WO2000052436A1

WO2000052436A1 - Measuring device

Info

Publication number: WO2000052436A1
Application number: PCT/SE2000/000427
Authority: WO
Inventors: Thomas Eriksson
Original assignee: STUDSVIK INSTRUMENT AB
Current assignee: STUDSVIK INSTRUMENT AB
Priority date: 1999-03-04
Filing date: 2000-03-03
Publication date: 2000-09-08
Anticipated expiration: 2001-09-04
Also published as: AU3687900A

Abstract

An arrangement for measuring conditions in an environment with hot gas flows (150) comprises a hollow pole shaped probe (100) provided with at least one measuring device (113). The probe (100) is intended to be partly arranged in the hot environment and partly arranged to be accessible in an area outside the hot environment. The arrangement further comprises at least one essentially tube shaped channel (103) for transport of heat absorbing medium (160) between the probe (100) and the area outside the hot environment. The channel (103) is at least partly arranged in the hollow probe (100). The probe (100) is separable in its direction of elongation (X) in at least a first (101) and a second (102) probe section. The first probe section (101) is located in the hot environment.

Description

MEASURING DEVICE

TECHNICAL FIELD

The present invention relates to arrangements and methods for measuring conditions in environments characterized by hot gas flows, such as conditions for corrosion on devices within furnaces.

STATE OF THE ART

Corrosion is a collective term for the chemical attacks which a material is subject to when exposed in a certain environment. The chemical resistance of the material to a certain environment and the mechanical stress the material is subject to are in combination often criteria for which materials to use in a given application. The environment may be seemingly harmless, such as in the case of atmospheric corrosion, but also of a much more aggressive nature, such as in many industrial applications.

Thermodynamically, metallic materials are unstable and easily form oxides, sulfides, carbides etc. Usually, in a dry oxygen atmosphere at room temperature this instability has no practical implication since the reaction rate is low. But the chemical reaction rate increases with temperature, whereby stronger corrosive attacks are to be expected on materials exposed to aggressive environments at high temperature. A typical example of an environment in which the corrosive conditions are of economic interest is the over heater region in an energy producing furnace. The over heater in a furnace mainly consists of a large number of steam pipes in a tight configuration in order to enable highest possible yield of energy between the burning gas and the steam in the pipes. In operation, the over heater is difficult to monitor with respect to possible corrosion. Because of it's central role in the production it is of importance to enable monitoring of corrosion and the conditions for the appearance of corrosion. It shall be noted, however, that other factors may also be of interest to monitor in furnaces, such as direct mechanical wear in the form of erosion in so-called fluid bed furnaces.

That which is of interest while monitoring of, e.g., an over heater in a furnace is to obtain an estimate of the corrosion and, when appropriate, also the corrosion rate. This estimate may be considered in terms of the character of the coatings forming on, e.g., a tube of a measuring probe located in direct vicinity of the pipes of the over heater. Specific conditions that may be of interest are temperature and the rate of growth of the coatings on the steam pipes of the over heater. But also measurements of whether any coatings are in a solid or in a fluid state may be of interest. It is of great interest to enable measuring of conditions that are decisive for corrosion in these aggressive high temperature environments. Arrangements for measuring conditions for, e.g., corrosion on the steam pipes in the over heater in a furnace are often in the form of a rod shaped probe on which a number of measuring devices are arranged. The probe is preferably arranged such that the measuring devices are located in such vicinity of the steam pipes that the environment of the measuring devices and the pipes can be considered one and the same. In order to obtain as good results as possible it is of importance that the measuring probe and the steam pipes are kept at essentially one and the same temperature. For this purpose, the probe must be cooled by means of supplying, e.g., a cooling medium such as air or water. In many cases, the environment within the furnace does not allow cooling medium leakage. Hence, there is a need for a probe having a more or less circulating cooling system.

An example of a cooled measuring probe is to be found in the Swedish patent publication SE459281, in which it is shown in a preferred embodiment a hollow tubular probe for monitoring of coatings in hot gas flows. The probe consists mainly of a sealed probe tube, the outer surface of which is in contact with the hot gas. In order to enable control of the temperature of the probe an inner tube is arranged in the probe. A cooling medium, exemplified by air, is made to pass through the probe and out via the inner tube.

However, SE459281 illustrates an arrangement whose flexibility with respect to the arrangement of measuring devices is very limited. SE459281 only shows attached measuring devices that are fixed.

Furthermore, SE459281 avoids mentioning whether or not mechanical stress, created by differential thermal expansion of the components, affects the arrangement. In particular, a discussion of the attachment of the inner tube to the probe is avoided, as is any limitations of the function of the arrangement when the hot probe is expanding in length with respect to the comparatively cold inner tube.

SUMMARY OF THE INVENTION

A problem which the present invention intends to solve is how a measuring probe for hot environments shall be constituted in order to enable increased flexibility with respect to the arranging of measuring devices on the probe, in particular in connection with differential thermal expansion of the components of the probe.

A purpose of the present invention is to address and solve these problems and to show the use of an arrangement for measuring, e.g., the conditions for corrosion in an environment characterized by hot gas flows .

A purpose is achieved by an arrangement for measuring conditions in an environment with hot gas flows and comprises a hollow pole shaped probe provided with at least one measuring device. The probe is intended to be partly arranged in the hot environment and partly arranged to be accessible in an area outside the hot environment. The arrangement further comprises at least one essentially tube shaped channel for transportation of heat absorbing medium between the probe and the area outside the hot environment. The channel is at least partly arranged in the hollow probe. The arrangement is further characterized in that the probe is separable in its direction of elongation_. in at least a first and a second probe section. The first probe section is located in the hot environment. The tube shaped channel is arranged to be accessible in the area outside the hot environment and arranged to the first and the second probe section. The measuring device is removably attached between the probe sections.

Another purpose is achieved in that the tube shaped channel is arranged to the first probe section and arranged to the second probe section by means of at least one, in the direction of elongation of the probe, yielding connection device. The connection device is arranged to maintain a mechanical bias tension essentially in the direction of elongation of the probe between the tube shaped channel and the probe. The measuring device is fixed i^'n the direction of elongation to the probe by the mechanical bias tension.

Furthermore the purpose is achieved by a measuring system and a method in which an arrangement according to the above is part together with arrangements for data collection and data processing. An advantage of the invention is that, while at the same time enabling a flexible arrangement of measuring devices because a probe according to the invention may be separable into two parts and 'between the parts allow room for an arbitrary number of measuring devices, it provides for high quality measurements of corrosion conditions in environments with high temperatures. This is due to the fact that the arrangement can be kept at any temperature, such as the temperature of the steam pipes of a furnace, by use of controlled heat transport without allowing influence on the function by mechanical stress due to differential thermal expansion.

SHORT DESCRIPTION OF THE DRAWINGS

Figure 1 shows a schematic cross sectional view of a preferred embodiment of the invention, comprising a separable probe tube provided with measuring devices and a resiliently attached inner tube.

Figure 2 shows a schematic cross sectional view of a part of a probe tube with a number of measuring devices and isolators.

Figure 3 shows schematically an outline of a system comprising an arrangement according to the invention.

Figure 4 shows schematically a cross sectional view of another preferred embodiment of the invention, comprising a probe tube provided with measuring devices.

PREFERRED EMBODIMENTS

An arrangement for measuring conditions for corrosion in an energy producing furnace is shown in figure 1. The figure illustrates schematically a measuring probe 100 arranged in a furnace of which a side wall 116 is suggested in the figure. A hot gas flow 150 generated by the burning in the furnace represents a typical environment in which the invention is used. The measuring probe 100 is attached in a removable manner through the side wall 116 of the furnace by means of schematically illustrated attachment device 115. In order to increase the clarity, the measuring probe 100 is shortened in the figure. A typical length of a measuring probe 100 for use in a furnace is one to two meters.

Conditions that may be of interest and measured with the arrangement in figure 1 are temperature and electrical quantities measured using electrochemical techniques. The measured quantities are indicative of the corrosion and it's rate. In particular, the information relating to the state of the coatings is decisive in terms of the corrosive nature of the coatings. A liquid coating is more corrosive than a coating that is in a solid state.

Electrochemical methods for measuring corrosion are based on the phenomena that occur in an electrochemical cell. In simple terms, an oxidation takes place on one of the electrodes of the cell, i.e. an emission of electrons. Reduction takes place at the other electrode, i.e. capture of electrons. This transport of electrons causes an electric current to flow^'through the circuit, the size of which reflects the reactions taking place at the border between the electrode and the electrolyte. By measuring across a resistor with known resistance the voltage drop caused by the . generated current, the current can be calculated using Ohm's law. The development of different electrochemical methods are based on different techniques of measuring, in a representative manner, the often very complex reactions taking place at the border between the electrode and the electrolyte. Electrochemical methods hence require a presence of an electrolyte, such as salt melt or condensed fluid. It is hence a requirement that the corrosive environment generates an electrolyte. When using electrochemical information for in-situ measurements of corrosion, it is usually by way of simultaneous use of several electrochemical techniques. This multi-electrochemical technique may make use of electrochemical impedance measurements, linear polarization technique, zero- resistance technique and/or electrochemical noise measurements, all being techniques well known to a person skilled in the art.

Use of the arrangement according to the invention in electrochemical measurements will be further commented below in connection with figure 2, where the design and placement of the electric measuring devices is shown. As will be discussed in more detail below in connection with figure 2, the temperature may be measured with a thermoelement and any present melt may be measured electrochemically using two separated electrodes.

The main components of the measuring probe 100 are, as figure 1 illustrates in a cross-sectional view, a pole shaped probe tube, preferably of steel, having a circular cross-section. The probe tube is separable in it's direction of elongation X and comprises a first probe tube section 101 and a second probe tube section 102. Four electric measuring devices 113 are arranged between the probe tube sections 101,102. These measuring devices 113 are separated, in the sense of being electrically isolated, from each other and from the probe tube sections 101,102 by means of -five isolators 112. The measuring devices 113 are in the form of metallic sleeves and the isolators are in the form of ceramic rings and are fixed in their respective position along the measuring probe by a mechanical biasing tension which is present due to the attachment of an inner tube 103 to the probe tube sections 101,102 as will be described below.

The measuring devices and the isolators will be further discussed below in connection with figure 2.

Two lateral tubes are arranged on the second probe tube section 102, a first lateral tube 110 and a second lateral tube 111. These lateral tubes 110,111 partly perform the function of allowing access for electric connectors for the measuring devices 113 and partly to act as output means for heated cooling fluid 161, as will be discussed further below. An inner tube 103 is concentrically arranged within the probe tubes 101,102. The inner tube 103 has an outer connection portion 104 to which a source (not shown in the figure) of cooling fluid 160 is preferably connected. The inner tube 103 is connected within the probe tube sections 101,102 by means of, e.g., a threaded connector, to the first probe tube section 101 via an inner tube connector 105. In the vicinity of its attachment to the first probe tube section 101, the inner tube 103 is provided with a number of exit openings 109 through v/hich the cooling fluid 160 is made to pass from the inner tube 103, through the probe tube sections 101,102 and out through any or both of the lateral tubes 110,111.

The inner tube 103 is resiliently arranged to the second probe tube section 102 at the outer connection portion 104. This results in a mechanical biasing tension between the inner tube 103 and the probe tube sections 101,102 fixing the measuring devices and the isolators 112 in their respective positions between the probe tube sections 101,102. The resilience is established in this example by means of a washer assembly 108. The washer assembly 108 consists of a number of arched washers being in abutment with a flange 117 on the second probe tube section 102 and fixed in its position by threaded bolts 106 and a sleeve 107. Needless to say, other resilient arrangements known in the art may be used, such as a spring.

In order to achieve a plastically yielding arrangement, as opposed to a resilient arrangement, of the inner tube 103 to the second probe tube section 102, the washers 108 may of course be exchanged by, e.g., a plastic sleeve of an appropriate material. A situation in which this may be desirable is when a given mechanical biasing tension is to be maintained in the arrangement, such as when there exists an upper tension limit that is not to be exceeded. A combination of resilient and plastically yielding arrangements may be used to obtain an arbitrary varying character of the yielding of the arrangement.

During operation in an environment having hot gas flows 150, the first 101 and the second 102 probe tube section will be subject to heating from without by the gas flow 150 and cooling from within by the cooling fluid 160. The probe tube sections 101,102 and the inner tube 103 will then, depending on the magnitude of the flow of cooling fluid 160, obtain different temperatures.

An example of a hot environment is the over heater region of a furnace where the temperature may be around 900 degrees Celsius. Depending on the cooling, the probe tube sections 101,102 will in such an environment reach a temperature of about 650 degrees Celsius. The inner tube 103 obtains a significantly lower temperature, at least several hundreds of degrees lower than the temperature of the probe tube sections 101,102.

Due to the thermal expansion characteristics of steel, the probe tube sections 101,102 and the inner tube 103 will expand in volume. This expansion is most notable in the direction of elongation X of the tubes 101,102,103, and due to the large temperature difference between the probe tube sections 101,102 and the inner tube 103, these will obtain different expansions in length. A difference of one to two centimeters in length expansion between the probe tube sections 101,102 and the inner tube 103 is to be expected when the temperature difference is a few hundred degrees.

This difference in length expansion results in a pulling force along the inner tube 103 and the probe tube sections 101,102 which results in the measuring devices 113 and the isolators 112 are subject to a squeezing force which in addition to the applied biasing tension further keeps them together and also retains a sealing coupling between them.

The resilient arrangement 108 receives the difference in length expansion, the pulling force increasing with increasing difference in length expansion along the probe tube sections 101,102 and the inner tube 103. This may entail certain limitations with respect to a choice of materials to use for measuring devices 113 and isolators 112. In particular the isolators 112, preferably not made of steel, are usually of materials having a limited strength to withstand mechanical force. Hence, it may be desirable to provide a limiting means against excessive pulling forces in the arrangement by combining a connection capable of being deformed plastically with a resilient connection of the inner tube 103 as indicated above .

Figure 2 shows in detail a part of an arrangement similar to that in figure 1. A first probe tube section 201 and a second probe tube section 202 enclose a set of measuring devices 213 and isolators 212.

The measuring devices 213 are sleeve shaped and electrically conductive, and preferably metallic. An electrode 231 is attached to each of the measuring devices 213 in such a manner that electric contact is maintained via electric leads 232 between the measuring devices and electric measuring and processing equipment (not shown in figure 2) . The measuring devices 213 are electrically isolated from each other and from the probe tube sections 201,202 by means of ring shaped isolators 212. The isolators 212 are preferably made of material capable of withstand high temperatures while at the same time being electrically isolating. Examples of such materials are well known to a person skilled in the art, and are preferably exemplified by ceramic materials or teflon-like materials. As discussed above, coatings appear on the probe tube sections 201,202 and the measuring devices when an arrangement according to the invention is placed in, e.g., the over heater region of a furnace. The coatings act electrochemically as an electrolyte and it is hence possible to analyze them by means of the electric currents generated and received by the electrodes 231.

A very schematic sketch of a system 300 for monitoring of corrosion in an energy-producing furnace 300 is shown in figure 3. From a supply arrangement 302, a mixture of air and fuel is supplied to the furnace 301 in which it is incinerated in an incineration bed 303. Hot gas 304 passes by an over heater 305 through which steam 306 passes for further use in, e.g., a turbine/generator system (not shown) . After the passage by the over heater 305, cooled gas 307 may be transported to arrangements (not shown) for further exchange of heat. A pole shaped measuring probe 308, such as arrangements shown in figures 1 and 2, is arranged in proximity of the over heater 305 and arranged to be subject to the same flow of gas 304 as the over heater. Measuring devices arranged on the measuring probe, such as the measuring devices 213 in figure 2, are connected via electric leads 309 to a measuring and processing unit 310. An appropriate choice of measuring and processing unit 310 is obviously a computer having appropriate interface hardware and appropriately designed software.

Processing of the electric quantities emanating from the electric measuring devices, such as resistance, voltage and current takes place in the computer and is interpreted in terms of corrosion and rate of corrosion. By further connections 311 between the measuring and processing unit 310, appropriately provided with software, and the supply arrangement 302, a feedback may be provided such that the supply of air and fuel to the incineration bed 303 is controlled towards such a level that a minimization of corrosion is obtained.

In figure 4 it is shown a simplified measuring probe 400 which, in contrast to the separable probe 100 shown in figure 1, shows a probe 400 which is essentially non- separable. A probe tube 401 is, as previously shown, arranged through an opening in the side wall 416 of a furnace. Measuring devices 413 are arranged on the probe tube 401. These measuring devices are, as exemplified in this embodiment, in the form of sleeves which by using known techniques, e.g. soldering, are arranged on the probe tube 401. Other designs of the measuring devices 413, such as washers or plates, are assumed to be within the knowledge of a person skilled in the art. The measuring devices 413 are preferably arranged to be subject to a hot and corrosive environment during a time interval as described above, after which the probe 400 is removed from the hot environment and the measuring devices are analyzed with respect to, e.g., corrosion and erosion. Monitoring of the temperature of the probe 400 may be performed by using thermoelements (not shown in figure 4) arranged in the probe tube 401, as described above in connection with figure 2.

An inner tube 402 is arranged in the probe tube in order to transport a heat conveying fluid 460,461 via a lateral pipe 410 in the same way as illustrated above. However, the inner tube 402 in this embodiment is arranged to be freely movable at its outer connecting part 404 in the direction of elongation of the probe 400, while at the same time the movability in an orthogonal direction Y is minimized. This movable arrangement is achieved by means of a sliding sleeve 407 the function of which is to allow the inner tube 402 to slide in the direction of elongation X during differential heat expansion of the parts of the probe 400 as described above. The detailed design of the sliding sleeve 407, including any sealing means (not shown in figure 4) is considered to be within the field of knowledge of^' a person skilled in the art.

Claims

1. Arrangement for measuring conditions in an environment with hot gas flows (150) , comprising:

- a hollow pole shaped probe (100) provided with at least one measuring device (113,213), wherein the probe

(100) is intended to be partly arranged in the hot environment and partly arranged to be accessible in an area outside the hot environment,

- at least one essentially tube shaped channel (103,203) for transport of heat absorbing medium

(160,161) between the probe (100) and the area outside the hot environment, wherein the channel (103,203) is at least partly arranged in the hollow probe (100), the arrangement c h a r a c t e r i z e d in that: - the probe (100) is separable in its direction of elongation (X) in at least a first (101,201) and a second (102,202) probe section, wherein the first probe section (101,201) is located in the hot environment,

- the tube shaped channel (103,203) is arranged to be accessible in the area outside the hot environment,

- said at least one measuring device (113,313) is removably attached between the probe sections (101,102;201,202) .

2. Arrangement according to claim 1, further c h a r a c t e r i z e d in that:

- the tube shaped channel (103,203) is arranged to the first probe section (101,201) and arranged to the second probe section (102,202) by means of at least one, in the direction of elongation (X) of the probe yielding, connection device (108) which is arranged to maintain a mechanical biasing tension essentially in the direction of elongation (X) of the probe (100) between the tube shaped channel (103,203) and the probe (100),

- said at least one measuring device (113,313) being fixed in the direction of elongation (X) to the probe

(100) by the mechanical biasing tension.

3. Arrangement according to claim 2, further c h a r a c t e r i z e d in that the yielding connection device comprises a resilient device (108) .

4. Arrangement according to claim 2, further c h a r a c t e r i z e d in that the yielding connection device comprises a plastically deformable device.

5. Arrangement according to claim 2, further c h a r a c t e r i z e d in that the yielding connection device comprises at least one resilient device (108) and one plastically deformable device.

6. Arrangement according to any one of claims 3-5, further c h a r a c t e r i z e d in that the resilient device comprises at least one arched washer (108) .

7. Arrangement according to any one of claims 3-5, further c h a r a c t e r i z e d in that the resilient device comprises at least one spring.

8. Arrangement according to any one of claims 1-7, further c h a r a c t e r i z e d in that the tube shaped channel (103,203) is essentially concentrically arranged with respect to the probe (100) .

9. Arrangement for measuring conditions in an environment with hot gas flows (150), comprising:

- a hollow pole shaped probe tube (401) provided with at least one measuring device (413), wherein the probe (400) is intended to be partly arranged in the hot environment and partly arranged to be accessible in an area outside the hot environment,

- at least one essentially tube shaped channel (402) for transportation of heat absorbing medium (460,461) between the probe (400) and the area outside the hot environment, wherein the channel (402) is at least partly arranged in the hollow probe (400) , the arrangement c h a r a c t e r i z e d in that:

- the tube shaped channel (402) is arranged to a part of the probe (400) which is in the hot environment, - the tube shaped channel (402) is at least partly arranged to be accessible in the area outside the hot environment and movably arranged to the probe (400) in the direction of elongation (X) of the probe.

10. Arrangement according to claim 9, further ch a r a c t e r i z e d in that the tube shaped channel (402) is essentially concentrically arranged with respect to the probe tube (401) and fixed, by a sliding sleeve (407) , in a direction (Y) perpendicular to the direction of elongation (X) of the probe.

11. Arrangement according to any one of claims 1-8, further ch a r a c t e r i z e d in that the measuring devices (113,213) comprises at least a temperature sensor.

12. Arrangement according to any one of claims 9-10, further ch a r a c t e r i z e d in that at least one temperature sensor is arranged in the probe tube (401) .

13. Arrangement according to any one of claims 11-12, further cha r a c t e r i z e d in that the temperature sensor is a thermoelement.

14. Arrangement according to any one of claims 1-8, further c h a r a c t e r i z e d in that the measuring devices (113,213) comprises at least one sensor for electrical quantities.

15. Arrangement according to claim 14, further cha r a ct e r i z e d in that the measuring devices are electrically separated from each other with isolators .

16. Arrangement according to any one of claims 14-15, further ch a r a c t e r i z e d in that the measuring devices are sleeve-shaped.

17. Arrangement according to any one of claims 14-16, further c ha r a ct e r i z e d in that the isolators are ring-shaped.

18. Arrangement according to any one of claims 15-17, further c h a r a c t e r i z e d in that the isolators are ceramic.

19. System (300) for measuring conditions in an environment with hot gas flows (304), c h a r a ct e r i z e d by:

- at least an arrangement (308) according to any one of claims 1-18,

- at least an arrangement (310) for data collection and data processing,

- connector means (309) for connecting the measuring devices to the arrangement (310) for data collection and data processing.

20. Method for measuring conditions in an environment with hot gas flows, c h a r a c t e r i z e d in that a system (300) according to claim 19 performs the steps of:

- measuring a temperature,

- measuring at least one electrical quantity,

- collecting and processing of measured quantities obtained by the measuring.