Cement Energy and Environment

.. A. B. c. Figure 1: A typical example of fan deposition material indicating nature of the deposit, A. & B. shows photographs of the samples, C. & D. shows microphotograph captured by SEM. The build-up, once formed, was suspected to be breaking loose from the fan unevenly during the operation due to non-uniform thermal expansion gradients. The resulting unbalance in the dynamic fan assembly was causing high bearing vibration requiring shut down to avoid mechanical damages. The shut down frequency to remove this build-up from the fan rotor was proving to be very costly in terms of plant non-availability and increased maintenance costs. Present case study attempts to evaluate possible reasons of the fan deposition and characterize the deposit sample by analyzing it using various analytical techniques. Materials and methods: In order to characterize the nature of the problem, the samples were collected from various locations in the preheater system. Typical sample collection points included A. Gas and material outlet of Vlth stage (top) preheater cyclones B. Fan deposition sample C. Fan outlet sample apart from kiln feed. All the samples were collected in apparently steady state operation of the plant except the deposition sample, which could only be collected during shut down of the fan . All the relevant process data like gas and material temperatures, raw material feed rate, gas flow rate, fan vibration levels, velocities, RPM, etc. were recorded from the continuous data logger available in central control room of the unit. Typical average values of some of the process conditions are reported in table 1. The values reported in the table are averaged values of hourly collected values over the period of more than 45 days. The collected samples were subjected to various analyses like particle size distribution, X-ray diffraction, TG-DSC and chemical analysis for their characterisation. Evaluation of particle size distribution for fan deposition sample was not possible due to its hard bricklike structure . Typical particle size distributions of the collected samples, evaluated using Laser particle size analyzer; are shown in figure 2. From the particle size analysis it is observed that fan deposition results due to the particles having 8 _)