Figs. 48 and 49 show the arrangement of a Belgian retort-furnace, Fig. 48 representing a vertical section lengthways, and Fig. 49 a horizontal section. The illustrations, however, are given at different heights in order to show plainly the arrangement of the fire-place and the passage of the fire-gases.
The cast-iron retorts—sixteen in the apparatus shown—are placed in rows alongside and one after another, so as to be swept as uniformly as possible by the fire. As will be seen from Fig. 49 the firing is so arranged that only the upper portions of the retorts are touched by the flames. B is the actual fire-place, and A the ash-pit, both being furnished with closely fitting doors so that the fire may be properly regulated, and the retorts eventually be exclusively heated with gas.
Fig. 49.
The retorts are cylindrical in form, with one end closed. At the open end is fixed the frame or mouth-piece, which carries the door swung on a hinge. The door has a slight projecting rim, some two inches wide, which, with the surface of the frame, is ground perfectly true; on closing, the joint is made gas-tight by a lever arrangement.
The fire-gases escaping from B are distributed as uniformly as possible by the flues, a, carried underneath the pans, E, and finally pass out in the direction of the arrows through a chimney.
At the time when the extraction of fat was exclusively effected by boiling the bones, the pans E served for this purpose, and the spaces D, D1, D2, etc., alongside the pans, which were also heated by the fire-gases, were used for drying the bones. However, at present, the extraction of fat is, as a rule, effected by means of benzine or carbon disulphide, and it is advisable to replace the pans, E, by a bonekiln, and eventually to utilize any waste heat for heating the evaporators for glue-liquor.
Fixed to the upper portion of each retort is a pipe, and these pipes lead into a very wide iron-pipe, T. The products of destructive distillation escaping from the retorts combine in T, and besides having a very large diameter, this pipe must be considerably inclined to avoid the accumulation of products of distillation in it. To prevent the products of distillation from depositing in a crystalline form in T, the latter is covered with a bad conductor of heat.
The pipe T is connected with a series of condensing vessels, D, another series of vessels being placed alongside the first one, so that the vapors may be conducted, as desired, into either one of them. Two batteries of such condensing vessels are required, as one of them has from time to time to be disengaged in order to be cleansed.
If the products of distillation would have to overcome the entire pressure of the column of fluid in the condensing vessels, their escape from the retorts would be very much retarded. To avoid this, plates are arranged horizontally a few inches below the level of the fluid, and the pipes dip into the condensing vessels only far enough to permit the escaping vapors to pass under these plates. By this arrangement, the vapors sweep under the plates and are absorbed by the fluids, a strong pressure in the apparatus being thus avoided.