The combustion of pulverised coal at high temperatures and pressures in power stations produces different types of ash. The 'fine' ash fraction is carried upwards with the flue gases and captured before reaching the atmosphere by highly efficient electro-static precipitators. This material is known as 'fly ash', or Pulverised Fuel Ash (PFA). It is composed mainly of extremely fine, glassy spheres and looks similar to cement.
The 'coarse' ash fraction falls into the grates below the boilers, where it is mixed with water and pumped to lagoons. This material, known as Furnace Bottom Ash (FBA) has a gritty, sand-like texture.
The use of fly ash and FBA in construction has been established for decades. Applications range from providing the cementitious material in concrete, to use as a simple fill material or a lightweight aggregate in the manufacture of blocks – see our Products and Applications sections for further information on its many uses and benefits.
Ash direct from a power station, or excavated from lagoons can be of variable quality, so to ensure consistently high standards of product quality, particularly of blended products, ScotAsh utilises advanced ash beneficiation technology.
Our leading edge electrostatic separation plant was manufactured by STI of Baltimore to our specifications and installed in 2002. It works by separating the mineral ash from the carbon (basically powdered, unburnt coal) between two highly charged plates, enabling the carbon content of the ash to be controlled within strict parameters and to levels as low as 2%.
We process a significant proportion of the ash we receive from the power stations into low carbon fly ash, which provides us with a highly versatile core product, ideally suited to high grade cementitious applications.