EP4273447A1 - Steam generator - Google Patents

Abstract

Steam generator (1), comprising: a housing (2); a flow channel through which a heat exchange fluid, preferably flue gas, can flow from an inlet of the flow channel to an outlet of the flow channel, at least a portion of the flow channel being arranged as a first heat exchange element (3) in the housing (2); at least one second heat exchange element (4) arranged in the housing (2), through which water can flow to generate steam; a heat transfer medium arranged in the housing (2) to transfer heat from the heat exchange fluid flowing through the flow channel to the water flowing through the second heat exchange element (4) to generate steam, characterized in that the heat transfer medium is a salt bath, and the Cross section of the flow channel is larger at the inlet of the flow channel than at the outlet of the flow channel.

Description

TECHNICAL FIELD

The present invention relates to a steam generator for generating steam to generate energy, for example by means of a steam engine or a steam turbine. For this purpose, the steam generator can be coupled to a biomass furnace, biogas plant or a pellet heater, for example.

BACKGROUND

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 transfer medium is conducted past a heat exchanger, for example, in order to evaporate water flowing in the heat exchanger. The water vapor generated in this way can then be used to generate energy, for example in a steam engine.

To generate steam and energy efficiently, high pressures and associated high temperatures are required. This leads to thermal expansion of the heat exchanger and stresses in the material of the heat exchanger.

In the prior art, for example, DE 10 2010 046 804 A1 a tube bundle heat exchanger with a plurality of tube windings extending from a common outlet space for a heat exchange medium and into one common outlet space, each pipe winding comprising an alternating sequence of pipe sections and pipe bends and the pipe bends being designed as a deflection of 180 ° with respect to an assigned bend axis and having the same bending radii. This tube bundle heat exchanger is characterized in that along each tube winding the arch axes of pipe bends that are connected to the same pipe section are in an angular position to one another and the arch axes of pipe bends between which a pipe section, a pipe bend and another pipe section are arranged in direct succession, run parallel.

However, the efficiency here depends heavily on the distance of the tube bundle heat exchanger to the housing and strongly on the type of flow of the heat exchange fluid in the tube bundles to the thermal energy generated by fuel. This means that wall losses, which are generated by a flow past between the tube bundle heat exchanger and a surrounding housing without the heat exchanger being flowed through, cannot be prevented in such a configuration. The heat exchange efficiency is therefore not optimal.

Furthermore, according to such a configuration, it is not possible to compensate for stresses in the tube bundles due to thermal expansion generated by the high temperatures of the heat exchange fluid.

Also the DE 20 2007 017 403 U1 discloses a tube bundle heat exchanger, in particular for the heat exchange from heating gas to heating water or drinking water, the tube bundle heat exchanger having a water space through which a heating water flow or drinking water flow can flow and a heating gas space through which a heating gas flow can flow. The heating gas pipes forming the heating gas are parallel or can be flowed through in series.

The problems described above also occur here and the efficiency of the heat exchange is low because it is operated in direct current.

In addition, when generating steam with biomass in previously known steam generators, it is particularly critical to compensate for an undefined and possibly fluctuating energy content of the fuel mass (in contrast to, for example, coal) and thus the fluctuating steam parameters during steam generation. If the fluctuating energy content cannot be adequately compensated for, the steam temperature will fluctuate, which - for example when using steam turbines - can lead to impairment or even damage to these steam turbines.

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

However, such a design is no longer applicable at high pressures, for example over 250 bar, since there is a high risk of destruction, for example in the form of an explosion.

There is therefore a current need for a solution for a steam generator when used with biomass and high pressures, which is not only high pressure resistant, but can also be implemented easily and cost-effectively.

Apart from this, the property of a salt bath as an energy storage device over a longer period of time has so far only been known in foreign technical areas.

For example, revealed US 2012/067551 A1 an arrangement with which solar energy, which is collected by parabolic mirrors, can be stored in such a salt bath in a solar park with solar panels. At a later point in time, for example at night, the energy stored in the salt bath can then be used to generate electricity in phases without sunlight, thus ensuring constant electricity generation.

Even if one were to use salt baths as an intermediate heat transfer medium in a (high-pressure) steam generator, stability problems in the heat transfer can arise.

These are primarily due to local hotspots in the salt bath, for example at corners or during flow stalls.

This is particularly disadvantageous because it can cause permanent glowing of metal components of such a steam generator due to overheating and decomposition of the salt.

Such decomposed salt can corrode the metal of the remaining steam generator and cause leakage.

PRESENTATION OF THE INVENTION

It is therefore the object of the present invention to provide an efficient device for generating steam (a steam generator) in which, with a simple design and even with fluctuating energy content of the fuel, reliable operation can be guaranteed and a high level of effectiveness can be achieved, and the above disadvantages can be reduced or reduced can even be prevented.

This task is solved by a device with the features of claim 1. Preferred configurations can be found in the further claims of the following description and drawings.

According to one aspect, the steam generator has a housing and a flow channel through which a heat exchange fluid can flow from an inlet of the flow channel to an outlet of the flow channel.

At least a portion of the flow channel is arranged in the housing. This can be arranged as the first heat exchange element in the housing. In other words, the flow channel can be flowed through as a first heat exchange element from an inlet of the housing to an outlet of the housing in a first flow direction.

The steam generator also has a second heat exchange element arranged in the housing. Water can flow through this to generate steam.

In addition, a heat transfer medium is arranged in the housing.

In other words, the housing is filled with a heat transfer medium. The heat transfer medium is provided to transfer heat from a heat exchange fluid flowing through the flow channel to the water flowing through the second heat exchange element. This allows steam to be generated.

The heat transfer medium is a salt bath.

Furthermore, the cross section of the flow channel is larger at the inlet of the flow channel than at the outlet of the flow channel.

The “cross section of the flow channel” is to be understood as the internal dimension of the flow channel. If the flow channel is designed as a cylindrical tube, the “cross section is of the flow channel" is to be understood as the inner diameter of the pipe. In other words, the "cross section of the flow channel" is to be understood as the effective flow cross section of the flow channel.

The heat exchange fluid can be flue gas. In addition, the heat exchange fluid can be waste heat from a biomass furnace, biogas plant or a pellet heating system, which can flow through the flow channel or the first heat exchange element and thus through the steam generator.

Such a steam generator is able to exchange heat as homogeneously as possible due to the heat transfer medium, while local overheating can be prevented.

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.

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, as well as high-pressure steam flows in the range of 500 to 800 bar can be generated without the fluctuating Energy content of the biomass would be critical for the device itself.

A complex arrangement with an additional dam storage boiler to achieve low pressure losses is also unnecessary in such a design. This means that not only a particularly flexible but also cost-effective device for generating steam can be realized.

In addition, destruction or explosion can be reliably avoided because the salt is crystalline when at rest liquefied by the heating with or via the first heat exchange element through which the heat exchange fluid can flow, so that the salt melt is heated by the heat exchange fluid and the salt thus liquefies and absorbs energy.

This means that the salt bath acts as a liquid salt, for example as a nitrate melt, and thus improves the heat transfer from the heat exchange fluid to the water.

At the same time, by changing the cross section between the inlet and outlet of the flow channel, the energy input into the salt can be made as large as possible at the beginning. This can prevent local overheating or decomposition of the salt.

According to such a design, not only can a particularly flexible system be realized, which can generate steam pressure of up to 800 bar at a wide range of pressures, but also a particularly reliable and long-lasting steam generator can be achieved.

The operational safety of such a steam generator can also be further improved due to a larger cross section at the inlet of the flow channel compared to the outlet of the flow channel, since the initial flow velocities, for example of flue gas as a heat transfer fluid, can be reduced.

Thus, when entering the flow channel, there are lower flow velocities due to the larger cross section in the flow channel. This in turn allows overheating of the salt and potential decomposition of the salt bath to be prevented.

The heat exchange fluid can, as mentioned at the beginning, 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 an already known feed grate furnace or the exhaust gas from a biogas plant. This allows electricity to be generated from waste materials. Depending on the heat exchange fluid, different temperature ranges can occur in the steam generator.

Depending on the heat exchange fluid, different temperature ranges can occur in the steam generator. If the heat exchange fluid, also known as heating fluid, is produced in the steam generator by pellet combustion, this is usually between 600°C and 1000°C, preferably 900°C.

Separately, the homogeneous heat transfer properties of the salt bath enable flue gas temperatures of over 1000°C, in particular 1300°C and more, to be "run" without endangering the safety of the steam generator. Furthermore, the claimed embodiment enables a homogeneous heat transfer or heat input into the water to generate steam to be achieved even with fluctuating flue gas temperature peaks.

If exhaust gas from a biogas plant is used as a heat exchange fluid, temperatures of 450°C to 500°C, preferably 470°C, usually occur in the steam generator. In addition, salts can be used that change from a crystalline to a liquid state of aggregation, i.e. an operating state, at temperatures as low as 130°C - 150°C.

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

Due to the high energy storage capabilities of the salt bath used, it is possible that the pressure to be generated can only be regulated via the flow velocity by increasing the flow of the water flowing through the second heat exchange element. This can be done using a simple pump.

For example, if necessary, pressures of seven bar can be achieved (for example for the food industry) and shortly afterwards, by increasing the flow rate, pressures of up to 800 bar can be generated, without the need for other, additional or different resistant materials, configurations or arrangements must be provided.

A particularly flexible and multiple-use device for steam generation can therefore be provided with just one compact device and one housing.

In this case, steam generation is also independent of the heat source. Thus, the heat exchange fluid can not only be present as flue gas through the combustion of biomass, but the heat exchange fluid can also be generated, for example, through the combustion of fossil fuels, such as coal or natural gas. This heat exchange fluid can then flow through the first heat exchange element in a similar way to flue gas.

According to a further aspect, the first heat exchange element may have a ceramic jacket at least in a section at the inlet of the housing.

In other words, an area at the inlet of the first heat exchange element within the housing may have a Have ceramic layer.

Such a design is particularly valuable with a view to increasing the efficiency of steam generation, since high-temperature flue gas streams of, for example, 1000 ° C can be used to a particularly great extent due to their radiant energy. The ceramic insulation of the initial area of the first heat exchange element enables the thermal energy of the high-temperature flue gas to be transferred to the salt bath without running the risk of the salt bath decomposing. This means that the radiant energy of the high-temperature flue gas can be used particularly efficiently with high operational reliability.

The ceramic casing can preferably be formed from calcium aluminate.

In contrast, particularly preferably, at least a section of the first heat exchange element at the outlet of the housing may not have a ceramic casing in order to be able to use the remaining residual heat of the heat exchange fluid after the first heat exchange element flows through the housing to generate steam.

Here, the ceramic casing can be provided on an inside of the first heat exchange element. Thus, overstressing of the first heat immersion element, i.e. of the flow channel within the housing, particularly in the area of the flow entry into the housing, can be reliably prevented. This undoubtedly increases operational safety and ensures the longevity and reliability of the steam generator.

To further increase the energy input into the salt bath Ribs can also be provided on the outside of the first heat exchange element, at least in the area of the ceramic casing, preferably over the entire extent of the first heat exchange element. Such ribs can extend into the interior of the housing.

Accordingly, the ribs act like a ribbed heat exchanger and further increase the energy transfer from the heat exchange fluid (e.g. flue gas) to the salt bath.

According to such a configuration, the heat input into the salt bath can be adjusted as desired via the thickness of the ceramic casing and the size and distance of the ribs.

The ribs are preferably steel ribs.

An additional ceramic layer can also be provided on the housing itself in order to insulate the steam generator even more towards the outside of the housing and to maximize the energy input from the flow channel to the salt bath and then further to the water in the second heat exchange element. This minimizes potential heat loss and allows the process parameters to be adjusted to be even more stable.

According to a further aspect, the housing is supported on a base. A preheating section is provided in the flow channel. This preheating section is arranged in the base.

Accordingly, the steam generator is designed in such a way that the heat exchange fluid first passes through the preheating section of the flow channel and then through the first Heat exchange element flows in the section of the flow channel arranged in the housing.

Accordingly, the heat exchange fluid can first flow through the preheating section, which is arranged in the base, before it enters the housing of the steam generator.

Specifically, this means that the housing and the salt bath filled therein can be preheated by the preheating section with the largest possible cross section of the flow channel.

Since the cross section of the flow channel is largest at the inlet of the flow channel, i.e. at the inlet of the preheating section, the flow velocity of the heat exchange fluid is at the same time lowest, so that the salt bath can effectively be preheated from outside the housing without the lines of the flow channel being in the area within the housing, i.e. in the area of the first heat exchange element, are overused.

The base is preferably made of concrete.

This ensures secure and high-temperature-resistant support for the flow channel and the housing.

The housing is preferably made of stainless steel.

Due to this, high corrosion resistance can be ensured, even at higher temperatures, for example in the salt bath, and reliable and safe operation over a longer period of time can be made possible.

The preheating section of the flow channel is preferably made of ceramic. The preheating section of the flow channel is particularly preferably formed from calcium aluminate.

Furthermore, in a preferred embodiment, the preheating section can be divided into a first and a second half. The first and second halves can be made monolithic.

In this context, the “first half” is to be understood as the side/half of the preheating section of the flow channel facing the housing and the “second half” as the half/side facing away from the housing.

The first and second halves of the preheating section are preferably made from different ceramic materials.

It is particularly preferred that the first half of the preheating section has silicon carbide. As a result, an improved thermal conductivity of the first half of the preheating section cannot be achieved with higher temperature resistance and the desired thermal conductivity can be “set”. At the same time, the second half ensures improved insulation from the surroundings.

The ceramic design of the flow channel ensures that overloading of the flow channel is prevented even at very high heat exchange fluid temperatures (for example above 800 ° C) and thus safe and reliable operation of the steam generator can be ensured. At the same time, due to the ceramic properties, preheating of the salt bath via the flow channel or via the preheating section of the flow channel in the base is ensured.

Here, the term “preheating” or “preheating section” is to be understood as meaning that the salt bath is first heated through the preheating section and further heating then takes place in the section of the flow channel that flows through the housing.

However, the term “preheating” does not exclude the fact that the majority of the heat transfer from the heat exchange fluid to the salt bath already takes place in this preheating section of the flow channel. For example, the heat exchange fluid can enter the preheating section at 1300°C and transfer thermal energy to the salt bath via the ceramic configuration and the housing. The heat exchange fluid can then enter the housing itself with an exemplary temperature of approximately 600°C and leave it again with a residual heat temperature of approximately 500°C.

This means that the salt bath can also reach approx. 500°C in continuous operation.

In order to be able to use the residual heat of the heat exchange fluid of approximately 500 ° C, a tube-water heat exchanger, preferably with helical turns, can be provided in a preferred embodiment in order to further utilize the residual heat temperature of approximately 500 ° C can. This allows the overall efficiency of the steam generator to be increased even further.

By way of example, the preheating section of the flow channel can be a cast ceramic element in the base or a tube made of ceramic in the base.

In addition, analogously, the preheating section of the flow channel can be coated with a ceramic layer, particularly preferably a layer made of calcium aluminate.

In such a steam generator, the weld seams, for example of the housing and/or the flow channel in the area of the housing, often represent the most heavily loaded areas and the most critical points for leaks and corrosion.

In order to prevent leaks or corrosion, in a preferred embodiment a ceramic layer, for example in the form of thermal barrier sleeves, can be provided in the area of the weld seams.

This allows the steel to be additionally coated with a temperature-resistant layer. Accordingly, the flow channel or the housing can be protected from heat flux densities that are too high.

In addition, it can be achieved that heat energy can be introduced evenly and without “peaks” into the steel surfaces and accordingly into the salt.

The wall thickness of the preheating section preferably decreases along its direction of extension.

Even if the highest temperature of the heat exchange fluid is present at the inlet of the flow channel and thus at the inlet of the preheating section of the flow channel and at the same time the lowest flow speed, the risk of overloading the flow channel can be ensured and a stable heat transfer can be made possible.

In addition, due to the decreasing wall thickness, the degree of transfer to the housing and the salt bath located therein can be increased along the direction of extension of the preheating section. This means that as the extension increases, a higher degree of heat transfer and thus preheating of the salt bath can be ensured.

According to such an arrangement, the heat exchange fluid can ensure homogeneous heating and thus liquefaction of the salt bath due to the flow through the preheating section before the heat exchange fluid flows through the housing in the area of the first heat exchange element for further heat exchange.

The preheating section of the flow channel arranged in the base can contact the housing directly. However, for improved control of the heat transfer, a silicon carbide sand layer can optionally be provided in the base between the housing and the preheating section of the flow channel.

Such a layer has particularly good heat conduction properties and heat transfer properties.

This allows the heat input via the housing into the salt bath to be improved.

In a particularly preferred embodiment, silicon carbide sand can be filled into an intermediate membrane wall between the preheating section of the flow channel and the outside of the housing.

It is particularly preferred that the preheating section is arranged both on the underside of the housing and on one side of the housing and that heat exchange fluid, e.g. flue gas, flows through this area. The heat exchange fluid on the underside of the housing can serve as a kind of “tub heater” and the intermediate membrane wall can regulate the heat coupling in a side area of the housing.

The silicon carbide sand can be present alone or, if the heat transfer is to be reduced, mixed with quartz sand.

In particular, this achieves a cascade-shaped gradation of heat transfer from the ceramic of the preheating section to the silicon carbide sand layer, to the metal of the housing, to the salt bath and finally to metal pipes of the second heat exchange element and thus to the water.

The cross section of the flow channel in the preheating section is preferably constant.

In other words, the cross section of the preheating section is constant throughout the base and at the same time has the largest cross section of the flow channel.

To put it another way, this means that the preheating section has a constant and larger cross section than the flow channel within the housing, i.e. in the area in which it functions as the first heat exchange element.

Such a large, constant cross section of the preheating section of the flow channel ensures sufficient and safe preheating of the salt bath within the housing.

Preferably, the cross section of the flow channel is larger at an inlet of the section of the flow channel arranged in the housing than at the outlet of the section of the flow channel arranged in the housing.

In other words, the section of the flow channel, which is arranged as the first heat exchange element in the housing, has a larger cross section at the inlet than at the outlet.

The cross section can change iteratively, i.e. H. in stages, reduce. However, it is also possible for the cross section to decrease continuously along its direction of extension.

The flow channel preferably has several U-shaped pipe windings.

According to such a configuration, the flow channel can be "meandered" as much as possible from the inlet to the outlet and thus the potential surface for heat transfer to the housing in the preheating section or directly to the salt bath in the area within the housing can be reached.

Particularly preferably, the preheating section of the flow channel has at least one U-shaped pipe winding, so that the heat exchange fluid is guided from an inlet of the flow channel along the direction of extension of the housing in the base, with a U-shaped one at the end of the housing Change of direction is experienced and then returned towards the inlet of the housing in order to then continue to flow through the flow channel through the housing.

Furthermore, it is particularly preferred that at least one U-shaped tube winding is also provided in the area of the flow channel, which extends in the area of the housing.

This means that it can also be ensured in the area of the flow channel within the housing, i.e. in the area in which it functions as the first heat exchange element, that a high level of heat transfer can be achieved.

The U-shaped pipe windings are therefore preferably provided in the preheating section and/or the section of the flow channel which is arranged in the housing.

The steam generator preferably has several flow channels.

These flow channels preferably run parallel to one another and can each be flowed through by the heat exchange fluid.

Thus, the heat transfer surface on the flow channel in the preheating section and in the housing can be further increased, and thus a homogeneous and uniform heat transfer to the salt bath and thus also to the water intended for steam generation in the second heat exchange element can take place.

The salt bath preferably has a nitrate salt. The salt bath particularly preferably contains a potassium-sodium nitrate.

The nitrate salt is not only particularly cost-effective, but can also be used to store energy at high temperatures of the heat transfer medium, for example with flue gas up to 900 °C, without chemical decomposition. This ensures that the steam generator is designed to be as operationally reliable and efficient as possible.

At the same time, potassium sodium nitrate is also particularly temperature-stable and therefore suitable for efficient heat transfer and heat storage in the event of overheating.

This means, for example, that a salt bath temperature of 350° to 565°C can be present without posing a risk to the operational safety of the steam generator.

The heat transfer medium, here the salt bath, preferably covers at least the first heat exchange element and the second heat exchange element.

According to the configurations described above, a particularly reliable, efficient and inexpensive, as well as flexible steam generation can be realized, because the salt bath ensures high heat transfer at a wide range of temperatures and also has a "high forgivability" with regard to temperature fluctuations and fluctuating energy contents. This means that the salt bath enables a high level of heat homogeneity and can therefore counteract the problems described above of different steam temperatures and the variable energy content of the biomass used, for example.

In addition, the high initial cross-section of the flow channel ensures that the flow velocities are reduced at the start of heat transfer and thus heat hotspots, overheating or even decomposition of the salt bath can be prevented. In addition or as an alternative to this, the preheating section provided in the base ensures that the salt bath is preheated before the heat exchange fluid enters the housing and that heat can be transferred particularly efficiently to the water in the second heat exchange element to generate steam.

Due to this, stability problems can arise, for example due to a stall in the flow of the heat exchange fluid through the pipe or in the salt can be prevented and thus a homogeneous heat transfer can be ensured.

In addition, local hotspots, for example in corners of the housing or hotspots caused by the flow stalls described above, can be prevented. Accordingly, permanent glowing of the housing, the flow channel and/or the second heat exchange element and thus overloading of the salt, which would possibly decompose, can be prevented.

Because of this, attack on the metal by the decomposed salt can also be prevented.

This is ensured in particular by the fact that the energy input into the salt bath is highest only in the area of the inlet of the flow channel and decreases along the direction of extension of the flow channel.

BRIEF DESCRIPTION OF THE DRAWINGS

• Figur 1: eine isometrische Darstellung eines Dampferzeugers gemäß einer beispielhaften Ausführungsform, wobei die Oberseite des Gehäuses und die Seitenwand des Sockels zu Darstellungszwecken weggelassen worden bzw. geschnitten dargestellt sind.
• Figur 2: eine zu Darstellungszwecken leicht modifizierte schematische Querschnittsdarstellung des Dampferzeugers gemäß der beispielhaften Ausführungsform entlang der Schnittlinie A-A von Figur 1.

A steam generator according to an exemplary embodiment is described below using schematic drawings. Such steam generators are used, for example, to generate steam for energy generation, for example in a steam engine or a steam engine. Show it:

• Figure 1 : an isometric view of a steam generator according to an exemplary embodiment, wherein the top of the housing and the side wall of the base have been omitted or shown in section for illustrative purposes.
• Figure 2 : a schematic cross-sectional view of the steam generator according to the exemplary embodiment, slightly modified for illustration purposes, along section line AA of Figure 1 .

As already indicated in the previous paragraph Figure 2 In view of the proportions and the features shown, it is not completely identical to the isometric representation of the steam generator in Figure 1 .

This was done primarily to see the cross section of Figure 2 The present application highlights the core properties of the most important features of the steam generator and their design.

Specifically, for example, the width of the base is slightly increased in relation to the housing in order to better illustrate the flow channels contained in the base. The silicon carbide layer, described in more detail below, was also shown at a distance from the flow channel and the housing. However, the silicon carbide can also be filled into a cavity or recesses between the housing and the base, so that there is no distance from the silicon carbide layer.

The part of the flow channel running in the housing itself, hereinafter referred to as the first heat exchange element, and the corresponding pipes have also been shown enlarged for illustration purposes.

However, all these proportions can vary and are purely exemplary in nature in the figures.

It is understood that Figures 1 and 2 refer to the same embodiment and are not intended to contradict each other or be understood as alternatives or the like.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig. 1 represents a perspective view of a steam generator 1 according to an exemplary embodiment.

Fig. 1 It can be seen that the steam generator 1 has a housing 2 and a base 20. The base 20 is in Figure 1 shown opened by a section in order to better illustrate the flow path through the base 20, which will be described in more detail below.

The base 20 and the components contained therein are described in detail with reference to Fig. 2 described.

The in Fig. 1 Steam generator 1 shown comprises a housing 2 in which a flow channel and a second heat exchange element 4 are arranged.

A heat exchange fluid can flow through the first heat exchange element 3. In the following description of an embodiment, flue gas is used as an example of such a heat exchange fluid, which was generated by biomass combustion. Another example of such a heat exchange fluid would be the waste heat from a biogas plant.

The flue gas is led to the steam generator 1 via a funnel 13.

In this context, the housing 2 of the steam generator 1 has an inlet 6, to which the funnel 13 is connected, and an outlet 7. Accordingly, the flue gas can flow through the housing 2 from the inlet 6 to the outlet 7 through the flow channel. This flow direction is referred to as “first flow direction 5” in the described embodiment. This means that the flue gas flows through the housing 2 along the first flow direction 5 from the inlet 6 to Outlet 7 of housing 2.

In the embodiment described here, a preheating section 21 of the flow channel 3 is also provided. How Figure 1 As can be seen, the flue gas first flows through this preheating section 21 of the flow channel before it reaches the inlet 6 of the housing 2.

However, it is also possible that no preheating section is provided, so that the flue gas flows directly from the inlet 6 of the housing 2 along the first flow direction 5 to the outlet 7 of the housing 2.

In the embodiment shown, the first heat exchange element 3 has a plurality of tubes 8, that is, a plurality of flow channels, which extend along the direction of extension of the housing 2, that is, from the inlet 6 to the outlet 7 of the housing 2.

In the embodiment of the steam generator 1 shown, the housing 2 is designed "box-like", that is, it extends essentially along a depth direction of the housing 2 and has a rectangular cross section. However, the width and/or height as well as the depth of the housing 2 are not limiting for steam generation and can be configured according to space requirements and/or desired configurations. In the embodiment shown, the first flow direction 5 corresponds to the longitudinal extent of the housing 2.

In this embodiment, water flows through the second heat exchange element 4 to generate steam. In other words, the water in the second heat exchange element 4 is heated by the flue gas flowing from the first heat exchange element 3 or the flue gas flowing therein and thus from a liquid state to one brought to 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 steam generated. 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.

At this point it should be noted that, for illustration purposes, the cover of the housing 2 (on an upper side of it) is also in Fig. 1 has not been shown, so that the interior of the housing 2 in the isometric view of Fig. 1 is recognizable.

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

As can be seen from the figures, the second heat exchange element 4 has a plurality of tube windings 10 in the form of a tube. These tube windings 10 are, as in Fig. 1 can be seen, so arranged in the housing 2 that the second heat exchange element 4 extends essentially perpendicular to the first flow direction 5 from the inlet 6 of the housing 2 to the outlet 7 of the housing 2 and with U-shaped tube winding sections along the largest possible tube length and thus the tube surface its extension from the inlet 6 to the outlet 7 of the housing 2. In cross section through the steam generator Figure 2 For improved illustration, the second heat exchange element 4 is not shown.

That is, while the pipes 8 of the first Heat exchange element 3 extends in a straight line from the inlet 6 to the outlet 7 of the housing 2 after the flue gas has passed through the preheating section 21, the pipe of the second heat exchange element 4 has a plurality of pipe sections which run vertically in the embodiment shown, so that the pipe windings connected to U-shaped pipe winding sections 10 extend essentially perpendicular to the first flow direction 5 from the inlet 6 to the outlet 7 of the housing 2.

However, according to a further embodiment, not shown, it is also possible for the first flow direction 5 and the second flow direction to run essentially parallel to one another.

It is also possible for each pipe 8, i.e. the respective flow channels of the steam generator through which flue gas flows, to have at least one, preferably several, U-shaped pipe windings. If this is the case, the flue gas can, for example, from the inlet 6 of the housing (or, if provided, from the inlet of the preheating section 21 of the flow channel) first run along the first flow direction 5, then run through the U-shaped pipe winding in the opposite direction and thus in Flow back in the direction of inlet 6. Such a course is in Figure 1 and 2 shown. As can be seen from the preheating section 21 provided in the base 21 and the arrow shown therein, the flue gas first flows through a lower pocket 21a before it can flow back through a side pocket 21b via a U-shaped pipe winding. After the flue gas has flowed through the side pocket 21b of the preheating section 21, it is flowed into the plurality of tubes 8.

Specifically, this also means that the U-shaped Pipe windings of the flow channel 3 can be provided in the preheating section 21 and / or the section of the flow channel that is arranged in the housing. To explain the preferred embodiment, based on Fig. 2 , it is assumed that U-shaped pipe windings are provided both in the preheating section 21 and in the section of the flow channel which is arranged in the housing 2.

Such a flow pattern is also determined by the directional information in the respective pipes 8 in Fig. 2 and the preheating section 21 in the base 20 in Fig. 1 illustrated and will be explained in more detail below.

Furthermore, the arrow in the preheating section 21 in the base 20 of the steam generator makes it clear and unambiguous that the incoming flue gas first flows through a lower part of the base 20 in the preheating section 21, that is, through the lower pocket 21a, for heat transfer to the housing 2, then has a U-shaped tube winding, in order to then flow back laterally from the housing in a direction opposite to the first flow direction 5 through the side pocket 21b of the preheating section 21 for further heat transfer to the housing 2.

Fig. 1 also illustrates that the second heat exchange element 4 with the U-shaped tube windings 10 extends between the tubes 8 and the housing 2.

In the embodiment illustrated in the figures, the first flow direction 5 runs essentially along a horizontal direction, whereas the second flow direction runs essentially vertically. However, it is also possible to arrange the steam generator 1 "upright", so that a first flow direction 5 is in a vertical direction and the second flow direction is in Essentially runs in a horizontal direction. If the space requirement requires this, an inclined arrangement of the housing 2 is also conceivable.

In the in Fig. 1 and in Fig. 2 In the illustrated embodiment, the second heat exchange element 4 extends along several planes in a width direction, because the tube windings 10 of the second heat exchange element 4 extend essentially perpendicular to the first flow direction 5. Separately, however, it is also possible for the tube windings 10 of the second heat exchange element 4 to extend along a vertical direction in different planes in a height direction of the housing 2 between the tubes 8 of the first heat exchange element 3 or a mixture thereof within the housing 2 between the tubes 8 of the first heat exchange element 3.

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

As in Fig. 1 shown, this salt bath can be filled into the housing 2 via inlet connection 15. The salt bath thus fills the spaces between the first heat exchange element 3 and the second heat exchange element 4 in the housing 2 and can fill it completely. Accordingly, this salt bath can serve as a heat transfer medium and energy storage in order to increase the homogeneity of the energy transfer.

The salt bath can have a nitrate salt, in particular a potassium-sodium nitrate.

Furthermore, the flow channel within the housing can be in the in Fig 1 The embodiment shown, i.e. the first heat exchange element 3, has a tapering cross section within the housing 2. Accordingly, the cross section at an inlet 6 of the flow channel is larger than at an outlet 7 of the flow channel.

This narrowing of the cross section can be provided, for example, in the area of the U-shaped pipe windings of the flow channel. Alternatively, it is possible for the taper to take place along the first flow direction 5.

According to such an embodiment, a problem due to fluctuating steam parameters, which is due, for example, to non-constant fuel or its calorific value, can be prevented even at supercritical pressures of over 350 bar.

This means that even if, for example, flue gas with a temperature of 900 ° C enters the steam generator 1, the heat energy is first transferred to the heat transfer medium in the form of a salt bath. In the case of several second heat exchange elements 4, it is also possible for water not to flow through one of these heat exchange elements if it is not currently needed. Due to the arrangement of the heat transfer medium in the housing 2 of the steam generator 1, destruction or overheating of the empty pipe of the second heat exchange element 4 can be prevented, because the salt bath is not only intended as a heat transfer medium, but can also store heat energy and release it again if necessary. Such a salt bath is often referred to as “nitrate melt”.

This can be heated up to 565°C without decomposing.

In addition, for example in the food sector, a pipe 8 for seven bar steam, another pipe 8 for 16 bar steam and a third pipe 8 for high-pressure steam (for example 500 bar) for engines and turbines can be provided with the same device. This is controlled by the flow speed in the respective tubes 8 of the second heat exchange element 4.

In addition, due to the cross-sectional taper along the heat exchange fluid flow through the housing 2, the energy input into the salt bath is kept highest at the inlet of the flow channel and at the same time the flow velocity at the inlet of the flow channel is kept lowest.

This means that overloading of the salt bath can be prevented, even in high-temperature applications, and heat transfer can be achieved as homogeneously as possible. This means that energy can be stored without pressure without any operational risk or risk of overloading.

According to such an embodiment, a steam generator can be realized which can be operated permanently and safely at a maximum pressure of 0.1 bar on the molten salt.

Further protection can be achieved by providing stainless steel sheets (not shown) as a (safety) membrane. Even in the unlikely event of a leak or corrosion in the housing 2, the housing 2 is therefore additionally protected from the outside.

Furthermore, a monitoring device (not shown) can be provided on the housing 2 for process monitoring.

For example, such a monitoring device can be designed in the form of a tube provided on an upper side of the housing 2, which opens into a water bath.

If there were an (unlikely) leakage of the heat exchange fluid into the salt bath in the housing 2 and/or decomposition of the salt bath, for example, nitrogen oxides and/or oxygen would be released. The resulting gases could then be immediately detected by water bubbles in the water and appropriate safety measures taken.

In addition, the provision of a preheating section 21 in the base 20, which carries the housing 2, enables the majority of the heat input to take place via this preheating section 21 of the flow channel 3.

In Fig. 2 is the basic structure of the steam generator 1 analogous to the steam generator of Fig. 1 designed with slightly modified proportions. In the embodiment shown, the base 20 is made of concrete, preferably HT concrete.

Analogous to the representation of Fig. 1 , the cross section is in Fig. 2 along line AA from Figure 1 A heat exchange fluid flows through the flow channel shown from an inlet of the flow channel to an outlet of the flow channel and a section of the flow channel is arranged as a first heat exchange element 3 in the housing 2. Furthermore illustrated Fig. 2 a preheating section 21 of the flow channel, which is arranged in the base 20 and can be divided into the lower pocket 21a and the side pocket 21b connected by a U-shaped pipe coil.

In other words, the flow channel has a section in the housing 2 in which it functions as a first heat exchange element 3 and a preheating section 21 arranged upstream thereof and running through the base 20.

Thus, the steam generator of the illustrated embodiment is designed so that the heat exchange fluid first flows through the preheating section 21 of the flow channel and then through the section of the flow channel arranged in the housing 2 as the first heat exchange element 3. In the in Fig. 2 In the embodiment shown, the flow channel in the area of the base 20 is made of ceramic, in particular made of calcium aluminate.

As already mentioned, the in Fig. 2 shown embodiment, both the preheating section 21 and the section of the flow channel 3, which is arranged in the housing 2, have at least one U-shaped tube winding, so that the heat exchange fluid entering at the inlet of the flow channel 3 can flow through the flow channel parallel to the direction of extension of the housing and then can flow in the opposite direction again in the direction of the inlet of the flow channel parallel to it, in order to then be able to flow into the housing 2 of the steam generator through a further U-shaped pipe winding of the flow channel.

To illustrate the flow direction of the heat exchange fluid, the flow is along the direction of extension from the inlet of the flow channel along the housing, that is, along the first flow direction 5 of Fig. 1 , through an "X" and the flow in the opposite direction through a point (".") in Fig. 2 illustrated.

Analogous to this, as mentioned above, the section of the flow channel, which is arranged in the housing 2 and functions as the first heat exchange element 3, also has several U-shaped tube windings, so that the heat exchange fluid is guided through the housing over the longest possible extent can.

Thus, as indicated by the arrow in Figure 1 indicated, in such an embodiment, the heat exchange fluid first passes through the preheating sections 21 of the two shown here, parallel flow channels flow from the inlet of the preheating section 21 along the housing 2 through the lower pocket 21a on the outside of the housing and flow back in the opposite flow direction at the end of the housing 2 in the longitudinal direction through the side pocket 21b.

The heat exchange fluid then passes through the section of the flow channel arranged in the housing 2 and serving as the first heat exchange element 3. Consequently, the heat of the heat exchange fluid in the preheating section 21 can first be given off to the housing 2 and thus to the salt bath contained therein. This means that overstressing of the section of the flow channel in the housing (first heat exchange element 3) is excluded.

Beyond that is out Fig. 2 it can be seen that the cross section of the flow channel 3 is largest in the area of the preheating section 21. In other words, the cross section of the preheating section 21 is larger than the cross section of the flow channel 3 within the housing 2. Consequently, the heat input into the salt bath is greatest in the area of the preheating section 21 due to the reduced flow velocity and the salt bath can be preheated accordingly.

In order to optimize the energy input, as in Fig. 2 shown, a silicon carbide sand layer 22 may be provided between the housing 3 and the preheating section 21.

This ensures that heat transfer into the housing 2 is as homogeneous as possible.

In addition, the larger cross section of the flow channel 3 in the area of the preheating section 21 enables the flow velocity at the beginning of the flow through the flow channel 3 to be kept as low as possible.

It is also possible here that, for example, the cross section remains constant in the entire area of the preheating section 21 of the flow channel and is reduced only in the area of the first heat exchange element 3.

Analogous to this, it is also conceivable that the cross sections of the preheating section 21 and/or cross sections of the flow channel, in the section in which it serves as the first heat exchange element 3, reduce continuously or gradually.

Analogously, it is possible for the wall thickness of the preheating section 21 to be reduced along its direction of extension. In this way, initial overheating can be avoided and uniform heat transfer to the housing or the salt bath contained therein can be achieved over the extent of the preheating section 21.

REFERENCE SYMBOL LIST

1

Steam generator

2

Housing

3

first heat exchange element

4

second heat exchange element

5

first flow direction

6

Inlet of the housing

7

Outlet of the housing

8th

Pipe

10

Pipe windings of the second heat exchange element

13

funnel

15

Inlet connection

20

base

21

Preheating section

21a

lower pocket

21b

side pocket

22

Silicon carbide sand layer

Claims (15)

Steam generator (1), comprising: a housing (2); a flow channel through which a heat exchange fluid, preferably flue gas, can flow through from an inlet of the flow channel to an outlet of the flow channel, wherein at least a portion of the flow channel is arranged as a first heat exchange element (3) in the housing (2); at least one second heat exchange element (4) arranged in the housing (2), through which water can flow to generate steam, a heat transfer medium which is arranged in the housing (2) in order to transfer heat from the heat exchange fluid flowing through the flow channel to the water flowing through the second heat exchange element (4) in order to generate steam, characterized in that the heat transfer medium is a salt bath, and the cross section of the flow channel is larger at the inlet of the flow channel than at the outlet of the flow channel. Steam generator (1) according to one of the preceding claims, wherein the housing (2) is formed from stainless steel. Steam generator (1) according to claim 1 or 2, wherein the first heat exchange element (3) has a ceramic jacket, preferably made of calcium aluminate, at least in a section at the inlet (6) of the housing (2). Steam generator (1) according to claim 3, wherein the ceramic casing is provided on an inside of the first heat exchange element (3), and at least in the area of the ceramic casing, preferably over the entire extent of the first heat exchange element (3), ribs, preferably steel ribs, are provided on the outside of the first heat exchange element (3), which extend into the interior of the housing. Steam generator (1) according to one of the preceding claims, wherein the housing (2) is supported on a base (20), wherein the flow channel has a preheating section (21) which is arranged in the base (20), and wherein the steam generator (1) is designed such that the heat exchange fluid flows first through the preheating section (21) of the flow channel and then through the section of the flow channel arranged in the housing (2) as the first heat exchange element (3). Steam generator (1) according to claim 5, wherein the base (20) is made of concrete, and/or the preheating section (21) of the flow channel is made of ceramic, preferably made of calcium aluminate. Steam generator (1) according to claim 5 or 6, wherein the wall thickness of the preheating section (21) decreases along its direction of extension. Steam generator (1) according to one of claims 5 to 7, wherein a silicon carbide sand layer (22) is provided in the base (20) between the housing (2) and the preheating section (21) of the flow channel. Steam generator (1) according to one of claims 5 to 8, wherein the cross section of the flow channel in the preheating section (21) is constant. Steam generator (1) according to one of the preceding claims, wherein the cross section of the flow channel is larger at an inlet (6) of the section of the flow channel which is arranged in the housing (2) than at the outlet (7) of the section of the flow channel, which is arranged in the housing (2). Steam generator (1) according to one of the preceding claims, wherein the flow channel has a plurality of U-shaped pipe windings (10). Steam generator (1) according to one of claims 5 to 11, wherein the flow channel has several U-shaped pipe windings (10), and the U-shaped pipe windings (10) are provided in the preheating section (21) and/or the section of the flow channel which is arranged in the housing (2). Steam generator (1) according to one of the preceding claims, wherein the steam generator (1) has several of the flow channels through which the heat exchange fluid can flow parallel to one another. Steam generator (1) according to one of the preceding claims, wherein the salt bath has a nitrate salt, preferably potassium sodium nitrate. Steam generator (1) according to one of the preceding claims, wherein the heat transfer medium covers at least the first heat exchange element (3) and the second heat exchange element (4).

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