Title of Invention

AN IMPROVED COOLING SYSTEM FOR USE IN HOOD ANNEALING FURNACE FOR COOLING OF HOT GASEOUS MEDIUM

Abstract An improved cooling system for cooling of hot gaseous medium such as hot dusty gases comprising at least one cooler shell having inlet end through which the hot gaseous medium is cooled and an outlet end through which the cooled hot gaseous medium is released for subsequent use/application having a plurality of water tubes through which cool water is passed to effectuate the cooling of said hot medium, said water tubes having a diameter in the range of 24mm to 26mm and having a wall thickness of 3mm to 4mm.
Full Text The present invention relates to for,cooling of hot gaseous medium and also to a hood annealing furnaces having such gas cooling systems.
It is known that in batch annealing furnaces, there is base over which an equipment known as diffuser is used as base plate for loading the coils for annealing and converting the velocity head into pressure head for creating requisite pressure required for the flow/circulation of hot inert gas. Coils to be annealed are kept over the diffuser and are covered with a cylindrical stainless steel cover known as inner cover, for isolating the coils from atmosphere. Proper sealing is provided at the base inner cover interface. The mode of sealing varies with furnace design, in some such furnace designs materials of these sealing is ceramic, special rubber and come of the design even sand is used as sealing material because pressure inside the cover is quite low. Furnace is put over the inner cover, air is purged out and the nitrogen hydrogen mixture is filled as protective gas inside the inner cover. A base fan circulates the protective gas through out the annealing_cycle viz heating, soaking and cooling cycle, in some design of furnaces during cooling cycle, inner cover protective gas is passed through protective gas coolers which are water tube coolers, in which cooling water is passed through tubes and hot gases are passed through coolers shell. At the exit side of the cooler bent pipes (commonly known as J pipes) are provided through which cooled gas is passed to the inner cover. This process continues till the inner cover temperature comes down to 120°C
Reference is invited to accompanying Fig 1 which schematically illustrates an existing hood annealing furnace provided with such known cooling arrangement. As shown in Fig. 1 the known hood annealing furnace consists of

a base frame (16) where coils are placed , a base fan (6) mounted motor (14) which circulates protective gas, two numbers of coolers (15) which cools the protective gas during cooling period and the cold gas in turn brings down the temperature of the coils, inner cover (2) made of stainless steel which covers the stack of coils, a refractory lined outer cover (5) which acts as a heat shield for the furnace, burner (8) for burning gaseous fuel which is the input heat to the furnace, and flue gas outlet (12) for exhaust of burnt gaseous products.
In the known art for placement of the coils the outer cover and inner covers are removed Base trough (7) is placed on the base Maximum four numbers of coils are

placed one above the other with convector plate (4) in between. Inner cover ts then placed over the coils. Sand sealing is done at the base. After that outer cover is placed, fuel air mixer is introduced in the furnace and ignited by the burner (8). The heating cycle starts at this point. The burnt gas after heating the coils go out through flue gas outlet via ejector (11). During heating cycle, coolers are kept inoperative. After heating is over, soaking is done for a certain period. After soaking, cooling starts. During cooling cycle, the coolers are made operative by opening a valve in the cooler circuit. Base, base fan inner cover constitute a equipment for annealing.
It has however, been experienced that in conventional base trough, in which diffuser vanes are placed for better circulation of protective gas due to non provision of placing the diffuser vanes in a proper manner, the vanes get disturbed at the time of placement of coils resulting into ineffective conversion of velocity heads, into pressure heads. In particular, improper arrangement of the diffuser vanes in the conventional art caused anomalous distribution-of velocity and pressure head leading to poor circulation of protective gas through coolers, this resulted higher cooling time. Also, there was improper cross sectional area at the inlet and exit of diffuser vanes in the known art
Also, in conventional scheme, the cooling pipes are more in numbers and dia of cooler tubes are less. The industrial water containing suspended particulates enter into the cooler tubes resulting into chokage of the same. The deposition of muck is another factor for chokages of tubes. Moreover, the shell of the cooler through which gas passes get blocked due to ingress of sand for sealing purpose. In particular, in conventional art, choking used to take place in the tubes as well as in the shell. The choking of the tube was due to smaller diameter of the tube and deposition of muck. The choking of the shell is due to ingress of sealing sand inside the shell. Heat transfer was not proper due to the above reasons and due to the corrosion, pipe life was short. Furthermore, in conventional J pipe design, there being no passage for taking out the deposited sand, the problem of choking by way of deposition of sand was also found to be common In particular, in conventional art, J pipe was not having withdrawal facility of removing sand which used to get deposited in the cooler shell.
It is thus the basic objective of the present invention to provide for an improved cooling system for industrial use especially for gases laden with considerable quantity of dust which would have good cooling efficiency and would avoid the problems/shortcomings of known cooling systems discussed above
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Another object of the present invention is directed to provide an improved cooling system for use in hood annealing furnaces which would have improved cooling efficiency and would avoid the problems/shortcomings of known cooling systems used in hood annealing furnaces.
Yet another object of the present invention is directed to provide for an improved cooling system for use in hood annealing furnaces which would favour effective heat transfer and consequent better cooling efficiency.
Yet another object of the present invention is directed to avoid problems of anomalous distribution of velocity and pressure head and thereby favour better circulation of protective gas through coolers and reduce cooling time.
Yet further object is directed to provide for an improved cooling system which would have facilities for better maintenance and in particular withdrawal of depositions/dust from the system.
Yet further object of the present invention is directed to a system for improving cooling efficiency in hood annealing furnaces by way of modifications in the furnace base to thereby eliminate problem of ingress of sand in cooler shell experienced in the known art.
Statement of Invention
Thus in accordance with one aspect of the invention there is provided an improved cooling system for cooling of hot gaseous medium such as hot dusty gases comprising :
At least one cooler shell having inlet end through which the hot gaseous medium to be cooled is introduced and an outlet end through which the cooled hot gaseous medium is released for subsequent use/application, said cooler shell having a plurality of water tubes through which cool water is passed to effectuate the cooling of said hot medium, said water tubes having a diameter in the range of 25mm to 26mm and havbing a wall thickness of 3mm to 4mm;
Strainer means for the incoming cooling water entering said water tubes;
Inlet pipes at said inlet end of said cooler being provided height of 100mm to 150mm;
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A modified J pipe at the said outlet end of said shell to facilitate cleaning and maintenance of said cooler shell;
means for effective diffusion of said hot gaseous medium gases for better circulation of the hot air through the said water tubes for better cooling ends
according to another aspect of the invention there is provided a hood annealing furnace having the improved cooling system comprising :
a base frame for providing the coils to be annealed;
a base fan mounted motor for circulation of protective gas ,
an inner cover to cover the stock of coils to be annealed
a refractory lined outer cover as a heat shield for said furnace;
burner for burning gaseous fuel as the input heat to said furnace;
a flue gas outlet for exhaust of the burnt gaseous product;]
atleast one cooling system as disclosed in the last preceding paragraph
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means for effective diffusion of said hot gaseous medium gases for better circulation of the hot air through the said water tubes for better cooling ends.

The objects and advantages in the invention and its mode of attaining will hereinafter be described in greater detail with reference to non-limiting exemplary embodiments thereof discussed in relation to the following accompanying drawings wherein
Fig. 2 shows schematically the protective gas cooler in accordance with the present invention.
Fig. 3 illustrates modifications in furnace base in accordance with the present invention.
Fig 4 illustrates the arrangement of fixing of vanes at the entry and exit points of the cooller system in accordance with the present invention.
Fig 5 illustrates modifications in J-pipes proposed in accordance with the present invention
Rference is first invited to Fig. 2 which shows the improved protective gas cooler in accordance with the present invention. As illustrated in said figure the .protective gas cooler is shown to comprise of. outer shell, water tubes flanges for gas outlet, inlet, water inlet, outlet pipes, side jackets

The base of the furnace has also been modified in accordance with this invention so as
to completely eliminate the ingress of sand in the cooler shell. The modified furnace
base takes care of problems encountered in assemblies of diffusers in the base. Such a
modified furnace base construction is illustrated in greater detail by way of
accompanying figure 3. As shown in Fig 3 the modified base of the furnace comprises
of diffuser, gas holes
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Reference is now invited to Fig 4 which illustrates the arrangement of diffusers in the modified base of the furnace in accordance with the present invention. As illustrated in said figure the vanes are arranged to provide proper profile and cross-sectional area at the entry and exit of the protective gas flow to achieve proper pressure of the gas (hot medium) into the cooler and for achieving better heat efficiency In particular, as

illustrated in said figure guiding plates have been provided by welding cleats in order to facilitate proper positioning of the vanes. Conversion of velocity head to pressure head is adequate in such configuration leading to higher amount of protective gas flow through coolers thereby achieving reduced cooling time
Reference is next invited to accompanying figure 5 which shows the modified J pipe connecting the cooler to the furnace whereby it would now be possible to maintain and clean the cooler shell at regular intervals. This provides for in particular, the withdrawal of depositions in the shell thereby avoiding the problem of shell jamming experienced in the known art.
Thus the cooler of the present invention provides for the following advantages vis-a-vis conventional coolers known in the art.
In earlier design of coolers, coolers are provided with more number of tubes of lesser diameter and wall thickness. These tubes were provided with huge number of fins for increasing the surface area and subsequently heat transfer but in existing system these parameters became unproductive, as gas flow used to stop after few months of operation due to choking. More number of tubes were a problem for cleaning where as smaller diameter was a constant source for choking of the tubes especially when untreated industrial water is used for the cooling. Thinner wall thickness of mild steel tubes in such environment was leading to early punctunng of the tubes and quality problems of the annealed coils The problem was decreased gas flow and subsequent stoppage of gas flow making the coolers inoperatives. The cooler of the invention have been modified (Fig. 2) in such as way that choking of water tubes will be drastically reduced, choking of cooler shell shall be eliminated and cooler longivity will be enhanced (at least five times).
Also, modification in furnace bases as discussed hereinbefore (Fig. 3) has completely eliminated the ingress of sand in cooler shell. The modified furnace base takes care of the problems encountered in assembly of diffusers on the bases
Proper profile and cross sectional area at entry and exit of the protective gas flow is essential for getting proper pressure of the gas Fixing of the vanes (Fig 4) of the present invention has assured the requisite pressure for gas flow
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Moreover, through design modifications in bases ingress of sand has been eliminated due to gravity fall, but ingress of finer sand particles with protective gas in not ailed out completely. To take care of this eventuality J pipe (the pipe which carries cool gas from cooler to furnace) has been modified in accordance with the invention (Fig. 5), so that at regular intervals, cooler shell may be cleaned.
In particular, in the cooling system of the present invention choking of the tube was overcome by way of
I. use of higher diameter of the tubes with increased pipe thickness ; and
II. use of strainer in the incoming cooling water line.
The above modifications make heat transfer very effective and enhance pipejfe. Also, choking of the shell has been overcome by the present invention by way of I. increase height of the inlet pipe of the cooler

II removal of huge number of fines from water tubes and
III. introduction of an .inspection ^maintenance pocket jn,the_J_pipe
Moreover, guiding plates have been provided by welding cleats in order to facilitate proper positioning of the vanes. Conversion of velocity head to pressure head is adequate in such configuration leading to higher amount protective gas flow through coolers. This result in reduced cooling time. Withdrawal facility has also been provided in the J pipe in accordance with the present invention
In view of the abovesaid, the present invention provides for the following .
i A protective gas coolers with bigger inner diameter and higher wall thickness
even going against the normal convention of higher heat transfer (provision of fins, less inner diameter and more number of tubes for greater heat transfer surface area, thinner tubes for better heat transfer), especially for dusty condition.
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II. Improved coolers suitable for use not only in annealing furnaces, but can be used in any industry especially where gases are laden with considerable quantity of
dust.
III. The modification in furnace bases to prevent ingress of sand and any powder/granules, wherever gas flow is taking place.
iv. Modification in J pipe for easy maintainability of such equipment wherever dusty
gas is passing through the equipment, v Modified protective gas cooler, which completely eliminates the problem of shell
jamming, reduces drastically the choking of water tubes, enhances the heat
transfer rate and increases the longivity of coolers.
vi. Improved arrangement for fixing of vanes so that conversion from velocity head to pressure head is optimum with improved gas flow.
vii. Modification in J pipe has been carried out so that choking of cooler shell does not take place
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WE CLAIM :
1. An improved cooling system for use in hood annealing furnace for cooling of hot gaseous medium comprising
at least one cooler shell having inlet end through which the hot gaseous medium to be cooled is introduced and an outlet end through which the cooled hot gaseous medium is released for subsequent use/application, said cooler shell having a plurality of water tubes through which cool water is passed to effectuate the cooling of said hot medium, said water tubes having a diameter in the range of 24mm to 26mm and having a wall thickness of 3mm to 4mm ,
strainer means for the incoming cooling water entering said water tubes ;
inlet pipes at said inlet end of said cooler being provided height of 100 to 150mm,
a modified J pipe at the said outlet end of said shell to facilitate cleaning and maintenance of said cooler shell ;
means for effective diffusion of said hot gaseous medium gases for better circulation of the hot air through the said water tubes for better cooling ends
2) An improved cooling system as claimed in claim 1 wherein said water tubes are adapted and arranged to facilitate cleaning of the cooler tubes.
3} An improved cooling system as claimed in any one of claims 1 or 2 wherein said 'J' pipe is provided/adapted to facilitate withdrawal of deposited sand/dust from said shells
4) An improved cooling system as claimed in any one of claims 1 to 3 wherein said 'J' pipe is provided with an inspection and maintenance pocket.
5} An improved cooling system as claimed in any one of claims 1 to 4 wherein said means for effective diffusion of hot gaseous medium for better circulation of said hot
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gaseous medium comprise an arrangement of diffusion vanes provided at the inlet and outlet of said cooler shell
6) A cooling system as claimed in claim 1 wherein said diffusion vanes are
arranged on a base portion such that cross-sectional area at the inlet and outlet of
said diffusion vanes provide for proper distribution of velocity and pressure head for
effective circulation of the hot gaseous medium in said shell for cooling purposes.
7) An improved cooling system as claimed in any one of claims 1 to 6 wherein there
is provided guiding plates to facilitate proper positioning of all said vanes.
8) An improved cooling system as claimed in claim 7 wherein said guiding plates are
supported by welding cleats
9) A hood annealing furnace having the improved cooling system as claimed in claim 1
comprising
a furnace base having base frame for providing the coils to be annealed ;
a base fan mounted motor for circulation of protective gas , an inner cover to cover the stock of coils to be annealed a refractory lined outer cover as a heat shield for said furnace ; burner for burning gaseous fuel as the input heat to said furnace , a fuel gas outlet for exhaust of the burnt gaseous product , and at least one improved cooling system as claimed in any one of claims 1-8.
10) A hood annealing furnace as claimed in claim 9 wherein said furnace base is
adapted to eliminate ingress of sand in said cooler shell
11) A hood annealing furnace as claimed in claim 9 wherein said modified J pipe at
the outlet end of said shell of the cooling system operatively connects said improved
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cooling system to said furnace for supplying of cool protective gas from said cooler to said furnace
12) An improved cooling system for cooling of hot gaseous medium and a hood annealing furnace having said cooling system substantially as herein described and illustrated with reference to the accompanying figures.


Dated this 12th day of February 1999.

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An improved cooling system for cooling of hot gaseous medium such as hot dusty gases comprising at least one cooler shell having inlet end through which the hot gaseous medium is cooled and an outlet end through which the cooled hot gaseous medium is released for subsequent use/application having a plurality of water tubes through which cool water is passed to effectuate the cooling of said hot medium, said water tubes having a diameter in the range of 24mm to 26mm and having a wall thickness of 3mm to 4mm.

Documents:

00111-cal-1999 abstract.pdf

00111-cal-1999 assignment.pdf

00111-cal-1999 claims.pdf

00111-cal-1999 correspondence.pdf

00111-cal-1999 description(complete).pdf

00111-cal-1999 drawings.pdf

00111-cal-1999 form-1.pdf

00111-cal-1999 form-2.pdf

00111-cal-1999 form-3.pdf

00111-cal-1999 form-5.pdf

00111-cal-1999 pa.pdf

111-cal-1999-granted-abstract.pdf

111-cal-1999-granted-assignment.pdf

111-cal-1999-granted-claims.pdf

111-cal-1999-granted-correspondence.pdf

111-cal-1999-granted-description (complete).pdf

111-cal-1999-granted-drawings.pdf

111-cal-1999-granted-examination report.pdf

111-cal-1999-granted-form 1.pdf

111-cal-1999-granted-form 2.pdf

111-cal-1999-granted-form 3.pdf

111-cal-1999-granted-form 5.pdf

111-cal-1999-granted-letter patent.pdf

111-cal-1999-granted-pa.pdf

111-cal-1999-granted-reply to examination report.pdf

111-cal-1999-granted-specification.pdf


Patent Number 195169
Indian Patent Application Number 111/CAL/1999
PG Journal Number 30/2009
Publication Date 24-Jul-2009
Grant Date 02-Sep-2005
Date of Filing 12-Feb-1999
Name of Patentee STEEL AUTHORITY OF INDIA LIMITED
Applicant Address RESEARCH & DEVELOPMENT CENTRE FOR IRON & STEEL, ISPAT BHAWAN, LODHI ROAD
Inventors:
# Inventor's Name Inventor's Address
1 KEDAR NATH PANDEY RDCIS/SAIL, DORANDA, RANCHI-834 002
2 TAPAS KANTI DUTTA RDCIS/SAIL,DORANDA,RANCHI-834 002
3 NIRMAL KUMAR KAKKAR RDCIS/SAIL,DORANDA,RANCHI-834 002
4 KIRTIPRASAD VERMA RDCIS/SAIL,DORANDA,RANCHI-834 002
5 ASIM KUMAR SAHU RDCIS/SAIL,DORANDA,RANCHI-834 002
6 BHARAT CHANDRA ROY RDCIS/SAIL,DORANDA,RANCHI-834 002
7 JAI PRAKASH NARAYAN RDCIS/SAIL,DORANDA,RANCHI-834 002
PCT International Classification Number C21D 1/74
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA