EP0977964B1 - Continuous-flow steam generator and method for starting same - Google Patents

Description

The invention relates to a once-through steam generator according to the preamble of claim 1. Such Steam generator is known from EP 0 308 728 A1.

In a once-through steam generator, the heating of a number of evaporator tubes, which together form the gas-tight peripheral wall of a combustion chamber, leads to complete evaporation of the flow medium in the evaporator tubes in one pass. After its evaporation, the flow medium - usually water - is supplied to the superheater tubes connected downstream of the evaporator tubes and overheated there. In contrast to a natural circulation steam generator, a continuous steam generator is not subject to any pressure limitation, so that live steam pressures far above the critical pressure of water (P _crit = 221 bar) - where there is only a slight difference in density between liquid-like and steam-like medium - are possible. A high live steam pressure promotes high thermal efficiency and thus low CO ₂ emissions from a fossil-fired power plant.

Such a continuous steam generator can be built in or be designed in a two-pass design. With a once-through steam generator Steam generator tubes are usually in the draft type to form the perimeter wall of one Throttle cable welded together gas-tight, the throttle cable is arranged vertically. The the surrounding wall of the throttle cable Forming steam generator tubes usually include both Evaporator tubes as well as these on the fluid side downstream superheater tubes. In a lower area the throttle cable is usually a combustion chamber with a number provided by burners for fossil fuel.

In a continuous steam generator in two-pass design are common also steam generator pipes to form the surrounding wall of a vertically arranged first gas train gastight welded together. This type is the first Throttle cable, however, on the hot gas side via a horizontal gas cable followed by a second vertically arranged throttle cable, the Surrounding wall also formed by steam generator tubes is, and that of the heating gas usually from top to bottom is flowed through. A continuous steam generator in two-pass design shows in comparison to a continuous steam generator in draft type usually has a lower height and differentiates differ from this in a number of design parameters.

For a continuous steam generator in two-pass design, these are the peripheral wall of the first gas train forming steam generator tubes usually designed as evaporator tubes, whereas Steam generator tubes designed as superheater tubes the peripheral wall of the second throttle cable and / or part of one Wall heating surface of the horizontal throttle cable. In other words: those assigned to the horizontal throttle cable and those to the second gas cable Steam generator tubes are those assigned to the first throttle cable Steam generator tubes usually on the flow medium side downstream. To this end, the first throttle cable assigned steam generator tubes on the output side into one of them common outlet collector, via a water-steam separator and over a number of in the horizontal throttle arranged heating surfaces an entry collector for the steam generator pipes assigned to the second throttle cable is.

In the continuous steam generator known from EP 0 308 728 A1 are a number of for the flow of a flow medium steam generator tubes connected in parallel with each other connected to an evaporator heating surface, the part is a peripheral wall of the first throttle cable. This leads to the steam generator tubes forming the evaporator heating surface on the output side in a common one, in a comparison lower to a lower edge of the horizontal throttle cable Outlet collector at a height.

With such an arrangement, in particular also with a warm start called after a comparatively short downtime before igniting the burner when Filling of steam generator tubes of the still warm continuous steam generator with cold feed water considerable temperature differences between those assigned to the first throttle cable Steam generator tubes and a peripheral wall of the horizontal train assigned steam generator pipes occur. such Temperature differences can in particular at a connection point, on the one peripheral wall of the first throttle cable is welded to a wall of the horizontal train, impermissible Cause heat stress. Because of such thermal stresses is, especially with frequent starts, the life of such a continuous steam generator as a result high alternating loads only limited. The thermal stresses occur particularly after a short The continuous steam generator comes to a standstill, for example after a night standstill, because then the continuous steam generator usually one compared to temperature of the feed water has an elevated temperature.

A continuous steam generator is shown in FIG. 2 in US Pat. No. 2,982,267 shown, in which a first evaporator pipe in lower part of the first throttle cable on the flow medium side Type bulkhead heating surface immediately downstream and in one Space within the first throttle cable above one Combustion chamber is arranged. However, this heating surface is a combination of evaporator heating surface and superheater heating surface and only the evaporator part is the water-steam separator downstream.

The invention is therefore based on the object in To specify the two-pass type of continuous steam generator, which is particularly long even with frequent starting operations Has lifespan. In addition, a particularly inexpensive method is said to start up such a once-through steam generator can be specified.

Regarding a once-through steam generator of the type mentioned above This object is achieved in that the Outlet collector, a bulkhead heating surface on the flow medium side is immediately connected, the bulkhead heating surface in a space within the first throttle cable above one Combustion chamber is arranged and the bulkhead heating surface a water-steam separation device on the flow medium side is connected downstream.

Under the bulkhead heating surface there is a number of for the Flow of the flow medium connected in parallel, in one common entry and exit collector to understand opening steam generator tubes, wherein the steam generator tubes close together in one plane lie and thus a number of plate-like heating surfaces form, which are suspended within the throttle cable.

The invention is based on the consideration that for a particularly long lifespan of the once-through steam generator too in the case of frequent starting operations, the thermal tensions between the Boundary wall of the first throttle cable and the walls of the horizontal throttle cable should be kept particularly low. To the temperature differences between the immediately before starting the burner, fill it with cold feed water, the steam generator tubes assigned to the first throttle cable and the with a warm start still relatively hot walls of the Horizontal throttle cable must be kept particularly low.

For this purpose, on the one hand, the outlet manifold is the one of the first gas train assigned steam generator tubes in such a dimensioned Height arranged that a direct contact of the front steam generator tubes filled with cold feed water with the walls of the horizontal throttle cable still hot during a warm start is avoided. On the other hand, for one particularly effective cooling of the horizontal throttle cable Steam generator pipes already during start-up Heating surfaces provided for steam generation are particularly large dimensioned. For this is the one that forms the evaporator heating surface Steam generator pipes as additional to steam generation provided heating surface downstream of the bulkhead heating surface.

The bulkhead heating surface is within a room area of the first throttle cable above that provided in the first gas cable Combustion chamber arranged. The bulkhead heating surface is therefore in one especially when starting up the continuous steam generator highly heated room area arranged and contributes in particular to a large extent for steam generation. Thus, too a large one when the continuous steam generator is started up Amount of steam generated, which leads to a particularly effective cooling of the steam generator tubes provided as evaporator tubes downstream steam generator tubes designed as superheater tubes contributes.

For particularly low thermal stresses between the wall heating surfaces of the first gas train and the wall heating surfaces of the horizontal gas train is in a room area above that in the first Throttle cable arranged burner and below the lower edge the throttle cable advantageously an approximately horizontal Dividing line between when filled with water and provided with steam-filled steam generator pipes when starting up. This dividing line can be designed in this way be that the thermal stresses occurring at this point are kept particularly low. A meeting of the Start-up of differently cooled heating surfaces in the transition area from the first throttle cable to the horizontal throttle cable thus safely avoided.

For this purpose, one that evaporates during operation Flow medium through which the evaporator tubes flow evaporated flow medium through superheater tubes decoupling water-steam separator on the fluid side downstream of the bulkhead heating surface.

Advantageous embodiments of the invention are the subject of subclaims.

In a further advantageous embodiment, a steam-side one Outlet of the water-steam separator to an inlet header for a number of others designed as superheater tubes Steam generator pipes connected, these steam generator pipes the upper part of the perimeter wall of the first Form the throttle cable, and this inlet collector in one lower compared to the lower edge of the horizontal throttle cable Height is arranged.

Regarding the method for starting such a once-through steam generator in two-pass design, the task mentioned solved by after the onset of water the steam generator tubes forming the evaporator heating surface whose flow medium flow rate is temporarily reduced becomes.

When a continuous steam generator is started up, a Part of the non-evaporated contained in the evaporator tubes Fluid or water replaced by steam. This Process takes place during start-up and leads to a briefly increased flow medium throughput at the outlet of the Evaporator tubes, also known as water emissions. The water output must usually from the continuous steam generator are dissipated and therefore cause heat loss for the continuous steam generator.

In a particularly favorable method for starting a Pass-through steam generator should therefore especially the water output be kept low. This is for the one shown above Continuous steam generator can be reached by before igniting the burner is assigned to the peripheral wall of the first throttle cable Steam generator pipes first up to a height of downstream outlet collector with unevaporated Flow medium to be filled. Excess unevaporated Fluid or water can be bypassed Bulkhead heating surface via a bypass valve directly to the water-steam separator be directed. With the ignition of the The burner becomes the steam generator tubes designed as evaporator tubes initially an initial mass flow of flow medium or feed water supplied. The flow medium evaporates in the steam generator tubes opening into the outlet header partially, the non-evaporated flow medium into the bulkhead heating surface downstream of the outlet header arrives. Since this is also used as an evaporator heating surface designed and can thus be fed with unevaporated flow medium the undevaporated flow medium can get there evaporated there without harmful effects become. Adequate cooling of all steam generator tubes is guaranteed, the feed water mass flow for a particularly low water output use of water output temporarily reduced becomes.

The flow medium throughput is advantageously achieved by the steam generator tubes forming the evaporator heating surface after its lowering proportional to the heat output of the Continuous steam generator set.

The advantages achieved with the invention are in particular in that by at a height between the first Accelerator cable assigned burners and the lower edge of the horizontal throttle cable arranged outlet collector of the evaporator heating surface an almost horizontal dividing line between the Start-up with water-filled steam generator tubes and with Steam-filled steam generator tubes in one to avoid them created particularly favorable area of thermal stresses is. The occurrence of thermal stress in the transition area from the first accelerator cable to the horizontal accelerator cable safely avoided, so that the once-through steam generator is a special long service life even with frequent starts having. The bulkhead heating surface also ensures that when starting, a sufficiently large evaporator heating surface is available to a particularly high Generate steam mass flow and thus safe cooling to ensure all steam generator tubes. Through the bulkhead heating surface is also a temporary storage for Unevaporated ejected from the evaporator heating surface when starting up Flow medium created. That in the bulkhead heating surface came unevaporated flow medium evaporated there so that the from the continuous steam generator when starting up amount of water to be discharged due to the water output especially is low.

FIG 1

schematisch einen Durchlaufdampferzeuger in Zweizugbauart,

FIG 2

einen Ausschnitt aus einer Umfassungswand des Durchlaufdampferzeugers nach Figur 1, und

FIG 3

einen Eintrittssammler und einen Austrittssammler des Durchlaufdampferzeugers nach Figur 1.

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

FIG. 1

schematically a continuous steam generator in two-pass design,

FIG 2

a section of a peripheral wall of the once-through steam generator according to Figure 1, and

FIG 3

an inlet header and an outlet header of the continuous steam generator according to Figure 1.

The same parts have the same reference symbols in all the figures Mistake.

The continuous steam generator according to Figure 1 comprises a number of burners 2 for a fossil fuel, which are shown in FIG are shown schematically based on their main axes. The Burners 2 are arranged in a combustion chamber 4, through a lower part of the peripheral wall 6 of a vertically arranged first throttle cable 8 is formed. The surrounding wall 6 goes at the lower end of the first throttle cable 8 formed by it into a funnel-shaped bottom 10.

The continuous steam generator 1 according to FIG. 1 is of the two-pass type executed. For this purpose, the first throttle cable 8 is for combustion of the fossil fuel fuel gas a horizontal throttle cable 12 is followed by a second throttle cable 14. The second throttle cable 14 is also arranged vertically.

The peripheral wall 6 of the first throttle cable 8 is made of steam generator tubes 16.17 built that gas-tight on its long sides connected to each other, for example welded. In The surrounding wall 18 of the second throttle cable is of an analog design 14 also from steam generator tubes, not shown built up on their long sides gastight with each other are connected. The horizontal throttle cable 12 in turn comprises a number of steam generator tubes, not shown, to the surrounding wall, which is also gastight arranged heating surfaces 20 are combined. As shown in Figure 1, are the surrounding wall 6 of the first gas train 8 forming steam generator tubes 16, 17 vertically arranged. Alternatively, the steam generator tubes 16, 17 but also rising obliquely in the manner of a screw winding be arranged around the first throttle cable.

The surrounding wall 6 of the first in a lower area Accelerator cable 8 forming steam generator tubes 16 are used as evaporator tubes designed and to a number of evaporator heating surfaces 22 summarized, each part of the perimeter wall 6 of the first throttle cable 8. The steam generator pipes 16 of each evaporator heating surface 22 are for the flow of Water connected as a flow medium in parallel and are with their entry ends to a common, not shown Entry collectors and with their exit ends to a common one Outlet collector 24 connected.

The outlet header 24 is one on the flow medium side Bulkhead heating surface 26 connected. The bulkhead heating surface 26 is from a number of, not shown, for the flow of the flow medium connected in parallel Steam generator tubes built, the input side to one common entrance collector 28 and on the exit side to one common outlet collector 30 are connected. The the Bulb heating surface 26 forming steam generator tubes are tight arranged side by side in a plane and form a number of plate-like heating surfaces within the first throttle cable 8 or the horizontal throttle cable 12 suspended are.

The bulkhead heating surface 26 is a water-steam separation device on the flow medium side 34 downstream, the steam side Outlet 36 to an inlet header 38 for a number further, only indicated in Figure 1 for a better overview Steam generator tubes 17 is connected. The others Steam generator tubes 17 are designed as superheater tubes and to a number of superheater heating surfaces, not shown summarized the 32 in the upper room Form the peripheral wall 6 of the first throttle cable 8. In the flow path between the outlet header 24 and the water-steam separator 34 is bypassing the bulkhead heating surface 26 also one that can be shut off with a bypass valve 40 Bypass line 42 switched.

As shown in Figure 2, the steam generator tubes 16,17 in an area at the level of the outlet collector 24 and the Entry collector 38 in a toothed arrangement in the surrounding wall 6 of the first throttle cable 8 is mounted. For that are the in the lower area the surrounding wall 6 of the first throttle cable 8 forming steam generator tubes 16 in two groups of Steam generator tubes 16a and 16b combined, the a larger group assigned to the first group Have length than that assigned to the second group Steam generator tubes 16b. The same applies in the upper room area the surrounding wall 6 of the first throttle cable 8 forming steam generator tubes 17 in two groups of steam generator tubes 17a and 17b, with those assigned to the first group Steam generator tubes 17a have a greater length than the steam generator tubes 17b assigned to the second group.

Each of the comparatively shorter steam generator tubes 17b is above a comparatively longer one Steam generator tube 16a arranged, each of the comparatively longer steam generator tubes 17a above each a comparatively shorter steam generator tube 16b is. As shown in Figure 3, both open out comparatively shorter steam generator tubes 16b as well comparatively longer steam generator tubes 16a in the outlet header 24, being for the comparatively longer Steam generator pipes 16a each have a feed pipe section 16c is provided. Both the comparatively shorter ones are analogous Steam generator tubes 17a as well as the comparatively longer ones Steam generator tubes 17b connected to the inlet header 38.

Due to the interlocking arrangement of the steam generator tubes 16.17 in the area of the outlet collector 24 and the inlet collector 38 is also with different heating and / or different cooling of the steam generator tubes 16 in comparison to the other steam generator tubes 17, a temperature equalization guaranteed. The thermal stresses that occur are therefore kept particularly low.

As can be seen from Figure 1, the other steam generator tubes 17 on the flow medium side in the horizontal gas flue 12 arranged heating surfaces 20 the surrounding wall 18 of the second throttle cable 14 forming steam generator tubes downstream. Both the heating surfaces 20 of the horizontal throttle cable 12 forming steam generator tubes as well as the surrounding wall 18 of the second throttle cable 14 forming steam generator tubes are intended as superheater tubes and with regard to their interpretation depending on the location of their arrangement Adjusted heating gas and flow medium parameters.

The outlet manifold 24, in which the evaporator heating surface 22 forming steam generator tubes 16 lead into one in Comparison to a lower edge 44 of the horizontal throttle cable 12 lower height. The one as superheater tubes trained further steam generator tubes 17 upstream together Entry collector 38, on the other hand, is at a height between the outlet header 24 and the lower edge 44 of the Horizontal throttle cable arranged, that is in a compared to Outlet collector 24 larger and compared to the lower edge 44 of the horizontal throttle cable 12 lower height. Alternatively, you can the entry collector 38 but also in a compared to the Outlet collector 24 can be arranged at a lower height.

To start the continuous steam generator 1 are before Ignite the burner 2 assigned to the first throttle cable 8 in steam generator tubes forming the surrounding wall 6 16 initially up to the level of the downstream Outlet collector 24 with unevaporated flow medium, so filled with water. The bypass valve 40 is in this Operating status open. When the burner 2 is ignited the steam generator tubes 16 designed as evaporator tubes initially an initial mass flow of feed water is supplied. The feed water that is supplied evaporates in the outlet collector 24 partially emitting steam generator tubes, the unevaporated rest of the feed water into the Outlet collector 24 downstream bulkhead heating surface 26 arrives. This is also designed as an evaporator heating surface and thus without harmful effects with undevaporated Feed water feedable. The unevaporated rest of the feed water is thus largely evaporated in the bulkhead heating surface 26. Part of the exiting from the outlet header 24 Mass flow can, if necessary, via the bypass line 42 be fed directly to the water-steam separator 34.

Because of the in addition to the as evaporator tubes designed steam generator tubes 16 as an evaporator heating surface The bulkhead heating surface 26 provided is the total for steam generation available heating surface is therefore special large. Adequate steam production for safe cooling all downstream of the water-steam separation device 34, Steam generator tubes designed as superheater tubes is thus even when only a small mass flow is supplied Feed water guaranteed.

In order to avoid the exit from the bulkhead heating surface 26 during start-up, the rest of the unevaporated water discharge To keep feed water particularly low, that will Steam generator tubes 16 supplied mass flow of feed water thereby in an initial phase of the start-up process from an initial value starting with temporarily reduced initially. To its lowering is fed to the steam generator tubes 16 Mass flow of feed water proportional to the heat output of the continuous steam generator 1 set.

Due to the height between those assigned to the first throttle cable 8 Burners 2 and the lower edge 44 of the horizontal throttle cable 12 arranged outlet manifold 24 of the evaporator heating surface 22 is an approximately horizontal dividing line between the steam generator tubes 16 filled with water when starting up and the steam generator tubes 17 filled with steam. Thermal stresses between adjacent wall parts of the Throttle cables 8, 12, 14 can therefore mainly in the vicinity of this horizontal dividing line occur by the outlet header 24 and defined by the entry collector 38 is. The occurrence of thermal stress in a transition area from the first throttle cable 8 to the horizontal throttle cable 12 safely avoided so that the once-through steam generator 1 a particularly long lifespan even with frequent starts having. In addition, due to the interlocking arrangement the steam generator tubes 16, 17 in the area of the outlet header 24 and the entry collector 38 even with different Heating and / or different cooling of the steam generator tubes 16 compared to the other steam generator tubes 17 ensures a uniform temperature. The occurring Thermal stresses are therefore kept particularly low.

The bulkhead heating surface 26 also ensures that when starting up a sufficiently large evaporator heating surface Is available to ensure safe cooling of the steam generator tubes 16 downstream of the flow medium, steam generator tubes designed as superheater tubes 17 to ensure. Through the bulkhead heating surface 26 is above also a buffer for when starting off the evaporated heating surface 22 expelled undevaporated flow medium created. That got into the bulkhead heating surface 26 undevaporated flow medium evaporates there, so that the water output of the once-through steam generator 1 when starting up and the associated heat loss is particularly low.

Claims (4)

1. Once-through steam generator (1), with a first gas flue (8) which is followed on the fuel-gas side, by way of a horizontal gas flue (12), by a second gas flue (14), a number of steam generator tubes (16) connected in parallel for a flow medium to flow through them being connected to one another to form a gas-tight evaporator heating surface (22) which is part of a containing wall (6) of the first gas flue (8), and the steam generator tubes (16) which form the evaporator heating surface (22) opening on the outlet side into an outlet header (24) which is common to them and which is arranged at a lower height in comparison with the bottom edge (44) of the horizontal gas flue (12), characterized in that the outlet header (24) is followed directly, on the flow-medium side, by a bulkhead heating surface (26), the bulkhead heating surface (26) being arranged in a region of space (32) within the first gas flue (8) above a combustion chamber (4), and the bulkhead heating surface (26) being followed, on the flow-medium side, by a water/steam separating device (34).
2. Once-through steam generator (1) according to Claim 3, in which a steam-side outlet (36) of the water/steam separating device (34) is connected to an inlet header (38) for a number of further steam generator tubes (17) guided in the containing wall (6) of the first gas flue (8), the said inlet header being arranged at a lower height in comparison with the bottom edge (44) of the horizontal gas flue (12).
3. Method for starting up a once-through steam generator (1) according to either of Claims 1 and 2, in which the flow-medium throughput of the steam generator tubes (16) forming the evaporator heating surface (22) is temporarily reduced after the commencement of an ejection of water from the said tubes.
4. Method according to Claim 5, in which, after being reduced, the flow-medium throughput through the steam generator tubes (16) forming the evaporator heating surface (22) is set in proportion to the firing heat capacity of the once-through steam generator (1).

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