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] Description

[0002] Method for monitoring the condition of heat exchanger pipes of a heat recovery steam generator and heat recovery steam generator

[0003] The invention relates to a method for monitoring the condition of pipes carrying water or steam in at least one heat exchanger arranged in an exhaust gas stream 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. Furthermore, the invention relates to a heat recovery 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.

[0004] Heat recovery steam generators, often referred to as HRSGs (Heat Recovery Steam Generators), are known in the art in various designs. They are used to use the hot exhaust gas from an upstream process to generate steam and normally comprise an exhaust duct in which several heat exchangers are arranged downstream, usually in the form of a superheater, an evaporator and a feedwater preheater. Leaks in the water or steam-carrying pipes of the heat exchangers can result in unannounced downtimes due to malfunctions, which must 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 position 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 that are distributed around the entire heat recovery steam generator. Leaks cause a change in the ambient noise, which is then detected by the sensors. Sensors positioned closer to the location of the leak detect stronger noise changes than sensors positioned further away. In this way, leaks can also be located using sensors. A disadvantage of the known acoustic detection systems, however, is that several hundred sensors have to be arranged and wired around the heat recovery steam generator, which is both very complex and expensive.

[0005] 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.

[0006] 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, characterized in that 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 which record a measured variable representing the moisture content of the exhaust gas flow, 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 and in this way cause 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 water vapor 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 that significantly fewer sensors are required, and they 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.

[0007] 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.

[0008] 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 to be sufficiently high to reliably indicate that a leak actually exists, and sufficiently low to allow sufficient time to plan and carry out repair work to eliminate the leak.

[0009] According to one embodiment of the present invention, the sensors detect the measured variable at measuring points that are 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 relatively 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.With knowledge of the flow characteristics of the exhaust gas through the exhaust pipe and of 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.

[0010] Preferably, the measuring points are arranged in the manner of a grid, evenly distributed over the cross section of the exhaust gas flow, which leads to a simple structure and reliable statements.

[0011] Advantageously, the measuring points are positioned downstream of the heat exchanger through which the exhaust gas flow last flows, in particular exclusively downstream of the heat exchanger through which the exhaust gas flow last flows. This results in the exhaust gas temperature being minimal in the region of the measuring points, which allows the use of inexpensive sensors, since they do not require high temperature resistance.

[0012] 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.

[0013] Alternatively or additionally, an optical detection system is used for detection according to the invention.

[0014] 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 flows, 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 from the recorded video images. Preferably, at least two video cameras are positioned on opposite sides of the exhaust gas duct and directed at opposite inner surfaces of the exhaust gas duct, thereby enabling better localization of the leak.

[0015] Alternatively or additionally, the optical system can have 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 flowed. 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 laser beams emitted adjacent to one another, which are 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.Furthermore, the present invention creates 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 feed water preheater, characterized in that 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 that a control is provided which is connected in terms of data technology to the sensors and / or the optical detection system and is set up to carry out the method according to the invention.

[0016] The sensors are preferably humidity sensors.

[0017] Advantageously, a support grid is provided for the sensors, extending across a cross-section of the exhaust duct, with the sensors being 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.

[0018] Preferably, the holding grid is arranged downstream of the last heat exchanger.

[0019] 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.

[0020] 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;

[0021] Figure 2 is a sectional view along the line I I- II in Figure 1;

[0022] Figure 3 is a view analogous to Figure 1, schematically showing damage to pipes of various heat exchangers of the heat recovery steam generator and the resulting water vapor clouds;

[0023] Figure 4 is a sectional view taken along the line IV-IV in Figure 3; and

[0024] Figure 5 is a schematic plan view of a downstream region of a heat recovery steam generator according to a further embodiment of the present invention.

[0025] The same reference numerals refer to the same or similar parts or components.

[0026] Figure 1 shows a waste heat 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.

[0027] The heat recovery steam generator 1 comprises a housing 3, through which an exhaust gas duct 6 extends, which has an exhaust gas inlet 4 and an exhaust gas outlet 5 and opens downstream into a chimney 7 via a diffuser. Within the exhaust gas duct 6, three heat exchangers 8, 9 and 10 are arranged one behind the other in the flow direction 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. During operation of the heat recovery steam generator 1, hot exhaust gas from an upstream process is introduced into the exhaust gas duct 6 in the direction of the arrow 11 through the exhaust gas inlet 4, for example the hot exhaust gas from a gas turbine process. The exhaust gas flows through the exhaust duct 6 in the direction of the arrows 12 , enters the chimney 7 through the exhaust outlet 5, flows through it in the direction of the arrows 13 and is finally discharged into the environment.On its way through the exhaust duct 6, the exhaust gas gives off heat to feedwater which is passed in countercurrent through pipes 14 of the heat exchangers 8, 9 and 10 in order to gradually superheat this feedwater. More precisely, 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 steam generated 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 a generator 17, for example.

[0028] 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 in this way to minimize downtime and maintenance times.

[0029] 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 gas duct 6, which sensors 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 gas duct 6 at a plurality of measuring points. Alternatively or additionally, sensors can also be used which do not directly detect the moisture content, but rather, for example, detect a measured variable that is proportional to the moisture content. In the embodiment shown, the sensors 18 are provided on a holding grid 19 which extends over a cross-section of the exhaust gas duct.The sensors 18 are positioned in a matrix-like manner at equal intervals on the holding grid 19. The holding 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 the heat exchangers 8, 9 and 10. In principle, further holding 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 different cross-sections of the exhaust duct 6. In the present case, a second holding grid with sensors 18 held thereon is positioned downstream of the first holding grid 19, wherein these sensors 18 are only intended to verify the measured values ​​detected by the upstream positioned sensors 18 and thus form a redundant arrangement. The sensors 18 are data-linked to a controller 20.

[0030] Figures 3 and 4 schematically show damage 21, 22 and 23 on a pipe 14 of the three heat exchangers 8, 9 and 10, respectively. The damage 21 causes 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 damage 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 is indicated schematically in Figure 3 by the dashed lines and in Figure 4 by the circles 24, 25 and 26 of different sizes.Circle 24 outlines the area in which sensors 18 record an increase in the moisture content of the exhaust gas caused by damage 21, circle 25 the area in which sensors 18 record an increase in the moisture content of the exhaust gas caused by damage 22, and circle 26 the area in which sensors 18 record an increase in the moisture content of the exhaust gas caused by 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 damage 21, 22, 23 from sensors 18, which is indicated in Figure 4 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 on the registered level 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 the maintenance personnel to search for the leak and minimizes the maintenance time.

[0031] During operation of the heat recovery steam generator 1, the sensors 18 record the moisture content of the exhaust gas at predetermined intervals or continuously. The recorded measured values ​​are then forwarded to the controller 20, where the recorded measured values ​​are compared with at least one stored limit value. The at least one limit value can be a fixed limit value that has been set as a function of 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 recorded measured values ​​exceeds the at least one limit value, an alarm is triggered to alert the operating personnel to the detected leak.Furthermore, the position of the leak is calculated and communicated to the operating personnel. The measured values ​​recorded by the sensors 18 arranged on the rear support grid 19 in the direction of exhaust gas flow are used to verify the measured values ​​recorded by the sensors 18 arranged on the front support grid 19 in order to minimize false alarms and / or to take over the function of failed sensors 18 of the first support grid 19.

[0032] The inventive monitoring of the condition of water or steam-carrying pipelines 14 is characterized in 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 temperature of the exhaust gas 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 about 2g / 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 moisture sensors.

[0033] Figure 5 shows 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. However, instead of the sensors 18, 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 embodiment shown, 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.

[0034] If, in the event of a leak, areas of the pattern are obscured by a cloud of water vapor, 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 position of the leak is calculated and communicated to the operating personnel.

[0035] 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. With a suitable selection of the positions of the lasers and light detectors, the position of the leak can also be calculated.

[0036] 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 can be derived therefrom by those skilled in the art without departing from the scope of the invention.

Claims

Patent claims 1. Method for monitoring the condition of water or water vapor-carrying pipelines (14) of at least one heat exchanger (8, 9, 10) arranged in an exhaust gas stream of a waste heat steam generator (1), in particular, viewed in the downstream direction, a heat exchanger serving as a superheater, an evaporator and a feedwater preheater, characterized in that the presence of water vapor within the exhaust gas stream is automatically detected using sensors (18) that detect a measured quantity representing the moisture content of the exhaust gas stream and / or using an optical detection system, and an alarm is triggered in the event of detection.

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

3. Method according to claim 2, characterized in that the measured values ​​recorded by the sensors (18) are compared with at least one stored limit value and, if at least one of the recorded measured values ​​exceeds the limit value, the alarm is triggered.

4. Method according to claim 2 or 3, characterized in that the sensors (18) detect the measured quantity at measuring points which are arranged distributed over a cross-section of the exhaust gas flow .

5. Method according to claim 4, characterized in that the measuring points are arranged in a grid-like manner, evenly distributed over the cross-section of the exhaust gas flow.

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

7. Method according to one of claims 4 to 6, characterized in that 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 the calculated position is output to the operating personnel.

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

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

10. Waste heat steam generator (1) with an exhaust gas duct (6) in which at least one heat exchanger (8, 9, 10) having pipes (14) carrying water or steam is arranged, in particular, viewed in the downstream direction, a heat exchanger designated as a transfer- a heat exchanger serving as an evaporator and as a feedwater preheater, characterized in that sensors (18) and / or an optical detection system are provided within the exhaust gas duct, which are designed to detect the presence of water vapor in an exhaust gas passed through the exhaust gas duct, and that a control unit (20) is provided which is connected to the sensors (18) and / or the optical detection system (27) by means of data technology and which is set up to carry out the method according to one of the preceding claims.

11. Waste heat steam generator (1) according to claim 10, characterized in that the sensors (18) are humidity sensors.

12. Waste heat steam generator (1) according to claim 10 or 11, characterized in that a retaining grid (19) for receiving the sensors (18) is provided, the sensors being positioned at uniform intervals on the retaining grid (19) over a cross-section of the exhaust gas duct (6).

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 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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