when you open the vent if because you is thinking the drum is cool low temperature less 250F and pressure less 2 psig, (when you open the vent for an operator expert he can tell you if the drum still hot; for the sound or amount of the steam , etc) and then the operator procedure to drain the drum (there is some refinery after opening the vent they open the top flange) this take between 20 t0 30 minute
when you open de vent is because you have low pressure less tan 1 or 2 psig after that the pressure en the coke drum reduce amost to atmosfhere after that this people open the top flange
As per U.S. EPA Refinery New Source Performance Standard 40 CFR 60, Subpart Ja, Federal Register May 14, 2007, all new, modified, or reconstructed Cokers after May 14, 2007,
require complying with a minimum of 5 psig before venting coke drums.
our drum is drained and vented (at the end of quenching cycle) to atmosphere at the coke drum ovhd pressure and temperature of about 1kg/cm2g and a70oC (or below).. the drum is opened when pressure is less than 0.05kg/cm2g..
Some refineries start the drainig whitout open the vent, with the drum still connected whith the blown down and pressurized. Then after some time, when the pressure get low the operator isolate the drum and open the vent. There is a risk of hot spots and send HC to atmosphere by the blow down but you gain a valuble time.
