Hydrocarbon Processing - March 2021 - 42

Petrochemical Technology
pipe grades are to be made (e.g., PE 100
pipes or black pipes), thus justifying the
installation of a dedicated extruder for
pipe grades.
An extruder with a motor or drive of
15 MW-20 MW is considered very large
and are typically single-speed extruders
because variable-speed extruders with
such large motors are extremely expensive. Additionally, the specific energy
index of an extruder package defined as
Kwh/kg (kilowatt hour/kilogram) of capacity becomes high and cost prohibitive
due to energy or electricity costs.
The extruder capacity is nominally
specified by screw diameter. Established
extruder package vendors have successfully demonstrated operation with
380-mm-450-mm screw diameters with
improved filling efficiency. Mega compounders, as they are called, have nearly
reached a torque limit for standardized
throughput rate with respect to specific
energy, especially for LLDPE and HDPE
for certain applications at approximately
100 t/hr.
A single extruder capacity up to
100 t/hr is considered a proven and reliable scale-up. This would imply that
components downstream of the processing section are designed for a capacity higher than 100 t/hr. Therefore, it is
logical that a reactor or plant capacity
of 80 t/hr-85 t/hr (or the equivalent to
700,000 tpy) is achievable with operational reliability if an extruder capacity of
100 t/hr is considered a proven scale-up.
Silos and pneumatic conveying. Silos are generally made either of stainless
steel or Al/Al alloys. These pressure-less
vessels are fabricated onsite. The number
and size of silos are decided by the client based on their operating philosophy.
However, each silo with a capacity of
700 t-1,000 t is common in the industry
with 24 hr-48 hr of combined installed
storage space for blending and storage
determining the number of silos.
Pellet pneumatic conveying. Product

pellets are pneumatically conveyed from
the extruder to blending/storage silos and
conveyed from silos to warehouse for bagging or packaging.
The pneumatic conveying of pellets
is largely dictated by the principle of
velocity to prevent solids from settling
during transportation by conveying.
42

MARCH 2021 | HydrocarbonProcessing.com

Consequently, pipeline sizes increase
proportionately to capacity and tend to
become large. This is not as evident in
straight pipelines; it is piping elements
like bends, diverter valves, rotary feeders,
etc., that really set the limitation on the
confidence of the scale-up and the proven-ness of the components. Generally,
pneumatic conveying capacity up to 120
t/hr is considered proven due to reliable
scale-up, although capacities up to 140 t/
hr appear promising in the future.
Single-line capacity challenges
ahead. This discussion suggests that sin-

gle-line capacities for PE and PP plants
are expected to range from 500,000 tpy-
700,000 tpy at the higher end of the spectrum. Plant capacities will be dictated by
product mix and the technology selected.
Technology selection is guided by factors
that include:
* Flexibility
* Versatility
* Product range
* Catalyst range and productivity
* Product transition time
* Proven capacity of critical
equipment, such as the reactor,
extruder, etc.
This is of course over and above the usual
CAPEX and OPEX parameters.
Takeaway. PE faces a greater challenge

due to the nature of a wide spectrum of
product application, ranging from LLDPE, MLLDPE, MDPE, MM-HDPE
and HM-HDPE to bi-modal HDPE. No
single technology is expected to encompass the entire range in equal measure for
various reasons. This has necessitated licensees to seek a judicious combination
of technologies to cover the entire product range, or to focus on a selective product range. The conceivable combinations
can be but are not limited to:
* Fluidized-bed gas phase +
loop slurry
* Fluidized-bed gas phase + CSTR
* Two fluidized-bed gas phases
with swing capability
* Two-loop slurry: SL + ADL.
The single-line capacity of these technologies can be expected to advance to
the range of 550,000 tpy-750,000 tpy
soon with an emphasis on energy efficient design.
PP has an advantage over PE in that
all PP technologies offer a full product

range. If ethylene is unavailable, only a
homopolymer PP plant can be installed
with the provision to add an impact copolymer PP reactor later-Lummus
Novolen in an exception, as its two-reactor technology can produce the entire
product range. All PP technologies are
expected to advance toward a 550,000
tpy-750,000 tpy range soon with an emphasis on energy efficient design.
It is conceivable that the challenge of
large-capacity plants can be partly overcome by installing one or more smallcapacity, high-value speciality plants that
are ethylene or propylene derivatives
other than the usual PE and PP. The new
trend of diverting part of the ethylene
and propylene to produce more valueadded speciality chemicals looms bright
on the horizon and will emerge sooner
than later. Plant size will be conveniently
smaller and, accordingly, CAPEX will decrease with relatively higher returns. Elements of business risks accompanying
large single-line capacity will be replaced
by opportunities.
LITERATURE CITED
LyondellBasell, online: https://www.lyondellbasell.
com/en/search/?q=hostalen
2
Mitsui
Chemicals,
online:
https://jp.
mitsuichemicals.com/en/search/?q=cx
3
Chevron Phillips Chemical, online: https://www.
cpchem.com/search?search=martech
4
Univation Technologies, online: https://www.
univation.com/en-us/unipol.html
5
LyondellBasell, online: https://www.lyondellbasell.
com/en/search/?q=spheripol\
6
Mitsui
Chemicals,
online:
https://jp.
mitsuichemicals.com/en/search/?q=hypol
7
W. R. Grace and Co., online: https://grace.com/
en-us/capabilities/Pages/unipol-plant-and-processoverview.aspx
8
Lummus Technology, online: https://www.
lummustechnology.com/Process-Technologies/
Petrochemicals/Polypropylene-Production
1

JAYANT D. DIVEY works as a
Polyolefins Technology Consultant
supporting technology evaluation
and selection, process design and
troubleshooting for new grassroot as
well as operating petrochemicals
plants. Prior to that, he retired as
Senior Vice President from Reliance Industries Ltd.,
where he was responsible for polyolefins technologies.
He has four decades of extensive experience in
practically all HDPE, LLDPE, LDPE and PP technologies.
He also worked as technology manager in FCC light
olefins, handling C2, C3, C4 and C5 chemicals. His areas
of interest and expertise range from polyolefins
catalysts and reaction systems to products. He has led
many projects from concept to commissioning,
including design basis to engineering. He holds a B.
Tech (BS) degree from the Laxminarayan Institute of
Technology Nagpur University, and an M.Tech (MS)
degree from the Indian Institute Technology Bombay,
India, both in chemical engineering.

https://www.lyondellbasell.com/en/search/?q=hostalen https://www.lyondellbasell.com/en/search/?q=hostalen https://jp.mitsuichemicals.com/en/search/?q=cx https://jp.mitsuichemicals.com/en/search/?q=cx https://www.cpchem.com/search?search=martech https://www.cpchem.com/search?search=martech https://www.univation.com/en-us/unipol.html https://www.univation.com/en-us/unipol.html https://www.lyondellbasell.com/en/search/?q=spheripol https://www.lyondellbasell.com/en/search/?q=spheripol https://jp.mitsuichemicals.com/en/search/?q=hypol https://jp.mitsuichemicals.com/en/search/?q=hypol https://grace.com/en-us/capabilities/Pages/unipol-plant-and-processoverview.aspx https://grace.com/en-us/capabilities/Pages/unipol-plant-and-processoverview.aspx https://grace.com/en-us/capabilities/Pages/unipol-plant-and-processoverview.aspx https://www.lummustechnology.com/Process-Technologies/Petrochemicals/Polypropylene-Production https://www.lummustechnology.com/Process-Technologies/Petrochemicals/Polypropylene-Production https://www.lummustechnology.com/Process-Technologies/Petrochemicals/Polypropylene-Production http://www.HydrocarbonProcessing.com

Hydrocarbon Processing - March 2021

Table of Contents for the Digital Edition of Hydrocarbon Processing - March 2021