Castle Cement’s Ketton Works replaced coal for firing of its rotary kilns, with Profuel, an alternative fuel comprised of cardboard, paper, plastics, textiles and carpet and other green fuel waste materials.
In 2002 the company built a £4m ($7.56m), three-stage Profuel preparation plant that required conveying and weighing of the Profuel material as well as pulverised fuel ash (PFA) that is heated along with calcium oxide, silica, aluminium and iron in horizontal rotary kilns at 1600°C (2940° F).
The company chooses 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 (0.8 in) in diameter, are conveyed from two 300 cu m (10,590 cu ft) bunkers through two enclosed rotary weigh feeders to two sluice valve hoppers at a rate of 5000 kg/h (11,000 lb/h).
Rotary weigh feeders continuously weigh and meter the material whose bulk density fluctuates due to type and ratio of waste being fed.
The pulverised 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 m (6.2 ft) in length, and the other 6.3 m (20 ft) in length.
Each conveyor is dedicated to transport PFA at the rate of 1000 kg/h (2200 lb/h) 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) , 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 tons/day, and the other with a capacity of 2400 tons/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 odour.
Any residue becomes locked into the crystalline structure of the cement. The Profuel preparation plant allows Ketton Works to produce 1.2m tons of cement annually in an environmentally friendly manner.