US3687116A

US3687116A - Process steam heaters

Info

Publication number: US3687116A
Application number: US140409A
Authority: US
Inventors: Kenneth Holt
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1971-05-05
Filing date: 1971-05-05
Publication date: 1972-08-29
Anticipated expiration: 1989-08-29

Abstract

This invention relates to process stream heaters. These heaters comprise a furnace chamber through which a number of tubes carrying the process stream to be heated pass. These tubes must be free to expand along their length but should not distort away from position since such distortion might result in uneven and insufficient heating. According to the invention this distortion is prevented where there are adjacent pairs of rows of tubes by means of a tube guide system comprising a zig-zag lattice made up of a number of clamping bars. Adjacent bars are pivoted to one another near their ends and the tubes nest in and are trapped in the V-shaped openings of the zig-zag lattice. In this way, the tubes are left free to expand and more relatively to one another along their lengths but any attempted distortion of a tube away from its axial position tends to cause pivoting of the clamping bars retaining that tube in place so that the lattice tends to lock more tightly onto other tubes so restraining that tube attempting to distort.

Description

waited States atet [451 Aug. 29, 1972 Holt [54] PROCESS STEAM HEATERS [72] Inventor: Kenneth Holt, Twyford, England [73] Assignee: Foster Wheeler Corporation, Livingston, NJ.

[22] Filed: May 5, 1971 [21] Appl. No.: 140,409

[52] US. Cl ..122/356, 122/510 [51] Int. Cl ..F22b 37/24 [58] Field of Search ..122/240 R, 356, 510

[56] References Cited UNITED STATES PATENTS 3,026,858 3/ 1962 Fleischer ..122/510 3,127,876 4/1964 Olson ..122/356 X 3,240,204 3/1966 Wiesenthal ..122/240 3,384,053 5/1968 Fleischer ..l22/5l0 Primary Examiner-Kenneth W. Sprague Attomey-John Maier, III, Marvin A. Naigur and John E. Wilson [57 ABSTRACT This invention relates to process stream heaters. These heaters comprise a furnace chamber through which a number of tubes carrying the process stream to be heated pass. These tubes must be free to expand along their length but should not distort away from position since such distortion might result in uneven and insufficient heating. According to the invention this distortion is prevented where there are adjacent pairs of rows of tubes by means of a tube guide system comprising a zig-zag lattice made up of a number of clamping bars. Adjacent bars are pivoted to one another near their ends and the tubes nest in and are trapped in the V-shaped openings of the zig-zag lattice. In this way, the tubes are left free to expand and more relatively to one another along their lengths but any attempted distortion of a tube away from its axial position tends to cause pivoting of the clamping bars retaining that tube in place so that the lattice tends to lock more tightly onto other tubes so restraining that tube attempting to distort.

9 Claims, 5 Drawing Figures PATENTEDwszs 1912 SHEET 3 [IF 3 PROCESS STEAM HEATERS This invention relates to process stream heaters which are used to heat various processing feed streams in a processing plant such as an oil refinery.

BACKGROUND TO THE INVENTION These heaters generally comprise a furnace chamber provided with one or more burners and through this chamber extend a number of tubes carrying the stream to be heated.

The mounting of these tubes is not simple because one must allow for them to expand along their length. On the other hand they should retain their positions relatively to one another so as to ensure even and sufficient heating. The restraining of the tubes in this way is made more difficult by the fact that uneven coking may occur in them and accordingly they may bend from their designed position; Additionally one or more of the burners in the heater might fail so subjecting different tubes to different heating effects.

Since the tubes are of quite large diameter, e. g. 8 inches, any attempt to restrain them in place will involve extremely large forces. Thus, one way of restraining them would be to link them to the walls of the heater. The-great disadvantage of doing this, however, is that the walls would then need to be of massive construction to resist the forces likely to be placed in them by the tubes and this solution would, therefore, entail a considerable increase in the cost of the heater and also in the time and complexity of its construction.

It is, therefore, an object of the invention to provide a relatively simple way of restraining the tubes relatively to one another in such heaters.

THE INVENTION According to the invention there is provided a tube guide system for a pair of rows of tubes in a heater, the system comprising a number of clamping bars, pairs of which are pivoted to one another at positions near their ends so as to form a roughly zig-zag lattice with the tubes nesting in the troughs defined between crests of the zig-zag lattice, the size of the openings of the troughs between the ends of clamping bars being less than the diameter of the tubes so that the latter are trapped in place, whereby the tubes are free to expand relatively to one another along their lengths but any attempted distortion of a tube away from its axial position tends to cause pivoting of the clamping bars retaining that tube in place so that the lattic tends to lock more tightly onto other tubes and so restrains the tube attempting to distort.

Such a tube guide system is very simple and cheap to install and relies upon the strength of other tubes to prevent a particular tube from distorting. Therefore no special reinforcing of the walls of the heater are required. When there are a relatively large number of tubes in the rows, the system can rely entirely upon the tubes themselves to restrain one another, but when there are relatively few tubes it is often desirable to link the ends of the tube support system to opposed walls of the heater for additional support to the tubes. The force placed on the end walls is quite small, however, and so they need very little if any reinforcement.

Although the tube guide system of the invention is very eifective in preventing distortion of an particular tubes or a number of tubes, away from their axis, it

leaves the tube free for thermal expansion and contraction independently of one another along their lengths.

To hold the tubes at the ends of the rows in place, end clamping members are required which extend sufficiently around the last tubes and co-operate with the clamping members to lock them in position and which are pivoted to the last clamping bar. When the tube guide system is to be linked to the walls of the heater, these end clamping members are linked to the wall.

The tubes in the pairs of rows of tube will normally be spaced and arranged so that their longitudinal axis lay on a triangular pitch arrangement since this ensures a fairly uniform heating of each tube right the way round its circumference. The invention is equally ap plicable, however, to the case when the tubes are pitched on a square pattern or any other pattern.

In order to support the tube guide support system, the clamping bars of the system should rest on support members fixed to the outside of the tubes so as to retain the system roughly horizontal.

The tube guide system of the invention is particularly useful in heaters where there are four upright sets of tubes through the furnace heating chamber, these tubes all being formed by bending one length of tubes, two lengths of tubes or all being separate lengths of tubes. The four upright sets of tubes can be positioned so that a set extends up near opposite side walls while the remaining two sets extend up side by side in the middle of the chamber between the side walls. The tube guide system is then eminently suitable for restraining the tubes of the two sets extending up the center of the chamber.

BRIEF DESCRIPTION OF THE DRAWINGS An embodiment of a tube support system according to the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-section through a heater employing the system of the invention;

FIGS. 2 and 3 are enlarged plan views taken in the line A-A of FIG. 1 showing the tubes in their normal position and in an exagerated position showing attempted distortion of a tube, respectively;

FIG. 4 is an elevational detail in the direction of the line B-B of FIG. 2; and

FIG. 5 is a diagrammatic plan view showing the tube arrangement within the heater of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The heater 10 shown in the drawings comprises a furnace heating chamber 12 defined by side walls 14 covered with insulation 16 and a floor 18. From the top of the chamber an outlet 20 leads to a stack. In the floor 18 are provided burners (not shown).

Within the chamber 12 are a number of tubes 22 each bent so as to make 4 upright passes. The tubes 22 have upright passes 24 and 26 adjacent side wall 14, two

central passes

28 and 30 in the middle of the chamber and the

passes

24 and 28, and 26 and 30 respectively, are joined at their tops by

horizontal passes

32 and 34, while the

passes

28 and 30 are joined at their lower ends by a U bend 36. As shown best in FIG. 4 the

passes

24 and 28, and 26 and 30 are staggered relatively to one another so that the tubes in the central passes 28 and 3b are spaced on a triangular pitching.

The tubes 22 are supported by a cross bar 40 in the floor 18 on which the bends 36 rest and are restrained by pegs d2 projecting from the tubes into the bar 40 and at the lower ends of the

passes

24 and 26.

it is important to restrain the

central passes

28 and 30 both relatively to one another so as to maintain substantially uniform even heating and in their central positions so that unduely large forces are not applied to the side walls 14. If they are so restrained then the upper ends of the

passes

24 and 26 need only simply I sliding guides 50 allowing upward thermal expansion and contraction of the tubes of the

passes

24 and 26 and no large forces will be applied to the side walls ld.

The tube guide system 60 of the invention provides this effective restraint upon the tubes of the central passes 28 and 3t) and the system is shown in more detail in FIG. 2.

The system comprises a number of clamping bars 62, pairs of which are pivoted to one another near their ends by pivot pins 64 (FIG. 3). Nuts and bolts can be used instead of the pins 64. The clamping bars 62 are thus assembled into a horizontal zig-zag configuration and the tubes of the

passes

28 and 30 are nested in the troughs formed by the zig-zag configuration. The distance between the ends of the clamping bars 62 defining a trough, i.e., the distance x, is less than the diameter of the tubes so that the latter are trapped in the troughs.

The tubes of the

passes

28 and 30 have small supports 66 welded to their circumference and the clamping bars 62 simply rest on these.

At the ends of the system, end clamping members 68 are provided. As can be seen they are shaped so as to encompass sufficient of each end tube to trap it in place. The members 68 are pivoted to the final clamping bar 62.

Normally the system 60 will maintain the tubes of the passes 28 and 39 in their correct position on its own, but if relatively few tubes are present it may be desirable to link the end member 68 through pivoted links 70 to front and rear walls 72.

The system 60 restrains the tubes in the following way as will be described in connection with FIGS. 2 and 3. if one of the tubes 128 tries to bend away from the upright position through uneven heating because a burner (not shown) has failed or because of coking in the tube, it will try to move in the direction of the arrow 1%. When this happens, because it is trapped in the trough formed by the bars 62, it attempts to pivot the bars 162 which encircle it in the direction of the arrows 132. in attempting to pivot relatively to one another, the bars 162 by a kind of scissors effect grip all the more tightly on the tubes near to the defecting tube 128. Therefore, to distort, the tube 12% it must at the same time bend all of the tubes in the pass 30 and although some slight deflection will occur it will be sufficiently small to be unimportant.

it will therefore be realized that, although the system 64) is very simple and cheap, it is extremely effective in restraining the tubes of the passes 28 and 39 in place. In addition it puts very little, if any, additional forces on the walls id and 72 of the heater and so these walls do not need costly strengthening.

Although the system gives very effective restraint in the horizontal sense, it leaves the tubes in the passes 28 and 34), plenty of freedom for thermal expansion and contraction even if adjacent tubes expand differently because of say difierent coking within the tubes or if a burner fails and different tubes then expand lengthwise by varying amounts.

A latitude of modification, change and substitution is intended in the foregoing disclosure and in some instances some features of the invention will be employed without a corresponding use of other features. Accordingly it is appropriate that the appended claims be construed broadly and in a manner consistent with the spirit and scope of the invention herein.

I claim:

1. A process stream heater comprising a furnace heating chamber, at least a pair of rows of parallel tubes, said rows extending side by side across said chamber, said pair of rows of tubes being restrained by means of a tube guide system comprising:

a. a number of clamping bars,

b. pivot means being provided between adjacent pairs of said bars, said pivot means being provided near ends of said bars leaving free ends projecting beyond said pivot means, whereby said adjacent clamping bars are pivoted to one another,

c. adjacent pairs of said bars defining V-shaped openings so that said clamping bars constitute a roughly zig-zag lattice,

d. said tubes of said rows nesting in said V-shaped openings and being trapped in said openings by free ends of damping bars,

whereby said tubes are free to expand and move relative to one another along their lengths but any attempted distortion of a tube away from its axial posi' tion tends to cause pivoting of said clamping bars retaining that tube in place so that said lattice tends to lock more tightly onto other tubes so restraining that tube attempting to distort.

2. A process stream heater according to Claim 1 further comprising at said ends of said lattice end clamping members, means for pivoting said end clamping members to said clamping bars at at said end of said lattice, said end clamping members comprising an arm by means of which said member is pivoted to said adjacent clamping bar, and a pair of lugs having part circular shaped recesses in which tubes are arranged to nest and be trapped in place.

3. A process stream heater according to claim 2 further comprising opposed side walls defining said furnace heating chamber and pivot means pivotally linking said end clamping members to said opposed side walls.

d. A process stream heater according to claim 1 in which said tubes in each of said pair of rows of tubes stagged relative one another so that their longitudinal axis are arranged on a triangular pitch.

5. A process stream heater according to claim 1 further comprising support members fixed to said tubes, said clamping bars resting on said support membets.

6. A process stream heater according to claim 1 comprising opposed side walls defining said further heating chamber, an upright substantially parallel row of tubes extending rear to each opposed side wall and said pair of rows of parallel tubes extending side by side across the furnace heating chamber, said pair of row of tubes being restrained by said tube guide system.

7. A process stream heater according to claim 6 in which all of said rows of tubes have been formed by bending lengths of tubes so that corresponding tubes in all rows are connected by series flow.

8. In a process stream heater a pair of rows of parallel tubes extending side by side which are restrained by a tube guide system comprising:

a. a number of clamping bars,

b. pivot means being provided between adjacent pairs of said bars, said pivot means being provided near ends of said bars leaving free ends projecting

Claims

1. A process stream heater comprising a furnace heating chamber, at least a pair of rows of parallel tubes, said rows extending side by side across said chamber, said pair of rows of tubes being restrained by means of a tube guide system comprising: a. a number of clamping bars, b. pivot means being provided between adjacent pairs of said bars, said pivot means being provided near ends of said bars leaving free ends projecting beyond said pivot means, whereby said adjacent clamping bars are pivoted to one another, c. adjacent pairs of said bars defining V-shaped openings so that said clamping bars constitute a roughly zig-zag lattice, d. said tubes of said rows nesting in said V-shaped openings and being trapped in said openings by free ends of damping bars, whereby said tubes are free to expand and move relative to one another along their lengths but any attempted distortion of a tube away from its axial position tends to cause pivoting of said clamping bars retaining that tube in place so that said lattice tends to lock more tightly onto other tubes so restraining that tube attempting to distort.

4. A process stream heater according to claim 1 in which said tubes in each of said pair of rows of tubes stagged relative one another so that their longitudinal axes are arranged on a triangular pitch.

5. A process stream heater according to claim 1 further comprising support members fixed to said tubes, said clamping bars resting on said support members.

6. A process stream heater according to claim 1 comprising opposed side walls defining said further heating chamber, an upright substantially parallel row of tubes extending near to each opposed side wall and said pair of rows of parallel tubes extending side by side across the furnace heating chamber, said pair of row of tubes being restrained by said tube guide system.

8. In a process stream heater a pair of rows of parallel tubes extending side by side which are restrained by a tube guide system comprising: a. a number of clamping bars, b. pivot means being provided between adjacent pairs of said bars, said pivot means being provided near ends of said bars leaving free ends projecting beyond said pivot means, whereby said adjacent clamping bars are pivoted to one another, c. adjacent pairs of said bars defining V-shaped openings so that said clamping bars constitute a roughly zig-zag lattice, d. said tubes of said rows nesting in said V-shaped openings and being trapped in said openings by free ends of clamping bars.

9. In the heater of claim 8 support member fixed to said tubes, said clamping bars resting on said support members.