INVESTIGATION ON EFFECTIVENESS PARAMETERS IN RESIDUE UPGRADING METHODS
ABSTRACT In recent decade, the residue upgrading processes are developed for producing light cuts because
the demand of heavy fuel oil is decreasing in world. This paper presents the effectiveness parameters on heavy residue upgrading methods to select
the optimum condition for various feedstock specifications.
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Petroleum & Coal
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Petroleum & Coal 51 (4) 229-236, 2009
INVESTIGATION ON EFFECTIVENESS PARAMETERS IN RESIDUE
A. Dehghani, M. Sattarin, H. Bridjanian, Kh. Mohamadbeigy
Research Institute of Petroleum Industry, Tehran, Iran – P.O. Box 14665-
137, Email: firstname.lastname@example.org
Received February 22, 2009, December 1, 2009
In recent decade, the residue upgrading processes are developed for producing light cuts because
the demand of heavy fuel oil is decreasing in world.
This paper presents the effectiveness parameters on heavy residue upgrading methods to select
the optimum condition for various feedstock specifications.
Key w ords: Residue upgrading; Heavy crude oil; High sulfur crude oil.
1. I ntroduction
Due to the recently imposed restrictions of : meeting the growing market of cleaner
fuels, gradual substitution of light low-sulfur refinery feed by heavy high-sulfur one (due
to its scarcity), and the decreasing demand for heavy fuel oil , serious challenges have
raised in the petroleum refining industry.
Therefore, it is currently developed ways to upgrade heavy oil or residue to light product
to add value so that necessitates using processes for conversion of heavy high-sulfur
refining residues into (mostly) lighter low-sulfur products , which are generally called as
residue upgrading processes. The final product slate requirement, the refining product
values and the price difference between light and heavy crude oils are three major factors in
the selection of these processes. By recent high crude oil prices, the later two factors are
significantly increased and the investment profitability of residue upgrading plants has
The International Energy Agency (IEA) has predicted 70% growth in worldwide demand
for primary sources of energy by 2030. The IEA expects 88% of this increased demand to
be met by oil, natural gas, and coal. While production from other renewable sources is
expected to almost double, these sources will still meet only 2.5% of overall demand. Oil
will consequently remain a dominant factor in energy through this century.
There has been an extended substitution program of petroleum-derived fuels by natural
gas; therefore, the future refining schemes in some of refineries should be revised.
2. Upgrading processes
It‘s developed upgrading methods for conversion of low value-high sulfur heavy residue
to clean-valuable light fuels as following.
2.1 Breaking heavy molecules into lighter ones ( carbon rejection processes) ,
such methods are (usually) non-catalytic thermal and low pressure processes, in
which Poly-Nuclear Aromatics (PNA) form coke. Coking, residue fluid catalytic cracking
(RFCC) and advanced visbreaking are some examples of these processes. They have
flexibility for feedstock specification like atmospheric residue with up to 20% Conradson
carbon and 10,000 ppm metal content (Ni+ V).The capital and operating costs of these
processes are low, but their light products yields are also low.
2.2. Adding hydrogen to light molecules ( hydrogen addition technologies) ,
which are catalytically processes, hydrocracking and hydro-visbreaking is the examples of
these processes. Their main feature is “product quality”. Some of their innovative types
can accept feeds (Atmospheric Residue) with up to 38% Conradson carbon and about
4000 ppm metal content (Ni+ V). Their capital and operating costs are high, but their
light products yields are also high . Coking, solvent extraction, residue fluid catalytic
cracking (RFCC), hydrocracking, advanced visbreaking, gasification and finally residue
hydrocracking are the dominant residue conversion processes. Combinations of them are
also becoming increasingly attractive for large volume applications. Some of the relevant
processes are briefly reviewed [1-2].
2.2.1 Delayed coking
Delayed coking process completely converts the residues into gas oil, distillates, lighter
hydrocarbons and coke. This process can handle residues of heaviest, contaminated crude
oils, and has the lowest capital cost among high conversion processes; besides has suitable
flexibility. Nowadays, about one-third of installed residue upgrading plants all over the
world are by delayed coking. It is noteworthy to mention that some of the liquid fuels
produced by delayed coking should be intensely hydrotreated, which have their own
2.2.2 Solvent de-asphalting ( SDA)
In this process a paraffinic solvent (C3 , C4 , C5 or a mixture of them ) is used to separate
(physically) the vacuum residue feed, into a De- Asphalted Oil (DAO) (usually 35-75
vol.% ) and a De-Oiled Asphalt (DOA). The first stream is a higher value product and is
normally used as a hydrocracker feed, an FCCU feed or a lube oil blending agent .DOA is
a low value asphalthene rich pitch stream ,and contains most of the contaminants ( i.e.,
Conradson carbon) and can be used as a heavy fuel constituent , a delayed coking feed
or a gasification feed [3-4].
Recently, another version of this process is developed (Critical Solvent De-asphalting),
which uses critical state solvents for the best separation of lighter liquid products from
all kinds of heavy residues (supercritical extraction), specially with coking or gasification
for the elimination of SDA pitch .
This method has a considerable energy conservation. The integrated processing of delayed
coking and solvent de-asphalting is also proposed . Generally speaking, it is usually advised
to select heavy residue which are as paraffinic as possible and with less contaminant
2.2.3 Residue fluidized catalytic cracking ( RFCC)
This process is a version of FCCU, which can handle heavy residue as its feed. Its
products slate may be focused on: gasoline, gasoline/diesel, propylene or petrochemicals.
Around 24% of the global residue upgrading capacity belongs to this process. It can accept
feeds (Atmospheric Residue) with up to 7% Conradson carbon and about 12 ppm metal
content (Ni+ V) [2-4]. In other words, to some extents it is driven by sweet crude oil availability.
Recently, some catalyst manufacturers have claimed to produce catalysts which can tolerate
up to about 8500 ppm metal contents (Ni+ V) and have better product slates .
This is a mild thermal cracking process, in which the residue’s viscosity is reduced and
the residue is partially converted into lighter hydrocarbons and coke . About 26 % of
the global residue upgrading capacity is occupied by this process. There is also a version
of this process called Deep Thermal Conversion, which produces a very heavy residue
(bitumen blowing unit feed) and a lot of heavy to light liquid fuels, instead of fuel oil
product of traditional visbreaking unit . Recently, the conversion of Visbreaker units
into delayed coking ones is also suggested. For a one million metric ton per year (approximately
23,000 barrels per day) visbreaker unit; 68 million $ installed cost (instead of 84 million
$ for a grassroots one of similar capacity) was required to be converted into a coking
unit. 60 % of the existing equipment was re-used. The incremental cost was 112 million$
and the simple payback period was very attractive (about seven months) . Another non-
catalytic version of visbreaking (called Hydro-visbreaking) exists, which is done under 100
to 260 bar hydrogen pressure and about 430oC temperature. Due to its lower coke for-
mation and more stable products, higher conversions than straight visbreaking can be
Gasification is a conversion by a partial oxidation of a carbon containing gas, liquid or
solid into the synthesis gas, in which the major components are hydrogen and carbon
monoxide. In the past, its main applications were in the petrochemical industry in the
production of ammonia, methanol and hydrogen. But it has been widely used in petroleum
refineries and integrated combined cycle power generation plants (IGCC). Its wide spectrum
feed (from natural gas to heaviest high metals and sulfur petroleum or coal derived
pitches) can even contain agricultural residues, worn out automotive tires, un-recyclable
polymer wastes, sewage sludge, biomass, municipal garbage, etc. Therefore, a major
economic advantage of destroying waste material, plus a lot of steam and electricity can
be gained by gasification, which is now very important for our municipalities. All the sulfur
content of the feed(s) is also converted into H2S, which can easily be separated by the
well-known amine treating process .This advantage is very important, because the main
factor of heavy residue price reduction is their sulfur content, mainly due to the environmental
regulations .In other words, by using IGCC, there is no need to expensive refining of
heavy fuels. A key benefit of IGCC is the lowest SOx and NOx emission of any liquid/ solid
feed power generation technology. Table-1 expresses this fact well:
Table 1 Air emissions (mg/Nm3) 
European Standards for
conventional power station
Also, IGCC represents the most promising technology for CO2 capture (sequestration).
Each ton of gasification feed requires one ton of oxygen, which requires an air separation
plant construction .But, nitrogen and rare gases are its other valuable and saleable products,
which compensate for a large fraction of its costs. Produced syngas can be used for the
production of : power and steam (30% of global capacity), petrochemical products
[ammonia, ammonium nitrate, urea (fertilizer), methanol, ethanol, dimethylether (DME),
acetic acid, etc. -45% of cumulative global capacity], transportation fuels(via Fischer-
Tropsch reaction- now 25% of global capacity) and even hydrogen . Rarely, a feed
with a price higher than 10 $/barrel is used for gasification.
2.2.6 Residue hydrocracking
Heavy residue is refined under high temperature and pressure, by using a robust catalyst
to remove sulfur, nitrogen, metals, olefins, condensed aromatic, oxygen, etc., and converted
into high quality lighter fuels. Good quality products make this family of processes, one
of the best options for residue upgrading, however higher crude prices (e.g., 30 $ / barrel)
improves its economy. Feed Conradson carbon (which comprises asphalthenes, metals
and minerals) under 30 % is usually suitable for it .The feed conversion is relatively high
(50 to 75 % ) [4-5].
From the reactor design point of view the following categories are usually observed:
Fixed bed units designed for vacuum residue processing, now run on lighter feed or
atmospheric residue for FCC feed. This is due to the short catalyst life (6 months or less)
of fixed-bed designs; on the contrary to the large catalyst volumes used (LHSV typically
between 0.5 to 1.5). Although some licensors have tried to conquer it by some innova-
tive developments. However, the refining industry has remained cautious about these proc-
esses, such that by now, only about 17.5 % of the residue upgrading global capacity be-
longs to them [2, 4].
Ebullated bed technologies were first introduced in the 1960’s to overcome problems
of catalyst ageing and mal-distribution in fixed bed designs. In this design, feed and hydrogen
enter at the reactor bottom, thus expanding the catalyst bed. Even though the catalyst
performance can be kept constant by replacing it continuously. Due to the back mixing
effect of ebullation desulfurisation and hydro-conversion are lower obtainable in the
fixed-bed design. Nowadays, most commercial ebullated bed units operate in the 70 to
85 % desulfurisation and 50-70 % volume conversion of non-distillable (+ 538oC). By
R&D, some improvements in catalyst and reactor have been made. Now; this technology
is well developed with 12 commercial plants in service . Before the application of the
ebullated bed technologies, the hydro-processing upper limit of metal contaminants were
taken as 200 ppm. But this technology increased that limit to 460 ppm. The asphaltene
upper limit increased from 12-19 % to 28 % , as well .
Novel technology, recently, for residues with up to 4000 ppm metals (Ni+ V) content
and about 38 wt.% asphaltenes, a new process is developed by several companies,
which is slurry hydrocracking. This route can have a very high feed conversion(more
than 95 % with recycle) (Table 2).
Table 2 Performance of ebullated bed and slurry hydrocracking processes [11-12]
60 - 95 70 - 98 N.A. 40 - 75 40- 92
Slurry HC > 82 > 99 > 41 > 95 > 99
In other words, this process demonstrates feedstock flexibility, together with almost
Table 3 Product slate of slurry hydrocracking (wt. % ) 
(C5 - 170oC)
(170 - 350oC)
Vacuum Gas Oil
(350 - 500oC )
9.9 - 15.1 4.9 - 14.0 26.9 - 39.1 23.3 - 34.9 8.5 - 24.4
Slurry hydrocracking vacuum gas oil and DAO products are suitable feedstocks for
conventional FCCU and hydrocracker . For obtaining maximum yield of transportation
fuels, the hydrocracking /delayed coking scheme should be used .
3. Economic analysis
The fluctuation of crude oil and refinery products price is a key parameter in economic
investigation of upgrading processes.
The crude oil price is increased more than 60 $ / barrel, therefore, it's very important
to consider world demand and also new marketing for refined products.
However there is no unique for the residue upgrading and it should be considered all
concepts for each case to select suitable upgrading method.
In below, it's presented some cases to describe various conditions:
Case I .
For a U.S. Gulf coast location with midyear 1998 construction, total fixed cost increases in
the order: delayed coking < RFCC < residue hydrocracking. Plant profitability is a strong
function of product values. Return on investment (ROI) for each of the three processes
ranges from less than 10% /yr to 24% /yr based on midyear 1998 product and feedstock
values (crude oil around $14/b). ROI's improve to the 30-38 % /yr for each process based
on November 1999 values (crude oil about $25/b) .
Case I I .
It's demonstrated a comparison of three carbon rejection processes in following example .
The capital cost of residue upgrading schemes based on gasification continues to decrease
steadily. The capital cost of gasification for power generation Integrated Gasification
Combined Cycle (IGCC), is now reported to be in the range of 850-950 $/kW, compared
to 1500-2500 $/kW, about the period 1987-1992. Gasification application has an approxi-
mately 10% grow rate per year, based on the syngas production .
Plant 1 Delayed coking on an FCC-based refinery
In this plant, vacuum bottom is upgraded into transportation fuels (naphtha and middle
distillates), FCCU feed gas oil and (fuel grade) coke.
Plant 2 I ntegrated gasification combined cycle ( I GCC) on an FCC-based refinery
In this plant, vacuum residue and FCCU slurry are consumed for power generation
(usually in the range of 987 to 1,836 MWe), without any appreciable amount of pollutants
emission. Besides, there are many cases of petrochemicals, transportation fuels or
hydrogen production in this option .It is noteworthy to remind that even in natural gas
abundant areas, this process is a good choice.
Plant 3 RFCCU w ith atmospheric residue hydro-treatment
The entire atmospheric residue is hydro-treated and sent to an RFCCU (without any
vacuum distillation). Hydro-treatment removes metal content (30-40 ppm wt maximum
economic limit), reduces the products sulfur content and improves the RFCCU yield.
To obtain more transportation fuels rather than electricity, RFCCU or delayed coking
should be used. The choice between the two depends on many site-specific factors.
RFCCU has also the advantage of using unsaturated LPG's by Alkylation, MTBE or DIPE
(Di-Isopropyl Ether) processes.
3.1.Capital investment and operating costs
In each plant, 220,000 Barrels per day has been taken .The crude oil price is assumed
between 16 to 24 $ / barrel .The coke price is taken conservatively as Zero $/ton (by using
the current trade price of 20 $/ton, the Delayed coking option IRR is improved by
3% ).The analysis includes the primary residue upgrading plant, plus the plant required to
refine its products (for example additional FCCU capacity). The power price is taken as 5
IGCC has the largest capital cost, $ 800 Million of which is due to the power generation
train. The annual operating cost is also the highest ($ 150 Million). But the product reve-
nue is also high (Table 4).
Table 4 - Three carbon rejection residue upgrading schemes 
AR HDS /
Capital cost ($ million) 485 - 623* 1,353 - 2,103* 703 - 705*
Operating cost ($ million per year)
Operating Cost ($ /barrel AR feed)
40 - 50*
138 - 230*
3.7 - 5.0*
2.4 - 2.7*
Product Revenue, ($ million per year) 861 - 932* 1,079 - 1,404* 987 -1,020*
* Depending on the crude oil heaviness
By the assumptions made , all the three above options have positive rates of return
(IRR) between 7 to 20% (AR HDS has the higher IRR, then IGCC and delayed coking) .For
cheaper , heavier crude slates , the delayed coking and IGCC become more economically
attractive , and also more operationally flexible from the crude selection point of view
.The IRR is very sensitive to the atmospheric residue price, and each 1$ / barrel change
of its price can change IRR by 2% to 8% (for delayed coking). IRR values are pre-tax
ones and do not include the owner’s costs .
Case I I I .
There is another case study by a different reference , which compares four residue
upgrading schemes (Table 5); obviously by its own assumptions.
Table 5 - Comparison of four Residue Upgrading Schemes 
Case I V.
This reference  (Table 6) has the following assumptions:
• 100,000 barrels per day grass roots crude oil processing (Arabian Heavy) in each of
the plants studied.
• 3.50 $ / M Btu gas price
• product slate to liquid intermediate products and solids / pitch
• capital recovery at 15 % ROI
• US Gulf Coast location
• primary conversion unit about 20 % of total capital
• operating cost not including crude oil feedstock costs
Table 6 - Comparison of some residue upgrading schemes 
Visbreaking/Critical solvent Deas-
( $ / Barrel)
Hydrocracking, (60 % Conversion)
Hydrocracking, (90 % Conversion)
4. Discussion and results
The projected global demand of refined products shows an appropriate situation for
the residue conversion processes construction, especially for hydro-processing ones
LPG NaphthaGasoline Jet/ Diesel/ LSFO HSFO
Figure 1 Global Incremental Demand Growth 
There is a promising future for middle distillates and gasoline producing upgrading
processes. However, there is a stability limit for the high conversion region of the ebullated
bed hydrocracking process (Fig. 2) . Likewise , due to the increasing natural gas prices
, hydrogen production from residue , via gasification can be economical. With such a
processing scheme, there is a balance point between the hydrogen consumption and
production, which limits the residue conversion level (to e.g. 83 % as in Fig.3). There-
fore, this promotes the slurry hydrocracking processes.
Million tons per year
Figure 2 Stability Limit for ebullated bed hydrocracking conversion level 
Figure 3 Hydrogen balance point 
Considering the above various economic cases (albeit using their own assumptions
and conditions), the following results can be realized:
• Delayed coking is a non-expensive (capital & operating costs)-relatively high conversion
process , and for refineries with coke export capabilities can be an interesting route
However , the gradually tightening regulations for the environmental protection dictates
progressively cleaner fuels , and the related costs may affect the economic feasibility
of this process in the future.
• Integrated Gasification and Combined Cycle (IGCC) is becoming cheaper and can be a
good final solution for refining heavy residues .Besides all other benefits , it neatly destructs
industrial, agricultural and municipal wastes and be a very economical-yet clean-
heavy residue upgrading method.
• Both RFCCU and hydrocracking processes seem to have a promising future, but slurry
hydrocrackers can be the best one in the coming decade .This should be considered by
refineries which are constructed new hydrocracking plants. Of course, RFCCU is a
lower cost one .The main RFCCU product which is gasoline contains aromatics, olefins
(and sometimes di-olefins), that produce ozone in the vehicles exhaust gas .But due
to their high octane numbers, they cannot be neglected. Therefore, their concentration
in gasoline is specified and limited .As an example, in California State of United States,
the standard olefin volume percent in motor gasoline was decreased from 9.5 % to
6% . On the other hand, the reduction of olefins in gasoline will increase its Volatile
Organic Compounds (VOC) pollution, (most probably) due to the aromatics increase
necessity, to compensate for the high octane number of olefins. In other words; there
should be an environmentally safe blending constituent to substitute olefins. Such a
valuable and useful compound is the branched paraffin (iso-paraffin), which is mainly
produced via the Alkylation or (Light Naphtha) Isomerisation processes. Today, Alkyla-
tion is done by sulfuric acid or solid boron flourides catalysts. Also, hydrogenation of
dimerized (oligomerized) butylenes (iso-octene or polymer gasoline) can be used.
• Visbreaking units
- Due to the low conversion of this process and limited future market for fuel oil, it is
appropriate to convert them into Delayed Coking or Hydro-Visbreaking plants.
- Combining these latter two processes with the aforementioned ones, would have a
still better result, with a relatively low cost.
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