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Publication numberUS3723079 A
Publication typeGrant
Publication dateMar 27, 1973
Filing dateJul 23, 1971
Priority dateJul 23, 1971
Publication numberUS 3723079 A, US 3723079A, US-A-3723079, US3723079 A, US3723079A
InventorsSeitzer W
Original AssigneeSun Research Development
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Stabilization of coal
US 3723079 A
A process for stabilizing dried lignitic and subbituminous coal against spontaneous combustion which comprises treating said dried coal at about 175 DEG to about 225 DEG C. with oxygen in an amount of from about 0.5 percent to about 8 percent by weight of said coal and rehydrating the oxygen treated coal with water in an amount of from about 1.5 percent to about 6 percent by weight of said oxygen treated coal.
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Unite States atent r 1 Seitzer [54] STABILIZATION OF COAL [75] Inventor: Walter H. Seitzer, Marcus Hook,

[73] Assignee: Sun Research and Development Co.,

Philadelphia, Pa.

[22] Filed: July 23, 1971 [21] Appl. No.: 165,728

[52] US. Cl. ....44/l R, 44/1 G [51] Int. Cl..; ..C10l 5/00 [58] Field of Search ..44/1 R, l G, 6,10 D, 10 E [56] References Cited UNITED STATES PATENTS 1,219,155 3/1917 Rigby 44/1 R [4 1 Mar. 27, 1973 Fernholtz ..44/l G Ford ..44/1O E Primary Examiner-C. F. Dees Attorney-George L. Church et a1.

[57] ABSTRACT 2 Claims, N0 Drawings STABILIZATION or COAL Dried lignitic and subbituminous coals are unstable to storage in that they are subject to air oxidation and combust spontaneously. Thus, in order to enhance storage stability special treatments must often be used. For example, coal piles are often arranged in a particular manner to obtain safe storage; e.g., thin layers which are compacted with sloping sides at a maximum angle of 14, smooth final surfaces, and top surface continually smoothed as coal is removed from the top only. Other approaches to prevent spontaneous combustion during storage involves chemical treatment of the coal; e.g., coating the coal with petroleum products and their emulsions, spraying with calcium bicarbonate or aqueous hydroquinone or amines. Such treatments, however, are either not completely effective or are excessively expensive for a low priced commodity such as coal.

Numerous investigations have been made on the oxidation of coal with an objective toward improving its stability. One such study concluded that use of oxygen to form oxidized zones on the surface and in the interior of the mass of brown coals imparted protection against further oxidation (Szadeczky-Kardoss, E., Ungar., Z. Berg u. Huettenwessen, 77, 241-7, 253-60, 1944). My experimental work confirms this effect with oxygen treatment, but 1 have found this technique to be an incomplete solution to the storage stability problem. In my experiments 1 find that this oxygen treatment coal and thus, the process of the invention will use from about 0.5 pounds to about 8 pounds of oxygen per 100 pounds of coal treated. It will be also understood that air is a suitable source of oxygen and that pure oxygen,

delays somewhat the time until spontaneous combustion might occur, but the treatment does not greatly extend the safe storage period.

1 have now found a means to significantly improve the storage stability of dried lignitic and subbituminous coal and this is accomplished, in accord with my invention, by the process which comprises treating said dried coal at a temperature between about 175 C. and about 225 C. with oxygen in an amount of from about 0.5 percent to about 8 percent by weight of said coal and rehydrating the oxygen treated coal with water in an amount of from about 1.5 percent to about 6 percent by weight of said coal.

The coals used in the process of the invention will be, as indicated, lignitic and subbituminous coals and will include North Dakota lignite, Powder River subbituminous coal, Wyodak coal, and the like. Such coals usually contain from about 20 to 40 percent water as they come from the mine, but for use in subject process they will first be dried to a water level of about I percent to about 10 percent by weight and this is readily done simply by flowing hot flue gas through the coal. The process of the invention is applicable to coal of any size, but will, of course, be of most value with the smaller sizes since they have the greater surface area and are most subject to oxidation.

In carrying out the process of the invention it is important to control the amount of oxidation since I have found that excessive oxygen actually decreases the stability of the dried coal. The process of the invention requires that the oxygen treatment be controlled so that its uptake is between about 0.5 percent and about 8 percent by weight of the coal treated. As a guide in carrying out this controlled oxidation it should be understood that an oxygen uptake of 1 percent corresponds to about 1 pound ofoxygen per 100 pounds of while operable, is somewhat expensive for use in the process.

r The-oxygen treatment may be carried out by any conventional technique which will distribute the oxygen over the surface of the coal. In a preferred method, the dried coal is treated with air in a rotary drum burner, the temperature of treatment being from about C. to about 225 C. Not all of the oxygen in the air will be reactive with the coal since about onehalf of the available oxygen will be carried out of the burner. This is readily compensated for by adjusting air flow, drum rotation speed, and coal volume in accord with known techniques available to the skilled art worker. The oxygen level of the gas used for the oxidation treatment should be at least about 10 percent and as the oxidation proceeds about 45 percent of the oxygen is converted to water, about 45 percent to CO and about 10 percent to CO.

The rehydration of the coal with water is readily accomplished by a spraying technique, although when smaller amounts are treated, the coal particles may be simply agitated with the required amount of water to effect distribution on the surface. As indicated, the amount of water used will be between about 1.5 percent and about 6 percent by weight of the oxygen treated coal. In a preferred technique the hot coal emerging from the oxygen treating step is cooled to a temperature between about 150 and about 50 C. by heat exchange with the hot gas oxygen supply, and then the cooled coal is sprayed with water. Empirical techniques are easily employed in the selection of type of spray nozzle, water pressure, time of spray, etc. in order to place from about 1.5 percent to about 6 percent water on the coal.

After the water treatment the stabilized coal is handled, transported and stored by conventional methods and prolonged storage stability of the treated coal is evident.

in order to more fully illustrate the invention the following examples are given:

Test Procedure Dried Wyodak coal of 14 mesh size is placed in a stirred container equipped with an oxygen inlet, an outlet which is connected in series to a drying tube, a CuO catalyzed converter at 800 C. to convert CO to C0,, an Ascarite tube for C0, absorption, and then connected through a pump to the input for oxygen recycle. The stirred coal is heated to 200 C. as oxygen is passed through the system and recycled. The amount of oxygen used is measured with appropriate gas flow meters.

The oxidized coal is cooled and wetted with the desired amount of water, thorough distribution being obtained by agitation. Then the rehydrated coal is placed in a Dewar flask fitted at the bottom with a sparging tube to pass oxygen through the coal and equipped with a temperature measuring device. The coal (450g) in Dewar flask (70 mm. [.D.) is about 200 mm. in depth and oxygen is passed through it at 63 C. at a rate of ml/min. The time for combustion of the coal to occur is noted as shown by the sudden temperature increase and is taken as a measure of stability.

The following tables illustrate the effects of the process:

TABLE I Ex. nov Coal treatment Hours to combustion No oxygen, No water 1 6 l% 0,, No water 6.0 7% 0,, No water 4.8

8% 0,, No water 4.5

No oxygen, 6% water 4.3

4% 0 1.5% water 9 0 4% 0 3% water Never com busts illustrative of the invention:

TABLE 11 Ex. no. Coal Treatment Hours to Combustion 8. No oxygen. 6% water 4.3 9. 4% 0, +6% water Never combusts l0. 7% 0, 6% water Never co'mbusts l l. 8% O, 6% water Never combusts It is clear from the above data that the process of the invention provides a means to prevent spontaneous combustion of coal during storage and makes a valuable contribution to the art.

The invention claimed is:

l. A process for stabilizing dried lignitic and subbituminous coal against spontaneous combustion which comprises treating said dried coal at about to about 225 C. with oxygen in an amount of from about 0.5 percent to about 8 percent by weight of said coal and rehydrating the oxygen treated coal with water in an amount of from about 1.5 percent to about 6 percent by weight of said oxygen treated coal.

2. The process of claim 1 where the amount of water is from about 3 percent to about 6 percent.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US1219155 *Jan 11, 1913Mar 13, 1917Nils TestrupTreatment of lignite and the like.
US1426723 *Sep 23, 1916Aug 22, 1922Margaret J ThompsonProcess and apparatus for the conversion of peat, lignite, and other carbonaceous substances into artificial coal
US1577902 *Dec 22, 1924Mar 23, 1926Fernholtz Machinery CompanyBlock or briquette of lignite and method of making the same
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4043763 *Jan 7, 1977Aug 23, 1977Suntech, Inc.Stabilization of dried coal
US4192650 *Jul 17, 1978Mar 11, 1980Sunoco Energy Development Co.Process for drying and stabilizing coal
US4213752 *Nov 6, 1978Jul 22, 1980Suntech, Inc.Coal drying process
US4401436 *Dec 21, 1981Aug 30, 1983Atlantic Richfield CompanyProcess for cooling particulate coal
US4402706 *Dec 21, 1981Sep 6, 1983Atlantic Richfield CompanyMethod and apparatus for oxidizing dried low rank coal
US4498905 *Aug 31, 1984Feb 12, 1985Atlantic Richfield CompanyMethod for deactivating and controlling the dusting tendencies of dried particulate lower rank coal
US4501551 *Nov 10, 1983Feb 26, 1985Atlantic Richfield CompanyMethod for producing a dried particulate coal fuel from a particulate low rank coal
US4645513 *Jun 21, 1985Feb 24, 1987Idemitsu Kosan Company LimitedProcess for modification of coal
US5254139 *Aug 5, 1991Oct 19, 1993Adams Robert JMethod for treating coal
US5468265 *Aug 12, 1993Nov 21, 1995Rja AssociatesMethod for treating coal
US5863304 *Aug 15, 1995Jan 26, 1999Western Syncoal CompanyStabilized thermally beneficiated low rank coal and method of manufacture
US6090171 *Jan 21, 1999Jul 18, 2000Western Syncoal CompanyStabilized thermally beneficiated low rank coal and method of manufacture
US7695535Dec 22, 2005Apr 13, 2010River Basin Energy, Inc.Process for in-situ passivation of partially-dried coal
US8197561Sep 24, 2009Jun 12, 2012River Basin Energy, Inc.Process for drying coal
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EP2287279A1 *Mar 11, 2005Feb 23, 2011Evergreen Energy Inc.Method and apparatus for thermally upgrading carbonaceous materials
U.S. Classification44/608, 44/620, 44/501
International ClassificationC10L9/06, C10L9/00
Cooperative ClassificationC10L9/06
European ClassificationC10L9/06