An Improved Furnace for Recovering in an Inodorous Manner the Salts Contained in the Lyes Used in the Manufacture of Wood-fibre.
Year: 1887

page_text: Date of Application, 28th Mar., 1887.
Specification Accepted, 29th Apr., 1887.
An Improved Furnace for Recovering in an Inodorous Manner
the Salts Contained in the Lyes Used in the Manufacture of
Wood-fibre.
I CARL FERDINAND DAHL, of 10 Langenmarkt, Danzig, Prussia, Engineer,
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:-
The aqueous alcaline lyes resulting from the manufacture of wood fibre contain the
incrusting substances of the wood, straw, fibres of alfa or other vegetable substances,
from which the cellulose has been abstracted by boiling with caustic soda. In order
to recover the precious salts contained in the lyes in as pure a condition as possible
the lyes are inspissated and the incrusting substances destroyed by a melting process,
in which the alkalis result in the form of melted salts, and are introduced again in
this form into the circle of manufacture. In the said melting process the incrusting
substances are removed in the form of imperfectly burnt or smouldering gases
("Schuelgase") which cannot he led away through chimneys into the open air on
account of their piercing bad odour and of their other offensive properties which must
entirely be destroyed. There is already a danger, that such smouldering gases will
be produced during the inspissation, and this can be avoided only by special
arrangements.
This invention has for its object to prevent the production of the smouldering gases
during the inspissation of the lyes to destroy the gases produced by the melting pro-
cess, and in general to avoid entirely all the inconveniences hitherto inet with in the
recovering of alcalis. I attain this purpose by a particular process of evaporation
and by the complete combustion of the smouldering gases in such a manner that the
combustion gases which are thus obtained are free from bad odours, and are used for
evaporating the lyes.
Referring to the accompanying four sheets of drawings showing the construction
of the furnace. I will now describe the process which takes place in the furnace.
The recovery of the salts contained in the lyes takes place in three stages and the
operations effected during these processes are the following.
1. The evaporation of the water in kettles, boilers, pans and the like, until the lyes

page_text: are concentrated to from 35 to 40° Bé, the fire gases being led to the lye in the
counter-currentin such a manner that first the gases escaping into the flue and which
have been cooled to about 150° C., come directly in contact with the concentrated
lyc.
2. The inspissation of the concentrated lyes to the consistency of mud in a fire-
proof vat by an open fire, so that the smouldering gases which are produced, flow at
a right angle into an auxiliary fire arranged beside the vat and are thus intimately
mixed with heated air and completely burnt, whereupon they are led underneath the
boiler.
3. The reduction into gas of the incrusting substances, in melting down the salts in
a retort shaped furnace which is connected with the inspissating vat in such a manner
that the gases mixed with previously heated air enter into the main fire of the vat,
are then burnt, and aid in this way the inspissation of the lye.
The evaporation of the water begins in the steam kettles A and A (see figures 1, 4,
7, 8 and 11). These two kettles (which are constructed and completely fitted accord-
ing to legal requirements) are each divided by two partitions d d¹ (fig. 1) into three
compartments abc; these partitions & are of such a height that the
in the first two compartments may enter without being throttled into the third com-
vapour produced
partment and then into the dome. The raw weak lye is forced into the compartmet c.
As the combustion gases arriving from-the vat and the secondary fire strike first against
these compartments of the kettles, the plates e (figs. 1 and 11) are hung concentrically
to the casing of the kettles in these compartments in order to prevent the salts from
burning and attaching themselves to the bottoms of the kettles, as an extremely quick
circulation of the weak lye is thereby produced along the hottest place of the shell
the kettles, as shown by the arrow in Fig. 11; the formation of incrustations
will entirely be prevented by this simple means, especially at this most dangerous
place.
The steam kettles are placed in a postion which is a little inclined forward, so that,
the larger the quantity of water lost by the lye, the larger will be the quantity of lye
gathered in the compartment c on the partition of the compartment b, and on the
bottom, owing to the greater specific weight of. the lye. This heavier lye passes
through a pipe arranged in the partition d into the compartment b, where the
evaporation of the water is continued; the lye, the weight of which has still increased
and which is accumulated on the bottom, passes through the pipe finto the
compartment a, where the lye remains until it has obtained a certain degree of
thickness.
The difference of this thickness depends on the composition of the lyes; the
degree to which the lye is evaporated in the kettles is previously determined by
examination.
These kettles must naturally frequently be cleaned; to facilitate this operation the
front wall of the same is provided with a man-hole, and corresponding therewith two
man-holes are also cut into the partitions & d; these holes are closed during the
working of the apparatus by means of plates which are fixed to the partitions d by
sash fasteners.
To withdraw the lye from the three compartments of the kettles at once, for cleaning
the latter, or for any other purpose, I arranged in the compartment a, as well as in
the compartments b and c near the partitions d, d', blow off pipes.
The pressure in the kettles is kept at a low degree and a pressure of one kilogram
above the atmospheric pressure will be sufficient to blow-off the lye. The vapour
produced in the kettles is freed in the domes from any lye that may still adhere
thereto; for this purpose two perforated plates are arranged in the dome one over the
other (see figure 1), which are both covered with a layer of iron shavings whereby
all the foreign parts will be retained when the vapor passes through the said
layer.
The pure water vapor is employed either for caustifying the fresh lye or for drying 5
purposes and for further evaporating the lye withdrawn from the kettles.

page_text: The lye inspissated in the kettles is withdrawn at certain intervals from the com-
partment a by means of the blow-off-pipes g and g' (figs. 1, 7 and 10) in quantities of
about 250 liters and conveyed through the pipe (fig. 7) into the boiler B. This
boiler (figs. 1, 3, and 7) consists of a vessel which is made of wrought iron and pro-
vided with a conical neck and an upright tube by which the vapour produced by the
evaporation of the lye passes through the roof into the open air. To prevent the
formation of smouldering gas the evaporation is carried out entirely without any
pressure.
The heating in the boiler is effectuated by the vapour produced in the kettle in
evaporating the lye; this vapour flows through a serpentine or worm, the arrange-
ment of which is shown in the figures 1 and 3. Under normal conditions 30 per
cent. of water is abstracted from the raw lyc, and in the boiler the lye further loses
23 per cent. of its original weight. From the boiler 13 the lye is drawn off into the
uppermost of the 4 open evaporating pans C.
0
These 4 pans (fig. I and fig. 3) are open flat vessels made of wrought iron and
having shovel shaped bent up ends; they are walled in behind the ketiles and below
the boiler and placed in an alternating way one over the other in such a manner, that
the fire-gases, which have circulated round the kettles in the direction of the arrow
(figs. I and 8) pass over the upper pan in the direction of the arrow and flow in their
way to the chimney over the surface of the lower pan and at the same time along the
bottom of the upper pan. In their way along the kettles the gases are by means of
suitable draught regulating devices cooled as much as is generally possible during the
working, that is to say to about 150° C in consequence of the principle of the counter
currents and owing to the circumstance that by the smokeless gases the walls of the
kettles are always free from flying ashes and remain consequently highly capable of
transmitting heat. At the aforesaid temperature the fire-gases may directly come in
contact with the lye without causing the formation of smouldering gases from the
same. The walling in of these pans offers the great advantage that the gases arriving
from the kettles, which otherwise would escape, without being utilized, into the
chimney, abstract by the direct contact from the inspissated lye still further 15 per
cent. of its original content of water. The inspissating-process of the lye in the pans
can be observed from the rear front of the furnace through working holes which
ordinarily are closed by doors (figs. 1, 9) and through which the pans may easily be
cleaned. Owing to the particular arrangement of the four pans one above the other,
the lye passes from one pan always into the pan beneath and is finally introduced
from the lowest pan through the pipe D, which can be closed by means of a cock, into
the inspissating vat, which must therefore lie at a sufficient distance below
the last pan, so that the lye which is already thickly liquid, may easily flow
down. The flat form of the pan is necessary as in deeper pans the salts will
easily be fixed on the bottom so that no heat can pass through the same, while the
shape of the pans, shown in the drawing and bent up on the ends is particularly
advantageous for cleaning the pans from the outside and also for the flowing over of
the lyes. The inspissating vat E (figs. 1, 2, 4) consists of a flat vaulted box made of
brick-work and lined with refractory material in which the lye stands almost up to
the fire bridge. The fire place F which is provided with a plane grate, serves to
produce the fame which is introduced by natural draught into the vat and passes,
guided by the low vaulted ceiling of the box, closely over the lye, whereby a further
quantity of water will be evaporated. But as the incrusting substances contained in
the lye also begin to be decomposed under the open flame and to develope large
quantities of smouldering gases which must be prevented from escaping; a second
fire place G (figs. 1, 3, and 11) having also a plane grate, is arranged on the wall of
the inspissating vat which is opposite to the fire-place F. The grate of this fire-place (+
is arranged at such a depth that a free flame will already exist where the mixture of
smouldering and fire gases enter into the vat. The gas-mixture arriving from the
vat enters at a right angle into the flame of the fire place G and will surely burn if a
sufficient quantity of air be introduced, and this air is added to the gas mixture already
in the vat.

page_text: To preserve the walls of the inspissating vat as long as possible notwithstanding
the high degree of heat, the refractory walls are cooled from the outside by arranging
therein intermediate spaces H, (air channels see fig. 1) which are to be considered
as generators. These intermediate spaces communicate on one side with the open air
and discharge on the other side at H₁ from the ceiling into the fire place F and
at Hthrough into the partition between the vat and the auxiliary fire place.
As the air in these intermediate spaces is highly heated, the cold air will energetically
push in from without; there will consequently be in the vat so large a surplus of
heated air in the gases that at the entrance of the smoulding gases into the flame
of the fire place a complete combustion of the said gases will take place, so that
not only all the stinking substances will certainly be destroyed but the whole quantity
of heat contained in the carbon of the smouldering gases will be utilized for the
evaporation in the kettles. There is but one condition, namely, that the mixture of
the gases does not contain a large quantity of water vapour.
Through the doors J, (figs. 2, 4, 7) which are inscried in the longitudinal wall of
the yat, the lye is continuously stirred up during the inspissation; whereby the
dephlegmation of the lye and the development of the smouldering gases is enlivened.
When the lye has attained the consistency of a viscid mud, the fire of F is reduced
and the lye is pushed or rabbled into the tightly closed box K which is placed before
the vat. The side doors J of the vat are of particular construction. To prevent
noxious gases escaping from the furnace and entering into the building when stirring
up the lye and in rabbling the same, the door is opened only for a moment when the
rabbles are introduced or withdrawn. During the working, the door is closed and the
handle of the rabble or rake is moved in a small indentation in the door, while
the workman may look into the vat through an inspection hole. The bottom of the
closure J communicates through the pipes (fig. 1) with the box K so that the
mud can be introduced into the box without opening for that purpose the doors of
the closure.
The hot inspissated mud of the lye still continuously develops smouldering gases
which are led through a pipe from the box underneath the grate of the fire-place F
and carried away into the flame by the air, which flows in. When the mud is cooled,
the cover of the box, which has hitherto been tightly closed, is opened and the lye
having now the consistency of molten asphaltum is tapped off by means of spades
and thrown through the working holes M into the melting furnace, which is arranged
beside the inspissating vat and separated from the same by the fire-place F (see figs. 2
and 7).
The bottom of the furnace L which is also made of refractory material and which
has the form of a retort, is constructed in such a way that it inclines from all points
towards the orifice of exit for the recovered salts. The ceiling is vaulted over the
furnace and as low as possible (see figs. 1, 5 and 6). On the small wall of the retort,
opposite to the inspissating vat on the fore-front of the furnace is the fire place N
of the melting furnace, beside and above the orifice for the salts; the flame of this
fire place is compelled by the construction of the fire place to flow from the orifice
through the whole furnace and the working is a continuous one, while the melting lye
slipping down on the sloping bottom is always replaced by other lumps of mud
subsequently thrown into the furnace.
In inclting down these lumps the last rest of water (12%) is evaporated by the
flame and the incrusting substances which detach from the melting salts are
completely reduced into gas, as the muddy mass slides from all points of the furnace
towards the orifice which is the hottest place of the furnace. The salt freed from the
incrusting substances flows out continuously. To destroy with certainty the large
quantities of smouldering gases which are here produced, and to utilize in the furnace
itself the considerable quantity of latent heat which is therein, the gases are led from
the melting furnace into the fire place F of the inspissating vat. As the combustion
would not immediately take place for want of air it is necessary to previously supply
the smouldering gases with the air necessary for their combustion; this is effectuated
in the same manner as shown in the inspissating vat. The wall between the fire-

page_text: place F and the melting furnace encloses an air-channel communicating by an air-
shaft arranged beneath the furnace with the atmosphere (see figs. 1, 5, 6). The air
channel O discharges laterally and from below in several holes into the opening PP
which puts the melting furnace in communication with the fire-place F (figs. 1 and 2).
The air passing through this channel and highly heated by the hot masonry in escaping
from the air-channel meets directly the smouldering gases whereby a whirl is produced
which intimately mixes the gas and air; this hot mixture flows into the fire-place
where it burns immediately without smoke when the air supply is sufficient.
The circulation of the fire gases in the furnace is generally as follows. The flame
of the fire place of the melting furnace produces a large quantity of smouldering
gases by the volatilization of the incrusting substances; in the burner P, these gases
are sufficiently mixed with air to be consuined immediately after their entrance into
the fire-place F. All these fire-gases pass through the inspissating vat and take off
from the lye which is therein, a large quantity of smouldering gases; the gases mix
then with the introduced previously heated air and escape from the inspissating vat
at a right angle into the open flame of the auxiliary fire-place G. There is in
consequence of the introduced hot air such a surplus of oxygen in the gas mixture,
that a complete combustion will take place; the hot smokeless gases now pass
underneath the kettles, flow simultaneously below and along the two kettles from the
rear to the fore end divide here in returning on the exterior sides of the boiler (figs. 1
and 8) and pass together over the pans C. Although on account of the large heating
surface which the steam kettles offer in consequence of the arrangement of the
same, and of the quality of the gases, heat has been withdrawn from the fire-gases in
a larger quantity than can be ordinarily obtained in steam boilers yet the pans fake
off from the gases, which have 150° of heat, and strike against the first pan, such a
quantity of heat, that the gases escape into the chimney with a temperature which is
absolutely necessary to maintain a sufficiently powerful draught in the furnace. In
comparison with the hitherto used systems of recovering salts in retort-furnaces, this
new method offers, apart from the complete inodorous working of the furnaces,
considerable economy of combustibles by utilizing the fire gases to an extent never
hitherto attained.
•
In the above described normal process the evaporation of the lye and the mud in
the several stations takes place as follows:-
Kettles 30% boiler 23% Pan 15% Inspissating vat 20% Melting furnace 12%.
Alterations in the strength of the lye and modifications in the attendance of the
several apparatus have however a certain influence on the intensity of the evaporation.
In the case of lyes originally particularly strong or which contain larger
quantities of turpentine or sulphide of sodium, the above described process must he
somewhat modified and the inspissation in the steam kettles must be suppressed.
Such lyes would develop in steam kettles a large quantity of smouldering gases which
would escape, when forced into the boiler, through the upright tube into the open air
and produce a pernicious effect.
These lyes are worked in such a manner that the inspissating process begins in the
boiler in charging the steam-kettle with pure water and in utilizing otherwise in the
workshop the large excess of water vapor resulting therefrom. Or the ketiles may
be supplied with weak wash lyes, having only about 3° Be and which are in this way
duly concentrated without particular expense being caused by the inspissation.
A main condition in the whole device is the regular course of the evaporation in the
kettles, boilers, and vats. During this first part of the process at least two thirds of
the quantity of water must be abstracted from the lye which according to the above
explanations will take place under normal conditions. If too aqueous lyes are
introduced into the inspissating vat, the produced mixture of fire, smouldering gases
and previously heated air would absorb so large a quantity of water vapor that the
auxiliary fire would not be able to effectuate a complete combustion, so that smoulder-
ing gases would escape into the open air.
The introduction of this evaporation, which allows of the entrance into the

page_text: inspissating vat of only weakly aqueous lyes is an advantage of the new system, which
causes the excellent working of the furnace.
The small production of water-vapor in the vat does not prevent the combustion of
the smouldering gases and the furnace, apart from its other advantages, is for these
reasons, of great importance with respect to hygiene, as the absence of any bad smell
is of the utmost importance for the whole cellulose industry.
Having now particularly described and ascertained the nature of my said invention
and in what manner the same is to be performed, I declare that what I claim is :
In order to recover the salts contained in the lyes which are used in the manufacturo
of cellulose
1. The construction of a furnace in which in an inodorous manner the greatest
quantity of water is first abstracted from the weak lye in steam kettles, boilers, and
pans, so that in the succeeding evaporation of the inspissated lye by means of open
fires the smouldering gases which are produced by the reduction into gas of the
incrusting substances, have attained such a degree of dryness that after addition of
previously heated air they are completely burnt by an auxiliary fire and in this way
not only completely destroyed but also utilized in the furnace for heating purposes.
2. In the aforesaid furnace for dephlegmating the raw lye in an inodorous manner,
the arrangement of two steam kettles which are divided, by partitions extending into
the vapor chamber, into several compartments; owing to the inclined position of the
kettles the weak lye introduced into the highest compartment moves through pipes
arranged in the partitions, by its increasing specific weight continuously forward, and
is forced, after a further abstraction of about one third of the amount of water con-
tained in the lye, from the kettles into an open wrought iron boiler, in which a further
considerable abstraction of the water contained in the lye is effected by the vapor in
tension produced by the proper evaporation of the lye, this vapor being led from the
boilers into the heating worm of the boiler.
3. For further concentration of the lye, the application of several flat wrought iron
inspissating vats, which in their two extremities are bent up like shovels, and are
arranged in the furnace underneath the boiling apparatus one above the other, in an
alternating manner, so that the lye discharged from the boiler flows into the upper
pan and from thence into the lower one, and so on, while the fire gases which have
already been cooled on the kettles come in direct contact with the lye, in such a way,
that arriving from the kettles they pass over the first pan and flow then, on their
further way from above downwards, between the surface of a lower pan and the
bottom of the upper pan for the purpose of utilizing the fuel as completely as
possible.
4. To inspissate the viscid lye; the arrangement of a fire proof vat having on each
end a fire place, one of which serves to inspissate the strongly concentrated lye and
the other to burn the nitrogen and the smouldering gas produced by the inspissation,
so that the fire gases of the inspissating fire and the gases of the vat incet the
flame of the auxiliary fire at a right angle, while heated air is introduced through the
vault of the fire bridge and the side walls.
5. A reservoir for receiving the mud of the lye, consisting of a receiver which can
be closed by means of a detachable cover, and into which the lye, inspissated to the
consistency of mud, is discharged from the vat by means of rakes; the said receiver
being provided with a lateral tube for leading the smouldering gases underneath the
grate of the inspissating fire-place.
6. An aperture putting the receiver in communication with the inspissating vat by
means of a slide and closing the vat on the outside by a flap, which may be turned
upwards and hang down in a sloping direction, the flap being provided with a hole or
passage for the handle of the rake so that in withdrawing the stinking mud of the lye
neither cold air can enter into the vat nor gases escape into the atmosphere.

page_text: 7. For recovering salts from the mud of the lye, the arrangement of a fire proof
rotort (melting furnace), the sole of which inclines from all points towards the exit for
the recovered salts and in which the melting of the mud is effected by means of a fire-
place arranged beside the said exit, and the flame of which is directed downwards
from the vaults upon the lye, so that the latter will completely be melted and conse-
quently the incrusting substances which are freed by the melting process, will entirely
he reduced into gas; the produced smouldering gases are then utilized, and for that
purpose the retort is set in the furnace, in such a manner, that the gases escaping from
the retort meet the air heated in the hollow walls of the furnace and are then led into
the inspissating fire of the vat to be burnt and utilized in the inspissation of the
concentrated lyc.