The document discusses the use of oxygen for sulfur recovery and BTX (benzene, toluene, xylene) destruction in Claus plants, highlighting its advantages for flexible operation and increased capacity with minimal capital investment. The study reviews pilot plant and simulation research on burner designs that effectively eliminate BTX contaminants while optimizing combustion processes, demonstrating significant potential cost savings. BOC's technology advancements, including a kinetic computational fluid dynamics model, enable better understanding and management of reactions in sulfur recovery operations.

1. Oxygen: the Solution for Sulfur Recovery and BTX
By
Jason Norman
BOC
Murray Hill, NJ
Stephen Graville and Richard Watson
BOC
Sheffield, UK
ABSTRACT
Oxygen has been in use in sulfur recovery units for more than twenty years. Oxygen allows for flexible
sulfur plant operation for expanded capacity, peak shaving and turndown with minimal capital investment;
this is beneficial in assisting an industry under pressure to increase gas capacity for the power generation
sector. BTX contaminates, which cause serious problems with sulfur plants, can readily be destroyed
with the use of oxygen. This article reports pilot plant and simulation studies conducted to evaluate burner
design features for BTX destruction. The use of oxygen has been evaluated as a cost effective means of
destroying BTX compared to alternative approaches whilst providing the additional option to increase
sulfur plant capacity up to 180% of design.
BACKGROUND
BTX (Benzene, Toluene, and Xylene) are common contaminants in Claus plant feed gases originating
from associated and some natural gases. Whilst not difficult to destroy in a conventional combustion
process, the fact that the associated acid gas often contains much less than 60% H2S means that the
temperature in the Claus furnace is often too low for effective BTX destruction. Failure to remove the
BTX, either upstream or in the reaction furnace, leads to carbon and hydrocarbon contamination in the
catalyst beds with subsequent loss of activity, high pressure drop in the first catalytic bed and a need to
change out catalyst on a frequent basis. Bypassing some of the process gas around the furnace to
increase the furnace temperature is not possible since BTX is then passed directly to the catalyst beds.
The conventional way of handling the problem within the reaction furnace, for air-based plants, is to
preheat the feed gas (and air) either directly or indirectly. Indirect pre-heat is less efficient thermally and
requires the use of direct-fired heaters, or gas to gas heat exchangers if an external source of heat is
available. If the heat required for preheat is taken from the Claus unit itself, less steam is available for
amine stripping and difficulties can arise during start-up. In either case, preheating is energy intensive
and has a significant effect on the cost and the complexity of the Claus unit. Furthermore, as highlighted
in a paper by Chen[1], the heat required to preheat the air and / or acid gas streams tends to increase
operating costs of the plant. If preheat is to be retrofitted to an existing burner / furnace configuration, the
increase in gas volume to the burner may lead to mixing and pressure drop issues.
Adding natural gas to the Claus feed is more attractive from an efficiency point of view, but this can
significantly increase the size and cost of the Claus unit. If the added methane is not effectively burnt it
too can add to problems with carbon deposition. The reducing nature of the furnace also tends to result
in higher CO and COS concentrations due to incomplete combustion of the methane if added directly to
the feed acid gas.
Oxygen enrichment or total replacement of the combustion air with oxygen is an elegant and cost
effective solution to the BTX problem and this paper will concentrate on illustrating the benefits and
potential cost savings that can be achieved. It will also describe the programme of test work carried out
by BOC on it’s 4 ton per day Claus pilot plant to collect the data which forms the basis of the evaluation
work.
1

2. BOC SURE™ PROCESSES
BOC began developing oxygen using burners and processes for application in Claus units in the mid
80’s. Much of this work was aimed initially at the refining Claus market, but its applicability to gas
recovery Claus was always recognised. BOC offers a complete range of options from simple enrichment,
where oxygen is added to the combustion air before it reaches the burner, through burner replacement,
which allows higher enrichment levels and mixes oxygen directly with feed gas at the burner tip, to pure
oxygen using processes. In the latter case, BOC’s Double Combustion process allows pure oxygen use
even on high combustible content refinery feeds. Three plants now operate successfully with pure
oxygen.
Since the feed streams derived from most gas recovery operations (incl. POX) contain less than 60% H2S
by volume (often much less) pure oxygen can be used without process modifications such as Double
Combustion. The parts of BOC’s SURE™ portfolio most applicable to gas operation therefore are the
SURE™ burner design and related technologies that can have a significant effect on BTX destruction.
BOC SURE™ BURNERS
Burner development is regarded as a core competency within BOC. Our experience has been built up
over many decades and in a wide range of user industries.
The tip-mixed design was chosen because of its safety and flexibility and because it generally has a
much lower pressure drop than the pre-mixed alternative. As the name implies, oxygen (and air in the
case of lower levels of enrichment) does not mix with the acid gas until they leave the burner tip. Keeping
the feed gas, oxygen (and air) apart in this way, facilitates the creation of zones of different temperature
and stoichiometry within the flame. In this way, the flame is used as a chemical reactor and the burner is
staged to promote the beneficial reactions that aid the destruction of unwanted contaminants such as
BTX. It should be noted that, within the flame, localised temperatures in excess of 2000oC might exist.
This is achieved without any risk to the furnace refractory or any other part of the Claus plant. Since the
BTX destruction reactions are kinetically limited, higher localised temperatures result in much greater
destruction rates.
Burner-furnace matching is of major importance and in order to evaluate this fully, BOC has developed a
three-dimensional kinetic computational fluid dynamics (CFD) model of the Claus furnace. This model
has been fully validated with data from BOC’s 4TPD pilot plant, from commercial installations using
SURE™ technology and from small-scale laminar flow reactor work where applicable.
BOC’s burner and process technology has been in commercial use for approximately 12 years and has
proved highly successful. Burners are designed and produced to exacting standards in order to meet the
requirements for oxygen use and to satisfy the design standards of the user industry. The burners have
been developed to ensure optimum performance no matter what the feed composition may be. These
designs have been obtained after extensive research examining the key parameters associated with
good contaminant destruction and burner / furnace operation within the refinery and gas plant industries.
To do this, a purpose built Claus burner development facility was constructed, a brief description of which
follows.
BOC Burner development facility
The burner development facility comprises a commercial-scale 4TPD Claus pilot plant with one thermal
and one catalytic stage (see Figure 1). Based on the former Courtaulds site in Trafford Park,
Manchester, UK, this unit was operated for a period of three years. The plant was equipped with
sophisticated in-furnace sampling and gas temperature measuring devices (see Figure 2), some of which
were developed by BOC specifically for this application.
The plant was able to simulate virtually any feed stream including high ammonia and BTX contaminated
options. The programme looked at the performance of all SURETM burner designs and the complete
range of oxygen use up to 100%. The work on the pilot facility was supplemented by additional small-
2

3. scale laminar flow reactor work carried out both within BOC and by external R&D organisations. Further
information relating to the facility is available from Graville et al. [2-5].
Realising that the burner requirements may be different between gas plant and refinery operations, a
programme of work specifically geared to examine BTX destruction was undertaken. This consisted of a
range of operating conditions that included:
varying BTX and H2S concentrations in the feed gas to the burner
varying levels of oxygen enrichment
natural gas addition as an alternative and in combination with oxygen enrichment
varying the burner design and modes of operation
Figure 1 BOC SURE™ burner development facility
Figure 2 Gas sampling from within the reaction furnace
3

4. Full furnace profiles of the different species within the furnace were measured using gas chromatography.
Corresponding temperature measurements were taken with in situ thermocouples protruding into the
furnace flow area, refractory thermocouples, sacrificial thermocouples and suction pyrometry. This data
was then used to help develop and validate a kinetic CFD model that is described below. Using this
model, burner / furnace matching can be performed and process optimisation techniques examined and
implemented.
Claus reaction furnace models
Many models used in the design of Claus units rely upon equilibrium assumptions to represent the
chemistry occurring within the reaction furnace. This is adequate if the species being examined are not
kinetically limited and one can assume the reactants to be perfectly mixed. In instances where kinetic
limitations predominate, such as ammonia and BTX destruction, the equilibrium assumption is erroneous
and will often predict far greater destruction levels than actually occurs within the furnace. Some models
try to overcome this through empirical relationships taken from commercial plant however, due to the
large number of variables between different plants, this too can give misleading results.
An alternative to relying purely on equilibrium assumptions is to incorporate kinetic expressions for those
species whose reactions are deemed to be kinetically limited within the reaction furnace. Unfortunately,
kinetics alone are not sufficient to obtain an accurate picture of the reaction furnace chemistry. In many
processes, especially combustion, turbulence and mixing play an important role in the overall reaction
pathways undertaken. Therefore, both the kinetics and mixing properties need to be combined and
solved simultaneously.
BOC has, over the last twelve years, developed a 3D model of the reaction furnace and associated
chemistry [6]. The model uses a modified computational fluid dynamics code (CFD). Using this code, the
chemistry, thermodynamics, fluid flow, turbulence and radiation can be solved simultaneously. The
solution process is complex and requires relatively powerful computers to obtain a solution in a timely
manner. Having obtained a solution however, a great deal of information can be extracted from the
model. One caveat with this type of model is that the results are only as good as the various sub-models
used to describe the Claus process. To this end, a great deal of effort has been expended ensuring that
these are accurate; the sub-models for the furnace chemistry are, by necessity, particularly complex. As
far as BTX is concerned, those reactions associated with its destruction have appended an already
complex set of chemical reactions used to represent the sulfur chemistry. BTX chemistry relevant to this
work is discussed below.
BTX chemistry
The reaction pathways associated with the aromatic components within the reaction furnace have been
the issues of some debate within the industry. Since oxygen is present, the assumption that the
hydrocarbons are oxidised to CO2 is often thought to prevail. However, experience shows that invariably
the oxygen requirement is less than stoichiometric for the amount of hydrocarbon present leading to
incomplete or partial oxidation. Furthermore, in the flame region of the furnace, the H2, H2S and reactive
flame radicals are competing for the available oxygen. As such, the relatively large aromatic molecules
with associated large bond energies tend to fair badly in the battle for oxygen resulting in a different set of
reactions occurring to those of hydrocarbon oxidation. An investigation was therefore conducted
examining the possible reaction pathways for these higher hydrocarbon species.
Experiments detailing higher hydrocarbon decomposition reaction rates are well documented [7-10] and
various reaction pathways have been proposed. Figure 3 illustrates an initial decomposition step for p-
xylene derived from Hippler et al.[8]. In this scheme, the initial decomposition of p-xylene is initiated
through collision with another molecule (M) within the system. This either leads to a methyl group being
removed from the ring or, more likely, the removal of an H atom. Once initiated, toluene is eventually
formed from 4-methylphenyl reactions. In a similar manner, toluene thermally decomposes to benzene
[9].
4

5. CH2 CH2
H3C CH3
+ H H2
+
CH3
M
H CH 3 CH 3 M
M
CH 2
CH3 H3C CH3
CH3 M
CH2C 6H4CH2 + H + M
+ CH 3 CH4 +
H3C
CH 3 CH3
CH 3 M
CH3 CH2
H, M +
CH3
Figure 3 Thermal decomposition of p-xylene through 4-methylphenyl to toluene
Examination of the various reaction enthalpies of the dissociation channels for the larger hydrocarbon
molecules, shows that xylene tends to have lower reaction enthalpies than toluene (Table 1). Toluene, in
turn, has lower reaction enthalpies than those associated with the relatively stable benzene ring. As a
consequence, once sufficient energy is supplied to decompose xylene, benzene tends to be formed
relatively quickly; in the experimental programme of work undertaken, in furnace sampling rarely showed
any species other than benzene downstream of the main flame reaction front.
The deactivation potential varies with different hydrocarbon components; In catalyst deactivation
experiments, Cravier et al.[11] found that xylene and toluene were particularly efficient at deactivating
Claus catalysts with xylene being capable of significant catalyst deactivation within a matter of hours. In
commercial units where catalyst deactivation occurs over a relative long time, the main contributor is
likely to be benzene [12]. Where extremely rapid deactivation of the catalyst occurs, toluene and xylene
would be the main contributors however, such events would normally be associated with ‘non-standard’
operation.
Parent molecule Reaction products ∆H298/kJmol-1
p-xylene p-methyl-benzyl + H 353.2
C7H7+ CH3 423.8
toluene benzyl + H 356.1
phenyl + CH3 426.4
benzene phenyl + H 464.2
Table 1 Reaction enthalpies for aromatic hydrocarbon dissociation channels
Using fundamental chemical kinetic packages, the break-up of the large aromatic rings and the
associated kinetics have been investigated. Using this information, sensitivity studies examining the key
reaction pathways were conducted and a series of key reaction steps determined. Before these could be
incorporated into the CFD model however, the inclusion and interaction with sulfur chemistry was
required. This work has therefore examined and included CS2, S2, H2 and COS chemistry.
COS and CS2
The chemistry associated with CS2 and COS alone is particularly complex as is illustrated in Figure 4. In
this case, the main source of CS2 comes from reaction of methane with sulfur species in the reactor. In
5

6. the case of BTX, the methyl radical serves as the main precursor to CS2, this being produced during the
initial decomposition of the larger aromatic structures.
COS + CO + SO2
S2
CH4 + 2S2 CS2 + CO2 2COS CO + 0.5S2
H2O SO2
H2S COS + H2S COS + S2O
CO2 H2O SO2
COS + H2O CO2 + H 2S CO2 + S2O CO2 + S3
CS2 S3
CO2 S3
CO2 + H 2 CO + H 2O H2 + 0.5S2 COS + S3 3S2
Figure 4 Reaction pathways for COS and CS2 chemistry (adapted from Clark et al.[13,14])
In addition to the main stable species that are shown in the above scheme, many flame-generated
radicals are also present and these play a key role in the overall formation and destruction of each stable
species. Such radicals include H, SH, S, OH, CH, CH2, CH3 and SO. To include the effect of all species,
a large kinetic model containing over 250 reactions was used. This large scheme was checked with
experimental work available within the literature and external and internal bench scale experiments. For
complexity reasons, it is prohibitive to model all of the reactions present in the fundamental kinetic model
within the CFD model. Further studies determining the key reaction pathways were repeated and a
simplified model of the reaction chemistry suitable for use within the CFD model was derived.
Using this global kinetic model, a comparison of BTX destruction at two different temperatures is shown
in Figure 5. Here, the top graph represents the system at 1000oC whereas the lower represents the
same system at 1100oC. Xylene initially present reacts to form toluene and benzene. The toluene curve
(inverted triangles) shows an initial formation peak and subsequent destruction to benzene and other
products. Benzene formed is destroyed albeit at a slower rate than toluene. This figure clearly illustrates
that a 100oC change in operating temperature has a marked effect on the rates of BTX destruction;
benzene and toluene are still present after 2s residence time. This sensitivity to temperature and
residence time illustrates why Claus furnace models relying on equilibrium assumptions often have errors
in their BTX representation.
6

7. Figure 5 Comparison of BTX destruction at 1000oC and 1100oC
The reduced reaction scheme used in the simulation above has been incorporated into the CFD model to
enable the mixing and fluid dynamics to be coupled with the chemistry. An overview of this is shown in
Figure 6.
7

8. CH 3 CH3
M,H,CHx M,H,CHx H2O
CO + H 2
CH 3
Sulphur chemistry model
Hy drocarbon S2 H2O, SO2
Pool
CS2 COS
Figure 6 BTX chemistry and tie-in to existing CFD sulfur model
Results from the BOC burner test facility, described earlier, have been used to validate the BTX CFD
model. The overall technique adopted ensures that the chemical models used are validated at each step
from fundamental level through to the global reaction pathways incorporated in the CFD. The next
section describes some of the CFD validation work whilst illustrating the importance of good burner
design and the effect this can have on BTX destruction.
Validation of the CFD model
Figure 7 Illustration of 3D section of reaction furnace showing burner, hot flame region and inner
refractory temperature variation
A full 3D simulation of the BOC burner development facility reaction furnace was performed for a gas
stream comprising 40% H2S, 59.3% CO2 and 0.7% xylene firing through a burner using 100% oxygen as
the oxidant. The inside furnace refractory temperature, hot gas zone and burner location are illustrated in
Figure 7. For this particular firing configuration, acid gas passes through and around the acid gas burner.
Pure oxygen, fed through the central regions of the burner reacts rapidly with the combustible species
liberating thermal energy. With the BTX chemistry and sulfur sub-models in place, the predicted
temperature, H2S and SO2 variation within the furnace obtained are shown in Figure 8. The figures here
represent a slice through the middle of the reaction furnace.
8

9. Figure 8 Predicted contours of temperature, sulfur dioxide and hydrogen sufide
Intense combustion regions result in a relatively short flame with peak temperatures around 1900oC. In
this figure, the red end of the scale depicts higher temperatures and concentrations. Oxidation of the
sulfur species initially liberates SO2 the profiles of which follow maximum temperature relatively closely.
The hottest region of the flame consumes virtually all of the H2S, that which is not oxidised tends to be
dissociated to H2 and associated species.
Downstream of the main reaction zone, the temperature drops fairly quickly to give bulk gas temperatures
of around 1050oC, which agree well with experimental observations. Using the model, it is possible to
confirm that refractory temperatures throughout the furnace remain below the material temperature limits.
This is not as great a concern for gas plant feed streams owing to the low H2S concentrations and high
CO2 levels in the feed. In this example, the high temperature region of the flame is shrouded by a staged
feed gas stream, which ensures the refractory temperature remains well within material design limits.
In Figure 9, xylene, toluene and benzene concentrations are depicted together for the same case. The
initial break-up of the xylene molecules leads to some formation of toluene part of which subsequently
forms benzene. As far as kinetics are concerned, the xylene destruction is faster than toluene and
benzene, complete destruction occurring before the first sampling port of the test facility. Benzene takes
longer to be fully removed owing to the stability of the benzene ring. The scale in this figure is not
common but serves merely to illustrate the high and low concentration regions within the furnace.
In this example, the high temperatures associated with the flame region give very high BTX destruction
rates. Even though xylene is depicted to pass around some of the flame, there is sufficient temperature,
mixing and time for the key reactions to proceed. Even with a relatively low bulk gas temperature of
1050oC, the high levels of feed xylene (7000ppmv) are completely destroyed using pure oxygen whilst
ensuring refractory temperatures remain well with design limitations.
9

10. Figure 9 Decomposition of xylene to toluene and subsequent formation and destruction of benzene
Figure 10 illustrates a comparison between predicted and measured benzene concentrations for this
case. Benzene is illustrated here since it was the only component measured within the furnace at the
sampling locations. The burner is located at the left end of the figure. Considering the complexity of the
BTX chemistry and sampling and analysis errors, the model gives good agreement with measured
values. The lower plot, depicting the predicted values, is slightly conservative with respect to benzene
destruction, which is favourable for design purposes. The figure illustrates that complete BTX destruction
is obtained.
Figure 10 Comparison between measured (top) and predicted (bottom) levels of benzene (ppmv)
10

11. The results from the model described above provide a large amount of data, far more than is presented
here. Using this CFD model different burner designs and operating conditions have been examined and
the effects and dependencies these have, within the Claus reaction furnace, have been determined. With
a validated model, this can be done without necessarily having to build and test each burner design. The
next section illustrates an example where the CFD model is used to examine some of the differences
between general oxygen enrichment and specific oxygen enrichment through a purpose-built burner.
Oxygen enrichment options
At levels below 28%v/v, oxygen addition to the reaction furnace can be performed through either general
enrichment, lancing or a purpose built burner. Above 28%v/v, oxygen compatibility requires different
materials to be used and purpose built oxygen equipment is normally supplied. Oxygen requirement is
normally determined through process modelling of the type discussed previously. Due to the nature of
this analysis tool, only general enrichment can be considered. Using the CFD model however, different
burner designs and firing configurations can be examined and the best solution determined.
In this example, the same burner is fired in two different modes. The feed stream is the same as the
previous example i.e. 40% H2S, 59.3% CO2 and 0.7% xylene. In this case however, oxygen enrichment
to 28%v/v is utilised as opposed to 100% in the previous example. In dropping from 100% oxygen to
28%, the difference is made up with nitrogen from air and as a consequence, the furnace operating
temperature will drop from the previous example. The two firing options considered are:
1. GENERAL: General enrichment of the air fed to burner to a level of 28%v/v oxygen
2. SPECIFIC: Pure oxygen feed to the burner gun with separate air being fed to an air annulus. The
quantity of oxygen used is the same as case 1 thus giving the 28%v/v overall oxygen levels.
Figure 11 Comparison of temperature profiles for the two firing configurations. Top = general
enrichment. Bottom = Pure oxygen addition to same level of overall enrichment
Figure 11 illustrates that, with the SPECIFIC mode of operation, the maximum gas temperature is higher
than the GENERAL case by approximately 300oC. As a consequence of this, the maximum rates of BTX
destruction are higher. Bulk gas temperatures on the other hand, are virtually the same. Figure 12
depicts the xylene destruction for the two configurations. The general enrichment case obtains
approximately 81% destruction of the feed xylene whereas the specific enrichment case achieves 94%
destruction. Although in each case, xylene breakthrough would occur, the concentrations are less with
the purpose-built burner. Bulk gas temperatures are ~980oC and one would normally expect some HC
11

12. breakthrough at these temperatures and feed concentrations. In practise, an increase in oxygen
enrichment would be sufficient to destroy all of the BTX.
Through using CFD modelling and pilot plant testing, BOC has been able to design SURE™ burners that
are optimised for BTX destruction. As such, the amount of required oxygen to achieve complete
destruction is less than is required for general enrichment. In a similar manner, a purpose built burner
offers the same benefits over oxygen lancing for higher levels of oxygen enrichment.
The decision as to whether to use oxygen or not should not therefore be based solely on the oxygen
requirement predicted by industry standard process simulations since these only account for the general
enrichment option. With correctly design equipment, oxygen usage can be less and a reduction in
operating costs can be gained.
Figure 12 Comparison of xylene concentrations for the two different firing configurations
The economics of oxygen use
Oxygen use within Claus units treating gas plant acid gases offer two main advantages. The first is the
ability to completely destroy BTX without the need for natural gas addition or preheat. The second is the
opportunity to increase the plant throughput due to the removal of diluent nitrogen associated with the air
stream. The benefits of this can either be realised through debottlenecking existing plants or reduced
plant size for grass roots units. Since the concentrations of H2S are relatively low in gas plants, higher
levels of oxygen enrichment are achievable within the single furnace without furnace overheating. For
materials reasons, oxygen enrichment above 28% v/v would require dedicated oxygen equipment in
these instances. In cases where the acid gas is reasonably strong, in excess of 70% H2S, alternative
technologies, such as BOC’s Double Combustion, can be used to control the higher associated
temperatures.
For grass-roots installations of equivalent throughput, there are capital, space and complexity savings to
be made with a pure oxygen system over an air-based unit. This is mainly as a result of the removal of
air associated nitrogen from the system; an oxygen-based plant treating a 40% H2S feed would be
approximately 55% of the normal size of an equivalent air based unit. In cases where additional fuel gas
and air are required for BTX destruction purposes, the size of the air-based unit is necessarily larger and
the oxygen-based unit can be significantly less than 50% of the air-based plant. In addition to the above-
mentioned savings, the main air blower would not be required since the air separation plant would
provide oxygen already compressed to the required pressure. A small packaged air blower could be
used for start-up conditions. The use of oxygen also enables catalyst savings to be made owing to the
smaller sized units. This is of additional benefit in plants using proprietary catalysts.
12

13. In spite of the on cost of oxygen, the operating costs can also be lower than that of an equivalent air-
based plant as shown in Table 2. Three options for achieving the required temperature of 1100oC have
been evaluated:
preheat acid gas and air up to 500oC
add fuel gas into feed to reaction furnace
pure oxygen feed
Net requirement Preheat Fuel gas Oxygen
Fuel gas 100% 95% 25%
(Heating/RGG/incinerator)
Electrical 100% 123% 16%
(Air fans)
Net production Preheat Fuel gas Oxygen
Steam LP 3.5 Barg 100% 122% 83%
(Condensers/coolers)
Steam MP 23 Barg 100% 98% 65%
(WHB/reheaters)
Table 2 Operating costs for different process options
The fuel gas and power requirements are very much larger for the fuel gas and preheat processes when
compared to oxygen usage. The flip side of the coin is that there is a net increase in steam production for
the preheat and fuel gas processes. However, the value of the steam will be limited by the cost of
providing boiler feed water (typically BFW costs are a third of the value for steam production) and the
demand for a steam supply on site.
The major operating benefit using pure oxygen is seen in fuel gas (natural gas) savings. Obviously the
cost of fuel gas determines the relative savings in operating costs achieved. In order to provide the
oxygen for BTX destruction, an air separation unit (ASU) has been assumed as the supply. If the power
requirements of the ASU to produce the required oxygen can be met with integrated power generation,
then the cost of oxygen supply can be reduced by approximately 50% further. In order to do this, an
equivalent natural gas requirement of 25% of the preheat case, would be required as a fuel source.
For a grass-roots system, both capital and operating cost savings can lead to oxygen being an
economically attractive alternative to other technologies. In the instance of retrofitted oxygen supply to
destroy BTX, the economics become more dependent upon local gas prices and the local cost of oxygen
which in turn is dependent upon demand requirements.
Conclusions
• An extensive programme of work has been conducted aimed at improving the understanding of Claus
plant operation and the controlling parameters for BTX destruction. A greater understanding of the
chemistry associated with BTX and sulfur has been achieved and this work has resulted in a kinetic
model that has been incorporated into a customised CFD package. Through extensive testing over a
range of different operating conditions, the model has been validated on a commercial scale pilot
facility.
• In conjunction with pilot plant experiments, modelling work has examined and optimised SURE™
burner designs specifically for BTX destruction. The design of burners enables more efficient
contaminant destruction than can be achieved using general enrichment and lancing techniques to
the same level of enrichment. Consequentially, operating costs can be less when SURE™
equipment is used.
• Converting a gas plant sulfur recovery unit to oxygen can provide an additional 80% increase in
capacity at a marginal capital cost. The added benefits of more reliable operation with good
contaminant destruction can also be attained.
• In addition, to the capital savings, a significant reduction in energy consumption can be achieved.
Virtually all the electrical power cost would be incorporated in the oxygen cost (for over the fence
supply). Additional energy would not be required for pre-heating and the fuel gas supply for the
13

14. incinerator would be greatly reduced. In these instances, the cost of oxygen can be offset against
these operating cost savings making oxygen enrichment an attractive alternative to other
technologies.
References
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Conference, Canmore, Canada, 2001.
2. Graville, S.R. and Watson, D. ‘BOC Burner Development Technology’, In: Proceedings of the
Brimstone Sulfur Recovery Symposium, Vail, US, 1997.
3. Graville, S.R. and Watson, D. ‘Optimising the use of Oxygen in Claus Plants’, In: Proceedings of the
Brimstone Sulfur Recovery Symposium, Canmore, Canada, 2001.
4. Graville, S.R., Norman, J.S. and Watson, D. ‘Claus Plant Reaction Furnace: Misconceptions’, In:
Proceedings of the Brimstone Sulfur Recovery Symposium, Vail, US, 1998.
5. Graville, S.R., Norman, J.S. and Watson, D. ‘Contaminant destruction using the BOC SURETM
burner’, In: Proceedings of the Brimstone Sulfur Recovery Symposium, Vail, US, 1999.
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Combustion, The Combustion Institute, pp789-797, 1984.
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Fifth Symposium (International) on Combustion, The Combustion Institute, pp875-882, 1994.
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thermal decomposition of aromatic hydrocarbons’ In: Twentieth Symposium (International) on
Combustion, The Combustion Institute, pp799-806, 1984.
10. Muller-Markgraf, W. and Troe, J. ‘Shock wave study of benzyl UV absorption spectra: Revised
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The Combustion Institute, pp815-823, 1986.
11. Crevier, P.P, Clark, P.D., Dowling, N. I. and Huang, M. ‘Quantifying the effect of individual aromatic
contaminants on a Claus Catalyst’, In: Saudi Aramco Journal of Technology, pp46-54, 2001.
12. Klint, B. ‘Hydrocarbon destruction in the Claus SRU reaction furnace’, In: Proceedings of the
Laurance Reid Gas Conditioning Conference, Norman, Oklahoma, US, Feb. 2000.
13. Clark, P.D., Dowling, N.I. and Huang, M. ‘Mechanisms of CO and COS formation in the Claus
furnace’, ASRL quarterly bulletin, July-Sept. 1999.
14. Clark, P.D., Dowling, N.I., Huang, M., Cooper, J. and Butlin, G. ‘The chemistry of sulfur recovery by
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