GB2035535A - Supporting heat exchange tubes - Google Patents

Abstract

A method of supporting vertical reformer tubes, 2, wherein the tubes are arranged in groups each group communicating to a common header 6 via individual expansion pigtails 7, which method comprises providing at the lower ends of the tubes and in contact therewith a support member, 10 such as a beam, for carrying at least part of the weight of the tubes without significant reaction being the imposed on the headers when the headers are raised to their operational temperature. Outlet headers and support members are maintained at about the same temperature, and constructional materials are selected to minimise differential expansion therebetween. Positioning of the outlet pipework with respect to fixed supports can be optimised to minimise or compensate for differential thermal expansion of the pipework. Large volumes of flue gas can be handled through tunnels running across the width of the reformer box via openings in the floor of the reformer box. <IMAGE>

Description

SPECIFICATION Reformer tube support method The present invention relates to a method of supporting a plurality of vertical reformer tubes.

In traditional reformer design, the reformer tubes are arranged in rows partially supported and partially suspended from the furnace steelwork in fixed positions relative to the centre-line of the furnace. When the furnace is raised to its operational temperature, considerable expansion of the materials of the furnace and its associated pipework take place. The vertical expansion of the reformer tubes is considerable and because the material of the tubes becomes relatively weak at the high operational temperature of the tubes care must be taken to ensure that no stresses are imposed upon the tubes during their vertical movement.

To carry material in and out of the reformer tubes, inlet and outlet headers are provided which are connected to the respective ends of the tubes, generally by means of expansion pigtails. These expansion pigtails are flexible pipes which have a large length to diameter ratio and which are of sufficient length to accommodate the relative movements between the tubes and their headers, whilst at the same time have to be strong enough to carry any imposed loads, such as their own weight at their usual operational temperatures, e.g. up to 850"C. Because of the relatively large amounts of movement which have to be accommodated in traditional reformer design, and because of reduced material strength, it is not possible to design the outlet pigtails to operate at the higher temperatures, e.g.up to 1 000 C, which are now desired for the reformer tube outlets, whilst maintaining the traditional design of reformer.

In one traditional design, the vertical reformer tubes have their outlet ends below the floor of the reformer box in a chamber which is open to the air in order to allow necessary cooling of the tube supports, which are generally made of mild steel, to take place. The outlet headers and the major part of the outlet pigtails are enclosed within lagging boxes to avoid the loss of heat from the product leaving the reformer tubes, and careful lagging of the portions of the reformer tubes and the pigtails lying outside the reformer box and the lagging box is also needed.

The present invention seeks to overcome this disadvantage of traditional reformer design.

In accordance with the present invention there is provided a method of supporting a plurality of vertical reformer tubes, wherein the tubes are arranged in groups, each group communicating to a common header via individual expansion pigtails, which method comprises providing at the lower ends of the tubes and in contact therewith a support member for carrying at least part of the weight of the tubes without significant reaction being imposed on the headers when the headers are raised to their operational temperature.

In one embodiment, the lower ends of the tubes of each group, and the expansion pigtails and the header associated therewith are enclosed within an annex attached to the reformer box through which the reformer tubes pass. Preferably the support member is in the form of a beam, the tube ends resting on the shorter side thereof, which beam is supported by props passing through the wall of the annex. It is desirable that each header and the lower ends of the tubes associated therewith are positioned so as to minimise the relative movement between the ends of the individual pigtails connecting them on raising the header, tubes and pigtails to their respective operational temperatures.

In addition it is preferred that the material of each header and of the pigtails are selected so as to minimise the relative movement between the ends of the individual pigtails connecting each header to the lower ends of the tubes associated therewith, on raising the header, tubes and pigtails to their respective operational temperatures.

Transfer mains are provided in communication with the outlet headers which in this preferred arrangement extend vertically through the floor of each annex. The transfer mains can then be supported at a level relative to the annex and relative to the props associated therewith so as to minimise differential vertical movement between each header and the tubes associated therewith on raising the tubes, transfer mains, props and header to their respective operational temperatures. In addition, it is also possible for each header and the lower ends of the tubes associated therewith to be positioned so as to minimise the relative movement between the ends of the individual pigtails connecting them on raising the header, tubes and pigtails to their respective operational temperatures.

By adopting the method of supporting the reformer tubes of the present invention, it becomes possible to redesign the flue gas outlet connections from the reformer box. Traditionally, the flue gas has been taken out along tunnels constructed within the reformer box which run parallel to the tube rows and are usually connected and discharged into a convection zone at one end of the furnace.

With large furnaces, the flue gas tunnels have to be enlarged and the walls of the tunnels begin to be undesirably stressed due to the pressure differential across the walls of the tunnels. In addition, the enlargement of the flue gas tunnels in order to accommodate increased amounts of flue gas begin to inter fere with disposition of the reformer tubes within the reformer box.

By using the present reformer tube support method, it becomes possible to lead the flue gases from the reformer box out through openings in the floor of the reformer box into tunnels running across the width of the reformer box. Preferably the openings are shaped so as to direct the flue gas from the reformer box into the tunnels at an acute angle to the centre-line of the tunnels.

One embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-sectional view of part of the lower portion of a reformer furnace incorporating vertical reformer tubes supported in accordance with the method of the invention; Figure 2 is an enlarged view of Fig. 1 showing the lower end of one of the reformer tubes; Figure 3 is a sectional view through part of the lower portion of the reformer furnace of Fig. 1 taken along a line parallel to the rows of reformer tubes; Figure 4 is a cross-sectional plan view of the reformer furnace of Fig. 1 showing the outlet pipework beneath the floor of the reformer box.

In the illustrated reformer furnace, the furnace wall 1 encloses a reformer box through which pass a large number of reformer tubes 2. These tubes are aligned in rows and carry reactants through the reformer furnace from the top to the bottom thereof, the highest temperature being attained at the lower end of the reformer tubes. An outlet main 3 runs across the width of the reformer furnace and is connected to the lower ends of the reformer tubes by means of line mains 4 and transfer mains 5. The lower ends of the reformer tubes 2 are connected in groups by means of a common outlet header 6 which is connected to the transfer mains 5. In order to allow relatively movement between the outlet header 6 and the lower ends of the tubes 2, individual outlet expansion pigtails 7 are provided between them.

Each outlet header, together with its associated pigtails, as well as the lower ends of its respective reformer tubes, are enclosed within a reformer annex 8 which lies immediately below the floor of the reformer box. Steelwork 9 is provided to support the reformer tubes at their lower ends beneath the reformer annex 8. The lower ends of the reformer tubes rest on a supporting beam 10 which in turn is supported by a number of beam props 11 extending through the wall of the reformer annex 8 to the steelwork 9.

Beneath the outlet pipework, a number of flue gas tunnels are provided into which flue gas passes from the reformer box through flue gas openings 13 provided in the floor of the reformer box.

In the illustrated embodiment, the lower ends of the reformer tubes, the outlet headers and the outlet pigtails are placed together in enclosed annexes 8 which are essentially extensions of the reformer box, and which are maintained substantially at the outlet header temperature. These annexes fulfil much the same function as the traditional lagging boxes, but there is no need to insulate the space enclosed by the annexes from the reformer box. Similarly, unlike prior arrangements, there is no need thermally to insulate the lower ends of the reformer tubes after passing through the floor of the reformer box.Because of the high operational temperatures of the outlet pigtails and the outlet headers, they are made of a high temperature alloy, such as an lncolloy. The supporting beam 10 as well as the beam props 11 are also made of this alloy since they have to withstand the high outlet header temperatures, whilst at the same time carrying at least part of the weight of the reformer tubes without significant deformation. Once the beam props 11 have passed through the wall of the annex 8 their temperature will have been reduced sufficiently to enable them to be directly attached to the steelwork 9, without the steelwork being overheated. As in prior arrangements, the supporting steelwork beneath the furnace floor is open to the circulation of cooling air.

From Fig. 2, it will be seen that the lower end of the reformer tube 2 is at the same height as the outlet header 6, and as close to it as possible. By this arrangement, vertical movement during expansion of these components is compensated and the relative lateral movement between the two is minimised. The outlet pigtail 7 is long enough to allow this relative movement to take place without imposing any stresses upon the header or tube, whilst at the same time being long enough to allow 'nipping-off' in the event of a reformer tube failure.

The outlet main, tine main, and transfer main are generally constructed of mild steel with a refractory lining on the inner surface thereof. By arranging for each transfer main to enter the annexes parallel to the length af the beam props 11, lateral movement between the transfer mains and the tube support system can be eliminated. Vertical differential expansion will, however, take place, but the transfer mains can be supported at a level relative to the floor of each annex which will make their effective vertical expansion relative to this level the same as the vertical expansion of the beam props 11.

- In large furnaces, expansion of the outlet main 3 and the line main 4 becomes significant, and allowance must be made for sideways movement of the transfer mains relative to the tube supporting steelwork 9. Compensation for this movement can be made by linking the supports for the beam props to their associated transfer mains and allowing the props to slide in unison with the outlet mains relative to the supporting steelwork.

Movable seals are then provided in the floors of the annexes to accommodate the sideways movement of the transfer mains and the associated props.

The supporting beams 10 will, of course, expand, but since they are disposed in parallel to the outlet headers 6, no lateral movement between them will take place. In addition, by constructing the supporting beams and the headers of the same material, relative lengthwise thermal expansion is also compensated.

By using this arrangement, the stressing of the lower ends of the reformer tubes, the outlet pigtails and the outlet headers is minimised. The described reformer tube supporting system can be used either to support part of the weight of the tubes or to transfer to the associated steelwork an access of tension imposed on the tubes by the suspension system at the top of the furnace. In either case, bending moments imposed on the outlet headers are considerably reduced, and outlet header temperatures of up to 1 000 C can be accommodated.

By adopting the reformer tube supporting arrangement shown in the drawings, it is possible to rearrange the outlet system for the reformer reactants. This rearrangement also permits the redesign of the flue gas outlet system. By providing outlet openings 1 3 in the base of the reformer box, the flue gas can be conveyed underneath the floor of the furnace without the need for ducting within the reformer box itself. This allows for much higher volumes of flue gas to be handled than was considered possible with traditional flue gas tunnels. In addition, the discharging of the flue gas from the furnace box can take place at multiple locations with the arrangement shown in the accompanying drawings.

The collecting efficiency and predictability of the flow pattern of the flue gas are also increased by arranging the flue gas openings 1 3 to direct the flue gas from the reformer box into their respective flue gas tunnels 1 2 at an acute angle to the centre-line of the tunnels. The particular angle of entry will normally depend upon the pressure differential across the flue gas opening and the volume flow rate of flue gas moving through the flue gas tunnels 1 2 past the openings 1 3.

Claims (12)

1. A method of supporting a plurality of vertical reformer tubes, wherein the tubes are arranged in groups, each group communicating to a common header via individual expansion pigtails, which method comprises providing at the lower ends of the tubes and in contact therewith a support member for carrying at least part of the weight of the tubes without significant reaction being imposed on the headers when the headers are raised to their operational temperature.

2. A method as claimed in Claim 1 wherein each header and the lower ends of the tubes associated therewith are positioned so as to minimise the relative movement between the ends of the individual pigtails connecting them on raising the header, tubes and pigtails to their respective operational temperatures.

3. A method as claimed in Claim 1 or Claim 2 wherein the material of each header and of the pigtails are selected so as to minimise the relative movement between the ends of the individual pigtails connecting each header to the lower ends of the tubes associated therewith, on raising the header, tubes and pigtails to their respective operational temperatures.

4. A method as claimed in any one of the preceding claims wherein the lower ends of the tubes of each group and the expansion pigtails and the header associated therewith are enclosed within an annex attached to the reformer box through which the reformer tubes pass.

5. A method as claimed in Claim 4 wherein the support member is in the form of a beam, the tube ends resting on the shorter side thereof, which beam is supported by props passing through the wall of the annex.

6. A method as claimed in Claim 4 or Claim 5 wherein transfer mains are provided extending vertically through the floor of the annex parallel to its associated props and in communication with the header, the transfer mains being supported at a level relative to the annex and relative to the props associated therewith so as to minimise differential vertical movement between each header and the tubes associated therewith on raising the tubes, transfer mains, props and headers, to their respective operational temperatures.

7. A method as claimed in any one of Claims 4 to 6 wherein each transfer mains is linked to the props associated therwith so that the transfer mains and the said props move in unison, and wherein the transfer mains and the said props are movably sealed into the floor of the annex.

8. A method of supporting a plurality of vertical reformer tubes substantially as hereinbefore described with reference to the accompanying drawings.

9. A reformer including a plurality of vertical reformer tubes, wherein the reformer tubes are supported in accordance with a method as claimed in any one of the preceding claims.

10. A reformer as claimed in claim 9 wherein flue gas from the reformer box through which the tubes pass is arranged to leave the reformer box through openings in the floor of the reformer box and pass into at least one tunnel running across the width of the reformer box.

11. A reformer as claimed in claim 10 wherein the openings are shaped so as to direct flue gas from the reformer box into the or each respective tunnel at an acute angle to the centre-line of the tunnel.

12. A reformer comprising a plurality of vertical reformer tubes substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.