Comparative Assessment of Post-Combustion CO2 Capture Processes: Chilled Ammonia and Amine Scrubbing Technologies Applied to Natural Gas Compression Stations

Post-combustion CO2 capture is a key mitigation pathway for natural gas compression and processing infrastructure; the chilled ammonia process (CAP) and advanced amine-based capture (AAC) are the most technologically mature commercial options. Methods: This study presents a technical and economic comparison of CAP and AAC, combined with historical field emission measurements (11 June 2013) at two Romanian natural gas compression stations (S.N.G.N. Romgaz S.A., Mediaș, Romania): Cristur (downstream of a CAP unit) and Brateiu (uncaptured baseline), using a Multilyzer NG Series 213 analyzer (SYSTRONIK Elektronik und Systemtechnik GmbH, Illmensee, Germany). As the stations were not sampled under a controlled before/after protocol, the comparison is cross-sectional. Results: Flue gas CO2 was lower at Cristur (at or below detection limit) than at Brateiu (6.8%), but this reading could not be reconciled with the analyzer’s own O2-based calculation formula and is reported as an unresolved historical data-quality issue rather than as evidence of capture performance; co-pollutants (NO, NOx, CO) were also lower at Cristur. An independent van’t Hoff-based thermodynamic estimate, anchored to ammonia-specific literature data, yields a CAP capture efficiency of 89.6–90.3% at typical operating temperature. A theoretical mass balance, using representative flow rates and literature capture efficiency, estimates 42,600–85,200 t CO2/year captured. Literature capture costs range from 40 to 77 EUR/t (CAP) and 47 to 90 EUR/t (AAC), both largely below the current EU ETS price (81.35 EUR/t, June 2026), though no net economic benefit is quantified due to missing capital and ancillary cost data. Conclusions: CAP is thermodynamically capable of high CO2 removal efficiency; the historical field data are directionally consistent but do not independently validate this. Beyond the historical dataset itself, this study contributes a reusable diagnostic cross-check for flue gas analyzer CO2 readings, a recalibrated ammonia-specific thermodynamic estimation method, and a transparent framework for assessing capture technologies from incomplete legacy data; it is presented as a historical, illustrative case study and methodological reference for future, instrumentally verified monitoring campaigns.