High-accuracy hydrocarbon dew point (HCDP) data are of utmost importance in natural gas operations. They are key to the reliability of pipeline systems, the development of equipment, and the fulfillment of custody transfer tariffs. Still, two errors—pressure regulation and gas chromatograph (GC) uncertainties)—usually cause phase diagram calculations to go wrong. The association of these factors with HCDP results is important in addressing their effect and increasing the reliability of the operations.
Pressure Regulation Errors
Gas-Chromatographs are operated at near atmospheric pressures, while natural gas samples are taken from pipelines at pressures of more than 500 psi (35 Bar) or more. Therefore, before the analysis, pressure of the sample needs to be reduced to about 20 psi, which corresponds to the GC's typical operating range. This step, called pressure regulation, is a substantial source of error.
During the regulation of the pressure, the composition of the gas sample can be modified. Dew point, heavy hydrocarbons which are considered the key components, are highly sensitive to these modifications. The changes in composition accompanying pressure reduction may cause more than 20°C (about 35°F) discrepancies in the phase diagram calculations. This level of uncertainty is one of the main factors affecting the HCDP reliability and, at the same time, tends to lead to wrong operational decisions.
GC Uncertainty
Gas chromatographs are important devices used to measure the composition of hydrocarbon mixtures. Nevertheless, their high efficiency is restricted with heavy hydrocarbons such as those in the C6+ and C9+ fractions. These elements are crucial for the hydrocarbon dew point measurement, which means that the inaccurate reading of these elements will result in inaccurate phase diagram calculations.
The uncertainties in GC measurements can add another 20-30°C to the overall error in determining the HCDP. This situation is additionally worsened when the uncertainties are not independent of each other. For instance, software used for the calculation of phase diagrams can give different results, which will increase the overall error margin. As a result, GC data is the only source for phase calculations, and this adds a lot of risk to the project, especially sinceHCDP measurements are crucial for the safe operation of pipelines and the associated equipment such as compressors.
ZEGAZ Instruments’ Approach
ZEGAZ Instruments provides high-quality equipment for hydrocarbon dew point analysis. These products such as HCD5000™ and DewPoint Duo™ can directly measure hydrocarbon and water dew points via a state-of-the-art CEIRS(™) technology. In contrast to conventional gas chromatography (GC) methods, ZEGAZ Instruments' analyzers afford real-time data accuracy without pressure regulation or compositional analysis estimations. This direct measurement method sidesteps numerous errors that pressure regulation and GC uncertainty usually bring, hence more trustworthy HCDP measurements are achieved.
Through utilizing ZEGAZ Instruments' devices, operators may easily avoid the restriction of GC analysis thus, the possibility of spending huge sums of money on mistakes will be decreased, and the overall system performance will be benefited as well.
Combined Impact
Errors induced by pressure regulation combined with gas chromatograph (GC) uncertainties can really add up to inaccurate HCDP calculations. These mistakes are quite costly both in terms of revenue lost and costs accrued due to damage to equipment.Wrong phase diagrams can cause condensation of liquids in the pipeline, compressors, and power plants, which will mean loss in efficiency and safety. Presence of liquids will also create significant uncertainties in gas property and flow measurements.
Conclusion
Gas Chromatography (GC) pressures regulation errors and GC accuracy improvement are the main things to focus on while getting hydrocarbon phase diagrams of high accuracy. Although GCs are still the main devices for chemical analysis and BTU measurements, the fact that they have some limitations must be pointed out especially those with the heavier hydrocarbons. Operators should focus on the actual measurement of HCDP rather than guesstimations using GC-based data.Through this, the industry will be able to get more precise HCDP readings that will in turn provide profitable results and less losses to the operations.
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