Keeping One's Cool
Lately, natural refrigerants have increasingly been used in process cooling. Ammonia makes up the largest proportion - over 40 percent - followed by carbon dioxide and hydrogen.
"For many users, energy efficiency is the most important criterion in selecting the appropriate refrigerant," explained Georges Hoeterickx, executive board member of Eurammon, a joint European initiative of companies, institutions, and individuals who advocate an increased use of natural refrigerants. "Because ammonia has proven efficient and effective, many companies choose to use this traditional natural refrigerant."
REMOTE COOLING FOR ECONOMIC REFRIGERATIONThe Bayer chemicals group, for instance, commissioned York's refrigeration specialists to build an ammonia-based refrigeration plant. The job was part of Bayer's extension of the remote cooling system at its primary plant in Leverkusen, Germany, one of the largest production plants in the world. Here, in roughly 600 buildings scattered on more than three square kilometers, Bayer manufactures pharmaceuticals, dyes, rubber, polyurethanes and organic and inorganic products.
The heat generated by all production-related processes is dissipated via a remote refrigeration plant with several refrigeration centers. Three different temperature levels are available for this process: -5°, -20° and -45°C. Decentralized cascade chillers, also hooked up to the main supply, provide temperatures of -45° and below. Bayer uses the remote refrigeration plant, which comprises several large units, to economically generate cooling energy and ensure a steady supply.
At the refrigeration plant, two rotary screw compressor units provide cooling energy. The ammonia is liquefied in water-cooled condensers and fed into the liquid line via a subcooler and high-pressure pumps as needed to supply the consumer loads. The superheated ammonia gas is returned via a network into a suction separator and then returned to the suction side of the compressor. The plant's refrigeration output exceeds 5 megawatts.
AIR-COOLED AMMONIA-BASED PLANTLundbeck Pharmaceuticals, a Danish drug manufacturer, needed to expand its production capacity in Seal Sands, England, due to increased demand. The production processes requires adhering to precisely specified temperature gradients. There is a large variation in temperatures, from -85°C to +260°C. Lundbeck turned to Star Refrigeration for solution.
The plant builders produced two factory built, skid-mounted air-cooled ammonia systems that each supply one loop with cooling energy. Factory packaging significantly reduced onsite assembly and facilitated the production startup.
The low temperature cycle at +5° cools 400 mÂ³/hr of the coolant Therminol D12. Its refrigeration output is 1.4 megawatts. The low temperature cycle chills 50 mÂ³/hr of Therminol D12 to -25°, with an output of 220 kilowatts.
Both cycles use soundproof rotary screw compressors and fully welded plate-and-shell evaporators, which assist in the design of a system with a very small refrigerant charge. The refrigeration systems have tanks for storing the secondary refrigerant, which helps to bridge downtimes and facilitates maintenance work. Star Refrigeration equipped the plant with modern controls, including ammonia detectors.
ONE-STEP PROCESS COOLING AND AIR CONDITIONINGThe German company Dresen + Bremen built an ammonia-based process cooling plant for a leading German sweets manufacturer. On its factory premises in Halle/Westfalen, the company erected a production building that required a system for cooling processes as well as air conditioning the premises.
Following a detailed economic feasibility study that weighed the pros and cons from an installation-engineering point of view, the operator chose an ammonia-based refrigeration plant.
"The plant uses a minimum of energy and is reliable thanks to its redundant structure," said Norbert Hackmann of Dresen + Bremen. "The additional investment compared to CFC chillers pays for itself in four years. What's more, the operator benefits from the positive image of ammonia as a natural refrigerant."
Besides ensuring a controlled dissipation of heat during the production of chocolate, bonbons, and gummy candies, the refrigeration system keeps the machines cool. At the heart of the centralized system are four RPM-regulated rotary screw compressors.
Two liquid cycles at temperatures between +5° and +11° supply cooling energy to the consumer loads. Cold water circulates in the process cooling cycle, while propylene glycol is used in the air conditioning. Plate heat exchangers handle the energy transfer, based on the principle of gravity feed evaporation.
The evaporating temperature is +3° in each case, while the condensation temperature is +33°. The waste heat from the rotary screw compressors is used to heat the process water via a self-contained glycol cycle. The refrigeration plant is housed in a steel machine room on the roof. Once the two-step system extension is complete, the refrigeration output will be nearly
2 megawatts in the production area, and nearly 3 megawatts for the air conditioning.
A LOOK AHEAD"We also see great potential in manufacturing cooling energy in the -30° to -100° range, especially in the chemicals and pharmaceuticals industry," said Eurammon's Hoeterickx. "Natural refrigerants, including hydrocarbons and carbon dioxide, are high-performance. In process cooling, refrigeration facilities are closely interconnected with such environmentally friendly alternatives."
For more information, visit www.eurammon.com. This article was prepared by Eurammon.
Sidebar: Defining TermsAmmonia (R-717) has been used successfully as a refrigerant in industrial refrigeration plants for over 125 years. It is a colorless gas that liquidizes under pressure and has a biting odor. In coolant technology, ammonia is synthetically produced for use in refrigeration. Ammonia has no ozone depletion potential and no direct greenhouse effect. While flammable, ammonia is only combustible to a limited degree.
In refrigeration, CO2 (R-744) has a long-standing tradition that reaches well back into the 19th century. It is a colorless gas, liquid under pressure, with a slightly sour odor and taste. CO2 has no ozone depletion potential and a negligible direct greenhouse effect when used as a refrigerant in closed cycles. It is non-combustible, chemically inactive, and heavier than air. Carbon dioxide occurs naturally in vast quantities.
Publication date: 01/09/2006