Shell Chemicals, Rotterdam, The Netherlands
Intrinsically Safe Process Control
Shell Chemie Moerdijk, which is situated approximately 30 kilometers from Rotterdam, manufacturers various chemicals from crude oil. For product-specific transfer and dispatch, Shell Moerdijk uses an intrinsically safe process control solution with Process Interface modules from Phoenix Contact.
For filling and transportation, Shell part owns a tank park, eight quays with transfer distributors for ships, a shunting yard for railroad cars, and three loading/weighing platforms for tankers. The 1500 to 2000 ships, approximately 13,000 tankers, and more than 3000 railroad cars that are required for transport emphasize the considerable quantities that are processed annually.
When modernizing the factory, 250 intrinsically safe HART transmitters were installed for 4-20 mA signals in addition to approximately 500 NAMUR sensors. Availability requirements and restricted space meant that a reliable and compact I/O concept was needed. Shell therefore opted for a Process Interface solution.
Jumper Structure Promotes Flexibility
Process Interface combines the jumper level and interface level in one control cabinet
At Shell, signals from the field are first transmitted to a jumper cabinet and then coupled with terminal blocks according to preset functions. The jumper cabinet enables test measurements and diagnostic procedures to be carried out, usually by interrupting the circuit using isolating blade terminals. The input signals are transferred from the jumper cabinet to a second converter or interface cabinet via a remote cable. The interface cabinet contains signal converters for converting current into voltage and isolation converters for explosive and non-explosive areas. The voltage signals are transmitted from the interface cabinet to the control system.
The Process Interface Concept
The conceptual design of the Process Interface is a further development of the above jumper structure and is based on two main components: a basic terminal with a width of 12.4 mm (0.488 in.) and electronics modules in the same width that can be plugged in and keyed. By integrating these functions, the jumper and interface level are combined in one control cabinet. Another feature is the isolating blade terminal on the basic terminal, which has test points for diagnostic purposes. The supply voltage can be jumpered, e.g., using an insertion bridge, and the terminals are modular.
Functions can be adapted by inserting the appropriate electronics modules, e.g., transmitter/supply isolator or NAMUR switching amplifier. Pre-wiring the basic terminal ensures that flexible reserves are maintained. Process Interface components are marked with [EEx ia]II C, which indicates that they are approved as appropriate parts for all zones and gases and certified according to the ATEX 100a Directive, which comes into force on July 1, 2003.
Process Interface in use at Shell
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