The patented MAC (Magaldi Ash Cooler) Dry Bottom Ash System, is a unique system for dry extraction, cooling and handling of bottom ash from pulverized coal-fired boilers.
With almost a hundred of systems installed worldwide, the MAC Dry Bottom Ash system is the world's leading dry bottom ash handling system for utility boilers.

The success of the MAC system can be attributed to the following benefits over traditional wet bottom ash system

Eliminates water usage in cooling and conveying bottom ash

Reduces carbon content in bottom ash

Captures heat energy from ash and returns to boiler

Provides for potential sale of dry, low carbon ash

Reduces operational and maintenance costs compared to conventional wet systems

Fully automatic system from boiler throat to storage silo

The Mac system has been installed in both new boiler and retrofit projects on many different boiler types and makes in a wide range of operating conditions.

The main component of the MAC system is the MAC extractor, which is designed to operate in harsh conditions including exposure to high temperature and shock loads caused by the fall of large clinkers.

The MAC extractor is connected to the boiler throat through a refractory-lined hopper or a transition chute, which provides a volume for temporary ash storage. The hopper is available with bottom doors which can be closed to isolate the MAC extractor and for ash storage. The hopper or transition chute is connected to the boiler throat by a high temperature mechanical seal that allows for boiler expansion.

The key element of the MAC extractor is the Magaldi Superbelt steel belt conveyor, which receives and extracts bottom ash falling from the boiler. The Superbelt is enclosed inside the sealing casing of the Mac extractor.

During the conveying of ash on the Magaldi Superbelt, ash is cooled by a small, controlled amount of ambient air that flows by natural draft into the MAC casing through inlet valves. In addition the air provides oxygen to the unburned ash allowing a more complete combustion and return of heat to the boiler. Data from existing installations indicate reverse air flow does not disturb the combustion process and does not influence NOx formation.

From the MAC extractor, the cooled ash is discharged onto a crusher, which reduces the large ash clinkers to a size suitable for conveying to a silo. Any ash fines that fall on the MAC casing floor are swept off by the spill chain, a small scraper conveyor installed under the Magaldi Superbelt.