11 Steps to Create a Virtual System Model

By Dominik Fry, P.E.  | Engineered Software, Inc.

In recent years, plant processes have become more intricate with a host of supervisory control and data acquisition (SCADA) solutions to achieve the precision control necessary to deliver a finished product. Control rooms have upgraded from analog to digital, with displays giving the operator data.

Operators can now tell which pumps are operating, various tank levels, concentrations, flow rates and much more. This is great for operators trying to hit a certain target. It can be tough on the health of the system. When there are issues, pinpointing the broken equipment is easy. However, determining the root cause of the problem is much harder.

Determining how a system interacts can be difficult. Processes and components change as upgrades are implemented over time. The new Department of Energy (DOE) standards for pumps and new motors are a challenge for the entire pumping industry. You cannot simply swap out an old motor for a new one anymore. There are operational challenges such as different-sized baseplates on new motors. There are also elements that change how the system will work, such as startup current, horsepower (hp) and slip.

With a more efficient motor, you could potentially have higher energy costs due to a higher pump speed. Now figure into the mix all the tweaks the operator is making and ask: Is your system really working smarter? Just because a control room looks high tech does not mean the underlying system is functioning as designed.

Fluid flow software provides a clear picture of how a piping system operates by calculating the flow rates and pressures in the system. Initially, this software was mainly used to design the piping system, but recently, more plant personnel are using this software to simulate the operation of existing fluid piping systems.

1. Paint a Total Picture

To be effective in the plant operating market, the fluid flow software provides the user with enough information to design, build, operate and maintain the system throughout the plant’s life. This will show the conditions or positions to achieve a certain set point and the effects on the entire system. A valve position may change for a lower set point, but this may trigger warnings if it makes the pump run outside its acceptable operating range, or if minimum or maximum flow velocities are exceeded.

2. Visualize Connections

Providing the user with a clear picture of how the items in a piping system are connected is a must. Piping schematics show the connection between location of tanks, pumps, components, control valves and pipelines. A piping schematic identifies each item in the system using the project’s equipment naming convention.

3. Calculate Flow Rates, Pressures

Fluid flow software calculates the balanced flow rates and pressures in piping systems. It can handle open- or closed-loop systems, as well as series, branching and parallel flow paths. Sizing rules and design limits assist the user in optimizing or warning for individual pipelines during the design process. Set up and save various operating scenarios so the user can see how the system operates under a variety of expected operating conditions.

This approach also allows the user to optimize the piping system as it is being built, providing a better final design. Using these calculation techniques, the user can quickly build the piping system model without having to get involved with the program’s inner workings.

4. Communicate Specifications

Communication is necessary to ensure the various groups involved in the project have a clear understanding of how the piping system is to be built and operated. To ensure a system is built to meet the requirements of the end user, specification documents are developed outlining the methods for each item’s design, construction and testing.

During the design process, the information must be checked and reviewed by other members of the design team. After the system design is completed, the owner of the piping system must review the information. The ability to communicate with others ensures everyone involved with the project has access to all the information needed to design, build, operate and maintain a fluid piping system.

5. Build the System Model

Building the system model involves entering the details about each item in the piping system. Much of the information needed to build the model is obtained during the design process. It is always best to create the model during the design process and keep the model current through construction and startup. This allows users to turn over a completed piping system model
to the client as part of the required design package.

6. Provide a Design Document

Project files provide the user with the ability to store and update piping system design details as they become available. For example, when doing a preliminary design, the pipe diameter and number of isolation and check valves are determined. The length of pipe and number of elbows are approximated. Once the pipe routing is completed, the exact length of pipe and number of elbows are known, and the piping system model can be updated.

At the end of the design phase, the engineering documents can be turned over to construction for use in building the system.

7. Create a Construction Document

During construction, the design documents are used to build and test the system. Field changes are often necessary to accommodate changes in pipe routing or changes in the system design. If the modifications involve adding pipe length, elbows or adjustments to the pipe sizes, the system model can be updated, and calculations can be done to show the effect these changes have on the piping system operation.

During plant startup and testing, the software provides the plant startup engineers with a model that shows how the system will operate. This information is useful during startup because much of the equipment testing is conducted with the equipment running in abnormal operating conditions. A copy of the design model can be created, and the operating conditions can be adjusted to reflect how the test will be run.

The software also can be used while flushing the piping system to remove construction debris. A copy of the piping system model can be created, and the startup engineer can insert the strainers, filters and piping jumpers needed to flush the system. A fluid flow analysis can then calculate the flush velocities for each flush path. In addition, the fluid flow analysis can calculate if a pump is operating off its pump curve due to abnormal operating conditions encountered during the flushing operations.

Finally, the program can calculate the valve positions needed to balance the flow rates in the piping system.

8. Validate the Piping Model

After the system is built and put into operation, the piping model should be validated. The plant instrumentation shows how the plant is operating. If the model matches the observed plant operating conditions, the model accurately reflects the actual system operation and it is a valid model.

Once the validation is performed for a variety of operating conditions, the model can be used to predict system operation under any possible set of operating conditions.

9. Troubleshoot System Operations

After the system has been turned over to the operating plant, the model can be used to troubleshoot system operations. If the predicted results of the piping system model do not agree with the observed operating data, then the model is incorrect or something in the piping system is not operating as designed.

A piping system lineup can be created so the model is set up exactly like the real system is operating. By comparing the observed values of the operating system with the piping system model, one can quickly isolate the problem and, more importantly, determine what can be done to return the system to normal operation.

10. Make Plant Improvements & Modifications

During the life of the plant, adjustments will be made to the system because of process changes, the addition of new loads or the need to increase capacity. Using the existing piping system model, the project engineer can see how the required changes will affect the operation of the system.

11. Train for Operations

Plant operating personnel need to know how the plant will operate during a variety of conditions. They can either gain that experience by putting the plant into that condition, or they can simulate the operation.

In many cases, the piping system is infrequently operated at given conditions, such as startup or shutdown, making it difficult for operating personnel to obtain necessary experience. In other cases, the system cannot be run in that condition due to operational requirements.

Conclusion

A thorough understanding of your piping system allows for more a more effective and safe use of resources. Individual components can be tuned to run in their most efficient range, which also increases mean time between failure (MTBF). This allows the end user to have a firm understanding of the limitations of the system.

Together, these translate to a safer work environment where maintenance can be planned rather than hurried in an emergency. This also allows for engineers and operators to test the system and make any potential mistakes in the model, rather than in real life. As a result, the model is a valuable design document for anyone involved with the system. If the model is started during the design phase, updated during construction and maintained for the life of the plant, a clear picture of the piping system operation is always available.