This operation simulates the separation of oversize solids from undersize solids in a slurry using a centrifugal sieve. Centrifugal sieves are used widely in the starch industry for starch extraction and fiber dewatering.
● Centrifugation Procedure in a Centrifugal Sieve
First, the available material for this operation is split into a liquid/solid phase and a gaseous phase. This is done based on the specified physical state options at the procedure level (through the “Default PS Calc. Options” dialog) and on the temperature and pressure of the feed stream.
Subsequently, each liquid/solid phase pure component is identified as being either liquid or solid depending on whether the respective Removal % is zero or positive. For each solid component, the Removal % indicates the percentage of the available liquid/solid phase flow of that component (if any) that is discharged to the selected output stream. This can be either the Oversize stream or the Undersize stream. The rest of the available liquid/solid phase flow of that component is discharged to the other output stream (the one that was not selected).
The Solids Mass % of the selected output stream indicates the total solids % (by mass) in that stream. The percentage of available liquid that is split to the selected output stream can be calculated by first multiplying the total solids flow in that stream by (1- Solids Mass %) / Solids Mass % and then dividing by the total flow of available liquid for this operation. For each liquid component, a percentage equal to the above liquid split is sent to selected output stream and the rest is sent to the other output stream (the one that was not selected).
The operating throughput is based on the flow of the liquid/solid phase components of the feed stream. If the equipment size option is in Design Mode, the user specifies the maximum equipment throughput. If the operating throughput exceeds the maximum equipment throughput, then, the program assumes multiple, identical units operating in parallel with a total throughput equal to the operating throughput.
If the equipment size option is in Rating Mode, the user specifies the rated throughput of the equipment and the number of units. If the operating throughput per unit exceeds the rated throughput of the equipment, a warning message is displayed advising the user to increase the number of units or use larger equipment.
In terms of power consumption, the following specification options are available:
a) Set Specific Power
b) Set Total Power
c) Set Power Per Unit
If option (a) is selected, the power consumed per operating throughput is specified and the total power and power per unit are calculated. If option (b) is specified, the total power consumed by the operation is specified and the specific power and power per unit are calculated. If option (c) is selected, the power consumed per equipment unit is specified and the specific power and total power are calculated.
It is assumed that a percentage of total power input equal to the specified “Power Dissipation to Heat” is converted into sensible heat of material and increases its temperature. Hence, the outlet temperature must be such that the outlet enthalpy is equal to the sum of the inlet enthalpy and the above heat source due to power dissipation.
The built-in and user-defined equipment purchase cost models are based on the rated mass throughput. By default, the built-in equipment purchase cost model is used to calculate the equipment purchase cost. This is based on a modified version (based on vendor data) of the cost correlation for horizontal basket centrifuges described in Coulson and Richardson’s Chemical Engineering Series, Volume 6, 4th Ed. (2005). This model uses the constraint that the smallest equipment available on the market has a rated mass throughput of 22 MT/h. If the rated throughput is smaller than this value, then the equipment purchase cost will be based on this value and not on the rated throughput.
1. Coulson and Richardson’s Chemical Engineering Series, Volume 6, 4th Ed. (2005).
The interface of this operation has the following tabs:
● Oper. Cond’s, see Centrifugation in a Centrifugal Sieve: Oper. Conds Tab
● Labor, etc, see Operations Dialog: Labor etc. Tab
● Description, see Operations Dialog: Description Tab
● Batch Sheet, see Operations Dialog: Batch Sheet Tab
● Scheduling, see Operations Dialog: Scheduling Tab