Thermofor Catalytic Cracking Unit J
S. C. E-ISTWOOD, C. V. HORNBERG, i S D A. E. POT.4S
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Socony- P‘ucuurna Laboratories, Division of Socori? I.aciciina Oil Co., I n c . , Research and Developmerit D e p a r t m e n t , Paulsboro, .Y. J .
n e ‘l’lieriiiofor catalytic cracking pilot unit described is used primarily for the study of process variables and the c\aluation of charge stocks. These studies proTide the information required to conduct commercial operations a t the highest economic level, thereby obliating expensive full-wale experimentation. The pilot unit is used also to compare new catalysts with those in present commercial senice. I t is one of several pilot units which were employed in the original development of the Thermofor process t o obtain basic engineering information on catalyst f l v ~ characteristics, cracking yields, and catalyst regeneration. This engineering information was used to design a n integrated unit to produce 500 barrels per day, wrhich preceded the first full-scale commercial installation of the process in 19G.
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RGINIRATID CAlALYST HOPPER
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Figure 1.
Simplified Flow Diagram ,of Reactor and Kiln
Figure 2.
1685
Pilot Unit
1686
INDUSTRIAL AND ENGINEERING CHEMISTRY
T
HE Thermofor catalytic cracking process has been described in detail ( 2 , 3,4. Its essential elements are a reactor for continuously contacting hydrocarbon feed with a moving bed of granular catalyst to effect part,ial conversion of the hydrocarbons, and a kiln for removing carbon x-hich is deposited on t,he catalyst in the cracking operation, by controlled combustion with air. T h e catalyst flows by gravity through both vessels, n-hich stand side by side, and is transferred from the bottom of one t,o the top of the other by means of bucket elevators. The system is illustrated by the simplified flow diagram shown in Figure 1. Commercial units have charging capacities ranging from 4000 to 20,000 barrels per day and catalyst circulation rates ranging from 75 t o 150 tons per hour. T h e pilot unit is designed to simulate and study the reactor part of t,he commercial Thermofor catalytic cracking system. T h e related operations are conducted batchwise in separate laboratory equipment for simplicity and economy. Thus, the spent catalyst is regenerated for re-use in a small Thermofor kiln which is operated int,erniitt,eritly arid the liquid product froni the reactor is fractionated in batch stills to provide the desired fractions for yield and quality determinations. Furthermore, the time required to establish equilibrium conditions on the pilot unit is minimized by divorcing the catalyst regeneration and product fractionation from the reactor operation. PILOT UNIT
Vol. 39, No. 1 2
the reactor are condensed and the total liquid condensate, or "synthetic crude," is separated from the cracking gas. T h e cracking gas passes through a back-pressure control valve to a gas meter and is vented after sampling. The synthetic crude flows through a water separator and, if the operation is of the once-through type, is discharged through a level control valve into a product accumulator. I n the case of recycle operation, the synthetic crude is fed into a two-tower fractionating system where a recycle stock is separated and returned to the reactor. Carbon dioxide is employed as seal gas on the catalyst inlet and outlet lines t o prevent the escape of oil vapors from the reactor a t these points. The carbon dioxide feed to the top seal leg enters a t the bottom of t,he catalyst preheater and a portion of it is withdrawn from the top to dehydrate the descending catalyst, thereby simulating freshly regenerated catalyst typical of commercial operation. EQUIPMENT
The equipment operating above 600 F.-Le., the catalyst and oil preheaters, react,or, and connecting piping-is fabricated from 18-8 stainless steel. T h e other parts of the unit are constructed of carbon steel. The major pieces of equipment are described below. . CATALYST PREHEATEB. T h e design of the catalyst preheater is shown in Figure 5. Heat is supplied by four 1.5-kx. heaters,
The pilot unit occupies a floor space 13 feet square and has an over-all height of 28 feet. I t has a maximum oil charge capacity of 2 barrels per day, a catalyst throughput rate up to 60 pounds REPRESSURING per hour, and can be operated a t pressures u p t o 50 pounds per HOPPER SUPPORT square inch gage and temperatures up to 1100" F. The minimum , CATALYST quantity of catalyst required to operate the unit continuously is 450 pounds. T h e oil charge requirement varies between 15 and 30 gallons for each run. The general layout of the pilot unit is shown in Figure 2 with the oil feed system on t,he lower left side, the reactor in the center, and the gas meter a n d fractionating toivers on the right. T h e operator is adjusting the variable-speed drive x-hich controls the catalyst rate t,hrough the unit. S L I P J O I N T M The flow of oil ahd catalyst through the pilot unit is shon-n dia_ WATER _ DROP ~ OUT_ POT _ grammatically in Figure 3 and described below. WATER CATALYST FLOW. Catalyst f l o w by __ BURET gravity from the supply hopper a t the top of the unit through the catalyst preheater and reactor. A catalyst meter P A R T I C COh below the reactor discharges the catalyst a t the desired rate into the spent catalyst receiver. A11 the piping between vessels is 1.5 inches in inside diameter or larger to assure free flow of 4- t o 10-mesh commercial catalysts used in t h e Thermofor process. .4s the unit is operated under pressure ( 5 t o 20 pounds per square inch gage), a pressure lock system is provided at the top and bottom of the unit t o permit charging and discharging catalyst Rithout interrupting t h e operation of the reactor. L Figure 4 shows the laboratory ThermoBACK CO, FOR for kiln used for regenerating t h e spent PRLSSJRE A CONTROLLCR REPRESSURING catalyst from t h e pilot unit. OIL FLOW.T h e oil feed is charged by means of a Hills McCanna Type RM2F pump from burets through t h e oil preSYSlEM heater and into the reactor. Process 1 .INU 1 cb, eteam is added at regulated rates as deSYNTHCTI; CRUDE sired by pumping water from a buret T O RECEIVER O R f RACTIONATORS through a vaporizer to join the oil stream PROCESS in the preheater. T h e hot vapors from WATER Figure 3. Flow Diagram of Pilot Unit
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December 1947
INDUSTRIAL AND ENGINEERING CHEMISTRY
one of Tvhich is provided wit,h voltage control, so that the heat input can be varied manually from 0 to 6.0 kw. This preheater has 9.2 square feet of heat transfer surface including the internal fins, and i h capable of heating 60 pounds per hour of catalyst (0.25 average specific heat) from 100' to lloOo F. REACTOR.T h e design of the reactor assembly is sh0n-n in Figure 6. The reaction zone is 3 inches in diamet'er by 18 inches long and has a volume of 1.75 gallons. This reactor is designed t o operate adiabatically along its entire length, so as t'o duplicate the tempi,rature pattern that occurs in a commercial Thermofor catalytic. cracking reactor as the result of the cndotherniic heat of crackirlg. This is accomplished by dividing t,he reactor zone into five sections of equal length and providing each section n-ith an individually controlled electric heater wound on the first layer of insulation to prevent heat loss from the reactor proper. d t ' the mid-point of each adiahatic section one thermocouple is attached to shell of reactor and another is embedded in the center of first layer of inwlation on the reactor. The electric heater is adjusted so that tlie teniperature readings a t these t x o points are balanced to n-ithin 10' F. The average cracking temperature is obtained by iritvgrating the temperature pattern through the reactor. Thr: imctor is designed t o permit operation with either concurrent or countercurrent flow of oil and catalyst. K i t h vaporized feid stocks either type of flow may be used. However, only concuri~entf l o r is employed n-ith stocks which are not completely vaporized and a nozzle is used to distribute the oil on the catalyst. The iiozzle with auxiliary equipment is sh0Tv-n in Figure 7 . The purge section below the reaction zone (Figure 6) simulates commercial operation as t o catalyst residence time and temperaturc, the only difference being that carbon dioxide is used instead of steam in the pilot unit. (?.~T.ILY.ST METER. A special catalyst meter is used t'o control tlie rate of flow of catalyst through the reactor. Comnicrcially thi.q i q accomplished by a valve in the catalyst discharge line from the reactor. The use of a special mechanical device in the pilot unit is necessitated by the fact that the desired small flow rates cannot be controlled by orifices. Such a device must also be capable of handling commercial-size catalysts n-ithout crushing. The design of the catalyst meter is shown in Figure 8. This nirter can deliver 4-t o 10-mesh size catalyst without breakage a t a rate ranging from 8 t o 60 pounds per hour. OIL PREHE.ITER. The oil preheater consists of a 4-inch outside dimieter helix coil made of 44 feet of '/,-inch pipe concentrically supported Ivithin a 6-inch diameter shell 45 inches long. Heat is supplied by means of five 2-kn-. electric heaters nrapped on the shell in parallel. This shell in effect acts as a radiant' heater. Proccss steam enters the oil preheater coil a t a point about 15 feet from the outlet. ('OSDENSISG Si-smir. A two-stage condensing system is used to cool the cracked vapors from the reactor (see Figure 3). Tube and shell-type condensers are used in both stages to prevent frcquerit fouling Kith catalyst fines and to facilitate cleaning. Although only a small amount of catalyst fines is carried out of the reactor by the cracked vapors, i t would be sufficient t o plug a helical coil condenser. The first stage or "partial condenser" operates a t about 260" F., while the second stage or "final condenser" operates a t cooling water temperature. Both condensers are operated with the pressure in the shell side higher than t h a t in the tube side, so that any leaks which develop immediately shorn up as unaccounted for water in the product. \Then processing waxy stocks the condensate from the first condenser is n-ithdrarr-n hot to a separate receiver; ot,herwise this stream passes t o t.he second condenser where the total liquid product and cracking gas are separated. The liquid product from the final condenser passes through a water settler and the waterfree synthetic crude is discharged by a float control valve to a product accumulator. FR.4CTIorATIso TOWERS. Two packed ton-ers Rhich have a fractionating efficiency equivalent t o about 10 theoretical plates
1687
Figure 4. Thermofor Kiln
are used in recycle operations to prepare the desired boiling range recycle fraction continuously from the synthetic crude. In thia type of operation the condensed s>-ntheticcrude is fed through a preheater into the first tower wbere unstabilizeti gasoline i s taken overhead. The bottoms flow into a second tower where a gas oil fraction is taken overhead for recycling xhile the bottoms are rejected. If desired, t,he total bottoms from the first ton-er may be recycled t'o the reactor without use of the second tower. All recycling is done continuously and automatically with a minimum of liquid holdup in the system. The unit. is supported rigidly at the top of the USIT SVTPPORT. catalvst supply hopper and a t the top of the reactor. The catalyst, feed line from the supply hopper enters the catalyst prelicatcr through a packed slip joint, permitting upward expansion ahove the reactor. Expansion don-nmard from this point is provided for by counterweight, suspension of the bottom of the unit. Ausiliary equipment such as oil preheater, product condensers, and fractionating towers are suspended from the main support of the unit. Heat loss from the reactor is minimized by inserting '/,-inch mica betn-een the reactor and its supports. KILX. -2 Thermofor kiln is used t o regenerate catalysts for several pilot units. I t p-ill regenerate about 300 pounds per hour
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I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Vol. 39, No. 12
INDUSTRIAL AND ENGINEERING CHEMISTRY
December 1947
TABLE
1.
COMPARISON OF
Cuini.aricon Charge stock
PILOT U X I T THERYOFOR CATALYTIC C R A C K I N G (Concurrent Bow operation) 1 2 3 Paraffinic Paraffinic Paraffinic Light gas oil Light gas oil H e a v y gas oil
COM1fERIChL AXD
(:rayit), A . P . I . .$nilin? point, F, .Suliur, :7c u t Carbon residue, 5 x t , .4.8.T.M. di-tillation. F I.R.P. 10 L; SO C,
q0q End point
Catalyst a c t i v i t y O p y a t l n g conditions Catalyst inlet teiiiprrat2re F. inlet temperature, F. I o t a l space velocity, I-i'hr./l' Recycle ratio, recg-cle,'freah feed C n t a l p t 'total oil, vo:unie Oil llnrtial p r e s i n r e ( a v . ) . p.c.i.p T o t a l presSure, p , ? i.p.b
ci!
Ca-free liqiiid recovers, D r y pas, c'c wt. Coke, 5 1vt.
R
vo1.
r. a t 90% motor gaiqline Bielrl. r: volnine of f r e ~ l i - f e ~ d O c t a n e rating. F-2 clear 1 re. TEL I 3 cr. TEL
10 ttV1' 3jGC
F-I
DATA 4 Saphthenic Heavy gas oil
33.5 170 0.31 0.03
34.1 172 0.32 0.02
31 . O 174 0 43 0 7(J
27.4 155 0.31 0.;1
370 512 601 712 730
395 511 590 672 714
392 453 608 801
472 548 fi40 817
Plant Pisnt Pilot 11ixed p h a s e 1 1 i x d phase Alixed plia-e
l'iior I l i x c d phase
Vapor
Pilot Vapor
Plant Vapor
Piiot Vapor
3i i
36.0
36.6
36.0
31 0
3 5 , (1
36 0
1.10 0.59 1.84 .i4 5 4
939 851 1.10 0.59 1.87 6.0 10.0
955 666 1.69 0.74 1.22 9.5 9 . .j
955 866 I , 62 0.ii 1.26 7.2 10 0
1000 870 0.76
I001 877 0 78
9G7 827 1.03
i
0 00
I1
26.6 9.7 3.3 4.3 99.2 6.I 4.7
34.2 Z.5.8 il.5 4.83.i 100.0 6.4 5 1
49.0 36.1 i.6 3.2 3.9 99.8 6,2 3.5
47 8 36.0 9.2 3.0 4.0 100.0 6.0 3.3
3b 7 48.2 5 4 1 7
33.7 47.6 6.3 3.4 4.6 97.6 7.3 4 2
39,9 52.8
Plant
K-nit T y p e of feed
1689
935 848
n nq
5.4
97.4 7.2 3.2
30.0
4,:
;:: 102.1
3.9 3 .0
$172 833
us
n
42.0 46.2 8 1
2.i 3.1 in1 5 .r1 2 3 8
38 3
56.3
. j l ,3
48.1
3s 6
37.7
42 9
I? 5
+
79 8 84.7 87.2
80.8 54.9 88.3
80.0 84.6 87.9
80.3 85.2 87.9
80.3 84.4 86.0
80.0 82.9 86.1
79.6 84.1 87.2
so n
c,lear 1 cC, 'rEL T 3 CC. T E L
89.8 94.: 96.r
90.i 94.8 97.5
89.9 94.4 97.1
89.8 94.0 96.4
92 2 9.7.4
89.2 93 8 VF . .5
88.1 93.5 96 2
lJi.3 9.5.: nx 4
+
I);,6
8.5 87.
0
