US2270717A - Process of transferring heat - Google Patents

Description

tinuously, is heated to a high temperature, usual- Patented Jan. 20, 1942 UNITED STATES PROCESS OF TRANSFERRING HEAT Vladimir L. Shipp, New York, and John Happel, Brooklyn, N. Y., asslgnors to Socony-Vacuum Oil Company, Incorporated, New York, N. Y., a corporation of New York No Drawing. Application May 22, 1940, Serial N0. 336,592

3 Claims.

This invention has to do with the art of heating and heat transfer. It is concerned with those processes wherein a fluid medium, circulated under pressure, is heated in one portion of a cycle and utilized to deliver heat in another portion of the cycle, the whole object of the process being to deliver heat to apparatus isolated from the furnace or other means wherein the fluid medium is heated. Commercial systems of this type commonly utilize a heavy mineral oil fraction as the fiuid'heat transfer medium. This invention is specifically directed to such processes using oil as a heat transfer medium.

This application is a continuation in part of our copending application Serial No. 211,698, flled June 3, 1938.

The object of this invention is to provide such a process which is free from the hazards, disadvantages, and costs coincident to the degradation of the oil used as a fluid heat transfer medium.

The equipment utilized in such processes is well known and consists of a fired furnace or other type of heater in which the oil, circulating conly not higher than about 550" F. to about 6002?; The hot oil is circulated to the point whereheat is to be applied, e. g., to the jacket of a kettle in which some reaction or process is conducted, and is then returned to the furnace.

In general, such systems have used a very heavy oil, the oil preferred heretofore being the best grade Pennsylvania on parafflnic type lubricating oil of high flash point, known to the trade as cylinder stock. heretofore thought necessary'for the oil was the possession of a high flash point believed to indicate freedom from fire iiisk. Such systems, using the oil heretofore recommended as best,

have encountered difllculties inoperation, which, 40

while not serious atylow temperatures in well I designed apparatus, become crucial at higher temperatures and/or with poor design. A very important difficulty is that of a great tendency 21) oil nature.

The principafrequirement 35 5 the phenomenon of decomposition referred to herein is of the same nature as thermal crack ing of hydrocarbon, the heat transfer oils are called upon to withstand the temperatures to which they are exposed for periods ranging into 10 years rather than hours or minutes as in cracking. I

This inventioni s based upon the discovery that the selection of oils upon. the basis of high flash point is entirely erroneous, and that the use of m oils of entirely different characteristics,-as described rein, leads to entirely unexpected results an benefits in a manner contrary to the prior teaching of the art.

This invention is based upon the use of a high 2.0 temperature refractory oil of a low gravity, of

narrow boiling range, but not capable of pro- ,iiucing a substantial amount of vapors at the temperature of operation, of low viscosity, and

of a gas oil nature rather than of a lubricating Such a material will have a flash point materially lower than the material heretofore used.

To contrast one such new material with that heretofore used, the following tabulation shows comparative data on a typical old-style material and a typical new material.

TABLE I Old type New type Gravit A, P. I 24.2 19.3 Flash Q, C.) F. 590 310 Fire F 690 360 Vise. Saybolt Universal I 100 F .seconds 79 At 210 F do 221 Per cent distilled oilt 400 F 0 0 At 500 F 0 0 Such oils may be obtained conveniently as disof the oil to deteriorate and become possessed of 45 tillates from residual oil produced by cracking a lower flash point, and hence more susceptible to ignition and more dangerous to use. Another important difficulty is the appearanceof coke,

carbonaceous impurities, and sludge in such oils under use, the deposit of which greatly decreases 60 the heat transfer capacity of the apparatus, and which necessitates continuous straining during use and promotes clogging, burning, coking, and erosion of apparatus. Another dimculty is the tendency of such oils, in use, to liberate hydrocarbon gases. avoided by following the teaching of this invention;

Eurther, present demands for extension of the 5 all cases, however, they may be described as ma- All of these disadvantages may be terials of a gas oil nature derived from hydrocarbon stocks which have been subjected to cracking, or, more shortly, as cracked mineral oil fractions having certain physical characterfield of the process to temperatures of about 60 istics.

The refractory nature of the new type fluid heat transfer medium is well demonstrated by its superiority in use, as demonstrated by the following comparison of new and old type oils after each has been heated at 650 F. for a period of five hours under apressure sufiicient to prevent substantial vaporization.

Note that the old type oil has suffered serious degradation resulting in the formation of light, low boiling material (per cent distilled off) sufiicient to materially increase the hazard attendant upon its use. It also has over three times as much carbon and sludgy material.

Of great importance is the difference in viscosity of the oils of old and new type, the new type oil having a viscosity so much lower than the old that very material savings in pumping costs are possible. Of additional interest is the fact that the oils of the new type are higher in specific heat than the oils heretofore used.

The advantages claimed for the new type of oil are capable of complete substantiation based upon actual use. In commercial operation it has been found that savings due to power and increased heat transfer efficiency amounted to 25 and that, rather than forming sludge, the new type oil was actually dissolving and freeing and removing from the system sludge and coke deposited therein by the former oil. Also, oils of the new type, after twenty months continued use, show no appreciable changes in gravity, viscosity, color, presence of lower boiling materials,- or of. sludge originating from the oil.

The oils of the new type may be defined as oils which do not form material amounts of fixed gases when exposed for substantial lengths of time to elevated temperatures. For example, they may be tested for such gas formation by being heated -to and held at temperatures in the range GOO-700 F. in a vessel connected with a condenser, and the fixed gas noncondensible at atmospheric pressure and temperature, so formed can be collected and measured. Comparative data from such a test, carried out on an old type and a new type oil follows:

From this it may be observed that these new oils may be deflnedas oils which are substantially resistant to thermal decomposition, as evidenced by formation of normally non-condensible gaseous products, upon prolonged exposure to temperatures within the range GOO-700 F- In this connection, it may be re-' markedthat it is quite definitely established in the art of thermal decomposition of hydrocarbons that results obtained from comparatively short exposure to active cracking temperatures may be obtained also by much longer exposure to much lower temperatures. Consequently, to

those skilled in the art, the above noted evolu- I tion of measurable quantities of gas in the above old oil at temperatures above 600 F. is a reaction of the same character as that giving sludge, coke, reduction of flash, gas evolution, and similar degradation in the old oil when exposed for periods of months and years to temperatures around 500-550 F.

Oils of the new type may also be defined by means of physical characteristics, the most outstanding of which is that for a given gravity, they are possessed of viscosities and boiling ranges substantially lower than those normally associated with naturally occurring mineral. oil fractions of similar gravity.

A less highly indicative characteristic of such oils is their aniline point, a chemical characteristic, defined as the lowest temperature at which the oil is completely miscible with an equal volume of aniline. For comparison, a typical oil of the old type has an aniline number of 115 C., while a typical oil of the new type has an aniline number of 68 C. In general, the useful characteristics of oils of the new type with which this invention is concerned will be associated with aniline points of C. or less.

Oils at present preferred for the uses above outlined will, in general fall within the range of properties outlined below:

TABLE IV Gravity A. P. I 0 to 30 Initial boiling point, "F 5'75 to 850 Viscosity at F. (seconds S. U. V.) 60 to 250 Aniline point 80 C. or lower.

The initial boiling point of such oils should be suinciently high so that no generation of vapors under the conditions obtaining in the heating system will occur, and to this end, this property must be correlated somewhat with intended use. For most present conditions, an initial boiling point of about 575 F. (A. S. T. M. method) will be sufficient, although for use at higher temperatures, this should be correspondingly higher. 7

We claim:

1. The method of applying heat at temperatures ranging from 600 F. to around 700 F. comprising continuously circulating a fluid heat transfer medium in a closed cycle, applying heat to said medium in one portion of said cycle and removing useful heat from it at another portion of the cycle, in which the fiuid heat transfer medium is a cracked mineral oil fraction, substantially resistant to thermal decomposition, as evidenced by formation of normally non-condensible gaseous products, upon prolonged exposure to temperatures within the range GOO-700 F. conforming .to the following specification:

Gravity A. P. 1..-; 0 to 30 Initial boiling point, F 575 to 850 Viscosity at 100 seconds Saybolt Universal 60 to 250 Aniline point 80 C. or lower.

2. The method of applying heat at temperatures ranging from 600 F. to around 700 F. comtransfer medium in a closed cycle, applying heat to said medium in one portion of said cycle and removing useful heat from it at another portion posure to temperatures within the range 600-700 F., having an initial boiling point of at least 575 F., and a viscosity not greater than about 250 seconds Saybolt Universal at 100 F.-

3. The method of applying heat at temperatures ranging from'600 F. to around 700'F. comprising continuously circulating a fluid heat transfer medium in a closed cycle, applying heat -to said medium in one portion of said cycle and removing useful heat from another portion of the cycle, in which the fluid heat transfer medium is a cracked mineral oil fraction of gas oil nature, having an initial boiling point of at least 575 F., and substantially resistant to thermal decomposition, as evidenced by formation of normally non-condensible gaseous products upon prolonged exposure to temperatures within the range 600-700 F., and a viscosity not greater than of the order of about 250 seconds Saybolt Universal at 100 F.

VLADIMIR L. SHIPP. JOHN HAPPEL.