Evaporative Dryer

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Navigation: Models ➔ Energy Transfer Models ➔ Evaporative Dryer


General Description

The Evaporative Dryer is used to remove the water from the solids in the feed stream. The model will use the user defined moisture remaining in the cake to calculate the amount of water to be evaporated off. Any liquid impurities will remain in the cake moisture. The unit also allows for some solids loss with the evaporated moisture.

NOTES:

  1. This model assumes that the energy required for the drying and evaporation of water is supplied by an EXTERNAL source, therefore the user does not have to supply a heating stream, such as hot gas.
  2. The feed to the model is normally a slurry stream, with minimal vapours.
  3. In Build 138 or earlier, the model assumes that the cake has a minimum of at least 0.1% moisture.
  4. The model is intended for water only in product. All aqueous species in the feed should be converted to solids in the Reaction Block (user needs to define).

Diagram

Evaporative-Dryer-Image001.gif

The diagram shows the default drawing of the Evaporative Dryer, with all of the streams that are required for operation of the unit.

The physical location of the streams connecting to the dryer is unimportant. The user may connect the streams to any position on the unit.

Inputs and Outputs

Label Required
Optional
Input
Output
Number of Connections Description
Min Max.
Feed 1 Required In 1 20 The feed to the Evaporative Dryer
Moisture/Vapour Required Out 1 1 The evaporated moisture outlet from the unit
Cake Required Out 1 1 The Solids 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 streams connected to the 'Feed' inlet will flow out of the 'Dried Solids' outlet, with no change in temperature or composition;
  • No heating will occur and no water will be evaporated;

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

Model Theory

The Evaporative Dryer is based on the user-defined variables of cake moisture content and solids loss. Any impurities within the liquid feed to the unit will remain in the cake moisture, i.e. only the water will be evaporated from the cake.

Assumptions

  • Only water is evaporated from the feed stream. All other liquid impurities remain in the cake moisture.
  • The only liquid species expected to be in the final cake is Water. All aqueous species in the feed should be converted to solids in the Reaction Block (user needs to define), otherwise the final cake moisture requirement may not be achieved.
  • In Build 138 or earlier, the final dryer cake contains between 0.1 and 99% moisture, i.e. not all of the water is evaporated
  • In Build 139 or later, the final dryer cake contains between 0 and 99% moisture, i.e. all of the water can be evaporated
  • Energy is supplied by an EXTERNAL source.

Flowchart

The following shows the sequence of events if sub model options are switched on. See next heading for more information.

Evaporative-Dryer-Image002.gif

Data Sections

The default access window consists of several sections,

  1. Dryer tab - Contains general information relating to the unit.
  2. RB - Optional tab, only visible if the Reactions are enabled in the Evaluation Block.
  3. QFeed - Only available in Build 139 or later. Optional tab, only visible if ShowQFeed is enabled. This page shows the properties of the mixed stream as the feed to the dryer.
  4. QCake - Only available in Build 139 or later. Optional tab, only visible if ShowQCake is enabled. This page shows the properties of the final Cake stream.
  5. QVapour - Only available in Build 139 or later. Optional tab, only visible if ShowQVapour is enabled. This page shows the properties of the final Vapour stream.
  6. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  7. Links tab, contains a summary table for all the input and output streams.
  8. Audit tab - Contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.

Evaporative Dryer Page

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

Tag (Long/Short) Input / Calc Description/Calculated Variables / Options
Tag Display This name tag may be modified with the change tag option.
Condition Display OK if no errors/warnings, otherwise lists errors/warnings.
ConditionCount Display The current number of errors/warnings. If condition is OK, returns 0.
GeneralDescription / GenDesc Display This is an automatically generated description for the unit. If the user has entered text in the 'EqpDesc' field on the Info tab (see below), this will be displayed here.
If this field is blank, then SysCAD will display the unit class ID.

Requirements

On Tick Box This allows the user to switch the model on or off. All feed reports to cake.
UseOriginalMethod Tick Box Only available in Build 139 or later. If enabled, model will behave the same in current Build as it did in Build 138 or earlier. This is for backward compatibility and it is recommended that this option be disabled to enable new functionality to be used.
TemperatureReqd / T_Reqd Input The required temperature of the dryer. Both the dryer cake and the moisture streams will exit the unit at this temperature.
SolidsLossMethod
(Only available in Build 139 or later, with UseOriginalMethod disabled)
Solids Loss The user can specify the fraction of solids that will be sent to the Vapour stream. This will be calculated after reactions have occurred.
Vapour Solids Frac The user can specify the target fraction of solids in the Vapour stream.
Vapour Solids Conc The user can specify the target concentration of solids in the Vapour stream.
Vapour Cake Frac The user can specify the fraction of the final cake (solids and liquids) in the Vapour stream.
Vapour Cake Conc The user can specify the concentration of the final cake (solids and liquids) in the Vapour stream.
SolidsLossReqd Input The required fraction of solids that will be lost with the evaporated moisture (to the Vapour stream). This will be calculated after reactions have occurred. If SolidsLossMethod is displayed, then this field will only be shown if SolidsLossMethod = Solids Loss.
Vapour.SolidFracReqd Input Only available if SolidsLossMethod = Vapour Solids Frac. The required fraction of solids in the final Vapour stream.
Vapour.SolidConcReqd Input Only available if SolidsLossMethod = Vapour Solids Conc. The required concentration of solids in the final Vapour stream.
Vapour.CakeFracReqd Input Only available if SolidsLossMethod = Vapour Cake Frac. The required fraction of cake (solids and liquids) in the final Vapour stream.
Vapour.CakeConcReqd Input Only available if SolidsLossMethod = Vapour Cake Conc. The required concentration of cake (solids and liquids) in the final Vapour stream.
Cake.MoistureMethod
(Only available in Build 139 or later, with UseOriginalMethod disabled)
Water In Cake The user can specify the target fraction of water in the cake. The model will try to achieve this by evaporating water.
Liquor In Cake The user can specify the target fraction of liquid in the cake. The model will try to achieve this by evaporating water. This may not be achievable if there are liquids other than water present in the final cake.
CakeMoistReqd / Cake.H2OFracReqd Input The required water content of the final dryer cake. If Cake.MoistureMethod is displayed, then this field will only be shown if Cake.MoistureMethod = Water In Cake.
Cake.LiquidFracReqd Input Only available if Cake.MoistureMethod = Liquor In Cake. The required liquid content of the final dryer cake.
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.
OperatingP - NOTE: this pressure is applied to the (combined) feed, before sub-models (if any).
Method AutoDetect If there are any liquids AND no vapours present in the feed, outlet streams will take the highest pressure of the feeds. Else (eg. some vapours present) outlet streams will take the lowest pressure of the feeds.
LowestFeed Outlet streams will take the lowest pressure of the feeds.
HighestFeed Outlet streams will take the highest pressure of the feeds.
Atmospheric Outlet streams 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 Outlet streams will be at the user specified pressure.
IgnoreLowMassFlow / IgnoreLowQm Tick Box This option is only visible if the AutoDetect, LowestFeed or HighestFeed methods are chosen. When calculating the outlet pressure and temperature of the tank, 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 tank 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. This is user specified pressure.
Result Calc The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure).

Options

TrackAqueous Tick Box Only available in Build 139 or later. Allows warning messages be displayed if there are aqueous species in the product streams other than H2O.
ShowQFeed Tick Box Only available in Build 139 or later. QFeed and associated tab pages (eg. Sp) will become visible, showing the properties of the combined feed stream. See QFeed. This will be prior to any reactions occurring.
ShowQCake Tick Box Only available in Build 139 or later. QCake and associated tab pages (eg. Sp) will become visible, showing the properties of the final Cake stream. See QCake.
ShowQVapour Tick Box Only available in Build 139 or later. QVapour and associated tab pages (eg. Sp) will become visible, showing the properties of the final Vapour stream. See QVapour.

Results

Feed.MassFlow / Qm Calc Only available in Build 139 or later. The total mass flow of the feed to the unit.
Temperature / T Calc Only available in Build 139 or later. The temperature of the streams leaving the unit. This should be equal to T_Reqd.
SolidsLoss Calc Only available in Build 139 or later. The calculated fraction of the solids which is lost to the vapour stream. This should be equal to SolidsLoss_Reqd.
CakeMoist Calc Only available in Build 138 or earlier. The calculated cake moisture (includes water and other liquid species) in the final dryer cake.
Cake.SolidFrac / Sf Calc Only available in Build 139 or later. The calculated fraction of solids in the final dryer cake.
Cake.LiquidFrac / Lf Calc The calculated fraction of liquids (includes water and other liquid species) in the final dryer cake.
Cake.WaterFrac Calc The calculated fraction of water (excluding any other liquid species) in the final dryer cake.
Vapour.SolidFrac / Sf Calc Only available in Build 139 or later. The calculated fraction of solids in the vapour stream.
Vapour.SolidConc Calc Only available in Build 139 or later. The calculated concentration of solids in the vapour stream.
Vapour.MassFlow / Qm Calc Only available in Build 139 or later. The total mass flow of the vapour stream.
Vapour.SteamMassFlow / SteamQm Calc Only available in Build 139 or later. The mass flow of steam in the vapour stream.
WaterEvaporated Calc The amount of water evaporated.
RctHXReqd / Power.RB Calc In Build 138 or earlier, only visible if Reactions are enabled in the unit. The energy required to added or removed to the reaction block via one of the heat exchange options.
EnergyReqd / Power.Evap Calc The energy required to evaporate the water and heat both product streams to the final dryer temperature, after reactions (including any heat exchange) have occurred.
TotalEnergyReqd / Power.TotalReqd Calc The total energy required to evaporate the water and heat both product streams to the final dryer temperature. This will include any heat exchange required as part of the reaction block. It is the sum of the two previous fields.
The unit assumes that all of this energy is supplied by an EXTERNAL energy source.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

  DLL:
HeatExchange.dll
Units/Links Heat Transfer: Evaporative Dryer
DLL:(Build138 or earlier)
Separ1.dll
Units/Links Separation: Evaporative Dryer
or Group:
Energy Transfer
Units/Links Heat Transfer: Evaporative Dryer
Group:(Build138 or earlier)
Mass Separation
Units/Links Separation: Evaporative Dryer

See Model Selection for more information on adding models to the configuration file.


Insert into Project

  Insert Unit Heat Transfer Evaporative Dryer
Insert Unit (Build138 or earlier) Separation Evaporative Dryer

See Insert Unit for general information on inserting units.

Example Project

Copper Flash Furnace Example