The decision to use the new I/O technology came late in the planning process. Southern States had looked at a standard fieldbus system incorporating wiring all the way from the I/O point into the cabinet in the control room, but when the new field junction cabinets and I/O system became available, the company opted for them, as they appeared to promise big savings in engineering and construction costs, as well as increased reliability.
The characterization modules (CHARMs) enable I/O anywhere in the plant regardless of signal type—from a local I/O cabinet to remote enclosures. In the Wilbara project, Southern States terminated the total I/O among 10 junction boxes located throughout the plant, running all the signals from each junction box to the control room and I/O cards via two Ethernet cables. Traditional marshalling cabinets were completely eliminated, decreasing the amount of field wiring by half and cutting wiring cost by 40% (Figures 1 and 2).
The electronic marshalling technology eliminated one of the most tedious and costly tasks that almost invariably become a part of any plant construction or expansion project: late engineering changes. The I/O system's flexibility showed its value in several cases where an I/O point was located in a different cabinet from that originally planned, and it was very easy for the team to relocate the I/O module and reconfigure it in the control system.
The Results Are In
Plant operation has been reliable, aided by the system's redundant controllers and CIOC, dual Ethernet communications and smart transmitters in key areas.
Emerson provided all the field devices, including valves, transmitters, thermocouples, RTDs and flowmeters. Among these, the company's mass flowmeters now allow truck and rail car tanks to be filled with acid in a very streamlined process. By tying the truck scale in with the flowmeter, operators input the target weight and, with the press of a button, can fill the tank accurately and concurrently print the loading bill. This dramatically reduces traffic, while increasing both reliability and throughput. The control system and field devices all came from a single supplier with local representation, an added reliability assurance.
FAT had an added component of key operator/supervisor training. These operators and supervisors became our mentors during operator training and site commissioning. The digital control system's ease of understanding and operation reduced operator training and costs, with training completed in two weeks.
Southern States achieved substantial capital cost savings, with construction and wiring costs 50% less than a standard DCS.
The start-up schedule was met by taking advantage of the characterization modules' flexibility when field I/O changes were implemented during construction. I/O additions were quicker and less costly because of the Ethernet communications backbone already in place. One of the changes made in the I/O during construction concerned a point originally planned for location in the field, which ended up requiring location in the control room where the system controller is. Connection in the new location was extremely quick and easy.
Integration with Southern States' business systems is still a work in progress, but the production data now available is showing the way to continuous improvement. The digital automation system provides a wealth of production data that every segment of the corporation can use, enabling Southern States to provide outstanding quality, predict required maintenance quicker, control the process better and make better business decisions.
The gamble to entrust a new plant start-up and ongoing process automation to a single supplier and its new electronic marshalling technology clearly paid off. The new plant is producing roughly 575 tons of sulfuric acid per day, versus around 150 tons per day at the old plant with the same number of personnel. Recent state SO2 and acid mist emissions tests fell significantly below requirements. Further, the Wilbara plant is delivering as much or more steam per month to its neighboring customer as promised in its contract. The construction, wiring and change management savings provided by the electronic marshalling technology, along with subsequent reliability and performance have served as a model for future plant automation engineering.
Using this state-of-the-art technology, Southern States Chemical's new Wilmington plant stands as the crown jewel of the company.