Advanced High-Efficiency Column Internals for Layout and Height Optimization of FPSO TEG Contactor and Reducing TEG Loss

Abstract

Objectives/Scope Gas dehydration is a vital step in the processing of natural gas, where triethylene glycol (TEG) is commonly employed as a desiccant to decrease and control the water content, ensuring the safe processing and transmission of natural gas streams [Abdulrahman, R. K., 2014, Anyadiegwu, C., 2014, Chebbi, R., 2019, Khan, M. A., 2012, Mokhatab, S., 2019, Wang, X., 2013]. The traditional layout of TEG gas dehydration typically consists of an inlet scrubber, a TEG contactor vessel, and an outlet scrubber [Bahadori, A., 2014, Chebbi, R., 2019, Viteri, R., 2006]. The inlet scrubber is responsible for removing any liquid carryover to meet the specifications for the gas stream entering the TEG contactor. The TEG contactor, which serves as the central component of gas dehydration systems, carries the crucial mass transferring section for achieving efficient and effective gas dehydration. The outlet scrubber aims to capture free liquid TEG carryover in the dry gas stream, thereby minimizing TEG loss [Gupta, A., 1996, Trueba, L. J., 2011]. This research paper focuses on a case study involving the design of a TEG contactor for an offshore floating production, storage, and offloading (FPSO) facility. Designing the TEG contactor for an FPSO platform presents several challenges, such as limited footprint and equipment height, motion effect caused by sea waves, and stringent performance requirements. To reduce the footprint, piping complexity, and overall weight of the high-pressure gas-side equipment, the design integrates the gas inlet scrubber and outlet scrubbers into the TEG contactor (i.e., one integrated TEG contactor served the functions of three vessels of inlet scrubber, TEG contactor, and outlet scrubber). The integrated inlet scrubber incorporates proprietary inlet vane diffusers, a mesh pad, and proprietary demisting cyclones. Similarly, the integrated outlet scrubber consists of a mesh pad and demisting cyclones to minimize TEG losses. The integration of the inlet and outlet scrubbers leads to an increased height of the TEG contactor, resulting in higher weight and cost. Therefore, it is essential to develop innovative approaches for the internal design of the TEG contactor to optimize its height while maintaining or improving process performance. Given the significant influence of TEG contactor internals on separation efficiency and dehydration performance, the design approach aims to meet the height optimization requirement while enhancing process performance. In this study, high-efficiency vessel internals with advanced features for height reduction and motion effect mitigation were designed for the integrated TEG contactor. In the integral scrubber section, the demisting cyclones were integrated into the chimney trays, significantly reducing the overall height requirement. Moreover, the distances between vessel internals and level settings at various sections were justified for reduction. Wave baffles, liquid protection plates, and level instrument dampening were incorporated into/recommended to the design to mitigate the impact of FPSO motion. To ensure desirable gas flow distribution and process performance, the process efficiency of the innovative internal design was verified using computational fluid dynamics (CFD) [Lu, Y., 2009, Olaleye, O., 2022]. CFD analysis was also employed to investigate the effect of FPSO motion on liquid levels and level instrumentation, confirming that the overall design efficiently diminishes motion effects with satisfactory liquid level response.