Seawater Simulations

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Introduction

The IAPWS-08 Seawater Property Package is based on the Seawater-Ice-Air (SIA) library. The Seawater-Ice-Air (SIA) library contains the TEOS-10 subroutines for evaluating a wide range of thermodynamic properties of pure water (using IAPWS-95), seawater (using IAPWS-08 for the saline part), ice Ih (using IAPWS-06) and for moist air (using Feistel et al. (2010a), IAPWS (2010)).

TEOS-10 is based on a Gibbs function formulation from which all thermodynamic properties of seawater (density, enthalpy, entropy sound speed, etc.) can be derived in a thermodynamically consistent manner. TEOS-10 was adopted by the Intergovernmental Oceanographic Commission at its 25th Assembly in June 2009 to replace EOS-80 as the official description of seawater and ice properties in marine science.

A significant change compared with past practice is that TEOS-10 uses Absolute Salinity SA (mass fraction of salt in seawater) as opposed to Practical Salinity SP (which is essentially a measure of the conductivity of seawater) to describe the salt content of seawater. Ocean salinities now have units of g/kg.

Absolute Salinity (g/kg) is an SI unit of concentration. The thermodynamic properties of seawater, such as density and enthalpy, are now correctly expressed as functions of Absolute Salinity rather than being functions of the conductivity of seawater. Spatial variations of the composition of seawater mean that Absolute Salinity is not simply proportional to Practical Salinity; TEOS-10 contains procedures to correct for these effects. More information about the SIA library can be found here.

Setup

Create a new simulation. Add "Water" and "Salt" compounds to it.

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Add the Seawater Property Package to the simulation. The Flash Algorithm setting is irrelevant because the Seawater PP has its own flash algorithm.

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Add a Material Stream to the simulation and set the amount of salt and water in the stream. Solubility in terms of kg salt per kg water can be easier entered if you switch input mode to "Mass Flows". Maximum solubility supported by the seawater property calculation routines is 0.12 kg salt per kg water.

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When the Stream is calculated, the equilibrium phases will be displayed with all the required properties calculated, so you can go forward simulating your process with salt water. If maximum solubility is exceeded, the excess salt will precipitate to a solid phase.

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Ignore maximum salinity limit setting

The Seawater Property Package has a user-defined setting to ignore the maximum supported salinity value (0.12 kg/kg) for calculations. If enabled, it doesn’t display any warnings and the calculated salinity will be sent directly to the property calculation routines without further check. If disabled, the maximum value of 0.12 will be used if the calculated salinity is higher, and a warning message will be displayed in the flowsheet log window.

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