US3652426A

US3652426A - Process and apparatus for removal of volatile matter by electrical resistance heating

Info

Publication number: US3652426A
Application number: US866790A
Authority: US
Inventors: Thaddeus J Oleszko
Original assignee: Marathon Oil Co
Current assignee: Marathon Oil Co
Priority date: 1969-10-06
Filing date: 1969-10-06
Publication date: 1972-03-28
Anticipated expiration: 1989-03-28
Also published as: DE2045531B2; DE2045531A1; DE2045531C3

Abstract

Volatile matter can be removed from material containing volatile matter removable by heat, e.g., coal and coke by delivering the material to a hearth so as to form a bed, touching the bed with downwardly projecting members disposed above the hearth, e.g., rabbles, moving the hearth and rabbles in relation to each other so as to cause movement of said material from the point of delivery of said material onto said hearth toward point of exit from said hearth, imposing an electrical potential between a point on the projecting members and a spaced point in the bed of material so as to cause heating by electrical resistance and thus remove at least a portion of the volatile matter. Preferably, the volatile matter is oxidizable and can be oxidized within a chamber enclosing the hearth so as to deliver additional heat to the bed causing additional devolatilization.

Description

United States Patent Oleszko [4 Mar. 28, 1972 [s41 PROCESS AND APPARATUS FOR REMOVAL OF VOLATILE MATTER BY ELECTRICAL RESISTANCE HEATING [72] Inventor: Thaddeus J. Oleszko, Neuotting, Germany [73] Assignee: Marathon Oil Company, Findlay, Ohio [22] Filed: Oct. 6, 1969 211 Appl. No.: 866,790

[52] [1.8. CL ..202/2l6, 202/265, 202/269, 201/19, 201/33, 13/2, 13/23 [51] Int. Cl. ..Cl0b 1/00, C10b 7/20, 801d 3/00, 1105b 11/00, C10b 19/00, 1105b 3/60 [58] Field otSearch ..l3/2,20,21,23,34,25,9,

[56] References Cited UNITED STATES PATENTS 1,225,396 5/1917 Benjamin ..201/19 X 1,806,027 5/1931 Smalley ..13/2 3,459,867 8/1969 Estes ..l3/9 3,475,286 10/1969 Kemmerer, Jr. et a1. ..201/33 X 1,384,878 7/1921 Wingett ..202/l17 X 1,449,834 3/1923 Pehrson ..13/21 1,680,630 8/1928 Okell ..13/23 2,127,542 8/1938 Stitzer ..201/l9 COKE SOAKING PIT 2,448,886 9/1948 Hopkins ..l3/23 X 1,634,479 7/1927 Wickenden et a1. .....13/21 X 2,676,006 4/ 1954 Martin ..263/26 3,025,385 3/1962 Tanaka .....l3/20 X 3,227,627 1/1966 Asquini.... 201/32 X 3,448,012 6/1969 Allred ...201/33 X 3 ,470,068 9/ 1969 Kemmerer ..24/3 3 Primary Examiner-Norman Yudkofi Assistant Examiner-G. 'J. Sofer Attorney-Joseph C. Herring, Richard C. Willson, Jr. and Jack L. l-lummel [57] ABSTRACT Volatile matter can be removed from material containing volatile matter removable by heat, e.g., coal and coke by delivering the material to a hearth so as to form a bed, touching the bed with downwardly projecting members disposed above the hearth, e.g., rabbles, moving the hearth and rabbles in relation to each other so as to cause movement of said material from the point of delivery of said material onto said hearth toward point of exit from said hearth, imposing an electrical potential between a point on the projecting members and a spaced point in the bed of material so as to cause heating by electrical resistance and thus remove at least a portion of the volatile matter. Preferably, the volatile matter is oxidizable and can be oxidized within a chamber enclosing the hearth so as to deliver additional heat to the bed causing additional devolatilization.

13 Claims, 5 Drawing Figures SO-ROTARY DISCHARGE TABLE SHEET 1 OF 4 PATENTED MAR 2 8 I972 INVENTO? PATENTED m8 I912 ATTORNEY PATENTEQMAR28 I972 SHEET 3 OF 4 Fig. 3-

/IVVENTO/? THADDEUS' J. OLESZKQ ATTORIVE SHEET H []F 4 AIR COOLING CONDUITS RABBLES Fig.4

INVENTOR. THADDEUS J. OLESZKO PROCESS AND APPARATUS FOR REMOVAL OF VOLATILE MATTER BY ELECTRICAL RESISTANCE HEATING CROSS REFERENCES TO RELATED APPLICATIONS BACKGROUND or THE INVENTION 1 Field of the Invention The present invention relates to the devolatilization of materials by electrical resistance heating. The invention is particularly applicable to coking of coal and to calcining of coal or petroleum cokes. Among the pertinent United States Patent subclasses are the following: 13-25; 201-19; 202-16; 202-18; 202-265; 202-270; and 263-21.

2. Description of the Prior Art British patent 1,055,857, equivalent to U.S. Pat. 'No. 3475286, teaches apparatus comprising a hearth and projecting members, which apparatus is adaptable to the practice of the present invention. This patent teaches nothing concerning resistance heating of the bed. U.S. Pat. No. 3,227,627 and Ser. No. 613,145, filed Feb. I, 1967, now U.S. Pat. No. 3448012, both also teach apparatus adaptable to the practice of the present invention, but do not teach any sort of resistance heating. U.S. Pat. No. 2,127,542 shows a process for carbonizing coal by passing an electrical current between electrodes located in contact with a charge of coal. U.S. .Pat. No. 1,680,630 to Okell teaches an electrical resistance furnace in which one ofthe electrodes rotates in order to agitate the material in the furnace by means of gas discharged from orifices within the electrode. None of this prior art shows projecting members which fulfill the dual function of acting as electrodes and also serve to move the material between the entrance point to the hearth and the exit point from the hearth.

SUMMARY 1. General Statement of the Invention The invention involves the resistance heating of a bed of material which contains volatile matter removable by heat, which material has limited conductivity to electricity. This resistance heating is accomplished by imposing a potential between a downwardly projecting member which touches the bed and a point on the bed spaced away from the member. This electrical heating is relatively localized and, for a relatively short time, raises the temperature of the material lying near the pointat which the downwardly projecting member, e.g. rabble or plow is contacting the bed. The quality of calcined coke, e.g. the grain density and the coefficient of thermal expansion of the graphite resulting from graphitization of the calcined coke, has been found to be dependent upon the maximum temperature to which the coke has been raised during calcination. Thus, premium quality coke must be raised to temperatures generally in excess of 2,300 F, and preferably in excess of 2,600 F. This can be accomplished in apparatus such as that taught by the first three references mentioned in the above Description of the Prior Art. Such apparatus accomplishes the heating of the material to be devolatilized by means of oxidation either of auxiliary fuel, e.g. natural gas supplied in burners, or by the oxidation of a portion of the volatile matter itself in instances where such volatile matter is oxidizable. This oxidation is accomplished within the chamber generally located above the hearth and having walls which are adapted to reflect heat and to deliver heat to the bed of material laying on the hearth. However, where the material is to be calcined to a high grain density and therefore must be raised to temperatures of 2,400 F. or more, the arch temperatures (the temperatures at the walls of the chamber which are generally the maximum temperatures within the chamber), must be at least 2,700 to 3,000 F. Such temperatures require relatively expensive special high-temperature refractories to be used in the construction of the chamber walls. The present invention permits localized additional heating by electricity to be applied to each portion of the bed for a short time interval. Therefore, the present invention pennits increasing of the maximum temperature to which the material being calcined is subjected without increasing the arch temperature. By permitting lower arch temperatures, the invention permits the use of less expensive lower-temperature refractory materials in the construction of the chamber. 7

Because the downwardly projecting members, e.g. plows or rabbles of the invention can be set to project deeply into the bed and to contact or come into close proximity with, every particle being calcined, the electrical heating provides a uniformity which is not generally achieved by the radiant heating utilized in prior furnace installations. In such radiant heating, the heat is delivered to the top of the bed by reflection downward from the walls and sides of the chamber. Thus the top of the bed inherently receives more heat than those particles of the materials which lie beneath the surface. In preferred embodiments of the invention, the plow-like downward projecting members turn the bed over and simultaneously heat it by acting as electrodes for the electrical resistance heating.

A further problem in prior calcining apparatus was the difficulty in heating above about 2,500 F. by means of auxiliary heat supplied by gas burners. In many commercial instances, the oxidizable volatile matter within the material is sufficient to heat the material up to temperatures in the range of 2,200 F. to 2,400 F. However, to achieve the increased temperatures necessary to produce high-quality calcined coke, natural gas is sometimes burned in burners located within the chamber which encloses the hearth. Additional quantities of air must be injected into the chamber in order to oxidize this gas. Since the air is generally available at a temperature in the range of 0 to 100 F., a great deal of heat is utilized in increasing the temperature of the combustion air up to the furnace temperature. Thus, in attempting to heat the bed above about 2,400 F. by means of auxiliary fuel gas, the preheating of the additional air necessary to burn the fuel gas requires approximately percent of the heat given off by the fuel gas burned. Thus, 5 b.t.u.s of heating value of fuel gas must be burned to increase the heat within the furnace by l b.t.u. The present invention avoids this inefficiency since electrical resistance heating is accomplished without the addition of any air. Therefore, the air can be introduced in sufficient amounts to burn the oxidizable volatile matter and to raise the bed temperature to, for example, 2,200 F. without the addition of excessive amounts of oxidation air. The electrical resistance heating of the invention can then be utilized to raise the temperature of the bed up to the 2,500 F. or so required for the production of high quality calcined coke.

The combined electrode-plows of the present invention may be utilized for materials which yield only non-oxidizable volatile matter. In fact, the invention may be employed as the sole source of heating of the material in specialized circumstances, particularly where some conductive material is mixed with the coke to improve electrical properties at lower temperatures. v

2. Utility of the Invention The present invention permits the production of high quality cokes and other calcined materials. Coal can be coked, coal-coke can be calcined, delayed orfluid petroleum coke can be calcined, and other materials, carbonaceous or noncarbonaceous, can be devolatilized by the apparatus and processes of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a vertical section to a furnace embodying the invention.

FIG. 2 is a section showing details of the rabbles and rabble holding means of FIG. 1.

FIG. 2A shows an alternate electrical circuit.

FIG. 3 is a schematic diagram showing details of the rotary hearth and the rabbles of FIGS. 1 and 2.

FIG. 4 is similar to FIG. 2 but shows an alternate electrode arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a furnace according to the invention having a rotary hearth with an inner hearth surface 11 sloping from the outer periphery downwardly to a central axially extending soaking pit l2 integral with and depending from the hearth 10. The rotary hearth 10 is supported on space rollers 13 mounted on a furnace frame 14 and is driven by a motor and a rack and pinion drive in conventional manner for rotary hearth furnaces. A curb 15 extends vertically above the hearth surface 11 at its outer periphery and carries a trough 16 with sand 17. A liquid may be used instead of sand if preferred.

The furnace frame 14 carries roof beams 20 which support a refractory roof having a central flue 22. Roof 21 has a depending wall 23 carrying flange 24 which extends into the sand 17 carried in trough 16 forming a rotary sand seal between the roof 21 and hearth 10. The roof 21 is provided with air ports 25 receiving air from duct 26 mounted on the furnace frame 14. The ports 25 direct air downwardly towards the hearth-Side walls 23 of the roof are provided with ports 27 receiving air from duct 28 also mounted on the frame 14. The ports 27 direct air generally across the hearth in a radial direction. Burners 29 are provided in the roof to bring the furnace to operating temperature. A feed chute 30 passes through the roof 21 adjacent the side wall 23 and is provided with a vertically adjustable delivery end 31 extending to a point adjustably selected to deliver a selected thickness of feed on the hearth surface 11. A radially extending U-shaped rabble pit 32 is provided with electrical insulation 38 adapted to slidably receive rabbles 34. Rabbles 34 may be solid or of hollow plate-like structures with inner vertical baffles for air or liquid cooling depending upon the temperature involved. Each baffle is provided with inlet and outlet coolant conduits 37, which also act as support for the rabbles. Coolant such as raw air is delivered to the inlet and into the rabble 34 on one side of the baffle, then under the baffle to the opposite side of the rabble and out through the outlet pipe 37. Rabble carriers having vertical adjustment screws at each end are provided so as to adjust the distance between the end of the rabble and the hearth 11.

A rotary discharge table 50 is provided beneath the soaking pit 12 to receive the output of the pit. A fixed discharge spout or plow 51 is mounted in frame 14 between the soaking pit l2 and the discharge table 50. The spout 51 is provided with a peripheral trough 52 carrying sand 53 into which a depending flange 54 on the soaking pit extends to form a sand seal.

Referring now to the electrical aspects of the invention, the last three rabbles which the material encounters on its way toward the outlet 10, are attached to

electric wires

81, 82, and 83, respectively, and are electrically insulated from all of the other parts of the apparatus. Electrical insulating means is inserted into the water supply conduits of these rabbles.

Wires

81 and 83 are connected to one side of a source of direct current. Wire 82, connected to the middle of the three rabbles, is connected to the other side of the source of direct current and such a potential difference is maintained as necessary to overcome the resistance between the center and either of the end two of the three rabbles, to result in the necessary or desired temperature rise. The voltage is regulated by means of suitable electrical gear on the alternating current side of the rectifiers, or properly regulated alternating current can be used without rectification as shown in FIG. 2A. Alternative methods, such as connecting all of the rabbles to one pole of the direct current source and connecting electrodes placed within the bed (either depending from above or set into the bed) and connected to the other pole could be used as shown in FIG. 4.

The furnace described above operates as follows. The burners 29 are fired to bring the furnace up to the desired chamber temperature which depends upon the nature of the material being devolatilized or calcined. The material to-be devolatilized or calcined, in this instance delayed petroleum coke, is fed through feed chute 30 and is continuously spread to the desired thickness, in this instance a bed depth of approximately 6 inches and width along the outer periphery of hearth surface 11. As the hearth rotates, the material encounters the rabbles 34. Each set of rabbles deflects material striking it into the next adjacent concentric ring so that the flow of material from the periphery of the hearth surface 11 to the soaking pit 12 is generally in spiral concentric rings, each of greater width so that as the rings become smaller the area becomes greater providing a uniform depth. These concentric spiral rings are diagrammatically illustrated in FIG. 3, together with the relative position of each rabble with respect to such rings. The vertical position of the rabbles determines the residual amount of material which is to be left on each ring as the hearth rotates. The rabbles tend to cause mixing and inversion of the bed several times as the material moves downwardly from the hearth periphery to the soaking pit. This permits a more uniform heating and devolatilization and provides a more uniform product.

In this embodiment, the arch temperature at the hottest point in the chamber is approximately 2,500 F. and the temperature measures at the top of the coke bed is approximately 2,300 F. This is too low a temperature to provide a high grain density quality coke suitable for ready conversion into graphite, e.g. graphite annodes for electro-chemical uses.

As the coke encounters each of the first five rabbles itis turned over and subjected to heat radiated from the roof 21' and the side walls 23. Volatiles are removed through the action of this heat and these escape into the furnace chamber where they mix with air from ports 25 and 27 causing combustion at a point spaced a distance above the surface of the coke bed. This combustion is sufficient to maintain the arch temperature of the furnace at the 2,500 F. temperature mentioned previously, and therefore the burners 29 are turned'off.

The total residence time of an average particle of coke on the hearth is approximately 25 minutes. As the average particle of coke contacts the sixth rabble, the first electrically heated rabble, its temperature is approximately 2,300 F. As the bed is turned over by the sixth, seventh, and eighth rabbles electrical current flowing between the sixth and seventh and the seventh and eighth rabble heats the bed between these rabbles momentarily as each portion of the bed passes under the rabbles. The maximum temperature to which each particle is exposed averages approximately 2,500 F. This additional 200 temperature greatly improves the grain density of the finished product. The 200 F temperature boost consumes approximately 50 kilowatt-hours per ton of calcined coke treated. In general, the electrical consumption will amount to roughly 25 kilowatt-hours per ton per F. which the coke is raised above the temperature in the general range of 2,500 F. Losses in conversion and losses dependent on the various characteristics of the material being calcined can vary the energy requirement by several times. In general, the addition of 200 F. will require electricity costing from about $0.80 to about $4.00 per ton, based on electric scale of $0.1 per kilowatt-hour. While this is a relatively expensive method of applying heat, it is competitive on a cost basis with the inefficient application of heat by auxiliary burners at temperatures above 2,000" F. due to the energy absorbed in preheating combustion air.

By using isolation transformers the rabbles lend themselves to being used as electrodes with minimum insulation problems. The control of necessary power to give the proper temperature rise to the coke is accomplished by the use of a saturatable core reactor. Either direct or alternating current can be used but the point is resistance heating as a principle. The electrical circuit diagrams of FIGS. 2 and 2a show two alternate circuits but others will be evident to those skilled in the art.

MODIFICATIONS OF THE INVENTION It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art by a reading of the specification and which are to be included within the spirit of the claims appended hereto.

What is claimed is:

l. A continuous process for removing volatile matter from limitedly electrically conductive material such as coke or coal which yields such volatile matter under heat comprising continuously delivering such material through an entrance point to an annular hearth, moving said material toward a point of exit from said hearth by rabbles projecting downward, disposed above the hearth and extending into the material, said projecting rabbles and said hearth moving relative to each other to turn and move the material, causing electrical resistance heating of said material-at the point of contact of at least one of said projecting rabbles with the material lying on the hearth, said resistance heating being caused by imposing an electrical potential between a conductive portion of said projecting rabble and a point within said material lying on said hearth which point is spaced from said projecting member, removing at least a portion of said volatile matter from said material by means of said electrical resistance heating said volatile material being oxidizable and additional heat being delivered to the material on said hearth by burning at least a portion of said oxidizable volatile matter above the surface of the material after it has been removed from said material.

2. The process of claim 1 wherein the material is coke.

3. The process of claim 1 wherein the material is coal.

4. The process of claim 1 wherein the material is petroleum coke.

5. The process of claim 1 wherein the material is delayed petroleum coke.

6. The process of claim 1 wherein the heat derived from the oxidation of the volatile matter is sufficient to heat the material lying on the hearth to a maximum temperature in the range of 2,000-2,600 F. and wherein said electrical resistance heating increases the maximum temperature to which said material lying on the hearth is heated to a temperature above that obtainable by oxidation alone of said volatile matter in the apparatus being used.

7. Apparatus for treating limitedly electrically conductive material such as coke or coal which contains volatile matter removable by heat' comprising an annular hearth, a central material outlet from said hearth, means for delivering material to the hearth to form a bed of material upon the hearth, downwardly projecting rabbles disposed above the hearth and extending into said material, at least one of said projecting rabbles having at least a submerged portion thereof electrically conductive, means for moving the hearth and projecting rabbles relative to each other, said projecting rabbles being disposed to move material on the hearth progressively toward the central material outlet during the relative movement between the hearth and said projecting rabbles, electrical means for imposing an electrical potential between said electrically. conductive portion of said rabble where said rabble contacts said bed, and a point in said bed spaced from said point where said bed contacts said projecting member said hearthbeing located in a chamber, wherein at least a portion of said volatile matter is oxidizable and wherein means are provided for burning at least a portion of said oxidizable volatile matter within said chamber and above the surface of said material so as to deliver additional heat to said bed.

8. Apparatus of claim 7 wherein said material outlet includes a soaking pit having discharge means at the bottom thereof.

9. Apparatus of claim 7 wherein said projecting members comprise rabbles. I

10. Apparatus of claim 7 wherein said projecting members are plow-shaped to promote turning over of the material as the material is progressively advanced toward said material outlet. 11. Apparatus of claim 7 wherein said hearth 1S downwardly inclined in the direction from its point of receiving said material into said bed toward said material outlet so as to promote movement of the bed as it is progressively advanced toward said material outlet.

12. Apparatus of claim 7 wherein said hearth is substantially circular and wherein said projecting members are substantially radially arranged.

13. Apparatus of claim 12 wherein said projecting members are plow-shaped to promote turning over of the material as the material is progressively advanced toward said material outlet, and wherein said material outlet is located substantially at the center of said circular hearth.

Claims

2. The process of claim 1 wherein the material is coke.
3. The process of claim 1 wherein the material is coal.
4. The process of claim 1 wherein the material is petroleum coke.
5. The process of claim 1 wherein the material is delayed petroleum coke.
6. The process of claim 1 wherein the heat derived from the oxidation of the volatile matter is sufficient to heat the material lying on the hearth to a maximum temperature in the range of 2,000*-2,600* F. and wherein said electrical resistance heating increases the maximum temperature to which said material lying on the hearth is heated to a temperature above that obtainable by oxidation alone of said volatile matter in the apparatus being used.
7. Apparatus for treating limitedly electrically conductive material such as coke or coal which contains volatile matter removable by heat comprising an annular hearth, a central material outlet from said hearth, means for delivering material to the hearth to form a bed of material upon the hearth, downwardly projecting rabbles disposed above the hearth and extending into said material, at least one of said projecting rabbles having at least a submerged portion thereof electrically conductive, means for moving the hearth and projecting rabbles relative to each other, said projecting rabbles being disposed to move material on the hearth progressively toward the central material outlet during the relative movement between the hearth and said projecting rabbles, electrical means for imposing an electrical potential between said electrically conductive portion of said rabble where said rabble contacts said bed, and a point in said bed spaced from said point where said bed contacts said projecting member said hearth being located in a chamber, wherein at least a portion of said volatile matter is oxidizable and wherein means are provided for burning at least a portion of said oxidizable volatile matter within said chamber and above the surface of said material so as to deliver additional heat to said bed.
8. Apparatus of claim 7 wherein said material outlet includes a soaking pit having discharge means at the bottom thereof.
9. Apparatus of claim 7 wherein said projecting members comprise rabbles.
10. Apparatus of claim 7 wherein said projecting members are plow-shaped to promote turning over of the material as the material is progressively advanced toward said material outlet.
11. Apparatus of claim 7 wherein said hearth is downwardly inclined in the direction from its point of receiving said material into said bed toward said material outlet so as to promote movement of the bed as it is progressively advanced toward said material outlet.
12. Apparatus of claim 7 wherein said hearth is substantially circular and wherein said projecting members are substantially radially arranged.
13. Apparatus of claim 12 wherein said projecting members are plow-shaped to promote turning over of the material as the material is progressively advanced toward said material outlet, and wherein said material outlet is located substantially at the center of said circular hearth.