4 replies to this topic

Hi to all,

Could you please tell me exactly the difference between DCS and ESD? How can I identify on P&IDs the instruments and controls associated to DCS and the ones associated to ESD? I have to confess that I'm a bit confused about instrumentation, interlocks and controls and I'd like to shed more light on my doubts.

Since in the short period I'll be involved in the HAZOP review of the project on which I am working, could you also suggest me some good books or sources of informations on the subject?

Thank you in advance for all the help and suggestions.

Best regards,

Andrea

[Padmakar Katre]

Dear Let me take the previlage to answer your question,
The DCS stands for Distributed Control System which is the mean to control your plant operations by using the the distributed(spread across your plant) controllers throught the system with having the Network for comminication and monitoring the system. You jys google the term and you will find more information on the same.
ESD stands for the Emergency Shut-Down. This is the way of shutting down the plant inthe event of abnormality in plant operation which could lead to dangerous situation. The same is achiver by triggering the interlock system which will take the emergency shut-down.
Just to understand the differnce between the indications which are local or DCS try to know the difference in the notation/legends of the same. There are certain instruments which are just for local indiacation(field) and some are having the DCS indications. The interlock are the safety measures which gets active in the event of an abnormality to save your unit.
Hazop the term is very very broad and a nice experience for any process engineer to have. To know about the technique how Hazop is carried out you can go through some literature available. I suggest you if your organization has any copy of the Hazop of any facility before go thorugh it and you will come to know. And I hope this will even give you and idea regarding your preparedness for the upcoming Hazop. All the best.
Hope this could help a little.

[mishra.anand72@gmail.com]

Dear Andrea

Hw r u?? u belong to south Italy or North Italy?? I like Italians. They r just like friends; always needing information. u saw PIDs?? Conventionally round one is used for local instrumentation and square block surrounding round one is used for remote indication. DCS is nothing but remote operation of plant. Process pages r developed from PIDs and incorporated in DCS which is in technical jargon is called HUMAN MACHINE INTERFACE. All the instrumentation is channelised into network and brought to Computer Screen which is in technical jargon is called CONSOLE/PANEL/BOARD at which operator surf through PROCESS GRAPHICS and manipulates process parameters for plant operation. Do u hv copy of PROCESS GRAPHICS?? Interlocks r indicated in DCS in sepatate pages and indication of whether interlock is active is also indicated in PROCESS GRAPHICS. Interlocks r nothing but CAUSE & EFFECT avoiding maloperation, damage to machine and/or humans. Further to this, u will see PROCESS ALARMS which is nothing but alert to board man; deviation from operating intent.

ESD is nothing but cutting the feed; in some cases power also to concerned unit. Do u no anybody who hv used ESD?? Emergency can not be defined. May be fire in unit, heavy leaks activating need of ESD. Can v leave this??

The HazOp concept is to review the plant in a series of meetings, during which a multidisciplinary team - design Engineer, process engineer, operation & maintenance supervisor & safety engineer -methodically "brainstorms" deviation from plant design intent, following the structure provided by the guide words - less, more - and the team leader's experience. Do u hv experience in attending meetings?? Can u follow team leader?? This one results from the interaction of the team and their diverse backgrounds. Consequently the process requires that all team members participate and team members must refrain from criticizing each other to the point that members hesitate to suggest Ideas. If u do not want ideas, go ahead and criticise. what do u say?? do ppl mean this one??

Just take it easy. Hv working folders.

Hv a great time in meeting.

Thank u in advance?? Share ur experience about discussion held in HAZOP meetings, if u remember us.

Never Mind

Wish u gud luck

Thanks a lot to you both! I capitalized your guidances and suggestions. HazOp was nothing more nothing less than what you described: indeed it was a good experience to see the things from different points of view (commissioning, operation and technical units points of view, which complete the picture of a process engineer).

Mishra I'm from south italy

Thanks again for your help

[Whit123]

Hi to all,

Could you please tell me exactly the difference between DCS and ESD? How can I identify on P&IDs the instruments and controls associated to DCS and the ones associated to ESD? I have to confess that I'm a bit confused about instrumentation, interlocks and controls and I'd like to shed more light on my doubts.

Since in the short period I'll be involved in the HAZOP review of the project on which I am working, could you also suggest me some good books or sources of informations on the subject?

Thank you in advance for all the help and suggestions.

Best regards,

Andrea

DCS is short form for Distributed Control System, as you must be already knowing by now. The process measuring instruments transmit the values (say pressure,flow,temperature,level,etc) to controllers located away from the process. These controllers then process the data and depending on how you program it generate outputs to different kinds of final elements (like control valves, drives,etc) to control the plant. All of this is visualized on Operator stations (these days many are just PCs that run the visualization software of the DCS). The controllers, associated communication network and the operator/engineering stations together form the DCS.
The Emergency Shutdown System (ESD) is a separate system used to safely shutdown a process plant in case of an emergency (including a failure of the DCS, which means you are running the whole plant blindly without any info-very dangerous indeed). Since the ESD is completely separate and made of very reliable stuff, the chances of both the ESD and DCS failing at the same time is very low.ESD systems are now referred to as SIS (Safety Instrumented Systems).
If you need to find out more you can check out the Safety Instrumented Systems course
There is a free demo available for download and the info that you seek, you will get there.
HAZOP is short for Hazard and Operability Study, which seeks to analyze what could go wrong in a process. So the process plant is broken down into small parts (only conceptually)to analyze what can go wrong. So certain guide words are used, like "no flow", "reverse flow", "high flow" to analyze for example a pump operation. Then each consequence is written next to the abnormal condition (called a deviation). If the consequence is going to be dangerous, then we have to have a "mitigation" for it, in other words, have some safety interlock or alarm or operator action, that will nullify this deviation. After the entire HAZOP is over, you will find a large list of "action plan items" that you must implement in order to make your plant safe.
Hope this helps you
Cheers!

Edited by Whit123, 10 April 2010 - 04:28 AM.