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[Movers]

Hello.

 

Do you know which parameters have impact on speed of steam cracker radiant coils carburization?

 

Is it possible that oxygen level in the flue gas is one of such parameters?

 

Regards

Edited by Movers, 26 June 2020 - 07:32 AM.

[Tdha]

Hi Movers,

 

my answer may be a little late, but might be useful for others.

 

Carburization occurs because during the high temperature operation carbon from the hydrocarbon feedstock can diffuse into the wall and form brittle carbides on grain boundaries. Carborization predominantly occurs on the feedstock (inner) side of the tube.

 

Factors affecting:

1. Type and concentration of feedstock: light hydrocarbons for mainly catalytic coke which is very dense and hard. Heavier feeds like gas oil form mainly porous pyrolytic coke
2. Operation temperature: the higher the tube metal temperature, the higher the rate of diffusion. This effect becomes critical in cases where local hot spots occur due to flame impingement, bent tubes get closer to burners or thicker coke layer/forein object sticks to the inner tube wall
3. Quality of radiant tube: metallurgy improves over time. Nowadays alumina alloys represent the cutting edge technology, where a protective alumina layer is formed on the surfaces and acts as a primary barrier for carburization
4. I do not think that number of heating ups/shut-downs really affect speed of carburization, but they have significant contributions to tube quality degradations via other mechanisms (metal dusting, appearance of microcracks along grain boundaries, etc.)
5. I once had a short discussion with an old, experienced engineer from Shell who said that in case of high CO-levels in radiant zone (due to inaccurately operated or badly maintained burners) might have some minor carburization effect from flue gas side as well, but I never heard any example from the industry

 

Sincerely,

Tamás

Edited by Tdha, 30 August 2024 - 02:07 AM.