Early claims about the wonders of wireless technologies, which often failed to live up to expectations, soured many technical professionals on their use. But Marc Ayala, control system specialist at Akzo Nobel Industrial Specialties Inc.'s Houston plant, gave wireless a second chance. Now he raves about the cost savings and "rock solid" integrity of the wireless technology that his company uses in conjunction with its automated control system.
The Swedish company touched off its venture into using wireless technology with its control system in June 2002 when it acquired Crompton Corp. of America's Industrial Specialties business, which included a Houston plant that manufactures agricultural and oilfield chemical surfactants. For the past several years, the Houston site has been undergoing a plantwide project to replace pneumatic and/or electronic analog field instruments, as well as a legacy, single-loop controller-based control system, with a next-generation, fully integrated automation system.
A hybrid control system, comprising several panel-based single-loop controllers and on/off switches, used to run the plant's mostly batch-oriented processes. Several years ago, operators realized that the plant's aging and increasingly unreliable systems were starting to negatively impact the company's ability to meet customer commitments. Spare parts for the legacy control system with pneumatic instrumentation were becoming hard to find. Nearly all of the 10 plant areas had its own control room, and the legacy control system did not make it easy to coordinate plant-area controls or collect plantwide process history data.
A low-power wireless transmitter/receiver is mounted near field storage tanks.
Akzo Nobel decided to replace the legacy system with the DeltaV automation system from Emerson Process Management, Systems Division, based in St. Louis. Availability of technical support from Puffer-Sweiven, the local Emerson representative in Stafford, Texas, was a key factor, as was the automation system's intuitiveness and field-proven record for controlling batch and/or continuous processes.
The first modernization project included replacement of all pneumatic field instruments and the legacy control system associated with an on-line blending operation. The project was relatively small; it involved about 120 input/output (I/O) points. A pneumatic-to-current and a current-to-pneumatic converter was used to couple each of the pneumatic field instruments to the legacy single-loop controller-based control system. Akzo Nobel decided to implement the blending project on a turnkey basis because of its limited in-house expertise, supported by Puffer-Sweiven's engineering and installation services.
A second automation project opportunity arose just as the first turnkey project neared completion: to replace all pneumatic field instruments, a few 4-20 mA instruments and the legacy control system associated with an oxylation unit. Although management could back the purchase of hardware/software and field instrumentation for the automation system, it could not justify outsourcing the entire project. After the first project went so well, however, the team was confident that it could hit a tight one- to two-month window for engineering and installing the new automation system on the oxylation unit ," despite the fact that the second project included almost double the I/O and required redundancy for controllers, communications and power supplies.
After soliciting input from the operators on how to best transition from panel-based instrumentation to a Windows-based operator station, the company learned that replicating the single-loop controller panels and face plates on the operator displays would be the way to go. Using the Intellution-based graphics builder software package of the new automation system, Akzo Nobel built a customized face plate, which was nearly identical to the legacy system, that could be reused for each loop.
During the oxylation unit changeover, Ayala expected a few surprises, especially when his team started to test the system by producing water batches. The team produced the first batch, however, without doing the customary rework. Everyone thought that was a coincidence, but Ayala says that they were able to produce batch after batch without reworking or restripping any of the manufactured product. He estimates that rework elimination saves two to three hours per batch, which in turn increases production capacity by at least 20 percent.
Based on their hands-on experience with oxylation unit implementation, Ayala and his team now know their processes more intimately than before. This puts them in a better position to apply automation technology to other plant applications on their own, which saves money.
DeltaV's data historian has also improved employee productivity, especially the operators'. Authorized users now have instantaneous access to real-time and/or historical data, which has been useful for analyzing and optimizing the process for raw materials and energy usage, for example.
Akzo Nobel control systems specialist Marc Ayala inspects a wireless transmitter/receiver connected to DeltaV I/O modules.
Wireless technology keeps costs down
Akzo Nobel cautiously considered using wireless technology. Ayala, who had tested a wireless technology that did not work at distances of more than a few hundred feet and experienced serious interference problems from the radio towers adjacent to the plant, understands how reliability ," as well as security ," concerns have impeded the technology's acceptance. He took another look at wireless, though, when the plant needed to add two temperature measurements for monitoring and keeping historical data on the temperature of a raw material. The material is stored in an awkwardly located storage tank to which it would be difficult and costly to route wires.
After extensive research, site visits and discussions, Akzo Nobel installed the HS-900 wireless monitoring system, based on ISM (Industrial, Scientific and Medical) spread-spectrum bands, from OMNEX Control Systems, Port Coquitlam, British Columbia, Canada. The 900-megahertz-band Frequency Hopping Spread Spectrum-based transmitter/receiver set can provide 4-20mA current to the temperature transmitter. It can be mounted in Class I, Division II, Groups A/B/C/D environments and supports Hart communications. Each transmitter/ receiver pair uses digitally encrypted communications to maintain security.
Ayala's team pondered whether to interconnect the OMNEX system with DeltaV. That approach, Ayala says, was more cost-effective than pulling wires and running new conduit. In fact, his team estimated that labor costs to prepare the path for wires alone would have been 10 times the price of a wireless transmitter/receiver.
In general, the use of wireless technology for process monitoring and control purposes has been limited to supervisory control and data acquisition applications that cover large distances.
Nevertheless, Ayala's team had no trouble integrating the OMNEX system with its input cards and setting it up. The effort was worthwhile.
"The wireless integration to our DeltaV has enabled alarming, trip points and intercommunications from the actual wireless in the field, which is over 1,300 feet away," says Ayala.
The plant has installed 10 receiver/ transmitter sets for temperature monitoring and, in one application, for closed-loop control on a slow-acting temperature control loop using steam.
For more information about Emerson Process Management, Select 494, or for OMNEX Control Systems, Select 495, in Chemical Processing's on-line reader service.