EVAPORATION 



343 



detail. WTiat is \\Titten of the accessories is applicable to the other types 

 also. 



Vertical Submerged Tube Evaporator. — A cell of this type, Fig. i88, 

 consists of a cast-iron or steel shell of over-all height up to twenty feet, and 

 of diameter in the largest units yet built in sugar factories up to 15 feet ; 

 ver\' large plants of 28 ft. diameter are in use in other industries. The height 

 is independent of the diameter of the apparatus. 



The shell is divided into two non-communicating parts by the "tube plates 

 a a and by the tubes b b ; the space between the tube plates and around the 

 tubes forms a chamber, the calandria, mto which steajn from the main or a 

 pre\aous vessel is admitted. The 

 space above the upper tube plate 

 is called the vapour space, c, and 

 is continuous through the tubes, 

 with the space below the bottom 

 tube plate. This space is dead 

 space, and has no evaporating 

 function, but is necessary as a 

 part of the structure of the ap- 

 paratus. At d is seen the pipe 

 conducting the vapour to the next 

 cell. At e are indicated the pipes 

 which remove the condensed water 

 from the calandria, and at f pipes 

 which vent the incondensible 

 gases from the calandria to the 

 vapour space to the next effect, 

 or even directly to the condenser. 

 At g is shown the pipe which con- 

 ducts the juice to the next effect, 

 at h the juice inlets, at j the entry 

 of steam to the calandria, in this 

 case shown as a steam belt sur- 

 rounding the calandria. At k is 

 a gauge glass indicating the level 

 of the liquid. 



Steam Distribution. — The steam 

 may enter at the side at one place 



only, or the vapour pipe may divide into two or more branches. The steam 

 belt may be arranged round the calandria and may be separated from the tubes 

 b\' a slotted or perforated partition. A flared nozzle to the steam pipe and 

 the omission of tubes so as to form steam lanes is claimed in Maxwell's 

 patent (12809, 1S89), and both of these have become standard practice. 

 Steam distribution is also sometimes obtained b}^ the use of internal baffles, 

 whereby a definite passage is given to the steam. 



Another method of steam distribution is seen in Vi\den and Dujardin's 

 patent (2286, 1884), Fig. 189, in which the centre lines of the vapour pipes are 

 coincident with the vertical axes of the cells. This is the first British patent 

 illustrating the modem form of evaporator. 



The velocity of steam in vapour pipes is usually calculated at from 

 50 to 100 feet per sec, and 100 to 200 feet per sec. in the pipe to the condenser. 



Fig. 188 



