According to the study conducted with the processes of limestone dissociation
and magnetite oxidation (Fig. 5 and Fig. 6) with regard to the residual moisture in the
pellets, it has been established that when the presence of the residual moisture, the
magnetite oxidation and limestone dissociation are significantly slowed down.
Therefore, in order to prevent the process inhibition during the pellets preheating, it is
necessary to dry the pellets completely within the drying zone as much as possible
before they are transported into the preheating zone.
Figure 6. Dependence of the magnetite oxidation degree on the content of the
residual moisture within the pellets layer
Analysis on the mutual influence of the firing temperature and the gas flow
rate on pellets firing. The initial data chosen for the dedicated analysis were as
follows: the rate of gas filtration in the firing zone was 0.8 m/s, 1.0 m/s, 1.2 m/s; the
pellets layer depth was 300 mm; the length of the firing zone was 20 m; the velocity of
the carriages was 2 m/s; the temperatures of gas in the firing zone were 1230
o
C,
1250
o
C, 1280
o
C. The results of the study are reported as the data presented in Table 6.
Table 6 The firing zone: maximum temperature of the pellets within the depth of
the layer depends on the gas temperatures and the gas flow rates
Gas
temperature,
о
С
1230
1250
1280
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
Maximum
temperature, %
1229
1230
1230
1249
1250
1250
1279
1280
1280
300
1223
1226
1228
1243
1246
1248
1272
1278
1279
240
1210
1218
1223
1229
1237
1243
1257
1271
1277
180
1190
1203
1213
1207
1222
1232
1234
1268
1272
120
1170
1183
1197
1188
1200
1216
1215
1244
1246
60
With the increase (up to 1280
o
C) in the gas temperature acting in the firing zone,
the maximum temperature of pellets within the depth of the layer strongly depends on
the gas flow rate (Fig. 7).
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