FIELD OF THE INVENTION
The present invention relates to an apparatus to find out optimised cooling
methods for producing coke of compatible strength and methods generated
thereof. More particularly the invention relates to find out through various
quenching methods with the help of the said apparatus, the strength
characteristics of coke after it is pushed from coke oven chamber.
BACKGROUND OF THE IVNENTION
Metallurgical coke is an essential and important raw material for blast furnace.
The various measures like coal properties, coal preparation and operating
conditions are being practiced for upgrading quality of coke. These technological
measures are not sufficient because upon different type of cooling the physico-
mechanical properties of coke changes differently. It is due to the fact that
depending on the type of cooling, the stress in pieces of various sizes and shapes
acts in different ways. An increase in stress leads to formation of cracks and
micro-fissures resulting decreases of coke strength.
For this purpose special type of equipment is developed to study change in coke
properties using different methods of quenching. With this type of equipment it
is possible to study different methods of quenching with small quantity of hot
coke.
The dominant method of the existing art of cooling coke is wet quenching. The
production of each metric ton of coke yields 0.3-0.4m3 of chemically
contaminated water. The formation of such drainage cannot be prevented since
the by product coking process requires a large quantity of water. The water is
introduced for the technological process together with the raw material (with a
coal blend) and is also formed during the coking process.
The waste water of coke production leaving the biochemical installation cannot
be discharged directly into water bodies. The purified effluents are transferred
for quenching of the coke pushed from coking chambers. Its heat is completely
spent on the vaporization of water into atmosphere and as a consequence
substantial amount of heat is wasted, and with such cooling method strength
characteristics of the coke are also impaired.
Another disadvantage in wet quenching is encountered with formation of harmful
substances into the atmosphere due to vigorous evolution of components form
the coke and also due to the residual content of ammonia and other substances
in the water supplied for quenching.
Coke production by dry quenching method provides heat recovery from sensible
heat of hot coke and also improves the quality of metallurgical coke resulting in
reduced coke rate in blast furnaces, which in turn increases the productivity of
blast furnaces. Hot coke slowly cooled with inert gas (Nitrogen) generates
substantial amount of steam which can be recovered and used. The slow cooling
of coke prevents cracks from occurring and ensures uniform coke size. In dry
quenching method the process does not require water and is not involved with
drainage of water causing pollution as encountered in wet quenching method.
In the conventional coke oven practice of wet quenching of coke the final
temperature of the coke mass before pushing is of the order of 950-1100° C.
This coke is to be quenched and cooled to 25-100° C to prevent its combustion
and facilitate transportation. Considering that 700,000 to 800,000 Kcal of heat
input is required per tonne of coke production during carbonization of coal, the
loss in heat by wet quenching amount of 360,000-420,000 Kcal per tonne of
coke.
The prior art investigations carried out by different authors have shown that the
electric resistivity, the heat of wetting, reactivity, volume changes and other
physico-mechanical and physico-chemical properties reflect changes in the
structure of coke at different energy levels.
In high temperature range, where the structure is denser and more strongly
stressed, at the coke pushing temperature (1000 to 850° C) the quenching rate
must be minimal as possible. When the final temperature range from 850 to
650° C is maintained the coke structure is still quite stressed and the temperature
gradient between the surface of the coke and center being rather high, the
quenching rate can be increased slightly.
When the final temperature range from 650 to 200° C is maintained the rate of
quenching may be increased to such an extent as to prevent the generation of
stress exceeding the ultimate strength of the coke.
In coke quenching in the pouring stream the bulk mass of coke is polydispersed.
It is essential to provide a uniform cooling of each block, irrespective of coke size
and shape in such cooling condition. However, this is impossible to realize
during quenching system of an immovable coke charge. For practical reasons
quenching conditions are created not in the static state but in the dynamic,
flowing state.
In the conventional process of coke production the first stage of quenching
proposed was a bin with a recuperative heat exchanger. In this system it is
possible to provide conditions for isothermal exposure prior to cooling and to
utilize the coke heat to produce power generating steam. The developed
method of the first stage of coke quenching made it possible to provide a
uniform descent of the entire mass of coke through the cross section of the bin,
its mixing during the flow of the coke charge and uniform cooling throughout the
entire volume from 1000 to 650° C at a rate of 2.6° C / min, is about 42% lower
than in the case of coke quenching in dry quenching installation. The second
stage proposed is a rotary drum type heat exchanger, in which the remaining
coke heat can be used for other heat and mass transfer process, including the
vaporization of water. The internal arrangements in drum type heat exchanger
in the form of grid blades and cutoff diaphragms provide the required interaction
of the heat emitting coke surface with the coolant under dynamic conditions in
the moving stream.
During carbonization in a coke oven fissures in the coke are generated due to
stress that arises from the differential contraction rates in adjacent layers of
coke, which are at different temperatures typically longitudinal, i.e. perpendicular
to the oven walls. Additionally, mainly transverse fissures are formed during
pushing. These fissures result in breakage along their lines during subsequent
handling which episode determine the size distribution of the product coke. But
not all the fissures lead to breakage at this early stage, so that a number of them
remain in the coke lumps.
In an early study Mott and Wheeler showed that the greater the number of initial
fissures in a piece of coke, the weaker it was in a shatter test.
It has not yet been established conclusively to what extent residual fissures
influences the mechanical strength of cokes. In part, the difficulty in assessing
their role lies in the lack of comprehensive methods of characterization, which
enable Assuring to be quantified and compared.
It is quite evident from the analysis of coke made through various quenching
methods described above that the strength characteristics of coke depends not
only on the selection of coal and preparation of coal blends for coking, but also
on the method of quenching of coke after it is pushed from coke oven chamber.
The present invention is aimed to solve the difficulties of prior arts as narrated
above to solve the long standing and extent problem in coke quenching to find
out appropriate cooling method.
DESCRIPTION OF THE INVENTION
It is therefore an object of the invention to propose an apparatus to find out
optimised cooling method of producing coke of compatible strength and methods
generated thereof.
Another objective of the invention is to find out a suitable means to maintain
quality of coke produced by cooling method instead of going for maintaining
coke strength through residual fissures determination.
Yet another objective of the invention is to find out suitable cooling method for
wet quenching, dry quenching or normal cooling or in combination of wet, dry or
normal cooling according to high and low temperature cooling to ascertain
quality of coke produced and ensuring no strength loss of coke due to
proceeding through wrong choice of cooling method.
The present invention will be better understood by the following description with
reference to the accompanying drawings in which.
Figure 1 relates to a schematic diagram of a quenching
apparatus for quenching samples of coke.
Figure 2 shows effect of quenching conditions
on coke strength after reaction.
Figure 3 shows effect of quenching conditions on coke reactivity index.
Figure 4 shows effect of quenching conditions on coke mean size.
Figure 5 shows effect of quenching conditions on minus 40 mm coke size.
Figure 6 shows effect of quenching conditions on plus 40 mm coke size.
For this investigation, only the samples of coke made with plant coal blend was
used. Six sets of experiments for different types of cooling were carried out in
carbolite oven and the resultant cokes were cooled at different rates in the
specially designed apparatus (See Fig. 1).
The coal blend was charged into an electrically heated carbolite oven (0)
supported on a movable platform (C) and then carbonized at flue temperature -
1000° C under stamp charging conditions. The heating rate and the
carbonization time were kept identical for all the tests. The said oven is
encircled by a heat resisting jacket (J) from its bottom to the upper half of the
oven.
The apparatus (Fig. 1) is designed and fabricated for studying the effect of
different rate of cooling on coke strength. The main cylindrical chamber made of
stainless steel has a perforated bottom (1) for draining out the water through a
suction means (2) and is provided with external gas heating arrangements (3).
The oven is adapted to cool the coke with gas. The top opening of the
cylindrical chamber is covered tightly with a stainless steel lid (L) provided with a
thermo well (4). A circular ring type gas burner (not shown) is connected with
the heating channel (3) to heat the chamber whenever required. The
thermocouple (not shown) inserted in the thermo well measures the temperature
of the pushed coke during cooling. The main container (0) was heated upto
800° C before receiving the pushed coke. The cokes pushed out from each
test were subjected to different types of cooling as given under
1. Quenching with water
2. Normal cooling i.e. no external cooling medium was used.
3. Normal cooling upto 400° C then water quenched.
4. Coke quenched with 10% moist blend.
5. Coke quenched with N2 upto 400° C then water quenched.
6. Coke quenched with N2 (5 lit / min) only.
Figures 2 to 6 show the parameters in the ordinates in percentages with respect
of six different types of cooling method, herein denoted in the abscissa as
quenching conditions. The parameters used are coke strength after reaction
(CSR), coke reactivity index (CRI), coke mean size, -40 mm coke size, plus 40
mm coke sizes.
The starting material utilized in the process may be derived from any coal source
which is suitable for metallurgical coke making and coke quality parameter can
be determined by standard practice.
For evaluation of quality of coke on cooling the said parameters are compared
with the No. 1 method I.e. quenching with water the carbonized coke from
1000° C.
Good quality coke is assessed of having higher CSR and optimum CRI. CSR of
coke has inverse relation with CRI i.e. lower CRI and higher CSR. The
compatible higher CSR is obtained by No. 2 and No. 6 method of cooling. It is
also observed that other conditions like normal cooling upto 400° C then water
quenching (3), quenching with 10% moist blend (4) and coke quenched with N2
upto 400° C and then water quenched (5), are comparably better than water
quenched system.
Coke mean size percentage of the cooled coke as observed from the graph in
Figure 4 is in the range of 54 to 61 % and the coke mean size for No. 2 and No.
6 method of cooling are observed as 56% and 61% respectively.
Minus 40 mm size coke size achieved in the six quenching conditions are found
between 8% to 17%, lower 8% being formed in quenching condition No. 6 and
higher 17% in quenching conditions Nos. 2 and 5.
Plus 40 mm size % of coke achieved on cooling is observed in the range of 83.5
% to go 90.8 %. The said test datas reveal the fact that +40 mm size is
minimum for quenching condition Nos. 2 and 5 and highest 90.8 % for cooling
method No. 6.
The gas permeability in blast furnace is one of the most important requirement
served by coke, is largely dependent on the size of coke. Due to various
mechanical, chemical and thermal factors the initial coke size grading can not be
retained in the blast furnace and other steel making furnace. The final size
distributions at various zones in blast furnace are considerably influenced by the
initial size grading of coal. Over size coke should be eliminated as far as
practicable as oversize is characterized by poor thermal stability. A smaller coke
owing to its higher surface area is more susceptible to degradation. Keeping all
the above factors in view coke size range and coke mean size should be chosen
according to other raw material used and operating condition of blast furnace.
Figures 4, 5 and 6 indicate the effect of cooling condition on size of coke.
Maximum mean size, plus 40 mm size and minimum minus 40 mm size of coke
was achieved when coke was cooled with nitrogen. Overall it can be said that
slow cooling is beneficial for quality of coke.
Considering all the aspects from above test results it is recommended that
methods of cooling No. 2 and 6 are most suitable for carbonized coke cooling.
But the present invention qualify an improved process guides to produce
metallurgical grade of coke applicable to all the above six quenching conditions
on precise process control to be maintained with slow cooling rate when
quenched in water and slow cooling rate in dry quenching also when quenched
from higher temperature.
The quenching conditions No. 1 and 6 i.e. water quenching and dry quenching
are known in the art.
The proposed invention has developed methods of cooling of carbonized coke at
high temperature (1000° C) of different combinations of quenching conditions
No. 2 to 5 through characterize evaluation from test results to maintain
compatible coke strength after carbonization to produce metallurgical grade
coke.
The invention as narrated hereinabove and illustrated with an exemplary
embodiment of the invention should not be read and construed in a restrictive
manner as various modifications of the apparatus, adaptations and alterations of
the constructive parts of the apparatus and method steps, coke sizes and
process control steps are possible within the scope and limit of the invention as
defined in the encompassed appended claims.
WE CLAIM
1. An apparatus to find out optimized cooling methods for producing compatible strength of
coke comprising a cylindrical chamber with a perforated bottom for draining out water
adapted to cool pushed coke and a gas heating arrangement (3) to heat the chamber, a
stainless steel lid (L) to cover sealingly the cylindrical chamber, wherein an oven (0)
being electrically heated to carbonize the coal blend when charged into the oven,
subjecting the cokes on carbonization from the oven to different types of cooling method
as given under;
1. Quenching with water, from a high temperature of 1000° C.
2. Normal cooling i.e. no external cooling medium was used,
3. Normal cooling upto 400° C then water quenched,
4. Coke quenched with 10% moist blend,
5. Coke quenched with N2 upto 400° C then water quenched,
6. Coke quenched with N2 (5 lit / min) only,
Comparing test results of the cooled and quenched coke from parameters coke strength
after reaction (CSR), coke reactivity index (CRI), and CSR on coke mean size and greater or
less of 40 mm coke size with No. 1 quenching condition i.e. water quenching from high
temperature of 1000° C, to find out optimized cooling method among No. 2 to No. 6 as
defined above to produce metallurgical grade coke on cooling carbonized high temperature
coal blend.
2. The apparatus to find out optimized cooling method as claimed in claim 1, wherein the
oven (0) is an electrically heated carbolite oven, supported on a movable platform (C)
and carbonized at flue temperature of 1000° C under stamp charging conditions.
3. The apparatus as claimed in the preceding claims, wherein the heating rate and
carbonization time were kept identical for all the test methods of cooling in the oven
encircled by a heat resisting jacket (J) from its bottom to the upper half of the oven.
4. The apparatus as claimed in the preceding claims, wherein the cylindrical lid (L) is
provided with a thermo well (4) in which a thermocouple is inserted in the well (4) to
measure the temperature of the pushed coke during cooling.
5. The apparatus as claimed in the preceding claims, wherein the oven (0) is heated upto
800° C before receiving the pushed coke, the oven being heated electrically and also by a
circular ring type gas burner when connected with the heating channel (3) whenever
required.
6. Method to find out optimized cooling method for producing coke of compatible strength
generated by the apparatus as claimed in claim 1 comprising:
- charging the coal blend for each set of test, into an carbolite oven (0); heating the oven
electrically;
- carbonizing the charge at flue temperature of 1000° C under stamp charging conditions;
- maintaining the heating rate and carbonization time identical for all the tests;
- providing the oven an arrangement to cool the coke with gas;
- covering the top opening of the cylindrical chamber tightly with a stainless steel lid (L);
- providing a thermowell to the lid (L) to measure the temperature of pushed coke during
cooling by a thermocouple inserted in the said thermowell (4); wherein the oven (0) is
heated upto 800° C by a circular ring type gas burner connected with the heating channel
(3), before receiving the pushed coke when the cokes pushed out from each test is
subjected to different types of cooling as given below under the different parameters and
is compared with the No. 1 method to evaluate the quality of coke,
1. Quenching with water, from a high temperature of 1000° C.
2. Normal cooling i.e. no external cooling medium was used,
3. Normal cooling upto 400° C then water quenched,
4. Coke quenched with 10% moist blend,
5. Coke quenched with N2 upto 400° C then water quenched,
6. Coke quenched with N2 (5 lit / min) only.
7. The method as claimed in claim 7, wherein the test results find that No. 2 and No. 6 are
the best methods of cooling with higher C5R of 57 % and 56 % and lower CRI of 29 %
and 30 % respectively when coke mean size percentage of the cooled coke for No. 2 and
No. 6 method of cooling are 56% and 61% respectively.

This invention relates to an apparatus to find out optimized cooling method of carbonized coke
and methods generated thereof comprising a cylindrical chamber adapted to cool pushed coke
with a perforated bottom for draining out water and a gas heating arrangement (3) to heat the
chamber, a stainless steel lid (L) to cover sealingly the cylindrical chamber, the oven (0) being
electrically heated to carbonize the coal blend when charged into the oven, subjecting the cokes
on carbonization from the oven to different type of cooling method as given under.
1. Quenching with water, from a high temperature of 1000° C.
2. Normal cooling i.e. no external cooling medium was used,
3. Normal cooling upto 400° C then water quenched,
4. Coke quenched with 10% moist blend,
5. Coke quenched with N2 upto 400° C then water quenched,
6. Coke quenched with N2 (5 lit / min) only,
Comparing test results of the cooled and quenched coke from parameters coke strength after
reaction (CSR), coke reactivity index (CRI), and CSR on coke mean size and greater or less of 40
mm coke size with No. 1 quenching condition i.e. water quenching from high temperature of
1000° C, to find out optimized cooling methods of No. 2 to No. 6 cooling method as defined
above to produce metallurgical grade coke on cooling carbonized high temperature coal blend.