Washing the Char coal. — The anirnal charcoal used in these filte,rs is rarely pre pared in the sugar factory itself ; but usu ally it there undergoes a washing operation, as well as a process termed " revivification." The washing is as follows. After having been sub jected to fermentation, or to a treatment with alkali at 100° (212° F.), the black is washed with water till it ceases to communicate the least turbidity. Nume rous machines have been introduced for carrying out these con ditions, the main ob jects being to cleanse thoroughly, employ a minimum of labour, and avoid disintegra tion of the black. A typical form is Kluze mann's, Fig. 1318. It consists of a chamber divided by low parti tions into compart ments d, in which slowly revolve arms c mounted on shafts b, and terminating in flexible iron blades. The black falls from the hopper a into the lowest part of the ma chine ; it is successively passed from one com partment to the next by the revolving arms, each time attaining a higher level, finally reaching the upper end e, whence it is ejected completely washed. The water admitted by the pipe f passes in a contrary direc tion through the black, and runs out at g. The machine is cheap and efficient, and washes about 15 tons per 24 hours.
Schreiber, of St. Quentin, has introduced a novel form of washer, in which the black is placed in contact with a stream of water by means of its own sp. gr., without the intervention of any mechanical appliance to cause its disintegration. The machine consists of horizontal air-tight cylinder, 6 ft. long, and 28 in. diam., turning in external supports by means of toothed wheels engaging ln toothed rings on the cylinder ; in the interior of the cylinder, are two paddles or curves, and it is prolonged by a cylindrical part of less diameter. The pipe conveying water enters the cylinder at the axis of this smaller part. The black enters at the other end. In the centre of tho oylinder, revolves an endless acrew, which catches up the bla.ck; and an annular space is left throughout the cylinder for the passage of the water. During the rotation of the cylinder, the black is continually lifted by the paddles by the simple act of rotation, and at the same time a certain quantity of water is taken up, and falls back into the same bath with the black. In this movement, the grains of black traverse the water, and the washing is effected without shock or injury. The paddles are so inclined, that the black entering at one end is propelled along one side to the other end, returning in the same manner along the other side, and escaping finally at the end where it entered. The machine is spoken of in the highest terme.
Revivification.—By " revivification " of the charcoal, is meant the sepamtion from it of those saccharine and other matturs which it absorbs in the filtering process, thus rendering it fit for re-use. With this object, it is fermented to destroy the organic matters; washed with acid, with hot water, with cold water, and with steam ; dried ; and finally calcined in furnaces of very various construction. These all consist essentially of a system of cast-iron or earthenware pipes, heated
to dull-redness, and closed at bottom by a method permitting the black to be withdrawn without ulmitting air, which would immediately cause the combustion of the red-hot carbon. This last condition is the one difficulty, and each maker strives to overcome it in a particular way.
Schreiber's kiln, shown in section in Fig. 1319, consists of a drier, vertical undulating pipes for the calcination, and inclined cooling-tubes terminating in boxes for regulating the discharge of the tubes. It is surrounded with masonry. On each aide of the fire a, are placed the rows of cast-irou undulating pipes b, each composed of three pieces, fitting one within another. They are prolonged downwards by fiat cast-iron tubes o, serving to cool the black, and forming an angle of 45° with the vertical pipes b. At the top, are similar undulating pipes d, with lateral openings forming venetian blinds in front, and crowned by a hopper e for holding the supply of black for the kiln. This forms the automatic drier. The undulating pipes b serving for the revivification are plated iusido aud out with slabs of fire-brick ; these protect the iron from the tire, and regulate the trans mission of heat, preventing the temperature exe..eding 375°-450° (707°-842° F.), beyond which the black might be vitrified. The black is collected in the hopper e above ; thence it descends into the driers d, enters the revivifiers b at about 90° (194° F.), and, when the operation is complete, °salvos by the refrigerating-tubes c. A fire of coke or other fuel being lit in the furnace a, the flame spreads throughout the whole space of the fire-chamber f included between the two series of ilre-slah coated tubes b and an arch at top, passes downwards, divides into two chambers right and left, heats the backs of the tubes, and again rises into a single flue passing through the drier d. The kiln is easy to build and manage, and turns out a black of suporior quality.
The Ruelle kiln, Fig. 1320, has several advantages, and differs from most others in its general arrangement. It consists as usual of a series of cast-iron revivifying- and cooling-tubes. The whole of these aro arranged hi 11 bunch centred around a vertical axis, and suffer a slow, circular automatic movement of 2 rev. per hour, within a cylindrical furnace flanked by a lateral fire. The black is fed in a thin stream at the upper part of the kiln, and traverses the tubes, which are in turn presented to the fire, so that they are successively brought to a dull-red beat, thus ensuring regularity in the roasting, and avoiding those excesses of temperature which are always to be feared with fixed tubes. The rotary movement enables the discharge to be made automatically; each time a pipe reaches a certain point it meets a cam, which opens the outlet. A little elevator carries away the black as fast as discharged. The waste heat from the furnace circulates beneath a platform for performing the preliminary desiccation. This form of kiln is much used.