Abstract

With current technology, the majority of natural gas is transported from points of production to points of consumption in one of two ways, via pipeline or as liquefied natural gas (LNG). Pipeline networks are expensive to build, lay and maintain, such that only overland or somewhat shorter undersea routes can be considered. Cryogenic liquefaction of natural gas serves to permit transport over intercontinental distances, thereby allowing access to a much larger and more diverse market. The principal benefit of transporting natural gas in liquid state is the 600-fold reduction in volume that occurs with the vapor-to-liquid phase change.

Both transport mediums require some form of gas sweetening treatment to reduce or remove impurities such as water, carbon dioxide, and hydrogen sulfide. For pipelines, however, the tolerance to contaminants is several orders of magnitude higher than for the liquefaction process.

The stringent specifications applied to natural liquefaction for contaminant removal are necessary to prevent blockages in the system caused by solids development. Such gas purification not only removes the components mentioned above, but also heavier hydrocarbons. Almost all natural gases contain some components which solidify when natural gas is transformed to LNG at atmospheric pressure. Inert gases, such as argon and helium, are also removed during the cryogenic process.

A cryogenic gas separation technology has been developed at Curtin University to sweeten gas using the cryogenic distillation principles [1,2].The technology results in a compact module, known as the Cryocell, which is portable and can be easily accommodated on production platforms; it is energy efficient and can process a wide variation in feed gas composition.

Up to 70% carbon dioxide as a contaminant of the natural gas volume has been successfully removed down to less than 200 PPM during laboratory trials.

Introduction

Natural gas liquefaction (LNG) is a mature technology for monetizing remote gas. Over the past 30 years, tremendous technology advances in LNG plant configuration, efficiency, equipment design and materials of construction have been recorded. The capacity range for a single onshore LNG train, is around 4.2 MMTPY.

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