Mintek

C H A P T E R   3


ADVANCED FEATURES

  • Editing and Adding Thermodynamic Data
  • Recovering the Erased Equilibrium File
  • Using Recycle Streams
  • Summary of Recycle Operation
  • Entrainment
  • Bypass Streams
  • Summary of Bypass
  • Using Total Feedrate
  • Multi-Stage Equilibrium
  • Multi Unit Simulation
  • Editing the Pyrosim.cfg File
  • Renaming of Phases
  • Interpreting the Active Screen
  • Mineralogy
  • Activity Coefficients


  • This chapter discusses other Pyrosim features which will not necessarily be used by all users.

    Editing and Adding Thermodynamic Data
    One of the most common errors made is to forget to select certain key species when selecting the thermodynamic data for a system. This section describes how data can be added to the THERMDAT.EXT data-base created with Thermo or Pyromake.

    This option has been disabled in Pyrosim version 1.50 (all registered users of Pyrosim version 1.50 are also registered users of Thermo). If you have an old version of Pyrosim then please read on.

    Choose Setup/Thermo Data to add or alter data of a specific data-base. The following warning appears.

    Figure19
    Figure 19: The warning shown before editing the thermodynamic data file

    Press Y to continue. Select the compound to edit using the cursor keys to move the cursor and Enter to select the compound. If you wish to add a new compound to the list move to the pointer and press Enter. From there just follow the prompts.

    Figure20
    Figure 20: Editing a known species, to add new species just go to the end of the list

    After selecting the compound to be edited follow the prompts as they appear.

    Figure21
    Figure 21: The compound data

    Once the compound data has been entered the user is prompted for the phase data.

    Figure22
    Figure 22: Modifying the phase data

    Simply move to the value to be changed and insert the new value.

    × If equilibrium specifications already exist and the list of species in the data-base is extended, all equilibrium specification files are erased once F10 is pressed. It is therefore recommended that a printout of all equilibrium specifications be made before new data is added (Document/Equilibrium).

    Pyrosim only allows three new species to be added to the data-base at a time, to add more restart Pyrosim and repeat the procedure.

    Recovering the Erased Equilibrium File
    There are two ways of regenerating the deleted equilibrium specification files. The option first is to merely re specify all the species present at equilibrium (Setup/Equilibrium), using the printout as reference.

    The second is to use an undelete utility like the DOS command undelete (DOS ver. 3.* and higher, just type UNDELETE EQUIL*.*). This will recover the equilibrium specification as it was before the new species were added. The new species can then be added to the correct phase by editing the equilibrium file in the normal manner (Setup/Equilibrium).

    The current version of Pyrosim does not allow the user to add any additional thermodynamic data to the main data-base (THERMO.DAT). For more information on extended data bases contact Mintek's Pyrometallurgy Division.

    Using Recycle Streams
    In certain operations some product streams are recycled as feed streams to a previous unit operation, e.g., in matte smelting and converting the converter slag is often recycled to the furnace.

    All recycle streams are marked (Setup/Analyses) as *->PhaseNumber, where Phase is the phase under consideration and Number is the unit where this stream is a product e.g., *->Slag3 indicates that the slag from unit 3 is a recycle stream.

    The stream is given any arbitrary initial analyses (Pyrosim will automatically replace this arbitrary analysis with the correct assay after the calculation has been performed).

    For the first iteration, the feedrate of this stream is set to 0. After the calculation, press the F2 key which will automatically save the analyses of all streams marked with *->PhaseNumber.

    The flowrate of the product e.g., the slag stream from Unit 3 can be checked on screen (Summary) and this value can now be entered as a feedrate. The process is repeated, until the input is equal to the output or a certain percentage of recycle is reached (thus allowing for a purge stream), with F2 being pressed after each iteration.

    Figure23
    Figure 23: A screen printout showing an example with a recycle stream

    The figure above shows a hypothetical two stage process where the slag product from stage 2 is recycled to the first stage. The recycle stream is thus not shown on the flow diagram but the streams are reported in the report.

    Pyrosim automatically converges the recycle loop using successive substitution. Currently 100% of any stream designated as a recycle stream is recycled (request for a bleed/purge steam should be directed to Rodney Jones).

    Summary of Recycle Operation

    Entrainment
    In processes involving the formation of more than one liquid phase, clean separation of the different phases seldom occurs since there tends to be entrainment of the different phases in one another.

    To simulate this physical phenomenon you must edit the last lines of the file NEWCALC.EXT. There you will find the following lists:

    Entrainment factors for each unit:

    1 Solids in Slag; 2 Slag in Solids; 3 Solids in Metal; 4 Metal in Solids
    5 Solids in Matte; 6 Matte in Solids; 7 Slag in Metal; 8 Metal in Slag
    9 Slag in Matte; 10 Matte in Slag; 11 Metal in Matte; 12 Matte in Metal

    0,0,0,0,0,0,0,0,0,0,0,0
    0,0,0,0,0,0,0,0,0,0,0,0
    0,0,0,0,0,0,0,0,0,0.13,0,0
    0,0,0,0,0,0,0,0,0,0,0,0

    The descriptions above (1-12) relate to each number in the list. The four lists of numbers relate to each unit (out of a possible four present) in a flowsheet. If you had a single unit model, you would only need to consider the first list of numbers.

    Therefore the 0.13 in the list above represents 13% of the Matte entrained in the Slag in unit 3.

    This describes the entrainment option for Pyrosim version 1.50.

    Bypass Streams
    In many operations a certain fraction of the feed bypasses the reaction unit. Pyrosim allows up to 9 different fractions of bypass. All the different bypass streams are combined as a Dust phase in the Flowrates output.

    To activate this facility, all feed materials that bypass a unit to a certain degree are indicated as ##NumberName (Setup/Analyses), where Number is any integer from 1 to 9 and Name is the name of the stream, e.g. ##3Air. For materials having the same fraction of bypass (they) must have the same integer value.

    Bypass factors are also found in the NEWCALC.EXT file, just above the entrainment factors.

    0,0,0,0,0,0,0,0,0
    For example if 15 per cent of ##3CO bypasses a unit, the third number in must be set to 0.15.

    Figure24
    Figure 24: Dust flow signifies the bypass stream. Also shown is the convention used for labelling bypass streams

    Summary of Bypass

    This describes the bypass operation for Pyrosim version 1.50.

    Using Total Feedrate
    For processes having many different feed materials, it can be a tedious task adding up the feedrates to complete a total material balance.

    To overcome this problem, an external facility was added to the program, which can be activated by the DOS command PYROSIM \TOTAL. For all units in the operation that have external feed sources (not linked feed streams), the total feed rate will then be displayed.

    Figure25
    Figure 25: The total function sums the flowrates of feeds to a process

    Multi-Stage Equilibrium
    The multi-stage equilibrium model (Model) was allows for up to 99 units to be linked in a co-current arrangement.

    Pyrosim does not support counter-current flow since the solution procedure would be an iterative one, co-current arrangement is solved sequentially which is computationally far faster. The model can be operated under temperature or energy control (Operation).

    The phases present in the multi-stage equilibrium model (Setup/Equilibrium/Multi-stage) are specified exactly as for any other equilibrium model.

    All feed materials that are to be split between stages must be marked as -->Name, e.g.,-->Air (Setup/Analyses). When Calculate is pressed, the user will be prompted to give the number of equilibrium stages in series.

    All gaseous products are combined as one final Gas products stream.

    This unit is also discussed briefly in the previous chapter under the heading Choosing a model.

    Multi Unit Simulation
    Multi-unit processes are calculated in sequential order. Therefore, if the process contains four stages the first three stages will have to be recalculated before any changes made to the last unit can be analysed. To save time the following feature has been incorporated.

    What is involved is that the conditions of the streams entering the last unit are updated and retained. These are then fed to a final unit (the previous units being discarded). Thus the process flow sheet is reduced to a single unit, allowing quick optimisation of this final unit.

    The procedure to be followed is listed below. Note that every step must be meticulously followed, otherwise errors will occur.

    Figure26
    Figure 26: A diagram of multi-unit model development

    This feature is worth mastering for models containing more than three or four units.

    Editing the Pyrosim.cfg File
    The configuration file of Pyrosim has the following format:

    Figure27
    Figure 27: Editing the PYROSIM.CFG file

    Pyrosim supports outputs to 5 different printers.

    The correct printer can be selected under Setup/Printer ,and by pressing F10, the printer configuration will be saved in the PYROSIM.CFG file. If the correct printer has not been selected and the user has completed a simulation, the Printer option in the document menu allows the printer configuration to be changed temporarily. This printer set-up is not saved and the printer setting return to its previous setting if Pyrosim is exited.

    × The configuration file is a source of error generation (normally Error 7 or 9). Make sure that the limits in points 1) and 2) are not exceeded.

    ¤ With the VIDRAM utility you can free up more memory (approximately 70 kb) to support larger models. This allows you to re-specify the maximum number of materials, species and elements present in your system.

    Maxmaterials is the number of feed materials allowed to be present.

    Specieslimit is the number of species allowed per phase, e.g. for the above configuration file a maximum of 70 species can be present in any of the phases.

    Renaming of Phases
    By editing the file NEWCALC.EXT (DOS command: edit NEWCALC.EXT, where EXT is the suffix used in Thermo or Pyromake), the first nine lines of the file will look similar to the following:

    Figure28
    Figure 28: The beginning of the file NEWCALC.EXT

    If for example, you want to redefine the metal phase as a 'carbide' phase, merely replace "Metal" with "Carbide" and save the file. The NEWCALC.EXT file is only generated once Pyrosim has done a simulation. Take care not to tamper with the rest of the file.

    Do not change the name of the Slag phase. This phase should always represent an oxide phase as the elemental analyses express some compounds in this phase in the form of basic oxides.

    Interpreting the Active Screen
    Once Calculate has been pressed and the program is busy with an iteration, the active screen can provide information regarding the simulation. By looking at the kmoles/h of the different species, those having a value of zero can be removed from the equilibrium specification (Setup/Equilib). This will speed up iterations, especially if many species have been selected.

    × It is however dangerous to tamper with the equilibrium specifications since species may form under different operating conditions.

    ¤ The convergence factor (less than 0.00001) will show which phases do not form, since the value of the convergence factor of the corresponding phase(s) will become very large, while w will tend to zero.

    If a pure solids phase has been selected in the equilibrium file and it does not form, w will reach zero and iterations will continue but not converge. No error message will be displayed and this phase(s) must be removed from the equilibrium specification (Setup/Equilib) in order for the simulation to converge.

    A simulation can be terminated at any time by pressing the Esc key. The results of such a simulation must not be trusted.

    Figure29
    Figure 29: The active screen

    The w factor indicates to what extent the mass balance has been satisfied, when w is close to one Pyrosim is close to the solution.

    Mineralogy
    If the mineralogy of the sample is not available, the chemical analyses of the feed material can be converted to a mineralogical analyses.

    Although this will not affect the predicted equilibrium compositions (because the equilibrium distribution is dependent on the moles of each element present , which remain the same), the energy requirements for the process will increase. The mineralogical analyses results in a more stable feed material, i.e., more energy is required to break the chemical bonds.

    Activity Coefficients
    Activity coefficients can now be added to account for non ideal behaviour of components in phases.

    Using DOS Edit, or a similar text editor, create four files, called ACT001.EXT,....ACT004.EXT (where EXT is your three character identifier).

    The files should contain the following lines:

    rem: Phase number, species number, a + bT (K)
    1
    1,1,1,0

    Each file (ACT001.EXT...ACT004.EXT) contains the activity coefficient data for a unit (1-4). The first line beginning with rem, is a remark which explains the format of the data which follows. The second line contains a number representing the number of activity coefficient expressions which follow. The last line shown implies that the activity coefficient of the first species in the first phase is equal to 1, and that there is no dependence on temperature.

    If you wished to include activity coefficient data for carbon and iron in a metal phase in unit 2 the ACT002.EXT would need to be edited to look something like:

    rem: Phase number, species number, a + bT (K) 
    2
    3,1,0.9,0
    3,2,0.99,0.001

    This is assuming that the first two species (e.g. C and Fe) in the metal phase (third phase) have activity coefficients. The activity coefficient for carbon is (arbitrarily) fixed at 0.9 (and is independent of temperature); the activity coefficient for iron is given by 0.99+0.001*T(K).

    Note that this facility contains a limitation regarding the order of components present in each phase. If, for example, boron (B) was also present in the equilibrium selection, and was present at equilibrium, then carbon and iron would be the second and third components present in the metal phase. The ACT002.EXT file would then need to be manually updated. If however, boron was selected in the equilibrium specification, but was not present at equilibrium, then carbon and iron would remain the first and second compounds in the metal phase and ACT002.EXT would not need to be updated. It is hoped that this feature will soon be incorporated into the menu structure of Pyrosim.


    Contact Information
    Pyrometallurgy Division, Mintek,
    200 Hans Strijdom Drive, Randburg, 2125, South Africa
    Private Bag X3015, Randburg, 2125, South Africa.

    Phone: +27 (11) 709-4642
    Fax: +27 (11) 793-6241


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    Copyright © 1996-97 George la Grange, Mintek, glg@pyro.mintek.ac.za
    19 June 2001