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Early Event Prediction with Geometric Process Control: Compressor Surge

Adverse events such as surge in compressors, breaks in paper, glass, and film manufacturing, and pack-offs in oil well drilling cause upsets, unproductive downtime, equipment wear, and can be a major expense in operations. Avoiding these events is a key part of the design and operation of many process systems. Often the otherwise most economic operating conditions (fastest throughput or most energy efficient) are exactly the conditions which increase the likelihood of adverse events. Thus, a common operating goal is to operate near event conditions while minimizing the chances that these events will occur. Further complicating the problem is that the mechanisms leading to events are rarely fully understood and the ideal operating conditions can be very sensitive to process operations.


Drilling Better Wells Cheaper and Faster

The control of a drill in realtime is demanding on the skills and experience of the drill operator and is variable across operating shifts because different operators have different levels of skill and experience.This paper describes and demonstrates a radically different approach and a solution to the problem by modelling the operating envelope of the drill operation as a multi-dimensional solid object so that the operating problem becomes a geometric problem of operating always as an interior point of the envelope.

The method is part of the overall technology known as Geometric Process Control (GPC) which is becoming well-established in downstream process industries and has already achieved success in problem-solving and offshore process improvement applications with several major North Sea operators. It has won awards for Innovation from EPSC, IChemE, IET and the CIA (Chemical Industries Association).


Operator Alarms are the First Line of Defence

Operator Alarms should be the first line of defence in every plant but all too often are more of a nuisance than an aid to the operator. This exposes safety alarms to more process excursions with the consequent increase in probability of a Failure upon Demand detracting from the plants overall safety capability. Poor operator alarms also contribute to poor process economics. The situation has arisen because there has never been a fundamental understanding of how alarm limits relate to process control and to process operating objectives.

We have identified that the Operating Envelope of a batch or continuous process is the missing factor that unites all three topics. Operator Alarms are inter-related by positioning them on the boundary of an operating envelope which is today approximated by an alarm window or hypercube. Understanding and using the geometric relationship between an operating envelope and its approximating hypercube eliminates many false alarms. This substantially improves the credibility of the alarm system to the operator and allows earlier annunciation with more time for the operator to respond.

The paper describes the methods used, including a simple visual method for Alarm Rationalisation that quickly delivers large sets of Consistent Alarm Limits, and the extension to full Alert Management with highlights from the Field Trials to indicate the overall effectiveness of the method in practice. .


A New Method for Defining and Managing Process Alarms and for Correcting Process Operation when an Alarm Occurs

A new mathematical treatment of alarms that considers them as multi-variable interactions between process variables has provided the first-ever method to calculate values for alarm limits. This has resulted in substantial reductions in false alarms and hence in alarm annunciation rates in field trials. It has also unified alarm management, process control and product quality control into a single mathematical framework so that operations improvement and hence economic benefits are obtained at the same time as increased process safety.

The paper describes the methods used, including a simple visual method for Alarm Rationalisation that quickly delivers large sets of Consistent Alarm Limits, and the extension to full Alert Management with highlights from the Field Trials to indicate the overall effectiveness of the method in practice. 

This substantially improves the credibility of the alarm system to the operator and allows earlier annunciation with more time for the operator to respond. Field Trials have been and are being conducted at IneosChlor and Mallinckrodt Chemicals, both in the UK, of the new Geometric Process Control (GPC) method for improving the quality of both process operations and product by providing Process Alarms and Alerts of much high quality than ever before. The paper describes the methods used, including a simple visual method for Alarm Rationalisation that quickly delivers large sets of Consistent Alarm Limits, and the extension to full Alert Management with highlights from the Field Trials to indicate the overall effectiveness of the method in practice. .


Using Alarms to Achieve Management Objectives

In this paper we show that Alarm Limits and Operating Limits should be the same and that this will allow Alarm Limits and their rationalisation to benefit from the well-developed economic understanding already in existence for Operating Limits


Consistent Alarms Improve Process Economics and Increase Process Safety

There has never been a scientific method for finding process operating alarm limits other than a few strength-of-materials calculations of safety limits which are outside the scope of this paper. Almost all previous work on Alarm Rationalization has started from the Process Alarm Log and proceeded from there based upon qualitative judgements. We present our scientific method for determining safer and more profitable operating alarm limits based upon process historical data and demonstrate this technique with implementation examples.

We have identified that the Operating Envelope of a batch or continuous process is the missing factor that unites all three topics. Operator Alarms are inter-related by positioning them on the boundary of an operating envelope which is today approximated by an alarm window or hypercube. Understanding and using the geometric relationship between an operating envelope and its approximating hypercube eliminates many false alarms. This substantially improves the credibility of the alarm system to the operator and allows earlier annunciation with more time for the operator to respond.

Field Trials have been and are being conducted at IneosChlor and Mallinckrodt Chemicals, both in the UK, of the new Geometric Process Control (GPC) method for improving the quality of both process operations and product by providing Process Alarms and Alerts of much high quality than ever before. The paper describes the methods used, including a simple visual method for Alarm Rationalisation that quickly delivers large sets of Consistent Alarm Limits, and the extension to full Alert Management with highlights from the Field Trials to indicate the overall effectiveness of the method in practice.


The Rationale for Alarm Rationalization

Quantifying the economic value of an Alarm System, or even the value of rationalising it, has rarely been attempted. Few, if any, plants actually know the value, as opposed to the cost, of their alarm systems hence they can not justify and do not see a need to initiate projects involving additional expenditure on, for instance, alarm rationalisation or on-going continuous improvement of the alarm systems. Requirements for such projects come from outside the plant either compelled by legislation or coerced by the need to be seen to have adhered to Best Practice in case litigation should follow a plant incident. In the absence of a value-understanding, project justification degrades to the need for just-enough compliance with the legal or Best Practice requirement and may be seen as an imposition deserving of less than their full enthusiasm by those most closely involved with the plant and who are already fully and gainfully occupied in meeting production and up-time targets. Unfortunately these are the very people most essential to any rationalisation or improvement of an Alarm System.


New Alarms and Alerts from Operating Envelopes drive economic benefits as well as Safer Processes

Few, if any, plants actually know the value, as opposed to the cost, of their alarm systems hence they can not justify and do not see a need to initiate projects involving additional expenditure on, for instance, alarm rationalisation or on-going continuous improvement of the alarm systems. The root cause has been lack of a fundamental understanding of alarms exemplified by the fact that there has never previously been a general method to find values at which to set the alarm limits, although this is where many or most of the problems of alarm systems begin and therefore could end.

In this paper we show that Alarm Limits and Operating Limits are linked by an Operating Envelope. They should in principle be the same, thus allowing Alarm Limits and their rationalisation to benefit from the well-developed economic understanding already in existence for Operating Limits. That they are not the same today is probably because it was not previously possible to see, compare and work with Operating Envelopes.


Defeating an Old Adversary - Cement Kiln Balls

For reasons not well understood kilns – pulp, cement, etc. – form balls. Although creative solutions, including use of the 04 gauge shotgun kept in a certain pulp mill’s control room, have been devised for their elimination such balls frequently grow without bound.
Beyond rework of product caught in the kiln when it became choked by large objects – which can also damage refractory material in the cement case – this drives a throughput penalty from frequent start-ups and shutdowns that can be the operational bane of a plant’s existence. Hence, although blasting pulp balls out of existence can provide a diversion for the control room staff and viable clinker is generally made (albeit at high cost) in cement kilns that are cycled up and down, prevention is a far superior solution. Unsurprisingly, this proved easier said than done at a major cement manufacturer’s facility where two large kilns were freakishly affected -–winter and summer, without apparent pattern or reason – by unexpected ball formation which considerably restricted output.


The Missing Link between Operator Alarms, Process Control and KPI’s

Operating Envelope is one of those phrases that everyone uses and understands until they are asked to describe and define an operating envelope for their process. Then they discover that the words they need just don’t exist in English (and probably not in any other language either), that they can’t draw a picture of an operating envelope and that even with advanced mathematics they can’t describe an envelope of their process with equations. So how have plants managed to operate all these years without being able to know whether they were operating inside or out¬side of the nebulous and undefined Envelope within which they achieve all of their product and KPI objectives?


 

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