Accuracy and consistency of on-line natural gas analysis

The accuracy and consistency of on-line natural gas analysis using the gas chromatography method was investigated systematically and carefully. Since the gas chromatography method is a comparative method, the calibration gas, the performance of the analyzer and the choice of calibration gas composition are critical factors to obtain accuracy and consistency of on-line analysis. The gravimetric preparations of calibration gases, especially EffecTech procedures, were elaborated detailedly. At the same time, the performance of analyzer was studied. Specifically, the detailed bias error and uncertainty calculations were described and interpreted. Generally, bias errors and uncertainties cannot be combined in a satisfactory manner and as such, they are usually compared. However, it is now common practice to accept errors in the measurement of component amount fractions provided their effect does not give rise to unacceptable errors in physical properties.