Facility and method for the forced carbonation of a fine fraction of a recycled concrete

Abstract

The invention relates to a facility (1) for the forced carbonation of a fine fraction of a recycled concrete, the facility comprising: - a carbonation reactor (2) in which the fine fraction is able and intended to be brought into contact with a carbon dioxide-containing gas; - a first, water-spraying device (11) capable of increasing the moisture content of the fine fraction; - a conditioning device (16) capable of managing the temperature and relative humidity of the carbon dioxide-containing gas, the facility comprising a computer control unit (6) capable of controlling the first, spraying device (11) and the device (16) for conditioning the carbon dioxide-containing gas.

Description

[0001] DESCRIPTION

[0002] TITLE: Installation and process for forced carbonation of a fine fraction of recycled concrete

[0003] Technical field of the invention

[0004] The invention relates to an installation and a method for forced carbonation of a fine fraction from a previous process for dissociating recycled concrete. More specifically, the invention relates to an installation and a method for trapping carbon dioxide in recycled concrete.

[0005] Technical background

[0006] Carbon dioxide is a greenhouse gas. The amount of carbon dioxide gas in the Earth's atmosphere has an impact on climate change.

[0007] There are several techniques for reducing carbon dioxide emissions. One of these techniques involves trapping carbon dioxide in recycled concrete, particularly from the deconstruction of old buildings or structures.

[0008] Recycled concretes contain hydrated cement paste. Hydrated cement paste can, to some extent, be used as a carbon dioxide sink. In other words, hydrated cement paste can be used to capture carbon dioxide by coming into direct contact with it, thereby reducing the amount of this greenhouse gas in the atmosphere. In order to properly charge these recycled concretes with carbon dioxide, they are exposed to carbon dioxide for several hours. This is incompatible with an industrial production rate.

[0009] Aware of the problem, and in order to achieve industrial production rates, attempts have been made to reduce the exposure time of the fine fraction to carbon dioxide to a few dozen minutes. Mixers designed to create agitation have been used, however, the rate of carbon dioxide capture of recycled concrete has proven insufficient, reducing the efficiency of the process and therefore the interest of these operations.

[0010] Thus, current techniques remain perfectible. The challenge is to be able to charge recycled concrete with carbon dioxide at industrial rates, that is, in a few dozen minutes at most. The objective is to remove the technological barrier that hinders the use of recycled concrete by industrialists as a carbon dioxide sink.

[0011] Summary of the invention

[0012] For this purpose, a forced carbonation installation for a fine fraction of recycled concrete is proposed firstly, the installation comprising:

[0013] - a carbonation reactor in which the fine fraction is suitable and intended to be brought into contact with a gas containing carbon dioxide,

[0014] - a first water spraying device capable of increasing the humidity level of the fine fraction, and

[0015] - a conditioning device capable of managing the temperature and relative humidity of the gas containing carbon dioxide, the installation comprising a computer control unit capable of controlling the first spraying device and the device for conditioning the gas containing carbon dioxide.

[0016] Various additional features may be provided alone or in combination:

[0017] - the first spraying device is arranged upstream of the carbonation reactor in the direction of movement of the fine fraction or inside said carbonation reactor in the vicinity of the inlet of the fine fraction;

[0018] - the installation comprises a first device for measuring the humidity level in the fine fraction, said first measuring device being arranged upstream of the carbonation reactor, in the direction of movement of the fine fraction;

[0019] - the installation comprises a second device for measuring the relative humidity and / or the temperature of the gas in the carbonation reactor;

[0020] - the installation comprises a circuit for injecting gas containing carbon dioxide into the carbonation reactor, said circuit for injecting gas containing carbon dioxide being fluidically connected to a supply of fumes from combustion;

[0021] - the carbon dioxide gas injection circuit comprises, arranged in the following order according to the direction of movement of the carbon dioxide gas:

[0022] - an outlet dryer intended to dry the fine carbonated fraction at the outlet of the carbonation reactor,

[0023] - an air separation device capable of separating the gas containing carbon dioxide on the one hand from the fine carbonated and dried fraction on the other hand, said separation device comprising a first outlet through which the fine carbonated and dried fraction is intended to be evacuated,

[0024] - a volumetric distribution system capable of managing the volume of gas containing carbon dioxide sent to the carbonation reactor,

[0025] - a device for conditioning the gas containing carbon dioxide capable of modifying the relative humidity and / or the temperature of the gas containing carbon dioxide,

[0026] - a device for injecting gas containing carbon dioxide into the carbonation reactor.

[0027] The invention secondly relates to a method for forced carbonation of a fine fraction from recycled concrete, this method being capable of implementing an installation as previously described, the method comprising the following steps:

[0028] - a step of conditioning the fine fraction so that said fine fraction has a predetermined humidity level substantially equal to a set value, and

[0029] - a step of conditioning the gas containing carbon dioxide so that the relative humidity and / or the temperature of said gas are substantially equal to set values,

[0030] - a step of feeding the carbonation reactor with the fine fraction coming from recycled concrete comprising hydrated cement paste, said fine fraction having a particle size less than or equal to 16 millimeters, said fine fraction having been previously conditioned during the step of conditioning the fine fraction,

[0031] - a step of injecting the gas containing carbon dioxide into the carbonation reactor, said gas having been previously conditioned during the gas conditioning step,

[0032] - a carbonation step of the fine fraction in the carbonation reactor.

[0033] Various additional features may be provided alone or in combination:

[0034] - the method comprising a step of measuring the humidity level in the fine fraction, the measurement being compared to a set value, method in which the quantity of water injected upstream of the carbonation reactor is adjusted so that the humidity level in the fine fraction is substantially equal to the set value;

[0035] - method comprising a step of measuring the relative humidity and / or the temperature of the gas in the carbonation reactor, the measurement(s) each being compared to a set value, in which method the relative humidity and / or the temperature of the gas containing carbon dioxide is or are modified during the gas conditioning step so that the relative humidity and / or the temperature in the carbonation reactor is or are each substantially equal to the set value;

[0036] - method comprising a step of drying the fine fraction using fumes from combustion at the outlet of the carbonation reactor, the fine fraction being dried after having been carbonated;

[0037] - the carbon dioxide injected into the carbonation reactor comes from fumes from combustion;

[0038] - the process comprises an air separation step carried out using the air separation device, during which step the fine dry and carbonated fraction is separated from the fumes;

[0039] - the method comprises a volumetric distribution step so as to send a predetermined quantity of carbon dioxide to the gas conditioning device;

[0040] - the temperature in the carbonation reactor is between 30°C and 80°C, preferably 40°C;

[0041] - the relative humidity of the gases in the carbonation reactor is between 40% and 100%;

[0042] - the residence time of the fine fraction in the carbonation reactor is between 20 minutes and 120 minutes;

[0043] - the pressure inside the carbonation reactor is substantially equal to atmospheric pressure; - the fine fraction has a particle size less than or equal to 6 millimeters.

[0044] Brief description of the figures

[0045] Other characteristics and advantages of the invention will appear during the reading of the detailed description which follows for the understanding of which one will refer to the attached drawing in which:

[0046] [Fig 1] Figure 1 is a schematic representation of an installation according to the invention.

[0047] Detailed description of the invention

[0048] Figure 1 shows a forced carbonation plant 1. Plant 1 comprises a carbonation reactor 2. Carbonation reactor 2 is intended to receive a fine fraction of recycled concrete. Carbonation reactor 2 is capable of bringing the fine fraction into contact with carbon dioxide.

[0049] "Recycled concrete" means concrete from the deconstruction of buildings or civil engineering structures, as well as waste from concrete production units, for example, but not limited to, tank washing residues and mixer bottoms.

[0050] A fine fraction corresponds to the fraction of recycled concrete that has been attritioned or ground and whose particle size is less than or equal to 16 millimeters. The fine fraction advantageously has a particle size less than or equal to 6 millimeters. The carbonation reactor 2 has an inlet 9 through which the fine fraction enters and an outlet 10 through which the fine fraction is discharged.

[0051] The installation 1 comprises a first water spraying device 11 capable of spraying water onto the fine fraction. In Figure 1, the first spraying device 11 is arranged upstream of the carbonation reactor 2 in the direction of movement of the fine fraction. According to an alternative embodiment not shown, the first spraying device 11 is arranged inside the carbonation reactor 2, in the vicinity of the inlet 9.

[0052] The first spraying device 11 is fluidically connected to a water tank 3.

[0053] The first spraying device 11 makes it possible to spray water directly onto the fine fraction so as to increase its humidity level.

[0054] By acting on the humidity level of the fine fraction at the inlet 9 of the carbonation reactor 2, the fine fraction is placed in the best conditions to be charged with carbon dioxide during its stay in said carbonation reactor 2. By conditioning the fine fraction so as to obtain an optimal humidity level in it, the chemical reactivity of the carbon dioxide with the fine fraction in the carbonation reactor 2 is improved. It thus becomes possible to obtain carbonation of the fine fraction at an industrial rate.

[0055] Advantageously, the installation 1 comprises a first device 7 for measuring the humidity level of the fine fraction. The measuring device 7 is arranged upstream of the carbonation reactor 2. The measuring device 7 is arranged upstream of the spraying device 11 as shown in FIG. 1. In a variant not shown in FIG. 1, the measuring device 7 can be arranged downstream of the spraying device 11. It is a sensor capable of communicating the data obtained at the unit 6 in real time.

[0056] The fine fraction initially has a moisture content less than or equal to a determined set value. By "initially" is meant before the first spraying device 1 1 in the direction of movement of the fine fraction.

[0057] The carbonation reactor 2 is in the form of a rotating drum 4. The rotating drum 4 is driven in rotation by means of at least one motor, not shown in the drawings.

[0058] Advantageously, the installation 1 comprises a computer control unit 6. The unit 6 makes it possible to control the installation 1.

[0059] Advantageously, the installation 1 comprises a second device 8 for measuring the relative humidity and the temperature of the gases in the carbonation reactor 2. This is a sensor measuring the relative humidity and the temperature of the gases in the carbonation reactor 2 and capable of communicating the data obtained to the unit 6 in real time.

[0060] Advantageously, the installation 1 comprises an outlet dryer 13. The outlet dryer 13 is capable of drying the fine carbonated fraction. Drying the fine carbonated fraction makes it suitable for transport and storage.

[0061] The outlet dryer 13 is arranged at the outlet 10 of the carbonation reactor 2. The outlet dryer 13 thus arranged is capable of drying the fine carbonated fraction as soon as it leaves the carbonation reactor 2. Advantageously, the outlet dryer 13 is fluidically connected to a supply 14 of fumes from a combustion. This combustion is for example that of the burner of a cement kiln. Thus the fumes from the kiln, loaded with carbon dioxide, are cooled in the outlet dryer 13 and at the same time humidified. This has an advantage because these fumes contain carbon dioxide and will be brought into contact with the fine fraction in the carbonation reactor 2 as will be described later. The applicant has in fact determined after testing that the carbonation reaction is more efficient when the carbon dioxide is at a low temperature.

[0062] Advantageously, the installation 1 comprises a circuit 60 for injecting gas containing carbon dioxide. This circuit 60 comprises, arranged in the following order according to the direction of movement of the fumes:

[0063] - an outlet dryer 13,

[0064] - an air separation device 17,

[0065] - a volumetric distribution system 20,

[0066] - a device 16 for conditioning the gas containing carbon dioxide,

[0067] - a device 15 for injecting gas containing carbon dioxide.

[0068] The elements 13, 17, 20, 16, 15 are successively connected to each other in a fluid manner.

[0069] The circuit 60 is fluidically connected to a flue gas supply 14. Thus the flue gases are conveyed to the carbonation reactor 2 and injected into it.

[0070] The installation 1 advantageously comprises an air separation device 17 arranged downstream of the fine fraction outlet dryer 13 in the direction of movement of the fumes and the fine fraction represented by the arrow 24. From the outlet dryer 13, the fumes transport the fine fraction to the air separation device 17. The air separation device 17 makes it possible to separate the fine fraction from the fumes. At a first outlet 18 of the air separation device 17, the carbonated fine fraction is evacuated while at a second outlet 19 of the air separation device 17, the fumes are sent towards the conditioning device 16. The air separation device 17 is advantageously of the cyclone type and may additionally comprise a dynamic separator.

[0071] Advantageously, the installation 1 comprises a volumetric distribution system 20. The volumetric distribution system 20 is arranged between the air separation device 17 and the conditioning device 16. The volumetric distribution system 20 makes it possible to manage the volume of fumes sent to the device 15 for injecting gas into the carbonation reactor 2 in order to send only the necessary quantity of fumes into said carbonation reactor 2. Thus, only the fumes that will be conveyed to the carbonation reactor 2 are conditioned. The rest of the fumes are evacuated to an exhaust.

[0072] The conditioning device 16 makes it possible to regulate the humidity level and the temperature of the gas containing carbon dioxide. Indeed, since relative humidity and temperature are important factors in the carbonation reaction, their management is carried out optimally using the conditioning device 16.

[0073] By optimizing the temperature and relative humidity of the gases in the enclosure of the carbonation reactor 2, the carbonation reaction is accelerated, which makes it possible to reduce the residence time of the fine fraction in said carbonation reactor 2.

[0074] The increase in the relative humidity of the gas is achieved directly by adding water or water vapor. The reduction in the relative humidity of the gas is obtained by condensation of the water vapor. The conditioning device 16 is thus fluidically connected to the water tank 3 in particular so that said device 16 can draw water therefrom. Advantageously, the conditioning device 16 is capable of cooling and heating the gas containing carbon dioxide to obtain an optimal temperature. The conditioning device 16 is thus capable of modifying the temperature of the gas containing carbon dioxide.

[0075] The conditioning device 16 is arranged between the volumetric distribution system 20 and the gas injection device 15. The conditioning device 16 thus arranged makes it possible to manage the relative humidity and the temperature of the gas containing carbon dioxide before said gas is injected into the carbonation reactor 2.

[0076] In a preferred embodiment, the carbonation reactor 2 has a length substantially equal to 15 meters and a diameter of 1.6 meters. The carbonation reactor 2 is arranged so as to form an angle substantially equal to 2 degrees with the horizontal. The rotation speed is substantially equal to 1.5 revolutions per minute.

[0077] In the following a forced carbonation process using the installation will be described.

[0078] The fine fraction arrives in the installation 1 via an inlet 22. The process includes a step of conditioning the fine fraction. The fine fraction has a particle size less than or equal to 16 millimeters. The fine fraction results from the grinding or attrition of recycled concrete. The fine fraction of recycled concrete, that is to say that whose particle size is less than 16 millimeters, is used for carbonation because its properties are suitable for loading with carbon dioxide. The particle size of the fine fraction is advantageously less than or equal to 6 millimeters, its properties then being optimal for loading with carbon dioxide. The fine fraction comprises hydrated cement paste. This hydrated cement paste has carbon dioxide capturing properties. This step of conditioning the fine fraction consists of managing the humidity level of the fine fraction upstream of the carbonation reactor 2.The humidity level is managed via a water injection operation on the fine fraction. The water injection operation upstream of the carbonation reactor 2 is carried out by means of the first spraying device 11 which makes it possible to spray the fine fraction with water. This conditioning of the fine fraction makes it possible to improve its carbon dioxide capture properties.

[0079] Advantageously, the method comprises a step of conditioning the gas containing carbon dioxide. During this conditioning step, the gas containing carbon dioxide is conditioned by regulating its temperature and its relative humidity in order to obtain an optimal temperature and relative humidity in the carbonation reactor 2. This step is carried out by means of the conditioning device 16. The relative humidity corresponds to the ratio of the partial pressure of the water vapor and the saturated vapor pressure in the carbonation reactor 2. The challenge is therefore to maintain an optimal temperature and relative humidity in the carbonation reactor 2 in order to increase the kinetics of carbon dioxide capture by the fine fraction. The method comprises a step of feeding the carbonation reactor 2 with the fine fraction conditioned during the step of conditioning the fine fraction.

[0080] Advantageously, the method comprises a step of injecting the gas containing carbon dioxide into the carbonation reactor 2. In the embodiment shown in the drawing, fumes from combustion in a furnace and containing carbon dioxide are injected into the carbonation reactor 2.

[0081] Advantageously, the method comprises a step of carbonation of the fine fraction in the carbonation reactor. This step is carried out by bringing the fine fraction into direct contact with the gas containing carbon dioxide in the carbonation reactor 2.

[0082] The method advantageously comprises a step of measuring the moisture content in the fine fraction. This step is carried out by means of the first device 7 for measuring the moisture content in the fine fraction. The measurements obtained are sent to the control unit 6.

[0083] Control unit 6 compares the measurements with a predetermined setpoint value. Several scenarios can then appear:

[0084] - the measured humidity level is lower than the set value, the control unit 6 then commands the first spraying device 11 to spray water onto the fine fraction;

[0085] - the measured humidity level is equal to the set value, the control unit 6 commands the first injection device not to spray water on the fine fraction.

[0086] The method advantageously comprises a step of measuring the relative humidity and the temperature in the carbonation reactor 2 by means of the second measuring device 8. The measurements obtained are sent to the control unit 6. The control unit 6 compares the measurements with set values. The control unit 6 then commands the conditioning device 16 to condition the gas containing carbon dioxide so that its relative humidity and its temperature are substantially equal to said set values.

[0087] Advantageously, the relative humidity in the carbonation reactor 2 is between 40% and 100%. The set value of the relative humidity is thus included in this range. The applicant has determined that a relative humidity included in this range makes it possible to obtain carbonation reaction kinetics that are sufficiently rapid to obtain industrial rates.

[0088] Advantageously, the temperature in the carbonation reactor 2 is between 30 and 80°C. The temperature setpoint is thus within this range. The applicant has determined that a temperature within this range makes it possible to obtain carbonation reaction kinetics that are sufficiently rapid to achieve industrial production rates.

[0089] When the fine fraction has completed its stay in the carbonation reactor 2 and is therefore carbonated, it is dried by means of the outlet dryer 13. As previously mentioned, the hot gas used in the outlet dryer 13 and which passes through the material, comes from combustion, for example that of a cement kiln.

[0090] With reference to Figure 1, the fumes leaving the outlet dryer 13 transport the fine fraction to the air separation device 17. The fine carbonated and dry fraction is evacuated through the first outlet 18. The fumes are evacuated through the second outlet 19.

[0091] The method comprises a step of volumetric distribution of the fumes. At the outlet of the air separation device 17, the fumes are sent to the volumetric repair system 20. During this step, the volumetric distribution device sends a given quantity of fumes to the conditioning device 16. The remainder of the fumes is evacuated through an exhaust 25. Indeed, it is advantageous to condition only the necessary quantity of fumes in order to maximize the overall efficiency of the installation.

[0092] At the outlet of the volumetric distribution system 20, the fumes are sent to the conditioning device 16 in order to regulate their relative humidity and their temperature. Indeed, and to the extent that the fumes are used as gas containing carbon dioxide in the carbonation reactor 2, it is advantageous to condition them to obtain the favorable and optimal conditions for the carbonation reaction in the carbonation reactor 2.

[0093] The combustion fumes, previously conditioned and then decarbonized, i.e. discharged at least in part of their carbon dioxide in the carbonation reactor 2, are then evacuated by an exhaust outlet not shown in FIG. 1. In an alternative embodiment, the decarbonized fumes can be sent to another element of the installation.

[0094] Advantageously, the residence time of the fine fraction in the carbonation reactor 2 is between 20 minutes and 120 minutes. This duration is acceptable in the context of industrial production and allows, within the framework of the invention, a carbon dioxide loading rate of the fraction sufficient in quantity. Advantageously, the pressure in the carbonation reactor 2 is substantially equal to atmospheric pressure. The installation 1 is thus made less dangerous, less complex and less expensive than a pressurized installation.

[0095] Advantageously, the fumes comprise at least 5% carbon dioxide by mass or volume. Such fumes allow an efficient carbon dioxide loading rate in terms of quantity and speed.

Claims

CLAIMS 1. Installation (1) for forced carbonation of a fine fraction of recycled concrete, the installation comprising: - a carbonation reactor (2) in which the fine fraction is suitable and intended to be brought into contact with a gas containing carbon dioxide, - a first water spraying device (11) capable of increasing the humidity level of the fine fraction, and - a conditioning device (16) capable of managing the temperature and relative humidity of the gas containing carbon dioxide, the installation comprising a computer control unit (6) capable of controlling the first spraying device (11) and the device (16) for conditioning the gas containing carbon dioxide.

2. Installation (1) according to claim 1 in which the first spraying device (11) is arranged upstream of the carbonation reactor (2) in the direction of movement of the fine fraction or inside said carbonation reactor (2) in the vicinity of the inlet of the fine fraction.

3. Installation (1) according to any one of claims 1 or 2, in which it comprises a first device (7) for measuring the humidity level in the fine fraction, said first measuring device (7) being arranged upstream of the carbonation reactor (2), in the direction of movement of the fine fraction.

4. Installation (1) according to any one of the preceding claims, in which it comprises a second device (8) for measuring the relative humidity and / or the temperature of the gas in the carbonation reactor (2).

5. Installation (1) according to claim 4, in which it comprises a circuit (60) for injecting gas containing carbon dioxide into the carbonation reactor (2), said circuit (60) for injecting gas containing carbon dioxide being connected fluidically to a supply (14) of fumes from combustion.

6. Installation (1) according to claim 5 in which the circuit (60) for injecting gas containing carbon dioxide comprises, arranged in the following order according to the direction of movement of the gas containing carbon dioxide: - an outlet dryer (13) intended to dry the fine carbonated fraction at the outlet of the carbonation reactor (2), - an air separation device (17) capable of separating the gas containing carbon dioxide on the one hand from the fine carbonated and dried fraction on the other hand, said separation device (17) comprising a first outlet (18) through which the fine carbonated and dried fraction is intended to be evacuated, - a volumetric distribution system (20) capable of managing the volume of gas containing carbon dioxide sent to the carbonation reactor (2), - a device (16) for conditioning the gas containing carbon dioxide capable of modifying the relative humidity and / or the temperature of the gas containing carbon dioxide, - a device (15) for injecting the gas containing carbon dioxide into the carbonation reactor (2).

7. Method for forced carbonation of a fine fraction from recycled concrete, this method being capable of implementing an installation (1) according to any one of claims 1 or 2, the method comprising the following steps: - a step of conditioning the fine fraction so that said fine fraction has a predetermined humidity level substantially equal to a set value, and - a step of conditioning the gas containing carbon dioxide so that the relative humidity and / or the temperature of said gas are substantially equal to set values, - a step of feeding the carbonation reactor (2) with the fine fraction coming from recycled concrete comprising paste of hydrated cement, said fine fraction having a particle size less than or equal to 16 millimeters, said fine fraction having been previously conditioned during the stage of conditioning the fine fraction, - a step of injecting the gas containing carbon dioxide into the carbonation reactor (2), said gas having been previously conditioned during the gas conditioning step, - a step of carbonation of the fine fraction in the carbonation reactor (2).

8. Method according to claim 7, this method implementing an installation according to claim 3, this method comprising a step of measuring the humidity level in the fine fraction, the measurement being compared to a set value, method in which the quantity of water injected upstream of the carbonation reactor is adjusted so that the humidity level in the fine fraction is substantially equal to the set value.

9. Method according to any one of claims 7 or 8, this method implementing an installation according to claim 4, this method comprising a step of measuring the relative humidity and / or the temperature of the gas in the carbonation reactor, the measurement(s) each being compared to a set value, method in which the relative humidity and / or the temperature of the gas containing carbon dioxide is or are modified during the gas conditioning step so that the relative humidity and / or the temperature in the carbonation reactor is or are each substantially equal to the set value.

10. Method according to any one of claims 7 to 9, this method implementing an installation according to claim 6, this method comprising a step of drying the fine fraction by means of fumes from combustion at the outlet of the carbonation reactor, the fine fraction being dried after having been carbonated. 1 1. Method according to any one of claims 7 to 10, the method implementing an installation according to one of claims 5 or 6, method in which the carbon dioxide injected into the carbonation reactor comes from fumes from combustion.

12. Method according to claim 7 to 11, comprises an aeraulic separation step carried out by means of the aeraulic separation device (17), a step during which the fine dry and carbonated fraction is separated from the fumes.

13. Method according to any one of claims 7 to 12, the method implementing an installation according to claim 6 in which the method comprises a volumetric distribution step so as to send a predetermined quantity of carbon dioxide to the gas conditioning device (16).

14. Method according to any one of claims 7 to 13 in which the temperature in the carbonation reactor (2) is between 30°C and 80°C, preferably 40°C.

15. Method according to any one of claims 7 to 14 wherein the relative humidity of the gases in the carbonation reactor is between 40% and 100%.

16. Process according to any one of claims 7 to 15, in which the residence time of the fine fraction in the carbonation reactor is between 20 minutes and 120 minutes.

17. Method according to any one of claims 7 to 16 wherein the pressure inside the carbonation reactor is substantially equal to atmospheric pressure.

18. Method according to any one of claims 7 to 17 in which the fine fraction has a particle size less than or equal to 6 millimeters.

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