Off-Design and Surge Analysis of Centrifugal Gas Compressor

Centrifugal gas compressors are key assets in gas industries. Off-design performance conditions can turn the compressor closer to the surge region, which causes backward flow of gas, an unfavorable phenomenon that damages seals, bearings, impellers, and shafts because of intense vibration. Additionally, it shortens the compressor's lifespan, decreases energy efficiency, increases seal clearance, and causes unstable flow and pressure. The novelty of this study lies in developing a comprehensive off-design surge analysis methodology that evaluates compressor performance and surge within a range of operating conditions, beyond conventional design conditions. Unlike existing studies that lies on conventional performance maps and limited operating conditions, the proposed method provides a reliable assessment of surge prediction, operational stability, and reducing energy losses. In this research work, ASPEN HYSYS Software was employed for simulation to evaluate compressor off design and surge conditions. This analysis is crucial for predicting surge and energy efficiency under varying operating conditions. The simulation model was validated using the original equipment manufacturer (OEM) provided performance curves at design point conditions using quantitative error metrics. The results demonstrated that operating the compressor near 20% surge control margin, using load variation control, significantly improved energy efficiency, reducing power consumption from 135,960kWh to 55,905 kWh during off-peak demand, when the load decreased from 99.89 to 73.49 MMSCFD. Similarly, the second stage operating near a 15% safety margin showed that load variation control reduced energy consumption from 232,880 kWh to 102,541 kWh as the load decreased from 217 to 187 MMSCFD. These significant energy consumption reductions highlight the significance of optimizing compressor operation under off-design conditions, which offers significant potential for lowering energy costs and enhancing overall energy efficiency while maintaining sufficient surge protection.