Maximizing Process Control Strategy – Workshop Model

In the industrial process control applications, there are a wide variety of concepts and designs, made to suite the application at hand. All sorts of parameters required to be monitored, controlled are factored in and a control strategy developed to suit the plant’s operational and process control and shutdown needs. However, my experience tells me that there seems to be a need for developing a strategy whereby the maximum benefits of a modern day control system is used, where complex calculations, sequences, functions, even curves and graphs are programmable within the system and maximize plant availability and control, with minimal manual intervention from Operations.

This can be achieved by involving process, process control and automation engineers, into a brainstorming exercise forum or workshop similar to a HAZOP or SIL to evaluate Since, my background of work has involved Conceptual, FEED, EPC as well as Automation Vendors side, I have observed that there is a need for maximizing the use of control system and minimizing the use of manual intervention of an Operator, especially considering the degree, depth, versatility of built-in functions, and speed with which this can be achieved in the modern Integrated Control and Safety Systems. In so looking at it from various perspectives, a clear picture emerges; one in which there is a need to develop a mechanism of capturing methods of evaluation, in a workshop setting environment, where every control strategy adopted, in process control, can be re-evaluated, after applying all the international standards, recommended practices, design procedures, engineering standards that go into a typical engineering design of process control.

This has a huge added benefit to production and operations, in terms of long term cost and running costs; and yet, involves nothing more than building a comprehensive workshop at developing better process control strategies and giving the plant key instrumentation and control systems. This in my experience, has not been done with many existing plants. Most control is rudimentary and at a very basic level and yet the modern control system is capable of so much more complexity of process control and even predictive hazardous situations which would lead to a trip or a shutdown. There is a tendency to slack on focusing on Process Control and relying on Safety and trips, ignoring to build in an inherently safe design of a plant that is more immune to trips because of a runaway process and an insufficiently designed control strategy or a whole set of strategies for a plant. Trip immunity in itself, as a concept, can prevent so many instances of expensive and long startup procedures of a continuous process plant that costs cannot be weighed in simplistic measures.

A plant and most equipment design life run into many decades, and yet, the downtimes are due to trips of process and equipment; not to mention the rudimentary design of control and shutdown loops. There is currently, very little focus on attempting to develop strategies around maximization of process control using the modern control systems and the experience and participation of Operations and Maintenance folks un a plant, Automation backgrounds of control engineers and process knowledge of process engineers to constructively build one, through means of a workshop.

Designing and implementation of a workshop, not only will begin a culture of selecting field instrumentation and control strategy wisely and in places where it would maximize plant availability and reduce downtimes, but also maximize the features and benefits which are already available within the modern day control and automation systems, which currently are grossly under-utilized and most process engineers and operations/maintenance personnel are not even aware of the kind of inherent capabilities, functions, computations which already exist.

The following bulleted points, as open questions, are based upon the most common questions around which a model of a workshop maybe built, which can then be used to maximise the use of control system in continuous operations by using more built in features, functions and capabilities, while minimizing manual intervention.

A very crucial point to be noted is to add, adequate Field instrumentation to facilitate the results which emerge out of such a workshop since it has the sanction of a better developed and well rounded process control strategies that can minimize human errors and plant and/or equipment downtimes/maintenance time and plant systems/units trips as well. More often than not, in my experience, plant operations and maintenance personnel expect miracles out of a control system itself, while ignoring the basic fact that a well rounded control system can only work in conjunction with the field input/output that it receives. Typically, any plant has more sensors than final control elements, since open loops are used for monitoring purposes. However, the question remains if the valuable inputs that are received by the control systems are in fact being used in complex calculations and predictability models or not?

The following questions can be used to build a workshop Concepts for Process Control Maximization. And these questions are broadly to be asked of every Open/Closed loop parameter in the plant.

• ? Can a parameter, already available before or after this control loop, which can be functioned or factored into this loop, be effectively used, in any way to achieve better controllability of this loop?
• ? Can a parameter, not currently in design, before or after this control loop, which can serve as a primary factor to achieve better controllability of this loop?
• ? Is this control strategy relying least on the Operator and more on control system to maximize loop availability itself (i.e. on automatic control without any manual intervention)?
•  Is this control strategy relying on the Operator monitoring the least number of process parameters and/or graphic pages (ideal being a single page)?
• ? Can the tuning of this loop PID Controller/(s), be influenced and pre-programmed by the functioning in of an equipment performance curve or characteristic, which enhances the equipment performance and reduces downtime?
• ? Can a function, parameter, a bias or additional instrumentation, be added to this control loop, which will reduce trips and shutdowns as a result of process parameter runaway, upstream or downstream, during steady state of plant operation?
• ? Can a function, parameter or a bias, be added to this control loop, which will enhance its controllability and performance, over time, during steady state of plant operation?
• ? Can IPS loops pertaining resulting due to this loop failure, or immideatly upstream/downstream of this loop be eliminated in any way, by way of additional field instrumentation, more control loops and/or cascade loops?
• ? Have auto-tuning PID controller possibilities of this loop been explored based on real-time or historical trends, or based on other affected control loops in vicinity?
• ? Have auto-tuning PID controller possibilities of this loop been explored based on real-time or historical trends, or based on other affected packaged equipment loops in vicinity?
• ? Can a prior experience of Operations, be factored in this loop, to have it more in automatic control mode?
• ? Can the predictability of plant equipment that is upstream/downstream of this loop, be factored and functioned into this loop to have it more under automatic control mode?
• ? Have the Operator Graphics been optimized from an operational control perspective, factoring in all the above, and giving maximum control of the screen and all related parameters, so that operations can be performed with minimal graphic navigation?
• ? Can a sequence of manual operations be converted to a “One Touch” operation via Operator screens, by use of additional field instrumentation which is placed strategically around an equipment/package/plant unit?
• ? Have field instrumentation and systems been added to equipment, static, rotating and packaged equipment sufficiently in order to have reports generated for production teams to have a better planned maintenance shutdown while keeping plant operational?
• ?Can instrumentation and measurement be added to record and report the heat and material balance and power of the plant end-to-end, to assist in plant efficiency and performance?
• ? Is there a possibility of using a Complex function at any other process unit/train, the parameters resulting of which can be applied to this loop for better functioning?
• ? Is there are feedforward/feedback/cascade loop possible to/from any parameter of this loop to/from other loops downstream of this loop that may benefit downstream process fluctuations?

The above are meant only as a starting point in exploring concepts aiming to maximize the utility of a Control system, from a better designed, fit for purpose plant operations. More features and questions may be explored and built into the workshop, to explore and enhance process control strategy for every loop in a plant.

In conclusion, the kind of questions that are asked within such a workshop should aim at utilising all existing field instrumentation to the maximum capacity and yet use more complex calculations, loop manipulations and control strategy design and make operator friendly graphics at the same time giving maintenance engineers the data access of all critical Rotating/Static equipment/unit, packaged units, valves/motors and all equipment used to continuously vary process parameters, so that there is maximum availability of the plant at any time; at the same time maximum utilisation of the enormous capabilities built in within the modern day control systems.