Material flow issues of cement, flyash, and slag in silos can be a real headache. Below is a list of typical flow rates for cement through various size butterfly valves and screw conveyors and a list of troubleshooting tips. Aerated cement has a typical flow rate of 74 pounds per cubic foot.
Cement Butterfly Valve Estimated Gravity Flow Rate:
8” Diameter = 144 Tons per Hour
10” Diameter = 226 Tons per Hour
12” Diameter = 325 Tons per Hour
14” Diameter = 443 Tons per Hour
Cement Screw Conveyor Estimated Delivery Rate:
8” Diameter = 80 Tons per Hour
10” Diameter = 115 Tons per Hour
12” Diameter = 200 Tons per Hour
Slag and flyash materials will flow and convey at a slower rate because of their aerated bulk densities being lower than cement. Slag has an aerated bulk density of 60 pounds per cubic foot and flyash at 45 pounds per cubic foot.
If you have a diminished flow check the following:
- Confirm all of the aeration pads are receiving 9 psi of dry air
- Confirm the butterfly valve is opening up vertical the entire way.
- Check the silo top dust collection unit to ensure it has air flow and is not packed full.
- Check the silo top for any signs of water being able to enter the silo.
- Empty the silo and confirm the cone section does not have buildup, a plugged cone, or chunks of hard material.
Tip: Proper aeration is key to material flow, condensation in air lines feeding aeration pads can cause major problems in a cement silo. In recent years more and more producers have installed low-pressure aeration blowers which drastically reduce the probability of water entering the silo cone through the aeration pads.