Hello Haliff,
It's a tough problem, but after thinking about it a bit more I propose the following;-
To control the limestone feed rate using the apron feeder speed, you will need to make sure that the limestone bin is kept roughly at the same level, so the flow out of the bin is relatively constant. You might then be able to "calibrate" the feeder speed
to give a rough limestone feed rate by experimentation. ie slightly increasing and decreasing the speed to see the effect on the raw meal and back calculate a corresponding percentage feed rate from the raw meal analysis. You would have to keep the other components
of the raw mix constant while you did these tests..
Alternatively, if it is possible to fill a truck(s) from the limestone apron feeder over a timed period, you could weigh them and estimate a rough feed rate in tonnes/hr.
Hope this helps,
Ted.