INDUSTRIAL A N D ENGINEERING CHEMISTRY
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Vol. 21, No. 5
The Progress of Industrial Heating by Oil Circulation' Alexander B. McKechnie PARBS-CRIMER COMPANY.
1102 OLD S o U M BLDD
NDUSTRIAL heating by oil circnlation has been suecessfully applied to high-temperature heating processes in many industries for about fifteen years. Naturally the equipment has gone through many important changes toward improvement, but the basic principle of operation is unchanged. The size of installations has increased as well as the number of processes to which it has been applied.
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Three Systems Installed in a Chemical Plant In 1919
, BOSTON, MASS
ing fluid and its tendency to carbonize when overheated in an improperly designed system. The absorber, or oil heater, should properly be considered the most important piece of equipment in the entire assembly making up a complete system, although there are other parts of major importance from both an engineering and operating standpoint which will he touched upon later. A correctly designed absorber must heat the circulating oil uniformly throughout its entire mass, and without overheatine a m Dortioii of it. To do this, the oil must b e k e p t moving a t a high velocity over the heating surface and the film of oil in contact therewith must be frequently changed by a proper arrangement of oil paaaeges. This requirement. takes into account the length and diameter of the heater tubes and tlie means for connecting them together, also the relation of the heating surface to the heat.ing furnace. The design must also provide for high efficiency io the generation of the heat, as well as its absorption, and all parts must be readily accessible for inspection or repair. The circulating oil pump should produce a positive and non-pulsating discharge, so as to maintain a uniform and high velocity through the absorber tubes. Only pumps of the most substantial construction, designed for operation under the high temperatures required, can be successful in this work. There are many comniercial oils that have a high flash point, but other properties have to be considered in the selection of the right oil for this work. Some of these are the viscosity of the
Description of System
A heating system in which a high-flash oil is used as the transmitter of heat is analogous to a hobwater heating system, hut instead of depending upon thermal circulation to carry the heated oil to the point of heat consumption, a circulating pump is employed to give a high velocity of flow. These systems operate at practically negligible pressures of ahout 10 to 15 pounds on the hot-oil supply and return mains. Because of the low pressures it was at first considered a very easy task to build it heating plant and distributing system of this kind. Actual experience, however, proved the fallacy of this thought, and it was soon learned that circulating oil undcr high temperatures up to 600" F. (316" C.) could only be handled in equipment of the most rugged construction, properly designed to avoid leakage and provide for expansion stresses. I n addition to the problems brought about by the fugitive properties of high-temperature oil, there was also another requiring greater consideration-namely, the delicate nature of the circulab I
Received February 25, 1929.
Seeflonal View of Absorber Seftlng with Downward Draft
May, 1929
INDUSTRIAL A N D ENGINEERING CNEMISTRY
o i i - n e a t e d Tank car; weight "5 contents 80,ooo Pounds; Raised
oil, particularly its cold test, also its percentage of distillation at a fixed temperature, and the amount of free carbon produced when the oil is distilled to dryness. The oil recommended for t h k work is known as "Meprolene," and has been used successfully since these systems were first put into service. Meprolene has the following physical propertics: Specific gravity at BO' F. Flash p a t Pire pomt Specific heat at 60' F. Specific heat at BW' F.
0.905 5Qi' F. 5580 F. 0 46
0.71
With the exception of a rare instance or two, i t has not been found necessary to withdraw the circulating oil from a system and recharge with a fresh supply. For convenient and satisfactory operation there are a number of special and patented features, such as
497
temperature, but has also improved the quality of the finished product. A number of installations are in operation for tank-car heating, with materials that are only sufficiently fluid to pump at temperatures far beyond the range of steam. These particular installations require from 375" to 450" F. in t,he tank car, and the entire tank is raised to the full temperature before any of the material is pumped from it. The tank cars are especially designed with coils for circulating oil and are properly insulated so that the entire heating process is a very efficient one. These installations are for one or more tank cars per day, and the piping is so arranged that any number of tanks can be connected to the same system if necessary. It will be noted that many of these materials, such as asphalt, rosin, wax, etc., are substances which are ordinarily solid and require a high temperature to produce a state of fluidity that i d render them easilv trnnsuortahie thronsh tn P. . .43110 ~.~ pipe lines. As an accesiory to (he high-tempersture oil heating system, there is a full line of jacketed piping, cocks, and fittings, made in sizes ranging from I'/, to 4 inches, and larger sizes would be made on demand. I n liiglr-temperature installations t,he jacketed piping is heated with circulating oil; for medium temporatures steam is ordinarily used; and in other cases, such as chocolate and sirups in the confectionery trade, where only a miid temperature is required, hot water has proved to be entirely satisfactory. To meet the demands of the industries, these systems are built in many sizes ranging in capacity from 100,000to 2,800,000 B. t. u. per hour, and several absorbers may be connected in battery where necessary. Each different capacity is standardized with its own circulating oil pump and piping, expansion tank, and all specialties of the proper size. ~
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tois,. safety automatic shut-off valves, etc: Application in Chemical Plants ~~
Iacketed Pipine 3 X 4 Inches with Cocks Conneered to Two Jacketed Tanks. ranks and Piping Are Heated w i t h Hot Circulating 011
These systems have found wide use and large application in many chemical plant processes, particularly for high-temperature heating, evaporating, distilling, and subliming. I n connection with asphalt, it has been used in the higlitemperatlire work such its from 350" to 550" F. required for impregnating transformer coils, cable insulation, saturation of felts for asphalt shingles, paved culvert, coated and duplex papers, molded products, shipping cartons, battery boxes, etc. The starch industry has made several installations for starch roasting in the manufacture of gums and dextrins. WRXmelting and heating in molded products and the hightemperature heating in rosin purification have taken several systems. Two installations were made for distillation in the manufacture of toxic gases. I n the vegetable oil industry, where it is necessary even under high vacuum in the deodorizer to obtain temperatures in the vegetable oil ranging from 450" to 550" F., the system has not only proved satisfactory as a means for obtaining
A fair idea of the size and long life of some of these installations can he gained from the following table: KO.
I
B.
i. %.perhour
YCLVS
1
1,200,000 1,60(1,000 1 200 000
Chemicals AJphalt rhinples snd roofing Molded wax products
2
1.200.000 1:200:000
~ r ~ impregnation n ~ i Vesetable oil deodoririiig coated
1
I
1.200.wO
i,2on.nw
1
S00.000 200.0W
3
2.800.000
3
800,OW
5
Chemicsls Asphalt molded products Vepetable oil deadoiidng Chemicals
~
13 13 12 S ~ 5 ~ S S 9
11 5
10
This list only touches upon a few installations, but is representative of them all. The only moving parts of an installation are the circulating oil and the pump, and the oil naturally protects all metal with which it comes in contact. There is therefore no corrosion taking place, and as the systems are vented to the atmosphere and operate under extremely low pres-
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
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sures, there will be no reason for condemning them after a given number of years, as is the case with pressure equipment. From the condition of the systems which have now been
Vol. 21, No. 5
operating for twelve to Gfteen years, there is nothing to indicate any general wear, and there is every reason to believe that their life will be indefinitely long.
Crushing and Pulverization’ Lincoln T. Work DEPARTMENT O F CHEMICAL ENGINEERING, COLUMBIA UNIVERSITY, N B W YORK. N. Y.
S A basic operation useful to the engineering industries
surface and its comparison with energy, the fineness charin the preparation of materials, crushing presents an acteristics of the product as determined by its inherent interesting diversity and similarity of problems. nature and by the processes of crushing, and the behavior of Mineral ores are disintegrated to prepare them for roasting, materials under the forces of crushing. leaching, or flotation; coal is crushed to render it suitable The old yet unsolved question involved in the Kick us. for firing; rock minerals are pulverized to make them useful Rittinger dispute has been again revived and subjected to as fillers in rubber and in paints, and as ingredients of glass new test. MartinZhas compared the energy consumption in and pottery; and many other materials are reduced to a ball mill with the new surface developed. Silica sand was powder to prepare them for further treatment. Yet, with crushed with 1-inch steel balls in an 18 X 18 inch mill, and but few exceptions, the chief aim is to produce surface. surface was measured by the rate of solution in hydrofluoric Equipment is equally diversified in the many types and acid. The energy input was recorded as the difference construction features of mills. Nevertheless, the problem between that required for driving the mill with and without a always before engineers is to select the machine that will charge of sand. As a result of comparing those values with deliver the desired product a t lowest power, maintenance, and the corresponding new surface developed, he concluded that (‘in ordinary tube mill grinding the surface produced is acculabor cost. By its very complexity crushing has not been amenable to rately proportional to the work done.” Recognizing that fundamental scientific analysis. Such a study was limited possible errors might be introduced in the measurement of in the past by the lack of exact methods of measurement; work done in ordinary mills, Gross and Zimmerley3 have for, at least until recently, it has not been possible to measure crushed sand by utilizing the energy of a freely falling body. fineness accurately below sieve sizes or to evaluate the They have measured surface with their modification of the resistance of any material to grinding. Nevertheless, prog- hydrofluoric acid solution method, and they have found ress in the development of machinery has been made by that the new surface produced varied with the energy input. empirical methods, keen observation, and the available It is their conclusion that (‘when crushing quartz, the new surface produced is in methods of measuredirect proportion to t h e m e n t . Closed-circuit work input in accordcrushing with the aid ance with the Rittinger of liquid or air classil a w of c r u s h i n g . ” f y i n g equipment has However, i t should be come into common use. borne i n m i n d t h a t M a r k e d advancement these crushing methodsis to be noted in the measure the over-all field of the colloid mill. e n erg y accompanying The demand for finer disintegration, and that products or for more the dissolution test has uniform ones is being not yet been rigidly m e t . Y e t t h e evip r o v e d to m e a s u r e dence now available insurface. dicates a g r e a t loss Furthermore, energy of energy i n c r u s h Figure 1-Conical Disk Mill A and B , crushing disks D pulley i n p u t h e s been coming a n d p u lve r i zing . E: eccentric bearing C, shaft and casing pared with surface The trend Of the future Reprinted from “Principles of Chemical Engineering,” by Walker, Lewis, and McAdams, energy and found to will undoubtedly be published by McGraw-Hill Book Company. toward a more scienbe greatly in excess of tific study of the fundamental principles of crushing and the calculated energy needed to develop the new surface. of classification, to lower power costs and to produce the SURFACE ENERGY CRUSEUNG desired type of fineness; toward the wise selection of OBSERVER MILL Calcd. by: Value EFFICIENCY Ergs/@. cm. Per cent materials and the design for simplicity to insure mini920 1.3 Rolls Edser Gaudin mum maintenance; and toward the scientific selection of Martin Ball Martin 310 0.06 920 3.0 Gross and Zimmerley Stamp Edse: suitable size units and the use of automatic controls to miniGross and Zimmerley Stamp Martin 310 l.o mize operating labor. The values of surface energy are somewhat in doubt; Principles of Crushing but their order of mamitude indicates that a large proportion of the energy input isdissipated as heat or sound. Recent studies in the fundamental principles of crushing 2 Martin, Trans. Inst. Chem. Eng. (Brit.), 4 , 42 (1926). have followed three lines: measurement Or calculation Of t Gross and Zimmerley, Am. Inst. Mining Met. Eng., Tech. Publ. 127
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Received March 5, 1929.
(1928).
