bulk material - hopper silo control

Dear,

please check picture, we have phosphate material in a silo with four discharge outlets and it is filling hopper based on rotary type level switches.

I want to check if the system is feasible, based on the phosphate level detected in the hopper by the rotary type level switches (either high or low level), the discharge outlets are closed or opened to allow filling of the hopper.
are the rotary type level switches the right type of levels to be used? and what about using time for opening and closing the discharge outlets if the level in the hopper is monitored using a radar guide type level transmitter?
your feedback is valuable.

thank you!

Are the rotary type level switches the right type of levels to be used?

Click to expand...

For phosphate handling in this humid part of the world, the rotary bin indicators always cause problems sooner or later. On a wet rainy day, the phosphate forms clumps that will jam up most rotary devices.

Is your picture true as to the shape of the silo? With a flat bottom, feeding out will be difficult. In every fertilizer plant that I worked on, we used cone-shaped silos with one big feeder at the bottom, usually a rotary screw feeder. Here the silos need large vibrators attached to the outside to keep the phosphate flowing. Even with the vibrators, the operators kept a large sledge hammer on hand for jams.

Maybe in your area, the humidity is not be a big problem.

Dear Lancie,
thank you, actually where the plant will be used has very low precipitations (such as 5mm) and average relative humidity is 50%. is the rotary paddle wheel a reliable system to be used in such applications?

Second, yes you are right, the silo has a conned shape, and it is discharge into the hopper using 4 discharge valves.

thank you, actually where the plant will be used has very low precipitations (such as 5mm) and average relative humidity is 50%. is the rotary paddle wheel a reliable system to be used in such applications?

Click to expand...

Yes, they will work until the motor burns out. The ones I have seen work by continually rotating while not covered, and when covered the wheel is blocked by the material, which sigals the material is up to that level. As long as the material does not cling to the wheel and set up like concrete (blocking the wheel even after the level has fallen below the wheel) then that type of bin level indicator will work okay.

Thinking about past experiences, the bindicator type level switch seems to work best where it is uncovered often. For example, the High Level switch is often uncovered, and the rotary wheel-type in that location will run a long time, but the Low Level switch is often covered and stopped, so the material tends to clump up around the paddle. Perhaps the slight heat from the stalled motor causes the material to set up. Then for the rare times when the paddlewheel is uncovered, it does not break free and start rotating again. Then it will not indicate a low level even when the material drops below it.