Method of and Apparatus for Producing Fresh Water from Water Containing Salts.
Year: 1896

page_text: Date of Application, 23rd Nov., 1896-Accepted, 20th Feb., 1897
COMPLETE SPECIFICATION.
Method of and Apparatus for Producing Fresh Water from Water
Containing Salts.
We, HERMANN PAPE and WILHELM HENNEBERG, both of Hohe Bleichen 36,
Hamburg, in the German Empire, Engineers, do hereby declare the nature of this
uvention and in what manner the same is to be performed. to be particularly
described and ascertained in and by the following statement:-
The production of fresh water from water containing salts by means of
evaporating apparatus is the more difficult, the greater is the percentage of salt
contained in the water, in particular because the walls of the evaporating
apparatus which are heated by combustion gases or by steam become rapidly
incrusted if the water contains a large percentage of salts, and this greatly hinders
the evaporation.
If it be desired to reduce such incrustation to as low a degree as possible, or to
avoid it entirely, it is essentially necessary to effect the production of the fresh
water to the least possible extent by the direct action of the said heating surfaces
and as much as possible by indirect means.
According to the present invention, this is effected as follows:-
1. Either by heating the salt water to a high degree under pressure, and then
reducing such, pressure step by step in several pressure reducing vessels connected
in series, whereby fresh water vapour is produced, which is then condensed to
liquid form."
2. Or the salt water is heated to boiling point at atmospheric pressure and is
then cooled by an air current which thus becomes heated and saturated with
moisture, this being separated in liquid form on the cooling of the saturated 'air.
3. Or by the combined use of the said method of reduction of pressure and that
of air circulation.
On the accompanying drawings are shewn various arrangements for carrying out
the said methods.
In Figure 1 of the drawings is shewn an arrangement with five generators for
fresh water vapour, and the same number of condensers. The generators AI
to A III work under a pressure which is greater than atmospheric pressure and the
generators A IV and AV work under vacuum.
The pressure is highest in generator AI and decreases stepwise to the
generator A V; in consequence hereof there also exists in each of the generators,
a different temperature of the fresh water vapour generated therein, such
temperature being highest in generator Al and lowest in generator AV.
The salt water flows from the raised reservoir B through the condensers CV CIV
to the circulation pump D, the steam of C'V and CIV is thus condensed that
of CV having been generated under a higher vacuum than that of CIV. The
quantity of salt water flowing to the pump D is so proportioned, that on issuing
from the condensers, it has as nearly as possible the same temperature as that of
the steam entering CV and CIV.
The fresh water produced from the said steam in CV and C IV, is withdrawn
by the vacuum pumps E" and E' and discharged 'into the collecting tank for fresh
water F.
The salt water heated in the condensers C and C now enters the circulating
pump. D and is, there subjected to a pressure corresponding to that in the

page_text: generator A. But before the salt water can pass into the generator A', it must
pass through the condensers C C and C; here it condenses tho. vapour
from A, A aud A 1 and has its temperature correspondingly raised step by step;
so that the salt water enters the generator A' with a temperature which is almost
equal to that of the steam. At the same time all the steam or vapours generated
in AI to A III are condensed, and the waters of condensation are caused by the
pressure to which they are respectively subjected, to flow automatically, without the
aid of pumps, into the fresh water tank F.
The water entering generator A' has, in being subjected to the preliminary
heating, produced no steam, as the circulating pump imparts to the salt water so
high a pressure, that it cannot boil at the temperature which it has attained.
In consequence herecf there are formed on the heating.surfaces of the condensers
no deposits, or hardly any, particularly if the brine salts have been previously
removed by means of soda.
After the salt water has entered generator A¹, a certain amount of steam must
be produced by direct heating, thus producing steam. The remaining salt water,
the quantity of which is very considerable relatively to the quantity of the steam
produced, now passes into the generator A", and thence seriatim into the other
generators. In each of these a reduction of pressure takes place and in consequence
hereof steam must be produced the quantity of which with proper adjustment of
the differences of pressure, should respectively be about equal to the quantity of
steam. In none of the generators A to A are there any heating surfaces that
have to be heated externally, and consequently the solid salts produced by the
evaporation collect on the bottom of the generators, without in any way interfering
with the evaporation. The concentrated salt lye ultimately produced is pumped
out of the generator AV by means of a pump, D₁ and only has the temperature
corresponding to the boiling point of the salt water in vacuo.
Figure 2 shews an arrangement in which the heating of the salt water is effected
in the same way as above described, but without the use of vacuum.
The arrangement here is such that the water of condensation formed in the
several condensers does not flow directly into the fresh water tank F, but is made
to flow first through the condenser of a lower stage of temperature, in order to
become farther cooled therein.
The bot salt lye which flows off from generator A is in this case employed for
the preliminary heating of the circulating water in the preliminary heater G, while
the salt water from tank B', is heated in the preliminary heater G by the
condensed fresh water, before this passes to the fresh water tank F. Only so
much salt water enters the tank B of the circulating water as is equal to the
quantity of fresh water produced; the circulating water flows in a circuit and the
excess of salt separates in crystalline form.
Fig. 3 shews a similar arrangement to Figure 2, but in place of the generator A¹
heated with coal or wood fuel there is employed a generator A' heated by means of
high pressure steam.
The circulating water does not in this case flow in a circuit, but the last
concentrated salt lye flows away freely. The fresh water flows from condenser CIT
through a filter H into the fresh water tank F.
Figure 4 shews the arrangement in which a circulating air current is employed
for extracting fresh water from hot salt water.
This salt water flows off from the generator A in which steam is produced by
reduction of pressure, after the salt water has been heated to a high degree in the
condensers C and C
The condenser C is heated by boiler steam. The hot salt lye flowing off from A
is then subjected to the action of an air current in the enclosed tanks I, which
current is produced by a fan b in a direction contrary to that of the flow of the
salt lye. The lye is thus cooled and the air is heated and at the same time its
percentage of moisture increases, the vapour given off by the lye being taken up
The air is hottest and contains moisture, when it reaches the inlet of

page_text: the hot salt lye at X, and it will be evident that any cooling of the air taking
place after it has passed that point, must at once result in the formation of aqueous
mist and the collection of the condensed moisture into drops, which fall out of the
air current.
This cooling is best effected by causing the salt water that is to be employed
for the production of fresh water, or the cooled salt lye to flow over the closed
apparatus J, in which the current of warm air saturated with moisture flows.
When the air is sufficiently cooled and the said watery mist has been formed, the
wet air is filtered through porous fabrics, asbestos cloth, metal turnings or the like
at K, a further cooling being effected by means of cooling pipes K', whereby the
aqueous mist is precipitated in the form of water, which collects at the bottom of
the compartiment, from which the air deprived of the greater part of its moisture
passes back to the fan b.
The collecting water is discharged through a pipe L to a fresh water tank F..
The cooled and comparatively dry air is then forced by the fan over and in
contact with the salt lye contained in the receptacles I, in order to repeat the above
described operation which consequently constitutes a continuous closed circuit.
By this means all loss of moisture is prevented and the salt water can be practically
entirely converted into fresh water and crystallised salts, which latter are
precipitated on to the bottom of the chamber J in which the hot salt lye
is cooled.
The mother liquor remaining after the crystallisation of the salt is withdrawn
by the pipe D, and is raised thereby so as to be discharged over the chamber J
whence it falls into the tank B'; from this the warmed water is drawn by the
pump D', which propels it through the condensers C and C into the generator A
and thence back into the chamber J, so that the salt water flows in a complete
closed circuit.
Instead of this arrangement the salt lye may be discharged from the tank B' and
new salt water be continuously introduced by the pump D if it be not desired to
convert the salt water entirely into fresh water and salt crystals.
Having now particularly described and ascertained the nature of this inven-
tion and in what manner the same is to be performed, we declare that what we
claim is
1. The method of producing fresh water from water containing a large
a considerable
proportion of salts, wherein the salt water is first heated to
degree under pressure, and is then subjected to a lower pressure so
liberate steam or aqueous vapour, which is then condensed to water, substantially
as described.
as to
2. Apparatus for carrying out the process referred to in the first claim, combined
and operating, substantially as herein described with reference to Figures 1, 2
and 3 of the drawings.
3. The method of producing fresh water from water containing a large
proportion of salts, wherein the salt water is first heated to about boiling point,
and a current of air is then caused to pass in a closed circuit over and in contact
with the said heated salt water, whereby the air becomes saturated with moisture
whereupon the air current is cooled so that the moisture is condensed and separated
therefrom, substantially as described.
4. Apparatus for carrying. out the process referred to in the third claim,
combined and operating substantially as described with reference to Figure 4 of
the drawings.
Dated this 23rd day of November 1896.
ABEL & IMRAY,
Agents for the Applicants.