Blue Circle Cement's Westbury plant in the UK is the first cement works in the country to receive the international ISO14001 award for environmental management, following what is thought to be around pound 15 million (US$23.8 million) being spent on environmental improvements.

A major part of the works revolved around improved dust control with almost 50 dust collectors working on this one site.

Blue Circle has committed itself to standardize its entire dust control system, utilizing advanced reverse-jet technology, and allowing continuous plant operation. A significant part of this commitment revolves around the renewal of the electrostatic precipitators situated in the kiln exhaust stream and the upgrading of dust control equipment.

The installation has been phased in over a number of years, and the last of the more traditional shaker-type units has now been replaced by automatic reverse-jet technology. The equipment has been employed wherever continuous filtration of high dust concentrations at high filtration velocities and constant levels of resistance are required.

Several Dalamatic high-performance units, using the reverse-jet principle, have been provided by DCE Ltd. to be sited both internally and externally at discharge points. This principle is based around a seal frame that consists of a formed plate containing a series of parallel slots into which a number of flat, pad-shaped filter elements are inserted.

Each filter element consists of a felted fabric pad supported on a rigid mesh frame or insert in the open end, where an integral sheet steel header incorporating a sealing ring is welded. When the filter is assembled, clamps compress the sealing ring between the flange and the seal-frame slot to give an airtight seal, ensuring correct alignment of the filter pads.

A jet tube is located along the mouth of each insert header and connected via a diaphragm valve to the compressed-air distribution manifold. This valve is linked to a solenoid-operated pilot valve governed by an electronically or pneumatically controlled timer. The modules are assembled into a case and built up to the precise size and configuration of Dalamatic required.

The dust-laden air is drawn through filter pads, so that the dust is captured on the outer surface of the fabric. The air passes through the fabric and out of the insert header on the clean side of the filter.

To maintain continuous operation, each pad is regularly cleaned by a reverse jet of compressed air. A timer activates pilot valves in sequence at predetermined intervals on a continuous cycle. The pilot valves, in turn, open the diaphragm valves.

A short burst of compressed air is released and injected by the jet tube through the insert header into the filter pad. This causes a momentary reversal of the air flow and the effect is a brief controlled inflation of the pad to dislodge the accumulated dust cake into the collection facility.

Blue Circle has been carrying out assessments of the environmental aspects of cement production at Westbury since the late 1980s, with the official Environmental Management System put in place at the beginning of 1995.

Other factors influencing the award to Blue Circle at the Westbury Plant were the reduction of fuel consumption, the examination and trial of alternative fuels, including tires and domestic waste, and the return of kiln dust to the kilns.

The staff at Westbury, however, cannot rest on its laurels. The plant will be subject to six monthly inspections by the government Environment Agency, and the emphasis must be on maintaining the standard.