Jacketed Industrial Glass Heat Exchanger v are mounted horizontally and joined H. C. BATES by return bends. The spacing must referred to in a previous reCorning Glass works, Corning, N. y* fit that of the bends, and for this p o r t ' h a s been f u r t h e r reason s o m e a d j u s t m e n t in the studied, and, because of its adaptability to heat transfer problems with very corrosive media, the supports is necessary. The weight is carried on the metal results are considered to be of interest. The initial work jackets, and the glass, supported by the packing, is cradled in with this equipment was intended to determine whether or them. Figure 2 shows that the supports hold the jackets in the not glass piping could be packed in jackets, connected to others by return bends so that multiple units might be exact spacing of the U-bends and allow for endwise motion to assembled and be serviceable in plant-scale equipment. The fit in with slight variations in pipe lengths as may be desired. problem involved devising packing so that water, steam, Inlet and outlet connections to the jackets are also made suffietc., could be circulated in the jackets and the fluids circu- ciently flexible so as not to strain the glass. The method of lated in the piping without leakage and in such a way that the support shown provides the necessary flexibility for easy niovements resulting from temperature or pressure would not adaptation, but any other method that accomplishes the same cause breakage. Ais0 a methbd of supporting individual units to fit the glass pipes and bends and not unduly strain the glass was necessary. The next step was to determine how the rates of heat transfw varied with thickness of glass and velocity of flow of the water and how thin the wall could he made and still have sufficient strength
T
HE jacketed heat exchanger
&
DESCRIPTION O F THE G N I T
An individual unit consists of a straight length of upset-end pipe made of Pyrex chemical resistant glass, which is enclosed in a metal jacket and connected to the next pipe by a glass return bend. The thin-walled pipes to be mentioned later are made as shown in the lower part of Figure 1. The heavy-walled, upset-end s e c t i o n s are fused a t A and B to the central thin-walled part of the pipe. This p r o v i d e s h i g h heat transfer rate through the main body of the pipe and ruggedness a t the ends where i t is required. The pipe is packed in the jacket by means of s t u f i g boxes. T h e s e a r e p r o v i d e d w i t h standard nipe threads to fit regular metal Diping. Thebetails are shown in the upper pari of Figure 1. The latter is a standard type of stuffing box designed for use with glass piping having upset ends. The seal is made by use of a nicely fitting rubber ring. The rubber is protected against extrusion under the temperature and pressure conditions by means of s p 1i t a s b e s t o s gaskets, two on each side. I t is not necessary to tighten the packing very much to make a seal, and this looseness allows for t h e slippage which accompanies heating and cooling. This motion may amount to as much as 0.15 i n c h a n d must be accommodated. The units FIGURE2. SUPPORTS FOR HOLDING AND U-BENDS IN PLACE JACKETS
1 Bates, R. C . , Chem. & Met. Eng., 40, 512-13
(1933).
5TD.
/Ron
P/PE
FIGURE 1. DIAGRAM OF PIPEAND JACKET
results is entirely satisfactory. Figure 3 shows a complete heat exchanger.
MECHANICAL STRESSES During the Drogress of the exDerimenta1 work i t developed that themechanick stresses were not severe and that, in v'lew of the fact that the main body of the piping was protected against accidental impacts, very light walls might be considered. The piping, however, must be capable of withstanding the internal pressure of the fluid, the external pressure of the medium in the jackets, and the stress due to the weight of the pipe full of liquid when supported in the packing near the ends. The recommended internal pressures for different Ti-all thicknesses are shown in Table I. Table I must not be considered as giving the maximum pressure resistance of the piping but merely recommendations based on the tensile strength of the glass itself with a factor of safety and with the understanding that mechanical stress must be applied through the flanges to prevent leaks at the gaskets While Table I gives pressures up to 100 pounds per square inch, it is conceivable that special requirements for gaskets may be such that it will be impossible to make leak-proof joints a t the higher pressures. The glass itself is strong enough for the pressures shown. Because of the uncertain 273
INDUSTRIAL AKD ENGINEERING
214
CHEMISTRY
Vol. 27, No. 3
TABLEI. RECOMMENDED INTERNAL PRESSURES WALL THICKNESS Inch 0.040 0.050 0.060 0.070 0.080 0.000
INTERNALPRESSURE AT DIAVETER OF: 1 inch 1 . 5 inches 2 inches Pound8 per square inch 40 27 20 50 34 25 60 40 30 io 46 35 80 53
2
-I
0.100 0.110 0.120 0.130
50 55 60 65
The load of the liquid in the pipe places a limit on the lengths which may be used since the pipe can be supported conveniently only near the ends. This feature involves the density of the liquid to be used in the pipe, the density of the glass, the diameter and wall of the pipe, and the tensilc strength of the glass. Table I1 shows recommended over-all lengths for various wall thicknesses and under different conditions of operation for jacketed pipes with heavy ends. If the heat exchanger is to be used for condensing a vapor, the cooling water will exert a buoyant force on the pipe; if it is used for cooling another liquid, only the weight of the glass and the difference in the weight of the chemical and the cooling medium need be considered. The values in Table I1 were obtained from the equation for fiber tension in a cylinder supported freely a t points 5 inches from the ends and containing liquids as specified. A conservative value for tensile strength was used, and the results were checked by mounting pipes and filling with liquids. Therefore the use of piping with wall and length specifications as shown in Table I1 is quite safe.
HEATTRANSFER COEFFICIENTS It is desirable to know heat transfer coefficients in order t o compute area requirements. A large number of measurements
FIGURE 3. COMPLETE HEATEXCHANGER clamp stresses, however, it is good engineering to take precautions against injury from accidental breakage. The jacket pressure which is external to the glass pipe will not cause trouble (from collapsing) even with the thinnest walls, u p to 100 pounds per square inch, and higher pressures are not usually required.
have been made with glass piping of different wall thicknesses under varying conditions. The results have been plotted graphically and the values condensed into Tables I11 and IV. Table I11 gives results of heat transfer from steam to cold water through the walls of the glass piping. Table IV is similar except that the transfer is from hot water to cold water. The liquid velocity is that of the hot water and the supply was such that velocities were limited to 1.0 foot per second.
TABLE11. RECOMMENDED OVER-ALLLENQTHS FOR JACKETED PIPIXGWITH HEAVYENDS (In inches)
IN.
DENSITY OF WALL
(WATER) L I Q U I D = 1 GRAY/CC.= 0.036 L B . / C U . L I Q U I D I N S I D E , STEAX O U T S I D E LIQUID INSIDE, W A T E R OUTSIDE
THICKNIDSS 1-in.pipe 1.5-in. pipe 2-in. pipe 1-in. pipe 1.5-in. pipe 2-in. pipe 0,040 0.050 0.060 0.070 0,030 0,090 0.100 0.110 0.120 0.130
TABLE111. GLASS
92 98 103 107
96 104 110 115 119 120 120
111
113 116 118 120 120
... ... ...
VAPOR TO
97 106 113 119 120 120
120 120
120 120
.... .. ... ... ... ... ...
,..
...
... .,. ...
...
LIQUIDTR.4NSFER EXCHANGERS
IN
... ... ...
... ...
...
OVER-ALLCOEFFICIENT OF HEATTRANSFER, X , AT LIQUID VELOCITY ( F T . / ~ E c .OF: ) 0.5 1.0 1.5 2.0 2.6 3.0 B . t. u. per square f o o t p e r hour per O F. 122 03 76 64 55 48 43 39
131 95 79 66 57 50 44 40
138 103 82 68 58 51 45 40
... ... ...
...
LIQUID I N S I D E , 8TEAM OUTSIDE
LIQUID INSIDE, W 4TER OUTSIDE
1-in. pipe 1.5-in. pipe 2411. pipe 1-in. pipe 1.5411. pipe 2-in. pipe 103 105 77 78 97 i4 113 110 83 85 101 79 117 120 89 91 110 84 120 120 94 96 115 88 120 98 100 120 92 105 120 102 96 106 109 99 109 113 ... 102 106 113 116 ... ... 109 116 120 ... ...
...
I N JACKETED HE.4T JACKETED HEAT T A B LI~v . LIQUIDTO LIQUIDTRANSFER EXCHANGERS
TEICKNEEB0 Inch
LO7 84 69 59 51 46 40 37
120 120
DENSITY O F LIQUID= 1.83 GRAM/CC.= 0.0% LB./CU. IN. (HISO%)
145 107 84 70 59 52 46
41
150 103 86 71 60 52 46 41
OVER-ALL
K,
0
1.0
GLASS THICKNESS Inch 0.040
0,060 0.080 0.100 0.120 0.140 0.160 0.180
C O E F F I C I E N T OF HEAT T R A X S F E R , INSIDEL I Q U I D VELOCITY (FT./SEC.)O F : 0.2 0.4 0.6 0.8 B. t . u. per square foot per hour p e r ' F . 94 72 85 41 58 76 61 70 50 37 64 53 59 34 45 55 47 52 40 31 49 42 46 37 29 43 38 41 27 33 39 35 37 25 31 36 32 34 24 29
hT
99
so
66
57 _.
50 44
40 ~.
36
INDUSTRIAL AND ENGINEERING
March, 1935
For liquids with vjscosities similar to that of water, the coefficients shown in Tables I11and IV for different wall thicknesses and liquid velocities may be safely used in computing area requirements. For the effect of viscosity on film coefficients, textbooks on the subject should be consulted. Tables I11 and IV show clearly the advantage to be gained by using thin-walled pipes. Between 0.06 and 0.04 inch there is a gain of 24 per cent for liquid to liquid and 31 per cent for vapor to liquid transfer at 1.0 foot per second. Between 0.18 and 0.16 inch the difference is 10 per cent in each case. The effect of increasing the velocity of flow is also apparent. For
CHEMISTRY
275
thicknesses of about 0.16 inch there is little advantage in using velocities higher than 1.0 foot per second. For thinner pipes the over-all coefficient increases u p to and beyond 3.0 feet per second for vapor to liquid transfer. Heat exchangers of the type described are being used in industrial plants. Information as to the heat transfer capacities and other details of these commercial installations cannot be given because of lack of space. However, they are all operating in a highly satisfactory manner. RECEIVED October 29,
1934.
Sweetening of Gasoline with Alcoholic Alkali and Sulfur B. A. STAGNER, 11.21 South Hi!l Street, Los Angeles, Calif.
S
UBSTAXTIALLY all gasoinasmuch as a small percentPracfically all cracked gasoline and much of line produced by cracking’ age of t h e a l k y l sulfides is the straight-run gasoline must be “sweetened” for and much of that produced r e c o n v e r t e d t o mercaptans the r e m o d of the mercaptans. The method here by straight distillation contain d u r i n g the distillation. The described accomplishes complete sweetening by a small amount of mercaptans two stages of sweetening thus brief agitation of the gasoline with small proporyield a slightly better q u a l i t y as an impurity. The amount of the mercaptans, expressed for of gasoline. tions of elementnry sulfur and a solution of The ideal method of handling simplicity as their content of sulcaustic soda in methanol. No emulsions are fur. varies from almost, zero to as t h e mercaptans would be jormed. The alcohol can be recocered. Valumuch, in extreme cases, as 0.25 to extract them c o m p l e t e l y able by-products are also formed. The adtunper cent b y weight of the gasofrom the g a s o l i n e , but the tages of the process are discussed. line. The amount depends onithe petroleum industry still awaits stock used and, in cracked gasoa n economical procedure line, on the temperature of the CI mking. The mercaptans of commensurate with the snnall improvement attained. seven or fewer carbon atoms have a n objectionable odor; SEW METHOD OF SWEETETING and although the mercaptans themselves are not corrosive to metals, they are all extremely corrosive in the presence of It has been discovered ( 3 ) that, when elementary sulfur elementary sulfur and are, therefore, not tolerated in gasoline. and mercaptans are brought together in solution in gasoline For many years the mercaptans have been eliminated in intimate contact with a very small amount of an alcoholic by treating the gasoline with “doctor solution,” which is an solution of anhydrous alkali, they react instantly with each alkaline aqueous solution of sodium plumbite, and a care- other; and if proper proportions of the sulfur and mercaptans fully determined quantity of elementary sulfur; the sulfur are brought together under this condition, they are both required is not definitely proportional to the mercaptan sulfur totally eliminated as such. No lead is required. It is thus but varies to some extent with the type of mercaptans. possible to remove mercaptans from gasoline by adding the The sulfur oxidizes the mercaptans to alkyl disulfides and requisite amount of elementary sulfur and anhydrous alcoholic doubtless converts Lome of the disulfides to trisulfides. The alkali solution, or to remove elementary sulfur from gasoline finished gasoline gives negative reactions for mercaptans in by adding the requisite amount of mercaptans, or preferably the doctor test and for elementary sulfur (corrosiveness) in a definite amount of gasoline which contains mercaptans, the copper strip test. and the anhydrous alcoholic alkali. Frequently a refinery The reaction of this sweetening process is often expressed may have one type of gasoline bearing elementary sulfur and as follows: another type bearing mercaptans. A proper blending of these two types agitated with water-free alkali will free the PRSH S KazPbOz = R,S, PbS PN:LOH mixture of both substances. A. higher proportion of free sulfur is required than the equaIt is found to be much more economical of time and retion indicates, and Ott and Reid ( 2 ) have s h o r n that be- agent to apply the anhydrous alkali in solution in alcohol, qides lead sulfide other insoluble lead compounds are formed, preferably methanol. The alcohol serves to disperse the such as Pb2S(SR)z, I’bZ(OH)&, Pbz(OH)& etc. The alkyl alkali throughout the gasoline in a fine state of division, sulfides remain dissolved in the gasoline. They are usually doubtless molecular; and the alkali, if added in the minimum considered innocuous in the gasoline except that they in- amount, is almost completely exhausted in the reaction with crease slightly the total sulfur content, the detonation, and the sulfur and mercaptans. The quantity of alcoholic alkali the color instability. These alkyl sulfides have higher boiling solution required is dependent on the degree of sourness of the points than the original mercaptans, and, if the gasoline is gasoline, but it is surprisingly small-one pint per barrel in first sweetened and then distilled, some of the sulfides are left a typical California cracked gasoline, as described later in in the still. An additional sweetening is necessary, however, this paper. The essential reaction is thau oi oxidizing the mercaptans 1 T h e present production of cracked gasoline in the United States is about 160,000,000 barrela per year. by sulfur, the mercaptans being converted to alkyl disulfides
+ +
+
+
