The Integration of New NCS system with Natural Gas Carrier and Liquefaction Process

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The Integration of New NCS system with Natural Gas Carrier and Liquefaction Process

Introduction and Objectives

Natural Gas Capture and Sequestration (NCS) is defined as a system of technologies that integrates three stages: natural gas capture, transport and geologic storage. Natural Gas transport is usually done by pipelines; however, it is also possible by ships. There are several key factors that make shipping natural gas attractive. Firstly, the initial investment required for this method of transport is much less expensive than pipeline construction. Secondly, natural gas shipping is a discrete transport solution that offers more flexibility in transporting over long distances, compared to a pipeline that maintains a continuous flow (Dubel and Wackertapp, 1983). Thirdly, shipbuilding can be customized to suit client's demand and do not require much lead-time. Finally, natural gas shipping has less stringent regulatory approval issues when compared to pipelines, for which said approvals can represent significant problems in NCS project development. In spite of these advantages, ship transport has been regarded as a short-term measure only for demonstration projects because pipelines are considered a more economical solution, especially for short distances and large amounts of natural gas transport.

IPCC SRCCS and other research concluded that the break-even distance, i.e. the distance for which the costs per transport mode are the same, is in the range between 1,000 km and 1,500 km for transporting 6Mt/yr. This paper will review recent technical development which can make natural gas shipping more cost effective and will suggest that natural gas shipping should be considered as a competitive alternative for natural gas transport in shorter distance than 1,000km as well.

New approach on NCS system integration

Background : Natural gas compression Technologies

The NCS chain is divided into capture, transport and storage. In further detail, the capture stage is divided into a natural gas capturing stage from the source and later in to a natural gas compressing stage having suitable pressure for pipeline transport (typically about more than 10 MPa or 20 MPa). It is a conventional approach to compress the natural gas using multiple stage centrifugal compressor. Meanwhile, natural gas has to be liquefied to render it possible for transport by ship which is not necessary in pipeline transport. This liquefaction stage makes natural gas shipping economically less competitive to pipeline. Recently, GE Oil and Gas conducted a study to understand the possibilities and limitations of various natural gas compression strategies including a compression only approach and a refrigerated compression/pumping approach (Dubel and Wackertapp, 1983). In this study, GE Oil and Gas grouped those different compression strategies according to the density of the compressed natural gas and the pressure at which natural gas liquefaction actually took place.

Figure 1

Compression Only: It was the simplest option in terms of the number of components required, with only four compression sections required. No pump was needed since, neither a liquid nor a dense supercritical phase wass present at any point during the compression ...