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Title:
HEAT EXCHANGE SYSTEM OF A SOLAR THERMAL POWER PLANT AND USE OF THE HEAT EXCHANGE SYSTEM
Document Type and Number:
WIPO Patent Application WO/2014/131443
Kind Code:
A1
Abstract:
The inventions refers to a heat exchange system of a solar thermal power plant with least one closed heat storage container and at least one heat transfer fluid of the solar thermal power plant, wherein the closed heat storage con- tainer contains at least one reactant of a reversible chemical reaction and/or at least one reaction product of the reversible chemical reaction, a chemical reaction equilibrium of the reversible chemical reaction is sensitive to thermal energy, the closed heat storage container and the heat transfer fluid are thermally contacted to each other such that thermal energy for affecting the chemical reaction equilibrium can be exchanged between the closed heat storage container and the heat transfer fluid. Additionally a use of the heat exchange system in a solar thermal power plant for transferring solar energy into electrical energy is provided with following steps: a) Transferring solar energy into thermal energy; b) Storing the thermal energy while an excess of thermal energy; and c) Releasing stored thermal energy for generating electrical energy.

Inventors:
TAMAR YAIR (IL)
Application Number:
PCT/EP2013/053934
Publication Date:
September 04, 2014
Filing Date:
February 27, 2013
Export Citation:
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Assignee:
SIEMENS AG (DE)
SIEMENS CONCENTRATED SOLAR POWER LTD (IL)
International Classes:
F01K3/00; F03G6/00; F22B1/00; F28D20/00
Foreign References:
US20110100356A12011-05-05
EP0907006A11999-04-07
Other References:
WENTWORTH W E ET AL: "Simple thermal decomposition reactions for storage of solar thermal energy", SOLAR ENERGY, PERGAMON PRESS. OXFORD, GB, vol. 18, no. 3, 1 January 1976 (1976-01-01), pages 205 - 214, XP025451358, ISSN: 0038-092X, [retrieved on 19760101], DOI: 10.1016/0038-092X(76)90019-0
Attorney, Agent or Firm:
SIEMENS AKTIENGESELLSCHAFT (München, DE)
Download PDF:
Claims:
Patent claims

1. Heat exchange system (1) of a solar thermal power plant with least one closed heat storage container (10) and at least one heat transfer fluid (11) of the solar thermal power plant, wherein

- the closed heat storage container (10) contains at least one reactant (101) of a reversible chemical reaction and/or at least one reaction product (102) of the reversible chemi- cal reaction;

- a chemical reaction equilibrium of the reversible chemical reaction is sensitive to thermal energy;

- the closed heat storage container (10) and the heat trans¬ fer fluid (11) are thermally contacted to each other such that thermal energy for affecting the chemical reaction equi¬ librium can be exchanged between the closed heat storage con¬ tainer (10) and the heat transfer fluid (11) .

2. Heat exchange system (1) according to claim 1, wherein the chemical reaction equilibrium comprises at least one partial reaction which exothermic or endothermic.

3. Heat exchange system according to claim 1 or 2, wherein the reversible chemical reaction is a decomposition and com- position reaction of ammonium chloride.

4. Heat exchange system according to one of the claims 1 to 3, wherein

- the heat exchange system comprises a plurality of closed heat storage containers;

- each of the plurality of closed heat storage containers contains the reactant (101) of the reversible chemical reac¬ tion and/or the reaction product (102) of the reversible chemical reaction.

5. Use of the heat exchange system in a solar thermal power plant for transferring solar energy into electrical energy with following steps: a) Transferring solar energy into thermal energy; b) Storing the thermal energy while an excess of thermal en¬ ergy; and

c) Releasing stored thermal energy for generating electrical energy .

Description:
I

Description

HEAT EXCHANGE SYSTEM OF A SOLAR THERMAL POWER PLANT AND USE OF THE HEAT EXCHANGE SYSTEM

BACKGROUND OF THE INVENTION

1. Field of the invention This invention relates to a heat exchange system of a solar thermal power plant and a use of the heat exchange system.

2. Description of the related art

A solar thermal power plant (sun field power plant) which is based on the concentrated solar power technique comprises a solar collector unit. For instance, the solar collector unit comprises a parabolic trough collector with parabolic mirrors and a heat receiver tube. The heat receiver tube is arranged in a focal line of the mirrors. By sunlight reflecting surfaces of the mirrors the sunlight is focused to the heat receiver tube. The heat receiver tube comprises a core tube, which is filled with a heat transfer fluid, e.g. a thermo-oil or molten salt. Via the core tube of the heat receiver tube the energy of the sunlight is coupled into the heat transfer fluid. Solar energy is converted to thermal energy.

Subsequently, the thermal energy which is absorbed by the heat transfer fluid is used for water steam generation (via a heat exchanger) . By the water steam a turbine is driven. The turbine is coupled to a generator for producing electricity.

In order to have the possibility to produce electricity in the night or while a period of low sun intensity various thermal energy storage (TES) systems are used. For instance, such a thermal energy storage system comprises a phase change material (PCM) . By changing a state of the material thermal energy can be stored or can be released.

The phase change material is in thermal contact with the heat transfer fluid. The storing takes place while the sun shines. In the night, stored thermal energy is exchanged from the TES to the heat transfer fluid. By this, electricity can be pro ¬ duced in the night. SUMMARY OF THE INVENTION

It is an object of the invention to provide a possibility for efficiently storing thermal energy which can be used in solar thermal power plants.

This object is achieved by the invention specified in the claims .

For achieving the object a heat exchange system of a solar thermal power plant with least one closed heat storage con ¬ tainer and at least one heat transfer fluid of the solar thermal power plant is provided, wherein the closed heat storage container contains at least one reactant of a re ¬ versible chemical reaction and/or at least one reaction prod- uct of the reversible chemical reaction, a chemical reaction equilibrium of the reversible chemical reaction is sensitive to thermal energy, the closed heat storage container and the heat transfer fluid are thermally contacted to each other such that thermal energy for affecting the chemical reaction equilibrium can be exchanged between the closed heat storage container and the heat transfer fluid.

Additionally a use of the heat exchange system in a solar thermal power plant for transferring solar energy into elec- trical energy is provided with following steps:

a) Transferring solar energy into thermal energy;

b) Storing the thermal energy while an excess of thermal en ¬ ergy; and c) Releasing stored thermal energy for generating electrical energy .

More than one reactant (educt) and more than one reaction product is possible. The reactant or the reaction product acts as heat storage material.

The reversible chemical reaction comprises at least two par ¬ tial reactions: A forward reaction and a backward reaction. By the forward reaction the reactant is transformed into the reaction product. On the other way around, by the backward reaction the reaction product is transferred into the reac ¬ tant . The heat transfer fluid and the closed heat storage container are thermally coupled together. By this an exchange of ther ¬ mal energy between the heat transfer fluid and the heat storage container is possible. For instance, the heat storage container and the heat transfer fluid are in direct contact to each other. In order to enable an efficient heat exchange a container wall of the container comprises a container material with a relatively high heat conductivity. For instance the container material comprises a metal. Moreover for the case of direct contact, the container mate ¬ rial of the container wall is inert towards the heat transfer fluid and the reactant and reaction product of the chemical reaction. No chemical reaction takes place between the container material and a material of the heat transfer fluid or the reactant or the reaction product which are placed in an interior of the heat storage container. In this case, stainless steel is a very good container material.

An interior space of the heat storage container and the heat transfer fluid are separated from each other. So, no exchange of substances is possible. The chemical reaction is sensitive to thermal energy. The re ¬ versible chemical reaction comprises at least one partial re ¬ action which is exothermic and at least one partial reaction which is endothermic. While an exothermic reaction thermal energy is released whereas thermal energy is consumed while an endothermic reaction.

In a preferred embodiment the reversible chemical reaction is a decomposition and composition reaction of ammonium chlo- ride. Ammonium chloride (solid) is the reactant which under ¬ goes the decomposition reaction (forward reaction) . Reaction products of this decomposition reaction are ammonia (gaseous) and hydrochloric acid (gaseous) . While the backward reaction, ammonia and hydrochloric acid react to ammonium chloride.

The decomposition reaction takes place at temperatures of more than 345 °C. This partial reaction is an endothermic re ¬ action. Thermal energy can be absorbed (stored) by this par ¬ tial reaction.

The composition reaction of ammonium chloride takes place at temperatures of less than 345 °C. This partial reaction is an exothermic reaction. Thermal energy is released while this partial reaction takes place.

Preferably a plurality of the heat exchange system comprises a plurality of closed heat storage containers, wherein each of the plurality of closed heat storage containers contains the reactant of the reversible chemical reaction and/or the reaction product of the reversible chemical reaction. By this a very efficient heat exchange system can be provided: The more heat storage container, the higher the thermal energy which can be exchanged (surface effect) . For summarizing the invention: The problem is solved by introducing Encapsulated Equilibrium Energetically Active

Chemical Reactions (EEEACR) to the system. One of the features in the system is a capsulate (container) in which the reactants and/or products of chemical reaction are accommodated. The reaction implies the following specifi ¬ cations :

- It is an equilibrium reaction.

- One of the partial reactions of the equilibrium reaction is endothermic the other partial reaction is exothermic.

- The temperature (T) at which the energy is needed is de ¬ rived from the temperature which is defined by the equation (1) :

AH., is the enthalpy change during the reaction,

is the entropy change during the reaction

In a system containing this capsulate following takes place: The heat will be transferred into a capsulate. According to Le Chatelier's principle, the presence of the heat will force to reaction to reach a new equilibrium, enhancing the endothermic reaction, thus, absorbing the heat. When the heat is needed to be used, a cold heat part of the system will be brought to contact with the capsulate. According to Le

Chatelier's principle, the loss of the heat will force to re ¬ action to reach a new equilibrium, enhancing the exothermic reaction, thus, emitting the heat.

BIEF DESCRIPTION OF THE DRAWING

Further features and advantages of the invention are produced from the description of an exemplary embodiment with reference to the drawing. The drawing is schematic. The figure shows the a heat storage system.

DETAILED DESCRIPTION OF THE INVENTION Given is a heat exchange system 1 of a solar thermal power plant with a plurality of closed heat storage containers 10 and with a heat transfer fluid 11 of the solar thermal power plant. The heat transfer fluid is a thermo-oil . The container walls 103 of the heat storage containers 10 comprise container materials which is stainless steel.

The closed heat storage containers 10 contain a reactant 101 of a reversible chemical reaction and reaction products 102 of the reversible chemical reaction. The reversible chemical is the decomposition/composition of ammonium chloride. Solid ammonium chloride is the reactant. Ammonia and hydrochloric acid are the reaction products. Reactant and reaction products are located in the interior of the heat storage containers. The container material of the container wall of the heat storage container is stainless steel . The forward reaction (decomposition reaction of ammonium chloride into ammonia and hydrochloric acid) is endothermic and takes place at temperatures of more than 345°C. By pro ¬ moting the forward reaction thermal energy can be stored. The backward reaction (composition reaction of ammonium chloride out of ammonia and hydrochloric acid) is exothermic and takes place at temperatures of less than 345°C.

The heat storage system is used in a solar thermal power plant for transferring solar energy into electrical energy, whereby following steps are carried out: a) Transferring so ¬ lar energy into thermal energy; b) Storing the thermal energy while an excess of thermal energy; and c) Releasing stored thermal energy for generating electrical energy.