WO2002008141A1

WO2002008141A1 - Method and apparatus for the production of a building material

Info

Publication number: WO2002008141A1
Application number: PCT/NL2001/000557
Authority: WO
Inventors: Cornelis Gerardus Sebastiaan Duijn; René Hendrik Jan OSTERMEIJER; Johan Jurriaan Weber
Original assignee: Du-Mat Trade Bv
Current assignee: Du-Mat Trade Bv
Priority date: 2000-07-21
Filing date: 2001-07-19
Publication date: 2002-01-31
Anticipated expiration: 2003-01-21
Also published as: NL1015771C2; EP1301447A1; AU2001280259A1

Abstract

The invention relates to a method and apparatus for the production of a building material of substantially inorganic, solid waste, such as such as bottom ash, kettle ash and/or fly ash, containing heavy metals. At least a part of the heavy metals in the waste is immobilised and the waste is washed preferably after immobilisation.

Description

Method and apparatus for the production of a building material

The invention pertains to a method and apparatus for the production of a building material of substantially inorganic, solid (i.e. having a dry weight of 20 % by weight) waste, such as bottom ash, kettle ash and/or fly ash, containing heavy metals.

Such a method is known, for example from Dutch patent application no. 8903092. Said publication discloses a method for reducing the leachability of granular material substantially consisting of an inorganic binder and a filler, which contains contaminants such as heavy metals. In order to reduce the extent to which leaching of the granular material takes place, for example by rain water in those cases where the granular material is deposited, or by the mixing water in those cases where said granular material is used as a filler, for example in concrete or the like, the finished granular material is sealingly coated with of a water-insoluble and water- repellent material . Examples of such a material are water- impermeable and/or water-repellent polymer compositions, which preferably consist of a bituminous material, such as tar, pitch or asphalt.

The object of the present invention is to provide an improved method of the kind referred to in the first paragraph, by means of which a building material is obtained which meets recent and possibly future legal requirements, and which in principle does not require the addition of a water-insoluble and water-repellent material .

In order to accomplish that objective, the method and the apparatus according to the invention are characterized in that at least a substantial part of the heavy metals in the waste is immobilised and in that the waste is washed with water. In this manner a building material is obtained wherein Xe extent to which leaching out of heavy metals and salts takes place has been strongly reduced without the presence of a water- insoluble and water-repellent material being required. Preferably, the heavy metals that are present in the waste are immobilised before the waste is washed. In that case the washing water that is being discharged will only contain small amounts of heavy metals, if at all, and it can more easily be processed or be used in other processes or, depending on the geographic situation of the plant in which the method according to the invention is used, on the nature of the salts and on the local legislation, be discharged into the sea.

If the waste contains a fraction of fine particles, such as fly ash or sludge or dredgings, for example, or substantially consists thereof, (the larger part of) said fine particles is preferably converted into an aggregate during said immobilisation process. Such an aggregate (which is also indicated by the term granulate) can already function as a building material by itself. Instead, it is also possible to add the fly ash aggregate to a flow of coarse particles, such as bottom ash from a waste incinerating plant or pan oven desulphurisation slag from a blast-furnace.

The invention furthermore pertains to a construction element comprising a building material obtained by using a method as described above, as well as to apparatus which at least comprises equipment for immobilising a part of the heavy metals in the waste and for washing said waste.

The invention will now be explained in more detail with reference to the appended figures, which schematically show a number of embodiments of the method according to the present invention.

Figure 1 shows a number of possibilities for refining coarse bottom ash.

Figure 2 shows a method for the production of a building material from kettle ash and fly ash. Figure 3 shows a method for the production of a building material from coarse bottom ash.

Figure 4 shows various methods for the production of a building material from a combination of kettle ash and fly ash on the one hand and coarse bottom ash on the other hand. Figure 1 shows the process of refining coarse slag from an incineration plant for domestic waste and comparable industrial waste. Such slag is usually inhomogeneous both as regards the material composition and as regards the particle size distribution (particle size ranging from 0 mm to 300 - 500 mm) and requires more or less intensive refining before it can be used for producing a building material therefrom.

The very coarse parts, such as paving stones, for example, (wet) telephone directories, bicycle wheels and the like, can be removed from the slag by passing the coarse waste incinerator slag over a bar screen. Said removed very coarse parts can subsequently be separated by means of a magnet into coarse ferrous parts and coarse non-incinerated waste, which can be returned to the waste incineration plant.

Ferrous parts can be removed from the slag that has passed the bar screen, likewise by means of a magnet, which parts can be reused, just like the aforesaid coarse ferrous parts .

Subsequently, the fraction (indicated by the term "excess") that may cause damage to the equipment in the installation for the production of the aforesaid building material can be removed from the main flow via a further screen. After having passed said screen, the particles in the main flow are smaller than 60 mm, preferably smaller than 40 mm. Now, further processing of the main flow into a building material can take place directly; according to another possibility, organic particles, such as paper, polystyrene foam and plastic are removed, for example by means of an air separator, such as the Windzifterunit ® of DUOS B.V., which particles can subsequently be returned to the waste u ω |vj DO μ> H

( l o in O o ot

ω ω DO to > cπ o un o cπ o (Jl

ash and fly ash aggregate thus treated can be used as a building material, which meets the current strict legal requirements . For the sake of completeness it should be noted that both the immobilisation step and the washing step can be carried out more or less intensively. Said intensity can be selected in dependence on, among other things, the waste to be processed and on the current local and environmental legislation (which may vary according to time and to geographical location) . Instead of using the aforesaid baths, it is also possible, for example, to use a flow-up column, a washing/dewatering screen or a washing/dewatering screw.

Figure 3 shows a process for the processing of coarse waste incinerator slag, wherein a refining step as shown in Figure 1 is carried out first. Then the waste is stored for a period of for example six weeks, so that any organic material that is present therein will decay. Said decaying process can be accelerated by adding suitable bacteria to the waste. The immobilisation and washing steps are carried out in a manner which is substantially similar to the above-described methods. The main differences are the smaller amount of cement to be added, because the cement, in connection with the size of the slag particles, only needs to coat a relatively small surface area (for the purpose of enhancing the immobilisation process) and does not need to contribute to the formation of an aggregate; the small amount of water to be added, or the absence thereof, because coarse waste incinerator slag is relatively moist; and, as regards the washing step, the quenching and cooling of the slag, which does not play any significant role in the case of an aggregate consisting of fly ash and kettle ash.

Figure 4 shows a number of routes for the processing of kettle ash and fly ash on the one hand and coarse waste incinerator ash on the other hand, wherein the stage at which the respective waste flows are combined varies. In the case of route A, the kettle ash and the fly ash are mixed with the slag after the immobilisation step, and the obtained mixture is further processed in a manner which substantially corresponds to the manner of processing that is shown in Figure 3. This route can be used in particular if the kettle ash and fly ash contains a large amount of heavy metals in proportion to the slag, which is usually the case, and if said ash is relatively small-sized. In that case the immobilisation process can be optimized for the kettle ash and fly ash without this waste flow having any significant effect on the efficiency of the immobilisation of the mixed waste flow.

In the case of routes B and B ' , mixing of the immobilised and washed kettle ash and fly ash takes place after quenching and cooling of the slag, just before refining of the slag (route B) or just before storage of the slag (route B') .

Route C concerns the mixing of finished aggregate of kettle ash and fly ash, for example obtained by means of the process that is shown in Figure 2, on the one hand and finished aggregate of slags, for example obtained by means of the process that is shown in Figure 3, on the other hand. Integration of one or more steps for the processing of kettle ash and fly ash can lead to a reduction of the amount of equipment and storage sites that are required for said processing and, in addition, it can lead to a more uniform product . Within the framework of the invention, washing is preferably carried out in 1 to 3 steps with a total LS ("Liquids to Solids ratio") ranging between 2.0 and 5.0. In order to keep the amount of waste water within bounds, an LS ranging between 2.5 and 3.0 is preferred.

Example

Three samples of a homogeneous fly ash from an AVI were immobilised, aggregated and washed in the following manner so as to obtain a product having a particle size distribution as is common with bottom ash (Demi = demineralised water; LS = Liquid to Solids ratio; Cement = CEM II 32.5/B-M; Phosphate monocalcium phosphate) :

The leaching (in mg/kg) of a number of heavy metals and salts from the aggregates thus obtained was tested in accordance with EN 12456:1996 procedure B and compared with the requirements for a category 2 building material in accordance with the Nederlandse Bouwstoffenbesluit (BsB) (Dutch Building Materials Order) of 23 November 1995:

Sample B meets the stringent criteria of the aforesaid Bouwstoffenbesluit . Samples A and C meet all criteria, except for bromide, so that a higher LS can be used during one or more washing steps for these samples .

When using the method according to the invention, a clean building material is obtained in an efficient manner, which building material is suitable, for example, for non- shaped applications (for example as a fill material or road- metalling material) and shaped applications (for example concrete or asphalt layers or stabilisation layers) .

The invention is not restricted to the embodiments as described above, of course, and it can be varied without departing from the scope of the claims.

Claims

1. A method for the production of a building material of substantially inorganic, solid waste, such as bottom ash, kettle ash and/or fly ash, containing heavy metals, characterized in that at least a part of the heavy metals in the waste is immobilised and in that the waste is washed with water.

2. A method according to claim 1, wherein the heavy metals in the waste are immobilised before the waste is washed.

3. A method according to claim 2, wherein the waste contains a fraction of fine particles, such as fly ash, or substantially consists thereof, and wherein the larger part of said fine particles is preferably converted into an aggregate during said immobilisation process.

4. A method according to any one of the preceding claims, wherein cement is added during said immobilisation.

5. A method according to any one of the preceding claims, wherein the waste contains a fraction of coarse particles, such as bottom ash, or substantially consists thereof, and wherein said coarse particles are refined prior to the immobilisation of the heavy metals in the waste, in such a manner that particles which are larger than 60 mm and preferably particles which are smaller than 40 mm are removed therefrom.

6. A method according to claim 5 , wherein ferrous metal particles, non-ferrous metal particles and/or organic particles are removed from the coarse particles during said refining process .

7. A method according to any one of the preceding claims, wherein an aggregate of immobilised, fine particles is mixed with coarse particles and wherein the obtained mixture is subsequently washed with water.

8. A method according to any one of the claims 3 - 6, wherein fine particles and coarse particles undergo the aforesaid treatments separately and wherein the obtained aggregate of fine particles is subsequently mixed with the coarse particles in order to thus form a combined aggregate.

9. A method according to any one of the preceding claims, wherein the waste is stored so as to allow at least a part of the organic particles that are present in the waste to decompose prior to the immobilisation of the heavy metals in the waste.

10. A construction element comprising a building material obtained by using a method according to any one of the preceding claims .

11. Apparatus for the production of a building material of substantially inorganic, solid waste, such as bottom ash, kettle ash and/or fly ash, containing heavy metals, characterized in that said apparatus at least comprises equipment for immobilising a part of the heavy metals in the waste and for washing the waste .