EP1188021B1 - Fossil-fuel heated steam generator, comprising denitrification device for heating gas - Google Patents

Description

The invention relates to a steam generator with a denitrification device for heating gas and with a combustion chamber for fossil fuel, the hot gas side via a horizontal gas train and a vertical gas train denitrification is followed by heating gas.

document US 3527261 For example, discloses a steam generator in a compact design with a horizontal gas train and a downstream vertical gas train, but without denitrification.

In a power plant with a steam generator, the fuel gas generated during the combustion of a fossil fuel is used for the evaporation of a flow medium in the steam generator. The steam generator has evaporator tubes for the evaporation of the flow medium, the heating of which leads with heating gas to an evaporation of the flow medium guided therein. The steam provided by the steam generator can in turn be provided, for example, for a connected external process or else for the drive of a steam turbine. If the steam drives a steam turbine, usually a generator or a working machine is operated via the turbine shaft of the steam turbine. In the case of a generator, the power generated by the generator may be provided for feeding into a composite and / or island grid.

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

Steam generators are usually designed with a combustion chamber in a vertical construction. This means that the combustion chamber is designed for a flow through the heating medium or heating gas in approximately vertical direction. Heizgasseitig the combustion chamber can be followed by a horizontal gas train, wherein the transition from the combustion chamber in the horizontal gas train, a deflection of the Heizgasstroms takes place in an approximately horizontal flow direction. However, such combustors generally require due to the temperature-induced changes in length of the combustion chamber, a scaffold on which the combustion chamber is suspended. This requires a considerable technical effort in the production and installation of the steam generator, which is the greater, the greater the height of the steam generator.

A particular problem is the design of the enclosure wall of the gas flue or combustion chamber of the steam generator with respect to the pipe wall or material temperatures occurring there. In the subcritical pressure range up to about 200 bar, the temperature of the peripheral wall of the combustion chamber is essentially determined by the height of the saturation temperature of the water , This is achieved, for example, by the use of evaporator tubes which have a surface structure on their inside. For this purpose, in particular innberippte evaporator tubes into consideration, their use in a continuous steam generator, for example, from the above cited essay is known. These so-called finned tubes, i. Tubes with a ribbed inner surface have a particularly good heat transfer from the tube inner wall to the flow medium.

For nitrogen oxide reduction of the fuel gas of the fossil fuel, the process of selective catalytic reduction, the so-called SCR process, can be used. In the SCR process, nitrogen oxides (NO _x ) are reduced to nitrogen (N ₂ ) and water (H ₂ O) by means of a reducing agent, such as ammonia, and a catalyst.

In a steam generator designed for an SCR process, a denitrification device for heating gas with a catalytic converter is usually arranged after the heating gas duct designed as convection draft, where usually the heating gas has a temperature of about 320 to 400 ° C. The catalyst of the denitration device for heating gas serves to initiate and / or maintain a reaction between the reducing agent introduced in the heating gas and the nitrogen oxides of the heating gas. The reducing agent required for the SCR process is usually injected with air as a carrier stream into the hot gas flowing through the gas train. However, the nitrogen oxide emission of the steam generator is usually dependent on the type of fossil fuel burned. In order to comply with the statutory limits, therefore, usually the einzudüsende amount of reducing agent is varied depending on the fossil fuel used.

However, a denitrification device for heating gas arranged on the output side after the convection pass requires considerable design and production effort for the respective steam generator. Because the denitrification must be placed there in the steam generator, where it can exert a particularly high cleaning effect on the fuel gas at all operating conditions of the steam generator. This is usually the case where the heating gas has a temperature in the range of about 320 to 400 ° C. In addition, the production cost of a steam generator increases when this addition to conventional components additionally has a denitrification.

The invention is therefore an object of the invention to provide a fossil-fired steam generator of the type mentioned above, which requires a particularly low design and manufacturing costs, and in the particularly reliable cleaning of the fuel gas of the fossil fuel is guaranteed before they leave the steam generator on the output side.

This object is achieved by the combustion chamber of the steam generator comprises a number of arranged in the height of the horizontal flue burners, the vertical gas flue for an approximately vertical flow of the heating gas from bottom to top and denitrification of heating gas for an approximately vertical flow of the fuel gas top down is designed.

The invention is based on the consideration that a producible with particularly low manufacturing and assembly costs steam generator should have a executable with simple means suspension structure. A scaffold for the suspension of the combustion chamber to be created with comparatively little technical effort can be accompanied by a particularly low overall height of the steam generator. A particularly low height of the steam generator can be achieved by the combustion chamber is designed in a horizontal design. For this purpose, the burners are arranged in the height of the horizontal gas flue in the combustion chamber wall. Thus, the combustion chamber is flowed through during operation of the steam generator in approximately horizontal direction of the heating gas.

For a particularly reliable cleaning of the fuel gas of the fossil fuel, the denitrification device for heating gas should be arranged on the output side after the vertical gas train. On the output side after the vertical gas train, namely, the heating gas to temperatures at which a cleaning of the fuel gas is particularly effective with little technical effort. It should be noted that for a particularly low height of the steam generator Entstickungseinrichtung for heating gas should be designed for an approximately vertical flow of the fuel gas from top to bottom. This results in an injection of the liquid required in the SCR process with ammonia components along the main flow direction of the fuel gas possible, whereby the vertical extent of the denitrification precipitates particularly low.

In a steam generator with a combustion chamber, which can be flowed through in nearly horizontal main flow direction of heating gas, but now flow the hot gases after leaving the Horizontalgaszugs in the vertical gas train downwards. In order to allow the heating gas in the denitrification for heating gas to flow approximately vertically from top to bottom, therefore, a channel for the heating gas is required, in which the heating gas on the output side after the vertical gas is passed from bottom to top and then in the durchströmbare from top to bottom Denitrification device for heating gas to arrive. This additional channel is not required if the vertical gas flue is designed for an approximately vertical flow of the heating gas from bottom to top and provided for the heating gas Entstikkungseinrichtung for an approximately vertical flow of the heating gas from top to bottom.

Advantageously, the purified fuel gas leaving the denitrification device for heating gas can be used to heat air in an air preheater. The air preheater should be arranged in a particularly space-saving manner directly below the Entstickungseinrichtung for heating gas. The preheated air is to be supplied to the burners of the steam generator for the combustion of the fossil fuel. If warm air is supplied to the burners as opposed to cold air during combustion of the fossil fuel, the overall efficiency of the steam generator increases.

The denitrification device for heating gas advantageously comprises a DeNO _x catalyst. For then a reduction in nitrogen oxide of the hot gas leaving the steam generator can be carried out in a particularly simple manner, for example with the method of Selective Catalytic Reduction.

The enclosing walls of the combustion chamber are advantageously formed of gas-tight welded together, vertically arranged evaporator tubes, each of which a number can be acted upon in parallel with flow medium.

Advantageously, a peripheral wall of the combustion chamber is the end wall and two surrounding walls of the combustion chamber are the side walls, wherein the side walls are each subdivided into a first group and a second group of Verdamperrohre, the end wall and the first group of Verdamperrohre be acted upon in parallel with flow medium and the be acted upon in parallel flow medium, the second group of evaporator tubes upstream of the flow medium. This ensures a particularly favorable cooling of the end wall.

Advantageously, each of the evaporator tubes, which can be acted upon in parallel with flow medium, is preceded by a common inlet collector system on the flow medium side and a common outlet collector system connected downstream. A designed in this embodiment steam generator allows reliable pressure equalization between the parallel connected evaporator tubes and thus a particularly favorable distribution of the flow medium in the flow through the evaporator tubes.

In a further advantageous embodiment, the tube inner diameter of a number of evaporator tubes of the combustion chamber is selected depending on 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 gas-side predefinable heating profile. With the effect thereby effected 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 guided into the evaporator tubes flow medium advantageously has a number of evaporator tubes on its inner side in each case a mehrgängiges thread forming ribs. In this case, a pitch angle α between a plane perpendicular to the tube axis and the flanks of the arranged on the tube inside ribs is advantageously less than 60 °, preferably less than 55 °.

In a heated, designed as an evaporator tube without Innenberippung, a so-called smooth tube, evaporator tube can namely no longer be maintained by a certain vapor content of the required for a particularly good heat transfer wetting the tube wall. If there is no wetting, there may be a partially dry pipe wall. The transition to such a dry pipe wall leads to a kind of heat transfer crisis with deteriorated heat transfer behavior, so that in general increase the pipe wall temperatures at this point particularly strong. In an internally ribbed pipe, however, this crisis of heat transfer now occurs only at a steam mass content> 0.9, ie shortly before the end of the evaporation, compared to a smooth pipe. This is due to the spin experienced by the flow through the spiral ribs. Due to the different centrifugal force, the water is separated from the vapor component and pressed against the pipe wall. As a result, the wetting of the pipe wall is maintained up to high vapor contents, so that there are already high flow velocities at the location of the heat transfer crisis. This causes a good heat transfer despite the heat transfer crisis and as a consequence low pipe wall temperatures.

A number of the evaporator tubes of the combustion chamber advantageously has 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, for example, internals in be the evaporator tubes, which reduce the pipe inside diameter at a point inside the respective evaporator tube.

In this case, also prove to be means for reducing the flow in a multiple parallel lines piping system advantageous, through which the evaporator tubes of the combustion chamber flow medium can be supplied. In this case, the line system can also be connected upstream of an inlet collector system of evaporator tubes which can be acted upon in parallel with flow medium. In one line or in several lines of the line system, for example, throttle valves can be provided. With such means for reducing the flow of the flow medium through the evaporator tubes, an adjustment of the flow rate of the flow medium can be caused by individual evaporator tubes to their respective heating in the combustion chamber. As a result, temperature differences of the flow medium at the outlet of the evaporator tubes are particularly reliably kept particularly low.

The side walls of the horizontal gas flue and / or the vertical gas flue are advantageously formed of gas-tight welded together, vertically arranged steam generator tubes, each of which a number can be acted upon in parallel with flow medium.

Adjacent evaporator or steam generator tubes are advantageously welded together via metal bands, so-called fins, gas-tight. The fin width affects the heat input into the steam generator tubes. Therefore, the fin width is preferably adapted depending on the position of the respective evaporator or steam generator tubes in the steam generator to a gas-side prescribable heating and / or temperature profile. As a heating and / or temperature profile, a typical heating and / or temperature profile determined from empirical values or else a rough estimate, such as a step-shaped heating and / or temperature profile, be given. Due to the suitably chosen fin widths, heat input into all evaporator or steam generator tubes is achievable even with very different heating of different evaporator or steam generator tubes, so 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 steam generator on a particularly long life.

In the horizontal gas train, a number of superheater heating surfaces are advantageously arranged, whose tubes are arranged approximately transversely to the main flow direction of the heating gas and connected in parallel for a flow through the flow medium. These arranged in a hanging design, also referred to as Schottheizflächen, superheater heating surfaces are heated predominantly convective and downstream of the evaporator tubes of the combustion chamber downstream of the combustion chamber. As a result, a particularly favorable utilization of the heating gas heat is ensured.

Advantageously, the vertical gas train has a number of convection heating surfaces, which are formed from tubes arranged approximately transversely to the main flow direction of the heating gas. The tubes of a convection heating surface are connected in parallel for a flow through the flow medium. These convection heating surfaces are heated predominantly convection.

In order to further ensure a particularly complete utilization of the heat of the hot gas, the vertical gas train advantageously has an economizer.

Advantageously, the burners are arranged on the end wall of the combustion chamber, that is on that surrounding wall of the combustion chamber, which is opposite to the outflow opening to the horizontal gas flue. Such a trained steam generator can be adapted in a particularly simple manner to the Ausbrandlänge of the fuel. Under burn-off length of the fossil fuel while the fuel gas velocity in the horizontal direction at a certain average heating gas temperature multiplied by the burn time t _{A of} the fossil fuel to understand. The maximum burn-out length for the respective steam generator results in the steam output of the steam generator at full load, the so-called full-load operation of the steam generator. The burn-out time t _A, in turn, is the time that, for example, a pulverized coal particle needs to completely burn out at a certain average heating gas temperature.

In order to keep material damage and an undesirable contamination of the horizontal gas flue, for example due to the entry of molten ash of a high temperature, particularly low, the defined by the distance from the end wall to the inlet region of the horizontal flue length L of the combustion chamber is advantageously at least equal to the burn-out length of the fuel Full load operation of the steam generator. This length L of the combustion chamber will generally be greater than the height of the combustion chamber, measured from the funnel upper edge to the combustion chamber ceiling.

und $$\mathrm{L}\left(\mathrm{W},{\mathrm{T}}_{\mathrm{BRK}}\right)\mathrm{=}\left({\mathrm{C}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{4}}\right)\mathrm{W}\mathrm{+}{\mathrm{C}}_{\mathrm{5}}{\left({\mathrm{T}}_{\mathrm{BRK}}\right)}^{\mathrm{2}}\mathrm{+}{\mathrm{C}}_{\mathrm{6}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{7}}$$

mit

• C₁ = 8 m/s und
• C₂ = 0,0057 m/kg und
• C₃ = -1,905 · 10^-4 (m · s) / (kg°C) und
• C₄ = 0,286 (s · m) / kg und
• C₅ = 3 · 10^-4 m/ (°C)² und
• C₆ = -0,842 m/°C und
• C₇= 603,41 m.

The length L (indicated in m) of the combustion chamber is for particularly favorable utilization of the combustion heat of the fossil fuel in an advantageous embodiment as a function of the BMCR value W (indicated in kg / s) of the steam generator, the burn-out time t _A (indicated in s) of the fuel and the outlet temperature T _BRK (indicated in ° C) of the heating gas selected from the combustion chamber. BMCR stands for Boiler maximum continuous rating and is the internationally commonly used term for the highest continuous output of a steam generator. This also corresponds to the design performance, ie the power at full load operation of the steam generator. In this case, given a BMCR value W of the steam generator for the length L of the Combustion chamber approximately the greater value of the two functions (I) and (II): $$\mathrm{L}\left(\mathrm{W},{\mathrm{t}}_{\mathrm{A}}\right)\mathrm{=}\left({\mathrm{C}}_{\mathrm{1}}\mathrm{+}{\mathrm{C}}_{\mathrm{2}}\mathrm{\cdot }\mathrm{W}\right)\mathrm{\cdot }{\mathrm{t}}_{\mathrm{A}}$$

and $$\mathrm{L}\left(\mathrm{W},{\mathrm{T}}_{\mathrm{BRK}}\right)\mathrm{=}\left({\mathrm{C}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{4}}\right)\mathrm{W}\mathrm{+}{\mathrm{<figure-callout\; id="5"\; label="C"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C</figure-callout>}}_{\mathrm{5}}{\left({\mathrm{T}}_{\mathrm{BRK}}\right)}^{\mathrm{2}}\mathrm{+}{\mathrm{C}}_{\mathrm{6}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{7}}$$

With

• C ₁ = 8 m / s and
• C ₂ = 0.0057 m / kg and
• C ₃ = -1.905 · 10 ^-4 (m · s) / (kg ° C) and
• C ₄ = 0.286 (s · m) / kg and
• C ₅ = 3 × 10 ^-4 m / (° C) ² and
• C ₆ = -0.842 m / ° C and
• C ₇ = 603.41 m.

By "approximate" is meant a permissible deviation of the value defined by the respective function by + 20% / - 10%.

The advantages achieved by the invention are in particular that has a particularly small footprint through the horizontal combustion chamber and designed for an approximately vertical flow direction of the fuel gas from bottom to top vertical gas train of the steam generator. This particularly compact design of the steam generator allows for integration of the steam generator in a steam turbine plant particularly short connecting pipes from the steam generator to the steam turbine.

FIG 1

schematisch einen fossil beheizten Dampferzeuger in Zweizugbauart in Seitenansicht und

FIG 2

schematisch einen Längsschnitt durch ein einzelnes Verdampferrohr und

FIG 3

ein Koordinatensystem mit den Kurven K₁ bis K₆.

An embodiment of the invention will be explained in more detail with reference to a drawing. Show:

FIG. 1

schematically a fossil-heated steam generator in Zweizugbauart in side view and

FIG. 2

schematically a longitudinal section through a single evaporator tube and

FIG. 3

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

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

The steam generator 2 according to FIG. 1 is associated with a power plant not shown, which also includes a steam turbine plant. The steam generated in the steam generator 2 is used to drive the steam turbine, which in turn drives a generator for generating electricity. The electricity generated by the generator is provided for feeding into a network or an island network. Furthermore, a diversion of a subset of the steam for feeding into an external process connected to the steam turbine plant may be provided, which may also be a heating process.

The fossil-heated steam generator 2 is advantageously designed as a continuous steam generator. It comprises a horizontally constructed combustion chamber 4, the heating gas side via a horizontal gas train 6 a vertical gas train 8 is connected downstream. 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. As a result of the funnel 5, as the steam generator 2 is operated, ash from the fossil fuel B can be discharged into a deashing device 7 arranged below it. The enclosure walls 9 of the combustion chamber 4 are formed from gas-tight welded together, vertically arranged evaporator tubes 10. In this case, a surrounding wall 9, the end wall 9A and two enclosing walls 9 are the side walls 9B of the combustion chamber 4 of the steam generator 2. In the in FIG. 1 shown side view of the steam generator 2, only one of the two side walls 9B visible. The evaporator tubes 10 of the side walls 9B of the combustion chamber 4 are divided into a first group 11A and a second group 11B. The evaporator tubes 10 of the end wall 9A and the first group 11A of the evaporator tubes 10 are acted upon in parallel with flow medium S. Also, the second group 11B of the evaporator tubes 10 can be acted upon in parallel with flow medium S. In order to achieve a particularly favorable flow characteristics of the flow medium S through the Umfassungswände 9 of the combustion chamber 4 and thus a particularly good utilization of the heat of combustion of the fossil fuel B, the evaporator tubes 10 of the end wall 9A and the first group 11A strömungsmediumsseitg the evaporator tubes 10 of the second group 11B upstream.

The side walls 12 of the horizontal gas flue 6 and / or the side walls 14 of the vertical gas flue 8 are formed from gas-tight welded together, vertically arranged steam generator tubes 16 and 17, respectively. Of the steam generator tubes 16, 17 while a number in parallel with flow medium S can be acted upon.

The end face 9A and the first group 11A of the evaporator tubes 10 of the combustion chamber 4 upstream of the flow medium side, a common inlet header system 18A for flow medium S and downstream of an outlet header system 20A. Likewise, the second group 11B of the side walls 9B of the evaporator tubes 10 is preceded by a common inlet header system 18B for flow medium S downstream of an outlet header system 20B and downstream of an outlet header system 20B. The entry collector systems 18A and 18B each comprise a number of parallel entry collectors.

For supplying flow medium S into the inlet header system 18A of the end face 9A of the combustion chamber 4 and the first group 11A of the evaporator tubes 10 of the side walls 9B of the combustion chamber 4, a piping 19A is provided. The conduit system 19A includes a plurality of parallel-connected conduits, each connected to one of the inlet header of the inlet header system 18A. The outlet header system 20A is connected on the output side to a line system 19B, which is suitable for feeding flow medium S into the Intake collector of the inlet header system 18B of the second group 11B of the evaporator tubes 10 of the side walls 9B of the combustion chamber 4 is provided.

In the same way, the steam generator tubes 16, which can be acted upon in parallel with flow medium S, of the side walls 12 of the horizontal gas flue 6 are preceded by a common inlet header system 21 and are followed by a common outlet header system 22. In this case, a line system 25 is provided for supplying flow medium S into the inlet header system 21 of the steam generator tubes 16. The line system 25 also includes a plurality of parallel lines, which are each connected to one of the inlet header of the inlet header system 21. On the input side, the line system 25 is connected to the outlet header system 20B of the second group 11B of the evaporator tubes 10 of the side walls 9A of the combustion chamber 4. The heated flow medium S leaving the combustion chamber 4 is thus guided into the side walls 12 of the horizontal gas flue 6.

This embodiment of the continuous-flow steam generator 2 with inlet collector systems 13A, 18B and 21 and outlet collector systems 20A, 20B and 22 provides a particularly reliable pressure equalization between the parallel-connected evaporator tubes 10 of the combustion chamber 4 and the parallel steam generator tubes 16 of the horizontal gas flue 6 in FIG the way possible that each parallel-connected evaporator or steam generator tubes 10 and 16 have the same total pressure loss. This means that in a more heated evaporator tube 10 or steam generator tube 16 compared to a less heated evaporator tube 10 or steam generator tube 16, the throughput must increase.

The evaporator tubes 10 have - as in FIG. 2 shown on its inside ribs 40, which form a kind multi-threaded and have a rib height R. In this case, the pitch angle α between a perpendicular to the tube axis Level 42 and the flanks 44 of the arranged on the tube inside ribs 40 is less than 55 °. As a result, a particularly high heat transfer from the inner wall of the evaporator tubes to the flow medium S guided into the evaporator tubes 10 is achieved at the same time as particularly low temperatures of the tube wall.

The tube inner diameter D 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. In this way, the 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 tubes 10 are kept particularly low.

Adjacent evaporator or steam generator tubes 10, 16, 17 are gas-tight welded together in a manner not shown by fins. By a suitable choice of the fin width namely the heating of the evaporator or steam generator tubes 10, 16, 17 can be influenced. Therefore, the respective fin width is adapted to a gas side specifiable heating profile, which depends on the position of the respective evaporator or steam generator tubes 10, 16, 17 in the steam generator. The heating profile can be a typical heating profile determined from empirical values or else a rough estimate. As a result, temperature differences at the outlet of the evaporator or steam generator tubes 10, 16, 17, even with very different heating of the evaporator or steam generator tubes 10, 16, 17 are kept particularly low. In this way, material fatigue are reliably prevented, which ensures a long life of the steam generator 2.

As means for reducing the flow rate of the flow medium S, a part of the evaporator tubes 10 are equipped with throttling devices which are not closer in the drawing are shown. The throttling devices are embodied as pinhole diaphragms reducing the inner diameter of the pipe D and, during operation of the steam generator 2, reduce the throughput of the flow medium S in underheated evaporator tubes 10, whereby the flow rate of the flow medium S is adapted to the heating. Furthermore, as a means for reducing the flow rate of the flow medium S in the evaporator tubes 10 of the combustion chamber 4, one or more lines of the conduit system 19 and 25 with throttle devices, in particular throttle valves, equipped, which is not shown in detail in the drawing.

When boring the combustion chamber 4, it should be noted that the heating of the individual, gas-tight welded evaporator tubes 10 during operation of the steam generator 2 is very different. Therefore, the design of the evaporator tubes 10 with respect to their Innenberippung, fin connection to adjacent evaporator tubes 10 and its inner tube diameter D chosen so that all evaporator tubes 10 despite different heating have approximately the same outlet temperatures of the flow medium S and sufficient cooling all evaporator tubes 10 for all operating conditions of the steam generator. 2 is guaranteed.

These properties of the steam generator are ensured, in particular, when the steam generator 2 is designed for a comparatively low mass flow density of the flow medium S flowing through the evaporator tubes 10. By a suitable choice of the fin connections and the tube inner diameter D is also achieved that the proportion of friction pressure loss in the total pressure loss is so low that sets a natural circulation behavior: Stronger heated evaporator tubes 10 are flowed through stronger than less heated evaporator tubes 10. This also ensures that the comparatively strongly heated evaporator tubes 10 near the burner specifically - based on the mass flow - absorb almost as much heat as the comparatively weakly heated evaporator tubes 10, which are arranged in comparison closer to the combustion chamber end. Another measure to adapt the flow through the evaporator tubes 10 of the combustion chamber 4 to the heating, is the installation of throttles in a part of the evaporator tubes 10 or in a part of the lines of the conduit system 19. The internal ribbing is designed such that a sufficient cooling of Evaporator pipe walls is ensured. Thus, all the evaporator tubes 10 have approximately the same exit temperatures of the flow medium S with the above-mentioned measures.

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

The vertical gas flow 8, which can be flowed through from bottom to top by heating gas G, has a number of convection heating surfaces 26 which can be heated predominantly convectively 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 flow through the flow medium S and integrated into the path of the flow medium S, which is not shown in detail in the drawing. In addition, an economizer 28 is disposed in the vertical gas train 8 above the convection heating surfaces 26. The economizer 28 is connected on the output side via a line system 19 to the evaporator tubes 10 associated with the inlet collector system 18. In this case, one or more lines (not shown in detail in the drawing) of the line system 54 may have throttle bodies for reducing the flow rate of the flow medium S.

On the output side, the vertical gas train 8, which can be traversed from bottom to top in approximately vertical main flow direction 24 with heating gas G, is followed by a short connecting duct 50. The connecting channel 50 connects the vertical gas train 8 with a housing 52. In the housing 52, a denitrification 54 for heating gas G is arranged on the input side. The denitrification device 54 for heating gas G is connected via a feed 56 to an air preheater 60. The air preheater 60 in turn is connected via a flue gas channel 62 to an electronic filter 62.

The denitrification device 54 for heating gas G is operated by the selective catalytic reduction process, the so-called SCR process. In the catalytic purification of the heating gas G of the steam generator 2 according to the SCR method, nitrogen oxides (NO _x ) are reduced to nitrogen (N ₂ ) and water (H ₂ O) by means of a catalyst and a reducing agent, for example ammonia.

To carry out the SCR process, the denitrification device 54 for heating gas G comprises a catalyst designed as DeNO _x catalyst 64. The DeNO _x catalyst is arranged in the flow region of the heating gas G. For introducing ammonia-water as reducing agent M into the heating gas G, the denitrification device 54 for heating gas G has a metering system 66. In this case, the dosing 66 comprises a reservoir 68 for ammonia water and a compressed air system 69. The dosing system 66 is disposed above the DeNO _x catalyst 64 in the denitrification 54.

The steam generator 2 is designed with a horizontal combustion chamber 4 with a particularly low height and thus can be built with very low production and assembly costs. For this purpose, the combustion chamber 4 of the steam generator 2 to a number of burners 70 for fossil fuel B, which are arranged on the end wall 11 of the combustion chamber 4 in the height of the horizontal gas flue 6.

So that the fossil fuel B, for example, coal in solid form, to achieve a particularly high efficiency particularly completely burns out and material damage of the heating gas seen first Überhitzerheizfläche 23 of Horizontalgaszuges 6 and pollution thereof, for example, by entry of molten ash with high temperature, particularly reliable prevented are, the length L of the combustion chamber 4 is selected such that it exceeds the burn-out length of the fuel B at full load operation of the steam generator 2. The length L is the distance from the end wall 9A of the combustion chamber 4 to the inlet region 72 of the horizontal gas flue 6. The burn-out length of the fuel B is defined as the fuel gas velocity in the horizontal direction at a certain mean heating gas temperature multiplied by the burn-out time t _{A of} the fossil fuel B. The maximum burn-out length for the respective steam generator 2 results during the full-load operation of the steam generator 2. The burn-out time t _{A of} the fuel B, in turn, is the time required, for example, by a pulverized coal grain of medium size to completely burn out at a specific average heating gas temperature.

$$\mathrm{L}\left(\mathrm{W},{\mathrm{T}}_{\mathrm{BRK}}\right)\mathrm{=}\left({\mathrm{C}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{4}}\right)\mathrm{W}\mathrm{+}{\mathrm{C}}_{\mathrm{5}}{\left({\mathrm{T}}_{\mathrm{BRK}}\right)}^{\mathrm{2}}\mathrm{+}{\mathrm{C}}_{\mathrm{6}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{7}}$$

mit

• C₁ = 8 m/s und
• C₂ = 0,0057 m/kg und
• C₃ = -1,905 · 10^-4 (m · s) / (kg°C) und
• C₄ = 0,286 (s · m) / kg und
• C₅ = 3 · 10^-4 m/ (°C)² und
• C₆ = -0,842 m/°C und
• C₇ = 603,41 m.

In order to ensure a particularly favorable utilization of the heat of combustion of the fossil fuel B, the length L (indicated in m) of the combustion chamber 4 in dependence on the outlet temperature of the heating gas G from the combustion chamber 4 T _BRK . (indicated in ° C), the burn-out time t _A (indicated in s) of the fuel B and the BMCR value W (indicated in kg / s) of the steam generator 2 suitably chosen. BMCR stands for Boiler maximum continuous rating. The BMCR value W is an internationally commonly used term for the highest continuous output of a steam generator. This also corresponds to the design performance, ie the power at full load operation of the steam generator. This horizontal length L of the combustion chamber 4 is greater than the height H of the combustion chamber 4. The height H is thereby from the funnel upper edge of the combustion chamber 4, in FIG. 1 marked by the auxiliary line with the end points X and Y, measured up to the combustion chamber ceiling. In this case, the length L of the combustion chamber 4 is determined approximately by the two functions (I) and (II) $$\mathrm{L}\left(\mathrm{W},{\mathrm{t}}_{\mathrm{A}}\right)\mathrm{=}\left({\mathrm{C}}_{\mathrm{1}}\mathrm{+}{\mathrm{C}}_{\mathrm{2}}\mathrm{\cdot }\mathrm{W}\right)\mathrm{\cdot }{\mathrm{t}}_{\mathrm{A}}$$

$$\mathrm{L}\left(\mathrm{W},{\mathrm{T}}_{\mathrm{BRK}}\right)\mathrm{=}\left({\mathrm{C}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{4}}\right)\mathrm{W}\mathrm{+}{\mathrm{<figure-callout\; id="5"\; label="C"\; filenames="imgf0001.png"\; state="\{\{state\}\}">C</figure-callout>}}_{\mathrm{5}}{\left({\mathrm{T}}_{\mathrm{BRK}}\right)}^{\mathrm{2}}\mathrm{+}{\mathrm{C}}_{\mathrm{6}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{7}}$$

With

• C ₁ = 8 m / s and
• C ₂ = 0.0057 m / kg and
• C ₃ = -1.905 · 10 ^-4 (m · s) / (kg ° C) and
• C ₄ = 0.286 (s · m) / kg and
• C ₅ = 3 × 10 ^-4 m / (° C) ² and
• C ₆ = -0.842 m / ° C and
• C ₇ = 603.41 m.

Approximately this is to be understood as a permissible deviation of +20% / - 10% of the value defined by the respective function. In this case, the larger value from the functions (I) and (II) for the length L of the combustion chamber 4 always applies to any desired but fixed BMCR value W of the steam generator.

• K₁: t_A = 3s gemäß (1),
• K₂: t_A = 2,5s gemäß (1),
• K₃: t_A = 2s gemäß (1),
• K₄: T_BRK = 1200°C gemäß (2),
• K₅: T_BRK = 1300°C gemäß (2) und
• K₅: T_BRK = 1400°C gemäß (2).

As an example for a calculation of the length L of the combustion chamber 4 as a function of the BMCR value W of the steam generator 2 are in the coordinate system according to FIG. 3 six curves K ₁ to K ₆ drawn. The following parameters are assigned to the curves:

• K ₁ : t _A = 3s according to (1),
• K ₂ : t _A = 2.5s according to (1),
• K ₃ : t _A = 2s according to (1),
• K ₄ : T _BRK = 1200 ° C according to (2),
• K ₅ : T _BRK = 1300 ° C according to (2) and
• K ₅ : T _BRK = 1400 ° C according to (2).

• von W = 80 kg/s eine Länge von L = 29 m gemäß K₄,
• von W = 160 kg/s eine Länge von L = 34 m gemäß K₄,
• von W = 560 kg/s eine Länge von L = 57 m gemäß K₄.

To determine the length L of the combustion chamber 4 are thus, for example, for a burnout time t _A = 3s and an outlet temperature T _BRK = 1200 ° C of the heating gas G from the combustion chamber. 4 to use the curves K ₁ and K ₄ . This results in a given BMCR value W of the steam generator 2

• of W = 80 kg / s a length of L = 29 m according to K ₄ ,
• of W = 160 kg / s a length of L = 34 m according to K ₄ ,
• of W = 560 kg / s a length of L = 57 m according to K ₄ .

• von W = 80 kg/s eine Länge von L = 21 m gemäß K₂,
• von W = 180 kg/s eine Länge von L = 23 m gemäß K₂ und K₅,
• von W = 560 kg/s eine Länge von L = 37 m gemäß K₅.

For the burnout time t _A = 2.5 s and the outlet temperature of the heating gas G from the combustion chamber T _BRK = 1300 ° C, for example, the curves K ₂ and K _{5 are} used. This results in a given BMCR value W of the steam generator 2

• of W = 80 kg / s a length of L = 21 m according to K ₂ ,
• of W = 180 kg / s a length of L = 23 m according to K ₂ and K ₅ ,
• of W = 560 kg / s a length of L = 37 m according to K ₅ .

• von W = 80 kg/s eine Länge von L = 18 m gemäß K₃,
• von W = 465 kg/s eine Länge von L = 21 m gemäß K₃ und K₆,
• von W = 560 kg/s eine Länge von L = 23 m gemäß K₆.

The burn-out time t _A = 2s and the outlet temperature of the heating gas G from the combustion chamber T _BRK = 1400 ° C, for example, the curves K ₃ and K _{6 are} assigned. This results in a given BMCR value W of the steam generator 2

• of W = 80 kg / s a length of L = 18 m according to K ₃ ,
• of W = 465 kg / s a length of L = 21 m according to K ₃ and K ₆ ,
• of W = 560 kg / s a length of L = 23 m according to K ₆ .

During operation of the steam generator 2, the burners 70 are supplied with fossil fuel B and air. The air is preheated in the air preheater with the residual heat of the fuel gas G, and then, which is not shown in detail in the drawing, compressed and fed to the burners 70. The flames F of the burner 70 are aligned horizontally. As a result of the design of the combustion chamber 4, a flow of the heating gas G produced during combustion is generated in an approximately horizontal main flow direction 24.

The heating gas G passes through the horizontal gas flue 6 in the vertical gas fl ow from bottom to top with hot gas G. 8. On the output side after the vertical gas train 8, the heating gas G passes through the connecting channel 50 in the denitration 54 for fuel G. About the denitrification 54 for fuel gas G is a function of the fuel type of the steam generator 2 operating fuel B, a certain amount of ammonia water as reducing agent M injected by means of compressed air into the fuel gas G. This is necessary since the degree of separation of the nitrogen oxides (NO _x ) depends on the type of fuel of the fossil fuel B operating the steam generator 2. In this way, a particularly reliable denitrification of the hot gas G is ensured under all operating conditions of the steam generator 2.

The purified fuel gas G1 leaves the denitrification 54 for fuel gas G via a feed 56, which opens into the air preheater 58. In the air preheater 58, a preheating of the burners 70 for the combustion of the fossil fuel B air supplied. The heating gas G leaves the air preheater 58 via the flue gas channel 60 and passes through the electronic filter 62 into the environment.

Flow medium S entering the economizer 28 passes via the line system 19A into the inlet header system 18A, which is assigned to the end wall 9A and the evaporator tubes 10 of the first group 11A of the side walls 9B of the combustion chamber 4 of the steam generator 2. The resulting in the vertically arranged, gas-tight welded together evaporator tubes 10 of the combustion chamber 4 of the steam generator 2 steam or a water-steam mixture is collected in the outlet collector system 20A for flow medium S. From there, the steam or the water-vapor mixture passes via the line system 19B in the inlet header system 18B, which is associated with the second group 11B of the evaporator tubes 10 of the side walls 9B of the combustion chamber 4. The resulting in the vertically arranged, gas-tight welded together evaporator tubes 10 of the combustion chamber 4 of the steam generator 2 steam or a water-steam mixture is in the outlet collector system 20B collected for flow medium S. From there, the steam or the water-vapor mixture passes through the line system 25 in the steam generator tubes 16 of the side walls 12 of the horizontal gas train associated with inlet collector system 21. The resulting in the evaporator tubes 16 steam or water-steam mixture passes the outlet collector system 22 into the walls of the vertical gas flue 8 and from there in turn into the superheater heating surfaces 23 of the horizontal flue 6. In the superheater heating 23 further overheating of the steam, which is then a use, for example, the drive of a steam turbine is supplied.

In the steam generator 2 is ensured by the choice of the length L of the combustion chamber 4 in response to the BMCR value W of the steam generator 2 that the heat of combustion of the fossil fuel B is utilized particularly reliable. In addition, the steam generator 2 by its horizontal combustion chamber 4 and the denitrification device 54 immediately downstream of the vertical gas train 8 has a particularly small footprint. In this case, a particularly reliable denitration of the heating gas G is ensured in a particularly simple manner in all operating states of the steam generator 2.

Claims (20)

1. Steam generator (2) with a nitrogen removal device (54) for fuel gas (G) and with a combustion chamber (4) for fossil fuel (B), which is followed on the fuel-gas side, via a horizontal gas flue (6) and a vertical gas flue (8), by the nitrogen removal device (54) for fuel gas (G), the combustion chamber (4) comprising a number of burners (70) arranged level with the horizontal gas flue (6), and the vertical gas flue (8) being designed for an approximately vertical flow of the fuel gas (G) from the bottom upward and the nitrogen removal device (54) for fuel gas (G) being designed for an approximately vertical flow of the fuel gas (G) from the top downward.
2. Steam generator (2) according to Claim 1, with an air preheater (58), in which the purified fuel gas (G1) leaving the nitrogen removal device (54) for fuel gas (G) can be used for the heating of air.
3. Steam generator (2) according to Claim 1 or 2, in which the nitrogen removal device (54) for fuel gas (G) comprises a DeNO_x catalyst (64).
4. Steam generator (2) according to one of Claims 1 to 3, in which the containment walls (9) of the combustion chamber (4) are formed from vertically arranged evaporator tubes (10) welded to one another in a gastight manner, in each case a number of the evaporator tubes (10) being capable of being acted upon in parallel by flow medium (S).
5. Steam generator (2) according to one of Claims 1 to 4, in which one containment wall (9) of the combustion chamber (4) is the end wall (9A) and two containment walls (9) are the side walls (9B) of the combustion chamber (4), the side walls (9B) being subdivided in each case into a first group (11A) and a second group (11B) of evaporator tubes (10), the end wall (9A) and the first group (11A) of the evaporator tubes (10) being capable of being acted upon in parallel by flow medium (S) and preceding, on the flow-medium side, the second group (11B) of the evaporator tubes (10) capable of being acted upon in parallel by flow medium (S).
6. Steam generator (2) according to one of Claims 4 and 5, in which, in each case, the evaporator tubes (10) capable of being acted upon in parallel by flow medium (S) are, on the flow-medium side, preceded by a common inlet header system (18A, 18B) and followed by a common outlet header system (20A, 20B).
7. Steam generator (2) according to one of Claims 1 to 6, in which the tube inside diameter (D) of a number of the evaporator tubes (10) of the combustion chamber (4) is selected as a function of the respective position of the evaporator tubes (10) in the combustion chamber (4).
8. Steam generator (2) according to one of Claims 1 to 7, in which a number of the evaporator tubes (10) carry on their inside in each case ribs (40) forming a multiflight thread.
9. Steam generator (2) according to Claim 8, in which a pitch angle (α) between a plane (42) perpendicular to the tube axis and the flanks (44) of the ribs (40) arranged on the tube inside is smaller than 60°, preferably smaller than 55°.
10. Steam generator (2) according to one of Claims 1 to 8, in which a number of the evaporator tubes (10) in each case have a throttle device.
11. Steam generator (2) according to one of Claims 1 to 10, in which a line system (19A, 19B) is provided for feeding flow medium (S) into the evaporator tubes (10) of the combustion chamber (4), the line system (19A, 19B) having a number of throttle devices, in particular throttle fittings, in order to reduce the throughflow quantity of the flow medium (S).
12. Steam generator (2) according to one of Claims 1 to 11, in which the side walls (12) of the horizontal gas flue (6) are formed from vertically arranged steam generator tubes (16) which are welded to one another in a gastight manner and a number of which are in each case capable of being acted upon in parallel by flow medium (S).
13. Steam generator (2) according to one of Claims 1 to 12, in which the side walls (14) of the vertical gas flue (8) are formed from vertically arranged steam generator tubes (17) which are welded to one another in a gastight manner and a number of which are in each case capable of being acted upon in parallel by flow medium (S).
14. Steam generator (2) according to one of Claims 1 to 13, in which adjacent evaporator or steam generator tubes (10, 16, 17) are welded to one another in a gastight manner via fins, the fin width being selected as a function of the respective position of the evaporator or steam generator tubes (10, 16, 17) in the combustion chamber (4) of the horizontal gas flue (6) and/or of the vertical gas flue (8).
15. Steam generator (2) according to one of Claims 1 to 14, in which a number of superheater heating surfaces (50) are arranged in a suspended form of construction in the horizontal gas flue (6).
16. Steam generator (2) according to one of Claims 1 to 15, in which a number of convection heating surfaces (52) are arranged in the vertical gas flue (8).
17. Steam generator (2) according to one of Claims 1 to 16, in which an economizer (28) is arranged in the vertical gas flue (8).
18. Steam generator (2) according to one of Claims 1 to 17, in which the burners (70) are arranged on the end wall (9A) of the combustion chamber (4).
19. Steam generator (2) according to one of Claims 1 to 18, in which the length (L) of the combustion chamber (4), defined by the distance between the end wall (9A) of the combustion chamber (4) and the inlet region (72) of the horizontal gas flue (6), is at least equal to the burnup length of the fuel (B) during full-load operation of the steam generator (2).
20. Steam generator (2) according to one of Claims 1 to 19, in which the length (L) of the combustion chamber (4) is selected as a function of the BMCR value (W), of the burnup time (t_A) of the burners (70) and/or of the outlet temperature (T_BRK) of the fuel gas (G) from the combustion chamber (4), approximately according to the two functions (I) and (II) $$\mathrm{L}\left(\mathrm{W},{\mathrm{t}}_{\mathrm{A}}\right)\mathrm{=}\left({\mathrm{C}}_{\mathrm{1}}\mathrm{+}{\mathrm{C}}_{\mathrm{2}}\mathrm{\cdot }\mathrm{W}\right)\mathrm{\cdot }{\mathrm{t}}_{\mathrm{A}}$$

    

    
    and $$\mathrm{L}\left(\mathrm{W},{\mathrm{T}}_{\mathrm{BRK}}\right)\mathrm{=}\left({\mathrm{C}}_{\mathrm{3}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{4}}\right)\mathrm{W}\mathrm{+}{\mathrm{C}}_{\mathrm{5}}{\left({\mathrm{T}}_{\mathrm{BRK}}\right)}^{\mathrm{2}}\mathrm{+}{\mathrm{C}}_{\mathrm{6}}\mathrm{\cdot }{\mathrm{T}}_{\mathrm{BRK}}\mathrm{+}{\mathrm{C}}_{\mathrm{7}}$$

    

    
    where

    C₁ = 8 m/s and

    C₂ = 0.0057 m/kg and

    C₃ = -1.905 · 10^-4 (m · s) / (kg°C) and

    C₄ = 0.286 (s · m) / kg and

    C₅ = 3 · 10^-4 m/(°C)² and

    C₆ = -0.842 m/°C and

    C₇ = 603.41 m,

    the respectively higher value of the length (L) of the combustion chamber (4) applying to a BMCR value (W).

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