CANE SUGAR. 



The great majority of vacuum pans in use at the present day consist of a 

 vertical cylindrical iron body of approximately equal length and width ; this 

 is often called the belt and is covered on the top by a spherical or conical cap 

 called the dome ; on the dome is placed the head box whence leads the vapour 

 pipe to the pump ; the lower portion of the pan is formed by an inverted cone 

 called the saucer or well ; the massecuite is discharged by a door at the centre 

 of the well. In what may be referred to as the Standard type of vacuum pan, 

 the heating surface consists of a number of helical copper coils, reaching from 

 the bottom to a little above the centre of the pan, and so arranged as to divide 

 the heating surface as uniformly as possible. In Fig. 189 is shown a view 

 partly in section and partly in elevation of a modern pan. The coils are seven 

 in number and are 4 J inches in diameter ; they are supported by stay rods 

 fixed to the side of the pan ; they each pass through the side of the pan and 

 communicate with the steam pipe/; each coil has its own valve i whereby 

 steam can be admitted to any or all of them ; connection is also made to a 

 second pipe (not shown) carrying exhaust steam, so that this can be utilized 

 when available. In modern practice the maximum length of coil used is one 

 about 200 times the diameter ; beyond this length it is found that the con- 

 densed water does not leave the pipe fast enough to obtain an efficient heating 

 surface. The syrup is brought into the pan by the pipe I controlled by the 

 valve shown at a ; this pipe reaches down to the bottom of the pan, so that the 

 lighter syrup enters at the bottom and rising upwards becomes uniformly dis- 

 tributed ; each coil is closed by a flange d at its lowest point, which carries a 

 smaller pipe conveying the water of condensation to a steam trap or separator ; 

 at e is shown a pipe connected to the main steam whereby steam is introduced 

 to the interior of the pan for the purpose of removing sugar after a strike ; at 

 k is a manhole giving access to the pan, at g the vacuum gauge, at c a sight 

 glass, and at b the cock for breaking vacuum ; in the pan shown there are 

 approximately 1,000 square feet heating surface, the vessel holding when full 

 30 tons of massecuite. Special points with regard to this type of pan are 

 that the coils are often made double, alternately right and left handed 

 helices, and that the condensed water is trapped at every fifty feet or so 

 of coil. 



Vertical Tube Pan. A view of this pan is shown in Fig. 190, and 

 is often referred to as a calandria pan. The main portion of the heating surface 

 is contained in the vertical tube belt, the tubes of which are generally about 

 four inches in diameter ; the coil shown in the lower portion of the pan is for 

 the purpose of graining when only a small quantity of syrup is used for that 

 purpose ; it is also necessary so as to distribute the heating surface over the 

 lower portion of the apparatus. Frequently the upper tube plate of the 

 calandria is made sloping slightly downwards at an angle from the circum- 

 ference towards the centre of the pan with the object of preventing an accumu- 



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