Optimal Energy Integration and Off-Design Analysis of an Amine-Based Natural Gas Sweetening Unit

The present paper focuses on the efficiency enhancement of the energy-intensive natural gas (NG) sweetening process in the context of upstream natural gas production. A bi-level heat integration scheme is proposed including direct recycling of available high-temperature waste heat and harnessing the excess low-temperature waste heat in an optimized organic Rankine cycle (ORC) for power production. The energy performance of the whole model was studied under a range of possible reservoir conditions. A particle swarm optimization (PSO) algorithm was adopted to simultaneously optimize the parameters of the heat recovery network as well as the ORC cycle parameters. Finally, in order to account for the impact of perturbations of the heat source and sink, an off-design performance analysis was conducted using real-time data from an industrial plant. The proposed integration methodology was found to be effective across most of the reservoir conditions covered in this study. At optimal integration, a reduction of 40% up to 100% in heating requirements of the amine process was reported, as well as a net electricity production of 30% up to 190% of the electrical demand of the background process. The use of propane (R290) as a working fluid resulted in the highest energy output, whereas higher carbon number fluids allowed a better energy/working pressure trade-off. The off-design analysis allowed for the quantification of the impact of operational fluctuations of the background process on integration performance. Energy savings resulting from direct heat integration were found to range from 68% up to 103% of the expected design value, whereas the ORC net energy output respective to the use of R290, R600a, and R601a was found to range from 60% to 132%, 47% to 142%, and 52% to 135%.