A novel application of TERA framework for gas compressor station performance analysis using thermal modelling assumptions

Abstract

Gas compressors are critical yet energy-intensive components of pipeline networks. Accurately predicting their performance is a significant design and operational challenge, profoundly affected by the thermal behaviour of the transported gas. This study introduces a novel application of a techno-economic and environmental risk analysis (TERA) framework to determine gas compressor performance under three distinct gas flow temperature assumptions: isothermal, intermediate, and non-isothermal. The analysis, performed in MATLAB R2024a, integrates thermodynamic gas properties, pipeline hydraulics (via the Weymouth equation), and compressor characteristics, explicitly accounting for ambient temperature and altitude variations at each compressor station along the pipeline route. The results demonstrate that the common assumption of isothermal flow yields fixed but potentially inaccurate operating points. In contrast, non-isothermal analysis, which ties gas temperature to fluctuating ambient conditions, reveals significant operational dynamics. Specifically, compressor power demand peaks at 15:00 hours during the hottest season and reaches its lowest point at 06:00 hours during the coldest season, directly correlating with ambient temperature cycles. This fluctuation, which can critically impact design and fuel consumption, is entirely masked in isothermal and intermediate models. Furthermore, the findings show that for every 1% increase in the non-isothermal ambient temperature, the compressor suction pressure decreases by an average 0.1% and the compressor power demand increases by an average 0.3%, corresponding to an average increase of 0.3% in the polytropic head. A ±5% parametric sensitivity analysis confirms that inlet temperature exerts the strongest influence on power demand (±1.5%), followed by mechanical efficiency (±1.0%), pressure ratio (±0.8%), and gas composition (±0.4%). The total estimated annual operational cost for the 18-station pipeline network under isothermal conditions is approximately USD 90.66 million; however, a sensitivity analysis assuming a +10% increase in power demand during daily peaks reveals that operational costs could be underestimated by more than USD 56,000 per year for a single station, demonstrating that the isothermal assumption risks substantial under-estimation of long-term operational expenditures (OPEX). This study provides, for the first time, a comparative analysis of these three scenarios within a unified TERA framework, delivering crucial insights for selecting appropriately sized compressors. The MATLAB model was validated against Aspen HYSYS, showing excellent agreement with a maximum deviation of only 0.348% and a mean absolute deviation of 0.035% across all 18 stations. Therefore, this work offers a robust methodological advance that can assist designers in optimising the design and operation of existing or new long-distance natural gas transmission pipelines, leading to improved economic and operational outcomes.