NL8302120A - Underground gasification of coal - by introducing a chemical physical crushing agent, esp. ammonia, prior to ignition - Google Patents

Abstract

Underground gasification of coal is carried out by (a) drilling two bores at a distance from each other into the coal bed; (b) making a passage between the two bores; (c) igniting the coal and (d) maintaining the burning and gasification of the coal via one of the boreholes and adding a medium or media which are reactive with coal and removing a gas with calorific value via the other borehole. The process is characterised, by before igniting the passage, inserting a medium (I) which chemical/ physically crushes the coal. The medium and at least part of the crushed coal are then removed. Pref. (i) the (I) is circulated through both boreholes and entrained coal particles are removed from the medium above ground; (ii) and (I) is chosen from alkali solns, and organic hydrogen donors such as anthracene oils, alcohols, amines, acetone, hydrogen peroxide and ammonia; (iii) when using ammonia, the relationship between the prevailing temp. and press. is chosen to satisfy the vapour pressure curve; (iv) crushed coal is removed from the medium with a liq. or gas stream.

Description

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Applicant: Stichting Steenkoolbank Nederland, with its registered office in Heerlen

Postal address: Postbus 151, 6470 ED Eygelshoven Authorized representative: Dr.ir. J. Stuffken

Short designation: "Method for underground gasification of coal"

The invention relates to a method for gasifying carbon layers present there below ground level, wherein: a. At least two boreholes are spaced apart into the carbon layer to be gasified? 5 b. a connection is made between the two boreholes in the coal layer? c. the cabbage is ignited; d. Burning and gasification of the coal is maintained by supplying a carbon reactive medium or media through one of the boreholes and discharging a calorific gas through the other borehole 10 to ground level.

The principle of underground gasification of coal according to the above method is generally known. The connection between the two boreholes can be made in different ways. It is best known to do this by breaking the carbon between the boreholes under very high liquid or gas pressure and / or providing the passage according to the layering (so-called "fracturing"). Another possibility which enables the current state of the art is direct drilling of one or both boreholes # such that the last part thereof is drilled according to the plane of the coal layer. A variant of this # is described in NL-O.A. 7713455 where the last part of one of the boreholes is widened to increase the chance of hitting the other borehole (making the connection). The broadening takes place by mechanical means, but the use of chemical / physical crushing is not excluded. This must then take place before the connection is established.

It will be clear that the passage obtained by "fracturing" or by directional drilling (or a combination of these) is of low passage. Not too large diameters can be used for directional drilling.

It is also important with "swelling" coal that the passage is not too narrow. After all, by heating, as a result of the gasification, this coal will swell and, if the passage is too narrow, will clog the connection between the two boreholes.

The part of the invention is to enlarge a passage once established - such that a sufficiently large gas passage is ensured after ignition of the coal layer.

According to the invention this is achieved if the passage is filled before ignition with a medium which chemically / physically pulverizes the coal, after which the medium and at least part of the pulverized coal are removed.

Of course, for practical reasons, at least one of the drill holes will be filled with the medium. Preferably, however, a circulation of the medium is effected via both drill holes. Because there is initially a narrow passage (with the aim of increasing it), the medium will have a high speed, whereby carbon particles that are sufficiently crushed can be entrained and can be separated from the medium above ground level.

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Obtaining a sufficiently large passage between two boreholes has hitherto been a major problem in developing the underground gasification of coal seams. In particular for planar layers, the present invention represents significant progress.

Suitable media are: alkaline solutions, organic hydrogen donors (eg anthracin oil), alcohols, amines, acetone, hydrogen peroxide, but ammonia is preferred. Preferably, a pressure is chosen which, in view of the prevailing rock temperature in the compound, is such that the relationship between (prevailing) temperature and pressure satisfies the vapor-tension line, i.e. gas-liquid equilibrium is achieved.

An additional advantage of the use of ammonia is shown in patent no. 165212, which relates to above-ground gasification of coal. The coal becomes more reactive by treatment with ammonia. Of course, this is also advantageous for starting up the underground gasification.

Most cabbage varieties can be treated in this way. Coal reacts best ("hard coal"). The type of coal, time, pressure and rock temperature, as well as the medium used, all play a role. For example, an optimal result is obtained with a carbon with a volatile matter content of about 20% with ammonia at a pressure of 25 bar, if the rock temperature at a depth of 1200 meters is 58 ° C. Optimal conditions can of course be simulated above ground using an autoclave and a sample of coal.

Optionally, the medium can effect the desired temperature regime in the coal to be crushed by heat transfer.

The invention is illustrated by way of example with a drawing.

In the drawing show: fig, 1: a section through a coal layer with a connecting borehole? fig. 2: same place no. the crushing treatment; Fig. 3: a sectional view of a carbon layer in which a passage has been forced by the application of hydraulic pressure; fig. 4: same place nS. the crushing treatment.

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In Fig. 1, the coal layer, 2 is the roof rock, 3 is the floor rock, 4 is a borehole, 5 is the cavity after applying the present method, 6 is a "fracturing" passage, and 7 is the cavity after applying the method.

If after the application of the method still too much crushed coal remains, it can still be removed after a removal of the medium by a liquid or gas stream. Residues of (reactive) crushed coal can be an advantage when starting the gasification process.

8302120

Claims (6)

7 »-5“ - X. Method for the gasification of cage hedges present there below ground level, wherein: a. At least two boreholes are spaced apart into the cage to be gasified; 5 b. a passage is made between the two boreholes in the Hague. c. the cabbage is ignited; d. combustion and gasification of the coal is maintained by supplying one of the boreholes with a carbon reactive medium or media and discharging gas of a calorific value through the other borehole, which is characterized by before ignition, fill the passage (,) with a medium which chemically / physically crushes the coal, after which the medium and at least part of the crushed coal are removed. 2. Method according to claim 1, characterized in that a circulation of the medium is effected via both boreholes and the entrained carbon particles are separated from the medium above ground level. 3. Process according to claim 1 or 2, characterized in that the medium is selected from alkaline solutions, organic hydrogen donors (such as anthracin oil), alcohols, amines, acetone, hydrogen peroxide and ammonia. 4. Process according to claims 1-3, characterized in that ammonia is used, such that the relationship between prevailing temperature and pressure satisfies the vapor pressure line. 5. Process according to claims 1-4, characterized in that after removing the medium, crushed carbon is removed with a liquid or gas stream. 6. Method as described and further explained. 8302120