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Key Design Features For A Successful SRU Operation Implemented with Oxygen Enrichment Technology

Vincent W. Wong, Arnold E. Sanchez, Jason Flowers and Thomas K. Chow

Fluor Energy and Chemicals

Dave Sikorski, and Nick Roussakis HEC Technologies

0 ABSTRACT Environmental, legislative, economical and existing plant arrangement all conspire to place demanding constraints on increasing sulfur processing capacity. One reliable and cost-effective technology which can meet these challenges is oxygen enrichment. This paper will demonstrate the economic benefits, highlight the technical challenges, and provide an example of the feasibility of O2 enrichment.

1 INTRODUCTION Many refineries and gas plants throughout the world wish to expand current sulfur processing capacity. This is being driven by several factors. Regulations on the sulfur content in fuels have become increasingly stringent. Specifications (e.g. ultra low sulfur diesel) require lower levels of sulfur in products. There has also been a shift toward heavier, increasingly sour feedstocks as light and sweet feedstocks are becoming scarce and more expensive. Finally, environmental agencies have instituted stricter regulations on sulfur emissions from oil, gas, and chemical processing facilities. All of these factors have led to the need for increased hydro-desulfurization in many plants. The net effect is that SRUs/TGTUs are required to process a greater quantity of sulfur while achieving higher recovery efficiency. In some of these facilities, the feed to the SRU possesses undesirable characteristics such as a dilute H2S concentration and/or presence of contaminants including ammonia (NH3), mercaptans, cyanides, and aromatics such as benzene, toluene, and xylene (BTX). To achieve the desired increases in sulfur processing capacity and efficiency while maintaining smooth, continuous and dependable operation in the presence of feed contaminants, it is necessary to select and implement reliable and cost-effective technologies. Oxygen enrichment frequently provides the most economical solution to all of the aforementioned issues. The basis of the technology lies in removing all or part of the nitrogen typically carried in the combustion air and replacing it with oxygen. Table 1 illustrates how oxygen enrichment increases SRU capacity.

Table 1: Oxygen Enrichment Technology for SRU Capacity Expansion

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H2S + ½ O2 + x N2 → H2O + S + x N2

% O2 x Tail Gas Flow Rate Capacity Increase (%)

20 2 1 + 2 = 3 0

50 0.5 1 + 0.5 = 1.5 100

100 0 1 200

The nitrogen present in the combustion air is a diluent that does not participate in the reactions. Oxygen enrichment increases SRU capacity by reducing the nitrogen diluent to make room for more acid gas feed. Removal of the nitrogen diluent also enables the reaction furnace to achieve a higher temperature, which aids the destruction of the feed contaminants. Oxygen enrichment technology provides the flexibility to meet a wide variety of applications in both grassroots and existing plants1. Different levels of oxygen enrichment can be utilized depending on plant configurations, processing capacity requirements, plot space availability, feed gas compositions, and desired operating scenario. Oxygen enrichment technology was first implemented on a commercial scale in the mid-1980’s. Today there are over 200 operating Claus plants effectively utilizing various levels of oxygen enrichment. Commercial applications have achieved successful operation in a wide range of SRU capacities – from small-scale plants to up to a nominal 1000 MTPD, although it has been considered for much larger plants. The technology has proven to be extremely versatile and has been successfully applied to both existing plants and grassroots facilities. The potential advantages of oxygen enrichment are numerous and substantial, both from a process and an economic point of view. When properly implemented, the technology can provide significant capital cost savings in addition to improved operation of the SRU and the downstream Tail Gas Treating Unit (TGTU). Another benefit of oxygen enrichment is its remarkable versatility. That is, the appropriate configuration and level of enrichment can be custom-tailored to each individual project based on new or existing plant configurations, desired capacity expansion, plot space availability, and feed gas compositions.

2 ECONOMIC BENEFITS OF OXYGEN ENRICHMENT TECHNOLOGY

2.1. Effect of Oxygen Enrichment on Capital Costs With larger sulfur processing requirements, plant operators are faced with two choices to handle the increased load: (1) build new facilities, or (2) expand the processing capacity of existing facilities. Regardless of which option is selected, oxygen enrichment can provide the most economical solution.

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2.1.1 Grassroots Facilities Perhaps the most important benefit of oxygen enrichment technology is the substantial capital cost savings realizable through reduced equipment sizes that can be achieved in the design of a new unit. The cost associated with oxygen usage is a major factor when considering application of oxygen enrichment. Overall economics of the technology depend heavily on the cost of oxygen, which varies significantly from site to site. Pipeline oxygen supply is usually cost-effective when available, while the economics of on-site air separation will likely be attractive if the co-produced nitrogen commands a premium and/or there plant oxygen demand is very high. The capital cost reduction achieved through smaller equipment may outweigh the cost of an on-site oxygen generation facility (particularly for lean gas feeds). Table 2 illustrates the extent of the savings that can be realized through incorporation of oxygen enrichment technology in a large scale plant. Both options are capable of processing the same sulfur tonnage during normal operation. The process configuration is a two-stage Claus plant followed by a hydrogenation/amine type TGTU. For the purpose of this analysis, it has been assumed that a new dedicated oxygen supply system must be installed. If excess oxygen were available on-site, the savings would be even greater.

Table 2: Cost savings achievable via oxygen enrichment in a new 1000 TPD SRU/TGTU facility.

Air Only

O2 Enrichment

Configuration 4 x 250 TPD trains 2 x 500 TPD trains Differential Total Installed Cost1

Base Base – 50%

Differential Net Capital Cost2

Base Base – 45%

Differential Operating Cost (NPV)3,4

Base Base + 20%

NPV of Total Savings for 20 Year Life Cycle5

Base Base – 40%

Notes: 1. Does not include cost of an oxygen supply system. 2. Considers cost of new, dedicated oxygen supply system. 3. Operating cost based on steam cost of $6/tonne, power cost of

$25/MWh, and 8000 operating hours per year. 4. NPV based on a 20 year plant life, an 8% discount rate, and 2% per

year escalation. 5. Considers capital cost and operating costs for a 20 year plant life cycle.

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For this study, application of oxygen enrichment reduces operating costs through decreased cooling duties and fuel gas consumption as well as increased saturated HP steam production. However, these savings are offset by the relatively large power requirement of the oxygen supply system (in this case, a cryogenic ASU). Nevertheless, the large savings in capital cost far outweigh the increased operating cost for the oxygen enrichment option. The overall saving achievable through implementation of oxygen enrichment is approximately 40%.

2.1.2. Revamp Units

For the revamp of an existing unit, oxygen enrichment technology provides a relatively quick, simple, and cost-effective method to incrementally increase sulfur processing capacity without requiring the substantial investment of time, money, and plot space necessary to construct a new sulfur plant. Table 3 provides capital cost comparisons for increasing SRU/TGTU capacity in an existing 100 MTPD facility via construction of a new unit versus implementation of oxygen enrichment.

Table 3: Cost of increased capacity in an existing 100 TPD SRU/TGTU.

Increase in SRU Capacity

Estimated Cost for New SRU/TGTU, $MMUSD1

Estimated Cost for Revamp Using Oxygen Enrichment, $MMUSD2

25 – 30% 18 < 1 70 – 80% 32 2

150 – 160% 45 7 Notes: 1. Based on United States Gulf Coast, 2nd Quarter 2009 US dollars excluding site preparation, contingency, escalation, owner’s cost, license fees, catalysts and chemicals cost. 2. Does not include any oxygen supply cost.

2.1.3. Cost-Effective Spare SRU Capacity Environmental regulations in certain parts of the world frequently dictate that the SRU must be in operation in order for refining/gas processing units to run at full capacity. If SRU capacity is decreased (due to a planned or unplanned outage of one of the units), it is generally not acceptable to flare sulfur-containing gases to the atmosphere for an extended period of time. Therefore, if spare SRU capacity is not included, the remainder of the plant’s processing capacity must be significantly reduced or even shutdown when an SRU is down. Oxygen enrichment provides an economically-attractive route to provide spare SRU capacity. Consider, for example, a 1000 TPD SRU/TGTU facility discussed in Table 2. Assume the plant is configured with four identical air-blown SRUs each capable of processing 250 TPD. A fifth train (also with a capacity of 250 TPD) would likely need to be included to provide spare capacity in the event that one of the units was down. Oxygen enrichment provides a method by which to circumvent the necessity for a spare SRU/TGTU.

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Instead of four operating and one spare trains, the facility could be designed with four total units. During normal operation, all four trains would operate on air only at a capacity of 250 TPD. However, if one of the SRUs/TGTUs were out of commission, oxygen enrichment could be applied in the remaining three units to maintain 1000 TPD (full capacity) throughput. Oxygen enrichment can be applied without the need for any additional equipment other than an oxygen burner in each of the SRU trains. The differential cost between an air-only burner and an oxygen-enriched air burner is very minimal, thus the increase in capital cost of the oxygen enrichment option is almost negligible. As indicated in Table 3 above, the cost of implementing oxygen enrichment is quite small relative to the cost of installing an extra SRU/TGTU unit.

2.2. Improved Logistics of Equipment Transportation and Procurement Reduced equipment sizes by implementing oxygen enrichment provide logistical advantages for transportation and procurement. First, smaller equipment is easier and less expensive to transport. This becomes particularly important for plants at remote sites where new infrastructure must be constructed specifically for equipment delivery. Secondly, as equipment gets close to and/or beyond normal fabrication limits, the number of potential suppliers decreases. This means a supplier may have to be selected based on ability to build sufficiently large equipment rather than on technical qualifications and experience. Furthermore, decreased competition between suppliers frequently results in increased costs and decreased control over delivery times. The ability to select between numerous suppliers provides substantial benefits to both cost and project schedule.

2.3. Decreased Plot Space Requirement Oxygen enrichment technology can be particularly valuable when utilized in facilities with space constraints. Whether the application lies in revamping an existing unit or building a new SRU, the compact footprint associated with oxygen enrichment can help to alleviate many common problems.

2.4. Short Schedule for Implementation As mentioned previously, long SRU outages are extremely undesirable because the remainder of the plant will likely have to decrease or shutdown production when the SRU is unavailable to process acid gas. If a slight increase in sulfur processing capacity is necessary to maximize plant production, the operator will certainly prefer not to wait for the construction of a new SRU. Fortunately, low-level oxygen enrichment can be implemented without shutting down the unit. An oxygen diffuser can simply be tapped into the main air supply line2. When higher levels of oxygen enrichment are desired, the necessary burner and piping modifications can be made within the timing of a normal turnaround.

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3 PROCESS AND OPERATIONAL BENEFITS OF OXYGEN ENRICHMENT TECHNOLOGY

Although the increase in sulfur processing capacity and the capital cost savings are typically the driving force behind the implementation of oxygen enrichment, application of the technology also helps to improve the performance of the unit. Some of the areas in which oxygen enrichment provides process benefits are highlighted in the following sections. 3.1. Improved Contaminant Destruction

Contaminant destruction in the Claus reaction furnace is typically dependent upon what are referred to in the industry as the “three T’s”: temperature, turbulence, and residence time. Oxygen enrichment can provide benefits in each of these areas, and thus is an ideal choice to ensure destruction of a variety of contaminants encountered in SRU feeds. 3.1.1. Benzene, Toluene, and Xylene (BTX) Destruction

Benzene, toluene, and xylene (BTX) are examples of contaminants that can have adverse effects on a sulfur plant. If not destroyed in the reaction furnace, these heavy hydrocarbons can lead to loss of catalyst activity in downstream reactors, increased pressure drop through reactor beds, and/or production of off-spec “black” sulfur. The keys to BTX destruction lie in achieving sufficiently high temperature, long residence time, and thorough mixing of all gas streams in the reaction furnace. Oxygen enrichment provides an excellent method by which to achieve the desired process parameters. Oxygen enrichment reduces volumetric flow through the furnace compared to air-only operation at the same sulfur processing capacity. Therefore, a smaller furnace in an oxygen-enriched SRU can provide sufficient residence time for contaminant destruction compared to the furnace necessary in an air-only unit. When revamping an existing SRU (where the size of the reaction furnace is pre-determined), application of oxygen enrichment can provide increased residence time without the need for a time-consuming and expensive modification of the existing reaction furnace.

Typically, temperatures in excess of 2200°F (1200°C) are desirable to ensure complete BTX destruction in the reaction furnace. One of the methods to achieve a sufficiently high temperature is to co-fire natural gas to the furnace. However, there are a number of negative side effects associated with this option. A slight decrease in overall sulfur recovery efficiency is frequently observed due to the increased formation of undesirable side products such as COS and CS2. Furthermore, the dilution effect from the addition of more inert gas and water results in less favorable Claus equilibrium. The larger volumetric gas flow necessitates increased equipment sizes, thereby driving up the capital cost of the unit. Finally, supplemental fuel gas operation requires increased operator attention and represents an added operating cost3.

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Oxygen enrichment technology ensures BTX destruction without any of the adverse side effects. Reactions responsible for the destruction of BTX are kinetically limited4. Therefore, the high localized flame temperatures produced in an oxygen-enriched unit are ideal for guaranteeing that BTX destruction reactions proceed to completion. 3.1.2. Ammonia (NH3) Destruction The requirement for additional hydrotreating and hydrocracking processing steps in fuel production has resulted in increased levels of ammonia present in feed streams to many SRUs. Removal of this contaminant in the Claus reaction furnace is essential for successful operation, as incomplete destruction can result in plugging and/or corrosion of downstream equipment. Oxygen enrichment can be utilized to achieve the necessary residence time, high combustion temperatures (2650°F or higher), and thorough mixing required for ammonia destruction. Depending upon the composition of the feed, oxygen enrichment may enable sufficiently high reaction furnace temperatures to be attained without the need of using some of the proprietary technologies. However, for very lean acid gas feeds, such as for some gasification applications, it is possible that preheating the acid gas and utilizing 100% oxygen enrichment is still not sufficient to achieve the required temperature in the reaction furnace. In this situation, oxygen enrichment can be applied in conjunction with the proprietary technologies to ensure the sufficient temperature is attained. 3.2. Improved Sulfur Recovery Efficiency 3.2.1. Effect of Oxygen Enrichment on Sulfur Conversion Removal of the nitrogen in the combustion air results in a decrease in the total volume of gas carried through the process. This means that the partial pressure of H2S in the process gas is increased, which in turn leads to higher conversion in the catalytic converters in the SRU. Similarly, the increased H2S partial pressure in the gas feed to the amine absorber enables a higher degree of H2S absorption in the column. As a result, less sulfur is discharged to the atmosphere and overall sulfur recovery efficiency is improved.

3.2.2. Effect of Oxygen Enrichment on COS

Sames et al. have obtained plant data indicating that COS production in the reaction furnace increases with increasing temperature between 2200°F (1200°C) and 2710°F (1490°C)5. Others have postulated that COS formation increases with temperature to a maximum level, then levels off and eventually decreases at higher temperatures. Regardless of which theory is correct, it appears that the high temperatures provided by oxygen enrichment likely increase COS production in the reaction furnace to some extent.

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However, the same study5 reports that the amount of COS formed in the waste heat boiler (WHB) accounts for 62 to 71% of the total combined COS formation in both the WHB and the reaction furnace. Fortunately, there are proposed design parameters to decrease the COS formation in the WHB. Through the combined implementation of small diameter tubes in the WHB and operation of the WHB at maximum allowable gas mass velocity, simulation results have shown that up to a 50% reduction in total COS production can be achieved6. Proper design of the WHB can dramatically limit the amount of COS formation in this portion of the SRU, more than offsetting the increased production in the reaction furnace.

3.2.3. Effect of Oxygen Enrichment on CS2 Work by Clark et al.7 indicates that at sufficiently high temperatures, CS2 is not observed in the effluent of the Claus thermal section. Another study by Sames et al.8 reports complete destruction of CS2 at temperatures above 2750°F (1510°C). Destruction of this component is particularly important because each mole of CS2 carries two moles of sulfur. Therefore, the prevention of CS2 formation by attaining a hot flame in the reaction furnace using oxygen enrichment outweighs the potential to slightly increase COS formation. 3.3. Operational Considerations

3.3.1. Improved Tolerance to Process Disturbances

In the event of an upset in upstream units, an SRU with oxygen enrichment capability has the flexibility to process a wide variety of feeds. Should the disturbance result in an increased flow of acid gas to the SRU, increasing the extent of oxygen enrichment can provide additional capacity in the unit. If a higher concentration of contaminants necessitates an increased reaction furnace temperature, increased oxygen enrichment can also satisfy this demand.

3.3.2. Relief of Tight Pressure Profile

One of the challenges of sulfur plant design is the limited overall pressure drop provided by the acid gas feed. Since the pressure drop through equipment is proportional to the square of the gas flow rate, the substantial reduction in flow rate achieved via oxygen enrichment can provide a decrease in the pressure drop through the unit. Without the ability to use oxygen enrichment to decrease the overall pressure drop, it would be necessary to incur the additional capital cost and operating expense of an acid gas or tail gas booster blower.

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4 CFD Validation of Oxygen Enriched Reaction Furnace/Burner Design

HEC has previously presented the need to consider the extreme temperatures that can occur in reaction furnaces and burners even for air only operation (13). Even when operating with low levels of oxygen enrichment, the risks associated with extreme temperatures increase considerably. Since reaction furnace systems involve mixing and chemical reaction in a flowing system, computational fluid dynamic (CFD) modeling is a logical method for evaluating system behavior. CFD is a more cost effective method than the construction and testing of air or water flow (cold flow) models. HEC has previously presented the advantages of CFD over cold flow methods in properly assessing the effects of combustion generated density gradients on system flow pattern and mixing (14). CFD is the numerical solution of discretized differential equations of fluid flow. Convergence involves iteratively balancing energy, mass and momentum at every volume element in the system. The hydraulic domain is typically broken down into five to twelve million volume elements. Smaller elements yield greater accuracy but increase the total number elements and thus reduce the speed of the computation. As a result, it is important to be able to vary the grid density to enhance resolution in the zones where high gradients exist. The converged CFD simulation yields a three dimensional numerical map that includes among others the forecasted velocity, species concentration and temperature distributions. To achieve a reasonable representation of the system within the time line of the design cycle, an optimum combination of fluid dynamic and chemical thermodynamic equivalence must be obtained. The appropriate turbulent viscosity model (14) as well as the chemical reaction schemes and associated models must be properly selected to ensure that a stable, representative solution is obtained in a reasonable period of time. HEC has been using CFD in reaction furnace applications for more than 14 years. Validated by field observations and incorporating the latest R&D results from sulfur research facilities, HEC has yielded significant experience in optimizing the 3D numerical simulation of the reaction furnace. In this section HEC presents an example of design evolution for oxygen enriched operation. The case simulations are based on an actual reaction furnace and burner that were designed for a refinery SRU. The unit was designed to operate in two key modes; air only or with up to 27 mole% oxygen enrichment. In order to ensure good NH3 destruction during air only operation, the unit was designed with acid gas bypass to enhance zone 1 temperature. All of the simulations were based on zero heat loss (adiabatic) and no consideration of radiation. The CFD code used was CFX-v12.1 and the hydraulic domain consisted of seven million volume elements.

Since reaction furnace furnaces are designed with an overall oxygen equivalence (% of stoichiometric oxygen) of about 33 to 40 percent (depending on NH3 and hydrocarbon levels), the oxygen is in fact the limiting reactant. After the oxygen is completely consumed, all combustion effectively ceases. In the case of a flare

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stack burning a hydrocarbon gas in the open air, the hydrocarbon consumption envelope effectively defines the flame boundary. In a reaction furnace it is the oxygen consumption envelope that effectively defines the flame boundary.

Figure 1A shows the cut away oxygen concentration profile for a fast mixing burner installed on the subject reaction furnace. The speed of mixing is evident in the fact that the oxygen plumes disappear within a very short distance of the air/acid gas injection plane (burner near field) and well away from the refractory hot face.

While keeping all input variables constant but changing the trajectory characteristics of the 27 mole% O2-air stream, the fast mixing profile of figure 1A is transformed into the very poor mixing scenario shown in figure 1B. The failure of the air and acid gas to mix efficiently causes the enriched oxygen stream to survive beyond the choke ring that segregates zones 1 and 2.

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For preliminary evaluation, radiation and conductive heat transfer through the refractory is omitted to obtain a worst case hot face temperature profile and provide an effective method to evaluate the mixing within the reaction vessel. The adiabatic temperature distribution provides the best visualization for reaction furnaces mixing because with the zero heat loss assumption, the temperature at any point in the numerical model is determined by the effective air/acid gas ratio at the specific location.

Figure 2A shows the temperature distribution forecast for air only operation of the subject reaction furnace. Of particular interest is the fact that the corner zones display a gas temperature range significantly higher than the fully mixed (Tmixed) zone 1 temperature of 2508°F. This is due to the fact that the CFD simulation predicted that most of the combustion would take place in a zone where the air/acid gas equivalence is closer to stoichiometric than the fully mixed condition. While the peak gas temperature predicted by the CFD simulation (CFDmax) was 3097°F, the stoichiometric reaction temperature calculated by detailed chemical thermodynamics was 3245°F.

The temperature distribution presented in figure 2B is a CFD forecast of the same burner as 2A but the air stream has been adjusted to about 27 mole% O2 and the air/acid gas ratio and bypass fraction were changed to reflect the higher oxygen concentration. The significant upward shift in the corner zone temperature is striking. The peak gas temperature forecasted (CFDmax) of 3707°F was more than 600°F greater than the peak forecasted for the air only case. The fully mixed and stoichiometric reaction temperatures calculated by chemical thermodynamics were 2481°F and 3757°F respectively.

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Figures 3A and 3B display the CFD forecast of the gas temperature distribution at the hot face of the refractory (hydraulic boundary). The air only case predicted a peak gas temperature of 3097°F while the oxygen enriched simulation predicted a peak hot face gas temperature of 3508°F. In both cases the temperatures presented would represent and an unacceptably high temperature condition for refractory design.

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For initial evaluation, radiation and conjugate heat transfer models are not required. The inclusion of radiation reduces the peak gas and peak refractory surface temperatures while increasing gas and surface temperatures in the cooler zones. Heat loss through the refractory reduces the interior surface temperatures; the degree depends primarily on the assumed refractory thermal resistance, ambient air temperature, wind velocity and rain shield configuration. Even when taking into account the temperature mitigating effects of radiation and heat loss, the risks associated with the hot face temperature extremes of the oxygen enriched case resulted in the rejection of the specific burner design represented by figures 2A/B and 3A/B. Since the refractory is such a critical component in the reaction furnace, it is useful to consider both adiabatic and heat loss cases when validating a new system design. This is especially true even for low level oxygen enrichment applications since flame temperatures can significantly exceed the maximum capability of the hot face refractory material. Figure 4A reveals the temperature distribution corresponding to the oxygen distribution case presented in figure 1B. The peak temperature zones occur at the enriched air/acid gas interface. Due to the poor mixing, the peak temperature zone disperses very slowly and extends well into zone 2. As shown in figures 4A and 4B, simulation of this burner design forecasted that the extreme temperature zones would stay well away from the refractory. However, the likely problems presented by the poor mixing flame configuration include poor NH3 destruction, cold shell corrosion and flame impingement on the waste heat boiler tube sheet. This mixing scenario was presented to illustrate the fact that design validation can often involve investigating design and performance extremes as a means of converging to the optimum for oxygen

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enriched applications. As with the previous configuration, the burner design associated with figures 1B and 4A/B was also rejected.

The gas temperature at the refractory hot face for the optimum design is presented in figure 5. Like the burner in figure 1A, the proprietary design in figure 5 demonstrates excellent mixing, however the peak hot face gas temperature is well within acceptable limits for refractory durability and operational performance.

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It must be noted that the application presented in this paper involved very low level oxygen enrichment. The risks associated with high temperatures increase significantly as the oxygen enrichment level increases. Even though CFD only represents an approximation of system behavior, it is a valuable tool for design validation in oxygen enrichment applications. The following points should be kept in mind:

1. System designs for oxygen enriched operation, even low level, must be properly

evaluated to ensure safe and efficient operation of a reaction furnace.

2. CFD is an effective tool for validating system designs.

3. Design evaluations must not only consider the fully mixed system temperatures, but must also consider the risks posed by extreme temperature zones.

4. Whenever possible, CFD predictions should be compared to global performance factors to continuously validate/update the empirical parameters of CFD codes.

5 CONCLUSION

Increasingly sour feedstocks, limits on sulfur content in fuels, and stringent environmental regulations have necessitated increased sulfur processing capacity and improved sulfur recovery efficiency in refineries and gas plants around the world. Oxygen enrichment technology has proven to be the most economical solution to these challenges for many operators. By replacing some or all of the nitrogen present in combustion air with oxygen, flow rates through the SRU/TGTU can be substantially reduced. In the design

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of a new unit, this translates to smaller equipment and thus a reduced capital cost. When applied to a revamp, oxygen enrichment can provide a cost-effective incremental capacity increase. Utilizing smaller equipment due to oxygen-enrichment may provide added benefits to a project. For instance, procurement is generally easier because more suppliers may qualify. Also, the smaller equipment is easier and less costly to transport. Furthermore, smaller equipment is desired in facilities where there are plot space constraints. Finally, oxygen-enrichment technology can be implemented in a short schedule. This well-proven technology not only provides economic benefits, but can also improve the operation of the SRU/TGTU. Enhanced contaminant destruction, sulfur recovery efficiency, reliability, and robustness of operation have all been realized through implementation of this technology. One of the key aspects to ensure successful operation of an oxygen-enriched unit lies in the design of the reaction furnace and burner. Computational fluid dynamics (CFD) modeling can be utilized to model the velocity profiles, species concentrations, mixing characteristics, and temperature profile within the reaction furnace, thereby guaranteeing a design that will provide the desired performance. As a result of its remarkable flexibility, oxygen enrichment technology can be applied to a wide variety of projects. Feeds that are lean in H2S and rich in CO2 allow high levels of oxygen enrichment without the need for complicated temperature-moderating technologies. The extent of oxygen enrichment can be custom-tailored for successful application in both new and existing facilities depending on the plant configuration, processing capacity requirement, plot space availability, feed gas compositions, and desired operating scenario.

ACKNOWLEDGEMENT: HEC Technologies would like to thank Dr. Anthony Corriveau of Stream Function Inc for his tireless efforts and useful suggestions in the generation of the CFD material for this paper.

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