US1866388A - Heat exchange - Google Patents

Description

July s, 1932.

W. H. ARMACOST HEAT EXCHANGE Filed May 16, 1929 2 Sheets-Sheet l CEB um :gm-:xm 11Y 'um :az-.1a 'am g am crm :1:21a am :arno mnh 2 @im :Q tri-ISI :aL-1a om; amg am are: crm g una ccf: crm afb @zu @gm ma.

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ATTORNEY.

Patentes July s, 1932 WILBUR H. ARMACOST, F NEW YORK, N. Y., ASSGNOR T0 TEE SUPERHEATER COM.-

PANY, 01E"l NEW YORK, N. Y..

HEAT EXCHANGE Application led May 16,

My invention relates to heat exchange and has for its general purpose the provision of method and means whereby overheating of a fluid being heated may be prevented and s an improved temperature control of such fluid obtained.

More specifically the invention relates to heat exchange effected through the heating by combustion gases of a continuously flowing stream of fluid and effects its purpose by the simultaneous addition to and abstraction of heat from the fluid being heated. The invention is particularly applicable in the heating and cracking of petroleum in tube stills and will therefore be illustrated and described as applied to this use although it isY to be understood that the invention is equally as well applicable to other uses.

In the accompanying drawings in which preferred forms of the invention have been shown, Fig. 1 is a vertical section taken through a tubular heater constructed in accordance with the invention; Figs. 2, 3 and 4 are fragmentary sections on an enlarged scale 4-4 of Fig. 1; Fig. 5 is a view similar to Fig. 1 showing a second form of heater, and Fig. 6 is a fragmentary section on a reduced scale taken on line G-G of Fig. 5.

Referring now to Fig. 1, the heater comprises the usual refractory casing formed y walls 1 and 2, and roof 3, said casing being divided by the bridge wall 4 into combustion chamber 5, and heating chamber 6, these chambers being placed in communication by way of the passage 7 at the top of the heater. The heater may be fired by any desired means, and in the example shown an oil burner is indicated at 8 for this purpose. The spent combustion gases leave the heater at the bottom of chamber G, passing through the breeching 9 to stack 10. f In the form shown, the fluid heating means comprises a plurality of tubes 11 located transversely of the chamber 6 and serially connected by return bends 12. The inlet to the bank of tubes 11 is at 13 while the discharge is at 14. A portion of the path of flow between 13 and 14is formed by a double tubed heat exchanger comprising a. plurality taken respectivel y on the lines 2-2, 3-3, and

1929. Serial No. 363,677.

of tubes 15 serially connected by means of suitable return bends 17, said tubes being larger in diameter than the tubes 11. Within tubes 15 a second series of smaller tubes 16 are concentrically arranged and serially connected by meansv of return bends 18.

The tubes 15 at each end of the heat eX- ehanger are connected to tubes 11 by means of suitable fittings 19 and 20, each of these fittings being provided with suitable openings 21 and 22 through which the ends 23 and 24 of the series of inner tubes 16 extend by Way of fluid tight joints. As appears clearly in Figs. 2, 3, and 4, the tubes 15 are of such size that their free cross-sectional area outside the tubes 16 is substantially equal to the cross-sectional area of tubes 11, so that the said exchanger' does not restrict the flow through the heating means as a Whole.

rIhe return bends 17 and 18 and the fittings 19 and 20 have been diagrammatically shown as removably attached, but such construction is not essential to the exercise of the invention.

'In the apparatus just described the fluid to be heated is preferably introduced through the inlet 13 and discharged at 14, as with the flow through the heater in this direction, the benefit of counterflow heat exchange is secured. Through a portion of the path of flow through the heater, however, the fluid being heated is subjected to a simultaneous abstraction of heat due to the circulation of a colder fluid through the series of internal pipes 16 in the heat exchanger. By means of this arrangement, the rise in temperature of the fluid being heated may be controlled as desired at any point in its course through the heater, depending upon where the heat exchanger is located in the path of flow. For example, it may be desirable to raise a certain oil. to a given temperature, hold it at substantially that temperature for a predetermined length of time, and then further raise its temperature. The manner in which this object can be accomplished by the apparatus shown in Fig. 1 is obvious. Steam is frequently used in conjunction with oil heating and cracking processes, and in such or similar cases the cooling fiuid used in the exchanger may be water to be generated into steam or steam to be reheated or superheated.

Again it may be desirable to heat a. fluid, the nature of which is such that it can not be heated in tubes exposed directly to the intense heat of combustion gases. Fluids of this nature, such as certain vegetable oils, may readily be heated without danger of over-heating by passing them through the set of internal tubes 16, the latter being located at a oint in the heatin apparatus where the uid in the outer tu es 15 does not exceed the maximum temperature to which the fluid inthe inner tubes may be safely heated.

In Fig. 5 another arrangement of heater is shown in which the cooling fluid passing through the internal tubes of the heat exchan er is a portion or all of the same fluid whic is subsequently heated in the outer tubes of the exchanger. The arrangement shown in thisfgure further provides means whereby the heating tubes may be used to protect surfaces exposed to direct radiant heat such as the roof of the combustion chamber without danger of overheating ,the iiuid contained in such tubes.

In this form the bank of tubes 11 connected by return bends 12 discharges to the outer tubes 15 of a double tubed heat exchanger located at the discharge end of the path of flow, and comprises a plurality of serially connected double tubed elements arranged below the roof 3 of the heater and extending from the chamber 6 into the chamber 5.

The inlet pipe 25, feeding the tubes 11', is provided with a branch 26 passing through the fitting 28 to connect the inner tubes 16 of the exchanges with the inlet pipe 25. At the other yend of the heat exchanger, pipe 27 passing through a similar fitting connects the other end of the series of inner tubes 16 with the inlet pipe 25 so that this series of inner pipes forms'a by-pass with respect to a portion of the inlet pipe 25.

The fitting 28 is attached to the discharge end of the outer tubes 15 and is provided 4with an outlet branch 29 through which the heated iiuid is finally discharged. A diaphragm control valve 30 is inserted in the inlet line 25between points where -pi es 26 and 27 join this line and is controlled y a thermostat 31 placed in the outlet branch 29. In addition, the burner 10 is preferably kcontrolled by a diaphragm valve 32 acting in response to a thermostat'33 placed atthe dis- .charge end of the bank'of heating tubes 11.

In the operation of this apparatus the final discharge temperature is regulated through the action of thermostat 31 controlling valve 30 which in turn determines the amount of Huid which is by-passed through the inner a tubes of the heat exchanger on its way to the heater. If the temperature at the thermostat 31 rises beyond the desired point, valve 30 will be opened and more fluid will be bypassed through the heat exchanger, thereby abstracting additional heat and reducing the total amount of heat absorption at this point in the exchanger. This action will tend to raise the temperature of the fluid Where it enters `the bank of tubes 11 so that the fluid would enter the heat exchanger at a higher temperature and the effect of the control by the thermostat 3l would be in a large measure lost. However, if due to the rise in the inlet temperature in the tubes 11 the fluid discharged therefrom to the exchanger exceeds a certain desired temperature, the thermostat 33 will act to reduce the combustion rate to compensate for such rise.

The advantages of the construction just described willI be largely obvious as it will be apparent that the fluid in tubes 15 may be exposed to gases of high temperature without danger of overheating of the fluid therein due to the fact that this fluid absorbs such heat as a transmitting rather than a retaining agent. By suitable proportioning of the diameters of the inner and outer tubes of the exchanger, the amount of heat retained by the fluid passing through the annular space between tubes 15- vand 16 and the fluid velocity can be controlled as desired and during its flow through the heat exchanger this fiud can be held at substantially constant temperature or may be heated or even cooled by a predetermined amount.

It will be understood that while in both forms illustrated the tubes are shown serially connected from end to end of the heater, other specific arrangements of the tubes may be employed, giving for example a series-parallel flow of fluid through the heater.

While the apparatus illustrated is the most suitable of which I am at present aware for carrying the invention into effect, it will be obvious that the herein described method may be practiced in other than tubular heaters, and the invention is, therefore, to be considered as in no way limited by the apparatus shown, but is to be considered as embracing all that may fall within the scope of the appended claims.

I claim: d Y

1. In the operation of continuous flow fluid heaters, that improvement which consists in by-.passing a part of the fluid to be supplied to the heater and passing said part through a portion of the heaterjn heat exchange relation with the fluid being heated and out of contact therewith and mixing said part with the'iiuid from which it was separated while in a confined stream and before the iiuid reaches its final temperature.

2. In the operation of continuous flow fluid heaters, that improvement which consists in by-passing a part of the fluid to be supplied Lacasse to the heater, passing said part through a portion of the heater in heat exchange relation With the fluid being heated, and controlling the amount of fluid by-passed in' response to the temperature of the fluid discharged from the heater.

3. In apparatus of the class described, the combination with a combustion chamber' and a heating chamber, of continuous flow fluid heating means located in said chamber and comprising a heat exchanger portion extending from said heating chamber into said combustion chamber, said exchanger being formed by an outer conduit through which the fluid to be heated is passed, an inner con'- duit through Which a cooling fluid is passed, and a connection for introducing fluid from said inner conduit into a portion of the heating means in Which the temperature of the fluid is less than the final temperature attained by the fluid in the heating means.

4. In apparatus of the class described, a heater comprising a setting forming a combustion chamber and a heating chamber in communication at their upper ends to provide a serial combustion gas flow therethrough, a fluid heating conduit comprising a plurality of serially connected tubes located in said heating chamber, and a heat exchanger formed by a plurality of serially connected outer tubes receiving the fluid from said first named tubes and a plurality of serially connected inner tubes adapted to receive a cooling fluid, said exchanger extending from the heating chamber int-o the combustion chamber and a connection for introducing fluid from said inner tube .portion of the heat exchanger into a portion of the heating conduit in Which the temperature of the fluid is less than the final temperature attained by the fluid in the apparatus.

5. In apparatus of the class described, the combination With a setting having a roof and forming a combustion chamber and a heating chamber in communication adjacent to the roof, of means for protecting said roof comprising a heat exchanger formed of outer and inner tubes, a connection for supplying a fiuid to the outer tubes, a connection for supplying a cooling iuid to the inner tubes and a connection for introducing fluid from said inner tube portion of the heat exchangervinto the outer tube portion thereof.

6. In apparatus of the class described, means for protecting a surface exposed to radiant heat comprising a heat exchanger located between said surface and the source of heat, said exchanger comprising a plu rality of connected outer tubes arranged to forma screen for said surface and a plurality of connected tubes within said outer tubes, and supply and discharge connections for both outer and inner tubes, said discharge for the inner tubes arranged to deliver to said supply connection for the outer tubes.

7 In apparatus of the class described, the combination With a passage adapted to convey combustion gases, of a bank of heating tubesl located in said passage, aheat exchanger comprising concentrically arranged inner and outer tubes located between the inlet end of said passage and said tube bank, a connection from the discharge end of said bank of tubes to the outer set of tubes of said exchanger, and a connection from the discharge end of the inner tubes of said exchanger to the inlet of said bank of tubes.

8. In apparatus of the class described, the combination With a passage adapted to convey combustion gases, of a set of serially connected heating tubes located in said passage, some of said tubes being of lar er diameter than others of said tubes, an a set of serially connected tubes located Within said large diametered tubes, the diameters of said last named tubes beingsuch that the free cross-sectional area through said firstA named set of tubes is substantially constant throughout its entire length.

9. In apparat-us of the class described, the combination of a setting forming a combustion chamber and a heating chamber, of a bank of tubes located in said heating chamber, a double-tubedv heat exchanger located between said bank of tubes and the inlet of said chamber, the outer tubes of said exchanger being connected with the discharge end of said bank 4of tubes, an inlet conduit leading to said bank of tubes, conduits connecting the inner tubes of said heat exchanger in parallel with said inlet conduit,

a valve controlling the flow of fluid through said inner tubes, a discharge conduit leading from the outer tubes, and a thermostat located in said discharge conduit for controlling said valve.

l0. In the. art of heating fluids, the process consisting in flowing a stream of fluidto be heated toward a heating zone, splitting off from said stream a portion thereof, passing said portion in heat exchanging relation With said stream Within said zone to prevent overheating of the stream, but Without mixing said portion with the stream during the heat exchanging step, and mixing said portion with the remamder of the stream at a point in the stream path prior to that at which the -fiuid obtains its highest temperature.

l1. The process as set forth in claim 10 and in which the relative size of the portion split off from the stream is varied in accordance With the final temperature of the stream.

12. The process as set forth in claim ll0 13. The process as set forth in claim l0 and inwhich the relative size of' the portion split o' from the stream is varied in accordance with the nal temperature of the stream while `the split-0H portion is surrounded by the stream during the heat interchange step.

WILBUR H. ARMACOST.I f

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