SIMULTANEOUS DEHYDRATION AND COKING USING FLUIDIZED SOLIDS G.W. HODGSON', BEN MATCHEN2,W. S. PETERSON, AND P. E. GISHLER NATIONAL RESEARCH COUNCIL OF CANADA, OTTAWA, CAN.
THE
n,orld's largest single reserve of oil exists in the Athabasca oil sands of northern Alberta. Differing sharply from the other oil fields of the province, this deposit is an unconsolidated silica sand formation saturated with a heavy black oil. The full extent of the deposit is not knomi, but examination of outcrops and core drillings for 60 miles along the Athabasca River indicates that t>hcdeposit underlies a t least 1500 square miles. Because the viscosity of the oil is excessive, it cannot be produced by normal methods and resort must be made to less conventional methods. Various government agencies and private organizations have carried out research work directed toward the development, of this petroleum resource. Blair ( 2 ) has reviewed t'he production methods that have been studied and has proposed a sequence of operations for obtaining a marketable oil from the oil sands. The calculated production cost indicates t'hat development of this vast resource is economically practical. The sequence of operations calls for open-pit mining of the deposit and recovery and processing of the contained oil to yield a product equivalent to a No. 2 fuel oil. Until present met,hods of oil recover?- in situ are improved, open-pit mining must be practiced, although this limits the extent of the deposit that, is amenable to development. Preliminary core drilling has shown one A-square mile area-the Mildred-Ruth Lakes area, 20 miles north of McMurray-with an indicated oil content of over 1 billion barrels. The average thickness of oil-sand deposit t,here is 140 feet lying under about 60 feet of overburden. The oil content of the sand is 13.6y0by weight. (In addition to the oilsaturated sand, there are irregular pools containing 18 to SO% oil by weight. These pools are the exception rather than the rule and should not unduly influence any process designed to recover oil from the Alberta oil sands.) Two general methods of recovering oil from the mined sand are well known. One is a direct distillat,ion of oil from the sand in a fluidized bed to produw a clean, dry colrer distillate in a single operation (5). The other mcthod makes use of water as a partition agent for separating the oil from the sand in a flotation step. It exists in two forms, the hot-water process ( 3 ) and t,he cold-water process ( i ). The watcr-separation processes rejept the bulk of the sand a n d produce an unaltered crude oil containing considerable emulsified water. Hot-water separation yields a product of 64% oil, 32% n-ater, and 4% solids. The removal of the water and solids is necessary before this can be considered a suitable crude feedst,ock t o a refinery. The present paper describes one method of accomplishing this. It involves feeding the wet crude oil produced by water separation directly t o a fluidized sand bed maintained a t about 500" C. 1 2
Present address, Research Council of Alberta, Edmonton, Can. Present address, McRIaster Universit.y, Hamilton, Can.
Simultaneous dehydration and coking take place yielding a clean, dry oil, the properties of nhich diffrr markedly fiom thow of the oil in the charging stock. The problem was tahen dirrctl? to the pilot plant scale. The pilot plant used for this dehydration-coking study vim a modification of that used in the direct distillation of oil from the raw sand (6). The experiments were designed to determine the feasibility of charging the primary product of the hot-water separation process to a fluidized-solids still. A study was made of the manner in which the solids and water contained in the charge are removed and of the influence of variables, mainly temperature, on oil yield and quality. Stili and Burner Designs A l l o w Simultaneo.us Dehydration and Coking
The pilot plant layout was influenced by the restricted space available. The area is 17 X 19 feet with 18 feet of headroom. The plant had a capacity of about 2 gallons per hour. Most 'of t,he equipment is located on the mezzanine floor with the standpipes and risers extending through a well almost to ground level. The instrument panel is located a t ground level. The still and burner and the collection system are shown in Figure 1. The floor plan is shown in Figure 2 and the flow sheet in Figure 3. The still and burner were of stainless steel, 6 feet, long with diameters of 6 and 9 inches, respectively. Starting beds consisted of sand obtained from the direct distillation of oil from bituminous sand in a fluidized bed (6).The same lot of sand was used for all experiments with make-up sand added as required. The depth of fluidized bed in the &ill and burner was 30 and 36 inches, respectively. The warmed wet crude charge stock was pumped directly into the lower part of a fluidized sand bed. The oil and water flashed off and passed to the collection system. -4hot cyclone removed the bulk of the entrained solids. The line to the electrical precipitator was water-jacketed to cool the off-gases and vapors to about 130" C. The bulk (75 to 8A%), of the oil condensed as fine droplets suspended in the gas stream. These were removed by the electrical precipitator. The water vapor and light oil were then condensed in a finned cooler and collected. Charcoal scrubbers removed the light ends. The still temperature was usually maintained a t 500" C. or higher. At this temperature, coking of the bitumen in the feed resulted in the deposition of a thin coke layer on the surface of the sand part,icles. This "coked sand" was continuously wit,hdrawn from the still down t'he still standpipe and was picked up by the preheated air stream and blown into the burner. Combustion of the coke raised the temperature of the sand in the burner. This heated sand was recycled to the still to supply the heat' required for the dehydration-coking step. 1492
June 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
The pilot plant is similar in some respects t o a catalytic cracking plant. The still and burner function much t h e same as a reactor and regenerator, except t h a t simultaneous dehydration and coking rather than catalytic cracking take place. The differences are as follows: Charge Stock. I n a catalytic cracker the preheated charge stock is usually a distillation cut of a crude oil plus cycle stock, and it is fed t o the base of the still riser. It is vaporized either in a preheater or by the recycled catalyst, and t h e vapors serve as fluidizing gas. The oil of t h e wet crude charging stock, however, was a high boiling material very sensitive to thermal shock. Attempts were made t o feed it to the base of the still riser where it contacted sand at 700" C. The charge would rapidly cool the sand t o about 500" C., and any irregularity in flow rate of the hot sand caused temperature fluctuations t h a t resulted in excessive coking. The charge was therefore fed into the cone a t the base of the still. Three other design changes were made: the still grid was removed; the end of the feed tube was extended about an inch past the wall of the cone so t h a t the oil was readily picked up by the violently agitated bed particles which were a t 500" C. or higher; and a small spiral agitator was rotated in the delivery tube to prevent coke build-up. Process gas was recycled in an amount sufficient to carry the recycle sand up t h e still riser. The remainder of the fluidizing gas was supplied by the vaporization of water and oil of the charge stock. Auxiliary Heat. The unit was too small to be thermally selfsufficient. Part of the heat was therefore supplied electrically. Heat was supplied directly to the shell of the burner. On the still side, electric heat served t o maintain adiabatic conditions. Calculations indicated that, on a larger scale, the coke and process gas would be adequate t o carry the process. I n this work, propane, when required, was used as a n auxiliary heat source in the burner since it was more convenient t o use than process gas. Collection System Recovers 95% of Oil Product
An external hot cyclone separator removed dust from the oil vapor stream, This permitted a study of the dusting tendency of the solids (mainly fine silica and clay) contained in the charge stock. The choice of oil collection system was dictated by severd factors: a short lining-out time to steady-state conditions was desirable; electrical precipitators had been found very satisfactory for recovering suspended materials from gas streams; and the collection system adopted permitted the recovery of products in a simple fashion, when and as formed. After the first hour, a steady state was reached. About 95% of the oil product was collected hourly. The remainder consisting essentially of gasoline waa recovered from the charcoal scrubbers by steam stripping at the end of the run. Instruments and Sampling Control Process end Product
The two main controls were those for still bed temperature control and still bed level control. A temperature recordercontroller actuated by a thermocouple in the still bed, controlled t h e flow of hot burnt sand t o t h e still by adjusting the position of the slide valve at t h e base of the burner standpipe. The still bed depth was controlled by a bellows type differential pressure recorder-controller, which operated t h e slide valve at the base of the still standpipe.
1493
Figure 1. Pilot Plant
A six point recorder recorded the temperature of the two fluidized beds, the two preheaters and the two risers. Aside from this, temperatures were recorded hourly a t 36 other positions on the plant. Pressure drops at 21 positions were recorded hourly. Continuous still and burner off-gas samples were taken hourly. Continuous hourly coked sand samples were taken from the still standpipe for carbon and hydrogen determinations. Spot samples of burnt sand were taken hourly from the burner standpipe. Cyclone dust was removed from still and burner cyclones periodically and sampled for carbon and hydrogen determinations. A large sample of process gas (still off-gas) was collected near the end of a run for Podbielniak analysis. After a run, a composite oil sample was made u p for distillation analysis and determination of sulfur content, viscosity, and density. For some samples, composition of the oil was also studied. This included determination of the asphaltenes, resins, and oily material and also t h e aromatic, unsaturate, and paraffin plus naphthene content, Charge Stocks Contained
4 to 95% Solids
The charge stock was wet oil t h a t had been produced at Bitumount. Three lots of oil were available: Lot 1: Experiments 37, 39, and 40, stored for 5 years Lot 2: Experiment 45, stored for 1 year and similar t o Lot 1 Lot 3: Experiment 35, stored for 1year, high solids Solids in the oil consisted almost entirely of finely divided material, largely silica with some clay materials. Any coarse sand included in t h e oil at the time of production had settled out during storage. Some water had separated out of the older lot of oil during storage, but this deficiency was made u p by adding water t o the oil prior t o charging it to the fluidized distillation unit. The third lot of oil was termed a "mud" because of its high solids content. It was obtained from the Bitumount operations and consisted of a mixture of various settler underflows. As in the other two lots of wet oil, all t h e coarse sand had settled out leaving finely divided quartz and clay minerals. Table I shows the composition of the three lots of charge stock. Solids analysis was by ignition and water by ASTM distillation. Solids recovery. One of the objects of combining the fluidized solids process with the hot water process was t h a t the solids in the oil sand could be handled conveniently. The hot water
INDUSTRIAL AND ENGINEERING CHEMISTRY
1494
MEZZANINE FLOOR PLAN
GROUND FLOOR PLAN Floor Plan of Pilot Plant
Figure 2.
TABLE I. CHARGE STOCKS Expt. No. Feed Lot No. Solids, yo Water, % Oil, b y diff.,
35 3
37
39
1
1
24.7 19.4 55.9
3.5 30.2 66.3
3.1 30.8 66.1
40 1 2.9 33.0 64.1
45 2
3.5 38.1 58.4
method removed the rocks, mining debris, and the bulk of the sand. The residual sand and cla) left in the oil entered the fluidized solids bed and thereby tended to increase the bed inventory. It wa9 reasonable to believe that any sand of the same size as the fluidized bed sand would simply increase the bed inventory. I t was not clear what would happen t o the finer material in the charge stock.
TABLE 11. Expt. No. Feed solids, lb. Recovered solids, lb. Still cyclone Oil Burner cyclone Burner filter Total Stillgas rate, ft./sec.
SOLIDS
RECOVERY
35 9 52
37 169
39 2 66
40 3.00
45 3.30
4.69
0.51 0.12 1.07
0 31
1.34
1.59 0.81 1.28
2.07 0.29 1.31
0.41
1.61 __ 0.38 7.09 0 66
0.19 1.89 0 8G
1.27
0.31 3.23 1.00
0.12 3.80 1 17
Vol. 44, No. 6
0
2
3.73 1.07
Table I1 s h o m that linear gas rates of more than 0.8 foot per second in both the still and the burner were sufficiently great to elutriate the finely divided feed solids from the fluidized beds, and the t x o gas streams tended to carry slightly more solids out of the tv-o fluidized beds than were introduced into the system in the wet oil feed. S e t particle size distribution of the fluidized sand beds remained unchanged during processing of the wet oil. About half the feed solids were carried over to the burner. This was probably caused by inclusion of the fine particles in the coke deposits on t,he coked sand in the still, Following the combustion of the coke in the burner, the fines were released and escaped with the burner gases. Water Recovery. A second objective in combining the processes wva8 that the water associated with the primary separation product of the hot water method could be simply and effectively removed. Operation of the fluidized solids pilot plant showed that flash distillation of the wet oil occurred smoothly with no
indication of froth formation which is characteristic of conventional dehydration of this wet oil by distillation. Table 111 s h o w that the water was collected readily from the still condensate with virtually no emulsion loss. The final oil product from the fluidized solids plant contained about 0.2% water. O i l Products Recovered as Liquid Distillate, Coke, and
Gas
The third reason for combining the two processes was that treatment in the fluidized bed resulted in a partial coking of the oil. The coking operation resulted in the formation of three products. The major part of the oil in the feed was recovered as a liquid distillate and the remainder as coke and gas. Coke formation w&s measured indirectly. All the coke, apart from that left on sand and dust samples, was burned in the plant process. The burner off-gas rate was measured, and the concentration of carbon dioxide and carbon monoxide was determined. The amount of coke burned was calculated. From a knowledge of the amount of oil processed the fraction of oil going to coke could be calculated. Incidental to the calculation of coke production was the calculation of still residence time and recycle rate of the sand. Table IV shows the carbon and hydrogen analyses of the various plant materials. In general, the coke production amounted to 8 to 10% of the charged oil. The still residence time of the sand was of the order of about 20 minutes and was dependent on the temperature differential betxeen the still and burner, and the throughput of the plant.
TABLE 111. WATERRECOVERY Expt. S o . Water in, lb. Charging- stock W a t e r o u t , lb. Condenser water layer Dispersed in oil Total
35
37
39
40
45
7.17
14.6
26.4
34.4
36.3
6.77 0 1 6.87
13.3 0.3 13.6
24.2 0.2
34.0 0.3 34.3
32 9 0.1
- - 21.4
Gas formation was measured by metering the gas going t o waste to keep the gas inventory of the system constant. Before each experiment was begun, the pilot plant was thoroughly checked for gas leaks. However, in operation, some gas mas knov-n to escape through sample cocks, but the volume, as measured a t various times, was small. Table V shows a typical
INDUSTRIAL A N D ENGINEERING CHEMISTRY
June 1952
18b
-
nocEw WECT
Am
TANK
01s HOLDER
Figure 3. F l o w Sheet for Reemery of Oil from Wet Bitumen ~
TABLE IV. COKEPRODITTIOX Exyt. No. Burner nfl-gu. R COI
35
co
Coked m d 7 ' C and R Burnd mnb, C and I3 Still dud, % $and H
I 63 0 12 0 454 003
15.2
Rcaidcnwtimefor~ndinrrtillbed,urin.33.G
37
39
40
45
3 30 4 25 7.030 6.1. 0 79 0.40 0.12 0.3 0.590 0.570 0.649 0.41
m:i
26'6
21.'i
0.03 18.8
..
23.2 19.3 16.0
Including propme burned.
TABLE V. WASTEGASANALYSIS Per C a t ?$etbsne Etlrvlcoe Ethke Propylene Propane Imbut me n-Ruunc
8.81 0.23 Nil
Iwpontrne n P mune 6 compoundr
Nil
Carbon monoxide Hydrogen Nitrogen (by dib.)
0.85
om 0.14
-
Per Cant 0.12 0.53
was greater than at the lowor temperature 6 t h I2 ud 7% at 560" and 517' C., reepectively. The nature of the bitumirwxls sand oil mdernmt a mmidtrable change in the still reaction. Not only did the rLcadty .Id gravity change as iodicsted,but tbe eompositaa d the o&+d oil was altered considerably. The q h l t e a e h & m d tbt dl wae reduced fromabout 20 to .bout 1% It ir b d k d thrth .high molecular weight n u t 4 of which the asphdhe t.ctiolli. composed is the le& nsdily dietilbd in the OPrJia and ss a result is subjected to tbe mast thcrmrlmtion. For thie reason, the bephaltenea prahbly M the anrce mtcri.l for the coke and gaa formed in tbe still reaIt mas faral
0 .po
Nd
0.50
3.88 85.1
TABLE VI. TFLUPER~.~-RE fimcrs Expt. so.
3T
Still temp., C. C Duration b u p dte. hrib./hr.
Oil yield. vol. % Coke $bo. r t . %
rnalyeis of the gas purged from the system. It includea the nitrogen bled to precleure tape. The quantity of proteas gris formed varied with still operating temperature. Under optimum opera1 ing conditione it was a h t 0% by weight.
GM. veld., wt. 011 lMpeCliOD W.la
517
wet crude
%
a. 0 la.I) m.4
0.2 0.49 56.0 14.7 4.1
25 1 15.6 4.1
8.1 4.0
146
Ekperimenta were conducted a t a E&of temperatures to determine the effect on the distillrrte oil yield and quality. The data are &own in Table VI. The coke yield WM virtually inded e n t of the still temperalure. The gnu yield i n r d with rising lemperatum, and the oil yield decreased. An 84% oil yield wm indicated. Table VI ala0 &owe that the viscoeity of the didillate oil decreased with increaee in temperature. The gravity of the. oil changed only slightly, remaining at about 16 'A.P.1. Sulhrr content appeared independent of temperatwe. The high lrulfur indiclttes the need for a hydrogenation step (8). Distillation of the oil rshowed that at higher temperatures the.&linsproduction
20 SO 40 50 80 70 80
4m 567
8.2 6.2
03 I.?6
1s 278
rn
63a
4aD 668 CII &?$
m
em
ppoduet.
lrcva i
am 646 6R2
6m
'b kDetrrmined e d on oil content ai Iced. on Cottmll oil.
denastion or polymerhat&
.w w
3.8 12.7 M.6
3s-3
StillT -AllR o d & m d ( r lYkld
39
UI
#z
.
h
INDUSTRIAL AND ENGINEERING CHEMISTRY
1496
Vol. 44, No. 6
thenes. However, the sulfur content of OF OIL FRACTIONS FROM PILOT PLANT PRODUCT PRODUCED the cuts is high and ita effect on the TABLE VII. INSPECTION separation has not been studied. The AT 510' C. aromatics were desorbed from the silica Distillation Range, F. gel by methanol. The results are inI.B.P. 356to 464to 536to 608to 644to cluded in Table VII. Composite to356 464 536 608 644 750 Residue O
Sp. gr. a t 60' F . Refractive index Sulfur! % Viscosity kin. os. At 100b F.
A4 210° F.
Distillate Val. %, Wt. % (calcd.) 'AsDhaltenea.. 5.4 Resins % o i l y daterial, % Aromatics % Acid soluthe, % Acid insoluble, %
0,954
....
4.0'
52.0 5.2
0.7875 1.4384 1.71
0.8477 1.4680 1.87
0.8747 1.4815 2.12
0.9000 1 ,4952 2.70
0.9218 1.5098 3.03
2.1 1.06
1.88 0.87
2.91 1.15
5.14 1.59
9.81 2.27
'
0.9465 1.5252 3.61 28.7 4.0
1.003 .. . . 4.74 4550 54
Process Costs Vary with Water Content
Wet crude bitumen produced by the hot water process can be dehydrated 0.5 Nil Nil Nil Trace Trace 22.6 and coked simultaneously and continu1.40 1.74 2.2 6.7 3.9 72.5 92.7 98 98 97.6 97.0 94.5 ously by flash distillation in a fluidized 11.4 33.3 12.4 18.4 .... 4.9 38.4 ... 44.8 41.3 39.0 39.6 , . . . 38.6 ... 29.5 sand bed. A high yield of clean, dry 37.1 48.6 42.1 50.3 47.3 .... 25.0 ... coker distillate is obtained. The propa Excludes gasoline c u t . ,* erties of this distillate are very similar to those of distillate obtained from the TABLE VIII. HEATREQUIRED TO DISTILL1 POUND CONTAINED BITUMEN AT 500' C. fluidized processing of raw bituminous sand (6). The optimum yields and (Base temp. = 0' C.) operating conditions were found to be Analysis. % Wt., Lb. Heat, B.t.u. ~ ~ t ~ l BituBituBituHeat, in the temperature range 500" to Feed Type men Solids HoO men Solids HIO men Solids HzO B.t.u. 525' C. As the temperature is reduced Wet bitumen 71 9 20 1 0.127 0.28 717 27 433 1177 below this, the incomplete removal of 71 4 25 1 0.056 0.35 717 12 542 1271 63 4 33 1 0.063 0.52 717 13 806 1536 the heavy ends causes the ooked sand to 56 4 40 1 0.071 0.71 717 15 1100 1832 lose its free flowing properties. Bituminoussand 15 85 0 1 5.67 0 717 1210 0 1927 15 82 3 1 5.47 0.2 717 1170 310 2197 The solids content of the feed can be 13 87 0 1 6.69 0 717 1420 0 2137 very high without causing difficulty in 13 84 3 1 6.47 0.23 717 1380 356 2453 coking in a fluidized bed. For example, raw bituminous sand feed, which averages about 85% solids and 14% bituof the unsaturated compounds formed in the still reaction. They men, has been treated successfully (6). In this latter case, heat appear as asphaltenes because of their solubility characteristics requirements are high because of the high ratio of solids (plus and not necessarily because of their chemical structure. some water) to bitumen. In the coking of wet bitumen, the ratio Oil Composition. The coker distillate produced from wet of solids to bitumen is much lower, however the ratio of water to crude feed and from bituminous sand feed gave similar yields and bitumen is at the same time higher. At the temperature of the had similar properties such as viscosity, gravity, and boiling still, the water has an enthalpy of over 1500 B.t.u. per pound point curves. A sample of coker distillate selected for detailed while the sand hacs a value of somewhat over 200 B.t.u. per pound. analysis was produced using bituminous sand feed a t a still temDehydration-coking costs for the water separated bitumen are perature of 510' C.-low enough to produce a high yield of oil therefore closely related t o the water content, with the solids but not so low that the successful operation of the plant was content playing a minor role. This is illustrated in Table VI11 jeopardized. It is believed that a detailed analysis of coker diswhere heat requirements for different compositions of feed are tillate using wet crude feed will show similar results. The coker shown including, for comparison, data on raw bituminous sand. distillate waa vacuum distilled into seven cuts and the following It was found that the solids content of the feed did not appear determinations were made on each cut as well as on the comto change the bed inventory. This suggested the use of a coarse posite: specsc gravity, refractive index, sulfur content, viscoscatalyst in place of the inert sand. Some exploratory runs with ity; asphaltene, resin, and oily material; and aromatic, acida silica alumina catalyst have been made. Much higher yields of soluble, and acid-insoluble material. gasoline, process gas, and coke were obtained with a resultant The asphaltenes, resins, and oily material were determined as reduction in the total oil yield. This work is continuing. follows~
.... ,...
3.3 2.7
6.8 6.0 Nil 1.66
5.7 5.2
8.2 7.7
4.5 4.3
A 5-gram sample was dissolved in 50 ml. of benzene. This was evaporated to a small volume and poured into a large excess of nentane. The asphaltenes (including asphaltous acids and angydrides) precipitated out aa a flocculent brownish powder This was allowed to settle overnight, then filtered off washed with a small amount of cold n-pentane, dried a t 105" C., and weighed. When dried the asphaltenes were brown to black in color. They had a specific gravity of 1.110 and a molecular weight of about 3000. '
Resins and oily material were determined chromatographically using fuller's earth as adsorbent. The oily material was desorbed by n-pentane and the resins by a 9:l benzene-methanol solution. To determine the oomposition of the various cuts, the following procedure was used: A 50-ml. sample was measured into the top of a column containing activated silica gel. The paraffins, naphthenes, and olefins were swept through with n-pentane. A saturated solution of phosphorus pentoxide in sulfuric acid at 0' C. separated this material into acid soluble and acid insoluble. Normally, this method is used to determine olefins and parafEns plus naph-
16.7 16.6
50.3 53.0 1.03 26.6 71.7 ,
References
(1) Adkins, W.E.,World Petroleum, 20,40-5 (December 1949). (2) Blair, S. M., Government of Provinoe of Alberta, Edmonton, Can., Rept. on Alberta Bituminous Sands (1950). (3) Clark, K. A., Can. Oil and Gas Ind., 3,46-9 (September 1950). (4) Hume, G. S., Trans. Can. Inst. Mining & Met., 50, 298-334 (1947). (5) Peterson, W. S.,and Gishler, P. E., Petroleum Engr., 23, C66-C74 (April 1951). (6) Warren, T.E.,and Bowles, K. W., Eng. J.,6,597-600 (1947). (7) Warren, T. E., and Burrows, E. J., Can. Oil and Gae Ind., 3, 32 (January 1950).
RECEIVED for review February 27, 1952. ACCEPTED March 28. 1952. Contribution from the Chemical Engineering Section, National Research Council, Ottawa, Can. Information in this paper was p r a e n t e d at the Athabasca Oil Sands Conference, Edmonton, September 1951 and is contained in the Proceedings available from the Government of the Province of hlberta, Edmonton, Can.
