WO2012028502A2

WO2012028502A2 - Solar-thermal continuous flow steam generator comprising a steam separator and star distributor which is connected downstream for solar tower power stations with direct evaporation

Info

Publication number: WO2012028502A2
Application number: PCT/EP2011/064518
Authority: WO
Inventors: Jan BRÜCKNER; Martin Effert; Joachim Franke
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-09-03
Filing date: 2011-08-24
Publication date: 2012-03-08
Also published as: DE102010040216A1; WO2012028502A3

Abstract

The invention relates to a solar-thermal continuous flow steam generator (21) comprising a water separation system (23) and evaporator pipes which are connected on the flow medium side and upstream of the water separation system (23) and overheating pipes which are connected on the flow medium side and downstream of the water separation system (23). Said water separation system (23) comprises a plurality of water separating elements (24), each of said elements (24) comprising an end flow piece (26) which is connected to the respective upstream-connected evaporator pipes, which changes into a water guiding pipe piece (27) when viewed in the longitudinal direction. A number of outflow pipe pieces (28) branch off in the transitional area and are connected to an inlet connector (33) of the respective downstream-connected overheating pipes, and a distributor element (34) is arranged on the evaporator side between the respective water separation element (24) and the inlet collector (33). The invention also relates to a solar tower power station (1).

Description

description

Solar thermal continuous steam generator with a steam separator and downstream star distributor for solar tower power plants with direct evaporation

The invention relates to a solar thermal steam generator, in particular for a solar tower power plant, with a Wasserabscheidesystem and the Wasserabscheidesystem flow medium side upstream evaporator tubes and the Wasserabscheidesystem downstream side superheater tubes, wherein the Wasserabscheidesystem comprises a number of Wasserabscheideelementen, each of the Wasserab ^¬ sheath elements one with the respectively upstream Ver ^¬ steamer tubes connected inflow pipe piece includes, seen in its longitudinal direction merges into a Wasserableitrohrstück, wherein in the transition region a number of Abströmrohrstücken branches, which are connected to an inlet header of the respective downstream superheater tubes, and wherein the steam side between the respective Wasserabscheideele ^¬ ment and the inlet collector a Distributor element is arranged.

The steadily rising energy demand and climate change must be tackled with the use of sustainable energy sources. Solar energy is such a sustainable energy source. It is climate-friendly, yet inexhaustibly and is not a burden for is a descendant genera ^¬ tions.

Therefore, solar thermal power plants are one of the SUST ^¬ term alternatives to conventional power generation. Until now, solar thermal power plants were lectors with Parabolrinnenkol- or executed Fresnel collectors. Another option is direct evaporation in so-called solar tower power plants. A solar thermal power plant with solar tower and direct evaporation consists of a solar field, a solar tower and a conventional power plant part. in which the thermal energy of the water vapor is converted into electrical ^¬ specific energy.

The solar field consists of heliostats that focus the Sonnenstrah ^¬ Assembly at one housed in the solar tower absorbers. The absorber consists of a heating surface in which the irradiated solar energy is used to heat supplied feed water, to evaporate and possibly also to overheat. The generated steam is then expanded in a conventional power plant part in a turbine, optionally reheated and then condensed and fed back to the absorber. The turbine drives a generator, which converts the mechanical energy into electrical energy.

In a solar tower power plant, the solar energy input is limited by the size of the heliostat field. Part of the radiation is reflected by the absorber and is lost to the thermodynamic power plant process. These losses increase with the size of the heating surface. Therefore, for a given thermal performance compact absorbers with the smallest possible heating surface are desirable. By concentrating the incident solar energy on small areas, this leads to very high heat flux densities, generally higher heat flux densities than in fossil-fired thermal power plants. Therefore, with the concept of direct evaporation in a solar tower power plant, the cooling of the absorber heating surface is of central importance. To minimize the Heizflächengröße is be interpreted ^¬ gen on maximum heat flux densities. The upper limit of the allowable heat flux is determined by the pipe material and the quality of Kühlungsme ^¬ mechanisms.

The invention is therefore based on the object to provide a solar thermal ^¬ steam generator of the type mentioned above for maximum heat flow. Furthermore, a correspondingly improved solar tower power plant with high thermodynamic efficiency is to be specified. This object is achieved by the features of claim 1. For a high thermodynamic efficiency thermal power plants are operated at high (ia supercritical) pressures. For this purpose, the evaporator must be designed as Durchlaufheizflächen because they are subject to no pressure limit, in contrast to a natural or forced circulation steam generator, so that live steam pressures far above the critical pressure of water are possible. This high live steam pressure promotes a high thermodynamic efficiency of a power plant.

During low load operation or during startup, such a continuous steam generator is usually operated with a minimum flow of flow medium in the evaporator tubes in order to ensure reliable cooling of the evaporator tubes. For this purpose, just at low loads of, for example, less than 40% of the design load, the pure mass flow through the evaporator usually no longer suffices for cooling the evaporator tubes, so that an additional throughput of flow medium is superimposed on the passage of flow medium through the evaporator in circulation. The operationally provided ^¬ ne minimum flow of fluid in the evaporator tubes is thus not completely evaporated during startup or low load operation in the evaporator tubes, so that at ei ^¬ ner such operating mode at the end of the evaporator tubes still unvaporized flow medium, in particular a water-steam mixture available is.

Since the evaporator tubes of the continuous steam generator after ^¬ connected superheater tubes are usually designed for a flow unevaporated flow medium, continuous steam generators are usually designed so that even when starting and in low load operation, a water ingress into the superheater tubes is safely avoided. For this purpose, the evaporator tubes are usually connected to the nachge ^¬ switched superheater tubes via a Wasserabscheidesystem. The water separator causes a separation emerging from the evaporation ^¬ ferromagnetic lead at start or in low-load operation of water-steam mixture into water and steam. The steam is fed to the downstream of the water separator reheater tubes, whereas the separated water can can be fed to the evaporator tubes or discharged via an expander, for example, via a circulating pump as ^¬.

The o.g. Water separation can be achieved, for example, by so-called cyclone separators. Cyclone separators are relatively large, thick-walled components.

Due to the design, a feedthrough of these cyclone separators with water is only possible to a limited extent. Thus, the heating surface that can be used for evaporation must lie in the flow direction in front of the separators and is thus limited. This has the consequence that the live steam temperature can be controlled only in small limits by the feedwater quantity. For a size ^¬ ren Control range Desuperheaters are required.

The water separation system may include a plurality of water separation elements integrated directly into the tubes. Here, each may in particular the parallel ge ^¬ switched evaporator tubes a Wasserabscheideelement conces- be classified. The Wasserabscheideelemente may alternatively be designed as so-called T-piece Wasserabscheideelemente to the above cyclone separators. Each T-piece Wasserabscheideelement each case includes an associated with the vor ^¬ connected evaporator tube Einströmrohrstück, which is seen in its longitudinal direction merges into a Wasserableitrohrstück, wherein in the transition region branches off a connected to the downstream superheater tube Abströmrohrstück. By this construction, the T-piece Wasserabscheideelement for inertial separation of the flowing from the upstream evaporator tube in the Einströmrohrstück water-steam mixture is designed. Because of its comparatively higher inertia flows namely ^¬ place preferably in the axial extension of the Einströmrohrstücks further and thus enters the Wasserableitrohrstück and from there further into a normally be castle ^¬ NEN collecting the water content of the flowing in a ^¬ strömrohrstück flow medium at the transition. The vapor portion of the flowing in Einströmrohrstück water-steam mixture, however, can follow a set ^¬ zwungenen deflection due to be ^¬ ner comparatively lower inertia better and thus flows over the Abströmrohrstück to the downstream superheater tube section.

In a continuous-flow steam generator with such a designed water separation water separation can be performed without herein are subject ^¬ membered collection of flowing out of the evaporator tubes of flow medium through the distributed integration of the separation of water into the individual tubes of the tube system of the once-through steam generator. For a direct transfer of the flow medium in the downstream superheater tubes is possible.

The transfer of flow medium to the superheater tubes is not limited to vapor By design, in addition, but can now also be a water-steam Ge ^¬ mixing continued at the superheater tubes by the Wasserabscheideelemente be fed. Thus, the evaporation end point may be required, neinverschoben in the superheater tubes hi ^¬. Thus, a particularly high operating ^¬ Liche flexibility even in start-up or low load operation of the continuous steam generator can be achieved. In particular, the live steam temperature can be controlled in comparatively large limits by influencing the feedwater quantity.

However, to be considered in such systems is that due to the integration of the water separating a comparatively high number of individual pipe sections or elements is required in the individual tubes in particularly in the area of the deposition ^¬ system. For this reason, in the inventive Durchlaufdampferzeu- ger before the T-piece separator a collection of the flow medium of each of a plurality of evaporator tubes and the steam side between the respective Wasserabscheideelement and the inlet header arranged a distributor element.

The invention proceeds from the consideration that by the distributed water separation that occurs in the above-beschrie ^¬ surrounded construction separately in each of the parallel connected evaporator tubes, can result in a relatively large number of tee-Wasserabscheideelementen to design problems in the industrial application , Due to the space problems that may bring with it the need to accommodate such a large number of water separation elements, such a construction due to the high design ^effort associated with it also considerable ^¬ cost and bring limitations of the geometric parameters of the continuous ^{steam generator} with it.

A reduction of the design ^{effort of} the continuous steam generator could be achieved by a simpler design of the water separation system. For this purpose, the number of Wasserabscheideelemente used can be reduced. However, in order to obtain the advantages of decentralized water separation, such as the possibility of feeding with water-steam mixture, the basic design in the form of T-piece water separation elements should be maintained. The combination of the two aforementioned concepts can be achieved by a collection of the flow medium from a plurality of evaporator tubes in each case a Wasserabscheideelement.

Due to a reduced number of T-piece Wasserabscheideele ^¬ ments a direct steam-side forwarding to the inlet header of the downstream superheater tubes, however, lead to inhomogeneities in the distribution of the various superheater tubes. Therefore, after the exit of Damp ^¬ or fes the water-steam mixture from the T-piece Wasserab- element sheath, a uniform distribution on the nachge ^¬ switched superheater tubes to achieve steam side Zvi ^¬ rule of each Wasserabscheideelement and the A ^¬ arranged a distributor element occurs collector.

Advantageously, the geometric parameters of a number of outlet pipes are chosen such that a homogeneous flow distribution is ensured on the inlet header of the respectively downstream superheater pipes. As a result, a homogeneous entry is already achieved in the inlet header, which accordingly continues in the nachgeschalte ^¬ th superheater tubes. The output pipes may have, for example the same diameter and be guided in gleichmä ^¬ lar intervals parallel to one another in the inlet header.

In an advantageous embodiment, the distributor element is designed as a star distributor, ie it comprises a baffle plate, an inlet tube arranged perpendicular to the baffle plate and a number of outlet tubes arranged in a star shape around the baffle plate in its plane. The inflowing water impinges on the baffle plate and is distributed in a symmetrical manner perpendicular to the inflow direction and gelei ^¬ tet in the output tubes.

In this case, the baffle plate is circular in a particularly advantageous Ausges ^¬ tion and the output tubes arranged concentrically to the center of the baffle plate at equal intervals to the respective adjacent outlet tubes. In this way, a particularly homogeneous distribution is ensured on the various output ^¬ pipes.

Advantageously between five and 20 output ^¬ tubes per distributor element are provided. With a smaller number, a sufficient homogenization of the entry of steam or water-steam mixture in the inlet header of the superheater could no longer be guaranteed, while a higher number of problems in the geometrical configuration. tion of the distributor element may be, in particular if the ^¬ ses is designed as a star distributor.

The solar thermal steam generator is integrated in a particularly advantageous embodiment with its Verdampferheizflache in a solar tower power plant and directly to steam generation by focused solar radiation acted upon.

The advantages achieved by the invention are in particular that a uniform distribution of the flow medium is achieved on the superheater tubes even at a much ge ^¬ ringeren number of Wasserabscheideelementen by the vapor-side arrangement of an additional distribution element between the respective Wasserabscheideelement and the inlet header of the superheater.

These measures make it possible to reduce the number of water separation elements in the first place. This be ^¬ indicates a significantly lower manufacturing costs and a comparatively lower complexity of the pipe system of the continuous steam generator and it is particularly high ^¬ be triebliche flexibility in starting or Schwachlastbe ^¬ driving distance.

The use of conventional cyclone separators and their temperature monitoring can be omitted.

The homogeneous temperature distribution over the downstream superheater tubes leads to significantly lower mechanical loads as a result of different thermal expansion of the individual superheater tubes.

At the same time, all advantages of using T-piece Wasserabscheideelementen obtained, such. B. the possibility of forwarding water-steam mixture to the superheater tubes, which allows a needs-based control of the fresh steam temperature at the steam outlet of the continuous steam generator by the control of the introduced flow medium amount. When feeding the steam separator with water, water-steam mixture or steam, the entire superheater can also be used as an evaporator. Thus, the live steam tempera ture down to the saturation temperature on the Speisewas sermenge be influenced so that the usual one sprayers can be omitted.

Further, in appropriate operation, the Temperaturtran- the superheater outlet header can be redu ^¬ sheet to a minimum SIENT, resulting in a shortening of the startup time.

The number of required steam separators is considerably reduced by the connection of star distributors.

The inventive design of solar thermal steamer generators will be explained in more detail with reference to the drawings.

In detail show:

1 shows a solar tower power plant,

2 shows an evaporator of a solar thermal Dampferzeu gers according to the prior art,

3 shows an evaporator of an inventive solar thermal continuous steam generator and

4 shows a vapor separator with downstream star distributor for forced flow steam generators in solar tower power plants with direct evaporation.

Corresponding parts are provided in the figures with the same reference numerals.

1 shows a solar tower power plant 1. The solar tower power plant 1 comprises a solar tower 2, at the vertically upper end of an absorber 3 is arranged. A heliostat 4 with a number of heliostats 5 is on the ground at de Solar Tower 2 placed around. The heliostat 4 with the heliostat 5 is designed for focusing the direct solar radiation 6. In this case, the individual heliostats 5 are arranged and aligned such that the direct solar radiation 6 is focused by the sun in the form of concentrated solar radiation 7 onto the absorber 3. In the solar tower power plant 1, the solar radiation is thus concentrated by a field individually tracked mirror, the heliostat 5, on the top of the solar tower 2. The absorber 3 converts the radiation into heat and returns it to a Wärmeträgerme ^¬ dium, for example water, from which supplies the heat to a conven tional ^¬ power station process with a steam turbine.

In FIG 2, an evaporator 8 of a known solar thermal see circulation steam generator 9 with direct evaporation Darge ^¬ represents, which is integrated as an absorber 3 in the solar tower 2 of FIG 1.

The steam generator tubes 10 on the input side with an input distributor 11 and enters the outlet side fluidly connected with an outlet collector ^¬ 12th Overflow pipes 13 connect the outlet header 12 with a drum 14, into which a feedwater line 15 opens. In the feedwater pipe 15, a feedwater pump 16 is connected. A steam line 17 and a downpipe 18 branch off from the drum 14. In the downpipe 18, a circulation pump 20 is connected. The downpipe 18 opens into the inlet manifold 11. In operation of the solar heated circulating steam ^generator 9, the circulation pump sucks 20 boiler water from the drum 14 and pushes it into the inlet manifold 11. There, the boiler ^¬ water is distributed to the plurality of heat-transmitting tubes 10. The evaporator 8 is divided into parallel Heizflä- chenrohre. The heat-transferring tubes 10 are heated by the concentrated solar radiation 8, wherein the heat-transferring tubes 10 deliver the heat to the boiler water. The resulting steam / water mixture is over the Outflow collector 12 and the overflow pipes 13 are guided into the unheated drum 14 and separated there into saturated dry steam as far as possible and into the circulating water ^flowing back to the evaporator 8. The feed water supply is controlled so that the water level in the drum 14 remains constant.

The saturated steam leaves the drum 14 via the steam line 17 and can be overheated in a further heating surface and then delivered as live steam of a steam turbine not shown for generating electrical energy.

In operation of a solar thermal steam generator is to provide be ^¬ Sonders critical in dependence on the existing heat In ^¬ bots of the primary solar radiation always exactly the required feed water mass flow through the Absorberheizfläche, available to the required or desired fluid state at the absorber outlet, respectively, at the evaporator outlet ^¬ 13 also during unsteady processes, in particular in cloud passage through the heliostat 4 to be guaranteed ^¬ th.

3 shows the principle of a solar thermal cycling ^¬ steam generator 21, wherein the force of the flow of the water / steam flow through the evaporator of a feed pump sixteenth The feed water is conveyed by the feed pump 16 into the inlet manifold 11 and successively the evaporator 8 and the superheater 22 are flowed through (in solar thermal power plants typically eliminates a feedwater pre-heater). The heating of the feed water to the saturated steam temperature, the evaporation and overheating take place continuously in one pass, so that no drum is needed. Between evaporator 8 and superheater 22 a Wasserabscheidesystem 23 is provided for the circulation process when starting the system.

With forced circulation steam generators very large steam outputs can be generated in a relatively small space. By the By eliminating the separating drum, supercritical pressures can also be achieved with the continuous steam generator and thus very high efficiencies can be achieved.

To explain the solar thermal steam generator 21 according to the invention in the solar tower power plant 1 with direct evaporation, FIG. 4 shows the water separation system 23 to which the flow medium vaporized in the steam generator tubes is supplied. In Wasserabscheidesystem 23 not yet evaporated water is collected and removed. This is necessary in particular in the on ^¬ driving operation, if for safe cooling of the evaporator tubes, a larger amount of flow medium must be pumped, as can be evaporated in an evaporator tube run. The generated steam is optionally distributed to the superheater tubes.

The Wasserabscheidesystem 23 comprises a number of T-piece Wasserabscheideelementen 24. In each case a number of evaporator tubes opens into a common transition pipe piece 25, each of which a T-piece Wasserabscheideelement 24 nachge ^{¬ is} switched. The T-piece water separation element 24 comprises an inflow pipe piece 26, which, viewed in its longitudinal direction, merges into a water discharge pipe piece 27, wherein an outflow pipe piece 28 branches off in the transition region. The Wasserableitrohrstück 27 opens into a collector 29. To the collector 29 is connected via connecting lines 30, a collecting container 31 (bottle) downstream. To the sump 31, an off ^¬ let valve 32 is connected, via which the separated What ^¬ ser either discarded or can be fed to the evaporation circuit again.

In the T-piece water separation element 24, flow medium enters through the inflow pipe piece 26. The proportionate water flows due to its inertia in the following in the longitudinal ^¬ direction Wasserableitrohrstück 27. The vapor, however, follows due to its lower mass of the forced by the pressure ratios deflection in the outflow pipe piece 28. The Abströmrohrstück 28, the Überhit tube via an inlet header 33 are connected downstream.

If necessary, the outlet valve 32 can be closed and thus an overfeed of the T-piece Wasserabscheideelemente 24 are brought about. In this case still unevaporated water enters the superheater tubes, so that they can still be used for further evaporation, d. h., The evaporation end point can be moved into the superheater tubes, which allows a relatively higher flexibility in the operation of the continuous steam generator 21.

In order to enable a particularly simple construction of the Durchlaufdampf- generator 21, a relatively smaller number of ge ^¬ T-piece Wasserabscheideelementen 24 should be used. To the resulting inhomogeneities in the allocation on the superheater tubes for For ^¬ same and thus allow such a design in the first place, are interposed in the way of star distributors the T-piece 24 Wasserabscheideelementen distributor elements 34th These provide for a pre-distribution of the flow medium in the event of over-feeding of the T-piece Wasserabscheideelemente 24 to the inlet header 33rd

In the constructed as a star distributor manifold elements 34, the flow medium impinges on a circular baffle plate and impinges from there in a star shape, concentrically-arranged symmetrically output pipes 35. Due to the symmetrical Anord ^¬ voltage to each output tube is in this case 35 allocated approximately the same amount of flow medium. These open at equal intervals in the inlet header 33, so that there is already a pre-distribution of the flow medium over the entire width of the inlet header 33.

With a direct introduction of the flow medium via a single line per T-piece Wasserabscheideelement 24, the flow medium in the inlet manifolds 33 could not be distributed evenly, as these due to their width are not suitable for such a homogeneous distribution of example, ^¬ a single supply line.

By designed as a star distributor distribution elements 34 thus a simpler and thus more cost-effective design of the continuous steam generator 21 is possible because a comparatively smaller number of T-piece ^{Wasserabscheide ¬} elements 24 can be used. Furthermore, temperature differences are better compensated by better mixing of the flow ^¬ medium compared to a fully decentralized water separation with a larger number of T-piece Wasserabscheideelementen 24 and thus achieves a more homogeneous temperature distribution to the subsequent superheater tubes.

Claims

claims

Solar thermal continuous steam generator (21) for a solar tower power plant (1), with a Wasserabscheidesystem and the Wasserabscheidesystem (23) flow medium side upstream evaporator tubes and the Wasserabscheidesystem (23) flow medium side downstream superheater tubes, said Wasserabscheidesystem (23) comprises a number of Wasserabscheideelementen (24) wherein each of the Wasserabscheideelemente (24) comprises a connected to the je ^¬ Weils upstream evaporator tubes Einströmrohrstück (26), seen in its longitudinal direction in a Wasserableitrohrstück (27) passes, wherein in the transition region a number of Abströmrohrstücken (28) branches, the an inlet header (33) of the respectively downstream superheater tubes are connected, and wherein a distributor element (34) is arranged on the vapor side between the respective Wasserab ^¬ sheath element (24) and the inlet header (33).

Solar thermal continuous steam generator (21) according to claim 1, wherein the geometric parameters of a number of outlet pipes (35) of the respective distributor element (34) are selected such that a homogeneous Strö ^¬ tion distribution is ensured on the inlet header (33) of the respective downstream superheater tubes.

3. Solar thermal continuous steam generator (21) according to claim 1 or 2, wherein the respective distributor element (34) has a baffle plate, a perpendicular to the baffle plate to ^¬ ordered input pipe and a number of star-shaped arranged around the baffle plate in the plane of the output ^¬ tubes (35). includes.

4. Solar thermal continuous steam generator (21) according to claim 3, wherein the baffle plate is circular and the outlet pipes (35) concentric with the center of the baffle plate are arranged at equal intervals to the respective adjacent output tubes (35).

5. solar thermal continuous steam generator (21) according to one of claims 1 to 4, ^wherein the respective distributor ^¬ element (34) between five and 20 outlet pipes (35) summarizes.

6. solar tower power plant (1) with a solar thermal continuous steam generator (21) according to any one of the preceding claims.