U.S. patent application number 15/202520 was filed with the patent office on 2016-10-27 for air preheater and method for preventing corrosion and blockage of the same.
The applicant listed for this patent is Hotant Thermal Technology (Jiangsu) Co., Ltd.. Invention is credited to Ronge HE, Maoling LIU, Xuelue QIAN.
Application Number | 20160313076 15/202520 |
Document ID | / |
Family ID | 51274982 |
Filed Date | 2016-10-27 |
United States Patent
Application |
20160313076 |
Kind Code |
A1 |
QIAN; Xuelue ; et
al. |
October 27, 2016 |
AIR PREHEATER AND METHOD FOR PREVENTING CORROSION AND BLOCKAGE OF
THE SAME
Abstract
An air preheater, including a flue; an air channel; a first
segment for producing secondary air; a second segment for producing
primary air; a third segment for anti-condensation of ammonium
bisulfate; and a fourth segment for curing of ammonium bisulfate.
The flue and the air channel are disposed on the downstream of a
denitration device. The first segment, the second segment, the
third segment and the fourth segment are disposed in that order
along the gas flow direction. The first segment, the second
segment, the third segment and the fourth segment each include a
phase-change heat exchanger. The phase-change heat exchanger
includes a heat absorption segment disposed in the flue, a heat
release segment disposed in the air channel, an ascending tube and
a downcomer which are configured to connect the heat absorption
segment and the heat release segment.
Inventors: |
QIAN; Xuelue; (Zhenjiang,
CN) ; LIU; Maoling; (Zhenjiang, CN) ; HE;
Ronge; (Zhenjiang, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hotant Thermal Technology (Jiangsu) Co., Ltd. |
Zhenjiang |
|
CN |
|
|
Family ID: |
51274982 |
Appl. No.: |
15/202520 |
Filed: |
July 5, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/CN2014/075792 |
Apr 21, 2014 |
|
|
|
15202520 |
|
|
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F23L 15/045 20130101;
F23J 2219/10 20130101; F28D 15/0266 20130101; Y02E 20/348 20130101;
F23J 15/06 20130101; F28F 19/00 20130101; F23J 2215/10 20130101;
F23L 15/02 20130101; Y02E 20/34 20130101 |
International
Class: |
F28F 19/00 20060101
F28F019/00; F23L 15/02 20060101 F23L015/02; F23J 15/06 20060101
F23J015/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 7, 2014 |
CN |
201410006896.4 |
Claims
1. An air preheater, comprising: a flue; an air channel; a first
segment for producing secondary air; a second segment for producing
primary air; a third segment for anti-condensation of ammonium
bisulfate; and a fourth segment for curing of ammonium bisulfate;
wherein the flue and the air channel are disposed on a downstream
of a denitration device; the first segment for producing secondary
air, the second segment for producing primary air, the third
segment for anti-condensation of ammonium bisulfate and the fourth
segment for curing of ammonium bisulfate are disposed in that order
along a gas flow direction; the second segment for producing
primary air, the third segment for anti-condensation of ammonium
bisulfate, and the fourth segment for curing of ammonium bisulfate
each comprise a phase-change heat exchanger; the phase-change heat
exchanger comprises a heat absorption segment disposed in the flue,
a heat release segment disposed in the air channel, an ascending
tube and a downcomer which are configured to connect the heat
absorption segment and the heat release segment; the heat release
segment is disposed higher than the heat absorption segment, and
the phase-change heat exchanger is provided with a cycling medium;
and a wall surface temperature of the third segment for
anti-condensation of ammonium bisulfate is higher than a dew
temperature of the ammonium bisulfate; a wall surface temperature
of the fourth segment for curing of ammonium bisulfate is lower
than a solidification point temperature of the ammonium
bisulfate.
2. The air preheater of claim 1, wherein the air preheater further
comprises an acid-dew resistant segment disposed on a downstream of
the fourth segment; the acid-dew resistant segment also comprises
the phase-change heat exchanger, and a wall surface temperature of
the acid-dew resistant segment is higher than an acid dew point
temperature.
3. The air preheater of claim 2, wherein the heat absorption
segment in the second segment for producing primary air, the heat
absorption segment in the third segment for anti-condensation of
ammonium bisulfate, the heat absorption segment in the fourth
segment for curing of ammonium bisulfate, the heat absorption
segment in the acid-dew resistant segment each are provided with a
temperature sensor.
4. The air preheater of claim 2, wherein the cycling medium in the
second segment, in the third segment, in the fourth segment, and in
the acid-dew resistant segment is water, Freon, or heat transfer
oil.
5. The air preheater of claim 1, wherein the first segment for
producing secondary air is a segment of a regenerative air
preheater.
6. The air preheater of claim 1, wherein the first segment for
producing secondary air comprises the phase-change heat exchanger,
and the cycling medium in the second segment for producing primary
air is water, Freon, or heat transfer oil.
7. A method for preventing corrosion and blockage of an air
preheater, the air preheater being disposed on a downstream of a
denitration device, the method comprising: 1) introducing flue gas
in a flue to an upstream of the air preheater, and allowing the
flue gas to pass a first segment for producing secondary air, a
second segment for producing primary air, a third segment for
anti-condensation of ammonium bisulfate and a fourth segment for
curing of ammonium bisulfate in that order; introducing air in an
air channel to a downstream of the air preheater, and allowing the
air to pass the fourth segment for curing of ammonium bisulfate,
the third segment for anti-condensation of ammonium bisulfate, the
second segment for producing primary air, and the first segment for
producing secondary air; 2) adjusting a wall surface temperature of
the third segment for anti-condensation of ammonium bisulfate to be
higher than a dew temperature of the ammonium bisulfate, and
adjusting a wall surface temperature of the fourth segment for
curing of ammonium bisulfate to be lower than a solidification
point temperature of the ammonium bisulfate; 3) gasifying the
ammonium bisulfate in the flue prior to and in the third segment
for anti-condensation of ammonium bisulfate; curing the ammonium
bisulfate in and after the fourth segment for curing of ammonium
bisulfate, the ammonium bisulfate being cured on a wall surface of
a pipe of the fourth segment and a wall surface of a downstream
pipe of the fourth segment; and 4) eliminating solid ammonium
bisulfate on the wall surface of the pipe of the fourth segment and
on the wall surface of the downstream pipe of the fourth segment.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of International
Patent Application No. PCT/CN2014/075792 with an international
filing date of Apr. 21, 2014, designating the United States, now
pending, and further claims priority benefits to Chinese Patent
Application No. 201410006896.4 filed Jan. 7, 2014. The contents of
all of the aforementioned applications, including any intervening
amendments thereto, are incorporated herein by reference. Inquiries
from the public to applicants or assignees concerning this document
or the related applications should be directed to: Matthias Scholl
P.C., Attn.: Dr. Matthias Scholl Esq., 245 First Street, 18th
Floor, and Cambridge, Mass. 02142.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention relates to an air preheater and a method for
preventing corrosion and blockage of the same.
[0004] 2. Description of the Related Art
[0005] Conventional flue gas denitration technology employs ammonia
gas as a reducing agent. The reducing agent reacts with sulfur
trioxide in the flue gas to yield ammonia bisulfate. Following the
denitration process, an air preheater is provided to recycle heat
energy.
[0006] Typically, the air preheater is of a regenerative type, as
shown in FIG. 1, and includes a high temperature segment, a medium
temperature segment, and a low temperature segment. Ammonium
bisulfate exhibits strong viscosity in the medium temperature
segment and the low temperature segment, and tends to adsorb dust
particles and, as a result, block the air preheater. This increases
the gas flow resistance, lowers the heat transfer efficiency, and
adversely affects operation of the air preheater.
SUMMARY OF THE INVENTION
[0007] In view of the above-described problems, it is one objective
of the invention to provide an air preheater that has good
corrosion resistant property. The air preheater is particularly
practicable following a selective catalytic reduction (SCR)
denitration.
[0008] To achieve the above objective, in accordance with one
embodiment of the invention, there is provided an air preheater,
comprising a flue and an air channel disposed on a downstream of a
denitration device, a first segment for producing secondary air, a
second segment for producing primary air, a third segment for
anti-condensation of ammonium bisulfate, and a fourth segment for
curing of ammonium bisulfate. The first segment for producing
secondary air, the second segment for producing primary air, the
third segment for anti-condensation of ammonium bisulfate and the
fourth segment for curing of ammonium bisulfate are disposed in
that order along a gas flow direction. The second segment for
producing primary air, the third segment for anti-condensation of
ammonium bisulfate, and the fourth segment for curing of ammonium
bisulfate each comprise a phase-change heat exchanger. The
phase-change heat exchanger comprises a heat absorption segment
disposed in the flue, a heat release segment disposed in the air
channel, an ascending tube and a downcomer which are configured to
connect the heat absorption segment and the heat release segment.
The heat release segment is disposed higher than the heat
absorption segment, and the phase-change heat exchangers are
provided with a cycling medium. A wall surface temperature of the
third segment for anti-condensation of ammonium bisulfate is higher
than a dew temperature of the ammonium bisulfate. A wall surface
temperature of the fourth segment for curing of ammonium bisulfate
is lower than a solidification point temperature of the ammonium
bisulfate.
[0009] In a class of this embodiment, the air preheater further
comprises an acid-dew resistant segment disposed on a downstream of
the fourth segment for curing of ammonium bisulfate. The acid-dew
resistant segment comprises the phase-change heat exchanger, and a
wall surface temperature of the acid-dew resistant segment is
higher than an acid dew point temperature.
[0010] Preferably, the heat absorption segment in the second
segment for producing primary air, the heat absorption segment in
the third segment for anti-condensation of ammonium bisulfate, the
heat absorption segment in the fourth segment for curing of
ammonium bisulfate, the heat absorption segment in the acid-dew
resistant segment are provided with a temperature sensor.
[0011] In a class of this embodiment, the cycling medium in the
second segment for producing primary air, the third segment for
anti-condensation of ammonium bisulfate, the fourth segment for
curing of ammonium bisulfate, and the acid-dew resistant segment is
water, Freon, or heat transfer oil.
[0012] Preferably, the first segment for producing secondary air is
a high temperature segment of a regenerative air preheater.
[0013] Preferably, the first segment for producing secondary air
comprises the phase-change heat exchanger, and the cycling medium
in the second segment for producing primary air is water, Freon, or
heat transfer oil.
[0014] Advantages of the air preheater according to embodiments of
the invention are summarized as follows:
[0015] In the air preheater, the reaction of the escaped ammonia
and the sulfur trioxide only produces gaseous and solid ammonium
bisulfate, and no liquid ammonium bisulfate is produced, thus the
air preheater is effectively prevented from blockage and corrosion
caused by liquid ammonium bisulfate. Therefore, the service life of
the air preheater is prolonged; the heat transfer efficiency of the
boiler is improved; thus ensuring the stable and safe operation of
the machine set.
[0016] It is another objective of the invention to provide a method
for preventing the air preheater from corrosion and blockage. The
air preheater is disposed on a downstream of a denitration device
using SCR denitration technology. The method can prevent the
corrosion and blockage of the heating surface of the air
preheater.
[0017] To achieve the above objective, in accordance with another
embodiment of the invention, there is provided a method for
preventing an air preheater from corrosion and blockage, the method
comprising: [0018] a) introducing flue gas in a flue to an upstream
of the air preheater, and allowing the flue gas to pass a first
segment for producing secondary air, a second segment for producing
primary air, a third segment for anti-condensation of ammonium
bisulfate and a fourth segment for curing of ammonium bisulfate in
that order; introducing air in an air channel to a downstream of
the air preheater, and allowing the air to pass the fourth segment
for curing of ammonium bisulfate, the third segment for
anti-condensation of ammonium bisulfate, the second segment for
producing primary air, and the first segment for producing
secondary air; [0019] b) adjusting a wall surface temperature of
the third segment for anti-condensation of ammonium bisulfate to be
higher than a dew temperature of the ammonium bisulfate, and
adjusting a wall surface temperature of the fourth segment for
curing of ammonium bisulfate to be lower than a solidification
point temperature of the ammonium bisulfate; [0020] c) gasifying
the ammonium bisulfate in the flue prior to and in the third
segment for anti-condensation of ammonium bisulfate; curing the
ammonium bisulfate in and after the fourth segment for curing of
ammonium bisulfate, the ammonium bisulfate being cured on a wall
surface of a pipe of the fourth segment and a wall surface of a
downstream pipe of the fourth segment; and [0021] d) eliminating
solid ammonium bisulfate on the wall surface of the pipe of the
fourth segment and on the wall surface of the downstream pipe of
the fourth segment.
[0022] Advantages of the method according to embodiments of the
invention are summarized as follows:
[0023] Using the method, the wall surface temperature of the third
segment and the fourth segment can be accurately controlled, so
that the ammonium bisulfate is cured on the wall surface of the
pipe of the fourth segment and the wall surface of the downstream
pipe of the fourth segment, then the solid ammonium bisulfate is
eliminated by blowing equipment. As a result, the air preheater is
effectively prevented from blockage and corrosion, thus ensuring
the safe, reliable, and stable operation of the boiler.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The invention is described hereinbelow with reference to the
accompanying drawings, in which:
[0025] FIG. 1 is a schematic diagram of an existing air
preheater;
[0026] FIG. 2 is a schematic diagram of an air preheater in
accordance with one embodiment of the invention; and
[0027] FIG. 3 is a schematic diagram of an air preheater in
accordance with another embodiment of the invention.
[0028] In the drawings, the following reference numbers are used:
1. Hue; 2. Air channel; 3. First segment for producing secondary
air; 4. Second segment for producing primary air; 5. Third segment
for anti-condensation of ammonium bisulfate; 6. Fourth segment for
curing of ammonium bisulfate; 7. Heat absorption segment; 8. Heat
release segment; 9. Ascending tube; 10. Downcomer; 11. Acid-dew
resistant segment; and 12. Temperature sensor.
DETAILED DESCRIPTION OF THE EMBODIMENTS
[0029] For further illustrating the invention, experiments
detailing an air preheater and a method for preventing corrosion
and blockage of the same after selective catalytic reduction (SCR)
denitration are described below. It should be noted that the
following examples are intended to describe and not to limit the
invention.
[0030] As shown in FIG. 2, an air preheater comprises a flue 1 and
an air channel 2 disposed on the downstream of a denitration
device, a first segment for producing secondary air 3, a second
segment for producing primary air 4, a third segment for
anti-condensation of ammonium bisulfate 5, and a fourth segment for
curing of ammonium bisulfate 6 disposed in that order along a gas
flow direction. The second segment for producing primary air 4, the
third segment for anti-condensation of ammonium bisulfate 5, and
the fourth segment for curing of ammonium bisulfate 6 each comprise
a phase-change heat exchanger. The phase-change heat exchanger
comprises a heat absorption segment 7 disposed in the flue 1, a
heat release segment 8 disposed in the air channel 2, an ascending
tube 9 and a downcomer 10 which are configured to connect the heat
absorption segment 7 and the heat release segment 8. The heat
release segment 8 is higher than the corresponding heat absorption
segment 7, and the phase-change heat exchanger is provided with a
cycling medium. A wall surface temperature of the third segment for
anti-condensation of ammonium bisulfate 5 is higher than a dew
temperature of the ammonium bisulfate. A wall surface temperature
of the fourth segment for curing of ammonium bisulfate 6 is lower
than a solidification point temperature of the ammonium
bisulfate.
[0031] High-temperature flue gas (between 350 and 440.degree. C.)
in the flue 1 enters an upstream of the assembled air preheater,
and passes the first segment for producing secondary air 3, the
heat-absorbing segment 7 of the second segment for producing
primary air 4, the heat-absorbing segment 7 of the third segment
for anti-condensation of ammonium bisulfate 5, and the
heat-absorbing segment 7 of the fourth segment for curing of
ammonium bisulfate 6. The high-temperature flue gas releases heat
when passing the air preheater and heats the cycling medium in the
heat absorption segment 7 of all phase-change heat exchangers. The
cycling medium in all phase-change heat exchangers absorbs heat
released by the flue gas and generates a lift force because of a
density difference, thus the cycling medium in the heat absorption
segment 7 enters the heat release segment 8 via the ascending tube
9, and after releasing heat to the air, the cycling medium in the
heat release segment 8 is back to the heat absorption segment 7 via
the downcomer 10, hereby a self-cycle is realized and no external
power is needed. Because the pipe wall temperature of the third
segment for anti-condensation of ammonium bisulfate 5 and the pipe
wall temperature of an upstream of the third segment for
anti-condensation of ammonium bisulfate 5 are higher than the dew
temperature of the ammonium bisulfate (between 0 and 200.degree.
C.), and the pipe wall temperature of the fourth segment for curing
of ammonium bisulfate 6 and the pipe wall temperature of a
downstream of the fourth segment for curing of ammonium bisulfate 6
are lower than the solidification point temperature (147.degree.
C.) of the ammonium bisulfate, the reaction of escaped ammonia and
sulfur trioxide only generates gaseous and solid ammonium bisulfate
in the air preheater, no liquid ammonium bisulfate is produced, and
the air preheater is effectively prevented from blockage and
corrosion caused by liquid ammonium bisulfate. Therefore, a flue
gas temperature is decreased; an air leakage is reduced; a service
life of the air preheater is prolonged; a heat transfer efficiency
of a boiler is improved; and finally a stable and safe operation of
a machine set is ensured. Preferably, cycling media in the second
segment for producing primary air 4, the third segment for
anti-condensation of ammonium bisulfate 5, the fourth segment for
curing of ammonium bisulfate 6, the acid-dew resistant segment 11
is selected from water, Freon, or heat transfer oil. In actual
operation, a suitable cycling medium solution is determined
according to different temperatures.
[0032] Preferably, when the pipe wall temperature of the downstream
of the fourth segment for curing of ammonium bisulfate 6 is too
low, an acid dew corrosion happens, thus along the flue gas flow
direction, the downstream of the fourth segment for curing of
ammonium bisulfate 6 is provided with an acid-dew resistant segment
11. The acid-dew resistant segment 11 comprises the phase-change
heat exchanger, comprising the heat absorption segment 7, the heat
release segment 8, the ascending tube 9 and the downcomer 10. The
wall surface temperature of the acid-dew resistant segment 11 is
higher than an acid dew point temperature (between 0 and
100.degree. C.), thereby effectively preventing the acid dew
corrosion, decreasing an energy consumption of the boiler, and
saving energy and reducing emission to the largest extent.
[0033] In addition, the air is divided into two paths after heated
by the second segment for producing primary air 4, as shown in
FIGS. 2-3, the first path is used as a primary air for a
pulverizing system, and the second path is heated by the first
segment for producing secondary air 3 and is used as secondary air
of the boiler, which means the primary air is not heated by the
first segment for producing secondary air 3. Heat saved by the
primary air can be used to heat materials in the third segment for
anti-condensation of ammonium bisulfate 5, the fourth segment for
curing of ammonium bisulfate 6, the acid-dew resistant segment 11,
or a combination thereof.
[0034] Prior to starting the assembled air preheater, the air in
the acid-dew resistant segment 11, the fourth segment for curing of
ammonium bisulfate 6, the third segment for anti-condensation of
ammonium bisulfate 5, and the second segment for producing primary
air 4 is exhausted, so that no non-condensable gas exists in
cycling pipes of the phase-change heat exchangers, and the blockage
caused by water or gas is avoided. When the boiler is operated at a
rated load, the flue gas temperature after denitration is between
350 and 440.degree. C. and is gradually stable, and water volumes
in the cycling pipes of the acid-dew resistant segment 11, the
fourth segment for curing of ammonium bisulfate 6, the third
segment for anti-condensation of ammonium bisulfate 5, and the
second segment for producing primary air 4 are adjusted according
to the flue gas temperature after denitration, a temperature of the
primary air, and a temperature of the secondary air;
correspondingly, steam pressures in the phase-change heat
exchangers are adjusted and determined, then saturation
temperatures are determined, and wall surface temperatures of the
segments are determined. Preferably, the heat absorption segment 7
in the second segment for producing primary air 4, the heat
absorption segment 7 in the third segment for anti-condensation of
ammonium bisulfate 5, the heat absorption segment 7 in the fourth
segment for curing of ammonium bisulfate 6, the heat absorption
segment 7 in the acid-dew resistant segment 11 are provided with a
temperature sensor 12 adapted to detect the wall surface
temperatures of the segments.
[0035] Preferably, in the example, as shown in FIG. 2, the first
segment for producing secondary air 3 is a high temperature segment
of a regenerative air preheater. Optionally, the first segment for
producing secondary air 3 can also be a phase-change heat
exchanger, as shown in FIG. 3, the first segment for producing
secondary air 3 also comprises the heat absorption segment 7, the
heat release segment 8, the ascending tube 9, and the downcomer 10,
and the cycling medium in the first segment for producing secondary
air 3 is water, Freon, or heat transfer oil.
[0036] A method for preventing the air preheater from corrosion and
blockage after an SCR denitration is also provided in the
invention, and the method comprises: [0037] a) introducing flue gas
from the flue 1 to an upstream of the air preheater, and allowing
the flue gas to pass the first segment for producing secondary air
3, the second segment for producing primary air 4, the third
segment for anti-condensation of ammonium bisulfate 5, and the
fourth segment for curing of ammonium bisulfate 6 in that order;
introducing air from the air channel to a downstream of the air
preheater, and allowing the air to pass the fourth segment for
curing of ammonium bisulfate 6, the third segment for
anti-condensation of ammonium bisulfate 5, the second segment for
producing primary air 4, and the first segment for producing
secondary air 3; [0038] b) adjusting the wall surface temperature
of the third segment for anti-condensation of ammonium bisulfate 5
to be higher than a dew temperature of the ammonium bisulfate, and
adjusting the wall surface temperature of the fourth segment for
curing of ammonium bisulfate 6 to be lower than a solidification
point temperature of the ammonium bisulfate; [0039] c) gasifying
the ammonium bisulfate in the flue 1 prior to and in the third
segment for anti-condensation of ammonium bisulfate and an upstream
of the third segment for anti-condensation of ammonium bisulfate;
curing the ammonium bisulfate in and after the fourth segment for
curing of ammonium bisulfate 6, the ammonium bisulfate being cured
on a wall surface of a pipe of the fourth segment and a wall
surface of a downstream pipe of the fourth segment; and [0040] d)
eliminating solid ammonium bisulfate on the wall surface of the
pipe of the fourth segment and on the wall surface of the
downstream pipe of the fourth segment 6.
[0041] Advantages of the air preheater and the method are
summarized as follows: [0042] 1. Using the method, the wall surface
temperature of the third segment and the fourth segment can be
accurately controlled, so that the ammonium bisulfate is cured on
the wall surface of a heat exchanger, meanwhile avoiding
condensation of the ammonium bisulfate on the wall surface of the
heat exchanger; then the solid ammonium bisulfate is eliminated by
the blowing equipment. As a result, the air preheater is
effectively prevented from blockage and corrosion, thus ensuring
the safe, reliable, and stable operation of the boiler, and the
corrosion caused by the ammonium bisulfate in a medium temperature
segment and a low temperature segment of the regenerative air
preheater is completely prevented. [0043] 2. The acid-dew resistant
segment 11 is provided, and the wall surface temperature of the
acid-dew resistant segment 11 is controlled so as to prevent the
acid dew corrosion, decrease the energy consumption of the boiler,
and save energy and reduce emission to the largest extent. [0044]
3. The phase-change heat exchanger is employed, and the flue gas
temperature is decreased to a lower level than the flue gas
temperature of the regenerative air preheater. [0045] 4. The air is
directly divided into two paths following the second segment for
producing primary air 4, and the primary air does not enter the
first segment for producing secondary air 3, thus the heat is
saved. [0046] 5. The air leakage problem of the regenerative air
preheater in the prior art is solved by using the phase-change heat
exchanger.
[0047] Therefore, the phase-change heat exchanger compensates for
the shortcomings in the prior art, featuring high industrial
value.
[0048] Unless otherwise indicated, the numerical ranges involved in
the invention include the end values. While particular embodiments
of the invention have been shown and described, it will be obvious
to those skilled in the art that changes and modifications may be
made without departing from the invention in its broader aspects,
and therefore, the aim in the appended claims is to cover all such
changes and modifications as fall within the true spirit and scope
of the invention.
* * * * *