The diatomaceous earth (D.E.) is delivered to the brewery in 100,000 lb pneumatic hopper cars, and is blown into one of two 90 ft hoppers. The bin vent is protected by a bag filter as are all subsequent hopper and slurry tank vents. When precoat or body feed tanks need D.E. the silo valve opens and a screw conveyor transfers the powder to a 100 lb scale hopper. The hopper is then pressurised and the D.E. blown into the slurry tank. At the beginning of each week the operator selects which slurry tanks are to be used and hand controls the fill up to 85% of tank capacity. When the filter goes on steam the slurry tanks are automatically refilled. The automatic proportioning of the body feed is accomplished with a Waukesha peristaltic pump, controlled by a variable speed motor. The pump rotates between 5-44 rpm. The pump itself may be flushed by hand or automatically when the filter is off steam. The pump starts to operate automatically at 5 rpm when filter is about to start, and will stay in the 5 rpm mode during any recycle or until the filter control system calls for higher D.E. dosages. Control is via a turbidity meter on the beer inlet of the filter, and a differential pressure cell. Information is fed into a programmable logic controller which calculates the D.E. dosage rate and the D.E. dosing pump speed. The rate of increase in pressure on the filter is targetted so that a load of 2700 lbs D.E. is achieved at the same time as the differential pressure reaches 50 psi. A density meter on the body feed tank is used for dosage calculations and to indicate any malfunctions. All information is exhibited to the operator on a CRT screen. Spent filter cake is dropped into a tank and pumped to an Ametex vacuum filter. The filtrate is discharged to drain and the cake falls into a dumping wagon. The entire system is totally automatic once it is started at the beginning of each week.
Keywords: automatic beer brewery filter aid filtration precoating