What Is Alternative Fuel Substitution Rate?

The alternative fuel substitution rate is the share of a cement kiln's total thermal energy supplied by alternative fuels (waste-derived and biomass fuels) instead of conventional fossil fuels such as coal and petroleum coke. It is measured on an energy basis, as a percentage, and is the same metric the industry calls the thermal substitution rate (TSR) or, loosely, the alternative fuel rate (AFR). The global average sits at roughly 8-10% [1], the EU average is about 52% [2], and leading European plants run above 80%, with several at 90-100% [3].

One disambiguation worth making early: in a kiln-fuels context, AFR means the alternative fuel substitution rate, not the air-fuel ratio of the burner combustion, and not the share of supplementary cementitious materials in the cement (that is clinker substitution, a separate metric covered under supplementary cementitious materials). This piece deals only with the thermal-energy substitution rate at the kiln.

A rising alternative fuel substitution rate changes the flame, the draft, and the false-air sensitivity of a kiln, which is where sealing performance starts to matter. If you are raising your substitution rate and want the combustion-air path under control, our engineering team can map your inlet and outlet sealing against the new fuel profile through Oswal's integrated false air control. Contact us to walk through your configuration.