Varying gas composition impacts performance and component lifetime of internal combustion engines, gas turbines and fuel cell-based machines. By measuring the optical fingerprints of C1-C5 alkanes, the Precisive 5 Gas Analyser enables real-time and high-accuracy fuel gas analysis, according to the firm’s founder and president, Vidi Saptari.
"With an update rate of 5 seconds or less reporting the full hydrocarbon composition information and its low operational requirements, it makes a formidable alternative to industry-standard analysers," Saptari told Gas to Power Journal.
Elaborating on the rising fuel type variety and operators' need to swiftly analyse gas quality, he said gas-powered engines traditionally run on a number of fuel sources such as natural gas, syngas, coke oven gas, LPG, landfill gas and biogas.
Unconventional gas sources such as coal bed methane, shale gas, gas hydrates and tight gas reservoirs, increase the spread in its composition and characteristics. Furthermore, synthetic mixtures and blends are introduced into the pipeline such as during peak shaving to maintain the energy content during seasons of high demand, therefore varying gas consistency.
Stressing the importance of stable fuel properties to maintain chemical kinetics of the combustion process, Saptari said: "Non-optimal fuel properties result in lower efficiency, higher emissions and/or decreased component life, whereas fuel properties that are out of the specified range could result in catastrophic failures or unsafe operating conditions."
Variable gas quality puts combustion stability at risk
There is also a risk 'engine knocks' in stationary IC installations: "As the flame propagates in the combustion chamber, the un-burnt fuel mixture ahead of the flame may be compressed causing rapid increase in pressure, temperature and density. This causes high frequency pressure oscillations in the chamber and produces a sharp metallic noise called engine knock," he explained.
In the case of turbines, the fuel compositional variation may give rise to flashback, blowout, auto-ignition or combustion instability, all of which strongly depend on fuel composition.
The popular lean premixed turbine combustors operate near lean limit to minimize CO (carbon monoxide) and NOx (nitrous oxides) emissions. "However, near the lean limit, these combustors are highly susceptible to flashbacks and blowout," he pointed out. Flashbacks are a phenomenon whereby the flame propagates upstream or in reverse direction.
Flow-through, real time, online sensor for multiple fuels
To help maintain performance and efficiency of gas turbine components, Boston-headquartered Precisive has developed and patented an industry-first all-optical analyser based upon Tunable Filter Spectroscopy (TFS) providing real-time specifiation of hydrocarbon components. Close to 2000 units have been deployed for the measurement of C1 – C5 alkane gases in natural gas and hydrocarbon processing industries to-date.
A standard ‘Precisive 5 Gas Analyzer’ is a stand-alone unit ready for installation in Div 2 and Zone 2 areas with native digital Modbus TCP/IP communication over multiple channels with absolute concentrations across CO2 and Hydrocarbons, BTU calorific value, and Wobbe Index.
The optical analyser provides:
- Fast response time (down to a 1 second update rate)
- Comprehensive measurement including C1 – C5 composition information, calorific value and Wobbe index calculations
- Permanent calibration at the factory – for life.
- No carrier gas, fuel gas or other consumable requirements
- Excellent accuracy and linearity throughout a wide measurement range
- Compact (large shoe-box sized) with 24VDC power or AC weighing less than 26lbs (~12kg)
- Stand-alone analyzer with negligible maintenance and low operation costs
The only other widely deployed analyser technology that provides the actual speciated hydrocarbon composition information is a gas chromatograph, Saptari pointed out.
"However, due to the need to physically separate the constituents, not only does it need a continuous supply of expensive carrier gas, it is slow, with a measurement cycle time of typically 5 minutes depending on the design," he cautioned, concluding "For real-time control, this is not sufficient."