Carl Stumpe checks a DeltaV controller's analog I/O module. The controller is mounted in cabinet space that used to hold DCS equipment.
The DeltaV digital architecture is designed to accept I/O from digital bus networks directly into modules as native I/O. Additional interfaces, lookup tables and subroutines are not needed to communicate with Foundation Fieldbus, AS-I bus, Devicenet, Profibus DP and Hart digital signals. The digital architecture provides easy access to information present in BASF's existing HART transmitters and new Foundation Fieldbus devices.
A surprisingly high percentage of existing instruments were Hart Smart. Using Hart communication, the team extracted 70 new measurements from existing transmitters. Each Coriolis flowmeter, for example, now reports flow, density and temperature.
In addition, 350 Hart instrument configurations were automatically backed up in the asset-management database. BASF chose Emerson's AMS since it easily integrates into the DeltaV network. Past calibrations are maintained, and new calibrations are easily downloaded. While the new features were a factor in the decision to move to a new DCS platform, the company initially underestimated their usefulness. The new automation system's advanced control options, better diagnostics, superior analysis, optimization and asset-management software are being used to reduce variability and maintenance costs, and speed troubleshooting.
DeltaV's peer-to-peer communication between controllers and operator stations allowed consolidation of existing LCNs into a single, facility-wide control network. Power failures or disruptions in one unit do not affect another unit on the same network. By combining multiple networks, BASF reduced system administration and upgrade expenses.
Virtual FAT developed
BASF's answer to overcoming the FAT problem was to develop a two-stage, software-based method. In the first stage, control module functionality was tested using Chesterfield, Mo.-based Mynah Technologies' Mimic simulation software. During this phase, items checked out included new controllers; a workstation loaded with Mimic simulation software; the network linking the controllers; and the workstation.
The second stage of FAT testing used a BASF-designed test fixture to assist with the point-by-point checkout of each module's I/O connections, thereby taking the place of field loop-checking. Art England, instrumentation engineer, designed the fixture. "We knew the wiring connections from the existing instruments to the termination panels were working with the previous DCS. So, we just had to confirm that the Flexconnect cable between the DeltaV and the Termination panels operated properly," he says. To do this, he designed a test fixture that simulated a termination panel with instruments attached.
A classic loop check requires a board engineer and field technician. Oftentimes, the board engineer will be waiting on the field technician, or vice versa. With England's technique, one person in the test lab can efficiently conduct loop checks. The tester confirms that the module responds properly to changes made at the adjacent test fixture. Since field devices and associated wiring were untouched by the retrofit, there was no need to perform field checks after the system was installed. This method was effective, with only two valves found to be operating improperly during startup.
In other words, FAT and traditional loop check were never conducted. Simulation software and Flexconect testing were combined to efficiently replace the classic FAT and loop check. The testing allowed for trouble-free startup immediately after the DCS installation. BASF calls this multi-stage technique "virtual FAT," or VFAT.
In new construction, loop checking requires about one to two weeks per controller. With the VFAT technique, spot-checking of instruments took just four hours per controller. Use of VFATs and Flexconnect technology guaranteed the quick cutover the company required.
Self-directed operator training
To assist in a smooth transition, new graphics were designed to look as much like the old graphics as possible. During training, operators suggested improvements, including better module descriptions, improved alarm schemes, more descriptive graphics names, minor graphic modifications, etc.
Operations personnel received only three hours of formal instruction. The remaining class time allowed the operators to train themselves on the process by running the Mynah simulation.
Simulation also ensured that the interlocks performed properly. Many of the interlocks at SAR are built around a specific startup sequence and they change as the sequence progresses. Using the simulator, the team tested interlocks for each phase of the startup. To test the first-out functions, several extensive, multiple-initiator trip scenarios were simulated. In the past, interlocks would have been checked during water batching, which is expensive and time consuming. The Mynah simulation software provided a convenient, inexpensive alternative.
Simulation also helped BASF optimize certain control schemes. The configuration of five cascade loops were changed because they never had worked well, but were too difficult to modify on the old system. The new control schemes were tested with Mimic before they were implemented.
Reaping the benefits
At press time, the DeltaV system has replaced three LCNs with a single distributed Ethernet network that connects 17 controllers and 15 consoles. As more of the BASF site is converted to DeltaV, the layout will expand, change and be integrated to best fit the site's requirements.
Complete replacement of the legacy control system has enabled BASF to implement modern technology in any area of the converted plants. The Hannibal site is taking advantage of DeltaV's integrated asset-management, controller-resident model predictive control, and advanced diagnostics to improve efficiency. The new control system's compatibility with Foundation Fieldbus, Profibus DP, Devicenet, AS-I Bus and Hart technology have cut new project costs. The adoption of digital automation technology has allowed BASF's Hannibal facility to meet all three of its original goals of boosting output, cutting costs and improving quality.
Carl Stumpe is the instrumentation and electrical lead engineer at BASF's Hannibal, Mo., site.
Using FlexConnect and simulation software, the team was able to rapidly cut over processes with thousands of I/O points. Preplanning and support were critical to the project's success.Plant personnel had become comfortable with the existing DCS, so there was some concern about switching to a new control system. The Mimic simulation software played a role in allowing personnel to become familiar with the new automation technology. This was essential for a smooth startup. Areas of special concentration in simulation training included pulling up interlocks; navigating between graphics; simulating equipment shutdown; and alarm management.Factory acceptance testing (FAT) procedures have not changed significantly since the introduction of DCS. The classic technique of hardware checkouts at the vendor's site, followed by extensive loop checking at the customer's site, is inefficient for large-scale DCS retrofits. An efficient FAT is essential to speed startup and reduce project cost.Cost was only one factor in selecting a new DCS platform. Another factor was the ability to mount small, powerful controllers adjacent to the equipment being controlled.The decision to go with a new DCS platform proved to be the most cost-effective option by a 2-to-1 margin. In prior DCS retrofits, instruments were rewired to new controllers. Designing and installing new marshalling panels, loop diagrams and I/O terminations was expensive and, after the conversion, existing controllers, termination boards and cabinets had to be ripped out. In addition, each device required a thorough loop check.Configuration of the DeltaV automation system was largely automated. The team developed a program to convert point parameters into a flat file, which was imported into standardized DeltaV modules. One of the challenges with this approach was that the new modules had many more features than the legacy system. For example, Hart data are brought into the modules at a channel level, so transmitter range and diagnostic information is tied to the analog input signal. Default module settings were set up to uniformly act on these additional data.Once the team chose its automation strategy, implementation was the next step. Complicating the effort was that the new and old DCS were of different manufacture and vintage.Although it was challenging to abandon preconceived notions about DCS architecture and function, the DCS team at Hannibal decided to start with a clean slate and evaluate all automation options. They wanted to identify the most capable and cost-effective automation system available; one that would be compatible with future upgrades.