Patent Publication Number: US-2013233301-A1

Title: Apparatus and method for producing superheated steam by means of a solar-thermally operated reheater and use of the superheated steam

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2011/067027 filed Sep. 29, 2011, and claims the benefit thereof. The International Application claims the benefits of German Application No. 10 2010 041 734.3 DE filed Sep. 30, 2010. All of the applications are incorporated by reference herein in their entirety. 
    
    
     FIELD OF INVENTION 
     The invention relates to an apparatus for producing superheated steam by means of solar energy and to a method for producing superheated steam using the apparatus. In addition a use of the superheated steam is specified. 
     BACKGROUND OF INVENTION 
     The use of solar-thermal power stations as an alternative to conventional power generation is a way of ameliorating the existing carbon dioxide problem. In such cases solar energy (energy from the sun), i.e. electromagnetic radiation of the sun, is converted into electrical energy. 
     Currently a majority of solar-thermal power stations are embodied as solar-thermal power stations with indirect evaporation. In such cases solar arrays with parabolic dish collectors serve as receivers of the thermal energy. As an alternative to the parabolic dish collectors, Fresnel collectors are used as receivers of the solar energy. Solar towers are also used instead of solar arrays. 
     A solar-thermal power station with indirect evaporation has a steam generator. The steam generator comprises a heat-transfer circuit (primary circuit) with a heat-transfer medium and a water/steam circuit (secondary circuit) with water. The water and the steam function as the working fluid. 
     The heat-transfer medium of the heat-transfer circuit, for example a thermo oil or molten salt, takes up the solar energy in the form of heat (thermal energy). The heat-transfer medium is heated up. The heat taken up by the heat-transfer medium is transferred with the aid of feed water preheaters, evaporators and superheaters to the water or to the steam of the water/steam circuit. In this case superheated steam is produced. The thermal energy stored in the superheated steam is used for obtaining electrical energy. The process involves the conversion of thermal energy into electrical energy. 
     The thermal energy of the superheated steam is converted into electrical energy in the “conventional” part of the solar-thermal power station, for example with the aid of the steam turbine, via which a generator is driven. 
     For optimum utilization of the turbine potential the steam is superheated once more after its evaporation in a high-pressure turbine. This is done with the aid of a reheater. After the superheating the steam is evaporated again in a low-pressure turbine. This process does not exclude the possibility of there being small portions of liquid water after the first evaporation of the steam. This water/steam mixture causes undesired deposits (salt flecks) of the heating surface and erosion in the turbine by drops hitting the inlet blades of the steam turbine. 
     SUMMARY OF INVENTION 
     An object is to demonstrate how, with the aid of solar energy, superheated steam with a small proportion of water can be efficiently obtained, which can be used for the generation of electrical energy. 
     To achieve the object an apparatus for producing superheated steam by means of solar energy is specified, having at least one heat-transfer medium circuit with a heat- transfer medium for taking the solar energy in the form of heat and at least one water/steam circuit with water and/or steam for forming the superheated steam, wherein in the water/steam circuit the water and/or the steam can flow in a flow direction, the heat-transfer circuit and the water/steam circuit are thermally coupled to one another via at least one heat exchanger for producing the superheated steam, in the water/steam circuit at least one water separator for separating water and steam from one another is disposed in the flow direction upstream of the heat exchanger, so that essentially only steam can get to the heat exchanger and the heat exchanger and the water separator are disposed in a common reheater pressurized container. 
     To achieve the object a method for producing superheated steam using the apparatus is also specified, with the following method steps: a) Provision of the heat-transfer medium, b) Conversion of solar energy into a heat of the heat-transfer medium, c) Provision of a water/steam mixture of the water/steam circuit, d) Separation of water from the water/steam mixture with the aid of the water separator and d) Transmission of the heat of the heat-transfer medium to the remaining steam of the water/steam mixture, wherein the superheated steam is generated. 
     In accordance with a further aspect of the invention a use of the superheated steam produced with the method described for obtaining electrical energy is specified, wherein a steam turbine is driven with the aid of the superheated steam. 
     Usually connecting pipes, through which the saturated steam is carried from the water separator into the heat exchanger, are used between the water separator and the heat exchanger. In some cases, even with very slight cooling, condensation (formation of liquid water) of the saturated steam occurs. By contrast, in accordance with the present invention, no connecting pipes between water separator and heat exchanger of the reheater are used. The water separator and the heat exchanger are disposed in a single container, so that the saturated steam which is obtained by the water separation goes directly into the heat exchanger of the reheater. To this end the water separator and the heat exchanger are preferably disposed immediately adjacent to one another. 
     The separated water is preferably fed back again to the water/steam circuit. One or more pumps are used for this purpose for example. 
     The efficiency with which a downstream steam turbine is operated is increased with the reheater. With the reheater thermal energy is introduced into the steam of the water/steam circuit. To introduce the thermal energy the reheater is operated solar-thermally. The reheater has a reheater water pipe for accepting the steam. For reheating hot heat-transfer medium heated up with the aid of solar energy (electromagnetic radiation which is emitted by the sun and which strikes the surface of the earth) bypasses the reheater water pipe. Reheater water pipe and heat-transfer medium are coupled thermally to one another. The passage of the heat-transfer medium past the pipe means that the steam in the reheater water pipe is superheated. 
     To cause the heat-transfer medium to bypass the reheater water pipe, a heat-transfer pump is used or a number of heat-transfer pumps are used. The heat-transfer medium is pumped past the water pipe. Preferably the reheater has a vertical structure, so that the hot heat-transfer medium can flow from “the top to the bottom” through the heat exchanger. The vertical structure of the reheater also utilizes a natural movement of the steam in the reheater water pipe from “the bottom to the top”. 
     In one particular embodiment the heat exchanger is disposed vertically above the water separator. Here too the natural movement of the steam is utilized. In addition the separated water can be drained off in a simple manner and supplied again to the water-steam circuit for further use. 
     In accordance with one particular embodiment the heat exchanger has a least one reheater water pipe for carrying the steam of the water/steam circuit. In this case the reheater water pipe has at least one pipe shape chosen from the group straight shape, U shape and helix shape. An efficient exchange of heat is ensured with the U shape and the helix shape in particular. 
     A switch of the heating medium to the inside of the pipe is also conceivable as well. The heat-transfer medium flows in the reheater heat-transfer medium pipes. The steam of the steam circuit flows past outer walls of the reheater heat-transfer pipes. In such cases heat is transferred. In one particular embodiment the heat exchanger has at least one reheater heat-transfer pipe for carrying the heat-transfer medium of the heat-transfer medium circuit. In this case the reheater heat-transfer medium pipe has at least one pipe shape selected from the group straight shape, U shape and helix shape. Here too the U shape and the helix shape ensure an especially efficient heat exchange. 
     It is especially efficient for a plurality of reheater water pipes disposed in parallel to one another to be present. A bundle of reheater water pipes exists. For a given pipe volume a (total) pipe surface via which the heat coupling of the heat-transfer medium and of the steam takes place, is greater for a reheater water pipe bundle by comparison with a single reheater water pipe. 
     In a reheater water pipe bundle the steam is for example distributed via a distributor to the reheater water pipes. Superheated steam is produced separately in each of the reheater water pipes. The superheated steam produced in the individual reheater water pipes is collected again in a collector. The superheated steam is subsequently conveyed onwards to a steam turbine. 
     For further improving the efficiency with which the heat of the heat-transfer medium can be transmitted to the steam of the reheater water pipe, it is advantageous to influence the direction of flow (and the speed of flow) of the heat-transfer medium. The heat-transfer medium can be channeled past the reheater water pipe or the reheater water pipes. For this purpose, in accordance with one particular embodiment, a plurality of diverter plates is present for changing the direction of flow of the heat-transfer medium. 
     In accordance with one particular embodiment a plurality of reheaters is present. Preferably the plurality of steam generators are connected together in parallel to a larger reheater unit. 
     The invention will be described in greater detail below with reference to a number of exemplary embodiments and the associated figures. The figures are schematic and do not represent true-to-scale diagrams 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a first example of an apparatus for producing superheated steam, viewed from the side. 
         FIG. 2  shows a second example of an apparatus for producing superheated steam, viewed from the side. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
     The starting point is an apparatus  1  for producing superheated steam  30  by means of solar energy. The apparatus has the following components: A heat-transfer circuit  2  with a heat-transfer medium  20  for taking up the solar energy in the form of heat and a water/steam circuit  3  with water and/or steam for producing superheated steam. In this case the water and/or the steam can flow in the water/steam circuit in the direction of flow  33 . 
     To produce the superheated steam, the heat-transfer circuit and the water/steam circuit are coupled thermally to one another via at least one heat exchanger of at least one reheater  4 . Hot heat-transfer medium  22  is introduced into the reheater. Cold heat-transfer medium  23  exits from the heat exchanger of the reheater and is available again to take up solar energy. 
     A water separator  5  for separating water and steam from one another is disposed in the water/steam circuit upstream from the heat exchanger, so essentially only steam can get into a heat exchanger. The heat exchanger and the water separator are disposed in a common reheater pressurized container. 
     The water  50  separated in the water separator is fed back again to the water/steam circuit. 
     Example 1 
     Here the steam (after evaporation from a first steam turbine) is conveyed into the water separator. The saturated steam flows out of the water separator directly into a bundle of reheater water pipes with a U shape. The U-shaped pipes are disposed in the form of a circle and are placed so that two part pipe plates are formed with the connections. These part pipe plates are placed offset (independently of one another. This avoids heat stresses resulting from high temperature differences. By the use of deflection plates the flow speed of the heat-transfer medium in the outer area is increased and thereby the transfer of heat improved. 
     Example 2 
     The structure of the apparatus is similar to that of example 1. Instead of U-shaped pipes, reheater water pipes with a helix shape are installed in the bundle. To reduce the flow cross-section the bundle is divided into two parts. The functional principle is comparable with that of the U-shaped pipe arrangement. 
     In accordance with a further example not shown, reheater water pipes with a U-shape and reheater water pipes with a helix shape are used. 
     Further examples, likewise not shown, include the carrying of the fluid heat-transfer medium inside the pipes. Reheater heat-transfer pipes with a U shape and/or reheater heat-transfer pipes with a helix shape are used. The steam of the water/steam circuit can flow past the outer surfaces of the reheater heat-transfer pipes, which results in an exchange of energy. 
     The apparatus described is used for production of superheated steam by means of solar energy. In this case the following method steps are performed: a) Provision of the heat-transfer medium, b) Conversion of solar energy into heat of the heat-transfer medium, c) Provision of a water/steam mixture of the water/steam circuit, d) Separation of water from the water/steam mixture with the aid of the water separator and d) Transfer of the heat of the heat-transfer medium to the remaining steam of the water/steam mixture, wherein the superheated steam is produced. 
     The superheated steam produced is conveyed onwards to a steam turbine for obtaining electrical power.