Carbon dioxide (CO₂) dynamics in Exhaust Gas Boiler (EGB) systems: Distinguishing measurement artifacts from true emission reduction

Implementing Exhaust Gas Boilers (EGBs) for waste heat recovery is a key strategy to improve thermal efficiency in power generation and thereby reduce carbon dioxide (CO₂) emissions. However, field measurements often show a misleading decrease in CO₂ concentration downstream of the EGB, which can be misinterpreted as direct emission removal. This study distinguishes genuine CO₂ mitigation, achieved through fuel savings, from apparent reductions due to measurement artifacts. Operational data from reciprocating-engine-based power plants equipped with EGBs were analyzed under baseline (simple cycle) and EGB-engaged (combined cycle) modes. Mitigation was quantified using specific emission intensity (kg CO₂/MWh), while anomalies were assessed through oxygen balance, condensation correction, and time‑series modeling (SARIMAX) with fleet validation (DTW clustering). Results indicate a 24.4% reduction in specific CO₂ emissions, confirming that mitigation arises from improved fuel efficiency rather than in-stream capture. In contrast, the 31.6% apparent concentration drop downstream was explained by air ingress (+37.1% O₂ increase) and wet-to-dry basis conversion following condensation (0.8–1.2 L/h). An uncertainty margin of ±3.5% accounted for fuel variability and sensor drift. SARIMAX decomposition (R² = 0.87) and DTW clustering validated the mitigation signal across engines, with one outlier flagged due to sensor drift. These findings show that accurate emissions accounting in waste heat recovery must rely on fuel consumption and mass-flow data rather than volumetric concentrations. Conclusions are restricted to natural gas reciprocating engines with EGB retrofits; broader applicability requires further validation.