EP1554522B1 - Operating method for a horizontal steam generator - Google Patents

Description

The invention relates to a method for operating a steam generator with an evaporator through-flow surface arranged in a heating gas duct which can be flowed through in an approximately horizontal heating gas direction, comprising a number of steam generator tubes connected in parallel to flow through a flow medium, each of which has an approximately vertical flow through the flow medium in the downstream direction Downcomer pipe and a this downstream of the flow medium side, arranged approximately vertically and by the flow medium in the upward direction durchströmbares riser pipe, wherein the evaporator Durchlaufheizfläche is designed such that a more compared to another steam generator the same evaporator Durchlaufheizfläche more heated steam generator tube compared to the other steam generator tube higher throughput having the flow medium.

In a gas and steam turbine plant, the heat contained in the relaxed working fluid or heating gas from the gas turbine is used to generate steam for the steam turbine. The heat transfer takes place in a heat recovery steam generator connected downstream of the gas turbine, in which a number of heating surfaces for water preheating, steam generation and steam superheating is usually arranged. The heating surfaces are connected in the water-steam cycle of the steam turbine. The water-steam cycle usually comprises several, e.g. three, pressure stages, each pressure stage may have a Verdampferheizfläche.

For the gas turbine as a heat recovery steam generator downstream of the gas turbine steam generator come several alternative Design concepts, namely the design as a continuous steam generator or the design as a circulating steam generator, into consideration. In a continuous steam generator, the heating of steam generator tubes provided as evaporator tubes leads to an evaporation of the flow medium in the steam generator tubes in a single pass. In contrast, in a natural or forced circulation steam generator, the recirculated water is only partially vaporized when passing through the evaporator tubes. The water which is not evaporated is fed again to the same evaporator tubes after separation of the steam produced for further evaporation.

In contrast to a natural or forced circulation steam generator, a continuous steam generator is not subject to any pressure limitation, so that it is possible for live steam pressures far above the critical pressure of water (P _Kri ≈ 221 bar) - where no differentiation of the phases water and steam and thus no phase separation is possible. can be designed. A high live steam pressure promotes a high thermal efficiency and thus low CO ₂ emissions of a fossil-fired power plant. In addition, a continuous steam generator in comparison to a circulating steam generator a simple construction and is thus produced with very little effort. The use of a designed according to the flow principle steam generator as heat recovery steam generator of a gas and steam turbine plant is therefore particularly favorable to achieve a high overall efficiency of the gas and steam turbine plant with a simple design.

Particular advantages in terms of the manufacturing effort, but also in terms of required maintenance offers a heat recovery steam generator in horizontal construction, in which the heating medium or heating gas, ie the exhaust gas from the gas turbine, is guided in approximately horizontal flow direction through the steam generator. In a steam generator in horizontal construction, the steam generator tubes of an evaporator heating surface However, depending on their positioning be exposed to a very different heating. In particular, at the output side connected to a common collector steam generator tubes of a continuous steam generator, a different heating individual steam generator tubes to a combination of steam flows with widely divergent steam parameters and thus undesirable efficiency losses, in particular to a comparatively reduced effectiveness of the affected heating surface and thereby reduced steam generation lead. In addition, a different heating of adjacent steam generator tubes can, in particular in the junction area of collectors, lead to damage to the steam generator tubes or to the collector. The desirable use of a continuous-flow steam generator designed as a downheating steam generator for a gas turbine can thus bring about considerable problems with regard to a sufficiently stabilized flow guidance.

From the EP 0 944 801 B1 a steam generator is known, which is suitable for a design in horizontal design and also has the advantages of a continuous steam generator mentioned. For this purpose, the evaporator heating surface of the known steam generator is connected as Durchlaufheizfläche and designed such that a more heated compared to another steam generator tube Durchlaufheizfläche same steam generator tube has a higher compared to the other steam generator tube throughput of the flow medium. By continuous heating surface is generally to be understood a heating surface, which is designed for a flow according to the flow principle. The flow medium supplied to the evaporator heating surface interconnected as a continuous heating surface is thus completely evaporated in a single pass through this continuous heating surface or through a heating surface system comprising a plurality of continuous heating surfaces connected in series.

The interconnected as Durchlaufheizfläche evaporator heating surface of the known steam generator thus shows in the nature of the flow characteristics of a Naturumlaufverdampferheizfläche (natural circulation) with occurring different heating individual steam generator tubes a self-stabilizing behavior that without the need for external interference to an alignment of the outlet temperatures also differently heated, flow medium side connected in parallel Steam generator tubes leads.

In order to achieve a particularly low load in a steam generator in such a construction by thermally induced stresses especially with regard to the water and / or vapor distribution of the flow medium particularly low manufacturing and assembly costs, the evaporator Durchlaufheizfläche the steam generator in the Art a U-shaped construction of a number of parallel to the flow of the flow medium steam generator tubes may be formed, each having an approximately vertically arranged, from the flow medium in the downward flow-through downpipe piece and this downstream of the flow medium side, approximately vertically arranged and flow medium through-flow in the upward direction riser piece. As has been found, in such a construction, the flow through the Durchlaufheizfläche favors - flow-promoting - pressure contribution on the geodetic pressure of the water column located in the downpipe of each steam generator tube water column available.

However, such a construction could in principle favor the occurrence of flow instabilities in the operation of the evaporator Durchlaufheizfläche, which could lead to operational disadvantages. Although it is by the supply of the Durchlaufheizfläche forming steam generator tubes with relatively low mass flow density and the associated relatively low friction pressure loss a natural circulation characteristic of the flow in the steam generator tube achievable, which has a stabilizing effect on the flow. Nevertheless, it is desirable to contribute to a stabilization of the flow conditions during operation of the evaporator Durchlaufheizfläche especially in such a construction with downward flow-through pipe section.

The invention is therefore based on the object to provide a method for operating a steam generator of the type mentioned above, with a relatively high degree of flow stability in the operation of the evaporator Durchlaufheizfläche can be achieved in a relatively simple manner.

With regard to the method, this object is achieved in that the flow medium of the evaporator Durchlaufheizfläche is supplied such that it has a flow rate of more than a predetermined minimum speed in the downcomer of the respective steam generator tube.

The invention is based on the consideration that a particularly high flow stability and thus a particularly high level of operational safety for the steam generator of the type mentioned above can be achieved by consistently suppressing possible causes for self-adjusting flow instabilities. As has been found, one of these possible causes may be the occurrence of vapor bubbles in the downcomer of the respective steam generator tube. If, in fact, vapor bubbles should form in the downcomer piece, they could rise in the water column located in the downcomer piece and thus perform a movement counter to the flow direction of the flow medium. To prevent such, the flow direction of the flow medium oppositely directed movement of possibly existing vapor bubbles consistently, by a suitable specification of the operating parameters, a forced entrainment of the vapor bubbles in the actual flow direction be ensured of the flow medium. This can be achieved by feeding the evaporator pass-through heating surface with flow medium in a suitable manner, wherein a sufficiently high flow velocity of the flow medium in the steam generator tubes brings about the desired entrainment effect on the possibly existing or forming vapor bubbles.

Advantageously, the flow rate of the flow medium in the downcomer piece of the respective steam generator tube is adjusted such that in the permissible operating range in any case a take-over of possibly existing vapor bubbles is ensured. For this purpose, the flow velocity required for entrainment of the vapor bubbles, optionally increased by a suitably selected safety impact, is advantageously set as the minimum velocity for the flow velocity of the flow medium in the downcomer of the respective steam generator tube.

The setting of a sufficiently high flow rate of the flow medium in the downcomer of the respective steam generator tube is possible in a particularly simple manner by the flow medium is supplied to the downcomer of the respective steam generator tube in teilverdampftem state and / or with a certain minimum enthalpy. For this purpose, the flow medium is advantageously partially pre-evaporated prior to its entry into the evaporator Durchlaufheizfläche that it has a vapor content and / or an enthalpy of more than a predetermined minimum steam content or a predetermined minimum enthalpy when entering the evaporator Durchlaufheizfläche.

The advantages achieved by the invention are in particular that by the now provided, at least partially pre-evaporation of the flow medium prior to its entry into the formed from substantially U-shaped steam generator tubes Durchlaufheizfläche according to specifiable Criteria a desired vapor content and / or a desired enthalpy of the flow medium is adjustable. By a suitable choice of the vapor content and / or the enthalpy of the flow medium flowing through the flow heating surface above a predetermined minimum steam content and / or a predetermined minimum enthalpy, a sufficient flow velocity of the flow medium can be ensured in the downer piece of the respective steam generator tube Durchlaufheizfläche. The flow rate of a water-steam mixture is in fact higher with the same mass flow rate, the greater the vapor content and thus the specific volume of the mixture.

The flow rate of the water-steam mixture can be set in particular so high that possibly present in the downpipe section of each steam generator tube existing steam bubbles reliably and can be transferred to the respective downcomer branch piece of riser pipe. Even with the U-shaped design of the steam generator tubes of the evaporator Durchlaufheizfläche thus one of the flow direction of the flow medium opposite movement of the vapor bubbles is safely excluded, so that a particularly high flow stability and thus a particularly high operational safety for the steam generator with such a designed evaporator Durchlaufheizfläche is guaranteed.

Figur 1

in vereinfachter Darstellung im Längsschnitt die Verdampfersektion eines Dampferzeugers in liegender Bauweise,

Figur 2

den Dampferzeuger nach Figur 1 ausschnittweise in Aufsicht,

Figur 3

den Dampferzeuger nach Figur 1 im Ausschnitt entlang der in Figur 2 dargestellten Schnittlinie,

Figur 4

den Dampferzeuger nach Figur 1 im Ausschnitt entlang der in Figur 2 darstellten Schnittlinie, und

Figur 5

ein Enthalpie- bzw. Strömungsgeschwindigkeits-Massenstromdiagramm.

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

FIG. 1

in a simplified representation in longitudinal section the evaporator section of a steam generator in horizontal construction,

FIG. 2

the steam generator after FIG. 1 partially in supervision,

FIG. 3

the steam generator after FIG. 1 in the clipping along the in FIG. 2 illustrated section line,

FIG. 4

the steam generator after FIG. 1 in the clipping along the in FIG. 2 represented cutting line, and

FIG. 5

an enthalpy flow chart.

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

The in FIG. 1 shown with an evaporator section steam generator 1 is downstream in the manner of a heat recovery steam generator of a gas turbine not shown exhaust. The steam generator 1 has a surrounding wall 2, which forms a in a nearly horizontal, indicated by the arrows 4 Heizgasrichtung x fuel gas channel 6 for the exhaust gas from the gas turbine. In the Heizgaskanal 6 is a number - in the exemplary embodiment two - arranged by the flow principle evaporator heating surfaces 8, 10, which are connected in series for the flow of a flow medium W, D.

The multistage evaporator system formed from the evaporator pass-through heating surfaces 8, 10 can be acted upon by unevaporated flow medium W, which evaporates in a single pass through the evaporator pass-through heating surfaces 8, 10 and is discharged as vapor D after exit from the evaporator pass-through heating surface 8 and usually to the further Overheating superheater heating is supplied. The evaporator throughflow heating surfaces 8, 10 formed evaporator system is connected in the non-illustrated water-steam cycle of a steam turbine. In addition to this evaporator system are in the water-steam cycle of the steam turbine, a number of others, in FIG. 1 not shown heating surfaces connected, which are, for example, superheater, Medium-pressure evaporator, low-pressure evaporator and / or can act to preheater.

The evaporator Durchlaufheizfläche 8 of the steam generator 1 comprises in the manner of a tube bundle a plurality of parallel to flow through the flow medium W steam generator tubes 12. In each case a plurality of steam generator tubes 12 to form a so-called pipe layer in Heizgasrichtung x seen side by side, so that in FIG. 1 in each case only one of the juxtaposed steam generator tubes 12 a pipe layer is visible. The thus juxtaposed steam generator tubes 12 each an associated inlet header 14 upstream and a common outlet header 16 downstream of the flow medium side.

The evaporator pass-through heating surface 8 is designed such that it is suitable for feeding the steam generator tubes 12 with a comparatively low mass flow density, the steam generator tubes 12 having a natural circulation characteristic. In this natural circulation characteristic, a more heated steam generator tube 12 compared to another steam generator tube 12 of the same evaporator pass-through heating surface 8 has a higher throughput of the flow medium W compared to the other steam generator tube 12. To ensure this with particularly simple design means in a particularly reliable manner, the evaporator Durchlaufheizfläche 8 comprises two flow medium side connected in series segments. In the first segment, each steam generator tube 12 of the pass-through heating surface 8 comprises an approximately vertically arranged downpipe piece 20 which can be flowed through by the flow medium W. In the second segment, each steam generator tube 12 comprises a riser tube piece downstream of the downcomer 20, downstream of the downcomer 20 and downstream of the flow medium W 22nd

The riser piece 22 is connected to its associated downcomer piece 20 via an overflow piece 24.

Each steam generator tube 12 of the evaporator pass-through heating surface 8 has, as in FIG. 1 can be seen, a nearly U-shaped shape, wherein the legs of the U through the downpipe piece 20 and the riser pipe piece 22 and the connecting sheet through the overflow 24 are formed. In a steam generator tube 12 designed in this way, the geodetic pressure contribution of the flow medium W in the region of the downcomer piece 20-in contrast to the region of the riser piece 22-produces a flow-promoting and not a flow-inhibiting pressure contribution. In other words, the water column located in the downpipe piece 20 of the unvaporized flow medium W "pushes" the flow through the respective steam generator tube 12, instead of impeding it. As a result, the steam generator tube 12 as a whole has a comparatively low pressure loss.

In the approximately U-shaped construction, each steam generator tube 12 is suspended or fixed respectively in the inlet region of its downcomer piece 20 and in the exit region of its riser piece 22 in the manner of a hanging construction on the ceiling of the heating gas duct 6. The spatially lower ends of the respective downcomer piece 20 and the respective riser piece 22, which are interconnected by their overflow piece 24, however, are not directly spatially fixed to the heating gas duct 6. Length expansions of these segments of the steam generator tubes 12 are thus tolerable without risk of damage, the respective overflow 24 acts as a strain curve. This arrangement of the steam generator tubes 12 is thus mechanically very flexible and insensitive to thermal stresses occurring in relation to differential strains.

When steam generator 1 in horizontal construction and using the evaporator Durchlaufheizfläche 8 with substantially However, in general, U-shaped steam generator tubes 12 have vapor bubbles in the downcomer 20 of a steam generator tube 12. These vapor bubbles could ascend contrary to the flow direction of the flow medium W in the respective downpipe piece 20 and thus hinder the stability of the flow and also the reliable operation of the steam generator 1. To prevent this reliably, the steam generator 1 is designed for feeding the evaporator throughflow heating surface 8 with already partially evaporated flow medium W.

In this case, a supply of the flow medium D, W is provided in the evaporator Durchlaufheizfläche 8 such that the flow medium D, W in the downcomer piece 20 of the respective steam generator tube 12 has a flow rate of more than a predetermined minimum speed. This in turn is dimensioned such that due to the sufficiently high flow rate of the flow medium D, W in the respective downpipe piece 20, the steam bubbles present there reliably entrained in the flow direction of the flow medium D, W and transferred via the respective overflow piece 24 into the respective downstream riser piece 22. Compliance with a sufficiently high flow rate of the flow medium D, W in the downpipe pieces 20 of the steam generator tubes 12 is ensured by the fact that the supply of the flow medium D, W in the evaporator Durchlaufheizfläche 8 with a sufficiently high vapor content and / or with a For this purpose, a sufficiently high enthalpy is provided.

In order to enable the supply of the flow medium D, W with suitable parameters in the already partially vaporized state, the evaporator Durchlaufheizfläche 8 of the steam generator 1 is the flow medium side as further Durchlaufheizfläche the evaporator Durchlaufheizfläche 10 upstream. The evaporator continuous heating surface 10 is thus designed in the manner of a pre-evaporator, so that the evaporator system is formed by the further evaporator Durchlaufheizfläche 10 and this downstream of the flow medium side evaporator Durchlaufheizfläche 8. The provided in the manner of a pre-evaporator further evaporator Durchlaufheizfläche 10 is spatially arranged in the comparatively colder space region of the Heizgaskanals 6 and thus the heating gas side downstream of the evaporator Durchlaufheizfläche 8. On the other hand, the evaporator pass-through heating surface 8 is arranged in greater proximity to the inlet region of the heating gas duct 6 for the heating gas flowing out of the gas turbine and thus exposed to a comparatively strong heat input by the heating gas during operation.

The further evaporator passage heating surface 10 is in turn also formed by a number of parallel to the flow of the flow medium W steam generator tubes 30. The steam generator tubes 30 are aligned substantially vertically with their longitudinal axis and designed for a flow through the flow medium W from a lower inlet region to an upper outlet region, ie from bottom to top. In order to ensure a particularly high stability of the flow for the further evaporator continuous heating surface 10 in the manner of a self-stabilizing operating behavior, the evaporator Durchlaufheizfläche 10 is also designed such that a more compared to another steam generator tube 30 more heated steam generator tube 30 a compared to further steam generator tube 30 higher throughput of the flow medium W has.

In order according to the concept provided for by the evaporator Durchlaufheizfläche 8 and by this upstream of the flow medium side further evaporator Durchlaufheizfläche 10 evaporator system, namely in the design case, the input-side feeding the evaporator Durchlaufheizfläche 8 with partially pre-evaporated, a sufficiently high steam content and / or a sufficiently high enthalpy Flow medium D, W, the further evaporator Durchlaufheizfläche 10 is suitably dimensioned. In this case, in particular a suitable choice of material and a suitable dimensioning of the steam generator tubes 30, possibly also different from each other, but also a suitable positioning of the steam generator tubes 30 are taken into account relative to each other. Especially with regard to these parameters, the further evaporator Durchlaufheizfläche 10 is dimensioned such that in the operating case in the hereafter connected evaporator Durchlaufheizfläche 8 inflowing flow medium D, W requires a flow rate of more than the entrainment of existing in the respective downpipes 20 vapor bubbles Minimum speed has.

As has been found, the high operational safety designed according to the design is particularly achievable in that the heat absorption during operation is essentially distributed equally to the evaporator throughflow heating surface 8 and to the further evaporator throughflow heating surface 10. The evaporator Durchlaufheizflächen 8, 10 and these forming steam generator tubes 12, 30 are therefore dimensioned in the exemplary embodiment such that in the operation of the entire heat input into the evaporator Durchlaufheizfläche 8 forming steam generator tubes 12 in about the heat input into the further evaporator Durchlaufheizfläche 10th forming steam generator tubes 30 corresponds. Taking into account the mass flows occurring in the process, the further evaporator through-flow heating surface 10 has a number of steam generator tubes 30 suitably selected with regard to the number of steam generator tubes 12 of the throughflow heating surface 8 downstream of them.

The further evaporator Durchlaufheizfläche 10 forming steam generator tubes are designed for a flow through the flow medium W from bottom to top. In this case, the further evaporator continuous heating surface 10 in the manner of a Tube bundle a number of seen in Heizgasrichtung x successively arranged pipe layers 32, each of which is formed of a number of juxtaposed in Heizgasrichtung x steam generator tubes 30, and of which FIG. 1 in each case only one steam generator tube 30 is visible. The steam generator tubes 30 of each tube layer 32 are each preceded by a common inlet collector 34 aligned with its longitudinal direction substantially perpendicular to the heating gas direction x. The inlet collector 34 are connected to an in FIG. 1 only schematically indicated water supply system 36 is connected, which may include a distribution system for needs-based distribution of the influx of flow medium W to the inlet header 34.

On the output side and thus in an area above the heating gas channel 6, the steam generator tubes 30 forming the further evaporator passage heating surface 10 open into a number of associated outlet collectors 38. Each of the outlet collectors 38, substantially parallel to each other and juxtaposed, of which FIG. 1 only one is visible, is aligned with its longitudinal axis substantially parallel to the heating gas x direction. The number of outlet headers 38 is adapted to the number of steam generator tubes 30 in each tube layer 32.

Each outlet header 38 is an inlet header 14 of the further evaporator Durchlaufheizfläche 10 flow medium side downstream evaporator Durchlaufheizfläche 8 assigned. Due to the U-shaped configuration of the evaporator Durchlaufheizfläche 8 is the respective inlet header 14 as well as the respective outlet header 38 above the Heizgaskanals 6. The flow medium side series connection of the evaporator Durchlaufheizfläche 8 with the other evaporator Durchlaufheizfläche 10 is in a particularly simple manner possible by integrating each outlet header 38 with its respective inlet collector 14 into a structural unit 40. By the structural or structural unit 40 is an immediate overflow of the flow medium W from the other evaporator Durchlaufheizfläche 10 in the evaporator Durchlaufheizfläche 8 allows, without a comparatively complex distribution or connection system would be required.

As in FIG. 2 is shown in plan view in section, the steam generator tubes 30 are each two adjacent pipe layers 32 in a direction perpendicular to the Heizgasrichtung x seen offset from each other, so that there is a substantially diamond-shaped basic pattern with respect to the arrangement of the steam generator tubes 30. In this arrangement, the outlet headers 38, of which in FIG. 2 only one is shown, positioned such that in each outlet header 38 from each pipe layer 32 each a steam generator tube 30 opens. It can also be seen that each outlet header 38 is integrated with an associated inlet header 14 for the downstream of the evaporator Durchlaufheizfläche 10 evaporator continuous flow surface 8 to a structural unit 40.

FIG. 2 is further removed that the evaporator Durchlaufheizfläche 8 forming steam generator tubes 12 also form a number of x seen in Heizgasrichtung x consecutive pipe layers, the seen in Heizgasrichtung x first two pipe layers are formed from the riser pipe sections 22 of the steam generator tubes 12, the output side in the Outlet collector 16 for the vaporized flow medium D open. The next two pipe layers seen in the direction of heating gas x, however, are formed from the downpipe pieces 20 of the steam generator tubes 12, which are the input side connected to a respective associated inlet collector 14.

FIG. 3 shows in side view fragmentary the inlet region of the steam generator tubes 12 and the outlet region of the steam generator tubes 30 in the respectively associated Building unit 40, on the one hand the outlet header 38 for a number of the further evaporator Durchlaufheizfläche 10 forming steam generator tubes 30 and on the other hand the inlet header 14 for each two of the evaporator Durchlaufheizfläche 8 forming steam generator tubes 12 comprises. It is particularly clear from this representation that flow medium D, W flowing out of the steam generator tubes 30 and entering the outlet header 38 can flow over directly into the inlet header 14 assigned to the evaporator throughflow heating surface 8. When overflow of the flow medium D, W bounces this first against a bottom plate 42 of the inlet header 14 comprehensive structural unit 40. As a result of this impact is a turbulence and very intimate mixing of the flow medium D, W, before this from the inlet collector 14 into the downpipe pieces 20 of associated steam generator tubes 12 passes.

As shown in the illustration FIG. 3 In addition, it is particularly clear that designed as inlet header 14 for the steam generator tubes 12 end portion of the structural unit 40 is designed such that the outflow of the flow medium W in the steam generator tubes 12 for all steam generator tubes 12 from a single plane perpendicular to the longitudinal direction of the structural unit 40 out. In order to make this possible also for two steam generator tubes 12, which, with regard to their actual spatial positioning, are assigned to two different tube layers arranged one behind the other in the direction of the heating gas x, each steam generator tube 12 is assigned an overflow piece 46. In this case, each overflow piece 46 runs obliquely to the heating gas direction x and connects the upper region of the respective associated steam generator tube 12 with the respective outlet opening 48 of the inlet collector 14. By this arrangement, all the outlet openings 48 of the inlet collector 14 can be positioned in a common plane perpendicular to the cylinder axis of the structural unit 40 be so that already due to the symmetrical arrangement of the outlet openings 48 in relation to the flow path of the flow medium D, W a uniform distribution of the entering into the steam generator tubes 12 flow medium D, W is guaranteed.

To further clarify the pipe guides in the area of their entries or exits in or out of the structural unit 40 is in FIG. 4 a number of such structural units 40 shown in front view, wherein the in FIG. 2 is based on IV line section. It can be seen that the two in FIG. 4 Structural units 40 on the left, which are shown in the region of their end formed as inlet header 14 for the downstream steam generator tubes 12, are each connected via the overflow pieces 46 to the downstream downcomer pieces 20 of the steam generator tubes 12.

In comparison, the two are in FIG. 4 shown on the right structural units 40 each in the area of their outlet collector 38 for the steam generator tubes 30 of the further evaporator Durchlaufheizfläche 10 formed front portion. In this case, it can be seen that the steam generator tubes 30, which in each case lead one after the other from the tube layers 32 into the structural unit 40, are guided into the structural unit 40 in a simple angled manner.

The steam generator 1 after FIG. 1 and with the special designs according to the FIGS. 2 to 4 is designed for a particularly safe operation of the evaporator Durchlaufheizfläche 8. For this purpose, it is ensured during operation of the steam generator 1 that the substantially U-shaped evaporator continuous heating surface 8 is supplied with flow medium D, W at a flow rate of more than a predetermined minimum speed. This ensures that in the downpipe pieces 20 of the Durchlaufheizfläche 8 existing steam generator tubes entrained existing vapor bubbles and spent in the respective downstream riser 22 piece. In order to ensure a sufficiently high flow rate when flowing into the evaporator Durchlaufheizfläche 8 flow medium D, W, the feeding of the evaporator Durchlaufheizfläche 8 takes place using this upstream further evaporator Durchlaufheizfläche 10 such that the flowing into the evaporator Durchlaufheizfläche 8 flow medium D, W has a vapor content or an enthalpy of more than a predefinable minimum steam content or more than a predeterminable minimum enthalpy. To comply with this suitable operating parameters, the evaporator Durchlaufheizflächen 8.10 are designed or dimensioned such that in all operating points of the vapor content or the enthalpy of the flow medium D, W when entering the evaporator Durchlaufheizfläche 8 above suitably predetermined characteristics is, as example in the FIGS. 5a . 5b are shown.

The FIGS. 5a . 5b show in the manner of a family of curves with the operating pressure as a crowd parameter, the functional dependence of the at least to be set vapor content X _min and the minimum to be set enthalpy H _min as a function of the design selected mass flow density ṁ. Shown here is as a curve 70, the design criterion in each case for an operating pressure of p = 25 bar, whereas the curve 72 is provided in each case for an operating pressure of p = 100 bar.

For example, it can be seen from these curves that in partial load operation at a design mass flow density ṁ of 100 kg / m ² s and an intended operating pressure of p = 100 bar, it should be ensured that the vapor content X _min in the flow medium 8 flowing through the flow heating surface 8 has a value of should occupy at least 25%, preferably about 30%. In an alternative representation of this design criterion can also be provided that the enthalpy of the flow medium W flowing through the continuous heating surface 8 should have at least a value of H = 1750 kJ / kg under the above-mentioned operating conditions. With regard to their dimensioning, that is, for example, with regard to the type, number and design of the steam generator tubes 30 forming them, taking into account the thermal space available within the heating gas duct 6 for their spatial positioning, the heat supply to these boundary conditions is provided customized.

Claims (3)

1. Method for operating a steam generator (1) with a continuous heating panel (8) of the evaporator arranged in a heating gas channel (6) through which a heating gas (x) can flow in a more or less horizontal direction, which comprises a plurality of pipes of a steam generator (12) connected in parallel for the throughflow of a flow medium (W) which each have a more or less vertical down pipe (20) through which the flow medium (W) can flow in a downward direction and have a riser pipe (22) connected downstream with respect to the down pipe on the flow medium side and which is more or less vertical and through which the flow medium (W) can flow in an upward direction, wherein the continuous heating panel of the evaporator (8) is arranged in such a way that one pipe of the steam generator (12) which is hotter than the other pipe of the steam generator (12) of the same continuous heating panel of the evaporator (8) has a flow medium (W) rate which is higher than that of the other pipe of the steam generator (12), characterised in that the flow medium (W) of the continuous heating panel of the evaporator (8) is supplied in such a way that, in the part of the down pipe (20) of the respective pipe of the steam generator (12), it has a flow velocity of more than a predetermined minimum flow velocity.
2. Method according to claim 1 in which, as the minimum flow velocity, the flow velocity required for the entrainment of the steam bubbles generated in the relevant part of the down pipe (20) is predetermined.
3. Method according to claim 1 or 2, wherein the flow medium (W) is advantageously partially pre-evaporated before entering the continuous heating panel of the evaporator (8) in such a way that, on entering the continuous heating panel of the evaporator (8), it has a steam content and/or an enthalpy of more than one predetermined minimum steam content or a predetermined minimum enthalpy.

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