Suspensoid Cracking Pilot Plant J. W:FLANhGAN Imperial Oil Limited, Sarnia, Ontario, Canadu
A pilot plant of three gallons per hour capacity has been constructed for the study of the suspensoid catalytic cracking process. The flow plan, equipment, and operation of the plant are described. Product yield and quality data from pilot plant runs can be used to predict yields and product quality for runs on oommercial units.
into gasoline, fuel oil, and cracked tar. The catalyst is filtered from the tar and either discarded or regenerated for further use. A complete description of the process and refinery equipment is available in the literature (2-4). Suspensoid cracking was put into commercial operation at the Sarnia Refinery of Imperial Oil Limited during the first year of the war. Four tube-and-tank cracking coils were modified for injection of the catalyst slurry, and a tar filter plant was constructed. The pilot unit described here was completed and put into operation in December 1945, to study various catalysts, feed stocks, and operating variables for suspensoid cracking.
S
USPENSOID catalytic cracking is a simple and flexible pro(*ess for the catalytic conversion of petroleum hydrocarbons
to gasoline and other useful products. Natural or synthetic catalyst in an oil or water slurry is charged with the feed to the reaction zone of a conventional thermal cracking coil. Feed stock may be varied from naphtha to heavy gas oils and vacuum distillates. The quantity of catalyst used is quite small, from 2 to 10 pounds per barrel of total feed. The products are fractionated
PILOT COIL PROCESS
A simplified flow plan of the pilot cracking coil is shown in Figure 1. Throughput is of the order of 3 to 4 (U. S.)gallons per hour and is limited by the capacity of the fractionating towers.
PRESSURE REGULATOR
c
FRESH FEED' *
1I
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WET I-
O'S *
.
1
-
li
all
I
SLURRY RESERVOIR
SLURRY -MIXER PISTON
>
--
U
SLURRY PUMP
I
GASOLINE
SLURRY OIL
--SLURRY
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r
-7
8
+--
SLURRY
TAR 4CATALYST
PRESSURE REGULATOR
U QUENCH DRUM
_ I
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FLASH TOWER
WATER SEPARATOR T-l
1,STIRRER GASOLINE
Figure 1.
I
WATER
Simplified Flow Plan of Suspensoid Cracking Pilot Plant 211
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INDUSTRIAL AND ENGINEERING CHEMISTRY
Yol. 41, No. 1
i for the pu1pose. Oute cylirrdrical tanki hold 8000 gallons each of heavy naphtha, interniediate ga3 oil, and h w v y g a i oil for hlrndiny into feed s t o r k The terd inixei are made up irt , whic*h R I C placwl in d steainhrated 'not bo\ adJaci.rlt to the building. From here -the icwi is pumped to thf. t t d tir;un- rnside n h e n required. At the pi (-sent tirile, x ~000-~dlOU tank for light naphtha storage and three t500-galloii tanks for feed mixing are bring added to allon bl(~iid1Iit: and storage of larger quantitiili ot bteain, cornpiebbed air r, and city watei a i ( hupplied i n the hi~iltiing froin I(-finery m a i m KQ UlPhZENT
All p i p ~ l ~used g for llqU1d h?d10. (arbon stresnlr within the plant j b 0.25-inch extra-heavy carbon steel pipe, with the exception of the 0 125-inch stainless steel slurry linc from the rnixeri t o the coil inlet The slnallrr internal diameter of thls line produwi a higher slurry velocitv with less ~clttling of catalyst. Thc. as line from the fractionating is 1nadc3 from 0.5-inch standa~tl
Feed Drums. Each feed d r u m is fabricated fiom a 3.5-foot Iengih of IO-inch 5tandard pipe sealed ai thr bottom with B %elding cap. The l o p of the drum i s closed by a blind Rang( Figlire 2. Qiiriirh, dlurrj, a r i d keed Pumps (left to r i g h t . f o r e g r o u n d ) , Feed Drum ( r i g h t . background) through nllic-h projrcts a stirrei shaft, driven by a 0.25-h.p. Lightnin' mixer mounted 011 top of the flange. Desigri p t e s u r e io1 the diurnv i i 200 pound< per square inch. T h e Feed aiid slurry oil 1 mixers are duplicated to allow recharging of oiie while the other is on streani, thereby drums are insulated and stearn-traced to allot\ heavy and v, ax\ p e r m i t h g continuous operati.oi3. ieFd ~ t o c k ?to be kept fluid. &pdVity i q approximwtely 13 Fresh feed is pumped froin the feed druiri t o the coil inlet. each. Both d r u m are (I Mith high p e w r e sight Slurry oil from the ryservoir is pumped t80the slurry inixer,?wrhil(~ rallhrated in galloni. the c,atalyst slurry from t8hemixers is injected into the fresh fceti J Oil Reservoirs and Quench Drums. The d u r ~ yoil stream a t the coil inlet. or i i kiiig zone of the coil. ndard pipe, and the que1 rtwrvoirs are made from 8-inch The coil is immersed iii a lten lead baths to provitlr ilium from 10-inch standard pip Both reservoirs and heat to vaporize the fred an vtwaking reaction. t o take drum ale sealed a t the bottom by a welded plate, with place in the presence of the catalyst. iwwwl by ft loose fitting lid t o keep out rluit. Blurry 011 i ( w 3 1 At, the coil outlet, the va,pors are watw-qurnchcd froin ~ O V W \ i ) ~ r hdve \ a capacity of 7 gallons each while the quench drurll 1000" F. t,o approximat 'F. The tar and catalyst settle out liolds 14 galloni. 211 are fitted with staiidsrd gage gla in the flash pot and arc1 a w i i ; t h e uncontle:lsed vapoia flash h1 atrd i n gallons Over through the press t r o l l t ~1,o t,iie l'ra,ct,ionatingsysl em. Pumps. Three electrically-drivrn Milton-Roy pumps ( L ' l g ~ i e Two towera are used for fract,innation wjth draw-off o f gas oil 1) equipped nritli double ball-cheisb ~ a l ~ are e s used For feed, from the, bottom of T-1 (Figure I ) a i d of dcbutanized gasoliiir * l n ~ oil, y and quench. The t o t d r e d pump 16 a duplex recipicrfrom the bottom of T-2. The overhead vapors from T-I are ( ating type with variable stidce t o deliver up to 10 gallon5 pel cooled to condense out water in the wat'er separator. V e t gas hour against a hack pressure of 1600 pounds ppr square inch. Thc consisting of butane and light,er fractions passe3 overhead froin zluiiy oil and quench pumps are similar single-unit pumps de,T-2 through the presruic cont,rnllw to the gas in hvering up fn 5 gallon, prr houi. ically-driven gear piimp of 400-gallon per hour capnc PJANT LAYOU'I' it\ IS u-ed for pumping fred from outsidc the building into ( t i ( feed drums and slurry oil reaervoii y. The pilot plant occupies practically all the tlooi. space of 700 q u a r e feet, i n a huilcling 20 feet ii) hright , a-hich wa,s esprc-iallg Slurry Mixers. T o overcome erosion of chcc~k salves en-
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INDUSTRIAL A N D E N GINEERING CHEMISTRY
January 1949
Figure 3.
Slurry Mixers
countered when pumping a mixture of oil and catalyst, the slurry injection system was designed so that the slurry does not come into direct contact with the pump. Oil from the slurry oil reservoir is pumped into the slurry mixer (Figure 3). This consists of a %foot vertical cylinder fabricated from 8-inch double extraheavy pipe. The walls are machined and honed to an internal diameter of 7 inches. Both ends are sealed with high pressure flanges; the bottom flange supports a parking gland for the st,irrer
Figure 4.
213
shaft, and the top flange a gland through which the piston rod passes. Inside the cylinder, a close fitting piston is pumped down by the slurry oil, forcing the slurry below the piston out through the slurry line t o the coil. The piston has a total travel of 29 inches, equivalent to approxiniately 5 gallons of slurry. On reaching the bottom of its travel the piston is pulled up by B 1-ton chain falls attached to the rod; it sucks in fresh slurry from a filling spout. The slurry is kept in suspension below the piston by a 6-inch propeller mounted on the stirrer shaft projecting through the bottom packing gland. Both stirrers are belt-driven from a 5-h.p. 500-r.p.m. electric motor mounted between the slurrj inixtm. Design pressure for the niixcw is 1500 pounds per sqns,re inch. Coil and Lead Baths. The lead baths consist of five boxlike open-top compartments (Figure 4 ) 18 inches square by 18 inches deep; the level of the molten lead is maintained about 4 inches from the top of the box. The compartments are joined by troughs through which the coil runs, still beneath the surface of the molten lead. The five cnmpartmmts are built into an iron box 7%-hichia lined with insulating firebrick, and covered with loose Ltsbestob insulation to a depth of approximately 5 inches over the molten lead. Each compartment has two 5-kw. electric heaters, one connected direct t o the 110-volt supply, the other t o a 5-kv.-amp variable ratio transformer across the supply. The direct heater k used when any large increase in temperature is needed; the variable heaters maintain the required temperature for each bath The first two compartments a t the inlet end supply preheat t u the feed and slurry at a temperature of 800" F.; the other three constitute the cracking zone where the reaction takes place a9 higher temperatures. . The coil is welded from 20-foot lengths of 0.125-inch 18-8 stainless steel pipe, wound into five sections and each immersed in a separate compartment of the lead baths. Each section consists of seventeen turns of 8-inch diameter across the face of the coil. The sections are made up separately and thcn welded together to form the coil. By using different coils the slurry may be pumped into the teed stream a t the coil inlet, or passed through separate preheat sections and into the feed a t the cracking zone. This allows study OB the optimum point of injection for the catalyst. Quench Injection. To prevent uncontrolled cracking taking place in the flash pot, the vapors are cooled by quench injection in the transfer line between the coil outlet and the flash pot Both water and heavy gas-oil have been used as quench. R a t e r
CoiI and Lead Baths
Spare coils are shown on top of insulation fur the lead baths
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INDUSTRIAL AND ENGINEERING CHEMISTRY FRACTIONATING SYSTEM
has proved more satisfactory because it can be separated easily
f r o m the hydrocarbon whereas t.he gas-oil affects the quality of the products. Flash Pot. I n the refinery suspensoid cracking units, the coil outlet pressure is controlled by an orifice in the vapor-catalyst line a t thc entrance to the fractionating towers. On the small scalp unit, where it is necewary to use a control valve, considerahlc erosioii of the valvt, takes place when the c a t a l p t passes through ir,. T o overcome this a flash pot m s built at the coil. outlcr ; t,hia a,llows the tar and catalyst to settle out, while the uncwniirr~aedva,porx flash over through thi. pi~:s~sure controllrr t,o t h e irtlrtioiiation towers. The flash pot consist-: of a, 15-jnch colunrn of 5-inch ciwliiiig :vi1 tubing, closed at the bottom with a blind flange, which suppnrts a scraper to loosen any catalyst on the m-alls. A high pressure sight glass allows the liquid level in the flash pot to be seen for withdrawal of ta.r and catalyst through a cooler to atmosphere, or through a cross-over line to fractionating tower T-I (Figure 1). Thewhole system, being at coil outlet pressure, is built for operation up tmo1500 pounds per square inch pressure. The flash pot is insulated with a Kichrorne wire winding embtdded in the insula,tion. This winding, connrcted to a 2-kv.-anip. variable ratio t ransformer, provides heat for amdinhatic opcration of the flacjli pot.
VOl. 41. No. 1
The fractionating system (Figure 5) consists of two 3-inch diameter towers, 8 feet in height. Vapor from the flash pot enters the middle of T-1 (Figure 1). Gas-oil is withdrawn from t>hr bottom of T-1 while the overhead passes through the water sixparator condenser. Here water and gasoline condense out, and the gasoline and gas flow into the middle of T-2. Both towers are packed with 0.25-inch Raschig rings, n-ith the exception of a section of disks-and-doughnut,s in t,he lowcr half of' T-1. This unpacked sect,ion is to prevent tower plugging when t a r and catalyst are brought t,hrough the crossover line from Lht, tarpot. T h e t o w m arc insulated and wound with Nichrome resistance wire to give adiabatic heating conditions. The insulation consists ol a layer of alundum cement, around which the Nichrome wire is wound; then the whole is covered with two 1-inch layers of Sil-0-Cel concrete and magnesia insulation. Reboiler heat' is provided by a Nicbrome-wire winding underneath the cement on the bott'om skin of T-I. (Figure 1) and by a 1000-watt int>ernal blade heater on T-2. Both reboilers are controlled by 2-kv.amp. variable ratio transformers, as are the adiabatic heaters. The quench water is removed in the water separator between T-1 and T-2 (Figure 1) after the water and gasoline have been condensed in the overhead vapors from T-1. The water separator consists of a 3-inch column 4 feet in height, with attached sight glass for viewing the level of the gasoline-TTater interface. The water is withdrawn continually from the lower layer, while gasoline from the upper layer flows into T-2, together with the uncondensed gas. An air-cooled coil mounted inside the top of the tower condenses sufficient liquid for reflux to T-I; a water-cooled condenser on the \.;et, gas line provides reflux for T-2. GAS MEASUREMENT AND C O L L E c r i m
The wet gas from T-2 (Figure I) consisting of butanes and lighter gases passes through the tower pressure cont,roller to a steam heater which serves to evaporat,e any liquid condensed in the sudden expansion from 100 pounds pressure t o atmospheric. The gas passes through a water bubbler bottle to saturate it with water vapor and then through a 100-cubic foot Ret test meter. This met,er has proved satisfactory for gas measurement exccpt in very cold \Teather vihen moisture in the discharge line t o the atmosphere freezes and causes a large back pressure on the meter. Two 3-gallon bombs filled with water are attached to the gas discharge line; these, are allovc.ed to empty at a specified rate, as viewed in attached sight glasses, l o obtain samples of the gas over any required period. All gas lines are 0.5-inch st>andardpipe. IlVSTRURIENTATION
Figure 5 .
Fractionating Tow-ers
Three-section w a t e r reparator gage glass ( r i p h t . backgrorsrrd)
The iiistrunientat,ion in the pilot plant, is conventional. While air to the reflux condenser on T-1 (Figure 1) is controlled manually, a recording temperature regulator adjusts the amount of water to the reflux condenser on T-2; thus the amount.
January 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
219
of reflux produced is controlled. This temperature regulator is mounted on the control panel (Figure 6) and is operated by the top tower temperature of T-2. Chromel-alumel thermocouples are set in each of the lead baths; iron-constantan thermocouples are used for liquid, skin, and insulation temperatures of the flash pot, and top, middle, and bottom of each tower. Separate recorders are mountcd on the control panel for bath and tower temperatures. The recording pressure regulators on the control panel operate control valves on the flash pot vapor line and on the wet gas line to maintain the coil outlet pressure and tower pressure. Iri addition, pressure gages are fitted on the feed drums, towers, flash pot, and feed, slurry, and quench inlet lines t o the coil. Liquid levels are controlled manually with the aid of sight glasses on the flash pot, fractionating towers, and water separator. OPERATION
The operation of the pilot plant requires three three-man shifts, plus two daymen for feed make-up, product blending, and general cleaning. Each shift is in charge of a chemist, who has with him an experienced operator and helper from the refinery. A test run generally consists of a 24-hour period a t the speci6ed conditions. Approximately 5 to 6 hours are required to reach steady operation, before the test is ready to begin. During the test all liquid products are saved, and feed, product, temperature, and pressure readings are recorded every hour. Two gas bombs are filled during each 8-hour period of the test, to give a composite gas sample. On completion of the test, coke in the coil is burned out by raising the bath temperatures to 1150" F. and blowing air through it. The air is supplemented with blasts of high pressure nitrogen every half hour t o clear away any loose catalyst. This burning-out generally requires about 6 hours; during this time the towers are steamed, and the feed drums and slurry mixers are flushed out in preparation for the next run. The total liquid products from the test run are blended together and a sample sent to the laboratory for distillation to determine product yields and quality. The gas samples are analyzed by Podbielniak low temperature distillation and olefins are determined by Orsat analysis and checked by an infrared spectrophotometer. MECHANICAL AND OPERATIONAL DIFFICULTIES
Slurry Mixers-Stirrers. A large part of the mechanical troubles that have arisen have occurred with the slurry mixers. Various stirrer speeds, types of packing, and methods of lubricating the packing around the stirrer shaft have been tried. At high speeds of rotation, the packing soon burns out and leakage of slurry through the gland becomes excessive. Attempts were made to provide lubrication by means of a by-pass line from the top of the mixers, supplying slurry oil to the packing gland at slightly above the pressure in the lower section of the mixer. This system allowed a large part of the slurry oil to by-pass the piston and dilute the slurry. At present, the stirrers are beltdriven from a 5-h.p. motor a t a speed of 500 r.p.m. The packing consists of layers of asbestos and metallic foil, lubricated with graphite grease. This has proved fairly satisfactory, allowing even naphtha slurries to be used with a minimum of trouble. Homever, i t is usually necessary t o install a new stirrer shaft and change the packing every 2 weeks. Slurry Mixers-Walls. After several months' operation, build-up of catalyst on the walls of the slurry mixers causes the pistons to stick. No remedy has been found except to clean the walls every 2 months. Slurry Mixers-Pistons. Leakage of oil past the pistons was overcome by using three neoprene rings interspaced with steel rings on each piston. The compression is adjusted by means of
Figure 6.
Control Panel
Trmperatura and pressure controllers (foreground); variable rntio tranuformers and switches for lead beth and tower heaters (harhgroirnd)
a flange on top of the piston; this expands the rings to fit closely against the cylinder walls. Catalyst Settling and Coking. Major operational difficulties have been the settling of catalyst in the slurry line from the mixer to the coil and formation of coke in the coil. Settling of catalykt has been prevented largely bv using a 0.125-inch inside diameter slurry line, and if necessary increasing the slurry rate for heavier catalysts. Experience with coking indicates that it occurs directly upstream of the quench inlet point, on the transfer line It is believed that quench injection directly in the flash pot will cut down hoke formation in the w i l and transfer line.
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CONCLIJSIOX
The pilot, plant tests may be divided into two sections; st,iidies on new catalysts, feed stocks, and operat,ing conditions; and runs to check refinery tests on the commercial units. Within the ltccuracy of the laboratory work-up, refinery and pilot plant, runs check with respect t o yields, product dist'ribution, and quality. Thus I,he Sarnia suspensoid cracking pilot' plant can be used to predict product yields and quality. Because of inherent differences in design, such as the &io of coil diameter to volume, i t iu necessary to check operability under extreme conditions in a(xt,uaI refinery units. LIl'ERA'rUKE ClTEll
(1) Caesar, C. II., Petrolezim~lilefiner,26, 727 (1947). ( 2 ) Foster, A. L.,Oil Gas J . , 42, No. 5 2 , 43 (1944, (3) Oil and Gas Journal, 44, No. 47, 135 (19461. (4) Purvin, R. L., W o d d Petroleum, 19, No. 4, 69 (1948). RECEIVED October 18, 1948. Presented before the technical srsstons of aht Chemical Institute of Canada. J u n r 7-10. 1948
