A COST EFFECTIVE SYSTEM FOR ADDITION OF TAR DECANTER SLUDGE IN
COAL CHARGE ON THE BELT CONVEYOR IN COKE MAKING PLANT
Field of invention
This invention relates to an improved, simple and cost effective system for addition of
tar decanter sludge with coal charge on the belt conveyor. It particularly relates to an
inexpensive on-line plough arrangement on belt conveyor for mixing of tar decanter
sludge with coal charge, before they are charged into coke oven for making of coke.
Background of the invention
In coke making process in Coke Oven (CO),coke oven gas, containing many toxic
organic compounds, is generated. This CO gas is then subjected to recover some
useful by-products. Tar Decanter Sludge (TDS) is one of the by-products of coke oven
gas, which was dumped in open field as waste material as a conventional practice for
many years. TDS is a solid hazardous waste produced as a by-product of tar separation
from flushing liquor in coke ovens. Due to increasing open-field dumping costs with
added stringent environmental regulations, now a days, dumping of the hazardous TDS
in open fields has become a difficult issue for steel industries. Hence, attention has
focused on effectively re-cycling the TDS in the manufacturing process as a resource
material instead.
Handling TDS is also a difficult issue because of its sticky and easy melting nature. In
summer days, it melts to spread the fields and pollutes the environment. The generation
of TDS at Bokaro Steel Plant is approximately 200 tons per month. Five numbers of
decanters of capacity 700 m3 each are installed to separate flushing liquor and crude
tar. The decanters are provided with hoppers of capacity around 2 tons each to receive
Tar Decanter Sludge (TDS) which is taken out by scrapper conveyor from the
decanters. TDS pots of capacity around 4 tonnes are placed beneath the hopper and
the sludge is emptied into them. The TDS pots are then lifted by a dumper and taken
out on road for disposal at the open field at extreme end of plant boundary.
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Almost all of the existing systems for addition of tar decanter sludge with coal charge
require huge, complicated and costly equipment with large open area near the coke
oven plant. But at Bokaro Steel Plant, availability of necessary space for a new
installation of the conventional tar decanter sludge addition system was not there. Over
and the above space constraint, requirement of capital cost investment was high.
Hence, a necessity was felt to develop a simple and cost effective system for addition of
tar decanter sludge with coal charge on a belt conveyor at Bokaro Steel Plant. It would
also help to eliminate the earlier practice of dumping the hazardous TDS in open fields
andalso to utilize the useful carbon value of the TDS in making of useful coke.
Description of the prior arts
The following statements describe the prior arts for the process for adding tar-decanter
sludge with coke oven feed:
1. Tar decanter sludge was directly added to the coal, after or while it is being
charged in the coke oven, without pre-mixing of sludge and coal. In these cases
the tar decanter sludge is added at the top of the coal bed after the entire charge is
added to the coke oven or added at the bottom, before the coal is charged to the
coke oven. And in some cases the sludge is added intermittently during charging
the coke oven with coal interferes during the charging operation.
The above all options of adding tar decanter sludge with coal charge without any
pre-mixing of the materials result in unsatisfactory process of making coke, due to
non- uniformity of distributed coal-sludge mixture in coke oven and hence carbon
value of the sludge could not be utilized efficiently in the coking operation.This nonuniformity
of mixture of coal and sludge has also led to deterioration of coke oven
inner walls.
2. In another prior art, premixing of sludge andcoal was achieved by a mixing
operation in a proper mixer and uniform particle sizing was achieved in a crushing
mill. Even,though this art of addition of sludge in coal ensures proper mixing of
sludge with coal, but the requirement of these huge mechanical equipments, such
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as hammer mill, spiral mixer etc., makes the sludge addition system, more costly
and complex.In addition to the increased cost of the system, installation of these
mechanical equipments also requires large spaces near the coke oven site. Even
though this art ensures uniform mixture of sludge and coal, the input sized coal
charge is required to be subjected to un-necessary re-crushing along with the
bigger sized sludge agglomerates in the hammer mill, causing generation of coal
charge fines. This finer coal charge in coke oven deteriorates the quality of coke
produced.
3. Taken into consideration of both draw-backs of the above prior inventions and
space &cost limitations in Bokaro steel Plant, an improved method and a system
for addition of sludge in coal charge, which is simple and cost effective, has been
successfully designed, developed and installedtherein which has also recently
been published in “Recycling of Tar Decanter Sludge through the Addition of
Coke Oven Batteries in Charge Coal Feed” by Y. Singh, S. T. Selvan, S. K.
Ghosh, and A. K. P. Singh in ( Sustainable development and Planning IV, Vol.2) -
WIT Transactions on Ecology and the Environment –Vol 120, Pages 895-900
(2009)
In the above referred prior art at serial number 3 there is a reference of an use of a
plough arrangement on the belt conveyor for premixing of sludge with coal charge
before the mixture is charged into the coke oven,but the details of which was not
disclosed. In order to get a thorough and intimate mixture of the tar decanter sludge with
coal for better efficiency there is a need for the development of an appropriate design
and structure of the same.
Objects of the invention
The object of the invention is to develop an appropriate design and structure of the
plough arrangement on the belt conveyor for more efficient premixing of tar decanter
sludge with coal charge before the mixture is charged into the coke oven in order to
provide a more efficient premixing system for the enhancing the ultimate efficiency in
producing coke.
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Another object of the invention is to provide for a method for efficient premixing of tar
decanter sludge with coal using the said plough arrangement.
Brief description of the accompanying drawings
Figure1 shows the process flow diagram indicating the material flow for addition of tar
decanter sludge with coal.
Figure 2 shows the arrangement of ploughs on top of the Y20 belt conveyor with
different shapes and patterns of the invention installed at the sinter plant in Bokaro Steel
Plant.
Description of the Invention
According to this invention there is provided a simple and cost effective system for
premixing of tar decanter sludge with coal before they are charged into coke making
oven by direct addition of the sludge on to a moving belt conveyor carrying coal wherein
a plough arrangement on the top of the belt conveyor is provided for in-situ thorough
mixing of the sludge with the coal charge on the belt conveyor characterised in that the
plough arrangement is made of light polymer liner plates of different sizes and shapes
at different locations on the belt conveyor.
The polymer liner plates of the invention are fabricated in different patterns and
positioned on top of the belt conveyor by hanging from the top in a staggered manner.
All the plough plates are firmly hanged from the top of the belt conveyor and they
protrude into the coal charge of the belt conveyor. The plough plates are provided
before and after the charging points of the tar decanter sludge.The plough plates (
indicated by numeral 1 of Figure 2 of the accompanying drawings) is shaped in inverted
“V” and is located just before the discharge point of the screw conveyor. Immediately
after the charging of the tar decanter sludge on top of the coal charge and at the middle
of the conveyor two nos. of plough plates (indicated by numeral 2 in the Fig. 2) at both
extreme sides of the belt conveyor are positioned in such a way that the diverted coal
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charge sideways is converged back into the middle line of the belt conveyor. In the said
arrangement of the invention, just after the plough plates (2), three nos. of plough plates
(3) are positioned firmly across the width of the belt conveyor. Next to the above plates
four nos. of plough plates (4) are positioned at staggered way covering across the width
of the belt conveyor for re-digging and mixing of the charges. At the end again two nos.
of plough plates (5) are positioned suitably for re-converging of sludge and coal mixture
towards centre of the belt conveyor. All along the total distance of charging and mixing
area of the belt conveyor, suitable polymer made skirts are provided at both sides of the
belt conveyor to prevent spillage of material on the sides of the belt conveyor.
The invention includes a method for in-situ premixing of tar decanter sludge with coal
before they are charged in coke making plant by direct addition of the sludge on to a
moving belt conveyor carrying coal wherein the plough arrangement provided according
to this invention is used. Further, the feed rate tar decanter sludge in the belt conveyor
is directly controlled by speed variation of the screw conveyor and the feed rate is
varied according to the coal charge transportation rate by the belt conveyor. The steam
traced screw conveyor directly charges the tar decanter sludge from the sludge bunker
on the running belt conveyor.
Stating in details,the system mainly consists of a steam traced storage hopper, steam
traced screw conveyor and mono-rail hoists. No other major mechanical equipment is
used in this system. The storage hopper is positioned at a height through suitable
structural supports. The TDS pots with tar decanter sludge, brought from the tar
decanters,are lifted from ground level by the main-hoists up to top of the storage hopper
and then tilted by the auxiliary hoist at about 1400 to empty the sludge in to the storage
hopper. The inlet opening of the hopper is fully covered with steam pipes’ grid to
prevent the bigger agglomerated sludge enter in to the hopper. If any bigger sludge
lumps in the charge, they are trapped on the top of the steam pipes’ grids and get
slowly melted by steam through the grid pipes and hencefall into the hopper. From the
bottom opening of hopper, the sludge is then transported through the steam traced
screw conveyor and charged on to the existing belt conveyor, which carries coal charge
to the coke oven. The absence of all major mechanical equipments in this improved
system makes the system simpler and more cost effective.
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Polymer liner platesof different sizes are fabricated in different patterns and positioned
on top of the belt conveyor by hanging from the top in a staggered manner. The suitably
arranged polymer plates based plough patterns helps to mix the sludge with coal charge
at in-situ condition, while the belt conveyor transportsthe material to the coke oven.
While uses for most of the coal tar by-products have been found, the coal tar sludge still
remains as waste products. Tar decanter sludge (TDS) is classified as a hazardous
waste that must be recycled within the coke oven plant in an appropriate manner or to
be disposed-off to an approved open and secured land. In Bokaro Steel Plant, it was the
earlier practice of disposing the TDS in open remote landfills. At later stage, the
disposal of hazardous tar sludge in open field has become difficult issue as it was
coming under close scrutiny by stringent norms of various environmental regulatory
agencies. Under this compulsion, re-cycling of the tar decanter sludge in coke making
process was found only option. By this, the carbon value of the tar sludge is also being
utilized in useful coke making process.
However, all the established methods/techniques for addition of tar decanter sludge in
coal charge in coke oven were found unsuitable to Bokaro Steel Plant conditions. The
huge requirement of cost and space for implementation has made the earlier methods
for addition of tar decanter sludge in coal charge as unfavorable to Bokaro Steel Plant.
Other site restrictions exits at Bokaro Steel Plant, have added up to the unfavorable
conditions. This situation has helped to develop this new invention, the improvedmethod
for addition of tar decanter sludge in coal charge, which is simple in design, that doesn’t
require much space and also inexpensive due to absence of major equipments in the
system.
In this invention,tar decanter sludge (TDS) from the tar decanters is collected in sludge
pots and charged directly in to the steam traced,storage bunker by the mono-rail hoists.
The top opening of the storage hopper is provided with steam pipes’ grid. The bigger
sized sludge, trapped on the surface of steam traced pipe grid gets melted by heat and
could enters in to the hopper. Steam traced screw feeder of suitable capacity, provided
below the hopper, transports the sludge from the hopper to the exiting belt conveyor,
which carries coal charge to the coke oven. A slide gate provided between the bottom of
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the hopper and entry chute of the screw feeder, along with screw speed of the screw
feeder, controls the feed rate of the sludge to the belt conveyor. In this invention, the
requirement of major mechanical equipments for charging of TDS and heating
arrangement such as hammer mills, electrical heaters etc., are eliminated and hence
made this system as inexpensive for both installation and maintenance.
After the addition of the TDS on top of the coal charge on the belt conveyor, the sludge
and coal charge are mixed through suitably positioned plough arrangements.
Throughout the length of this region, where sludge addition and plough for mixing of
sludge and coal happens, suitably designed skirts on both sides of the belt are provided
to prevent material spillage on the sides. The load cell provided below the belt conveyor
measures the feed rate of coal charge and controls the speed of the screw feeder to
regulate the feed rate of the tar decanter sludge from the storage bunker. In this
invention, major and complicated equipments, necessary for pre-mixing of sludge and
coal such as mixers are eliminated by simply designed in-situ ploughs.
Describing Figure 1 of the accompanying drawings the Tar Decanter Sludge (TDS) from
the tar decanter is collected in the main hopper, located near the tar decanters. From
the bottom charging main hoppers, tar decanter sludge is collected in portable TDS pots
(1). Each TDS pot is provided with suitable lifting hooks for lifting and a tilting hook
facilitating easy discharging of TDS out of the pot. The filled up TDS pots are
transported from tar decanter site on a dumper vehicle to the site at TDS addition
system in coke oven. The TDS pots are unloaded from the dumper as early as possible;
so that the dumper is relieved for it’s another trip. The filled up TDS pot is lifted from
ground to suitable height by means of main hoist. After lifting the TDS pot to suitable
height, the same will be tilted by means of auxiliary hoist for complete discharge of
sludge to the TDS storage bunker (2). The pot is tilted upto 140º for complete discharge
of sludge from the pot. After discharge of the sludge, the TDS pot will be brought down
to the ground by means of the main hoist. The monorail hoists will be released after
keeping the pot either on the ground or on the Dumper directly.
The TDS storage bunker (2) of suitable capacityis installed at a height and near the
existing Y-20 belt conveyor at coke oven. The Y-20 belt conveyor transports coal
charge to coke oven. The TDS storage bunker is provided with steam traced jackets, to
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keep the TDS in hot condition for its smooth flow ability. Top of the storage bunker has
a mesh of steam carrying pipe of suitable size for initial heating of the falling sludge
from the TDS pot for easy flow to the bottom. The steam pipe mesh also ensures the
bigger agglomerated sludge is not entering inside the hopper. The trapped bigger sized
sludge on the top of the mesh gets melted due to steam and then fall in to the hopper.
A screw conveyor (3) of suitable capacity, provided below the bunker, transports the
sludge from bunker to Y-20 belt conveyor (4). The screw conveyor is also provided with
steam jacketing arrangement for maintaining the TDS in warm condition for their
flowability. The feed rate of the screw conveyor is varied according to the feed rate of
coal charge in Y-20 belt conveyor. A manual slide gate is also provided in between the
bunker outlet and the screw conveyor, to ensure smooth discharge of TDS from the
bunker.
The discharge chute of the screw conveyor is positioned in such a way that the TDS is
charged at middle of the Y-20 belt conveyor width. Suitable arrangement has been
made to discharge the sludge over the coal charge in conveyor belt. Appropriate
ploughing arrangements before and after the sludge feeding point on Y-20 conveyer is
provided so that the discharged sludge is contained in the coal feed and does not come
in contact of the belt on onward transportation.
Suitable electro-mechanical system provided for sensing the presence of coal on Y-20
conveyor belt, and interlocking the screw feeder with Y-20 belt, ensures that the sludge
is not fed on empty belt.
Describing Figure 2 of the drawings the ploughs are made of light weight polymer
plates. All the ploughs are firmly hanged from the top of the Y-20 belt conveyor and they
protrude in to the coal charge of Y-20 belt conveyor. The protruding depth of ploughs
can also be varied manually according to the requirement. Ploughs are provided before
and after the charging point of the tar decanter sludge by screw conveyor. An inverted
“V” shaped plough (1) is located just before the discharge point of the screw conveyor,
so that it can create sufficient space on the coal charge of the Y-20 belt conveyor for
charging the TDS. Immediately after the charging of TDS on top of the coal charge and
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at the middle of the Y-20 conveyor, two nos. of ploughs (2) at both extreme sides of the
Y-20 belt are positioned, in such a way that the sideways diverted coal charge is
converged back in tomiddle line of Y-20 belt conveyor. Just after the above ploughs (2),
three nos., of ploughs (3) are positioned firmly across the width of the belt conveyor for
plough and mixing of coal and sludge. Next to the above ploughs, four nos., of ploughs
(4) are positioned at staggered way covering across the width of the Y-20 belt conveyor
for re-digging and mixing of the charges.At the last, two nos., of flat ploughs (5) are
positioned suitably for re-mixing of sludge and coal. All along the total distance of
charging and mixing area of Y-20 belt conveyor, suitable polymer made skirts are
provided at both sides of the belt conveyor to prevent spillage of material on the sides of
the belt conveyor. The above arrangement of ploughs along with exiting two drops of Y-
20 belt conveyor ensures sufficient pre-mixing of TDS with coal charge, well before they
are finally charged in to coke ovens.
In this invention, tar decanter sludge (TDS) from the tar decanters is collected and
transported in sludge pots on open transport vehicle to the site,where the tar decanter
sludge addition system is installed. From the vehicle, TDS pot is lifted directly up to the
top of the storage hopper by main hoist of the mono-rail hoists. By the use of auxiliary
hoist, the pot is tilted to maximum slope for easy discharge of the sludge in to the
storage bunker. The storage bunker is provided with steam jackets all around its sides
for maintaining suitable temperature on its wall for sludge’s flow ability. The top of the
storage hopper is provided with a pipes’ grid/mesh, through which steam passes to
maintain suitable temperature. The pipes’ grid at top opening of the storage bunker also
acts as a mechanical screen, to prevent the bigger sized sludge agglomerates entering
in to the hopper by trapping them at the top itself. The trapped bigger sized sludge
agglomerates on the surface of steam traced pipe grid in the process, gets melted by
hot steam pipes and finally falls back in to the bunker. Steam traced screw feeder of
suitable capacity, provided below the hopper, transports the sludge from the bunker to
the existing belt conveyor, which transports coal-charge to the coke oven. A mechanical
slide gate provided between the bottom of the bunker and input chute of the screw
feeder, along with regulated speed of the screw feeder, controls the feed rate of the
TDS to the belt conveyor.
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Immediately before and after the addition of the sludge on top of the coal charge on the
belt conveyor, the sludge and coal-charge are mixed efficiently in-situ condition by
suitably positioned plough arrangement. Throughout the length of this sludge addition
and mixing region of the belt conveyor, is suitably provided with side skirts to prevent
the materials spillage on the sides of the belt. The suitably designed and positioned
ploughs, are made of polymer plates in different patterns. These plough patterns along
with two level drops of thebelt conveyor on its routes before the coke ovens, ensures
sufficient pre-mixing of sludge and coal charge, before they are charged in to coke oven
batteries. The ploughs are firmly hanged from the top through structural, in such a way
that they could dig in to coal-charge material on the belt conveyor by sufficient depth
and does not touch the surface of belt conveyor. The digging depth of the ploughs can
be varied manually according to the process requirement. The load cell provided below
the belt conveyor measures the feed rate of coal charge and regulates the speed of the
screw feeder to control the feed rate of the tar decanter sludge from the storage bunker.
When there is no material i.e., coal-charge on the belt conveyor or conveyor is not
running, the belt-weigh on load sensor ensures stopping of the feeding of the TDS on
the belt conveyor.
Design Basis
The installed “System for addition of Tar Decanter Sludge (TDS) with Coal-charge” has
been designed, developed and manufactured, taken in to consideration of the following
input data:
Description Specifications
Total TDS production at plant 8 tons per day
TDS addition rate with coal-charge 5 tons per day
Specific gravity of TDS
Viscosity of TDS
1.28
1100 CPS
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Tar specific gravity
Tar viscosity
TDS temperature for flowability
1.18
550 CPS
750C to 850C
Benefits of the invention:
 The earlier practice of dumping the hazardous Tar Decanter Sludge (TDS) in an
open field has been eliminated and hence this invention has helped to
preventenvironmental pollutions. It also eliminated the dumping costs of TDS.
 Carbon value of the waste material i.e., TDS is efficiently utilized in the process
of coke making.
 A simple and cost effective system for addition ofTDS with coal-charge on a
running belt conveyor at in-situ condition has been newly developed. No crushing
equipments are used in this invention.
 Mixing of TDS with coal-charge is achieved on-line in the belt conveyor itself
through simple designed polymer ploughs provided from top of the belt conveyor.
No separate mixing equipments are used in this invention.
From the above disclosure of the invention it is apparent that several additional
embodiments beyond those described herein are possible which can be carried out by a
person skilled in the art and the same are also included within the broad ambit of the
invention claimed herein.
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We Claim:
1. A simple and cost effective system for in-situ premixing of Tar Decanter Sludge
with coal before they are charged into coke making oven by direct addition of the sludge
on to a moving belt conveyor carrying coal wherein a plough arrangement on top of the
belt conveyor is provided for in-situ thorough mixing of the sludge with the coal charge
on the belt conveyor characterised in that the plough arrangement is made of light
polymer liner plates of different sizes and shapes at different locations on the belt
conveyor.
2. A system as claimed in claim 1, characterised in that the polymer liner plates are
fabricated in different patterns and positioned on top of the conveyor belt by hanging
from the top in a staggered manner.
3. A system as claimed in claims 1 & 2, characterised in that all the plough plates
are firmly hanged from the top of the belt conveyor and protrude into the coal charge of
the belt conveyor.
4. A system as claimed in claims 1 to 3, characterised in that the plough plates are
provided before and after the charging points of the tar decanter sludge.
5. A system as claimed in claims 1 to 4, characterised in that the plough plate (1) is
shaped in inverted “V” and is located just before the discharge point of the screw
conveyor.
6. A system as claimed in claims 1 to 5, characterised in that immediately after the
charging of the sludge on top of the coal charge and at the middle of the conveyor two
nos. of plough plates (2) at both extreme sides of the belt conveyor are positioned in
such a way that the sideways diverted coal charge is converged back into middle line of
the belt conveyor.
7. A system as claimed in claims 1 to 6, characterised in that just after the plough
plates (2), three nos. plough plates (3) are positioned firmly across the width of the belt
conveyor.
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8. A system as claimed in claims 1 to 7, characterised in that next to the said plates
(3) four nos. of plough plates (4) are positioned at staggered way covering across the
width of the belt conveyor for re-digging and mixing of the charges.
9. A system as claimed in claims 1 to 8, characterised in that at the last, again two
nos. of flat plough plates (5) are positioned suitably for removing the sludge and coal.
10. A system as claimed in claims 1 to 9, characterised in that all along the total
distance of charging and mixing area of the belt conveyor suitable polymer made skirts
are provided at both sides of the belt conveyor to prevent spillage of material on the
sides of the belt conveyor.
11. A method for in-situ premixing of tar decanter sludge with coal before they are
charged in coke making plant by direct addition of the sludge on to a moving belt
conveyor carrying coal wherein plough arrangement on top of the belt conveyor is
provided for in-situ thorough mixing the sludge with the coal on the belt conveyor
characterised in that the plough arrangement of claims 1 to 10 is used.
12. A method as claimed in claim 11, wherein feed rate of the tar decanter sludge in
the belt conveyor is directly controlled by speed variation of the screw conveyor and the
feed rate is varied according to the coal charge transportation rate by the belt conveyor.
13. A method as claimed in claims 11 & 12, wherein steam traced screw conveyor
directly charges the tar decanter sludge from the storage bunker on the running belt
conveyor.