The operation of carbonizing woolen rags for the purpose of obtaining pure wool, through the destruction of the vegetable substances contained in the raw material, maybe divided into two parts, viz., the immersion of the rags in acid, with subsequent washing and drying, and the carbonization properly so called. The first part is so well known, and is so simple in its details and apparatus, that it is useless to dwell upon it in this place. But the second requires more scientific arrangements than those that seem to be generally adopted, and, as carbonization is now tending to constitute a special industry, we think it is of interest to give here a typical plan for a plant of this kind. It will be remarked that this plan contains all the parts in duplicate. The object of this arrangement is to permit of a greater production, by rendering the operation continuous through half of the apparatus being in operation while the other half is being emptied and filled.
Figs. 4 and 5 give plans of the ground floor and first story, and Figs. 1, 2, and 3 give vertical sections. The second story is arranged like the first, and serves as a drier. As we have said, there is a double series of chambers for carbonization, drying, and work generally. These two series are arranged on each side of a central portion, which contains the heating and ventilating apparatus and a stone stairway giving access to the upper stories. The heating apparatus is a hot air stove provided with a system of piping. The rags to be carbonized or the wool to be dried are placed upon wire cloth frames.
The carbonization is effected in the following way: When the heating apparatus has been fired up, and has been operating for about half an hour, the apertures, i, are opened so as to let the air in, as are also those, m, which allow the hot air to pass into the chambers. The hot air then descends from the top of the chamber into the wool or rags, and, becoming saturated and heavier, descends and makes its exit from the chamber through an aperture, n, near the floor, whence it flows to the central chimney. This latter, which is built of brick or stone, contains in its center a second chimney (formed of cast or forged iron pipes) that serves to carry off into the atmosphere the products of combustion from the heating apparatus. The heat that radiates from these pipes serves at the same time to heat the annular space through which the vapors derived from the wool are disengaged.
The air, heated to 40° or 50°, is made to pass thus for several hours, until the greater part of the humidity has been removed. The temperature is then raised to 80° or 90° by gradually closing the apertures that give access to the ventilating chimney. In order that it may be possible to further increase the temperature during the last hour, and raise it to 90° or 120°, an arrangement is provided that prevents all entrance of the external air into the heating apparatus, and that replaces such air with the hot air of the chamber; so that this hot air circulates in the pipes of the stove and thus becomes gradually hotter and hotter. The hot vapors that issue from the lower chamber rise into the upper one, where they are used for the preliminary drying of another part of the materials.
The hot air stove should be well lined with refractory clay, in order to prevent the iron from getting red hot, and the grate should be of relatively wide surface. All the pipes should be of cast iron, and all the joints be well turned. Every neglect to see to such matters, with a view to saving money, will surely lead in the long run to bad results.
PLAN OF WORKS FOR CARBONIZING WOOL. (Scale 1-200.)
The mode of work indicated here is called the moist process. It necessitates the use of a solution of sulphuric acid, but, as this latter destroys most colors, it cannot be used when it is desired to preserve the tint of the woolen under treatment. In this case recourse is had to the dry process, which consists in substituting the vapors of nitric acid heated to 115° or 125° for the sulphuric acid. The arrangement of the rooms must likewise be different. The chambers, which may be in duplicate, as in the preceding case, are vaulted, and are about three yards long by three wide and three high. The rags are put into wire cages that have six divisions, and that are located in the middle of the chamber, where they are slowly revolved by means of gearings. Under the floor are the heating flues, and upon it is a reservoir for holding the vessel that contains the acid to be vaporized. The arrangements for the admission of air and carrying along the vapors are the same as in the other case.
Great precaution should be taken to have the flues so constructed as to prevent fire. - Bull, de la Musee de l'Industrie.