Situ multi-channel combustion gas analyzer

• US 4,560,873 A
• Filed: 06/17/1983
• Issued: 12/24/1985
• Est. Priority Date: 06/17/1983
• Status: Expired due to Term

• Current Assignee: Teledyne Monitor Labs, Inc. (Teledyne Technologies Incorporated)
• Original Assignee: Lear Siegler, Inc. (LSS Holdings LLC)
• Inventors: McGowan, Gerald F., Ketchum, Ronald L., Polhemus, Carl E., Price, Gerald W.
• Primary Examiner(s): Smith, Alfred E.
• Assistant Examiner(s): Hannaher, Constantine
• Application Number:
  US06/505,201
• Time in Patent Office: 921 Days
• Field of Search: 250/339, 250/343, 250/341, 250/351, 356/438, 356/439
• US Class Current: 250/339.09
• CPC Class Codes: G01N 2021/3129 Determining multicomponents by multiwavelength light
• CPC Class Codes: G01N 2021/536 Measurement device mounted at stack
• CPC Class Codes: G01N 2021/8571 using filtering of sample fluid
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01N 21/8507 Probe photometers, i.e. with optical measuring part dipped into fluid sample
• CPC Class Codes: G01N 2201/1215 for interfering gases

Abstract

Apparatus is disclosed to accurately measure and analyze multiple component interfering gases which coexist in the stack gas effluent generated from a combustion process which utilizes a non-dispersive, narrowband infrared absorption technique. The apparatus includes a probe in the stack with an optical measurement cavity (34) through which the stack gases are passed. A transceiver (14) mounted to the probe includes an optical portion operatively associated with the measurement cavity including a chopped light source (54), (60), (62) for projecting beams of light into the measurement cavity and a detector (86) for detecting the attenuation of the gases to provide a measure of the extent of absorption of each gas of interest. A control unit, preferably remote from the transceiver, preferably a programmed digital computer, and preferably via a J-box (18) converts the electric outputs to a corresponding % modulation and in turn corrects for temperature, pressure and interference between gases. The results may be displayed on a front panel (174) or used, for example, to maximize efficiency in a combustion process.

Claims

1. Apparatus for measuring multiple component interfering gases contained in flue gases issuing from a stack due to combustion, comprising:

a probe for mounting to extend through the wall of a stack including a measurement cavity through which combustion gases in the stack can pass;

a transceiver mounted to said probe externally of said stack including an optical means and electric circuit means,

said optical means having a chopped light source for projecting a succession of beams of light of different selected wavelengths one at a time into said probe, a detector for continuously detecting any attenuation of each of the light beams by said gases in said probe for providing a measure of the extend of absorption of each gas of interset in each of a plurality of separate channels, and a zero absorption channel providing a reference for the other channels,

said electric circuit means providing an electric output representing each of said absorption measurements; and

control means coupled to said transceiver including first means for continuously converting said electric output to a corresponding percent modulation output for each of said gases of interest, for continuously correcting each of said percent modulation outputs for temperature, of correcting each of said percent modulation outputs for pressure, for correcting said percent modulation output for interference between measured gases, and to provide corrected continuous outputs representing the concentration of each of said measured gases,

said control means including automatic calibration means for continuously purging said measurement with dry air to provide zero values that are used in calculating said percent modulation and means to couple a gas valve into said measurement cavity for the purpose of obtaining a gain factor for continuously correcting the measured results.

2. Apparatus as set forth in claim 1 wherein said measured gases are CO, CO₂ and H₂ O.

3. Apparatus as set forth in claim 1, wherein said electric circuit portion includes an automatic gain control to normalize said output signal from said detector to remove source, detection and contamination variations.

4. Apparatus as set forth in claim 1, wherein said percent modulation output is defined as 100(1-I/Io) I=light remaining after attenuation, I_o =total available light.

5. Apparatus as set forth in claim 1, including a junction box mountable on said stack adjacent said transceiver electrically coupled to said transceiver and arranged to transfer transceiver outputs to said control unit and control unit outputs to said transceiver.

6. Apparatus as set forth in claim 1, including means for displaying said corrected outputs.

7. Apparatus as set forth in claim 1, including means for converting said corrected outputs to selectable digital-to-analog converter recorder outputs.

8. Apparatus as set forth in claim 1, including means for using selected of said corrected outputs from said control means to adjust the fuel/air ratio to the burner of a furnace to maximize the efficiency of the combustion process in the furnace.

9. Apparatus for measuring multiple component interfering gases contained in flue gases issuing from a stack due to combustion, comprising:

a probe for mounting to extend through the wall of a stack including a measurement cavity through which combustion gases in the stack can circulate;

a transceiver mounted to said probe externally of said stack including an optical portion and an electric circuit portion,

said optical portion having a light source and a rotary filter wheel with a narrow band filter corresponding to the primary absorption wavelength of each gas of interest for a selected number of separate gas measurement channels, a reference channel, and a total absorption channel, for projecting a succession of beams of light of different selected wavelengths one at a time into said probe, and a detector for continuously detecting any attenuation of the light beams by said gases in said probe for providing a measure of the extend of absorption of each gas of interest in each of said channels, said total absorption channel eliminating background noise and drift and said zero absorption channel providing a reference for the other channels,

said electric circuit portion providing an electric output representing each of said absorption measurements; and

a control unit coupled to said transceiver including first computing means for continuously converting said electric output to a corresponding percent modulation output for each of said gases of interest and second computing means for continously correcting each of said percent modulation outputs for temperature, for correcting each said output for pressure and moisture, for correcting said percent modulation output for interference between measured gases, for correcting said percent modulation output for non-linearity, for calibrating, ranging and averaging each of said percent modulation outputs, and to provide corrected continuous outputs representing the concentration of each of said measured gases,

said control unit including an automatic calibration means for continously purging said measurement with dry air to provide zero value that are used in calculating said percent modulation and means to couple a gas valve into said measurement cavity for the purpose of obtaining a gain factor for continuously correcting the measured results.

10. Apparatus as set forth in claim 9, wherein said transceiver includes sample and hold means to produce a sample and hold signal from said filter wheel to sample and hold a normalized signal for each of said channels.

11. Apparatus as set forth in claim 10, wherein said sample and hold means includes a notch in said wheel opposite each filter sensed by a sensor to identify which filter is opposite said light source.

12. Apparatus as set forth in claim 10, wherein said light source emits infrared radiation from an electrically heated metallic source through said rotating filter wheel with filters defining said separate channels, said radiation being directed onto a beam splitter which reflects the beam down the probe through a measurement cavity, the radiation being absorbed in a manner characteristic of the gases present.

13. Apparatus for measuring multiple component interfering gases contained in flue gases issuing from a stack due to combustion, comprising:

a probe for mounting to extend through the wall of a stack through which combustion gases in the stack can pass;

a transceiver mounted to said probe externally of said stack including an optical means and electric circuit means;

said optical means having a chopped light source for projecting beams of light of different selected wavelengths into said probe, a detector for detecting any attenuation of the light beams by said gases in said probe for providing a measure of the extend of absorption of each gas of interest in each of a plurality of separate channels, and a zero absorption channel providing a reference for the other channels,

said electric circuit means providing an electric output representing each of said absorption measurements; and

control means coupled to said transceiver including first means for converting said electric output to a corresponding percent modulation output for each of said gases of interest, for correcting each of said percent modulation outputs for temperature and pressure, for correcting said percent modulation output for interference between measured gases, and to provide corrected outputs representing the concentration of each of said measured gases,

said control means including a programmed digital computer using a table iterative solution having channel percent modulation with respect to gas concentration output for a family of temperatures of each of said measured gases.

14. Apparatus as set forth in claim 13, wherein said measured gases are H₂ O, CO and CO₂ and a seven-table iterative solution is used in said control unit.

15. Apparatus for measuring multiple component interfering gases contained in flue gases issuing from a stack due to combustion, comprising:

a probe for mounting to extend through the wall of a stack through which combustion gases in the stack can pass;

a transceiver mounted to said probe externally of said stack including an optical means and electric circuit means,

said optical means having a chopped light source for projecting beams of light of different selected wavelengths into said probe, a detector for detecting any attenuation of the light beams by said gases in said probe for providing a measure of the extend of absorption of each gas of interest in each of a plurality of separate channels, and a zero absorption channel providing a reference for the other channels,

said electric circuit means providing an electric output representing each of said absorption measurements; and

control means coupled to said transceiver including first means for converting said electric output to a corresponding percent modulation output for each of said gases of interest, for correcting each of said percent modulation outputs for temperature and pressure, for correcting said percent modulation output for interference between measured gases, and to provide corrected outputs representing the concentration of each of said measured gases,

said control means providing a compensated CO measurement value equal to ##EQU4## that is insensitive to the dilution effects of excess air.

16. Apparatus for measuring multiple component interfering gases contained in flue gases issuing from a stack due to combustion, comprising:

a probe for mounting to extend through the wall of a stack through which combustion gases in the stack can pass;

a transceiver mounted to said probe externally of said stack including an optical means and electric circuit means,

said optical means having a chopped light source for projecting beams of light of different selected wavelengths into said probe, a detector for detecting any attenuation of the light beams by said gases in said probe for providing a measure of the extend of absorption of each gas of interest in each of a plurality of separate channels, and a zero absorption channel providing a reference for the other channels,

said electric circuit means providing an electric output representing each of said absorption measurements; and

control means coupled to said transceiver including first means for converting said electric output to a corresponding percent modulation output for each of said gases of interest, for correcting each of said percent modulation outputs for temperature and pressure, for correcting said percent modulation output for interference between measured gases, and to provide corrected outputs representing the concentration of each of said measured gases,

said control means providing an efficiency measurement value %CE=%CE Dry flue gas×

%CE combustibles×

1/100 where;

%CE Dry flue gas=K₁ [0.964+0.000135% EA) - (0.000207+1.68×

10^-6 ×

%EA) T_s ]100

T_s =flue gas exit/stack temperature °

F. K₁ =fuel sensitivity factor;

oil=1.0, Natural gas=0.91 ##EQU5## % O_2D =% dry oxygen ##EQU6## K₂ =Ratio of total heat loss to all unburned combustibles to that only due to CO, ideally unity

CO=ppm of carbon monoxide corrected to dry basis stoichiometric conditions.