p
rbw---
. .
o f b i ~ d p p e d u o e s a %inch pipe llrppe welded at the &set. The retort is joined at the bottom by &sage to an offnet, truncated dieemgaging member whiah 0Ont.isa the inverted weir. The stirring element, whiah occupiw &upper one fonrth of the retort,in made of twe &inch Ienstha of 0.Ylfrinh stainlea a h 1 weld rod, bent an ahown and I . * c a o o v s b r ~ u a t . Q C L l r a d J M p r d m i n tbe umtd 8t.ta u limited to t a c 4 - M ’to Ooaara which in tmn m taoW to tbs ahnIt. dpit6hin modibsdKoppen oven,the Currsn broed of 0250 x 0.069 inch iltabkw stsal tubing to fit over the rounded end of a 6xed ahdt of ooa,.nddekyeddrumookers. h u y , m b . Alignmentoffhsdryythusformedw .#sotiso b h e u ~d k t e d towcud d t d o p m t d ~oamplishadby a themnowell of 0.1% X 0086 inch steinlns mntiopR(IcDcm” (4-6) in which pitch w spreadand mtedina thin 6lm on a contact ooke which mrvm M the heatsom. The tubing which coutaioe thrw gladnmhted !28 B and 5 &age thermocouples npnced 6 inch- apart. The thmowell may he Diao Co., now a dirbion d Pitt.boab oaaaolldation Coal Co., probed M much M 8 inched from ita u d nference pwition-i,e., t a l s continuous robry-kiln caking pmcea (8) on a semimth the tip opposite ths d e inlet. The rotating &inwshdt, m b acah for eeveral yeam in the 1940’s. ‘‘Tk aonatruation of a rotuty kiln, amall enough for evaluation fued shaft, rmdthemnowd eaah are sealed outaide the &rt by not fesaible. Cr&pEimmtal qwl$ltiw of md tar pi-. small glen& madeFmm atandard brasstuhecompresaion fit+. The stirrer ahdt in m e c t e d by d v e d joint to a p1wbwore, thaulthonbeliwedtbat themsthod of t r M c k n‘ 0I sui(able gear motor tbat pmdum 62?.p.m. at 43 hch-pbtmda of ” m r a a mmiaat moa to a thin Bim d pitch would he dmib, toque. The retmt ia m p p r t e d on a line raoL by 0.50-inch xcampli&il m a robry hiln or gmvity-flow vertical round mds welded to the retort Banpe. dt.a,dtwevaluation of the eaet of t.3mpmbne on pmdnct distribution and propertiw in one tJpe d system Heat loaa from the retott ia mmpermated hy three reeiatsnce windings, ea& of IO00 wattd oapdty controlled by a vsliabls would he applicablato the other. !mnaforn~~nnd c a d l i n g ofhelidly coiled Nichmme V reaiat For them reamom a d moving bed contact ookino qapMtua anw airs wound around the retort Owr b layer of 0.016inch sheet mu developed and ued over a range of temperaturen to coke d c a and W d e d in h d u m cement, A themaeonple ia espimental md tar pitEhes d a heavy petmleum reddue. h t e d ab the mter of eaoh winding betwean the retort nail and @c&nt m a W bdanced mobtained on lem than om pound ita miaa sheath. The retort m well lagged w i t h a I-Inch layer dF4tfh Iaed Durior a typicd chow material halanoe period Dimulsted and it. weight eaoh of high teaaperptore and 85%ma(pleds b l d insulstion. A 4 pound. of coke fourtb heater of Nichrome V &his permahenay instdled on iDsMsolmrved at the mduion of the run liquid pmdnuots the dieengaging mxnb Mow the 0ange and controlledfrom two wam rawvered in amounts dicimt for &tillation and inapstion *iqwPmwb* oassppmsohpoetab dipnal eo& of co!iing thae pirsaa Q dlr(.rJuJ3b liquid produat.forthe ohanid market and a
,
pa
ywhrn br*lc( Cddna Appamhvs 0-
on h s lhan O m Pound oi liquid hd
The Bow of uteri& is traced on the schemati0 flow diagram shown in Figwe 1. Coke pellets flow by gravity from a hopper Unongh a @eater into the retort, w b m they ure wetbd by pitah through t8e mtlon of a etirrer. Coke and vapom move down& tlnvugh tbe retort to an invertad weir whera they are reppstw Ths coke, atripped by nitrosen PUW gas, p ~ s e out s twatgh a ndidn Bm controllel into a d v e r . Make gas. +a@+&, and n-i pttgs gas are led thmugh a etepwim condeyz3tion trsin -oc of a p a i knockout pot at 2400 a pstg-moled oondprmpo;and dry iw-ac%tonecooled traps. Glass 401plag insertsdin $he e@nent line fmm eacb trap m o v e fog ahplh, and(heCles0p M spot sampled, metered, and vented. Theretort, collamlM entjrely ofTYpe304 staid= Bteal e&&b of an lainch section of %inah ached& 40 pipe (Figu?e Bbort d o n a of Bnaller diameter pipe m welded at the ?). @p, M ,duxvn, to provide for entrance of the pitch feed line. .Liner Wt, and pmheated mke. A thenrewell of0.125 X 0.025 iach ltsinlessteel tubing extendB into the cokeinlet port through
c.,
.bintJlemmmplea Insulstionoftbispartofthelstortia m o n d h and m& eakntially Oi asbwton cloth paaS held in plaosbYsskaQtapa The cake prtaesC conalsts of */,-inch stainleas e t d p i p 27 inohw long which is wnne~tedto the retort by a +&le iron d o n and to the hopper at the top threugha glam pipeuightglass. Two 1OOO-watt Nichmme V ribbon Haiatance windings, perme nentJy installed and cantrolled M in the rat& heatsrs, provide d c i e n t Qpacrty to heat (to 850‘ C.) a atream of coke pellets Bowing at 10 gram8 per minuta. The ahort seolion of 8 J & c h stdnlesa asel pipe, welded to the retort but conaidered part of the coke preheatm, w heated by a third,permanently inadled winding. COMeded in & with thin heater w a short, removable length of a s b e s t o w o v e r e d Ghromel rasiatanoe wire that prevents heat loas from the union. Glsss aspirator bottles of I-liter oapacity serve M combination receive&oppera These are c a d by 1-inch bore rubber tubing through abort pipe inaertS to similar ruhber tubing permsnenUy attached to the dght g l w above the pmheater and to the funnel spout of the solid.flow controller. Tbia Pmmngemmt pmvidea a dmple and rapid meslul of intedmghg hopper and receiver. Obuervation of the edida Bow rate in made hy weighing each receiver at the tims of change.
I N D U S T R Z A L A N D E M 6 1[ N E E B I N G C H E M I S T R Y
vPt-*Irlo-l
8
,
-,
PILOT PLANTS ~
The solids flow controller consists of a 5.5-inch diameter aluminum drum, 1.5 inches wide with 0.0625-inch rims and a knurled tread, mounted on a shaft just below a J/Anch pipe stand leg. Clearance between the stand leg and knurled surface is adjusted to about twice the average coke pellet diameter. The drum is rotated a t a predetermined speed through worm gears
w
-RECEIVER-
THERMOCOUPLES
SKIN
1-13
STREAM 14-17
HOPPER
Nt
~I-COKE
PREHEATER
AMPLE
VENT
PI FEEDER
location of skin and stream thermocouples so that a temperature differential between preheated coke and the mixing zone of the retort could be observed and maintained. The unit is lined out with continuous circulation of coke pellets preheated to about 25" to 40" C. above the retort skin temperatures. Vnder these conditions the bed temperatures in the mixing zone are about 15 to 20" C. below that of the preheated coke. When pitch feeding is begun, however, the temperature of the mixing zone drops immediately to that of the skin or slightly higher. The temperature differential is consistent with the coke-to-pitch weight ratio employed and an estimated heat of vaporization of the pitch feed. A description of the experimental procedure follow: All parts of the apparatus are heated overnight under nitrogen purge to the desired temperature levels. A weighed batch (1800 to 2000 grams) of previously devolatilized coke pellets i b charged to the unit, and the temperature of the bed is brought to the predetermined coking temperature. Coke withdrawal arid stii ring of the top of the bed are begun, and the unit is lined out at the desired coke preheat and bed temperatures. At the same time pitch feed is heated in a 600-ml. beaker to 5 to 7" C above the feeder jacket temperature, drawn into the pitch feed cylinder and given approximately an hour to reach temperature equilibrium. The pitch feeder is started and transfer line valve opened. A t a typical pitch feed rate of 0.97 to 0.98 gram per minute about 10 minutes are required to fill the transfer line. A burst of fog in the glass condenser and a perceptible drop in the temperature of the top of the mixing zone in the coker indicate that pitch has
SOLIDS FLDW CONTROLLER
RECEIVER- HOPPER-
Figure 1.
b'
N STRIPPED &HEATED COKE
PITCH KNOCKOUT POT
Schematic Flow Diagram of Miniature Moving Bed Coking Apparatus
%INCH PIPE RY BEARING DRY
driven by an 82-r.p.m. gear motor. A typical drum revolution of 0.5 per minute results in a coke flow rate of 8.3 0.3 gram per minute over 3- to Cminute intervals. A gross change in flow rate is accomplished by changing worm gears, and minor changes are made by adjusting the clearance between stand leg and drum. The drum is enclosed in a gas-tight, metal box which is tested a t pressures well in excew of the water actually observed. A builtin metal funnel delivers solids from the rotating drum to a receiver as described above. Pitch was pumped from a continuous, nonpulsating, syringetype feeder identical with that previously described by Jones et al. (3)of this laboratory except for the method of heating. In this application the steam jacket was replaced by a n electrically heated air jacket to permit feeding of pitches having softening points as high as 150' C. ring and ball. Connection between the 2-inch diameter glass cylinder and the metal transfer line is made through a 0.25-inch glass pipe flange using a glass-to-metal adapter with a silicone interface gasket. The usual pressure gage or spring-loaded check valve as a safety precaution against pressure buildup due to plugging is not feasible for handling heavy pitches. Instead a small bellows, filled with hydraulic fluid and equipped with a small pressure gage, is inserted between the piston rod and the worm drive clutch to indicate instantaneously and continuously any resistance to movement of the piston. Preheated Coke Pellets Furnish Heat for Vaporization a n d Coking
A principal objective of the work described here was to supply, by means of preheated coke pellets, the heat required for partial vaporization of pitch and for subsequent coking of the unvaporized fraction. Particular attention was paid to the January 1954
P ~ E S S U R ETAP Y l N C H PIPE PROBE THERMOWELL
/I "kl" ll
'MINIMUM ANGLE
Figure 2.
Retort
reached the coke bed, marking the beginning of the run. In a typical run of 3.5 to 4.0 hours, several probes of the coke bed temperature are made and pressure drop, met test meter data are recorded at frequent intervals. Several sets of spot gas samples are taken. Each time the coke hopper empties, the rubber sleeve between solids flow controller and the receiver is pinched off, the receiver is weighed, and the two bottles are interchanged, providing a coke flow rate data point. At the conclusion of the run, pitch feed is stopped and withdrawn from the transfer line into the feed cylinder while the flow of coke continues. When tar fog subsides (usually after 2 to 3 minutes) the nitrogen purge rate is reduced, and the pitch knockout pot and condenser are drained, removed, and weighed.
INDUSTRIAL AND ENGINEERING CHEMISTRY
13
ENGINEERING AND PROCESS DEVELOPMENT The cold traps are removed, wiped dry, weighed, and returned to empty Dewar flasks. A small nitrogen purge is sent through the traps to a gas holder, and the temperature of the traps is increased in stages to 60' C. by addition of water to the Dewar flasks. After 30 minutes a t 60" C. the cold traps are wiped dry and weighed. Meanwhile the pitch feed rate is calibrated under run conditions, and contact coke is drained from the apparatus, weighed, and the unit is cooled overnight under nitrogen purge. On the following day the retort is opened a t the flange and inspected; any accumulation of coke pellets is removed and weighed. Generally, about 20 grams of agglomerated coke pellets are found above the stirrer near the pitch feed inlet tube. Experience showed that these agglomerates were formed in the first few minutes of the run and contained less than 1% of the pitch feed as coke. Petroleum Feed Stock Yields Two Distillate Cuts and a Residue Liquid feed to a run is based on calibration of the feeder under operating conditions. Liquid products are combined from the pitch knockout pot, condenser, and cold traps after stabilizations and are distilled through a 1-inch by 3 - f O O t Vigreaux column with reflux head and electrically heated air jackets. In the petroleum feedstock, two distillate cuts, corresponding roughly to crude gasoline and gas oil, and a residue are obtained. Holdups in the various recovery vessels, measured by weight difference from the cleaned apparatus, are assigned to the various liquid products as follows: Holdup in the pitch pot amounts to about 1% of the feed and is assigned to the +360° C. residue; holdup in the condenser comprises about 2% of the feed and is credited equally to the crude gasoline and gas oil distillate fractions. Recovery of cold trap contents after stabilization is essentially quantitative, but any holdup is credited to the crude gasoline yield. 100
90 80 70 60
SO
Properties of 18% Reduced Kuwait Crude
Gravity OAPI Specific 'gravity 140/25O C. Softening point' R & B 0 C. Carbon residue,' Conradson, wt. % Ultimate analysis Hydrogen Carbon Nitrogen sulfur Hydrogen t o carbon mole ratio
Table II.
6.0
0.955 42 20.9 10.30 84,OO 0.31 5.37 1.47
Contact Coking of 18% Reduced Kuwait Crude
Run No. Temperature O C. Preheated hoke pellets Coke bed average Preheated pitch Knockout pot skin Coke flow rate grams per minute Pitch feed rate' grams per minute External coke 60 pitch weight ratio Calculated vapor residence time, sec. Nitrogen purge prtrtial pressure, atm. Duration of run, minutes Product distribution distribution. wt. % 91, of feed Gas Ca and light& Cruhe gasoline c4+ t o 2000 C. Crude gas oil, i00-360'' C. Pitch, +360° C. Coke Total
41
42
43
39
523 503 204 250 8.2 0.97 8.4 40 0.57 240.0
575 550 219 250 8.3 0.98 8.5 32 0.46 241.3
617 582 213 250 8.4 0.97 8.7 29 0.42 235.1
627 588 219 254 9.3 0.98 9.5 23 0.42 234.0
6.5 15.1 17.4 41.6 18.5
15.1 22.4 15.9 26.9 17.0
21.5 26.2 10.0 16.8 20.2
24.1 27.1 9.1 14.5 21.8
99.1
97.3
94.7
-
-
h
&
~
-
96.6
and weighed just before use to correct for any observed increases due to adsorption of atmospheric moisture and carbon dioxide. The surface of the coke was smooth, and a substantial proportion of the pellets was round, contributing significantly to the smooth flow characteristics observed. Product gases were analyzed by Orsat, Tutweiler, infrared, and gravimetric techniques and calculated on a carbon monoxidecarbon dioxide-, oxygen- and nitrogen-free basis. Gas yields calculated from Orsat, Tutweiler, and infrared analyses were in good agreement with those calculated from gravimetric analyses. The latter method analyzed for carbon dioxide, carbon, and hydrogen according to a procedure published recently by these laboratories (I). Coking of Reduced Petroleum Crude Furnished Operating Data
40
30 20 10
530
Figure 3.
550 570 590 610 COKE PREHEAT TEMPERATURE, 'C.
630
Effect of Temperature on Product Distribution
Stabilization gas from the dry ice-acetone cooled traps is principally Cp-Ce olefins and is reported as crude gasoline. The weight loss of the traps after stabilization is usually in good agreement with that calculated from gravimetric and infrared analyses and represents, generally, from 3 to 5 weight % of the pitch feed. The yield of green coke is determined by measuring the weight increase of circulation coke a t the conclusion of a run. Coke pellets used in this work comprise an 8 X 16 mesh fraction of product coke from the rotary kiln coker operated by the Disco Co. A large batch of coke is devolatiliaed a t 800" C. in the moving bed unit and collected in separate weighed batches of approximately 4 pounds. Each batch was stored under nitrogen
14
Table 1.
A sample of 18% reduced Kuwait crude, furnished by the Gulf Research and Development Co., was coked a t several coke preheat temperatures ranging from 500" to 650' C. Inspections on the feed stock are shown in Table I. Experimental conditions, yields, and distribution of products are presented in Table 11. The yields of gas and crude gasoline increased by a t least 100% as the coking temperature was raised from 525" to 625' C., while those of crude gas oil and recycle pitch decreased by about 50%. At the lower temperatures the yield of coke decreases with increasing temperature, being controlled apparently by the proportion of heavy pitch remaining on the coke after the lighter constituents are flashed. This effect is overcome a t the higher temperatures by increased vapor phase cracking, resulting in a minimum coke yield a t 550" to 570" C. These data, adjusted to recovery basis, are shown graphically in Figure 3. Inspections of the light and heavy distillates, pitch, and product gas are presented in Table 111. The decrease of hydrogen to carbon mole ratio and increase in specific gravities of the distillates with increasing temperature indicate increased aromatization of the liquid products with increasing temperature, probably due to selective cracking of the paraffinic constituents. The product pitch was softer than the feed a t the lower coking temperatures but harder a t the higher temperatures. The distribution of sulfur in the products is of interest and is pre-
INDUSTRIAL AND ENGINEERING CHEMISTRY
Vol. 46, No. 1
*
PILOT PLANTS Table 111.
Product Analyses
Run KO. Coke preheat temperature, C. Gas, to Cs, Mole %,smoothed data Hydrogen sulfide Hydrogen Methane Ethane Propane Ethylene Propylene Stabilized crude gasoline, C; to 2009 c . Specific gravity, 25/25' C. Hydrogen Carbon Sulfur Hydrogen to carbon mole ratio Crude gas oil 200-360O C. Specific grivity, 25/26' C. Hydrogen Carbon Sulfur Hydrogen t o carbon mole ratio Pitch residue $360° C. softening ploint, R & B, 0 C. Hydrogen Carbon Sulfur Hydrogen t o carbon mole ratio
Table IV.
41
42
43
39
523
575
617
627
6.5 1.4 32.2 19.8 12.1 11.5 16.5
4.8 3.2 34.3 18.1 9.6 15.0 15.0
2.8 4.6 38.9 16.5 7.0 17.2 13.0
2.5 5.0 39.9 15.8 6.5 17.7 12.6
0.751 13.62 85.72 0.68 1.91
0.763 12.58 86.78 0.62 1.74
0.802 11.63 87.52 0.83 1 . GO
0,831 10.75 88.05 1.18 1.47
0.873 11.88 84.55 -3.41 1 .69
0.901 11.16 84.98 3.78 1.57
0,970 9.17 85.13 5.60 1 .29
1.004 8.37 85.62 5.90 1 .17
14 9.97 84.20 5.66 1.42
30 8.35 84.01 7.29 1.19
78 7.33 83.46 8.91 1.06
~~
L 00
6.49 83.87 9.31 0.930
Sulfur Content and Distribution in Products
Run No. Coke preheat temperature, C. Sulfur, wt. % in gas (as HIS) Stabilized crude gasoline Crude gas oil Pitch residue Coke plus loss Distribution of feed sulfur, n t . % Gas (as HtS) Stabilized crude gasoline Crude gas oil Pitch residue Coke plus loss
41 623 7.5 0.68 3.41 5 66 10 1 9 2 11 43 35
42 575 5.3 0.62 3.78 7.29 10.6 16 3 11 36 34
43 617 3.5 0.83 5.60 8.91 10.8 15 4 10 28 43
39 627 3.2 1.18 5.90 9.31 11.1 15 6 10 25 44
sented in Table IV. Sulfur in the gas was calculated as hydrogen sulfide. Sulfur content of the coke was obtained by difference, since direct analysis of the thin film of product coke was not feasible. The concentration of feed sulfur shifts from the pitch at the lower coking temperatures to the coke a t the higher temperatures. It is possible, of course, for some sulfur to be lost by reaction with the metal retort. A noticeable effect of temperature on the rate of coking was observed in this study. ,4t a temperature 15' C. lower than those reported in this work the coke left the agitated zone with its
surface still wet with pitch, resulting in agglomeration of the bed below the stirrer. Residence time in the stirred zone is estimated a t 30 to 35 minutes. In other runs, a t 15' to 30" 0. higher than those reported, the pitch coked before it could be mixed with incoming coke resulting in an agglomerate plug across the pitch feed opening. Thus the time required to set up a semicoke ranges from a few seconds or minutes to a half hour or more in the temperature range 525' to 650" C. for this particular feedstock. For experimental coal tar pitches studied, a similar effect of temperature on the rate of coking was observed but a t a slightly lowered temperature range. In general higher yields of coke than those reported for the petroleum feed stock reflected the lower hydrogen to carbon mole ratios of the coal tar pitches as compared with that of the reduced Kuwait crude. Finally the effect of temperature on product distribution was less pronounced for coal tar pitch than for the petroleum residue. Summary
A miniature moving bed contact coking apparatus has been described from which basic process data were obtained from less than 1 pound of liquid feed. The effect of temperature on product distribution and properties was presented for the singlepass coking of a heavy petroleum residue. The apparatus and technique described appear to have utility in fields other than the coking of coal tar and petroleum pitches. Specifically the unit currently is being used, without agitation of the bed, for vapor phase contact catalytic studies, in which a catalyst of changing activity is involved. Literature Cited (1) Barthrtuer, G. L., Haggerty, Alice, and Friedrich, R. J., Anal.
Chem., 25, 256-9 (1953). (2) Davies, Caleb, Jr. (to Pittsburgh Consolidation Coal Co.), U. S. Patent 2,575,587 (Nov. 20, 1951). (3) Jones, B. W., Jones, S. A , , Neuworth. M. B.. IND.ENG.CHEM.. 44, 2233-4 (1952). (4) Miller, Max B. (to Max B. Miller & Co.), U. S. Patedts 2,314,112 (March 16, 1943), 2,323,501 (July 6, 1943), and 2,364,492 (Dec. 5, 1944). (5) Rex, Walter A. (to Standard Oil Development Co.), U. S. Patent 2,608,526 (Aug. 26, 1952). (6) Smoley, E. R., and Schutte, A . H., Petroleum Processing, 7, 348 (March 1952). RECEIVED for review June 15, 1953. ACCEPTEDSeptember 24, 1953. Presented before the Division of Petroleum Chemistry, 123rd LMeeting, A M E R I C A N CEMICAL S O C I E T Y , L O S Angeles, Calif.
END OF PILOT PLANT SECTION
January 1954
INDUSTRIAL A N D ENGINEERING CHEMISTRY
15
