US 2788956 A
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E. F- PEVERE ET AL GENERATION OF CARBON MONOXIDE AND HYDROGEN 4 April 16, 1957 2,788,956
BY UNDERGROUND GASIF'ICATION OF COAL I Filed Aug. 3, 1955 med SmePuefO GENERATION 01 MONOXIDE' HYDROGEN BY UNDERGROUND GASIFICA- TION F COAL I a Ernest'F. Pevere, Reac ing-mu Hom ny. Hess, Glenliam, N". Y., assignurs-to The. Texas Company; New York, N. Y., a corporation. of Delaware Application August 3, 1955, Serial No. 526,163 fiGlaiins". '(Cl.-262-"-$) This application relates-tothe partial combustionof coal inunderground seams. in one of itsmore specific aspects, the invention relates to a method for preparing coal beds for'underground gasification. 7
Since 1933', the underground gasification-of coal has been seriously investigated and exploited by a special Russian trust, Podzem, and extensive Russian literature has grown out of this work. A reviewin-English by Chel-tin was published in Collary Garden 162, 1193-6 (1936) and Fuel Economist ll, 331- (l 936). Since. the end of World War II, this problem has been seriously examined in England, France, Belgium and the UnitedSta'tes. A review by M. L. Kastems'appeared in Chemical and Engineering News, March 24,. 1952.
Underground gasification of coal hasbeen carried out in a number of cases with encouraging results. In preparing the coal seam forgasification, it is generally necessary to drive two parallel main drifts through .the:coal seam, one as an inlet andthe other as an outlet, and to connect these shafts with one or more-lateral drifts at right angles to the main drifts. A combustion-supporting gas, e. g. air, oxygen or'other gas' con'taining'free oxygen is introduced through one of the main drifts and products of combustion are withdrawn through the other. Steam or carbon dioxide may be used in conjunction with air, oxygen, or a mixture of air and oxygen as the gasifying medium or combustion-supporting gas. Combustion is initiated by igniting the .co'al along the path of flow, usually at the lateral cross drifts. The main drifts may be used alternately as inlets and outlets. Afterthe coal seam is fired, air or oxygen is blown through the corridorto bring the surface of the coal tofthe desired temperature, and then steam is blown in either alone or withair or oxygen. If steam alone is used, the flow of steam must be periodically interrupted and the coal seam'firedwith combustionsupporting gas to maintain .the required temperature. A mixture of steam with oxygen or air may be used for continuous gasification. Thegas produced generallyhas a low B. t. u. value, a result which is not unexpected due to poor contact of the coal with the steam and oxygen.
It has been proposed previously to prepare a portion of a coal seam for gasification by breaking the coal loose from the bed by mining methods and then passing the reacting gases through the lumps ofcoal. Although this procedure results in effective contact between thecoai and thegases it obviously is a costly one. By the process of this invention the coal seam is prepared for underground g'asifica'tion insuch-a way that intimate contact between the coal and the gaseous reactants isobtained without the necessity of mining the coal from the seam.
In accordance with this inventiona mineral acid having solvent power for one or more' of the constituents of the coal is brought into contact with theicoal seameffecting solution of coal substance; Preferably, theacidi. is permitted to drip onto the coal at a pluarlity of points. The acid forms a multitude of passages through the coal which are irregular in shape and which are very permeable to gaseous reactants used for the gasification of coal.
In a specific embodiment of. the presentinvention a main channel or passageway is drilled throughan upper portion of the coal seam, preferably as near as possible to the top-of the seam, while a second-"main passageway Patented Apr. 16; 1957 stantially parallel to the upper passageway. In general, the passageways are parallel to the bedding; plane of the coal seam. Theprocess of the invention remains the samefor an inclined seam as for a horizontal seam. The acid is introduced through the upper main passageway or drift. The acid percolates downward through. the coal seam and eventually reaches the lower main passageway. Intermediate .passagewaysparallel to the main passageways may be :provided and are particularly-advantageous in thick beds.
In .a preferred embodiment of. the present invention strong sulfuric acid containing percent sulfuric acid by weight is introduced slowlyinto contact with the coal in the=upper partof. the. seam- Strong sulfuric acid may be introduced through the passageway-into contact with the coalseam through a steel .tube. The tube may be perforated to distribute the acid along the desired section of the passageway. With other acids other types of acid resistant tubing. are required, e. g. plastic or synthetic rubber tubes.
St-rongmineral acids, e. g. hydrochloric, hydrofluoric, nitric, and sulfuric acids, are useful in the processof this invention. The acid concentration should exceed 30 weight percent. Higher concentrations of sulfuric and nitric acids are desirable. Sulfuric acid in. excess. of 90 weight percent is preferred.
Selective gasification of'the coal seam may be accomplished'by treating. sections of the seam with acidv and leaving pillar-s or untreated sections of the coal seam between treated sections. One or more of the treated sections may be ignited while others are blocked off.
Preferably the-reaction is initiated in an upper passageway, the gasification proceeding downwardly through the c'oal b'ed to a lower passageway. As indicated above, exit passageways may be provided at varying depths and are particularly useful inthick seams of coal.
Firing of the coal may be initiatedin any of a number of ways, fo'rexample by pumping a colloidal or semicolloidal dispersion of phosphorus in water, or phosphorus in carbon disulfide into the upper part of the pretreated section of the coal. As the carrier liquid trickles downwardly through the treated section, phosphorus is deposited on .thelco'al. Afterthe bed has been pretreated with the phosphorus solution, an oxygen-containing gas is'introduced which, upon contact with the phosphorus, ignites simultaneously and thereby ignites the coal. Once the reaction commences it isself sustaining so long as an adeguate supply of oxygen-containing gas is provided.
The" figure is a diagrammatic sectional view through a section of the earth illustrating the application of the process of this invention to underground gasification of coal.
With reference to the figure, a well 1 is drilled into or through the coalseam. A main passageway 2 is then drilled along the upper part of the coal seam. Means for horizontal drilling and directional drilling-are known in the art. Generally, a deflecting device known as a whipstock is positioned in the well 'at the desired depth and a rotating drill bit on a flexible conduit is operated fromth'e whipstock' to effect horizontal 'or near-horizontal drilling. After a horizontal bore Zof the desired length. has been drilled, the bit is removed, the whipstock is lowered and a second bore 3 is drilled through the coal seam parallel to and below bore 2. Bore 3 forms the second main passageway. Obviously a number of such passageways may be drilled through the coat seam. The portion of well 1 below bore 2 is then filled with cement 4. A second well 6 is drilled into the coal seam to intersect passageway 3-. Well 6 may be enlargedat its lower end'b'y means of explosive charges.
A conduit 7, closed at its end andprovid'e'd witha series ofperforations 8; is; theniutr'oduced into the-upper main passageway 2. Strong mineral acid, e. g. sulfuric acid, is
pumped through conduit 7 from which it escapes through perforations 8 into section AA' of the coal seam. The 7 necting the upper main passageway 2 with the lower main passageway 3. Similarly, other sections of the coal seam, e. g. section BB' may be acid treated. Following acid treatment, an ignition agent may be introduced through pipe 7. Following preparation pipe 7 is withdrawn from the well bore. A combustion supporting gas is then introduced through one of the wells, preferably through well 1 into the upper horizontal pasageway 2. The coal seam is, ignited at the top of the treated section. The oxygen-containing gas stream passes down through channels formed by the acid in the treated section. As the coal is consumed, combustible gas comprising carbon monoxide and hydrogen is generated. The combustible gas, together with volatile constituents distilled from the coal, is collected in the lower pasageway 3 and produced through well 6 to the surface.
The coal seam may be ignited initially in any suitable manner, as by electrical means or by a squib or incendiary shell, placed in contact with the coal in the horizontal passageway 2.
Air or relatively pure oxygen may be employed as the source of oxygen-containing gas. Relatively pure oxygen is preferred from the standpoint of producing gas which contains a minimum amount of nitrogen and other inert constituents. Once combustion is well established, steam may be introduced either continuously, in admixture with oxygen or oxygen-containing gas, or intermittently as in gas making apparatus with alternate blast and blow gas make cycles. Steam helps to control the temperature in the formation and produces hydrogen.
It will be understood that although passageway 2 is preferred as the input passageway for the combustionsupporting gas, either main passageway 2 or 3 may be used as the input pasageway while the other is used as the outlet passageway. It will also be understood that either of the main passageways may be drilled through well 6.
i In an alternative procedure, channels between passageways 2 and 3 are first made by hydraulic fracturing of'the coal seam between the passageways. In this case, hydraulic fluid under pressure, suitably water or oil with or without thickeners or viscosity increasing additives, is introduced through well 6 into passageway 3 under sufficient pressure to fracture the coal seam and form cracks extending upwardly toward or even as far as passageway 2. Similarly, hydraulic fluid under pressure may be introduced through well 1 into the upper passageway 2,
fracturingthe coalseam between bores 2 and 3. The
liquid is withdrawn, the grains of sand or gravel serve to help prevent thecracks from closing. Following hydraulic fracturing, acid is introduced through passageway 2 onto the top of the coal seam. The acid per- .colates down through the fissures, forming auxiliary passageways'interconnecting the main passageways. The gasifying medium may be readily passed through the auxiliary passageways.
Spent acid may be withdrawn from the coal seam through passageway 3 and well 6. Ordinarily it is not necessary to separately withdraw the spent acid. Acid recovery is efiected by processing the product gas. Fresh acid thus may be made up for additional treatment opcrations. Sulfuric acid is a preferred acid because of the natural occurrence of sulfurin coal. Obviously, many modifications and variations of the invention, as herein'before set forth, may be made without departing from the spirit and scope thereof and therefore only such limitations should:be made as are'indicated in the appended claims.
Weclaimz. 1. In a process forthe underground gasification of coal in which an exothermically-reacting gas is introduced into contact with the coal in situ, the coal is reacted with said gas, and gaseous products of reaction are withdrawn from the coal bed, the improvement which comprises forming a first main passageway through an upper portion of the 'coal bed along the seam, forming a second main passageway through a lower portion of the coal bed along the seamsubstantially parallel to and below said first passageway, fonning aum'liary passageways interconnecting said main passageways by introduction of strong mineral acid through said first passageway into contact with said coal eifecting solution of coal substance in said acid, and
thereafter supplying reactant gas to one of said main passageways, and withdrawing gaseous products from the other of said main passageways.
2. A process as defined in claim 1 wherein said acid is sulfuric acid.
3. A process as defined in claim 1 wherein said acid is nitric acid.
4. A process as defined in claim 1 wherein said acid is hydrochloric acid.
5. In a process for the underground gasification'of coal wherein a combustion-supporting gas is introduced into contact with the coal in situ, the coal is ignited, and gaseous products of reaction are withdrawn from the coal bed, the improvement which comprises forming a first main passageway through an upper portion of the coal bed along the seam, forming a second main passageway through a lower portion of the coal bed along the seam substantially parallel to and below said first passageway, and introducing strong mineral acid through said first main passageway into contact with the bed of coal at a plurality of selectedpoints along said first main passageway thereby effecting solution .of coal substance and forming auxiliary vpasageways interconnecting said main passageways,
. 6. In a'pro'cess for .the underground gasification of coal wherein a combustion-supporting gas isintroduced into contact with the coal in situ, the coal is ignited, and gaseous products of reaction are withdrawn from the coal bed, the improvement which comprises forming a first main passageway through an upper portion of the coal bed .along the seam, forming a second main passageway through a lower portion of the coal bed along the seam substantially parallel to and below said first passageway, introducing liquid under pressure through at least one of said mainpassageways eflecting fracturing of said coal seam and forming fluid permeable channels interconnecting said main passageways, withdrawing said fracturing liquid and introducing a strong mineral acid into said first main passageway and through said channels into said secondmain passageway effecting solution of coal substance in said strong mineral acid, withdrawing reaction products of said acid from said coal bed, introducing combustion-supporting fluid through one of said main passageways, and withdrawing gaseous products of reaction from the other of said main passageways.
References Cited in the file of this patent UNITED STATES PATENTS 2,630,306 I Evans Mar. 3', 1953