What is the main function of an ash pond in a coal-fired power plant?

The main function of an ash pond in a coal-fired power plant is to manage bottom ash and fly ash. When coal is burned for energy, the non-combustible materials that remain are classified as ash, which comes in two main types: bottom ash, which settles at the bottom of the furnace, and fly ash, which is carried away with flue gases. An ash pond is specifically designed to collect and store these byproducts safely.

This function is critical for environmental management, as proper handling of ash reduces the risk of air and water pollution. The ash is typically mixed with water in the pond, which helps to suppress dust and provides a method for managing its physical and chemical properties. Furthermore, the storage allows for potential further utilization of ash, such as in construction materials, or for compliance with regulations governing hazardous waste disposal.

In contrast, the other options do not accurately represent the role of an ash pond. For example, storing excess coal pertains to fuel management rather than ash disposal, purifying water for cooling systems does not involve ash management, and facilitating air mixing is a combustion process, distinct from ash handling. Therefore, the accurate answer emphasizes the ash pond's crucial role in addressing the byproducts of coal combustion.