US2240372A - Superheater element - Google Patents

Description

April 29, 1941.

A. HUET 22403.72

SUPERHEATER EUEMENT Filed June 4, "1940 I INVENTOR. ANDRE Hu: 7.

ATTORNEY.

Patented Apr. 29, 1941 SUPEEHEATE-R ELEMENT Andre Huet, Paris, France Application June 4, 1940, Serial No. 338,718 In France May 25, 1939 1 Claim.

The present invention relates to improvements in tubular super-heating elements intended to be disposed in the flues of aboiler and more particularly in a locomotive boiler.

In locomotive super-heater elements wherein the steam in saturated state passes rearwardly to the neighborhood of the firebox of the boiler by a tube, or assembly of tubes, which will be referred to as the inlet tubes, and then flows forwardly through a tube herein called the outle tube which extends back towards the superheater header, the outlet tube contains steam at higher temperature than the inlet tube or tubes and consequently is submitted to linear displacement greater than that of the inlet tubes. This difference of distortion or expansion is accentuated when the outlet tube is disposed nearly in the axis of the flue; also, when, because of the disposition of the inlet tubes, or their shape, or both, the outlet tube is shielded against cooling that would otherwise result from radiation of heat in a direction towards the surface of the flue.

Because of these differences of expansion the outlet tube during use of the superheater exerts on the inlet tube or tubes a considerable force susceptible of surpassing the elastic limit of the inlet tubes at the temperature of operation and to produce in these tubes a permanent elongation. When during subsequent cooling of the superheater the outlet tube reverts to its normal length the inlet tube remains extended because of having been subjected to permanent elongation. Thus, it is submitted to a pressure at its extremity with the possibility of permanent distortion. The repetition of phenomena of this nature produces substantial deformation in the inlet tubes which can cause obstruction in the flue, render difllcult the extraction and reinsertion of the superheating elements and eventually renders the superheater elements useless.

The consequence of these differences of expansion are particularly to be feared when the part of the inlet tubes located in the flue is made up of a series of parts, some of which are more rigid than others, because then the deformation is produced in the less rigid parts, flexing these more than if the deformation were distributed over the entire length of the elements located in the flue.

An object of the present invention is to provide a superheating element so formed as to alleviate these disadvantages.

According to the invention the inlet tube, or each of the inlet tubes of a superheating element, is provided with an expansion bend in one of its less rigid parts, preferably that part which is at least heated. When possible the expansion bend is formed in a part of the inlet tube located outside of the flue. This expansion bend lends itself to the movements in question without being submitted to permanent deformation and at the same time to not obstruct the natural path of the gases in the flue.

This bend may, according to the invention, be formed in one or in several :planes and even have the form of a helix.

In elements consisting of several inlet tubes arranged in a circle and grouped about the outlet tube the expansion bend is formed in portions of the inlet tubes located outside the flue in the boiler smokebox.

Where the space in the smoke box does not provide room for expansion bend in the inlet tube of the element it may be located in the flue in the form of a spiral so .alined with other parts of the inlet tubes as to create the least possible obstruction to the gases.

In the drawing:

Figure 1 is a longitudinal sectional view through a boiler flue showing a superheating element embodying the invention.

Figure 2 shows the same element in plan view.

Figures 3 and 4 are sections on the lines 3-3 and 4-4 in Fig. 1.

Figures 5 and 6 are views similar to Figs. 1 and 2 of another type of superheating element embodying the invention.

Figure 7 is a sectional view on line 1-! in Fig. 5.

In the superheater represented in Figs. 1 to 4 the outlet tubes consist of a series of small tubes provided with longitudinal fins and disposed about a larger outlet tube. The numeral l designates a flue of a locomotive boiler in which are located the assembly of small tubes 2 provided with longitudinal fins 3 as well as the large outlet tube i. These tubes are joined together at their inner ends by a bree-ches piece 5. At their opposite ends the small tubes 2 are connected by a breeches piece ii to a section I connected to the saturated steam header while the outlet tube t has an extension 3 for discharging the superheated steam into the superheated steam headers. The position of the headers is fixed with respect to front tube sheet It] of the boiler.

As a general rule the fins 3 do not extend to the breaches piece 5, the end portion of the small tubes 2 near the firebox being exposed to gases at very high temperature in which it is now useful to increase the absorption of heat and where the fins could not be sufficiently cooled by the steam. It follows that under the influence of differences of expansion which have been mentioned previously, the permanent deformation of the small tubes are localized, especially when these tubes are not provided with curves of expansion in this portion near the breeches piece 5 where the metal is veiy hot.

In a superheater element according to the invention the small tubes 2 are provided with an expansion bend 9 located between the front flue sheet and the breeches piece 6. This bend accommodates the elastic deformation sufficiently to permit the small tubes 2 to follow the large tube 4 in its expansions without being subjected to permanent elongation. As the bends 9 are more easily deformable than the other parts of the tubes 2, it is these portions that become subjected to permanent deformations, if any should be produced by improvident circumstances such as excessive temperature. As shown in Figs. 1 and 2, the bends in the four tubes 2 are located with respect to the axis of the flue outlet in such manner as not to block it and thus leave a free passage for the gases leaving the tube.

In a superheating element represented by Figs. 5 to '7 the saturated steam lead is connected by a breeches piece H to two small tubes l2 joined at two diametrically spaced points to an annular conduit l3 from the other end of which extend the two small tubes I4 joined by a breeches piece 15 to the outlet tube 4 which is disposed substantially coincident with the axis of the annular conduit I3. The small tubes I2 in portions located in front of the tube sheet are formed with expansion bends. Here again the bent portions are so spaced as not to block the flue outlet, but contrary to the preceding case where each bend is in a plane, here they have been given a twist of to increase their flexibility.

What I claim is:

In a tubular heat exchange: superheater element disposed in the flue of a fire tube boiler and having a, plurality of inlet sections joined outside the flue by a breeches piece and disposed about an outlet section for superheated steam, said inlet and outlet sections communicating at their inner ends and their outer ends: being rigidly connected to saturated and superheated steam headers, respectively; and expansion bends formed in each inlet section from portions thereof contiguous to said breeches piece.

ANDRE I-IUET.

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