Pulverized coal (PC) power plants have feeders that measure the mass flow rate of the pulverized coal particles as it enters the burner section in the boiler. The orifice of the feeder is calibrated to certain mass flow rate of the pulverized coal.
Sometimes the only weight of the coal storage above the feeder is measured. During steady state operation the the loss of weight is more or less similar to the coal mass flow to the boiler
A team of colleagues work on this topic. They use rod sensors where an electrostatic principle is applied. If you are interested you can read more about it here http://ieeexplore.ieee.org/document/7210198/?reload=true