Hydrocarbon Processing - November 2021 - 77

Valves, Pumps and
Turbomachinery
J. PRUSHA, Emerson Automation Solutions,
Marshalltown, Iowa
Control valve design challenges
for green diesel processes
Green (or renewable) diesel is a biofuel
that offers several advantages over biodiesel,
so many refineries are increasingly
including it in their production portfolios.
The downstream portion of the refining
process is very similar to traditional diesel
hydrotreating processes, making modifications
less onerous than switching to the
production of a totally different fuel.
While similar, there are some process
differences between green diesel and
standard diesel that are more difficult to
handle for the critical control valves in the
unit. This article discusses the green diesel
process, and it offers suggestions for
choosing the best valves for reliable, safe
and profitable production.
Biodiesel vs. green diesel. Biodiesel
has its roots from experiments conducted
in the 1930s, and it has been produced in
quantity since the 1980s. It uses a transesterification
process to convert various
vegetable oils and/or animal fats into fatty
acid methyl esters (FAME). The burn characteristics
of FAME are like diesel fuel, but
it is chemically different and tends to gel in
colder temperatures. This gelling limits the
amount of FAME that can be blended to
10%-20% of the total diesel volume, and,
even then, the fuel can be troublesome to
handle during colder winter months.
Green diesel is a more recently introduced
process that starts with the same
collection of vegetable oils and/or animal
fats, but the result is a product chemically
identical to diesel. Since diesel and green
diesel are the same in terms of end product,
there is no blending restriction, and
any engine can operate on 100% green
diesel. FIG. 1 compares biodiesel, green
diesel and regular diesel.
FIG. 1. Like biodiesel, green diesel can be created from various vegetable oils and animal
fats. However, unlike biodiesel, green diesel has the same chemical composition and physical
properties as standard diesel and can be used as a direct replacement.
The significantly increased blending
rates for green diesel enable producers to
achieve much lower carbon intensity in
their final product. Carbon intensity is a
method of measuring how much carbon
is emitted in the production and burning
of a particular fuel. Gasoline, jet fuel and
diesel derived from crude oil have a carbon
intensity of about 100. Biofuels derived
from non-crude oil feedstocks have
substantially lower carbon intensity values-as
low as 20, depending on the raw
materials used as feedstock. The overall
carbon intensity often drives regulatory
credits, so the low carbon intensity and
high blend rates of green diesel offer attractive
incentives for refineries to switch
at least some of their production.
The green diesel process. Green diesel
can be created from a large variety of
renewable feedstocks (FIG. 2). There is no
significant advantage in production yield
from one type of feedstock to the other,
and each takes about 7.5 lb-8.5 lb of raw
material to create a gallon of fuel.
The production of green diesel starts
with pretreatment (FIG. 3). Feedstocks
must be separated and treated differently
to convert them into a common intermediate,
which feeds the hydrotreater processing
unit downstream.
Hydrocarbon Processing | NOVEMBER 2021 77

Hydrocarbon Processing - November 2021

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