EP1166015A1

EP1166015A1 - Fossil-fuel fired continuous-flow steam generator

Info

Publication number: EP1166015A1
Application number: EP00922444A
Authority: EP
Inventors: Eberhard Wittchow
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1999-03-31
Filing date: 2000-03-20
Publication date: 2002-01-02
Anticipated expiration: 2020-03-20
Also published as: CA2368972A1; CA2368972C; DE19914760C1; JP4489307B2; DK1166015T3; RU2224949C2; CN1344360A; DE50006755D1; JP2002541419A; US6715450B1; KR20010112293A; EP1166015B1; KR100694356B1; WO2000060283A1; ES2222900T3; CN1193191C; ATE268882T1

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

description

Fossil-heated continuous steam generator

The invention relates to a once-through steam generator which has a combustion chamber for fossil fuel, which is followed by a vertical gas flue on the hot gas side via a horizontal gas flue, the peripheral walls of the combustion chamber being formed from vertically arranged evaporator tubes welded together in a gastight manner.

In a power plant with a steam generator, the energy content of a fuel is used to evaporate a flow medium in the steam generator. The flow medium is usually conducted in an evaporator circuit. The steam provided by the steam generator can in turn be provided, for example, for driving a steam turbine and / or for a connected external process. If the steam drives a steam turbine, a generator or a working machine is usually operated via the turbine shaft of the steam turbine. In the case of a generator, the current generated by the generator can be provided for feeding into a network and / or island network.

The steam generator can be designed as a continuous steam generator. A continuous steam generator is known from the article "Evaporator concepts for Benson steam generators" by J. Franke, W. Köhler and E. ittchow, published in VGB Kraftwerkstechnik 73 (1993), No. 4, pp. 352-360 Pass-through steam generator leads the heating of steam generator pipes provided as evaporator pipes to an evaporation of the flow medium in the steam generator pipes in a single pass.

Pass-through steam generators are usually designed with a combustion chamber in a vertical design. This means that the combustion chamber is designed for a flow through the heating medium or heating gas in an approximately vertical direction. On the heating gas side, a horizontal gas flue can be connected downstream of the combustion chamber, with the heating gas flow being deflected into an approximately horizontal flow direction during the transition from the combustion chamber to the horizontal gas flue. However, such combustion chambers generally require a framework on which the combustion chamber is suspended due to the temperature-related changes in length of the combustion chamber. This requires considerable technical effort in the manufacture and assembly of the once-through steam generator, which is greater the greater the overall height of the once-through steam generator. This is particularly the case with continuous steam generators, which are designed for a steam output of more than 80 kg / s at full load.

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

The design of the peripheral wall of the gas flue or combustion chamber of the once-through steam generator poses a particular problem with regard to the pipe wall or material temperatures that occur there. In the subcritical pressure range up to approximately 200 bar, the temperature of the peripheral wall of the combustion chamber essentially depends on the level of the saturation temperature of the water determines, 'when a wetting of the inner surface of ^the' evaporator tubes can be ensured. This is achieved, for example, by using evaporator tubes which have a surface structure on the inside. In addition, there are in particular ribbed inside Evaporator tubes into consideration, the use of which in a once-through steam generator is known, for example, from the article cited above. These so-called finned tubes, ie tubes with a finned inner surface, have a particularly good heat transfer from the inner tube wall to the flow medium.

Experience has shown that it cannot be avoided that thermal stresses occur between adjacent tube walls of different temperatures when the continuous steam generator is in operation when these are welded together. This is the case in particular in the connection section of the combustion chamber with the horizontal gas flue downstream of it, that is to say between evaporator tubes of the outlet region of the combustion chamber and steam generator tubes of the inlet region of the horizontal gas flue. These thermal stresses can significantly shorten the lifespan of the once-through steam generator and, in extreme cases, even pipe tears can occur.

The invention is therefore based on the object of specifying a fossil-fired once-through steam generator of the type mentioned above, which requires a particularly low manufacturing and assembly outlay and, during its operation, temperature differences at the connection of the combustion chamber with the horizontal gas flue downstream thereof are kept small. This should be the case in particular for the evaporator tubes of the combustion chamber which are directly or indirectly adjacent to one another and steam generator tubes of the horizontal gas flue downstream of the combustion chamber.

This object is achieved according to the invention by the through steam generator ugs having a combustion chamber with a number of in the height of the Horizontalgasz ^'arranged burners, where a ^"plurality of evaporator tubes is respectively paral- lel acted upon by the flow medium, and in the exit region of the combustion chamber, a number of Evaporator tubes that can be acted upon in parallel with flow medium in front of their Entry into the respective peripheral wall of the combustion chamber is guided through the combustion chamber.

The invention is based on the consideration that a continuous steam generator that can be produced with particularly low manufacturing and assembly costs should have a suspension construction that can be carried out with simple means. A scaffold for suspending the combustion chamber that can be created with comparatively little technical effort can go hand in hand with 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 designing the combustion chamber in a horizontal construction. For this purpose, the burners are arranged at the level of the horizontal gas flue in the combustion chamber wall. Thus, when the continuous steam generator is operating, the heating gas flows through the combustion chamber in an approximately horizontal main flow direction.

When operating the continuous steam generator with the horizontal combustion chamber, temperature differences at the connection of the combustion chamber with the horizontal gas flue should also be particularly small in order to reliably avoid premature material fatigue as a result of thermal stresses. These temperature differences should be particularly small, in particular between directly or indirectly adjacent evaporator tubes of the combustion chamber and steam generator tubes of the horizontal gas flue, so that material fatigue as a result of thermal stresses is particularly reliably prevented in the outlet region of the combustion chamber and in the inlet region of the horizontal gas flue.

The inlet section of the evaporator tubes charged with flow medium now has a comparatively lower temperature during operation of the once-through steam generator than the inlet section of the steam generator tubes of the horizontal gas flue downstream of the combustion chamber. Comparatively cold flow flows into the evaporator tubes medium in contrast to the hot flow medium that enters the steam generator tubes of the horizontal gas flue. The evaporator tubes are therefore colder in the inlet section when the continuous steam generator is operating than the steam generator tube in the inlet section of the horizontal gas flue. Material fatigue as a result of thermal stresses is therefore to be expected at the connection between the combustion chamber and the horizontal gas flue.

If, however, cold, but preheated, flow medium enters the evaporator tubes of the combustion chamber, the temperature difference between the inlet section of the evaporator pipes and the inlet section of the steam generator pipes will no longer be as great as would be the case if cold flow medium entered the evaporator pipes Would be the case. The temperature difference can be reduced even further if the tube in which the flow medium is preheated by heating is connected directly to the evaporator tube connected directly or indirectly to the steam generator tubes of the horizontal gas flue, or is a part of the same. For this purpose, a number of the evaporator tubes are guided through the combustion chamber before they enter the peripheral wall of the combustion chamber. This number of evaporator tubes is assigned to a plurality of evaporator tubes that can be acted upon in parallel with flow medium.

The side walls of the horizontal gas flue and / or the vertical gas flue are advantageously formed from steam generator tubes which are welded to one another in a gastight manner and are arranged vertically and in each case can be acted upon in parallel with flow medium.

Advantageously, a common inlet manifold system is connected upstream of a number of evaporator tubes connected in parallel to the combustion chamber and a common outlet manifold system for flow medium is connected downstream.

A continuous steam generator designed in this embodiment enables reliable pressure equalization between a number of evaporator tubes which can be acted upon in parallel with flow medium, so that in each case all evaporator tubes connected in parallel between the inlet header system and the outlet header system have the same total pressure loss. This means that the throughput must increase in the case of a multi-heated evaporator tube in comparison with a less-heated evaporator tube. This also applies to the steam generator tubes of the horizontal gas flue or the vertical gas flue, which can be acted upon in parallel with flow medium, which advantageously are preceded by a common inlet header system for flow medium and a common outlet header system for flow medium is connected downstream.

The evaporator tubes of the end wall of the combustion chamber can advantageously be acted upon in parallel with flow medium and upstream of the evaporator tubes of the surrounding walls, which form the side walls of the combustion chamber, on the flow medium side. This ensures particularly favorable cooling of the strongly heated end wall of the combustion chamber.

In a further advantageous embodiment of the invention, the inner tube diameter of a number of the evaporator tubes of the combustion chamber is selected as a function of the respective position of the evaporator tubes in the combustion chamber. In this way, the evaporator tubes in the combustion chamber can be adapted to a heating profile which can be predetermined on the hot gas side. As a result of the influence on the flow through the evaporator tubes, temperature differences of the flow medium at the outlet from the evaporator tubes of the combustion chamber are kept particularly low.

For a particularly good heat transfer from the heat of the combustion chamber to the flow medium guided in the evaporator tubes, a number of the evaporator tubes advantageously has ribs forming a multiple thread on the inside thereof. This is advantageously a Pitch angle α between a plane perpendicular to the pipe axis and the flanks of the ribs arranged on the inside of the pipe is less than 60 °, preferably less than 55 °.

In a heated evaporator tube designed as an evaporator tube without internal ribbing, a so-called smooth tube, the wetting of the tube wall required for a particularly good heat transfer can no longer be maintained from a certain steam content. 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 the pipe wall temperatures generally rise particularly sharply at this point. In an internally finned evaporator tube, however, in comparison to a smooth tube, this crisis of heat transfer only occurs when the vapor mass content is> 0.9, ie shortly before the end of the evaporation. This is due to the swirl that the flow experiences through the spiral ribs. Due to the different centrifugal force, the water and steam are separated and transported to the pipe wall. As a result, the wetting of the tube wall is maintained up to high steam contents, so that high flow velocities are already present at the location of the heat transfer crisis. Despite the heat transfer crisis, this causes relatively good heat transfer and, as a result, low pipe wall temperatures.

A number of the evaporator tubes of the combustion chamber advantageously have means for reducing the flow of the flow medium. It proves to be particularly advantageous if the means are designed as throttle devices. Throttling devices can, for example, be built-in components in the evaporator tubes that reduce the inside diameter of the tube at one point inside the respective evaporator tube. Means for reducing the

Flow in a line system comprising several parallel lines as advantageous, through which the evaporator tube ren the combustion chamber flow medium can be supplied. The line system can also be connected upstream of an inlet header system of evaporator tubes which can be acted upon in parallel with flow medium. For example, in one line or in several lines of the line system

Throttle fittings may be provided. Such means for reducing the flow of the flow medium through the evaporator tubes can be used to adapt the throughput of the flow medium through individual evaporator tubes to their respective heating in the combustion chamber. As a result, additional temperature differences of the flow medium at the outlet of the evaporator tubes are kept particularly low.

Adjacent evaporator or steam generator tubes are advantageously gas-tightly welded to one another on their long sides via metal strips, so-called fins. These fins can already be firmly connected to the tubes in the tube manufacturing process and form a unit with them. This unit formed from a tube and fins is also referred to as a fin tube. The fin width influences the heat input into the evaporator or steam generator tubes. Therefore, the fin width is preferably adapted to a heating profile that can be predetermined on the hot gas side, depending on the position of the respective evaporator or steam generator tubes in the continuous steam generator. A typical heating profile determined from empirical values or a rough estimate, such as, for example, a step-shaped heating profile, can be specified as the heating profile. Due to the suitably chosen fin widths, even with very different heating of different evaporator or steam generator tubes, heat input into all evaporator or steam generator tubes can be achieved in such a way that temperature differences of the flow medium at the outlet from the evaporator or steam generator tubes are kept particularly small. In this way, premature material fatigue is a result of Reliably prevents thermal stress. As a result, the once-through steam generator has a particularly long service life.

A number of superheater heating surfaces are advantageously arranged in the horizontal gas flue, which are arranged approximately perpendicular to the main flow direction of the heating gas and whose tubes are connected in parallel for a flow through the flow medium. These superheater heating surfaces, also known as bulkhead heating surfaces, are predominantly convectively heated and are connected downstream of the evaporator tubes of the combustion chamber on the flow medium side. This ensures a particularly favorable utilization of the heating gas heat.

The vertical gas flue advantageously has a number of convection heating surfaces which are formed from tubes arranged approximately perpendicular to the main flow direction of the heating gas. These tubes of a convection heating surface are connected in parallel for a flow through the flow medium. These convection heating surfaces are also predominantly convectively heated.

In order to continue to ensure a particularly complete utilization of the heat of the heating gas, the vertical gas flue 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 burnup of the fossil fuel-gas velocity in the horizontal direction ^"at a certain average temperature Heizgastem- is multiplied by the burnup time t _A of the flame to understand the fossil fuel. The maximum burnout length for the respective continuous steam generator is at the steam output M at full load of the once-through steam generator, the so-called full load operation. The burnout time t _{A of} the flame of the fossil fuel is in turn the time which, for example, a coal dust grain of medium size takes to completely burn out at a certain mean heating gas temperature.

In order to keep material damage and undesired contamination of the horizontal gas flue particularly low, for example due to the entry of molten ash of a high temperature, the length of the combustion chamber defined by the distance from the end wall to the inlet area of the horizontal gas flue is advantageously at least equal to the burnout length of the fossil fuel at Full load operation of the continuous steam generator. This horizontal length of the combustion chamber will generally be at least 80% of the height of the combustion chamber, measured from the top edge of the funnel, if the lower region of the combustion chamber is funnel-shaped, up to the combustion chamber ceiling.

The length L (specified in m) of the combustion chamber is advantageous for a particularly favorable utilization of the heat of combustion of the fossil fuel as 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. Given the 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 ) = (Ci + C ₂ • M) • t _A (I) and

L (M, T _BRK ) = (C ₃ ^'" • T _BRK + C ₄ ) M + C ₅ (T _BR κ) ² + C _δ ^• T _BRK + C7 (II) with

C ₂ = 0.0057 m / kg and

C ₃ = -1, 905 ^• 10 ^"4 (• s) / (kg ^! 'O and

C ₄ = 0.286 (s • m) / kg and

Cs = 3 • 10 ^"' ' m / (° C) ² and c ₆ = -0.842 m / ° C and

C ₇ = 603.41 m.

“Approximately” is to be understood here as a permissible deviation of the length L of the combustion chamber from the value defined by the respective function by +20% / - 10%.

The lower region of the combustion chamber is advantageously designed as a funnel. In this way, the ash produced during the operation of the continuous steam generator during the combustion of the fossil fuel can be removed particularly easily, for example into a deashing device arranged under the funnel. The fossil fuel can be solid coal.

The advantages achieved by the invention are, in particular, that by guiding some evaporator tubes through the combustion chamber before they enter the peripheral wall of the combustion chamber, temperature differences in the immediate vicinity of the connection between the combustion chamber and the horizontal gas flue are particularly small during operation of the continuous steam generator. The thermal stresses caused by temperature differences between immediately adjacent evaporator tubes of the combustion chamber and steam generator tubes of the horizontal gas flue at the connection of the combustion chamber to the horizontal gas flue therefore remain far below the values when the continuous steam generator is in operation, for example where there is a risk of pipe rips. This enables the use of a horizontal combustion chamber in a once-through steam generator even with a comparatively long service life. By designing the combustion chamber for an approximately horizontal main flow direction of the heating gas, a particularly compact construction of the continuous steam given. When the continuous steam generator is integrated into a power plant with a steam turbine, this also enables particularly short connecting pipes from the continuous steam generator to the steam turbine.

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

1 schematically shows a fossil-fueled continuous steam generator in a two-pass design in side view and

2 schematically shows a longitudinal section through a single evaporator tube,

3 shows a coordinate system with the curves Ki to Kg,

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

5 shows a coordinate system with the curves Ui to U. ₄

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

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. The continuous steam generator 2 is designed for a steam output at full load of at least 80 kg / s. The steam generated in the continuous steam generator 2 is used to drive the steam turbine, which in turn drives a generator to generate electricity. The current generated by the generator is intended for feeding into a network or an island network.

The fossil-heated once-through steam generator 2 comprises a combustion chamber 4 which is constructed in a horizontal construction and which a vertical throttle cable 8 is connected downstream on the gas side via a horizontal throttle cable 6. The lower region of the combustion chamber 4 is formed by a funnel 5 with an upper edge corresponding to the auxiliary line with the end points X and Y. Through the funnel 5, when the continuous steam generator is operating, 2 ashes of the fossil fuel B can be discharged into a deashing device 7 arranged underneath. The surrounding walls 9 of the combustion chamber 4 are formed from gas-tightly welded, vertically arranged evaporator tubes 10, of which a number N can be acted upon in parallel with flow medium S. A peripheral wall 9 of the combustion chamber 4 is the end wall 11. In addition, the side walls 12 of the horizontal gas flue 6 and 14 of the vertical gas flue 8 are also formed from vertically arranged steam generator tubes 16 and 17 which are welded together in a gastight manner. A number of steam generator tubes 16 and 17 can each be acted upon in parallel with flow medium S.

A number of the evaporator tubes 10 of the combustion chamber 4 is an inlet header system 18 for the fluid medium

Flow medium S upstream and an outlet header system 20 connected downstream. The entry collector system 18 comprises a number of parallel entry collectors. In this case, a line system 19 is provided for supplying flow medium S into the inlet inlet system 18 of the evaporator tubes 10. The line system 19 comprises a plurality of lines connected in parallel, each of which is connected to one of the inlet collectors of the inlet collector system 18.

In the same way, the steam generator tubes 16 of the side walls 12 of the horizontal gas flue 6, which can be acted upon in parallel with flow medium S, are preceded by a common inlet collector system 21 and followed by a common outlet collector system 22. In this case, a line system 19 is also provided for supplying flow medium S into the inlet header system 21 of the steam generator tubes 16. The line system also includes several lines connected in parallel, which are each connected to one of the entry collectors of the entry collection system 21.

This configuration of the continuous-flow steam generator 2 with inlet header systems 18, 21 and outlet header systems 20, 22 enables a particularly reliable pressure compensation between the evaporator tubes 10 of the combustion chamber 4 connected in parallel or the steam generator tubes 16 of the horizontal gas flue 6 connected in parallel in such a way that all of the evaporator or steam generator tubes 10 or 16 connected in parallel have the same total pressure loss. This means that the throughput must increase in the case of a more heated evaporator tube 10 or steam generator tube 16 in comparison to a less heated evaporator tube 10 or steam generator tube 16.

As shown in FIG. 2, the evaporator tubes 10 have an inner tube diameter D and on their inner side fins 40 which form a kind of multi-start thread and have a fin height C. The pitch angle α between a plane 42 perpendicular to the pipe axis and the flanks 44 of the ribs 40 arranged on the inside of the pipe is less than 55 °. As a result, a particularly high heat transfer from the inner walls of the evaporator tubes 10 to the flow medium S guided in the evaporator tubes 10 and at the same time particularly low temperatures of the tube wall are achieved.

The inner tube diameter D 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. In this way, the once-through steam generator 2 is adapted to the different degrees of heating of the evaporator tubes 10. This design of the evaporator tubes 10 of the combustion chamber 4 ensures in a particularly reliable manner that temperature differences of the flow medium S are kept particularly small when they emerge from the evaporator tubes 10. As a means of reducing the flow rate of the flow medium S, part of the evaporator tubes 10 are equipped with throttling devices, which are not shown in the drawing. The throttling devices are designed as perforated diaphragms which reduce the inner tube diameter D at one point and, when the continuous steam generator 2 is operating, bring about a reduction in the throughput of the flow medium S in less heated evaporator tubes 10, as a result of which the throughput of the flow medium S is adapted to the heating.

Furthermore, as means for reducing the throughput of the flow medium S in the evaporator tubes 10, one or more lines of the line system 19 (not shown in more detail) are equipped with throttle devices, in particular throttle fittings.

Adjacent evaporator or steam generator tubes 10, 16, 17 are welded together in a gas-tight manner on their longitudinal sides via fins in a manner not shown in the drawing. The heating of the evaporator or steam generator tubes 10, 16, 17 can be influenced by a suitable choice of the fin width. The respective fin width is therefore adapted to a heating profile which can be predetermined on the hot gas side and which depends on the position of the respective evaporator or steam generator tubes 10, 16, 17 in the continuous-flow steam generator 2. The heating profile can be a typical heating profile determined from empirical values or a rough estimate. As a result, temperature differences at the outlet of the evaporator or steam generator tubes 10, 16, 17 are kept particularly small, even when the evaporator or steam generator tubes 10, 16, 17 are heated to very different degrees. In this way, material fatigue are due to thermal stresses reliably prevented, long life gewährlei- stet ^"of the once-through steam generator. 2 When piping the horizontal combustion chamber 4, it must be taken into account that the heating of the individual evaporator tubes 10, which are welded to one another in a gas-tight manner, is very different when the continuous steam generator 2 is operating. For this reason, the design of the evaporator tubes 10 with regard to their internal fins, their fin connection to adjacent evaporator tubes 10 and their inner tube diameter D is selected such that, despite different heating, all evaporator tubes 10 have approximately the same outlet temperatureή of the flow medium S and adequate cooling of all evaporator tubes 10 for all Operating states of the continuous steam generator 2 is guaranteed. A reduced heating of some evaporator tubes 10 during the operation of the continuous steam generator 2 is additionally taken into account by the installation of throttle devices.

The inner tube diameter D of the evaporator tubes 10 in the combustion chamber 4 are selected as a function of their respective position in the combustion chamber 4. Evaporator tubes 10, which are exposed to greater heating during operation of the continuous steam generator 2, have a larger inner tube diameter D than evaporator tubes 10, which are heated to a lesser extent during operation of the continuous steam generator 2. Compared to the case with the same inner tube diameters, this means that the throughput of the flow medium S in the evaporator tubes 10 with a larger inner tube diameter D is increased and temperature differences at the outlet of the evaporator tubes 10 are reduced as a result of different heating. Another measure to adapt the flow through the evaporator tubes 10 with the flow medium S to the heating is the installation of throttle devices in a part of the evaporator tubes 10 and / or in the line system 19 provided for the supply of the flow medium S. In contrast, the heating depends on the throughput of the To adapt flow medium S through the evaporator tubes 10, the fin width can be selected depending on the position of the evaporator tubes 10 in the combustion chamber 4. All of the measures mentioned ken, despite strongly different heating of the individual evaporator tubes 10, approximately the same specific heat absorption of the flow medium S guided in the evaporator tubes 10 during operation of the continuous-flow steam generator 2 and thus only slight temperature differences of the flow medium S at their outlet. The internal fins of the evaporator tubes 10 are designed in such a way that particularly reliable cooling of the evaporator tubes 10 is ensured in spite of different heating and flow through with flow medium S in all load states of the continuous steam generator 2.

The horizontal gas flue 6 has a number of superheater heating surfaces 23 designed as bulkhead heating surfaces, which are arranged in a suspended construction approximately perpendicular to the main flow direction 24 of the heating gas G and whose pipes are connected in parallel for a flow through the flow medium S. The superheater heating surfaces 23 are predominantly convectively heated and are connected downstream of the evaporator tubes 10 of the combustion chamber 4 on the flow medium side.

The vertical gas flue 8 has a number of convection heating surfaces 26 which can be heated predominantly by convection and which are formed from tubes arranged approximately perpendicular to the main flow direction 24 of the heating gas G. These tubes are each connected in parallel for a flow through the flow medium S. In addition, an economizer 28 is arranged in the vertical throttle cable 8. On the output side, the vertical gas flue 8 opens into a further heat exchanger, for example an air preheater and from there via a dust filter into a chimney. The components downstream of the vertical throttle cable 8 are not shown in the drawing.

The once-through steam generator 2 is configured with a horizontal combustion chamber 4 with ^"extremely low overall height and can therefore be set at a particularly low manufacturing and assembly costs. For this purpose, the combustion chamber 4 of the pass-through steam generator 2 a number of burners 30 for fossil Fuel B, which are arranged on the end wall 11 of the combustion chamber 4 at the level of the horizontal gas flue 6. The fossil fuel B can be solid fuels, especially coal.

So that the fossil fuel B, for example coal in solid form, burns out particularly completely in order 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 heating gas side and contamination thereof, for example due to the introduction of molten ash at high temperature , are prevented particularly reliably, the length L of the combustion chamber 4 is selected such that it exceeds the burnout length of the fossil fuel B during full-load operation of the continuous steam generator 2. 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 speed in the horizontal direction at a specific mean heating gas temperature multiplied by the burnout time t _A 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 time certain average 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 "the burnout time" depending on the outlet temperature T _BRK (specified in ° C.) of the heating gas G from the combustion chamber 4 t _A (given in s) of the flame F of the fossil fuel B and the steam output M

(specified in kg / s) of the continuous-flow steam generator 2 at full load. This horizontal length L of the combustion chamber 4th is at least 80% of the height H of the combustion chamber 4. The height H is measured from the upper edge of the funnel 5 of the combustion chamber 4, marked in FIG. 1 by the auxiliary line with the end points X and Y, to the ceiling of the combustion chamber. The length L of the combustion chamber 4 is approximately determined by the functions (I) and (II):

L (M, t _A ) = (Ci + C ₂ • M) • t _A (I) and L (M, T _BRK ) = (C ₃ ^• T _BRK + C ₄ ) M + C ₅ (T _BRK ) ² + C ₆ ^• T _BRK + C7 (II) with

Ci = 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, this is to be understood as a permissible deviation of the length L of the combustion chamber 4 by +20% / - 10% from the value defined by the respective function. When designing the continuous steam generator 2, the larger value from the functions (I) and (II) for the length L of the combustion chamber 4 applies for a predetermined steam output M of the continuous steam generator 2 at full load.

As an example of a possible design of the continuous steam generator 2, for some lengths L of the combustion chamber 4, depending on the steam output M of the continuous steam generator 2 at full load in the coordinate system according to FIG. 3, six curves Ki. drawn up to Ke. The following parameters are assigned to the curves:

Ki: 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 Ki and K ₄ are thus to be used, for example, for the burnout time t _A = 3s 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 in a given 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, from M = 560 kg / s a length of L = 57 m K ₄ .

The curve K drawn as a solid line always applies.

For the burnout time t _A = 2.5s of the flame F of the fossil

Fuel B and the outlet temperature of the heating gas G from the combustion chamber T _BR κ = 1300 ° C, the curves K ₂ and K5 are to be used, for example. This results in a given 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 K5.

Up to M = 180 kg / s, the part of the curve K ₂ that is drawn as a solid line and not the curve K ₅ drawn as a dashed line in this value range of M applies. For values of in 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 _BR κ = 1400 ° C. of the heating gas G from the combustion chamber 4 are assigned, for example, the curves K ₃ and Kg. This results in a given 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, 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 Kβ

For values from M to 465 kg / s, the curve K ₃ drawn as a solid line in this area and not the curve Kς 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 KQ drawn as a solid line and not the part of the curve K drawn as a broken line applies.

So that comparatively small temperature differences occur between the outlet region 34 of the combustion chamber 4 and the inlet region 32 of the horizontal gas flue 6 during the operation of the continuous-flow steam generator 2, the evaporator tubes 50 and 52 are guided in a special way in the connecting section Z marked in FIG. This connecting section Z is shown in detail in FIG. 4 and comprises the outlet area 34 of the combustion chamber 4 and the inlet area 32 of the horizontal gas flue 6. The evaporator tube 50 is the evaporator tube 50 of the peripheral wall 9 of the combustion chamber 4 welded directly to the side wall 12 of the horizontal gas flue 6 and that Evaporator tube 52 is the immediately adjacent evaporator tube 52 of the peripheral wall 9 of the combustion chamber 4.

These two evaporator tubes 50 and 52 emerge from the common inlet header system 18 together with the evaporator tubes 10 connected in parallel. Then, however, both the evaporator tube 50 and the evaporator tube 52 are initially opposed in an approximately horizontal direction led to the main flow direction 24 of the heating gas G outside the combustion chamber 4. Then they enter the combustion chamber 4 and do not immediately become part of the peripheral wall 9 of the combustion chamber 4 when they enter the combustion chamber 4. Namely, they are returned to the area along the main flow direction 24 of the heating gas G in the combustion chamber 4, on which they are branched outside of the combustion chamber 4 from their approximately vertical course in order to run opposite to the main flow direction 24 of the heating gas G. Only after this loop are they welded into the peripheral wall 9 of the combustion chamber 4, so that they are part of the peripheral wall 9 of the combustion chamber 4.

By means of this special pipe routing, the evaporator pipes 50 and 52 are preheated during operation of the once-through steam generator 2 before they enter the peripheral wall 9 of the combustion chamber 4. The flow medium S guided in them is therefore heated and thus preheated during operation of the continuous steam generator 2, so that it enters the peripheral wall 9 of the combustion chamber 4 at a comparatively higher temperature than that in the directly connected to the evaporator tubes 50 and 52 adjacent evaporator tubes 10 of the combustion chamber 4 is the case. As a result of this special pipe routing via evaporator pipes 50 and 52, the evaporator pipes 50 and 52 in the inlet section E have a comparatively higher temperature when the continuous steam generator 2 is operating than the evaporator pipes 10 directly adjacent to them of the surrounding wall 9 of the combustion chamber 4. As a result, the continuous steam generator 4 is in operation 2 temperature differences at the connection 36 between the combustion chamber 4 and the horizontal gas flue 6 kept particularly low particularly reliably.

As an example of possible temperatures T _{s of} the flow medium S in the evaporation 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 Ui to ü _{4 are} entered. Uj. 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 of the combustion chamber 4. It is clear from the curves drawn that the special pipe routing of the evaporator tubes 50 and 52 in the inlet section E in the peripheral wall 9 of the combustion chamber 4 can significantly reduce the temperature difference from the steam generator tubes 16 of the peripheral wall 12 of the horizontal gas flue. 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 at the connection 36 between the combustion chamber 4 and the horizontal gas flue 6 are ensured during operation of the continuous steam generator 2.

When the continuous steam generator 2 is operated, the burners 30 are supplied with fossil fuel B, preferably coal in solid form. The flames F of the burner 30 are aligned horizontally. Due to the design of the combustion chamber 4, a flow of the heating gas G generated during the combustion is generated in an approximately horizontal main flow direction 24. This passes through the horizontal gas flue 6 into the vertical gas flue 8 oriented approximately towards the floor and leaves it in the direction of the chimney (not shown in more detail).

Flow medium S entering the economizer 28 enters the inlet header system 18 of the evaporator tubes 10 of the combustion chamber 4 of the continuous-flow steam generator 2. In the vertically arranged, gas-tightly welded evaporator tubes 10 of the combustion chamber 4 of the once-through steam generator 2, the evaporation and possibly a partial overheating of the flow medium S takes place. The resulting steam or a water-steam mixture is collected in the outlet collector system 20 for flow medium S. From there, the steam or the water-steam mixture reaches the superheater heating surfaces 23 of the horizontal gas duct 6 via the walls of the horizontal gas flue 6 and the vertical gas flue 8. In the superheater heating surfaces 23, the steam is further overheated, which is then used, for example by the drive a steam turbine.

With the special guidance of the evaporator tubes 50 and 52, temperature differences between the outlet region 34 of the combustion chamber 4 and the inlet region 32 of the horizontal gas flue 6 are particularly small during operation of the once-through steam generator. A choice of the length L of the combustion chamber 4 as a function of the steam output M of the continuous steam generator 2 at full load ensures that the heat of combustion of the fossil fuel B is used particularly reliably. In addition, the continuous steam generator 2 can be built due to its particularly low overall height and compact design with particularly low manufacturing and assembly costs. A scaffold that can be constructed with comparatively little technical effort can be provided. In a power plant with a steam turbine and a continuous steam generator 2 having such a low overall height, the connecting pipes from the continuous steam generator to the steam turbine can also be designed in a particularly short manner.

Claims

claims

1. continuous steam generator (2) with a combustion chamber (4) for fossil fuel (B), the hot gas side is followed by a horizontal gas flue (6), a vertical gas flue (8), the combustion chamber (4) having a number of in the amount of Horizontal gas flue (6) arranged burners (30) and the peripheral walls (9) of the combustion chamber (4) are formed from vertically arranged evaporator tubes (10) welded to each other in a gas-tight manner, a plurality of the evaporator tubes (10) each parallel to the flow medium ( S) can be acted upon and in the outlet area (34) of the combustion chamber (4) a number of the evaporator tubes (10) which can be acted upon in parallel with flow medium (S) before they enter the respective peripheral wall (9) of the combustion chamber (4) through the combustion chamber (4 ) is performed.

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 gas-tightly welded to one another, vertically arranged steam generator tubes (16) which can be acted upon in parallel with flow medium (S).

3. continuous steam generator (2) according to claim 1 or 2, wherein the side walls (14) of the vertical gas flue (8) from gas-tightly welded, vertically arranged, parallel with flow medium (S) actable steam generator tubes (17) are formed.

4. continuous steam generator (2) according to any one of claims 1 to 3, in each of which a plurality of evaporator tubes (10) which can be acted upon in parallel with flow medium (S) upstream of the flow medium on the common inlet collector system (18) and -a common outlet collector system - stem (20) is connected downstream.

5. continuous steam generator (2) according to any one of claims 1 to 4, in each of which a number of steam generator tubes (16, 17) of the horizontal throttle cable (6) or the vertical gas cable (8) which can be acted upon in parallel with flow medium (S) on the flow medium side, a common inlet collector -System (21) upstream and a common outlet collector system (22) is connected downstream.

6. continuous steam generator (2) according to any one of claims 1 to 5, in which a peripheral wall (9) of the combustion chamber (4)

Front wall (11), the evaporator tubes (10) of the front wall (9) can be acted upon in parallel with flow medium (S).

7. continuous steam generator (2) according to any one of claims 1 to

6, in which the evaporator tubes (10) of the end wall (11) of the combustion chamber (4) are connected upstream of the other peripheral walls (9) of the combustion chamber (4) on the flow medium side.

8. continuous steam generator (2) according to any one of claims 1 to

7, in which the inner tube diameter (D) of a number of the evaporator tubes (10) of the combustion chamber (4) is selected depending on the respective position of the evaporator tubes (10) in the combustion chamber (4).

9. continuous steam generator (2) according to one of claims 1 to 8, in which a number of the evaporator tubes (10) on their inside each carry a multi-thread ribs (40).

10. continuous steam generator (2) according to claim 9, in which a pitch angle (α) between a plane perpendicular to the pipe axis (42) and the flanks' (44) of the ribs (40) arranged on the inside of the pipe is less than 60 °, preferably small is less than 55 °.

11. continuous steam generator (2) according to any one of claims 1 to

10, in which a number of the evaporator tubes (10) each have a throttle device.

12. continuous steam generator (2) according to any one of claims 1 to

11, in which a line system (19) for supplying flow medium (S) into the evaporator tubes (10) of the combustion chamber (4) is provided, the line system (19) for reducing the flow of the flow medium (S) having a number of Throttle devices, in particular throttle fittings.

13. continuous steam generator (2) according to any one of claims 1 to

12, in which adjacent evaporator or steam generator tubes (10, 16, 17) are welded together in a gas-tight manner via fins, the fin width depending on the respective position of the evaporator or steam generator tubes (10, 16, 17) in the combustion chamber (4), the horizontal throttle cable (6) and / or the vertical gas cable (8) is selected.

14. continuous steam generator (2) according to any one of claims 1 to

13, in which a number of superheater heating surfaces (23) are arranged in a hanging construction in the horizontal gas flue (6).

15. continuous steam generator (2) according to any 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 steam generator (2) according to any one of claims 1 to 15, wherein the burners (58) on the end wall (11) of the combustion chamber (4) are arranged.

17. continuous steam generator '(2) according to one of claims 1 to 16, wherein the by the distance from the end wall (11) of the combustion chamber (4) to the inlet region (32) of the horizontal gas flue (6) defined length (L) of the combustion chamber ( 4) at least is equal to the burnout length of the fuel (B) during full load operation.

18. Continuous steam generator (2) according to one of claims 1 to 17, in which the length (L) of the combustion chamber (4) as a function of the steam output (M) at full load, the burnout time (t _Ä ), the flame (F) of the fuel (B) and / or the outlet temperature (T _BRK ) of the heating gas (G) from the combustion chamber (4) approximately according to the two functions (I) and (II)

L (M, t A) = (Ci + C ₂ ^• M) ^• t _A (I) and

L (M, T BRK) ⁼ (C ^• T _BR κ + C ₄ ) M + C ₅ (T _BRK ) ² + c ₅ ^• : _BRK + C7 (II) with

C_ = 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 _s = -0.842 m / ° C and c ₇ = 603.41

is selected, the larger value of the length (L) of the combustion chamber (4) applying to a given steam output (M) at full load.

19. continuous steam generator (2) according to one of claims 1 to 18, wherein the lower region of the combustion chamber (4) is designed as a funnel (5).