Needle Coke is a premium grade, high value
petroleum coke, used in the manufacturing of
graphite electrodes for the arc furnaces in the
metallurgy industry. Its hardness is due to the
dense mass formed with a structure of carbon
threads or needles oriented in a single direction.
Needle coke is highly crystalline and can provide
the properties needed for manufacturing graphite
electrode. It can withstand temperatures as high
as 28000C.
Needle Coke (Pictorial view of SEM)
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Unlike other petroleum products, there is no standard specification
for needle coke and it is categorized under various grades depending
on the properties. Directionally, the desired properties of needle coke
for manufacturing of premium quality graphite electrodes are lower
coefficient of therml expansion(CTE), lower sulfur and ash content,
higher real density, etc.
Only few companies in the world manufacture needle coke using their own proprietary technology.
The needle coke technology available with few companies (e.g.Conoco etc.)
is usally not availbale for licensing.
Availability of delayed coker units in refineries and
absence of any manufacture in India, impelled Indian Oil to work in the development of needle coke
technology. By developing this novel technology
and producing needle coke in its Guwahati
refinery, IndianOil has become the pioneer in this
technology in India.
The technology is primarily focused on production
of needle coke in any existing delayed coker unit
using heavier hydrocarbon streams without any
costly pre-treatment. Formation of needle coke
requires specific feedstocks, special coking and
also special calcination conditions. If feedstocks
are suitable for needle coke, process conditions
for coking and calcination are selected to improve
the properties and yield of the needle coke.
Typical yield of needle coke is 18-30 wt% of
fresh feed.
The maximum limits of sulfur and ash in calcined
needle coke are 0.6 and 0.3 wt% respectively.
Higher sulfur content of coke can cause the
puffing of electrode. High ash content can
increase the resistivity and decrease electrode
strength. The calcined coke with higher sulfur and
ash content is not considered suitable for
manufacturing of graphite electrode even if other
properties meet the quality of premium grade
coke. Thus, the quality and price of needle coke
are highly dependent on the properties of
feedstock used for coking.
Refineries having delayed coker unit either
processing low sulfur crude and/or having a
residue hydrotreater unit and/or having RFCC/
FCC unit processing low sulfur feed are suitable
for considering this technology.
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 Typical Process Conditions |
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Process conditions for production of needle coke
are not unique and need to be optimised
depending on feed properties and plant
hardware constraints, if any. Typical ranges of
operating conditions are as below :
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Coil outlet temperature:
470 to 510 ºC |
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Recycle ratio: 0.2 to 0.8 |
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Cycle time: 18 to 36 hrs |
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Coke drum pressure: 1.5
to 9.5 kg/cm2 (g) |
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