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as the high stage for e.g. R-744 or R-170 cascade systems. The systems can also be used for cooling plastic machines or other machinery. 5.3.6 Ice slurry Ice slurry has been used for special applications and installations for many years. Especially in the deep mines in South Africa Ice slurry technology has been used as an alternative to having refrigeration systems in the mine itself. Ice slurry is being used for quick cooling of especially big fish like big types of tuna for which a quick cooling down is very critical. Circulating the ice slurry around the fish cools them down much faster than ice and consequently gives a much longer shelf-life. 5.3.7 Absorption Absorption systems using aqua-ammonia can be used for low temperature applications, reaching temperatures as low as -60°C (Colibri, 2017). This is because the ammonia is used as the refrigerant, with water as the absorbent. Absorption systems can be provided from 12 kW to 12 MW or more for process systems. Water-lithium bromide (LiBr) systems can only be used above freezing because the water is the refrigerant, and the LiBr is the absorbent. Absorption systems are only effective if there is an abundant source of heat at high temperature to drive the system. It is not normally economic to burn fossil fuel for the sole purpose of driving the regenerator of an absorption system, particularly in low temperature systems, because the heat rejection plant is significantly larger than for an equivalent duty, electrically driven vapour compression system. Absorption systems are primarily used for process cooling in food, beverage, chemical and pharmaceutical plants where waste heat to drive the system is readily available. There is an increase in the food industry, where local on-site power generation is used, and provides a source of waste heat. This has been particularly noted in developing countries such as India and China, where increased food production is being achieved but the electrical infrastructure is under construction. In these cases chilling is normally achieved with vapour compression plant, but with some absorption cooling available to increase the cooling capacity when the generator is running. Also in many other Article 5 countries where the electrical grid is not robust enough for a large capacity refrigeration system, it makes sense to use absorption systems. In countries where natural gas downstream piping infrastructure exist and where gas prices are reasonable compared to electricity, direct fired chillers are used to produce chilled water for industrial applications. Those are normally double effect units. Countries with a shortage or unreliable electric supply use direct fired chillers in industrial cooling. Examples are in India, Pakistan, Bangladesh and China. Those units are generally fuel oil fired or gas fired. Indirect fired absorption units are used primarily in applications where excess boiler capacity is available in summer months and where steam or hot water are generated by a co-generation application. Those units are normally single effect and are fired at water or steam temperatures of 90°C to 120°C. The efficiency of those units is compared to those of vapour absorption in chapter 9. The lithium bromide-water chillers are all water cooled. . 5.4 Options for existing equipment Systems using HCFC-22 have been converted to zero ODP refrigerants, but it is difficult to replicate the operating conditions of HCFC-22 and therefore conversions often involve an element of equipment replacement. Before committing to any large scale retrofit project, serious 2018 TOC Refrigeration, A/C and Heat Pumps Assessment Report 111PDF Image | Heat Pumps Technical Options
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