Kongsberg Density Profile Measurement System

LNG DENSiTy PROFiLE MEASUREMENT SySTEM

The KONGSBERG Density Profile Measurement System is an

extension module to the K-Gauge CTS, allowing the Radar 

Tank Gauge to be used as a combined level gauge and

densimeter. The system offers a world’s first in-situ and online

LNG density measurement system, and comes with built-in LNG

aging tool.

The function both estimates the current LNG composition and

predicts future composition. Gross Calorific Value (GCV) and

the theoretical LNG density value by revised Klosek McKinley

equation..

Functional description

K-Gauge DPMS offers a cost effective way to gain improved

knowledge and information of the LNG stored. Online and

continuous LNG density monitoring and trend functions provide

an added value for the users of the K-Gauge Custody Transfer

Measurement System for LNG carriers and LNG FSRUs.

By use of the KONGSBERG Radar Tank Gauges and stand

pipes installed in the tanks for level gauging, the DPMS soft

ware module provides density monitoring and reporting, LNG

aging calculation and GCV estimation.

For LNG carriers, the LNG density, aging and GCV information

are helpful tools to prepare for the Custody Transfer operation,

and an easy verification when getting the official composition

report from the terminal. For LNG FSRUs the density profile

monitoring and trend function are helpful tools to continuously

monitor the boil-off process and the density and temperature

profile in the tanks to prevent roll-over incidents to happen.

The possibility to accurate measure the density offers a back

up, and verification, to the currently dominating method to de

termine the density in cargoes transferred to/from LNG carriers

and FSRUs.

Aging and the possibility to monitor the profile of density in the

cargo down the tank can help to predict a possible roll-over

accident by improving the decision basis for the operator. The

operator performing cargo operation will, by means of the den

sity information together with level and temperature measure

ment, become better equipped to make the correct decisions to

prevent roll-over accidents.

Density measurements

Density is a measurement of mass per unit of volume. Because

LNG is not a pure substance, the density varies between the

different gas fields due to different composition.

The traditional way of obtaining the density of LNG as input to

the CTS report, is by taking liquid samples that are vapourized

and sent to a gas chromatograph to analyze the composition.

The density is then calculated by using the revised Klosek

McKinley equation, where the composition of the LNG found by

the gas chromatograph forms the input.

The chemical composition of LNG is a function of the source

and type of processing/aging. it is a mixture of mainly methane,

ethane, propane and butane with small amounts of heavier

hydrocarbons. Besides the hydrocarbons, mainly Nitrogen exist,

which is an important component to watch due to its altered

properties compared to the hydrocarbons. Methane is by far the

major component, usually over 85 % by volume.

With KONGSBERG radar based densimeter, the density of the

LNG is monitored continuously as long as the sensing part of

the pipe is immersed in LNG. This is done at each immersed

segment in the tank, and can be presented for each tank or

averaged over several tanks. By knowing only the N2

content to

certain accuracy, the uncertainty of the density measurement is

reduced to a level well below the uncertainty of today’s accept

ed standards.

Accurate density measurement is possible regardless of the

tank atmospheric conditions. High instrument accuracy and

flexible software ensure continuously monitoring of the density

and its change both in cases with natural and forced boil-off and

re-liquefaction.

The density calculated from the gas composition found at

laboratories (by use of gas chromatograph), can be verified

by the radar based density measurement, hence it will also be

a confirmation of the input to the gross calorific value (GCV)

calculation. The density meter has a built in aging model that is

continuously adjusted by the updated inputs from the accurately

measured temperatures and the day-by-day change of the den