GB686375A - Improvements in or relating to a process and apparatus for evaporating liquids - Google Patents

Abstract

<PICT:0686375/III/1> Aqueous solutions, particularly those which are heat sensitive such as orange juice, are evaporated under reduced pressure, by heat-exchange with a compressed refrigerant gas such as ammonia, the liquefied refrigerant discharged from the heating-element of the evaporator is cooled and used as cooling-liquid in a surface condenser for the water-vapour evolved from the solution, whereby the refrigerator is re-vaporized; the vaporized refrigerant is re-compressed and returned to the heating-element of the evaporator, and some heat is continuously discharged from the system by heat-exchange of the liquid refrigerant with cooling-water and/or by condensing part of the water-vapour in a jet condenser, in order to maintain a uniform pressure of the refrigerant gas delivered to the evaporator. In Fig. 1, the evaporator comprises three tubular units 11 of the falling-film recirculation type connected in series as described in Specification 682,170 The evaporation is connected to a condenser 35 by pipes 17 and 26. Orange juice, supplied through pipe 54, is freed from air in film-type deaerator 55 which is evacuated by pump 57; and the deaerated juice is introduced through pipe 34 into the evaporator where it is evaporated at 60 DEG F under a vacuum of 28 inches to 29 1/2 inches Hg. by heat-exchange with ammonia gas at 205 p.s.i.g. (180 DEG F) which is supplied to the evaporator through pipe 17. Concentrated orange juice is withdrawn from the evaporator by pump 31, while the vaporized water passes through pipe 26 to condenser <PICT:0686375/III/2> 35. Partially condensed ammonia at 102 DEG F is withdrawn from the evaporator through pipe 41. Assuming that cooling-water is available at a temperature (say 80 DEG F) higher than the water-vapour (60 DEG F) the ammonia is passed through condenser 42 and cooler 43 which are supplied with the cooling-water by pump 44. The pump is controlled by diaphragm-valves 70 and 73 in accordance with the pressure of the ammonia-gas in pipe 17. The water is discharged from the condenser 42 through pipe 46. The liquid ammonia at about 85 DEG F then flows through pipe 47 to receiver 48 where is is cooled by flashing-off part of it through pipe 52 to the suction side (75 p.s.i.g.) of compressor 53. The liquid ammonia is then introduced via pipe 50 into the tubes of condenser 35 wherein it vaporizes at 50 DEG F, and, in doing so, condenses the water-vapour on the outsides of the tubes. The condensed water collects in tank 37, and is withdrawn therefrom by pump 38. The vaporized ammonia is withdrawn from the condenser through pipe 51, and is passed to the compressor for recirculation to the evaporator. Air is withdrawn from condenser 35 by ejector 40. In the event that cooling water below 60 DEG F is available, the jet condenser shown in Fig. 7 is connected by pipe 74 to condenser 35 in place of ejector 40. The jet condenser is supplied with cooling water through line 79; and as it spills over weir 80 and falls over splash-plates 81, it will condense the water-vapour entering the jet condenser from condenser 35. Water is discharged from the jet condenser by means of barometric leg 82; and air is ejected by steam-ejector 84. The amount of cooling water supplied to the jet condenser is controlled by diaphragm-valve 78 so that enough compressed ammonia is delivered into pipe 17 to accomplish a uniform amount of evaporation per hour. When the jet condenser is used for removing heat from the system, the liquid ammonia is cooled by partial flash evaporation before it is introduced into condenser 35. Specifications 686,376 and 686,377 also are referred to.