The progression of wireless networking from accepted to mainstream is probably nowhere more evident than at ConocoPhillips’ Sweeny refinery in Old Ocean, Texas. The 8,000-acre facility has used a variety of wireless technologies since the 1980s, but recently reorganized and standardized on Honeywell Process Solutions’ (HPS) OneWireless platform.
Alan Autenrieth, control systems team leader, and his colleagues at ConocoPhillips showed how Sweeny has implemented HPS tools over the past three years during his presentation, “Wireless’eering: Enabling Your Future with OneWireless,” at the June 2008 Honeywell Users Group meeting in Phoenix.
Autenrieth emphasized that wireless—like any networking method—is only useful if it successfully serves the needs of the application where it’s deployed. These basic needs include security management and diagnostics, fault tolerance, OPC and ISA compliance, bandwidth flexibility and the ability to work with a portfolio of sensing devices and to share data across multiple systems.
“After employing various forms of wireless applications since 1984, our facility had three wireless transmitter manufacturers, four types of wireless networks and no exchange between them,” said Autenrieth. “We wanted to quit having to start over from scratch with each new wireless job, and we did it by pulling everything under one wireless umbrella. Several other companies are introducing products that support wireless, so it’s important to compare to determine if they offer as complete a package as OneWireless. If emerging technology products are marketed as being compliant with the ISA SP100, then they should be compatible with OneWireless.”
To achieve their goals of wireless unification, Sweeny’s engineers also had to solve several logistical issues. For example, the plant’s operators needed alarms to be in front of them in any location. They also needed to be able to access operating procedures when in the field, as well as graphical displays of tank levels, pumps and other devices. And the system has to run with the same reliability as the control system, added Autenrieth.
ConocoPhillips partnered with Honeywell to cover about half of Sweeny’s geography with 13 OneWireless multinodes, which have 2.4 GHz WiFi and 5.5 GHz radios. One of the first benefits the plant gained resulted from adding transmitters to 38 skin thermocouples on its thermal reactors. The costs of the wired and wireless transmitters themselves were within 10% of each other, but with wireless, the plant saved $200,000 in hardwiring costs.
A second benefit was in OneWireless’ support of the plant’s layer of protection analysis evaluations. “We looked at different options to support 15-minute response time to alarms with one operator in each of two tank farms and found it would have taken $1.25 million to make the existing approach more robust,” said Autenrieth. “Instead, we put mobile Process Knowledge System (PKS) tablets in the operators’ trucks.”
Sweeny presently operates four mobile Experion PKS stations and 32 transmitters. So far, the plant’s wireless network has had only two multinode interruptions in more than 14 months of operation. In fact, ConocoPhillips has identified for installation an additional 120 level gauges with 60 temperatures, 23 digital transmitters for pump stops and 45 transmitters for pipeline monitoring.
To make its wireless network secure, Autenrieth first established an internal policy governing its process control network, firewalls, network topology and access to it. Besides dividing its network into time-synchronized functional realms separated by firewalls and “demilitarized zones” (DMZs), Sweeney and HPS also installed active network snooping tools to check for pings and detect other attempts to probe or intrude on its network. They also added sufficient server capabilities so these separate network areas could continue to run if their connections were ever severed.
When designing a wireless network, Autenrieth advised other users to perform a site survey to find the right places to install wireless nodes in their applications. “If you have some other wireless technologies in place, this can reduce the cost of doing a new wireless survey,” he added.
On the physical side, Autenrieth recommends using poles and support structures for the wireless transmitters that can withstand local weather conditions. For example, Sweeny’s antennas were installed on poles and supports that can survive the 125-mph winds that accompany the region’s frequent hurricanes. “The poles also need to be on stable platforms. We’ve found that the three-leg Rohn type is best,” he said. Because these wireless components operate at 24 V, there are many ways to power them. In fact, Sweeny uses solar power, with battery and collector capacities consistent with the area’s solar conditions.
Autenrieth added that developers should design their network to allow for future expansion, especially by installing DMZs with added port capacity, while still segregating different network areas to prevent viruses from spreading. “You also have to design for potential failures, so it’s important to arrange your multinodes to give the mesh network multiple pathways and then use utility power and UPSs and solar where you can,” he explained. “However, we advise against installing SIL-rated systems on wireless without considering failure mitigation.”
To make sure paths between multinodes are clear, Autenrieth added that installers must watch out for trees, line poles, buildings and even long expanses of water, which can cause reflections and interference.