We have to take gypsum out of a rectangular silo and we are not sure if a rotary valve is necessary between the silo and a screw conveyor. At the moment we have problem of ratholing and bridge as well, thanks in advance for any help.

I would suggest installation of an acoustic cleaner and sounding the horn periodically to combat the ratholing problem.

We are facing problem of poor fluidity of cement while extracting cement from silo even with fresh cement stock. We are having only Ordinary Portland Cement grinding with no water cooling facility in mill. Cooling takes place only in O-sepa. Since the last two months we started water spray in mill inlet to control mill outlet product temperature of around 108 to 113 deg C. Product temp. entering to silo is around 85 deg C and at outlet 72 to 75 deg C. Humidity is around 40 to 60 per cent in air because of coastal area. Please highlight some of the possible causes for such phenomenon and also give the method normally applied to determine moisture content in cement. As additional information we are using mineral gypsum 5 to 5.5 per cent in the cement.

I suggest you should raise the mill outlet temperature setpoint of the PID loop controlling the water injection rate. This should allow more water to be driven off the gypsum in the cement mill. At the same time you shouod attempt to maximise the cooling in the O-Sepa.