DuPont Fluoroproducts Improves Operations at Fayetteville Facility With Siemens PCS 7
For decades, DuPont™ Tedlar® polyvinyl fluoride (PVF) film has protected the delicate wiring and components of photovoltaic modules. Widely used as backing sheets, Tedlar® PVF film has set the solar energy standard for strength, weather and UV resistance and moisture barrier properties.
To keep up with the growing needs of the photovoltaic energy market, DuPont Fluoroproducts (DuPont) recently completed an expansion of its Fayetteville, N.C., plant to augment other PVF manufacturing facilities.
DuPont Technology Associate Jim Simmons was given the assignment to work with the DuPont design organization to select and install the distributed control system (DCS) that would automate the Tedlar® operation. Simmons knew he needed a DCS that could accommodate more than 600 DuPont approved field devices from multiple vendors adding up to more than 1100 I/O points.
After a comprehensive analysis of available technology, DuPont chose Siemens SIMATIC® PCS 7 DCS, including four pair of redundant S7 400 controllers, three S7 300 PLCs for skid control, and a redundant client/server architecture with four dual monitor operator stations.
"I knew that Siemens PCS 7 had a lot of the capabilities in the various field bus technologies I wanted for this project," Simmons said. "While I couldn't guarantee we would be ahead of schedule, I was confident we would be on time. The idea that it could be faster was enough of a carrot."
And faster it was. The project team cut eight weeks, off the allotted commissioning time. Originally scheduled to begin production on Nov. 22, 2007, the plant in Fayetteville began producing product Sept. 11, 2007.
"Our outside consultant evaluated our initial Nov. 22 schedule and determined it was 83 percent shorter than the best of the best for project execution time in the industry. So we even bettered that," Simmons said. "The mechanical installation was completed on Aug. 31, but we did not begin introducing process material until Sept. 6, because we decided to take time off for Labor Day weekend. It would have been even earlier if we had worked through it."
Open and Flexible
In the past, Simmons worked with traditional 4-20 mA wiring on other DuPont installations and did not spend much time learning about digital field bus technology because it was not applicable to his operation. However, his vision was to save time by using field bus to connect all devices and instrumentation back to the PCS 7 DCS.
"There are four categories of traditional field devices that we connected to the PCS 7 control system - process instrumentation, motors and drives, discrete block valves, as well as process analyzers and auxiliary equipment," Simmons said. "My goal was to identify the field bus technology that was best suited for each category of field device. PCS 7 is ideal because it offers all of those capabilities and it all connects into the system using a common field bus backbone (PROFIBUS DP)."
The first field device category at the Fayetteville facility to connect to the PCS 7 system was process instrumentation - primarily transmitters that measure pressure, temperature, level, flow and density. The category also included control valves, which control the process variables that are measured by the transmitters.
Simmons said he found support within DuPont's guidelined instrumentation vendors for PROFIBUS PA. At the time of the installation DuPont had a blend of four vendors for temperature, pressure, level and flow - ABB*, Siemens, Emerson* and Endress+Hauser*. Flowserve* control valves were used with Siemens SIPART PS 2 positioners. In some instances where a transmitter was not compatible with PROFIBUS PA, Simmons used HART communications and traditional 4-20 mA connections. Loop checkout of all the fieldbus instrumentation was performed using the Process Device Manager (PDM) tool.
The second category for devices is motor control, which includes both fixed and variable speed motors. The approved supplier for motor control technology at the site is Rockwell Allen-Bradley*.
The fixed speed motor starters were all supplied with DeviceNet connectivity, which is a fieldbus commonly used with Allen Bradley's motor control centers. To bring the data into the system, Siemens utilized a gateway from HMS called "Anybus" that connects DeviceNet to the PROFIBUS DP backbone.
The Siemens team developed symbols and faceplates to display all of the DeviceNet supplied motor data within the HMI. Now, operators in the control room can instantly access start/stop, run status, field switch status, and the current that the motor is drawing on faceplates on the PCS 7 OS operator console.
"I now have an entire motor control center that has 15-20 motor starters off of one, four conductor cable," Simmons said. "If the overload trips, I can open up the faceplate and see what the overload cause was. I can also see how long before the overload can be reset and then reset it from the console.
Our rules state that we can reset it once, but if it trips again we have to get an engineer involved," Simmons continues. "But being able to reset after a single trip in the middle of the night instead of shutting the plant down is worth a lot of money. It could easily add up to millions."
The variable speed motors have built-in PROFIBUS DP connections. This provides DuPont with the ability to use the speed of the motor to control flow instead of a control valve, which saves money by eliminating the energy losses which occur when flow is throttled through a control valve.
"I found a tremendous benefit in the openness of PCS 7 and PROFIBUS for motor control," Simmons said. "First, there were far fewer wires to connect, which sped up check out time and reduced the potential for wiring errors. Furthermore, the digital communication and the presentation of the information on the PCS 7 faceplates allow us to do more effective troubleshooting and diagnostics."
In the past, Simmons says if a fault occurred on a drive, operators would be required to physically go to the site of the trip and scroll through an error list to find the appropriate two digit fault code. The operator would then look up the code in a drive manual to determine the cause of the fault.
"Now if a drive trips, we can open a faceplate to see the fault code and the English word description of that fault," Simmons said. "In some situations, it is not uncommon for the drive to trip out because of the way the process is run. The operator can reset that fault from the control system and restart the motor without leaving the control room."
The third field device category is automated block valves that open and close to direct process flow. Simmons says since the valves require only a few pieces of communication data, he chose Actuator Sensor Interface (ASi) to communicate to the PCS 7 system. Information from the faceplates at the workstation assures operators that the valves have moved to the appropriate position and are either fully opened or closed.
The final category includes Siemens gas chromatograph process analyzers and other pieces of equipment such as the site's 100-ton chiller, two substations and heat trace circuit control panels. Simmons chose Modbus to supply information back to the PCS 7 system since it is commonly used with these types of equipment.
"All of these field bus technologies are compatible with PCS 7," Simmons said. "If I am not using field bus it is because that device is not field bus capable."
Responsiveness and Teamwork
Simmons attributes the success of the start up to a number of factors, but points to a "Let's get it done" attitude that permeated throughout the combined Siemens and DuPont team.
"It was a close knit effort and a lot of work done in a little time," Simmons said. "Whenever we came across a problem, someone from Siemens was on site and took care of it. We never placed blame. It was always "let's go." Siemens did all of the configuration work and was on site all eight weeks we were doing check out plus two weeks of start up."
An example of this teamwork and responsiveness came unexpectedly as the team was preparing for start up. As technicians were making the PROFIBUS DP communications to the Allen-Bradley variable speed drives, a sample drive was energized to ensure the communications to PCS 7 were in good order. The Siemens representative found that the sample drive communicated using 32 bit words for speed and power. The drives that had been tested at Spring House communicated using 16 bit words.
"Because the Siemens person was on site, he was able to diagnose what was going on with the drive and made another version of the function block that was mapped properly for 32 bit word communications," Simmons said. "If we tried to figure this out on our own, we would have stumbled around in the dark for a long time. That could have made a difference in amount of time we cut out of the schedule."
New Plant Planned, Same Technology
The new facility has exceeded all expectations. In addition to the entire project being more than $6 million under budget, the fast commissioning and start up allowed DuPont to make Tedlar® PVF eight weeks earlier than expected. Simmons vision for a field bus controlled plant has come to fruition.
Success breeds success. Simmons says the company is planning to duplicate control system and field bus communications in another, identical facility.
"I'm moving out of my support role and back into the project role right next door," He said. "The intent is to make the new facility identical to this one. We are going to make a copy of the configuration and change the prefix parts of tag names and everything else will be the same.
"As I've told many people, I have been very pleased with our relationship with Siemens and I'm fully invested in using PCS 7 and the field bus technologies it accommodates."
* ABB is a trademark of ABB Ltd. Emerson is a trademark of Emerson Electric Company. Endress+Hauser is a trademark of Endress+Hauser AG. Rockwell Allen Bradley is a trademark of Rockwell Automation. Flowserve is a trademark of Flowserve Corporation. Siemens Energy & Automation, Inc., is not in any way associated or affiliated with ABB, Emerson, Endress+Hauser or Rockwell Allen Bradley.
Tedlar® is a trade mark of DuPont.