Method for monitoring the state of heat exchanger pipelines of a waste heat steam generator, and waste heat steam generator

Abstract

The invention relates to a method for monitoring the state of pipelines (14), which conduct water or steam, of at least one heat exchanger (8, 9, 10), 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, said at least one heat exchanger being arranged in the exhaust gas flow of a waste heat steam generator (1). The invention is characterized in that the presence of steam within the exhaust gas flow is automatically detected using sensors (18) 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. The invention additionally relates to a waste heat steam generator (1) designed to carry out the method.

Description

[0001] The invention relates to a method for monitoring the condition of water- or steam-carrying pipes of at least one heat exchanger arranged in an exhaust stream of a heat recovery steam generator, in particular, viewed downstream, a heat exchanger serving as a superheater, an evaporator, and a feedwater preheater. Furthermore, the invention relates to a heat recovery steam generator with an exhaust duct in which at least one heat exchanger having water- or steam-carrying pipes is arranged, in particular, viewed downstream, a heat exchanger serving as a superheater, an evaporator, and a feedwater preheater.

[0002] Heat recovery steam generators, often referred to as HRSGs (Heat Recovery Steam Generators), are known in various designs in the prior art. They utilize the hot exhaust gas from an upstream process to generate steam and typically comprise an exhaust duct containing several heat exchangers, usually in the form of a superheater, an evaporator, and a feedwater preheater, arranged downstream. Leaks in the water or steam-carrying piping of the heat exchangers can result in malfunction-related, unannounced downtimes, which should be avoided. Accordingly, it is desirable to be able to identify such leaks as early as possible to give maintenance personnel sufficient time to locate the location of a leak, determine its extent, and plan and carry out repair work.In the past, acoustic detection systems have been established in this context. These systems monitor the noise environment of a heat recovery steam generator using a large number of acoustic sensors distributed throughout the heat recovery steam generator. Leaks cause a change in the ambient noise, which is then detected by the sensors. Sensors positioned closer to the leak detect stronger noise changes than sensors positioned further away. In this way, a leak can also be located using sensors. A disadvantage of the known acoustic detection systems, however, is that several hundred sensors must be distributed throughout the heat recovery steam generator and wired, which is both very complex and expensive. Document US10082087 discloses a method for monitoring a heat recovery steam generator according to the prior art.

[0003] Based on this prior art, it is an object of the present invention to provide an alternative method and an alternative waste heat steam generator of the type mentioned at the outset, in which in particular the problems mentioned above are reduced.

[0004] To achieve this object, the present invention provides a method for monitoring the condition of water or steam-carrying pipes of at least one heat exchanger arranged in an exhaust gas flow of a heat recovery steam generator, in particular, viewed in the downstream direction, a heat exchanger serving as a superheater, an evaporator and a feedwater preheater, wherein the presence of water vapor within the exhaust gas flow is automatically detected using sensors (18) which record a measured variable representing the moisture content of the exhaust gas flow and / or using an optical detection system, and in the event of detection, an alarm is triggered which informs the personnel of the leak.The present invention therefore proposes using, instead of acoustic sensors, sensors that detect a measured variable representing the moisture content of the exhaust gas stream, in particular the moisture content of the exhaust gas itself, and / or an optical detection system to detect a pipeline leak. If a leak occurs in a pipeline carrying water or water vapor, portions of the water or water vapor flow into the exhaust gas, thereby causing an increase in the moisture content of the exhaust gas, which is then detected by the sensors. Alternatively or additionally, the water vapor flow in the exhaust gas, which forms a water vapor cloud or plume spreading downstream from the location of the leak, can be detected by an optical detection system.Compared to conventional acoustic sensors, the sensors used in this invention have the primary advantage of requiring significantly fewer sensors, which need to be positioned locally within the exhaust duct rather than distributed throughout the heat recovery steam generator. This results in lower costs and significantly lower maintenance requirements. The same applies to an optical detection system.

[0005] The sensors are preferably humidity sensors, in particular commercially available humidity sensors, which is conducive to a simple and inexpensive technical implementation of the method according to the invention.

[0006] According to one embodiment of the present invention, the measured values ​​recorded by the sensors are compared with at least one stored limit value, and if at least one of the recorded measured values ​​exceeds the limit value, an alarm is triggered. The predefined limit value is advantageously selected sufficiently high to reliably indicate that a leak actually exists, yet sufficiently low to allow sufficient time to plan and carry out repair work to eliminate the leak.

[0007] According to one embodiment of the present invention, the sensors detect the measured variable at measuring points distributed across a cross-section, preferably a single cross-section, of the exhaust gas flow. Such an arrangement of the sensors is advantageous in that only a comparatively small number of sensors are required, thereby simplifying the design of the detection system and minimizing costs. Furthermore, such an arrangement also enables leaks to be localized.By knowing the flow behavior of the exhaust gas through the exhaust line and any water vapor cloud or plume entrained with the exhaust gas, which can be determined, for example, in a simulation using suitable software, the location of the leak can be determined based on the positions and number of sensors that detected an increase in the moisture content of the exhaust gas, as well as the increase in moisture content detected by the individual sensors. The further a leak is from the position of the sensors in the direction of flow of the exhaust gas, the more sensors distributed across the cross-section of the exhaust duct will detect an increase in moisture content. The closer a leak is to the position of the sensors in the direction of flow of the exhaust gas, the greater the increase in moisture content detected by the corresponding sensors.

[0008] Preferably, the measuring points are arranged in a grid-like manner, evenly distributed over the cross-section of the exhaust gas flow, which leads to a simple structure and reliable results.

[0009] Advantageously, the measuring points are positioned downstream of the heat exchanger through which the exhaust gas flow last passed, in particular exclusively downstream of the heat exchanger through which the exhaust gas flow last passed. This results in the exhaust gas temperature being minimal in the area of ​​the measuring points, which allows for the use of inexpensive sensors, as these do not require high temperature resistance.

[0010] According to one embodiment of the present invention, in the event of an alarm, the position of a leak is calculated based on a comparison of the measured values ​​determined at different measuring points and output to the operating personnel.

[0011] Alternatively or additionally, an optical detection system is used for detection according to the invention.

[0012] According to one embodiment of the present invention, the optical detection system has at least one video camera, wherein the at least one camera is preferably positioned downstream of the heat exchanger last through which the exhaust gas flow passed, for the reasons already mentioned. Advantageously, the at least one video camera is directed at an inner surface of the heat recovery steam generator provided with a predetermined pattern. If such a pattern is partially obscured by a passing cloud or plume of water vapor, this can be detected based on the recorded video images. Preferably, at least two video cameras are positioned on opposite sides of the exhaust duct and directed at opposing inner surfaces of the exhaust duct, thereby enabling better localization of the leak.

[0013] Alternatively or additionally, the optical system can comprise at least one laser, which is directed in particular at an associated light detector arranged on an inner surface of the heat recovery steam generator, wherein the at least one laser and the associated light detector are preferably positioned downstream of the heat exchanger last through which the exhaust gas flow passed. The presence of water vapor in the exhaust gas flow can also be detected by obscuring the light detector by a water vapor cloud or plume. Advantageously, a cross-section of the exhaust gas duct is covered by a plurality of adjacently emitted laser beams directed at corresponding light detectors, thereby enabling the position and size of the water vapor cloud or plume to be determined and thus the leak to be localized.

[0014] Furthermore, the present invention provides a waste heat steam generator with an exhaust gas duct in which at least one heat exchanger having pipes carrying water or steam is arranged, in particular, viewed in the downstream direction, a heat exchanger serving as a superheater, an evaporator and a feedwater preheater, wherein sensors and / or an optical detection system are provided within the exhaust gas duct, which are designed to detect the presence of water steam in an exhaust gas conducted through the exhaust gas duct, and wherein a control system is provided which is connected in terms of data technology to the sensors and / or the optical detection system and is designed to carry out the method according to the invention.

[0015] The sensors are preferably humidity sensors.

[0016] Advantageously, a support grid is provided for the sensors, extending across a cross-section of the exhaust duct, with the sensors positioned on the support grid, in particular at regular intervals. Such a support grid ensures simple and cost-effective installation of the sensors across the cross-section of the exhaust duct.

[0017] Preferably, the retaining grid is arranged downstream of the last heat exchanger.

[0018] The optical detection system advantageously comprises at least one camera and / or at least one laser. The at least one camera and the at least one laser can be positioned in the exhaust duct as previously described with reference to the method according to the invention.

[0019] Further features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. Figure 1 is a schematic side view of a heat recovery steam generator according to an embodiment of the present invention; Figure 2 is a sectional view along the line II-II in Figure 1 ; Figure 3a view analogous to Figure 1 , which schematically shows damage to pipes of various heat exchangers of the heat recovery steam generator and resulting steam clouds; Figure 4 a sectional view along the line IV-IV in Figure 3 and Figure 5 is a schematic plan view of a downstream region of a heat recovery steam generator according to another embodiment of the present invention.

[0020] The same reference numbers refer to the same or similar parts or components.

[0021] Figure 1shows a heat recovery steam generator 1 according to an embodiment of the present invention, which is used in a known manner to generate superheated steam from feed water using hot exhaust gas from an upstream process, which steam is used to operate a steam turbine 2.

[0022] The waste heat steam generator 1 comprises a housing 3 through which an exhaust duct 6 extends, having an exhaust gas inlet 4 and an exhaust gas outlet 5, which opens downstream into a chimney 7 via a diffuser. Within the exhaust duct 6, three heat exchangers 8, 9, and 10 are arranged one behind the other in the direction of flow of the exhaust gas, with the heat exchanger 8 serving as a superheater, the heat exchanger 9 as an evaporator, and the heat exchanger 10 as a feedwater preheater.

[0023] During operation of the heat recovery steam generator 1, hot exhaust gas from an upstream process, such as the hot exhaust gas from a gas turbine process, is introduced into the exhaust duct 6 through the exhaust inlet 4 in the direction of arrow 11. The exhaust gas flows through the exhaust duct 6 in the direction of arrows 12, enters the chimney 7 through the exhaust outlet 5, flows through it in the direction of arrows 13, and is finally discharged into the atmosphere. On its way through the exhaust duct 6, the exhaust gas transfers heat to feedwater flowing countercurrently through pipes 14 of the heat exchangers 8, 9, and 10, in order to gradually superheat the feedwater. More specifically, feedwater, which is fed to the heat exchanger 10 positioned at the downstream end of the exhaust duct 6 via a feedwater pump 15, is first preheated by the exhaust gas.The preheated feedwater is then fed to a steam drum 16, which feeds the pipes 14 of the heat exchanger 9 with the preheated feedwater. The feedwater is then evaporated in the heat exchanger 9. The generated steam is then fed to the pipes 14 of the heat exchanger 8 and superheated there. The superheated steam is finally fed to the steam turbine 2, which drives, for example, a generator 17.

[0024] During operation of the heat recovery steam generator, it is desirable to monitor the condition of the pipes 14 of the heat exchangers 8, 9 and 10 in order to detect any leaks that may occur as early as possible and thus minimize downtime and maintenance times.

[0025] To monitor the condition of the pipes 14, the heat recovery steam generator 1 in the present embodiment comprises a plurality of sensors 18 arranged within the exhaust duct 6, which are designed to detect a measured variable representing the moisture content of the exhaust gas flow. The sensors 18 are designed as moisture sensors and positioned such that they detect the moisture content of the exhaust gas flow conducted through the exhaust duct 6 at a plurality of measuring points. Alternatively or additionally, sensors can also be used that do not directly detect the moisture content, but rather, for example, detect a measured variable that is proportional to the moisture content. In the illustrated embodiment, the sensors 18 are provided on a support grid 19 that extends across a cross-section of the exhaust duct. The sensors 18 are positioned on the support grid 19 in a matrix-like manner at regular intervals.The support grid 19 is arranged downstream of the last heat exchanger 10, so that the sensors 18 detect the moisture content of the exhaust gas after it has passed through all heat exchangers 8, 9, and 10. In principle, additional support grids 19 with sensors 18 attached to them can be provided within the exhaust duct 6 in order to detect the moisture content of the exhaust gas at various cross-sections of the exhaust duct 6. In the present case, a second support grid with sensors 18 attached thereto is positioned downstream of the first support grid 19, whereby these sensors 18 are only intended to verify the measured values ​​detected by the upstream sensors 18, thus forming a redundant arrangement. The sensors 18 are data-linked to a controller 20.

[0026] The Figure 3 and 4schematically show damages 21, 22 and 23, each on a pipe 14 of the three heat exchangers 8, 9 and 10. The damages 21 cause water or water vapor to escape from the pipes 14 and be entrained by the hot exhaust gas, forming clouds of water vapor, which increases the moisture content of the exhaust gas. It has been shown that the area over which the sensors 18 detect an increase in the moisture content of the exhaust gas becomes larger with increasing distance of the damages 21, 22, 23 from the sensors 18, since the water vapor is distributed more and more in proportion to the distance traveled within the exhaust duct 6, which in Figure 3 schematically by the dashed lines and in Figure 4by the differently sized circles 24, 25 and 26. Circle 24 outlines the area in which the sensors 18 record an increase in the moisture content of the exhaust gas caused by the damage 21, circle 25 the area in which the sensors 18 record an increase in the moisture content of the exhaust gas caused by the damage 22, and circle 26 the area in which the sensors 18 record an increase in the moisture content of the exhaust gas caused by the damage 23. Furthermore, it has been found that the intensity of the increase in the moisture content of the exhaust gas increases with decreasing distance of the damage 21, 22, 23 from the sensors 18, which in Figure 4indicated by the density of the hatching of circles 24, 25, 26. Based on the position and number of sensors 18 registering an increase in the moisture content of the exhaust gas and the registered magnitude of the increase in the moisture content of the exhaust gas, the position of the leak can be determined accordingly, which makes it easier for maintenance personnel to locate the leak and minimizes maintenance time.

[0027] During operation of the heat recovery steam generator 1, the sensors 18 measure the moisture content of the exhaust gas at predetermined intervals or continuously. The measured values ​​are then forwarded to the controller 20, where they are compared with at least one stored limit value. The at least one limit value can be a fixed limit value determined depending on the operating conditions, such as the outside temperature, the air humidity, the type of fuel used in the upstream process, etc. Alternatively or additionally, the limit value can also be defined, for example, as the maximum permissible increase in the moisture content of the exhaust gas within a predetermined period of time. If at least one of the measured values ​​exceeds the at least one limit value, an alarm is triggered to alert the operating personnel to the detected leak.Furthermore, the location of the leak is calculated and communicated to the operating personnel. The measured values ​​recorded by the sensors 18 arranged at the rear support grid 19 in the direction of exhaust flow are used to verify the measured values ​​recorded by the sensors 18 arranged at the front support grid 19, thereby minimizing false alarms and / or taking over the function of failed sensors 18 of the first support grid 19.

[0028] The inventive monitoring of the condition of water or steam-carrying pipelines 14 is characterized by the fact that the number of sensors can be significantly reduced compared to conventional acoustic monitoring, thereby saving costs. If the sensors 18 are arranged at the downstream end of the heat recovery steam generator 1, inexpensive commercially available sensors 18 can be used, since the exhaust gas temperature there is comparatively low and lies within the permissible temperature range of inexpensive commercially available sensors. The desired monitoring accuracy can also be achieved using inexpensive commercially available sensors.It has been found that a 1% leakage rate based on the mass flow flowing through a pipe 14 caused by a damage 21 to a pipe 14 of the first heat exchanger 8, which leads to an escaping water vapor mass flow of approximately 2 g / s, results in 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, which can be detected by inexpensive commercially available humidity sensors.

[0029] Figure 5shows a section of a heat recovery steam generator 1 according to a further embodiment of the present invention, the structure of which basically corresponds to the structure of the first embodiment. Instead of the sensors 18, however, an optical detection system 27 is provided, which in this case comprises two video cameras 28, which are preferably cooled in order to protect them from the hot environment. In the illustrated embodiment, the video cameras 27 are positioned on opposite sides of the exhaust duct 6 and are each directed at inner surfaces of the exhaust duct 6, which in this case are provided with a predetermined pattern, such as a pattern in the form of grid lines. The video cameras and the patterns can be positioned at different heights of the exhaust duct 6, but this is not absolutely necessary.

[0030] If, in the event of a leak, areas of the pattern are obscured by a water vapor cloud, this is registered by image recognition software contained in the controller 20 and an alarm is triggered. Based on the size and position of the obscured pattern areas, the location of the leak is calculated and communicated to the operating personnel.

[0031] It should be noted that, alternatively or in addition to the video cameras 27, the optical detection system 27 may also comprise lasers with associated light detectors positioned on the inner walls of the exhaust duct 6, even if this is not shown here. The presence of a water vapor cloud in the exhaust stream is detected in this case when the incidence of the laser light on the light detectors is attenuated or interrupted by a water vapor cloud. By appropriately selecting the positions of the lasers and light detectors, the location of the leak can also be calculated.

[0032] Although the invention has been illustrated and described in detail by the preferred embodiment, the invention is not limited to the disclosed examples and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention as defined in the appended claims.

Claims

1. Method for monitoring the state of water- or steam-conducting tubes (14) of at least one heat exchanger (8, 9, 10), in particular a heat exchanger serving as a superheater, a heat exchanger serving as an evaporator and a heat exchanger serving as a feedwater preheater when viewed in the downstream direction, said at least one heat exchanger being arranged in an exhaust gas flow of a heat recovery steam generator (1), wherein the presence of steam within the exhaust gas flow is detected automatically using sensors (18) that measure a measured quantity representing the moisture content of the exhaust gas flow and / or using an optical detection system, characterized in that an alarm is triggered in the event of a detection.

2. Method according to Claim 1, characterized in that the sensors (18) are moisture sensors.

3. Method according to Claim 2, characterized in that the measured values measured by the sensors (18) 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. Method according to Claim 2 or 3, characterized in that the sensors (18) measure the measured quantity at measurement points which are arranged in distributed fashion over a cross section of the exhaust gas flow.

5. Method according to Claim 4, characterized in that the measurement points are arranged in the style of a grid in uniformly distributed fashion over the cross section of the exhaust gas flow.

6. Method according to Claim 4 or 5, characterized in that the measurement points are positioned downstream of the last heat exchanger (10) through which the exhaust gas flow flows, in particular positioned exclusively downstream of the last heat exchanger (10) through which the exhaust gas flow flows.

7. Method according to any of Claims 4 to 6, characterized in that in the event of an alarm, the position of a leak is calculated on the basis of a comparison of the measured values ascertained at different measurement points, and the calculated position is output to operating staff.

8. Method according to any of the preceding claims, characterized in that the optical system (27) comprises at least one video camera (28), the said video camera in particular being directed at an inner surface of the heat recovery steam generator (1) furnished with a predetermined pattern, with the at least one video camera (28) preferably being positioned downstream of the last heat exchanger (10) through which the exhaust gas flow flows.

9. Method according to any of the preceding claims, characterized in that the optical detection system (27) comprises at least one laser, the said laser in particular being directed at an associated light detector arranged on an inner surface of the heat recovery steam generator (1), with the at least one laser and the associated light detector preferably being positioned downstream of the last heat exchanger (10) through which the exhaust gas flow flows.

10. Heat recovery steam generator (1) having an exhaust gas channel (6), in which at least one heat exchanger (8, 9, 10) comprising water- or steam-conducting tubes is arranged, in particular a heat exchanger serving as a superheater, a heat exchanger serving as an evaporator, and a heat exchanger serving as a feedwater preheater when viewed in the downstream direction, wherein sensors (18) and / or an optical detection system designed to detect the presence of steam in an exhaust gas guided through the exhaust gas channel are provided within the exhaust gas channel, characterized in that provision is made for a controller (20) data-connected to the sensors (18) and / or to the optical detection system (27) and configured to carry out the method according to any of the preceding claims.

11. Heat recovery steam generator (1) according to Claim 10, characterized in that the sensors (18) are moisture sensors.

12. Heat recovery steam generator (1) according to Claim 10 or 11, characterized in that provision is made of a holding grid (19) accommodating the sensors (18), in that, over a cross section of the exhaust gas channel (6), are positioned at regular intervals on the holding grid (19).

13. Heat recovery steam generator (1) according to Claim 12, characterized in that the holding grid (19) is arranged downstream of the last heat exchanger (10).

14. Heat recovery steam generator (1) according to any of Claims 10 to 13, characterized in that the optical detection system (27) comprises at least one video camera (28) and / or at least one laser.

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