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Examples of applications that could benefit from Geometric Process Control (GPC)
The main thrust of GPC is the reduction of variability in process operations because that will allow operation nearer to your best all of the time rather than some of the time. But we make it much easier for you and your engineers by using geometry instead of algebra or calculus to let you see, explore and model Operating Windows and Operating Envelopes using pictures containing hundreds of process variables instead of spreadsheets full of numbers. You can interrogate these pictures, and add your own calculations if you wish, to investigate, refine and test operating envelopes and operating windows to meet objectives for Safe Operating Limits (SOL), Reliability Operating Limits (ROL), Integrity Operating Windows (IOW), Operator Alarm Limits, Operator Alerts, KPIs, MPC Constraint Envelopes, Environmental Compliance Envelopes and more for continuous, batch and grade-change processes. The real-time process operator display shows the current process operating point across many process variables superimposed upon the Operating Envelope and Operating Window giving the operator his long-wanted “where am I” picture across many process variables, sometimes described as “radar for process operators”. Here is an example for a crude oil distillation column from an oil refinery:

Schematic diagram of the processes in a crude oil distillation unit

Gas Turbine Process

The image above is the process operator's real-time view of a CDU described with just 20 process variables and showing 30 hours of operation in just 6 seconds (in practice, the display might update once or twice per minute). You can see the envelope moving up and down with the change between day-time and night-time ambient conditions. The process operating point is shown as black dots coming via OPC from the DCS; the Operating Window is represented by the two horizontal grey lines with the individual Operating Limit values shown. The green zig-zag lines show the available space around the operating point within which the CDU’s operating objectives can be achieved. The instruction to the operator is “keep the black dots between the green lines”. Occasionally one of the boxes under the plot flashes red indicating an Alert when operation has strayed outside the Operating Envelope and operating objectives are no longer being achieved. The Alert is often accompanied by corrective advice in blue advising the operator how to adjust some of the manipulable variables to correct the violation and get back inside the Envelope where conventional regulatory and MPC controls can take control again. The picture looks the same for batch processes (see the picture at the top of this page) except that there is often a visible ‘jump’ as the process changes from one phase's Operating Envelope to the next (or from one mode's Operating Envelope to the next for a multi-mode continuous process or multi-grade polymer process). To get here required the use of PPCL’s offline C Visual Explorer (CVE) product, the other main component of GPC, and the real-time C Process Modeller (CPM) product in the no-maths, 3-step procedure outlined below:

Methods employed to build an operating envelope model using the CVE / CPM software suite provided by PPCL

Keep reading! You need to know a lot more about the capabilities of CVE and may decide that that is as far into GPC as you want to go at first. But once you realise how often your process strays outside the operating envelope you will soon realise that you need CPM as well to enforce operation inside an operating envelope.

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