH OIL, SAID QUENCH OIL BEING MAINLY RESIDUAL OIL WITHDRAWN FROM THE QUENCHING AND FRACTIONATING ZONE BELOW THE POINT AT WHICH SAID MIXTURE IS PASSED INTO SAID QUENCHING AND FRACTIONATING ZONE, THEN COOLED AND A PORTION OF THE COOLED QUENCH OIL CIRCULATED TO THE CRACKED PRODUCTS LEAVING THE CRACKING ZONE AND ANOTHER PORTION OF COOLED QUENCH OIL PASSED TO AN UPPER PART OF SAID QUENCHING AND FRACTIONATING ZONE, A THIRD PORTION OF THE THUS CIRCULATED QUENCH OIL BEING PURGED AND REPLACED BY A MORE STABLE GAS OIL WHICH LOWERS THE TAR CONTENT OF THE QUENCH OIL.