US2504150A - Coking expanding coals - Google Patents

Description

April 1s, 195o Filed Feb. 18, 1947 PRESSUEEf POUNDS PE2 SQUARE. INCH M. PERcH 25045150 COKING EXPANDING GOALS 2 Sheets-Sheet 2 La? 9 Wl fao e V r 7 /l 5 l l/./ 4 /I/ 3 2 f56 Z .b 4 .J 6 7 9 HOURS AFTER CHARGING Slwcntor mzcHAEL Psecf/ I Cittorneg Patented Apr. 18, 1950 COKING EXPANDING COALS Michael Perch, North Arlington, N. J., signor to Kappers Company, Inc., Pittsburgh, Pa., a corporation oi Delaware Application February 18, 1947, Serial No. 729,328

3 Claims. l

The present invention relates to the coking oi' coals in by-product coke ovens, and has reference more particularly to novel procedure for the utilization of expanding coals and expanding coal mixtures in such coke ovens.

The problems encountered by the expansion of coal during coking has long been known in the industry and has been subjected to much study in an effort to alleviate the condition. The development of the modern horizontally elongated coke oven and oi' high temperature coking, and the enhanced productive capacity of coke ovens obtainable thereby, has increased the importance of the problem since such higher rates of coking develop higher expansion pressures within the oven.

Coals and coal mixtures are considered expanding if they exert, during the process of coking, such pressuresagainst the walls of the oven chamber that they either damage the oven ,walls or affect deleteriously their useful life. On the basis of their experience, coke-oven operators have in general arbitrarily set an expansion pressure of two pounds per square inch as the highest pressure permissible against coke oven walls.

Methods for reducing coal expansion pressures by altering the physical and general characteristics of the selected coal and coal mixtures have been uniformly unsuccessful because they also deleteriously aii'ect the quality of the coke produced therefrom. A recent method, disclosed and claimed in copending application of Powell, Serial No. 612,160, provides a means for reducing to within safe limits the final expansion pressures of coals which expand during the latter part of their coking period, at which time, it is believed. the plastic seams produced in the coal during coking join to form a continuous plastic envelope which entraps thereinpressure producing gases. The Powell method substantially prevents the closure of the plastic seams. However, the expanding characteristic of some coals and coal mixturesl is so pronounced that greatly excessive pressures may develop during the first period of coking when the Powell method is ineffective to reduce expansion pressures.

The primary object of the present invention is .the provision of a method whereby highly expanding coals and coal mixtures can be coked at customary. high temperatures in the usual byproduct coke ovens without damage to the ovens other operative advantages or results as may be found to obtain in the processes or apparatus hereinafter described or claimed.

According to the present invention, expanding coal or expanding coal mixtures are admixed with a minor quantity of pitch and there is disposed along any surface of an oven charge constituting such an admixture a stratum of solid fuel that is itself either non-coking or non-agglomerating or forms during coking a weak, gas permeable plastic seam. The striking eifect of the described combination in the reduction of the expansion of highly expanding coals is particularly surprising inasmuch as the use of either pitch admixture alone or of the stratum alone provides no appreciable reduction in the expansion of these coals. The stratum can constitute an entire and uniform layer in the plane of one surface of the coal charge, or it can be a series of broken layers constituting only a portion of any particular plane of the charge, or it can be a single layer not entirely covering one surface of the charge. or it may be one or more layers in one or more heating planes of the oven charge. The stratum or layer can consist of any inert non-coking material through which gases can readily permeate, especially coke, of which one preferred example is breeze. oxidized coal is another suitable non-coking material.

The pitch can be a mineral pitch or a coal tar pitch, such as roofing pitch or fuel pitch, the latter being preferred because it is considerably less expensive. Suitable coal tar pitch is defined in the Standards of the ASTM, Part II, page 612, (1944) as Black or dark-brown solid cementitious residues which gradually liquefy when heated and which are produced by the partial evaporation or fractional distillation of tars. The aforesaid preferred coke breeze which may be used for the present coking method is defined in the Standards of the ASTM, Part III, page 61, (1944) as follows: The iine screenings from crushed coke or from coke as taken from the ovens, of a size varying in local practice but usually passing a 1/2 inch or inch screen opening. The successful operation of the present invention is of course not restricted to employment of the defined coke size. Particulate coke of larger sizes and mixed sizes arealso. effective in the combination of this invention. It is obviously necessary to avoid coke pieces too large to enter the charging hole without diiliculty, or so large that the void spaces between them would permit radiation of heat through the stratum and form a, plastic seam at the underlying coal surface.

Dangerous expansion-pressures have been defined arbitrarily by those experienced in cokeoven operation as those which exceed a pressure of two'pounds per square inch on the oven walls.

coking are measured in standard test ovens.

The apparatus that was employed in the hereinafter reported tests is the movable-wall oven illustrated and described in Proceedings of the ASTM 43, p. 310 (1943). Pressures exerted by coking coals below the said limit are identified in the claims as pressures of a normal value and mbelievedtobebeneiicialandtobeanim portant factor in the production of a high quality coke having stable physical characteristics.

In the accompanying drawings forming a part of the speciilcation,

Fig. 1 is a fragmental, elevational view in vertical section of coke-oven chambers and their accompanying dues and crossovers taken longitudinally of the coke-oven battery and at right angles to the horizontal extension of the individual ovens, and showing one oven as charged and another oven at an intermediate period during coking, and illustrating a` stratum of coke at the top of the ovens to prevent, in combination with admixed pitch, the development of high pressure in the oven,

Pig. 2 shows curves with coal expansion pressures plotted against coking time of an expanding coal, which was coked according to standard practice in one instance, with admixed pitch only in another, and with a superimposed layer of breeze in another, and

Figs. 3 and 4 are curves showing coal expansion pressures plotted against coking time of the same expanding coal which was coked according to the method of invention. Y

Referring now to the drawings, Fig. 1 illustrates a preferred embodiment of the invention whereby a highly expanding coal, admixed with pitch, is coked without exerting excessive expansion pressures. In this instance, after levelling, a layer of coke breeze is added to an oven charge comprising expanding coal and a 'minor quantity of coal-tar pitch. A layer of breeze approximately no greater in thickness than the width of oven chamber is formed across the top of the ovenV charge. Fig. 1 shows two oven chambers, one chamber 2, which is represented as just having been charged, and an adjacent oven chamber 4, in which the oven charge is partially coked. Each chamber is formed by two longitudinally extending flued, masonry walls B, and an oven sole 8 and a masonry roof IU. The ovens are also supplied with regenerators I2, air and waste heat ports I4 and I6, respectively. and with fuel gasburner nozzles I8.

As is the well known process in the heating of reversible regenerative coke ovens, air is passed through checkerwork in the said regenerator I2 and is flowed therefrom through air ports I4 into "on" flues 20 wherein the air intermingles with, and burns fuel gas introduced through the said burner nozzles I8. The burning mixed gases iiow through crossover ducts 22 and descend on the opposite side of an oven chamber through an "oil" flue' 2B. The waste heat ows from the latter flue through ducts I8 into another set of regenerators I2 to preheat the checkerbrick contained therein.

The described technology of coking coal in horizontal coke ovens of an improved design provide uniformity of heating and the delivery of heat from all sides of the oven chamber, thus causing the formation of the described plastic envelope. In addition, highly expanding coals form highly viscous plastic seams which themselves exert considerable expansion pressures.

A' completely sealed, uninterrupted plastic envelopc surrounding and enclosing the central portion of the coal-charge cannot be formed 4 when, as illustrated in Fig. 1, a non-coking fuel Is positioned as slayer 24 adjacent and between heating walls, jbecause no plastic seam can be formed in the non-coking fuel, and because the layer insulates the underlying surface of the coal `charge from heat which otherwise would be radiated from the adjacent heating wall. A layer of coke breeze is particularly eiective to permit escape of gases from the underlying coke charge, for the said breeze is substantially. uninuenced by the coking heat. The layer 24 of coke breeze can be introduced into the oven chamber through charging holes 26 after the oven has been charged with coal.

The hereinbefore described viscous and pressure exerting plastic seam of highly expanding coal appears to be altered by the admixture with the coal of minor quantities of pitch and, hence, a plastic seam 28 as shown in Fig. 1 represents a seam which has been so altered by the pitch addition that it in itself develops only minor expansion pressures.

The layer 24 which is disposed on the top of the charge in each of the oven chambers can also constitute coke pieces of larger size than breeze, or may be coke of mixed sizes.

Fig. 2 illustrates by curves the expansion pressures developed during the coking of 1) a highly expanding low-volatile coal (curve 30), (2) the same coal to which has been added 10% by weight of the coal of coal-tar pitch '(curve 32), and (3) the same coal upon the upper surface of an voven charge of which a 7" deep layer of coltev breeze has been addedI (curve 34). It can be seen from the curves that neither the expedient of admixed pitch nor of a stratum of a solid fuel is effective alone to reduce the expansion pressures of highly expanding coals. A realization of the extremely dangerous pressures exerted by this coal will be had when the line 35, indicatingthe arbitrarily set limit for safe coal expansion, is noted on the figure.

Figs. 3 and 4 illustrate the expansion curves exhibited by the same expanding coal when it has been admixed with pitch and protective solid fuel stratum has been distributed over the top of the oven charge. As shown, the greatly excessive expansion pressures to be observed in Fig. 2 have been completely eliminated and, instead, there remains only moderate pressures well within the limit of 2 lbs. per sq. in., andV conducive to the production of high quality coke.

The data and test conditions from which the results reported by the described curves were obtained are given in the following specific examples.

Example 1 An expanding coal was selected, which had the following pulverization:

Per cent by weight On 41" screen 0.5 Through 1A," and on t/a" screen 11.8 Through 1/8" and on 11g" screen 46.6 Through 1*," screen 41.1

The coal had a bulk density of 49.7 lbs. per cu. ft. and a moisture of 1.5% by weight. When coal was coked for about 81/2 hours in the aforementioned movable wall oven which had an average ue temperature of 2473 F., a maxi" mum pressure of 10.1 lbs. per sq. in. was developed. The expansion-pressure curve is shown as curve 30 of Fis. 2.

Example 2 The'same coal as was used in Example 1, but having a slightly higher bulk density. 52.6 lbs. per cu. ft., due perhaps to its lower moisture con-- tent of less than 1%, was coked in the aforesaid movable wall oven which had during the test an average nue temperature -of 2453 F. A layer of coke breeze 7 deep was distributed over the top of the oven charge immediately after charging. The expansion pressure that was developed exceeded the limit of the apparatus at 11.9 lbs. per sq. in. The curve 34 of Fig. 2 illustrates the expansion pressure developed by this example.

Example 3 The same expanding low volatile coal as was employed in Example 'l and having a moisture content of less than 1% and a bulk density of 51.4 lbs. per sq. in. was mixed with 10% by weight of coal-tar pitch. The admixture was coked in the aforesaid movable wall oven and the expansion pressure exceeded the limit of the apparatus at 11.5 lbs. per sq. in.

The expansion pressures observed during this test are illustrated in curve 32 of Fig. 2. From the foregoing specific examples it can be seen that a highly expanding coal cannot be effectively treated for elimination of excessive expansion pressures by admixing pitch alone or by providing a protective stratum of solid fuel against one of the surfaces of the coal charge without admixture with pitch.

The remarkable and unexpected effect o1 the A use of pitch and the protective stratum in com bination is shown in the following examples.

Example 4 The said low volatile coal, having a bulk density oi 50 lbs. per cu. ft. and moisture of less than 1% and a pulverization of 93.3% through a 1/8" screen, was mixedwith 10% by Weight of coal-tar pitch. The admixture was charged to the aforesaid movable wall oven and a layer of coke breeze`7 deep was added to the top of the charge. vThe charge was coked at an average ue temperature of 2462 F. and exhibited a maximum coal expansion pressure of 1.29 lbs. per sq. in. The coke produced was of ysuperior quality. The coal expansion pressures exhibited during this test are illustrated in Fig. 3.

Example The said coal having a bulk density of 47 lbs. per cu. ft., a moisture of 1%, and a pulverization of 86.9% through a 1;/8" screen was mixed with by weight of coal-tar pitch. The admixture was charged into the aforesaid movable wall oven and a layer o1 coke breeze 10" deep was added to the top of the charge. The charge was coked for approximately 8 hours at an average flue temperature of 2495 F. and a maximum expansion pressure of 0.7 1b. per sq. in. was recorded. Fig. 4 illustrates the expansion pressures observed in this test.

Example 6 Another low volatile coal which. when coked alone, exhibits an excessively dangerous coal expansion pressure of a degree equal to the coal used in the above specific examples was coked in admixture with 10% ot fuel pitch and with a layer of breeze 8" deep on the coal charge. A maximum expansion pressure of 1.82 lbs. per sq. in. was recorded.

Example 7 7.5% by weight o1' pitch was mixed with the coal used in Example 1 and was coked with an 8" layer of breeze thereon as an upper layer. For this particular coal having extremely expanding characteristics the use of 7.5% of pitch appears to be the minimum proportion providing a safe expansion pressure because a maximum expansion pressure of 2.17 lbs. per sq. in. was produced in this example and the test was performed under conditions which produce the highest obtainable coking pressures.

Example 8 The coal employed in Example 1 was mixed with 10% by weight of coal-tar pitch and was coked with a superimposed six-inch layer of coke breeze. The maximum expansion pressure-exhibited was slightly over 2 lbs.v per sq. in. and consequently this appears to be a lower limit of thickness which will provide safe coking pressures when one uses the aforesaid highly expanding coal in admixture withv 10% of pitch and when the protective layer vconstitutes coke breeze.

The extremely expanding nature of the coals selected for the above testing causes the reported results to establish thereby the substantially ultimate limits in respect of the minimum of pitch to be added and minimum thickness of protective layer to be employed for any expanding coal. It is obviously within the skill of the art to determine the expansion pressure exhibited by any untreated coal or coal mixture and to 'add a correct proportion of pitch and a correct depth oi' a -protective layer.

The expansion pressure exhibited by a selected coal or coal mixture increases with increase in coking temperature and therefore the problem hereinbefore described of excessive expansion pressures is most pressing when the high temperatures of modern coking practice are employed. However, it is clearly within the scope of the present invention to employ the elements of the disclosed combination in lesser proportion zvhen it is preferred to use lower coking temperaures.

Although in the hereinbefore described Fig. 1 the stratum there illustrated is shown to be rectangular in cross section, the stratum of invention need not be so and equally good results have been obtained when the stratum was triangular in cross section with the apex pointing down or, in another instance, when the cross section of the stratum roughly conformed to the cross sec- 'tion of an inverted truncated cone.

The invention as hereinbeforeset forth is embodied in particular form and manner but may be variously embodied within thev scope of the claims hereinafter made.

I claim:

l. In a method of carbonizing coal in an externally heated horizontally elongated coke oven having sidewalls which are susceptibleoi' injury when subjected to pressure in excess of 2 lbs. per square inch, the method of preventing injury to the side walls during carbonization of an expanding coal of the type which when carbonized in an oven in the usual manner has created therein said expanding coal to nll a major portion of the oven, mixing pitch with the coal charge in the amount of substantially 7.5 to by weight oi the coal charge to reduce swelling of the plastic zone, driving heat through the opposite sides oi the coal body to make it plastic and coke it within the temperature rangefor high temperature coking, and providing during the carbonization period a covering for a surface of the coal body coni sisting of a porous layer of granular material of such composition and thickness as to provide a structure of the coal being carbonized and the material thereon to permit the ready escape therethrough of gas generated by the coal carbonization without .developing a pressure in excess of 2 lbs. per square inch against the oven walls during the coking period.

2. In a process of carbonizing coal Ain an externally-heated horizontally-elongated intermittent coke oven having sidewalls which are sussubstantially uninterrupted highly impermeable plastic zone surrounding and enclosing the central portion of the coal-charge and which when carbonized in the usual manner also causes pressures in excess of said normal value to be exerted againstthe oven side walls during a substantial part of the carbonizing period prior to the latter part of the carbonizing period because of the swelling of the plastic zones in the coal-charge, y

said method comprising charging said oven with coal of the type identified above and to which there has been added pitch in the amount of substantially 7.5 to 10% of the weight of the coalcharge to thereby reduce the swelling of the plastic zones in said coal-charge to such a degree as to prevent pressures in excess of said normal value being exerted against the oven side walls prior to the latter part of the carbonizing period, and preventing the formation in said coal-charge during the latter part of the carbonizing period of an uninterrupted highly impermeable plastic zone by providing over at least a substantial part of the above-identified coal-charge a porous layer of granular material of such composition that a highly impermeable plastic zone does not develop within said layer as a result of exposure of said layer to the temperatures encountered in said oven and of such thickness as to prevent heat radiated from the roof of said oven and from the uper portion of the side walls of said oven from developing a highly impermeable plastic zone across the top of said coal-charge.

3. A method of carbonizing in an externallyheated horizontally-elongated intermittent coke oven having side walls which are susceptible of injury when subjected to pressure in excess of a normal value coal of a type which when carbonized in the usual manner causes pressures in excess of said normal value to be exerted against the oven side walls during the latter part oi the `carbonizing period because oi. the formation during the latter part of the carbonizing period oi a substantially un-interrupted highly impermeable plastic zone surrounding and enclosing the central portion of the coal-charge and which when carbonized in the usual manner also causes pressures in excess of said normal value to be exerted against the oven -side walls during a substantial part of the carbonizing period prior to the latter part of the earbonizing period because of the swelling of the plastic zones in the coal-charge,

said method comprising charging said oven with coal oi the type identiiled above and to which has been added pitchin the amount of at least '1.5% of the weight of the coal-charge to thereby reduce the swelling of the plastic zones in said coalcharge to such a degree as to prevent pressures in excess of such normal values being exerted against the oven side walls prior to the latter part4 of the carbonizing period, and preventing the formation in said coal-charge during the latter part ofA the carbonizing period of an uninterrupted A coal-charge the material of said covering layer remains substantially more permeable to gases emitted from said coal-charge than the plastic zone formed in said coal-charge, said covering layer being of such thickness as to prevent heat radiated from the roof of said oven and from the upper portions of the side walls of said oven from developing in the upper portion of said coalcharge a plastic zone which can cooperate with the plastic zones developed in the lower portions of said coal-charge to restrict the escape of gases from the portion of the coal-charge within said plastic zone, whereby the gases evolved from the central portion of said coal-charge during carbonization of said coal-charge may readily escape without building up to pressures which cause said coal-charge to exert pressures in excess of said normal value on the side walls of said oven.

MICHAEL PERCH.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 955,970 Korting Apr. 26, 1910 1,268,628 Rusby et al. June 4, 1918 1,512,577 Blythe Oct. 21, 1924 1,593,208 Culmer July 20, 1926 2,018,664 Fitz et al. Oct. 29, 1935 2,382,809 Otto Aug. 14, 1945 FOREIGN PATENTS A Number Country Date v 322,341 Great Britain C. A. Dec. 5, 1929 842,550 France Aug. 24. 1938

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