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Petroleum Refining – Chapter 10: Residue Upgrading
10-1
Chapter 10 Residue Upgrading (Heavy Oil Processing)
Introduction
Heavy oil processing includes
• Desulfurization of High Sulfur Atmospheric or Vacuum Residue → ARDS (Chapter 8).
• Thermal Cracking of Low Sulfur Vacuum Residue → Delayed Coker
• Hydrocracking of High Sulfur Vacuum Residue → H-Oil & Isomax
• Catalytic Cracking of Low Sulfur Atmospheric or Vacuum Residue → RFCC
• Extraction of oil from vacuum residue → Solvent deasphalting (SDA)
• Conversion of coke into gas → KRW Gasification
• (if the viscosity is too high) Viscosity reduction of vacuum residue → Visbreaking
Figure 10-1. Types of residue processing schemes.
CDU
&
VRU
H-Oil or
Isomax
CDU
ARDS
RFCC Residue
Residue
Residue
Delayed
Coker
CDU
ARDS
VRU
Residue
Residue
Residue
Coke
HCR
VGO
CGO
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-2
1. Delayed Coker
Figure 10-2. The Delayed Coker Unit
Introduction
• A severe thermal cracking process (high temperature reactions, no catalyst).
• Converts heavy HC's into light HC's
• Simplified reaction,
Figure 10-3: Simplified Thermal Cracking Reaction.
• Gases and coke (carbon) are side products of thermal cracking.
• Types of thermal cracking processes
1. Flexi-coking.
2. Fluid Coking (simplified version of flexi-coking).
3. Vis-breaking (mild thermal cracking operation).
4. Delayed coker (most widely used).
• In 1997 KNPC MAB1 commissioned a two-train delayed coker unit capable of processing
a total of 60,000 BPSD of hot vacuum residue (2 X 30,000). Each coker train has 2
heaters and 4 coke drums (one heater serving 2 drums).
1 28% of US refineries had cocking facilities in 1990. Very few delayed coking units actually
exist outside the US. Only two exist in the middle-east (one in KNPC-MAB and one in
Egypt).
CH4 + 9 C
C20H26
C10H22
+
gas coke
Petroleum Refining – Chapter 10: Residue Upgrading
10-3
• MAB delayed coker can also process vacuum residue from MAA refinery.
• The process is "controlled thermal cracking" to produce gas, liquid distillates on
continuous basis and solid coke on a semi-continuous basis. The coke drums are filled
and emptied on a time cycle, whereas, the fractionator facilities are operated
continuously.
Advantages
• The important contributions of Coker Units to the overall Refinery Operations are;
1. Conversion of the “bottom of the barrel” - low value fuel oil stocks to more valuable
middle distillates.
2. Produce a high quality “needle coke” (from stocks such as heavy catalytic gasoils &
decanted oils from the FCC unit).
3. Significant amount of gas production (up to 25 MMSCFD) which helps minimizing
oil firing and natural gas imports.
1. Improve the quality of the feed to the FCC and the HCR (Hydrocracker) units
through reducing metal and carbon content of the CGO feed to these units which
reduces coke formation on the catalyst allowing increased throughputs for FCC and
longer turnaround for the HCR.
4. Generation of 450# steam (up to 144,000 lbs/hr) from waste-heat for use in the
refinery’s steam network.
• Disadvantage – Products contain olefins
FEED
• Usually Vacuum Residue.
• Any other heavy stream in the refinery like atmospheric Residue, aromatic gasoils1 and
thermal tars2.
PRODUCT
Table 10-1: Products of the Coker Units at MAB refinery.
PRODUCT
YIELD WT % ON
FEED
DESTINATION
10% RR
Operation
30% RR
Operation
Gas (C4)
Light Naphtha (C5-160)
Heavy Naphtha (160-300)
Kerosene (300-480)
Diesel (480—680)
Gasoil 680+
Green coke
7.3
3.0
6.7
14.1
23.3
26.3
19.3
8.0
3.0
7.0
16.7
25.2
17.0
23.0
Refinery Fuel Gas System
Merox Unit
Naphtha Hydrotreater/Merox Unit and/or storage
Kero Hydrotreater and/or storage
Diesel Hydrotreater/FO pool and/or storage
FO pool and/or to FCC Hydrocracker
Storage
1 Other heavy product streams can be sent to the delayed coker (instead of being blended into
heavy fuel oil, the market for which is becoming more limited). 2 The heavy products from the FCC unit (HGO) and the alkylation unit (tar) can be sent to the
coker for processing.
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-4
PROCESS DESCRIPTION
• Hot fresh liquid feed (vacuum residue) is charged to the fractionator 2-4 trays above the
bottom vapor zone, where the coker drum vapors are injected.
• This accomplishes the following:
1. Hot vapors from the coke drum are quenched by the cooler feed liquid thus
a. preventing any significant amount of coke formation in the fractionator.
b. condensing a portion of the heavy ends which are recycled.
c. stripping (vaporizing) the light material from the fresh liquid feed.
2. The fresh feed liquid is further preheated making the process more energy efficient.
• The fresh feed combined with recycle oil from the coker fractionator bottom is charged to
the coker heaters.
Heater
• The thermal cracking of such heavy stocks results in unwanted deposition of coke in the
heaters.
• Employing high velocities in the heaters (minimum residence time) and using steam (to
lower the HC partial pressure) allows raising the oil temperature above the coking point
without significant coke formation in the heaters.
• The oil stock is moved from the heater into one of the two coke drums.
Coke drums
• Providing an insulated (coke) drum on
the heater effluent allows sufficient
time for the coking to take place in the
drums instead of the heater. Hence, the
term "delayed" coking.
• Usually 4 coke drums and 2 heaters are
provided, but units having 2 drums
with one heater are also possible.
• The coke drums are large enough to
take in heater effluents for a period of
24 hours while releasing the vapors in
these stocks continuously.
• The vapors from the coke drums in
service are sent to the fractionator.
• These vapors are quenched
a. by gasoil at coke drum top (to
control fractionator feed gas
quality)
b. by vacuum residue feed at fractionator bottom section (to control gasoil endpoint
and fractionator bottoms stock quality).
Fractionator
• Vapors comprising of steam and thermal cracking products (gas, naphtha, kerosene,
diesel, and gasoil) from the top of the coke drum return to the base of the fractionator.
• The fractionator works in the same way as conventional crude oil fractionator column and
separates the various distillates from the feed (coke drum overhead gases).
• The vapors flow up through the quench trays (numbers 1– 4).
Petroleum Refining – Chapter 10: Residue Upgrading
10-5
• Above the fresh feed entry in the fractionator, 2-3 additional trays below the gasoil draw
off tray exist. These trays are refluxed with partially cooled gasoil to quench and provide
fine trim control of the gasoil endpoint and minimize entrainment of any fresh feed (or
recycle) liquid into the gasoil product.
• The fractionator overhead gases are compressed, cooled and sweetened (by MEA wash)
before going to the fuel gas system.
• The overhead naphtha is sent to a stabilizer and splitter to produce light and heavy naphtha
streams.
• Coker kerosene, coker diesel and coker gasoil are side-draw products from the
fractionator.
• The fractionator bottoms are sent back as recycle to join the fresh feed.
• The rate of recycle oil (fractionator bottoms to coke drum) / (fresh feed rate) is called
‘recycle ratio’. This is an important operating variable of the coker unit and is unusually
between 10%, 30% and 100%.
Pumparound
• Upper and lower pumparound reflux systems are provided below the kerosene and gasoil
draw-off trays to improve kerosene/diesel separation and Gasoil endpoint.
• Pumparrounds also help recover heat at a high temperature level and minimize the low-
temperature level heat removal by the overhead condenser heat (that cannot normally be
recovered by heat exchange and is rejected to the atmosphere through a water cooling
tower or fin-fan coolers).
• Pumparrounds function in the same way described in the crude unit fractionator.
Side Strippers
• There are three side strippers; for kerosene, diesel and gasoil.
• They function in same manner described in the crude distillation unit.
• The gasoil side draw for example employs 6-8 tray stripper with steam introduced under
the bottom tray for vaporization of light ends to control the IBP of the gasoil.
• Steam and vaporized light ends are returned from the top of the gasoil stripper to the
fractionator 1-2 trays above the draw-off tray.
Figure 10-4. Coke formation model; how coke forms in the Drum
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-6
Figure 10-5: Delayed Coking Unit
Kerosene
Diesel
HAT
Recycle Oil (R) Recycle Ratio = R/F
Petroleum Refining – Chapter 10: Residue Upgrading
10-7
Figure 10-6: Delayed coking unit at MAB refinery.
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-8
Coke drum operation & decoking cycle
• While one drum is being used for coke formation, the other drum will be undergo
decoking.
• After completing 24 hours of coking service where the coke drum is 70 to 75% filled to
keep a safe margin from the top, the heater effluent is switched to the empty coke drum.
• The first coke drum is then isolated, steamed to remove HC vapors for safety, gradually
cooled by steam water mixture then filled with water, and drained.
• The drum heads are then removed and coke in the drums are cut by high pressure water
jets (3000 psi) from the top and the drum will be emptied out.
• Decoking is done either by mechanical drill or reamer, or hydraulic system (which is
more common).
Table 10-2. Coking decoking time schedule
Drum #1 Duration Drum # 2 Duration
Fill drum with coke 24 hrs Switch & Steam out
Cool
Drain
Unhead & decoke
Head up and test
Heat up
Spare (idle) time
3 hrs
3 hrs
2 hrs
5 hrs
2 hrs
7 hrs
2 hrs
Total 24 hrs
• Usual design factors allow 20% increase in capacity by shortening coking cycles from 24
to 20 hrs.
• Moderate debottlenecking modification projects will allow coking cycles a slow as 16-18
hrs.
• Shorter cycle time is not desirable
1. Lead to a lower (bad) yield of liquid products (because higher pressure is needed in
the drum & fractionating tower to prevent too high vapor velocities, and fractionator
and compressor overloading).
2. Can result in a shorter drum life because of additional drum stresses due to more rapid
temperature cycles (21-18 hrs reduced drum life by 25%).
Hydraulic Decoking System
• A small diameter hole (18-24″ diameter) called “rat hole” is first cut all the way through
the bed top to bottom using a special jet. This is to allow the main drill to enter and permit
movement of coke and water through the bed.
• Several high-pressure (2000 – 4500 Psig) water jets are lowered into the coke bed on a
rotating drill steam.
• The main bulk of coke is cut from the drum, usually beginning at the bottom. (Some
prefer to begin at the top of the drum to avoid the chance of dropping large pieces of coke
which, can trap the drill stem and cause problems in subsequent coke handling facilities).
• The drum is then inspected, boxed up, steamed and then gradually warmed up to make it
ready for another ‘switch over’.
• The water and coke particles fall from the bottom nozzle of the coke drum through a
moveable discharge chute and down a sloping surface into the coke pit.
Petroleum Refining – Chapter 10: Residue Upgrading
10-9
• The excess water in the coke pit flows through a bank of coke filters (to separate the
fines) then into a sump (بالوعة).
• The clarified water from the sump can be reused in the unit.
Figure 10-7. Coke removal via hydraulic decoking
Figure 10-8
Figure 10-9
First Boring Tool for Hydraulic Decoking Final Cutting Tool for Hydraulic Decoking
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-10
Operating variables
1. Heater outlet temperature.
2. Fractionator pressure.
3. Temperature of vapors rising to the gasoil draw-off tray (HAT temperature).
4. The carbon content of the feed (determined by Conradson / Ramsbottom Carbon
residue tests).
1. Heater outlet temperature:
Higher outlet temperature increase (cracking & coking) reactions.
- increase yields of naphtha and coke
- decrease yield of gasoil
2. Fractionator pressure:
An increase is fractionator pressure has the same effect as increase in the heater
outlet temperature because more recycle is condensed in the fractionator and
returned to the heater and coke drums.
3. Carbon content of the feed
Higher Carbon Content results in the production of more coke and less volatiles.
4. HAT temperature.
If the temperature is increased, more heavies will be drawn off in the gasoil leaving
less material to be recycled to the furnace.
Table 10-3. Relation of operating variables in delayed coking.
Independent variables increase
HOT1 P2 Feed CR3 HAT4
Gas yield
Naphtha yield
Coke yield
Gasoil yield
Gasoil EP
Gasoil metals content
Coke metals content
Recycle quantity
+
+
+
-
c
c
c
c
+
+
+
-
-
-
+
+
+
+
+
-
c
c
c
c
-
-
-
+
+
+
-
- 1 Heater outlet temperature. 2 Fractionator pressure. 3 Conradson carbon residue ASTM test. 4 The temperature of the vapors rising to the gasoil draw-off tray in the fractionator. c No significant effect.
Petroleum Refining – Chapter 10: Residue Upgrading
10-11
Figure 10-10. Figure. Coking and Decoking cycle
Types of coke
• Depends on
1. The process used.
2. The operating conditions.
3. Feedstock properties.
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-12
1. Green coke:
- Also known as (sponge) coke because it looks like black
sponge (hard, porous, irregular shaped lumps ranging in
size from 30 cm down to fine dust).
- Contain high MW hydrocarbons left from incomplete
carbonization reactions (trapped in the pores).
- Incompletely carbonized molecules are referred to as
volatile materials in the coke (expressed on a moisture-
free basis).
- Grades:
A. Fuel grade coke. (used as fuel)
B. Anode grade coke. (used as anodes for aluminum production or electrodes for
steel production)
2. Needle coke: (more valuable)
- Derives its name from its microscopic elongated crystalline structure.
- It is produced from highly aromatic feedstocks (like FCC cycle oil, etc.) when a
coking unit is operated at high pressures (100 psig) and high recycle ratios (1:1).
- It is preferred over sponge coke for use in electrode manufacture because of its lower
electrical resistivity and lower coefficient of thermal expansion.
- Sold for a higher value than sponge coke.
3. Shot coke:
- Produced unintentionally during operational upsets or when processing very heavy
residues such those from California and Venezuela. It is also produced from high
sulfur residues.
- Named shot coke because of the clusters of shot-sized pellets (حبيبات أو كرات) which
characterize it.
- Those shot clusters can grow large enough to plug the coke drum outlet (>20 cm).
- Shot coke is undesirable because it does not have the high surface area of sponge coke
or the useful properties of needle coke.
- It is sold for lower price than sponge and needle coke.
Petroleum Refining – Chapter 10: Residue Upgrading
10-13
Uses of coke
1. Fuel
2. Manufacture of graphite.
3. Manufacture of anodes for electrolytic cell reduction of alumina.
4. Manufacture of electrodes for use in electric furnace production of elemental
Phosphorus, Titanium dioxide, and Silicon Carbide.
5. Direct use as chemical carbon source for manufacture of Calcium Carbide and Silicon
Carbide.
Figure 10-11. Commercial uses of petroleum coke
Coke handling facilities
• The coke collected in the coke pit is reclaimed by an overhead bridge crane with
clamshell bucket and is transferred to a drainage pad located adjacent to the coke pit
where it is left in a pile to permit additional water to drain from the coke back into the pit.
• After draining for a minimum of 24 hours, the coke is then reclaimed from the drainage
pad by the bridge crane and transferred to a movable crusher car.
• The crushed coke from the crusher (5 cm or smaller in size) is discharged on to a belt
conveyor system for transferring the coke to stock-pile it in a warehouse for shipping.
Fuel
(40%)
Aluminum
Electrodes (40%)
Fuel
Graphite
Products (10%)
Chemicals
(10%)
Carbide Compounds
Acetylene
Specialty Chemicals
Dry Cells
Brushes for electrical motors
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-14
Figure 10-12: coke pit and drainage
Figure 10-13. Coke belt conveyor system
Petroleum Refining – Chapter 10: Residue Upgrading
10-15
Coke Calcination
• In practice, the coke formed contains some volatile matter or high boiling hydrocarbons.
• To complete the carbonization process and reduce the volatile matter from petroleum coke
to a very low level, it is calcined in a furnace at 1800 – 2400 ºF, to increase the profit margin
per BBL of feed.
Green Coke 𝐶𝑎𝑙𝑐𝑖𝑛𝑎𝑡𝑖𝑜𝑛
𝐻𝑒𝑎𝑡 Calcined Coke
• Even after calcination, minor amounts of hydrogen remain in the coke.
• Removal of moisture and volatile combustion matter (VMC) improves physical properties
(such as density, electrical conductivity, and oxidation characteristics).
• Important Variables are
1. Heating rate
2. VMC/air ratio
3. Final Calcination temp
Table 10-4. World Calciner Capacity (KMT) excluding ex-communist affiliated.
Calcinating capacity has been
shutting down since the 80’s
Current capacity can only operate at
about 90-95% of nameplate
Region 1980
Capacity
1995
Capacity
U.S. 6,829 5,575
Europe 1,425 1,545
Canada 460 460
Cen. /S/ America 420 600
Mid. East / Africa 0 255
Asia 820 1,090
Total 9,954 9,525
–
Table 10-5. Calcined Coke Property Ranges
Calcined coke properties have
different implications.
For example, sulfur is a pollutant,
metals can both contaminate the
aluminum and they contribute to air
or CO2 burn and thus pot
productivity. Density and sizing
relate to the anode properties that
can be manufactured from the coke.
Properties Values
Sulfur, wt% S 1.0 – 3.0
Vanadium, ppm V 50 – 350
Nickel, ppm Ni 50 – 250
Iron, ppm Fe 100 – 400
Silicon, ppm Si 50 – 250
Calcium, ppm Ca 50 – 200
Real Density RD 2.02 – 2.11
Particle Density PD 0.82 – 0.92
Sizing - -
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-16
Figure 10-14. Coke Calcination Process
Coke Gasification processes
1. Shell gasification process
2. Texaco gasification process
3. KRW Gasification Process
Coke gasification can be used to produce syngas, a mixture of carbon monoxide (CO) and
hydrogen (H2) gas. During gasification, the coke is mixed with oxygen and steam while also
being heated and pressurized. During the reaction, oxygen and water molecules oxidize the
coke into carbon monoxide (CO), while also releasing hydrogen gas (H2).1
C (as Coke) + O2 + H2O → H2 + CO
1. Syngas is used to fire gas turbines to produce electricity
2. Syngas can be converted into methanol, which can be blended into fuel directly or
converted to gasoline via the methanol to gasoline process.
3. Hydrogen obtained from gasification can be used for various purposes, such as powering
a hydrogen economy, making ammonia, or upgrading fossil fuels. If hydrogen is the
1 This process has been conducted in both underground coal mines and in the production of town gas. In the
past, coal was converted to make coal gas (town gas), which was piped to customers to burn for illumination,
heating, and cooking.
Petroleum Refining – Chapter 10: Residue Upgrading
10-17
desired end-product, however, the syngas is fed into the water gas shift reaction, where
more hydrogen is liberated.
CO + H2O → CO2 + H2
4. Syngas can also be converted into transportation fuels, such as gasoline and diesel,
through the Fischer-Tropsch process. If the refiner wants to produce gasoline, the syngas
is collected at this state and routed into a Fischer-Tropsch reaction. Gasification
combined with Fischer-Tropsch technology is currently used by the Sasol chemical
company of South Africa to make motor vehicle fuels from coal and natural gas.
Coke Liquefaction
• Coke can be converted into synthetic fuels equivalent to gasoline or diesel by various
direct liquefaction processes which do not require gasification.
• In the direct liquefaction processes, the coke is either hydrogenated or carbonized.
• Hydrogenation processes are the Bergius process, the SRC-I and SRC-II (Solvent Refined
Coal) processes, the NUS Corporation hydrogenation process and several other single-
stage and two-stage processes.
• In the process of low-temperature carbonization, coke is cooked at temperatures between
360 and 750 °C (680 and 1,380 °F). These temperatures optimize the production of coal
tars rich in lighter hydrocarbons. The coal tar is then further processed into fuels.
• Coke liquefaction methods involve carbon dioxide (CO2) emissions in the conversion
process which needs to be dealt with.
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-18
2. RFCC UNIT
INTRODUCTION
• Residue Fluid Catalytic Cracking (RFCC) has many licensors such as Total, Ashland
& UOP, Nippon Oil Co. Ltd./ Nippon Petroleum Refining Co., Ltd.
• Here we select Shell FCC for processing of atmospheric and vacuum residue.
• 3 RFCC units will be deployed in ZOR refinery in late 2019.
FEATURES & APPLICATIONS
• High flexibilities for feedstocks (vacuum distillates to atmospheric residues) and
products (gasoline, lower olefins, and middle distillates modes of operation).
• Cost-effective power recovery and electricity generation option.
Figure 10-15. Comparison of delayed coking, catalytic cracking and crude oil distillation
process Yields
PROCESS DESCRIPTION
Preheated feed charge is atomized and mixed with the hot regenerated catalyst (Figure
10-16). After reaction in a riser, oil vapors and catalyst are separated in a separator,
followed by a set of cyclones. This combination of separator/cyclones allows only a
few seconds residence time between riser exit and fractionator quench, which
Cat
Gasoline
(50%)
Resid (15%)
Gases
(10%)
Cat Cracking Whole Crude Coking
% Cat
Cracking
Feed
% Whole
Crude % Coker
Feed
Coke (5%)
Gases (20%)
LFO (15%)
HFO (10%)
Gases (3%)
SR Gasoline
(25%)
LFO (25%)
HFO (32%)
HFO (20%)
Coker Gasoline
(20%)
LFO (25%)
Coke (25%)
Petroleum Refining – Chapter 10: Residue Upgrading
10-19
minimizes thermal after-cracking. Spent catalyst is immediately stripped of
hydrocarbons in a multistage stripper. The stripped catalyst gravitates through a short
stand-pipe into a single vessel, catalyst regenerator.
The surplus combustion heat can be removed via ca t a l ys t coolers. Regenerative flue
gas passes via a cyclone/swirl tube combination to a power recovery turbine. From the
expander turbine the heat in the flue gas is further recovered in a waste heat boiler.
Depending on the environmental conservation requirements, a deNOxing, deSOxing and
particulate-emission control device can be included in the flue gas train.
Key design features contained in Shell FCC technology are:
Reactor
• Vertical reactor riser featuring a high-performance feed injection/vaporization
system requiring low steam rate and low pressure drop, lift-pot and riser internals.
• A separation device at the end of the riser, allows segregation of catalyst and
hydrocarbons followed by a set of cyclones (to separate the catalyst from products).
This combination minimizes the thermal after-cracking.
Stripper
• Pre-stripping of the catalyst removes adsorbed hydrocarbons.
• Secondary stripping of the catalyst to crack, desorb and displace remaining
hydrocarbons from the catalyst to minimize coke plus hydrocarbons on the catalyst
before discharge into the regenerator.
Regenerator
• Regenerator can achieve very low carbon levels on regenerated catalyst. The
regenerator can operate in partial CO-combustion mode. Complete CO-combustion
mode is achieved with additives.
• The regenerator is designed to allow moderate and high-temperature operation (up
to 750 ºC) with minimum catalyst deactivation using the catalyst inlet and outlet
devices, the cyclone system and the air distributor capable of sustained high
performance at these moderate temperatures.
• Regenerator is supplied with heat removal facilities (catalyst coolers).
Reactor/stripper/regenerator
Shell’s FCC units are designed such as to have relatively low elevations. Shell's
standpipe design gives a smooth catalyst circulation. The additional heat balance
flexibility (catalyst coolers) combined with the robust catalyst circulation give the unit
significant flexibility (to processing heavier feeds and attain higher conversion).
Power recovery and power generation
• The power recovery technology includes a separator that removes all catalyst > 20µ
from the hot flue gas.
• The single regenerator flue gas overhead system allows full power recovery from
the coke burned in the regenerator.
• Residue processing can make the FCC unit a net exporter of power.
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-20
Shell FCC technology is characterized by
1. a smooth and safe operation,
2. a high flexibility with respect to range of feed quality /feed rate/product slate,
3. a low energy consumption,
4. a run length of minimum three years and
5. short maintenance shutdowns.
OPERATIONAL DATA
An example of current performance data of a Shell LR FCC unit is given in Table 10-6.
Table 10-6. Typical performance data of a LR-FCC unit.
Intake 9500 t/d
Riser Temperature 520 ºC
Regenerator temperature 670 ºC
Ni on catalyst
1250 ppmw
V on catalyst 2700 ppmw
Feedstock properties
Feed A Feed B
Density,15/4 ºC 0.911 0.942
API gravity 18.2 13.4
Viscosity at 100 ºC cSt 57 19.3
Sulfur %wt 1.1 1.3
Basic nitrogen ppmw 320 650
Conradson carbon %wt 1.2 4.7
Aromatics index (*) %wt 15.9 18.2
Yields, %wt on feed
C2-minus (incl. H2S) 3.0 3.3
C3-total 5.4 4.7
C4-total 10.2 8.3
Gasoline (C5 – 221 ºC TBP) 49.5 46.2
LCO (221 – 370 ºC TBP) 20.1 19.1
HCO + slurry (>370 ºC TBP) 5.9 10.8
Coke 5.9 7.6
Gasoline quality
RON-O 92.0 93.0
MON-O 80.0 80.5
(*) Proprietary measure for the aromatics content of the feed.
Petroleum Refining – Chapter 10: Residue Upgrading
10-21
Figure 10-16. RFCC reactor/regenerator details.
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-22
Figure 10-17. RFCC Process Flow Diagram.
Petroleum Refining – Chapter 10: Residue Upgrading
10-23
3. ISOMAX (RCD Unibon BOC)
INTRODUCTION
• RCD Unibon BOC (Black Oil Conversion) is process for upgrading vacuum bottoms by
molecular weight reduction and contaminant removal.
• Single-stage or a two-stage versions of RCD Unibon process are available.
• The feed is high sulfur vacuum reside (HSVR).
• Isomax is a fixed bed combined hydrodesulfurization/hydroconversion (hydrocracking)
process.
• In MAB refinery isomax feed is high sulfur vacuum residue.
• Licensed by UOP Inc.
• This process has been discontinued and replace by UOP unionfining process
Feed & Products
Table 10-7: ISOMAX capacity in Kuwait.
Refinery Name Unit Throughput
(BPSD)
Feed
MAB Isomax
(RCD Unibon)
02 35,000 High sulfur vacuum residue from old
crude unit (14.3 API 4.3%S).
Total 102,000
Table 10-8: Product characteristics form Isomax unit in MAB.
Product Name (cut point) Characteristics Destination
API S
Naphtha (IBP – 320)
Distillate (320 – 680)
Low Sulfur atmospheric residue
(670/680+)
62.4
32.5
18.8
-
0.4
1.5
Storage/Naphtha HTU
Storage/Diesel HTU
Storage/Vacuum units
Process description of RCD Unibon BOC (Black Oil Conversion)
• The RCD Unibon (BOC) process is used to upgrade high sulfur vacuum residue.
• There are several possible flow scheme variations for the process.
1. Standalone (MAB old refinery).
2. Combined with a thermal conversion unit (not in Kuwait).
1. Standalone Isomax
• The Isomax is a two-stage, fixed-bed catalyst process (Figure 10-18Error! Reference
source not found.).
• Each stage has a separate hydrogen recycling system.
• Exact conditions depend on the feedstock (distillates/residue) and product
requirements.
• Conversion may be balanced to provide desired product yields, and recycling can be
taken to extinction if necessary.
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
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2. ISOMAX combined with thermal conversion
• In this configuration (Error! Reference source not found.), hydrogen and a vacuum
residuum are introduced separately to the heater and mixed at the entrance to the
reactor.
• To avoid thermal reactions and premature coking of the catalyst, temperatures are
carefully controlled, and conversion is limited to approximately 70% of the total
projected conversion.
• The removal of sulfur, heptane-insoluble materials, and metals is accomplished in the
reactor.
• The effluent from the reactor is directed to the hot separator.
• The overhead vapor phase is cooled and condensed, and the hydrogen separated
therefrom is recycled to the reactor.
• Liquid product goes to the thermal conversion heater, where the remaining conversion
of nonvolatile materials occurs. The heater effluent is flashed, and the overhead
vapors are cooled, condensed, and routed to the cold flash drum.
• The bottoms liquid stream then goes to the vacuum column, where gasoil is recovered
for further processing and the residuals are blended into the heavy fuel oil pool.
HW. Delayed coker material balance
HW. FCC material balance
Petroleum Refining – Chapter 10: Residue Upgrading
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Figure 10-18: Simplified schematic diagram of a two stage Isomax Hydrocracking standalone process
Prof. Tareq Albahri 2018 Kuwait University Chemical Engineering
10-26
Figure 10-19: Simplified schematic diagram of Isomax Hydrocracking process combined with thermal conversion.
