Solar thermal power plant having continuously heated pipe system
Patent Information
- Application Number
- EP2024720754
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2023-04-18
- Filing Date
- 2024-04-09
- Publication Date
- 2026-02-11
Smart Images
Figure DE2024100293_24102024_PF_FP_ABST
Abstract
Description
[0001] SOLAR THERMAL POWER PLANT WITH
[0002] COMPLETELY HEATED PIPE SYSTEM
[0003] The present invention relates to a solar thermal power plant with a piping system in which a heat transfer medium is guided, comprising a plurality of absorber tubes for absorbing solar energy coupled in with the aid of collector mirrors, wherein the absorber tubes are connected to form a collector loop which connects a distribution line for supplying cold heat transfer medium to a collecting line for discharging heated heat transfer medium, wherein the collector loop has electrically conductive tube walls which are divided into electrical circuits by means of spaced electrical bridges, wherein the electrical bridges alternately have an earth short circuit and a current source for supplying current to the tube walls in sections.
[0004] Such a solar thermal power plant is already known from CN 103 712 358 A. Reference is also made to WO 2017 / 002262 A1 and WO 2017 / 002252 A1.
[0005] In solar thermal power plants based on concentrating tracking mirror technology, molten salt is often used as the heat transfer medium. This typically has a freezing point above 230°C and should always remain in a liquid state. Before the salt is poured into the piping system, it must also be preheated to avoid or minimize thermally induced mechanical stresses, as these stresses can damage the pipeline beyond a critical level.
[0006] Another reason for heating pipelines is the accidental freezing of molten salt in the pipes. To remelt the frozen salt in such a case, the pipeline requires a heater with sufficient power, at least equal to the melting enthalpy of the salt.
[0007] There are various ways to heat pipelines. The most common method is trace heating. This involves placing an electrically insulated metal heating cable around the pipeline and applying a defined operating voltage. The electrical current induced by the voltage, combined with the electrical resistance of the heating cable, generates heat, which warms up the adjacent pipeline.
[0008] Another option for heating pipes is so-called Joule Heating. This involves applying an electrical voltage to the pipe itself, and the induced current flows in the pipe wall, where it generates heat with the pipe's electrical resistance. The advantage of this is that the heat generated is located directly where it's needed—in the pipe itself. Another advantage is the uniform heat distribution across the entire pipe cross-section, whereas with trace heating, the heat is predominantly distributed at the contact point between the pipe and the heating cable, resulting in lower efficiency and potentially hot / cold spots.
[0009] The challenge with Joule Heating is ensuring proper electrical insulation of the pipe. This means ensuring that there are no electrically conductive connections between the pipe and its support or casing, as these could misdirect the current.
[0010] Joule heating is also already known in principle in the field of solar thermal power plants, for example through DE 10 2013 108 311 A1 .
[0011] Against this background, the present invention is based on the object of specifying a solar thermal power plant which has reliable piping, but can nevertheless be manufactured inexpensively in terms of effort and material use and whose operating costs are reduced compared to known solar thermal power plants.
[0012] This object is achieved by a solar thermal power plant according to the features of independent claim 1. Useful embodiments of such a solar thermal power plant can be found in the subsequent dependent claims.
[0013] A solar thermal power plant is provided with a piping system through which a heat transfer medium is conducted, comprising a plurality of absorber tubes for absorbing solar energy coupled in by means of collector mirrors. The absorber tubes are connected to form a collector loop, which connects a distribution line for supplying cold heat transfer medium to a collecting line for discharging heated heat transfer medium. According to the invention, this is characterized in that the collector loop has electrically conductive tube walls that are divided into electrical circuits by spaced-apart electrical bridges. The electrical bridges alternately have a ground short circuit and a current source for supplying current to the tube walls in sections.
[0014] This design allows the collector loop to be divided into multiple circuits as needed. For this purpose, electrical bridges are placed at a distance from each other between the two absorber tubes contained in a collector loop. Each of these bridges is assigned a current source, while the two adjacent bridges are assigned a short circuit or a current sink, i.e., a ground short circuit. In a heating mode, the current source first energizes the bridge, then the absorber tubes, and finally the adjacent bridge with the ground short circuit. Due to their internal resistance, the absorber tubes heat up, and the heat transfer medium contained within them is thawed or at least heated as needed.
[0015] In a specific design, the absorber tubes can be connected to each other via connecting piping, which forms an electrical bridge, with or without a ground short circuit. Since the heat transfer medium must be transferred from one absorber to the other at the ends of the absorber tubes anyway, this connecting piping can itself be used as an electrical bridge, eliminating the need for a separate line.
[0016] Preferably, the collector loop may further comprise a riser as an electrically conductive connecting element to the distribution line and a downpipe as an electrically conductive connecting element to the collecting line, wherein the riser is connected to the downpipe via at least one electrical bridge.
[0017] To utilize the advantages of Joule Heating described above for the pipe sections adjacent to the absorbers and their connecting piping, Joule Heating can be extended to include additional circuits. The particular challenge here, in addition to the aforementioned electrical insulation of the pipe, lies in the definition and interconnection of the individual circuits and thus heating circuits. Pipe branching, different pipe diameters and wall thicknesses, insulation layer thicknesses, as well as internal components such as sensors or valves, play a decisive role in determining the temperature of each pipe section, either due to varying ohmic resistances or due to different thermal losses. The goal is to achieve a similar temperature in all pipe sections.The resulting current path can be influenced by the defined design of electrical bridges and grounding potentials.
[0018] Furthermore, in a specific design, the distribution line and the collecting line can have electrically conductive pipe walls that are divided into electrical circuits by spaced electrical bridges. The electrical bridges alternately provide a ground short circuit and a current source for supplying current to the pipe walls in sections. This also applies the basic idea of Joule Heating to the area of large distribution and collecting lines, which combine the heat transfer medium from the individual collector loops and represent the overlying transport level.
[0019] Accordingly, several similar collector loops arranged parallel and / or opposite each other can be arranged to connect the header and the distribution line. This results in a complex piping system within which the absorber tubes, in which the heat transfer medium is normally heated by solar radiation, are heated at a first level, while the heat transfer medium is supplied and removed at the level above. The distribution line and header, the so-called headers, therefore have a considerably greater capacity than the collector loops themselves and thus have a significantly larger pipe cross-section.
[0020] Therefore, it seems sensible for the pipe cross-sections and material cross-sections within a collector loop, preferably within all collector loops, to be consistently the same, and preferably made of the same material or material with the same electrical resistance. This enables consistent temperatures at consistent heating currents in the solar thermal power plant. However, for header heating, it is advisable to adapt the dimensions to the pipe sizes.
[0021] Finally, it may be preferable for the pipes of the collector loops and / or the distribution line and / or the collecting line to be electrically and / or thermally insulated, at least in sections. While the insulation protects against energy losses, it also simultaneously provides protection against damage and injuries caused by heat or electric shock. Suitable insulation is therefore advisable.
[0022] The invention described above is explained in more detail below using an exemplary embodiment.
[0023] It shows
[0024] Figure 1 shows an absorber tube with collector mirrors directed onto it in a side view,
[0025] Figure 2 shows a piping system with partial heating of the collector loops in a schematic representation, as well as
[0026] Figure 3 shows a schematic representation of the piping system according to Figure 2 with complete heating.
[0027] To illustrate this relationship, Figure 1 shows a supporting structure on which an absorber tube 1 is arranged elevated above a number of collector mirrors 2. The collector mirrors 2 serve to concentrate incoming sunlight and direct it onto the elevated absorber tube 1. A molten salt, whose melting point is above 230 °C and which can be heated to over 500 °C in the system, serves as the heat transfer medium in the absorber tube 1. The heat transfer medium initially flows through the elongated absorber in one direction, is then returned in the opposite direction via connecting piping 12 into a second, parallel and similarly designed absorber tube 1, where it leaves the collector loop 8 thus formed.
[0028] Figure 2 shows this in a schematic representation. The solar field according to the invention has a modular structure consisting of several parallel collector loops through which the molten salt flows and is heated during the day thanks to the concentrated solar radiation. The pipeline within a collector loop, a so-called loop, is connected via a riser 6 to a distribution line 4, the so-called cold header, and a downcomer 7 to a collecting line 5, the so-called hot header. Figures 2 and 3 show sections from a schematic representation of an overall system, which comprises numerous collector loops 8, 13 and other infrastructure.
[0029] In a first step, only the absorber pipes 1 can be heated to heat the piping system 3 using Joule Heating. The pipe sections of riser 6, downpipe 7, distribution pipe 4, and manifold 5 are each heated with Trace Heating. These pipe sections are initially only wrapped with a heating wire, and the heat is supplied from the outside.
[0030] Specifically, an electrical bridge 9 is created, which is arranged centrally on the two absorber tubes 1 combined to form a collector loop 8. A further electrical bridge 9 is inserted at the end of the absorber tubes 1 facing the header lines, the connecting piping 12 at the end of the absorber tubes 1 facing away from the header lines 4 and 5 serves not only to transmit the heat transfer medium but also as a further electrical bridge 9. This results in a first electrical circuit for heating the piping from the power source 11 via a first absorber tube 1 and the connecting piping 12, the second absorber tube 1 and the electrical bridge back to the power source 11. A second electrical circuit also starts at the power source 11 and runs via a first absorber tube 1, but then takes the path via the further electrical bridge 9 with an earth short circuit 10 and back via the second absorber tube to the power source 11.Further collector loops 13 can be connected in parallel to this collector loop 8.
[0031] Finally, Figure 3 shows a piping system 3 continuously heated by Joule heating. It comprises the circuits of Figure 2, but also forms an electrical bridge 9 with a power source 11 between the downpipe 6 and the riser 7, as well as further electrical bridges 9 between the distribution line 4 and the manifold 5, which are alternately provided with a power source 11 and a ground short circuit. Electrical circuits for heating all components are always formed between two electrical bridges 9 and thus also heat the riser 6 and the downpipe 7, as well as the two header lines, namely the distribution line 4 and the manifold 5.
[0032] This system heats the entire solar field's piping system (3) seamlessly. No hot or cold spots occur on any part of the piping system (3); instead, the pipes heat up evenly along their entire length.
[0033] The above describes a solar thermal power plant that has reliable piping, yet is inexpensive to manufacture in terms of effort and material usage, and whose operating costs are lower than those of conventional solar thermal power plants. LIST OF REFERENCE SYMBOLS 1 Absorber tube
[0034] 2 collector mirrors
[0035] 3 Piping system
[0036] 4 distribution line
[0037] 5 Collecting line 6 Riser line
[0038] 7 Downpipe
[0039] 8 collector loop
[0040] 9 electric bridge
[0041] 10 Earth short circuit 11 Power source
[0042] 12 Connecting piping
[0043] 13 additional collector loops
Claims
PATENT CLAIMS 1. Solar thermal power plant with a piping system (3) in which a heat transfer medium is guided, comprising a plurality of absorber tubes (1) for absorbing solar energy coupled in by means of collector mirrors (2), wherein the absorber tubes (1) are connected to a collector loop (8) which connects a distribution line (4) for supplying cold heat transfer medium to a collecting line (5) for discharging heated heat transfer medium, wherein the collector loop (8) has electrically conductive tube walls which are divided into electrical circuits by means of spaced electrical bridges (9), wherein the electrical bridges (9) alternately have an earth short circuit (10) and a current source (11) for supplying current to the tube walls in sections, characterized in that the collector loop (8) has a riser (6) as an electrically conductive connecting element to the distribution line (4) and a downpipe (7) as an electrically conductive connecting element to the collecting line (5), wherein the riser (6) is connected to the downpipe (7) is connected via at least one electrical bridge (9), so that heating circuits also heat the riser pipe (6) and the downpipe (7).
2. Solar thermal power plant according to claim 1, characterized in that the absorber tubes (1) are connected to one another via a connecting piping (12) which forms an electrical bridge (9), with or without an earth short circuit (10).
3. Solar thermal power plant according to one of the preceding claims, characterized in that the distribution line (4) and the collecting line (5) have electrically conductive pipe walls which are connected by means of spaced electrical bridges (9) are divided into electrical circuits, wherein the electrical bridges (9) alternately have an earth short circuit (10) and a current source (11) for supplying current to the pipe walls in sections.
4. Solar thermal power plant according to one of the preceding claims, characterized in that several similar collector loops (8, 13) arranged at a distance from one another in parallel and / or opposite one another connect the collecting line (4) and the distribution line (5) to one another.
5. Solar thermal power plant according to one of the preceding claims, characterized in that the pipe cross-sections and the material cross-sections within a collector loop (8), preferably within all collector loops (8, 13), are always the same and are preferably made of the same material or material with the same electrical resistance.
6. Solar thermal power plant according to one of the preceding claims, characterized in that the pipes of the collector loops (8, 13) and / or the distribution line (4) and / or the collecting line (5) are at least partially electrically and / or thermally insulated.