Precipitator3 Dynamic Mode

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Precipitation3 Model Theory - Growth Model Theory - PSD Model Options Data Sections Dynamic Mode Batch Operations (Probal)

Latest SysCAD Version: 29 November 2021 - SysCAD 9.3 Build 139.29945

Related Links: Alumina 3 Bayer Species Model


Dynamic Operation

The Precipitator3 may be operated in Dynamic mode. This is new to Build 136 and provides a large range of new precip circuit modelling capability, such as:

  • Batch operation with no feed.
  • Parameter tuning (agglomeration and growth constants) using lab data from batch experiments.
  • Transient operation through changes in feed flow and composition.
  • Modelling of control strategies for commissioning and upset recovery.
  • Steady state operation reproducing ProBal results

A working ProBal precipitator project may be converted to Dynamic by editing the configuration file to allow for Dynamic. Some additional work may be needed to seed the tanks appropriately and control strategies may need modification, but the Dynamic model uses the same parameters as the ProBal Model.

This first release of the Dynamic Precip model operates as an overflow tank. (If you need to run the tank at lower levels, adjust the tank volume). Some of the cooling operations are unavailable, but will be developed in future releases. The classifying precipitator is not implemented in dynamic mode.

A typical scenario might involve filling a tank over a period of time, running at steady state conditions, stopping the feed (and outflow) to run as a batch precipitation, then draining the tank. Precipitation and particle size changing will still occur even with no feed or product flows (though this may be disabled).

The following additional capability is available:

  • The Tank now has surge volume. The parameter tag TankVol refers to the volume of the tank when filled. Separately the level of the tank is reported, so a tank may be filled from empty or drained.
    • From Build 139, tank level control may be enabled with an Underflow connection.
  • In a dynamic scenario, either the inflow or outflow may be zero.
    • If the outflow is zero, the tank is filling
    • If both inflow and outflow are zero, the tank is operating as a batch precipitator.
    • If the inflow is zero, the tank is draining.
  • The user can specify the initial contents of a tank using a Preset Image.
  • There are additional results/Tags only relevent to dynamic models
    • Level Tank Level
    • MtAcc Change in tank mass since last iteration
    • MassRateOfChange QmAcc Net Inflow/Outflow of material from tank, positive if total mass is increasing
    • YieldRate Mass rate of precipitation per unit volume
  • The tank outflow may be specified in two ways;
    • By overflow: the tank will fill as long as the level is less than the specified tank volume (100% level). Once filled, the volume will remain fixed and any further inflow will be compensated by removing material from the tank to maintain the specified volume.
    • By underflow: with an Underflow connection, the outflow can be controlled by Capacity or Pull as defined in the underflow line. A product connection is still required to receive overflow in case of tank spillage. Level control may also be enabled, in which case the underflow line should be left unrestricted and controlled via the tank LevelControl settings.
  • From Build 139, two Bypass options are provided:
    • TankBypass: Allows full tank bypass from feed to product, while allowing contents to continue reacting.
    • Bypass: Bypasses feed to product, representing short-circuiting, capped at 95%. Can only occur when tank is overflowing, otherwise feed is added to tank contents.

Notes

  • In batch operation, the total mass in the tank will remain fixed. However the total volume may change, since precipitation continues and precipitated material has a higher density than dissolved material, resulting in a slightly reduced volume.
  • Some operations (Classification, evaporation, external cooling) are not available in Dynamic at this stage.
  • The Yield in steady state operation is the difference in gpl THA solids between feed and product. In Dynamic this may be meaningless, eg in batch operation. It is still reported, but only valid if the tank is close to steady state. The YieldRate (kg/s/m^3) directly reports changes in precipitated mass, so is valid in both dynamic and steady state.
  • If a tank is Off then the feed reports directly to the product stream and no precipitation takes place in the contents. It is possible to bypass the feed directly to product (while the tank undergoes batch precipitation) by enabling TankBypass.
  • Thermal override works with specified tank temperature. Temperature drop also works provided there is sufficient flow in the feed - this allows compatibility with Probal models. If there is no flow, then the tank temperature is unchanged.