US 3518181 A
Description (OCR text may contain errors)
H. F. TSE 3,518,181 PYROLYTIC METHODS OF TREATING BITUMINOUS TAR SANDS June 30, 1970 AND PREHEATING OF THE SAME Filed July 26, 1967 INVENTOR HAROLD F. TSE 8 0 United States Patent 3 518,181 PYROLYTIC METHDS 0F TREATING BITU- MINOUS TAR SANDS AND PREHEATING OF THE SAME Harold F. Tse, Bala Cynwyd, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jerse y Filed July 26, 1967, Ser. No. 656,160
Int. Cl. C10g 1/00 US. Cl. 208-11 2 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a method for the processing of tar sands. Large deposits of these sands are found as the Athabasca deposits in northern Alberta, Canada. The evaluated portion of these deposits occupies about five and one-half million acres and is buried by zero to 2000 feet of overburden. It has been estimated that these deposits consist of about 600 billion barrels of reserves in place, 350 billion barrels of recoverable reserves of raw tar sand oil and over 250 billion barrels of upgraded synthetic crude oil. See page 1 of the K. A. Clark Volume edited by M. A. Carrigy, Research Council of Alberta, October, 1963. The recoverable reserves estimate is just about equal to the world-wide reserves estimate of conventional oil, sixty percent of which is in the Middle East.
The tar sands are primarily composed of a fine quartz sand having a particle size greater than that passing a 325 mesh screen. The quartz sand is impregnated with a viscous bitumen in quantities of from 5 to 21 weight percent of the total composition. More typically, the bitumen content is from 8 to 15 percent. This bitumen is quite viscous6 to 8 API gravity--and contains typically 4.5 percent sulfur and 38 percent aromatics. Its specific gravity at 60 F. ranges typically from about 1.00 to about 1.06.
In addition to the bitumen and quartz sand, the tar sands contain clay and silt in quantities of from 1 to 50 weight percent of the total composition. Silt is normally defined as material which will pass a 325 mesh screen but which is larger than 2 microns. Clay is material smaller than 2 microns including some siliceous material of that size.
Various methods of handling tar sands to recover the desired petroleum products have been utilized. For example, the hot and cold water processes have been employed to remove bitumen followed by subsequent proc essing of the bitumen to obtain the desired hydrocarbon products. Petroleum has also been recovered from the sands by pyrolytic methods such as thermal or catalytic cracking or coking. The present invention relates to an improvement to the processing of tar sands and specifically to pyrolytic methods of handling the sands.
At room temperature, tar sands are a viscous mass that will pack and form agglomerates under their own Weight. This property causes the sands to pack in process feed hoppers or conveyors. It has now been observed that when the sands are heated to above about 200 F., they flow readily and do not pack. Under these conditions, the
3,518,181 Patented June 30, 1970 agglomerates of sand disintegrate and flow freely. They can then be transported without difliculty.
It has also now been observed, and surprisingly so, that when heated above about 380 F., the sands become viscous again and tend to reagglomerate. It is therefore proposed to facilitate the transportation of tar sands,
through conveyors or feed hoppers or the like, by preheating the sands to a temperature within the range of about 200 to about 380 F. Within this range, the bituminous sands are surprisingly free flowing and can be easily handled for feeding into a process for recovering hydrocarbons. The process is therefore describable as an improvement to pyrolytic methods of treating tar sands comprising preheating the tar sands to a temperature in the range of about 200 to about 380 F. and feeding the preheated tar sands into the pyrolytic treating process.
The drawing consists of two figures each schematically representing the present invention as applied to a pyrolytic method for treating tar sands.
In this specification, the term pyrolytic treating will be used to describe any process for handling tar sands to recover hydrocarbon products therefrom which process is characterized by chemical and physical decomposition of bitumen by the action of heat. Exemplary of these pyrolytic treatments are coking, retorting, thermal cracking and catalytic cracking and the like, some of which will be described in detail infra.
It is thought that when the bituminous sands are heated to about 200 F., the viscosity of the bitumen on the surface of the sand particles is reduced thereby reducing the sands tackiness to the point where they flow freely. At about 380 F. another change takes place. At this temperature it may be that asphaltenes and resins, suspended in the bitumen of reduced viscosity, begin to soften and thereby cause an increase in viscosity of the whole bituminous sand. There is no intent to be limited by this explanation for the operation of the present invention.
Those processes to which the present improvement can be applied include thermal cracking, catalytic cracking and coking among others. In thermal cracking, the bitumen in the sands is vaporized at a temperature between about 750 and 1300 F., preferably between about 800 and 0 F. At this temperature hydrocarbons in the bitumen vaporize. The hydrocarbon vapors can be stripped from the heated sands by means of a countercurrently flowing purge gas, preferably superheated steam.
In one specific exemplary thermal cracking process, preheated bituminous tar sands are passed into a distilling and cracking zone where they are maintained at a temperature at which hydrocarbons in the sands vaporize. The vaporized hydrocarbons are recovered and coked solids, produced by pyrolysis of the tar sands, are passed from the distillatingand cracking zone into a decoking zone where carbonaceous residue is burned off. With decoking the solids are heated to an elevated temperature. At least a portion of these heated solids are then recycled and mixed with fresh tar sands to initiate cracking.
In one specific exemplary catalytic cracking process, the preheated tar sands are mixed with a stream of hydrocarbon vapors, obtained as described infra, and with heated particles of primarily a finely-divided light catalyst. The mixture is introduced into the lower portion of an elevated distilling and cracking zone. The catalyst particles are of a lower density and smaller size than the sand of the tar sands. The cracking catalyst can be. any of the well known types of catalyst, such as silica-alumina, silicamagnesia, silica-zirconia or a natural catalyst such as Superfitrol.
In the distilling and cracking zone, a fluidized contacting is effected between the catalyst, hydrocarbon vapor and tar sands to distill additional hydrocarbon vapor from the tar sands and to crack some of the vapors. The resulting hydrocarbon vapors are discharged from an upper portion of the distilling and cracking zone, and catalyst and spent sand are withdrawn from the fluidized bed and passed to a stripping zone where the catalyst and sand particles are contacted with an inert, heated, stripping medium. The stripping catalyst and sand particles are then passed to a regeneration and classification zone where they are contacted with free oxygen at a velocity sutficient to maintain fluidization of the sand particles. Simultaneously, the burning of a portion of the caribonaceous matter from both catalyst and sand is effected and a classification and separation is caused between the catalyst and sand. A stream of primarily catalyst is withdrawn from the regeneraiton and classification zone and cornmingled with a hydrocarbon vapor stream, at least a portion of which has been recovered from the distilling and cracking zone. The commingled stream is then mixed with fresh preheated tar sands and passed to the distilling and cracking zone.
The improvement of the present inventionpreheating the tar sands to between 200 to 380 F.can be applied -to any of the processes described above and also to any pyrolytic process that is used for handling tar sands. The improvement is to preheat the sands to between 200 to 380 F. at which temperature the sands flow freely without agglomeration or stickiness. Preferably this range is 250 to 350 F. and within this range, the preferred temperature for treating the sands will vary with the bitumen content of the particular sand. For example, with a sand of high bitumen content, the preferred preheating temperature lies within the range of 250 to 280 F. and for medium bitumen content sands, the preferred temperature is 280 to 300 F. and for a very low bitumen content sands, the preferred temperature of preheating can be up to 350 F.
The improvement of the present invention can be more easily described with reference to the figures of the drawing which represent two embodiments of the present invention.
In the drawing, FIG. 1 shows the improvement of the present invention applied to a thermal cracking process. Tar sands are fed, in line 1, to the preheating zone 2. In the preheat zone, the sands are heated to between 200 to 380 F. depending upon the bitumen content of the particular sand charged. Heating to this range makes the sand less viscous and reduces agglomeration so that delivery to the reaction zone 4 through line 3 is facilitated. Line 3 represents any means used for charging tar sands into a pyrolytic zone such as the thermal cracking zone 4. Line 3 can represent a screw conveyor or a feed hopper or the like. Regardless of what means is utilized for delivering the sands, handling of the sands is greatly facilitated by preheating to this range.
The preheated tar sands are passed into the thermal cracking zone 4 where they are maintained at a temperature at which hydrocarbons vaporize. The vaporized hydrocarbons are recovered through 5 and coked solids from the sands are passed from the distillation and cracking zone 4 via line 6 to decoking zone 7 where carbonaceous residue is burned from the spent sand. Decoking heats the solids so that they can be withdrawn from the decoking zone 7 via 8 and recycled back to be mixed with tar sands for preheating or mixed via line 9 for cracking in the thermal cracking zone 4 or all of a portion of the spent sand can be discarded via 10.
FIG. 2 of the drawing shows a catalytic cracking process utilizing the improvement of the present invention. Tar sands are fed via line 11 to the preheat zone 12 Where they are heated to between 200 to 380 F. The tar sands are withdrawn from the preheat zone 12 via line 13, mixed with a stream of hereinafter described hydrocarbon vapors from 14 and with heated particles of a finelydivided light catalyst added from 15. The mixture is introduced into the lower portion of an elevated distilling and cracking zone 16. In the zone 16 a fluidized contacting is effected between the catalyst, hydrocarbon vapor and tar sands to distill hydrocarbon vapor from the sands and to crack some of the vapors. The resulting vapors are discharged via line 17. A portion of the vapors are recycled via line 14 to be mixed with fresh sands in line 13 while the remainder of the vapor is recovered from line 18 as product. Catalyst and spent tar sands are withdrawn from zone 16 via line 19 to stripping zone 20 where the particles are contacted with an inert, stripping medium which is recovered via line 21. The stripped catalyst and sand are passed through line 22 to a regeneration and classification zone 23. A stream of primarily catalyst is withdrawn from zone 23, via line 15 to be mixed with fresh tar sands and recycled vapors from lines 13 and 14. Spent sand is recovered from zone 23 via line 24.
The following is an example of the improvement of the present invention as applied to a thermal cracking process. Bituminous tar sands containing about 10 percent by weight bitumen are mined in chunks and heated to a temperature of about 270 to 290 F. at which temperature lumps break down and the sands become easily transportable. The sands are transported in a screw conveyor from the preheat to the thermal cracking zone. The feed to the thermal cracker is characterized by its free flowability and uniform consistency. The consistency allows for more thorough cracking in the thermal cracking zone and the free fiowability reduces wear on the screw conveyor system. At the cracking zone, the tar sands are mixed with decoked recycle spent sand from which the hydrocarbons have previously been stripped. The hot recycle sand is at a temperature of l200 F..while the fresh feed sand is at about 250 F. The weight ratio of hot recycle sand-to-fresh feed is adjusted so that the mixture is at about 950 F. when charged to the thermal cracking zone. In the cracking zone, the mixture is held for an average residence time of 7 minutes at 950 F. The mixture is also contacted in the zone with superheated steam. The steam is regulated to give a flow rate of about 8400 pounds per hour. Small concentrations of hydrocarbon purge gas are added from time to time. Stripped vaporized hydrocarbons are passed with the purge gas to a hydrocarbon recovery unit wherein they are washed free of entrained sand and condensed to separate an oil fraction for storage and a normally gaseous fraction, a portion of which is returned to the cracking zone as purge gas. Hydrocarbon gas is recycled from the recovery unit back to the cracking zone to supplement the steam purge gas, while the stripped solids mixture continuously passes out of the zone to a rotary coke burner. In the coke burner, the solids mixture is continuously decoked by burning the carbonaceous residues in contact with preheated air, the solids being heated to 1200 F. by such burning. Some of the decoked hot solids are recycled for reuse in heating fresh tar sand. The excess hot decoked sand is passed into an air preheater and into direct contact with fresh air, preheating the air, which then passes into the entry end of the cracking zone. The excess hot decoked sand is then passed into a blow case and contacted with water, whereby steam is created. The steam pneumatically forces the sand through a waste line into a waste pile located out of the system.
This example illustrates the improvement of the present invention in combination with a pyrolytic method of treating tar sands and illustrates the improved delivery of tar sands to the pyrolytic zone made possible by the present invention in reducing equipment Wear and in giving improved feed quality for better processing.
What is claimed is:
1. In a pyrolytic method for recovering hydrocarbons from bituminous tar sands comprising the steps of (a) feeding tar sands to a pyrolytic zone by the method of mechanically causing said tar sands to flow to said pyrolytic zone; said tar sands having been mixed with hereinafter specified recycle of hot solids; (b) maintaining said sands in said pyrolytic zone at a temperature sutficient to vaporize hydrocarbons from said tar sands to leave carbonaceous residue on the spent tar sands; (c) passing spent tar sands from said pyrolytic zone to a decoking zone and thereafter burning carbonaceous residue from said spent tar sands to provide hot decoked solids having a temperature sufficient to decompose said bituminous tar sands and (d) recycling at least a portion of hot decoked solids to be mixed with fresh tar sands for feeding into the pyrolytic zone; the improvement which comprises prior to the feeding step preheating the bituminous tar sands to a temperature between 200380 F. to increase fiowability and reduce agglomeration of said bituminous tar sands.
2. Method of claim 1 in which the bituminous tar sands are preheated to between 250-300 F.
References Cited UNITED STATES PATENTS OTHER REFERENCES Blair, S. M., Report on the Alberta Bituminous Sands, 1950, p. 24.
DELBERT E. GANTZ, Primary Examiner T. H. YOUNG, Assistant Examiner