US2174184A - Method for digesting solid car - Google Patents

Description

Sept. 26, 1939. w. MCK; BYWAT'ER' 2,174,184

METHOD FOR DIGESTING SOLID CARBONACEOUS MINERALS Filed May 11, 1938 INVENTOR ATTOR Y Patented Sept. 26, 1939 PATENT OFFICE METHOD FOR DIGESTING SOLID CAR- BONACEOUS MINERALS Wilfred McKinley Bywater, Weehawken, N. J., assignor to The Barrett Company, New York, N. Y., a. corporation of New Jersey Application May 11, 1938, Serial No. 207,350

Claims.

This invention relates to the manufacture of heat-digestion products from carbonaceous mineral materials such as bituminous coal, cannel coal, shale, and the like under conditions 'such that a substantial but regulated amount of decomposition of the carbonaceous mineral materials takes place during the digestion.

In the past it has been proposed to prepare such products by introducing the mineral material into a tank containing a body of a hydrocarbon liquid, such as coal tars, high-boiling coal tar oils, and coal tar pitches, or various petroleumtars and oils, and then to heat the tank externally to bring the temperature of the mixture to between 300 and 400 C. Such processes were subject to the disadvantage that since a much higher temperature prevailed at the tank wall suriaces than in the body of liquid, solid material in contact with the surfaces was subjected to more intense heat-treatment thansolid material at a distance therefrom and conseuuently overheating. and even charring of the solid material occasionally occurred, and deposit of carbonaceous scale on the walls of the vessel resulted.

Moreover, successful operation of the digestion process requires careful control to effect the desired degree of decomposition of-the mineral undergoing digestion, e. g. coal. It has been found that if the digestion is carried out so that no decomposition or only incipient decomposition of the coal occurs, products are obtained of a quite different nature from those desired. It, however, the time and temperature of digestion oi a given coal are increased, a relatively sudden change occurs in the consistency of the product together with marked evolution of typical volatile coal-decomposition products and a reduction in the content of volatile combustible matter in the digested mineral.

Commercially desirable products are obtained by carrying the digestion to or beyond the point x dilutes the desired and characteristic final product with material approaching ordinary pitch in character.

direct-fired tank-still process, it has been proposed to circulate the liquid hydrocarbon through a body of coal or other carbonaceous mineral material. In the process thus proposed the hydrocarbon liquid fiowecl in a circuit involving a heater and a digestion chamber, so that heating of the liquid was accomplished at a point out of contact with the main body of coal which it was desired to subject to the digestion treatment. This process was found to overcome the disadvantages of overheating, excessive decomposition and the formation of carbonaceous scale on heating surfaces. In operation of the process on a large In order to overcome the disadvantages of the v scale, however, it was frequently found that after a run a varying percentage of the coal remained in the digestion chamber in a partially digested condition. Since the properties oi the desired product depend to a considerable extent on the content oi digested coal, this had two disadvantages:

(ll the properties oi the product of the original batch could not be accurately predicted because its digested-coal content was the difference between the coal introduced (less volatile decomposition products) and the varying residue in the digester, and there was no way of determining accurately beforehand the proportion of the! coal that would remain as residue;

(2) in formulating succeeding batches it was impossible to maize allowance for the varying residue in the digester, part of which would be dispersed in each following batch, for there was no ready means for measuring or weighing the residue in situ.

Still another disadvantage encountered lay in the fact that the partialy digested coal possessed a semi-liquid, livery, or jclly -liire character such that it formed a more or less resistant protective coating onfragments oi undigested coal, and contact oi liquid therewith was diminished. As a consequence the digestion was appreciably prolonged.

"While the above discussed disadvantages are not of a nature to make the process unworkable, they lead to products of widely variant properties and make it uneconomical for producing products to close specifications.

In accordance with the present invention it has been found that the desired degree of decomposition of the carbonaceous mineral can be effected, Wh le the disadvantages of both the direct-fired tank-still digestion and the methodinvolving circulation oi" liquid hydrocarbon through the carbonaceous mineral may be eliminated, by subiecting the mineral in a finely divided condition to heating while suspended in a' turbulent stream of the liquid. 'Ihis is accomplished by mixing the finely divided mineral with the hydrocarbon liquid and the mixture at a velocity above its critical velocity through a ,tubular heater or equivalent heating device.

By'the process of this invention it is possible to prepare compositions, suitable for use as paving compositions, road binders, block fillers, roofing compositions, water-proof paints, etc., possensing not only a high degree of uniformity throughout a particular batch but having a minimum of variation between batches.

Apparatus for conducting the process of the present invention is illustrated in the accompanyim thawing.

The ninneral I designates a tank for mixing the carbonaceous mineral material and' the liquid hydrocarbon. An agitator l, driven by motor I, may be provided for stirring the contents of tank I. The agitator 2 may be provided with a drag chain I for cleaning the walls of the tank, if desired, especially if the tank is arranged with external heating means (not shown) to bring it to reaction temperature. The agitator may either rotate or oscillate, as desired. A pipe I leads from tank I, near the bottom thereof, to

pump I. From pump a pipe I, having avalve 0, leads to a tubular heating coil 0 arranged to be heated by hot combustion gases. An outlet pipe I. having avalve II is dispoud on pipe I between the ,pump and the heating coil. A re- .turn line "leads from the heating coil back to I has an inlet pipe It provided with a valve It for introducing hydrocarbon liquid and a hopper II, which has a suitable closure It, for the introduction of solid carbonaceous mineral matter. If preferred, a star valve or other suitable closure permitting introduction of solid material while avoiding escape of substantial quantitiesofvaporamaybe providedinplaceofthe simple closure ll.

Avapor pipe ll leads fromtank I to condenser II cooled by water, tar to be used-in a succeeding digestion, or another suitable cooling medium. Oondensate outlet II leads to oil storage (not shown);

Athermometerwelillisdisposedintank I to indicate the temperature of the liquid therein.

pparatus may be provided with the customary clean outs. traps, insulation, etc.

'lheaboveapparatus maybeoperatedinthe following manner:

moo gallons of topped-tar-and-heavy-tar-oil- 7 having an initial boiling point aroimd C.ar'echargedtotank I throughinlet ll; is then closed. Pump 8 is started as enough of the mixture is introduced to pump supplied. The mixture is circulated through heating coil 9 and recirculated to the extent necessary to heat it to a temperature around 150 C. as indicated by the thermometer in well 20. Finely divided coal, having a particle size not over 0.3 cm. in diameter is then introduced at I 5, the agitator being operated to 'mix the coal withthe liquid contents of tank I When the desired amount of coal has been added, normally 5% to'45% of 'the tar-tar-oilmixture, depending upon the type of product it is desired to produce, the temperature of the mixture in tank I may have risen to between 170 and 210 C. and the mixture leaving coil 8 may be at atemperature between 200 C. and 250 C. as recorded by the thermometer in well Ila. Agitation of the contents of the still and circu lation of the tar containing suspended coal particles are continued until the desired maximum digestion temperature, usually somewhere between 300 and 320 0., is obtained.

For illustration a tubular heater containing 93 tubes each 2% inches in diameter and about 8% feet long connected serially by return bends was found to attain the desired temperature, measured from the time of completing the coal charge, in from 5 to 6 hours. The average linear velocity of the mixture (topped-tarand heavy- 'oil-mixture plus 20% of coal particles of less than 0.3 'cm. diameter) through the heater was 11 to 12 feet per second, as compared with a critical velocity for the mixture in this apparatus believed in the neighborhood of 1 foot per second. Since the critical velocities of the tarcoal mixtures of commercial importance at the digestion temperature are in the same neighborhood, it may be said that in general the average linear velocity of the mixture within 1% inch of the heating surface should be above 1 foot per second. This generalization, however, would not include those cases where turbulence is induced by use of surfaces other than heating surfaces or by use of heating tubes of substantially smaller than 2% inch diameter or otherwise.

The temperature at Ila at the start may be 80 to '75? or more above that at 20. Fairly satisfactory products have been produced when the mixture has been permitted to absorb heat at about this rate throughout the process and it is possible to maintain a diilerential of as much as 100' between the temperatures at Ila and 20. However, it is preferred to avoid so high a temperature diii'erence, at least near the maximum digestion temperature. It has been found" that a temperature difference of about 20 makes the most satisfactory products.

For an apparatus of the above proportions handling an 8000-8500 gallon charge containing coal which undergoes the desired conversion at about 305' C., the temperatures measured by thermometers at Ila and llfrespectively may correspond as follows:

lie 20 Donna Duran mas 100i!) 110 2:05:20 am His-= 810 2001110 3181: 8 8061i: 6

themaximum temperature to be attained by the mixture, for the gas-to-liquid temperature difierence becomes radically less as the temperature of the liquid rises. In case the gases are at high temperatures on the order of 1000 to 2000 C. the reduction in heating efiect as a consequence of reduced temperature difference will be small and to keep the liquid temperature down the liquid may, be circulated at an increased rate or the heat supply may be reduced, as by diluting the combustion gases with air or cutting the flow of fuel. In this manner the maximum temperature of the liquid at I2a may be kept within 10 or 20 of the maximum liquid temperature in the tank as recorded at 20.

The following example illustrates the preparation of a coal-digestion product by the process of the present invention:

6889 gallons of a digestion medium consisting of topped high-temperature, bituminous coal tar and heavy creosote oil were charged to tank I as above described. The temperature was brought up to somewhat above. 150 C. by circulating the tar-oil mixture through heating coil 9 by means of pump 6 from and to tank I. While the mixture was being circulated, 18,671 pounds bituminous coal, ground to pass a 10 mesh screen, were gradually introduced into tank I and there agitated with the tar-oil mixture. The liquid flow through coil 9 was maintained at 'a constant average rate of 11.60 linear feet per minute during the digestion. Laboratory tests having previously been made to determine suitable digestion temperature for the coal in question to secure the desired degree of coal decomposition, heating and circulation were continued to bring the contents of tank I as recorded at 20 to 304 C. over a period of several hours; at the same time the the following properties.

Melting point C '10 Penetration at (200 gms., 30 seconds) l4- 25 (100 gms., seconds) 30 46.1 (50 gms., 5 seconds) 80 Slide test at 40 -C. ('7 hours, 30 angle, /2

inch cube) "inches" 2 I claim:

1. The method of producing from coal and petroleum tars, pitches of lower temperature susceptibility than ordinary tar pitches of the same melting point, comprising suspending finely pulverized coal in regulated amount in a liquid comprising tar, of the group consisting of coal tar and petroleum tar, or its distillation products,

which liquid is capable of forming pitch on distillation, agitating said liquid and mechanically suspended coal, recirculating said liquid and coal through a heating coil to effect the decomposition of the coal, and continuing the decomposition process until a pitch product of the desired melting pointand temperature susceptibility is obtained.

2. The method of digesting bituminous coal in a coal-tar digestion medium, which comprises preparing a mixture of the digestion medium containing the coal suspended therein in finely divided form, withdrawing a portion of the mixture, passing a stream thereof while free from added reagents through a heating zone at a rate such that the average velocity of the mixture within one and a quarter inch of the heating surface is above one foot per second, returning it to the main body of the mixture and mixing it therewith, and continuing said operation only until the temperature of the main body of the mixture has reached but not exceeded a digestion temperature between 300 and 400 C.

3. The method of producing from tar, pitches of lower temperature susceptibility than ordinary tar pitches of the same melting point, comprising suspending finely pulverized coal in regulated amount in a liquid comprising bituminous coal tar or its distillation products, which liquid is capable of forming pitch on distillation, agitating said liquid and mechanically suspended coal, recirculating said liquid and coal through aheating coil to effect the decomposition of the coal, and continuing the decomposition process until a pitch product of the desired melting point and temperature susceptibility is obtained.

4. The method of producing from coal tar, pitches of lower temperature susceptibility than ordinary tar pitches of the same melting point, comprising suspending finely pulverized coal in regulated amount in a liquid comprising coal tar and creosote oil, which liquid is capable of forming pitch on distillation, agitating said liquid and mechanically suspended coal, recirculating said liquid and coal through a heating, coil to effect f the decomposition of the coal, and continuing the decomposition process until a pitch product of the desired melting point and temperature susceptibility is obtained.

5. The method of digesting bituminous coal in a coa1tar digestionmedium, which comprises preparing a mixture of a digestion medium comprising bituminous coal tar and heavy creosote oil containing the coal suspended therein in finely divided form, withdrawing a portion of the mixture, passing a stream thereof while free from added reagents through a heating zone at a rate such that the average velocity of the mixture within one and a quarter inch of the heating surface is above one foot per second, returning it to the main body of the mixture and mixing it therewith, and continuing said operation only until the temperature of the main body of the mixture has reached but not exceeded a digestion temperature between 300 and 400 C.

WILFRED McKINLEY BYWATER.

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