EP2564117B1 - Steam generator - Google Patents

Description

The invention relates to a forced once-through steam generator with a combustion chamber with a surrounding at least partially made of gas-tight welded steam generator tubes Umfassungswand, wherein within the combustion chamber at least two at least partially formed of further steam generator tubes inner walls are arranged, which are connected in series flow medium side via an intermediate collector. Steam generators with steam generator tubes are for example from the EP 0 320 403 A1 . EP 0 561 220 A1 . CN 1 061 653 A . US Pat. No. 6,675,747 B1 and EP 0 064 092 A1 known.

A steam generator is a closed, heated vessel or piping system designed to produce high pressure, high temperature steam for heating and service purposes (eg, for operation of a steam turbine). At particularly high steam outputs and pressures such as in power generation in power plants water tube boilers are used, in which the flow medium - usually water - is located in steam generator tubes. Also in the solid combustion water tube boilers are used, since the combustion chamber, in which the heat is generated by combustion of the respective raw material, can be arbitrarily designed by the arrangement of pipe walls.

Such a steam generator in the design of a water tube boiler thus comprises a combustion chamber, the surrounding wall is at least partially formed of tube walls, ie gas-tight welded steam generator tubes. On the flow medium side, these steam generator tubes initially form an evaporator, into which the unevaporated medium is introduced and evaporated. The evaporator is usually arranged in the hottest region of the combustion chamber. He is downstream of the flow medium, if necessary, a device for separating water and steam and a superheater, in the steam is further heated above its evaporation temperature to be used in a following heat engine such. B. a steam turbine to achieve high efficiency. The evaporator can be preceded by a preheating device (so-called economizer) on the flow medium side, which preheats the feed water by utilizing waste or residual heat and thus likewise increases the efficiency of the overall system.

Depending on the design and geometry of the steam generator further steam generator tubes can be arranged within the combustion chamber. These can be summarized or welded to an inner wall, for example. Depending on the desired arrangement of steam generator tubes or inner walls within the combustion chamber, it may be necessary to interconnect interior walls on the flow medium side in succession and to connect their steam generator tubes via an intermediate collector. In the intermediate collector, the medium flow from the upstream inner wall combines and it serves as an inlet header for the downstream inner wall.

In certain operating conditions, however, it may already come in the intermediate collector to a vapor content greater than zero. With such a vapor content, a uniform distribution of the medium to the downstream inner wall with a simple collector is not possible, so that water-steam segregation can occur. Individual pipes of the downstream inner wall can thus already have such high vapor contents or enthalpies at their inlet that overheating of these pipes is very likely. Such overheating can lead to pipe damage during prolonged operation.

The object of the invention is therefore to provide a forced flow steam generator, which allow a particularly long service life and a particularly low repair requirements of the steam generator.

This object is achieved by the features of independent claim 1. In this case, the flow medium at an inlet of the intermediate collector upstream Inner wall at a lower temperature than the flow medium at an entrance of the enclosure wall.

The invention is based on the consideration that a particularly long service life and a particularly low repair susceptibility of a steam generator could be achieved by avoiding overheating of the steam generator tubes by excessively high vapor contents or enthalpies. In this case, these high levels of steam occur in particular by the fact that in intermediate collectors already teilverdampftes flow medium is distributed unevenly to the downstream steam generator tubes. This unequal distribution should therefore be prevented by avoiding a two-phase mixture of water and steam in the intermediate collector. This would be achievable by keeping the inner walls upstream of the intermediate collector untouched, so that the medium undercooled and enters the intermediate collector without further preheating. However, this solution has constructive disadvantages. Therefore, rather, the temperature of the flow medium should be reduced at the entrance to the steam generator.

However, a reduction in the inlet temperature of the flow medium leads to a lower efficiency of the steam process. This is not desirable, moreover, such reduction in less heated steam generator tubes or pipe walls without intermediate collector - especially in the Umfassungswänden the steam generator - not necessary. Therefore, in these steam generator tubes to improve the efficiency no reduction of the inlet temperature should take place. This can be achieved by the flow medium at an inlet of the intermediate collector upstream inner wall has a lower temperature than the flow medium at an entrance of the enclosure wall.

The combustion chamber of the steam generator advantageously has a fluidized-bed firing device. The firing takes place in a fluidized bed of crushed, solid fuel and hot combustion air. The fuel will suspended above the nozzle bed and fluidized. The shredded fuel particles have a large surface area, so that a good burnout can take place. The strong turbulent flow results in a very good momentum and heat exchange, so that a uniform temperature prevails in the fluidized bed. In fluidized bed combustion very low nitrogen oxide emissions can be maintained.

In comparatively large-scale steam generators with fluidized bed combustion, the flow inlet-side lower combustion zone should be divided into two. By such a "pant-leg" design, a better mixing of the fuel mixture and thus lower possible distribution problems are achieved.

Therefore, the intermediate collector in a further advantageous embodiment, two upstream in the combustion chamber symmetrically arranged, at least partially formed from further steam generator tubes inner walls upstream of the flow medium side. In such steam generators in the pant-leg design an intermediate collector is required at the transition to the upper combustion zone, so that in particular here the described problems of uneven redistribution occur particularly strongly. Lower temperatures at the entrances of the intermediate collector upstream inner walls are therefore of particular advantage here.

In particular, fluidized bed boiler with pant leg design have been often performed as a drum boiler, ie the heated medium is separated at the outlet of the evaporator in a water-steam drum in water and vapor content. In such steam generators, the problem mentioned at the outset takes a back seat due to the higher medium flow. However, the embodiment described above also allows a design as a forced flow boiler, which brings several advantages: forced flow steam generators can be used for both subcritical and supercritical pressure without changing the process technology. Only the wall thicknesses The pipes and collectors must be dimensioned according to the intended pressure. Thus, the continuous flow principle meets the globally recognizable trend towards increasing efficiencies by increasing the steam conditions. Furthermore, an operation of the entire system in sliding pressure is possible. In sliding pressure mode, the temperatures in the high-pressure section of the turbine remain constant over the entire load range. Due to the large dimensions in terms of diameter and wall thickness of the component, the turbine is much more heavily loaded than the boiler components. This results in Gleitdruckbetrieb advantages in terms of load change speeds, number of load changes and starts. Advantageously, the steam generator is therefore designed as a forced flow boiler.

To improve the efficiency or to optimize the Heizflächenanordnung the entrances of the perimeter walls and the inner walls of a steam generator upstream of a preheater, a so-called economizer. This uses waste heat to preheat the flow medium. Due to the lower exhaust gas temperature generated by the use of waste heat so a higher overall efficiency of the steam generator is achieved. A particularly simple construction of a steam generator is therefore possible by the different temperature at the inner wall and the peripheral wall of the steam generator is achieved by structural measures on the preheater, d. H. by providing media with different degrees of preheating. For this purpose, the preheating device is designed such that for the entry of the intermediate collector upstream inner wall certain flow medium undergoes a lower heat input than the specific for the entrance of the enclosure wall flow medium. For this purpose, the preheating may comprise a plurality of preheaters, which are connected accordingly.

In an advantageous embodiment, a bypass line branches off before the flow medium-side inlet of a preheater, which leads into the inlet of an intermediate collector upstream inner wall or the intermediate collector upstream inner walls opens. As a result, a bypass of the preheater of the preheating device is achieved in a structurally simple manner and thus achieves a lower heat input into the bridged part of the flow medium. The bridged part of the flow medium can then be mixed with a part of the unbridged part in the desired amount and it is thus achieved a particularly simple reduction in the temperature of the inner walls supplied flow medium.

Advantageously, the bypass line comprises a flow control valve. In this way, the amount of the branched flow medium is particularly easy to adjust during operation and it is a simple temperature control allows.

In a further advantageous embodiment, the inlet of the inner wall or the inner walls flow medium side, a first preheater upstream and upstream of the entrance of Umfassungswand flow medium side, a second preheater, wherein the first preheater has a lower heat input than the second preheater. This embodiment with two preheaters connected in parallel makes it possible to control the temperature of the flow medium for the inner walls or the perimeter wall separately by appropriate design of the two preheaters.

In a further advantageous embodiment, the inlets of the inner wall or the inner walls and the inlet of Umfassungswand flow medium side, a first preheater upstream and the entrance of Umfassungswand flow medium side is connected in series to the first preheater, a second preheater. In this way, the entire flow medium first flows through a first preheater before dividing the flow medium to produce the different temperatures. While a part of the flow medium is supplied to the inlet of the inner walls, is another part fed to another preheater and then the Umfassungswand.

The advantages achieved by the invention are in particular that the problem of water-steam segregation in the intermediate collector is reliably avoided by the use of two media with different degrees of supercooling for feeding the various evaporator parts (enclosing walls and inner walls). In contrast to a solution with reduced enthalpy of entry for all evaporator parts, the evaporator does not have to be increased or only slightly enlarged in order to ensure a sufficiently high outlet enthalpy at the evaporator. In this case, the special design of the preheater shows structurally particularly simple ways to provide feedwater with different degrees of subcooling available. Overall, a particularly high life of the steam generator is achieved at the same time high efficiency.

• FIG 1 schematisch den unteren Teil der Brennkammer eines Zwangdurchlaufdampferzeugers mit Wirbelschichtfeuerung mit teilweise überbrückter Vorwärmeinrichtung,
• FIG 2 den Durchlaufdampferzeuger aus FIG 1 mit parallelen Vorwärmern, und
• FIG 3 den Durchlaufdampferzeuger aus FIG 1 mit seriellen Vorwärmern.

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

• FIG. 1 schematically the lower part of the combustion chamber of a forced once-through steam generator with fluidized bed combustion with partially bridged preheating device,
• FIG. 2 the continuous steam generator FIG. 1 with parallel preheaters, and
• FIG. 3 the continuous steam generator FIG. 1 with serial preheaters.

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

The steam generator 1 in a schematic representation according to the FIG. 1 is designed according to the invention as forced circulation steam generator. He includes several, formed from steam generator tubes and from bottom to top flowed through tube walls, Namely a perimeter wall 2 and symmetrically arranged, inclined aligned inner walls 4, which is connected via an intermediate collector 6 flow medium side, a further inner wall 8. The continuous steam generator 1 is thus designed in the so-called "pant-leg" design.

Through each of the enclosure wall 2 and the inner walls 4 associated entries 10, 12 occurs flow medium in the pipe walls. In the interior 14, a solid fuel is burned in the manner of a fluidized bed combustion and thus reaches a heat input into the tube walls, which causes heating and evaporation of the flow medium. If the medium now enters all tube walls with the same enthalpy, a high vapor content can already be created in the intermediate collector 6 such that an uneven distribution takes place on the tubes of the inner wall 8 and the tubes with high steam content overheat here.

In order to avoid the consequent disadvantages, such as, for example, a shorter service life or a higher susceptibility to repair, the flow medium fed to the intermediate collector 6 has a lower temperature than that supplied to the surrounding wall 2. In the steam generator 1, a preheating device 16 is provided, which ensures different heat inputs into the different medium flows.

The preheating device 16 after the FIG. 1 includes a preheater 18, the flow medium side, a branch point 20 is connected upstream. A portion of the flow medium is thus passed around the preheater 18 in a bypass line 22. In the flow-medium-side direction, the preheater 18 is initially followed by a further branching point 24, from which a line is led to the inlets 10 of the surrounding wall 2. A part of the preheated flow medium is thus supplied to the enclosure wall 2. One another part of the preheated flow medium is guided in a line which meets in a mixing point 26 with the bypass line 22. Here, a medium slightly lower temperature is achieved by the mixing of the medium streams, which then the inlets 12 of the inner walls 4 is supplied. By a flow control valve 28 in the bypass line 22 while the amount of bridged flow medium and thus the temperature of the inner walls 4 supplied flow medium can be easily controlled.

An alternative embodiment of the invention shows FIG. 2 , The steam generator 1 is here except for the preheater 16 for FIG. 1 identical. The preheating device 16 comprises at its flow-medium-side inlet a branch point 30 from which two lines lead into two preheaters 18, 32. The outlet of the preheater 18 is connected to the inlets 10 of the enclosure wall 2, while the preheater 32 is connected to the inlets 12 of the inner walls 4. The preheater 32 is now configured such that it has a lower heat input into the flow medium than the preheater 18. Thus, a lower temperature is achieved at the entrances 12 of the inner walls 4 than at the entrances 10 of the enclosure wall 2. By suitable design of the preheater 18th , 32 the temperature is adaptable to the desired boundary conditions.

A further embodiment of the invention is in FIG. 3 shown. Again, the steam generator 1 is up to the preheater 16 for FIG. 1 identical. The preheating device 16 comprises after its flow-medium-side inlet first a preheater 18, in which the entire flow medium is heated. Then branches off a bridging line 22, which opens into the inlets 12 of the inner walls 4. Another part of the flow medium is fed into a further, downstream preheater 32. Here it is further heated and then the Umfassungswand 4 performed. Due to the additional heating in the preheater 32, this medium has a higher temperature than that guided in the inner walls 4.

Claims (7)

1. Forced-flow steam generator (1) with a combustion chamber having a peripheral wall (2) formed at least partly from gas-proof, welded steam generator pipes, wherein at least two inner walls (4, 8) formed at least partly from additional steam generator pipes are arranged inside the combustion chamber, which are connected one behind the other on the flow medium side by an intermediate collector (6), wherein an economiser (16) is provided in the forced-flow steam generator (1), which ensures varying heat inputs into different flow mediums so that during operation of the forced-flow steam generator the flow medium has a lower temperature at an inlet (12) of the inner wall (4) connected upstream of the intermediate collector (6) than the flow medium at an inlet (10) of the peripheral wall (2), and wherein during operation of the force-flow steam generator the temperature of the flow medium at the inlet (12) of the inner wall (4) connected upstream of the intermediate collector (6) is reduced to such an extent that a two-phase mixture comprising water and vapour is prevented in the intermediate collector (6).
2. Steam generator (1) according to claim 1, in which the combustion chamber has a fluidised-bed firing device.
3. Steam generator (1) according to one of the previous claims, in which two inner walls (4) arranged symmetrically in the combustion chamber at least partly formed from the further steam generator pipes are connected upstream of the intermediate collector (6) on the flow medium side.
4. Steam generator (1) according to claim 1, in which a bridging line (22) branches off before the flow medium-side inlet of an economiser (18) which opens out into the inlet (12) of an inner wall (4) connected upstream of the intermediate collector (6) or the inner walls (4) connected upstream of the intermediate collector (6).
5. Steam generator (1) according to claim 4, in which the bridging line (22) includes a flow regulation valve (28).
6. Steam generator (1) according to claim 1, in which a first economiser (32) is connected upstream of the inlets (12) of the inner wall (4) or the inner walls (4) on the flow medium side and a second economiser (18) is connected upstream of the inlet (10) of the peripheral wall (2) on the flow medium side, wherein the first economiser (32) has a lower heat input than the second economiser (18).
7. Steam generator according to claim 1, in which a first economiser (18) is connected upstream of the inlets (12) of the inner wall (4) or the inner walls (4) and the inlet (10) of the peripheral wall (2) on the flow medium side and wherein a second economiser (32) is connected upstream of the inlet (10) of the peripheral wall (2) on the flow medium side in series with the first economiser (18).

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