AKO Pinch Valves used in Cement Plant

For over 15 years, AKO pinch valves have been used successfully by Blue Circle (Lafarge) in the manufacture of cement. In the mill house, which is unavoidably an environment of high temperature and abrasive dust, the standard rubber sleeves in the pinch valves last for at least 18 months before routine replacement.

At the Hope Valley (England) Cement Works, in the mill house where limestone clinker is milled into cement, at normal temperatures of 2200°F, the elevators transport finished cement at rates of 200 tons/hour. Entrained in the cement are small numbers of nibs milling medium (17mm manganese balls), These are removed at the head of the elevator, where the cement enters a centrifugal separator, via a nib trap, where the nibs are extracted from the flow of cement.

The collected nibs are conveyed through an air slide incorporating an AKO pinch valve. The discharge side of the valve empties onto a vibratory screen where any stray cement adhering to the nibs is filtered back into the elevator. The used nibs are then dumped. By the time the nibs pass through the pinch valve they have absorbed heat from the hot cement but their temperature is still below the allowable range of the high temperature pinch valve sleeves.

Two 600 HP cement mills together use four elevators, each equipped with 8 inch pinch valves, giving a combined production of over 200 tons/hour.

Because of the high operating temperatures the pinch valve sleeves are exposed to, the Blue Circle maintenance engineers routinely replace the sleeves at intervals of about 18 months, Any inadvertent increase in cement temperature could have a baking effect on the rubber, thereby shortening its life. AKO engineers are presently working to develop an alternative sleeve material which will extend the working life and reduce maintenance efforts.

Elsewhere in the plant, other AKO valves are used. The 500 ton capacity storage and discharge silo loads outgoing cement into rail wagons. The conical lower section of the silo is equipped with aerator lines to assist gravity flow. Divided into 4 circumferential sectors, the aerators operate sequentially on a timer, using sixteen 2 inch diameter AKO valves to control the bursts of compressed air.