The modern plant manager has plenty to worry about, what with keeping aging plant and equipment running, getting the most out of resources and complying with an almost never ending deluge of environmental, safety and health requirements.
“All this and the manager needs to keep a competitive edge too,” points out Business Development Manager with Invensys Process Solutions Dr Paul W Seccombe.
The answer, he believes, is simulation: “Its justification lies in the fact that simulation is much more than just training.”
To begin with, a simulator can be used to validate design and control strategies, assess process equipment design, and analyse process operability. The next stage is control testing, where it helps with activities such as controller pre-tuning and graphic display improvement.
Personnel training is obviously important, especially in terms of interface familiarisation, start-up training, emergency response training and C&I diagnostic training.
Finally, simulation improves plant performance by allowing alarm management, advanced process control pre-tuning and operation procedure optimisation.
However, even when faced with these apparent advantages, many plant managers will still ask themselves why they should bother with operator training simulation (OTS). Seccombe's response is to highlight the risks versus the opportunities.
“Risks include outages and damage to the plant, which can involve substantial costs. There is also the challenge of knowledge management, which can be very serious where aging staff are involved. The use of an OTS provides a platform to capture this knowledge in a formal, documented manner. On the opportunity side, OTS allows you simulate control checkout, improve knowledge via operator training and, overall, to operate the plant as efficiently as possible.”
In order to achieve success, however, the plant manager needs to invest in the best simulation modelling software and the best DCS/PLC simulation available.
Invensys’ answer to this is its SIM4ME simulator solution architecture, its DynSim (dynamic process simulation) real object oriented modelling and its FSIM, TRISIM: ExactFIT approach to simulating control systems.
The point here is that Invensys’ simulator solutions offer ‘virtual stimulation’ solutions, incorporating real DCS graphics and control systems connected through the SIM4ME environment to the Dynsim process models. Not like the competition, which he says offers ‘cartoon graphics with Fortran code for the DCS under the hood’. And DynSim works beyond steady state, calculating mass, energy and accumulation along with all typical dynamic constraints. All these solutions incorporated within SIM4ME remove unknowns, giving greater confidence in the results.
“There are a number of reasons why Invensys has chosen to go down this route,” he explains. “Firstly, models are easy to construct so changes are similarly easy to track and control. No detailed programming skills are required. In addition, just one user interface handles all OTS needs, including engineering and model building. The model configuration itself resides in an open database, which makes it portable for the future.”
In terms of DCS simulation, Invensys uses a technique that it calls ‘virtual stimulation’ rather than full simulation or full emulation.
On one level, the ideal solution would appear to be a full simulation that uses real DCS hardware and controllers.
The advantages are obvious – direct use of controls and graphics, actual cabinet hardware, full engineering functions and control checkout. The downsides are quite dramatic, however.
First is the very high cost and secondly the fact that real controllers do not support simulation functions such as start, stop, snapshot, speed up or slow down very well.
Then there is the full emulation option. Here, custom software is written to mimic control function and operator graphics. It has the advantage of low hardware cost, portability and reusability.
However, while emulation may have a low cost initially, the exact function of the DCS controllers is not 100percent replicated and can struggle to keep up with the latest versions. As a result, the maintenance cost of keeping an emulated solution up to date can lead to significant costs in the future.
Invensys’ take on this is to use virtual stimulation in which it ‘ports’ controller software to run on the PC and uses real operator stations. Although this does require the use of real DCS operator/engineering stations, it gives exact control function, can be used for control checkout and uses actual controls and graphics.
“With data from the DynSim models, the DCS and the ESD – and SIM4ME at its heart – this revolutionises modular simulation DCS and process simulation models. It uses the same HMI as a real system, the same source code as a real system and users can have as many ‘engines’ as they want,” explains Seccombe.
With the control algorithms being ported or compiled for a desktop computer the ‘virtual’ controller enjoys reduced maintenance costs and long-term maintainability.
The bi-directional transfer of both controls and graphics again lowers maintenance costs, means that OTS is always up to date, and always available for check out control, improvement and testing. All these factors are key on a new plant, or one going through a significant upgrade.
Another important factor is the improved training environment. It eliminates the hassles that emulated controllers can cause in the simulation environment, allows users to go fast, slow, forwards and backwards, and allows for trainee performance monitoring (TPM).
“With TPM you can use as many key performance indicators (KPIs) as you want, so performance can be marked against KPI score. In my opinion, an operator score of 75–80percent is acceptable bearing in mind the type and severity of exercises you are putting the operators through. You can then follow the operator's progress with respect to his or her personal development training.”
Three month ROI
There is no doubt that OTS already produces real savings. Take for example the full OTS designed for the Iberdrola CCGT plant at Castellon in north eastern Spain.
This brand new plant consists of two 800MW gas turbines, uses FoxboroI/A DCS for plant control and GE MkVI control for gas and steam turbines. The purpose of the simulator was threefold – operator training, C&I training, and test bed control.
“As DCS/simulator schedules were tightly linked throughout the project, the company got early delivery and better quality. In fact operator training was considered to be the added benefit! Also, the project’s return on investment (ROI) was under three months.”
The economic justification is as follows: 800MW of power is being produced at roughly US$30/MwH. So that is US$24000 of generation. Each control trip found during an outage can take anything from 1–4 hours to resolve if it is straightforward. More complicated problems can take a whole day to sort.
“If the simulator uncovers control or operation glitches that save only two days outage, the opportunity is there to save over US$1m. Throw the simulator away – you just made your money back.
“At the end of the day, if you consider recent events in the industry, we are in the business of potentially saving not only damage to the plant, and improving operations, but also human life,” he concludes.