Optimized LNG Storage Tanks for Fleet-Size Refueling Stations with Local LNG Liquefiers

Abstract

The capacity of a liquid natural gas (LNG) storage tank in a LNG fleet-size refueling station is determined in part by the desire to have fuel capacitance to meet uneven fuel-use patterns during the day/week, to allow for maintenance and unexpected equipment failure, and to take advantage of off-peak feedstock prices. These considerations drive the selection of the LNG storage tank size upwards. On the other hand, the cost of conventional LNG storage tanks, restrictions due to safety codes, the size of the refueling skid, the installation costs, fuel quality variations due to weathering effects, and site preparation costs all drive the selection of the LNG storage tank size downward. Conventional LNG storage tanks for local refueling stations with a capacity of ~1000 DEG/day are made of either 304L stainless steel or 9% Ni-steel inner shells with carbon steel outer shells (DEG = Diesel-Equivalent-Gallons, or approximately 1.7 L LNG). The tanks are double-walled with thermal isolation provided by vacuum and superinsulation or, in some cases, perlite. The tanks are extremely thermally efficient and therefore a relatively expensive component of a refueling station. We have performed a thermoeconomic analysis to determine the optimum level of tank technology to apply to a LNG storage vessel for a local refueling station. One key result is that a local liquefier allows the use of a much less efficient and less expensive LNG storage tank, thus reducing the cost of delivered LNG fuel.