U.S. patent number 3,763,915 [Application Number 05/164,814] was granted by the patent office on 1973-10-09 for evaporative treatment of liquids by submerged combustion.
This patent grant is currently assigned to Copper Refineries Pty. Limited. Invention is credited to George Alan Denman, Thomas Joseph Goding, Norman William Irvine, John Geoffrey Lagerche, Graham Douglas Moffett, Ian James Perry, Bruce Dunstan Watson.
United States Patent |
3,763,915 |
Perry , et al. |
October 9, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
EVAPORATIVE TREATMENT OF LIQUIDS BY SUBMERGED COMBUSTION
Abstract
Method and apparatus for the evaporative treatment of liquid
usable in the electrolytic refining of copper in which fuel is
burned in an open-bottomed otherwise closed chamber in which the
bottom of the chamber is below the surface of a bath of said
liquid, the interior surfaces of the chamber are cooled by
application of cooling media to the chamber exterior, the interior
surfaces of the chamber are periodically flushed by steam to remove
accumulation thereon and the precipitated matter is removed from
the bath.
Inventors: |
Perry; Ian James (Queensland,
AU), Watson; Bruce Dunstan (Queensland,
AU), Lagerche; John Geoffrey (Queensland,
AU), Denman; George Alan (Queensland, AU),
Irvine; Norman William (Queensland, AU), Goding;
Thomas Joseph (Queensland, AU), Moffett; Graham
Douglas (Queensland, AU) |
Assignee: |
Copper Refineries Pty. Limited
(Townsville, Queensland, AU)
|
Family
ID: |
3692420 |
Appl.
No.: |
05/164,814 |
Filed: |
July 21, 1971 |
Foreign Application Priority Data
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Jul 22, 1970 [AU] |
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1923/70 |
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Current U.S.
Class: |
159/16.2;
159/13.4; 159/DIG.13 |
Current CPC
Class: |
B01D
1/14 (20130101); Y10S 159/13 (20130101) |
Current International
Class: |
B01D
1/14 (20060101); B01D 1/00 (20060101); B01d
001/14 () |
Field of
Search: |
;159/16A,4A ;23/281 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Yudkoff; Norman
Assistant Examiner: Sofer; J.
Claims
We claim:
1. Apparatus for evaporatively concentrating a liquid to recover
matters dissolved therein, comprising:
a. a tank to contain the liquid to be concentrated,
b. an open-bottom chamber, consisting of a side wall and a roof,
mounted on said tank so that its open bottom is submerged below the
surface of the liquid in said tank,
c. a fuel burner mounted on said roof and arranged to direct the
products of combustion produced into said chamber through an
aperture in said roof,
d. means for injecting fuel and air for the combustion thereof into
said burner,
e. a steam distribution header mounted in said chamber immediately
below said roof,
f. means to feed steam into said header, and
g. a plurality of outlet nozzles on said header by which steam is
directed onto the walls and roof of the chamber, and which are so
spaced along said header as to ensure that a condensate curtain
formed on the interior of said wall is circumferentially continuous
before reaching, said chamber walls and/or roof being jacketed to
provide for circulation of a coolant about said chamber for
producing said condensate curtain.
2. The apparatus of claim 1 wherein said rim is slotted or of
saw-toothed shape whereby combustion gases may enter said bath as a
large number of small streams to reduce bath turbulence, and
wherein the submerged rim is surrounded by an open-bottomed annular
duct having a circumferential outer wall which is similarly slotted
or saw-toothed to provide further outlets through which said
combustion gases are discharged into said bath liquor.
3. The apparatus of claim 1 wherein said bath is in the form of a
tank which receives liquor to be purified near the level of the
roof of said tank and which possesses a concentrated liquor
take-off pipe at or near the floor level of said tank, and means
which maintain the level of concentration liquor substantially
constant whereby said last-mentioned level is maintained above said
chamber open bottom at which said combustion gases are discharged,
said tank including a roof plate which separates a plurality of
said chambers, and said roof having an opening therein constituting
an intake end of a flue adapted to take off exhaust gases after the
latter have bubbled their way through the bath liquor.
4. The apparatus of claim 1 wherein said means for injecting fuel
and air defines a refractory duct, said duct being furnished with
nozzles for injection thereinto of fuel and air.
Description
This invention relates to the evaporative treatment of liquids to
concentrate them and remove matters dissolved therein. Such
treatment may be carried out merely to concentrate, purify or
re-condition the liquid, or merely to recover the dissolved matter,
or with both of those ends combinedly in view.
The invention is applicable generally to the treatment of liquids
for the purposes indicated. However, it is presently expected that
the invention will be particularly advantageous in the treatment of
electrolyte as used in the electrolytic refining of copper; to
re-condition the electrolyte for re-use and to recover from it
matters of commercial importance which accumulate in it as a result
of its sustained use in the copper refining process. Because of
this expectation the invention will be further described herein
primarily in terms of that particular use but is not to be regarded
as restricted thereto.
In the electrolytic refining of copper the most commonly used
electrolyte is a solution of sulphuric acid and copper sulphate and
the copper anodes usually contain nickel as an impurity at levels
less than 1 percent.
This Ni content is, of course, freed during the electrolytic
migration, but if it is not removed from the electrolyte it will
accumulate and increasingly contaminate the deposited cathode
copper by occlusion of electrolyte during deposition. It is thus
necessary for the Ni concentration in the electrolyte to be kept
sufficiently low to ensure no more than an acceptable proportion
(for example, 2 ppm) of Ni in the cathode copper. There are, of
course, a number of other soluble impurity elements, such as
arsenic, iron and calcium, which are not wanted in the electrolyte
and these may be removed along with, or prior to the removal of,
the Ni content but the present discussion is largely in terms of
the Ni ingredient because its recovery (in the form of NiSO.sub.4)
is of considerable commercial importance.
Thus the main objects of the present invention, in its application
to the electrolytic refining of copper are:
A. the efficient refining of copper.
B. the recovery in marketable form of a valuable Ni by-product,
and
C. the achievement of objectives (a) and (b) in a manner and with
apparatus which are simple yet highly effective by comparison with
the prior art.
The purification of an electrolyte, viewed with sufficient
generality as to be common to the prior art and the present
invention, comprises two stages. The first stage accomplishes the
removal of copper and arsenic, electrolytically or otherwise, and
thus prepares the feed liquor for the second stage, viz. the
concentration process to which this invention applies. This stage
two feed liquor consists of a solution of sulphuric acid, nickel
sulphate, iron sulphate, calcium sulphate and small proportions of
other materials.
It will be understood that the function of the purification circuit
is to keep the concentration of alien matters (that is, matters
such as nickel sulphate which are valuable but unwanted in or alien
to the electrolyte) in the electrolyte in actual use in the
electrorefining circuit, down to an acceptable level; and hence
only a sufficient fraction of the refining electrolyte must be
treated in the purification circuit so as to remove an amount of
impurity equal to the input of that impurity to the refinery. It is
a feature of the present invention that, because of its efficiency,
purification plant may be on a relatively small scale compared with
the prior art. In an experimental practicing of this plant it was
found that a satisfactory alien matter concentration was not
exceeded, with the continuous withdrawal of 3 gals/min. from a
total refinery pump output of 1,620 gals/min.
The purification circuit is, in effect, a subcircuit in parallel
with the refining circuit; the purification circuit has a liquid
intake pipe which branches from the output pipe of the refinery
pump and a discharge pipe by which finally purified electrolyte is
fed back into the intake pipe leading back to the refining circuit
pump.
It will be appreciated that any second stage purification in
essence consists in heating the electrolyte so to concentrate the
liquid by driving off excess water and to bring the salts dissolved
in the electrolyte to a state of saturated solution so that upon
subsequent cooling a satisfactory removal of the dissolved salts is
effected. The crystals are precipitated partly in the evaporator
and partly by subsequent cooling and thus may be removed and the
concentrated liquid, freed of at least its most damaging
impurities, can then be returned to the refining circuit for
re-use.
It might appear from this that second stage purification is a
relatively simple procedure, but that is not so; it has long been a
severe problem in the industry and many different expedients have
been adopted in the past, but so far as we are aware none of these
prior expedients, although they are still widely in use, has been
entirely satisfactory. Thus it is an object of this invention to
remedy or substantially remedy the prior art shortcomings.
One commonly used second stage purification incorporates the use of
an ordinary tubular heat exchanger applying heat by means of steam
or heated gases. This is satisfactory up to a point, but it rapidly
becomes inefficient through accumulation of solid encrustations, in
that keeping one of the heat exchange surfaces (that having liquid
under treatment in contact with it) clean is a major task which
virtually prohibits continuous operation.
Another common method is to heat the solution in heavy steel or
cast iron pans by means of flame heating underneath the pan, but
this again involves the same disabilities as just referred to in
connection with tubular heat exchangers, and in an endeavour to
avoid these disabilities it has been proposed to direct hot gases
into the solution in order to transfer heat directly to it. The
direct heating method, however, necessitates the use of nozzles or
the like dipping into the solution, or other devices to introduce
the hot gases thereto, but this method does not avoid the build up
of solid sulphate or like deposits on the nozzles or the like and
the intense local heat to which the encrustations are then
subjected causes the sulphates (nickel and iron, for example) to
decompose giving off sulphur trioxide. This escapes into the
atmosphere where it becomes an obnoxious pollutant and, in general,
this is one of the more serious effects of some of the prior art
methods known to us, in that the hot gases leaving the evaporating
system, by reason of air pollution, are a serious disadvantage.
A further disability of the prior methods involving encrustation of
solids on the heating or heat transfer equipment, is that their
presence is highly detrimental in point of thermal efficiency,
because an insulating layer of salts crystallises or settles out in
the heat exchange vicinity. This in turn causes inefficiency of
heat transfer with consequent excessive heating of the exchange
medium and consequent reaction with the free H.sub.2 SO.sub.4
present in, and in continuous supply to, the salt layer and, as
previously indicated, the salt layer and entrapped H.sub.2 SO.sub.4
are heated beyond decomposition temperature with unavoidable
SO.sub.3 generation.
It is a further object of the present invention to avoid the
disabilities recited above by use of a method and apparatus of high
thermal efficiency which reduces discharge of SO.sub.3 or other
pollutant matters to the atmosphere to a level which is acceptable
having regard to the laws concerned to prevent atmospheric
pollution, while enabling efficient recovery of values, such as
nickel sulphate and/or the effective elmination of other
impurities.
A further advantage due to the present invention is that it permits
second stage purification to be carried out continuously during the
process of electrolytic refining and the first stage purification
of the electrolyte involved in the refining process.
In its broadest aspect the invention consists in a method of
evaporatively concentrating a liquid and removing dissolved matter
therefrom, comprising the steps of: burning fuel in an
open-bottomed, otherwise closed, chamber whereof the bottom rim is
below the surface of a bath of said liquid so that the products of
combustion are discharged directly into the liquid, cooling the
interior surfaces of said chamber by application of cooling media
to the chamber exterior, flushing said interior surfaces
sufficiently to clear therefrom solid particles tending to
accumulate thereon, and removing solid matter precipitated in said
bath.
One embodiment of the invention defined in the preceding paragraph
will now be described with reference to the accompanying drawing,
in which similar reference indicate corresponding parts, and in
which:
FIG. 1 shows a plan view of a combustion chamber,
FIG. 2 shows, in front elevation and partly in section, a view
along the line 2--2 of FIG. 1 and,
FIG. 3 shows, in side elevation, a tank containing a bath of liquor
in which three of said combustion chambers are partially
submerged.
Upon referring to the drawings, it will be seen that a combustion
chamber 1 surrounded by a jacket 2 terminates in a skirt 3 in which
a plurality of slots such as 4 is formed. A mounting flange 6,
fixed to the outer wall of said water jacket 2, permits the chamber
1 to be mounted with respect to a tank hereinafter described. Above
the roof 7 of the chamber is mounted anair manifold 8 from which a
refractory spacer 9 separates the burner tile 10 which communicates
with an oil burner 11. Beneath the roof 7, a steam spray ring 12 is
mounted with a plurality of steam nozzles 13 depending therefrom.
Said chamber is adapted to be partially immersed in said bath so
that liquor therein rises to the level 14.
The medium used to flush the interior surfaces such as 15 of the
chamber 1 may be water directly sprayed on to those surfaces, but
is preferably steam emitted from the nozzles 13 which by
condensation on the cooled inner surfaces of the chamber provides a
film-like stream of water which runs down the walls and acts as a
solvent or parting layer which prevents solids from building up as
encrustations on that surface. Obviously the addition of flush
water, in any form, to the bath of liquid under treatment increases
the amount of water to be driven off so that the required level of
concentration of the liquid is maintained. Therefore, it is
preferable for the flush medium to be applied sparingly, for
example, by short intermittent blasts of steam directed towards the
walls of the chamber.
A presently preferred apparatus for carrying out the invention
comprises the chamber 1 having a cylindrical wall as shown, with
its open bottom terminating the skirt 3 being adapted to dip into a
bath of the liquid to be subjected to second stage purification.
The oil burner 11 employs any suitable liquid fuel such as diesel
distillate injected via suitable nozzles thereinto together with
the air necessary for its combustion. Because the fuel is liquid,
it may be burnt under controlled conditions so that the products of
combustion will be virtually oxygen and ash free. The jacket 2 is
supplied with a coolant such as water circulated continuously
therein by means of a suitable pump which derives the water from a
cooling tower or the like.
The circulation rate of the cooling water is preferably such as
will maintain the chamber walls at a temperature such that the
effluent temperature of the cooling water does not exceed
85.degree.C. The effluent heat of the cooling water may be
advantageously employed by using it in a heat exchanger as
pre-heating counter current to the liquor leaving the first stage
of purification on its way to the second stage. The roof of the
combustion chamber may be water cooled in much the same manner as
just described with reference to the chamber walls, but, for
preference, roof cooling is effected by use of the manifold 8 as a
pre-heating feed duct for the air necessary for fuel combustion in
the burner chamber.
Discharge of steam within the chamber may be carried out in several
different ways, but for preference, the tubular steam spray ring 12
is mounted in the chamber 1 immediately below the roof 7 thereof.
The outside diameter of this ring is preferably such as to be
almost equal to the internal diameter of the chamber. Steam is fed
to the ring from any conventional source of supply and the ring is
furnished with a plurality of nozzles 13 by which the steam is
directed onto the walls and roof of the chamber, the nozzles being
sufficiently closely spaced as will ensure that the condensate
curtain formed on the inner wall of the chamber is
circumferentially continuous before it reaches the bottom rim of
the container which dips into the liquor to be treated. The
preferred steam supply is saturated steam at a nozzle pressure of
about 100 lbs/ins.sup.2.
The preferred bath has a liquid capacity equal to 450 gallons, and
a feed liquor input of about 3 gals. per min. The internal
dimensions of the chamber 1 are preferably about 20 inches in
height and 26 inches in diameter are under these conditions a
suitable rate of steam infeed is intermittently discharged into the
chamber in the form of short bursts each of about 1 min. duration
alternating with inactive intervals of 2 hours duration.
The skirt 3 of the chamber is preferably multitudinously slotted or
of sawtooth shape so that the combustion gases will enter the bath
as a large number of small streams, thus to reduce what might
otherwise be excessive bath turbulence, and for preference the
submerged skirt is surrounded by an open bottom annular duct or
inverted channel 5 having a circumferential outer wall which is
similarly slotted or sawtoothed to provide a still greater
multiciplicity of outlets through which combustion gases are
discharged into the bath liquor.
The operation is preferably conducted continuously at a constant
concentration in the bath so that the rate of addition of feed
liquor just balances the rate of evaporation of water plus the
runoff of concentrated liquor. In practice this is preferably
achieved by continuous addition of feed liquor and intermittent
discharge of concentrated liquor so that the level in the bath
alternates between upper and lower limits. In the preferred method
of operation, the concentration of sulphuric acid is maintained
above that which will corrosively attack the steel components.
By intermittent agitation (e.g. by means of a suitably designed
rabble and drive 20) those salts which precipitate in the bath are
maintained in suspension and are thus removed with the concentrated
liquor. This hot saturated solution plus precipitate from the bath
is then cooled thereby precipitating the major part of the salts
which are to be removed. The cooled liquor is separated from the
precipitated salts by settling, filtration or the like, and the
purified liquor is directed back into the intake pipe leading to
the refining circuit.
As shown in FIG. 3, a tank 16 contains a bath 17 of liquor which
rises to the level 14. This tank receives at a level near its roof
via the inlet 18 the liquor to be purified, and at its lower or
floor level has a concentrated liquor take-off pipe 19. Means may
be provided for ensuring that the level of concentrated liquor in
the bath is maintained substantially constant and that the level is
maintained above that at which the combustion gases are discharged
into it. The tank 16 includes a roof plate 21 to which a plurality
of (in this case, three) chambers such as 1 are attached by means
of the mounting flange 6. Each said chamber is fitted through an
opening in the roof 21 which is equipped with a flue or the like
for taking off the exhaust gases after they have bubbled their way
through the bath 17.
* * * * *