Method of monitoring oxygen concentrations in gas streams

Claim 1

A method of monitoring oxygen concentration in a gas mixture, said method comprising the following steps: (1) passing at a predetermined pressure a sample of the gas to be analyzed through a leak-tight optical absorption cell having high transparency in the 325-600 nm range and maintained at a predetermined temperature above 100° C., said optical absorption cell being placed in the path of a visible light beam; (2) sealing off said optical absorption cell at said predetermined pressure; (3) establishing by means of a light detector the base absorbance of the gas to be analyzed or zeroing the light detector to eliminate said base absorbance; (4) introducing into said optical absorption cell nitrogen oxide, NO, at a pressure at least equal to twice the partial pressure of oxygen in the gas sample, within the range of 0.01 to 0.2 MPa; (5) determining the absorbance, at a predetermined wavelength within the 325-600 nm range, of nitrogen dioxide, NO 2 , formed by reaction of oxygen with nitrogen oxide, NO; and (6) calculating the oxygen concentration in the gas sample from said absorbance; with the proviso that the above step (3) may be performed at any time prior to the introduction of nitrogen oxygen into the optical absorption cell, whether or not the cell is sealed off.

Claim 2

A method of monitoring oxygen concentration in a gas mixture, said method comprising the following steps: (1) passing at a predetermined pressure a sample of the gas to be analyzed through a leak-tight optical absorption cell having high transparency in the 325-600 nm range and maintained at a predetermined temperature above 100° C., said optical absorption cell being placed in the path of a visible light beam; (2) sealing off said optical absorption cell at said predetermined pressure; (3) establishing by means of a light detector the base absorbance of the gas to be analyzed or zeroing the light detector to eliminate said base absorbance; (4) introducing into said optical absorption cell nitrogen oxide, NO, at a pressure at least equal to twice the partial pressure of oxygen in the gas sample, within the range of 0.01 to 0.2 MPa; (5) determining the absorbance, at a predetermined wavelength within the 325-600 nm range, of nitrogen dioxide, NO 2 , formed by reaction of oxygen with nitrogen oxide, NO; and (6) calculating the oxygen concentration in the gas sample from said absorbance; with the proviso that the above step (3) may be performed at any time prior to the introduction of nitrogen oxygen into the optical absorption cell, whether or not the cell is sealed off.