In a paper mill with a re-causticizer feeding a lime mud recycling system having a lime kiln with an inlet adapted to receive lime mud, apply heat thereto, process the lime mud into lime in granular form and discharge the granular lime to a kiln outlet and a lime mud feed system adapted to wash, filter and feed lime mud to the lime mud inlet of the kiln, the improvement comprising a camera proximate the kiln outlet imaging granular lime and providing outlet images of granular lime exiting the kiln, a processor analyzing the outlet images of the granular lime and providing pebble size distributions for granular lime exiting the kiln, as well as a controller communicating with the processor comparing pebble size distributions of granular lime exiting the kiln with predetermined prescribed operating parameters for the pebble size distribution for the granular lime exiting the kiln and issuing (I) a notification and/or (II) a control signal prompting remedial action when the pebble size distributions for the granular lime exiting the kiln is outside of the predetermined prescribed operating parameters for pebble size distributions for granular lime exiting the kiln.