The detection and characterization of molecular gases in a sample is a relatively difficult challenge. Usually, this task is relegated to expensive and time-consuming processes like mass spectrometry and gas chromatography. Furthermore, numerous industrial applications require such gas-phase analysis for pollution and process control; for example, in large, natural-gas-fired turbine electricity generators, large quantities of natural gas are mixed with air and burned. Because natural gas comes from a variety of sources, the composition of the gas changes often. If the composition of natural gas were known a-priori, turbine efficiency could be improved by adjusting the fuel/air mixture and other operating parameters. This control capability requires measurement of the components of the natural gas to better than 0.1% accuracy, with the measurement being performed at least once every second. There is currently no commercially available sensor or sensing system that can measure all of the natural-gas components in one second.
Industries utilizing natural gas, gasifier syngas, biogas, landfill gas, or any type of fuel gas can benefit from knowing the composition of a fuel gas mixture in real time. Natural gas — the most common fuel — can have significant variation in hydrocarbon composition in areas supplied by multiple sources. The “opportunity fuels,” such as biogas and landfill gases, also have significant variation in quality, and operators often use natural gas as a backup fuel. There is a need for a sensing system that is able to quickly and reliably identify, characterize, and determine the concentration of the various gases in a gas mixture.
The current invention meets this need by providing a gas sensor system capable of accurate and continuous readout of the relative mole percent of all major fuel-gas components including H2, CO, CO2, CH4, C2H6, and C3H8, along with O2, N2, and water vapor. The sensor system is based on Raman spectroscopy, and has been developed to utilize low laser powers, and low-resolution spectrometers and detectors to reduce cost while giving readouts in one second or less. This sensor system will greatly benefit the power industry, as well as other industries utilizing gaseous input or output streams by enabling faster, smarter control to increase process efficiency and reduce emissions.
The gas analyzing sensor characterizes gaseous fuel, exhaust gases, or other process gas streams and reports concentrations of all majority gases to 0.1% in one second or less. The sensor relies on novel techniques to enhance usually weak spontaneous Raman emissions from the gases being sampled, enabling the application of Raman spectroscopy to rapid gas analysis. The invention provides a gas composition measurement system that is fast, accurate, cost-effective, and capable of continuously measuring the concentrations of gases in a mixture, such as natural gas, at elevated system pressures.
Real-time capability enables turbine operators to switch from one fuel to another with continuous adjustment of the fuel/air ratio for optimum operation efficiency and flameout prevention. Current field-unit prototypes are rated for pressures between 10 psi and 800 psi, and gas temperatures up to 200 °C for regulated or direct pipeline measurement.