Kingfisher Industrial has demonstrated its ability to provide solutions to problems of wear, due to impacts and sliding abrasion, and to deliver improved efficiency via increased mass flow, on the coal handling plant at Didcot A power station in Oxfordshire. The combination of Kingfisher’s ceramic, metallic and polymer linings on hoppers, transfer chutes, bunkers, feeders and trifurcator sections, is providing greatly improved wear life from the Didcot coal handling and combustion plant; at the same time reducing maintenance and improving coal throughput.
Didcot A is a tri-fuel power station in Oxfordshire, owned and operated by RWE npower. The station, which began commercial operation in 1970, can generate 2,000MW of electricity – enough power to meet the needs of some 2- million people.
Didcot A was originally designed as a coal-fired station. Three of the four 500MW generating units have now been converted to dual-firing, enabling the station to use natural gas as an alternative to coal. In addition, the station has the capability to use biomass fuels such as sawdust and wood chips on all four units.
Kingfisher’s involvement at Didcot A began upon receipt of the coal, at the coal reception hoppers where the fuel is stored following delivery via train. “If it was just coal that was being handled then it’s relatively easy to manage,” said Kingfisher MD John Connolly. “However, because there are foreign particles – metallic, wood, and debris, mixed in with the coal, protection measures have to be taken to ensure that this contamination doesn’t become a problem throughout the rest of the plant. It’s also important to get the material away very, very quickly in order to reduce the cost of any waiting time associated with the unloading operation thus avoiding demurrage costs.
In order to aid discharge of the coal, we’ve lined the coal reception hoppers with a combination of K-FLOW ferritic stainless steel and also our K-Plas polyethylene lining. We’ve used the various grades of material and various thicknesses to counter both the impact and friction induced abrasion, and the wear associated with discharging the material from the rail wagons.”
Once discharged, the coal is fed onto the conveyor belt; it then goes through a series of transfer chutes. These coal transfer chute are used take coal from the unloading station and it can fed directly up to the station bunkers or it can be stockpiled for storage and reclamed at a later stage. Eventually all product is fed back onto conveyors and discharged onto the tripper conveyor that feeds the bunkers. As the transfer chutes are subject to impact, friction and sliding induced abrasion, Kingfisher has lined these units with its ceramic range of lining materials. This combination of K-ALOX, K-BAS and K-ZAS materials supplied in various thicknesses offers resistance to all the different types of wear encountered and guarantees long term protection (10-12 years-plus) against perforation of the fabrication, and against any discharge onto the floor.
The station coal bunkers, which are fed from the transfer chute, have also been optimised by Kingfisher. Here, the main problem was the amount of discharge that was being achieved into the feeders, as a result of whole combination of different bunker lining materials. Continual discharge into the feeders is very important in guaranteeing that the correct amount of tonnage is fed down to the coal mill to ensure an efficient milling process, and correct distribution up to the burners.
“What Didcot wanted here was to achieve mass flow,” said John Connolly; “so we re-designed some of the internal geometry of the bunkers using radius sections, and then we lined them with our K-FLOW ferritic stainless steel. We applied this material using traditional welding and mechanical fixing, which provided a totally seamless lining inside the bunker. This delivers a high degree of wear protection, due to its true hardness of about 240 Brinell. It also gives them a very low coefficient of friction, as a result of the polished stainless steel finish. In addition, the fact that the lining is fully welded prevents any internal corrosion taking place in the internal steel substrate.”
Also as part of the project of achieving improved mass flow, Kingfisher was tasked with removal of the existing volumetric feeders, and the installation of new units. The feeders weigh and distribute coal at different rates, ensuring that between 30 and 40 tonnes per hour of coal is always discharged into the mill at any one time.
From the gravimetric feeders, the coal is deposited downward into the mills. On top of the mills are three piping ducts. One of these handles coal into the mill itself; the remaining two provide the outlets for coal that has already been milled. As the coal comes down into the mill, it is feed out onto a rotating table, and then ground down. This results in a micron sized powder, which is dried and conveyed with a primary air flow prior to exiting the mill vertically via the two pulverised fuel outlets, which are lined with protecting using a range of ceramic and metallic liners.
The wear protected pipework that initially conveys the pulverised coal vertically, eventually turns through 90 degrees, then conveys the coal horizontally to a trifurcator. The trifurcator is a mass flow device that divides the coal flow equally among three legs. Because of the amount of wear that takes place in these legs, and in the associated pipework itself, all are lined with Kingfisher’s range of K-Alox, K-BAS, K-CAST, K-SIL ceramic and K-HARD metallic materials. These offer the key benefit of countering the different amounts of wear that occur in bend sections, triffucators, non return valves (NRV’s) and likewise within the burners, where abrasion is at its greatest.
Summing up the project, John Connolly said: “What we have demonstrated at Didcot A is that wear protection is one of the key technologies in helping operators meet the requirements for reliable, efficient equipment in the power generation industry. At Kingfisher Industrial we are leading the way by introducing new materials to combat the abrasive effects of both coal and ash; and we are continually increasing the warranty periods offered, based upon the extended lengths of time our existing systems have been operating within the industry. We aim to continue improving what we offer the industry, and feel confident that our portfolio of services will continue to grow and assist power utilities in meeting its key performance targets.”