**1. Introduction**

As the most widely used critical common technology in the chemical industry, distillation is widely used in petroleum, natural gas, chemical, pharmaceutical, and environmental protection, and other industries. Furthermore, it occupies a considerable proportion of industrial production [1]. In the 21st century, with the increasing depletion of onshore oil and gas resources and the continuous breakthrough of offshore oil and gas exploration and exploitation technologies, the natural gas industry has begun to extend to the sea [2,3]. The distillation tower is the core equipment of the natural gas pretreatment process, and its operation has a significant impact on the gas purification effect, gas quality, and economic benefits [4]. Therefore, the development of offshore distillation and the realization of stable and efficient distillation towers on offshore platforms have become inevitable trends in the development of the distillation industry [5–9]. However, due to the influence of ocean wind and waves, floating devices will produce three angular motions of rolling, pitching, and yawing, and three displacement motions of swaying, surging, and heaving. The movement of offshore platforms is shown in Figure 1. The sloshing that has the greatest influence on the hydrodynamic performance of a traditional distillation tower is rolling (pitching) [10–12]. Therefore, it is of great significance to understand the performance of the tower under rolling motion.

**Citation:** Tao, J.; Zhang, G.; Yao, J.; Wang, L.; Wei, F. Study on the Hydrodynamic Performance of a Countercurrent Total Spray Tray under Sloshing Conditions. *Processes* **2023**, *11*, 355. https://doi.org/ 10.3390/pr11020355

Academic Editors: Elio Santacesaria, Riccardo Tesser and Vincenzo Russo

Received: 22 November 2022 Revised: 9 January 2023 Accepted: 19 January 2023 Published: 22 January 2023

**Copyright:** © 2023 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/).

**Figure 1.** Movement of offshore platform. (**a**) Movement of offshore platform; (**b**) rolling motion.

Research on the influence of sloshing on equipment has mainly concentrated on the design calculation and load analysis of ships and tanks [13–16], while research on its effect on towers is relatively rare. Ma [4] carried out an experimental study on bubble cap trays and valve trays on a sloshing platform. The results showed that the performance of the trays decreased significantly with increasing rolling amplitude, and they could not work when the rolling amplitude exceeded 3◦. Cheng [17] studied the hydrodynamic performance of LBJ (low backmixing jet) and DLJ (double-layer jet) trays under sloshing conditions and found that their ability to resist sloshing was improved compared to that of traditional trays. Zhang et al. [18] studied the influence of offshore sloshing on a packed column and found that the liquid accumulated obviously near the wall on the tilt side. The flow field parameters in the column changed significantly after the inclination exceeded 3◦. Weedman et al. [19] studied the performance of several different packed columns under tilting conditions. Due to the high length–diameter ratio of the distillation column, the separation efficiency decreased rapidly under slight tilting conditions. Di et al. [20] studied the effects of ship motion on the mass transfer area in structured packed columns for offshore gas production. The results confirmed that the mass transfer area will decrease under any typical ship motion. Yang et al. [21] proposed a small air separation plant with a dual-column distillation process and carried out experiments under offshore conditions, providing engineering guidance for the design of cryogenic distillation columns for offshore applications. China University of Petroleum [22–28] conducted an experimental study on a packed column and plate tower on a sloshing platform and analyzed the influence of sloshing on the distribution and flow of gas and liquid in the tower. It was found that rolling motion was the most influential form of sloshing with regard to the hydrodynamic performance of the tower, and the arrangement of partitions could reduce the influence of sloshing on the liquid in the tower.

It can be seen that offshore conditions seriously affect the hydrodynamic performance of packed column and plate towers. The reason for this is that the tilt scale of the tower has a significant amplification effect on the uneven liquid distribution in the tower. For a plate tower with gas–liquid cross-flow contact, the liquid on the tray flows horizontally and cannot be blocked in the flow direction. Thus, the unevenness of liquid on the plate becomes severe with an increasing diameter of the tower under the tilt state. For a packed column with gas–liquid countercurrent contact, the liquid in the column flows vertically downward; by increasing the height of the column, the liquid will deviate to one side of the column during falling into the tilt state. Therefore, the traditional onshore distillation tower cannot maintain high performance under harsh conditions such as sea waves and typhoons [28].

Now, people mainly use different types of packed columns to solve the effect of offshore sloshing on distillation columns. Compared to a packed column, a plate tower has the advantages of a large operating range, suitability for large tower diameters, and convenient maintenance. However, it is impossible to block the liquid in the direction of liquid flow, which limits the application of traditional plate towers in the sea. If the plate tower can be made to resist sloshing, the plate tower will have greater advantages under some working conditions. Therefore, it is of great significance to study the applicability of plate towers under offshore conditions.

To solve the bottlenecks in existing plate towers—their low operational flexibility and poor resistance to sloshing under sloshing conditions—we propose a new type of total spray tray (TST) [29–31] with gas–liquid countercurrent contact and with the liquid flow in the tower guided by a three-dimensional space barrier. Under rolling conditions, the hydrodynamic performance of this TST was studied experimentally. The variation law of the hydrodynamic performance of the tower plate under offshore conditions is analyzed. Its operational flexibility range is clarified. Its ability to adapt to offshore sloshing conditions is explored, providing technical support for the design optimization of tower equipment on offshore platforms.

## **2. Materials and Methods**
