# Sugar Mud Filter

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## General Description

The mud Filter is used to recover sugar from the mud solids and fibre from the clarifier underflow before it is disposed of. The mud filter includes options for the evaporation of water and for heat loss to the environment.

Clarifier underflow mud (at approximately 30% solids mass fraction) is fed onto the filter and wash water is (optionally) sprayed onto the mud. Most of the mud and fibre are retained on the filter and leaves as filter cake and most of the sugar solution is washed out and leaves the unit in the filtrate stream. There is also an optional Vent stream out and any vapors coming into the system and any water vapor from evaporation leave via the vapor line connection.

The unit is assumed to have perfect mixing before separation. Water, mud solids, fibre and solutes are then split independently to the outlet streams to match the specified operating criteria.

## Input and Output Connections

The connections to the mud filter are as below;.

 Label Required / Optional Input /Output Number of Connections Description Min Max. Feed Required In 1 5 Feed streams to the mud filter. Wash Water Optional In 0 5 Wash Water to the mud filter. Filter Cake Required Out 1 1 High solids filter cake out. Filtrate Required Out 1 1 Filtrate out. Vent Optional Out 0 1 Vapour Outlet Stream containing all Vapors - NB required if vapors are present.

## Behavior when Model is OFF

The mud filter may be turned Off by de-selecting the On tick box in the access window.

When the unit is off the following behavior occurs:

• All input feed streams are perfectly mixed together and exit via the filter cake stream. There is no environmental heat loss however, energy is conserved and product temperature will be adjusted accordingly if Feed streams are at different temperatures. There is no interaction with the wash stream.
• All wash water streams are perfectly mixed together and exit via the filtrate stream with no interaction with the feed streams.
• NB any gases in any of the input streams will remain with those streams when the unit is off and are not sent to the Vent stream.

## Physical Model

Feed - The only required input stream connection to the mud filter is the Feed stream (there may be up to 5 feed streams). All feed streams to the mud filter are assumed to mix perfectly. The feed streams must contain some solids and some sucrose(aq) or a warning will be displayed.

Wash Stream - The wash stream is optional and if present, may have zero flow. The wash stream can contain solutes or solids (although would normally be just water).

Environmental Heat Transfer - Several options for environmental heat transfer are included in the model. Heat exchange with the environment is included in the energy balance calculations.

Evaporation - Evaporation is included as an option in the model and the enthalpy of vaporization is included in the energy balance calculations.

Gases - If there are gases in any of the feed streams or if there is evaporation taking place then a Vent stream connection is also required and all gases are split to the vent stream. If there are gases and no vent is connected all gases are sent to the Filtrate stream and a warning will be displayed. NB there is no warning displayed if gases are present in the feed streams and a vent is connected.

Product Streams Output stream connections are required for the Cake and "Filtrate" Streams. The mud solids (all solids except fibre), fibre, water and solutes are all split independently to meet the required filter performance criteria.

Product Temperature - Feed streams and wash streams may all be at different temperatures and have different compositions, the filter may exchange heat with the environment and water may evaporate during operation. All of these effects (including enthalpy of dilution/concentration, mixing or evaporation) are included in the energy balance and product temperature calculation. All product streams (cake, filtrate and vent) are assumed to be at the same temperature.

## Environmental Heat Exchange Options

The mud filter may lose heat to the environment. The heat loss options are set from a drop down list and include;

1. None - No Environmental Heat Exchange occurs.
2. Fixed_Loss - A Fixed Heat Flow Rate to the Environment is specified by the user.
3. Ambient - A Heat Loss Constant is specified and heat loss is calculated as heat loss constant times the temperature difference between the product stream and ambient temperatures, $Q_{EnvLoss} = Constant \times \left(T_{prod} - T_{amb}\right)$
4. SetTprod - A Product Temperature is specified and the required heat loss is calculated. NB This will force the product temeprature to be whatever value is specified and may result in heat gain to the unit which is probably not physically realistic.

For all the above options the heat flow is displayed. The Heat Flow is displayed for all options and heat flow from the mud filter to the environment is positive in sign. NB If a negative heat flow is reported, it indicates heat flow to the mud filter from the environment.

## Evaporation Option

The sugar mud filter has the option of evaporation of water from the juice. The evaporation rate is a user input. If no evaporation is required this can be simply set to zero. An approximate heat loss rate due to evaporation is displayed. The Heat Flow is displayed is positive for heat loss due to evaporation.

## Solids Separation

When the unit operation is solved, all feed and wash streams into the mud filter are assumed to be perfectly mixed, any evaporation occurs and then the mud solids, fibre, water and solutes are split as per the inputs. Most of the solids are retained on the filter and leave in the filter cake stream. The fraction of mud solids retained and the fraction of fibre retained are each user specified inputs.

The mud solids includes all solid material except for fibre. The SysCAD Sugar Properties Model includes a MudSolids species, however the calculated mud solids also includes any other solids except fibre that are present in the system. The retained fraction of mud solids and fibre go to the filter cake stream and all other solids and fibre goes with the filtrate stream. The calculations for mud and fibre retention are based on material in the feed streams only and do not include any solids in the wash stream. If there are any solids in the wash stream they assumed to be retained on the filter and leave with the filter cake.

## Liquid Separation

The liquid in the feed is usually juice from crushing and has a significant concentration of sucrose. Some of this liquid is drawn through the filter while most solids are retained on the filter - this will occur even if there is no wash stream connected. Some of the feed liquid will also be washed form the filter cake through displacement wash water. In this unit operation all wash and feed streams are mixed and then the water and the solutes are split separately to meet the required operating parameters for cake moisture and either cake POL or wash efficiency.

Cake moisture is defined as water per total cake mass;

$Cake\,Moisture=\frac{Mass\,{{H}_{2}}O}{Total\,Cake\,Mass}$

Cake POL and POL in feed and wash streams is defined as mass of aqueous sucrose to total mass;

$Cake\,POL=\frac{Cake\, Mass\,Sucrose}{Cake\,Total\,Mass}$

Wash Efficiency is defined as the fraction of sucrose recovered into the filtrate stream;

\begin{align} & {{\eta }_{wash}}\text{ = }\frac{\text{(Sucros}{{\text{e}}_{Feed}}\text{ + Sucros}{{\text{e}}_{Wash}}\text{- Sucros}{{\text{e}}_{Cake}}\text{)}}{\text{(Sucros}{{\text{e}}_{Feed}}\text{ + Sucros}{{\text{e}}_{Wash}}\text{)}}\,\,\,\,\text{or}\,\,\,\frac{Sucros{{e}_{Filtrate}}}{\text{(Sucros}{{\text{e}}_{Feed}}\text{ + Sucros}{{\text{e}}_{Wash}}\text{)}}\, \\ & \, \\ \end{align}

The amount of water remaining with the filter cake is controlled to achieve the specified filter cake moisture content and the balance minus any evaporation is sent to the filtrate stream. The fraction of sucrose required to achieve the target cake POL or to achieve the specified wash efficiency is calculated and that fraction used to split all of the solutes to the cake and filtrate streams.

## Flow Chart

The process is shown schematically in the flow chart below for the mud filter. Feed and wash streams are perfectly mixed and material exits via the filter cake and filtrate streams. All gases exit via the vapour stream. Heat is exchanged with the environment.

## Mud Filter Access Pages

### MudFilter

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

 Tag / Symbol 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). TackStatus Tickbox Option to display warnings. Environmental Heat Loss EnvLossMethod None No heat exchange with the environment. FixedLoss User specified environmental heat loss rate. Ambient Heat loss determined as a constant times temperature difference from ambient. Set_Tprod Final Product Temperature specified by user. ThermalLossRqd Input The Required Environmental Heat Loss Rate - This is only visible if the FixedLoss Method is selected. ThermalLossAmbient Input The Environmental Heat Loss Rate Coefficient(kW/K) - This is only visible if the Ambient Method is selected. FixedProductT Input User Specified Product Temperature - This is only visible if the Set_Tprod Method is selected. Env_Heat_Loss Display Actual heat Loss to the Environment - positive value is heat from filter to environment. Evaporation Loss EvaporationLossQm Input User specified evaporation rate. ApproxEvapHeatLoss Display Approximate rate of heat loss due to evaporation. Select Wash Calculation Method FixedCakePOL Tickbox ON Select Fixed Cake POL method Tickbox OFF Select Required Wash Efficiency method. Fixed Cake POL method displays when method selected WashEfficiency Display Wash efficiency of filter. FilterFeedPOL Display Feed stream POL. WashWaterPOL Display Wash water POL. TargetCakePOL Input Cake POL set point. CakePOL Display Actual cake POL. FiltratePOL Display Filtrate POL. Required Wash Efficiency displays when method selected WashEffRequired Input Required wash efficiency of filter. WashEfficiency Display Wash efficiency of filter. FilterFeedPOLQm Display Mass flow feed stream POL. WashWaterPOLQm Display Mass flow wash water POL. Cake Moisture FilterFeedMoisture Display Moisture content of feed stream. CakeMoistureSP Input Required filter cake moisture. CakeMoisture Display Actual cake moisture. Solids Separation MudSolidsRetention Input Required Mud Solids retention mass fraction. CakeMudSolidsQm Display Cake mud solids mass flow. FiltrateMudSolQm Display Filtrate mud solids mass flow. FibreRetention Input Required mass fraction of fibre retained in filter cake. CakeFibreQm Display Filter Cake fibre mass flow. FiltrateFibreQm Display Filtrate fibre mass flow. CakeTotalSolids Display Cake total solids mass fraction. CakeMudSolids Display Cake mud solids mass fraction. FiltrateTotalSolids Display Filtrate total solids mass fraction. FiltrateMudSolids Display Filtrate mud solids mass fraction. CakeTotSolidsQm Display Cake total solids mass flow. FiltrateTotSolidsQm Display Filtrate total solids mass flow.

### Data Access Page

The second tab has the name Data and displays some results and information for the screening process.

 Tag / Symbol Input / Calc Description DATA TAB Temperatures T_Feed Display Temperature of all feed streams mixed together. T_Wash Display Temperature of all wash streams mixed together. T_PRoduct Display Temperature of product streams - cake filtrate and vent are at the same temperature. Fibre FeedFibreFrac Display Mass fraction of fibre in the feed. CakeFibreFrac Display Mass fraction of fibre in the cake. FiltrateFibreFrac Display Mass fraction of fibre in the filtrate. FiltrateSolConc@25 Display Filtrate solids concentration @ 25°C. CakeSolConc@25 Display Cake solids concentration @ 25°C. POL Mass Fraction FilterFeedPOL Display Filter Feed POL. WashWaterPOL Display Wash Water POL. CakePOL Display Cake POL. FiltratePOL Display Filtrate POL. Brix Flows FilterFeedBrix Display Filter feed Brix. WashWaterBrix Display Wash water Brix. CakeBrix Display Cake Brix. FiltrateBrix Display Filtrate Brix. FilterFeedBrixQM Display Filter feed Brix mass flow. WashWaterBrixQm Display Wash water Brix mass flow. CakeBrixQm Display Cake Brix mass flow. FiltrateBrixQm Display Filtrate Brix mass flow. Purity FilerFeedPurity Display Filter feed purity. WashPurity Display Wash water purity. CakePurity Display Purity of filter cake stream. FiltratePurity Display Purity of filtrate stream.

## Warnings

 Warning Message Comments Vapour in Feed or Wash Streams and NO Vent Connected! Vent stream must be connected if gases are present. No Sucrose in Feed - Check Stream Compositions! Sucrose(aq) must be present in the feed stream . No Solids in FilterFeed - Check Stream Compositions! Feed stream must have some solids - can be MudSolids, fibre or any other solid. WashWater Pol > FilterFeed Pol - Check Stream Compositions! Wash water has higher sucrose concentration than feed stream. Required Cake Pol NOT Achieved! Unable to achieve required cake POL, check set point or stream compositions. Required Cake Moisture NOT Achieved! Specified cake moisture cannot be achieved, check set points and stream compositions and flows. Energy Balance Error! Unable to balance energy - check required heat flows, evaporation rate and stream temperatures.

## Adding this Model to a Project

Insert into Configuration file

Sort either by DLL or Group.

 DLL: SugarUnits.dll → Units/Links → Sugar: Sugar Mud Filter or Group: Sugar → Units/Links → Sugar: Sugar Mud Filter