# Optimal Energy Integration and Off-Design Analysis of an Amine-Based Natural Gas Sweetening Unit
## 2 Energy Assessment of the Background Process  
Data collected from three different natural gas upstream production facilities operated by the Algerian national oil company, Sonatrach, were analyzed in order to assess the energy demand in the upstream processing chain and identify the units with the highest potential for integration. Energy demand as well as the quality and quantity of waste heat from each unit are presented in Table 1. Due to confidentiality concerns, heating requirements and waste heat quantity are presented as a ratio to the sweetening unit. The results show that the amine-sweetening unit features the highest thermal energy demand within the NG processing chain. This observation matches many research papers concluding that despite its maturity and large utilization, high energy intensity has always been reported as a major drawback of amine-based sweetening units [16]. On the other hand, the analysis revealed that the turbine-driven NG compression unit is associated with the highest quantity and quality of waste heat because of its high power demand as well as its inherent low energy conversion efficiency. Table 1 also indicates that the amount of waste heat available from the compression step is available at a higher temperature than the amine unit's requirement. Consequently, heat and process integration emerges as an appropriate solution to bridge the energy efficiency gap in the upstream processing of natural gas, and the compression/amine-based sweetening units are the ideal candidates for this integration. These units were set to be the scope of our study and are considered as the background process. The inlet natural gas compression process is a crucial step in the processing chain as it maintains a stable plant pressure over the years of production by compensating for the natural decrease in reservoir pressure. On the other hand, the amine-based NG sweetening process, which is equally important, reduces the CO\({}_{2}\) content in order to meet the transport specification, i.e., less than 2 mol-%. The available data collected from industry are restricted to a narrow range of reservoir pressures and CO\({}_{2}\) contents. Therefore, in order to study the potential of the proposed integration over a wider range of conditions, AspenHysys V11 was used to build a model of the targeted processes, which includes a turbine-driven compression station and an amine-based sweetening unit. MDEA/DEA was selected as the working solvent for this study because of the advantages it presents such as stability and high absorption capacity. The operating pressure of the absorber and regenerator was set to 80 bar and 2 bar, respectively. A feed of 10 MMSCM/Day of sour natural gas was considered for this study, with sixteen scenarios spanning a range of CO\({}_{2}\) molar content from 4 to 10 mol-% and an admission pressure at the turbine inlet ranging from 30 to 60 bar, which corresponds to compression ratios ranging from 2.66 to 1.33. The compression unit considered in this study is turbine-driven using natural gas as a fuel. It was modeled using the Peng-Robinson equation of state [17] and was validated against data from Siemens SGT series openly provided by the manufacturer [18]. The estimated overall efficiency of the turbine-driven compressor as well as the exhaust gas flow rate was compared to manufacturer data, and a deviation of less than 2% was observed for both factors. On the other hand, the amine unit was modeled using an equilibrium approach based on the Li-Mather empirical model [15; 19] and was then validated against industrial data. The predicted CO\({}_{2}\) content in sweet gas, reboiler duty, and temperature