IMPROVEMENTS IN APPARATUS FOR INCREASING THE DRAFT IN THE CHIMNEYS OF STEAM SHIPS
Year: 1878

page_text: PROVISIONAL SPECIFICATION left by John Clayton Mewburn at the Office
of the Commissioners of Patents on the 6th November 1878. A communication
from abroad by Alexander Friedmann, of Vienna, Austria, Engincer.
JOHN CLAYTON MEWBURN, of 169, Fleet Street, in the City of London, Patent
Agent and Consulting Engineer. "IMPROVEMENTS IN APPARATUS FOR INCREASING
THE DRAFT IN THE CHIMNEYS OF STEAM SHIPS." [A communication from abroad by
Alexander Friedmann, of Vienna, Austria, Engineer.]
The production of steam in steam ships is essentially dependent upon the draft
of the chimney of the steam boilers.
On the 29th January, 1874, Letters Patent, No. 373, were granted to my present
correspondent, Alexander Friedmann, in the Specification of which he described the
fitting and use in the chimneys of steam ships of a compressed air blast apparatus
to assist or increase the draft. The principle of assisting the draft of chimneys of
steam boilers of steam ships by means of compressed air has therefore already been
made known by him, and he also described in the aforesaid Specification a special
apparatus for carrying out this principle. Now the present Invention consists of
improved apparatus for carrying out the principle, that is to say, of assisting the
draft in the chimneys of steam ships by an air blast apparatus. In fact it has been
found that the air blast apparatus described in the aforesaid Specification is a great
obstruction whenever the chimney works solely with its natural draft.
According to the present Invention the compressed air is made to escape around
the whole inner circumference of the chimney, the gases near the inner surface of
the chimney being especially slow in ascending. For this purpose there is formed
in the chimney of the steam boilers of steam ships and around the inner circum-
ference of the said chimney an annular orifice, through which compressed air from
a fan or other blowing apparatus enters the chimney, so that the said compressed
air sweeps the inner circumference of the part of the chimney situated above the
annular orifice, and drives or draws up first the combustion gases which are in
stagnation against and near the inner surface of the chimney and gives an impulse
also to the rest of the ascending gases, thus increasing the velocity of ascension of

page_text: the whole of the combustion gases, and therefore also the draft of the chimney.
Further, the inner surface of the chimney beginning at the place where the com-
pressed air enters is made slightly converging for a moderate distance, so that the
inner diameter of the chimney becomes gradually smaller. From the point where
the inner diameter of this part of the chimney is the smallest the chimney is for a
short distance cylindrical, and then begins to diverge until it becomes again of
ordinary diameter.
Thus the whole chimney is as it were transformed into a very large vacuum-
ejector, similar to the ejector of Smith's vacuum brake, with the difference that the
driving medium instead of being steam is compressed air entering a very large
annular nozzle, and that the inner diameter of the said nozzle is formed by tho
surface of the chimney below the annular orifice, and the outer diameter of the
annular nozzle by the inner surface of the chimney above the air inlet. This
annular air inlet or air nozzle can be arranged near the upper edge of the chimney,
and then the apparatus is essentially a lifting or sucking apparatus, rarefying the
gases of nearly the whole volume of the chimney, and thus utilizing nearly all the
natural ascending force of the gases (due to their being hot and therefore specifically
lighter than the air). This situation of the annular air nozzle will be preferable
especially in commercial or passenger steamers. For war steamers however it may
be preferred to arrange the apparatus at a lower part of the chimney so as to
prevent its being destroyed during an engagement, and to enable it to be utilized
as a reserve in case the part of the chimney above the deck gets damaged. The
best height however to place the apparatus is such that the end of the diverging
part of the chimney above the annular air nozzle shall coincide with the upper edge
of the chimney. As the apparatus is intended to increase the natural draft of the
chimney it is evident that it will often be employed only as a reserve, and then it
is important to protect the annular orifice from being obstructed or incrusted while
not in use by the deposits of the smoke. For this purpose the apparatus is arranged
so that either the converging part of the chimney which forms the outer diameter
of the annular nozzle of the air inlet or that part of the chimney which forms the
inner diameter of the annular nozzle of the air inlet is movable, and thereby capable
of closing the annular orifice. This may be effected either by lowering the part
above or by raising the part beneath the annular orifice. The cleansing of the
apparatus may be provided for in the same way.