EP2625390B1 - Fossil-fired steam generator - Google Patents

Description

The invention relates to a fossil-fired steam generator for a steam power plant with a number of flow path forming, flowed through by a flow medium M economizer, evaporator and superheater heating in a plurality of pressure stages, in which in a high-pressure stage an overflow line is connected on the input side to the flow path and leads to a flow medium in a middle-pressure stage upstream of a superheater heating in the flow path arranged injection valve.

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 fed to a steam turbine.

The publication DE19849740 discloses a fossil fired steam generator of the prior art.

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 stage, the flow medium first passes through economizers on its flow path, using residual heat to preheat the flow medium, and then various stages of evaporator and superheater heating surfaces. 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 flows into the high-pressure part of the steam turbine, where it is expanded and fed to the following pressure stage of the steam generator. There it is overheated again 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 usually 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. The injection is usually controlled by the temperature deviation from a predetermined temperature setpoint at the outlet of the superheater of the respective pressure stage.

Modern power plants not only require high levels of efficiency but also the most flexible mode of operation possible. Apart from short start-up times and high load change speeds, this also includes the possibility of compensating for frequency disturbances in the power grid. To meet these requirements, the power plant must be able to provide more power, for example, 5% and more within a few seconds.

Such power changes of a power plant block in the second range are possible only by a coordinated interaction of steam generator and steam turbine. The contribution that the fossil-fueled steam generator can make is the use of its storage, d. H. of the steam but also of the fuel storage, as well as rapid changes of the control variables feedwater, injection water, fuel and air.

This can be done, for example, by opening partially throttled turbine valves of the steam turbine or a so-called step valve, whereby 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.

However, a permanent throttling of the turbine valves to provide a reserve always leads to a loss of efficiency, so that for an economic 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 may have a significantly 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 excessively impaired. At the same time, the short-term increase in output should be possible without invasive structural modifications to the overall system, regardless of the design of the fossil-fueled steam generator.

This object is achieved according to the invention in that the overflow line has two supply lines, of which the first branches off the flow medium side from a high-pressure preheater and the second fluid side branches off behind the high-pressure preheater.

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 required Temperature setpoint to achieve. Accordingly, results from a higher enthalpy of the injection water a comparatively larger amount of steam.

Such an increase in enthalpy is possible by the water not at the feed pump itself, d. H. is removed before the high pressure preheaters, but only after a high pressure preheater. If the temperature setpoint is reduced in such an interconnection, this results in a comparatively larger amount of steam and thus a greater release of power. 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. Particularly in the case of reheating, it is entirely possible in the lower load range for the enthalpy behind a high-pressure preheater to be too large in view of the desired overcooling of the injection water and, under certain circumstances, wet steam to form in the case of open injection fittings at the injection point. This steam can block the injection valve in the worst case, so that the injection mass flow can not be maintained.

This should be counteracted by the enthalpy of the injection water can be controlled as needed. This can be achieved by mixing the injection water withdrawn behind a high-pressure preheater with a small proportion of injection water withdrawn before the high-pressure preheater, 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 a high-pressure preheater to the overflow line to the injection valve of the reheat.

Advantageously, the second supply line branches off from the flow medium side behind all high-pressure preheaters. 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 Design branches off the first supply fluid side from all high-pressure preheaters. Because of the removal in the coldest area, a reduction in the temperature of the injection medium can be achieved, even at a small admixing amount, which ensures a sufficient distance to the boiling line. 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 one of the supply lines and arranged in the other supply line, a flow control valve. The mixture is then in a particularly simple manner on the determination of the injection quantity on the one hand, which is adjusted by the injection control valve and is provided in part via the supply line with the check valve, the check valve prevents backflow from the high pressure path in the low pressure path. On the other hand, the admixing of the medium of the other temperature is controlled via the flow control valve of the other supply line.

In a particularly advantageous embodiment, a check valve is arranged in the first supply line and arranged in the second supply line, a flow control valve. That is, the check valve is located in the supply line with the medium of the lower temperature level. Advantageously, moreover, the first supply line branches off from a feed pump. Since under these circumstances, only upstream of the flow control valve, the flow medium has a relatively higher pressure, it is possible that the entire water path of the injector is at a relatively lower pressure level. In addition, such an arrangement simplifies the control, and it is furthermore possible to use the currently used feed pumps with a corresponding branch for the reheat injection, since even in the present case, the cool medium can be coupled in the same place.

In a further advantageous embodiment, a flow measuring device is arranged downstream of the branch of the second supply line in the flow path flow medium side. Under these circumstances, the withdrawal quantity need not be taken into account for the feedwater control via additional measurement or separate balancing.

In an advantageous embodiment, a steam power plant comprises such a fossil-fired steam generator.

The advantages achieved by the invention are, in particular, that a sufficient supercooling of the injection water can always be ensured by the mixing of injection water for reheating from leads before and after Hochdruckvorwärmern one hand, on the other hand with regard to the provision of an immediate reserve in absolutely safe injection operation without vapor formation a maximum can be realized on additional power relief 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, should the use of the injection system for increasing the power used. The desired benefit release can be among these Circumstances then even with less, in the best case, even without any additional throttling can be achieved. 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.

FIG 1

strömungsmediumsseitig schematisch den Hochdruck- und Mitteldruckteil eines fossil befeuerten Dampferzeugers mit optimierter Einspritzwasserzuleitung,

FIG 2

strömungsmediumsseitig schematisch den Hochdruck- und Mitteldruckteil eines fossil befeuerten Dampferzeugers mit Einspritzwasserzuleitung in alternativer Ausgestaltung,

FIG 3

ein Diagramm mit Simulationsergebnissen zur Verbesserung der Sofortreserve eines fossil befeuerten Dampferzeugers durch Erhöhung der Einspritzwasserenthalpie der Zwischenüberhitzung in einem oberen Lastbereich, und

FIG 4

ein Diagramm mit Simulationsergebnissen zur Verbesserung der Sofortreserve eines fossil befeuerten Dampferzeugers durch Erhöhung der Einspritzwasserenthalpie der Zwischenüberhitzung in einem unteren Lastbereich.

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

FIG. 1

flow medium side schematically the high-pressure and medium-pressure part of a fossil-fired steam generator with optimized injection water supply,

FIG. 2

flow medium side schematically the high-pressure and medium-pressure part of a fossil-fired steam generator with injection water supply line in an alternative embodiment,

FIG. 3

a diagram with simulation results to improve the immediate reserve of a fossil-fired steam generator by increasing the injection water enthalpy of reheating in an upper load range, and

FIG. 4

a diagram with simulation results to improve the immediate reserve of a fossil-fired steam generator by increasing the injection enthalpy of reheating in a lower load range.

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

From the fossil-fired steam generator 1 are in the FIG. 1 the high-pressure part 2 and the medium-pressure part 4 are shown. The FIG. 1 schematically represents a part of the flow path 6 of the flow medium M. The flow medium M is first fed by a feed pump 8 in the high-pressure part 2. There it is first brought by Hochdruckvorwärmern 10 to an elevated temperature, which can be operated for example with bleed steam. This is followed by economizer heating surfaces 12, in which flue gas waste heat is usually used for further heating of the flow medium, and evaporator heating surfaces 14, in which the flow medium is evaporated by means of the heat obtained from fossil fuel. The spatial arrangement of the individual heating surfaces 12, 14 in the hot gas duct is not shown and may vary. The illustrated heating surfaces 12, 14 may each represent a plurality of serially connected heating surfaces, which are not shown differentiated due to the clarity.

After leaving the evaporator heating surfaces 14 possibly existing residual moisture is deposited in a Wasserabscheideeinrichtung not shown and fed the remaining steam not shown superheater. Subsequently, the superheated steam is expanded in the high pressure section of a steam turbine. Subsequently, the flow medium M flows into the central pressure part 4 of the steam generator, where it is overheated again in a number of reheater heating surfaces 16 and then fed to the medium-pressure part of the steam turbine.

In front of the reheater heating surfaces, an injection valve 18 is arranged on the flow medium side. Here cooler and unevaporated flow medium M for controlling the outlet temperature at the outlet 20 of the medium-pressure part 4 of the fossil-fired steam generator 1 can be injected. The introduced into the injection valve 18 amount of flow medium M is controlled by an injection control valve 22. The flow medium M is supplied via a previously branched off in the flow path 2 overflow 24.

To the injection system not only to control the exit temperature, but also to provide an immediate To be able to use power reserve, the injection system is designed for an increase in the enthalpy of the injection water as required. For this purpose, the overflow line 24 has a first supply line 26, which branches off directly in the feed pump 8 and feeds flow medium M at a relatively low temperature to the overflow line 24. This ensures adequate subcooling of the injection medium. The first supply line 26 also includes a check valve 28 which prevents backflow of fluid from the injection system.

Furthermore, the overflow line has a second supply line 30 whose flow is controlled by a flow control valve 32. The second supply line branches off behind all high-pressure preheaters 10 in front of the economizer heating surfaces 12, so that here flow medium M is introduced into the overflow line 24 with a comparatively higher temperature. As a result, a considerable increase in steam quantity is achieved with a comparatively larger injection and the power of the downstream steam turbine is increased. In this case, the flow measuring device 34 is arranged in the flow path 6 behind both branches of the supply lines 26, 30, so that the quantity of the branched flow medium M for the feedwater control need not be taken into account here.

FIG. 2 shows an alternative embodiment, which is essentially the FIG. 1 corresponds, but here the locations of flow control valve 32 and check valve 28 are reversed. The first supply line 26 thus has a control valve 32 and the second supply line 30 a check valve 28. This embodiment is also possible, however, the entire injection path for higher pressures is interpreted. In addition, an additional branch 36 is provided for the first supply line 26, since due to the higher pressure level, flow medium M can not be decoupled at any point of the feed pump 8.

FIG. 3 shows a diagram with simulation results using the interconnection described. Is applied the percent additional power in relation to full load 38 versus time 40 in seconds after a sudden decrease in the temperature setpoint for the temperature at the exit 20 of the mid-pressure member 4 by 20 ° C at 95% load. Here, the curve 42 shows the results without heated injection fluid, so according to the usual system, the curve 44, the results with as described above interconnected injection system. In FIG. 2 It can be seen that the maximum of the curve 44 is higher than the curve 42. The additionally released power is thus higher.

FIG. 4 is opposite FIG. 3 only slightly modified and shows the simulated curves 42, 44 for 40% load, all other parameters coincide FIG. 3 Here, both curves 42, 44 show a flat course and in addition a comparatively high power increase about 60 seconds after changing the setpoint, which then rapidly drops again to go to the maximum of the flat course , Overall, the curve 44 is higher in each time range than the curve 42. Thus, a higher power deduction is also possible here, in spite of the load at only 40% sufficient subcooling of the injected medium is guaranteed.

A steam power plant equipped with such a fossil-fueled steam generator 1 is capable of rapidly increasing the output via an instant power output of the steam turbine, which serves to support the frequency of the composite power network. The fact that this power reserve is achieved by a double use of the injection fittings in addition to the usual temperature control, a permanent throttling of the steam turbine valves to provide a reserve can be reduced or eliminated, whereby a particularly high efficiency is achieved during normal operation.

Claims (8)

1. Fossil-fired steam generator (1) for a steam power station with a number of economiser, evaporator and superheater heating surfaces (12, 14, 16) forming a flow path (2) through which a flow medium M flows in a plurality of pressure stages (2, 4), in which, in a high-pressure stage (2), an overflow line (24) is connected to the flow path (2) on its inlet side and leads to an injection valve (18) disposed upstream in the flow path (2) from a superheater heating surface (16) in a medium-pressure stage (4) on the flow medium side,
   characterised in that
   the overflow line (24) has two supply lines (26, 30) of which the first branches off on the flow medium side upstream from a high-pressure preheater (10) and the second on the flow medium side downstream from the high-pressure preheater (10).
2. Fossil-fired steam generator (1) according to claim 1,
   characterised in that
   the second supply line (26) branches off on the flow medium side downstream from all high-pressure preheaters (10).
3. Fossil-fired steam generator (1) according to one of the preceding claims,
   characterised in that
   the first supply line (30) branches off on the flow medium side upstream from all high-pressure preheaters.
4. Fossil-fired steam generator (1) according to one of the preceding claims,
   characterised in that
   a check valve flap (28) is disposed in one of the supply lines (26, 30) and a throughflow regulation valve (32) is disposed in the other supply line.
5. Fossil-fired steam generator (1) according to one of the preceding claims,
   characterised in that
   a check valve flap (28) is disposed in the first supply line (26) and a throughflow regulation valve (32) is disposed in the second supply line (30).
6. Fossil-fired steam generator (1) according to claim 5,
   characterised in that
   the first supply line (26) branches off from a feed pump (8).
7. Fossil-fired steam generator (1) according to one of the preceding claims,
   characterised in that
   a throughflow measurement device (34) is disposed in the flow path (2) on the flow medium side downstream from the branch of the second supply line (30).
8. Steam power station with a fossil-fired steam generator (1) according to one of the preceding claims.

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