Evaporative Dryer

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Navigation: Main Page -> Models -> Mass Separation Models


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. The model assumes that the cake has a minimum of at least 0.1% moisture.

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

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 final dryer cake contains between 0.1 and 99% moisture, i.e. not all of the liquid is 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. Info tab - Contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
  4. Links tab, contains a summary table for all the input and output streams.
  5. 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
Common Data on First Tab Page

Requirements

On Tick Box This allows the user to switch the model on or off. All feed reports to cake.
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.
SolidsLossReqd Input The fraction of feed solids that will be lost with the evaporated moisture.
CakeMoistReqd Input The required moisture 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...
Method 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 Species tab page of the Plant Model.
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.
RequiredP outlet streams will be at the user specified pressure.
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.
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 Display The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure).

Results

CakeMoist Calc The calculated fraction of liquids in the final dryer cake.
WaterEvaporated Calc The amount of water evaporated.
EnergyReqd 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.
RctHXReqd Calc 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.
TotalEnergyReqd 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:

Separ1.dll

Units/Links

Separation: Evaporative Dryer

OR

Group:

Mass Separation

Units/Links

Separation : Evaporative Dryer

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

Insert into Project

 

Insert Unit

Separation

Evaporative Dryer

See Insert Unit for general information on inserting units.