GB2196725A

GB2196725A - Honeycomb heat shield for heat exchangers

Info

Publication number: GB2196725A
Application number: GB08720968A
Authority: GB
Inventors: Nino Elia
Original assignee: Ansaldo SpA
Current assignee: Ansaldo SpA
Priority date: 1986-10-29
Filing date: 1987-09-07
Publication date: 1988-05-05
Anticipated expiration: 2007-09-07
Also published as: DE3732682A1; GB8720968D0; FR2606131A1; NL8702518A; IT1200308B; GB2196725B; IT8612568A0

Description

GB2196725A 1 SPECIFICATION flow of the primary fluid, avoiding any stagna

tion of the same.

Honeycomb heat shield for heat exchangers The aims and advantages of the invention are indicated in the following description re

The subject matter of this invention consists 70 ferred to embodiments chosen by way of of a honeycomb type heat shield for heat ex- example only with particular reference to the changers. attached drawings in which:

Independently of their concept, which may Figure 1 is an axial section of a steam gen- be based on straight, "U"-shaped or helical erator, limited to its upper end, in which a pipes, etc., heat exchangers (steam generator 75 heat shield according to the invention is posi or otherwise) may require heat shields or tioned against the upper tube plate; other devices in special areas of the tube Figure 2 shows the heat shield already illusplate to protect the latter in the presence of trated in Figure 1, on a larger scale and up different phenomena linked with the operating side down; status of the component. 80 Figure 3 is a view on 111-111 of Figure 2; More in particular, it is sometimes necessary Figures 4 and 5 show portions of blades of to protect ptirts of the tube plates which have the heat shield, of the first and second series, a high degree of stress or structural peculiari- equipped with complementary slits; ties such as welds or other types of joints, Figure 6 shows in perspective the two from variations in temperature or in the flow 85 blades of figures 4 and 5, after assembly to rate of the fluid circulating outside the tube one another.

bundle; the purpose of this is to prevent these With particular reference to the attached variations from creating stresses which are drawings: 10 indicates the shell of a steam not permissible and thus damage. generator equipped with a tube plate 11 with In the case of heat exchangers with straight 90 vertical pipes which pass through an upper pipes, the part of the tube bundle to which tube plate 12, beyond which there is a steam the shielding according to the invention may header 13 fitted with a discharging outlet 14.

be applied is normally the area in which the Entry of the primary fluid, which circulates pipes are joined to the tube plate. According around the pipes of the tube bundle 11 takes to the invention, the heat shield is supported 95 place through the inlet 15 located approxi by a cylindrical ring, coaxial to the shell of the mately half way up the steam generator.

exchanger, located for example in proximity to The flow (A) of the primary fluid entering the upper tube plate, and equipped with slits the steam generator does not hit directly to allow access inside the ring of a fraction of against the tube bundle 11, in order to avoid the flow of primary fluid which rises inside the 100 thermal shocks to the pipes of the bundle it annular interspace created by the outer wall of self. For this purpose the tube bundle is sur said ring. rounded by a sleeve or ring, called the lower This fraction of the flow of primary fluid ring 16, which creates an annular interspace drops down again lapping against the outside 17 between the outer surface of the ring itself of the pipes of the tube bundle and passing 105 and the inner surface of the shell 11, into through the heat shield arranged inside said which the whole flow (A) of the primary fluid ring which forms its support. entering through the inlet 15 is channeled up- The heat shield consists of at least a double wards.

series of blades which intersect one another The lower ring 16 ends at a suitable dis- to form a honeycomb structure so as to cre- 110 tance from the upper tube plate, from which a ate, for at least a fraction having the height of second sleeve or ring, called the upper ring, the ring, a prismatic cell for each pipe of the protrudes downwards. The lower edge of this tube bundle. upper ring is separated from the upper edge In the simplest embodiment, the two series of the lower ring 16 by a slit or gap 21 - of blades which intersect one another form a 115 through which a fraction (B) of the flow (A) of plan of diamond shapes. the primary fluid flows downwards among-the For this purpose, each of the two series of pipes of the tube bundle.

blades has slits reaching for half of their The above flow (B) corresponds almost to height, able to accommodate the thickness of the totality of the flow (A).

the blades of the second series, also slit for 120 The remaining fraction (C) of the flow (A) half their height. rises towards the other along the interspace As an alternative, the connection of the two 22 existing between the upper ring 20 and series of blades may be made by welding, or the shell 11 and enters inside the upper ring another means of joining. 20 through slits or openings 23 positioned The load loss caused by the presence of 125 just below the tube plate 12 in the upper ring the above heat shield causes the quantity of 20.

heat given up by the primary fluid at the In this way the fraction (C) of the flow (A) height of the heat shield to be reduced; in comes into contact with the pipes of the tube spite of this, even this area of the pipes of bundle in correspondence with their upper the tube bundle is surrounded by a constant 130 portion, and then falls downwards until it 2 GB2196725A 2 meets up with the main fraction (B) at the In this case the heat shield is divided up height of the slit 21. into two parts, of which the upper part 120 Already in this way the upper ends of the has a smaller height than the lower part 220, pipes of the tube bundle 11, being hit by a as shown in figure 2. Both the upper and the reduced current of the primary fluid and which 70 lower parts of the heat shield are made up of has to follow a longer path than the main parts which slot into one another as illustrated current (B) are to some degree protected from in figures 4 to 5, although other solutions are direct contact with the primary fluid entering clearly possible.

through the inlet 15. Although for descriptive reasons this inven- If a further reduction of the quantity of heat 75 tion has been based on the above descrip- given up by the primary fluid to the pipes of tions and illustrations, many changes and vari the tube bundle in correspondence with their ations may be brought about within the scope upper portion and which ends against the up- of the invention. For instance, the blades per tube plate 12, is required, according to 31,32 could be formed as a single casting the invention, inside the upper ring 20 a heat 80 and only intersect in the geometrical sense.

shield 30 is provided made up of at least two

Claims

series of intersecting blades, indicated in the CLAIMS figure by numbers

31 and 32. Said blades 31 1. A heat shield for a heat exchanger having and 32 are fixed at their ends to the upper a chamber for containing a first fluid and a ring 20 and are equipped with slits 33 and 34 85 number of tubes passing through the chamber, which for the first extend from the top down- for bringing a second fluid into heat exchange wards for half of their height and for the sec- relationship with the first fluid, the heat shield ond from the bottom upwards for half of their comprising a plurality of series of intersecting height. blades which form cells in a generally honey- It is therefore possible to cross the blades 90 comb-like formation such that the heat ex- of the first and second series in a comb-like changer tubes can pass through the cells.

manner, as shown in figure 6, so as to form a
2. The heat shield of Claim 1, wherein there honeycomb sort of structure, in this case with are two series of the intersecting blades, the cells 35 having a rhomboid transverse section. cells being of rhomboid, square or rectangular Subsequently, the blades 31,32 are welded 95 cross-section.

together. Each cell, open at the bottom and at
3. The heat shield of Claim 1, wherein there the top, is passed through by a pipe of the are three series of the intersecting blades, the tube bundle 11, so that due to the presence cells being of triangular or hexagonal cross of the claimed shield the cross-section through section.

which the fraction (C) of the primary fluid 100
4. The heat shield of any of the preceding passes is smaller than that of a transverse Claims, wherein each series comprises a plu section of the lower ring 16, which is not rality of continuous blades each formed with fitted with a heat shield. It is to this reduced slits where they intersect, the slits extending section that the minor value of the fraction (C) for half the height of the blade and having a of the flow of primary fluid in the upper part 105 width substantially equal to the thickness of of the steam generator is due, in addition to the blade.

the greater length of the path and to the pres-
5. The heat shield of Claim 4, wherein there ence of the slits 23, of a lesser extension as are two series of the intersecting blades, in compared to the practically continuous slit 21. the first series the slits extending from the The fraction (C) of the flow of fluid which 110 upper edge to the centre of the blade and in passes through the claimed heat shield is the second series extending from the lower however sufficient to prevent stagnation of edge to the centre of the blade.

primary fluid in the upper part of the tube
6. The heat shield of any of the preceding bundle. Claims, wherein the blades are welded to one It is worthwhile to stress the fact that the 115 another.

shape of the prismatic cells defined by the
7. A heat shield, substantially as herein de- blades 3 1 and 32 of the heat shield 30 may scribed with reference to, and as shown in, be other than rhomboid. the accompanying drawings.

As an alternative, square or rectangular
8. A heat exchanger having a chamber for shapes may be made, depending on the lattice 120 containing a first fluid and a number of tubes defined by the position of the pipes forming passing through the chamber, for bringing a the tube bundle. second fluid into heat exchange relationship In addition to this, the series of blades may with the first fluid, and also having the heat even be three instead of two, and in this case shield of any of the preceding Claims posi the prismatic cells to be formed may be trian- 125 tioned such that the heat exchanger tubes gular or hexagonal. It should be remembered, pass through the cells of the heat shield.

finally, that according to a preferred embodi-
9. The heat exchanger of Claim 8, wherein ment, it is advisable for the slits 23 to be the outside of the chamber is defined by a located at a certain distance from the lower shell, and the blades of the heat shield have surface of the tube plate 12. 130 their ends supported by a cylindrical ring hav- 3 GB2196725A 3 ing a smaller diameter than the shell so that there is an annular space around the ring, the wall of the ring being provided with openings to permit the first fluid to circulate around the tubes.
10. The heat exchanger of Claim 8 or 9, and having at least one tube plate, there being two of the heat shields, a first heat shield being positioned immediately adjacent the tube plate and the other heat shield being spaced from the first heat shield.
11. The heat exchanger of Claims 9 and 10, wherein both heat shields are within the same cylindrical ring, the openings in the ring lead- ing into the space between the two heat shi- elds.
12. A heat exchanger, substantially as herein described with reference to, and as shown in, the accompanying drawings.

Published 1988atThe Patent Office, State House, 66/71 High Holborn, London WC 1 R 4TP. Further copies may be obtained from The Patent Office, Sales Branch, St Mary Cray, Orpington, Kent BR5 3RD.

Printed by Burgess & Son (Abingdon) Ltd. Con. 1/87.