Temporary shutdown of co-combustion devices

Claim 1

An improved method of temporarily shutting down a CO-combustion device that is fed with the flue gas continuously discharged from a cracking process wherein a hydrocarbon feed is catalytically cracked in the absence of added hydrogen, said cracking process comprising circulating an inventory of particulate cracking catalyst in a cracking apparatus comprising a cracking zone coupled by conduit means with a regeneration zone; contacting said feed and catalyst under cracking conditions in said cracking zone to form cracked products and catalyst contaminated by coke deposits; combusting said coke deposits with air in said regeneration zone and continuously discharging therefrom flue gas containing from about 4 to 9 volume percent CO; the improvement, whereby reducing or eliminating air pollution from said continuously discharged flue gas, which comprises: introducing into said circulating inventory of cracking catalyst a trace amount of metal combustion promoter selected from compounds of platinum, iridium, osmium, palladium, rhodium, ruthenium or rhenium, said amount being effective to reduce the CO content of said flue gas continuously discharged from said regeneration zone to less than about 1 volume percent; increasing the flow rate of said air sufficient to effect said reduction of CO content during said temporary shutdown of said CO-combustion device; and subsequently reducing said increased flow rate of said air whereby terminating said temporary shutdown and restoring normal operation of the CO-combustion device.