US2461365A - Production of shaped and carbonized articles from coal - Google Patents

Description

Patented 8,

rnonoo'rrou or SHAPED AND CARBONIZED ARTICLES FROM COAL John Godolphin Bennett, David Blythe Foster, Charles Desmond Greaves, and George Cordery Phillpotts, London, and Marcello Pirani and William Julianus Kramers,

Kingston-on- Ihaznes, England, assignors to C. D. Patents Limited, London, England, a British company No Drawing. Applicationflctober 17, 1945,

Serial No. 622,934 In Glttt- Britain NOVCllibel 2, 1944 8 Claims. 1

The invention relates to processes for the production from bituminous coal of shaped articles, predominantly carbon in composition with a density greater than that of the original coal and with properties which render such articles useful in various arts and industries. Thus the product may be made by the processes herein described to have a tensile strength of 3,000- 6,000 lbs. per square inch and upwards, considerable resistance to being shattered, a structure free from bubbles and of a porosity in methyl alcohol of less than per cent; it may also be made to contain not less than 97 per cent of carbon on the dry, mineral-matter-free basis, to be inert to most chemicals, substantially unafiected by boiling toluene, or aniline, unaffected by heat, in a non-oxidising atmosphere, up to 2,600 C., to have good'electrical conductivity, and to show reflectance in oil from a polished surface higher than that exhibited by anthracite. According to the present invention, articles of the character referred to are made from bituminous coal, without requiring the use of an added binding material, by taking advantage of the agglutinating power of suitable coals themselves (particularly suitable coking coals), to effect the binding of the material and to promote its strength. The process comprises moulding followed by carbonization, and involves fine comminution and intimate mixture of the material, the moulding of the same to shape under pressure which usually is considerable, and subsequent carbonizatio-n of the shaped article in a non-oxidizing atmosphere, under a carefully controlled firing schedule. Successful results are obtained by adjustment and regulation of certainfactors ofthe process particularly of the firing rate, as will presently be explained. The process, it may be added, may involve the feature that the non-oxidizing atmosphere consists of or contains one or another gas or vapour, thecharacter of which may considerably affect the properties of the-final product.

One of the difiiculties to be overcome is the fact that the most strongly agglutinating' coals: when heated to the stage of thermal decomposition,

evolve gases and vapours and tendto swell. This 4 firing may be carried out at a very slow rate of increase, particularly in passing through the plastic range, so that the volatile matters are not generated too rapidly and can escape without setting up critical internal pressures. It is important, also, that the comminution ofthe material should be neither too coarse nor too.

fine. If the particles are coarser than an op timum value, internal pressures tend to beset up inside the particles, and. with comminuticn finer than the optimum pressures tend to'be set up between the particles, both'eiiectstending'tc make the mass swell. Also, compacting'the mass only lightly is a means for avoiding swelling, so'that suilicient space is left between the par;

ticles for the escape of gases or vapours.

For the purposes of the present invention, however, the factors'whi ch promote strength in the degree of fineness, so that the individual par ticles can-be brought into the closest possible contact; to compressthe mass under very pressure-into a desired shape, analogous to the process of powder metallurgy to conduct the fir ingat a rate of: temperature rise as rapid as possible; and during the carbonization, to errsure that the atmosphere surrounding-the article is rich in hydrocarbons, especially unsaturated hydrocarbons. But it so happens that all these strength-promoting factors tend, whether separately or in combination,. to produce swelling if they are allowed to operate without restriction.

' It has now been found; however, that a strong, unswollen product can be-gmade bya; careful and balanced choice of these strength-promoting and swell-inhibiting factors, Adequate strength carr be produc-zed by the use of some" only of the strength-producing factors, whilst V swelling canbe prevented by the use of some only of the items of the anti-swelling e'Xpedients-s The process'herein described is based to a considerable extent upon the use ofsuch a corhbh nation of these two sets of factors as is found" to be" most suitable for the production ofpairticu-lar typesof articles; a certain amount ofcompromise between the opposed elements: being,

practised.

high agglutinating power; to commi-nute the coal to a very' 'high The object of the invention is the provision of methods, for the production of articles of the character referred to, which shall-be eifective, readily controllable, and comparatively inexpensive and speedy. The process may involve the use of a swell-inhibiting agent, under certain conditions, as when the tendency to intumesce of the coal operated upon exceeds a certain value, or it may be practised without the use of such agent under other conditions, as when the swelling tendency is below such value or when the rate of firing is considerably reduced.

Possible swell-inhibiting agents may be of various characters. One type consists of materials which appear to be inert. These appear to have little or no effect beyond that which follows from a reduction of the amount of volatile matter as a fraction of the weight of the preformed product. This type will be referred to as diluents. sists of a weakly caking coal. This acts to some extent as a diluent, but'it contributes its own small agglutinating power to the mixture, and evolves gaseous products during the firing, (the temperature range at which the most rapid evolution takes place being, however, somewhat different for the two coals). Such materials as the above may be employed in the present invention, when required, but in other cases no inhibitor will be used within the scope of the present invention.

The invention, at least in its preferred form, is based on a number of discoveries and observations of a more detailed character than those mentioned above, and, to said understanding of the process, these will now be referred to briefly.

Firstly, in coal which when treated by the procedure described in British Standard Specification No. 1016 evolves from about 13% to 30% of its weight in volatile form calculated on a dry ash-free basis, there seems to be a general relation between the percentage of such volatiles and the tendency of the coal to intumesce, and We have found that for the process of this invention there exists a specially favourable percentage range. Coals within such range can be comminuted, moulded, and fired, in the manner described herein, without the addition of an antiswell agent, without any harmful swelling, and with the production of good products. Likewise, coal having a higher percentage of volatiles can be diluted by the addition of enough of an inert material of the character described or of a weakly caking coal to bring the volatile percentage down to about the same figure, with very much the same effect, the diluent being ground to about the same degree of fineness as the coal, and the rate of firing and the other steps of the process being similar to those practised in the case in which no diluent was used. The specially favourable percentage range referred to is 18/22.

Secondly, the material to be moulded must be finely comminuted and intimately mixed, and the mixture must be moulded under a pressure at least sufficient to enable the shaped article to be handled and transferred undamaged from the mould to the furnace in which it is fired, and preferably under a pressure of at least 2 tons per square inch. Considerable variations of the degree of comminution and amount of pressure are possible, with accompanying variations of firing rate.

Thirdly, if the moulded body is fired at suitable rates, up to a suificiently high temperature, in a non-oxidizing atmosphere, the carbonaceous ma- One modification of this type conterial remaining will pass through a series of chemical changes, to give an optical reflectivity in oil which may be a considerably higher figure even than that for anthracite; but the rate of firing, while the temperature is being raised through the zone in which the coal is plastic, must be above a minimum figure, below which an amorphous material is produced.

For example, using the technique described by Seyler in his Melchett Lecture to the Institute of Fuel in 1942, a Welsh coal suitable for the process is found to consist mainly of a constituent (Seylers No. 6) having an optical reflectance in oil immersion of 1.62%. Anthracite, which has the highest optical reflectance of naturally occurring coals, has an optical reflectance in oil of 2.34%. The product made in accordance with the process of the invention is found to contain a substantial proportion of a material having optical reflectance in oil from 4.95% up to 5.2% (hereinafter referred to as alpha material) which is not found in any naturally occurring coal. It has, moreover, been found that the presence of this material of high optical reflectance is an important factor in conferring strength and other desired properties. If, however, the rate of firing is too slow, the proportion of material of high reflectance is diminished, and it is replaced by a black material which is usually described as amorphous carbon and is of low optical reflect-' ance. The products consisting entirely or almost entirely of this black material of low optical refiectance are weak and unsuitable for use in commerce, and for this reason excessively slow rates of firing must be avoided. The material of high reflectance referred to is carbon in an elementary form which, when the process is carried out in a preferred manner, occurs in a proportion of at least 30% by weight of the product, or of the carbonaceous material contained in the product in case a substantial proportion of the product is non-carbonaceous, as when a non-carbonaceous swell-inhibiting agent is used in the process, as is hereinafter described.

Fourthly, the rate of firing must be sufficiently slow during that temperature range in which the coal is plastic and is also evolving gases, to avoid swelling, and likewise during that temperature range in which the coal is no longer plastic but is still evolving gases, i. e., above about 500 C. sufiiciently slow to avoid formation of cracks. We have made the important discovery that to give the best results in respect of strength, however, the firing rate should be substantially as rapid as possible, conformably with avoidance of swelling, through the range in which the coal is both plastic and is evolving gases. This firing rate must be slower when the powder is comminuted more finely, or when a higher moulding pressure is used, or when articles of thicker section are made, than when less fine comminution or less pressure are used or thinner section articles are made.

Fifthly, useful articles for some purposes can be produced by firing only to about 550? 0., but for articles of considerable toughness and strength, the firing should be continued to at least about 650 C.-850 C.

Sixthly, the gas envelope in which the article is surrounded during carbonization exerts a marked influence on the process, which varies considerably with dii erent gases. For example, excellent results are obtained in some cases when carbonizing in an envelope composed of or containing ethylene or other unsaturated hydrocarenemas bon gas or vapour, with deposition of carbonwithin the interstices and on the internal faces of particles within the body, and in some cases an article which is defective, for example, in tensile strength, can be improved considerably by re-firing it in such a selected atmosphere.

The invention will now be described in greater detail.

The first consideration is choice of a suitable coal. Mechanically strong bodies may be produced from bituminous coal by carbonization, as a general principle, provided that the coal agglutinates into a coherent mass during carbonization. Different coals vary considerably in agglutinating power, and when this is below a certain figure the addition of an agglutinating agent or binder may be used to produce suitable co-- hesion, such binders being, for example, the products of coke manufacture, tars, pitches, etc. Such additions, however, are not required in the present process and generally are not desired, for a number of reasons. The coal chosen must be one in which the temperature ranges in which softening and thermal decomposition occur are suitably related to each other. If a coal decomposes largely before it softens, no strong coherent body can be produced by the present process. Therefore, low rank or young coals cannot be used, such as lignites or the lignitous coals, in which the decomposition temperature is very low. Likewise very high rank or old coals of the anthracite group are excluded, because as is well known they do not soften but decrepitate, i. e., break up into small fragments, when heated to decomposition temperatures.

The coals which have been found to be best adapted for use in the present invention are bituminous coals, having a volatile matter content which lies between about 13 and 39 per cent, calculated on a dry ash-free basis. Differences exist between coals of this type sufficiently Wide to predetermine the treatment to be employed. A gradation of such coals in composition with increasing rank will usually show a steady decrease in the intensity of the anti-swelling factors required to produce unswollen products. Thus considering the following strongly swelling coals:v

Vola- Agglutina- Swelling tiles Flxed ting Value No.

' A 24 67.2 (74) 24 9 B 22 75.4 (77.5) 29 9 C 20 78.4 (79.5) 16 9 In this table, given by way of example, (and elsewhere, unless otherwise stated), the volatiles and the bracketed values for fixed carbon are ash-free, the agglutinating values are as determined by British Standard Specification No. 795, and the swelling numbers are as determined by British Standard Specification No. 1016.

As to these coals, a dilution, by the addition of an agent of the character described, of 10 per cent in the case of coal A, and of about 5 per cent in. the case of coal B and no dilutionin the case of coal C, will give unswollen products at the same firing rate which produces an un-,

swollen product from coal C, the other factors of the process being treated similarly, and in the manner herein described. In coal 0, the'percentage of volatiles is 20, while in coal A, when diluted by mixing 90 per cent coal with 10 per cent of, say, pitch coke, the percentage is 2 1.6,

V 8.. and in coal B, when diluted with 5 per cent of pitch coke, the percentage is 20.9, the diluent having almost reduced the percentage of volatiles to what seems to be the specially favourable percentage shown by coal C. It will be seen that careful selection 'of the coal employed, and. a thorough understanding of its characteristics, are needed for the practice of the described process.

The coal selected is first cornminuted to a fine powder, so that, for example, more than 95 ,per cent byweight of the particles pass through a 200 mesh B. S. sieve. This is fairly close to the optimum fineness for the prevention of swelling, it being believed that the optimum for a typical coking coal is 80-90% through 260 mesh B. S. S. This is optimum because with coarser particles internal pressures are set up inside the particles, on carbonizatiomand with finer particles having a greater surface volume ratio pressures are set up between the particles, with effects tending. to make the mass swell.

In many cases a much finer comminution can be efiecteci, with advantage to the strength of the product. Thus the coal may be so comminuted that at least 69 per cent by weight of the particles are smaller than 16 microns, or so that the specific surface exceeds 15,009 sq. ems. per

gramme, both of these measurements being as determined by the photo-electric sedimentation method, which is described in the Proceedings of the Conference on the Determination of ever 'the coal is comminuted to any such degree of fineness, the firing rate will require to be cor- V respondingly slower, as is explained hereafter.

The swell-inhibiting agent, which maybe required when theswelling tendency of the coalis greater than desired, may be an inert filler, which seems to act solely as a diluent, or it may be a weakly-coking coal, or even a non-colring coal. 0f the last two, each contributes a small agglutinating power. e

If the agent is of the inert type,it may be a carbonaceous material such as pitch coke, or coke breeze. Graphite may be used, and is of particular value for special purposes; as when good electrical conductivity is wanted, or when special shapes are required which require fluidity in the moulding stage, in which case graphite may be added and be useful both as a lubricant and as a swell-inhibitor. Higher rank coals. such as anthracite, which seem to approximate to an inert filler, may also be used. V

Or the diluent may be a non-carbonaceous material, as for example, a solid pulverulent' material which does not melt within thefiring temperature range, such as, for example, silica in any of its'nurnerous forms, siliceous minerals such as clays, mica, granite, etc nietallic oxides such as alumina, and metal powders. When selecting one of the many possible agents of this type, regard should be'had to thepcssibility that there may be some decompositionicf theagent during the firing operation. Such decomposition is not necessarily undesirable, provided that the products of decomposition do not oxidize the-coal substance or otherwise affect the'properties of the article, particularly in respect ofstrength or r distortion. a Next, as to comrninution of the agents, the

selected agent is ground in any suitable grinder to a degree of sub-division which may be determined experimentally to be best in a particular case, and which usually is atleast sufficient to pass 90-95 per cent by weight of the particles through a 200 mesh B. S. sieve. In some cases it is found that, as in the case of the coal the agent may be further comminuted so that at least 60 per cent by weight of the particles are smaller than 10 microns or so that the specific surface exceeds at least 15,000 sq. ems. per gramme, with a resulting increase of tensile strength of the product.

The grading of the particle sizes when comminuted to pass, say, 95 per cent through a 200 mesh B. S. sieve will generally be such as to secure a satisfactory degree of close packing, but if desired the coal and/or agent may be further graded as to particle size, in accordance with known principles, to obtain an improved degree of close packing.

As to mixing, it is essential that powders of coal and mixtures of coal with swell-inhibiting agents be mixed intimately. The ordinary methods of mixing which are sufiicient, for example, in preparing a blend of coals for coke manufacture or briquetting are quite inadequate for the process of the present invention. The strength of the finished article may fall considerably if there is inadequate or faulty mixing. Mixing methods should be used which can be relied upon to break down any agglomerates and to ensure as far as possible perfectly uniform distribution.

As to the moulding pressure, considerable variation is possible in different cases, as will be explained hereafter, but there must always be enough pressure to enable the cold-shaped product to be transferred from the mould to the firing furnace without damage, and also enough to ensure desired strength in the product. In general, good results are obtained with pressures of, say, 3 to 4 tons per square inch. If complicated shapes are required, pressures up to 6 tons per square inch or higher may be necessary. As during the moulding of the article no curing process is involved, the time of moulding may be quite short, and it is usually not necessary to maintain the pressure for more than 10 or 15 seconds. The moulding is normally carried out at room temperature, but for certain mixtures it may be desirable to mould Warm, say up to As alternatives to moulding, extrusion or similar techniques usedin the plastics and ceramics industries may be employed. In general, the ordinary technique which is used for the moulding of synthetic resins and of dry powders is suitable, except that temperatures higher than atmospheric need not be used. Preferably the mould is designed with slightly greater clearance for the plunger than is customary with the usual moulding powders of the plastics industry.

As to the firing rate, it is evident that heating in itself is an agglomerating factor, enabling carbonization and particle re-arrangement to take place, but that rapidity of increase of temperature is a swelling factor, if time enough is not allowed for the escape of volatile matter generated at temperatures at which volatiles come off, particularly between about 300 C. to 500 C. In most cases the strongest products will be produced by heatin through this range as rapidly as possible to avoid rather narrowly the swelling of the product, as can readily be determined by test. The'firing schedule may be varied somewhat'by the nature of the coal or the mixture,

the degree of comminution, the moulding pres- If however a coal of coal mixture having a volatile content of 27% were to be used, the following schedule would be preferable;

C. per minute rise Up to 300 C /2-1 300500 C 500-850C 2-3 Whilst for a great many coals the foregoing schedule-s will be a satisfactory guide, it is import-ant to remember that proximate and ultimate analyses are not a reliable guide to indi vidual behaviour and, more especially, to the extent of the decomposition temperature range in any given coal.

By firing totemperatures higher than 850 C. increased electrical conductivity is obtained. In such case the firing schedule above 1000 C. may be as rapid as is convenient.

A further matter of considerable importance in the process is that of the firing atmosphere. The heating of the shaped articles and their subsequent cooling must be conducted under nonoxidizing conditions, not only to prevent the coal from burning, but also because oxidation may tend to weaken the agglutinating power of the compacted mass. This may conveniently be achieved by packing the article within a protective mass of granular or powdered material which evolves non-oxidizin gas or vapours during the firing operation. A suitable material for this purpose is a coal of high volatile content with little or no caliing property, such as the British coal, Warwickshire Brights. A bed of this powdered material is made and may be slightly compressed, and the moulded article may then be laid in a depression within the bed which has been made, for example by tamping with a solid former of the same shape as the article. If the moulded article is hollow, the interior of the article is filled with the same powdered material. The exposed surface or surfaces of the articles are then covered with the powder, the latter being firmly but gently pressed down.

1+ is also possible to secure the necessary protection by passing a gas stream through the furnace, for example, hydrogen, carbon monoxide, ordinary town gas, or hydro-carbon vapours. In such case the article should be placed on an even support, preferably of fine, loose, granular ma terial such as sand 01' charcoal. And care should be taken to see that the gas composition all round the article is as uniform as possible.

Whichever method of protection is employed, and it will of course be understood that any suitable method or combination of methods may be used if desired, it is essential that the access of atmospheric oxygen or other oxidizing gases, even carbon dioxide, to the surface of the article should be prevented.

The nature of the firing atmosphere during carbonization exerts a positive influence on the process, and has a considerable effect on the nature of the product, as will be referred to hereafter. This atmosphere may be maintained at normal pressure, or a part or the whole of the firing operation may be conducted with the atmosphere at pressure either above or below normal.

Some examples of the practice of the invention, employing a carbonaceous swell-inhibiting agent of diluen character, will now be given.

1. 80 parts by weight of a strongly coking Welsh coal having a volatile content .of 24% and of swelling number 9 containing 8% ash, (90.4% carbon, 4.9% hydrogen, 1.9% nitrogen, and 2.8% oxygen, on Parrs basis), was comminuted so as to pass through a 240 mesh B. S. sieve. 20 parts by weight of graphite (95%) which had been separately comminuted to the same degree of fineness was employed as the swell-inhibiting agent, and the coal and graphite powders were thoroughly mixed together in a ball mill for two hours.

The mixture was then moulded cold into small howls about 1% deep by 5%" diameter at the rim, under a pressure of 3 tons per square inch,

the pressure being applied slowly (for example, a travel of 1 inch in seconds) and then immediately released. The bowls were then placed in a copper box insidean electrical furnace and covered all over with a high-volatile non-caking coal of a size to pass through a inch mesh B. S. sieve. The temperature of the furnace was raised to 800 C. at a rate of 1 C. per minute, the furnace was then allowed to cool, and the bowls were removed from the furnace when the temperature had fallen to about 250 0.

The bowls so made were of good strength, unswollen and undistorted, the overall shrinkage being in the neighbourhood of It should be noted that the temperature was raised uniformly-x;

to 800 C. in this and some other examples, given hereafter, as a. matter of convenience, to avoid resetting of apparatus. It was found that the rate of 1 C. rise per minute through the plastic temperature range and up to 550 C, would give satisfactory results, and it therefore followed that this rate could not be too rapid for the firing up to the beginning of plasticity and beyond 550 C. The rate of firing could have been increased to about 2 C. per minute, up to 300 C. and to about 23 C. per minute from 550 to 800 C., with an equally good product and a saving of time.

2. 80 parts of the same coal as in Example 1 was comminuted the same as in. Example 1. For the swell-irmibiting agent, parts of pitch coke and 10 parts of powdered cuprene were taken, the pitch coke being comminuted so as to pass 100% through a 200 mesh B. S. sieve and 90% through a 240 mesh B. S. sieve, and the powdered cuprene being made by allowing gaseous acetylene to deposit on metallic copper at an elevated tem perature. The coal, pitch coke, and cuprene were intimately mixed in a ball mill for three hours, and the rest of the process was exactly the same as in Example 1, except that small bars of about /2" thick were moulded and that the non-oxidiz ing atmosphere was different. As to the latter, the moulded bars were placed on a firebrick support inside an electrical furnace, and a current of hydrogen was passed over the bars, the volume flow of the hydrogen being just sufficient to maintain the non-oxidizing atmosphere around the bars.

3. As an example of the process whenemployinc a weakly caking coal as the swell-inhibiting agent, 70 parts of the strongly coking Welsh coal described in connection with Example 1 was comminuted as in Example 1 and mixed, the same as in Example 1, with 30 parts of a Yorkshire weakly caking coal having a volatile content of 34% and separately comminuted so that per cent passed through a 200 mesh B. S. sieve. The mixture was pressed into flat plates having a thickness of at a moulding pres-sure of 4 tons per square inch, the procedure as to moulding being the same as in Example 1, and also the arrangement to produce the non-oxidizing atmosphere. The rate of firing was, however, different, the temperature of the furnace being raised at the rate of 2 per minute to 300 C'., then at per minute to 500 C. and thereafter at 1 per minute to 700 C. The product was about the same as thatof Example 1.

Two examples of the'process when a non-carbonaceous swell-inhibiting agent of the diluent character is used.

4. 66 parts by weight of a strongly coking Welsh coal diiferent from the one used in Example 1, were comminuted so as to pass 90% through a 200 mesh B. S. sieve.

The characteristics of thi coal were: volatiles 20%, swelling number 9, ash 1.1% (90.9% carbon, 4.6% hydrogen, 1.6% nitrogen, 2.9% oxygen and errors on Parrs basis). Y

34 parts by weight of commercial silica of about equal fineness to the coal, was used as the swell-inhibiting agent, the coal powder and silica being intimately mixed in a ball mill for 8 hours.

The mixture was moulded the same as in Examh ple 2, into bars of the same size, andthese were subjected to a non-oxidizing atmosphere in an electric furnace in the same way as in Example 1. The furnace was raised to 850 C'Qat the rate of 2 C. per minute, and the bars removed when the temperature had fallen to 200 C. The product was exceptionally hard, strong, unswollen and undistorted.

, 5. This example'is the'same as No. 4 in all respects except that 60 parts of the coal were taken, with 40 parts of elemental silicon, of about the same degree of fineness as the coal, and that the firing rate was 3 C. per minute. The product was a strong, hard undistorted material, throughout the mass of which were distributed small, highly reflective facies. This material had a hardness exceeding 5on the Moh scale.

Reference will now be made to the practice of the invention when no swell-inhibiting agent is used, after which comment on. the various ex'ame ples will be given. The process may be carried out without any agent, with coal of the same character as in the previous examples, when considerably slower firing with or without a lower moulding pressure is employed. It can also be carried out-without an anti-swell agent when a coal having a proportion of volatiles below 18% is employed, preferably with a higher moulding pressure than in the examples in which an agent was used, and preferably withv a more rapid firing scheduler 6. As an example of the use of the higher volatile coal without an anti-swell agent, the same Welsh coking coal as in Example 1 was comminuted so that per cent passed through a 200 .mesh B. S. sieve. The coal powder was pressed into flat plates having a thickness of A at a moulding pressureof 2 tons per square inch,

which were: almost sealed with clay luting and confined space.

fired in an electric furnace, non-oxidizing atmosphere outside the boxes being provided by a current of town gas passed over the-boxes at a vol ume' flow just sufficient to maintain the atmosphere. The atmosphere within the boxes was composed of the volatiles of the coal itself, liberated by the carbonization of the plates in a The firing schedule from -300 C. was 1% per minute, from SOD-500 C. /7" per minute, and from 500-850 C. per minute, the plates being removed when the furnace temperature had fallen to about 200 C. The product was very much the same as in Example 1. V

7. As an example of the use of a coal without the addition of a swell-inhibiting agent, a South Wales dry steam coal containing 4% ash (92% carbon, 4.1% hydrogen, 1.5% nitrogen, 2.4% oxygen and errors on Parrs basis) and a moisture content 0.6% and volatiles 13.6%, was comminuted to pass a 200 mesh B. S sieve and mixed thoroughly. The resultant powder was pressed at tons per square inch into plates 4 x 2% x A, which were then placed on a firebrick support inside an electrical furnace. A current of ethylene was passed through the furnace at such a rate that the gaseous contents of the furnace would be changed once in every ten minutes. The rate of firing up to 550 C. was about 0. per minute and somewhat slower thereafter up to 850 C., the slower rate after 550 C. being due solely to furnace characteristics and not to any necessity for slower, firing. The plates were removed from the furnace after the latter had cooled to 200 C. They were undistorted and fairly strong. 7

In Example 3 in which a weakly-caking coal is used to inhibit swelling, the conditions are somewhat different from those in the other examples. In the other examples the inhibitor seems to act merely as a diluent, and materials which behave in that way may be used throughout a wide range, provided that they do not introduce complications into the process, as by decomposing and oxidizing the coal substance. A weakly caking coal, however, is not merely a diluent, since it has a small agglutinating value of its own. The volatiles of coals of difierent "rank are not evolved over exactly the same temperature range. It appears that the effect of the use of ordinary diluents is to reduce proportionally the amount of volatiles seeking to escape, at the same time, per unit of exit surface, whilst when a weakly-caking coal, or other material which evolves volatiles at other temperatures, is used, it seems that this material acts wholly or chiefly as a diluent at the temperatures at which the strongly-coking coal is evolving volatiles most rapidly, whilst it evolves its own modicum of volatiles over another temperature range. Strength should to some extent be added to the product by the agglutinating value of the weakly-caking coal.

It may also be remarked that in Example 3 the firing rate through the plastic temperature range was substantially as rapid as possible, with the avoidance of swelling, as determined by test, while the degree of comminution and the pressure applied in moulding were similarly determined experimentally, in accordance with the contrasting necessities of providing strength and avoiding swelling, in each case. Thus the eifect of variation in each factor can be determined for any particular case, and adjustments made by further tests for combinations of factors. For instance, test pieces are made and fired with a standardized procedure except that different proportions of a particular anti-swelling agent are mixed with a given coal, and the tensile strength, shatter resistance, and other desirable qualities of the product determined, to ascertain the effect of varying such proportions, other conditions being equal. The same procedure can be followed with variations of the degree of comminution of either or both the coal and the agent, and with variations of the pressure applied in moulding, and with variations in the firing rate, and'in the nonoxidizing atmosphere provided. It is evident however that items of procedure which seem the best when less than all are applied together may require adjustment when test is made with all of the tentatively-determined optimum values in use.

As has been stated above, some procedure to prevent oxidation of the article during the can bonization is essential, and also the product obtained can be varied to a considerable extent by the nature of the atmosphere which may be provided. In this connection, it should be noted that pressure within the mass is relieved, during carbonization, partly by the outward diffusion of the volatiles as they are evolved, and partly by the decomposition, under considerable pressure, of hydrocarbons, with deposition of carbon within the interstices of the mass and with production of hydrogen Whose rate of difiusion is more rapid than that of the parent hydrocarbons. By this carbon deposition the product is strengthened and made more dense. It is also thought that hydrogen diffusing towards the periphery of the article combines to some extent with liquid or solid hydrocarbons and produces more volatile hydrocarbons which can more readily escape and thus further relieve the internal pressure.

It would appear that, for the purpose of obtainin good carbon deposition and making a strong article, the non-oxidizing atmosphere should consist of or contain an unsaturated hydrocarbon gas or vapour such for example as ethylene or other olefine or benzene, or other readily cracked hydrocarbons (whether saturated or unsaturated). Whilst such vapours may scour away certain unsaturated constituents evolved from the coal, the latter will be replaced by another unsaturated substance such as ethylene, which eiiect would not be obtained when the nonoxidizing atmosphere is provided by a gas such as hydrogen or methane.

It is found that an ethylene atmosphere always tends to the production of the alpha material referred to above which is lustrous grey, with a high tensile strength and a conchoidal fracture. This material is also marked by higher density, higher reflectivity and greater homogeneity than the M material. The same material tends to be produced when the article is carbonized in an atmosphere which comprises the lower temperature decomposition products of coal.

The use of hydrogen to maintain a non-oxidizing atmosphere tends to the production of the black material referred to as M, which is also produced when the proportion of swell-inhibiting agent is in excess of that minimum necessary to inhibit swelling for a given rate of firing.

When a coal having a comparatively low volatile content and agglutinating value is to be moulded, as in the case of Example '7 given above, it is especially desirable to carry out the firing of the moulded article in an atmosphere of a hydrocarbon which can permeate into the moulded article and which decomposes within the firing temperature range so as to deposit carbon on the internal faces and in the interstices within the article. As stated, such an atmosphere can suitably consist of or contain an unsaturated hydro carbon gas or vapour such for example as ethyl-- ene or other olefine or benzene, or other readily cracked hydrocarbons, whether unsaturated or saturated. With this process for the treatment either of high or low volatile-content coal, in order to avoid the dilution by volatile matters evolved from the coal of a relatively expensive vapour such as ethylene, it will often be found advantageous to carry out an initial firing operation, for example up to 450 C., in the presence of a cheaper non-cxidizing gas such asordinary town gas, which may with advantage be freed from oxygen and sulphur, and then to submit the fired article, with or without cooling, to a further firing operation in the presence of ethylene vapour, for example up to about 850 C.

This latter method, in addition to yielding an article which has an especially low porosity, provides for improved control over the process. For example when the non-oxidizing means in the first stage is a gas such as hydrogen or ordinary town gas, the hydrogenation and the scouring away of unsaturated constituents both of the coal substance and of the surrounding atmosphere can be tolerated, and hence the volume flow of the gas may be sufficient to remove any danger of burning of the article as the result of the ingress of atmospheric oxygen. Further, the ethylene or other gas or vapour which is used in the second stage will be relatively free from contamination and therefore may be recycled, thus re ducing the cost of the process. It will of course be understood that the article must be exposed to these hydrocarbon gases or vapours sufficiently long for the desired amount of deposition to take place, such deposition being accelerated at high temperature. However, at a firing temperature above about 1,000 C. it is probable that the efficiency of the process will be impaired by the deposition of carbon outside the article, for example on the oven walls.

The two stages of firing above-described are especially suitable for the treatment of coal of high volatile content. In the case of very weakly agglutlnating coals the shaped articles may lack sufficient strength to withstand a firing operation unless the hydrocarbon gas or vapour is introduced at the outset. And since many of these very weakly agglutinating coals are also of low volatile content, the deposition of carbon on the inner surfaces of the material or in the voids between them will not be seriously interfered with. nor will it be necessary to use an excessive quantity of gas or vapour.

We claim:

1. The process of producing useful shaped articles which comprises preparing an intimate mixture of finely comminuted material composed at least predominantly of coal which contains volatiles in the proportion of about 13 to 30% on a dry ash-free basis, moulding from the resultant mixture an article of the desired shape under a pressure of the order of at least two tons per square inch, at least sufficient to enable the shaped article to be transferred undamaged from the moulding machine to a furnace, releasing the pressure, producing test pieces from said mixture, firing the test pieces in a non-oxidising atmosphere to a temperature of at least 550 C. and controlling the rate of firing in such manner as to produce a fired test piece free from cracks and free from a cellular structure Visibie to the naked eye, thereafter firing the moulded article under the conditions and at the rate at which the last-named test piece was fired to produce an article having the properties of the last-named fired test piece and cooling the article in a non-oxidising atmosphere.

2. process of producing ale. articles which comprises prepai fi an intimate mixture of finely comrninuted coal which contains volatiles in the proportion of about 13 to 36% on a dry ash-free basis with a pulverulent sweli-im hiciting agent of diluent character, moulding from the result-ant mixture an article of the desired shape uric. -r a pressure of the or er of at least two tons per square inch, least sufiic znt to on able the shaped article to be. transferred 1111- dal .aged from the mo 1g machine to a furnace, releasing the pres e,'prco.ucing test pieces from said mixture, firing the test pieces in a non oxidising atmosphere to a temperature of at least 550 C. and controlling the rate of firing in such manner to produce a fired test piece free from cracks and free from a cellular structure visible to the naked eye, thereafter firing the moulded article under the conditions and at the rate at which the last-named test piece was fired to produce an article having the properties of the fired test piece and cooling the article in a non-oxidizatmosphere.

The process of producing useful shaped articles which comprises preparing an intimate mixture of finely cc-inminuted material containat least a major proportion of coal which contains Volatiles in the proportion of about 13 to 38% on a dry ash-free basis, moulding test pieces from said mixture under a pressure of the order a of at least two tons per square inch, firing said test pieces in a non-oxidising atmosphere to a temperature of at least 556 0., controlling'the rate of firing of said test pieces in such manner as to produce afired test piece free from cracks and free from cellular structure visible to the naked eye, moulding some of the mixture of which said last named test piece was made to desired shape, under a pressure of the order of at least two tons per square inch, releasing the pressure, transferring the moulded article from the moulding machine to a furnace, firing the same in a like atmosphere and at the rate at which the last named test piece was fired to a temperature of about 550 C. and continuing the firing to temperaturecf at least between 650 C. and 850 0., to produce an article having freedom from cracks and cellular structure in like degree as said last named test piece, and cooling the article in a non-oxidising atmosphere.

l. The process of producing useful shaped articles which comprises preparing an intimate mixture of finely comminuted coal which contains volatiles inthe proportion of about 13 to 30% on a dry ash-free basis with finely 00111- rninuted coal of less agglutineting power, mould ing from the resultant mixture an article of the desired shape under a pressure of the order of at least two tons per square inch, at least sufficient to enable the shaped article to be trans- 1 ferred undamaged from the moulding machine to a furnace, releasing the pressure, producing test pieces from said mixture, firing the test pieces in a non-oxidising atmosphere to a temperature of at least 550 C. and controlling the rate of firing in such manner as to produce a fired test piece free from cracks and free from .a cellular structure visible to the naked eye,

thereafter firing the moulded article under the conditions and at the rate at which the last named test piece was fired to produce an article having the properties of the fired test piece, and cooling the article in a non-oxidising atmosphere.

5. The process of producing useful shaped articles which comprises, preparing an intimate mixture of finely comminutecl material containing at least a major proportion of coal which contains volatiles in the proportion of about 13 to 30% on a dry ash-free basis, moulding from the resultant mixture an article of the desired shape under a pressure of the order of at least two tons per square inch, at least sufiicient to enable the shaped article to be transferred undamaged from the moulding machine to a furnace, releasing the pressure, producing test pieces from said mixture, firing the test pieces in a non-oxidising atmosphere containing a gaseous hydrocarbon decomposable at temperatures attained in firing, to a temperature of at least 550 C. and controlling rate of firing in such manner as to produce a fired test piece free from cracks and free from a cellular structure visible to the naked eye, thereafter firing the moulded article under the conditions and at the rate at which the last-named piece was fired to produce an article having the properties of the fired test piece, and cooling the article in a non-oxidising atmosphere.

6. The process of producing useful shaped articles which comprises, preparing an intimate mixture of finely cornminuted material containing at least a major proportion of coal which contains volatiles in the proportion of about 13 to 30% on a dry ash-free basis, moulding from the resultant mixture an article or the desired shape under a pressure of the order of at least two tons to the square inch, at least sufiicient to enable the shaped article to be transferred undamaged from the moulding machine to a furnace, releasing the pressure, transferring the said article to a furnace, firing it in a non-oxidising atmosphere to a temperature of at least 550 C. at rates which include substantially as rapid a firing through the temperature range within which the coal is plastic and is evolving volatiles as is possible with avoidance of swelling, to produce an article free from cracks and free from a cellular structure visible to the naked eye, as determined by having previously fired test pieces moulded from such mixture under like pressure and fired in a like atmosphere, with rates of firing controlled so as to produce a test piece fired at the above mentioned rates and having the above mentioned properties of the said moulded articles, and cooling the article in a non-oxidising atmosphere.

7. The process of producing useful shaped articles which comprises, finely comminuting coal which contains volatiles in the proportion of about 13 to 30% on a dry ash-free basis, producing samples of the same intimately mixed with different proportions of a puverulent swell-inhibiting agent of diluent character similarly comiii mlnuted, moulding portions of said samples to produce test pieces, under a pressure of the order of at least two tons per square inch, firing said test pieces in a non-oxidising atmosphere to a temperature of at least 550 C., controlling the rate of firing of said test pieces in such manner as to produce a fired test piece free from cracks and free from cellular structure visible to the naked eye, moulding some of the mixture of which said last named test piece was made to desired shape, under a pressure or the order of at least two tons per square inch, releasing the pressure, transferring the moulded article from the moulding machine to a furnace, firing the same under the conditions and at the rate at which the last named test piece was tired to produce an article having the properties of said last named test piece, and cooling the article in a non-oxidising atmosphere. 7

8. The process of producing useful shaped articles which comprises preparing an intimate mixture of finely comminuted material containing at least a major proportion of coal which contains volatiles in the proportion of about 13 to 30% on a dry ash-free basis, moulding from the resultant mixture an article of the desired shape under a pressure of the order of at least two tons per square inch, releasing the pressure, transferring the moulded article from the moulding machine to a furnace, firing it in a non-oxidising atmosphere to a temperature above the temperature range within which the coal is plastic and is evolving volatiles, and controlling the rate of firing, as previously determined by firing test pieces moulded from said mixture under like pressure and fired in a like atmosphere, in such manner as to produce an article free from cracks and free from a cellular structure visible to the naked eye, replacing said non-oxidising atmosphere by another non-oxidising atmosphere which is richer in gaseous hydrocarbon-s decomposable at temperatures up to 850 C. than said first named atmosphere, subjecting said article to a further firing in said second atmosphere up to a temperature of at least 550 (3., and cooling the same in a non-oxidising atmosphere.

. JOHN GODOLPHIN BENNETT.

DAVID BLY'II-IE FOSTER. CHARLES DESMOND GREAT/ES. GEORGE CORDERY PHILLPOTTS. MARCELLO PIRANI.

WILLIAM JULIANUS KRAMERS.

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

UNITED STATES PATENTS Number Name Date 1,840,491 Dietsche Jan. 12, 1932 1,856,680 Williams et a1. June 3, 1932 1,904,568 Taylor Apr. 18, 1933 2,370,350 Heuberger Feb. 27, 1945 2,416,476 Fuchs Feb. 25, 1947