US2336151A - Pressure treatment of coking coals - Google Patents

Description

Dec. 7, 1943. w. J. KRUPPA PRESSURE TREATMENT OF COKING COALS Filed July 2, 1940 w u L Wa/,4M a KfW/AM,

ATTORNEY.

Patented Dec. 7, 1943 UNITED: STATES PATENT oFFlcE PRESSURE TREATMENT F COKING GOALS William Joseph Krupna, Hamden, Conn., assigner, by mesne assignments, to American Cyanamid Company, New York, N. Y., a corporation of Maine Application 2,1940, Serial No. 343,518

Claims.

4 ing characteristics'of such coals by oxidation. In

these oxidation processes it is necessary that the oxidation be controlled so that the coal when carbonized willhavesuiiicient caking characteristics to form a firm bond during carbonization. The prior proposed methods of oxidizing such coals Vhave the serious disadvantage thatthe temperature of the coal must be raised to about 150 C. and maintained at that temperature for a period of 24 to 120 hours depending upon the type of coal being treated. 'I'he prior oxidation processes are diicult to control accurately.

In accordance with the present invention I have found that `even the most strongly caking and swelling coals can be oxidized to the desired reduction of its caking powers in a very much shorter time and under conditions which are more easily controlled than the proposed prior oxidation processes. My improved method broadly comprises subjecting ground coal to'an oxidation treatment at elevated temperatures and pressures. Satisfactory oxidation is /accomplished with many coals in from 3 to 6 hours by employing a temperature `of about 150 C. and carrying the oxidation out in a tightly sealed vessel under air pressure oi' about 50 lbs. per square inch. In

general as the pressure is decreased for a given coal the amount of swelling inhibition in a unit of time is likewise decreased. The pressure and time of treatment varies with the coal being treated. Most bituminous coals can be treated suillciently, to produce non-swollen carbonized briquettes with coal tar or pitch as a binder, in

a period of 4 hours at 50 lbs. air pressure per` coal under air pressure speeds up the rate of oxi-` over 50 lbs. per square inch have very little elect on increasing the rate of oxidation, i. e., the rate of oxidation increases with the pressure up to its maximum of about 50 lbs. per square inch after -which further increase in pressure does not produce a further substantial reduction in the time requirement. Pressures higher than 50 lbs. per square inch are required only with coals that require larger quantities of oxygen to bring about the desired swelling inhibition, than can be forced into the pressure treating vessel at 50 lbs. per square inch. One type of coal, for example, could not be suillciently oxidized in 4 hours with 45 lbs.

- per square inch pressure unless the air in the treating vessel was changed several times. However, when this coal was treated for 4 hours at 150 lbs. pressure no air change was required indicating that the increased pressure in this case served only to supply suiiicientoxygen to produce the same eiect in the same time which 45 lbs. pressure produced when the air in the coal container was changed several times. Apparently the effectof this air change was to supplythe coal with suillcient oxygen to bring about the desired reduction of the coals swelling characteristics.

If the air is mixed with OXygen or if oxygen gas is used alone the temperature and pressure may be adjusted to bring about the desired changes in which case the time may bedecreased a or 'the temperature and pressure decreased. In place of air, oxygen, oxygen mixtures or other suitable oxidizing gases may be used or mixtures of such gases, air being preferred because` of its cheapness.

The present invention is not limited to' any particular neness to which the coal is ground. I have found however that it has an effect on the time of treatment required under the same conditions of pressure and temperature. 'I'he temperature also has an effect on the `time of treatment, in general the higher the temperature the shorter the time of treatment required. Reasonable changes in the iineness of the coal and the temperature are not as effective in reducing the time requirement for sufficient oxidation as increasing the pressure from atmospheric to 5 0 lbs. per square inch. This is one of the important advantages of the present invention as it permits the degree of oxidation to be very easily and accurately controlled in applying the process to difdation. I have found, however, that pressures of ferent oxidation requirements.

The process is interfered with somewhat by coals that give off moisture or volatiles diu'ing the treating process. When such coals are to b e treated they are first thoroughly dried and raised to the oxidizing temperature before the pressure treatment begins. The oxidation process is more easily controlled and results are more consistent. Many coals, however, which are dry or contain very little volatile'substance can be treated directly without rst drying. Without limiting the invention by a particular explanation the interference is probablyl due to thefact that some coals more than others start to decompose about 100 C. and give oiI water along with other volatile constituents as the temperature is raised. This water is not surface moisture alone but the result of the decomposition of some part of the coal itself. With some coals it has been found thatwhen put into a tightly sealed coal pressure treater and the temperature raised to about 150 C. with no provision for the escape of moisture consistent results are not obtained with the pressure treatment oxidation process. However, when these coals were first dried and raised to the desired temperaturein an air stream outside the coal treater and then put into the coal treater and given al pressure treatment, satisfactory and consistent results were always attainable.- In a preferred lembodiment of the present invention, therefore, it is important that the coal be dried and brought up to the reacting temperature to eliminate the moisture, both external and internal before the pressure treatment begins. Briefly my improved process is carried out as follows: The coalis dried, ground to proper flneness and brought up to the desired reacting temperature (11S-200 C. depending 'upon the c oal and the nal state of oxidation required) outside the pres- I' y elevated pressure of from 20 to 150 lbs. per square inch depending upon the coal being treated and the iinal state of oxidation required. 'I'he coal is allowed to remain under this pressure and at substantially the same temperature (H-200 C.) at which it was introduced into the container for a period of about 4 hours. or less depending upon the coal and the final stateof oxidation and swelling inhibition desired. After the re- The hot dry'coal is charged into The coal is fedinto the pulyerizer I by means of a suitable feeder 2 as illustrated in the drawing. The coal in the pulverizer is ground so that the material iiner 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 iiue 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 the pulverizer which contains suitable separation equipment asan 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 a cyclone type dust collector 1 whereabout 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.

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

.The coal in the cyclone collector I is dry and at a temperature equal to or somewhat lower than that desired in the treaters.A The temperature is controlled by the amount and temperature of flue gas drawn into the pulverizer I from the pulverizer furnace 4. A screen analysis'of this coal shows it to range in particle size from about 88% less than 28 mesh to about 10% less than 200 mesh.

quired lapse of time the coal is discharged from y the pressure treating container and is .ready for any suitable carbonization treatment.

The invention will be described more particularly -in conjunction with the drawing which is a i semi-diagrammatic elevation of suitable plant burgh .seam coal,'containing about 35% volatile matter, and which 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 through the plastic temperature range without swelling. The coal as delivered to the plant is of lowsurface moisture content.

'Il'his hot coal is then fed out of the bottom of the cyclone colletcor 'I by means of a pulverized coal pump I0. In order to pump the pulverized coal and cause it to travel through a conveyor pipe II the coal is aerated by the introduction of airthrough the air line I2 into the coal conduit asvsho'wn. The amount of air required for proper: aeration is on the order of about 51% by weightof the coal conveyed. 'Ihis airrequired for aeration is rst heated to any desired temperature inthe air heater coil I3 and provides to further raise or control the coal temperaturel desired. The length of this conduit and the temperature of steam or oil used in its jacket is suiilcient 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 lbs. per .square inch pressure. '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 rst treater is iilled, the coal valve I5 in the coal conduit is closed and the valve to the next treater is opened. The rst treater is immediately put under 50 lbs. per square'inch air pressure and allowed to stand for 4 hours under that pressure.

The air introduced into the treaters may or may not be preheated. .It is an advantage however that hot air can be used as the temperature of the coal is more easily maintained. also be mixed with oxidizing gases if desired.

After an elapsed time of about 4 hours the coal .is discharged from the coal treater Il into the treated coal bin I6 from whence asuitablefeeder I'l conveys the treated coal to the fluxing and briquetting equipment.v The badly swelling and caking bituminous coals which normally cannot be successfully coked are in accordance with the present invention altered to such an extent that they can be coked by any of the ordinary carbonization processes. Because of the desirability, however, i'or finely grinding the coal in carrying out my'processes the practicall methods of coking should be limited to compressing, briquetting, and agglomerating processes prior to carbonization. In the case of briquettes the coal can be compressed into a briquette with or without a binder and carbonized at an intense rate to obtain a\ compact and unswollen briquette.4 In agglomerating processes the coal after oxidation can be iiuxed with a small amount of cheap adhesive and rolled through a tubular mill to agglomerate it into balls which can then be charged into an ordinary coking'oven and coked without interference of swelling or caking while passing through the plastic temperature range.

In the manufacture of briquettes from the bituminous coals there are at least two difficulties which are encountered: first, the coalhas a tendency to be plastic and swells and this results in the production of a very poorly formed briquette of low specific gravity and in many instances the caking tendency is so strong that the briquettes cannot be separated one from another; secondly, the compressed briquettes must have sufficient head load bearing strength so that the underly- The air may ing briquettes will not be crushed by the weight ofthe briquettes above them.

The preoxidatlon treatment of the present invention overcomes the difliculties due to caking and swelling. The head load bearing ability o1. the briquettes is not extensively associated with oxidation. It is an advantage of the present invention however that the pre-oxidation does not reduce the head load bearingV ability of briquettes and in some instances increases it so that the binders usually employed in manufacturing briquettes from a good quality coking coal can be used with my pre-oxidized coal and moreover the degree of oxidation can be controlled so that the coking characteristcs of .the coal may be more readily amenable to the use of various binders; for example, a highly swelling coking coal can be oxidized to the point that the coking characteristics of the coal are changed to something on the order of a Beckley seam coal and sullte liquor can be used as a binder. In this type of coal there is still enough plasticity remaining so that the briquettes are firmly bound by the suliite liquor and they will bear a. sufficient head load. Such coal, however, cannot be successfully used with pitch and tar binders to produce a briquette having suitable head load bearing ability. If pitch or tar is to be used as a binder the coal is preferably oxidized to such an extent that it corresponds to Peace and partners A and B- coals. These are British weakly coking coals, the A described as Thorne /dry cleaned smalls" containing about 36.1% volatiles, 58.5% fixed car` bon and 5.4% ash. B is described as Alerton main washed smalls" containing about 35.6% volsether or slumping. It

through the plastic range as contrasted to un treated coals in which the temperature rise cannot be more than about 1/2 C. per minute through the plastic temperature range.

It is therefore an' advantage of the present. invention that when badly caking or coking coal is oxidize'd the coking characteristics of the coal are altered to such an extent that when briquetted the briquettes can be carbonized at higher rates of temperature rise through the plastic temperature range without fusing, swelling, sticking tohas been found that the extent of oxidation required to achieve this end varies somewhat with the binder to be used in the briquetting operation. When coal tar or pitch is used as a binder the oxidation should be carried f. to such an extent that a test briquette of the oxiing in the non-binder briquette test is allowed.

When molasses or other carbohydrate material 'is used as a binder the degree of oxidation should be approximately the same as for sulte liquor. In general it has been found that with all other conditions being the same the time of oxidation treatment to produce sufficient swelling inhibition when sulte liquor binder is used is only about 3A of that required to produce sulcient inhibition with coal taror pitch as a binder.

The following specific tests carried out on dif.

ferent coking coals will serve to further illustrate the operativeness of the present invention and also the exibility of the invention when applied to different coking coals.

'I'he following tests were conducted on the Hillman Coal Companys emerald coal and Berwind-VVhites ocean coal, both of which are Pittsburgh seam coals and are highly melting coals. These coals cannot be run in ordinary briquetting carbonization plants at a temperature rise of more than 1/2 C. per minute through the plastic temperature range and will not bear more than a 4 foot head load using sulflte liquor.

'Ihe coals were rst ground so that about 90% passed through a 28 mesh screen, the ground coal was then dried at a temperature of about C. until all of the surface moisture and that of constitution formed at or below 150` C. had been removed. The hot dry coal was then highly swelling,v

charged into the pressure treaters and subjected to a pressure of 50 lbs. per square inch at the temperature of 150 C. for a period of 4 hours.

Briquettes were made from the treated coal using no binders and while the binding prop- `erties were not very good the briquettes could be binder and subjected to carbonization. `The suliite liquor bound briquettes were unswollen, well bonded, hadsuiilcient head load strength to bear a six foot head load and produced briquettes of good density. Briquettes were likewise made from the treated coal using 4% molasses as a binding substance. The briquettes were well bonded and upon carbonization the swelling and caking was satisfactory in that the carbonization could be carriedout at a temperature rise of at least 21/2 C. per minute through the plastic temperature range but the head load bearing strength was somewhat weaker. The pretreated coal when made into briquettes using about 5% pitch or coal tar as a binding material produced briquettes having a good bond and. excellent swelling and coking properties but with poor head load resistance. Upon experimentation it was discovered that it the pitch or coal tar` bound .briquettes were heated in air at a tem? perature of about 200 to 240 C. for a period of ffrom minutes to 1 hour prior to the carbonization treatment the briquettes had excellent head load bearing strength.

This heat treatment in an oxidizing atmosphere of the tar or pitchbound `briquettes previ-v, ous to their carbonization isl-an important step in briquetting operations using the pref-oxidized coals ofthe present vention. Tar and' pitch are by-products oi.' caking' operations and are therefore not only readily available but are also cheap. Tar and pitch bound briquettes however.

are not suitable in general'for carbonization processes in which the briquettes must bear a] super-.imposed head 1oad,.i. e., they have very@- assalti' at a temperature of about 115' C. and charged into the pressure treater and held at a temperature of 115 C. for 3 hours under 50 lbs. per square inch air pressure. i The briquettes from this coal bound with 4% sulnte liquor dry substance and carbonized at 2% C. rise per minute through the plastic temperature 'range produced very hard, clean, undistorted briquettes `with a diametric shrinkage of about 1%. Coal "E was `subiectedto the same treatment as coal "C and produced equally exciellent sulte liquor bound briquettes,being very hard, dense, clean, undistorted and with a Yliametric shrinkage of about 5%. Coal F when subjected to oxidation.V under conditions similar to coals "C" and E could not be economically carbonized in the form of briquettes and theoxidation procedure was accordingly altered somewhat. The coal F was ground and dried l at a temperature of 150 C. for 4 hours under lbs. air pressure. while atV the ,same time allowing a small quantity of air to bleed through the coal and then out of -the container. Briquettes made from this treated coal: with 4% sulte liquor dry substance and carbonized at 1.2%? C. rise per minute through the plastic temperature range were'very hard, dense, and clean with a diametric shrinkage of about-,8%. Bri- `.fq'uette'sinade without binders were unswollen .3o

'and poorlyf bonded which shows that the treat'- ment destroyed almost completely the fusing poor head loadl strength, but if these briquettes r are first'heated in an oxidizing atmosphere for from 15 minutes. to 1 hourat a temperature from 200 to 240 C. they'will bear super-imposed. loads up to 6 feet and thus make their carbonization in large quantities a. practical process.

The above tests were also carried out on a straight Beckley coal which is considered to be a coking coal well adapted for forming briquettes. In each instance the pre-treated Pittsburgh seam Vcoals resulted in the production of briquettes which were equivalent in quality to those produced from the Beckley coal and in most instances were of a better quality.

Tests 'were also conducted on 'certain Britishcoals of the Peace and partners class.- Some of these coals, specifically "A and "B can be successfully run at economical rates in briquetting processes without pretreatment, however,

the coals C, E, and F cannot be made into briquettes and carbonized by the usual processes because of their extreme swelling characteristics. Coal C is described as Thrislington washed `nu containing about 33.2% volatiles, 63.8% xed carbon, 3.00% ash and is strongly coking.

E is described as Waterhouses unwashed coal containing about 26.4% volatiles, 69.6%

fixed carbon, 4.00% ash and is strongly cokin'g.v "F is strongly coking low ash coal containing about 28.3% volatiles, 68.9% fixed carbon and 2.80% ash. When the C, E, and F" coals are pre-treated in accordance with the present invention the swelling properties are altered to such an extent that they can economically be briquetted` and carbonized. The treatment 'of these 3 coals iollowed the same general procedure as that described in connection with the Pittsburgh seam coals with only slight variations to compensate for the degree of oxidationto which each of the coals should be subjected. For example, coal C was ground and dried v vproperty of the coal. The abovetreatment `of 'coal- F indicates that there was insuilicient oxygen present at a pressure of 50 lbs. and at a temperature of 150 C. to suilciently alter the caking characteristics of the coal and hence the bleeding of air through the coal during the pres'- sure treatment served to supply the necessary oxygen. This is further evidenced by the fact that the sarnel coal ground and dried at a temperature of 150 C. and then subjected to air pressure of 150 lbs. per'square inch and held at the temperature of 150 C. for 4 hours resulted in the production of oxidized coal which could be successfully briquetted. This type of coal can be altered more readily by using a gas having stronger oxidizing properties than air.

Tests were conducted on the pre-treated coals C, E," and F" in briquetting operation using binders other than suliite-liquor. The results in general are the same as previously described in connection with the Pittsburgh seam coals.

The present invention is of course not limited to' the treatment of the particular'coals as described but is generally adaptable for the treatment of coals capable of coking but which because of undue plasticity', swelling and caking properties cannot be coked by the ordinary briquetting and carbonization processes to produce a dense coked product. The .improved results of the invention can be obtained in connection with any such coal by subjecting the hot pulverized coal at a temperature of between 115 and 150 C., dependent upon the coal and ,the nal state ol oxidation desired, and thensubjecting it to an oxidizing gas at elevated pressures of from20 to l- 150 lbs.\pressure for 3 to 6 hours, again dependknown briquette carbonizing processes, at a tem- .perature rise of at least 21/2" C. per minute through the plastic temperature range and without interference from swelling and caking.

What I claim is: 1. A method of coking badly swelling and caking coals which comprises pulverizing and drying the coal and then subjecting it to a, controlled oxidation treatment in the presence of air pressure of from 45 to 150 lbs. per square inch and at a temperature of from 115 to 200 C. depending upon the coal and the degree of oxidation required and subsequently converting said treated coal into coke by carbonizing at a temperature rise of about 21/ C. per minute through the plastic temperature range.

2. A method of coking badly swelling and caking coals which comprises pulverizing and drying the coal and then subjecting it to a controlled oxidation treatment in the presence of air pressure of from` 45 to 150 lbs. per square inch and at a temperature of from 115 to 200 C. from 3 to 6 hours depending upon the coal and the degree of oxidation required and subsequently converting said treated coal into coke by carbonizing at a temperature rise of about 21/2 C. per minute through the plastic temperature range.

3. A method of coking badly swelling and caking coals which comprises pulverizing the coal, drying the coal, and then subjecting it to a ccntrolled oxidation treatment in the presence of` air pressure of from 45 to 150 lbs. per square inch and at a temperature of from 115 to 200 C. from 3 to 6 hours depending upon the coal and the degree of oxidation required and subsequently converting said treated coal into coke by carbonizing at a temperature rise of about 21/2 C. per minute through the plastic temperature range.

4. A method of coking Pittsburgh seam coal which comprises pulverizing the coal, drying in the atmosphere at 150 C. and then subjecting the dry coal to a controlled oxidation treatment in the presence of air pressure of 50 lbs. per square inch and at a. temperature of 115 C., said pressure and temperature being maintained for a period of about 4 hours and subsequently converting said treated coal into coke by carbonizing at a. temperature rise of about 21/ C. per minute through the plastic temperature range.

5. A method of making carbonized briquettes from coking coals which comprises subjecting a pulverized, substantially dry, badly swelling and caking coal to a controlled oxidation treatment in the presence of an oxidizing gas pressure of from 45 to 150 pounds per square inch and at a temperature of from 115 to 200 C. to effect a reduction ofthe swelling and caking properties thereof, subsequently compressing into briquettes and subjecting said briquettes to carbonization at a temperature rise of about 21/2 C. per minute through the plastic temperature range.

6. A method of making carbonized briquettes from caking coals which coals cannot normally be compressed into briquettes and carbonized at a temperature rise of more than 1/2" C. per minute through the plastic temperature range without badly swelling and caking, which comprises.

the steps of pulverzing and drying said coal and then subjecting the dried, pulverized coal to a controlled oxidation treatment in the presence of air pressure of from 45 to 150 pounds per square inch and at a temperature of from to 200 C. to effect a reduction of the swelling and caking properties thereof, forming briquettes of said treated coal and subjecting the briquettes to a carbonization treatment at a temperature rise of at least 21/.2 C. per minute through the plastic temperature range.

7. A process according to claim 6 in which the pulverized coal is subjected to oxidation in the presence of air pressure of about 50 lbs. per

square inch and at a temperature of about C. for a. period of about 4 hours.

8. A process according to claim 6 in which sulte liquor is used as a binder in trie formatipn of .,MM f f j briquettes.

9. A process according to claim 6 in which mo'-` lasses is used as a binder in the formation of briquettes.

l0. A process according to claim 6 in which coal tar is used as a binder in the formation o1 briquettes.

WILLIAM JOSEPH KRUPPA.

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