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Generation of Respirable Coal Dust                                135

           Table 9.6 Matrix of Partial Correlation Between Respirable Dust Production and Coal Seam
           Properties (ROM Coal)

            Coal Properties                   Partial Correlation with RDI
            Moisture                           0.204
            Ln ash                             0.393
            Volatile matter                    0.191
            Fixed carbon                        0.523
            Fixed carbon/volatile matter        0.575
            Hardgrove Grindability Index        0.216




           2. The RosineRammler graph distribution parameter, n, was also rank dependent. The value for
              n was 0.68, 0.84, 0.90, and 0.95 for semianthracite, low-volatile coal, high-volatile bitumi-
              nous coal, and subbituminous coals, respectively. This is similar to findings by Thakur (refer
              to Chapter 8 in the book).
           3. High-rank coals produce a higher proportion of submicron dust particles.



           9.6.2  Jha’s Studies
           Jha [8] collected coal samples and airborne respirable dust samples from the coal
           mines for his study. He basically correlated the rate of coal mining with the rate of
           respirable dust production. The respirable dust concentration was measured with a
           personal, gravimetric sampler. Statistical analyses of data showed the following corre-
           lation matrix.
              Data in Table 9.6 compare well with similar data in Table 9.4 and reconfirm
           Thakur’s [6] findings. The only difference is that Jha [8] found a significant correlation
           with the Hardgrove Grindability Index, which the other two studies [6,7] did not.



           9.7   Impact of Cutting Bit Wear on Respirable Dust
                 Production


           Although it is generally true that the breaking machinery does not have much influence
           on respirable dust production, the cutting bit design and consequent specific energy of
           producing a ton of coal has a direct impact. New, sharp bits have a lower specific
           energy consumption (Kwh/ton) compared with older, damaged bits. Figure 9.8 shows
           how a new cutting bit can get damaged in the course of operation.
              Khair [9] did a laboratory test to confirm this and found a 26% increase in respirable
           dust production as the bit got dull and damaged (with a weight loss of 15%). It is
           recommended that a cutting bit should be replaced when it loses 7% weight.
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