US2843462A - Heat treating fluid coke briquettes - Google Patents

Description

July 15, 1958 J. w. BROWN HEAT TREATING FLUID COKE BRIQUETTES Filed July 27, 1955 muqzma} 1% Em; l F vw w: Iv mm m Iv Iv mzow uztfiz mzow MXOO 0541 James W. Brown Inventor By X C'Wflomey r 2,843,462 lQe Patented July 15, 1958 HEAT TREATING FLUID COKE BRIQUETIES James W. Brown, Mountainside, N. 1., assignor to Esso Research and Engineering Company, a corporation of Delaware Application July 27, 1955, Serial No. 524,747

3 Claims. (Cl. 44-24) This invention relates to improvements in the heat hardening of fluid coke briquettes. More particularly it relates to a process of this nature wherein the briquettes are heat hardened by treating them countercurrently with upflowing inert gases. The binder materials are cracked and the tar condensate is utilized as additional binder.

There has recently been developed an improved process known as the fluid coking process for the production of fluid coke and the thermal conversion of heavy hydrocarbon oils to lighter fractions, e. g. see Patent No. 2,725,349, granted November 29, 1955, and Patent No. 2,721,169, granted October 18, 1955. For completeness the process is described in further detail below although it should be understood that the fluid coking process itself is no part of this invention.

The fluid coking unit consists basically of a reaction vessel or coker and a heater or burner vessel. In a typical operation the heavy oil to be processed is injected into the reaction vessel containing a dense, turbulent fluidized bed of hot inert solid particles, preferably coke particles. A transfer line or staged reactors can be employed. Uniform temperature exists in the coking bed. Uniform mixing in the bed results in virtually isothermal conditions and effects instantaneous distribution of the feed stock. In the reaction zone the feed stock is partially vaporized and partially cracked. Effluent vapors are removed from the coking vessel and sent to a fractionator for the recovery of gas and light distillates therefrom. Any heavy bottoms is usually returned to the coking vessel. The coke produced in the process remains in the bed coated on the solid particles. Stripping steam is injected into the stripper to remove oil from the coke particles prior to the passage of the coke to the burner.

The heat for carrying out the endothermic coking reaction is generated in the burner vessel, usually but not necessarily separate. A stream of coke is thus transferred from the reactor to the burner vessel, such as a transfer line or fluid bed burner, employing a standpipe and riser system; air being supplied to the riser for conveying the solids to the burner. Sufficient coke or added carbonaceous matter is burned in the burning vessel to bring the solids therein up to a temperature suflicient to maintain the system in heat balance. The burner solids are maintained at a higher temperature than the solids in the reactor. About 5% of coke, based on the feed, is burned for this purpose. This may amount to approximately 15 to 30 wt. percent of the coke made in the process. The net coke production, Which represents the coke make less the coke burned, is Withdrawn.

Heavy hydrocarbon oil feeds suitable for the coking process include heavy crudes, atmospheric and crude vacuum bottoms, pitch asphalt, other heavy hydrocarbon petroleum residua or mixtures thereof. Typically such feeds can have an initial boiling point of about 700 F. or higher, an A. P. I. gravity of about to 20, and a Conradson carbon residue content of about to 40 wt. percent. (As to Conradson carbon residue see A. S. T. M. test D-189-41.)

A problem in the marketing of the fluid coke product is the small size of the particles, predominantly, i. e. about 6090 wt. percent in the range of 20 to mesh. The production of substantially larger particles is inconsistent with satisfactory operation of the fluid bed. On the other hand industrial requirements for coke often necessitate particles having a diameter of about at least inch to 1 inch.

These fluid coke particles have accordingly been compacted into briquettes using various carbonaceous binder substances. The agglutinating carbonaceous binder substances that can be utilized include suitable hydrocarbon binders, such as asphalt and other heavy petroleum residues, aromatic tars, e. g. vacuum reduced thermal tars, heavy ends of coal tar, such as coal tar pitches having a minimum softening point of about C., and heavy ends from the coking operation, i. e., 1000 F. scrubber bottoms. Some specific trade examples of the binders are Elk Basin vacuum residum F. softening point), Enjay 160 Asphalt and Hawkins coker bottoms. These substances are utilized in an amount of about 5 to 25 wt. percent based on the coke charge and preferably 8 to 15 wt. percent.

This invention is especially suited to utilization of lowvalue petroleum residues which are inferior binders unless specially treated. Normally, when a petroleum residue is decomposed by heating, the carbonaceous residue is less than from a more aromatic binder such as from coal tar. It has now been found, however, that the conditions desirable for the heat hardening of fluid coke agglomerates are also the conditions best suited to converting a petroleum residue into a good binder with high cokeforming potentialities. The most important condition is a slow rate of heating. A binder so treated has less tendency to soften during subsequent heating and is also more susceptible to additional treatments, to be described later, which reduce its tendency to soften during heating.

The important advantage of using a petroleum residue is the low cost relative to other available binders. For example, when 10% binder is used in agglomeration the cost saving would be in the range of $1.00 to $3.00 per ton of coke agglomerated.

The fluid coke can be used as is to make briquettes, but the behavior of briquettes during heating and the strength of the final products are improved by grinding part or all of the coke to produce finer particles. .This mixture with binder is then 'briquetted by molding in a hydraulic press at a pressure of about 2,000 to 20,000 p. s. i. Pressures of 2000 to 6000 p. s. i. are usually adequate. Roll presses such as those commonly employed to make briquettes from coal and other materials can be used. Such machines are described in the Chemical Engineering article Agglomeration, October 1951. The mixtures pass directly to the pressing rolls.

These briquettes require heat hardening at temperatures of above 700 F. to decompose the binder to a carbonaceous residue and to produce adequate strength and cohesion. Heating up to 16002000 F. is usually desirable to devolatilize the coke. F. range, however, because of the melting of the binder material results in the deformation of the compactions and also adherence to each other. In addition elevated.

temperatures tend to destroy the binder by preferential Heating in the 200 700".

ening the briquettes'by countercurrently contacting them with hot inert gases. The briquettes are thus heat hardened without deformation or oxidation. The binder materials are cracked. A tar fraction is condensed and this condensate is then used as a superior additional binder for the briquetting operation. Further details follow.

Part of the fluid coke is ground so as to pass through a 100 mesh screen. The amount of grinding to be done depends on the desired strength of the agglomerates as well as on the quality of the binder with which it is to be mixed. High viscosity binders are especially difficult to mix with fine coke. The fluid coke is admixed with the binder material at a temperature in the range of 200 to 400 F.

The mixture is then molded under pressure as also explained above but at a lower temperature than the mixing step, i. e., 150 to 250 F. The resultant briquettes are then sent to a heating zone, e. g., a shaft furnace, where they are heated to a temperature in the range of 1200 to 2000 F., preferably 1600 to 2000 F. by countercurrent contacting with hot inert gases which enter the furnace at a temperature in the range of 2000 to 3000 F. The rate of heating the agglomerates is 2 to 15 F./min. depending on binder quality and agglomerate strength. The heating time is in the range of 1 to 10 hours. The hot inert gases include materials like CO CO, N etc. Preferably the inert gases are flue gases from combustion systems. The combustible material can be fluid coke itself or an extraneous fuel such as fuel oil or natural gas. The combustion is supported by an oxygen containing gas such as air but the combustion should take place with a deficiency of oxygen so as to assure the absence of oxygen in the furnace.

The inert gases as well as evolved cracked binder vapors are then removed from the heat treating zone and cooled. The conditions are controlled such as to condense a fraction having a minimum boiling point in the range of 400 to 700 F. This is most conveniently accomplished by introduction of a quench medium which may be water, steam or condensed, cooled hydrocarbons. The temperature of the quench can be adjusted so as to condense the desired hydrocarbons without condensing water which would form emulsions. Subsequent cooling to a convenient temperature around 80 to 100 F. removes much of the water vapor and light hydrocarbons. The condensate is highly aromatic, lower boiling and less viscous than the binder material used originally. In general, the poorer the original binder, the more cracked binder will be recovered for use in the condensation step. The condensate would normally have a boiling range from about 500 F. to well over 1000 F.

At the temperature of mixing with the coke around 200 to 400 F., the recycle binder has a viscosity of 40 to 200 Saybolt Seconds Furol. Its gravity is usually less than A. P. I. and displays a high coke-forming tendency when heated. This condensate is then recycled to the mixing operation to facilitate the latter and conveniently the inert gases after reheating are returned to the heat treating operation.

The recycle condensate thus utilized is in the range of 2 to 10 wt. percent based on the fluid coke charged to the briquetting operation.

This invention will be better understood by reference to the following example and description in connection with the flow diagram shown in the drawing.

Referring now to the flow diagram, fluid coke is fed through line 1 into mixing zone 15 wherein it is admixed with 10 wt. percent scrubber bottoms from fiuid coking of heavy Elk Basin vacuum pitch from line 2 at a temperature of 250 F. The resultant mixture together with wt. percent of the recycle binder from line 14 passes through line 3 into briquetting zone 4 where it is molded at a temperature of 150 F. and a pressure of 4000 p. s. i. The resultant briquettes leave by way of line 5 and are slowly passed downward as a moving bed through .4. shaft furnace heating zone 6. The briquettes are countercurrently contacted with upflowing flue gas from auxiliary furnace 11 and line 12 and are thus hardened by slowly heating to 1800 F. at an average rate of 5 F. per minute. The heat hardened briquettes are cooled before removal by introducing wet steam through line 17. Finished briquettes may also be cooled by introducing water or recycle gas into line 17. The cooled, heat hardened briquettes are withdrawn from line 13 by a feeding mechanism 18.

The binder undergoes cracking at the heat hardening temperature and cracked binder vapors along with flue gases are removed overhead through line 7. Quench material such as water or recycled binder is introduced through line 16 so as to condense a condensate having a minimum boiling point of 500 F. No difl'iculty is encountered in quenching provided it takes place quickly and provided the temperature is above that at which water condenses. A venturi-type quench is the preferred apparatus. In separation zone 8 the uncondensed vapor is separated from the condensate. The latter is recycled through line 14 to mixing zone 15. 5 wt. percent binder based on the fluid coke charge is recycled in this manner.

The flue gases are then quenched in venturi-scrubber 19 to remove remaining condensable hydrocarbons which are collected in separator 20. Flue gases are then vented through line 9 or recirculated by line 10, compressor 21, furnace 11 and line 12 back to heating zone 6.

The conditions usually encountered in a fluid coker for fuels are also listed below so as to further illustrate how the fluid coke was prepared.

Conditions in fluid coker reactor The advantages of this invention are apparent to the skilled in the art. A distinct saving in expensive binder material is provided. Improved mixing of binder and fluid coke is obtained. This improves the strength of the agglomerate. Briquettes are heat hardened Without deformation or surface disintegration.

The reduction in deformation tendency is partly attributable to the improved mixing and partly to the better properties of the recycle binder. Furthermore, the cracked binder is especially susceptible to additional treatments to fuither decrease the amount of deformation encountered. Such treatments include air blowing, treatment with chemicals such as sulfuric acid or thermal pretreating such as a short heating on a moving belt prior to introduction into the shaft furnace. In the case of thermal pretreatment the recycle binder tends to set into a hard form because of its unsaturated chemical nature.

The coke agglomerates produced by use of the recycle binder have a more porous structure than those produced from binders which display a smaller amount of thermal cracking. The porous structure makes this coke especially reactive in metallurgical use.

The process of this invention also has utility in preparing other compactions such as pellets and extrusions and from other fine solids besides fluid coke.

It is to be understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. A process for preparing stable briquettes from fluid coke particles which comprises the steps of admixing the particles with an agglutinating carbonaceous binder at a temperature in the range of 200 to 400 F.; molding the resulting mixture into briquettes at a lower temperature, one in the range of 150 to 250 F. and a pressure in the range of 2000 to 20,000 p. s. i.; heat hardening the briquettes at a temperature in the range of 1200 to 2000 F. in a heating zone at a heating rate of 2 to 15 F. 1 min. by countercurrently contacting them with upflowing inert gases at a temperature in the range of 2000 to 3000 F., the total heating time being in the range of 1 to 10 hours; withdrawing evolved, cracked binder vapors along with inert gases from the heating zone; cooling the vapors so as to obtain a condensate having a minimum boiling point in the range of 400 to 700 F., the boiling point and viscosity of the condensate being less than that of the agglutinating carbonaceous binder; recycling this condensate as additional binder to the admixing step and withdrawing stable briquettes from the heating zone, the total amount of binder utilized being in the range of 5 to 25 wt. percent based on the fluid coke particles of which the condensate represents 2 to 10 wt. percent based on the coke particles.

References Cited in the file of this patent UNITED STATES PATENTS 1,667,358 Robeson Apr. 24, 1928 1,972,944 Morrell Sept. 11, 1934 2,556,154 Kern June 5, 1951 2,709,676 Krebs May 31, 1955 2,776,935 Jahnig et a1. Jan. 8, 1957 OTHER REFERENCES Residual Oils Fluid Coked to Eliminate Heavy Fuel Problem, Voorhees and Martin, Proceedings of A. P. I., 1953, see. III, pages 39-46.

Attesting Officer UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,843,462 July 15, 1958 James Wo Brown It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

0 o Column 5, line 6, for "15 .F(, 'l mine" read 15 Fa/mino Signed and sealed this 28th day of October 19580,

ttest:

KARL AXLINE ROBERT c. WATSON Commissioner of Patents

Claims (1)

1. A PROCESS FOR PREPARING STABLE BRIQUETTES FROM FLUID COKE PARTICLES WHICH COMPRISES THE STEPS OF ADMIXING THE PARTICLES WITH AN AGGLUTINATING CARBONACEOUS BINDER AT A TEMPERATURE IN THE RANGE OF 200* TO 400*F., MOLDING THE RESULTING MIXTURE INTO BRIQUETTES AT A LOWER TEMPERATURE, ONE IN THE RANGE OF 150* TO 250*F. AND A PRESSURE IN THE RANGE OF 2000 TO 20,000 P. S. I.; HEAT HARDENING THE BRIQUETTES AT A TEMPERATURE IN THE RANGE OF 1200* TO 2000*F. IN A HEATING ZONE AT A HEATING RATE OF 2* TO 15*F. 1 MIN. BY COUNTERCURRENTLY CONTACTING THEM WITH UPFLOWING INERT GASES AT A TEMPERATURE IN THE RANGE OF 2000* TO 3000*F. THE TOTAL HEATING TIME BEING IN THE RANGE OF 1 TO 10 HOURS; WITHDRAWING EVOLVED, CRACKED BINDER VAPORS ALONG WITH INERT GASES FROM THE HEATING ZONE; COOLING THE VAPORS SO AS TO OBTAIN A CONDENSATE HAVING A MINIMUM BOILING POINT IN THE RANGE OF 400* TO 700*F., THE BOILING POINT AND VISCOSITY OF THE CONDENSATE BEING LESS THAN THAT OF THE AGGLUTIATING CARBONACEOUS BINDER; RECYCLING THIS CONDENSATE AS ADDITIONAL BINDER TO THE ADMIXING STEP AND WITHDRAWING STABLE BRIQUETTES FROM THE HEATING ZONE, THE TOTAL AMOUNT OF BINDER UTILIZED BEING IN THE RANGE OF 5 TO 25 WT. PERCENT BASED ON THE FLUID COKE PARTICLES OF WHICH THE CONDENSATE REPRESENTS 2 TO 10 WT. PERCENT BASED ON THE COKE PARTICLES.

Images