But this competition among inventors, whatever the incentive, has not been without benefit, because to-day, by means of very simple improvements in details, such as the addition of circulators and increased area of connexions, what may be taken to be the standard type of multiple-effect evaporator (that is to say, vertical vacuum pans fitted with vertical heating tubes, through which passes the liquor to be treated, and outside of which the steam or vapour circulates) evaporates nearly double the quantity of water per square foot of heating surface per hour which was evaporated by apparatus in use so recently as 1885 - and this without any increase in the steam pressure.
This consideration should be carefully, remembered in the future by the planter who may require an evaporator and by the engineer who may be called upon to design or construct it, and more especially by a constructor without practical experience of the working of his constructions.
In places where work is carried on day and night throughout the week, the standard type of evaporator lends itself more readily to cleaning operations than any other.
The modern distilling plant consists of two main parts termed the evaporator and condenser; in addition there must be a boiler (sometimes steam is run off the main boilers, but this practice has several disadvantages), pumps for circulating cold water in the condenser and for supplying salt water to the evaporator, and a filter through which the aerated water passes.
The water level is maintained in the evaporator until it contains a certain amount of salt.
The water vaporizes and is led from the dome of the evaporator to the head of the condenser.
A ton, and where steam is raised by coal, as in a beetroot factory, it might pay to adopt a quintuple-effect apparatus, but on a cane-sugar estate, where the steam necessary for the evaporator is raised by burning the megass as fuel, and is first used in the engines workifig the mills, the exhaust alone passing to the evaporator, there would be very little, if any, advantage in employing a quadruple effect instead of a triple effect, and practically none at all in having a quintuple-effect apparatus, for the interest and sinking fund on the extra cost would more than counterbalance the saving in fuel.
The clear juice thus obtained is evaporated in a multiple-effect evaporator and crystallized in a vacuum pan, and the sugar is purged in centrifugals.