US3294070A

US3294070A - Gas-cooled reactors

Info

Publication number: US3294070A
Application number: US355797A
Authority: US
Inventors: Bell Alan
Original assignee: Foster Wheeler Inc
Current assignee: Foster Wheeler Inc
Priority date: 1963-04-08
Filing date: 1964-03-30
Publication date: 1966-12-27
Anticipated expiration: 1983-12-27
Also published as: GB1078393A

Description

Dec. 27, 1966 A. BELL GAs-cooLED REAcToRs 2 Sheets-Sheet l Filed March 30, 1964 INVENTOR. ALAN BELL ATTORNE Y Dec. 27, 1966 A. BELL 3,294070 GAS COOLED REACTORS Filed March 50, 1964 2 Sheets-Sheet 2 INVENTOR.

ALAN BELL NIU lma( M mfom@ ATTORNEY United States Patent O 3,294,070 GAS-CLED REACTORS Alan Bell, Coolrham, England, assignor to Foster Wheeler gororation, New Yorlr, N.Y., a corporation of New Filed Mar. 30, 1964, Ser. No. 355,797

Claims priority, application Great Britain, Apr. 8, 1963,

Claims. (Cl. 122-32) This invention relates to a once-through forced circulation tubular steam generator, and in particular to a final evaporation and superheating section of a once-through generator. The terms water and steam are used herein to denote any suitable liquid and its vapour.

Such steam generators generally include preheating, evaporating and superheating sections connected in series. The steam and water mixture produced in the evaporator may be very heterogeneous and there is then the danger that the mixture may pass through the superheater without 'complete evaporation of its water content. It is to the solution of that problem that the present invention is directed.

In a steam generator in accordance with the invention, the steam and water mixture produced in a tubular evaporator is passed to .a tubular superheater in which it is subjected to high speed turbulent ow in order to improve the homogeneity of the mixture before being subjected to lower speed ow for evaporation of the dispersed water and the finally desired superheating.

Preferably the high speed turbulent flow is effected by passing the whole of the mixture flowing from the evaporator through a single tube. This can be important because, if the mixture from the evaporator is offered alternative paths, there may be segregation of 'water and steam from the mixture With the result that the streams passing over the said paths will be of different composition.

It is important that suflicient heat transfer surface is provided to allow evaporation lof any water in the steam to occur. This :can be conveniently achieved by providing as long as ow path for the steam-water mixture as possible. To this end, the mixture can be iiowed at high speed from one end to the other of the superheating section and then back again before being flowed at the lower speed Vin the original direction to the superheated steam outlet. In the preferred form of the invention, the mixture is flowed iii-st through a single tube of relatively large diameter disposed along the axis of the superheating section, then in the opposite direction through two tubes the aggregate cross-section of which is approximately equal to the cross-section of the single tube and which are connected thereto in parallel and finally in the original direction through a number of relatively small diameter tubes surrounding the other tubes and connected in parallel with the intermediate tubes.

The rate of heat transfer in the nal stage of ow through the superheater section should be as high as possible and this can be achieved by making that flow turbulent, the turbulence here being thus for a different purpose from that for which turbulence is created in the initial stage of superheating.

An example of the invention will now be described with reference to the accompanying drawings in which:

FIGURES 1 and 1A are sectional elevation views of an element in accordance with the invention;

FIGURE 2 and FIGURE 3 are enlarged cross-sections .taken on the lines II-II and III-III respectively of FIG. 1; and

FIGURE 4 is an elevation section view of a steam generator using an element in accordance with the invention.

The element 12 shown in FIGS. 1 and 1A may, in practice, have an overall length of about 25 and may be arranged vertically side-by-side as shown in FIG. 4 with a large number of identical elements within a shell or casing 14 to form a steam generator 16. Each element comprisesra preheating section 118, a steam generating section 20, and a steam superheating section 22 connected together for series flow of fluid through the element.

The preheating and steam generating sections may be identical and comprise (FIGS. 1 and 2) nineteen substantially straight tubes 24 connected at their ends to tube plates 26 to form a cluster 28 of tubes. The two sections are connected together in series by welding an intermediate header member 30 between adjacent tube plates of each section. To the tube plate at the other end of the preheating section is attached a header 32 for receiving the water to be evaporated.

The -superheater section 22 comprises a cluster of nineteen tubes (FIG. 3) generally designated 34 c-onnected at their ends to tube plates 36 and 38 respectively. The section is connected in series with the steam generating section 26 through an intermediate header 46 in which is provided a funnel shaped baille 44 which serves to direct the mixture yfrom the steam generating section into the central tube 46 of the tube cluster. The fluid leaving this central tube is deflected by a hemispherieal member 48 attached to the tube plate 38 into two tubes 50 adjacent the central tu'be 46. The iiuid flows through these two tubes in a direction opposite to the flow through the central tube 46 and at the outlet thereof is deected by .the bafiie 44 into the remaining sixteen tubes 52 of the cluster 18 through which it flows in the same direction as through the central tube 46. The uid finally leaves the cluster through a header 54.

In the arrangement described above, the steam and water mixture produced in the nineteen parallel tubes of the evaporator section is on leaving that section caused to flow through the single tube 46 of the superheater section and then through the two adjacent tubes Sti. The speed of the mixture owing through that part of the superheater section constituted by the

tubes

46 and 50 is thus considerably higher than through the evaporator section and by adjusting the rate at which water is supplied to the element, the `speed of the mixture through the tubes 46 and 5() may be made sufficient to cause the ow through them to be highly turbulent. This improves the homogeneity of the mixture and the homogeneity is still further improved by the change in direction twice imposed on the ow through the superheater section. On leaving the two tubes 50, the mixture flows through the remaining sixteen tubes 52 of the superheater section where the velocity of flow is reduced to that through the evaporator section.

The tubes of each section may all be of the same diameter. Preferably, however, the central tube 46 of the tube cluster 34 through which the mixture leaving the evaporating section is flowed is of a diameter such that its cross-sectional area is approximately equal to the sum of the eross-sectional areas of the two tubes 50. This has the advantage of enabling each tube cluster to be composed of nineteen tubes, evenly and closely pitched on their end tube plates. In a typical example of the element described above, the inside diameter of the central tube 46 is 1" and that of the remaining tubes of the superheater section is v1/2.

It will be appreciated that the tubes of the heat exchange elements need not be exactly arranged as described and shown here. For example, the tube arrangement described in the co-pending application Serial No. 276,048, filed April 23, 1963, now Patent No. 3,195,517 may be used in the preheating and steam generating sections. Also the single tube which .forms the rst part of the flow path through the superheating section need not be the central tube of the cluster, although this arrangement is the easiest to construct.

As shown in FIG. 1, all the tubes except the central tube 46 are provided with means 56 in the form of iluted bars for increasing the turbulence of the fluid flow through them. This improves the heat input into each tube and enables the overall length of the heat exchange element to be kept short.

Although not illustrated here, the vapour generating section 20 may be constructed as shown in our copending application Serial No. 276,048, led April, 1963, now Patent No. 3,195,517 with a central water downcomer tube.

Any number of the heat exchange elements may be arranged in any desired manner within a shell or casing to form a steam generator. An example is shown in FIG. 4. In the unit of FIG. 4, a plurality of the tube systems of FIGS. 1-3 extend between lower and upper collecting `headers 58 and 60, the

small headers

32 and 54 being joined to the collecting headers by lower and

upper risers

62 and 64. A rectangular shell 66 surrounds the tube systems, provided with a gas inlet 68 at the top thereof. The gas tlow is essentially longitudinal of the elements, i.e., parallel to the tube axes. As shown the

headers

32 and 54 are staggered for this purpose, but in addition, the headers and spacer plates 70 (to be described) cause a partial cross ilow.

A typical generator may consist of a plurality of units bolted together, each unit being shop assembled. One unit may contain nineteen tubes. The generator then with a length of about 25 feet will provide a heating surface comparable to that of a conventional unit a hundred feet plus. In gas cooled nuclear stations, the saving in pressure vessel volume and thickness should be apparent. The size of the casing in any given case can be kept to a minimum by arranging the elements close together so that there is as little lost casing space as possible. This is assisted by having the tubes arranged on the tube plate as shown in FIGS. 2 and 3, by using

intermediate headers

30, 40 which have a circular or hexagonal cross-section and by springing or otherwise deforming the tubes of each section so as to achieve uniform distribution of the tubes of the elements over the cross-section of the casing. This may be done as shown in FIGS. 1, 1A and 2 by spacer plates 70 whose detailed construction and method of assembly on each tube cluster is described in our copending Application Serial No. 243,926, tiled December 1l, 1962, now Patent No. 3,227,142.

Although the invention has been described with relation to specific embodiments, it is to be understood that many variations are within the spirit and scope of the invention as claimed.

What is claimed is:

1. In a forced circulation boiler having a tube system including in series preheating, evaporating and superheating sections, the improvement comprising in said superheating section a plurality of tubes in a cluster including a center tube and rst and second sets of tubes substantially parallel to, coextensive with and removed from said center tube on opposite sides thereof, the center tube having a cross-sectional area of flow substantially less than the cross-sectional area of ilow in the evaporating section, -said cluster of tubes delining a circular array encompassing the center tube, said rst set of tubes being two tubes on opposite sides of the center tube, said crosssectional areas of the center tube and first set of tubes being substantially equal, means for directing the llow from the evaporating section to said center tube, second means for directing the ilow from the center tube to said rst set of superheating section tubes, and third means -for directing the ilow therefrom to the second of said sets of tubes so that the ow leaves the superheating section at lan end removed from the evaporating section.

2. In a forced circulation boiler, a tube system comprising a plurality lof tube elements,

each element including in series a preheating section, an

evaporating section, and a superheating section, the sections being axially aligned,

each section comprising a center tube and inner and outer `circular arrays of tubes, the tubes being substantially parallel and coextensive,

inlet and outlet headers for each element communicating with the preheating and superheating sections respectively,

intermediate headers communicating the sections with each other, the center tube of the superheating section including a funnel-shaped baille disposed in the header intermediate the evaporating and superheating sections arranged to direct the flow from the evaporating section into the center tube, the center tube having a cross-sectional area of ilow substantially less than the cross-sectional area of llow in the evaporating section,

the superheating section further including a hemispherical shaped baille to direct the flow from the center tube to two tubes adjacent and on opposite sides of the center tube,

the funnel-shaped baille further being arranged to direct the flow from said two tubes to the remaining tubes of the superheating section, whereby the ow enters the outlet header at an end of the element removed from the inlet header.

3. A boiler according to claim 2 further including means for increasing turbulence in said remaining tubes of the superheating section.

4. A boiler according to claim 1 wherein said means for directing the ow from the evaporator section to said center tube includes a funnel-shaped baille.

5. In a forced circulation boiler having a tube system including in series preheating, evaporating and superheating sections, the improvement comprising in said superheater section a plurality of tubes in a cluster including a center tube and rst and second sets of tubes substantially parallel to, coextensive with and removed from said center tube on opposite sides thereof, the center tube having a cross-sectional area of ilow substantially less than the cross-sectional area of flow in the evaporating section, means including a lfunnel-shaped battle for directing the ilow from the evaporating section to said center tube, second means including a hemi-spherical-shaped baille for directing the flow from the center tube to said first set of superheating section tubes, and third means coextensive with said funnel-shaped baille for directing the ow therefrom to the second of said sets of tubes so that the flow leaves the superheating section at an end removed from the evaporating section.

References Cited by the Examiner UNITED STATES PATENTS 2,083,679 6/1937 Adams 165-158 X FOREIGN PATENTS 1,205,952 8/ 1959 France. 1,231,3'11 4/ 1960 France. 1,250,438 12/:1960 France.

909,537 10/ 1962 Great Britain.

KENNETH W. SPRAGUE, Primary Examiner.

Claims

1. IN A FORCED CIRCULATION BOILER HAVING A TUBE SYSTEM INCLUDING IN SERIES PREHEATING, EVAPORATING AND SUPERHEATING SECTIONS, THE IMPROVEMENT COMPRISING IN SAID SUPERHEATING SECTION A PLURALITY OF TUBES IN A CLUSTER INCLUDING A CENTER TUBE AND FIRST AN SECOND SETS OF TUBES SUBSTANTIALLY PARALLEL TO, COEXTENSIVE WITH AND REMOVED FROM SAID CENTER TUBE ON OPPOSITE SIDES THEREOF, THE CENTER TUBE HAVING A CROSS-SECTONAL AREA OF FLOW SUBSTANTIALLY LESS THAN THE CROSS-SECTIONAL OF FLOW IN THE EVAPORATING SECTION, SAID CLUSTER OF TUBE DEFINING A CIRCULAR ARRAY ENCOMPASSING THE CENTER TUBE, SAID FIRST SET OF TUBES BEING TWO TUBES ON OPPOSITE SIDES OF THE CENTER TUBE, SAID CROSSSECTIONAL AREAS OF THE CENTER TUBE AND FIRST SET OF TUBES BEING SUBSTANTIALLY EQUAL, MEANS FOR DIRECTING THE FLOW FROM THE EVAPORATING SECTION TO SAID CENTER TUBE, SECOND MEANS FOR DIRECTING THE FLOW FROM THE CENTER TUBE TO SAID FIRST SET TO SUPERHEATING SECTION TUBES, AND THIRD MEANS FOR DIRECTING THE FLOW THEREFROM TO THE SECOND OF SAID SETS OF TUBES SO THAT THE FLOW LEAVES THE SUPERHEATING SECTION AT AN END REMOVED FROM THE EVAPORATING SECTION.