Evaporative Dryer

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

Diagram

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.

Flowchart

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

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

Class: Dryer The first tab page in the access window will have this name.

Tag (Long/Short)	Input / Calc	Description/Calculated Variables / Options
Common First Data Section
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.

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

	DLL:	Separ1.dll	→	Units/Links	→	Separation: Dryer
OR	Group:	Mass Separation	→	Units/Links	→	Separation : Dryer

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

Insert into Project

Insert Unit

→

Separation

→

Dryer

See Insert Unit for general information on inserting units.