Method for monitoring the condition of heat exchanger conduits in a waste heat steam generator and waste heat steam generator

Abstract

The present invention relates to a method for monitoring the condition of at least one heat exchanger (8, 9, 10) arranged in the waste gas stream of a waste heat steam generator (1), in particular the water or steam conduit (14) of the heat exchanger which, viewed in the downstream direction, serves as a superheater, an evaporator and a feed water preheater, characterized in that the presence of water vapor in the waste gas stream is detected using a sensor (18) detecting a measurement representative of the humidity content of the waste gas stream and / or automatically using an optical detection system, and an alarm is activated upon detection.

Description

Technical Field

[0001] The present invention relates to a method for monitoring the condition of conduits guiding water or steam in at least one heat exchanger arranged in the waste gas stream of a waste heat steam generator, in particular a heat exchanger functioning as a superheater, an evaporator, and a feedwater preheater when viewed in the downstream direction. The present invention also relates to a waste heat steam generator having a waste gas channel in which at least one heat exchanger including a conduit guiding water or steam is arranged, in particular at least one heat exchanger functioning as a superheater, an evaporator, and a feedwater preheater when viewed in the downstream direction.

Background Art

[0002] Waste heat steam generators, often abbreviated as HRSGs ("Heat Recovery Steam Generator"), are known in the prior art in various configurations. They serve to utilize the high-temperature waste gas stream from an upstream process for steam generation and usually comprise a waste gas channel in which a plurality of heat exchangers are arranged when viewed in the downstream direction, and these heat exchangers are typically in the form of a superheater, an evaporator, and a feedwater preheater. If there is a leak in the conduits of the heat exchanger carrying water or steam, unannounced interruption times related to failures may occur, which should be avoided. Therefore, it is desirable to detect such leaks as early as possible, identify the location of the leak for the maintenance staff, determine its extent, and provide the maintenance staff with sufficient time to plan and carry out repair work. In the past, an acoustic detection system has been established for this purpose, and the noise environment of the waste heat steam generator is monitored using a plurality of acoustic sensors distributed throughout the waste heat steam generator. The leak causes a change in the ambient noise, which is detected by the sensors. In this case, the sensors arranged closer to the leak location detect a greater change in noise than the sensors arranged farther away. In this way, it becomes possible to locate the leak by the sensors. However, a drawback of the known acoustic detection system is that hundreds of sensors have to be distributed and wired on the waste heat steam generator, which is very cumbersome and costly.

Summary of the Invention

[0003] Starting from such prior art, the object of the present invention is to provide an alternative method and an alternative waste heat steam generator of the type described at the beginning, which particularly reduces the problems mentioned above. [Means for solving the problem]

[0004] To address this problem, the present invention provides a monitoring method for monitoring the condition of a water or steam conduit in at least one heat exchanger located in the exhaust gas flow of a waste heat steam generator, particularly a heat exchanger that functions as a superheater, evaporator, and feedwater preheater when viewed downstream, characterized in that the presence of steam in the exhaust gas flow is automatically detected using a sensor (18) that detects a measured quantity representing the humidity of the exhaust gas flow and / or using an optical detection system, and an alarm is activated upon detection to alert staff to the leak. The present invention further proposes the use of a sensor and / or an optical detection system, instead of an acoustic sensor, that detects a measured quantity representing the humidity of the exhaust gas flow, particularly the humidity of the exhaust gas flow itself, to detect leaks in the conduit. If there is a leak in the water or steam conduit, the water or steam component flows into the exhaust gas flow, thus causing an increase in the humidity of the exhaust gas flow, which is then detected by the sensor. Alternatively, or in addition to the above, the steam flow in the exhaust gas flow that forms a steam cloud or steam band propagating downstream from the location of the leak can also be detected by the optical detection system. Compared to conventional acoustic sensors, the sensors used according to the present invention have the particular advantage of requiring significantly fewer sensors. These sensors do not need to be distributed across the waste heat steam generator, but only need to be placed locally within the exhaust gas channel. This results in lower costs and significantly reduced maintenance expenses. The same applies to optical detection systems.

[0005] It is advantageous that the sensor is a humidity sensor, particularly a commercially available humidity sensor, which is beneficial for a simple and cost-effective technical implementation of the method according to the present invention.

[0006] According to one configuration of the present invention, a measurement detected by a sensor is compared to at least one stored limit value, and an alarm is triggered if at least one of the detected measurements exceeds the limit value. It is advantageous that the predefined limit value is selected to be high enough to provide reliable certainty regarding the actual presence of a leak, and low enough to leave sufficient time for planning and carrying out repair work to correct the leak.

[0007] According to one configuration of the present invention, sensors detect measurements at measurement points distributed across the cross-section of the exhaust gas flow, preferably across individual cross-sections of the exhaust gas flow. Such a sensor arrangement is advantageous because, on the one hand, it requires relatively few sensors, thereby simplifying the structure of the detection system and minimizing costs. On the other hand, leak localization is also possible with such a configuration. Knowledge of the flow behavior of the exhaust gas flow through the exhaust gas conduit, and the vapor cloud or band carried with the exhaust gas flow, which can be obtained, for example, within the scope of simulation using appropriate software, makes it possible to estimate the location of a leak based on the location and number of sensors that detect an increase in the humidity of the exhaust gas flow, and the increase in humidity measured by each sensor. As the leak moves away from the sensor location in the direction of the exhaust gas flow, the increase in humidity is perceived as more sensors are distributed across the cross-section of the exhaust gas channel. The closer the leak is to the sensor location in the direction of the exhaust gas flow, the greater the increase in humidity measured by the corresponding sensor.

[0008] It is advantageous for the measurement points to be arranged in a grid pattern, uniformly distributed across the cross-section of the exhaust gas flow, which results in a simple structure and reliable evidence.

[0009] It is advantageous to position the measurement point downstream of the last heat exchanger through which the exhaust gas flow passes, and especially only downstream of the last heat exchanger through which the exhaust gas flow passes. This minimizes the temperature of the exhaust gas flow in the region of the measurement point, eliminating the need for high-temperature resistant sensors and enabling the use of cost-effective sensors.

[0010] According to one embodiment of the present invention, when an alarm is triggered, the location of the leak is calculated based on a comparison of measurements obtained at multiple measurement points and output to the operating staff.

[0011] Alternatively, or in addition thereto, according to the present invention, an optical detection system is used for detection.

[0012] According to one configuration of the present invention, the optical detection system comprises at least one video camera, which, for the reasons stated above, preferably is positioned downstream of the last heat exchanger through which the exhaust gas flow passes. It is advantageous that at least one video camera be directed toward the inner surface of the waste heat steam generator having a predetermined pattern. If such a pattern is partially obscured by a steam cloud or band moving alongside it, this can be detected based on the captured video image. It is advantageous that at least two video cameras be positioned on either side of the exhaust gas channel, directed toward the mutually opposing inner surfaces of the exhaust gas channel, thereby allowing for better localization of leaks.

[0013] Alternatively, or in addition to the above, the optical system may comprise at least one laser, which is directed in particular to an associated photodetector located on the inner surface of the waste heat steam generator, and at least one laser and associated photodetector are preferably located downstream of the last heat exchanger through which the exhaust gas flow passes. The presence of steam in the exhaust gas flow can also be detected by obscuring the photodetector with a steam cloud or band. It is advantageous to have the cross-sections of the exhaust gas channels emanating adjacent to each other and covered by a number of laser beams directed to corresponding photodetectors, thereby enabling the determination of the location and size of the steam cloud or steam band, and thus the location of leaks.

[0014] The present invention also provides a waste heat steam generator having an exhaust gas channel, wherein at least one heat exchanger having water or steam conduits is arranged in the exhaust gas channel, particularly downstream, the heat exchanger functions as a superheater, evaporator, and feedwater preheater, and the exhaust gas channel is provided with a sensor and / or optical detection system designed to detect the presence of steam in a gas guided through the gas channel, and a controller configured to perform a method according to the present invention, which is data-connected to the sensor and / or optical detection system.

[0015] Preferably, the sensor is a humidity sensor.

[0016] A retaining grid is provided that extends across the cross-section of the exhaust gas channel and accommodates sensors, and it is particularly advantageous if the sensors are arranged at regular intervals on the retaining grid. Such a retaining grid ensures that sensors can be installed easily and cost-effectively across the cross-section of the exhaust gas channel.

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

[0018] It is advantageous for the optical detection system to include at least one camera and / or at least one laser. The at least one camera and the at least one laser can be arranged in the waste gas channel as already described in the context of the method according to the invention.

Brief Description of the Drawings

[0019] Further features and advantages of the invention will become apparent from the following description with reference to the accompanying drawings.

[0020] [Figure 1] A schematic side view of a waste heat steam generator according to an embodiment of the invention is shown. [Figure 2] A cross-sectional view taken along line II-II of FIG. 1 is shown. [Figure 3] A view similar to FIG. 1 is shown, schematically showing damage to the conduits of a plurality of heat exchangers in the waste heat steam generator and the resulting steam cloud. [Figure 4] A cross-sectional view taken along line IV-IV of FIG. 3 is shown. [Figure 5] A schematic plan view of the downstream region of a waste heat steam generator according to a further embodiment of the invention is shown.

[0021] Hereinafter, the same reference numerals denote the same or similar parts or components.

Embodiments for Carrying Out the Invention

[0022] FIG. 1 shows a waste heat steam generator 1 according to an embodiment of the invention, which generates superheated steam from feed water by using the hot waste gas flow of a previous process as is known, and is used to drive a steam turbine 2.

[0023] The waste heat steam generator 1 includes a housing 3 through which a waste gas channel 6 having a waste gas inlet 4 and a waste gas outlet 5 extends and opens to a downstream chimney 7 via a diffuser. In the waste gas channel 6, three heat exchangers 8, 9, and 10 are sequentially arranged in the flow direction of the waste gas stream. The heat exchanger 8 functions as a superheater, the heat exchanger 9 functions as an evaporator, and the heat exchanger 10 functions as a feed water preheater.

[0024] During the operation of the waste heat steam generator 1, a high-temperature waste gas stream from a previous process, for example, a high-temperature waste gas stream from a gas turbine process, is introduced into the waste gas channel 6 through the waste gas inlet 4 in the direction of arrow 11. The waste gas flows through the waste gas channel 6 in the direction of arrow 12, enters the chimney 7 through the waste gas outlet 5, flows through the chimney in the direction of arrow 13, and is finally discharged into the environment. During the process of passing through the waste gas channel 6, the waste gas dissipates heat in a countercurrent manner to the feed water guided through the conduits 14 of the heat exchangers 8, 9, and 10, and gradually superheats this feed water. More specifically, the feed water supplied to the heat exchanger 10 located at the downstream end of the waste gas channel 6 via the feed water pump 15 is first preheated by the waste gas stream. Then the preheated feed water is supplied to the steam drum 16, and the steam drum supplies the preheated feed water to the conduits 14 of the heat exchanger 9. Then the feed water is evaporated in the heat exchanger 9. The generated steam is subsequently supplied to the conduits 14 of the heat exchanger 8, where it is superheated. The superheated steam is finally guided to the steam turbine 2 to drive, for example, the generator 17.

[0025] During the operation of the waste heat steam generator, it is desirable to monitor the states of the conduits 14 of the heat exchangers 8, 9, and 10, detect possible leaks that may occur as early as possible, and thereby minimize the interruption time and maintenance time.

[0026] To monitor the condition of the conduit 14, the waste heat steam generator 1 of this embodiment is equipped with a number of sensors 18, which are positioned within the exhaust gas channel 6 and designed to measure a value representing the humidity of the exhaust gas flow. In this case, the sensors 18 are designed as humidity sensors and are positioned to measure the humidity of the exhaust gas flow guided through the exhaust gas channel 6 at multiple measurement points. Alternatively, or in addition to this, it is also possible to use sensors that do not directly measure humidity, but rather measure a value proportional to humidity, for example. In the illustrated embodiment, the sensors 18 are mounted on a retaining grid 19 extending across the cross-section of the exhaust gas channel. In this case, the sensors 18 are positioned in a matrix at regular intervals on the retaining grid 19. The retaining grid 19 is positioned downstream of the last heat exchanger 10, and the sensors 18 are configured to measure the humidity of the exhaust gas flow after it has passed through all the heat exchangers 8, 9, and 10. Basically, additional retaining grids 19 are provided within the exhaust gas channel 6 along with sensors attached to them, allowing for measurement of the humidity of the exhaust gas flow at various cross-sections of the exhaust gas channel. In this case, the second holding grid to which the sensor 18 is attached is located downstream of the first holding grid 19, and these sensors 18 are intended to verify the measurements taken by the sensors 18 located upstream, thus forming a redundant configuration. The sensors 18 are data-coupled to the controller 20.

[0027] Figures 3 and 4 schematically illustrate damages 21, 22, and 23 to the conduits 14 of the three heat exchangers 8, 9, and 10, respectively. Damage 21 causes water or steam to leak out of conduit 14 and is carried by the hot exhaust gas flow, forming a water vapor cloud, thereby increasing the humidity of the exhaust gas flow. As a result, the area in which sensor 18 detects the increase in humidity of the exhaust gas flow increases as the distance between damages 21, 22, and 23 and sensor 18 increases, as more steam is distributed in proportion to the distance traveled within the exhaust gas channel 6. This is schematically illustrated by the dashed line in Figure 3 and the circles 24, 25, and 26 of different sizes in Figure 4. In this case, circle 24 roughly indicates the region where sensor 18 shows an increase in the humidity of the exhaust gas flow caused by damage 21, circle 25 roughly indicates the region where sensor 18 shows an increase in the humidity of the exhaust gas flow caused by damage 22, and circle 26 roughly indicates the region where sensor 18 records an increase in the humidity of the exhaust gas flow caused by damage 23. It has also become clear that the increase in the humidity of the exhaust gas flow increases as the distance between damages 21, 22, and 23 and sensor 18 decreases, which is indicated in Figure 4 by the density of the hatching in circles 24, 25, and 26. The location and number of sensors 18 recording the increase in the humidity of the exhaust gas flow, and the recorded levels of the increase in the humidity of the exhaust gas flow, make it possible to reasonably estimate the location of the leak, facilitating the investigation of the leak by maintenance staff and minimizing the maintenance period.

[0028] During operation of the waste heat steam generator 1, the sensor 18 detects the humidity of the exhaust gas flow at predetermined intervals or continuously. The detected values ​​are transmitted to the controller 20, where they are compared to at least one stored limit value. The at least one limit value is a fixed limit value defined according to operating conditions, such as external temperature, humidity, and the type of fuel used in the upstream process. However, instead of, or in addition to, the limit value may be defined, for example, as the maximum allowable increase in the humidity of the exhaust gas flow over a predetermined period. If at least one of the detected values ​​exceeds at least one limit value, an alarm is activated to draw the attention of the operating staff to the detected leak. Furthermore, the leak location is calculated and output to the operating staff. The values ​​detected by the sensor 18 located on the rear retaining grid 19 in the direction of the exhaust gas flow are used to verify the values ​​detected by the sensor 18 located on the front retaining grid 19, thus minimizing false alarms and / or substituting for the function of a faulty sensor 18 on the first retaining grid 19.

[0029] The monitoring of the condition of the water or steam conduit 14 according to the present invention has the advantage of significantly reducing the number of sensors compared to conventional acoustic monitoring, thereby saving costs. By placing the sensor 18 at the downstream end of the waste heat steam generator 1, the temperature of the exhaust gas flow is relatively low, and a cost-effective commercially available sensor 18 within the temperature range can be used. The required monitoring accuracy can also be achieved using a cost-effective commercially available sensor. With respect to the mass flow rate through the conduit 14, a 1% leakage rate caused by damage 21 to the conduit 14 of the first heat exchanger 8, resulting in an emerging steam mass flow rate of about 2 g / s, is accompanied by a 2-2.5% increase in the humidity of the exhaust gas flow immediately downstream of the first heat exchanger 8, and a 1-1.5% increase in the humidity of the exhaust gas flow immediately downstream of the third heat exchanger 10, and therefore at the location of the sensor 18, which can be measured by a cost-effective commercially available humidity sensor.

[0030] Figure 5 shows a cross-sectional view of a waste heat steam generator 1 according to another embodiment of the present invention, the structure of which is basically the same as that of the first embodiment. Instead of the sensor 18, an optical detection system 27 is provided here, in which case the optical detection system comprises two video cameras 28, which are preferably cooled to protect them from high-temperature environments. In the illustrated embodiment, the video cameras 27 are positioned on both sides of the exhaust gas channel 6 and are directed inward into the exhaust gas channel 6, where a predetermined pattern, for example, in the form of a mesh line, is provided in this example. The video cameras and pattern can be positioned at different levels within the exhaust gas channel 6, but this is not a requirement.

[0031] If a leak occurs, the pattern area is obscured by a water vapor cloud, which is recorded by the image recognition software included in the controller 20, triggering an alarm. The location of the leak is calculated based on the size and position of the obscured pattern area and output to the operating staff.

[0032] It should be noted that the optical detection system 27 may also include, as an alternative to or in addition to, the video camera 27, a laser with an associated photodetector positioned on the inner wall of the exhaust gas channel 6, even if not illustrated in this example. In this case, the presence of a vapor cloud in the exhaust gas flow is detected when the incident laser beam to the photodetector is attenuated or blocked by the vapor cloud. It is also possible to calculate the location of the leak by appropriately selecting the positions of the laser and photodetector.

[0033] Although the present invention is illustrated and described in more detail by preferred exemplary embodiments, the present invention is not limited to the disclosed embodiments, and those skilled in the art can derive other modifications therefrom without departing from the scope of protection of the present invention. [Explanation of Symbols]

[0034] 1. Waste heat steam generator 2 Steam Turbine 3 Housing 4. Exhaust gas inlet 5. Exhaust gas outlet 6. Exhaust gas channels 7 Chimney 8 Heat exchanger (superheater) 9. Heat exchanger (evaporator) 10. Heat exchanger (feedwater preheater) 14 Conduit 15 Water supply pump 16 Steam drum 17 Generators 18 sensors 19 Holding Grid 20 controllers 27 Optical detection systems

Claims

1. A method for monitoring the condition of water or steam conduit (14) in at least one heat exchanger (8, 9, 10) located in the exhaust gas flow of a waste heat steam generator (1), The presence of water vapor in the exhaust gas flow is automatically detected using a sensor (18) that detects a measured value representing the humidity of the exhaust gas flow. When water vapor is detected, an alarm is triggered. The at least one heat exchanger (8, 9, 10) includes a first heat exchanger (8, 9) having a first water or steam conduit (14), and a second heat exchanger (9, 10) located downstream of the first heat exchanger (8, 9) and having a second water or steam conduit (14). The sensor (18) detects measurement values ​​at measurement points distributed across the cross-section of the exhaust gas flow, The measurement points are arranged in a grid pattern, uniformly distributed across the cross-section of the exhaust gas flow. The measurement point is located downstream of the second heat exchanger (9, 10) through which the exhaust gas flow passes. If an alarm occurs, the location of the leak in the first water or steam conduit (14) or the second water or steam conduit (14) is calculated based on the number of sensors (18) that detected an increase in the humidity of the exhaust gas flow. The method is characterized in that the calculated position is output to the operating staff.

2. The method according to claim 1, characterized in that the sensor (18) is a humidity sensor.

3. The measured value detected by the sensor (18) is compared with at least one stored limit value. An alarm is triggered if at least one of the detected measurements exceeds the limit value. The method according to feature 2.

4. The method according to claim 1, characterized in that the location of the leak is calculated based on the number of sensors (18) that detected an increase in the humidity of the exhaust gas flow and the amount of increase in humidity measured by the sensors (18).

5. A waste heat steam generator (1) having an exhaust gas channel (6), wherein at least one heat exchanger (8, 9, 10) having a conduit (14) for guiding water or steam is arranged, A sensor (18) designed to detect the presence of water vapor in the exhaust gas flow being guided through the exhaust gas channel is provided in the exhaust gas channel. The at least one heat exchanger (8, 9, 10) includes a first heat exchanger (8, 9) having a first water or steam conduit (14), and a second heat exchanger (9, 10) located downstream of the first heat exchanger (8, 9) and having a second water or steam conduit (14). The sensor (18) detects measurement values ​​at measurement points distributed across the cross-section of the exhaust gas flow, The measurement points are arranged in a grid pattern, uniformly distributed across the cross-section of the exhaust gas flow. The measurement point is located downstream of the second heat exchanger (9, 10) through which the exhaust gas flow passes. A controller (20) is provided which is data-connected to the sensor (18) and is configured to perform the method according to any one of claims 1 to 4. A waste heat steam generator (1) characterized by the following:

6. The waste heat steam generator (1) according to claim 5, characterized in that the sensor (18) is a humidity sensor.

7. The waste heat steam generator (1) according to claim 5 is characterized in that a retaining grid (19) for housing the sensors (18) is provided, and the sensors (18) are arranged at regular intervals on the retaining grid (19) across the cross-section of the exhaust gas channel (6).

8. The waste heat steam generator (1) according to claim 7, characterized in that the retaining grid (19) is located downstream of the second heat exchangers (9, 10).

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