Method and apparatus for nox analysis
AssigneeE. I. Du Pont de Nemours and Company
InventorsJohn R. Reader, Jr., James L. Seago, James A. Williamson, Jr.
Life of this patent
Estimating the term…
Abstract
Apparatus and method for NO.sub.x analysis in which a sample gas is introduced into a sample cell and mixed with oxygen to induce conversion of NO to NO.sub.2. After a given time, prior to complete conversion of NO to NO.sub.2, the absorbance and the time rate of change of absorbance is measured. The time rate of change of absorbance is indicative of the initial NO concentration in the sample gas; and the sum of the absorbance and the time rate of change of absorbance is indicative of the initial NO.sub.x concentration in the gas. A better indication of the initial NO.sub.x concentration can be obtained from the sum of the absorbance and the square root of the time rate of change of absorbance.
Claims15
An apparatus for determining the amount of NO.sub.x in a sample gas, comprising:
- a. a gas-tight sample cell having windows transparent to radiation of a wavelength in the range of about 410 to about 600 nm.;
- b. means for introducing a known volume of sample gas into said cell;
- c. radiation source means for passing radiation of a wavelength in the range of about 410 to about 600 nm. through said cell;
- d. means for detecting the intensity of the radiation emerging from said cell;
- e. means for introducing at least about 2 atmospheres of an oxygen-containing gas into said cell to form a gas mixture with the sample gas;
- f. means for maintaining the gas mixture at a substantially constant temperature;
- g. means for maintaining the gas mixture at a substantially constant pressure;
- h. means for measuring, at a given time, the time rate of change of the absorbance of radiation by the gas mixture in said cell and generating a signal proportional to the measured absorbance;
- i. means for measuring, at the same time, the time rate of change of the absorbance of radiation by the gas mixture in said cell and for generating a signal proportional to the measured time rate of change of absorbance, the sum of the measured absorbance and the measured rate of change of absorbance being indicative of the initial NO.sub.x content of the sample gas;
- and
- j. means for summing the two generated signals.
An apparatus for determining the amount of NO.sub.x in a sample gas, comprising:
- a. a gas-tight sample cell having windows transparent to radiation of a wavelength in the range of about 410 to about 500 nm.;
- b. means for introducing a known volume of sample gas into said cell;
- c. radiation source means for passing radiation of a wavelength in the range of about 410 to about 600 nm. through said cell;
- d. means for detecting the intensity of the radiation emerging from said cell;
- e. means for introducing at least about 2 atmospheres of an oxygen-containing gas into said cell to form a gas mixture with the sample gas;
- f. means for maintaining the gas mixture at a substantially constant temperature;
- g. means for maintaining the gas mixture at a substantially constant pressure;
- h. means for measuring, at a given time, the absorbance of radiation by the gas mixture in said cell and for generating an electrical signal proportional to the measured absorbance;
- and
- i. means for measuring, at the same time, the time rate of change of the absorbance of radiation by the gas mixture in said cell and for generating an electrical signal proportional to a power, between about 0.4 and about 0.6, of the measured time rate of change of absorbance;
- the sum of the measured absorbance and the power of the measured rate of chanage of absorbance being indicative of the initial NO.sub.x content of the sample gas.
A method for measuring the concentration of NO.sub.x in a sample gas comprising the following steps:
- a. introducing a known volume of the sample gas into a gas-tight sample cell;
- b. introducing at least about 2 atmospheres of an oxygen-containing gas into the cell to form a gas mixture with the sample gas;
- c. controlling the temperature and pressure of the gas mixture;
- d. passing detecting radiation of a wavelength between about 410 to about 600 nm. through the gas mixture in the cell, said detecting radiation being of a wavelength strongly absorbed by NO.sub.2 ;
- and
- e. measuring, at the same given time, the absorbance and the time rate of change of absorbance of the detecting radiation passing through the cell by the gas mixture in the cell, the sum of the measured absorbance and the measured time rate of change of absorbance being indicative of the initial NO.sub.x content of the sample gas.
Dependencies are inferred from the claim text.