EP1141625A1

EP1141625A1 - Fossil fuel fired continuos-flow steam generator

Info

Publication number: EP1141625A1
Application number: EP99964411A
Authority: EP
Inventors: Joachim Franke; Rudolf Kral; Eberhard Wittchow
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1998-12-18
Filing date: 1999-12-06
Publication date: 2001-10-10
Anticipated expiration: 2019-12-06
Also published as: KR20010082364A; JP2002533643A; CN1192186C; RU2212582C2; DE19858780C2; DK1141625T3; JP3571298B2; US6446580B2; US20020000208A1; ES2179696T3; CA2355101C; CA2355101A1; DE59901884D1; DE19858780A1; ATE219828T1; EP1141625B1; CN1330751A; KR100685074B1; WO2000037851A1

Abstract

The fossil fuel fired continuous-flow steam generator has a gas turbine combustion chamber for fossil combustibles. On the heating gas side a vertical gas extractor is mounted downstream of a horizontal gas extractor. The walls surrounding the combustion chamber are composed of vertical evaporator tubes that are welded together. During operation the temperature differences between adjacent evaporator tubes of the combustion chamber are kept as low as possible. The burners are arranged at the level of the horizontal gas extractor. For a number of evaporator tubes which can be simultaneously impinged by the flow medium the ratio of the steam generating capacity M (in kg/s) at full load and of the sum A (in m2) of the inner cross-sectional surfaces of the same evaporator tubes is less than 1350 (in kg/sm2).

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, where the peripheral walls of the combustion chamber are made of gas-tightly welded, vertically arranged evaporator tubes.

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 a vaporizer 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 αe article "Evaporator concepts for Benson steam generators" by J. Franke, W. Kohler and E. ittchow, published in VGB Kraftwerktechmk 73 (1993), volume 4, pp. 352-360 A continuous steam generator leads the heating of steam generator tubes provided as evaporator tubes to an evaporation of the flow medium in the steam generator tubes in a single pass.

Pass-through steam generators are usually designed with a combustion chamber in a vertical design. This means that l the combustion chamber is designed for a flow through the etching 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 the length of the combustion chamber. This requires a considerable technical effort in the manufacture and assembly of the once-through steam generator, which is all the greater, the greater the overall height of the once-through steam generator. D it 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 well above the critical pressure of water (pkπ ⁼ 221 bar) - where there is only a slight difference in density between liquid-like and steam-like medium - are possible. A honey fresh steam pressure favors a high thermal efficiency and thus low CO ₂ emissions of a fossil fuel-fired power plant, which can be fired, for example, with hard coal or lignite as fuel.

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 wall or material temperatures that occur there. In the subcritical pressure range up to about 200 bar, the temperature of the peripheral wall of the combustion chamber essentially depends on the level of the saturation temperature - Water temperature determined if wetting of the inner surface of the evaporator tubes can be ensured. This is achieved, for example, by using evaporator tubes that have a surface structure on the inside. In addition, there are in particular male ribs 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 lined inner surface, have a particularly good heat transfer from the inner tube wall to the flow medium.

Experience has shown that the peripheral wall of the combustion chamber cannot be heated differently. Due to the different heating of the evaporator tubes, the outlet temperatures of the flow medium from multi-heated evaporator tubes can therefore generally be higher in continuous steam generators than in the case of normal or mm-heated evaporator tubes. This can result in temperature differences between adjacent evaporator tubes, which can lead to hot voltages that reduce the lifespan of the continuous steam generator or can even cause pipe tears

The invention is therefore based on the object of specifying a fossil-heated once-through steam generator of the type mentioned above, which requires a particularly low outlay in terms of manufacture and assembly, and during the operation of which temperature differences between adjacent evaporator tubes of the combustion chamber are also kept particularly low.

This object is achieved according to the invention in that the continuous steam generator has a combustion chamber with a number of burners arranged at the height of the horizontal gas flue and is designed such that for each of a number of evaporator tubes which can be acted upon in parallel with flow medium, the steam output M (given in kg / s ) at full load and the sum of the internal cross-sectional areas A (specified in m ² ) of this evaporator tubes, which can be acted upon in parallel with flow medium, is less than 1350 (specified m kg / snr). 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 the combustion chamber that can be constructed with comparatively little technical effort can be accompanied by a particularly small baffle of the continuous steam generator. A particularly small construction 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 in the height 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.

In the case of a horizontal combustion chamber, however, when the continuous steam generator is in operation, the region of the combustion chamber seen on the hot gas side is heated comparatively less than the front region of the combustion chamber seen on the hot gas side. In addition, for example, an evaporator tube in

Heating more near the burner than an evaporator tube arranged in a corner of the combustion chamber. In extreme cases, the heating in the front area of the combustion chamber can be about three times greater than in the rear area. Be the usual mass flow density in the Verdampferrohren- given in kg / m ² s, and based on 100% steam power (full load) - 2000 kg / m ² to s is the mass flow rate in a multi-tube heated and rises in a less heated tube , each based on the average mass flow of all pipes. This behavior is caused by the relatively high proportion of the friction pressure loss in the total pressure drop of the evaporator tubes. In addition, due to the particularly low height of the combustion chamber, the relative differences in length of the evaporator tubes are considerably larger than in the case of a vertical combustion chamber. This additionally reinforces the differences in heating and in the loss of friction pressure of the individual evaporator tubes. However, in order to keep approximately the same temperatures between To ensure neighboring evaporator tubes, the continuous steam generator should be designed such that s ch automatically sets a higher flow rate of the flow medium in a comparatively more heated evaporator tube than in a comparatively less heated evaporator tube. This is generally the case when the geodetic pressure drop Δp _G (specified in bar) of an evaporator tube with medium heating is a multiple of its frictional pressure loss Δp _R (specified in bar). The condition for an increase in throughput in a comparatively more-heated evaporator tube with a constant mass flow is:

where Δp _B (specified in bar) is a change in the pressure drop, ΔQ (specified in kJ / s) a change in heating, M (specified in kg / s) the mass flow and K (specified in (bar s) / kJ) is a constant. The condition formulated in this inequality indicates that with a constant mass flow, the total pressure loss Δ (Δp _G + Δp _R + Δp _B ) (given in bar) decreases in the case of additional heating ΔQ, ie must become mathematically negative. Thus, if the same total pressure loss prevails in a number of evaporator tubes, then the flow rate of the flow medium must increase in a multi-heated evaporator tube compared to a less-heated evaporator tube in accordance with the above inequality.

Comprehensive calculations have now surprisingly shown that the condition formulated in the inequality for continuous steam generators with a horizontal combustion chamber is met if the quotient of the steam output M (specified m kg / s) of the continuous steam generator at full load and off for a number of evaporator tubes connected in parallel the sum of the internal cross-sectional areas A (specified in m ² ) of these evaporator tubes connected in parallel is not greater than 1350 (specified in kg / sm ² ). So formulated mathematically: M

- <1350.

A

The steam output M at full load of the pass-through steam generator is referred to as a permissible steam generation boiler or as a maximum continuous ratmg (BMCR), and the _j eweilige Innenquerschnittsflacne an evaporator tube is relative to a horizontal section.

Advantageously, a number of parallel evaporator tubes of the combustion chamber are connected upstream of a common inlet header system and a common outlet header system for the flow medium. A continuous steam generator designed in this embodiment enables reliable pressure equalization between a number of evaporator tubes connected in parallel, so that in each case all evaporator tubes 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 compared to a less-heated evaporator tube in accordance with the above inequality.

The evaporator tubes of the end wall of the combustion chamber are advantageously connected upstream of the flow medium on the flow medium side of the evaporator tubes of the surrounding walls which form the side walls of the combustion chamber. 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. With the effect this has on the flow through the evaporator tubes temperature differences at the outlet of 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. In this case, a pitch angle α between a plane perpendicular to the tube axis and the flanks of the ribs arranged on the inside of the tube is advantageously less than 60 °, preferably less than 55 °.

In a heated evaporator tube designed as an evaporator tube without an internal covering, 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 generally the pipe wall temperatures rise particularly sharply at this point. In a male finned evaporator tube, however, this crisis of heat transfer only occurs in comparison with a smooth tube when the steam mass content is> 0.9, i.e. shortly before the end of the

Evaporation, on. This is due to the swirl that the flow experiences through the spiral ribs. Due to the different centrifugal forces, the water and steam are separated and transported to the pipe wall. As a result, the wetting of the pipe wall is maintained up to high steam contents, so that high flow rates 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. Daoe proves to be particularly advantageous if the means are designed as throttling devices. Throttle means may be, for example internals in the evaporator tubes, the decrease at a location inside the _j eweiligen Verdampferronrs the pipe inner diameter. Means for reducing the flow in a line system comprising a plurality of parallel lines also prove to be advantageous, through which flow medium can be supplied to the evaporator tubes of the combustion chamber. The line system can also be connected upstream of an entry collector system of evaporator tubes which can be acted upon in parallel with the flow medium. Throttle fittings can be provided in one line or in several lines of the line system. With such means for reducing the flow of the flow medium through the

Evaporator tubes can be brought about an adjustment of the flow rate 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.

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 the flow medium.

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 output in 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 Pass-through steam generator adapted to a heating profile that can be specified on the hot gas side. 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 at the outlet of the evaporator or steam generator tubes are kept particularly low. In this way, premature material fatigue is reliably prevented. 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 pipes 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 heated convectively.

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 is 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 fuel. The burnout length of the fuel is understood to mean the heating gas velocity in the horizontal direction at a specific mean heating gas temperature multiplied by the burnout time t _A of the fuel flame. The maximum burn-out 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 fuel in turn is the time which, for example, a coal dust of medium size takes to completely burn out at a certain average 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 fuel under 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 to the top of the combustion chamber.

The length L (specified in) of the combustion chamber is advantageously 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 _3R

(specified m ° C) of the heating gas selected from the combustion chamber. For a given steam output M of the continuous steam generator at full load for the length L of the combustion chamber approximately the larger value of the two functions (1) and (2):

L (M, t _A ) = (d + C ₂ W) t _A and

L (M, T _BRK ) = (C ₃ T _BR -r C ₄ ) W - ^< - CS (BK) ⁺ Ce T _B RK ⁺ C-

Ci = 8 m / s and

C ₂ = 0.0057 m / kg and

CC ₃₃ == --11 ,, 990055 1100 ^{~ "4} " ((mm ss)) // ((kkgg ° ^α CC) and

C ₄ = 0, 28 6 (sm) / kg and

C ₅ = 3 10 ^{~ 4} m / (° C) ² and

C _s = -0.842 m / ° C and

CC ₇₇ == 660033,, 4411 ..

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

The advantages achieved by the invention are, in particular, that through the suitable choice of the ratio between the steam output of the once-through steam generator or full load for a number of evaporator tubes connected in parallel and the inner cross-sectional areas of this evaporator tube, the throughput of the flow medium can be adjusted particularly well Evaporator tubes to the heating and thus almost the same temperatures at the outlet of the evaporator tubes are guaranteed. The heat tensions in the peripheral wall of the combustion chamber caused by temperature differences between adjacent evaporator tubes remain far below the values during operation of the continuous steam generator, for example where there is a risk of ripping cracks. This means that the use of a horizontal combustion chamber in a once-through steam generator is also possible with a comparatively long service life. The design of the combustion chamber for an approximately horizontal main flow direction of the heating gas also makes it particularly compact Design of the continuous steam generator 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 and

3 shows a coordinate system with the curves K _x to Kβ -

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

The continuous steam generator 2 according to FIG. 1 is assigned to a power plant, not shown, which also includes a steam turbine system. The continuous steam generator is designed for a steam output at full load of at least 80 kg / s. The steam generated in the continuous-flow 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-fueled once-through steam generator 2 comprises a combustion chamber 4 which is constructed in a horizontal construction and which is followed by a vertical gas flue 8 on the hot gas side via a horizontal gas flue 6. The surrounding walls 9 of the combustion chamber 4 are formed from vertically arranged evaporator tubes 10 welded to one another in a gastight manner, of which a number N can be acted upon in parallel with flow medium S. there 13 is a peripheral wall 9 of the combustion chamber 4, the end wall 11. In addition, the side walls 12 of the horizontal gas train 6 and 14 of the vertical gas train 8 can also be formed from vertically arranged steam generator pipes 16 and 17, which are welded together in a gastight manner. In this case, the steam generator tubes 16 and 17 can each be acted upon in parallel with flow medium S.

An inlet header system 18 for a number of the evaporator tubes 10 of the combustion chamber 4 is on the flow medium side

Flow medium S is connected upstream and an output collector system 20 is 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 collecting manifold 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.

The evaporator tubes 10 have - as shown in FIG. 2 - 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 R. 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 particularly reliable that temperature differences at the outlet of the evaporator tube 10 are kept particularly low.

As a means of reducing the flow of the flow medium S, some of the evaporator tubes 10 are equipped with throttling devices, which are not shown in the drawing. The throttling devices are designed as perforated orifices which reduce the inner diameter D of the pipe 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 pipes 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 detail. 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 side 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 low, even when the evaporator or steam generator tubes 10, 16, 17 are heated to very different degrees. In this way, material fatigue is reliably prevented, which ensures a long service life of the continuous 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, 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 temperatures and sufficient cooling of all evaporator tubes 10 is ensured for all operating states of the continuous steam generator 2 is. A reduced heating of some evaporator tubes 10 during 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 subjected to greater heating during operation of the once-through steam generator 2, have a larger inner tube diameter D than evaporator tubes 10, which are heated less when the once-through steam generator 2 is in operation. Compared to the case with the same inner tube diameter, 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 pipes 10 and / or in the line system 19 provided for the supply of flow medium S. In contrast, the heating to 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 above-mentioned measures result in heating of the individual being very different Evaporator tubes 10 have 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 at their outlet. The interior of the evaporator tubes 10 is 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 22 in the form of bulkhead heating plates, which are arranged in a hanging construction approximately perpendicular to the main flow direction 24 of the heating gas G and the pipes of which are connected in parallel for flow through the flow medium S. The superheater heating surfaces 22 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 26 of the heating gas G. These pipes are connected in parallel for 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 flows into a further warm-up exchanger, for example into 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 more detail in FIG. 1.

The continuous steam generator 2 is designed with a horizontal combustion chamber 4 with a particularly low overall height and can therefore be set up with particularly little production and assembly effort. For this purpose, the combustion chamber 4 of the once-through steam generator 2 has a number of burners 30 for fossil fuels Fuel B, which are arranged on the end wall 11 of the combustion chamber 4 at the height of the horizontal gas flue 6.

To ensure that the fossil fuel B burns out completely completely in order to achieve a particularly high degree of efficiency, and material damage to the first superheater heating surface 22 of the horizontal gas flue 6, as seen on the heating gas side, and contamination thereof, for example by the introduction of molten ash at a high temperature, is prevented particularly reliably L of the combustion chamber 4 is selected such that it exceeds the burnout length of the 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 entry region 32 of the horizontal gas flue 6. The burnout length of the 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 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 to completely burn out at a certain 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 (given in s) the

Flame F of the fuel B and the steam output M (specified in kg / s) of the once-through steam generator 2 are selected as suitable at full load. 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 measured from the top edge of the funnel of the combustion chamber 4, marked by the line with the end points X and Y in FIG. 1, to the top of the combustion chamber. The Lange L der Combustion chamber 4 is approximately determined by functions (1) and (2):

L (M, t _A ) = (Ci + C ₂ ^• M) ^• t _A (1) and

L (M, T _BRK ) = (C ₃ ^• T _BRK + C ₄ ) M + C ₅ (T _BRK ) ² + C ₆ ^• T _BRK + C7 (2) 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- = 603.41 m.

Approximately, this is to be understood as a permissible deviation of +20% / - 10% from the value defined by the respective function. When designing the once-through steam generator 2 for a given steam output M of the once-through steam generator 2 at full load, the larger value from the functions (1) and (2) applies to the length L of the combustion chamber 4.

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

Ki: t _A = 3s according to (1),

K ₂ : t _A = 2.5 s according to (1),

K ₃ : t _A = 2s according to (1),

K ₄ : T _BRK = 1200 ' ³ C according to (2),

K ₅ : TBRK = 1300 " ³ C according to (2),

K ₆ : T _BRK = 1400 ' ^D C according to (2). To determine the length L of the combustion chamber 4, the curves Ki and K ₄ are thus to be used, for example, for a burnout time t _A = 3 s and an 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, 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 according to K .

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 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 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 K ₅ .

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 M that 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 fuel B and the exit temperature of the heating gas G from the combustion chamber T _BRK = 1400 ° C. are assigned to the curves K ₃ and K ₆ , 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 = 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 _s -

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 Kς drawn as a solid line and not the part of the curve K ₃ drawn as a dashed line applies.

In order for a higher throughput of the flow medium S to set itself automatically in a multi-heated evaporator tube 10 than in a less heated evaporator tube 10 during operation of the continuous steam generator 2, the quotient of the steam output M (given in kg / s) of the continuous-flow steam generator 2 at full load and the sum A (indicated in m ² ) of the inner cross-sectional area of the number N of these evaporator tubes 10, which can be acted upon in parallel with flow medium S, each having an inner tube diameter D _N such that the condition

is satisfied. The number 1350 is given in kg / sm ² and D _{N is} the inside diameter of the Nth evaporator tube 10 with i = 1 to N.

When the continuous steam generator 2 is operated, the burners 30 are supplied with fossil fuel B. The flames F of the burner 30 are aligned horizontally. Due to the construction of the combustion chamber 4, a flow of the combustion gas G generated in approximately horizontal main flow direction 24 generated. 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 reaches the inlet header system 18 of the evaporator tubes 10 of the combustion chamber 4 of the continuous-flow steam generator 2 via the convection heating surfaces 26 arranged in the vertical gas flue 8. In the vertically arranged, gas-tightly welded evaporator tubes 10 of the combustion chamber 4 of the continuous 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 passes through the walls of the horizontal gas flue 6 and the vertical gas flue 8 into the superheater heating surfaces 22 of the horizontal gas flue 6. In the superheater heating surfaces 22, the steam is further overheated, which is then used, for example the drive of a steam turbine.

By limiting the quotient from the steam output M of the continuous-flow steam generator 2 at full load and the sum of the internal cross-sectional areas F to the value 1350 kg / sm ² for a number N of evaporator tubes 10 connected in parallel, particularly small temperature differences between adjacent evaporator tubes are particularly simple 10 guaranteed at the same time particularly reliable cooling of the evaporator tubes 10 in all load conditions of the continuous steam generator 2. In addition, the series connection of the evaporator tubes 10 is designed in particular for utilizing the approximately horizontal main flow direction 24 of the heating gas G. By choosing 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), which has a combustion chamber (4) for fossil fuel (B), the hot gas side is followed by a vertical gas flue (8) via a horizontal gas flue (8), the peripheral walls (9) of the combustion chamber (4) are formed from vertically arranged evaporator tubes (10) welded to one another in a gas-tight manner and the combustion chamber (4) comprises a number of burners (30) arranged at the height of the horizontal gas flue (6) and is designed such that a number (N ) of evaporator tubes (10) which can be acted upon in parallel with flow medium (S) and which derive from the steam output (M) (specified in kg / s) at full load and from the sum (A) (specified in m ² ) of the internal cross-sectional areas of these in parallel with flow medium ( S) loadable evaporator tubes (10) formed quotient is less than 1350 (specified in kg / sm ² ).

2. Continuous steam generator (2) according to claim 1, in each of which a number of evaporator tubes (10) which can be acted upon in parallel with flow medium (S) upstream of the combustion chamber (4) on the flow medium side each have a common inlet collector system (18) for flow medium (S) and a common outlet collector system (20) is connected downstream.

3. continuous steam generator (2) according to claim 1 or 2, wherein the evaporator tubes (10) of the end wall (11) of the combustion chamber (4) on the flow medium side upstream of the evaporator tubes (10) of the other surrounding walls (9) of the combustion chamber (4).

4. continuous steam generator (2) according to any one of claims 1 to 3, wherein the tube inner diameter (D) of a number of the evaporator tubes (10) of the combustion chamber (4) depending on the respective position of the evaporator tubes (10) in the combustion chamber (4th ) is selected.

5. continuous steam generator (2) according to any one of claims 1 to 4, in which a number of the evaporator tubes (10) each carry a multi-thread ribs (40) on their inside.

6. Continuous steam generator (2) according to claim 5, in which a 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 60 °, preferably smaller than 55 °; is.

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

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

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

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

9. continuous steam generator (2) according to any one of claims 1 to 8, in which the side walls (12) of the horizontal throttle cable (6) from gas-tightly welded, vertically arranged, parallel with flow medium (S) actable steam generator tubes (16) are formed.

10. continuous steam generator (2) according to one of claims 1 to 9, in which the side walls (14) of the vertical throttle cable (8) from gas-tightly welded, vertically arranged, • parallel with flow medium (S) actable steam generator tubes (17) are formed.

11. continuous steam generator (2) according to one of claims 1 to 10, in which adjacent evaporator or steam generator tubes (10, 16, 17) are welded together gas-tight 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) of the horizontal gas train (6) and / or the vertical throttle cable (8) is selected.

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

11, in which the horizontal gas flue (6) has a number of superheater heating surfaces (22) arranged in a hanging construction.

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

12, in which a number of convection heating surfaces (26) is arranged in the vertical gas flue (8).

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

13, in which the burners (30) are arranged on the end wall (11) of the combustion chamber (4).

15. continuous steam generator (2) according to any one of claims 1 to 14, wherein the by the distance from the end wall (11)

The combustion chamber (4) to the inlet area (32) of the horizontal gas flue (6) has a defined length (L) of the combustion chamber (4) which is at least equal to the burnout length of the fuel (B) when the steam generator (2) is operating at full load.

16. continuous steam generator (2) according to any one of claims 1 to 15, wherein the length (L) of the combustion chamber (4) as a function of the steam output (M) at full load, the burnout time (t _A ) of 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 functions

L (M, t _A ) = (Ci + C ₂ M) t _A and

L (M, T _BRK ) = (C ₃ T _BR + C ₄ ) M + C ₅ (T _BR ² + C ₆ T _BRΛ + O 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 ₇ = 603.41 m

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