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LNG Sampling

Oct 26, 2007

The rising value of liquid hydrocarbons and in particular Liquid Natural Gas (LNG) is causing receipt terminal operators to become a lot more interested in the quality of LNG they are receiving from suppliers.

LNG is a notoriously difficult cargo to transport as well as being held at the extremely low temperature of -161oC; it can also “age” during the voyage. This ageing process effectively changes the physical composition of the LNG between the import and export terminals.

The actual effect of this “aging” process is not fully known, various models have been used to try and predict the changes but these are not always accurate. It is generally agreed that the only reliable way to determine the change in composition between buyer and seller is to accurately measure the volume, density and the BTU (British Thermal Unit) energy value of the LNG being transferred

Due to the unique temperature requirements of LNG it is significantly challenging to measure, in order to keep it in it liquid form it must be kept at -161oC. Any change in temperature, pressure or process conditions will cause the LNG to flash off into gas. The gas will vaporise preferentially with the light ends coming off first, this will significantly bias the measurement accuracy of any sampling or online analysing devise.

Traditionally LNG has been sampled using complicated, expensive and difficult to operate continuous sampling systems but Jiskoot Ltd have designed and manufactured a unique LNG sampling system, the IsoFraction that eliminates the problems associated with the older technology.

The IsoFraction sampling system is designed to be insensitive to changes in line press, loading rates or process conditions and as a consequence it provides the only method that does not require operator intervention to ensure accuracy of total batch sampled, it is the only LNG system that is fully automatic.

The Jiskoot IsoFraction LNG sampling system has been validated in a significant number of field trials to deliver a performance of better than +0.2% variance in terms of density and BTU this performance is delivered as a consequence of Jiskoot’s experience in handling super cooled hydrocarbons and hydrocarbons with high vapour pressure in their sampling business.

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