To optimize plant performance and prevent expensive turbine damage, rapid control is critical for industrial power markets covering multiple energy sources. Maintaining turbine efficiency is an even higher priority today because of lower emission requirements and varying fuel sources due to the increase in unconventional natural gas sources, such as shale. Plant gas sources are primarily composed of methane, but typically there are extensive variations in higher hydrocarbons (C2+) as well. In fact, in some cases, over 18 percent variation has been recorded with fluctuations from 10 percent to 16 percent within one minute. Turbines have to be more flexible and need to present the above criteria over a wide range of loads because gas turbine power plants are often used only for peak loads.
Methane and higher hydrocarbons like ethane and propane behave differently during combustion. The variability of fuel sources can sometimes pose challenges for control and optimization, especially for combined cycle turbines with lower emissions. While a gas chromatograph can provide all the required measurements, the speed of response it provides is sometimes not sufficient for effective control.
The solution can often be a process gas analyzer (PGA) with a specific configuration of optical benches and filters that provide continuous measurement and the rapid response that’s required. In addition, an approximate calorific value (BTU) can be provided as long as the higher hydrocarbons are low in content. If this is not the case, the BTU value will be underestimated but never overestimated. Such values cannot be used for custody transfer but they may be adequate to prevent turbine damage and optimize performance. If the operator knows the variation of C2+ in the fuel sources, then that will substantially minimize the error.