MANUFACTURING

Air Products and Chemicals, Inc.

Closed-Cycle Air Refrigeration

View PDF Document Text Only Version

In 1995, as a result of the public’s concern about damage to the ozone layer caused by liquid refrigerants (which contained chlorofluorocarbons and hydro-chlorofluorocarbons), researchers were attempting to find safer refrigeration technologies. Air Products and Chemicals, Inc. and its joint venture partner, Toromont Process Systems Inc., applied for cost-shared funding from the Advanced Technology Program (ATP) to develop a high-risk, ultra-cold refrigeration technology. Called closed-cycle air refrigeration (CCAR), their proposed technology was based on using benign compressed air at high pressure as the refrigerant. Technical success would require advances in several refrigeration system parts, as well as the ability to combine them to maintain high pressure levels. If successful, ultra-cold systems would enable safer and more environmentally friendly food processing, which would result in improved food taste, quality, and safety. Spillover applications might include the ability to condense and capture harmful volatile organic compound vapor emissions in the chemicals, metals, and auto industries and other applications in the petrochemical and pharmaceutical industries.

The joint venture was unable to obtain commercial funding due to high technical risk. Therefore, ATP awarded cost-shared funds for a project that began in 1995. After the project met all its technical milestones, in 1998 Air Products and Toromont successfully evaluated a pilot refrigeration unit for several months at a Kodak manufacturing plant. The pilot system met or exceeded all specifications for refrigeration capability, reliability, and efficiency. The technology led to several industry publications and presentations.

However, after the project ended in 1999, the food industry was unwilling to adopt the new technology due to cost. Toromont ended its involvement in the project, because CCAR did not fit competitively into its product stream. Air Products applied the ATP-funded compression technology to manufacture liquid oxygen and liquid nitrogen. As of 2005, the company was marketing a promising new application: a marine-based liquid natural gas (LNG) recovery system that uses a modified closed-cycle refrigeration system on tanker ships to recapture LNG that would otherwise be lost to evaporation.

COMPOSITE PERFORMANCE SCORE
               (based on a four star rating)
* *

Research and data for Status Report 95-01-0150 were collected during November – December 2005.

Liquid Refrigerants Were Problematic Basic refrigeration technology works by compressing a fluid, typically a refrigerant that contains chlorofluorocarbons (CFCs) and hydro-chlorofluorocarbons (HCFCs) and then allowing it to expand. Compressing the fluid in one chamber heats the fluid and its surroundings. Expanding the fluid in a

different chamber cools it down along with its surroundings. As a result of this process, heat from one area is pumped to another area, similar to the process used in an ordinary refrigerator. Problems with this basic cooling technology include the impact the refrigerants have on the environment through leakage and when disposed of, as well as the technology’s inability to achieve ultra-cold temperatures.

Conventional mechanical refrigeration systems can effectively cool to -70°F, but not below. Ultra-cold temperatures can be obtained with liquid nitrogen and carbon dioxide cryogenic systems, but these systems cost much more than mechanical refrigeration. (Cryogenic systems are those that operate at very low temperatures.) In the 1990s, public concern about the environmental problems caused by refrigerant fluids was growing because CFCs and HCFCs were known to deplete the ozone layer. Researchers were attempting to develop alternative refrigerants, including propane, argon, krypton, and xenon. Each of these alternatives was problematic, however. For example, propane is explosive, and inert gases, while stable, are costly. Another alternative, which is benign, safe, and readily available, is air. When compressed under high pressure, air becomes a compressed fluid. Existing air-based systems, such as those used in aircraft, relied on an open cycle in which compressed, dehumidified cold air was blown into a cooling chamber and then exhausted into the open air. Moisture had to be removed, because ice particles on turbine blades could damage the rotating blades. More air had to be compressed and dehumidified to replace the air lost in the process, which resulted in high energy costs. In the 1990s, public concern about the environmental problems caused by refrigerant fluids was growing because CFCs and HCFCs were known to deplete the ozone layer. The chief competition for air-cooled systems were ammonia-based systems. Ammonia enjoys many advantages. First, it is readily available, inexpensive, and capable of absorbing large amounts of heat when it evaporates. Second, it is environmentally compatible; it neither depletes ozone nor contributes to global warming and requires less energy than other refrigerants when used in large industrial systems. Third, ammonia-based refrigeration has a proven safety record, in part because of its easily detectable odor.^1 However, in the event of a leak, it can pose significant danger to occupational health and safety in a confined space, despite its low lethality.

Air Products Proposes Closed-Cycle Air Refrigeration Researchers at Air Products and Chemicals, Inc. believed that if a closed-cycle air refrigeration (CCAR) system could be developed, it could compete economically with other liquid refrigerants and provide an environmentally safer alternative. This system would be sealed and would reuse the refrigerant, similar to the system in a traditional refrigerator. CCAR would require high-risk improvements in the expander, compressor, seals, and heat exchanger components in order to achieve the required high pressure levels (82 atmospheres of pressure) and ultra-cold temperatures (-70°F to -150°F). Combining all these components in a new refrigeration system would be challenging, but would avoid the problems posed by open-cycle air (ice formation and energy loss) and ammonia systems (occupational safety risk). Air Products formed a joint venture with Lewis Energy Systems (later renamed Toromont Process Systems, Inc.) and applied for cost-shared funding from ATP in 1995. Air Products is a large industrial gas producer that supplies oxygen, nitrogen, argon, hydrogen, and helium and related equipment for their production. Toromont assembles complex pieces of refrigeration equipment for use in chemical, petrochemical processes. Because of the high technical risk of CCAR, the joint venture partners would not have undertaken the project without ATP support. The two companies viewed the U.S. food processing industry as their primary potential market. If successful, CCAR ultra-cold temperatures would result in substantial savings for food processors through faster chilling at lower cost compared to cryogenic refrigeration. The technology would achieve the following: · Reduce environmental emissions and impacts by using benign air as the refrigerant · Reduce weight loss in food due to minimized evaporation · Improve food taste and quality due to reduced dehydration

¹“Ammonia: The Natural Refrigerant of Choice” (an International Institute of Ammonia Refrigeration (IIAR) green paper)
http://www.iiar.org/f-green.cfm.

· Enhance food safety by reducing the amount of time processed foods would need to be cooled, during which bacteria grows · Reduce diesel emissions that resulted while transporting the liquid nitrogen and carbon dioxide used in conventional refrigeration (estimated at 12,000 to 14,000 roundtrip truck deliveries per year) ATP awarded cost-shared funding to the Air Products and Toromont joint venture in 1995 for a three-year project. Faster Freezing Raises Food Quality and Safety The process of freezing food involves several steps. Water, which freezes at 32°F, comprises 55 to 95 percent of the food mass. However, the water content is not pure; it is a solution that contains fats and other organic materials that lower the freezing temperature by acting as an antifreeze. After some of the water has frozen, ice crystals form. Larger crystals break down food texture and lower the product’s quality. The remaining solution becomes more concentrated, and the freezing point drops. Faster freezing in colder temperatures plunges the product through the freezing temperature range quickly, which reduces the formation of ice crystals, thus improving quality and consistency. The closed-cycle air refrigeration (CCAR) system would be sealed and would reuse the refrigerant, similar to the system in a traditional refrigerator. Vapor evaporates from hot cooked foods, leading to dehydration. Rapid freezing reduces this loss of moisture, which results in juicier food. When cooked food is processed, it reaches a “danger zone” during the cooling process (141°F down to 40°F), when harmful bacteria can form. Ultra-cold temperatures cool food more rapidly, which improves safety. Joint Venture Team Meets Technical Goals The joint venture team made significant technical progress in the aluminum core exchanger technology, the ability to operate at high pressure, and the single-stage compander. (A compander is a [com]pressor and

ex[pander] mounted on one shaft.) Air Products met all its goals and developed a functioning CCAR system (see Figure 1). Figure 1. Diagram of the CCAR system’s key components and connections. The system uses dry, high-pressure air as the working fluid. As a closed system, it does not need continuously remove moisture from fresh air. From the Economic Case Study of December 2001, by Thomas Pelsoci, at http://www.atp.nist.gov/eao/gcr_819.pdf CCAR’s technical accomplishments included the following: · Achieved high pressure (1,200 pounds per square inch gauge, or psig), temperatures below –150°F, and compander shaft speeds of 30,000 revolutions per minute (rpm) (increased from 7,200 rpm at project start). High pressure leads to higher potential energy and a greater cooling effect. · Designed a single-stage compander (at a cost that was lower than cryogenic systems, which use multi-stage compressors and expanders). The Air Products Cryomachinery Laboratory used three-dimensional rapid prototyping technology from subcontractor 3D-Cam, Inc. This approach reduced the time and cost of building prototypes for testing. · Used a low compression ratio (compressor output to expander output) of 1.6 to 1 (cryogenic machines operate at 8-to-1 ratios). Low compression ratios increase operational efficiency. · Developed low-leakage dry gas seals to prevent air from escaping at the compressor shaft. Subcontractor Flowserve designed the compressor shaft seal. Prior to this project, no seals existed that could handle these process conditions. Better seals would function more efficiently and would last longer.

· Developed a high-efficiency, high-pressure aluminum plate core heat exchanger (the temperature difference between return air from the load exchanger and high-pressure air exiting the cooling system varied no more than 2°F to 3°F). Greater efficiency would provide a greater cooling effect with the same energy consumption. Subcontractor Chart Heat Exchangers designed the heat exchanger. In 1998, the team bench tested the CCAR system at Air Products’ Cryomachinery Laboratory and at a Kodak facility in Rochester, NY during a nine-month pilot program. Kodak, a potential end user, was planning to use industrial refrigeration to capture solvents such as methylene chloride used in photography, as well as liquid natural gas (LNG) applications. Kodak was also seeking environmentally friendly and economical refrigeration alternatives that they could use in the future. The pilot system ran for 6,000 hours, and Kodak engineers stated that CCAR met or exceeded all of the following acceptance criteria: · Reduced Size. The pilot system occupied one-quarter of the footprint of Kodak’s existing units. · Unit Output. The output specification was 50 tons of refrigeration. (A ton of refrigeration measures the refrigeration capacity needed to freeze one ton of water.) The pilot system operated at 60 tons of refrigeration, exceeding specifications by 20 percent. · System Reliability. Reliability was predicted at 95 percent. The pilot system operated at 98 percent reliability, exceeding specifications by 3 percent. · Refrigeration Temperatures. The temperature specification was –100°F. Temperatures consistently maintained ± 2°F of the specification. · Coefficient of Performance (COP). COP measures the relative efficiencies of different refrigeration systems. The pilot system maintained a .75 COP level at –70°F, comparable to conventional mechanical systems. At –100°F, the CCAR system operated at the specified 0.66 COP (conventional mechanical units cannot reach this temperature). Reducing the load by 40 percent reduced CCAR

efficiency by only 3 percent, compared with a 37-percent efficiency reduction in a conventional mechanical system. Higher pressure leads to greater efficiency. · Noise Level. CCAR met Occupational Safety and Health Administration regulations by operating at less than 85 decibels. The ATP-funded technology succeeded technically but could not compete economically. Toromont left the joint venture in 1998, toward the end of the project, because CCAR could not cost-effectively compete with other liquid refrigerants. Competitors had developed a new lower cost carbon-dioxide-based system, which reached –55°F. Food processors compromised on temperature and decided that carbon dioxide met their needs at a lower cost. Natural Refrigerants Are the Future of Refrigeration Although CCAR has not been commercialized in the food processing industry, the concept of using air as a refrigerant is valid, nonetheless. The technology won two technical awards: finalist for the Kirkpatrick Award by Chemical Engineering Magazine in November 1999, which recognized CCAR’s “step-out” performance levels; and an energy conservation award from the Industrial Energy and Technology Conference in 2001. The pilot system ran for 6,000 hours, and Kodak engineers stated that CCAR met or exceeded all acceptance criteria. Furthermore, using air is consistent with the intent of the Montreal Protocol and other initiatives that address greenhouse gases and other environmental issues. The 1987 Montreal Protocol on Substances that Deplete the Ozone Layer was signed by more than 150 countries to reduce the use of CFCs. The goal was to protect the ozone layer by decreasing and eventually eliminating the use of ozone-depleting substances like CFCs. "The future is going to be in natural refrigerants--carbon dioxide, ammonia, even air and water," stated engineer Ronald P. Vallort, chairman of the International Institute of Ammonia Refrigeration.^2 While relatively low domestic energy costs

²Higgins, Kevin T. "Refrigeration, Naturally." Food Engineering, Vol. 75, No. 11, November 2003.

in recent years have discouraged application of high-efficiency innovations in refrigeration, U.S. food companies are applying high-efficiency principles in new plants being built in Asia, South America, and elsewhere, where costs are higher, Vallort says. Alternative Applications Found for CCAR Technology Air Products has found ways to benefit from the key technical advances achieved during the ATP-funded CCAR project in the following applications: · Improved Dry Gas Seals. Because seals performed successfully under the severe CCAR operating conditions (1,200 psig, –150°F, and 30,000 rpm shaft speeds), Air Products expects increased industry acceptance of these seals. · High-Pressure Core Heat Exchanger. The high-efficiency aluminum plate core heat exchanger has potential applications in the petrochemical, air separation, and natural gas industries. · Improved Casting Technology. Rapid prototyping technology developed for CCAR with advanced materials can reduce the time and cost of building prototypes. After the ATP-funded project ended, Air Products continued developing the technology for large air-separation units to manufacture liquid oxygen and nitrogen. The company, which sells approximately $2 billion in liquid oxygen and nitrogen annually, is one of the top U.S. liquid nitrogen suppliers. The liquefiers rely on the ATP-funded compander, which saves approximately 3 percent in energy costs compared to other units on the market. The CCAR technology won two technical awards: finalist for the Kirkpatrick Award by Chemical Engineering and an energy conservation award from the Industrial Energy and Technology Conference. As of 2005, Air Products was marketing a modified air-cycle refrigeration application that is based on CCAR: a

liquid natural gas (LNG) recovery system for marine transportation. As shown in Figure 2, worldwide consumption of LNG has increased from approximately 40 quadrillion British thermal units (Btus) in 1970 to nearly 100 quadrillion in 2004. (Btus measure the amount of heat required to raise the temperature of one pound of water by 1°F.) Figure 2. As of 2004, global LNG consumption was approximately 100 quadrillion Btus, up from 40 quadrillion in 1970. Growth is expected to continue. Source: Air Products presentation to the American Chemical Society, September 2005. LNG is condensed 600 times to a liquid form, cooled to –250°F, and transported on specially constructed tanker ships. During transport, some of the gas evaporates, normally about 0.15 percent of cargo volume per day. As global energy demand has grown, distributors want to recapture the lost LNG. In addition, the desire to reduce carbon gases in the atmosphere makes recapturing LNG attractive. As of 2005, Air Products was marketing a modified air-cycle refrigeration application (based on the ATP-funded CCAR) to reliquefy the evaporating LNG in order to recover the gas. The Air Products LNG recovery system has a 75-percent smaller footprint than comparable systems, which is a significant advantage on a ship where space is at a premium. The market for this technology is rapidly increasing; the global LNG tanker fleet has grown from 100 vessels in 1997 to 175 in 2005, with 400 anticipated by 2015. As new tankers are built, this technology is being considered. Conclusion From 1995 to 1999, Air Products and Chemicals, Inc. and Toromont used ATP funding support to develop ultra-cold closed-cycle air refrigeration (CCAR), using high-pressure, environmentally benign air as a

refrigerant. They accomplished all of their technical goals and evaluated a pilot system at a Kodak facility for nine months in 1998. The partners shared their knowledge through publications and presentations and received two technical awards. The pilot plant operated at –100°F, with 98-percent reliability, and at 60 tons of refrigeration capacity. The market for ultra-cold food refrigeration changed when the project ended in 1999, and competitors had designed a refrigeration system based on carbon dioxide as the refrigerant. Although this carbon-dioxide system could only reach –55°F, the system’s cost was much lower than CCAR. Users made a quality sacrifice to achieve lower cost. Air Products went on to modify and use the CCAR knowledge for two alternative applications: manufacturing liquid nitrogen and liquid oxygen (an annual $2 billion business for Air Products) and reliquefying evaporated gas from liquid natural gas (LNG) for marine shipping. In 2005, the company was beginning to market its LNG reliquefaction system for tanker ships. Reliquifying LNG will save energy by reducing evaporation loss to the atmosphere and thus reducing the cost to consumers.

PROJECT HIGHLIGHTS
Air Products and Chemicals, Inc.

Project Title: Closed-Cycle Air Refrigeration (Development of Closed Cycle Air Refrigeration Technology for Refrigeration Markets) Project: To design, fabricate, and pilot test a new form of industrial refrigeration equipment using dry air as the working fluid in a closed cycle at high pressures. Duration: 8/1/1995 - 1/31/1999 ATP Number: 95-01-0150 Funding (in thousands): ATP Final Cost              $2,056    32.3% Participant Final Cost        4,301    67.7% Total                            $6,357 Accomplishments: The joint venture of Air Products and Chemicals, Inc. and Toromont Process Systems, Inc. successfully developed and demonstrated closed-cycle air refrigeration (CCAR) technology that delivered high-pressure (1,200 pounds per square inch gauge, or psig), ultra-cold refrigeration in the 70°F to –150°F range. The team achieved the following key technical advances with CCAR: · Low-leakage dry gas seals to prevent air from escaping at the compressor shaft. · High-efficiency, high-pressure aluminum plate core heat exchanger (the temperature difference between return air from the load exchanger and high-pressure air exiting the cooling system varied no more than 2°F to 3°F). Greater efficiency provides a greater cooling effect with the same amount of energy. · Innovative three-dimensional rapid prototyping technologies to produce a single-stage compressor and expander (at a cost that was lower than cryogenic systems, which use multi-stage compressors and expanders). This approach reduced the time and cost of building prototypes and meant that fewer prototypes were needed. Compander shaft speeds reached 30,000 revolutions per minute (rpm), up from 7,200 rpm at project start. (A compander is a [com]pressor and ex[pander] mounted on one shaft.) · Low compression ratio (compressor output to expander output) of 1.6 to 1 (cryogenic machines operate at 8-to-1 ratios).

A pilot CCAR system was subjected to a nine-month test at a Kodak facility in 1998. The pilot system cost-effectively delivered ultra-cold refrigeration for food processing, volatile organic compound recovery, and liquid natural gas (LNG) applications. The pilot system met or exceeded all of the following design specifications: · The pilot plant operated at 60 tons of refrigeration, exceeding specifications by 20 percent. (A ton of refrigeration measures the refrigeration capacity needed to freeze one ton of water.) · The pilot plant operated at 98-percent reliability, exceeding specifications by 3 percent. · Temperatures were maintained within ± 2°F of the specified –100°F. · The pilot system maintained a .75 Coefficient of Performance (COP) level at –70°F, comparable to conventional mechanical units. COP measures the relative efficiencies of different refrigeration systems. At –100°F, the unit operated at the specified 0.66 COP (conventional mechanical units cannot reach this temperature). Reducing the load by 40 percent reduced CCAR efficiency by only 3 percent, compared with a 37-percent efficiency reduction in a conventional mechanical system. · CCAR met Occupational Safety and Health Administration noise-level regulations by operating at less than 85 decibels. The ATP-funded CCAR prototype won the following two awards for Air Products and Chemicals: · Finalist for the Kirkpatrick Award by Chemical Engineering Magazine in November 1999. The magazine recognized CCAR’s “step-out” performance levels. · Received an energy conservation award from the Industrial Energy and Technology Conference in 2001. Commercialization Status: CCAR technology has not been commercially accepted because of a change in market demand. In addition, the cost of equipment construction was higher than anticipated. Nevertheless, Air Products has developed two commercial applications based on the ATP-funded technology: a modified closed-cycle refrigeration system for use in manufacturing liquefied nitrogen

PROJECT HIGHLIGHTS
Air Products and Chemicals, Inc.

and oxygen and an LNG reliquefaction system. The company sells approximately $2 billion in liquid oxygen and nitrogen annually. The ATP-funded compander used in the liquefiers saves approximately 3 percent in energy costs compared with the previous system. As of 2005, Air Products was marketing an LNG reliquefaction system for marine transport, which uses a modified closed-cycle refrigeration system that is based on CCAR. Outlook: The outlook for closed-cycle refrigeration systems is good. Air Products expects to continue using modified closed-cycle refrigeration systems in producing liquid oxygen and nitrogen, as well as LNG reliquefaction on board marine vessels. Composite Performance Score: * * Company: Air Products and Chemicals, Inc. 7201 Hamilton Boulevard Allentown, PA 18195-1501 Contact: E. F. Kiczek Phone: (610) 481-4705 Company: Toromont Process Systems, Inc. 10815 Telge Road Houston, TX 77095 Contact: Mark Rossiter Phone: (281) 345-5080 Subcontractors: · 3D-Cam, Inc. Chatsworth, CA · Flowserve Irving, TX · Chart Heat Exchangers La Crosse, WI

Publications: CCAR gained attention through the following publications: · “Proprietary Internal Study on Dehydration Modeling and Test Results.” Air Products and Chemicals, 1999. · “CCAR Breakthrough Technology for Food Freezing.” Air Products and Chemicals, 2000. · “The Future of Refrigeration: Some Cool Ideas.” The Economist, March 20, 2003. · Higgins, Kevin T. "Refrigeration, Naturally." Food Engineering, Vol. 75, No. 11, November 2003. http://www.foodengineeringmag.com/CDA/ ArticleInformation/features/BNP__Features__ Item/0,6330,111806,00.html Presentations: · Kiczek, E. F. "Closed Cycle Air Refrigeration." American Institute of Chemical Engineers Conference, Atlanta, GA, March 2000. · Sherman, Scott. “World Energy is Global Growth Business.” American Chemical Society, Washington, DC, September 2005.

---

Research and data for Status Report 95-01-0150 were collected during November – December 2005.
Also see the Economic Case Study of December 2001, by Thomas Pelsoci, at http://www.atp.nist.gov/eao/gcr_819.pdf