WO2012062708A2

WO2012062708A2 - Fossil fueled steam generator

Info

Publication number: WO2012062708A2
Application number: PCT/EP2011/069558
Authority: WO
Inventors: Martin Effert; Frank Thomas
Original assignee: Siemens Aktiengesellschaft
Priority date: 2010-11-10
Filing date: 2011-11-07
Publication date: 2012-05-18
Also published as: DE102010043683A1; WO2012062708A3

Abstract

The invention relates to a fossil fueled steam generator (1) for a steam power plant having a plurality of economizer, evaporator, and superheater heating surfaces (10, 12, 14, 16, 18) that form a flow path (4) and through which a flow medium (M) flows, wherein an overflow line (30) is connected to the input side of the flow path (4) in a high-pressure stage (2), and leads to an injection valve (20, 22) disposed upstream of a superheater heating surface (16, 18) in the flow path (4) on the flow medium side in the high-pressure stage (2), wherein the efficiency of the steam process should not be unduly compromised. At the same time, a short-term power increase should be made possible regardless of the type of construction of the fossil fueled steam generator, without invasive constructive modifications to the overall system. To this end, the overflow line (30) has two infeed lines, wherein the first infeed line (32) branches off downstream of an economizer heating surface (10) on the flow medium side and the second infeed line (36) branches off upstream of the economizer heating surface (10) on the flow medium side.

Description

description

Fossil fired steam generator

The invention relates to a fossil-fueled steam generator for a steam power plant with a number of forming a flow, flowed through by a flow medium Ecom- mizer, evaporator and superheater heating, in which in a high-pressure stage, an overflow line is connected to the inlet side with the flow path and to a in the High-pressure stage flow medium side before a superheater heating in the flow path arranged injector leads. It also ^relates to a method for operating such a steam generator.

A fossil-fueled steam generator produces superheated steam using the heat generated by burning fossil fuels. Fossil fueled steam generators are mostly used in steam power plants, which are mainly used for power generation. The steam is supplied to a steam turbine ^¬ leads.

Analogous to the various pressure stages of a steam turbine, the fossil-fueled steam generator also comprises a plurality of pressure stages with different thermal states of the respectively contained water-steam mixture. In the first (high) pressure level, the flow medium passing through the flow path on its first economizer, use the residual heat to Vorwär ^¬ mung of the flow medium, and then various levels of dene ^¬ evaporator and superheater. In the evaporator, the flow medium is evaporated, then separated any residual moisture in a separator and further heated the remaining steam in the superheater. Thereafter, the superheated steam in the high pressure part of the steam turbine flows, is there decompressed, and the following print ^¬ stage of the steam generator is supplied. There it is again over ^¬ heated and fed to the next pressure part of the steam turbine. Due to a wide variety of external influences, the heat output transferred to the superheaters can fluctuate greatly. Therefore, it is often necessary to control the superheat temperature. Usually, this is achieved in the high-pressure stage as well as in the medium-pressure stages for reheating mostly by injection of feed water before or after individual Überhitzerheizflächen for cooling, ie, an overflow branches off from the main stream of the flow medium and leads to there correspondingly arranged injection valves, namely injection coolers. The injection is customarily controlled by the temperature deviation from a predetermined temperature setpoint at the outlet of the superheater ^¬ About the respective pressure stage.

Not only high efficiencies are required of modern power plants, but also a very flexible Betriebswei ^¬ se. This includes not only short start-up times and high load change speeds and the ability to compensate for frequency interference in the power grid. To meet these requirements, the power plant must be able to provide additional services such as 5% or more within we ^¬ niger seconds.

Such power changes of a power plant ^block in the se ^¬ customer area are possible only by a coordinated interaction of steam generator and steam turbine. The contribution of fossil fuel-fired steam generator can do this is by using his memory, ie the steam but also the fuel storage, as well as rapid changes in the controlling variable ^¬ SEN feedwater, injection water, fuel and air.

This can be done, for example, by opening partially angedros ^¬ selter turbine valves of the steam turbine or a so genann ^¬ th stage valve, thereby the vapor pressure is lowered in front of the steam turbine. Steam from the steam storage of the upstream fossil-fueled steam generator is thereby stored and fed to the steam turbine. With this Measure, an increase in performance is achieved within a few seconds.

A permanent throttling of the turbine valves for Vorhal ^¬ tion of a reserve, however, always leads to a loss ^¬ efficiency, so that for an economical driving the degree of throttling should be kept as low as absolutely necessary. In addition, some types of fossil-fueled steam generators, such. B. forced flow steam generator ^¬ ger under circumstances, a considerably smaller storage volume than z. B. natural circulation steam generator. The difference in the size of the memory in the method described above has an influence on the behavior of power plant block power changes.

It is therefore an object of the invention to provide a fossil-fired steam generator of the above type, in which the efficiency of the steam process is not impaired over ^¬ taken. At the same time short-term Leistungsstei ^¬ delay should fired regardless of the design of fossil

Steam generator without invasive structural modifications to the Ge ^¬ overall system are made possible.

This object is achieved according to the invention, by the transfer ^¬ strömleitung has two feed lines, wherein the first supply line branches off the flow medium side behind an economizer from ^¬ and the second supply line branches off the flow-medium side upstream of the economizer.

The invention is based on the consideration that injections of feedwater can make a further contribution to the rapid change in performance. By additional injections in the superheater namely the steam mass flow can be increased. In terms of control, injections are triggered by reducing the temperature setpoint at the outlet of the respective pressure stage. The higher the enthalpy level of the injection water, the more injection mass flow is needed to meet the newly demanded to reach the temperature setpoint. Thus, results from a higher Enthalpieniveau of the injection water, a ver ^¬ tively larger amount of steam.

Such an increase in enthalpy is possible by the water is not removed at the Economizereintritt, but only behind an economizer heating. Is reduced at a sol ^¬ chen interconnection of the temperature set point, this therefore has a comparatively large amount of steam and thus a greater power delivery result. It should be noted, however, that in the entire load range, the injection water has a sufficient distance to the boiling point of the steam and thus a satisfactory supercooling. Straight z. B. in the starting operation, it is quite possible in the lower load range that the enthalpy behind an economizer can be too large in view of the desired supercooling of Einspritzwas ^¬ sers and forms in the case of open injection fittings at the injection point may wet steam. This steam can block the injection valve in the worst case, so that the injection mass flow can not be maintained. Also, the pressure difference between sampling and injection point may be too low under certain circumstances.

This should be counteracted by controlling the enthalpy of the injection water as needed. This is he ^¬ reichbar by the withdrawn behind an economizer injection water is mixed with a small percentage of samples taken prior to injection point the injection of water, so that the desired enthalpy of the injection water can be adjusted in this way. For this purpose, two supply lines each lead from the flow medium side before and behind an economizer heating surface to the overflow line to the injection valve of the high-pressure stage. Thus, the injection water can be removed in front of the economizer during start-up and in circulation operation and switchover to the removal behind the economizer in load operation with frequency support. Advantageously, the first supply line branches off on the flow medium side behind all economizer heating surfaces. As a result, the greatest possible enthalpy for the injection water is ensured, so that an optimum with regard to the amount of steam and release of power is achieved. In a further advantageous embodiment, the second supply line branches off on the flow medium side from all economizer heating surfaces. By taking in the coldest region, a reduction in the temperature of the inlet can in fact already at low addition amount are injection medium reaches that sufficient Ab ^¬ was a guaranteed to boiling. Overall, the greatest possible temperature variance can be achieved by removing before and after all high-pressure preheaters.

In an advantageous embodiment, a check valve is arranged in the first supply line and arranged in the first and / or the second supply line, a flow control valve. This allows in a particularly simple manner, the adjustment of the injection quantity from each of the two supply lines, wherein the non-return valve prevents backflow of medium of lower temperature. Such a design made ^¬ light, a realization of the invention with particularly simple means.

In a further advantageous embodiment, a flow measuring device is arranged in the first supply line and in the flow path on the flow medium side between the branch of the first and the second supply line. Thus, the evaporator mass flow can be determined by subtraction in a particularly simple manner. In particular, in a forced once-through steam generator, the knowledge of the evaporator mass flow is necessary because in low-load operation, a minimum mass flow must be set.

In an advantageous embodiment, a steam power plant comprises such a fossil-fired steam generator. With regard to the method in which flow medium is removed from the flow path in a high-pressure stage and is arranged in the high-pressure stage upstream of a superheater ^heating surface in the flow path injection ^¬ valve, the object is achieved by depending on the operating condition of the steam generator flow medium with different enthalpy is removed. ^¬ advantage adhesive enough, is taken from the full load state flow medium with a higher enthalpy than in a partial load condition.

The advantages achieved by the invention are in particular that by the possibility of using injection water for high pressure superheating from supply lines before and after the economizer on the one hand always a sufficient supercooling of the injection water can be guaranteed even in low load operation, on the other hand with respect to Be ^¬ provision of immediate reserve With absolutely safe injection operation without vapor formation, a maximum of additional power release can be realized via a correspondingly increased injection quantity. Alternatively, the load of all the affected components such as injection point, heating surfaces and turbine can be reduced at the same power release compared to previous concepts, since for the same power release a lesser drop in temperature of the steam is expected.

In addition, the interconnection and the associated increase in the power deduction by using the injection system is independent of other measures, so that, for example, throttled turbine valves can be additionally opened to increase the power increase of the steam turbine yet. The effectiveness of the procedure remains largely unaffected by these parallel measures.

It should be emphasized that with a fixed requirement for additional power, the degree of throttling of the turbine valves can be reduced, the use of the injection system for the power increase should be used come. The desired performance release can then be achieved under these circumstances with less, in the best case even completely without additional throttling. Thus, the plant can be operated in the usual load operation, where it must be available for an immediate reserve, with a relatively greater efficiency, which also reduces the operating costs.

An embodiment of the invention will be described with reference to a

Drawing explained in more detail. Therein, the figure shows flow-medium side, schematic view of the high-pressure section of a ^{fossil-fueled} steam generator be optimized with Einspritzwasserzulei ^¬ processing.

From the fossil-fired steam generator 1, only the high pressure stage 2 is shown in the figure, which is connected upstream of the high pressure part of a steam turbine, not shown in detail. The steam generator 1 also includes other, not shown, pressure levels. The figure shows schematically a part of the flow path 4 of the flow medium M. The medium flow ^¬ M is initially fed through a feed pump 6 into the high-pressure stage 2 ^¬. There it is first brought from high ^¬ pressure preheaters 8 to an elevated temperature, which can be operated for example with bleed steam. This is followed by economizer 10, in which usually flue gas waste heat is used for further heating of the Strö ^¬ mung medium and evaporator heating surfaces 12, in which the flow medium M is evaporated using the heat produced from fossil fuel. The spatial Anord ^¬ voltage of the individual heating surfaces 10, 12 in the hot gas channel is not shown and may vary. The heating surfaces 10, 12 shown may each representative of a multi ^¬ number series-connected heating surfaces are provided, which are not shown differentiated on the basis of clarity.

After exiting the evaporator 12 is possibly existing residual moisture in a non-illustrated Water Separator (separator or drum) deposited and the remaining vapor of a first superheater 14, which are shown in the figure in the figure in the figure for simplicity with the evaporator heating surfaces 12 for simplicity. This is followed by further superheater heating surfaces 16, 18 and finally the overheated steam is expanded in the high-pressure section of a steam turbine. Subsequently, the Strö ^¬ mung medium M flows into the not shown medium-pressure part of the steam generator, where it heating surfaces in a number of reheater is superheated again and is then fed to the with ^¬ teldruckteil the steam turbine.

Before the two last superheater heating surfaces 16, 18, an injection valve 20, 22 is arranged in each case on the flow medium side. Here, cooler and unevaporated flow medium M to be injected to control the outlet temperature at the outlet 24 of the high-pressure stage 2 of the fossil fuel-fired steam generator 1, a ^¬. The amount of flow medium M inserted ^¬ brought into the injection valves 20, 22 is controlled via a respective single injection control valve 26, 28th The flow medium M is then fed through a previously branching in the flow path 4 About ^¬ strömleitung 30th

To use the injection system not only to control the outlet temperature, but also to provide an immediate power reserve, the injection system for a required, increasing the enthalpy of the water injection ^¬ is designed. For this purpose, the overflow line has a first supply line 32, which branches off behind all economizer heating surfaces 10, so that here flow medium M with comparatively higher temperature is introduced into the overflow line 30. Thereby, a considerable amount of steam increase is achieved at a comparatively larger ^¬ A injection and the performance of the downstream steam turbine increases. The flow of the first supply line 32 is controlled by a flow control valve 34. In order to ensure sufficient undercooling of the injection ^medium , especially in low-load operation or during start-up, the overflow line 30 has a second supply line 36 which branches off on the flow medium side between economizer heating surfaces 10 and high-pressure preheaters 8 and supplies flow medium M with a relatively low temperature to the overflow line 30. Thus, in these load conditions always sufficient subcooling of the injection medium ensures ^¬ who. The flow through the second supply line 36 is regulated by a flow control valve 38.

Furthermore, the first supply line 32 has a check valve 40, which reliably prevents a return flow of colder medium from the second supply line 36 into the region behind the economizer heating surfaces 10. A first flow measuring device 42 is located directly in front of the economizer heating surfaces 10, d. H. arranged after the branch of the second supply line 36; a second flow measuring device 44 is arranged in the first supply line 32. By difference formation, the flow through the evaporator heating surfaces 12 can thus be determined comparatively easily.

A equipped with such a fossil fuel-fired steam generator 1 steam power plant is able to provide a so ^¬ diate power delivery of the steam turbine fast an increase in power, which serves to support the composite frequency of the power system. Because it is power ^¬ reserve achieved by a double use of the injection valves in addition to the usual temperature control, a permanent throttling of the steam valves for providing ^¬ position a reserve can be reduced or eliminated, whereby a particularly high efficiency is achieved during normal operation.

Claims

claims

1. Fossil-fired steam generator (1) for a steam power plant with a number of a flow path (4) forming, flowed through by a flow medium M economizer, evaporator and superheater heating surfaces (10, 12, 14, 16, 18), wherein in a high-pressure stage (2), an overflow line (30) on the input side to the flow path (4) and to one in the high-pressure stage (2) the flow-medium side upstream of a superheater heating surface (16, 18) in the flow path (4), ^¬ arranged injection valve (20, 22) leads,

wherein the overflow line (30) has two supply lines, wherein the first supply line (32) branches off downstream of an economizer heating surface (10) and the second supply line (36) branches off in front of the economizer heating surface (10) on the flow medium side.

2. Fossil-fired steam generator (1) according to claim 1, wherein the first supply line (32) branches off on the flow medium side behind all economizer heating surfaces (10).

3. Fossil-fired steam generator (1) according to one of the preceding claims, in which the second feed line (36) branches off on the flow medium side in front of all economizer heating surfaces (10).

4. Fossil-fired steam generator (1) according to one of the preceding claims, wherein in the first supply line (32) a non-return valve (40) is arranged.

5. Fossil-fired steam generator (1) according to one of the preceding claims, in which in the first and / or in the second supply line (32, 36) each have a flow control valve (34, 38) is arranged.

6. Fossil-fired steam generator (1) according to any one of the preceding claims, wherein in the first supply line (32) a flow meter (44) is arranged.

7. Fossil-fired steam generator (1) according to one of the preceding claims, wherein in the flow path (4) on the flow medium side between the branch of the first and the second supply line (32, 36) a flow measuring device (44) is arranged.

8. Steam power plant with a fossil-fired steam generator

(1) according to any one of the preceding claims.

9. A method for operating a fossil-fired steam generator (1) for a steam power plant with a number of a flow path (2) forming, flowed through by a flow medium M economizer, evaporator and superheater heating surfaces (10, 12, 14, 16, 18), in the case of a high-pressure stage

(2) flow medium is taken from the flow path (4) and is guided to an injection valve (20, 22) arranged in the high-pressure stage (2) in front of a superheater heating surface (16, 18) in the flow path (4);

depending on the operating state of the steam generator (1) flow medium M is taken with different enthalpy.

10. The method of claim 9, wherein in the full load condition flow medium M is removed with higher enthalpy than in a part-load condition.