WO2013167249A1

WO2013167249A1 - Fill level measurement for molten salt

Info

Publication number: WO2013167249A1
Application number: PCT/EP2013/001306
Authority: WO
Inventors: Andrew Lochbrunner
Original assignee: Linde Aktiengesellschaft
Priority date: 2012-05-10
Filing date: 2013-05-02
Publication date: 2013-11-14
Also published as: DE102012009336A1

Abstract

The invention relates to a fill level sensor (1) which is designed to measure a fill level in a container (2) with molten salt and which has a sensor (11) that is at least partly electrically conductive and a fixing structure (12), wherein the fill level sensor (1) can be fixed to the container (2) by means of said fixing structure. At least one insulating structure (131 - 133) is arranged between the sensor (11) and the fixing structure (12), said insulating structure having a mica-containing material. The invention likewise relates to a fill level measuring device (10) with a corresponding fill level sensor (1) and a control unit (14), to a container (2) with such a fill level measuring device (10), and to the use of a mica-containing material as an insulator in a fill level sensor (1).

Description

description

Level measurement for molten salt

The invention relates to a level sensor, which is adapted to measure a level in a container with a molten salt, a level measuring device with a corresponding level sensor and a control unit, a container with such a level measuring device and the use of a mica-containing material as an insulator in a level sensor.

State of the art

Salt melts with temperatures of up to 600 ° C are suitable as heat carriers in a wide variety of chemical processes. The focus here is on classic applications that work at a high temperature level, for example in melamine or aluminum oxide production. For example, salt mixtures with a melting point of about 142.degree. C. are used.

Salt melts, in addition to liquid metals, are the only heat carriers for temperatures above about 400 ° C. Other heat carriers, such as thermal oils, can generally no longer be used in these temperature ranges. However, molten salts are also advantageous in lower temperature ranges compared to thermal oils, since the latter have a relatively high vapor pressure and are highly flammable. When suitable as heat transfer salts are, for example, sodium and potassium nitrates. Such salts have a higher heat storage capacity than thermal oils and are significantly cheaper.

Salt melts are also used as heat carriers in solar thermal energy, for example in so-called parabolic trough power plants. In such applications, sunlight is focused by suitable concave mirrors on an absorber tube. A heat transfer medium flows through the absorber tube and is heated accordingly. The heat can be released, for example, in a downstream steam generator to a water-steam cycle and converted by steam turbines and generators into electricity. The efficiency of power generation depends largely on the maximum paint working temperature of the heat carrier used. The higher its temperature, the better the utilization of the steam turbine.

In appropriate applications, molten salts can also be used for heat storage. For example, a suitable molten salt can be heated up to 565 ° C during the day by solar radiation, and at night, just like a battery, it can release the stored heat. Here, for example, salt melts with a melting temperature of 220 to 240 ° C are used. In particular, in such storage systems, but also in classical applications, the determination of the level of molten salt in the containers used is required. A corresponding filling level should preferably be monitored automatically, so that, for example, falling below a minimum level can be detected and signaled simply and reliably. Salt melts in solar thermal applications, for example, are often pumped from cold to hot areas and vice versa, so that the fill levels present in the respective containers can change rapidly and faults must be detected.

A mechanical or hydrostatic level measurement is often not possible due to the high temperatures of 565 ° C and more in molten salt. For this reason, conventional conductive measuring probes are also only of limited suitability for level measurement. However, a reduction in the temperature for level measurement is also not without problems, since the salt melts can thereby partially solidify. This leads to unreliable values.

The present invention therefore has as its object to provide a way of measuring the level of molten salt at high temperature.

Disclosure of the invention

The invention proposes a level sensor adapted for measuring a level in a molten salt container, a level measuring device with a corresponding level sensor and a control unit, a container with such a level measuring device, and the use of a mica-containing material as an insulator in a level sensor the characteristics of the pending claims. Preferred embodiments are subject of the dependent claims and the following description.

Advantages of the invention

An inventive level sensor is set up to measure a level in a container with a molten salt. It has an at least partially electrically conductive measuring sensor and a fastening structure by means of which the filling level sensor can be fastened to the container. At least one insulating structure is arranged between the measuring sensor and the fastening structure. This according to the invention has a mica-containing material.

Minerals of the mica group, or mica for short, are phyllosilicates with the chemical composition DG ₂ , 3 [TO ₁₀ ] X2. Here, D denotes a 12-coordinate cation (K, Na, Ca, Ba, Rb, Cs, NH ₄ ⁺ ), G a 6-coordinate cation (Li, Mg, Fe ²⁺ , Mn, Zn, Al, Fe ³⁺ , Cr, V, Ti), T is a 4-coordinate cation (Si, Al, Fe ³⁺ , B, Be) and X is an anion (OH ^" , F ^" , Cl ^" , O ^2" , S ^{2 ").} mica are constructed layered and parallel to the layer packets cleavable. Within the framework of this application are in particular the outstanding dielectric, thermal and mechanical properties of micas of interest. the melting point of muscovite, so-called light or clay mica, for example, is at 1320 ° C In general, mica materials are stable at temperatures of 600 ° C and more.

As already mentioned, level sensors are generally known as capacitive and / or conductive sensors, but have hitherto hardly been suitable for use in salt melts. This is due, in particular, to the fact that the materials used are generally not suitable for use with the high temperatures of molten salts. Although level sensors of the type described could in principle be formed with ceramic insulators, which likewise have sufficient temperature resistance. However, such level sensors are only partially suitable for use in salt melts, in particular for use in storage tanks in solar thermal energy, since relatively large sensors must be used in this case due to the large volumes of the containers. Here, however, ceramics proves to be too fragile. In contrast, the invention provides a filling level sensor which can be formed both thermally resistant and unbreakable and is therefore particularly suitable for use in solar thermal energy. To be particularly advantageous for use in a level sensor of the type described above, a micaceous material has proven, which is formed as a muscovite or phlogo- pithaltiger composite material.

Composite materials have so-called reinforcing materials, which are impregnated, for example, with synthetic resins and then cured under heat and pressure. As reinforcing materials in such composites, for example, cellulose paper, mica paper, fabrics such as cotton, glass, carbon, synthetic fibers and / or glass slabs are known. As explained, the use of mica materials is particularly advantageous in the context of the invention. Examples of resins which may be used are polyester, epoxide, phenolic, polyimide, silicone, melamine, vinyl ester, and / or cyanate ester resins. Silicone can be used in particular within the scope of the invention. By selecting suitable reinforcing materials and / or resins, materials having the respective desired mechanical, electrical and / or thermal properties can be created. Corresponding composite materials can be produced in different shapes and sizes, either as raw or finished parts.

Particularly advantageous is the use of muscovite or phlogopite, because such materials have particularly good heat resistance and insulation properties. A sold under the trade mark ^® Pamitherm composite material with a silicone matrix and a muscovite reinforcing material in the form of a mica paper is temperature-resistant, for example 450-800 ° C and in the form of sheets having a thickness up to 60 mm. A filling level sensor according to the invention advantageously comprises an insulating structure which encloses at least a part of the measuring sensor coaxially at least partially. This allows a corresponding area of a probe to be isolated from surrounding structures, thereby avoiding erroneous measurements. This is of particular importance in molten salts. A filling level sensor according to the invention advantageously has a measuring sensor which is designed as a closable tube which can be filled with a fluid and / or partially evacuated. This results in a weight saving. A corresponding fill level sensor is advantageously designed as a conductive fill level sensor. A corresponding production of capacitive level sensors is possible in principle. An illustrated level sensor can also be operated optionally as a capacitive or conductive level sensor by being controlled by a corresponding control unit in each case suitable. A conductive level sensor can be designed very simply and operated as a so-called "level switch". If such a conductive level sensor immerses in a conductive liquid, a signal is output.

A fill level measuring device according to the invention has at least one previously explained fill level sensor and a control unit, which is set up to apply a voltage between the at least one fill level sensor and the container and / or to detect a current. For example, such a level measuring device may be formed with two level sensors, which are arranged at different heights and / or their sensors have different lengths. As a result, e.g. a minimum and maximum level are detected.

An inventive container is adapted to receive a molten salt and has a level measuring device as previously explained. Such a container therefore benefits from the advantages explained above.

This is especially true when a corresponding container is designed as a storage container of a solar thermal system and therefore can be filled with molten salt, which reaches the previously explained temperatures. The advantages of the invention result from the use of a mica-containing material in a corresponding insulating structure in a filling level sensor, for which protection is therefore also desired.

The invention will be explained in more detail below with reference to the accompanying drawings, which show a preferred embodiment of the invention. Short description of the drawing

Figure 1 shows a level sensor according to a particularly preferred embodiment of the invention in a schematic representation.

Figure 2 shows a container according to a particularly preferred embodiment of the invention in a schematic representation. In the figures, corresponding elements with identical reference numerals are given. A repeated explanation is omitted.

Embodiment (s) of the invention In FIG. 1, a filling level sensor according to a particularly preferred embodiment of the invention is shown in a schematic illustration in longitudinal section and denoted overall by 1. The level sensor 1 has an elongated sensor 11, which is shown shortened in the figure. The measuring sensor 11 may, for example, be designed as a closable tube with a tube wall 111 and an interior space 112 which can be filled and / or evacuated with a fluid and be closable by means of a closure 113. As a material for the probe 1, for example, stainless steel can be used. The sensor 11 may be connected to a fastening structure 2, which is not explained here in more detail, which may also be made of stainless steel. The attachment structure 12 has fastening screws 121, a cover cap 122 and / or a stopper 123, for example.

Between the sensor 11 and the mounting structure 13 a plurality of hatched drawn insulating structures 131, 132, 133 are arranged. The insulating structures 131, 132 and / or 133 may be made of a mica-containing material. At least one insulating structure 131 can thereby coaxially surround the measuring sensor 1 in an area shown shortened here. As a result, a secure insulation is ensured, so that only the tip of the probe 11 comes into contact with a molten salt.

FIG. 2 shows a container 2 which is equipped with a fill level measuring device designated by 10. The container 2 is for receiving a molten salt 21 furnished. The molten salt 21 can, as illustrated in FIG. 2 by dashed lines, be present at different heights in the container. The levels 211 and 212 correspond, for example, a minimum and a maximum level. When a minimum fill level 211 is exceeded, a sensor 11 of a first fill level sensor 1 L is immersed in the molten salt 21. A sensor 11 of a second level sensor H does not initially contact the molten salt. When a maximum level 212 is exceeded, the measuring sensor 1 of the second level sensor 1 H is also immersed in the molten salt 21. A control unit 14 is designed to apply in each case a voltage between the first level sensor 1 L and the container 2 or the second level sensor 1 H and the container 2 via corresponding lines 141, 142 and 143 and to detect corresponding currents. When falling below a minimum level 211 in this case no current can be detected, since the circuits between the level sensors 1 H and 1 L and the container 2 are interrupted. The control device 14 may be designed to output an underfill signal in this case. Between the minimum level 21 1 and the maximum level 212, a circuit between the first level sensor 1 L and the container 2 is closed. The control unit 14 may signal a normal operation in this case.

If the fill level of the molten salt 21 exceeds the maximum fill level 212, a current flow can be detected both between the first fill level sensor 1 L and the second fill level sensor 1 H and the container 2. The control unit 14 may output an overfill signal in this case. LIST OF REFERENCE NUMBERS

1, 1L, 1H level sensor 10 level measuring device

11 sensors

12 mounting structure 14 control device 111 wall

2 interior

113 closure

121 screw connection

122 protective cap

123 stoppers

131, 132, 133 insulating structure 141, 142, 143 lines

2 containers

21 salt melt

211 minimum level

212 maximum level

Claims

claims

1. Fülistandssensor (1), which is adapted to measure a level in a container (2) with a molten salt, and an at least partially electrically conductive probe (11) and a mounting structure (12), by means of which the Fülistandssensor (1 ) is attachable to the container (2), wherein between the sensor (11) and the mounting structure (12) at least one insulating structure (131 - 133) is arranged, which comprises a micaceous material.

2. Fülistandssensor (1) according to claim 1, wherein the micaceous material is formed as muskovit- and / or phlogopithaltiger composite material.

3. Fülistandssensor (1) according to claim 2, which is formed as a composite material with a silicone matrix and a muscovite reinforcing material.

4. Fülistandssensor (1) according to any one of the preceding claims, wherein the at least one insulating structure (131 - 133) at least partially coaxially surrounds at least a portion of the measuring sensor (1 1).

5. Fülistandssensor (1) according to any one of the preceding claims, wherein the measuring sensor (1) is designed as a closable tube, which can be filled with at least one fluid and / or at least partially evacuated.

6. Fülistandssensor (1) according to one of the preceding claims, which is designed as a conductive and / or capacitive Fülistandssensor (1).

7. level measuring device (10) with at least one Fulistandssensor (1 H, 1 L) according to any one of the preceding claims and with a control unit (14) which is adapted to between the at least one Fulistandssensor (1 H, 1 L) and the container (2) to apply a voltage and / or to detect a current.

8. container (2) which is adapted to receive a molten salt (21) and a level measuring device (10) according to the preceding claim.

9. Container (2) according to the preceding claim, which is designed as a storage container of a solar thermal system.

10. Use of a giimmerhaltigen material in an insulating structure (131 - 133) in a level sensor (1) according to one of claims 1 to 6.