Note: Descriptions are shown in the official language in which they were submitted.
~5D~7~
This invention relates to a process for producing
coke, and more particularly to a process for producing
needle coke.
It is known in the art ~c produce coke from a wide
variety of feedstocks by a delayed coking procedure. Such
procedures have been directed to the production of both
anode grade coke, and to a premium quality coke, often
referred to as needle coke.
U.S. Patent No. 4,108,798 describes an improved pro-
cessfor producing a needle coke (a highly crystalline petro-
leum coke) wherein the petroleum feedstock is initially heat
soaked in the presence of sulfur, followed by controlled thermal
cracking and separation of non-crystalline substances from
the cracked`feedstock. The thus treated feedstock is then
subjected to delayed coking to produce highly crystalline
petroleum coke.
The present invention is directed to the production of
coke by a delayed coking procedure.
In accordance with the present invention, a coking
feedstock is subjected to delayed coking at coking temperatures
lower than those normally employed in the art.
After the coke drum has been filled to a desired level,
introduction of feedstock is discontinued~ as normally prac-
tised in the art, and in accordance with the invention, the
contents of the drum are heated at a temperature which is
higher than the temperature employed during the coking step
or stage, to remove volatile combustible matter therefrom,
-- 1 --
~5~
and thereby produce a coke having a reduced coefficient of
thermal expansion tCTE). Although the present invention has
applicability to a wide variety of delayed coking procedures
for producing coke, the present invention has particular
applicability to the production of a needle coke and most
particularl~ a high ~uality crystalline coke from a feed-
stock which has been pretreated by thermal soaking, and/or
cracking and/or removing of non-crystallin~ substances.
For example, a process employing all three steps is des-
cribed in U.-S. Patent No. 4,108,798.
More particularly, in accordance with the general
teachings of the present invention, delayed coking is accom-
plished by the general procedure known in the art wherein
coking feedstock is continuously heated in a coking heater
and introduced into a coke drum until the contents reaches
a desired fill level, followed by taking the coke drum off-
stream for removal of coke, except that in accordance with
the present invention, the coke drum is operated at lower
temperatures of from 415C to 455C, preferably of from 240C
to 450C, and after the coke drum is taken off-s~ream; i.e.,
the coking feedstock is no longer introduced into the coke
drum, the contents of the off-stream coke drum are heated at
a temperature which is at least 10C greater than the
coking temperature (preferably at least 15C and most pre-
ferably at least 20C greater than the coking temperature)
and which temperature is at lea~t 450C, preferably at
least 460C and no greater than 500C, preferably no greater
than 480 C (preferably by passing a heated non-coking
vapor through the contents of the drum) for a time to pro-
duce a coke having a volatile combustible matter content of at
~L~5~71~7
least 4%, preferably at least 5~, and no greater than 10%,
preferably no greater than 8%, all by weight. The time re-
~uired for producing the coke with such volatile combustible
mattar content after taking the drum "off-stream" will vary
with the coke produced, the feedstock employed for producing
such coke a~d the heating temperatur~; however, in most cases
such reduction can be accomplished by ~'off-stream" heating
for a time period in the order of from four hours to 24 hours.
The subsequent off-stream heating of the contents of
the coke drum is accomplished by ~he use of a non-coking
vapor. Any one of a wide variety of materials which are
not suitable for:the production of coke may be employed
for such heating and as representative examples of suitable
materials, there may be mentioned light coker distillate,
lS coker gases ~Cl-C4 hydrocarbons), steam, nitrogen and other
non-coking gases except gases which are oxidizing gases. The
selection of a suitable gas for accomplishing the heating is
deemed to be within the scope of those skilled in the art from
the teachings herein. It is to be understood that in some
cases it may be possible to accomplish such heating by
means other than passing a heated gas through the coke drum
contents; however, for most commercial operations, the pre-
ferred and most practical manner of heating the coke drum
contents is by use of superheated vapors.
It is to be understood that in some cases the heating
of the coke drum contents may be accomplished with a material,
which is capable of forming coke, such as a heated coker
~59~
recycle or coker recycle plus relatively low concentrations
of coker ~eedstock; however, in most cases the quality of
the coke produced by the use of such materials is lower
than the ~uality produced by the use of a non-coking material.
Thus, in accordance with the present invention, the
delayed coking is conducted at a temperature lower than
normally used in the art until the coke drum is filled to
the desired level, a~d after--taking the drum off-stream-the
contents thereof are heated at a higher temperature to effect
a reduction in the volatile combustible matter content there-
of. The o~Lnation produces a final product which when
calcinad has a reduced CTE. The specific temperatures em-
ployed in each of the coking steps and subse~uent off-stream
heating will vary with m particular feedstock as well as
the desired CTE for the final product. In general, it has
been found that the use of lower temperatures within the
hereinabove described general range of coking temperatures
produces a final product with a lower CTE; however, with some
feeds higher temperatures within the hereinabove described
general range of working temperatures are required to achieve
a suitab~e rate of reaction.
As hereinabove noted, thepresent invention isparti-
cularly applicable to the production of a highly crystalline
coke (needle coke), and most particularly to the productivn
of a highly crystalline petroleum coke from a petroleum feed-
stock which has been pretreated in accordance with the teachings
of U.S.P. NO. 4,108,798 or U~S.P. 4,199,434.
-- 4
7(:)7
In accordance with the overall process of the present
invention, the feed~tock is initially heat-soaked in the pre-
sence of sulur, followed by heating the heat-soaked feedstock
to a higher temperature to effect controlled ~hermal cracking
thereof, which enhances the aroma~icity of the feedstock. The
material from the thermal cracking then treated to separate
non-crystalline substances therefrom, followed by heating o
the coking feedstock, free of non crystalline ~ubstances, in a
coking heater to provide coke drum temperatures in the order
of from 415C to 455C, and after filling of the coke drum,
which is taken off-stream, the content:s thereof are heated at
a temperature which is at least lO~C greater than the coking
temperature and which temperature is from 450C to 500C, for
a time sufficient to reduce the volatile combustible matter
content thereof to a value as herinabove described.
The ~eedstocks which are generally employed for the
production of coke in accordance with the invention are heavy
petroleum feedstocks, such as a distillation residue derived
from a crude oil, lube oil extract and hydrodesulfurized lube
extract, a cracking residue or a hydrodesulfurized product of
a residue from the distillationor cracking of petroleum.
Preferred feedstocks are the so-called pyrolysis fuel oils or
black oils which are the residual heavy black oils boiling
above pyrolysis gasoline; i.e., boiling above 187 to 218 C
which àre produced together with olefins in the pyrolysis
of liquid hydrocarbon feeds, catalytic cracker decant oils,
thermally cracked tars, lube oil extract and its hydrodesul-
furized product, coal tar or pitch distillates and the like.
In general, such feedstocks have low sul~ur content, i.e.,
sulfur content of 1.5 wt.~ or less, preferably of 0.8 wt.
or less. Blends of æuch feeds may be employed.
The feedstock is initially soaked in the presence of at
least 30 parts per million of sulfur, with such sulfur preferably
being provided by adding sulfur (generally in the fvrm of at
least one member selected from the group consisting of elemental
sulfur, mercaptan and carbon di~ulfide). In most cases, the
added sulfur does not exceed 200 ppm. The soaking is generally
effected or at least 5 minutes, and most generally from 5
to 120 minutes. The soaking temperature is generally in the
order of from 230 to 315C. It is to be understood that if
the requisite sulfur is present in the feed, sulfur need not
be added thereto. In some cases, it may be possible to achieve
the desired results by soaking at a temperature of from 230
to 315C without the use of sulfur. It is believed that the
soaking step improves the overall operation by polymerizing
polymerizable components.
The soaked feedstock is then heat treated to effect
controlled thermal cracking thereof and to thereby increase
the aromaticity (reduce API gravity). The heat treatment to
effect cracking, which follows the initial thermal soaking,
is performed by heating the feedstock, generally in a tubular
heater, under a precsure in the order of from 4 to 50 kg/cm2G
to an outlet temperature in the order o~ from 450 to 595C.
The crac~ing is effected ~or a period of time to increase the
aromaticity, with such cracking generally being in the order
of from 15 to 120 seconds. In general, the API gravity is
decreased by at least 1 ~based on the material boiling
above 260 C.).
~s~
Sub~equent to the heat treating, the feedstock may be
processed to remove no~-crystalline substances, and non-dis-
tillable heavy components, with s~ch separation generally
being easily accomplished by the use of high t:emperature
flashing, with such flashing generally being at a temperature
of 380 to 510C under a pressure of from 0.1 kg/cm2(A) to
2 kg/cm2G. In the flashing, the non-crystalline substances
can bP selectively removed as a pitch bottoms. The material
recovered as the coking feedstock yenerally boils within the
ran~e of from 260C to 538C. Lighter components from the
feedstock, such as gas, gasoline and gas oil may be separately
recovered.
The coking fQedstock, which has been pretreat~d, as
hereinabove described, is then subjected to delayed coking
by the general procedure known in the art, except that in
accordance with the present invention, it has been found
that the coking temperature should be controlled to temper-
atures lower than those generally used in the art. The
optimum coking temperature varies with each feedstock. The
coking pressure is generally in the order of from 2 to 10
kg/cm G.
Subsequent to fllling of the coke drum, the drum is
taken off-stream and the contents heated at a temperature
which is at least 10C greater than the coking temperature
and which temperature is from 450C to 500C for a time suf-
ficient to reduce the volatile combustible matter content
-
to the values as hereinabove described.
Although the herinabove described embodiment is
particularly preferred, it is to be understood that one or
~L59~ 37
more of the steps for pretreating the feed may be eliminated,
with the coking procedure of the present invention, in such
~ases, also providing an improvement in the coke quality,
although in most cases the combination of the three pre-
treating steps, in combination with the controlled eoking
heater outlet temperatures and subsequent ~ff-stream heating
to reduce the volatile combustible matter content producing
the highest ~uality coke. Thus, for example, the initial
soaking may be eliminated, and/or the cracking of the feed-
stock may be eliminated and/or the separation of non-crystalline
components may be eliminated within the spirit and scope of the
present invention, provided that the coking
- 7a -
,>j
~ ~5~
heater is op~rated a~ ~he hereinabove clescribed temper-
atures and the c~ntents thereof heat treated off-stream
as hereinabove described, to produce a coke having the
hereinabove described volatility.
U.s. Patent 4,199,~34, ~or example, discl~ses pre-
treating a coking feedstock by the combination of soaking
~t a firs~ temperature in the presence of sulfur, followed
by heating at a higher temperature to reduce API gravity.
U.S. Patent 3,687,840 discloses pretrea~ing a coking feed
in the presence of sulfur.
The invention will.~e further described with respect
to an embodLment thereof i~lustrated in the accompanying
drawing wherein:
The drawing is a simplified schematic representation
of a flow diagram for effecting the process of the present
invention.
Referring now to ~he drawing, a feed, in
line 10, ~s introduced into a soaking drum, schematically
generally ~ndicated as 12, with su~fur, if required, being
introduced into the drum 12 through line 13. In drum 12,
the feed is thermally soaked, as hereinabove described,
w~th such soaking effecting polymerization of highly un-
sa~urated compounds.
The soaked feedstock is wi.thdrawn from drum 12 through
line 14 and introduced into a coil 15 in a thermal cracking
~ '7~'7
heater 16 wherein the fe~d is subjected to thermal cracking
conditions, as hereinabove described, in ~rder to increase
~hè overall aroma~icity thereof (reduce API gravi~y). The
cra~ke1 feedstock is withdrawn from coil 15 in line 17,
quenched with a light gas oil, ~btained as hereinabove des-
cribed, in line 18, and the combined stream passed through a
pressure reduction valve 19 into a vacuum flash tower, sch~-
matically genèrally indicated as 21. The vacuum flash tower
i5 operated at temperatures and pressures to separate from
the feed non-crystalline sùbstances,
and other heavy components. In general, the flash tower is
operated at a temperature in the order of from 380 to 510~C,
and at a pressure in the o~der of from 0.1 kg~cm2A to
2 k~/cm G.
lS A heavy pitch-like bottoms is recovered from tower 21
through line 22. A light gas oil is recovered from tower 21
through line 23, with a portion thereof being employed in line
18 as a quench oil. Naphtha and lighter gases are recovered
from the flash tower through line ~4.
The pretreated coking f~edstock, which is recovered
through line 25 is generally those components which are within
a boiling temperature range in the ~rder of from268~' to 538~C
and such components are introduced into a coker combination
fractionator tower, ~chematically generally indicated as 27.
~5 ~he coker combination fractionator tower 27 is
operated, as known in the art, to recover the coking feedstock
bottoms, and to also reCGVer lighter componentS, which are
~ 3'~
gerJera~ly not empl~yed in the co~.ing eedstock, suc~. as a
heaYy c~ker gas oil in line 28, a light coker ~as oil in
line 29 and coker naphtha and gases in line 31. The coker
com~inati~n fractionating tower 27, as known in the art,
S is also provided with coke drum overhead vapors throush line
32.
Bottoms withdràwn from the tower 27 ~hrough line 34
is passed through a ~oking heater, of a ~ype k~own in the
art, and schematically generally indicated as 35, and the
heate~ material i introduced into a coke drum, schematically
~enerally indic~ted as 36. The coke drum is operated at the
temperatures and pre~sures hereinabove described. Overhead
vapors are withdrawn from coke drum 36 through line 38, an~
aft~r quenc~ing by a portion of the light gas oil in li~e 39,
such ~verhead ~apors are introduced into the coker fraction-
ator 27 through line 32.
After the coke drum is filled, as known in the art,
the coke drum is taken "o~f-line;" i.e., the drum is ~o longer
provided with coking ~Pedstock. The off-line drum is in-
dicated as 36' ~n the drawin~.
In accordanre with the present invention, the ~ff-line
drum 36' is heated to a higher temperature to reduce the
volatile combustible matter ~ontent thereof and reduce
the CTE. As ~hown in the drawing, superheated gas, such
as light coker distillate, naphtha, coker gas, etc. is
introduced into the cokin~ drum 36' through line 101,
with such gas generally ~eing at a temperatur~ ~nd ~ressure
sufficient to mai~tain the off-line drum 369 at
- 10 -
the tempera~ures hereinabove described for reducing the
volatile ~ombust~ble matter content. In general, the vapor
is introduced at a temperature in the order of from 450 to
525DC and Qt a pressure i.~ the order of from 2 to l0Kg/cm2G
~he vapor introduced through line 101, as well as volatile
matter driven of~ ~rom the drum oDn~ents is withdrawn fr~,off-lin~
coXe drum 36 ' thr~ugh line 102, and introduced into a quench
tower, schematically generally indicated as 103, desi~ned and
operated to recover the non-coking vapor to be employed in
o~f-line drum 36'. In quench tower 103, lighter components
are recovered through line 104, as a gas; the material ~o
be used as the drying gas is recovered through line 105, as
a liquid; and heavier components are recovered througl~ line
106. A portion of the material in line 105 is passed through
line 107, includina a cooler 108 for i~troduction into tower
103 throu~h line 109 , as reflux. ~he remaini~g portion in
line 111 is heated in heater 112 to effect vaporization thereof
for use as ~ drying gas. The heated material from heater 112
is introduced into ~ ~eparator 115 to separate unvaporized
material which is withdrawn through line 116. Superheated
vapor is withdrawn from separator 115 thro~gh line 101
for introduction into the "off-line" drum
to pr~vide a co~e having a volatile combustible matter
content, as hereinabove described.
- 11 -
, .,
~L~S4~ 7
In one modiication, the vapor for the drying step
S could be recovered from the coker combination tower a~d the
material wi~hdrawn from the of~-~ine drum is returned t~
the coker combination towex. Thus, in such an ~peration,
the coker combination tower is employed for both the "on-
line~ and "off-line~ coke dr~ms.
Similarly, although the preferred embodiment has
been described with reference to pretreating the feed by
tl) a low temperature oak to polymerize ~nsaturates; (2)
thermal crackin~ to increase aromatic content (reduce API
gravity); and ~3) separation of pitch, the invention is
15 also applîcable to coke production without such pretreatment
and to coke production which employs one or more of such pre-
trea~ment ~teps.
-- 12 --
The present inv~ntion will be further described
with respect to the following examples:
EXAMPLE 1
Decant oils having the properties summarized
in Table 1 were added with 50 parts per million of sulfur and
heat soaked at a temperature of 260~C. The feedstock so treated
was introduced into a tube of 6 mm inner diam~ter and thermally - -
cracked at a temperature of 500~C under a pressure of 20 kg/cm2G
~The residence time was 78 seconds on the cold oil basis.)
The feedstock was then introduced into a flash ~ower maintained
at 480C under normal pressure and non-volatile substances
were removed from the bot~om of the flash tower as pitch.
The oil obtained by cooling the overhead effluent was used
as the coking feedstock.
TABLE 1
Specific gravit~, 15/4C 1.0187
API gravity 7.4
Asphaltenes (C7 insolubles) 1.6 wt%
Conradson carbon 5.7 wt~
Sulfur content 0O75 wt~
Ash 0.01 wt~
Delayed coking was carried out under the conditions shown
in Table 2, using the oil obtained under the above-
mentioned conditions. The coke drum which was about 30 cm in
inner ~iameter and about 50 cm in height was placed in a molten
salt bath and was so designed as to permit external heating.
After the drum was filled, the drum was taken off-stream and
heated, as tabulated.
j4 ~
e
a
c~ ~ ~ h
bl
Q~
.r~ ~ ~ ~ ~ ~
~ A
_~ E ~
o ~ ~! ~ ~ ~ ~h .e
b ~ .1 0
o " 8
O ~o r~ ¢~ ,J~
h ~ C
C~ 3
O~
c J ~ y E U ,~ ¦ E
E ~ ~ E c
.
Runs A through C shown in Table 2 were per-
for~ed by the process according tc the present in-
Yention, while runs D through E were performed under
different conditions: the off-stream temperature in
run D was lower; and the on-stream coking temperature
in run E was higher than those used in the process
of this invention. Green coke obtained under these
conditions was calcined at 1, 400C by the ordinary
method, and calcined coke was pulveriæed. Each
sample of calcined coke was blended with coal tar
pitch as a b~nder and the mix was extruded in~o rods
to ma~e electrodes. The electrodes were baked at
1,000C and graphitized at 3,000C. The coefficient
of thermal expansion ~CTE)
in the direction parallel to the extrusion was measured.
The measurements obtained are shown in Table 3.
Table 3
A B C D E
CET (xlO~6/C)in 0.79 0.74 0.89 1.31 1.21
the direction parallel
to the extrus ion
~100 to 400C)
-
~5~ '7
The green coke which was ~btained in run D
contained a lot of pitchy substance in the upper por-
tion. It melted and foamed during calcining and ~,ad
a very poor appearance. The green coke obtained in
run E was a spongy one having a lot of foan,.
As is clear from Table 3, the cokes obtained
by the p~ocess of this invention ~ad very high quality.
EXAMrLE I I
Decant oils having the properties shown in
Table 4 were pretreated under the conditions su~marized
in Ta~le 5 to obtain a coking feedstock.
Table 4
Specific gravity, 15/4C 1.0192
Asphaltenes (C~ lnsolubles) 3.7 wt~
Conradson carbon 6.4 wt~
: 5ulfur content 0.64 wt%
Ash 0.0l wt~
Table 5
Soaking Amount o~ sulfur added 50 ppm
Temperature 270C
Reside~ce time 15 min
Crackinq Tube inner diameter 6 mm
Outlet temperature 490C
Pressure 22 kg/cm2G
R~sidenee time 7B sec
Flashing Temperature 4B0C
Pressure Atm.
-- 16 --
~ ~ 5~ ~O ~
The material bala~tce in the pretreatment W25
shown ir. Table 6.
Table 6
Pitch 11.1 ~t~
Coker feedstock (290C ~ 84.3 wt~
Disti~late (290C ) 2.4 wt~
C~acked gas & loss 2.2 wt~
CoXin~ was performed on the feedstocks so ob-
tained under the conditions summarized in Table 7,
and the YCM content o~ green coke so derived is also
sho~n in the same table.
Table 7
Run No. F G H
On~Stream Temp. (DC) 43~ 440 ~47 430
Delayed Pr~ss. (kg/cmZG) 5 5 5 5
Time ~hr) 24 24 24 24
~ecycle ratio 0.6 0.6 0.6 0.6
QI ~n coke drum 3 3 4 4
Off-Stre~n Temp. 1C) 460 460 447 430
Heating ~ime (~r) 6 6 6 6
Heated vapor STM STM STM STM
G~een coke VC.~ 6.2 5.8 11.7 23.6
lw~ )
~ 17
7~
Runs F and G were performed b~ the process
~f this invention, while run ~ was performed at a
hiyher ~n-stream c~kin~ te~p~rature than the in-
vention, and xun I at a lower ~ff-stream heatir.~
temperature, than that of the inventiDn. Ele~trodes
were made from coke obtained under the conditi~ns
sum~arized in Table 7 and graphitized at 3,OD0C.
The C~E or graphitized electrodes are sh~n .-
in Table 8.
:
._ :
Table 8 . `
i:
~un No. F G H
CTE (xlO S/C)
in the direc~ion 0.86 1.00 1.1~ 1.33
parallel to the
extrusion
(100-400C)
As is clear from Table 8, coke obtained by the
process of this invention had a very high quality. .:
:.
~XAMPLE III
Pyrolysis tar obtained as a by-product in the
thermal cracking of gas oil was pretreated under the
~onditions ~u~marized in Table 9 and coke made fro.
the coking feedst~ck so refined.
- lB -
:~5~ 7
Table 9
Soaking Amount of sul:Eur added 100 ppm
Temperature 260 C
Residence time 20 min
Cracking Tube inner dlameter 6 mm
Outlet temperature 470C
Pressure 25 kg/cm2G
Residence tlme ~bas~d on cold oil) 62 sec
Flashing Temperature 460 C
Pressure Atm.
Coking was per~ormed on this coking feedstock
under the conditions summarized m Table 10.
Table 10
Run No. J K L M
On-StXeam T~mp. (C) 435 460 440 445
Delay~d Coking .,
Pressu~e 6.5 6.5 6.5 6.5
~kg/cm G)
Time ~hr) 24 24 24 24
Recy~le 1.0 1.0 1.0 loO
ratio
Off-Stream
Heating Temp. ~ C)460 460 460 460
Time (hr) 8 8 8 8
HeatPd Coker light No~e (ex- Light Light
vapor distillate ternal Coker Cokex
Distillate Distillate
Green Coke VCM
(.wt~ percent) ~ 6.7 5.4 6.3 5.7
~5~ 7
Ru~ J was performed by the process of this
inve~tion, whereas run K was performed at a higher
on-s~ream coking temperature than in run J.
Electrodes were made from coke in the same way as in
Example I, and the CTE of electrodes graphi-
tized at 3,000C was measured. The results of
measurement are shown in Table II~
Table ll
Run No. J ~ L M
CTE (xlO /C)
in the direction
parallel to the 0.731.38 0.87 0,99
extrusion
(100-400C)
- 20 -
~ 7
EXAMPLE IV
Hydrodesulfurized decant oil having the properties shown in
Table 12 was pretreated under the same conditions as shown in
Table 5 of Example II to obtain a coking feedstock.
Table 12
Specific Gravity, 15/4 /C 1.0142
Asphal~enes (C7 insolubles) 0.2 wt. percent
Conradson Carbon 2.6 wt. percent
Sulfur Content 0.52 wt. percent
Ash 0.01 wt. percent
Coking was performed on this coking feedstock under the con-
ditions s~mmarized in Table 13, and the VCM content of green
coke so derived is also shown iTl the same Table.
Table 13
Run No. N O P
On-stream Temp. (C) 2 445 455 465
Delayed Pres.(K~/C~ G 6.5 6.5 6.5
Coking Time(hr) 24 24 24
Recycle Ratio 1.0 1.0 1.0
Off-stream Temp.(C) 465 455 465
Heating Time(hr) 6 2 6
Heated Vapor Coker Light Coker Light
Distillate Steam Distillate
Green Coke VCM
(PCT) 7.8 12.5 5.2
Run N was performed by the process of this invention, while
Run P was performed at a higher on-stream coking temperature-
than specified in the invention. Run O was performed at an on-
stream coking temperature of 455C and then after the drum was
filled, the contents of the drum were purged with non-heated
steam for 2 hours, without the use of a tem~perature greater
than the coking temperature. Electrodes were made from coke
obtained under the conditions summarized in Table 13 and gra-
phitized at 3000~C. The CTE values of graplhitized electrodes
are shown in Table 14.
-20a-
~ ~ ~4
Table 14
Run No. N O P
CTE in the direction parallel 0.83 1.22 1.19
to the extrusion (100 to 400C)
As is clear from Table 14, coke ~btained by t:he process of
this invention (Run N) had a very high quality.
- -20b-
~5~ 7
The present invention is particularly advantage~us
in that by employing the com~inatisn ~f del~yed co~ing at
a lower temperature than normally used in the art, follo~ed
by off-stream heating of the coke drum contents, at a
higher temperature to produce a coke with a
~peci~ied VCM content, the coke thus produced(af~er cal-
cining and ~raphitizing) has a lower CT~. If the coke is
produced at the lower temperatures, follcwed by calcination
and graphitization (no off-s~ream heating in the coke drum
at controlled temperature to provide a VCM content as here-
inabove described, prior to calcination~, the CTE of the
graphitized coke is higher than that provided in accordance
with the invention.
The invention, as hereinabove described, is particularly
applicable to the production of needle coke (CTE ~ 1.35 x 10 6/oC
measured at 100 - 400C, and also super needle coke CTE
C 1.1 xlO~6/C~ea~ured at 100 - 400C).
3~
The present invention has particular applicability
~-o the c:oking of a feedstock which has been pretreated b~
(1) thermal sc:~aking at 230 - 3150C, generally in the
presence of sulfur lalthough in some cases sulfur is not
required) to decrease the tendeney to depos~t coke and/or
polymer in su~sequent lines or equipment and/or (2~ thermal
crac~ing at 450 to 595C to increase aromaticity and/or
(3) ~eparation of non-crystalline substances. ~lthough
pretreatment is not required and/or pretreatment by use of
only one or two o~ the pretreatment steps may ~e employed,
~n general, ~he best results ~lowest CTE~ are achieved by
use o~ the three pretreatment steps in combination with the
coking at controlled temperatures, followed by off-stream
hea~ing ~o reduc~ VCM conten~.
(
-- 2~ --
