steam generator

Abstract

The steam generator (1) comprises a housing (2); a first heat exchange element (3) located within the housing through which a heat exchange fluid, preferably flue gas, can flow; at least one second heat exchange element (4) located within the housing through which water can flow to generate steam; and a heat transfer medium in the form of a salt bath located within the housing (2) 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) to generate steam. The steam generator further comprises an agitator (5) located within the housing (2) and reaching into the heat transfer medium, the agitator (5) being configured to create flow in the heat transfer medium by agitating it during operation of the steam generator (1).

Description

Technical Field

[0001] The present invention relates to a steam generator for generating steam, and the steam generator can be used, for example, for energy generation using a steam engine or a steam turbine. For this purpose, the steam generator can be connected, for example, to a biomass combustor, a biogas plant, or a pellet heater.

Background Art

[0002] In order to generate steam, a steam generator is generally used. The steam generator usually has a combustion chamber (fire chamber) for heating or burning fuel to generate heat. Alternatively, it is also possible to utilize the still-high-temperature exhaust gas of a biogas plant to supply the necessary heat. This heat passes through, for example, a heat exchanger in the form of a heat exchange fluid and evaporates the water flowing through the heat exchanger. The steam thus generated can be used for energy generation, for example, in a steam engine.

[0003] For efficient steam generation and energy generation, high pressure and, accordingly, high temperature are required. This results in the heat load of the heat exchanger and the stress in the material of the heat exchanger.

[0004] In the prior art, for example, from Patent Document 1, a shell-and-tube heat exchanger is known that includes a number of tube coils starting from a common inlet chamber for a heat exchange fluid and merging into a common outlet chamber. Each tube coil includes an alternating arrangement of tube portions and tube bending portions. The tube bending portions are formed as curves of 180° with respect to the arranged bending axis and have the same bending radius. This shell-and-tube heat exchanger is characterized in that along each tube coil, the bending axes of the tube bending portions connected to the same tube portion form an angle with each other, the bending axes of the tube bending portions extend parallel to each other, and between them, tube portions, tube bending portions, and further tube portions are arranged directly continuously.

[0005] However, in this case, the efficiency depends heavily on the distance between the shell-and-tube heat exchanger and the housing, and the type of flow of the heat exchange fluid within the tube bundle relative to the thermal energy generated by the fuel. In other words, in such a configuration, it is not possible to prevent wall losses caused by flow between the shell-and-tube heat exchanger and the surrounding housing without flowing through the heat exchanger. Therefore, the heat exchange efficiency is not optimal.

[0006] Furthermore, in such a configuration, it is impossible to compensate for the stress within the tube bundle caused by thermal expansion resulting from the high temperature of the heat exchange fluid.

[0007] Patent Document 2 also discloses a shell-and-tube heat exchanger, particularly for heat exchange from fuel gas to heating water or drinking water. The shell-and-tube heat exchanger has a water chamber through which a flow of heating water or drinking water passes, and a fuel gas chamber through which a flow of fuel gas passes. In this case, the fuel gas pipes that form the fuel gas can pass through in parallel or in series.

[0008] In this case, the aforementioned problems still occur, and furthermore, because heat exchange is performed using direct current, the efficiency of heat exchange is reduced.

[0009] Furthermore, when generating steam using biomass in known steam generators, it is particularly important to compensate for the uncertain and potentially fluctuating energy content of the combustible material (in contrast to coal, for example) and, consequently, the fluctuating steam parameters during steam generation. If the fluctuating energy content cannot be adequately compensated for, fluctuations in steam temperature will occur, which may lead to a decrease in the function or damage to steam turbines, for example, when using them.

[0010] Therefore, known configurations use an additional steam storage boiler to achieve low pressure loss and to counteract fluctuations.

[0011] However, at high pressures exceeding, for example, 250 bar, the risk of destruction, such as explosions, increases, making such configurations no longer applicable.

[0012] Therefore, for steam generators using biomass at high pressure, there is a need for a solution that is not only resistant to high pressure and safe, but also easily and inexpensively implemented.

[0013] Regarding this, only Patent Document 3 has so far disclosed a first solution in the field of steam generators that solves the aforementioned problem of fluctuations in the energy content of the combustible material while simultaneously achieving high operational safety. This is achieved by interposing a salt bath as a heat transfer medium between a first heat exchange element that guides a heat exchange fluid and a second heat exchange element that guides water for generating steam in a (high-pressure) steam generator.

[0014] However, even with this configuration, there is a possibility of stability issues arising in heat transfer.

[0015] This is mainly due to localized high-temperature regions within the salt bath, such as corners of the steam generator housing or when the flow stalls.

[0016] This is disadvantageous because it can lead to the sustained burning of the metal components of the steam generator due to overheating, as well as the decomposition of salt.

[0017] These decomposed salts can corrode the metal in the steam generator, potentially leading to leaks.

[0018] To address this problem, Patent Document 3 discloses a pump configured to flow a salt bath while a steam generator is in operation.

[0019] However, even with such a pump, the uneven temperature field within the salt bath persists due to the pump's placement, limiting the extent to which the aforementioned problems can be solved.

[0020] Furthermore, such a pump arrangement only results in a very local circulation of the salt bath during the operation of the steam generator. Therefore, even with the arrangement of Patent Document 3, local high-temperature regions can still continue to occur in the salt bath.

[0021] Furthermore, since the pump consumes a large amount of power, it has an adverse effect on the overall efficiency and economy of the steam generator.

Prior Art Documents

Patent Documents

[0022]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0023] Therefore, an object of the present invention is to provide an efficient device (steam generator) for generating steam, which has a simple structure, can ensure reliable operation even when the energy content of the combustible material fluctuates, can obtain high efficiency, and can reduce or prevent the above-mentioned drawbacks.

Means for Solving the Problems

[0024] This problem is solved by a device having the features of claim 1. Preferred embodiments are described in the following claims, description, and drawings.

[0025] According to one aspect of the present invention, the steam generator has a housing. Inside the housing, a first heat exchange element through which a heat exchange fluid can flow is provided.

[0026] The heat exchange fluid is preferably flue gas. Furthermore, the heat exchange fluid may be waste heat generated from biomass combustion, a biogas plant, or a pellet heater, and the waste heat can flow through the first heat exchange element, and therefore the steam generator. In other words, the heat exchange fluid may be, for example, combustion gas generated when a fuel in the form of undried, low-quality biomass is burned in the combustion chamber of a known propulsion grate combustion device, or exhaust gas from a biogas plant. This makes it possible to generate electricity from residual materials.

[0027] Depending on the heat exchange fluid, a variety of temperature ranges can occur within the steam generator. Such a heat exchange fluid can be understood as a heating fluid, fuel gas, or general combustion gas, and typically has a temperature between 600°C and 1200°C, preferably 1000°C.

[0028] Separately, as detailed below, the homogeneous heat transfer characteristics of the salt bath allow the steam generator to be "operated" without compromising safety even when the temperature of the heat exchange fluid exceeds 1000°C, especially above 1300°C.

[0029] When using exhaust gas from a biogas plant as a heat exchange fluid, the temperature of the heat exchange fluid, i.e., the gas temperature, is typically between 450°C and 500°C, preferably 470°C, in the steam generator.

[0030] Furthermore, the housing is provided with a second heat exchange element through which water can flow to generate steam. In this case, the water may be water, preheated water, or saturated steam.

[0031] Furthermore, the heat transfer medium is arranged in the form of a salt bath within the housing, thereby transferring 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.

[0032] In other words, the housing is filled with a salt bath as a heat transfer medium. The heat transfer medium is provided to absorb heat from the first heat exchange element and release it to the second heat exchange element. This heats the water flowing through the second heat exchange element, which can generate steam.

[0033] Furthermore, the heat transfer medium is used as a "buffer" to compensate for fluctuations in heat input from the first heat exchange element to the salt bath, which acts as the heat transfer medium, due to variations in the energy content of the combustion material. In other words, such a steam generator offers "high tolerance" to temperature fluctuations and variations in energy content. That is, even when the temperature peak of the heat exchange fluid fluctuates significantly, the salt bath ensures uniform heat transfer or heat input to the water for steam generation.

[0034] The steam generator further includes an agitator. This agitator is located in the housing and reaches into the heat transfer medium. In other words, the agitator is at least partially surrounded by the heat transfer medium. The agitator is configured to create flow within the heat transfer medium by agitating it during the operation of the steam generator.

[0035] In this context, the concept of "flow" is understood to mean the movement of the heat transfer medium within the housing during the operation of the steam generator, as the heat transfer medium begins to move, preferably in a circulating motion, within the housing.

[0036] Specifically, the circulation of this heat transfer medium within the housing provides a much more uniform temperature field than, for example, using a pump with the heat transfer medium. At the same time, localized overheating can be prevented.

[0037] Furthermore, by circulating the heat transfer medium within the housing using the stirring device according to the present invention, a uniform temperature field with a very high heat transfer coefficient can be obtained. In this case, a particularly high heat transfer coefficient occurs at a (high) pressure of 250 bar or more, preferably 300 bar or more.

[0038] With this configuration, it is possible to keep the temperature difference between the heat transfer medium and water or steam in the second heat exchange element to 1°C or less.

[0039] This further prevents temperature differences within the salt bath from occurring throughout the entire extension of the housing, thus preventing the formation of localized high-temperature regions or significant differences in the efficiency of heat transfer from the salt bath to the water in the second heat exchange element.

[0040] Such a uniform temperature field within the salt bath also enables uniform heat transfer within the salt bath. This allows for particularly flexible configurations of the steam generator or its housing. Specifically, this means that the steam generator housing can have a variety of shapes and geometric structures without the risk of localized high-temperature regions or excessively large temperature gradients in the heat transfer medium. This is also positive, as it reduces the calculation and design burden required to design an efficient steam generator.

[0041] In this case, a salt that already transitions from a crystalline aggregated state to a liquid aggregated state, i.e., an operating state, at 130°C to 150°C or 235°C can be used as the heat transfer medium. The heat transfer medium is preferably a nitrate, and particularly preferably potassium nitrate-sodium nitrate or potassium nitrate-sodium nitrate-calcium nitrate.

[0042] Nitrates are not only particularly low-cost, but they can also be used for heat transfer without chemical decomposition, even when the heat exchange fluid is at high temperatures, such as flue gas up to 900°C. For example, potassium nitrate-sodium nitrate can be used continuously at salt bath temperatures up to 560°C without the risk of decomposition. Therefore, a steam generator can be constructed that is as reliable and efficient as possible.

[0043] In addition, potassium nitrate-sodium nitrate exhibits particularly excellent temperature stability and is therefore suitable for efficient heat transfer and heat storage. Consequently, salt bath temperatures ranging from 350°C to 565°C can be used without compromising the operational safety of the steam generator.

[0044] The heat transfer medium preferably covers at least the first heat exchange element and the second heat exchange element.

[0045] In other words, in this configuration, both the first and second heat exchange elements are completely surrounded by the heat transfer medium. This allows the salt bath to achieve high heat transfer at various temperatures, and the agitator prevents localized temperature peaks within the salt bath, thus enabling particularly safe, efficient, low-cost, and flexible steam generation.

[0046] In the heat exchanger of this steam generator, a steam pressure of 50 bar to 800 bar, preferably 30 bar to 500 bar, and particularly preferably 30 bar to 180 bar, can be generated, but also a lower pressure of 4 bar to 10 bar.

[0047] In other words, because such a device uses a salt bath for heat transfer, it can be used with particular flexibility. For example, it can be used at low pressures in the 7 bar range for food production, or at high-pressure steam flows in the 500-800 bar range, without fluctuations in the biomass energy content becoming a significant problem for the device itself.

[0048] Furthermore, this configuration eliminates the need for the complex setups common in prior art that included additional steam storage boilers to achieve low pressure loss. Consequently, a steam generator that is not only particularly flexible but also low-cost can be realized, and such a steam generator can be implemented in a particularly compact structure.

[0049] Unlike known heat exchangers / steam generators, multiple piping systems, i.e., multiple second heat exchange elements, may be provided within the housing and surrounded by a salt bath, arranged parallel to each other. In other words, multiple steam generation conduits are provided within the housing and surrounded by a heat transfer medium. Correspondingly, even when only one steam generator is operating, i.e., operating in only one housing through which the heat exchange fluid flows, it is possible to generate steam at different pressures simultaneously. For example, in a single steam generator housing, due to the numerous second heat exchange elements, steam at 7 bar, 11 bar, 100 bar, and 200 bar can be generated as needed. That is, for example, it is possible to provide a pure steam rail for food processing and a higher-pressure rail for a steam engine or turbine for power generation.

[0050] Preferably, the stirring device is configured to generate turbulence within the heat transfer medium by stirring the heat transfer medium during the operation of the steam generator.

[0051] Such turbulence enhances the "swirling" of the heat transfer medium, enabling particularly efficient heat transfer. Preferably, the first heat exchange element can be passed through by the heat exchange fluid from the inlet to the outlet of the housing in the first flow direction. In this case, heat transfer from the heat exchange fluid to the heat transfer medium and heat transfer from the heat transfer medium to the water flowing within the second heat exchange element can occur along the first flow direction.

[0052] In this case, it is preferable that the cross-section of the first heat exchange element at the inlet of the housing is larger than that at the outlet of the housing.

[0053] In this case, the "cross-section of the first heat exchange element" is understood as the internal dimension. If the "first heat exchange element" is formed as, for example, a cylindrical tube, the "cross-section of the first heat exchange element" is correspondingly understood as the inner diameter of the tube. In other words, the "cross-section of the first heat exchange element" is understood as the effective flow cross-section of the first heat exchange element.

[0054] By changing the cross-section between the inlet and outlet of the housing, the initial energy input to the heat transfer medium can be designed to be as large as possible. In addition, localized overheating or decomposition of the heat transfer medium can be prevented, thereby improving operational safety. This is because increasing the cross-section of the flow reduces the initial flow velocity of the heat exchange fluid. Therefore, the flow velocity of the flue gas when it flows into the first heat exchange element is reduced. Correspondingly, overheating and possible decomposition of the heat transfer medium can be prevented.

[0055] In this regard, the flexibility of the steam generator is particularly advantageous, as it allows for particularly easy control of the generation of the desired steam pressure.

[0056] Preferably, the stirring device has a plurality of stirrs. Each of these stirrs reaches into the heat transfer medium. The stirrs may be dispersed along a first flow direction. Particularly preferably, the stirrs are evenly dispersed along the first flow direction.

[0057] By providing multiple agitators along the first flow direction, it is possible to more intensively homogenize heat transfer and efficiently avoid localized high-temperature regions within the heat transfer medium.

[0058] Furthermore, it is preferable that the stirring device has a control device configured to individually control multiple stirrers.

[0059] This allows the stirring speed of the stirrers to be adapted as flexibly as possible to the temperature of the flue gas and salt bath in the region of each stirrer.

[0060] In this case, it is preferable that the control device is configured to control the agitators so that the stirring speed of each agitator is less than 150 revolutions per minute while the steam generator is in operation. In other words, the control device is configured to control the agitators so that they operate at the lowest possible rotational speed while the steam generator is in operation, ensuring efficient and high heat transfer without creating localized high-temperature areas within the housing.

[0061] By reducing the stirring speed of each agitator in this way, it becomes possible to configure a particularly energy-efficient steam generator while maintaining the lowest possible temperature gradient within the salt bath, unlike the known use of a single pump.

[0062] Preferably, the control device may be configured to control the stirrers so that, during operation of the steam generator, at least one stirrer stirs in the opposite direction to at least one additional stirrer.

[0063] Controlling the agitator in this way increases turbulence within the heat transfer medium, thereby promoting heat transfer in the salt bath. Correspondingly, the increased turbulence in the salt bath also improves the uniformity of heat transfer to the water in the second heat exchange element.

[0064] Similarly, the control device may be configured to control the agitator on the inlet side of the housing to agitate at a higher agitation speed than the agitator on the outlet side of the housing while the steam generator is in operation.

[0065] Similar to the above description regarding the inlet cross-section which is larger than the cross-section of the first heat exchange element at the outlet of the housing, this configuration also prevents overloading of the heat transfer medium on the inlet side of the housing, i.e., in the region where the heat load is greatest because the temperature of the heat exchange fluid is highest.

[0066] In particular, as the stirring speed increases, higher heat transfer is achieved from the first heat exchange fluid to the heat transfer medium, and within the heat transfer medium itself, thereby further improving the temperature uniformity of the heat transfer medium within the housing.

[0067] Preferably, the control device may be configured to control the agitators so that their stirring speed decreases along the first flow direction during operation of the steam generator. In other words, the first agitator on the housing inlet side can rotate faster than agitators further away from the housing inlet along the first flow direction.

[0068] Therefore, the temperature input to the heat transfer medium is further homogenized and remains constant across the first flow direction, even if the temperature of the heat exchange fluid decreases.

[0069] Each agitator may have multiple stirring blades, each of which is positioned in the region where the agitator reaches into the heat transfer medium. The stirring blades are provided to create flow within the heat transfer medium by stirring it during the operation of the steam generator.

[0070] In other words, a stirring blade is understood to be a "vane" that can move, for example, a heat transfer medium.

[0071] It is preferable that the numerous stirring blades of the agitator be distributed and arranged over the area in which the agitator reaches the heat transfer medium.

[0072] In this case, it is particularly preferable that all stirring blades of the agitator have uniform dimensions. Furthermore, it is especially preferable that the stirring blades are evenly distributed by the heat exchange fluid in the longitudinally extending portion of the agitator in the region where the agitator is immersed in the heat exchange fluid. This makes it possible to generate a uniform temperature field with excellent energy efficiency even with stirring blades that have short radially extending portions.

[0073] It is preferable that the agitator on the inlet side of the housing has larger stirring blades than the agitator on the outlet side of the housing.

[0074] Even with this configuration, it is possible to prevent overloading of the heat transfer medium at the housing inlet, i.e., the region where the heat exchange fluid has the highest temperature. This is because the agitator located at the inlet, with its larger agitation blades, particularly promotes uniformity of the temperature field within the heat transfer medium.

[0075] Preferably, the first heat exchange element may have a plurality of tubes extending along a first flow direction, with each agitator extending between the tubes.

[0076] Since multiple agitators between the tubes of the first heat exchange element work together with the salt bath provided as the heat transfer medium, it is possible to generate steam uniformly regardless of the heat source. Accordingly, a steam generation device that is particularly flexible and versatile can be realized with just one compact device.

[0077] Particularly preferred is that the tube of the first heat exchange element is a smooth tube, i.e., a tube without ribs and protrusions.

[0078] This is particularly advantageous because any ash residue or other deposits that may occur in the heat exchange fluid cannot accumulate on the first heat exchange element. This significantly reduces the inspection interval of the steam generator and ensures the sustained high efficiency of the steam generator.

[0079] Depending on the application, the housing may be made of stainless steel or black steel. When stainless steel is used, high corrosion resistance is guaranteed even at relatively high operating temperatures, enabling reliable and safe operation of the steam generator over a relatively long period.

[0080] Preferably, the first heat exchange element has a plurality of U-shaped tube coils, the tube coils arranged such that the heat exchange fluid passes through the first heat exchange element multiple times along a first flow direction and in the opposite direction to the first flow direction.

[0081] Particularly preferably, the U-shaped tube coil of the first heat exchange element is configured such that the heat exchange fluid flows through the first heat exchange element from the top to the bottom of the housing, or from the bottom to the top of the housing.

[0082] Regardless of the selected flow path within the housing, the heat transfer surface from the heat exchange fluid to the salt bath within the housing can be maximized.

[0083] In the following, a steam generator according to an exemplary embodiment will be described based on schematic drawings. Such a steam generator is used, for example, in steam engines or other devices to generate steam for energy production. The following diagram shows the example. [Brief explanation of the drawing]

[0084] [Figure 1] This figure shows a cross-section of a steam generator according to an exemplary embodiment. [Modes for carrying out the invention]

[0085] Figure 1 shows a steam generator 1 according to an exemplary embodiment of the present invention. Figure 1 shows a cross-section of the steam generator 1, with the cross-sectional axis extending along the longitudinal direction of the steam generator (i.e., the first flow direction A, which will be described in detail later), thereby allowing the interior of the steam generator to be seen. In other words, Figure 1 can also be understood as a side view of the steam generator, with the side walls removed along the longitudinal direction to allow the interior of the steam generator to be seen.

[0086] The steam generator shown in Figure 1 has a housing 2 with a bottom wall, a top wall, a rear wall, and two side walls. As mentioned at the beginning, the front wall of the housing 2 is not visible in order to explain the inside of the steam generator 1.

[0087] In the illustrated embodiment, the housing 2 is configured in a "box shape." That is, the housing 2 basically extends along its longitudinal direction and has a right-angle cross-section.

[0088] However, with the configuration of the steam generator 1 according to the present invention, the width and / or height and length of the housing 2 do not impose any limitations with respect to steam generation and can be set according to the required space and / or desired configuration.

[0089] Housing 2 has an entrance 6 on the side wall of Housing 2 shown on the left side of Figure 1, and an exit 7 on the opposite side of Housing 2 shown on the right side of Figure 1.

[0090] A first heat exchange element 3 is located inside the housing 2. This first heat exchange element 3 can be permeated by a heat exchange fluid. In the detailed description of preferred embodiments herein, the heat exchange fluid is flue gas. Another example of such a heat exchange fluid is waste heat from a biogas plant.

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

[0092] In other words, in the illustrated embodiment, the first flow direction A corresponds to the longitudinal direction of the housing 2.

[0093] In other words, with this configuration, the first heat exchange element 3 in the form of a number of tubes 10 can be passed through by flue gas from the inlet 6 to the outlet 7 in the first flow direction A, and thus can release thermal energy into the steam generator 1.

[0094] In the following explanation, flue gas produced by biomass combustion is used as an example of a heat exchange fluid. Another example of such a heat exchange fluid is waste heat from a biogas plant.

[0095] Figure 1 does not show the U-shaped tube section that extends the flow path of flue gas through the first heat exchange element 3. Multiple tubes 10 arranged within the housing 2 can be connected to each other by the U-shaped tube section, thereby extending the flow path through the first heat exchange element 3. In the example shown in Figure 1, the flue gas not only flows in from the left side wall, i.e., the inlet 6 of the housing, along the first flow direction A to the outlet 7 of the housing 2 on the side wall of the housing 2 shown on the right side of Figure 1, but rather, through the U-shaped tube section, the flue gas flows into the tube from the inlet 6, completely along the longitudinal direction of the housing 2 to the side of the outlet 7, and then in a further tube 10, it is guided in the opposite direction to the first flow direction A, from the side of the outlet 7 of the housing 2 to the side of the inlet 6 of the housing 2, and the flue gas can flow again along the first flow direction A, from the side of the inlet 6 of the housing 2 to the side of the outlet 7 of the housing 2, through a further U-shaped tube section.

[0096] In this context, flue gas may be introduced, for example, from the bottom of housing 2 and discharged from the top of housing 2. Similarly, the reverse configuration is also possible. That is, flue gas may flow in from the top of housing 2, through a U-shaped tube section, through housing 2 along the first flow direction A, flow through housing 2 in the opposite direction to the first flow direction A, and then discharged again from housing 2 at the bottom.

[0097] In the illustrated embodiment, the inlet 6 and outlet 7 are located on the side walls of the housing. However, the present invention is not limited thereto. Similarly, the inlet 6 and outlet 7 may be located on the front and rear walls, or the bottom and top walls of the housing, or in combination thereof.

[0098] Separately, in the embodiment shown in Figure 1, a second heat exchange element 4 is located within the housing 2. This second heat exchange element 4 can be permeated by water to generate steam. In other words, the water in the second heat exchange element 4 is (indirectly) heated by the first heat exchange element 3 or the flue gas flowing through the first heat exchange element 3, and thus changes from a liquid state to a steam state. This steam can then be used, for example, for power generation. In this case, the current can be used in a steam engine and / or steam turbine supplied with the generated steam.

[0099] In the illustrated embodiment, the second heat exchange element 4 is configured as a single tube that extends in a coil shape through the housing 2 of the steam generator 1.

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

[0101] As is evident from the figure, the second heat exchange element 4 is in the form of a tube and has a plurality of tube coils 12. As can be seen in Figure 1, these tube coils 12 are located within the housing 2, and the second heat exchange element 4 extends from the inlet 6 of the housing 2 to the outlet 7 of the housing 2, substantially perpendicular to the first flow direction A, and the U-shaped tube coil portions are arranged so that the largest possible tube length and thus tube surface area can be obtained along the extending direction from the inlet 6 to the outlet 7 of the housing 2.

[0102] While the tube 10 of the first heat exchange element 3 extends linearly (longitudinally) from the inlet 6 to the outlet 7 of the housing 2, the tube of the second heat exchange element 4, in the illustrated embodiment, has multiple tube sections that extend vertically. As a result, the tube coil 12 connected to the U-shaped tube coil section extends substantially perpendicular to the first flow direction A from the inlet 6 to the outlet 7 of the housing 2.

[0103] In further embodiments not shown, the cross-section of the first heat exchange element 3 at the inlet 6 of the housing 2 may be larger than that at the outlet 7 of the housing 2. This makes it possible to reduce the flow velocity of the flue gas as a heat exchange fluid when it flows into the housing 2.

[0104] Furthermore, the housing 2 contains a heat transfer medium to transfer heat from the heat exchange fluid (in this case, 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. In this embodiment, the heat transfer medium is a salt bath that completely covers the first heat exchange element 3 and the second heat exchange element 4 within the housing 2.

[0105] As shown in Figure 1, this salt bath can be filled into the housing 2 through the inlet nozzle 13. Thus, the salt bath can fill the gap between the first heat exchange element 3 and the second heat exchange element 4 within the housing 2, completely filling the housing 2. Correspondingly, this salt bath can function as a heat transfer medium and energy storage device, improving the homogeneity of energy transfer.

[0106] Salt baths may contain nitrates, particularly potassium nitrate-sodium nitrate, or potassium nitrate-sodium nitrate-calcium nitrate.

[0107] In further embodiments not shown, the heat transfer medium may be a thermo-oil placed inside the housing for heat transfer, particularly homogeneous heat transfer.

[0108] However, the following exemplary embodiments assume the use of a salt bath as the heat transfer medium.

[0109] As can be derived from Figure 1, an embodiment of the present invention has a stirring device 5 in the housing 2. The stirring device is provided to cause the salt bath to flow by stirring the salt bath while the steam generator is in operation. This improves heat transfer from the first heat exchange element 3 to the salt bath, heat transfer within the salt bath, and heat transfer from the salt bath to the second heat exchange element.

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

[0111] In this configuration, the three agitators 8 are fixed to the upper surface of the housing 2 by mounting fixtures 11 and can reach the interior of the housing 2 through flanges, particularly sealed flanges. However, the arrangement of the agitators 8 of the agitator 5 is not limited to fixing them to the upper surface of the housing. Similarly, the agitators could be positioned on the sides or bottom of the housing, from which they could reach the salt bath inside the housing.

[0112] In the following, we assume that the stirring device 5 is located on the upper surface of the housing, as shown in Figure 1.

[0113] In this configuration, the multiple stirrers 8 are arranged in a dispersed manner along the first flow direction A so that they can stir the salt bath.

[0114] In other words, the stirring device 5, in the form of multiple stirrers 8, is configured to create a flow in the salt bath by stirring the salt bath while the steam generator 1 is in operation. In this case, the stirrers 8 are equipped with motors, and each motor is equipped with a metal tube that extends into the salt bath, thereby allowing the rotational force of the motor to be transmitted to a metal rod.

[0115] The region in which the metal rod of the agitator 8 is located within the salt bath in the housing 2 is provided with numerous stirring blades 9. The stirring blades 9 of the agitator 8 are arranged such that each agitator 8 extends between the tube 10 of the first heat exchange element 3 and the tube coil 12 of the second heat exchange element 4.

[0116] In this regard, in the preferred embodiment shown in Figure 1, the stirring blades 9 of each stirrer 8 have uniform dimensions, i.e., uniform blade dimensions. Furthermore, multiple stirring blades 9 may be dispersed along the metal rod of the stirrer 8 within the region where the metal rod reaches into the salt bath. However, in this case, for illustrative purposes, Figure 1 shows only two stirring blades 9 at the height position of each stirrer 8. These stirring blades 9 stir the heat transfer medium, in this case the salt bath, during the operation of the steam generator 1, thereby creating a flow, preferably turbulence, in the salt bath and ensuring homogeneous heat transfer.

[0117] In the preferred embodiment shown in Figure 1, all agitators 8.1, 8.2, and 8.3 dispersed along the first flow direction A are equipped with agitation blades of the same size in each agitator 8.

[0118] However, separately, in further embodiments not shown, a stirrer 8.1 located on the side of the inlet 6 of the housing 2 may have larger stirring blades 9 than a stirrer 8.2 or 8.3 located further away from the inlet 6 of the housing 2 when viewed in the first flow direction A.

[0119] Furthermore, a control device (not shown) is provided to control the multiple stirrers 8 of the stirring device 5.

[0120] Such a control device is configured to control each agitator individually. Therefore, for example, all the motors of agitator 8 can be operated at the same rotational speed or at different rotational speeds, and accordingly, the salt bath can be stirred at different intensities, thereby causing the salt bath to flow.

[0121] In this case, in order to enhance turbulence, or non-laminar flow, within the salt bath, the control of the agitators may be designed such that at least one of the three agitators 8.1, 8.2, and 8.3 shown in Figure 1 operates in the opposite direction to the remaining agitators. Specifically, for example, the agitator at the inlet 6 of housing 2, i.e., agitator 8.1, and the agitator at the outlet 7 of housing 2, i.e., agitator 8.3, rotate clockwise due to the operation of their motors, while agitator 8.2 in the center of Figure 2 rotates counterclockwise.

[0122] Similarly, the agitator on the inlet 6 side of housing 2, i.e., agitator 8.1, may be operated at a higher speed than the other agitators. This allows for particularly good heat transfer of the flue gas at its highest temperature, i.e., heat transfer at the inlet 6 of housing 2, to the salt bath, and the temperature of the salt bath is homogenized without the risk of localized high-temperature regions forming, especially in the inlet 6 area.

[0123] By using stirrers that move, or flow, the salt bath regardless of the actual rotational speed of each stirrer's motor, effective homogenization of the salt bath becomes possible with particularly high energy efficiency, meaning low power consumption of only a few hundred watts.

[0124] In this case, operating all stirrers at a stirring speed of less than 150 revolutions per minute is sufficient to obtain 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, and particularly preferably less than 1°C along the first flow direction A.

[0125] In further embodiments not shown, a plurality of steam generators shown in Figure 1 are connected in series in a cascade manner, and the steam generator comprises a housing 2, a first heat exchange element 3 and a second heat exchange element 4 located in the housing 2, and a heat transfer medium covering these heat exchange elements, together with an agitator 5 provided therein. In such embodiments, for example, flue gas having a high temperature of about 900°C flows into the first steam generator as a heat exchange fluid, transferring heat to a salt bath inside the first steam generator, and the salt bath is stirred by the agitator, thereby uniformly transferring the temperature to the second heat exchange element 4.

[0126] In this first steam generator, the agitator is used in particular to obtain a uniform temperature field along the first flow direction A within the salt bath housing 2. In this process, flue gas near the bottom of housing 2 flows into housing 2, is guided along the first flow direction A through a U-shaped tube section, is guided in stages upward in the opposite direction to the first flow direction A, and then flows out again at the highest point of the ceiling wall region of housing 2 of the first steam generator.

[0127] Next, the flue gas, having already released a first portion of its thermal energy into the salt bath in the first steam generator, is guided to a second steam generator having the same configuration as the first steam generator. However, in this case, the flue gas flows into the housing 2 from near the lid, i.e., from the upper surface of the housing 2, through the U-shaped tube section, is guided through the housing along the first flow direction A, is guided in the opposite direction of the first flow direction A, and finally flows out again from the second steam generator in the area of ​​the bottom wall of the housing 2.

[0128] In contrast to the first steam generator, in the second steam generator, the agitator 8 within the second steam generator may operate at a clearly lower level, making it possible to achieve a temperature gradient along the vertical line of the housing 2 in the salt bath, and thus clearly set the exhaust temperature of the flue gas at the outlet of the second steam generator.

[0129] In this context, the first steam generator, into which flue gas with a clearly higher temperature flows, can be filled with potassium nitrate-sodium nitrate as a heat transfer medium, while the second steam generator, through which the gas flows next, is filled with nitrate.

[0130] In other words, in this embodiment, the high-temperature steam generator is located upstream of the low-temperature steam generator. Similarly, it is possible that the second steam generator is used only for heating the second heat exchange element and no longer reaches a temperature sufficient for a change in the condensation state of water. In the second (low-temperature) steam generator, the presence of stratification of the salt bath is controlled primarily by stirring; that is, the stirrer can control whether a temperature gradient exists along the vertical line of the housing or whether the entire salt bath is homogeneous, as in the upstream high-temperature steam generator. [Explanation of symbols]

[0131] 1. Steam generator 2 Housing 3. First heat exchange element 4. Second heat exchange element 5. Stirring device 6 Housing entrance 7 Housing exit 8. Stirrer 9. Stirring blades 10 tubes 11 Mounting hardware 12 Tube Coils 13 Inlet nozzle

Claims

1. Housing (2); A first heat exchange element (3) is located within the housing (2) and can be permeated by a heat exchange fluid, preferably flue gas; At least one second heat exchange element (4) disposed within the housing (2) through which water can flow to generate steam; and A heat transfer medium in the form of a salt bath, placed within the housing, 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) to generate steam; In a steam generator (1) having, A stirring device (5) is provided on the housing (2) and reaches into the heat transfer medium. The steam generator (1) is characterized in that the stirring device (5) is configured to generate a flow within the heat transfer medium by stirring the heat transfer medium during the operation of the steam generator (1).

2. The steam generator (1) according to claim 1, wherein the stirring device (5) is configured to generate turbulence in the heat transfer medium by stirring the heat transfer medium during the operation of the steam generator (1).

3. The steam generator (1) according to claim 1 or 2, wherein the first heat exchange element (3) can be passed through by the heat exchange fluid from the inlet (6) of the housing (2) to the outlet (7) of the housing (2) in a first flow direction (A).

4. The steam generator (1) according to claim 3, wherein the cross-section of the first heat exchange element (3) at the inlet (6) of the housing (2) is larger than that at the outlet (7) of the housing (2).

5. The steam generator (1) according to claim 3 or 4, wherein the stirring device (5) has a plurality of stirrers (8) that each reach into the heat transfer medium and are dispersed along the first flow direction (A), preferably evenly distributed.

6. The steam generator (1) according to claim 5, wherein the stirring device (5) has a control device configured to individually control a plurality of stirrs (8).

7. The steam generator (1) according to claim 6, wherein the control device is configured to control the stirrers (8) so that the stirring speed of each of the stirrers (8) is less than 150 revolutions per minute during the operation of the steam generator (1).

8. The steam generator (1) according to claim 6 or 7, wherein the control device is configured to control at least one agitator (8) so as to agitate in the opposite direction to at least one further agitator (8) while the steam generator (1) is in operation.

9. The steam generator (1) according to any one of claims 6 to 8, wherein the control device is configured to control the agitator (8.1) on the inlet (6) side of the housing (2) to agitate at a higher stirring speed than the agitator (8.3) on the outlet (7) side of the housing (2) during operation of the steam generator (1).

10. The steam generator (1) according to any one of claims 6 to 9, wherein the control device is configured to control the agitator (8) such that the stirring speed of the agitator (8.1, 8.2, 8.3) decreases along the first flow direction (A) while the steam generator (1) is in operation.

11. Each of the aforementioned agitators (8) has a plurality of stirring blades (9) arranged in the region where the agitator reaches the heat transfer medium, The steam generator (1) according to any one of claims 5 to 10, wherein the stirring blade (9) is provided to generate a flow in the heat transfer medium by stirring the heat transfer medium during the operation of the steam generator (1).

12. The steam generator (1) according to claim 11, wherein the plurality of stirring blades (9) are distributed over the entire area in which the stirrer reaches the heat transfer medium, and preferably the stirring blades (9) of the stirrer (8) have uniform dimensions.

13. The steam generator (1) according to claim 11 or 12, wherein the agitator (8.1) on the inlet (6) side of the housing (2) has a stirring blade (9) that is larger than the agitator (8.3) on the outlet (7) side of the housing (2).

14. The first heat exchange element (3) has a plurality of tubes (10) that extend along the first flow direction (A), Each of the agitators (8) extends between the tubes (10), as described in any one of claims 5 to 13, for the steam generator (1).

15. The steam generator (1) according to any one of claims 1 to 14, wherein the salt bath comprises a nitrate, particularly preferably potassium nitrate-sodium nitrate, or potassium nitrate-sodium nitrate-calcium nitrate.

Images