CH642142A5 - Method for preventing the overcooling of condensate in the pipes of a reheater - Google Patents

Description

The present invention relates to a method according to the preamble of claim 1 and to a reheater which is suitable for carrying out this method and which, in a one-stage embodiment, is particularly suitable for nuclear nuclear power steam turbine power plants.

The steam from a fossil fuel boiler is generally hot and dry and contains enough energy to operate a high pressure turbine. Subsequently, the steam is generally reheated in the boiler, so that it can perform useful work first in medium pressure and then in low pressure stages. The vapor from a nuclear-powered steam generator or reactor, on the other hand, generally has a relatively low temperature and is saturated. After it has passed through a high-pressure turbine stage, the steam generated by nuclear energy contains so much moisture that it has to be freed from it and should preferably also be reheated in order to increase its enthalpy so that it can reliably perform further useful work.

Various types of water separator reheaters are already known, see e.g. See, for example, US Pat. No. 3,712,272. The water separator reheater known from this patent contains two reheater sections, each with a bank or a bundle of U-shaped tubes, which extend longitudinally into a pressure-resistant jacket and a head piece for introducing a heating fluid (steam ) to the pipes and to withdraw the fluid (condensate) from the pipes. The head piece is provided with a vertical guide plate which is arranged substantially in the middle of the head piece and which divides an inlet and an outlet section. One end of each tube communicates with the inlet section and the other end with the outlet section. In operation, saturated heating steam is fed into the U-shaped tubes through the inlet portion of the header, flows through and exits the tubes through the outlet portion of the header, and all of the condensate that forms in the after-heater tubes becomes one Discharge directed, which is provided in the outlet section.

Another example of a water separator post-heater which contains two post-heater tube bundles is known from US Pat. No. 3,713,278. In this known construction, the head piece is provided with a substantially horizontal separating or guide plate, which is essentially in the middle of the head

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stiicks is arranged and this is divided into an upper inlet section to large amounts of flushing steam in the pipes and a lower outlet section. To return the U-shaped heating element. The inlet ends of in one

Bends of the pipes therefore run in the vertical direction. vertical plane, U-shaped tubes can be used

A water separator post-heater, which has a single post-different openings, in order to better contain heating tube bundles, is known from US Pat. No. 3,593,500. s ensure that enough steam is supplied to the individual pipes - with all these known water separators - after-heater - to avoid undercooling of condensate. Structures can condense under certain operating conditions. The live steam, which upstream of the high pressure turbine draws significant amounts of the reheat steam in the am, serves as the heating fluid (steam) for the tube bundles with the greatest load. If the whole del. In a nuclear reactor or steam generator, the steam that enters these pipes condenses completely before the pipe ends, fluctuations in the live steam pressure over the loading area, and supercooled condensate can accumulate. range of the turbine minimal. A way is provided in order to supply the Proble steam jet pump which occurs during the supercooling of condensate with live steam, the upstream and the associated instabilities are known from the throttle valve or the throttle valves of the feeder. It is already known that the pipe openings and piping of the pipe bundle are removed. Furthermore, pipe bundle flushing has a beneficial influence and makes the above 15 problems from the outlet part of the head piece of the pipe bundle easier. Pipe openings are known from the US-PS low pressure suction port of the steam jet pump vorese-3 073 575. In tube bundle rinsing, as z. B. in the hen. These measures describe the pressure of the propellant steam US Pat. No. 3,724,212, the purge flow is typically at least 1.5 times (and up to 10 usually diverted to a lower point in the system for steam jet pumps) than that of the purge steam . With such a pressure, however, there is considerable thermodynamic loss. The steam jet pump produces a ratio of at least 1.5

US Pat. No. 3,830,293 discloses a method for recycling (which is also used as a high-pressure thermocompressor, i.e. as a thermo-

of purge steam in tube-shell heat exchangers, which can be called a high AP compressor) that

Tube bundles work, known. Substantially more flushing steam is drawn off in the steam supply line than motive steam is supplied to the tube bundle with a small pressure difference (approx. 0.7 to. For the outlet or exhaust steam of the steam jet pump,

1.4-105 pa or about 10 to 20 psid) working thermocompressor 25 which has a medium pressure, pipes to its sor are used to recirculate the purge vapor in the feed into the inlet chamber of the head of the pipe collar.

To effect tube bundles. The amount of dels provided by this technique.

Recirculated scavenging steam is not sufficient, however. These measures can avoid rinsing steam throughputs in the cooling of the condensate, since the low pressure of around 50 to 100% of the tube bundle throughput,

Difference on the thermocompressor makes it very ineffective 30, which is determined by the heat to be given off, and there is no information that an alternative such partial load conditions can easily be achieved, in which the

Source for higher pressure steam is desirable or necessary - inlet flow is throttled and high purge steam throughput is dig. are needed. The known problems regarding the

Accordingly, the invention relates to supercooling and the associated insta

The underlying principle is that the supercooling of condensate in the tube bundle is largely avoided in this way. To avoid del afterheating. the flushing steam through the tube bundle or tubes

This task is recirculated or recirculated by the method characterized in claim 1, the further

Method or the post-heating test-suppression of the condensate supercooling resolved with zer. a minimum of thermodynamic losses. To remove

In the preferred embodiments of the present invention, any non-condensable gases that accumulate

Invention is one with a high pressure difference between propellants, a small emptying is expediently provided

See steam and suction steam working steam jet pump. At high powers, in which the pipe bundle uses considerable amounts of flushing steam in the down- or the pipe bundles, heating steam no longer becomes the first stage of a two-stage reheat-pressure pipe bundle, the heat output of the numerous zeros can also be recirculated. For the drive or operation of the steam 45 U tubes of the bundle easily through different tube openings

jet pumps use relatively small amounts of high-pressure flushing in conjunction with a relatively low flow rate.

steam from the high pressure tube bundle of the second stage use speed of flushing steam, which det to a lower. For this operation two tube bundles are required, the point of the system is derived, easily adjusted or changed

work with significantly different pressures. be evened out. Under these conditions, the

In another embodiment of the invention, the steam jet pump is so, albeit with less efficiency

Continue working undercooling of condensate in a one-stage reheater in order to avoid a renewed start-up in a later or reheater according to the invention, essentially changing the load.

Chen avoided that for the operation of a high-pressure fresh air throttled in the following embodiments of the invention are explained in more detail with reference to the drawing.

steam is used to show with minimal thermodynamic 55

Losses of much larger amounts of flushing steam than was previously possible in FIG. 1, a somewhat schematic vertical cross-sectional view, to feed back and keep it in circulation. of a two-stage reheater and associated system parts

The invention thus enables supercooling of cones in accordance with one embodiment of the invention;

2 a somewhat schematic vertical cross-sectional view of thermodynamic losses can be prevented by fio a single-stage post-heater and associated system parts one live steam, which is upstream of the throttle according to a preferred embodiment of the invention,

valve or the throttle valves in the feed line for that and

3 was a vertical cross section of a steam jet pump,

len steam jet pump operating with a high pressure difference, as can be used in the device according to FIG. 2,

used. 65 The reheater 10 shown in FIG. 1 contains one

In a preferred embodiment of the present invention pressure vessel 12, which typically has a plurality of steam inlets 13

These advantages are achieved in that contains one and several steam outlets 14 so that the single-stage reheater to be dried is provided with a steam jet pump and steam to be reheated is more easily passed through.

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that can.

The moisture entrained by the steam supplied is substantially completely removed by water separating plates 15 in a known manner. The water separator plates have a very large surface area with so-called “wobble plates” and an associated drainage system (not shown), which collects the water running off the plates and forms a path for the removal of the water from the jacket or pressure vessel 12.

Immediately above the water separating plates 15, several reheaters 16 and 17 are arranged in the way of the steam flowing from the steam inlets 13 to the steam outlets 14.

The post-heater 16 of the first stage contains a tube bundle 18 and a head piece 19. The post-heater 17 of the second stage contains a tube bundle 20 and a head piece 21. The tube bundles 18 and 20 each contain a number of U-shaped tubes 22, between which and a heat transfer takes place through the jacket-side steam. The U-tubes 22 each carry saturated vapor of high pressure, the origin of which is still to be discussed, and each contain an almost horizontal section 23, a round, vertically oriented U-bend section 24 and an almost horizontal outlet section 25. The head pieces 19 and 20 each contain a baffle or partition plate 32 which divides the respective head piece into an upper inlet chamber 33 or 35 and a lower outlet chamber 34 or 36, the latter having a small drain opening. Each tube of the tube bundles 18 and 20 has an inlet end which communicates with the upper inlet chamber of the associated head piece, while its other end is connected to the lower outlet chamber of the same head piece. Saturated steam, the pressure of which is substantially higher than the jacket-side steam, is fed to the inlet chamber 33 of the headpiece of the first stage through a pipeline 40, which contains a valve 42 and comes from a tap of a high-pressure turbine, not shown. The steam flows through the tubes 22 of the reheater 16 and in the process releases heat to the jacket-side steam, wherein it condenses at least partially in the tubes. The resulting condensate enters the outlet chamber of the head piece and is discharged through a drain line 44, while the remaining steam is fed to the suction side of a steam jet pump 70 and an emptying line 51 via a pipeline 49.

Saturated steam is supplied to the inlet chamber 35 of the second stage reheater 17 which is taken upstream of the high pressure turbine by a ling 50 and is throttled by valve 52 at part load conditions and has a pressure which is substantially above the pressure of the saturated steam the inlet chamber 33 of the reheater 16 is supplied. The steam then flows from the inlet chamber 35 through the tubes 22 of the reheater 17, giving off heat to the jacket-side steam with at least partial condensation. The resulting condensate exits into the outlet chamber 36 and is fed through a pipe 74 to a drain tank 47, while the excess steam is fed through a pipe 71 to the steam jet pump 70 as motive steam.

The steam jet pump 70, which is supplied with motive steam by the working steam from the pipeline 71, promotes a greater mass flow of exhaust steam from the line 72 and delivers a larger mass flow of flushing steam via the line 73 to the inlet chamber 33 of the head piece 19 of the reheater 16. This steam flow is sufficient for the flushing of the tube bundle 18 of the reheater 16 and essentially prevents undercooling of the condensate with the associated instabilities.

The advantages of this flushing of the first post-heater tube bundle can be retained if the second post-heater stage is switched off and the post-heater is practically operated as a single-stage post-heater. For this purpose, an arrangement with a pipeline 75 and a valve 76 is provided, which make it possible to operate the steam jet pump 70 with a part of the high-pressure steam that is available from the main steam source. The valve 52 and the valve 77 are then closed, as a result of which the second reheater stage is separated from the steam flow. The valve 76 is opened, so that undistorted steam with a pressure which is substantially higher than the pressure in the line 40 drives the steam jet pump 70 as a propellant and supplies the desired flushing steam for the reheater 16.

Under the circumstances described above, one then has a two-stage post-heater, the high-pressure stage of which is switched off, so that the device works as a single-stage post-heater, in which the exhaust steam is returned or recirculated in the working tube bundle for rinsing purposes by means of a steam jet pump, which causes a high pressure difference becomes. A single-stage reheater designed for such an operation will of course have a different configuration. An optimized arrangement for such an operation of the reheater is shown in FIG. 2, in which parts of the same function as in FIG. 1 are provided with the same reference numerals.

The reheater 10 shown in FIG. 2 again contains a pressure vessel 12, which typically has a plurality of steam inlets 13 and a plurality of steam outlets 14, so that the steam to be dried and heated can be passed through more easily. Above the steam inlets 13 and inlet fillings (not shown), water separating panels 15 of a known type are arranged, through which practically all of the moisture which the incoming steam carries is separated off.

The post-heater 16 contains a tube bundle 18 and a head piece 19. The tube bundle 18 contains a plurality of U-tubes 22 which are in heat exchange with the jacket-side steam flowing through the post-heater and each carry saturated high-pressure steam, the origin of which is still to be discussed. Each U-tube of the bundle 18 has a nearly horizontal inlet section 23, a curved, vertically arranged U-shaped bend section 24 and a nearly horizontal outlet section 25. The head piece 19 contains a partition plate 32 which it into an upper inlet chamber 33 and a lower outlet chamber 34 divided. Each U-tube of the tube bundle 18 is connected at one inlet end to the upper inlet chamber of the head piece and at the other end to the lower outlet chamber of the same head piece. Since the flow paths of all U-tubes of a given tube bundle are connected in parallel, there is the same pressure difference (driving force) between the inlet and the outlet section on all tubes.

Main steam, which is taken upstream from the high-pressure turbine, is available for operation via a pipeline 50 for the reheater 16. The pipeline 50, which leads to the inlet chamber 33 of the head piece 19, contains a supply-side valve 42 and at least one throttle valve 43. The steam then flows through the U-pipes 22, whereby it has two longitudinal paths along and parallel to the longitudinal axis of the jacket or pressure vessel 12 flows and travels down a curved path when it reaches the end of the first horizontal flow path and then flows back to the outlet chamber 34 of the header 19. As the U-tubes 22 pass through, a certain proportion of the steam contained in the tubes condenses and the condensate flows together with the uncondensed steam to the outlet chamber, where it flows through the drain line 44 to a collecting tank 45 located outside the pressure vessel 12. The liquid phase in the collecting tank 45 can be fed via line 48 to a feed water preheater or a main condenser. To compensate for the pressure in the outlet chamber 34 of the

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A vent or equalization pipe 49 is provided in the head piece and the collecting tank 45. A pipeline 72 is connected to the pipeline 49, through which the exhaust steam emerging from the tube bundle is fed to a steam jet pump 70. A pipeline 51 is also connected to the pipeline 49 in order to be able to continuously discharge non-condensable gases through a valve 78 and exhaust steam through a valve 79 to points of lower pressure in the system.

The live steam, indicated by an arrow A, used as heating steam and entering through the heating steam inlet pipeline 50, which contains a steam source inlet valve 42 and at least one throttle valve 43, is generally taken upstream of the high pressure steam turbine.

The pressure of this live steam used as heating steam is relatively high and essentially constant over the entire load range. In pressurized water reactors, the live steam pressure can also drop somewhat in practice with increasing load. The jacket-side steam, which comes from the outlet of the high-pressure turbine, on the other hand, has a pressure which increases substantially linearly with the turbine load to a value of about 1 A of the live steam pressure at full load. If the live steam were introduced as heating steam through the inlet pipeline 50 into the tube bundle 18 in the load area, the difference between the temperature of this heating steam (which typically has a pressure of the order of 7 MPa or 1000 psia) and that of the jacket-side steam would be too large under part-load conditions, much more than 100 ° C or about 200 ° F. With these high temperature differences in part-load operation, considerable problems arise due to deformation of the tube bundle as a result of the thermal expansion due to the temperature differences, and severe condensate supercooling can occur in the tubes. In order to alleviate these difficulties, the live steam used as heating steam in the inlet pipe 50 in the present device is typically throttled by the valve 43 in part-load operation.

Only one valve 43 is shown, but in practice several such valves can be used. A whole series of methods for throttling the heating steam are known; typically, the valve or valves 43 are controlled by the high pressure turbine outlet steam pressure such that the pressure of the steam for the tube bundle 18 increases linearly from a low load value to the live steam pressure in the range of 50 to 80% of the turbine load. The term “throttled steam” is to be understood here to mean steam whose pressure is reduced at part load of the associated turbine.

As the jacket-side steam entering the pressure vessel 12 flows from the steam inlets 13 over the U-tubes 22 of the bundle 18 and is increasingly heated, the temperature difference between the tube-side steam and the jacket-side steam continuously decreases. An important problem with which the invention is particularly concerned resides in the changing temperature difference between this jacket-side steam and the tube-side steam when the jacket-side steam is heated. The jacket-side steam can also carry a certain residual water content beyond the water separating panels 15, which must be evaporated by heat transfer from the lower rows of pipes of the tube bundle 18 before the steam can begin to overheat. Since the temperature difference between the tube-side and the jacket-side steam is greatest at the lower tubes of the tube bundle 18 and water has to be evaporated there as well, the greatest heat transfer can obviously occur at these lower tubes of the tube bundle, which in turn requires that the outer U - Tubes in vertically oriented superheater tube bundles are supplied with larger amounts of steam on the tube side.

Since the inlet ends of all U-tubes in connection with the inlet chamber 33 of the head piece and the outlet ends of all U-

Pipes are connected to the outlet chamber 34 of the head piece 19, there is necessarily the same pressure difference on all U-pipes. The outer (vertical) U-tubes are therefore usually not supplied with enough steam to cover the 5 heat demand. In these pipes, the steam condenses completely before the end of the pipes and downstream of the point at which the last steam is condensed, the condensate is supercooled to meet the need for heat to be released. On the other hand, a two-phase saturated mixture emerges from the inner io (vertical) U-tubes, which carry more steam than is theoretically required, into the outlet chamber 34 of the head piece 19. As is well known, the most varied problems can arise from the occurrence of supercooled liquid. Two major problems are ruptures in tube-to-tube welding and instability of the system as a whole.

It is Z. B. from US-PS 3 073 575 that you can reduce the supercooling by constricting certain pipes in a suitable manner and thereby adapting the throughput 20 of the tube-side steam to the amount of heat actually required for heat transfer. This can reduce supercooling and the associated instabilities in steam heat exchangers. One way to address the problem outlined above is to design the pipe openings accordingly.

The opening or cross-sectional dimensioning is one of the measures for eliminating the problem of different condensation in the U-tubes of a post-heater tube bundle and thus largely avoiding the condenser cooling. The conceptually simplest way to avoid this problem, however, is to pass a sufficient amount of saturated steam in excess through the tube bundle over the amount theoretically necessary for the reheating and thereby flush all the U-tubes. However, this measure is normally not applicable in terms of efficiency, since it represents an intolerable waste of energy. A more practical solution is the use of additional partitions in the header, as is known from US Pat. No. 3,996,897. In the device described there, the supplied steam enters a subdivided inlet section of the head piece of a horizontally oriented tube bundle and flows through the lower half of the U-pipes to a reflux section of the head piece, where the condensate, which is found in the first two longitudinally «Passages through which U-tubes have formed is derived. The saturated steam is then reintroduced into the tubes of the tube bundle, it enters the upper half of the tube bundle and returns to the opposite section of the head piece, from which the accumulated condensate is thus discharged again. Such a device represents a “four-pass arrangement” and reduces the risk of condensate flooding and the resulting thermal cycles.

In a "four-pass arrangement" known from US Pat. No. 3,755,919, the post-heater contains a separate distributor 55 in order to let the saturated steam, which has already made one pass, run again through certain U-tubes of the post-heater tube bundle.

Unfortunately, the gradation of the flow cross-sections and the other measures discussed above do not normally provide a complete solution to the problem of condensate subcooling and the associated instabilities in water separator reheaters. One reason why the gradation of the opening or flow cross-sections no complete solution is possible. r, 5 that a predetermined opening arrangement can indeed be calculated and designed for a distribution of the steam flow over the various pipes, so that it meets the theoretical need for heat to be transferred in a specific operating state

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cover, but is not ideally designed for all operating conditions. A cross-sectional or aperture arrangement that is ideal for one set of conditions may not be suitable for another set of conditions, e.g. B. when changing the load values of the turbine or in the case of a single-stage reheater, when the heating steam is throttled at partial load.

The present invention can be applied either with a graduated opening or cross-sectional dimensioning (or equivalent measures) or independently thereof, in order to improve the operation of post-heaters, in particular for steam turbine generator systems, in particular to substantially avoid supercooling of condensate and the associated instabilities.

It has long been known that steam lines for removing unwanted water and the like can be purged by passing high pressure gas or steam through them. One can therefore avoid undercooling of condensate in post-heater tube bundles by increasing the supply of saturated steam from the input steam source to the tube bundle by a predetermined amount in excess of the amount that is theoretically required for the post-heating of the jacket-side steam at a certain load becomes. If a sufficient excess of saturated steam is removed from the tube bundle steam source, condensate hypothermia can be practically avoided even without special dimensioning of the opening or flow cross sections. On the other hand, it is essential that the steam generated for use in a steam turbine system is used well and a maximum amount of work in the necessary functions of the steam turbine is taken from it, for example when reheating steam in a reheater, before preheating the feed water its supply to the steam generator or reactor and when using the end product of a condenser as feed water for the system. The safe use of high-temperature, high-pressure steam, the heating unit of which could be used more productively and better, for purging, can significantly impair the efficiency of the system as a whole. Since steam turbines typically have a lifespan of over 30 and often up to 40 years, wasting a significant percentage of steam for purposes such as largely preventing condensate supercooling in reheater tube bundles can be extremely costly in terms of the primary energy unnecessarily used for such purposes over the years .

According to the present invention, steam which is returned to the inlet of the tube bundle is used as the rinsing vapor for largely avoiding condensate supercooling in reheater tube bundles. The kinetic energy or drive power is supplied by heating or live steam, which is taken upstream of the throttle valve 43 or the corresponding throttle valves. The recirculated purge steam is useful as opposed to the steam that is diverted to a feed water preheater (which represents a point of lower energy in the system), so that the invention effectively improves the reliability of the operation of the reheater without sacrificing the operating efficiency of the system seriously suffers as a whole. The use according to the invention of pipe-side exhaust steam represents practically a significant improvement over the known practice, in which smaller amounts of flushing steam than are required for virtually complete removal of the condensate supercooling are led to a feed water preheater or a similar point of low pressure in the turbine cycle .

As shown in FIG. 2, a steam jet pump with a high AP is used in the device according to the invention in order to return rinsing steam to the inlet chamber 33 of the head piece 19 of the reheater 16 in such a way that sufficient excess high-pressure steam is available for the individual U-tubes 22 of the bundle 18 stands in order to substantially avoid supercooling of condensate even in those pipes where the greatest temperature difference occurs.

The drive fluid for the steam jet pump 70 is supplied through a pipeline 71, it is the heating steam that is available in the heating steam line 50 upstream of the throttle valve 43 or the throttle valves. This steam, which has a pressure of approximately 7 MPa (1000 psia), drives the steam jet pump 70, which supplies the rinsing steam for the reheater 16. In general, the proportion of steam used for this purpose is only about 5 to 10% of the theoretically necessary amount of steam that must be supplied to the inlet chamber of the reheater 16 to cover the heat requirements of the tube bundle 18. The steam jet pump 70, of which an exemplary embodiment is shown in more detail in FIG. 3, is therefore operated with high pressure motive steam, so that it sucks a larger amount of exhaust steam as motive steam through the line 72 from the outlet chamber 34 of the head part of the reheater 16. The unified flow, i.e. H. the purge steam leaves the steam jet pump 70 at a medium pressure which causes the desired strong purge flow at the entrance of the reheater.

The steam jet pump 70, which is supplied with suction or low pressure steam via the conduit 72 from the outlet chamber 34 of the reheater 16 and motive steam via the conduit 71, generates a steam flow through the conduit 73 into the conduit 50, which throttled heating steam into the inlet chamber 33 of the header of the reheater 16, or directly into the inlet chamber 33.

The method and the device according to the invention, by means of which more purging steam is supplied, by which undercooling of the condensate and the associated instabilities are essentially prevented, are very economical and have a high thermodynamic efficiency. Not only will the above be achieved, but the overall efficiency of the system will also be improved under partial load conditions, since the amount of purge vapor derived from preheater 16 to a lower point in the system, such as the feedwater preheater, significantly reduces, thereby reducing the less efficient use of the hot Steam is kept to a minimum.

It is not necessary to take special precautions, such as through special valves, to ensure that only a small part, for example 2 to 10% of the steam in the heating steam line, is used as motive steam for the steam jet pump 70. Under the present conditions, the steam jet pump is self-limiting, it works in throttle mode and only absorbs as much steam as is necessary to keep the available flushing steam in circulation.

Another advantage of the device according to the invention is that the system can easily be adapted to commercially available steam jet pumps, the operating parameters of which are well known.

To achieve the goal of avoiding condensate hypothermia and the associated instabilities, a larger amount of flushing steam is generally required than would be expected when recirculating with a low-pressure steam jet pump (steam jet pump with low AP). However, the high pressure steam jet pump (high AP steam jet pump) used in accordance with the present invention is capable of effecting these throughputs of the recirculation flow. The high pressure steam jet pump is also smaller and it is easy to increase the suction power by increasing the motive steam flow.

Another advantage is that the high AP steam jet pump used in the present invention

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does not reduce the pressure in the inlet chamber of the header. A low pressure steam jet pump, on the other hand, results in a lower header pressure because it represents a flow resistance in the steam inlet line. Reducing the header inlet pressure lowers thermal efficiency because the steam temperature is correspondingly lower.

Commercially available steam jet pumps can be used for the practical implementation of the invention, as are available, for example, from Ametek Corporation, Schutte and Koerting Division, Cornwells Heights, Pennsylvania, V. St. A. A typical steam jet pump is shown in FIG. 3.

The steam jet pump shown in FIG. 3 contains a motive steam inlet 81, a nozzle 82, a steam suction inlet 83, a body or mixing area 84 and a diffuser and outlet section 86.

In the simplest case, a steam jet pump with a fixed nozzle is used to implement the present invention. In a preferred embodiment of the invention, however, a steam jet pump with an adjustable nozzle is used, as shown in FIG. 3. The nozzle 82 is adjusted by means of a rotary head 88, which is used for the axial adjustment of a shaft, at the end of which there is a valve needle 89 with which the cross section of the inlet side of the nozzle 82 can be reduced. With this additional degree of freedom, the extent of the flushing can be set as is desirable for a specific operating mode, or different settings can be selected for different systems.

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The special exemplary embodiments described can of course be modified in a wide variety of ways. Instead of returning the purge steam by means of heating steam, as was described using the example of the throttled single-stage reheater, the invention can of course likewise be used in the same way in any other reheater with a tube bundle arrangement which is fed with high-pressure steam, which is considerable in a certain load range is throttled. In the case of a two-stage reheater which works according to the same principle, the rinsing flow in the tube bundle, which works with the higher pressure, will be recirculated. In addition, other tube bundle configurations, such as known straight tube bundles, can also be used instead of the U-tube bundles described. Instead of the high-pressure steam jet pump described as a pump device for the recirculation of the flushing steam in the reheater tube bundle, it is also possible to use any other equivalent pump device which fulfills the functional requirements placed on the high-pressure steam jet pump, such as a turbine or paddle wheel compressor.

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2 sheets of drawings

Claims (8)

642 142 PATENT CLAIMS 1. A method for preventing undercooling of condensate in the tubes (22) of a reheater (10) provided with a water separator, in which steam flowing on the jacket side of the tubes of a heating element is dewatered and heated by heat exchange with saturated heating steam flowing in the tubes (22) , in which method the saturated heating steam introduced into the pipes has a higher pressure than the saturated steam supplied on the jacket side, characterized in that the heating steam is throttled and introduced into the heating element (16) at reduced pressure; that part of the heating steam emerging from the heating element (16) is fed to the low-pressure inlet of a pump device (70) operating with a high pressure difference; that motive steam is supplied to the pump device (70); that the motive steam in the pump device (70) is expanded isentropically and entrains the heating steam at the outlet of the heating element (16) and that the flushing steam emerging from the outlet (73) of the pump device (70) of the inlet chamber (33) of the heating element (16 ) is supplied in order to prevent undercooling of condensate in the tubes (33) of the tube bundle (18) of the heating element under partial load conditions. 2. The method according to claim 1, characterized in that the ratio of the pressure of the driving steam to the pressure of the heating steam emerging from the heating element (16) is at least 1.5: 1. 3. reheater for performing the method according to claim 1, with a vapor-tight pressure vessel (12), an arrangement (13) for introducing cool, wet, jacket-side steam into the container, a device arranged in the container (15) for separating Water from the jacket-side steam, with a heating element (16) arranged in the container and used to increase the temperature of the dewatered jacket-side steam, which has an inlet chamber (33), an outlet chamber (34) and a plurality of essentially parallel heat exchange tubes connected between them , (22), which form a tube bundle (18) and run for heat exchange with the jacket-side steam in the longitudinal direction of the container, and with a device (50) for feeding the heating element with saturated heating steam of a temperature and a pressure which is greater than the temperature and pressure of the saturated jacket-side steam are characterized by a device (43) for throttling the Heizda mpfes for the heating element and an arrangement with which a flushing steam can be fed to the inlet chamber (33) in order to prevent undercooling of condensate in the tubes (22) under partial load conditions, which arrangement a steam jet pump (70) for high pressure difference, a first Line (72), with which heating steam can be fed from the outlet chamber (34) to the low-pressure inlet of the steam jet pump (70), a second line (71) for feeding the high-pressure inlet of the steam jet pump with motive steam, around the latter upstream of the throttle device (43) to remove the heating steam and has a third line (73) through which the flushing steam emerging from the steam jet pump (70) can be fed to the inlet chamber (33). 4. reheater according to claim 3, characterized in that the steam jet pump (70) is provided for a ratio of the pressure at the high pressure inlet to the pressure at the low pressure inlet of at least 1.5: 1. A post-heater according to claim 3, characterized in that means are provided which partially obstruct the flow of steam into the inlet ends of the tubes (22), so that a greater flow of saturated steam enters the tubes which are more stressed by heat transfer than those other tubes in the tube bundle. 6. reheater according to claim 3, characterized. that the tubes (22) of the tube bundle (18) are U-tubes which run in a substantially vertical plane, and that the inlet chamber (33) and the outlet chamber (34) are separate chambers of a single head piece (19). 7. reheater according to claim 3, characterized in that the steam inlet arrangement (13) along one side of the pressure vessel (12) and at least one steam outlet arrangement (14) along another side of the pressure vessel (12) and the device (15) for separating of water is arranged adjacent to the steam inlet arrangement (13), and in that: a head piece (19) is arranged at a first end of the tube bundle (18) and is tightly connected to the ends of the tubes (22) forming the tube bundle and at least one Contains partition plate (32) which divides the head into several chambers (33, 34), at least one of which forms an inlet chamber (33) and another forms an outlet chamber (34) to which the corresponding ends of the tubes (22) are connected . 8. reheater according to claim 3, characterized in that the steam jet pump for combining the high-pressure propellant steam with the low-pressure heating steam to a purge steam flow medium pressure contains no moving parts (Fig. 3).