SODA RECOVERY

357

Each effect has three chambers, the bottom one being very shallow, the top
one being much larger. The centre chamber is composed of a number of
upright tubes connecting the top and the bottom, through which the liquor
is agitated by means of the vacuum. The steam to assist the evaporation of
this liquid is passed through the centre chamber, but on the outside of the
tubes. The last effect or concentrator is constructed in the same manner as

FIG. 155.—Two SCOTT ROTARY FURNACES WITH PATENT SODA GRATES

[George Scott and Sons

Nos. I and 2, but the steam for this concentrator is new steam, procured
entirely from the main steam range. This ensures that the thickened liquor
is passing to the furnace at the highest temperature, the drop in temperature
being from the third to the first effect in this arrangement.

Where the drop in temperature is from the first to the third effect, the
thickened liquor requires to be run to a steam-heated storage tank to increase
its temperature, thereby making it more fluid and easy to bum.

The liquor has then been concentrated from about 4° Tw. to 60° Tw. (200°
to 230° F.) by evaporation, and passes onwards to the rotary furnace (Fig. 155)*
This consists of a revolving firebrick-lined steel shell, whose internal diameter

AA