SINTERED LIGHTWEIGHT AGGREGATES

This invention relates to lightweight aggregates produced by sintering furnace ash.

Our co-pending International Patent Application WO2010/100468 discloses a method and apparatus for producing a lightweight aggregate for the construction industry from fly ash, which is a fine residue recovered from the gasses of burning coal during the production of electricity.

The apparatus comprises a screw-conveyor for delivering controlled quantities of the pulverised fly ash to a mixer unit, where it is mixed with a certain amount of water. The mixture is then fed by a conveyor at a controlled speed into a pelletiser, which rotates around an inclined axis such that the mixture is formed into pellets which are eventually discharged from the pelletiser by continued rotation thereof.

The pellets are then conveyed to a sintering device, such as a sinter strand, where they are formed into a bed on top of a movable grate or mesh. The bed of material, which contains carbon, is then is ignited from above and moved away from the ignition source over a downdraft, which causes the ignition to propagate downwardly through the bed of material in a controlled manner to fully combust the material. The resultant sintered material is both strong and lightweight and thereby lends itself to use as an aggregate for the building industry.

Such apparatus is only suitable for processing fine ash recovered from the exhaust gases of certain coal fired furnaces. In a travelling gate boiler, both fine ash and clinker is removed from the boiler either by sluicing or by using drag chain. Ash recovered from such boilers is unsuitable for use with the apparatus disclosed in International Patent Application WO2010/100468 due to the presence of the clinker in the ash.

The practice of disposing of fly or other furnace ash in landfill sites is widespread in some countries and this has the undesirable effect of contaminating the surrounding environment. We have realised that the recovery of fly or other furnace ash from landfill sites for conversion into lightweight aggregates can have both economic and environmental benefits. However a problem of using such ash is that it forms into wet clumps in landfill sites when exposed to water and can contain other particulate matter or solids.

We have now devised an apparatus for producing lightweight aggregate which alleviates the above-mentioned problems.

In accordance with the present invention, there is provided an apparatus for producing a lightweight aggregate from furnace ash, the apparatus comprising means for grinding the furnace ash to be processed, a pelletiser for receiving the ground furnace ash and for forming pellets thereof and means for sintering the pellets to form the lightweight aggregates.

The provision of the grinding means prior to the pelletiser allows the output from travelling grate boilers to be processed since the coarser clinker contained therein is ground to a suitable consistency for feeding to the pelletiser. The provision of the grinding means prior to the pelletiser also allows for the processing of furnace ash recovered from landfill sites by grinding the clumps and other matter to a suitable consistency for feeding to the pelletiser.

The matter received by the grinding means can be of varying degrees wetness and as a result the ground furnace ash output from the grinding means has a corresponding water content. Since the degree of wetness of the material in the pelletiser is crucial to the formation of pellets, means are preferably provided for drying the ground furnace ash and for mixing the dried furnace ash with water prior to the pelletiser. The initial drying of the ground ash then allows a controlled amount of water to be added to produce material suitable for reliable pelletisation.

Preferably means are provided between the drying means and the pelletiser for diverting the output of the drying means away from the pelletiser if the output contains particles over a certain size.

Preferably the apparatus comprises an input for re-introducing the diverted output of the drying means back into the grinding means.

A problem of producing surplus furnace ash is that it has to be stored in a location where some will blow away and contaminate the surrounding environment. Hitherto, this problem has been solved by adding water to the ash to allow for stockpiling.

Preferably are provided for mixing conditioned ash with the output from the grinding means. The production of matter of a suitable wetness for pelletisation can thus be achieved by appropriate blending of the ground and conditioned ash.

Also in accordance with the present invention there is provided a method of producing a lightweight aggregate from furnace ash, the method comprising grinding the furnace ash, feeding the ground ash to a pelletiser and sintering the pellets produced by the pelletiser.

Preferably the furnace ash is ground in a wet condition.

Preferably the ground ash is dried prior to feeding it to the pelletiser.

Preferably water is added to the dried ash prior to or during the pelletisation step.

Preferably the ground ash is mixed or blended with conditioned ash prior to the pelletisation step.

Embodiment of the present invention will now be described by way of examples only and with reference to the accompanying drawings, in which:

Figure 1 is a block diagram of a first embodiment of apparatus in accordance with the present invention for producing a lightweight aggregate;

Figure 2 is a block diagram of a second embodiment of apparatus in accordance with the present invention for producing a lightweight aggregate; and

Figure 3 is a block diagram of a third embodiment of apparatus in accordance with the present invention for producing a lightweight aggregate.

Referring to Figure 1 of the drawings, there is shown an apparatus in accordance with the present invention for producing a lightweight aggregate from either furnace ash A recovered from a landfill site and/or conditioned furnace ash B. The apparatus comprises a grinding device 10 for receiving the recovered furnace ash A. The

grinding device 10 grinds any clumps or other particles in the ash to a suitable consistency for processing. The output of the grinding device 10 is fed to a blender or mixer 1 1 where the ground is mixed to the desired consistency with the ash B.

The output of the blender or mixer 1 1 is fed to apparatus of the kind disclosed in International Patent Application WO2010/100468, which basically comprises a pan pelletiser 12 and a sintering device 13 for igniting the pellets to produce a lightweight aggregate.

The provision of the grinding means 10 prior to the pelletiser 12 allows for the processing of furnace ash recovered from landfill sites by grinding the clumps and other matter to a suitable consistency for feeding to the pelletiser 12.

Referring to Figure 2 of the drawings, there is shown an apparatus in accordance with the present invention for producing a lightweight aggregate from furnace ash C output from a travelling grate boiler. The apparatus comprises a grinding device 10 for receiving the furnace ash A. The grinding device 10 grinds the larger clinker particles in the ash to a suitable consistency for processing. The output of the grinding device 10 is fed to a dryer 14 where the ground ash is dried. The dryer may use heat recovered from a sintering device 13 of the apparatus.

The output of the drier 14 is fed to apparatus of the kind disclosed in International Patent Application WO2010/100468, which comprises a mixer which mixes a weighed quantity of the ground ash with water. The output of the mixer is fed at a controlled rate into a pan pelletiser 12. A sintering device 13 ignites the pellets produced by the pelletiser to produce a lightweight aggregate.

Referring to Figure 3of the drawings, there is shown another embodiment of apparatus in accordance with the present invention for producing a lightweight aggregate from furnace ash C output from a travelling grate boiler. The apparatus is similar to the apparatus of Figure 2 and like parts are given like reference numerals. In this embodiment the output from the grinding device 10 is fed to a sorting device 15 arranged to only allow particles above a certain size to progress towards the pelletiser 12. Larger particles are fed back to the grinding device 10 for further grinding.

The provision of the grinding means 10 allows the output from travelling grate boilers to be processed since the coarser clinker contained therein is ground to a suitable consistency for feeding to the pelletiser 12.

CLAIMS
1. An apparatus for producing a lightweight aggregate from furnace ash, the
apparatus comprising means for grinding the furnace ash to be processed, a
5 pelletiser for receiving the ground furnace ash and for forming pellets thereof
and means for sintering the pellets to form the lightweight aggregates.
2. An apparatus as claimed in claim 1, comprising means for drying the ground
furnace ash and for mixing the dried furnace ash with water prior to the
10 pelletiser.
3. An apparatus as claimed in claim 2, comprising means disposed between the
drying means and the pelletiser for diverting the output of the drying means
away from the pelletiser if the output contains particles over a certain size.
15
4. An apparatus as claimed in claim 3, comprising an input for re-introducing the
diverted output of the drying means back into the grinding means.
5. An apparatus as claimed in any preceding claim 1, comprising means for
20 mixing conditioned ash with the output from the grinding means.
6. A method of producing a lightweight aggregate from furnace ash, the method
comprising grinding the furnace ash, feeding the ground ash to a pelletiser
and sintering the pellets produced by the pelletiser.
25
7. A method as claimed in claim 6, in which the furnace ash is ground in a wet
condition.
8. A method as claimed in claim 6 or 7, in which the ground ash is dried prior to
30 feeding it to the pelletiser.
9. A method as claimed in any of claims 6 to 8, in which water is added to the
dried ash prior to or during the pelletisation step.
35 10. A method as claimed in any of claims 6 to 9, in which the ground ash is mixed
or blended with conditioned ash prior to the pelletisation step.