Process Research In Liquefied Gas Desulfurization System

This study aimed to investigate excessive hydrocarbon content in acidic gas from liquefied gas desulfurization system in a LPG refinery and a technical improvement has been proposed.In this refinery, LPG desulfurization extraction tower was put into production in2003with the original design capacity:LPG feed rate:38.8t/h, methyl diethanolamine (MDEA):18t/h. In2007, the device became overloaded:LPG feed rate:45～52t/h, amine:22t/h. from that time, the acidic gas from the recycling device at the top of regeneration tower contained7.12%of C3and C4, which further escalated to12.43%～37.17%in2008. The acidic gas is not suitable for Sulfur device since its hydrocarbon content exceeds the maximal level of4%. Meanwhile, the catalysts in the pre-removing mercaptan tower (T-5203) and removing mercaptan tower(T-5204)had to be replaced once every year rather than once every two years due to faster saturation and hardening of the catalyst. these greatly increase the production cost, making it inapplicable for long term use.(normally two years for agent replacement annually)The study analyzed several factors that may contribute to increased level of hydrocarbon content, such as too short retaining time during settling phase at the bottom of LPG extraction tower, too small volume of flash tank to fit rich liquid flash distillation settlement, overload of amine, etc. Corresponding improvement was first provided, followed by system simulation using ASPEN PLUS and operating optimization. The final improvement was eventually made by taking into consideration both real situation and possible cost:increasing the volume of flash tank and changing its internal structure. Also, changing the condition of flash distillation from high temperature to low one in order to reduce its pressure. The improvement can bring a solution to both high level of hydrocarbon content and short life time of the catalyst.