DE102010041754A1 - Apparatus and method for generating superheated steam by means of solar energy based on the forced flow concept with helical water / steam guide and use of the superheated steam - Google Patents

Abstract

The invention relates to a device and a method for generating superheated water vapor by means of solar energy. A steam generator based on the forced flow concept is used. The generation of superheated steam, with which, for example, a steam turbine is driven, takes place within a water pipe in several stages, namely via feed water preheating, evaporation and superheating. Helical-shaped water pipes are used to guide the water or the water vapor. The thermal energy required to generate superheated water vapor is provided by a heat transfer medium heated by solar energy. To increase the efficiency of the generation of the superheated steam, tube bundles are used, among other things. With regard to larger steam generator units, a large number of steam generators are connected in parallel.

Description

The invention relates to a device for generating superheated steam by means of solar energy and a method for generating superheated steam using the device. In addition, a use of the superheated steam is indicated.

The use of solar thermal power plants as an alternative to conventional power generation is a way to defuse the existing carbon dioxide problem. This is solar energy (solar energy), d. H. electromagnetic radiation of the sun, converted into electrical energy.

Currently, the majority of solar thermal power plants are designed as solar thermal power plants with indirect evaporation. Solar fields with parabolic trough collectors serve as receivers of the solar energy. As an alternative to the parabolic trough collectors, Fresnel collectors are used as receivers of solar energy. Instead of the solar fields, solar towers are also used.

A solar thermal power plant with indirect evaporation has a steam generator. The steam generator includes a heat transfer circuit (primary circuit) with a heat transfer medium and a water / steam circuit (secondary circuit) with water. The heat transfer medium of the heat transfer circuit, such as a thermal oil or a salt melt, absorbs the solar energy in the form of heat (thermal energy). The heat transfer medium is heated. The heat absorbed by the heat transfer medium is transferred to the water of the water / steam circuit with the help of feedwater preheaters, evaporators and superheaters. In this case, superheated steam is generated. The stored in superheated steam thermal energy is used to obtain the electrical energy. It comes to the conversion of thermal energy into electrical energy.

The conversion of the thermal energy of the superheated steam into electrical energy takes place in the "conventional" part of a solar thermal power plant, for example with the aid of a steam turbine.

Object of the present invention is to show how efficiently superheated steam can be obtained with the help of solar energy, which can be used for the production of electrical energy.

To solve the problem, a device for generating superheated steam by solar energy is specified, comprising at least one heat transfer circuit with a heat transfer medium for receiving the solar energy in the form of heat and at least one water / steam cycle with water, wherein the heat transfer circuit and the water / steam cycle are thermally coupled to each other via at least one steam generator, by the steam generator a forced flow concept is realized with feed water preheater, evaporator and superheater, at least one water pipe for receiving the water is present Water pipe and the heat transfer circuit in the region of the feedwater preheater for heating befindlichem in the water pipe, liquid water by means of heat of the heat transfer medium are thermally coupled together, the water pipe and the heat transfer circuit in the evaporator to transfer the befindli in the water pipe chen, heated liquid water in water vapor by means of heat of the heat transfer medium are thermally coupled together, the water pipe and the heat transfer circuit in the superheater to overheat the water vapor located in the water pipe by means of heat of the heat transfer medium are thermally coupled together and the water pipe in at least one of the areas has a helical shape (helical structure).

To achieve the object, a method for generating superheated steam using the device with the following steps is given: a) providing the heat transfer medium, b) converting solar energy into heat of the heat transfer medium and c) transferring the heat of Heat transfer medium to the water of the water / steam cycle, wherein the superheated steam is generated.

According to a further aspect of the invention, a use of the superheated steam generated by the described method for obtaining electrical energy is specified, wherein with the aid of superheated steam, a steam turbine is driven.

The idea underlying the invention is to use solar energy for the formation of superheated steam, so the electromagnetic radiation emitted by the sun and which hits the earth's surface. For this purpose, a suitable steam generator system is provided. The steam generator or the steam generator system are based on the concept of forced circulation. Within the water pipe (pipe, in which the water of the water / steam cycle is located) takes place the transfer of liquid water in superheated steam. These are the heat transfer medium and the water thermally coupled with each other. It comes to the exchange of heat between the heat transfer medium and the water. This is preferably accomplished by the heat transfer medium flowing past the water pipe or being conducted past it. The exchange of heat takes place by heat conduction indirectly via the water pipe.

The difference to natural circulation concepts lies in the forced circulation concept in the water supply: The water of the water / steam cycle is always on the tube side, ie in the tube interior of the water ear. Since preheating, evaporation and overheating take place in the same water pipe, in contrast to the natural circulation concepts, a steam drum is not necessary.

The generation of the superheated steam takes place in several stages, namely via the feedwater preheating, the evaporation (formation of water vapor) and the overheating of the water vapor.

The water pipe for guiding water / resp. Water vapor has at least partially a helical construction. The water pipe is shaped as a helix (screw, helix, cylindrical spiral or helix) with a helical axis. The water pipe "winds" around the helical axis.

The helical design is particularly suitable for use with HPS heating (high performance solar thermal, eg molten salt as heat transfer medium) and allows a much larger temperature spread due to a "thermoelastic" structure. An occurring thermal expansion can be much better (more elastic) absorbed by the helical structure.

Preferably, the heat transfer circuit has a central heat transfer medium supply pipe, which is arranged along a helical axis of the water pipe. Through the heat transfer medium supply pipe, the heat transfer medium is provided to the steam generator. A supply of the hot heat transfer medium via an inner central tube allows a particularly space-saving compact design.

In order to simplify a start-up of the system, it is advantageous to provide at least one device for separating liquid water from the steam. This device comprises, for example, a separation vessel attached to the outlet of the superheater. Until the desired steam parameters are reached, the water vapor is passed on to a condenser of the separation vessel. The separated water is returned to the water / steam cycle, for example, by means of a pump.

In addition, the steam generator may have an intermediate superheater (intermediate superheat stage). With the intermediate superheater, an efficiency is increased with which a downstream steam turbine is operated. With the intermediate overheating stage, additional thermal energy is introduced into the water vapor. The introduction of the thermal energy can be done arbitrarily, for example by means of fossil fuels. Preferably, however, the intermediate overheating stage is operated solar-thermally: The intermediate superheater has an intermediate superheater water pipe for receiving the water vapor. For intermediate overheating hot, heated by means of solar energy heat transfer medium is guided past the intermediate superheater water pipe. Intermediate superheater water pipe and heat transfer medium are thermally coupled together. By passing the heat transfer medium, the water vapor in the intermediate superheater water pipe is additionally overheated. Preferably, the intermediate superheater water pipe is shaped as a helix.

For the feedwater preheating, evaporation and overheating can each be provided a separate heat transfer circuit. Preferably, however, a single, common heat transfer circuit is present for the feedwater preheating, evaporation and overheating. In this case, the heat transfer circuit is designed such that the heat transfer medium can successively flow past the water pipe in the region of the superheater, in the region of the evaporator and in the region of the feedwater preheater. Water pipe and heat transfer medium are brought into contact with each other.

The feedwater preheater, the evaporator and the superheater can be arranged arbitrarily to each other, for example horizontally. In order to effect the flow of heat medium through the water pipe, for example, a heat transfer pump or a plurality of heat transfer pumps is used. The heat transfer medium is pumped past the water pipe.

According to a particular embodiment, the feedwater preheater, the evaporator and the superheater are arranged vertically one above the other, for example, stacked one above the other. By a vertical structure, the Vorbeiströmen the heat transfer medium to the water pipe can be caused solely by the force acting on the heat transfer medium gravity. In addition, at least one heat transfer pump can be used to influence the flow of heat medium (flow direction and / or flow velocity) past the water pipe. In the vertical structure are preferably the Superheater above, the evaporator in the middle and the feedwater preheater below. The heat transfer medium flows from top to bottom first in the area of the superheater, then in the area of the evaporator and finally in the area of the feedwater preheater past the water pipe. With the aid of hot heat transfer medium, the overheating, with the help of slightly cooled heat transfer medium, the evaporation and with the help of "cold" heat transfer medium, the feed water preheating takes place. Thus, the amount of heat required for the particular stage is provided in a simple manner on the heat transfer medium.

The vertical construction of the steam generator is advantageous not only with regard to the flow of the heat transfer medium from "top to bottom". In addition, the vertical structure exploits a natural movement of the water vapor from "bottom to top".

For thermal coupling of the water pipe and the heat transfer medium, the feedwater preheater, the evaporator and the superheater each have their own pressure vessel (preheating pressure vessel, evaporator pressure vessel and superheater pressure vessel). In these pressure vessels, the water pipe is arranged. The water pipe is led through the pressure vessels. In the case of a single, common heat transfer circuit, the pressure vessels are preferably connected to one another such that the heat transfer medium can flow successively through the superheater pressure vessel, through the evaporator pressure vessel and through the preheating pressure vessel.

According to a particular embodiment, the water pipe is arranged in a single pressure vessel for thermal coupling of the water pipe and the heat transfer medium together, through which the heat transfer medium can flow with at least one particular flow direction. The common pressure vessel has at least one heat transfer medium inlet and at least one heat transfer medium outlet. Hot heat transfer medium is introduced into the pressure vessel via the heat transfer medium inlet and heat carrier medium cooled down via the heat transfer medium outlet. The heat transfer medium inlet is preferably in the region of the superheater and the heat transfer medium outlet in the region of the feedwater preheater.

Within the common pressure vessel, the heat transfer medium may be fed in one-pass with a flow direction or more generously with a plurality of different flow directions through the pressure vessel. One-way and Mehrzügigkeit the flow of the heat transfer medium may be provided in particular in the preheating pressure vessel, in the evaporator pressure vessel and / or in the superheater pressure vessel. Generous means that the heat transfer medium flows past the water pipe several times in each case in the region of the superheater, in the region of the evaporator and / or in the region of the feedwater preheater. In the case of the helical design, the generosity functions, for example, by changing the media guide between cylindrical areas, which at the end in each case have a reversal with semi-toroidal hoods into the adjoining (adjacent) cylindrical area. The individual functional units could be accommodated in the separate cylindrical areas.

It is particularly efficient if a plurality of parallel arranged water pipes is present. There is a water pipe bundle. For a given volume of pipe, a (total) pipe surface over which heat coupling of the heat transfer medium and water takes place is higher for a water pipe bundle compared to a single water pipe.

In a water pipe bundle, for example, the water is distributed via a distributor to the water pipes of the evaporator. In each of the water pipes, the production of superheated steam takes place separately. About a collector, the recovered in the individual water pipes, superheated steam is brought together again. The combined, superheated steam is then forwarded to a steam turbine.

To further increase the efficiency with which the heat of the heat transfer medium can be transferred to the water of the water pipe, it is advantageous to influence the flow direction (and the flow velocity) of the heat transfer medium. The heat transfer medium can be routed channeled on the water pipe or on the water pipes over. The channeling is done by, for example, a radially arranged pipe support. The pipe support is, for example, a radial perforated plate or web strips with semicircular recesses. A further improvement is achieved by the construction of the water tube bundle in cylinders with counter-wound helix tubes. There are crossed helices. A coiled strands forming in the heat transfer medium outside along the helical water pipes is thereby prevented.

For this purpose, according to a particular embodiment, a plurality of Umleitblechen for changing the flow direction of the heat transfer medium is present.

A further embodiment of the device relates, for example, to the provision of an additional heat carrier connection in the region of the evaporator. This connection is located at the outlet of the evaporator. The resulting additional hot heat transfer medium flow provides for faster settings of a design-related evaporation endpoint in the water pipes. When the desired superheated steam parameters are reached, this additional connection can be disabled. An additional amount of heat then connected to the additional heat transfer medium can be used, for example, for an intermediate overheating.

According to a particular embodiment, a plurality of steam generators are present. Preferably, the plurality of steam generators are connected in parallel to a larger steam generator unit.

With reference to several embodiments and the associated figures, the invention will be described in more detail below. The figures are schematic and do not represent true to scale figures.

1 shows a circuit diagram of a solar parabolic trough power plant.

2 shows a vertically placed steam generator without separation vessels in a side view.

3 shows a vertically placed steam generator with separation vessel in a lateral cross-section.

4A and 4B show the operating principle of the evaporator.

Given is a device 1 for generating water vapor by means of solar energy. The device has a heat transfer circuit 2 and a water / steam cycle 3 on.

The circuits are over at least one steam generator 4 thermally coupled with each other. An exchange of heat can take place via the steam generator, so that the water is transferred from the liquid phase into the gaseous phase as water vapor ( 1 ).

With the steam generator is a forced flow concept 44 with feedwater preheater 41 , Evaporator 42 and superheater 43 realized. There is at least one water pipe 30 for receiving water. The water pipe is helical.

To transfer heat through the solar panel 11 on the heat transfer medium 20 is transferred to the heat transfer circuit, the water pipe and the heat transfer circuit in the area 40 the feedwater preheater for heating located in the water pipe, liquid water by means of heat of the heat transfer medium thermally coupled together.

Likewise, the water pipe and the heat transfer circuit in the area 41 the evaporator for transferring the heated liquid water in the water pipe in water vapor by means of heat of the heat transfer medium is thermally coupled together. In addition, the water pipe and the heat transfer circuit in the area 41 the superheater for thermally overheating the water vapor in the water pipe by means of heat of the heat transfer medium is thermally coupled together.

To increase the respective heat transfer efficiency, the water pipe is helically shaped in the region of the superheater. The water pipe has a helix in this area. In an alternative embodiment, the water pipe is helically shaped in one of the other regions (evaporator, feedwater preheater) or in all regions.

Example 1:

Feedwater preheaters, evaporators and superheaters are vertically stacked in a common pressure vessel 43 stacked ( 2 ). The pressure vessel has a heat transfer medium inlet 430 and a heat transfer medium outlet 431 on. Hot heat transfer medium is supplied through the heat transfer medium inlet, and spent heat transfer medium, ie cooled heat transfer medium, is discharged through the heat transfer medium outlet. The heat transfer medium is a thermal oil. In an alternative embodiment, the heat transfer medium is a salt melt.

Within the pressure vessel, the heat transfer medium flows with a vertical flow direction from top to bottom of the heat transfer medium inlet in the direction of heat transfer medium outlet.

According to the present embodiment, there is no separation vessel for separating liquid and gaseous phases of the water.

Example 2:

In contrast to the previous example is a separation vessel 37 for the separation of the liquid and gaseous phase of the water ( 3 ). The separation vessel has a separator (cyclone separator) 33 for the separation of liquid and gaseous water. The separated water is returned to the water / steam cycle. This is done by gravity or, as shown in Figure, by means of a pump 36 ,

The 4A and 4B the operating principle of the steam generator with forced circulation concept is to be taken from. 4A shows the steam generator in a lateral cross-section. 4B shows the evaporator in plan view A and in cross sections along the connecting lines BB and CC ( 4A ). In the presentation is - contrary 2 - A central heat transfer medium supply pipe available.

In the pressure vessel, a plurality of helically shaped water pipes is present. The water pipes are coiled in each case in the same direction in individual cylinders and arranged coiled in opposite directions in each adjacent cylinder and tube bundles 32 summarized. The water pipes are over the distributor 34 supplied with water. The superheated steam formed in the water pipes is supplied by the collector 35 merged again and to the steam turbine 12 forwarded.

Via a central, arranged along the helical axes of the water pipes heat transfer medium supply pipe 50 the liquid, hot heat transfer medium is introduced into the steam generator.

According to the present examples, the heat transfer medium is passed through the pressure vessel einschubig. According to further, not shown embodiments, the heat transfer medium is passed mehrzügig within at least one of the areas through the respective pressure vessel.

In non-illustrated embodiments, the feedwater preheater, the evaporator and the superheater are each arranged in a separate pressure vessel. In this case, the water pipes are helically shaped in each of the pressure vessel.

Furthermore, in addition to the steam generator, an intermediate overheating stage (intermediate superheater) 13 available to increase the efficiency of the downstream steam turbine. The intermediate stage is also operated solar-thermally. The intermediate superheater has an intermediate superheater water pipe for receiving the water vapor. For intermediate superheating hot, heated by means of solar energy heat transfer medium is guided past the intermediate superheater water pipe. Intermediate superheater water pipe and heat transfer medium are thermally coupled together. Also, the intermediate superheater water pipe is helically shaped. Alternatively, the intermediate superheater water pipe is shaped differently, for example meandering. In another alternative, the intermediate superheater water pipe is straight throughout. It is not bent.

The device described is used to generate superheated steam by means of solar energy. The following process steps are carried out: a) providing the heat transfer medium, b) converting solar energy into heat of the heat transfer medium and c) transferring the heat of the heat transfer medium to the water, wherein the superheated steam is generated.

The generated, superheated steam is forwarded to a steam turbine for the production of electricity.

Claims (10)

Contraption ( 1 ) for generating superheated steam by means of solar energy, comprising - at least one heat transfer circuit ( 2 ) with a heat transfer medium ( 20 ) for receiving the solar energy in the form of heat and - at least one water / steam cycle ( 3 ) with water, wherein - the heat transfer circuit ( 2 ) and the water / steam cycle ( 3 ) via at least one steam generator ( 4 ) are thermally coupled to each other, - by the steam generator ( 4 ) a forced-circulation concept ( 44 ) with feedwater preheater ( 40 ), Evaporator ( 41 ) and superheater ( 42 ), - at least one water pipe ( 30 ) is present for receiving the water, - the water pipe ( 30 ) and the heat transfer circuit ( 2 ) in the area ( 40 ) of the feedwater preheater for heating in the water pipe ( 30 ), liquid water by means of heat of the heat transfer medium ( 20 ) are thermally coupled together, - the water pipe ( 30 ) and the heat transfer circuit ( 2 ) in the area ( 42 ) of the evaporator for transferring the in the water pipe ( 30 ), heated liquid water in water vapor by means of heat of the heat transfer medium ( 20 ) are thermally coupled together, - the water pipe ( 30 ) and the heat transfer circuit ( 2 ) in the area ( 42 ) of the superheater to overheat the water pipe ( 30 ) located by means of heat of the heat transfer medium ( 20 ) are thermally coupled together and - the water pipe ( 30 ) in at least one of the areas ( 40 . 41 . 42 ) has a helix shape. Device according to claim 1, wherein at least one device ( 37 ) is present for the separation of liquid water from water vapor. Apparatus according to claim 1 or 2, wherein a single heat transfer circuit is provided, which is configured such that the heat transfer medium can successively flow past the water pipe in the region of the superheater, in the region of the evaporator and in the region of the feedwater preheater. Device according to one of claims 1 to 3, wherein the feedwater preheater, the evaporator and the superheater are arranged vertically one above the other. Device according to one of claims 1 to 4, wherein for thermal coupling of the water pipe and the heat transfer medium together, the water pipe is arranged in a single pressure vessel through which the heat transfer medium with at least one particular flow direction ( 21 ) can flow. Device according to one of claims 1 to 5, wherein a plurality ( 32 ) is provided by parallel arranged water pipes. Apparatus according to any one of claims 1 to 6, wherein there are a plurality of steam generators. Device according to one of claims 1 to 7, wherein the heat carrier circuit, a central heat transfer medium supply tube ( 50 ), which is arranged on a helical axis of the water pipe. A method for producing superheated steam using a device according to any one of claims 1 to 8, comprising the following steps: a) providing the heat transfer medium, b) converting solar energy into heat of the heat transfer medium and c) transferring the heat of the heat transfer medium to the water of the water / steam cycle, wherein the superheated steam is generated. Use of the superheated in accordance with the method of claim 12 water vapor for the production of electrical energy, wherein with the aid of the superheated steam, a steam turbine ( 12 ) is driven.

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