US1886262A - Distillation of carbonaceous materials - Google Patents

Description

Patented Nov. 1, i 1932 l, area HAEALE) NIELSEN, OF BEOMLEY, AND BRYAN LAING, OF PETTY FRANCE, WESTMINSTER, ENG-LAND DIib'IEILLATION OF CARBONAGEOUS MATERIALS No Drawing. Griginal application filed November 21, 1927, Serial No. 234,904, and in Great Britain December 4, 1926.

This invention is a division of my pending application'Serial No. 23%,904, filed November 21, 1927, and relates to the distillation, with bye-product recovery, of carbonaceous materials, such as coal, lignite, brown coal,

peat, wood, shale and the like.

lin oroer to distil carbonaceous materials for the purpose of oil recovery the amount of heat which is necessary per unit of weight to effect thevnecessary thermal changes is well known and varies from 200 to 300 kg. cal. per kg. of dry coal. If, however, this iigure is analyzed or resolved it becomes apparent that the amount of heat required to penetrate in a given time from the periphery to the centre of each particle or piece of coal or through any thickness of fuel bed so as to effect the necessary thermal changes actually depends upon the following main factors or considerations :(l) The mean temperature difference which exists atany stage in the seating process between the heating medium and the material undergoing treatment; (2) The total superficial area of material exposed to the action of the heating gases; (3) A co-cfiicient of heat tran ference or transmission which includes a time factor; and l) The distance through which the heat has to enetrate. Consequently, the total thermal work effected is a.

function of these four factors. Since, however, the oil vapours are very susceptible to temperatures higher than those at which they are liberated from the carbonaceous material, it is necessary, if cracking or decomposition of the said vapours is to be reduced or practically eliminated, that the vapours, after being liberated at the particular temperature at which they are evolved, should not pass into zones which are at higher temperatures or be brought into contact with highly heated surfaces, as, if cracking oc curs to any extent, the yield of oils is reduced, while the heavy oils which result from the process are unsuitable for lubricating purposes. in order to reduce or eliminate cracking we have found that it is necessary to modify one or more of the four aforesaid factors, but this must be carried on in such a way that the total thermal work ef- Serial No. 356,599,

fected remains the same. For example, the surface exposed to the action of the heating gases or the heating medium may be increased by crushing the coal very finely so that the distance throu h which the heat has to travel from the centre to the periphery of each coal particle is greatly diminished, but in such cases special precautions, such as the provision of stirring and agitating devices, must also be taken to maintain the fuel in thin layers and prevent a dense or thick bed of material being formed. it is not, however, always expedicnt toicrush finely the coal which has to be distilled, especially the so-called non-coking coals which do not ag= glolnerate, and in such instances the time factor might be increased. There is, however, for practical reasons, only a permissible reduction possible in the time, factor, as, if the rate of heating is substantially reduced, not only is the throughput of the apparatus diminished and the cost of the process increased, but the properties of the resultant coke are detrimentally affected. 7 Further more, and when dealing with so-called coking coals which agglomerate and form large pieces during heating, it will be clear that, although they may have been admitted into the distillation apparatus in a finely powdered form, such agglomeration wi l result in the distance from the outside to the centre of the mass being considerably increased.

One feature of the present invention is based upon the discovery that, if the temperature difference which exists between that which prevails the centre and the outside of a piece of coal, or an agglomeration or bed of the same, exceeds a given figure, cracking of the oil vapours evolved at the centre of the coal particle or piece, or'of the agglomeration thereof, or of a dense fuel bed, occurs when the vapours reach the hotter external surface of the coal particle, agglomeration or fuel bed; This fact we find to be the main contributing cause of excessive cracking de spite other precautions that may be taken to avoid it, and we have discovered that the chief reason why high quality lubricating oils have not heretofore been obtained by coal distillation processes is due to the fact that both the time factor and the mean temperature difference which exists between that which prevails at the centre and that which exists at or outside the surface or periphery of a piece of coal, or else between the exterior surface and the interior portions of a fuel bed of any given thickness, have not been so controlled as to result in the production of a primary oil rich in hydrogen from which a high class lubricating oil can be obtained.

According to this feature of the present invention the process of distilling solid carbonaceous materials is carried on in sucha manner that, for any given size of particle or piece of carbonaceous material or for given thickness of fuel bed, the periodor time factor of distillation is so controlled that at any stage in the distillation process a temperature difference exceeding 120 C. to 150 (1., but preferably of the order of 'C. to C, is not allowed to exist between the temperatures prevailing at the centre and at the periphery of any given size of particle or piece, or any given thickness of fuel bed. For example, when distilling bituminous black coal of sizes below 2 mesh or cube, we have found that, in order to maintain a range of temperature difference of approximately 100 C. between the temperatures prevailing at the inside and the outside of the coal particles, the duration of the distillation period must be about two hours; raw coal, after being subjected to a preliminary pre-heating or drying treatment, being allowed to enter the retort at a temperature of 150 C. and the solid residue, after distillation, leaving the retort with a temperature of 550 C. The heating medium, which may be constituted by producer or water gas or by any heated and inert or relatively inert gas or by combustion gases, is preferably brought into direct contact with the carbonaceous material, although external heating or a combination of internal and external heating may be used, and should be of such a volume that it carries with it in the form of sensible heat the required heat units to effect the thermal changes in the solid material within the prescribed temperature and time limits. In the case of internal heating the heating medium preferably travels in countercurrent to that of the coal, and may enter the retort at approximately 650 C. and leave the same at approximately 100 C. to 110 C. In the case of external heating the temperature of the heating gases progressively increases from the point where the carbonaceous material enters the retort to the outlet thereof, and stirring or agitating devices are preferably provided by means of which the ma terial is kept in constant motion and in thin layers so as to promote uniform heating, and to allow of the removal, without passing into hotter zones, of the vapours and gases at the temperatures at which they are evolved,

while also to prevent overheating of the coal particles due to prolonged contact with the externally heated metal or brickwork of the retort. Subject to the process being carried on in the aforesaid manner, that is to say, in such a manner that a temperature difference exceeding 150 C. does not exist between the centre and the periphery of any given size of coal piece or particle, or any given thickness of fuel bed, excessive and disadvantageous cracking of the oil vapours does not occur, and we have been able to produce from the so-called crude oils resulting from the distillation of bituminous coal a lubricating oil of a standard equivalent to that obtained from the finest well oils. The determination of the length of retort to be used and the duration of the heating process are matters of simple calculation and naturally vary with the nature, size and character of the 1 material undergoing distillation. In the case of externally heated retorts, the volume and temperature of the gas which is necessary to produce the required heat gradient from the inlet to the outlet of the retort in a given time is also easy of determination, and by increasing or diminishing the speed of rotation of the stirring or agitating devices where such are employed, or varying the temperature gradient, for example by by-passing heating gases either at higher or lower temperatures as required to different points in the distillation apparatus,overheating of the material can be avoided. Provision may also be made for withdrawing the'evolved vapours at or about the temperature at which they are evolved, or for preventing them, for example by drawing them off in uniflow with the heating gases and in countercurrent to the solid material, from passing into hotter zones' where cracking may occur, precautions being also taken to prevent them from passing into cooler zones where condensation may take place. 7

Another feature of the present invention relates to processes of distilling carbonaceous materials of the kind in which a distilling medium, such as water, producer or combustion gas (after being superheated if necessary) is passed through an apparatus, such as a rotary retort, in direct contact with, and in contrafiow to, the solid carbonaceous materials so that the so-called sensible heat of the distilling medium is employed to distil off the Volatilizable and condensable oils contained therein, the inert heating gas containing the volatilizable oils being subsequently passed through condensers, scrubbers, oil washers, etc., for the purpose of recovering in liquid form the said condensable oils.

According to this feature of the present invention the temperature zones throughout the length of the retort are graduated or controlled so that the said oils are distilled off at the temperatures at. which they volatilize and are then Withdrawn from the apparatus in unifiow with the heating medium either at one end or at different points along the length thereof and at temperatures at which no excessive cracking can occur, while the volume of inert gas whose sensible heat is employed as thedistilling medium is so controlled as to lower the vapour pressure of the volatilizable oils as much as possible.

We have found that, provided carbonaceous materials are treated in this manner, and provided a sufiicient quantity or volume of the inert heating gas is employed to carry with it in the form of sensible heat the total heat requirements for the distillation process, it is possible to obtain an increased yield of the heavier and more valuable oils, while if the aforesaid precautions to prevent overheating and to secure exact temperature regulation are observed, it is also possible to obtain an increased yield of heavier oils with a high viscosity, both lighter and heavier oils produced by this process having properties and a composition hitherto unobtainable by low temperature distillation processes. A. cording to this feature of the present invention the volume of gas employed for distillation purposes is of such a magnitude (e. g., 35,000 up to 100,000 cubic feet per ton ofcarbonaceous material) that the vapour tension or so-called partial pressure of the heaviest oil fractions present in the carbonaceous materials is lowered sufliciently to enable such oils to be liberated in vapour form from the carbonaceous materials at temperatures not exceeding 450 C. to 500 C.

V7 hen distilling materials containing a very large percentage of oil such as oil shales or torbanites the volume of the distilling medium employed is preferably such that, after having efl ected distillation of the material, it may be cooled down to approximately C. to 100 C. without causing the heaviest or highest boiling point fraction to condense; in other words, the distilling gas carrying the oil vapours may .be of such a magnitude that the oils will not separate out or condense within the distillation apparatus or the dust extractor at temperatures as low as 80 C. to 100 C. Generally speaking, the conditions to be observed, in the case of internal heating by means of an inert gas, are (l) the volume of inert heating gas, although such as to carry with it through and from the retort the vapours evolved during the distillation period without allowing the heaviest oil fractions to reach their so-called dew point until actual condensation of the condensable volatile products, or any desired fraction thereof, is desired, is so controlled that the vapour-tension of the volatilizable oils is lowered so that the heaviest oil fractions are liberated in vapour form from the solid materials at temperatures not exceeding 450 C. to 500 C., and 2) the time factor and temperature gradient are so controlled that a temperature difference exceeding 150 C. is avoided between the temperature prevailing at the centre and the periphery of any given size of material or thickness of fuel bed.

In order to maintain the requisite temperature gradient or to increase the volume of the heating or carrying gas at any point in the heat treatment, or to maintain any desired temperature in the dust extractor or in any of the condensers, additional volumes of gases at the desired temperatures may be ad mitted at any stage in the'process to the combined heating and retort gases or vapours,-

or a heating or cooling medium may be applied as and when required at any particular stage in the process. For example, the retort used for carrying on the distillation process may be of the type hereinafter described.

We have also found that, by controlling the temperature gradient so that'the heaviest oil fractions are liberated in vapour form from the carbonaceous materials at temperatures not exceeding 450500 (1., coking or agglomeration of the solid materials does not take place to the same extent as occurs with any usual process or distillation. For example, when distilling Esthonian shale, which shale, when normally treated, melts to a semi-liquid or pitch-like conglomeration, we have found that, after the .oil vapours have been evolved and removed, the carbonaceous residue is discharged from the retort in a solid form, the pieces being of a shape and size approaching that it which they were originally charged into the retort, that is to say, no agglomeration has been observed and the individual pieces have retained their original size and shape more or less unaltered. It would thus appear that, owing to the large volume of gas passed through the retort, the vapour tension of the various oil fractions was so lowered that the oil vapours in the example under consideration were evaporated from the solid material without causing the solid material to melt or pass through the so-called sticky period during the heating process. In other Words, the formation of the conglomerated mass which normally results when coking bituminous coals are distilled by any usual process, is avoided, and the materia when subjected to the present process of distillation, behaves in a similar or substantially similar manner to earthy brown coals, lignites and non-coking coals.

We have also found that it is essential, in order to obtain a freely burning solid carbonaceous residuum, that the volatilizable oils should, as aforesaid, be withdrawn from the retort without excessive cracking, as not only processes, but, if excessive cracking occurs, graphitic carbon is deposited on the solid material, which coats the microscopic and sub-microscopic cells and cell walls with a highly impervious carbon film which is difficult to oxidize and which reduces to a marked degree the readiness to combustibility as well as the reactivity of the resultant fuel. It is also essential that, as aforesaid, the oil yielding and volatilizable constituents should be expelled from the solid material at as low a temperature as possible, that is to say, at temperatures ranging from 185 C. to 580 C. We have found that the solid residue produced by the present process can be burnt in open domestic firegrates and is more readily ignitable than the ordinary semicoke obtained by any of the usual processes of low temperature distillation and far more readily combustible than ordinary so-called gasworks coke or gas oven coke. This property of the solid carbonaceous residue obtained by the aforesaid process appears to be due to the fact that the original cell structure of the raw material is left intact and the deposition of an inert carbon film on the residual fuel is avoided, while the thinness of the cell walls is maintained, so that a very large superficial surface is made available for attack by oxygen either combined or in a free state.

We have also found that a fusible or coking coal, which on distillation passesthrough a so-ealled plastic state, can be given the same degree of reactivity, etc., as a so-called non-coking or non-ca-king coal, that is to say, be made to retain its original cell structure by being subjected to a preliminary heat treatment by gases containing sufiicient oxidizing constituents, free oxygen and the like to an extent which will stop fusing and agglomeration.

The preliminary treatment may consist in drying and/or pre-hea-ting the coal or carbonaceous material in a so-called coal dryer, rotary or otherwise. During these operations the carbonaceous material is subjected to the action of a hot gas, such as combustion gases, for example, containing a. percentage of free oxygen of the order of from 2% to 8% which will suffice to oxidize some of the so-called coking constituents to the desired degree and thereby influence their coking power.

As a detailed description of one method of carrying on the present process and involving all of the features previously described, the following example is given: A bituminous coal was distilled by means of a controlled volume of an inert gaseous heating medium (i. e. superheated water gas) which was brought into direct contact with the coal in a rotary retort, the raw coal, after preheating to a temperature of about 150 C., having a volatile content of 30%. The volume of water gas used was of the order of 55,000 cubic feet and entered the retort at a temperature of 750 C. and a pressure of by water gauge. It was observed that oil began to distil ofi at 210 C. together with a small volume of gas and at or about 570 C. all the oil-giving or condensable hydrocarbons were removed from the material under distillation.

The quantity of products obtained per ton of raw materials at this temperature (570 C.) was 20 gallons of oil.

15 gallons of ammoniacal liquor.

2,500 cubic feet of stripped retort gas combined with water gas.

The volatile matter still present in the solid material was reduced to 10%.

Microscopic research showed that practically no deposit of graphitic carbon was present.

It was also found that, on account of the fact that cracking did not take place owing to exact temperature regulation, to the fact that the oil yielding volatilizable constituents were carried off in unifiow with the heating gases, and to the fact that the volume of heat ing gas employed was controlled, a primary oil was obtained containing a large percentage of the more valuable high boiling fractions or lubricating oils rich in hydrogen.

The neutral oil which was obtained after removal of the acidic and basis constituents was considerably richer in hydrogen than that obtained by other methods of coal distillation. A large yield of lubricating bases of a specific gravity approaching that of water was also obtained from which a lubricating oil was extracted by the treatment hereinafter described which was of a character and quality hitherto unobtainable by any previous method of coal distillation. The neutral oil produced had the following characteristic properties :Hydrogen percent-age by weight, 9.5% up to 11.5%. Heavy lubricating bases having a hydrogen percentage above 9%by weight and a specific gravity ranging from 0.95 up to 1.080, at 15 C. The total yield, after fractional distillation and refining, of oils having properties similar to the following derivatives from well oils and adapted for similar purposes, was as follows Boiling point (degrees centigrade) Per cent Petroleum ether 90 Petroleum naphtha 90120 3.0 Petroleum benzine 120150 6.0 Kerosene 150300 40.0 Lubricating oils 300420 30.0

Melting point (degrees centigrade) Paraffin wax 4565 4.0

In order to produce a high grade lubricating oil that portion of the distillate, boiling over 300 (3., was then subjected to further treatment. To this end the tar acids were removed by caustic soda, and the resultant oil refined with sulphuric acid. The refined oil was then distilled and the first 25 per cent. yielded up during the distillation process was in this instance added to the so-called kerosene fraction. The remainder was then passed through a filter press at about 5 C. and the paraffin wax extracted. The waxfree oil after distillation gave lubricating oils of a rather dark red colour and amarked green fluorescence. The yield of all grades of lubricants by the aforesaid treatment amounted to about of the total original crude oil. The amount of lubricating oil equivalent to so-calledspindle oil was of the order of 5% of the original crude oil. On

7 testing the lubricating oil so obtained it was retort contained about 10% volatile matter found that at normal temperatures, namely from 12 C. to 18 (3., it had a so-called static coefficient of friction of from 0.1 up to 0.185.

The residual solid fuel discharged from the and was exceedingly reactive and easily oxidized, either by free oxygen or the combined oxygen present in metallic ores, such as iron or copper oxides and the like, or in steam. Consequently, the solid carbonaceous residue resulting from the present process is of greater value for domestic use or industrial processes than the comparatively speaking nonreactive carbon material hitherto produced by low temperature distillation.

As the carbonaceous residue from certain coals, particularly those of a non-coking variety, may be producedin a friable state, it is eminently suitable for use, after crushing, as powdered fuel, owing to its high clegree of reactivity and free burning properties.

A. suitable form of apparatus for carrying on the present process by internal heating comprises a long rotary retort, which may be composed Of metal or refractory material, or metal lined or covered with refractory ma terial containing semi-circular partitions of metal or refractory material which extend inwardly from diametrically opposite points of the casing of the retort at suitable distances 7 apart along the length thereof together, if desired, With one or more partitions extending diametrically across the retort. The inert or relatively inert gas maybe constituted by combustion gases or preferably by producer or water gas, which, as it is generated in the producer, is withdrawn therefrom and, after,

if necessary, being superheated, is passed through the retort indirect contact with the carbonaceous materlals so as toutilize its socalled sensible heat for the purpose of distilling off at low or moderate temperatures from the raw carbonaceous materials passing through the retort the volati-lizable and condensable oils contained therein, the inert heating gas admixed with the retort gas and containing the volatilized oils being subsequent- 1y passed through condensers, scrubbers, oil washers, etc., for the purpose of condensing and recovering in liquid form the said oils. The so-called stripped gas consisting of the combined retort and producer or water gas which remains after the'oils have been condensed therefrom is an enriched gas suitable for heating or illuminating purposes, but if desired the stripped gas may be employed, after superheating, as the distilling medium and recirculated through the retort in direct contact with the carbonaceous materials undergoing treatment therein.

The carbonaceous materials after the oil yielding and volatilizable constituents have been driven off at temperatures ranging from C. to 580 C. may be subjected to a high temperature ranging from 580 C. to 1200 C. so as to expel the permanent gases from the material and reduce its volatile content to from 1 to 1%. The process ofvhigh temperature distillation can be carried on as a conases or with the combined retort and heatin D gases before, during, or after the same have been brought into contact with the solid carbonaceous material undergoing distillation for the purpose of polymerizing or facilitating the polymerization of resinous bodies,

prior to condensation or during condensation and while the oils are still wholly or partially in the vapour state. VVe'havefound that. provided a quantity of oxygen is admixed with the distillation gases or with the oil vapours (e. g. approximately 3% to 7% of oxygen) the oils which are obtained, after fractional distillation and refining of the primary yield, are more stable and retain their colour and valuable properties longer than other oils where polymerlzation only takes place after refining or after prolonged stand- 111g.

lVe claim An oil of a lubricating character obtained from tar oils derived from coal having a specific gravity ranging from 0.95 to 1.08 at from 12 C. to 18 (1, and a static co-eflicient of friction of from 0.1 up to 0.85.

In testimony whereof we have afiixed our signatures.

HARALD NETLSEN. BRYAN LAING.