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Posted On: 03/07/2006

Turpene plant pumped in Panama City

PlantServices.com

When Thomas Roe was hired as maintenance supervisor at the Arizona Chemical plant in Panama City, Fla., the company already had decided in 2000 to upgrade the plant with a Moore APACS distributed control system (DCS) to help operators refine crude sulfite turpentine. Among the challenges for Roe, who has since been promoted to senior energy engineer, was to replace and interface an antiquated motor control center (MCC) lineup handling 194 water-feed pump motors used in the turpene process.

The old MCCs were causing big problems. Some had been installed in 1958, the rest dated back to the 1940s. Downtime from malfunctions and insulation failures were costing the company more than $50,000 a year. And every time a problem arose and controls were replaced, technicians were exposed to danger as the decades-old MCCs were designed without protective barriers.

Roe decided that the new MCCs must provide historical information to improve predictive maintenance. The lineup should be easy to wire, commission, and maintain with the DCS, and minimize exposure to electrical hazards by isolating the power busbars.

Arizona Chemical had Class A buying agreements with two well-known MCC and automation vendors, but Roe says neither provided the solution he needed to complete the MCC replacement project.

“Siemens was the only company that had a dependable interface with the approved DCS,” Roe says. “The other companies’ recommendations involved too much wiring, their communications systems had too many restraints, and they just couldn’t give us the historical motor data we needed.”

Roe selected Siemens’ Tiastar MCC for the upgrade. A 2002 installation included five Tiastar MCCs with 158 full-voltage, non-reversing (FVNR) starters with AS-Interface Slim Line modules, and 43 FVNR starters with Simocode overloads. The installation was completed within a planned two-week outage, primarily because Roe eliminated hundreds of hours of wiring and commissioning time by choosing Profibus and AS-interface communications instead of conventional hard wiring.

Roe says if the plant chose a standard, hardwired MCC lineup, eight wires would need to be connected to each of 194 motors, going back and forth from the MCC to the control room 100 ft. away.

“We had only two weeks to complete the entire MCC upgrade,” Roe says. “We tore out the panelboards, put in the DCS, replaced the existing MCCs, removed the wires and installed Profibus, and tied it all back into the DCS in those two weeks.

“We installed only four, ½-in. diameter Profibus cables. If we hardwired, we would have had to pull 1,552 wires and drill through concrete to access that much conduit. Hardwiring would have taken seven electricians more than two weeks to finish 3,100 terminations. Also, hardwiring would have cost an additional $30,000 in labor and material.”

A second installation, completed in 2004, included seven MCCs with 108 FVNR starters with AS-Interface and 92 with Simocode devices.

The AS-Interface Slim Line modules act as remote I/O devices inside the starter units and communicate back and forth over the AS-interface bus. The Simocode device, an intelligent overload relay, provides operators with detailed information regarding the process using Profibus-DP protocol. The AS-Interface network acts as a slave network on the Profibus network.

The microprocessor inside the Simocode device communicates with Profibus to provide more than 40 different readings including current, motor protection, fault codes, shutdown explanations, the day’s highest current and extensive historical data. The communication was configured within the DCS with links to the individual cells in the starters in each MCC.

When Arizona Chemical’s operators do not require this level of information, 31 AS-Interface blocks may be connected to each Profibus drop. “This gives us the ability to bring out a lot of I/O inexpensively into the MCC, including start and stop functions,” says Roe.

Arizona Chemical realized immediate and significant time and labor by using Profibus during the check out and startup phases, says John Richardson, automation specialist with Siemens Energy & Automation. “Checking out the Profibus communications was simply a matter of making sure the green indication light was on,” Richardson says. “In fact, the Panama City plant technicians started the MCC twice and went through the complete check out twice because they didn’t believe it could check out so fast.”

Richardson says the option of having power and communication over two wires further reduced wiring time and costs of the new MCCs. In addition, AS-interface bus lets Roe and technicians at the plant perform remote start/stop with just those two wires.

Safety also is improved. “The Tiastar MCCs are fully insulated so when the panels are opened, the bus is not staring right at you,” Roe says. “They have shutters so when electricians pull a controller out, the bus is not exposed, which is a major improvement.

“The Tiastar smart MCCs, communications via Profibus, and our experience with Siemens’ automation technology have eliminated plant downtime and saved labor and material costs,” Roe says. “We now have more options to migrate to a more sophisticated DCS, like Siemens PCS 7, when the time is right.”