First Gaining Experience and then Implementing Large-Scale Digital Bus Projects

Jack Murray, a member of Emerson’s Metals, Mining, and Minerals industry team, shared a paper he had co-written with an Alcan Gove bauxite mine and alumina refinery staff member and Emerson fieldbus consultant, Sudhir Jain. Alcan was recently purchased by Rio Tinto.

Their paper, Fieldbus Technology on a Large Scale Mineral Project, describes Alcan’s path from the 4-20mA analog world to a digital bus communications world. Alcan’s investigation of the benefits of moving from analog to digital began in 1999. They had seen possible ways to reduce their project costs and improve operations by using digital busses.

Their first step, like most when undertaking something new, was a small step. They chose to implement Foundation fieldbus in a non-critical area of an existing facility. Their initial installation consisted of 20 I/O. They chose fieldbus devices from a number of automation suppliers to obtain a greater breadth of experience. They also chose Profibus DP for their motor control centers and variable speed drives.

This experience proved beneficial when the decision was made in 2004 to nearly double refinery capacity to meet growing demand. The project consisted of 5,000 field devices and 15,000 total I/O including motors and drives. They used a DeltaV system and the two digital busses, Foundation fieldbus and Profibus DP, for which they gained experience to connect the majority of this I/O. A key part of their decision was to work with Sudhir during the front end engineering design (FEED) process to assist in the segment design, training of key personnel, and to establish wiring best practices and standards.

Sudhir related to me how they developed new hazard analysis procedures (CHAZOP, short for control HAZOP) to ensure that failure of any bus segment would not leave a critical part of the plant unmonitored or uncontrolled. Segment segregation practices were developed to address the findings from this analysis. They also had a 3D model of the plant site, so that questions of distance and pathways could be quickly addressed to help rapidly advance the engineering effort.

They chose a modular construction approach using pre-assembled modules (PAMs). These modules were assembled and fitted off-site and fully pre-commissioned before they were delivered to the plant site. These PAMs were self-contained units and included process vessels, piping, pumps, instrumentation and valves, all fully wired and tested.

The digital busses fit into this modular approach with test procedures developed and a portable DeltaV system used to test field devices and fieldbus segments within the PAMs. Once delivered to the plant site, it was much faster to hook up fully tested segments than to individually terminate and retest devices as had to be done on their analog-based projects.

The project team followed elements of the Construction Industry Institute (CII)
PepC model. The paper describes this model:

In the new model procurement transactions for the most critical elements of the project (indicated by capital P) happen first and to a large extent define the next step, the main body of the engineering effort for the rest of the project (Capital E). This is followed by procurement of the materials for the rest of the project (small p), followed by the actual construction (capital C).

This model helped Alcan take advantage of the expertise of the suppliers involved in the project and aligned with their globally distributed engineering and procurement practices. It also supported their modular approach and the use of PAMs.

As with most every bus-based project, they documented savings in cabinet space, installation and commissioning. The real value was in the accelerated project timeline. In five fiscal quarters, 95% of the engineering, 76% of the PAM fabrication, and 54% of the on-site construction was completed. Alcan was able to meet their aggressive project schedules and get production on-line sooner.

Update: Welcome readers of Carl Henning’s PTO PROFIblog. I’m not sure about the “voice of reason” part, but like Carl, I certainly agree that the benefits from the digital bus technologies outweigh the change in status quo from the analog world.

Read the Crossing the Chasm article to which Carl refers and judge for yourself. Feel free to let me know what you think.

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