For our Delayed Coker Unit after quenching drum some portion of hydrocarbon is coming from the vent lines while opening of the vents to continue draining. We checked the quench oil lines to be sure the valves are leaking but quench oil valves are not leaking. We tried to put steam by opening the steam connection just upstream of the vent valves during quenching. It helped but for this time, we have some problem with quenching of the drum. The drum overhead line is not cool down enough during quenching.
Can anyone help to identify reasons why hydrocarbon is coming from vent?