FORM 2
THE PATENT ACT 1970
(39 OF 1970)
&
The Patent Rules, 2003
COMPLETE SPECIFICATION
(See Section 10 and Rule 13)
1 TITLE OF THE INVENTION :
A METHOD FOR REHEATING OF INDIVIDUAL OVENS AFTER SHUT DOWN FOR NON-RECOVERY COKE OVEN.
2 APPLICANT (S)
Name : JSW STEEL LIMITED.
Nationality : An Indian Company.
Address : Jindal Mansion, 5-A, Dr. G. Deshmukh Marg, Mumbai - 400 026,
State of Maharastra, India.
3 PREAMBLE TO THE DESCRIPTION
COMPLETE
The following specification particularly describes the invention and the manner in which it is to be performed.

FIELD OF THE INVENTION
The present invention relates to a method for reheating of individual coke oven after shutdown without using any external heat source. More particularly, the present invention is directed to providing a method for reheating of individual oven of non recovery coke oven after repair/shutdown with reduced time for normalizing. Advantageously, following the method of reheating according to the present invention, oven could be normalized (at 900°C) in about 7 days as compared to about 11 days time by conventional practice using diesel burner for reheating of coke oven. The method of reheating of non recovery coke oven after shutdown/repair is thus economical without needing any external heat source, adapted to ensure uniform heating with reduced time of normalizing in a safe and reliable manner, favoring cost effective application in shutdown/maintenance of coke ovens in steel plants.
BACKGROUND ART
It is well known in the existing art that coke making technology comprises two types - one is recovery and another is non-recovery type of coke making. In recovery type, the byproducts are recovered where as in non-recovery type, heat of the flue gas is generally utilized for utilities like captive power generation. Conventionally, applicants' have the facility of two non recovery coke ovens each of 0.6 Mtpa capacity, wherein the oven temperature is maintained at 1250°C to 1350°C which is on the higher side of the thermal sustainability of the oven refractory lining. It is also experienced in the existing practice that individual ovens are often shut down for repair of damaged refractory lining. On an average 5/6 ovens remain in shutdown condition for repair/preventive maintenance. After repair of individual shut down ovens, reheating is done to make ready the oven (at 400°C) for coal cake charging. Then the oven is normalized by attaining the oven temperature of 900°C.
Conventionally, Oven reheating is done using diesel burner and also burning wood inside the oven. The individual oven doors are closed and sealed properly. Additional wood is also fed continuously through the window to raise the oven temperature to desired level. It takes almost 7 days to achieve the desired temperature (400°C) for charging. Then the coal cake is charged and after another 4 days, the coke will be

ready to be pushed out and the oven will attain the normalized temperature of 900°C. So, in total 11 days are required to normalize the oven thermal condition. There has been therefore a need in the art to develop a method for reheating of individual coke oven after shut down for non recovery coke oven without using external heat source and normalize the oven thermal condition with substantial reduction in time in a safe and reliable manner. The method would ensure on one hand uniform and faster reheating of the coke oven after repair/shutdown and on the other hand avoid use of expensive heating involving external fuel/heat source to thereby reduce down time of coke oven and improve productivity in coke oven.
OBJECTS OF THE INVENTION
The basic object of the present invention is thus directed to a method for reheating of individual ovens after shutdown for non recovery coke oven with reduced time for normalizing of oven without use of any external heat source in safe and reliable manner.
Another object of the present invention is directed to a method for reheating of individual ovens after shutdown for non recovery coke oven wherein heating using diesel burners or burning wood inside oven will not be required thus avoiding any additional cost.
A further object of the present invention is directed to a method for reheating of individual ovens after shutdown for non recovery coke oven wherein requirement of skilled manpower is avoided.
A still further object of the present invention is directed to a method for reheating of individual ovens after shutdown for non recovery coke oven wherein oven is normalized in 7 days compared to 11 days by conventional reheating process.
A still further object of the present invention is directed to a method for reheating of individual ovens after shutdown for non recovery coke oven wherein a standardized procedure is adopted to favour uniform heating which is easy to follow and is safe.

A still further object of the present invention is directed to a method for reheating of individual ovens after shutdown for non recovery coke oven wherein production of coke during oven reheating is achieved as an added benefit.
A still further object of the present invention is directed to a method for reheating of individual ovens after shutdown for non recovery coke oven wherein after initial isolation and sealing and keeping the individual oven airtight for predetermined time duration, specially compacted coal cake is charged and then controlled heating is carried out with control on primary air and oven draft to achieve desired/targeted crown and under flue temperature in successive steps in order to minimize the oven normalizing time.
SUMMARY OF THE INVENTION
Thus according to the basic aspect of the present invention there is provided a method for reheating of individual ovens after shut down/repair for non-recovery coke oven comprising:
a) sealing and maintaining the oven airtight for atleast 72 hours (3 days);
b) providing specially compacted coal cake for charging; and
c) subjecting the compacted coal cake to heating such as to normalize the oven by about 96 hours (4 days).
A further aspect of the present invention is directed to a method for reheating of individual ovens wherein the step of sealing and maintaining the oven airtight comprises
(i) door and primary air window sealing;
(ii) isolating the oven from the battery by individual damper isolation valve and maintained minimum draft for the particular oven;and
(iii) keeping the oven airtight for 72 hrs (3 days).
A still further aspect of the present invention is directed to said method for reheating of individual ovens wherein the said step of providing compacted coal cake for reheating of the oven comprises

(i) charging the coal cake of about 24 tons with moisture of about 10% and (ii) carrying out the cake Compaction in two layers, with 10 tons each and lastly 4 tons of loose layers.
According to yet another aspect of the present invention directed to said method for reheating of individual ovens wherein the step of subjecting the compacted coal cake to heating such as to normalize the oven by about 96 hours (4 days) comprises carrying out the heating stepwise and observing to confirm oven status at each stage as per the following steps and conditions noted in the following table:

Steps Action Hours
after
charging Primary Air (P/A) opening (Pusher side,
Quenching side) Draft, (-mm of water
column) Things to be checked to
understand the status of the
oven (by physical
observation) Temperature Target (°C)

From
(hour) To
(hour)


Crown Under Flue
1 0 6 (Full Closed, Full Closed) Min After Charging up to 6 hrs
P/A is (Full Closed, Full Closed) from both the sides 400 325
2 6 8 (Full Open, 1/4 Open) Min At 6 hrs Brick plug of the
P/A opening has to be
removed 400 325
3 8 12 (Full Open, 1/4 Open) Min Through out the cake bed is
red hot and flames are
started to ignite 400-435 325-350
4 12 28 (Full Open 1/2/ Open) 4 Oven readiness will be medium flames 440-495 355-395
5 28 36 (Full Open, V2 Open) 5 Oven readiness will be high flames 500-575 400-455
6 36 48 (Va Open, V2 Open) 6 Oven readiness will be high flames 580-675 460-500
7 48 60 (V2 Open, VA Open) 7 Oven readiness will be high flames 680-725 510-555
8 60 72 (VA Open, 1/4 Open) 8 Oven readiness will be medium flames 730-780 560-600
9 72 80 (1/4 Open, Full Close) 9 Oven readiness will be minimum flames 785-850 605-655
10 SO 96 {V4 Open, Full Close) 6 Oven readiness will be light flames 855-900 660-700

A still further aspect of the present invention is directed to a method for reheating of individual ovens wherein the oven attains the normalization temperature of 900°C in total of about 7days after repair.
According to yet another aspect of the present invention directed to said method for reheating of individual ovens wherein the normalization of the oven is achieved free of any external heat source.
The present invention and its objectives and advantages are described in greater details with reference to following non limiting illustrative drawing and example.
BRIEF DESCRIPTION OF ACCOMPANYING FIGURE
Figure 1: is the graphical plot of the variable parameters e.g. crown temperature (CR), under flue temperature (UF) and the draft (DF) during reheating of shutdown oven after repair plotted against time in no. of hours taking zero hour as the charging time.
DETAILED DESCRIPTION OF THE INVENTION WITH REFERENCE TO FIGURE AND EXAMPLE
The present invention is directed to providing a method for reheating of individual non recovery coke oven after repair/shutdown, with reduced time for normalizing without using any external heat source favoring uniform heating in a simple, safe and cost effective manner.
To achieve the desired objective, a standardized reheating method for the individual shutdown oven is developed for non recovery type coke oven wherein the procedure comprising three stages to implement the reheating of oven after repair. The reheating procedure shall be better illustrated with the help of following Example.

EXAMPLE I:
According to an exemplary embodiment for reheating of individual oven of non recovery coke oven, following stages are implemented:
1. Before charging of coal cake:
During this stage following activities are undertaken:
(i) Door and primary air window of individual oven are sealed.
(ii) Oven is isolated from the corresponding battery by means of individual damper
isolation valve and minimum draft is maintained for the particular oven.
(iii) Oven is kept in air-tight condition for 72hours (3 days).
Thus in this stage the required temperature for coal charging at 400°C is attained within 72 hrs or 3 days time.
2. Making special coal cake to be charged:
(i) The coal cake of 24 tons with moisture content of 10% is charged.
(ii) The cake compaction is done in two layers of lOtons each and finally 4 tons of
loose coal layers.
3. After charging of coat cake:
(i)The specially compacted coal cake as obtained from previous stage is charged
inside the coke oven;
(ii) Process parameter like the primary air and draft pressure in mm of water column
is continuously monitored in steps;
(iii) The target temperature and oven status is achieved in each step and then next
step follows other wise conditions to be held for the particular step.
(iv) The oven is normalized in 96 hours or 4 days by the standardized reheating as
described above.

The newly developed standard method of reheating of individual shut down oven for non-recovery coke oven after coal cake charging, the oven status as well as the target temperature, corresponding to each step with specified time duration in hours is illustrated in the following Table I.
TABLE I:

Steps Action Hours after
charging Primary Air (P/A) opening (Pusher side,
Quenching side) Draft, (-mm of
water column) Things to be checked to
understand the status of the
oven (by physical
observation) Temperature Target
(QC)

From (hour) To (hour)


Crown Under Flue
1 0 6 (Full Closed, Full Closed) Min After Charging up to 6 hrs
P/A is (Full Closed, Full Closed) from both the sides 400 325
2 6 8 (Full Open, VA Open) Min At 6 hrs Brick, plug of the
P/A opening has to be
removed 400 325
3 8 12 (Full Open, 1/4 Open) Min Through out the coal cake
bed is red hot and flames
are started to ignite 400-435 325-350
4 12 28 (Full Open, 1/2 Open) 4 Oven readiness is medium flames 440-495 355-395
5 28 36 (Full Open, 1/2 Open) 5 Oven readiness is high flames 500-575 400-455
6 36 48 (1/2 Open, 1/2 Open) 6 Oven readiness is high flames 580-675 460-500
7 48 60 (V2 Open, VA Open) 7 Oven readiness is high flames 680-725 510-555
8 60 72 (1/4 Open, VA Open) 8 Oven readiness is medium flames 730-780 560-600
9 72 80 (VA Open, Full Close) 9 Oven readiness is minimum flames 785-850 605-655
10 80 96 (1/4 Open, Full Close) 6 Oven readiness is light flames 855-900 660-700
Thus the total time required to normalize the oven after shutdown/repair is (3+4=) 7 days,

Reference is now invited to the accompanying Figure 1 that shows the crown temperature(CR) under flame temperature (UF) and the draft(DF) of the individual shut down oven when subjected to the standard heating procedure as described above and it is observed that it takes only (3 days + 4 days=) 7days to reach oven normalized temperature of 900°C. In the above graph zero hour is taken as the charging time of the coal cake in the oven after initial isolation and sealing airtight for 72 hours. Thereafter, by adjusting and controlling process parameters e.g. the primary air and the draft, oven temperature rises to the desired level in steps by monitoring the oven status according to the steps shown in Table I above.
It is thus possible by way of the present invention to providing a method for reheating of individual coke oven after shutdown/repair with reduced time for normalizing by isolation, sealing and keeping the oven airtight for predetermined time and thereafter charging specially compacted coal cake inside oven, followed by controlled heating by controlling the primary air and the draft to thereby reaching the oven normalized temperature within reasonably shorter period of time compared to conventional reheating of oven using external heat source. The method of reheating of the non recovery coke oven according to the invention is thus simple, fast, safe and economic favoring wide scale application and use in coke oven batteries in steel plant with improved productivity.

WE CLAIM:
1. A method for reheating of individual ovens after shut down for non-recovery coke
oven comprising:
d) sealing and maintaining the oven airtight for atleast 72 hours (3 days);
e) providing compacted coal cake for reheating of the oven; and
f) subjecting the compacted coal cake to heating such as to normalize the oven by about 96 hours (4 days).
2. A method for reheating of individual ovens as claimed in claim 1 wherein the step
of sealing and maintaining the oven airtight comprises
(i) door and primary air window sealing;
(ii) isolating the oven from the battery by individual damper isolation valve and maintained minimum draft for the particular oven; and (iii) keeping the oven airtight for 72 hrs (3 days).
3. A method for reheating of individual ovens as claimed in anyone of claims 1 or 2 wherein the said step of providing compacted coal cake for reheating of the oven comprises (i) charging the coal cake for about 24 tons with moisture of about 10% and (ii) carrying out the cake Compaction in two layers, with 10 tons each and lastly 4 tons of loose layers.
4. A method for reheating of individual ovens as claimed in anyone of claims 1 to 3 wherein the step of subjecting the compacted coal cake to heating such as to normalize the oven by about 96hours (4 days) comprises carrying out the heating stepwise and observing to confirm oven status at each stage as per the following steps and conditions noted in the following table:


5. A method for reheating of individual ovens as claimed in anyone of claims 1 to 4 wherein the oven attains the normalization temperature of 900°C in total (3+4=) 7days after shutdown/repair.
6. A method for reheating of individual ovens as claimed in anyone of claims 1 to 5 wherein the normalization of the oven is achieved free of any external heat source.
7. A method for reheating of individual ovens after shut down for non-recovery coke oven substantially as herein described and illustrated with reference to the accompanying examples.