Gasification in Petroleum Refinery of 21st Century
Oil & Gas Science and Technology - Rev. IFP, Vol.
Gasification in Petroleum Refiner y of 21st Centur y
E. Furimsky 0
0 IMAF Group , 184, Marlborough Avenue, Ottawa, Ontario - Canada , K1N 8G4
steam with electricity offers the flexibility to respond to market demands. Gasification technology is
commercially proven. Among several types, entrained bed gasifiers are the gasifiers of choice. A number
of commercial projects in Europe, Asia and United States use a gasifier employing either a slurry feeding
system or a dry feeding system.
Keywords: Gasification, petroleum residues, IGCC, electricity and chemicals, petroleum refinery emissions.
The evolution of supply and demand patterns and technical
considerations indicate difficulties for disposing of refinery
residues in the medium and long term [
]. This is caused by
a continuous decrease in the volume of conventional crudes
which have to be replaced by heavier crudes. This is illustrated
on the results in Figure 1 showing a continuous increase in the
gravity and sulphur content of crudes which have been
processed in United States refineries between 1983 and 1995
. These trends have been continuing until now and it is
anticipated that they will continue into the next century. The
higher volume of heavy crudes results in the higher yield of
residues. There are several options available to refiners for the
residue disposal. This includes either using the residues
without further processing or converting them into higher
demand products using carbon rejection and/or hydrogen
addition technologies. In some parts of the world, residues can
be blended with a gas oil and sold as a heavy fuel oil.
However, this outlet is drying out because of a continuous
increase in the sulphur and metal contents of the residues. A
further processing to obtain additional liquids is an attractive
option being practiced by many refineries. The choice of the
upgrading technology has to be thoroughly evaluated. Thus,
according to Tamburrano [
], at least nine factors have to be
taken into consideration. The stiffer legislative restrictions
suggest that choice of the technology will be environmentally
Higher production of residual fuel
Higher sulfur content
In the case of the hydrogen addition technologies,
problems with disposal of the spent catalysts have to be
solved because of their classification as hazardous wastes [
Significant increase in coke production per unit of
processed crude in United States between 1980 and 1990
indicated on coking technology gaining on importance, i.e.,
during this period, the coke production increased by 70% [
Since that time, the coke production has been steadily
increasing. The sulphur content of coke has been increasing as
well. This has resulted in a steady decrease in the price of the
coke. Today, price per one ton of coke is less than $10 inspite
of its highest heating value compared with the other solid fuels.
Visbreaking is being widely practiced in other countries (e.g.,
Italy), whereas the suitability of deasphalting for the residue
upgrading has been recognized as well [
]. The trends in the
yield and sulphur content observed for coke are similar for the
residues produced from both visbreaking and deasphalting.
After a thorough evaluation of several factors, gasification
was identified to be an answer to problems with the disposal of
refinery residues [
]. This technology can convert any solid or
semi-solid carbonaceous material to synthesis gas. This
includes intermediate refinery streams, asphalt, petroleum coke
and even various refinery sludges. The raw gas produced in the
first step is cleaned to remove sulphur compounds and
particulates. The former are converted into pure sulphur in the
Claus plant, while particulates are recycled to the gasifier.
Thus, almost 100% carbon conversion can be achieved. Metals
(vanadium and nickel) are concentrated in the slag/ash,
saleable for metal recovery. Thus, no solid byproduct is left for
disposal. The clean synthesis gas can be converted to valuable
products such as electricity, steam, hydrogen and chemicals.
Gasification technology is commercially proven and used in
many parts of the world. It is now being considered for the
final conversion of refinery residues in Europe, United States
and Asia. Electricity appears to be product of the main interest.
For this purpose, the integrated gasification combined cycle
(IGCC) technology is being applied. This technology can be
readily integrated with a petroleum refinery. Thus, most of the
components of an IGCC plant are part of a typical refinery.
This is indicated by the simplified flowsheet of an IGCC plant
(Fig. 2), which shows that the gasifier and feedstock
preparation units may be the only units of the IGCC island not
yet operated by the refinery. This ensures the availability of the
qualified operators. Besides electricity generation, part of the
synthesis gas can be converted to hydrogen for the refinery
consumption or chemicals. Also, steam required for the
refinery operation can be produced by the IGCC plant.
The integration of gasification with refineries offers new
business opportunities to offset potential loss of a share of
traditional refiner’s market due to the introduction of
reformulated gasoline containing oxygenates like MTBE,
TAME, methanol, etc., as well as agricultural fuels like ethanol
and biodiesel. Trends around the world indicate on the
deregulation of the electricity market, one of the most lucrative
and steady market. This enables petroleum refineries to enter
this market either alone or in a partnership with utilities.
The environmental performance of IGCC technology is
unmatched by competing means of dealing with low value
refinery residues. Typical emissions from competing
technologies for electricity generation were estimated by
] and are shown in Table 1. It is evident that the
emissions from IGCC plants are the lowest and are in the
range of those from combined cycle burning natural gas. The
environmental acceptability was the major concern before the
start of the construction of the IGCC plant at the El Dorado
refinery in Kansas, United States [
]. In this case, the project
had to obtain environmental permits including the prevention
of significant deterioration permit. The environmental agencies
such as United States Environmental Protection Agency (EPA)
and Kansas Department of Health and Environment (KDHE)
were involved together with Texaco. After necessary permits
were received, the press release stated “Texaco and KDHE set
a national precedent for using refinery waste products for
fuel”. The major commercial projects in different stages of
development and construction are listed in Table 2. Strict
environmental regulations were the driving force behind the
choice of IGCC technology for commercial projects in Italy. In
particular, the limits set by the European Community Large
Combustion Plant Directive for new large plants have been
extended to the existing plants. For this reason, in Italy,
production of electricity from residue gasification is eligible
for subsidies and incentives.
and exhaust stack
Exhaust Steam turbine
Clean fuel gas
Comparison of typical emissions from power generating technologies
using petroleum coke (lb/MWh, 100% capacity, 5wt.% sulphur) [
Natural gas Gasification
comb. cycle comb. cycle
FGD and SCR
Power (500 MW)/steam/H2
Power (500 MW)/steam/H2
Power (250 MW)/steam
1 FUNDAMENTAL ASPECTS OF GASIFICATION
Gasification has been used commercially for many years. A
wide range of gasification conditions can be attained by
properly matching the feedstock with a type of gasifier. Thus,
any solid, semisolid or liquid organic material can be gasified
in accordance with environmental regulations. The simplified
flowsheet in Figure 3 indicates potential final products
produced from the synthesis gas obtained during gasification
as the first step. Only a cursory account of this topic will be
given in this review. Thus, an extensive information on
various aspects of gasification can be found in the literature.
In this regard, reports published by IEA [
] provide an
excellent description of gasification technology.
Gasification is a partial oxidation process in which
carbonaceous solids react with oxygen, enriched air or air
according to the overall reaction:
CnHm + n/2 O2 fi nCO + m/2 H2
The overall reaction can be summarized in several basic
chemical reactions such as gasification with O :
C + 1/2 O fi
H = – 123.1 kJ/mol
combustion with O :
gasification with CO2:
gasification with steam:
C + O fi
H = – 405.9 kJ/mol
C + CO2 fi 2 CO
H = 159.7 kJ/mol
C + H2O fi
CO + H2
H = 118.9 kJ/mol
O2 or air
Slate of potential final products from gasification.
In overall, gasification is a controlled combustion in O2
depleted atmosphere. In this case, most of the O2 fed to the
gasifier is consumed in Reactions (1) and (2). These reactions
generate heat to increase temperatures at which chemical
bonds are broken and gasification Reactions (3) and (4)
become favorable. If the gas is considered for a subsequent
synthesis, the water-gas shift Reaction (5), i.e.:
CO + H2O fi
H + CO2
H = – 40.9 kJ/mol
also becomes important for adjusting H2/CO ratio.
Otherwise, the primary objective is to maximize content of
combustibles such as CO and H2. CH4 can also be formed at
low gasification temperatures. Sulphur in the feed is
converted mainly to H S and small amount of COS. Traces
of S2 and CS2 can also be formed. Most of the nitrogen in the
feed is converted to N2. However, small amounts of HCN
and NH3 are also formed. HCl is the main Cl-containing
product formed during gasification.
Gasification medium has a major impact on calorific value
(CV) of gasification products. When air is used, a low CV
products are obtained because of a significant dilution effect,
whereas a medium CV gas is obtained in the case of O2 or O2
enriched air. However, the use of air eliminates the air
separation unit on the site though in some refineries such unit
may be already in the operation. The O2 concentration in the
gasification medium has an impact on the gasifier design.
Thus, high O2 concentrations are used to attain high
gasification temperatures required for certain feedstocks.
Steam can be added with O2 to maintain heat balance of the
combustion and gasification reactions in the gasifier. A direct
gasification in the steam only yields a medium CV gas.
However, in this case, an external source of heat is required for
the gasification reactions to occur. A direct CO2 gasification
may have a potential if a cheap source of CO2 is available.
Also in this case, an external source of heat would be required.
At high temperatures, CO2 formed during combustion
(Reaction (2)) will be converted to CO in the secondary
gasification reaction (Reaction (3)).
Under certain conditions, gasification may be divided into
two stages, i.e., primary gasification and secondary
gasification. The former involves devolatilization of the feedstock. The
secondary gasification involves gasification of the char from
the devolatilization according to the reactions described above.
In this regard, an efficient contact of the gasification medium
with the hot char is crucial to attain high enough temperatures.
Otherwise, the targeted composition of the gas produced as
well as the form of solid residue cannot be obtained.
Temperature is directly related to the physical state of ash in
the gasifier. There are three types of the operation, i.e., dry ash,
ash agglomerating and slagging. During the dry ash operation
(below 1000°C), the ash is removed dry without sintering.
Depending on the composition of mineral matter, the ash
agglomeration occurs between 1000 and 1200°C. As ash
becomes sticky, the particles form agglomerates which are
withdrawn at a controlled rate to maintain a steady state in the
gasifier. Slagging of ash begins above 1200°C. It is essential
that the fusion properties of the feedstock mineral matter are
suitable for the slagging operation. Thus, it may be difficult to
slag mineral matter which has a high fusion temperature unless
a fluxing agent is added to decrease the temperature. High
temperatures (~1500°C) used during slagging operations
ensure high reaction rates, high gasification conversions, good
quality gas and high feedstock throughputs. Slagging operation
is also suitable for a great variety of the feedstocks.
2 ORIGIN OF REFINERY RESIDUES FOR GASIFICATION
The flowsheet of the refinery processing a conventional crude
is shown in Figure 4a [
]. The crude oil entering the refinery
is first desalinated before being processed by atmospheric
distillation. The liquid fractions are further treated to meet the
specification of transportation fuels and fuel oils. In this case,
the atmospheric residue represents a small portion of the crude
entering the refinery. In some situations, the atmospheric
residue can be directly utilized as a heavy fuel oil. A vacuum
gas oil can be obtained if the atmospheric residue is subjected
to vacuum distillation. The vacuum residue usually meets the
specifications of asphalt, a marketable construction material.
Thus, in the case of some conventional crudes, an almost
complete utilization may be achieved, leaving no residue. In
such situations, there may be little economic incentive for an
additional conversion of vacuum residues to liquid products.
Besides increasing yields of liquid fractions by subjecting the
atmospheric residue to vacuum distillation, the additional
liquids can be obtained by further upgrading the residue from
vacuum distillation. The typical upgrading options, such as
coking and deasphalting are included in the flowsheet of the
refinery shown in Figure 4b [
]. In this case, the upgrading
processes generate the final residue such as coke and asphalt,
which may be converted to usable products, i.e., it can be
either combusted or gasified to generate electricity or other
The type of crude oil processed by the refinery and the
conditions to which the crude oil is subjected determine the
characteristics of the final residue. In the latter case, the
selected process is essential. For heavy crudes, the upgrading
of vacuum residues can significantly increase the yield of
liquids per unit of crude entering the refinery. The best known
upgrading technologies which generate the final residues can
be divided into thermal processes and solvent extraction and/or
precipitation processes. Catalytic hydroprocessing upgrading
processes may not generate final residues. Thus, the residual
pitch produced may be further upgraded to liquid products and
final residues, e.g., coke or asphalt. Visbreaking (thermal or
hydrogen) and coking (delayed, fluid and flexi) are typical
thermal processes, whereas deasphalting is the best known
solvent treating process [
]. The typical yields of the
final residues generated by these processes are shown in
Table 3 . In this case, the vacuum residue obtained from
the Light Arabian crude was used as the feedstock for the
corresponding process. Besides residues from vacuum
distillation of the virgin crude, the feedstock for the upgrading
process can originate from vacuum distillation of
hydrocracked products [
]. The world residue upgrading
capacity, including both carbon rejection processes and
hydrogen addition processes is shown in Table 4 [
former accounts for almost 80% of the total capacity, not
including the residue FCC capacity.
LPG fuel gas
Flowsheet of petroleum refinery; with residue upgrading option.
3 PROPERTIES OF THE FINAL RESIDUES
The primary focus will be on the properties which influence
the gasification performance and feedstock preparation. The
compositional data obtained from the proximate and ultimate
analysis, ash composition, ash fusion and heating value of the
feedstock provide essential information for predicting
gasification performance. Also, this information is crucial for
the material selection for critical parts of the IGCC plant. The
physical properties, such as particle size distribution,
grindability and slurrability are important for feedstock
preparation. A vast database on the same properties of coals
is available in the literature. A similar database for the final
refinery residues is less extensive. However, by ash playing
an insignificant role compared with the coals, predictions of
the behavior of the final residues during gasification are more
accurate. If the final residue is in the solid phase, such as
cokes, the feedstock preparation and feeding are quite
straightforward. In the case of visbreaking tars and pitches,
specially designed systems are available to enable feeding in
the molten phase. In some cases, a gas oil may be added as a
diluent to improve feeding to the gasifier.
It is believed that the most detailed information on properties
of petroleum cokes was published by Bryers [
compositional data and ash analysis, published in this article
are reproduced in Tables 5 and 6, respectively. Important
information on properties of the delayed coke was published
by Bechtel [
]. Although properties of the feed influence
properties of the coke, the effect of processing conditions is
quite evident from the results in Table 5. In this regard, the
content of volatiles, carbon and hydrogen are the best
indicators of the severity to which the coke was subjected. As
one would predict, based on the process conditions, the content
of volatiles and hydrogen was largest for delayed coke and
lowest for flexicoke. The significant difference in H/C ratio
among the cokes indicates the degree of aromatization. Also,
this reflects the difference in the severity of the processes. This
may have a direct effect on the gasification reactivity, if the
same particle size of the delayed and flexicokes is used for
comparison. Thus, the reactivity of the latter is significantly
lower. Properties of the feed from which the cokes were
prepared influenced parameters such as the content of ash,
nitrogen and sulphur.
The chemical composition of the cokes ashes is entirely
determined by the properties of the mineral matter contained in
the feed from which the cokes were derived. In this regard, the
high content of NiO and V2O5 in the ashes from the delayed
coking and flexicoking would indicate more conventional type
feeds compared with the fluid coke, in which case SiO2, Al2O3
and Fe2O3 account for most of the ash. Thus, the small amount
of clay like species are usually present in heavier crudes. The
ash composition determines the fusion properties.
Ash fusion, °C
Ash fusion, °C oxid. atm ID ST (sph.)
brittle and can be readily crushed, as indicated by the
Hardgrowe index exceeding 80. As rather high viscosities
suggest, feeding of such materials in a molten phase could be
difficult. However, there are some asphalts from deasphalting
having a softening point lower than 100°C [
the type of solvent and solvent/oil ratio, the origin of the
deasphalted feedstock determines the properties of the
asphalt. The type of deasphalting process can have an impact
on the properties of the asphalt as well.
The fusion temperatures in the reducing atmosphere are of
primary importance because they are an indication of the
slagging tendency of the ash during entrained bed gasification.
It is evident from these results that the ashes from the delayed
coking and flexicoking will not slag without the addition of a
fluxing agent in the Texaco gasifier. However, the information
published by Shell  suggests that more than 90% of the ash,
having a composition similar to that of the flexicoking ash,
slagged in the Shell gasifier. This slag was classified as
nonleachable. In view of the high vanadium and nickel content,
these ashes and slags can be considered as a high value
byproduct saleable to metal reclaimers. The disposal of the
gasification slags is of little concern because they are
nonleachable. As can be predicted, the high content of vanadium is
responsible for the significant decrease in fusion temperatures
in the oxidizing atmosphere. Therefore, the fusion
temperatures of the delayed coke’s ash in the oxidizing
atmosphere shown in Table 6 [
] should be reexamined.
With respect to feeding, the particle size of the coke is
crucial. In entrained bed gasifiers, the mean particle diameter
is about 40 microns. Therefore, significant crushing will be
required for the delayed coke which is produced in the form
of large lumps, compared with the fluid and flexi cokes which
are produced in a powder form. Nevertheless, the Hardgrove
index in Table 5 shows a lower hardness for the delayed coke
than for the fluid coke. The particle size is perhaps the main
parameter in narrowing down the gasifier selection to the
entrained bed in the case of the fluid and flexi cokes.
3.2 Other Final Residues
In this case, the asphalt from deasphalting, visbreaking tar
and in some circumstances even vacuum residues may be
included among the final residues for gasification. The
choice depends on the overall operating strategy of a
refinery. The elemental analysis of several gasification
feedstocks tested as liquid feedstocks is shown in Table 7
]. The H/C ratio of these materials is significantly higher
than that of cokes suggesting that some liquids can still be
produced, e.g., by coking. Nevertheless, for various reasons,
the refiner may decide to include these materials among the
From the feeding point of view, physical properties such
as the softening point, viscosity and pumpability are equally
important as is the particle size for the solid feedstocks. In
this regard, the asphalt from deasphalting deserves attention
because its properties can be, to a great extent, influenced by
the operating conditions applied during deasphalting. The
results in Table 8 show the effects of different solvent on the
asphalt properties from the Rose deasphalting process using
the vacuum residue derived from the Light Arabian crude
]. In this case, the asphalt can be handled as a solid and
fed into the gasifier in a pulverized form or in a water slurry
form. Thus, at ambient temperatures, the asphalt is very
A wide range of properties of vacuum residues and
visbreaking tars (vacuum residue of visbreaking product) can
be found in the literature. The softening point of these materials
varies between 50 and 100°C but rarely exceeds 100°C. They
can be fed into the gasifier in a liquid form, although in some
case, the addition of a viscosity depressant may be required. An
example of the effect of visbreaking on the properties of the
visbreaking tar compared with that of the vacuum residue from
which the tar was derived is shown in Table 9 [
]. It is to be
noted that the vacuum residue is much heavier than the tar.
Parameters such as gravity and viscosity are of particular
interest. Thus, while the gravity of the tar has increased (API
gravity decreased), the overall viscosity was reduced
significantly suggesting improved pumpability of the tar
compared with the vacuum residue. In this case, the tar
accounts for more than 80% of the original vacuum residue.
3.3 Refinery Sludges
A variety of sources from petroleum refineries generate large
volumes of different waste oil sludges, such as tank
bottom/cleaning sludge, dissolved and induced air flotation
skimmings and impoundment sludge. According to the EPA
regulations, these sludges are included among so called
Kwastes (Table 10). The sludges contain oil, emulsion, water
and solids. The ratio of these phases vary from one application
to another and from site to site. The difficult part of the sludge
is the oil-water-solid emulsion phase, which is always present.
This phase represents a distinct phase for separation in
combination with water and solid phases. The emulsion phase
is stable and cannot be broken by centrifugal and filtration
methods but can be partly destabilized by heating. The
customary method of refinery sludge management involves
storage in ponds and tanks, from where it has to be taken for
final disposal. Some disposal and utilization options for
refinery sludges were discussed by Kanakamedala and Islam
]. In addition, the current EPA regulations allow utilization
of the waste sludges in the coker units. It is believed that the
injection of the sludges into an entrained bed gasifier would
provide an even more efficient method for sludge utilization.
This point was raised by Falsetti et al. [
] while discussing
gasification of petroleum coke in the Texaco gasifier. In this
case, the sludge could enter the system during the preparation
of the coke-water slurry to be fed to the gasifier.
4 GASIFICATION PROCESSES
Gasification processes may be operated either at a near
atmospheric pressure or at an elevated pressure. The effect of
pressure up to about 3.0 MPa (440 psi) on product composition
is small although the equilibrium considerations suggest on
slowing down the decomposition of steam and CO2 with
increasing pressure. Many of the downstream units operate at
elevated pressures. Then, if the gasifier operates at a near
atmospheric pressure, the raw gas has to be compressed for the
further processing. The cost of this compression may exceed
the cost of an atmospheric gasifier compared with the
pressurized gasifier. Therefore, most of the advanced
commercial or near commercial gasifiers operate at elevated
pressures. The simplicity of gasification chemistry is
overridden by the mechanical complexity as well as the
material requirements. A steady and uninterrupted feeding of
the feedstock must be maintained to ensure a continuous
operation. Further, a proper mixing of the feedstock with
gasification medium in the gasifier must be achieved to obtain
high conversions. Expensive refractory linings are needed to
prevent corrosions by slags in the advanced gasifiers.
Superalloys have to be used for some heat recovery systems to
prevent corrosions by sulphur, chlorine and alkalis and erosion
by particulates. Several types of commercial gasifiers are
available to deal with these problems.
The technical literature on gasification processes is rather
]. In this review, a brief summary will only be
given with the emphasis on commercial gasifiers.
Fixed bed gasifier, also referred to as a moving bed
gasifier, requires a feedstock particle size of 2 to 50 mm and
can be used with air, oxygen and steam which are introduced
into the bottom of the reactor. Feedstock is fed from the top,
ash or slag leaves the bottom and produced gas exits at the
top. Depending on the gasification medium, the bottom of the
reactor can be operated either in a dry mode or in a slagging
mode. In the former case, temperature in the gasification
zone is in the range of 800 to 1050°C whereas in the slagging
mode, the temperature may approach 1400°C. Reactors can
be operated at pressures ranging from 0.1 to 3.0 MPa.
Residence time is in the order of 1 to 3 h. This type of
gasifiers may not be suitable for gasification of refinery
residues, such as the fluid coke and flexi coke as well as
visbreaking tar and asphalt from deasphalting.
In the fluidized bed gasifier, feedstock is injected into the
bottom and reactant gases can be injected at two levels to
maximize carbon conversion. The temperature in the
fluidized bed gasifier may approach 1200°C if oxygen is
used as gasification medium. The main problem of the
fluidized bed systems is the extent of carbon conversion and
the carry-over of the fine particles. Normally, this carry-over
has a high carbon content and has to be collected and
recycled to the gasifier. Also, the required average particle
size (approximately 8 mm) of the feedstock exceeds that of
the fluid coke and flexi coke. For delayed coke, the suitable
particle size may be attained. However, low reactivity of the
delayed coke may require a long residence time which
translates into lower throughputs. Little information indicates
on the use of the fluid bed gasifier for the gasification of the
visbreaking tars and asphalt from deasphalting. High overall
conversions can be achieved if the fluid bed gasification is
combined with the combustion of the carried-over fines. In
this case, both fluid coke and flexi coke can be used as
feedstock. To a certain extent, limestone can be injected into
the fluidized bed of the feedstock for the in situ sulphur
capture. However, for feedstocks containing more than
5wt.% sulphur, the use of limestone in the fluid bed
combustor is not recommended [
]. Several types of the
fluid bed gasifiers, e.g., U-Gas, HTW and KRW are available
commercially. The gasification of petroleum coke containing
about 2wt.% sulphur with the limestone injection was
successfully demonstrated in KRW gasifier.
Entrained bed gasifiers require a pulverized feedstock of
which about 90% is less than 200 mesh. This suggests that
the fluid coke and flexi coke require only a little preparation.
The feedstock can be injected either dry or in the form of a
water slurry. Semisolid feedstocks, such as visbreaking tars
as well as the asphalt from deasphalting can be injected in a
molten phase. The injection ports can be either at the side or
at the top of the reactor. In a dry feeding mode, the feedstock
is screw-fed from lock hoppers to burners where the
gasification medium (air, oxygen or steam) convey the
feedstock at a velocity in excess of flame propagation rates
into the reactor. Pumps are used for the injection in a slurry
mode and the feedsstocks in a molten phase. Once in the
reactor, particles are rapidly devolatilized and lose any
inherent characteristics of the original feedstock. The high
operating temperature effectively destroys all hydrocarbons,
tars, oils and phenols which may be formed during the
devolatilization. This reduces gas purification and eliminates
water condensate contamination problems. The rapid
reaction rate requires control to prevent an excess of oxygen,
should the feeding be interrupted. There is no reservoir of
carbon as is available either in the fluidized bed or fixed bed.
The temperature of gasification flame may exceed 1500°C.
As the result of the high temperature, most of the mineral
matter in the feedstock is melted and removed in the form of
a slag. Residence time is in the order of 1 s. The units are
usually operated at high pressures. As indicated above, the
combination of factors such as high temperatures, high
content of contaminants in the vapor phase and molten
mineral matter results in special material requirements.
Several types of the commercial entrained bed gasifiers
are available for selection of one which fulfils best the
performance, economic and environmental requirements.
With respect to the gasification of refinery residues, the
entrained bed gasifiers are the gasifiers of the choice. For the
purpose of this study, these gasifiers will be discussed in
more details. The best known slurry feeding entrained bed
gasifiers are Texaco and Destec, whereas the best known dry
feeding systems are Shell and Prenflo gasifiers. High
temperatures attained in these gasifiers make them suitable
for the gasification of less reactive feedstocks such as the
petroleum coke and oil sand coke. In the case of the slurry
fed gasifiers, refinery wastes such as K-, D- and F-wastes can
be cogasified with the coke. A wide range of liquid and
semisolid materials can also be gasified.
Prior to their utilization, gasification products have to be
cleaned to remove particulates and sulphur. For this purpose,
conventional cleaning systems are being used commercially.
In this case, the gas is cooled and then scrubbed to remove
particulates. A low temperature steam can be recovered
during the low temperature cooling of the particulate free
gas. Also, this gas can be used to preheat water for fuel gas
saturation prior to combustion in the turbine or to preheat
boiler feed water. In refinery, this gas can be used to preheat
other streams. The particulate free gas enters the COS
hydrolyzer where most of the COS is converted to H2S in the
presence of a catalyst. This fuel gas then enters the acid gas
removal section where more than 95% of sulphur is removed.
For this purpose, various commercial processes operated at
about 100°C, e.g., Selexol, Sulfinol, Stretford, etc. are
available. Attempts are being made to develop a hot gas
clean-up process operating above 400°C. The selection of the
process depends on the system parameters and concentration
of acid gases. After desorption from the scrubbing agent, the
acid gases enter Claus process for recovery of elemental
sulphur. An additional treatment of the tail gas from the
Claus process is needed to meet environmental regulations.
This is carried out in the Scot process. It is noted that most of
the components of the gas cleaning systems are in the
operation in refineries for purifying refinery gas prior to their
use either as petrochemical feedstocks or combustion fuel.
4.1 Texaco and Destec Gasifiers
Texaco and Destec are the most advanced slurry fed gasifiers.
In the Texaco process, the solid feedstock such as coke is
pulverized and slurried in a wet grinding mill to produce a
pumpable slurry containing between 55 and almost 70% of
solids. The slurry water consists of the recycled condensate
from raw gas cooling and a make-up water. The slurry is fed to
the gasifier through a specially designed nozzle together with
oxygen. The slurry fed system provides high feeding reliability
which is critically important for pressurized systems. However,
the use of the slurry feeding system introduces a thermal
penalty since some of the heat of combustion must be utilized
to convert the slurry water to steam. As the water requirements
for the slurry production increase, the oxygen consumption
increases and quality of the gas decreases. It is therefore
critical for the economy of the Texaco process that the solid
concentration in the slurry is high. In this regard, in the solid
concentration range, low rank coals and lignites are at the low
end and cokes at the high end. It is expected that for cokes, the
solid concentration in the slurry can approach 70% [
Semisolid feedstocks such as vacuum residues and visbreaking
tars as well as liquid hydrocarbon feedstocks can be injected in
a molten or liquid form without requiring the slurry
preparation. The synthesis gas production from the delayed
and fluid petroleum cokes is compared with two United States
coals in Table 11 [
]. The solid carbon concentration in the
slurry is 53, 48 and 41 for the petroleum cokes, Pittsburgh 8
and Utah coals, respectively. In this case, the size of the plant
approaches that of the Cool Water gasification plant in
California, i.e., about 100 MW electricity.
Texaco gasifier is a cylindrical refractory lined vessel
mounted on the top of the radiant cooler. It has no movable
parts, so its maintenance is simple. It operates at temperatures
ranging from 1200 to almost 1400°C and pressure of about
30 atm. Depending on the final product, three versions of the
Texaco process are available for commercial uses. The
differences among these versions are based on the extent of
heat recovery from hot gasifier products. In the case of the
radiant + convective design (Fig. 5), hot gasifier products exit
gasifier at the bottom and enter radiant cooler that generates
high pressure steam. At the bottom of the radiant cooler, slag
drops into a quench pool of cooling water prior to its removal,
while gas flows to a convection type exchanger, where
additional high pressure steam is generated. Cooled gas is
further treated to remove particulates and sulphur to make it
suitable for combustion turbine. High pressure steam generated
in the radiant and convective coolers is injected into the steam
turbine. This version of the Texaco process, termed as a full
heat recovery design, is used for IGCC applications in which
electricity is the main final product. Radiant only design
incorporates radiant cooler only. Thus, no convective cooler is
provided. Also, both the slag and the gas are quenched at the
bottom. Cooled gas flows directly to the downstream units.
These heat recovery design configurations significantly
influence the degree of integration required by the IGCC plant.
The main difference is in the quantity of high pressure steam
which has an impact on the overall thermal efficiency of the
plant. In the case of the total quench design, both the radiant
and convective coolers are eliminated. This design offers a
flexibility for coproduction of hydrogen, chemicals and
electricity. Such design of the Texaco gasifier was used in the
El Dorado refinery for gasification of petroleum coke and
refinery sludges [
]. There is a significant difference in the cost
of these designs being the highest for the full recovery and the
lowest for the direct quench design.
Destec gasifier comprises two stages, i.e., a slagging first
stage and a non-slagging second stage. In both sections, the
preheated oxygen and slurry are fed and atomized through two
opposing burner nozzles. The slagging section is a horizontal
refractory lined vessel in which the feedstock slurry is partially
combusted with oxygen. High temperatures (approaching
1400°C) ensure almost complete gasification of the feedstock
while mineral matter is fused to a molten slag and drops to the
bottom from where it is continuously removed. The hot
gasification products from the slagging section enter the
second non-slagging section which is a vertical
refractorylined vessel. Additional slurry is injected to the second stage to
cool the gas. Also, in this section, the feedstock undergoes
devolatilization and pyrolysis thereby generating additional gas
of a higher heating value because no oxygen is introduced into
the second stage. The endothermic gasification reactions occur
as well. Particles of the unreacted feedstock are carried out
with the gas. The temperature of the gas exiting the second
stage may approach 1000°C. This gas enters the heat recovery
Coal grinding and
Flowsheet of gasification system employing Texaco gasifier with full heat recovery option.
boiler where a high pressure steam is produced. After the heat
recovery, the particles are removed by a filter and recycled to
the gasifier. The units downstream of the syngas cooler are
similar as those shown in Figure 5.
There is no information in the technical literature
indicating the use of the Destec gasifier for gasification of the
petroleum coke and/or other refinery residues. A low
volatility and reactivity of the petroleum coke suggest that
the contribution of the second stage to the overall gasification
will be small though a high carbon conversion in the first
stage can be achieved. Nevertheless, high volatile low rank
coals were the predominant feedstocks used during the all
stages of the development of this gasifier. It is believed that
some reactor modifications would be needed to make the
Destec reactor more suitable for the gasification of petroleum
coke. However, because of the slurry feeding system
employed, the Destec gasifier may be used for cogasification
of coal with refinery sludges.
4.2 Shell and Prenflo Gasifiers
These are the most advanced dry fed entrained bed gasifiers.
In this case, coal is first pulverized and dried, if necessary, to
less than 5% moisture content before is being conveyed
pneumatically under nitrogen and pressurized in the
lockhoppers. Then, the coal is fed to the gasifier together with
oxygen and steam (if used) through two pairs of the
horizontally opposed burners. Temperature in the gasifier can
readily exceed 1500°C. At such temperatures, even a high
fusion temperature mineral matter can be slagged. The
vertical Shell gasifier shown in Figure 6 employs a water
cooled membrane wall covered with a protective layer of a
refractory and frozen slag. This arrangement allows recovery
of the part of the heat generated in the gasifier in the form of
superheated high pressure steam. Most of the molten slag is
drained from the gasifier through a slag tap at the bottom and
collected in the water bath. Part of the slag is entrained with
the gas as a fly slag. The hot raw gas is first quenched with
recycle product gas to about 930°C to solidify entrained fly
slag. The gas and fly slag then flow to a convective gas cooler
where most of the sensible heat of the gas is recovered as a
superheated high pressure steam. Entrained fly slag and ash are
then removed from the partially cooled raw gas using cyclones
and filters. The gas is then cooled further and scrubbed of any
residual solids in a wet scrubber system. Captured solids are
recycled to the gasifier or mixed with the gasifier slag for
disposal. The solids free raw gas is then passed over a COS
hydrolysis catalyst and subsequently treated with a chemical
solvent to remove all sulphur compounds. The clean fuel gas is
normally reheated and may be saturated with water before
being used in the combustion turbine.
The Shell gasifier used as part of the Demkolec project in
the Netherlands gasifies about 2500 t/d of coal in a single
unit. This is the largest commercial gasifier in the world. The
primary objective of this project was to demonstrate a
number of factors which are part of the technical risk
considerations. This includes the design of the membrane
wall and refractory life, syngas cooler design, feeding
Cool gas for quenching
Schematic of Shell gasifier with syngas cooler.
reliability, gas recycle reliability and solids collection
operability. It appears that all these issues have been resolved
during the initial stages on the demonstration.
A high solid feedstock flexibility of this gasifier should be
noted. This results from the dry feeding system. Thus, any
feedstock which can be pulverized can be readily gasified.
With respect to the gasification of petroleum coke, the Shell
gasifier is perhaps the most suitable, compared with the other
gasifiers. However, a low ash content in the coke may require
the addition of a mineral matter to the coke to ensure
formation of the protective layer of slag on the membrane
wall, at least during the initial stages of the operation. A
significant modification of the feeding system would be
required to enable feeding of vacuum residues and
visbreaking tar, as well as that of refinery sludges. However,
there are some indications on the Shell’s development of an
upscaled coannular burner to handle extremly viscous
feedstocks such as visbreaking tars.
Prenflo is a dry feed pressurized entrained flow gasifier, a
further development of the Koppers-Totzek process. Some
features of the feeding system and the gasifier are similar as
that of the Shell gasifier. Dry pulverized feedstock (less than
100 microns) is pneumatically transported with nitrogen to
the gasifier where it is gasified with oxygen and steam. The
gasifier is lined with water cooled refractory to withstand the
temperature of up to 2000°C and has similar features as Shell
gasifier. Raw gas leaves the gasifier and enters a radiant
cooler directly above the gasifier. The radiant boiler has
pendent tube walls protruding into the interior of the boiler,
forming several flow channels for heat transfer enhancement.
The waste heat boiler generates high pressure and
intermediate pressure steam to be used in the steam turbine.
Two ceramic candle filters are used for the removal of
particulates before the gas enters Venturi scrubber to remove
chlorine and alkalis from the gas. Separated particulates are
recycled directly to the burner of the gasifier.
The IGCC plant employing the Prenflo gasifier is now
under construction in Puertollano Spain as part of the
Elcogas project. The throughput of the gasifier is similar as
that of the Shell gasifier used in the Demkolec project. The
primary feedstock will be the 50/50 blend of the petroleum
coke supplied from the adjacent refinery and a high ash
(about 45%) local raw coal. Similarly as in the case of the
Shell gasifier, all kinds of solid feedstocks can be gasified. It
is indicated that future testing will verify the use of liquid
fuels, principally low value waste streams. With this option
available, suitability of the Prenflo gasifier for integration
with a refinery can be significantly enhanced.
4.3 Other Entrained Bed Gasifiers
commercial entrained flow gasifiers, i.e., air blown gasifier
developed in Japan by CRIEPI and the GSP gasifier
developed in Germany. The former employs two stage
reactor and dry feeding system. The GSP gasifier has similar
features as Shell gasifier. There is no information in the
literature indicating the use of these entrained flow systems
for gasification of refinery residues.
5 DESCRIPTION OF IGCC PLANT
An overall block flow diagram of an IGCC plant employing
the Texaco gasifier is shown in Figure 2. The plant consists
of several major sections, i.e., feedstock preparation,
gasification, gas clean-up, sulphur recovery, heat recovery,
turbines and water treatment. In view of the above
discussion, the description of the plant will consider the
gasifiers such as Texaco, Shell and Prenflo. The operating
characteristics of these gasifiers are given in Table 12. Thus,
little information is available on the commercial gasification
of refinery residues using the other gasfiers. A common
feature of these gasifiers are high temperatures (approaching
1500°C) which ensure high gasification rates. The plant
layout shown in Figure 2 considers electricity as the only
final product, i.e., the full heat recovery option.
5.1 Full Heat Recovery Option without Coproduction
It is again emphasized that entrained flow gasifiers are
gasifiers of the choice for refinery residues as supported by
the available information. There are at least two other
In this case, all synthesis gas produced and heat recovered are
used for the production of elctricity. With this option, the
overall thermal efficiency of the power generation via IGCC
exceeds 40%. This represents a decrease in CO2 emissions
per unit of the electricity generated besides the decrease in
the other emissions as indicated in Table 1.
Preparation of the solid feedstock in the first step is
influenced by the feeding system employed. A wet grinding
is used for the slurry feeding system. The wet grinding has
some safety advantages over the dry grinding. Also, an oil
contaminated water and/or sludges can be added already
during the slurry preparation stage. The dry grinding is
performed under the blanket of nitrogen. The overall water
requirements of the plant are significantly lower in the case
of a dry feeding system. In some cases, this fact may
influence the choice of the gasifier. Specially designed
nozzles and pumps are used for the injection of the liquid and
molten feedstocks, wehreas the lockhopper systems are used
for the dry feeding.
A common feature of the entrained bed gasifiers are high
tempereatures which ensure high gasification rates. The heat
recovery systems around the gasifier represent the major
difference among the Texaco, Shell and Prenflo gasifiers. In
the full heat recovery mode, the Texaco system employs a
radiant and convective cooler which generate a high pressure
steam. In the case of the Shell gasifier, the gasifier products
approaching 1500°C are quenched by a recycled gas to about
900°C before entering the syngas cooler to generate a high
pressure steam in addition to the high pressure steam
generated in the reactor membrane walls. For the Prenflo
system, a radiant cooler comprising suspended tubes is
placed on the top of the gasification section. In the full heat
recovery mode, only Shell gasifier employs a direct quench
of the hot gasifier products. It appears that the Prenflo system
may achieve a higher thermal efficiency than the Texaco and
Shell gasifiers because of the direct heat recovery from the
hot gasifier products. In the Texaco gasifier, the heat is
recovered in the radiant cooler as well, however, part of the
heat is lost due to the evaporation of the slurry water. The
different features of the gasifiers suggest the different
requirements on the material. For example, the suspended
tubes in the Prenflo radiant boiler will be exposed to much
more corrosive and erosive atmosphere than the tubes in the
syngas cooler of the Shell system. Therefore, the long run
performance of the Prenflo gasifier on a large commercial
scale still has to be demonstrated. In this regard, most of the
commercial experience has been gained with the Texaco and
Destec gasifiers, however, the Shell gasifier may soon reach
the same level of confidence assuming that all phases of the
Shell process demonstration as part of the Demkolec project
are successfully completed.
The raw gas leaving the high temperature heat recovery unit
contains a small amount of particulates which are removed in
the particulate removal system such as cyclones and filters.
Shell and Prenflo have successfully tested ceramic filters on a
near commercial scale. The fly slag can be recycled back to the
gasifier or conveyed to a fly slag lock-hopper. After purging
with a high pressure nitrogen, the lock-hopper is depressurized
and the fly slag conveyed to the storage. In the case of Texaco
gasifier, the raw gas from the syngas coolers is water washed
in the carbon scrubber to produce a particulate free saturated
gas. The particulate free syngas enters sulfur removal units
Before utilized in the combustion turbine, the clean gas
after exiting the acid gas removing unit is moisturized to
reduce NOx formation. The gas turbine is equipped with the
heat recovery steam generators to recover waste heat from
the combustion gases. High, intermediate and low pressure
steam is produced. In addition, similar kinds of steam
generated in the gasification plant, i.e., high pressure steam
produced in the reactor’s walls (Shell and Prenflo) and
radiant cooler (Texaco) as well as in the syngas cooler,
intermediate pressure steam produced by further cooling of
the gasifier products as well as from the Claus waste heat
boiler and low pressure steam. All high pressure steam is
utilized in the steam turbines. Part of the intermediate
pressure steam can also be used in the steam turbine while
the rest is used for heaters in the gasification plant and other
parts of the petroleum refinery. All low pressure steam
requirements in the gasification plant are supplied from the
5.2 Partial Heat Recovery and Coproduction
In this configuration, part of the steam recovered from the
heat recovery steam generators and/or part of the synthesis
gas is used to produce other final products. The former may
be used to satisfy requirements of the petroleum refinery or
sold to an adjacent industry. Also, in a site specific case,
steam can be used for the district heating. The direct quench
mode of the Texaco gasifier is ususally chosen when
coproduction is equally or more important than electricity
generation. In this case, after being quenched, the gas is
saturated with steam required for the water-gas shift reaction
to adjust H2/CO ratio for the subsequent synthesis. If H2 is
the final product, the water-gas shift is performed in several
steps. The product of every step enters the CO2 scrubber. In a
specific situation, CO2 can be used, e.g., for the enhanced oil
recovery. There could be some other options for the
utilization of CO2 [
Conversion of the synthesis gas to fuels is commercially
proven. Thus, one commercial plant in Sasol in South Africa
has been producing transportation fuels for many years,
while the other at Great Plains, United States, produced the
synthetic natural gas. Of course, viability of these routes is
dictated by the economics which are today unattractive.
There are several commercial plants in the world producing
ammonia from the synthesis gas made by gasification. Also,
the commercial plant operated by the Tennessee Valey
Authority in United States has been producing oxyganets for
several years. Studies are in the advanced stages, to evaluate
synthesis gas for the direct reduction of iron ore [
suggests that there is a potential for the integration of the
gasification technology with petroleum refinery and
steelmaking. There are several commercial Texaco gasifiers
in operation in China using refinery residues as feedstocks,
producing ammonia and chemicals as final products [
6 INTEGRATION OF PETROLEUM REFINERY WITH
The addition of the gasification process to the petroleum
refinery does not require significant modification of the
refining cycle. Thus, the gasifier only marginally influences
the conventional refinery configuration by being positioned
in a cascade with upgrading processes such as visbreaking,
coking and deasphalting. At the same time, the electricity
generated can have a significant impact on the refinery
product mix. Besides electricity, hydrogen can be produced
for the refinery requirements. Most of the units down stream
gasifier, i.e., gas clean-up, Claus plant, heat recovery
systems, steam and gas turbines, etc. are part of a typical
refinery operation. It is emphasized that power generation
within a refinery is not a new activity and is in reality widely
practiced. However, refinery power plants usually supply
power only for internal consumption. With the development
of IGCC plants, only a small fraction of the power generated
by the refinery will be consumed internally with the rest
being sold to the external consumers. The revenues from the
sale of electricity can have a significant impact in economic
terms. In a medium sized refinery (10 Mt/y) operating a
visbreaker, this can represent over 30% of the total refinery
income if all of the visbreaking tar is used for electricity
In most cases, the environmental factors appear to be the
driving force behind installing a gasification plant on the
refinery site. However, it may be worthwhile to evaluate the
integration from the point of view of the economic benefits
as well. The integration scheme for any new grassroots
refinery will depend on the crude charged and available
markets for electricity, vacuum pitch, coke and liquid fuels.
For existing refineries, capacities and the potential of
debottlenecking these units may be an important
consideration in selecting the optimal scheme. Nevertheless,
the addition of an upgrading unit and a gasifier to the refinery
ensures more efficient processing of crude oil and the
flexibility to meet the changing demand patterns and fuel
A general analysis of several cases published by Iqbal
et al. [
] showed that bottom upgrading adds substantial
value to the operating economics of a refinery. For example,
the cash operating margin per barrel of crude charge to the
refinery improved significantly, as shown in Table 13. The
most significant increase in operating margin was achieved
between the base case and the base + deasphalting + gasifier
case. As expected, the annual cash operating margin, defined
as positive cash flow in thousands of dollars per year per
million dollars of capital investment, as well as the gain in
operating margin on per million dollars of additional
investment for base case, have also increased significantly
(Table 14). All these estimates (Tables 13 and 14) are in
second quarter 1995 dollars. This brief overview indicates a
great potential for the integration of petroleum refinery with
the gasification of the final residues. In addition, the
environmental problems with the residues are solved as well.
The information in Tables 13 and 14 is the only
information of its kind found in the literature, therefore, a
more detailed description of the cases appears to be desirable.
In the base case configuration the vacuum residue is not
processed further, but it is blended with FCC slurry oil and
cycle oil to produce a 4% sulphur heavy fuel oil. The vacuum
tower design achieves a vacuum gas oil cut of 1075°F
(580°C) to minimize residue production.
The flowsheet for the case involving base case + coker +
gasification is shown in Figure 7. The study assumes the
processing of 120 000 bpd of a Venezuelan crude. At first,
only base case + coker will be examined. In this case, the
vacuum residue is upgraded in a delayed coker to give liquid
products and petroleum coke. The intermediate liquid
Refinery with coker, LSR-light straight run naphtha, HSR-heavy straight run naphtha, SR diesel-straight run diesel, VGO-vacuum gas
oil, coker GO-coker gas oil, GOHT-gas oil hydrotreater, LCO-light cycle oil, DSLHT-diesel hydrotreater, NC4-normal butane-IC4-iso
butane, MTBE-esterification unit, C3-propane/propene mixture from FCC, C4-butane/butene mixture from FCC, RFG reg-regular
grade reformulated gasoline, RFG prem-premium grade reformulated gasoline, gaso-gasoline, DSL-diesel, FCC-fluid catalytic
cracking unit, NHT-naphtha, C4 ISOM-butane, isomerization unit, ALKY-alkylation unit [
streams from the coker are hydrotreated in a similar way as
in the base case. These products add to the total amount of
products available for sale. The steam and hydrogen required
for the coker and additional hydrotreatment are generated
within the plant, whereas electricity is purchased from
outside. When a gasifier is added, problems with petroleum
coke, i.e., storage, handling, marketing, etc. are eliminated.
The coke is converted to syngas containing mainly CO and
H2. After cooling and desulphurization, the syngas is steam
reformed to yield a mixture of H2 and CO2. High purity H2 is
recovered by pressure swing adsorption for use in the
refinery. The remainder of the syngas is combusted in a
turbine to generate power. High pressure steam is generated
by cooling the gas turbine exhaust. This steam is expanded in
a steam turbine to generate additional power and the lower
pressure steam is used in the refinery.
The addition of deasphalting and a gasifier to the base case
requires a slight modification of the flowsheet (Fig. 8). At
first, butane is used to split the residue into the deasphalted oil
(DAO) and asphaltenes. The conditions are selected to ensure
that the amount of metals in DAO oil is low for smooth
hydrotreatment and subsequent FCC of DAO. Also in this
case, steam and hydrogen are generated internally and power
purchased from outside. When the gasifier is added, the
asphaltenes are converted to syngas, similarly as in the case
of petroleum coke. If the asphaltene production is higher than
that of coke (e.g., because of DAO quality requirements), the
gasifier capacity is higher, i.e., more power is generated for
export compared with the coke case. On the other hand, in
some cases, it may be possible to choose the operating
conditions of the deasphalting unit to produce more DAO and
less asphaltenes and correspondingly higher liquid yields than
a coker operating on the same feed. It appears that the
integration analysis published by Iqbal et al. [
] assumes a
generic type of delayed coker and Shell gasification process
(SGP), whereas the Residual oil supercritical extraction
(Rose) process was chosen for the deasphalting unit. The
visbreaking case was not included.
In a similar study, Quintana and Falsetti [
] used a
Texaco gasifier for processing a 565°C vacuum residue
derived from the Mayan crude, i.e., the total refinery capacity
was 22 000 t/d producing 8100 t/d of the residue. The
residue was further treated by either deasphalting (Rose) or
delayed coking. Some parameters estimated in this study are
shown in Table 15.
Refinery with solvent deasphalting, Rose-residue oil supercritical extraction unit, DAO deasphalted oil, other abbreviations
as in Figure 7 [
Some parameters from integration of Texaco gasifier [
Parameter Deasphalting Delayed coking
Both the deasphalted oil and liquid products from delayed
coking were hydrotreated using a T-Star process. The
visbreaking case was not included in this analysis. In the
following, the commercial projects in United States and
Europe will be discussed in more details.
6.1 Commercial Projects in United States
The El Dorado Texaco project is a unique case of installing a
relatively small gasification unit to obtain economic benefits
and to solve environmental problems in a refinery. At the
present time, the El Dorado refinery in Kansas, United States,
is a 100 000 bbl/d complex comprising crude and vacuum
distillation units, isomerization, alkylation, reforming, FCC,
delayed coking, hydrotreating, H2 production, gas
liquefaction and distillation, sulphur recovery, aromatics
complex, phenol and acetone production [
]. The flowsheet
of the refinery is shown in Figure 9. The project team has
evaluated several options to meet the refinery’s utility
requirements in compliance with environmental regulations,
i.e., both the economic and regulatory pressures being
imposed on refiners were taken into consideration. The
gasification power plant offered a number of benefits over
the other alternatives. The nominal rating of the plant is
40 MW and the turbine’s exhaust heat produces about
180 000 lb/h of 600 psi and 150 psi of superheated steam. It
meets all of the refinery’s power requirements and 40% of its
steam needs. The gasifier enabled the refinery to shut down
one of its fired boiler which was used for steam production.
The unit was sized to utilize the excess coke (about 120 t/d).
Thus, inspite of its small size, the unit is not considered to be
a demonstration unit for the Texaco process but rather a
No. 1 cat Aromatics
commercial unit. A combination of various economic and
environmental factors showed that the direct quench mode of
the Texaco gasifier was the most suitable for the plant. The
duration of the project, starting with the detailed enigineering
work and ending with the start-up was about two years at a
total cost of $80 million.
Significant reductions of SOx and NOx emissions was
achieved by replacing the previously performed offsite
combustion of 120 t/d coke by gasification. In addition, four
other streams of refinery wastes (Table 16) totaling about
10 t/d are being incinerated in accordance with EPA
regulations. Also, a theoretical decrease in emissions is
associated with the power which the local utility is no longer
generating for refinery usage. Other important environmental
factors relevant to the project were discussed in the
The addition of the gasification plant resulted in
significant economic benefits. Previously, the refinery was
spending $12 to 14 M/y on power purchases from the local
utility. The refinery now pays only a few million dollars a
year for stand-by services. In addition, the refinery is saving
about $1 M/y in waste shipment and disposal and almost
$1 M in nitrogen costs. Steam production costs have been
reduced by more than half. Other benefits result from oxygen
enrichment of the sulphur plant which will enable the
refinery to process a wider range of high sulphur crudes
when the sweet/sour differential becomes attractive.
A new petroleum coke gasification plant at the Star
Enterprise refinery at Delawere City will gasify more
2000 t/d of fluid coke to generate 225 MW electricity.
Another plant is being considered by Koch Ref. Co. This
plant will convert a low value, high sulphur petroleum coke
to power, hydrogen and steam.
6.2 Projects in Italy
There are several IGCC projects in Italy, each at a different
]. All are planned to be constructed in refineries and
to use heavy residues as feedstock. Italy has suddenly
become the cutting edge of this technology in refineries for
residue disposal. These projects represent an attempt by
refineries to enter the fastest growing and perhaps the most
profitable energy business of future-electricity [
There are several factors favoring the integration of IGCC
technology with petroleum refineries in Italy. First of all, the
refining industry in Italy is characterized by widespread use
of visbreaking processes. Thus, among 18 refineries in
operation, 11 have visbreaking plants giving a total
conversion capacity of almost 20 Mt/y [
]. This represents a
visbreaking tar availability of about 8 Mt/y from which it
would be possible to obtain almost 4400 MW of electricity.
Currently, the tar is used to produce a high sulphur heavy oil
(HSHO) by blending it with heavy gas oil in about 70/30
ratio (tar/gas oil). The disposal of the tar via gasification frees
up the gas oil which may be used to produce transportation
fuels. An IGCC plant of 500 MW will consume about 1 Mt/y
of tar. The diluent distillate freed up in this case is around
400 000 t/y [
]. It is evident from the simplified flowsheet
of IGCC integration with the visbreaker that streams leading
to the HSHO can be eliminated.
Meeting environmental standards is another driving force
for implementing IGCC technology in Italy. In particular, the
limits set by the EC Large Combustion Plant Directive for
new large plants have been extended to the existing plants.
This will result in a significant decline in the consumption of
HSHO in Italy, using conventional methods. Because of its
environmental benefit in disposing of the visbreaking tar, the
production of electricity via IGCC in refineries is eligible for
subsidies. In 1994, the price of electricity was fixed at
130 lires/kWh of which 50 lires represented subsidies. The
price is guaranteed in the first 8 years of investment and then
revised according to inflation. Also, the quantities of
electricity are supplied to Italian electric utilities according to
a long term commitment.
The change of product slate which results from a change
in the refinery configuration is shown in Table 17 for a
typical medium size (10 Mt/y) Italian refinery operating a
]. The refinery has an internal consumption of
about 30 MW. If only 75% of the visbreaking tar produced is
gasified, the refinery power consumption represents only 6%
of the total power capacity installed (about 500 MW).
The construction of a 512 MW IGCC plant is underway on
the site of the Isab refinery located in Priolo Gargallo near
Siracusa in Sicily [
]. The plant is constructed by a
consortium of Snamprogeti and Foster Wheeler Italiana under
a $730 million lump sum turn key contract. Commercial
operation is planned for November 1999. The visbreaking tar
will be gasified to produce steam and hydrogen for internal
refinery consumption. a high purity sulphur will be sold to
agricultural and chemical industries. The Italian power utility
(Enel) will purchase electricity under a long term purchase
agreement. Edison Mission Energy, subsidiary of Edison
International owns 49% of the project and ERG Petroli, owner
of the Isab refinery owns 51%.
Edison International led the development of a 100 MW
Cool Water plant the first near commercial IGCC plant, in
A 276 MW Anonima Petroli Italiana (API) project
located at Falconara, will gasify 7700 bbl/d of visbreaking tar
to produce electric power for sale to a local utility [
addition, steam will be produced for internal refinery
consumption and a high purity sulphur for export. The
ownership of the plant includes API [51%] and ABB (25%)
with Morgan Stanley being the financial adviser. Saras
project, scheduled for commercial operation in 1999, will be
the world’s largest IGCC plant at 550 MW. The plant will be
constructed at the Saras Oil Refinery in Sarroch, Sardinia
]. A consortium including Nuovo Pignone (80%
owned by General Electric), Turbotechnica and
Snamprogetti was selected as the turnkey supplier for the
project by Sarlux, a joint venture between Saras and Enron.
6.3 Other Projects
The Shell plant at Pernis, The Netherlands, will gasify tar from
a vacuum residue visbreaker [
]. The gasifier will be supplied
by Shell Lurgi. The plant comprises three Shell gasifier parallel
trains with 550 t/d capacity each. The so-called trigeneration
plant will produce power with cogenerated heat and synthesis
gas for high value chemicals [
]. H2 will be used in a new
hydrocracker which is an integral part of the project. The
remainder of the syngas will be used for power generation
(approximately 80 MW) most of which will be sold to the
national grid. Medium and low pressure steam will be
produced as required by the refinery. Three less efficient and
less environmentally friendly boilers will be phased out.
Commercial operation on syngas is scheduled for 1997.
A 300 MW (net) IGCC plant is being commissioned at
Puertollano, Spain, about 200 km south of Madrid, at an
elevation of approximately 700 m above see level [
plant is being built by Elcogas, a consortium of the leading
European utilities from Spain, France, England, Portugal and
Italy. The feedstock for the plant is a 50/50 mixture of
petroleum coke and lignite containing about 45% ash. The
coke will be supplied from the Repsol refinery located about
1 km from the power plant and the coal mine which is
approximately 6 km from the plant. About 2600 t/d of the
mixture will be gasified. The highly integrated IGCC system
with separate generators for the gas and the steam turbine,
was selected where the total air for the air separation unit is
delivered from the air compressor of the gas turbine. The
primary objective of the plant is to demonstrate its high
thermal efficiency, i.e., an overall thermal efficiency of 45%
is being projected. About 77 t/d of flake sulphur is available
for sale. It is projected that the environmental emissions from
the IGCC plant will be far below the current European
standards. According to the most recent information [
Total, Électricité de France (EdF) and Texaco have launched
a joint project to build an IGCC plant next to Total’s
320 000 bbl/d refinery in Normandy, France. Feedstocks will
include a high-sulfur heavy oil, used lube oil, petroleum coke,
and various refinery wastes. About 20% of the 365 MW of
electric power produced by the IGCC plant will be for Total’s
onsite operation, whereas the remaining 80% will be sold to
EdF. It is projected that the plant will be on stream in 2003 at
the estimated total cost of about FF 4 billion.
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Final manuscript received in August 1999