A METHOD AND APPARATUS FOR DRYING COLOUR PASTE AND OTHER STRONGLY AQUEOUS MATERIALS
Year: 1884

page_text: I EMIL PASSBURG Engineer residing at Moscow in the Empire of Russia do
hereby declare the nature of said Invention for "A METHOD AND APPARATUS FOR
DRYING COLOUR PASTE AND OTHER STRONGLY AQUEOUS MATERIALS," 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 a process for drying in vacuo strongly aqueous bodies,
in particular such bodies which are subject to decomposition when exposed to
intense heat.
The Invention chiefly consists: 1, in introducing the heat, required for the
evaporation, into the interior of the vacuum apparatus, not only from the outside
by direct radiation, but by means of separate bodies serving as heat reservoirs.
2, in bringing the substances to be dried into immediate or almost immediate
contact with the heat containing bodies or heat reservoirs, so as to obtain a sufficient
transinission of heat, without causing the materials to be dried to adhere to the
walls or to form products of torrefication.
I have previously elaborated a process for drying moist refined sugar in the
vacuum apparatus by first strongly heating the sugar, then placing the same into
the vacuum apparatus, and subsequently heating the apparatus further from
without, which process I also tried in the treatment of other aqueous bodies.
I have, however, found that this process, although successful in treating refined
sugar containing only about 4 per cent. of water, is not commercially successful for
drying bodies containing a considerably larger quantity of water.
On closer examination I found that the heat, admitted from without through the
steam or heating water, had almost no effect towards accelerating the drying
process, and that it is almost exclusively the heat stored up in the crystals of the
blocks of sugar, which causes the evaporation of the water contained in the refined
sugar and replaces the heat of evaporation which has been consumed and which is
but low in the vacuum.
When the heat stored up in the body in course of drying, is used up, the
operation of drying continues so slowly, that the process offers no further
advantages.

page_text: The means which I have invented for drying solid and pulpy bodies, (which are
subject to decomposition when exposed to strong heat), by aid of a vacuum and
with economy of fuel, are substantially as follows:
A separate heat reservoir capable of holding at least as much latent or stored
heat as required to evaporate the total quantity of water in the partial (and as
high as possible) vacuum to be produced, is placed into the vacuum apparatus
simultaneously with the material to be dried and before the vacuum is established,
the heating surfaces of this heat reservoir having been brought into close contact
with the material to be dried.
The beating reservoir must be of such a construction as to easily but gradually
give off the heat.
It is preferable to introduce an excess of heat, that is to say, considerably more
than would be theoretically required for evaporation.
The process of evaporation is thereby considerably accelerated.
The loss of heat should be prevented by suitable jackets.
The drying apparatus may consist of any suitable reservoir adapted to be
hermetically closed by a lid or door and which is sufficiently strong to resist the
exterior pressure after the formation of the vacuum.
It is advantageous to surround this drying apparatus with a steam jacket for the
purpose of preventing loss of heat, and condensation of steam in the interior.
The amount of heat required for evaporation is stored up in the heat reservoir
by exposing the latter to high temperature in a specially constructed oven.
For the purpose of storing the-heat I advantageously employ sand, metal
shavings, tiles; furthermore caustic soda, caustic potash, calcic chloride-and-other
salts (in a solid or dissolved state) the solutions of which are good conductors of
heat and not subject to rapid cooling.
The sand or other material is contained in flat easily closed metallic boxes which
are preferably arranged in superposed tiers or rows on angle irons of the carriage
illustrated by Fig. 1, of the accompanying Drawings, in which position the heat
reservoirs permanently remain.
The carriage containing the heat reservoirs is moved into the furnace, Figs. 6
and 7, and exposed (for about 1 to 12 hours) to a temperature of 200° to 300° Celsius
until the carriage and its contents have become heated to a temperature approaching
the above, whereupon the carriage is conducted into the chamber J, Fig. 8.
The material to be dried is kept ready in the chamber J, having been spread in
thin layers on sheet iron trays, on sieves or equivalent devices, and it is placed
with the latter on the heat reservoirs of the carriage.
The carriage is now at once conducted into the drying apparatus B₁ B₂ B, Fig. 8.
After this a partial (and as high as possible) vacuum is produced by means of an
air pump connected with the apparatus, and is maintained until the materials are
dried.
By this treatment the water is subjected to a rapid evaporation.
The temperature and quantity of the sand or other heat storing substance or
appliance depends on the quantity of water contained in the materials to be dried,
also on the vacuum produced, and lastly on the special nature of the drying
substances.
Organic bodies containing their water in cellular tissues and membranes dry less
easily than bodies which contain their water only mechanically distributed between
separate component parts or crystals.
The quantity of sand and the heat required for the treatment of each separate
substance will be ascertained by experiments.
The following description relates by way of example to the drying of moist
paints or colour paste.
Several kinds of paint contain up to 70 per cent. of water and are of a cohesive
greasy nature.
The moist paint is spread by means of a paint press N, Fig. 8, in layers of
5 to 20 millimetres thickness, on thin metallic sheets, wire gauze or covered frames,

page_text: fed forward by the horizontal platform or endless apron P Fig. 8, or an endless
chain. The metallic plates or trays covered with paint are conveniently arranged
on the table S mounted on wheels. After the heat reservoirs have taken up the
desired amount of heat, the carriage containing the same is conducted through the
passage H H into the chamber J, where the trays etc. covered with the paint are
removed from the table S to the carriage, where they are introduced into the
intervals formed or left between the superposed boxes, so that each tray or frame
covered with paint is placed on the top of a sand receptacle.
From 3 to 4 kilogrammes of sand are generally sufficient for 1 kilogramme of
moist paint containing about 69 per cent. of water.
The carriage (or carriages) thus filled is now at once placed into the drying
apparatus, the latter is hermetically closed and the vacuum is produced by means
of a pump or equivalent appliance. The evaporation begins immediately, the
moist paint having been already heated during the operation of placing the trays
in the carriage, so that the water contained in the paint has already reached the
boiling point corresponding to the partial vacuum.
A further absorption of heat from the hot sand is merely applied for the
evaporation of the water in the moist paint, so that the paint will not be heated to
a higher temperature than 50° during the whole operation of drying.
Consequently, the considerable heat of the sand has no injurious effect whatever
on the material to be dried, as long as the same is moist.
When the drying process of the material is nearly terminated, the heat stored
up in the sand is so far consumed that the remaining temperature of the sand will
have no injurious effect on the dried substances.
The supply of heat, and-as long as the pump maintains the vacuum-also the
evaporation, remains uninterrupted until the drying is complete.
During 2 to 3 hours of operation of the air pump, up to 69 per cent. of the
70 per cent. of water contained in the paint will be evaporated.
The valve controlling the air pump is now closed, air allowed to enter the
apparatus and after opening the door, the carriages with the dried paint are
conducted into the chamber L Fig. 8. The trays with the paint are now removed
from the heat reservoirs, which remain on the carriages, the dry paint is removed
from the trays and brought into the mill Q, where it is ground to powder.
If instead of the tough pulpy products, paint of a granulous sandy nature is to
be dried which contains the water between the component parts, the paint may be
placed in pans instead of on sieves or covered frames, and the material may be
placed in the pans in layers of 5 centimetres thickness.
Paint of this nature will be dried in 1 to 2 hours.
After the paint has been removed from the trays, the latter are again conducted
to the paint press by means of the carrier P and here covered with a fresh quantity
of moist paint.
The carriage with the heat reservoirs which have now become cool, is rolled
back into the furnace and again heated.
The operations may be continuously carried on in such manner that while one
set of carriages with the cooled reservoirs is again heated in the furnace, another
set of carriages containing paint is in the vacuum apparatus.
Figa. 1 to 4 represent a drying apparatus suitable for the above described
process.
The apparatus may be kept heated from outside by the exhaust steam of the air
pump.
The drying apparatus consists substantially of a horizontal cylindrical body A
made of iron, surrounded by a steam jacket B and provided with doors C and D.
The apparatus is connected with the air pump by means of the pipe E, and the
steam jacket is provided with inlet and outlet valves F and G for the steam and
with a thermometer and a vacuum gauge.

page_text: The apparatus contains rails which permit the carriage, holding the materials to
be treated, to roll in and out. The construction of the furnace is illustrated by
Figs. 6 and 7.
In a similar manner I apply this process for drying meat, vegetables, fruit and
other highly aqueous bodies.
For the production of meat powder it may be recommended to pass the meat
through the mincing machine before drying, and to spread the minced meat on
galvanized, nickel plated, or tin plated trays which are then placed on the heated
sand receptacles. Notwithstanding the high temperature of the heat reservoirs,
the albumen contained in the meat does not coagulate during the above described
process. The dried pieces are then ground. The meat retains its complete
nutritive value and its taste, after 50 to 60 per cent. of water have been extracted
from the saine.
Comparatively thick slices cut off a joint may be dried in the course of a few
hours. By treating the meat with saltpetre before drying, its red colour may be
retained.
Fruit (such as apples and pears) may be dried in the same way as meat by
treating the fruit in the manner described above whether the same be left intact or
divided into slices.
The same process may be applied to vegetables, such as roots and potatoes, and
to glue, fish and other substances.
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:
1. The process of drying colour paste and other strongly aqueous, gelatineous,
or semi liquid materials in vacuo by introducing into the vacuum apparatus a heat
reservoir consisting chiefly of hot sand, hot solutions of alkalies or salts and
containing stored heat more than suflicient for the total evaporation in vacuo, and
placing such heating reservoir as closely as possible in contact with the materials
to be dried.
2. The combination of the appliances illustrated by Figs. 1 to 8, comprising a
preliminary heating apparatus or oven provided with rails for the carriage
supporting the heating reservoir, a carriage or carriages holding the heat reservoirs
arranged in sections or superposed tiers, and the vacuum apparatus connected with
the oven by rails and serving for the reception of the loaded carriage or carriages.
The whole substantially as described.