US2761824A

US2761824A - Method of treatment of solid carbonaceous materials

Info

Publication number: US2761824A
Authority: US
Publication date: 1956-09-04
Anticipated expiration: 1973-09-04

Description

terial containing volatilizable constituents. ject of this invention is to provide an improved process United States Patent METHOD. OF TREATMENT 0F SOLID CARBONACEOUS MATERIALS du Bois Eastman, Whittier, Calif., and Leon P. Gaucher, Tuckahoe, N. Y., assignors to The Texas Company, New York, N. Y., a corporation of Delaware Application April 30, 1952, Serial No. 285,246

7 Claims. (Cl. 202-12) This invention relates to a process for the treatment of solid carbonaceous materials containing volatilizable constituents. The present invention involves a novel 'method for distilling, or volatilizing, volatilizable constituents fiom solid carbonaceous materials. This in- .vention also involves a method for reducing the particle sizeof coal and other similar carbonaceous materials The process of the present invention is especially useful for the recovery of valuable volatilizable constituents, for example, coal and wood distillates, from solid carbonaceous materials containing the same. As applied to coal, the invention provides a novel process for carbonizing, or partly carbonizing, the coal while, at the same time, eifecting pulverization of the coal. Relatively high recovery of volatilizable constituents may be obtained. Wood and various solid fossil fuels such as oil shale and coals, including anthracite, lignite, and bituminous coals, may be treated in the process of this invention.

An object of this invention is to provide an improved process :for recovering volatiles from carbonaceous ma- Another obfor carbonizing' coal. Still another object of this invention is to provide a process for the production of smokeless fuel from a solid carbonaceous material containing volatile constituents.

For the sake of simplicity, in the following detailed description of the invention, the process will be described as applied specifically to the treatment of coal. The application of the process to solid carbonaceous teed materials other than coal will be evident to one skilled in the art from the detailed description of this invention and the illustrative'examp'les of'its application to coal.

In accordance with this invention a solid carbonaceous material, e. g., coal, in granular or particle form, is adslurry the heating zone. Vaporization of the water results in a great increase in volume which, in

turn, greatly increases the velocity of flow of the stream throughthe tubular heating zone. are suspended in the steam resulting from vaporization. As. this dispersion flows through the heating zone in The solid particles highly turbulent flow, the solid particles are subjected to numerous collisions with one another and with the wall of the pipe resulting in pulverization of the solid.

2,761,824 Patented Sept. 4, 1956 2 At the same time, heating the solid particles in the presence of steam results in volatilization [of at least a part of the volatilizable constituents therefrom while retaining the carbon in condition for subsequent use as 'a fuel.

.still type furnace.

The temperature required for recovery of volatiles from the solid carbonaceous material depends upon the particular material undergoing treatment and to the extent of distillation or carbonization desired. In general, a temperature of at least 700 'F. is necessary to obtain appreciable recovery of volatiles. The temperature may range upward to about 1,200? F. or higher, the upper limit being determined usually by apparatus limitations.

The extent of recovery of volatiles is greater, at a given temperature and pressure, than in normal process, probably as the result of two factors. First, the material is pulverized in passing through the heating zone, and second, the presence of steam results in increased distillation due to the partial pressure effect of the steam.

The quantity of water admixed with the solid to form a fluid slurry may vary consider-ably. A minimum of about 35 per cent water by volume is required, based upon the apparent volume of the granular solid. With coal, a fluid slurry may be prepared from approximately equal parts of coal and water by weight. The liquid content of the slurry may be controlled by first mixing the solid with a quantity of water in excess of the re quired amount and thereafter removing excess water in a conventional thickener, e. g., a Dorr thickener. The slurry may be readily pumped with suitable equipment, for example, with a piston pump of the type commonly used for handling drilling mud in well drilling operations.

The size of the solid particles used for the preparation of the slurry'is generally determined by apparatus limitations. The particles must have an efiective diameter less than /3 the diameter of the passageways through which they are passed. Generally, the maximum particle size is limited by other apparatus limitations. Particles which are too large may, for example, interfere with the operation of the check valves in the pump. In general, it is preferable to use particles smaller than /4 inch in average diameter. With most equipment, particles smaller than about inch in diameter are more satisfactory for smooth operation of the equipment. Coal may be crushed mechanically to particle sizes on the order of A3 inch in diameter with a relatively small expenditure in power. Further reduction of size by conventional mechanical means becomes progressively more expensive, pulverization requiring large expenditures of power.

The process possesses important advantages over conventional pulverization in that the amount of mechanical preciable savings may be thus realized, as compared with conr'enti'onal mechanical pulverization.

The heating may most effectively be carried out in a tubular heater, for example, a coil of pipe or a pipe- The slurry is fed into the heating zone, or heated tube, at a rate at least suificient to prevent settling of thesolid particles. The linear velocity of the slurry at the inlet to the heating zone should be in excess of about /2 foot per second, preferably in excess of 1 foot per second, and may range as high as 10 feet per second. The velocity of the gaseous dispersion of powdered solidin steam, resulting in vaporization, depends upon the pressure and temperature to which the dispersion is subjected, as well as the rate at which slurry is supplied to the heating zone. The velocity of the gaseous dispersion increases as the dispersion approaches section and the remainder as a vapor section.

on vaporization and volatilization is Well known.

the outlet of the heating zone, due to the gradually decreasing pressure. The difference in pressure between the inlet and the outlet of the heating zone may, for example, amount to 100 pounds per square inch gauge or more. Preferably a velocityabove' about 60 feet per second is attained within the heating zone. V'elocities 'on the order of 2,000 to"3,00Q-feet per second, for extained at the outlet of the heating zone.

One section of the heating zoneacts as a vaporizing The solid and vapors in the vapor section may be heated to any desired extent. Since most of the pulveriza'tion and distillation takesplace in the vapor section of the tube, a relatively long path of how in the vapor section is desirable. The vapor section may comprise a heated or unheated tubular conduit through which the dispersion is passed at relatively high velocity. While, for convenience of construction, 'it isgenerally desirable to provide tubular coils, it has been found that there is little difference in the degree of size reduction obtained in a coil and in a straight tube of the same diameter.

Pressure and temperature are inter-related; their effect Genorally it is desirable to maintain the pressure at the outlet ot the vapor section at a low value to provide large vapor volume and high velocity and to maintain the a partial pressure of the volatiles at a relatively low value.

It is, however, sometimes desirable to operate the heating zone at an elevated, pressure in orderto make the gases or the pulverized solid available at elevated pressure as feed for a subsequent associatedprocess.

Following discharge from the heating zone, the steam and volatilized constituents are separated from the solid particles as vapors. Thesevapors may be condensed and treated for recovery of the volatilized constituents inconventional manner. The separation of gases and vapors from the solid particles may be accomplished in various ways as is known in the art; cyclone separators. and classifiers for example, are generally effective for this separation. Cottrell precipitators or filters may be used for the removal of fine particles from the vapor stream. if desired, a part of the vapor may be discharged from the separator with the pulverized solid to act as a fluid carrier for the solid.

Particles of solid separated from the vaporous dispersion may be returned to the slurry preparation step for recycling. In some instances it is desirable to recycle coarse particles of solid for further treatment. These coarse particles may be separatedfrom the fine particres in a classifier as is known inthe art. In one specific example, a slurry is made up of the recovered solid particles with water, and the coarser particles separated from the finer particles in a classifier of the type known as a Dorr classifier. The slurry of large particles withdrawn from the classifier is returned to the heating zone.

The heated pulverized solid is dry' in appearance when.

separated from the vapors. Additional stripping of vapors from the solid particles may be readily accomplished by contacting the hot solid particles with a dry gas. Further distillation of the heated solid particles may be accomplished in a similar manner. Stripping the solid particles with gas may be conveniently carried out by maintaining a dense phase fluidized bed of the solid material through which the gas is passed as the fiu'idizing medium. If desired, the solid separatedfrom'the dispersion may be subjected to brlquetting; A number of satisfactory methods of briquetting solid particles are known in the art. A suitable binder, for example, oil or tar of coal or petroleum origin, may beadded to the solid as an aid in the briquetting. The briquetting may be done with 4 the hot solid obtained on separation of the vapors therefrom following discharge from the heating zone. Some coals, e. g., bituminous coals containing relatively large quantities of volatiles, maybe suitable for hot briquetting without an added binder.

The invention will be more readily understood from the accompanying drawings and the following detaileddescription of a preferred mode of operation'of the process.

The figure is a diagrammatic elevational view showing a suitable arrangement of apparatus for carrying out one modification of the process of this invention.

With reference to the drawing, coal from hopper 6 is admixed with water from line 7 in mixer 8. A mixture of coal and water is passed to a thickener 9 where the concentration of solids and liquid in the resultingslurry is adjusted. Excess Water is drawnoil the thickener through line 11 from which it may be returned, if desired, to the mixer. The slurry is passed by pump 12 through heating coil 13' of relatively great length compared to its diameter in furnace 14.

The heating coil suit bly is arranged as a. helix and may be constructed in sections disposed in a plurality'of furnaces. A'valve 15 may be provided in the heating coil to permit operation of a latter portion of the coil, relative to flow therethrough, at a pressure somewhat lower than the pressure in the first portion of the'coil. Operation in this manner is sometimes advantageous in that expansion and rapid vaporization may take place as a result of pressure reduction at the valve. The valve 15 may take the form of a plate orifice, Venturi, ba fiie,.or a combination of such devices for reducing pressure.

The gasiform stream of vapors and powdcredfcoal,

resulting from the action of the heating coil, is discharged from the heating coil through line 16 and passed into a separator 18. The separator 18 may be operated at substantially atmospheric pressure or at an elevated pressure substantially the same as the pressure existing at the outlet of the heating coil. The powdered solid carbonaceous material is separated from at least a portion of the steam and vapors in separator 18 and discharged therefrom through line 19.

Powdered solid carbonaceous material from separator 18 is passed through line 19 into a storage hopper. 21. This storage hopper may be maintained. at av pressure corresponding to the pressure in separator 18.

The steam and other'vapors separated from the solid carbonaceous material are dischargedfromthe separator 18 through line 23. Control'of the pressure in the separator 18 may be eflected by valve 24. The vapors .and gases discharged'from separator ,18 are'passed' into a scrubber 26, preferably operated at elevatedv pressure.

The scrubber may be a tray-type contacting. tower wherein the gases and vapors introduced through line 23 are countercurrently contacted with a'liquid scrubbing medium, suitably water. Water, for example, is introduced to the scrubber by line 27 at a point at the top of the tower.

Fixed gases, generally comprising nitrogen and gaseous hydrocarbons, are discharged from the scrubber: by

line 28. The pressure maintained in thescrubber," andv if desired, the pressure maintained in separator 18 and heating coil 13, is controlled by means of. a regulating valve 29,. In the scrubber, tar and readilycondensible oils distilled from the coal are condensed. Water, containing recovered volatile constituents, is withdrawrrtfrom At least a portion of the water and recovered volatile? constituents are withdrawn'from the scrubber through line 33 for further treatment to effect separation of volatile constituents fromthe water and separation'of the constituents into various fractions, for example, 'a-rn otor fuel fraction, a light oil fraction, a middle oil fraction,-

and a tar fraction- Example Greek lignite containing 31 per cent water on an as received basis and having a particle size such that 90 to 95 per cent passed a 40 mesh screen (Tyler scale) was mixed with Water to form a slurry containing approximately 40 per cent lignite by weight. An analysis of the lignite (dry basis) showed:

Weight per cent Carbon 54.1 Hydrogen 4.5 Oxygen 24.4 Nitrogen 1.8 Sulphur 1.0 Ash 14.1

The slurry was passed through four gas-fired preheaters in series where vaporization of the water and superheating of the resulting steam took place. The heaters were each made up of 100 feet of one-half inch extra heavy steel pipe in the form of a helical coil. The dispersion of solid particles in superheated steam was passed through a cyclone separator where steam, containing volatilized constituents from the lignite, Was separated from the residual solid. A pressure of 200 pounds per square inch gauge was maintained on the cyclone separator. The temperature at the outlet of the heaters (the temperature in the cyclone separator) was 800 F.

It was found that 70 pounds of carbon dioxide and 80 pounds of tar was liberated from the lignite. The total residence time in the system was about one minute. The tar fraction includes all the condensible oils distilled from the lignite. This was not analyzed. The uncondensed gases liberated by the heating had the following composition:

Mol per cent Carbon dioxide 88 Carbon monoxide 7 Methane 3 Hydrogen 1 Nitrogen 1 The solid product was much improved as fuel, especially because of elimination of carbon dioxide and moisture therefrom. In gasification tests, it gave results comparable to the better bituminous coals.

Obviously many modifications and variations of the invention as above set forth may be made without departing from the spirit and scope thereof and only such limitations should be imposed as are indicated in the appended claims.

We claim:

1. In a process for the recovery of volatilizable constituents from a solid carbonaceous material containing said constituents, the improvement which comprises forming a slurry of said solid material in granular form with sufiicient water to produce a fluid mixture, passing the resulting mixture into a tubular heating zone at a velocity within the range of from about /2 to about 10 feet per second, vaporizing substantially all of the water from said slurry in said heating zone thereby forming a dispersion of solid particles in the resulting steam, driving at least a portion of the volatilizable constituents from the suspended solid particles while maintaining the carbon of said material in condition for subsequent use as a fuel by heating said dispersion to a temperature between 700 and 1,200 E, separating the resulting vapors comprising steam and volatilized constituents from said solid material, and recovering volatilized constituents from the steam.

2. A process as defined in claim 1 wherein said solid carbonaceous material is oil shale.

3. A process as defined in claim 1 wherein said solid carbonaceous material is bituminous coal.

4. A process as defined in claim 1 wherein said solid carbonaceous material is wood.

5. In a process for the recovery of volatilizable c0nstituents from lignite containing said constituents, the improvement which comprises forming a slurry of lignite in granular form with sufiicient water to produce a fluid mixture, passing the resulting mixture into a tubular heating zone at a velocity within the range of from about /2 to about 10 feet per second, vaporizing substantially all of the water from said slurry in said heating zone thereby forming a dispersion of solid particles of lignite in the resulting steam, driving at least a portion of the volatilizable constituents from the suspended solid particles while maintaining the carbon of said material in condition for subsequent use as a fuel by heating said dispersion to a temperature between 700 and 1,200 E, separating resulting vapors comprising volatilized constituents and steam from said solid particles of residue, and recovering volatilized constituents from the steam.

6. A process for treating a solid carbonaceous material containing carbon and volatile constituents to recover said volatile constituents and leave said carbon in condition to be used as a fuel, said process comprising forming a flowable slurry by mixing particles of said material with water; passing said slurry into a tubular heating zone of relatively great length compared to the diameter thereof; heating said slurry in said zone to a temperature suflicient to vaporize all of said water and form a flowing dispersion of said particles in steam; reducing the size of the said particles by passing said dispersion through said tubular heating zone at a velocity in excess of 60 feet per second while concurrently driving off said volatile constituents but retaining said carbon in condition for subsequent use as a fuel by heating said dispersion to a temperature between 700 and 1,200 F.; separating said carbon while still hot from said volatile constituents mixed with steam; and recovering said volatile constituents from said steam.

7. A process in accordance with claim 6, also comprising stripping volatile constituents from said separated carbon by contacting said carbon with a flowing gas stream while still hot.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Kalbach: Fluidization in Chemical Reactions, Chemical Engineering, January 1947, McGraw-Hill, pages 108.

Claims

1. IN A PROCESS FOR THE RECOVERY OF VOLATILIZABLE CONSTITUENTS FROM A SOLID CARBONACEOUS MATERIAL CONTAINING SAID CONSTITUENTS, THE IMPROVEMENT WHICH COMPRISES FORMING A SLURRY OF SAID SOLID MATERIAL IN GRANULAR FORM WITH SUFFICIENT WATER TO PRODUCE A FLUID MIXTURE, PASSING THE RESULTING MIXTURE INTO A TUBULAR HEATING ZONE AT A VELOCITY WITHIN THE RANGE OF FROM ABOUT 1/2 TO ABOUT 10 FEET PER SECOND, VAPORIZING SUBSTANTIALLY ALL OF THE WATER FROM SAID SLURRY IN SAID HEATING ZONE THEREBY FORMING A DISPERSION OF SOLID PARTICLES IN THE RESULTING STEAM, DRIVING AT LEAST A PORTION OF THE VOLATILIZABLE CONSTITUENTS FROM THE SUSPENDED SOLID PARTICLES WHILE MAINTAINING THE CARBON OF SAID MATERIAL INCONDITION FOR SUBSEQUENT USE AS A FUEL BY HEATING SAID DISPERSION TO A TEMPERATION BETWEEN 700 AND 1,200* F., SEPARATING THE RESULTING VAPORS COMPRISING STEAM AND VOLATILIZED CONSTITUENTS FROM SAID SOLID MATERIAL, AND RECOVERING VOLATILIZED CONSTITUENTS FROM THE STEAM.