EP0067079A1 - Process and installation for the underground gasification of coal - Google Patents

Abstract

The invention relates to the gasification of coal. An oxygen jet (21) with a dart (22) coming into impact with the coal is produced in situ with an envelope (30) of steam. The combustible gas is extracted in a current (F ') flowing against the current of the oxygen jet and is brought back to the surface through the same borehole which served for the arrival of oxygen. Application to underground and in situ gasification of coal.

Description

The invention relates to a method of underground gasification of coal, according to which a gasifying agent is led through a borehole, which is sprayed in situ towards a coal seam, where a combustible gas is extracted. resulting from an incomplete combustion of said coal, which is led to the surface in a current flowing against the current and: around the jet of gasifying agent and which is led to the surface through said borehole. We know that this ensures the formation of combustible gas generally comprising at least carbon monoxide, and very variable amounts of methane. The advantage of this process is to use only one borehole for the admitted products and the fuel withdrawn, but the problem posed is that of avoiding any additional combustion reaction between the gasifying agent and the combustible gas resulting from incomplete combustion and, for this purpose, we were led either to continuously advance the head delivering the gasifying agent until arriving in the immediate vicinity of the coal front where combustion takes place, which has drawbacks control and thermal shock, or to dilute the gasifying agent in projected protection capsules circulating by gravity towards the combustion front.

The present invention aims to simplify the means used to ensure the in situ gasification of coal, in particular localized at very great depth, by considerably simplifying the means used and by ensuring precise control of the phenomenon of incomplete combustion.

According to the invention, the jet of gasifying agent is a gas jet and an annular sheet of an insulating fluid is emitted between said jet of gasifying agent and said stream of combustible gas flowing in co-current of said jet of gasifying agent.

Preferably the fluid of the annular ply is water, if necessary, in the form of water vapor. In this way, thanks to the isolation of the gasifying jet, it is possible to ensure a significant distance between the head delivering the gasifying agent and the combustion front, while avoiding any complementary reaction of complete combustion. In addition, we can, by means of measurements suitable, check the incomplete combustion zone perfectly and therefore obtain a gas of constant quality.

The invention also relates to an installation for the implementation of this method.

• - la figure 1 est une vue schématique à l'endroit de la zone de combustion incomplète ;
• - la figure 2 est une vue schématique du forage ;
• - la figure 3 est une vue schématique à échelle agrandie de l'extrémité du conduit aboutissant à la buse d'injection ;
• - la figure 4 est une vue schématique du mode opératoire ;
• - la figure 5 est une vue schématique d'une variante de buse ;
• - la figure 6 est une vue en coupe axiale de la figure 5.

The invention will now be described by way of example with reference to the accompanying drawings in which:

• - Figure 1 is a schematic view at the location of the incomplete combustion zone;
• - Figure 2 is a schematic view of the drilling;
• - Figure 3 is a schematic view on an enlarged scale of the end of the conduit terminating in the injection nozzle;
• - Figure 4 is a schematic view of the operating mode;
• - Figure 5 is a schematic view of a variant of the nozzle;
• - Figure 6 is an axial sectional view of Figure 5.

Referring to Figures 1 and 2, we see that a nozzle 1 at the end of a pipe 2 placed in a borehole 3 extending from the surface 4 to a coal seam 5 occurs in an area median of the coal seam 5. This nozzle 1 consists of a preferably supersonic nozzle 10 of diverging convergent shape and of a co-axial pipe 11 which is also connected to the pipe 2 which is in the form of a double tube, one central connected to the central nozzle pipe 10, the other co-axial connected to the co-axial pipes. nozzle 11, the axial nozzle line 10 is supplied with pressurized oxygen, while the annular ducts 11 are supplied with pressurized water vapor.

The nozzle operates as follows: through its orifice 20, a concentrated jet of oxygen 21 and directional elongated and has a supersonic velocity dart 22, the Extremists _- Mite comes into impact with the coal, while the water vapor flows around the jet 21 in an annular curtain 30 which extends at least over a large part of the extension of the directive jet 21. The oxygen, at the point of impact, causes incomplete combustion of coal. An annular stream of combustible gas 23 at high temperature rises according to the arrows FF ′ around the oxygen jet-water vapor curtain assembly. During its journey, the gas cools on contact with the carbon layer and water vapor: the resulting chemical reactions greatly increase its calorific value. This combustible gas is taken up at the bottom of the borehole by a second annular pipe 6 formed by an envelope 7 surrounding the double tubular pipe 2 at a distance. It is noted that water vapor constitutes not only an active element in incomplete combustion, but also plays a decisive role in avoiding contact between the combustible gas and oxygen sting; without this curtain of water vapor, or other means of separation, the combustible gas would oxidize during this course at the oxygen level, which, of course, would make impossible the partial gasification sought. This is all the more true since the directive jet of oxygen 21 can have a very great extension in the axial direction, since the distance between the dart 22 and the nozzle 1 can be several tens of meters.

• On procède au forage comme indiqué à la figure 2 jusqu'à parvenir à la veine de charbon 5 et à ce moment, on introduit les tubulures 2 et 6 en équipant la tubulure 2 du dispositif à joints tournants représenté à la figure 3. Dans cette position, les sections coudées 40 et 41 sont mises en alignement et l'on procède à la première étape de combustion partielle qui consiste à partir du niveau du sol, à accroître la longueur de la tubulure 2 pour se déplacer le long d'une zone médiane de la veine 5, la buse de tête 11 provoquant par combustion incomplète une galerie de mine 50, qui est une sorte de forage "à l'oxygène" dans le plan de la veine de charbon et ce forage peut atteindre plusieurs centaines de mètres. Cette opération s'effetuant par adjonction de tubulures au niveau du sol et correction permanente de la direction d'avancée par contrôle de la zone de combustion grâce à un thermomètre optique 51 (figure 1) solidaire de la buse 11 et qui permet de vérifier si l'impact du jet d'oxygène se produit bien sur la couche de charbon. Une fois la galerie de mines 50 formée, on procède à des opérations de combustion latérale (figure 4) le long de cette galerie en réorientant les parties de conduites 40 et 41 de façon à diriger la buse 11 dans l'extension transversale la plus importante de la veine de charbon 51 et l'on procède ensuite à des combustions incomplètes dans des plans transversaux perpendiculaires à la galerie de mine 50, assurant ainsi soit des cavités de combustion 52, 53, 54 et 52', 53', 54' décalées les unes des autres ou, le cas échéant, une large cavité qui s'étend de part et d'autre de la galerie de mine 50.

In practice, as shown in Figure 3, the composite oxygen and water vapor nozzle is placed at the end of a double tube 2 which has two successive sections 40 and 41 each having a right angle bend 42 and 43, these two sections 40 and 41 being connected by two rotary joints 44 and 45. In practice, the procedure is as follows:

• The drilling is carried out as indicated in FIG. 2 until reaching the coal seam 5 and at this time, the tubes 2 and 6 are introduced by equipping the tube 2 with the rotary joint device shown in FIG. 3. In this position, the bent sections 40 and 41 are brought into alignment and the first stage of partial combustion is carried out which consists, starting from ground level, of increasing the length of the pipe 2 to move along an area median of the vein 5, the head nozzle 11 causing by incomplete combustion a mine gallery 50, which is a kind of drilling "with oxygen" in the plane of the coal seam and this drilling can reach several hundred meters . This operation is carried out by adding tubing at ground level and permanent correction of the direction of advance by monitoring the combustion zone using an optical thermometer 51 (Figure 1) integral with the nozzle 11 and which makes it possible to check whether the impact of the oxygen jet does indeed occur on the layer of carbon. Once the gallery of mines 50 has been formed, lateral combustion operations are carried out (FIG. 4) along this gallery by reorienting the parts of pipes 40 and 41 so as to direct the nozzle 11 in the largest transverse extension of the coal seam 51 and one then proceeds to incomplete combustions in transverse planes perpendicular to the mine gallery 50, thus ensuring either combustion cavities 52, 53, 54 and 52 ', 53', 54 'offset from each other or, where appropriate, a large cavity which extends on either side of the mine gallery 50.

This incomplete combustion operation which takes place inside the mass of coal, which has not undergone any random preparation such as a fracturing can therefore be carried out with the greatest chances of success, since this mass of coal has then a mass uniformity which makes incomplete combustion reproducible from one place to another. It is further noted that the optical control device 51 makes it possible, by laterally oriented combustion operations, to verify that one is still in a middle position of the coal seam, because this control device 5f makes it possible to detect immediately any drop in temperature when the sting 22 of the directive jet of oxygen 21 meets the rock.

• - On a vu qu'un des rôles de la vapeur d'eau était d'isoler le jet d'oxygène des gaz résultant de la combustion incomplète. Ce rôle peut aussi être assuré par un gaz neutre, comme le gaz carbonique.
• - Au lieu d'opérer par une injection continue d'oxygène avec une enveloppe gazeuse d'isolement, on peut également opérer par des successions d'injections d'oxygène , puis d'hydrogène et dans ce cas il n'est plus nécessaire d'assurer une protection gazeuse du jet d'hydrogène actif.
• - On peut également mettre en oeuvre une injection plus complexe comprenant un jet central d'oxygène, enveloppé d'un jet annulaire intermédiaire de vapeur d'eau, ou de gaz carbonique, et d'un jet annulaire périphérique d'hydrogène ou de vapeur d'eau (notamment si le jet intermédiaire est autre que de la vapeur d'eau), comme représenté aux figures 5 et 6, où l'on voit un débouché de buse supersonique 61 pour l'oxygène, une couronne annulaire de débouché 62 pour de la vapeur d'eau, ou de l'eau, circulant à grande vitesse, et une fente annulaire 63 pour de la vapeur d'eau en écoulement laminaire.

It is noted that the invention can be implemented in different forms, some of which are listed as examples:

• - We have seen that one of the roles of water vapor was to isolate the oxygen jet from the gases resulting from incomplete combustion. This role can also be fulfilled by a neutral gas, such as carbon dioxide.
• - Instead of operating by a continuous injection of oxygen with a gaseous isolation envelope, one can also operate by successive injections of oxygen, then of hydrogen and in this case it is no longer necessary to '' provide gas protection for the active hydrogen jet.
• - It is also possible to implement a more complex injection comprising a central oxygen jet, surrounded by an annular jet intermediate water vapor, or carbon dioxide, and a peripheral annular jet of hydrogen or water vapor (especially if the intermediate jet is other than water vapor), as shown in Figures 5 and 6, where one sees an outlet for a supersonic nozzle 61 for oxygen, an annular ring for an outlet 62 for water vapor, or water, circulating at high speed, and an annular slot 63 for water vapor in laminar flow.

Claims (13)

1. Method of underground gasification of coal, according to which a gasifying agent is led through a borehole, which is sprayed in situ in the direction of a coal seam, where a combustible gas resulting from incomplete combustion of said coal, which is brought to the surface in a current flowing against the current and around the jet of gasifier and which is led to the surface through said borehole, characterized in that the jet of gasifying agent is a gas jet and in that an annular sheet of an insulating fluid is emitted between said jet of gasifying agent and said stream of combustible gas flowing co-current of said jet of agent gasifier. 2. Method of underground gasification of coal, according to claim 1, characterized in that the fluid of the annular sheet is water, if necessary in the form of water vapor. 3. Method of underground gasification of coal according to claim 1, characterized in that the fluid of the annular layer is a neutral gas, for example carbon dioxide. 4. A method of underground gasification of coal according to claim 1, characterized in that the gasifying agent is oxygen, optionally periodically replaced by hydrogen. 5. Method of underground gasification of coal according to claim 1, or 2 or 3, characterized in that a second gas, such as water vapor, carbon dioxide or hydrogen, is injected into the outer periphery of said annular fluid layer of isolation. 6. Method of underground gasification of coal according to any one of claims 1 to 5, characterized in that one first performs such an initial operation of gasification in line to form a mine gallery with median extension in the vein of coal, and in that one then successively performs a plurality of lateral gasification operations spanning along and on either side of said mine gallery. 7. Gasification process according to any one of claims 1 to 5, characterized in that the water vapor layer results from the vaporization of water injected at the head of the borehole, heating by heat exchange with the combustible gas going back to the area. 8. Installation for the underground gasification of coal, for the implementation of the method according to any one of claims 1 to 7, comprising a first tube extending through a borehole 'to the level of a vein of coal, at the end of this tubing a displaceable nozzle adapted to form a directive jet of gasifying fluid, characterized by a second tube in said bore extending to the nozzle for forming the directive jet of gasifying fluid. 9. Installation for the underground gasification of coal according to claim 8, wherein the nozzle is equipped with axial sliding means, characterized in that the nozzle is arranged at the end of a double rotating joint. 10. Installation according to claim 8, characterized in that the second tube is arranged coaxially with the first tube. 11. Installation for the underground gasification of coal according to claim .10, characterized in that the axial gas injection nozzle is of the axial convergent-divergent type. 12. Installation for the underground gasification of coal according to claim 11, characterized in that the nozzle has an annular duct in communication with the second pipe. 13. Installation for underground gasification of coal according to claim 11, characterized in that the nozzle has a second annular conduit externally to said annular conduit, in communication with a third drill pipe.

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