METHOD FOR MONITORING CONDITION OF HEAT EXCHANGER PIPE OF 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 state of at least one heat exchanger arranged in the waste gas flow of a waste heat steam generator, in particular the water or steam conducting conduits of the heat exchanger, which, viewed in the downstream direction, act as a superheater, an evaporator and a feed water preheater.The present invention also relates to a waste heat steam generator having a waste gas channel in which at least one heat exchanger, comprising a water or steam conducting conduit, in particular at least one heat exchanger, which, viewed in the downstream direction, acts as a superheater, an evaporator and a feed water preheater, is arranged. [Background technology]

[0002] Waste heat steam generators, often abbreviated as HRSG ("Heat Recovery Steam Generator"), are known in the prior art in various configurations. They serve to utilize a high-temperature waste gas flow from an upstream process for steam generation and usually comprise a waste gas channel in which, viewed in a downstream direction, several heat exchangers are arranged, usually in the form of superheaters, evaporators, and feedwater preheaters. Leaks in the conduits of the heat exchangers carrying water or steam can result in unannounced downtimes associated with failures, which should be avoided. It is therefore desirable to detect such leaks as early as possible, providing the maintenance staff with sufficient time to locate the leak, determine its extent, and plan and carry out repair work. Acoustic detection systems have been established for this purpose in the past, in which the noise environment of the waste heat steam generator is monitored using several 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, sensors located closer to the leak location detect a larger change in noise than sensors located further away. In this way, the leak can be located by the sensors. However, a drawback of known acoustic detection systems is that hundreds of sensors must be distributed and wired on the waste heat steam generator, which is very cumbersome and expensive. Summary of the Invention [Problem to be solved by the invention]

[0003] Taking this prior art as a starting point, the object of the present invention is to provide an alternative method and an alternative waste heat steam generator of the type mentioned at the outset, in which in particular the above-mentioned problems are reduced. [Means for solving the problem]

[0004] To solve this problem, the invention provides a method for monitoring the condition of at least one heat exchanger arranged in the waste gas stream of a waste heat steam generator, in particular a water or steam conduit of a heat exchanger that, viewed in the downstream direction, functions 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 automatically using a sensor (18) that detects a measured quantity representative of the humidity content of the waste gas stream and / or an optical detection system, and an alarm is activated on detection, making staff aware of the leak. The invention further proposes the use of a sensor that detects a measured quantity representative of the humidity content of the waste gas stream, in particular the humidity content of the waste gas stream itself, instead of an acoustic sensor, and / or an optical detection system, to detect leaks in the conduit. In the event of a leak in the water or steam conduit, water or water vapor components will flow into the waste gas stream and thus cause an increase in the humidity content of the waste gas stream, which is then detected by the sensor. Alternatively or additionally, the flow of steam in the waste gas stream forming a steam cloud or steam zone propagating downstream from the location of the leak can also be detected by an optical detection system. In comparison with conventional acoustic sensors, the sensors used according to the invention have the advantage in particular that significantly fewer sensors are required, which do not have to be distributed over the waste heat steam generator, but only locally in the waste gas channel, which results in lower costs and significantly reduced maintenance costs. The same is true for optical detection systems.

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

[0006] According to one configuration of the invention, the measured values ​​detected by the sensor are compared with at least one stored limit value and an alarm is activated if at least one of the detected measured values ​​exceeds the limit value. It is advantageous for the predefined limit value to be selected high enough so that there is a reliable certainty regarding the actual presence of a leak, but small enough so that sufficient time remains for the purpose of planning and carrying out repair work to correct the leak.

[0007] According to one embodiment of the invention, the sensors detect measured values ​​at measuring points distributed over the cross section of the waste gas flow, preferably over the individual cross sections of the waste gas flow. Such an arrangement of sensors is advantageous, since on the one hand, relatively few sensors are required, which has the effect of simplifying the construction of the detection system and minimizing the costs. On the other hand, localization of leaks is also possible with such an arrangement. Knowledge of the flow behavior of the waste gas flow through the waste gas conduit and of the vapor cloud or band carried along with the waste gas flow, which can be obtained, for example, within the scope of simulation with suitable software, makes it possible to estimate the location of the leak based on the position and number of sensors which detect an increase in the humidity content of the waste gas flow, as well as the increase in the humidity content measured by the individual sensors. The further the leak is from the position of the sensor in the flow direction of the waste gas flow, the more sensors are arranged to be distributed over the cross section of the waste gas channel, and the greater the increase in the humidity content measured by the corresponding sensor. The closer the leak is to the position of the sensor in the flow direction of the waste gas flow, the greater the increase in the humidity content measured by the corresponding sensor.

[0008] The measuring points are advantageously arranged in the manner of a grid in a uniformly distributed manner over the cross section of the waste gas flow, which results in a simple construction and reliable evidence.

[0009] It is advantageous if the measuring point is arranged downstream of the last heat exchanger through which the waste gas stream flows, in particular only downstream of the last heat exchanger through which the waste gas stream flows, as this minimizes the temperature of the waste gas stream in the area of ​​the measuring point, allowing the use of cost-effective sensors, since the sensors do not have to be resistant to high temperatures.

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

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

[0012] According to one configuration of the invention, the optical detection system comprises at least one video camera, which for the reasons mentioned above is preferably arranged downstream of the last heat exchanger through which the waste gas stream flows. Advantageously, the at least one video camera is directed towards an inner surface of the waste heat steam generator which is provided with a predefined pattern. If such a pattern is partially obscured by a steam cloud or band moving nearby, this can be detected on the basis of the captured video images. Advantageously, at least two video cameras are arranged on either side of the waste gas channel and directed towards mutually facing inner surfaces of the waste gas channel, which allows a better location of the leak.

[0013] Alternatively or additionally, the optical system may comprise at least one laser, which is in particular directed to an associated photodetector arranged on the inner surface of the waste heat steam generator, the at least one laser and the associated photodetector being preferably arranged downstream of the last heat exchanger through which the waste gas stream flows. The presence of steam in the waste gas stream may also be detected by obscuration of the photodetector by a steam cloud or band. Advantageously, a cross section of the waste gas channel is covered by a number of laser beams emitted adjacent to one another and directed to corresponding photodetectors, thereby enabling the determination of the position and size of the steam cloud or band and thus the location of the leak.

[0014] The present invention also provides a waste heat steam generator having a waste gas channel in which at least one heat exchanger with a water or steam conduit is arranged, in particular a heat exchanger functioning as a superheater, evaporator, feed water preheater, seen in the downstream direction, characterized in that a sensor and / or optical detection system designed to detect the presence of steam in the gas guided through the gas channel is provided, and a controller configured to execute the method according to the present invention is provided in data connection to the sensor and / or optical detection system.

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

[0016] Advantageously, a retaining grid is provided which extends across the cross section of the waste gas channel and accommodates the sensors, the sensors being arranged in particular at regular intervals on the retaining grid, which ensures a simple and cost-effective installation of the sensors across the cross section of the waste gas channel.

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

[0018] Advantageously, the optical detection system comprises at least one camera and / or at least one laser, which may be arranged in the waste gas channel, as already explained in the context of the method according to the invention. [Brief description of the drawings]

[0019] Further features and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings.

[0020] [Figure 1] 1 shows a schematic side view of a waste heat steam generator according to one embodiment of the present invention. [Diagram 2] A cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 2 shows a diagram similar to FIG. 1 , illustrating diagrammatically damage to conduits of multiple heat exchangers within a waste heat steam generator and the resulting steam cloud; [Figure 4] 4 shows a cross-sectional view taken along line IV-IV in FIG. [Diagram 5] 4 shows a schematic plan view of a downstream region of a waste heat steam generator according to a further embodiment of the present invention;

[0021] Hereinafter, the same reference numerals indicate the same or similar parts or components. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0022] FIG. 1 shows a waste heat steam generator 1 according to one embodiment of the present invention, which uses a hot waste gas stream from a previous process to generate superheated steam from feedwater, as is known, for driving a steam turbine 2.

[0023] The waste heat steam generator 1 comprises a housing 3 through which extends a waste gas channel 6 having a waste gas inlet 4 and a waste gas outlet 5, which opens via a diffuser into a downstream chimney 7. Arranged in the waste gas channel 6 in the flow direction of the waste gas stream are three heat exchangers 8, 9 and 10, one after the other, with heat exchanger 8 functioning as a superheater, heat exchanger 9 as an evaporator and heat exchanger 10 as a feedwater preheater.

[0024] During operation of the waste heat steam generator 1, a hot waste gas stream from a previous process, for example a gas turbine process, is introduced into the waste gas channel 6 through the waste gas inlet 4 in the direction of the arrow 11. The waste gas flows through the waste gas channel 6 in the direction of the arrow 12, through the waste gas outlet 5 into the chimney 7, and then through the chimney in the direction of the arrow 13, and is finally discharged into the environment. In the process of passing through the waste gas channel 6, the waste gas dissipates heat in countercurrent to the feed water guided through the conduit 14 of the heat exchangers 8, 9 and 10, superheating it step by step. More precisely, the feed water, which is supplied to the heat exchanger 10 located at the downstream end of the waste gas channel 6 via the feed water pump 15, is preheated for the time being by the waste gas stream. The preheated feed water is then supplied to the steam drum 16, which supplies the preheated feed water to the conduit 14 of the heat exchanger 9. The feed water is then evaporated in the heat exchanger 9. The steam produced is then fed into conduit 14 of heat exchanger 8 where it is superheated. The superheated steam is ultimately directed to steam turbine 2 to drive, for example, a generator 17.

[0025] During operation of the waste heat steam generator, it is desirable to monitor the condition of the conduits 14 of the heat exchangers 8, 9 and 10 in order to detect any possible leaks as early as possible, thereby minimizing downtime and maintenance time.

[0026] To monitor the state of the conduit 14, the waste heat steam generator 1 in this embodiment comprises a number of sensors 18, which are arranged in the waste gas channel 6 and designed to measure a measurement value representative of the humidity content of the waste gas stream. In this case, the sensors 18 are designed as humidity sensors and are arranged to measure the humidity content of the waste gas stream guided through the waste gas channel 6 at a number of measuring points. Alternatively or in addition, it is also possible to use sensors which do not directly measure the humidity content but, for example, measure a measurement value which is proportional to the humidity content. In the illustrated embodiment, the sensors 18 are arranged on a holding grid 19 which extends across the cross section of the waste gas channel. In this case, the sensors 18 are positioned on the holding grid 19 at regular intervals in a matrix. The holding grid 19 is arranged downstream of the last heat exchanger 10, the sensors 18 being arranged to measure the humidity content of the waste gas stream after it has passed through all the heat exchangers 8, 9 and 10. Basically, further holding grids 19 with sensors attached to them are arranged in the waste gas channel 6, so that the humidity content of the waste gas stream at various cross sections of the waste gas channel can be measured. In this case a second retaining grid with sensors 18 mounted thereon is placed downstream of the first retaining grid 19, these sensors 18 only serving to verify the measurements taken by the upstream placed sensors 18 and are therefore intended to form a redundant configuration. The sensors 18 are data coupled to a controller 20.

[0027] Figures 3 and 4 show diagrammatically the damages 21, 22, and 23 to the conduits 14 of each of the three heat exchangers 8, 9, and 10. The damage 21 causes water or steam to escape the conduit 14 and be carried by the hot waste gas stream forming a water vapor cloud, thereby increasing the humidity content of the waste gas stream. As a result, the area over which the sensor 18 detects an increase in the humidity content of the waste gas stream increases as the distance between the damages 21, 22, 23 and the sensor 18 increases, as more steam is distributed in proportion to the distance it travels within the waste gas channel 6. This is shown diagrammatically by the dashed lines in Figure 3 and by the different sized circles 24, 25, 26 in Figure 4. In this case, circle 24 generally indicates an area where sensor 18 indicates an increase in the amount of humidity in the waste gas stream caused by damage 21, circle 25 generally indicates an area where sensor 18 indicates an increase in the amount of humidity in the waste gas stream caused by damage 22, and circle 26 generally indicates an area where sensor 18 records an increase in the amount of humidity in the waste gas stream caused by damage 23. It has also been found that the increase in the amount of humidity in the waste gas stream increases as the distance between the damages 21, 22, 23 and sensor 18 decreases, and in Figure 4 this is shown by the density of the hatching in circles 24, 25, 26. The location and number of sensors 18 recording the increase in the amount of humidity in the waste gas stream, and the recorded level of increase in the amount of humidity in the waste gas stream can be used to correspondingly infer the location of the leak, facilitating maintenance staff's investigation of the leak and minimizing maintenance periods.

[0028] During operation of the waste heat steam generator 1, the sensors 18 detect the humidity content of the waste gas stream at predefined intervals or continuously. The detected measured values ​​are transmitted to the controller 20, where the detected measured values ​​are compared with at least one stored limit value. The at least one limit value is a fixed limit value defined depending on the operating conditions, e.g. external temperature, humidity, type of fuel used in the upstream process, etc. However, alternatively or in addition, the limit value may be defined, e.g., as a maximum permissible increase in the humidity content of the waste gas stream within a predefined period of time. If at least one of the detected measured values ​​exceeds the 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 of the leak is calculated and output to the operating staff. The measured values ​​detected by the sensors 18 arranged on the rear retaining grid 19 in the flow direction of the waste gas stream are used to verify the measured values ​​detected by the sensors 18 arranged on the front retaining grid 19, thus minimizing false alarms and / or substituting the function of a failed sensor 18 on the first retaining grid 19.

[0029] The condition monitoring of the water or steam conduit 14 according to the invention has the feature that the number of sensors can be significantly reduced compared to conventional acoustic monitoring, thereby saving costs. The arrangement of the sensor 18 at the downstream end of the waste heat steam generator 1 allows the use of cost-effective commercially available sensors 18 within the temperature range, where the temperature of the waste gas stream is relatively low. The required monitoring accuracy can also be achieved using cost-effective commercially available sensors. In terms of the mass flow rate flowing 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 emergent steam mass flow rate of about 2 g / s, is accompanied by a 2-2.5% increase in the humidity content of the waste gas stream immediately downstream of the first heat exchanger 8, and a 1-1.5% increase in the humidity content of the waste gas stream immediately downstream of the third heat exchanger 10, and thus at the location of the sensor 18, which can be measured by a cost-effective commercially available humidity sensor.

[0030] 5 shows a cross-sectional view of a waste heat steam generator 1 according to another embodiment of the invention, the structure of which basically corresponds to that of the first embodiment. Instead of the sensor 18, an optical detection system 27 is provided here, which in this case comprises two video cameras 28, which are preferably cooled in order to protect against the high temperature environment. In the illustrated embodiment, the video cameras 27 are arranged on both sides of the waste gas channel 6, each directed towards the inside of the waste gas channel 6, which in this example is provided with a predetermined pattern, for example a pattern in the form of a mesh line. The video cameras and the pattern can be arranged at different levels in the waste gas channel 6, but this is not a requirement.

[0031] If a leak occurs, the pattern area will be obscured by the water vapor cloud, which will be recorded by image recognition software contained in the controller 20 and an alarm will be activated. The location of the leak will be 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 comprise, as an alternative or in addition to the video camera 27, a laser with an associated photodetector arranged on the inner wall of the waste gas channel 6, even if not shown in this example. In this case the presence of a vapour cloud in the waste gas stream is detected when the laser light incident on the photodetector is attenuated or blocked by the vapour cloud. By appropriate selection of the positions of the laser and the photodetector it is also possible to calculate the location of the leak.

[0033] Although the present invention has been shown and described in more detail by means of preferred exemplary embodiments, the invention is not limited to the disclosed examples, and those skilled in the art can derive other variants therefrom without departing from the scope of protection of the invention. [Explanation of symbols]

[0034] 1 Waste heat steam generator 2. Steam turbine 3. Housing 4 Waste gas inlet 5 Waste gas outlet 6 Waste gas channel 7. Chimney 8 Heat exchanger (superheater) 9 Heat exchanger (evaporator) 10 Heat exchanger (feed water preheater) 14 Conduit 15 Water Pump 16 Steam Drum 17. Generator 18 Sensors 19 Retaining Grid 20 Controller 27 Optical Detection Systems

Claims

1. 1. A method for monitoring the condition of at least one water or steam conduit (14) of a heat exchanger (8, 9, 10) arranged in the waste gas stream of a waste heat steam generator (1) and functioning, in particular as viewed downstream, as a superheater, an evaporator and a feed water preheater, comprising: the presence of water vapor in the waste gas stream is detected automatically using a sensor (18) that detects a measurement representative of the amount of humidity in the waste gas stream and / or using an optical detection system; An alarm is activated when water vapor is detected, A method comprising:

2. 2. The method of claim 1, wherein 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 activated if at least one of the detected measurements exceeds the limit value; 3. The method of claim 2 .

4. 4. The method according to claim 2 or 3, characterized in that the sensor (18) detects measured values ​​at measuring points distributed over a cross section of the waste gas flow.

5. 5. The method according to claim 4, wherein the measurement points are arranged in a grid pattern and uniformly distributed over the cross section of the waste gas flow.

6. 6. The method according to claim 4 or 5, characterized in that the measuring point is arranged downstream of the last heat exchanger (10) through which the waste gas stream flows, in particular only downstream of the last heat exchanger (10) through which the waste gas stream flows.

7. If an alarm occurs, a location of the leak is calculated based on a comparison of the measurements detected at a plurality of the measurement points; The calculated position is output to an operating staff.

7. The method according to claim 4, wherein the first and second electrodes are arranged in a first direction.

8. the optical detection system (27) comprises at least one video camera (28); said video camera (28) being directed towards the inner surface of the waste heat steam generator (1) which is provided with a particular pattern; At least one said video camera (28) is preferably positioned downstream of the last heat exchanger (10) through which the waste gas stream flows.

8. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

9. an optical detection system (27) comprising at least one laser, said laser being directed in particular at an associated photodetector arranged on the inner surface of the waste heat steam generator (1); The at least one laser and associated photodetector are preferably positioned downstream of the last heat exchanger (10) through which the waste gas stream flows.

9. The method according to claim 1, wherein the first and second electrodes are arranged in a first direction.

10. A waste heat steam generator (1) having a waste gas channel (6), in which at least one heat exchanger (8, 9, 10) having a conduit (14) for conducting water or steam is arranged, in particular in which, viewed in the downstream direction, the heat exchanger functions as a superheater, an evaporator and a feed water preheater, a sensor (18) and / or an optical detection system is provided, designed to detect the presence of water vapor in the waste gas stream guided in the waste gas channel; a data connection to said sensor (18) and / or said optical detection system (27); A controller (20) is provided that is configured to carry out the method according to any one of claims 1 to 9, A waste heat steam generator (1).

11. Waste heat steam generator (1) according to claim 10, characterised in that the sensor (18) is a humidity sensor.

12. A waste heat steam generator (1) as claimed in claim 10 or 11, characterized in that a retaining grid (19) is provided which houses the sensors (18) and is arranged at regular intervals on the retaining grid (19) across a cross section of the waste gas channel (6).

13. 13. Waste heat steam generator (1) according to claim 12, characterized in that the retaining grid (19) is arranged downstream of the last heat exchanger (10).

14. Waste heat steam generator (1) according to any one 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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