IT202100008858A1 - METHOD AND EQUIPMENT FOR PREPARING A GRANULAR MIXTURE FOR THE PRODUCTION OF CERAMIC TILES - Google Patents

Description

Description

METHOD AND EQUIPMENT FOR PREPARING A DOUGH

GRANULAR FOR THE PRODUCTION OF CERAMIC TILES

Technical field

The present invention relates to a method and plant for preparing a granular body for the production of ceramic tiles. Known art

? the need to mass-produce products of ceramic material, in particular products such as tiles and the like, has been known for some time.

Ceramic tiles are usually produced with a standardized technological system, which provides for the continuous dosage of raw materials to mix the various components destined to form part of the body. These are normally materials with very different physical and rheological characteristics: for example plastic materials, fluxes, stabilizers, etc. Each component is used to control one or more? qualitative parameters of the product, such as the stability? in green, in dry, in cooking, to obtain the quality? desired of the fired ceramic tiles, for example made tangible by the color of the mixture, by the capacity of absorption of? water, from the regularity? dimensional, the absence of surface defects and many other measurable parameters.

The production process then proceeds with the wet or dry grinding of the mixture of raw materials.

In the case of dry milling, the raw materials, mixed according to a specific recipe, are ground in a roller or hammer mill, without adding water. Subsequently, the ground mixture is granulated, for example in a rotating drum, adding, only in this phase, a specific but reduced quantity. of water.

In the case of wet grinding, on the other hand, the raw materials are added with a large quantity of water, usually equal to 35% of the total weight, to form an aqueous suspension called "slip". The amount of water added to solid raw materials can vary according to the dough, for example it can? reach over 40%.

Wet grinding usually takes place using mills, in which the mixture of raw materials is fed, together with a specific quantity? of water, and it comes out ground, with residues between 3 and 8%, through a 63 micron sieve. These average reference values, for example, refer respectively to the production of porcelain stoneware and red-body flooring.

Wet grinding has significant advantages over dry grinding. In fact, it requires less frequent plant maintenance, exploits the disintegrating power of water and, compared to dry grinding, offers the possibility of to sieve to the previously mentioned fine particle sizes. Furthermore, the resulting dough is not subject to the possible reclassification due to the difference in the specific weight of the raw materials in subsequent transports.

Furthermore, while dry milling requires raw materials to be selected from a small number of materials, wet milling allows for the most wide choice of recipes, to obtain, as previously described, the control of the various process parameters and the desired final result.

It should be emphasized that the non-extreme grinding and the mixing obtainable with the dry process are not optimal and that also the sieving result can be problematic. Consequently, even the vitrification of a product obtained with a dry process can be problematic.

Therefore, wet grinding ? generally preferred, allowing you to obtain high quality products? and resistance. In particular, with wet grinding it is possible to obtain products with high vitrification, even below 0.2% water absorption, with minimal surface defects, and also in large formats, without too many complications in the production process.

The wet process, however, requires the extraction of large quantities of water, to bring the ground mixture back to the humidity level, usually around or below 8%, necessary for forming the tiles.

For this reason, in the known plants, which perform wet grinding, very bulky and operationally expensive apparatuses are used, which operate the extraction of the excess water. These are the atomizers, which carry out the extraction of water from the slip, feeding the latter under pressure, at about 27 bar, in the nebulised state, in counter-current with a flow of hot air at about 500°C.

The atomizer has considerable economic and environmental disadvantages, due to the huge consumption of energy, water, as well as? to dust and CO2 emissions.

First of all, in fact, the rapid counter-current drying process, carried out by the atomizer, requires large volumes of fuel, usually natural gas. Can you? estimate that the cost of this operation is about 0.18 ?/m<2>. Can you? calculate that in ceramic plants of the known type the heat consumption values are on average about 440 kcal/kg in the atomisation process, 90 kcal/kg in the drying process after the forming phase, and 490 kcal/kg in the firing phase . In this case we consider an average product in which the slip fed into the atomizer has a percentage of water equal to 35% at the entrance and at the exit equal to 8%. In this regard, we only mention the fact that humidity levels? differences in output or input affect the consumption of thermal energy. For example, an increase in water in the slip entering the atomizer or a decrease in the humidity content? in the output dough, equal to a percentage point, can? lead to an increase of about 4% in the consumption of thermal energy.

In addition, the actual consumption can fluctuate, depending on the efficiency of the system, up to total values, which can increase by as much as 20%.

Taking into consideration, for example, a production line of 10,000 m<2>/day, for the production of a product of 21 kg/m<2>, one can calculate that for atomization it is necessary to consume 92,400,000 kcal/day:

daily thermal energy consumption = 440x21x10000= 92,400,000 kcal/day Considering a lower calorific value of about 8,400 kcal/Nm<3 > of natural gas, the daily consumption ? given by:

daily consumption of natural gas = 92400000 ? 8400= 11,000m<3>

At an average price of natural gas in Italy equal to 0.19 ?/Nm<3>, we obtain:

methane gas cost/day = 0.19x11,000 = 2,090 euro/day For a production of 10,000 m<2>/day, we therefore obtain a cost equal to 2090 ? 10000 ?0.21?/m<2 >(daily methane gas cost/m<2>) Therefore, in one year, considering an average of 340 working days, the total cost for methane gas is:

0.21 ? 340 ? 10,000 = 714,000.00 ?/year for productions of 10,000 m<2>/day. For a comparison on the calculation of the economic impact of the use of the atomizer in the tile production processes, you can also consider what emerges from the research published in 2005 in the report ?Costs by type and average revenues in the Italian ceramic tile industry? by Assopiastrelle, the national association of manufacturers of ceramic tiles and refractory materials. This research shows how in 2004 the cost of total thermal energy in the production of glazed porcelain, in particular, ? was estimated at an average of 0.76 ?/m<2>.

Considering that on average 44% of thermal energy consumption comes from the use of atomizers, starting from the Assopiastrelle data, we arrive at an estimate of the relative economic impact of around 0.33 ?/m<2>, therefore well higher than previously estimated.

As far as water consumption is concerned, the use of sprayers in production plants certainly involves a high ecological cost.

In fact, in known processes, the atomizer must extract about 27% of the initial water content from the slip. The extracted water? materially visible in the white plumes that emerge from the factories and which testify to how it is substantially dispersed in the environment.

Can you? calculate that about 0.45 liters of water/kg of mix are emitted into the atmosphere, i.e., considering about 21 kg of mix/m<2>, what? equivalent to 9.45 liters of water/m<2>. In a production line that produces 10,000 m<2>/day, can one? then calculate that they are issued, that is? dispersed, 94,500 liters of water/day, therefore 32,130,000 liters/year.

It should also be considered that dust also comes out of the atomizer chimney, in addition to the combustion fumes and the extracted water.

Through the use of suitable filtering media, such as bag filters, ? possible to reduce the emission levels, but not more than 20 mg/Nm<3>.

Although the emission value may appear very low, in reality, the enormous volumes of air involved, equal for example to about 140,000 Nm<3>/h in a 14,000 liter/h atomizer, involve a considerable emission of dust into the atmosphere with a high content of silica, therefore of particles, how ? known, very dangerous to health.

Approximately, for an atomizer of 14,000 litres/h, can one? to calculate:

approx. kg/h of dust.

The dust emitted by the ceramics are mainly silicon, whose effect on the lungs is? known to cause both silicosis, tuberculosis and tumours, as also emerges from the study by the National Health Service ?Evaluation of exposure to free crystalline silica in some production sectors in Emilia Romagna summary of results / NHS ? 2005?, in which, in particular, the high risks for workers in the ceramic tile manufacturing sector are highlighted. In addition to the workers? Inside the factories, ? It is important to consider the exposure of the population, and therefore the potential negative impacts on health, of the release of these harmful dusts into the atmosphere.

In the end, ? important to highlight how the production plants that include atomizers also emit high quantities? of CO2.

In practice, you can? consider, for example, that the Sassuolo district uses approximately 442,000,000 m<3 >of gas, the combustion of which produces 1.8 kg of CO<2 >for every m<3 >of methane. The approximate calculation of CO2 emitted by the atomizers? therefore of about 790,000 tons/year, equal to about 2,300 tons per day.

We are therefore dealing with considerable emissions, with a negative impact on the environment, which should not be overlooked.

Presentation of the invention

The task of the present invention ? that of solving the aforementioned problems, devising a method and a plant for the preparation of a granular mixture for the production of ceramic tiles which allows to minimize, in particular, the consumption of thermal energy and water.

In the context of this task, ? a further object of the invention is to provide a method and a plant for the preparation of a granular mixture for the production of ceramic tiles capable of minimizing the environmental impact, in particular with regard to the emission of dust and carbon dioxide.

Another purpose of the invention? that of providing a method and a plant for the preparation of a granular body for the production of ceramic tiles that are able to maximize energy savings.

A further purpose of the invention ? that of supplying a plant for the preparation of a granular mixture for the production of ceramic tiles of reduced size compared to plants of the known type, certainly reliable in operation, versatile in use, as well as? relatively cheap cost.

The aforementioned aims are achieved, according to the present invention, by the method for preparing a granular mixture for the production of ceramic tiles according to claim 1, as well as by the from the plant according to claim 8. The method according to the invention provides for preparing, according to a specific recipe, a quantity dosed of solid raw materials, suitable for the production of ceramic tiles.

The method then envisages proceeding with wet grinding of the recipe, by means of a known type of wet grinding apparatus, adding to this quantity? dosed a certain percentage by weight of water, in order to obtain a slip, then an aqueous suspension of particles of solid materials. This percentage by weight corresponds to an initial moisture content? of the slip, which can? for example be equal to, or included in an interval of a few percentage points around 35%.

According to an advantageous prerogative of the method, the slip is subsequently fed into a tank of a stirring group, containing a plurality of? of grinding bodies and operable in rotation along a longitudinal axis.

The method then provides for stirring, then homogenizing, and grinding the fed slip, by activating the tank in rotation around the longitudinal axis, thus obtaining a dough with a desired moisture content.

The method then envisages transferring the mixture obtained from the stirring group to a unit? granulator, to granulate the mix and obtain a granular mix suitable for the production of ceramic tiles.

The aforementioned tank? loaded with grinding bodies, for example spheres, preferably of sintered alumina.

The method can providing for the extraction, or sieving, of the mixture treated by the stirring unit by means of filtering means, for example cyclones.

The mixture obtained includes the same quantity dosed of solid materials and a quantity? residual water, that is? a desired content preferably around 2 - 5%.

According to a particular aspect, in the stage of shaking and grinding the method can? foresee the? further phase of regulating the humidity content? of the slip to obtain the desired content, by feeding a controlled flow, in particular counter-current, of an operating fluid through the tank by a heat recovery unit, configured to recover the operating fluid produced at outlet from a baking oven for the production of ceramic tiles, prepared in function, and/or by a cogeneration group arranged, in order to dry the slip and extract from it by evaporation a quantity in excess of water, cos? to obtain the dough with the desired moisture content.

In practice, the method pu? expect to separate from the slip the amount? in excess of water, by thermal separation means, through the same stirring group.

Preferably, therefore, the stirring group uses quotas of thermal energy made available through the heat recovery group from other phases of the tile production process, for example and mainly from the firing phase in the kiln.

Preferably the? Thermal energy recovered? in the form of hot air coming from the cooling areas of the cooking oven itself or from the flue gas outflow chimney.

The method can foresee, for the thermal extraction of the excess water, the use of recovered thermal energy produced alternatively, if for example the plant does not have a cooking oven, from a cogeneration group set up in the plant. By cogeneration group is meant a system for the production of electrical energy, comprising means such as for example turbines or endothermic engines, suitable for generating electrical energy, and for recovering the heat generated by them as exhaust gas and/or cooling air.

According to a particular aspect, the method pu? provide for the provision of an auxiliary device for feeding the thermal energy used to extract the aforesaid portion of excess water, for example comprising a burner which acts on the flow of operating fluid, in particular hot air, in a pipe of the heat recovery unit, for at least temporarily compensate for any lack of hot recovery air, due to production stops of the furnace or furnaces connected to it, or to the temporary shutdown of the aforementioned cogeneration group.

If necessary, according to a further particular aspect, the phase of separating the quantity? in excess of water by means of separation of the thermal type pu? be preceded by an intermediate phase, in which the separation of a part of the quantity? excess water to be extracted. The mechanical separation carried out in this intermediate phase, for example by means of a filter press or similar means, involves the reduction of the percentage of water in the slip, and the obtaining of a mixture with an intermediate humidity content, but still requires a subsequent phase, from part of the agitator group, to bring the humidity content? to the desired level. Furthermore, it must be considered that the water extracted mechanically in the aforementioned intermediate phase is rich in water-soluble substances, in particular salts. So it doesn't? directly reusable in the process, but preferably requires decantation or other processing to eliminate or reduce the content of these substances. For example, in the event that the salt content is greater than a certain threshold value, this extracted water is not? reused, but is disposed of.

The method can further comprise the step of chopping the dough with an intermediate moisture content using a chopping unit.

Furthermore, the method can understand the further phase of recovering at least in part the aforementioned quantity? in excess of water, extracting it by condensation from the stirring group, and to use it at least in part for the initial phase of preparation of the slip and/or for the phase of wetting and regranulating the mix. According to a prerogative of the invention, the stirring group comprises a rotary tank, with continuous or discontinuous operation.

According to a particular aspect, the method pu? provide advantageously to recover, at least in part, preferably totally, by means of condensation, the quantity? in excess of water possibly separated from the stirring unit, by means of a water recovery unit, and to reuse the condensate upstream of the process as grinding water in the wet grinding equipment. Through the water recovery group ? what? possible to recover a considerable part of the process water, for example estimated at around 60%.

The method allows to obtain a powder of suitable particle size, avoiding the use, for example, of a pin mill or similar means.

The method preferably envisages successively humidifying the powder obtained to a final humidity content of appropriate, for example between 6% and 8%, and to re-granulate it by granulating means of the known type.

This step makes it possible to obtain a granular mix which is suitable, in terms of physical shape and moisture content, for loading known type of forming equipment, such as, for example, presses for forming ceramic tiles.

The method can Finally, plan to store the granulated mixture in units? containers, silos for example, to allow their subsequent use, according to known operating steps in the ceramic tile production sector.

According to a particular embodiment, the method pu? provide for the further phase of feeding a further quantity into the tank of the agitator group? dosage of raw materials in powder obtained by dry grinding, thus forming? in this a semi-liquid mixture with a lower humidity content. In this case, the stirring unit optimizes the energy required to mix this semi-liquid mixture.

Basically, the method according to the invention has the advantage of avoiding the use of spray dryers or atomizers for extracting the water from the slip. There? involves a considerable saving in the consumption of energy resources and water, as well as? a considerable reduction in the environmental impact of ceramic production.

In practice, therefore, the method makes it possible to reduce the emission of extremely harmful dust with a high silica content, such as ? known, for the organism, and of CO2.

The plant according to the invention, adapted to implement the aforementioned method, comprises at least one apparatus for the wet grinding of a determined quantity? dosed solid raw materials of a mixture of a certain amount? dosed solid raw materials and a weight percent of water, according to an initial moisture content, for the production of a slip, an agitator unit connected to the wet grinding equipment and configured to agitate and grind the slip. The stirring unit comprises a tank containing a plurality of of grinding bodies, for example spheres, preferably of sintered alumina, and operable around a longitudinal axis, preferably substantially horizontal, to obtain from the slip a mixture with a desired moisture content.

The plant also includes a unit? granulator configured to receive the aforementioned mix from the agitator unit, so as to obtain a granular mix suitable for ceramic production.

The tank of the agitator unit ? configured to be fed with an operating fluid to extract by evaporation a quantity? in excess of water from the slip and get cos? a dough having the desired moisture content. The system can include at least one oven for baking the dough, configured to produce the heating operating fluid at the outlet, and/or a cogeneration group for the production of electricity, from which it is It is preferably possible to recover thermal energy, and a thermal recovery unit, configured to recover the operating fluid produced at the outlet of the cooking oven and, alternatively or additionally, from the cogeneration unit, so as to thus feed, at least partially, the agitator group.

The aforesaid tank preferably comprises a casing, for example a cylindrical one, which can be operated in rotation around the aforesaid longitudinal axis, preferably horizontal.

Advantageously, the stirring unit according to the invention can allow the regulation of? humidity? of the slip in a dynamic way, avoiding, thanks to the action of the grinding bodies, the aggregation of the material and, therefore, the necessity? of further treatments for its reduction to a fine powder, suitable for subsequent regranulation.

A further advantage lies in the fact that the dynamic effect of the grinding bodies achieves a further grinding of the material fed inside the stirring group according to the invention. There? therefore it allows to increase the granulometry of the slip coming out of the wet grinding equipment. Consequently, this equipment can produce a greater quantity? of slip to parity? of energy consumption.

The aforementioned method, according to the cited particular aspect, also allows to exploit considerable quantities of recovered thermal energy, at relatively low temperatures.

The mentioned particular aspect, for the regulation of the humidity? of the slip, also exploits the effect of the dragging motion operated by the agitator unit on the slip. In fact, thanks to this motion, the material to be dried has a higher speed? on the countercurrent, relatively to the operating fluid, optimizing cos? the heat exchange.

At the same time, the heating of the grinding elements and of the slip due to the effect of the preferably counter-current flow of operating fluid, according to the same particular aspect, produces its adhesion to the grinding elements and the subsequent detachment, due to the mechanical action of the same elements , which continually collide inside the casing.

The fed slip is continuously subjected, inside the agitator group, to the crushing action of the grinding bodies, thus to be reduced to the desired particle size.

At the same time the action of the grinding bodies to which ? continuously subjected the mixture determines the elimination of the evaporative boundary layer which is usually created between the material to be dried and the operating, drying fluid, thus facilitating? the drying process.

Furthermore, the action of the grinding bodies also determines the leakage of the interstitial water, thus making the interaction of the operating fluid with the water itself is possible, facilitating its evaporation.

The system can also understand? mechanical separation means, functionally interposed between the wet grinding apparatus and the agitator group, to extract a part of the aforementioned quantity from the slip. of excess water.

Preferably, the aforementioned mechanical separation means comprise a filter press or similar mechanical extraction means.

The system can further comprising a chopping unit for the dough separated from the slip, for example a sheeter or a reel mill or similar means.

The system can usefully include at least one water recovery group, configured to recover the aforementioned quantity? in excess of water, in particular extracted from the stirring unit.

Preferably the aforementioned water recovery group? configured to recover, by condensation, the amount? in excess of water or part of it, removed from the slip by means of the agitator unit.

The aforementioned water recovery group pu? feed in addition or alternatively the aforementioned unit? granulator.

The aforementioned plant is therefore more? compact and relatively more cost-effectiveness of a plant of the known type, for the production of ceramic tiles, in which atomizers are used.

Furthermore, the plant according to the invention minimizes energy expenditure, in particular the consumption of thermal energy, and the environmental impact, thus preserving the environment and the health of the population.

In fact, a considerable portion of the process water, which would otherwise be dispersed into the environment, is recycled and the emission of dust is reduced, which, on the other hand, is released into the environment in large quantities. high, even after filtering, from the chimneys of the atomizers in plants of the known type.

Brief description of the drawings

The details of the invention will become more apparent from the detailed description of a preferred embodiment of the method for preparing a granular body for the production of ceramic tiles, illustrated by way of example in the attached drawing, in which:

Figures 1 to 3 respectively show a flow diagram, representative of the operating steps envisaged by the method according to the invention, in different embodiments;

figure 4 schematically shows a plant for the production of ceramic tiles according to the invention;

figure 5 schematically shows a further embodiment of the plant for the production of ceramic tiles according to the invention. Embodiments of the invention

With particular reference to figures 1 and 4, the method according to the invention ? feasible, for example, by a plant 10 for the production of ceramic tiles comprising at least one unit 1 for dosing the raw materials, at least one apparatus 2 for the wet grinding of the raw materials, for the production of an aqueous suspension, usually denominated ? slip?, a mixing unit 3 of the slip, for obtaining a mixture having an amalgamated and, in particular, a desired moisture content. The plant also preferably comprises a heat recovery unit 4 of thermal energy, preferably coming from an oven 40 for cooking the mixture obtained and formed or, in addition or alternatively, from a possibly envisaged cogeneration unit 41.

Dosing unit 1, of known type, is configured to dose, by means of a continuous weighing system, the different raw materials of a given recipe for the production of ceramic tiles. The dosing group 1 therefore allows to obtain a quantity dosed with pre-established raw materials.

The wet grinding device 2, also known, can be made, for example, by a ball mill, configured to add to the quantity? dosed of raw materials dosed a certain percentage by weight of water, in order to obtain, after grinding, the slip. This percentage by weight can be equal to 35%, or included in an appropriate range, for example of a few percentage points, around this value. A high percentage of water in the slip makes wet grinding easier. There? ? convenient, in particular, if ? Is there sufficient thermal energy available to then reduce, in the successive phases described below, the humidity content? of the slip to the desired value for the mix. In cases where, however, ? the thermal energy available to subsequently reduce the humidity content is relatively small, then ? Is it possible to envisage introducing a more water content into the slip? low, for example around 30%, possibly inserting deflocculant substances.

Is the term ?water? used hereafter? to also mean an aqueous solution or mixture to which additives are added, to adjust certain properties? of the solution or mixture itself, or of the mixture to be obtained.

Wet grinding equipment 2 can be associated downstream with a sieving and iron removal unit 21 of a known type, to treat the ground slip in a suitable manner for the subsequent steps.

The stirring unit 3, located downstream of the wet grinding apparatus 2 and possibly to the unit 21, is configured to receive the slip in liquid form, with the portion of water deriving from wet grinding or, as described below, with a portion of water reduced from that of wet grinding, following an intermediate mechanical separation process. In this case, the slip with a reduced amount of water can eventually be minced, as described below, before being introduced into the stirring group (see figure 5).

Alternatively, the stirring unit 3 can be fed partially with slip in liquid form coming from wet grinding and partially with substances in powder form, produced in the known way by dry grinding.

The stirring unit 3 according to the invention primarily performs the function of stirring, then of mixing, the liquid mixture, in particular the slip, fed to it.

The stirring group 3 then performs a grinding function, thanks to the action of the grinding bodies.

Finally, the stirring group 3 can? preferably perform a regulating function of the humidity content? present in the feed mixture. Preferably it can consider adjusting this parameter from an initial input content to a desired final content, in particular by drying the feed mix.

Pi? precisely, the stirring group 3 comprises a particular tank which internally defines a chamber containing within it a plurality of of grinding bodies, for example spheres, preferably of sintered alumina.

The tank which forms the stirring group 3 according to the invention? operable in rotation, advantageously according to a horizontal axis, and ? preferably configured to be crossed by a flow of an operating fluid, preferably hot air. This flow of operating fluid ? preferably made available by the heat recovery unit 4, to adjust the humidity content? of the slip, in particular therefore to dry it properly.

The rotation of the tank produces the effect of dragging the grinding bodies into motion, together with the slip inserted inside the chamber. In practice, the rotation of the tank with the grinding bodies has the effect of agitating, in particular mixing, the slip.

The dragging of the grinding bodies also has the advantageous effect of grinding the slip.

Again, with regard to the aforementioned regulation function of the humidity level, when is the operating fluid? introduced inside the tank of the agitator group, contact with it can? produce adhesion of the slip to the bodies and to the internal wall of the chamber defined inside the tank itself. Subsequently, the grinding bodies exert a mechanical action on the slip and therefore it separates from the bodies themselves and from the internal wall of the chamber to then be extracted by the stirring group 3.

The rotary motion of the tank then has the effect of dynamically moving the slip inserted inside the chamber towards the operating fluid, increasing the speed? relationship between the slip and the operating fluid itself, therefore the effectiveness of the heat exchange in the context of the regulating function of the agitator group 3. Thanks to this dynamic action, the interaction between the slip driven into motion by the rotation of the tank and the flow operational does not present? gray areas?, but involves every part of the product.

Furthermore, again thanks to the aforementioned dragging motion, the grinding bodies exert a continuous crushing action on the product, thus tending to eliminate an evaporative boundary layer on the particles of the latter and increasing the thermal interaction with a drying effect.

The same squeezing action causes the interstitial water to come out, thus making direct interaction of water with the operating fluid is possible, thus facilitating its evaporation.

Furthermore, it should be noted that the motion in which the grinding bodies are dragged produces itself a quantity of heat, useful for contributing to the regulation of humidity? of the product placed inside the chamber.

Furthermore, the mechanical action of the grinding bodies allows to obtain a perfectly blended mixture, even if the tank is partially fed with product in liquid form, coming from wet grinding, and partially with product in powder form, coming from grinding dry, as described in detail below.

The stirring group 3, in particular, can forming a first casing, preferably cylindrical, which internally defines the chamber for containing the slip to be treated.

The stirring group 3 preferably also comprises a second casing, also preferably cylindrical, arranged externally to the first casing, so as to define with it an interspace, configured for the passage of the operating fluid. In that case? It is possible to operate, by feeding the operating fluid inside the interspace, the heating, substantially by conduction, of the first internal casing and, therefore, of the chamber and of what is contained therein.

Preferably the stirring unit 3 comprises valve means, configured to keep the chamber of the tank in a vacuum or semi-vacuum condition. In that case, can a condenser device should also be provided for the recovery of the evaporated water.

The agitator group 3 can? further comprising filtering means 31, for example of the type of a bag filter or a cyclone, for sucking in the operating fluid and recovering any residual dust leaving the stirring unit. The heat recovery unit 4 comprises means for conveying a flow of operating heating fluid leaving the cooking oven 40 and/or the cogeneration unit 41 which may possibly be present in the plant.

Regulator group 3 can? be advantageously associated with the aforementioned heat recovery unit 4, so to receive, at least in part, the thermal energy accumulated in the cooling air leaving the cooking oven 40 or other units, as described below.

The cooking oven 40 mentioned ? preferably of the known type, with rollers.

In particular, thanks to the aforementioned heat recovery unit 4 ? possible to recover, in a firing kiln of 10,000 m<2>/day, approximately 1,200,000 kcal/day using the cooling air which, in known plants, is instead expelled into the atmosphere.

The heat recovery group 4 can? fully recovering from the cooking oven 40 the thermal energy required by the process according to the invention.

For prudential purposes, ? For? It is possible to envisage associating the regulator unit 3 with an auxiliary device 42 for the production of thermal energy to meet a possible additional request or to serve in the event of failure or incomplete recovery from the cooking oven 40.

The plant 10 can? usefully also comprise a water recovery unit 5 which can be associated with an air flow at the outlet of the regulator unit 3, configured to extract from it, by means of a condensation device 51, a respective amount of water.

The water recovery unit 5 can? be associated with the regulator group 3, to recover the aforementioned quantity? of excess water or at least part of it, for reuse for example in the wet grinding apparatus 2.

The plant 10 can? also include a unit? wetting/granulating machine 6, to bring the dough, with the desired moisture content, to a physical form suitable for forming in known equipment, such as presses.

For this forming, in fact, particular physical characteristics are required, for example the flowability of the powders and humidity.

The plant 10 can? otherwise? include, in the section dedicated to the preparation, containment means of a known type, such as silos, in which the pulverized and granulated material can be stored until used in the production process.

The plant 10 can? further comprise a dust recovery unit 7, configured to convey the dust recovered from the filtering means 31 or from other parts of the plant, for example from the recovery of broken or unfired tiles, from storage silos, from presses, inserting them in percentages suitable for subsequent firing during the slip mixing stage.

The method for preparing a granulated body for the production of ceramic tiles, according to the invention, and the operation of the plant which implements it are easily understood from the preceding description.

The method according to the invention envisages arranging the apparatus 2 for the wet grinding of raw materials suitable for the preparation of a granular mixture.

The furnace 40 for firing ceramic products is also preferably set up for operation.

In a first phase of preparation, according to a specific recipe, the quantity is prepared. dosed of solid raw materials, suitable for the production of ceramic tiles.

The quantity of the product is then mixed and ground using the wet grinding apparatus 2. dosed of raw materials with the determined percentage by weight of water, in order to obtain the ground slip.

Subsequently the humidity content? of the ground slip is regulated by the regulator unit 3 according to the invention, using the operating fluid, in particular hot air, preferably recovered by the heat recovery unit 4 at the outlet of the prearranged cooking oven 40, preferably coming from cooling areas of the cooking oven 40. In addition, the regulator group 3 can? provide to be powered by the auxiliary power supply device 42, to make up for the lack or variations in availability? of thermal energy recovered from the furnace 40 and/or from the cogeneration group 41, if present.

The method can foresee to operate, through the aforementioned water recovery group 5, the recovery of this quantity? of excess water, extracting it, by means of condensation, during the drying process.

Furthermore ? it is possible to draw in the operating fluid, in particular air, leaving the regulator unit 3, and to filter it through the filtering means 31, to recover any residual dust.

? it is further possible to activate the dust recovery unit 7, configured to convey the dust recovered from the aforementioned filtering means 31, as well as from other phases of the plant, for example from the recovery of broken, unfired tiles, from storage silos, from presses , in percentages suitable for subsequent firing, adding them when mixing the slip.

The method can preferably plan to pulverize, wet and regranulate the dried mixture through the unit? wetting/granulating machine 6. In particular, ? is it possible to reuse the aforementioned quantity? in excess of water, once recovered, to wet the dried and pulverized mixture, in the granulation phase.

Is it obtained like this? a granular mix suitable for subsequent shaping.

The method can Finally, plan to store the granulated mixture in units? containment, silos for example, to allow their subsequent use.

According to a workaround, ? It is possible to envisage that the method is implemented by a plant for the production of a granular mixture for the production of ceramic tiles, comprising, in addition or as an alternative to a cooking oven 40, a cogeneration group 41, configured to produce and recover energy thermal.

In that case, ? It is possible to envisage that the heat recovery unit 4 is fed by the thermal energy produced by the cogeneration unit 41, to produce the drying process which generates the desired mix at the output of the regulator unit 3.

For the rest, as far as applicable, the method does not differ from what was previously described.

The plant that can? implement the method according to this alternative solution pu? produce the dried dough, advantageously even in the absence of an operating baking oven 40.

According to a further embodiment illustrated in figures 2 and 5, the system 10?, otherwise similar to what has been described previously, can further comprise a mechanical separation unit 8 of the excess water from the slip, interposed between the wet grinding apparatus 2 and the regulator unit 3.

The mechanical separation group 8 ? instead configured to mechanically separate the solid part of the slip from a quantity? in excess of water, therefore leaving the wet grinding apparatus 2.

The mechanical separation group 8 can? be made using a known type of filter press or equivalent equipment.

The mechanical separation group 8 can? be configured to reduce the slip to a mixture in which the share by weight of water ? reduced to at least 18%.

? should be noted that the part of water extracted mechanically from the slip can? transport salts and other water-soluble substances. If the excess water was extracted by evaporation, these substances would remain in the mix and would subsequently be ceramicised during the firing process.

To reuse the excess water extracted mechanically from the slip ? it is therefore necessary to carry out a treatment by means of flocculation and/or decantation, as well as to properly dispose of the residual substances.

The aforementioned water recovery unit 5 can? what? be associated also? to the mechanical separation group 8, for the recovery of a further quantity? of excess water, separated from the slip.

The plant 10? can? further comprise a chopping unit 9, interposed between the mechanical separation unit 8, if provided, and the regulator unit 3 (see figure 3). For example, the shredder group 9 can? be made using a sheeter or a reel mill or other known equipment, suitable for the purpose.

The chopping unit 9 reduces the mixture resulting from the mechanical separation of part of the excess water to a size suitable for introduction into the regulator unit 3 according to the invention.

As regards the implementation of the method according to the invention according to this embodiment , described with reference to the further embodiment described for the plant 10?, in addition to what has been previously described ? It is possible to envisage that between the mixing of the slip and the relative drying by means of the regulator group 3, a preliminary extraction phase of a part of the excess water is interposed, for example by means of the aforementioned mechanical extraction group 8. After the partial extraction of the ?excess water, through the mechanical extraction unit 8, ? is it possible to predict that the mixture is cos? obtained is reduced to a smaller particle size, by means of the cited shredding unit 9.

The method can provide advantageously to recover, at least in part, the part of the quantity? in excess of water separated mechanically, by means of the water recovery group 5, and to reuse it, for example, for mixing a new slip.

Alternatively, as shown in Figure 3, ? It is possible to provide for feeding the regulator unit 3 with a mixture in semi-liquid form, resulting from the slip obtained from the grinding performed by the wet grinding apparatus 2, and from a material in powder form, produced by a dry grinding apparatus. In this case, the rolling of the grinding bodies of the regulator unit 3 produces a dynamic effect which allows both the dry product and the wet product to be optimally mixed, so as to obtain a homogeneous mixture.

It should be noted that the mixing of the two portions of mixture, dry and wet, is particularly difficult. However, thanks to the primary dynamic action of the grinding bodies driven into rotation, the stirring group 3 can carry out its dynamic action on the mixture, obtaining an optimal mixing with minimum energy consumption.

Advantageously, in this case the quantity? of humidity? introduced overall in the mixture to be mixed is less, cos? to get more easily for the final mix the humidity content? desired ending.

In that case? Is it possible to predict that the humidity content? of the mixture introduced into the tank is close to or substantially equal to the humidity content? desired. Consequently, can be modulated in a corresponding way the flow of operating fluid in the tank, cos? to further reduce or maintain this humidity content?. In the latter case, when not ? Is it necessary to reduce the humidity content? inside the tank, a quantity? of supplementary water can? possibly be added only in the granulation phase.

The method according to the invention therefore achieves the aim of reducing heat consumption and the environmental impact of the ceramic tile production process. The method for preparing a granular body for the production of ceramic tiles according to the present invention therefore achieves the aim of minimizing, in particular, the consumption of thermal energy and water, thus maximizing energy saving.

Furthermore, the method according to the invention and the plant which implements it are capable of minimizing the environmental impact, in particular by considerably reducing the emissions of dust and carbon dioxide.

The system described by way of example ? susceptible to numerous modifications and variations according to different needs.

In the practical implementation of the invention, the materials used, as well as the shape and dimensions can be any according to the needs.

Where the technical characteristics mentioned in each claim are followed by reference marks, such reference marks have been included for the sole purpose of enhancing the understanding of the claims and consequently they are not limiting on the scope of each element identified by way of example by these reference marks.

Claims (18)

Claims 1. Method for the preparation of a granular body for the production of ceramic tiles, including the following steps: to. prepare a quantity? dosed of solid raw materials; b. grind by means of an equipment (2) for wet grinding said quantity? dosed solid raw materials, adding to it a determined percentage by weight of water, in order to obtain a slip with an initial humidity content; c. to feed said slip inside a tank of an agitator group (3), containing a plurality? of grinding bodies and operable in rotation along a longitudinal axis; d. agitate and grind said slip fed, activating said tank in rotation around said longitudinal axis, thus obtaining? a dough with a desired moisture content; And. transferring said mixture from said stirring group (3) to a unit? granulator (6), to granulate said mixture and obtain a granular mixture suitable for the production of ceramic tiles. 2. Method according to claim 1, characterized in that said desired humidity content? ? less than 10%, preferably between 2 and 5% by weight. 3. Method according to claim 1 or 2, characterized in that said step of d. shake and grind provides for the further step of regulating said humidity content? of said slip to obtain said desired content, feeding a controlled flow of an operating fluid, in particular against the current, through said tank by means of a heat recovery unit (4), configured to recover said operating fluid produced at the outlet from a furnace firing (40) for the production of said ceramic tiles, set up for operation, and/or by a cogeneration unit (41) set up, so as to dry said slip and extract from it by evaporation a quantity in excess of water, cos? to obtain said dough at said desired moisture content; 4. Method according to claim 3, characterized in that between step b. grind and phase c. feed said slip into said stirring group (3), ? the intermediate stage is foreseen to separate a part of said quantity? in excess of water from said slip, by means of a mechanical separation group (8), to obtain a mixture with an intermediate humidity content? to be fed inside said stirring group (3). 5. Method according to claim 4, characterized in that following the step of separating said part of said quantity? in excess of water comprises the further step of chopping said dough by means of a chopping unit (9). 6. Method according to one of the claims from 3 to 5, characterized in that it comprises the further step of recovering at least in part said quantity? in excess of water, extracting it by condensation from the stirring unit (3), and to use it at least in part for step b. add to that amount? dosed of raw materials a certain percentage by weight of water and/or for the phase of e. wet and regranulate said mixture. 7. Method according to claim 1, characterized in that said step of c. feeding said slip inside said tank of said agitator group (3) comprises the further step of feeding a further quantity? dosed of raw materials in powder obtained by dry grinding. 8. Plant for the preparation of a granular mixture for the production of ceramic tiles, comprising at least one apparatus (2) for the wet grinding of a mixture of a determined quantity? dosed of solid raw materials and a percentage by weight of water, to obtain a slip, a stirring group (3) connected to said equipment (2) for wet grinding to receive said slip and configured to stir and grind said slip, said stirring group (3) comprising a tank containing a plurality? of grinding bodies, preferably of sintered alumina, and operable in rotation around a longitudinal axis, to obtain from said slip a mixture with a desired humidity content, a unit? granulator (6) configured to receive said mixture from said stirring group (3), so as to obtain a granular mixture suitable for the production of ceramic tiles. 9. Plant according to claim 8, characterized in that said longitudinal axis of said tank ? essentially horizontal. 10. Plant according to claim 8 or 9, characterized in that said tank is configured to be fed with a preferably counter-current flow of an operating fluid to evaporate an amount in excess of water from said slip and get cos? a mixture having said desired humidity content, said plant comprising at least one oven for cooking (40) of said mixture, configured to produce said heating operating fluid, and/or a cogeneration group (41) for the production of thermal energy, and a heat recovery unit (4), configured to recover said operating fluid output from said cooking oven (40) and, alternatively or in addition, from said cogeneration unit (41), so as to thus feeding, at least partially, said stirring group (3). 11. Plant according to claim 10, characterized in that said tank of said stirring group (3) comprises an internal casing defining a chamber for receiving said slip, and a further casing, external to said casing, a cavity being defined between said casing and said further casing, for receiving said operating fluid. 12. Plant according to claim 11, characterized in that said stirring group (3) comprises valve means configured to create a vacuum or semi-vacuum condition inside said casing. 13. Plant according to one of the claims from 10 to 12, characterized in that said stirring group (3) comprises condensation means for extracting said quantity? in excess of water from said slip fed inside said casing in a vacuum or semi-empty condition. 14. Plant according to one of claims 10 to 13, characterized in that it further comprises a group for the mechanical separation (8) of an excess portion of the water of said slip, interposed between said wet grinding apparatus (2) and said stirring group (3), said mechanical separation group (8) comprising a filter press or equivalent means. 15. Plant according to claim 14, characterized in that it further comprises a chopping unit (9) for said slip subjected to mechanical separation of water, said chopping unit (9) comprising a sheeter or a reel mill or similar means. 16. Plant according to claim 10 or 15, characterized in that it comprises at least one water recovery group (5), configured to recover said quantity? in excess of water, extracted from said stirring group (3) and fed it to said apparatus (2) for wet grinding and/or to said unit? wetting/granulating machine (6). 17. Plant according to one of the preceding claims, characterized in that it comprises an apparatus for dry grinding, configured to feed said stirring group (3) with a quantity dosed raw material powder. 18. Plant according to one of the preceding claims, characterized in that said desired humidity content? ? less than 10%, preferably between 2 and 5%.