Note: Descriptions are shown in the official language in which they were submitted.
i Q
APPARATUS AND METHOD FOR DELIVERY OF
COMBUSTION AIR IN MULTIPLE ZONES
Field of the Invention
The present invention relates to feeding of
combustion air to a combustion device. In particular, the
invention relates to air registers which surround a fuel
nozzle and which deliver combustion air to be mixed with
the fuel fed to the combustion device by the fuel nozzle.
In this way a fuel-air mix is provided to support
combustion.
- 2 -
Background of the Invelltion
In the burning of fuels using burners fed by
air registers, it has become known in the industry to
divide the combustion air into an inner ignition zone
and an outer, supplemental zone which concentrically
surrounds the inner ignition zone. The purpose of
the divided zones is -to separate the high intensity
mixing necessary for good ignition stability at the
center of the fire from the smoother air flow at the
perimeter, where it is important to avoid the nitrous
oxide production of a very hot, intense flame.
The present invention is directed to enhancing
and improving multiple zone combustion by providing
an air register apparatus, method, and overall
arrangement in which enhanced control over the
characteristics of the combustion in the inner and
outer zones may be achieved.
The present invention extends and improves upon
certain enhanced flow characteristics, flow
measurability, and flow control as provided in U.S.
Patent No. 4,504,216 to Donald K. Hagar et al. In
that patent, an air register is disclosed utilizing
an inwardly spiralling scroll passageway which
organizes the air flow, which air flow may be
measured and controlled by a simple ups-tream valve
remote from the hostile environment of the furnace.
Reference is made to the aforesaid U.S. Patent No.
4,504,216 for a more complete discussion of this
subject matter.
4~
- 3 - ~3~
As further background, reference is also made
to Chapter 9 of "Steam/Its Generation and Use" by the
Babcock and Wilcox Company, 1978 ed., which discusses
and illustrates the use of air registers for
supplying combustion air to a combustion device.
Again, reference is made to this Babcock and Wilcox
publication for a more complete discussion of the
background, context and environment of the present
invention.
Summary of the Invention
It is an object of the present invention to
provide an improved apparatus, method, and arrange-
ment for delivery of combustion air to a combustion
device in multiple zones.
It is another object of the present invention
to provide an apparatus, method, and arrangement for
controllably delivering combustion air to an inner
ignition zone in the combustion device and for
separately, controllably delivering combustion air to
an outer supplemental zone.
It is another object of the present invention
to provide an apparatus, method, and arrangement
which provides a first, discrete stream of air
having measurable and controllable characteristics
which govern combustion
_ 4 - ~ 3
characteristics in an inner ignition zone and delivering a
second, separate, discrete stream of air having measurable
and controllable characteristics which govern combustion
characteristics in an outer, supplemental zone.
It is yet another object of the invention to provide
an improved air register apparatus, method, and
arrangement which delivers a larger amount of air flow and
velocity at an inner ignition zone than the proportionate
share of the register outlet area for that ignition zone,
thereby concentrating combustion air where it is needed
for ignition stability.
It is yet another object of the present invention to
provide an air register apparatus, method, and arrangement
in which combustion in the supplemental zone may be
modulated based on an accurate measurement of air flow
through a portion of the air register, which measurement
of air flow represents the entire air flow through that
particular register portion, to thus enhance stability of
the flame procluced by the air register when used with an
associated fuel nozzle.
It is another object of the present invention to
provide an air register apparatus, method and arrangement
in which the sum of: 1) air flow through the inner
ignition zone register portion and 2) air f~ow through the
supplemental reyister portion can be adjusted
proportionally to fuel flow for a specific burner among a
set burners to optimize the combustion product by that
~ t S , , } ;;~J
particular burner irrespective of the condition of other
burners.
It is yet another object of the present invention to
provide an air register apparatus and arrangement in which
vanes in the air register are capable of producing nearl~
the same tangential air flow velocity at the small, inner
ignition zone as at the large, outer supplemental zone.
These and other objects, purposes and advantages of
the present invention will be apparent from the detailed
description which follows and ~rom the drawing.
The objects of the invention are achieved by an air
register for feeding combustion air to a combustion device
having a register body with two register portions, one
register portion being an inner zone register portion for
supplying combus~ion air to the ignition zone of the
combustion device, the other register portion being a
supplemental zone register portion for supplying
combustion air to the supplemental zone of the combustion
device.
The ignition zone reyister portion has an ignition
zone register inlet for combustion air, an ignition zone
register outlet for combustion air, an ignition zone
register scroll section, and an ignition zone register air
valve. The ignition zone register air valve is disposed
adjacent the ignition zone register inlet and upstream of
the ignition 7.0ne register scroll section. The ignition
zone register scroll section and ignition zone register
air valve are in communication with each other, such that
the ignition zone register air valve controls the flow of
combustion air through the ignition zone register scroll
section. The ignition zone register scroll section has an
ignition zone register scroll passageway which spirals
S inwardly in the direction of combustion air flow
therethrough.
The supplemental zone register portion has a
supplemental zone register inlet for combustion air, a
supplemental zone register outlet for combustion air, a
supplemental zone register scroll section, and a
supplemental zone register air valve. The supplemental
zone register air valve is disposed adjacent the
supplemental zone register inlet and upstream of the
supplemental zone register scroll section. The
supplemental zone register scroll section and the
supplemental zone register air valve are in communication
with each other such that the supplemental zone register
air valve controls the flow of combustion air through the
supplemental zone register scroll section. The
supplemental zone register scroll section has a
supplemental zone register scroll passageway which spirals
inwardly in the direction of combustion air flow
therethrough.
The ignition zone register por-tion and the
supplemental zone register portion are so coupled to each
other and so disposed with respect to each other that the
ignition zone register portion controllably delivers
combustion air to the air ignition zone, and the
- 7 - 1 ~
supplemental zone register portion controllably delivers
combustion to the outer supplemental zone. In this way
combustion in the inner ignition zone and combustion in
the outer supplemental zone may be separately controlled.
In the use of the present invention, a first air
stream is created which has measurable characteristics
representing the characteristics of a first portion of
combustion air fed to the combustion device, which first
combustion air portion supports and governs combustion in
the ignition zone. A second air stream is created having
measurable characteristics representing characteristics of
a second portion of combustion air fed to the combustion
device, which second combustion air portion supports and
governs combustion in the supplemental zone. That is,
each discrete stream of air through a different portion of
the register has its own measurable characteristics which
govern combustion characteristics in its associated zone
within the combustion device. This in turn facilitates
separate control of the characteristics of combustion in
the two zones by adjusting a simple air valve associated
with the particular air stream to be adjusted, which air
valve is located away from the hostile environment of the
furnace upstream of an inwardly spiralling scroll
passageway.
According to the present invention, one or both of
the register portions include a set of spirally twisting
vanes in the scroll section. The vanes are mutually so
disposed as to represent a truncated cone having a small
~ 3 ~
radius end and a large radius end. The vanes each have an
angle of incidence relative to incoming air flow which
varies with the radius of the truncated cone such that the
vanes at the small radius end of the truncated cone direct
flowing air to a higher angular velocity than do the vanes
at the large radius end of the truncated cone. The large
radius end of the truncated cone is closer to the
combustion device than is the small radius end. Vanes of
this type are advantageous in both of the register
portions, but they are especially advantageous in the
ignition zone register portion, where they effect an
acceleration of the air flow in the ignition zone.
Brief Description of the Drawing
Fig. 1 is a side elevation of a register according to
the present invention in which register a fuel nozzle is
installed, the overall combination of the register and
fuel nozzle providing a burner for supplying a fuel-air
mix to the furnace or other combustion device.
Fig. 2 is an exploded perspective view of the
register of the present invention, showing two major
portions of the register separated from each other.
Fig. 3A is an end elevation viewed from the furnace
side of the ignition zone register portion of the register
of the present invention.
Fig. 3B is an end elevation viewed from the furnace
side of the supplemental zone register portion of the
9 ~ 3 ~
register of the present invention. Fig. 3B also shows the
fuel nozzle in place in the center of the register.
Fig. 4 is a plan view of the valve actuating
mechanism for operating the air valves of the register of
the present invention.
Fig. 5 is a perspective view showing an ignition zone
register vane assembly used in the register of the present
invention, Fig. 5A shows the truncated conical shape of
the assembly of Fig. 5, and Figs. 5B and 5C are
fragmentary, detail, sectional views showing certain parts
of the vanes of the vane assembly of Fig. 5.
Fig. 6 is a perspective view showing a supplemental
zone register assembly used in the register of the present
invention, Fig. 6A shows the truncated conical shape of
the assembly of Fig. 6, and Figs. 6B and 6C are
fragmentary, detail, sectional views showing certain parts
of the vanes of the vane assembly of Fig. 6.
Fig. 7 is a schematic diagram showing a plurality of
registers according to the present invention, along with
their associated fuel nozzles (to provide burners) in a
windbox.
Detailed Description of the Preferred Embodiment
In the following description and in the drawing, like
reference numerals, used among the various figures of the
drawing refer to like elements or features.
- 10 ~
Referring to Figs. 1 and 2, reference numeral 10
generally refers to the air register of the present
invention. Air register 10 feeds combustion air to a
combustion device 12 (Fig. 7~ such as a furnace which
fires a boiler to produce steam for generating electricity
in a power plant. Air register 10 feeds the combustion
air in such a manner as to provide an inner ignition zone
16 (Fig. 1), where fuel is first ignited, and an outer,
supplemental zone 18 (Fig. 1), where the main combustion
in the combustion device or furnace 12 takes place.
Air register 10 includes a register body 20 having
two register portions, namely, an ignition zone register
portion 22 for supplying combustion air to the ignition
zone 16 of the combustion device and a supplemental zone
register portion 24 for supplying combustion air to the
outer, supplemental zone 18 of the combustion device 12.
The exploded perspective view of Fig. 2 illustrates a
substantial part of the ignition zone register portion 22
at the upper left and the supplemental zone register
portion 24 at the lower right.
Ignition zone register portion 22 has an ignition
zone register inlet 30 for combustion air and an ignition
zone register outlet 31 for combustion air. As will be
seen in Figs. 1 and 2/ ignition zone register outlet 31 is
disposed generally at the furnace side of supplemental
zone register portion 24. That is, supplemental zone
register portion 24 has extending concentrically axially
through the center thereof an ignition zone register
, r~j ~
outlet barrel 32 which receives the output of ignition
zone register portion 22 so as to discharge the combustion
air of ignition zone register portion 22 into the furnace
at the furnace side of supplemental zone register portion
24. The ignition zone register outlet barrel 32 receives
combustion air from ignition zone register portion 22 via
intermediate discharge opening 33 in the part of ignition
zone register portion 22 included in the subassembly shown
at the upper left of Fig. 2.
Ignition zone register portion 22 includes an
ignition zone register scroll section 34 for directing air
from ignition zone register inlet 30 to intermediate
discharge opening 33, through ignition zone register
outlet barrel 32 and thence to ignition zone register
outlet 31. The flow of air through ignition zone register
inlet 30 is controlled by a simple ignition zone register
air valve 36 in the form of a butterfly valve having a
simple pivotal valve member 37 which regulates the amount
of air which may flow into scroll section 34 through inlet
30. Ignition zone register air valve 36 is disposed
adjacent ignition zone register inlet 30 and upstream of
(in terms of the direction of air flow) the ignition zone
register scroll section 34.
The ignition zone register scroll section 34 and
ignition zone register air valve 36 are in communication
with each other such that the ignition zone register air
valve 36 controls the flow of combustion air through the
ignition zone register scroll section 34. The ignition
~ 3 ~
- 12 -
zone register scroll section 34 has an ignition zone
register scroll passageway 38 (Fig. 3A) which spirals
inwardly in the direction of combustion air flow
therethrough. This flow of combustion air through scroll
passage 38 is represented by the arrow 39 shown in phantom
lines in Fig. 3A. Ignition zone register scroll
passageway 38 has an ever diminishing cross sectional area
in the direction of air flow 39 in a manner analogous to
the ever diminishing cross sectional area of the
passageway in a Nautilus shell in a direction of advance
toward the interior of the shell.
The function of the scroll passageway of diminishing
cross-section is to maintain a constant air flow velocity
throughout the register portion. Air flowing through a
register tends to lose velocity through friction loss and
back-pressure. The ever-diminishing cross section of the
inwardly spirally scroll section, however, offsets this
tendency through a nozzle-like tendency to accelerate the
flow of air through the scroll passageway. Once the air
in the register portion reaches the first vane in the vane
assembly disposed in the scroll section (which vane
assembly will be described later,) the air flow velocity
will then remain constant through the register. This, in
turn, minimizes expansion and contraction of the flowing
air, which in turn minimizes pressure drop and energy loss
through the register. This also maintains the same inlet
conditions for each succeeding vane in the vane assembly
~ 13 - ~ 3 ~
to achieve uniformity in the flow, including uniform flow
around the entire periphery of the outlet opening.
Supplemental zone register portion 24 has a
supplemental zone register inlet 40 for combustion air and
a supplemental zone register outlet 41 for combustion air.
Supplemental zone register outlet 41 is concentrically
disposed coaxially with, but radially outside of, ignition
zone register outlet 31. Both ignition zone register
outlet 31 and supplemental zone register outlet 41 take
the form of annular openings, supplemental zone register
outlet 41 representing a coaxial annular band outside of
and immediately contiguous with the annual band
representing the ignition zone register outlet 31.
Supplemental zone register outlet 41 feeds combustion air
into the combustion device 12 for supporting and
controlling combustion in the outer, supplemental zone 18,
whereas ignition zone register zone outlet 31 provides
combustion air for supporting and controlling combustion
in the inner, ignition zone ~6 of combustion device 12.
Supplemental zone register portion 24 includes a
supplemental zone register scroll section 44 (Fig. 3B~
into which combustion air flows under the contxol of a
supplemental zone register air valve 46 (Figs. 2 and 4.)
Supplemental zone register air valve 46 is disposed
adjacent supplemental zone register inlet 40 and upstream
of (in the direction of combustion air flow) the supple-
mental zone register scroll section 44.
- 14 _ 131~0
Supplemental zone register scroll section 44 and
supplemental zone register air valve 46 are in communi-
cation with each such that the supplemental zone register
air valve 46 controls the flow of combustion air through
supplemental zone register scroll section 44. Supple-
mental zone register air valve 46 takes the form of a
simple, opposed louver valve having a pair of pivotal
valve members 47a, 47b (Figs. 2 and 4) which swing
arcuately to adjust the amount of air flowing into
supplemental zone register inlet 40 and thence through
supplemental zone register scroll section 44.
Supplemental zone register scroll section 44 has a
supplemental zone register scroll passageway 48 which
spirals inwardly in the direction of combustion air flow
therethrough. Such flow of combustion air through
supplemental zone register scroll passageway 48 is
represented by arrow 49 shown in phantom lines in Fig. 3B.
Supplemental zone register scroll passageway 48 has an
ever diminishing cross section analogous to that the
passageway through a Nautilus shell, as described in more
detail in connection with ignition zone register scroll
passageway 38.
Ignition zone register portion 22 and supplemental
zone register portion 24 are so coupled to each other and
so disposed with respect to each other that ignition zone
register portion 22 controllably and measurably delivers
combustion air in flow path 39 to the inner, ignition zone
16, and the supplemental zone register portion 24
- 15 -
controllably and measurably delivers combustion air in
flow path 49 to the outer, supplemental zone 18. In this
way, combustion in the inner, ignition zone 16 and
combustion in the outer, supplemental zone 18 may be
separately controlled.
Ignition zone register portion 22 has a central axis
50a, and supplemental zone register portion 24 has a
central axis 50b. Each register portion 22, 24 spirals
inwardly about and toward its central axis 50a, 50b. Axis
50a of ignition zone register portion 22 and an axis 50b
of supplemental zone register portion 24 are coextensive
with each other.
As may best be appreciated from Fig. 2, a substantial
part, but preferably not the entirety, of ignition zone
register portion 22 is disposed in axial series with
respect to supplemental zone register portion 24. That
is, a substantial part of ignition zone register portion
22 is disposed axially next to supplemental zone register
portion 24 in contiguous relationship therewith. In the
preferred embodiment shown and described herein, one
element, which is functionally part of ignition zone
register portion 22, is, howe~er, physically part of ~he
subassembly which comprises supp'emental zone register
portion 24 and which is shown at the lower right of Fig.
2. This particular element which is functionally a part
of ignition zone re~ister portion 22 is ignition zone
register outlet barrel 32. When the substantial part of
ignition zone register 22 shown at the upper left of Fig.
~31~
- 16 -
2 is coupled with supplemental zone register portion 24,
intermediate discharge opening 33 will be in registry with
ignition zone outlet barrel 32, such that air flow 39
through ignition zone register scroll section 44 will pass
through intermediate discharge opening 33 and through
ignition zone register outlet barrel 32 to be discharged
into the furnace or other combustion device 12 at ignition
zone register outlet 31 on the furnace side of ignition
zone register outlet barrel 32.
It will thus be apparent that a part other than the
aforesaid substantial part of ignition zone register
portion 22 (the substantial part being represented by the
subassembly shown at the upper left of Fig. 2, the other
part being represented by the ignition zone register
outlet barrel which is part of the subassembly shown in
the lower right of Fig. 2) is disposed radially within the
supplemental zone register portion 24. This other part,
i.e., ignition zone register outlet barrel 32, provides a
conduit through which combustion air for supporting and
controlling combustion in the ignition zone as discharged.
Outlet barrel 32 preferably tapers radially inwardly along
an axial path away from ignition zone register scroll
section 34, i.e., in a direction toward the furnace or
combustion device 12. This helps to further accelerate
and concentrate air flow 39 in the ignition zone register
portion 22 prior to discharge into the comhustion device
12.
- 17 - ~3~
The result is higher air flow velocity with lower
differential pressure between the inlet and outlet, as
compared with known arrangements. In other words, for a
given inlet to outlet differential pressure, the
arrangement of the present invention provides a higher air
flow velocity than known devices. Also, the present
invention permits control and adjustment of tne kinetic
energy at the outlet with a constant inlet-to-outlet
differential pressure, i.e., the kinetic energy at the
outlet may be varied while the inlet-to-outlet
differential pressure remains constant. As already
indicated, a high kinetic energy in the ignition zone is
desirable. With the arrangement of the present invention,
this kinetic energy may be independently varied in
relation to that of the outer, supplemental zone without
changing the inlet-to-outlet differential pressure
Combustion device 12 to which combustion air is fed
by air register 10 receives fuel from a fuel nozzle 52,
which in turn receives fuel from a fuel supply 53 (Figs. 1
and 7). Example of fuels which may be supplied by fuel
supply 53 and injecting into combustion device 12 by fuel
nozzle 52 include: pulverized coal entrained in
pressurized air (known as "primary" air which is different
from "secondary" air, referred to herein as "combustion
air"); oil; and natural gas.
Body 20 of air register 10 includes a mounting tube
54 for mounting fuel nozzle 52 with respect to body 20 so
that ignition zone register outlet barrel 32 coaxially
- 18 -
surrounds fuel nozzle 52 in mounting tube 54 to create an
ignition zone register outlet passage 56 between ignition
zone register outlet barrel 32 and fuel nozzle 52 or, more
precisely, mounting tube 54 in which fuel nozzle 52 is
disposed. Because outlet barrel 32 tapers radially
inwardly toward combustion device 12, outlet passage 56
takes the form of an ever diminishing annular space in a
direction toward combustion device 12. That is, ignition
zone register outlet passage 56 has an ever diminishing
cros~ section in a direction toward the ignition zone
register outlet.
The ignition zone register scroll passageway 38 and
the supplemental zone register scroll passageway 48 are
isolated from communication with each other during the
flow of combustion air from the inlet to the outlet of
each register portion 22, 24. That is, air flow 39 in
ignition zone register portion 22 is isolated from air
flow 49 in supplemental zone register 24. This
facilitates separate and independent control over
combustion at the ignition zone and combustion at the
outer, supplemental zone in combustion device 12. This
independent control is effected in the ignition zone 16 by
ignition zone register air valve 36 and in the
supplemental zone 24 by supplemental zone register air
valve 46.
Also contributing to separate control of the ignition
zone register air flow 39 and supplemental zone register
air flow 49 is a flow measuring instrument 60 in the
- 19 - 1~
ignition zone register scroll section 34 which sends
through line 61 an output signal representative of
characteristics of the air flow 39 in ignition zone
register scroll section 34 and a flow measuring instrument
62 in supplemental zone register scroll section 44 which
sends a signal through line 63 representative of
characteristics of the air flow 49 in supplemental zone
register scroll section 44.
The inwardly spiralling scroll passageway 38 of
ignition zone register portion 22 organizes air flow 39
such that insertion of a measuring instrument into an
appropriate part of ignition zone register scroll
passageway 38 results in a measurement which is
representative of the total air flow through the ignition
lS zone register scroll passageway 38. This is entirely
unlike conventional air registers in which air is admitted
around the circumferenc~ of the air register. The result
in conventional air registers is that no discrete air flow
passageway or air flow path is provided which represents
overall air flow to thereby frustrate any attempt to
measure characteristics of the flow and, based on such
measurements, to control air flow through the air register
and in turn control combustion.
These same desirable characteristics for the ignition
zone register portion 22 hold true as well for the
supplemental zone register portion 24. That is, with the
device of the present invention, measurements
representative of the entire air flow through the
- 20 - ~3~
supplemental zone register portion 24 may be taken in a
very simple manner via instrument 62 as a result of the
organization of flow 49 into a single, inwardly spiralling
path through a passageway 48 of ever diminishing cross
section. The measurements taken with respect to air flow
49 then become the basis for controlling that flow in a
manner such that the conirol is based on an accurate
representation of the entirety of the flow thxough the
supplemental zone register portion 24.
What is more, not only may the flows 39, 49 through
register portions 22, 24 be accurately measured and
controlled, but also these flows may be accurately
measured and controlled separately and independently of
one another. That is, combustion air flow 39 which
supports combustion in the inner ignition zone 16 may be
independently adjusted to provide high intensity mixing in
ignition zone 16 so as to provide good ignition stability
at the center of the flame. By the same token, air flow
49 for supporting combustion in the outer supplemental
zone 18 may be independently adjusted to provide a
smoother air flow around the perimeter to avoid the
nitrous oxide production typical of a very hot, intense
flame.
The arrangement according to the present invention
provides for minimum shear between the ignition zone and
supplemental zone at full load firing, where nitrous
oxides from high combustion intensity have been the
greatest problem in known devices. The shear between
- 21 ~ 6 ~ ~
zones results from the different flow characteristics of
the two zones in known devices. The flow in the ignition
zone is rapid, intense and swirling, while the flow in the
supplemental zone is less intense, slower, has a
relatively low degree of swirl and is generally axial in
known devices. The interface between these two types of
flows in known arrangements creates the aforementioned
shear, which in turn creates an undesirably high
combustion intensity at full load. The arrangement of the
present invention produces minimum shear between the
ignition zone and supplemental zone to minimize
undesirable combustion intensity and nitrous oxide
production at full locad. While the arrangement of the
present invention causes a higher flow velocity in the
ignition zone than in the supplemental zone, as do prior
art arrangements, the present invention provides for the
combustion air to emerge into the respective zones 16, 18
in parallel, i.e., at helixes that nearly match one
another, to reduce shear between zones 16, 18.
Zones 16, 18 include innermost and outermost regions.
That is, ignition zone 16 includes an innermost region 116
and an outermost region 216. Similarly, supplemental zone
18 includes an innermost region 118 and an outermost
region 218.
Disposed within ignition zone register scroll section
34 is an ignition zone register vane assembly 70 (Fig. 5)
which includes a set of spirally twisting, ignition zone
register vanes 71. Toward the furnace side of ignition
1 3 ~
- 22 -
zone register portion 22, vanes 71 terminate in and are
mounted in a large radius mounting ring 74 representing a
large radius end 75 of vane assembly 70. At an end most
remote from the furnace, vanes 71 terminate in and are
mounted in a small radius mounting ring 76 representing a
small radius end 77 of vane assembly 70. ~anes 71 and
rings 74, 76 are mutually so disposed as to represent a
truncated cone 78 (Fig. 5A,) which truncated cone has an
axis 79 which is coaxial and coextensive with central axis
50a of the ignition zone register portion 22.
Disposed within the supplemental zone register scroll
section 44, is a supplemental zone register vane assembly
(Fig. 6.) Supplemental zone register assem~ly 80
includes a set of spirally twisting supplemental zone
register vanes 81 which terminate at and are mounted in a
large radius mounting ring 84 disposed on the furnace side
of supplemental zone register portion 24. Mounting ring
84 represents a large radius end 85 of supplemental zone
register vane assembly 80. Opposite large radius mounting
ring 84 is a small radius mounting ring 86 remote from the
furnace side of supplemental zone register portion 24.
Small radius mounting ring 86 represents a small radius
end of the supplemental zone register vane assembly 80.
Supplemental zone register vanes 81 and mounting rings 84,
86 are mutually so disposed as to represent a truncated
cone 88 (Fig. SA) which truncated cone 88 has an axis 89
which is coaxial with and coextensive with central axis
50b of supplemental zone register portion 24.
- 23 -
It is to be understood that many of the fundamental
advantages of the present invention are independent of the
use of spirally twisting vanes 71, 81. That is, many of
the advantages of the present invention would still remain
even if vanes such as those disclosed in U.S. Patent No.
4,504,216 were used in the present context, which vanes
will be referred to as axial vanes. Use of axial vanes in
lieu of spirally twisting vanes would reduce initial
capital expenditures for users of registers according to
the present invention.
Nevertheless, the most desireable arranement,
irrespective of initial capital cost, is the use of
spirally twisting vanes in both the ignition zone register
portion 22 and supplemental zone register portion 24.
The next most desireable arrangement, and a good
compromise between optimum performance and initial capital
cost, is the use of spirally twisting vanes 71 for the
ignition zone register portion 22 and axial vanes for the
supplemental register portion 24.
In use, spirally twisting vane assemblies 70, 80 help
direct air flows 39, 49 in optimum, swirling paths as
these air flows approach the outlets 31, 41 of their
respective register portions 22, 24. In particular, the
ignition zone register vanes 71 have angles of incidence
97a, 97b (Figs. 5B and 5C) relative to incoming air flow
39 which varies with the radius of the truncated cone 78,
such that the ignition zone register vanes 71 at the small
radius end 77 of the truncated cone 78 are at an angle of
- 24 - ~3~
incidence ~7a (Fig. 5B) to direct flowing air to a higher
angular velocity than do the same ignition zone register
vanes 71 when they are disposed at the large radius end 75
of the truncated cone, which vanes 71 at the large radius
end are disposed at the angle of incidence 97b (Fig. 5C).
Similarly, supplemental zone r~gister vanes 81 have
angles of incidence 98a, 98b (Figs. 6B and 6C) relative to
incoming air flow 49 which vary with the radius of the
truncated cone 88 such that the supplemental zone register
vanes 81 at the small radius end 87 of truncated cone 88
are at an angle of incidence 98a to direct flowing air 49
to a higher anguiar velocity than do the same supplemental
zone register vanes 81 at the large radius end 85 of the
truncated cone 88, which vanes 81 at the large radius end
are disposed at an angle of incidence 98b (Fig. 6C)
relative to the air flow 49. Preferably, angles of
incidence 98a and 97b are the same to minimize turbulence
at the boundary between ignition zone register outlet 31
and supplemental zone register outlet 41.
With this arrangement of vanes, nearly the same
tangential air flow velocity is produced in the radially
innermost region 116 ignition zone 16 as in the radially
outermost region 218 of supplemental zone 18 when the
ignition zone air valve and supplemental zone air valve
are both fully open. This, in turn, results in an
improved fuel-air mix at the core of the fire 99 ~Fig. 7)
produced by each combined air register and fuel nozzle
(i.~., by each burner.)
-25- ~31~
As a result of centripetal acceleration of air flow,
to which the spirally twisting vanes make a sub-stantial
contribution, air flow velocity is higher at the outermost
region 216 of the ignition zone 16 than at the innermost
region 118 of the supplemental zone 18. Air flow velocity
diminishes in the ignition zone from the inside out, i.e.,
from the innermost region 116 to the outermost region 216,
when spirally twisting vanes are used. The result is
that, as already indicated, the tangential velocity of air
10 flow is approximately the same at the innermost region 116
of the ignition zone 16 as at the outermost region 218 of
the supplemental zone 18.
The significance of this is that more combustion
occurs toward inner part of the fire 99 than would
15 otherwise be possible, i.e., less of the fuel has to
migrate to the outside of fire to mix with air for
ignition. The effect is a tighter, more contained fire 99
with improved combustion characteristics, particularly in
terms of lower production of oxides of nitrogen.
The high centripetal acceleration produced in the
ignition zone 16 when spirally twisting vanes are used in
the ignition zone register portion 22 results in czpture
of the fuel by the accelerating air in that zone. The
result is that the mixing energy at the center of the
25 fire, i.e., at the innermost region 116 of ignition zone
16 (where the mixing energy is normally low in
conventional burners) is approximately the same as at the
outside of the fire, i.e., at the outermost region 218 of
- 26 -
the supplemental zone 18 (where the mixing energy is
normally relatively high in conventional burners). That
is, and as already indicated, in a burner using a register
according to the present invention, the fuel does not have
to travel to the outside of the fire to mix with
sufficient air to ignite.
When fuel must migrate to the outside of the fire to
ignite, the advantages of staged combustion, i.e., the
advantages of combustion in multiple zones, is lost. The
present invention takes full advantage of staged
combustion by supplying high velocity air for mixing with
fuel at the innermost region 11~ of ignition zone 16 to
approximately the same extent at any given point in that
region as at the outermost region 218 of the supplemental
zone 18.
By intensifying the mixing of fuel and air at the
center of the fire, the present invention provides
conditions by which the fuel is ignited with a substantial
deficiency of oxygen. Thus, in turn, suppresses the peak
flame temperature in the supplemental zone and therefore
reduces the ability of the burner to form oxides of
nitrogen.
Others have sought to achieve similar results by
withholding air at the burner and then adding air later at
a different place. With the present invention, however,
this is unnecessary. With the present invention, the fuel
is held in tighter in the supplemental zone, and
particularly the outermost region 218 thereof, than in
- 27 - ~3~
conventional arrangements. This results in a longer
elapsed time before final combustion, which in turn makes
for a burner with low nitrous oxide production.
The mechanism for operating air valves 36, 46 will
now be described. An overall valve actuating mechanism
for air valves 36, 46 i5 designated generally by reference
numeral 100 and illustrated in Fig. 4. Mechanism 100
includes an ignition zone register actuating portion
generally designated by reference numeral 102 and a
supplemental zone register actuating portion generally
designated by reference numeral 104.
Ignition zone register actuating portion 102 includes
a hollow rotatable shaft 102 to which is affixed an
actuation arm 122. Movement of actuator arm 122 either
via an automatic control system or through a human
operator in response to measured conditions (such as
provided by flow measuring instrument 60) results in
rotation of shaft 120 which is suitably journaled in
register body 20. Rotation of shaft 120, in turn, results
20 in swinging of crank arm 124 to move connecting rod 126.
This, in turn, causes valve member 37 of ignition zone
register air valve 36 to pivot about its journal 128 to
adjust the opening of ignition zone register air valve 36.
Supplemental zone register actuating portion 104
includes a rotatable shaft 140 (Fig. 4) which is journaled
within hollow rotatable shaft 120 and concentric
therewith. Actuation arm 142 is affixed to shaft 140 so
that movement of actuation arm 142 in response to a
~1 3 ~
- 28 -
condition such as measured by instrument 62 will result in
rotation of shaft 140 to swing crank arms 144a, 144b. The
swinging of crank arm 144a results in movement of
connecting rod 146 to in turn swing valve member 47a about
its journal 148a. Simultaneously, swinging of crank arm
144b results in movement of connecting arm 146b to swing
valve member 47b about its journal 14~b. This swinging
movement of valve members 47a, 47b adjusts the opening of
supplemental zone register air valve 46 to control the air
flow 49 through supplemental zone register portion 24 and
specifically through the supplemental zone register scroll
passageway 38 thereof.
As is customary, and according to one embodiment of
the invention, more than one air register 10 according to
the present invention will fire a single furnace 14 or
other combustion device 14, and this is illustrated
schematically in Fig. 7. As shown there, multiple
registers according to the present invention, which
registers are designated lOa, lOb, lOc and lOd are
disposed in a single windbox 150. Windbox 150 acts as a
plenum chamber to supply air to all of the air registers
lOa, lOb, lOc, lOd. The registers have ignition zone
register portions 22a, 22b, 22c, 22d and supplemental zone
register portions 24a, 24b, 24c, 24d corresponding to
those previously described.
Windbox 150 receives a stream of air 151 produced by
a forced draft fan 152 and regulated by a regulating
damper 154 operating by a control 156. While, according
- 29 -
to this one embodiment of thP invention, multiple
registers are used in a single windbox, particularly where
the invention is to be used in conventional power plants
for generating electricity with fossil fuels, other
embodiments of the invention may involve other contexts
which do not include windboxes or multiple registers in a
windbox.
By the arrangement of the present invention, air flow
is improved by using an ignition zone register portion in
addition to the supplemental zone register portion 24.
As indicated, the ignition zone register portion 22 feeds
a tapered outlet barrel 32 and it produces a higher
velocity output of combustion air than would otherwise be
available. Specifically, in a prototype, 25~ of the total
air flow through the overall register 20 was produced
through 20% of the overall outlet area without any
increase in pressure drop across the register. While
existing burners achieve higher velocity by using a larger
than proportionate share of area at the exit, the present
invention concentrates air where it is needed in the inner
ignition zone for ignition stability.
Whereas existing schemes also control the amount of
combustion air by regulating the flow of air produced by
the forced draft fan 152 which feeds the windbox, the
present invention entails regulating the windbox-to-
furnace differential pressure not only by the forced draft
fan but also by controlling the air flow by modulating the
supplemental zone of the active registers. Utilizing this
_ 30 ~
scheme, the present invention maintains a constant
ignition zone flow volume and kinetic energy. This
enhances the stability of the flame at low firing range
and creates an opportunity for elimination of the use of
an additional fuel ~such as the use of oil or gas in a
combustion device for burning pulverized coal) to
stabilize the flame, which additional fuel is an expensive
necessity with present register designs.
In use, the present invention supplies combustion air
to a combustion device 12 by feeding air from a common
source or common supply, which in the particular
embodiment shown and described involves windbox 150 with
its forced draft fan 152. At each air register 10, the
air fed from the common supply is divided into at least
two discrete flow paths 39, 49 to produce at least two
flows, each of which is susceptible of accurate flow
measurement, one flow being measured by instrument 60, the
other by instrument 62. These flows are indeed actually
measured, a balance between the flows is selected, and the
20 flows are regulated to maintain the selected balance.
Flows are then discharged into the combustion device 12
such that one discharged flow, i.e., that of ignition zone
16, is concentrically surrounded by the other flow, i.e.,
that of supplemental zone 18.
According to the present invention, the two flows are
handled and directed such that one of the flows, i.e.,
flow 39 through the ignition zone register portion 22,
produces a predictably higher kinetic energy of combustion
- 31 - ~3,~
air in the combustion device 12 at the inner ignition zone
16 than does the other flow into its associated zone,
i.e., flow 49 into the outer supplemental zone 18, when
the flows are discharged into the combustion device.
Thus, the flow 39, which produces the predictably higher
kinetic energy of combustion air in the ignition zone 16
of the combustion device, is the flow which is
concentrically surrounded by the other flow, i.e., the
flow 49, when the flows have been discharged into the
combustion device.
In operation, the use of the air register according
to the present invention entails directing a first
discrete stream of air, i.e., that of flow path 39,
through inwardly spiraling ignition zone register scroll
passageway 38, such that the air flow or air stream 39 has
measurable characteristics which govern combustion
characteristics in ignition zone 16. This air stream 39
is discharged into combustion device 12 after it has
passed through ignition zone register scroll passageway
38, such that the discharged air stream 39 supports and
governs combustion in ignition zone 16.
A second discrete air flow or air stream 49 is
directed through inwardly spiraling supplemental zone
register scroll passageway 48, such that the air stream 49
has measurable and controllable characteristics which
govern combustion characteristics in the supplemental zone
18. Air stream 49 is discharged into the combustion
device 12 after it has passed through the supplemental
- 32 -
zone register scroll passageway 48, such that the
discharged air stream 49 supports and governs combustion
in the supplemental zone.
Characteristics of the combustion in the ignition
zone 16 are controll~d by adjusting ignition zone register
air valve 3~ disposed upstream of the ignition zone
register scroll passageway 38. Character-istics of the
first air stream 39 are measured by measuring instrument
60 in the ignition zone register scroll passageway 38, and
the aforementioned control of the combustion in the
ignition zone is executed in response to the measurement
of the air flow in the air stream 39.
Similarly, characteristics of combustion in the
supplemental zone 18 are controlled by adjusting
supplemental zone register air valve 46 disposed upstream
of the supplemental zone register scroll passageway 48.
Characteristics of the air stream 49 are measured with
measuring instrument 62 in supplemental zone register
scroll passageway 46. The aforementioned control of the
characteristics of combustion in the supplemental zone is
executed in response to this measurement of the air flow
in the air stream 49.
While the present invention has been illustrated and
described by way of a specific, preferred, exemplary
embodiment, it will be understood that many additional
embodiments, variations and modifications utilizing in the
present invention are possible within the spirit and scope
of the appended claims.
