Flash Fire Problem (workshop)

[Freeman]

Flash Fire Problem (workshop)

Professor Silveston from Waterloo University Canada came to Universiti Teknologi Malaysia for an assignment. While he was around, he gave a workshop on problem solving.

I would like to share one problem that he gave and I want to see some ideas. Please feel free to gave your opinion on the answer for the problem.

Flash Fire Problem

Heavy naphtas are converted into high octane gasoline in platformer. By products of the reaction include LPG and hydrogen rich gas containing 6-80% by volume hydrogen. The products from the platformer reactor (at 700 psig and 500 oC) are heat-exchanged with the naptha feed to the reactor. This preheats the feed. The platforming catalyst is rapidly fouled and must be generated by blowing with steam or waste gas. Thus the process is cyclic. A battery of reactors maintains a steady flow.

In three weeks since the startup, there have been four flash fires along the flanges of the heat exchanger. The plant manager claims that because of the differential expansion within the heat exchanger, because of the diameter of the exchanger and the stream hydrogen is rich these flash fires are bound to occur. The maintainance mean have broken 6 bolts trying to get the flange tighter, but they just cannot get it tight enough. The excahanger costs 0,000 and the whole plant costs #39 million. The technical manager says that the plant must be safe in 3 days.

What will you do?
What are the actions?
Can you think and share with us your action plan...

[Vijay.hse]

I guess we are talking about Combined Feed Exchangers (CFE) of UOP CCR Platformer. Is that a vertical one? Generally the "girth" flange can have issues of bad sealing. Are the fires mentioned in flanges all over the CFE? Or is it at a particular flange? Do you have proper gaskets in place? From the fact that several bolts were broken - it seems that there is no proper bolt tightening procedure (measuring torque) is not existent. I am not sure whether the CFE is leak checked before putting it in service. I would seek expert advice of mechanical engineers / CFE fabricator to resolve the flange issue (assuming it is at a particular flange). I would install steam snuffing rings around the flanges with valves at grade in order to mitigate the consequences in case of flash fires.
Cheers
Vijay

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As "Vijay" mentioned there should be a known torque reached when tightening the bolts and the sequence of bolt tightening should also be done as normal industrial practice, the type of gasket should be checked. Is this the first start up for the unit? Has the same problem occurred in previous start ups? Has there been any modifications on the unit ? if so, you may want to check the temperature gradients of the CFE before and after the modifications, if any.

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