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.
[Illustration: 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_.
* * * * *