Steam generator

Abstract

There is provided a steam generator (1) having: a housing (2); a first heat exchange element (3) arranged in the housing, through which a heat exchange fluid, preferably a flue gas, can flow; at least one second heat exchange element (4) arranged in the housing, through which water can flow in order to generate steam; and a heat transfer medium in the form of a salt bath arranged in the housing (2) in order to transfer heat from a heat exchange fluid flowing through the first heat exchange element (3) to water flowing through the second heat exchange element (4) in order to generate steam. The steam generator further comprises a stirring device (5) which is arranged on the housing (2) and protrudes into the heat transfer medium, the stirring device (5) being designed to generate a flow within the heat transfer medium by stirring the heat transfer medium during operation of the steam generator (1).

Description

TECHNICAL FIELD

[0001] The invention relates to a steam generator for generating steam, which can be used, for example, for the generation of energy by means of a steam engine or a steam turbine. To this end, the steam generator can be coupled, for example, to a biomass furnace, a biogas plant or a pellet heating appliance. BACKGROUND

[0002] In order to generate water vapor, steam generators are generally used. The steam generators mostly have a combustion chamber in which a fuel is heated or combusted in order to generate heat. Alternatively, it is also possible to utilize the still hot exhaust gas of a biogas plant in order to provide the required heat. The heat is guided, for example, past a heat exchanger in the form of a heat exchange fluid in order to thereby evaporate water flowing in the heat exchanger. The water vapor thus generated can then be used for the generation of energy in a steam engine.

[0003] In order to generate steam and energy efficiently, a high pressure is required and, in connection therewith, also a high temperature. This results in a high thermal load of the heat exchanger and in stresses occurring in the material of the heat exchanger.

[0004] In the prior art, a tube bundle heat exchanger is given, for example, by DE 10 2010 046 804 A1, which has a plurality of tube coil structures which are led out of a common inlet chamber for the heat exchanger fluid and open into a common outlet chamber, each tube coil structure comprising a sequence of alternating tube segments and curved tubes, and each curved tube being configured as a 180° turning structure about a matching bending axis and having the same bending radius. This tube bundle heat exchanger is characterized in that, along each tube coil structure, the arc axes of the curved tubes connected on the same tube segment are in a certain angular position with respect to one another, and the bending axes of the following (two) curved tubes extend parallel, between which one tube segment, one curved tube and a further tube segment are arranged in direct sequence.

[0005] Here, however, the efficiency is largely dependent on the distance of the tube bundle heat exchanger to the housing and largely on the flow type of the heat exchange fluid in the tube bundle with respect to the thermal energy generated by the fuel. That is to say, wall losses which occur due to the flow past between the tube bundle heat exchanger and the surrounding housing in the absence of a flow through the heat exchanger are unavoidable in this design. As a result, the heat exchange efficiency is not optimal.

[0006] Furthermore, according to this design, stresses in the tube bundle cannot be compensated by thermal expansion due to the high temperature of the heat exchange fluid.

[0007] DE 20 2007 017 403 U1 also discloses a tube bundle heat exchanger, in particular for heat exchange from a fuel gas to heating water or drinking water, having a water chamber flowable through by a heating water flow or a drinking water flow and a fuel gas chamber flowable through by a fuel gas flow. Here, the fuel gas tubes forming the fuel gas can be flowed through in parallel or in series.

[0008] Here, too, the problems explained above arise and, in addition, the efficiency of the heat exchange is low, since this heat exchange is operated in counterflow.

[0009] Furthermore, in the steam generators known hitherto for generating steam from biological substances, it is particularly critical that the energy content of the fuel, which is not as certain and can fluctuate as, for example, coal, is compensated and, as a result, fluctuating steam parameters are compensated when generating steam. If the fluctuating energy content cannot be sufficiently compensated, fluctuations in the steam temperature can occur, which can lead to an influence on or even damage to the steam turbine, for example, when using a steam turbine.

[0010] The design solutions known hitherto use an additional steam storage boiler for this reason, in order thereby to achieve a small pressure loss and to counteract the fluctuations.

[0011] But such design solutions can no longer be used, for example, at high pressures of more than 250 bar, since there is a high risk of a destructive, for example, explosive, failure.

[0012] There is therefore a need for a solution for a steam generator when using biological substances and high pressures, which is not only pressure-resistant and safe, but also simple and economical to implement.

[0013] To this end, only EP 4 134 609 A1 discloses a first solution in the field of steam generators, which attempts to solve the problem of the fluctuating energy content described above while at the same time achieving a high operating safety. This is achieved in that, in a (high-pressure) steam generator, a salt bath as a heat transfer medium is interposed between a first heat exchange element, which guides a heat exchange fluid, and a second heat exchange element, which guides water for generating steam.

[0014] But in this design solution, too, problems of stability in the heat transfer arise.

[0015] The cause of the problems lies primarily in local hot spots in the salt bath, for example, at the corners of the steam generator housing or at flow separations.

[0016] This is disadvantageous, since it can lead to the metal parts of such a steam generator being constantly red-hot due to overheating and to a decomposition of the salt.

[0017] The salts thus resolved can attack the metal of the steam generator and cause leaks to occur.

[0018] To prevent this, EP 4 134 609 A1 discloses a pump which is designed to put the salt bath in motion during operation of the steam generator.

[0019] But this pump can only limit the problems described above, because due to the pump arrangement an inhomogeneous temperature field still exists inside the salt bath.

[0020] Furthermore, this pump arrangement only achieves a pure point-like circulation of the salt bath during operation of the steam generator, so that local hot spots can still occur in the salt bath in the arrangement of EP 4 134 609 A1.

[0021] Furthermore, the pump also entails a high power consumption, which has a negative effect on the overall efficiency and economy of the steam generator. SUMMARY

[0022] It is therefore the object of the present application to provide a highly efficient device for generating steam (steam generator) in which, with a simple design and with a setup which can also be ensured in the event of fluctuations in the energy content of the fuel, a reliable operation can be ensured, a high efficiency can be achieved and the disadvantages described above can be mitigated or even avoided.

[0023] The object is achieved by a device having the features of claim 1. Advantageous design solutions are given in the other claims, the following description and the figures.

[0024] According to one aspect of the application, the steam generator has a housing. In the housing, a first heat exchange element is provided, through which a heat exchange fluid can flow.

[0025] The heat exchange fluid is preferably flue gas. Furthermore, the heat exchange fluid can be waste heat from a biomass furnace, a biogas plant or a pellet heating device, which can flow through the first heat exchange element and thus through the steam generator. That is to say, the heat exchange fluid can be, for example, combustion gases from the combustion of fuel in the form of, for example, low-grade biomass which has not been dried in a combustion chamber of a known push grate furnace (Vorschubrostfeuerung) or exhaust gases of a biogas plant. From this, a flow consisting of residues can be produced.

[0026] In connection with the heat exchange fluid, different temperature ranges can occur in the steam generator. This can also be understood as the heat exchange fluid, which is heated by the fluid or the combustion gas or generally the combustion gas, usually has a temperature of between 600°C and 1200°C, preferably 1000°C.

[0027] Irrespective of this, the uniform heat transfer properties of the salt bath explained in detail below make it possible to "use" heat exchange fluids with temperatures of more than 1000°C, in particular 1300°C and more, without endangering the safety of the steam generator.

[0028] If the exhaust gas of a biogas plant is used as heat exchange fluid, a heat exchange fluid temperature, i.e. a gas temperature, of 450°C to 500°C, preferably 470°C, usually occurs in the steam generator.

[0029] Furthermore, a second heat exchange element is provided in the housing, through which water can flow in order to generate steam. This can relate to water, preheated water or saturated steam.

[0030] Furthermore, a heat transfer medium in the form of a salt bath is provided in the housing in order to transfer heat from the heat exchange fluid flowing through the first heat exchange element to the water flowing through the second heat exchange element in order to generate steam.

[0031] In other words, the housing is filled with a salt bath as heat transfer medium. The heat transfer medium is designed to absorb heat from the first heat exchange element and to release heat to the second heat exchange element. Thereby, water flowing through the second heat exchange element can be heated and steam can be generated.

[0032] Furthermore, the heat transfer medium acts as a "buffer" in order to compensate for fluctuating heat input from the first heat exchange element to the salt bath as heat transfer medium due to fluctuating energy content of the fuel. That is, this steam generator provides a "high degree of tolerance" in terms of temperature fluctuations and fluctuating energy content. That is, even when the temperature peaks of the heat exchange fluid fluctuate strongly, uniform heat transfer or heat input into the water for generating steam can be achieved due to the salt bath.

[0033] Furthermore, the steam generator also has a stirring device. The stirring device is provided on the housing and extends into the heat transfer medium. In other words, the stirring device is at least partially surrounded by the heat transfer medium. The stirring device is designed to generate a flow within the heat transfer medium during operation of the steam generator in such a way that the heat transfer medium is stirred.

[0034] Here, the expression "flow" means that the heat transfer medium is put in motion, preferably in a circulating motion, in the housing, so that the heat transfer medium in the housing is moved during the operation of the steam generator.

[0035] In particular, the circulation of the heat transfer medium in the housing achieves a significantly more uniform temperature field compared to the case in which, for example, a pump is used in the heat transfer medium. At the same time, local overheating can be avoided.

[0036] Furthermore, the circulation of the heat transfer medium in the housing according to the application by means of the stirring device achieves a uniform temperature field with very high heat transfer coefficients. Particularly high heat transfer coefficients occur here at (high) pressures of more than 250 bar, preferably more than 300 bar.

[0037] With this design, it is possible to achieve a temperature difference of 1 °C or less between the heat transfer medium and the water or steam in the second heat exchange element.

[0038] This in turn makes it possible to prevent temperature differences in the salt bath in the extension of the housing and thus to prevent local hot spots or to prevent a significantly varying efficiency of the heat transfer from the salt bath to the water in the second heat exchange element.

[0039] This uniform temperature field in the salt bath furthermore achieves a uniform heat transfer in the salt bath itself. Thereby, it is possible to design the steam generator or the housing of the steam generator particularly flexibly. In particular, this means that the housing of the steam generator can have various different shapes and geometries without there being a risk of local hot spots or too strong temperature gradients in the heat transfer medium. This is also advantageous because thereby less calculation and design expenditure is required for designing a highly efficient steam generator.

[0040] Here, salts can be used as heat transfer medium which already change from the crystalline state to the liquid state at 130 °C - 150 °C or 235 °C, that is to say a change in the operating state occurs. The heat transfer medium can preferably be a nitrate, particularly preferably potassium-sodium nitrate or potassium-sodium-calcium nitrate.

[0041] Nitrate salts are not only particularly economical, but can also be used for heat transfer at high temperatures of the heat exchange fluid, for example for flue gases of up to 900 °C, without chemical decomposition occurring. In this way, for example, potassium-sodium-ammonium salts can be used durably and without the risk of decomposition in salt baths of up to 560 °C. Thereby, a design of the steam generator is achieved which is as operationally reliable and efficient as possible.

[0042] At the same time, the potassium sodium ammonium salt is particularly temperature-stable and thus suitable for efficient heat transfer and heat storage. Thereby, for example, salt bath temperatures of 350 °C to 565 °C can be present without posing a threat to the operational reliability of the steam generator.

[0043] The heat transfer medium preferably at least covers the first heat exchange element and the second heat exchange element.

[0044] That is to say, according to this design, both the first heat exchange element and the second heat exchange element are completely surrounded by the heat transfer medium. Thereby, a particularly operationally reliable, efficient, advantageous and flexible steam generation can be achieved, since the salt bath achieves a high level of heat transfer at different temperatures and local temperature peaks in the salt bath can be prevented due to the stirring device.

[0045] In the current heat exchange arrangement of the steam generator, a pressure can be generated which is between 50 bar and 800 bar, preferably between 30 bar and 500 bar, particularly preferably between 30 bar and 180 bar, but also a pressure which generates a steam pressure of 4 bar to 10 bar.

[0046] That is to say, this arrangement can be used particularly flexibly due to the salt bath which performs the heat transfer and can both generate low pressures in the range of, for example, 7 bar for food production and also high-pressure steam flows in the range of 500 bar to 800 bar, while the energy content of the biological substance fluctuates unimportantly for the device itself.

[0047] An arrangement in the form of a complex steam storage boiler with additional steam losses, as is common in the prior art so far, is not necessary in this design. Thereby, a device for generating steam can be achieved which is not only particularly flexible, but also economical, which can furthermore be achieved particularly compactly.

[0048] Furthermore, in contrast to the heat exchangers / steam generators known to date, a plurality of second heat exchange elements, i.e. a plurality of tubes arranged parallel to one another in the housing, can be arranged in the housing, and these tubes are surrounded by the salt bath. In other words, a plurality of steam generation tubes is arranged in the housing and surrounded by the heat transfer medium. Accordingly, in the operation of only one steam generator, i.e. with one housing through which the heat exchange fluid flows, steam having different pressures can be generated at the same time. In this way, for example, steam having a pressure of 7 bar, 11 bar, 100 bar and 200 bar can be generated on demand in only one steam generator housing on the basis of a plurality of second heat exchange elements. That is to say, for example, a pure steam line is provided for food production, and further high-pressure lines are provided for steam engines and turbines for generating electricity.

[0049] Preferably, the stirring device is designed to generate a turbulent flow within the heat transfer medium by stirring the heat transfer medium during operation of the steam generator.

[0050] This turbulent flow enables particularly efficient heat transfer, since the turbulence causes the heat transfer medium to undergo an increased degree of "eddy current".

[0051] Preferably, the heat exchange fluid can flow through the first heat exchange element in a first flow direction from an inlet of the housing to an outlet of the housing.

[0052] Here, therefore, in the first flow direction, heat transfer from the heat exchange fluid to the heat transfer medium and heat transfer from the heat transfer medium to the water flowing in the second heat exchange element can take place.

[0053] It is preferred here that the cross section of the first heat exchange element is larger at the inlet of the housing than at the outlet of the housing.

[0054] The "cross section" of the first heat exchange element here refers to the internal dimensions. If the "first heat exchange element" is designed, for example, as a cylindrical tube, the "cross section of the first heat exchange element" accordingly refers to the internal diameter of the tube. In other words, the "cross section of the first heat exchange element" refers to the effective flow cross section of the first heat exchange element.

[0055] By means of the change in the cross section between the inlet and the outlet of the housing, the energy input into the heat transfer medium at the beginning can be designed to be as large as possible. At the same time, local overheating or decomposition of the heat transfer medium can be prevented, and the operating reliability is increased. The reason for this is that the initial flow speed of the heat exchange fluid can be reduced as a result of the larger flow cross section. As a result, there is a lower flow speed when the flue gas enters the first heat exchange element. Overheating of the heat transfer medium and possible decomposition of the heat transfer medium can accordingly be prevented.

[0056] At this point, the flexibility of the steam generator is particularly advantageously implemented, and the generation of a desired steam pressure can be particularly simply controlled.

[0057] Preferably, the stirring device has a plurality of stirring mechanisms. Each of the stirring mechanisms extends into the heat transfer medium. The stirring mechanisms can be arranged distributed along the first flow direction. The stirring mechanisms are particularly preferably arranged uniformly distributed along the first flow direction.

[0058] The arrangement of a plurality of stirring mechanisms along the first flow direction enables a more uniform effect on the heat transfer and contributes to efficiently avoiding local temperature hotspots in the heat transfer medium.

[0059] It is furthermore preferred that the stirring device has a control device which is designed to individually control the plurality of stirring mechanisms.

[0060] It is thereby possible to implement an adaptation of the stirring speed of the stirring mechanisms to the current temperature of the flue gas and the current temperature in the salt bath in the region of the respective stirring mechanism as flexibly as possible.

[0061] It is preferred here that the control device is designed to control the stirring mechanisms during operation of the steam generator such that the stirring speed of each stirring mechanism is less than 150 revolutions per minute. That is to say, the control device is designed to control the stirring mechanisms during operation of the steam generator such that the stirring mechanisms are operated at as low a rotational speed as possible in order to efficiently ensure a high heat transfer in the housing without the occurrence of hotspots.

[0062] This low stirring speed of each stirring mechanism makes it possible, unlike in the case of the hitherto known use of a single pump, to implement a particularly energy-efficient design of the steam generator which still has as low a temperature gradient as possible in the salt bath.

[0063] The control device is preferably designed to control the stirring mechanisms during operation of the steam generator such that at least one stirring mechanism is stirred counter to at least one further stirring mechanism.

[0064] Such a manipulation of the stirring mechanisms enhances the turbulence within the heat transfer medium and thereby promotes the heat transfer within the salt bath. Correspondingly, it is also possible to increase the uniformity of the heat transfer to the water in the second heat exchanger element by the enhanced turbulence in the salt bath.

[0065] The control device can likewise be designed to control one stirring mechanism on the inlet-side of the housing during operation of the steam generator such that this stirring mechanism is stirred at a higher stirring speed than one stirring mechanism on the outlet-side of the housing.

[0066] Similar to the above embodiment of the inlet cross-section being larger than the cross-section at the outlet of the housing with respect to the first heat exchange element, in this configuration, an overload of the heat transfer medium can also be prevented in the region of the inlet side of the housing, i.e. in the region with the highest thermal load due to the highest temperature of the heat exchange fluid.

[0067] In particular, due to the higher stirring speed, a higher heat transfer from the first heat exchange fluid to the heat transfer medium and within the heat transfer medium itself can be achieved, so that the temperature uniformity of the heat transfer medium in the housing can be further improved.

[0068] The control device can preferably be designed to control the stirring means during operation of the steam generator such that the stirring speed of the stirring means decreases gradually along the first flow direction. In other words, the first stirring means at the inlet side of the housing can rotate faster than the stirring means further away from the inlet of the housing along the first flow direction from the inlet of the housing.

[0069] Thereby, the heat input into the heat transfer medium can be further homogenized and the heat input can be kept constant in the first flow direction with decreasing temperature of the heat exchange fluid.

[0070] Each stirring means can have a plurality of stirring blades which are arranged in the region in which the stirring means projects into the heat transfer medium, respectively. The stirring blades are arranged in order to generate a flow within the heat transfer medium by stirring the heat transfer medium during operation of the steam generator.

[0071] That is, the stirring blades are, for example, "blades" which are able to put the heat transfer medium into motion.

[0072] The plurality of stirring blades of one stirring means is preferably arranged distributedly in the region in which the stirring means projects into the heat transfer medium.

[0073] Here, all stirring blades of one stirring means are particularly preferably of uniform size. Furthermore, it is particularly preferred that the stirring blades are arranged uniformly distributed in the region in which the stirring means is in the heat exchange fluid over the longitudinal extension of the stirring means through the heat exchange fluid. Thereby, due to the stirring blades with a radially shorter extension dimension, a uniform temperature field can still be generated with high energy efficiency.

[0074] It is preferred that one stirring means on the inlet side of the housing has larger stirring blades than one stirring means on the outlet side of the housing.

[0075] According to this design, it is also possible to prevent an overload of the heat transfer medium at the inlet of the housing, that is to say in the region in which the heat exchange fluid has the highest temperature. The reason for this is that the stirring means at the inlet promote the uniformity of the temperature field in the heat transfer medium particularly effectively due to the larger stirring blades.

[0076] Preferably, the first heat exchange element can have a plurality of tubes which extend in the first flow direction, wherein each stirring means extends between the tubes.

[0077] Due to the plurality of stirring means between the tubes of the first heat exchange element, in cooperation with the salt bath provided as heat transfer medium, it is possible to achieve a uniform generation of steam independently of the heat source. Accordingly, a particularly flexible and multipurpose useable device for generating steam can be realized with only one compact device.

[0078] The tubes of the first heat exchange element are particularly preferably smooth tubes, that is to say tubes without ribs, protrusions or similar structures.

[0079] This is particularly advantageous, since possible residual ash or possible other deposits of the heat exchange fluid cannot deposit in the first heat exchange element. As a result, the maintenance intervals of the steam generator can be significantly reduced and a continuous high efficiency of the steam generator is ensured.

[0080] Depending on the specific application, the housing can be formed from stainless steel or black steel. In the case of the use of stainless steel, a high corrosion resistance can be ensured even at higher operating temperatures and a reliable and safe operation of the steam generator over a longer period of time is achieved.

[0081] The first heat exchange element preferably has a plurality of U-shaped tube coil structures which are arranged in such a way that the heat exchange fluid passes through the first heat exchange element a plurality of times in the first flow direction and in the reverse direction of the first flow direction.

[0082] The U-shaped tube coil structures of the first heat exchange element are particularly preferably designed in such a way that the first heat exchange element is flowed through by the heat exchange fluid from the upper side to the lower side of the housing or from the lower side to the upper side of the housing.

[0083] As a result, the heat transfer surface from the heat exchange fluid to the salt bath in the housing can be maximized independently of the selected flow through the housing. BRIEF DESCRIPTION OF DRAWINGS

[0084] In the following, a steam generator according to an exemplary embodiment is explained with reference to the schematic drawings. Such a steam generator is for example used in a steam engine or a steam engine, for example in order to generate steam for the purpose of energy extraction. Therein: Figure 1 A cross-sectional view of a steam generator according to an exemplary embodiment is shown. Detailed Implementation

[0085] Figure 1 A steam generator 1 according to an exemplary embodiment of the present invention is shown. For this purpose, Figure 1 A cross-sectional view of the steam generator 1 is shown, with the axis of the cross section extending along the longitudinal direction of the steam generator (i.e., along the first flow direction A, which will be described in detail later), so that the internal structure of the steam generator is visible. That is to say, Figure 1 This can also be understood as a side view of the steam generator, in which the sidewalls along the longitudinal extension direction have been removed so that the internal structure of the steam generator is visible.

[0086] according to Figure 1 The steam generator has a housing 2, which has a bottom wall, a top wall, a rear wall, and two side walls. As mentioned earlier, the front wall of the housing 2 is not visible in order to show the internal structure of the steam generator 1.

[0087] In the illustrated embodiment, the housing 2 is designed to be "box-shaped". That is, the housing extends substantially along the longitudinal direction of the housing 2 and has a rectangular cross-section.

[0088] However, due to the design scheme of the steam generator 1 according to the present invention, the width and / or height and length of the housing 2 are not limited for generating steam and can be configured according to space requirements and / or design expectations.

[0089] The housing 2 is in the housing 2 Figure 1 The left side wall shown in the middle has an inlet 6 and is located in the housing 2. Figure 1 The opposite side wall shown on the right has an outlet 7.

[0090] A first heat exchange element 3 is disposed within the housing 2. A heat exchange fluid is capable of flowing through the first heat exchange element 3. In the present detailed description of a preferred embodiment, the heat exchange fluid is flue gas. Another example of such a heat exchange fluid is waste heat from a biogas plant.

[0091] exist Figure 1 In the embodiment shown, the first heat exchange element 3 is implemented via a plurality of tubes 10. These tubes extend from the inlet 6 of the housing 2 to the outlet 7 of the housing 2 along a first flow direction A.

[0092] That is, in the embodiment shown, the first flow direction A corresponds to the longitudinal extension direction of the housing 2.

[0093] That is to say, the first heat exchange element 3 enables the flue gas to flow through in the first flow direction A from the inlet 6 to the outlet 7 in the form of the plurality of tubes 10 and thereby releases heat energy to the interior of the steam generator 1 by this design.

[0094] In the following description, flue gas is used as an example of a heat exchange fluid, which is generated by the combustion of biological material. Another example of such a heat exchange fluid is waste heat of a biogas plant.

[0095] In Figure 1 , the U-shaped tube sections, which extend the flow path of the flue gas through the first heat exchange element 3, are not shown, so that the plurality of tubes 10 arranged in the housing 2 can be connected to each other by U-shaped tube sections, so that the flow path can be extended through the first heat exchange element 3 and in the example shown in Figure 1 , the flue gas does not flow in at the left-hand side wall of the housing, i.e. at the inlet 6, and once through the housing 2 in the first flow direction A to the outlet 7 of the housing 2 at the right-hand side wall of the housing shown in Figure 1 . Rather, the flue gas flows at the inlet 6 through the U-shaped tube sections into the tubes, flows completely through the housing 2 in the longitudinal extension to the side of the outlet 7, is then guided in the other tube 10 from the side of the outlet 7 of the housing 2 to the side of the inlet 6 of the housing 2 in the opposite direction to the first flow direction A, and then the flue gas can flow again from the side of the inlet 6 of the housing 2 in the first flow direction A to the side of the outlet 7 of the housing 2 through another U-shaped tube section.

[0096] In this case, the flue gas can be introduced, for example, at the lowermost section of the housing 2 and discharged at the uppermost section of the housing 2. The opposite design can also be used: the flue gas can enter at the uppermost section of the housing 2, be guided through the housing 2 in the first flow direction A by U-shaped tube sections, be guided through the housing 2 in the opposite direction to the first flow direction A, and be discharged again at the lowermost section of the housing 2.

[0097] In the shown embodiment, the inlet 6 and the outlet 7 are arranged in the side walls of the housing. However, the application is not limited thereto. It is also conceivable that the inlet 6 and the outlet 7 can be arranged on the front wall and the rear wall of the housing or on the bottom wall and the top wall and also in a mixed form of the above-mentioned ways.

[0098] Irrespective thereof, in Figure 1In the embodiment shown in the figures, the second heat exchange element 4 is located in the housing 2. Water can flow through the second heat exchange element 4 in order to generate steam. In other words, the water in the second heat exchange element 4 is heated (indirectly) by the flue gas flowing through the first heat exchange element 3 or, respectively, in the first heat exchange element and is thereby converted from a liquid state into a steam-like state. The steam can then be used, for example, to generate a flow. Here, the flow can be used in a steam motor and / or a steam turbine which is supplied with the generated steam.

[0099] In the embodiment shown, the second heat exchange element 4 is designed as a single tube which extends through the housing 2 of the steam generator 1 in the form of a winding.

[0100] In this embodiment, the flow direction of the water in the second heat exchange element 4 is referred to as the "second flow direction".

[0101] As can be seen in the figures, the second heat exchange element 4 has a plurality of tube windings 12 in the form of a tube. As can be seen in Figure 1 These tube windings 12 are arranged in the housing 2 in such a way that the second heat exchange element 4 extends substantially perpendicular to the first flow direction A from the inlet 6 of the housing 2 to the outlet 7 of the housing 2 and achieves as great a tube length and, thus, as great a tube surface as possible along the extension of the U-shaped tube winding sections from the housing inlet 6 to the housing outlet 7.

[0102] The tube 10 of the first heat exchange element 3 extends linearly (in the longitudinal direction) from the inlet 6 to the outlet 7 of the housing 2, whereas the tube of the second heat exchange element 4 has a plurality of tube sections which extend vertically in the embodiment shown, so that the tube windings 12 connected with the U-shaped tube winding sections extend substantially perpendicular to the first flow direction A from the inlet 6 to the outlet of the housing 2.

[0103] In another embodiment not shown, the cross section of the first heat exchange element 3 can be larger at the inlet 6 of the housing 2 than at the outlet 7 of the housing 2. Thereby, the flow speed of the flue gas as heat exchange fluid can be reduced upon entering the housing 2.

[0104] Furthermore, a heat transfer medium is arranged in the housing 2 in order to transfer heat from the heat exchange fluid (flue gas) flowing through the first heat exchange element 3 to the water flowing through the second heat exchange element 4 in order to generate steam. Here, in the embodiment shown, the heat transfer medium is a salt bath which completely covers the first heat exchange element 3 and the second heat exchange element 4 in the housing 2.

[0105] As Figure 1As shown, the salt bath can be injected into the housing 2 through the inlet pipe 13. Thus, the salt bath fills the intermediate space between the first heat exchange element 3 and the second heat exchange element 4 within the housing 2 and can completely fill the housing. Accordingly, the salt bath can be used as a heat transfer medium and an energy accumulator to improve the uniformity of energy transfer.

[0106] The salt bath may contain nitrates, especially potassium-sodium nitrate or potassium-sodium-calcium nitrate.

[0107] In another embodiment, not shown, the heat transfer medium may be heat transfer oil, which is disposed in the housing for heat transfer, particularly uniform heat transfer.

[0108] However, in the exemplary embodiment below, a salt bath is used as the heat transfer medium.

[0109] like Figure 1 As shown, this embodiment of the invention has a stirring device 5 on the housing 2. The stirring device is configured to keep the salt bath in motion during steam generator operation by agitating the salt bath. This improves heat transfer from the first heat exchange element 3 to the salt bath, heat transfer within the salt bath itself, and heat transfer from the salt bath to the second heat exchange element.

[0110] The stirring device 5 is in Figure 1 The embodiment shown is implemented with multiple stirring mechanisms, namely three stirring mechanisms 8.1, 8.2, and 8.3. Each of the stirring mechanisms extends into the heat transfer medium covering the first heat exchange element 3 and the second heat exchange element 4.

[0111] Here, the three stirring mechanisms 8 are fixed to the upper side of the housing 2 by the suspension structure 11, and can extend into the interior of the housing 2 via flanges, especially sealing flanges. However, the arrangement of the stirring mechanisms 8 of the stirring device 5 is not limited to being fixed to the upper side of the housing. It is also conceivable that the stirring mechanisms are located on the side of the housing or even in the bottom region of the housing, and can extend into the salt bath inside the housing from there.

[0112] The following discussion takes the setting of the stirring device 5 on the upper side of the shell as a starting point, such as... Figure 1 As shown.

[0113] The plurality of stirring mechanisms 8 are arranged in a distribution along the first flow direction A, thereby enabling the stirring of the salt bath.

[0114] In other words, the stirring device 5 is designed in the form of a plurality of stirring mechanisms 8 which, during operation of the steam generator 1, generate a flow in the salt bath by stirring the salt bath. Here, the stirring mechanisms 8 are provided with a motor on which a metal tube (rod) which extends into the salt bath is arranged, so that the rotational force of the motor can be transmitted to the metal rod.

[0115] In the region of the metal rod of the stirring mechanism 8 which is located in the salt bath in the housing 2, a plurality of stirring blades 9 are arranged. The stirring blades 9 of the stirring mechanism 8 are arranged in such a way that each stirring mechanism 8 extends between the individual tubes 10 of the first heat exchange element 3 and the individual tube coil structures 12 of the second heat exchange element 4.

[0116] In this case, in the preferred embodiment shown in Figure 1 , the stirring blades 9 of each stirring mechanism 8 are provided with uniform dimensions, that is to say with uniform blade dimensions. Furthermore, a plurality of stirring blades 9 can be arranged distributed along the metal rod of the stirring mechanism 8 in the region which projects into the salt bath.

[0117] However, in the present case, in Figure 1 , only two stirring blades 9 are drawn in one height position of each stirring mechanism 8 for the sake of illustration. It is these stirring blades 9 which, during operation of the steam generator 1, generate a flow, preferably a turbulent flow, of the salt bath by stirring the heat transfer medium, here the salt bath, and thereby ensure uniform heat transfer.

[0118] In the preferred embodiment shown in Figure 1 , all stirring mechanisms 8.1, 8.2, 8.3 which are distributed in the first flow direction A are provided with stirring blades of the same size on each stirring mechanism 8.

[0119] Irrespective of this, however, in another embodiment which is not shown, the stirring mechanisms 8.1 on the side of the inlet 6 of the housing 2 can also have larger stirring blades 9 than the stirring mechanisms 8.2 or 8.3 which are arranged further away from the inlet 6 of the housing 2 in the first flow direction A.

[0120] Furthermore, for the purpose of controlling the plurality of stirring mechanisms 8 of the stirring device 5, a control device which is not shown is provided.

[0121] This control device is designed to control the individual stirring mechanisms separately. Thereby, for example, all motors of the stirring mechanisms 8 can be operated at the same or at different rotational speeds, and accordingly stir and thereby set in motion the salt bath with different intensities.

[0122] Here, for the purpose of intensifying the turbulent flow, that is to say for the purpose of intensifying the non-laminar flow, in the salt bath, the control device of the stirring mechanisms can be designed in such a way that, in the region of the metal rod of the stirring mechanism 8 which is located in the salt bath,Figure 1 At least one of the three stirring mechanisms 8.1, 8.2, and 8.3 shown in Figure 2 can operate in the opposite direction to the other stirring mechanisms. That is, specifically, for example, a control device can be envisioned in which the stirring mechanism at the inlet 6 of the housing 2, i.e., stirring mechanism 8.1, and the stirring mechanism at the outlet 7 of the housing 2, i.e., stirring mechanism 8.3, rotate clockwise by the operation of their motors, while the stirring mechanism 8.2, located in the middle in Figure 2, rotates counterclockwise.

[0123] It is also conceivable that the stirring mechanism on the inlet 6 side of the shell 2, namely the stirring mechanism 8.1, operates at a higher speed than other stirring mechanisms. This means that heat transfer at the inlet 6 of the shell 2 can be transferred to the salt bath with the highest flue gas temperature, and this homogenizes the salt bath temperature, while there is no risk of local hot spots, especially in the area of ​​the inlet 6.

[0124] In contrast, the actual rotational speed of the motors of each stirring mechanism allows for the use of stirring mechanisms that place the salt bath in motion, i.e., in flow, enabling the salt bath to be effectively homogenized with particularly high energy efficiency, i.e., with a small power consumption of a few hundred watts.

[0125] Here, operating all stirring mechanisms at a stirring speed of less than 150 rpm is sufficient to achieve a salt bath with a negligible temperature gradient along the first flow direction A, that is, a salt bath with a temperature gradient of less than 10°C, preferably less than 5°C, along the first flow direction A.

[0126] In another embodiment, not shown, multiple such... ​ The steam generators shown are cascaded and connected in series. These steam generators have a housing 2, a first heat exchange element 3 and a second heat exchange element 4 disposed in the housing 2, and a heat transfer medium covering the heat exchange elements, along with a stirring device 5 disposed in the heat transfer medium. In this embodiment, flue gas, for example, as the heat exchange fluid, enters the first steam generator at a high temperature of about 900°C and transfers heat to a salt bath located in the first steam generator. The salt bath is kept in motion by the stirring mechanism, thereby enabling the temperature to be uniformly transferred to the second heat exchange element 4.

[0127] In the first steam generator, the stirring mechanism is specifically used to achieve a uniform temperature field of the salt bath within the housing 2 along the first flow direction A. Here, the flue gas can flow into the housing 2 near the bottom and be gradually guided upward through the housing 2 via a U-shaped pipe section along the first flow direction A and in the opposite direction to the first flow direction, until the flue gas re-flows out at the top of the housing 2 of the first steam generator.

[0128] Next, the flue gas, which has already released its first portion of thermal energy to the salt bath in the first steam generator, is guided into a second steam generator, which has the same configuration as the first steam generator. But at this point the flue gas enters the housing 2 in the vicinity of the roof, that is to say at a location on the upper side of the housing 2, and is guided through the housing via the U-shaped tube section in the first flow direction A and counter to the first flow direction, until the flue gas flows out of the second steam generator again at the region of the bottom wall of the housing 2.

[0129] In contrast to the first steam generator, in the second steam generator the stirring means 8 in the second steam generator can be operated significantly less intensively, so that a certain temperature gradient in the vertical direction of the housing 2 within the salt bath can be achieved and the outlet temperature of the flue gas at the outlet of the second steam generator can thus be determined with certainty.

[0130] In this case, potassium-sodium-nitrate (Kalium-Natrium-Nitrat) is filled as heat transfer medium in the first steam generator, into which the flue gas enters at significantly higher temperatures, and the second steam generator, through which the flue gas is subsequently flowed through, is filled with nitrate in contrast.

[0131] In other words, in this embodiment a high-temperature steam generator is provided upstream of a low-temperature steam generator. Likewise, the second steam generator can be used only for heating the second heat exchange element and does not reach the temperatures for the phase change of water at all. In the second (low-temperature) steam generator, the salt bath is present in a stratified structure mainly by means of stirring, that is to say, by means of the stirring means it can be controlled whether a temperature gradient in the vertical direction of the housing is present or whether the entire salt bath should be present uniformly as in the high-temperature steam generator upstream.

[0132] List of reference signs 1 steam generator 2 housing 3 first heat exchange element 4 second heat exchange element 5 stirring device 6 inlet of the housing 7 outlet of the housing 8 stirring means 10 tube 11 suspension structure 12 tube coiling structure 13 inlet connection

Claims

1. Steam generator (1) having: a housing (2); a first heat exchange element (3) arranged in the housing (2), through which a heat exchange fluid, preferably flue gas, can flow; at least one second heat exchange element (4) arranged in the housing (2), through which water can flow in order to generate steam; and a heat transfer medium in the form of a salt bath, which is arranged in the housing in order to transfer heat from the heat exchange fluid flowing through the first heat exchange element (3) to the water flowing through the second heat exchange element (4) in order to generate steam; characterized in that the steam generator has a stirring device (5) which is arranged on the housing (2) and projects into the heat transfer medium, the stirring device (5) is designed to generate a flow within the heat transfer medium by stirring the heat transfer medium during operation of the steam generator (1), the stirring device (5) is designed to generate a turbulent flow within the heat transfer medium by stirring the heat transfer medium during operation of the steam generator (1), the heat exchange fluid can flow through the first heat exchange element (3) in a first flow direction (A) from an inlet (6) of the housing (2) to an outlet (7) of the housing (2), the cross section of the first heat exchange element (3) is larger at the inlet (6) of the housing (2) than at the outlet (7) of the housing (2), the stirring device (5) has a plurality of stirring mechanisms (8) which each project into the heat transfer medium and are arranged distributed, preferably uniformly distributed, in the first flow direction (A), the stirring device (5) has a control device which is designed to control the plurality of stirring mechanisms (8) individually, the control device is designed to control the stirring mechanisms (8) during operation of the steam generator (1) such that the stirring speed of each stirring mechanism (8) is less than 150 revolutions per minute, the control device is designed to control the stirring mechanisms (8) during operation of the steam generator (1) such that at least one stirring mechanism (8) stirs counter to at least one further stirring mechanism (8), the control device is designed to control one stirring mechanism (8.1) on the side of the inlet (6) of the housing (2) during operation of the steam generator (1) such that this stirring mechanism stirs at a higher stirring speed than one stirring mechanism (8.3) on the side of the outlet (7) of the housing (2), the control device is designed to control the stirring mechanisms (8) during operation of the steam generator (1) such that the stirring speed of the respective stirring mechanisms (8.1, 8.2, 8.3) decreases gradually in the first flow direction (A). ​ ​ ​ ​ ​ ​ ​ 2. Steam generator (1) according to claim 1, wherein ​ 3. Steam generator (1) according to any one of the preceding claims, wherein, ​ 4. Steam generator (1) according to claim 3, wherein ​ 5. Steam generator (1) according to claim 3 or 4, wherein ​ 6. Steam generator (1) according to claim 5, wherein ​ 7. Steam generator (1) according to claim 6, wherein ​ 8. Steam generator (1) according to claim 6 or 7, wherein ​ 9. Steam generator (1) according to any one of claims 6 to 8, wherein, ​ 10. Steam generator (1) according to any one of claims 6 to 9, wherein, ​ 11. Steam generator (1) according to any one of claims 5 to 10, wherein, Each stirring device (8) has a plurality of stirring blades (9) which are arranged in the region in which the stirring device projects into the heat transfer medium, the stirring blades (9) being arranged in order to generate a flow in the heat transfer medium by stirring the heat transfer medium during operation of the steam generator (1).

12. Steam generator (1) according to claim 11, wherein The plurality of stirring blades (9) are arranged distributed over the region in which the stirring device projects into the heat transfer medium, and the individual stirring blades (9) of a stirring device (8) preferably have uniform dimensions.

13. Steam generator (1) according to claim 11 or 12, wherein One stirring device (8.1) on the side of the inlet (6) of the housing (2) has larger stirring blades (9) than one stirring device (8.3) on the side of the outlet (8) of the housing (2).

14. Steam generator (1) according to any one of claims 5 to 13, wherein, The first heat exchange element (3) has a plurality of tubes (10) which extend in the first flow direction (A), and each of the stirring devices (8) extends between the plurality of tubes (10).

15. Steam generator (1) according to any one of the preceding claims, wherein, The salt bath has nitrates, particularly preferably potassium-sodium nitrates or potassium-sodium-calcium nitrates.

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