GB2502373A

GB2502373A - Thermal scanner

Info

Publication number: GB2502373A
Application number: GB1209403.3A
Authority: GB
Inventors: Bernard Robbins; David Martin Farrell
Original assignee: Rowan Technologies Ltd
Current assignee: Rowan Technologies Ltd
Priority date: 2012-05-21
Filing date: 2012-05-28
Publication date: 2013-11-27
Anticipated expiration: 2032-05-28
Also published as: GB201208909D0; GB201209403D0; GB2502373B

Abstract

A non-intrusive thermal scanner system for monitoring the fireside conditions of a wall 100, such as walls of power station boilers or furnaces as well as walls of pipelines and storage vessels. The system comprises a plurality of temperature sensors 10 arranged to provide an array 15 on an external side of the wall 100 the array defining a monitoring area (30) on the wall. At least one non-intrusive heat flux sensor 50 is also provided. A control system (20) is configured to scan the array 15 of sensors 10 in sequence. Also disclosed is a method of non-intrusive monitoring of the fireside conditions of a wall.

Description

NON-INTRUSIVE SCANNER

FIELD OF THE INVENTION

The present invention relates to a non-intrusive thermal scanner system for monitoring the fireside conditions of a wall and a method of non-intrusive integrity monitoring of the fireside conditions of a wall using non intrusive technology (NT) techniques. In particular, the invention relates to the monitoring of fireside conditions of a boiler tube wall.

BACKGROUND OF THE INVENTION

The monitoring of fireside (i.e. internal) conditions of a wall is important in understanding the health and performance of plant systems. Such monitoring may be particularly useful in enhancing knowledge and awareness to provide smoother operations and maximising efficiency. Such monitoring may be used to monitor boiler walls (for example the walls of power station boilers or furnaces) as well as walls of pipelines, storage vessels and the like.

Fireside conditions may typically be monitored using intrusive sensors which require a portion of the wall (typically a section of tube from a boiler tube wall) to be removed and replaced with a replacement section of wall material (typically a tube of the same material as the original wall). Thermocouples are embedded in the replacement section at the fireside of the wall (typically in the fireside crown of the tube). By providing a pair of thermocouples it is possible to measure both the point temperature and the fireside wall heat flux. It will be appreciated that the installation of such intrusive sensors incurs significant cost and increased risk for the plant integrity. Specialist welding may also be required to install the replacement wall sections.

SUMMARY OF THE INVENTION

According to a first aspect the present invention provides a non-intrusive thermal scanner system for monitoring the fireside conditions of a wall wherein the system comprises a plurality of temperature sensors arranged to provide an array on an external side of the wall, the array defining a monitoring area on said wall; at least one non-intrusive heat flux sensor; and a control system configured to scan the array of sensors in sequence.

An array of temperature sensors may be used to map external wall surface temperatures. The external temperatures may be used to estimate the fireside wall temperature and/or heat flux. The provision of at least one non-intrusive heat flux sensor enables the accuracy of the estimates produced from the array to be increased. The control system may be arranged to estimate the fireside heat flux at each temperature sensor and may further be arranged to calibrate said estimate using heat flux measurements from the at least one non-intrusive heat flux sensor.

The control system may be arranged to control the scanning array and to acquire data from the sensors. The control system may be arranged to enable real time data capture and historical data analysis. Data from the scanner system may be plotted as linear traces (which may highlight events such as wall cleaning). Preferably, the control system is configured to provide a two dimensional map of the fireside conditions of the monitoring area. It will be appreciated that the provision of a two dimensional map is enabled by the provision of an array of sensors.

In one embodiment the invention provides a non-intrusive thermal scanner system for monitoring the fireside conditions of a tube wall (such as a boiler tube wall).

The array formed by the plurality of temperature sensors will depend upon the size and shape of the wall to be monitored and could for example be a linear array or a rectangular matrix (for example a rectangular matrix with a sensor at each node). Rectangular matrices are particularly suitable for providing a two dimensional mapping of a wall. The plurality of sensors may be pre-configured in an array connected with pre-installed wiring ready for connecting as an array on a wall (for example "chains" of sensors may be provided). The plurality of sensors may be spaced apart by at least one flexible conduit and arranged in a desired configuration for forming said array on an external side of the wall.

The at least one non-intrusive heat flux sensor may be arranged to be positioned on an external surface of the wall within the monitoring area.

Preferably, at least one non-intrusive heat flux sensor is provided within the array (for example the non-intrusive heat flux sensor may be a node within the array). The non-intrusive heat flux sensor may replace a temperature sensor within the array.

The non-intrusive heat flux sensor may comprise a plurality of electrodes arranged to be connected to the external surface of the wall and to directly measure the electrical characteristics of the wall.

The non-intrusive sensor may be used independently of the scanner system and as such according to a further aspect of the invention there is provided a non-intrusive heat flux sensor comprising a plurality of electrodes arranged to be connected to the external surface of the wall and to directly measure the electrical characteristics of the wall. Preferably the non-intrusive sensor is arranged to measure electrical characteristics of different parts of the wall at the sensor location.

The non-intrusive heat flux sensor preferably measures the resistance of the wall, for example it may use a four-terminal sensing arrangement for accurate measurement. The electrodes are preferably arranged to take electrical resistance measurements across different parts of the wall at the sensor location. Measurements from different parts of the wall may be used to measure the heat flux flowing through the wall. The plurality of electrodes may comprise a plurality of electrode pairs, each pair comprising a current supply electrode and a current sink electrode and being arranged to measure the resistance therebetween. In the case of a tube wall the electrodes may typically be arranged to measure the resistance of both the crown and the membrane. The electrodes may be arranged around a single tube or a small number of tubes. The distance between the electrodes may generally be short so as to limit the spreading of the current.

The resistance measurements from the non-intrusive heat flux sensor are used in a finite element model of the wall to calculate the heat flux in the wall.

Advantageously, this allows the heat flux across the whole fireside wall to be determined in contrast to the embedded thermocouples of intrusive heat flux sensors which only measure the heat flux at a point proximal to the embedded thermocouples.

The system may be configured to provide wall integrity scanning (for example the monitoring of wall erosion and/or corrosion) in addition to thermal scanning.

As such, the plurality of temperature sensors may be arranged to provide electrodes on the wall and the system is arranged to measure resistance between adjacent sensor locations (which are typically nodes within the array) for monitoring the wall integrity. The resistance measurements between sensor locations may be used to calculate at least one of fireside corrosion rate, fireside metal loss, remaining wall thickness or time to replacement. The control system may provide a two dimensional map of the fireside wall integrity of the monitoring area.

Preferably the control system may comprise a scanner control and data acquisition module and may further comprise a virtual network module and may further comprise an ORG module.

According to a further aspect of the present invention there is provided a boiler comprising a non-intrusive thermal scanner system according to embodiments of the invention, wherein the plurality of temperature sensors and the at least one non-intrusive heat flux sensor are attached to an external side of the boiler wall. The sensors are preferably welded to the external side of the boiler wall.

According to a further aspect of the invention there is provided a method of non-intrusive monitoring of the fireside conditions of a wall, wherein the method comprises: providing an array of temperature sensors on the non-intrusive external side of the wall; scanning the array of sensors; providing at least one heat flux sensor on the external side of the wall; and calculating the heat flux of the fireside wall from the heat flux sensor.

The step of providing at least one non-intrusive heat flux sensor on the external side of the wall may comprise measuring the resistance of wall and calculating the heat flux (for example using a finite element model). For example, the step of providing at least one non-intrusive heat flux sensor on the external side of the wall may comprise providing a plurality of electrodes on a portion of the external side wall and measuring the electrical resistance of parts of said portion of the side wall and calculating the heat flux of the fireside wall from the at least one non-intrusive heat flux sensor comprises providing a finite element model of the portion of the wall and calculating the heat flux through the whole fireside wall.

Preferably the method further comprises providing a two dimensional map of the fireside wall conditions within the area defined by the array of temperature sensors.

The method may comprise the additional steps of estimating the heat flux of the fireside wall across the array of temperature sensors; and refining said estimates using the heat flux calculation from the at least one non-intrusive heat flux sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a schematic of a typical thermal scanner system layout for use in embodiments of the invention; Figure 2 is a schematic of a control system for use in the sensor system of Figure 1; Figure 3 illustrates a two dimensional temperature map which may be produced by a thermal scanner system; Figure 4 is a schematic of the measurement of wall integrity using the system of figure 1; Figure 5 is a schematic of the location of heat flux sensors in a thermal scanner system; and Figure 5 is an image of a plurality of electrodes for a non-intrusive heat flux sensor positioned on the outer side of a wall.

DETAILED DESCRIPTION OF EMBODIMENT

As shown in figure 1, a nan-intrusive thermal scanner system 1 comprises a plurality of thermal sensors 10 arranged as a rectangular matrix 15 on the wall of a boiler (not shown). Each sensor 10 forms a node in the matrix 15 which defines the monitoring area 30. A single matrix 15 could for example comprise up to 250 sensor locations. In the schematic of figure 1 a single system 1 comprises two separate matrices 15a, 15b which may each be attached to different walls bOa, lOOb (or different regions of a single wall) of a boiler (alternatively a single system may monitor several boilers in a single plant). The sensors 10 are connected by pre-assembled wires 12 in flexible conduits so as to provide chains of sensors ready for connection to the wall 100 of the boiler. Typically, the sensors 10 forming the array may be approximately one metre apart. A single communication cable 14 is provided extending from the array 15 to the control system 20 which may for example be located in a control cabinet in a different area of the plant. The communication cable 14 could be several hundred meters long.

An electrode is welded to the external side of the wall 100 at each sensor location to which the pre assembled wiring may be easily connected. Node boxes 11 may be conveniently provided at some nodes of the matrix 15 to accommodate associated electronics (typically in a weatherproof box). Where ambient conditions exceed the operating limits the node box electronics may be located in a convenient cooler location.

The control system 20 comprises a scanner control and data acquisition module 22 which is arranged to control rapid scanning of the sensors in a pre determined sequence and to acquire the resulting data. The control system 20 also comprises modules for data access and analysis. An OPC module 23 allows the data to be made available to the plant historian. A virtual networking module 24 allows remote access to the data via plant network or other network connections. The control system may also comprise a data storage device for recording historical plant data from the scanner system.

Figure 3 shows a two dimensional map that can be generated by the non-intrusive thermal scanner system 1. The mapping may for example show the external wall temperature and can be used to readily compare or observe changes in thermal behaviour over time. The map represents the monitoring area 30 as defined by the matrix 15 and has the locations of the sensors 10 superimposed. The measured and estimated values for that node location may also be displayed in the overlay.

The thermal scanner system 1 may optionally also be arranged to perform plant integrity scanning (for example the monitoring of wall erosion and/or corrosion).

As shown schematically in Figure 4, integrity scanning uses electrical resistance techniques to measure between the electrodes 10 of the matrix 15.

During the measurement cycle current passes through the wall between the electrodes and spreads through the bulk metal of the wall. Any metal thinning (for example as a result of corrosion) hinders the passage of current through the fireside of the wall and therefore increases the measured resistance between the electrodes 10. The temperature data captured by the system is used to compensate the resistance value measured. Two dimensional maps may be generated to represent the wall integrity (in a similar manner to that of figure 3) -for example maps may be provided of fireside corrosion rate and/or the fireside metal loss and/or the wall thickness remaining.

Figure 5 schematically shows the inclusion of non-intrusive heat flux sensors 50 within the matrix 15 of temperature sensors 10 on the external side wall 100 of a boiler. The non-intrusive heat flux sensors 50 enable the heat flux of the wall, including the fireside of the wall, to be calculated and used to increase the accuracy of heat flux estimates produced form the non-intrusive thermal scanner system 1. In this example non-intrusive heat flux sensors 50 are included within the monitoring area defined by a 7-by-15 rectangular matrix.

is The non-intrusive heat flux sensors 50 have each replaced a node location within the matrix.

As shown in figure 6, each sensor 50 comprises a plurality of simple electrodes welded to the cold side tube of the wall 100. The electrodes are typically welded around a single tube as shown in Figure 6 (although it will be appreciated that they could be around a plurality of tubes). Electrodes are welded to both the tube 110 and the adjacent membranes 120. The electrodes are used to take resistance measurements across the different parts of the wall (for example the crown of the tube 110 and at the membrane 120) in the vicinity of the sensor 50. Careful placing of the electrodes 55 allows the current flow to be restricted to certain parts of membrane boiler tubes. The relative measurements of the different parts of the wall may then be used to provide the heat flux, for example the raw data in the form of resistance measurements is used in a finite element model of the wall to calculate the heat flux values.

Advantageously the finite element model provides the heat flux through the entire fireside tube section rather than only at the fireside crown as with intrusive thermocouple sensors. The finite element model can be easily tailored for the specific wall characteristics. For example the model may take account of different diameters of boiler tubes or tube shapes (for example circular or oval tubes). Additionally, weld overlays' (for example high-nickel alloys), which are frequently provided on the fireside walls of power station boilers to prevent excessive corrosion and subsequent failure of the tubes, may be included in the model.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes and/or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1. A non-intrusive thermal scanner system for monitoring the fireside conditions of a wall wherein the system comprises a plurality of temperature sensors arranged to provide an array on an external side of the wall, the array defining a monitoring area on said wall; at least one non-intrusive heat flux sensor; and a control system configured to scan the array of sensors in sequence.
2. A non-intrusive thermal scanner system as claimed in claim 1 wherein the control system is further configured to provide a two dimensional map of the fireside conditions of the monitoring area.
3. A non-intrusive thermal scanner system as claimed in either of claims 1 and 2, wherein the control system is arrange to estimate the fireside heat flux at each temperature sensor and to calibrate said estimate using heat flux measurements from the at least one non-intrusive heat flux sensor.
4. A non-intrusive thermal scanner system for monitoring the fireside conditions of a boiler tube wall comprising a non-intrusive thermal scanner system as claimed in any of claims claim 1 to 3.
5. A non-intrusive thermal scanner system as claimed in any of claims 1 to 4, wherein the plurality of temperature sensors are arranged to provide a rectangular matrix on an external side of the wall.
6. A non-intrusive thermal scanner system as claimed in any of claims 1 to 5, wherein the at least one non-intrusive heat flux sensor is arranged to be positioned on an external surface of the wall within the monitoring area.
7. A non-intrusive thermal scanner system as claimed in any of claims 1 to 6, wherein the at least one non-intrusive heat flux sensor comprises a plurality of electrodes arranged to be connected to the external surface of the wall and to directly measure the electrical characteristics of the wall.
8. A non-intrusive thermal scanner system as claimed in claim 7, wherein the plurality of electrodes are arranged to measure the electrical resistance across different parts of the wall.
9. A non-intrusive thermal scanner system as claimed in either of claims 7 and 8, wherein the at least one non-intrusive heat flux sensor uses a finite element model of the wall to calculate the heat flux from resistance measurements.
10. A non-intrusive thermal scanner system as claimed in any preceding claim, wherein the plurality of temperature sensors are arranged to provide electrodes on the wall and the system is arranged to measure resistance between adjacent sensor locations for monitoring the wall integrity.
11. A non-intrusive thermal scanner system as claimed in claim 10, wherein the resistance measurement is used to calculate at least one of fireside corrosion rate, fireside metal loss, remaining wall thickness or time to replacement.
12. A non-intrusive thermal scanner system as claimed in either of claims 10 and 11, wherein the control system is further configured to provide a two dimensional map of the fireside wall integrity of the monitoring area.
13. A non-intrusive thermal scanner system as claimed in any preceding claim, wherein the plurality of temperature sensors are spaced apart by at least one flexible conduit and arranged in desired configuration for forming said array on an external side of the wall.
14. A non-intrusive thermal scanner system as claimed in any preceding claim, wherein the control system comprises a scanner control and data acquisition module and a virtual network module and an OPC module.
15. A boiler comprising a non-intrusive thermal scanner system as claimed in any preceding claim, wherein the plurality of temperature sensors and the at least one non-intrusive heat flux sensor being attached to an external side of the boiler wall.
16. A method of non-intrusive monitoring of the fireside conditions of a wall, wherein the method comprises: providing an array of temperature sensors on the external side of the wall; scanning the array of sensors; providing at least one non-intrusive heat flux sensor on the external side of the wall; and calculating the heat flux of the fireside wall from the heat flux sensor.
17. A method of non-intrusive monitoring of the fireside conditions of a wall as claimed in claim 16, wherein, the step of providing at least one non-intrusive heat flux sensor on the external side of the wall comprises providing a plurality of electrodes on a portion of the external side wall and measuring the electrical resistance of parts of said portion of the side wall; and calculating the heat flux of the fireside wall from the at least one non-intrusive heat flux sensor comprises providing a finite element model of the portion of the wall and calculating the heat flux through the whole wall.
18.A method of non-intrusive monitoring of the fireside conditions of a wall as claimed in either of claims 16 and 17, wherein the method further comprises: providing a two dimensional map of the fireside wall conditions within the area defined by the array.
19.A method of non-intrusive monitoring of the fireside conditions of a wall as claimed in any one of claims 16, 17 and 18, wherein the method further comprises: estimating the heat flux of the fireside wall across the array of temperature sensors; and refining said estimates using the heat flux calculation from the at least one non-intrusive heat flux sensor.