With up to 113 million litres of highly flammable fuels on site, the new Darwin Industry Fuel Terminal's operators selected a highly specified Pilz Programmable Safety System to oversee a very basic yet critical device: the emergency stop.
The terminal replaces the Stuart Park Tank farm and will store jet fuel, aviation gas, petrol and diesel for three oil companies.
The scale of the project is impressive, with 23 km of internal fuel pipes planned for the terminal. The fuel is pumped from ships at the wharves into 11 major fuel tanks, with another 25 tanks providing for products like additives. From there, fuel is transferred to the fleet of bulk tankers supplying distributors and petrol stations. In the event of a spill or other emergency shutdown, a Pilz Programmable Safety System (PSS) with fibre optic SafetyBUS p safe field bus takes control. Fibre optic cabling is important in such a hazardous area to avoid the risk of sparks associated with copper wiring. Once triggered by a safety breach, the PSS/SafetyBUS p combination shuts down the entire plant, de-energises all machinery and communicates with the plant's standard operations programmable logic controller (PLC). Three types of emergency switches are monitored by the PSS network: the traditional e-stop button, tank mounted high level sensors and emergency release couplings at the wharf.
In total, there are 80 digital inputs and 48 outputs, including a set of monitored redundant relays for each pump, managed by the PSS. Diagnostics are fed through to a Citect Supervisory Control and Data Acquisition (SCADA) system for display. While the application is rated at Category 2 according to AS4024.1, the safety conscious terminal operator specified that any safety system should match the calibre of the Category 4 (and SIL 3) approved Pilz PSS with SafetyBUS p.
A logic-driven safety controller, the Pilz Programmable Safety System (PSS) offers optimum safety levels and real flexibility as the plant develops and changes. In combination with safe bus system SafetyBUS p, the PSS can be extended to many thousands of safety circuits. An open technology based on the CAN bus system, SafetyBUS p enables users to incorporate field modules from other manufacturers and network programmable safety systems for more than 1000 I/O over 3.5 kilometres, which can then be bridged to multiply the I/O and bus length.
From a designer's perspective, the Pilz PSS also offers significant configuration and operational benefits over conventional safety relays with its TUV approved standard function blocks and diagnostic tools. In fact, Pilz has developed a software package specifically for tank farm installations, which includes the evaluation of e-stop devices, deadman switches, level monitoring, gas detection, plus the monitoring and control of flaps and valves.
Supporting terminal contractor, Henry Walker Eltin (HWE), with specialist engineering expertise, Simon Engineering's Colin Millen is responsible for the installation of the safety system. Although this was his first project with a PSS, Colin was surprised by its ease of use.
"Pilz delivered excellent support in the form of a knowledgeable and succinct training session," he said. "I found the PSS was easy to put together - it worked pretty much straight out of the box." Commissioning of the new $55 million Darwin Industry Fuel Terminal is scheduled for June 2005.