Process Control for Practitioners Hardcover – October 14, It is your complete reference for improving control-loop performance, solving process control problems, and designing control strategies. Jacques F. Smuts, Ph.D., has been a process control practitioner since the. OptiControls is proud to announce the release of its flagship book, Process Control for Practitioners – How to Tune PID controllers and Optimize. The importance of process control. Control theory basics. Components of control loops and ISA symbology. Controller algorithms and tuning. Process control.
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Important Terms and Objective of Automatic Process Control / 3. Regulatory . To do good process control there are at least three things the practitioner. This technology guide of industrial process control techniques Process control keeps processes within specified boundaries and minimises variations. experiences of the Advanced Process Control Group at the. Department of .. reason or other, many practitioners are still not confident about the long term.
The book is targeted primarily for use in the continuous process industry, but even predominantly batch plants have continuous controllers and often have sections of the process which are continuous. My experience is mainly in the oil and petrochemicals industries and, despite every effort being taken to make the process examples as generic as possible, it is inevitable that this will show through. However this should not be seen as a reason for not applying the techniques in other industries.
Many started there and have been applied by others to a wide range of processes. It is hoped that the academic world will take note of the content.
While some institutions have tried to make their courses more relevant to the process industry, practitioners still perceive a huge gulf between theory and practice. Of course there is a place for the theory. Many of the modern control technologies now applied in the process industry are developed from it.
And there are other industries, such as aerospace, where it is essential. The debate is what should be taught as part of chemical engineering. Very few chemical engineers benefit from the theory currently included. Indeed the risk is that many potentially excellent control engineers do not enter the profession because of the poor image that theoretical courses create.
Further, those that do follow a career in process control, can find themselves working in an organisation managed by a chemical engineering graduate who has no appreciation of what process control technology can do and its importance to the business.
Preface xi It is the nature of almost any engineering subject that the real gems of useful information get buried in amongst the background detail.
Listed here are the main items worthy of special attention by the engineer because of the impact they can have on the effectiveness of control design. Understanding the process dynamics is essential to the success of almost every process control technique.
These days there is very little excuse for not obtaining these by plant testing or from historically collected data. There are a wide range of model identification products available plus enough information is given in Chapter 2 for a competent engineer to develop a simple spreadsheet-based application.
Often overlooked is the impact that apparently unrelated controllers can have on process dynamics. Their tuning and whether they are in service or not, will affect the result of steptests and hence the design of the controller. Any changes made later can then severely disrupt controller performance. How to identify such controllers, and how to handle their effect, is described in Chapters 2 and 8. Of particular importance in the proportional-on-PV algorithm. It is probably the most misunderstood option and is frequently dismissed as too slow compared to the more conventional proportional-on-error version.
In fact, if properly tuned, it can make a substantial improvement to the way that process disturbances are dealt with — often shortening threefold the time it takes the process to recover.
This is fully explained in Chapter 3. Controller tuning by trial and error should be seen as an admission of failure to follow proper design procedures, rather than the first choice of technique. To be fair to the engineer, every published tuning technique and most proprietary packages have serious limitations. Chapter 3 presents a new technique that is well proven in industry and gives sufficient information for the engineer to extend it as required to accommodate special circumstances.
Derivative action is too often excluded from controllers. Understandably introducing a third parameter to tune by trial and error might seem an unnecessary addition to workload. It also has a poor reputation in the way that it amplifies measurement noise, but, engineered using the methods in Chapter 3, it has the potential to substantially lessen the impact of process disturbances. Tuning level controllers to exploit surge capacity in the process can dramatically improve the stability of the process.
However the ability to achieve this is often restricted by poor instrument design, and, often it is not implemented because of difficulty in convincing the plant operator that the level should be allowed to deviate from SP set-point for long periods. Chapter 4 describes the important aspects in sizing and locating the level transmitter and how the conventional linear PID algorithm can be tuned — without the need even to perform any plant testing. It also shows how nonlinear algorithms, particularly gap control, can be set up to handle the situation where the size of the flow disturbances can vary greatly.
While many will appreciate how signal conditioning can be applied to measurements and controller outputs to help linearise the behaviour, not so commonly understood is how it can be applied to constraint controllers.
Doing so can enable constraints to be approached more closely and any violation dealt with more quickly. Full details are given in Chapter 5.
Many engineers are guilty of installing excessive filtering to deal with noisy measurements. Often implemented only to make trends look better they introduce additional lag and can have a detrimental impact on controller performance. Chapter 5 gives guidance on when to install a filter and offers a new type that actually reduces the overall process lag. Split-ranging is commonly used to allow two or more valves to be moved sequentially by the same controller.
While successful in some cases the technique is prone to problems with linearity and discontinuity. A more reliable alternative is offered in Chapter 5. Feedforward control is often undervalued or left to the MVC. Chapter 6 shows how simple techniques, applied to few key variables, can improve process stability far more effectively than MVC. A commonly accepted problem with MVC is that, if not properly monitored, they become over-constrained.
Chapter 8 offers a range of monitoring tools, supplementary to those provide by the MVC vendor, which can be readily configured by the engineer. There are many examples of MVC better achieving the wrong operating objective; unbeknown to the implementer they are reducing process profitability. Rather than attempt to base the cost coefficients on real economics they are often adjusted to force the MVC to follow the historically accepted operating strategy. Some MVC are extremely complex and it is unlikely that even the most competent plant manager will have considered every opportunity for adopting a different strategy.
Chapter 12 shows how properly setting up the MVC can reveal such opportunities. Indeed many of them are so inaccurate that process profitability would be improved by decommissioning them. Chapter 9 shows how many of the statistical techniques that are used to assess their accuracy are flawed and can lead the engineer into believing that their performance is adequate. It also demonstrates that automatically updating the inferential bias with laboratory results will generally aggravate the problem.
Simple monitoring of on-stream analysers, described in Chapter 9, ensures that measurement failure does not disrupt the process and that the associated reporting tools can do much to improve their reliability and use. Preface xiii. Compensating fuel gas flow measurement for variations in pressure, temperature and molecular weight requires careful attention. Done for accounting purposes, it can seriously degrade the performance of fired heater and boiler control schemes.
Chapter 10 presents full details on how it should be done. Manipulating fired heater and boiler duty by control of fuel pressure, rather than fuel flow, is common practice.
However it restricts what improvements can be made to the controller to better handle process disturbances. Chapter 10 shows how the benefits of both approaches can be captured. Fired heater pass balancing is often installed to equalise pass temperatures in order to improve efficiency. Chapter 10 shows that the fuel saving is negligible and that, in some cases, the balancing may accelerate coking. However there may be much larger benefits available from the potential to debottleneck the heater.
Chapter 11 describes how these schemes work and, using the tuning method in Chapter 3, how they might be implemented in the DCS. A common failing in many distillation column control strategies is the way in which they cope with changes in feed rate and composition.
Often only either the reboiler duty or the reflux flow is adjusted to compensate — usually under tray temperature control. Chapter 12 shows that failing to adjust both is worse than making no compensation.
Other common misconceptions include the belief that column pressure should always be minimised and that the most economic strategy is to always exactly meet all product specifications. There are many pitfalls in executing an advanced control project. Significant profit improvement opportunities are often overlooked because of the decision to go with a single supplier for the benefits study, MVC, inferentials and implementation.
Basic controls, inferentials and advanced regulatory controls are not given sufficient attention before awarding the implementation contract. The need for long-term application support is often underestimated and poor management commitment will jeopardise the capture of benefits.
Chapter 13 describes how these and many other issues can be addressed. Gaining the knowledge and experience now contained in this book would have been impossible if it were not for the enthusiasm and cooperation of my clients. I am exceedingly grateful to them and indeed would welcome any further suggestions on how to improve or add to the content.
Myke King July , Isle of Wight About the Author Myke King is the founder and director of Whitehouse Consulting, an independent consulting organisation specialising in process control. He has over 35 years experience working with over clients from more than 30 countries. As part of his consulting activities Myke has developed training courses covering all aspects of process control. To date, around delegates have attended these courses. To support his consulting activities he has developed a range of software to streamline the design of controllers and to simulate their use for learning exercises.
His course included process control taught as part of both mechanical engineering and chemical engineering. At the time he understood neither!
Fortunately he quickly discovered that the practical application of process control bore little resemblance to the theory he had covered at university. He later became head of the process control section and then moved to operations department as a plant manager. This was followed by a short period running the IT section. The company was sold to Honeywell where it became their European centre of excellence for process control.
It was at this time Myke set up Whitehouse Consulting. At the lowest level is the process itself. Understanding the process is fundamental to good control design. While the control engineer does not need the level of knowledge of a process designer, an appreciation of how the process works, its key operating objectives and basic economics is vital.
In one crucial area his or her knowledge must exceed that of the process engineer, who needs primarily an understanding of the steady-state behaviour. The control engineer must also understand the process dynamics, i. Next up is the field instrumentation layer, comprising measurement transmitters, control valves and other actuators. This layer is the domain of instrument engineers and technicians. However the control engineer needs an appreciation of some of the hardware involved in control.
He or she needs to be able to recognise a measurement problem or a control valve working incorrectly and must be aware of the accuracy and the dynamic behaviour of instrumentation. Above the field instrumentation is the DCS and process computer.
These will be supported by a system engineer. So he or she needs to be well-trained in this area. These are vertical shaft kiln, rotary quality, increased production, improved fuel efficiency, lime kiln and fluidized bed lime kiln. Out of these majority of increased refractory life, improved kiln information gathering paper industries globally use rotary lime kiln. A rotary lime kiln and processing.
The absence of closed loop controls results operating conditions and frequent disturbances, unreliable and in inefficiencies in fuel consumption and variation in reburned inaccurate process sensors, accurate dynamic kiln process lime quality . The potential for reducing the overall costs of the operators, which can cause kiln upsets at each shift change. The benefits associated with theoretical and practical issues associated with MPC technology. Although respectively.
Ufuel, udamper, YFET and YBET represents fuel flow DMC was conceived for multivariable constrained control, rate manipulated variable, damper percentage opening while GPC is primarily suited for single variable, and possibly manipulated variable, front end temperature controlled variable adaptive control .
In the present investigation, a multivariable, linearized, time Table1 delayed model of an industrial lime kiln process is controlled Tuning parameters for analyzing the effect of change in using MPC strategy and the effects of variation on controller controller setting by varying control horizon only. Tuning parameter Value Control interval time units 1 II.
Secondary objectives include minimization of the energy Coefficient of ufuel rate weight 0. Coefficient of udamper weight 0 temperature of the hot lime within specified bounds. The Coefficient of udamper rate 0. The manipulated variables are the fuel flow rate Coefficient of YFET weight 1 and the damper percentage opening for air flow rate .
Response speed to robustness 0.
The settling time is same for FET set-point responses Effect of varying ratio of control horizon to prediction horizon for control horizon values of 2 and 3. The peak time in former on closed loop response for FET is visualized in three cases. Effect of varying ratio of control horizon to prediction although the response is very close for control horizon as 5. Effect of varying ratio of control horizon to prediction horizon As the ratio of control horizon to prediction horizon can be on closed loop response for FET set point by varying control varied also by keeping fixed control horizon and varying horizon with fixed prediction horizon of value 10 is investigated.
Next attempt is to investigate the effect of The control horizons are selected as 1, 2 and 5 which give the this ratio using these possibilities. Effect of ratio of control horizon to prediction horizon Now the effect of ratio of control horizon to prediction horizon on closed loop response for FET set point on closed loop response for FET set point is seen by varying prediction horizon with fixed control horizon of value 2. The peak times are 4, 5 and 6 seconds Tuning parameter Value respectively and peak amplitudes are 1.
The best response achieved is that for Coefficient of ufuel rate weight 0.