Circumix - Dense Slurry Mixer

Basic and optional material streams

Circumix- basic material streams

Fly ash collection and inlet 

The fly ash must be collected in dry form. Dry pneumatic fly ash conveying system to transport fly ash into storage silo(s) is recommended. The purposes of the silo(s) are to provide buffer capacity in emergency situations. 

Fly ash is generally classified as fine and coarse ash. In may happen that separate collection of the two types for quality classification is required. Circumix can be easily integrated even if two separate collection systems are in place.

Make-up water 

Make-up water shall be continuously available within the specified pressure range to be used by the Circumix process in order to ensure the appropriate solid water ration in the mixture. The make-up water can be fed from the process water system or from practically any1 plant waste water sources such as FGD waste water, wet cooling tower blowdown, thickener overflow streams.

1 A few restrictions apply, please refer to our office.

Circumix- optional material streams

Bottom ash (wet/dry collection; particle size of max 15-25 mm (3/4"-1")) 

The bottom / bed ash (BA) can be collected by any of the usual methods:

  • Wet: Bottom / bed ash, as wet granulate may be removed from under the boiler with water filled ash scraper / drag chain conveyor / jet ejectors / etc...
  • Dry: Bottom / bed ash may be removed from under the furnace by an air cooled belt conveyor system that allows proper afterburning and cooling of the BA particles, with less radiative heat losses of the furnace (e.g. the Magaldi system).

Bottom ash is reclaimed from the furnace as a mostly amorphous and glassy material that is then crushed to less than 20-25 mm particle size. The particles do not contain soluble compounds and are, usually, transported as lean ash – water slurry, in case of wet BA handling. Due to the use of too much water in such systems the Circumix requires that an additional facility needs to be applied in order to reduce water content up to 1:3 - 1:5. For this purpose we recommend that a thickener is used. The thickened bottom ash slurry can be fed into the Circumix mixer. BA thickener is in our product portfolio. Please contact if interested in further information. 

In case of dry bottom ash handling the BA is collected in dry BA silos. Depending on the distance between these BA silos and the Circumix mixers the bottom ash can either be transported in dry form or as BA slurry with 1:3-1:5 ash to water ratio. 

FGD gypsum (slurry in weight w:s=1:1 solid to water ratio) 

Various techniques are used for removing sulphuric oxides from flue gases. One solution is the recirculating fluidized bed firing where pulverized limestone is introduced already in the furnace in order to capture sulphuric oxides. Excess limestone and calcium sulphite are removed with the bed ash. 

The most widely applied technology is, however, the wet scrubbing where hazardous gaseous pollutants are removed by injected limestone and water slurry. The product is gypsum with 10 to 15 per cent water content. Although this is marketable, in many cases it is simply landfilled. Another by-product is the heavily polluted waste water that is blown down from the scrubber. 

The quantity and quality of gypsum and waste water primarily depends on the sulphur content of coal. The amount of by products from desulphurization, though substantial, usually does not exceed 20 per cent of fly ash. 

The generated FDG gypsum can be added to the Circumix mixer as slurry with preferably 1:1 solid to water ratio. 

Other solutions may be applied. For further details, please contact us. 

Waste water for make-up purposes 

Other waste waters such as FGD waste water, wet cooling tower blow down can be used as make-up water although some rare limitations may apply.