EP1166015B1 - Fossil-fuel fired continuous-flow steam generator - Google Patents

Abstract

A continuous-flow steam generator includes a combustion chamber with evaporator tubes for fossil fuel. The combustion chamber is followed on the fuel-gas side, via a horizontal gas flue, by a vertical gas flue. When the continuous-flow steam generator is in operation, temperature differences between the exit region of the combustion chamber and the entry region of the horizontal gas flue are to be particularly low. For this purpose, of a plurality of evaporator tubes capable of being acted upon in parallel by a flow medium, a number of the evaporator tubes are led through the combustion chamber before their entry into the containment wall of said combustion chamber.

Description

The invention relates to a once-through steam generator, which has a combustion chamber for fossil fuel, which a vertical gas flue on the heating gas side via a horizontal gas flue is connected downstream, the peripheral walls of the combustion chamber made of gas-tightly welded, vertically arranged Evaporator tubes are formed.

In a power plant with a steam generator, the Energy content of a fuel to vaporize one Flow medium used in the steam generator. It will Flow medium usually in an evaporator circuit guided. The steam provided by the steam generator in turn can be used, for example, to drive a steam turbine and / or provided for a connected external process his. If the steam drives a steam turbine, then usually a generator via the turbine shaft of the steam turbine or operated a work machine. in case of a Generator can the current generated by the generator for Infeed into a network and / or island network provided his.

The steam generator can be designed as a continuous steam generator his. A continuous steam generator is from the top "Evaporator concepts for Benson steam generators" by J. Franke, W. Köhler and E. Wittchow, published in VGB Kraftwerkstechnik 73 (1993), No. 4, pp. 352-360. At a Pass-through steam generator conducts the heating of evaporator tubes provided steam generator pipes for evaporation of the flow medium in the steam generator tubes in one one-time run.

Continuous steam generators are usually equipped with a combustion chamber executed in vertical construction. This means that the combustion chamber for a flow of the heating medium or heating gas designed in an approximately vertical direction is. On the heating gas side, the combustion chamber can use a horizontal gas flue be connected downstream, the transition from Combustion chamber in the horizontal gas flue a redirection of the heating gas flow takes place in an approximately horizontal flow direction. However, such combustors generally require due to the temperature-related changes in length of the combustion chamber a scaffold on which the combustion chamber is suspended. This requires considerable technical effort in the Manufacture and assembly of the once-through steam generator, the order the greater the overall height of the once-through steam generator is. This is particularly the case with continuous steam generators the case for a steam output of more than 80 kg / s Are designed for full load.

A continuous steam _generator is not subject to any pressure limitation, so that live steam pressures well above the critical pressure of water (p _kri = 221 bar) - where there is only a slight difference in density between liquid-like and vapor-like medium - are possible. A high live steam pressure promotes high thermal efficiency and thus low CO ₂ emissions from a fossil-fired power plant, which can be fired with hard coal or lignite as a fuel, for example.

The design of the surrounding wall poses a particular problem the throttle cable or combustion chamber of the once-through steam generator with regard to the pipe wall or material temperatures occurring there in the subcritical pressure range up to the temperature of the surrounding wall of the Combustion chamber essentially on the level of the saturation temperature of water determined; when wetting the inner surface the evaporator tubes can be ensured. This is done, for example, by using evaporator tubes achieved a surface structure on the inside exhibit. In addition, there are in particular ribbed inside Evaporator tubes into consideration, their use in a once-through steam generator for example from the article cited above is known. These so-called finned tubes, i.e. Tube with a ribbed inner surface, have a special good heat transfer from the inner pipe wall to the flow medium.

Experience has shown that it cannot be avoided that during operation of the continuous steam generator between neighboring pipe walls of different temperatures occur, if they are welded together. This is particularly so at the connection section of the combustion chamber with the your downstream horizontal throttle cable, the case between Evaporator tubes of the outlet area of the combustion chamber and Steam generator tubes of the entry area of the horizontal throttle cable. Through these thermal stresses, the life of the Continuous steam generator can be significantly shortened, and in extreme cases even pipe rips can occur.

The invention is therefore based on the object of a fossil-fired To specify continuous steam generators of the type mentioned above, a particularly low manufacturing and assembly cost requires, and temperature differences during its operation at the connection of the combustion chamber with yours downstream horizontal throttle cable are kept low. This is intended in particular for each other directly or indirectly adjacent evaporator tubes of the combustion chamber and steam generator tubes of the horizontal gas flue downstream of the combustion chamber be the case.

This object is achieved by the continuous steam generator a combustion chamber with a number of in the height of the horizontal gas flue arranged burners, a plurality of the evaporator tubes each in parallel can be acted upon with flow medium and in the outlet area the combustion chamber using a number of in parallel Evaporator tubes acted upon by the flow medium in front of their Entry into the respective surrounding wall of the combustion chamber is guided through the combustion chamber.

The invention is based on the consideration that one with special low manufacturing and assembly costs Pass-through steam generator one that can be carried out with simple means Should have suspension structure. One with comparative low technical effort for scaffolding the suspension of the combustion chamber can be accompanied by a particularly low overall height of the once-through steam generator. A particularly low overall height of the once-through steam generator can be achieved by using the combustion chamber in a horizontal design is executed. For this purpose, the burners are at the level of the horizontal gas flue arranged in the combustion chamber wall. Thus flows when operating the once-through steam generator, the heating gas in approximately horizontal main flow direction through the combustion chamber.

When operating the continuous steam generator with the horizontal The combustion chamber should also join the combustion chamber with the horizontal throttle cable temperature differences in particular be low to premature material fatigue as a result of Avoid thermal stresses reliably. These temperature differences should be in particular between each other immediately or indirectly adjacent evaporator tubes of the combustion chamber and steam generator tubes of the horizontal throttle cable especially be small, so in the exit area of the combustion chamber and material fatigue in the entry area of the horizontal throttle cable particularly reliable as a result of thermal stresses are prevented.

The inlet section of the flow medium Evaporator tubes now point to the operation of the once-through steam generator a comparatively lower temperature than the inlet section of the steam generator tubes of the Horizontal gas flue downstream of the combustion chamber. In the evaporator tubes comparatively cold flow medium occurs a in contrast to the hot flow medium that in the steam generator tubes of the horizontal throttle cable enters. So are the evaporator tubes when operating the once-through steam generator colder than the steam generator tubes in the inlet section in the inlet section of the horizontal throttle cable. With that at the connection between the combustion chamber and the horizontal gas flue Material fatigue as a result of thermal stresses expect.

Now do not step into the evaporator tubes of the combustion chamber cold but preheated flow medium, so will the temperature difference between the inlet section of the Evaporator tubes and the inlet section of the steam generator tubes are no longer as large as when entering of cold flow medium in the evaporator tubes Would be the case. The temperature difference can still be further decrease if the pipe in which by heating the The flow medium is preheated directly to the indirect one or directly with the steam generator tubes of the horizontal gas flue connected evaporator tube connected or but is part of it. For this is a number of evaporator tubes before entering the perimeter wall of the Combustion chamber led through the combustion chamber. Here is this Number of evaporator tubes in parallel with a plurality Flow medium assigned to evaporator tubes.

The side walls of the horizontal throttle cable and / or the vertical throttle cable are advantageously made of gas-tight welded together, vertically arranged, each parallel to the flow medium actable steam generator tubes formed.

Advantageously, a number of each connected in parallel Evaporator tubes of the combustion chamber a common one Entry collector system upstream and a common one Outlet collector system for flow medium downstream. A continuous steam generator designed in this embodiment namely enables reliable pressure equalization between a number of flow media that can be acted upon in parallel Evaporator tubes so that they are all parallel connected evaporator pipes between the inlet header system and the outlet header system have the same total pressure drop exhibit. This means that with a more heated one Evaporator tube compared to a less heated one Evaporator tube the throughput must increase. This also applies to the steam generator tubes which can be acted upon in parallel with flow medium the horizontal throttle cable or the vertical throttle cable, to which advantageously a common entry collector system upstream for flow medium and a common Outlet collector system for flow medium downstream is.

The evaporator tubes of the end wall of the combustion chamber are advantageous Flow medium can be applied in parallel and the evaporator tubes of the surrounding walls that form the side walls form the combustion chamber, upstream of the fluid medium. As a result, cooling is particularly favorable strongly heated end wall of the combustion chamber guaranteed.

In a further advantageous embodiment of the invention is the inside diameter of a number of evaporator tubes the combustion chamber depending on the respective position of the evaporator tubes selected in the combustion chamber. That way the evaporator tubes in the combustion chamber to a hot gas side predeterminable heating profile adaptable. With the resultant Influence on the flow through the evaporator tubes are particularly reliable temperature differences of the flow medium at the outlet from the evaporator tubes of the combustion chamber kept particularly low.

For a particularly good heat transfer from the heat of the Combustion chamber on the flow medium in the evaporator tubes advantageously has a number of evaporator tubes a multi-start thread on the inside forming ribs. This is advantageously a Pitch angle α between a perpendicular to the pipe axis Level and the flanks of those arranged on the inside of the pipe Ribs less than 60 °, preferably less than 55 °.

In a heated, as an evaporator tube without internal fins, a so-called smooth tube, executed evaporator tube can namely from a certain steam content to that for someone special good heat transfer required wetting of the pipe wall can no longer be maintained. If there is no wetting there may be a dry pipe wall in places. The Transition to such a dry pipe wall leads to a so-called heat transfer crisis with deteriorated heat transfer behavior, so that generally the tube wall temperatures rise particularly sharply at this point. In one internally finned evaporator tube now occurs in comparison this crisis of heat transfer only contributes to a smooth tube a steam mass content> 0.9, i.e. shortly before the end of the Evaporation, on. This is due to the twist that experiences the flow through the spiral ribs. by virtue of the difference in centrifugal force becomes water Steam component separated and transported to the pipe wall. As a result, the wetting of the pipe wall up to high steam contents maintained so that at the site of the heat transfer crisis there are already high flow velocities. The causes a relatively good heat transfer despite the heat transfer crisis and as a result, low tube wall temperatures.

A number of the evaporator tubes of the combustion chamber advantageously has Means for reducing the flow of the Flow medium. It turns out to be special favorable if the means are designed as throttle devices are. Throttle devices can, for example, internals in the evaporator tubes, which are in one place inside the Reduce the inner tube diameter of the respective evaporator tube. Means to reduce the Flow in a multi-parallel lines Pipe system as advantageous, through which the evaporator tubes flow medium can be supplied to the combustion chamber. It can the pipe system also an entry collector system from Evaporator tubes that can be acted upon in parallel with flow medium be upstream. In one line or in several Lines of the line system can, for example Throttle fittings may be provided. With such means of reduction the flow of the flow medium through the Evaporator tubes can be adapted to the throughput of Flow medium through individual evaporator tubes at their respective Bring heating to the combustion chamber. Thereby are additional temperature differences of the flow medium particularly reliable at the outlet of the evaporator tubes kept low.

Adjacent evaporator or steam generator tubes are on their Long sides advantageously via metal strips, so-called Fins, welded together gastight. These fins can already in the manufacturing process of the pipes with the Connected pipes and form a unit with them. This unit, formed from a tube and fins, will also referred to as fin tube. The fin width affects the Heat input into the evaporator or steam generator tubes. Therefore the fin width is preferably dependent on the position of the respective evaporator or steam generator tubes in the Continuous steam generator to a heating profile that can be specified on the hot gas side customized. A heating profile can be a Typical heating profile determined from experience or a rough estimate, such as a step-like one Heating profile. By the suitable selected fin widths is also very different Heating various evaporator or steam generator tubes a heat input in all evaporator or Steam generator pipes can be reached in such a way that temperature differences of the flow medium at the outlet from the evaporator or steam generator tubes are kept particularly low. On this way premature material fatigue is a result of Reliably prevents thermal stress. As a result, the Continuous steam generators have a particularly long service life.

There are advantageously a number in the horizontal throttle cable arranged by superheater heating surfaces that are approximately vertical arranged to the main flow direction of the heating gas and their Pipes for a flow of the flow medium in parallel are switched. These are arranged in a hanging construction, also referred to as bulkhead heating surfaces are mainly heated by convection and are on the flow medium side downstream of the evaporator tubes of the combustion chamber. This is a particularly favorable use of Heating gas heat guaranteed.

The vertical throttle cable advantageously has a number of Convection heating surfaces, which are approximately perpendicular to the Main flow direction of the heating gas arranged tubes formed are. These pipes of a convection heating surface are for a flow of the flow medium connected in parallel. These convection heating surfaces also become predominantly convective heated.

To continue to make full use of the heat To ensure the heating gas, the vertical throttle cable advantageously has an economizer.

The burners are advantageously arranged on the end wall of the combustion chamber, that is to say on the side wall of the combustion chamber which lies opposite the outflow opening to the horizontal gas flue. A continuous steam generator designed in this way can be adapted in a particularly simple manner to the burnout length of the fossil fuel. The burnout length of the fossil fuel is to be understood as the heating gas velocity in the horizontal direction at a specific mean heating gas temperature multiplied by the burnout time t _{A of} the flame of the fossil fuel. The maximum burnout length for the respective continuous steam generator results from the steam output M at full load of the continuous steam generator, the so-called full load operation. The burn-out time t _{A of} the flame of the fossil fuel is in turn the time that, for example, a medium-sized coal dust particle takes to completely burn out at a certain average heating gas temperature.

To material damage and unwanted pollution of the Horizontal throttle cable, for example due to the entry of molten ash of a high temperature, particularly low to hold is by the distance from the front wall Length defined to the entry area of the horizontal throttle cable the combustion chamber advantageously at least equal to the burnout length of the fossil fuel at full load operation of the Through steam generator. This horizontal length of the combustion chamber will generally be at least 80% of the amount Combustion chamber, measured from the top of the funnel, if the lower part of the combustion chamber is funnel-shaped is up to the combustion chamber ceiling.

For a particularly favorable utilization of the heat of combustion of the fossil fuel, the length L (specified in m) of the combustion chamber is advantageously a function of the steam output M (specified in kg / s) of the continuous steam generator at full load, the burnout time t _A (specified in s) of the flame of the fossil fuel and the outlet temperature T _BRK (specified in ° C) of the heating gas from the combustion chamber. For a given steam output M of the continuous steam generator at full load, the length L of the combustion chamber approximately applies to the larger value of the two functions (I) and (II): L (M, t A ) = (C 1 + C 2 · M) · t A and L (M, T BRK ) = (C 3 · T BRK + C 4 ) M + C 5 (T BRK ) 2 + C 6 · T BRK + C7 With
C ₁ = 8 m / s and
C ₂ = 0.0057 m / kg and
C ₃ = -1.905 · 10 ^-4 (m · s) / (kg ° C) and
C ₄ = 0.286 (s · m) / kg and
C ₅ = 3 · 10 ^-4 m / (° C) ² and
C ₆ = -0.842 m / ° C and
C ₇ = 603.41 m.

Under "approximate" is a permissible deviation the length L of the combustion chamber by the respective function to understand the defined value by +20% / - 10%.

The lower region of the combustion chamber is advantageously as Funnel formed. In this way, when operating the Continuous steam generator in the combustion of the fossil Ashes are easily removed, for example, one located under the funnel Ash removal. With fossil fuel it can are coal in solid form.

The advantages achieved with the invention are in particular in that by guiding some evaporator tubes through the combustion chamber before it enters the surrounding wall the combustion chamber, temperature differences in the immediate Surrounding the connection of the combustion chamber with the horizontal gas flue especially when operating the continuous steam generator turn out small. The difference in temperature between immediately adjacent evaporator tubes of the combustion chamber and steam generator tubes of the horizontal throttle cable Thermal stresses at the connection of the combustion chamber with the Horizontal gas flues therefore remain in operation of the once-through steam generator far below the values where, for example there is a risk of pipe rips. So that's the Use of a horizontal combustion chamber in a once-through steam generator even with a comparatively long service life possible. By designing the combustion chamber for approximately horizontal main flow direction of the heating gas also a particularly compact design of the once-through steam generator given. This enables the continuous steam generator to be integrated in a power plant with a steam turbine also particularly short connecting pipes from the once-through steam generator to the steam turbine.

FIG 1

schematisch einen fossilbeheizten Durchlaufdampferzeuger in Zweizugbauart in Seitenansicht und

FIG 2

schematisch einen Längsschnitt durch ein einzelnes Verdampferrohr,

FIG 3

ein Koordinatensystem mit den Kurven K₁ bis K₆,

FIG 4

schematisch die Verbindung der Brennkammer mit dem Horizontalgaszug und

FIG 5

ein Koordinatensystem mit den Kurven U₁ bis U₄.

An embodiment of the invention is explained in more detail with reference to a drawing. In it show:

FIG. 1

schematically a fossil-heated continuous steam generator in two-pass design in side view and

FIG 2

schematically shows a longitudinal section through a single evaporator tube,

FIG 3

a coordinate system with the curves K ₁ to K ₆ ,

FIG 4

schematically the connection of the combustion chamber with the horizontal gas flue and

FIG 5

a coordinate system with the curves U ₁ to U ₄ .

Corresponding parts are in all figures with the provided with the same reference numerals.

The fossil-heated continuous steam generator 2 according to FIG. 1 is assigned to a power plant, not shown, which also includes a steam turbine plant. Here is the Continuous steam generator 2 for a steam output at full load of at least 80 kg / s. The one in the once-through steam generator 2 generated steam is used to drive the steam turbine used, which in turn a generator for power generation drives. The electricity generated by the generator is provided for feeding into a network or an island network.

The fossil-fueled continuous steam generator 2 comprises an in horizontal design combustion chamber 4, the hot gas side a vertical throttle cable 8 via a horizontal throttle cable 6 is connected downstream. The lower area of the combustion chamber 4 is through a funnel 5 with an upper edge corresponding to the Auxiliary line with the end points X and Y formed. By the Funnel 5 can operate the continuous steam generator 2 Ashes of the fossil fuel B in an arranged below Deashing device 7 are removed. The surrounding walls 9 of the combustion chamber 4 are welded together gas-tight, vertically arranged evaporator tubes 10 are formed, a number of which are N in parallel with flow medium S is acted upon. A surrounding wall 9 is the Combustion chamber 4 the front wall 11. In addition, the side walls 12 of the horizontal throttle cable 6 and 14 of the vertical gas cable 8 of gas-tightly welded, vertically arranged Steam generator tubes 16 and 17 formed. Are there a number of steam generator tubes 16 and 17 each in parallel can be acted upon with flow medium S.

A number of the evaporator tubes 10 of the combustion chamber 4 an inlet header system 18 for Flow medium S upstream and an outlet collector system 20 downstream. Entry collector system 18 includes a number of parallel entry collectors. It is for supplying flow medium S into the inlet header system 18 of the evaporator tubes 10, a line system 19 is provided. The line system 19 comprises several connected in parallel Lines, each with one of the entry collectors of the entry collector system 18 are connected.

In the same way, the flow medium S can be acted upon in parallel Steam generator tubes 16 of the side walls 12 of the Horizontal throttle cable 6 a common inlet collector system 21 upstream and a common outlet collector system 22 downstream. S is for supplying flow medium into the inlet header system 21 of the steam generator tubes 16 a line system 19 is also provided. The pipe system also includes several lines connected in parallel, each with one of the entry collectors of the entry collection system 21 are connected.

Through this configuration of the continuous steam generator 2 with Entry collector systems 18, 21 and exit collector systems 20, 22 is a particularly reliable pressure compensation between the evaporator tubes 10 connected in parallel Combustion chamber 4 or the steam generator tubes connected in parallel 16 of the horizontal throttle cable 6 possible in such a way that all parallel connected evaporator or steam generator tubes 10 or 16 have the same total pressure drop. This means that with a more heated evaporator tube 10 or steam generator tube 16 compared to one less heated evaporator tube 10 or steam generator tube 16 the throughput must increase.

The evaporator tubes 10 have - as shown in Figure 2 - an inner tube diameter D and ribs on the inside 40, which form a kind of multi-start thread and one Have rib height C. The pitch angle α is between a plane 42 perpendicular to the pipe axis and the flanks 44 of the ribs 40 arranged on the inside of the tube are smaller than 55 °. This results in a particularly high heat transfer from the Inner walls of the evaporator tubes 10 to that in the evaporator tubes 10 guided flow medium S and at the same time special low pipe wall temperatures reached.

The inner tube diameter D of the evaporator tubes 10 of the combustion chamber 4 depends on the respective position of the evaporator tubes 10 selected in the combustion chamber 4. In this way the continuous steam generator 2 is different strong heating of the evaporator tubes 10 adapted. This interpretation the evaporator tubes 10 ensures the combustion chamber 4 particularly reliable that temperature differences in the flow medium S particularly when leaving the evaporator tubes 10 are kept low.

As a means to reduce the flow of the flow medium S are part of the evaporator tubes 10 with throttling devices equipped, which are not shown in the drawing are shown. The throttling devices are called the inner pipe diameter D perforated shutters at one point executed and cause the operation of the continuous steam generator 2 a reduction in the throughput of the flow medium S in less heated evaporator tubes 10, whereby the Throughput of the flow medium S is adapted to the heating.

Furthermore, as a means of reducing the throughput of the Flow medium S in the evaporator tubes 10 one or more Lines of the line system, not shown 19 with throttle devices, in particular throttle fittings, fitted.

Adjacent evaporator or steam generator tubes 10, 16, 17 are in a manner not shown in the drawing their long sides welded together gas-tight over fins. With a suitable choice of fin width namely the heating of the evaporator or steam generator tubes 10, 16, 17 are influenced. Therefore, the respective one Fin width on a heating profile that can be specified on the hot gas side adapted from the position of the respective evaporator or steam generator tubes 10, 16, 17 in the continuous steam generator 2 depends. The heating profile can be based on empirical values determined typical heating profile or be a rough estimate. This means temperature differences at the outlet of the evaporator or steam generator tubes 10, 16, 17 even with very different heating the evaporator or steam generator tubes 10, 16, 17 particularly kept low. In this way, material fatigue is considered Consequences of thermal stress reliably prevented what a long life of the continuous steam generator 2 guaranteed.

When piping the horizontal combustion chamber 4, it must be taken into account that heating the individual, each other gas-tight welded evaporator tubes 10 when operating the Pass-through steam generator 2 is very different. therefore is the design of the evaporator tubes 10 in terms of their Internal fins, their fin connection to neighboring evaporator tubes 10 and their inner pipe diameter D are selected that all evaporator tubes 10 despite different Heating approximately the same outlet temperatures of the flow medium S have and sufficient cooling of all Evaporator tubes 10 for all operating states of the continuous steam generator 2 is guaranteed. A minor heating of some Evaporator tubes 10 during operation of the continuous steam generator 2 is achieved by installing throttling devices additionally considered.

The inner tube diameter D of the evaporator tubes 10 in the Combustion chamber 4 are dependent on their respective position selected in the combustion chamber 4. Evaporator tubes show 10, one in the operation of the once-through steam generator 2 exposed to greater heating, a larger pipe inside diameter D on as evaporator tubes 10, which are in operation of the continuous steam generator 2 are heated less. This is compared to the case with the same inner pipe diameters achieved that the flow rate of the flow medium S in the evaporator tubes 10 with a larger inner tube diameter D increases and thus temperature differences at the outlet the evaporator tubes 10 due to different heating be reduced. Another measure, the flow the evaporator tubes 10 with flow medium S to the heating to adapt, the installation of throttle devices in one Part of the evaporator tubes 10 and / or for the supply of Flow medium S provided line system 19. In contrast the heating to the throughput of the flow medium S. to adjust the evaporator tubes 10, the fin width in Depending on the position of the evaporator tubes 10 in the Combustion chamber 4 can be selected. Effect all of the above measures despite strongly different heating of the individual Evaporator tubes 10 have approximately the same specific heat absorption of the flow medium guided in the evaporator tubes 10 S during the operation of the continuous steam generator 2 and thus only slight temperature differences of the flow medium S at their exit. The internal fins of the evaporator tubes 10 is designed so that a particularly reliable Cooling of the evaporator tubes 10 despite different heating and flow through with flow medium S in all load conditions of the continuous steam generator 2 is guaranteed.

The horizontal throttle cable 6 has a number of bulkhead heating surfaces trained superheater heating surfaces 23, which in hanging construction approximately perpendicular to the main flow direction 24 of the heating gas G arranged and their tubes for a flow through the flow medium S in parallel are switched. The superheater heating surfaces 23 are predominant heated by convection and are on the flow medium side Evaporator tubes 10 downstream of the combustion chamber 4.

The vertical throttle cable 8 has a number of predominantly convective heatable convection heating surfaces 26, which come from approximately perpendicular to the main flow direction 24 of the heating gas G arranged tubes are formed. These pipes are for a flow through the flow medium S in parallel connected. There is also an economizer in the vertical throttle cable 8 28 arranged. The vertical throttle cable 8 opens on the output side in another heat exchanger, for example in one Air preheater and from there via a dust filter into one Stack. The components downstream of the vertical throttle cable 8 are not shown in the drawing.

The continuous steam generator 2 is horizontal Combustion chamber 4 with a particularly low overall height and thus with particularly low manufacturing and assembly costs be set up at. For this purpose, the combustion chamber 4 of the once-through steam generator 2 a number of burners 30 for fossil Fuel B on the end wall 11 of the combustion chamber 4th are arranged at the level of the horizontal throttle cable 6. In which fossil fuel B can be solid fuels, trade coal in particular.

So that the fossil fuel B, for example coal in solid form, burns out particularly completely to achieve a particularly high degree of efficiency and material damage to the first superheater heating surface 23 of the horizontal gas flue 6, as seen on the hot gas side, and contamination thereof, for example due to the introduction of molten ash at high temperature, is prevented particularly reliably are, the length L of the combustion chamber 4 is selected such that it exceeds the burnout length of the fossil fuel B when the continuous steam generator 2 is operating at full load. The length L is the distance from the end wall 11 of the combustion chamber 4 to the inlet area 32 of the horizontal gas flue 6. The burnout length of the fossil fuel B is defined as the heating gas velocity in the horizontal direction at a specific mean heating gas temperature multiplied by the burnout time t _{A of} the flame F. of the fossil fuel B. The maximum burn-out length for the respective continuous steam generator 2 results when the respective continuous steam generator 2 is operating at full load. The burn-out time t _{A of} the flame F of the fuel B is in turn the time it takes, for example, a medium-sized coal dust grain to completely burn out at a specific medium Heating gas temperature required.

In order to ensure particularly favorable utilization of the heat of combustion of the fossil fuel B, the length L (specified in m) of the combustion chamber 4 is dependent on the outlet temperature T _BRK (specified in ° C.) of the heating gas G from the combustion chamber 4; the burnout time t _A (specified in s) of the flame F of the fossil fuel B and the steam output M (specified in kg / s) of the continuous steam generator 2 at full load are selected appropriately. This horizontal length L of the combustion chamber 4 is at least 80% of the height H of the combustion chamber 4. The height H is marked from the top edge of the funnel 5 of the combustion chamber 4, in FIG. 1 by the auxiliary line with the end points X and Y, to Combustion chamber ceiling measured. The length L of the combustion chamber 4 is approximately determined by the functions (I) and (II): L (M, t A ) - (C 1 + C 2 · M) · t A and L (M, T BRK ) = (C 3 · T BRK + C 4 ) M + C 5 (T BRK ) 2 + C 6 · T BRK + C7 With
C ₁ = 8 m / s and
C ₂ = 0.0057 m / kg and
C ₃ = -1.905 · 10 ^-4 (m · s) / (kg ° C) and
C ₄ = 0.286 (s · m) / kg and
C ₅ = 3 · 10 ^-4 m / (° C) ² and
C ₆ = -0.842 m / ° C and
C ₇ = 603.41 m.

Approximately here is a permissible deviation of the Length L of the combustion chamber 4 by +20% / - 10% from the respective Understand function defined value. The following applies to the design of the continuous steam generator 2 for a given Steam output M of the continuous steam generator 2 at full load the larger value from functions (I) and (II) for the Length L of the combustion chamber 4.

K₁: t_A = 3s   gemäß (I),

K₂: t_A = 2,5s   gemäß (I),

K₃: t_A = 2s   gemäß (I),

K₄: T_BRK = 1200°C   gemäß (II),

K₅: T_BRK = 1300°C   gemäß (II),

K₆: T_BRK = 1400°C   gemäß (II).

As an example of a possible design of the continuous steam generator 2, six curves K ₁ to K _{6 are} drawn for some lengths L of the combustion chamber 4 as a function of the steam output M of the continuous steam generator 2 at full load in the coordinate system according to FIG. The following parameters are assigned to the curves:

K ₁ : t _A = 3s according to (I),

K ₂ : t _A = 2.5s according to (I),

K ₃ : t _A = 2s according to (I),

K ₄ : T _BRK = 1200 ° C according to (II),

K ₅ : T _BRK = 1300 ° C according to (II),

K ₆ : T _BRK = 1400 ° C according to (II).

To determine the length L of the combustion chamber 4, the curves K ₁ and K ₄ are thus to be used, for example, for the burnout time t _A = 3 s of the flame F of the fossil fuel B and the exit temperature T _BRK = 1200 ° C. of the heating gas G from the combustion chamber 4. This results at a predetermined steam output M of the continuous steam generator 2 at full load
from M = 80 kg / s a length of L = 29 m according to K ₄ ,
from M = 160 kg / s a length of L = 34 m according to K ₄ ,
from M = 560 kg / s a length of L = 57 m according to K ₄ .

The curve K ₄ drawn as a solid line always applies.

For the burnout time t _A = 2.5 s of the flame F of the fossil fuel B and the exit temperature of the heating gas G from the combustion chamber T _BRK = 1300 ° C., the curves K ₂ and K _{5 are to} be used, for example. This results at a predetermined steam output M of the continuous steam generator 2 at full load
from M = 80 kg / s a length of L = 21 m according to K ₂ ,
from M = 180 kg / s a length of L = 23 m according to K ₂ and K ₅ ,
from M = 560 kg / s a length of L = 37 m according to K ₅ .

The part of the curve K ₂ which is drawn as a solid line and not the curve K ₅ drawn as a dashed line in this value range of M applies to M = 180 kg / s. For values of M which are greater than 180 kg / s, the part of the curve K ₅ that is drawn as a solid line applies and not the curve K ₂ drawn as a dashed line in this value range of M.

The burnout time t _A = 2s of the flame F of the fossil fuel B and the outlet temperature T _BRK = 1400 ° C. of the heating gas G from the combustion chamber 4 are assigned, for example, the curves K ₃ and K ₆ . This results at a predetermined steam output M of the continuous steam generator 2 at full load
from M = 80 kg / s a length of L = 18 m according to K ₃ ,
from M = 465 kg / s a length of L = 21 m according to K ₃ and K ₆ ,
from M = 560 kg / s a length of L = 23 m according to K ₆ .

For values from M to 465 kg / s, the curve K ₃ drawn as a solid line in this area and not the curve K ₆ drawn as a dashed line in this area applies. For values of M which are greater than 465 kg / s, the part of the curve K ₆ drawn as a solid line and not the part of the curve K ₃ drawn as a broken line applies.

So that between the exit region 34 of the combustion chamber 4 and the entry area 32 of the horizontal throttle cable 6 during operation of the continuous steam generator 2 comparatively small temperature differences occur, the evaporator tubes 50 and 52 in the connection section Z marked in FIG. 1 in particular Led way. This connecting section Z is in Figure 4 shown in detail and includes the exit area 34 of the combustion chamber 4 and inlet area 32 of the horizontal gas flue 6. The evaporator tube 50 is the immediate one welded to the side wall 12 of the horizontal throttle cable 6 Evaporator tube 50 of the peripheral wall 9 of the combustion chamber 4 and the evaporator tube 52 is the evaporator tube immediately adjacent to this 52 of the peripheral wall 9 of the combustion chamber 4.

These two evaporator tubes 50 and 52 join together the evaporator tubes 10 connected in parallel from the common entry collector system 18. Then, however both the evaporator tube 50 and the evaporator tube 52 initially opposite in an approximately horizontal direction to the main flow direction 24 of the heating gas G outside of Combustion chamber 4 out. Then they enter the combustion chamber 4 and will not be immediately upon entering the combustion chamber 4 is part of the peripheral wall 9 of the combustion chamber 4. They are namely along the main flow direction 24 of the heating gas G in the combustion chamber 4 up to the area returned to where it is outside the combustion chamber 4th are branched off from their approximately vertical course in order to opposite to the main flow direction 24 of the heating gas G to get lost. Only after this loop are they in the surrounding wall 9 the combustion chamber 4 welded so that it are part of the peripheral wall 9 of the combustion chamber 4.

Due to this special pipe routing, the Continuous steam generator 2, the evaporator tubes 50 and 52 in front preheated their entry into the peripheral wall 9 of the combustion chamber 4. The flow medium S carried in them becomes heated during operation of the once-through steam generator 2 and thus preheated so that it has a comparatively higher temperature enters the peripheral wall 9 of the combustion chamber 4, than this in the in the directly to the evaporator tubes 50th and 52 adjacent evaporator tubes 10 of the combustion chamber 4 of the Case is. Through this special pipe routing of the evaporator pipes 50 and 52 have the evaporator tubes 50 and 52 in the inlet section E when operating the continuous steam generator 2 a comparatively higher temperature than that of them directly adjacent evaporator tubes 10 of the surrounding wall 9 of the combustion chamber 4. As a result, the continuous steam generator is in operation 2 Temperature differences at connection 36 between the combustion chamber 4 and the horizontal gas flue 6 particularly reliably kept particularly low.

As an example of possible temperatures T _{s of} the flow medium S in the evaporator tubes 10 of the combustion chamber 4 or the steam generator tubes 16 of the horizontal gas flue 6, the coordinate system according to FIG. 5 for some temperatures T _s (specified in ° C.) as a function of the relative tube length R (given in%) the curves U ₁ to U _{4 are} entered. U ₁ describes the temperature profile of a steam generator tube 16 of the horizontal gas flue 6. U _2, on the other hand, describes the temperature profile of an evaporator tube 10 along its relative tube length R. U ₃ describes the temperature profile of the specially guided evaporator tube 50 and U ₄ describes the temperature profile of the evaporator tube 52 of the surrounding wall 9 the combustion chamber 4. It can be seen from the graphs that the special pipe routing of the evaporator pipes 50 and 52 in the inlet section E in the peripheral wall 9 of the combustion chamber 4 allows the temperature difference to the steam generator pipes 16 of the peripheral wall 12 of the horizontal gas flue to be significantly reduced. In the example, the temperature of the evaporator tubes 50 and 52 in the inlet section E of the evaporator tubes 50 and 52 can be increased by 45 Kelvin. As a result, particularly small temperature differences in the inlet section E of the evaporator tubes 50 and 52 and the steam generator tubes 16 of the horizontal gas flue 6 are ensured at the connection 36 between the combustion chamber 4 and the horizontal gas flue 6 during the operation of the continuous steam generator 2.

During operation of the continuous steam generator 2, the burners 30 fossil fuel B, preferably coal in solid Shape, fed. The flames F of the burner 30 are horizontal aligned. Due to the design of the combustion chamber 4 becomes a flow of the heating gas generated during combustion G in approximately horizontal main flow direction 24 generated. This reaches the horizontal throttle cable 6 in the vertical throttle cable 8 and approximately aligned with the floor leaves this in the direction of the fireplace, not shown.

Flow medium S entering the economizer 28 arrives in the inlet header system 18 of the evaporator tubes 10 of the Combustion chamber 4 of the once-through steam generator 2. In the vertical arranged, gastight welded evaporator tubes 10 of the combustion chamber 4 of the once-through steam generator 2 finds the evaporation and possibly a partial one Overheating of the flow medium S instead. The resulting one Steam or a water-steam mixture is in the outlet collector system 20 collected for flow medium S. Of there the steam or the water-steam mixture passes through the Walls of the horizontal throttle cable 6 and the vertical gas cable 8 in the superheater heating surfaces 23 of the horizontal throttle cable 6. In the Superheater heating surfaces 23 further overheat the Steam, which is subsequently used, for example by the Drive a steam turbine, is supplied.

With the special guide of the evaporator tubes 50 and 52 fall temperature differences during operation of the continuous steam generator between the outlet area 34 of the combustion chamber 4 and the entry area 32 of the horizontal throttle cable 6 in particular low. Here is a choice of the length L of the combustion chamber 4 as a function of the steam output M of the once-through steam generator 2 at full load ensures that the heat of combustion of the fossil fuel B is particularly reliable is exploited. The continuous steam generator can also be used 2 due to its particularly low height and compact Construction with particularly low manufacturing and assembly costs build. It can be a comparatively small The technical complexity of the scaffold can be provided. at a power plant with a steam turbine and a continuous steam generator 2 having such a low overall height can also connect the connecting pipes from the once-through steam generator designed for the steam turbine in a particularly short manner his.

Claims (19)

1. Continuous-flow steam generator (2) with a combustion chamber (4) for fossil fuel (B) which is followed on the fuel-gas side, via a horizontal gas flue (6), by a vertical gas flue (8), the combustion chamber (4) comprising a number of burners (30) arranged level with the horizontal gas flue (6), and the containment walls (9) of the combustion chamber (4) being formed from vertically arranged evaporator tubes (10) welded to one another in a gastight manner, a plurality of the evaporator tubes (10) being capable of being acted upon in each case in parallel by flow medium (S), and, in the exit region (34) of the combustion chamber (4), a number of the evaporator tubes (10) capable of being acted upon in parallel by flow medium (S) being led through the combustion chamber (4) before their entry into the respective containment wall (9) of the combustion chamber (4).
2. Continuous-flow steam generator (2) according to Claim 1, in which the side walls (12) of the horizontal gas flue (6) are formed from vertically arranged steam generator tubes (16) welded to one another in a gastight manner and capable of being acted upon in parallel by flow medium (S).
3. Continuous-flow steam generator (2) according to Claim 1 or 2, in which the side walls (14) of the vertical gas flue (8) are formed from vertically arranged steam generator tubes (17) welded to one another in a gastight manner and capable of being acted upon in parallel by flow medium (S).
4. Continuous-flow steam generator (2) according to one of Claims 1 to 3, in which, in each case, a plurality of evaporator tubes (10) capable of being acted upon in parallel by flow medium (S) are, on the flow-medium side, preceded by a common entry header system (18) and followed by a common exit header system (20).
5. Continuous-flow steam generator (2) according to one of Claims 1 to 4, in which, in each case, a number of steam generator tubes (16, 17) of the horizontal gas flue (6) or of the vertical gas flue (8) which are capable of being acted upon in parallel by flow medium (S) are, on the flow-medium side, preceded by a common entry header system (21) and followed by a common exit header system (22).
6. Continuous-flow steam generator (2) according to one of Claims 1 to 5, in which one containment wall (9) of the combustion chamber (4) is the end wall (11), the evaporator tubes (10) of the end wall (9) being capable of being acted upon in parallel by flow medium (S).
7. Continuous-flow steam generator (2) according to one of Claims 1 to 6, in which the evaporator tubes (10) of the end wall (11) of the combustion chamber (4) precede the other containment walls (9) of the combustion chamber (4) on the flow-medium side.
8. Continuous-flow steam generator (2) according to one of Claims 1 to 7, in which the tube inside diameter (D) of a number of the evaporator tubes (10) of the combustion chamber (4) is selected as a function of the respective position of the evaporator tubes (10) in the combustion chamber (4).
9. Continuous-flow steam generator (2) according to one of Claims 1 to 8, in which a number of the evaporator tubes (10) carry in each case, on their inside, ribs (40) forming a multiflight thread.
10. Continuous-flow steam generator (2) according to Claim 9, in which a pitch angle (α) between a plane (42) perpendicular to the tube axis and the flanks (44) of the ribs (40) arranged on the tube inside is smaller than 60°, preferably smaller than 55°C.
11. Continuous-flow steam generator (2) according to one of Claims 1 to 10, in which a number of the evaporator tubes (10) in each case have a throttle device.
12. Continuous-flow steam generator (2) according to one of Claims 1 to 11, in which a line system (19) is provided for supplying flow medium (S) into the evaporator tubes (10) of the combustion chamber (4), the line system (19) having a number of throttle devices, in particular throttle accoutrements, for reducing the throughflow of the flow medium (S).
13. Continuous-flow steam generator (2) according to one of Claims 1 to 12, in which adjacent evaporator or steam generator tubes (10, 16, 17) are welded to one another in a gastight manner via fins, the fin width being selected as a function of the respective position of the evaporator or steam generator tubes (10, 16, 17) in the combustion chamber (4), of the horizontal gas flue (6) and/or of the vertical gas flue (8).
14. Continuous-flow steam generator (2) according to one of Claims 1 to 13, in which a number of superheater heating surfaces (23) are arranged in a suspended form of construction in the horizontal gas flue (6).
15. Continuous-flow steam generator (2) according to one of Claims 1 to 14, in which a number of convection heating surfaces (26) are arranged in the vertical gas flue (8).
16. Continuous-flow steam generator (2) according to one of Claims 1 to 15, in which the burners (58) are arranged on the end wall (11) of the combustion chamber (4).
17. Continuous-flow steam generator (2) according to one of Claims 1 to 16, in which the length (L) of the combustion chamber (4), defined by the distance from the end wall (11) of the combustion chamber (4) to the entry region (32) of the horizontal gas flue (6), is at least equal to the burnup length of the fuel (B) in the full-load mode.
18. Continuous-flow steam generator (2) according to one of Claims 1 to 17, in which the length (L) of the combustion chamber (4) is selected as a function of the steam power output (M) under full load, the burnup time (t_A) of the flame (F) of the fuel (B) and/or the exit temperature (T_BRK) of the fuel gas (G) from the combustion chamber (4) approximately according to the two functions (I) and (II) L (M, tA) = (C1 + C2 · M) · tA and L (M, TBRK) = (C3 · TBRK + C4)M + C5 (TBRK)2 + C6 · TBRK + C7 with
       C₁ = 8 m/s   and
       C₂ = 0.0057 m/kg   and
       C₃ = -1.905 · 10^-4 (m · s)/(kg°C)   and
       C₄ = 0.286 (s · m)/kg   and
       C₅ = 3 · 10^-4 m/(°C)²   and
       C₆ = -0.842 m/°C   and
       C₇ = 603.41 m,
    the in each case higher value of the length (L) of the combustion chamber (4) applying to a predetermined steam power output (M) under full load.
19. Continuous-flow steam generator (2) according to one of Claims 1 to 18, in which the lower region of the combustion chamber (4) is designed as a funnel (5).

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