Milk processor seeks energy savings through innovation

Compagnie des Fromages is part of the Bongrain Group, the world's fifth-largest milk-processing company and an employer of 18,870 people. Compagnie des Fromages was seeking to reduce its energy usage and CO₂ emissions by investing in a facility designed by Cofely Axima. Energy savings were achieved via a process that heats and cools within a single cycle, and also through the use of key components - a Vilter single-screw compressor from Emerson Climate Technologies and a Leroy-Somer variable-speed drive from Emerson Industrial Automation.

“We conducted an energy audit with the Compagnie des Fromages’ plant in the town of Vire,” says Jean-Yves Druillennec, Sustainable Development Manager for Cofely Axima-GDF Suez. The audit, which was based on a series of measurements, provided a snapshot of the Vire plant’s consumption levels and suggested replacing its four piston compressors, which provided only cooling, with a thermorefrigerating pump, a thermodynamic heat-transfer system that can cool and heat at the same time.

The refrigeration system makes it possible to provide cooling capacity to the evaporator and heating capacity to the condenser. When 1000 kW of chilled water is produced at Vire, 1300 kW of energy is recovered at the same time and combined with just 100 kW of electricity to heat water to 62°C. All the energy produced and used is fully recovered. A 150 m³ buffer storage unit allows energy to be used to produce hot water as needed by the process (particularly during cleaning operations). With the previous system, this water was heated by gas, which has a much higher carbon footprint. In addition, the heat produced was rejected to the atmosphere by a cooling tower instead of being recovered and re-used. The new system saves 9000 m³ of water a year and has reduced use of the cooling tower, which, with its plumes of steam, was viewed negatively by local residents.

At the heart of the system are a 390 kW motor and a variable-speed drive, that power a single-screw compressor with 1000 kW of cooling capacity. The refrigerant circulated in the system is ammonia (NH₃), a natural heat-transfer medium . Cooling and heating are simultaneously produced for one third of the time. To raise the water temperature from 15 to 58°C, with a combined coefficient of performance (COP) of 7.67, the ammonia, after having removed heat from the cold side to produce chilled water, is compressed to achieve the right pressure and temperature. As this temperature is much higher than the usual temperature for a conventional cooling system, the ammonia condenses at 59°C. The water is heated by transferring the heat from the ammonia via the condenser and other heat exchangers located at various points in the system for heat-optimisation purposes.

During the remaining time, chilled water is produced conventionally with a COP of 5.75. Ultimately, the system will recover all the heat extracted during the production of chilled water.

Chilled water at 1-7°C and 200 m³ of hot water at 60°C are produced daily at the Vire plant. To do this, the old system consumed an average of 820 kW of energy per ton of production per year. With the new system, this level is now only 560 kW.

“The process for producing heat with less grid electricity is not the only source of energy savings,” says Jean-Yves Druillennec. “The use of much more energy-efficient components is the other source.”

One of these components is the Dyneo LSRPM, a permanent-magnet synchronous motor which significantly increases efficiency to levels approaching 98%. The low losses of the magnet-rotor technology considerably reduce heating of the bearings. As a result, they need to be lubricated much less often and the life of the motor is increased.

Another component is the Vilter single-screw compressor, which uses a single screw and two star-shaped gaterotors. The compressor is designed to balance the single screw both radially and axially. This balance ensures that very low loads are placed on the bearings, thus achieving a high level of reliability with considerably reduced vibration and noise levels. The key to the single-screw compressor’s high energy efficiency is its Parallex slide system, which allows the compressor to run at optimum efficiency throughout its capacity range. The capacity and volume slides (with an expanded volume ratio of 1.2 - 7.0) move independently of each other under all operating conditions, eliminating over or under compression and saving motor horsepower. “What makes these compressors stand out is their ability to independently adjust their capacity and volume ratio. That makes a real difference under partial load conditions. Depending on the application, they can be as much as 10% more efficient,” says Jean-Yves Druillennec.