US 3928161 A
The invention pertains to improved gas analyzers including solid electrolyte oxygen analyzing devices whereby through the use of a protective fitter-shield exhibiting suitable porosity for the diffusion of gases and sufficient strength to withstand particulate impingement a solid electrolyte analyzer may be inserted directly into a gas stream of environment such as a flue, stack or boiler in the presence of particulate matter such as fly ash, cinder, etc. to provide instantaneous, in situ, measurement of oxygen while preventing damaging contact of the particulate matter with the oxygen analyzer. Further included is a gas deflecting device associated with the porous protective shield to establish a gas flow pattern about the protective shield to prevent direct contact by large particulate matter in the gas flow while directing the gas flow in such a manner across the surface of the protective shield to provide a cleaning action.
Description (OCR text may contain errors)
States Patent [191 clntyre et al.
[ Dec. 23, 1975  Assignee: Westinghouse Electric Corporation,
22 Filed: Mar. 22, 1974 211 Appl. No.: 454,031
Related US. Application Data  Division of Ser. No. 247,368, April 25, 1972.
 US. Cl. 204/195 S; 204/1 T Primary ExaminerT. Tung Attorney, Agent, or FirmM. P. Lynch [5 7] ABSTRACT The invention pertains to improved gas analyzers including solid electrolyte oxygen analyzing devices whereby through the use of a protective fitter-shield exhibiting suitable porosity for the diffusion of gases and sufficient strength to withstand particulate impingement a solid electrolyte analyzer may be inserted directly into a gas stream of environment such as a flue, stack or boiler in the presence of particulate matter such as fly ash, cinder, etc. to provide instantaneous, in situ, measurement of oxygen while preventing damaging contact of the'particulate matter with the oxygen analyzer. Further included is a gas deflecting device associated with the porous protective shield to establish a gas flow pattern about the protective shield to prevent direct contact by large particulate matter in the gas flow while directing the gas flow in such a manner across the surface of the protective shield to provide a cleaning action.
3 Claims, 5 Drawing Figures  Int. Cl. G01N 27/46  Field of Search 204/1 T, l95 S  References Cited UNITED STATES PATENTS 3,48l,855 12/1969 Kolodney et al. 204/195 S 3,546,086 12/1970 Sayles 204/195 S 3,619,381 1l/ l971 Fitterer 204/1 T 3,768,259 10/1973 Carnahan et al. 204/195 S 1,11,11,11: I '11 n- I I US. Patent Dec. 23, 1975 SheetlofZ 3,928,161
US. Patent Dec. 23, 1975 Sheet 2 of2 3,928,161
6 QE r 3 h GAS MEASURING PROBE FOR INDUSTRIAL APPLICATIONS This is a division of application Ser. No. 247,368 filed Apr. 25, 1972.
BACKGROUND OF THE INVENTION Oxygen analyzers presently being marketed for industrial applications generally require a relatively clean gas sample in order to avoid oxygen analyzer failure due to damage caused by foreign matter or unacceptable operation caused by build-up of foreign matter about the oxygen sensor. The limitations of the presently available oxygen analyzers precludes the use of the oxygen analyzer for direct measurements within coal-fired furnaces and boilers wherein large amounts of particulate matter are present. The adaptation of conventional solid electrolyte oxygen analyzers for measurement of oxygen in environments containing foreign matter generally requires the use of a gas sampling system intermediate the source of gas and .the oxygen analyzer to perform the function of cleaning and preconditioning the gas sample which is extracted from the working environment and subsequently supplied to the. gas analyzer. Although this technique has been widely used, it requires continuous maintenance SUMMARY OF THE INVENTION The invention described herein in conjunction with the exemplary embodiment of the drawings relates to a solid electrolyte oxygen analyzer probe assembly inserted within a'porous refractory shield comprised of ceramic or metal in the form of a cylinder or a thimble wherein the shield provides rapid diffusion of the oxygen to the solid electrolyte oxygen sensor for'rapid in.
situ measurement of the oxygen present within 'an industrial environment, such as a furnace, boiler, stack,
etc. The protective shield prevents the passage of dust and particulate matter, such as fly ash, from contacting the oxygen sensing element while allowing the rapid diffusion of the hot gases to reach the sensing element. In industrial environments containing significant percentages of particulate matter and matter of significant size, a gas deflector element is positioned relative to the gas flow to deflect the large particles from direct contact with the protective shield while at the same time directing theflow of gas across the surface of the protective shield to provide a wiping or cleaning action, thus avoiding build-up of foreign matter on the protective shield, which could result in restriction of the diffusion of the oxygen gas through the protective shield tov the oxygen sensing element.
While the embodiment chosen to illustrate the porous protective shield is that of an oxygen analyzer, it. is apparent that the protective shield is equally applicable to gas analyzers in general when subjected to environments containing particulate matter.
The invention will become more readily apparent from the following exemplary description in connection with the accompanying drawings.
2 DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of a typical applica- DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is illustrated a typical embodiment of a solid electrolyte oxygen probe-assembly 10 inserted within the wall 12 of a furnace F to monitor the oxygen content of the furnace-environment. The furnace F is provided with an insertion-flange 14 providing entry from outside the wall 12 into the furnace environment. The probe assembly l0'is secured 'to the furnace flange 14 by means of flange 16. The probe assembly 10 is comprised of solid electrolyte oxygen sensor assembly 20, porous protective shield 50 and tubular extension member 60 forpositioning the combination of the oxygen sensor assembly 20 and'protective shield 50 within the stationary tubular support member 70. Supporting apparatus for the operation of the solid electrolyte oxygen cell assembly 20 is typically illustrated in US. Pat. No. 3,546,086, entitled Device For Oxygen Measurement, issued Dec. 8, 1970 and assigned to the assignee of the present invention. This includes an interconnect assembly for supplying oxygen reference gas from reference source 82 to the cell assembly '20 as well as providing signal leads for a temperature sensing element in the cell assembly 20 for monitoring cell temperature by temperature controller 84. The electrical signal developed by the solid electrolyte electrochemical cell assembly 20 in response to the oxygen content of the furnace environment is transmitted to 'the EMF measuring or recording apparatus 86. through the interconnect assembly 80. While the signal developed by the cell assembly 20 is indicated as being utilized for record or measurement purposes, it is equally applicable for use as a feedback signal to control a combustion apparatus as illustrated in US. Pat. No. 3,404,836, entitled Heat Generating Apparatus, and issued Oct. 8, 1968. The'scheme of interconnections of the probe-assembly 10 with units 82,84 and 86 is illustrated in'FIG. 1A. 1
There is illustrated in FIG. 2 a sectioned schematic representation of the combination of the solid electrolyte oxygen sensor assembly 20 and the protective shield assembly 50. The oxygen sensor assembly 20 is comprised of solid electrolyte cell assembly 30 which is secured to the tubular extension member 60 and which in turn is fixedly'secured within a tubular insulating member 40 by the clamp 42. The tubular thermal insulating member 40 is in the form of a tubular can typically constructed of inner and outer walls 43 and 44 within which is packed a thermal insulating material 45 which functions to effectively insulate the temperature sensitive oxygen solid electrolyte cell assembly 30 from heat transfer from the temperature environment existingwithinthe furnace environment. Attached to the tubular member 40 are spring members 46 which in conjunction with the cylindrical sealing collar 47 function to stably align and position the combination of the oxygen sensor assembly 20 and the protective shield assembly 50 within the stationary tubular member 70. The sealing collar 47 which is in the form of a collar positioned about the tubular thermal insulating member 40 is illustrated as comprised of the same thermal insulating material utilized within the walls of the tubular thermal insulating member 40 and provides an effective diameter sufficient to provide essentially a force-fit of the combination of assemblies 20 and 50 within the tubular member 70. The sealing collar 47, in addition to providing alignment of the assembly combination, also serves to provide a barrier whereby particles in the furnace environment are prevented from traveling within the tubular member 70, thus avoiding a build-up of foreign matter which could adversely affect the insertion and removal of the probe assembly 10. The thermal insulating material utilized within the tubular thermal protection device 40 and used as the sealing collar 47 can be one of many thermal insulating materials available including Fiberfrax insulation, which is a product of the Carborundum Company. The efiective diameter of the sealing collar 47 can be varied by the positioning of the adjustable clamp 48.
The solid electrolyte cell assembly 30 is comprised of a solid electrolyte member 31 illustrated in the form of a disc sealed to form the closed end of tubular support member 32 which has the opposite end secured to the tubular extension member 60. Disposed on opposite surfaces of the solid electrolyte member 31 are electrode members 33 and 34. The material composition of the solid electrolyte can be satisfied by any of many compositions of materials well known in the art which support oxygen ion conductivity. Such material compositions are described in U.S. Pat. No. 3,400,054 issued Sept. 3, 1968. A requirement for the electrode members 33 and 34 is that they provide sufficient electronic conductivity and operable at elevated temperatures. The prior art typically represents the electrodes as being porous platinum coatings. In selecting the material for the tubular support member 32 for an oxygen probe assembly for use in industrial applications, the prime considerations are the materials resistance to the corrosion and a need to match as closely as possible the thermal coefficient of expansion of the tubular material with that of the solid electrolyte. Materials satisfying these requirements include 446 Stainless, Ebrite 26-1 Hastelloy B, lnconel X, etc. Investigations have shown that the Ebrite 26-1 provides characteristics compatible with conventional solid electrolyte material composition to satisfy the requirements of corrosion resistance and matching coefficients of thermal expansion to insure an integral seal between the solid electrolyte member 31 and the tubular support member 32.
A heater assembly 35 positioned within the tubular support member 32 provides uniform operating temperature for the solid electrolyte cell assembly. Electrical leads 35A from the heater assembly 35 extend within tubular member 60, through interconnect member 80 to temperature controller 84.
Entry tube 36 extending from the interconnect member 80 of FIG. 1 includes at least four longitudinal passages therein whereby an electrical lead member 37 is brought in contact with electrode 32 and leads for temperature measuring element 38 are carried to the temperature controller 84 to provide input information for controlling the operation of the heater. assembly 35. The fourth longitudinal passage in the entry tube 36 permits the passage of a reference oxygen supply, such as air, exhibiting a known oxygen content from the reference gas supply 82 to the surface of the solid electrolyte member 31 occupied by the electrode 33 and exhausted back through interconnect member 80.
A suitable composition for the solid electrolyte 31 includes a composition of zirconia and oxides of cal-' cium or related material which provides sufficient oxygen ion conduction to render the solid electrolyte useful for oxygen gas measurement.
The use of electrically conductive material for the tubular support member 32 permits the extension of the electrode member 34 to electrical contact with the tubular member 32 thus permitting the use of the tubular member 32 as an electrical conductor to conduct the signal developed by the solid electrolyte member in response to oxygen differential pressure. The use of a metal material for the tubular extension member provides additional conduction of the signal to the interconnect member at which electrical contact is made by a lead extending to the signal measuring circuit 86.
As described in the referenced U.S. patents, the operation of the conventional solid electrolyte oxygen cell is such that the electrolyte member 31 will respond to a difference in oxygen pressure between that of the oxygen reference present at electrode 33 and that of the environment present at electrode 34 by generating an EMF signal which is monitored by the remote measuring apparatus 86 and interpreted as a measurement of the oxygen content of the unknown environment present at electrode 34. In the instant application, the environment present at the electrode 34 corresponds to the furnace environment which is conducted through the porous protective shield member 52 of the protective shield assembly 50 by diffusion and is introduced into a gas cavity define'd by an end portion of a heatconductive cap 64 and the surface of the solid electrolyte member 31 upon which electrode 34 is disposed through apertures 62 in the heat-conductive cap 64. The construction and the operation of the solid electrolyte member 31 in conjunction with electrodes 33 and 34 in response to varying oxygen environments is clearly described in the referenced patents and will therefore not be described in detail in this application.
The heat conductive cap 64 serves primarily to conduct heat produced by the heater assembly 35 to the end cap portion 64A of the heat conductive cap 64. The end cap 64A serves as a stable temperature barrier whereby the gas in the gas cavity is maintained at a relatively stable temperature corresponding to that required for the desired operation of the oxygen cell assembly. An annular air space is included to serve as an insulating barrier which essentially eliminates short circuit of the thermal conduction from the heat conductive cap to the solid electrolyte 31 through the tubular support member 32 and assures conduction of the heat to the closed end portion 64A. Of secondary importance, is the mechanical protection provided the relatively fragile solid electrolyte 31 by the closed end heat conductive cap during handling of the oxygen sensor assembly prior to insertion within the furnace environment. The heat conductive cap can be fabricated from any suitable material exhibiting the thermal conduction characteristics required, such as, 304 Stainless Steel, 446 Stainless Steel, Ebrite 26-1, etc.
The protective shield assembly 50 includes a mechanical support structure 54 which is fixedly secured to end piece 49 of the open ended tubular insulating member 40. The mechanical structure 54 includes end plate 55 and leg members 56 and 57 extending between the end plate 55 and the end piece 49. An adjustable clamping assembly 58 associated with the end plate 55 serves to apply controlled force against the closed end of the tubular porous member 52 to effectively seal the open end of the tubular porous member 52 against sealing member 59. The sealed positioning of the open end of the tubular porous member 52 against the sealing member 59 effectively isolates the oxygen sensor assembly 30 from contact by foreign matter present in the fumace environment. The use of a material which will readily support oxygen diffusion at elevated temperatures for the porous member 52 assures the sensitivity of the oxygen sensor assembly to the oxygen content of the fumace environment. The requirements for selecting a material exhibiting desirable mechanical characteristics suitable to enable the porous member to withstand impingement by foreign matter while at the same time providing rapid gas diffusion can be satisfied by selecting a porous refractory material such as a ceramic material or a metal having a porosity sufficient to prevent passage of dust and particulate matter while permitting the desired level of gas diffusion. A commercially available porous refractory material in the form of an extraction thimble produced and marketed by Fisher Scientific satisfies the requirement of the porous member 52.
Referring to FIG. 3, there is illustrated a section of the embodiment of FIG. 2 illustrating the position and configuration of the leg members 56 and 57 of the mechanical support structure 54 and the orientation of the leg members relative to the gas flow within the fumace environment. The configuration of the leg member 56 is such as to form a deflecting member resulting in a gas flow pattern as illustrated. The deflector configuration of the leg member 56 serves two purposes:
a. prevents direct impingement of large particulate matter on the surface of the porous member 52; b. establishes a sweeping air flow across the outside surfaces S1 and S2 of the porous member 52 to effectively provide a wiping or cleaning action, thus eliminating a build-up of particulate matter on the surfaces 81 and S2 of the porous member 52 which could ultimately seal the pores of the member 52 thus preventing rapid diffusion of oxygen gas therethrough. Field tests of the configuration illustrated in FIG. 3 resulted in a build-up of particulate matter PM as illustrated. While the deflector configuration of the leg member 56 is simply illustrated as a right angle member, it is apparent that numerous configurations are available to provide the desired gas flow pattern.
In FIG. 4, there is illustrated an alternate implementation of the porous member 52. The single porous member 52 of the illustration of FIG. 2 is replaced by two porous members 152 and 154. Instead of relying solely on diffusion of the gas from the furnace environment for contacting the oxygen sensor assembly 30, a gas flow path is established as illustrated by the arrows such that gas which is diffused through porous member 152 and subsequently monitored by the oxygen sensor assembly is ultimately diffused through porous member 154 and exhausted to the furnace environment through the apertures 71 of the stationary tubular members and 73. It is obvious that the direction of the gas flow can be reversed.
1. In a solid electrolyte electrochemical cell assembly adapted for monitoring gas constituents at elevated temperatures wherein the solid electrolyte electrochemical cell is a solid electrolyte member having a first electrode disposed in contact with a first surface of the solid electrolyte member and a second electrode disposed in contact with the opposite surface of the solid electrolyte member, said solid electrolyte electrochemical cell forming the closed end of a tubular member, the improvement for heating said solid electrolyte electrochemical cell, wherein said improvement comprises:
heating means inserted within said tubular member and disposed adjacent to the surface of the solid electrolyte member contacted by the first electrode and remote from the solid electrolyte surface contacted by said second electrode for directly heating said tubular member and the electrolyte surface contacted by said first electrode, and
heat conductive means in thermal contact with the external surface of said tubular member and having an end portion extending adjacent and parallel to and spaced apart from the electrolyte surface contacted by said second electrode to define there-between a gas cavity and to heat said electrolyte surface contacted by said second electrode, said heat conductive means including apertures therethrough to permit the flow of gas containing constituents. to be monitored to enter said cavity and contact said electrolyte surface contacted by said second electrode.
2. In a solid electrolyte electrochemical cell assembly as claimed in claim 1 wherein said heat conductive means being a cap of heat conductive material having side walls heat conductively coupled to the walls of said tubular member.
as claimed in claim 2 further including a thermal shield surrounding the heat conductive cap.