Gas detection system

• US 3,925,666 A
• Filed: 07/29/1974
• Issued: 12/09/1975
• Est. Priority Date: 11/14/1973
• Status: Expired due to Term

• Current Assignee: Colin J. Allan, John G. Bayly
• Original Assignee: Colin J. Allan, John G. Bayly
• Inventors: Allan, Colin J., Bayly, John G.
• Primary Examiner(s): Lawrence, James W.
• Assistant Examiner(s): Grigsby, T. N.
• Application Number:
  US05/492,458
• Time in Patent Office: 498 Days
• Field of Search: 250/338,393,343,221,226 356/51,201,75 350/285 340/258B,237R,242
• US Class Current: 250/338.5
• CPC Class Codes: F17C 13/12 Arrangements or mounting of devices for preventing or minimising the effect of explosion flame traps A62C4/00 ; Other safety measures
• CPC Class Codes: G01M 3/38 by using light G01M3/02 takes precedence
• CPC Class Codes: G01N 21/39 using tunable lasers
• CPC Class Codes: G01N 33/0027 concerning the detector
• CPC Class Codes: G01N 33/0044 Sulphides, e.g. H2S
• CPC Class Codes: Y02E 60/32 Hydrogen storage
• CPC Class Codes: Y02P 90/45 Hydrogen technologies in production processes

Abstract

The gas detection system provides for the effective detection of gas leaks over a large area. It includes a laser which has a laser line corresponding to an absorption line of the gas to be detected. In the instant case, a He-Xe laser scans a number of retroreflectors which are strategically located around a D2O plant to detect H2S leaks. The reflected beam is focussed by a telescope, filtered, and passed into an infra-red detector. The laser may be made to emit two frequencies, one of which corresponds with an H2S absorption line; or it may be modulated on and off the H2S absorption line. The relative amplitude of the absorbed light will be a measure of the H2S present.

Claims

1. An apparatus for monitoring a known gas in the atmosphere around a plant area comprising:

a. a first number of reflector means mounted in a spaced manner in the plant area;

b. first detector means positioned at a first predetermined location in direct line of sight with each first reflector means, the first detector means including;

i. light source means providing a collimated beam having at least a wavelength which corresponds to an absorption line of the gas;

ii. means for cyclically directing the bean onto each first reflector means at a first scan rate; and

iii. means for receiving the reflected beam indicating the presence of the gas in the beam path as a function of any absorption of the corresponding wavelength;

c. a second number of reflector means mounted in a spaced manner in the plant area; and

d. second detector means positioned at a second predetermined location in direct line of sight with each second reflector means such that the lines of sight between the second detector means and the second reflector means overlap with the lines of sight between the first detector means and the first reflectors means to form a grid, the second detector means including;

i. light source means providing a collimated beam having at least a wavelength which corresponds to an absorption line of the gas;

ii. means for cyclically directing the beam onto each second reflector means at a second scan rate; and

iii. means for receiving the reflected beam indicating the presence of the gas in the beam path as a function of any absorption of the corresponding wavelength.

2. An apparatus as claimed in claim 1 wherein said second scan rate is greater than said first scan rate such that the first detector is sensitive to a small quantity of said gas and the second detector provides a fast response to a large quantity of said gas.

3. An apparatus as claimed in claim 1 wherein said gas to be monitored is H2S and the light source means includes a He-Xe laser.

4. An apparatus for monitoring a known gas in the atmosphere around a plant area comprising:

a. first number of reflector means mounted in a spaced manner along a first section of the perimeter of the plant area;

b. a second number of reflector means mounted in a spaced manner along the remaining second section of the perimeter of the plant area;

c. a third number of reflector means mounted in a spaced manner along the perimeter of the plant area such that the third reflector means overlap a portion of said first and second section;

d. a fourth number of reflector means mounted in a spaced manner along the perimeter of the plant area such that the fourth reflector means overlap the remaining portion of said first and second sections; and

e. first, second, third and fourth detector means positioned at spaced locations outside the plant area in direct line of sight of said first, second, third and fourth reflector means respectively, each of said detector means including;

i. light source means providing a collimated beam having at least a wavelength which corresponds to an absorption line of the gas;

ii. means for cyclically directing the beam onto each corresponding reflector means at a predetermined scan rate; and

iii. means for receiving the reflected beam indicating the presence of the gas in the beam path as a function of any absorption of the corresponding wavelength.

5. An apparatus as claimed in claim 4 which further includes:

control means for maintaining the scan rate of said third and fourth detector means greater than the scan rate of said first and second detector means.

6. As apparatus as claimed in claim 4 wherein said gas is H2S and the light source includes a He-Xe laser.