Simulation of rollover in stratified LNG storage tanks

Pooya Arjomandnia

    Research output: ThesisMaster's Thesis

    2274 Downloads (Pure)

    Abstract

    [Truncated abstract] One of the major petroleum exports produced in Australia is Liquefied Natural Gas (LNG), which is a highly processed and purified natural gas. It is stored as a cryogenic liquid at temperatures of about -162°C and pressures slightly above atmospheric. "Rollover" is one of the major issues concerning the safety and mechanical stability of storage and transportation facilities for LNG. Addition of a new LNG mixture to an existing LNG without adequate mixing can result in the formation of separate strata with different densities due to differences in temperature and composition, within the storage tank. Heat leaks through the bottom and the wall of a storage tank, cause temperature changes in the stored LNG layers. Rollover refers to the rapid mixing of stratified LNG layers due to the equalization of their mass densities over time caused by heat and mass transfer between the layers. Rollover leads to the release of an abnormal amount of vapour into the storage tank, which endangers its mechanical stability and may result in a loss of valuable product through venting, with associated environmental pollution. In this Thesis, the fundamental issues associated with rollover are reviewed, a summary of past simulations plus their limitations is given, and a new program for simulating rollover is presented. The new simulation links the software packages REFPROP 8.0 and Mathematica 7.0; the former is used to calculate the physical properties of LNG as a function of temperature, pressure, and composition, and the latter is used to solve the coupled ordinary differential equations describing the material and energy balance relations for each strata. Importantly the software REFPROP 8.0 uses the most accurate available model, the GERG-2004 Equation of State 1, to calculate the thermodynamic properties of the LNG. The model also allows different correlations and analogies to be used to calculate the coefficients of heat and mass transfer between the
    Original languageEnglish
    QualificationMasters
    Publication statusUnpublished - 2010

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