TCE Functionality Overview
|Thermodynamic Calculation Engines (TCEs)||TCE Add-Ons|
|TCE Functionality Overview||TCE Species Mapping||TCE Configuration Options||AQSol Add-On||ChemApp FACTSage Add-On||PHREEQC Add-On||OLI Add-On|
Latest SysCAD Version: 21 September 2021 - SysCAD 9.3 Build 139.29552
Workflow - Using TCE Add-Ons in a SysCAD Model
To use these add-ons in a model, this requires placing at least one Model Configuration unit onto the flowsheet and performing the configuration. Multiple model configurations can be used. Then, unit models are added which use the configurations. These unit models can be integrated directly into the process model, i.e. reactors, evaporators, flash tanks, reverse osmosis units, etc., or used to calculate the equilibrium compositions of streams without affecting the model, i.e. side calculations. There is also a direct calculation unit operation which enables direct testing of the model for specific situations (analogous to using the software directly for single point calculations).
To summarize, the use of these models in a flowsheet involves the following steps:
- Model configuration:
- selecting the database file to use with the specific thermodynamic software
- performing mapping between species in the SysCAD configuration and species within the thermodynamic software and database file
- if required, modifying how the model is used within the process model, such as adjusting how solids and gases are formed to account for supersaturation.
- Adding units:
- Dropping unit operations onto the flowsheet
- If applicable, selecting the model configuration to use for the unit model
- Setting parameters for the thermodynamic calculation specific to the TCE being used and the unit operation being simulated.
- Adding required species for mapping:
- The use of thermodynamic software often results in the generation of species which are not in the project. Users need to add additional species to the project database from either the SysCAD default database, from hardwired species, or from other data sources. SysCAD provides clear messages and useful functionality to guide the user in adding the required species.
- For aqueous species, these may be in the form of neutral species or ions. There is functionality in place within SysCAD to automatically determine how ions are used to build SysCAD species. Ionic species do not require full thermodynamic information as they are used as intermediates in the building of SysCAD species. The SysCAD species are apparent species, and the ions are true chemical speciation predicted by the thermodynamic software.
Note that multiple types of TCE software can be loaded in a single flowsheet. For example, in a sulfide mineral smelting plant with an acid plant and flue gas scrubbers, one could use ChemApp to model the smelting operations and OLI to model offgas scrubbing and the metallurgical acid plant. Treatment of waste water could be modelled using AQSol and/or PHREEQC. Each of these software packages have their strengths, and the flexible SysCAD architecture allows for use of each of them as appropriate, alongside standard SysCAD unit operations.
A simplified illustration of the interaction between a model configuration, an engine, and a unit operation is shown in the figure below. The database is loaded into the configuration. User settings which consist of convergence tolerances, saturation indices, exclusion of solids, etc., is provided to the configuration. This is then used by the engine when it receives a task from a unit operation. The task from the unit operation will specify which model configuration to use.
SysCAD TCE Models User Functionality
When a TCE-enabled unit is placed on a SysCAD sheet and linked to a model configuration, it provides much more than just a calculation node in your process model. A number of analysis and reporting features are embedded within each unit, including:
- parametric sweeps: The user can generate plots of chemical speciation, enthalpy, pH, and many other parameters as a function of temperature. For side calculations, the effect of adding or removing a species can also be plotted.
- deportment: the deportment of elements between different phases can be viewed and exported to better understand what is occurring within a complex operation. Deportment calculations can be used as control parameters, i.e. calculate the lime addition required to precipitate 90% of magnesium sulfate from a stream.
- elemental balances: elemental balances are shown for both the TCE balance (i.e. the green control volume in the above figure), and the SysCAD balance (i.e. the black control volume in the above figure). This is an important tool for diagnosing mapping issues when developing a model.
- heat balances: a summary of the heat balance is shown for identifying heat sources and sinks. The overall heat requirements for the specific calculation done within a unit are clearly displayed.
- warning/error messages: clear warning and error messages specific to each unit are clearly displayed. Details and suggestions on how to fix the errors/warnings are written to the message log.
Solving TCE Models - Multithreading (Parallel Computation)
Each TCE used within a process flowsheet is accessed by unit operations that incorporate embedded calculations. Multiple TCEs are loaded to allow for parallel computation. The engines are instructed by the unit operations what database file (i.e. model configuration) to use. The engines then load the database (if not already loaded) and perform the computation as requested. The information is then returned to the unit operation for use in the process model. Optimizations are incorporated in the selection of a suitable engine to minimize the number of database loads that are required, as this can be computationally expensive. See the figure below for a graphical representation of the situation where there are 5 engines and two database files available for one TCE type. The dashed lines represent communication between TCE-embedded unit operations and the calculation engines. Note that not all of the unit operations use TCE-embedded calculations.