GB2082750A

GB2082750A - Thermal Shield Plate Construction for Heat Exchanger

Info

Publication number: GB2082750A
Application number: GB8125786A
Authority: GB
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1980-08-25
Filing date: 1981-08-24
Publication date: 1982-03-10
Also published as: JPS642879B2; DE3133385C2; GB2082750B; JPS5741594A; DE3133385A1

Abstract

A thermal shield plate construction for a heat exchanger for cooling a fluid of high temperature used with a cooled type fast neutron breeder reactor, which is used for providing a protection from heat to welds formed between heat exchange tubes (9) and tube sheets (4, 8), and comprises thermal shield plates (11) each split at least radially into a plurality of pieces of the thermal shield plates, with end portions of the adjacent pieces being formed with stepped portions (21) respectively, which, when superposed one over the other, have the same thickness as the thermal shield plates (11). The structural features can avoid the disadvantages of the prior art namely that the effects achieved in shielding the parts from heat are reduced by the fluid of high temperature seeping through the gaps between the thermal shield plates and that excessively high stress is produced in the welds between the heat exchange tubes and the tube sheets. <IMAGE>

Description

SPECIFICATION Thermal Shield Plate Construction for Heat Exchanger Background of the Invention Field of the Invention This invention relates to a heat exchanger, and more particularly it is concerned with a thermal shield plate construction suitable for use with tube sheet sections exposed to serve thermal shocks.

The invention can be incorporated in all the heat exchangers provided with thermal shield plates, and has particular utility for application in an intermediate heat exchanger, steam generator, etc., for increasing the effects achieved by the thermal shield plates, to thereby improve the performance of thermal power and nuclear power plants.

Description of the Prior Art The prior art comprises Japanese Patent No.

907122 (Patent Publication No. 34775/77) which provides, in a heat exchanger comprising heat transer tubes attached to tube sheets of the heat exchanger for permitting a heat receiving fluid to flow therethrough, and a zone defined between a shell of the heat exchanger and the heat transfer tubes for a heating fluid of high temperature to flow therein, a plurality of thermal shield plates split and arranged such that the heat transfer tubes are interposed between the adjacent pieces of the thermal shield plates. The prior are disclosed in this Japanese patent which is shown in Fig. 2 and 3 suffers the disadvantage that, as subsequently to be described in detail, the heating fluid seeps between the thermal shield plates.

Summary of the Invention This invention has been developed for the purpose of obviating the aforesaid disadvantage of the prior art and minimizing a reduction in the effects achieved by the thermal shield plates of the prior art. Accordingly the invention has as its object the provision of a thermal shield plate construction of a heat exchanger capable of effectively providing a shield against heat by eliminating the gaps hitherto present between the adjacent thermal shield plates, to thereby avoid seeping of a fluid of high temperature between the thermal shield plates.

According to the invention, there is provided a thermal shield plate construction of a heat exchanger comprising a plurality of heat transfer tubes, tube sheets supporting the heat transfer tubes, and thermal shield plates provided in the vicinity of the tube sheets, whereby heat exchange can take place between heat exchange mediums through the heat transfer tubes, wherein said thermal' shield plates are formed with a plurality of apertures for inserting the heat transfer tubes therein and each said thermal shield plate is split at least radially into a plurality of pieces in such a manner that end portions of the adjacent pieces are formed with stepped portions respectively which, when superposed one over the other, have the same thickness as the thermal shield plates.

Brief Description of the Drawings Fig. 1 is a sectional view of a heat exchanger in its entirety in which the present invention can have application: Figs. 2 and 3 are detailed views showing a thermal shield plate construction of the prior art, Fig. 2 being a vertical sectional view taken along the line li-Il in Fig. 3 and Fig. 3 being a sectional view taken along the line I-I in Fig. 2; Figs. 3 and 4 are detailed views of the thermal shield plate construction comprising one embodiment of the invention, Fig. 4 being a vertical sectional view taken along the line IV- IV in Fig. 5 and Fig. 5 being a sectional view taken along the line Ill-Ill in Fig. 4: and Fig. 6 is an exploded view in explanation of the thermal shield plate with respect to a portion A showing in Fig. 5.

Description of the Preferred Embodiment Fig. 1 shows the construction of a heat exchanger in which the invention can have application. As shown, the heat exchanger comprises an outer shell 1 having a primary sodium inlet nozzle 2 and a primary sodium outlet nozzle 6. A secondary side upper end plate 3 is unitary with an upper tube sheet 4 to define therein a secondary side upper plenum 5 formed at its upper portion with a secondary sodium outlet nozzle 7. Heat transfer tubes 9 are connected at an upper end to the uDDer tube sheet 4 and at a lower end to a lower tube sheet 8, and thermal shield plates 11 are mounted in the vicinity of each tube sheet.

An outer shroud 10 having an inlet window 12 in an upper portion and an outlet window 13 in a lower portion is mounted to surround the outer side of the transfer tubes 9. A secondary sodium inlet tube 15 extends through the secondary upper end plate 3, upper tube sheet 4 and lower tube sheet 8 and has a lower end portion opening in a secondary side lower plenum 14.

Primary side sodium of high temperature is introduced through the primary sodium inlet nozzle 2 into the outer shell 1 and discharged through the inlet window 12 formed in the outer shroud 10 into the outer shroud 10 where it descends while exchanging heat with the secondary sodium ascending in the heat transfer tubes 9, before passing through the outlet window 13 in the lower portion of the outer shroud 10 and flowing out of the heat exchanger through the primary sodium outlet nozzle 6.

Meanwhile secondary side sodium of low temperature is introduced through the secondary sodium inlet tube 15 into the heat exchanger and flows to the secondary side lower plenum 14 where it reverses the direction of flow and flows into a heat transfer tube 9 in the lower tube sheet 8, before ascending while exchanging heat with the primary sodium secondary side upper plenum 5, from which it is discharged to outside through the secondary sodium outlet nozzle 7.

In the heat exchanger of this construction, thermal shield plates 11 are mounted to cope with the use of liquid metal sodium of high heat transfer rate as a coolant and to reduce thermal stress that might be produced in the tubes and tube sheets in the vicinity of welds and upper and lower sides of the tube sheets due to sudden temperature changes in the primary side sodium and the secondary side sodium.

Before describing in detail the thermal shield plate construction according to the invention, a thermal shield plate construction of the prior art will be outlined by referring to Figs. 2 and 3, to enable the invention to be thoroughly understood.

As shown, the thermal shield plates 1 are formed with apertures for receiving the multiplicity of heat transfer tubes 9, and gaps between the apertures and the heat transfer tubes 9 are almost eliminated when the heat exchanger is in operation. The upper and lower tubesheets 4 and 8 support the thermal shield plates 11 through thermal shield plate support studs 18, to form a stagnant sodium layer between the upper and lower tube sheets 4 and 8 and the thermal shield plates 11, to thereby avoid a thermal impact that might otherwise be applied to the upper and lower tube sheets 4 and 8 and welds between the tubes and tube sheets as well as the upper and lower sides of the tube sheets by sudden changes in temperature. The upper and lower tube sheets 4 and 8 are formed with tube supports 17 for welding the heat transfer tubes 9 thereto.The thermal shield plates 11 are split peripherally at regular intervals into thermal shield plate frieses 11 of concentric circular shape which are arranged in an orderly manner as shown in Fig. 3. The thermal shield plate pieces 11 radially adjacent each other are each formed with semicircular cutouts 20, and the semicircular cutouts 20 of the radially adjacent thermal shield plate pieses 11 cooperate with each other to define full circles serving as the apertures for permitting the heat transfer tubes 9 to extend therethrough.Spacers 16 and built in to support the thermal shield plates 11 of the upper and lower layers with a predetermined spacing interval therebetween at all times, and the thermal shield plates 11 are supported by the upper and lower tube sheets 4 and 8 through the thermal shield plate support studs 1 8. The thermal shield plate construction of the prior art has suffered the disadvantage that there are the possibilities of a fluid of high temperature seeping through the gap in the adjacent thermal shield plate pieces, so that the effect of shielding tubes and tube sheets from heat might be unable to be achieved and excess stress might be produced in the upper and lower tube sheets and portions of the tubes and tube sheets close to the welds.

One embodiment of the invention will now be described by referring to Figs. 4-6. Parts similar to those shown in Figs. 2 and 3 are omitted. The thermal shield plates 11 are each split circumferentially and radially into a plurality of thermal shield plate pieces as shown in Fig. 5 which are formed with a plurality of apertures for inserting the heat transfer tubes 9.The support studs 1 8 are each inserted into stepped portions 21 at ends of the adjacent thermal shield plate 1 As shown in Fig. 6, the stepped portions 21 are constructed such that when the stepped portions 21 of the adjacent thermal shield plate pieces 11 are superposed one over the other thb overlapping stepped portions 21 have the same thickness as the thermal shield plate pieces 11. lt is essential that the overlapping stepped portions 21 have the same width as the thermal shield plate pieces 11 because, if there is a distinction in thickness, it would be necessary to work on the thermal shield plates individually which is troublesome and the current of fluid flowing along the thermal shield plates would be adversely affected.Moreover, what is important is that high thermal stress would be produced depending on the thickness of the overlapping end portions. The spacers 1 6 are used to keep the thermal shield plates 11 apart from each other and the thermal shield-plates 11 and the upper and lower tube sheets 4 and 8 from each other at predetermined spacing intervals. The thermal shield plates 11 are plural in number with respect to each of the tube sheets 4 and 8, and the thermal shield plates 11 near the center are rings of small outer diameters.

Since the thermal shield plates 11 are assembled by weldably joining the heat transfer tubes 9 to the upper and lower tube sheets 4 and 8 starting with the secondary sodium inlet tube 1 5 side and moving toward the outer shroud 10 in Fig. 1 while conducting tests on the welds formed, the thermal shield plates 11 near the center are small in diameter as aforesaid and can be handled with ease, making it unnecessary to split same circumferentially.

The stepped portions 21 of the thermal shield plate pieces 11 are connected together by screws 1 9. This offers the advantage that the thermal shield plates 11 can be each formed as a single ring and the support studs 1 8 can be reduced in number.

With regard to the width of each thermal shield plate 11 as viewed radially, the stepped portions 21 are superposed one over the other, thereby.

eliminating the risk that the thermal shield plate pieces 11 might individually suffer damage.

From the foregoing description, it will be appreciated that according to the invention the adjacent thermal shield plate pieces are formed at their ends with stepped portions which are superposed one over the other, to eliminate the gap that might otherwise exist radially between the adjacent thermal shield plate pieces to enable thermal shield to be satisfactorily effected. The thermal shield plate pieces obtained by splitting each thermal shield plate are each formed with apertures for inserting the heat transfer tubes therein, thereby simplifying the operation because formation of an aperture can be effected more readily than formation of a semicircle and joining the two semicircles together.

in the invention, the volume of the fluid of high temperature seeping between the thermal shield plates and the tube sheets can be greatly reduced, thereby minimizing occurrence of excessively high thermal stress in the structure concerned.

When the thermal shield plates have a small diameter, no trouble may occur in the operation of assembling a heat exchanger even if the thermal shield plates are not split circumferentially if they are merely split radially. In such case, the thermal shield plates may have only to be split radially, without reducing the aforesaid effects attributed to the embodiment shown in Figs. 4-6 and described hereinabove.

In the embodiment shown in Figs. 5 and 6, circumferentially abutting portions of the thermal shield plate pieces do not coincide with each other radially. This arrangement has the effect of relieving mutual interference of the pieces that might otherwise occur due to thermal deformation, for example, when the four end surfaces of the thermal shield plate pieces about against one another.

Claims

1. A thermal shield plate construction of a heat exchanger comprising a plurality of heat transfer tubes, tube plates supporting the heat transfer tubes, and thermal shield plates provided in the vicinity of the tube sheets, whereby heat exchange can take place between heat exchange medium through the heat transfer tubes, wherein said thermal shield plates are formed with a plurality of apertures for inserting the heat transfer tubes therein and each said thermal shield plate is split at least radially into a plurality of pieces in such a manner that end portions of the adjacent pieces are formed with stepped portions respectively which, when superposed one over the other, have the same thickness as the thermal shield plates.

2. A thermal shield plate construction as claimed in claim 1, wherein said thermal shield plates are each split both circumferentially and radially into a plurality of pieces.

3. A thermal shield plate construction as claimed in claim 2, wherein the thermal shield plates near the center are in the form of a single ring.

4. A thermal shield plate construction as claimed in any one of claims 1-3, wherein the stepped portions of the adjacent pieces of the thermal shield plates have, when superposed one over the other, a constant thickness.

5. A thermal shield plate construction as claimed in any one of claims 1, 2, and 4, wherein said pieces of the thermal shield plates have abutting ends which do not coincide with each other radially.

6. A thermal shield plate construction substantially as hereinbefore described with reference to, or as illustrated in Figures 4 to 6 of the accompanying drawings.