Steam generator

Abstract

The invention relates to a steam generator (1) which comprises a housing (2) with an inlet (6) and an outlet (7), a first heat exchange element (3) which is arranged in the housing (2) and through which a heat exchange fluid, preferably flue gas, can flow in a first flow direction (A) from the inlet (6) to the outlet (7), and at least one second heat exchange element (4) which is arranged in the housing (2) and through which water can flow in order to generate steam. Furthermore, a salt bath is provided for absorbing and transferring thermal energy, wherein the salt bath is received in the housing (2) in order to absorb thermal energy and transfer same to the water flowing through the second heat exchange element (4) in order to generate steam. The steam generator additionally comprises an electric heating device (14) for heating the salt bath.

Description

[0001] STEAM GENERATOR

[0002] TECHNICAL FIELD

[0003] The present invention relates to a steam generator for temporarily storing energy and generating steam, which can be used, for example, to generate energy using a steam engine or a steam turbine. For this purpose, the steam generator can be coupled, for example, to a biomass furnace, biogas plant, or pellet heater.

[0004] BACKGROUND

[0005] Steam generators are generally used to generate steam. These steam generators usually have a combustion chamber (the furnace) in which fuel is heated or burned to generate heat. Alternatively, the still-hot exhaust gas from a biogas plant can be used to provide the required heat. This heat, in the form of a heat exchange fluid, is passed past a heat exchanger, for example, to evaporate water flowing in the heat exchanger. The resulting steam can then be used to generate energy, for example in a steam engine.

[0006] Efficient steam and power generation requires high pressures and, consequently, high temperatures. This leads to thermal stress on the heat exchanger and stresses in the heat exchanger material.

[0007] In the prior art, for example, DE 10 2010 046 804 A1 discloses a tube bundle heat exchanger with a plurality of tube windings which emanate from a common outlet space for a heat exchange fluid and open into a common outlet space, wherein each tube winding comprises an alternating sequence of tube pieces and tube bends, and wherein the tube bends are designed as a deflection of 180° with respect to an associated bend axis and have identical bending radii. This tube bundle heat exchanger is characterized in that along each tube winding, the bend axes of tube bends which are connected to the same tube piece are at an angle to one another, and the bend axes of tube bends between which a tube piece, a tube bend and another tube piece are arranged in direct succession run parallel.

[0008] However, the efficiency depends heavily on the distance between the shell-and-tube heat exchanger and the housing, as well as on the flow pattern of the heat exchange fluid in the shells and the heat energy generated by the fuel. This means that wall losses, which are caused by flowing past the shell-and-tube heat exchanger and a surrounding housing without flowing through the heat exchanger, cannot be prevented in this design. Thus, the heat exchange efficiency is not optimal.

[0009] Furthermore, according to such a design, it is not possible to compensate for stresses in the tube bundles caused by thermal expansion caused by the high temperatures of the heat exchange fluid.

[0010] DE 20 2007 017 403 Ul also discloses a tube-bundle heat exchanger, in particular for heat exchange between heating gas and heating water or drinking water. The tube-bundle heat exchanger has a water chamber through which a heating water flow or drinking water flow can flow, and a heating gas chamber through which a heating gas flow can flow. The heating gas tubes forming the heating gas can flow through the water chamber in parallel or in series.

[0011] The problems described above also arise here, and the efficiency of the heat exchange is low because it is operated in cocurrent. Furthermore, when generating steam with biomass in previously known steam generators, it is particularly critical to compensate for the undefined and potentially fluctuating energy content of the fuel mass (in contrast to coal, for example), and thus the fluctuating steam parameters during steam generation. If the fluctuating energy content cannot be adequately compensated, the steam temperature fluctuates, which - for example, when using steam turbines - can impair or even damage these steam turbines.

[0012] For this reason, previously known designs use an additional steam storage boiler in order to achieve low pressure losses and counteract the fluctuation.

[0013] However, such a design is no longer applicable at high pressures, for example above 250 bar, as there is a high risk of destruction, for example in the form of an explosion.

[0014] There is therefore a need for a solution for a steam generator for use with biomass and high pressures, which is not only high pressure resistant and safe, but also simple and cost-effective to implement.

[0015] To date, only EP 4 134 609 A1 discloses a first solution in the field of steam generators which addresses the above-described problems of the fluctuating energy content of the fuel mass while simultaneously ensuring high operational reliability. This is achieved by interposing a salt bath as a heat transfer medium between a first heat exchange element carrying the heat exchange fluid and a second heat exchange element carrying the water for steam generation in a (high-pressure) steam generator. The use of such a salt bath as a heat transfer medium in a steam generator was previously unknown in the technical field of steam generation devices.

[0016] Such salt baths have so far only been used in the remote technical field of solar power plants. For example, US 2012 / 067551 A1 discloses an arrangement with which solar energy, collected by parabolic mirrors in a solar park with solar panels, can be stored in such a salt bath. At a later time, for example, at night, the energy stored in the salt bath can then be used to generate electricity during periods of no sunlight, thus ensuring constant power generation.

[0017] There is therefore still a need for a steam generator that can not only ensure reliable operation and achieve high efficiency with a simple design and even with fluctuating energy content of the fuel mass, but also the need to expand the range of applications of steam generators.

[0018] PRESENTATION OF THE INVENTION

[0019] It is therefore an object of the present invention to provide an efficient device for steam generation (a steam generator) in which reliable operation can be ensured and high efficiency achieved with a simple design, even with fluctuating energy content of the fuel mass. Furthermore, not only should the above-mentioned disadvantages be reduced or even eliminated, but also electricity generation using such a steam generator in conjunction with a steam engine or a steam turbine should be implemented particularly efficiently.

[0020] This object is achieved by a device having the features of claim 1. Preferred embodiments can be found in the further claims, the following description and the drawings.

[0021] According to one aspect of the present invention, a steam generator comprises a housing. The housing comprises an inlet and an outlet. A first heat exchange element is arranged in the housing. A heat exchange fluid can flow through the first heat exchange element in a first flow direction from the inlet to the outlet.

[0022] The heat exchange fluid is preferably flue gas. Furthermore, the heat exchange fluid can be waste heat from a biomass furnace, biogas plant, or pellet heating system, which can flow through the first heat exchange element and thus through the steam generator. The heat exchange fluid can therefore be, for example, a combustion gas from the combustion of a fuel, for example in the form of undried, low-quality biomass, in a combustion chamber of a conventional moving grate furnace, or the exhaust gas from a biogas plant. This allows electricity to be generated from residual materials.

[0023] Depending on the heat exchange fluid, different temperature ranges can occur in the steam generator. Such a heat exchange fluid, which is also referred to as a heating fluid or heating gas, or generally a combustion gas, typically has a temperature between 600 °C and 1200 °C, preferably 1000 °C.

[0024] Separately, the homogeneous heat transfer properties of the salt bath, which will be explained in more detail below, allow temperatures of the heat exchange fluid of over 1000 °C, in particular 1300 °C and more, to be "run" without endangering the safety of the steam generator.

[0025] If exhaust gas from a biogas plant is used as a heat exchange fluid, temperatures of the heat exchange fluid, i.e. gas temperatures, of 450 ° C to 500 ° C, preferably 470 ° C, usually occur in the steam generator.

[0026] In addition, a second heat exchanger element is provided in the housing, through which water can flow to generate steam. This can be water, preheated water, or saturated steam.

[0027] Furthermore, a salt bath is incorporated into the housing for optimized absorption and transfer of (heat) energy. In other words, the housing is filled with a salt bath as a heat transfer medium. The salt bath is specifically incorporated into the housing to absorb heat energy and transfer it to the water flowing through the heat exchange element to generate steam.

[0028] The salt bath is therefore designed for the temporary storage (absorption) and transfer from one heat exchange element (here, the first heat exchange element) to another heat exchange element (here, the second heat exchange element). In other words, the salt bath serves, among other things, for the temporary storage of energy by initially "coupling" it into the salt bath. Furthermore, the salt bath is designed to transfer the coupled heat to the second heat exchange element. This allows the water flowing through the second heat exchange element to be heated and steam to be generated.

[0029] In addition, the salt bath serves as a "buffer" to compensate for the fluctuating heat input, e.g. from the first heat exchange element due to the fluctuating energy content of the fuel mass and / or the subsequent electrical heating device described in more detail, to the salt bath. Such a steam generator therefore offers a "high degree of forgiveness" with regard to temperature fluctuations and fluctuating energy contents. This means that even with strongly fluctuating temperature peaks, e.g., of the heat exchange fluid, a homogeneous heat transfer or heat input into the water for steam generation can be achieved thanks to the salt bath. The steam generator also has an electrical

[0030] Heating device for heating the salt bath to .

[0031] The electric heating device is designed to convert additional electrical energy from outside the steam generator into thermal energy and store it temporarily in the salt bath, for example, for several hours or days. With appropriate housing insulation and sufficiently large quantities of salt (e.g., 30 tons of salt), storage for weeks is even possible.

[0032] The electrical heating device thus enables additional energy in the form of thermal energy to be coupled into the salt bath and stored there temporarily by converting electrical energy into thermal energy and transferring it to the salt bath.

[0033] To date, only configurations known for solar power generation involve heating a salt bath using solar energy, and then using the stored heat energy to generate electricity at a later time, e.g., at night, by generating steam and then using the steam in a steam turbine or steam engine. This allows voltage peaks in pure power generation to be balanced out, and electricity can be produced even when the sun isn't shining.

[0034] However, unlike the state of the art, steam generators that can additionally heat such a salt bath using electrical energy and thus not only contribute to the actual, homogeneous steam generation, but also have an energy storage function, are not known.

[0035] In the present configuration, surplus electricity generated, for example, by wind or solar energy can be temporarily stored without having to feed it directly into the power grid for a low price per kilowatt hour.

[0036] Furthermore, the salt bath of the steam generator not only serves to produce steam homogeneously with high reliability and low risk, but also as a temporary energy storage device which – unlike conventional batteries – is hardly exposed to aging processes and therefore hardly any loss of efficiency over the operating period. This makes it possible to create a particularly efficient and sustainable solution for intermediate energy storage and steam generation, e.g. for downstream power generation. Longevity is also significantly increased by storing energy in salt compared to conventional accumulators or batteries. Furthermore, the price for energy storage, i.e. the price per stored kilowatt or megawatt hour, is significantly lower in a salt bath than with conventional battery storage systems. Accordingly, the steam generator can be understood as a device for the temporary storage of energy and generation of steam.

[0037] The present invention is therefore based on the core idea of ​​providing a steam generator, which can generate steam as homogeneously as possible, with an additional electrical heating device, so that temporarily excess energy can be stored in the salt bath in the form of heat and can be used at a desired time to generate steam and thus, for example, by means of a steam turbine or steam engine to generate electricity.

[0038] Preferably, the salt bath is accommodated in the housing to absorb thermal energy from the heat exchange fluid flowing through the first heat exchange element and / or from the electrical heating device.

[0039] Accordingly, depending on the application, either the

[0040] Steam generators can be used purely for generating steam by transferring energy from the heat exchange fluid flowing through the first heat exchange element to the salt bath and from the salt bath in turn homogeneously to the water flowing in the second heat exchange element to heat it and thus generate steam.

[0041] If, for example, no steam and / or the electricity generated from it is required, but electrical energy, i.e., electricity, from an external energy source is to be temporarily stored for later use, the steam generator can also be used as a battery. The battery function is achieved by heating the salt bath predominantly or even exclusively with the electric heater instead of the heat exchange fluid.

[0042] Independently of this, parallel operation is also conceivable, whereby energy is transferred from the heat exchange fluid and from the electrical heating device to the salt bath.

[0043] Preferably, the electric heating device is designed to heat the salt bath using an external energy source, in particular from a photovoltaic system and / or a wind turbine.

[0044] This allows (electrical) energy from an external energy source to be fed into the steam generator, particularly its salt bath, by converting electrical energy into thermal energy and temporarily storing it in the form of heat. This again demonstrates that the steam generator in question has been supplemented with a battery function.

[0045] This is particularly advantageous when generating electricity using renewable energies, since in times of high energy availability, for example when there is strong wind in the case of wind power, or strong solar radiation in the case of solar energy, the surplus electricity does not have to be fed into the power grid immediately, but can be used to generate steam and therefore electricity using the steam generator at a desired time in the future, for example when the wind dies down or there is no solar radiation at night.

[0046] Preferably, the electrical heating device is an electrical resistance heater.

[0047] The electric heater can therefore also be understood as an ohmic resistance heater, in which electricity is converted into thermal energy. This means that the electric heater generates heat by flowing current through a conductor with electrical resistance. Due to the resistance, the conductor heats up, and the electrical energy is converted into thermal energy, which, in this case, is transferred from the electric heater to the salt bath contained in the housing. Thus, excess electricity from an external energy source can be temporarily stored in the form of thermal energy in the steam generator's salt bath.

[0048] Preferably, the electrical heating device is arranged on the housing in such a way that it extends into the salt bath.

[0049] The electric heating device is therefore in direct contact with the salt bath, ensuring efficient heat transfer to the salt bath. This allows for a high overall efficiency of the device.

[0050] In an alternative embodiment, it would also be conceivable for the electrical heating device to be arranged on the housing and for the heat energy to be transferred to the salt bath by heating the housing itself.

[0051] Preferably, the electric heating device comprises a heating rod extending into the salt bath.

[0052] Particularly preferably, this heating rod can have an elongated main extension direction and a circular cross-section. The heating wire extends spirally through the interior of the heating rod along the main extension direction of the heating rod.

[0053] Regardless of the geometric design, the design of the heating rod, which extends into the salt bath, enables cost-effective and, above all, efficient heating of the salt bath.

[0054] The heating element is preferably designed with a surface made of steel in accordance with EN 1.4571.

[0055] This is a particularly corrosion-resistant steel, so that even in contact with the hot salt bath, which is liquid under operating conditions, there is no danger whatsoever, even during long periods of operation at high operating temperatures.

[0056] However, the design of the heating element surface that comes into contact with the salt bath is not limited to steel according to EN 1.4571. Depending on the salt mixture or heat exchange fluid used, it is also conceivable to use other types of steel or even titanium for the surface that reaches into the salt bath.

[0057] surface of the heating element.

[0058] The steam generator preferably further comprises a stirring device. This is arranged on the housing and extends into the salt bath. In other words, the stirring device is at least partially surrounded by the salt bath. The stirring device is designed to generate a flow within the salt bath by stirring the salt bath during operation of the steam generator.

[0059] The term "flow" is to be understood in this context as meaning that the salt bath in the housing is set into motion, preferably a circulating motion, so that the salt bath moves in the housing during operation of the steam generator. Specifically, this circulation of the salt bath in the housing achieves a significantly more homogeneous temperature field than, for example, when using a pump in the salt bath. At the same time, local overheating can be prevented.

[0060] Furthermore, the circulation of the salt bath in the housing by means of a stirring device creates a homogeneous temperature field with a very high heat transfer coefficient. This is advantageous both for heat transfer from the heat exchange fluid to the salt bath and from the electric heating device to the salt bath. Particularly high heat transfer coefficients occur at (high) pressures of over 250 bar, preferably over 300 bar.

[0061] By means of such a design, the temperature difference between the salt bath and the water or steam in the second heat immersion element can be 1 ° C or less.

[0062] This also makes it possible to prevent a temperature difference in the salt bath across the extension of the housing and thus to prevent the occurrence of local hotspots or strongly diverging efficiencies of the heat transfer from the salt bath to the water in the second heat exchange element.

[0063] Such a homogeneous temperature field in the salt bath also enables homogeneous heat transfer in the salt bath itself. This enables a particularly flexible design of the steam generator or the steam generator housing. In concrete terms, this means that a steam generator housing can have a wide variety of shapes and geometries without the risk of local hotspots or excessively strong temperature gradients in the salt bath. This in turn is positive because it requires less calculation and design effort to design an efficient steam generator. Salts can be used as the salt bath which change from a crystalline to a liquid state, i.e. an operating state, at temperatures as low as 130°C - 150°C or 235°C. The salt bath can preferably be a nitrate salt, particularly preferably a potassium sodium nitrate or a potassium sodium calcium nitrate.

[0064] The nitrate salt is not only particularly cost-effective, but can also be used for heat transfer at high heat exchange fluid temperatures, such as flue gas temperatures of up to 900°C, without chemical decomposition. For example, potassium sodium nitrate can be used continuously and without risk of decomposition at salt bath temperatures up to 560°C. This allows for the most reliable and efficient steam generator design possible.

[0065] At the same time, potassium sodium nitrate is particularly temperature-stable, making it ideal for efficient heat transfer and storage. For example, a salt bath temperature of 350°C to 565°C can be used without compromising the operational safety of the steam generator.

[0066] Preferably, the salt bath covers at least the first heat exchange element and the second heat exchange element.

[0067] According to such a design, both the first and second heat exchange elements are completely surrounded by the salt bath. This allows for particularly reliable, efficient, cost-effective, and flexible steam generation, as the salt bath enables high heat transfer at various temperatures, and the stirring device prevents local temperature peaks in the salt bath.

[0068] In the present heat exchange arrangement of the steam generator, pressures between 50 and 800 bar, preferably 30 to 500 bar, particularly preferably 30 to 180 bar, but also lower pressures between 4 and 10 bar steam pressure can be generated.

[0069] This means that such an arrangement can be used particularly flexibly due to the heat-transferring salt bath and both low pressures in the range of, for example, seven bar for food production and high-pressure steam flows in the range of 500 to 800 bar can be generated without the fluctuating energy content of the biomass being critical for the device itself.

[0070] A complex arrangement with an additional dam storage boiler, as was previously common in the state of the art to achieve low pressure losses, is also unnecessary in such a design. This allows for the realization of not only a particularly flexible and reliable, but also cost-effective steam generation device, which can also be implemented in a particularly compact design.

[0071] In contrast to previously known steam generators, it is also possible to provide a plurality of pipes arranged parallel to one another in the housing, i.e. a plurality of second heat exchange elements, which are surrounded by a salt bath. In other words, a plurality of steam generation lines are provided in the housing and surrounded by the salt bath. Accordingly, when only one steam generator is in operation, steam can be generated at different pressures at the same time. For example, thanks to the large number of second heat exchange elements, steam can be generated at 7 bar, 11 bar, 100 bar and 200 bar in a single steam generator housing, as required. This means that, for example, a pure steam rail can be provided for food production and a further high-pressure rail for a steam engine or a turbine for power generation.

[0072] Due to the flow through the first heat exchange element along the first flow direction from the inlet of the housing to the outlet of the housing, a heat transfer can take place across the first flow direction from the heat exchange fluid to the heat transfer medium, here the salt bath, and from the salt bath to the water flowing in the second heat exchange element.

[0073] It is preferred 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.

[0074] The "cross-section of the first heat exchange element" is to be understood as an internal dimension. If the "first heat exchange element" is designed, for example, as a cylindrical tube, the "cross-section of the first heat exchange element" is to be understood as the internal diameter of the tube. In other words, the "cross-section of the first heat exchange element" is to be understood as the effective flow cross-section of the first heat exchange element.

[0075] By changing the cross-section between the inlet and outlet of the housing, the energy input from the heat exchange fluid into the salt bath can be designed as large as possible at the beginning. At the same time, local overheating or decomposition of the salt bath can be prevented and operational reliability increased. This is due to the fact that the initial flow velocities of the heat exchange fluid can be reduced due to the larger flow cross-section. This results in lower flow velocities when the flue gas, for example, enters the first heat exchange element. Accordingly, overheating of the salt bath and its potential decomposition can be prevented.

[0076] The flexibility of the steam generator is particularly advantageous and the generation of the desired steam pressure is particularly easy to control.

[0077] The stirring device preferably has a plurality of agitators. Each of these agitators extends into the salt bath. The agitators can be distributed along the first flow direction. Particularly preferably, the agitators are evenly distributed along the first flow direction.

[0078] Preferably, the first heat exchange element comprises a plurality of tubes extending parallel to one another along the first flow direction. The electric heating device extends between the tubes in the salt bath.

[0079] Due to the arrangement of the electric heating device between the tubes in the salt bath as a heat transfer and temporary storage medium, steam can be generated homogeneously regardless of the heat source. Accordingly, a particularly flexible and multi-applicable steam generation device can be created with just one compact device. Furthermore, the steam generator can be used as a temporary "battery" or "accumulator", which, unlike conventional lithium-ion batteries, can be used over a long operating time with a consistently high level of efficiency and negligible aging process. Furthermore, significantly more cost-effective (temporary) energy storage can be achieved without strategic materials such as lithium.

[0080] This makes it possible to create a particularly durable and sustainable steam generator with energy storage function.

[0081] Particularly preferably, the tubes of the first heat exchange element can be smooth tubes, i.e. tubes without fins, projections or the like.

[0082] This is particularly advantageous because it prevents potential ash residue from a heat exchange fluid or any other deposits from accumulating in the first heat exchange element. This drastically reduces service intervals for the steam generator and ensures consistently high efficiency. Depending on the application, the housing can be made of stainless steel or carbon steel. Using stainless steel ensures high corrosion resistance, even at higher operating temperatures, and enables reliable and safe operation of the steam generator over a longer period.

[0083] The second heat exchange element is preferably designed in the form of a plurality of pipes in fluid communication. Water can flow through the pipes in a second flow direction to generate steam. Such a second heat exchange element thus consists of a plurality of pipes connected in series and connected to one another, which are in fluid communication with one another in such a way that water flowing through this second flow direction is converted into a vaporous aggregate state by indirect heating by means of the salt bath and the heat exchange fluid and / or the electric heating device.

[0084] The pipes preferably extend through the housing with U-shaped pipe windings such that the pipes run substantially perpendicular to the first flow direction. In other words, the pipes of the second heat exchange element extend through the housing with U-shaped pipe windings such that the second flow direction and the first flow direction run substantially perpendicular to one another.

[0085] Preferably, pressure relief valves, particularly preferably mechanical pressure relief valves, are provided on the pipes, which are arranged such that the volume within the pipes between two pressure relief valves is a maximum of two liters each. Even more preferably, the pressure relief valves are arranged such that the volume within the pipes between two pressure relief valves is in a range between 1.8 and 1.9 liters, most preferably 1.87 liters. Here, the "volume within the pipes" refers to the internal flow diameter of the series-connected and connected pipes of the at least one second heat exchange element and its extension length.

[0086] The term "pressure relief valve" is to be understood as a valve which is designed in such a way that it can interrupt the flow in the pipes of the second heat exchange element by allowing the water flowing through the pipes to escape when a predetermined pressure limit within the pipe is reached and / or exceeded. This means that water or steam can escape from the sections of the second heat exchange element which are individually sealed off with pressure relief valves in the event of excess pressure from the pipes. Accordingly, a maximum load with potentially excessive pressure in the water / steam can be limited to a pipe volume of two liters.

[0087] Accordingly, there cannot be an area in the second heat exchange element in which the internal pipe volume is more than two liters without a pressure relief valve provided in between.

[0088] The pressure relief valves ensure that all pipes containing the pressurised water used to generate steam are separately sealed off at least every two litres of pipe volume, and the volume per such "pull" is < 2 litres.

[0089] According to such an arrangement, in the event of (local) overpressure situations that could be potentially dangerous for the steam generator, relief can occur because the water or steam can escape from the second heat exchange element through the pressure relief valves.

[0090] In addition, the relevant load range is limited to a maximum pipe volume of less than or equal to two liters, so that such a steam generator is no longer subject to the "Pressure Equipment Directive 2014 / 68 / EU" and its categorization in categories 1 to 4.

[0091] This is due to the fact that such a steam generator falls outside the requirements for categorisation under the Pressure Equipment Directive due to the limited volume range of each water or steam carrying element (here the second heat exchange element).

[0092] Since any pipe section of one or more pipelines in fluid communication has a maximum volume of two liters between two of the pressure relief valves, no approval is required and routine mandatory maintenance no longer has to be carried out.

[0093] In particular, the presence of a mechanical pressure relief valve means that no electronic components, controls, sensors or the like are required, while still ensuring safe operation of the steam generator and / or automatic opening of the valve when the pressure in the water or steam pipes reaches and / or exceeds a certain pressure value. For example, such a mechanical pressure relief valve can be pre-tensioned with a spring, so that when the prevailing pressure within the pipes exceeds the force acting on the spring, the pressure relief valve opens automatically against the spring force, allowing water to escape from the pipes of the at least one second heat exchanger element.

[0094] Preferably, a plurality of second heat exchange elements are provided in the housing, through which water can flow parallel to one another to generate steam.

[0095] Furthermore, the provision of a plurality of second heat exchange elements through which water can flow parallel to one another in the second flow direction makes it possible to draw off or generate different water / steam temperatures from the steam generator. This can be controlled in particular via the flow rate of the water through the respective second heat exchange elements. Furthermore, a plurality of second heat exchange elements arranged parallel to one another in the housing make it possible to increase the amount of heated water generated without having to increase the overall volume or the dimensions of the steam generator housing.

[0096] BRIEF DESCRIPTION OF THE DRAWINGS

[0097] A steam generator according to an exemplary embodiment is described below using a schematic drawing. Such steam generators are used, for example, to generate steam for energy production, in particular electricity generation, for example in a steam engine or steam motor. It shows:

[0098] Figure 1: a cross-sectional view of a steam generator according to an exemplary embodiment.

[0099] DESCRIPTION OF THE PREFERRED EMBODIMENT

[0100] Figure 1 illustrates a steam generator 1 according to an exemplary embodiment of the present invention. Figure 1 shows a cross-sectional view of the steam generator 1, wherein the section axis runs along the longitudinal extent of the steam generator (i.e., along the first flow direction A, which will be explained in more detail later), in order to make the interior of the steam generator visible. Figure 1 can therefore also be understood as a side view of the steam generator, in which a side wall has been removed along the longitudinal extent in order to make the interior of the steam generator visible.

[0101] The steam generator according to Figure 1 has a housing 2 with a

[0102] floor wall, a ceiling wall, a rear wall and two side walls. As mentioned at the beginning,

[0103] Illustration of the interior of the steam generator 1, the front wall of the housing 2 not visible.

[0104] In the embodiment shown, the housing 2 is designed in a "box-like" manner. This means that it extends essentially along a longitudinal direction of the housing 2 and has a rectangular cross-section.

[0105] However, due to the inventive design of the steam generator 1, the width and / or height as well as the length of the housing 2 are not limiting for steam generation and can be configured according to space requirements and / or desired design.

[0106] The housing 2 has an inlet 6 on the side wall of the housing 2 shown on the left in Figure 1 and an outlet 7 on the opposite side wall of the housing 2 shown on the right in Figure 1.

[0107] A first heat exchange element 3 is arranged within the housing 2. A heat exchange fluid can flow through this 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 would be the waste heat from a biogas plant.

[0108] 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 a first flow direction A from the inlet 6 of the housing 2 to an outlet 7 of the housing 2.

[0109] In the embodiment shown, the first flow direction A corresponds to the longitudinal extent of the housing 2. This configuration allows flue gas to flow through the first heat exchange element 3 in the form of a plurality of tubes 10 in the first flow direction A from the inlet 6 to the outlet 7, and can thus release thermal energy into the interior of the steam generator 1.

[0110] In the following description, flue gas generated by biomass combustion is used as an example of a heat exchange fluid. Another example of such a heat exchange fluid would be the waste heat from a biogas plant.

[0111] Not shown in Figure 1 are U-shaped pipe sections which extend the flow path of the flue gas through the first heat exchange element 3 in such a way that a plurality of pipes 10 arranged in the housing 2 can be connected to one another by U-shaped pipe sections, so that the flow path through the first heat exchange element 3 can be extended and in the example shown in Figure 1 the flue gas not only enters at the left side wall, i.e. at the inlet 6 of the housing, and flows once 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 in Figure 1.Rather, the flue gas enters the pipe at the inlet 6 through the U-shaped pipe sections, runs completely through the longitudinal extent of the housing 2 to the side of the outlet 7, is then guided in a further pipe 10 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, before it can run through a further U-shaped pipe section again from the side of the inlet 6 of the housing 2 to the outlet 7 of the housing 2 along the first flow direction A.

[0112] In this context, the flue gas can, for example, be introduced at a lowest section of the housing 2 and expelled at a highest section of the housing 2. A contrary design is also possible: the flue gas can enter at a highest section of the housing 2, be guided through U-shaped pipe sections through the housing 2 along the first flow direction A and opposite to the first flow direction A through the housing 2, and be expelled again at a lowest section of the housing 2.

[0113] In the embodiment shown, inlet 6 and outlet 7 are arranged in the side walls of the housing. However, the present invention is not limited thereto. It would also be conceivable for inlet 6 and outlet 7 to be provided on a front wall and a rear wall of the housing, or on a bottom wall and a ceiling wall, as well as mixtures thereof.

[0114] Separately, in the embodiment shown in Figure 1, a second heat exchange element 4 is located in the housing 2. Water can flow through this second heat exchange element 4 to generate steam. While in the preferred embodiment, a flue gas flows as a heat exchange fluid in the first heat exchange element 3, the second heat exchange element 4 is filled with water, or water flows through the second heat exchange element to be heated by the device.

[0115] For this purpose, the water in the second heat exchange element 4 is heated (indirectly) by the first heat exchange element 3 or the flue gas flowing therein and / or the electric heating device 14 described in more detail below, and thus converted from a liquid state into a vaporous state. This steam can then be used, for example, to generate electricity. The electricity can be used in a steam engine and / or a steam turbine, which is fed with the generated steam.

[0116] In the embodiment shown, the second heat exchange element 4 is designed as a single tube which extends with windings through the housing 2 of the steam generator 1. According to a further embodiment not shown, it is also possible to provide a plurality of second heat exchange elements 4 in the housing 2, through which water can flow parallel to one another. In this way, different steam pressures or the like can be achieved. In addition, for example, the steam from one second heat exchange element can be used for production purposes, heating, etc., while the steam from another second heat exchange element is used to generate electricity.

[0117] In this embodiment, the flow direction of the water in the second heat exchange element 4 is referred to as the “second flow direction”.

[0118] As can be seen from the figures, the second heat exchange element 4 in the form of a tube has a plurality of tube windings 12. These tube windings 12 are, as can be seen in Figure 1, arranged in the housing 2 in such a way that the second heat exchange element 4 extends essentially perpendicular to the first flow direction A from the inlet 6 of the housing 2 to the outlet 7 of the housing 2 and, with U-shaped tube winding sections, achieves the greatest possible tube length and thus tube surface area along its extension from the inlet 6 to the outlet 7 of the housing 2.

[0119] While the tubes 10 of the first heat exchange element 3 extend straight (in the longitudinal direction) from the inlet 6 to the outlet 7 of the housing 2, the tube of the second heat exchange element 4 has a plurality of tube sections which, in the embodiment shown, run vertically, so that the tube windings 12 connected to U-shaped tube winding sections extend substantially perpendicular to the first flow direction A from the inlet 6 to the outlet 7 of the housing 2.

[0120] As can be seen in Figure 1, the cross-section of the first heat exchange element 3 at the inlet 6 of the housing 2 is larger than at an outlet 7 of the housing 2. This makes it possible to reduce the flow velocity of the flue gas as heat exchange fluid upon entering the housing 2.

[0121] A heat transfer medium is also arranged in the housing 2 in order to transfer heat from the heat exchange fluid flowing through the first heat exchange element 3 (here flue gas) to the water flowing through the second heat exchange element 4 in order to generate steam. In the described 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 in the housing 2.

[0122] Accordingly, this salt bath can serve as a heat transfer medium and energy storage in order to increase the homogeneity of energy transfer and to control the temporary availability of steam more flexibly.

[0123] As shown in Figure 1, this salt bath can be filled into the housing 2 via an inlet nozzle 13. The salt bath can contain a nitrate salt, in particular a potassium-sodium nitrate or a potassium-sodium-calcium salt.

[0124] In a further embodiment not shown, the heat transfer medium can be a thermal oil which is arranged in the housing for homogeneous heat transfer.

[0125] In the following exemplary embodiment, however, a salt bath is assumed as the heat transfer medium.

[0126] As can be seen from Figure 1, the steam generator has a stirring device 5 on the housing 2. The stirring device is provided to set the salt bath in motion during operation of the steam generator by stirring it. This improves the heat transfer from the first heat exchange element 3 to the salt bath, from the electrical heating device 14 (described in more detail below) to the salt bath, the heat transfer within the salt bath itself, and from the salt bath to the second heat exchange element 4.

[0127] In the embodiment shown in Figure 1, this stirring device 5 is implemented in the form of a plurality of stirrers, i.e., three stirrers 8.1, 8.2, and 8.3. Each of these stirrers extends into the heat transfer medium covering the first heat exchange element 3 and the second heat exchange element 4.

[0128] Here, the three agitators 8 are attached to the top of the housing 2 by means of suspensions 11 and can extend into the interior of the housing 2 via a flange, in particular a sealed flange. However, the arrangement of the agitators 8 of the agitator device 5 is not limited to attachment to the top of the housing. It is also conceivable to arrange the agitators on the side of the housing or even in the bottom area of ​​the housing and from there extend into the salt bath in the housing.

[0129] In the following, as shown in Figure 1, it is assumed that the stirring device 5 is arranged on the top side of the housing.

[0130] The plurality of agitators 8 are arranged distributed along the first flow direction A so that agitation of the salt bath can be achieved.

[0131] In other words, the stirring device 5 in the form of a plurality of agitators 8 is designed to generate a flow within the salt bath by stirring the salt bath during operation of the steam generator 1. The agitators 8 are provided with a motor, each of which is provided with a metal tube extending into the salt bath, so that a rotational force of the motor can be transmitted to the metal rod.

[0132] In the area where this metal rod of the agitator 8 is located within the salt bath located in the housing 2, a plurality of agitator blades 9 are provided. The agitator blades 9 of the agitators 8 are arranged such that each of the agitators 8 extends between the tubes 10 of the first heat exchange element 3 and the tube coils 12 of the second heat exchange element 4.

[0133] Furthermore, the embodiment according to Figure 1 shows that the steam generator has an electric heating device 14 for additional heating of the salt bath. Accordingly, the salt bath is accommodated in the housing to absorb thermal energy from the flue gas flowing through the first heat exchange element and / or from the electric heating device.

[0134] This allows for the creation of a steam generator with an additional energy storage function, i.e., a battery function. Unlike conventional batteries, however, the salt bath results in negligible aging processes, thus creating a particularly sustainable and long-term solution for temporarily storing energy, for example, for later power generation using the generated steam.

[0135] Here, the electric heating device 14 can be operated using an external energy source 15, such as a photovoltaic system and / or a wind turbine, to heat the salt bath by means of the electric heating device 14. Thus, among other things, excess electricity, for example from a photovoltaic or wind turbine, can be (temporarily) stored in the salt bath and contributes to steam generation.

[0136] As can be seen from the side view of the steam generator in Figure 1, the exemplary embodiment of the electric heating device 14 is realized by three heating rods 14 distributed here along the first flow direction A, which are arranged on the housing such that they each extend into the salt bath (not shown). Specifically, a flange, in particular a sealed flange, is provided on the housing, which ensures the arrangement of the heating rods 14 in contact with the salt bath and their extension through the salt bath.

[0137] In Figure 1, the heating rods extend from the top of the housing 2. It is understood, however, that this is not the only possible arrangement for the heating rods 14. It is also conceivable for them to extend laterally, i.e., along the first flow direction, through the interior of the housing and thus through the salt bath.

[0138] In the preferred embodiment shown in Figure 1, the surface of the heating rod 14(s) in contact with the salt bath is made of steel according to EN 1.4571. Depending on the selected fluid and / or salt bath, it is also possible to provide heating rods with a titanium surface or heating rods made of titanium. However, the following description of the preferred embodiment assumes steel according to EN 1.4571.

[0139] In addition, the external energy source 15, here for example the generator of a wind power plant / wind turbine, is connected by power lines 16 to the respective heating rods of the electrical heating device 14.

[0140] In a further embodiment not shown, it is also conceivable that mechanical pressure relief valves are arranged on the pipes of the second heat exchange element 4 or the second heat exchange elements 4 such that the volume within the pipes between two pressure relief valves is a maximum of two liters. In this case, the pressure relief valves of each second heat exchange element 4 are arranged on the top side of the housing outside the housing 2, so that in the event of an overpressure situation, at a corresponding opening of the valve, water or steam from the respective second

[0141] Heat exchange element 4 can flow.

[0142] LIST OF REFERENCE SYMBOLS

[0143] 1 steam generator

[0144] 2 housings

[0145] 3 First heat exchange element

[0146] 4 Second heat exchange element

[0147] 5 Stirring device

[0148] 6 Housing inlet

[0149] 7 Outlet of the housing

[0150] 8 agitator

[0151] 9 stirring blades

[0152] 10 pipe

[0153] 11 Suspension

[0154] 12 pipe winding

[0155] 13 Inlet nozzles

[0156] 14 electric heating device (heating rod)

[0157] 15 external energy source

[0158] 16 power line

[0159] A first flow direction

Claims

CLAIMS 1. Steam generator (1), comprising: a housing (2) with an inlet (6) and an outlet (7); a first heat exchange element (3) arranged in the housing (2), through which a heat exchange fluid, preferably flue gas, can flow in a first flow direction (A) from the inlet (6) to the outlet (7); at least one second heat exchange element (4) arranged in the housing (2), through which water can flow to generate steam; a salt bath for absorbing and transferring thermal energy, wherein the salt bath is accommodated in the housing (2) in order to absorb thermal energy and to transfer it to the water flowing through the second heat exchange element (4) to generate steam; characterized by an electrical heating device (14) for heating the salt bath.

2. Steam generator (1) according to claim 1, wherein the salt bath is accommodated in the housing (2) to absorb thermal energy from the heat exchange fluid flowing through the first heat exchange element (3) and / or from the electric heating device (14).

3. Steam generator (1) according to claim 1 or 2, wherein the electrical heating device (14) is designed to heat the salt bath using an external energy source (15), in particular from a photovoltaic system and / or from a wind turbine.

4. Steam generator (1) according to one of the preceding claims, wherein the electrical heating device (14) is an electrical resistance heater.

5. Steam generator (1) according to one of the preceding claims, wherein the electric heating device (14) is arranged on the housing (2) in such a way that it extends into the salt bath.

6. Steam generator (1) according to one of the preceding claims, wherein the electrical heating device (14) comprises a heating rod extending into the salt bath.

1. Steam generator (1) according to claim 6, wherein the heating rod has a surface made of steel according to EN 1.4571.

8. Steam generator (1) according to one of the preceding claims, further comprising a stirring device (5) which is arranged on the housing (2) and extends into the salt bath, wherein the stirring device (5) is designed to generate a flow within the salt bath by stirring the salt bath during operation of the steam generator (1).

9. Steam generator (1) according to one of the preceding claims, wherein 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).

10. Steam generator (1) according to one of the preceding claims, wherein the first heat exchange element (3) comprises a plurality of tubes (10) extending parallel to one another along the first flow direction (A), and the electrical heating device (14) is located between the tubes (10) in the salt bath.

11. Steam generator (1) according to one of the preceding claims, wherein the salt bath comprises a nitrate salt, preferably a potassium-sodium nitrate or a potassium-sodium-calcium nitrate.

12. Steam generator (1) according to one of the preceding claims, wherein the second heat exchange element (4) is designed in the form of a plurality of pipes in fluid communication, and wherein, preferably, the pipes extend through the housing (2) with U-shaped pipe windings (12) such that the pipes run substantially perpendicular to the first flow direction (A).

13. Steam generator (1) according to claim 12, wherein pressure relief valves, preferably mechanical pressure relief valves, are arranged on the pipes such that the volume within the pipes between two pressure relief valves is a maximum of two liters each.

14. Steam generator (1) according to one of the preceding Claims, wherein a plurality of second heat exchange elements (4) are provided in the housing (2), through which water can flow parallel to one another.

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