Citation: Saied, O.; Abdellatif, A.; Shaaban, S.; Elsafty, A.F. Efficient Energy Recovery Scenarios from Pressure-Reducing Stations Intended for New Al-Alamein City in Egypt. Energies 2022, 15, 9077. https:// doi.org/10.3390/en15239077 Academic Editor: Phillip Ligrani Received: 22 October 2022 Accepted: 25 November 2022 Published: 30 November 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article Efficient Energy Recovery Scenarios from Pressure-Reducing Stations Intended for New Al-Alamein City in Egypt O. Saied 1 , A. Abdellatif 1, * , S. Shaaban 1 and A. F. Elsafty 2 1 Mechanical Engineering Department, Arab Academy for Science and Technology and Maritime Transport, Sheraton Branch, Cairo 11736, Egypt 2 Mechanical Engineering Department, Arab Academy for Science and Technology and Maritime Transport, Al-Alamein Branch, El-Alamein 51718, Egypt * Correspondence: a_abdellatif@aast.edu Abstract: Worldwide concerns over energy optimization and harnessing have sparked a variety of research on utilizing wasted energy. Natural gas, in particular, has been an essential energy commodity for domestic and industrial applications. This paper approaches the same principle throughout the Egyptian natural gas conventional national grid. The real case of Egypt’s Al-Alamein city gas line extension is analytically studied for energy harness. Thus, this paper aims to study the replacement of conventional energy-wasting pressure-reducing stations with power-producing expander generator systems to utilize pressure reduction in electricity generation. The mathematical equations that describe the energy recovery processes are presented. Reliable commercial software is used to verify the possible implementation of turbo expander stations in three scenarios. Each scenario is defined, and its main components and numerical parameters are introduced. Hence, the resulting energy outputs and applicability of all scenarios are compared to provide adequate energy recovery solutions. Keywords: natural gas; turbo expander; energy recovery; New Al-Alamein city; energy optimization 1. Introduction Worldwide concerns over energy optimization and waste energy recovery have sparked initiatives for various research. The main aim has been to harness wasted en- ergy in common industrial applications. One of those approaches is to utilize natural gas transmission lines with their rich gas flows and high pressure for electricity generation [1]. This can be achieved at the consumer destination, where expander generators can replace conventional pressure-reducing valves. Expander generators are turbomachinery expansion turbines that allow the passage of gaseous fluids at high pressure through guided vanes and impellers that utilize pressure drops to reach isentropic gaseous expansion. Then, the shafts are rotated at fixed speeds for stable electricity generation. This effectively enhances traditional systems in hopes of rais- ing efficiency, fuel saving and generating electricity from energy-dissipating conventional systems [2]. A figure that describes the main components of the turbo expander is shown in Figure 1. The utilized expander generator works with the same principle as the turbo expander. The main difference lies in replacing the compressor with a generator attached to the expander shaft. On the contrary, conventional pressure-reducing valves rely on isenthalpic expansion through which pressure is converted to velocity through a Joule–Thomson effect, causing friction, heat dissipation and wasted flow velocity [3]. Global research has shown an interest in energy recovery applications in general and in expander generator replacements of conventional systems in particular. Energies 2022, 15, 9077. https://doi.org/10.3390/en15239077 https://www.mdpi.com/journal/energies