Method and apparatus for siloxane measurements in a biogas

A system for monitoring one or more silicon-containing compounds in a biogas, the system comprising:

• a source of a first beam of radiation;
• an interferometer receiving the first beam of radiation from the source and forming a second beam of radiation comprising an interference signal;
• a sample cell in optical communication with the interferometer;
• a flow mechanism establishing a first flow of a non-absorptive gas having substantially no infrared absorptions in a specified wavelength range of interest and a second flow of the biogas through the sample cell;
• a cooled detector in optical communication with the sample cell, the cooled detector receiving:
• a first interference signal propagating through the non-absorptive gas in the sample cell;
• and
• a second interference signal propagating through a sample gas in the sample cell, the sample gas comprising the biogas;
• a processor in electrical communication with the cooled detector, the processor configured to calculate a total concentration of the one or more silicon-containing compounds in the biogas based on:
• a first absorption spectrum based on a ratio of the first interference signal and the second interference signal;
• a set of surrogate absorption spectra based on, at least, individual absorption spectrum for each of a subset of one or more silicon-containing compounds selected from a larger set of known silicon-containing compounds with known concentrations;
• and
• a housing in which the source, the interferometer, the sample cell, the cooled detector and the processor are disposed.

A computer readable product, tangibly embodied on a non-transitory information carrier or a machine readable storage device, and operable on a digital signal processor for a biogas detection system, the computer readable product including instructions operable to cause the digital signal processor to:

• receive a first spectral measurement of a non-absorptive gas in a sample cell, the non-absorptive gas having substantially no infrared absorptions in a specified wavelength range of interest;
• receive a second spectral measurement of a sample gas comprising a biogas in the sample cell, wherein the biogas includes one or more siloxane compounds;
• generate a first absorption spectrum based on a ratio of the first spectral measurement and the second spectral measurement;
• generate a set of surrogate absorption spectra based on, at least, individual absorption spectrum for each of a subset of one or more silicon-containing compounds selected from a larger set of known silicon-containing compounds with known concentrations;
• and
• perform a multiple regression analysis using the first absorption spectrum and the set of surrogate absorption spectra to calculate a total concentration of the one or more siloxane compounds in the biogas.