This article was printed in CONTROL's May 2009 edition.
By Dan Hebert, Senior Technical Editor
In many hybrid industries such as food processing, PLCs have ruled the roost for years. However, there are some hybrid applications where PLCs don’t provide enough processing power, data handling and communications. In those instances, PC-based control can be the best alternative.
For example, McCain Foods in New Brunswick, Canada, is the world’s largest producer of french fries and other oven-ready frozen food products. Its 20,000 employees and 55 production facilities in 12 countries span six continents. McCain processes 1 million pounds of potatoes each hour and sells one-third of the world’s frozen french fry products.
McCain prides itself on being ahead of the curve in product creation and delivery. It was the first company to create a french fry that would stay as fresh as when it was made—even after being frozen and shipped worldwide.
This forward-looking philosophy has not only helped McCain create frozen foods, but also has enabled the company to embrace technological innovations in its manufacturing facilities. One such innovation was first implemented at its Easton, Maine, plant and is now serving as the model for all the company’s frozen food processing plants.
Reducing Refrigeration Costs
Precise temperature control is critical in food processing. In fact, refrigeration costs in a typical food processing plant can be up to 70% of total energy consumption. McCain had designed and implemented an automated control system in its Easton plant,but the company was looking for even better ways to manage energy distribution, cut usage and reduce greenhouse gas emissions.
So, McCain turned to systems integrator TechCold International (TCI), also based in New Brunswick, to assist in updating its refrigeration control systems. As early as 2002, TCI and McCain agreed the Easton plant would be a good facility at which to develop and customize a new kind of controller. This special controller would connect to the existing infrastructure and target specific areas for energy management. The new controller also would work alongside McCain’s existing PLCs, but provide the algorithms to make the cooling process more efficient.
This is one of the many industrial refrigeration compressors used in McCain Food's processing plant. TCI’s PC-based controls help optimize operation and reduce energy consumption.
Using a second controller along with a PLC would also provide a level of redundancy. If the controller was not accessible for any reason, the control system could simply revert to PLC-based control with no disruption to plant operations.
The result of those discussions was a two-year partnership that provided the impetus for the design and development of a prototype solution that became TCI’s enhanced refrigeration control system. McCain has since standardized many of its plants on the TCI prototype, which was greatly modified in the ensuing years. The TCI system is now deployed in 20 McCain facilities in Canada, the United States, England and some European Union countries. The company is also looking to expand the TCI system into its plants in South Africa, Australia and New Zealand.
PC-Based Control is the Answer
The partnership began with a kick-off meeting between TCI and personnel from the Easton plant. “We were met with some skepticism,” says Ernie Adsett, TCI’s president. “McCain already had a sophisticated control system based on an Allen-Bradley ControlLogix PLC, which they considered to be top of the food chain. They weren’t sure we could significantly cut their energy consumption and deliver an acceptable return on investment by adding another layer of control.”
TCI’s idea was to take the McCain facility from simply using a PLC-based system to one with a more intelligent, finer level of PC-based control. McCain was interested in using the new control system not only to reduce energy use, but also to operate its equipment more efficiently.
TCI had two goals for the PC-based enhanced refrigeration control system. The first was to reduce energy consumption and demand by usingadvanced control algorithms. The second was to provide a standardized system common to all McCain plants.
To accomplish the first goal, TCI found that PC-based control was the best option. TCI’s advanced refrigeration control scheme is written in a language that’s easily executed by a PC. Executing the advanced control algorithm in a PLC may have been possible, but it would have been unwieldy and impractical.
“We’re using a high-speed PC-based industrial processor based on a Microsoft Windows environment. The PC allows us to create a sophisticated model of the complete refrigeration system in real time to determine capacity and efficiencies,” notes Adsett.
“We can optimize five to 10 compressors working on a certain line, run all different scenarios and come up with a set of compressors that is the most efficient. We can then switch to these compressors by using all the equations to generate efficiencies, something a PLC can’t easily do,” adds Adsett.
The second goal, standardization across many different types of food processing facilities, also required a PC. Standardization reduces servicing and implementation costs, and it also provides easier ongoing remote monitoring and upgrades.