U.S. patent application number 12/838037 was filed with the patent office on 2010-11-04 for plenum crusher dust injection.
This patent application is currently assigned to Solvay Chemicals, Inc.. Invention is credited to William E. Stuble, Alain Vandendoren.
Application Number | 20100279241 12/838037 |
Document ID | / |
Family ID | 39330419 |
Filed Date | 2010-11-04 |
United States Patent
Application |
20100279241 |
Kind Code |
A1 |
Vandendoren; Alain ; et
al. |
November 4, 2010 |
PLENUM CRUSHER DUST INJECTION
Abstract
Methods for heating a solid material comprising a granular
material are provided. Dust is removed from the granular material
before it is heated. The dust is injected into the exhaust gas from
the heater. The heated dust is recovered and combined with the
heated granular material.
Inventors: |
Vandendoren; Alain; (Green
River, WY) ; Stuble; William E.; (Green River,
WY) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Assignee: |
Solvay Chemicals, Inc.
|
Family ID: |
39330419 |
Appl. No.: |
12/838037 |
Filed: |
July 16, 2010 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11591162 |
Nov 1, 2006 |
7771690 |
|
|
12838037 |
|
|
|
|
Current U.S.
Class: |
432/16 |
Current CPC
Class: |
F27D 17/008 20130101;
C01D 7/126 20130101; F27B 7/20 20130101 |
Class at
Publication: |
432/16 |
International
Class: |
F27B 15/12 20060101
F27B015/12 |
Claims
1. In a process for heating a solid material comprising a granular
material using a kiln, the improvement comprising: injecting a dust
material into an exhaust gas stream which exits an outlet of the
kiln and enters a first particulate capture device; wherein the
exhaust gas stream is of a temperature sufficient to affect a
desired change in the dust material; and recovering a recovered
dust material from the first particulate capture device.
2. The process of claim 1, further comprising introducing the
recovered dust material with a heated granular material for further
processing.
3. The process of claim 1, wherein the exhaust gas stream is of a
temperature sufficient to dry or calcine the dust material.
4. The process of claim 1, wherein the dust material is derived
from an ore.
5. The process of claim 1, wherein the dust material is lime,
cement, gypsum, coal or a mineral.
6. The process of claim 1, wherein the kiln is a rotary
type-kiln.
7. The process of claim 1, further comprising: crushing the solid
material to form the dust material and the granular material;
separating the dust material from the granular material; injecting
the granular material into the kiln; and heating the granular
material.
8. The process of claim 7, wherein the solid material is lime,
cement, gypsum, coal or a mineral.
9. The process of claim 8, wherein the solid material is trona.
10. The process of claim 1, wherein at least 90 wt % of the dust
material has a particle size less than 100 mesh, and at least 90
wt. % of the granular material has a particle size greater than 100
mesh.
11. The process of claim 1 wherein the temperature of the exhaust
gas stream exiting the calciner is between about 300.degree. F. and
about 500.degree. F.
12. The process of claim 1, further comprising: crushing the solid
material in a crusher device to form the dust material; collecting
the dust material from the crusher device in a second particulate
capture device; and pneumatically transferring the dust material
from the second particulate capture device to the exhaust gas
stream.
13. A process for heating a solid material comprising: a. removing
a dust material from a solid material comprising a granular
material and a dust material, said dust material having a particle
size smaller than a particle size of the granular material; b.
introducing the granular material into a heater; c. heating the
granular material in the heater; d. injecting the dust material
into an exhaust gas stream from the heater; and e. recovering the
injected dust material.
14. The process of claim 13, wherein the heater is a rotary
type-kiln.
15. The process of claim 13, further comprising: capturing the dust
material from the solid material in a particulate capture device;
and pneumatically transferring the dust material from the
particulate capture device to the exhaust gas stream.
16. The process of claim 13, further comprising introducing the
dust material into the exhaust gas stream in a plenum of the
particulate capture device.
17. In a process for heating a solid material comprising a granular
material using a kiln, the improvement comprising: separating the
solid material into a fine particle size part and a coarse particle
size part; injecting the coarse particle size part at a first
location of the kiln, wherein the first location is at the hot end
of the kiln; and injecting the fine particle size part at a second
location of the kiln, wherein the second location is downstream of
the first location.
18. The process of claim 17, further comprising introducing a flame
at the first location of the kiln, and wherein the second location
is downstream of the flame.
19. The process of claim 18, wherein the second location is at the
cool end of the kiln.
20. The process of claim 18, wherein the second location is an
exhaust duct exiting the kiln.
Description
RELATED APPLICATIONS
[0001] The present patent document is a divisional application of
application Ser. No. 11/591,162, filed Nov. 1, 2006, which is
hereby incorporated by reference.
FIELD OF THE INVENTION
[0002] A process for heating dust material is provided.
BACKGROUND
[0003] Trona ore is a naturally occurring mineral that consists
primarily of sodium sesquicarbonate
(Na.sub.2CO.sub.3--NaHCO.sub.3-2H.sub.2O) and about 4 to 12 percent
insoluble materials consisting mainly of shale. In the vicinity of
Green River, Wyoming, trona ore deposits are found at depths
ranging form about 800 to 1800 feet underground. The main trona bed
varies from 8 to 18 feet in thickness and other beds of less
thickness separated by layers of shale are usually found above the
main trona bed. Although some solution mining techniques are now
being used, trona ore is frequently mechanically mined and carried
to the surface for further processing.
[0004] Various processes for the production of sodium carbonate
from sodium sesquicarbonate are known. In the "monohydrate
process," trona ore is crushed, calcined to convert sodium
bicarbonate values to sodium carbonate, and dissolved; the solution
is filtered, treated with activated carbon to remove soluble
organic compounds, and evaporated to crystallize sodium carbonate
monohydrate. The monohydrate is dried to produce anhydrous sodium
carbonate. See, for example, U.S. Pat. No. 2,962,348, which
describes a typical monohydrate process.
[0005] When crude trona is crushed, a broad distribution of
particle sizes is obtained. Typical sizing, expressed throughout in
terms of U.S. Standard Sieves, illustrate this. As discussed in
U.S. Pat. No. 3,869,538, ore crushed to 100%-3/8 inch mesh is
typically 0%+3/8 inch, 25%+4 mesh, 80%+100 mesh, and 90%+270 mesh.
At 100%-1/4 inch mesh, a typical distribution of 0%+1/4 inch, 10%+4
mesh, 50%+16 mesh, 75%+100 mesh, and 90%+325 mesh. Ore crushed to
pass 8 mesh 100% will typically be 0%+8 mesh, 20% +20 mesh, 35%+40
mesh, 50%+100 mesh, 65%+200 mesh, and 80%+400 mesh. Using the
entire product from a crushing circuit provides more efficient use
of the raw material than if the product is separated into fractions
of narrower range.
[0006] The smallest particles of trona formed when crude trona is
crushed are referred to as trona dust. Handling of trona dust is
problematic for a number of reasons including environmental, health
and maintenance hazards due to the low density of these small
particles. For example, containment of trona dust is difficult when
it is transferred from the crusher and loaded onto the calciner
feed belt. Dust is kicked up during this process, resulting in
inefficient transfer of the trona dust to the calciner and
unnecessary exposure to the trona dust. Trona dust frequently has
to be cleaned from the equipment and processing unit.
[0007] In addition, processing of trona dust in conjunction with
granular trona decreases the efficiency of the calciner as compared
to processing granular trona alone. Processing trona dust in a
rotary kiln-type calciner increases slag, causes refractory brick
damage, increases formation of soluble silica and organics, and
reduces the feed end temperature of the calciner thereby reducing
heat transfer to larger ore size particles. Because there is a
temperature gradient in a rotary kiln-type calciner, over
calcination occurs in the hot end of the calciner, especially near
the surface of particles, which become overexposed to the hot
gases. Fine particles collected from the calciner therefore contain
a higher level of soluble organic compounds than the coarse
particles in the product.
[0008] U.S. Pat. No. 3,869,538 describes a method of calcining
crushed trona of broad size range to crude sodium carbonate in a
fluid bed calciner at 125-225 .degree. C. A more uniform
temperature in the fluid bed calciner results in fine particles not
becoming over calcined, and no concomitant increase in formation of
soluble organic material is obtained. Soluble organic materials are
but one problem of processing trona dust.
[0009] In addition to the trona processing industry, dust
processing and recycling is important the cement, alumina, clay and
lime industries, for example. U.S. Pat. Nos. 5,007,823 and
6,241,514 describes methods and apparatus, respectively for dust
recycling, particularly with application to cement dust. In both of
these patents, the dust is recycled back to the kiln in combination
with an enriched oxygen atmosphere to facilitate processing of the
dust. What is needed are improved methods which address all of the
previously discussed issues for handling, processing, and recycling
dust, in particular, trona dust to form sodium carbonate.
BRIEF SUMMARY
[0010] In one embodiment, a process for heating a solid material
comprising a granular material using a kiln is provided. The
improvement comprises injecting a dust material into an exhaust gas
stream which exits an outlet of the kiln and enters a first
particulate capture device; and recovering a recovered dust
material from the first particulate capture device. The exhaust gas
stream is of a temperature sufficient to affect a desired change in
the dust material. The process improvement may further comprise
introducing the recovered dust material with a heated granular
material for further processing. In other aspects the process
improvement may further comprise crushing the solid material to
form the dust material and the granular material; separating the
dust material from the granular material; injecting the granular
material into the kiln; and heating the granular material. In other
aspects, the process improvement may further include crushing the
solid material in a crusher device to form the dust material;
collecting the dust material from the crusher device in a second
particulate capture device; and pneumatically transferring the dust
material from the second particulate capture device to the exhaust
gas stream. The desired change may be drying or calcination. The
dust material may be lime, cement, gypsum, coal, a mineral, trona
or derived from an ore.
[0011] In another embodiment, a process for preparing soda ash from
crude trona by calcining crude trona is provided. The improvement
comprises injecting trona dust into an exhaust gas stream from an
outlet of a calciner; calcining the trona dust in the exhaust gas
stream to form calcined trona dust; and recovering the calcined
trona dust. In some aspects, the process improvement may further
comprise injecting the trona dust prior to or at a first
particulate capture device; and collecting the calcined trona dust
captured in the first particulate capture device. In other aspects,
the process improvements may further comprise crushing the solid
material in a crusher device to form the dust material; collecting
the dust material from the crusher device in a second particulate
capture device; and pneumatically transferring the dust material
from the second particulate capture device to the exhaust gas
stream. In some aspects, the injecting comprises pneumatically
transferring the trona dust with a first gas.
[0012] In another embodiment, a process for preparing soda ash from
crude trona by calcining crude trona is provided. The improvement
comprises injecting trona dust into an exhaust gas stream from an
outlet of a calciner; calcining the trona dust in the exhaust gas
stream to form calcined trona dust; and recovering the calcined
trona dust. In some aspects, the improvement further comprises
injecting the trona dust prior to or at a first particulate capture
device; and collecting the calcined trona dust captured in the
first particulate capture device. In other aspects, the improvement
further comprises crushing a trona ore to form trona dust and
crushed trona; separating the trona dust from the crushed trona;
injecting the crushed trona into the calciner; calcining the
crushed trona to form calcined crushed trona; and combining the
calcined crushed trona and the calcined trona dust to form combined
calcined trona. In other aspects, the improvement further comprises
collecting the trona dust in a second particulate capture device;
and pneumatically transferring the trona dust from the second
particulate capture device to the exhaust gas stream.
[0013] In another embodiment, a process for preparing soda ash from
crude trona by calcining crude trona is provided. The process
comprises removing a trona dust from a crushed crude trona feed
being fed to a calciner; injecting the removed trona dust into an
exhaust gas stream from the calciner to form calcined trona dust;
and recovering the calcined trona dust. In some aspects, the
process further comprises capturing the trona dust from the crushed
crude trona feed in a particulate capture device; and pneumatically
transferring the trona dust from the particulate capture device to
the exhaust gas stream. In other aspects, the process further
comprises dissolving the recovered calcined trona dust in a
solvent; and crystallizing the dissolved trona dust to form sodium
carbonate. In yet other aspects, the process further comprises
separating the crystallized trona dust from a filtrate; and drying
the crystallized trona dust.
[0014] In another embodiment, a process for heating a solid
material comprising granular material using a kiln is provided. The
process comprises removing a dust material from a solid material
comprising a granular material and a dust material, said dust
material having a particle size smaller than a particle size of the
granular material; introducing the granular material into a kiln;
heating the granular material in the kiln; injecting the removed
dust material into an exhaust gas stream from the kiln; and
recovering the injected dust material. In some aspects the process
further comprises capturing the dust material from the solid
material in a particulate capture device; and pneumatically
transferring the dust material from the particulate capture device
to the exhaust gas stream.
[0015] In another embodiment, a process for heating a solid
material comprising a granular material using a kiln is provided.
The process improvement comprises separating the solid material
into a fine particle size part and a coarse particle size part;
injecting the coarse particle size part at a first location of the
kiln, wherein the first location is at the hot end of the kiln; and
injecting the fine particle size part at a second location of the
kiln, wherein the second location is downstream of the first
location.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic representation of a process for
calcining dust material in combination with granular material.
[0017] FIG. 2 is a schematic representation of one embodiment of a
process for calcining dust material.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] Dust is created in a number of industries where a crude
material is crushed into smaller particles for further processing.
For economical and environmental reasons, it is advantageous to
process this dust. Processing may include heating the dust to
affect a desired change such as drying or calcination.
[0019] In the trona industry, trona ore is calcined to afford soda
ash according to the following chemical equation:
2Na.sub.2CO.sub.3.NaHCO.sub.3.2H.sub.2O.fwdarw.3Na.sub.2CO.sub.3+CO.sub.-
2+5H.sub.2O.
As used herein, calcination refers to the process of heating a
material to a temperature to afford a change in the chemical or
physical constitution.
[0020] FIG. 1 illustrates one method for calcining dust material in
which dust material 10 is combined with granular material 12. The
dust material and granular material are combined prior to entering
the calciner on a calciner feed belt, for example. The combined
feed is fed to a rotary calciner 14 which is fueled with a natural
gas or coal fed calciner burner 16. Both the loading of the crusher
dust onto the feed belt and feeding dust to the calciner kicks up
dust material. This method not only results in inefficient
processing of the dust material, but also poses environmental,
health and safety concerns.
[0021] The dust material and granular material are calcined in the
rotary calciner. The larger particles are then dropped on to a
conveyor belt and delivered to processing equipment. Dust particles
which are carried off by the calciner exhaust gas are collected in
an electrostatic precipitator 18. The calcined dust particles and
calcined granular particles are combined for further
processing.
[0022] In an improved process for heating dust material and
granular material, the dust material and granular materials are
introduced separately into the process. In particular, the dust
material may be introduced at any point downstream of the point of
introduction of the granular material and prior to or at the plenum
of the particulate capture device. As used herein, downstream
refers to a location along the processing route that is after an
upstream location. The direction of the processing route is the
direction which the material to be processed travels. Both the
granular material and dust material may be introduced into a heater
such as a calciner or kiln. However, the dust material may be
introduced downstream of where the granular material is introduced.
For example, the granular material may be introduced at the front
end or hot end of the calciner. The dust material is introduced
into the calciner at a location downstream of the front end of the
calciner.
[0023] In one embodiment, FIG. 2 illustrates an improved process
for handling and processing dust material. The dust material and
trona ore granular material are introduced separately for
calcination. The trona ore granular material 22 is fed to the
calciner 24 at the hot end or flame end of the rotary calciner by
suitable means such as a calciner feed belt. The dust material 20
is introduced at a separate and downstream location from that of
the trona ore granular material. The dust material may be
introduced into the exhaust gas stream of the calciner, prior to or
at the plenum of the particulate capture device such as at point
21.
[0024] When the dust material is introduced into the exhaust gas
stream, it may be preferable to introduce the dust material in such
a manner as to avoid dust exiting through the calciner spill and
disrupting the calciner spill temperature controls. In other words,
it may be preferable to introduce the dust such that it is
effectively carried to the particulate capture device.
[0025] The exhaust gas may be of any suitable composition and
temperature. A suitable temperature is one which affects the
desired change in the dust material, for example calcination or
drying. For calcination, the exhaust gas temperature is at least
about 300.degree. F., preferably between about 300 and about
500.degree. F., more preferably between about 300 and about
400.degree. F., even more preferably between about 350.degree. F.
and 400.degree. F. After injection of the dust material, the
temperature of the exhaust gas may decrease less than about
100.degree. F., preferably less than about 50.degree. F., more
preferably less than 20.degree. F., alternatively between about 10
and about 50.degree. F.
[0026] In other embodiments, the dust material may be introduced
directly to the calciner, although at a location downstream of that
where the granular material is introduced. For example, the
granular material may be introduced at the front end or hot end of
the calciner. The dust material may be introduced into the calciner
downstream of the front end of the calciner, for example at point
23 in FIG. 2. In some embodiments, it may be preferable to
introduce the dust material downstream of the flame of a calciner
burner. In other embodiments it may be preferable to minimize
contact of the dust material with a calciner burner flame.
[0027] Preferably the dust material is pneumatically transferred by
suitable means including, for example, a dilute phase transporter
or dense phase transporter. In one aspect, a blower, dust feeding
pump and pipe are used to pneumatically transfer the dust material.
Any suitable gas or combination of gases can be used to transfer
the dust particles. Preferably air is used to pneumatically
transfer the dust particles. The transfer gas may be of any
suitable temperature such as ambient temperature. Preferably the
gas has a suitable temperature to avoid condensation in the duct or
piping. The gas temperature may be at least 100.degree. F.,
preferably between about 100 and about 250.degree. F., more
preferably between about 150 and 200.degree. F. The dust particles
are pneumatically transferred with a suitable gas pressure. The gas
pressure may be between about 5 and about 10 PSIG, preferably
between about 6 and about 8 PSIG.
[0028] In one example, when calcining a granular trona feed of
about 325 tph, the pneumatic transfer gas has a volumetric flow
rate between about 1500 and about 3000 ACFM (Actual Cubic Feet per
Minute) depending on the amount of trona dust being transferred,
preferably between about 1650 and about 1800 ACFM for transfer of
15 tph trona dust and between 2500 and 3000 ACFM for transfer of 30
tph trona dust. The pneumatic transfer gas flow may transport dust
particles at any suitable rate such that the particulate capture
device is not overloaded and the dust material is calcined, heated
or dried. For a calciner fed with about 200 tph coarse trona, the
rate of dust transfer may be less than 30 tph, preferably between
about 1 and about 20 tph, more preferably about 15 tph. The
percentage of dust injection to granular feed is often less than 20
wt. %, frequently less than 15 wt. %, preferably less than 10 wt.%,
depending on the operating conditions and waste heat available in
the calciner exhaust gas. The percentage of dust injection may be
more than 2 wt.%, or preferably more than 5 wt.% of the granular
feed.
[0029] The process of the present invention is applicable to any of
a variety of materials which are heated. Heating may alter a
material in a variety of ways including drying or calcination.
Suitable materials include, but are not limited to ores, minerals,
lime, cement, gypsum, coal, trona ore, phosphate, aluminum oxide,
manganese carbonate, petrol coke, and sea water magnesite.
[0030] Any suitable heater known to one skilled in the art may be
used in the present invention. Examples of heaters include, but are
not limited to calciners, kilns, ovens, dryers, tumble dryers,
fluidized bed dryers. The heater may be of any suitable
configuration including stationary, a rotary-type or vertical-type.
The heater may be fueled by any of a variety of fuels, including,
but not limited to natural gas, electricity, coal or fuel oil.
Preferably, the combustion products are compatible with, do not
excessively contaminate, or react with the heated dust product.
[0031] The process of the present invention affords several
advantages. For example, the improved process represents a cost
savings by utilizing waste energy in the exhaust gas. The energy
savings realized by the invention may range between 0.3 and 1.3
MMBTU/t trona dust injected, but more typically is expected to be
between 0.5 and 1.0 MMBTU/t dust. Additional cost saving is
realized by more efficient heat transfer to the granular material
at the fend end (flame end) of the calciner which may allow the
calciner to operate at a lower discharge temperature. Further
advantages include reduction in the formation of soluble silica and
organics in the calcined trona dust since the dust is not exposed
to the hot flame, and reduction in slagging and refractory brick
damage since the trona dust is not introduced in the hot end of the
calciner.
[0032] The dust material has a particle size less than about 100
U.S. mesh, preferably less than about 200 U.S. mesh, more
preferably less than about 270 U.S. mesh.
[0033] The granular material has a particle size greater than about
200 U.S. mesh, preferably greater than about 100 U.S. mesh, more
preferably greater than about 40 U.S. mesh.
[0034] In some embodiments, the process may further comprise
crushing a solid material to form the dust material and granular
material; and separating the dust material and granular material.
The dust material may be collected in a particulate capture device
such as a bag house. In some embodiments, the dust material may be
pneumatically transferred from the particulate capture device used
to collect the dust after crushing to the calcining or heating
process equipment.
[0035] In some embodiments, the process may further comprise
recovering the dust material from a particulate capture device.
Particulate capture devices are known to one skilled in the art and
include electrostatic precipitators, baghouses, air classifiers,
and cyclonic separators. The material recovered from the
particulate capture device and the processed granular material may
be combined for further processing or processed separately. Further
processing steps for the processed granular, processed dust
material, or combination thereof may include: dissolving the
material in a solvent, crystallizing the material from a solvent,
separating the crystallized material from a filtrate, drying the
crystallized material.
EXAMPLES
[0036] Provided below are non-limiting examples of the processes
disclosed herein.
[0037] After crude trona ore is crushed, it is separated into
granular and dust material. A typical particle size analysis of the
dust and granular materials is shown in Tables 1 and 2 below,
respectively.
TABLE-US-00001 TABLE 1 Screened trona dust material characteristics
U.S. Mesh Size Wt. % +100 2.6 -100 + 140 2.3 -140 + 200 5.0 -200 +
270 12.3 -270 + 325 6.4 -325 + 400 6.8 -400 + 450 7.4 -450 + 500
10.8 -500 + 635 9.5 -635 36.9 100.0
TABLE-US-00002 TABLE 2 Screened trona granular material
characteristics U.S. Mesh Size Wt. % + 5/16 0 - 5/16 + 1/4 30.7
-1/4 + 4 12.2 -4 + 8 17.7 -8 + 40 20.2 -40 + 100 9.5 -100 + 200 4.2
-200 5.5 100.0
Example 1
[0038] A test run is conducted wherein trona dust from a crusher
baghouse is pneumatically transferred to the exhaust gas of a
gas-fired rotary calciner at a rate of about 30 tph using 2700 ACFM
air at 110.degree. F. The granular trona material is fed to the
calciner at a rate of 325 tph. The exhaust gas flow rate is about
650,000 pph. The exhaust gas temperature is 378.degree. F. at the
exit of the calciner before trona injection and 293.degree. F.
after the trona injection point at the plenum of an electrostatic
precipitator. Samples are collected from the calciner spill and
electrostatic precipitators. A particle size analysis of the
calciner spill shows that about 83-94 wt % of the material is +100
mesh (about 17-6 wt % is -100 mesh). About 97 wt.% of the recovered
trona dust is -100 mesh. None of the samples contain detectable
NaHCO.sub.3. Energy efficiency is improved as compared to a run
without trona dust.
[0039] The above examples are illustrative only, and should not be
interpreted as limiting since further modifications of the
disclosed embodiments will be apparent to those skilled in the art
in view of this teaching. All such modifications are deemed to be
within the scope of the invention described herein and defined by
the following claims.
* * * * *