Application of partially diabatic divided wall column to floating liquefied natural gas plant

The offshore operation of chemical plant requires the compactness of process equipments due to its harsh environment. A DWC (divided wall column), a compact ternary separator, is a good candidate for distillation process in the offshore operation. In this study the DWC is applied to the offshore FLNG (floating liquefied natural gas) plant, but high utility cost is required in the application because of the large difference of boiling points among feed components. A partially diabatic DWC is proposed for the reduction of the operating cost here, and its design procedure is presented along with performance and economic evaluations and the examination of thermodynamic efficiency as well. The heating duty of the proposed DWC including tray heat transfer is 35% less than that of the conventional system, and the cooling duty is 18% less. The evaluation indicates that some 16% less utility cost is used in the DWC compared with the conventional system, though 7% more investment is required. The exergy loss is reduced by 12%, and the thermodynamic efficiency is improved by 3.3 percentage point over the conventional system.