After a second, and sometimes a third carbonatation and filtration, the
juice is carried to the evaporators, commonly called the “effects,”
usually four (4) large air-tight vessels furnished with heating tubes
running from 3000 to 7000 square feet in each vessel. A partial vacuum
is maintained in these evaporators which makes the juice boil out at a
low temperature, thus preventing discoloration, and to a large degree
the destruction of sugar which will come about by high temperature.
There always is, however, some unavoidable loss of sugar in this
apparatus. The juice passes along copper pipes from first to last
vessel, becoming thicker as it does so. It comes into the first vessel
at 10% to 12% sugar and is pumped out of the last one so thick that it
contains about 50% of sugar.]
[Illustration: VACUUM PANS.
After a careful filtration, the juice that comes from the evaporators,
and is called thick juice, is pumped to large tanks high up in the
building, and from these is drawn into vacuum pans. These are large
cylindrical vessels from 10 to 15 feet in diameter and from 15 to 25
feet high, with conical top and bottom, built air-tight. Around the
inner circumference they are furnished with 4- to 6-inch copper coils,
which have a heating surface of 800 to 2000 square feet. Exhaust steam
is used in the evaporators, live steam in the pans, the juice in both
being boiled in a vacuum to prevent discoloration and reduce losses.
After considerable thickening by this evaporation, minute crystals
begin to form. When sufficient of these have formed, fresh juice is
drawn in and the crystals grow, the operator governing the size of
the crystals to suit the trade. If small crystals be desired, a large
quantity of juice is admitted at the outset, while if large crystals
are desired, a small quantity of juice first is admitted, and, as it
boils to crystals, fresh juice gradually is added to the pan, and the
crystals are built up to the desired size. The operator of this pan,
known as the “sugar boiler,” is one of the must important men in the
factory. The water furnished the condensers of these vacuum pans and
the evaporator goes to the beet sheds and is used for floating in the
beets. It amounts to from 3,000,000 to 8,000,000 gallons every 24
hours, depending upon the size of the factory, and must be very pure.]
[Illustration: HOW SUGAR IS GRANULATED