Process simulation can be an invaluable tool to compare alternatives and justify the cost for manufacturing and manufacturing-related processes.
Simulation is sometimes used interchangeably with modeling, but simulation is the result of running a model. The model comes first; that model is then used to perform simulation studies. Typically, a process model is used to either reproduce a historical period (for validation purposes) or to extrapolate data to predict the future (for what-if studies). Users may perform many simulations with a single model exploring additional alternatives or replication with each simulation.
The main purpose of the computer model for manufacturing and manufacturing-related processes, such as batch documentation, material replenishment/warehousing, and quality testing laboratories is to act as a substitute (from a behavioral standpoint) for the real thing.
It may be too expensive or disruptive to experiment on the real process; or perhaps the real process does not yet exist and is still being designed. Regardless of the scenario, a computer model can perform experiments or ‘what-if’ studies that can add to the understanding of the real-world system and can identify and compare alternatives that improve the system in some way, usually to reduce costs or increase the throughput.
Another argument for using computer-based modeling is that the real-world system is often very complicated involving many interactions between variables that may be unknown or poorly defined with significant variability that tends to hide the underlying relationships. A good model is a simplified version of the true system that captures the essential relationships while leaving out unimportant details. If variability exists and can be quantified, then this can be included in the model to provide a more realistic result.
Benefits of simulation
With these definitions of process modeling and simulation, what benefits can we expect from this technology? There are two places where it really shines:
Design phase – The facility is being designed or will soon be designed. It’s best to start as early as possible in the design process. Changes to the design, prompted by process simulation results, are more cheaply made early in the design.
Renovation – A facility exists already and it needs to be improved in some way. Typical objectives are increasing throughput, reduce manufacturing costs, lower inventories or some combination of these. The improvements that come out of a study for an existing facility may or may not include equipment changes. Sometimes improvements can be made simply by changing the operating procedures or product scheduling alone.
Simulation used in the design phase or new facility
Process modeling of a new design can provide the right number and size of necessary processing and supporting equipment. This is particularly valuable for equipment shared by multiple-unit procedures such as clean-in-place (CIP) skids, utility system designs and powder bins and tablet totes in an oral solid dosage (OSD) facility. The overall production process may have an equipment bottleneck; the model will identify the bottleneck and ensure it does not constrain production to a value less than the business objectives for the facility.
The model also will examine other potential bottlenecks. If their constraint is close to the desired bottleneck, then schedule disruptions or other variability may result in a constraint lower than the design, effectively substituting a more restrictive bottleneck for the desired one.
Changes occur frequently during the design process. Engineers find better alternatives and management may change the product mix of volumes the facility will be expected to make. In these instances, having a process model of the design is especially beneficial. The model can be used to evaluate the alternatives and ensure the changes are cost effective while maintaining the desired throughput. Staffing levels and shift schedules can also be compared with a model. This helps with cost justification of the design change.
Modeling during facility renovation
A model of an existing facility can provide the same benefits as in a design model with two important differences. First, there is historical data that can be used to give a better model and to validate the performance of the model against. This helps to prevent process modeling errors and provides greater confidence in the model results. Secondly, the model is more likely to be used for operational decisions, such as production schedules and shift schedules.
Equipment changes are still possible, but the scale of the possible changes may be lower if the facility footprint is fixed. Intermediate inventories may be fixed for the same reason, creating other problems for manufacturing. Models of existing facilities tend to be more realistic and detailed, which requires more engineering time to build, validate and use the model.
A process model, at the right detail level and properly validated, is a valuable tool to compare alternatives and justify their cost. These benefits apply to new facilities during the design phase and to existing facilities that need renovation or operational changes. Further benefits accrue when each facility has an up-to-date model. Usually good decisions must be made quickly and this is only possible if the time and effort has been invested in a process model beforehand.
Philip Lyman, PhD director, process simulation, CRB. This article originally appeared on CRB’s website. CRB is a CFE Media content partner. Edited by Chris Vavra, associate editor, Control Engineering, CFE Media and Technology, [email protected].
MORE ANSWERS
Users may perform many process simulations with a single model exploring additional alternatives or replication with each simulation.
Process modeling and simulation is valuable in the design phase and during renovations.
A process model is a valuable tool to compare alternatives and justify project costs.
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CAPTIONS FOR PRINT
CTL2005_MAG2_IMG_IP_CRB_Simulation: A process model is a computer representation of a real-world system or process. Courtesy: CRB
CTL2005_MAG2_IMG_IP_CRB_Simulation_ATMPFacility: Process modeling of a new design can provide the right number and size of necessary processing and supporting equipment. Courtesy: CRB
