Recently, Operator Training Simulators have become more a necessity than a luxury in the process industry. That is why investments for the purpose of operators training are increasing in all industries. On many industry sites, OTS systems are being developed at least for the most important units. However, anytime the investment plan is put at the table, numerous questions occur. 
Investment in OTS system is rarely a small one. It can be hard to evaluate the exact benefits, although there is always a long list of evidence why it is important and even necessary. 
Also, the way from the point of an idea to the full successful development and integration with the working environment, is full of challenges. Both investor and the vendor enters a labyrinth of questions, doubts, and uncertain answers. Through the way out of the labyrinth, it is easy to take the wrong way and get lost. The main reason that this projects are so complex lies in the fact that OTS is truly the integration of so many different knowledge areas: process knowledge, process control and control system knowledge, knowledge of process modeling, equipment knowledge and more. All those fields are complex enough on their own. When they are put together in a single system, a number of challenges can be overwhelming. Together with that comes a great value that OTS doubtlessly has. 

The aim of this article is to go through the major points that need to be addressed on time, to avoid problems, overpaid project and get the system to suit defined objectives. 

OTS functionality

The human error which is found to be the main cause of major accidents that have taken place in the past is the main driving force behind setting up such real time training simulators. Training simulators enable training of the operators on normal and emergency conditions including all types of scenarios that would arise in a plant and also unit start-ups and shut-downs. The scenario based training helps the plant operator to handle a crisis in an efficient manner with the ultimate goal of safe and efficient operation of the plant.

Operator Training Simulator is including modeling and simulation of all process equipment enabling that behind every measurement stands the process model. It also covers the original process graphics, control system, safety system, display of alarms and indications and all other parts of the control strategy included in the real unit.
OTS has become a well accepted medium of knowledge transfer and is a major step towards enhancing the skill set of the operators.

Critical points to be clarified when starting an OTS project

1. Clear definition of the objectives

This is the most important question that comes right at the beginning of the project that will with high probability define the successful outcome of the project. Therefore, it is very important to have a consensus of all the team members on this question.

Some of the questions related to defining the OTS objectives are defined with this checklist:

• What is the way OTS will be used in everyday working life? 
• Is it going to be used only for operator's training or for the engineering studies as well? 
• How the future training of operators is going to look like? 
• What are the most important safety issues that operators need to be trained for?
• Who will be their trainer and what is the principle of the exercises that will be defined for operators?
• How much the accuracy of the simulation model is important?
• What is acceptable accuracy?
• What are the most important sections on which the accuracy should be as good as possible?
• Analysis of the data available for the OTS development: are historical data of an existing unit or project design data going to be used?
• Are there any problems related to the reliability of any of those data?  
• What are expected OTS maintenance activities and needs?

Answers to this questions will help the investor to define both modeling platform and narrow the choice of an appropriate vendor.
In cases where these questions are not clarified at the beginning of the project, the result may be the wrong choice of a platform or a vendor, realized in the later phase of the project. At that point is too late to go back in steps. That is why this point is the most important point of the whole project.

2. Definition of fidelity and modeling platform

This step looks into more details as a natural step forward from the point 1. Clearer list of assumptions needs to be addressed here. When talking about OTS, their fidelity is one of the terms that most often comes up as an important decision to make. On the market, there are:

• Low fidelity models,
• Medium fidelity models,
• High fidelity models.

What very often makes a confusion is a misinterpretation and mixing of the terms fidelity with model accuracy. However, the fidelity doesn't have to be related to accuracy at all, it relates to the characteristics and the type of the simulation model used as the OTS platform. Therefore, low fidelity models define very simple tieback connection of the DCS elements. Their main purpose is to be able to connect and test control system with the help of defined measurement coming from a very simple model.
Medium fidelity models are using some of the basic chemical engineering equations but only to the point that does not cross the defined limit of complexity, both mathematical and thermodynamical. They can also use data-driven models and, therefore, can be quite accurate. However, with limited application outside of the defined operating area they are applicable only for operational purposes. That can be more than enough in many situations, mostly because of their flexibility and a lower price. However, their application is limited in cases of a more complex processes. 
High fidelity models have become the most accepted ones, especially for more complex units, the kind that are found in refining and petrochemical industry. Their characteristic is an application of rigorous process simulators such as Unisim, Hysys, Dynsim etc. Although their chemical engineering solid base is very important for a definition of process models, with their application, one should be aware of the complexities and challenges which are brought to the operational environment of an OTS system. This has to do with all the complications related to mathematical and calculation challenges and convergence problems.  Column and reactors are typical examples for this kind of problems. When columns are reactors are calculated for design purposes, those problems can be solved. However, when we are talking about operational activities in OTS life, where the operation is defined by the speed of a control system, the typical response of the OTS control system is on the level of 1 second. This can put a huge load on the simulation part and it is not a surprise that with hundreds and thousands of equations calculated simultaneously, sometimes the result is not possible to find. Because of the highly defined system with all the mathematical and thermodynamic equations, it is also the case that those models, although are high-fidelity are not necessary the most accurate. However, with adequate assumptions and simplification, those challenges can be bridged successfully. It is important to have this in mind while making the choices of the platform and to ask the vendor the right questions. Related to that, next checklist should be clarified checklist:

• What kind of models are used to model all process elements such as heat exchangers, valves, pumps, flash vessels etc. What kind of assumptions are defined?
• How the column and reactors are modeled? What assumptions are taken into account and what are possible problems of the simulations?

3. Definition of priorities

List of priorities should clarify important variables, expected process responses, error tolerance and robustness of particular process equipment and/or sections. Basic engineering logic is telling us how it is not possible to define all elements of the model with the same and/or highest accuracy. Therefore, priorities need to be defined so that it is clear when there comes the modeling problem, which variable is going to be prioritized over some other.

4. Definition of testing procedures

At the beginning of the project, it is very good to make a draft of how the OTS is going to be tested for acceptance. How it is going to be tested for steady state error tolerance and how for a dynamic. Although, the thorough test procedure is defined in later project phases, it is very helpful to have this draft in mind on the beginning of the project and to discuss it with the potential vendor. This is helping to predict possible deviations and priorities and reduce risks of an unsuccessful testing. 

With an OTS, the ability to model the plant will have a great impact on safety and staff effectiveness, since it allows personnel to be trained for safety-critical scenarios or events, and therefore improving the economical operation of the plant. Good project preparation is a crucial step in successful finalization of the project that will allow great knowledge transfer and certify the operators for competence.

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