A New or Improved Process and Apparatus for Drying, Cooling, and Feeding or Conveying Superphosphate and other Materials.
Year: 1899

page_text: Date of Application, 15th May, 1899- Accepted, 8th July, 1899
A New or Improved Process and Apparatus for Drying, Cooling, and
Feeding or Conveying Superphosphate and other Materials.
A communication from abroad by Dr. F. LORENZ, successor to Dr. J. Lutjens,
of Hanover, in the Empire of Germany.
I, ALFRED GEORGE BROOKES, of 55 and 55; Chancery Lane, in the County of
London, Chartered Patent Agent, 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 methods hitherto adopted for drying superphosphate were attended with
the inconvenience that they yielded a hot product which, being collected in a
large bulky heap, was only capable of giving off its heat very slowly. Now
it is precisely when superphosphate lies in a heap that it is particularly apt to be
injuriously affected by heat, as superphosphate in a heated condition has a ten-
dency to ball" or lump together. Owing to the pressure to which the heaped-up
superphosphate is subjected, as a result of its own weight, especially where it is
kept in store for any length of time, the caking of it proves to be an extremely
objectionable feature, and one that necessitates the repetition of a costly disin-
tegrating process.
This drawback has been partly remedied by the scraping or shaving process
covered by the Specification of the Application for Letters Patent dated the
2nd May 1899, No. 9260, whereby the superphosphate was reduced to powder
immediately after leaving the decomposing chambers. The superphosphate, how-
ever, obtained by this process, contains about 14 per cent. moisture, a condition
in which it no longer meets the requirements of the present day, many users
of superphosphate desiring it to contain only about 10 per cent. of moisture."
But the most serious disadvantage, attaching to all processes hitherto known,
resides in the fact that the kiln-dried superphosphates, collected in tall heaps,
retain their heat for a very long time, caking in consequence, and readily lead-
ing to a state of chemical recession or retroaction; the phosphoric acid, which
had been made soluble, becoming insoluble again.
This return of the phosphoric acid to the insoluble state, after it has been
rendered soluble by the preliminary decomposing process in a proportion which
has frequently been observed to attain 1 per cent. and more, constitutes a loss
to the manufacturer, since what is paid for by users of superphosphate is merely
the proportion of phosphoric acid, soluble in water, which the superphosphate
contains.
This invention relates to a process whereby a cold fine grained material, dried
down to 10 per cent. of moisture, is directly obtained from the superphosphate
as, it leaves the decomposing chambers; such material being proof against any
danger of either caking or chemical recession (i.e. a return to the insoluble
condition). In carrying out this process, the superphosphate, after having been
divided on leaving the chambers by means of disintegrating or comminuting

page_text: apparatus, such as the scraping machine covered by the said application for
British Patent is subjected to the action, firstly, of hot compressed air, which
dries the product scraped to powder; and next, of cold compressed air, which acts
as a cooling blast upon the heated and dried powder.
The construction of the apparatus, employed in performing this process, is
such that the compressed air serves the double purpose of drying and moving
the superphosphate.
In point of fact, prior to the introduction of the scraping process covered by
the said Application for British Patent, means for transporting the material
from one part of the apparatus to another, in three successive stages, had to be
provided at considerable expense; for the material was to be conveyed.
1. From the decomposing chambers to the place of delivery, or collector;
2. From such collector to the drying chambers and back to the collector; and
again
3. From the collector to the disintegrators and back to the collector.
One object of the scraping process referred to was to reduce the number of
these transporting stages to one, since, by that process, the warm material issu-
ing from the decomposing chambers was immediately converted into a dry
readily dispersing powder; and the product obtained was. powdered superphos-
phate containing about 14 per cent. of moisture; which, indeed, is suitable for
many purposes, though, of late, many customers have been asking for superphos-
phate containing a proportion of moisture reduced to, say, 10 per cent.
Now whenever it was desired thus to reduce the amount of moisture in the
product, powdered by the scraping appliance, to 10 per cent. or thereabouts, an
additional transporting device or conveyor had to be inserted into the working
machinery, and the material had to be moved through the following two stages.
1. From the decomposing chambers to the scraping mechanism; and
2. From the scraping machine to the drying chamber and then to the place of
delivery or storage.
By employing the arrangement herein described, in conjunction with the
scraping process referred to in the said previous application for the purpose of
drying superphosphate, it is readily feasible to obtain within a few minutes super-
phosphate containing any low percentage of moisture that may be demanded at
the time-say about 10 per cent.-by moving the material only once, in a con-
tinuous manner and by purely mechanical means: commencing at the decom-
posing chambers and ending where the material is collected, ready to be forwarded
to customers for immediate use; such material being liable neither to aggregate
into lumps nor to retroact chemically by rendering insoluble the phosphoric acid
previously made soluble.
The improved apparatus is represented in the accompanying drawings in which
Fig. 1 is a longitudinal section thereof, while,
Fig. 2 shows one form of the perforated bottom or floor employed.
The drying apparatus consists of an inclined trough or channel a which is
divided into two compartments by a diaphragm or drying surface proper c,
bulging out at the top, in the upward direction. The lid covering the upper
compartment is left wide open at its raised end, for the reception of the
material while at its lower end, an adjustable door or hinged valve f leaves
an aperture only just sufficient for the discharge of the material as it is dried.
Into the lower compartment a³, which is tightly closed and from which the
external air is entirely shut out, hot compressed air is admitted through the
air supply pipe ; such air being allowed to escape again through the apertures
of the perforated bottom or floor whereon the dry material, supplied through
the charging hopper c, is spread out in even layer.
As will be seen from the drawings the trough or channel is inclined at any
suitable angle to the horizon. The currents of air, issuing from the lower air
compressing chamber through the perforations of the floor c, therefore necessarily

page_text: move the material down the inclined trough, while at the same time they raise,
permeate, loosen, heat and dry it.
The material, at this juncture, is acted upon by two forces, viz.:
1. The power of the compressed air, which raises the material off the drying
surface in the direction of its motion; and
2. Gravity, whereby it is caused to drop back on to the drying surface.
Hence there results either a leaping movement of the dried material; or, where
the two forces acting thereon balance each other, the material, carried by an
elastic cushion of air, will slide along in an even and uniform manner, in the
forward and downward direction.
The parts of the material, which are thus made continually to change their
relative position to each other, are, firstly, heated by contact with the drying
floor c; secondly, the particles, in order that they may undergo a general dry-
ing action and be thereby freed from the main part of their moisture, are raised,
traversed, loosened, broken up, heated and dried by the blast divided into a
number of single currents; and lastly, the blast, in passing through the upper
compartment a, in the upward direction, must once more pass over the material,
though in the direction opposite to that in which the material moves, as the
upper part of the trough has only a small outlet aperture left by the hinged
valve fat its lower end for the discharge of the material, and acts as a chimney
owing to the inclined direction it imparts to the current of heat.
Thus the exchange of heat takes place in a three fold manner.
1. By contact of the material with the hot surface c.
2. By immediate and close contact of the material with the currents of the
hot blast, all parts thus constantly receiving a supply of fresh, dry, hot air at
the same time; and
3. By contact with the hot air referred to in the preceding paragraph, which,
in the compartment a¹, moves in the direction opposite to that taken by the
material; all the benefit which the heat is still capable of affording being here
derived from it.
Owing to the circumstance that the compressed air acts at an angle to the
direction in which the material is moved along, and serves to stir up such
material so as to make it loose and light; and also to the fact that the air, after
having performed its work, leaves the drying channel in the reverse direction
to that in which the material moves; the velocity of the material is so regulated
that it remains in the drying apparatus for a period of time sufficiently long for
its desiccation.
In the drawings two channels are shown to be arranged one above the other,
which arrangement is adopted where it is desired to treat the material with hot
compressed air in one channel, and with cold compressed air in the other channel,
so as to cool it and at the same time subject it to a final stage of drying. Accord-
ingly, the hot material drops, from the upper trough a onto a second, or lower
trough g, exactly similar in construction to the first, into the lower compressed-
air-chamber h of which cold blast is forced through the branch tube or jet i.
Both the air and material here move precisely as they do in the first trough;
the material being quite cooled down by the blast and at the same time freed
from another considerable portion of its moisture. Where the charging hopper
is placed in a raised position, the hot air escaping from the upper trough may
furthermore be utilized in a preparatory stage of drying; flues being provided
for carrying off the air after it has effected its object.
The arrows marked in full lines indicate the direction of motion of the air,
while the dotted arrows signify the direction in which the material to be dried
is fed along.
The lower end of the second trough may be constructed in the shape of a
sieve, such as k, so that cold, sifted material may be collected in the tilting
wagon or in the sacks employed in forwarding the superphosphate to customers
while the coarser fragments, if any, are carried further on and deposited in the

page_text: j
waggon'm; or, if preferred, the finishing sieve k may be arranged as a detached
contrivance.
Instead of arranging the two troughs, one below the other they may both be
combined into a single apparatus wherein one part of the material shall be treated
with hot compressed air and the other part with cold compressed air; or the
arrangement may be divided into a number of sections adapted to operate. either
separately or in conjunction with each other.
The drying floor c may consist of slotted or otherwise suitably perforated
plates, or sieves, overlapping after the manner of scales; the particular construc-
tion depending upon, the nature of the material to be treated.
In Fig. 2 is shown one form of such drying floor c, it here consists of a number
of superposed scale shaped plates c,,, etcetera forming, as it were a flight
of steps, between which compressed air passes into the chamber through which
the material travels along; the material being thereby moved forward in the
required direction, as illustrated in the drawing. The successive scales or steps
are rivetted or otherwise suitably joined together; while upright rods serve to
keep them at proper distances apart.
The portion of the drying floor c, situated in front of the compressed-air-inlet
pipe d, is as indicated in Fig. 1-more inclined to, the horizontal than the
remaining parts of the said floor; and is moreover conveniently curved.
The
advantage of this arrangement is that part of the current of compressed air is
blown through such curved drying floor direct into the space wherein the material
travels and gives the initial impulse to the material in its required direction of
motion; while the remaining part of the compressed air, whereof the flow con-
tinues through the compartment, is deflected therein from its original direction
and spread out so that as it enters the upper compartment a, its expansion has
the effect of loosening and drying the material and of maintaining it in motion.
Where it is desired to accelerate the motion of the material being dried, a rock-
ing or shaking movement may, by suitable mechanical appliances, be imparted
to the trough, say, in the manner suggested in the drawings, or by means of
rocking conveyors, rollers or the like."
It is clear that by the arrangements described a great saving is effected in
practice all the hand labour required being limited to one single transporting
stage, while all the remaining stages of treatment of the material, viz. the
drying, cooling and sifting of the same, combine into one purely mechanical
operation requiring but a very brief space of time for its performance.
It will be understood that this process as well as the apparatus employed
in carrying it out, is applicable not only to the drying of superphosphate, but
to all cases where the object is simultaneously to dry and feed along any given
material.
Having now particularly described and ascertained the nature of my said in-
vention, and in what manner the same is to be performed, I declare that what
I claim is
1. A new or improved process for simultaneously drying and feeding along
superphosphate and other materials, the main feature of which is that the dis-
integrated or comminuted superphosphate is dried by hot compressed air, and,
immediately afterwards, cooled and fed along by cold compressed air, for the
purpose of extracting from the superphosphate before it reaches the place where
it is collected or stored-besides moisture the heat which would tend to restore
the phosphoric acid, previously made soluble, to an insoluble condition.
2. Apparatus for the performance of the process referred to in the 1st Claim;
the main feature of such apparatus being that within. a feeding channel or the
like, a slotted or perforated drying floor is so arranged that the compressed air
admitted into its lower compartment, as it passes through the perforations into
the upper compartment, moves along and dries the material under treatment,
at the same time time loosening such material.

page_text: 3. Apparatus for carrying out the process referred to in the 1st Claim; the
main feature of such apparatus being, that the slotted or perforated drying floor
consists of plates superposed or overlapping after the manner of scales, through
the spaces between which the compressed air enters the chamber wherein the
material is travelling, thereby imparting motion to such material in the required
direction.
4. Apparatus for carrying out the process referred to in the First Claim; the
main feature of such apparatus being that the portion of the drying floor situated
in front of the compressed-air-inlet pipe, is more inclined to the horizon than
the remaining part of said floor, and, if necessary, curved; for the purpose of
adding to the power of the part of the current of compressed air which is
admitted through the aperture of the portion of the floor that is more sloping
than the rest; while the remaining part of the compressed air continues to flow
through the lower compartment, and there, in virtue of its pressure, passes
through the perforations of the portion of the floor which is less inclined, and
then expands.
Dated the
Toth day say
1055.
WM. BROOKES & SON,
55/56, Chancery Lane, London, Agents for the Applicant.