Hydrocarbon Processing - April 2021 - 26

Clean Fuels
hydrotreating unit, these feedstocks must be in liquid
form. That requires steam or electric heat tracing
systems that raise the temperature of pipes, tanks and
vessels to liquefy the fats and oils. The addition of
significant heat tracing capacity will likely be required
for both existing hydrotreating infrastructure, as well as
the rail, truck or barge piping and equipment used to
store and transfer feedstock into the unit.
Any of these factors could potentially give a refiner pause on
a renewable diesel conversion project. More likely, they will provide insight on the right way to move forward.
As they proceed, refiners must be prepared to face issues beyond these technical considerations. In an LCFS environment,
renewable diesel projects must be able to account for the carbon
they emit. Therefore, refiners must approach these projects holistically, measuring carbon intensity at every step along the path.
From the farm fields to the end product's final delivery, producers must look for ways to lower the carbon intensity at each step.
Despite these challenges, the transition to renewable diesel
will continue. The time for refiners to consider their options
is now.

has the potential to create a corrosive environment.
Another special consideration for renewable feedstocks
is the potential for polymerization in the feed train.
When hydrogen is absent, renewable feedstocks can
polymerize, which causes gumming and fouling in the
equipment. The addition of hydrogen could make the
equipment susceptible to high-temperature hydrogen
attack. One option is to update feed-side metallurgy
to protect against corrosive conditions. Another is
to create two separate pre-heat trains, with separate
systems for liquid recycle and fresh feed.
* Water and carbon dioxide (CO2) production-
Renewable diesel reactions produce water and CO2 in
much larger quantities than petroleum hydrotreaters,
creating potential carbonic acid corrosion concerns
downstream of the reactor. Metallurgy upgrades may
be required in the reactor effluent air cooler system.
Consideration must be given to the handling, treatment
and disposal of the extra water and CO2 produced in
these reactions. For example, if water is routed to the
refinery's sour water stripper, it may produce high
concentrations of carbonic acid in the sour water streams,
impacting how the water is treated and reused.
* Heat tracing-The vegetable oils and animal fats used
as feedstock become waxy and solidify at ambient
temperatures. To load them into trucks and rail cars
for shipment and, later, unload and charge them to a

ERIN CHAN is a Process Department Manager and Associate
Process Engineer at Burns & McDonnell, focusing on quality and
technical excellence for oil, gas and chemicals projects. She is a
leader in process design and engineering for innovative
renewable fuels and refining projects.

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Hydrocarbon Processing - April 2021

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