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Product category: Machine Safety Monitoring and Control
News Release from: Pilz Automation Technology | Subject: Programmable safety systems
Edited by the Engineeringtalk Editorial Team on 03 September 2004

Safety upgrade provides reliability as a
bonus

Programmable safety systems improve boiler safety and reliability, saving a Scottish distillery thousands of pounds.

Programmable safety systems improve boiler safety and reliability, saving a Scottish distillery thousands of pounds Pilz has worked alongside Elite Control Systems, a system integrator, to improve the availability and reliability of steam boilers for an Edinburgh distillery, thereby saving the distillery thousands of pounds

The North British Distillery Company, Edinburgh's last remaining working distillery, operates 24 hours per day producing 64 million litres of whisky and neutral spirit every year for blends such as Famous Grouse and J and B, as well as for gin and vodka.

Steam is used extensively in the production process, for cooking the grain, mashing, distillation, and as the heat source for disc dryers.

Any interruption to the steam flow almost inevitably results in downtime - which can easily cost GBP 5000 per hour.

A pair of Wellman Robey boilers, each with two burners, provides the steam for the entire site at a rate of 50 tonnes per hour.

When the plant is running at maximum output there is little spare capacity available from the boilers, so a fault with any of the four burners is likely to lead to part of the plant being shut down.

Owing to the use of cam timers and electromechanical relays to control the burners, breakdowns were occasionally causing problems.

Additionally, it was rare for the burners to light first time following any routine maintenance or planned shutdowns.

Not only was the hardware unreliable, but fault-finding was troublesome and spare parts were hard to obtain for the obsolete cam timers.

Consequently, it was often necessary to call out a technician from the boiler supplier in order to restart the boilers, adding further to the direct costs of such problems.

In an attempt to improve matters, and bring the boilers up to the current site standards, five potential suppliers were invited to tender for upgrading the boiler control systems.

Of the proposals received, that from Elite Control Systems offered the technologically best solution.

At the heart of this was the Pilz programmable safety system (PSS), with one of these replacing the cam timers and relays for each burner management system.

The four PSS units were to be linked to an Allen-Bradley ControlLogix supervisory PLC that would replace the existing Seprol PLC.

System visibility was to be provided by Intellution's iFIX Scada (supervisory control and data acquisition) package in place of the existing Scada tool.

The Pilz PSS uses triple diverse redundancy, which makes it suitable for use in applications up to IEC61508 SIL 3 and BS EN954-1 Category 4.

Expansion modules enable the PSS central processor unit (CPU) to communicate with digital and analogue I/O on the plant, as well as other nonsafety controllers.

In the case of the North British Distillery project, the PSS is a 3100-series modular system comprising a power supply, CPU, one digital input module, one test pulse input/output module, and two relay output modules.

The I/O modules are wired directly to the field terminals and burner combustion control units, replacing some 31 electromechanical relays, and there is a link to the supervisory PLC and Scada package to provide process visibility, especially during start-up and shutdown.

When North British Distillery issued the invitation to tender, it provided a copy of a consultant's report, but this made no direct mention of safety integrity levels.

However, Elite Control Systems was deemed to be one of the potential suppliers to give this aspect of the project a high level of consideration.

When asked by Elite, North British Distillery stated that the burner management system should comply with the requirements of IEC61508 SIL 1, and this was confirmed by an independently chaired hazard and operability study.

Elite worked in partnership with Pilz who provided an independent safety consultant to chair the study.

Prior to commencing any design work, a manufacturing quality plan was prepared, which, once agreed with the client, was swiftly followed by a functional requirements specification.

This was also agreed with the client before the software test procedures were written and approved, then the electrical schematics were prepared and approved.

Once these steps were complete, the software could be written.

One of the factors to be taken into account during the tendering process was that all installation and commissioning had to take place within the summer 2003 and Christmas 2003 scheduled shutdowns, with minimal risk to production.

Elite therefore proposed to implement the PSS upgrade during the summer, together with replacing some signal cables that were suspected of causing problems due to interference from adjacent power cables.

The situation was then to be monitored prior to Phase 2 at Christmas, which would include the PLC upgrade and new Scada system.

Despite the limited time available on site, Elite was confident that the PSS upgrade would function as intended.

The software was therefore written as a direct copy of the cam timer and relay logic of the existing system, rather than using pre-written standard function blocks available from Pilz.

Once the software was written and the test routines agreed, Elite used PICS (Programmable Industrial Control Simulation), a PC-based modelling and simulation package, to thoroughly test the control algorithms prior to even arriving on site.

Compared with traditional lamp-and-switch boxes, PICS is far more flexible, allowing what-if scenarios to be tested with ease.

Factory acceptance tests for the boiler control project were completed with the PICS system running at Elite's premises.

As a result of this detailed planning and exhaustive preparation, the installation and commissioning ran smoothly, despite the control cabinets being found to contain several undocumented modifications.

Installation and commissioning for Phase 1 took just over one week, while Phase 2 was completed in just four days.

Both phases were finished ahead of schedule, substantiating Elite's initial confidence that they could meet the time demands.

"Elite did an excellent job".

"Right from the start they were knowledgeable and professional in all aspects of the planning and execution of the project", said Jim Davie, Assistant Engineering Manager at North British Distillery.

"But proof of their expertise was borne out when, after the system was commissioned, the burners all lit first time".

He went on to say that the first-time lighting of the boilers was a rare event indeed with the original system.

He goes on: "We have had no problems since".

"In fact, we have cut by 75% the number of times the boiler supplier has been called on site, which has led to direct savings in maintenance costs".

However, despite the success of the project, Elite ensured there was backup by instigating a 24/7 support package, offering total peace of mind to those responsible for running the plant.

Jim Davie concludes: "We are very pleased with the outcome of this project".

"Now that the upgrade is complete, we have a steam supply that is more reliable, saving us thousands of pounds in reduced downtime and service calls".

"This project has also resulted in a safer plant that is user-friendly".

"I would not hesitate to contact Elite again should we have any other projects requiring a system integrator".

Brian Sneddon, Sales Manager at Elite, adds: "Thanks to our pre-planning, the whole project ran like clockwork, despite the invitation to tender containing known gaps that had to be filled during the tendering and specification phases".

"Compared with the alternatives, using the PSS was cost-effective and user-friendly".

"The PSS was easy to integrate with both the existing and upgraded supervisory PLCs and Scada systems, so we were able to meet the customer's specification in a straightforward way".

"However, safety is only one of the many fields of Elite expertise and experience".

"That said, we have a set of competencies that places us in a better position than most to advise customers and carry out projects that have safety implications".

"We have a reputation for being highly professional and innovative in everything we do, working with customers to provide them with cost-effective solutions that match their needs".

"The project with North British Distillery illustrates this well".

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