U.S. patent number 3,841,614 [Application Number 05/312,523] was granted by the patent office on 1974-10-15 for apparatus for preheating steel ingot or blooms by the use of high-speed jet streams as well as heating furnace using the same.
This patent grant is currently assigned to Kawasaki Jukogyo Kabushiki Kaisha. Invention is credited to Ryuzo Okuno.
United States Patent |
3,841,614 |
Okuno |
October 15, 1974 |
APPARATUS FOR PREHEATING STEEL INGOT OR BLOOMS BY THE USE OF
HIGH-SPEED JET STREAMS AS WELL AS HEATING FURNACE USING THE
SAME
Abstract
Apparatus for preheating substances such as steel ingots, slabs,
blooms, billets or the like to be treated in a reheating furnace by
the use of high-speed jet streams is provided with a casing which
consists of two parts, one of them being a high-speed jet zone of a
hot fluid having a high temperature which has been exhausted from
the said reheating furnace and the other a convection zone (or a
high-speed jet zone) connected with the said jet zone. A conveyor
operates to successively feed the said substances to be treated
such as steel ingots or blooms into the said casing and to
successively extract the thus treated substances from the said
casing. The present invention also relates to a reheating furnace
for industrial use which is provided within a part of its
combustion zone with a numer of jet nozzles being equipped to the
upper and lower portions of the said combustion zone (high-speed
jet zone) each at a determined distance from substances to be
treated, wherein a high temperature exhaust gas which has been fed
from another combustion zone is jetted from the said nozzles under
high speed into the said high-speed jet zone whereby a heat
transfer is efficiently conducted therein between the said gas
streams and the said substances by utilizing the high coefficient
of heat transfer occurred on the surface of the said substances due
to the said high-speed gas streams.
Inventors: |
Okuno; Ryuzo (Kobe,
JA) |
Assignee: |
Kawasaki Jukogyo Kabushiki
Kaisha (Kobe-shi, Hyogo, JA)
|
Family
ID: |
26339643 |
Appl.
No.: |
05/312,523 |
Filed: |
December 6, 1972 |
Foreign Application Priority Data
|
|
|
|
|
Dec 6, 1971 [JA] |
|
|
46-98908 |
Jan 11, 1972 [JA] |
|
|
47-5669 |
|
Current U.S.
Class: |
432/64; 432/133;
432/164; 432/171 |
Current CPC
Class: |
B21B
45/023 (20130101); F27B 9/10 (20130101); F27B
9/38 (20130101); B21B 45/0203 (20130101); F27B
9/22 (20130101); B21B 45/004 (20130101); F27D
7/00 (20130101); F27B 2009/3638 (20130101); F27D
2003/0046 (20130101); F27D 2009/0089 (20130101); F27D
2003/0051 (20130101); F27B 2009/126 (20130101); F27M
2001/1552 (20130101); F27B 2009/122 (20130101); F27D
2003/008 (20130101) |
Current International
Class: |
F27D
7/00 (20060101); F27B 9/22 (20060101); F27B
9/00 (20060101); F27B 9/10 (20060101); B21B
45/02 (20060101); B21B 45/00 (20060101); F27B
9/30 (20060101); F27B 9/38 (20060101); F27B
9/36 (20060101); F27D 3/00 (20060101); F27B
9/12 (20060101); F27D 9/00 (20060101); C21d
009/100 () |
Field of
Search: |
;266/5H
;432/121,123,126,133,171 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lake; Roy
Assistant Examiner: Bell; Paul A.
Attorney, Agent or Firm: Sughrue, Rothwell, Mion, Zinn and
Macpeak
Claims
What is claimed is:
1. A preheating apparatus for treating substances such as steel
ingots, blooms, slabs, billets or the like to be treated in a
reheating furnace, the improvement comprising:
a casing defining a chamber having at a first end means forming a
high-speed jet zone of a hot fluid having a high temperature which
has been exhausted from said reheating furnace and at a second end
a convection zone connected with the said jet zone;
means for directing said exhaust gases from said reheating furnace
to said jet nozzles; and
a conveyor which operates to successively feed the said substances
into the said casing and to successively extract the thus treated
substances from the casing,
wherein; heat transfer is conducted on the surface of the said
substances by a high coefficient of heat transfer occurring on the
said surface by the impingement of the said hot jet streams.
2. The preheating apparatus of claim 1 wherein said high speed jet
zone at said first end comprises a plurality of jet nozzles located
on each side of said substances to be treated to direct the high
temperature exhaust fluid toward the surface of said substance and
means for directing said exhaust gases from said reheating furnace
to said jet nozzles.
3. The preheating apparatus of claim 1 wherein said casing forms a
first chamber containing the high-speed jet zone and a separate
second chamber containing the convection zone, said first and
second chambers being interconnected via a duct having pumping
means connected thereto to pump said high temperature exhaust fluid
from said first chamber to said second chamber.
4. The preheating apparatus of claim 3 wherein said first and
second chambers contain a plurality of jet nozzles to direct the
high temperature exhaust fluids at both sides of said substances to
be treated.
5. In an industrial furnace having a plurality of independent, fire
proof combustion chambers and conveying means inside of said
combustion chambers for transporting materials to be reheated, the
improvements comprising:
a. a preheating chamber adjacent the first combustion chamber
through which the material to be reheated passes,
b. a plurality of jet nozzles in said preheating chamber to direct
high temperature exhaust gas from the industrial furnace onto both
sides of the material to be reheated so as to raise the temperature
of the material to approximately 500.degree.C,
c. means to prevent said high temperature exhaust gas from entering
said combustion chamber after passing through said nozzles, and
d. means to direct the high temperature exhaust gas from the
industrial furnace to said jet nozzles.
6. The improved industrial furnace of claim 5 wherein said nozzles
are composed of fire proof brick.
7. The improved industrial furnace of claim 5 wherein said means to
prevent the high temperature exhaust gases from entering the
combustion chamber comprises a high-speed gas curtain between said
preheating chamber and said combustion chamber.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The subject matter of the present invention resides in a
pre-heating apparatus in which heat transfer is conducted between
the substances to be treated such as steel ingots or blooms around
which a large number of nozzles are arranged, and high-speed jet
streams which gush out from the said nozzles, by utilizing the high
coefficient of heat transfer on the surface of the said substances
which results from the said jet streams.
As to the coefficient of heat transfer on a plate to which jet
streams are blown off, it has been proved that a considerably high
heat transfer may be achieved on the surface of the said plate by
various experimental results or by means of the experiments on jet
streams conducted by Gardon, Cobonpue, etc.
As the well known experimental equation of Gardon and Cobonpue
illustrates, the average coefficient of heat transfer (hm) on the
surface of a plate, to which the jet streams gushing out from the
arranged nozzles flow vertically, is as follows:
Num = hmx/.lambda. = 0.286 uax/.gamma. .sup.0.625
Where
hm is defined with respect to the difference between the
temperature of air before flow into the nozzles and the temperature
of the plate,
ua is the flow speed in the center of the jet streams at the
position of the plate,
x is a distance between the respective nozzles,
.lambda. is a thermal conductivity, and
.gamma. is a coefficient of kinematic viscosity.
The present invention also resides in a heating operation of the
said substances such as steel ingots or blooms by means of a
continuous type reheating furnace for industrial use which is
provided within a part of its combustion zone a number of jet
nozzles being equipped to the upper and lower portions thereof each
at a distance from the said substances, wherein a high temperature
exhaust gas is introduced directly from another combustion zone to
the said nozzles and then is jetted therefrom under high speed into
the said high-speed jet zone whereby the substances are preheated
by means of thus jetted high temperature and high-speed jet
streams.
2. Description of the Prior Art
The conventional preheating apparatus in the prior art techniques
are explained in the following: In the industrial furnaces for
heating which have hitherto been used, a heat energy involved in an
exhaust gas is recovered by preheating air for combustion, by using
a heat exchanging apparatus (=recuperator), for the purpose of
decreasing the specific heat consumption of the furnace (=rate of
necessary heat quantity Kcal per ton of blooms to be treated). In
this case, however, the temperature of the exhaust gas at the
outlet of the recuperator is about 700.degree. - 800.degree. C.
Thus, a large amount of heat energy is in fact thrown away. For
example, in the case of five-zone type continuous reheating furnace
(=pusher type furnace) having a heating capacity of 170 T/H, the
specific heat consumption thereof is about 430 kcal/kg, and it is a
common knowledge that in the case of walking beam type furnaces
which have rapidly developed in these days, the same unit is about
500 kcal/kg (due to a larger water cooling loss than the case of
the former pusher type furnaces).
With respect to the conventional reheating furnace (including a
walking beam type furnace), the specific heat consumption thereof
is represented by the following equation:
Qz = .epsilon.Q = Qn + Qw + Qs + Qk + Qabs 1.
where;
Qz: total heat quantity required in the furnace in kcal/h
Qn: net heat quantity required to heat the steel substance in
kcal/h
Qw: heat quantity released through wall, etc. (loss of heat
quantity) in kcal/h
Qs: heat quantity released and radiated through shutter, etc. in
kcal/h
Qk: loss of heat quantity due to water cooling skid, etc. in
kcal/h
Qabs: heat quantity of exhaust gas being thrown away in kcal/h
In case the capacity of the furnace is D kg/h, then the specific
heat consumption Ws of the furnace is represented as follows:
Ws = Qz/D Kcal/kg 2.
That is, the above is a proportion of the heat quantity required
per kg of the steel substance to be treated, on the basis of the
total heat quantity.
On the other hand, the necessary quantity of fuel Bf is represented
by the following:
Bf = .SIGMA.Q/Hu = (Qn + Qw + Qs + Qk + Qabs/Hu) 3.
One embodiment for heat calculation is shown in the following, with
respect to the five-zone pusher type furnace of 170 T/H.
__________________________________________________________________________
Necessary net quantity of heat Qn=34.9.times.10.sup.6 kcal/hr 47%
Wall loss, etc. Qw + Qs=2.8.times.10.sup.6 kcal/hr 3.5% Water
cooling loss (skid) Qk=10.6.times.10.sup.6 kcal/hr 14.5% Exhaust
gas loss Qabs=25.9.times.10.sup.6 kcal/hr 35% .epsilon.Q = Qz =
74.2 .times. 10.sup.6 kcal/hr 100%
__________________________________________________________________________
Specific heat consumption Ws=Qz/D= 74.2.times.10.sup.6
/1.7.times.10.sup.5 = 435 Kcal/kg D: treated value 170,000 kg/hr.
Fuel consumption value (heavy oil) Hu=9,800 Kcal/kg Bf = Qz/Hu =
74.0 .times. 10.sup.6 /9,800 = 7,600 Kg/hr
Thus, the necessary amount of heavy oil per hour is 7,600 kg/hr. In
this case, the exhaust gas loss occupies 35 percent of the total
heat quantity. It is noted that this has a great significance to
affect the amount of the specific heat consumption.
As is understood from the above equations, it is necessary, in
order to decrease the specific heat consumption and the fuel
quantity, to reduce the heat quantity of exhaust gas which has been
exhausted from a reheating furnace. The said value depends upon the
furnace to be used, and in general, is 35 - 40 percent.
In the conventional technical arts, a heat recovery has hitherto
been tried by using a recuperator in a flue for the exhaust gas, as
a countermeasure for the above defects. However, even if some heat
recovery is achieved in the recuperator, as a practical matter the
heat quantity of 35 - 40 percent is still exhausted.
SUMMARY OF THE INVENTION
The present invention improves such uneconomical operation as in
the conventional means wherein a large amount of heat energy
contained in an exhaust gas is thrown away.
It is a primary object of the present invention to impart a heat
energy contained in a high temperature fluid into substances to be
treated so as to elevate the temperature of the said substances, by
jetting the said high temperature fluid from nozzles onto the
substances under high speed, and by utilizing the high coefficient
of heat transfer occurred on the surface of the said
substances.
Still another object of the present invention is to preheat
substances which are fed into a reheating furnace, by utilizing an
exhaust gas which has been exhausted from a generally used
industrial heating furnace as a high temperature fluid, directly or
via a heat exchanging device.
Further, the present invention reduces the heat energy contained in
the exhaust gas which has been exhausted from a reheating furnace
for the purpose of eliminating the defects of the conventional
furnaces as explained above, by increasing the heat transfer effect
or the coefficient of heat transfer in a convection or a preheating
zone which is connected with an outlet for the exhaust gas.
More precisely, the present invention is based upon the application
of such phenomenon to a heating furnace that a high coefficient of
heat transfer may be attained on a surface of a plate onto which
jet streams are blown. Thus, the present reheating furnace
comprises a plurality of jet nozzles which are provided in the
upper and lower portions of its combustion zone (say preheating
zone), the materials to be treated being conveyed between the said
upper and lower nozzles, whereby a high temperature exhaust gas
which has been forwarded from another combustion zone is jetted
from the respective nozzles thereby to efficiently carry out the
heat transfer between the said substances and the said gas.
By virtue of the provision of the said jet nozzles, in the
combustion zone, heat transfer may efficiently be carried out
between the substances to be treated and the high temperature
exhaust gas in the said zone (hereunder referred to as a jet zone),
and thus the temperature of the exhaust gas is extremely lowered.
Accordingly, great advantage may result therefrom, such as decrease
of specific heat consumption of the furnace, economization of fuel,
etc.
DETAILED DESCRIPTION OF THE INVENTION
In the present apparatus for preheating, the pressure of an exhaust
gas which has a temperature of 700.degree. - 800.degree. C. and
which has been passed through a recuperator is elevated by means of
a hot gas blower and then is fed into jet nozzles which are
arranged around the substances to be treated in the preheating
apparatus. From the said nozzles the high-speed exhaust gas having
the said high temperature is jetted and a direct heat transfer is
conducted on the surface of the substances, by utilizing the high
coefficient of heat transfer (150 - 200 kcal/m.sup.2 h.degree.C) on
the said surface which results from the jet streams fed from the
nozzles, thereby elevating the temperature of the substances to
about 500.degree. C. In this case, the temperature of the exhaust
gas becomes lower than 400.degree. C. after the said heat transfer
treatment. In such case that the temperature of the exhaust gas is
400.degree. C., the exhaust gas loss Qabs is as follows:
Qabs = 10.4 .times. 10.sup.6 kcal/hr
The exhaust gas loss Qabs is as follows:
Qabs = 10.4 .times. 10.sup.6 Kcal/hr
Therefore, in such case that the aforementioned values are employed
for Qn, Qw+Qs and Qk, respectively, the total heat quantity Qz' is
as follows:
Qz' = 58.7 .times. 10.sup.6 Kcal/hr
Thus, the specific heat consumption thereof (Ws' ) in the said case
is as follows:
Ws' = Qz'/D = (58.7 .times. 10.sup.6)/(/1.7 .times. 10.sup. 5) =
345 Kcal/Kg
This value shows that the reduction of the said unit amounts to
about 20 percent of that of the conventional furnace. With regard
to the fuel consumption value Bf', the same is as follows:
Bf' = 58.7 .times. 10.sup.6 /9,800 = 6,000 Kg/hr
Therefore, against 7,600 Kg/hr of previous time the fuel amount of
1,600 Kg/hr will be economized.
In case that the operation period is set for average 6,000 hours
per year and that unit price of the heavy oil to be used is 7
yen/kg, the economized value of the fuel amounts to the
following:
6,000 .times. 1,600 .times. 7 = 67,200,000 yen/year
Now, some preferable embodiments of the present invention will be
explained with reference to the drawings attached hereto, wherein
like numerals designate like elements in the several
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partly cut-away, side elevation of a preheating
apparatus embodying the present invention.
FIG. 2 is a sectional view taken about line II -- II of FIG. 1.
FIG. 3 is a sectional view taken about line III -- III of FIG.
1.
FIG. 4 is a partly cut-away, side elevation of another modification
of the preheating apparatus according to the present invention.
FIG. 5 is a sectional view of a conventional five-zone continuous
pusher type reheating furnace.
FIG. 6 is a sectional view of a reheating furnace which is provided
with jet nozzles in its preheating zone, embodying the present
invention.
FIG. 7 is a sectional view of a walking beam type furnace to which
the jet nozzles of the present invention are applied.
FIG. 8 is an enlarged sectional view of jet nozzle parts.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring to FIG. 1, FIG. 2 and FIG. 3, the substances 1 to be
preheated which are put on fixed beams 4 are successively conveyed
in the apparatus, by the upper and lower movement and the front and
rear movement of walking beams 3, that is, the rectangular movement
of the same, via wheels 8 located on inclined rails 7.
Posts 2 of the walking beams 3 are connected with a driving beam in
a lower portion of the apparatus, piercing a lower portion of a
casing 10. In the piercing portion, gas seal boxes 6 and seal
plates 18 are provided so as to prevent from a gas leakage in the
apparatus.
Each of the posts 2 and the walking beams 3 is covered with heat
shielding plates 5, since these are exposed to a high temperature
gas. On the beams, casting rails 3' are equipped on both of the
fixed beam side and the walking beam side thereof so as to prevent
oxidation erosion.
The preheating apparatus is divided into two parts at the center
thereof, and in the high temperature side is a jet zone a wherein a
number of nozzles are provided at the upper and lower portions.
This jet zone a is a main part of the present apparatus, and is
composed of a casing box 10. The exterior surface of the casing box
is coated with an insulating material 19 and the interior casing is
made of a heat resistant steel plate to which nozzles 9 are fixed.
The other part of the apparatus is a convection current zone b. The
exhaust gas fed into the jet zone a is thereafter introduced into
this zone b wherein a heat supply is conducted by the convection
current of the said gas. Thus, the convection current zone b has
such a role as conducting an auxiliary heat supply therein. Since
the gas temperature of the interior part of the zone b is
considerably high, such as about 500.degree. C., the interior
surface of the casing in this part is coated with an insulating
material 11 so as to prevent, as much as possible, oxidation
erosion of the casing and heat loss from the wall. An exhaust gas
port 13 is equipped on one end of the zone b, from which the
exhaust gas is removed and is introduced into a chimney.
In each feeding inlet and extracting outlet of the present
apparatus, a nozzle 17 is provided wherein a jet film of an air or
high temperature gas and the gas in the interior of the apparatus
is sealed by the said jet film. The substances 1 to be preheated
are fed to the front of the apparatus by means of a rollgang 15 and
then are conveyed into the interior thereof by means of the walking
beams 3.
At the extracting outlet, the preheated substances are extracted by
means of an extractor 16. In addition, a pusher may also be used
for the said feeding and conveying means.
FIG. 4 shows another embodiment of the present preheating apparatus
wherein a jet zone a and a convection current zone b are entirely
separated from each other. The pressure of the high temperature gas
which has been exhausted from the jet zone a is elevated further by
means of a hot gas blower and the said gas is fed into nozzles
which are arranged in the corresponding parts of the convection
current zone b. In this zone b, high temperature jet streams also
gush out from the nozzles to supply heat to the substances to be
treated. In this apparatus, a two-stage jet zone a is provided, for
the purpose of increasing the heat recovery efficiency and of
compactly integrating the whole apparatus. Like elements to that of
FIG. 1 carry like numerical designations.
As explained in the above, the furnace efficiency is improved and
the specific heat consumption thereof is lowered, by the use of the
present apparatus. According to the present apparatus, the
temperature of the exhaust gas which is exhausted from the
industrial heating furnace may be lowered, and so the expense for
the attendant equipments in the works may be decreased. Thus, the
present apparatus includes various merits. In addition, the present
invention may be utilized for any and every apparatus for
preheating substances by the use of high-speed jet streams.
Next, some embodiments of the reheating furnaces according to the
present invention will be explained in the following:
FIG. 5 is a sectional view of a conventional five-zone continuous
heating furnace. This furnace is a pusher type furnace which is
provided with a soaking pit bed at the extraction outlet part and
which consists of five combustion zones in all in the upper and the
lower portion.
In the said FIG. 5 a' is a soaking zone, b' is a heating zone, and
c' is a preheating zone.
Substances 1' to be treated are pushed into the furnace from the
side of the preheating zone by means of a pusher and are forwarded
to the extraction outlet part, sliding on the skid pipe 2' which is
supported by post pipes 3' and being heated successively. The
temperature of each combustion zone varies, depending upon the
quality of the substances to be treated, and, in general, in the
case of normal steels, a' is 1,250.degree. - 1,300.degree. c., and
b' and c' are 1,300.degree. - 1,350.degree. C., respectively.
Referring to FIG. 6, a number of jet nozzles 34 composed of
refractory materials are provided in upper and lower portions of a
preheating zone c, each with a determined distance from the
substances to be heated. The constitution of the nozzle section is
shown in the enlarged FIG. 8.
The jet zone is a hanging ceiling type zone which consists of a
conventional refractory body 35 and anchor bricks 36. In the part
of the refractory body 35, nozzles 34 are inserted.
To ceiling large size crawl beams 40 is fixed a small size beam 38
by means of hanging metal fittings 39, and the anchor bricks 36 are
fixed via a brick hanging metal fitting 37 thereby to support the
refractory body 35. On the other hand, the nozzles 34 are supported
by a refractory body metal fitting 43 via a joint duct 42 leading
to a forwarding duct 41 for the high temperature exhaust gas being
coated with a refractory material in its interior part.
In the furnace of FIG. 6 the means for feeding and supporting the
substances 1 to be treated are the same as those of FIG. 5.
As to the constitution of the furnace, it is possible to provide
the heating zone b and the jet zone c thereof, as being completely
separated from each other. In addition, it may also be possible, as
shown in the embodiments of the present invention, to integrally
constitute the two zones, a partition wall being provided in the
center therebetween. Thus, the two zones may be kept independent by
means of the jet film gushing from a nozzle 45.
The high temperature exhaust gas is collected in a header 46 at the
end part of the heating zone and is introduced into the forwarding
duct 41 by means of the hot gas blower or the present pressure
elevating device.
FIG. 7 shows a walking beam type furnace embodying the present
invention wherein a combination of a pusher and a walking beam is
used. In addition, the walking beam may also be used in the whole
length of the furnace.
According to the use of the present apparatus, the following
effects may be attained:
The temperature of exhaust gas after recuperator is now
850.degree.C and it is applied directly to the jet zone.
In this case, when jet speed W.sub.N is 85 m/s, according to the
test result of jet flow group conducted by the inventor of the
present invention and other people the average heat transfer
coefficient
.alpha.m = 185 Kcal/m.sup.2 h.degree.C is obtained.
Based on this value, when the substance to be fed to the furnace is
preheated from normal temperature up to 450.degree.C, average
temperature difference .DELTA.tm is 590.degree.C and heat transfer
area A is 120m.sup.2 (total of the upper and lower surfaces).
In this case, the heat quantity Qj absorbed by the substances,
including jet zone is as follows:
Qj = A .alpha. m .DELTA.tm
= 120 .times. 185 .times. 590
= 13.1 .times. 10.sup.6 Kcal/hr.
Here, Ql is the total loss of water cooling loss, etc. Therefore,
exhaust gas loss Qabs Kcal/hr can be obtained by subtracting the
aforementioned Qj from the heat quantity corresponding to the
exhaust gas temperature of 850.degree.C (Q' = 24.2 .times. 10.sup.6
Kcal/hr).
Qabs = (Q' - Qj - Ql)
= (24.2 - 13.8) .times. 10.sup.6 Kcal/hr
= 10.4 .times. 10.sup.6 Kcal/hr.
In this case, the temperature of exhaust gas is approximately
400.degree.C. This value agrees with the aforementioned exhaust gas
loss Qabs.
Applying the present invention to the above mentioned 170 T/H
reheating furnace, the following data are obtained.
By installing the jet zone according to the present invention in
the feeding portion of conventional reheating furnace and
preheating the steel ingot or steel piece to be fed to the furnace
making use of high temperature exhaust gas exhausted from furnace,
the following effects can be obtained.
1. Utilizing effectively the high temperature exhaust gas, heat
quantity of exhaust gas loss is lowered by more than 20 percent. In
one embodiment example, specific heat consumption is reduced from
435 Kcal/Kg to 345 Kcal/Kg and the big economization of fuel
consumption from 7,600 Kg/hr down to 6,000 Kg/hr becomes
possible.
2. Any burners which have been required in the preheating zone of
the conventional furnaces are unnecessary in the present
furnace.
3. The exhaust gas temperature is about 400.degree. C., and thus
the use of any recuperator is unnecessary.
Thus, the present invention has various merits say for drastic
economization of expenses, etc.
* * * * *