Field Test Report: NETL Portable Raman Gas Composition Monitor - Initial Industrial tests at NETL and General Electric (GE)
NETL has developed new technology which enables the use of Raman spectroscopy in the real-time measurement of gas mixtures. This technology uses a hollow reflective metal-lined capillary waveguide as a gas sampling cell which contains the sample gas, and efficiently collects optical Raman scattering from the gas sample, for measurement with a miniature spectrometer. The result is an optical Raman “fingerprint” for each gas which is tens or hundreds of times larger than that which can be collected with conventional free-space optics. In this manner, the new technology exhibits a combination of measurement speed and accuracy which is unprecedented for spontaneous Raman measurements of gases. This makes the system especially well-suited to gas turbine engine control based on a-priori measurement of incoming fuel composition. The system has been developed to produce a measurement of all of the common components of natural gas, including the lesser nitrogen, oxygen, carbon-dioxide, and carbon monoxide diluents to better than 1% concentration accuracy each second. The objective of this task under CRADA 10-N100 was to evaluate the capability of a laser Raman capillary gas sensor for combustion fuels. A portable version of the Raman gas sensor, constructed at NETL, was used for field-trials conducted in a cooperative research effort at a GE facility. Testing under the CRADA was performed in 5 parts. Parts 1-4 were successful in testing of the Raman Gas Composition Monitor with bottled calibration gases, and in continuous monitoring of several gas streams at low pressure, in comparison with an online mass spectrometer. In part 5, the Raman Gas Composition Monitor was moved outdoors for testing with high pressure gas supplies. Some difficulties were encountered during industrial testing including the condensation of heavy hydrocarbons inside the sample cell (in part 5), communication with the GE data collection system, as well as some drift in the optical noise background. The difficulties with liquid contaminants will be overcome through the use of prodigious sample-cell heating and additional line filtration including liquid ingress-protection. The communication problem was resolved through site-specific troubleshooting of the MODBUS data tags.