MAR® SYSTEM

Bearing the well known MAC® System working concept in mind, it is possible to focus on the MAR® System one.
The MAR® System allows to recycle the dry bottom ash and the fly ash collected by the electrostatic precipitator (ESP) sections with the highest UBC (UnBurned Carbon) content.

The ash to be recycled is temporarily stored in a silo. Then, from this silo, the ash can be conveyed to the coal feeder level in two different ways:

1) Pneumatically, through different systems (vacuum, pressurized conveyance or using ejectors).

2) Mechanically, through suitable MAGALDI conveyors and bucket elevators.

Referring to the solution 1), the ash to be recycled is pneumatically conveyed to a cyclone. In the cyclone the finest ash fraction is directly drafted into the combustion chamber due to its negative pressure, while the coarse ash fraction is dosed to the coal feeders and then passes through the coal pulverizers before being injected into the boiler by the coal burners.

The choice to recycle the ash through the coal pulverizers is driven by the possibility to reduce the bottom ash grain size up to a value comparable with the ESP fly ash one. Besides, the ash enters the combustion chamber near hot areas that means a fraction of the UBC contained in the recycled ash, can burn thanks to high temperatures and proper residence time.

Referring to the solution 2), the cyclone is not required given that the chosen ash is conveyed to the coal feeder level by suitable MAGALDI conveyors. Then this ash can be dosed to the coal feeders, for instance, by vibro-feeders before going into the boiler with the same path of the previous solution 1).

The choice of the MAR® System configuration mainly depends on the specific project and boiler designer. The MAR® System can be implemented, as a retrofit, downstream the 80 MAC® Systems already in operation in the world.