IMPROVEMENTS IN APPARATUS FOR EVAPORATING SOLUTIONS IN CONTACT WITH AIR OR OTHER GAS
Year: 1880

page_text: LETTERS PATENT to Sydney Pitt, of Sutton, in the County of Surrey, for
an Invention of " IMPROVEMENTS IN APPARATUS FOR EVAPORATING SOLUTIONS
IN CONTACT WITH AIR OR OTHER GAS." A communication from abroad by
the Société pour l'Exploitation des Brevets Piccard, of Genova, Switzerland.
•
PROVISIONAL SPECIFICATION left by the said Sydney Pitt at the Offico
of the Commissioners of Patents on the 22nd June 1880.
SYDNEY PITT, of Sutton, in the County of Surrey. "IMPROVEMENTS IN
APPARATUS FOR EVAPORATING SOLUTIONS IN CONTACT WITH AIR OR OTHER GAS."
[A communication from abroad by the Société pour l'Exploitation des Brevets
Piccard, of Geneva, Switzerland.]
In many industries it is necessary to carry on the evaporation of liquids in
contact with the air. For example, salt in large crystals can only be obtained on
the surface of a liquid evaporated in contact with air without boiling. In ordinary
salt evaporating pans brine is evaporated in contact with air, and the vapour
produced by burning fuel under the pan passes off into the atmosphere. The heat
contained in the vapour which is disengaged is thus lost.
To utilize the greater part of the heat contained in the vapour disengaged from
a liquid which is being evaporated it is necessary either to conduct this vapour
into contact with the sides of a vessel containing a liquid which evaporates at a
lower temperature (this is the principle of the apparatus known as multiple effect
apparatus employed in sugar works and other industries), or else to reheat this
vapour by compression; it can then even keep up the temperature of the liquid
from which it was disengaged. These processes are both known, but if applied to
the treatment of a mixture of air and vapour they present difficulties and sources
of loss which render their use very little advantageous and even impossible.
The first process is used at some salt works where a small portion of the vapour
admixed with air is utilized under a second pan called vapour pan, in which tho

page_text: liquid has only to be warmed to a lower temperature than that of the mixture of
air and vapour. The temperature of the mixture is lowered by contact with the
sides of the pan, part of the vapour condenses and yields its heat to the sides of
the pan and the liquid it contains, but as the lowering of temperature sustained by
the mixture is small only a small portion of the vapour it contains is condensed,
whilst the greater portion instead of being utilized remains mixed with the air
which must necessarily be passed away.
This is the cause of the small yield of the vapour pans now used. The same cause
would have to be encountered in any other arrangement of multiple performance
apparatus treating a mixture of air and vapour, and would prevent any
advantageous result being obtained from it.
The treatment of a mixture of air and vapour by compression would be still less
economical. The presence of air would necessitate a loss of a large excess of
mechanical force over what would be necessary when treating pure vapour.
The process which it is now sought to protect has for its object to permit
pure vapour to be obtained even when the evaporation takes place in presence
of air.
The process is as follows:-Over an ordinary salt pan a current of air is passed,
which becomes charged with the vapour of water by passing over the surface of
liquid kept at a certain temperature. At the outlet from the pan this air, nearly
if not entirely saturated with vapour, is conducted through a shower of liquid
which is at a lower temperature than the air charged with vapour coming from the
pan. This colder rain of liquid will lower the temperature of the mixed air and
vapour, and part of the water vapour will be condensed. If the air deprived by
condensation of a portion more or less considerable of the vapour which it has
taken from the solution were allowed to escape into the atmosphere the vapour
still contained in the evacuated air would be lost.
To avoid this loss this air which has been slightly cooled, and deprived by its
cooling of a portion of the moisture which it contained, may be again conducted
over the pan, be thereby warmed and caused to take up a fresh charge of
vapour.
The intermediate liquid which is made to fall in a rain will have condensed
some of the vapour, and in doing so will have absorbed the latent heat of this
vapour; it is thereby warmed and at the same time increased in volume by the
quantity of water which it has condensed.
If now a quantity of vapour equal to that which has been condensed is
withdrawn from the intermediate liquid the intermediate liquid will be brought
back exactly to its original state both as regards volume and temperature. The
operation can then he recommenced, and the intermediate liquid be used over and
over again to condense vapour out of its admixture with air, and to produce a
quantity of vapour equal to that which it has condensed.
It is casy to obtain the vapour disengaged from the intermediate liquid free
from air, and so obtain pure vapour, that is to say, without admixture of air. This
vapour can then be used for producing a new evaporation by the employment
either of the principle of multiple effects or of compression of the vapour.
In place of the intermediate liquid being made to fall as a rain it might be
brought into contact with the saturated air in any other manner. This contact
need not also be direct; the intermediate liquid might be made to circulate through
a tubular or other surface condenser. In this case the vapour condensed in the
condenser would have to be separately drawn off. The main characteristics of the
above process consist in evaporating a solution in contact with air, in condensing
the vapour so obtained admixed with air by the contact of this mixture with an
intermediate liquid, and in obtaining freo from air the vapour of this liquid, so
obtaining pure vapour possessing all the heat of the vapour produced admixed with
air. Also preferably in effecting the return of the air so partially deprived of
vapour over the surface of the evaporating pan and maintaining a constant

page_text: circulation. The heat of the pure vapour may be utilized in any known way
either by the application of the principle of compression, or of multiple effect, or
in other suitable manner. The above process, which admits of obtaining a vapour
free from air, although the evaporation which has produced it took place in
presence of air, constitutes a new and important inanufacturing process susceptible
of numerous applications, not only for the manufacture of large grained salt, but
also for the evaporation of any other liquid, whether it is required to obtain from
it a solid residue or to concentrate the liquid, or even if the object is to collect
condensed vapour as a liquid which has been rectified or distilled in the presence of
air or other gas.
SPECIFICATION in pursuance of the conditions of the Letters Patent filed
by the said Sydney Pitt in the Great Seal Patent Office on the 21st December
1880.
SYDNEY PITT, of Sutton, in the County of Surrey. "IMPROVEMENTS IN
APPARATUS FOR EVAPORATING SOLUTIONS IN CONTACT WITH AIR OR OTHER GAS."
A communication from abroad by the Société pour l'Exploitation des Brevets
Piccard, of Geneva, Switzerland.
In many industries it is necessary to carry on the evaporation of liquids in
contact with the air. For example, salt in large scale like crystals can only
be obtained on the surface of a liquid evaporated in contact with air without
boiling.
In ordinary salt evaporating pans brine is evaporated in contact with air, and
the vapour produced by burning fuel under the pan passes off into the atmosphere.
The heat contained in the vapour which is disengaged is thus lost.
To utilize the greater part of the heat contained in the vapour disengaged from
a liquid which is being evaporated it is necessary either to conduct this vapour
into contact with the sides of a vessel containing a liquid which evaporates at a
lower temperature (this is the principle of the apparatus known as multiple effect
apparatus employed in sugar works and other industries), or else to reheat this
vapour by compression; it can then even keep up the temperature of the liquid
from which it was disengaged. These processes are both known, but if applied to
the treatment of a mixture of air and vapour they present difficulties and sources
of loss which render their use very little advantageous, or perhaps impossible.
'I he first process is used at some salt works where a small portion of the vapour
admixed with air is utilized under a second pan called a vapour pan, in which the
liquid has only to be warmed to a lower temperature than that of the mixture of
air and vapour. The temperature of the mixture is lowered by contact with the
sides of the pan, part of the vapour condenses and yields its heat to the sides of the
pan and the liquid it contains, but as the lowering of temperature sustained by

page_text: the mixture is small only a small portion of the vapour it contains is condensed,
whilst the greater portion instead of being utilized remains mixed with the air
which must necessarily be passed away.
This is the cause of the small yield of the vapour pans now used. The same
cause would have to be encountered in any other arrangement of multiple per-
formance apparatus treating a mixture of air and vapour, and would prevent any
advantageous result being obtained from it.
The treatment of a mixture of air and vapour by compression would be still less
economical. The presence of air would necessitate a loss of a large excess of
mechanical force over what would be necessary when treating pure vapour.
The process which it is now sought to protect has for its object to permit pure
vapour to be obtained even when the evaporation takes place in presence of air.
The process is as follows:-Over an ordinary salt pan a current of air is passed
which becomes charged with the vapour of water by passing over the surfaco of
liquid kept at a certain temperature. At the outlet from the pan this air, nearly
if not entirely saturated with vapour, is conducted through a shower of liquid
which is at a lower temperature than the air charged with vapour coming from the
pan. This colder rain of liquid will lower the temperature of the mixed air and
vapour, and part of the water vapour will be condensed. If the air deprived by
condensation of a portion more or less considerable of the vapour which it has
taken from the solution were allowed to escape into the atmosphere the vapour
still contained in the evacuated air would be lost.
To avoid this loss this air which has been slightly cooled, and deprived by its
cooling of a portion of the moisture which it contained, should be again conducted
over the pan, to be thereby warmed and caused to take up a fresh charge of
vapour.
The intermediate liquid which is made to fall in a rain will have condensed
some of the vapour, and in doing so will have absorbed the latent heat of this
vapour. It is thereby warmed and at the same time increased in volume by the
quantity of water which it has condensed.
If now a quantity of vapour equal to that which has been condensed is with-
drawn from the intermediate liquid the intermediate liquid will be brought back
exactly to its original state both as regards volume and temperature. The operation
can then be recommenced, and the intermediate liquid be used over and over again
to condense vapour out of its admixture with air, and to produce a quantity of
vapour equal to that which it has condensed.
It is easy to collect the vapour disengaged from the intermediate liquid free from
air and so obtain pure vapour, that is to say, without admixture of air. This
vapour can then be used for producing a new evaporation by the employment
either of the principle of multiple effects or of compression of the vapour.
In place of the intermediate liquid being made to fall as a rain it might be
brought into contact with the saturated air in any other manner. This contact
need not also be direct; the intermediate liquid might be made to circulate through
a tubular or other surface condenser. In this case the vapour condensed in the
condenser would have to be separately drawn off.
In the following explanation of the apparatus for carrying out the system above
explained it is assumed that the regeneration of the heat of the vapour will be
effected by compression. It will be seen afterwards that without making any
change in the apparatus itself the principle of multiple effects is applicable.
For clearness and facility in explaining the Drawing hereunto annexed tem-
peratures and pressures are marked thereon by way of example.. It is hardly
necessary however to say that the apparatus may be worked under other conditions.
of temperature and pressure.

page_text: a is a salt pan, which may be constructed in iron, wood, cement, or other
material, as it is not exposed directly to the fire.
b is a casing over the pan.
c is a fan causing the air to circulate by the pipes l, i, and passing successively
over the pan a, and through the shower condenser d.
d is the shower condenser; it is provided with a number of perforated shelves,
which receive the intermediate liquid as it passes in at the top.
The process remains precisely the same if in place of causing the intermediate
liquid to descend as rain it be brought into contact with the saturated air in any
other way. It is not essential that the contact should be direct; the intermediate
liquid may be made to circulate in a tubulár apparatus operating as a surface
condenser.. In this case the condensed vapour can be collected separately.
e, vessel through which the intermediate liquid is made to pass, and in which it
is evaporated. This liquid may be pure water, or a saline solution or other liquids
may be employed.. The level of the intermediate liquid in the vessel e will vary
with the pressure of the vapour emitted by this liquid.
pump by which the intermediate liquid is made to circulate in the pipes n
and m between the shower condenser d and the vessel e, where the evaporation of
the intermediate liquid takes place. Any description of pump or circulating
apparatus may be employed.
g, a compresser or pump withdrawing the vapour from the vessel e by the
tube o, and forcing it by the pipe p into the space surrounding the tubes in the
boiler h.
This pump is not employed when the principle of multiple effects is applied, as
will be presently explained. Consequently this pump is not an essential part of
the apparatus.
h, boiler in which the solution to be evaporated is made to circulate; it is here
heated by contact with the tubes and surfaces enclosing the space into which the
vapour of the intermediate liquid is compressed.
It is not essential that this boiler should be tubular; its surfaces may be
otherwise arranged.
The liquid to be evaporated circulates continually by
boiler h to the pan a, and from the pan to the boiler.
simply from the heating of the solution in the boiler h.
rendered more active by mechanical means.
the pipes rand & from the
This circulation will result
Or the circulation may be
t is a pipe leading steam from a steam generator into the boiler h. This direct
admission of steam serves at the commencement of working to raise the liquid to
be evaporated to the desired temperature, and during the continuance of the
operation to maintain the temperature to compensate losses of heat.
q, outlet pipe for the hot distilled water. This hot water will serve to heat the
cold solution before it enters the pan. For this purpose the hot distilled water is
made to pass in one direction through a temperature interchanger, which is
traversed in the other direction by the solution as it passes to the pan.
This temperature interchanger being a well known appliance is not represented
in the Drawing.
In order to minimise loss of beat the apparatus should be clothed with felt or
other material which is a bad conductor.
When salts are deposited by evaporation at the bottom of the pan a they are
removed from time to time by hand, the casing b being opened for the purpose;
or the salt may be raked out by known mechanical appliances.
The apparatus above described may be utilized in many different ways, according
to circumstances, as, for example, where water power is available the compresser g
will be worked by this means, and then the evaporation will be obtained with the
expenditure of little or no fuel.
When water power is unattainable the compressor g will be worked by a steam
engine. Or a series of apparatus like that described above will be combined and
used as a battery or multiple effects apparatus.

page_text: In this last case the steam from a boiler or the exhaust steam from an engino
will be led by the pipe p into the boiler / of the first apparatus, whilst the vapour
from the vessel e will be conducted by the pipe o in to the boiler / of a second
apparatus working at a lower temperature.
The pipe o of the second apparatus will conduct the vapour from its vessel e into
the boiler of a third apparatus working at a still lower temperature, and so on
until the end where the pipe o of the last apparatus delivers its vapour into a
condenser.
To define shortly the process which is the object of the present Patent, it
consists in evaporating a solution in contact with air, in condensing the vapour
so obtained admixed with air by the contact of this mixture with an intermediate
liquid, and in collecting free from air the vapour of this liquid, so obtaining pure
vapour possessing all the heat of the vapour produced admixed with air. Also
preferably in effecting the return of the air so partially deprived of vapour over
the surface of the evaporating pan and maintaining a constant circulation.
The heat of the puro vapour may be utilized in any known way, either by the
application of the principle of compression or of multiple effect, or in other suitable
manner.
The above process, which admits of obtaining a vapour free from air, although
the evaporation which has produced it took place in prosence of air, constitutes a
new and important manufacturing process susceptible of numerous applications,
not only for the manufacture of large grained salt, but also for the evaporation of
any other liquid, whether it is required to obtain from it a solid residue or to
concentrate the liquid, or oven if the object is to collect condensed vapour
as a liquid which has been rectified or distilled in presence of air or other gas.
I claim more especially the above described process of evaporation in contact
with air, having as a characteristic feature the employment of an intermediate
liquid serving to collect the heat contained in the vapour formed in the evapo-
ration, and either in combinatin or not with the continuous circulation of the
same quantity of air from the pan to the intermediate liquid, and vice versa.
In witness whereof, I, the said Sydney Pitt, have hereunto set my hand and
seal, this Soventeenth day of December, in the year of our Lord One thousand
eight hundred and eighty.