Improved instrumentation probe

Abstract: An instrumentation probe comprises a tubular housing for enclosing a sensing element, the tubular housing being adapted to project into a process stream. The tubular housing is surrounded by an outer casing that has its longitudinal axis transverse to the longitudinal axis of the tubular housing and which outer casing is aerodynamically shaped to be substantially non-disruptive of the flow of the process stream while protecting the tubular housing from erosion.

Description: The present invention relates to instrumentation probes for use in erosive process streams and especially for sensing temperature in erosive process streams. BACKGROUND OF THE INVENTION There are many industrial processes in which it is desirable to sense conditions existing in a process stream by means of a sensor mounted within an instrumentation probe. Typical instrumentation probes consist of a generally tubular housing which projects into a process stream for sensing conditions in the process stream. An early thermometer design for use with jet engine hot gases is described in GB-A-610317. One embodiment comprises a generally air-foil body having inlet apertures on its leading edge to cause hot gases to stream into the body and around a temperature sensor located in close proximity to the inlet apertures. After flowing round the sensor the hot gases pass along the interior of the body and exit through outlet apertures at the trailing edge thereof. In practice, process streams frequently contain erosive particles, as is the case, for example, in fluid catalytic cracking and similar processes. These erosive particles erode the probe over time, which is highly undesirable. Considerable effort, therefore, has been directed in the process industry toward developing erosion-resistant alloys and erosion-resistant coatings for instrumentation probes. Notwithstanding these activities, there still remains a need for improved erosion and corrosion resistant instrumentation probes. Therefore, it is an object of the present invention to provide improved instrumentation probes for use especially in erosive environments. It is another object of the present invention to provide improvements in instrumentation probes for retrofitting of existing sensor probes. According to the present invention, an instrument probe for use in erosive process streams comprises: an outer casing having a bore therethrough transverse to its longitudinal axis; and a tubular housing, adapted to receive and enclose a sensing element, located in the bore and secured therein by welded plug means, whereby that portion of the tubular housing which, in use of the probe, would otherwise be in contact with a process stream is totally enclosed by the outer casing and plug means; and wherein the outer casing of the probe has a substantially air-foil shape with (i) a leading curved edge that is at a distance from the axis of the tubular housing in the range of from 2 to 4 times the radius thereof, and (ii) a trailing edge that is at a distance from the axis of the tubular housing in the range of from 2 to 2.5 times the radius thereof, but not more than distance (i); whereby, in use, the outer casing is substantially non-disruptive of the process stream flow. In another aspect the invention provides a conduit or container for the passage of an erosive process stream, in combination with the afore-defined instrument probe located therein with the said outer casing of the probe aligned to have its leading edge substantially directed towards the direction from which the process stream will flow in use, and its trailing edge substantially directed towards the direction to which the process stream will flow in use after passing the location of the trailing edge. These and other embodiments of the present invention, as well as other objects and advantages thereof, will be apparent from the "Detailed Description" which follows, as is illustrated in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic fragmentary illustration of an improved instrument probe of the present invention installed in a riser conduit positioned in a vessel through which conduit an erosive process stream is passed. Figure 2 is a side elevation of the outer casing of an instrument probe of the present invention, showing a particularly preferred aerodynamic design of the casing. Figure 3 is a cross-sectional view taken along lines A-A of Figure 2. DETAILED DESCRIPTION OF THE INVENTION Figure 1 is a schematic illustration of an instrument probe of the present invention having an aerodynamically shaped outer casing 10 located in a riser conduit 5 through which an erosive process fluid flows. In the embodiment shown in Figure 1, the riser conduit 5 is positioned within a reactor vessel having a wall 11. As can be seen by the arrows, process fluid flowing through the reactor is directed to flow around the outer casing 10 in a substantially aerodynamic fashion, so as to be substantially non-disruptive of the flow of fluid through the riser conduit 5, thereby preventing erosion of the housing within the casing 10 containing the sensor. In a particularly preferred embodiment of the present invention, the outer casing 10 of the instrument probe has a substantially air foil design and particularly the design shown in Figure 2. As is shown in Figure 3, the instrument probe includes a tubular housing member 14 of sufficient length to extend from a point within the conduit 5 to a location external the conduit 5. In this particular instance where the conduit containing the process stream is located within a vessel, the tubular housing 14 is preferably sufficiently long to extend to a location external the reactor vessel wall 11. As shown, the end of the tubular housing 14 that extends into the process stream to be sensed is surrounded by outer casing 10. As can be seen from Figures 2 and 3, the outer casing has a substantially aerodynamic shape, especially an outer shape 10 similar to an air foil. Thus, the outer casing 10 has three sections: a first section 16; a middle second section 17 and a third section 18. Preferably, the outer casing 10 is a solid unit with a cylindrical tubular opening therein which is transverse to its longitudinal axis and has a diameter sufficient to be able to readily receive and remove tubular housing 14. The outer casing 10, preferably, is welded to the tubular housing 14 at the first end 15 of housing 14 by weld 27. The outer casing 10 optionally and preferably is also welded to the conduit 5 by welds 8. In the embodiment shown in Figure 3, the conduit 5 and the reactor vessel wall 11 are each provided with a refractory lining 6. Importantly, as can be seen in Figure 2, the casing 10 of the probe has a first section 16 with a curved leading edge 26 and a third section 18 with a curved trailing edge 28. Also as can be seen in the figures, the first section 16 of the outer casing 10 is slightly longer in length than the third section 18 of the casing 10. Indeed, as shown in Figure 2, in a particularly preferred embodiment of the present invention, the length from leading edge 26 to the center of the cylindrical opening in outer casing 10 is from 2 to 4 times the radius of the cylindrical opening; whereas, the length from the trailing edge 28 to the center of the cylindrical opening is about 2 to 2 1/2 times the radius of the cylindrical opening. In the embodiment shown in Figure 3, a mounting plate 34 is provided to secure the tubular housing 14 to the conduit 5 and to effectively provide a gas seal between the interior and the exterior of conduit 5. Also as is shown, the mounting plate 34 is fastened to the wall of conduit 5 by means of welds and optionally and preferably the tubular housing 14 is welded to mounting plate 34. As is shown in Figure 3, a sensing element such as a thermocouple 32 is located within a tubular housing 14, extending substantially inward toward weld 27, thereby providing the primary means for measuring temperature within the process stream. The second end 25 of the tubular housing 14 is provided with conventional means 36, such as a threaded end, for connection to external equipment and devices. As will be readily appreciated, the outer casing 10 can be separately fabricated and placed over conventional thermocouple probes in use by welding at points such as 27 and 8, shown in Figure 3. In the practice of the present invention, the outer casing 10 will be made from metals such as 316 stainless steel; however, optionally it may be also coated with erosion resistant coating such as carbides, borides and aluminides, alloys of iron, nickel, cobalt, especially wear resistant alloys of cobalt-chromium and tungsten, and ceramics such as magnesia-stabilized zirconia. Although the invention has been described specifically in connection with a riser conduit positioned within a reactor, it should be readily appreciated that the improved instrument probe is equally useful in fluid coking apparatus such as transfer lines, catalyst regenerators and the like, as well as other erosive environments requiring instrument probes.

Claims: An instrument probe for use in erosive process streams comprising: an outer casing (10) having a bore therethrough transverse to its longitudinal axis; and a tubular housing (14), adapted to receive and enclose a sensing element (32), located in the bore and secured therein by welded plug means (27), whereby that portion of the tubular housing (14) which, in use of the probe, would otherwise be in contact with a process stream is totally enclosed by the outer casing (10) and plug means (27); and wherein the outer casing (10) of the probe has a substantially air-foil shape with (i) a leading curved edge (26) that is at a distance from the axis of the tubular housing (14) in the range of from 2 to 4 times the radius thereof, and (ii) a trailing edge (28) that is at a distance from the axis of the tubular housing (14) in the range of from 2 to 2.5 times the radius thereof, but not more than distance (i); whereby, in use, the outer casing (10) is substantially non-disruptive of the process stream flow. An instrument probe as claimed in claim 1, further comprising a sensing element (32) located in the tubular housing (14). An instrument probe as claimed in claim 1 or claim 2, wherein the outer casing (10) is provided with an erosion-resistant coating. A conduit or container (5), for the passage of an. erosive process stream, in combination with an instrument probe according to any preceding claim located therein with the said outer casing (10) of the probe aligned to have its leading edge (26) substantially directed towards the direction from which the process stream will flow in use, and its trailing edge (28) substantially directed towards the direction to which the process stream will flow in use after passing the location of the trailing edge (28).

Inventors: SHAW DONALD FRANCIS, TAMMERA ROBERT FRANK, SHAW, DONALD FRANCIS, TAMMERA, ROBERT FRANK
Applicants: EXXONMOBIL RES & ENG CO, EXXONMOBIL RESEARCH AND ENGINEERING COMPANY
Application year: 1993
Main classification: G01K13
IPC codes: G01K13