rate of 0.8 m/s, the pellets does not have time to dry up much within their layer. As the
consequence, the processes in the preheating zone and, in their turn, in the firing zone
are being slowed down and this negatively affects the quality of pellets and the process
productivity (Fig. 2).
Figure 2. Dependence of the residual moisture amount on the temperature of the gas
in the drying zone and the rate of gas flow in the depth of the layer
(layer middle part and its bottom)
Analysis of the mutual influence of the preheating temperature and the
length of the preheating zone on the degree of limestone decomposition and the
magnetite oxidation. In order to study how the preheating temperature and the
preheating zone length are capable of influencing the process, the experimental
research has been carried out with the initial data chosen for the analysis as follows.
The research was carried out with three different rates of gas filtration supplied into the
preheating zone (0.8 m/s, 1.0 m/s, 1.2 m/s) and three different gas temperatures were
reached within the preheating zone (1000
o
C, 1050
o
C, 1100
o
C). The unchangeable
parameters in the experiment were the depth of the pellets layer (300 mm), the length
of the preheating zone (10 m) and the velocity of the carriages (2.25 m/s). Different
degrees of limestone decomposition have been studied with this experiment (Table 2)
and those for the magnetite oxidation have been also revealed (presented in Table 3).
Table 2 The preheating zone: the dependence of the limestone decomposition
degree on the gas temperature and the gas flow rate in the depth of the pellet layer
Gas
temperature,
о
С
1000
1050
1100
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
Degree of
limestone
decomposition,
%
100
100
100
100
100
100
100
100
100
300
100
100
100
100
100
100
100
100
100
240
41.3
95.8
100
66.7
100
100
85.5
100
100
180
4.3
35.5
89.1
3.4
60.2
100
14.1
79.7
100
120
1.3
2.1
34.1
1.1
4.1
57.9
3.2
11.2
77.1
60
The limestone of the lower part of the layer remained almost completely non-
dissociated at the gas flow rate of 0.8–1.0 m/s under conditions of all above heating
Middle of the layer
0
1
2
3
4
340
380
420
460
Drying temperature (°С)
Re
sid
u
al moisture
(%)
1,2
1
0,8
Bottom of the layer
0
1
2
3
4
5
6
7
8
340
380
420
460
Drying temperature (°С)
Re
sid
u
al moisture
(%)
1,2
1
0,8
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