Batch Centrifuge

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Navigation: Models -> Mass Separation Models


General Description

The Batch Centrifuge is used to separate the solids from the liquids in the feed stream. The user may connect one or two wash streams to the Batch Centrifuge. These streams will displace a calculated amount of feed liquid from the cake, based on flows and the user-defined wash efficiency.

The model is designed so that it may simulate the following batch operation:

  1. The feed slurry is fed to the unit until the solids load reaches a predetermined point, and the feed is then stopped.
  2. The cake is washed, with either one or two washes.
  3. The washings stream, or streams, from the Batch Centrifuge may be handled as follows:
    • They may be combined with the filtrate;
    • They may be removed in a single stream; or
    • They may be removed individually from the unit.
    In Steady State mode the model determines how the washings are removed based on the streams that are connected to the unit.
  4. The cake is then removed and the slurry feed is restarted.

The model allows reactions to be specified via a reaction file. The reactions occur before the separation takes place and any solids generated by the reaction(s) are included in the separation calculations.

The user may also specify an environmental heat loss from the Batch Centrifuge. The temperature of the solids and liquids is calculated after any reactions and/or heat loss has occurred.

Diagram

BatchCentrifuge.png

The diagram shows the default drawing of the Batch Centrifuge, with all of the streams that can be connected to the unit.

Both the Wash Water streams and the Washing Streams are Optional.

The physical location of the streams connecting to the unit 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 slurry feed to the Batch Centrifuge
Wash Water 1 Optional In 0 1 The first wash stream
Wash Water 2 Optional In 0 1 The second wash stream
Filtrate 1 Required Out 1 1 The Filtrate from the unit.
Cake 1 Required Out 1 1 The solid discharge from the unit.
Wash 1 Optional Out 0 1 The first washing stream from the unit. If this connection is not present, the washings 1 will be added to Filtrate.
Wash 2 Optional Out 0 1 The second washing stream from the unit. If this connection is not present, the washings 2 will be added to Filtrate.
Vent Optional Out 0 1 Vent Stream (Vapour only).

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 'Cake' outlet;
  • All streams connected to the 'Wash Water' inlets will flow straight out of the 'Filtrate' outlet;
  • No mixing will occur.

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


Model Theory

The Batch Centrifuge operates simply as a solids / liquids separation unit with the added facility of up to two cake washes. See Example for the illustration of material splits with the various connections.


Flowchart

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

BatchCentrifugeFlowchart.png

Data Sections

  1. BatchCentrifuge tab - This first tab contains general information relating to the unit.
  2. PC - Optional tab that is visible if EB.Solubility.On is enabled on the first tab. (Available from SysCAD 9.3 Build137.21979 and later.)
  3. MU - Optional tab, or multiple tabs if more than 1 Makeup is selected. Only visible if one of more Makeup is enabled in the Evaluation Block. (Available from SysCAD 9.3 Build137.21979 and later.)
  4. RB - Optional tab, only visible if the Reactions are enabled.
  5. EHX - Optional tab, only visible if the EnvironHX is enabled.
  6. Evap - Optional tab that is visible if Evaporator is enabled. (Available from SysCAD 9.3 Build137.21979 and later.)
  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.


Batch Centrifuge Page

Unit Type: BatchCentrifuge - 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 Tickbox Switch the model on or off. If the unit is 'Off' then the Feed reports to cake solids outlet and all wash streams report to filtrate.
SolidsToFiltrate Input The required solids loss to the liquid stream(s) as a fraction of the feed solids. (This will not take into account any solids from the wash streams.)
CakeMoistureReqd / CakeMoistReqd Input The required fraction of liquid in the cake.
WashEfficiencyReqd / WashEffReqd Input The efficiency of washing. This is the mass fraction of the liquor in the cake displaced by the wash.
Reactions List Only visible in earlier builds of SysCAD. In the latest build of SysCAD, this has been moved to the EB (Evaluation Block group).
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.
EnvironHX List Only visible in earlier builds of SysCAD. In the latest build of SysCAD, this has been moved to the EB (Evaluation Block group).
This can be used to switch on Environmental Heat Exchanger (EHX). If this is 'On' then the associated page, EHX may become visible and may be configured.
OperatingP...
Method Atmospheric The unit will operate at Atmospheric pressure. All of the outlet streams will be at this 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 The unit will operate at the lowest pressure of the feeds. All of the outlet streams will be at this pressure.
HighestFeed The unit will operate at the highest pressure of the feeds. All of the outlet streams will be at this pressure.
RequiredP The unit will operate at the user specified pressure. All of the outlet streams will be at this 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).

EB (Flow Evaluation Block)

The Evaluation Block section is only available from SysCAD 9.3 Build137.21979 onwards.

Solubility.On Tickbox Allows the user to switch on any predefined solubility curve to adjust the composition of material in the unit. This sub model has been added to this unit operation in Build137.

.

EvalSequence Calc 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, VLE.
Makeups Input The number of makeup blocks required. Extra dropdown options Makeup1, Makeup2, etc will be added to allow these to be switched on. This sub model has been added to this unit operation in Build137.
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. This sub model has been added to this unit operation in Build137.

Options

TrackStatus Tick Box Allows warning messages be displayed if requirements are not met. For example, if there are solids present in the wash water, then the SolidsToFiltrate requirements may not be met. See Hints and Comments below.

Results

Cake.LiquidFrac / Cake.Lf Calc The cake moisture content.
Cake.SolidFrac / Cake.Sf Calc The cake percent solids.
Filtrate.SolidFrac / Filtrate.Sf Calc The percent solids in the filtrate.
Filtrate.SolidConc25 Calc The filtrate solids concentration measured at 25°C.
Filtrate.SolidConc Calc The filtrate solids concentration measured at Temperature.
WashComponent / WashComp Input Choose Component/species from the drop down list for the calculation of Wash efficiency on a concentration base. (OPTIONAL)
CompWashEfficiency1 / CompWashEff1 Calc The calculated wash efficiency of the unit based on concentration.
WashEff = (Conc Feed -- Conc Cake post wash 1) / (Conc Feed -- Conc wash1)
CompWashEfficiency1 / CompWashEff2 Calc The calculated wash efficiency of the unit based on concentration.
WashEff = (Conc Feed -- Conc Cake post wash 2) / (Conc Feed -- Conc wash2)

Example

FEED AND CENTRIFUGAL SETTINGS
Feed Solids Flow Feed Liquids Flow Required Solids Loss Required Cake Moisture Wash Efficiency
10 t/h 20 t/h 1% 10% 90%


CONNECTION OPTIONS AND RESULTS
OPTIONS CONNECTION DETAIL Wash Water RESULTS
No Washing Feed, Filtrate, Cake None Cake
Filtrate
9.9tph solids 1.1tph feed liquids
0.1tph solids 18.9tph feed liquids
Single wash,
combined wash and filtrate take-off
Feed, Wash water 1,
Filtrate, Cake
Wash Water 1 = 2tph Cake
Filtrate
9.9tph solids, 0.11tph feed liquids, 0.99tph wash1 liquids
0.1tph solids, 19.89tph feed liquids, 1.01tph wash1 liquids
Single wash,
Separate washing take-off
Feed, Wash water 1,
Filtrate, Cake, Wash 1
Wash Water 1 = 2tph Cake
Filtrate
Wash 1
9.9tph solids, 0.11tph feed liquids, 0.99tph wash1 liquids
0.09tph solids, 18.9tph feed liquids
0.01tph solids, 0.99tph feed liquid, 1.01tph wash1 liquids
Two washes,
Single washing take-off
Feed, Wash water 1, Wash water 2,
Filtrate, Cake, Wash 1
Wash Water 1 = 2tph
Wash Water 2 = 2tph
Cake
Filtrate
Wash 1
9.9tph solids, 0.01tph feed liquids, 0.1tph wash1 liquids, 0.99tph wash2 liquids
0.083tph solids, 18.9tph feed liquids
0.017tph solids, 1.09tph feed liquid, 1.9tph wash1 liquids, 1.01tph wash2 liquids
Two washes,
Two washing take-off streams
Feed, Wash water 1, Wash water 2,
Filtrate, Cake, Wash 1, Wash 2
Wash Water 1 = 2tph
Wash Water 2 = 2tph
Cake
Filtrate
Wash 1
Wash 2
9.9tph solids, 0.01tph feed liquids, 0.1tph wash1 liquids, 0.99tph wash2 liquids
0.082tph solids, 18.9tph feed liquids
0.009tph solids, 0.99tph feed liquid, 1.01tph wash1 liquids
0.009tph solids, 0.1tph feed liquid, 0.89tph wash1 liquids, 1.01tph wash2 liquids

Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 

DLL: (prior to Build137.21979)

Separ1.dll

Units/Links

Separation: Centrifuge - Batch Centrifuge

 

DLL: (Latest build)

Separation.dll

Units/Links

Separation: Centrifuge - Batch Centrifuge

OR

Group:

Mass Separation

Units/Links

Separation : Centrifuge - Batch Centrifuge

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

Insert into Project

 

Insert Unit

Separation

Centrifuge - Batch Centrifuge

See Insert Unit for general information on inserting units.

Hints and Comments

  1. There may be mass entering or leaving the unit via the Reaction Block source or sink, so if the outgoing mass is not the same as the incoming mass, this may be a place to check first.
  2. SysCAD assumes NO solids are present in the wash water. Any solids in the wash water will not be used in the calculations and will be reported directly to the Cake.
  3. The Scandrett efficiency is only a displayed variable in this model. Users requiring certain Scandrett efficiency can control the wash efficiency to obtain the desired results.
  4. This model has been revised in Build137.21979. It has been moved from Separ1.dll to Separation.dll. More evaluation blocks were implemented (to feed stream only, excluding wash streams).