(92f) Optimization of Marine CNG Transport for Stranded Gas

While liquefied natural gas (LNG) is the dominant technology for marine transport of natural gas, compressed natural gas (CNG) is an economically attractive alternative for transportation of relatively small amounts of natural gas over short distances (up to 6 Bcm/year transported over 2000 km, respectively).  Because the main capital expenditure in a CNG project is on marine transport vessels, accounting for more than 3/4 of potential CNG projects, careful design of CNG transport fleets and compatible distribution schedules is important.  Design through numerical solution of an all-encompassing optimization problem would be feasible but complicated and intuitive unappealing, in that it would provide little insight into the guiding principles of CNG transport system design.  In this work, a structured optimization framework is applied to potential marine CNG transport.  A case study for transport from a source in the Trinidad/Venezuela area to island countries in the Caribbean is used to illustrate related concepts.  Two general patterns emerge in the results:  A "hub-and-spoke" pattern for servicing of the largest four consumption markets (Puerto Rico, Dominican Republic, Jamaica, and The Bahamas) and a cyclical "milk-run" pattern for the remaining (smaller) markets.  Furthermore, a general guiding principle emerges that favors medium rather than large-size CNG transportation vessels, such that a closer approximation of the ideal (but infeasible) optimum of a two-way CNG pipeline can be achieved.