U.S. patent application number 15/953703 was filed with the patent office on 2018-12-20 for ammonia-adding system for ammonia-based desulfurization device.
The applicant listed for this patent is Jiangnan Environmental Protection Group Inc.. Invention is credited to Jing Luo, Jingyong Wang, Jun Zhang.
Application Number | 20180361308 15/953703 |
Document ID | / |
Family ID | 59227514 |
Filed Date | 2018-12-20 |
United States Patent
Application |
20180361308 |
Kind Code |
A1 |
Luo; Jing ; et al. |
December 20, 2018 |
AMMONIA-ADDING SYSTEM FOR AMMONIA-BASED DESULFURIZATION DEVICE
Abstract
Ammonia-adding apparatus and methods for ammonia-based
desulfurization use multi-stage control, calculate a theoretical
amount of ammonia based on gas amounts provided by an inlet
continuous emission monitoring system (CEMS) and an outlet CEMS of
the ammonia-based desulfurization device or associated gas amounts,
a SO.sub.2 concentration provided by the inlet CEMS, and a
predetermined SO.sub.2 concentration of the outlet CEMS. The
apparatus and methods calculate a corrected theoretical amount of
ammonia using half of the ratio of the actual amount of added
ammonia to the actual amount of removed sulfur dioxide as a
correction coefficient for the theoretical amount of ammonia; add
an ammonia absorbent equivalent to the corrected theoretical amount
of ammonia to the ammonia-based desulfurization device through an
ammonia metering means and an ammonia control valve, and
automatically control the actual ammonia flow rate based on the
actual SO.sub.2 concentration and a change trend provided by the
outlet CEMS.
Inventors: |
Luo; Jing; (NanJing, CN)
; Wang; Jingyong; (NanJing, CN) ; Zhang; Jun;
(NanJing, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Jiangnan Environmental Protection Group Inc. |
Grand Kayman |
|
KY |
|
|
Family ID: |
59227514 |
Appl. No.: |
15/953703 |
Filed: |
April 16, 2018 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15661186 |
Jul 27, 2017 |
10099170 |
|
|
15953703 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B01D 2252/102 20130101;
Y02A 50/20 20180101; B01D 53/50 20130101; B01D 53/1412 20130101;
B01D 53/346 20130101; Y02A 50/2346 20180101; B01D 2252/103
20130101; B01D 53/1481 20130101; B01D 53/1493 20130101 |
International
Class: |
B01D 53/14 20060101
B01D053/14 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 14, 2017 |
CN |
201710446925.2 |
Claims
1. Apparatus for adding ammonia to an absorption solution in a
flue-gas desulfurization system, the apparatus comprising: an
emission monitoring system configured to provide a measure of an
output sulfur dioxide characteristic; valves configured to: add
ammonia to the absorption solution at a base rate that is
proportional to: a) a target sulfur dioxide removal rate; and b) a
correction coefficient that includes a ratio of cumulative ammonia
added to cumulative sulfur dioxide removed; and, then, control
ammonia addition to the absorption solution to a second rate based
on the measure of the output sulfur dioxide characteristic; and a
distributed control system configured to: receive a sulfur dioxide
concentration at an outlet of the desulfurization system; and set
the correction coefficient to a different value in response to the
sulfur dioxide concentration.
2-26. (canceled)
27. The apparatus of claim 1 wherein the valves include a main
ammonia dispensing valve and an auxiliary ammonia dispensing valve,
the auxiliary valve configured to dispense ammonia at a rate that
is the base rate minus a rate at which ammonia is dispensed through
the main valve.
28. The apparatus of claim 27 wherein the auxiliary valve is
further configured to change its rate of dispensing ammonia based
on the measure of the output sulfur dioxide characteristic.
29. The apparatus of claim 28 wherein; the measure of the sulfur
dioxide characteristic is a rate of change of sulfur dioxide
emission rate at the outlet of the desulfurization system; and the
auxiliary valve is further configured to change its rate based on a
predefined relationship between: the rate of change of sulfur
dioxide emission at the outlet; and a fine adjustment value.
30. The apparatus of claim 29 wherein: the valves configured to add
ammonia includes: the main valve being configured to: pass ammonia;
and be controlled with coarse control; and the valves configured to
control ammonia addition includes: the auxiliary valve being
configured to: pass ammonia; and be controlled with fine
control.
31-39. (canceled)
40. The apparatus of claim 1 wherein the correction coefficient is
defined as: one half of: a ratio of actual molar number of added
ammonia to actual molar number of removed sulfur dioxide.
41. The apparatus of claim 40 wherein the valves are further
configured to regulate the base rate to be: no less than 90% of a
product of: ammonia stoichiometrically required by the target sa
lfaar dioxide removal rate and the correction coefficient; and no
more than 110% of the product.
42. The apparatus of claim 41 wherein: the target sulfur dioxide
removal rate depends on a predetermined outlet sulfur dioxide
concentration; and the ammonia stoichiometrically required is: (
gas amount corresponding to an inlet of the desulfurization system
, Nm 3 / h ) ( SO 2 concentration at the inlet mg / Nm 3 ) - ( gas
amount corresponding to the outlet of the desulfurization system ,
Nm 3 / h ) ( predetermined SO 2 concentration at the outlet , mg /
Nm 3 ) ( 1 , 000 mg / g ) ( 1000 g / kg ) ( 64 mg SO 2 / 34 mg NH 3
) . ##EQU00002##
43. The apparatus of claim 42 wherein the gas amount corresponding
to the inlet of the desulfurization system is received from an
inlet continuous electronic monitoring instrument.
44. The apparatus of claim 42 wherein the SO.sub.2 concentration at
the inlet of the desulfurization system is received from an inlet
continuous electronic monitoring instrument.
45. The apparatus of claim 42 wherein the gas amount corresponding
to the outlet of the desulfurization system is received from an
outlet continuous electronic monitoring instrument.
46. (canceled)
47. The apparatus of claim 30 further configured to: measure at
least one of: a gas amount corresponding to an inlet of the
desulfurization system; and a gas amount corresponding to the
outlet of the desulfurization system; and substitute the at least
one measured one of the gas amount corresponding to the inlet and
the gas amount corresponding to the outlet for the other one of the
gas amount corresponding to the inlet and the gas amount
corresponding to the outlet.
48. The apparatus of claim 47 wherein the other one is subject to a
gas amount correction calculation based, at least partly, on a gas
flow characteristic.
49. The apparatus of claim 48 wherein the flow characteristic is
temperature.
50. The apparatus of claim 48 wherein the flow characteristic is
pressure.
51. The apparatus of claim 48 wherein the flow characteristic is
water content.
52. (canceled)
53. Apparatus for adding ammonia to an absorption solution in a
flue-gas desulfurization system, the apparatus comprising: an
emission monitoring system configured to provide a measure of an
output sulfur dioxide characteristic; valves configured to: add
ammonia to the absorption solution at a base rate that is
proportional to: a) a target sulfur dioxide removal rate; and b) a
correction coefficient that includes a ratio of cumulative ammonia
added to cumulative sulfur dioxide removed; and, then, control
ammonia addition to the absorption solution to a second rate based
on the measure of the output sulfur dioxide characteristic; and a
distributed control system ("DCS") configured to calculate an
amount of required ammonia; wherein the DCS uses a processor to
calculate the amount, the processor configured to calculate the
amount based on: characteristics of gases associated with flue gas,
the characteristics provided by an inlet continuous emission
monitoring system ("CEMS") and an outlet CEMS of the
desulfurization system; an SO2 concentration provided by the inlet
CEMS; and a predetermined SO2 concentration of the outlet CEMS.
54. The apparatus of claim 53 wherein the characteristics include
boiler activity characteristics from a boiler with which the
desulfurization system is operated.
55. The apparatus of claim 54 wherein the valves include a main
ammonia dispensing valve and an auxiliary ammonia dispensing valve,
the auxiliary valve configured to dispense ammonia at a rate that
is the base rate minus a rate at which ammonia is dispensed through
the main valve.
56. The apparatus of claim 55 wherein the auxiliary valve is
further configured to change its rate of dispensing ammonia based
on the measure of the output sulfur dioxide characteristic.
57. The apparatus of claim 56 wherein: the measure of the sulfur
dioxide characteristic is a rate of change of sulfur dioxide
emission rate at the outlet of the desulfurization system; and the
auxiliary valve is further configured to change its rate based on a
predefined relationship between: the rate of change of sulfur
dioxide emission at the outlet; and a fine adjustment value.
58. The apparatus of claim 57 wherein: the valves configured to add
ammonia includes: the main valve being configured to: pass ammonia;
and be controlled with coarse control; and the valves configured to
control ammonia addition includes: the auxiliary valve being
configured to: pass ammonia; and be controlled with fine
control.
59. Apparatus for adding ammonia to an absorption solution in a
flue-gas desulfurization system, the apparatus comprising: an
emission monitoring system configured to provide a measure of an
output sulfur dioxide characteristic valves configured to: add
ammonia to the absorption solution at a base rate that is
proportional to: a) a target sulfur dioxide removal rate; and b) a
correction coefficient that includes a ratio of cumulative ammonia
added to cumulative sulfur dioxide removed; and, then, control
ammonia addition to the absorption solution to a second rate based
on the measure of the output sulfur dioxide characteristic; and a
distributed control system ("DCS") configured to calculate an
amount of required ammonia; wherein the DCS uses a processor to
calculate the amount, the processor configured to calculate the
amount based on: characteristics of flue gas, the characteristics
provided by an inlet continuous emission monitoring system ("CEMS")
and an outlet CEMS of the desulfurization system; an SO2
concentration provided by the inlet CEMS; and a predetermined SO2
concentration of the outlet CEMS.
60. The apparatus of claim 59 wherein the valves include a main
ammonia dispensing valve and an auxiliary ammonia dispensing valve,
the auxiliary valve configured to dispense ammonia at a rate that
is the base rate minus a rate at which ammonia is dispensed through
the main valve.
61. The apparatus of claim 60 wherein the auxiliary valve is
further configured to change its rate of dispensing ammonia based
on the measure of the output sulfur dioxide characteristic.
62. The apparatus of claim 61 wherein: the measure of the sulfur
dioxide characteristic is a rate of change of sulfur dioxide
emission rate at the outlet of the desulfurization system; and the
auxiliary valve is further configured to change its rate based on a
predefined relationship between; the rate of change of sulfur
dioxide emission at the outlet; and a fine adjustment value.
63. The apparatus of claim 61 wherein: the valves configured to add
ammonia includes: the main valve being configured to: pass ammonia;
and be controlled with coarse control; and the valves configured to
control ammonia addition includes: the auxiliary valve being
configured to: pass ammonia; and be controlled with fine
control.
64. Apparatus for adding ammonia to an absorption solution in a
flue-gas desulfurization system, the apparatus comprising: an
emission monitoring system configured to provide a measure of an
output sulfur dioxide characteristic; valves configured to: add
ammonia to the absorption solution at a base rate that is
proportional to: a) a target sulfur dioxide removal rate defined as
a difference between: 1) a product of: a gas flow rate
corresponding to an inlet of the desulfurization system and an
inlet SO.sub.2 concentration; and 2) a product of: a gas flow rate
corresponding to an outlet of the desulfurization system and a
predetermined SO.sub.2 outlet concentration; and b) a correction
coefficient that includes a ratio of cumulative ammonia added to
cumulative sulfur dioxide removed; and, then, control ammonia
addition to the absorption solution to a second rate based on the
measure of the output sulfur dioxide characteristic; and a
distributed control system configured to: receive a steam
generation rate from a boiler that produces the flue gas; and
calculate an amount of required ammonia based, at least partly, on
the steam generation rate, wherein the gas flow rate corresponding
to the inlet is evaluated as the steam generation rate.
65. The apparatus of claim 64 wherein the valves include a main
ammonia dispensing valve and an auxiliary ammonia dispensing valve,
the auxiliary valve configured to dispense ammonia at a rate that
is the base rate minus a rate at which ammonia is dispensed through
the main valve.
66. The apparatus of claim 65 wherein the auxiliary valve is
further configured to change its rate of dispensing ammonia based
on the measure of the output sulfur dioxide characteristic.
Description
[0001] This application claims priority under 35 U.S.C. .sctn. 119
of Chinese Patent Application No. 201710446925.2, filed on Jun. 14,
2017, which is hereby incorporated herein in its entirety.
TECHNICAL FIELD
[0002] The present invention belongs to the field of environmental
protection technologies, and in particular to an ammonia-adding
system for an ammonia-based desulfurization device.
BACKGROUND
[0003] At present, limestone desulfurization process and
ammonia-based desulfurization process are mainstream processes in
the whole world for removing sulfur dioxide from gases. In the
limestone desulfurization process, large quantities of waste water
and gypsum residues are produced during desulfurization, and a lot
of investment and operating costs are required to treat these waste
water and waste residues. Also, in the limestone desulfurization
process, while 1 ton of sulfur dioxide is removed, about 0.7 ton of
carbon dioxide is produced synchronously. With ammonia-based
desulfurization process, basically no waste water or waste residue
is produced, and added ammonia desulfurizer is converted into a
useful ammonium sulfate fertilizer, thus it is more environmentally
friendly. However, the existing ammonia-based desulfurization
process often has the problems, such as ammonia escape, aerosol
formation, etc.
[0004] Chinese patents CN 1283346C and CN 1321723C disclose a
process for removing SO.sub.2 from coal-fired flue gas by using
ammonia as a removal agent, in which the SO.sub.2 concentration in
the clean gas is less than 100 mg/Nm.sup.3. However, the amount of
ammonia escaping in the clean gas can be up to 12 mg/Nm.sup.3.
[0005] Chinese Patent CN 100428979C discloses an ammonia-based
desulfurization process with crystallization inside a tower and an
apparatus thereof, wherein the desulfurization tower is designed to
be of a multi-section structure, successively including an
oxidation section, a crystallization section, a cooling absorption
section, a main absorption section, and a dehydration-demisting
section from bottom to top. In the process, the evaporating ability
of flue gas is utilized for crystallization to reduce operation
energy consumption, the SO.sub.2 concentration in the clean gas is
less than 200 mg/Nm.sup.3, and the ammonia content in the clean gas
can be as low as 3 mg/Nm.sup.3.
[0006] Chinese patent application No. CN 201710154157.3 discloses a
method and a device for ammonia-based removal of sulfur oxides and
dust from gas, wherein the device consists of a gas purification
and removal system, an oxidation system, an ammonium sulfate
post-processing system, an ammonia supply system and an auxiliary
system, and uses a process of multipoint ammonia addition and
multi-stage control, thereby significantly inhibiting ammonia
escape and aerosol formation, and achieving efficient
desulfurization and dedusting effects.
[0007] Chinese patent application No. CN 201610322999.0 discloses a
pH-based automatically adjusting ammonia addition system, mainly
including a control cabinet, an aqueous ammonia tank, a first
aqueous ammonia pump, a second aqueous ammonia pump, a pressure
transmitter, an electromagnetic flowmeter, an electric control
valve and a pH transducer, wherein the control cabinet is
respectively connected to the pressure transmitter, the
electromagnetic flowmeter, the electric control valve, and the pH
transducer; the control cabinet is connected to the first aqueous
ammonia pump and the second aqueous ammonia pump; the inlet end of
the first aqueous ammonia pump is connected to the aqueous ammonia
tank and the outlet end of the first aqueous ammonia pump is
respectively connected to an inlet of an ammonia addition chamber
and an inlet of a circulating pump; the first aqueous ammonia pump
is respectively connected to the pressure transmitter, the
electromagnetic flowmeter, the electric control valve and the pH
transducer; the inlet end of the second aqueous ammonia pump is
connected to the aqueous ammonia tank and the outlet end of the
second aqueous ammonia pump is respectively connected to the inlet
of the ammonia addition chamber and the inlet of the circulating
pump; the second aqueous ammonia pump is respectively connected to
the pressure transmitter, the electromagnetic flowmeter, the
electric control valve and the pH transducer; and the electric
control valve is respectively connected to the inlet of the ammonia
addition chamber and the inlet of the circulating pump.
[0008] An automatic ammonia-adding system with stable and reliable
system operation, a high automation degree and a simple process and
being applicable to an ammonia-based desulfurization device is
still required to achieve automatic multipoint ammonia addition and
multi-stage control in the ammonia-based desulfurization device,
and inhibit ammonia escape and aerosol formation.
[0009] It would therefore be desirable to provide improved
apparatus and methods for adding ammonia to a flue gas
desulfurization system to overcome shortcomings in the prior
art.
SUMMARY
[0010] An object of the disclosure is to provide an ammonia-adding
system with stable and reliable system operation, a high automation
degree and a simple process and being applicable to an
ammonia-based desulfurization device. The automatic ammonia-adding
system may be used with a method and a device for ammonia-based
removal of sulfur oxides and dust from gas disclosed in Chinese
patent application No. CN 201710154157.3.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Objects and advantages of the invention will be apparent
upon consideration of the following detailed description, taken in
conjunction with the accompanying drawings, in which like reference
characters refer to like parts throughout, and in which:
[0012] FIG. 1 is a schematic diagram of an embodiment in accordance
with the principles of the invention.
[0013] FIG. 2 is a control scheme of automatic ammonia addition in
accordance with the principles of the invention.
[0014] The drawings are exemplifications of the principles of the
invention and are not intended to limit the invention to the
particular embodiments illustrated.
DETAILED DESCRIPTION
Definitions
[0015] "Ammonia recovery" means that fraction or percentage of
ammonia added to a gas cleaning process that is subsequently
captured and extracted from the process.
[0016] "Dust" means a particulate material fine enough to waft
along gaseous flows, when handled, processed, or contacted. It
includes but is not limited to aerosols, including solid aerosol
particles and liquid aerosol particles, soot, charcoal,
non-combusted coal, fine minerals, sand, gravel, salts, and any
combination thereof.
[0017] "NO.sub.x" means a chemical species containing nitrogen and
oxygen.
[0018] In the event that the above definitions or a description
stated elsewhere in this application is inconsistent with a meaning
(explicit or implicit) that is commonly used, set forth in a
dictionary, or stated in a source incorporated by reference into
this application, the application and the claim terms in particular
are understood to be construed according to the definition or
description in this application, and not according to the common
definition, dictionary definition, or the definition that was
incorporated by reference. In the event that a claim term can only
be understood if it is construed by a dictionary, a definition set
forth in the Kirk-Othmer Encyclopedia of Chemical Technology, 5th
Edition, 2005, (John Wiley & Sons, Inc.) shall control, if
provided therein.
[0019] Apparatus and methods for adding ammonia to an absorption
solution in a flue gas desulfurization system are provided.
[0020] The apparatus and methods may involve an automatic
ammonia-adding system for an ammonia-based desulfurization device.
The apparatus may automatically calculate a theoretical amount of
ammonia based on gas amounts provided by an inlet Continuous
Emission Monitoring System (CEMS) and an outlet CEMS of the
ammonia-based desulfurization device (or associated gas amounts), a
SO.sub.2 concentration provided by the inlet CEMS, and a
predetermined SO.sub.2 concentration of the outlet CEMS. The
apparatus may calculate a corrected theoretical amount of ammonia
using half of the ratio of the actual amount of added ammonia to
the actual amount of removed sulfur dioxide as a correction
coefficient for the theoretical amount of ammonia. The apparatus
may add an ammonia absorbent equivalent to the corrected
theoretical amount of ammonia (for example, within one or more of
the ranges .+-.10%, .+-.5%, .+-.3%, .+-.2% the corrected
theoretical amount) to the ammonia-based desulfurization device
through an ammonia metering means and an ammonia control valve, and
then may control the actual ammonia flow rate based on the actual
SO.sub.2 concentration and a change trend provided by the outlet
CEMS as a feedback.
[0021] The gas amounts of the inlet and outlet CEMS (or associated
gas amounts, such as boiler activity characteristics from a boiler
with which the desulfurization device is operated), the SO.sub.2
concentrations of the inlet and outlet CEMS, and the data of the
ammonia metering may be uploaded to a distributed control system to
calculate the actual amount of added ammonia and the actual amount
of removed sulfur dioxide, and then calculate the theoretical
amount of ammonia, the correction coefficient for the amount of
ammonia, and the corrected theoretical amount of ammonia.
[0022] The theoretical amount of ammonia, the correction
coefficient for the theoretical amount of ammonia, and the
corrected theoretical amount of ammonia may be calculated as
follows:
theoretical amount of ammonia=(gas amount of the inlet CEMS or
associated gas amount (Nm.sup.3/h)*inlet SO.sub.2 concentration
(mg/Nm.sup.3)-gas amount of the outlet CEMS or associated gas
amount (Nm.sup.3/h)*predetermined SO.sub.2 concentration of the
outlet CEMS (mg/Nm.sup.3))/1000/1000/64*34 kg/h
correction coefficient for theoretical amount of ammonia=actual
molar number of added ammonia/actual molar number of removed sulfur
dioxide/2
corrected theoretical amount of ammonia=theoretical amount of
ammonia*correction coefficient for theoretical amount of
ammonia
[0023] The apparatus may use an outlet SO.sub.2 concentration as a
term in the correction coefficient for the theoretical amount of
ammonia. Different correction coefficients can be set according to
different ranges of the SO.sub.2 concentration, such as 20-30,
50-80, 120-170 mg/Nm.sup.3 and so on.
[0024] The apparatus may use a slope of a temporal curves of the
outlet SO.sub.2 concentration value to determine the outlet
SO.sub.2 concentration change trend. Different further correction
coefficients can be used for different observed slopes (for
example, when the slope takes on values such as less than 0, 0-1,
1-2, etc.).
[0025] The methods may include adding ammonia to the absorption
solution at a base rate that is proportional to: a) a target sulfur
dioxide removal rate; and b) a correction coefficient that includes
a ratio of cumulative ammonia added to cumulative sulfur dioxide
removed. The methods may include; after the adding, controlling
ammonia addition to a second rate based on a measured output sulfur
dioxide characteristic.
[0026] The methods may include dispensing ammonia through a valve
at 90-99% the base rate.
[0027] The valve may be a main ammonia dispensing valve. The
methods may include dispensing ammonia through an auxiliary ammonia
dispensing valve at a rate that is the base rate minus the rate at
which ammonia is dispensed through the main ammonia dispensing
valve.
[0028] The main valve may have a throughput setting. The methods
may include quantifying a rate of change of sulfur dioxide at an
inlet of the system; and determining that the rate of change is not
greater than a threshold. The controlling may include,
simultaneously: maintaining the main valve at the throughput
setting; and adjusting the auxiliary valve.
[0029] The threshold rate of change may be 2%.
[0030] The method may include quantifying a rate of change of
sulfur dioxide at an inlet of the system; and determining that the
rate of change is greater than a threshold. The controlling may
include: resetting the main valve from the throughput setting to a
new throughput setting; and, simultaneously: maintaining the main
valve at the new throughput setting; and adjusting the auxiliary
valve.
[0031] In the adding, the target sulfur dioxide removal rate may be
defined as a difference between: (a) the product of: (i) a gas flow
rate corresponding to an inlet of the system and (ii) an inlet
SO.sub.2 concentration; and (b) the product of: (i) a gas flow rate
corresponding to an outlet of the system and (ii) a predetermined
SO.sub.2 outlet concentration.
[0032] The methods may include receiving at a distributed control
system ("DCS") a steam generation rate from a boiler that produces
the flue gas; and evaluating the gas flow rate corresponding to the
inlet as the steam generation rate. The evaluating may include
using the steam generation rate, or a term proportional to the
steam generation rate, as a proxy, in a targeted sulfur dioxide
removal rate calculation, for the gas flow rate corresponding to
the inlet.
[0033] The method may include receiving at a distributed control
system ("DCS") a steam generation rate from a boiler that produces
the flue gas; and evaluating the gas flow rate corresponding to the
outlet as the boiler load. The evaluating may include using the
steam generation rate, or a term proportional to the steam
generation rate, as a proxy, in a targeted sulfur dioxide removal
rate calculation, for the gas flow rate corresponding to the
outlet.
[0034] The methods may include receiving at a distributed control
system ("DCS") a boiler air flow rate from a boiler that produces
the flue gas; and evaluating the gas flow rate corresponding to the
inlet as the boiler air flow rate. The evaluating may include using
the boiler air flow rate, or a term proportional to the boiler air
flow rate, as a proxy, in a targeted sulfur dioxide removal rate
calculation, for the gas flow rate corresponding to the inlet.
[0035] The methods may include receiving at a distributed control
system ("DCS") a boiler air flow rate from a boiler that produces
the flue gas; and
evaluating the gas flow rate corresponding to the outlet as the
boiler airflow rate. The evaluating may include using the boiler
air flow rate, or a term proportional to the boiler air flow rate,
as a proxy, in a targeted sulfur dioxide removal rate calculation,
for the gas flow rate corresponding to the outlet.
[0036] The methods may include receiving at a distributed control
system ("DCS"), from a continuous emission monitoring system, a
flue gas inlet flow rate corresponding to an inlet of the system;
and evaluating the gas flow rate corresponding to the inlet as the
flue gas inlet flow rate.
[0037] The methods may include receiving at a distributed control
system ("DCS"), from a continuous emission monitoring system, a
flue gas outlet flow rate corresponding to the outlet of the
system; and evaluating the gas flow rate corresponding to the
outlet as the flue gas outlet flow rate.
[0038] The methods may include measuring the flue gas inlet flow
rate. The methods may include measuring the flue gas outlet flow
rate.
[0039] In the adding, the correction coefficient may be defined as:
one half of: a ratio of actual molar number of added ammonia to
actual molar number of removed sulfur dioxide. The actual molar
numbers may be tallied over a time period. The time period may be a
period of days, a period of weeks, a period of months, a period of
years, or any other suitable period.
[0040] The adding may include regulating the base rate to be: (a)
no less than 90% of a product of: (i) ammonia stoichiometrically
required by the target sulfur dioxide removal rate and (ii) the
correction coefficient; and (b) no more than 110% of the
product.
[0041] The adding may include regulating the base rate to be: (a)
no less than 95% of a product of: (i) ammonia stoichiometrically
required by the target sulfur dioxide removal rate and (ii) the
correction coefficient; and (b) no more than 105% of the
product.
[0042] The adding may include regulating the base rate to be: (a)
no less than 98% of a product of: (i) ammonia stoichiometrically
required by the target sulfur dioxide removal rate and (ii) the
correction coefficient; and (b) no more than 102% of the
product.
[0043] The targeted sulfur dioxide removal rate depends on a preset
outlet sulfur dioxide concentration. The ammonia stoichiometrically
required may be:
( gas flow rate corresponding to an inlet of the system , Nm 3 / h
) ( SO 2 concentration at the inlet , mg / Nm 3 ) - ( gas flow rate
corresponding to an outlet of the system , Nm 3 / h ) ( preset SO 2
concentration at outlet , mg / Nm 3 ) ( 1 , 000 mg / g ) ( 1000 g /
kg ) ( 64 mg SO 2 / 34 mg NH 3 ) . ##EQU00001##
[0044] The methods may include receiving, at a distributed control
system ("DCS"), from an inlet continuous electronic monitoring
instrument, the gas flow rate corresponding to the inlet of the
system.
[0045] The methods may include receiving, at a distributed control
system ("DCS"), from an inlet continuous electronic monitoring
instrument, the SO.sub.2 concentration at the inlet of the
system.
[0046] The methods may include receiving, at a distributed control
system ("DCS"), from an outlet continuous electronic monitoring
instrument, the gas flow rate corresponding to the outlet of the
system.
[0047] The controlling may include: receiving at a distributed
control system ("DCS") a sulfur dioxide concentration at an outlet
of the desulfurization system; and changing the correction
coefficient in response to the sulfur dioxide concentration.
[0048] The valve may be a main ammonia dispensing valve, and the
methods may include dispensing ammonia through an auxiliary ammonia
dispensing valve at a rate that is the base rate minus the rate at
which ammonia is dispensed through the main ammonia dispensing
valve. The methods may include changing the rate of dispensing
through the auxiliary ammonia dispensing valve in response to a
predefined relationship between: (a) a rate of change of sulfur
dioxide emission rate at an outlet of the system; and (b) a fine
adjustment value. The fine adjustment value may correspond to a
throughput setting of the auxiliary valve. The fine adjustment
value may correspond to a change in a throughput setting of the
auxiliary valve.
[0049] The controlling may include changing the correction
coefficient in response to a sulfur dioxide concentration at an
outlet of the desulfurization system.
[0050] The method may include measuring only one of: (a) the gas
flow rate corresponding to the inlet of the system; and (b) the gas
flow rate corresponding to the outlet of the system; and evaluating
the other one as the measured one. The evaluating may include using
the measured rate as a proxy, in a targeted sulfur dioxide removal
rate calculation, for the rate not measured.
[0051] The methods may include receiving at a distributed control
system ("DCS") a flue gas characteristic; and correcting the other
rate based on the flow characteristic. The other rate may be the
rate not measured. The flow characteristic may be a flue gas
temperature. The flow characteristic may be a flue gas pressure.
The flow characteristic may be a flue gas water content.
[0052] The absorption liquid may include at least one ammonia or
amine based compound, including but not limited to ammonium salts,
ammonium ions (NH4.sup.+), ammonium sulfate, ammonium sulfite, and
any combination thereof. The liquid may be water.
[0053] The apparatus and methods may include an oxidation section,
an absorption section and a fine particulate control section in the
absorption tower.
[0054] The apparatus may include an ammonia-adding system for an
ammonia-based desulfurization device. The apparatus may use
multi-stage control. The apparatus may include a processor. The
processor may calculate a theoretical amount of required ammonia
based on flue gas amounts provided by an inlet continuous emission
monitoring system ("CEMS") and an outlet CEMS of the ammonia-based
desulfurization device or associated gas amounts, an SO.sub.2
concentration provided by the inlet CEMS, and a predetermined
SO.sub.2 concentration of the outlet CEMS. The processor may
calculate a corrected theoretical amount of ammonia using half of
the ratio of the actual amount of added ammonia to the actual
amount of removed sulfur dioxide as a correction coefficient for
the theoretical amount of ammonia. The apparatus may provide
addition of an ammonia absorbent equivalent to the corrected
theoretical amount of ammonia .+-.10% to the ammonia-based
desulfurization device through an ammonia metering means and an
ammonia control valve. The apparatus may automatically control the
actual ammonia flow rate based on the actual SO.sub.2 concentration
and a change trend. One or both of the actual SO.sub.2
concentration and the change trend may be provided by the outlet
CEMS as a feedback.
[0055] The apparatus may include an absorption tower, an ammonia
supply system, an ammonia control valve, an ammonia metering means,
a circulating pump, an inlet CEMS, an outlet CEMS and an oxidation
section.
[0056] The gas amounts of the inlet and outlet CEMS or associated
gas amounts, the SO.sub.2 concentrations of the inlet and outlet
CEMS, and the data of the ammonia metering may be uploaded to the
DCS to calculate the actual amount of added ammonia and the actual
amount of removed sulfur dioxide, and then calculate the
theoretical amount of ammonia, the correction coefficient for the
amount of ammonia, and the corrected theoretical amount of
ammonia.
[0057] The theoretical amount of ammonia, the correction
coefficient for the theoretical amount of ammonia, and the
corrected theoretical amount of ammonia may be calculated as
follows:
Theoretical Amount of Ammonia:
[0058] theoretical amount of ammonia=(gas amount of the inlet CEMS
or associated gas amount (Nm.sup.3/h)*inlet SO.sub.2 concentration
(mg/Nm.sup.3)-gas amount of the outlet CEMS or associated gas
amount (Nm.sup.3/h)*predetermined SO.sub.2 concentration of the
outlet CEMS (mg/Nm.sup.3))/1000/1000/64*34 kg/h
Correction Coefficient for Theoretical Amount of Ammonia:
[0059] correction coefficient for theoretical amount of
ammonia=ratio of actual molar number of added ammonia to actual
molar number of removed sulfur dioxide/2
Corrected Theoretical Amount of Ammonia:
[0060] corrected theoretical amount of ammonia=theoretical amount
of ammonia*correction coefficient for theoretical amount of
ammonia.
[0061] An outlet SO.sub.2 concentration gradient (change in
concentration per unit of time) may be a term in the correction
coefficient for the theoretical amount of ammonia.
[0062] A slope of curve of the outlet SO.sub.2 concentration value
may be evaluated to assess an outlet SO.sub.2 concentration change
trend.
[0063] The ammonia absorbent supplied by the apparatus may be one
or more of liquid ammonia, aqueous ammonia and gas ammonia.
[0064] The apparatus may include one or more ammonia control
valves. The apparatus may include two ammonia control valves. The
apparatus may include a plurality of ammonia control valves having
different control abilities.
[0065] A control valve with a large control ability may be used to
control the corrected theoretical amount of ammonia. A control
valve with a small, or fine, control ability may be used for
automatic feedback adjustment and control.
[0066] The apparatus may include a flow meter or a metering pump
for metering or adding ammonia.
[0067] The inlet CEMS may output one or more of water content,
temperature and pressure of the flue gas.
[0068] The outlet CEMS may output one or more of water content,
temperature and pressure of the flue gas.
[0069] A boiler may be associated with the desulfurization device.
The boiler may receive heat from hot gas that is then exhausted as
flue gas for treatment by the desulfurization device. The apparatus
may substitute for one or both of the inlet and outlet CEM gas
amounts a boiler steam generation rate (tons per unit of time, for
example) (a "boiler load") and a boiler air amount.
[0070] The apparatus may substitute the inlet CMS gas amount for
the outlet CMS gas amount. The apparatus may substitute the outlet
CMS gas amount for the inlet CMS gas amount.
[0071] One or more of the water content, temperature and pressure
data of the inlet and outlet CEMS may be used for gas-amount
correction.
[0072] Some embodiments are discussed with reference to FIG. 1. In
some embodiments, the apparatus may include ammonia supply system
2, ammonia control valve 3, ammonia metering means 4, inlet CEMS 7
and outlet CEMS 8. In some embodiments, the apparatus may include
absorption tower 1, ammonia supply system 2, ammonia control valve
3, ammonia flow meter 4, circulating pump 6, inlet CEMS 7, outlet
CEMS 8 and oxidation section 9.
[0073] The apparatus may provide an ammonia absorbent, which may be
one or more of liquid ammonia, aqueous ammonia and gaseous
ammonia.
[0074] The apparatus may include one or more ammonia control
valves. The apparatus may include two or more ammonia control
valves. The valves may have different control abilities. For
example, one or more of the valves may have large (coarse) control
ability, and one or more of the valves may have fine control
ability. A control valve with a large control ability may be used
to control 90-99% amount of ammonia. A control valve with a small
control ability may be used for automatic feedback adjustment and
control.
[0075] In some embodiments, the ammonia metering means may include
one or both of a flow meter, e.g. a volumetric flow meter or a mass
flow meter, and a metering pump.
[0076] In some embodiments, the measured items for the inlet CEMS
may include one or more of a gas amount (flow rate), a gas SO.sub.2
concentration, a gas water content, a gas dust content, a gas
temperature, and a gas pressure.
[0077] In some embodiments, the measured items for the outlet CEMS
may include one or more of a gas amount, a gas SO.sub.2
concentration, a gas water content, a gas dust content, a gas
temperature, a gas pressure, a gas nitrogen oxide content, and a
gas free ammonia content.
[0078] In some embodiments, associated gas amounts, e.g. gas
amounts calculated from a boiler load, a boil air volume or other
parameters may be used to substitute for one or both of a CEMS gas
inlet amount and a CEMS gas outlet amout. In some embodiments, one
of a CEMS gas inlet amount and a CEMS gas outlet amount can be
substituted for the other. In some embodiments, one or more of a
gas water content, a gas temperature and a gas pressures of the
inlet or outlet CEMS can be used for gas amount correction
calculation.
[0079] In some embodiments, an ammonia-based desulfurization device
using apparatus and methods may include one or more of the
following illustrative process steps:
[0080] A raw flue gas enters from the middle-lower part of an
absorption tower.
[0081] An ammonia supply system provides supplemental ammonia
absorbent via an ammonia control valve to predetermined
ammonia-adding points, such as an oxidation section of an
absorption tower, a circulating pump, etc., thereby achieving
automatic ammonia addition to the desulfurization system.
[0082] The circulating washing liquid (ammonia absorbent) may be
concentrated (crystallized) in a cooling-and-washing process, and
then processed to an ammonium sulfate product through an ammonium
sulfate post-processing system.
[0083] The raw flue gas is emitted from a flue gas outlet on the
top of the tower after cooling-and-washing, washing for
desulfurization, and removing fine particulate matters by a washing
liquid circulated by a circulating pump.
[0084] A specific illustrative embodiment of the apparatus and
methods is now described with reference to FIG. 1 and FIG. 2,
wherein the automatic ammonia-adding system includes an absorption
tower 1, ammonia supply system 2, ammonia control valve 3, ammonia
metering means 4, circulating pump 6, inlet CEMS 7, outlet CEMS 8
and oxidation section 9.
[0085] A Distributed Control System (DCS) automatically calculates
a theoretical amount of ammonia using a microprocessor based on gas
amounts provided by inlet CEMS 7 and outlet CEMS 8 (or associated
gas amounts), an SO.sub.2 concentration provided by the inlet CEMS
7 and a predetermined SO.sub.2 concentration of outlet CEMS 8;
calculates a corrected theoretical amount of ammonia using half of
the ratio of the actual amount of added ammonia to the actual
amount of removed sulfur dioxide as a correction coefficient for
the theoretical amount of ammonia; adds an ammonia absorbent
equivalent to the corrected theoretical amount of ammonia (for
example, within one or more of the ranges .+-.10%, .+-.5%, .+-.3%,
.+-.2% the corrected theoretical ammount), to the ammonia-based
desulfurization device through ammonia metering means 4 and ammonia
control valve 3; and then automatically controls the actual ammonia
flow rate based on the actual SO.sub.2 concentration and change
trend provided by the outlet CEMS 8 as a feedback, thereby
achieving automatic ammonia addition.
[0086] Different correction coefficients can be set according to
different ranges of the SO.sub.2 concentration (such as 20-30,
50-80, 120-170 mg/Nm.sup.3, and so on).
[0087] A slope of a curve of the outlet SO.sub.2 value may be used
as a basis for calculation, and different correction coefficients
can be set at different slopes (the outlet SO.sub.2 concentration
change trend, e.g. less than 0, 0-1, 1-2, etc.).
[0088] The ammonia absorbent supplied by the ammonia supply system
2 may be 20% aqueous ammonia.
[0089] Dual control valves may be used to control automatic ammonia
addition. The inlets of ammonia control valves 3 may be connected
to ammonia supply system 2. Outlets of ammonia control valves 3 may
be connected to ammonia addition points, such as oxidization
section 9 and the circulation pump 6. The amount of ammonia added
through the main ammonia control valve may be, for example, 98% of
the corrected theoretical amount of ammonia.
[0090] The measured items for inlet CEMS 7 may include one or more
of a gas amount, a gas SO.sub.2 concentration, a gas water content,
a gas dust content, a gas temperature and gas pressure.
[0091] The measured items for outlet CEMS 8 may include one or more
of a gas amount, a gas SO.sub.2 concentration, a gas water content,
a gas dust content, a gs temperature, a gas pressure, a gas
nitrogen oxide content, and a gas free ammonia content.
[0092] Ammonia supply system 2 may include one or more of an
aqueous ammonia tank, an aqueous ammonia unloading pump, an aqueous
ammonia supply pump, an accident spray device and a breathing gas
washing tank. An aqueous ammonia having a concentration of 20 wt.-%
may be supplied as an ammonia absorbent. The ammonia metering means
may include a mass flow meter.
[0093] An illustrative ammonia-based desulfurization process using
the apparatus and methods may include one or more of the following
steps: [0094] Raw flue gas 5 enters from the middle-lower part of
the absorption tower 1. [0095] Ammonia supply system 2 provides
supplemental aqueous ammonia absorbent, via main ammonia control
valve 31 and an auxiliary ammonia control valve 32, to ammonia
addition points, such as oxidization section 9 and circulation pump
6.
[0096] A circulating washing liquid may be oxidized, then
concentrated to a solid content of 10-20 wt.-% in a
cooling-and-washing process, and then processed to an ammonium
sulfate product through an ammonium sulfate post-processing
system.
[0097] Gas 5 then may be emitted from a flue gas outlet on the top
of the tower successively after cooling-and-washing, washing for
desulfurization, and removing fine particulate matters by a washing
liquid circulated by circulation pump 6.
[0098] In the ammonia-based desulfurization process, illustrative
ammonia addition control steps are as follows:
1) uploading the gas amounts of inlet CEMS 7 and outlet CEMS 8 (or
associated gas amounts), the SO.sub.2 concentrations of inlet CEMS
7 and outlet CEMS 8, and ammonia metering data to the distributed
control system (DCS), wherein the water content, temperature and
pressure data of the inlet CEMS and the outlet CEMS can be used for
the gas amount correction calculation; 2) predetermining the outlet
SO.sub.2 concentration by the DCS; 3) calculating the theoretical
amount of ammonia; 4) calculating the correction coefficient for
the theoretical amount of ammonia; 5) calculating the corrected
theoretical amount of ammonia 6) controlling the ammonia flow rate
to be 98% of the corrected theoretical amount of ammonia through
mass flow meter 4 and main ammonia control valve 31; 7) acquiring
the actual SO.sub.2 concentration of the outlet CEMS by the DCS; 8)
controlling auxiliary ammonia control valve 32 based on the actual
SO.sub.2 concentration and change trend of the outlet CEMS as a
feedback to allow the outlet SO.sub.2 concentration to tend towards
the predetermined SO.sub.2 concentration; and 9) acquiring the
actual ammonia flow rate, and integrating the actual ammonia flow
rate over time; and acquiring the actual amount of removed sulfur
dioxide, and integrating the actual amount of removed sulfur
dioxide over time, by the DCS to conduct the next round of
control.
[0099] The apparatus and methods may improve the automation degree
of an ammonia-based desulfurization device through automatic
ammonia addition, may have SO.sub.2 concentration and total dust in
the outlet clean flue gas that do not exceed standards because of
inlet gas amount and SO.sub.2 concentration fluctuations, and may
reduce investment by making use of measured quantities at the inlet
and outlet CEMS, automatic statistics and the computing function of
the distributed control system.
[0100] Under the conditions that the SO.sub.2 concentration is not
more than 30000 mg/Nm.sup.3 and the total dust concentration is not
more than 50 mg/Nm.sup.3 in the raw flue gas, the ammonia-based
desulfurization device may achieve a SO.sub.2 concentration in the
clean flue gas of no more than 35 mg/Nm.sup.3, a total dust
(including aerosol) concentration of no more than 5 mg/Nm.sup.3, an
ammonia escape of no more than 3 mg/Nm.sup.3, and an ammonia
recovery of no less than 99%.
[0101] The following embodiment is provided for the purpose of
illustration, not limitation.
Embodiment 1
[0102] A raw flue gas was treated using the apparatus and methods,
as shown in FIG. 1, wherein 1 is an absorption tower, 2 is an
ammonia supply system, 3 is an ammonia control valve, 4 is a mass
flow meter as an ammonia metering means, 5 is the raw flue gas, 6
is a circulating pump, 7 is an inlet CEMS, 8 is an outlet CEMS, and
9 is an oxidation section. The gas amount of the raw flue gas is
360,000-510,000 Nm.sup.3/h, the SO.sub.2 concentration is
1,000-30,000 mg/Nm.sup.3, and the total dust concentration is 15-30
mg/Nm.sup.3.
[0103] An ammonia absorbent supplied by ammonia supply system 2 is
liquid ammonia.
[0104] Dual control valves, i.e, a main ammonia control valve 31
and an auxiliary ammonia control valve 32, are used to control
automatic ammonia addition, wherein the inlets of the ammonia
control valves 3 are connected to the ammonia supply system 2, the
outlets of the ammonia control valves 3 are connected to the
ammonia addition points, such as the oxidization section 9 and the
circulation pump 6, and the amount of ammonia added through the
main ammonia control valve 31 is 99% of the corrected theoretical
amount of ammonia.
[0105] The measured items for the inlet CEMS 7 include gas amount,
SO.sub.2 concentration, NO.sub.x content, water content, dust
content, temperature and pressure.
[0106] The measured items for the outlet CEMS 8 include gas amount,
SO.sub.2 concentration, water content, dust content, temperature,
pressure, nitrogen oxides content and free ammonia content.
[0107] The ammonia supply system 2 includes a liquid ammonia
spherical tank, an ammonia unloading compressor, an ammonia supply
pump and an accident spray device, and the ammonia metering means 4
is a mass flow meter.
[0108] Raw flue gas 5 enters from the middle-lower part of
absorption tower 1, and is then emitted from the flue gas outlet on
the top of the tower successively after cooling-and-washing,
washing for desulfurization, and removing fine particulate matters
by a washing liquid circulated by circulating pump 6.
[0109] Ammonia supply system 2 provides supplemental liquid ammonia
absorbent through main ammonia control valve 31 and auxiliary
ammonia control valve 32 to the ammonia addition points, such as
oxidization section 9 and circulation pump 6.
[0110] The circulating washing liquid is oxidized, then
concentrated to a solid content of 15 wt.-% in the
cooling-and-washing process, and then processed to an ammonium
sulfate product through an ammonium sulfate post-processing
system.
[0111] Illustrative control steps were as follows:
[0112] 1) acquiring relevant data by a DCS: an inlet gas amount of
395000 Nm.sup.3/h, an inlet SO.sub.2 concentration of 2112
mg/Nm.sup.3, an outlet gas amount of 405000 Nm.sup.3/h, an outlet
SO.sub.2 concentration of 24 mg/Nm.sup.3, an actual cumulative
amount of added liquid ammonia of 1940 t, and an actual cumulative
amount of removed sulfur dioxide of 3653 t;
[0113] 2) predetermining the outlet SO.sub.2 concentration of 23.9
mg/Nm.sup.3 by the DCS;
[0114] 3) calculating a theoretical amount of
ammonia=(395000*2112-405000*23.9)/1000/1000/64*34=438 kg/h;
[0115] 4) calculating a correction coefficient for the theoretical
amount of ammonia=1940/34/3653*64=0.9997;
[0116] 5) calculating a corrected theoretical amount of
ammonia=438*0.9997=437.85 kg/h
[0117] 6) controlling the ammonia flow rate to 433.47 kg/h through
mass flow meter 4 and main ammonia control valve 31;
[0118] 7) acquiring the actual SO.sub.2 concentration of the outlet
CEMS 23.9 mg/Nm.sup.3;
[0119] 8) controlling auxiliary ammonia control valve 32 based on
the actual SO.sub.2 concentration and change trend of the outlet
CEMS 8 as a feedback to control the outlet SO.sub.2 concentration
to 23.5 mg/Nm.sup.3; and [0120] 9) acquiring actual total ammonia
flow rate of 438 kg/h and integrating and acquiring the actual
amount of removed sulfur dioxide and integrating, to conduct the
next round of control.
[0121] When a change rate of a product of the inlet gas amount and
the inlet SO.sub.2 concentration was less than or equal to 2%, the
openness degree of main ammonia control valve 31 was left
unchanged, and the actual SO.sub.2 value of outlet CEMS 8 was
controlled to 20-25 mg/Nm.sup.3 through the auxiliary ammonia
control valve 32. When the change rate of the product of the inlet
gas amount and the inlet SO.sub.2 concentration was more than 2%,
the openness degree of main ammonia control valve 31 was calculated
and adjusted according to the above steps, and the actual SO.sub.2
value of outlet CEMS was controlled to 20-25 mg/Nm.sup.3 by
controlling auxiliary ammonia control valve 32.
[0122] The resulting clean flue gas had the following
characteristics:
[0123] SO.sub.2: 23.6 mg/Nm.sup.3;
[0124] total dust (including aerosol): 1.9 mg/Nm.sup.3;
[0125] ammonia escape: 0.55 mg/Nm.sup.3; and
[0126] ammonia recovery: 99.4%.
[0127] The present disclosure illustrates principles of the
invention and is not intended to limit the invention to the
particular embodiments illustrated. All patents, patent
applications, scientific papers, and any other referenced materials
mentioned herein are incorporated by reference in their entirety.
The principles of the invention encompass any possible combination
of some or all of the various embodiments mentioned herein,
described herein and/or incorporated herein. The principles of the
invention encompass any possible combination that also specifically
excludes any one or some of the various embodiments mentioned
herein, described herein and/or incorporated herein.
[0128] All ranges and parameters disclosed herein are understood to
encompass any and all subranges subsumed therein, and every number
between the endpoints. For example, a stated range of "1 to 10"
should be considered to include any and all subranges between (and
inclusive of) the minimum value of 1 and the maximum value of 10;
that is, all subranges beginning with a minimum value of 1 or more
(e.g. 1 to 6.1), and ending with a maximum value of 10 or less
(e.g. 2.3 to 9.4, 3 to 8, 4 to 7), and to each number 1, 2, 3, 4,
5, 6, 7, 8, 9, and 10 contained within the range. All percentages,
ratios and proportions herein are by weight unless otherwise
specified.
[0129] Thus, apparatus and methods for adding ammonia to a
desulfurization system have been provided. Persons skilled in the
art will appreciate that the present invention can be practiced by
other than the described embodiments, which are presented for
purposes of illustration rather than of limitation. The present
invention is limited only by the claims that follow.
* * * * *