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Last update: 06/03/2020

Dry discharge system

In times of diminishing resources and increased environmental awareness, the bottom ash that remains on the grate after combustion, in particular the ferrous and non-ferrous metals contained in the bottom ash should be recycled. Dry discharge offers significant advantages in this respect. Not only are the recoverable metals of a better quality, the fine fraction can also be separated from the coarse fraction more effectively and recycled separately.

The MARTIN dry discharge system consists of the following components:

  • MARTIN ram-type discharger
  • Air separator enclosed in housing
  • Dust removal system
  • Air system

The MARTIN ram-type discharger is operated without water. The bottom ash is discharged in dry form and conveyed directly to an air separator, where it is transported by means of gravity and vibration. The bottom ash is divided into three product streams by means of air separation in several stages:

  • Coarse fraction with recyclable metal content
  • Fine fraction (containing almost no metal)
  • Bottom ash dust

The fine fraction and bottom ash particles are < 4 mm in size.


The air separation area is fully enclosed. Negative pressure is set in the enclosure using the air supply system to prevent false air from entering the furnace and dust from getting into the boiler house.


The exhaust air from the air separator is conveyed into a dust removal system (e.g. a cyclone separator), where the fine fraction is separated. The exhaust air and the bottom ash dust can be supplied to the combustion process as part of the overfire air.


The coarse fraction can be recycled and used in road construction, for example, after the ferrous and non-ferrous metals have been removed. The fine fraction can either be recycled or delivered to a landfill.


The MARTIN dry discharge system offers the following advantages:

  • There is no water consumption (saving water and transport costs)
  • The metals obtained are of better quality
  • Most of the bottom ash is recycled
  • The coarse fraction has a reduced dust content and can be transported