Improvements in and relating to the Construction of Digesters or Boilers for use in the Manufacture of Paper Pulp.
Year: 1890

page_text: Date of Application, 28th Jan., 1890-Accepted, 1st Mar., 1890
COMPLETE SPECIFICATION.
Improvements in and relating to the Construction of Digesters or
Boilers for use in the Manufacture of Paper Pulp.
I, WILLIAM WALLACE KEYS, residing at Waldemere Avenue, near Iranistan
Avenue, in the City of Bridgeport County of Fairfield and State of Connecticut,
one of the United States of America, Manufacturer, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
It is well known that the digesters employed in the manufacture of paper-pulp
from woody-fibre, are huge hollow structures which must not only possess great
strength for enabling them to successfully resist the requisite high steam pressures,
but they must also be of such a character that the pulp developed therein, will not
be impaired by that discoloration always resulting from the presence of iron in the
acid solutions.
Long prior to our present invention, we believe it had been satisfactorily
determined that cast-iron would be unreliable for affording the requisite strength,
in digesters especially in view of the fact that their great size necessitated their
construction in many parts or sections, bolted together, and the liability to derange
ment by the expansion and contraction due to frequent alterations in heating and
cooling.
Iron or steel boiler plate has therefore been relied upon as an outer wall or shell
for affording the requisite strength, but as wrought iron or steel plates are even
more liable to corrosion than cast iron, those plates have always been employed in
the construction of an outer shell, in combination with some other metal in plate
or sheet form, applied as a lining with a view to not only protecting the outer shell
against destructive corrosion, but what is of even greater consequence, preventing
the discoloration and ruin of the paper pulp, which always results from the presence
of iron in the corrosive liquids employed.
A digester having double walls composed of a boiler plate shell and any kind
of a protecting lining composed of metal or an alloy, is one which obviously
involves many fine and critical points in its mechanical construction, as well as an
expenditure of much costly skilled labor. However perfect, such a double walled
digester may have been initially, the combination of a metallic lining and an outer
metallic shell involves much liability of derangement at the numerous joints and
seams, solely because of the unequal expansion and contraction obviously incident
to large structures composed of many parts or sections bolted or rivetted together,
and especially in one embodying inner and outer cylinders which are not only of
different diameters and thickness, but are respectively composed of metals which
are radically unlike as to their expansive and contractile characteristics.
Lead has heretofore been mainly if not wholly relied upon for lining digesters,
and although that metal is voraciously destroyed by the acid solutions until well
coated with lead salts, the pulp, is not seriously impaired by the presence of the
lead the use of lead however demands constant watchfulness and close inspection
of the interior of a digester after each cooking operation, and frequent repairs, and
even under the greatest possible vigilance, serious losses are liable to and do quite
frequently occur, because of such defects in the lining as result in the ruin or dis-
coloration of pulp whenever the acid solutions gain access to the interior surface of
the outer shell.
It has been heretofore proposed to line the iron shells of digesters with lead bronze
as a substitute for lead. While lead bronze would no doubt be preferable to pure lead
in some respects, a digester lined with such bronze would like any other lined digester
involve similar unequalities as to expansion and contraction, and also as to complexity

page_text: as a mechanical structure, as well as to that liability of straining and leaking at the
inevitably numeroas soldered or brazed joints or seams in the lining, and a consequent
liability of exposure of the iron shell to the corrosive action of the acid solutions, with
resultant damage and loss in the discoloration of the pulp.
A paper pulp digester embodying our invention differs structurally from any
heretofore known to us in that it has solid walls, is composed of sections each of which
is a casting of solid homogeneous metal, and we are the first to devise a wood pulp
digester which does not involve those mechanical complexities in construction to
which we have referred, nor any liability of damaged pulp, nor any necessity for
frequent and close inspection, nor the constant outlay for repairs with the serious loss
of service incident thereto, all of which are well known to be attendant upon the use
of all wood paper pulp digesters as heretofore constructed.
This structural novelty in our digesters is rendered possible because the cast
sections are composed of a practically non-corrosive bronze of extraordinary strength,
or in other words, a bronze which is free from oxides and sub-oxides.
Some of the digesters made by us are so large in diameter that a mounted horseman
can freely ride through a detached cylindrical section, and we have discovered that
we can cast such sections of de-oxidized bronze, and have them homogeneous and
solid throughout while avoiding undue bulk and weight, and to have them as strong
or stronger than the best iron or steel outer shells heretofore used, and also so as to
involve no mechanical labor in the construction of the walls of the digester other
than that required in merely facing the flanges of the cast sections, and the applica-
tion of bolts thereto. All of these advantages would be unavailable, had we not also
discovered that the deoxidized bronze can effectually resist the corrosive action of the
acid solutions; so thoroughly in fact, that after upwards of twenty months of
continuous use, our novel digesters at their inner exposed surfaces bear neither
optical indications of corrosive action, nor any enlargement in diameter which is
measureable by ordinary callipering.
The discoloration of a charge of pulp involves a loss so great that to avoid that
liability ordinary lined digesters are cooled down after each cooking operation to
admit of a critical inspection of the lining, and the making of such repairs as are
frequently required, whereas our novel digesters may be and are in practice promptly
charged after each discharge of finished pulp, thus indicating that one of our digesters
is equal in practical effective service to two or more ordinary lined digesters of the
same size. Economy in steam is also of great practical consequence, and the use of
our novel digesters involves a minimum expenditure thereof because they need
never be cooled down and can be operated constantly, night and day, without as
yet any known limit to their durability and capacity for continuous service.
De-oxidized bronze suitable for digesters can be produced as follows-viz.:
After the copper is well melted in crucibles its surface is kept well covered for from
thirty minutes to an hour, with scraps or small pieces of animal horn to the depth of
an inch or two and thereafter the tin is added in proportions of say one part of tin
to nine parts of copper.
The accompanying drawing represents partly in elevation and partly in section a
paper pulp digester constructed in accordance with our invention.
As shown in the drawings our novel digester has solid walls composed of several
parts, viz.: a cap or dome, a pit or base, and certain intervening cylindrical parts,
and each of these parts or sections is a casting of solid homogeneous de-oxidized
bronze.
The sections, A, are circular in cross-section and provided at each end with flanges, B.
These sections are secured together by bolts, a, passed through said flanges and
clinched by nuis, b. The dome or cap section, C, having a flange, D, is similarly bolted
to the upper flange of the section below. A cap, E, is bolted to the top of the dome by
bolts, c, and nuts, d. The pit, F, has a flange, G, bolted to the lower flange of the
adjacent section by the bolts, a, and nuts, b.
Pieces, H, are placed side by side to constitute a false bottom in the pit, F. The
pieces, H, are composed of bronze and are perforated as seen at, g. At the side of

page_text: the pit is a bronze steam connection, I, and a blow-out, J, and cover-plate, K, for
the steam connection is composed of bronze and is hinged to the pit and secured in
closed position by the bolts, h, and nuts, i. The pieces, H, are inclined and lead
down to the mouth, L, of the pit.
The wood or vegetable matter to be made into pulp is introduced within the digester
at the top of the dome, while the acid is run in through the inlets, M. When the pulp
has become sufficiently cooked both the acid and the pulp settle at the bottom of the
digester, the pulp gravitating through the mouth, L, of the pit, while the acid partly
follows the course of the pulp, but mainly percolates through the perforated bottom
sections, H, within the chamber, N, and is led thence to any suitable receptacle. The
object in thus separating the acid and pulp is to facilitate the massing of the latter
and at the same time to afford egress to a greater amount of pulp in a given time.
Steam being introduced through the connection, I, the pulp, as it drops through the
mouth of the pit, is blown through the opening, J, into the usual receptacle (not
shown). It is obvious that no iron or steel should be used in or about the apparatus
where it will be liable to exposure to contact with liquids employed within the
digester.
Having now particularly described and ascertained the nature of our said
invention and in what manner the same is to be performed we declare that
what we claim is-
1st. The paper pulp digester substantially as hereinbefore described, consisting of
several flanged sections bolted together, each section being a solid homogeneous
casting composed of bronze which is substantially non-corrosive under contact with
hot acid solutions and has sufficient strength to withstand the heavy steam pressures
requisite in the manufacture of wood-pulp, substantially as and for the purpose
specified.
2nd. A paper pulp digester having solid walls composed of cast de-oxidized bronze,
substantially as and for the purpose specified.
anuary lou.
JENSEN & SON,
77, Chancery Lane, London, W.C., Patent Agents.