Process automation snapshot

At Cameco Corp.’s Cigar Lake Mine in Saskatchewan, the single-shaft test mine is being expanded into a full production facility. High-grade (19% U3O8) ore will be crushed and ground underground. Ore slurry will be pumped to the surface, loaded into special containers, and trucked offsite for further processing. Mine construction began a year ago and is phased for projected completion in 2007.

The process automation project is also phased, with Invensys supplying the control system to date.

The first phase of the distributed control system completed last fall features several remote control centres with Foxboro I/A Series systems and Modicon PLCs. On surface, the concrete plant for construction of the new No.2 shaft contains a small control centre, and the expansion of the freeze system (see p. 18) contains the other first phase control centre.

Second phase underground process operations, including jet boring operations, crushing, grinding, clarification and thickening, will be controlled from a main underground control room at the 480-m level. Additional control systems at surface will support the ore slurry load-out process, first- and second-stage water treatment plants and other auxiliary services, all connected to a main surface control room to be located in the ore load-out building.

The distributed control system incorporates several DIN-rail mounted field control processors (FCP270) located separately in cabinets at each process area. The field control processors communicate with HART protocol field devices using HART I/O modules and two types of field device system integrator modules (FDSI). These are I/O signal processors that consolidate signals from Ethernet devices and serial-based protocols.

The integrator module technology permits the control and supervision of many types of field-mounted sensors and devices — Foxboro, third party and other specialized sensors and equipment. Many RTD temperature points are required to monitor the freezing of the orebody. These RTD points are wired to eight-point RTD modules, which connect to the Modbus RTU RS-485 networks and interfaces with the field device system integrators using Modbus protocol. Field device integrators of another type, using Modbus TCP/IP protocol, tie into numerous Modicon PLCs dedicated for discrete controls.

In all, the control system comprising Foxboro I/A series and multiple Modicon PLCs will handle about 5,500 I/O points.

The field control-based architecture allows nearly all primary control actions to occur close to or within a machine or process. This means shorter and more secure I/O signal transmissions, less chance for I/O line or connection failure, and greater reliability of control data flowing to the rest of the system.

At the next control layer, the distributed control processors connect using high-speed Ethernet switches with main supervisory control rooms above and below ground. The control system employs I/A Series Version 8 software running on Microsoft XP-based computers to support applications for performance management, alarm management, and other operational and management roll-up applications, along with process operator interface via LCD monitors.

Since the McArthur River mine control system was implemented in the late 1990s, there have been technical improvements that are now benefiting the Cigar Lake automation system, mainly in the field control processors, field device system integrators and high speed communication network. Today’s processors have more streamlined internal (ASIC) design, standardize on Ethernet as the protocol of choice, and can be updated or upgraded on-line. These developments translate into optimized reliability for the field environment, and the ability to be reconfigured for changing needs and future technology migration.

Supported by people, processes and technology, Cigar Lake will mine ore over a life of 20-30 years, with the first phase of mining lasting about 15 years after production commences.

Meng Yap is industry sales manager for the Mining & Metal division of Invensys Systems Canada, Inc. in Dollard des Ormeaux, Que., and can be reached at meng.yap@ips.invensys.com.