WO2011070248A1

WO2011070248A1 - Carbon core preparation method

Info

Publication number: WO2011070248A1
Application number: PCT/FR2010/000816
Authority: WO
Inventors: Pierrick Defossez; Eric Gaucher
Original assignee: Brgm
Priority date: 2009-12-08
Filing date: 2010-12-07
Publication date: 2011-06-16
Also published as: FR2953593B1; FR2953593A1; PL2510330T3; EP2510330A1; EP2510330B1; ES2554655T3; CA2781819A1; PT2510330E

Abstract

The present invention in particular relates to a carbon core preparation method, characterized in that the method includes the steps of: (i) grinding a carbon sample so as to obtain a powder having a particle size between 0.1 and 800 μm; (ii) adding water to the powder obtained in step (i) so as to obtain a mixture including 20% to 30% water; (iii) placing the mixture, obtained in step (ii), in a mold; (iv) applying a pressure greater than 0.5 Mpa to the mixture, contained in said mold, so as to obtain a block; and (v) reinforcing the block, obtained in step (iv) under oedometric conditions so as to obtain a sample having a void ratio similar to that of the carbon, from which the sample used in step (1) was formed.

Description

PROCESS FOR PREPARING A CARROT OF CHARCOAL

The present invention relates in particular to a process for preparing a coal core. The present invention also relates to a method for measuring ^one adsorption of CO ₂ comprising the use of coal core according to the invention.

The storage of C0 ₂ in coal seams represents a real scientific challenge given the chemistry and the complex structure of the coals. Coal "macerates", structural equivalents of rock minerals, have varied organic origins and therefore behave differently. Each is part of a specific porosity range and has an affinity specific to gases. Thus, the composition of the coal, and particularly its organic fraction, seems to determine the adsorption capacity of the gases.

The understanding of C0 ₂ injection processes in coal does not stop with modeling of transport or adsorption. It has been shown that C0 ₂ is an organic solvent that can interact with the carbon matrix, which it then modifies physically and chemically. These changes are associated with the relaxation, the rearrangement of the macromolecular structures of the coal which cause a swelling of the material and thus a poral resizing. The volume increase by adsorption of C0 ₂ at 15 atm can reach 4% for some coals. It has been noticed that a correlation exists between a lower C0 ₂ content and an increase in swelling.

Moreover, in a coal in place under lithostatic stress, the movement of macromolecules is very slow. The percolation of C0 ₂ acts as a plasticizer, which promotes the rearrangement of the molecules, modifies the structure of the coal and leads to a reduction of its permeability.

The understanding of all these mechanisms and complex phenomena is essential to find the appropriate technical means to circumvent the difficulties and to make accessible the great potential of C0 ₂ storage of coal deposits.

In this perspective, it is essential to know the chemical and mechanical behavior of coal during the percolation of C0 ₂ .

The science of rock mechanics developed in the middle of the last century. His tests are done on coal as on any other rock. They require a sample from the drilling of the material called "carrot".

The standard coal test, as part of a C0 ₂ storage study, consists of gas percolation in a specimen of material subjected to given vertical and lateral stresses. Over the course of the experiment, we study the morpho-structural evolution of the core, in particular the evolution of its void index, its swelling and its fracturing.

Unfortunately, the material, in most cases, does not lend itself very well to coring. Coal is of a friable nature. It is not uncommon to have to drill dozens of blocks before you can extract a solid core. There are extreme cases where a sample is rejected because the test can not be performed. However, there is no known link between the ease of a coal to be cored and its ability to store gas, so no sample should be discarded under this pretext. In addition, the carrot obtained with more or less luck is not necessarily representative of the material; proof is the low repeatability of the experiment, which is a reflection of the heterogeneity of the material. Otherwise, large-scale, in-situ mechanical testing is time-consuming and costly.

The application US2009 / 295034 describes a preparation process for obtaining an activated carbon monolith used for storing natural gas. The disclosed method comprises a first step of activating charcoal powder by heating in the presence of potassium hydroxide. Then the activated carbon powder is molded in the presence of a binder (polytetrafluoroethylene or PTFE).

Lozano-Castello et al. (2002) has also described a preparation method for obtaining an activated carbon monolith for use in the storage of methane. The process described consists of hot molding a mixture comprising coal powder and a binder. Among the binders described are sodium salts derived from Humic Acid (HAS), polyvinyl alcohol, phenolic resins, waterlink sutcliff carbon, cellulose binders and Teflon.

The present invention proposes to solve the above problem by allowing the preparation of a coal core, usable in particular in the context of a study on C0 ₂ storage, from a coal sample. The coal core obtained by the process according to the invention has CO2 adsorption properties similar to that of the coal from which it was prepared. Advantageously, the process according to the invention operates at ambient temperature and does not require the use of a binder. This makes it possible to obtain an economical method of energy consumption and a final product containing only components present natively in the coal sample used to produce the coal core according to the invention.

The method according to the invention allows the creation of a carrot from the original non-coreable rock. Then, the use of the cores obtained by the process according to the invention makes it possible to easily compare the physical behaviors of several coals during the percolation of gases, whether or not they are carotable.

Thus, the present invention provides a method for preparing a coal core, which is remarkable in that it comprises the steps of:

(i) milling a sample of coal to obtain a powder having a particle size of between 0.1 and 800 μπι,

(ii) adding water to the powder obtained in step (i) so as to obtain a mixture comprising from 15 to 30% of water,

(iii) placing the mixture obtained in step (ii) in a mold,

(iv) applying to the mixture, included in said mold, a pressure greater than 0.5 MPa, in order to obtain a block,

- (v) applying to the block, obtained in step (iv), a consolidation in oedometric condition so as to obtain a sample having a vacuum index similar to that of the coal from which the sample used in step ( i).

According to a preferred embodiment, the method according to the invention comprises a step of measuring the void index of the coal sample used in step (i).

The grinding performed in step (i) can be carried out by any means known from the prior art. Among the possible means include crushers or ring grinders. The applicant was able to demonstrate that the desired particle size could be easily achieved using a roller mill. Thus, according to a preferred embodiment of the invention, step (i) is carried out by means of a roll mill.

In step (ii), water is added to the powder obtained in step (i) in order to obtain a mixture comprising from 15 to 30% of water (weight / weight). The studies carried out by the applicants have made it possible to demonstrate that a lesser quantity of water does not make it possible to obtain a block having sufficient cohesion and that a greater quantity of water causes problems of saturation and expulsion of water. water during step (iv). According to a preferred embodiment of the invention, said mixture comprises between 20 and 30% water and quite preferably between 23 and 27% water.

The mixture obtained in step (ii) is then placed in a mold. This mold is preferably cylindrical. Among the molds that can be used in the context of the present invention, mention may be made of the conventional oedometric cells used during the geomechanical tests. According to a preferred embodiment of the invention, said cylinder has an inside diameter of between 10 and 100 mm and very preferably between 40 and 60 mm.

According to another preferred embodiment of the invention, the mixture placed in the mold does not comprise a binder and in particular no polytetrafluoroethylene or PTFE, sodium salts derived from Humic acid (HAS), poly (vinyl alcohol ), phenolic resins, waterlink sutcliff carbon or cellulose binders and teflon.

According to an even more preferred embodiment of the invention, the mixture placed in the mold comprises only water and the powder obtained in step (i).

In step (iv) the mixture present in the mold is compacted. This compacting can be carried out indifferently in one or more steps. It is possible, for example, to carry out a first manual compaction and a second compaction using a press. The pressure applied during this step (iv) is greater than or equal to 0.5 MPa, a lower pressure does not provide a block having sufficient cohesion. According to a preferred embodiment of the invention, the pressure applied in step (iv) is greater than or equal to 0.9 MPa and according to a most preferred embodiment greater than or equal to 1 MPa. This step can be done through a press. Among the presses that can be used in the context of the present invention, mention may be made of MECMAN type presses. For the sake of clarity, it is specified that the various pressure indications present in this application correspond to the pressure measured at 20 ° C.

According to one embodiment ^'of the invention, the method comprises an additional step (iv') wherein the block obtained in Step (iv) is placed in a usable cutting shoe at a. oedometric test.

The oedometric test is well known to those skilled in the art. It notably makes it possible to measure and determine the consolidation parameters of the clay materials and their swelling characteristics. The compressibility test carried out with an oedometer allows the evaluation of the settlements of a soil, a structure, as well as their evolution over time. The measurements make it possible to establish compressibility curves (loading and unloading), and consolidation curves.

The oedometer comprises an indeformable metal cylinder, in which the test sample is placed between two porous stones intended to allow consolidation of the soil by dissipation of interstitial pressures. The sample is taken by means of a cutting kit and is placed under water so as to avoid desiccation of the soil. Said cutting kit makes it possible to obtain a sample having a compatible format with said metal cylinder.

In the context of the present invention, the block obtained in step (iv) will be subjected to consolidation under oedometric conditions which will make it possible to modify its structure and its mechanical properties in order to bring them closer to that of the coal from which the sample is derived. used in step (i).

During step (v), the block obtained in step (iv) will undergo a series of pressure bearing along a load plane. The person skilled in the art is able to determine, depending on the oedometer used, the load plan which makes it possible to obtain a coal core having the desired void number.

The tests carried out by the applicant have made it possible to demonstrate that it is advantageous for the consolidation under oedometric condition carried out in stage (v) to comprise at least one pressure level greater than 80 MPa, even more advantageously greater than 90 Mpa and quite advantageously greater than 100 Mpa.

The void ratio is the ratio of the void volume to the volume of the solid phases in a sample.

The method of obtaining the void index is based on several AFNOR standards:

- Standard NF P 94-053 which allows the determination of the density of a block of coal. In summary, said block of coal is weighed and then covered with a layer of paraffin. A second weighing makes it possible to determine the paraffin mass. A third hydrostatic weighing of the paraffin-coated sample allows the volume of the paraffin-coated sample to be calculated. Since the volume of paraffin is known, the total volume of the sample Vt is deduced therefrom.

- The standard NF P 94-054 which allows the determination of the solid particles density. In summary, this This test makes it possible to obtain, among other things, the density of the grains by helium pycnometry ps. This density is the result of the division of the mass of a coal sample by its volume ps = ms / Vs. Thus one can know precisely the volume of solid in a Vs coal sample.

The void index e is defined as the quotient: Vv / Vs with Vv the volume of the voids equal to Vt (obtained thanks to the standard NF P 94-053) to which we subtract Vs (obtained thanks to the standard NF P 94 -054)).

Vv = (Vt-Vs) / Vs

e = Vv / Vs

In the context of the present invention, the term similar means that the ratio between the void index of the core obtained after step (v) and the index of the voids of the coal from which the sample used in step (i) is between 0.9 and 1.

In order to allow the use of the coal core, obtained in step (v), in a CO2 adsorption measurement process, the process according to the invention may advantageously comprise a step (ν ') of eliminating The water present in the core obtained in step (v). According to a preferred embodiment of the invention, said step (ν ') comprises a step of passing a gas stream through the coal core obtained in step (v). Among the gases that can be used in the context of step (v '), mention may be made especially of nitrogen.

According to a preferred embodiment of the invention, the steps of the process according to the invention are carried out at a temperature below 100 ° C. and in a still more preferred embodiment at room temperature.

The present invention also relates to a coal core which is remarkable in that it is obtained by process according to the invention.

The present invention also relates to a method for measuring the CO ₂ adsorption capacity of a coal remarkable in that it comprises the use of a coal core according to the invention. The present invention also relates to a method for measuring the water permeability of a coal remarkable in that it comprises the use of a coal core according to the invention. The present invention also relates to a method for measuring the nitrogen permeability of a coal remarkable in that it comprises the use of a coal core according to the invention. The present invention also relates to a method for measuring the CO ₂ gas permeability of a coal remarkable in that it comprises the use of a coal core according to the invention. The present invention also relates to a method for measuring the supercritical CO ₂ permeability of a coal that is remarkable in that it comprises the use of a coal core according to the invention.

The present invention also relates to the use of a coal core according to the invention for measuring the CO 2 adsorption capacity.

Example:

Grinding phase

- The blocks of coal are first crushed roughly with a hammer and then placed in a roll mill surmounted by a 10L jar 45% filled with teflon balls (about 20Kg). The sample volume introduced is equal to 40% of the volume of beads. The duration of grinding is about ten minutes at maximum speed (300rpm).

This method makes it possible to obtain 2 kg of sample whose particle size ranges from 1 μπι to approximately 800 μιτι; wide range which guarantees a good cohesion of the block after the molding phase.

Molding phase

- 20 to 30% water (wt / wt) is added to the powder.

- The mixture is then homogenized and placed in a mold. (diameter = 50mm, H = 300mm). The content of the mold is packed by hand and then with a small MECMAN 2t press with a force of 2000daN, a preconsolidation constraint of the OOMP.

- The block obtained is placed in a cutting kit used during an oedometric test (H = 25mm, diam = 50mm). The surface of the specimen is leveled to obtain a perfect cylinder.

- Finally, the specimen is placed in press to recompact the surface layers of the block.

Oedometric test

- The sample thus prepared is studied like any rock core during a conventional oedometer test. The density of the natural block and that of the sample are compared by measurements of P-wave traversing speeds. This is precisely described in the AFNOR XP standard P94-090-1 of December 1997.

At the end of this test, the sample has the same void index as a block of natural coal. It has a density equivalent to the speed of sound measurement. The core obtained has a water content between 10 and 15% and this can be removed by a stream of dry gas (nitrogen type) before measuring the permeability to C0 ₂ .

Claims

1 - Process for the preparation of a coal core, characterized in that it comprises the steps of:

(i) grinding a carbon sample to obtain a powder having a particle size of between 0.1 and 800 μιτι,

(ii) adding water to the powder obtained in step (i) so as to obtain a mixture comprising from 20 to 30% of water,

(iii) placing the mixture obtained in step (ii) in a mold,

2 - Process for the preparation of a coal core according to one of the preceding claims, characterized in that the mixture placed in the mold in step (iii) comprises only water and that the powder obtained at step (i) · 3 - Process for preparing a coal core according to one of the preceding claims, characterized in that step (i) is carried out by means of a roll mill. 4 - Process for preparing a coal core according to one of the preceding claims, characterized in that the pressure applied in step (iv) is greater than or equal to 1 MPa.

5 - A method for preparing a core of coal according to one of the preceding claims, characterized in that it further comprises a step (iv ') of placing the block obtained in step (iv) in a kit cutter for use in an oedometric test.

6 - A method for preparing a coal core according to one of the preceding claims, characterized in that it further comprises a step (ν ') of removing the water present in the core obtained in the step ( v). 7 - Process for the preparation of a coal core according to one of the preceding claims, characterized in that step (ν ') comprises a step of passing a stream of gas through the coal core obtained at the stage ( v).

8 - Coal core characterized in that it is obtained by a process according to one of claims 1 to 7. 9 - Process for measuring the adsorption capacity of CO2 of a coal, characterized in that it comprises the use of a coal core according to claim 8 or obtained by a process according to one of claims 1 to 7.

Use of a coal core according to claim 8 for measuring the CO 2 adsorption capacity of a coal sample. 11 - Use of a coal core according to claim 8 for measuring the water permeability of a coal sample.

12 - Use of a coal core according to claim 8 for measuring the permeability to nitrogen

13 - Use of a coal core according to claim 8 for measuring the CO ₂ gas permeability of a coal sample.

14 - Use of a coal core according to claim 8 for measuring the supercritical CO ₂ permeability of a coal of a coal sample.