Distributed Control

DCS and IT blend abilities

How to take advantage of the increasingly homogenizing abilities of distributed control and information technology systems

By Jim Montague, executive editor, Control

Over time, many human spouses, as well as pets and their owners, reportedly come to resemble each other. So, in the case of distributed process control versus IT-style technologies, it's not so much one beating or replacing the other, but rather each exchanging capabilities, and both looking more alike and serving in similar ways.

This is why each new DCS, PLC or other process control project seems to add more mainstream computing and networking functions, which are increasingly indispensable in the varied and complex situations where distributed control is employed. However, while IT-based solutions have made inroads into data collection, monitoring, SCADA, networking and support areas of process applications, IT's methods have been slower to penetrate core process controls.

"The landscape of the industries we serve is changing as  consumer tools come in due to their computing power," says Beth Parkinson, market development director for connected enterprises at Rockwell Automation. "These devices are more mobile and can display data and even video immediately, and users want to use them in their business and manufacturing environments, too. This is forcing operations technology (OT) and information technology (IT) to converge, so operators can access capabilities like video views in their plants."

For instance, the methanization plant at Aguas Andinas' Planta La Farfana wastewater facility in Santiago, Chile, recently upgraded from a flooded-screw compressor and conditioning system to SCS Energy's sliding-vane compressor, conditioning and biogas separation skids in its pipeline. However, the compressor, biogas separator and waste gas flare each have their own PLC, and are managed by a balance-of-plant PLC that also controls the compressor and overall process. The plant produces high-BTU natural gas from anaerobic digester gas, which it sends to Santiago's Metrogas utility.

To coordinate the methanizer's four PLCs, SCS Energy and system integrator Tactical Controls LLC in Oceanside, Calif., implemented an Ignition server and software from Inductive Automation, which communicates with the four PLCs through KepServerEX and a MySQL server for historical logging and SCADA system data.

"Ignition provides fine-grained control of the new compressor system, and observation and start/stop control of other systems in the plant," says Bruce Gibbens, Tactical founder and manager. "Each HMI screen uses templates, indirection and UDTs for rapid development and a high degree of consistency between systems and screens. Valves, motors, analog values, PID loops and even subsystems utilize templates and indirect pop-up windows for display and control."

Migration nurtures IT

Naturally, one of the best times to begin streamlining tasks with IT-aided tools is during DCS migrations. For example, Total Petrochemical & Refining USA's Port Arthur refinery processes a mixture of crudes with conversion capabilities centering on coking, fluid catalytic cracking (FCC) and reforming technologies, and has a capacity of 174,000 bpd of transportation fuels. It's also capable of exchanging feedstock and utilities with an adjacent naphtha steam cracker, which is a joint venture between Total and BASF.

However, though Total had been modernizing parts of its 20- to 30-year-old TDC 2000 control system, it was still over capacity with 18,000 active I/O on eight Data Hiways, and unit segregation had been lost. To complete the upgrade and expand the refinery, Total undertook a deep conversion project (DCP) with hot cutovers to move individual loops to a new Experion Process Knowledge System (PKS), while the unit continues to operate on stream. The DCP added 12,000 I/O, two new operator consoles in greenfield units, and nine new DCS controllers in brownfield process areas. Total worked with Honeywell Process Solutions to enable console operators to interact transparently with different generations of DCS systems. Forty-five legacy consoles were replaced in the refinery's central control and local control rooms, and approximately 400 existing operator graphics were migrated to the current DCS. The facility's two legacy control communication networks were divided into four networks, and a fault-tolerant Ethernet backbone was installed refinery-wide.

The new open-automation architecture at the Port Arthur refinery allows multiple Experion PKSs on different operating units to communicate, exchange data and work together seamlessly. Personnel can connect directly to information and control networks, providing full and immediate access to critical data. Experion is easily integrated with human-machine interfaces (HMIs) throughout the facility, and communicates with all controllers and network modules.

Leg up for process safety

Beyond participating in DCS upgrades, IT-style strategies can also help users implement support efforts, such as process safety, and accomplish them more easily. For example, Sasol's integrated chemical plant in Sasolburg, South Africa, has migrated the burner management system (BMS) for a distillation column furnace on its wax work-up production process because the old BMS was at the end of its life. Running continuously with scheduled shutdowns two to five years apart, this furnace is critical to Sasol's wax production, and its failure could cost more than $150,000 per day.

Consequently, Sasol worked with Emerson Process Management and local business partner Aveng Automation and Control Solutions (A&CS) to migrate the old system to DeltaV SIS for Burner Management during the plant's annual, scheduled shutdown in 2014. This solution was seamlessly integrated into the plant's DeltaV DCS that Sasol adopted in 2012.

DeltaV SIS for Burner Management allows the furnace to go safely through all relevant states from start-up to operation and shutdown when needed. It comes with IEC 61508 TÜV-certified function blocks that simplify logic configuration, testing and troubleshooting. An intuitive, graphical control environment conveys critical information in one glance, so operators can understand furnace conditions in real time, place burners and igniters in and out of service safely and quickly, and initiate other timely actions to maintain safe operating conditions (Figure 1).

Communication leads to control

Because the IT side is already so closely paired with networking, it should be no surprise that communication tools can also assist DCS and other process control efforts. For instance, the Joint Water and Wastewater Authority, Vogtland in Germany consists of about 300 potable water plants and 300 wastewater plants serving 40 communities with about 240,000 residents. To better coordinate and control its plants, ZWAV recently used the OPC UA standard to establish machine-to-machine (M2M) communications between the small, intelligent, embedded controllers at its facilities.

Real objects, such as pumps, were modeled in TwinCAT IEC 61131-3 PLC software from Beckhoff Automation as complex objects with interactive possibilities. Thanks to an OPC UA server integrated in the controller, these objects are automatically available externally as complex data structures for semantic interoperability. The result is decentralized intelligence that can make decisions independently, transmit information to neighboring systems via wireless routers, and query equipment status and values for its own process. With standard PLCopen function blocks, the devices can independently initiate communication from a PLC to other devices such as OPC UA clients, while also responding to their requests or requests from higher-level SCADA, MES and ERP systems via OPC UA servers (Figure 2). OPC UA's authentication, signing and encryption security mechanisms were used, as well as a mobile, closed radio group to ensure data integrity.

"Replacing the former proprietary solution with a combined OPC UA client/server solution in embedded controllers saved ZWAV more than 90% per device on initial licensing costs, and minimizing service assignments in the field saved even more," says Silvio Merz, divisional manager for electrical/process technology at ZWAV. "For the engineering part, better standardization resulted in efficient engineering, cost reductions, reuse of technology and equipment, improved transparency, increased availability, increased choice of providers and greater interoperability."

Control going virtual

Finally, once IT-style tools pick up steam in controllers and DCSs, their momentum can pull process applications into performing many data processing chores on servers, virtual platforms and cloud-based services.

To upgrade its Omaha plant to more dynamic controls and flexible recipes, Syngenta Crop Protection worked with system integrator Interstates Control Systems Inc. in Sioux Center, Iowa, to implement Rockwell Automation's primary and secondary domain controllers and servers, including ProductionCentre SQL running Java for shop-floor interfaces and FactoryTalk Directory as the backbone for other FactoryTalk-based services. All these servers reside on ESXi virtualization servers running VMWare software. Syngenta also adopted a thin-client computing strategy and PanelView stations for all production sites and stations.

The plant's six active formulation facilities and five tanks farms manufacture fungicides, herbicides, insecticides and protective coatings for seeds. Syngenta Systems Engineer Darrell Hanson reports its migration to Rockell Automation began with its packaging lines in 2008, liquid continuous unit in 2010 and some of the tank farms in 2012-14. Future conversions will include the plant's continuous granular unit, more tank farms and its water treatment plant.

"Our new PLCs are programmed modularly, so recipes can control groups of equipment following the ISA S88 standard," explains Hanson. "New recipes are set up by formulation engineers, instead of PLC programmers. Orders are entered into Campaign Manager software by QA lab personnel for each batch to be produced, and operators start and control all batch functions using FactoryTalk. All data is recorded using FactoryTalk Historian, and batch reports and KPIs are viewed with FactoryTalk VantagePoint. We're adding 10 new products every year, and our old hard-coded PLCs just couldn't cut it, so we had to get to a more flexible recipe management and control system.

"Admittedly, there's some paper we can't get away from, and so we still use physical batch tickets, but all our data is recorded on FactoryTalk Historian. FactoryTalk Batch gives us more flexibility in combining formulations, such as combining lighter and heavier or more and less dense materials. Our HMIs can still see deviations and errors, but now we can automatically adjust for greater accuracy, and view batch reports with better trends, X-Y plots and all sorts of charts."