METHOD FOR MONITORING THE STATE OF HEAT EXCHANGER PIPELINES OF A WASTE HEAT STEAM GENERATOR, AND WASTE HEAT STEAM GENERATOR

Abstract

A method for monitoring the state of pipelines, which conduct water or steam, of at least one heat exchanger, in particular a heat exchanger designed as a superheater, a heat exchanger designed as an evaporator, and a heat exchanger designed as a feed water preheater. When viewed in the downstream flow direction, the at least one heat exchanger is arranged in the exhaust gas flow of a waste heat steam generator. The presence of steam within the exhaust gas flow is automatically detected using sensors which detect a measurement variable that represents the moisture content of the exhaust gas flow and/or using an optical detection system, and if steam is detected, an alarm is triggered. A waste heat steam generator is designed to carry out the method.

Claims

1. A method for monitoring a state of water- or steam-conducting tubes of at least one heat exchanger, said at least one heat exchanger being arranged in an exhaust gas flow of a heat recovery steam generator, comprising: detecting a presence of steam within the exhaust gas flow automatically using sensors that measure a measured quantity representing a moisture content of the exhaust gas flow and/or using an optical detection system, and triggering an alarm based on a detection of the presence of steam.

2. The method as claimed in claim 1, wherein the sensors are moisture sensors.

3. The method as claimed in claim 2, wherein the measured values measured by the sensors are compared with at least one stored limit value, and the alarm is triggered if at least one of the measured values exceeds the limit value.

4. The method as claimed in claim 2, wherein the sensors measure the measured quantity at measurement points which are arranged in distributed fashion over a cross section of the exhaust gas flow.

5. The method as claimed in claim 4, wherein the measurement points are arranged in a style of a grid in uniformly distributed fashion over the cross section of the exhaust gas flow.

6. The method as claimed in claim 4, wherein the measurement points are positioned downstream of the last heat exchanger through which the exhaust gas flow flows.

7. The method as claimed in claim 4, wherein in the event of detecting the alarm, a position of a leak is calculated on a basis of a comparison of the measured values ascertained at different measurement points, and the calculated position is output.

8. The method as claimed in claim 1, wherein the optical system comprises at least one video camera.

9. The method as claimed in claim 1, wherein the optical detection system comprises at least one laser.

10. A heat recovery steam generator comprising: an exhaust gas channel, in which at least one heat exchanger comprising water- or steam-conducting tubes is arranged, sensors and/or an optical detection system designed to detect the presence of steam in an exhaust gas guided through the exhaust gas channel provided within the exhaust gas channel, and a controller data-connected to the sensors and/or to the optical detection system and configured to carry out the method as claimed in claim 1.

11. The heat recovery steam generator as claimed in claim 10, wherein the sensors are moisture sensors.

12. The heat recovery steam generator as claimed in claim 10, further comprising: a holding grid accommodating the sensors provided over a cross section of the exhaust gas channel, and positioned at regular intervals on the holding grid.

13. The heat recovery steam generator as claimed in claim 12, wherein the holding grid is arranged downstream of the last heat exchanger.

14. The heat recovery steam generator as claimed in claim 10, wherein the optical detection system comprises at least one video camera and/or at least one laser.

15. The method as claimed in claim 1, wherein the heat exchanger comprises as a superheater, an evaporator, and a feedwater preheater when viewed in a downstream direction.

16. The method as claimed in claim 6, wherein the measurement points are positioned exclusively downstream of the last heat exchanger through which the exhaust gas flow flows.

17. The method as claimed in claim 8, wherein the video camera is directed at an inner surface of the heat recovery steam generator furnished with a predetermined pattern, and/or is positioned downstream of the last heat exchanger through which the exhaust gas flow flows.

18. The method as claimed in claim 9, wherein the at least one laser is directed at an associated light detector arranged on an inner surface of the heat recovery steam generator, and/or wherein the at least one laser and the associated light detector are positioned downstream of the last heat exchanger through which the exhaust gas flow flows.

19. The heat recovery steam generator as claimed in claim 10, wherein the heat exchanger comprises as a superheater, an evaporator, and a feedwater preheater when viewed in a downstream direction.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the drawing:

[0022] FIG. 1 shows a schematic side view of a heat recovery steam generator according to one embodiment of the present invention;

[0023] FIG. 2 shows a sectional view along the line II-II in FIG. 1;

[0024] FIG. 3 shows a view analogous to FIG. 1, which schematically shows damage to tubes of different heat exchangers in the heat recovery steam generator and steam clouds resulting therefrom;

[0025] FIG. 4 shows a sectional view along the line IV-IV in FIG. 3; and

[0026] FIG. 5 shows a schematic plan view of a downstream region of a heat recovery steam generator according to a further embodiment of the present invention.

DETAILED DESCRIPTION OF INVENTION

[0027] Hereinafter, the same reference signs denote the same or similar parts or components.

[0028] FIG. 1 shows a heat recovery steam generator 1 according to one embodiment of the present invention, which in a known manner serves the generation of superheated steam from feedwater by using hot exhaust gas of an upstream process, and this superheated steam is used to drive a steam turbine 2.

[0029] The heat recovery steam generator 1 comprises a housing 3, through which an exhaust gas channel 6 having an exhaust gas inlet 4 and an exhaust gas outlet 5 extends; via a diffuser, said exhaust gas channel opens into a downstream chimney 7. In the flow direction of the exhaust gas, three heat exchangers 8, 9 and 10 are arranged in succession within the exhaust gas channel 6 in the present case, with the heat exchanger 8 serving as a superheater, the heat exchanger 9 serving as an evaporator and the heat exchanger 10 serving as a feedwater preheater.

[0030] During the operation of the heat recovery steam generator 1, hot exhaust gas from an upstream process, for example the hot exhaust gas from a gas turbine process, is introduced through the exhaust gas inlet 4 into the exhaust gas channel 6 in the direction of the arrow 11. The exhaust gas flows through the exhaust gas channel 6 in the direction of the arrows 12, enters the chimney 7 through the exhaust gas outlet 5, flows through said chimney in the direction of the arrows 13 and is ultimately released into the surroundings. On its path through the exhaust gas channel 6, the exhaust gas dissipates heat to feedwater guided through tubes 14 of the heat exchangers 8, 9 and 10 in counter flow in order to superheat said feedwater in stages. In more detail, feedwater supplied to the heat exchanger 10 positioned at the downstream end of the exhaust gas channel 6 via a feedwater pump 15 is initially preheated by the exhaust gas. The preheated feedwater is then supplied to a steam drum 16, which feeds the tubes 14 of the heat exchanger 9 with the preheated feedwater. The feedwater is then evaporated in the heat exchanger 9. The steam created is subsequently supplied to the tubes 14 of the heat exchanger 8, where it is superheated. The superheated steam is subsequently guided to the steam turbine 2, which for example drives a generator 17.

[0031] It is desirable to monitor the state of the tubes 14 of the heat exchangers 8, 9 and 10 during the operation of the heat recovery steam generator, in order to detect possibly arising leaks as early as possible and thus minimize downtime and maintenance times.

[0032] For the purpose of monitoring the state of the tubes 14, the heat recovery steam generator 1 of the present embodiment comprises a multiplicity of sensors 18 which are arranged within the exhaust gas channel 6 and which are designed to measure a measured quantity representing the moisture content of the exhaust gas flow. In the present case, the sensors 18 are embodied as moisture sensors and positioned in such a way that they measure the moisture content of the exhaust gas flow, which is guided through the exhaust gas channel 6, at a multiplicity of measurement points. As an alternative to that or in addition, it is also possible to use sensors that do not measure the moisture content directly but for example instead measure a measured quantity that is proportional to the moisture content. In the depicted embodiment, the sensors 18 are provided on a holding grid 19 which extends over a cross section of the exhaust gas channel. In this case, the sensors 18 are positioned in the style of a matrix at regular intervals on the holding grid 19. The holding grid 19 is arranged downstream of the last heat exchanger 10 such that the sensors 18 measure the moisture content of the exhaust gas after the latter has passed through all heat exchangers 8, 9 and 10. In principle, further holding grids 19 with sensors 18 attached thereto can be provided within the exhaust gas channel 6 in order to measure the moisture content of the exhaust gas at various cross sections of the exhaust gas channel 6. In the present case, a second holding grid with sensors 18 held thereon is positioned downstream of the first holding grid 19, with the intention being that these sensors 18 merely verify the measurement values measured by the sensors 18 positioned upstream and thus form a redundant arrangement. The sensors 18 are data-coupled to a controller 20.

[0033] FIGS. 3 and 4 schematically show instances of damage 21, 22 and 23 to a respective tube 14 of the three heat exchangers 8, 9 and 10. The instances of damage 21 lead to water or steam emerging from the tubes 14, being carried along by the hot exhaust gas and forming steam clouds in the process, whereby the moisture content of the exhaust gas increases. It has transpired that the region over which the sensors 18 detect an increase in moisture content of the exhaust gas increases with increasing distance between the instances of damage 21, 22, 23 and the sensors 18 since the steam is distributed more and more in a manner proportional to the distance traveled within the exhaust gas channel 6; this is indicated schematically by the dashed lines in FIG. 3 and by the circles 24, 25 and 26 of different size in FIG. 4. In this case, the circle 24 sketches out the region in which the sensors 18 record an increase in moisture content of the exhaust gas caused by the damage 21, the circle 25 sketches out the region in which the sensors 18 record an increase in moisture content of the exhaust gas caused by the damage 22 and the circle 26 sketches out the region in which the sensors 18 record an increase in moisture content of the exhaust gas caused by the damage 23. It has also transpired that the intensity of the increase in moisture content of the exhaust gas increases with decreasing distance between the damage 21, 22, 23 and the sensors 18; in FIG. 4, this is indicated by the denseness of the hatching of the circles 24, 25, 26. Using the position and number of sensors 18 registering an increase in moisture content of the exhaust gas and using the registered level of increase in moisture content of the exhaust gas, it is possible to correspondingly infer the position of the leak, facilitating the maintenance staff's search for the leak and minimizing the maintenance duration.

[0034] The sensors 18 measure the moisture content of the exhaust gas at predetermined intervals or continuously during the operation of the heat recovery steam generator 1. The measured values that were measured are then transmitted to the controller 20, where the measured values that were measured are compared with at least one stored limit value. The at least one limit value can be a fixed limit value which was defined in a manner depending on the operating conditions, for example the external temperature, the humidity, the type of fuel used in the upstream process, etc. In an alternative to that or in addition, however, the limit value might also be defined, for example, as a maximal admissible increase in moisture content of the exhaust gas within a predetermined time period. An alarm is triggered should at least one of the measured values that were measured exceed the at least one limit value, in order to draw the operating staff's attention to the detected leak. Further, the position of the leak is calculated, and this is output for the operating staff. The measured values measured by the sensors 18 arranged on the rear holding grid 19 in the flow direction of the exhaust gas are used to verify the measured values measured by the sensors 18 arranged on the front holding grid 19, in order to thus minimize false alarms and/or adopt the function of failed sensors 18 on the first holding grid 19.

[0035] Monitoring the state of water- or steam-conducting tubes 14 in a manner according to the invention is distinguished in that the number of sensors can be reduced significantly in comparison with conventional acoustic monitoring, whereby costs are saved. Arranging the sensors 18 at the downstream end of the heat recovery steam generator 1 allows the use of cost-effective commercially available sensors 18 since the exhaust gas temperature is comparatively low there and located within the admissible temperature range of cost-effective commercially available sensors. The sought-after monitoring accuracy can also be attained using cost-effective commercially available sensors. It has transpired that, in relation to the mass flow flowing through a tube 14, a 1% leak rate caused by damage 21 to a tube 14 of the first heat exchanger 8 and leading to an emerging steam mass flow of approximately 2 g/s entails a 2-2.5% increase in the moisture content of the exhaust gas immediately downstream of the first heat exchanger 8 and a 1-1.5% increase in the moisture content of the exhaust gas immediately downstream of the third heat exchanger 10 and accordingly at the position of the sensors 18; this can be measured by cost-effective commercially available moisture sensors.

[0036] FIG. 5 shows a detail of a heat recovery steam generator 1 according to a further embodiment of the present invention, the structure of which fundamentally corresponds to the structure of the first embodiment. However, instead of the sensors 18, an optical detection system 27 is provided here; in the present case, it comprises two video cameras 28 which are preferably cooled in order to be protected from the hot environment. In the depicted embodiment, the video cameras 27 are positioned on opposite sides of the exhaust gas channel 6 and are each directed at inner sides of the exhaust gas channel 6 that are provided with a predetermined pattern in the present case, for example with a pattern in the form of mesh lines. The video cameras and the patterns can be positioned at different levels in the exhaust gas channel 6, but this is not mandatory.

[0037] If regions of the patterns are concealed by a steam cloud in the case of a leak, then this is registered by image recognition software contained in the controller 20, and an alarm is triggered. The position of the leak is calculated on the basis of the size and position of the concealed pattern regions and output to the operating staff.

[0038] Attention is drawn to the fact that the optical detection system 27 may also comprise lasers with associated light detectors positioned at the inner walls of the exhaust gas channel 6 as an alternative or in addition to the video cameras 27, even if this is not depicted in the present case. In this case, the presence of a steam cloud in the exhaust gas flow is detected when the incidence of the laser light on the light detectors is attenuated or interrupted by a steam cloud. It is also possible to calculate the position of the leak in the case of a suitable choice of the positions of lasers and light detectors.

[0039] Even though the invention is illustrated and described more closely in detail by way of the preferred exemplary embodiment, the invention is not limited by the disclosed examples, and a person skilled in the art is able to derive other variations therefrom, without departing from the scope of protection of the invention.