Method Of And System For Gasifying Underground Deposits Of Coal

Abstract

An underground coal deposit is provided with two separate channel systems and respective regions of the deposit are progressively combusted. The combustion heat expels high-value gases which are withdrawn through one of the channel systems, and the subsequent gasification of the coal from which the high-value gases have been thus expelled, results in the formation of lower-value combustion gases which are also withdrawn, but separately and through the other channel system.

Description

BACKGROUND OF THE INVENTION

The present invention relates to the gasification of underground deposits of coal, and more particularly to a novel method of gasifying underground deposits of coal and to a system for carrying the present method into effect.

The gasification of underground deposits of coal, that is the recovery of usable gases by combusting the underground coal deposits in situ, is already known. It is customary to blow air through shafts or holes which extend to a coal deposit, and to ignite the coal in the bottom zone of the respective shaft. The combustion results in the formation of carbon monoxide gas which is withdrawn by way of a second shaft extending through the underground deposit of coal and to the surface.

The difficulty with the prior art is that the primary combustion zone travels continuously through the coal deposit, being entirely uncontrollable as to speed and direction. Moreover, the gas which is obtained in this manner has only a relatively low heating value, that is the gas is a low-value gas in terms of its BTU value.

In my prior U.S. Pat. No. 3,506,309 I have disclosed a method and system for gasifying underground deposits of coal, which constitute an improvement over the above-outlined state of the art. In that disclosure I utilize a network of underground channels which are provided more or less at random in the coal deposit, without having definite orientations, and the coal deposit is combusted with the gas being withdrawn through these channels. However, the coal deposit or field cannot with that approach be systematically and completely gasified, aside from the fact that the only gas which can be recovered is hot carbon monoxide gas. It is, however, desirable to provide for the complete, systematic and controlled combustion of the coal deposit, and to have the system according to which such combustion is carried out operate not only with hot waste gas but also with air, hot steam, or mixtures of these with one another or with the hot waste gas.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide further improvements over the prior art.

More particularly it is an object of the present invention to provide an improved method of gasifying underground deposits of coal.

An additional object of the invention is to provide an improved system of gasifying underground deposits of coal.

In pursuance of these objects, and of others which will become apparent hereafter, one feature of the invention resides in a method of gasifying underground deposits of coal which, briefly stated, comprises the steps of providing in an underground coal deposit a first and a separate second channel system, progressively combusting respective regions of the coal deposit with the resulting expulsion due to the combustion heat of high-value gases, and the formation of lower-value hot combustion gases. The high-value gases and the lower value gases are withdrawn, separately from one another and each through one of the first and second channel systems, respectively.

In this manner I achieve the desired improvement over the prior art, including my aforementioned prior U.S. patent. I now can separately withdraw high-value gases as well as the lower-value gases resulting from combustion of the coke which remains after expulsion of the high-value gases. In fact, I can so control the pressure relationships in the separate channel systems that the gases become mixed and/or that only a desired fraction of the respective gases is withdrawn.

I can carry out the degasifying process, that is the expulsion of high-value gases, by itself and carry on the actual gasification process only to the extent necessary for obtaining the heat required for the degasifying process. This could be advantageous if the coal deposit is of the type which is rich in high-value expellable gases but is similarly rich in ash. Depending upon the content of volatile substances in the coal, up to one-third and more of the caloric value of the coal can be obtained in this manner in the form of high-value gases. The caloric value obtained in this manner is more than 5,000 cal/m.sup.3 by contrast to a caloric value of only about 1,500 cal/m.sup.3 in accordance with the previously known gasification methods. This is true particularly if the coal of the deposit has a relatively high water content and steam or water enters into the degasification space from the gasifying space and so increases the proportion of heavy hydrocarbons. This can be controlled by appropriately controlling the pressure relationships between the gasification and the degasification spaces.

The terms high-value gas and lower-value gas as used herein refer, of course, to the BTU content of the gases. Thus, a high-value gas may for instance have on the order of 10,000 kg. cal/m.sup.3 whereas a lower-value gas may have on the order of 5,000 kg. cal/m.sup.3.

According to the invention the combustion gases which result from the gasification of a coke, that is the lower-value gases, can also be used at another location of the underground deposit for heating the not-yet-combusted coal in this region sufficiently to effect expulsion of the higher-value gases therefrom; in other words, this results in a conversion of the coal into coke which will subsequently be combusted to yield the lower-value combustion gases. This means that two or more operating locations in the underground deposit or field can alternately cooperate with one another in such a manner that the volatile components (higher-value gases) are being expelled in one region by the heat of the combustion gases yielded during the combustion of coke in another region, that is coal from which the higher-value combustion gases had previously been expelled.

It is advantageous to provide throughout the coal seam or deposit various bore holes for the removal of the higher-value gases, so that the expelled gases can be withdrawn ahead of (as seen with respect to the travel of) the fire front, or above the latter. These bore holes can then be separated from the channel system and closed as the fire front approaches them.

The air required for the combustion is advantageously although not necessarily advanced to the combustion front via an already completely or partially combusted region of the deposit, that is a region which is still hot from the combustion, so that the air is thereby preheated and is supplied in this preheated state either directly to the combustion zone or to a burner whose hot waste gases are reduced at the combustion front to form a combustible gas.

In order to be able to carry out the method with a desired degree of precision and control, it is advantageous to subdivide the coal deposit or the region thereof which is to be processed according to the present invention, with a plurality of at least substantially parallel channels which subdivide the deposit into adjacent sectors. Each of the channels is then provided with one or more fire dams which separate the adjacent sectors from one another. The fire dams may be provided with closable openings through which the supply and/or removal of gases can be effected.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as toits construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a perspective diagrammatic view illustrating an embodiment of the invention, with the roof overlying the diagrammatically shown coal deposit having been omitted for the sake of clarity;

FIG. 2 is a vertical section through FIG. 1;

FIG. 3 is a diagrammatic top-plan view of FIG. 2;

FIG. 4 is a fragmentary vertical sectional detail view illustrating a further embodiment of the invention;

FIG. 5 is a fragmentary detail view, on an enlarged scale, illustrating a detail of FIG. 5; and

FIG. 6 is a fragmentary partly vertically sectioned detail view, also illustrating a detail of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Discussing the drawing in detail, and firstly FIGS. 1--3, it will be seen that here the coal deposit is subdivided by at least substantially parallel galleries 2 into a plurality of adjacent sectors 1a, 1b and 1c. The adjacent sectors are separated from one another, and the galleries protected, by fire dams 4 which extend longitudinally into the galleries and are provided with openings 5 for the combustion air and 6 for the removal of expelled high-value gases. The openings 6, which are the outlets of appropriate channels or pipes extending into the respective sectors, communicate with a collecting pipe or channel 3.

Each of the sectors (this is shown by way of example only for sector 1b in FIG. 1) is subdivided again approximately midway intermediate its sides, that is approximately midway intermediate the distance a, by a longitudinally extending channel 7 through which the lower-value gases are to be withdrawn which result from combustion of the coal deposit. The channel 7 communicates (see FIG. 2) with one or more bore holes or shafts 8 which in turn communicate with the surface.

If, as has been suggested in FIG. 2, the dimensions of the coal deposit 10 are particularly substantial, then bore holes or shafts 9 may be sunk from above where they are connected at the surface by non-illustrated connecting conduits.

The gasification, that is the combustion with resultant formation of combustion gases, of the coal deposit takes place approximately in the region 1 and the portions of the coal seam 10 located above this region will drop down into this space as combustion proceeds, with the overlying stratum or roof 11 descending in conformance with such break-ins. The result is a communication between the degasification and gasification zones, that is the zones where high-value gases are expelled and the zones where lower-value combustion gases originate, and by appropriately controlling the pressures in these zones (over or underpressures) an advantageous mixture of the two types of gases can be obtained for withdrawal. In FIG. 2 the higher-value gases may be withdrawn from the bores 9 and the lower-value ones from the bores 8.

FIG. 3 shows that the galleries 13, 13' which extend from shafts 12, 12' delimit the coal field or deposit over a rather large extend, for instance over a distance of 10 kilometers. Between them are provided the galleries 2 of FIG. 1, and the channels 7. The spacing amounts to about 400 meters, although this can be varied (this is the distance a shown in FIG. 1) so that in such a case each sector 1a, 1b or 1c would contain approximately 6 million tons of coal, assuming a thickness of the seam of 1.5 meters. The provision of the fire dams 4 assures that each sector can be prepared for combustion without any danger, while an adjacent sector is already in the process of being combusted.

The gases serving for combusting purposes, for instance combustion air, are supplied from the galleries 2 and move along the combustion front where they become converted into combustible gases to leave the gasification zone through the channel 7 which may be provided with wooden supports to reduce expenses and to assure that these, also, will eventually become combusted. If the supply of combustion air is admitted at appropriate locations, the air will always move along the shortest path, that is directly along the face of the seam, at the combustion front or fire front.

As soon as the fire front reaches the vicinity of the next passage 6, the latter is separated from the collecting passage 3, and this can be effected automatically in dependence upon the gas quality as will be discussed later. A premature break-in of the roof does not disadvantageously influence the gas stream, because sufficient space will always remain for the gas to pass.

Calculations show that a combustion of up to 2,000 tons per day can be expected with the present invention, meaning that a field of the size mentioned earlier would be gasified in approximately ten years.

One of the particular advantages of the present invention is that the preparation of pipeline gas, that is gas which can be supplied to remote locations via a pipeline, is thus made not only very simple but also very rapid. It is possible, for instance, to separate the gases still underground into high-value gases of for instance between 10,000 kg. cal/m.sup.3 to 6,000 kg. cal/m.sup.3, and into a lower-value gas of for instance 6,000 - 4,000 kg. cal/m.sup.3 and a still lower-value gas of for instance less than 4,000 kg. cal/m.sup.3.

FIGS. 4-6 show a further embodiment of the invention. Certain elements in these Figures have been identified with the same reference numerals as in FIGS. 1-3.

In this embodiment the seam or coal deposit will be provided with bore holes accommodating channels or tubes 40, 40a, 40b. Adjacent ones of these tubes (for instance the tubes 40 and 40a or the tubes 40a and 40b) may be spaced at distances of e.g. 2 meters. The tubes themselves will be provided with perforations or apertures over that portion of their length which is accommodated in the bore holes, within the coal seam, to permit the entry of gas into the tubes. The tubes 40, 40a, 40b in turn are connected with tubes 41 and 42 extending longitudinally in the galleries 2 and with one of them (the tube 41) being intended for high-value gas and the other of them (the tube 42) for lower-value gas.

An exhaustor 44, which may be of any known construction, is connected with tube 41 via a throttling device 43 and withdraws gas from tube 41 to blow it to the surface where it may be introduced into a pipeline or the like. Another throttling device 45 connects the tube 42 with an exhaustor 47 which is provided for the same purpose. By appropriately operating the throttling devices 43 and 45, the pressures in the tubes 41 and 42 can be controlled as desired (underpressure is preferred), thereby permitting the control of the relative quantity of gas which enters into the respective tubes. Such a control can for instance be effected by manometers 47 and 48. The tube 40 is connected with the tubes 41 and 42 in the manner illustrated in FIGS. 5 and 6, via the illustrated box B.

It will be appreciated that as the fire front advances to the tube 40, the tube will be destroyed. Before the value of gas recovered drops below a certain level, for instance below 4,000 kg. cal/m.sup.3, the entire box B is dismantled to be disconnected from the tube 40 and is then reassembled and for instance connected with the next tube 40a or 40b, and of course in each instance again with the tubes 41 and 42. This means that only two or three such boxes B are necessary at each operating location. The tube 40 is capped or otherwise closed after removal of the box B.

As FIGS. 5 and 6 show, the tube 40 (or 40a or 40b) is connected in box B via a tube 49a with an apparatus 49 which is a known measuring instrument determining the gas value or the methane percentage of the gas. The device 49 is provided with a plurality of terminals 51, 52, 53 and 54 and with an element 50 operatively associated with these terminals and supplying electric current to them. Electrically operated valves 55 and 56 are provided and are connected in circuit with the terminals so as to be controlled by signals originating thereat. The arrangement may for instance be such that when the gas value is sensed to be between 10,000 and 6,000 kg. cal/m.sup.3, the valve 56 is opened and the valve 56 is closed, whereas for instance between a 6,000 and 4,000 kg. cal/m.sup.3 the valve 56 is closed and the valve 55 is opened. Under 4,000 kg. cal/m.sup.3 both valves 55 and 56 may be closed.

In thin coal seams or deposits the tubes 40, 40a and 40b may be arranged horizontally or near-horizontally, and in thicker seams they may be arranged vertically or near-vertically. However, they may of course also be arranged both vertically and horizontally (for instance alternating tubes 40, 40a or 40a, 40b) if this is desired or determined to be advantageous.

What is important is to keep in mind that the present invention permits the recovery of gases having a higher caloric value than was previously the case, and permits such recovery in a simple and rather inexpensive manner, and with a minimum of effort.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of applications differing from the types described above.

While the invention has been illustrated and described as embodied in the gasification of underground deposits of coal, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

Claims

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims:

1. A method of gasifying underground deposits of coal, comprising the steps of forming in an underground coal deposit a first conduit system including at least one channel which extends along a face of the deposit; forming in said coal deposit a second conduit system having a plurality of inlets which are located in said deposits inwardly spaced from said face by a substantial distance; combusting said coal deposit so that the fire front extends along said face and consumes said deposit in direction inwardly of said face, whereby the heat of combustion expels high-value gases from said coal deposit whereas said combustion results substantially only in the formation of lower-value combustion gases; withdrawing said high-value gases through said inlets which are inwardly spaced from said face; withdrawing said lower-value combustion gases through said channel which extends along said face and the fire front; and terminating the withdrawal of said high-value gases through respective ones of said inlets when the fire front reaches the same.

2. A method as defined in claim 1; further comprising the step of regulating the withdrawal of said gases so as to admit only a desired fraction of at least one of said high-value and lower-value gases into the respective conduit system.

3. A method as defined in claim 2, wherein the step of regulating the withdrawal comprises regulating the relative pressures in said conduit systems.

4. A method as defined in claim 1; further comprising the step of circulating the hot combustion gases into heat-exchanging proximity with as yet uncombusted regions of said coal deposit to thereby expel high-value gases therefrom preliminary to combusting of the respective region.

5. A method as defined in claim 1; further comprising the steps of supplying combustion air into the combusting coal deposit, and of pre-heating such combustion air.

6. A method as defined in claim 5, wherein the step of pre-heating said combustion air comprises circulating the combustion air into heat-exchanging proximity with a respective at least partially combusted hot region of said coal deposit.

7. A system for the gasification of underground coal deposits, comprising first conduit means, including a channel formed in an underground coal deposit and bounded on one side by a face of the deposit along which the latter is to be combusted so that the resulting fire front consumes said deposit in direction inwardly of said face; a fire dam provided in said channel and extending along said face with spacing therefrom to form with said face a passage for the withdrawal of low-value combustion gases resulting from the coking of said coal deposit; second conduit means, including a plurality of second conduits which extend through said coal deposit and have inlet openings located within said coal deposit inwardly spaced from said face by a substantial distance, so as to permit the withdrawal through said inlet openings of high-value gases which are expelled from the coal of said deposit by the heat of the approaching fire front; and means operative at will for preventing the passage of gases through respective ones of said second conduits as the same are reached by said fire front.

8. A system as defined in claim 7; and further comprising supply means for supplying combustion air into said passage.