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SELECTING THERMODYNAMIC PROPERTY METHODS

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A key requirement of process design is the need to accurately reproduce the various physical properties that describes chemical species. The property packages available in HYSYS allow you to predict properties of mixtures ranging from well defined light hydrocarbon systems to complex oil mixtures and highly non-ideal (non-electrolyte) chemical systems.

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PHYSICAL PROPERTIES The physical properties required for modeling and simulation often includes, Molecular reaction and kinetic data. Thermodynamic properties Transport properties

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MOLECULAR REACTION & KINETIC DATA In this case Critical properties are, Rate equation Activation energies Reaction mechanism

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THERMODYNAMIC PROPERTIES Enthalpy Entropy Fugacity coefficient Gibbs free energy

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TRANSPORT PROPERTIES Diffusion coefficient Thermal conductivities Viscosities

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HYSYS provides enhanced equations of state (PR and PRSV) for rigorous treatment of hydrocarbon systems; semi empirical and vapour pressure models for the heavier hydrocarbon systems; steam correlations for accurate steam property predictions; and activity coefficient models for chemical systems. All of these equations have their own inherent limitations.

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So HYSYS includes following methods for the estimation of Physical properties, Equations of state Activity models Chao-Seader based empirical methods Vapour pressure models an Miscellaneous methods.

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EQUATIONS OF STATES

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The table lists some typical systems and recommended correlations.

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PENG-ROBINSON EOS For oil, gas and petrochemical applications, the Peng- Robinson EOS (PR) is generally the recommended property package.

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It rigorously solves any single, two-phase or three-phase system with a high degree of efficiency and reliability, and is applicable over a wide range of conditions, as shown in the following table.

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the Peng-Robinson equation of state supports the widest range of operating conditions and the greatest variety of systems. The Peng-Robinson and Soave-Redlich-Kwong equations of state (EOS) generate all required equilibrium and thermodynamic properties directly.

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PR AND SRK The PR equation of state applies a functionality to some specific component-component interaction parameters. Key components receiving special treatment include He, H 2, N 2, CO 2, H 2 S, H 2 O, CH 3 OH

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The PR or SRK EOS should not be used for non ideal chemicals such as alcohols, acids or other components. They are more accurately handled by the Activity Models (highly non ideal) or the PRSV EOS (moderately non-ideal).

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LEE KESLER PLÖCKER EQUATION The Lee Kesler Plöcker equation is an accurate general method for non polar substances and mixtures.

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ACTIVITY MODELS

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Although equation of state models have proven to be very reliable in predicting properties of most hydrocarbon based fluids over a large range of operating conditions, their application has been limited to primarily non-polar or slightly polar components. Polar or non-ideal chemical systems have traditionally been handled using dual model approaches.

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EXTENDED AND GENERAL NRTL With a wide boiling point range between components. where you require simultaneous solution of VLE and LLE, and there exists a wide boiling point range or concentration range between components.

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CHAO SEADER MODELS

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VAPOUR PRESSURE MODELS

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MISCELLANEOUS MODELS

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VAPOUR PRESSURE MODEL The Vapour Pressure options include the Modified Antoine, BraunK10, and EssoK packages

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MISCELLANEOUS - SPECIAL APPLICATION METHODS Amines Property Package

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STEAM PACKAGE HYSYS includes two steam packages: ASME Steam NBS Steam Both of these property packages are restricted to a single component, namely H2O.

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ASME Steam accesses the ASME 1967 steam tables. The limitations of this steam package are the same as those of the original ASME steam tables, i.e., pressures less than psia and temperatures greater than 32°F (0°C) and less than 1500°F. Selecting NBS_Steam utilizes the NBS 1984 Steam Tables, which reportedly has better calculations near the Critical Point.

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ASSIGNMENT

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PUMP Pumps are used to move liquids. The pump increases the pressure of the liquid. Water 120 C and 3 bar is fed into a pump that has only 10% efficiency. The flow rate of the water is 100 kgmole/h and its outlet pressure from the pump is 84 bar. Using Peng-Robinson equation of state as a fluid package, determine the outlet temperature of the water.

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RESULTS This example shows that pumping liquid can increase their temperature. In this case, the pump was only 10% efficient and it caused 18°C in the temperature of the water. The less efficient a pump is, the greater the increase in the temperature of the fluid being pumped. This arises because in a low efficient pump, more energy is needed to pump the liquid to get the same outlet pressure of a more efficient pump. So the extra energy gets transferred to the fluid.

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COMPRESSOR Compressors are used to move gases. The compressor increases the pressure of the gases. A mixture of natural gas (C1, C2, C3, i-C4, n-C4, i-C5, n-C5, n-C6, C7 ) at 100 C and 1 bar is fed into a compressor that has only 30% efficiency. The flow rate of the natural gas is 100 kgmole/h and its outlet pressure from the compressor is 5 bar. Using Peng-Robinson equation of state as a fluid package, determine the outlet temperature of the natural gas. If the outlet temperature is 400 C, what is the efficiency of the compressor?

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