111111111111111111111111111111111111111111111111111111111111111111111111111
US006479025B2
(12) United States Patent
Denham, Jr. et al.
(10) Patent No.:
(45) Date of Patent:
US 6,479,025 B2
Nov. 12,2002
(54) PROCESS FOR THE PRODUCTION OF
SODIUM CARBONATE
(73) Assignee: Environmental Projects, Inc., Casper,
WY(US)
Related U.S. Application Data
(60) Provisional application No. 60/058,643, filed on Sep. 11,
1997.
(75) Inventors: Dale Lee Denham, Jr., Arvada, CO
(US); Rudolph Pruszko, Green River,
WY (US); Wayne C. Hazen, Denver,
CO (US)
* 12/1994 423/206.2
* 7/1996
94/27725
96/22398
FOREIGN PATENT DOCUMENTS
3,819,805 A 6/1974 Graves et al. 423/206
3,869,538 A 3/1975 Sproul et al. 423/206
3,904,733 A 9/1975 Ganey et al. 423/206
3,933,977 A 1/1976 Ilardi et al. 423/206
3,936,372 A 2/1976 Frangiskos 209/3
4,022,868 A 5/1977 Poncha 423/184
4,202,667 A 5/1980 Conroy et al. 23/302
4,283,277 A 8/1981 Brison et al. 209/166
4,286,967 A 9/1981 Booth et al. 23/298
4,299,799 A 11/1981 Ilardi et al. 423/206
4,324,577 A 4/1982 Sepehri-Nik 71/33
4,341,744 A 7/1982 Brison et al. 423/206
4,375,454 A 3/1983 Imperto et al. 423/206
4,814,151 A 3/1989 Benke 423/206
5,139,749 A * 8/1992 White 423/171
5,238,664 A 8/1993 Frint et al. 423/206
5,470,554 A 11/1995 Schmidt et al. 423/206
5,911,959 A * 6/1999 Wold et al. 423/206.2
5,989,505 A * 11/1999 Zolotoochin et al. 423/206.2
6,010,672 A * 1/2000 Turner 423/206.2
* cited by examiner
WO
WO
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.c. 154(b) by 0 days.
(21) Appl. No.: 09/151,694
(22) Filed: Sep. 11, 1998
(65) Prior Publication Data
us 2001/0007650 A1 Jul. 12, 2001
( *) Notice:
Primary Examiner~teven Bos
(74) Attorney, Agent, or Firm~heridan Ross Pc.
(51)
(52)
(58)
Int. CI? COlD 7/00; C22B 26/10
U.S. CI. 423/206.2
Field of Search 423/210, 206.2,
423/421
(57) ABSTRACT
References Cited
U.S. PATENT DOCUMENTS
(56)
2,704,239 A *
3,244,476 A
3,425,795 A
3,479,133 A
3,498,744 A
3,528,766 A
3,655,331 A
3,717,698 A
3/1955
4/1966
2/1969
11/1969
3/1970
9/1970
4/1972
2/1973
Pike 423/190
Smith et al. .. 23/63
Howard et al. . 23/63
Warzel ...... 23/63
Frint et al. . 23/63
Coglaiti et al. 23/63
Seglin et al. . 23/63
Ilardi et al. 423/206
A process for the production of sodium carbonate monohydrate
is disclosed. The process includes heating a feed
stream containing trona and insoluble impurities in a calcining
apparatus to a temperature of less than about 3500 C.
to form anhydrous sodium carbonate. The anhydrous
sodium carbonate is contacted with a saturated sodium
carbonate brine solution to form sodium carbonate monohydrate
crystals. Sodium carbonate monohydrate crystals
are separated from insoluble impurities.
23 Claims, 7 Drawing Sheets
FIG. 1
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SETTLING TEST ON TRONA CALCINED IN CO2
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- Temperature 300 C
- - - Temperature 450 C
_. Temperature 600 C
TIME (HRS)
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SETTLING TEST ON NON-MAGNETIC PRODUCT FROM
TRONA CALCINED IN CO2
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SUMMARY OF DATA FROM CALCINING TRONA IN C02 AND AIR
CALCINATION TEMPERATURE, DEGREES C
150 300 450 600
CO2 C02 NM AIR CO2 C02 NM AIR CO2 C02 NM AIR CO2 C02 NM AIR
THICKENING TESTS:
SOLUTION COLOR SLIGHT SLIGHT SLIGHT YELLOW YELLOW AMBER AMBER YELLOW SLIGHT COLORLESS COLORLESS COLORLESS
FOAM SLIGHT SLIGHT SOME SOME SOME MUCH MUCH SOME SLIGHT NONE NONE NONE
HOURS TO:
1/2 OF VOLUME 0.8 0.3 1.3 2.9 0.6 1.9 4.0 1.3 3.5 6.4 2.1 24.0
1/3 OF VOLUME 1.5 0.4 2.5 4.8 0.8 3.0 6.7 1.5 12.0 19.0 3.4
1/4 OF VOLUME 3.0 0.5 4.5 12.0 0.9 4.3 19.0 2.3 24.0 13.0
FINAL VOL., ml 78 53 82 112 54 75 127 52 140 175 125 237
RATIO OF HOURS TO:
1/2 OF VOLUME 2.7 1.0 4.3 9.7 2.0 6.3 13.3 4.2 11.7 21.3 7.0 80.0
1/3 OF VOLUME 3.8 1.0 6.3 12.0 2.0 7.5 16.8 3.8 30.0 47.5 8.5
1/4 OF VOLUME 6.0 1.0 9.0 24.0 1.8 8.6 38.0 4.6 48.0 26.0
FINAL VOL., ml 1.5 1.0 1.5 2.1 1.0 1.4 2.4 1.0 2.6 3.3 2.4 4.5
FINAL%SOLIDS 35. 27. 36. 26. 28. 37. 20. 24. 19. 14. 9. 11.
NA2C03 IN FINAL THICKENED PULP
DIST. % 6 4 5 9 4 5 11 4 12 15 11 20
RATIO 1.5 1.0 1.4 2.3 1.0 1.3 3.0 1.2 3.1 4.0 2.8 5.3
INSOL FROM GROUND CALCINE
wr. %PLUS 500 48.2 74.7 53.1 41.6 63.6 53.9 41.1 50.5 35.1 29.4 55.6 35.0
LEACH SOLUTION ASSAYS
mg/l Si <3 <3 9 3 18 9 117 60
mg/l ORGANIC C 24 51 66 459 63 57 < 15 30
gil AI <1 <1 <1 <1
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u.s. Patent Nov. 12, 2002 Sheet 5 of 7 US 6,479,025 B2
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u.s. Patent Nov. 12, 2002 Sheet 6 of 7 US 6,479,025 B2
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US 6,479,025 B2
2
BRIEF DESCRIPTION OF THE DRAWINGS
60
FIG. 1 is a graph illustrating the settling characteristics of
trona calcined in a CO2 atmosphere at various temperatures;
FIG. 2 is a graph illustrating the settling characteristics of
trona calcined in an air atmosphere at various temperatures;
FIG. 3 a graph illustrating the settling characteristics of
55 trona calcined in a CO2 atmosphere at various temperatures
and treated to remove magnetic impurities; and
FIG. 4 is a table providing data for various settling and
compositional characteristics of trona calcined in a variety
of temperatures and atmospheres.
FIG. 5 is a side view of an indirect heat calcining
apparatus of the present invention.
FIG. 5A is an illustration of a one-piece exhaust port
containing an expansion chamber.
FIG. 6 is a plan view of an indirect heat calcining
65 apparatus of the present invention.
FIG. 7Ais an illustration of a bed plate having a fluidizing
gas inlet holes.
collection chute which is connected to the calcining chamber.
The apparatus can also include a plurality of holes on the
bed plate and a gas inlet for introducing a fluidizing gas into
the apparatus through the bed plate holes. The apparatus can
5 include an exhaust port located above the calcining chamber.
The exhaust port can also include an expansion chamber for
slowing the velocity of gas exiting the calcining apparatus.
The indirect heating element of the apparatus can be, for
example, coils within the calcining chamber which conduct
10 the heated fluid through the chamber. Thus, the indirect
heating element can include a fluid inlet port and a fluid
outlet port. The apparatus can also include a plurality of
calcining zones which are defined by compartmental walls.
The present invention includes a calcining process for
15 treating a saline mineral which includes introducing the
saline mineral to a calcining chamber, heating the saline
mineral to a temperature of less than about 350° by contacting
it with an indirect heating element and removing the
calcined material from the chamber. In this embodiment, the
20 calcining chamber can include a bed plate located below the
indirect heating element and having a plurality of bed plate
holes and a gas inlet for introducing a fluidizing gas into the
chamber through the bed plate holes. The calcining apparatus
can also include an exhaust port located above the
25 calcining chamber which can have an expansion chamber
for slowing the velocity of exiting gas. The apparatus can
also include a plurality of calcining zones defined by compartmental
walls.
Other processes of the present invention include processes
30 for calcining material and subsequent processing of the
material. For example, such processing can include
purification, such as crystallization.
An additional process of the present invention is a method
for reducing the emission of pollutants during calcining.
35 This process includes heating a saline mineral in a calcining
vessel wherein the calcination step produces a gas comprising
water vapor and a pollutant. The calcining gas is
removed from the calcining vessel to an outlet and at least
a portion of the water vapor in the calcining gas is con-
40 densed.
In this manner, a portion of the pollutants in the calcining
gas are removed. This process can also include the use of a
heat source for calcining which is not in direct fluid communication
with the material to be calcined. In further a
45
aspect, the material is calcined at temperatures less than
about 250° C.
SUMMARY OF THE INVENTION
CROSS REFERENCE TO RELATED
APPLICATIONS
BACKGROUND OF THE INVENTION
1
PROCESS FOR THE PRODUCTION OF
SODIUM CARBONATE
A variety of industrial processes involve the use of
calcination to thermally decompose materials either to aid in
the purification of materials or for use in an industrial
process. Generally, calcination processes involve exposing
the materials to be calcined to heat to thermally decompose
the materials. Thus, calcination differs from thermal drying
of materials in which free water is driven off by exposure to
increased temperatures. In contrast, calcination involves
changing the chemical composition of the material.
A number of apparatus are known for calcination processes.
For example, rotary direct-fired calciners use an open
flame as a heat source and therefore, necessitate the use of
combustion air. Also, vertical fluid bed calciners use heated
gas in direct contact with the material to be calcined.
Despite the well-known use of calcination, a number of
problems exist in the use of conventional calcination processes.
For example, the emission of by-products such as
particulates causes pollution concerns. Additionally, a number
of calcination processes are not energy efficient because
much of the energy from the process is released to the
atmosphere in the form of heat.
Further, many calcination processes which operate at high
temperatures, such as use of open flame calciners, unevenly
heat the material to be calcined. For example, in open flame
rotary calciners, material contacting the flame may experience
a temperature close to 1000° c., even though the
average temperature in the calciner may be significantly
below that temperature. In this manner, some particles may
not be fully calcined and some may be combusted.
Alternatively, some larger particles may be calcined on the
outside, but not on the inside of the particle. This type of
disadvantage can also have significant negative effects on 50
downstream processing because the material exiting the
calcination process is not uniform in its chemical composition.
Therefore, subsequent processing will have more variable
results than if the material from the calcination process
was uniform in nature.
As a result of the above disadvantages of known calcination
technology, there remains a need for improved calcination
apparatus and methods of use.
The present invention relates to an apparatus for the
calcination of materials and uses therefor.
One embodiment of the present invention is an indirect
heat calcination apparatus for calcining materials. The apparatus
includes a feed inlet, a calcining chamber which is
interconnected to the feed inlet, an indirect heating element
within the calcining chamber to transfer heat from a heated
fluid to the material, a bed plate located below the indirect
heating element within the calcining chamber, and a product
This application claims priority under 35 U.S.c. §119 (e)
to U.S. provisional application Ser. No. 60/058,643, filed
Sep. 11, 1997 and under 35 U.S.c. §120 to U.S. patent
application Ser. No. 08/967,281, filed Jul. 3, 1997 and
PCT/US94/05918, filed May 25, 1994.
FIELD OF THE INVENTION
US 6,479,025 B2
4
In a further embodiment of the present invention, the step
of calcining is conducted by heating a feedstream in an inert
atmosphere to produce a calcined material. The term inert
atmosphere refers to any atmosphere which is less oxidizing
5 than air. For example, an inert atmosphere can be an
atmosphere of carbon dioxide. Alternatively, the carbon
dioxide can also include water vapor and/or air. As discussed
in m ore detail below, some gaseous by-products of
calcination, such as carbon dioxide and water vapor gener-
10 ated as part of a calcining gas in some processes can be
recycled and used as a fluidizing gas in a fluidized bed
calciner.
The calcining step is preferably performed utilizing an
indirect heating process in a calcining vessel such as a
fluidized bed reactor. In the indirect heating process, the
15 combustion gases from the heat source are not in direct fluid
communication with the material being calcined, but rather
provide heat to the material by conduction through, for
example, heating coils, as described in more detail below.
The step of indirectly heating material for calcining
20 comprises the steps of heating a fluid and bringing the heated
fluid into thermal communication with material in the calcining
vessel. As used in this invention, a "fluid" refers to a
gas or a liquid medium. This step can be accomplished
utilizing a heat source which provides the heated fluid to
25 coils positioned within the interior of the calcining vessel. In
one embodiment, the heat source is a steam boiler and the
fluid is steam. Alternatively, the fluid may comprise oil or
any other appropriate medium. The step of heating the fluid
can comprise the steps of combusting an energy source to
30 produce heat and combustion gas, transferring at least a
portion of the heat to the fluid, and directing at least a portion
of the combustion gas through a combustion gas outlet
which is not in direct fluid communication with the calcining
vessel.
Referring to FIG. 5 there is shown one embodiment of an
indirect heat calcination apparatus of the present invention.
The indirect heat calcination apparatus 10 includes an indirect
heating element 14 located within the calcining chamber
16 for providing indirect heat to the material. The indirect
40 heating element 14 can be any conduit that allows a fluid to
flow within its walls while facilitating the transfer of heat
from the fluid to the material. As described above, the fluid
is heated to a desired temperature and enters the indirect
heating element 14 at an inlet port 18 and travels through the
45 entire length of the indirect heating element 14 and exits
through the outlet port 22. As the fluid travels through the
indirect heating element 14, heat is transferred from the fluid
to the indirect heating element 14 and ultimately to the
material to be calcined. In this manner, the material is
50 calcined without being exposed to a direct flame or heating
fluid. Typically, a sufficient amount of material is added to
the indirect heat calcination apparatus 10 to cover the entire
indirect heating element 14 within the calcining chamber 16.
However, a smaller amount of the material can be calcined
55 using the apparatus of the present invention.
In order for an efficient heat transfer to occur, it is
preferred that the indirect heating element 14 be made from
a material which is a good heat conductor. Preferably, the
material of indirect heating element 14 is selected from the
60 group consisting of a metal such as copper, steel, iron,
nickel, zinc, stainless steel and mixtures thereof; ceramics;
and composites. More preferably, the material of indirect
heating element 14 is selected from the group consisting of
steel and stainless steel and most preferably, is stainless
65 steel.
As described above, the fluid for providing the heat for
calcination can be any liquid or gas which can be heated to
In various embodiments of the present invention, processes
and apparatus involve the use of a calcining step with
low temperature heating of the feedstream at temperatures
lower than conventional calcination, such as in direct fired
rotary kiln calciners. More particularly, the calcining step of
the present invention includes heating a feedstream to a
temperature of less than about 3500 c., more preferably less
than about 2500 c., and more preferably at a temperature
from about 1200 C. to about 2500 C. As used herein,
reference to heating a feedstream to less than a certain
temperature refers to raising the temperature of the particles
in the feedstream within the stated temperature constraints,
and not to the temperature of the ambient atmosphere in the
calciner or to the temperature of the heat transfer medium.
Moreover, reference to heating a feedstream to less than a
certain temperature requires that no substantial portion of
particles in the feedstream be heated in excess of the stated
temperature constraints. Thus, it should be recognized that
while substantially the entire feedstream is maintained
within the temperature constraints, particles which actually
come into contact with a heat transfer surface, such as a
heated tube, may exceed the temperature constraints. More
particularly, however, no more than about 15 wt. % of the
feedstream should be heated in excess of the stated temperature
constraints, more preferably no more than about 10
wt. %, and most preferably no more than about 5 wt %. In
another aspect, no portion of the material in the feedstream
is heated in excess of about 4500 C.
Calcination in accordance with these temperature constraints
of the present invention provides a number of
previously unrecognized significant benefits. As discussed in 35
more detail below, the amount of pollutants from the calcination
process is reduced with low temperature calcination.
For example, low temperature calcination does not volatilize
as many organic compounds from insoluble impurities as
mid and high temperature calcination. Thus, fewer volatile
organic compound (VOC) pollutants are generated by calcination.
Also, fewer soluble organic compounds, such as
sulfonates, are generated. Additionally, benefits in subsequent
processing are obtained.
In a preferred embodiment, the calcination temperature
constraints are more readily achieved by controlling the
particle size and particle size distribution of particles in the
feedstream. By having a relatively small particle size with a
relatively narrow particle distribution, particles in the feedstream
can be evenly heated to meet the temperature constraints
as discussed above. More particularly, the feedstream
to the calciner is typically comminuted to reduce the
particle size. For example, the feedstream can be comminuted
to a particle size of less than about Y4 inch,
alternatively, less than about 6 mesh, and alternatively, less
than about 20 mesh. In addition, the feedstream is preferably
sized into multiple size fractions for calcining. More
particularly, the feedstream is sized into 3 or more size
fractions, more preferably 5 or more size fractions, and most
preferably 7 or more size fractions. In this manner, it is more
likely that sufficient heating of all the particles will occur to
completely calcine them without excessively heating
smaller particles in excess of the temperature constraints
identified above. Thus, in a further embodiment, the present
process includes calcination of at least about 95 wt. % of the
feedstream, more preferably, at least about 98 wt. %, and
most preferably, at least about 99.5 wt. %.
3
FIG. 7B is an illustration of bed plate having a fluidizing
gas inlet holes and a gas-flow deflector.
DETAILED DESCRIPTION OF IRE
INVENTION
US 6,479,025 B2
5
a sufficiently high temperature required for calcination. Such
fluids include water, steam, oil, and gases, including air. For
calcining trona, preferably the fluid is steam.
Again referring to FIG. 5, it is preferred that the fluid inlet
port 18 is located above the fluid outlet port 22. This
arrangement ensures that a lower amount of energy is
required to operate the indirect heating element 14 because
gravity aids in removing fluid from the indirect heating
element 14. Moreover, when a gas such as steam is used, it
is possible that some of it may condense to a liquId form as
the heat is transferred to the indirect heating element. The
presence of a condensed liquid within the indirect heating
element 14 reduces the amount of heat transferred to the
indirect heating element 14 because some of the energy will
be used to heat the condensed liquid. In order to reduce this
problem, the inlet port 18 is located above the outlet port 22
to facilitate the removal of any condensed liquid.
The indirect heating element 14 can be positioned within
the apparatus 10 such that the indirect heating element 14
traverses back and forth across the apparatus and from top
to bottom. This arrangement provides a large indirect heating
element surface area. However, even with this
arrangement, the amount of surface area of the indirect
heating element 14 is limited; therefore, not all of the
material particles will come in direct contact with the
indirect heating element 14 when the material is stationary
within the apparatus. Although all of the particles can be
heated to a desired calcination temperature by prolonged
exposure to the indirect heating element 14 and allowing the
heat to transfer from one particle to another and eventually
reaching an equilibrium, this method of stationary indirect
heat calcination requires a large amount of energy and time
rendering the apparatus rather inefficient. To expedite the
calcination process and/or to reduce the amount of energy
required, substantially all of the particles within the calcining
chamber 16 can be made to be dynamic, i.e., nonstationary
within the calcining chamber 16, during at least a
portion of the calcination process. Any method of creating a
dynamic motion of the particles can be used such as stirring,
shaking and agitating.
In one particular embodiment, the particles are placed on
top of the bed plate 26 and are fluidized by a fluidizing gas
which is introduced into the calcining chamber through a
plurality of bed plate holes 30. This fluidization process
causes a juggling effect of the particles and allows more
particles to come in a direct contact with the indirect heating
element 14, resulting in a relatively even distribution of heat
among the material particles. In addition, this fluidization
process can be used to separate the particles based on the
difference in density. The juggling effect provided by the
fluidizing gas allows relatively heavy particles to settle to
the bottom of the pile while allowing relatively light particles
to "float", i.e., concentrate, to the top of the pile.
The primary heat transfer mechanism is the material to
coil contact and not the material to fluidizing gas contact.
Therefore, the fluidization gas velocity and volume has to be
low or kept to a minimum to maximize the contact of the
material to the indirect heating coils. This concept is contrary
to current technology where the coils in a fluid bed
calciner are used to heat the fluidizing gas which in turn is
used to heat the material. In such a process, large volumes
of fluidizing gas is required for the heat transfer to the
material to take place.
The indirect heat calcination apparatus of the present
invention can also include a gas plenum 34. The gas plenum
34 may be located underneath the bed plate 26 to provide a
6
substantially equal gas pressure throughout the bed plate
holes 30. These holes can be angled, vertical or perpendicular
to the direction of gas from the plenum to the calcination
bed. Angled holes will aid in the direction of flow of material
5 through the calcining zone. In this embodiment, the angle of
the hole must be greater than the angle of repose of the
material being calcined to prevent material from falling into
the hole. Moreover, the presence of a gas plenum 34 in the
apparatus 10 also reduces a possibility of particles falling
through the bed plate holes 30 and blocking the flow of
10 fluidizing gas into the apparatus. In operation, the fluidizing
gas is introduced into the apparatus 10 through a gas inlet 38
into the gas plenum 34. As some materials are calcined, the
density of the material decreases. With the lower density, the
amount of fluidization gas needed decreases. Therefore,
15 individual flow controls for the fluidizing gas to each
calcining zone is preferred. In one particular embodiment,
fluidizing gas is heated to about the same temperature as the
temperature of the heating coils to prevent cooling of
material particles and/or to maintain the temperature above
20 the dew point. In this manner, condensation of water in the
fluidizing gas is avoided.
The indirect heat calcination apparatus 10 of the present
invention can also include an exhaust port 42 to prevent
excess pressure build-up within the apparatus or to remove
25 any volatile compounds which are released or generated
from the material during the calcination process. The
exhaust port is located above the material level to allow the
fluidizing gas to fluidize the material particles. Since the
particles are not all identical size, it is expected that some of
30 the lighter particles, e.g., smaller particles or the material
dust, will be carried into the exhaust port 42.
In order to reduce the amount of particles removed from
the apparatus by the action of the fluidizing gas, the indirect
heat calcination apparatus 10 of the present invention can
35 also include an expansion chamber 46 which is located
below or near the exhaust port 42. The cross-sectional area
of the expansion chamber 46 is larger than the crosssectional
area of the calcining chamber 16, and as a result the
velocity of gas, i.e., the flow rate, decreases as the fluidizing
40 gas flows from the calcining chamber 16 into the expansion
chamber 46. This decrease in the fluidizing gas flow rate
results in some of the solids carried upward into the expansion
chamber 46 by the fluidizing gas to settle and drop back
down into the calcining chamber 16, thus reducing the
45 particulate emission from the calcination apparatus. The
expansion chamber is even more important in a case where
the material releases vapor upon during calcining. This is the
case with trona, where carbon dioxide and water vapor are
released. This release of vapors increases the volume of
50 fluidizing gas in the calciner bed and therefore increases the
velocity of the fluidizing gas. This effect further entrains
particles that can be returned to the calciner bed with the use
of an expansion zone. Moreover, the exhaust port 42 can be
fitted with other. apparatus to collect any material that is
55 released through the exhaust port 42. For example, a condenser
can be fitted to the exhaust port 42 to condense and
collect water vapor or other useful materials, a filter can be
fitted to further reduce the amount of particulate matter that
is released into the environment, or a gas collector can be
60 fitted to collect or recycle the fluidizing gas or other gases
which may be released through the exhaust port 42.
Alternatively, the exhaust port 42 and the expansion chamber
46 can be a single unit piece, i.e, the expansion chamber
46 can be an integral part of the exhaust port 42 as shown
65 in FIG. 5A.
A process for indirect heat calcination of a material using
the apparatus of the present invention will now be described
US 6,479,025 B2
7 8
compartment wall 74, the material overflows into the third
calcination zone 62. At least a portion of the material in the
third calcination zone 62 then flows into the fourth calcination
zone 66 through the opening 86. The calcined material
then overflows into the product collection chute 90 where it
is collected.
Having a multiple calcination zone provides a longer
average residence time for material within the indirect heat
calcination apparatus 10. The desired average residence time
depends on a variety of factors including the temperature of
the indirect heating element 14, the feed rate, the particle
size of the feed, the completeness of calcination of the
feedstream and the amount of time required to calcine the
material. The underflow/overflow design forces contact of
the material being calcined with the coils.
Referring again to FIG. 6, as the material flows into the
second calcining zone 58, the fluidizing gas can be used to
provide a density separation as described above. In this
manner, the lighter materials will be concentrated on the top
portion and the denser materials will be concentrated on the
bottom portion. In the case of trona ore being calcined, this
means that the lighter anhydrous sodium carbonate and/or
trona will be on the top portion and the heavier impurities
such as shortite, shale and/or pyrite will be concentrated in
the bottom portion. A similar density separation can be
achieved in the fourth calcining zone 66. By allowing a
means for removing the bottom impurity concentrated portion
in the second and/or the fourth calcination zones, a
substantially purified calcined material can be collected
through the product collection chute 90.
Alternatively, all the flow of the material from one calcining
zone to another calcining zone can be made to
proceed over the compartmental walls, thus eliminating a
need for openings 82 and 86. One way this can be accomplished
is by increasing the fluidizing gas flow directly
adjacent to the compartment wall to the point where all
material including high density material is forced to overflow
the compartmental wall. In order to prevent back-flow
40 of the materials, the successive compartment walls can be
lower in height than the previous compartment wall. In this
manner, each successive calcining zone will contain less
amount of heavier impurities.
As shown in FIG. 7A, the bed plate holes 30 can simply
be an opening, in which case the direction of the gas flow is
substantially perpendicular to the opening of the bed plate
holes 30 or can be determined by the direction of gas-flow
prior to entering the bed plate holes 30.
Alternatively, as shown in FIG. 7B, the bed plate holes 12
can also include a gas flow deflector 94 which is placed
above the bed plate holes 30. The deflector 94 can serve a
multiple purposes. For example, it can be designed to
prevent any particles from entering, or falling through, the
bed plate holes 30. Another way to achieve this result is to
punch holes in the plate at an angle. In addition, the
movement of the particles towards the product collection
chute 90 can be facilitated by using the gas flow deflector 94
to introduce the fluidizing gas in the direction towards the
product collection chute 90. Thus, the average residence
time of the particles can be controlled by using the fluidizing
gas and the gas flow deflector 94.
The materials calcined using the indirect heat calcination
apparatus of the present invention have unique product
characteristics because of the use of low heat and relatively
even heating of the particles during the calcination process.
In addition, the materials can be further processed, including
dry separation such as density separation, electrostatic
in reference to FIG. 6 which illustrates the indirect heat
calcination apparatus having four different calcining zones
54, 58, 62 and 66, that are separated by three compartmental
walls 70, 74 and 78. The material can be pretreated, e.g.,
comminuted, size separated and/or dried, prior to being 5
calcined using the indirect heat calcining apparatus of the
present invention. In a typical operation, a feedstream of
comminuted material is introduced into the apparatus 10
through a feed inlet 50. In order to reduce the amount of
agglomeration of particles due to the moisture that is present 10
in the calcining atmosphere, the indirect heat calcining
apparatus 10 can also include a predried-gas inlet (not
shown) near the feed inlet 50 for reducing the moisture level
of the particles or moisture in the atmosphere from coming
in contact with particles. Alternatively, the first calcining 15
zone 54 can be used as both a pre-drying region as well as
the first calcining zone. However, if a separate predried-gas
inlet is used, the diameter of the predried-gas inlet is selected
to ensure that a sufficient gas flow rate is maintained to
provide a sufficient level of pre-drying. Factors influencing 20
the diameter of the predrying-gas inlet include the particle
size of the material, the moisture level of the calcining
atmosphere, density of the material, and the desired gas flow
rate. Pre-heating with dry fluidization gas is used to allow
material of a lower temperature to enter the calciner and mix 25
into the material bed before condensation can occur on the
entering material. Condensation on the material can cause
agglomerates to form or caking. The temperature of this gas
is less than the calcining temperature, but above the dew
point for the material's moisture content. It is also important 30
not to let the material reach a temperature above the calcination
temperature before it is fluidized, otherwise moisture
released during calcination can cause the particle to cake. To
limit the temperature in the first calcining zone to prevent
condensation and caking of material, the amount of heating 35
element, such as coils, for conducting heating fluid in the
first calcining zone can be less than in other zones. In
addition, the first calcining zone can also include already
calcined material to reduce the amount of gas released from
calcination in the first zone.
The primary purpose of heating the material with the
pre-drying gas is to reduce the amount of moisture present
where the ore enters the calciner. Thus, although some of the
material may be calcined during this pre-drying process, the
majority of the material is not calcined by this pre-drying 45
process. Drying the material reduces the agglomeration, thus
maintaining the high surface area of the particles which is
desired for indirect heat calcination. Particles having a high
surface area to volume ratio can be calcined more quickly
and/or more efficiently than the particles having a low 50
surface area to volume ratio.
The rate of pre-dried gas flow depends on a variety of
factors including the feed rate, the particle size and the
density of impurities and/or the material being calcined.
As the materials are introduced into the first calcining 55
zone 54, they are fluidized by a fluidizing gas and are heated
by the indirect heating element 14. The materials then flow
to the second calcining zone 58, the third calcining zone 62
and the fourth calcining zone 66, in a successive manner.
Although FIG. 6 shows each calcining zones having its own 60
gas inlet 38 and flow control (not shown), the apparatus can
have less than one gas inlet per calcining zone for providing
the fluidizing gas to the entire bed plate 26 of the apparatus
10. As more material is fed to the first zone 54, at least a
portion of the materials in the first zone 54 flows in to the 65
second zone 58 through the opening 82. As the height of the
feedstream in the second zone 58 reaches the top of the
9
US 6,479,025 B2
10
separation, magnetic separation, calorimetric separation;
and wet separation such as recrystallization methods and
evaporative crystallization methods.
The utilization of indirect heating for calcining material
provides significant benefits in that it significantly reduces
the amount of gas flowing through the fluidized bed because
no combustion gas flows through the bed. In this manner, a
significantly lower amount of particulates from the material
are entrained and need to be removed from exhaust gas from
the calcining operation. More specifically, the amount of gas
required for fluidization is typically about 80% less than the
amount of gas produced during the combustion necessary to
produce sufficient heat for the calcining process (e.g., utilizing
natural gas in a steam boiler). Accordingly, by utilizing
a source of gas for fluidization which is different than the
combustion gases, a smaller amount of fluidizing gas can be
used. Further, the smaller amount means that the fluidizing
gas will flow at lower velocities, thereby potentially reducing
particulate entrainment even further. In addition, less
fluidizing gas means that less gas needs to be scrubbed for
particulates before emission, thereby reducing the costs of
the calcining process.
It is well known that some calcining processes produce
calcining gas having a significant amount of water vapor.
For example, in the instance of calcining trona to produce
anhydrous sodium carbonate, calcining three moles of trona
produces five moles of water and one mole of carbon
dioxide. In order to reduce the amount of calcining gas
exiting the system, the process may further comprise the step
of condensing at least a portion of the water vapor from the
calcining gas by, for example, cooling the calcining gas.
Such condensation step will reduce the calcining gas volume
by as much as %ths, thereby reducing the amount of
calcining gas which must be treated. In addition to reducing
the volume of gas exiting the system, the condensing step
also has a scrubbing effect on the calcining gas by removing
particulates from the calcining gas. It is believed that the
amount of particulates removed is proportional to the
amount of gas removed (i.e., as much as %ths or more in the
case of trona). It is estimated that the particulate emission
from a process for calcining trona ore in a direct-fired rotary
calciner is typically about 6 lbs/ton of feed. By practice of
the present process, including indirect calcination and condensing
water from calcining gas, the particulate emissions
from calcination of trona ore can be less than about 3 lbs/ton
of feed, more preferably less than about 1.5 lbs/ton of feed
and most preferably less than about 1 lbs/ ton of feed.
In a preferred embodiment, the condensing step for condensing
water from gas produced during calcining comprises
two stages. In the first stage, a small amount (e.g., less
than about 5%) of the water vapor within the calcining gas
is condensed to significantly reduce the particulate content
of the gas. The first stage can be performed utilizing a
water-cooled condenser, such as a tubed condenser. In the
second stage, as much as 80% of the water vapor is
condensed. Because of the reduction in particulate content
resulting from the first stage, the water condensed from the
second stage is essentially distilled water grade. A third stage
may be added to further scrub particulates from the gas. For
example, a high-efficiency venturi scrubber or electrostatic
precipitator may be used.
The water which is removed during the condensing steps
can be utilized for other processes. For example, the condensed
water may be cooled (e.g., using air coolers) and then
recycled and used as the cooling medium to condense
further water vapor from the calcining gas by bringing the
cooled water into thermal communication with the precondensed
calcining gas. Further, the condensed water could
be utilized for processes in other areas of a facility which
involve the use of water. The condensed water may also be
treated and utilized for almost any other appropriate
5 purpose, such as for general water usage in the facility (e.g.,
for cleaning, drinking water, etc.).
Calcining gas which is produced during the calcining
process may be removed from the calcining vessel through
a calcining gas outlet, and at least a portion of the calcining
10 gas (proportional to the amount of CO2 produced in the
calcining process) may be expelled through a stack. The
expelled gas is preferably heated prior to exiting through the
stack to inhibit condensation and plume formation at the
stack outlet. For example, the expelled gas can be mixed
15 with hot combustion gas from heating fluid for indirect
calcination.
Another portion of the calcining gas may be recycled back
to the inlet of the calcining vessel and utilized for heating
and fluidizing additional material for calcining. Preferably,
20 this gas is recycled and/or heated after the above-noted
condensation step, thereby resulting in dry gas as the heating
and fluidizing medium. The recycled gas may be heated
(e.g., by steam coils) in order to bring the gas up to a
temperature prior to entry into the calcining vessel. In one
25 embodiment, the recycled gas temperature is between about
120° C. and about 200° c., and is preferably about 140° C.
This recycling of gas is beneficial in that it utilizes latent
heat within the calcining gas as part of the energy required
for calcining, rather than heating ambient temperature gas up
30 to calcining temperature. Further, such recycling reduces the
gas requirements and emissions of the process by eliminating
the need for fresh gas.
In a further embodiment of the present invention, a
density separation is conducted in the calcining vessel. As
35 some materials are calcined, they lose mass while impurities
in the material do not. In this manner, the apparent density
of the calcined material is less compared to the impurities
and can, therefore, be separated on a density separation
basis. For example, as trona, containing impurities such as
40 shale, pyrite and/or shortite, is calcined, the sodium carbonate
particles lose mass and become less dense, thereby,
creating a significant density difference between the anhydrous
sodium carbonate and the impurities. Thus, in a
fluidized bed, the anhydrous sodium carbonate will migrate
45 to the top of the bed and the denser impurities will migrate
to the bottom. For example, an average apparent density of
calcined trona is less than about 1.6. An average density of
a bottom impurity stream in this embodiment is greater than
about 2.1, more preferably greater than 2.3, and most
50 preferably greater than about 2.5. Thus, a further aspect of
the present invention is to calcine trona and remove a
particle stream comprising impurities from the bottom of the
calciner bed. As will be appreciated, depending on how
much of an impurity stream is taken, the impurity stream
55 may include some sodium carbonate. However, a bottom
stream will contain primarily impurities, such as shale,
pyrite and/or shortite, and the concentration of sodium
carbonate in top stream is greater than in the bottom stream.
More particularly, the concentration of sodium carbonate in
60 the top stream will be at least about 96 wt. %, more
preferably at least about 98 wt. %, and most preferably at
least about 99 wt. %.
After calcination of materials, subsequent processing of
some sort is typically conducted on the material. Often, such
65 subsequent processing involves purification. In a preferred
embodiment of the present invention, the material being
calcined is a saline mineral, and the calcined saline mineral
US 6,479,025 B2
11 12
In particular, sodium carbonate monohydrate crystals
having a crystal size of greater than about 150 mesh, more
preferably greater than about 100 mesh, and more preferably
greater than about 80 mesh, can be obtained by the present
5 process. By forming large sodium carbonate monohydrate
crystals, significant advantages are obtained. For example,
the ability to recover purified crystals on a size separation
basis is enhanced. Larger crystals enable greater recovery
yields when separating crystals from smaller insoluble
10 impurities, such as in the case of recovering sodium carbonate
from a feedstream of trona ore. Thus, in a further
aspect of the invention, the crystallization process is conducted
in the absence of procedures, such as grinding or
shearing, which significantly reduce crystal size in the
15 crystallization operation.
As noted, a preferred method of recovery of sodium
carbonate crystals is on a size separation basis. Such a basis
involves the separation of sodium carbonate monohydrate
crystals from impurities based on differences in size between
20 the sodium carbonate monohydrate crystals and the impurities.
Typically, impurities which can occur in the trona
feedstream include iron-bearing materials, dolomite, shale,
shortite, searlesite and northupite. It will be recognized that
the size of insoluble impurities will not be affected by the
25 recrystallization process. Thus, the initial particle size of an
insoluble impurity will be the minimum particle size at
which size separation of crystals can occur. Moreover, the
particle size of insoluble impurities can be reduced prior to
introduction into the brine solution by grinding the feed-
30 stream to smaller sizes. Typically, the feedstream has a
particle size of minus 100 mesh and more preferably minus
200 mesh. The size separation is typically conducted at a
size from about 80 mesh to about 150 mesh, and even more
particularly at about 100 mesh.
A significant advantage of the low temperature calcination
process described above is that subsequent recovery of
impurities is made easier. It has been determined that low
temperature calcination makes the insoluble impurities less
likely to break down into ultrafine particle sizes, such as less
40 than about 500 mesh. Thus, ease of subsequent recovery and
denaturing of the particles is significantly increased.
Size separation can be affected by any known appropriate
method. For example, screening or elutriation can be used.
45 In the instance of screening, the oversize material from a
first screening may be transferred to a repulping operation
for suspension of crystals in the oversize fraction by adding
clean liquor to a repulp tank to obtain a more efficient
screening in a second size separation.
Upon introduction of a feedstream into a saturated brine
solution, a problem which can be encountered is clumping
and poor dispersion of sodium carbonate. In another
embodiment of the invention, in order to avoid clumping and
to allow for adequate dispersion of the sodium carbonate
55 within the brine solution, the brine solution is agitated
during introduction of the feedstream containing sodium
carbonate. In another embodiment, the feedstream may be
preheated to a temperature above about 175° C. and blown
into the brine solution.
Once sodium carbonate monohydrate crystals are separated
from the saturated brine solution, the crystals are
dewatered, such as by centrifugation. The crystals can then
be converted to the anhydrous form of sodium carbonate
after dewatering for use in industry, such as in the produc-
65 tion of glass. Conversion of sodium carbonate monohydrate
to the anhydrous form after dewatering provides significant
advantages over conversion while in a slurry. To convert to
is subsequently processed by purification in a crystallization
process. In a further preferred embodiment, the saline mineral
is trona. By way of example, a particular crystallization
process for purification of saline minerals will be described
in detail. Use of the present calcination process and apparatus
(specifically, low temperature calcination) provides
significant benefits in terms of crystallization processes for
saline minerals, including among other things, larger crystals.
As used herein, the term "saline mineral" refers generally
to any mineral which occurs in evaporite deposits. Saline
minerals that can be beneficiated by the present process
include, without limitation, trona, borates, potash, sulfates,
nitrates, sodium chloride, and preferably, trona.
The purity of saline minerals within an ore depends on the
deposit location, as well as on the area mined at a particular
deposit. In addition, the mining technique used can significantly
affect the purity of the saline minerals. For example,
by selective mining, higher purities of trona ore can be
achieved. Deposits of trona ore are located at several locations
throughout the world, including Wyoming (Green
River Formation), California (Searles Lake), Egypt, Kenya,
Venezuela, Botswana, Tibet and Turkey (Beypazari Basin).
For example, a sample of trona ore from Searles Lake has
been found to have between about 50% and about 90% by
weight (wt. %) trona and a sample taken from the Green
River Formation in Wyoming has been found to have
between about 80 and about 90 wt. % trona. The remaining
10 to 20 wt. % of the ore in the Green River Formation
sample comprised impurities including shortite (1-5 wt. %)
and halite, and the bulk of the remainder comprises shale
consisting predominantly of dolomite, clay, quartz, kerogen
and iron, and traces of other impurities. Other samples of
trona ore can include different percentages of trona and
impurities, as well as include other impurities. The present
process can also be used with feedstreams having lower 35
impurity contents, including impurity levels as low as 0.1%
by weight.
The crystallization process described herein is particu1arly
well adapted for use with feedstreams having high
contents of insoluble impurities. For example, the present
invention is suitable for use with feedstreams having greater
than about 4% by weight insoluble impurities, more particularly
greater than about 15% by weight insoluble
impurities, and even more particularly greater than about
30% by weight insoluble impurities. The present process can
also be used with feedstreams having lower impurity
contents, including impurity levels as low as 0.1% by
weight.
The sodium carbonate resulting from calcination of trona,
as described above, is treated by purification in a crystalli- 50
zation process to remove insoluble impurities. A first crystallization
process includes contacting the calcined feedstream
comprising sodium carbonate and insoluble
impurities with a saturated sodium carbonate brine solution,
the saturated sodium carbonate brine solution being maintained
at a temperature between about 35° C. and about 112°
c., more preferably between about 85° C. and about 112° c.,
and most preferably between about 95° C. and about 112°
c., to form sodium carbonate monohydrate crystals and
separating the sodium carbonate monohydrate crystals from 60
the saturated sodium carbonate brine solution, preferably on
a size separation basis. The sodium carbonate monohydrate
crystals which are removed from the brine solution can be
dewatered, dried and eventually converted to anhydrous
sodium carbonate. Such a process is described generally in
U.S. Pat. No. 3,948,744 to Frint, which is hereby incorporated
by reference.
US 6,479,025 B2
13 14
EXAMPLE
The following example illustrates the effect of calcining
temperature and atmosphere on the settling of insoluble
impurities in trona ore.
Trona ore having a particle size of less than 20 mesh was
calcined at 1500 c., 3000 c., 4500 c., or 6000 C. in an
dissolving the small crystals, such as by the addition of wash
water, and then making a solidlliquid separation to remove
solid impurities from the dissolved crystals. Then, the solution
can be recycled to other points in the process for use in
5 washing, etc., so that the solution ultimately returns to the
crystallization unit for recovery of dissolved sodium carbonate.
Alternatively, the water in the sodium carbonate
solution could be driven off (e.g., by heating) to recover the
sodium carbonate by crystallization.
When insoluble impurities are removed by a solid/liquid
separation, most typically, the waste stream is sent to a
clarifier, settling tank or other gravity purification apparatus.
As illustrated below in the Example section, calcination in
accordance with the present invention and in particular, in
15 accordance with temperature constraints results in faster and
more compact settling of insoluble impurities. This result
provides significant cost and operational advantages in the
process. Because the settling of impurities occurs more
quickly and thus, is more efficient, the capital requirements
20 for a plant using this process are significantly lower. In
addition, the resulting muds have a higher solids content and
therefore, can be readily disposed of. More particularly,
insoluble impurities produced by the process of the present
invention, in the absence of a fiocculant or other settling aid,
25 can settle to a final density of at least about 20% solids, more
preferably to a final density of at least about 25% solids, and
most preferably to a final density of at least about 30%
solids.
A second crystallization process includes dissolving the
30 anhydrous sodium carbonate in solution to form a sodium
carbonate solution. At least a portion of insoluble impurities
present in the calcined sodium carbonate are separated from
the sodium carbonate solution. Sodium carbonate monohydrate
crystals are then formed from the sodium carbonate
35 solution. This process is generally discussed in U.S. Pat. No.
3,644,331 to Seglin et aI., which is incorporated herein by
reference. The sodium carbonate monohydrate crystals
which are produced can be dewatered, and eventually converted
to anhydrous sodium carbonate by drying or calcin-
40 ing.
Embodiments of the present invention can be conducted
in combination with other processes known for treating
saline minerals and in particular, trona ore. For example,
such other processes are generally described in the published
45 Patent Cooperation Treaty applications PCT/US96/00700
for METHOD FOR PURIFICATION OF SALINE MINERALS
and in PCT/US94/05918 for BENEFICIATION OF
SALINE MINERALS, the disclosures of which are incorporated
herein by reference in their entirety. More
50 particularly, separation steps, such as magnetic separation,
electrostatic separation, and density separation, can be conducted
in conjunction with processes as described herein in
detail. Similarly, separation steps based on other properties
can be used as well. For example, for ores or treated ores in
55 which fractions having different colors or sizes corresponding
to differences in purity, separations can be made on the
basis of such properties, as well.
The following experimental results are provided for purposes
of illustration and are not intended to limit the scope
60 of the invention.
the anhydrous form while in a slurry, the temperature of the
slurry must be above the boiling point of water. Thus, the
process needs to be conducted in a pressurized system. The
equipment necessary for such systems introduces significant
cost and complexity compared to the present process.
The size of the monohydrate crystals may be effected by
varying the feed rate and/or temperature of the anhydrous
sodium carbonate introduced to the saturated sodium carbonate
brine solution and by varying the crystal size distribution
of the sodium carbonate monohydrate seed. 10
Furthermore, appropriate residence times of sodium carbonate
monohydrate crystals in the brine solution for crystallization
can be selected by those skilled in the art. It should
be recognized, however, that longer residence times will
result in larger monohydrate crystals which can have significant
advantages with respect to recovery, as discussed
above. It is believed that residence times of the sodium
carbonate monohydrate crystals in the brine solution could
be as little as fifteen minutes, but can be significantly longer
as well. In one preferred embodiment, the residence time of
the crystallization can be greater than about one and a half
hours, more preferably greater than about three hours and
more preferably greater than about five hours. It will be
recognized that residence time corresponds to feed rate into
the crystallizer. In a further embodiment, the feed rate into
the crystallizer is less than about 0.4 lbs. of anhydrous
sodium carbonate per minute per gallon, more preferably
less than about 0.3 lbs. per minute per gallon and even more
preferably, less than about 0.2 lbs. per minute per gallon.
For example, by maintaining a crystal size distribution
with a high degree of uniformity of size, crystals can be
efficiently grown to a large size. That is, if crystal size
distribution is widely spread over a great number of small to
large crystals, while some new crystal growth will be
efficiently spent on making large crystals larger, some such
growth will be inefficiently spent on making small crystals
grow to a size that will still not be recovered because it will
be below the size separation cutoff. Thus, a further aspect of
the present crystallization process is to maintain a narrow
crystal size distribution of sodium carbonate monohydrate
seed crystals. This aspect of the invention is particularly
important when the feedstream includes insoluble impurities
because adequate crystal growth is necessary to obtain
crystals having a larger size than the insoluble impurities.
This aspect of the invention can be accomplished by a
variety of techniques. For example, by removing small
crystals, either continuously or intermittently, from the crystallization
vessel, the crystal size distribution will be narrowed
with the average crystal size of the remaining crystals
being greater than before removal. More specifically, crystals
having a crystal size less than about 150 mesh, more
particularly less than about 200 mesh and even more particularly
less than about 400 mesh can be removed for this
purpose.
In a further embodiment of the present invention, after
recovery of sodium carbonate from the saturated brine
solution, sodium carbonate in the non-recovered portion can
also be kept in the system for subsequent recovery. As will
be appreciated, the non-recovered portion comprises
insoluble impurities and residual sodium carbonate monohydrate
crystals having a particles size smaller than the size
separation cutoff. For example, when recovery is made on a
size separation basis, the non-recovered portion will have
crystals with a size below the size separation cutoff. In this
instance, the non-recovered portion can be treated to recover 65
sodium carbonate values from crystals which are smaller
than the size separation cutoff. Such a treatment can include
US 6,479,025 B2
15 16
* * * * *
(ii) transferring at least a portion of the heat to the fluid;
and
(iii) directing at least a portion ofthe combustion gas
through a combustion gas outlet
which is not in direct fluid communication with said
calcining vessel.
9. The process of claim 8, wherein said step of heating
said feedstream further comprises the steps of:
removing calcining gas from said heating step through a
calcining gas outlet; and
combining at least a portion of said calcining gas with at
least a portion of said combustion gas.
10. The process of claim 9, further comprising the steps
15 of removing said calcining gas from said heating step and
condensing at least a portion of water vapor from said
calcining gas.
11. The process of claim 10, wherein particulates are
removed from said calcining gas during said condensing
20 step.
12. The process of claim 10, wherein said step of condensing
at least a portion of said water vapor comprises the
step of condensing said portion of water vapor by cooling
said calcining gas.
13. The process of claim 1, further comprising the step of
separating a portion of said impurities from said trona before
step (a) by a process selected from the group consisting of
magnetic separation, electrostatic separation, density
separation, colorimetric separation and size purification.
14. The process of claim 1, wherein the temperature of
said saturated sodium carbonate brine solution is from about
35° C. to about 112° C.
15. The process of claim 1, wherein the temperature of
said saturated sodium carbonate brine solution is at least
35 about 95° C.
16. The process of claim 1, wherein said separation of said
sodium carbonate monohydrate crystals from said saturated
sodium carbonate brine solution is by size separation.
17. The process of claim 16, wherein said sodium car40
bonate monohydrate crystals separated from said saturated
sodium carbonate brine solution have a particle size of at
least about 100 mesh.
18. The process of claim 16, wherein a non-recovered
portion from said size separation step comprises insoluble
45 impurities and said sodium carbonate monohydrate crystals
having a particle size of less than about 100 mesh.
19. The process of claim 18, further comprising the step
of dissolving said sodium carbonate monohydrate crystals
from said non-recovered portion and separating said
50 insoluble impurities from said dissolved crystals.
20. The process of claim 19, further comprising the step
of recycling said dissolved sodium carbonate monohydrate
crystals from said non-recovered portion by introducing a
stream containing said dissolved sodium carbonate mono-
55 hydrate crystals from said non-recovered portion into said
saturated sodium carbonate brine solution.
21. The process of claim 16, further comprising the step
of drying or calcining said separated sodium carbonate
monohydrate crystals and converting said separated sodium
60 carbonate monohydrate crystals to anhydrous sodium carbonate
crystals.
22. The process of claim 1, further comprising the step of
gravity purification of said impurity stream.
23. The process of claim 22, wherein said impurity stream
65 has a final density of at least about 20% solids.
atmosphere of either CO2 or air. The ore was then ground to
minus 100 mesh, and water was added to completely dissolve
all soluble components (i.e., sodium carbonate) of the
material. Some of the samples were first treated by magnetic
separation before the settling test. The samples were then 5
allowed to settle in graduated cylinders. The volume of
settled solid materials was recorded over time to evaluate
settling characteristics of the samples. Observations were
made regarding the color of the liquid. The final solids
content of the various samples, and the sodium carbonate 10
content of the thickened pulp were determined. The results
of the various settling tests are illustrated in the graphs in
FIGS. 1-3 and the chart in FIG. 4.
The foregoing description of the present invention has
been presented for purposes of illustration and description.
Furthermore, the description is not intended to limit the
invention to the form disclosed herein. Consequently, variations
and modifications commensurate with the above
teachings, and the skill or knowledge of the relevant art, are
within the scope of the present invention. The embodiment
described hereinabove is further intended to explain the best
mode known for practicing the invention and to enable
others skilled in the art to utilize the invention in such, or
other, embodiments and with various modifications required
by the particular applications or uses of the present invention.
It is intended that the appended claims be construed to 25
include alternative embodiments to the extent permitted by
the prior art.
What is claimed is:
1. A process for producing sodium carbonate from a
feedstream containing trona and insoluble impurities, com- 30
prising the steps of:
(a) heating said feedstream in a calcining apparatus to a
temperature of less than about 350° C. to form anhydrous
sodium carbonate, wherein a heat source in said
calcining apparatus is not in direct fluid communication
with said feedstream;
(b) contacting said anhydrous sodium carbonate with a
saturated sodium carbonate brine solution for a residence
time to form sodium carbonate monohydrate
crystals;
(c) separating at least a portion of said sodium carbonate
monohydrate crystals from at least a portion of said
insoluble impurities to form an impurity stream; and
(d) allowing insoluble impurities to settle from said
impurity stream to form a recycle stream.
2. The process of claim 1, wherein said temperature of
heating is from about 120° C. to about 250° C.
3. The process of claim 1, wherein said calcining apparatus
is a fluidized bed reactor.
4. The process of claim 1, further comprising the step of
comminuting said feedstream to provide a comminuted
feedstream before step (a).
5. The process of claim 4, wherein particles in said
comminuted feedstream have a particle size of less than
about Y4 inch.
6. The process of claim 4, wherein said feedstream is
sized into 3 or more size fractions.
7. The process of claim 1, wherein said heating step
comprises the steps of:
heating a fluid; and
bringing the heated fluid into thermal communication
with said feedstream.
8. The process of claim 7, wherein said step of heating
said fluid comprises the steps of:
(i) combusting an energy source to produce heat and
combustion gas;