Chemical Engineering April 2020 - 14

Newsfront
A Push for 'Green' Crackers
S
Today's steam crackers are bigger than ever - those of tomorrow might be carbon neutral
TechnipFMC
team cracking is a key process
of the petrochemical
industry, whereby naphtha
or other petroleum-based
feedstock is thermally broken down
(cracked) into smaller building-block
compounds, such as ethylene, propylene,
butadienes and BTX (benzene,
toluene and xylenes), which are
then processed into plastics, rubber
and other polymers and chemicals.
The feedstock is cracked within milliseconds
as it flows through the furnace
tubes at temperatures of around
850°C. Crackers are large, complex
units with multiple furnaces - sometimes
as many as ten - that are integrated
with many different process
units for separating and purifying the
different olefins, which in turn are processed
into products. Hence, crackers
are at the heart of the aptly named
petrochemical complex (Figure 1).
Although crackers will operate with
the most economical feedstock, depending
on the location, all crackers
have one thing in common: today's
cracker furnaces use fossil fuels to
heat the tubes to the high temperatures
required. As a result, the steam
cracker is a major source of CO2
emissions resulting from the combustion
of fuels. In order to achieve
the goals agreed upon in the Paris
Agreement,
Europeans are working
to reduce the carbon footprint of
their crackers. In the short term, that
means improving the efficiency of the
furnaces. For the future, efforts are
underway to develop new, alternative
ways for making olefins, including
the use of electricity derived from
solar or wind power generation.
Steam-cracker trends
" One main trend has been the increase
in the size of plants worldwide, "
says Jim Middleton, manager
of Technology and Ethylene Product
Line Leader, TechnipFMC plc (London,
U.K.; www.technipfmc.com).
14
" Clients have been
aiming to maximize
the size of plant that
can be designed as a
single train, to maximize
economies of
scale. " Plants producing
1.5-1.8 million
tons/yr of ethylene
from liquid and
mixed-feed crackers,
and 1.5-2.0 million
ton/yr of ethylene
from ethane gas crackers are becoming
the norm for producers who
are not feed- or product-constrained,
he says.
" In North America, the focus has
been on producing ethylene from
ethane derived from shale gas, and
on capital efficiency. Elsewhere in
the world, the focus has been mainly
on naphtha, and particularly on an
increasing proportion of LPG [liquefied
petroleum gas] feeds, " continues
Middleton. " In both Asia and
Europe, some world-scale cracker
projects are being designed based
on imported ethane feedstock, "
adds Dennis Mayfield, vice president
Process Technology, TechnipFMC.
" In the Middle East, the trend reflects
the shortage of ethane availability,
directing the investment into liquid
feed or mixed ethane and liquid feed
steam crackers. Ethane crackers in
this region are expected when LNG
[liquefied natural gas] producers expand
their production facilities, " contributes
Yvon Simon, head of Technologies
Department, TechnipFMC.
" [Petroleum] refinery operators
outside the U.S. have been looking
to move into the production of olefins
to maintain capacity in response
to the anticipated slow growth in the
demand for fuels, " says Middleton.
" There is a trend to develop integrated
refineries and steam cracker
complexes or petrochemical refineries.
The ultimate development of
FIGURE 1. Steam crackers are part of large petrochemical complexes,
such as Chevron Phillips Chemical Co.'s Cedar Bayou plant in Baytown
Texas. CPChem's 1.5-million m.t./yr ethane cracker started up in 2018
such a trend is the crude-to-chemicals
concept. Oil-to-chemicals projects
have been discussed, but few
of these projects have moved to the
implementation stage, " says Simon.
" In Europe, the focus is on sustainability,
particularly CO2 reduction and
capture, energy efficiency and recycling
of plastics, " says Middleton.
Steam-cracker improvements
" TechnipFMC has developed and
implemented two particular new patented
developments in furnace radiant
coils - a Three Lane coil design and a
Swirl Flow Tube design. Both of these
offer improved run lengths and/or capacity
for cracking furnaces. Both of
these developments are in commercial
operation, " says Middleton.
" Radiant coil designs have evolved
over the past few decades to meet
greater industry demands, " explains
Mayfield. " This journey has been
characterized by numerous small
steps, as well as several vital, groundbreaking
innovations. The triple-lane
concept is the latest development
in this lineage. It has several merits
over preceding and competing developments,
including:
it
reduces
peak tube-metal temperatures; it is a
simple and elegant way to improve
run length, capacity and selectivity;
it can be applied in revamps and
new furnaces; and it is suitable for all
cracker feeds, from ethane to VGO
[vacuum gas oil], " says Mayfield.
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Chemical Engineering April 2020

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