US1458964A - Process of manufacture of coke for metallurgical uses - Google Patents

Description

June 19, 1923.

A. H. BAILLE-BARRELLE PROCESS OF MANUFACTURE OF COKE FOR METALLURGICAL USES Filed May 28 1921 2 Sheets-Sheet 1 Fig. 3

m. M m m H A June 19, 1923. 1,458,964

A. H. BAlLLE-BARRELLE PROCESS OF MANUFACTURE OF COKE FOR METALLURGICAL USES Filed May 28 1921 2 Sheets-Sheet 2 Fig/F men/1:01 wille -Bwzme Lle,

Jiws.

- Patented 1 9," v

] UNITED;STATES PATENT!OFFICE.

' 3mm: BAILLE-BARR ILLE, creams-Eamon or irniquracrunn or coim FOR METAILURGICAL' uses.

Application filed ma as, 1s21.- Serial n. 473,341.

"To it may concern:

-' I Be it known that I, ANDRITHENRI BAIlLLE BABBELLE, 'a citizenof the Republic of France, and residing at Paris, Seine Department, No, 126 Rue de Provence, in the Re public of France, have invented certain new and. useful Improvements in Processes of Manufacture ofCoke for Metallurgical'Uses,

of which the following is a specification. 10

This invention relates to a process of manufacture of coke for metallurgical uses. In theknown coking process, when the coal is fed into a coke oven which is brought to a high temperature, this will efi'e'ct the immediate distillation of the coal coming in contact with the oven walls, whereupon vapors of a tarry nature are produced-which condense within the massof coal which has not had sufficient time to become heated. In

/ gases and to heat.

this manner there is constituted at a short distance from each wall of the coke oven 2'.

regiontermed screen region, which 'is very rich in tar and is entirely impervious. to The said region which becomes completely destroyed at the outer side which is submitted-to the action of the 'heat, is formed anew at the inner side there.-

o'f,- and thus moves gradually towards the center of the furnace, leaving between this region andthe oven wall a certain amount of perfectly formed coke, while the coal situated between the said screen region and the center of the furnace has not as yet undergone any appreciable decomposition.

The thickness of the. said coking region is very small, this being at most 2 or 3 centimeters. By measuring the temperatures at any desired point within the mass of coal in 'a coke oven which is heated in the known manner, it willbe observed that the temperature will reach 100 C. rather rapidly, then remains stationary and will thereafter rise very slowly until the point under consideration is attained by the said coking region. In this casethe temperature rises rapidly, or in 4 to 5 hours, from 200 or 300 to 800- or 900 ,C. and then increases very slowly up tq the final temperature of the operation. It will therefore be noted that the coal is. coked in successive layers in I which the variations of heat are very rapid.

. "When applied to coal whose decomposition is attended by phenomena of considerable changes in volume, a rocess of this kind will afford only a '00 e of inferior quality, for at each instant the. coaltinclecom osition which is enclosed between" the shel ofalready-formed coke and the inner mass of non-decomposed coal, is prevented from undergoing free expansion and contraction, thereby givin rise to" considerable local tensions and resu ting in a product of a cracked and fragile nature analogous to a badly annealed glass. In the special case 'of coal which becomes reduced in volume in the coking process, the first'layer of coke surrounding a corewhich may be put out of shape will become broken in pieces, and subsequently such pieces will serve as a support,

for the successive films of coke in formation.

At the end of the operation the process will yield long needle-likemasses disposed perpendicular to the oven walls, these being --more or less intermingled but-not adhering to each other. Coke of this character, which is very fragile, is known as cokeformed in needle-like crystals, and is unsuitable. for

use in large blast furnaces.

The said phenomenon of the screen region is produced not only upon feedingcoal into a coke-oven which is sufficiently heatedto elfect a sudden distillation of the outer layers, but it likewise occurs underv all circumstances in which in the case of a. mass of coal submitted .tothe action of heati'n the interval of temperature wherein .con- 'den sable volatile products. are given offthere exists a suflicient difference of temperature between two portions of the mass whereby one portion is enabled to serve as a condensation region for the vapors given ofi by theother. The phenomenon when once started will increase very rapidly in extent, for when the said screen is once formed, the lack of equilibrium of temperature which gave rise thereto must 'necessarily go on increasing.

, The process according to this invention iii pors are observed at the same time.

Fig. 1 is a horizontal sectional view through a coal mass, the dotted and indicated lines representing the standard curve of variations of temperature,

Figs. 2 to 4 inclusive are diagrams indicative of the temperature curves of the furnace, the surface and the center of the coal mass.

The said process will be more particularly described hereunder as applicable to the coking of coal of the variety termed Fettkohl, that is, having the character of the coal obtained from the lower region of Sarrebruck.

By gradually heating such Fettkohl out of contact with air, the following phenomena are observed:

1. Between ordinary temperature and 330 C. the coal loses water as well as very small quantities of non-combustible gases (occluded air, CO and remains practically unchanged. Its percentage of volatile substances and its agglutinating power are only reduced by a small amount, but this on condition that the coal shall be heated in an entirely neutral atmosphere, inasmuch as the smallest admission of air, at temperatures above 100, would give rise to a rapid oxidation which in the case of certain varieties of coal may proceed as far as a complete combustion. This represents the phase of heating underneutral conditions.

2. The decomposition of the coal appears to commence about 330 C. at which temperature the beginning of the disengagemerit of gas and the appearance of tar va- This decomposition takes place without any change in the physical state, and all that might happen in certain cases would be that the coal would lose all cohesion and would fall in powder, but this effect is marked by a considerable diminution of the agglutinating power. This represents the phase of the first decomposition or the transition phase, and it ends at about 400 C.

3. Between 400 and 420 (1., the action whereby volatile substances are given off (gases and tars), is now observed to increase at a rapid rate. The coal changes its physical state, beingtransformed for a certain time into the pasty state, whereupon it becomes agglomerated and is subsequently solidified. This represents the phase of agglomeration, or the coking phase.

4. From 420 to the final temperature of the operation, the product obtained from the solidification of the coal paste is transformed into coke suitable for metallurgical purposes. This transformation is effected without any other change in physical state, or even, any change in structure, inasmuch as the substance which is obtained at the end of the third phase loses only its volatile sub-- stances while contracting and increasing in sible in order to lessen the effects of oxidation. It is advisable to make use of coke ovens which are made gas-tight as far as possible and to maintain the same at a slight excess of pressure therein. It is likewise advantageous to reduce the duration of the phase of the first decomposition. In fact, the l ettkohl begins to decompose at about 330 C. and even though the first decomposition is not made manifest on the outside save by a slight amount of volatile substances given off, it nevertheless modifies the essential properties of this coal, and in particular its aptitude for melting and its agglutinating power may entirely disappear. In order to prevent this agglutinating power from descending below the minimum limit necessary for obtaining a suitably agglomerated coke, it is required to pass through the interval of temperature from 330 to 440 within a time not exceeding H hours, H representing a number which 'is to be determined experimentably for each variety of coal. The duration of this phase of agglomeration or coke formation, which is the most essential, should be situated between two limiting points. Examination of the phenomena taking place during this period leads to the following conclusion: The rate of heating during the phase of agglomeration should lie between the two extreme values V and V, V being a minimum rate compatible with a suitable agglomeration, and V a maximum rate compatible with obtaining a homogeneous mass of coke without spongy formation.

Above 420 C. the coke contracts and Y, in '-this case the contraction will take place throughout the entire mass at the same time i .and without giving rise to local tensions which are the primary cause of cracking. But by reason of the slowness of the exchanges of temperature throughout the mass of coal, it isfoundfpreferable to adopt extremely low ratesiof heating. In practice it is not essential that the coke for metallurgical uses shall be entirel free from cracks, and it will suffice to suitably reduce the amount of cracking of the F ettkohl coke in order to enable its use for metallurgical purposes.

In practice, .it is fou nd the following conditions:

-1. At the time when the outer shell begins to contract, it. is required to allow a 'sufiicient thickness of plastic pasty mass between this shell and the main bodyof the coal which is. not as yet melted and cannot lose its shape, whereby the said shell is en- 'abled'to contract without bursting, that is, it

should possess from the beginning of the contractlon phase a regular temperature curve whose rate is below g r'centimeter between the-inner and outer part of the said.

- space.

. 2. The phaseof contraction occurs'lin such. manner that at each instant the masses having the same rate of heating shall be pro-.

vided in .suflicient amount'in order that. the

internal tension efi'ects arising 'from .un-

equal contraction' shall produce cracks of large size. which" are widely spaced apart, on the contrary to a network of small crackling. such as is formed by the contraction of thin-layers successively, submitted to .the in which ascreen finally stated'as .followsfv outer shell of the coke mass is not to be I cal use follows through'in less than hours,

1.1 The phaseof contraction is'not' to be commenced, that is, the temperature .of the brought to more than 420, before the in terior has exceeded 420N) -N being equalto g 1/2 L. '(Inwhich L represents the width. of the coke oven measured in centimeters).

2. The. "phase of contraction is to be passed through at a rate of speed suchthat-the difl ferenceof temperature from exterior to interior' shall in all cases remainlequal to N, for should this difference tendfl'to increase from the start, experience shows that it will then continue to increase until the interior reaches 500550, and after this time it suddenly-commences to decrease, whereby the temperature at the central part will very soon become almost the same asjat the outer part. 'The rate of heating at the central part is considerably higher than that of the outer shell, and consequently the interior of the coke mass will become very much cracked. But if the initial difference N has atenf dency to decrease from the start, the tem-" perature at'the center will very gradually become equalto that of the exterior, thereby producing a grade of coke which is but very slightly cracked. I

To recapitulate, the conditions requiredt obtain a ood quality of coke, for metallurgiom .Fettkohl, may be stated as 1. Oxidation of the coal is to 'beavoided durin the neutral phase." 2. he transition hase..is to be passed suflicient to obtain the operation is" carried out upon considerable masses as-inthe-actual industry:

.passed throu h "3. t The agglomeration phase is to be. passed through at'a'. rate of' speed-comprised between the 'rat'es'V and Vf.

, From. the sam- 10:;-

ployed whose'jrate is below g? percentimeter,

' the contraction" in phase, a temperature curve is to bet embetween the exterior and'the'lcenter of the coke'mass.

a 5. The phase ofcontraction is to be passed through aitfa rate of speed a; such that the difference of'temperature' between the center and the ,to increase.-

exterior have no tendency According to havebeen'foun'd the {coeflicients' H, V,

side, V=159 per hour.

, astjz-whiii' have beenhitherto carried -out'. WithJrelatively small "masses,\the' folliuwnig approximate values .The r ule'sto; be followed-forthe cokingi of Fettkohl may bemo're simply stated when tion to atemperaturenotunder-(420 N) wherein no point shall 'be allowed to exceed 420? i then the temperature :of th'e'mas's is nerthat at no'time duringthis second period of operation shall the maximumteme perature, difference between two. points of the mass go beyond N.

Under these conditions-a suitable coke to be gradually raised toxTOOE in such manwithout cracks will be obtained. Thiscoke will be furthermore 'ina better state of agglomeratlon if .the following is carried out:

1. No point of the'said mass shall'ha've the phase of agglomeration ata speed be ow '0.

2 No point thereof: shall have remained more than H hours between 330 and 400.

3. The coal shall. not have been oxidized. To conform to these rules, it appears advantageous vto carry out the operation follows: The small coal or slack of the .Fettkohl variety is disposed and very sfro ly pounded down in coke. ovens having a.wi th of' 2. Qentiinete'rs wherein the temperatureis maintainedat 320 until the-interiorof the .cok'e' .mass" .shall have attained 700. During a .:series. 'of testsiupon -coal containing 15% water, which was pounded downina "sheet metal receptacle of 24 centimeters width, it was found that the optimumd I tion' of treatment-1 at constant temperature is 18 hours at 320 and 6 hours at 700 C. The standard curve of variations of temperature in the said space with reference to the time is thus determined in a very complete manner, and the same is represented in the accompanying drawings together with the curves for the heating effects which were actually observed for the exterior and the center of the coke mass. A, B C. D indicates the temperature curve of the furnace, and a, b, c, (l and a, I), c, d the temperature curves for the surface and the center of the coke mass respectively.

This optimum curve may be modified to a certain extent. It is evident that the iso thermic line for 320 may be replaced by any suitable curve situated thereunder on the sole condition that the second part of the curve shall not be attainedbefore the interior of the coke 'mass shall have reached 150. Experiments have also shown that- N may vary between 130 and 240, and that the rate of heating at the center of the mass is subject to variations between 14 and 20 per hour. It is likewise possible to replace the inclined straight line by a series of steps which are spaced apart by about 100.

' The heating could be carried out in various types of coke ovens such for instance as impelling ovens, tunnel ovens, Hofimann ovens and in general all types of coke ovens wherein the temperature may be varied Within a considerable range.

Claims- I 1. A process of manufacture of coke for metallurgical uses, consisting in the operation of raising the coke as rapidly as possible to the temperature after which it commences to agglomerate, and then in heating the same gradually and with a suitable degree of slowness whereby there shall not exist at any moment such differences of temperature between any two points in the mass of coal as would be suscept ble of giving rise to the phenomenonv of the screen region, and lastly, when the coal has become agglomerated throughout the entire mass thereof, in heating the same rapidly to the final temperature which is required for giving 05 substantially the whole amount of the volatile substances.

2. A process of manufacture of coke for metallurgical uses, consisting in the operation of rapidly heating the coal to the temperature of 400 C. whereupon it commences to decompose, in raising the temperature of the coal from 400 to 420 C. in 8 hours or less, in maintaining the degree of heating in such manner that the rate 'of heating of the coal during the phase of agglomeration shall be at least equal to 15 C.- per hour, the temperature of the outer shell of the coal mass not being raised above 420 until the center of the mass has attained 420l l, N being approximately equal to-the product of 15 C. by one-half the thickness of the mass measured in centimeters, and in efiecting the final heating in such manner that the temperature difference betweenthe surface and the center of the mass shall not exceed N".

3. A process for the-manufacture of coke for metallurgical uses, consisting in the operation of heating a mass of coal of approximately 25 centimeters thickness and well pounded down, in such manner that the temperature of the coke oven shall be maintained at approximately 320 C. until the center of the mass shall have attained approximately 150 C., and then gradually raised by 15 C. per hour up to approxi-i mately 700 C., remaining at that temperature until the interior of the coke mass shall have attained 700 C. i

4. In a process of manufacture of metallurgical coke, the operation whereby the heating is so efi'ected that at the instant when the surface of the coal is at the temperature of agglomeration T,the center of the mass shall be at the temperature TN, N being approximately equal to the product of 15 C. by one-half the thickness of the mass measured in centimeters, and that subsequently the temperature difference between the surface and the center of the mass shall not exceed N".

In testimony, that I claim the foregoing as my invention I have signed my name in presenceof a subscribing witness.

ANDRfi HENRI BAlLLE-EARRELLE.

Witness MAURICE

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