Gas Driers KO Drum Design Shortfall

Abstract

Abstract The objective of this paper is to describe a deterioration that was observed in the performance of molecular sieve type Gas Driers, to summarize the work that was done to identify the root cause, to describe the modifications that were implemented to resolve this problem, and to explain the extent to which these modifications were effective in resolving this problem. During early 2012 the pressure drop across the Gas Driers in two trains within the onshore gas processing facility in Ras Laffan began increasing at a faster rate than usual. This change correlated with an increase in the CO2 content of gas feeding the concerned Gas Driers. Through liaison with molecular sieve vendors, it was established that the accelerated rate of bed deterioration had been caused by liquids carryover from the upstream Driers Inlet Separator co-inciding with an increase in CO2 content of the gas. Since it was preferred to maintain the increased CO2 concentration of the gas, efforts were made to re-design the Driers Inlet Separator to minimize liquid carryover into the Gas Driers. The effectiveness of gas/liquid separation in the existing Driers Inlet Separator was first assessed by means of computational fluid dynamics (CFD) studies conducted by a third party. These studies demonstrated that the separation efficiency of liquids from gas in the existing vessel was inadequate, and that the effectiveness of separation could be greatly enhanced by implementation of various internal modifications without the need to replace the existing vessels. It was proposed to remove the existing vane pack from within this vessel and to install new internals including a vane type inlet distributor, mesh pad, and cyclone separators. The effectiveness of these new internals was first demonstrated using proprietary software by the same third party. Upon completion of detailed engineering, these internals were manufactured and installed within the existing vessels. The rate at which molecular sieve deterioration occurs downstream of these modified Driers Inlet Separators was assessed, and details regarding the methodology for this assessment as well as the outcome of the assessment are provided. This paper will be of interest to anyone involved in the design or operation of molecular sieve Gas Driers and upstream gas/liquid separation facilities. It will provide useful information regarding the importance of effective gas/liquid separation upstream of these Gas Driers, especially when the CO2 concentration of the gas is high. This paper also describes novel internals modifications that can be considered for implementation in existing two or three phase separators that do not provide adequate separation of liquids from gas.