US1794507A - Fluid heater - Google Patents

Description

FLUID HEATER Filed Deo. 4. 1929 2 Sheets-Sheet 1 INVENTORA ATTom/Ey.

March 3, 1931. w. H. ARMAcosT FLUID HEATER 2 Sheets-Sheet 2 Filed Dec. 4, 1929 I N VEN TOR.

ATTRNEY.

Patented Mar. 3, 1931 UNITI-:D STATE-s PATENT `ol-Flcla e 'WILIB'UR H. ARMACOST, 0F NEW Y0RK,VN. Y., ASSIGNOR '.lO THE SUPERHEATER '.PANY, OF NEW YORK, N. Y.

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FLUID HEATER Application filed December 4, 1929, Serial No. 411,485, and in` Great Britain May 16, 1929.

My invention relates to fluid heaters and has particular reference to heaters of this type operating under extreme conditions of temperature and pressure. The invention is particularly useful when incorporated in the design of steam superheaters operating in conjunction with power boilers, and this form of apparatus has therefore been chosen as the illustrative embodiment to be hereinafter described. It will be understood however, that the invention is not intended to be restricted to use with superheaters, but is equally applicable to other comparable forms of heating apparatus.

This case is a continuation in part of United States application Serial` Number 346,279 filed on March 12,1929, and as to mattercommon to that case and the present one the filing date of the former is claimed for purposes of priority.

The increasing use of higher operating pressures in modern power plants has resulted in the production of steam having a high saturation temperature, which, upon being superheated to the desired degree, may attain a total. temperature of 800 deg. F. and over. In some instances superheated steam at temperatures considerably in excess of 800 deg. F. is required. In order to obtain steam temperatures of this magnitude, it is necessary to place the superheater in a zone of intense heat and the severity ofthe service when the steam ltemperature is so high has made the use of ordinary carbon steelv tubing impractical. It is a known fact that the heat transfer characteristics of asuperheater may be improved by the use of very small diameter tubing, which operates to increase the velocity of the steam through the superheater and to present a greater area of heating surface per unit volume of steaml With a superheater constructed of such small tubing, extreme conditionsA of pressure and temperature could be withstood by ordinary'tubing, but such construction isnot practically possible because of the excessive pressure dropl entailed by the reduction in the size of the tubing to a diameter which will give otherwise satisfactory service. In order to meet this condition, tubing made of special alloy steels has beenemployed, particularly in the last pass lof the superheater, in which the steam conveyed therethrough is at or 'near its maximum temperature. tion, however, is extremely expensive and the principal object of the present invention is the provision of an improved form of superheater, by means of which steam may be superheated to extreme temperatures and at high pressures without resorting to the use of expensive special materials. I

The invention has been illustrated as embodied in a superheater installed in lan interdeck, cross-drum boiler of standard type,.al though it is to beunderstood that the invention may equally well be applied to superheaters in other locations in such boilers and in conjunction with other types of boilers. In .the drawings, Fig. 1 is a sectional view showing the boiler and superheater arrange- `ment; Fig. 2 is a fragmentary section illustrating a modified form of superheater applied in the same position as the superheater shown in Fig. 1; Fig. 3 is a section on line 3--3 of Fig. 1; Fig. 3a is a section similar to that of Fig. 3 illustrating a modification; and Fig. 4 is a section on line 4-4 of Fig. 2; Figs. 3, 3a and 4 being on a considerably enlarged scale.

Referring now to Fig. 1, the boiler'comprises spaced banks or decks of horizontally inclined steam generating tubes 1 and 2 which are vfed f rom the Asteam and Water drum 3 through heaters 4 and 5, and the connecting nipples 6 and 7. Headers 8 and 9, together with nipples l0 and circulators 11, serve to connect the discharge end of tubes 1 and 2 to the steam and water drum. Bailes 12 and 13 servev to direct the combustion gases'over the tube banks in three passes in the usual manner. n

The superheater is shown in the usual interdeck location in the space between tube banks land 2 in the first pass, and comprises an inlet header 14 connected with the steannspace of drum 3 by means of pipe 15, van outlet header 16, and a plurality of tubular superheating units 17 of the multi-loop type. The inlet portions of these superheater units are of thel diameter which would normally be This construcemployed, but adjacent to their outlet ends each unit is bifurcated as at '18 and the remainder of each unit comprises two tubes 17a and 17?) of smaller inside diameter connecting the bifurcation 18 with the outlet header 16. In the form shown it Will be noted that one loop of the four-loop unit vis made of the small tubing, but the relative lengths of the small tubing and the large tubing will vary in accordance with the specific conditions for Which the individual super heater is designed. Also, the relation of the inside diameter of tubes 17 a and 17 b to the diameter of the major portion of the tubing 17 Will vary With individual designs. In some instances the increase Vin heat transfer eiiiciency due to the use of the small tubing may be sufficient so that the combined sectional area of tubes 17 a and 17 b may be made equal to the sectional area of tube 17. In that case there is no increase in steam velocity through'the small-tube section as compared With the main portion of the unit and the only increase in pressure drop Will be that due to the increase in the surface area. In some instances it is possible that the increase in heat transfer eiiiciency due to the greater area per unit volume of the smaller tubes Will permit the use of tubing of a size such that the combined cross-sectional area of tubes 17 a and 17 b Will even be greater than that of tube 17, while in other instances it Will be necesl sary to provide an increase of steam velocity through the last pass by making the combined tube area smaller than the area of the tube 17. In the form illustrated'in Figs. 1 and 3 the sum of the inside areas of the tWo branches 17a and 17?) of the bifurcated part is the same as the area of the single larger pipe, or approximately so. As will be readily appreciated by those skilled in the art, the relative lengths and diameters of the tubes 17ay and 17 b Will be determined by calculation in each individual case in order to provide a superheater which Will meet the conditions of steam temperature and pressure drop imposed When employed With the gas temperature, volume and velocity available. In the great majority of instances less than half the total area of heating surface Will be of the small diameter tubing, and it is generally desirable to hold the proportion of heating surface formed of the small tubing to a minimum in order to prevent undue pressure drop through the superheater.

In Figs. 2 and 4 a form of superheater is shown Which is particularly suited for conditions vvhere an increase in steam velocity is required. In this form the superheated header 14 and the outlet header 16 are connected by a plurality of multi-loop units 17. which instead of being bifurcated near theiil outlet ends, as are the' units 17 shown in Fig.y

1, have their internal diameter reduced at approximately the same point to provide a last pass or loop formed by a single small diametered tube 1.70.

While any desired method of joining the large and small diameter pipes together may be employed, the elimination of joints in high pressure piping makes it desirable that the superheater units be made integral, and the bifurcated joint shown in Fig. 1 may convenientl be made by the process disclosed in U. S. Iratent No. 1,169,209 granted to C. H. True, et. al. on January 25, 1916, While the tubes 17 and 17C, shown in Fig. 2, may conveniently be joined integrally through the medium of a forged return bend manufactured by the process outlined in the above patent, supplemented by the process disclosed in Patent No. 1,255,355 issued to C. H. True, et al. on February 5, 1918.

From an inspection o-f Fig. 4 it will be noted that the Wall thickness of the pipe 170 is greater than that of the pipe 17. In fact it is shown, and in practice' is preferably selected, such that the outside diameters of the two are the same or substantially so. This thickening has the advantage of increasing the life of the pipe, and When the tWo outside diameters are the same it presents the furtherV` great advantage, when the unit is manufactured by the patented process mentio-ned, that it simplifies the manufacture and obviates the necessity of special dies, which Would otherwise be required.

In installations in accordance with Figs. 1 and 3 the gauge of the tubes in the bifurcated part may evidently also be greater than that of the pipe in the single pipe part. This is illustrated in Fig. 3a.

The advantages accruin from the use of this invention may be brie y summarized as follows: The major portion of the superheater units may be made or ordinary carbon steeltubing of the size and thickness normally employed, as the temperature of the steam flowing through the first portion of the units is sufficiently low to provide ample cooling for them. Ordinary carbo-n steel may also be employed for the remaining portion of the units as the decreased diameter of the tubing used in this portion of the units results in an increase in the heat transferiyefiiciency, by means of which the necessary cooling effect can be obtained from the more highly superheated steam in this portion of the superheater. This increase in the heat transfer eiliciency, Which results in increasing the effectiveness of a given temperatured steam as a cooling agent, also permits the placing of the discharge end of the superheater units in a Zone of more intenseheat. Because of this factor itisv possible to arrange a superheater as shown in the accompanying drawings, so that eounterlow between the steam and the heating gases may be employed.

Heretofore, when eXtreme conditions of temperature Were encountered, it has been in tion of the gas path.

many cases necessary to forego the advantages of a counter-flow arrangement in order to obtain the cooling effect of the lowest temperature steam in the .portion of the super-heater units located in the hottest por- It will be clear that advantages need not be taken of this possibility of using the counter-flow arrangement, but that on the contrary my invention is likewise advantageous when the flow of gases and the flow of the stream are in the same general direction.

Because of the increased heat transfer efficiency of the small diametered tubes and the fact that the super-heater may be most advantageously arranged with respect lto the gas flow, a considerable reduction in the total amount of heating surface necessary to produce a given degree of superheat may be ob- .1- tained. This results not only in a saving of superheater material, but also in many instances results in a substantial saving because of the more compact boiler arrangement possible with the smaller superheater.

Vhile in accordance with the patent statutes I have described preferred forms of my invention, it is to be understood that they are illustrative only and that the invention embraces all such forms of apparatus as may fall Within the scope of the appended claims. I claim:

1. In apparatus of the class described, the

pass, each of said units comprising an inletl portion Jformed of a single tube and an outlet portion serially connected therewith formed of a single tube of the same external but smaller internal diameter than said inlet tube.

3. In apparatus of the class described, the combination with means defining a pass for Y combustion gases, of a plurality of multi-loop tubular heating units disposed generally transversely of the gas flow through the pass, each of said units being formed with at least the last loop thereof composed of tubing having an internal diameter less than the internal diameter of the remaining loops and having a greater ywall thickness than the remaining loops.

4. Apparatus of the class described comprising an inlet header, an outlet header, and a plurality of integral tubular heating units connecting said headers, each of said units comprising a single bifurcated tube connected at one end to the inlet header and a pair of tubes of smaller diameter than said single tube connecting the bifurcation with said outlet header, the cross-sectional area of said single tube being at least as great as the combined cross-sectional areas of said pair of' tubes.

V5. A superheater unit comprising an inlet portion formed by a tube bifurcated at one end and an outlet portion formed by a pair of tubes joinedto the bifurcated end of said first named tube, the combined crosssectional area of said small diametered pipe being less than the cross-sectional area of said bifurcated pipe.

6. Apparatus of the class described comprising an inlet header, an outlet header, and a plurality ofintegral tubular heatingunits connecting said headers, each of said units comprising a single bifurcated tube connected at one end to the inlet header and a pair of tubes ot' smaller diameter but greater wall thickness than said single tube connecting the bifurcation with said outlet header, the cross-sectional area of said single tube being at least as great as the combined cross-sectional areas of said pair of tubes.

7. The combination with a boiler having a bank of horizontally inclined steam-generating tubes and a baffle defining a transverse gas pass over said tubes, of a superheater located in said pass above said tube bank, said superheater comprising a plurality of multiloop tubular units disposed generallytransverselyof the gas flow, each unit comprising an inlet portion formed by a single tube and an outlet portion comprising a tube having a smaller diameter but a greater wall thickness than said first named tubes and serially connected therewith.

WILBUR H. ARMACOST.

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