# Optimal Energy Integration and Off-Design Analysis of an Amine-Based Natural Gas Sweetening Unit
## 1 Introduction  
In recent years, environmental awareness and stringent regulations have pushed many industrial sectors to explore alternative sources of energy as well as efficient technologies for its conversion. Driven by its high-energy intensity and low emission rate compared to other fossil fuels, natural gas is playing the role of a bridge fuel to complement the renewable-based global energy mix. Natural gas currently accounts for 25% of the global primary energy consumption, and its global demand is forecasted to increase by 30% between 2020 and 2050 [1; 2]. However, despite its advantages, the natural gas value chain is impacted by its high energy consumption and the large amounts of waste heat generated along its production and processing that are discharged into the atmosphere. Recovering and converting this wasted energy into useful work can result in considerable economic savings and alleviate the energy burden of the natural gas industry. Waste heat is estimated to represent 20% to 50% of industrial energy consumption, 50% of which is difficult to harness due to its low temperature [3]. As a result, severaltechnologies were investigated in the literature for both high-grade and low-grade waste heat recovery in industrial processes, such as direct heat integration, organic Rankine cycles, Kalina cycles, heat pumps, and absorption chillers, among others [4]. Direct heat integration (DHI) is the most efficient way for the recovery of high-grade waste heat in industrial processes. On another hand, the organic Rankine cycle (ORC) allows the recovery of low-grade waste heat and presents many advantages over other thermodynamic cycles such as simplicity in terms of design and implementation, reliability, and moderate operating conditions [5], which promote this technology as a suitable candidate for low-grade waste heat recovery. In recent years, ORC has found applications in many industrial sectors including glass, cement, geothermal, and solar-based processes with a power output ranging from 10 kW to 20 MW [6]. DHI and ORC applications in the energy-intensive oil and gas sector have also attracted research attention; several papers discussed advanced integration strategies for NG processing units based on heat exchanger networks. [PERSON] et al. [7] proposed the integration of dehydration and condensate stabilization units, whereas [PERSON] et al. investigated the simultaneous optimization of the design parameters and heat integration for NG purification units [8]. Moreover, [PERSON] et al. [9] focused on using ORC as a waste heat recovery method from multiple streams in oil refineries, whereas [PERSON] et al. [10] investigated the use of ORC to enhance the energy efficiency of offshore oil production facilities. Similarly, in the natural gas industry, [PERSON] and [PERSON] [11] examined the integration of waste heat from natural gas liquefaction turbines with an optimized ORC. [PERSON] et al. [12] integrated a two-stage ORC to recover cold energy from natural gas regasification units, whereas [PERSON] et al. [13] investigated the feasibility of ORC integration in natural gas compression stations. In contrast to down- and midstream natural gas processing, which have been thoroughly studied in the literature, we have noticed that the impact of using ORC integration in the upstream processing of natural gas is scarcely cited. As presented in Figure 1, the upstream processing of natural gas consists of primary compression, elimination of impurities such as Mercury, CO\({}_{2}\), and H\({}_{2}\)O from the raw feed, and primary separation in order to meet transport specifications. Among these steps, CO\({}_{2}\) removal, known as natural gas sweetening and which is based on solvent absorption/regeneration, was found to feature the highest energy demand.