Fly Ash Treatment and Utilization
Fly ash is a fine, powdery material composed of the finely divided mineral particles that are driven out of the combustion chamber with the flue gases during combustion of pulverized coal. The components of fly ash can vary depending on the geological characteristics of the coal that was burned and the type of boiler and pollution control equipment used at the power plant. Since coal is the most commonly used fossil fuel, the amount of fly ash generated from coal combustion is large, and thus it is important to ensure that it is treated and utilized appropriately.
The handling and use of fly ash has evolved significantly over the years and the development of regulatory Acts and regulations for ash storage, use and disposal has had a major impact on the industry. Typically, fly ash is stored and handled in either an ash yard, deep well injection, or surface impoundment. Regardless of the disposal method, the fly ash must be tested and treated to meet the air and water regulatory requirements.
The most common form of treatment is concentrated chemicals, followed by biological treatments and ozone treatments. The common objective of these treatments is to reduce the concentrations of acid gases in the fly ash, to reduce the formation of leachate and the release of contaminants into the environment. In some cases, treatments are aimed at increasing the usable life of the ash and enabling its reuse.
In order to assess the effectiveness of a fly ash treatment program, it is important to measure the impact it has on both the environment and human health. This can be done through a variety of tests, including analysis of the ash for hazardous constituents, analysis of leachates, and determination of potential air emissions. Also of importance is the evaluation of the potential for leaching or spreading of hazardous constituents from the treated fly ash through land disposal.
The most common and generally accepted form of utilization for fly ash is in cement and concrete. Fly ash is a great source of pozzolanic material and is often used to replace Portland cement in concrete mixes. The use of fly ash in this form can result in cost savings and a reduction of emissions associated with manufacturing concrete. Fly ash has also been used in roadbeds and embankment, as a soil amendment, and for reclamation projects.
Although fly ash generally has no direct benefit for the environment beyond its potential for use as a material or fuel, studies have recently indicated that certain types of fly ash may be beneficial when used as a land application. Benefits can be indirect, such as the potential improvement of soil structure and fertility and reduction in runoff, or direct, such as the potential removal of heavy metals from the soil.
Fly ash treatment and utilization is a complex process and further research is needed to fully assess the environmental and human health implications of different treatment technologies and utilization methods. With the right regulations and proper disposal and reuse of fly ash, many of its negative effects can be reduced or eliminated, and its benefits maximized.
