Waste heat recovery (WHR) has the potential to significantly improve the efficiency of process industries such as in the oil and gas sector, and reduce their environmental impact. The design of an effective WHR strategy requires a comprehensive plant energy audit, but examples of such information are lacking in the published literature. In this paper a detailed energy audit is presented for a major natural gas (NG) processing facility in the Middle East, to identify sources of waste heat and evaluate their potential for on-site recovery. Waste heat sources are quantified and evaluated in terms of grade (i.e., temperature), rate, accessibility (i.e., proximity to potential on-site WHR applications), and impact of potential WHR on the performance and safety of existing facilities. Based on the audit undertaken, conceptual WHR strategies are proposed, focusing on utilities enhancement, i.e., process cooling/heating, electrical/mechanical power generation, and steam production. In addition, to permit the techno-economic feasibility evaluation of the proposed WHR strategies in modeling work undertaken in parallel with this study, the operating parameters of waste heat producing equipment are compiled, along with the cooling/heating loads and electric power/fuel consumption of WHR-enhanced processes.
A total of 689 MW of waste heat is identified in the plant, which consists of 526 MW gas turbine (GT) and 56 MW gas generator exhaust gases, 10 MW flared gases, 5 MW excess process steam, 88 MW process gas air-cooler heat dissipation, 2 MW furnace exhaust gases, and 1 MW steam turbine outlet steam. Waste energy in the form of excess propane cooling capacity is also identified. The total amount of waste heat meeting the rate, grade, accessibility and minimal performance-and-safety-impact criteria defined for potential WHR in this study is of approximately 547 MW, most of which is produced by GTs. Only 174 MW of GT waste heat is presently re-utilized, in addition to excess propane cooling capacity. Novel absorption refrigeration-based WHR strategies are proposed to recover the available GT waste heat. These strategies were found to be thermodynamically and economically feasible in an accompanying study, and to lead to substantial energy and cost savings for the plant.