This invention is directed to a crystallizer, a process and an apparatus
which are particularly suitable for producing high purity sodium chloride.
As discussed in detail in Sodium Chloride: The Production and Properties of
Salt and Brine, Dale W. Kaufmann, 1971, pages 15-21, sodium chloride
crystals are generally in the form of a simple cube without any modifying
faces. However, the presence of certain foreign substances in the solution
from which salt is crystallizing may cause modifications. Skeleton-type
crystals (either octahedrons or combinations of octahedron and cube) may
result from rapid crystal growth without the presence of a foreign
substance. Further, hopper-shaped cubes can be produced by rapid crystal
growth which is parallel to octahedron and dodecahedron faces. By filling
out the cube edges and corners, hopper-shaped depressions are formed at
the center of each of the cube faces. Such hopper-shaped cubes are
particularly preferred where rapid dissolving is desired, such as in some
food and seasoning applications and certain agricultural and chemical
uses.
High purity is another frequently desired characteristic of sodium
chloride. High purity may be desired in combination with rapid
dissolution, as in the situations mentioned above, or high purity may be
wanted for uses such as water softening.
Historically, high purity sodium chloride is manufactured in heated
enclosed evaporators to vaporize solvent water. Production of brine from
sodium chloride requires energy, typically obtained from fossil fuels. In
order to reduce fossil fuel usage in sodium chloride production, various
arrangements of brine heaters and evaporators have been designed and
operated. Typical arrangements to enhance efficiency employ multi-effect
evaporation and vapor recompression.
Sodium chloride produced in steam heated enclosed vessel evaporators is
usually granular in size and cubic in crystal geometry. However, as
mentioned above, sodium chloride crystal geometry is not necessarily
cubic. For example, the Alberger process and the grainer process produce
hopper-shaped crystals by open pan methods. Dentritic salt may be produced
in enclosed vessels by introducing foreign substances (crystal habit
modifiers) into the contained brine. Flat flakes may be produced by the
compression of granular sodium chloride.
Solar vaporization of the aqueous solvent in a brine to produce "solar
salt" is an ancient, low-cost alternative to the earlier presented methods
of sodium chloride production. In its simplest form, solar salt is
produ ed by exposing aqueous sodium chloride brines to sunlight,
evaporating some or all of the aqueous solvent to cause concentration and
thus crystallizing dissolved constituents (such as sodium chloride). The
major disadvantage of solar salt is the reduced sodium chloride purity
when compared to vacuum evaporated sodium chloride.
Another well-known process, sometimes, referred to as the "salting out"
process, provides a relatively low energy, low cost method for the
production of sodium chloride. In a salting out process, two or more
aqueous solutions, each containing a single solute, or more typically,
multiple solutes, are combined. When combined, the resulting aqueous
mixture contains two or more solutes such that the solubility of one or
more of the solutes is exceeded. For example, U.S. Pat. No. 3,832,143
discloses methods for making table-grade sodium chloride by mixing two
brines having two distinct magnesium chloride concentrations, but each
substantially saturated with respect to sodium chloride, to form a crystal
crop of table-grade sodium chloride and a brine depleted in sodium
chloride. The saturated brines may be prepared by solar evaporation of
initial or starting brines such as ocean brines and Great Salt Lake
brines. Specifically, Example II of U.S. Pat. No. 3,832,143 teaches mixing
in a reactor crystallizer a first brine containing, among other things,
1.2 wt. percent Mg, 8.0 wt. percent Na and 14.8 wt. percent Cl and a
second brine containing, among other things, 7.4 wt. percent Mg, 0.6 wt.
percent Na and 20.2 wt. percent Cl. First a slurry, then substantially
pure NaCl, are produced. U.S. Pat. No. 3,832,143 also discloses recycle of
the depleted brine through the solar evaporation system. It should
additionally be noted that U.S. Pat. No. 3,772,202 discloses use of a
solar pond to concentrate a bitterns brine which contains NaCl but
predominates in magnesium chloride. U.S. Pat. No. 3,852,044 discloses a
solar evaporation system which produces sodium crystals, potassium
minerals and an aqueous solution concentrated at least near magnesium
chloride saturation.
SUMMARY OF THE INVENTION
In one embodiment, the current invention is drawn to a flow-through sodium
chloride crystallizer comprised of a vertically oriented crystallizer body
having at least two segments of different cross-sectional area, at least
two inlets for the introduction of saturated MgCl2 brine at a minimum
of two distinct vertical locations having different cross-sectional areas
along the crystallizer body, at least two inlets for the introduction of a
saturated NaCl brine at a minimum of two distinct vertical locations
having different cross-sectional areas along the crystallizer body, at
least one lower outlet for removal of NaCl crystals and at least one upper
outlet for removal of spent brine.
The current invention also entails an apparatus for the production of a
saturated MgCl2 brine and NaCl crystals of varying segregated purity
comprising:
(a) at least one flow-through sodium chloride crystallizer comprised of a
vertically-oriented crystallizer body having at least two segments of
different cross-sectional area, at least two inlets for the introduction
of saturated MgCl2 brine at a minimum of two distinct vertical
locations having different cross-sectional areas along the crystallizer
body, at least two inlets for the introduction of a saturated NaCl brine
at a minimum of two distinct vertical locations having different
cross-sectional areas along the crystallizer body, at least one lower
outlet for removal of NaCl crystals and at least one upper outlet for
removal of spent brine;
(b) a spent brine MgCl2 reconcentration system; and
(c) means for transporting said spent brine from said upper outlet to said
spent brine MgCl2 reconcentration system.
Further, the current invention discloses a process for the preparation of a
NaCl crystals of varying, segregated purity comprising:
(a) introducing an upper saturated MgCl2 brine stream into a
vertically oriented crystallizer body at an upper segment of said
crystallizer body;
(b) introducing a lower saturated MgCl2 brine stream into said
crystallizer body at a lower segment of said crystallizer body, said upper
segment having a greater cross-sectional area than said lower segment;
(c) introducing an upper saturated NaCl brine stream into said crystallizer
body at said upper segment of said crystallizer body;
(d) introducing a lower saturated NaCl brine stream into said crystallizer
body at said lower segment of said crystallizer body;
(e) allowing said brine streams introduced in steps (a) through (d) to mix
in said crystallizer body to produce NaCl crystals and a spent brine
stream;
(f) removing said spent brine stream from the upper portion of said
crystallizer body; and
(g) removing said NaCl crystals from the lower portion of said crystallizer
body.
As used in this Summary of the Invention, "saturated MgCl2 brine" and
"saturated NaCl brine" have the definitions provided below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of one embodiment of the flow-through sodium chloride
crystallizer of the current invention.
FIG. 2 is a schematic of one embodiment of the apparatus of the current
invention for producing NaCl crystals.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein, the following terms have the definitions provided.
The phrase "saturated MgCl2 brine" refers to a substantially saturated
brine having MgCl2 as a principal component and may contain lesser
amounts of other inorganic components including but not limited to
compounds and/or ions of Na, K, Ca, SO4 and Br.
The phrase "saturated NaCl brine" refers to a substantially saturated brine
having NaCl as a principal component and may contain lesser amounts of
other inorganic components including but not limited to compounds and/or
ions of Mg, K, Ca, SO4 and Br.
The sodium chloride crystallizer of the current invention will be described
with reference to FIG. 1.
FIG. 1 illustrates schematically the preferred embodiment of the sodium
chloride crystallizer. At a minimum, the sodium chloride crystallizer is
comprised of a vertically oriented crystallizer body 11 and the various
inlets 16 though 19 and outlets 20 and 21 further described below.
Crystallizer body 11 is comprised of upper segment 12, lower segment 13
and transition segment 14. Upper segment 12 has a greater cross-sectional
area than that of lower segment 13. Although the current invention is not
limited to the following specifications, it is typical for the
cross-sectional area ratio of upper segment 12 to lower segment 13 to be
about 2/1 to about 25/1 and preferably about 3/1 to about 6/1. Transition
segment 14 is provided to supply fluid communication between upper segment
12 and lower segment 13. Optionally, crystallizer body 11 may have a
second transition segment 15 below lower segment 13.
Upper saturated MgCl2 brine inlet 16 and lower saturated MgCl2
brine inlet 17 are positioned at distinct vertical locations along
crystallizer body 11, with the caveat that such locations have different
cross-sectional areas. Although in FIG. 1 upper saturated MgCl2 brine
inlet 16 is located in upper segment 12 and lower saturated MgCl2
brine inlet 17 is located in lower segment 13, it is possible, for
example, to position upper saturated MgCl2 brine inlet 16 in
transition segment 14 and lower saturated MgCl2 brine inlet 17 in
optional second transition segment 15. Upper saturated MgCl2 brine
inlet 16 and lower saturated MgCl2 brine inlet 17 are fed
respectively by upper MgCl2 brine conduit 22 and lower MgCl2
brine conduit 23.
Upper saturated NaCl brine inlet 18 and lower saturated NaCl brine inlet 19
are positioned along the crystallizer body 11, with the caveat that such
locations have different cross-sectional areas. Although in FIG. 1 upper
saturated NaCl brine inlet 18 is located in upper segment 12 and lower
saturated NaCl brine inlet 19 is located in optional second transition
segment 15, it is possible, for example to position upper saturated NaCl
brine inlet 18 in transition segment 14 and lower saturated NaCl brine
inlet 19 in lower segment 13. Upper saturated NaCl brine inlet 18 and
lower saturated NaCl brine inlet 19 are fed respectively by upper NaCl
brine conduit 25 and lower NaCl brine conduit 26. Lower outlet 20 is
positioned in either the optional lower transition segment 15 or
(particularly if lower transition segment 15 is not present) in lower
segment 13.
Lower outlet 20 is provided for the removal of a slurry of high purity
(typically greater than 99.80% purity) sodium chloride. Also, a
surprisingly high percentage of such sodium chloride will be in the form
of hopper-shaped cubes. Conduit 28 is provided for further transport of
the slurry. Typically, the sodium chloride slurry is transported to
dehydration equipment (such as centrifuges) for removal of water from the
slurry. Upper outlet 21 is provided for the removal of spent brine from
the sodium chloride crystallizer.
In addition to the components described above, the crystallizer of the
current invention may be comprised of additional segments of varying
cross-sectional area, additional transition segments and additional inlets
and outlets for the MgCl2 brines, NaCl brines, slurries, and
crystallized sodium chloride.
The apparatus and process of the current invention may be further described
with reference to FIG. 2. The apparatus of the current invention is
comprised of one or more sodium chloride crystallizer body 11. Sodium
crystallizer body 11 is illustrated in detail at FIG. 1 and described in
detail above. Each sodium chloride crystallizer body 11 is fed by at least
two saturated MgCl2 brine streams through upper saturated MgCl2
brine inlet 16 and lower saturated MgCl2 brine inlet 17. Inlets 16
and 17 are supplied via upper MgCl2 brine conduit 22 and lower
MgCl2 brine conduit 23, respectively. Conduits 22 and 23 may be fed
from one saturated MgCl2 brine conduit 24 (as shown in FIG. 2) or
from separate saturated MgCl2 brine supply sources.
Each sodium chloride crystallizer body 11 is also fed by at least two
saturated NaCl brine streams through upper saturated NaCl brine inlet 18
and lower saturated NaCl brine inlet 19. Inlets 18 and 19 are supplied via
upper NaCl brine conduit 25 and lower NaCl brine conduit 26, respectively.
Conduits 25 and 26 may be fed from one saturated NaCl brine conduit 27 (as
shown in FIG. 2) or from separate saturated NaCl brine supply sources.
A slurry of sodium chloride crystals in brine is removed from crystallizer
body 11 via lower outlet 20 and transported via conduit(s) 28 to a system
suitable and adapted for removing brine from the sodium chloride crystals.
An illustrative brine removal system shown in FIG. 2 is comprised of wash
vessel 29, centrifuge 30 and dryer 31. The brine removed from wash vessel
29 and centrifuge 30 may be recycled back to crystallizer body 11 via
conduits 32 and 33, and, eventually conduit 27.
Spent brine is removed from crystallizer body 11 via upper outlet 21 and
routed for further handling via conduits 34 and 35. The spent brine is
preferably reconcentrated in MgCl2 for recycling to crystallizer 11.
Many means are available to reconcentrate such streams. Preferably, the
spent brine is reconcentrated by a solar evaporation system substantially
similar to the one illustrated at FIG. 2 and described below; however, the
spent brine may be first removed to holding tank 36 prior to
reconcentration. A solar evaporation system requires at least one solar
pond. Most preferably, the solar evaporation system of the current
application is comprised of first solar evaporation pond 37, second solar
evaporation pond 38 and third solar evaporation pond 39. As described in
detail in Example 1 below, a three stage system to reconcentrate
MgCl2 provides three batches of NaCl segregated by purity. In a
preferred embodiment, the NaCl from the first solar pond has an
approximately 99.0 to 99.7% purity, the NaCl from the second solar pond
has an approximately 98.5% to 99.0% purity and the NaCl from the third
solar pond has a purity of less than about 96.0%. Optionally, the solar
evaporation system may contain a spent brine holding tank 36 and a
reconstituted storage tank 40. Alternatively, it may also be desirable to
provide filter 41 and saturator 42 for solids removal and storage tank 43
for holding the reconstituted, filtered saturated MgCl2 brine prior
to supply to crystallizer body 11 via conduits 24, 22 and 23.
One method of supplying NaCl saturated brine for supply to crystallizer
body 11 is illustrated at FIG. 2. The method involves preparing "pickle
brine" (brine which has undergone fractional crystallization in a
so-called "lime pond" to remove a preponderance of the contaminant calcium
sulfate) then storing it at the proper sodium concentration in NaCl brine
tank 44. Additionally, it may be desirable to provide filter 45 and
saturator 46 for solids removal and storage tank 47 to hold the filtered
sodium saturated brine prior to supply to crystallizer 11 via conduits 27,
26 and 25.
As demonstrated by the examples and data which follow, the crystallizer,
apparatus and process of the current disclosure produce high purity NaCl
crystals. Additionally, a surprisingly high percentage of high purity NaCl
crystals produced by the crystallizer, apparatus and/or process of the
current invention are hopper-shaped cubes.
EXAMPLE 1
Process Material Balance
The process of the current invention is demonstrated by the material
balance described in this Example 1. It is understood that this material
balance is only an exemplary process within the scope of the current
invention. It is intended only as one working example of the current
invention. Neither this Example 1 nor the following examples are intended
to limit the scope of this invention.
This Example 1 is discussed with reference to FIGS. 1 and 2 and Table 1.
This material balance was based on a daily production of 500 tons
hopper-shaped NaCl as output (through one or more conduit(s) 28) from one
or more crystallizer body 11. The composition of the NaCl product stream J
(in slurry form) is detailed in Table 1. Approximately 50 to 80% of the
NaCl crystals are hopper-shaped cubes. The hopper-shaped NaCl product may
be further treated in wash vessel 29, centrifuge 30 and dryer 31 to
produce dried, purified hopper-shaped salt granules.
In operation a substantially saturated NaCl brine (1020 gpm) of composition
I is introduced into one or more crystallizer body 11 via conduits 25 and
26 to mix with a substantially saturated MgCl2 brine (870 gpm) of
composition H which is introduced into crystallizer body 11 via conduits
22 and 23. The spent brine of composition A is removed via conduit 34 and
transported via conduit 35. Most desirably the spent brine is
reconstituted and recycled to the one or more crystallizer body 11. Any
reconstitution means which will provide an appropriate saturated
MgCl2 brine for the crystallizer body 11 is acceptable in the current
process. However, a solar evaporation system is employed for this Example
1.
In operation of the solar evaporation system, spent brine may be
transported directly to first solar pond 37. Alternatively, the spent
brine may be sent to spent brine holding tank 36 prior to introduction
into first solar pond 37. First solar pond 37 is of sufficient size to
allow concentration of the brine to composition C. First solar pond 37
produces approximately 146,842 tons per year of about 99.6% purity cubic
NaCl having composition B, a brine of composition C and about 155 million
gallons per year water of evaporation. Brine of composition C is further
concentrated, which is accomplished in this example by use of secondary
solar pond 38 and tertiary solar pond 39. The brine of composition C is
transferred to secondary solar pond 38 having dimensions to produce a
brine of composition E. Secondary solar pond 38 produces 108,216 tons per
year of about 99.5% purity cubic NaCl having composition D, a brine of
composition E and about 101 million gallons per year water of evaporation.
The brine of composition E is transferred to tertiary solar pond 39 having
dimensions to produce a brine composition G. Tertiary solar pond 39
produces 45,360 tons per year of mixed salts having composition F, a brine
of composition G and about 25 million gallons per year water of
evaporation. The mixed salts are predominantly chloride and sulfate salts
of sodium, potassium and magnesium. They may be discarded or treated for
further recovery of the salts. The brine of composition G is typically
sent to reconstituted storage tank 40 prior to treatment in filter 41 and
saturator 42, then holding in storage tank 43 prior to use in crystallizer
body 11. It should be noted that in addition to producing a saturated
MgCl2 brine stream, the tertiary solar evaporation system of this
Example produces NaCl of size and shape equivalent to that produced by
conventional solar evaporation but segregated into three distinct
purities.
In its preferred embodiment, the saturated NaCl brine stream I is prepared
by producing a so-called "pickle" brine in a "lime pond" (not shown) to
remove the impurity calcium sulfate from the brine by fractional
crystallization. The pickle brine of composition P may be stored in NaCl
brine tank 44, treated in filter 45 and saturator 46, then stored in
storage tank 47. The brine transferred from saturator 46 to storage tank
47 may have the composition I or it may have a composition so that when
mixed with composition K in storage tank 47 the output of storage tank 47
will have the composition I.
In order to produce "make-up" saturated MgCl2 brine of concentrations
to replenish the recycled saturated MgCl2 brine for feed to
crystallizer body 11, a portion of the "pickle brine" of composition P may
be treated by solar evaporation processes similar to the evaporation
process of solar ponds 37, 38 and 39. The portion of "pickle brine" is
treated seriatum in solar ponds 50, 51 and 52 to produce brines of
composition Q, R and S. Additionally, approximately 210,600 tons per year
of "conventional" solar salt is produced from solar pond 50. A portion of
the "conventional" solar salt crop (approximately 31,200 tons per year)
may be dissolved in tank 48 to produce a substantially saturated NaCl
solution of Composition N. Brine filter 49 may be used to remove suspended
particulate contaminants. Brine of composition N may be mixed with brine
of composition M removed from centrifuge 30 to provide co-mingled brine of
composition L. This co-mingled brine may be used to wash the salt produced
in crystallizer body 11 free of adhering mother liquor to produce a
washed, purified NaCl of purity greater than 99.8%.
EXAMPLE 2
Crystallizer of the Current Invention
A crystallizer similar to that illustrated in FIG. 1 was employed. With
reference to FIG. 1, the crystallizer body had the following dimensions.
The saturated MgCl2 brine streams and the saturated NaCl brine streams
were introduced at locations as illustrated in FIG. 1. The operating data
are provided at Table 2 for these separate runs through the
above-described crystallizer.
Runs A-C were conducted at ambient temperature and pressure. The NaCl
product from Runs A-C, as determined by microscopic evaluation was
approximately 75 wt. % hopper-shaped cubes and 25 wt. % simple cubes.
EXAMPLE 3
Comparative Example of the Salting Out Process
This Example 3 demonstrates a "salting out" process generally of the type
described in U.S. Pat. No. 3,822,143. A funnel-shaped vertical reactor was
employed. From top to bottom, the reactor comprised a 6.0"
long×18.0" I.D. top section, a 12" long×18.0" I.D.×3.25"
I.D. transition section and a 24" long×3.25 elutrating leg.
Substantially saturated MgCl2 brine and substantially saturated NaCl
were simultaneously fed through separate inputs into the base of the
vertical reactor. The mixed brine was then circulated from the top of the
reactor into the bottom of the elutrating leg. The time of the runs varied
between 4 to 12 hours. The saturated MgCl2 brine input and the
saturated NaCl input were each fed to the reactor at a rate of 0.066 gpm.
The total flowrate to the reactor varied between 2.13 and 3.13 gpm. The
circulation flowrate to the elutrating leg varied between 2.14 and 3.0
gpm. The NaCl product produced this salting out process as determined by
microscopic evaluation was approximately 40 wt. % simple cubes, 60 wt. %
agglomerated cubes and essentially no hopper-shaped cubes.
which are particularly suitable for producing high purity sodium chloride.
As discussed in detail in Sodium Chloride: The Production and Properties of
Salt and Brine, Dale W. Kaufmann, 1971, pages 15-21, sodium chloride
crystals are generally in the form of a simple cube without any modifying
faces. However, the presence of certain foreign substances in the solution
from which salt is crystallizing may cause modifications. Skeleton-type
crystals (either octahedrons or combinations of octahedron and cube) may
result from rapid crystal growth without the presence of a foreign
substance. Further, hopper-shaped cubes can be produced by rapid crystal
growth which is parallel to octahedron and dodecahedron faces. By filling
out the cube edges and corners, hopper-shaped depressions are formed at
the center of each of the cube faces. Such hopper-shaped cubes are
particularly preferred where rapid dissolving is desired, such as in some
food and seasoning applications and certain agricultural and chemical
uses.
High purity is another frequently desired characteristic of sodium
chloride. High purity may be desired in combination with rapid
dissolution, as in the situations mentioned above, or high purity may be
wanted for uses such as water softening.
Historically, high purity sodium chloride is manufactured in heated
enclosed evaporators to vaporize solvent water. Production of brine from
sodium chloride requires energy, typically obtained from fossil fuels. In
order to reduce fossil fuel usage in sodium chloride production, various
arrangements of brine heaters and evaporators have been designed and
operated. Typical arrangements to enhance efficiency employ multi-effect
evaporation and vapor recompression.
Sodium chloride produced in steam heated enclosed vessel evaporators is
usually granular in size and cubic in crystal geometry. However, as
mentioned above, sodium chloride crystal geometry is not necessarily
cubic. For example, the Alberger process and the grainer process produce
hopper-shaped crystals by open pan methods. Dentritic salt may be produced
in enclosed vessels by introducing foreign substances (crystal habit
modifiers) into the contained brine. Flat flakes may be produced by the
compression of granular sodium chloride.
Solar vaporization of the aqueous solvent in a brine to produce "solar
salt" is an ancient, low-cost alternative to the earlier presented methods
of sodium chloride production. In its simplest form, solar salt is
produ ed by exposing aqueous sodium chloride brines to sunlight,
evaporating some or all of the aqueous solvent to cause concentration and
thus crystallizing dissolved constituents (such as sodium chloride). The
major disadvantage of solar salt is the reduced sodium chloride purity
when compared to vacuum evaporated sodium chloride.
Another well-known process, sometimes, referred to as the "salting out"
process, provides a relatively low energy, low cost method for the
production of sodium chloride. In a salting out process, two or more
aqueous solutions, each containing a single solute, or more typically,
multiple solutes, are combined. When combined, the resulting aqueous
mixture contains two or more solutes such that the solubility of one or
more of the solutes is exceeded. For example, U.S. Pat. No. 3,832,143
discloses methods for making table-grade sodium chloride by mixing two
brines having two distinct magnesium chloride concentrations, but each
substantially saturated with respect to sodium chloride, to form a crystal
crop of table-grade sodium chloride and a brine depleted in sodium
chloride. The saturated brines may be prepared by solar evaporation of
initial or starting brines such as ocean brines and Great Salt Lake
brines. Specifically, Example II of U.S. Pat. No. 3,832,143 teaches mixing
in a reactor crystallizer a first brine containing, among other things,
1.2 wt. percent Mg, 8.0 wt. percent Na and 14.8 wt. percent Cl and a
second brine containing, among other things, 7.4 wt. percent Mg, 0.6 wt.
percent Na and 20.2 wt. percent Cl. First a slurry, then substantially
pure NaCl, are produced. U.S. Pat. No. 3,832,143 also discloses recycle of
the depleted brine through the solar evaporation system. It should
additionally be noted that U.S. Pat. No. 3,772,202 discloses use of a
solar pond to concentrate a bitterns brine which contains NaCl but
predominates in magnesium chloride. U.S. Pat. No. 3,852,044 discloses a
solar evaporation system which produces sodium crystals, potassium
minerals and an aqueous solution concentrated at least near magnesium
chloride saturation.
SUMMARY OF THE INVENTION
In one embodiment, the current invention is drawn to a flow-through sodium
chloride crystallizer comprised of a vertically oriented crystallizer body
having at least two segments of different cross-sectional area, at least
two inlets for the introduction of saturated MgCl2 brine at a minimum
of two distinct vertical locations having different cross-sectional areas
along the crystallizer body, at least two inlets for the introduction of a
saturated NaCl brine at a minimum of two distinct vertical locations
having different cross-sectional areas along the crystallizer body, at
least one lower outlet for removal of NaCl crystals and at least one upper
outlet for removal of spent brine.
The current invention also entails an apparatus for the production of a
saturated MgCl2 brine and NaCl crystals of varying segregated purity
comprising:
(a) at least one flow-through sodium chloride crystallizer comprised of a
vertically-oriented crystallizer body having at least two segments of
different cross-sectional area, at least two inlets for the introduction
of saturated MgCl2 brine at a minimum of two distinct vertical
locations having different cross-sectional areas along the crystallizer
body, at least two inlets for the introduction of a saturated NaCl brine
at a minimum of two distinct vertical locations having different
cross-sectional areas along the crystallizer body, at least one lower
outlet for removal of NaCl crystals and at least one upper outlet for
removal of spent brine;
(b) a spent brine MgCl2 reconcentration system; and
(c) means for transporting said spent brine from said upper outlet to said
spent brine MgCl2 reconcentration system.
Further, the current invention discloses a process for the preparation of a
NaCl crystals of varying, segregated purity comprising:
(a) introducing an upper saturated MgCl2 brine stream into a
vertically oriented crystallizer body at an upper segment of said
crystallizer body;
(b) introducing a lower saturated MgCl2 brine stream into said
crystallizer body at a lower segment of said crystallizer body, said upper
segment having a greater cross-sectional area than said lower segment;
(c) introducing an upper saturated NaCl brine stream into said crystallizer
body at said upper segment of said crystallizer body;
(d) introducing a lower saturated NaCl brine stream into said crystallizer
body at said lower segment of said crystallizer body;
(e) allowing said brine streams introduced in steps (a) through (d) to mix
in said crystallizer body to produce NaCl crystals and a spent brine
stream;
(f) removing said spent brine stream from the upper portion of said
crystallizer body; and
(g) removing said NaCl crystals from the lower portion of said crystallizer
body.
As used in this Summary of the Invention, "saturated MgCl2 brine" and
"saturated NaCl brine" have the definitions provided below.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic of one embodiment of the flow-through sodium chloride
crystallizer of the current invention.
FIG. 2 is a schematic of one embodiment of the apparatus of the current
invention for producing NaCl crystals.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As used herein, the following terms have the definitions provided.
The phrase "saturated MgCl2 brine" refers to a substantially saturated
brine having MgCl2 as a principal component and may contain lesser
amounts of other inorganic components including but not limited to
compounds and/or ions of Na, K, Ca, SO4 and Br.
The phrase "saturated NaCl brine" refers to a substantially saturated brine
having NaCl as a principal component and may contain lesser amounts of
other inorganic components including but not limited to compounds and/or
ions of Mg, K, Ca, SO4 and Br.
The sodium chloride crystallizer of the current invention will be described
with reference to FIG. 1.
FIG. 1 illustrates schematically the preferred embodiment of the sodium
chloride crystallizer. At a minimum, the sodium chloride crystallizer is
comprised of a vertically oriented crystallizer body 11 and the various
inlets 16 though 19 and outlets 20 and 21 further described below.
Crystallizer body 11 is comprised of upper segment 12, lower segment 13
and transition segment 14. Upper segment 12 has a greater cross-sectional
area than that of lower segment 13. Although the current invention is not
limited to the following specifications, it is typical for the
cross-sectional area ratio of upper segment 12 to lower segment 13 to be
about 2/1 to about 25/1 and preferably about 3/1 to about 6/1. Transition
segment 14 is provided to supply fluid communication between upper segment
12 and lower segment 13. Optionally, crystallizer body 11 may have a
second transition segment 15 below lower segment 13.
Upper saturated MgCl2 brine inlet 16 and lower saturated MgCl2
brine inlet 17 are positioned at distinct vertical locations along
crystallizer body 11, with the caveat that such locations have different
cross-sectional areas. Although in FIG. 1 upper saturated MgCl2 brine
inlet 16 is located in upper segment 12 and lower saturated MgCl2
brine inlet 17 is located in lower segment 13, it is possible, for
example, to position upper saturated MgCl2 brine inlet 16 in
transition segment 14 and lower saturated MgCl2 brine inlet 17 in
optional second transition segment 15. Upper saturated MgCl2 brine
inlet 16 and lower saturated MgCl2 brine inlet 17 are fed
respectively by upper MgCl2 brine conduit 22 and lower MgCl2
brine conduit 23.
Upper saturated NaCl brine inlet 18 and lower saturated NaCl brine inlet 19
are positioned along the crystallizer body 11, with the caveat that such
locations have different cross-sectional areas. Although in FIG. 1 upper
saturated NaCl brine inlet 18 is located in upper segment 12 and lower
saturated NaCl brine inlet 19 is located in optional second transition
segment 15, it is possible, for example to position upper saturated NaCl
brine inlet 18 in transition segment 14 and lower saturated NaCl brine
inlet 19 in lower segment 13. Upper saturated NaCl brine inlet 18 and
lower saturated NaCl brine inlet 19 are fed respectively by upper NaCl
brine conduit 25 and lower NaCl brine conduit 26. Lower outlet 20 is
positioned in either the optional lower transition segment 15 or
(particularly if lower transition segment 15 is not present) in lower
segment 13.
Lower outlet 20 is provided for the removal of a slurry of high purity
(typically greater than 99.80% purity) sodium chloride. Also, a
surprisingly high percentage of such sodium chloride will be in the form
of hopper-shaped cubes. Conduit 28 is provided for further transport of
the slurry. Typically, the sodium chloride slurry is transported to
dehydration equipment (such as centrifuges) for removal of water from the
slurry. Upper outlet 21 is provided for the removal of spent brine from
the sodium chloride crystallizer.
In addition to the components described above, the crystallizer of the
current invention may be comprised of additional segments of varying
cross-sectional area, additional transition segments and additional inlets
and outlets for the MgCl2 brines, NaCl brines, slurries, and
crystallized sodium chloride.
The apparatus and process of the current invention may be further described
with reference to FIG. 2. The apparatus of the current invention is
comprised of one or more sodium chloride crystallizer body 11. Sodium
crystallizer body 11 is illustrated in detail at FIG. 1 and described in
detail above. Each sodium chloride crystallizer body 11 is fed by at least
two saturated MgCl2 brine streams through upper saturated MgCl2
brine inlet 16 and lower saturated MgCl2 brine inlet 17. Inlets 16
and 17 are supplied via upper MgCl2 brine conduit 22 and lower
MgCl2 brine conduit 23, respectively. Conduits 22 and 23 may be fed
from one saturated MgCl2 brine conduit 24 (as shown in FIG. 2) or
from separate saturated MgCl2 brine supply sources.
Each sodium chloride crystallizer body 11 is also fed by at least two
saturated NaCl brine streams through upper saturated NaCl brine inlet 18
and lower saturated NaCl brine inlet 19. Inlets 18 and 19 are supplied via
upper NaCl brine conduit 25 and lower NaCl brine conduit 26, respectively.
Conduits 25 and 26 may be fed from one saturated NaCl brine conduit 27 (as
shown in FIG. 2) or from separate saturated NaCl brine supply sources.
A slurry of sodium chloride crystals in brine is removed from crystallizer
body 11 via lower outlet 20 and transported via conduit(s) 28 to a system
suitable and adapted for removing brine from the sodium chloride crystals.
An illustrative brine removal system shown in FIG. 2 is comprised of wash
vessel 29, centrifuge 30 and dryer 31. The brine removed from wash vessel
29 and centrifuge 30 may be recycled back to crystallizer body 11 via
conduits 32 and 33, and, eventually conduit 27.
Spent brine is removed from crystallizer body 11 via upper outlet 21 and
routed for further handling via conduits 34 and 35. The spent brine is
preferably reconcentrated in MgCl2 for recycling to crystallizer 11.
Many means are available to reconcentrate such streams. Preferably, the
spent brine is reconcentrated by a solar evaporation system substantially
similar to the one illustrated at FIG. 2 and described below; however, the
spent brine may be first removed to holding tank 36 prior to
reconcentration. A solar evaporation system requires at least one solar
pond. Most preferably, the solar evaporation system of the current
application is comprised of first solar evaporation pond 37, second solar
evaporation pond 38 and third solar evaporation pond 39. As described in
detail in Example 1 below, a three stage system to reconcentrate
MgCl2 provides three batches of NaCl segregated by purity. In a
preferred embodiment, the NaCl from the first solar pond has an
approximately 99.0 to 99.7% purity, the NaCl from the second solar pond
has an approximately 98.5% to 99.0% purity and the NaCl from the third
solar pond has a purity of less than about 96.0%. Optionally, the solar
evaporation system may contain a spent brine holding tank 36 and a
reconstituted storage tank 40. Alternatively, it may also be desirable to
provide filter 41 and saturator 42 for solids removal and storage tank 43
for holding the reconstituted, filtered saturated MgCl2 brine prior
to supply to crystallizer body 11 via conduits 24, 22 and 23.
One method of supplying NaCl saturated brine for supply to crystallizer
body 11 is illustrated at FIG. 2. The method involves preparing "pickle
brine" (brine which has undergone fractional crystallization in a
so-called "lime pond" to remove a preponderance of the contaminant calcium
sulfate) then storing it at the proper sodium concentration in NaCl brine
tank 44. Additionally, it may be desirable to provide filter 45 and
saturator 46 for solids removal and storage tank 47 to hold the filtered
sodium saturated brine prior to supply to crystallizer 11 via conduits 27,
26 and 25.
As demonstrated by the examples and data which follow, the crystallizer,
apparatus and process of the current disclosure produce high purity NaCl
crystals. Additionally, a surprisingly high percentage of high purity NaCl
crystals produced by the crystallizer, apparatus and/or process of the
current invention are hopper-shaped cubes.
EXAMPLE 1
Process Material Balance
The process of the current invention is demonstrated by the material
balance described in this Example 1. It is understood that this material
balance is only an exemplary process within the scope of the current
invention. It is intended only as one working example of the current
invention. Neither this Example 1 nor the following examples are intended
to limit the scope of this invention.
This Example 1 is discussed with reference to FIGS. 1 and 2 and Table 1.
This material balance was based on a daily production of 500 tons
hopper-shaped NaCl as output (through one or more conduit(s) 28) from one
or more crystallizer body 11. The composition of the NaCl product stream J
(in slurry form) is detailed in Table 1. Approximately 50 to 80% of the
NaCl crystals are hopper-shaped cubes. The hopper-shaped NaCl product may
be further treated in wash vessel 29, centrifuge 30 and dryer 31 to
produce dried, purified hopper-shaped salt granules.
In operation a substantially saturated NaCl brine (1020 gpm) of composition
I is introduced into one or more crystallizer body 11 via conduits 25 and
26 to mix with a substantially saturated MgCl2 brine (870 gpm) of
composition H which is introduced into crystallizer body 11 via conduits
22 and 23. The spent brine of composition A is removed via conduit 34 and
transported via conduit 35. Most desirably the spent brine is
reconstituted and recycled to the one or more crystallizer body 11. Any
reconstitution means which will provide an appropriate saturated
MgCl2 brine for the crystallizer body 11 is acceptable in the current
process. However, a solar evaporation system is employed for this Example
1.
In operation of the solar evaporation system, spent brine may be
transported directly to first solar pond 37. Alternatively, the spent
brine may be sent to spent brine holding tank 36 prior to introduction
into first solar pond 37. First solar pond 37 is of sufficient size to
allow concentration of the brine to composition C. First solar pond 37
produces approximately 146,842 tons per year of about 99.6% purity cubic
NaCl having composition B, a brine of composition C and about 155 million
gallons per year water of evaporation. Brine of composition C is further
concentrated, which is accomplished in this example by use of secondary
solar pond 38 and tertiary solar pond 39. The brine of composition C is
transferred to secondary solar pond 38 having dimensions to produce a
brine of composition E. Secondary solar pond 38 produces 108,216 tons per
year of about 99.5% purity cubic NaCl having composition D, a brine of
composition E and about 101 million gallons per year water of evaporation.
The brine of composition E is transferred to tertiary solar pond 39 having
dimensions to produce a brine composition G. Tertiary solar pond 39
produces 45,360 tons per year of mixed salts having composition F, a brine
of composition G and about 25 million gallons per year water of
evaporation. The mixed salts are predominantly chloride and sulfate salts
of sodium, potassium and magnesium. They may be discarded or treated for
further recovery of the salts. The brine of composition G is typically
sent to reconstituted storage tank 40 prior to treatment in filter 41 and
saturator 42, then holding in storage tank 43 prior to use in crystallizer
body 11. It should be noted that in addition to producing a saturated
MgCl2 brine stream, the tertiary solar evaporation system of this
Example produces NaCl of size and shape equivalent to that produced by
conventional solar evaporation but segregated into three distinct
purities.
In its preferred embodiment, the saturated NaCl brine stream I is prepared
by producing a so-called "pickle" brine in a "lime pond" (not shown) to
remove the impurity calcium sulfate from the brine by fractional
crystallization. The pickle brine of composition P may be stored in NaCl
brine tank 44, treated in filter 45 and saturator 46, then stored in
storage tank 47. The brine transferred from saturator 46 to storage tank
47 may have the composition I or it may have a composition so that when
mixed with composition K in storage tank 47 the output of storage tank 47
will have the composition I.
In order to produce "make-up" saturated MgCl2 brine of concentrations
to replenish the recycled saturated MgCl2 brine for feed to
crystallizer body 11, a portion of the "pickle brine" of composition P may
be treated by solar evaporation processes similar to the evaporation
process of solar ponds 37, 38 and 39. The portion of "pickle brine" is
treated seriatum in solar ponds 50, 51 and 52 to produce brines of
composition Q, R and S. Additionally, approximately 210,600 tons per year
of "conventional" solar salt is produced from solar pond 50. A portion of
the "conventional" solar salt crop (approximately 31,200 tons per year)
may be dissolved in tank 48 to produce a substantially saturated NaCl
solution of Composition N. Brine filter 49 may be used to remove suspended
particulate contaminants. Brine of composition N may be mixed with brine
of composition M removed from centrifuge 30 to provide co-mingled brine of
composition L. This co-mingled brine may be used to wash the salt produced
in crystallizer body 11 free of adhering mother liquor to produce a
washed, purified NaCl of purity greater than 99.8%.
TABLE 1
__________________________________________________________________________
Description of Flowstreams of the Material
Balance of Example 1
Flow-
Composition (% By Weight) Flowrate
stream
Mg+2
Na+
K+
Ca+2
Cl-1
SO4-2
H2 O
(tons/yr.)
__________________________________________________________________________
A 4.56 3.18
0.69 16.74
3.03
71.76
3,821,810
B .06 39.14
.05
0.06
60.53
0.16 155,880
C 5.76 1.93
1.57 18.10
3.66
68.98
2,888,496
D 0.11 39.09
0.08
0.08
60.38
0.26 112,392
E 6.94 1.08
1.48 19.60
4.35
66.55
2,247,192
F 0.08 39.03
0.06
0.10
60.43
0.30 99,648
G 7.50 0.64
0.87 21.00
3.72
66.27
1,995,840
H 7.50 0.68
0.77 21.04
3.84
66.17
287.136*
I 1.02 8.75
0.56 15.56
1.90
72.21
306.662*
J 1.05 8.73
0.49 15.70
1.71
72.31
42.155*
K 0.01 9.20
0.36 15.85
1.24
72.58
57.138*
L NOT DETERMINED
M NOT DETERMINED
N 0.01 10.51
0.01
0.01
16.23
0.01
73.22
15.43*
O 0.02 0.01
0.03 99.94
11.102*
P 1.08 8.65
0.60 15.50
2.05
72.12
1,796,400
Q 1.50 7.40
0.80 15.10
3.00
72.20
R 3.50 5.50
2.20 14.20
6.70
67.66
S 7.50 0.50
0.80 20.50
3.80
66.90
71,539
__________________________________________________________________________
*Indicates "tons/hr." rather than "tons/yr.
EXAMPLE 2
Crystallizer of the Current Invention
A crystallizer similar to that illustrated in FIG. 1 was employed. With
reference to FIG. 1, the crystallizer body had the following dimensions.
______________________________________
Upper Segment 12
27" long × 2" I.D.
Lower Segment 13
44" long × 1" I.D.
Transition Segment 14
2.75" long × 2" I.D. × 1" I.D.
Second Transition
1.75" long × 1" I.D. × 0.375" I.D.
Segment 15
______________________________________
The saturated MgCl2 brine streams and the saturated NaCl brine streams
were introduced at locations as illustrated in FIG. 1. The operating data
are provided at Table 2 for these separate runs through the
above-described crystallizer.
TABLE 2
______________________________________
Crystallizer Operating Data
A B C
______________________________________
Run Length (Hours) 5.0 3.5 15.0
Upper Saturated MgCl2 Brine (gpm)
0.055 0.033 0.067
Lower Saturated MgCl2 Brine (gpm)
0.040 0.034 0.023
Upper Saturated NaCl Brine (gpm)
0.055 0.033 0.073
Lower Saturated NaCl Brine (gpm)
0.058 0.034 0.027
Mg++ Conc. in Saturated MgCl2 Brine
7.0 7.0 7.5
(wt. %)
Na+ Conc. in Saturated NaCl Brine
9.0 9.0 9.0
(wt. %)
Specified Velocity in Upper Segment 12
0.25 0.16 0.23
(in/sec)
Specified Velocity in Lower Segment 13
0.48 0.33 0.25
(in/sec)
Total Lower Feed (gpm)
0.10 0.07 0.05
Total Upper Feed (gpm)
0.11 0.07 0.14
______________________________________
Runs A-C were conducted at ambient temperature and pressure. The NaCl
product from Runs A-C, as determined by microscopic evaluation was
approximately 75 wt. % hopper-shaped cubes and 25 wt. % simple cubes.
EXAMPLE 3
Comparative Example of the Salting Out Process
This Example 3 demonstrates a "salting out" process generally of the type
described in U.S. Pat. No. 3,822,143. A funnel-shaped vertical reactor was
employed. From top to bottom, the reactor comprised a 6.0"
long×18.0" I.D. top section, a 12" long×18.0" I.D.×3.25"
I.D. transition section and a 24" long×3.25 elutrating leg.
Substantially saturated MgCl2 brine and substantially saturated NaCl
were simultaneously fed through separate inputs into the base of the
vertical reactor. The mixed brine was then circulated from the top of the
reactor into the bottom of the elutrating leg. The time of the runs varied
between 4 to 12 hours. The saturated MgCl2 brine input and the
saturated NaCl input were each fed to the reactor at a rate of 0.066 gpm.
The total flowrate to the reactor varied between 2.13 and 3.13 gpm. The
circulation flowrate to the elutrating leg varied between 2.14 and 3.0
gpm. The NaCl product produced this salting out process as determined by
microscopic evaluation was approximately 40 wt. % simple cubes, 60 wt. %
agglomerated cubes and essentially no hopper-shaped cubes.
