Method and apparatus for real-time monitoring of furnace flue gases

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.

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, H2O, 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.

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.