144 Meat refrigeration Table 7.5 Energy and cost requirements for beef plant freezing 3000 cartons per freezers blast ezer Freezing time(h Freezer load (kw 53 Power consumption (kW) Capital cost Annual capital charges Annual energy costs Annual labour cost Total annual cost Source: De Jong. 1994 a net electricity cost of NZso10 per kilowatt hour, a capital recovery over 10 years and an interest rate of 12% 7.4 Cryogenic freezing Cryogenic freezing uses refrigerants, such as liquid nitrogen or solid carbon dioxide, directly. The method of cooling is essentially similar to water-based evaporative cooling, cooling being brought about by boiling off the refrig erant, the essential difference being the temperature required for boiling As well as using the latent heat absorbed by the boiling liquid, sensible heat is absorbed by the resulting cold gas. Owing to very low operating temperatures and high surface heat fer coefficients between product and medium, cooling rates of cryogenic systems are often substantially higher than other refrigeration systems. Most systems use total loss refrigerants, i.e. the refrigerant is released to the atmosphere and not recovered. Alternatively dichlorodifluoromethane (CCl, F2)(otherwise known as Freon 12, R 12 or F12) may be used in a recovery and recycle system, however, R 12 is not generally accepted in all countries. Because of environmental and economic factors total loss refrig erants must be both readily available and harmless, which limits the choice to atmospheric air and its components, liquid nitrogen(LN) and liquid or solid carbon dioxide(cO2) The particular ch cs of total loss refrigerants that may be regarded as advantages dvantages are listed in Table 7.6. eezing is used for small products such as burgers, ready meals, and so on. The most common method is by direct spraying of liquid nitrogen onto a food product while it is conveyed through an insu lated tunnela net electricity cost of NZ$0.10 per kilowatt hour, a capital recovery over 10 years and an interest rate of 12%. 7.4 Cryogenic freezing Cryogenic freezing uses refrigerants, such as liquid nitrogen or solid carbon dioxide, directly. The method of cooling is essentially similar to water-based evaporative cooling, cooling being brought about by boiling off the refrig￾erant, the essential difference being the temperature required for boiling. As well as using the latent heat absorbed by the boiling liquid, sensible heat is absorbed by the resulting cold gas. Owing to very low operating temperatures and high surface heat trans￾fer coefficients between product and medium, cooling rates of cryogenic systems are often substantially higher than other refrigeration systems. Most systems use total loss refrigerants, i.e. the refrigerant is released to the atmosphere and not recovered. Alternatively dichlorodifluoromethane (CCl2F2) (otherwise known as Freon 12, R.12 or F12) may be used in a recovery and recycle system, however, R.12 is not generally accepted in all countries. Because of environmental and economic factors total loss refrig￾erants must be both readily available and harmless, which limits the choice to atmospheric air and its components, liquid nitrogen (LN) and liquid or solid carbon dioxide (CO2). The particular characteristics of total loss refrigerants that may be regarded as advantages or disadvantages are listed in Table 7.6. Cryogenic freezing is mainly used for small products such as burgers, ready meals, and so on. The most common method is by direct spraying of liquid nitrogen onto a food product while it is conveyed through an insu￾lated tunnel. 144 Meat refrigeration Table 7.5 Energy and cost requirements for beef plant freezing 3000 cartons per day Four-batch air Automatic air Manual plate freezers blast freezers Energy analysis Freezing time (h) 38 38 17 Freezer load (kW) 573 477 400 Power consumption (kW) 689 570 462 Economic analysis (NZ$000) Capital cost 1500 2200 2000 Annual capital charges 266 389 354 Annual energy costs 463 383 310 Annual labour cost 60 0 90 Total annual cost 789 772 754 Source: De Jong, 1994