(14d) Flowsheet Simulation of Solids Processes

Flowsheeting program packages are now commonly used in Chemical Engineering for the design of processes involving fluids. The simulation of processes which involve solids or solids and fluids is not as advanced. In solids processing it is still common practice to design one apparatus separately from the other. There is a lack of suitable methods to combine single apparatus models to a process and to treat this process as a whole. There are several reasons for this situation: The characterization of solids requires more parameters (e.g. size, porosity, humidity, shape, ?) than a fluid which may be characterized by a few concentrated parameters i.e. temperature, pressure and concentration. Several of these additional parameters are distributed parameters e.g. the particle size distribution. Furthermore, secondary parameters, e.g. the particle size dependent moisture after a drying step, have frequently to be considered. For these reasons, the flow structures of simulation packages for fluid processes do not provide a sufficient support for the treatment of solids processes. In the present paper the simulation system ?SolidSim', which has been developed by a group of eleven institutes from seven different German universities, is described. SolidSim is a simulation system especially designed for the simulation of processes including solids, but will also be able to take account to a limited extent of fluid processes. At the present state of development modules are available for classification (sifter, sieve, stream classifier, general classifier), particle size reduction (crusher), crystallisation and dissolution, liquid-solid separation (thickener, filtration, decanting centrifuge, hydrocyclone), gas-solid separation (gas cyclone, filter, scrubber, electrostatic precipitator), agglomeration (fluidized bed granulator), drying (convection drying), conveying (dilute and dense conveying) and different general modules (pump, blower, heat exchanger, heater and cooler, mixer and splitter). With financial support from the CAPE OPEN Laboratories Network (COLaN) Aspen Technology Inc. modified for its version 12.1 of Aspen Plus ® a CO compliant interface which permits an exchange of informations with SolidSim. SolidSim may now be used as a normal unit inside the Aspen Plus® flowsheeting system, the SolidSim subflowsheet may be viewed in the Aspen unit dialogue and parameter values can be assigned to SolidSim units via the Aspen GUI. SolidSim has been applied successfully to the simulation of an industrial plant for the separation of a highly contaminated solids fraction from sludge dredged from the harbour of Hamburg. In this case the contamination of the particulate solids with heavy metals is depending on the particle size. The flowsheet simulation permits to vary and optimize the arrangement of classification and dewatering equipment.