Taking fieldbus into hazardous areas

The benefits that fieldbus digital communication technologies bring to industrial control and automation are well documented - reduced wiring and installation costs, better diagnostics, for example.

Some sectors of the process industries, however, have been slower than others in embracing fieldbus, particularly those involved with hazardous area operations that call for intrinsically safe (IS) systems. But, as more advanced equipment comes on to the market, the mood is changing.

Speciality chemicals manufacturer Avecia UK, for example, is close to commissioning a new plant at its Grangemouth, Scotland, site that will feature fieldbus technology in hazardous areas. The project, for which ABB Automation is control system contractor, follows recent fieldbus trials on two Avecia plants producing agrochemicals and pharmaceuticals intermediates.

The applications engineering for the trials was handled by ABB and its 'channel partner' in Scotland, J W Fairbairn, who used ABB's AC800 FieldControllers with integrated Profibus communications to monitor the use of steam, water and nitrogen.

The installation includes intrinsically-safe Profibus PA flow and temperature instrumentation from ABB and third-party vendors, together with ABB S800 remote I/O for converting into Profibus traditional 4-20mA signals from existing pressure transmitters.

The AC800 FieldController is said by ABB to be the first instrument of its type to cater for the most commonly-used fieldbus protocols as an integral part of the system, and to provide Avecia with a cost-effective entry level for Profibus, Avecia's preferred protocol.

Critical control

The new project, scheduled for completion in June, involves the critical area of process control, for which ABB and Fairbairn now have most of the engineering tools required already in place. According to Ken Fairbairn, his company is undertaking 'the complete integration of fieldbus with the Siemens control system specified by Avecia'.

Avecia's new plant is effectively 'a greenfield site located in an existing building', says Fairbairn. At another greenfield pharmaceutical plant in Ireland the other main process fieldbus technology, Foundation fieldbus, is also now being installed on an intrinsically-safe application. Last November pharmaceuticals producer Bristol-Myers Squibb announced a contract with Fisher-Rosemount to provide the process automation for its major new plant near Dublin, with Portsmouth-based Kværner as main contractor.

The project, known as the Cruiserath Bulk Manufacturing Facility, is for multi-purpose batch manufacture of healthcare products, and involves F-R's DeltaV automation system with over 1000 instrumentation and control points. As part of the £1.7million order, intrinsically-safe or flameproof Rosemount pressure, temperature and flow instruments are being supplied - with the key components networked together using Hart and Foundation fieldbus communications.

DeltaV forms part of F-R's PlantWeb architecture, which also includes the AMS (asset management solutions) software platform to enable PlantWeb to use diagnostic information from field devices to manage plant assets.

According to Ian Wright, md of Fisher-Rosemount UK and Ireland operations, 'the adoption of this technologically advanced approach to the control of a major new plant shows the forward thinking of the engineers in Bristol-Myers Squibb and Kværner. It comes as a result of extensive field trials and cooperative evaluation work across the world'.

Meanwhile, in the USA PlantWeb was the choice of, among others, Bayer Corporation's Agriculture Division for a pilot plant at its Kansas City site in Missouri. The PlantWeb solution was a logical extension of a previously installed DeltaV control system. When installed in conjunction with Foundation fieldbus, it allowed Bayer to utilize more effectively existing plant space due to small component size, reduced wiring requirements and reduced I/O component count.

'One of the areas in which we could confirm substantial savings from the PlantWeb architecture was field checkout and commissioning time,' says Ferrill Ford, the plant's process control system lead engineer. 'The Foundation installation required only five minutes per device for checkout and commissioning.'

One of the largest on-going projects involving a hazardous area fieldbus installation is Shell's Malampaya development in the Philippines. This is a deep-water gas-to-power project to supply natural gas to power plants throughout the country. Gas delivery is scheduled for January 2002.

There will be five sub-sea wellheads, an offshore gas processing platform, a 500km long 24in gas pipeline and an onshore gas treatment plant with despatch centre. Tying all this together will be the DeltaV automation system, ASM software and Foundation-based instrumentation.

'The technical and commercial challenges for the automation system on this project are considerable,' says Dick Wismeijer, Shell's principal process control, instrumentation and telecomms engineer for the project. 'With DeltaV, though, we have been able to pursue a truly open system field-based architecture, using Windows NT, Foundation fieldbus and OPC [OLE for process control], offering a host of competitive applications and sub-system integration opportunities, in contrast to the classical proprietary DCS 'control-room-centric' interface topology.'