(79g) Measurements and Simulations of Natural Gas Separation Performance for a Pilot-Scale, High-Pressure, Cryogenic Scrub Column Fitted with Oldershaw Trays

Authors: 
May, E. F., University of Western Australia
Sage, V., CSIRO
Young, B. R., University of Auckland
Burke, N., CSIRO
A critical part of LNG processing is the removal of heavier hydrocarbons (Natural Gas Liquids or NGLs) from the gas stream prior to liquefaction. Understanding and accurately controlling this process is critical for optimal performance in terms of product quality, throughput, and reliable operation. LNG processing conditions offer up a different set of challenges compared to ambient and above ambient distillation. These challenges include models that do not adequately describe behaviour at extremes of temperature and pressure (typically <-60 °C and >40 bar), and a lack of empirical data describing the useful operating window for cryogenic hydrocarbon distillation. To better address these challenges, a unique pilot distillation facility [1] has been developed to replicate empirically the industrial-scale units. The random packing internals used previously were upgraded to tray internals as is usually employed industrially (27 Oldershaw trays were employed). The separation performance achieved was explored across a variety of operating conditions (temperature, pressure, inlet and outlet flows). Steady-state and dynamic models of the column were implemented within the process simulation software VMGSim. These models were validated with the experimental results and used to determine the column efficiency.

Results thus far indicate that under moderate conditions (-40 °C and 40 bar) there is little difference in performance between trays and random packing. Experiments with Oldershaw trays conducted at lower temperatures (-60 °C and 45 bar) resulted in a better separation performance when compared to experiments with trays run at higher temperatures. The design performance of the Oldershaw trays was confirmed by observations of liquid pooling as inferred from the response of the temperature sensors located above each tray. The results of varying feed flow rate to investigate its effect on tray efficiencies and determine the flood point will be presented and discussed. Future work, including operating at lower temperatures and higher pressures; as well as potential opportunities for collaboration will also be highlighted.

[1]. Hazewinkel, P., Sage, V., Khamphasith, M., Burke, N., May, E. F. A New Pilot-scale facility for testing high pressure cryogenic distillation in LNG applications. 2018 AIChE Spring meeting and 14th Global congress on process safety proceedings, Orlando, Florida, USA, April, 2018