What are the causes of carbon build-up on hydrocarbon reforming catalysts?

When the surface of reforming catalyst is slightly carbonized, because of the carbon covering the active centre, the activity decreases and the heat absorption decreases, and then there are spots, hot strip, and the aromatics in the exit tail gas increase; when the catalyst is seriously carbonized, it shows that the bed resistance increases rapidly, and the surface temperature of reforming furnace tube rises quickly, until the red tube appears. The causes of catalyst carbon accumulation are generally as follows.
(1) Raw material
The index of hydrocarbon raw material exceeds the standard, the aromatic hydrocarbon is too high, the olefin is too high, the specific gravity is too large, as well as the sulphur content, chlorine content and other poisonous substances exceed the standard, which leads to the poisoning of catalyst.
(2) Water-carbon ratio disorder.
Feed fluctuations, temperature, pressure fluctuations cause the water-carbon ratio to reduce to below the normal value, the water-carbon ratio down to a certain extent will lead to carbon accumulation in the conversion process.
(3) Uneven combustion of the converting furnace nozzle, resulting in one-sided heating of the furnace tube or local high temperature will also cause the conversion of the catalyst will be carbonised to different degrees.
(4) Repeated oxidation and reduction of the catalyst during repeated starts and stops of the process, resulting in a decrease in the catalyst activity, which in turn causes carbon build-up on the catalyst. This will cause carbon deposits on the catalyst.
(5) The catalyst is not effectively protected because the feed is not removed in time during the emergency stoppage.