Mexican cold-storage operator Frialsa is leading its country’s adoption of NH<sub>3</sub> /CO<sub>2</sub> systems that are safer and 15%-20% more energy efficient than conventional ammonia equipment.
Two natural refrigerants, ammonia and carbon dioxide, have each proven to be highly effective working fluids, NH<sub>3</sub>favoring the industrial sector, CO<sub>2</sub> the commercial sector.
But a growing number of end users in North America in both sectors are finding that the marriage of the two natural refrigerants within a single refrigeration system can offer advantages that each refrigerant can’t necessarily deliver alone.
The first North American cold storage operator to embrace the concept of a combined NH<sub>3</sub>/CO<sub>2</sub> cascade refrigeration systems, United States Cold Storage, now has them in 12 of its 36 facilities. On a smaller scale, two food processing companies, Imuraya and Wholesome Harvest Baking, are using Mayekawa’s NewTon NH<sub>3</sub>/CO<sub>2</sub>packaged system for freezing applications.
And even in food retail, four U.S. supermarkets have installed an ammonia/CO<sub>2 </sub>cascade system, including a Piggly Wiggly store in Columbus, Georgia.
South of the border, the natural-refrigerant tandem is also bearing fruit, as Frialsa Frigorificos, Mexico’s largest cold-storage operator, has made NH<sub>3</sub>/CO<sub>2</sub> its standard refrigeration system. Starting in 2010, Frialsa now uses this technology at five of its 24 facilities.
Four of the five plants – in Monterrey, Tepeji del Rio, Toluca, and Veracruz – were constructed with an NH<sub>3</sub>/CO<sub>2</sub>cascade system from M&M Refrigeration, while at the fifth – in Culiacán Sinaloa – an expansion of the facility has been equipped with a packaged NH<sub>3</sub>/CO<sub>2 </sub>unit from Tewis (installed by Bohn). Frialsa plans to install NH<sub>3</sub>/CO<sub>2</sub>cascade system this year at two new plants encompassing 26 million cu. ft.
In Tepeji, the main, 9.8-million-cu.-ft. building and its NH<sub>3</sub>/CO<sub>2</sub> system were constructed in 2014, and Frialsa is working on a 5-million-cu.-ft. expansion of the facility expected to open this summer. The expansion will also be served by the main building’s NH<sub>3</sub>/CO<sub>2</sub> system.
Overseeing Frialsa’s transition to NH<sub>3</sub>/CO<sub>2 </sub>technology is Ricardo García, director of engineering and projects, who joined Mexico City-based Frialsa in 1994. He is responsible for all of Frialsa’s environmental projects, including management of energy generated at wind farms and delivering 50% of electricity needs at 12 Frialsa warehouses.
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<strong>Less ammonia, less risk</strong>
In NH<sub>3</sub>/CO<sub>2</sub> cascade systems, ammonia, a potentially toxic chemical, is confined to the engine room, vastly reducing the charge compared to what is used in conventional ammonia systems, and greatly improving the safety of plant employees. Ammonia is employed simply to condense CO<sub>2</sub> into a liquid, which is the only refrigerant channeled to the cooling and freezing areas.
For example, at the Tepeji plant, the engine room, which is located next to – but outside of – the main storage building, employs about 1,100 lbs. of ammonia (in concert with about 30,000 lbs. of CO<sub>2</sub>), compared with 10,000-15,000 lbs. of ammonia at conventional facilities. (Frialsa’s other NH<sub>3</sub>/CO<sub>2 </sub>cascade systems use a similar amount of ammonia and CO<sub>2</sub>.)
This year, Frialsa installed its first ultra-low-charge ammonia/CO<sub>2</sub> packaged unit to support the expansion of its Culiacán Sinaloa plant. Frialsa is contemplating using the packaged unit in future expansions of its four NH<sub>3</sub>/CO<sub>2</sub>warehouses, García said. The unit contains only about 200 lbs. of ammonia and roughly 10,000 lbs. of CO<sub>2</sub>; like the M&M system, it confines ammonia to the high side and uses only CO<sub>2</sub> in the cooling/freezing areas. “It could be on the roof, but we are putting it on the ground outside the building,” said García.
In addition to cost and energy considerations, it is very important for Frialsa to remove ammonia from cooling and freezing rooms. “When you think about ammonia leaks, we decided to put it just in the engine room – there is less ammonia, and less risk,” said García. “We’re fine with ammonia, but if you can reduce the amount, it is a great relief.”
Using CO<sub>2</sub> in the freezing and cooling areas rather than ammonia also helps safeguard stored food products in the event of a refrigerant leak. “A lot of our customers are happy about that,” said García. “Our insurance company is, too.” Some of Frialsa’s customers specifically request storing their products at facilities that use NH<sub>3</sub>/CO<sub>2</sub>refrigeration.
Government regulations are another factor favoring adoption of NH<sub>3</sub>/CO<sub>2</sub>. In Mexico, anything over 22 lbs. of ammonia can qualify an industrial facility as “high risk” by the Ministry of Labor and Social Welfare (STPS), said Garcia.
But low-charge systems require less documentation and less demanding emergency plans than a conventional ammonia plant. “If we have a leak, we have ammonia just in the engine room; we don’t have to move all the people outside the building, as we would do if there was an ammonia leak in the building.”
STPS’s safety requirements and enforcement are very similar to those set in the U.S. by the Environmental Protection Agency and the Occupational Safety and Health Administration, noted Garcia. And, as in the U.S., governmental inspections at facilities that use ammonia have been stepped up in Mexico, he said.
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