Furnace decoke

[coolcando]

Friends,

We operate NG fired furnaces to crack petrochemical feedstocks to various products.

Over a period of time, furnace tubes gets coated (inside surface) with carbon.

To remove this carbon and improve thermal efficiency ,
we take this furnace offline (shut off supply and product valves) and pass hot air in the furnace tubes. With further heat supplied by firing NG burners, carbon gets oxidized and converted to CO/CO2.Air is supplied to the tubes, downstream of the feedstock valve.

Now this decoking product is entered right into the firbox to complete the combustion and leaves the furnace alongwith flue gas thro' stacks. The decoke product is routed to firbox just upstream of main product valve(which is closed during this operation).

However only one furnace is offline at a time and others are operatiing .And there is a common product header which collects cracked gas from each furnace.

There is a huge safety issue here. When this perticular furnace is decoking and if the product discharge valve is passing, the cracked gas in common header may enter the furnace firebox and explosion is inevitable.

What is the best way to positively isolate decoking product from common cracked gas header ???


Any help will be appriciated.

 

[djack77494]

I've seen decoking piping such that spectacle blinds or Figure 8's were used to provide positive isolation between normal process and decoking gases.
Doug