Improvements in and in Apparatus for the Decomposition of Alkaline Nitrates.
Year: 1895

page_text: Date of Application, 9th Apr., 1895
Complete Specification Left, 6th Feb., 1896-Accepted, 7th Mar., 1896
PROVISIONAL SPECIFICATION.
Improvements in and in Apparatus for the Decomposition of
Alkaline Nitrates.
We, HENRY KENNETT BAYNES, Gentleman, and THE CHEMICAL AND
ELECTROLYTIC SYNDICATE, LIMITED, both of 6, Clements Lane, Lombard
Street, in the City of London, do hereby declare the nature of this invention to
be as follows:-
This invention relates to the process of decomposing alkaline nitrate for the
production of nitric acid and caustic alkali, or as an incidental step in making
chlorine for the purpose of recovering the nitric acid used in the process and
obtaining caustic alkali as a by-product.
In either case, the decomposition of the alkaline nitrate is effected by subjecting
the nitrate, in intimate admixture with ferric oxide, to heat in such manner as to
produce a copions evolution of nitrous fumes in the presence of heated air, or
heated air and steam, and form an alkaline ferrite convertible into ferric oxide and
caustic alkali.
It has, heretofore, been endeavoured to effect the decomposition of the nitrate
by subjecting the mixture to the action of heat, not only externally but also
But all
internally, by blowing heated air, or air and steam, through the mass.
attempts to so furnace the mixture of nitrate and oxide in the mass have resulted
in the fluxing of the greater part of the nitrate which accumulates at the lower
part of the retort to such an extent as to render the mixture non-homogeneous
and, for the greater part, impermeable to the heated current, thus rendering the
reaction very partial and incomplete and, therefore, impracticable on a commercial
scale.
The present invention consists of a continuously acting method and apparatus
whereby every individual particle of the mixture is exposed on all sides to
repeatedly renewed contact with heated surfaces, so that all clogging or massing
of the mixture is prevented and the reaction is rendered most perfect and
complete, so as to obtain the greatest possible evolution of nitrous fumes. The
furnacing of the mixture (formed by grinding together the nitrate and ferric
oxide) is effected by subjecting the mixture, not in the mass, as heretofore, but in
a loose pulverulent condition, in a continuous stream of small quantities at a time,
maintained continuously or intermittently in a state of motion, to frequently
repeated contact with the heated surfaces of the retort from which the adherent
particles are as frequently removed, so as to ensure as many points of contact as
possible of every individual particle with the licated surfaces of the retort, the
product of the decomposition being removed as fast as the reaction proceeds,
so as to be prevented from interfering mechanically with the portions still
undecomposed.
The operation is preferably performed in an externally-heated, slowly-revolving,
retort provided with internal ribs or projections to raise the particles in its
revolution and allow them to fall into contact with fresh surfaces, the retort being
set at a slight angle from the horizontal so as to cause the particles to travel
slowly through the retort by repeatedly falling, as above mentioned, the detachment

page_text: and showering down of the adhering particles being effected by the effect of inter-
mittent jarring or shock produced by the blows of a hammer which is periodically
raised and allowed to fall on the retort in its revolution. An Archimedean screw
conveyor, or other means, would be provided for feeding in the mixture at the
upper end of the retort at a rate commensurate with the rate of progress through
the retort, and means are provided for drawing off the nitrous fumes as they are
evolved, admitting air for conveying the fumes and supplying oxygen, and of
admitting steam, the fumes being recovered as commercial nitric acid by means
of the usual washing and condensing or concentrating apparatus. The product of
the decomposition is discharged from the retort in a pulverulent state into a
suitable closed receiver, and if the decomposition is not completed by a single
passage through the retort the product may be reground aud again subjected to
the operation, the ultimate product of complete decomposition being an alkaline
ferrite which is subsequently decomposed by heating it with water whereby ferric
oxide is precipitated for use over again whilst the alkaline base enters into solution
and is recovered as caustic alkali by evaporation in the ordinary way.
Dated a
1
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.
BET DIE DIEUIFICATION.
Improvements in and in Apparatus for the Decomposition of
Alkaline Nitrates.
We, HENRY KENNETT BAYNES, Gentleman, and THE CHEMICAL AND
ELECTROLYTIC SYNDICATE LIMITED, both of 6, Clements Lane, Lombard
Street, in the City of London, 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 :--
This invention relates to the process of decomposing alkaline nitrate either for
the purpose of producing nitric acid and caustic alkali, or for the purpose of
recovering the nitric acid used to form alkaline nitrate in the process of making
chlorine and obtaining caustic alkali as a by-product which was described in the
Specification of previous Letters Patent dated the 21st day of May 1891; No. 8692.
The decomposition is in auy case effected by subjecting the nitrate in intimate
admixture with ferric oxide, to heat in such manner as to produce a copious
evolution of nitrous fumes and form an alkaline ferrite convertible into ferric oxide
and caustic alkali.
It has heretofore been endeavoured to effect the decomposition of the nitrate by
subjecting the mixture to the action of heat not only externally but also internally
by blowing heated air, or air and steam through the mass. But all attempts to sɔ
furnace the mixture of nitrate and oxide in the mass in a stationary retort have
resulted in the fluxing of the greater part of the nitrate which by accumulating in
the fluxed condition at the lower part of the retort renders the mixture non-
homogeneous, and, for the greater part, impermeable to the heated current, thus
rendering the reaction very partial and incomplete, and, therefore, impracticable
on a commercial scale. Not only is the reaction incomplete when it is attempted
to treat the mixture in the mass, but even if it were treated in a comparatively
small quantity and kept constantly in motion by raking or by turning over in a
revolving horizontal retort, the undecomposed particles would gradually become
more and more isolated by the solid products resulting from the reaction of the
particles which have been most exposed to the heat and therefore less and less
acted on so that the progress of the reaction becomes more and more retarded and
therefore more and more difficult to carry to completion.

page_text: The present invention consists of a continuously acting method and apparatus
whereby every individual particle of the mixture is exposed on all sides to
repeatedly renewed contact with heated surfaces so that all clogging or massing of
the mixture is avoided and the solid products of the decomposition are carried
away and thus prevented from hampering the reaction of the undecomposed
particles and thus the reaction is rendered most perfect and complete, and is
accompanied by the greatest possible evolution of nitrous fumes. The furnacing
of the intimate mixture of finely divided ferric oxide and alkaline nitrate is effected
by subjecting the mixture in a loose pulverulent condition and in small quantities
to frequently repeated contact with the surface of the retort which is maintained
at a red heat the particles adhering to the retort being detached at each transfer
from one hot surface to another and the solid product of the decomposition being
removed from the zone of action and discharged as the reaction proceeds, so
that it cannot interfere mechanically with the reaction of the portions still
undecomposed.
The operation is preferably performed in a cast iron retort such as represented
in the accompanying drawings, forming part of this Specification, wherein
Figure 1 is a longitudinal elevation of the retort and furnace, partly broken
away to shew the interior, and
Figure 2 is a cross section of the retort.
Figures 3 and 4 are detail sections shewing a modification.
The retort A is heated to a cherry-red heat by a furnace within which it is
revolved, the retort being provided internally with longitudinal ribs or projections C
to raise the particles in its revolution and allow them to fall so as to bring them
repeatedly into contact with fresh surfaces, the retort being slightly inclined from
the horizontal so as to cause the particles to travel slowly through the retort by
repeatedly falling to and fro across the retort, as above mentioned. The retort is
mounted upon roller bearings D arranged externally of the furnace and it is driven
by spur or other suitable gear E and supported against end thrust by rollers F.
The forcible detachment and showering down of those particles which by partial
fluxing become liable to adhere to the sides of the retort, is brought about by the
effect of intermittent jarring or shock produced by the blows of hammers H which
are periodically raised by wipers h turning with the retort and allowed to fall on
the retort in its revolution, two hammers actuated alternately by two sets of wipers
being employed. An Archimedean screw conveyor G receives the mixture from a
hopper and feeds it into the upper end of the retort at a rate commensurate with
the rate of progress of the mixture through the retort. The nitrous fumes as fast
as they are evolved are swept out by air (or air and steam) forced into the retort
at the lower end whereby the fumes are conveyed through an outlet I at the upper
end of the retort to the usual condensers and other apparatus employed for
recovering the fumes as commercial nitric acid. The outlet pipe I for the air and.
gases may either be formed by the spindle of the screw conveyor G which in that
case projects, together with the casing G¹ in which it works, axially into the upper
end of the retort as in Figure 1 or the outlet pipe may be separate from and above
the conveyor as in Figures 3 and 4.
In order to allow for the free expansion of the retort by heat, and yet maintain
a sufficiently tight joint to withstand the internal pressure of the gases, an end
face joint is made at K between the flanged upper end of the retort and a spring
pressed part L provided with stuffing box and gland M through which the
casing G of the screw conveyor passes into the retort. The spring pressed part L
may be in the form of a collar as in Figure 1, surrounding the conveyor casing G¹
which is turned cylindrical externally to admit of the longitudinal sliding motion
of the stuffing box upon it, the collar being pressed up by the springs / to keep the
face joint K air tight. The joint between the rotating and stationary part of the retort
being thus made by turned metallic rubbing faces in a plane perpendicular to the
axis, no side binding in consequence of unequal expansion of the retort by the heat can
occur since there is perfect freedom for lateral deviation of the retort, there being

page_text: ample clearance between the screw casing G' and the retort whilst between the
stuffing box M and the screw casing G' which are both stationary parts the only
motion which takes place is the slight longitudinal one to allow for expansion and
contraction. In this way is maintained the perfectly tight joint necessary to admit
of internal air pressure being used to sweep out the fumes. The tubular spindle I
of the screw conveyor works in ordinary stuffing boxes ii and is driven by any
suitable
gear. It opens into a stationary box N whence a pipe conveys the gases
to the condensing plant.
In Figures 3 and 4 the outlet I is separate from the conveyor, both being
mounted in a cover L making a spring pressed face joint with the end of the retort
.as in the former case.
The lower end of the retort passes through a stuffing box into a chamber
provided with a spout o which dips into any suitable receiver wherein the solid
product of the decomposition which is still in a pulverulent state is received, the
matter therein collected serving to seal the mouth of the spout against the escape
of gas. To allow for any possible unequal expansion of the retort by the heat the
chamber is suspended freely by springs O' or otherwise supported so as to be
free to yield to any deviation of the retort and so prevent leakage of gases and side
binding of the retort in the stuffing box.
P is the inlet for air, or air and steam, blown in under sufficient pressure to carry
the fumes off as fast as they are generated.
.
The ultimate product of complete decomposition is an alkaline ferrite which is
subsequently decomposed by heating it with water whereby ferric oxide is obtained
for use over again whilst the alkaline base enters into solution and is recovered as
caustic alkali by evaporation in the ordinary way.
In conclusion it may be mentioned that the ferric oxide employed should be as
pure as possible in order that pure caustic alkali may be obtained; as regards the
proportion of ferric oxide in the mixture it must be sufficient to prevent the nitrate
from fluxing when furnaced; say two of oxide to one of nitrate, the proportion
being however subject to variation according to the physical properties of the
oxide.
As regards the rate of feed it has been found that with a retort 18 inches in
diameter having a length of 6 feet exposed to the furnace at an inclination equal
to a rise of 1 inch in the foot and revolving at a rate of 4 to 5 revolutions per
minute, the rate of feed for the mixture corresponding to 25 to 30 lbs. nitrate of
soda (ie. 75 lbs. to 90 lbs. mixture) per hour has given excellent results, but the
invention is in no way limited in this respect, these being merely working
directions which would necessarily vary according to circumstances.
Having now particularly described and ascertained the nature of the said inven-
tion, and in what manner the same is to be performed, we declare that what we
claim is :-
:-
1. The herein described continuous method of decomposing alkali nitrate in
admixture with ferric oxide which consists in subjecting the pulverulent mixture in
the form of a thin stream, film, or layer, to frequently repeated contact with the
heated surface of a retort wherein it is repeatedly showered down and through
which it is caused to travel, substantially as specified.
2. In the generation of nitrous fumes by the decomposition of an alkaline nitrate
in admixture with ferric oxide, the method of sweeping out the nitrous fumes
as fast as they are generated, by blowing air or air and steam into the retort, as
specified.
3. The apparatus for effecting the decomposition of alkaline nitrate by the
herein described method, consisting of a retort provided with longitudinal internal
ribs mounted to revolve upon an inclined axis and provided with means of
continuously feeding the matter to be treated and of separately removing the
gaseous and solid products of the decomposition, substantially as specified.
4. The combination, with an inclined revolving retort used for decomposing

page_text: alkaline nitrate as described, of means of periodically producing a shock or jar as
by a blow for the purpose of detaching the particles adherent to the surface of the
retort, substantially as specified.
Dated this 6th day of February 1896.
A. M. & WM. CLARK,
53, Chancery Lane, London, Chartered Patent Agents.