Title of Invention	A STEAM GENERATOR WITH A NITROGEN REMOVAL DEVICE FOR FUEL GAS
Abstract	A steam generator (2) has a nitrogen removal device for fuel gas (G) and a combustion chamber (4) 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 steam generator is to have a particularly low space requirement and ensure particularly reliably a removal of nitrogen from the fuel gases (G) of the fossil fuel (B). For this purpose, the combustion chamber has a number of burners (70) arranged level with the horizontal gas flue (6). Moreover, the vertical gas flue (8) is 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) is designed for an approximately vertical flow of the fuel gas (G) from the top downward.

Title of Invention

A STEAM GENERATOR WITH A NITROGEN REMOVAL DEVICE FOR FUEL GAS

Abstract

A steam generator (2) has a nitrogen removal device for fuel gas (G) and a combustion chamber (4) 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 steam generator is to have a particularly low space requirement and ensure particularly reliably a removal of nitrogen from the fuel gases (G) of the fossil fuel (B). For this purpose, the combustion chamber has a number of burners (70) arranged level with the horizontal gas flue (6). Moreover, the vertical gas flue (8) is 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) is designed for an approximately vertical flow of the fuel gas (G) from the top downward.

Full Text	The invention relates to a steam generator with a nitrogen removal device for fuel gas and with a combustion chamber for fossil fuel which is followed on the fuel-gas side, via a horizontal gas flue and a vertical gas flue, by the nitrogen removal device for fuel gas. 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. For the evaporation of the flow medium, the steam generator has evaporator tubes, of which the heating by fuel gas leads to an evaporation of the flow medium carried in them. The steam provided by the steam generator may, in turn, be provided, for example, for a connected external process or else for driving a steam turbine. When the steam drives a steam turbine, a generator or a working machine is normally operated via the turbine shaft of the steam turbine. Where a generator is concerned, the current generated by the generator may be provided for feeding into an interconnected and/or island network. The steam generator may in this case be designed as a continuous- flow steam generator. A continuous-flow steam generator is known from the paper "Verdampferkonzepte fur Benson-Dampferzeuger" ["Evaporator concepts for Benson Steam Generators"] by J. Franke, W. Kohler and E. Wittchow, published in VGB Kraftwerkstechnik 73 (1993), No. 4, p. 352-360. In a continuous-flow 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 form of construction. This means that the combustion chamber is designed for the heating medium or fuel gas to flow through in an approximately vertical direction. In this case, the combustion chamber may be followed, on the fuel-gas side, by a horizontal gas flue, a deflection of the fuel-gas stream into an approximately horizontal flow direction taking place at the transition from the combustion chamber into the horizontal gas flue. In general, however, because of the thermally induced changes in length of the combustion chamber, combustion chambers of this type require a framework on which the combustion chamber is suspended. This necessitates a considerable technical outlay in terms of the production and assembly of the steam generator, this outlay being the higher, the greater the overall height of the steam generator is. A particular problem is the design of the containment wall of the gas flue or combustion chamber of the steam generator with regard to the tube-wall or material temperatures which occur there. In the subcritical pressure range to about 200 bar, the temperature of the containment wall of the combustion chamber is determined essentially by the height of the saturation temperature of the water. This is achieved, for example, using evaporator tubes which have a surface structure on their inside. Consideration is given, in this respect, to, in particular, internally ribbed evaporator tubes, of which the use in a continuous-flow steam generator is known, for example, from the abovementioned paper. These what may be referred to as ribbed tubes, that is to say tubes with a ribbed inner surface, have particularly good heat: transmission from the tube inner wall to the flow medium. To reduce the nitrogen oxides in the fuel gas of the fossil fuel, the method of selective catalytic reduction, what is known as the SCR method, may be used. In the SCR method, nitrogen oxides (NOx) are reduced to nitrogen (N2) and water (H2O) with the aid of a reducing agent, for example ammonia, and a catalyst. In a steam generator designed for an SCR method, a nitrogen removal device for fuel gas, with a catalyst, is conventionally arranged downstream of the fuel-gas duct which is designed as a convection flue and where the fuel gas normally has a temperature of about 320 to 400°C. The catalyst of the nitrogen removal device for fuel gas serves for initiating and/or maintaining a reaction between the reducing agent introduced in the fuel gas and the nitrogen oxides of the fuel gas. The reducing agent required for the SCR method is in this case usually injected, together with air as a carrier stream, into the fuel gas flowing through the gas flue. However, as a rule, the nitrogen oxide emission of the steam generator depends on the type of fossil fuel burnt. In order to adhere to the legally prescribed limit values, therefore, the reducing agent quantity to be injected is normally varied as a function of the fossil fuel used. However, a nitrogen removal device for fuel gas, arranged downstream of the convection flue on the outlet side, requires a considerable outlay in structural and production terms for the respective steam generator. This is because the nitrogen removal device has to be arranged in the steam generator in a place where it can exert a particularly high purifying effect on the fuel gas in all the operating states of the steam generator. This is normally the case where the fuel gas has a temperature in the range of about 320 to 400oC. Moreover, the outlay in terms of the production of a steam generator increases when the latter has, as well as conventional components, a nitrogen removal device in addition. The object on which the invention is based is, therefore, to specify a fossil-fired steam generator of the abovementioned type, which requires particularly low outlay in structural and production terms and in which a purification of the fuel gas of the fossil fuel is ensured particularly reliably, before these leave the steam generator on the outlet side. This object is achieved, according to the invention, in that the combustion chamber of the steam generator comprises a number of burners arranged level with the horizontal gas flue, the vertical gas flue being designed for an approximately vertical flow of the flue gas from the bottom upward and the nitrogen removal device for fuel gas being designed for an approximately vertical flow of the fuel gas from the top downward. The invention proceeds from the notion that a steam generator capable of being erected at a particularly low outlay in production and assembly terms should have a suspension structure capable of being produced by simple means. A framework, to be erected at a comparatively low technical outlay, for the suspension of the combustion chamber may at the same time be accompanied by a particularly low overall height of the steam generator. A particularly low overall height of the steam generator can be achieved by the combustion chamber being designed in a horizontal form of construction. For this purpose, the burners are arranged, level with the horizontal gas flue, in the combustion chamber wall. Thus, when the steam generator is in operation, the flue gas flows through the combustion chamber in an approximately horizontal direction. For a particularly reliable purification of the fuel gas of the fossil fuel, the nitrogen removal device for fuel gas should be arranged downstream of the vertical gas flue on the outlet side. To be precise, downstream of the vertical gas flue on the outlet side, the fuel gas has temperatures at which a purification of the fuel gas takes place particularly effectively at a low technical outlay. It must be remembered, in this case, that, for a particularly low overall height of the steam generator, the nitrogen removal device for fuel gas should be designed for an approximately vertical flow of the fuel gas from the top downward. It is thereby possible for the liquid necessary in the SCR method, together with ammonia fractions, to be injected in the main flow direction of the fuel gas, with the result that the nitrogen removal device has a particularly small vertical extent. However, in a steam generator with a combustion chamber, through which fuel gas can flow in an approximately horizontal main flow direction, the fuel gases, after leaving the horizontal gas flue, flow downward in the vertical gas flue. In order to cause the fuel gas to flow approximately vertically from the top downward in the nitrogen removal device for fuel gas, it is therefore necessary to have a duct for the fuel gas, in which the fuel gas is guided from the bottom upward downstream of the vertical gas flue on the outlet side, in order then to enter the nitrogen removal device for fuel gas, through which said fuel gas is capable of flowing from the top downward. This additional duct is not necessary when the vertical gas flue is designed for an approximately vertical flow of the fuel gas from the bottom upward and the nitrogen removal device provided for the fuel gas is designed for an approximately vertical flow of the fuel gas from the top downward. Advantageously, the purified flue gas leaving the nitrogen removal device for fuel gas can be used for the heating of air in an air preheater. The air preheater should in this case be arranged directly below the nitrogen removal device for fuel gas in a particularly space-saving way. The preheated air is to be supplied to the burners of the steam generator for the combustion of the fossil fuel. When hot air, in contrast to cold air, is supplied to the burners during the combustion of the fossil fuel, the overall efficiency of the steam generator rises. The nitrogen removal device for fuel gas advantageously comprises a DeNOx catalyst. This is because a reduction in the nitrogen oxides of the fuel gas leaving the steam generator can then be carried out in a particularly simple way, for example by means of the method of selective catalytic reduction. The containment walls of the combustion chamber are advantageously formed from vertically arranged evaporator tubes 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. Advantageously, one containment wall of the combustion chamber is the end wall and two containment walls of the combustion chamber are the side walls, the side walls in each case being subdivided into a first group and a second group of evaporator tubes, the end wall and the first group of evaporator tubes being capable of being acted upon in parallel by flow medium and, on the flow- medium side, preceding the second group of evaporator tubes capable of being acted upon in parallel by flow medium. A particularly favorable cooling of the end wall is thereby ensured. Advantageously, the evaporator tubes capable in each case of being acted upon in parallel by flow medium are, on the flow-medium side, preceded by a common inlet header system and followed by a common outlet header system. A steam generator designed in this configuration allows reliable pressure compensation between the parallel-connected evaporator tubes and therefore a particularly favorable distribution of the flow medium during the flow through the evaporator tubes. In a further advantageous refinement, the tube inside 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- The evaporator tubes in the combustion chamber can thereby be adapted to a heating profile predeterminable on the gas side. By the influence brought about thereby on the flow through the evaporator tubes, temperature differences at the outlet of the evaporator tubes of the combustion chamber are kept low in a particularly reliable way. For a particularly good transmission of the heat of the combustion chamber to the flow medium guided in the evaporator tubes, a number of the evaporator tubes advantageously have on their inside in each case ribs forming a multiflight thread. In this case, advantageously, a pitch angle a between a plane perpendicular to the tube axis and the flanks of the ribs arranged on the tube inside is smaller than 60°, preferably smaller than 55°. To be precise, in a heated evaporator tube designed as an evaporator tube without internal ribbing, what may be referred to as a smooth tube, the wetting of the tube wall, necessary for a particularly good heat transmission, can no longer be maintained beyond a specific steam content. In the absence of wetting, there may be a tube wall which is dry at particular points. The transition to a dry tube wall of this type leads to a kind of heat transmission crisis with an impaired heat transmission behavior, so that, in general, the tube-wall temperatures at this point rise particularly sharply. In an internally ribbed tube, however, as compared with a smooth tube, this heat transmission crisis occurs only in the case of a steam mass content > 0.9, that is to say just before the end of evaporation. This is attributable to the swirl which the flow experiences due to the spiral ribs. By virtue of the differing centrifugal force, the water fraction is separated from the steam fraction and is pressed onto the tube wall. The wetting of the tube wall is thereby maintained up to high steam contents, so that high flow velocities prevail even at the location of the heat transmission crisis. This gives rise, despite the heat transmission crisis, to a good heat transmission and, consequently, to low tube-wall temperatures. A number of the evaporator tubes of the combustion chamber advantageously have means for reducing the throughflow of the flow medium. In this case, it proves to be particularly beneficial if the means are designed as throttle devices. Throttle devices may, for example, be fittings which are built into the evaporator tubes and which reduce the tube inside diameter at a point within the respective evaporator tube. In this case, it also proves advantageous to have means for reducing the throughflow in a line system which comprises a plurality of parallel lines and through which flow medium can be supplied to the evaporator tubes of the combustion chamber. At the same time, the line system may also precede an inlet header system of parallel evaporator tubes capable of being acted upon by flow medium. In this case, for example, throttle fittings may be provided in one line or in a plurality of lines of the line system. By such means for reducing the throughflow of the flow medium through the evaporator tubes, the throughput of the flow medium through individual evaporator tubes can be adapted to the respective heating of these in the combustion chamber. As a result, in addition, temperature differences of the flow medium at the outlet of the evaporator tubes can be kept particularly low in a particularly reliable way. The side walls of the horizontal gas flue and/or of the vertical gas flue are advantageously formed from vertically arranged steam generator tubes 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. Adjacent evaporator or steam generator tubes are advantageously welded to one another in a gastight manner via metal bands, what may be referred to as fins. The fin width influences the introduction of heat into the steam generator tubes. The fin width is therefore adapted, preferably as a function of the position of the respective evaporator or steam generator tubes in the steam generator, to a heating and/or temperature profile predeterminable on the gas side. In this case, the predetermined heating and/or temperature profile may be a typical heating and/or temperature profile determined from empirical values or else a rough estimation, such as, for example, a stepped heating and/or temperature profile. By means of the suitably selected fin widths, it is possible, even in the case of widely varying heating of different evaporator or steam generator tubes, to achieve an introduction of heat into all the evaporator or steam generator tubes, in such a way that temperature differences at the outlet of the evaporator or steam generator tubes are kept particularly low. Premature material fatigues are reliably prevented in this way. The steam generator consequently has a particularly long useful life. The horizontal gas flue advantageously has arranged in it a number of superheater heating surfaces, the tubes of which are arranged approximately transversely to the main flow direction of the fuel gas and are connected in parallel for a throughflow of the flow medium. These superheater heating surfaces, arranged in a suspended form of a construction and also designated as bulkhead heating surfaces, are heated predominantly convectively and follow the evaporator tubes of the combustion chamber on the flow-medium side. A particularly beneficial utilization of the fuel-gas heat is thereby ensured. Advantageously, the vertical gas flue has a number of convection heating surfaces which are formed from tubes arranged approximately transversely to the main flow direction of the fuel gas. The tubes of a convection heating surface are in this case connected in parallel for a throughflow of the flow medium. These convection heating surfaces, too, are heated predominantly convectively. In order, furthermore, to ensure a particularly full utilization of the heat of the fuel gas, the vertical gas flue advantageously has economizer. Advantageously, the burners are arranged on the end wall of the combustion chamber, that is to say on that containment wall of the combustion chamber which is located opposite the outflow orifice to the horizontal gas flue. A steam generator designed in this way can be adapted particularly simply to the burnup length of the fuel. The burnup length of the fossil fuel is understood as meaning, in this context, the fuel- gas velocity in the horizontal direction at a specific mean fuel- gas temperature, multiplied by the burnup time tA of the fossil fuel. The maximum burnup length for the respective steam generator is obtained in this case at the steam power output of the steam generator under full load, what may be referred to as full-load operation of the steam generator. The burnup time tA, in turn, is the time which, for example, a coal dust grain requires in order to burn up completely at a specific mean fuel-gas temperature. In order to keep material damage and undesirable contamination of the horizontal gas flue, for example due to the introduction of molten ash at high temperature, particularly low, the length L of the combustion chamber, defined by the distance between the end wall and the inlet region of the horizontal gas flue, is advantageously at least equal to the burnup length of the fuel during 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 top edge to the combustion chamber ceiling. In an advantageous refinement, for the particularly favorable utilization of the combustion heat of the fossil fuel, the length L (given in m) of the combustion chamber is selected as a function of the BMCR value W (given in kg/s) of the steam generator, the burnup time tA (given in s) of the fuel and the outlet temperature Tbrk (given in °C) of the fuel gas from the combustion chamber. BMCR stands for boiler maximum continuous rating and gives the term conventionally used internationally for the maximum continuous power output of a steam generator. This also corresponds to the design power output, that is to say the power output during full-load operation of the steam generator. In this case, with a given BMCR value W of the steam generator, approximately the higher value of the two functions (I) and (II) applies to the length L of the combustion chamber: "Approximately" is understood to mean in this case a permissible deviation of +20%/-10% from the value defined by the respective function. The advantages achieved by means of the invention are, in particular, that the steam generator has a particularly low space requirement on account of the horizontal combustion chamber and of the vertical gas flue designed for an approximately vertical flow direction of the fuel gas from the bottom upward. This particularly compact form of construction of the steam generator makes it possible, when the steam generator is incorporated into a steam turbine plant, to have particularly short connecting tubes from the steam generator to the steam turbine. An exemplary embodiment of the invention is explained in more detail by means of drawing in which: fig. 1 shows diagrammatically a side view of a fossil-fired steam generator of the dual-flue type, and fig. 2 shows diagrammatically a longitudinal section through an individual evaporator tube, and fig. 3 shows a coordinate system with the curves K1 to K6. Parts corresponding to one another are given the same reference symbols in all the figures. The steam generator 2 according to figure 1 is assigned to a power plant, not illustrated in any more detail, which also comprises a steam turbine plant. The steam generated in the steam generator 2 is in this case used for driving the steam turbine which itself, in turn, drives a generator for current generation. The current generated by the generator is in this case provided for feeding into an interconnected or an island network. Furthermore, a branch-off of a part quantity of the steam may also be provided for feeding into an external process which is connected to the steam turbine plant and which may also be a heating process. The fossil-fired steam generator 2 is advantageously designed as a continuous-flow steam generator. It comprises a combustion chamber 4 which is designed in a horizontal form of construction and which is followed on the fuel-gas side, via a horizontal gas flue 6, by a vertical gas flue 8. The lower region of the combustion chamber 4 is formed by a funnel 5 with a top edge corresponding to the subsidiary line having the end points X and Y. By means of the funnel 5, when the steam generator 2 is in operation, ash from the fossil flue B can be discharged into an ash removal device 7 arranged below said funnel. 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 this case, one containment wall 9 is the end wall 9A and two containment walls 9 are the side walls 9B of the combustion chamber 4 of the steam generator 2. Only one of the two side walls 9B can be seen in the side view, shown in figure 1, of the steam generator 2. The evaporator tubes 10 of the side walls 9B of the combustion chamber 4 are subdivided 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 capable of being acted upon in parallel by flow medium S. The second group 11B of the evaporator tubes 10 is also capable of being acted upon in parallel by flow medium S. In order to achieve a particularly favorable throughflow characteristic of the flow medium S through the containment walls 9 of the combustion chamber 4 and, consequently, a particularly good utilization of the combustion heat of the fossil fuel B, the evaporator tubes 10 of the end wall 9A and of the first group HA precede the evaporator tubes 10 of the second group 11B on the flow-medium side. The side walls 12 of the horizontal gas flue 6 and/or the side walls 14 of the vertical gas flue 8 are also formed from vertically arranged steam generator tubes 16 and 17 welded to one another in a gastight manner. At the same time, a number of the steam generator tubes 16, 17 can in this case be acted upon in parallel by flow medium S. The end face 9A and the first group 11A of the evaporator tubes 10 of the combustion chamber 4 are, on the flow-medium side, preceded by a common inlet header system 18A for flow medium S and followed by an outlet header system 20A. Likewise, the second group 11B of the side walls 9B of the evaporator tubes 10 are, on the flow- medium side, preceded by a common inlet header system 18B for the flow medium S and followed by an outlet header system 20B. The inlet header systems 18A and 18B at the same time in each case comprise a number of parallel inlet headers. A line system 19A is provided for feeding flow medium S into the inlet header system 18A of the end face 9A of the combustion chamber 4 and of the first group 11A of the evaporator tubes 10 of the side walls 9B of the combustion chamber 4. The line system 19A comprises a plurality of parallel-connected lines which are connected in each case to one of the inlet headers of the inlet header system 18A. The outlet header system 20A is connected on the outlet side to a line system 19B which is provided for feeding flow medium S into the inlet headers 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. In the same way, the steam generator tubes 16, capable of being acted upon in parallel by the flow medium S, of the side walls 12 of the horizontal gas flue 6 are preceded by a common inlet header system 21 and followed by a common outlet header system 22. In this case, a line system 25 is provided for feeding flow medium S into the inlet header system 21 of the steam generator tubes 16. Here, too, the line system 25 comprises a plurality of parallel- connected lines which are connected in each case to one of the inlet headers of the inlet header system 21. The line system 25 is connected on the inlet side 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 therefore guided into the side walls 12 of the horizontal gas flue 6. This configuration of the continuous-flow steam generator 2, with inlet header systems 18A, 18B and 21 and outlet header systems 20A, 20B and 22, makes it possible to have particularly reliable pressure compensation between the parallel-connected evaporator tubes 10 of the combustion chamber 4 or the parallel-connected steam generator tubes 16 of the horizontal gas flue 6, in that, in each case, all the parallel-connected evaporator or steam generator tubes 10 and 16 have the same overall pressure loss. This means that, in the case of an evaporator tube 10 or steam generator tube 16 heated to a greater extent, the throughput must rise, as compared with an evaporator tube 10 or a steam generator tube 16 heated to a lesser extent. As illustrated in figure 2, the evaporator tubes 10 have, on their inside, ribs 40 which form a type of multiflight thread and have a rib height R. In this case, the pitch angle a 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 55°. As a result, particularly high heat transmission from the inner wall of the evaporator tubes to the flow medium S guided in the evaporator tubes 10, at the same time with particularly low temperatures of the tube wall, is achieved. The tube inside 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. The steam generator 2 is thereby adapted to the different amounts of heating of the evaporator tubes 10. This design of the evaporator tubes 10 of the combustion chamber 4 ensures particularly reliably 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 welded to one another in a gastight manner via fins in a way not illustrated in any more detail. To be precise, the heating of the evaporator or steam generator tubes 10, 16, 17 can be influenced by suitable choice of the fin width. The respective fin width is therefore adapted to a heating profile which is predeterminable on the gas side and which depends on the position of the respective evaporator or steam generator tubes 10, 16, 17 in the steam generator. The heating profile may in this case be a typical heating profile determined from empirical values or else a rough estimation. As a result, even in the case of widely differing heating of the evaporator or steam generator tubes 10, 16, 17, temperature differences at the outlet of the evaporator or steam generator tubes 10, 16, 17 are kept particularly low. Material fatigues are thereby reliably prevented, thus ensuring that the steam generator 2 has a long useful life. As means for reducing the throughflow of the flow medium S, some of the evaporator tubes 10 are equipped with throttle devices which are not illustrated in any more detail in the drawing. The throttle devices are designed as perforated diaphragms reducing the tube inside diameter D and, when the steam generator 2 is in operation, bring about a reduction in the throughput of the flow medium S in evaporator tubes 10 heated to a lesser extent, with the result that the throughput of the flow medium S is adapted to the heating. Furthermore, as a means for reducing the throughput of the flow medium S in the evaporator tubes 10 of the combustion chamber 4, one or more lines of the line system 19 or 25 are equipped with throttle devices, in particular throttle fittings, this not being illustrated in any more detail in the drawing. In the tubing of the combustion chamber 4, it must be remembered that the heating of the individual evaporator tubes 10 welded to one another in a gastight manner differs greatly when the steam generator 2 is in operation. Consequently, the design of the evaporator tubes 10 in terms of their internal ribbing, fin connection to adjacent evaporator tubes 10 and their tube inside diameter D is selected such that, in spite of different heating, all the evaporator tubes 10 have approximately the same outlet temperatures of the flow medium S and sufficient cooling of all the evaporator tubes 10 is ensured for all the operating states of the steam generator 2. 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. What is achieved, moreover, by a suitable choice of the fin connections and of the tube inside diameters D is that the fraction of frictional pressure loss in the overall pressure loss is so small that a natural circulation behavior is established: evaporator tubes 10 heated to a greater extent have a higher throughflow than evaporator tubes 10 heated to a lesser extent. What is also achieved thereby is that the evaporator tubes 10 heated to a comparatively greater extent and located in the burner vicinity absorb specifically, with respect to the mass flow, approximately as much heat as the evaporator tubes 10 heated to a comparatively lesser extent, which, in comparison with them, are arranged nearer to the combustion chamber end. A further measure for adapting the throughflow of the evaporator tubes 10 of the combustion chamber 4 to the heating is for throttles to be built into some of the evaporator tubes 10 or into some of the lines of the line system 19. The internal ribbing is in this case designed in such a way that sufficient cooling of the evaporator tube walls is ensured. Thus, by means of the abovementioned measures, all the evaporator tubes 10 have approximately the same outlet temperatures of the flow medium S. The horizontal gas flue 6 has a number of superheater heating surfaces 23 which are designed as bulkhead heating surfaces and are arranged in a suspended form of construction approximately perpendicularly to the main flow direction 24 of the fuel gas G and the tubes of which are in each case connected in parallel for a throughflow of the flow medium S. The superheater heating surfaces 23 are heated predominantly convectively and follow the evaporator tubes 10 of the combustion chamber 4 on the flow-medium side. The vertical gas flue 8 through which fuel gas G is capable of flowing from the bottom upward has a number of convection heating surfaces 26 which are capable of being heated predominantly convectively and are formed from tubes arranged approximately perpendicularly to the main flow direction 24 of the fuel gas G. These tubes are in each case connected in parallel for a throughflow of the flow medium S and are integrated into the path of the flow medium S, this not being illustrated in any more detail in the drawing. Moreover, an economizer 28 is arranged in the vertical gas flue 8 above the convection heating surfaces 26. The economizer 28 is connected on the outlet side, via a line system 19, to the inlet header system 18 assigned to the evaporator tubes 10. In this case, one or more lines of the line system 24, which are not illustrated in any more detail in the drawing, may have throttle fittings in order to reduce the throughflow of the flow medium s. The vertical gas flue 8, through which fuel gas G is capable of flowing from the bottom upward in an approximately vertical main flow direction 24, is followed, on the outlet side, by a short connecting duct 50. The connecting duct 50 connects the vertical gas flue 8 to a housing 52. A nitrogen removal device 54 for fuel gas G is arranged on the inlet side in the housing 52. The nitrogen removal device 54 for fuel gas G is connected to an air preheater 60 via a feed 56. The air preheater 60, in turn, is connected to an electronic filter 62 via a smoke-gas duct 62. The nitrogen removal device 54 for fuel gas G is operated according to the method of selective catalytic reduction, what may be referred to as the SCR method. During the catalytic purification of the fuel gas G of the steam generator 2 according to the SCR method, nitrogen oxides (NO2) are reduced to nitrogen (N2) and water (H2O) with the aid of a catalyst and a reducing agent, for example ammonia. To carry out the SCR method, the nitrogen removal device 54 for fuel gas G comprises a catalyst designed as a DeNOx catalyst 64. The DeNOx catalyst is arranged in the flow region of the fuel gas G. To introduce ammonia water as reducing agent M into the fuel gas G, the nitrogen removal device 54 for fuel gas G has a metering system 66. In this case, the metering system 66 comprises a storage vessel 68 for ammonia water and a compressed-air system 69. The metering system 66 is arranged above the DeNOx catalyst 64 in the nitrogen removal device 54. A steam generator 2 is designed with a horizontal combustion chamber 4 having a particularly low overall height and can thus be erected at a particularly low outlay in production and assembly terms. For this purpose, the combustion chamber 4 of the steam generator 2 has a number of burners 70 for fossil fuel B, which are arranged, level with the horizontal gas flue 6, on the end wall 11 of the combustion chamber 4. So that the fossil fuel B, for example coal in solid form, burns up particularly completely in order to achieve particularly high efficiency and material damage to the first superheater heating surface 23, as seen on the fuel-gas side,, of the horizontal gas flue 6 and contamination of this, for example due to the introduction of molten ash at high temperature, are prevented in a particularly reliable way, the length L of the combustion chamber 4 is selected such that it exceeds the burnup length of the fuel B during full-load operation of the steam generator 2. The length L is in this case the distance from the end wall 9A of the combustion chamber 4 to the inlet region 72 of the horizontal gas flue 6. The burnup length of the fuel B is in this case defined as the fuel-gas velocity in the horizontal direction at a specific mean fuel-gas temperature, multiplied by the burnup time tA of the fossil fuel B. The maximum burnup length for the respective steam generator 2 is obtained during full-load operation of the steam generator 2. The burnup time tA of the fuel B is, in turn, the time which, for example, a coal dust grain of average size requires to burn up completely at a specific mean fuel-gas temperature. In order to ensure particularly favorable utilization of the combustion heat of the fossil fuel B, the length L (given in m) of the combustion chamber 4 is suitably selected as a function of the outlet temperature of the fuel gas G from the combustion chamber 4 TARK (given in °C), of the burnup time tR (given in s) of the fuel B and of the BMCR value W (given in kg/s) of the steam generator 2. In this context, BMCR stands for boiler maximum continuous rating. The BMCR value W is a term conventionally used internationally for the maximum continuous power output of a steam generator. This also corresponds to the design power output, that is to say to the power output during full-load operation of the steam generator. This horizontal length L of the combustion chamber 4 is in this case greater than the height H of the combustion chamber 4. The height H is in this case measured from the funnel top edge of the combustion chamber 4, marked in figure 1 by the subsidiary line having the end points X and Y, to the combustion chamber ceiling. In this case, the length L of the combustion chamber 4 is determined approximately via the two functions (I) and (II) "Approximately" in this case is understood to mean a permissible deviation of +20%/-10% from the value defined by the respective function. At the same time, in the case of an arbitrary, but fixed BMCR value W of the steam generator, the higher value of the functions (1) and (II) always applies to the length L of the combustion chamber 4. As an example of a calculation of the length L of the combustion chamber 4 as a function of the BMCR value W of the steam generator 2, six curves Ki to K^ are depicted in the coordinate system according to figure 3. Here, the curves are in each case assigned the following parameters: Thus, for example for a burnup time tR = 3s and an outlet temperature TBRK = 1200°C of the fuel gas G from the combustion chamber 4, the curves K1 and K4 are to be used to determine the length L of the combustion chamber 4. This results, in the case of a predetermined BMCR value W of the steam generator 2 of W = 80 kg/s, in a length of L = 29 m according to K4, of W = 160 kg/s, in a length of L = 34 m according to K4, of W = 560 kg/s, in a length of L = 57 m according to K4. For example, the curves K2 and K5 are to be used for the burnup time TA = 2.5s and the outlet temperature of the fuel gas G from the combustion chamber TBRK = 1300°C. This results, in the case of a predetermined BMCR value W of the steam generator 2 of W = 80 kg/s, in a length of 1 = 21 m according to K2, of W = 180 kg/s, in a length of L = 23 m according to K2 and K5, of W = 560 kg/s, in a length of L = 37 m according to K5. The burnup time tA = 2s and the outlet temperature of the fuel gas G from the combustion chamber Tbrk = 1400°C are assigned, for example, to the curves K5 and K6. This results, in the case of a predetermined BMCR value W of the steam generator 2 of W = 80 kg/s, in a length of L = 18 m according to K3, of W = 465 kg/s, in a length of 1 = 21 m according to K3 and K6, of W = 560 kg/s, in a length of L = 23 m according to K6. When the steam generator 2 is in operation, fossil fuel B and air are supplied to the burners 70. The air is in this case preheated in the air preheater by means of the residual heat of the fuel gas G and then, this not being illustrated in any more detail in the drawing, is compressed and supplied to the burner 70. The flames F of the burners 70 are in this case oriented horizontally. By virtue of the form of construction of the combustion chamber 4, a flow of the fuel gas G occurring during combustion is generated in the approximately horizontal main flow direction 24. The fuel gas G passes, via the horizontal gas flue 6, into the vertical gas flue 8 through which fuel gas 6 is capable of flowing from the bottom upward. Downstream of the vertical gas flue 8 on the outlet side, the fuel gas G passes, via the connecting duct 50, into the nitrogen removal device 54 for fuel gas G. Via the nitrogen removal device 54 for fuel gas G, a specific quantity of ammonia water is injected as reducing agent M into the fuel gas G with the aid of compressed air as a function of the type of fuel B operating the steam generator 2. This is necessary, since the degree of separation of the nitrogen oxides (NO5) depends on the type of fossil fuel B operating the steam generator 2. A particularly reliable removal of nitrogen from the fuel gas G is thereby ensured in all the operating states of the steam generator 2. The purified fuel gas G1 leaves the nitrogen removal device 54 for fuel gas G via a feed 56 which issues into the air preheater 58. A preheating of the air to be supplied to the burners 70 for the combustion of the fossil fuel B takes place ±n the air preheater 58. The fuel gas G leaves the air preheater 58 via the smoke-gas duct 60 and passes via 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 to 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 steam or a water/steam mixture occurring in the vertically arranged evaporator tubes 10 of the combustion chamber 4 of the steam generator 2 which are welded to one another in a gastight manner is collected in the outlet header system 20A for flow medium S. The steam or the water/steam mixture passes from there, via the line system 19B, into the inlet header system 18B which is assigned to the second group 11B of the evaporator tubes 10 of the side walls 9B of the combustion chamber 4. The steam or a water/steam mixture occurring in the vertically arranged evaporator tubes 10 of the combustion chamber 4 of the steam generator 2 which are welded to one another in a gastight manner is collected in the outlet header system 20B for flow medium S. The steam and/or the water/steam mixture passes from there, via the line system 25, into the inlet header system 21 assigned to the steam generator tubes 16 of the side walls 12 of the horizontal gas flue. The steam and/or the water/steam mixture occurring in the evaporator tubes 16 passes via the outlet header 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 gas flue 6. In the superheater heating surfaces 23, further superheating of the steam takes place, the latter subsequently being supplied for utilization, for example for driving a steam turbine. In the steam generator 2, the selection of the length L of the combustion chamber 4 as a function of the BMCR value W of the steam generator 2 ensures that the combustion heat, of the fossil fuel B is utilized particularly reliably. Moreover, the steam generator 2 requires a particularly small amount of space on account of its horizontal combustion chamber 4 and its nitrogen removal device 54 located directly downstream of the vertical gas flue 8. At the same time, a particularly reliable removal of nitrogen from the fuel gas G is ensured in a particularly simple way in all the operating states of the steam generator 2. We claims 1. A steam generator (2) with s nitrogen removal device (54) for fuel gas (G) having a combustion chamber (4) for fossil fuel (B) , which is followed on a fuel-gas side, via a horizontal gas flue (6) and a vertical gas flue (8), by a nitrogen removal device (54) for fuel gas (6), the combustion chamber comprising: a number of burners (70) arranged level with the horizontal gas flue (6), and wherein the vertical gas flue (8) is designed for substantially vertical flow of the fuel gas from a bottom thereof upward, and the nitrogen removal device (54) for the fuel gas (G) is designed for substantially vertical flow of the fuel gas (G) from a top thereof downward. 2. The steam generator (2) as claimed in 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. The steam generator (2) as claimed in claim 1 or 2, in which the nitrogen removal device (54) for fuel gas (G) comprises a DeNO. 4. The steam generator (2) as claimed in any 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 (8) 5. The steam generator (2) as claimed in any one of claims 1 to 4, in which jone 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 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 (5). 6. The steam generator (2) as claimed in 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 (5) 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. The steam generator (2) as claimed in lone 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. The steam generator (2) as claimed in 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. The steam generator (2) as claimed in claim 8, in which a pitch angle (a) 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 55o. 10. The steam generator (2) as claimed intone of claims 1 to 8, in which a number of the evaporator tubes (10) in each case have a throttle device. The steam generator (2) as claimed inlone 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). The steam generator (2) as claimed in/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). The steam generator (2) as claimed in/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). The steam generator (2) as claimed intone 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). The steam generator (2) as claimed in 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). The steam generator (2) as claimed in one of claims 1 to 15, in which a number of convection heating surfaces (52) are arranged in the vertical gas flue (8). The steam generator (2) as claimed in one of claims 1 to 16, in which an economizer (28) is arranged in the vertical gas flue (8). 18. The steam generator (2) as claimed in one of claims 1 to 17, in which the burners (70) are arranged on the end wall (9A) of the combustion chamber (4). 19. The steam generator (2) as claimed in 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. The steam generator (2) as claimed in 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 (tA) of the burners (70) and/or of the outlet temperature (Tbrk) of the fuel gas (G) from the combustion chamber (4), approximately according to the two functions (I) and (II) the respectively higher value of the length (L) of the combustion chamber (4) applying to a BMCR value (W). A steam generator (2) has a nitrogen removal device for fuel gas (G) and a combustion chamber (4) 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 steam generator is to have a particularly low space requirement and ensure particularly reliably a removal of nitrogen from the fuel gases (G) of the fossil fuel (B). For this purpose, the combustion chamber has a number of burners (70) arranged level with the horizontal gas flue (6). Moreover, the vertical gas flue (8) is 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) is designed for an approximately vertical flow of the fuel gas (G) from the top downward.

Full Text

The invention relates to a steam generator with a nitrogen removal
device for fuel gas and with a combustion chamber for fossil fuel
which is followed on the fuel-gas side, via a horizontal gas flue
and a vertical gas flue, by the nitrogen removal device for fuel
gas.
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. For the evaporation of
the flow medium, the steam generator has evaporator tubes, of
which the heating by fuel gas leads to an evaporation of the flow
medium carried in them. The steam provided by the steam generator
may, in turn, be provided, for example, for a connected external
process or else for driving a steam turbine. When the steam drives
a steam turbine, a generator or a working machine is normally
operated via the turbine shaft of the steam turbine. Where a
generator is concerned, the current generated by the generator may
be provided for feeding into an interconnected and/or island
network.
The steam generator may in this case be designed as a continuous-
flow steam generator. A continuous-flow steam generator is known
from the paper "Verdampferkonzepte fur Benson-Dampferzeuger"
["Evaporator concepts for Benson Steam Generators"] by J. Franke,
W. Kohler and E. Wittchow, published in VGB Kraftwerkstechnik 73
(1993), No. 4, p. 352-360. In a continuous-flow 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 form of construction. This means that the combustion
chamber is designed for the heating medium or fuel gas to flow
through in an approximately vertical direction. In this case, the
combustion chamber may be followed, on the fuel-gas side, by a
horizontal gas flue, a deflection of the fuel-gas stream into an
approximately horizontal flow direction taking place at the
transition from the combustion chamber into the horizontal gas
flue. In general, however, because of the thermally induced
changes in length of the combustion chamber, combustion chambers
of this type require a framework on which the combustion chamber
is suspended. This necessitates a considerable technical outlay in
terms of the production and assembly of the steam generator, this
outlay being the higher, the greater the overall height of the
steam generator is.
A particular problem is the design of the containment wall of the
gas flue or combustion chamber of the steam generator with regard
to the tube-wall or material temperatures which occur there. In
the subcritical pressure range to about 200 bar, the temperature
of the containment wall of the combustion chamber is determined
essentially by the height of the saturation temperature of the
water. This is achieved, for example, using evaporator tubes which
have a surface structure on their inside. Consideration is given,
in this respect, to, in particular, internally ribbed evaporator
tubes, of which the use in a continuous-flow steam generator is
known, for example, from the abovementioned paper. These what may
be referred to as ribbed tubes, that is to say tubes with a ribbed
inner surface, have particularly good heat: transmission from the
tube inner wall to the flow medium.
To reduce the nitrogen oxides in the fuel gas of the
fossil fuel, the method of selective catalytic reduction, what is
known as the SCR method, may be used. In the SCR method, nitrogen
oxides (NOx) are reduced to nitrogen (N2) and water (H2O) with the
aid of a reducing agent, for example ammonia, and a catalyst.
In a steam generator designed for an SCR method, a nitrogen
removal device for fuel gas, with a catalyst, is conventionally
arranged downstream of the fuel-gas duct which is designed as a
convection flue and where the fuel gas normally has a temperature
of about 320 to 400°C. The catalyst of the nitrogen removal device
for fuel gas serves for initiating and/or maintaining a reaction
between the reducing agent introduced in the fuel gas and the
nitrogen oxides of the fuel gas. The reducing agent required for
the SCR method is in this case usually injected, together with air
as a carrier stream, into the fuel gas flowing through the gas
flue. However, as a rule, the nitrogen oxide emission of the steam
generator depends on the type of fossil fuel burnt. In order to
adhere to the legally prescribed limit values, therefore, the
reducing agent quantity to be injected is normally varied as a
function of the fossil fuel used.
However, a nitrogen removal device for fuel gas, arranged
downstream of the convection flue on the outlet side, requires a
considerable outlay in structural and production terms for the
respective steam generator. This is because the nitrogen removal
device has to be arranged in the steam generator in a place where
it can exert a particularly high purifying effect on the fuel gas
in all the operating states of the steam generator. This is
normally the case where the fuel gas has a temperature in the
range of about 320 to 400oC. Moreover, the outlay in terms of the
production of a steam generator increases when the latter has, as
well as conventional components, a nitrogen removal device in
addition.
The object on which the invention is based is, therefore, to
specify a fossil-fired steam generator of the abovementioned type,
which requires particularly
low outlay in structural and production terms and in which a
purification of the fuel gas of the fossil fuel is ensured
particularly reliably,
before these leave the steam generator on the outlet side.
This object is achieved, according to the invention, in that the
combustion chamber of the steam generator comprises a number of
burners arranged level with the horizontal gas flue, the vertical
gas flue being designed for an approximately vertical flow of the
flue gas from the bottom upward and the nitrogen removal device
for fuel gas being designed for an approximately vertical flow of
the fuel gas from the top downward.
The invention proceeds from the notion that a steam generator
capable of being erected at a particularly low outlay in
production and assembly terms should have a suspension structure
capable of being produced by simple means. A framework, to be
erected at a comparatively low technical outlay, for the
suspension of the combustion chamber may at the same time be
accompanied by a particularly low overall height of the steam
generator. A particularly low overall height of the steam
generator can be achieved by the combustion chamber being designed
in a horizontal form of construction. For this purpose, the
burners are arranged, level with the horizontal gas flue, in the
combustion chamber wall. Thus, when the steam generator is in
operation, the flue gas flows through the combustion chamber in an
approximately horizontal direction.
For a particularly reliable purification of the fuel gas of the
fossil fuel, the nitrogen removal device for fuel gas should be
arranged downstream of the vertical gas flue on the outlet side.
To be precise, downstream of the vertical gas flue on the outlet
side, the fuel gas has temperatures at which a purification of the
fuel gas takes place particularly effectively at a low technical
outlay. It must be remembered, in this case,
that, for a particularly low overall height of the steam
generator, the nitrogen removal device for fuel gas should be
designed for an approximately vertical flow of the fuel gas from
the top downward. It is thereby possible for the liquid necessary
in the SCR method, together with ammonia fractions, to be injected
in the main flow direction
of the fuel gas, with the result that the nitrogen removal device
has a particularly small vertical extent.
However, in a steam generator with a combustion chamber, through
which fuel gas can flow in an approximately horizontal main flow
direction, the fuel gases, after leaving the horizontal gas flue,
flow downward in the vertical gas flue. In order to cause the fuel
gas to flow approximately vertically from the top downward in the
nitrogen removal device for fuel gas, it is therefore necessary to
have a duct for the fuel gas, in which the fuel gas is guided from
the bottom upward downstream of the vertical gas flue on the
outlet side, in order then to enter the nitrogen removal device
for fuel gas, through which said fuel gas is capable of flowing
from the top downward. This additional duct is not necessary when
the vertical gas flue is designed for an approximately vertical
flow of the fuel gas from the bottom upward and the nitrogen
removal device provided for the fuel gas is designed for an
approximately vertical flow of the fuel gas from the top downward.
Advantageously, the purified flue gas leaving the nitrogen removal
device for fuel gas can be used for the heating of air in an air
preheater. The air preheater should in this case be arranged
directly below the nitrogen removal device for fuel gas in a
particularly space-saving way. The preheated air is to be supplied
to the burners of the steam generator for the combustion of the
fossil fuel. When hot air, in contrast to cold air, is supplied to
the burners during the combustion of the fossil fuel, the overall
efficiency of the steam generator rises.
The nitrogen removal device for fuel gas advantageously comprises
a DeNOx catalyst. This is because a reduction
in the nitrogen oxides of the fuel gas leaving the steam generator
can then be carried out in a particularly simple way, for example
by means of the method of selective catalytic reduction.
The containment walls of the combustion chamber are advantageously
formed from vertically arranged evaporator tubes 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.
Advantageously, one containment wall of the combustion chamber is
the end wall and two containment walls of the combustion chamber
are the side walls, the side walls in each case being subdivided
into a first group and a second group of evaporator tubes, the end
wall and the first group of evaporator tubes being capable of
being acted upon in parallel by flow medium and, on the flow-
medium side, preceding the second group of evaporator tubes
capable of being acted upon in parallel by flow medium. A
particularly favorable cooling of the end wall is thereby ensured.
Advantageously, the evaporator tubes capable in each case of being
acted upon in parallel by flow medium are, on the flow-medium
side, preceded by a common inlet header system and followed by a
common outlet header system. A steam generator designed in this
configuration allows reliable pressure compensation between the
parallel-connected evaporator tubes and therefore a particularly
favorable distribution of the flow medium during the flow through
the evaporator tubes.
In a further advantageous refinement, the tube inside 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- The evaporator tubes
in the combustion chamber can thereby be adapted to a heating
profile predeterminable on the gas side. By the influence brought
about thereby on the flow through the evaporator tubes,
temperature differences at the outlet
of the evaporator tubes of the combustion chamber are kept low in
a particularly reliable way.
For a particularly good transmission of the heat of the combustion
chamber to the flow medium guided in the evaporator tubes, a
number of the evaporator tubes advantageously have on their inside
in each case ribs forming a multiflight thread. In this case,
advantageously, a pitch angle a between a plane perpendicular to
the tube axis and the flanks of the ribs arranged on the tube
inside is smaller than 60°, preferably smaller than 55°.
To be precise, in a heated evaporator tube designed as an
evaporator tube without internal ribbing, what may be referred to
as a smooth tube, the wetting of the tube wall, necessary for a
particularly good heat transmission, can no longer be maintained
beyond a specific steam content. In the absence of wetting, there
may be a tube wall which is dry at particular points. The
transition to a dry tube wall of this type leads to a kind of heat
transmission crisis with an impaired heat transmission behavior,
so that, in general, the tube-wall temperatures at this point rise
particularly sharply. In an internally ribbed tube, however, as
compared with a smooth tube, this heat transmission crisis occurs
only in the case of a steam mass content > 0.9, that is to say
just before the end of evaporation. This is attributable to the
swirl which the flow experiences due to the spiral ribs. By virtue
of the differing centrifugal force, the water fraction is
separated from the steam fraction and is pressed onto the tube
wall. The wetting of the tube wall is thereby maintained up to
high steam contents, so that high flow velocities prevail even at
the location of the heat transmission crisis. This gives rise,
despite the heat transmission crisis, to a good heat transmission
and, consequently, to low tube-wall temperatures.
A number of the evaporator tubes of the combustion
chamber advantageously have means for reducing the throughflow of
the flow medium. In this case, it proves to be particularly
beneficial if the means are designed as throttle devices. Throttle
devices may, for example, be fittings
which are built into the evaporator tubes and which reduce the
tube inside diameter at a point within the respective evaporator
tube.
In this case, it also proves advantageous to have means for
reducing the throughflow in a line system which comprises a
plurality of parallel lines and through which flow medium can be
supplied to the evaporator tubes of the combustion chamber. At the
same time, the line system may also precede an inlet header system
of parallel evaporator tubes capable of being acted upon by flow
medium. In this case, for example, throttle fittings may be
provided in one line or in a plurality of lines of the line
system. By such means for reducing the throughflow of the flow
medium through the evaporator tubes, the throughput of the flow
medium through individual evaporator tubes can be adapted to the
respective heating of these in the combustion chamber. As a
result, in addition, temperature differences of the flow medium at
the outlet of the evaporator tubes can be kept particularly low in
a particularly reliable way.
The side walls of the horizontal gas flue and/or of the vertical
gas flue are advantageously formed from vertically arranged steam
generator tubes 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.
Adjacent evaporator or steam generator tubes are advantageously
welded to one another in a gastight manner via metal bands, what
may be referred to as fins. The fin width influences the
introduction of heat into the steam generator tubes. The fin width
is therefore adapted, preferably as a function of the position of
the respective evaporator or steam
generator tubes in the steam generator, to a heating and/or
temperature profile predeterminable on the gas side. In this case,
the predetermined heating and/or temperature profile may be a
typical heating and/or temperature profile determined from
empirical values or else a rough
estimation, such as, for example, a stepped heating and/or
temperature profile. By means of the suitably selected fin widths,
it is possible, even in the case of widely varying heating of
different evaporator or steam generator tubes, to achieve an
introduction of heat into all the evaporator or steam generator
tubes, in such a way that temperature differences at the outlet of
the evaporator or steam generator tubes are kept particularly low.
Premature material fatigues are reliably prevented in this way.
The steam generator consequently has a particularly long useful
life.
The horizontal gas flue advantageously has arranged in it a number
of superheater heating surfaces, the tubes of which are arranged
approximately transversely to the main flow direction of the fuel
gas and are connected in parallel for a throughflow of the flow
medium. These superheater heating surfaces, arranged in a
suspended form of a construction and also designated as bulkhead
heating surfaces, are heated predominantly convectively and follow
the evaporator tubes of the combustion chamber on the flow-medium
side. A particularly beneficial utilization of the fuel-gas heat
is thereby ensured.
Advantageously, the vertical gas flue has a number of convection
heating surfaces which are formed from tubes arranged
approximately transversely to the main flow direction of the fuel
gas. The tubes of a convection heating surface are in this case
connected in parallel for a throughflow of the flow medium. These
convection heating surfaces, too, are heated predominantly
convectively.
In order, furthermore, to ensure a particularly full utilization
of the heat of the fuel gas, the vertical gas flue advantageously
has economizer.
Advantageously, the burners are arranged on the end wall of the
combustion chamber, that is to say on that containment wall of the
combustion chamber which is located opposite the outflow orifice
to the horizontal gas flue.
A steam generator designed in this way can be adapted particularly
simply to the burnup length of the fuel. The burnup length of the
fossil fuel is understood as meaning, in this context, the fuel-
gas velocity in the horizontal direction at a specific mean fuel-
gas temperature, multiplied by the burnup time tA of the fossil
fuel. The maximum burnup length for the respective steam generator
is obtained in this case at the steam power output of the steam
generator under full load, what may be referred to as full-load
operation of the steam generator. The burnup time tA, in turn, is
the time which, for example, a coal dust grain requires in order
to burn up completely at a specific mean fuel-gas temperature.
In order to keep material damage and undesirable contamination of
the horizontal gas flue, for example due to the introduction of
molten ash at high temperature, particularly low, the length L of
the combustion chamber, defined by the distance between the end
wall and the inlet region of the horizontal gas flue, is
advantageously at least equal to the burnup length of the fuel
during 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 top
edge to the combustion chamber ceiling.
In an advantageous refinement, for the particularly favorable
utilization of the combustion heat of the fossil fuel, the length
L (given in m) of the combustion chamber is selected as a function
of the BMCR value W (given in kg/s) of the steam generator, the
burnup time tA (given in s) of the fuel and the outlet temperature
Tbrk (given in °C) of the fuel gas from the combustion chamber.
BMCR stands for boiler maximum continuous rating and gives the
term conventionally used internationally for the maximum
continuous power output of a steam generator. This also
corresponds to the design power output, that is to say the power
output during full-load operation of the steam generator. In this
case, with a given BMCR value W of the steam generator,
approximately the higher value of the two functions (I) and (II)
applies to the length L of the combustion chamber:
"Approximately" is understood to mean in this case a permissible
deviation of +20%/-10% from the value defined by the respective
function.
The advantages achieved by means of the invention are, in
particular, that the steam generator has a particularly low space
requirement on account of the horizontal combustion chamber and of
the vertical gas flue designed for an approximately vertical flow
direction of the fuel gas from the bottom upward. This
particularly compact form of construction of the steam generator
makes it possible, when the steam generator is incorporated into a
steam turbine plant, to have particularly short connecting tubes
from the steam generator to the steam turbine.
An exemplary embodiment of the invention is explained in more
detail by means of drawing in which:
fig. 1 shows diagrammatically a side view of a fossil-fired
steam generator of the dual-flue type, and
fig. 2 shows diagrammatically a longitudinal section through an
individual evaporator tube, and
fig. 3 shows a coordinate system with the curves K1 to K6.
Parts corresponding to one another are given the same reference
symbols in all the figures.
The steam generator 2 according to figure 1 is assigned to a power
plant, not illustrated in any more detail, which also comprises a
steam turbine plant. The steam generated in the steam generator 2
is in this case used for driving the steam turbine which itself,
in turn, drives a generator for current generation. The current
generated by the generator is in this case provided for feeding
into an interconnected or an island network. Furthermore, a
branch-off of a part quantity of the steam may also be provided
for feeding into an external process which is connected to the
steam turbine plant and which may also be a heating process.
The fossil-fired steam generator 2 is advantageously designed as a
continuous-flow steam generator. It comprises a combustion chamber
4 which is designed in a horizontal form of construction and which
is followed on the fuel-gas side, via a horizontal gas flue 6, by
a vertical gas flue 8. The lower region of the combustion chamber
4 is formed by a funnel 5 with a top edge corresponding to the
subsidiary line having the end points X and Y. By means of the
funnel 5, when the steam generator 2 is in operation, ash from the
fossil flue B can be discharged into an ash removal device 7
arranged below said funnel. 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
this case, one containment wall 9 is the end wall 9A and two
containment walls 9 are the side walls 9B of the combustion
chamber 4 of the steam generator 2. Only one of the two side walls
9B can be seen in the side view, shown in figure 1, of the steam
generator 2. The evaporator tubes 10 of the side walls 9B of the
combustion chamber 4 are subdivided 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 capable of being acted upon in parallel by flow medium S. The
second group 11B of the evaporator tubes 10 is also capable of
being acted upon in parallel by flow medium S. In order to achieve
a particularly favorable throughflow characteristic of the flow
medium S through the containment walls 9 of the combustion chamber
4 and, consequently, a particularly good utilization of the
combustion heat of the fossil fuel B, the evaporator tubes 10 of
the end wall 9A and of the first group HA precede the evaporator
tubes 10 of the second group 11B on the flow-medium side.
The side walls 12 of the horizontal gas flue 6 and/or the side
walls 14 of the vertical gas flue 8 are also formed from
vertically arranged steam generator tubes 16 and 17 welded to one
another in a gastight manner. At the same time, a number of the
steam generator tubes 16, 17 can in this case be acted upon in
parallel by flow medium S.
The end face 9A and the first group 11A of the evaporator tubes 10
of the combustion chamber 4 are, on the flow-medium side, preceded
by a common inlet header system 18A for flow medium S and followed
by an outlet header system 20A. Likewise, the second group 11B of
the side walls 9B of the evaporator tubes 10 are, on the flow-
medium side, preceded by a common inlet header system 18B for the
flow medium S and followed by an outlet header system 20B. The
inlet header systems 18A and 18B at the same time in each case
comprise a number of parallel inlet headers.
A line system 19A is provided for feeding flow medium S into the
inlet header system 18A of the end face 9A of the combustion
chamber 4 and of the first group 11A of the evaporator tubes 10 of
the side walls 9B of the combustion chamber 4. The line system 19A
comprises a plurality of parallel-connected lines which are
connected in each case to one of the inlet headers of the inlet
header system 18A. The outlet header system 20A is connected on
the outlet side to a line system 19B which is provided for feeding
flow medium S into the
inlet headers 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.
In the same way, the steam generator tubes 16, capable of being
acted upon in parallel by the flow medium S, of the side walls 12
of the horizontal gas flue 6 are preceded by a common inlet header
system 21 and followed by a common outlet header system 22. In
this case, a line system 25 is provided for feeding flow medium S
into the inlet header system 21 of the steam generator tubes 16.
Here, too, the line system 25 comprises a plurality of parallel-
connected lines which are connected in each case to one of the
inlet headers of the inlet header system 21. The line system 25 is
connected on the inlet side 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 therefore guided into the side walls 12 of
the horizontal gas flue 6.
This configuration of the continuous-flow steam generator 2, with
inlet header systems 18A, 18B and 21 and outlet header systems
20A, 20B and 22, makes it possible to have particularly reliable
pressure compensation between the parallel-connected evaporator
tubes 10 of the combustion chamber 4 or the parallel-connected
steam generator tubes 16 of the horizontal gas flue 6, in that, in
each case, all the parallel-connected evaporator or steam
generator tubes 10 and 16 have the same overall pressure loss.
This means that, in the case of an evaporator tube 10 or steam
generator tube 16 heated to a greater extent, the throughput must
rise, as compared with an evaporator tube 10 or a steam generator
tube 16 heated to a lesser extent.
As illustrated in figure 2, the evaporator tubes 10 have, on their
inside, ribs 40 which form a type of multiflight thread and have a
rib height R.
In this case, the pitch angle a 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 55°. As a result, particularly high
heat transmission from the inner wall of the evaporator tubes to
the flow medium S guided in the evaporator tubes 10, at the same
time with particularly low temperatures of the tube wall, is
achieved.
The tube inside 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.
The steam generator 2 is thereby adapted to the different amounts
of heating of the evaporator tubes 10. This design of the
evaporator tubes 10 of the combustion chamber 4 ensures
particularly reliably 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 welded
to one another in a gastight manner via fins in a way not
illustrated in any more detail. To be precise, the heating of the
evaporator or steam generator tubes 10, 16, 17 can be influenced
by suitable choice of the fin width. The respective fin width is
therefore adapted to a heating profile which is predeterminable on
the gas side and which depends on the position of the respective
evaporator or steam generator tubes 10, 16, 17 in the steam
generator. The heating profile may in this case be a typical
heating profile determined from empirical values or else a rough
estimation. As a result, even in the case of widely differing
heating of the evaporator or steam generator tubes 10, 16, 17,
temperature differences at the outlet of the evaporator or steam
generator tubes 10, 16, 17 are kept particularly low. Material
fatigues are thereby reliably prevented, thus ensuring that the
steam generator 2 has a long useful life.
As means for reducing the throughflow of the flow medium S, some
of the evaporator tubes 10 are equipped with throttle devices
which are not illustrated in any more detail in the drawing.
The throttle devices are designed as perforated diaphragms
reducing the tube inside diameter D and, when the steam generator
2 is in operation, bring about a reduction in the throughput of
the flow medium S in evaporator tubes 10 heated to a lesser
extent, with the result that the throughput of the flow medium S
is adapted to the heating. Furthermore, as a means for reducing
the throughput of the flow medium S in the evaporator tubes 10 of
the combustion chamber 4, one or more lines of the line system 19
or 25 are equipped with throttle devices, in particular throttle
fittings, this not being illustrated in any more detail in the
drawing.
In the tubing of the combustion chamber 4, it must be remembered
that the heating of the individual evaporator tubes 10 welded to
one another in a gastight manner differs greatly when the steam
generator 2 is in operation. Consequently, the design of the
evaporator tubes 10 in terms of their internal ribbing, fin
connection to adjacent evaporator tubes 10 and their tube inside
diameter D is selected such that, in spite of different heating,
all the evaporator tubes 10 have approximately the same outlet
temperatures of the flow medium S and sufficient cooling of all
the evaporator tubes 10 is ensured for all the operating states of
the steam generator 2.
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. What is achieved, moreover, by a
suitable choice of the fin connections and of the tube inside
diameters D is that the fraction of frictional pressure loss in
the overall pressure loss is so small that a natural circulation
behavior is established: evaporator tubes 10 heated to a greater
extent have a higher throughflow than
evaporator tubes 10 heated to a lesser extent. What is also
achieved thereby is that the evaporator tubes 10 heated to a
comparatively greater extent and located in the burner vicinity
absorb specifically, with respect to the mass flow, approximately
as much heat as
the evaporator tubes 10 heated to a comparatively lesser extent,
which, in comparison with them, are arranged nearer to the
combustion chamber end. A further measure for adapting the
throughflow of the evaporator tubes 10 of the combustion chamber 4
to the heating is for throttles to be built into some of the
evaporator tubes 10 or into some of the lines of the line system
19. The internal ribbing is in this case designed in such a way
that sufficient cooling of the evaporator tube walls is ensured.
Thus, by means of the abovementioned measures, all the evaporator
tubes 10 have approximately the same outlet temperatures of the
flow medium S.
The horizontal gas flue 6 has a number of superheater heating
surfaces 23 which are designed as bulkhead heating surfaces and
are arranged in a suspended form of construction approximately
perpendicularly to the main flow direction 24 of the fuel gas G
and the tubes of which are in each case connected in parallel for
a throughflow of the flow medium S. The superheater heating
surfaces 23 are heated predominantly convectively and follow the
evaporator tubes 10 of the combustion chamber 4 on the flow-medium
side.
The vertical gas flue 8 through which fuel gas G is capable of
flowing from the bottom upward has a number of convection heating
surfaces 26 which are capable of being heated predominantly
convectively and are formed from tubes arranged approximately
perpendicularly to the main flow direction 24 of the fuel gas G.
These tubes are in each case connected in parallel for a
throughflow of the flow medium S and are integrated into the path
of the flow medium S, this not being illustrated in any more
detail in the drawing. Moreover, an economizer 28 is arranged in
the vertical gas flue 8 above the convection heating surfaces 26.
The economizer 28 is connected on the outlet side, via
a line system 19, to the inlet header system 18 assigned to the
evaporator tubes 10. In this case, one or more lines of the line
system 24, which are not illustrated in any more detail in the
drawing, may have throttle fittings in order to reduce the
throughflow of the flow medium s.
The vertical gas flue 8, through which fuel gas G is capable of
flowing from the bottom upward in an approximately vertical main
flow direction 24, is followed, on the outlet side, by a short
connecting duct 50. The connecting duct 50 connects the vertical
gas flue 8 to a housing 52. A nitrogen removal device 54 for fuel
gas G is arranged on the inlet side in the housing 52. The
nitrogen removal device 54 for fuel gas G is connected to an air
preheater 60 via a feed 56. The air preheater 60, in turn, is
connected to an electronic filter 62 via a smoke-gas duct 62.
The nitrogen removal device 54 for fuel gas G is operated
according to the method of selective catalytic reduction, what may
be referred to as the SCR method. During the catalytic
purification of the fuel gas G of the steam generator 2 according
to the SCR method, nitrogen oxides (NO2) are reduced to nitrogen
(N2) and water (H2O) with the aid of a catalyst and a reducing
agent, for example ammonia.
To carry out the SCR method, the nitrogen removal device 54 for
fuel gas G comprises a catalyst designed as a DeNOx catalyst 64.
The DeNOx catalyst is arranged in the flow region of the fuel gas
G. To introduce ammonia water as reducing agent M into the fuel
gas G, the nitrogen removal device 54 for fuel gas G has a
metering system 66. In this case, the metering system 66 comprises
a storage vessel 68 for ammonia water and a compressed-air system
69. The metering system 66 is arranged above the DeNOx catalyst 64
in the nitrogen removal device 54.
A steam generator 2 is designed with a horizontal combustion
chamber 4 having a particularly low overall height and can thus be
erected at a particularly low outlay in production and assembly
terms. For this purpose, the combustion chamber 4 of the steam
generator 2 has a number of burners 70 for fossil fuel B, which
are arranged, level with the horizontal gas flue 6, on the end
wall 11 of the combustion chamber 4.
So that the fossil fuel B, for example coal in solid form, burns
up particularly completely in order to achieve particularly high
efficiency and material damage to the first superheater heating
surface 23, as seen on the fuel-gas side,, of the horizontal gas
flue 6 and contamination of this, for example due to the
introduction of molten ash at high temperature, are prevented in a
particularly reliable way, the length L of the combustion chamber
4 is selected such that it exceeds the burnup length of the fuel B
during full-load operation of the steam generator 2. The length L
is in this case the distance from the end wall 9A of the
combustion chamber 4 to the inlet region 72 of the horizontal gas
flue 6. The burnup length of the fuel B is in this case defined as
the fuel-gas velocity in the horizontal direction at a specific
mean fuel-gas temperature, multiplied by the burnup time tA of the
fossil fuel B. The maximum burnup length for the respective steam
generator 2 is obtained during full-load operation of the steam
generator 2. The burnup time tA of the fuel B is, in turn, the time
which, for example, a coal dust grain of average size requires to
burn up completely at a specific mean fuel-gas temperature.
In order to ensure particularly favorable utilization of the
combustion heat of the fossil fuel B, the length L (given in m) of
the combustion chamber 4 is suitably selected as a function of the
outlet temperature of the fuel gas G from the combustion chamber 4
TARK (given in °C), of the burnup time tR (given in s) of the fuel B
and of the BMCR value W (given in kg/s) of the steam generator 2.
In this context, BMCR stands for boiler maximum continuous rating.
The BMCR value W is a term conventionally used internationally for
the maximum continuous power output of a steam generator. This
also corresponds to the design power output, that is to say to the
power output during full-load operation of the
steam generator. This horizontal length L of the combustion
chamber 4 is in this case greater than the height H of the
combustion chamber 4. The height H is in this case measured from
the funnel top edge of the combustion chamber 4, marked in
figure 1 by the subsidiary line having the end points X and Y,
to the combustion chamber ceiling. In this case, the length L of
the combustion chamber 4 is determined approximately via the two
functions (I) and (II)
"Approximately" in this case is understood to mean a permissible
deviation of +20%/-10% from the value defined by the respective
function. At the same time, in the case of an arbitrary, but fixed
BMCR value W of the steam generator, the higher value of the
functions (1) and (II) always applies to the length L of the
combustion chamber 4.
As an example of a calculation of the length L of the combustion
chamber 4 as a function of the BMCR value W of the steam generator
2, six curves Ki to K^ are depicted in the coordinate system
according to figure 3. Here, the curves are in each case assigned
the following parameters:
Thus, for example for a burnup time tR = 3s and an
outlet temperature TBRK = 1200°C of the fuel gas G from the
combustion chamber 4, the curves K1 and K4 are to be used to
determine the length L of the combustion chamber 4.
This results, in the case of a predetermined BMCR value W of the
steam generator 2
of W = 80 kg/s, in a length of L = 29 m according to K4,
of W = 160 kg/s, in a length of L = 34 m according to K4,
of W = 560 kg/s, in a length of L = 57 m according to K4.
For example, the curves K2 and K5 are to be used for the burnup time
TA = 2.5s and the outlet temperature of the fuel gas G from the
combustion chamber TBRK = 1300°C. This results, in the case of a
predetermined BMCR value W of the steam generator 2
of W = 80 kg/s, in a length of 1 = 21 m according to K2,
of W = 180 kg/s, in a length of L = 23 m according to K2 and K5,
of W = 560 kg/s, in a length of L = 37 m according to K5.
The burnup time tA = 2s and the outlet temperature of the fuel gas G
from the combustion chamber Tbrk = 1400°C are assigned, for example,
to the curves K5 and K6. This results, in the case of a predetermined
BMCR value W of the steam generator 2
of W = 80 kg/s, in a length of L = 18 m according to K3,
of W = 465 kg/s, in a length of 1 = 21 m according to K3 and K6,
of W = 560 kg/s, in a length of L = 23 m according to K6.
When the steam generator 2 is in operation, fossil fuel B and air are
supplied to the burners 70. The air is in this case preheated in the
air preheater by means of the residual heat of the fuel gas G and
then, this not being illustrated in any more detail in the drawing,
is compressed and supplied to the burner 70. The flames F of the
burners 70 are in this case oriented horizontally. By virtue of the
form of construction of the combustion chamber 4, a flow of the fuel
gas G occurring during
combustion is generated in the approximately horizontal main flow
direction 24.
The fuel gas G passes, via the horizontal gas flue 6, into the
vertical gas flue 8 through which fuel gas 6 is capable of flowing
from the bottom upward.
Downstream of the vertical gas flue 8 on the outlet side, the fuel
gas G passes, via the connecting duct 50, into the nitrogen removal
device 54 for fuel gas G. Via the nitrogen removal device 54 for fuel
gas G, a specific quantity of ammonia water is injected as reducing
agent M into the fuel gas G with the aid of compressed air as a
function of the type of fuel B operating the steam generator 2. This
is necessary, since the degree of separation of the nitrogen oxides
(NO5) depends on the type of fossil fuel B operating the steam
generator 2. A particularly reliable removal of nitrogen from the
fuel gas G is thereby ensured in all the operating states of the
steam generator 2.
The purified fuel gas G1 leaves the nitrogen removal device 54 for
fuel gas G via a feed 56 which issues into the air preheater 58. A
preheating of the air to be supplied to the burners 70 for the
combustion of the fossil fuel B takes place ±n the air preheater 58.
The fuel gas G leaves the air preheater 58 via the smoke-gas duct 60
and passes via 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 to 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 steam or a water/steam mixture occurring in the vertically
arranged evaporator tubes 10 of the combustion chamber 4 of the steam
generator 2 which are welded to one another in a gastight manner is
collected in the outlet header system 20A for flow medium S. The
steam or the water/steam mixture passes from there, via the line
system 19B, into the inlet header system 18B which is assigned to the
second group 11B of the evaporator tubes 10 of the side walls 9B of
the combustion chamber 4. The steam or a water/steam mixture
occurring in the
vertically arranged evaporator tubes 10 of the combustion chamber 4
of the steam generator 2 which are welded to one another in a
gastight manner is collected in the outlet header system
20B for flow medium S. The steam and/or the water/steam mixture
passes from there, via the line system 25, into the inlet header
system 21 assigned to the steam generator tubes 16 of the side walls
12 of the horizontal gas flue. The steam and/or the water/steam
mixture occurring in the evaporator tubes 16 passes via the outlet
header 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 gas flue 6. In the superheater heating surfaces 23,
further superheating of the steam takes place, the latter
subsequently being supplied for utilization, for example for driving
a steam turbine.
In the steam generator 2, the selection of the length L of the
combustion chamber 4 as a function of the BMCR value W of the steam
generator 2 ensures that the combustion heat, of the fossil fuel B is
utilized particularly reliably. Moreover, the steam generator 2
requires a particularly small amount of space on account of its
horizontal combustion chamber 4 and its nitrogen removal device 54
located directly downstream of the vertical gas flue 8. At the same
time, a particularly reliable removal of nitrogen from the fuel gas G
is ensured in a particularly simple way in all the operating states
of the steam generator 2.
We claims
1. A steam generator (2) with s nitrogen removal device
(54) for fuel gas (G) having a combustion chamber (4) for fossil
fuel (B) , which is followed on a fuel-gas side, via a horizontal
gas flue (6) and a vertical gas flue (8), by a nitrogen removal
device (54) for fuel gas (6), the combustion chamber comprising:
a number of burners (70) arranged level with the
horizontal gas flue (6), and wherein the vertical gas flue (8) is
designed for substantially vertical flow of the fuel gas from a
bottom thereof upward, and the nitrogen removal device (54) for
the fuel gas (G) is designed for substantially vertical flow of
the fuel gas (G) from a top thereof downward.
2. The steam generator (2) as claimed in 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. The steam generator (2) as claimed in claim 1 or 2, in
which the nitrogen removal device (54) for fuel gas (G) comprises
a DeNO.
4. The steam generator (2) as claimed in any 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 (8)
5. The steam generator (2) as claimed in any one of claims
1 to 4, in which jone 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 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 (5).
6. The steam generator (2) as claimed in 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 (5) 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. The steam generator (2) as claimed in lone 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. The steam generator (2) as claimed in 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. The steam generator (2) as claimed in claim 8, in which a
pitch angle (a) 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 55o.
10. The steam generator (2) as claimed intone of claims 1 to 8, in
which a number of the evaporator
tubes (10) in each case have a throttle device.
The steam generator (2) as claimed inlone 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).
The steam generator (2) as claimed in/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).
The steam generator (2) as claimed in/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).
The steam generator (2) as claimed intone 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).
The steam generator (2) as claimed in 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).
The steam generator (2) as claimed in one of claims 1 to 15,
in which a number of convection heating surfaces (52) are
arranged in the vertical gas flue (8).
The steam generator (2) as claimed in one of claims 1 to 16,
in which an economizer (28) is
arranged in the vertical gas flue (8).
18. The steam generator (2) as claimed in one of claims 1 to 17,
in which the burners (70) are arranged on the end wall (9A) of
the combustion chamber (4).
19. The steam generator (2) as claimed in 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. The steam generator (2) as claimed in 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 (tA) of the burners (70) and/or of the outlet temperature
(Tbrk) of the fuel gas (G) from the combustion chamber (4),
approximately according to the two functions (I) and (II)
the respectively higher value of the length (L) of the
combustion chamber (4) applying to a BMCR value (W).
A steam generator (2) has a nitrogen removal device for fuel gas (G)
and a combustion chamber (4) 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 steam generator is
to have a particularly low space requirement and ensure particularly
reliably a removal of nitrogen from the fuel gases (G) of the fossil
fuel (B). For this purpose, the combustion chamber has a number of
burners (70) arranged level with the horizontal gas flue (6).
Moreover, the vertical gas flue (8) is 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) is designed for an
approximately vertical flow of the fuel gas (G) from the top
downward.

Documents:

IN-PCT-2002-43-KOL-CORRESPONDENCE.pdf

IN-PCT-2002-43-KOL-FORM-27.pdf

in-pct-2002-43-kol-granted-abstract.pdf

in-pct-2002-43-kol-granted-claims.pdf

in-pct-2002-43-kol-granted-correspondence.pdf

in-pct-2002-43-kol-granted-description (complete).pdf

in-pct-2002-43-kol-granted-drawings.pdf

in-pct-2002-43-kol-granted-examination report.pdf

in-pct-2002-43-kol-granted-form 1.pdf

in-pct-2002-43-kol-granted-form 18.pdf

in-pct-2002-43-kol-granted-form 2.pdf

in-pct-2002-43-kol-granted-form 3.pdf

in-pct-2002-43-kol-granted-form 5.pdf

in-pct-2002-43-kol-granted-gpa.pdf

in-pct-2002-43-kol-granted-priority document.pdf

in-pct-2002-43-kol-granted-reply to examination report.pdf

in-pct-2002-43-kol-granted-specification.pdf

in-pct-2002-43-kol-granted-translated copy of priority document.pdf

IN-PCT-2002-43-KOL-PA.pdf

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Patent Number

225486

Indian Patent Application Number

IN/PCT/2002/43/KOL

PG Journal Number

46/2008

Publication Date

14-Nov-2008

Grant Date

12-Nov-2008

Date of Filing

09-Jan-2002

Name of Patentee

SIEMENS AKTIENGESELLSCHAFT

Applicant Address

WITTELSBACHERPLATZ 2, D-80333 MUNCHEN

Inventors:

#	Inventor's Name	Inventor's Address
1	PULEC, JOSEF	BUNZLAUER STRASSE 5, D-91074 HERZOGENAURACH
2	KARL, RUDOLF	AM LEITENWEG 28, D-92551 STULLN

PCT International Classification Number

F22B 21/34

PCT International Application Number

PCT/DE00/01941

PCT International Filing date

2000-06-13

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	199 29 088.2	1999-06-29	Germany