INDUSTRIAL AND ENGINEERING CHEMISTRY
766
In the course of an investigation of processing methods for the fabrication of a cosmetic hand, to be worn by amputees, from a synthetic elastomeric type latex (50 to 60% solids), it became necessary to devise a spray gun: which would be free from the troublesome difficulties experienced with conventional type of guns. DESCRIPTION AND OPERATION OF SPRAY GUN
Engineering details of the spray gun are shown in Figure 1. The body of the gun is Lucite and is drilled t o support three nozzles. One nozzle carries air, another water vapor or solvent vapor, and the third the emulsion or solution to be sprayed. Both the flow of air and the solvent vapor may be controlled: the air flow by a needle valve or diaphragm valve on the air inlet line and the flow of solvent by the adjustable needle valve of the Paasche nozzle shown. The position of the nozzles is adjustable, and they are held in place by set screws. During a typical spraying operation of 55 t o 65% solids latex (Figure l), a jet of air from the air nozzle passes over the Paasche nozzle creating a low pressure head and drawing water up into the tip of this nozzle. The air now leaving the Paasche nozzle is saturated with water vapor and passes over the nozzle containing the emulsion, which is drawn up into the tip and sprayed. The satu-
EngFnyring
VOl. 43, No. 3
rated vapor atmosphere is maintained over this nozzle preventing evaporation of water from the latex, subsequent clogging of the gun, and cobwebbing. I n practice, it has been found that almost complete throttling of the flow of water vapor by adjustment of the needle valve on the Paasche nozzle saturated the air sufficiently to maintain an even flow of the latex spray. For latices that are sensitive t o air, inert gas atmospheres such as nitrogen may be used. Application of the gun for spraying polymeric solutions containing organic solvents is carried out by allowing the pure solvents to saturate the air stream through the Paasche nozzle. The gun has been used successfully for spraying high solids latices of natural rubber, synthetic copolymer latices of ethyl acrylate and acrylonitrile, GR-S types and solutions of Nylon, Type FM-6501. Films 0.030 inch thick by 9 inches Iong by 7 inchep wide have been sprayed on a glass plate using ethyl acrylate-acrylonitrile copolymer latices. Of course, if lacquers are to be handled, i t would be advantageous to use metal for the body of the gun. ACKNOWLEDGMENT
Credit is due A. H. Brown of this laboratory for help in the design and construction of the gun. RECEIVED July 7, 1950.
Equilibrium Flash Still
p*cess development R.
B. S M I T H , T H O R P E DRESSER, H. F. H O P P ,
AND
T. H. P A U L S E N
SlNCLAlR REFINING CO.. HARVEY, ILL.
A n improved still was designed for the purpose of obtaining accurate and reliable flash distillation data, By the use of mercury vapor as the heat medium, isothermal cdnditions were obtained throughout the heating zone. This heat medium is easily maintained at any set temperature and can readily be manipulated to produce any temperature between 400' and 800' F. This leads to excellent operating characteristics. Data of greater accuracy and reliability have been obtained on this still than were heretofore obtainable, and the range of practical flash distillation was extended to higher boiling materials.
0
NE of the fundamental operations in petroleum refineries, and therefore in petroleum laboratories, is simple flash distillation. This type distillation is carried out a t a variety of points in refineries. Where flash pressures are atmospheric or somewhat above, reasonably reliable means are available for predicting operating conditions (1, 3, 4). However, it has been necessary in recent years to increase distillation temperatures and decrease distillation pressures continually in order to accomplish ultimate distillate recovery. As a result, difficulties have been encountered, not only in commercial equipment but also in the laboratory, because of questionable observations of temperature and pressure, superheating of feed stock, entrainment, and uneven operations generally. Reliable equilibrium flash data for these extreme conditions are important in the design and operation of this type refinery equipment. The still described herein was built in an effort t o supply such data. This laboratory still is practically isothermal; thus superheating and uncertainties regarding temperature are eliminated.
Entrainment is minimized by the design of the vaporizing zone and by the generous sizing of the still. Unusual smoothness and reliability of operation are realized because of the inherent advantages of saturated mercury vapor as the heat medium. This type of heat medium is ideal where isothermal conditions are required. Any apparatus immersed in this vapor closely approaches the saturation temperature because of the very high rate of heat transfer of the condensing vapor. There is little tendency t o superheat in a heating system of this type. Radiation losses are automatically compensated for by the condensation of the heat medium on the walls of the vapor jacket. Mercury vapor is not subject t o thermal decomposition, and its vapor pressure-temperature relationship is suitable for adaptation t o automatic temperature control. DESCRIPTION OF APPARATUS
Figure 1 is a simplified sketch showing the principal features of the apparatus. The construction material for the main apparatus is carbon steel. The space requirements of the apparatus proper are: width 5.5 feet, depth 3 feet, height 10 feet; adjacent t o it is a control panel 4 X 1.5 X 7 feet. A working space allowance of 2 feet for sides and back and 4 feet at the front should be made. The gross electrical load allowance is 15 kw. Oil Handling System. This still was designed for a feed rate of 0.5 gallon per hour. The feed line, from tanks and Zenith gear pump not shown, enter8 the top of the mercury vapor jacket and proceeds as a coil of tubing surrounding the still. The first four turns of this coil are 0.25 inch in diameter and serve t o heat the feed as a liquid to near the vaporizing temperature. The rerflaining turns are I-inch diameter tubing and total about 30 feet in length. This section is designed to give both negligible
March 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
767
FEED
Y
ENLAROEMENT
N2
SUPPW
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b
VENT
r
'I
0 @ @
@ @ @
STILL
@
PRESSURE CONTROL BLEED
MERCURY BOILER
@
DRY ICE TRAP
BOTTOMS RECEIVER PRIMARY CONDENSER
@
CLOSED MERCURY MANOMETER
@
DUBROVlN GAGE
KNOCK-BACK CONDENSER
@ @
MERCURY JACKET MANOMETER
MERCURY KNOCK-BACK VACUUM PUMP Figure 1, Equilibrium Flash Still
INDUSTRIAL AND ENGINEERING CHEMISTRY
768
pressure drop and large heat transfer surface, so that over a considerable length the stock is very nearly a t its final temperature and pressure. Thus all the va orization is considered to take place in the heating coil. WitE the turbulent flow conditions and large surface for contact in this section, an excellent situation exists for attaining equilibrium. This is in contrast t o the conventional flash still heater of relatively small diameter tubing, in which a large pressure drop results in sudden vaporization and large temperature drop a t the exit. This re uires heating to temperatures considerably in excess of the desirei vaporization temperature. When handling high boiIing or temperaturesensitive stocks, this type of heating results in serious thermal decomposition.
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WEIGHT
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OVERHEAD
Figure 2
The mixture of vapor and liquid enters the so-called “flashzone” tangentially a t E about mid-height on a 6-inch length of 6-inch pipe. At the 0.5-gallon-per-hour rate, this space results in low superficial velocities even a t 1 mm. of mercury pressure. Above this section is a 2-foot length of 4-inch pipe t o permit the settling of any entrainment which might exist. The vapors leave through a 1-inch diameter overhead line and pass into a primary condenser and thence t o a dual vacuum receiver eystem. The unvaporized portion of the feed drops t o the conical bottom of the flash zone and out through the residuum line into a single receiver. A small rise is provided in the residuum line to seal against the escape of vapors into the residuum receiver. Because the usual region of interest is above 600” F. and the residuum is frequently an asphalt, the construction of the residuum line was found to be rather critical. It is as short as possible, with low holdup volume t o minimize residence time as a protection against thermal decomposition. The line is accessible for cleaning in case of plugging. Insulation and compensating electrical windings are used to maintain temperatures, but temperatures are held as low as possible, consistent with good fluidity. Three points for temperature observation are provided, even though the line is short, t o assist the delicate control required. A shut-off valve must be provided in this line for use when exchanging receivers. A 0.25-inch blunt needle valve has been found most suitable because it is small and heat losses a t this point can be kept low t o avoid cold plugging. The residuum receiver is a bell fabricated of steel with two 2-inch view windows on a 45’ angle to the vertical set opposite each other. The steel bell avoids mechanical and thermal breakage associated with former glass bells. The residuum accumulates in a standard 1-pound grease can inside the bell. The bottom of the bell ig closed with a flat ‘/s-inch steel plate, sealed with a thin red rubber gasket lubricated with high temperature stopcock grease. Exchanging the receiving can requires only a few seconds, and during this time the residuum line valve is
Vol. 43, No. 3
closed, thus eliminating the considerable complications involved in using dual receivers on asphalts. Temperature Measurement. The most significant temperature point is that a t the flash zone. A thermowell is inserted through the residuum line and extends to the top of the tower. Temperatures are observed with two thermocouples in this n-ell: E at the flash zone and T a t the top of the tower near the vapor take-off. Another thermowell is inserted into the mercury vapor phase through the “mercury knockback condenser” and measures the mercury vapor temperature near the top of the tower a t H . When the still is lined out, points E, T , and H will agree. This uniformity of temperature is evidence of thermal equilibrium and reliability, and substantiates the accuracy and validity of the principal temperature observation, E. The mercury vapor heat medium system is operated to control the temperature a t E, and once set requires no further attention to maintain a fixed temperature. Temperature control is further discussed in connection with the mercury vapor system. For convenience in operating the still, temperatures are taken a t various points on the exterior of the shell and a t certain other points that will be mentioned in connection with the handling of the mercury vapor system. Pressure Measurement and Control. The flash zone pressure is one of the primary observations on this still. A special pressure-measurement tap is taken from the top of the tower leading through a knock-back condenser and trap to the primary pressure measurement instruments. A closed manometer is used for pressures above 20 mm. of mercury, and a Dubrovin gage ( 2 ) for pressures below 20 mm. of mercury. The Dubrovin gage gives an enlargement factor of 9 to 1. Since there is no continuous flow in this system, pressure measurements are considered to be quite reliable. In order to maintain the fixed gases in this system, a minute quantity of nitrogen is vented into it through a bubbler after a change in system pressure. Pressure control is through the overhead receiver system. After passing through the primary condenser, the condensed vapors run down into the receivers. The receivers are vented through a knock-back condenser and dry-ice trap t o the vacuum pump. Many of the automatic vacuum control devices extant have been tried out. The system in use consists of a fine-adjustment needle valve venting into the suction of the vacuum pump. This proves to be about as steady and reliable as the more complicated devices. The flash zone is the observation point for pressure control. When receivers are vented to atmosphere for the purpose of removing products, they are pumped back down t o within a millimeter or so of control pressure by a separate vacuum pump (not shown in sketch) before being returned to the controlled vacuum system, Mercury Vapor Heat Medium System. The main heat supply is t o the mercury boiler. The boiler is 3 feet of 4inch pipe, oriented horizontally, and is heated by five electric furnace sections. Two of these sections are controlled through a relay by the mercury jacket manometer a t the left of the sketch; the remaining sections are on hand control and are used in accordance with the gross heat demand as determined by the general teniperature level. Theoretically on this type still only a single heat supply is needed since the mercury vapor when up to the required saturation pressure will supply radiation demands. 9t temperatures up to about 730” F. the still is actually operated in this manner. However, a t higher temperatures the required boiler size would increase rapidly, and it is more expedient t o supply part of the radiation requirements directly with the usual adiabatic windings. Critical operation of these windings is not necessary to the maintenance of uniform temperatures because of the properties of the mercury vapor heating system. The adiabatic windings are insulated from the metal shell with a t least 2 inches of insulation and are operated 100” below the still temperature. The usual 2 t o 4 inches of insulation are added
March 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
I
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outside the adiabatic windings. The heat transferred through 2 inches of insulation by a 100 O F. differential places only a small load on the mercury boiler. The heat flux t o the boiler, below the liquid mercury level, is 20 watts per square inch. The sketch indicates the construction of a convection baffle inside the mercury boiler below the liquid level of the mercury which systematizes the flow of the liquid mercury and aids heat transfer. The mercury vapor is conducted into the jacket by a 2inch line, and condensate returns t o the boiler through the same line. The still was designed for a maximum temperature of 800" F. corresponding to 30 pounds per square inch gage mercury pres-
i 1.00 -
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-
FLASHED RESIDUUM FROM A MIDCONTINENT RED. CRUDE
B A
%
-
sure; the construction material is carbon steel throughout, and all closures are welded for absolute security against leaks. Although the outside vessel passed a hydraulic test a t 400 pounds per square inch gage and the inner vessel passed a t 1500 pounds per square inch gage, freedom from leaks was not assumed until after both vessels were cleaned and had passed the test of holding a pressure of 1mm. of mercury absolute for 16 hours. In using mercury as a heat medium, i t is necessary t o add 0.5% of titanium and 0.5% of magnesium t o serve as wetting agent and corrosion inhibitor (6). Because magnesium is present, oxygen must be excluded; this is accomplished by pumping down t o a good vacuum before applying the first heat and for a portion of a bring-up heat and then backfilling t o the desired operating pressure with nitrogen. Temperature Control. Temperature control is obtained by onoff operation of electrical elements on the mercury boiler using the mercury vapor jacket pressure manometer shown a t the left of Figure 1. The control point closes a circuit through the manometric mercury t o the terminal, G, at the bottom of the manometer t o turn off the control heaters by means of a relay switch. Opening this circuit turns the control heaters on. Other heaters on the mercury boiler are on hand control, and they are set so that the automatic control operates a t about 15-second intervals. If the control fails t o shut off the heaters, the alarm point set 5 or 10 mm. higher warns the operator by ringing a bell and lighting a signal lamp. The mercury vapor jacket pressure is communicated t o the control manometer through a small diameter line filled with nitrogen.. The mercury vapor-nitrogen interface is carried just outside the jacket between points U and L in the communicating line. These points are observed by thermocouples; L approximates H and E, the control temperature, and U a t a considerably lower temperature. The interface is adjusted for each operating temperature by addition or withdrawal of nitrogen from the manometer system. If the interface should rise too high, the operator may observe the sudden jump in temperature, U,or if too low, the sudden drop in L. Too low a n interface is merely bad operation, but too high a n interface is potentially dangerous. Therefore, if the operator fails t o see the jump in temperature, U, with too high a n interface, a dial type thermometer, W , with a built-in relay contact is placed above U. This is set 200" t o 300' F. below the operating temperature. If the mercury vapor-
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OVERHEAD AND RESIDUUM VIS COS IT1ES
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INDUSTRIAL AND ENGINEERING CHEMISTRY
1110
Vol. 43, No. 3
conveniently obtained in the laboratory by running isotherms a t various pressures. The runs were about 6 hours in duration and CRUDE were preceded by a short conditioning period. The operation Gravity, A.P.I. 22.9 of the still during a run was checked by making hourly weight Kinematic viscosity a t 122O F., os. 83.5 Flash, At 210° a F. F., os. balances. The general consistency of these data is much better 320 13.5 Fire F. 380 than any previously obtained on flash stills in this laboratory. R a d a b o t t o m carbon residue, wt. % ' 2.81 2.02 Insoluble in n-pentane, wt. % Several laboratory tests were Extraction sediment, wt. yo 0.24 utilized in checking the consistency of the data obtained TABLE11. EXPERIMENTAL FLASH DATAFOR MID-CONTINEKT REDUCED CRUDE a t the different flash temperaResiduum Residuum Overhead tures, such as the residuum Specific Viscosity Overhead Viscosity yield-specific gravity relationa t 210° F. Gravity, a t 122' F., Gravity Temp., Pressure, Overhead, Residuum, Wt. % 770/77d cs. Grams Grams Recovery A.P.I. Cs. O F . Mm. H g ship and the viscosity of the 0,9646 276.4 15.9 730 100 4579 2699 27.8 100.1 distillate and residuums (Fig0,9353 45.5 2525 8.5 400 4559 30.5 98.4 ures 4 and 5 ) . Each point rep0.9979 13447 29.5 680 2.5 2967 746 98.2 26.0 resents a separate run on the 5 0.9957 3826 26.5 2938 780 98.3 26.1 0,9860 1383 23.1 2796 26.7 954 99.9 10 shill. Enough runs were made 0.9733 495 17.8 2485 1180 27.6 25 100,5 0.9612 241.3 14.9 2315 1503 100.3 27.9 50 a t different operating condi0,9512 113.3 11.6 1952 1883 100.4 29.3 100 tions t o obtain considerable 0,9264 26.6 3040 99.2 31.9 400 779 6.3 o v e r l a p p i n g of yields. The 0.9853 1744 2543 26.6 23.5 630 2.5 894 100.0 5 0.9806 915 2424 21.0 1001 101.4 27.0 agreement among points at 0,9737 511 17.7 2010 997 101.8 27.4 10 different t e m p e r a t u r e s i s a 0.9621 207.3 1044 719 100.6 28.2 14.2 25 0.9498 125.7 11.1 1797 1727 100.1 29.1 50 severe test of consistency and 0.9402 53.4 1169 2001 30.5 8.5 100 99.6 0,9189 18.2 4.7 2893 33.7 400 99.5 284 shows that unusually reproducible results were obtained. 0.9758 610 2169 1035 27.0 18.4 580 2.5 99.0 0.9668 374 1914 27.4 5 1110 100,o 16.0 The line drawn through the 0.9571 178 1861 28.4 1339 10 100,5 13.6 0.9489 101.9 1408 29.5 1.596 25 100.0 10.1 residuum viscosities in Figure 0.9410 51.4 1325 2296 30.7 50 101.0 8.0 5 was derived independently 0,9298 28.5 2730 32.1 100.5 5.8 100 749 of the points shown by "sub0.9547 159.7 1810 1583 101.1 28.6 13.3 500 2.5 0.9460 92.3 1535 1857 99.7 29.5 9.9 0 tracting]' the viscosity of the 0 , 9 6 2 1 6 1 . 4 1308 2145 100.2 8 . 2 10 30.4 distillate (measured a t 210" F.) 0.9327 34.5 2577 31.6 6.8 25 856 100.0 0.9252 22.8 2798 33.1 4.5 50 47 1 101.1 from the viscosity of the feed 0,9417 72.2 1423 2043 450 2.5 99.2 30.0 8.7 using a viscosity b l e n d i n g 0.9380 47.6 1151 2401 5 100 1 30.7 7.0 chart. 0 , 9 3 0 2 32.5 851 10 32 5 . 7 2781 99.8 0
TABLE I.
PROPERTIES O F
25
400
2.5 5 10
45% MID-CONTINENT REDUCED
387
3227
100.0
33.8
4.0
0.9211
20.0
1160 754 368
2919 3250 3064
101.5 100.2 99.0
31.4 32.8 33.3
6.3 4.8 4.1
0.9348 0.9242 0.9226
40.2 26.5 21 .o
nitrogen interface rises t o this point a red signal light is turned on and a warning bell sounded. Above this signal is a mercury knock-back condenser cooled with water. It is difficult to drive mercury vapor through this condenser, but some splashing has been observed, so a trap is provided above it. No real emergencies have arisen in connection with these safety devices in a year's operation with many different operators, although the alarms have been actuated deliberately or during adjustment procedures. In discussing any mercury vapor heating system the question of the poisoning hazard always arises. The most important step in avoiding this hazard is to be sure there are no leaks, even the most minute, in the mercury system. It is also wise t o alert contact personnel t o the hazard, to practice good housekeeping and personal cleanliness, and t o check the atmosphere frequently and regularly with a mercury vapor detector. EXPERIMENTAL DATA
A program for investigating the flash vaporization characteristics of reduced crudes has given data that are reproducible and also check commercial operation. As an example, the data obtained in running a 45% mid-continent reduced crude is presented. The properties of this particular reduced crude are given in Table I. Engler distillation data obtained at 5 mm. of mercury are plotted in Figure 2. T h e flash data obtained on this stock are reported in Table 11 and Figure 3, where the flash temperature is plotted against per cent overhead for several isobars. These flash data were more
SUMMARY
The new type still described here gives reliable equilibrium vaDorization data in the temperature range 400" to 800' F., from atmospheric pressure t o approximately 1 mm. of mercury absolute. Typical data obtained on a heavy petroleum stock are presented t o illustrate the operation of this still and the consistency of the data obtainable. ACKNOWLEDGMENT
The advice of J. M. Wasmund, L. S. Dilleg, and R . E. Hyzer during the design of this still is appreciated. LITERATURE CITED
f l ) Edmister. mi. C.. Refiner. 28. No. 10. DD. 143-50 (1949). (2j Germann; F. E. E., &nd Gagos, K. A; I N DENG. . 'CKEM.,~ ~ N A L ED., 15, 285-6 (1943). (3) Packie, J. W., Trans. Am. Inst. Chem. Engrs., 37, 511 (1941). (4) Piroomov, R. S., and Beiswenger, G. A., Am. Petroleum Inst., Bull. 10, sec. 11, pp. 52-68 (1929). ( 5 ) Smith, A. R., and Thompson, E. C., Eke. Light and Power, 19, 58-66 (1941). RECEIVED June 12, 1950. Presented before the Division of Petroleuni CHEMICAL SOCIETY, Chicago, Ill. Chemistry, 118th Meeting of the AMERICAN
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