WO1991005998A1 - Detecteur de gaz - Google Patents

Detecteur de gaz Download PDF

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Publication number
WO1991005998A1
WO1991005998A1 PCT/GB1990/001611 GB9001611W WO9105998A1 WO 1991005998 A1 WO1991005998 A1 WO 1991005998A1 GB 9001611 W GB9001611 W GB 9001611W WO 9105998 A1 WO9105998 A1 WO 9105998A1
Authority
WO
WIPO (PCT)
Prior art keywords
temperature
component
catalyst
gaseous mixture
responsive
Prior art date
Application number
PCT/GB1990/001611
Other languages
English (en)
Inventor
Peter C. Foller
Original Assignee
Microsystem Design Specialists Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Microsystem Design Specialists Limited filed Critical Microsystem Design Specialists Limited
Publication of WO1991005998A1 publication Critical patent/WO1991005998A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
    • G01N25/22—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures
    • G01N25/28—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures the rise in temperature of the gases resulting from combustion being measured directly
    • G01N25/34—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures the rise in temperature of the gases resulting from combustion being measured directly using mechanical temperature-responsive elements, e.g. bimetallic
    • G01N25/36—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures the rise in temperature of the gases resulting from combustion being measured directly using mechanical temperature-responsive elements, e.g. bimetallic for investigating the composition of gas mixtures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N25/00—Investigating or analyzing materials by the use of thermal means
    • G01N25/20—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity
    • G01N25/22—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures
    • G01N25/28—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures the rise in temperature of the gases resulting from combustion being measured directly
    • G01N25/30—Investigating or analyzing materials by the use of thermal means by investigating the development of heat, i.e. calorimetry, e.g. by measuring specific heat, by measuring thermal conductivity on combustion or catalytic oxidation, e.g. of components of gas mixtures the rise in temperature of the gases resulting from combustion being measured directly using electric temperature-responsive elements

Definitions

  • This invention relates to apparatus and methods for the detection and monitoring of one or more components of a gaseous mixture and more particularly to a gaseous mixture.
  • components of gaseous mixtures with which this invention is concerned include ozone and chlorine dioxide.
  • ozone monitors Although reference will be made hereinbelow mainly to ozone monitors, it should be understood that the invention is applicable to other gases such as chlorine dioxide.
  • Ozone monitors are of use in various processes in which the gas ozone is used. Examples of such processes are the treatment of effluent in sewerage-treating facilities, purification of water which has been used in various chemical processes, the purification of bottled or potable water, the sterilisation of materials used in the medical and pharmaceutical industries, in the food industry (for instance, ozone is used to prolong the period for which seafoods remain fresh) and in the electronics industry, particularly the production of semi-conductors, where the highest level of contamination-free water is required.
  • Apparatus for monitoring the presence of ozone in a gas stream may provide information relating to such matters as ozone mass flow, ozone mass-flow rate, gas stream flow rate and ozone concentration.
  • Conventional ozone monitors incorporate amperometric or potentiometric electrochemical cells or may be in the form of ultra-violet spectrophotometers or be concerned with the measurement of the photochemical reaction of ozone with ethylene.
  • Aqueous-phase electrochemical sensors have proved unreliable since their electrodes and membranes are easily fouled, their internal solutions may become contaminated and the maintenance of the apparatus requires complex disassembly. The accuracy of such apparatus is low.
  • Ultra-violet spectrophotometers are expensive, require a reference gas, and incorporate optics which may easily become misaligned. They also require moving parts in the form of solenoid valves. In addition, the ultra-violet spectrum of ozone may be confused with that of other compounds present in the gas being monitored.
  • the photochemical approach is less common due to the need for a continuous supply of reagents and the ability to handle the exhaust products.
  • apparatus for detecting or monitoring a component of a gaseous mixture comprising: means for feeding the gaseous mixture along a flowpath; a catalyst support member located in said flowpath and having a catalyst supported thereon; temperature-responsive means located in said flowpath and forming part of an electric circuit for producing an electrical output relating to the temperature of said temperature-responsive means; and means for processing said output and displaying information relating to the amount of the component in the gaseous mixture.
  • the component may, for instance, be ozone or chlorine dioxide or may itself be a mixture of exothermically decomposable gaseous components.
  • the temperature-responsive means may be any suitable device having an electrical property which varies with temperature, an example being a thermocouple which responds to temperature change by a change in the voltage which the thermocouple generates.
  • the temperature-responsive means is a device whose resistance varies with temperature.
  • a resistance-temperature-measuring device or RTD.
  • An RTD may, for instance, be a thermistor, a bolometer or a platinum-resistance thermometer.
  • a platinum- resistive temperature device is preferred for the present invention since it gives a good linear response over a wide temperature range.
  • the catalyst may be any suitable catalyst which is capable of exothermically decomposing the component of the gas stream being monitored.
  • Ozone decomposing catalysts include cobalt oxide, Hopkalite and dispersed platinum.
  • a preferred material is manganese dioxide. The metal in manganese dioxide is in its highest oxidation state and does not catalyse the decomposition of other materials which may be present in the gas flow.
  • Apparatus in accordance with the present invention is capable of providing information relating to the concentration and mass-flow of ozone as well as the mass-flow rate of the gas stream which contains the ozone.
  • the accuracy of the apparatus is high, typically of the same order of known commercial mass-flow transducers, that is to say, within 1% to 2%. There are no moving parts in the apparatus, and the maintenance required is minimal.
  • a platinum-resistance thermometer device used in the present invention, may be provided encapsulated in a glass or ceramic housing.
  • the catalyst is located on the external surface of such a device.
  • the catalyst may be deposited on this external surface which is first pre-treated to make it more receptive to the application of the catalyst.
  • a wash-coat in the form of an aqueous slurry is first applied to the surface.
  • the slurry may be a dispersion of oxide materials, including alumina, in aqueous acetic acid.
  • the encapsulated RTD may be dipped into such a slurry in order to coat it.
  • Glass or ceramic-encapsulated RTDs can be etched with hydrofluoric acid before being dipped in the slurry in order to improve adherence.
  • the RTD may be heat-treated or fired at a temperature in excess of 300°C to provide a highly receptive surface with a large surface area onto which the catalyst itself may then be applied.
  • Application of the manganese dioxide catalyst to the wash-coat on the surface of the RTD housing may be carried out by thermal decomposition of the chloride or nitrate salt of manganese.
  • the wash-coated RTD element may be repeatedly dipped into a solution of the salt and then heated in air to a temperature in excess of 200°C.
  • catalytic materials such as platinum, cobalt oxide and Hopkalite can be applied to an RTD in a similar fashion. Powders of catalytic materials may alternatively be applied to an RTD by sintering with alumina or the plastics PDVF, FEP, TFE or TEF-PFA.
  • the present invention also provides a temperature-responsive catalytic device for use in the detection or monitoring of a component of a gaseous mixture, the device comprising temperature-responsive means having an electrical property whose value varies with the temperature of the device, encapsulation means encapsulating said temperature-responsive means and, located on the external surface of said encapsulation means, a catalyst capable of catalysing the exothermic decomposition of said component.
  • the present invention further provides a sensing head including the temperature-responsive device of the present invention together with one or more further temperature-responsive means and connection means for connecting the sensing head to means for processing the electrical outputs from said sensing head.
  • the present invention also provides a method for detecting or monitoring a component of a gaseous mixture, the component being capable of exothermic decomposition under the influence of a catalyst, the method comprising: feeding the gaseous mixture along a flowpath within which is located a catalyst for effecting exothermic decomposition of said component; allowing said gaseous mixture to contact the catalyst to effect exothermic decomposition of the component; causing the heat generated by said exothermic decomposition to raise the temperature of the temperature-responsive means located in said flowpath thereby to vary the electrical output of a circuit of which the temperature-responsive means forms a part; and feeding said electrical output to processing means for processing said output and displaying information relating to the amount of the component in the gaseous mixture.
  • Figure 1 is a schematic diagram showing the entire apparatus
  • FIG. 2 is a diagram showing in detail an RTD of use in the apparatus of Figure 1.
  • apparatus in accordance with the present invention includes one or more sensing heads 1,3, each of which contains a plurality of resistance-temperature-measuring devices (RTDs), such as 5 - 8 within sensing head 1.
  • RTDs resistance-temperature-measuring devices
  • These RTDs form part of an electrical circuit the outputs of which are fed to a monitor which includes all the components shown in Figure 1 to the right of the sensing heads.
  • this sensing head is provided with a gas stream inlet 11 and a gas stream outlet 12, the gas stream within sensing head 1 being caused to pass over the various RTDs located within the head.
  • RTDs 5 and 6 form part of a first electrical circuit 13.
  • RTD 5 is coated with an ozone decomposing catalyst, specifically manganese dioxide, and RTD 6 is a similar device but not carrying the catalytic coating.
  • a second electrical circuit 15 includes RTDs 7 and 8, the former being heated by means of an electrical current caused to flow through it and the latter being unheated. Neither of these RTDs is coated with catalytic material. As will be described in further detail below, the RTDs are located within sensing head 1 such that the gas flows sequentially over each RTD. In an alternative embodiment of the present invention, the sensing head may be arranged such that the RTDs lie in parallel flowpaths within the sensing head.
  • gas entering the sensing head 1 will cool the heated RTD 8, which is the last RTD in the flowpath. As a result, this RTD will have its electrical resistance altered.
  • the electrical output from circuit 15 can be processed to produce information relating to the gas-stream flow. Exothermic decomposition of ozone on the catalytic surface of RTD 6 causes the temperature of the RTD to rise and the resistance to alter.
  • the output from circuit 13 which, in effect, compares the resistance of RTD 6 with the reference RTD 5 may be processed to provide information relating to the concentration of ozone in the gas stream.
  • the above-referred to monitor includes circuitry represented by block 21 for effecting analogue-to-digital conversion of the outputs of the or each sensing head.
  • the resulting digital representations of the resistance readings are fed to circuitry represented by processing unit 23 which converts resistance data to flow and concentration data.
  • This data is fed directly to display device 25 where it can be displayed in the form of concentration (weight % of ozone in the gas stream) and flow (litres per/hr of the gas stream) .
  • the same data is also fed to circuitry represented by block 27 which calculates the mass flow and feeds the resultant data to display device 25 where it is displayed in terms of the amount of ozone in the gas stream (gm/hr).
  • a sensing head such as that indicated by 1 in Figure 1, includes a body which is formed from three separate PVC mouldings 31, 33 and 35. They are connected together by means of fixing bolts (not shown) passing through the three components and secured by locating nuts which are positioned in milled grooves 37 located in component 31.
  • the sensing head may be secured to, for instance, a bulkhead by means of bolts passing through bores 39 in component 31.
  • the sensing head body described above defines a flowpath 41 indicated by arrows.
  • Flowpath 41 extends from threaded inlet point 43 to a similarly threaded outlet point 45.
  • the flow path extends mainly through the middle component 33 of the sensor body. It follows an essentially rectangular-wave shaped path within which are located the four RTDs 5, 6 7 and 8.
  • Each RTD is located in a part of the flowpath which extends parallel of the longitudinal axis of the sensing head. It lies mainly within central component 33 but extends a short distance into upper component 35. Electrical connection extends from that end of the RTD located in upper component 35 via wire 51 through upper component 35 to the exterior of the sensing head.
  • the flowpath 41 is located mainly within middle component 33 and is effectively closed by means of lower and upper components 31 and 35.
  • the three body components are sealed together by means of a silicon-based sealant.
  • the above-described sensing head is particularly suitable for dealing with very low flow rates.
  • the length-wise flow along the RTDs is more uniform than would be the case with a cross-flow.
  • the particular sequence of the RTDs within the sensing head is not important except that it is preferred that the electrically heated RTD 8 should be the last RTD in the flow path. In this way, the sensing head may be kept as isothermal as possible.
  • the above-described apparatus may be used to monitor any concentration of ozone, from a concentration of the order of a few parts per million up to the safety limits for ozone in contact with catalytic surfaces which might be of the order of 10 to 15 weight %.

Abstract

Appareil pour détecter et contrôler un composant de mélange gazeux, par exemple ozone ou oxyde de chlore, susceptible de décomposition exothermique sous l'influence d'un catalyseur. Ledit appareil comprend un dispositif (1) déterminant le trajet du mélange gazeux dans lequel sont placés un catalyseur qui décompose ledit composant et un élément électrique (6) dont la propriété électrique varie avec sa température. Cet appareil comprend en outre des systèmes (21, 23, 25 et 27) de traitement des signaux électriques à la sortie du dispositif et d'affichage des informations relatives à la quantité du composant contenue dans le mélange gazeux.
PCT/GB1990/001611 1989-10-18 1990-10-18 Detecteur de gaz WO1991005998A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8923450.4 1989-10-18
GB898923450A GB8923450D0 (en) 1989-10-18 1989-10-18 Ozone monitor

Publications (1)

Publication Number Publication Date
WO1991005998A1 true WO1991005998A1 (fr) 1991-05-02

Family

ID=10664759

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1990/001611 WO1991005998A1 (fr) 1989-10-18 1990-10-18 Detecteur de gaz

Country Status (3)

Country Link
AU (1) AU6619090A (fr)
GB (1) GB8923450D0 (fr)
WO (1) WO1991005998A1 (fr)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5360266A (en) * 1992-07-03 1994-11-01 Robert Bosch Gmbh Control and analysis circuit device for measuring reaction heat
EP0740143A2 (fr) * 1995-04-05 1996-10-30 Hoechst Aktiengesellschaft Détecteur à cristal oscillateur
US6304327B1 (en) 1999-03-02 2001-10-16 Vulcan Chemicals Method and apparatus for photometric analysis of chlorine dioxide solutions
US6451272B1 (en) * 1999-12-21 2002-09-17 Ethicon, Inc. Monitoring of sterilant apparatus and method for monitoring sterilant
EP1308718A2 (fr) * 2001-11-02 2003-05-07 Ethicon, Inc. Dispositif et procédé de surveillance d'une vapeur ou d'un gaz oxydant
WO2006117328A1 (fr) * 2005-04-29 2006-11-09 Sig Technology Ag Procede et dispositif pour detecter des substances dans des milieux gazeux contenant de l'eau
AU2002301746B2 (en) * 2001-11-02 2008-05-29 Ethicon, Inc. Monitoring sterilant concentration in diffusion-restricted regions as a basis for parametric release
US10994254B2 (en) 2017-03-17 2021-05-04 Rasirc, Inc. System, device, and method for controlling mass flow of a catalytically reactive gas in a mixed gas stream

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB812607A (en) * 1955-08-08 1959-04-29 Robertshaw Fulton Controls Co Improvements in or relating to devices for determining the oxidising or reducing characteristics of an atmosphere
GB1498989A (en) * 1974-08-31 1978-01-25 Messer Griesheim Gmbh Method and apparatus for determining the ozone content of ozone-containing gas mixtures
DE3102330A1 (de) * 1981-01-24 1982-08-26 Krauss, Ralf, Palma de Mallorca Messgeraet zum quantitativen nachweis eines reaktiven gases, insbesondere ozon
US4835108A (en) * 1986-07-28 1989-05-30 The Babcock & Wilcox Company Method for measuring free oxygen in a combustible atmosphere

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB812607A (en) * 1955-08-08 1959-04-29 Robertshaw Fulton Controls Co Improvements in or relating to devices for determining the oxidising or reducing characteristics of an atmosphere
GB1498989A (en) * 1974-08-31 1978-01-25 Messer Griesheim Gmbh Method and apparatus for determining the ozone content of ozone-containing gas mixtures
DE3102330A1 (de) * 1981-01-24 1982-08-26 Krauss, Ralf, Palma de Mallorca Messgeraet zum quantitativen nachweis eines reaktiven gases, insbesondere ozon
US4835108A (en) * 1986-07-28 1989-05-30 The Babcock & Wilcox Company Method for measuring free oxygen in a combustible atmosphere

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5360266A (en) * 1992-07-03 1994-11-01 Robert Bosch Gmbh Control and analysis circuit device for measuring reaction heat
EP0740143A2 (fr) * 1995-04-05 1996-10-30 Hoechst Aktiengesellschaft Détecteur à cristal oscillateur
EP0740143A3 (fr) * 1995-04-05 1997-03-26 Hoechst Ag Détecteur à cristal oscillateur
US5866798A (en) * 1995-04-05 1999-02-02 Hoechst Aktiengesellschaft Crystal oscillator sensor
US6304327B1 (en) 1999-03-02 2001-10-16 Vulcan Chemicals Method and apparatus for photometric analysis of chlorine dioxide solutions
US6491881B2 (en) * 1999-12-21 2002-12-10 Ethicon, Inc. Monitoring of sterilant apparatus and method for monitoring sterilant
US6451272B1 (en) * 1999-12-21 2002-09-17 Ethicon, Inc. Monitoring of sterilant apparatus and method for monitoring sterilant
EP1308718A2 (fr) * 2001-11-02 2003-05-07 Ethicon, Inc. Dispositif et procédé de surveillance d'une vapeur ou d'un gaz oxydant
EP1308718A3 (fr) * 2001-11-02 2005-01-26 Ethicon, Inc. Dispositif et procédé de surveillance d'une vapeur ou d'un gaz oxydant
AU2002301746B2 (en) * 2001-11-02 2008-05-29 Ethicon, Inc. Monitoring sterilant concentration in diffusion-restricted regions as a basis for parametric release
AU2002301747B2 (en) * 2001-11-02 2008-12-18 Ethicon, Inc. Apparatus and method for monitoring of oxidative gas or vapor
WO2006117328A1 (fr) * 2005-04-29 2006-11-09 Sig Technology Ag Procede et dispositif pour detecter des substances dans des milieux gazeux contenant de l'eau
US10994254B2 (en) 2017-03-17 2021-05-04 Rasirc, Inc. System, device, and method for controlling mass flow of a catalytically reactive gas in a mixed gas stream

Also Published As

Publication number Publication date
GB8923450D0 (en) 1989-12-06
AU6619090A (en) 1991-05-16

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