Fig. 3.—Saltcake Muffle Furnace—Section (after Ost)
A Pan; B, F Pipes for hydrochloric acid vapour; D Shutter; E Muffle, O Coke fire.
Mechanical stirrers, despite their advantage from a health point of view, have not answered because of their short life.
The valuable bye-product of the sulphate process, hydrochloric acid, is led away separately from the pan and the muffle, as is seen, into one absorption system. The reason of the separation is that the gas from the pan is always the more concentrated. The arrangement of the absorbing apparatus is illustrated in [fig. 4].
Fig. 4a.—Preparation of Hydrochloric Acid—Plan (after Lueger)
- A, A´ Earthenware pipes
- B, B´ Sandstone cooling towers
- C, C Series of Woulff’s bottles
- D, E Condenser wash towers
Fig. 4b.—Elevation
The gases are led each through earthenware pipes or channels of stone pickled with tar (A´), first into small towers of Yorkshire flags (B), where they are cooled and freed from flue dust and impurities (sulphuric acid) by washing. They are next led through a series (over fifty) of Woulff bottles (bombonnes) one metre high, made of acid-resisting stoneware. The series is laid with a slight inclination towards the furnace, and water trickles through so that the gases coming from the wash towers are brought into contact with water in the one case already almost saturated, whilst the gas which is poorest in hydrochloric acid meets with fresh water. From the bombonne situated next to the wash tower the prepared acid is passed as a rule through another series. The last traces of hydrochloric acid are then removed by leading the gases from the Woulff bottles up two water towers of stoneware (D and E), which are filled partly with earthenware trays and partly with coke; above are tanks from which the water trickles down over the coke. The residual gases from both sets of absorbing apparatus now unite in a large Woulff bottle before finally being led away through a duct to the chimney stack.
Less frequently absorption of hydrochloric acid is effected without use of Woulff bottles, principally in wash towers such as the Lunge-Rohrmann plate tower.