RU2827748C1 - Steam generator - Google Patents

Abstract

FIELD: steam generators.

SUBSTANCE: steam generator comprises a prefabricated structure intended for transfer of heat energy removed from the core of the nuclear reactor by the coolant of the first circuit to the working medium of the second circuit. Superheated steam produced at the steam generator (SG) outlet is used further for transformation of thermal energy into mechanical energy, and then into electrical energy. Steam generator comprises a housing in the form of a vertical cylindrical chamber, an elliptical bottom, a cover, a primary coolant supply-discharge branch pipe, an internal device, inlet feed pipe and steam outlet branch pipe located in steam generator cover, steam generator pipe system, pipe sheets for pipe system attachment, inner and outer cylindrical screens, feed sections closed to feed chamber and located under steam generator cover, steam sections arranged above the pipe system, a collecting chamber of superheated steam, displacer located in central area of internal screen, gas removal system.

EFFECT: improving thermal-hydraulic efficiency and resource indices of internal device of steam generator.

1 cl, 3 dwg

Description

The invention relates to heat exchange technology, namely to steam generators, and can be primarily used as one of the elements of the component equipment included in reactor installations (RI). In particular, the invention can find application in nuclear power plants of ships, floating nuclear power plants (FNPP) and low-power nuclear power plants (LPNPP).

State of the art

Various designs of steam generators are known from the prior art, for example, steam generators according to Russian patents No. 2263845, 2221196, 27673, etc., which most often include a vertical body, a bundle of heat exchange tubes, and inlet and outlet coolant collectors.

The set of features that is closest to the set of essential features of the claimed solution is inherent in the known design of the PG-28 steam generator.

The technical description of the PG-28 s, as well as the circulation diagram of the coolant and working fluid are given in “STEAM GENERATOR PG-28 s. Operation Manual” IZHER.501421.008 RE 18.01.2008.

The known design contains a number of features that coincide with the essential features of the claimed invention: parameters of the fluid media of the first and second circuits (pressure, temperature, flow rates); materials of the structural elements of the SG.

PG-28 consists of:

- a tight-fitting body in the form of a welded vertical cylindrical chamber with a stamped elliptical bottom welded to it at the bottom, with a main pipe-in-pipe type branch pipe for supplying and discharging the coolant of the first circuit and fastening units on the metal-water protection tank (MWP);

- an internal device (ID) including a SG cover with units for supplying and removing the 2nd circuit medium and a coil-type pipe system with throttle packs. The cover assembled with the pipe system is welded to the upper part of the SG body.

The PG pipe system is made in the form of 100 cylindrical screw pipe coils, forming the heating surface of the economizer, evaporation and superheater sections. The coils are spaced using spacer strips installed during the winding of the coils using the group method; the coils are surrounded by a cylindrical shell on the outside. To remove gas from the upper part of the pipe system and to increase heat removal in the PG in case of emergency depressurization of the 1st circuit, 8 holes are made in the outer shell of the pipe system, evenly spaced around the circumference at a distance of 160 mm below the axis of the main branch pipe.

In the central part of the cover, a feed manifold for supplying feed water is installed. The feed chamber is formed by the lower surface of the SG cover and the tube sheet. The feed and steam manifolds are divided into 20 corresponding autonomous sections. In the tube sheet of the feed chamber, there are 20 holes for collector distribution feed pipes with a cross section of 22x2.5 mm.

Each of the 20 collector distribution feed pipes is closed to its section located in the feed chamber. The collector distribution pipe consists of two parts: the upper first one is made of austenitic stainless steel 0X18N10T, the lower second one, located under the tube plate of the feed collector and located in the volume filled with the coolant of the 1st circuit, is made of titanium alloy PT-7M. These pipes, made of metal alloys of different types, are connected to each other using a tight threaded joint. To ensure uniform heat exchange in the coil, the distribution of feed water flow in the throttle pipes is regulated by the length of the throttles located in them. From the bottom of each titanium pipe, 5 throttles emerge in the form of curved pipes, also made of titanium alloy PT-7M (4 of which are welded to the side wall, and one, straight - to the lower end of the pipe), forming a throttle pack. In turn, the throttles enter the throttle pipes.

Sectioning the pipe system by feedwater and steam makes the PG design repairable, i.e., when an inter-circuit leak occurs, it allows shutting off only the section in which the pipe system tightness is compromised by steam and feedwater (by installing welded repair plugs).

The generated superheated steam exits through a branch pipe welded to the toroidal collector in the SG cover and is fed into the main steam pipeline.

On the cover of the feed manifold, there are nozzles for gas removal, drainage of the cavity of the 1st circuit and sampling from the cavity of the 2nd circuit.

The disadvantages of the known invention are:

- sectioning of the feed manifold led to a weakening of the structure's strength due to the complication and change in the location of the throttle system, which led to massive failures in the operation of the pipe systems;

- due to the intensification of vibration processes, the feed pipe ruptures across its entire cross-section in the area of the lower weld of the threaded joint; as a result of mechanical action, the surface layer of the pipe is destroyed, leading to the destruction of the crystal lattice of the titanium alloy due to the penetration of free hydrogen atoms into the material (hydrogen embrittlement);

- the downcomer feed manifold is located vertically and is made as a straight pipe, unheated;

- the drainage pipe made of 0X18N10T stainless steel of the steam generator along the first circuit came into contact with one of the pipes of the downcomer feed manifold made of PT-7M titanium alloy, which was the cause of electrochemical corrosion;

- the specified temperature conditions for feed water are not favorable for pipes made of titanium alloy;

- a stagnant zone is structurally formed in the feed manifold due to the lack of coolant circulation, which leads to the absence of relief from axial stresses of feed pipes, throttles and throttle pipes during the downward movement of the second circuit medium and the formation of a gas cushion in the intertube space under the upper tube sheet;

- the connection of the throttle and steam pipes due to the difference in their flow cross-section is performed using a coupling with an expansion diffuser inside. In addition, the distribution of the throttle pipes for connection with the coil pipes is performed in the vertical plane depending on their belonging to a certain row with different bending angles and their subsequent withdrawal to a practically horizontal plane (at angles from 4° to 4.5°). Such a design scheme leads to the emergence of a zone of reverse movement of feedwater in the area of the diffuser expansion and a sharp increase in hydraulic resistance outside the linear dependence on the specified thermal power of the reactor.

The known design does not allow achieving the designated resource and service life of the pipe system, as well as the nominal power of the nuclear power plant in the event of failure of a certain number of sections of the steam generator.

Some of the above-mentioned shortcomings are due to the fact that the influence of vibration processes and the temperature regime in the second circuit on the strength of the feed manifold pipes was not taken into account.

Disclosure of invention

The technical problem that the claimed invention is aimed at solving is the elimination of the indicated disadvantages, namely, the increase in the thermal-hydraulic and resource indicators of the internal structure of the steam generator of the reactor plant.

The technical result of the present invention is to increase the thermal-hydraulic efficiency and service life of the internal device of the steam generator by changing the movement pattern of the coolant and working fluid.

The technical result of the claimed invention is achieved in that a steam generator is proposed, comprising a vertical body in the form of a welded vertical cylindrical chamber with a main branch pipe of the "pipe in pipe" type for supplying and removing the coolant of the first circuit and a rigidly connected elliptical bottom, an internal device with a fastening unit, an external and internal screen, a steam generator cover with units for supplying and removing the medium of the second circuit and a gas removal system and a coil-type pipe system separated from the upper part of the steam generator by a tube sheet and connected to feed chambers, feed sections with sectional pipes, the feed chamber is made in the form of a torus separately connected to each feed section by sectional pipes from the center of the pipe system which are carried out beyond the external screen of the internal device, wherein the outer side surface of this screen serves as a support for the feed coil pipes of the downcomer zone, wound around it from a vertical position with an average variable angle of 39÷42° relative to the horizontal, passing into the horizontal plane, the feed chamber is connected by feed pipes, in each downcomer feed coil pipe, a throttle is installed, the downcomer coil pipes are connected to the upcomer coil pipes in one horizontal plane using cylindrical adapters with a constant internal diameter, on the entire surface of the inner screen of the VU there are openings for collecting gas through gas removal pipelines, in each feed and steam section a detachable flange is installed for installing plugs, the number of section pipes, feed coil pipes and steam-generating coil pipes is in the range of 95÷105 pieces, the number of feed sections and steam sections is in the range of 19÷21 pieces.

The combination of the above essential features allows to increase the strength of the structure, increase the service life of the steam generator elements while increasing the resource indicators.

Brief description of the drawings

The essence of the invention is explained in the figures,

Fig. 1 shows a longitudinal axial section of the steam generator, Fig. 2 shows a cross-section of the steam generator pipe system with a top view, Fig. 3 shows a cross-section of the steam generator pipe system with a bottom view, demonstrating the horizontal layout of the first row.

The following reference designations are used in the figures: 1 - upper tube sheet; 2 - VU outer screen; 3 - VU inner screen; 4 - displacer; 5 - gas removal pipeline of the lowering zone of the coil tubes; 6 - gas removal pipeline of the lifting zone of the coil tubes; 7 - horizontal distribution zone of the coil tube system; 8 - collector pipe; 9 - annular channel of the main branch pipe for removing coolant from the SG; 10 - SG body; 11 - VU fastening unit; 12 - SG cover; 13 - lower tube sheet; 14 - steam cover; 15 - steam section; 16 - steam outlet branch pipe; 17 - feed chamber; 18 - feed section; 19 - feed pipe; 20 - lifting zone of steam-generating coil tubes; 21 - sectional pipe; 22 - collecting annular chamber of superheated steam; 23 - lowering zone of feed coil pipes; 24 - pipe of the main branch pipe for supplying coolant to the SG; 25 - pipes of the first row of horizontal distribution of the coil pipe system; 26 - central tube sheet; 27 - elliptical bottom.

The essence of the invention is as follows

The steam generator consists of: a SG body 10 in the form of a vertical cylindrical chamber; an elliptical bottom 27; a SG cover 12; a displacer 4 serving as a supporting structure for the internal device (ID) and located in the center of the ID; a DD fastening unit 11 serving to fasten the displacer 4 to the elliptical bottom 27; a main branch pipe 24 for supplying the coolant of the first circuit, located on the side surface of the SG body 10; an annular channel of the main branch pipe 9 for removing the coolant of the first circuit from the SG, formed by the outer surface of the main branch pipe 24 and the inner surface of the SG body 10, a feed pipe 19 for supplying the working fluid of the second circuit to the SG and a steam outlet branch pipe 16 located in the SG cover 12; an outer screen VU 2 of cylindrical shape, located between the lowering zone of the feed coil tubes 23 and the rising zone of the steam-generating coil tubes 20; an inner screen VU 3 of cylindrical shape, located between the displacer 4 and the rising zone of the steam-generating coil tubes 20; an upper tube sheet 1, having the shape of a ring with openings for the passage and fastening of sectional tubes 21 and installed between the inner side surface of the PG cover 12 and the outer side surface of the steam cover 14; a lower tube sheet 13, having the shape of a ring with openings for connecting sectional tubes 21 with the feed coil tubes of the lowering zone 23 and installed between the inner side surface of the PG casing 10 and the outer screen VU 2; a central tube sheet 26 installed under the steam sections 15 between the outer 2 and inner 3 screens and intended for the passage and fastening of the steam-generating coil tubes of the rising zone 20; twenty feed sections 18 connected to the feed chamber 17 by means of collector pipes 8 and located above the upper tube sheet 1 under the SG cover 12 along the periphery; one hundred sectional pipes 21 connecting the feed sections 18 with the pipes of the lowering zone 23, twenty steam sections 15 connected to the collecting annular chamber of superheated steam 22 by means of collector pipes 8 and located between the steam cover 14 and the central tube sheet 26; a zone of horizontal distribution of the coil tube system 7, located in the lower part of the SG body 10 above the elliptical bottom 27; gas removal pipeline 5 passing through the SG cover 12 under the lower annular tube sheet 13 and intended for gas removal from the annular space of the lowering zone of the feed coil tubes 23; gas removal pipeline 6 passing through the SG cover 12 under the central tube sheet 26 and intended for gas removal from the annular space of the rising zone of the steam-generating coil tubes 20. Gas removal is performed during preparation of the reactor plant for commissioning, before/after repair work, and after reducing the pressure in the primary circuit to perform process operations. Gases are released from the primary circuit coolant during ionization under the influence of gamma radiation, as well as when the pressure in the primary circuit is reduced.

The torus-shaped feed chamber 17, feed pipe 19 and feed sections 18 with section pipes 21 from the center of the pipe system, unlike the prototype, are taken out beyond the external screen VU 2. The outer side surface of this screen serves as a support for the feed coil pipes of the downcomer zone 23, wound around it from a vertical position with an average variable angle of 39°÷42° relative to the horizontal, turning into 0°, i.e. into the horizontal plane. This solution makes it possible to make the downcomer zone of the feed coil pipes heated, thereby increasing the overall heat exchange surface of the pipe system.

In the lowering zone of the feed coil pipes 23, relief from axial stresses of the pipe structure is provided by implementing a counter-current flow of the coolant of the first circuit, moving outside the pipes, and the working fluid of the second circuit, moving inside the pipes.

Compared to the prototype, the feedwater supply scheme from feed chamber 17 to feed sections 18 has been changed. Water is distributed through pipes to each section separately.

To ensure stable operation of the pipe system, a throttle is installed in each downcomer feed coil pipe. The total number of heat exchange pipes in the PG is at least 100. 5 heat exchange pipes are closed for each feed section.

The coil pipes of the lowering 23 and lifting 20 zones of the pipe system are made with the same flow section. Compared to the prototype, the scheme of the lowering coil pipes connection to the lifting coil pipes has been changed. It is implemented only in one plane in the horizontal distribution zone of the coil pipe system 7 using cylindrical adapters with a constant internal diameter, which significantly reduces the hydraulic resistance in the economizer zone of the VU and improves its hydrodynamics. Thus, the possibility of formation of a return flow (hydraulic plug) is eliminated and, as a consequence, the probability of occurrence of a swirling flow crisis inside the pipes in the lower economizer zone is reduced. The probability of occurrence of resonance effects in the PG pipe system is also reduced, which can lead to destruction of pipes in certain operating modes of the RU.

Compared to the prototype, the diameter of the internal screen VU 3 is reduced to a size that allows winding of the first row, consisting of three pipes Fig. 3. Holes are drilled along the entire length of the surface of the internal screen VU for collecting gas through gas removal pipelines 5 and 6, formed during the ionization of the coolant under the influence of gamma radiation.

Compared to the prototype, the most favorable temperature regime has been created and the stagnant zone of the primary coolant in the intertube space of the feed manifold has been eliminated, which leads to a decrease in the probability of "hydrogenation" of pipes made of PT-7M titanium alloy and an increase in the service life of the steam generator pipe system.

In order to increase labor productivity during repair work to search for, detect, and shut off leaky pipes, each feed and steam section is equipped with a split flange for installing plugs.

To evaluate the thermal-hydraulic efficiency of the steam generator, the efficiency criterion Ψ can be used, the numerical value of which is equal to the ratio of two characteristics of the devices under consideration - the modernized steam generator and its prototype. These characteristics are the ratios of two parameters: the specific thermal power of the reactor installation and the specific power for pumping the coolant. Calculations show that the value of the efficiency criterion *P significantly exceeds one and is estimated in the range of 1.8 < Ψ < 2.0.

In order to maintain the nominal parameters of superheated steam and the overall dimensions of the prototype steam generator body, the average winding angle of the downcomer feed coil pipes 23 is in the range of 39°÷42°. Accordingly, the number of section pipes 21, feed coil pipes 23 and steam-generating coil pipes 20 is in the range of 95÷105 pieces. The number of feed sections 19 and steam sections 15 is in the range of 19÷21 pieces.

Example of implementation

The scheme of movement of the coolant of the first circuit and the working fluid of the second circuit, declared in the invention is as follows: the coolant of the first circuit enters the steam generator through the internal pipeline of the main branch pipe 24 and rises into the upper cavity of the SG under the steam cover 14. Then the coolant descends down into the intertube space, washing from the outside and heating the steam-generating coil pipes of the lifting zone 20. Having passed from top to bottom the intertube space of the coils, the coolant rises up along the annular gap between the body 10 and the outer screen VU 3, transferring the remaining energy to the lowering zone of the feed coil pipes 23. Then, through the annular channel of the main branch pipe 9, it is removed from the SG.

The medium of the second circuit enters through the feed pipe 19 into the feed chamber 17, where it is distributed among twenty feed sections 18 and then, through the section pipes 21, it is distributed among 100 feed coil pipes located in the descending zone 23. Descending into them, the water is heated by the coolant of the first circuit to a temperature close to the saturation temperature. Then, having passed the lower horizontal distribution of the pipe system 7, it enters the lifting zone into the steam-generating coil pipes 20, where the feed water evaporates and is superheated to the required parameters. Superheated steam from the lifting coil pipes enters the channels of the steam sections 15, and from them - into the collecting annular chamber 22, and through the steam outlet branch pipe 16, is removed from the SG.

Claims (1)

A steam generator comprising a vertical casing in the form of a welded vertical cylindrical chamber with a main branch pipe of the "pipe in pipe" type for supplying and removing the coolant of the primary circuit and a rigidly connected elliptical bottom, an internal device with a fastening unit, external and internal screens, a steam generator cover with units for supplying and removing the medium of the secondary circuit and a gas removal system and a coil-type pipe system separated from the upper part of the steam generator by a tube sheet and connected to feed chambers, feed sections with sectional pipes, characterized in that the feed chamber is made in the form of a torus, separately connected to each feed section by sectional pipes from the center of the pipe system, which are extended beyond the external screen of the internal device, while the outer side surface of this screen serves as a support for the feed coil pipes of the downcomer zone, wound around it from a vertical position with an average variable angle of 39 ÷ 42 ° relative to the horizontal, turning into a horizontal plane, the feed chamber is connected to the feed coil pipes, a throttle is installed in each downcomer feed coil pipe, the downcomer pipes are connected to the upcomer coil pipes in one horizontal plane using cylindrical adapters with a constant internal diameter, there are openings on the entire surface of the VU internal screen for collecting gas through gas removal pipelines, a detachable flange for installing plugs is installed in each feed and steam section, the number of section pipes, feed coil pipes and steam-generating coil pipes is in the range of 95÷105 pieces, the number of feed sections and steam sections is in the range of 19÷21 pieces.