Heat exchange system with heat exchange tubes and method for exchanging heat by using the heat exchange system

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION The present invention refers to a heat exchange system with heat exchange tubes and a method for exchanging heat by using the heat exchange system.

2. DESCRIPTION OF THE RELATED ART

Despite the integration of renewable energy into the public electric energy system (power grid) a large share of elec ^¬ tricity is nowadays still generated by fossil energy sources. But the global climate change requires the further develop- ment of renewable energies.

The energy output of renewable energy sources like wind and solar is not constant throughout a day or throughout a year. Consequently, electricity which is generated by utilizing en- ergy from renewable energy sources fluctuates.

In order to manage this fluctuating electricity, heat (ther ^¬ mal energy) storage systems are developed for storing and re ^¬ leasing thermal energy (heat exchange system) . Such a heat exchange system comprises a heat exchange chamber with heat exchange chamber boundaries which surround a heat exchange chamber interior. The heat exchange chamber interior is filled with heat storage material like stones. The heat ex ^¬ change chamber boundaries comprise a first opening for guid- ing an inflow of a heat transfer fluid, e.g. air, into the heat exchange chamber interior and a second opening for guid ^¬ ing out an outflow of the heat transfer fluid out of the heat exchange chamber interior. For a charging mode, the heat exchange system additionally comprises a charging unit for heating the heat transfer fluid with the aid of excess electricity. The resulting hot heat transfer fluid is infused into the heat exchange chamber in ^¬ terior via one of the openings (e.g. first opening) of the heat exchange chamber boundaries. This opening defines a "hot" terminal of the heat exchange chamber. The hot heat transfer fluid is guided through the heat exchange chamber interior. By the guiding of the hot heat transfer fluid through the heat exchange chamber interior a heat transfer from the heat transfer fluid to the heat storage material is caused. Heat is stored by the heat storage material. Via the other opening (second opening) of the heat exchange chamber the resulting "cold" heat transfer fluid is guided out of the heat exchange chamber interior. Thereby, this opening of the heat exchange chamber boundaries defines a "cold" terminal (end) of the heat exchange chamber. The charging mode is stopped when the temperature at the cold terminal of the heat exchange chamber begins to rise above a predetermined temperature.

In a discharging mode of the heat exchange chamber this stored heat can be recovered: "cold" heat transfer fluid is infused into the heat exchange chamber interior via one of the openings of the heat exchange chamber boundaries. In this case, this opening defines a "cold" terminal. The cold heat transfer fluid is guided through the hot heat exchange cham- ber interior. By the guiding of the cold heat transfer fluid through the heat exchange chamber interior a heat transfer from the heat storage material to the heat transfer fluid is caused. Heat is released from the heat storage material. Via the second opening of the heat exchange chamber bounda ^¬ ries the resulting "hot" heat transfer fluid is guided out of the heat exchange chamber interior. Thereby, the second open- ing of the heat exchange chamber defines a "hot" terminal of the heat exchange chamber.

The resulting hot heat transfer fluid can be used for gener- ating steam with which a steam turbine is driven. Result of the described discharging mode: Heat is transformed back to electricity .

The discharging mode is stopped when the temperature at the cold terminal of the heat exchange storage begins to drop be ^¬ low a certain temperature.

For an efficiency of the heat exchange system it is important to control the flow of the heat transfer fluid through the heat exchange chamber interior.

SUMMARY OF THE INVENTION

It is an objective of the invention to provide a heat ex- change system with which the flow of the heat transfer fluid can easily be controlled.

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

A heat exchange system is provided with one heat exchange tube and at least one further heat exchange tube, wherein each of the heat exchange tubes comprises heat exchange tube walls which surround at least one heat exchange tube interior of the heat exchange tube. The heat exchange tube walls com ^¬ prise at least one first opening for guiding in an inflow of at least one heat transfer fluid into the heat exchange tube interior and at least one second opening for guiding out an outflow of the heat transfer fluid out of heat exchange tube interior. At least one heat storage material is arranged in the heat exchange tube interior of at least one of the heat exchange tubes such that a heat exchange flow of the heat transfer fluid through the heat exchange tube interior causes a heat exchange between the heat storage material and the heat transfer fluid. The heat exchange chamber concerning the state of the art is replaced by heat exchange tubes. With the aid of the heat exchange tubes it is easier to control the flow of the heat transfer fluid.

Preferably, the heat exchange tubes are arranged in a joint heat exchange compartment. The joint heat exchange compart ^¬ ment is preferably a horizontal heat exchange compartment which comprises a heat exchange compartment length which is at least twice of a heat exchange compartment width of the heat exchange compartment and/or which is at least twice of a heat exchange compartment height of the heat exchange com ^¬ partment. For instance, the heat exchange compartment length is selected from the range between 20 m and 300 m and the heat exchange compartment width and/or the heat exchange com ^¬ partment height are selected from the range of 1 m to 100 m.

The heat exchange tube walls can comprise different materi- als. Preferably, the heat exchange tube walls are made of steel .

A form of the heat exchange tubes can be different. For in ^¬ stance, the heat exchange tubes are straight or meander shaped.

In addition to the heat exchange system, a method for ex ^¬ changing heat by using the heat exchange system is provided. In an operating mode of the heat exchange system the heat ex- change flows of the heat transfer fluid is guided through the heat exchange tube interiors, wherein a heat exchange between the heat storage material and the heat transfer fluid is caused . Inside of the heat exchange tube the heat exchange can take place. In order to provide an efficient heat exchange, the heat exchange tube is preferably thermally insulated against the surroundings. The loss of heat is reduced by the thermal insulation. But, the heat exchange tubes should be thermally insulated from each other, too. This is advantageous in view of convection effects. Hence, in a preferred embodiment, the heat exchange tubes are thermally insulated from one another with the aid of a thermal insulator device. For instance, this device is thermal insulation plate. Alternatively, this device can be a thermal insulation wool like mineral wool.

In a preferred embodiment, the heat exchange tubes are verti- cally or horizontally oriented. For the last case, this re ^¬ sults in a "horizontal" heat exchange compartment. Prefera ^¬ bly, the heat exchange tubes are horizontally arranged above each other or the heat exchange tubes are vertically arranged side by side. The orientations of the heat exchange tubes are vertical or horizontal. A horizontal orientation of one of the heat exchange tubes and a vertical orientation of the other heat exchange tube is possible, too. In this case, the orientations of the heat exchange tubes are perpendicular to each other. In addition, deviations from an exact vertical, from an exact horizontal or from an exact perpendicular orientation of up to 10° are possible.

Preferably, at least two heat exchange tubes are arranged such that the heat transfer fluid passes the heat exchange tube interiors of the heat exchange tubes successively. So, the heat transfer fluid is guided subsequently through the heat tube interiors of the heat exchange tubes.

In a preferred embodiment, the heat exchange tube interiors of the heat exchange tubes are connected to each other by at least one connecting tube interior of at least one connecting tube. The heat transfer fluid is guided from one of the heat exchange tube interiors via the connecting tube interior to the other heat exchange tube interior. Preferably, the con- necting tube interior comprises the heat storage material.

In a preferred embodiment, the connecting tube is vertically or horizontally oriented and attached to a lateral surface of at least one of the heat exchange tubes. Horizontally orient ^¬ ed heat exchange tubes are connected together with the aid of the vertically oriented connecting tube whereas vertically oriented heat exchange tubes are connected together with the aid if horizontally oriented connecting tubes.

The heat transfer fluid is guided (led) into the heat ex ^¬ change tube interior via the first opening and is guided out of the heat exchange tube interior via the second opening. The first opening of the heat exchange tube boundaries is an inlet opening. The second opening of the heat exchange tube boundaries is an outlet opening. Thus, there are different areas of the heat exchange tube boundaries, namely an inlet area of the heat exchange tube boundaries with the first opening and an outlet area of the heat exchange tube bounda ^¬ ries with the second opening.

The operating mode of the heat exchange system is selected from the group consisting of charging mode with a heat trans- fer from the heat transfer fluid to the heat storage material and a discharging mode with a heat transfer from the heat storage material to the heat transfer fluid.

Depending on the operating mode, a specific opening can have the function of an inlet opening or the function of an outlet opening. The flow direction of the heat exchange flow depends on the operating mode. Preferably, during the charging mode the heat exchange flow is directed in a charging mode direc ^¬ tion, during the discharging mode the heat exchange flow is directed in a discharging mode direction and the charging mode direction and the discharging mode direction are opposed to each other (countercurrent operation) . But, a change of the directions of the heat exchange flow is not necessary. Charging mode direction and discharging mode direction com- prise the same direction (co-current operation) .

For instance, the heat exchange tubes are arranged above each other. For the charging mode, following flow direction is ad- vantageous : Flow through the upper heat exchange tube, through the connecting tube and through the bottom heat exchange tube . For the discharging mode, following flow direction would be advantageous: Flow through the bottom heat exchange tube, through the connecting tube and through the upper heat exchange tube . But, a change of the directions of the heat exchange flow is not necessary. Charging mode direction and discharging mode direction comprise the same direction (co-current operation) .

In countercurrent operation, switching from the charging mode to the discharging mode the direction of the heat exchange flow through the heat exchange tube interior is reversed and consequently, the function of the openings (inlet opening, outlet opening) at the respective opening is reversed, too. With such a solution it is especially advantageous to use the same heat transfer fluid for the charging mode and for the discharging mode. But of course, different heat transfer flu ^¬ ids for the charging mode and the discharging mode can be used, too. For the charging mode, the heat exchange system is equipped with at least one charging unit for heating the heat transfer fluid. In the charging mode with activated charging unit, the charging unit can be located upstream of the heat exchange chamber. In contrast to that, in the discharging mode with a deactivated charging unit, the charging unit can be located downstream of the heat exchange chamber.

Preferably, the charging unit comprises at least one electri ^¬ cal heating device which is selected from the group consist- ing of resistance heater, inductive heater, emitter of elec ^¬ tromagnetic radiation and heat pump. The electromagnetic ra ^¬ diation is preferably infrared radiation. A combination of different electrical heating devices is possible. With the aid of the electrical heating devices electricity is trans ^¬ formed into heat. This heat is absorbed by the heat transfer fluid and transported to the heat storage material in the heat exchange tube interior.

For instance, the electrical heating device comprises a re ^¬ sistance heater. This heater is located in the heat exchange inflow upstream of the heat exchange chamber. The heat trans ^¬ fer fluid is heated up before its entering of the heat ex- change chamber interior. The resistance heater comprises a large heat exchange area for an efficient heat exchange from the resistance heater to the heat transfer fluid. For in ^¬ stance, the large heat exchange area is formed by a grid of the resistance heater. A meander shaped resistance heater is possible, too. With such a measure, the heat transfer to the heat transfer fluid is enhanced. In addition, the possibility of the (not desired) occurrence of hot spots within the re ^¬ sistance heater is reduced. The heat exchange system is preferably equipped with at least one discharging unit for discharging the heat transfer fluid of the outflow from heat for production of electricity. Heat is removed from the heat transfer fluid. The removed heat is transformed into electricity. In a preferred embodiment, the transformation of heat into electricity is carried by a wa ^¬ ter/steam cycle for driving a turbine of a steam power plant.

The discharging mode can be realized when electricity prices and demand are high or when the production of renewable ener- gies is low. For that and in order to limit the costs which are connected to the invention, it is advantageous to use ex ^¬ isting power plants. So, the heat exchange system is a kind of retrofit system. For instance, well suited are CCPP (com ^¬ bined cycle power plant) since their heat recovery steam gen- erator (HRSG) is similar to the application proposed here. Nevertheless, hard coal, oil, gas, waste incineration, wood or lignite fired power plants can be used since the charging unit can be designed for high temperatures to match the tem- peratures used in the steam generator. In a hybrid mode the fuel can be used to increase the temperature from the temper ^¬ ature level of the heat exchange system to the operating tem ^¬ perature of the original furnace or boiler design.

In a preferred embodiment, the heat exchange system is equipped with a the flow adjusting element for adjusting heat exchange flow through the heat exchange tube interior, for adjusting the inflow into the heat exchange tube interior and/or for adjusting the outflow out of the heat exchange tube. The flow adjusting element comprises at least one ac ^¬ tive fluid motion device which is selected from the group consisting of blower, fan and pump and/or the flow adjusting element comprises at least one passive fluid control device which is selected from the group consisting of activatable bypass pipe, nozzle, flap, damper and valve. A multitude of these devices are possible as well as a combination of these devices. In addition, flow adjusting elements can be arranged serially or in parallel. For instance, two flaps are arranged at two openings in order to adjust the inflows of the heat transfer fluid into the heat exchange tube interior and con ^¬ sequently in order to adjust the temperature distribution in the heat exchange tube interior. The advantage of passive control devices is that they are cheap. In addition, passive control devices are very relia ^¬ ble. But preferably, active motion devices are used. By that, it is advantageous that driving units of the active fluid mo ^¬ tion devices like electrical motors and electrical equipment are located outside of the heat exchange flow with the (pos ^¬ sibly very hot) heat transfer fluid.

In a preferred embodiment, the flow adjusting element is a valve or a separator. Preferably, several of the separators are arranged in one of the heat exchange tube interiors such that the separators comprise alternating separator openings on top and on bottom of the heat exchange tube interior for guiding trough the heat transfer fluid. Preferably, the separator comprises at least one plate. The plate is located in the heat exchange tube interior. Due to the high temperatures, it is advantageous, that flow adjusting element comprises at least one thermal insulation layer. Preferably, the thermal insulation layer and/or the thermal insulation device (see above) comprise at least one thermal insulation material which is selected from the group consisting of ceramics, sinter, stones, foamed clay, mineral wool, mineral foam, mineral fibers and foam glass. Mixtures of these materials are possible, too.

In a preferred embodiment, at least one of the heat exchange tubes comprises a tube diameter which is selected from the range between 2 m and 8 m. But it has to be noted, that in view of a road transportation of the heat exchange tube diam ^¬ eters of less than 4.5 m are meaningful. Preferably, at least one of the heat exchange tubes comprises at least two part tubes which are connected to each other at longitudinal ends such that the two part tubes form the heat exchange tube with the tube interior. The two part tubes are connected to each other by at least one joint which is se- lected from the group consisting of screw joint, welded joint, flange connection and bayonet joint.

The heat storage material can be liquid and/or solid. For in ^¬ stance, a core of the heat storage material is solid and a coating of this solid core is liquid. Such a liquid coating can comprise ionic liquid.

The solid material comprises preferably bulk material. Mix ^¬ tures of different liquid materials and different solid mate- rials are possible as well as mixtures of liquid and solid materials . It is possible that the heat storage material is a thermo- chemical energy storage material: Thermal energy can be stored via an endothermic reaction whereas thermal energy can be released via an exothermic reaction. Such a thermo chemi- cal storage material is for instance the calcium ox ^¬ ide/calcium hydroxide system.

The heat storage materials can be arranged in one or more specific containers made of non-reactive container material. Non-reactive means that no chemical reaction between the heat storage material and the container material takes place dur ^¬ ing the heat exchange process.

In a preferred embodiment, the heat storage material compris ^¬ es at least one chemically and/or physically stable material. In the range of the operational temperature of the heat ex ^¬ change system the heat storage material does not change its physical and/or chemical properties. A physically stable ma ^¬ terial does not change its physical properties during the heat exchange. For instance, the heat storage material re ^¬ mains in a solid state in the operating temperature range. A chemically stable material does not change its chemical com ^¬ position during the heat exchange. For instance, such a chem ^¬ ically stable material is a phase change material (PCM) .

Moreover, a complex heat exchange system with different heat exchange tubes with different heat storage materials and/or different heat transfer fluids is possible, too. For In ^¬ stance, a heat exchange tube with stones as heat storage ma ^¬ terial and a heat exchange tube with a phase change material as a heat storage material are combined together.

In a preferred embodiment, the heat storage material compris ^¬ es sand and/or stones. The stones can be natural stones or artificial stones. Mixtures thereof are possible, too. Arti ^¬ ficial stones can consist of containers which are filled with heat storage material. This heat storage material is for in- stance a phase change material or a thermo-chemical storage material (see above) .

Preferably, the stones comprise gravels (pebbles) , rubbles and/or grit (splits) . The artificial material comprises pref ^¬ erably clinkers or ceramics. Again, mixtures of the mentioned materials are possible, too.

In order to provide a cheap energy storage material it is ad- vantageous to use waste material. Therefore, in a preferred embodiment, the artificial material comprises at least one by-product of an industrial process. For instance, the by ^¬ product is iron silicate. Iron silicate origins from a slag of copper production.

In a preferred embodiment, heat exchange channels are embed ^¬ ded in the heat storage material for guiding of the heat ex ^¬ change flow through the heat exchange tube interior. The heat storage material forms a heat exchange bed. The heat exchange bed comprises the heat exchange channels. The heat exchange channels are embedded into the heat storage bed such that the heat exchange flow of the heat transfer fluid through the heat exchange channels causes the heat exchange between the heat storage material and the heat transfer fluid. The heat exchange channels can be formed by interspaces (gaps) of the heat storage material. For instance, the heat storage materi ^¬ al comprises stones. The stones form the heat exchange bed with the heat exchange channels. In addition or alternative ^¬ ly, the heat storage material is porous. Open pores of the heat storage material form the heat exchange channels.

The heat transfer fluid is selected from the group consisting of a liquid and a gas. The gas is selected from the group consisting of inorganic gas and/or organic gas. The inorganic gas is preferably air. Mixtures of different liquids are pos ^¬ sible as well as mixtures of different gases. Preferably, the heat transfer fluid comprises a gas at ambi ^¬ ent gas pressure. Preferably, the gas at the ambient pressure is air. The ambient pressure (900 hPa to 1.100 hPa) varies such that the heat exchange flow through the heat exchange tube interior is caused.

For the guiding of the heat transfer fluid into the heat ex ^¬ change tube interior and for the guiding of the heat transfer fluid out of the heat exchange tube interior a pipe system (or channel system, ducting system) is used. This pipe system can be closed (with a closed loop) or can be open (with an open loop) .

For instance the heat transfer fluid is ambient air of the environment. The loop is an open loop. Air from the environ ^¬ ment is introduced into the heat exchange system and air of the heat exchange system is released to the surroundings. There is an air exchange during the operation of the heat ex ^¬ change system.

In contrast to that, there is no air exchange or a selective ^¬ ly adjustable air exchange during the operation in a closed loop. This has following specific advantage: In a situation with almost completely charged heat storage material, heat transfer fluid with remaining heat would be released to the environment in an open loop. The remaining heat is lost. In contrast to that, in a closed loop this heat transfer fluid with remaining heat stays in heat exchange system. The re ^¬ maining heat is not lost. Therefore, in a preferred embodi ^¬ ment, a closed loop is implemented and wherein the inflow comprises the outflow. The outflow is guided back into the heat exchange tube interior.

The temperature front is defined by neighboring cold and hot areas of the heat storage material in the heat exchange tube interior caused by the flow of the heat transfer fluid through the heat exchange tube interior. The temperature front is aligned perpendicular to the respective flow direc- tion of the heat exchange flow through the heat exchange tube. During the charging mode the heat exchange flow is di ^¬ rected in a charging mode direction wherein the temperature front moves along this charging mode direction. In contrast to that, during the discharging mode the heat exchange flow is directed in the discharging mode direction (opposite to the charging mode direction) wherein the temperature front moves along the discharging mode direction. In both cases, the temperature front of the heat exchange tube is migrating through the heat exchange tube to the respective hot/cold ends of the heat exchange tube. It is to be noted that in case of countercurrent operation, the hot (hot opening) end remains the hot end (hot opening) , independently from the mode (charging mode or discharging mode) .

The temperature front is a zone of strong temperature gradi ^¬ ent in the heat storage material, i.e. high temperature dif ^¬ ference between hot and cold areas. In this application it separates the hot (charged with heat) and the cold (not charged) zone in the heat exchange tube with the heat storage material. The temperature front develops due to the transfer of heat from the heat transfer fluid to the heat storage ma ^¬ terial during the charging mode and due to the transfer of heat from the heat storage material to the heat transfer flu- id during the discharging mode. Isothermal zones/lines devel ^¬ op ideally (e.g. without the influence of gravitation) per ^¬ pendicular to the main flow direction, i.e. zones/lines of constant temperature. In order to optimize the efficiency of the heat exchange sys ^¬ tem it is advantageous to ensure a uniform temperature front. There are just small variations concerning the temperature gradients perpendicular to the flow direction. In a vertical heat exchange tube with a flow direction top down, the tem- perature front is nearly uniform due to natural convection. So, in this case additional measures are not necessary. In contrast to that, natural convection leads to a non-uniform temperature front in a horizontal heat exchange tube. So, in this case additional measures could be meaningful (like usage of more openings or usage of more flow adjusting elements) .

Preferably, the heat exchange tube wall with one of the open- ings comprises a transition area with a tapering profile such that an opening diameter of the opening aligns to a first tapering profile diameter of the tapering profile and a chamber diameter of the heat exchange tube aligns to a second ta ^¬ pering profile diameter of the tapering profile. The transi- tion area comprises an increasing cross section from the respective opening towards the heat exchange tube. This is es ^¬ pecially advantageous for the first opening for guiding the heat transfer fluid into the heat exchange tube. The diameter of the transition area expands from the opening diameter of the first opening to the diameter of the heat exchange tube. With the aid of the tapering profile the inflow of the heat transfer fluid is guided into the heat exchange tube interi ^¬ or. The guided inflow is distributed to a wide area with the heat storage material. By this measure a capacity of the heat exchange unit (heat storage material which is located in the heat exchange tube) can be highly exploited. In addition, the efficiency of the heat exchange can be improved by adapting the heat exchange flow. Remark: For additionally adapting the heat exchange flow, a diffuser can be located at the first opening, especially in the transition area. By means of the diffuser an incident flow of the heat transfer fluid into the heat exchange tube interior can be adjusted. For instance, such a diffuser is formed by stones which are located in the transition area with the tapering profile.

For the case that the heat exchange tube comprises a number of first openings it is very advantageous to arrange a de ^¬ scribed transition area at that number of first openings. Thereby, the first openings can comprise a joint transition area or individual transition areas.

The transition area with the second opening for guiding the heat transfer fluid out of the heat exchange tube interior can be tapered, too. By this measure the guiding of heat flow out of the heat exchange tube interior of the heat exchange tube is simplified. In order to save space and in order to reduce the surface- volume ratio for a reduced heat loss, it is advantageous to implement a transition area as short as possible. The result is a short transition channel for guiding the inflow into the heat exchange tube interior. Besides an efficient usage of the capacity of the heat exchange tube a low space require ^¬ ment is connected to this solution.

The heat exchange system is especially adapted for operation at high temperatures of more than 300 °C. Therefore, in a preferred embodiment, an operating temperature of the operat ^¬ ing mode is selected from the range between 300 °C and 1000 °C, preferably selected from the range between 500 °C and 1000 °C, more preferably selected from the range between 600 °C and 1000 °C, 650 °C to 1000 °C and most preferably between 700 °C and 1000 °C. A deviation of the temperature ranges is possible. In this context, very advantageous is an upper lim ^¬ it of the temperature range of 900 °C and most preferably an upper limit of the temperature range of 800 °C. The heat ex ^¬ change system is a high temperature heat exchange system.

The proposed invention can be applied for renewable energy production as well as for conventional energy production. For instance, in order to increase the flexibility the steam cy ^¬ cle of fossil fired power plants (or nuclear power plants, etc.) it can be combined with the heat exchange system pro ^¬ posed here. In this case, the boiler of the steam cycle of the power plant can be operated with fuel when fuel costs are lower than electricity costs and the heat exchange system is charged in periods when electricity prices are low. Alterna- tively, the charging can take place during a period of excess production of energy.

Further advantages of the invention: - A structural strengthening of the heat exchange chamber re ^¬ sults due to coping with forces and strains from expanding heat storage material during the charging mode.

- A sharp temperature gradient and maintenance of high tem ^¬ perature are achieved.

- The manufacturing is quite easy.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention are produced from the description of exemplary embodiments with reference to the drawings. The drawings are schematic.

Figures 1 shows a heat exchange tube of the heat exchange system.

Figure 2 shows a temperature distribution of the heat ex ^¬ change tube of figure 1 in a charging mode.

Figure 3 shows the heat exchange system in a charging mode.

Figure 4 shows the heat exchanges system in a discharging mode .

Figure 5 shows the heat exchange tube in a different view to figure 1.

Figure 6 shows show a heat exchange compartment with heat ex ^¬ change tubes in a cross section in relation to a longitudinal extension of the heat exchange tubes. Figure 7 show the heat exchange system with two heat exchange tubes .

Figure 8 show a heat exchange tube with two part tubes.

DESCRIPTION OF PREFERRED EMBODIMENTS

Core of this invention is a heat exchange system 1 with at least two a heat exchange tubes 11 and 12 on a high tempera- ture level.

Heat storage material 121 (e.g. stones or sand) which is lo ^¬ cated in the heat exchange tube interior 112 of the heat ex ^¬ change tubes 11 and 12 can be charged and discharged with heat via a heat transfer fluid 13. Heat is stored by the heat storage material 121 and can be release from the storage ma ^¬ terial .

The heat exchange tubes are arranged in a joint heat exchange compartment 17 (figure 6) .

The temperature level of the stored heat is significantly higher compared to methods applied so far to increase the ef ^¬ ficiency. The temperature level lies between 300 °C and 800 °C, preferably between 550 °C and 650 °C. The thermal capaci ^¬ ty of the heat exchange system lies in the range between 0.3 GWh and 100 GWh, which causes a thermal power of 50 MW.

The heat exchange system 1 comprises a heat exchange tube 11 and at least one further heat exchange tube 12. The heat ex ^¬ change tubes 11 and 12 comprise heat exchange tube boundaries

111 which surround at least one heat exchange tube interior

112 of the heat exchange tube 11 and 12. The heat exchange tube boundaries 111 comprise at least one first opening 1111 for guiding in an inflow 132 of at least one heat transfer fluid 131 into the heat exchange tube inte ^¬ rior 112 and at least one second opening 1112 for guiding an outflow 133 of the heat transfer fluid 131 out of the heat exchange tube interior 112. At least one heat storage materi- al 121 is arranged in the heat exchange tube interior 112 such that a heat exchange flow 13 of the heat transfer fluid 131 through the heat exchange tube interior 112 causes a heat exchange between the heat storage material 121 and the heat transfer fluid 131.

With the aid of the proposed heat exchange system 1, thermal energy can be stored on a high temperature level during the charging mode. This stored thermal energy can be used during the discharging mode for the production of steam in a water steam cycle for reconversion into electrical energy.

The heat exchange tubes 11 are filled with solid heat storage material 121. The solid heat storage material comprises stones. Alternatively, sand is used.

There is a transition area 116 of the heat exchange tubes 11 and 12 with a tapering profile 1161. Thereby an opening diameter 1113 of the opening 1111 or 1112 aligns to a first ta ^¬ pering profile diameter 1162 of the tapering profile 1161 and a chamber diameter 117 of the heat exchange tube 11 aligns to a second tapering profile diameter 1163 of the tapering pro ^¬ file 1161.

The inflow 132 of the heat transfer fluid 13 is guided into the heat exchange tube interiors 112. The guided inflow 132 is distributed to a wide area of heat storage material 121. By this measure a capacity of the heat exchange unit (heat storage material 121 which is located in the heat exchange tube interior 112) can be utilized in an advantageous manner.

The transition area 116 is short. The short transition area 116 projects into the heat exchange tube 11. The result is a short transition channel for the guiding of the inflow 132 into the heat exchange tube interior 112 of the heat exchange tube 11.

The heat exchange system 1 is additionally equipped with at least one flow adjusting element 134 for adjusting a mass flow of the heat exchange flow 13 of the heat transfer fluid 131 through the heat exchange tube interior 11. The flow ad ^¬ justing element 134 is an active fluid motion device 1341 like a blower or a pump. Such a device enables a transporta- tion of the heat transfer fluid 131 through the heat exchange tube interior 112 of the heat exchange tube 11. The blower or the pump can be installed upstream or downstream of to the heat exchange tube 11. In the charging mode, the heat transfer fluid 131 enters the heat exchange tube 11 through a diffuser 1164. The diffuser 1164 comprises stones 1165 and is arranged at the transition area 116 of the heat exchange tube 11. The heat exchange flow 13 of the heat transfer fluid 131 is directed in the charging mode direction 135. The flow adjust ^¬ ing element 134, 1341 is advantageous installed upstream of the charging unit 200, 201 (figure 3) : Relatively cold heat transfer fluid passes the flow adjusting element 134, 1341 before absorbing heat from the charging unit.

For the charging mode, the heat transfer fluid 131 is heated up from ambient conditions by the electrical heating device 201 (charging unit 200) . This charged (heated) heat transfer fluid is guided into the heat exchange tube interior 112 of the heat exchange tube 11 for charging of the heat storage material. Thereby the heat exchange between the heat transfer fluid and the heat storage material takes place. With refer ^¬ ence 2000 the temperature front at a certain time of this charging process is shown (figure 2) . In addition, the temperature gradient 2001 which results in the temperature front is depicted. For the discharging mode the heat exchange system 1 comprises one or several heat exchange tubes 11 mentioned above, an ac ^¬ tive fluid motion device 1341 to circulate the heat transfer fluid 131 and a thermal machine for re-electrification, which can be a water/steam cycle 1003. The working fluid of this cycle is water and steam. The water/steam cycle 1003 has the function of a discharging unit 400. Essential components of the steam turbine cycle 1003 are a steam turbine 1006 and a generator 1004.

In the discharging mode, the heat exchange flow of the heat transfer fluid is directed into the charging mode direction 136. With the aid of the heat exchange system (heat exchanger, boiler) 1002 heat of the heat transfer fluid is transferred to the working fluid of the steam cycle 1003.

The heat exchange system 1 comprises a closed loop 1005. Heat exchange fluid which has passed the heat exchange tube inte ^¬ rior 112 is guided back into the heat exchange tube interior 112.

The heat exchange tubes 11 or 12 comprise separators (for in- stance welded in plates) with alternating openings on the top and bottom within the closed heat exchange tube, creating a labyrinth structure. Consequently air is forced to travel in vertical direction when passing through the heat exchange tubes .

Fig. 8 depicts the for instance 20 meter long part tubes of a heat exchange tube. These part tubes are connected together by flanges on respective ends. The result is a long heat ex ^¬ change tube .

The heat exchange tubes are thermally decoupled with insula ^¬ tion 15 in between to avoid temperature exchange between the heat exchange tubes (figure 6) . This facilitates keeping a sharp temperature gradient and high temperatures.

A cascading charging (one heat exchange tube after the other) is of advantage.

Fig. 7 depicts an upper and a lower horizontal heat exchange tube located and placed above each other. Several vertical connecting tubes 14 are located and connecting the upper heat exchange tube and lower heat exchange tube. The connecting tube interior of the connecting tube is filled with heat storage material. In such an embodiment, it is possible that the horizontal heat exchange tube are free of heat storage material. The heat storage material is just located in the vertical connecting tubes. These vertical connecting tubes form the heat exchange tubes.

In charging mode hot air would be guided through the upper pipe, further downwards through the vertical pipes and final- ly through the lower pipes. In this operation mode tempera ^¬ ture is dissipated to the storage material from the top to bottom resulting in a temperature profile hottest on top. Consequently there will be no convection, the high tempera ^¬ ture and sharp temperature gradient remains .

In discharging mode cold air is guided consecutively through the lower pipe, vertical pipe and finally through the upper pipe. This discharging from the bottom will keep temperatures on the top high and a sharp temperature gradient.

It is of course possible to include valves allowing for a control and cascaded charging of the storage. The valves can also be used to avoid air leakage.