SysCAD Modelling Guideline and Check List
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Latest SysCAD Version: 25 February 2021 - SysCAD 9.3 Build 138.28098
How does SysCAD Work?
A brief description of the SysCAD workflow is as follows:
- A project configuration file is set up with a set of user defined chemical compounds (done via SysCAD Database and configuration file.)
- A process flowsheet is created by inserting “Process Units” onto the Graphics Window. These process units are then linked together with Pipes
- SysCAD Process Units may include:
- When solving a SysCAD project, the SysCAD solver will build and solve a network of simultaneous equations internally. Users only need to supply information such as:
- Feeder information such as Feed rate, Temperature, Pressure and Composition. This is done through the Access Window, which can be viewed by right clicking on the unit operations.
- Configuration information of each Process Unit operation, such as reactions, mass separation, heat transfer, etc.
- Various controls to set constraints and/or set-points in the project.
- SysCAD can handle any number of complex recycle streams within a project.
- When a project is solved, mass and energy will be balanced at each process unit and node point in the project.
- SysCAD results can be reported using MS Excel for analysis.
- The user should have a clear scope prior to creating the SysCAD model. This includes knowing what outcome is needed from the model, whether it is for Mass or Energy Balance, Design or control logic testing. This will normally define the required SysCAD mode of operation (whether it is Steady State or Dynamic).
- Define and check all required species/chemical compound data in the project species database, SysCAD.93.db3. (This can be extended and changed at any stage of the project)
- Every SysCAD project MUST include water and steam and the user may not alter the properties of these two species.
- The user has complete control over the number and type of species that can be added to the database. In addition, the amount of data for each species can be very minimal, or extensive.
- The integrity of the species data has a direct effect on the accuracy of the final project. Therefore, it is very important that the data in the species database is reviewed and checked.
- It is not always possible to find comprehensive thermo-physical data for all species in a project. If data is unavailable for a species and it makes up only a very small fraction of the mass, then the effect on results will be limited. However, if the species is important in reactions or forms a relatively large fraction of the mass, then accuracy will be compromised.
- Setup the models configuration data. (This file has the cfg extension.)
- Use any existing Process Flow Diagrams (PFDs), or have a sketch / drawing of the process to be modelled. Go through each unit operation and determine which unit operations need to be simulated. Consider these while completing this step:
- Flowsheet naming conventions, recommend starting the flowsheet name with a number, so that they can be ordered by the process flow.
- Equipment naming conventions, unique naming rule applies.
- Stream naming conventions, unique naming rule applies.
- Flowsheet layout – includes borders and title blocks.
- Determine which SysCAD unit model best simulates each unit operation in the project. Reading through the Models help may be useful when choosing the most appropriate SysCAD unit models.
- Insert required unit models onto the graphics window and connect them as required. The graphical representation of unit models may be selected so that the SysCAD model closely resembles the PFD.
- Configure the SysCAD models – This includes all feed streams and all downstream unit operation configurations.
- Define any reaction - Reactions may be added to many unit models within SysCAD, including tanks, ties, pipes, etc. The actual species involved in the reactions must be correct, but the reaction extent types are also important when evaluating a project.
- Define and control points. - Controllers are the ‘brain’ of the model – they usually control how it responds to changes and allow the model to be used to run many different scenarios. It is vital that they are used intelligently.
- PID Controller - This is a Feed Back controller that mimics an actual plant based P&ID controller. This controller allows a modeller to control any value within the simulation by adjusting a suitable input field. This is a powerful tool, but should not be misused, as this type of controller will usually slow down the convergence speed of a steady state model. Therefore, they should be used sparingly, and only if a Feed Forward controller cannot be used.
- Set Tag Controller - This is a Feed Forward ratio controller.
- Makeup Source & Makeup Block Sub Model – The makeup blocks allows user to control the addition of reagents/utility to the plant.
- General Controller - This is used as a Feed Forward controller, as well performing calculations for control or display. For example, use this to calculate the overall recovery.
- Save the project often when changing or constructing the graphics, especially before solving or any major change.
- SysCAD is not a black box (nor a magic box) - it requires sensible inputs to give sensible answers. As a general rule: garbage in = garbage out, it only does what you tell it to do (whether you meant it or not).
- SysCAD may need to solve several thousand non-linear simultaneous equations to find a solution for large projects (much number crunching). So it is best to analyse what needs to be included in the model beforehand to avoid un-necessary complexity which can slow down the model.
- In general, the logic and control that applies to the real operating plant should be applied to controls in the model.
- SysCAD may not be able to find a valid solution if a model is incorrectly configured - users need to have enough knowledge of the operations to check the process criteria and assess the results.
- Use Find with Query to analyse and debug projects.
- Use reporting feature to create Mass and Energy Balance and to check if all project criteria have been met.
Project Check List
- Species Database and Configuration File:
- Species databases with very little or no missing data and all species will have references and have been checked.
- Configuration file contains all required species displayed appropriately for the project.
- Well laid out flowsheets, usually with a consistent border;
- Easy to follow flow lines;
- Units represented with appropriate symbols;
- Areas are grouped together;
- Flowsheets are labelled appropriately so that it is easy to navigate around the project;
- Units and pipes have consistent and appropriate tags (or names);
- Equipment Unit Models:
- Units are connected correctly;
- The correct options are selected where appropriate;
- Relevant input fields have been entered correctly;
- Feeders contain the correct species composition;
- Reactions and reaction extents are correctly specified;
- Reaction energy is specified by the user (using the override function) where insufficient data exists in the species database, or where the reaction energy is known from test work;
- Required reaction extents are achieved when the project is solved;
- Important control parameters are included in the control strategy;
- Reagent usage, including steam, cooling water, etc. will be controlled when there are changes to the plant feed rate or composition;
- Feed Forward controllers are used wherever possible, i.e. minimise the use PID controllers;
- Controllers are documented, including comments in any General Controller code;
- Controllers are stable;
- PID controllers meet their required set-points;
- Values that rely on operating conditions are not ‘hard-wired’ but are controlled to respond to changes.
- Model Criteria and Inputs Report:
- The project has an associated Model Criteria report; (See Example SysCAD Excel Reports)
- All important inputs to the model can be set from the Model Criteria;
- Inputs to the model are well laid out and comprehensive;
- Results Reports:
- Model Criteria Output Values - model outputs should be checked against the input criteria to ensure the model has been solved properly. (See Project Criteria Report)
- Other Key Process Indicators such as feed|product|reagents ratio - useful for cost analysis
- Stream Reports - Flow, Temperature, Density and so on - (part of default report - 04DetailedReport.xlsx);
- Total In and Out mass balance report - (part of default report - 04DetailedReport.xlsx);
- All Reactions and extents are generated and displayed - (part of default report - 04DetailedReport.xlsx);
- Other Model checking reports such as PID controllers, SetTag Controllers and so on - (part of default report -04DetailedReport.xlsx);
- All flowsheets are included in the report - Flowsheets can be copied by using the Copy bitmap command. Alternatively, user can use Windows Snipping Tool application to make a copy of the flowsheet.