SPECIALTY CHEMICALS
Why interest in ammonia refrigerants is surging Energy-saving and environmental attributes make ammonia a candidate to replace fluorochemical coolants MARC S. REISCH, C&EN NEW YORK CITY
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mmonia, the first refrigerant to maintains Ray Will, a fluorochemicals expert of concerns over their global warming and be used on a commercial scale, with consulting firm IHS Chemical. Toxicity ozone depletion potential, Nelson points is experiencing something of a concerns, which fluorochemicals do not out. Ammonia “meets the needs of environrenaissance. Long relegated to have, “outweigh everything else,” he says. mentally conscious end users,” he says, and large food warehouses and big industrial As Will sees it, using ammonia in large is likely to be around for many years. installations, ammonia is now showing up warehouses and at industrial sites away Because safety is a concern when it in supermarket refrigeration systems and from population centers isn’t a big probcomes to ammonia, refrigeration equipment convention center air conditioners. lem. Should a leak occur, it could disperse containing the pungent fluid typically goes Buoyed by these successes, a sturdy band without harm, he says. Any other use he outdoors, where tiny leaks aren’t noticeable, of equipment makers is pushing ammonia sees as a potential hazard. Nelson says. In addition, modern ammonia as an alternative to costly fluorochemi“You wouldn’t want to use ammonia in systems never bring ammonia indoors but cal-based refrigerants. An equally sturdy a small, indoor, self-contained refrigerause it to cool down a heat-transfer fluid, such band of fluorochemical makers, led by tion or climate cooling system,” admits as carbon dioxide or water mixed with a glyHoneywell International, is arguing against Caleb Nelson, business development vice col antifreeze, which does the work inside. the use of ammonia beyond large industrial president for Azane, a maker of ammonia It is those so-called “cascade” systems applications, pointing to the chemical’s refrigeration equipment. “You don’t want that are now showing up in a few U.S. supertoxicity. markets: two in California, Some backers tout amone in Texas, and, the most monia as a “natural” refrigPrice, toxicity stand out recent, a Piggly Wiggly that erant because it occurs in in competition between opened last September in nature. But just about all ammonia and HFOs Columbus, Ga. ammonia used commercialIn addition to superly today is made syntheticalmarkets, large hotel and ly by combining hydrogen convention spaces, such Ammonia Hydrofluoroolefins and nitrogen with a catalyst as McCormick Place in Price Low High under intense heat and Chicago, have seen ammoHeat-transfer efciency Excellent Very good pressure. nia-based equipment make Global warming potential None Very low From an environmental inroads, notes Doug Reindl, Ozone depletion potential None None angle, ammonia has formidirector of the Industrial Flammability Somewhat flammable Somewhat flammable Refrigeration Consortium at dable attributes. It doesn’t Toxicity High Low deplete Earth’s ozone layer the University of Wisconsin, or contribute to global Madison. Such applications Sources: OSHA, IIAR, Honeywell warming as some fluomore typically go to fluororochemicals do. From a purely economic people to smell it,” should even the tiniest carbon-based refrigerants, he points out. point of view, ammonia is an energy-saving leak occur. The latest crop of fluorochemical refrigcoolant that is widely available and cheap. But Azane, which makes ammonia erants, the HFOs, does look good, Reindl alBut anyone who has ever had a whiff chillers used in food processing and induslows. They are less toxic than ammonia and of an ammonia-based cleaner knows why trial water cooling applications, sees opseem to pose less risk to the environment it long ago disappeared from household portunities to replace equipment operating than their CFC and HCFC predecessors, refrigeration systems. It irritates the eyes with hydrochlorofluorocarbon (HCFC)-22, he says. But as HFOs are studied and used, and mucous membranes and is dangerous Nelson says. EPA is now enforcing a phaseissues may come to light that weren’t anticto life and health at 300 ppm, according to out of the refrigerant under the Montreal ipated, he points out. the Environmental Protection Agency. The Protocol on Substances that Deplete the That’s certainly happened before. Early agency also says that it is flammable at conOzone Layer. fluorochemical refrigerants, such as CFC-12, centrations of 15–28% by volume in air. Honeywell wants to replace HCFC-22 replaced methyl chloride, sulfur dioxide, and For these reasons, one long time observer with hydrofluoroolefins (HFOs), which various hydrocarbons because leaks could of the refrigerants market finds it hard to are more environmentally friendly fluolead to fires and death. Thought to be safe believe ammonia could make inroads into rochemicals, and blends that contain them. because it is non toxic and nonflammable, fluorochemicals’ domain. “Ammonia has But users of fluorocarbon refrigerants CFC-12 was among the first refrigerants reached all the penetration it’s going to get,” have seen variants come and go because banned under the Montreal Protocol for its
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ozone depletion potential. A string of fluorochemical variants and mixtures has come and gone since as shortcomings emerged. By contrast, ammonia has been used consistently as a commercial refrigerant for more than 150 years. The latest low-charge systems hold a fraction of the ammonia such systems traditionally required, making them more attractive to some supermarket and convention center uses. The International Institute of Ammonia Refrigeration (IIAR) can only provide an educated guess as to the number of ammonia refrigeration systems in the U.S. It counts about 12,000 such systems among the millions of installed refrigeration units country wide. System failures are a rarity. But when they happen, the fallout can be spectacular. A 2010 release of 14,500 kg of ammonia from the Millard Refrigerated Services warehouse in Theodore, Ala., exposed 800 people to the fumes and sent 152 of them to the hospital. Ammonia can pose a danger, admits IIAR Vice President Eric M. Smith. “But records show that these systems are pretty safe.” Ammonia’s pungent odor is actually its saving grace, Smith says. “People can smell it at 5 ppm,” long before concentrations become hazardous. On the other hand, fluorochemical refrigerants have no smell at all. “They are asphyxiants,” Smith says, and when they are released in enclosed spaces without ventilation, anyone nearby could suffocate. “We believe the number of deaths caused by synthetic refrigerants is equal to the number caused by ammonia. For both, deaths are rare,” he says. “You really can’t get away from ammonia’s toxicity issue,” counters Ron Vogl, global technical service leader for Honeywell. Yes, he admits, fluorochemicals can cause asphyxiation by displacing oxygen in a room. On the other hand, 10 minutes of exposure to ammonia at 2,700 ppm is lethal, according to the National Institutes of Health. And although new HFO refrigerants developed to replace their problematic predecessors are somewhat flammable, blends of those new HFOs with other fluorochemicals are nonflammable. “These blends have reduced global warming potential and are still allowed under existing government regulations,” says Tom Morris, a Honeywell business director. Given the infrastructure that’s in place and the familiarity service technicians already have with fluorochemicals, Morris sees the budding enthusiasm for ammonia as something of a fad. In another 25 years, he expects, ammonia will have a limited role in commercial refrigeration where it now has its niche. ◾
