How the PFR kiln works

A PFR (Parallel Flow Regenerative) kiln has two vertical shafts with a connecting crossover-channel. Both shafts work together. One burns the product, the other preheats the kiln feed.

In the burning shaft, combustion air is introduced at the kiln top and absorbs heat in the preheating zone from the limestone fill that was freshly supplied in the previous cycle.

The fuel is fed through vertical lances arranged evenly across the cross-section of the shaft. At the lower end of the lances, the fuel meets the combustion air and is ignited - this is also where the preheating zone ends and the combustion zone begins.

The flow in the preheating and combustion zones is in the co-current flow of process gases and kiln feed. 

In the cooling zone, cooling air is supplied in counterflow from the kiln discharge. The process gas and the supplied cooling air are fed together into the regenerative shaft via a crossover-channel (connecting channel to the second shaft).

In the regenerative shaft, the hot kiln gases subsequently heat up the limestone in the upper area (preheating zone) in counterflow and cool themselves down at the same time.

The material bed in the preheating zone of the regenerative shaft only has a limited heat absorption capacity. That is why the functionality of the shafts is changed by reversing the flow direction of the kiln gases at regular intervals: the previous regenerative shaft with the preheated limestone in the preheating zone becomes in turn the combustion shaft in which the cool combustion air absorbs the heat of this limestone again - and vice versa.

This allows the regenerative preheating of the limestone and thus the highest utilisation of the heat contained in the kiln gases.