Inventory of LNG terminals with vacuum insulated tanks.

One of most important concerns of operator of an LNG terminal is identification of the total amount of natural gas stored at the plant in any moment of its operation. Any uncertainty of the total has to be reasoned based on design and operation data. This paper presents investigation of the influences for uncertainty calculation used for LNG receiving terminals with vacuum insulated tanks. The calculation is based on the GUM (Guide to the expression of uncertainty in measurement) methodology. It uses data from equipment manufacturing and the installed instruments and information during operation (e.g. temperature measurement during loading). Inventory is not calculated as difference between inlet and outlet on the terminal boundaries but calculation of static inventory and uncertainty calculation is based on the measurement installed inside the terminal (e.g. pressure, differential pressure in the tanks …). Two main influences for uncertainty were identified – LNG level and the bottom impulse line for differential pressure measurement. This study can be used as guideline for operators to minimize uncertainty during inventory calculation (mass, volume and energy calculation) and put direction of development the instrumentation installed on the Tanks and the Terminals.