Any coal can be injected with the main requirements, from the viewpoint of chemical analysis being low sulphur, low phosphorus, low ash content and minimum fluctuation in composition.  The primary factor that influences the cost benefit of PCI is the amount of coke that can be replaced by the injected coal. Appendix A details various methods for calculating the replacement ratio of an injected coal base on its chemical analysis.

In Figure 1 different methods for calculating replacement ratio have been plotted against the dry ash free carbon content, which is a measure of the rank of a coal.  In this figure, all coal properties have been related back to the carbon content assuming a fixed ash content and using relationships between coal properties.  The figure does show that all methods used to determine replacement ratio give a maximum at around a carbon content of 90%. This is the main reason for the choice of LV coals for PCI.