Flare passive FTIR studies
Atmosfir have developed a capability through its unique spectral algorithm to provide flare combustion effeciency studies using state-of-the-art fast scanning passive FTIR (PFTIR) technology. A PFTIR is an analyzer that measures the infrared spectrum of the thermal radiation emitted by hot gases. The chemical constituents in the hot gases are identified and quantified by the shape and size, respectively, of each constituent’s emission spectrum. Bruker's SIGIS 2 (Scanning Infrared Gas Imaging System) is a scanning imaging remote sensing system based on the combination of an FTIR spectrometer with a single detector element and a scanner system with a large gimbal-mounted mirror on a rotating stage to direct the radiation from the target to the spectrometer telescope. An infrared and a visible camera are mounted to view through the gimbal-mounted mirror to produce infrared and visible images that overlay each other and the field of view of the FTIR detector to facilitate the alignment of the FTIR to the target. The instrument produces hyperspectral images in which an infrared spectrum is produced in each pixel. This is an imaging PFTIR (Passive Fourier Transform Infrared). The ability to view the plume makes it a powerful tool for making measurements of the chemical composition of flare plumes.
The main advances to method reliability with the new technology are:
1. Built in infrared camera that allows an overlay of the area of data collection for an infrared image.
2. Built in ambient and elevated black body calibration that was performed before each run. This is important for conversion the raw spectrum to accurate radiance spectrum when instrument ambient temperature is changing during the day.
3. Real-time analysis and visual software that allow you to evaluate in real-time detection with spectral validation for each direction (pixel) collected in 0.6 seconds. This visual plume mapping frame representation allows performing adjustments and all during the study for optimizing the spatial data collection programming before each run based on data and build up experience.
4. The duty cycle of the interferometer that allows:
a) Collection of 40 individual spectra in 25 seconds. Analyzing in real time for CO and CO2 for each pixel of the frame (e.g. 4x10 or 5x8) allows evaluating which pixels out of the 40 are in the plume of hot gases and which pixels are representing background in each frame. The in plume radiance spectra are averaged to generate the radiance sample spectrum, and the sky background radiance spectra are averaged to generate a sky background radiance spectrum. Both in plume radiance spectrum and a sky background radiance spectrum are included in calculation of the absorbance spectrum for each frame (25 seconds). Previous studies sampled a sky background couple of times a day and applied for the dataset of the day. They also collected data outside the plume as they track the plume for one minute in directions they assume the plume of full combustion was, and get one spectrum.
b) Collection of several pixels (4 in this study and about 6 repetitions in 30 minute run) around the tip of the flare for evaluating the atmospheric transmission for each run. In previous study this was performed in much lower frequency.