By WATSON SMITH, Lecturer in Chemical Technology in the Victoria
University, etc.
The Widnes Alkali Company, limited, to which I am indebted for
permission to describe this latest addition to a family of revolving
black ash furnaces, of late not only increasing in number, but also
individual size, has kindly allowed my friend, Mr. H. Baker, to
photograph the great revolver in question, and I have pleasure now in
throwing on the screen a picture of it, and also one of a revolver of
ordinary size, so as to render a comparison possible. The revolver of
ordinary size measures at most 18½ ft. long, with a diameter of 12½
ft. The boiling down pans connected with such a furnace measure 60 ft.
in length. Each charge contains four tons of salt cake, and some of
these revolvers get through 18 tons of salt cake per day and consume
13 cwt. of coal per ton of cake decomposed.
With regard to the larger revolver, it may be just said that the
Widnes Alkali Company has not at once sprung to the adoption of a
furnace of the immense size to be presently given, but in 1884 it
erected a revolver only about 3 ft. to 4 ft. short of the length of
that one, and having two discharging holes. The giant revolving
furnace to be described measures in length 30 ft. and has a diameter
of 12 ft. 6 in. Inside length is 28 ft. 6 in., with a diameter of 11
ft. 4 in. It is lined with 16,000 fire bricks and 120 fire-clay blocks
or breakers, weighing each 1¼ cwt. The bricks weigh per 1,000 about
four tons. The weight of salt cake per charge (i.e., contained in
each charge of salt cake, limestone, mud, and slack) is 8 tons 12 cwt.
For 100 tons of salt cake charged, there are also charged about 110
tons of lime mud and limestone and 55 tons of mixing slack. In a week
of seven days about 48 charges are worked through, weighing of raw
materials about 25 _tons per charge_. The total amount of salt cake
decomposed weekly is about 400 tons, and may be reckoned as yielding
240 tons of 60 per cent. caustic soda. As regards fuel used for
firing, this may be put down as 200 tons per week, or about 10 cwt.
per ton of salt cake decomposed. Also with regard to the concentration
of liquor from 20° Tw. to 50° Tw., there is sufficient of such
concentrated liquor evaporated down to keep three self-fired caustic
pots working, which are boiled at a strength of 80° Tw. Were it not
for this liquor, no less than seven self-fired pots would be required
to do this work, showing a difference of 80 tons of fuel.
[Illustration: A NEW MONSTER REVOLVING BLACK ASH FURNACE. (2 Figures.) ]
The question may be asked, "Why increase the size of these huge pieces
of apparatus?" The answer, I apprehend, is that owing to competition
and reduction of prices, greater efforts are necessary to reduce
costs. With automatic apparatus like the black ash revolver, we may
consider no very sensible addition of man power would be needed, in
passing from the smallest sized to the largest sized revolver. Then,
again, we may, reckoning a certain constant amount of heat lost per
each revolver furnace of the small size, consider that if we doubled
the size of such revolver, we should lose by no means double the
amount of heat lost with the small apparatus; but only the same as
that lost in the small furnace _plus_ a certain fraction of that
quantity, which will be smaller the better and more efficient the
arrangements are. Then, again, there is an economy in iron plate for
such a large revolver; there is economy in expense on the engine power
and on fuel consumed, as well as in wear and tear.
Just to mention fuel alone, we saw that with an ordinary large sized
revolver, the coal consumption was 13 cwt. per ton of salt cake
decomposed in the black ash process; but with the giant revolver we
have been describing, that consumption is reduced to 10 cwt. per ton
of cake decomposed.
[Illustration: A NEW MONSTER REVOLVING BLACK ASH FURNACE. (2 Figures.)]
The question will be probably asked, How is it possible to get a flame
from one furnace to carry through such a long revolver and do its work
in fusing the black ash mixture effectively from one end to the other?
The furnace employed viewed in front looks very like an ordinary
revolver fireplace, but at the side thereof, in line with the front of
the revolver, at which the discharge of the "crude soda" takes place,
there are observed to be three "charging holes," rather than doors,
through which fuel is charged from a platform directly into the
furnace through those holes.
The furnace is of course a larger one than furnaces adjusted to
revolvers of the usual size. But the effect of one charging door in
front and three at the side, which after charging are "banked" up with
coal, with the exception of a small aperture above for admission of
air, is very similar to that sometimes adopted in the laboratory for
increasing heating effect by joining several Bunsen lamps together to
produce one large, powerful flame. In this case, the four charging
holes represent, as it were, the air apertures of the several Bunsen
lamps. Of course the one firing door at front would be totally
inadequate to supply and feed a fire capable of yielding a flame that
would be adequate for the working of so huge a revolver. As an effort
of chemical engineering, it is a very interesting example of what
skill and enterprise in that direction alone will do in reducing
costs, without in the least modifying the chemical reactions taking
place.--_Journal Soc. Chem. Industry._
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