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Recently we faced an emergency in our one through hydro cracking unit. We experienced a tube rupture in our vacuum column re-boiler due to over heating and once we introduced emergency coil steam in re-boiler tubes, a major fire broke out in the furnace, leading to complete destruction of furnace. The logic behind introducing the emergency coil steam with pressure of 15 kg/cm 2 was if air will ingress through ruptured tube and make its way to vacuum column, it will lead to explosion of column. Kindly comment on this as it is not clear to us whether it was a right decision or should we wait to cool down the furnace?
 
Answers
25/02/2013 A: Balasubramanian Iyer, Nexen CNOOC Limited, balasubramanian.n@aol.in
Stop immediately the hydro carbon in the Tube Side by shutting of Pass flow valves/I/V.
Stop your Combustion air supply and introduce immediately the Box purging steam to remove any air inside other wise would be sucked in by the vaccuum tower suction and lead to major disaster. if you can isolate the Heater on both inlet and outlet that will be the best.
Then drop vaccuum slowly in the tower.
Introduction of Coil steam will push the Hydro carbon material in the coils into the furnace and can lead to major fire. This option can be opted only on isolating the Hydrocarbon feed to Furnace and introducing Coil Steam.
12/10/2012 A: keith bowers, B and B Consulting, kebowers47@gmail.com
The very first thing to do when a furnace tube ruptures and is badly leaking is to stop oil flow to the furnace, cut fuel gas, and start 'coil steam'. Simultaneously stop vacuum pumps/ejector steam on the vacuum unit. Simultaneously start nitrogen purge to vacuum tower to elevate the pressure to atmospheric. Steam can also be used to break the vacuum, but one must be absolutely certain it is dry steam with no water. Even a few gallons of water will instantly flash, causing a pressure surge that probably will upset the internals in the tower.
IF 'firebox snuffing steam' is available, use that to keep the fire down in the firebox. The best place for a fire is inside a furnace.
12/10/2012 A: Ralph Ragsdale, Ragsdale Refining Courses, ralph.ragsdale@att.net
My usual disclaimer on safety questions that I cannot resist answering: "Not a procedure for you to follow, just observations from my experience":
The usual method is to stop the flow to the furnace and let the fire burn out. If no valve on the transfer valve near the column, the inventory of the column would also be burned. Snuffing the fire while the firebox is hot can cause an explosion due to auto-ignition after vapors collect in the firebox.
You will agree that, if there is to be a fire in a plant, inside a furnace is the best place for it, other than a flare, of course.