FR2556239A1 - High-temperature pretreatment by means of an aqueous alkaline solution of natural materials using argillaceous gangue containing at least one upgradable fuel element - Google Patents

Abstract

High-temperature pretreatment process by means of an aqueous solution for so-called pretreatment of natural materials containing at least one upgradable fuel element, the gangue of which contains argillaceous compounds capable of forming a stable plastic suspension in the presence of water, characterised in that, for the purpose of permitting subsequent easy separations of the aqueous liquid and solid phases, on the gangue, the natural material containing at least one fuel element to be upgraded is brought into contact with an alkaline pretreatment solution containing at least 2.10 g/l of OH<-> ions and then the medium formed is immediately raised to the minimum pretreatment temperature of at least 120 DEG C in a time of at most 30 minutes taken from the time the natural material is brought into contact with the aqueous pretreatment solution.

Description

HIGH TEMPERATURE PRETREATMENT USING AN AQUEOUS SOLUTION
NATURAL CLAY GANGUE TATERIAL ALKALINE CONTAINING WALNUT
A VALUABLE FUEL ELEMENT
The invention relates to a process for the high temperature pretreatment, by means of an aqueous alkaline solution, of natural materials containing at least one recoverable fuel element such as, for example, coal, shale, coal, old residue from washing of Zharbon, lignite, petroleum, bitumen or peat, the gangue of which contains clay compounds capable of forming a stable plastic suspension in the presence of water.

By the expression “pretreatment”, the applicant intends to define a treatment prior to the extraction of the recoverable fuel element (s) from the natural material with the aim of subsequently conferring on the clay matrix, in the presence of an aqueous liquid phase, an ability to easy separation of the two phases.

For a long time now, it has been well known to those skilled in the art that clay compounds forming the gangue of certain fuel elements (which it would be desirable to exploit) have a real propensity to swell, then to disintegrate and finally to dissolve. dispersed in the form of fine crystals and small agglomerates in contact with an aqueous phase. This phenomenon, when it occurs during the phases of upgrading said fuel elements in an aqueous medium, that is to say during the separation of the fuel and its gangue, makes it very difficult to separate the aqueous and solid liquid phases on the fine fractions of the gangue after the extraction of the fuel to be upgraded, making the suspensions obtained unsuitable for settling and filtration, due to the swelling of the clays.

The clay compounds capable of forming a stable plastic suspension on contact with water, and frequently present in the aforementioned natural materials with clay matrix, may belong to the groups constituted by kaolinites, such as, for example, kaolinite, dickite, halloysite, disordered kaolinites, serpentines; the group of mica, such as, for example, muscovite, biotite, and paragonite, pyrophyllite and talc, illites and glauconite; the group of montmorillonites, such as, for example, beidéllite, stevensite, saponite, and hectorite; the chlorite group; the group of vermiculites; the group of interbedded clays whose unit structure is a combination of the preceding groups; the group of fibrous clays, such as, for example, attapulgite (palygorskite), sepiolite. These natural materials with clay matrix can also contain other compounds such as, for example, quartz, calcite (CaCO3), dolomite, gypsum, and certain shales with varying degrees of metamorphism.

Numerous processes for upgrading fuel elements contained in a matrix with little or no clay are well known to those skilled in the art, as well as their difficult transposition to fuel elements with a clearly argillaceous matrix.

Indeed, these processes can give rise to very large settling surfaces when the clay phase is in the presence of water, at the end of the upgrading operation. In addition, the clays present can, in some cases, also cause a higher consumption of reagents such as those intended for.

flotation operations, solvent extraction or separation in dense media.

A first type of drawback appears in the publication "Hydrocarbon Processing", pages 127 to 130, June 1981, of the "Standard Oil
Co ", which describes a process for treating tar sands, with a more or less clayey matrix, which requires a quantity of water all the greater as this clayey matrix is important. Indeed, this process consists in treating the sands. bituminous by means of an aqueous solution of sodium carbonate at 700 C to reduce the viscosity of the bitumen, then to carry out the extraction of the bitumen by means of an organic solvent, finally to recover the water intended to be recycled to the during an operation of separation of the liquid and solid phases carried out on the mineral phase, which has not been dissolved by the solvent. However, the application of such a process to a bituminous sand with a high clay content makes difficult the ultimate separation of the aqueous liquid and mineral solid phases, causing, as clearly expressed, a greater consumption of water.

Another type of drawback appears during the application of the well-known processes for treating coals or lignites when these fuels are found associated with a clay matrix.

Such a well-known process described in "Encyclopédie 0f Chemical
Technology "by Kirk-Othmer - 30 Editiofi, volume 6, pages 266-267, consists in separating the fuel from its gangue by a treatment in a dense medium or in a pulsed aqueous medium.

The products resulting from this separation are on the one hand the fuel freed from the aqueous phase by draining and on the other hand the gangue which is subsequently itself separated from its aqueous phase by settling, the surfaces necessary to achieve said settling is all the more important as the gangue is more clayey.

Such procedures, which have proved to be advantageous for the vlorization of certain fuel elements, are difficult to apply when it is a question of carrying out the valorization of fuel elements whose gangue is formed, among others, of clay compounds, because the application of such a process to a natural material containing clayey matrix leads, of course, to a correct enrichment of the fuel to be upgraded but also to obtaining a suspension of gangue resulting from the treatment of which it is difficult to ensure the separation of the phases. liquid and solid, regardless of the amount of flocculant added, because of its infiltration and even difficult to settle.

Thus, because of the aforementioned drawbacks, the Applicant, continuing its research, has found and developed a process for the high temperature pretreatment of natural material with argillaceous gangue, by means of an alkaline aqueous solution, allowing a very easy subsequent separation of the aqueous and solid liquid phases on the matrix.

The process according to the invention for the high temperature pretreatment of natural materials containing at least one recoverable fuel element, the gangue of which contains clay compounds capable of forming a stable plastic suspension in the presence of water is characterized in that in order to allow easy subsequent separations of the aqueous liquid and solid phases on the matrix, the natural material is brought into contact with the aqueous pretreatment solution, then the medium formed is immediately brought to the temperature of at least 1200 ° C. over a period of at most 30 minutes counted from the contact of the natural material with the aqueous pre-treatment solution.

However, it may happen that said natural materials have before grinding a quantity of water such that the solid particles tend to create agglomerates which prevent the good flow of these particles. has prior drying.

As has already been expressed, the aqueous solution of the pretreatment according to the invention is alkaline. This aqueous solution counteracts compounds which, when brought into contact with water, release OH ions. Such compounds are, for example, alkali metal hydroxides, alkaline earth hydroxides such as those of calcium and barium; alkaline carbonates such as those of sodium, potassium, and ammonium, ammonium carbonate possibly containing ammonium carbamate. Its OH concentration is at least 2.10-5g / 1.

Depending on the nature of the natural material, the reagent concentration of the alkaline pretreatment solution can vary within wide li
-5 moths. Thus, the OH concentration can vary between 2.10 girl -4 and 20 girl, but preferably between 2.10 gil and 12 girl.

As soon as the natural material and the aqueous pretreatment solution have the desired characteristics, they are brought into contact thus forming the pretreatment medium which takes the form of a suspension which is preferably prepared by the introduction. from the solid phase to the liquid phase.

The ratio of the liquid phase expressed in cubic meters to 12 solid phase expressed in tonnes of the ore (L / &, is at least equal to 0.6, is generally greater than 1, and is preferably chosen between 2 and 10.

According to one variant, which may prove to be of interest in the context of the process according to the invention, CO 2 gas may be blown into the reaction medium while the pretreatment is being carried out, or at the end of the pretreatment.

This insufflation can be done in a continuous or discontinuous manner according to a constant or variable flow rate. Thus, the injection of this CO 2 gas makes it possible, at the same time, to control and adjust the OH content of the reaction medium.

The temperature at which the pretreatment is carried out, which is at least 120 ° C., is therefore defined as the minimum pretreatment temperature; it is preferably chosen in the range of 140 C to 3000 C, depending on the nature of the clay matrix of the natural material.

The duration of the pretreatment is generally short, it being understood that the pretreatment time is all the shorter as the temperature is chosen within the high values of the corresponding interval.

This pre-treatment period breaks down into two periods: - a first period known as the temperature rise of the suspension
up to the minimum pretreatment temperature, this period of
to be very short: it is chosen between the instantaneous and
more than 30 minutes, and preferably between the instantaneous and
--plus 20 minutes, this time being counted from the setting in con
tact of the natural material with the aqueous pretreatment solution.

- a second so-called stay period at at least 120 C corresponds
at a duration preferably chosen in the interval of 30
minutes to 1 minute and does not need to exceed 60 minutes, because
the prolongation beyond 60 minutes of the stay at the temperature
chosen above the minimum pre-treatment temperature,
no longer improves the suitability for subsequent phase separation
aqueous and solid liquid on the matrix.

During the duration of the pretreatment, the suspension can be subjected to minimal mechanical agitation but agitation at least sufficient to oppose the settling of the largest grains of the solid phase.

The Applicant has in fact observed, during numerous experiments which led to the invention, that natural clay materials containing at least one fuel element brought into contact with an aqueous phase, the temperature of which is below 1200 ° C. and subjected to a prolonged mechanical stirring action, are very gradually disintegrated with production of extremely fine particles, the largest dimension of which is generally less than two microns, inhibiting the separation of the solid, aqueous and liquid phases on the matrix by the appearance of a suspension irreparably stable plastic.

Thanks to the pretreatment process according to the invention, the process of disintegration of the clays which occurs in the presence of an aqueous phase is inhibited in an almost irreversible manner allowing any subsequent treatment to be carried out subsequently and at the appropriate time. recovery, such as for example a flotation, a separation in a dense medium, a gravimetric separation, an extraction by organic solvent of the fuel element with pretreated clay gangue, which can include, without inconvenience, stages of agitation, storage, transfer and separation.

In addition, the pretreatment process according to the invention does not subsequently cause a limitation in the recovery yields of the fuel, whatever the type of treatment practiced, in an aqueous medium.

Finally, in order to facilitate the separation of the aqueous liquid and solid phases of the gangue suspension resulting from the pretreatment of the natural material according to the invention, then from its recovery treatment, it is desirable to introduce a flocculating agent in dilute aqueous solution, generally of a concentration at most equal to one gram per liter, in quantities not exceeding 500 grams per tonne of natural material, but always adapted to the desired results.

The advantages of the process according to the invention will be more perceptible thanks to the example given by way of illustration.

EXAMPLE
This example illustrates the good influence of the pretreatment according to the invention on a bituminous sand with a strongly argillaceous matrix.

To do this, we used a clay matrix bituminous sand having the following composition in percent by weight
Silica 59.9
of which quartz 42.8
A1203 10.8
CaO 1.7
Na20 1.3
KO 1.9
2
Bitumen 12.8
Binding H2O and miscellaneous 11.6
The clays were mainly made up of montmorillonite and illite.

In a first test illustrating the prior art, 100 g of this bituminous sand with clay matrix were suspended in 250 g of a stirred solution of Na2CO3 at a concentration such that the final pH of the suspension thus prepared was 8 , 6.

The temperature of the suspension thus prepared was 78 ° C. The medium maintained at this temperature was subjected to mechanical stirring for a period of 12 minutes.

20 g of kerozene were then introduced into the hot, stirred medium in order to extract the bitumen present.

After a standing time of 5 minutes to promote separation by settling of the organic and aqueous phases, it was collected at the top. the organic phase. Then, in order to simulate the recycling of the aqueous phase upstream of an industrial process, an attempt was made to separate the sandy and clay matrix from the aqueous phase by filtration.

To do this, a separation was carried out on a Büchner filter subjected to a vacuum of 500 millimeters of mercury, and the rate of separation of the liquid phase was measured in cubic meters .. hour.
Prior to passing the suspension over the filter, it was added with a flocculating agent at a rate of 20 milliliters of a 0.5 g / l solution of Floerger FA 10, prepared from an aqueous solution. at 2.5 g / l.

-2
The filtration rate was 0.04 mh. M
This filtration rate could not be significantly improved, even by a massive addition of flocculant: 100 cm 3 of the above-mentioned flocculant solution gave a filtration rate of 0.05 m.

hl.m'2
In a second test illustrating the good influence of the pretreatment according to the invention, 100 g of the same bituminous sand were introduced into a cylindrical autoclave with a total capacity of 500 milliliters, with 250 g of an aqueous alkaline pretreatment solution containing 2.10 girl of OH ions per tonne of clay, as an aqueous solution of NaOH. The suspension thus formed constituted the pretreatment medium.

The autoclave was placed in an electric furnace and subjected to oscillations in a vertical plane around its transverse horizontal axis.

The suspension was very quickly brought to the chosen temperature of 1800 ° C. in 5 minutes, and was maintained at this temperature for 5 minutes.

At the end of this time, the reactor was immersed in cold water in order to cause rapid cooling of the suspension.

After cooling to a temperature of 800 C, the medium obtained was subjected to carbonation in the same reactor by means of a continuous injection of CO 2 gas. the carbonation was stopped when the pH of the suspension reached the value of 8.6.

Then the operations of extraction by kerozene and filtration were carried out according to the protocol of the first test.

After adding the said suspension by means of 20 milliliters of the 0.5 glu solution of Floerger FA 10, mentioned above, the filtration rate on Büchner was found to be very markedly improved since it was 5.2 m³.h lm 2

Claims (10)

CLAIMS 1. High temperature pretreatment process using an aqueous solution known as pretreatment, of natural materials containing at least one fuel element, the gangue of which contains clay compounds capable of forming a stable plastic suspension in the presence of water, characterized in that, -in order to allow easy subsequent separations of the aqueous liquid phases and :: solid, on matrix the material. natural containing at least one recoverable fuel element is brought into contact with an alkaline pretreatment solution containing at least 2.10 g / l of OH ions then the medium formed is immediately brought to the minimum pretreatment temperature of at least 120t C in one time of at most 30 minutes counted from bringing the natural material into contact with the aqueous pretreatment solution. 2. A high temperature pretreatment method according to claim 1, characterized in that the natural material is subjected to preliminary drying. 3. A high temperature pretreatment process according to claim 1, characterized in that the ore is subjected to drying simultaneously with an operation of reducing its particle size. 4. A high temperature pretreatment process according to any one of claims 1 to 3, characterized in that the OH ion concentration of the aqueous pretreatment solution can vary between 2.0 5 g / l and 20 g / l, but preferably between 2.10 4g / l and 12 g / l. 5. A high temperature pretreatment process according to any one of claims 1 to 4, characterized in that the ratio of the liquid phase expressed in cubic meters to the solid phase expressed in tonnes of natural material is at least equal to 0, 6, generally greater than 1 and is preferably between 2 and 10. 6. High temperature pretreatment process according to any one of claims 1 to 5, characterized in that the minimum temperature herein pretreatment is preferably chosen from the range of 1400 C to 3000 C. 7. A high temperature pretreatment process according to any one of claims 1 to 6, characterized in that the time required for the temperature rise to the minimum pretreatment temperature is preferably between the instantaneous and at most 20 minutes. 8. A high temperature pretreatment process according to any one of claims 1 to 7, characterized in that the medium having reached at least the minimum pretreatment temperature is maintained at this selected temperature for a time of between 1 to 60 minutes. 9. A high temperature pretreatment process according to any one of claims I to 8, characterized in that, during the duration of the treatment, the aqueous medium resulting from contacting the natural material with the aqueous pretreatment solution. At least sufficient stirring is required to oppose the settling of the larger grains of the solid phase. 10. A high temperature pretreatment process according to any one of claims I to 9, characterized in that CO 2 gas is blown into the reaction medium while the pretreatment is carried out.