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A method and apparatus for monitoring the flue gases of a furnace combustion process is disclosed. A by-pass circuit that communicates a sample of flue gases to be monitored from a furnace, through a measurement chamber and back to the furnace or furnace exhaust duct is provided. The by-pass circuit

A method and apparatus for monitoring the flue gases of a furnace combustion process is disclosed. A by-pass circuit that communicates a sample of flue gases to be monitored from a furnace, through a measurement chamber and back to the furnace or furnace exhaust duct is provided. The by-pass circuit has a gas sampling probe with a fume inlet opening, the probe being positioned for withdrawing the sample to be monitored and transmitting it through the by-pass circuit. A measurement device is positioned in the measurement chamber and comprises an in situ optical device which provides real-time measurement of targeted flue gas species concentrations.

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We claim: 1. An apparatus for monitoring the flue gases of a furnace combustion process comprising, in combination: a by-pass circuit constructed and arranged to communicate a sample of flue gases to be monitored through a measurement chamber and through a return duct; the by-pass circuit having a

We claim: 1. An apparatus for monitoring the flue gases of a furnace combustion process comprising, in combination: a by-pass circuit constructed and arranged to communicate a sample of flue gases to be monitored through a measurement chamber and through a return duct; the by-pass circuit having a gas sampling probe having a fume inlet opening, the probe being positioned for withdrawing the sample to be monitored and transmitting it through the by-pass circuit; a measurement device positioned in the measurement chamber and comprising an in situ optical device constructed and arranged to facilitate real-time measurement of targeted flue gas species concentrations, the targeted species including at least one of O2 , CO, CO2, H2O, and H2, the measurement device further comprising an optical signal processor constructed and arranged to report a measured concentration to a controller that is constructed and arranged to control a process variable in relation to the measured concentration to optimize the process; and a vacuum drawing system constructed and arranged to draw the furnace flue gas to be monitored through the by-pass circuit. 2. The apparatus of claim 1, the by-pass circuit further comprising: a drop tube in communication with the probe and upstream a drop box; and the drop box being located at the end of the drop tube and positioned upstream from the measurement chamber, the drop box being constructed and arranged to remove particulates that may be present in the flue gases. 3. The apparatus of claim 1, wherein the vacuum drawing system comprises a particulate reducing subassembly operatively positioned in the return duct and including a particle filter, a condenser and a suction pump for vacuum drawing the flue gases through the by-pass circuit. 4. The apparatus of claim 1, wherein the probe is a filter-free probe. 5. The apparatus of claim 1, wherein the probe is positioned in the furnace. 6. The apparatus of claim 1, wherein the probe is positioned in the furnace exhaust duct. 7. The apparatus of claim 1, wherein the by-pass circuit is thermally insulated to prevent the flue gas from cooling to a temperature below its dew point along the length of the by-pass circuit. 8. The apparatus of claim 1, further comprising: an electrostatic precipitator constructed and arranged to remove particles from the flue gas sample, the precipitator being positioned upstream from the measurement chamber. 9. The apparatus of claim 8, further comprising: means for cooling the flue gas sample to a temperature of less than about 750 degrees F. 10. The apparatus of claim 9, wherein the means for cooling the flue gas sample to a temperature of less than about 750 degrees F. comprises: mixing the drawn flue gas sample with a stream of neutral, cooler gas which is not part of the process gas composition. 11. The apparatus of claim 10, wherein the neutral, cooler gas is nitrogen. 12. The apparatus of claim 1, wherein the measurement device uses an absorption-based technique to measure the flue gas sample. 13. The apparatus of claim 12, wherein the measurement device is a turnable diode laser. 14. The apparatus of claim 12, wherein the measurement device performs in situ dispersive, Fourier transform infrared (FTIR) spectrometry. 15. The apparatus of claim 12, wherein the measurement device performs non-dispersive, infrared (NDIR) spectrometry. 16. The apparatus of claim 1, the measurement device comprising: a transmitter module positioned at a launch position, constructed and arranged to launch a collimated beam of radiation along a line-of-sight path through the flue gas sample; a detector module positioned substantially opposed from the launch position, constructed and arranged to detect the beam; and an optical signal processor is further constructed and arranged to detect the attenuation obtained from the initial beam as the laser is tuned over a resonance absorption line of the targeted species. 17. The apparatus of claim 16, wherein the transmitter module and the detector module are both mounted on a rigid support. 18. The apparatus of claim 16, wherein the distance between the transmitter module and the detector module is between about one foot and about three feet. 19. An apparatus for monitoring the flue gases of a furnace combustion process comprising, in combination: a by-pass circuit constructed and arranged to communicate a sample of flue gases to be monitored through a measurement chamber and through a return duct positioned downstream from the measurement chamber, the by-pass circuit further having (a) a gas sampling probe having a fume inlet opening, the probe being positioned for withdrawing a sample of flue gases to be monitored; (b) a drop tube positioned between the gas sampling probe and a drop box, the drop tube having a length of less than about twenty-five feet; and (c) a drop box located at the end of the drop tube and positioned upstream from a remotely positioned measurement device, the drop box being constructed and arranged to remove particulates that may be present in the flue gases; an electrostatic precipitator positioned upstream from the measurement device and constructed and arranged to remove particles from the flue gas sample; means for cooling the flue gas sample to a temperature of less than about 750 degrees F.; a vacuum drawing system having a particle filter, a condenser and a suction pump for vacuum drawing the gas along the by-pass circuit; the remotely positioned measurement device comprising a tunable diode laser optical device constructed and arranged to facilitate real-time measurement of targeted flue gas species concentrations, the measurement device further comprising an optical signal processor constructed and arranged to report a measured concentration to a controller that is constructed and arranged to control a process variable in relation to the measured concentration to optimize the process; and the targeted species including at least one of O2, CO, CO2, H2O, and H2; and conduit means for venting the measured gas. 20. The apparatus of claim 19, wherein the probe is a filter-free probe. 21. The apparatus of claim 19, wherein the by-pass circuit is insulated sufficiently to prevent the flue gas from cooling to a temperature below its dew point along the length of the by-pass circuit. 22. The apparatus of claim 19, wherein the means for cooling the flue gas sample to a temperature of less than about 750 degrees F. comprises mixing the drawn flue gas sample with a stream of neutral, cooler gas which is not part of the process gas composition. 23. The apparatus of claim 22, wherein the neutral, cooler gas is nitrogen. 24. The apparatus of claim 19, wherein the fume inlet is positioned on a leeward side of the probe downstream with respect to flow of flue gases past the probe. 25. The apparatus of claim 19, wherein the remotely positioned measurement device comprises: a transmitter module positioned at a launch position, constructed and arranged to launch a collimated beam of radiation along a line-of-sight path through the flue gas sample; a detector module positioned substantially opposed from the launch position, constructed and arranged to detect the beam; and an optical signal processor constructed and arranged to detect the attenuation obtained from the initial beam as the laser is tuned over a resonance absorption line of the targeted species. 26. The apparatus of claim 25, wherein the transmitter and the detector module are both mounted on a rigid support. 27. The apparatus of claim 25, wherein the beam is transmitted in a direction that is substantially, perpendicular to a direction of gas sample flow. 28. The apparatus of claim 25, wherein the beam is transmitted in a direction that is substantially parallel to a direction of gas sample flow. 29. The apparatus of claim 25, wherein the probe is positioned in the furnace. 30. The apparatus of claim 25, wherein the probe is positioned in a furnace exhaust duct. 31. The apparatus of claim 25, wherein the process is electric arc furnace operation, and wherein the probe is positioned proximate to a separation gap positioned between a furnace elbow and a furnace exhaust duct. 32. A system for monitoring the off-gases of an electric arc furnace comprising, in combination: a by-pass circuit constructed and arranged to communicate a sample of off-gases to be monitored from a furnace exhaust duct, through a measurement chamber and through a return duct being positioned between the measurement chamber and the furnace exhaust duct, thereby being constructed and arranged to facilitate return of the sample to the furnace exhaust duct; the by-pass circuit further having (a) a gas sampling, filter-free probe having a fume inlet opening, the probe being positioned proximate to a separation gap in the furnace exhaust duct for withdrawing a sample of off-gases to be monitored; (b) a drop tube positioned between the gas sampling probe and drop box, the drop tube having a length of less than about twenty-five feet; and (c) a drop box located at the end of the drop tube and positioned upstream from the measurement device, the drop box being constructed and arranged to remove particulates that may be present in the off-gases; an electrostatic precipitator positioned upstream from the measurement device and constructed and arranged to remove particles from the off-gas sample; means for cooling the off-gas sample to a temperature of less than about 750 degrees F.; a vacuum drawing system including a particle filter, a condenser and a suction pump for vacuum drawing the gas along the sampling line; the measurement device comprising a tunable diode laser optical device constructed and arranged to facilitate real-time measurement of targeted off-gas species concentrations for targeted species including at least one of O2, CO, CO2, H 2O, and H2; the measurement device further comprising a transmitter module positioned at a launch position, constructed and arranged to launch a collimated beam of radiation along a line-of-sight path through the off-gas sample; a detector module positioned substantially opposed from the launch position, constructed and arranged to detect the beam; and an optical signal processor constructed and arranged to (a) detect the attenuation obtained from the initial beam as the laser is tuned over a resonance absorption line of the targeted species, (b) determine the concentration of the targeted species; and (c) report the concentration of the targeted species to a controller constructed and arranged to control at least one process variable in relation to the concentration of the targeted species to optimize the process; and conduit means for venting the measured gas directly into the exhaust duct. 33. A method for monitoring the flue gases of a furnace combustion process comprising, in combination: routing a sample of flue gas to be monitored from a furnace, through a measurement chamber and back to a return duct; launching a collimated beam of radiation along a line-of-sight path through the flue gas sample; detecting the beam; detecting the attenuation obtained from the beam as the laser is tuned over a resonance absorption line of the targeted species; determining the concentration of a targeted species; and reporting the concentration of the targeted species to a combustion process controller constructed and arranged to control at least one process variable in relation to the concentration of the targeted species to optimize the process. 34. The method of claim 33, wherein the targeted species includes at least one of O2, CO, CO2, H2O, and H2. 35. The method of claim 33, further comprising: the targeted species being only O2, and the process variable includes controlling the O2 level in the furnace to a desired set point and controlling the injection of oxidant into the furnace, thus controlling optimal burn out of CO, H2 and unburned hydrocarbons. 36. The method of claim 35, wherein the furnace combustion process is operation of an electric arc furnace.