A fieldbus presentation and demo to UK contractors

Interest is growing from EPCs in learning more about fieldbus systems: Nick Denbow reports on a well attended Reading event organised by the Fieldbus Foundation in the UK for these contractors.

With many end users now specifying fieldbus systems in the projects referred to contractors, these users are looking to contractors to provide expertise and input in the development of the project.

The Fieldbus Foundation UK Committee followed up this interest with a recent seminar at the Madejski conference centre in Reading, West of London.

While the location and the presentations were aimed at project managers and engineers in the local EPCs, the objective was to demonstrate what users can gain from fieldbus systems.

The growth in interest in fieldbus information and training at all levels from the EPCs was shown by the size of the audience: over 60 engineers had been sent along 6 or more contractors, and one or two major oil and gas users.

A show of hands indicated that around 70% had not previously worked on a fieldbus project to date, but they were keen to learn.

Travis Hesketh of Emerson Process Management stressed that while all new plant designs using Foundation Fieldbus do gain from the approximate 50% reduction in engineering drawings, plus the faster commissioning speed and accuracy, with less terminals, the major CAPEX benefits have been realised by offshore installations.

Here there is a real measureable benefit by taking advantage of the smaller system footprint and the lower system weight, from reduced cabling and cabinets.

However for the land based user, the real business benefits are now realised as in better OPEX performance, performance of the plant to get better efficiency and productivity by using the intelligence available via the instrumentation and the communications system.

Foundation fieldbus delivers meaningful intelligence information to operations and maintenance personnel, in time for them to react effectively to a poorly performing control loop or a maintenance request on a valve or transmitter.

Examples were presented of some of the intelligent information now available as standard from FF transmitters and valves, that can provide performance warnings before the plant operations are affected.

A warning of reduced pneumatic supply pressure at a control valve (resulting possibly from an air leak, which could be located by a maintenance visit); a dual-sensor temperature transmitter indicating that one probe had failed, but where the second sensor continued to provide valid measurement signals, keeping the plant going; and a pH transmitter that knows when the glass of the probe needs cleaning, and signals this as a developing maintenance requirement.

More interesting perhaps were the system monitoring tools that could identify control loops that display high variability, and list out all the loops where control had been switched to manual.

Andrew Tither from MTL reviewed the many different options now available for running fieldbus segments in hazardous areas, which include the FISCO options for Division 1 areas, and FNICO options for non-incendive Division 2 areas.

An explosion-proof approach allows the use of Exd field devices and Exe wiring for the junction boxes and field trunking, with other systems becoming available using field barriers at the end of Exe trunking.

Inevitably perhaps, the interest from the EPCs was in segment design, and the allocation of control, either for control in the field, or control back in the DCS.

Tony Alexander from Honeywell demonstrated the procedures used to build a control loop within a Foundation fieldbus segment, the need to load the DD files for each device, and how the devices should be allocated.

When setting up a control loop, another consideration has to be how often the loop control software runs, allocated between every 250msec and 16 secs.

Much of the EPC audience interest related to the allocation of devices and control functions to each segment, which looked like a major topic for its own specific seminar! Conventional design training brought out questions about segment calculators, which would allow the current and power limits in a segment to be summed in terms of the power available.

While many different segment calculators were available from the different manufacturers (all promised as a follow up on the conference summary CD), there is a significant variability in the current drawn by different devices: many devices are below 20mA, particularly if just acting as a simple transmitter, which can be as low as 11mA.

But similarly more modern complex transmitters are also low in current consumption.

IMPRESSIONS FROM THE REPORTER.

There were several topics that seemed to reflect the interests of the audience of EPC engineers (and some BP delegates) that possibly surprised the suppliers, and vice versa, which it was interesting to observe.

The audience was really interested in the decision over whether to undertake control in the field (often said to produce fast response and tight control), or control in the DCS/main system (requiring communication back to the Host system).

Honeywell confirmed that refineries tend to want to keep control back in the DCS, which was the same answer as came from Yokogawa, based on experience with nuclear installations, where the situation of each programmable device has to be separately evaluated.

On the other hand the ABB experience was reported that in practice around 20% of loops were controlled in the field.

The idea of having some form of Foundation Fieldbus ‘design tips’ on how to approach a FF project, and how to avoid the quoted installation hassles such as earthing problems and too much communications activity around the network, was taken up by the audience: it would certainly be a valuable document to build into a segment design engineer’s manual! The topic of network implementation was quoted as covered in documentation from the Foundation, along with installation standards.

Individual suppliers of host systems were quoted to have their own documentation and tools, to provided the processes and procedures to assist with the new aspects of the technology, such as segment design.

The supplier topic that went down badly with the EPC audience was the potential to provide multi-variable outputs from a single sensor, for example using a flowmeter also as a measurement point to measure process temperature.

This just did not seem to fit into a conventional box, so might need a little more promotion.

The EPC question that went down badly with the FF suppliers was a wish to know “How many people had recently evaluated a Foundation fieldbus solution for their project and rejected it, and why!” After an intake of breath, the suppliers could not seem to remember any such event!.

CONCLUSION: A day enthusiastically received by the EPC audience, showing a demand for further such events, to enable the expertise and enthusiasm from the suppliers to be passed to the EPC design engineers, and built into their project proposals with confidence.

While each supplier undoubtedly arranges training courses for clients and their operations engineers, the contractors possibly need to have some across the board training from FF, to enable them to make their own choice of host system, undertake the proposal work in-house, and push more fieldbus systems into the normal routine of smaller development projects or add-on sections to existing plants.

The INEOS ChlorVinyls use of fieldbus at Runcorn

In a Euro300M project at Runcorn, INEOS ChlorVinyls updated the control system for the major production of caustic soda and chlorine to a digital fieldbus system, described at the FF General Assembly.

The presentations by fieldbus users at the recent Foundation fieldbus General Assembly in Antwerp included a paper by Paul Young, the Automation Improvement Manager at INEOS ChlorVinyls, describing the implementation and results of applying fieldbus and other new technologies in a Euro300M improvement project at Runcorn.

INEOS ChlorVinyls is one of the major chlor-alkali producers in Europe, a global leader in chlorine derivatives and Europe’s largest PVC manufacturer.

Their “Genesis” project, through Fluor, was to replace the cellrooms, which produce caustic soda (1,200,000tpa) and chlorine (600,000tpa) by the electrolysis of brine.

The decision was made to adopt Foundation fieldbus communications with an Emerson DeltaV control system, and a HIMA SIS.

The site standard for instrumentation and control valves was based on Emerson equipment: 1223 fieldbus instruments were supplied, plus 143 HART instruments, for the process analysers and safety loop components.

AMS Asset Management Systems were implemented, with machinery health monitoring, to gain the benefits of predictive maintenance – the HART instruments on the SIS loops interfaced via an MTL Multiplexer.

Lastly, a Matrikon alarm management system was also installed.

INEOS ChlorVinyls had had an alliance with Emerson for many years prior to this project, dating back to the previous company names of ICI Chlorchemicals and Fisher-Rosemount.

This alliance had shown that the companies could together achieve improvements to plant performance, and also that the companies could work together effectively: INEOS ChlorVinyls had involved various DeltaV installations on site development projects.

Nevertheless there were significant potential risks in adopting the fieldbus approach to the Genesis project: notably these included the fieldbus design, installation and commissioning competence available, the risks of the new technology (such as potentially becoming obsolete, like Betamax) and the unique features of the application: what about the effects of the stray currents and magnetic fields in the cellrooms?

There were also concerns over whether the proposed heavy fieldbus segment loading would cause slow responses, and whether there might be a loss of a segment during operation.

After initial project discussions within the project team, it was decided that Emerson had significantly more segment design experience than that available in the Fluor project team, so Emerson were asked to take on that part of the design on behalf of Fluor.

A conservative approach was adopted overall to the segment design, and a limit of typically 8 instruments per segment was imposed, with a maximum of 4 valves per segment (originally the project had planned to use 12 instruments per segment and not be limited on valve numbers).

No loading issues have been seen as a result, and there have been no losses of segments during operation.

This was commented on later in the FF meeting by John Rezabeck of ISP Chemicals in Lima, Ohio, who reported that he had not seen any loss of a segment in 6 years, with around 80 fieldbus loops operating in the field.

Significant benefits came from having 35% less instrument drawings, and the site cabling installation was 1-2 weeks quicker than a conventional time-scale.

Fault finding was faster on installation, but the installation technician skills were limited initially: however an unexpected benefit was that loose field terminals were soon identified and located, by monitoring the noise present on each fieldbus segment.

A major problem was indeed found with the stray currents from the electrolysers, which did cause the loss of a digital segment, because of the earth free installation.

This caused a major diagnostic and solution headache, because even straightforward conventional HART equipped valves would not work on this application, when trialled as a fall-back solution.

This was resolved with the help of Emerson fieldbus experts by separating the mounting of the digital valve controllers from the valve bodies, using electrically insulating materials.

Overall, the start-up and commissioning went well, the modifications needed to get the plant on-line were implemented very quickly, and the result was that the timescale to plant operation was reduced by 2 weeks.

This was just the start of the work for Paul Young, charged in his role as Automation Improvement Manager with gaining significant further performance and efficiency benefits from the new fieldbus installation and investment.

The AMS system has been extensively used during pre-shutdown and shutdown testing.

This has minimised the time spent on invasive testing, and typically shaved a week of time off the whole shutdown test programme (therefore enabling improved plant productivity).

Perceived valve issues could be correctly diagnosed using the ValveLink software, and the AMS was used to perform valve scan and set-ups, without having to send the valve away to the workshop.

This was crucial in avoiding electrolyser damage when it became evident that there were sizing issues with one valve in this section of the system.

The target set for the Paul Young as responsible for operational improvements, in conjunction with the Emerson site engineer, was to gain GBP500k of further benefit from the available system technology.

Examples of the improvements achieved with the new control system were:.

* From the AMS Alerts triggered on saturated loops, it was identified that some transmitter ranges were incorrect on the chlorine interchangers.

* The evaporator temperature was the limiting factor on high produuction loads.

* The alkaline pumps were undersized for the high load situations.

* The compressor oil heaters were always on.

* The vibration alarm limits were set too high.

* AMS ValveLink is used continuously to monitor the most critical valves.

* Prior to the first major outage since the AMS installation, it was possible to identify just 7 of the 415 valves on site as needing overhaul, based on their condition.

* Poor valve performance in operation, prior to repair and replacement in the shutdown, was able to be improved by repair tuning.

* High accumulated valve travel on other valves highlighted control problem areas, and led to control improvements.

INEOS have learned a lot from this project, not the least of which has been that training in digital systems and fieldbus must be delivered to all engineers and technicians across the site.

The anticipated risks have been avoided or overcome, and given that the risks continue to be managed, Foundation fieldbus is now the site standard and will be adopted on future projects.

Finally, the effort spent on exploitation post project has been essential to get the most benefit and value out of the information delivered by the systems.

This report on the outline of the project by Paul Young is provided by Nick Denbow, based on the presentation and descriptive slides shown to the FF General Assembly in Antwerp in February 2008.