US2276362A - Vacuum treatment of coking coals - Google Patents

Description

March 17, w42. c. s. woLF VACUUM TREATMENT OF COKING GOALS Filed July 2, 1940 Patented Mar. 17, 1942 orion VACUUM TREATMENT OF COKING GOALS Clayton S. Wolf, New Haven, Conn., assignor, by mesne assignments, to American Cyanamid Company, New York, N. Y., a corporation of Maine Application July 2, 1940', Serial N0. 343,511

5 Claims.

The present invention relates to the treatment of coking coals and more particularly it relates to a method of treating badly swelling and caking coals to alter the coking characteristics thereof.

Many bituminous coals, such as high volatile bituminous coals, cake and swell badly when it 'is attempted to carbonize them in the production of coke. The swelling and caking characteristics proposed oxidation process involves subjecting the coal to a treatment at an elevated. temperature and maintaining the temperatureunder atmospheric conditions for varying lengths of time. In general, the process involves heating the coal to a temperature of about 150 C. and

maintaining that temperature for a period of 24 to 120 hours depending upon the type of coal being treated. An improved oxidation process is described and claimed'in the co-pending application Serial No. 343,518 led June 2, 1940, which comprises grinding the coal, raising the temperature of the coal to about 150 C. and then subjecting the heated coal to elevated air pressures of from about to 150 lbs. per square inch while maintaining a temperature of about 150 C. for a period of from 3 to 6 hours depending on the type of coal. While the above-described pretreating processes are useful in altering the coking characteristics of bituminous coals, they are somewhat cumbersome in that relatively long periods of time are consumed in. the treating process which materially slows down plant properature of the crushed coal toabout 150 C. and

maintaining at this temperature -until all o'f the surface moisture and that of constitution which maybe created at this temperature of .150 C. has been removed. 'I'his "can usually beaccomplished in about one hour. Some coals, however, are sufficiently dry ln their natural state and the drying is not necessary. The'd'ry crushed coal is then subjected to a vacuum equivalent to about 28 inches of mercury for about 15.to 30 minutes and then allowed to come to atmospheric pressure for a period of 3Q minutes to one hour. After which the coal is again subjected to a vacuum equivalent to about 28 inches of mercury for another 15 to 30 minutes. These alternative vacuum atmospheric treatments may be repeated a. v

number of times in some cases. During the above vacuum and atmospheric treatments of the coal the temperature is maintained at about C. When badly swelling and caking bituminousv coals, such as those of the Pittsburgh seam type and which normally cannot successfully be briquetted and carbonized,are subjected to my pretreating process the coal is altered to such an extent that it can successfully be formed into briquettes and carbonized at a temperature rise oi at least 2 C. per minute during the plastic temperature range.

I do not desire to limit the present invention by any particular theory or explanation as to why my pre-treating process alters the coking characteristics of swelling and caking coals. One possible theory is that the eiTect ls achieved by oxidation since it is known that oxidation processes produced similar changes. If the change is due to oxidation, it may be that the vacuum treatment breaks down and removes with the aid of 150 C. temperature the occluded liquid or gaseous films which surround each coal particle and thereby permits the oxygen of the air to react quickly with the coal ,at normal atmospheric pressures and that the second or successive evacuations may be necessary to remove such liquid or gaseous iilms again when they may have been formed by the oxidation f the coal when air was permitted to enter it again after the ilrstevacuation. I know of no other satisfactory explanation of why the alternate vacuum atmospheric treatment produces the effect. It may well be.

however, that the changes are not caused by oxidation at all but are merely due to a change in or the removal of certain volatile constituents from the coal itself.

It is well known that some coking bituminous coals can be ground to a neness o f say about 28 screen mesh and compressed into briquettes without the use of any binder and that the briquettes can be carbonized ln any conventional manner and the rate of temperature rise can be regulated to prevent excessive swelling while going through the plastic temperature range. For

each and every type of coking bituminous coal there can be determined a. maximum rate of temperature rise (degrees per minute) through the plastic temperature range above which the briquettes will swell. These rates v ary tremendously for different coals, being inthe order of a fraction of one degree C. a minute for some coals and as high as to 10 a minute for others. It is an advantage of the present invention that my pre-treatment of the coal'permits an appreciable increase in the rate of carbonization of briquettes without swelling, and particularly coals that swell at a very low rate temperature rise.

Suitable plants for carrying out the vacuum treatment process of this invention includebroadly any type of tank or treater in which coal can be charged and maintained at a substantially uniform temperature of about 150 C. and which will permit the formation of a vacuum in the treater surrounding the coal equivalent to about 28 inches of mercury and also having means for releasing the vacuum and permitting the coal to come in contact with air at atmospheric pressure while still beingmaintained at 150 C. The vacuum coal treaters may be used as individual units or they may form a series of such vacuum treaters so arranged that while one tank is being subjected to vacuum treatment another tank can be subjected to atmospheric treatment in which way it is possible to continuously provide treated coal to subsequent briquetting operations. The treaters may likewise form a unit in a complete coal treating plant which can be comprised of pulverizlng equipment, drying and preheating equipment, conveying means for introduction of the coal into the vacuum treaters foltreaters may also be designed so that the coal can be subjected to alternate elevated pressures.

The invention will be more fully described in connection with the drawing which is a semi-diagrammatic elevation of a suitable plant for carrying out the process. It should be understood, however, that in its broader aspects the present invention is not concerned with any particular plant for carrying out the process, and the draw.- ing represents only one such suitable plant arrangement.

Indescribing the method of carrying out the present invention in connection with the drawing, the description relates specifically to the treatment of a badly swelling and caking Pittsburgh seam coal, containing about volatile matter, and is to be oxidized to such an extent that the treated coal can be made into coal tar pitch briquettes and carbonized at a rate of about 21,? C. per minute temperature rise through thc plastic temperature range without swelling. The coal as delivered to the plant is of low surface moisture content.

The coal is fed into a pulverizer I by means of a suitable feeder 2 as illustrated in the drawing. The coal in the pulverizer is ground so that the material finer than 20 mesh is picked up by the stream of air entering the pulverizer from the larger fan 3, The temperature in the mill is controlled by an admixture of more or less of hot flue gases produced in the adjoining pulverizer furnace 4 by a combustion of coal, oil or gas. The air sweeps through the upper portion 5 of equipment as an integral part of the mill, the oversize dropping out of the air stream and returning to the grinding elements of the pulverizer. The air stream leaving the mill is conducted by means of the conduits 6 to the cyclone type dust collector 1 where `about 90 to 95% of the coal is separated from the hot air, the remainder returning to the larger fan. and thus to the mill for recirculation.

The smaller fan 8 removes air from the system and blows it through the concentrator collectors 9 where the remaining coal is substantially all removed and the waste air is then 'passed to the atmosphere. 'I'he iine coal collected in these concentrator collectors is returned to the mill as shown. -The amount of' air passing through the concentrator collectors 9 is the same as the amount drawn into the system from the pulverizer furnace 4, plus the water evaporated from the coal, plus the water formed by decomposition of some of the coal.

The coal in the cyclone collector 1 is rdry and at a temperature equal to or somewhat lower than thatdesired in the treaters. The temperature is controlled by the amount and temperature of ilue gas drawn into the pulverizer I from the pulverizer furnace 4. A screen analysis `the cyclone collector 1 by means of a pulverized coal pump I0. In order to pump the pulverized coal and cause it to travel through the conveyor pipe II, the coal is aerated by the introduction of air through the air line I2 into the'coal conduit as shown. The amount of air required for proper aeration is on the order of 5% by weight of the coal conveyed. 'I'his air required for aeration is first heated to any desired temperature in the air heater coil I3 and provides one method of producing accurate temperature control of the coal before its introduction into the coal treaters.

The coal is conveyed through the conduit II to the coal treaters I4. The conduit is preferably jacketed and steam or oil at temperatures of 150 C. or more is introduced into the jacket to further raise or control the coal temperature desired. The length of this conduit and the temperature of steam or oil used in its jacket is sunlcient to assure the delivery of coal-at exactly the proper temperature, in this example 150 C. to the coal treaters I4.

The treaters I4 are simple insulated tanks capable of withstanding an external pressure of at least 14 lbs. per square inch. In a large plant there would be a number of treaters as shown and in a smaller plant perhaps only two or even one. When the first treater is filled, the coal valve I5 in the coal conduit is closed and theA valve to the next treater is opened. The ilrst treater is subjected to a vacuum equivalent to 28 inches of mercury by means of the vacuum pump' and allowed to stand for about l5 minutes at the reduced pressure. The vacuum is then broken by opening the vent valve to the treater and the coal is allowed to remain in the presence of air at atmospheric pressure for about 30 minutes,

the pulverizer which contains suitable separation v after which it is again subjected to a vacuum equivalent to about 28jinches of mercury for a second period of about 15 minutes, after which the coal is discharged from the treater into the treated coal -bin I6 from whence a suitable feeder I1 conveys the treated coal to the fiuxing and smooth glazed surfaces.

2,276,362 .briquetting equipment. The process is repeated -may also be adaptable for applying `elevated air pressure to the coal instead of the air treatment at atmospheric pressures.-

' The invention will be described more in detail in connection with the following specific example, in which different types ofvcoking bituminous coals are treated in accordance with the present invention, briquetted and compared to the same type of coal without the pre-treatment.

Emerald coal of the Pittsburgh seam type was ground and screened on a 28 mesh screen. The ground coal was then dried under atmospheric conditions at a temperature of 150 C. for a period of 1 hour. The heated ground coal was then placed in avacuum coal treater which treater was then sealed and evacuated lto the equivalent of 28 inches of mercury and held there for 15 minutes.,v The vacuum was then disconnected and air allowed to enter the treater e until it reached atmospheric pressure. The coal was allowed to remain at atmospheric pressure for 30 minutes and was then evacuated again to 28 inches of mercury and held there for 30 minutes. The vacuum was again disconnected and the treater allowed to come to atmosphericpressure and the coal immediately removed for briquetting. Briquettes were made from the coal using no binders and at the same-time briquettes were made from the coal which had not been treated in any way other than grinding. Briquettes were also made from treated coal and untreated coal in which 5% sulflte liquor dry substance was used as a binder. The briquettes were then subjected to carbonization under the same conditions, the conditions being such that the rise in temperature during the plastic range was at a rate of 3.3 C. per minute. The briquettes which were made from the untreated coal using no binder were very badly swollen and diametrical measurements could not be made as the briquettes assumed the proportions of unmeasurable puff balls of strong, hard.

very porous coke. The briquettes made from the. treated coal with no binder permitted diametrii cal measurements and showed a swelling of about 25%. These briquettes were well bonded and had smooth glazed surfaces.

The sulfite liquor bound briquettes were also carbonized underidentical conditions. the conditions being such that the temperature rise through the plastic range was at a rate of 3.3 C. per minute. The sulte liquor bound briquettes from the untreated coal showed substantially no diametrical swelling or shrinkage, the bonding was good, and the surface of 'the briquettes was only vfair. being somewhat rough. The sulte liquor bound briuuettes made from the treated coal showed a very great improvement over` those from the untreated coal. 'I'he diametrical shrinkage was approximatel--f 7%, the bonding was excellent, and they had briquettes was, likewise, very good.

An analysis 'of the above results clearly shows The density of these coal. I

The present invention is not to be limited to I the'Pittsburgh seam type of coal employed in vof certain British coals such as that the coals pre-treated in accordance with the present invention result in the production of not only higher grade briquettes but also under/conditions which are commercially practical.

The untreated coal of the above type could not bel briquetted, using no binder, and carbonized with i out swelling or diametrical increases in volume except at a very low rate of temperature rise during thecarbonization, such carbonization be ing limited to between .3 and .8 C. perminutethrough the plastic range.' Whereas the treated coal briquettes with no binder were successfully carbonizedat .a temperature rise of v3.3" C. per minute through the plastic range with only a slight swelling. When `the temperaturev rise is reduced to-between 2 and .2l/2 C. per minute'. then this small diametrical increase or swelling can be eliminated. In briquetting operations, if

the temperature rise through the plastic range is somewhat less than 1 C. per minute, they' are l not commercially practical processes.v Itis readily seen, therefore, that such coals when pretreated in accordance with the present invention `are altered to such an extent that they can be briquetted and carbonized at astemperature of atleast 2 C. rise per minute and which iss'uffcient to permit the'carbonization to be carried out with commercial success. y

-It is also known that certain coking bituminous coals, which cannot be successfully vbriquet'ted and .carbonized using no binders because of swelling, can be successfully briquetted and carbonized with 4 or 5% sulfite liquor dry substance as .ablnder in the preparation of briquettes.. In

the above example it is clearly shown that when briquettes made from the'untreated vand treated coal, using sulte liquor as a binder, are compared the treated coal briquettes are muchbetter and present a better range of `operating conditions than those produced fromtheuntreated the example and the process is applicable to all coking bituminous coals having swelling 'and caking properties which made them unsuited for briquetting and coking. For example, the process y can be used to improve the conditions under which coal, such as the Beckley seam coals, can be brlquetted successfully without pre-treatment when sulfite liquor is used as a binder but cannot be successfully briquetted and carbonized when binders such as molasses, pitch, or coal tar i are used. vThe Beckley coals, therefore, may be pre-treated' in accordance with the present invention to very greatly improve conditions under which the coal can be briquetted and carbonized. The improved conditions resulting from the pretreatment are an increase in the rate of temperature rise through the plastic range over 4that normally employed without an increase in swelling or caking, and the coking characteristics of the coal are changed to wider choice of binders may be used.

The process may also be used in pre-treatment scribed as Waterhouses unwashed coal" c'onsuch an extent that. aI

Pease and which coals taining about 26.4% volatiles, 69.6% xed carbon, 4.00% ash and is. strongly coking. "F is a strongly coking, low ash coal containing about 28.3% volatiles, 69.9% xed carbon, and 2.80%

ash. These coals, however, when treated in acas those coals that are very highly volatile and have very great swelling and caking properties and coals in which binders such as pitch or coal tar are to be used, it may be desirable to subject the coal 'to a plurality of alternate vacuum and atmospheric treatments for varying lengths of time in order to alter the coking characteristics of 4a particular coal to render it best suited for a particular briquetting operation. The atmospheric treatment may also be replaced by a pressure treatment in the presence of air. The temperature may in some cases be lower than 150 C., and in some cases it may be necessary to use a higher temperature.

What I claim is:

1. A method of altering the coking characteristics o f swelling and caking coals which-comprises pulverizing the coal and subjecting to alternate vacuum and atmospheric treatments at an elevated temperature, said coal after such treatments being altered to such an extent that it can be carbonized at a faster rate without undue swelling than it could have been preceding such treatment.

2. A method of altering the'coking characteristics of swelling an caking coals which comprises pulverizing the coal, dryingfat a temperature of about C., subjecting the dry c'oal to a vacuum equivalent to about 28 inches of mercury. for a period of time, releasing the vacuum and allowing the coal to come in contact with'air at atmospheric pressure for a period of time, followed by a second vacuum treatment equivalent to about 28 inches of mercury for a short period of time while maintaining the coal at a temperature of about 150 C. during the alternate vacuum and atmospheric treatment, said vacuum and atmospheric treatments being for a period of time sufficient to alter the caking characteristics of the coal to such an extent that the coal can be carbonized at a faster rate withtact with air at atmospheric pressure for about 30 minutes followed by a second vacuum treatment equivalent to about 28 inches. of mercury for about 15 minutes while maintaining the coal at a temperature of about 150 C. during the alternate vacuumatmospheric treatment, said coal after such treatments being altered to such an extent that it can be-carbonized at a faster rate without undue swelling than it could have been preceding such treatment.

4. A method of making briquettes from caking coals which coals cannot normally be compressed into briquettes and carbonized at a temperature rise of more than about 1/2 C. per minute without badly swelling and caking which comprises pulverizing the coal and subjecting to alternate vacuum `and atmospheric treatments at anelevated temperature to reduce the swelling and leaking .properties thereof so that when compressed inter-briquettes. and subjected to carbonizationythe y'carbonization can be carried out at a .temperature rise of at least 21/2" C. per minute .through the plastic temperature range.

5. A method of making briquettes from coking coals which coals cannot normally be compressed into briquettes and carbonized at a temperature rise of more than about 1/2" C. per minute without badly swelling and caking which comprises pulverizing the coal, drying at a temperature of about 150 C., subjecting the dry coal to a vacuum equivalent to about 28 inches of mercury for about 15 minutes, releasing the vacuum and allowing the coal to come in contact with air at atmospheric pressure for about 30 minutes followed by a second vacuum treatment equivalent to about 28 inches of mercury for about 15 minutes while maintaining the coal at a temperature of about 150VC. during the alternate vacuum and atmospheric treatment to reduce the swelling and caking properties thereof so that when compressed into briquettes and subjected to carbonization the carbonization can be carried out at a temperature rise of at least 21/2 C. per minute through the plastic temperature range.

CLAYTON S. WOLF.

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