Petroleum and petrochemical processes are inherently complex, particularly if you're in northern Canada and dealing with extreme temperatures—36 to -50 °C—that can freeze product in its tracks. Oil sands companies in northern Canada—with eyes on 300 billion bbl of potentially recoverable crude—rely on firms like Bantrel Co. to ensure that the process facility designs, including the heat-conservation systems, are up to the task.

Bantrel has more than 25 years of experience providing multidisciplinary engineering, project management, procurement, and construction services to the petroleum, petrochemical, gas, and power industries. The company is heavily involved in the Canadian oil sands industry, where it is expected that more than $100 billion (Canadian) will be spent in new and expanded facilities in the next few decades.

Heat conservation systems have two major components: thermal insulation and heat tracing systems to maintain minimum hold temperatures in non-flowing lines for either freeze protection or viscosity maintenance. Traditionally, steam was the preferred heat-tracing medium; however, in the last decade, there has been a migration to electrical heat tracing (EHT) to help reduce life cycle costs.

EHT applications typically use individual or multipoint solid-state controllers located throughout the plant areas to measure and control the electric heater cables attached to the process piping and vessels. While electric tracing is much more cost-effective than steam, it poses additional risks.

For example, EHT systems often use multiple remote cabinet-grouped controllers with separate power supply sources. This makes maintaining the system a bit more hazardous, because power isolation usually occurs in another location. Also, fault isolation between controllers is not possible with multipoint designs. This situation has been further complicated with the introduction of centralized EHT buildings housing hundreds of EHT controllers switching megawatts of power.

Bantrel wanted to design new EHT control and monitoring systems that were safer, more maintainable, reliable, and more cost-effective than existing systems.

The company needed to develop a standard system for oil sands industry customers. EHT system failures have cost millions of dollars in the last several years. Cost of ownership is important; EHT systems represent one of the single largest electrical maintenance expenses in oil sands facilities. Bantrel worked with Rockwell Automation, to modify existing controls to meet EHT application design requirements.

At the new system's core is advanced control technology, including an Allen-Bradley 2100 IntelliCenter motor control-center (MCC) and an Allen-Bradley Redundant ControlLogix PLC System. Resistance temperature detectors (RTDs)—used to monitor pipe and vessel temperatures—are wired to 1794 Flex I/O modules. In turn, the modules are connected to the ControlLogix PLC system via ControlNet. DeviceNet is used within the MCCs for load control and system monitoring.

MCCs employ E3 Plus electronic overload relays. The E3 Plus overloads were modified to improve single-phase monitoring capabilities, and increase ground-fault sensitivity to the required 20-100 mA for EHT applications.

Maintaining a compact size was a key requirement. Because MCCs are typically located in buildings in the center of a facility, they can consume valuable floor space; smaller is better. Allen-Bradley 0.5SF plug-in wrapper unit designs are 6-in., half the height of a competitive unit. This small profile was achieved by using the E3 Plus relay and the Bulletin-100C IEC-style three-phase contactors rated for 30 A.

In an oil sands facility's single-process area, there can be thousands of RTDs monitoring temperature and movement of petroleum products within the piping and vessels. With the new system, it wasn't possible to reduce the number of RTDs, because it would simultaneously reduce the control and the number of heating options. Instead, the team worked to simplify RTD cabling.

To collect RTD temperature data required by ControlLogix, Rockwell Automation designed compact cabinets enclosing Flex I/O RTD input modules to integrate up to 120 RTDs into one ControlNet node. One ControlNet cable connects multiple RTD Input cabinets to the central ControlLogix System. To keep the temperature within a programmed range, the ControlLogix system then controls the MCC contactor units via DeviceNet.

Three-phase contactors were configured to switch three single-phase EHT loads based on flow patterns and temperature requirements. This allowed one-by-four conductor power cable per contactor to be run to a local distribution junction box rather than three-by-two cables required by conventional single point EHT control.

Safety, reliability

Cost-effectiveness—Savings were quickly realized by Bantrel and its customers through the use of standard control components and reduced wiring and installation costs of the new EHT system. Power and RTD cable is reduced by more than one-third, reducing long-term maintenance costs.

Increased safety—Low-voltage MCCs are inherently safer than conventional EHT control systems as the main disconnecting means is integral with the contactor wrapper unit. Also, conventional EHT control systems do not offer the safety features associated with draw-out MCC style metal-clad control gear.

Increased reliability—Traditional systems are plagued by failures, but the combination of proven ControlLogix and Flex I/O, used in conjunction with the MCCs for this EHT solution, greatly increases overall system reliability.

Improved productivity—Transmission of operational data and diagnostic information over DeviceNet keeps operation and maintenance personnel up-to-date on system performance and allows them to quickly pinpoint trouble spots.