Hydrocarbon Processing - August 2021 - 41

Process Optimization
cutters are typically from atmospheric
and vacuum distillation units (VDUs),
such as atmospheric gasoil (AGO), light
and heavy AGO and vacuum gasoil
(VGO). These cutters have a low aromaticity
of around 30%-50%. Typical
properties of blending components are
detailed in TABLE 2.
Considering asphaltene content and
aromaticity, VLSFO fuel oil blends can
be categorized as paraffinic blends, aromatic
blends and hybrid blends.
Paraffinic blends. These blends
typically use vacuum tower bottoms
and the cutter [e.g., light atmospheric
gasoil (LAGO), heavy atmospheric gasoil
(HAGO) or ultra-low-sulfur diesel
(ULSD)] (TABLE 3).
Vacuum residue (VR) from the VDU
can be blended with low-sulfur streams
to produce the required product, keeping
the resulting blend aromaticity above
40% by controlling the blend ratio and
the order of blending. Trim gasoil (TGO)
dropping in vacuum tower bottoms will
help achieve the required aromaticity.
With VR blended with distillate, the final
blending aromaticity could drop below
40% and lead to sludging, depending on
the blend ratio and the order of blending.
Aromatic blends. These blends typically
use " cracked " blend components,
such as visbreaker tar bottoms and highly
aromatic cutters (i.e., LCO and HCO).
Any aromatic blend will have an excess
of aromaticity (more than 50%) and be
stable (TABLE 4).
Hybrid blends. These blends typically
use paraffinic blend components such
as atmospheric tower bottoms, vacuum
tower bottoms, and mixtures of both paraffinic
cutters (such as AGO, LAGO and
HAGO) and aromatic cutters (i.e., LCO
and HCO). Depending on the blend recipe,
a hybrid blend is not always guaranteed
to have an excess of aromaticity (more
than 50%) and to be stable (TABLE 5).
The changes in fuel production result
in a different nature and quality of fuels.
New fuels (such as VLSFO) that are comGasoil
(10 ppm sulfur)
VR unit
Bunker tanks
VR residue
Blender
FIG. 4. KNPC's VR/ARD units.
pliant with the 0.5% sulfur limit are likely
to display a wide variability of physical
and chemical properties, even between
fuel batches of the same ISO specification.
Potential to produce VLSFO. The
considerable decrease of sulfur in fuel
content had a substantial effect on bunker
fuel production. In response to the
IMO regulation's significant reduction
in sulfur requirements, refineries must
make capital investments and use innovative
technologies/methods to reduce
the amount of sulfur and particulates in
fuel oil. Apart from this, HSFO production
must be minimized in anticipation
of a drop in value.
VLSFO must be compliant with ISO
8217:2017 to adhere to these IMO requirements.
The blending of available
components in refineries plays a vital
role in production. The major concern
is the compatibility between different
VLSFO blends. VLSFO blending is a
challenge from fuel oil stability and compatibility
points of view.
KNPC'S EXPERIENCE
WITH VLSFO PRODUCTION
KNPC has two refineries-Mina
Abdullah (MAB) and MAA. Both refineries
produce clean-burning fuels, conforming
to Euro 5 standards. As per design,
KNPC will produce a significant amount
of LSFO with viscosities of 380 cSt and
180 cSt. The components in the KNPC
refinery to produce LSFO are atmospheric
residue from the crude distillation units
(CDUs), treated residue (ARDR) from
the atmospheric residue desulfurization
Parameter
(ARD) units, VR from the VDUs, distillate,
and LCO and HCO from the FCCU.
The option of producing the desired
VLSFO product from atmospheric residue
is not possible due to high sulfur content
(> 4 wt%). Diverse options tried by
KNPC to produce VLSFO, along with associated
limitations and subsequent product
qualities, are presented in detail here.
The MAA refinery's Clean Fuels Project
ARD unit can produce residue with
a sulfur content significantly less than
0.5%, which is further processed in the
vacuum unit to keep feed sulfur at a minimum.
ARD distillate can be used as a cutter
to blend with VR bottoms.
Option 1: Hydrotreated ARDR. KNPC's
new ARD unit's (FIG. 3) product can be directly
supplied as BFO without blending
with another stream with sulfur less than
0.5 wt%. ARDR sulfur will depend on the
level of desulfurization, and will vary from
the start of run (SOR) to the end of run
(EOR). Typical properties of the ARD
unit's residue are detailed in TABLE 6.
To route ARDR to the appointed
VLSFO tanks, a project modification is
required with controls in the unit and
offsite area. The required project modification
is raised, and is expected to take a
long time for completion.
Impact. There will be a reduction in
the conversion unit feed rate (primarily
in the hydrocrackers, FCCUs and coker
units), since part of KNPC's ARDR will
not be processed in the vacuum re-run
units, thus resulting in VGO/TGO/VR
losses. Therefore, naphtha, aviation turbine
kerosene (ATK) and diesel production
will be reduced, as well.
TABLE 6. Typical properties of the ARD unit's residue
Unit
Carbon residue, Conradson
Sulfur, total
Density at 15°C
Viscosity at 50°C
Sludge, hot filtration
Hydrogen sulfide (H2
Vanadium
Ash
Sediment
Asphaltenes
CCAI
S), liquid phase
% mass
% mass
kg/l
cSt
% mass
ppm
mg/kg
% mass
% mass
% mass
Calculated
ARD
3.98
0.4
0.9259
173
0.036
0.02
5.3
0.02
0.04
1.72
795
Hydrocarbon Processing | AUGUST 2021 41
Hydrocarbon Processing - August 2021

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