The invention is in the field of coal carbonisation technology. More particularly it
relates to the processing of coal tar obtained from coke ovens for getting an
improved quality of extra hard pitch having a better coking value.
Tar obtained from high temperature carbonisation of coal in coke ovens is
dehydrated and heated in a pipe still furnace and distilled in an atmosphere
column (Bubble plate column) at a temperature of 290-300°C. The products from
the atmospheric column include residual light oils, taken as over heads, carbolic
oil, naphthalene oil, and light wash oil as side streams and road tar as bottom
product.
This road tar fraction is again heated to about 320 - 340°C in the lower section of
pipe still furnace and sent to pitch column, which is maintained, under vacuum of
100 mm Hg. The residual oil vapours from this column are separated into heavy
wash oil and anthracene oil in the anthracene column, which also operates under
vacuum. The bottom product of pitch column is a soft pitch, called running pitch
is limited, it is further heat treated in a pitch blower, where compressed air is
blown at a pressure of 4.5 - 5 Kg/cm^ for a period of 4 - 6 hrs., with or without
addition of anthracene oil, in order to increase its softening point and coking
residue. This final product is called extra hard pitch and is used making
electrodes for Aluminum Industries.
The extra hard pitch, produced as deschbed above, has low coking value which
is in the range of 52-53%, while the Electro metallurgical industry, especially
Aluminum industhes, require extra hard pitch with a coking value more than 56%.
Considering the need for improving the quality of the extra hard pitch for use as
binder in the preparation of electrodes, particularly for Aluminum industry, the
inventors concentrated their studies in the field of meeting the quality of extra
hard pitch.
As quality of extra hard pitch depends on the quality of soft pitch (running pitch),
the inventors further concentrated on the quality improvement of running pitch
being produced from road tar.
After performing several investigations, based on detailed analysis of road tar
and pitch as produced under different operating conditions, the inventors could
develop a process by which properties of running pitch can be modified for
making an extra hard pitch, having improved coking value, making the same
suitable as binder for electrodes in different Electro metallurgical processes.
Main object of the invention is, therefore, to produce an extra hard pitch having
improved coking value to make the same suitable as binder for eldctrodes in the
Electro-metallurgical processes. Coking value of conventional extra hard pitch
lies in the range of 52 - 53%, while the coking value of the inventive product is
more than 56% and is in the range of 56 - 57%. These and other improvement in
properties like softening point etc. are all achieved by the process of the
invention.
The invention provides a process for producing improved extra hard pitch having
improved coking value which comprises mixing anthracene oil with the road tar
fraction obtained as residue from fractionating column of coal tar distillation and
the mixture is heated before feeding to pitch column, maintained at a vacuum, for
distillation. The residual oil vapours separated during distillation are separated
into heavy wash oil and anthracene oil in the anthracene column, which also
operates under vacuum. Anthracene oil obtained from the column can be used in
this process.
The invention, therefore, provides a method of producing improved extra hard
pitch having improved coking value, which comprises mixing anthracene oil with
the road tar fraction, obtained as residue from fractionating column of coal tar
distillation, heating and injecting the mixture in the pitch distillation column
maintained at vacuum, air blowing the residue of this column in pitch receivers for
a period of 4-6 hrs. to get the product of the invention.
Percentage of anthracene oil mixed with the road tar fraction is in the range of
6 - 10% and the mixture is heated to a temperature of 350 - 370''C before
introducing in the pitch distillation column.
Improved properties of extra hard pitch of invention, as compared to conventional
extra hard pitch, are shown in Table 1.
Study on the use of anthracene oil and operating temperature and influence of
the same on the coking value of extra hard pitch is shown in Fig. 1 of the
accompanying drawing.
Detailed Description of the Process
For better understanding of the process the invention has been described with
reference to the flow sheet supplied in Fig. 2 of the accompanying drawing. In the
flow sheet the modification has been marked to locate the advantages.
In the process, as shown in the drawing, crude tar is pumped through a series of
heat exchangers in which it abstracts heat from road tar fraction and is pumped in
the dehydration tower at 140''C. The temperature of dehydration tower is
maintained by circulating hot dehydrated tar through a coil in its base. Dry tar is
pumped to the upper section of the coke oven gas fired pipe still furnace and
injected into the atmospheric pressure fractionating column at a temperature of
290 - SOCC. A portion of the road tar fraction, which is bottom product of
atmospheric column, after coming through heat exchanger as shown in the
drawing is mixed up with anthracene oil and is heated in the pipe still furnace and
then introduced into the pitch column at about 350 - 370°C. Pitch column is
maintained under vacuum and the residual oil vapours separated from pitch are
separated into heavy wash oil and anthracene oil in anthracene column, which

also operate under vacuum. Running pitch is collected from the base of the pitch
column. It appear that the elevated temperature of the mixture of road tar fraction
and anthracene oil in a specific concentration helps in the increasing the coking
residue and that anthracene oil prevents the increase in viscosity and quinolene
insoluble content. Extra hard pitch of the invention is produced by air blowing this
running pitch in pitch receivers at a pressure of 4.5 - 5 Kg/cm' for a period of
4-6 hrs., with or without further addition of anthracene oil.
WE CLAIM :
1. A method of producing improved extra hard pitch having improved coking
value, which comprises mixing anthracene oil with the road tar fraction,
obtained as residue from fractionating column of coal tar distillation, heating
and injecting the mixture in the pitch distillation column maintained at vacuum,
air blowing the residue of this column in pitch receivers for a period of 4-6 hrs.
to get the product of the invention.
2. A method of producing improved extra hard pitch as claimed in claim 1
wherein percentage of anthracene oil mixed with the road tar fraction is in the
range of 6- 10%.
3. A method of producing an improved extra hard pitch as claimed in claim 1
wherein the mixture is heated at a temperature of 350 - 370°C before
introducing the same in the pitch distillation column.
4. A method of producing an improved extra hard pitch as claimed in claim 1
wherein the percent of anthracene oil mixed with road tar fraction is 7%.
5. A method of producing an improved extra hard pitch as claimed in claim 1 in
which air blowing the residue of pitch distillation column is carried out at a
pressure of 4.5 - 5 Kg/cm^.
6. A method of producing an improved extra hard pitch as claimed in claim 5
wherein the mixture of anthracene oil and coal tar fraction is heated to a
temperature of 360°C before introducing the same in pitch distillation column.
7. A method of producing an improved extra hard pitch as claimed in claim 1
wherein anthracene oil produced from pitch distillation column is directly used
as a raw material for the invention.
8. A method of producing an improved extra hard pitch as claimed in claim 1
wherein the product produced has a coking value in the range of 56% to
57%.
9. A method of producing an improved extra hard pitch having improved
coking value substantially as herelndescribed and illustrated with
reference to the accompanying figures.

A method of producing improved extra hard pitch having improved coking value.
The method comprises mixing anthracene oil with the road tar fraction, obtained
as residue from fractionating column of coal tar distillation, heating and injecting
the mixture in the pitch distillation column maintained at vacuum, air blowing the
residue of this column in pitch receivers for a period of 4-6 hrs. to get the product
of the invention. The extra hard pitch produced by this process has improved
coking value in the range of 56% to 57%.