Anonymous
it all depends at what stage of the coke drum the heater has tripped . if the heater trips says after 5 -6 hrs after taking the coke drum inline then you can continue with the cold feed till the heater is back in service not more than 1-1.5 hrs from time of donw of the heater
After heater is taken in line can fill the drum with COT at 1-2 degree higher than the normal operating temperature