IMPROVEMENTS IN THE METHOD OF AND IN BOILERS OR APPARATUS FOR TREATING WOOD PULP AND OTHER VEGETABLE FIBRE
Year: 1884

page_text: I, DAVID OTTO FRANCKE of Korndal Mölndal in the Kingdom of Sweden,
Managing Director of the Kolndahls Fabrikers Aktiebolag, do hereby declare the
nature of my said Invention for IMPROVEMENTS IN THE METHOD OF AND IN
BOILERS OR APPARATUS FOR TREATING WOOD PULP AND OTHER VEGETABLE
FIBRE," and in what. manner the same is to be performed to be particularly
described and ascertained in and by the following statement :-
My Invention relates to the treatment of wood or other vegetable fibre with
solvent in boilers or apparatus for the production of pulp therefrom, and consists
firstly in applying direct steam to the mixture of fibre and solvent, instead of
heating the same by steam pipes as described in the Specification to my previous
Patent No 4419 of 1881, and secondly to an improved construction of the boiler or
boiling apparatus with lead lining as I will now describe.
Such boilers being constructed of iron or steel require to be lined with lead or
other metal that will protect them from the action of the lyes or solvents with
which the wood or other fibre is treated. These lead linings, in expanding by heat,
and not contracting on cooling in the same degree as the iron or steel boiler, aro
apt to become defective, causing injury to the boiler, and requiring frequent
repair.
My Invention relates to improved means whereby such defective places can be
readily indicated and localised and whereby the lining can be effectually supported
in such a manner as to enable any defective parts thereof to be readily removed
and replaced.
The accompanying Drawing shews my improvements applied to the construction
of rotating boiler which I prefer to employ for the above purpose. Fig. 1 is a side
elevation of the boiler, Fig. 2 is a part longitudinal section of the same to a larger
scale and Fig. 3 is a cross section.
The outer shell B of the boiler is of steel, made in several distinct lengths or
sections indicated by additional marks as B¹ B' each united to the next by what is
sometimes called a butt-joint; that is to say, the edge of one section abuts directly
against the edge of an adjacent section, and both sections are secured by rivetting,
brazing, welding or other efficient means to an enclosing ring B* of such width as
to lap sufficiently upon each section,

page_text: The inner shell M is of thick lead applied in distinct lengths or sections indicated
by additional marks as M' M² etc., united along their several edges.
The boiler is mainly cylindrical, but the ends are partially spheroidal terminating
in trunnions not represented, which are hollow and equipped with suitable stuffing
boxes and steam pipe connections lending from one or more boilers not shewn,
which supply steam at a high pressure.
D' D' are perforated pipes extending from the trunnions inward to points near
the centre of the boiler where their ends are each nearly closed by a perforated
plate. These pipes allow the steam received through the trunnions to be
introduced directly. into the contents of the boiler.
Manholes e properly reinforced and equipped with strongly secured covers allow
a man to enter the boiler, when required, to effect repairs. But my Invention
reduces the liability of the lead to require attention and in case of failure at any
point directs the workman to the point requiring attention.
The lead need not be pure; ordinary lead of commerce will suffice. I prefer
that the lead shall have a thickness of about one quarter of an inch.
From some cause, probably the difference in expansion and contraction between
-tho-lead-shell_and the outer shell, the lead shell is likely to fail after a period.
One steel-shell will outlast many lead-shells. When it is required to change the
lead shell it is cut out and removed through the manholes-or-trunnions without
difficulty. The introduction of the new shell requires some care but it can be
effected by rolling up the new lead and introducing it through the man-holes and
carefully unrolling and fitting to its place and joining the edges.
Between-the-lead-Mand the steel B' is a narrow space. The steel shell affords
the requisite strength for the entire structure-and the lead alone is presented to
contact with the contents of the boiler. As heretofore worked, the lead-lining of
-boilers is liable to failure by cracking so minutely as to be difficult of detection,
but a small quantity of fluid leaking from the interior of the boiler into the space-
between the lead lining and the steel induces great mischief.
When the lead lining is made, air will remain between the lead and the steel.
When the solution at a bigh temperature fills the lead lining, this air expands and
after one or two operations breaks the lead M. To avoid this, I provide a great
number of small orifices 6 through the steel plate to connect with the space between
the boiler and its lining which orifices let out the expanded air, as soon as the heat
rises inside the boilers, instead of breaking the lead.
The orifices b serve a double purpose. Sooner or later the lead boiler must
commence to give way by cracking; this cracking commences 50 minutely that
it is difficult to detect, and the solution or fluid which escapes through these
minute cracks would in a short time consume the steel. Steam penetrates easier
through these cracks than solution, consequently, when a crack in the lead under
the rotation is turned upward, the upper part of the boiler being filled with steam
the nearest orifice gives or throws out escaping steam and when turned down,
shews small drops of solution mixed with the dissolved parts of the wood. By
close observation of the orifices when steam from outside tho lead has shewn
itself, there is no difficulty in determining the whereabouts of the crack within
narrow limits.
If the steam is from the inside of the lead lining, it smells of the solution.
This it does not do if the escape results from moisture or air between lead and steel.
G are internal bracing rings, made each in two pieces and held distended by
wedges H, introduced at the joints. These bracing rings and wedges are made of
a composition such as brass, that will be unaffected by the solution and which will
have a greater expansion and contraction than iron. I take care to envelop each
with a thick covering of lead.
These internal bracing rings are arranged about three feet apart. They press
outwardly with sufficient force to support the weight of the upper portion of the
lead shell when the structure is empty and cold and press it firmly against the
interior of the iron or steel shell when it is filled and hot.

page_text: -
The apparatus will act best when the lead shell is made in a continuous band.
extending quite around the interior of the boiler, and of the proper width to reach
from one of the internal braces G to the next.
The wedges H which distend the internal braces G may be made of considerable
length and after being driven to set the braces tightly out against the inner face
of the lead, their ends should be smoothly cut off by any suitable cutting instrument.
It is important to leave no recesses to form a lodgement for the pulp as a retention
and reboiling of the pulp injures its color and mixing such with the next batch
will injure the whole.
The steam-pipes D¹ D³ are supported by brackets D* extended inward from the
internal braces G. The latter being made in sections can be easily removed
through the manholes and new ones introduced and brought to the proper positions
when required.
I provide each of the orifices b with a stop-cock b¹. Under ordinary conditions
theso cocks b¹ are all open and each is ready to discharge any fluid, whether hot air,
steam or solution which may seek to issue through the orifice b which it controls.
I is a sample cock controlling an orifice i made at a convenient point in the
boiler and through which small quantities of the contents of the boiler may be
drawn from time to time to examine its condition. The surfaces of the cock I
which are exposed to the solution are lead. The orifice i is reinforced by a bushing
of lead J having a head on the inner face and a head on the outer face. The cock
is secured by bolts tapped in holes in the steel shell B.
The apparatus acts as follows:-
As the boiler is rotated by mechanism not shewn, its contents are gently agitated.
The proper valves, not shewn, being operated steam at a sufficient pressure is
allowed to flow inward through the pipes D' D'. These pipes agitate the contents
of the boiler by being traversed through the same as the boiler slowly revolves and
deliver steam through orifices distributed along their whole length. Thus the heat
is delivered in the form of steam mingling directly with the contents of the boiler,
and imparting all the caloric thereto, rapidly raising the temperature of the boiler
until it is very nearly corresponding to that of the steam pressure employed.
The transfer of heat from tho steam to the contents of the boiler, results in the
production of considerable quantities of water due to the condensation of the
steam. It is therefore important at the commencement that the solution be strong,
though not stronger than from 4%, to 5 degrees Beaumé and not of sufficient
quantity to fill the boiler. As the work proceeds, the water added by the
condensation of the steam increases the volume and weakens the strength of the
fluid contents of the boiler. At the close of the operation, the boiler will be nearly
full.
By the ordinary method of treating wood with acid sulphite a large quantity of
sulphate forms and remains attached to the fibres of the pulp, which is practically
insoluble and adhering to the fibre, remains in the pulp. All known methods of
extracting it tend to darken the pulp and make it more difficult to bleach. I am
not confident as to the precise chemical reactions occurring but I have discovered
that the absence of highly heated surfaces reduces the evil. I believe the
production of sulphate depends on the existence of a higher temperature at some
points, higher than is necessary throughout the solution, and this will necessarily
occur when the heat has to be conveyed to the material through the metal of
steam pipes as was heretofore done. As by my method of heating by direct steam
any such heating of metal surfaces much above the mean temperature of the
solution is avoided, the above mentioned defect will be avoided. The steam pipes
are liberally perforated and allow a perfectly freo discharge of the steam. By the
above described means, I am enabled to produce a pulp, having, when dried, not
more than one per cent. of sulphate while ordinary methods produce pulp, holding
as high as 10 or 12 per cent. of the objectionable ingredient.
Lead is of such a nature that even with the care I take to give it expansion and
contraction, it is still shorter lived than the steel,

page_text: When a flaw occurs in any portion of the lead lining of sufficient magnitude to
induce a visible escape of steam from the nearest stop-cock b', the attendant marks
that stop cock and then closes all the stop cocks, thus preventing any serious loss
of the contents. As soon thereafter as practicable, a workman enters the boiler
and knowing, by the marked stop-cock, what part of the lead shell is defective,
solders or otherwise repairs the defect, introducing a new sheet of lead if required.
I have in my said Patent of Oct. 11th 1881 described a boiler having a portion
of each end occupied as steain space, with tubes connecting such spaces and in
which steam flowed from one chamber to another. Such apparatus imparted the
heat of the steam to the contents of the boiler only through the medium of the
metal of the tubes and of the tube sheets: A portion of the steam was necessarily
allowed to escape at the opposite end of the boiler, from that through which it was
received, in order to maintain the presence of steam on all the surfaces. My
present Invention, by introducing the steam directly imparts the heat of the steam
fully and effects the heating more rapidly and with less consumption of steam. It
also economises room by dispensing with the considerable steam spaces at each end
and by dispensing with a large proportion of the tube spaces.
It will be understood that the wood or analogous material to be treated,
previously made quite fine by mechanical means is introduced into the boiler with
the solution so as to fill the boiler-about-two-thirds full and then-it-is heated by
the direct application of steam to about 300° Fahr. or somewhat more-or-less and
rotated slowly from 10 to 15 hours. After being discharged from the boiler the
dissolved material may be removed by washing in a common rag engine. The
pulp-may-then be either made into paper directly by any ordinary or suitable
process, or it may be dried and stored or transported to-distant points.
Modifications may bé-made in the details without departing from the principle_
or sacrificing the advantages of the Invention.
Certain parts may be-used-without the whole. I can use the apparatus without
the stop cocks b', thus leaving the orifices b always open. I-can-inject direct steam
and effect thereby the efficient heating of the boiler, and with the economy of
space and the increase of fluid towards the close and the absence of sulphate due
to this mode of operation without the use of the independent lead shell. Or I can
use the latter without the direct steam. I can employ both without the bends in
the pipes providing other means for gently agitating the contents of the-boiler as
it revolves, or allowing the boiler to agitate by the simple friction of its smooth
inner surface. I prefer the whole as here shown.
The junctions of the edges of the lead plates to each other may be effected by
autogenous soldering, sometimes termed "burning "-I mean a partial melting of
the adjacent edges by a blow pipe flame or a very hot soldering iron or both, or by
other means of applying intense heat for a brief period along the line of junction.
This operation performed with proper skill will join the lead together and present
a continuous lead surface to the contents of the boiler.
The paper pulp produced in the above described boiler at a single operation, as
described, is substantially different from before known to me, in the fact that it
is not only relatively free from gypsum but it is more easily bleached and even
without bleaching it is of lighter color than any analogous product known to me.
It may be used for inany purposes requiring white or nearly white paper without
bleaching.
Having now particularly described and ascertained the nature of my Invention
and in what manner the same is to be performed, I declare that what I claim is :-
1. The method of treating wood and other vegetable fibre with direct steam
introduced into the boiler or vessel containing the fibro together with the lye or
solvent, substantially as and for the purposes herein set forth.
2. In iron or steel boilers or apparatus for treating wood or other vegetable
fibre the use of a loose lining of lead or other less corrodible metal held in position
by internal metal hoops or rings, so as to be free to expand and contract
independently of the outer shell of the boiler, substantially as herein described.

page_text: 3. In a boiler having an internal loose lining, the use of ventholes in the outer
shell of the boiler communicating with the spaco between it and the lining,
substantially as and for the purposes herein described.
4. In combination with the vent-holes in the outer shell of the boiler referred to
in the preceding claim, the use of stop cocks for closing the said holes substantially
as and for the purposes herein described.
5. The use in combination with a boiler for treating wood or other fibre with
solvents of internal perforated steam pipes such as D'Ds for the direct admission
of steam among the contents of the boiler substantially as herein described.
6. The use, in combination with the loose internal lining of a boiler, of bracing
rings G formed in two or more pieces and distended so as to hold the lining by
means of wedges such as H, substantially as herein described.
7. The use, in combination with a lead lined boiler for treating wood and other
fibre of a sample cock I, presenting only lead surfaces to the fluid, the hole in the
shell leading into which cock is protected by a lead bushing J.