Table 7 The cooling zone: the cooling rate of the pellets depends on the gas
temperature and the gas flow rate within the depth of the layer
Gas
temperature,
o
C
20
60
100
Pellet layer
depth, mm
Gas rate, m/s
0.8
1.0
1.2
0.8
1.0
1.2
0.8
1.0
1.2
Cooling rate,
o
C/min
78.5
78.68 78.75 76.12 76.25 76.25 73.68 73.75 73.75
300
77.93 78.37 78.56
75.6
76.05 76.11
73.1
73.3
73.35
240
76.87 77.68
78
75.36 75.62 75.65 72.79 72.91 72.96
180
75.18 75.81 77.12 74.85 75.13 75.32 72.56 72.61 72.68
120
83.14 85.21 85.78 80.71 83.14 83.28 78.07
80.5
80.35
60
Figure 8. The cooling zone: dependence of the cooling rate on the gas
temperature and the gas flow rate within the layer (top, middle and bottom)
The phenomenon of pellets insufficient cooling was observed at varying sets of
conditions: (i) cooling temperature of 60 °C and the gas flow rate of 0.8 m/s; (ii) the
cooling temperature of 100 °C and gas flow rates of 0.8 m/s or 1 m/s.
Analysis on the influence of pellets temperature at the exit from the firing
zone on the cooling rate. The following parameters of the cooling zone are
significantly influenced by the process of pellets cooling, namely, the cooling rate and
the final temperature of the pellets. Thus, when the layer of pellets enters the cooling
zone, the temperature of firing is responsible for the upper layer temperature while the
gas flow rate determines the temperature of the pellets located below the layer).
The influence of the principle parameters revealed for the firing process on
the pellets strengthening. Based on the fundamentals of the pellets firing, there have
been established four types of bonds capable of increasing their pellets strength. They
are the bonds that rely on magnetite oxidation (at the temperature above 200
o
C), on
Upper of the layer
72
74
76
78
80
0
25
50
75
100
Cooling temperature (°C)
Coolin
g r
ate
(de
g/min
)
1,2
1
0,8
Middle of the layer
72
74
76
78
80
0
25
50
75
100
Cooling temperature (°C)
Coolin
g r
ate
(de
g/min
)
1,2
1
0,8
Bottom of the layer
76
78
80
82
84
86
0
25
50
75
100
Cooling temperature (°C)
Coolin
g r
ate
(de
g/min
)
1,2
1
0,8
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