EP1086339B1 - Fossil fuel fired steam generator - Google Patents

Description

The invention relates to a once-through steam generator with a Combustion chamber for a fossil fuel that is on the hot gas side a horizontal throttle cable is followed by a vertical throttle cable.

The use of a steam generator usually serves to a flow medium carried in an evaporator circuit, for example, a water-water / steam mixture to evaporate. For this purpose, the steam generator has evaporator tubes whose Heating to evaporation of the flow medium contained therein leads.

Document US-A-3 527 261 discloses a natural circulation steam generator with a combustion chamber, the heating gas side via a horizontal gas flue a vertical gas flue is connected downstream.

Steam generators are usually used with a combustion chamber standing construction. This means that the combustion chamber for a flow through the heating medium or Heating gas is designed in an approximately vertical direction. On the heating gas side, the combustion chamber can use a horizontal gas flue be connected downstream, with the transition from the combustion chamber a diversion of the heating gas flow into the horizontal gas flue there is an approximately horizontal flow direction. This standing design of the combustion chamber requires due to the temperature-related changes in length of the combustion chamber Framework on which the combustion chamber is suspended. This requires a considerable technical effort in the production and Assembly of the steam generator, the bigger the bigger is the height of the steam generator.

The invention has for its object a fossil-fired Pass-through steam generator of the type mentioned above, the one requires particularly low manufacturing and assembly costs.

This object is achieved by the combustion chamber has a number of burners in the amount of Horizontal throttle cable are arranged.

The invention is based on the consideration that one with special low manufacturing and assembly costs Continuous steam generator a holding construction that can be carried out with simple means should have. One with comparatively little technical effort to create scaffolding for the suspension the combustion chamber can be accompanied by a special one low overall height of the once-through steam generator. A special one low overall height of the once-through steam generator can be achieved by the Combustion chamber is constructed in a horizontal position. For this are the burners at the level of the horizontal gas flue in the combustion chamber wall arranged. Thus the combustion chamber is in operation of the continuous steam generator in an approximately horizontal direction flowed through by the heating gas.

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

To material damage and unwanted pollution of the Horizontal throttle flue, for example due to ash deposits, to keep particularly low is the distance from the Front side to the entry area of the horizontal throttle cable defined Length of the combustion chamber advantageously at least equal to the burnout length of the fuel at full load of the continuous steam generator.

In an advantageous embodiment of the invention, the length L (specified in m) of the combustion chamber is a function of the BMCR value W (specified in kg / s) of the combustion chamber, the burnout time t _A (specified in s) of the fuel and the outlet temperature T _BRK (specified in ° C) of the working medium selected from the combustion chamber. BMCR stands for Boiler maximum continuous rating and BMCR value is the internationally used term for the highest continuous output of a steam generator. This also corresponds to the design power, i.e. the power at full load operation of the steam generator. Given the given BMCR value W, the greater the value of the functions approximately applies to the length L of the combustion chamber: L (W, t A ) = (C 1 + C 2 · W) · t A and L (W, T BRK ) = (C 3rd · T BRK + C 4th ) W + C 5 (T BRK ) 2 + C 6 · T BRK + C 7 With C. 1 = 8 m / s and C. 2 = 0.0057 m / kg and C. 3rd = -1.905.10 -4 (ms) / (kg ° C) and C. 4th = 0.2857 (s · m) / kg and C. 5 = 3 · 10 -4 m / (° C) 2 and C. 6 = -0.8421 m / ° C and C. 7 = 603.4125 m.

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

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

For a particularly good heat transfer from the heat of the Combustion chamber on the flow medium in the evaporator tubes advantageously has a number of evaporator tubes a multi-start thread on the inside forming ribs. This is advantageously a Pitch angle α between a perpendicular to the pipe axis Level and the flanks of those arranged on the inside of the pipe Ribs less than 60 °, preferably less than 55 °. In one heated, as an evaporator tube without internal fins, one so-called smooth tube, executed evaporator tube can namely from a certain steam content to the wetting of the Pipe wall can no longer be maintained. If there is no Wetting can be a dry pipe wall in places. The transition to such a dry pipe wall results in the way of a heat transfer crisis in one particular restricted heat transfer behavior, so that in general the pipe wall temperatures at this point in particular solid rising. But in an internally finned tube now in comparison to a smooth pipe this crisis of heat transfer only with a steam mass content> 0.9, i.e. short before the end of evaporation. This is due to the twist the flow through the spiral ribs experiences. Due to the different centrifugal force the water and steam are separated and sent to the pipe wall pressed. This will wetting the pipe wall up to maintain high steam levels so that at the location of the heat transfer crisis there are already high flow velocities. This causes a particularly good heat transfer and as a result, low pipe wall temperatures.

Adjacent evaporator or steam generator tubes are advantageous gas-tight via metal strips, so-called fins welded together. The fin width affects the Heat input into the steam generator tubes. Hence the fin width preferably depending on the position of each Evaporator or steam generator tubes in the steam generator a temperature profile that can be predetermined on the gas side is adapted. As a temperature profile can be determined from empirical values typical temperature profile or a rough estimate, such as a step profile. By the suitably chosen fin widths is also very strongly inhomogeneous Heating various evaporator or steam generator tubes a heat input into all evaporator or steam generator tubes so accessible that temperature differences especially at the outlet of the evaporator or steam generator tubes are kept low. In this way, premature material fatigue reliably prevented. As a result, the steam generator points a particularly long lifespan.

In a further advantageous embodiment of the invention is the inside diameter of the evaporator tubes of the combustion chamber depending on the respective position of the evaporator tubes selected in the combustion chamber. That way they are Evaporator tubes in the combustion chamber on a gas-definable Adaptable temperature profile. With the resultant Influence on the flow through the evaporator tubes is particularly significant reliable temperature differences at the outlet of the evaporator tubes the combustion chamber kept low.

The evaporator tubes of the combustion chamber are advantageous a common inlet header system for the flow medium upstream and a common exit collector system downstream. One designed in this configuration Steam generator enables reliable pressure equalization between the parallel evaporator tubes and thus a particularly even flow through the same.

The evaporator tubes on the front side of the combustion chamber are advantageous the evaporator tubes of the side walls of the Combustion chamber upstream of the flow medium. This is ensures a particularly favorable utilization of the heat of the burners.

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

The vertical throttle cable advantageously has a number of Convection heating surfaces, which are approximately perpendicular to the Main flow direction of the heating gas arranged tubes formed are. These pipes are for a flow through the Flow medium connected in parallel. These convection heating surfaces too are mainly heated by convection.

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

The advantages achieved with the invention are in particular in that by arranging the burner at the level of Horizontal throttle cable has a particularly low overall height for the steam generator is achievable. This also enables integration of the steam generator in a steam turbine system particularly short connecting pipes from the steam generator to the steam turbine. By designing the combustion chamber for a flow of the heating gas in an approximately horizontal direction a particularly compact design of the steam generator. The length of the combustion chamber is designed so that a particularly favorable use of the heat of the fossil Fuel is guaranteed.

FIG 1

schematisch einen fossil beheizten Dampferzeuger in Zweizugbauart in Seitenansicht und

FIG 2

schematisch einen Längsschnitt durch ein einzelnes Verdampfer- bzw. Dampferzeugerrohr und

FIG 3

ein Koordinatensystem mit den Kurven K₁ bis K₆.

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

FIG. 1

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

FIG 2

schematically shows a longitudinal section through a single evaporator or steam generator tube and

FIG 3

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

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

The fossil-heated steam generator 2 according to FIG. 1 is in a horizontal position Construction and advantageously as a continuous steam generator executed. It comprises a combustion chamber 4 on the hot gas side a vertical throttle cable 8 via a horizontal throttle cable 6 is connected downstream. The end face 9 and the side walls 10a the combustion chamber 4 are welded together in a gastight manner, vertically arranged, parallel with flow medium S acted upon evaporator tubes 11 formed. In addition can also the side walls 10b of the horizontal throttle cable 6 or 10c of the vertical throttle cable 8 made of gas-tightly welded together, vertically arranged steam generator tubes 12a or 12b. In this case, the steam generator pipes 12a, 12b also in parallel with the flow medium S acted upon.

The evaporator tubes 11 have - as shown in Figure 2 - ribs 40 on its inside, which are a kind of multi-course Form threads and have a rib height R. Here is the Pitch angle α between a perpendicular to the pipe axis Level 41 and the flanks 42 arranged on the inside of the tube Ribs 40 smaller than 55 °. This makes it special high heat transfer from the heat of the combustion chamber 4 the flow medium S guided in the evaporator tubes 11 at the same time particularly low temperatures of the pipe wall reached.

Adjacent evaporator or steam generator tubes 11, 12a, 12b are in a manner not shown in Figure 1 on fins welded together gastight. By a suitable one The choice of fin width can be used to heat the evaporator or steam generator tubes 11, 12a, 12b are influenced. Therefore the respective fin width depends on the Position of the respective evaporator or steam generator tubes 11, 12a, 12b in the steam generator to a gas-presettable Temperature profile adjusted. The temperature profile can a typical temperature profile determined from experience or a rough estimate. Thereby Temperature differences at the outlet of the evaporator or steam generator tubes 11, 12a, 12b even with very different ones Heating the evaporator or steam generator tubes 11, 12a, 12b especially kept Bering. In this way, material fatigue reliably prevents what a long life of the steam generator 2 guaranteed.

The inner tube diameter D of the evaporator tubes 11 of the combustion chamber 4 depends on the respective position of the evaporator tubes 11 selected in the combustion chamber 4. In this way is the steam generator 2 in addition to the different strong heating of the evaporator tubes 11 adapted. This interpretation the evaporator tubes 11 ensures the combustion chamber 4 a particularly reliable flow through the evaporator tubes 11 in such a way that temperature differences at the outlet the evaporator tubes 11 are kept particularly low.

When piping the combustion chamber, it must be taken into account that the heating of the individual, welded together gastight Evaporator tubes 11 during the operation of the steam generator 2 very much is different. That is why the design of the evaporator tubes 11 with regard to their internal ribbing, fin connection to neighboring evaporator tubes 11 and their inner tube diameter D chosen so that all the evaporator tubes 11 despite different heating approximately the same outlet temperatures have and sufficient cooling of the evaporator tubes 11 for all operating states of the steam generator 2 is guaranteed. This is ensured in particular by that the steam generator 2 for a comparatively low Mass flow density of the flow through the evaporator tubes 11 Flow medium S is designed. By a suitable one Choice of fin connections and inner tube diameter D is also achieved that the proportion of the loss of friction pressure of the total pressure loss is so low that there is a natural circulation behavior adjusts: More heated evaporator tubes 11 flows through more strongly than weakly heated evaporator tubes 11. This ensures that the comparatively strong heated evaporator tubes 11 in the vicinity of the burner specifically - related on the mass flow - absorb almost as much heat like the comparatively weakly heated evaporator tubes 11 at the end of the combustion chamber. The internal ribbing is included designed such that adequate cooling of the evaporator tube walls is ensured. Thus point to the above measures mentioned all evaporator tubes 11 approximately the same Outlet temperatures. For a steam generator with vertical Throttle cable is one such evaporator concept, for example from VGB-Kraftwerkstechnik 75 (1995), number 4, pages 353 - 359, known.

The evaporator tubes 11 of the combustion chamber 4 is on the flow medium side an inlet header system 16 for flow medium S upstream and an outlet collector system 18 connected downstream. This is a pressure equalization of the parallel Evaporator tubes 11 possible, the uniform Flow through the same causes.

To make particularly good use of the heat of combustion To reach fossil fuel B are the evaporator tubes 11 of the front 9 of the combustion chamber 4 the evaporator tubes 11 of the side walls 10a of the combustion chamber 4 on the flow medium side upstream.

The horizontal throttle cable 6 has a number of bulkhead heating surfaces trained superheater heating surfaces 22, which in hanging construction approximately perpendicular to the main flow direction 24 of the heating gas H arranged and their tubes for a flow through the flow medium S connected in parallel are. The superheater heating surfaces 22 become predominantly convective heated and are on the flow medium side of the evaporator tubes 11 downstream of the combustion chamber 4.

The vertical throttle cable 8 has a number of predominantly convective heatable convection heating surfaces 26 which come from approximately perpendicular to the main flow direction of the heating gas H arranged tubes are formed. These tubes are for one Flow through the flow medium S connected in parallel. Moreover is a high pressure preheater in the vertical throttle cable 8 or economizer 28 arranged. The vertical throttle cable opens on the output side 8 into a flue gas not shown or heat exchanger and from there via a dust filter into one Stack.

The steam generator 2 is special in a horizontal design low overall height and therefore particularly low Manufacturing and assembly costs can be set up. For this the combustion chamber 4 of the steam generator 2 has a number of Burners 30 for fossil fuel B on the front 9 of the combustion chamber 4 at the level of the horizontal gas flue 6 are arranged.

The length L of the combustion chamber 4 is selected so that the fossil fuel B burns out particularly completely to achieve a particularly high efficiency and material damage to the first superheater heating surface of the horizontal gas flue 6, as seen on the heating gas side, and contamination thereof, for example by the entry of ash, is selected in such a way that it the burnout length of the fuel B exceeds when the steam generator 2 is operating at full load. The length L is the distance from the end face 9 of the combustion chamber 4 to the inlet area 32 of the horizontal gas flue 6. The burnout length of the fuel B is defined as the heating gas speed in the horizontal direction at a specific mean flue gas temperature multiplied by the burnout time t _{A of} the fuel B. The maximum burn-out length for the respective steam generator 2 results when the steam generator 2 is operating at full load. The burn-out time t _{A of} the fuel B is in turn the time which, for example, a medium-sized coal dust particle takes to completely burn out at a certain average smoke gas temperature.

In order to ensure a particularly favorable utilization of the heat of combustion of the fossil fuel B, the length L (specified in m) of the combustion chamber 4, depending on the outlet temperature of the working medium from the combustion chamber 4 T _BRK (specified in ° C), is the burnout time t _A (specified in s) of the fuel B and the BMCR value W (specified in kg / s) of the combustion chamber 4 are selected appropriately. BMCR stands for Boiler maximum continuous rating. The BMCR value W is an internationally used term for the highest continuous output of a steam generator. This also corresponds to the design power, i.e. the power at full load operation of the steam generator. The length L of the combustion chamber 4 is approximately determined by the functions L (W, t A ) = (C 1 + C 2 · W) · t A L (W, T BRK ) = (C 3rd · T BRK + C 4th ) W + C 5 (T BRK ) 2 + C 6 · T BRK + C 7 With C. 1 = 8 m / s and C. 2 = 0.0057 m / kg and C. 3rd = -1.905.10 -4 (ms) / (kg ° C) and C. 4th = 0.2857 (s · m) / kg and C. 5 = 3 · 10 -4 m / (° C) 2 and C. 6 = -0.8421 m / ° C and C. 7 = 603.4125 m.

Approximately this is a permissible deviation +20% / - 10% of the value defined by the respective function to understand. It always applies to any but firm BMCR value of the combustion chamber 4 the larger value of the values L the Length L of the combustion chamber 4.

K₁: t_A = 3s   gemäß (1),

K₂: t_A = 2,5s   gemäß (1),

K₃: t_A = 2s   gemäß (1),

K₄: t_BRK = 1200°C   gemäß (2),

K₅ : t_BRK = 1300°C   gemäß (2) und

K₆: t_BRK = 1400°C   gemäß (2).

As an example of a calculation of the length L of the combustion chamber 4 as a function of the BMCR value W, six curves K ₁ to K _{6 are} drawn into the coordinate system according to FIG. The following parameters are assigned to the curves:

K ₁ : t _A = 3s according to (1),

K ₂ : t _A = 2.5 s according to (1),

K ₃ : t _A = 2s according to (1),

K ₄ : t _BRK = 1200 ° C according to (2),

K ₅ : t _BRK = 1300 ° C according to (2) and

K ₆ : t _BRK = 1400 ° C according to (2).

von W = 80 kg/s eine Länge von L = 29 m gemäß K₄,

von W = 160 kg/s eine Länge von L = 34 m gemäß K₄,

von W = 560 kg/s eine Länge von L = 57 m gemäß K₄.

To determine the length L of the combustion chamber 4, the curves K ₁ and K ₄ are thus to be used, for example, for a burnout time t _A = 3 s and an outlet temperature T _BRK = 1200 ° C. of the working medium from the combustion chamber 4. This results in the combustion chamber 4 at a predetermined BMCR value W

from W = 80 kg / s a length of L = 29 m according to K ₄ ,

from W = 160 kg / s a length of L = 34 m according to K ₄ ,

from W = 560 kg / s a length of L = 57 m according to K ₄ .

von W = 80 kg/s eine Länge von L = 21 m gemäß K₂,

von W = 180 kg/s eine Länge von L = 23 m gemäß K₂ und K₅,

von W = 560 kg/s eine Länge von L = 37 m gemäß K₅.

For the burnout time t _A = 2.5 s and the outlet temperature of the working medium from the combustion chamber T _BRK = 1300 ° C, curves K ₂ and K _{5 are to} be used, for example. This results in the combustion chamber 4 at a predetermined BMCR value W

from W = 80 kg / s a length of L = 21 m according to K ₂ ,

from W = 180 kg / s a length of L = 23 m according to K ₂ and K ₅ ,

from W = 560 kg / s a length of L = 37 m according to K ₅ .

von W = 80 kg/s eine Länge von L = 18 m gemäß K₃,

von W = 465 kg/s eine Länge von L = 21 m gemäß K₃ und K₆,

von W = 560 kg/s eine Länge von L = 23 m gemäß K₆.

The burnout time t _A = 2s and the outlet temperature of the working medium from the combustion chamber t _BRK = 1400 ° C are assigned to curves K ₃ and K ₆ , for example. This results in the combustion chamber 4 at a predetermined BMCR value W

from W = 80 kg / s a length of L = 18 m according to K ₃ ,

from W = 465 kg / s a length of L = 21 m according to K ₃ and K ₆ ,

from W = 560 kg / s a length of L = 23 m according to K ₆ .

When the steam generator 2 is operating, the burners 30 become more fossil Fuel B supplied. The flames F of the burners 30 are aligned horizontally. Due to the design of the combustion chamber 4 becomes a flow of the resulting from the combustion Heating gas H in approximately horizontal main flow direction 24 generated. This passes through the horizontal throttle cable 6 in the vertical throttle cable aligned approximately towards the floor 8 and leaves this in the direction of not shown Chimneys.

Flow medium S entering the economizer 28 arrives via the convection heating surfaces arranged in the vertical gas flue 8 into the intake manifold system 16 of the combustion chamber 4 of the steam generator 2. In the vertically arranged, gas-tight evaporator tubes 11 welded together Combustion chamber 4 of the steam generator 2 finds the evaporation and possibly a partial overheating of the flow medium S instead. The resulting steam or a water-steam mixture is in the exit collector system 18 for Flow medium S collected. From there the steam or the water-steam mixture in the walls of the horizontal throttle cable 6 and the vertical throttle cable 8 and from there again in the Superheater heating surfaces 22 of the horizontal throttle cable 6. In the Superheater heating surfaces 22 further overheat the Steam, which is subsequently used, for example by the Drive a steam turbine, is supplied.

Due to the particularly low height and compact design of the Pass-through steam generator 2 is a particularly low manufacturing and Assurance of the same guaranteed. One with comparative scaffolding can be created with little technical effort in particular by the level of the horizontal throttle cable 6 Burner 30 ensures the combustion chamber 4, the one Flow through the combustion chamber 4 in approximately horizontal Main flow direction 24 of the heating gas H. It is by a choice of the length L of the combustion chamber 4 in dependence from the BMCR value W of the combustion chamber 4 ensures that the The heat of combustion of the fossil fuel B is particularly reliable is exploited. In a steam turbine plant with the such a low-profile continuous steam generator 2 can also the connecting pipes from the continuous steam generator 2 the steam turbine can be designed in a particularly short manner.

Claims (16)

1. Once-through steam generator (2) having a combustion chamber (4) for a fossil fuel (B), downstream of which a vertical gas flue (8) is arranged on the heating-gas side via a horizontal gas flue (6), the combustion chamber (4) having a number of burners (30) which are arranged at the level of the horizontal gas flue (6).
2. Once-through steam generator (2) according to Claim 1, in which the burners (30) are arranged on the end face (9) of the combustion chamber (4).
3. Once-through steam generator (2) according to Claim 1 or 2, in which the length (L) of the combustion chamber (32), which is defined by the distance from the end face (9) of the combustion chamber (4) to the inlet region (32) of the horizontal gas flue (6), is at least equal to the burn-out length of the fuel (B) during full-load operation of the once-through steam generator (2).
4. Once-through steam generator according to one of Claims 1 to 3, in which the length (L) of the combustion chamber (4) (specified in m) is selected as a function of the BMCR value (W) of the combustion chamber (4) (specified in kg/s), the burn-out time (t_A) of the fuel (specified in s) and/or the outlet temperature (T_BRK) of the working medium from the combustion chamber (4) (specified in °C) approximately according to the equations L (W, tA) = (C1 + C2 · W) · tA    and L (W, TBRK) = (C3 · TBRK + C4) W + C5 (TBRK)2 + C6 · TBRK + C7    where C1 = 8 m/s    and C2 = 0.0057 m/kg    and C3 = -1.905 · 10-4 (m · s)/(kg°C)    and C4 = 0.2857 (s · m)/kg    and C5 = 3 · 10-4 m/(°C)2    and C6 = -0.8421 m/°C    and C7 = 603.4125 m in which case, for a BMCR value (W) of the combustion chamber (4), the respectively larger value of the length (L) of the combustion chamber (4) applies.
5. Once-through steam generator (2) according to one of Claims 1 to 4, in which the end face (9) of the combustion chamber (4) is formed from vertically arranged evaporator tubes (11) which are welded to one another in a gastight manner and to which flow medium (S) can be admitted in a parallel manner.
6. Once-through steam generator (2) according to one of Claims 1 to 5, in which the side walls (10a) of the combustion chamber (4) are formed from vertically arranged evaporator tubes (11) which are welded to one another in a gastight manner and to which flow medium (S) can be admitted in a parallel manner.
7. Once-through steam generator (2) according to Claim 6, in which a number of evaporator tubes (11), on their inside, in each case have ribs (40) forming a multi-start thread.
8. Once-through steam generator (2) according to Claim 7, in which a helix angle (α) between a plane (41) perpendicular to the tube axis and the flanks (42) of the ribs (40) arranged on the tube inside is less than 60°, preferably less than 55°.
9. Once-through steam generator (2) according to one of Claims 1 to 8, in which the side walls (10b) of the horizontal gas flue (6) are formed from vertically arranged steam-generator tubes (12a) which are welded to one another in a gastight manner and to which flow medium (S) can be admitted in a parallel manner.
10. Once-through steam generator (2) according to one of Claims 1 to 9, in which the side walls (10c) of the vertical gas flue (8) are formed from vertically arranged steam-generator tubes (12b) which are welded to one another in a gastight manner and to which flow medium (S) can be admitted in a parallel manner.
11. Once-through steam generator (2) according to one of Claims 1 to 10, in which adjacent evaporator or steam-generator tubes (11, 12a, 12b) 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 (11, 12a, 12b) in the combustion chamber (4), of the horizontal gas flue (6) and/or of the vertical gas flue (8).
12. Once-through steam generator (2) according to one of Claims 1 to 11, in which the tube inside diameter (D) of the evaporator tubes (11) of the combustion chamber (4) is selected as a function of the respective position of the evaporator tubes (11) in the combustion chamber (4).
13. Once-through steam generator (2) according to one of Claims 1 to 12, in which a common inlet-collector system (16) for flow medium (S) is connected on the flow-medium side upstream of the evaporator tubes (11) assigned to the combustion chamber (4), and a common outlet-collector system (18) is connected downstream of the said evaporator tubes (11).
14. Once-through steam generator (2) according to one of Claims 1 to 13, in which the evaporator tubes (11) of the end face (9) of the combustion chamber (4) are connected on the flow-medium side upstream of the evaporator tubes (11) of the side walls (10a) of the combustion chamber (4).
15. Once-through steam generator (2) according to one of Claims 1 to 14, in which a number of superheater heating surfaces (22) are arranged in a suspended type of construction in the horizontal gas flue (6).
16. Once-through steam generator (2) according to one of Claims 1 to 15, in which a number of convection heating surfaces (26) are arranged in the vertical gas flue (8).

Images