Dry bottom ash handling system cuts plant carbon emissions

Paul Boughton

A new 800 MW coal-fired plant in Germany has installed an 'eco friendly' dry bottom ash handling system.

Worldwide, the wet bottom ash handling is still the predominant procedure but growing environmental awareness in industrialised countries and increasing water shortage at many power plant sites are causing more and more a shift to the dry technique.

But there is an eco-friendly alternative to water: Clyde Bergemann's Drycon system uses fresh air to cool bottom ash while conveying. A special advantage of Drycon is the additional gain of heat energy from ash by using the re-burning effect.

German-based AE&E Inova awarded the contract for a dry bottom ash handling system at the new 800 MW hard coal fired Lünen power plant, located in North Rhine Westphalia, Germany to Clyde Bergemann.

In the Drycon, Clyde Bergemann applies a hydraulic driven Jaw Type Crusher/Slide Gate combination, located between the furnace and the Drycon system, which crushes hot ash lumps directly where they appear.

The hot cores of ash lumps got reduced to many small ones at once, falling down at the Drycon conveyor belt where air in counter-current flow fans the re-burning effect. This reduces the unburned carbon level and frees up additional thermal energy which is returned to the steam generating process within the boiler. This arrangement increases boiler efficiency, reduces coal usage and CO2 emissions.

Further on, compared to wet bottom ash handling, Drycon has lower life-cycle costs and as no precious water is wasted for ash cooling and conveying, all related water treatment costs are avoided. By using dry bottom ash handling, the ash quality is ready for sale to building and cement industry for re-use.

The scope of supply comprises engineering, delivery, erection and commissioning of Drtcon, crusher plant, ash conveying system, ash silo including steel works for storage and unloading facilities as well as supply of a control system which will be connected to the control room.

The Drycon system appeals by its rugged and modular design, both important features already being proved in numerous applications. A particular profitably support to economical plant operation provides the modular design. It ensures that the length-width ratio of the conveyor can be adjusted flexibly to the individual plant and process conditions. This guarantees efficient ash cooling at maximum extraction rate making Drycon to a technologically advanced solution for dry bottom ash handling.

Another feature is the conveying angle based on the chain based transportation. For example, in an Asian reference, a conveyor with an angle of 400 has been realised successfully. This constructive flexibility is important for both, new-builds and retrofits.

Besides Drycon, Clyde Bergemann offers a comprehensive range of solutions for fly and bottom ash conveying as well as for bulk-materials handling. Worldwide, Clyde Bergemann has built an installed base of over 500,000 MW in coal-fired power stations.

Clyde Bergemann GmbH is based in Wesel, Germany. www.clydebergemann.de

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