As shown in Figure 1, the incremental change in the amount of coke replaced by coal injection
decreases as the injection rate increases. In addition, as the injection rate increases, over about
140 kg/tHM, the quality of the coke must increase to ensure BF productivity is maintained. Using
the curve for all the data in Figure 1and a simple relationship between PCI rate and required coke
quality then the most economic injection rate can be determined for known PCI and coking coal
prices, as shown in Figure 2. If the 2005 coal prices into Japan are used then the economic
injection rate is determined to be about 115 kg/tHM, just below the average Japanese injection rate
for that year.
|
|
|
Figure 1 World coke and PCI rates. The estimated influence of HV and LV
coals on coke rate is determined based on the replacement ratio of typical
coals.
|
|
|
|
Figure 2 Influence of injection rate on BF total coal costs
|
