Castle Cement’s Ketton Works (Lincolnshire, UK) replaced coal for firing of its rotary kilns, with Profuel(tm), an alternative fuel comprised of cardboard, paper, plastics, textiles and carpet and other “green” fuel waste materials. In 2002 the company built a GBP4 million three-stage Profuel preparation plant that required conveying and weighing of the Profuel material as well as pulverized fuel ash (PFA) that is heated along with calcium oxide, silica, aluminum and iron in horizontal rotary kilns at 1600C.
The company chose to convey and weigh the Profuel materials differently than it did the PFA.
Green fuel waste that has been shredded and ground into particles approximately 20 mm in diameter, are conveyed from two 300 cu m bunkers through two enclosed rotary weigh feeders to two sluice valve hoppers at a rate of 5000 kg/h. 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 diameter flexible screw conveyors, one of which is 1.9 m in length, and the other 6.3 m in length. Each conveyor is dedicated to transport PFA at the rate of 1000 kg/h to one of two, 1-tonne capacity silos with automated loss-of-weight batching capability. In turn, the silos deposit 10 to 50 kg 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 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 1200 tonnes per day, and the other with a capacity of 2400 tonnes per day.
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 crystalline structure of the cement. The Profuel preparation plant allows Ketton Works to produce 1.2 million tonnes of cement annually in an environmentally friendly manner.
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