Indian Forest Records. 
tf 
[VOL. III. 
in vacuum pans into solid extracts. This is done in four ways, (1) b} 
Simple effect system, (2) by Double effect system, (3) by Triple effect 
system and (4) by Kestner's system. 
Simple Effect Vacuum Fan .—This consists of a closed pan made of 
copper or bronze in which the pressure is reduced by connecting it with 
the suction of a vacuum pump. Its shape is like that of the left-hand 
pan shown in Plate III. 
The “ calandria ” of the Simple effect pan is provided with two hori¬ 
zontal tubular bronze plates pierced with holes in which are fixed the 
tubes of a tubular bundle, whereby is formed a large heating surface. 
The tubular bundles are surrounded by a heating chamoer wueiein is 
introduced the steam from the boiler to evaporate the liquors which 
are passing through the tubes. Thus steam coming into the heating 
chamber condenses and gives up its latent heat to the tan liquors 
to be evaporated. The tan liquors then begin to boil under reduced 
pressure and thus yield a fresh amount of steam. The water condensed 
in the heating chamber is run off to feed the boiler. The steam from the 
boiling liquor is condensed in a surface condenser placed in front of the 
air pump at the exit from the pan. This device yields a corresponding 
quantity of condensed water which is used for extracting the material, 
while with a barometric or with an injection condenser, the steam mixed 
with the condensation water runs down the drain in sheer waste. The 
use of a surface condenser is, therefore, recommended in order to collect 
the distilled water from the boiling tan liquors for use in extraction 
without any extra cost. It may be pointed out here that the best results 
in tannin extract manufacture can only be obtained by the use of pure 
water. The condensed water from the evaporating vessels must be used 
for extraction purposes, and should surface condensers as mentioned 
above not be used, a special pump called the “ condensed water pump 
is required to collect it. 
Double Effect System-—' This type of vacuum pans consists of two pans 
communicating with each other in which the pressure is reduced at the 
exit of the second pan. The heating system is as in the Simple effect 
system ‘With this difference, that the quantity of steam generated bv 
boiling the liquor in the first pan is utilised to heat the tubular bundle 
of the second vessel and to boil the liquors therein. The steam rising 
from the boiling liquors of the second pan is then collected by surface 
ondensers from which it is pumped to the condensed water reservoir 
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