6,479,025 Process for the production of sodium carbonate

Patent Number/Link:

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

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

d•

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SETTLING TEST ON TRONA CALCINED IN CO2

SOOr'-----------------~---I

500

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~....

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-...J

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\Jl

0'1

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15 20 25

..... Temperature 150 C

- Temperature 300 C

- - - Temperature 450 C

_. Temperature 600 C

TIME (HRS)

~.-.-.-.-._.-.-.-. Isoocl

- - - - - - - - - - - - - - - - - -- - - .1450~o cl

........................................... ............. ~

" "

................

100

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FIG. 2

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SETTLING TEST ON TRONA CALCINED IN AIR

600 j I

~.....

~=.....

..... Temperature 150 C

500 h-. I-Temperature 300 C z0

....... ~ ....... - - - Temperature 450 C '""'"

~N . ....... .

: \ "- - - Temperature 600 C cN

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- "- C

-. : N \ "-

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:::-

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1150 cl

100~ ~.... _............•.. _..... _._-_ ..•.•.... __ .. 1300 cl I e

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(I) TIME (HRS)

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FIG. 3

SETTLING TEST ON NON-MAGNETIC PRODUCT FROM

TRONA CALCINED IN CO2

6001

' --------------~--------'------,i

----- Temperature 150 C 500 R- I -Temperature 300 C z0~

- - -Temperature 450 C ~'""N'"

-. Temperature 600 C c

.-.. 1'1 II

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=- ::::I I \'

~ 300 ~ "', ~

~.... 8 : 1\ ~ ...... 'I

0 S I , ...., I I

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Con :. \

"- -. -.- .-._---- 1600 cl ... _-------_._--

lOT'~ ------- 1450 cl

I I

1300 cl \Jl m:

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0'1 1150 cl 'l.

I ~I_h~__~_n,___~n~ __ ,

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00 5 10 15 20 25 30 \0 b

TIME (HRS) N(I)

FIG. 4

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

16 --t--___

FIG. 5

u.s. Patent Nov. 12, 2002 Sheet 6 of 7 US 6,479,025 B2

"'-I

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u.s. Patent Nov. 12, 2002 Sheet 7 of 7 US 6,479,025 B2

l.()

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C'JI __ __ a:.. _ II <0 0 __ ..u ~

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US 6,479,025 B2

BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

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. %.

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

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

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

US 6,479,025 B2

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;

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;