Moreover, the strength of pellets, as well as that of the sinter becomes greater with
more even porosity size and all the indicators evidence on this.
The next factor to be mentioned is the binder composition that has a crucial
influence on the temperature of the pellets being fired.
Certain role in strengthening the pellets plays the factor of time. The most
intensive process to increase the strength takes place during the first 5–20 minutes of
firing. A further increase in the firing time results in the much smaller increase in the
strength and may even lead to some worsening of it.
Eventually, among of all the parameters influencing the firing process, the drained
gas temperature and the gas flow rate are distinguished as the principle ones.
The principle parameters in pellets cooling. The certain effect on the strength
index of pellets has the cooling rate. Thus, pellets must be cooled at the rate not to
exceed 100 deg/min. At higher cooling rates, pellets lose their strength associated with
the development of the thermal stress.
Consequently, the following parameters are determined during the cooling
process: the temperature of the gas drained and the gas flow rate during pellets cooling.
Analysis on the mutual influence between the parameters of iron ore pellets
induration process. Mutual influence of the drying temperature and the rate of
gas flow on the process of pellets drying. Initial data for the analysis has been chosen
as written: the rates of gas filtration in the drying zone were 0.8 m/s, 1.0 m/s, 1.2 m/s;
the height of the pellets layer was 300 mm, length of the drying zone was 15 m, the
velocity of the carriages was 2.25 m/s, the gas temperatures in the drying zone were
350
o
C, 400
o
C, 450
o
C. The data obtained from the process conducted with the stated
data are presented in Table 1.
Table 1 The drying zone: residual moisture dependence on the gas temperature and
the gas flow rate within the layer
Gas
temperature,
о
С
350
400
450
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
Residual
moisture, %
0
0
0
0
0
0
0
0
0
300
0
0
0
0
0
0
0
0
0
240
3.3
0.6
0
1.4
0
0
0
0
0
180
5.5
3.7
1.4
4.3
1.8
0
3
0
0
120
6.9
5.7
4.1
6.1
4.4
2.1
5.3
2.9
0
60
When the gas temperature in the drying zone is as high as up 450 °C, the moisture
remains almost in the same amount within the pellets while the gas flow rate of 1.2 m/s
enables the pellets to dry completely through the entire depth of the layer.
After the drying zone, if the temperature is 350–400 °C the significant amounts
of moisture are present within the pellets. Under conditions of 350 °C and the gas flow
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