AIR POLLUTION – MONITORING MODELLING AND HEALTH

Fugitive Dust Emissions from a Coal-, Iron Ore- and Hydrated Alumina Stockpile 211
Measurements therefore show that threshold velocity u t.20 for FR2 must be larger than 18
m/s. According to the Greeley-Iversen scheme (described below) the threshold velocity u t.20
equal to 26.7 m/s is predicted if d 50 = 5 mm and u * t = 1.5 m/s. For FR3 the measured
threshold wind velocity u t.20 is 14.0 m/s (Figure 5–right). Since this is less than 18 m/s,
according to the G-I scheme the FR3 aerodynamic roughness length should be less than 300
μm and consequently, d 50 < 9 mm. This is not in contradiction with our measurements since
the maximum diameter of iron ore particles in FR3 is 3 mm.
41.6
41.2
20 25 30 35 40 45 50 Hz
40.8
Mass [kg]
-dm/dt [kg/s]
40.4
40.0
Iron Ore - FR 3
39.6
39.2
38.8
100
50
-50
-100x10 -3
0
1000
2000
3000
Time [sec]
4000
5000
10
5
Back wind velocity [m/s]
400x10 -6
300
-dm/dt [kg/s]
200
100
0
Iron ore
FR2
FR3
fit FR3
-dm/dt = 0.0000271 (u .20 - 13.96) 2
8
10
12
14
u .20 [m/s]
16
18
Fig. 5. -Left, FR3 iron ore mass loss measurement (red), its negative time derivative (gray)
and back wind velocity (blue). -Right, the mass loss from the test surface as a function of u .20
air velocity for FR2 (red) and FR3 (black).
4.3 Hydrated alumina
Hydrated alumina is a fine material with large erosion potential. It is usually extracted from
bauxite, which is mined for the production of aluminium. In the port, the alumina is
unloaded from ships using a continuous unloader and transported to silos where it is
stored. Experience tells that only a small wind velocity is sufficient to lift particles of
alumina into the air. Indeed, the alumina particles are small with diameters from 20-100 μm
and 3200 kg/m 3 density.
The fraction of alumina tested was taken directly from the storage facility. Already at
about 2.5 m/s (8 Hz) there is an observable mass loss (Figure 6 -left). It is notable that this
mass loss is constant in time at any given air velocity, suggesting that no major alteration
in surface morphology occurred during the test. Figure 6-right shows the results and
reveals that the threshold velocity for alumina at 0.20 m above the centre of the test vessel
is 2.45 m/s.