Combustibles sensor

• US 4,663,017 A
• Filed: 07/11/1985
• Issued: 05/05/1987
• Est. Priority Date: 03/02/1981
• Status: Expired due to Fees

• Current Assignee: Elsag International NV
• Original Assignee: Babcock & Wilcox Company (Babcock International Group PLC)
• Inventors: Ross, David F.
• Primary Examiner(s): TUNG, TA HSUNG
• Application Number:
  US06/754,668
• Time in Patent Office: 663 Days
• Field of Search: 204/1 S, 204/421-429, 204/409
• US Class Current: 204/409
• CPC Class Codes: G01N 27/407 for investigating or analysing gases G01N27/411 takes precedence
• CPC Class Codes: G01N 27/4073 Composition or fabrication of the solid electrolyte

Abstract

A modified zirconia oxygen sensor is disclosed wherein gas flows through inner (14) and outer tubes (12) and wherein one electrode (18) is attached to the inner surface of the inner tube (14), and the second electrode (16) is attached to the outer surface of the inner tube (14). The outer catalytic surface of inner tube (14) is made inert so that an oxygen potential difference is produced between the electrodes (16, 18) which results in a voltage output, as read by the oxygen analyzer (42), which is proportional to the initial level of the combustible in the gas. The utilization of inner (14) and outer tubes (12) wherein the portion of the gas sample contacting the active electrode (18) is maintained separate from the portion of the gas sample contacting the inactive electrode (16) prevents back or edge diffusion between the electrodes.

Claims

1. An apparatus for determining the presence of predetermined combustible constituents in an excess oxygen gas mixture, comprising:

an oxygen ion conductive solid electrolyte cell including a first solid electrolyte tube, having an inlet end and an outlet end and an inside and an outside surface;

a first electrode, attached to the outside surface of said first tube and a second electrode, attached to the inside surface of said first tube;

means for conducting a sample of said gas mixture simultaneously to said first and said second electrodes along separate paths having no gas diffusion between said paths, said means including a second tube, having an inlet end and an outlet end, surrounding said first tube such that a first portion of said gas mixture flows in the space defined between said first and said second tubes and in contact with said first electrode, and a second portion of said gas mixture flows through said first tube only and in contact with said second electrode, said first electrode supporting a first rate of catalytic combustion reactivity between said oxygen and said combustible constituents of said gas mixture, and said second electrode supporting a second rate of catalytic combustion reactivity between said oxygen and said combustible constituents of said gas mixture, said first rate being different from said second rate such that an oxygen potential difference between said first and said second electrodes is produced, said solid electrolyte cell developing an output signal corresponding to said oxygen potential difference which is indicative of the combustible constituents present in said gas mixture;

a venturi, formed integrally with the outlet end of said first tube and located downstream of said second electrode, said venturi having an outlet cross-sectional flow area less than 1/4 that of the inlet cross-sectional flow area of said inlet end of said first tube, for increasing the velocity of said second portion of said gas mixture exiting from said first tube over the velocity of said second portion of said gas mixture entering said first tube to minimize the diffusion of said second portion of said gas mixture back into the outlet end of said first tube; and

velocity increasing means, located at the outlet end of said second tube and downstream of said first electrode, for increasing the velocity of said first portion of said gas mixture exiting from the space defined between said first and said second tubes over the velocity of said first portion of said gas mixture entering said defined space to minimize the diffusion of said first portion of said gas mixture back into the outlet end of said second tube.

2. The apparatus as defined in claim 1 wherein said first tube is formed of a zirconia material, and said first and second electrodes are formed of platinum.

3. The apparatus as defined in claim 1 further including heating means surrounding said second tube, and temperature control means operatively connected to said heating means for maintaining the temperature of said gas mixture in contact with said electrodes at a substantially constant predetermined temperature.

4. The apparatus as defined in claim 1 further including a first plurality of orifices having a total inlet cross-sectional flow entrance area located at the inlet end of said second tube for admitting said first portion of said gas mixture to said defined space between said first and said second tubes, and wherein said velocity increasing means comprises a second plurality of orifices of sufficient cross-sectional flow area to form a total outlet cross-sectional flow exit area from said defined space of less than 1/4 of the total inlet cross-sectional flow entrance area of said first plurality of orifices.