In the heart of the Canadian prairies — Canada’s primary canola-growing region — canola crushing and oil refining plants flourish. Canola is harvested from the edible oilseed grown throughout the region before being processed into food-grade canola oil or pelletized meal for use as livestock feed. Canola is truly a “Made in Canada” crop (developed in western Canada in 1974), and it is often the nation’s most valuable one. Canada’s combined canola value chain — growers, seed developers, processors and exporters —generates approximately $23.2 billion (CAD 29.9 billion) in economic activity in Canada each year.[1]
When constructing a new canola crushing and oil refining plant capable of processing 2,500 metric tons of canola seed per day, one of the largest Canadian canola producers sought a process heating system capable of mitigating the unavoidable subfreezing temperatures affecting production during winter.
FIGURE 1. Heated lines installed on a pipe bridge demonstrate the project scale at the Canadian canola processing facility. Photos credit: Banner-Day (Click on image to enlarge.)
A design/build contracting firm was responsible for delivering pipe heating recommendations for this greenfield plant. They sought a robust solution to provide freeze protection for the piping exposed to the extremely cold conditions expected at the location. Trace element-type pipe heating was considered initially, but from experience, the project team was concerned with the cost of installation and the ongoing cost of ownership associated with trace element systems. Any costs would be further compounded by the expansive nature of the project — over a mile of heated pipe — as well as the numerous elevated-pipe locations.
The mechanical design company learned about impedance pipe heating through an end-user associate. To explore the technology, the design/build contractor researched the application and the use of impedance pipe heating with a provider. Influenced by the ease of installation, reliability, minimal maintenance requirements and overall cost of ownership, the contractor and end-user elected to implement impedance pipe heating.
Pipe Heating Provides Freeze Protection
The majority of the heated pipe throughout the plant is located in the often-harsh Canadian Great Plains, where temperatures can dip to -50°F (-45°C). During these cold periods, plant operations must be sustained. Refining processes and delivery of the product to storage tanks — and eventually to rail cars and trucks —require that temperatures be maintained to ensure the products flow easily. A reliable pipe heating system also is essential.
Based on the overall facility construction plan, the design of the impedance pipe heating systems occurred while the process pipe installation was being completed. Throughout the design process, engineers maintained close communications with mechanical personnel so that any necessary design alterations to the pipe heating systems were made to accommodate construction field changes. This was important because it helped maintain the project schedule.
Despite good planning, projects of this scope typically require field alterations, which are made on-site during construction. When this happens, designers and installers must be prepared to accommodate and respond to the circumstances at hand.
This project was no different. When the customer requested that a 15' section of previously undocumented field-installed pipe be heated, on-site personnel responded quickly. An adjacent system with available capacity was identified, and the extra 15' section was integrated.
FIGURE 2. At the canola crushing and refining plant, two heated lines provide freeze protection on a load-in tank. Photos credit: Banner-Day (Click on image to enlarge.)
Figures 1 and 2 provide views of the size and complexity of the pipe heating requirements throughout the plant. After all of the pipe heating systems were installed, they were labeled and documented with detailed drawings to enable maintenance personnel to identify and track them.
In addition, where needed, valves of an appropriate size and material can be heated as part of the pipe’s impedance heating system (figure 3). Impedance pipe heating systems utilize insulated pipe joints to define a system’s boundaries.
FIGURE 3. The impedance-heated, flanged valve serves as a dielectric isolator. Photos credit: Banner-Day (Click on image to enlarge.)
Often, flanged valves can be utilized as a convenient location for an insulated pipe joint system boundary. This eliminates the need to install a dedicated set of flanges. An insulated pipe joint typically includes the application of a full-face gasket and bolt sleeve insulators of sufficient dielectric strength.
Impedance Pipe Heating Basics
Impedance pipe heating is the generation of heat in a length of pipe. Heat is generated by the resistance to the flow of electric current through the wall of the pipe caused by the application of a low voltage AC potential across the length of the pipe being heated (figure 4).
FIGURE 4. Impedance pipe heating is the generation of heat in a length of pipe. Heat is generated by the resistance to the flow of electric current through the wall of the pipe caused by application of a low voltage AC potential across the length of the pipe being heated. Photos credit: Banner-Day (Click on image to enlarge.)
Viewed schematically, an impedance pipe heating system is represented as a simple series circuit. Calculations are rooted in the application of Joule’s Law in the form of
P = I2R
and with Watt’s Law in the form of
P = VI
where P is power, I is current, V is voltage and R is resistance. The appropriate amount of current and voltage are determined to generate the required amount of heat for a given process pipe heating application.
The purpose of an impedance pipe heating system is to provide heat to a liquid material or gaseous vapor flowing through a pipeline. Many products and ingredients transferred through pipelines are required to be maintained at a minimum temperature to ensure the integrity of the product, or that the viscosity of the material is kept sufficiently low to facilitate pumping efficiency. The heat generated by the impedance system can be used to:
- Thaw and warm up the product in a pipe to the process operating temperature.
- Maintain the temperature of the product in a pipeline.
- Elevate the temperature of a product flowing through a pipeline, in some cases.
Typical examples of products successfully heated with impedance pipe heating include asphalt, petroleum products, chemicals, waxes, molten metals, glues and adhesives, chocolate, shortenings, corn syrup, palm oil, peanut butter and honey.
In summary, for the Canadian canola processor, electric impedance pipe heating provided the refinery with a necessary and dependable freeze protection solution for their key processes. In addition, the system offered ease of installation and design flexibility. Other benefits include minimal maintenance requirements and a comparatively low cost of total ownership.
