An Improvement in the Treatment of Vegetable Fibre for Pulp Manufacture.
Year: 1891

page_text: Date of Application, 19th Aug., 1891-Accepted, 19th Sept., 1891
COMPLETE SPECIFICATION.
An Improvement in the Treatment of Vegetable Fibre for Pulp
Manufacture.
I, JOHN DAVIS TOMPKINS, of Brainard, in the County of Rennsselaer, State of
New York, 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 has heretofore been the practice to subject fibrous material from which paper
pulp is made to the successive action of various liquids within a closed vessel or
digester, and, while it is thus enclosed, to bring those liquids into intimate contact
with the material by spraying them in a downward direction thereon, or by
agitating the mass of material and liquids together, as by rotation of the
digester.
Both methods have been found in practice to be open to objection, the first, by
reason of the fact that the downwardly directed streams of liquid serve to pack the
material upon the bottom diaphragin of the digester, the effect of which is to cause
the material to act as a strainer or filtering mass, to gather the lignine, and other
substances picked up by the treating liquors, upon the top of the mass, and to
render the action of the liquids on the material uneven.
Thus when the mass is packed upon the bottom of the digester, its upper portion
must necessarily be much more affected than the lower portion, and hence, the
material is fully acted upon in one portion, partially acted upon in another portion,
and very little acted upon at the lowest part of the mass.
Again, agitation of the material and the liquids by rotation or other movement
of the digester tends, in a measure, to break up and destroy the fibrous character
of the pulp material thus acted on.
The object of my invention is to treat the material in a closed digester, and in
such a manner that no packing of the material will occur, the fibre is not injured,
the adventitious materials are separated therefrom, and all of the material is
brought into the best possible position to be evenly and effectively acted upon. I
accomplish this in the manner which I shall now describe.
Most of the materials from which paper pulp is made are of a lower specific
gravity than water, and hence tend to float in water or in the liquids commonly
employed to treat them. They also absorb the liquids in which they are immersed
and when thoroughly soaked, sink towards the bottom of the vessel in which they
are placed.
In practice, it has been found that if the materials can be kept in a suspended
condition in the treating liquid, they are most thoroughly and effectively acted upon,
and also that the strength of the treating liquid and the time required for treatment
may be materially reduced.
My improved method of treatment is based upon the theory that the material
from which the pulp is to be made should be suspended in the treating liquid while
in the digester and while thus suspended, subjected to the heating, cleansing or
chemical action of the suspending liquid.
In order to carry my improved process into practice, I have found it convenient
to make use of an apparatus which I shall now describe referring to the accom-
panying drawing, which is a vertical section of a digester with the tanks, pipes
pump etc. used in connection therewith shewn in elevation.
A is the casing or shell, preferably made of boiler plate of any convenient shape
or size. The interior of the shell may be lined with any acid resisting material
which will not be affected by the action of any of the chemical liquids used in the
digester. Central within the shell is the digesting chamber A¹ and at each end are

page_text: the chambers C, C³, separated from the digesting chamber by perforated walls or
diaphragms B B'. In the top of the digester is a manhole D, provided with a
closing plate d, through which the material to be treated may be introduced.
In the bottom of the shell, and connected with the digesting chamber is a
discharge pipe E, provided with a valve e, through which the treated material may
be withdrawn.
The chambers C and C¹ are connected together through the pipes F, F¹, and in
the lower part of the pipes F, F' outside of the shell, is interposed a pump G
adapted to deliver the liquid therefrom into the chamber C. Connected to the
eduction pipe F¹ and the purip is a pipe F3 which is connected with the upper
chamber C.
Normally the pump G draws its supply of liquid from the upper chamber C by
the pipe F, delivering it into the lower chamber C¹, but, by closing the valve i in
the pipe F, and opening the valves and 3, the pump draws its supply of liquid
from the lower chamber C¹ and delivers it into the upper chamber C.
The pipe F is the pipe through which the treating liquids are introduced into the
digester and norinally caused to circulate therein. These liquids are stored in
tanks which are connected to the pipe F by pipes H, I, J K, provided with the
valves h.
Obviously, instead of separate pipes, a flexible pipe with union may be connected
to any of the tanks. O is a steam pipe connected through the branch pipes 0' 0³
and valves n to the chambers C and C¹.
A waste steam pipe P connects the upper chamber C with any suitable water
tank or condenser. A similar pipe Q connects the upper chamber C with a tank
in which the bleaching gases may be stored.
L is a valve leading from the lower chamber C¹ through which the liquids may
be drawn off. T is a tester of the usual form connected to the side of the digesting
chamber, and V an air valve in the top of the chamber C.
The material to be treated is introduced through the man hole D, at the same
time the pump G is started, drawing the preliminary treating liquid from the tank
in which it is stored, through the pipe H, and delivering it into the chamber C¹, and
from thence in an upward direction through the perforations of the diaphragm B₁
the sum of the areas of which is made preferably somewhat less than the area of
the inlet pipe, so as to impart a certain velocity to the upwardly directed streams
of liquid transmitted through the perforations. These streams are projected against
the material as it is introduced into the digesting chamber, so as to spray the
material from below, as it falls. When sufficient quantity of material and liquid
have been introduced into the chamber, the valve in the pipe H is closed and the
pump G draws the liquid from the top chamber C and introduces it into the
lower chamber, from whence it is sprayed upward against the mass of material
in the digester, which, becoming soaked, tends to gravitate towards the lower
diaphragm B'.
The effect of the upwardly directed streams of liquid impelled from the pump
through the diaphragm is to overcome the gravity of the particles of material and
to hold them, so to speak, in suspension in the treating liquid.
As it is my purpose to keep the material in suspension in the treating liquid the
direction of flow or circulation of the treating liquid is always from below upward.
Sometimes, when treating certain classes of material, the light, feathery portions
tend to be carried upwards and to lodge against the surface of the diaphragm B,
impeding the circulation; in order to overcome this difficulty, I have arranged the
pump G and the communicating pipes, so that the direction of circulation of the
liquid within the digester can be reversed, the liquid being drawn from the lower
chamber C and delivered into the upper chamber C, and thence through the
diaphragm B in a downward direction upon the material, thus clearing the
diaphragm B from adhering particles of material. The reversed direction of
the circulator is continued only for the time necessary to clear the diaphragm.
I do not limit myself to any series of successive steps constituting a treating

page_text: process, as the steps may be varied and the treating liquid used of a different
character without departing from the nature of my invention. Usually, however,
I first subject the material to the action of highly heated water, which water may
be heated externally or may be heated within the digester by steam introduced by
the steam pipes 0 0¹ 0².
I prefer that the preliminary cooking of the material should be accomplished
with the temperature of the liquid below the boiling point, so as not to set the color
in the material and to effect the solution of the greater portion of the soluble
ingredients. After the preliminary cooking, which may be continued for from one
to four hours as required, the material may be washed and rinsed with one or with
several waters. After this cooking and washing, the material is treated to a second
cooking with any liquid of an alkaline character, as for instance a solution of caustic
potash or soda, suitable to the material acted upon. The character of the treating
liquids is so well understood that I do not consider it necessary to enter into any
specific description thereof.
The alkaline liquors may be heated by steam within the digester and the cooking
may be continued for from one to seven hours, as required. After the alkaline
cooking, the material is again washed and rinsed and its condition ascertained
through the tester T. The next step is the bleaching process of ordinary kind.
After the bleaching, any gases may be drawn off through the pipe Q and
discharged into any suitable receptacle. The material after being again washed
and rinsed is discharged through the pipe E.
In the cooking treatment with water and alkali and in the washing and rinsing
operations, the soluble ingredients of the material are taken up by the circulating
liquids, which thus have their specific gravity increased. In the treatment of pulp
material, as heretofore practised, the liquids being circulated downwardly, the
material becomes packed in the lower portion of the digester and the top portion
of the mass operated as a strainer to extract the thickened matters from the liquids,
so that all the gummy portion of the dissolved substances is deposited in the upper-
most portion of the compacted mass and this necessitated the transfer of the material
to a special washing machine after its removal from the digester.
My improved method of treatment differs in that all the substances extracted
from the pulp material are strained out at the lower side of the mass to which, by
their gravity, they naturally tend, and from which they can be removed through
the waste pipe L, or main discharge pipe E, before removal of the body of the
material treated.
I do not limit myself to the particular construction of digester or pipe circuits
shewn, as these may obviously be varied without departing from the nature of my
invention. The apparatus shewn and described is, however, that which I consider
best adapted to carry my invention into effect.
Having now particularly described and ascertained the nature of my said inven-
tion and in what manner the same is to be performed, I declare that what I
claim is :-
The herein described treatment of fibrous materials for their conversion into pulp
by suspending them in a constantly rising current of the treating liquids and
subjecting them while thus suspended to the heating, cleansing, and chemical action
of the suspending liquid.
Dated thin 10th day of s1001
ABEL & IMRAY,
Agents for the Applicant.