U.S. patent application number 14/295619 was filed with the patent office on 2014-10-30 for systems for recovering nitric acid from pickling solutions.
This patent application is currently assigned to ATI PROPERTIES, INC.. The applicant listed for this patent is ATI PROPERTIES, INC.. Invention is credited to James A. Moore.
Application Number | 20140322089 14/295619 |
Document ID | / |
Family ID | 45582055 |
Filed Date | 2014-10-30 |
United States Patent
Application |
20140322089 |
Kind Code |
A1 |
Moore; James A. |
October 30, 2014 |
SYSTEMS FOR RECOVERING NITRIC ACID FROM PICKLING SOLUTIONS
Abstract
In one embodiment, a system for treating a gas stream comprising
NO.sub.x produced from a used or spent acid pickling solution
includes a pickling apparatus, a first chamber, and a second
chamber. The pickling apparatus includes an inlet adapted for
introducing a reducing agent into contact with the acid pickling
solution, wherein the reducing agent reacts with free nitric acid
in the acid pickling solution to form NO.sub.x; and a headspace in
which gas comprising NO.sub.x collects. The first chamber includes
a first inlet communicating with the headspace, a second inlet
communicating with a source of ozone, and an interior volume
adapted to contact the NO.sub.x gas and the ozone. The second
chamber may include a third inlet communicating with a source of
water vapor, an interior volume adapted to contact the gaseous
effluent from the first chamber with the water vapor introduced
through the third inlet, and an outlet for collecting solubilized
nitric acid from the interior volume of the second chamber.
Inventors: |
Moore; James A.; (Beaver,
PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
ATI PROPERTIES, INC. |
Albany |
OR |
US |
|
|
Assignee: |
ATI PROPERTIES, INC.
Albany
OR
|
Family ID: |
45582055 |
Appl. No.: |
14/295619 |
Filed: |
June 4, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
13230889 |
Sep 13, 2011 |
8795620 |
|
|
14295619 |
|
|
|
|
13027312 |
Feb 15, 2011 |
8784762 |
|
|
13230889 |
|
|
|
|
Current U.S.
Class: |
422/170 |
Current CPC
Class: |
B01D 53/56 20130101;
C01B 21/40 20130101; C23G 1/36 20130101; B01D 2251/104 20130101;
B01D 2252/103 20130101; C23G 1/086 20130101; C23G 1/02
20130101 |
Class at
Publication: |
422/170 |
International
Class: |
B01D 53/56 20060101
B01D053/56 |
Claims
1. A system for treating a gas stream comprising NO.sub.x produced
from a used or spent acid pickling solution generated by treating a
material selected from a metal and a metal alloy, the system
comprising: a) a pickling apparatus selected from a pickling bath,
a pickling tank, and a pickling spray device, the pickling
apparatus including an acid pickling solution, the pickling
apparatus comprising an inlet adapted for introducing a reducing
agent into contact with the acid pickling solution, whereby the
reducing agent reacts with free nitric acid in the acid pickling
solution to form NO.sub.x, and a headspace in which gas comprising
NO.sub.x collects; b) a first chamber including an interior volume
a first inlet communicating with the headspace of the pickling
apparatus and adapted to convey at least a portion of the gas
comprising NO.sub.x from the headspace to the interior volume, a
second inlet communicating with a source of ozone, and wherein the
interior volume is adapted to contact the gas comprising NO.sub.x
with the ozone, thereby producing oxidation products including
nitrogen sesquioxide and nitrogen pentoxide, wherein at least a
portion of the nitrogen sesquioxide and nitrogen pentoxide react
with water in the first chamber to form nitric acid; and c) a
second chamber directly fluidly communicating with the first
chamber and receiving gaseous effluent from the first chamber, the
second chamber including a third inlet communicating with a source
of water vapor, an interior volume adapted to contact gases from
the first chamber with the water vapor, thereby solubilizing nitric
acid in the gaseous effluent from the first chamber with the water
vapor, and an outlet for collecting solubilized nitric acid from
the interior volume of the second chamber.
2. The system of claim 1, wherein the pickling apparatus includes
an acid pickling solution comprising nitric acid.
3. The system of claim 2, wherein the pickling apparatus is used to
treat surfaces of materials selected from stainless steel,
titanium, and titanium alloys.
4. The system of claim 1, wherein the first chamber includes a
static mixer adapted to mix the gas stream comprising NO.sub.x and
the ozone in the interior volume of the first chamber.
5. The system of claim 1, wherein the first chamber further
comprises a third inlet that communicates with a source of water
vapor.
6. The system of claim 1, wherein the source of ozone is an ozone
generator.
7. The system of claim 1, wherein the second inlet is located
adjacent the first inlet.
8. The system of claim 1, wherein a diameter of the first chamber
is at least 24 inches.
9. The system of claim 1, wherein the second chamber is a mist
eliminator.
10. The system of claim 1, wherein the inlet adapted for
introducing treating material into contact with the acid pickling
solution introduces the treating materials into the tank, bath, or
spray device.
11. The system of claim 1, wherein the pickling apparatus further
comprises a treating compartment in which the acid pickling
solution is contacted with the treating material.
12. The system of claim 1, wherein the outlet of the second chamber
fluidly communicates with the pickling apparatus so that
solubilized nitric acid from the interior volume of the second
chamber is conveyed to the pickling apparatus.
13. A system for treating a gas stream comprising NO.sub.x produced
from a used or spent acid pickling solution generated by treating
one of titanium and a titanium alloy, the system comprising: a) a
pickling apparatus selected from a pickling bath, a pickling tank,
and a pickling spray device, the pickling apparatus including an
acid pickling solution, the pickling apparatus comprising an inlet
adapted for introducing a reducing agent into contact with the acid
pickling solution, whereby the reducing agent reacts with free
nitric acid in the acid pickling solution to form NO.sub.x, and a
headspace in which gas comprising NO.sub.x collects; b) a first
chamber including an interior volume comprising a static mixer, a
first inlet communicating with the headspace of the pickling
apparatus and adapted to convey at least a portion of the gas
comprising NO.sub.x from the headspace to the interior volume, a
second inlet communicating with an ozone generator, and a third
inlet communicating with a source of water vapor, wherein the
interior volume is adapted so that the static mixer mixes the gas
stream comprising NO.sub.x and the ozone, thereby producing
oxidation products including nitrogen sesquioxide and nitrogen
pentoxide, wherein at least a portion of the nitrogen sesquioxide
and nitrogen pentoxide react with water in the first chamber to
form nitric acid; and c) a second chamber directly fluidly
communicating with the first chamber and receiving gaseous effluent
from the first chamber, the second chamber including a third inlet
communicating with a source of water vapor, an interior volume
adapted to contact gases from the first chamber with the water
vapor, thereby solubilizing nitric acid in the gaseous effluent
from the first chamber with the water vapor, and an outlet for
collecting solubilized nitric acid from the interior volume of the
second chamber.
14. The system of claim 13, wherein the pickling apparatus includes
an acid pickling solution comprising nitric acid.
15. The system of claim 13, wherein the pickling apparatus is used
to treat surfaces of materials selected from stainless steel,
titanium, and titanium alloys.
16. The system of claim 13, wherein the second inlet is located
adjacent the first inlet.
17. The system of claim 13, wherein a diameter of the first chamber
is at least 24 inches.
18. The system of claim 13, wherein the second chamber is a mist
eliminator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of, and claims
priority under 35 U.S.C. .sctn.120 to, co-pending U.S. patent
application Ser. No. 13/230,889, filed on Sep. 13, 2011, which in
turn is a continuation-in-part of, and claims priority under 35
U.S.C. .sctn.120 to, U.S. patent application Ser. No. 13/027,312,
filed Feb. 15, 2011. Each of the referenced previously-filed
applications is incorporated by reference herein in its
entirety.
TECHNICAL FIELD
[0002] The present disclosure is directed to systems and methods
for recovering free nitric acid from an aqueous pickling solution
including nitric acid.
BACKGROUND
[0003] Many manufacturing treatment and combustion processes
produce gases that include gaseous nitrogen oxides (NO.sub.x) and
other undesirable gaseous products. For example, processes for acid
pickling stainless steels and other alloys, which typically involve
immersing the alloys for a time in a bath of a strongly acidic
solution including nitric acid, result in gases above the bath that
include NO.sub.x. Federal and local environmental laws may limit
the content of NO.sub.x that is discharged into the atmosphere. In
the past decades, manufacturing companies have undertaken
considerable efforts to reduce the amount of NO.sub.x discharged
into the atmosphere.
[0004] One known method of removing NO.sub.x from a gas stream
includes contacting the gas stream with ozone to thereby oxidize
the NO.sub.x in the gas stream and form oxidation products such as
nitrogen sesquioxide and nitrogen pentoxide. The oxidation products
produced by the ozone treatment may be collected using aqueous
scrubbers, for example, stored on-site, and discarded as a liquid
waste stream. Discarding the liquid waste material may require
third-party waste collection and disposal services.
[0005] It would be advantageous to provide an alternative method
for removing NO.sub.x from the gases produced in an alloy pickling
process or other manufacturing treatment or combustion process that
results in a reduced amount of waste. More generally, it would be
advantageous to provide a method for removing NO.sub.x from a gas
stream produced in any process and that results in a reduced amount
of waste.
SUMMARY
[0006] One aspect according to the present disclosure is directed
to methods for treating a gas stream comprising NO.sub.x. The
methods include contacting a gas stream comprising NO.sub.x with
ozone to thereby form oxidation products including nitrogen
sesquioxide and nitrogen pentoxide. The methods further comprise
reacting at least a portion of the nitrogen sesquioxide and
nitrogen pentoxide with water to thereby form nitric acid, and
recovering at least a portion of the nitric acid.
[0007] An additional aspect according to the present disclosure is
directed to methods for treating a gas stream comprising NO.sub.x,
wherein the gas stream is produced in a process for pickling an
alloy including contacting the alloy with an acidic solution
comprising nitric acid. For example, the pickling process may
comprise at least one of immersing the alloy in an acidic solution
or spraying an acidic solution on the alloy. The methods comprise
contacting the gas stream comprising NO.sub.x with ozone to thereby
form oxidation products including nitrogen sesquioxide and nitrogen
pentoxide. The methods further comprise reacting at least a portion
of the nitrogen sesquioxide and nitrogen pentoxide with water to
thereby form nitric acid, and recovering at least a portion of the
nitric acid. In certain embodiments, at least a portion of the
recovered nitric acid may be recycled back to the acidic solution
used in the pickling treatment.
[0008] A further aspect according to the present disclosure is
directed systems for treating a gas stream comprising NO.sub.x. The
systems comprise a first chamber and a second chamber. The first
chamber includes a first inlet communicating with a source of a gas
comprising NO.sub.x, and a second inlet communicating with a source
of ozone. The first chamber also includes an interior volume
adapted to contact the gas comprising NO.sub.x gas with ozone,
thereby producing intermediate products including nitrogen
sesquioxide and nitrogen pentoxide. At least of portion of the
nitrogen sesquioxide and nitrogen pentoxide react within the first
chamber with water to form nitric acid. The second chamber receives
gases from the first chamber. The second chamber includes a third
inlet communicating with a source of water vapor and an interior
volume adapted to contact gases from the first chamber with water
vapor, thereby solubilizing nitric acid in the gases in the water
vapor. The second chamber further includes an outlet for recovering
at least a portion of the solubilized nitric acid.
[0009] In one particular embodiment of a system for treating a gas
stream comprising NO.sub.x according to the present disclosure, the
system is associated with an acid pickling apparatus for pickling
an alloy. Gases including NO.sub.x produced by the acid pickling
apparatus may be treated using the system so as to recover nitric
acid. Optionally, at least a portion of the recovered nitric acid
is recycled to the acid pickling apparatus.
[0010] An additional aspect according to the present disclosure is
directed to a method for recovering nitric acid from acid pickling
solution. The method includes introducing a treating material
comprising at least one chemical into a pickling solution
comprising free nitric acid. The treating material reacts with at
least a portion of the free nitric acid in the pickling solution
and produces NO.sub.x. A gas stream comprising at least a portion
of the NO.sub.x is contacted with ozone, thereby forming oxidation
products including nitrogen sesquioxide and nitrogen pentoxide. At
least a portion of the nitrogen sesquioxide and nitrogen pentoxide
is contacted with water, thereby forming nitric acid, and at least
a portion of the nitric acid is collected.
[0011] Yet another aspect according to the present disclosure is
directed to a system for treating a gas stream comprising NO.sub.x,
wherein the system includes a pickling apparatus, a first chamber,
and a second chamber. The pickling apparatus is selected from a
pickling bath, a pickling tank, and a pickling spray device. The
pickling apparatus including an acid pickling solution and
comprises: an inlet adapted for introducing a treating material
into contact with the acid pickling solution, wherein the treating
material reacts with nitric acid to form NO.sub.x; and a headspace
in which gas comprising NO.sub.x collects. The first chamber
includes: an interior volume; a first inlet communicating with the
headspace of the pickling apparatus and adapted to convey at least
a portion of the gas comprising NO.sub.x from the headspace to the
interior volume; and a second inlet communicating with a source of
ozone. The interior volume of the second chamber is adapted to
contact the gas comprising NO.sub.x with the ozone, thereby
producing oxidation products including nitrogen sesquioxide and
nitrogen pentoxide, wherein at least a portion of the nitrogen
sesquioxide and nitrogen pentoxide reacts with water in the first
chamber to form nitric acid. The second chamber directly fluidly
communicates with the first chamber and receives gaseous effluent
from the first chamber. The second chamber includes: a third inlet
communicating with a source of water vapor; an interior volume
adapted to contact gases from the first chamber with the water
vapor, thereby solubilizing nitric acid in the gaseous effluent
from the first chamber with the water vapor; and an outlet for
collecting solubilized nitric acid from the interior volume of the
second chamber.
[0012] It is understood that the invention disclosed and described
herein is not limited to the embodiments disclosed in this
Summary.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The characteristics of various non-limiting embodiments
disclosed and described herein may be better understood by
reference to the accompanying figures, in which:
[0014] FIG. 1 is a flow diagram showing certain steps of a
non-limiting embodiment of a method for treating a gas stream
comprising NO.sub.x gas according to the present disclosure;
and
[0015] FIG. 2 is a schematic representation of a non-limiting
embodiment of a system for treating a gas stream comprising
NO.sub.x gas according to the present disclosure.
[0016] FIG. 3 is a schematic diagram of an embodiment of a method
according to the present disclosure in which used or spent pickling
solution is mixed with a treating material that will react with
free nitric acid in the pickling solution to produce NO.sub.x.
[0017] FIG. 4 is a schematic diagram of an embodiment of a system
according to the present disclosure for treating a gas stream
comprising NO.sub.x with ozone and producing and recovering nitric
acid.
[0018] The reader will appreciate the foregoing details, as well as
others, upon considering the following detailed description of
certain non-limiting embodiments according to the present
disclosure. The reader may also comprehend additional details upon
implementing or using embodiments described herein.
DETAILED DESCRIPTION OF CERTAIN NON-LIMITING EMBODIMENTS
[0019] It is to be understood that the descriptions of the
disclosed non-limiting embodiments herein may have been simplified
to illustrate only those features and characteristics that are
relevant to a clear understanding of the disclosed embodiments,
while eliminating, for purposes of clarity, other features and
characteristics. Persons having ordinary skill in the art, upon
considering this description of the disclosed embodiments, will
recognize that other features and characteristics may be desirable
in a particular implementation or application of the disclosed
embodiments. However, because such other features and
characteristics may be readily ascertained and implemented by
persons having ordinary skill in the art upon considering this
description of the disclosed embodiments, and are, therefore, not
necessary for a complete understanding of the disclosed
embodiments, a description of such features, characteristics, and
the like, is not provided herein. As such, it is to be understood
that the description set forth herein is merely exemplary and
illustrative of the disclosed embodiments and is not intended to
limit the scope of the invention defined by the claims.
[0020] In the present disclosure, other than where otherwise
indicated, all numerical parameters are to be understood as being
prefaced and modified in all instances by the term "about", in
which the numerical parameters possess the inherent variability
characteristic of the underlying measurement techniques used to
determine the numerical value of the parameter. At the very least,
and not as an attempt to limit the application of the doctrine of
equivalents to the scope of the claims, each numerical parameter
described in the present description should at least be construed
in light of the number of reported significant digits and by
applying ordinary rounding techniques.
[0021] Also, any numerical range recited herein is intended to
include all sub-ranges subsumed within the recited range. For
example, a range of "1 to 10" is intended to include all sub-ranges
between (and including) the recited minimum value of 1 and the
recited maximum value of 10, that is, having a minimum value equal
to or greater than 1 and a maximum value equal to or less than 10.
Any maximum numerical limitation recited herein is intended to
include all lower numerical limitations subsumed therein and any
minimum numerical limitation recited herein is intended to include
all higher numerical limitations subsumed therein. Accordingly,
Applicant reserves the right to amend the present disclosure,
including the claims, to expressly recite any sub-ranges subsumed
within the ranges expressly recited herein. All such ranges are
intended to be inherently disclosed herein such that amending to
expressly recite any such sub-ranges would comply with the
requirements of 35 U.S.C. .sctn.112, first paragraph, and 35 U.S.C.
.sctn.132(a).
[0022] The grammatical articles "one", "a", "an", and "the", as
used herein, are intended to include "at least one" or "one or
more", unless otherwise indicated. Thus, the articles are used
herein to refer to one or more than one (i.e., to "at least one")
of the grammatical objects of the article. By way of example, "a
component" means one or more components, and thus, possibly, more
than one component is contemplated and may be employed or used in
an implementation of the described embodiments. Further, the use of
a singular noun includes the plural, and the use of a plural noun
includes the singular, unless the context of the usage indicates
otherwise.
[0023] Any patent, publication, or other disclosure material that
is said to be incorporated by reference herein, is incorporated
herein in its entirety unless otherwise indicated, but only to the
extent that the incorporated material does not conflict with
existing definitions, statements, or other disclosure material
expressly set forth in this description. As such, and to the extent
necessary, the express disclosure as set forth herein supersedes
any conflicting material incorporated by reference herein. Any
material, or portion thereof, that is said to be incorporated by
reference herein, but which conflicts with existing definitions,
statements, or other disclosure material set forth herein is only
incorporated to the extent that no conflict arises between that
incorporated material and the existing disclosure material.
Applicant reserves the right to amend the present disclosure to
expressly recite any subject matter, or portion thereof,
incorporated by reference herein.
[0024] The present disclosure includes descriptions of various
embodiments. It is to be understood that the various embodiments
described herein are exemplary, illustrative, and non-limiting.
Thus, the present disclosure is not limited by the description of
the embodiments. Rather, the invention is defined by the claims,
which may be amended to recite any features or characteristics
expressly or inherently described in or otherwise expressly or
inherently supported by the present disclosure. Further, Applicant
reserves the right to amend the claims to affirmatively disclaim
features or characteristics that may be present in the prior art,
but not necessarily expressly described herein. Therefore, any such
amendments would comply with the requirements of 35 U.S.C.
.sctn.112, first paragraph, and 35 U.S.C. .sctn.132(a). The various
embodiments disclosed and described herein can comprise, consist
of, or consist essentially of the features and characteristics as
variously described herein.
[0025] Various embodiments disclosed herein are directed to methods
of treating a gas stream comprising NO.sub.x. Such embodiments
include contacting a gas stream comprising NO.sub.x gas with ozone,
thereby forming oxidation products including nitrogen sesquioxide
and nitrogen pentoxide. At least a portion of the nitrogen
sesquioxide and nitrogen pentoxide reaction products are reacted
with water to form nitric acid, and at least a portion of the
nitric acid is recovered and optionally may be applied in some
useful purpose. Thus, in contrast to conventional methods for
treating NO.sub.x-containing gases, all or a portion of the
oxidation products resulting from the reaction of the
NO.sub.x-containing gas with ozone are not directly removed as a
waste stream using an aqueous scrubber. Instead, water is reacted
with at least a portion of the nitrogen sesquioxide and nitrogen
pentoxide oxidation products to form nitric acid, and at least a
portion of the nitric acid is recovered and may be recycled or
otherwise utilized. The nitric acid used in pickling of stainless
steel and other alloys, for example, is expensive and recycling at
least a portion of the acid may significantly reduce costs
associated with pickling, as well as reduce the amount of waste
fluids produced when the NO.sub.x-containing gases generated by the
pickling process are treated.
[0026] Embodiments of methods according to the present disclosure
may be further understood by reference to the flow diagram of FIG.
1. In a first step, gaseous NO.sub.x, which may be part of a gas
stream, and ozone are reacted to produce oxidation products. The
oxidation products may include nitrogen sesquioxide
(N.sub.2O.sub.3) and nitrogen pentoxide (N.sub.2O.sub.5). In a
second step, which may occur simultaneous with and/or removed in
time from the first step, at least a portion of the nitrogen
sesquioxide and nitrogen pentoxide react with water to form nitric
acid (HNO.sub.3). In a third step, at least a portion of the nitric
acid is recovered.
[0027] Various embodiments disclosed herein are directed to systems
for treating a gas stream comprising NO.sub.x with ozone and
producing and recovering nitric acid. One such embodiment is
schematically depicted in FIG. 2, wherein system 13 includes a
first chamber 1, a second chamber 2, and, optionally, a third
chamber 3. The chambers 1, 2, 3 may be regions of an apparatus that
communicate along a flow pathway. Alternatively, one or more of the
chambers 1, 2, 3 may be separate structures that communicate along
a flow pathway.
[0028] The first chamber 1 of system 13 receives an
NO.sub.x-containing gas stream and a gas stream including or
consisting of ozone gas and is adapted to mix the streams together.
First chamber 1 may include at least a first inlet 4 and a second
inlet 5, and includes an interior volume. In certain non-limiting
embodiments, the first chamber 1 may have a diameter of at least 24
inches. In certain non-limiting embodiments, the first chamber 1
may be at least 200 feet long. However, it will be understood that
the first chamber 1 may have any dimensions and design suitable for
mixing together the NO.sub.x-containing gas stream and the stream
including ozone and thereby facilitating reaction between the
NO.sub.x and the ozone. In certain non-limiting embodiments, the
temperature in the first chamber 1 may be less than 140.degree. F.
In certain non-limiting embodiments, the pressure in the first
chamber 1 may be 10.5 water column (inches) vacuum. In certain
non-limiting embodiments, the flow rate through the first chamber 1
of the NO.sub.x-containing gas and the gas including ozone may be
at least 500 cubic feet/min. It will be understood that the
conditions within the first chamber 1 may be selected to facilitate
reaction between the NO.sub.x-containing gas stream and the stream
including ozone and the further reaction of materials formed in the
first chamber 1 to produce nitric acid. The flow rate within the
first chamber 1 may be selected to permit adequate residence time
in the first chamber 1. If residence time within the first chamber
1 is not adequate, the NO.sub.x-containing gas stream and ozone may
have difficulty mixing and reacting. In such case, oxidation
products may not form in the first chamber 1, but instead might
form in the second chamber 2 or third chamber 3. In certain
non-limiting embodiments, the residence time in the first chamber 1
is at least 6 seconds.
[0029] The first inlet 4 communicates with a source of a gas
including NO.sub.x. The NO.sub.x-containing gas stream preferably
does not pass through a scrubber prior to passing through the first
inlet 4 into the first chamber 1. Instead, the NO.sub.x-containing
gas stream preferably passes directly through the first inlet 4
from the source generating the NO.sub.x-containing gas stream and
is not "pre-treated". The NO.sub.x-containing gas stream may be
generated from any process that produces NO.sub.x gases. For
example, in certain non-limiting embodiments, the NOx-containing
gas stream is generated during an alloy manufacturing or treatment
process or a combustion process. In certain non-limiting
embodiments, NO.sub.x-containing gas treated by a system according
to the present disclosure is produced in a pickling process for
treating metals and alloys. In one particular non-limiting
embodiment, the NO.sub.x-containing gas stream is generated in the
headspace above an acid pickling tank or bath that may include, for
example, nitric acid, and in which an alloy is immersed (i.e.,
"pickled") for a time to treat the alloy's surfaces. In certain
other non-limiting embodiments, the NO.sub.x-containing gas stream
is generated by a spray pickling process in which a spray of an
acid pickling solution is directed at surfaces of a metal or alloy.
In certain non-limiting embodiments, the NO.sub.x-containing gas
stream generated by an acid pickling process may have a temperature
in the range of ambient temperature to 140.degree. F. As is known
in the art, the acid solution used in an acid pickling tank, bath,
or spray is a solution that includes one or more strong acids and
which is used to remove surface impurities such as stains,
inorganic contaminants, rust, and scale, from metals and metal
alloys. In certain embodiments, the pickling tank, bath, or spray
may be used to remove surface impurities from materials selected
from titanium, titanium alloys, and stainless steels.
[0030] In certain non-limiting embodiments, the pickling bath may
include one or more strong acids selected from the group consisting
of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid,
hydrofluoric acid, and combinations thereof. In certain specific
non-limiting embodiments, the pickling bath may include one or both
of nitric acid and hydrofluoric acid. Person having ordinary skill
in the art may readily formulate a suitable pickling solution for a
particular metal or alloy and, therefore, it is not necessary that
the present description include a discussion of how to formulate or
apply a pickling solution for a particular metal or alloy. It will
be understood that embodiments of the method and system according
to the present disclosure may be used with any pickling formulation
that generates a NO.sub.x-containing gas. More generally, it will
be understood that certain embodiments of the method and system
according to the present disclosure may be used to process
NO.sub.x-containing gas produced by any process, apparatus, system,
or phenomenon.
[0031] In certain non-limiting embodiments of a method or system
according to the present disclosure used in connection with a
pickling process, the pickling solution within a pickling tank or
bath or used in a pickling spray may have a temperature of at least
140.degree. F. However, it will be understood that the pickling
solution may have any temperature suitable for pickling a metal or
alloy of interest. For example, in certain non-limiting
embodiments, the pickling solution may have a temperature less than
140.degree. F. In certain other non-limiting embodiments, the
pickling solution may have a temperature equal to or higher than
140.degree. F. In other non-limiting embodiments of a method or
system according to the present disclosure used in connection with
a pickling process, the pickling bath or tank may hold at least
5700 and as much as 15,000 gallons of pickling solution. However,
it will be understood that the pickling bath or tank may hold any
volume of pickling solution suitable for providing the desired
surface processing of a metal or alloy mill product of interest. As
previously noted, in certain other non-limiting embodiments of a
pickling process that generates NO.sub.x-containing gas, surface
impurities such as stains, inorganic contaminants, rust, and scale,
may be removed from metals and alloys using spray pickling. As used
herein, spray pickling refers to a process of spraying an acid
pickling solution on metal and/or metal alloy to remove surface
impurities. Spray pickling may minimize or reduce the volume of
acid that is used to treat the metal and/or metal alloy, but the
process may still produce significant volumes of
NO.sub.x-containing gas.
[0032] Again referring to the system 13 schematically illustrated
in FIG. 2, the first inlet 4 may further communicate with a source
of moisture (water). In certain non-limiting embodiments of system
13, the moisture and the NO.sub.x-containing gas stream enter the
first chamber 1 at the same location, which may be, for example,
inlet 4. In other non-limiting embodiments, the moisture and the
NO.sub.x-containing gas stream may enter the first chamber 1 at
different locations. In yet other non-limiting embodiments, all or
a portion of the moisture introduced into the first chamber 1 may
be part of the NO.sub.x-containing gas stream. For example, in
embodiments of the method and system described herein associated
with a pickling process or system, the NO.sub.x-containing gas
stream may be generated in the headspace of the acid pickling
solution and, therefore, may include a certain moisture content as
a result of evaporation of water from the acid pickling
solution.
[0033] The second inlet 5 to chamber 1 of the system 13
communicates with a source of ozone. The ozone source may be, for
example, an ozone generator or another known device that produces
ozone (not shown), or an ozone storage device. In certain
non-limiting embodiments, the ozone generating device may be
located "on-site" so that ozone may be produced when needed to
treat NO.sub.x-containing gas generated by a pickling process or
apparatus or another process or apparatus at the site. Because
ozone has a short half-life, the ozone preferably is generated
proximate the second inlet 5. For example, in certain non-limiting
embodiments, an ozone generator device or other ozone source may be
located near the second inlet 5. In other non-limiting embodiments,
the ozone source may be located near the first inlet 4 and the
second inlet 5. The ozone source may provide an ozone-containing
gas stream including ozone in any concentration suitable to treat
the particular NO.sub.x-containing gas stream that is being
introduced into the first chamber 1. In certain non-limiting
embodiments, the concentration of ozone in the gas stream
introduced into the first chamber 1 at second inlet 5 may be in the
range of 1 to 16 percent by volume.
[0034] In certain non-limiting embodiments of system 13, the second
inlet 5, at which a gas including ozone is introduced into the
first chamber 1 may be located adjacent (i.e., near to) the first
inlet 4 so that NO.sub.x entering the first chamber 1 at the first
inlet 4 contacts ozone introduced at the second inlet 5 and
suitably reacts to form oxidation products including nitrogen
sesquioxide and nitrogen pentoxide. Those having ordinary skill may
readily ascertain a suitable minimum, maximum, and/or range of
distances between the first inlet 4 and the second inlet 5 so that
the NO.sub.x in the NO.sub.x-containing gas stream and the ozone in
the ozone-containing gas stream react within the first chamber 1 to
a degree that results in the particular desired minimum reduction
in the concentration of NO.sub.x in the NO.sub.x-containing gas
stream entering the first chamber 1. The shape and size of the
interior volume of the first chamber 1 may be adapted to promote
contact between and thereby suitably react the NO.sub.x-containing
gas stream and the ozone to produce oxidation products including
nitrogen sesquioxide and nitrogen pentoxide. These reaction
products can be formed in the first chamber 1 by reaction of
nitrogen oxides (NO.sub.x, including NO.sub.x and NO.sub.2) and
ozone (O.sub.3) according to the following equations:
NO+O.sub.3.fwdarw.NO.sub.2+O.sub.2
NO.sub.2+O.sub.3.fwdarw.NO.sub.3+O.sub.2
NO.sub.3+NO.sub.2.revreaction.N.sub.2O.sub.5 A.)
NO+NO.sub.2.revreaction.N.sub.2O.sub.3 B.)
[0035] The degree to which the NO.sub.x in the NO.sub.x-containing
gas stream reacts with the ozone in the first chamber 1 to form
oxidation products including nitrogen sesquioxide and nitrogen
pentoxide depends on many factors including, but not limited to,
the flow rates of the gases, residence time, the concentration on
NO.sub.x and ozone in the respective gas streams, the temperatures
of the reactants, and the particular mixing action that occurs
between the gas streams within the first chamber 1. Those having
ordinary skill may suitably adjust or influence one or more of
these parameters to adjust the reaction rate occurring in the first
chamber 1 and achieve the desired level of conversion of NO.sub.x
in the NO.sub.x-containing gas stream.
[0036] In certain non-limiting embodiments of the system 13, the
NO.sub.x-containing gas stream is not treated in a scrubber prior
to being introduced into the interior volume of the first chamber 1
and contacting ozone therein. Also, in certain non-limiting
embodiments of a system according to the present disclosure, the
NO.sub.x-containing gas stream may be mixed with the
ozone-containing gas stream in the first chamber using a device
adapted to mix gas streams. For example, the NO.sub.x-containing
gas stream may be mixed with ozone-containing gas stream using a
static mixer. As used herein, the term "static mixer" refers to a
device that includes a series of fixed elements with a specific
geometric design so as to promote patterns of flow division and
radial mixing. A static mixer may be used to promote mixing of at
least two liquids or at least two gases, to disperse a gas into a
liquid, or to disperse at least two immiscible liquids. Although it
is believed that a static mixer is not required in the system 13,
providing a static mixer may improve system efficiency and reduce
the length of the first chamber 1 necessary to allow the gas
streams introduced into the first chamber 1 to mix and suitably
react. In certain non-limiting embodiments of the system 13, for
example, a static mixer may be located in or associated with the
first chamber 1 near the first inlet 4 and the second inlet 5. In
certain non-limiting embodiments of system 13, a static mixer may
be located immediately following the second inlet 5.
[0037] At least a portion of the nitrogen sesquioxide and nitrogen
pentoxide oxidation products formed in the first chamber 1 further
react with water in the interior volume of the first chamber 1 to
form nitric acid. As discussed above, water introduced into the
interior volume of the first chamber 1 may be, for example,
moisture that is already a component of the NO.sub.x-containing gas
stream introduced into the first chamber 1 at first inlet 4 and/or
water introduced into the first chamber 1 from one or more inlets
into the first chamber 1 that communicate with one or more water
sources. A possible water source 6 is indicated in FIG. 2. It will
be understood that the system 13 may be constructed in any suitable
way so that a sufficient concentration of water is present in the
first chamber 1 to suitably react with oxidation products in the
first chamber and form nitric acid. In certain non-limiting
embodiments, the first inlet 4 may be located near the water source
6. In certain other non-limiting embodiments, the first inlet 4 and
second inlet 5 may be located near the water source 6. It will be
understood that the particular design of the system 13 and the
first chamber 1 will influence the optimal positioning of the one
or more water inlets into the first chamber 1, if such is provided,
so as to optimally facilitate reaction of water and oxidation
products in the first chamber 1.
[0038] Again referring to FIG. 2, the second chamber 2 of system 13
may be located downstream (i.e., in the direction of gas flow) from
the first chamber 1. The first and second chambers 1, 2 preferably
are directly fluidly connected so that the effluent from the first
chamber 1 flows to the second chamber 2. The second chamber is
adapted to recover nitric acid from the effluent emerging into the
second chamber 2 from the first chamber 1. In certain embodiments
of the system 13, the second chamber 2 may be a mist eliminator
which, as is known to those having ordinary skill, is a device
including a large cross-sectional surface area adapted for
condensation of liquid from a mist introduced (e.g., injected) into
the mist eliminator. A mist eliminator preferably removes mist as a
liquid from a gas stream by reducing the velocity of gas as it
passes through the mist eliminator, thereby trapping the mist so
that it may be removed as a liquid via gravity.
[0039] As illustrated in FIG. 2, in certain non-limiting
embodiments, the second chamber 2 of system 13 may include a third
inlet 7, an interior volume, and an outlet 8 through which
solubilized nitric acid is collected or recovered from the interior
volume. The third inlet 7 communicates with a source of water vapor
which, in certain non-limiting embodiments, is sprayed into the
interior volume of the second chamber 2. The interior volume is
adapted to contact gaseous effluent from the first chamber 1 with
water vapor to thereby solubilize in the water vapor nitric acid in
the gaseous effluent from the first chamber 1. The solubilized
nitric acid is then collected as an aqueous nitric acid solution
and is extracted from the bottom of the second chamber 2 through
outlet 8. The concentration of the nitric acid may be adjusted by,
for example, controlling the volume of water that is introduced
into the system 13 over time. For example, introducing water into
the system 13 at a relatively high rate, as a component of the
NO.sub.x-containing gas stream and/or through one or more water
inlets associated with the first chamber 1, may dilute the nitric
acid formed in and recovered from the system 13. Alternatively,
introducing a lesser volume of water in the system 13 over time may
concentrate the nitric acid formed in and recovered from the system
13.
[0040] In certain embodiments, the recovered nitric acid is
recycled back to the process or apparatus that initially generated
the NO.sub.x-containing gas that is treated by the system 13. For
example, in the embodiment in which the system 13 is associated
with a pickling tank, bath, or spray that produces an
NO.sub.x-containing gas stream treated in the system 13, the nitric
acid recovered from the second chamber 2 may be piped or otherwise
transferred back to the pickling tank, bath, or spray and used to
pickle additional metal or alloy mill products. Alternatively, the
nitric acid recovered from the second chamber 2 may be stored,
sold, or properly disposed of, for example.
[0041] Again referring to FIG. 2, system 13 optionally includes a
third chamber 3 that is located downstream from the second chamber
2 and receives the gaseous effluent from chamber 2. In certain
non-limiting embodiments, the third chamber 3 may be a scrubber. A
scrubber is a device or system that extracts pollutants or other
materials from a gas stream. As is known in the art, a scrubber may
be a wet scrubber, which uses a liquid to remove materials from a
gas stream, or a dry scrubber, which uses a dry material to remove
materials from a gas stream. For example, the gaseous effluent from
chamber 2 may include un-reacted nitrogen oxides, nitric acid that
has not been captured by the second chamber 2, nitric acid produced
in regions of the system 13 beyond the second chamber 2, mercury,
sulfur oxides, and/or entrained particulates that one wishes to
remove from the gas stream exiting the second chamber 2, and such
materials may be fully or partially removed using a scrubber in the
third chamber 3. For example, nitrogen oxides that are not
converted to oxidation products in the first chamber 1 may pass
un-reacted through the second chamber 2 and enter the third chamber
3. Such un-reacted nitrogen oxides may be partially or fully
removed from the gas stream in chamber 3. Also, for example, nitric
acid that is not recovered in the second chamber 2 may enter the
third chamber 3 through conduit 9 and be partially or wholly
collected in the third chamber 3.
[0042] In certain non-limiting embodiments, the third chamber 3 may
include a fourth inlet 10, a terminal outlet 12 for releasing a gas
to the environment, and a second outlet 11 for collecting waste
from the interior volume of the third chamber 3. In embodiments in
which the third chamber 3 is a wet scrubber device, the fourth
inlet 10 may communicate with a source of a scrubber solution. The
scrubber solution may be, for example, a non-caustic solution, such
as water, or a caustic solution, such as a water/sodium hydroxide
solution. In certain non-limiting embodiments, the particular
scrubber solution may be recirculated through the scrubber to
neutralize non-recovered nitric acid passing into the third chamber
3. The first outlet 12 releases any nitrogen oxides (NO.sub.x) that
are not removed in the second chamber 2 or third chamber 3. The
second outlet 11 may be used for extracting wastes from the third
chamber 3, and the waste may be reused and/or disposed of, as the
case may be.
[0043] A NO.sub.x-containing gas stream treatment system
constructed as generally described in the present disclosure can
produce a significant volume of nitric acid in a 24 hour period.
For example, it is believed that an apparatus constructed as
generally shown in FIG. 2 could potentially recover as much as 1350
pounds/day of nitric acid (based on 100% acid) from a waste gas
stream including 1200 ppm NO.sub.x and flowing at a rate of 4,500
scfm (standard cubic feet per minute). Tests conducted on a
prototype system constructed as generally discussed according to
the present disclosure and having the general design shown in FIG.
2 successfully produced a significant volume of 42% (volume/volume)
nitric acid from a NO.sub.x-containing gas stream produced by an
alloy pickling apparatus.
[0044] An additional aspect of the present disclosure is directed
to a method for recovering nitric acid from an acid pickling
solution such as, for example, a used or waste ("spent") acid
pickling solution. A non-limiting embodiment of the method
comprises treating a gas stream comprising NO.sub.x wherein at
least a portion of the NO.sub.x in the gas stream is generated by
treating a used or spent acid pickling solution. During finishing
of stainless steel, for example, annealing and other finishing
processes are carried out in the presence of air, and a thin oxide
film forms on the surface of the stainless steel. In addition, a
zone that is depleted of chromium normally forms under the oxide
film when the steel is treated at high temperatures. The pickling
process is used to clean and condition the steel's surfaces.
Removal of the thermally grown oxide scale typically is
accomplished using shot blasting or electrolyte pickling in a
neutral salt. The chromium-depleted zone is removed by pickling in
an acid solution, which typically includes two or more acids. Some
amount of the bulk steel also may be removed during acid pickling
to provide the steel with a bright surface. The mixed acid solution
in the pickling bath, also referred to as pickling solution or
"pickling liquor", commonly is an aqueous solution including 90-160
g/L nitric acid and 10-40 g/L hydrofluoric acid, but may include
other acids instead of or in addition to hydrofluoric acid. The
nitric acid is a strong oxidizing agent and oxidizes the metals and
metal oxides, forming, for example, Cr.sup.3+, Ni.sup.2+, and
Fe.sup.3+ ions in the pickling solution. The hydrofluoric acid in
the pickling solution forms stable complexes with the metal ions.
The rate of pickling at a given time depends on the temperature of
the pickling bath, the concentration of free (i.e., unreacted) acid
in the pickling solution, and the concentration of dissolved
chromium and iron in the pickling solution. In order to maintain a
satisfactory pickling rate, a minimum concentration of free nitric
acid and hydrofluoric acid must be maintained in the pickling
solution.
[0045] Concentrated nitric acid and hydrofluoric acid can be added
to a pickling bath to maintain a sufficient free acid concentration
in the pickling solution. However, as the pickling process
proceeds, the metals content of the pickling solution increases.
Unless the metals content is reduced, it can reach a point at which
metal salts begin to crystallize out of solution and form a
strongly adhering sludge, necessitating that the pickling tank or
bath be drained and cleaned. Therefore, the composition of the
pickling solution must be adjusted over time to maintain a
sufficient concentration of free acid and avoid conditions
resulting in crystallization of metal salts. Spent pickling
solution includes significant concentrations of nitrate, fluoride,
and heavy metals, but also includes concentrations of free
(unreacted) nitric acid and free hydrofluoric acid. The free nitric
acid lost in spent pickling solution would be valuable if it could
be recovered and, for example, re-used in the pickling process or
in other applications. Techniques have been developed to treat
spent pickling solution to recover free nitric acid and free
hydrofluoric acid. In certain known pickling solution regeneration
systems, for example, spent pickling solution is passed through an
ion exchange resin bed to separate free acid from metal values. The
free acid may then be re-used in the pickling process or in other
applications. Nitric acid, however, is a strong oxidizing agent
and, therefore, has a tendency to oxidize ion exchange resins. In
such systems, therefore, the temperature and acid concentration of
the pickling solution must be closely monitored and controlled to
protect the resin bed from damage. If the temperature of the nitric
acid is too high, or if the acid is too concentrated, it will
aggressively attack the resin bed. Thus, pickling solution
regeneration systems typically include heat exchanger units to cool
the solution prior to contacting the resin bed. Also, suspended
solids must be removed from the spent pickling solution to prevent
the solids from physically clogging the resin bed. As such,
pickling solution regeneration systems typically also include media
filters and other types of filter units to isolate particulate
material from the solution before it contacts the resin bed. Given
the complexity of ion exchange resin-based pickling solution
regeneration systems, the systems tend to be costly and require
significant investment in terms of oversight and maintenance by
plant personnel.
[0046] The present inventor has developed a unique method for
recovering free nitric acid from pickling solution such as, for
example, a used or spent pickling solution. Rather than treat used
or spent pickling solution in an ion exchange regeneration system,
the used or spent pickling solution is chemically treated to
generate NO.sub.x from all or a portion of free nitric acid in the
solution. All or a portion of the NO.sub.x enters headspace above
the pickling bath, tank, or other pickling device and the
NO.sub.x-containing gas in the headspace may then be treated using
the method according to the present disclosure that is described
above, in which a gas stream comprising NO.sub.x is processed to
produce solubilized nitric acid. Therefore, according to one aspect
of the present disclosure, NO.sub.x gas is intentionally generated
by introducing a treating material into used or spent acid pickling
solution including free nitric acid. The acid pickling solution may
be in an acid pickling bath or tank, or may have been used in a
pickling spray device, for example. All or a portion of the
NO.sub.x generated by introducing the treating material into the
pickling solution enters headspace above the bath or tank or
associated with the spray device, and the resulting
NO.sub.x-containing gas stream is treated by the following method:
contacting the gas stream comprising NO.sub.x with ozone, thereby
forming oxidation products including nitrogen sesquioxide and
nitrogen pentoxide; reacting at least a portion of the nitrogen
sesquioxide and nitrogen pentoxide with water, thereby forming
nitric acid; and collecting at least a portion of the nitric acid.
Instead of introducing the treating materials into a bath, tank, or
spray device, for example, used or spent pickling solution may be
drained or piped from the pickling bath, tank, or spray device to
another tank or compartment where it is contacted with treating
material to generate NO.sub.x from the free nitric acid in the
solution, and then a gas stream including all or a portion of the
generated NO.sub.x is treated by the method according to the
present disclosure described above to thereby generate nitric
acid.
[0047] The pickling solution may be chemically treated in any
suitable way to generate NO.sub.x from all or a portion of the
liquor that is being treated. For example, the treating material
may include one or more chemicals that react with the free nitric
acid to form NO.sub.x, and the treating material may be mixed with
or introduced into the pickling solution being treated. Chemicals
that react with free nitric acid to form NO.sub.x include, for
example, ferrous sulfate, and other reducing agents such as, for
example, metals and alloys such as carbon steel and iron. In
particular, ferrous sulfate is a byproduct produced during sulfuric
acid pickling. Those having ordinary skill may identify other
reducing chemicals that may be used to convert free nitric acid to
NO.sub.x.
[0048] If, for example, used or spent pickling solution is being
treated by placing treating materials directly into a pickling bath
or tank holding the pickling solution, the treating material may be
introduced by a pipe or other inlet into the bath or tank in a
single batch or in a periodic or continuous fashion to react with
the free nitric acid in the pickling solution. The process of
reacting the treating material with the free nitric acid in the
pickling solution may be facilitated by, for example, mixing or
agitating the bath or tank to improve the reaction. In an
alternative embodiment, wherein all or a portion of the pickling
liquor in a pickling tank or bath is drained or piped from the
pickling bath or tank to a secondary tank or compartment to be
treated, the treating material may be introduced by a pipe or by
other means in a batch, periodic, or continuous fashion into the
secondary tank or compartment to react with free nitric acid in the
pickling solution. In yet another embodiment, used or spent
pickling solution may be removed from a pickling tank, bath, spray
device, or other pickling device and piped or transported to
another location for treatment with the treating material to
generate NO.sub.x from free nitric acid in the pickling solution,
and then the NO.sub.x-containing gas may be treated according to
the present disclosure to recover solubilized nitric acid.
[0049] In one non-limiting embodiment according to the present
disclosure, schematically shown in FIG. 3, used or spent pickling
solution is mixed with a treating material that will react with
free nitric acid in the pickling solution to produce NO.sub.x. In
certain non-limiting embodiments, the pickling solution
continuously flows from a pickling tank, bath, or spray device, for
example, through a pipe or other conduit, into a secondary tank or
compartment, where it is reacted, either in a batch operation or
continuously, with the treating material. A gas stream consisting
of or including all or a portion of the NO.sub.x formed by reaction
of the pickling solution and the treating material is reacted with
ozone to produce oxidation products that include nitrogen
sesquioxide (N.sub.2O.sub.3) and nitrogen pentoxide
(N.sub.2O.sub.5). In a step that may occur simultaneous with and/or
removed in time from the step of reacting the NO.sub.x with the
ozone, at least a portion of the nitrogen sesquioxide and nitrogen
pentoxide reacts with water to form nitric acid, and at least a
portion of the nitric acid is recovered.
[0050] Certain non-limiting embodiments according to the present
disclosure are directed to systems for treating a gas stream
comprising NO.sub.x with ozone and producing and recovering nitric
acid, wherein at least part of the NO.sub.x-containing gas stream
is NO.sub.x generated by treating used or spent acid pickling
solution with one or more chemicals to generate NO.sub.x from free
nitric acid in the pickling solution. One such embodiment is
schematically depicted in FIG. 4, wherein system 113 includes a
pickling tank 100, a first chamber 200, a second chamber 300, and,
optionally, a third chamber 400. Pickling tank 100 communicates
with first chamber 200 so that gases from pickling tank 100 may be
introduced into first chamber 200. The chambers 200,300,400 may be
regions of an apparatus that communicate along a flow pathway.
Alternatively, one or more of the chambers 200,300,400 may be
separate structures that communicate along a flow pathway.
[0051] Pickling tank 100 includes acid pickling solution 42
comprising an amount of free nitric acid. The pickling tank may be
of a conventional design, including a shroud or other suitable
structure to capture gases generated by the pickling process. A
treating material that reacts with free nitric acid in the pickling
solution to produce NO.sub.x is introduced into the pickling
solution through an inlet 30 in a wall of the pickling tank 100.
The treating material may be introduced in a batch, periodically,
or continuously, as appropriate, to generate NO.sub.x from free
nitric acid in the pickling solution 42 in the pickling tank 100.
All or a portion of NO.sub.x produced by the chemical reaction
enters the gases in the headspace 44 above the pickling solution 42
in the pickling tank 100. Although system 113 includes a pickling
tank 100, it will be understood that system 113 may be adapted to
include a different pickling apparatus, such as a pickling
apparatus including a picking bath or a pickling spray device.
Also, although system 113 is adapted so that treating material is
introduced into the pickling tank 100, it will be understood that
the system 113 may be modified so that pickling solution is
contacted with treating material in a separate secondary tank or
compartment associated with the pickling tank.
[0052] The first chamber 200 of system 113 receives a
NO.sub.x-containing gas stream and a gas stream including or
consisting of ozone gas and is adapted to mix the streams together.
In system 113, the NO.sub.x-containing gas is fed from the
headspace 44 of the pickling tank 100. However, it will be
understood that if, for example, pickling solution and treating
material are contacted in a secondary tank or compartment, then the
NO.sub.x-containing gas may be partially or wholly fed from the
secondary tank or compartment in which the reaction occurs. First
chamber 200 may include at least a first inlet 40 and a second
inlet 50, and includes an interior volume. In certain non-limiting
embodiments, the first chamber 200 may have a diameter of at least
24 inches. In certain non-limiting embodiments, the first chamber
200 may be at least 200 feet long. However, it will be understood
that the first chamber 200 may have any dimensions and design
suitable for mixing together the NO.sub.x-containing gas stream and
the stream including ozone and thereby facilitating reaction
between the NO.sub.x and the ozone. For example, the first chamber
200 may have a design and be operated as described in connection
with system 13 illustrated in FIG. 2. Accordingly, in certain
non-limiting embodiments, the temperature within in the first
chamber 200 may be less than 140.degree. F. In certain non-limiting
embodiments, the pressure in the first chamber 200 may be 10.5
water column (inches) vacuum. In certain non-limiting embodiments,
the flow rate through the first chamber 200 of the
NO.sub.x-containing gas and the gas including ozone may be at least
500 cubic feet/min. It will be understood that the conditions
within the first chamber 200 may be selected to facilitate reaction
between the NO.sub.x-containing gas stream and the stream including
ozone and the further reaction of materials formed in the first
chamber 200 to produce nitric acid. The flow rate within the first
chamber 200 may be selected to permit adequate residence time in
the first chamber 200. If residence time within the first chamber
200 is not adequate, the NO.sub.x-containing gas stream and ozone
may have difficulty mixing and reacting. In such case, oxidation
products may not form in the first chamber 200, but instead might
form in the second chamber 300 or third chamber 400 of system 113.
In certain non-limiting embodiments, the residence time in the
first chamber 200 is at least 6 seconds.
[0053] The NO.sub.x-containing gas stream preferably does not pass
from the headspace 44 of the pickling tank 100 through a scrubber
prior to passing through the first inlet 40 into the first chamber
200. Instead, the NO.sub.x-containing gas stream preferably passes
directly through the first inlet 40 from pickling tank 100 and is
not "pre-treated". Although system 113 includes acid pickling tank
100, it will be apparent that a different type of pickling
apparatus may generate the NO.sub.x-containing gas stream. For
example, the NO.sub.x-containing gas stream may be generated by a
spray pickling apparatus in which a spray of an acid pickling
solution is directed at surfaces of a metal or alloy. In certain
embodiments, the pickling tank, bath, or spray may be used to
remove surface impurities from materials selected from titanium,
titanium alloys, and stainless steels.
[0054] In certain non-limiting embodiments system 113, the pickling
solution (liquor) within pickling tank 100 has a temperature of at
least 140.degree. F. However, it will be understood that the
pickling solution may have any temperature suitable for pickling a
metal or alloy of interest. For example, in certain non-limiting
embodiments, the pickling solution may have a temperature less than
140.degree. F. In certain non-limiting embodiments of system 113,
the pickling tank 100 holds at least 5700 and as much as 15,000
gallons of pickling solution. However, it will be understood that
the pickling tank 100 may hold any volume of pickling solution
suitable for providing the desired surface processing of a metal or
alloy of interest.
[0055] Again referring to the system 113 schematically illustrated
in FIG. 4, the first inlet 40 may further communicate with a source
of moisture (water). In certain non-limiting embodiments of system
113, the moisture and the NO.sub.x-containing gas stream enter the
first chamber 200 at the same location, which may be, for example,
inlet 40. In other non-limiting embodiments of system 113, the
moisture and the NO.sub.x-containing gas stream may enter the first
chamber 200 at different locations. In yet other non-limiting
embodiments, all or a portion of the moisture introduced into the
first chamber 200 may be part of the NO.sub.x-containing gas
stream, generated as a result of evaporation of water from the
pickling solution 42.
[0056] Second inlet 50 to chamber 200 of the system 113
communicates with a source of ozone. The ozone source may be, for
example, an ozone generator or another known device that produces
ozone (not shown), or an ozone storage device. In certain
non-limiting embodiments, the ozone generating device may be
located "on-site" so that ozone may be produced when needed to
treat NO.sub.x-containing gas generated by a pickling process.
Because ozone has a short half-life, the ozone preferably is
generated proximate the second inlet 50. For example, in certain
non-limiting embodiments, an ozone generator device or other ozone
source may be located near the second inlet 50. In other
non-limiting embodiments, the ozone source may be located near the
first inlet 40 and the second inlet 50. The ozone source may
provide an ozone-containing gas stream including ozone in any
concentration suitable to treat the NO.sub.x-containing gas stream
that is being introduced into the first chamber 200 from the
pickling tank 100. In certain non-limiting embodiments, the
concentration of ozone in the gas stream introduced into the first
chamber 200 at second inlet 50 may be in the range of 1 to 16
percent by volume.
[0057] In certain non-limiting embodiments of system 113, the
second inlet 50, at which a gas including ozone is introduced into
the first chamber 200 may be located adjacent (i.e., near to) the
first inlet 40 so that NO.sub.x entering the first chamber 200 from
the pickling tank 100 at the first inlet 40 contacts ozone
introduced at the second inlet 50 and suitably reacts to form
oxidation products including nitrogen sesquioxide and nitrogen
pentoxide. Those having ordinary skill may readily ascertain a
suitable minimum, maximum, and/or range of distances between the
first inlet 40 and the second inlet 50 so that the NO.sub.x in the
NO.sub.x-containing gas stream and the ozone in the
ozone-containing gas stream react within the first chamber 200 to a
suitable degree. As discussed above in connection with the
description of system 13, the degree to which the NO.sub.x in the
NO.sub.x-containing gas stream reacts with the ozone in the first
chamber 200 to form oxidation products including nitrogen
sesquioxide and nitrogen pentoxide depends on many factors
including, but not limited to, the flow rates of the gases,
residence time, the concentration on NO.sub.x and ozone in the
respective gas streams, the temperatures of the reactants, and the
particular mixing action that occurs between the gas streams within
the first chamber 200. Those having ordinary skill may suitably
adjust or influence one or more of these parameters to adjust the
reaction rate occurring in the first chamber 200 and achieve the
desired level of conversion of NO.sub.x in the NO.sub.x-containing
gas stream.
[0058] In certain non-limiting embodiments of the system 113, the
NO.sub.x-containing gas stream is not treated in a scrubber prior
to being introduced into the interior volume of the first chamber
200 and contacting ozone therein. Also, in certain embodiments of
system 113, the NO.sub.x-containing gas stream is mixed with the
ozone-containing gas stream in the first chamber 200 using a device
adapted to mix gas streams. For example, the NO.sub.x-containing
gas stream may be mixed with ozone-containing gas stream using a
static mixer. Although it is believed that a static mixer is not
required in the system 113, providing a static mixer may improve
system efficiency and reduce the length of the first chamber 200
necessary to allow the gas streams introduced into the first
chamber 200 to mix and suitably react. In certain non-limiting
embodiments of the system 113, for example, a static mixer may be
located in or associated with the first chamber 200 near the first
inlet 40 and the second inlet 50. In certain non-limiting
embodiments of system 113, a static mixer may be located
immediately following the second inlet 50.
[0059] At least a portion of the nitrogen sesquioxide and nitrogen
pentoxide oxidation products formed in the first chamber 200
further react with water in the interior volume of the first
chamber 200 to form nitric acid. As discussed above, all or a
portion of water introduced into the interior volume of the first
chamber 200 at first inlet 40 may be, for example, moisture that is
already a component of the NO.sub.x-containing gas stream from the
pickling tank 100 and/or water introduced into the first chamber
200 from one or more inlets into the first chamber 200 that
communicate with one or more water sources. A possible water source
60 is indicated in FIG. 4. It will be understood that the system
113 may be constructed in any suitable way so that a sufficient
concentration of water is present in the first chamber 200 to
suitably react with oxidation products in the first chamber 200 and
form nitric acid. In certain non-limiting embodiments, the first
inlet 40 may be located near the water source 60. In certain other
non-limiting embodiments, the first inlet 40 and second inlet 50
may be located near the water source 60. It will be understood that
the particular design of the system 113 and the first chamber 200
will influence the optimal positioning of the one or more water
inlets into the first chamber 200, if such is provided, so as to
optimally facilitate reaction of water and oxidation products in
the first chamber 200.
[0060] Again referring to FIG. 4, the second chamber 300 of system
113 may be located downstream (i.e., in the direction of gas flow)
from the first chamber 200. The first and second chambers 200,300
preferably are directly fluidly connected so that effluent from the
first chamber 200 flows to the second chamber 300. The second
chamber 300 is adapted to recover nitric acid from the effluent
emerging into the second chamber 300 from the first chamber 200. In
certain embodiments of the system 113, the second chamber 300 may
be a mist eliminator which
[0061] As illustrated in FIG. 4, in certain non-limiting
embodiments, the second chamber 300 of system 113 may include a
third inlet 70, an interior volume, and an outlet 80 through which
solubilized nitric acid is collected or recovered from the interior
volume of the second chamber 300. The third inlet 70 communicates
with a source of water vapor which, in certain non-limiting
embodiments, is sprayed into the interior volume of the second
chamber 300. The interior volume of the second chamber 300 is
adapted to contact gaseous effluent from the first chamber 200 with
water vapor to thereby solubilize in the water vapor nitric acid in
the gaseous effluent from the first chamber 200. The solubilized
nitric acid is then collected as an aqueous nitric acid solution
and is extracted from the bottom of the second chamber 300 through
outlet 80. The concentration of the nitric acid may be adjusted by,
for example, controlling the volume of water that is introduced
into the system 113 over time. For example, introducing water into
the system 113 at a relatively high rate, as a component of the
NO.sub.x-containing gas stream and/or through one or more water
inlets associated with the first chamber 200, may dilute the nitric
acid formed in and recovered from the system 113. Alternatively,
introducing a lesser volume of water in the system 113 over time
may concentrate the nitric acid formed in and recovered from the
system 113.
[0062] In certain embodiments, the recovered nitric acid is
recycled back to the pickling tank 100. In such case, for example,
all or a portion of the nitric acid recovered from the second
chamber 300 may be piped or otherwise transferred back to the
pickling tank 100 and used to pickle additional metal or alloy.
Alternatively, the nitric acid recovered from the second chamber
300 may be stored, sold, or properly disposed of, for example.
Again referring to FIG. 4, system 113 optionally includes a third
chamber 400 that is located downstream from the second chamber 300
and receives the gaseous effluent from chamber 300. In certain
non-limiting embodiments, the third chamber 400 may be a scrubber.
As is known in the art, in certain embodiments the scrubber, if
present, may be a wet scrubber or a dry scrubber. The gaseous
effluent from second chamber 300 may include un-reacted nitrogen
oxides, nitric acid that has not been captured by the second
chamber 300, nitric acid produced in regions of the system 113
beyond the second chamber 300, mercury, sulfur oxides, and/or
entrained particulates that one wishes to remove from the gas
stream exiting the second chamber 300. Such materials may be fully
or partially removed using a scrubber in the third chamber 400. For
example, nitrogen oxides that are not converted to oxidation
products in the first chamber 200 may pass un-reacted through the
second chamber 300 and enter the third chamber 400. Such un-reacted
nitrogen oxides may be partially or fully removed from the gas
stream in third chamber 400. Also, for example, nitric acid that is
not recovered in the second chamber 300 may enter the third chamber
400 through conduit 90 and be partially or wholly collected in the
third chamber 400.
[0063] In certain non-limiting embodiments, the third chamber 400
may include a fourth inlet 110, a terminal outlet 120 for releasing
a gas to the environment, and a second outlet 111 for collecting
waste from the interior volume of the third chamber 400. In
embodiments in which the third chamber 400 is a wet scrubber
device, the fourth inlet 110 may communicate with a source of a
scrubber solution. The scrubber solution may be, for example, a
non-caustic solution, such as water, or a caustic solution, such as
a water/sodium hydroxide solution. In certain non-limiting
embodiments, the particular scrubber solution may be recirculated
through the scrubber to neutralize non-recovered nitric acid
passing into the third chamber 400. The first outlet 112 releases
any nitrogen oxides (NO.sub.x) that are not removed in the second
chamber 300 or third chamber 400. The second outlet 111 may be used
for extracting wastes from the third chamber 400, and the waste may
be reused and/or disposed of, as the case may be.
[0064] The system 113 illustrated in FIG. 4 is advantageous in that
it allows free nitric acid in the pickling solution 42 in pickling
tank 100 to be recovered and, if desired, re-used without the need
to control the temperature of the pickling solution 42 to a
temperature below a normal pickling operation operating
temperature. Also, the system 113 recovers free nitric acid from
the pickling solution 42 without the need to filter metallic solids
and other particulates from the pickling solution. As discussed
above in connection with system 13, a system constructed as
generally depicted in FIG. 4 can produce a significant volume of
nitric acid in a 24 hour period. An apparatus constructed as
generally shown in FIG. 4 could potentially recover as much as 1350
pounds/day of nitric acid (based on 100% acid) from a waste gas
stream including 1200 ppm NO.sub.x and flowing at a rate of 4,500
scfm (standard cubic feet per minute). It will be understood that
the NO.sub.x gas processed by system 113 may include NO.sub.x
generated by the normal pickling process and/or NO.sub.x produced
by introducing treating materials into the pickling solution 42.
Regardless of the source of NO.sub.x gas, the effect is to recover
and/or regenerate nitric acid used in the pickling process.
[0065] This disclosure has been written with reference to various
exemplary, illustrative, and non-limiting embodiments. However, it
will be recognized by persons having ordinary skill in the art that
various substitutions, modifications, or combinations of any of the
disclosed embodiments (or portions thereof) may be made without
departing from the scope of the invention. Thus, it is contemplated
and understood that the present disclosure embraces additional
embodiments not expressly set forth herein. Such embodiments may be
obtained, for example, by combining, modifying, or reorganizing any
of the disclosed steps, components, elements, features, aspects,
characteristics, limitations, and the like, of the embodiments
described herein. In this regard, Applicant reserves the right to
amend the claims during prosecution to add features as variously
described herein.
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