DE102010040211A1 - Solar thermal continuous steam generator for direct evaporation, in particular in a solar tower power plant - Google Patents

Abstract

The invention relates to a solar thermal once-through steam generator (9), in particular for a solar tower power plant (1), comprising an absorber (4) with steam generator tubes (10), a flow cross-section of the steam generator tubes (10) varying in the flow direction of a medium. The invention also relates to a solar tower power plant (1).

Description

The invention relates to a solar thermal continuous steam generator, in particular for a solar tower power plant, comprising an absorber with steam generator tubes. The invention further relates to a solar tower power plant with a solar thermal continuous steam generator.

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, inexhaustible and does not burden future generations.

Solar thermal power plants are therefore one of the sustainable alternatives to conventional power generation. So far, solar thermal power plants have been carried out with parabolic trough collectors or Fresnel collectors. Another option is the 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 energy.

The solar field consists of heliostats, which concentrate the solar radiation on an absorber accommodated in the solar tower. 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 interspersed 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 size of the heating surface, it must be designed for maximum heat flow densities. The upper limit of the permissible heat flow densities is determined by the pipe material and the quality of the cooling mechanisms.

Static and dynamic instabilities can occur in evaporator heating surfaces, which have caused damage in conventional power plants in the past. This risk is increased due to the high energy density of solar thermal systems.

There is therefore a need, especially in solar thermal power plants, to avoid instabilities in the evaporator heating surface of the absorber.

The invention is therefore based on the object to provide a solar thermal steam generator of the type mentioned above for the highest possible heat flow. Furthermore, a correspondingly improved solar tower power plant with high thermodynamic efficiency is to be specified.

This object is achieved according to the invention by the features of claim 1. For high thermodynamic efficiency, thermal power plants are operated at high (i.a., 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. In addition, a continuous steam generator in comparison to a circulating steam generator a simple construction and is thus produced with very little effort. Furthermore, it is known that especially the friction pressure loss of the two-phase flow or the steam path at the outlet of the system is destabilizing, which has a negative effect on the achievable mass flow densities of the water to be evaporated and thus also negatively on the recoverable heat flow. The proportion of this pressure loss in the total pressure loss of the system is therefore to minimize instability to minimize. For this purpose, it is proposed that the flow cross section along the tubes varies in order to stabilize the evaporator heating surface.

In an advantageous embodiment of the invention, the flow cross-section of the steam generator tubes increases in the flow direction of a medium.

It may be advantageous if the flow cross-section of the steam generator tubes in the flow direction of a medium due to a Reduction of a wall thickness of the steam generator tubes increased.

Alternatively, it may also be advantageous if the flow cross-section of the steam generator tubes increases in the flow direction of a medium as a result of an enlargement of a steam generator tube circumference.

With regard to the thermal engineering design of the solar thermal continuous steam generator this is expediently assembled in Einzelheizflächen by successively connected pipe parts, d. H. the evaporator of the continuous steam generator is divided into two evaporator parts. In this case, a medium side first evaporator part on no outlet collector. Likewise, this second downstream evaporator part has no inlet distributor. This evaporator construction saves costs due to the savings of collectors.

It is expedient if an inner diameter of a first pipe part on the medium side is smaller than an inner diameter of a second pipe part connected downstream of the first pipe part.

Advantageously, the pipe parts are connected directly to one another via a conically shaped connecting piece.

It is expedient if the first tube parts of the steam generator tubes are fluidically connected on the input side to an evaporator inlet with an inlet distributor.

Furthermore, it is expedient if the second tube parts of the steam generator tubes are connected to an outlet collector.

In this case, the outlet header is advantageously connected to a steam line, which leads the steam to Überhitzerheizflächen.

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

The advantages achieved by the invention are in particular that over a wide load range a stable operation and thus the reliable use is granted even for continuous steam generator in solar thermal power plants.

The proposed measure therefore increases the recoverable heat flow in the steam generator of a solar thermal power plant with solar tower.

Hereinafter, embodiments of the invention will be described with reference to a drawing. Show:

1 a solar tower power plant,

2 an evaporator of a solar thermal steam generator according to the prior art,

3 an evaporator of an innovative solar thermal continuous steam generator and

4 a constructed from two Einzelheizflächen evaporator of the continuous steam generator after 3 ,

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 includes a solar tower 2 , at the vertical upper end of an absorber 3 is arranged. A heliostat field 4 with a number of heliostats 5 is on the ground around the solar tower 2 placed around. The heliostat field 4 with the heliostats 5 is for a focus of direct solar radiation 6 designed. Here are the individual heliostats 5 arranged and aligned so that the direct solar radiation 6 from the sun in the form of concentrated solar radiation 7 on the absorber 3 is focused. At the solar tower power plant 1 Thus, the solar radiation through a field of individually traced mirrors, the heliostats 5 , on the top of the solar tower 2 concentrated. The absorber 3 converts the radiation into heat and releases it to a heat transfer medium, such as water, which supplies the heat to a conventional power plant process with a steam turbine.

In 2 is an evaporator 8th a known solar thermal circulating steam generator 9 shown with direct evaporation, as an absorber 3 in the solar tower 2 of the 1 is integrated.

The steam generator pipes 10 are input side with an entrance distributor 11 and on the output side with an outlet collector 12 fluidically connected. overflow tubes 13 connect the exit collector 12 with a drum 14 into which a feedwater pipe 15 empties. In the feedwater pipe 15 is a feedwater pump 16 connected. A steam line 17 as well as a downpipe 18 branches off the drum 14 from. In the downpipe pipeline 18 is a circulation pump 20 connected. The downpipe 18 flows into the entrance distributor 11 ,

In operation of the solar heated circulating steam generator 9 sucks the circulation pump 20 Boiler water from the drum 14 and press it into the entry manifold 11 , There, the boiler water on the variety of heat-transmitting tubes 10 distributed. The evaporator 8th is divided into parallel Heizflächenrohre. The heat transfer tubes 10 be through the concentrated solar radiation 8th heated, the heat transfer tubes 10 give off the heat to the boiler water. The resulting steam / water mixture is passed through the outlet collector 12 and the overflow pipes 13 in the unheated drum 14 directed and there in as dry saturated steam and in the evaporator 8th recirculating recirculating water separately. The feed water supply is regulated so that the water level in the drum 14 remains constant.

The saturated steam leaves the drum 14 over 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 the operation of a solar thermal steam generator, it is particularly critical depending on the available heat supply of the primary solar radiation always exactly the required feedwater mass flow through the Absorberheizfläche to make available to the required or desired fluid state at the absorber outlet, respectively at the evaporator outlet 13 also during unsteady processes, in particular during cloud passage through the heliostat field 4 to ensure.

To explain the solar thermal continuous steam generator according to the invention 21 in the solar tower power plant 1 with direct evaporation shows 3 the principle of a forced flow steam generator, in which the passage of the water / vapor stream through the evaporator of a feed pump 16 is enforced. The feed water is supplied by the feed pump 16 in the entrance distributor 11 promoted and successively become the evaporator 8th and the superheater 22 flows 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 8th and superheater 22 is for the circulation process when starting the plant a separator 23 intended.

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

4 shows a preferred embodiment of the evaporator 8th with two individual heating surfaces. These are realized by a first evaporator part 24 and a second evaporator part downstream of this medium side 25 ,

The two evaporator parts 24 and 25 are directly, ie without the interposition of an outlet header or entrance distributor, interconnected. This show the parallel tubes 10a the first evaporator part 24 an inner diameter d1, the opposite to the inner diameter d2 of the parallel tubes 10b the second evaporator part 25 is smaller (d1 <d2). The connection of the individual parallel tubes 10a and 10b the evaporator parts 24 respectively. 25 is in the example of 4 each with a conically shaped intermediate piece 26 produced. This intermediate or connecting piece 26 is conical to realize the diameter extension, preferably in the form of a truncated cone formed. On the output side are the parallel tubes 10b the second evaporator part 16 to the exit collector 12 connected.

When operating the solar thermal continuous steam generator 21 condensed water, so-called feed water flows from one of the (not shown) steam turbine downstream (not shown) capacitor via the feedwater line 15 in the entrance distributor 11 , From there, the feed water flows into the individual evaporator tubes 10a the first evaporator part 24 of the continuous steam generator 21 ,

In the continuous steam generator 21 generated steam is at the outlet of the continuous steam generator 21 ie in the exit collector 12 slightly overheated. Higher overheating is possibly carried out in another heating surface. The evaporation endpoint slides in this evaporator concept depending on the load operating point.

Claims (11)

Solar thermal continuous steam generator ( 21 ), in particular for a solar tower power plant ( 1 ) comprising an absorber ( 3 ) with steam generator tubes ( 10 ), characterized in that a flow cross-section of the steam generator tubes ( 10 ) varies in the flow direction of a medium. Solar thermal continuous steam generator ( 21 ) according to claim 1, wherein the flow cross-section of the steam generator tubes ( 10 ) in the flow direction of a medium increases. Solar thermal continuous steam generator ( 21 ) according to claim 2, wherein the flow cross-section of the steam generator tubes ( 10 ) in the flow direction of a medium due to a reduction a wall thickness of the steam generator tubes ( 10 ). Solar thermal continuous steam generator ( 21 ) according to claim 2, wherein the flow cross-section of the steam generator tubes ( 10 ) increases in the flow direction of a medium due to an increase in a steam generator tube circumference. Solar thermal continuous steam generator ( 21 ) according to one of the preceding claims, wherein the steam generator tubes ( 10 ) of pipe parts connected in series ( 10a . 10b ) are composed. Solar thermal continuous steam generator ( 21 ) according to claim 5, wherein an inner diameter of a medium side first pipe part ( 10a ) is smaller than an inner diameter of the first pipe part ( 10a ) downstream second tube part ( 10b ). Solar thermal continuous steam generator ( 21 ) according to claim 5, wherein the pipe parts ( 10a . 10b ) via a conically shaped connecting piece ( 26 ) are directly connected. Solar thermal continuous steam generator ( 21 ) according to one of claims 5 to 7, wherein the first pipe parts ( 10a ) of the steam generator tubes ( 10 ) on the input side at an entrance distributor ( 11 ) are fluidically connected. Solar thermal continuous steam generator ( 21 ) according to one of claims 5 to 8, wherein the second pipe parts ( 10b ) of the steam generator tubes ( 10 ) with an exit collector ( 12 ) are connected. Solar thermal continuous steam generator ( 21 ) according to claim 9, wherein the exit collector ( 12 ) is connected to a steam line, which leads the steam to superheater heating surfaces. Solar tower power plant ( 1 ) with a solar thermal continuous steam generator ( 21 ) according to any one of the preceding claims.

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