Cement Energy and Environment

• Mechanical factors aiding in the dust deposition on the fan chiefly consists of fan blade geometry. High RPM of fan blades resulting in high centrifugal forces act to hold dust particles in place on the back side of airfoil blades, backward curved, and backward inclined centrifugal fan rotor blades. Many a times, the build-up is caused as a direct result of the impact between the dust particles and the front side of the fan blades. The fine dust particles may actually melt/embed themselves into the relatively rough surface of the steel fan blades. Hence, generally the fan impeller is suggested to be designed in order to allow the smoothest possible flow lines in order to reduce impact energy of dust particles on the fan blades. Also flow turbulence and dead zones need to be avoided as they are privileged areas for dust deposition. This is generally achieved by using high efficiency fans. Therefore to select the fan of larger size at lower RPM is first priority due to A. larger size will reduce the number and the velocity of particle impact as there will be more space between the blades and B. lower speeds will reduce the unbalance forces induced by a non-uniform dust deposit. Oversized shaft, with high critical speed, is also many a times selected to reduce the effects of the unbalance forces on the bearings . Unbalance forces have to be considered for bearing selection and life time evaluation. Results and discussion: can be considered as an indication of increased iron, silica and alumina compounds. Similarly alkali in the fan deposition sample is observed to be increasing to a considerable extent. Chloride levels are also observed to be increasing drastically as compared to that in the kin feed sample. The increased chloride levels can possibly be traced back to water spraying system being utilized for efficient evaporative cooling of the exit gases in the pre-heater downcomer duct. In order to ascertain the preferential segregation of the alumina, iron and silica compounds in the deposit material, collected samples were subjected to X-ray diffraction analysis . Comparing X-ray diffractograms of top stage cyclone outlet sample, fan deposition material sample and fan outlet sample it is observed that preheater top cyclone gas outlet and fan outlet samples contained mainly components like calcite (CaC03), quartz (Si02) and free lime (CaO) along with traces of hematite (Fe20 3). Fan deposition sample on the other hand is found to contain considerable amount of Kaolinite (AI2(SiOs)(OH)4) and anhydrite (CaS04) in addition to expected compounds namely calcite , quartz, free lime and hematite (Figure 3). Comparing the three samples it is also be observed that the hematite quantities are getting increased to a considerable extent in fan deposition sample as compared to other two samples. From the above analysis it is reasonable to assume that the brick– red colour and hardness of the fan deposition sample is contributed by Hematite, Kaolinite and Anhydrite cumulatively. In the context of present problem collected samples were analyzed chemically in order to examine the extent of influence of chemical mechanism on the fan dust deposition. The chemical analysis of the samples in terms of oxides is reported in Table 2. It can be seen from the analysis that fan deposition sample is having considerably higher amounts of AI20 3 and Fe20 3 apart from slight increase in Si02, as compared to that in kiln feed and VJih stage cyclone gas outlet samples. On the other hand, the calcite particle concentration in the fan deposition sample is observed to be reducing substantially. Therefore brick red colour and hardness of the sample I00 ~p+.......,.._--a---ilr-a--~~~4 ,-- 90 = ~ 80 J 70 ·~ 60 I. ~ 50 ~ 40 . 30 5 20 -+- 1 n ee , 5 = . • ~Fan outlet, d50 = 11.84 U 10 -.!r- 6th stage Cyclone top, d50 = 12.63 --6th stage cyclone bottom, d50 = 38.74 o~~~~~~~~~~~ 0 100 200 300 400 Size, (~m) Figure 2: Parl1cle size distribution of collected samples 10