Castle Cement's Ketton Works replaced coal for firing its rotary kilns with Profuel, an alternative fuel comprised of cardboard, paper, plastics, textiles, carpet and other “green” fuel waste materials. In 2002 the company built a £4 million (US$7.56 million), three-stage Profuel preparation plant that required conveying and weighing of the material, as well as pulverized fuel ash (PFA), which is heated along with calcium oxide, silica, aluminum, and iron in horizontal rotary kilns at 2,940°F.

The company chose to convey and weigh the alternative fuel materials differently than it did the PFA. Green fuel waste that has been shredded and ground into particles approximately 20 mm (0.8 in.) in diameter are conveyed from two, 300-cu-meter (10,590-cu-ft) bunkers through two enclosed rotary weigh feeders to two sluice valve hoppers at a rate of 5,000 kg per hour (11,000 lb per hour). Rotary weigh feeders, as opposed to traditional belt and apron weigh feeders, continuously weigh and meter the material whose bulk density fluctuates due to type and ratio of waste being fed.

The pulverized fuel ash is conveyed from an 8-ton silo through a bifurcated discharge chute that charges the intake adapters of two, 114-mm- (4.5-in.-) diameter flexible screw conveyors, one of which is 1.9 meters (6.2 ft) in length, and the other 6.3 meters (20 ft) in length. Each conveyor is dedicated to transport PFA at the rate of 1000 kg per hour (2,200 lb per hour) to one of two, 1-ton-capacity silos with automated loss-of-weight batching capability. In turn, the silos deposit 10 to 50 kg (22 to 110 lb) shots of PFA into the intake adapters of two additional flexible screw conveyors that terminate at the same sluice valve hoppers as the above mentioned rotary weigh feeders.

Designed, manufactured, installed, and commissioned by Flexicon (Europe) Ltd., the flexible screw conveyor system satisfied the need to route the PFA material vertically, horizontally, and varied angles — over, under, and around pipes, piers, upright supports, and other equipment in place to process the Profuel materials — while containing dust.

From the sluice valve hoppers, the Profuel fuel-ash mixture is conveyed pneumatically to either of two horizontal rotary kilns, one with a capacity of 1,200 tpd, and the other with a capacity of 2400 tpd.

Profuel “green” fuel, possessing similar calorific value to coal, helps the UK government reach waste-recovery targets and reduce use of fossil fuels. It burns cleanly and completely in the kilns, with no black smoke or odor. Any residue becomes locked into the structure of the cement. The Profuel preparation plant allows Ketton Works to produce 1.2 million tons of cement annually in an environmentally friendly manner.

For more information, contact Flexicon Corp. at (+1) 610-814-2400; sales@flexicon.com; or www.flexicon.com