che_november-2024 - 29

gies include carbon capture, utilization
and storage (CCUS), hydrogen
fuel switching, renewable feedstock
adoption, steam-cracker enhancement
and process optimization.
Process simulation software is
a powerful tool to facilitate precise
modeling and optimization of complex
processes. In this article, a
process simulation software with
an
integrated
steam-cracker-furnace
model is used to investigate
various
decarbonization
overview
of
the
strategies
aimed at improving furnace energy
efficiency and reducing CO2
emissions, while providing a comprehensive
decarbonization
potential of steamcracking
furnaces.
Decarbonization strategies
There are various approaches for decarbonizing
steam crackers - some
of these approaches are aligned with
net-zero emissions, while others are
considered to be near-zero emissions.
Several net-zero strategies are
illustrated in Figure 2 and discussed
further in Refs 8 and 10-12.
Bio-based and recycled plastic
waste feedstock. Transitioning toward
decarbonization necessitates
a fundamental re-evaluation of feedstock.
Adopting a circular economy
approach,
energy
consumption
and carbon footprint reduction are
achieved by substituting conventional
fossil fuels with bio-based alternatives,
and waste plastics from
depolymerization or pyrolysis processes.
This approach not only mitigates
emissions, but also reduces
reliance on finite fossil resources,
thereby laying the groundwork for a
more sustainable lifecycle [12-15].
Thermal
efficiency.
Remarkable
evolution in the energy efficiency
of steam-cracker furnaces can be
obtained by improving two furnace
sections - the firebox and the combustion
section. Reduction of energy
consumption in the firebox can be
achieved by improving firebox radiation
efficiency, such as by increasing
emissivity,
changing coil type
and configuration and optimizing
the process conditions to increase
ethylene yield, including the steamto-hydrocarbon
ratio and coil outlet
pressure (COP).
Carbon-capture (CC)
efficiency
CC energy intensity
Energy savings
Emissions reduction
Margin improvement,
CT
Margin improvement,
CCC
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Coil configuration refers to how
the heat-exchange coils in the radiation
section are arranged within
the furnace to facilitate efficient heat
transfer. Applying specific coil or
tube types, such as ribbed tubes
and finned tubes, especially mixing-element
radiant tubes (MERT),
can improve heat transfer by either
increasing the heat-transfer area
(cross-sectional area) or heat-transfer
coefficient
directly. These tube
types help increase heat flux through
the axial profile and increase run
length [16, 17].
Pre-combustion
strategies. To
reduce the emissions associated
with energy-intensive combustion
processes, innovative technologies
to optimize combustion and
fuel switching (changing the ratio
of methane to hydrogen) can be
investigated, which consequently
also will
tion.
reduce energy consumpPre-combustion
strategies
enhance
combustion efficiency by
optimizing fuel composition before
entering the combustion burner to
achieve better fuel and air mixing.
This approach aims to maximize
Steam cracker KPI
Fuelgas consumption
rate
Fluegas flowrate
Severity (P/E)
Fluegas composition
(CO2, O2)
Energy intensity
Carbon intensity
Ratio of propylene to ethylene production rate
Molar composition of CO2 and O2 in fluegas
Total energy consumption per ethylene + propylene
production rate. Total energy consumption =
Total furnace fuel + Electrical consumption -
Steam export
CO2 emission generation per ethylene +
propylene production rate
(Fluegas CO2 rate - Captured CO2 rate) / Fluegas
CO2 rate
Reboiler energy consumption rate per captured
CO2 rate
Percentage change in energy consumption compared
to the base case (negative values indicate a
reduction in energy consumption)
Percentage change in emissions compared to the
base case (negative values indicate a reduction
in emissions)
Percentage change in margin compared to the
base case, taking carbon tax (CT) into account
Percentage change of margin by comparing new
case to base case, considering carbon capture
cost (CCC)
NOVEMBER 2024
Definition
combustion efficiency while minimizing
emissions from incomplete combustion,
improving fuel utilization
and consequently, increasing overall
furnace efficiency.
Incorporating hydrogen into the
fuel mix can lead to efficient combustion,
and consequently reduces
the carbon footprint, since hydrogen
has a high energy content and burns
with minimal emission. The hydrogen
required for hydrocarbon fuel
switching can be obtained through
various methods, including water
electrolysis, as well as steam methane
reforming (SMR) or auto-thermal
reforming (ATR) followed by CCUS
( " blue " hydrogen). Additionally, hydrogen
can be produced by the
gasification of fossil- or bio-based
fuels into synthesis gas (syngas; a
mixture of CO and hydrogen), with
subsequent conversion of syngas
to hydrogen and CO2 through the
water-gas shift (WGS) reaction. Another
source of hydrogen is from the
recycled hydrogen-rich byproducts
of the olefin plant itself.
Water electrolysis uses electricity
to split water molecules into hydroTABLE
1. KEY PERFORMANCE INDICATORS (KPIS) FOR STEAM-CRACKER
DECARBONIZATION STUDY
Unit
m.t./h, m3/h
m.t./h, m3/h
wt./.wt.
mol %
GJ/m.t.C2, C3
m.t.CO2/m.t.C2, C3
m.t./m.t.
GJ/m.t. CO2
%
%
%
%
29
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