Marine Transportation of Compressed Natural Gas A Viable Alternative to Pipeline or LNG

Abstract

Abstract The invention of the "Coselle" pressure vessel by Cran &Stenning of Calgary, Alberta, Canada and the development of the Coselle Compressed Natural Gas (CNG) Carrier promises to improve the economics of shipping natural gas over short sea routes, and from modest reserves. This invention also ignited renewed interest in CNG marine transportation and a few other concepts entered the scene: Enerseas' VOTRANS and TransCanada's GTM. The general promise from all these CNG concepts is to economically explore modest reserves in moderate daily volumes over shorter transportation distances, thus unlocking reserves which would remain stranded where either pipeline or LNG are considered. This paper provides an overview of current CNG technologies, compares those to pipeline and LNG and provides general insight regarding the commercialization of this concept. 1.0 Introduction LNG Carriers are currently the only commercial means of shipping natural gas by sea. While LNG Carriers are efficient at shipping large volumes of gas over long distances, the expense of the liquefaction plant and associated facilities make LNG too expensive for many markets. In numerous instances worldwide, gas reserves are located near potential markets, but the high cost of LNG liquefaction and transportation prevents its exploitation, especially when the gas reserves or market demand is small. The gas therefore remains "stranded". As already stated, the invention of the "Coselle" pressure vessel by Cran &Stenning of Calgary, Alberta, Canada and the development of the Coselle Compressed Natural Gas (CNG) Carrier, ignited renewed interest in CNG marine transportation and a few other concepts entered the scene: Enerseas' VOTRANS and TransCanada's GTM. It is believed that a CNG concept is generally more cost effective than the LNG and pipeline alternatives when initial gas volumes are modest; 5.4 × 106 to 13.4 × 106 Nm3/d (200 to 500 MMscfd), and distances are between 800 and 3,200 kilometres (500 and 2,000 miles). The scalability of the CNG system and the opportunity to reuse its major assets (the ships) makes the concept even more attractive. Fluor participated with seven other participants in 1999 in a Joint Industry Project to confirm the technical and economic feasibility of the CNG Coselle concept. At present, Fluor is conducting studies for various clients worldwide and actively seeking project applications for several CNG technologies. Fluor's proprietary CNG simulation model and results from an in-house case study pertaining to export options for Newfoundland gas are discussed as well. 2.0 Gas Utilization Alternatives There are four basic options to utilize offshore gas production and transport it from offshore to markets or to another location for further processing or utilization:Gas gathering and transmission to shore, in a gaseous phase, by pipeline.Volume reduction through either liquefaction or compression (LNG, CNG) followed by marine vessel transportation.Conversion to other products, by changing the "methane" molecule (methanol, synthetic crude), followed by marine vessel transportation to markets.Conversion to other energy form such as electric power and transmission by a subsea cable to shore.