Cement Energy and Environment

segregative accumulation of silica, alumina and iron compounds in the fan deposition sample. An endothermic peak at 707.6°C is likely to be of chlorite (a mineral from clay family having typical structure (Mg ,Fe)10AI2(Si ,AI}s02o(OH,F}1s}. Chlorite is also known to have exothermic peak characteri stics around 840°C [1 0, 11], which may be coinsiding with that corresponding to Mullite transformation. Additionally, in-spite of only marginal increase in the S03 content in the fan deposition sample as compared to other samples, presence of Anhydrite in the deposit sample points out the possible role played by the marginally higher su lphur content introduced in the system by Petcoke firing. 1 ~- ~----------- Although sulphur introduced through fuel is known to restrict itself in the kiln inlet area in the form of alkali-sulphur cycles or alkali sulphates in the clinker, local reducing conditions in the kiln or lack of intimate contact between flue gases and incoming feed can sometimes result in marginal increase in exit gas S02 concentrations. This S02 is therefore available for dry scrubbing by CaC03 predominantly present in the upper portions of preheater cyclones resulting in formation of fine particles of CaS04. Although CaC03 is perceived to be a rather ineffective scrubber of S02, the conditions like presence of water vapors , high gas temperatures and high calcite specific surface area are shown to be acting as accelerators for formation of CaS04 with considerably higher reaction rate constants [12, 13]. 00 = j. \.__...- ---------- ,, ' - ----........- ----- -050 8S _, I)J -SO 7$ - 70 - -2 00 100 400 500 600 700 eco 9t0 1000 Tel!l)ersure rc Figure 4: Thermal characteristics of preheater kiln feed sample indicating the presence of clay particles (Kaolinite) 100 :?CO 3CO 400 500 600 700 TcmpcrCitl.rc •c Figure 5: Thermal characteristics of fan outlet sample showing exothermic phase transformation of Kaolinite to Mullite (AI2Si20s) at around 895°C. IOOC 12