Hydrocarbon Processing - August 2022 - 23

Special Focus Refining Technology
W. ECHT, Merichem
Green refinery challenges: Small-scale
sulfur recovery
As the gavel dropped, signaling a historic agreement at the
conclusion of COP26 (2021 United Nations Climate Change
Conference) in Glasgow, Scotland, leaders from 197 nations
agreed to continue supporting the goal of limiting global warming
to 1.5°C above pre-industrial levels. The race is on!
Two initiatives that emerged from COP26 were the Mission
Innovation and Carbon Dioxide (CO2
) Removal Projects. Mission
Innovation-a collaboration among governments to unlock
affordable decarbonization pathways-seeks to accelerate
technologies that will reduce emissions by the sectors responsible
for 52% of current global emissions. The Netherlands and
India are leading a biorefinery program to make bio-based alternative
fuels and chemicals economically attractive. The other
initiative is the Carbon Dioxide Removal Project, which is led
by Saudi Arabia, the U.S. and Canada. The project's goal is to
net an annual reduction of 100 MMtpy of CO2
countries are following suit.
by 2030. Other
The biggest culprit. In November 2021, the Global Carbon
Project, a Global Research Project of Future Earth and a research
partner of the World Climate Research Programme, reported
that global CO2
decrease of 5.4% from 36.7 GtCO2
global fossil CO2
emissions from fossil fuels were 34.8 GtCO2
in 2019; however, projected
emissions in 2021 were forecast to rebound
close to their pre-COVID levels after an unprecedented drop in
2020. Emissions from coal and gas use are set to grow more in
2021 than they fell in 2020, but emissions from oil use remain
below 2019 levels.
In the U.S. alone, the U.S. Environmental Protection Agency
(EPA) reports that the transportation sector generates the largest
share of greenhouse gas (GHG) emissions (~ 23%). The
Intergovernmental Panel on Climate Change states that this
sector presents the most challenges to mitigation.
Energy transition and refinery restructuring. In the context
of fluctuating market conditions for traditional oil-derived
fuel markets, refiners are increasingly focused on the energy
transition to improve the profitability of their assets and secure
long-term operations, in tandem with reducing GHG emissions
and moving towards carbon neutrality. Many refineries around
the world are considering renewable fuels production at either
existing refineries that will continue to process crude oil, or at
facilities that are idle with existing infrastructure to accommodate
new processing units to refine (mainly) diesel and jet fuels
from sustainable sources, such as used cooking oils (UCO),
, a
duction of CO2
waste animal fats (tallow) and/or certified sustainable vegetable
oils, such as rapeseed.
With the new processing technologies, there is a co-proand
the need to maintain active catalyst in the
reaction system. A small amount of sulfur, usually in the form
of liquid disulfide oils, is added to the conversion reactors to
maintain catalyst activity. The sulfur is converted to hydrogen
sulfide (H2
the unwanted CO2
H2S. The resulting acid gas stream contains far less sulfur than is
practical to remove with a typical refinery sulfur recovery unit
(SRU) using Claus technology.
In its continued contribution to improving sustainable mobility,
a multinational oil and gas company based in Europe
uses a proprietary sulfur recovery technologya
to serve as the
SRU. This technology is a patented, wet scrubbing, liquid redox
system that uses a chelated iron solution to convert H2
S.
S
to innocuous, elemental sulfur. It is designed to remove about
4 metric tpd (tonnes per day) of sulfur from an acid gas with up
to almost 7 mol% H2
The processes. The hydrotreated vegetable oil (HVO) process
produces renewable fuels via hydrogenation and hydrocracking
of vegetable oils and animal fats using hydrogen and
catalysts at high temperatures and pressures. The oxygen is
stripped in a reactor with a catalyst that often requires sulfiding
to promote conversion chemistry and avoid catalyst deactivation.
Dimethyl-disulfude (DMDS), the most commonly used
chemical for sulfiding the catalyst, is converted to H2
oxygen from the feedstock is converted to CO2
S, and the
and water during
the deoxygenation reaction.
Hydrocarbon liquids exit the reactor and are routed to a
three-phase separator, where the water is removed and vapors
are collected for cleaning and recycling. The hydrocarbon liquids
are routed to an isomerization reactor before being separated
into various cuts to create light fuels, sustainable aviation
fuels and renewable diesel.
The vapors from the separator are often routed to an amine
unit to remove the H2
S and CO2
formed in the deoxygenation
reactor. The treated gas from the amine unit is rich in hydrogen
and recycled to the HVO process. A slipstream may be used as
fuel gas. Depending on what other units may be operating at the
refinery, additional acid gases may be processed in other amine
units at the site. The European refinery mentioned here utilized
large Claus units that had been previously idled.
Hydrocarbon Processing | AUGUST 2022 23
S) in the reactor system. An amine unit can remove
from the process, but this also removes the
Hydrocarbon Processing - August 2022

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