THE YEAR-BOOK OF THE COKE OVEN - Coke Oven Managers ...

Journey of Improvements in Beehive Coke Conversion for Better Quality
of Coke for Blast Furnaces
Dhirendra Prasad, P. C. Choudhary & Sandip Bhattacharya
1. Introduction
Tata Steel, Jamshedpur, India
Steel industry is cyclic in nature and demand for steel fluctuates according to the
economic scenario of country. In the course of high demand of steel, the iron
making capacity of Tata Steel, India was increased in several expansions
projects completed during year 2003, 2005 and 2008.
Enhanced capacity of blast furnaces at Tata Steel, India created the requirements
of additional metallurgical coke of 1 million tons per annum which was beyond
the coke making capacity of around 2.3 million tons per annum existed during
year 2003-04. The requirement of extra coke was further augmented due to
shutting down of some of the coke ovens at Tata Steel, India for rebuilding and
repairing. The requirement of additional coke was temporarily fulfilled by either
import or by coke conversion through beehive ovens (outsourcing). During
2003-06, Tata Steel had sourced 15000 to 20000 tons per month of metallurgical
coke through coke conversion route which further got increased to 35000 to
40000 tons per month (during 2007-08). Beehive coke ovens are situated in
Dhanbad and Ramgarh district in the state of Jharkhand, India. Tata Steel
supplied coals and received coke after conversion from various beehive coke
ovens through conversion agents at predetermined rate.
Coke supplied during initial period of coke conversion was not meeting the
quality requirements of blast furnaces. It created confusion and poor confidence
of procurement of coke through coke conversion route. A series of affirmative
actions were initiated to achieve the required levels of quality in converted
beehive coke. The present paper describes the journey of coke conversion from
bad to good period and various improvement initiatives undertaken to achieve
target levels of coke quality during the last one decade.
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2. Description of Beehive Coke Ovens
2.1 Basic design: Beehive coke ovens are very small in capacity. A battery
usually consists of 12 - 16 ovens and is arranged symmetrically back to back
with 6 - 8 ovens on one side. Normally the capacity of each oven varies from 5
to 6.5 tons of coal charge. The capacity of beehive ovens varies from about
1200 to 1600 tons coke per month per battery. A beehive oven generally
consists of 2 batteries and in some cases more than 2 batteries. The structure is
not exactly like a beehive but a rectangular box having an arched rooftop (figure
1). The front has a door, which is fixed between channels. The oven bricks are
made out of silica and there are no supporting members as in normal coke plant.
There are charging holes form the top.
Fig 1: Beehive Coke Oven
2.2 Heating system: There is no provision for external heating and it gets
heated due to burning of volatile matter in the coal. The heat content of the
burnt gases is utilized for heating the sole & arched rooftop. The sole is heated
from bottom because of burnt hot gases pass below it. The hot burnt gases flow
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from top of the charge to two flues, located at the bottom of the sole and then
through the chimney. Some oven pairs have individual chimneys while most of
them have common chimney. There are coarse & fine control devices for
controlling the draft in these chimneys.
2.3 Coal Crushing & Charging: The top of the battery has rail tracks running
along the length of the battery. Manually pushed trolleys are used for transfer &
charging of coal into the ovens. Each trolley has a capacity of about 1 ton. The
coal is crushed in small crushers and loaded into these trolleys. Normally 5-6
trolleys filled with coal is collected on the top near the charging hole before
charging is done.
2.4 Coke Pushing: The front door is lifted using a winch system to open the
oven. The hot coke is pulled out from the oven using a plough type of iron
structure. Manual scraping is done to remove remaining portion of coke from
inside the oven. The front door is lowered to close the oven. Quenching is done
manually using water hosepipe on the platform where the hot coke is pulled out.
2.5 Advantages & Disadvantages in Making Coke through Beehive Ovens:
Advantages:
1) Good quality, strong & blocky coke.
2) Low capital & operating cost.
3) Coke production is not connected with the availability of a market for byproducts.
4) Environmental friendly as it is emission free, no handling of effluents etc.
Hence creates no pollution issues.
Disadvantages:
1) No recovery of byproducts.
2) Lower coke yield due to partial combustion.
3) Production of quality coke only from good coking coals (blend of inferior
coal can't be used).
4) Lack of flexibility in operation.
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2.6 Specifications of Coals Supply:
Specification of coal supplied by Tata Steel for conversion is shown in table 1.
Coal Source Ash V.M. Moisture Coal in Blend
Imported 10 % max. 23.5 %
max.
8 % max (may
go up to 10%
during
monsoon)
50 % or (Semi
Soft - 30 %,
Jellinbah- 20
%)
Captive
(Jamadoba )
17 % max. 24 % max. 9.5 % max
(may go up to
10% during
monsoon)
50 %
Table 1: Specification of coal supplied by Tata Steel for conversion
3. Challenges
Problems were faced with respect to coke quality during initial stage of
conversion of coal to coke through beehive oven route. The CSR of coke which
is one of the vital parameters for coke quality was found varying significantly
from ovens to ovens and even within a beehive oven battery. Also, the CSR
values were low and varying in the range of 35-45. Blast furnace operators
refused to charge such low CSR coke in to the blast furnaces. Therefore,
challenge was taken to improve the CSR of beehive coke to above 60 as well as
its consistency.
As per the agreement between Tata Steel and conversion agent, maximum
allowed moisture in converted beehive coke received at Jamshedpur works was
10%. But, actual beehive coke moisture received at Jamshedpur works was
15.1% (average). The undersize (-10 mm) in coke was approximately 3.55%.
High moisture in beehive coke resulted in loss in coke yield, increased
transportation cost and finally caused increase in blast furnace fuel rate. High
fines in beehive coke resulted in coke yield loss and increased cost of
transportation. Hence, challenge was taken to reduce beehive coke moisture by
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5% and fines (undersize) by 2% by improvements in processes for coke
quenching and handling at beehive coke ovens.
4. Analysis Phase
A detailed cause and effect diagram (figure - 2) was prepared for a root-cause
analysis of possible reasons which could lead to poor quality as well as
inconsistency in the quality of coke from the beehive coke ovens.
Coal
Quality
Operating
Conditions
Dispatch &
receiving
High Moisture
High gap between pushing & charging
Lack of control of air supply
Deterioration on quality while loading
Variability in input coal quality & Mix-ups
Mode of transport
Poor coking property
Inadequate water for quenching
Delay/early coke pushing
Deterioration on quality while travel
Improper crushing fineness
No. of loading & receiving points
Supervision
Monitoring
Analysis & Improvement
Lack of storage facility
Poor oven design conditions
Inadequate control on leakage
Inadequate control on air supply
Improper blending
Lack of instrumentation
Lack of coke making knowledge
Lack of blending facility
Improper insulation
Lack of knowledge sharing
Long quenching time
Non-availability of timely
technical information
Pilferage
Sample collection & Preparation
Lack of knowledge on
coke quality parameters
Lack of awareness
training to operators
Large no. of stages
Sampling & quality control
Standard Procedures
Large no. of samples
Poor Coke
Quality
&
Inconsistency
Lack of instrumentation & testing facilities
Process
Control
Oven/Process
Design
Knowledge
& Training
Inspection
& Testing
Fig. 2: Cause and Effect Diagram for poor quality of Coke from
Beehive Coke Ovens.
Most of the beehive ovens were of basic design and had no instrumentation for
process control. One of major problems noticed that persons deployed as oven
operators were unskilled and not aware of fundamentals of metallurgical coke
making. Moreover, there was no penalty clause existed in commercial terms and
conditions with conversion agents to ensure supply of good quality and quantity
of coke from beehive ovens to Jamshedpur works.
After thorough analysis of previous coke conversion processes, it was found that
documented system was not available for coal management, carbonization and
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coke handling processes with beehive ovens operators. Written procedures were
also not found for quality assurance activities like sampling, sample preparation
and analysis of coal and coke. With respect to coal handling system, it was
observed that no distinct demarcation was being maintained between various
received coals (Semi Soft / Jamadoba/ HCC (imported hard coking coal) / WB
(west bokaro) and blended coal) in the premises of beehive ovens. Different
types of coal had no nameplates or display board for proper identification.
Various individual coals were dumped haphazardly near the blended coal. Coals
were stored in open areas which resulted in moisture gain during rains. It was
also observed that process was not followed for coal usage based on the
principle of “first in, first out” (FIFO) to avoid usage of weathered coal. Latest
received coals were being utilized first. Crushing fineness of blended coals was
inadequate. Stock management of various coals was poor.
Assessment of old practices of coke quenching and handling system at beehive
coke ovens was carried out. It was observed that the time elapsed between coke
pushing and coal charging was very high and varying. The heat condition of the
battery was poor which resulted in green coke pushing (un-carbonized / partially
carbonized coke). This might led to the weakening of coke and generation of
fines. Leakages through the door were noticed. In some of the ovens, whole
bricks from the door were collapsed before coke pushing. Poor sealing of doors
and opening of oven top covers was found in a number of ovens. Cracks on
walls were also observed. Carbonization time was not being adjusted according
to the coal moisture to get good quality of coke. After pushing from ovens, coke
was not quenched immediately due to unpreparedness of quenching system
which resulted in coke burning. Lots of green pushing was observed because of
poor process control.
It was observed that a single big hosepipe was being utilized for coke quenching
with water. This led to requirement of more volume of water for completing the
coke quenching because single stream of water could not cover entire hot coke
pile at a time. This resulted in high moisture (15-17%) in dispatched coke. High
moisture in coke resulted in sticking of fines on lump coke. It was also noticed
that for coke quenching, uncontrolled and continuous single stage quenching
operation was practiced. Quenching was being done continuously for 15-25
minutes duration. Also, the quenching of coke was practiced without dispersing
the red hot coke pile after the pushing. This caused inadequate quenching of hot
coke inside the pile and restricted removal of fines. Velocity of water in single
hosepipe was not sufficient to flush out the fines. Other observations were made
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like improper cleaning of platform and high tonnages of left out platform ash at
each of the beehive ovens. This caused sticking of fines on to lump coke.
Segregation of coke was not being done to separate out bad coke from good
coke after the completion of quenching although there were evidences of green
coke pushing. High percentages of moisture and fines in dispatched beehive
coke were due to inappropriate process of quenching and coke handling
operations at beehive coke oven.
Based on the root-cause analysis, requirement was felt for implementations of
beehive coke oven management systems for following purposes:
1. Improvements in coal receiving and handling system to
a. Avoid use of weathered coal.
b. Prevent mixing of various coals in a beehive oven.
c. Improve coal crushing fineness.
d. Ensure proper blending of coal as decided by Tata Steel.
2. Improvements in carbonization operations and coke handling system
to
a. Adjust carbonization time depending upon coal moisture to
get proper coke.
b. Improve heat condition of the battery.
c. Avoid green pushing (un-carbonized / partially carbonized
coal).
d. Proper sealing of doors and lifting of openings on oven top.
e. Avert delay in quenching of coke which may cause coke
burning.
f. Sorting of good quality coke for dispatch.
5. Improvement Phase
One of the major observations made during the analysis phase was lack of
proper information about the various operating conditions of the ovens.
Therefore, a format was designed and implemented to systematically capture
data for further analysis and improvements. Table 2 presents the format and
some typical data of beehive oven operation during initial period.
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Sl.
No.
Oven
No.
Wt. Of
Coal
Charge
( MT )
Charging
( A )
Pushing ( B )
Date Time Date Time
Carbon
-ization
(Hours)
Time
(B-A)
Next Charging
( C )
Date
Time
Time
between
pushing
to next
charging
(Hours),
(C-B)
Cycle
time ,
(Hours)
(C-A)
Empty
oven
temp.
prior to
charging
, ( 0 C)
Carbon
-ization
Temp.
( 0 C)
Quenching
time,
(Min.)
1 25 5.500 16.9.03 18.30 18.9.03 6.00 35.30 18.9.03 8.45 2.45 38.15 640ºC 935ºC 50
2 25 5.500 18.9.03 8.45 19.9.03 17.00 32.15 19.9.03 19.15 2.15 34.30 650ºC 943ºC 40
3 25 5.500 19.9.03 19.15 21.9.03 2.30 31.15 21.9.03 5.00 2.30 33.45 640ºC 940ºC 45
4 27 5.500 15.9.03 24.00 17.9.03 10.45 34.45 17.9.03 12.45 2.00 35.45 660ºC 960ºC 55
5 27 5.500 17.9.03 12.45 18.9.03 23.30 34.45 19.9.03 1.40 2.10 36.55 630ºC 950ºC 48
6 27 5.500 19.9.03 1.40 21.9.03 12.40 35.00 21.9.03 14.25 1.45 36.45 680ºC 975ºC 40
Table 2: Some typical data of beehive coke oven operation during initial period
Processes for coal receiving, storing, crushing, blending and charging were
developed and implemented across all beehive ovens at Dhanbad and Ramgarh
area. Quality assurance systems for coal handling, carbonization operation and
coke handling were developed and implemented in all beehive ovens. Written
procedures were made for quality assurance activities for incoming raw
materials (coal), in process materials (coal/coke) and product coke. Series of
training sessions were organized by Tata Steel experts for all staffs of beehive
ovens, conversion agency and third party quality assurance (QA) agency.
Frequent audits were conducted by Tata Steel personnel on various activities
starting from coal dispatch to coke received. Flow chart of various activities
under new quality assurance system starting from Tata Steel washeries to
beehive ovens for coke conversion and coke dispatch from beehive ovens to
Jamadoba siding and Jamshedpur works of Tata Steel India are represented in
figures 3 - 5.
Temporary/permanent sheds were erected for coal & coke storage to prevent
moisture gain during rains in all beehive ovens. For proper identification, coals
received from different sources were stock-piled source-wise with different
geometrical shapes and proper identification marks. Demarcation between
individual coals and blended coal were maintained. Individual coals were not
allowed to be stored nearer to blended coal to avoid mix-ups. The quantities of
crushed coal for blending were ensured according to the capacity of oven before
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charging. Crushing fineness of coal was improved by proper preventive
maintenance of crusher and screener (used for sieving the coal). The blending
ratio of different coals was maintained as per weight volume assessment on the
advice of Tata Steel experts.
The time gap between coke pushing & coal charging was brought down to 30-
40 minutes from 150 minutes by ensuring preparedness of resources like
availability of power for pulling out the coke, readiness of quenching system,
ensuring crushed coal for next charging etc. Heat condition of the battery was
improved by implementation of new process monitoring and control system.
Sealing of doors and openings on the oven top were ensured. Cracks on walls
were repaired. In the case of oven door collapse, use of castable was suggested
in place of bricks. More focus was given on maintenance and proper sealing of
oven doors. Adjustment of carbonization time was started depending upon coal
moisture to get proper coke. Operators were asked to observe the performance
of oven during carbonization while keeping secondary port holes (including side
ovens) open.
Oven temperature measurement was started on routine basis for better process
monitoring and control. Ovens operators were advised to maintain proper
records of various process parameters. Green pushing was eliminated by proper
process control of carbonization operation. It was ensured that the oven platform
(wharf) is kept free from foreign materials like oven clay, brick pieces, platform
ash / dust etc. before starting of discharging of oven. Required amount of
crushed coal was kept ready for next feed before the coke pushing operation. It
was sometimes found that some coke materials were still remained inside the
oven after the dragging of hot coke from the oven, this material was taken out
carefully and stocked separately with proper identification marks.
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Jamadoba washery Bheltand washery West Bokaro washery
Quantity check & physical
observation
Process of coal
loading
Quality check
Physical verification of empty
truck, tarpaulin, Wooden Plate
& rope
Truck entry for coal
loading
---
Checking of issue slip given by
conversion agent
Issue of loading slip ---
* Checking of weighment for
tare weight of truck
Truck weighment
(Tare)
Maintaining register and report
format of weighment truck and
reporting to concerned
authorities/QA agency
Checking by QA agency,
issued slip, gross & tare weight
of coal loaded truck & sample
collection during loading
* Coal loading into
the truck/ weighing
(Gross)
Sample preparation for analysis
of moisture, ash & V.M.
Checking of truck cover with
tarpaulin & proper sealing
Truck desptch to
Beehive coke ovens
Maintaining register and report
format in remarks column
Coal receipts to beehive ovens (Dhanbad
& Ramgarh area)
Remarks :- ( * ) Representative of Transporter to be present during the time of truck weighment (Gross & Tare) of coal & coke.
Fig. 3: Activities at Washeries of Tata Steel Ltd.
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Coal receipts at beehive ovens
(Dhanbad & Ramgarh area)
Quantity check & physical observation
Process of coal
receipt & dispatch to
beehive ovens
Quality check (Moisture, Ash & V.M.)
Physical verification of coal loaded trucks
and checking of issue/ dispatch slip,
tarpaulin, rope, wooden plates & sealing
Coal receipts at
beehive ovens and
coke dispatch from
beehive ovens
---
* Checking of weighment for gross & tare
weight of coal loaded trucks. Calibration
of beehive oven weighbridge checked
Truck weighment
Maintaining register and report format of
weighment truck and reporting to
concerned authorities/QA agency
Stock measurement of coal every month
end, physical verification of coal on day to
day basis
Stocking of coal
Source-wise sample collection during coal
unloading & sample preparation for
moisture, ash & V.M.
Calibration of pay loader bucket and
maintaining the number of buckets of
blended coal
Calibration of oven trolley, weighment of
charging coal per trolley checked, sample
collection in three shifts & sample
preparation for quality
Supervision for low quenching, maintaining
coking periods, checking of oven leakage
& sample collection in three shifts
Supervision for coke sizing at platform /
stock yard, segregating the under size
coke
Supervision for coke loading from
stockyard by 40mm fork shovel, checking
the issue memo & sample collection during
coke loading
Checking of truck cover with tarpaulin &
proper sealing
Supervision of coal
blending
Coal charging
Coke production
Sizing of coke
Coke loading
Truck dispatch
Maintaining register & blend format with
signature of beehive oven representatives,
conversion agent and QA agency
Maintaining register with oven wise coal
charged, maintaining charging format,
reporting day-wise to concerned
authority/office and analysis of ash &
V.M.
Maintaining register with oven wise coke
production, maintaining format of cooking
periods, reporting day-wise to concerned
authority/office and analysis of ash &
V.M.
Reporting of all day activities on daily
basis to offices and noted in reporting
format
Maintaining register as well as format of
loaded truck and reporting to concerned
authorities/office with daily observation.
Samples of quality part sent to Dhanbad
office for total moisture, ash & V.M.
Maintaining register and report format in
remarks column
Dispatch from beehive coke oven to Tata Steel Ltd.-Jamadoba
and Tata Steel Ltd. Works- Jamshedpur
Remarks :- ( * ) Representative of Transporter to be present during the time of truck weighment (Gross & Tare) of coal & coke.
Fig.4: Activities at Beehive Coke Ovens
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Coke receipt at Tata Steel Ltd. - Jamadoba
and Tata Steel Ltd. - Works Jamshedpur
Coke receipts at Jamadoba railway station siding (By road)
Coke receipts by road from Ramgarh & by rail from
Jamadoba Coal Processing Plant (JPCC) siding
Quantity check &
physical verification
Process
of coke
receipts
Quality check
Quantity check & physical verification
Physical verification
of loaded trucks,
checking of dispatch
memo, tarpaulin
cover, wooden plate
& rope sealing
* Weighment
checking for gross
& tare weight of
coke truck
Sample collection
during coke
unloading and size
analysis
Coke
receipts at
Jamadoba
railway
siding
Truck
weighment
Coke
trucks
unloading
at
Jamadoba
Railway
Siding
Physical verification of coke loaded trucks/wagons,
sample collection during coke unloading, size analysis
& sample preparation for quality
Maintaining registor as well as format of loaded
Maintaining register trucks/wagons and reporting to concerned
and report format of authorities/office with daily observation. Samples of
weighment truck and quality part sent to Dhanbad office for total moisture,
reporting daily basis
ash & V.M.
to concerned
authorities/office
Sample preparation
for quality and
analysis of total
moisture, ash &
V.M. at Dhanbad
office
System of Reporting
1. Daily - coal received, operation
monitoring, charing/production, coke
desptach & observation report (by Road).
Sample preparation
Physical verification
Coke
for quality and
of wagons, sample
3. Reporting of coke despatch/receipts
loaded /
analysis of total
collection during
quantity, quality & under size (-10mm),
despatched
moisture, ash &
wagon loading, size
ash% ( by Rail).
to wagons
V.M. at Dhanbad
analysis
office
4. Monthly - quantity report (GRN Sheet).
5. Monthly - quantity & quality report.
6. Abnormilities report.
7. Reporting of improved process controll.
Remarks :- ( * ) Representative of transporter to be present during the time of truck weighment (Gross & Tare) of coal & coke.
--
Quality check
2. Daily - quantity & quality report of
coal/coke despatch/receipts, charging &
production size analysis of coke
despatch/receipts and under size (-10mm),
ash % (by Road).
Fig.5: Activities at Jamadoba & Jamshedpur Siding.
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Quenching system was made ready before pushing (dragging) of coke.
Checking of water level in tank and condition monitoring of motor & pump
used for quenching was started. The reservoir containing quenching water was
cleaned periodically by the oven operators to make it free from contamination.
Pump with 10 HP motor was arranged in each beehive ovens for quenching of
hot coke mass with water. This ensured high pressure of water jet which helped
in flushing out of fines from coke lumps which generally contains high ash.
Proper preparedness helped in avoidance of delay in quenching of coke which
was causing coke burning earlier. Two hosepipes were provided in place of
single big hosepipe in all ovens. Quenching of hot coke mass was executed by
using two hosepipes. Quenching by two hosepipes helped in proper quenching
of hot coke mass simultaneously from two sides with less water. Two stage
quenching was implemented in all ovens. Total quenching time was kept at 6
minutes as against 40-50 minutes previously. In first stage coke was sprayed
with water for 3 minutes after pulling (dragging) it out from oven. Then the
partly cooled coke mass was spread out with the help of spikes. Again in second
stage, water spraying was carried out covering the entire coke mass for 2-3
minutes. Spot quenching was followed in the case of localized hot coke.
After quenching the hot coke with water, it was suggested to leave the coke
undisturbed on the platform for a period of 2-3 hours for further evaporation of
moisture. It helped in reduction of moisture in dispatched coke. Sizing of coke
lumps was conducted manually on platform or at stockyard, keeping the coke
size between +40 to -100 mm. After completion of process of sizing, the sized
coke was shifted from the platform to the stock yard by lifting it with the help of
a +40 mm forked shovel. This helped in reducing the fines in dispatched coke.
Finally sized coke loaded directly from the stockyard into the carriage by using
a + 40 mm forked shovel. The remaining materials (-40 mm coke fraction) left
at the stockyard were stored separately by lifting it with the help of plain shovel.
The size analysis of – 40 mm coke conducted on day to day basis at each
beehive oven. Subsequently, +10 mm size coke dispatched to Tata Steel
Jamshedpur works along with the sized coke (+ 40 to -100 mm).
After completion of loading, trucks used for transportation were covered with
tarpaulin and sealed with plastic seals with unique numbers and the same were
mentioned in the delivery slip/ memo. The rope used for sealing was tied with
double roll technique. This was implemented to eliminate any malpractices
during transportation of converted coke to Jamshedpur works. Truck-wise size
analysis of dispatched coke was conducted at each beehive oven before
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dispatching and was made available with the truck. Old contract with
conversion agents was modified and penalty clause was introduced for lower
CSR, higher moisture and fines in supplied beehive coke.
6. Results & Discussion
In improvement phase, several new systems were implemented which had given
positive results and helped in fulfilling the coke quality requirement of blast
furnaces. Initial period of improvements was focused on coal management and
proper process control of carbonization process which resulted in improvement
in CSR values as shown in figure 6 & 7.
Fig. 6: CSR values (individual data) of Beehive Coke from year 2003 to 2009
14

Fig. 7: CSR values (yearly average) of Beehive Coke from year 2003 to 2009
It can be observed from figures 6 & 7 that during starting period (year 2003) of
coke conversion, CSR values of beehive coke were at the levels of 35-45 with
high standard deviation. Then during year 2004, CSR values were gradually
improved and went above 60 with improvement in its standard deviation. After
that, CSR values were remained in the range of 60. During year 2007, some new
beehive ovens were introduced which resulted in some drop in CSR values.
After horizontal deployments of improvement initiatives in newly introduced
ovens, CSR values regained its original range of 60 and above. In the these
figures, standard deviation of CSR values was improved during year 2004 and
remained in the level of 3 till 2007. Afterward standard deviation has improved
in year 2008.
After achieving desired levels of CSR values, next improvement initiatives were
focused on coke quenching and handling system which resulted in reduction of
moisture and fines contents of beehive coke as depicted in figures 8 & 9.
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Fig. 8: Percentage of Moisture of Beehive Coke received before and after
implementation of Improvement Initiatives.
Fig. 9: Percentage of undersize in Beehive Coke received before and after
implementation of Improvement Initiatives.
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It can be seen from figures 8 & 9 that moisture and fines levels in beehive coke
received at Jamshedpur works were in the range of 14-16% and 3-4%
respectively before the implementation of improvement initiatives till August
2008. After implementation of various recommendations moisture and fines
levels had reduced to below 10% and 1.5% respectively. Time duration in coke
pushing to next coal charging had come down from over 150 minutes to 30-40
minutes due to readiness of coal charging arrangement. Quenching time was
reduced from over 40-50 to 6 minutes. This was primarily due to
implementation of two stage quenching technique and use of two hosepipes
simultaneously. This initiative had minimized burning of hot coke, hence, the
reduction in ash content and improvement in coke strength. Reduction in overall
cycle time had contributed significantly in maintaining a higher empty oven
temperature (gone up from 650-950 to 930-1050 o C or even more) prior to
charging. All these have contributed towards increasing the coke quality,
productivity and consistency.
7. Conclusion
Beehive coke oven management system was developed and implemented at
various beehive coke ovens batteries at Dhanbad and Ramgarh district of
Jharkhand, India which were contracted for coal to coke conversion for Tata
Steel. Significant improvements in coke quality in terms of coke CSR, moisture
and undersize have been achieved from beehive coke ovens by means of various
improvement initiatives discussed in the present paper.
The above work helped in fulfilling the blast furnace requirement from beehive
coke in terms of quality by giving more focus on process improvement, people
development and without any major investment. This has ensured the
procurement of good quality of coke through beehive coke conversion route
which is also the cheapest source available as compared to other sources like
import.
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