Sugar Fugal 2

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Latest SysCAD Version: 16 February 2024 - SysCAD 9.3 Build 139.34893


General Description

The Sugar Fugal2 unit operation is available with the Sugar add-on.

The Sugar Fugal2 is a type of centrifuge used to separate and wash molasses from sugar crystals. Massecuite is loaded into a porous walled basket in the fugal which is then spun at high speeds. The sugar crystals are retained in the basket and centrifugal force pulls the molasses out of the sugar crystals and through the basket walls where it is collected and removed. Water sprays may be used to wash further molasses from the sugar crystals during the process. Some sugar crystal may be dissolved by the wash water during this stage of the operation. The sugar is then plowed out of (removed from) the basket leaving a small fraction of the sugar on the walls. A basket wash spray is used to dissolve this remaining sugar and the the cycle is then repeated. The purged molasses, washings and basket washings may be collected into a single stream leaving the fugal or they may be split into a high and low purity stream leaving the fugal.

In reality a Sugar Fugal2 is a batch device. However, the cycle times are generally short (typically about 200 seconds) so the fugal may be approximated as a continuous operation for steady state modeling purposes.

The incoming feed to the fugal is a slurry of sugar crystals and mother molasses. The sugar crystal is assumed to be pure sucrose and all of the impurities are assumed to be in the molasses. The molasses is an aqueous mixture of water, sucrose and impurities. As molasses is removed from the cake, the massecuite purity of the cake increases. The purity of the cake is a measure of how much of the mother molasses has been removed from the cake. The purity of the molasses may also increase if sugar crystal is dissolved during the wash stage.

The Sugar Fugal2 process is described by the following steps;

Purge Molasses is removed by centrifugal force in the purge step. In this stage only molasses is removed and all crystal is assumed to remain in the basket along with some fraction of the mother molasses. The massecuite purity of the cake remaining in the basket (sugar crystals and retained molasses) rises as impurities are removed with the molasses. The amount of molasses retained with the cake determines the massecuite purity (NB the measure of cake purity is always the massecuite purity).

Wash An Optional Wash Stage is used to remove more of the impurities. In this stage wash water is sprayed onto the cake. Some of the molasses is removed by centrifugal force and some of the molasses is removed through displacement by the wash water. Some of the wash water may bypass through the cake with little interaction, some of the wash water may be retained in the cake and some of the wash wash water may dissolve some sugar crystals in the cake as it passes through.

The fraction of the impurities remaining in the cake are determined by specifying either (1) the cake purity rise or (2) the target cake purity.

The extent of dissolution of sugar crystals is determined by specifying either (1) the purity rise in the molasses or (2) the dry substance loss ratio. The dry substance loss is the ratio of dry substance in the fugal feed lost to the washings per mass of wash water. The solids loss includes some of the impurities and sucrose from the mother molasses and potentially some dissolved crystal.

The amount of water in remaining in the cake is specified as the moisture content which is the mass fraction of water in the cake after the wash stage.

When no wash is connected, there is no wash action and this step is skipped.

Basket Wash A user specified fraction of the feed sucrose crystal mass is assumed to remain in the basket after plow out. A fraction of the washed crystal and cake molasses mixture from the wash stage is retained in the basket to give the required crystal mass. The rest of the washed crystal/molasses mixture leaves the unit as product sugar. Basket wash water is sprayed onto the basket to dissolve the remaining sugar and the wash water sugar solution leaves as basket washings. The solubility of sucrose in the wash water is calculated. Generally the extent of dissolution should be 100% and all sucrose dissolved. However, if there is insufficient wash water or if the wash water is too cold, sugar will only dissolve to the limit of solubility. If this happens the basket washings will contain some sucrose crystal and a warning will be displayed.

Sugar Outlet Connection A sugar crystal product stream is always required for the washed sugar crystals.

Molasses Outlet Connections There are two outlet connection configurations for the molasses and washings from the fugal. The molasses, washings and basket wash streams may be sent out as a single combined stream of molasses or they may be split between a low purity and a high purity molasses outlet stream (for example purge molasses goes to a low purity outlet stream and washings and basket washings to a high purity outlet stream). In the model, a low purity connection is always required and the high purity stream is optional.

Molasses Split When there are two molasses outlet connections, the fraction of each stream (purge, washings and basket wash) to each connection may be specified. This option allows control over the sharpness of the cut between the outlet streams. This accounts for the fact that there is always some material retained in the trough and some mixing between the streams from the various stages of the process. In the model this is specified by the separation efficiency. For example, if the separation efficiency for the purge stream is 90%, then 90% of the purge flow will go to the low purity outlet connection and 10% will go to the high purity outlet connection.

Vapours Any vapours in the input streams are sent to the vent stream - a warning is displayed if there are vapours in any of the input streams or if there is evaporation and there is no vent connected.

Pressure The exit pressure of all streams is atmospheric pressure (NB the atmospheric pressure that is specified in the project - see Plant_Model#Environment_Tab).

Heat Loss The Sugar Fugal2 model includes optional heat loss to the environment. There are two different heat loss models available. The wash water is typically hotter than the massecuite and is sprayed onto the sugar. The environmental heat loss is taken from the wash water before it mixes with the massecuite. The total heat loss is calculated and then taken proportionally from the wash water streams based on their relative mass flows.

Evaporation The Sugar Fugal2 also includes the option to specify an evaporation rate from the wash water. The overall evaporation rate is taken from the individual wash water streams in proportion to relative mass flow. Heat loss and evaporation are included in the energy balance.

Energy The Fugal2 model conserves energy and calculates temperatures after the wash stage and after the basket wash. It is assumed that the cake and the washings are at the same temperature after wash and that the cake and basket washings are at the same temperature after the basket wash. The model allows for evaporation and environmental heat loss which are removed in proportion to mass from the wash and basket wash streams. An energy balance is solved simultaneously for the temperature at each stage taking into account the incoming temperatures of the sugar and wash streams, evaporation, heat loss to the environment and the enthalpy of dissolution for any dissolving sucrose.

Input and Output Connections

A number of the inputs and outputs for the sugar fugal are optional. You connect the ones that you want to use depending on how you want the unit to operate. NB it is possible to have some of the output connections in place and direct the flows elsewhere so that they are effectively unused.

Label Required / Optional Input /Output Number of Connections Description
      Min Max  
FugalFeed Required In 1 5 Massecuite Feed to the Fugal.
WashWater1 Optional In 0 5 Wash Water for Wash Stage.
BasketWash Optional In 0 5 Wash Water for Basket Wash Stage.
LowPurityMol Required Out 1 1 Lower Purity Molasses from Fugal.
HiPurityMol Optional Out 0 1 Higher Purity Molasses from the Fugal.
Sugar Required Out 1 1 Purged and Washed Sucrose Crystal.
Vent Optional Out 0 1 Vent outlet containing all Vapours - NB required if there are vapours present.

Behaviour when Model is OFF

The sugar fugal may be turned Off by deselecting the On tick box in the access window. When the unit is off the following behavior occurs:

  • If the unit has a valid feed stream (some mass flow and sucrose crystals present), then all material will flow through to the Product Sugar Stream with no changes or heat exchange.
  • If the feed stream is not valid (no mass flow or no sugar crystals), then all material will flow through to the Low Purity (Purge) Molasses stream with no changes or heat exchange.

NB any gases in either feed or wash water streams will remain with those streams when the unit is off.

Model Theory

The purge, wash, plow out and basket wash stages occur in sequence.

The feed massecuite to the fugal is a mixture of pure sucrose crystal plus mother molasses. Mother molasses is a mixture of aqueous sucrose, impurities and water. The impurities include all solutes that are not sucrose.

During the purge step molasses is removed from the feed massecuite until the massecuite remaining in the basket reaches a target purity. The molasses removed during purge is assumed to be the same composition as the mother molasses. There is no crystal lost from the bed in this step.

In the wash step the wash water is assumed to be pure water. In this step some molasses is removed, some sugar crystal may be dissolved by wash water and removed with the washings and some wash water may be retained in the crystal bed. The set points which determine the dissolution of crystal and the split of aqueous sucrose, impurities and water are;

  • The final massecuite purity target - this is specified either directly or by a purity rise from the purge step.
  • Either the feed solids mass loss to washings or the purity rise in the molasses to washings.
  • The moisture content of the cake remaining in the basket.

A set of algebraic equations for the above relations plus conservation of sucrose can be solved to determine the amount of dissolution and the final component masses in the cake and molasses. The temperature of the cake and molasses are assumed to be the same at the end of the wash stage and is calculated from conservation of energy.

After the wash step the cake is plowed out and sent the the final sugar stream. A small fraction of the cake remains in the basket and is washed out separately. The cake solids (crystal, sucrose and impurities) remaining in the basket are specified as a percentage of the feed crystal mass.

During the basket wash water is sprayed into the basket and the crystal in the remaining cake is (or should be) dissolved by the wash water. The saturation coefficient for the basket washings is calculated and the dissolution of crystal in the basket is limited to saturation in basket washings. If there is not adequate capacity to dissolve all of the crystal (insufficient water or temperature) then the undissolved crystal will go out with the washings and a warning will be displayed.

When there is environmental heat loss, the heat loss is removed from the wash water streams before they go into the basket. The heat loss is divided between the streams in proportion to their relative mass flows. Similarly with evaporation, the specified amount of evaporation is divided proportionally between the two wash streams before the wash water enters the basket. Heat loss and evaporation are included in the energy balance.

Data Sections

SugarFugal

Unit Type: SugarFugal - The first tab page in the access window will have this name. User inputs and results are displayed on this page.

In general, the control inputs are defined in terms of parameters that are normally measured in sugar factories.

Tag (Long/Short)
Input / Calc
Description
Common Data on First Tab Page

Requirements

On Tickbox Tickbox used to turn the unit ON or OFF (off behavior is described above).
TrackStatus Tickbox Option to display warnings.

Environmental Heat Loss

Method None No heat exchange with the environment.
FixedLoss User specified heat loss rate.
Ambient Heat loss determined as a constant times temperature difference from ambient. Qloss = ThermalLossAmbient * (Tprod - Tamb)
ThermalLossRqd Input The Required Heat Loss Rate - This is only visible if the FixedLoss Method is selected.
ThermalLossAmbient Input The Heat Loss Rate Constant (kW/K) - This is only visible if the Ambient Method is selected.
EnvHeatLoss Display This field displays heat flow to the environment (positive value is heat flow from Fugalto Environment.).

Evaporation Loss

EvapLossQm Input User specified evaporation rate (set to zero for no evaporation).
EvapHeatLoss Display Heat loss due to evaporation (latent heat of vaporisation).

Molasses Outlet Connections

The following inputs are only visible if both the HighPurity and LowPurity streams are connected.
Set Stage Fractions to High Purity Outlet

PurgeHPMol Input Fraction of Purge Molasses going to high purity outlet connection, balance to low purity molasses connection.
Wash01HPMol Input Fraction of Wash 1 Molasses going to high purity outlet connection, balance to low purity molasses connection.
BsktWashHPMol Input Fraction of Basket Wash Molasses going to high purity outlet connection, balance to low purity molasses connection.

Purity

The second tab page in the access window. Input Parameters, results and calculated data are displayed on this page.

Tag / Symbol
Input / Calc

Purge

CakePurityControl Mass Purity Rise User specified massecuite purity rise.
Target Mass Purity User specified massecuite purity target.
FeedMassPurity Display Massecuite purity of the feed stream.
PurgePurityReq Input Required purity after purging (this controls the amount of molasses that remains in the sugar).
PurgeMassPurity Display Actual purity after purge and before wash.
PurgePurityRiseReq Input Required purity rise of the purge molasses stream.
PurgePurityRise Display Purity rise of the purge molasses stream.
 
FeedMolPurity Display Purity of feed molasses (NB molasses not massecuite).
PurgeMolPurity Display Purity of purged molasses.
PurgeMolSSNCoeff Display Supersaturation coefficient of purged molasses.

Wash control Options

WashCakeControl Mass Purity Rise User specified massecuite purity rise.
Target Mass Purity User Specified massecuite purity.
MolassesControl Mol Purity Rise User specified molasses purity rise.
Solids Loss Ratio User specified molasses final sucrose supersaturation.
WashWaterRatio01 Display The Mass Ratio of Wash Water to feed massecuite (expressed as percent).
WashWater01Brix Display Brix of the Wash Water.
WashWater01Purity Display Purity of the Wash Water.
Wash01PurityIn Display Massecuite Purity into Wash Stage.
Wash01PurityRiseReq Input Target Massecuite Purity Out of Wash Stage 1 (must be > Purity in).
Wash01Purity Display Actual Massecuite Purity out of Wash stage.
Wash01PurRiseReq Input Required Massecuite purity out of Wash stage 1.
Wash01PurityRise Display Massecuite Purity out of Wash stage.
Wash01MoistReqd Display Cake moisture required after wash stage.
Wash01Moist Display Cake moisture after wash stage.
Wash01SolidsFrac Display Mass percentage of sugar crystal in the basket after Wash.
 
Wash01MolPurity Display Molasses Purity into Wash 1.
Wash01MolPurRiseReq Input Molasses Purity Rise Required through Wash Stage 1.
Wash01MolPurityRise Display Molasses Purity rise through Wash Stage 1.
Wash01DStoWWReqd Input The required solids loss ratio for Wash Stage 1.
Wash01DStoWW Display The calculated solids loss ratio for Wash Stage 1.
Wash01XtDissolved Display Mass Percentage of Sugar Crystal dissolved in Wash Stage 1.
Wash01SSN Display Molasses Sucrose Supersaturation out of Wash Stage 1.

Product Crystal

PodMolSSN Display Saturation coefficient of molasses in product cake.

Basket Wash

BsktWWtoMassRatio Display Mass ratio of Basket Wash Water to Feed Mass (expressed as percent).
BsktWashWtrBrix Display Basket Wash Water Brix.
BsktWashWtrPurity Display Basket Wash Water Purity.
BasketLossFrac Input Mass of Solids remaining in Basket after plow out as percent of Feed Crystal Mass.
BasketSolidsLoss Display Mass of Solids remaining in Basket after plow out.
BsktXtDiss Display Mass of sugar dissolved into basket washings NB should be the same as mass of sugar remaining when there is sufficient wash water.
WashingsXt Display Sugar Crystal remaining in basket washings NB a warning will be displayed if there is any crystal in the basket washings.
WashingsPurity Display Purity of the basket washings stream.
WashingsSSN Display Sucrose Supersaturation of basket washings stream.

Data Access Page

Class: Data - The second tab page in the access window will have this name. Results and calculated data are displayed on this page.

Tag / Symbol
Input / Calc

Product Crystal

FeedCrystal Display Mass Flow Rate of Sugar Crystal in Feed.
ProductCrystal Display Mass Flow Rate of Product Crystal.
CrystalDissolved Display Mass Fraction of Crystal Dissolved through Fugal.
ProductPurity Display Product Massecuite Purity.

Wash Water Mass Flows

WashWater01 Display Mass Flow of Wash Water to Wash Stage (before any evaporation).
BasketWash Display Mass Flow of Wash Water to Basket Wash (before any evaporation).

Stage Molasses Mass Flows

These are the properties of molasses from the different internal process stages - some streams may be combined before exiting the Fugal.

QmFeedMol Display Mass Flow of Molasses in Feed.
QmPurgeMol Display Mass Flow of Molasses in Purge Stream.
QmWash01Mol Display Mass Flow of Molasses in Washings.
QmBsktWash Display Mass Flow of Basket Washings.

Stage Molasses Purities

These are the properties of molasses from the different stages - some streams may be combined before exiting the Fugal.

PurityFeedMol Display Purity of Feed Molasses.
PurityPurgeMol Display Purity of Purge Stream.
PurityWash01Mol Display Purity of Washings.
PurityBsktWashMol Display Purity of Basket Washings.

Stage Molasses Brix

These are the properties of molasses from the different stages - some streams may be combined before exiting the Fugal.

BrixFeedMol Display Brix of Feed Molasses.
BrixPurgeMol Display Brix of Purge Stream.
BrixWash01Mol Display Brix of Washings.
BrixBsktWashMol Display Brix of Basket Washings.

Outlet Connection Molasses Flows

Only connected streams are displayed.

QmLPmolasses Display Mass Flow to Low Purity Molasses Connection.
QmHPmolasses Display Mass Flow to High Purity Molasses Connection.

Outlet Connection Molasses Purities

Only connected streams are displayed.

PurityLPmolasses Display Purity of Low Purity Molasses.
PurityHPmolasses Display Purity of High Purity Molasses.

Outlet Connection Molasses Brix

Only connected streams are displayed.

BrixLPmolasses Display Brix of Low Purity Molasses.
BrixHPmolasses Display Brix of High Purity Molasses.

Vent Mass Flow

VentQm Display Mass flow of Gases to Vent connection.

Mass Flows Page

Class: MassFlows - The third tab page in the access window will have this name. Results data are displayed on this page.


Tag / Symbol
Input / Calc
Description

Stage Solids

FeedSolids Display Mass Flow Rate of Solids in Feed.
PurgeSolids Display Mass Flow Rate of Solids in Purge Stream.
Wash01MolSolids Display Mass Flow Rate of Solids in Washings.
BsktWashingsSolids Display Mass Flow Rate of Solids in Basket Washings.
ProductSolids Display Mass Flow Rate of Solids in Product Cake.

Stage Sucrose

FeedSucrose Display Mass Flow Rate of Sucrose in Feed.
PurgeSucrose Display Mass Flow Rate of Sucrose in Purge Stream.
Wash01MolSucrose Display Mass Flow Rate of Sucrose in Washings.
BsktWashingsSucrose Display Mass Flow Rate of Sucrose in Basket Washings.
ProductSucrose Display Mass Flow Rate of Sucrose in Product Cake.

Stage Impurities

FeedImp Display Mass Flow Rate of Impurities in Feed.
PurgeImp Display Mass Flow Rate of Impurities in Purge Stream.
Wash01MolImp Display Mass Flow Rate of Impurities in Washings.
BsktWashingsImp Display Mass Flow Rate of Impurities in Basket Washings.
ProductImp Display Mass Flow Rate of Impurities in Product Cake.

Warnings

The model will report errors and warnings for the following conditions.

Warning Message Comments
Vapour in Feed or Wash Streams and NO Vent Connected When vapours are present in any input streams or evaporation is occurring a vent stream must be connected.
No Crystal in FugalFeed - Check Stream Compositions There must be sucrose crystal in the fugal feed stream.
FugalFeed is not a Sugar Species model The feed stream must be a sugar stream.
Purge Purity Target < Feed Purity Purge Purity Target must be greater than the Feed Purity.
Crystal in Basket Washings - insufficient Wash Water There is insufficient wash water available in the basket wash stage to dissolve all the sugar crystal remaining in the basket or the water is too cold.
Purge Target Purity NOT Achieved Purge purity target not achieved.
Wash01 Target Purity NOT Achieved The purity target is set lower than the feed to this stage.

Adding this Model to a Project

Add to Configuration File

Sort either by DLL or Group:

  DLL:
SugarUnits.dll
Units/Links Sugar: Sugar Fugal 2
or Group:
Sugar
Units/Links Sugar: Sugar Fugal 2

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


Insert into Project Flowsheet

  Insert Unit Sugar Sugar Fugal 2

See Insert Unit for general information on inserting units.