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GPAL Launches XINSTn to Reduce Fuel Costs due Poor Fuel Quality

Fuel costs amount to millions of dollars per year. Any decrease in the lower heating value (LHV) of the fuel supplied will result in operators of gas turbines paying extra for their fuel. In one instance, a 2% decrease in LHV resulted in increased fuel cost exceeding half a million dollars per year. Thus, means to track LHV changes is of paramount importance in detecting and eliminating such increases in costs, particularly in a deregulated market.

GPAL gas turbine performance monitoring and diagnostics systems detect faults by trending fault indices, which indicate change in component characteristics such as compressors and turbines(see www.gpal.co.uk/xpgt3.htm). The trends and patterns of these fault indices can also be used to detect measurement errors. For example, one component performance improves, while simultaneously another component performance decreases. Therefore, fault indices are also an excellent means of detecting instrument faults as discussed in www.gpal.co.uk/trial1.htm. Although all measurement errors can be detected by such analysis we can detect one measurement error on-line. XINSTn exploits this feature to detect LHV errors on-line and it gives an immediate indication of change in LHV thus alerting the operators of potential increase in fuel costs. XINSTn can also differentiate between fuel flow errors and changes in LHV. A typical variation in LHV during operation is shown in Figure 1 and will result in a significant increase in fuel cost and thus life cycle cost.

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Figure 1 the change in LHV with time during engine operation

XINSTn is applicable to any gas turbine configuration including water and steam injection. It is also applicable when using either gaseous or liquid fuels. No additional hardware or sensors are required other than those required for performance monitoring and diagnostics as described in www.gpal.co.uk/xpgt3.htm and is therefore a very low cost option. In gas transmission, it also acts as a very useful check on the quality of gas being transmitted as the fuel gas is usually taken from the transmission line.

XINSTn have been applied extensively in the exploration and production facilities in the UK off-shore sector and has successfully detected the changes in LHV. This occurs because in certain facilities the fuel gas composition changes significantly depending of what wells are employed in production. Swings in LHV as much as ±10% is possible and detectable using XINSTn, which has been successfully tested using natural gas and diesel.

With accurate fuel flow calculations, monitoring emissions using Parametric Emissions Monitoring Systems (PEMS) such as XEM gives meaningful results. PEMS that do not allow for such changes in LHV errors will inevitably give errors in emissions. The advent and widespread use of DLE gas turbines will also benefit from XINSTn. As the LHV swings combustion problems such as rumble and chugging can be predicted thus help prevent damage to combustion systems. Furthermore, flame out conditions can also be predicted and outputs from XINSTn can be used to prevent such conditions from occurring.

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Figure 2 shows fault pattern before adjusting for LHV changes

As an example, the fault index pattern in Figure 2 implies damage to both compressor and turbines. This result could also be due to measurement errors. After XINSTn analyses the fault pattern (on-line) we get the fault index pattern as shown by Figure 3, which indicates compressor fouling and no damage to the turbine. Importantly, the system also indicates a LHV error of about -2%.

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Figure 3 shows fault patterns after adjusting for LHV changes


2013 Gas Path Analysis