Potash Evaporator
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| Potash Species Model | Potash Solubility | Potash Properties Utility | Potash Evaporator |
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Related Links: Energy Transfer Models, Solid-Liquid Separator, Evaporator
General Description
The Potash Evaporator is only available to users with the Potash add-on.
The unit may be operated at a user defined temperature or pressure, or it may be part of a Flash Train. SysCAD will attempt to run the unit at equilibrium at the required temperature or pressure. This may involve vapour to be flashed in the unit, with a subsequent increase in concentration of the remaining solution.
If the user enables Solubility and selects Potash solubility, if either KCl or NaCl are above their saturation values they will precipitate out as the crystal product. Alternatively, the user may use the Reaction Block (RB) to set the precipitation reaction and extent.
The unit has a 'Body' and a 'Leg'. The Body section receives the main unit feeds, recycles solution to the heat exchangers and the overflow and vent streams come from this section. The crystals drop into the Leg section and are usually washed with the solution in the 'Leg Feed'. The product is then discharged from the Evaporator leg.
Operational Modes
There are two operational modes for the Potash Evaporator:
- as a stand-alone unit; or
- as part of a Flash Train.
The user sets the required operational mode of the Potash Evaporator. However, if the user sets the mode as Flash Train and the Potash Evaporator is NOT connected to another Evaporator (Embedded Shell), Barometric Condenser, Heat Exchangers of any Flash Train aware destination unit, the model will go to an error state.
Available Sub-Models
| Sub-Models | Feed Block | Body Block | Leg Block | Description |
| Solubility | No | Yes | Yes | May be enabled in the Body and Leg. This is required to automatically calculate the KCl and NaCl solubility. |
| Makeup Blocks (one or more) | Yes | No | No | This allows the user to control the addition of streams such as reagents or brine to the Potash Evaporator, often without having to use a PID or General controller. |
| Reaction Block (RB) | Yes | No | Yes | Allows the user to configure any number of reactions in the Feed or Leg of the Evaporator. |
| Environmental Heat Exchanger Block | Yes | No | No | Allows the user to add or remove energy from the Evaporator using a number of different methods. |
| Vapour Liquid Equilibrium Block | No | Yes | No | ALWAYS enabled in an Evaporator. This will attempt to ensure that the water and steam will be in equilibrium in the unit. |
Heat Exchange Options
The unit may also have connections to an Embedded or to an External Heat Exchanger.
Often Evaporators are operated by recycling the liquor through one or more heat exchangers. This model allows the user to embed these heat exchangers as part of the model. (This is often more efficient when carrying out the modelling calculations.)
The user sets the amount of flow to the heat exchanger, either as a fixed flowrate or as a fraction of the throughput. This flow will then be heated in either the embedded heat exchanger, or sent to an External heat exchanger via the Recycle outlet.
The user may select any of the following 3 options for heat exchange:
- None - no Heat Exchange is required.
- Embedded - The Embedded Heat Exchange model uses a Shell and Tube style heat exchanger. The user connects the Steam (or other cooling or heating medium) to the Embedded HX Shell input port and the Condensate (or return heat exchange medium) to the Embedded HX Shell output port. The recycle flow to the heat exchanger must to be specified, but this is handled internally within the unit.
- External - A recycle stream from the Potash Evaporator is heated, or cooled, in a separate Heat Exchanger unit. The user must connect the Recycle output port from the Potash Evaporator to an external heat exchanger. This recycle stream is then either heated or cooled and returned to the Potash Evaporator via the Recycle input port.
NOTES:
- The difference between the two heat exchange methods:
- With embedded heat exchange, the steam and condensate streams (or other heat exchange medium) are connected directly to Potash Evaporator via the Embedded HX Shell connections. The Recycle stream to the heat exchanger is handled internally within the unit.
- With external heat exchange, the recycle stream is sent to an external heat exchanger via the Recycle connection and returned to the Potash Evaporator via the Recycle connection.
- For both internal and external heat exchange the user must set the recycle flow to the heat exchanger.
Diagram
- The above 2 diagrams show the Potash Evaporator with and without an embedded heat exchanger.
- The physical location of the streams connecting to and from the Potash Evaporator is unimportant. The user may connect the streams to any position on the unit.
- When inserting a Potash Evaporator into a flowsheet, the user may choose a different symbol from the menu.
- Many of the above connections are optional. Please see the Input/Outputs table below for further information.
Inputs and Outputs
| Label | Required Optional |
Input Output |
Number of Connections | Description | |
| Min | Max | ||||
| Feed | 1 Required | In | 1 | 20 | Feed to the main body of the Potash Evaporator. |
| Leg Feed | Optional | In | 0 | 10 | Potash Evaporator Leg feed - this is often a wash stream for the crystals. |
| Embedded HX Shell | Optional | In | 0 | 10 | Inlet stream to the Shell side of Embedded Shell and Tube Heat Exchanger (often the steam inlet). |
| Recycle | Optional | In | 0 | 10 | Recycle stream from external Heat Exchanger(s). |
| Product | Required | Out | 1 | 1 | Product Slurry outlet - this stream flows from the evaporator leg and normally contains the crystals. |
| Vent | Required | Out | 1 | 1 | Vent outlet containing all Vapours from the unit. |
| Overflow | Optional | Out | 0 | 1 | Overflow liquor outlet - this stream flows from the body of the evaporator and normally contains very little solids. |
| Embedded HX Shell | Optional | Out | 0 | 1 | Outlet stream from the Shell side of Embedded Shell and Tube Heat Exchanger (often the condensate). |
| Recycle | Optional | Out | 0 | 1 | Recycle stream from the Potash Evaporator to external Shell and Tube Heat Exchanger(s). |
Behaviour when Model is OFF
If the user disables the unit, by un-ticking the On tick box, then the following actions occur:
- All material in streams connected to the 'Feed' inlet will flow straight out of the 'Product' outlet, with no change in phase or energy exchange with material flowing through the internal heat exchanger;
- All material in streams connected to the 'Embedded HX Shell' connections will have no change in phase or energy exchange with material flowing through the Potash Evaporator;
- No sub-models will be called.
So basically, the unit will be 'bypassed' without the user having to change any connections.
Model Theory
Vapour Liquid Equilibrium
The unit is configured to achieve vapour : liquid equilibrium at a required pressure (or temperature) using the user defined VLE method. Any solids that may be in the stream entering the unit are ignored in the flash calculations. However the enthalpy balance does include the solids. For further information on the theory for the VLE calculations see Vapour Liquid Equilibrium (VLE).
Solubility
If Potash Solubility is enabled in the Potash Evaporator then the solubility calculations will be performed simultaneously with the VLE calculations. Therefore, the product from the Potash Evaporator will contain liquid at, or below, the saturation value of KCl, NaCl and optionally CaSO4.
Flow Chart
Data Sections
The default access window consists of several sections:
- PotashEvaporator - The first tab contains general information that can be set by the user.
- Results - This tab contains the unit results.
- HX - Optional tab, only visible if an Embedded Heat Exchanger is selected. (In this case the Embedded HX Shell connections should be connected).
- RB - Optional tab, only visible if the Reactions are enabled in the Feed Evaluation Block.
- EHX - Optional tab, only visible if the EnvironHX is enabled in the Feed Evaluation Block.
- MU - Optional tab, or multiple tabs if more than 1 Makeup is selected. Only visible if one of more Makeup is enabled in the Feed Evaluation Block.
- PC - Optional tab, only visible if the Solubility is enabled in the Body Evaluation Block.
- VLE - Always visible. This is calcualted in the Body of the Evaporator.
- LPC - Optional tab, only visible if the Solubility is enabled in the Leg Evaluation Block.
- LRB - Optional tab, only visible if the Reactions are enabled in the Leg Evaluation Block.
- QFeed - Optional tab, only visible if ShowQFeed is enabled. This page shows the properties as a mixed stream of all of the Feed streams to the Potash Evaporator. This EXCLUDES the recycle from the external heat exchanger, if there is one.
- This is before any Evaluation Block models are evaluated.
- QBodyFeed - Optional tab, only visible if ShowQBodyFeed is enabled. This page shows the properties of the mixed stream as the feed to the Body of the Potash Evaporator.
- This is before any Evaluation Block models are evaluated.
- QRecycle - Optional tab, only visible if ShowQRecycle is enabled. This page shows the properties of the recycle stream sent to the Embedded Heat Exchanger. This is only relevant if an Embedded Heat Exchanger (Heater or Cooler) is used.
- This is AFTER the flash calculations, but before the split to slurry, overflow and vapour streams.
- QProd - This page shows the properties of the Potash Evaporator discharge as a single stream.
- This is AFTER the flash calculations, but before the split to slurry, overflow and vapour streams.
- Info tab - contains general settings for the unit and allows the user to include documentation about the unit and create Hyperlinks to external documents.
- Links tab - contains a summary table for all the input and output streams.
- Audit tab - contains summary information required for Mass and Energy balance. See Model Examples for enthalpy calculation Examples.
Potash Evaporator Page
Unit Type: PotashEvaporator - The first tab page in the access window will have this name.
Tag (Long/Short) |
Input / Calc |
Description
|
| Tag | Display | This name tag may be modified with the change tag option. |
| Condition | Display | OK if no errors/warnings, otherwise lists errors/warnings. |
| ConditionCount | Display | The current number of errors/warnings. If condition is OK, returns 0. |
| GeneralDescription / GenDesc | Display | This is an automatically generated description for the unit. If the user has entered text in the 'EqpDesc' field on the Info tab (see below), this will be displayed here. If this field is blank, then SysCAD will display the UnitType or SubClass. |
| Requirements | ||
| On | Tickbox | This variable in used to turn the unit ON or OFF. If this not ticked, the material will flow out of the Product outlet with no change in state, i.e. the unit acts as a pipe. |
| Mode | Stand Alone (Manual) | The Evaporator will act as a 'Stand Alone' unit and the user may set the required operating Pressure or Temperature. |
| Flash Train | The Evaporator Body will act as part of a Flash Train. In this mode the Evaporator vent must be connected to a steam consumer, such as a Barometric Condenser, Shell and Tube Heat Exchanger, Shell and Tube Heat Exchanger 2 or a Direct Contact Heater. The steam requirements of the steam consumer will drive the operating pressure of the Evaporator, therefore the user may NOT set the operating temperature or pressure. Note If the Evaporator does have an embedded Heat Exchanger, this can be set up separately as part of a Flash Train. | |
| OperatingP The user may only set the operating pressure or temperature of the Potash Evaporator if it is NOT part of a Flash Train. | ||
| Method | Atmospheric | This method is only available if 'Stand Alone' Mode is chosen. All flash calculations will be done 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 Environment tab page of the Plant Model. |
| RequiredP | This method is only available if 'Stand Alone' Mode is chosen. All flash calculations will be done at the user specified pressure (and saturated temperature @ P). | |
| RequiredT | This method is only available if 'Stand Alone' Mode is chosen. All flash calculations will be done at the user specified temperature (and saturated pressure @ T). | |
| Saturated | The OperatingP - Method will be set to Saturated if 'Flash Train' Mode is chosen. All flash calculations will be done at the saturated pressure. | |
| PressureReqd / P_Reqd | Input | This field is only visible if the RequiredP method is chosen. This is user specified flash pressure. |
| TemperatureReqd / T_Reqd | Input | This field is only visible if the RequiredT method is chosen. This is user specified flash temperature. |
| Result | Calc | The actual pressure used for the sum of the feeds which will also be the outlet pressure (unless further model options change the pressure). |
| MinFlashP | Input | This is only visible when 'Flash Train' Mode is chosen. The Minimum Flash Pressure. |
| TCorrection | Calc | This is only visible if the Mode = Stand Alone. |
| UseFeedP | Tickbox | This is only visible if the Mode = Stand Alone. If this field is enabled then all of the Evaluation Block calculations will be performed at the Feed pressure. Otherwise, if it is not enabled, the calculations will be performed at the final pressure. See also Model Theory. |
| Feed Evaluation Block | ||
| 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 auto evaluation sequence followed will be the order the sub models are listed below. |
| Makeups | Input | The number of Makeup Blocks required. Extra dropdown options Makeup1, Makeup2, etc. will be added to allow these to be switched on and off and prioritised in relation to the other sub-models. |
| 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 | Reaction Block (RB) - Enable or disable Reactions and set the sequence in relation to the other sub-models. 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 | Environmental Heat Exchanger (EHX) - Enable or disable Environmental Heat Exchange and set the sequence in relation to the other sub-models. 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. |
| Body Evaluation Block | ||
| Solubility.On | Tickbox | Only visible if Solubility has been defined for at least one species in the project. Allows the user to switch on any predefined solubility curve to adjust the composition of material in the unit. |
| [email protected] | Tickbox | Only visible if Phase Change at Temperature has been defined for at least one species in the project and Plant Model - Species Tab - PhaseChange@T = OFF. Allows the user to switch on any predefined phase changes at temperature in the unit. |
| 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 auto evaluation sequence followed will be the order the sub models are listed below. |
| VLEquilibrium | List | Vapour Liquid Equilibrium (VLE) - Enable or disable Vapour Liquid Equilibrium and set the sequence in relation to the other sub-models. If this is 'On' then the associated page, VLE becomes visible and may be configured. Note: This option may automatically adjust the species make-up. |
| Leg Evaluation Block | ||
| Solubility.On | Tickbox | Only visible if Solubility has been defined for at least one species in the project. Allows the user to switch on any predefined solubility curve to adjust the composition of material in the unit. |
| [email protected] | Tickbox | Only visible if Phase Change at Temperature has been defined for at least one species in the project and Plant Model - Species Tab - PhaseChange@T = OFF. Allows the user to switch on any predefined phase changes at temperature in the unit. |
| 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 auto evaluation sequence followed will be the order the sub models are listed below. |
| Reactions | List | Reaction Block (RB) - Enable or disable Reactions and set the sequence in relation to the other sub-models. 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. |
| Fraction of Leg Feed Liquid reporting to Evaporator Body | ||
| LegFeedLiqFracToBody / LegFeedToBody | Input | The required fraction of the liquid in the leg feed that reports directly to the Evaporator body. The remainder flows to the leg section. Note that all solids in the Leg Feed stream will always report directly to the leg. |
| Evaporator Heat Exchanger Options | ||
| HXType | None | The unit is not connected to a Heat Exchanger. No other fields are visible for the Heat Exchanger if this option is chosen. |
| External | The Evaporator is connected to an External Heat Exchanger unit. This external unit may be any type of SysCAD model. | |
| Embedded Heater | The Evaporator contains an Embedded Heater. If this option is chosen, an additional page HX becomes visible and the user configures the Heat Exchanger within the Evaporator. | |
| HX.HeaterCount | Input | The number of heaters. |
| HXOut.SplitMethod | Off | No flow is sent to the Heat Exchanger. |
| Ratio to Feed MassFlow | The flow to the Heat Exchanger (either Embedded or External) is a Ratio of the Feed mass. The composition and temperature of the stream to the Heat Exchanger is the same as the Combined Feed to the Evaluation Block. | |
| Ratio to Prod MassFlow | The flow to the Heat Exchanger (either Embedded or External) is a Ratio of the Product mass. The composition and temperature of the stream to the Heat Exchanger is the same as the Product from the Evaluation Block. Note: The Product mass includes both the Overflow and the Product streams. | |
| MassFlow | The flow to the Heat Exchanger (either Embedded or External) is a fixed mass flow. The composition and temperature of the stream to the Heat Exchanger is the same as the Product from the Evaluation Block. Note: The Product mass includes both the Overflow and the Product streams. | |
| VolumeFlow | The flow to the Heat Exchanger (either Embedded or External) is a fixed volumetric flow. The composition and temperature of the stream to the Heat Exchanger is the same as the Product from the Evaluation Block. Note: The Product mass includes both the Overflow and the Product streams. | |
| MassFlow Per Heater | The flow to each Heat Exchanger (either Embedded or External) is mass based. The composition and temperature of the stream to the Heat Exchanger is the same as the Product from the Evaluation Block. Note: The Product mass includes both the Overflow and the Product streams. | |
| VolumeFlow Per Heater | The flow to each Heat Exchanger (either Embedded or External) is volume based. The composition and temperature of the stream to the Heat Exchanger is the same as the Product from the Evaluation Block. Note: The Product mass includes both the Overflow and the Product streams. | |
| HXOut.RatioToFeedQm | Input | Only visible if SplitMethod = Ratio to Feed MassFlow. The flow to the Heat Exchanger (either Embedded or External) is Feed Flow times by this Ratio. |
| HXOut.RatioToProdQm | Input | Only visible if SplitMethod = Ratio to Prod MassFlow. The flow to the Heat Exchanger (either Embedded or External) is Product Flow times by this Ratio. Note: The Product mass includes both the Overflow and the Product streams. |
| HXOut.MassFlowReqd / QmReqd | Input | Only visible if SplitMethod = MassFlow. The required Product mass flow to the Heat Exchanger (either Embedded or External). |
| HXOut.VolumeFlowReqd /QvReqd | Input | Only visible if SplitMethod = Ratio to VolumeFlow. The required Product volumetric flow to the Heat Exchanger (either Embedded or External). |
| HXOut.EachHeaterQmReqd | Input | Only visible if SplitMethod = MassFlow per Heater. The required Product mass flow to each Heater (either Embedded or External). |
| HXOut.EachHeaterQvReqd | Input | Only visible if SplitMethod = VolumeFlow per Heater. The required Product volumetric flow to each Heater (either Embedded or External). |
| Overflow and Product Split | ||
| CalcSplitMethod | Simple Estimate | The model will do a simple estimate to calculate the liquid split required from the body to the leg to give the desired solids fraction in the product. |
| Iterative | The model will iteratively calculate the liquid split required from the body to the leg to give the desired solids fraction in the product. | |
| OFSolSaltsReqd | Input | The required solid salts species fraction in the overflow stream. Salts species include KCl, NaCl and MgCl2. |
| GypsumSplitMethod (Note: 'Gypsum' includes CaSO4.2H2O(s) and CaSO4(s)) |
Follow Solid Salts | The fraction of gypsum to the Overflow stream will be the same as the solid salts fraction to the Overflow stream. |
| All to OF | All of the gypsum from the Evaporator body will report to the Overflow stream. Note - there may be some gypsum in the Leg that reports to the Product stream. | |
| None to OF | None of the gypsum in the Evaporator body will report to the overflow stream, i.e. it will all report to the Product stream. | |
| User Frac to OF | The user may define the fraction of gypsum in the Evaporator body that will report to the Overflow stream. | |
| GypsumToOF | Input | Only visible if GypsumSplitMethod = User Frac to OF. The required fraction of gypsum in the Evaporator body that will report to the Overflow stream. |
| OtherSolidSplitMethod ('Other Solids' are any solid species that are not gypsum or salts, i.e. NOT KCl, NaCl, MgCl2 or gypsum.) |
Follow Solid Salts | The fraction of other solids to the Overflow stream will be the same as the solid salts fraction to the Overflow stream. |
| All to OF | All of the other solids from the Evaporator body will report to the Overflow stream. Note - there may be some other solids in the Leg that report to the Product stream. | |
| None to OF | None of the other solids in the Evaporator body will report to the overflow stream, i.e. they will all report to the Product stream. | |
| User Frac to OF | The user may define the fraction of other solids in the Evaporator body that will report to the Overflow stream. | |
| OtherSolidToOF | Input | Only visible if OtherSolidSplitMethod = User Frac to OF. The required fraction of other solids in the Evaporator body that will report to the Overflow stream. |
| ProductSolidFracReqd | Input | The required solids fraction in the Product Stream. |
| Options | ||
| VapStandardSpModel | Tickbox | This forces the vent stream to revert to the Standard species model. If this is NOT ticked, then the species model in the vent will be the same as the species model used in the Evaporator. Normally this is left ticked, as the vent contains steam and the Standard species model will calculate all of the properties of steam correctly. |
| ShowQFeed | Tick Box | QFeed and associated tab pages (e.g. Qm) will become visible if this is enabled. These tabs will show the properties of the combined feed stream to the Unit. These values are BEFORE the Evaluation Block is processed. |
| ShowQBodyFeed | Tick Box | QBodyFeed and associated tab pages (e.g. Qm) will become visible if this is enabled. These tabs will show the properties of the combined feed stream to the Evaporator Body. |
| ShowQRecycle | Tickbox | This is only visible if an Embedded Heater is used. If this option is ticked then the recycle stream to the Heat Exchanger is displayed as 'QRecycle' and the user may access properties of the stream feeding the Heat Exchanger. |
| ShowQProd | Tick Box | QProd and associated tab pages (e.g. Qm) will become visible if this is enabled. These tabs will show the properties of the product stream from the Unit, AFTER the Evaluation Block is processed, but BEFORE the stream is split to overflow and product. |
| ShowResultsTable | Tick Box | This adds a section in the Results Page showing a summary of QFeed, QBodyFeed and QProd Results. |
Results Page
Tag (Long/Short) |
Input / Calc |
Description
|
| Operating Conditions | ||
| TemperatureIn / Ti | Calc | The temperature of the combined Feed stream to the Evaporator. (This is a normally hidden field) |
| PressureIn / Pi | Calc | The pressure of the combined Feed stream to the Evaporator. (This is a normally hidden field) |
| VapFlashed.MassFlow / Qm | Calc | The quantity of flashed vapour. |
| LiqChange.MassFlow / Qm | Calc | The mass change of liquid in the evaporator. |
| BPE | Calc | The Boiling Point Elevation used in the Flash calculations in the Evaporator. |
| FlashT | Calc | The final temperature (the Flash Temperature) in the Evaporator. |
| FlashP | Calc | The final pressure (the Flash Pressure) in the Evaporator. |
| Flash Train Macro Model These extra fields are only visible if the unit is part of a Flash Train. | ||
| VapourMassFlow / VQm | Calc | The mass flow of flashed vapour. |
| PressureReqd / P_Reqd | Calc | The required flash pressure calculated by the Flash Train. |
| TotalPressChange / TotaldP | Calc | The total pressure change calculated by the Flash Train. |
| FeedSatP | Calc | The saturation pressure of the feed. |
| FlashTrain | Display | A unique tag assigned to the flash train by SysCAD. Each unit in the flash train will have the same tag in this block. |
| FlashTearBlock | Display | Displays the name of the tear block that is part of the Flash Train. |
| FlashTrainEqp | List | This contains a list of all of the equipment tags in this flash train. the list might be as follows: FT_EVAPORATOR_2_HX FT_EVAPORATOR_1_Evap |
| PAdvBase | Input | Additional damping or acceleration for calculated pressure change (DP) for the iteration. DP = DP * PAdvBase when PAdvExtra=0. |
| PAdvExtra | Input | Additional damping or acceleration for calculated pressure change (DP) for the iteration. DP = DP * (PAdvBase + PAdvExtra*(VQmReqd-VQm)/Max(VQmReqd,VQm)). |
| Summary of QFeed, QBodyFeed and QProd Results | ||
This Summary table is only visible when the ShowQResultsTable option has been ticked on the Potash Evaporator Tab. It shows the values of each of the following variables for
| ||
| Temperature / T | Calc | The Temperature in each stream. |
| MassFlow / Qm | Calc | The total mass flow in each stream. |
| SolidMassFlow / SQm | Calc | The mass flow of solids in each stream. |
| SolidFrac / Sf | Calc | The solids fraction in each stream - this includes all solids and gypsum. |
| SolSaltsQm | Calc | The mass flow of solid salts (KCl and NaCl) in each stream. |
| SolSaltsFrac | Calc | The mass frac of solid salts (KCl and NaCl) in each stream. |
| GypsumMassFlow / GypsumQm | Calc | The mass flow of Gypsum in each stream. |
| Summary of Input and Output Streams | ||
This Summary table shows the values of each of the following variables for the Feed and Product streams that are connected to the Evaporator. The possible streams are:
| ||
| Temperature / T | Calc | The Temperature in each stream. |
| MassFlow / Qm | Calc | The total mass flow in each stream. |
| SolidMassFlow / SQm | Calc | The mass flow of solids in each stream. |
| SolidFrac / Sf | Calc | The solids fraction in each stream - this includes all solids and gypsum. |
| SolSaltsQm | Calc | The mass flow of solid salts (KCl and NaCl) in each stream. |
| SolSaltsFrac | Calc | The mass frac of solid salts (KCl and NaCl) in each stream. |
| GypsumMassFlow / GypsumQm | Calc | The mass flow of Gypsum in each stream. |
| Results | ||
| LegBypass.MassFlow / Qm | Calc | The mass flow of material bypassed to the Leg. |
| BFeed.Temperature / T | Calc | The temperature of feed in the main body of the evaporator. |
| BFeed.Pressure / P | Calc | The pressure of feed in the main body of the evaporator. |
| Body.SolidsYield | Calc | The mass flow of solids in the Product - mass flow of solids in the Feed. |
| Leg.SolidsYield | Calc | The mass flow of solids in the Leg. |
| SolidsYield | Calc | The mass flow of solids in the Product - mass flow of solids in the Feed. |
| OF.AqSaltsFrac | Calc | Aqueous salts fraction in the Overflow. |
| Leg.SolidFrac / Sf | Calc | Solids fraction in the leg. |
| Leg.SolSaltsFrac | Calc | Solid Salts fraction in the leg. |
| Leg.AqSaltsFrac | Calc | Aqueous Salts fraction in the leg. |
| Internal Calculations | ||
| PrevLiqQmToUF | Calc | The amount of liquid mass flow to underflow in the previous iteration. |
| BodySolSaltsFracToLeg | Calc | Body solid salts fraction to leg. |
| BodyGypsumSolFracToLeg | Calc | Body solid gypsum fraction to leg. |
| BodyOtherFracToLeg | Calc | Body other solids (not including salts and gypsum) fraction to leg. |
| BodyLiqFracToLeg | Calc | Body Liquid fraction to leg. |
| CalcLegSplit.Iters | Calc | Number of iterations allow to calculate the split to leg. |
| Evaporator to External Heat Exchanger / Embedded Heater These extra fields are only visible if one of the Heat Exchanger options has been chosen on the first tab page. | ||
| HXOut.MassFlow / Qm | Calc | The mass flow to the specified Heat Exchanger. |
| HXOut.EachHeaterQm | Calc | The mass flow to the specified Heat Exchanger (per heater if more than one is used). |
| HXOut.VolFlow / Qv | Calc | The volume flow to the specified Heat Exchanger. |
| HXOut.EachHeaterQv | Calc | The volume flow to the specified Heat Exchanger (per heater if more than one is used). |
| HXOut.Temperature / T | Calc | The temperature of the stream to the specified Heat Exchanger. |
| Embedded Heater Recycle Loop convergence These extra fields are only visible if the Embedded Heater option has been chosen on the first tab page. | ||
| RecycleConvergeMethod | FullStream | User can select to solve the recycle loop using Full stream data (loop has to solve and converge all mass and energy terms.) |
| Stream Mass Only | User can select to solve the recycle loop using mass only. Loop will be solved when mass is converged, ignoring energy. | |
| Duty | User can select to solve the recycle loop using energy only. Duty from "shell" side of heat exchanger is added directly to the feed (recycle mass flow is not actually added). Loop will be solved when duty is matched, ignoring mass balance. | |
| MaxIterations / MaxIter (Global) | Input | The maximum number of iteration allowed within the recycle solver loop. Only shown for Stream Recycle Converge Methods. |
| IterSteps | Calc | The number of iteration used in the current step to solve the recycle loop. Only shown for Stream Recycle Converge Methods. |
| IterLastStep | Calc | The number of iteration used in the last step to solve the recycle loop. Only shown for Stream Recycle Converge Methods. |
| IterMaxInAStep | Calc | The maximum number of iterations (in a step) used to solve the recycle loop. Only shown for Stream Recycle Converge Methods. |
| IterTotal | Calc | The total number of iterations used to solve the recycle loop. Only shown for Stream Recycle Converge Methods. |
| FeedMaxDuty | Calc | The maximum amount of Duty that can be added to feed before temperature exceeds water critical temperature. Only shown for Duty Recycle Converge Method. |
| IterDuty | Calc | The number of iterations to apply duty and flash. When this is greater then 1 then the Duty from the condensing steam is applied in iterations, the values displayed on the VLE page reflect this. Only shown for Duty Recycle Converge Method. |
HX Page
HX - Optional tab, only visible if an Internal Heat Exchanger is selected. (In this case the Internal HX connections should be connected).
| Tag (Long/Short) | Input / Calc | Description/Calculated Variables / Options |
| Heater / Cooler Requirements | ||
| On | Tick Box | Switches the Embedded Heat Exchanger on/off |
| HeaterCount / NumofHeaters | Input | Specifies the number of embedded heat exchangers in the evaporator. This can also be changed on the first tab page. |
| Type | Fixed Heat Flow | This will exchange a fixed amount of heat between two streams. No phase change will take place automatically. |
| Sensible | This will allow sensible heat exchange between two streams. No phase change will take place. (not currently implemented) | |
| Condensing | Only visible when Embedded Heater is used. This is used to condense the steam. Steam must be connected to Embedded HX Shell (inlet). | |
| Evaporating | Only visible when Embedded Cooler is used. This is used to evaporate the water. Water (or another component with Predefined Flashing Data) must be connected to Embedded HX Shell (inlet). | |
| DutyReqd | Input | Only visible when Fixed Heat Flow method is used. The required fixed heat flow to be exchanged between the two streams. |
| CondensingMethod (Only visible when Type = Condensing) |
All | The Steam addition is manually specified by the user. All steam will condense. |
| All (Calc Demand) | The steam demand is calculated based on the user specified Heater HTC and Area (UA). User needs to set the steam flow based on the calculated amount. | |
| All-Demand General | The steam supply comes from (directly or indirectly) a Feeder with Demand.on selected. | |
| All-Demand Flashtrain | The steam supply comes from another process unit in Flash train mode (usually the vapour from the preceding evaporation stage) | |
| EvaporatingMethod (Only visible when Type = Evaporating) |
All | The component defined on the VLE Tab will fully evaporate. |
| All (Calc Demand) | The demand is calculated based on the user specified Cooler HTC and Area (UA). User needs to set the flow based on the calculated amount. | |
| All-Demand General | The flow supply comes from (directly or indirectly) a Feeder with Demand.on selected. | |
| UseOldDemandCalc | Tickbox | Visible with method set to any of the demand methods. Allows users to continue to use old demand calculations for backward compatibility. It is recommended to leave this unticked. |
| HTC | Input | Visible with method set to any of the demand methods. The user specified Heat Transfer Coefficient (HTC). |
| Area | Input | Visible with method set to any of the demand methods. The user specified heat transfer area per heat exchanger. |
| Heater / Cooler Results | ||
| Duty | Calc | The calculated Heat Exchanger Duty |
| TotalArea | Calc | Visible with method set to any of the demand methods. The total Area used (HX Area * number of HX). |
| UA | Calc | Visible with method set to any of the demand methods. The heat exchanger UA. |
| LMTD | Calc | The calculated log mean temperature difference. |
| TheoreticalDuty / TheorDuty | Calc | Visible with method set to any of the demand methods. The theoretical duty of the heat exchanger. |
| HeatFlow | Calc | The net heat flow to the unit. This should be zero as heat is merely exchanged (no external energy is added or removed). |
| Calculated Vapour/Liquid Flow Demand This group of tags is only visible when one of the demand methods is chosen. | ||
| DemandFlow.Reqd | Calc | The calculated demand flow to meet the Heat Exchanger requirements. When the HX is not in Demand General or Demand FlashTrain mode, use a General controller or SetTag Controller to get this value to set the Embedded HX Shell (in) flowrate. |
| DemandFlow.Actual | Calc | The actual demand flow to Heater Exchanger . |
| DemandFlow.Error | Calc | The difference between the required and actual vapour/liquid flows, (DemandFlow.Reqd - DemandFlow.Actual). This will warn the user if the amount of flow supplied doesn't match the heat exchanger requirements. Most common when the heater is not in Demand General or Demand FlashTrain mode and the steam flow is not controlled. |
| DemandFlow.RelErr | Calc | The relative difference between the required and actual vapour/liquid flows, (DemandFlow.Reqd - DemandFlow.Actual)/DemandFlow.Reqd. |
| Tube Side (Recycle Stream) | ||
| Tube.TemperatureIn / Ti | Calc | Tube in temperature. |
| Tube.TemperatureOut / To | Calc | Tube out temperature. |
| Tube.PressureIn / Pi | Calc | Tube in pressure. |
| Tube.MassFlow / Qm | Calc | The mass flowrate going through the tube side. |
| Shell Side (Condensing / Evaporating) | ||
| Shell.TemperatureIn / Ti | Calc | Shell in temperature. |
| Shell.TemperatureOut / To | Calc | Shell out temperature. |
| Shell.PressureIn / Pi | Calc | Shell in pressure. |
| Shell.MassFlow / Qm | Calc | The mass flowrate going through the Shell side. |
| Shell.DmdQm | Calc | Visible with method set to any of the demand methods. This is the amount of steam needed from connected flash train units (flash tank or steam feeders), not including any fixed amount of steam input. |
| Shell.FxdQm | Calc | Visible with method set to any of the demand methods. This is the amount of steam added in manually, thus not from connected flash train units. Note this portion of steam addition is not included in the pressure calculation of the flash train group. |
| Flash Train Macro Model
Note: Extra fields are visible if the unit is part of a Flash Train. These fields are described below. Please refer to Flash Train. | ||
| VapourMassFlowReqd / VQmReqd | Calc | The calculated mass flow of steam required by the Embedded Heater Condenser. |
| CondMassFlow / CondQm | Calc | The amount of steam condensed by the Embedded Heater Condenser. |
| MinSatPress | Calc | The minimum saturated pressure of steam that could satisfy the heating requirements of the Embedded Heater Condenser. |
| FlashTrain | Display | A unique tag assigned to the flash train by SysCAD. Each unit in the flash train will have the same tag in this block. |
| FlashTearBlock | Display | Displays the name of the tear block that is part of the Flash Train. |
| FlashTrainEqp | List | This contains a list of all of the equipment tags in this flash train. the list might be as follows: FT_EVAPORATOR_2_HX FT_EVAPORATOR_3_Evap |
| PAdvBase | Input | Additional damping or acceleration for calculated pressure change (DP) for the iteration. DP = DP * PAdvBase when PAdvExtra=0. |
| PAdvExtra | Input | Additional damping or acceleration for calculated pressure change (DP) for the iteration. DP = DP * (PAdvBase + PAdvExtra*(VQmReqd-VQm)/Max(VQmReqd,VQm)). |
Adding this Model to a Project
Add to Configuration File
Sort either by DLL or Group:
| DLL: | PotashUnits.dll |
→ | Units/Links | → | Heat Transfer: Evaporator - Potash OR PotashEvaporator (note1) | |
| or | Group: | Energy Transfer |
→ | Units/Links | → | Heat Transfer: Evaporator - Potash |
See Model Selection for more information on adding models to the configuration file.
Insert into Project Flowsheet
| Insert Unit | → | Heat Transfer | → | Evaporator - Potash OR PotashEvaporator (note1) |
See Insert Unit for general information on inserting units.
NOTE:
- Name change in Build139 and later.
Hints and Comments
- 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.
- The information in the VLE Section must be correct for the Evaporator to operate as required. If the VLE configuration requires information that is not available, then the flashing will not occur.