AIR POLLUTION – MONITORING MODELLING AND HEALTH

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206 Air Pollution <strong>–</strong> Monitoring, Modelling and Health 3.5 Sample preparation The coal and iron ore samples were separated into four and three size fractions, respectively, while hydrated alumina, which has a narrow grain size distribution, was taken directly from the cargo. 40.3 kg of the test coal, named ABK, which originates from Indonesia, was taken from the pile and fractionated as follows: - Fraction 1 (FR 1): grain size larger than 15 mm, 27.1% of the total mass, - Fraction 2 (FR 2): grain size between 5 and 15 mm, 25.8 % of total mass, - Fraction 3 (FR 3): grain size between 3 and 5 mm, 9.1 % of the total mass, - Fraction 4 (FR 4): grain size less than 3 mm, 38.0% of total mass of the coal sample. The majority of the coal with density of 1100 kg/m 3 in the pile was present in the finest, the FR4 fraction. The particle size distribution (relative number N of particles as a function of coal particle diameter d) of FR4 coal fraction was estimated by the following simple method. The particles were allowed to disperse according to size by dropping them through a horizontally directed stable air stream with a restricted cross section on to a horizontal metal plate. An average diameter of particles, d i , deposited along the metal plate in each bin was determined by optical microscopy and the mass m i of the deposit in each bin was measured accurately using a microbalance. In the log-log plot the N(d) is approximately a linear function of d suggesting that N is proportional to d -1.6 . The median diameter of the particle distribution, defined as the diameter that “splits” the number of particles into two halves, was d 50 =40 μm. Prior to making tests on the wind test track, a maximum cone angle for three of the finest coal fractions was measured. This was achieved by building up a cone on a flat surface until the angle at the top assumed the largest value. As the angle increases, the component of the weight force acting on a coal particle along the cone surface is increased. When this force becomes larger than the friction force, exerted by the surrounding particles, the particle will start to move downhill. This is important for estimating the threshold friction velocity on inclined surfaces. Obviously, the component of the weight force “helps” the wind to lift the particles if this is blowing downhill and vice-versa. FR4 FR3 FR2 Base diameter (cm) 20 20 20 Height (cm) 13.0 15.5 18.0 Angle 33.0° 37.8° 42.0° Table 2. Top cone half-angle α t for different coal fractions. The iron ore with 5000 kg/m 3 density was separated into three fractions: - FR 1: d > 7 mm, 25.5 % of the total mass, - FR 2: 3 mm < d < 7 mm, 29.2 % of the total mass, - FR 3: d < 3 mm, 45.2 % of the total mass.
Fugitive Dust Emissions from a Coal-, Iron Ore- and Hydrated Alumina Stockpile 207 4. Results and discussion 4.1 Coal For FR1 coal fraction no mass loss larger than 0.02 kg and no increase in PM10 or the BC signal for test wind velocities up to 18 m/s were detected during a time interval of 10 minutes and for an initial coal mass of 9 kg. 4.1.1 FR2 coal The average background concentration of PM10 during the FR2 measurement was 73 μg/m 3 but this did not correlate with the detected mass loss. The latter was detected only at the highest wind speeds i.e. > 45 Hz (16 m/s). The Aethalometer signal was also stable during the measurements, displaying average values of 1470 ng/m 3 and 1320 ng/m 3 for the IR and UV diode, respectively. The effect of buoyancy is to make the test vessel effectively lighter when the air stream is on and is larger for higher air velocities. This results in an offset of the mass signal and can be easily accounted for in the data analysis. 4.1.2 FR3 coal For FR3, a mass loss on a time-scale of a few minutes at a wind speed of u .20 =13.5 m/s (40 Hz) is observed (Figure 1). The effect of 18 m/s wind velocity was such as to remove approx. 20% of the material from FR3 from the vessel in 10 minutes. 15 20 25 30 35 40 45 50 Hz mass [kg] PM10 [g/m 3] 8.0 Coal fraction 3: 3 - 5 mm mass 7.5 derivative PM10 BC - IR 7.0 BC - UV 6.5 6.0 1500 1000 500 40x10 -3 30 20 10 0 -dm/dt [kg/s] 0 500 1000 1500 2000 seconds Fig. 1. Fraction 3 (FR3) measurement with a dry coal reporting the total mass (red, kg), the negative of its time derivative (gray, kg/s), PM10 concentration (green, μg/m 3 ), BC-IR (black) and BC-UV (pink) concentrations (ng/m 3 ) as a function of time. Narrow intervals between vertical dashed lines correspond to wind velocity zero. For the intervals between, the wind velocity is denoted by a frequency of the converter ν depending on u .20 in a linear fashion as presented in Section 3.4. The results also show a correlation between the increasing PM10 concentration and the negative time derivative of the mass (-dm/dt), which is not so prominent in the BC detection channel. In fact, there should be no PM10 signal since, in principle, FR3 should not 2500 3000 3500 2000 0 BC [ng/m 3 ]
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AIR POLLUTION - MONITORING, MODELLI
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Contents Preface IX Chapter 1 Urban
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Preface This book provides a compre
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AIR POLLUTION – MONITORING MODELLING AND HEALTH

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