Reverse Osmosis (RO) Unit

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This model is only available in SysCAD 9.3.


General Description

This model is designed to simulate a reverse osmosis membrane process, often used in water treatment, especially for desalination of sea water.

The user may specify the yield and efficiency of the process, as well as the outlet pressure requirements.

The unit expects the feed to be free of solids. If solids are fed to the unit, the user will receive a warning and any solids will be sent to the Brine stream.

If a vent stream is connected, then all gases will exit via the Vent. If gases are present and there is no vent connection then the user will receive a warning and all gases will be sent to the Brine stream.

Diagram

RO Unit.png

  • The diagram shows default drawing of the Reverse Osmosis unit with connecting streams.
  • The physical location of the streams connecting to the unit is unimportant. The user may connect the streams to any position on the unit.
  • When inserting a Reverse Osmosis unit into a flowsheet, the user may choose a different symbol from the menu.

Inputs and Outputs

Label Required
Optional
Input
Output
Number of Connections Description
Min Max.
Feed Required In 1 20 Inlet liquid feed stream to the unit, usually water with dissolved salts.
Product Required Out 1 1 Outlet product stream of the unit, usually purified water.
Brine Required Out 1 1 Outlet brine or waste stream of the unit.
Vent Optional Out 0 1 Optional gas outlet from the unit.

Behaviour when Model is OFF

If the user disables the unit, by un-ticking the On tick box, then the following actions occur:

  • All feed material will flow straight out of the Brine outlet;
  • No material will flow out of the Product or Vent outlets;
  • No sub-models will be called.

So basically, the unit will be 'bypassed' without the user having to change any connections.

Data Sections

The default access window consists of several sections:

  1. ReverseOsmosis - The first tab contains general information relating to the unit and allows the user to configure the unit
  2. PC - Optional tab, only visible if EB.Solubility.On and/or EB.PhaseChange@T.On is enabled on the first tab.
  3. RB - Optional tab, only visible if Reactions are enabled in the Evaluation Block.
  4. EHX - Optional tab, only visible if EnvironHX is enabled in the Evaluation Block.
  5. Evap - Optional tab, only visible if Evaporator is enabled in the Evaluation Block.
  6. MU - Optional tab, or multiple tabs if more than one Makeup is selected. Only visible if one of more Makeups are enabled in the Evaluation Block.
  7. Info tab - contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  8. Links tab, contains a summary table for all the input and output streams.
  9. Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

ReverseOsmosis

Unit Type: ReverseOsmosis - The first tab page in the access window will have this name.

Symbol / Tag
Input / Calc
Description
Common First Data Section
Requirements
On Tickbox This variable in used to turn the unit ON or OFF. If the unit is OFF, all feed will exit via the Brine outlet.
Model Simple User only needs to specify Yield and Overall efficiency. No setting of pressures. No sub-models can be used.
General User can choose from several efficiency methods and specify the outlet pressures. Sub-models can be used.
YieldReqd Input Required fraction of pure water in the feed which is recovered to the product stream.
EffMethod Only visible if Model selected is General
Overall User can specify a single efficiency of removal for all non-water liquid species.
Individual Phase User can specify an efficiency of removal for each individual liquid phase.
Impurity Frac User can specify the fraction of impurities in the product stream.
EfficiencyReqd Input Only available if Model is set to Simple, or with General Model, EffMethod is set to Overall. Required fraction of liquid species other than water that are recovered to the brine stream.
EfficiencyReqd.x Input Only available if EffMethod is set to Individual Phase. Required fraction of species in individual phase x (other than water) that are recovered to the brine stream.
ImpurityFracReqd / ImpFracReqd Input Only available if EffMethod is set to Impurity Frac. Required fraction of liquid species other than water in the product stream.
Pressure Requirements (Only visible if Model selected is General)
Prod.PressureReqd / P_Reqd Input Required pressure of the product stream.
Brine.PressDropReqd / PDropReqd Input Required pressure drop from the feed pressure to the brine stream.
OperatingP...
Method AutoDetect If there are any liquids AND no gases present in the feed, the unit pressure will be the highest pressure of the feeds. Else if there are Gases in any of the feed streams, the unit pressure will be the lowest pressure of the feeds.
LowestFeed The unit pressure will be the Lowest Feed pressure.
HighestFeed The unit pressure will be the Highest Feed pressure.
Atmospheric The unit will be at Atmospheric Pressure. The atmospheric pressure is calculated by SysCAD based on the user defined elevation (default elevation is at sea level = 101.325 kPa). The elevation can be changed on the Environment Tab page of the Plant Model.
RequiredP The unit pressure is specified by the user.
IgnoreLowMassFlow / IgnoreLowQm Tickbox This option is only visible if the AutoDetect, LowestFeed or HighestFeed methods are chosen. When calculating the unit pressure, SysCAD will ignore the low flow feed streams should this option be selected. The low flow limit is set in the field below.
LowMassFlowFrac / LowQmFrac Input This field is only visible if the IgnoreLowQm option is selected. This is the amount any stream contributes to the total flow. For example, if the total feed to the unit is 10 kg/s, and this field is set to 1%. Then any feed streams with less than 0.1 kg/s will be ignored in the pressure calculations.
PressureReqd / P_Reqd Input This field is only visible if the RequiredP method is chosen. The user enters the required operating pressure.
Result Calc This field displays the operating pressure of the unit.
EB... (Flow Evaluation Block) (Only visible if Model selected is General)
Solubility.On Tickbox Allows the user to switch on any predefined solubility curve to adjust the composition of material in the unit.
PhaseChange@T.On Tickbox Only visible if Phase Change at Temperature has been defined for at least one species in the project. Allows the user to switch on any predefined phase changes at temperature in the unit.
EvalSequence Display The sequence in which the sub models (which are part of the evaluation blocks) will be calculated. The sequence is determined by the priority selection for the individual sub-models.
Note: If the user chooses On-AutoSequence then SysCAD will determine the sequence of the sub-models. The sequence followed will be MU1, MU2, etc., RB, EHX, Evap.
Makeups Input The number of makeup blocks required. Extra dropdown options Makeup1, Makeup2, etc will be added to allow these to be switched on and off and prioritised in relation to the other sub-models.
MakeupX List This can be used to switch the Makeup Block (MU) on or off and prioritise it in relation to the other sub-models. If this is 'On' then the associated page, MUX becomes visible and may be configured.
Note: This field is only visible if the entry for 'Makeups' is greater than 0. If there is one makeup then X=1. If there are two makeups, then X=1 and X=2, etc.
Reactions List This can be used to switch on the Reaction Block (RB). If this is 'On' then the associated page, RB becomes visible and may be configured.
Note: The user does not have to configure a reaction file, even if this block is checked.
EnvironHX List This can be used to switch on the Environmental Heat Exchanger (EHX). If this is 'On' then the associated page, EHX becomes visible and may be configured.
Note: The user does not have to configure an environmental heat exchange, even if this block is checked.
Evaporation List This can be used to switch on the Evaporation Block (Evap). If this is 'On' then the associated page, Evap becomes visible and may be configured.
Note: The user does not have to configure an evaporator, even if this block is checked.
Residence Time
ResTime...
Calc Tickbox Allows the user to specify the volume of the unit, from which a residence time can be calculated.
Volume Input Only visible if the Calc option has been enabled. The operating volume of the unit. This will be used to calculate the apparent residence time in the unit. This is based on the volumetric flow of all outlets from the unit.
MassFlow / Qm Calc Only visible if the Calc option has been enabled. The mass flow of material from the unit.
Temperature / T Calc Only visible if the Calc option has been enabled. The temperature of the material leaving the unit.
Slurry Calc Only visible if the Calc option has been enabled. The residence time of the slurry in the unit.
Total Calc Only visible if the Calc option has been enabled. The residence time for the slurry and the vapours in the unit. If there are any vapours leaving the unit, then this value will be smaller than the Slurry figure.
Options
ShowQFeed Tick Box QFeed and associated tab pages (eg. Sp) will become visible, showing the properties of the combined feed stream. See Material Flow Section. This will be prior to any sub-model (eg reactions) actions.
TrackStatus Tick Box If this box is checked, the unit will flag warnings if gases are present but no vent connected, or if solids are present.
Separation Results
Yield Calc Fraction of pure water in the feed which is recovered to the product stream.
Efficiency Calc Fraction of liquid species other than water that are recovered to the brine stream.
Brine.PressDrop / PDrop Calc Pressure drop from the feed pressure to the brine stream.
Product
Prod.MassFlow Calc Total mass flow of the product stream.
Prod.WaterMassFlow Calc Mass flow of pure water in the product stream.
Prod.AqueousMassFlow Calc Mass flow of aqueous species in the product stream.
Prod.ImpurityFrac Calc Fraction of liquid species other than water in the product stream.
Prod.ImpurityConc Calc Concentration of liquid species other than water in the product stream.
Prod.VolFlow Calc Total volume flow of the product stream.
Prod.SolidMassFlow Calc Mass flow of solids in the product stream.
Prod.LiquidMassFlow Calc Mass flow of liquids in the product stream.
Prod.SolidFrac Calc Mass fraction of solids in the product stream.
Prod.LiquidFrac Calc Mass fraction of liquids in the product stream.
Prod.Temperature Calc Temperature of the product stream.
Prod.Pressure Calc Pressure of the product stream.
Prod.Density Calc Density of the product stream.
Brine
Brine.MassFlow Calc Total mass flow of the brine stream.
Brine.WaterMassFlow Calc Mass flow of pure water in the brine stream.
Brine.AqueousMassFlow Calc Mass flow of aqueous species in the brine stream.
Brine.ImpurityFrac Calc Fraction of liquid species other than water in the brine stream.
Brine.ImpurityConc Calc Concentration of liquid species other than water in the brine stream.
Brine.VolFlow Calc Total volume flow of the brine stream.
Brine.SolidMassFlow Calc Mass flow of solids in the brine stream.
Brine.LiquidMassFlow Calc Mass flow of liquids in the brine stream.
Brine.SolidFrac Calc Mass fraction of solids in the brine stream.
Brine.LiquidFrac Calc Mass fraction of liquids in the brine stream.
Brine.Temperature Calc Temperature of the brine stream.
Brine.Pressure Calc Pressure of the brine stream.
Brine.Density Calc Density of the brine stream.
GridDisplay Tickbox Toggles between showing the product and brine stream results in a grid (table) format or in a list. This is a global selection that will affect the display of results in other access windows.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

  DLL: Separation.dll Units/Links Separation: Reverse Osmosis
or Group: Mass Separation Units/Links Separation: Reverse Osmosis

See Project Configuration for more information on adding models to the configuration file.


Insert into Project

  Insert Unit Separation Reverse Osmosis

See Insert Unit for general information on inserting units.