Fly ash is a coal combustion product (CCP), a by-product of pulverized coal incineration in the process that generates electricity. Coarse particulates, such as bottom ash and boiler slag, settle at the bottom of the combustion chamber after incineration is complete. Fly ash rises up in the plant exhaust stacks with the flue gases and is removed by electrostatic precipitators and a fabric filter baghouse.
Fly ash is a supplementary cementitious material (SCM) and can be used as a partial substitute for portland cement in the production of concrete, reducing the need for and production of cement. How does this help lower the carbon footprint of concrete products? For each ton of fly ash used in place of traditional cement, approximately one ton of carbon dioxide emissions is avoided. This is due to the amount of energy required and carbon dioxide that is created by producing cement—both from the calcining process of the raw materials and the thermal heat from fossil fuels needed to manufacture the cement. For reference, one ton of CO2 is equivalent to about three months of emissions from an average automobile. The amount of fly ash used in concrete annually, saves around 13 million tons of extra carbon dioxide being generated.
Recycling fly ash from landfills or impoundments has other environmental benefits as well. One ton of coal ash is equivalent to the average solid waste produced by each American during a 455-day timeframe. Recycling the fly ash reduces space required for landfills. It reduces the amount of carbon dioxide produced by the trucks that need to transport the ash from the power plant to the landfill, as well as the earth-mover equipment it takes to safely bury it.
Recycling fly ash results in saving new raw materials from needing to be mined and also reduces carbon dioxide emissions. It also saves natural resources from being reduced or depleted.
Recycling fly ash from historic fly ash impoundments or landfills has other environmental benefits as well. Decades old fly ash landfills and impoundments were often built without liners. It allows for groundwater to seep in and come in contact with the fly ash. This can result in leaching of elements such as arsenic, boron, sulfites, lithium and others into the water table. Recycling the fly ash and incorporating it into a non-leaching material such as concrete eliminates the potential for groundwater contamination.
Not all fly ash is created equal though. Lower-quality fly ash can still be used to stabilize soils and reduce erosion. But the finer the particles used in concrete, the easier the concrete is to place and finish. Fine fly ash also contributes to a higher-strength product that is more resistant to the elements and wear.
This is where ST Technology & Equipment comes in. Our proprietary tribo-electrostatic belt separator is capable of handling a high throughput using very little energy. More importantly, it is able to separate fly ash down to very small particle sizes, providing operation with varying degrees of final product. The finer the fly ash, the higher the demand and price.