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Technical Cement Forum / NO Reduction in reburning conditions

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Gris 05/03/2008 21:05:30

NO Reduction in reburning conditions

Hello

I'd like to know about NO reduction in cement process, I have bee reading some articles related with NO reduction. The process that is mentioned is:

The injection reducing agent and promoters that can be added to reducing agent. The NO reduction capacity of solid fuels in reburning conditions.

My questios are:

In the combustion operation in cement process; what part of the operation is refered to "reburning conditions"?

What kind of "injection reducing agent" could be used in cement process in order to reduce NO emissions? , I think the "reducing agents are the alternative fuels, maybe; and the promoters are metals that acts as a "catalizador"......

Please tell me something about this.. If I am definitly lost about this.

Michael Clark 06/03/2008 10:09:56

You will also see reference to "staged combustion" in relation to NO reduction in cement kilns. This staged combustion is usually achieved by firing part of the fuel in an in-line precalciner in an exygen deficient zone at the base of the precalciner. A reducing atmosphere is created and this leads to reduction of the NO to nitrogen. The same effect can be achieved by mid-kiln fuel injection in long kilns or by firing some fuel in the inlet or gas riser of preheater kilns. This is the process of "reburning conditions" you are refering to.

Injection of reducing agents is the SNCR (selective non-catalytic reduction) process where ammonia water is injected into the preheater. The ammonia acts as a reducing agent converting NO to nitrogen again. Temperature is critical for this process so the point of injection into the preheater is very important.

If these topics are of interest I would recommend enrolling on the next CemNet Kiln Chemistry course.

Gris 06/03/2008 22:59:56

Hello Michael

Thanks a lot for your answer; with that I recognized the part of the process where ammonia or urea is injected into the in - line precalciner in order to reduce NOx emissions, but that is depend the type of process used to produce clinker.

The articles that I have been reading mentioned reburning conditions into entrained flow reactor, only combusting coal, and for this process the range of temperature is lower than the gas temperature at cement kiln, then the technology is couldn't used in cement process.

Michael Clark 07/03/2008 09:49:57

The temperatures in an in-line calciner are too high for ammonia or uea injection. That must be in the preheater. It is staged combustion that is conducted in the in-line precalciner.

I don't know which articles you have been reading, so its difficult to comment. However, it is correct that coal is fired in the staged combustion in cement kiln precalciners and not petroleum coke. This is because the NO reduction reaction is actually a free radical reaction and the necessary free radicals are produced from coal rather than petroleum coke.

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