Data that may affect the overall process schedule can be specified at the:
a) Operation Level (e.g. start time shift, setup time, etc.)
b) Procedure Level (e.g. number of cycles)
c) Recipe (or Process) Level (e.g. available annual operating time, cycle time slack, etc.)
Depending on how you intend to operate your process, you may set the operating mode to either batch or continuous (see also Process Operating Mode: Batch vs. Continuous). In most cases, the choice is clear. In typical continuous plants all steps are continuous and in typical batch plants all steps are batch. In some cases, a mixed operating environment exists. Some procedures operate in batch (cyclical) mode where there is a down time (or ‘off time’) while other procedures may be carried out continuously (i.e. they are ‘on’ all the time). Typically, the mode by which you produce your main product will dictate your choice for the process operating mode. If the overall operating mode is set to continuous, then no scheduling data are required at any level (operation, procedure or process) and all the Gantt Chart, Equipment Occupancy Chart and Resource Tracking Chart interfaces and menu options are disabled. The overall operating mode of a process is set from the Process Operating Mode Dialog.
For each operation (assuming the overall operating mode is batch) you must specify the following information:
a) Setup Time
b) Process Time (sometimes process time is calculated by SuperPro Designer, see Notes below)
c) Turnaround Time
d) Start or Finish Time Shift and
e) Start or Finish Time Reference Operation.
The operation-level scheduling information can always be set from the Operations Dialog: Scheduling Tab even though some of the above parameters may also appear on the ‘Oper. Cond’s’ tab of the operation’s i/o simulation dialog.
a) The process time of an operation could be calculated by the program instead of being set by the user. Typically (but not always) this may be the case when the hosting equipment resource is in rating mode (i.e., its size/capacity is specified). In some operations, the user has the choice instead of setting directly the process time to set some other rate variable (e.g. a transfer rate or a heating/cooling rate, etc.) and allow SuperPro Designer to compute the time required to archive a certain operating goal (e.g. transfer a given amount, or reach a specified temperature). For some purely cyclical unit procedures, such as chromatography, the process time is always calculated. For inherently continuous unit operations (such as pumping) that operate semi-continuously in a batch process, the process time is always specified. Finally, the process time could also be dictated by another operation, if a master-slave relationship is specified (see Note (d) below). In summary, a unit operation’s process time (and duration) assumes a value as:
- Set by User,
- Calculated based on other specifications (such as rates, etc), or
- Set by a Master-Slave Relationship.
b) Specifying the setup time, process time, turnaround time and/or number of cycles may affect the outcome of the scheduling calculations (process batch time, number of batches etc.) as well as some of the simulation results (sizing of process units, capital cost, etc.).
c) Oftentimes, the timing (duration) of an operation is totally dependent upon the duration of another operation (e.g. the transfer time to a filtration unit is totally regulated by the rate of filtration). In this case, you can establish a master-slave relationship between the two operations: i.e. designate the transfer operation to be the slave of the filtration operation. Having done that, then all three duration parameters of the transfer operation (setup time, process time and turnaround time) will be assumed as equal to the filtration’s equivalent times and whenever the filtration parameters change, the transfer operation's parameters will change as well. Even though any operation can be selected as a master operation, not all operations allow the option of becoming a slave operation. If a unit operation’s scheduling allows a master-slave relation, it is done through the operation’s ‘Cond’s’ tab. There could be multiple options for how the process time of the operation is determined. If setting a master-slave relation is one of them it would appear on that tab and when selected, it will activate a button labeled Setup. Clicking on this button, will bring up The Master-Slave Relationship Dialog that allows you to choose the master operation and specify how the master’s duration will be used to calculate the duration of the slave.
The main scheduling information that can be adjusted by the user at the procedure level is the number of cycles per batch and, under certain circumstances, the holdup time. As of version 9.0 when the operating mode of the entire recipe is batch then a procedure may also be set to cycle independently to the recipe and the main batch. Hence the time between consecutive cycle starts of the procedure or the number of cycles per main recipe cycle can be modified as well. All this information can be set through the Procedure Data Dialog: Scheduling Tab (Batch Process) (the dialog appears when selecting Procedure Data from the procedure’s command (or context) menu.)
Setting the number of cycles in a procedure to anything other than 1 implies the following:
a) the amount of material processed per batch will be divided equally amongst each cycle (thereby reducing the processing load per cycle),
b) the sequence of operations in that procedure will repeat themselves as many times as the number of cycles (possibly increasing the total procedure time).
For more on the procedure cycle, see Procedure Cycle and Cycle Duration.
When a batch procedure (like chromatography, batch filtration, batch distillation, etc.) is set to operate in a continuous process, SuperPro Designer needs to infer the amount of material that gets processed per cycle. In other words, the implicit assumption is that, in order for this procedure to function cyclically in an otherwise continuous environment, there must be a tank that accumulates material for a certain time (at least while the procedure is in progress) and then feed the next cycle of the procedure. This time we call holdup time (see also Holdup Time).
When the number of cycles of a procedure is greater than one then time elapsing between two consecutive cycle starts (handling material from the same batch) is the procedure’s cycle cycle time. This cycle cycle time is normally equal to the cycle duration. However, the user can specify a gap between cycles (if needed) thereby making the cycle cycle time longer than the cycle duration. A user may also force the cycle cycle time be less than the cycle duration, but of course this can only materialize if multiple equipment sets can be engaged in a staggered mode (the first equipment set starts the first cycle, then the second equipment set hosts the second cycle which starts before the first cycle is finished - still handling material from the same batch).
The procedure cycle time is that time that passes between two consecutive procedure starts (each start handling a different batch). Normally, this is equal to the recipe cycle time, as each procedure’s start is apart from the previous start by an amount of time that is equal to the recipe cycle time (time between consecutive batch starts). However, a procedure can be set to cycle independently from the main process (see Independently Cycling Procedure). In that case, the user can specify the time between consecutive starts of the procedure. For instance, if a procedure’s cycle time is set to be half of the recipe cycle time, then that procedure is completed twice for every main batch execution. It is also possible to set the number of cycles completed per cycle of the main recipe (relative frequency of starts) and that will determine indirectly the procedure’s cycle time.
For procedures set to cycle independently of the main recipe (see Independently Cycling Procedure), instead of setting the time between consecutive starts, the user can set the number of times the procedure is executed during the main recipe cycle time (aka equivalent procedure cycles). It is possible that number of times the procedure is carried out can be a non integer number as the procedure’s cycle durations may not fit exactly in the span of the recipe cycle time.
The following parameters, as they apply to the entire process, must also be specified:
a) the Available Annual Operating Time (AOTav),
b) the Number of Campaigns (k) and
c) one of the following: Number of Batches (NB), Recipe Cycle Time (RCT) or Recipe Cycle Time Slack (RCTS).
The recipe-level scheduling information can be set from the Recipe Scheduling Information Dialog accessed by selecting Tasks } Recipe Scheduling Information from the main menu.