1156 posts
Burning Question 51
We wish to know about oxygen enrichment in the cement kilns/precalciners. Please brief us about the expected merits and demerits. Are there any cement plants using this technique? If yes, then why is it not used commercially on regular basis in most of the cement plants.
Know the answer to this question? Join the community and register for a free guest account to post a reply.
1156 posts
Re: Burning
This is a big question! The merit is that the output of the kiln can be boosted by up to 15 per cent, the demerit is that the oxygen is expensive and therefore the costs of producing the additional clinker are higher. If market demand exists with good prices for cement then oxygen enrichment can be a good option. There are a number of kilns in the USA using oxygen enrichment of either the main burner or the precalciner. It is worth noting that CEMEX USA consider oxygen enrichment of precalciner firing to be their technology for which they have lodged a patent. You can find papers on oxygen enrichment in the proceedings of the IEEE conference in Vancouver 2001.
1156 posts
Burning Question 52
NOx control approaches applicable to the cement industry may be grouped in three categories: process modifications, combustion control, and NOx reduction controls. One process modification that can be quantified is the CemStar process, which is a small addition of steel slag to the raw kiln feed. Can you provide more information on CemStar?
1156 posts
Re: Burning
TXI have published various papers on their patented Cemstar process. The addition of steel slag or air cooled blast furnace slag boosts the output of the kiln with virtually no increase if fuel consumption as the slags have already effectively been clinkered and contains trace elements that mineralise the combination of the kiln feed into the clinker in the kiln. More product with the same amount of fuel burnt inevitably dilutes the NOx emissions per tonne of clinker produced. The mineralising effect may also lead to lower burning zone temperature, and less thermal NOx formation in the flame. The real crux of the technology is adjusting the chemistry of the kiln feed to maintain the desired clinker mineralogy when the slags are being added t the kiln inlet. With steel slag the iron oxide input is increased and has to be compensated by increasing the alumina and silca modulii. With air cooled blast furnace slag the material is deficient in lime therefore the LSF of the kiln feed has be increased. This inevitably increases the demand for high CaCO3 content in limestone and is often the limiting factor.