Working with Cofely Axima, a leader in industrial refrigeration and a subsidiary of GDF Suez, milk-processor La Compagnie des Fromages has improved its energy profile with the ability to generate heating and cooling in a single cycle.
Key process components are supplied by the Emerson Group, including a Vilter single-screw compressor from Emerson Climate Technologies and a Leroy-Somer variable-speed drive from Emerson Industrial Automation.
La Compagnie des Fromages is part of the Bongrain Group, the world’s fifth-largest milk-processing company and an employer of 18,870 people.
" We conducted an energy audit with la Compagnie des Fromages’ plant in the town of Vire," said Jean-Yves Druillennec, sustainable development manager for Cofely Axima – GDF Suez.
The audit was a snapshot of the plant’s consumption levels. It suggested replacing four piston compressors, which provided only cooling, with a thermo-refrigerating pump. A thermo-refrigerating pump is a thermodynamic heat-transfer system that cools and heats at the same time. Cooling capacity is supplied to an evaporator and heating capacity to a 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 degrees C. All energy produced and used is fully recovered. A 150 m³ buffer storage unit uses the energy to produce hot water, especially for cleaning operations. With the old system, this water was heated by gas. In addition, heat produced was vented to atmosphere at a cooling tower. Now, 9000 cubic meters of water a year is saved and cooling tower use reduced.
Milk system’s heart
At the heart of the system are a 390 kW motor and a variable-speed drive for a single-screw compressor with 1000 kW of cooling capacity. The refrigerant circulated in the system is ammonia (NH3), a common heat-transfer medium.
Cooling and heating take place simultaneously about one-third of the time. To raise the water temperature from 15 degrees C to 58 degrees C (with a combined COP of 7.67), the ammonia, after having removed heat from the cold side to produce chilled water, is compressed to achieve a certain pressure and temperature. The ammonia condenses at 59 degrees C. The water is heated by its transfer to it via the condenser and other heat exchangers.
At other times, 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 1.0 to 7.0 degrees C and 200 cubic meters of hot water at 60 degrees 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 Druillennec. "The use of much more energy-efficient components is the other source."
Motor technology
The Dyneo LSRPM is a range of permanent-magnet synchronous motors with technology patented by Leroy-Somer that it says increases efficiency to levels approaching 98 percent.
"It is 7 percent more energy efficient than high-efficiency induction motors. Electricity costs are expected to rise by 25 percent in the next five years," says Druillennec. "What sets this motor apart is that it is ideal for speed control. We noticed that some induction motors were under excessive load under non-steady-state conditions. We don’t have this problem with these motors. Had we used induction motors, they would have had to be oversized."
Vilter is a brand of Emerson Climate Technologies, which employs more than 16,000 people worldwide. Compression is accomplished by a single-screw compressor and two star-shaped gate rotors. The compressor balances the single screw both radially and axially to ensure very low loads are placed on the bearings, for reduced vibration and noise levels.
The key to the single-screw compressor’s high energy efficiency is the Parallex slide system that allows the compressor to run at optimum efficiency throughout its capacity range. Capacity and volume slides — with an expanded volume ratio of 1.2 to 7.0 — move independently of each other under all operating conditions, eliminating over- or under-compression.
Final words
"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 percent more efficient," says Druillennec.
Cofely Axima managed the project. Only the electrical wiring was contracted out. La Compagnie des Fromages’ process was down for only three hours during commissioning.
Cofely Axima is installing many systems in countries such as Thailand, Kuwait and Italy. "Our clients are interested only in solutions that pay for themselves in less than two years," Druillennec concludes.
