VMGSim User Manual - Separators6

7/25/2019 VMGSim User Manual - Separators6

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6/23/2016 Separators in Dynamics

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Separators in Dynamics

Main Flow sheet

PFD Stencil

General

Separators model pressure vessels in dynamics. The vessels may be use to separate phases, or merely as

buffer volumes.

There are four flavors of separators:

Separator

SeparatorLLVMultiFeedSep2MultiFeedSep3

In addion to allowing mulple feeds, the MulFeedSep allows the user to specify Duty or Outlet T and

DeltaP.


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Summary (Tab)

Main Data

InQ

The external duty applied to the separator (shown only for separators with mulple feeds).

Outlet T

Specifies the holdup temperature for the separator, which implies that the outlets will have the same

temperature unless there is pressure change because of kinec energy.

Delta P

A pressure drop that will be applied to all feed streams (if specified). This item is shown only for separators

with mulple feeds.

Percent Level

The level percent of the body height of the light liquid.

Level

The level of the light liquid.

Boot/Heavy % Level

The level percent of the boot height of the heavy liquid (main body if no boot specified).

Boot/Heavy Level

The level of the heavy liquid.

Heat Loss Calc Type

The type of heat loss calculaon required. Selecng anything other than None makes the Heat Loss Tab visible

where data can then be entered.

Entrainment Mode

The type of entrainment calculaon required. In dynamics, entrainment must be product based. Selecng an

entrainment opon makes the Entrainment tab visible, where data can then be entered.

Separator Configuration

For modeling purposes, a separator is assumed to be horizontal or vercal cylinder, with an oponal vercal

cylinder for the boot. If only the volume is specified, a default L/D of 2.0 will be assumed. For the boot, a

default L/D of 1.0 will be assumed.

Also, the separator head design is selected and the head geometry is specified respecvely.


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Orientation

The separator orientaon vercal or horizontal.

Slug Catcher

Enables selecon of Slug Catcher

Head Design

Ellipsoidal

This is used to model ellipcal heads with default axis rao = 2:1 on a separator.

None

This is used when ends are completely flat.

Custom

This is used to model torispherical heads of the separator with user specified crown radius and knuckle radius.

Flat

This is used to model flat heads. Here knuckle radius = min(0.06*OD, 3*thickness), crown radius = 1.3*OD.


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Dished

Here, ends are spherical secon with default crown radius = OD

DIN ToriSpherical

Here, knuckle radius = 0.1*OD, crown radius = OD.

Din SemiEllipsoidal

Here,knuckle radius = 0.154*OD, crown radius = 0.8*OD

ASME F&D

Here, knuckle radius = min(0.06*OD, 3*thickness), crown radius = OD.

Head Axis Ratio

This is used to model ellipcal heads on a separator. The value is the rao of the minor to the major axis for

the ellipse. A typical value would be 0.5, which implies that the ellipcal poron of the separator extends out

of the diameter beyond the tangent line.

Note that if this feature is used, the separator Length defines the distance between the tan lines. I.e. Total

Length = Length + Head Axis Rao * Diameter

If the separator has a boot, the Head Axis Rao applies to the boom of the boot also, and is based on the

Boot Diameter.

Reported levels are impacted by this opon. For a boot, the level is reported as a fracon of the distance from

the boom of the ellipcal head to the top of the boot. For a vercal separator, level is reported based on the

Total Length of the separator.

Length

The separator length.

Diameter

The separator diameter.

Volume

The total separator volume (including boot volume).

L/D Ratio

The length to diameter rao of the separator.

Thickness

The wall thickness (heads are assumed equal thickness)

Boot Length

The height of the boot.

Boot Diameter

The diameter of the boot.

Boot Volume

The boot volume.

Level Control


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Internal Level Ctl

Enables internal level control using the liquid product flowrate.

Boot Intern Lev Ctl

Enables boot internal level control using the heavy liquid product flowrate.

Upper Level Tap

The locaon of the level taps on the separator.

Lower Level Taps

The locaon of the level taps on the separator.

Upper Boot Level Taps

The locaon of the boot level taps on the separator.

Lower Boot Level Taps

The locaon of the boot level taps on the separator.

Material Summary

This frame shows the condions, composion and properes of the material at the inlet and outlet. The

Connected Stream/UnitOp displays the streams or units aached to the inlet and outlet of the unit operaon.

Advanced (Tab)

Geometry

Inclination

The separator angle of inclinaon 0 90 : Inlet is higher, 90 180 : Outlet is higher (See below for more

details).

Crown Radius

The radius of the crown poron of a torispherical head.

Knuckle Radius

The radius of knuckle poron of a torispherical head.

Spherical Limit


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The width of the spherical poron of a torispherical head.

Knuckle Height

The height of the knuckle poron of a torispherical head.

Crown Height

The height of the crown poron of a torispherical head.

Liquid Carryover

Terminal Vapor Velocity

An esmate of the terminal vapor velocity.

Vapor Velocity

The current vapor velocity in the separator.

More details for Separators Inclination


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Heat Loss (Tab)

Heat loss calculators are used to calculate heat loss from equipment such as separators and heat exchangers.

There are different calculators with varying levels of informaon requirements and fidelity. They are selected

by:

Heat Loss Calc Type

Simple Heat Loss

This models calculates heat loss using an overall Q = UA * delta T model.

Duty

Calculated duty.

UA

Overall heat transfer factor.

U

The overall heat transfer coefficient.

Area

The inner area for heat transfer.

Process T

The weighted average process side temperature.

Outside Data

Select between using the global ambient temperature and a specified value.

Ambient Temperature

The global ambient temperature.

Outside T

Use this to specify the temperature if Specify opon is selected.


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Outside T

The outside temperature either the user specified value or the ambient temperature.

Detailed Heat Loss

This model calculates heat loss based specified values for the equipment wall layers

Duty

Calculated duty.

Process TThe weighted average process side temperature.

Outside Temp Source

Select between using the global ambient temperature and a specified value.

Ambient Temperature

The global ambient temperature.

Outside T

Use this to specify the temperature if Specify opon is selected.

Layer Count

The number of layers of material in the equipment wall.

Heat Transfer Coeff

In this frame the Heat Transfer Coefficients are specified.

Inner HT Corr

Heat transfer correlaon for Inner Heat Transfer Coefficient. Choices are:


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Constant (default)

FreeConv Free Convection suitable for estimating heat transfer where velocities are low,such as for separators. If PhaseZone is selected (see below), heat transfer coefficients will becalculated on a phase basis. Otherwise an overall coefficient will be calculated using bulkproperties.

Inner HTC

The heat transfer coefficient between the process fluid and the inner wall.

Inner HTC Scale

Scale to be applied to the calculated Inner HTC value. Note that the reported HTC value is the unscaled value,

but that the scaled value will be used to calculate heat duty.

Outer HTC

The heat transfer coefficient between the outer wall and the surroundings.

Radiant Heat Transfer

Informaon related to the radiant heat transfer inside and outside the separator is defined within this frame.

Do Inner Radiant Calc

Checking this opon includes radiant heat transfer on the inside of the separator. The radiant heat transfer is

driven by an equaon taking into account the process temperature, inner wall temperature, inner process

emissivity, and the wall emissivity (Kern, 1950).

Inner Process Emissivity

The emissivity of the inner process fluid is entered here and should be a value between 0 and 1. Esmates of

this value can be determined based on consideraons such as fluid composion and average process

temperature (Bahadori and Vuthaluru, 2009).

Inner Wall Emissivity

The emissivity of the inner wall is entered in this signal port for internal radiant heat transfer calculaons. An

example would be an emissivity of 0.79 for an oxidized steel at ~600 C, or 0.28 for a mild molten steel surface

~1600 C (Hewi, Shires, and Bo, 1994).

Do Outer Radiant Calc

Checking this opon includes radiant heat transfer on the outside of the separator.

Radiant HT Method

The method used to calculate the radiant heat transfer on the outside of the separator.


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Grey Body

The same equaon as the inner radiant calculaon. The radiant heat transfer is driven by an equaon taking

into account the process temperature, outer wall temperature, outer process emissivity, and the wall

emissivity (Kern, 1950).

ISO Fire Heat

The radiant heat transfer is driven by an equaon taking into account the process temperature, outer wall

temperature, outer process emissivity, and the wall emissivity and absorpvity given in ISO/DIS 23251.

Outer Process Emissivity

The emissivity of the outer process fluid is entered here and should be a value between 0 and 1. Esmates of

this value can be determined based on consideraons such as fluid composion and average ambient

temperature (Bahadori and Vuthaluru, 2009).

Outer Wall Emissivity

The emissivity of the outer wall is entered in this signal port for outer radiant heat transfer calculaons.

Outer Wall Absorptivity

The absorpvity of the outer wall is entered in this signal point for outer radiant heat transfer calculaons.

This value is only used if the Radiant HT Method is set to ISO Fire Heat.

Detailed Heat Loss. Layers

Layer Name

A name for each wall layer. VMGSim provides default names.

Density

The wall material density. Required so that VMGSim can calculate the overall heat capacity. Default value

supplied is for mild steel.

Heat CapacityThe specific heat capacity for the wall material. Default value supplied is for mild steel.

Thermal Conductivity

The thermal conducvity for the wall material. Default value supplied is for mild steel.

Thickness

The wall thickness for each layer.

Walls Detailed


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Area

The area for heat transfer at each boundary between layers. If you have two layers, these would be the

boundaries between process/layer1, layer1/layer2 and layer2/outside.

For some equipment types such as separators, VMGSim calculates these based on the supplied equipment

geometry.

Duty

The heat flux across each layer boundary (correspond to the boundaries where areas are specified).

Temperature

The temperature at each layer boundary. For a two layer case, these boundaries would be located at layer1

inner, layer1/layer2, and layer2 outer.

PhaseZone Loss

This opon is available only for equipment types where detailed geometry informaon is available.

This model is similar to the detailed heat loss model, except that it allows for the specificaon of different

heat transfer coefficients depending on the fluid phase in contact with the equipment wall. It calculates and

reports heat loss for each zone, and also reports the overall heat loss.

The area associated with each zone is specified as a fracon of the overall area, and is calculated by the

VMGSim based on geometry and fluid levels.

Radiant Heat Transfer can be selected for PhaseZone Loss. In this case, the user must provide emissivies for

each phase zone.

Roof/Wall/Floor Zone Loss

This model is similar to PhaseZone loss. However, on the outside of the separator, the zones are the roof, wall,

and floor of the separator, rather than the vapor and liquid weed regions.

Depressuring (Tab)

Void Fraction Calculation

Void fracon calculators are used when performing depressuring studies. During a sudden depressuring of a

separator, vapor bubbles form in the liquid, causing the liquid to expand. As a result, a top blowdown may

have entrained liquid, even if the liquid surface was inially below the nozzle. The void fracon in the liquid

can be correlated as a funcon of the bubble rise velocity, and the vapor superficial velocity above theinterface.

The Depressuring tab on the separator allows the selecon of void fracon calculator: [Simple, Bubbly, Churn,

TopBias].

Simple is the default, which use the unexpanded liquid level to determine the vapor fracon in the nozzle.

Bubbly uses the formula

where is the average void fracon and C0 is a tuning constant.

Churn Turbulent uses the formula


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TopBias assumes that there is a dead zone at the boom of the liquid which does not expand. It uses the

same expansion formula as the Churn Turbulent model.

The Bubbly model assumes a uniform bubble distribuon i.e. the void fracon at the surface is the same as

the bulk void fracon. For the Churn/TopBias models, the void fracon at the surface is given by

Note that these correlaons are designed for a blowdown scenario they use only the vapor superficial

velocity and bubble rise velocity as correlang parameters. If you enable these correlaons for other

scenarios, such as normal vapor/liquid separaon, you will most likely significantly overpredict the liquid

expansion, and results may be incorrect.

Input Data

Void Frac Calc Type

Select one of [Simple, Bubbly, Churn, TopBias]. Simple is the default, and implies no liquid expansion.

Void Fraction

This is the calculate bulk void fracon.

Surface Void Fraction

This is the calculated surface void fracon.

Tuning Param

This is the C0 parameter in the formulas.

Frac Non Boiling

This is the height of the nonboiling region expressed as a fracon of the separator vercal dimension.

Reported Levels

Both the expanded levels and the equivalent clear liquid levels are reported.

Reference


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Fisher, H.G. et al, Emergency Relief System Design Using DIERS Technology, AIChE, 1992, pp 529

Fire Heat calculation

Fire heat calculaon allows the user to calculate the heat load on a pressure vessel in a fire scenario. The fire

heat input calculaons should normally be used in conjuncon with a heat loss model.

If no heat loss model is present, the calculated fire heat input duty is added directly to the process fluid in the

vessel. If a heat loss model is present, the fire heat input duty replaces the calculated duty between the outer

surface of the vessel and the surroundings.

As an alternave to a Fire Heat Calculaon, one can use Radiant Heat Transfer in the Detailed or PhaseZone

Heat Loss Model, and specify the outside temperature to be the esmated flame temperature.

Calculator Active

Check this to enable the calculaons.

Duty

The total calculated heat flux from the fire to the vessel.

Formula

Area Power

Q = (Const 2)*A(Const 1)

Generic

Q = Const 1 + Const 2 * Integrator Time + Const 3*(Const 4 T Vessel) + Const 5 * Weed Area Percent /Nominal Weed Area Percent

Radiant Heat Input

Q = Const 2


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This opon allows for addional heat input/losses from the vessel outer surface i.e. the net heat flux to

the outer surface in general will not match the specified value. If you need a fixed heat flux, choose one of

the two opons above.

This opon can be used, e.g to model solar radiaon on the outside of the vessel. The solar radiaon will be

balanced against all the other heat loss contribuons to determine net heat loss/gain.

Area Type

Total

The enre vessel surface area is used in the formula.

Wetted Nominal

The fracon of the area which is in contact with liquid on the process side is used. The user wishes to specify

this fracon.

Wetted Actual

The fracon of the area which is in contact with liquid on the process side is used. The simulator calculates

this fracon.

Area

The total area of the vessel.

Wetted Area

The area of the vessel which is in contact with liquid on the process side.

Const 1 Const 2

The correlang parameters for the heat calculaon formula.

Entrainment(Tab)

This tab is used to configure carryover for nonideal separators in which the products are not pure phases.

Calculation Type

Defines the type of specificaons used to define entrainment.

No Entrainment

The separaon is assumed to be ideal (no carry over).

Feed Based

Feed based is not available in dynamics.

Product Based

Enables variables to specify the amount of carry over in each product. These variables are contained in the

Sengs and Entrainment frames.

Basis can have any value from Mole, Mass and Actual Volume and it is used to define the basis of the

entrainment specificaon.

Specificaon Type must be Percent in dynamics.


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The number of variables in the Entrainment frame depends on the number of phases being used in the

separator. For example, a separator for 2 liquid phases with no solids will expose six variables labeled, Vap in

Light Liq, Vap in Heavy Liq, Light Liq in Vap, Light Liq in Heavy Liq, Heavy Liq in Vap, Heavy Liq in Light

Liq.

Nozzles (Tab)

Nozzles model the connecon points for unit operaons, and mirror the physical connecon points for

equipment. For many applicaons, the default sengs for nozzles provided by the simulator are sufficient,

and no user intervenon is required. Nozzle geometry impacts the simulaon in the following ways:

Where the phase fracon of the fluid leaving the equipment is determined by the nozzle locaon and

diameter e.g. a separator

When stac head calculaons are enabled. Nozzle elevaon will impact the stac head contribuons.


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Unit Op Elevation

The elevaon relave to ground for the reference line for the equipment. All other elevaons are relave to

this.

Fitting K

Specify this if you need addional pressure drop to account for fing losses. The pressure drop is calculated

from

For pipes, go to the Detail Tab, and either specify K there, or select the fing type.

Diameter

The nozzle diameter. For unit operaons that have physical dimensions, such as the separator, the diameter

defaults to 5% of the vercal dimension. For other unit operaons, the diameter defaults to 50 mm.

Elevation

Specify one of:

Elevation

The nozzle elevaon relave to the equipment baseline.

Elev. Rel Ground


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The nozzle elevaon above ground level (See below for more details).

Elev Percent

The elevaon is specified as a percentage of the vercal dimension of the equipment. This opon is

convenient, but can be used only for equipment such as separators that have a vercal dimension.

Efficiency

The type of efficiency calculaon required . Selecng Equilibrium will set all values to 100%, while selecng

Zero will set all values to zero.

This specificaon affects what percentage of the feed will be flashed together with the holdup contents, and

what percentage will bypass the flash and mix directly with the corresponding phase in the holdup.

See also the explanaon about holdup efficiencies in the secon below.

Static Head Calc Status

This reports whether stac head calculaons are enabled or not. To change the behavior, go to the flowsheet

form (Sengs | Do Stac Head Calcs).

Internal Static Head

This is the stac head difference between the nozzle and the holdup reference point. Nozzle pressure + stac

head = holdup reference pressure. Only calculated/reported if enabled on flowsheet form (Sengs | Do Stac

Head Calcs).

External Static Head

This is the stac head difference between the nozzle, and the nozzle on another unit operaon that is

connected to this nozzle. Upstream nozzle pressure + stac head = downstream nozzle pressure. Only

calculated/reported if enabled on flowsheet form (Sengs | Do Stac Head Calcs).

Kinetic Head Calc Status

This reports whether kinec head calculaons are enabled or not. To change the behavior, go to the flowsheet

form (Sengs | Do Kinec Head Calcs).

Kinetic dP

The difference in pressure between the nozzle and the holdup aributable to kinec energy. This is the actual

pressure recovered or lost. This may differ from reversible conversion because of entry/exit losses. Onlycalculated/reported if enabled on flowsheet form (Sengs | Do Kinec Head Calcs), and the nozzle diameter

is specified.

Velocity

This reports the calculated fluid velocity in the nozzle. The nozzle diameter must be specified for the

calculaon to take place.

Total Pressure

This reports the total pressure in Nozzle that includes stac head, choke pressure and pressure aributable to

kinec energy .

Enlarger Angle

Enlarger/Reducer Angle for feed nozzles can be specified here.


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More details for Nozzle Elevations

Holdup (Tab)

Init From

You can inialize the holdup using any stream in the simulaon. All properes except levels/mols will be


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inialized to the stream values.

The inializaon takes place once at the me that you make the selecon. You can repeat the inializaon

from the same stream by clicking the buon which appears once a stream has been selected.

Summary

Volume

The holdup volume. For most equipment, this is specified or calculated on the Summary Tab, and is reported

here for convenience.

T

The weighted average temperature in the holdup. Typing a value will inialize all phase temperatures to that

value.

P

The holdup reference pressure at which VLE calculaons are performed.

MoleFraction

This node can be expanded to view the bulk holdup composion. Clicking in the area to the right of the Mole

Fracon Label, or typing in any of the component cells brings up an edit box which allows eding/inializaon

of the holdup composion.

Duty

The heat duty applied to the holdup. This is either specified at the unit operaon level, or calculated by the

unit operaon.

Elevation

The reference elevaon for the holdup.

Total Mol Inv

The total number of mols present in the holdup.


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Phase Mol Inv

The number of mols of each phase present in the holdup.

Total Mass Inv

The total mass present in the holdup.

Phase Mass Inv

The mass of each phase present in the holdup.

Efficiency Type

Most simulaon modeling is performed using the assumpon that material is at thermodynamic equilibrium.

In reality, this may not be the case, because of low interfacial mass transfer. One way to model this is using

the concept of efficiencies. Efficiencies are used in steady state modeling to more accurately represent trays in

a disllaon column.

In dynamics, efficiencies can be specified for all unit operaons which processes material. The holdup tab

allows entry of nozzle efficiencies and holdup efficiencies. Nozzle efficiencies model the degree of equilibrium

reached between material entering the holdup and the material already in the holdup. Holdup efficiencies

model the movement towards equilibrium of the material already in the holdup. Efficiencies are specified ona perphase basis, since the degree of contact and rate of mass transfer may be different for each phase.


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Holdup Efficiencies

Holdup efficiencies are specified under Holdup|Efficiency.

Efficiency Type

Equilibrium All phase efficiencies are 100%.

None All phase efficiencies are 0%.

Time The first order time constant for each phase for reaching equilibrium.

Efficiency All phase efficiencies are the user specified value.

Mass Transfer-- A rigorous mass transfer model is used to model the departure from

equilibrium.If you want to model an approach to equilibrium over me, the recommended Efficiency Type is Mass

Transfer, as this uses a rigorous MaxwellStephan model for the mass transfer rates. Note that this model does

not take into account any separator internals to aid the approach to equilibrium.

To achieve beer customizaon of the approach to equilibrium, select Time or Efficiency. Time is the

recommended opon, as it is stepsize independent. This specifies a first order me constant i.e. the me

that it takes to proceed 68% of the distance towards equilibrium. If you select Efficiency, be aware that the

me to reach equilibrium will be impacted by the integrator stepsize, because the holdup contents will move

a fixed percentage towards equilibrium every me a flash calculaon is performed.

Nozzle EfficienciesNozzle efficiencies are specified under Nozzles|[Nozzle Name]|Efficiency.

Efficiency Type

Equilibrium All phase efficiencies are 100%.

None All phase efficiencies are 0%.

Efficiency Phase efficiencies are the user specified values.

Nozzle efficiencies can be specified for product nozzles as well. These efficiencies willbe used if the flow reverses (i.e. the product nozzle becomes a feed to the holdup). Ifyou have specified nozzle efficiencies for feed nozzles, it is best practice to specify

them for product nozzles as well.

Level


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The calculated liquid levels for the unit operaon/holdup. If the unit operaon has more than one holdup, it is

the levels associated with this holdup.

Equilibrium Results (Tab)

View the equilibrium results for the port selected in the pull down menu.

Notes (Tab)

A rich text editor where the user can store notes related to the unit op.

Copyright (c) 20022015 Virtual Materials Group, Inc. All Rights Reserved [email protected]

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