Fig 6.28
The following fields are available on this tab:
The location can have an alphanumeric name. This feature is useful for large flowsheets, because you can provide a different “location” name to different sections to make it more comprehensible.
Field Description
Name The alphanumeric description of the Control Valve (e.g. - FCV 1).
Location You may want to specify the location of the Control Valve in the plant.
Outlet Either type in the name of the pipe segment or select from the drop-down list.
At You can specify where the pipe segment is to be attached to the Control Valve.
Ignore Select the ignore checkbox to ignore this control valve in the calculations. Clear the checkbox to re-enable it.
7 Nodes 91
Conditions Tab
Fluid conditions are specified here.
Fig 6.29
The following fields are available on this tab:
Field Description Inlet
Pressure The pressure of the source on the upstream side of the valve. Valid values are between 0.01 and 600 bar.
It is recommended that a value for Outlet Temperature which corresponds to an isenthalpic flash from the upstream conditions down to the Allowable Back Pressure. This will give the highest probable entry temperature into the system which will in turn give the highest velocities.
Inlet Temp Spec.
The temperature specification of the source on the upstream side of the relief valve. Valid values are between -250oC and 1500oC.
You can select the fluid condition from the drop-down list on the left side. The available option are:
Actual - it uses the given inlet temperature as the actual fluid temperature.
Subcool - If this option is selected, enter the amount of subcooling.
Superheat - If this option is selected, enter the amount of superheat.
Allowable Back Pressure
The Allowed Back Pressure is the pressure that is allowed to exist at the outlet of a pressure relief device as a result of the pressure in the discharge system. It is the sum of the superimposed and built-up back pressure. Clicking the Set button calculates the Allowable Back Pressure as a function of the Inlet Pressure. Checking the Auto checkbox will automatically calculate the Allowable Back Pressure whenever the Inlet Pressure changes. Valid values are between 0.01
www.cadfamily.com EMail:[email protected]
The document is for study only,if tort to your rights,please inform us,we will delete
to 600 bar.
Outlet
Temperature This is the temperature of the source at the flange on the downstream side of the valve.
If the enthalpy method chosen is the Ideal Gas model, then this temperature is used to determine the enthalpy of the source at the entrance to the pipe network, otherwise this enthalpy is calculated from the upstream pressure and temperature. If the Set button was clicked and the enthalpy model is Peng Robinson, Soave Redlich Kwong or Lee Kesler then the outlet temperature will be calculated from the upstream temperature and pressure after isenthalpic expansion to the defined MABP. Valid values are between -250oC and 1500oC.
Field Description
Mass Flow This is the mass flow of the source. Valid values are between 0 and 100,000,000 kg/hr.
Flange
Diameter This is the diameter of the flange at the valve discharge.
The flange diameter may be left unknown in which case it will be assumed to be the same as the outlet pipe.
Composition Tab
The fluid composition is specified here.
Fig 6.30
The following fields are available on this tab:
Field Description
Basis This is the composition basis, which may be either Mol. Wt., Mole Fraction or Mass Fraction.
Mol. Wt. It is the molecular weight of the fluid. You can only enter data here if the
7 Nodes 93 composition basis selected is Molecular Weight. Valid values are between 2 and 500.
If the composition basis selected is Mole or Mass Fraction, the molecular weight is updated when you enter or change the component fractions.
Fluid Type If Molecular Weight is selected in the composition basis drop-down list, you need to select the Fluid Type to calculate a binary composition in order to match the molecular weight. If the two components of the specified fluid type are not found then the other components are used.
Component Fractions
This is the fluid composition in either mole or mass fractions. You can only enter data here if the composition basis selected is Mole or Mass Fraction.
When you exit the Source view, you will be prompted about the Invalid Composition if the sum of these fractions is not equal to one. You can normalize the composition by either manually editing the component fractions or by clicking the Normalize button.
If the composition basis selected is Molecular Weight, the component fractions are estimated when you change the molecular weight.
Clone Composition From
This button allows the copying of compositional data from another releif valve in the same scenario
Normalise Normalises the composition such that the sum of the component fractions is 1.
Methods Tab
Calculation methods are specified here.
Fig 6.31
www.cadfamily.com EMail:[email protected]
The document is for study only,if tort to your rights,please inform us,we will delete
The following fields are available on this tab:
Fields Description
VLE Method The options for the Vapor-Liquid Equilibrium calculations are as follows (see Appendix A - Theoretical Basis):
Compressible Gas - Real Gas relationship.
Peng Robinson - Peng Robinson Equation of State.
Soave Redlich Kwong - Soave Redlich Kwong Equation of State.
Vapor Pressure - Vapor Pressure method as described in API Technical Data Book - Volume 1.
Model Default - If this is selected, the Default method for the VLE method (as defined on the Calculation Options view) will be used.
Swage Group Fittings Loss Method
The available options are;
Equal Static Pressure – Pressure drop calculation is ignored and static pressure is balanced.
Calculated – Pressure drop is calculated in accordance with the Swage method.
Isothermal
Pressure Drop If this option is set to Yes, the inlet temperatures used for the size change calculations in the control valve will not update during iterative calculations for pressure loss i.e. a PT flash will be used to update the inlet properties. If the option is set to No then a more rigorous PH flash will be used to update the inlet properties.
The control valve will do one size change calculation from the defined flange diameter to the outlet pipe diameter. This will normally be an expansion.
Fields Description
Setting this option to Yes can speed up calculations in some cases at cost of a minor loss of accuracy.
Two Phase
Correction If this option is set to Yes then the pressure loss coefficient in two phase flow will be calculated using properties corrected for liquid slip. If set to No then the homogeneous properties of the fluid will be used in calculating the pressure loss coefficient.
Method The following options are available:
Compressible - pressure losses will be calculated assuming compressible flow through the connector at all times.
Incompressible (Crane) - pressure losses will be calculated assuming incompressible flow through the connector at all times.
Loss coefficients are calculated using Crane coefficients.
Transition - pressure losses will be calculated initially using the assumption of incompressible flow. If the pressure loss expressed as a percentage of the inlet pressure is greater than the defined
compressible transition value then the pressure drop will be recalculated using the compressible flow method.
Incompressible (HTFS) - pressure losses will be calculated assuming incompressible flow through the connector at all times. Loss
coefficients are calculated using HTFS correlations
The Incompressible method calculations are faster but will be less accurate at higher pressure drops. The Transition method can cause instabilities in some cases if the calculated pressure drop is close to
7 Nodes 95 the transition value.
Compressible
Transition This entry defines the pressure drop as a percentage of the inlet pressure at which compressible flow pressure drop calculations should be used. It applies only when the Transition method is selected.
Sizing Group
Sizing Method The four sizing method options available are:
API (1976) – American Petroleum Institute method in the 1976 edition of RP 520 pt 1. No account is made of liquid flashing as it passes through the relief valve, thus this method is not
recommended for either two phase or flashing fluids.
API (1993) – American Petroleum Institute method in the 1993 edition of RP 520 pt 1. Liquid flashing is handled by a simplified approach in which the fluid is flashed to the outlet pressure. The relative quantities of each phase at the outlet condition are then used at the inlet of the valve to determine the two phase capacity API(2000) – American Petroleum Institute method in the 1993 edition of RP 520 pt 1. This method is often referred to as the Diers or Leung method. This is the recommended method for all two phase fluids.
HEM – Homogeneous Equilibrium method.
Back Pressure Back pressure to be used for rating the relief valve. If this value is not specified then the maximum allowable back pressure is used.
Multiphase Cd Discharge coefficient to be used of relief valve in multiphase service Liquid Cd Discharge coefficient to be used for relief valves in liquid service Kb User defined back pressure correction factor. If this field is left blank
then the back pressure correction factor is calculated. This value should only be specified in exceptional cases.
Energy Balance Group Isentropic Flash
Select Yes to use an isentropic flash between the inlet and outlet otherwise an isenthalpic flash will be done
Isentropic Efficiency
Fractional isentropic efficency for the isentropic flash
Estimated
Fraction The initial estimates for the flow profile in looped systems are generated based on the assumption of vapor phase flow without any liquid knockout in the system. It is not uncommon for sources to pass through a knockout drum before connection to the main header (see Figure 6.17). Specification of an estimate of vapor fraction of the fluid at the knockout drum can considerably enhance the automatically generated flow profile.
If this value is not specified then it is assumed to be all vapor.
Vapor Mol.
Wt. Specify the estimated vapor molecular weight for the vapor fraction given above.
If this value is not specified then it is assumed to be the same as that of the total fluid.
www.cadfamily.com EMail:[email protected]
The document is for study only,if tort to your rights,please inform us,we will delete
Inlet Piping Tab
Details of the piping between the protected equipment and the inlet to the relief valve are specified here. This data is used to calculate the pressure drop in the inlet piping to ensure that it does not exceed the recommended limit of 3% of the inlet pressure. The diameter of the inlet piping is also used to calculate the inlet velocity of the source fluid when the Include Kinetic Energy option is selected in the Calculation Options view.
Fig 6.32
The available fields are:
Fields Description
Length The length of the inlet piping.
Elevation
Change The change in elevation of the inlet piping. This cannot be greater than the length of the piping.
Properties Group
Material The material of the inlet pipe either Carbon Steel or Stainless Steel.
Roughness The surface roughness of the inlet pipe. Whenever a material is selected, the absolute roughness is initialized to the default value for the material as defined on the Preferences view. Valid values are between 0.00001 inches and 0.1 inches.
Diameter Nominal
Diameter The nominal pipe diameter used to describe the inlet pipe size. For pipes with a nominal diameter of 14 inches or more, this will be the same as the outside diameter of the pipe.
Schedule If a pipe schedule other than “-” is selected, you will be able to select a nominal pipe diameter from the pipe databases. It will not be necessary to specify the internal diameter. If you select “-” you will be unable to select a nominal pipe diameter from the pipe databases and you will then have to specify both the internal diameter.
Internal The pipe diameter used for the pressure drop calculations.
7 Nodes 97 Diameter
Fields Description Use Pipe
Class Select this checkbox to restrict the sizes of the inlet piping selected by Flare System Analyzer to those defined by the Pipe Class tool.
Fittings Groups Loss
Coefficient Enter the A and B parameters for the following fittings “K” factor equation in which Ft is the friction factor for fully developed turbulent flow:
K = A + BFt .
Valid values are any positive number or 0.