Experimental analysis of ship motion effects on the performance of an absorption column equipped with structured packings

In the upstream sector of the modern offshore industry, mainly packed columns are used for gas purification purposes, such as the removal of CO2, SOx, NOx, and other impurities. Offshore conditions are known for their harsh environment conditions that pose extra challenges for stable process operations and can lead to inefficient separation. To make use of the newly explored offshore energy resources, floating vessels, namely, Floating Production Storage and Offloading (FPSO) units, are currently gaining dominance due to their technological and economic advantages over conventional offshore platforms. These floating vessels with their unique design can be operated in deeper locations by means of advanced technologies, i.e. mooring system and remote control mechanisms. Despite aforementioned facts, the impact of sea states and strong winds on the floating production systems cannot be fully suppressed, and these conditions affect the performance of onboard packed columns. To have a highly efficient separation process, the interfacial mass transfer area between the gas and liquid phases in packed columns must be sufficiently large, and for this reason, a uniform distribution of the phases in characteristic packing channels is required. However, realizing uniform flow distribution in the packings becomes more difficult during ship motions. When considering the geometric arrangement of column internals, structured packings are likely to have relatively better performance than random packings under these circumstances. Nevertheless, it is still unclear to what extent the flow distribution deviates from its ideal pathway under motion conditions and how this deviation degrades the separation performance.
In this study, most predominant sea conditions are considered to experimentally analyze the effect of ship motions on the mass transfer efficiency of packed columns. Therefore, air dehumidification with triethylene glycol (TEG) desiccant is chosen as an example of an absorption process in a structured packing column. To simulate typical motion conditions, an absorption column (DN150) equipped with Mellapak 250Y structured packings is placed on the mobile platform of a hexapod robot that mimics the six-degree-of-freedom ship motion. The mass transfer performance of the absorption column in the stationary upright position is first investigated by measuring the inlet and outlet humidity of the gas phase, and then the experimental results in static and dynamic inclination positions are compared to evaluate the relative deterioration of the efficiency. Furthermore, the impact of operating conditions, such as gas factor, liquid load, and TEG concentration, is explored.