WO2009033943A1

WO2009033943A1 - Process and plant for treating sludges resulting from the machining of articles of agglomerated stone material

Info

Publication number: WO2009033943A1
Application number: PCT/EP2008/061112
Authority: WO
Inventors: Dario Toncelli
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-09-10
Filing date: 2008-08-26
Publication date: 2009-03-19
Anticipated expiration: 2010-03-10
Also published as: ITTV20070149A1

Abstract

The sludges resulting from the machining of articles of agglomerated stone material, in particular slabs and blocks produced using the Bretonstone technology, after concentration, undergo drying and incineration so as to recover the water contained in the sludges and powders which are used as fillers during the same slab or block machining process.

Description

"Process and plant for treating sludges resulting from the machining of articles of agglomerated stone material"

The present invention relates to a process and a plant for treating the process sludges resulting from the manufacture and machining of agglomerated stone materials, in particular obtained using the so-called Bretonstone technology.

For many years it has been known to use this technology to produce directly slabs or panels of agglomerated stone material, especially with large dimensions, or blocks made of the same material, also commonly known as Bretonstone blocks.

The technology in question essentially envisages the preparation of a mix comprising a granulated stone material or the like, with a suitably selected particle size, and a binder consisting of a hardenable organic resin, with addition preferably, to the mix, of a very fine inorganic substance, called filler, preferably consisting of stone powders. The mix, which is deposited in the form of a thin layer on a temporary support or used to fill a suitable mould (in the case where a block must be produced), undergoes a vacuum compaction step and at the same time is subject to a vibratory movement of predetermined frequency, following which the rough-formed article is transferred for a step involving hardening of the binding resin by means of the action of heat and/or a catalyst. For further details regarding this technology reference may be made, for example, to the patents US 5,928,585, US 6,773,641 and to the patent applications US 2006/0,283,136, US 2006/0,119,002 and WO 2006/079 585 (to be regarded as incorporated herein by way of reference).

In the case of blocks these then undergo sawing by means of diamond-coated blades operating under a water flow in order to obtain slabs or panels.

Following manufacture of the slabs finishing operations such as sizing and polishing are then necessarily performed using special abrasive tools operating under a continuous water flow used to cool the tools of the sizing and polishing machines and at the same time eliminate the dust generated by machining. These abrasive tools in die most recent versions are composed of diamond-coated granules embedded in a metal or resin matrix.

These operations produce, as waste, a powder consisting of stone material (for example marble, granite, quartz, etc.) and hardened binding resin as well as associated additives, this powder remaining suspended inside the water of the aforementioned water flow. Furthermore in the case of the blocks the sawing operation is performed using diamond-coated blades also operating under a water flow within which a similar suspension of powders such as those mentioned above is formed.

The machining water containing said dispersed powders is treated with various substances (for example flocculating and anti-foaming agents) and passes into decanting apparatuses so that the powder may be deposited while the water is used again to supply the cooling circuits of the cutting, sizing and polishing tools.

The sludges, consisting of powder and water and collected inside decanting devices, are fairly fluid and contain a large quantity of water so that, during an initial phase of the disposal cycle, they are conveyed into concentrating apparatus such as centrifuges or more often filter presses so as to be able to extract as much water as possible, this water being then reintroduced into the cycle for machining the slabs of agglomerated stone material.

The filter -pressed sludges, which have a water content by weight varying between 15% and 30% depending on the type of filter press, are at present transferred to suitable storage and disposal centres with the associated complications and costs. Basically the machining sludges are essentially composed of the following:

- water used during machining of the slabs;

- materials forming the Bretonstone slab and therefore stone materials and binding resin in powder form;

- organic additives such as, for example, flocculating and anti-foaming agents which help the decantation process;

- a minimum and negligible amount of substances resulting from the machining tools, i.e. diamond and organic or metal binder.

The main object of the invention is to manage to eliminate the problem associated with disposal of the machining sludges and preferably be able to use them in the same process for the production of agglomerated stone material and in particular in Bretonstone technology.

In this way, in addition to eliminating the problem of their disposal, there is the further advantage of being able to reutilise the stone material powder as a filler during the cycle for production of the agglomerated article, where said filler must have a given and controlled fineness, with consequent savings in terms of energy and raw materials.

These and other objects are achieved with the present invention which envisages a process for treating and using sludges resulting from the machining of slabs of agglomerated stone material, in which the machining sludges, after at least one step involving mechanical elimination of the water content resulting in a concentrated sludge, undergo the following steps: (a) drying the concentrated sludge so as to remove, by means of evaporation, the water contained therein;

(b) calcinating the dried sludge, namely heating it to a temperature and for a sufficient amount of time to eliminate by means of combustion all the organic substances, resulting in a powder consisting of inorganic material;

(c) cooling, followed by breaking up, filtration and, where necessary, separation of the resultant powder; and

(d) using the powder as filler in the process for the manufacture of slabs of agglomerated stone material. In the preferred embodiment of the present invention said operation (b) involving calcination of the dried sludge is preferably performed at a temperature of between 450 and 650° C, preferably between 550 and 600° C, and kept at this temperature for several tens of minutes so as to be able to ensure that all the organic substances contained in the dried sludge are eliminated by means of combustion. The process envisages that the fumes produced during this operation undergo a post- combustion treatment at a temperature of about 950° C, with the aim of eliminating any organic compounds which are contained in the gases and are then introduced into the atmosphere, after suitable cooling with recovery of the energy.

Moreover, in a preferred embodiment of the invention, the process envisages that the water removed by means of evaporation during the drying step (a) is condensed, for example by means of a scrubber, and used to replenish the cooling circuit of the machines for machining of slabs of agglomerated stone material.

The step (d) involving use of the powder resulting from the process according to the invention envisages preferably a check as to the colour of the powder and transfer to storage silos for subsequent use as a filler during the cycle for manufacturing conglomerate slabs and/or blocks.

The plant according to the present invention in turn comprises a decanter and a concentrator for obtaining concentrated sludges and is characterized in that, downstream of said concentrator, it comprises a drier for removing the water by means of evaporation and an incinerator for eliminating, by means of calcination, the organic substances contained in the dried sludges, equipped with post-combustion unit. Preferably, the plant also comprises:

- a dispersion mill and a device for filtering the residual powders produced by incineration; - means for recovering the water obtained both from preliminary treatment of the sludges and drying of the concentrated sludge; and

- means for transferring said water to a line for machining the slabs of agglomerated stone material so as to supply the cooling circuit therewith.

The particle size of the powders of fine stone material which can be obtained depends not only on the nature of the said material but also on the grain of the tools used during the cutting and sizing/polishing operations.

Therefore, depending on the particle size of the filler needed for the required production of Bretonstone slabs and blocks, the most appropriate machining tools may be chosen. For example, it has been established that if a filler with a particle size less than 20 μm is required, the abrasive granules of the tools must be smaller than 100 mesh.

This therefore gives rise to a closed cycle since the sludges produced by machining of the slabs and blocks of agglomerated stone material and especially the Bretonstone slabs and blocks, after the drying and calcination treatment, are used in the cycle for production thereof. The filler thus obtained from the machining sludges satisfies a large part of the requirement and reduces the purchase volumes, resulting in an enormous economic advantage as well as eliminating the energy consumption associated with production of the fillers by means of grinding of stone extracted from quarries.

The colour of the powder obtained from calcination of the sludges requires special comment in that the agglomerated material is normally coloured: the resin is in fact mixed with pigmenting agents which may be of an organic or inorganic nature (normally metal oxides).

The organic pigments which may be present in the sludges are eliminated by means of combustion together with the organic binder and the organic additives during the high- temperature calcination step, so that the resultant powder has the same colour as the stone present in the manufactured article and therefore in the sludge, the stone normally having a very light and often white colour. The resultant filler therefore has a light/white appearance so that it is perfectly suitable for use in a mixture for manufacturing agglomerated stone materials of any colour. When, however, the pigments are of an inorganic nature, they are not eliminated during calcination of the sludges, so that the powder obtained from calcination of the sludges is not perfectly white, but slightly coloured. It therefore seems appropriate to select the powder depending on the colour and to store it in different silos. Subsequently, during manufacture of the agglomerated stone material the powders will be used depending on the colour of the article to be manufactured. The figure of the accompanying drawing shows a diagram of a plant according to the present invention.

More specifically it shows the end section of the plant for manufacturing slabs of agglomerated stone material, for example using the Bretonstone technology, comprising a sizing machine 10 (for example the machine manufactured and marketed under the name

Levibreton KC by Breton S.p.A.), the polishing machine 12 (for example the machine manufactured and marketed under the name Levibreton KGP by Breton S.p.A.) and the cutting machine 14 (for example the machine manufactured and marketed under the name Multibreton AC-AD by Breton S.p.A.). In the figure the arrow Fl indicates raw slabs entering the plant while the arrow F2 indicates the finished slabs leaving the plant. If the slabs are obtained by sawing blocks, frames for sawing the blocks into slabs are situated upstream of the abovementioned machines (even though not shown in figure). Said frames have been known for many years and are described for example in the patent GB 951389.

The reference number 16 denotes a common header for supplying cooling water to the abovementioned machines by means of the branch lines 16A, 16B and 16C, while the reference number 18 indicates a header for collecting, via the branch lines 18A, 18B and 18C, the machining sludges discharged from the machines in question and having the previously mentioned composition.

A line 20 for supplying sedimentation additives, which are drawn from a tank 22, is connected to the header 18.

The header 18 leads into a decanter 24 from where the supernatant fluid is removed via the line 26 and recycled along the line 28 to the header 16, if necessary together with the replenishing water supplied via the line 30. In this way the water extracted from the sludges is used along the same line for the manufacture of slabs of agglomerated stone material. The sludges discharged from the decanter 24 are transferred by means of the line 32 to the concentrator, such as a well-known filter press 34 of the conventional type, which has the function of extracting further water from the sludges and concentrating the latter.

The water recovered in this way is added by means of a line 35 to the line 26 and recycled together with the water recovered from the decanter 24. The concentrated sludges discharged from the filter press 34 are collected inside a settling tank 36 and from here transferred to a drier 38 inside which evaporation of the water still contained in the sludge is performed. The sludge is then transferred into an incinerator 40 operating at a temperature sufficient to produce calcination, namely ensure that all the organic substances contained in the sludges are eliminated by means of combustion. Both the drier and the incinerator are apparatus which are well-known in waste material treatment technology.

It is also envisaged that the drier and incinerator form a single incineration apparatus which performs both functions.

The water removed by means of evaporation during drying is condensed, for example by means of a scrubber 39, and recycled together with the water recovered from the decanter along the line 37.

The incinerator 40 operates at a temperature of between 450 and 650° C, and preferably between 550 and 600° C, and the sludge remains inside it for the time necessary to ensure the aforementioned complete combustion of the organic components. This time period is normally in the region of a few tens of minutes.

The fumes from the incinerator are conveyed to a post- combustion unit 42 operating normally at temperatures suitable for ensuring that the said fumes do not contain toxic substances (in particular dioxin), and therefore being operating at temperatures in the region of 950° C, and from there to a filter 44 which retains any powders contained in the said fumes.

The incinerator produces powders which, via the conveyor 46, are transferred to a dispersion mill 45, a separator device 47, if necessary, and then to a storage tank 48 so as to be used as filler in the process from manufacturing the agglomerated stone material, such as the Bretonstone process, and then recycled back into the plant for production of the slabs to be machined, i.e. those which reach the sizing machine 10.

The powders retained inside the filter 44 are also transferred to the storage tank 48 via the line 50.

As mentioned above, the plant may contain a section for checking the colour of the powder obtained from the incinerator 40 so as to use it in varying forms. In this case a plurality of tanks 48 are envisaged, one of these tanks being intended to receive substantially white or colourless powders, since obtained from slabs, colouring of which was performed using organic pigments, while the other tanks are intended for the powders resulting from the machining of slabs coloured with organic pigments, so that the powders after incineration are also coloured. The advantages of the invention as already mentioned above are as follows:

- elimination of the organic components of the machining sludges;

- complete absence of machining residual matter, so that the problem of disposal of the waste, essentially resulting from the organic components contained in the machining sludges, is completely eliminated, with consequent zeroing of the costs for the disposal centre; - a substantial reduction in the amount of filler to be acquired and therefore the overall cost of the raw materials from which the slabs and blocks are made; and

- a consequent reduction in the amount of stone to be extracted from the quarries in order to produce the filler, thereby helping safeguard the environment and save energy. The process for manufacturing agglomerated stone material, in particular Bretonstone slabs and blocks, is therefore an increasingly more ecological and environmentally friendly process, in particular if one considers that the resin to be used could be of an organic type as described in the patent application PCT/IB2007/051949.

It is very important to mention that the resin contained in the sludges, during the calcination process, acts as a fuel so that the energy balance nearly breaks even. In other words, the heat generated by combustion of the resin contained in the sludges is almost sufficient to ensure evaporation of all the water and heating of the dry residue to about 550-

600° C.

The gases generated during calcination and subsequent post-combustion may also pass through a heat exchanger so that the heat contained in them may be recovered and used to preheat the air necessary for the drying operation. The energy requirement for this treatment stage is therefore substantially reduced.

Claims

1. Process for treating and using sludges comprising the waste resulting from the machining of slabs or blocks of agglomerated stone material, in which the machining sludges, after at least one step involving mechanical elimination of the water content resulting in a concentrated sludge, undergo the following steps:

(a) drying the concentrated sludge so as to remove, by means of evaporation, the water contained therein;

(b) calcinating the dried sludge, namely heating it to a temperature and for a sufficient amount of time to eliminate by means of combustion all the organic substances, resulting in an inorganic material powder;

(c) cooling, breaking-up and filtration of the resultant powder; and

(d) using the resultant powder in the manufacture of conglomerate blocks or slabs.

2. Process according to Claim 1, characterized in that said step (b) of heating the dried sludge is performed at a temperature of between 450 and 650° C and for a time period of a few tens of minutes so as to ensure that all the organic substances contained in the dried sludge are eliminated by means of combustion.

3. Process according to Claim 2, characterized in that said step (b) of heating the dried sludge is performed at a temperature of between 550 and 600° C.

4. Process according to Claim 1, characterized in that, after the cooling step (c) and prior to the use step (d), the powder resulting from calcination also undergoes separation.

5. Process according to Claim 1, characterized in that the use step (d) envisages verification of the colour of the powder resulting from calcination and storage of the same powder for subsequent use as a filler in the cycle for manufacturing slabs and/or blocks of agglomerated stone material.

6. Process according to Claim 1, characterized in that all the water obtained from treatment of the sludges is recycled for use in the machining of the slabs or blocks of agglomerated stone material.

7. Plant for treating sludges comprising the waste from the machining of slabs or blocks of agglomerated stone material, the plant comprising a decanter (24) and a concentrator (34) for obtaining concentrated sludges and being characterized in that, downstream of said concentrator (34), it comprises a drier (38) for removal of the water by means of evaporation, an incinerator (40) for eliminating, by means of combustion, the organic substances contained in the dried sludges and a dispersion mill (45) for the powders resulting from said incinerator (40).

8. Plant for treating sludges according to Claim 7, characterized in the said incinerator (40) operates at a temperature of between 450 and 600° C and the dried sledges remain inside it for the time necessary to ensure the aforementioned complete combustion of the organic components.

9. Plant for treating sludges according to Claim 8, characterized in that the duration of the incineration treatment is in the region of a few tens of minutes.

10. Plant for treating sludges according to Claim 7, characterized in that it also comprises at least one of the following devices:

- a post-combustion unit (42) situated downstream of said incinerator and operating at temperatures suitable for ensuring that the fumes produced by the incinerator (40) do not contain toxic substances such as dioxin and therefore at a temperature in the region of 950°

C;

- a filter (44) for the powders resulting from said incinerator (40);

- means for collecting the water obtained from said decanter (24) and from said concentrator (34) and means (57, 35, 28) for transferring said water for use in the same machining of slabs or blocks of agglomerated stone material.