Playing it safe

Integrating basic process control with a smart Safety Instrumented System is becoming the norm for an ever-growing range of process plants. Mark Venables explains


Since last year’s dramatic fire at the Hertfordshire oil depot in Buncefield, there has been a renewed focus on process plant safety – particularly in the petrochemical industry.

All the key players in the field – Emerson Process Management, Siemens, Invensys, ABB, Yokogawa and Rockwell – have safety functionality built into their own proprietary platforms, but now more than ever this is becoming a product differentiator.

Emerson has won a contract with leading North American natural gas producer EnCana to apply its PlantWeb digital plant architecture to automate EnCana’s Steeprock natural gas processing plant in British Columbia.

The approach, integrating basic process control with a smart Safety Instrumented System (SIS), is designed to assist in processing 190 million cu ft/day of raw gas and will consist of two main components.

The first comprises two amine plants, one to remove CO2 from the raw sweet feed gas, and the second to remove CO2 and H2S from the raw sour feed gas. The second component will be a Claus process facility to extract elemental sulphur from the H2S using an amine process. The construction goal for plant start-up and commissioning is the end of this year and the beginning of 2007.

‘We see advantages to the SIS technologies, and to the predictive nature of the basic control system,’ said EnCana senior facilities engineer, Rajesh Udipi.

Emerson’s PlantWeb will integrate process control and smart SIS solutions based on the DeltaV digital automation system, AMS Suite predictive maintenance software and intelligent HART field instruments that include Fisher valves with Fieldvue digital valve controllers and Rosemount transmitters.

Emerson’s SIS uses digital intelligence to enable customer implementation of safer process plants. It automates proof testing, including partial valve stroking, to enable continuous and on-demand diagnosing of safety loop sensors, logic solvers and final control elements to ensure they perform on demand. The resulting high reliability of safety systems is aimed at reducing the risk of plant trips, to keep plants up and running.

At the same time, this approach minimises the costly and risky practices of ongoing manual proof tests.

Meanwhile in Colombia, Ecopetrol has selected Invensys Process Systems to implement Triconex TMR (triple-modular redundant) technology for burner management systems in its Cartagena refinery’s power plant, currently undergoing modernisation.

Located in the Mamonal industrial area on Colombia‘s north coast, the facility – with a capacity of 80,000 barrels a day – produces petrol, middle distillates, propane and fuel oil. Invensys will implement four Tricon TMR high-availability systems for burner management system applications at the plant’s steam generators (boilers).

These will protect new burners being installed as part of the modernisation. The new systems will increase control reliability and availability, make for improved boiler safety, and help bring the refinery into compliance with international SIL and SIS standards, such as represented by the National Fire Protection Association (NFPA).

The Triconex TMR technology employs three isolated, parallel control systems and extensive diagnostics integrated into one system. The system uses two-out-of-three voting to provide high-integrity, error-free, uninterrupted process operation. The TMR architecture eliminates any single point of failure and enables on-line maintenance, on-line programming downloads, self-calibration and fault localisation.

The industry-certified Triconex TMR controller regulates functions, with embedded, transparent diagnostics, and behaves as a single control device to the operator or engineer.

For the Shah Deniz project in the South Caspian Sea, Azerbaijan, ABB has supplied its safety controller and automation system technology for the major gas project that is part of the Caspian Sea development. The field includes an offshore platform, onshore terminal and pipeline. The Shah Deniz condensate field lies in the Caspian Sea, about 100km south of Baku in water ranging from 50m to 500m deep. From here a pipeline is being constructed to supply gas to Turkey.

ABB is supplying, installing and commissioning an integrated control and safety system (ICSS) for the new onshore gas terminal and offshore platform and the associated South Caucasus Pipeline (SCP). The ICSS comprises a process control system and an integrated safety system.

This consists of a fire and gas sub-system covering process and non-process areas, and a separate emergency shutdown sub-system for the process area. This will provide process control, emergency shutdown and fire and gas protection across all platforms.

The system architecture for both the terminal and the platform installations, while very similar to that for the oil processing facilities, incorporates some extra features. For instance, the project uses the latest AC800 technology with the introduction of the HI safety controller and 800xA (extended Automation) software.

‘Such is the timescale of the Caspian project, that new technology developments are inevitable,’ explained ABB project manager Rex Poulter. ‘The AC800 HI safety controller, for example, has several features over ABB’s Safeguard Controller which is used extensively on the Caspian project.’

One benefit is its size. Being some 50 per cent more compact than Safeguard, it has enabled ABB engineers to integrate it easily within the offshore platform, where space is at a premium.

The safety controller is based on the AC800 family of controllers and features more safety checking functions and reporting facilities, as well as greater I/O.

Being part of the AC800 family, the controller uses the same industry standard language, which complies with IEC standards, rather than being bespoke. This makes it more open and more easily understood. A key advantage of the overall system design is that, via gateways, the operator in the common control room can see any information relating to either the offshore platform or onshore terminal.

For this to be successful, every part of the installation needs to be consistent.

This has been achieved by writing common functional design specifications for process control, fire and gas, shutdown, graphics, operator interfaces and type circuits with a standard hardware build.