Real-time alkali monitoring system

A real-time alkali monitoring system for detecting two selected alkali emissions simultaneously from a light source in the presence of interfering background radiation, comprising:

• a bifurcated fiber optic cable having first and second branches attached to a common trunk and adapted at the common end to optically couple light from a light source to said cable;
• a first beam splitter disposed to intercept light passing from the end of said first branch of said cable and split the light into a first beam and a second beam;
• a second beam splitter disposed to intercept light passing from the end of said second branch of said cable and split the light into a third beam and a fourth beam;
• a first bandpass optical filter having a passband centered about a first selected emission line and having a bandwidth at least as wide as the first selected emission line and being disposed to intercept said first beam passing from said first beam splitter;
• a second bandpass optical filter having a passband centered about a wavelength identical to that of said first bandpass filter and a bandwidth substantially wider than the bandwidth of said first bandpass filter and being disposed to intercept said second beam passing from said first beam splitter;
• a third bandpass optical filter having a passband centered about a second selected emission line and a bandwidth at least as wide as the second selected emission line and being disposed to intercept said third beam passing from said second beam splitter;
• a fourth bandpass optical filter having a passband centered about a wavelength identical to that of said third bandpass filter and a bandwidth substantially wider than the bandwidth of said third bandpass filter and being disposed to intercept said fourth beam passing from said second beam splitter;
• a first light detector means for generating a first signal having an amplitude proportional to the intensity of light transmitted through said first bandpass filter;
• a second light detector means for generating a second signal having an amplitude proportional to the intensity of light transmitted through said second bandpass filter;
• a third light detector means for generating a third signal having an amplitude proportional to the intensity of light transmitted through said third bandpass filter;
• a fourth light detector means for generating a fourth signal having an amplitude proportional to the intensity of light transmitted through said fourth bandpass filter;
• a means for scaling one of the output signals from said first and second detectors and one of the output signals from said third and fourth detectors, and
• a means for calculating the difference between said scaled output signal from said first and second detectors and the difference between said scaled output signal from said third and fourth detectors and said other output signal from said third and fourth detectors to generate fifth and sixth output signals each having an amplitude proportional to the intensity of one of said emission lines being monitored.

A real-time alkali monitoring system for detecting two different selected alkali emissions simultaneously from a light source in the presence of interfering background radiation comprising:

• a quadfurcated fiber optic cable having first, second, third and fourth branches attached to a common trunk and adapted at the common end to optically couple light from a light source to said cable;
• a first bandpass optical filter having a passband centered about a first selected emission line and having a bandwidth at least as wide as the first selected emission line and being diposed to intercept light passing from the end of said first branch of said cable;
• a second bandpass optical filter having a passband centered about a wavelength identical to that of said first bandpass filter and a bandwidth substantially wider than the bandwidth of said first bandpass filter and being disposed to intercept light passing from the end of said second branch of said cable;
• a third bandpass optical filter having a passband centered about a second selected emission line and having a bandwidth at least as wide as the second selected emission line and being disposed to intercept light passing from the end of said third branch of said cable;
• a fourth bandpass optical filter having a passband centered about a wavelength identical to that of said third bandpass filter and a bandwidth substantially wider than the bandwidth of said third bandpass filter and being disposed to intercept light passing from the end of said fourth branch of said cable;
• a first light detector means for generating a first signal having an amplitude proportional to the intensity of light transmitted through said first bandpass filter;
• a second light detector means for generating a second signal having an amplitude proportional to the intensity of light transmitted through said second bandpass filter;
• a third light detector means for generating a third signal having an amplitude proportional to the intensity of light transmitted through said third bandpass filter;
• a fourth light detector means for generating a fourth signal having an amplitude proportional to the intensity of light transmitted through said fourth bandpass filter;
• a means for scaling one of the output signals from said first and second detectors and one of the output signals from said third and fourth detectors, and
• a means for calculating the difference between said scaled output signal from said first and second detectors and said other output signal from said first and second detectors and the difference between said scaled other output signal from said third and fourth detectors and said output signal from said third and fourth detectors to generate fifth and sixth output signals each having an amplitude proportional to the intensity of respective of said first and second emission lines being monitored.

A method for real-time monitoring of alkali concentrations in process streams, comprising:

• diverting a sample from a process stream to a combustion burner;
• combusting the sample to produce alkali flame emissions;
• transmitting the flame emissions to a pair of bandpass filters having passbands centered about the spectral emission line of an alkali species, the first bandpass filter having a bandwidth at least as wide as the selected emission line and the second bandpass filter having a bandwidth substantially wider than the bandwidth of the first bandpass filter;
• detecting the signals transmitted by each of the bandpass filters;
• scaling one of the detected signals, and
• calculating the difference between the scaled signal and the other detected signal to produce an output signal having an amplitude proportional to the intensity of the emission line being monitored.