US3662718A - Sodium heated steam generator - Google Patents

Abstract

A sodium heated steam generator having a tube sheet which is subject only to saturated or near saturated steam temperatures. Double-walled evaporative and superheated steam tubes extend through said tube sheet into the liquid metal. In both the evaporative and superheated steam tubes the saturated steam passes through the annular passageways which contact the tube sheet.

Description

United States Patent Creek et al.

[451 May 16, 1972 [54] SODIUM HEATED STEAM GENERATOR [72] Inventors: Ronald B. Creek, Northridge, Calif.; Karl A. Gardner, Chatanooga, Tenn.

[73] Assignee: The United States of America as represented by the United States Atomic Energy Commission 221 Filed: Mar. 2, 1971 21 Appl.No.: 120,151

[52] U.S.Cl ..l22/32, 122/34, l22/483 [51] Int. Cl ..F22b 1/16 [58] Field ofSearch ..l22/32, 33, 34,483

[56] References Cited UNlTED STATES PATENTS 3,076,443 2/1963 Coles et a1. "122/34 3,097,630 7/1963 Kinyon et al ..l22/34 3,267,907 8/1966 Glausser et al. 3,357,409. 12/1967 Williamson et al. ..l22/483 X Primary Examiner-Kenneth W. Sprague Attorney-Roland A. Anderson [5 7] ABSTRACT A sodium heated steam generator having a tube sheet which is subject only to saturated or near saturated steam temperatures. Double-walled evaporative and superheated steam tubes extend through said tube sheet into the liquid metal. In both the evaporative and superheated steam tubes the saturated steam passes through the annular'passageways which contact the tube sheet.

5 Claims, 3 Drawing Figures Ill ill

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Ronald B. Creek Karl A. Gardner SODIUM HEATED STEAM GENERATOR SOURCE OF THE INVENTION This invention was made in the course of or under a contract with the United States Atomic Energy Commission.

BACKGROUND OF THE INVENTION In the development of liquid metal breeder nuclear reactors, the liquid metal, having been heated as the result of the fission process within the reactor, may be employed within a heat exchanger to generate steam.

It is readily apparent that a heat exchanger in which a hot molten metal such as sodium is in heat exchange relationship with water and steam, critical problems arise having to do with the extremely high heat densities within the sodium and the resulting thermal gradients appearing in different regions in the heat exchanger, the vibrations and stresses induced by the changes in flow directions and velocities of the flowing liquid metal, and the existence within a single heat exchanger along with the aforementioned difficulties the existence of a low pressure region, e.g., the liquid sodium, and a'high pressure region, e.g., the water and steam.

SUMMARY OF THE INVENTION The present invention provides for a liquid metal heated steam generator in which the various aforementioned difficulties are effectively overcome with greater reliability, efficiency, and economy.

In accordance with a preferred embodiment of this invention, the steam, generator is divided into a high pressure steam/water side and a low pressure liquid metal side divided by a tube sheet which is maintained at saturated steam temperature for normal full load operating conditions. The entire high pressure steam/water inlet-outlet plenum is likewise maintained at saturated steam temperatures. This isothermal structure is obtained by a so-called split bundle bayonet tubing which provides appropriate flow routes for the sodium, water and steam. Hence, the tube sheet is not exposed to high inlet temperature sodium and exit steam.

Another important feature of the heat exchanger of this invention is that it can operate both as a once-through or a recirculating unit.

It is thus a principal object of this invention to provide liquid metal heated steam generation apparatus in which many of the problems associated with high heat densities are avoided.

Other objects and advantages of this invention will become evident from the following description of a preferred embodiment of thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIGS. 1 and 2, steam generator consists of an elongated cylindrical vessel 12 having a lower section 14 with a hemispherical bottom 15, an intermediate section 16, and an 'upper hemispherical closure section 18. Intermediate section 16 carries high pressure tube sheet 22 which divides vessel 12 into a high pressure region above sheet 22 and a low pressure region below. Section 16 has steam outlet nozzle 23 above tube sheet 22 for a purpose to be later described.

Lower section 14 is provided with a bottom inlet nozzle 24 for liquid metal and a side liquid metal outlet nozzle 26 located adjacent to the lower end of section 14.'Intermediate section 16 has a sodium-water reaction product vent nozzle 28 below tube sheet 22 but above the level of liquid metal 32.

Extending down from tube sheet 22 is a cylindrical bundle 34 of bayonet type tubes (the details of which are shown in FIG. 3 and will be described later) divided into a central superheater bundle 36 and an annular evaporator bundle 38, divided by a flow separator baffle 42. Tube supports 43a 43h provide suitable spacing elements for the tubes making up bundle 34 the details of which are not a part of this invention. Bafile 42 is connected at the bottom to the sodium inlet nozzle and separates the upward flow of liquid metal from the downward flow shown by arrows A. Baffle 42 terminates'at the upper end at 44 and is supported from tube sheet 22 by a plurality of support bars 45. It will be seen that an annular funnel shaped seal 46 just above inlet 24 between the wall of the lower section 12 and baffle 42 maintains separation between incoming and exhausting liquid metal 32. Between baffle 42 and the wall of vessel 12 is a cylindrical thermal shield 47.

Extending through and above tube sheet 22, evaporator bundle 38 terminates in an annular feedwater chest 48 whereas superheater bundle 36 terminates in-a low pressure tube sheet 52 which is supported within a cylindrical shell 54 having a hemispherical head 56 located above tube sheet 52. Tube sheet 52 separates a lower evaporator chamber. 55a within shell 54 from an upper superheater chamber 55b within head 56. Feedwater chest 48, which admits feedwater through inlet nozzle 57, surrounds and is mounted on shell 54. A ring of openings 58 is located in shell 54 below tube sheet 52 and 7 above feedwater chest 48. An annular seal 59, above steam chest 48, divides the space around shell 54 into upper and lower regions, for reasons to be later described.

Spherical head 56 has a superheater outlet tube 62 which extends out of closure section 18. The latter is also provided with saturated steam inlet nozzle 64 and an access port 66. Spherical head 56 is provided with a normally closed access port 68.

For details of the tubes comprising evaporator bundle 38 and superheater bundle 36 reference is made to FIG. 3, where a single tube arrangement for each bundle is shown for illustrative purposes. A typical evaporator tube assembly 78 consists of a tube 82 extending down from chest 48 where feedwater enters as illustrated by arrow C from feedwater chest 48. Tube 82 passes through and opens below tube sheet 22 into a closed tube 77 which extends down to the bottom of baffle 42. Tubes 77 and 82 are spaced from each other so that as indicated by arrows C the feedwater passes down through tube 82 for the length of evaporator bundle 38, reverses after exiting into tube 77 and passes up through the annular space between tubes 77 and 82, passing once again through tube sheet 22, emptying into the space surrounding shell 54 below seal 59. During the passage up through the annular space the feedwater becomes saturated steam which then passes out of steam generator 10 by way of nozzle 23. As shown in phantom, the saturated steam is carried from nozzle 23 through either a bypass line 83 or a steam drum S, to inlet nozzle 64. Valves V1, V2, and V3 control the flow path of the steam which upon re-entering exchanger 10 passes into lower superheater chamber 55a by way of openings 58 in shell 54.

Referring again to FIG. 3, the saturated steam, indicated by arrows B, enters a tube assembly 76 by way of an annular space within an outer tube 72 whose entrance is in tube sheet 22, and terminates below above sodium inlet nozzle 24. The steam flow reverses and passes up within a tube 74 which extends up through and spaced from tube sheet 22 to superheated steam chamber 55b where the superheated steam is combined from all of the tubes in superheater bundle 36 and then exits from generator 10 by way of superheated steam outlet nozzle 62, shown in FIG. 1. The arrangement of tubes just described wherein a first tube exits into a second tube in which the flow is reversed for flow in the annular space is referred to as a bayonet tube configuration.

Vessel 12 is supported by a cylindrical skirt 86 and integral base plate 88 attached at the junction of the lower hemispherical head 15 and the cylindrical portion of lower section 14.

It should be pointed out that while the walls of tubes 74,76, 78, and 82, and that of chamber 55b and feedwater chest 48 are illustrated as being solid it is understood that they may each comprise a double, thin wall construction with annular gaps, or dead space, between the double thin walls. This annular gap, or dead space, would serve in the case of evaporator tube assembly 78 as an insulator to minimize heat transfer to the feedwater as it flows to the bottom of the evaporator heat transfer tubing. This construction, well known in the art, provides a similar function in the bayonet tubes of the superheater bundle 36, and that of feedwater chest 48 and steam chamber 55b.

In the operation of steam generator 10, liquid sodium which is heated directly or indirectly in a separate heat source such as in a nuclear reactor, enters steam generator by way of inlet nozzle 24. The hot sodium flows upwardly (shown by arrows A) in the central region within baffle 42, passing in the spaces between the tubes forming superheater bundle 36. The sodium flows over the top edge 44 of baffle 42 and then down through the annular space formed by baffle 42 and thermal shield 47 filling the spaces between the tubes forming evaporator bundle 38. The liquid sodium leaves generator 10 by way of outlet nozzle 26.

Feedwater enters steam generator 10 by way of inlet tube 57, filling feedwater chest 48, passing into tubes 82 and down through tube sheet 22 into the region within the annular space formed by bafile 42 and thermal shield 47. At the lower end of the latter the feedwater reverses direction as shown in FIG. 3, passing up through the annular spaces between tubes 77 and 82. it is during the upward pass in the annular space that the water, being heated by second pass liquid sodium, is converted into saturated steam. The flow of feedwater and saturated steam is shown by arrows C.

The saturated steam passes out of generator 10 by way of outlet nozzle 23. From the phantom line it is seen that the steam is returned under normal operating conditions by line 83 to inlet nozzle 64. Valve V3 is open and valves V1 and V2 are closed. When it is desired to operate heat exchanger in a recirculating mode, valve V3 is closed and valves V1 and V2 opened to permit the saturated steam to pass through steam drum S where separation of water from steam takes place. Then only dry steam is piped back into the superheater section.

When the steam is returned to generator 10 by way of nozzle 64 into the lower superheater chamber 55a by way of openings 58 the steam, as shown in FIG. 3, enters tubes 72 of superheater bundle 36 at tube sheet 22, passing down the annular channel to be superheated by first pass, hot sodium. The superheated steam returns upwardly through inside tubes 74 directly into steam chest 55b, outlet nozzle 62 carrying the superheated steam out of generator 10.

It will be noted from the foregoing description, that an important advantage of this arrangement is that high pressure tube sheet 22 and the entire high pressure steam/water inletoutlet plenum within shell 54, with the exception of steam chest 55b operates as an isothermal structure at saturated steam temperature for normal full load operating conditions, while allowing the generation of superheated steam. The high pressure tube sheet is not exposed to high outlet temperature superheated steam. This construction minimizes the occurrence of extreme thermal gradients in tube sheet 22 and elsewhere which could affect adversely the useful life of this critical part of the heat exchanger. Other advantages of this arrangement are that the separate superheater and evaporation tube bundles greatly enhance stability, the unit is capable of operating both as a once-through or a recirculating unit, and the addition of a separate reheating cycle can be simply accomplished.

The space above liquid metal 32 is provided to absorb the expansion due to any sodium-water reaction and to permit these products to be vented through nozzle 28.

It is thus seen that there has been provided unique steam generation apparatus useful with liquid metal as a source of heat.

What is claimed is:

1. Liquid metal steam generation apparatus comprising:

a.apressure vessel; b. lower tube sheet means within said vessel dlVldUlg the latter into high pressure and low pressure regions;

c. means for circulating hot liquid metal through the low pressure region of said vessel;

d. means for supplying feedwater into the high pressure region of said vessel;

e. evaporative means including tube assemblies of annularly arranged inner and outer tubes extending from said high pressure region through said lower tube sheet means into said hot liquid metal within the low pressure region for carrying said feedwater within the inner tubes into said low pressure region, said tube assemblies carrying within the annular spaces said feedwater during evaporation back through said lower tube sheet means for discharge into the high pressure region as saturated steam;

f. superheater means for receiving said saturated steam from said evaporative means in said high pressure region for producing superheated steam, consisting of tube assemblies of annularly arranged inner and outer tubes extending into said hot liquid metal within said low pressure region for carrying within annular spaces said saturated steam which is superheated during passage therethrough and returning the superheated steam in the inner tubes through said lower tube sheet means, the latter thereby being subject only to saturated steam temperatures within said vessel; and

g. upper tube sheet means in said high pressure region spaced above said lower tube sheet means for receiving said superheated steam and delivering same from said steam generator.

2. The steam generator of claim 1 in which said liquid metal makes first and second passes through said low pressure region before leaving said pressure vessel, said evaporative means extending into the second pass of said liquid metal and said superheater means extending into the first pass of liquid metal.

3. The steam generator of claim 2 having means formed within said low pressure region for collecting and delivering out of said vessel the products of any water-liquid metal reaction.

4. The steam generator of claim 2 in which said upper tube sheet means includes a tube sheet with an upper chamber fonned above said tube sheet to receive said superheated steam and a lower chamber extending between said tube sheet and said lower tube sheet means for receiving the saturated steam from said evaporative means, and manifold means above said lower tube sheet means annularly arranged around said lower chamber for receiving feedwater and passing same into said evaporative means.

5. The steam generator of claim 4 having means external of said pressure vessel for receiving said saturated steam from said evaporative means and returning the saturated steam to said pressure vessel, the latter having further means to direct the saturated steam into said lower chamber.

Claims (5)

1. Liquid metal steam generation apparatus comprising: a. a pressure vessel; b. lower tube sheet means within said vessel dividing the latter into high pressure and low pressure regions; c. means for circulating hot liquid metal through the low pressure region of said vessel; d. means for supplying feedwater into the high pressure region of said vessel; e. evaporative means including tube assemblies of annularly arranged inner and outer tubes extending from said high pressure region through said lower tube sheet means into said hot liquid metal within the low pressure region for carrying said feedwater within the inner tubes into said low pressure region, said tube assemblies carrying within the annular spaces said feedwater during evaporation back through said lower tube sheet means for discharge into the high pressure region as saturated steam; f. superheater means for receiving said saturated steam from said evaporative means in said high pressure region for producing superheated steam, consisting of tube assemblies of annularly arranged inner and outer tubes extending into said hot liquid metal within said low pressure region for carrying within annular spaces said saturated steam which is superheated during passage therethrough and returning the superheated steam in the inner tubes through said lower tube sheet means, the latter thereby being subject only to saturated steam temperatures within said vessel; and g. upper tube sheet means in said high pressure region spaced above said lower tube sheet means for receiving said superheated steam and delivering same from said steam generator.

2. The steam generator of claim 1 in which said liquid metal makes first and second passes through said low pressure region before leaving said pressure vessel, said evaporative means extending into the second pass of said liquid metal and said superheater means extending into the first pass of liquid metal.

3. The steam generator of claim 2 having means formed within said low pressure region for collecting and delivering out of said vessel the products of any water-liquid metal reaction.

4. The steam generator of claim 2 in which said upper tube sheet means includes a tube sheet with an upper chamber formed above said tube sheet to receive said superheated steam and a lower chamber extending between said tube sheet and said lower tube sheet means for receiving the saturated steam from said evaporative means, and manifold means above said lower tube sheet means annularly arranged around said lower chamber for receiving feedwater and passing same into said evaporative means.

5. The steam generator of claim 4 having means external of said pressure vessel for receiving said saturated steam from said evaporative means and returning the saturated steam to said pressure vessel, the latter having further means to direct the saturated steam into said lower chamber.

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