About Power Station Ash

When coal is burnt in a modern pulverised fuel furnace, two types of ash are produced. The fine ash, which is recovered from the flue gas, is called fly ash (FA). This material comprises up to 90% of the total ash produced. The remainder consists of similar particles that have fused together into aggregate sized lumps. These fall to the bottom of the furnace and are known as furnace bottom ash (FBA).

 

Typical Fly Ash (FA) Material Properties

The fly ashes produced in Australian power stations are light to mid-grey in colour and have the appearance of cement powder. Particle sizes range from less than 1 μm (micrometer) to 200 μm and are irregular to spherical in shape. In Australia the majority of ash produced is categorised as Class F – being mainly silica and alumina (80-85%) and >10% CaO. Class F ash is highly pozzolanic and reacts with various cementitious materials.

Typical Furnace Bottom Ash (FBA) Material Properties

Bottom ash and boiler slag are formed when ash adheres as hot particles to the furnace walls, agglomerates and then falls to the base of the furnace where it is collected for disposal. Bottom ash and boiler slag comprise approximately 10% of the total ash produced and range in grain size from fine sand to coarse lumps. They have chemical compositions similar to fly ash.

 

  
 

 

Retaining Wall Backfill

As by-products of a very efficient industry, for a given power station, the types of ash have consistent properties and many potential uses. The coarse furnace bottom ash (FBA) is used as a sand replacement, aggregate for lightweight blocks, a road-base component, for agricultural drainage mediums and as engineered bulk fill.

 

Bottom Ash as Bowling Green sub-base
 

Utilisation in Australasia

In Australasia, about 85% of the current " beneficial use" of flyash is for partial cement replacement (between 10-20%) to enhance the properties of concrete and other building materials.

 

In supplying the power requirements for Australian households, around 12 million tonns of ash by-products are produced annually. Today, the cement and concrete industry through their channel members have and continue to build significant markets  for the beneficial use of FA and FBA.

 

 

Regardless of these achievements challenges still remain requiring the development of other high volume uses for the Ash Development Association (ADAA). 

Many new potential uses have been identified by research conducted in Australia and Overseas. The ADAA has, and continues to provide significant funding for research and development into uses for Australian coal ash.

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