Volatilization Property Of Alkali, Chlorine And Sulfur, And Their Effects On The Burnability

The use of cement kiln to co-dispose of solid industrial waste, such as garbage and sludge, is currently a hot area for research and practice. Industrial wastes containing potas-sium, sodium, chlorine, sulfur, will lead to circulation and enrichment in cement kiln because of their high volatile characteristics, and these elements will be of influence on the composi-tion of cement clinker and clinker hydration performance. In this paper, the volatile character-istics of potassium, sodium, chlorine, sulfur is studied and their influence on clinker calcining is discussed, which can play a guiding role in co-disposing of solid industrial waste, using of high alkali, chloride, sulfur content of raw materials.According to Gibbs free energy minimization principle, the volatile rate and equilibrium of alkali (K), chlorine and sulfur in the temperature range of 500℃-1400℃is calculated. The circulation and enrichment of those elements combined with the temperature distribution in the cement kilns are also discussed. The results showed that:(1) the volatile rate of Chlorine increases abruptly from 650℃to 800℃, and reaches almost 100% at temperatures higher than 800℃. Sulfur and alkali volatilize com-pletely at about 1300℃and the volatile rate increases abruptly at 1000℃-1200℃. In-creasing the content of chlorine can promote the volatilization of sulfur and alkali, espe-cially at lower temperatures between 650℃and 800℃.(2) The circulation and enrichment occur comparative seriously in two main regions: kiln hot end and the rise-pipe, the second last stage and the last stage preheater. The former one occurs mostly related with alkali and sulfur, while the latter one with chlorine. In order to reduce the probability of the buildups jam of the kiln system, sulfur-alkali ratio should be controlled at about 1.5.Furthermore, the effect of trace elements on the burnability, mineral composition and crystal morphology are investigated by XRD, SEM and chemical analysis. The results showed that: (1) K2CO3, Na2CO3, CaCl2 have a positive effect on the improving burnability at low temperatures (lower than 1300℃), and increasing the content of K2CO3, Na2CO3, CaCl2 makes this phenomenon even more apparent. But these elements show an adverse effect on the burnability at high temperatures (higher than 1350℃). A small amount of CaSO4 has a positive effect on the burnability at low temperatures (lower than 1300℃), but too much CaSO4 has a negative effect, especially at high temperature.(2)Potassium mineral is not found by XRD, because K2CO3 has high volatility, and po-tassium does not enter the lattice of clinker. Na2CO3 solid solves in C3A and forms NC8A3-CaCl2 produces the intermediate phase C11A7·CaCl2 and forms the low-temperature liquid phase. By SEM, crystalline grain size of adulterate alkali, chlorine changes little compared with the blank sample, but the crystal morphology is better. Adulterate sulfur forms a large crystal.(3) C3S formation process of adulterate alkali, sulfur meets the Ginstling equation, so C3S formation process is controlled by diffusion. Adulterate chlorine does not meet the Gin-stling equation. Adulteration can reduce the activation energy, and reduce the magnitude of activation energy:CaCl2> K2CO3> CaSO4> Na2CO3.From the above preliminary results, it is showed that circulation and enrichment of these elements is alleviated or avoided by modifying the key parts of the cement kiln, such as kiln hot end and the rise-pipe, the second last stage and the last stage preheater, and by controlling the chlorine content and sulfur- alkali ratio.Appropriate content of potassium, sodium, chlo-rine and sulfur do not show an adverse effect on the burnability.