Control Loop Case History 106

HOW PROCESS PLANTS CAN SUCCEED IN THESE TOUGH ECONOMIC TIMES

We are living through one of the worst worldwide economic crises of all times. There is huge uncertainty everywhere as to how long it will last, with world leading investment and financial gurus talking years. Even more scary is the fact that many people who are experts in the financial world are scared that we haven’t even seen the real “crunch” yet, and an even worse melt-down lies yet ahead.

To an engineer like myself, to whom economics and the ways of the financial world are really a grey area, it is incomprehensible that this has happened, and that we have found ourselves in this situation. When I did a management course in the late 1960’s, I was told that the economists had now so much scientific understanding, that it would be impossible for the world to ever again have a major recession, let alone a depression. However since that time we have suffered 3 fairly bad stock-market crashes. We have been repeatedly told that the only way to really make your savings increase is to invest in equities, and whatever you do, not to leave your money earning interest in the bank. After finding I did not have the time or knowledge, and was not too good in investing in the stock-market myself, I decided to invest through funds headed by experts who have a wealth of experience, huge research teams, and should be able to increase your funds dramatically. However my general experience on the whole is that in spite of being charged substantial fees (whether your funds did well or not), I probably would have been much better off leaving my money in something like a Money Market Fund, and cheerfully paying a large chunk of my earnings to our friendly SARS.

I also find it incomprehensible that the whole world is dependent on the economic health of the USA, which country is, and has been technically bankrupt for years, owing countries like Japan and China trillions of dollars. To an engineer it doesn’t make any sense. It certainly is like building skyscrapers on a quicksand without any foundations.

The sad thing about it is how it is affecting the lives of virtually all the people on Mother Earth. There is a huge shortage of skilled and experienced technical people in many countries in the world, and particularly in Southern Africa. The brain drain in our own South Africa has been alarming over the last few years.

People with process and control and instrumentation skills have always been in high demand. I have been told many times by these people, that one thing they are sure about is that they will never be out of a job.

However what has happened? Turnover of companies has dropped dramatically. They have to cut back, and make savings. How do they do this? Firstly they lay off people. In many cases they look at laying off the older people who can be got rid of more easily. Then they lay off the “last-in” people who were the most recent to join. Skills don’t seem to come into the equation.

I have quite a sad example of this. I had an excellent and highly experienced C&I consulting engineer who worked for a large mining group on a course in November last year. He is a man in his late 40’s. He wanted to leave South Africa, and his company said they could use him in Australia. He left with his family in December, full of plans on optimising the controls of the mines he would be responsible for in Australia. Things went well for him in January and February, and we corresponded quite a few times. In March he emailed me to tell me that the company has decided to suspend their Australian operations, and he has been made redundant. Terrible! Since then I have heard of quite a few very intelligent people with a lot of experience who have been retrenched.

Great! The companies concerned have saved themselves a lot of money. However they don’t seem to realise that one day, hopefully not too far in the future, things will, as they must do, swing the other way. When they want to start increasing production again they will find they have lost a huge base of skills and experience, which will severely hamper their growth.

Back to the present. The companies are laying off people, cutting back production, but they still haven’t managed to save enough money. So they look round for other ways of cutting budgets. To many companies the next most obvious thing is to cut all training. I find it unbelievable how many companies have done this. Once again this can only have a very adverse affect on these companies in the long run, particularly in the field of control, where there is already a huge dearth of knowledge. The other thing I have also seen is that there seems to be very little effort to try and improve plant efficiency. This normally involves calling in outside experts, which costs money. So they don’t go this route. It seems to be very short sighted.

However I was really encouraged a couple of days ago. The chief process manager of a large group of process plants asked me to meet him. He started off by telling me that he has been instructed by top management to cut back on all expenses by 10%. He then told them, that not only is he going to do that, but at the same time he is going to try and increase productivity by 10%.

How could he achieve this miracle? Very interesting. Basically he had realised that their plants were not running at all efficiently. Some of them, particularly some that were many years old, were using inefficient production and process methods, and were following bad practices that had been accepted as normal over the years. Several process refinements and improvements have already been made on some plants, and it could be seen how much more efficient certain processes had become with potentially huge savings, particularly in reagents. However it had also become apparent that these innovations depended largely on skilful operators, because the control systems were not performing well.

Unfortunately for a variety of reasons in their particular industry, the operators are relatively unskilled, and most are not highly educated. Therefore it has become imperative that to lower the reliance on operators, the working of the automatic control systems must be improved.

Virtually all their plants have fairly modern computerised control equipment installed. However the process experts and the existing C&I personnel have realised it is not working as it should, and that they would need outside assistance to find out how to improve things. Hence our meeting.

The company has already taken the decision that both process and C&I personnel need to work together on effecting improvements in the control side. This falls in exactly with what I have been preaching for many years. Firstly optimisation is a team effort and needs a high degree of cooperation between these departments to succeed. In every case that I have ever come across, optimisation efforts purely on the part of the C&I people does not work. Secondly there has to be full and enthusiastic support by both top and middle management. Without these two elements, any optimisation effort is doomed to failure.

The thinking at this stage is to initially start off with a really small, but full time optimisation team consisting of a senior process engineer, and a very bright C&I technician. They will initially undergo a 5 day classroom course on practical optimisation of regulatory control loops. After that they will undertake an audit in conjunction with the instructor on certain of the more important and critical control loops in some of their plants. Once that has been done, management will then decide on how to proceed further. If it goes as expected , a few more people will be trained and seconded to the team. There will also be some training given to quite a few other people of various disciplines in the various plants, so they can understand what is being done, and lend their support to the optimisation efforts. It is really also vitally important that plant personnel come on “board”. If they don’t understand what is happening, and start resisting changes, which is very human, then the whole optimisation exercise could be in jeopardy.

The whole thing to me shows the intelligent approach that process companies should be taking to improve things in these difficult times. All effort should be made to improve efficiency of production. It could be a “life-saver”.

To finish off I would like to reprint the following quiz which was originally published in Case History 17. This will give you some idea of how well your controls are working, and if there is a need to improve things:

Our experience shows that over 65% of feedback control loops in automatic are operating ineffectively, and less than 15% have anything close to optimum tuning parameters. It costs approximately R50,000 to automate a control loop. In spite of this, the poor state of the controls in a plant are generally accepted as normal. In fact very few people are even aware that the loops are not working properly.

To help you to judge approximately how well the loops in your plant are operating, we have devised the following quiz. This is based on experience taken from several hundreds of plants over a wide range of industries in various countries. Take a few minutes to study the questions. If necessary research them, and answer them as honestly as possible.

1. When your plant is running in a steady-state condition, are over 90% of the loops in automatic?
a) Yes b) No

2. During plant start up or shutdown, do the Operators put quite a few or even many loops into manual?
a) Yes b) No

3. How is tuning done in your plant?
a) Self tuning controllers.
b) Tuning package.
c) “Scientific” or semi-scientific methods (e.g. Ziegler - Nichols).
d) Trial and error.

4. If an Operator complains that a loop is not controlled properly, do your instrument technicians or engineers
a) Adjust the tuning parameters to try and improve matters?
b) Carry out a full loop analysis involving a series of open and closed loop tests to firstly determine why the loop is not behaving correctly?

5. Are there many filters on the transmitters, or on the process variable signals on the loops in your plant?
a) Yes b) No

6. The relationship between the Process Operators and instrument and control (I&C) department is
a) Good. The Operators trust the I&C people.
b) Bad. There is mistrust, and lack of co-operation.

7. The operation of a modern digital controller is complex, and most have numerous selectable options and features. Do your I&C people fully understand the PID functioning of the controller, including the algorithm, how it will effect tuning, and whether each of the P and the D actions operate on error or process variable?
a) They understand all these things.
b) They don’t understand the terms used in the question.

8. What equipment do your I&C department have to undertake loop analysis?
a) Some form of high speed, high resolution recorder.
b) Nothing special. They use the tuning screen of their SCADA system.

9. Is loop optimisation regarded as a discipline in your plant that must be regularly carried out?
a) Yes b) No

10. If you are using digital controllers and smart transmitters, is the scan rate of the controller set to be at least 2 to 5 times slower than the transmitter’s scan rate?
a) Yes b) No

11. If your control loops use a digital controller with a scan rate of 1 second or longer, are anti-aliasing filters set on your transmitters, particularly on very noisy measurements? (Note this does not refer to process variable filters set in the controller).
a) Yes b) No

12. Have your Operators received some elementary training on the practical operation of PID control?
a) Yes b) No

13. Have your I&C personnel performing loop optimisation received detailed training on the operation of the processes in your plant?
a) Yes b) No

14. Do the process people and the I&C people work as a team on optimising the loops?
a) Yes b) No

15. Are measuring instruments and transmitters calibrated and checked on a regular basis?
a) Yes b) No

16. Are valves “stroked”, and associated equipment, including pressure regulators, I/P converters, and positioners, checked on a regular basis?
a) Yes b) No

Score one point for each of the following answers:

You have serious problems in the feedback control loops in your plant, of which you may not even be aware. If this is the case, ask yourself why all that money was originally spent on automating the plant, if it is not working properly. Also enumerate the obtainable benefits if control was improved. These would include increased productivity, better quality, and decreased running costs. Would it not be worthwhile considering investing some time and money to improve the control? It will require commitment on the part of senior and middle management. You will also have to invest in some equipment and training.

If you have scored between 4 and 9:

Your controls are probably running better than most plants. However the score does show that improvements need to be made.

If you have scored between 0 and 3:

Your plant is definitely committed to optimisation, and your controls will be running really well. Your staff will be competent and well trained.

Index to articles

Michael Brown is a specialist in control loop optimisation, with many years of experience in process control instrumentation. His main activities are consulting, and teaching practical control loop analysis and optimisation. He gives training courses which can be held in clients' plants, where students can have the added benefit of practising on live loops. His work takes him to plants all over South Africa, and also to other countries. He can be contacted at:
Tel (011) 486-0567
Fax (011) 646-2385
E-Mail:  michael.brown@mweb.co.za