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Regulation Effects on Sulfur Removal Facilities

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Regulation Effects on Sulfur Removal Facilities Powered By Docstoc
					 Regulation Effects on
Sulfur Removal Facilities


              Mahin Rameshni, P.E.
             Chief Process Engineer

                 WorleyParsons
            125 West Huntington Drive
                Arcadia, CA, USA

               Phone: 626-294-3549
                 Fax: 626-294-3311
     E-Mail: mahin.rameshni@worleyparsons.com




           Sulfur Recovery Symposium
        Brimstone Engineering Services, Inc.
                Vail, Colorado, USA
                  September 2001
                         and
        AICHE’S 5th International Conference
                March 10-14, 2002
             Table of Contents

                                                                                                                                      Page
            Abstract......................................................................................................................... i



Section 1   Introduction .............................................................................................................1-1


Section 2   Global Petroleum Market .......................................................................................2-1
            2.1          Overview .....................................................................................................2-1
            2.2          Impacts from New Environmental Regulations in United States .............2-4



Section 3   Evaluation of Key Elements for Higher Sulfur Recovery .................................3-1
            3.1          Process Knowledge ...................................................................................3-1

            3.2          Existing Process Evaluation ......................................................................3-1
            3.3          Process Modifications/Optimizations.........................................................3-2
            3.4          Selection of New Technology to Increase Sulfur Recovery.....................3-3

            3.5          Evaluation of Existing Process Control/Possibilities of Additional ...............
                         New Controls ..............................................................................................3-5
            3.6          Process Monitoring.....................................................................................3-6
            3.7          Capital and Operating Costs......................................................................3-7
            3.8          Oxygen Enrichment Configurations...........................................................3-7
                         3.8.1        Low-level Oxygen Enrichment (<28% O2) ..................................3-7

                         3.8.2        Medium-level Oxygen Enrichment (28% to 45% O2) .................3-8
                         3.8.3        High-level Oxygen Enrichment (>45% O2) .................................3-8
                         3.8.3.1          Implementation of Oxygen Burning Processes.......................3-8

                         3.8.3.2          Conventional Configuration for High Capacity
                                          Expansion................................................................................3-11
                         3.8.3.3          Innovative Configuration for High-capacity
                                          Expansion................................................................................3-13
                         3.8.3.4          WorleyParsons Latest Development “PROClaus
                                          Process” ..................................................................................3-16




                                                                                                                                                  i
             Table of Contents

                                                                                                                                Page
Section 4   Conclusions.............................................................................................................4-1


Section 5   Bibliography ............................................................................................................5-1


            Appendix
            Acronyms and Abbreviations................................................................................... A-1



            Figures
            2-1          Crude Capacity Conversion Units .............................................................2-4
            3-1          Conventional SURE Double Combustion Configuration Reusing

                         Existing Reaction Furnace and WHB......................................................3-12
            3-2          Conventional SURE Double Combustion Configuration with New
                         Two-pass WHBs.......................................................................................3-13

            3-3          Parallel SURE Double Combustion Configuration Using Existing
                         Reaction Furnace and Waste Heat Boiler as Second Thermal Stage
                         Providing 150% Capacity Increase .........................................................3-15
            3-4          Parallel SURE Double Combustion Configuration with
                         New Reaction Furnace and Waste Heat Boilers Providing
                         150% Capacity Increase ..........................................................................3-15

            3-5          Parallel SURE Double Combustion Configuration Using
                         Existing Reaction Furnace and WHB as Second Thermal Stage
                         Providing 300% Capacity Increase .........................................................3-17
            3-6          Parallel SURE Double Combustion Configuration with
                         New Reaction Furnace and Waste Heat Boilers Providing
                         300% Capacity Increase ..........................................................................3-18
            3-7          Three-stage PROClaus Process Flow Diagram.....................................3-19


            Tables
            1-1          Worldwide Sulfur Recovery Requirements ...............................................1-2
            2-1          Crude Quality Profile for Western European Refineries...........................2-2
            3-1          Typical Sulfur Species in Claus Tail-gas Unit ...........................................3-1



                                                                                                                                       ii
 Table of Contents

                                                                                                   Page
3-2   Different Tail-gas Processes......................................................................3-4
3-3   Comparison of Tail-gas Cleanup Processes ............................................3-5
3-4   Tail-gas Cleanup Process..........................................................................3-5
3-5   Revamp Plants Comparison....................................................................3-10




                                                                                                          iii
  Abstract

The U.S. Environmental Protection Agency (EPA) announced a proposal for a 97%
reduction in diesel fuel’s sulfur content in mid-May 2000. This “touch” stance
translates into dropping the current 500-ppm level to 15 ppm. Fuel provisions
would go into effect in June 2006. The EPA believes it has designed its proposed
reduction “to include significant lead time for the introduction of new cleaner fuel
into the marketplace and to ensure no disruptions in fuel supply.” However, the
industry’s National Petrochemical and Refiners Association (NPRA), which
supports a 90% reduction in highway diesel sulfur levels (e.g., a new cap of 50
ppm), voices its concerns that investment requirements for compliance are
“immense.” The refining industry is already implementing a budget program to
reduce sulfur in gasoline in the same time frame. According to the NPRA,
“uncoordinated environmental programs will lead to frequent market disruptions
which affect all petroleum products.”

One objective of the Clean Air Act (CAA) in the United States is to improve air
quality. Managing emissions from mobile sources is becoming a more complex
situation. Processing methods to meet the recent sulfur-reduction specifications for
gasoline might also reduce octane in the gasoline blending streams. The drive
train of new car designs will actually determine future fuel specifications. The EPA
notes that “Refiners and car manufacturers must work together to develop engine
technologies and cleaner fuels so that the clean-air objectives are met. Fuel sulfur
concentration is a problem for new engine designs; sulfur interferes with the proper
functioning of advanced emission control technologies. Reductions to 30-ppm
sulfur is viewed as a ‘great first step’.” The super-clean vehicles of the future will
demand near zero or sulfur-free fuels. Refiners should be thinking about sulfur-free
fuels, because future cars will eventually require sulfur-free fuels. Fuel cell systems
for vehicles are being researched. Methanol and low-sulfur reformulated gasolines
are the most promising fuels for fuel cells. However, many challenges remain. For
example, fuel types, infrastructures, unit costs, and the size of fuel cells are yet to
be resolved. Refineries are already pushing the limit of total U.S. operating
capacity. The NPRA has stated that the EPA’s proposed rule to establish a 15-
ppm sulfur cap in 2006 goes too far. The association expressed concern that a 15-
ppm cap for diesel sulfur content effective in 2006 (from its current 500 ppm) will
sharply reduce available fuel supplies, leading to higher prices and increased
market volatility, which could have devastating consequences. Sulfur is the only
diesel fuel property that should be regulated because it is the only fuel property
that significantly impairs the efficiency of the heavy-duty engine emission control
devices.

Because of the environmental legislation of the European Union (EU), Western
European refiners will be required to make significant processing changes.
Although most refiners did not have a serious problem meeting the year 2000
requirements, a significant investment will be needed to attain 2005 standards for
gasoline and diesel. The current refinery configuration in Western Europe does not


                                                                                      i
  Abstract

support the production of the product slate demanded by local markets. European
refiners will have to make adjustments and investments to meet the EU’s
2000/2005 “clean” gasoline and diesel specifications. Unfortunately, the European
refining industry is plagued by gasoline surpluses that have contributed to low
profit margins. The sulfur content in gasoline specifications under European law is
150 and 50 ppmw (from the current 200-ppm gasoline, 500-ppm diesel) for the
year 2000 and 2005 limits, respectively.

In the United States, during the year 2005, the average legal limit for sulfur in
gasoline will dip to 30 ppm from a current 300 ppm and during the following year,
the limit for sulfur diesel will drop to 15 ppm.

One of the future options for diesel streams is a new type of catalyst, which could
mean a simple change of catalyst rather than the introduction of new sulfur
removal technology. A new desulfurization technology such as Phillips Petroleum’s
S-Zorb process for diesel could be introduced.

In Europe, the sulfur limit in gasoline will be 30 ppm from 2005 and a sulfur-free
limit of 10 ppm will be introduced between 2005 and 2011. Conformance to Auto-I
leads to a six percent increase in CO2 emissions whilst lowering the sulfur content
of gasoline to 10 ppm leads to a future 4.5 percent increase in carbon releases
from refineries.

Using conventional HDS units to deliver very low levels of sulfur depends on
design parameters such as operating partial pressure of hydrogen, which dictates
level of sulfur removal as well as catalyst life. In general, every refinery would need
to invest in additional HDS capacity plant to address the lower limits for diesel.

With the sulfur content of crude oil and natural gas on the increase and with the
ever-tightening sulfur content in fuels, the refiners and gas processors will require
additional sulfur recovery capacity. At the same time, environmental regulatory
agencies of many countries continue to promulgate more stringent standards for
sulfur emissions from oil, gas, and chemical processing facilities. It is necessary to
develop and implement reliable and cost-effective technologies to cope with the
changing requirements. In response to this trend, several new technologies are
now emerging to comply with the most stringent regulations. These advances are
not only in the process technology but also in the manner in which the traditional
modified Claus process is viewed and operated.

Typical sulfur recovery efficiencies for Claus plants are 90% to 96% for a two-
stage plant and 95% to 98% for a three-stage plant. Most countries require a sulfur
recovery efficiency in the range of 98.0% to >99.9%. Therefore, the sulfur
constituents in the Claus tail-gas must be reduced further.

The following key parameters affect the selection of the tail-gas cleanup process:

                                                                                     ii
      Abstract

(1)      Required sulfur recovery efficiency established by the environmental
         agency for different countries (e.g., the EPA or EU).
(2)      Feed gas composition, including H2S content, hydrocarbons, and other
         contaminants
(3)      Existing equipment and process configuration/modifications
(4)      Concentration of sulfur species in the stack gas
(5)      Ease of operation
(6)      Remote location
(7)      Sulfur product quality
(8)      Minimum unit modification for existing units
(9)      Costs (capital and operating)


Depending on the process route selected, an overall sulfur recovery efficiency of
98.0% to >99.9% is achievable. The latter recovery corresponds to less than 250
ppmv of SO2 in the offgas going to the thermal oxidizer before the offgas is vented
to the atmosphere.

In United States, oil and gas refineries are required to reduce the emissions of
sulfur levels to achieve 99.9% or higher sulfur recovery. The sulfur recovery
requirements in Canada increase from 98.5% for plants with a capacity of 50 tpd
up to 99% for plants with a capacity of 2,000 tpd. In South America, the sulfur
recovery requirements vary from 99.0% to 99.9%, depending on where the plant is
located.

The European countries are required to reduce the maximum levels of sulfur in
diesel and gasoline by environmental regulation agencies. However, the overall
sulfur recovery in most European countries is at least 98.5%. Germany requires
sulfur recoveries of 99.5% for plants with a high capacity and 99.8% for plants with
lower capacity.

This paper presents the regulation effects of sulfur removal on worldwide facilities,
ways to increase sulfur recovery the capacity, the global petroleum market and the
key parameters to improve the existing plants, as well as the design criteria for the
new plants to achieve the emission requirements established by environmental
regulatory agencies.

The major impacts on the sulfur recovery units worldwide are not more than a 15%
to 30% capacity increase, and that could be corrected by the minimum
modifications in sulfur plants. Oxygen enrichment seems to be the most cost-
effective process to increase the capacity in existing sulfur plants.


                                                                                   iii
Section 1         Introduction

            When crude oil is processed in refineries, sulfur contained in the oil is mainly
            recovered as H2S, which is converted to sulfur in the refinery Claus plant. Part of
            the sulfur in the crude oil accumulates in the refinery residues. The external use of
            heavy fuels is very restricted, and further upgrading the heavy residues to lighter
            hydrocarbons, or converting these residues to synthesis gas, requires additional
            processes and investment costs.

            Combustion of refinery residues, as well as incineration of Claus tail gases, results
            in offgases containing SO2. The environmental regulations in many countries
            require that most of the SO2 is removed from these flue gas flows. In response to
            this trend, several new technologies are now emerging to comply with the most
            stringent regulations. However, government regulations are only effective if
            compliance is monitored and if the regulations are strictly enforced. If gasoline that
            is exported for sale outside the United States, that gasoline is not subject to the
            requirements of the gasoline sulfur rule, including gasoline produced by a refiner
            located within the Gas Processing Associations (GPA).

            Whether the initiative arose from government inducement, public pressure, or
            internally from corporate philosophy, there has been a considerable increase in
            demand from industries for what are regarded as the key elements for achieving
            higher sulfur recovery efficiencies. These are:

            (1)       Process knowledge
            (2)       Existing process evaluation
            (3)       Process modifications/optimization/converting to a suitable process in
                      order to meet the new emission requirements for any unit involved with the
                      emission requirements
            (4)       Selection of a new technology for the new plant
            (5)       Evaluation of the existing process control/possibilities of additional new
                      controls
            (6)       Process monitoring
            (7)       Capital and operating costs


            To achieve the higher recovery expected of a modern sulfur recovery unit,
            advances in the modified Claus sulfur recovery process itself are being
            implemented. These process technology advances are as a result of the
            evaluation of the key parameters. Each key element will be evaluated individually
            in the following sections.

            Table 1-1 represents the worldwide sulfur recovery requirements for selected
            countries.

                                                                                              1-1
Section 1     Introduction

            Table 1-1—Worldwide Sulfur Recovery Requirements


                        Country               Overall Sulfur Recovery, %

            Asia
            Australia                                    99.9
            China                                        99.9
            India                                        99.0
            Indonesia                                    99.0
            Japan                                        99.9
            Kazakhstan                                   99.9
            Korea                                        99.9
            Pakistan                                    < 99.0
            Philippine                               95.0 to 99.9
            Singapore                                   < 99.0
            Taiwan                                       99.9
            Thailand                                     99.9
            Europe
            Italy                                    97.5 to 99.9
            Most European Countries                      98.5
            Austria                                      99.8
            Germany                                  99.5 to 99.8
            Russia                                       99.9
            United Kingdom (UK)                       98 to 99.5
            Middle East
            Abu Dhabi (UAE)                              98.0
            Egypt                                    99.0 to 99.9
            Iraq                                         99.0
            Kuwait                                       99.9
            Qatar                                        99.0
            Saudi Arabia                                 95.0
            North America
            Canada                                    98.5 to 99
            United States                                99.9
            South America
            Argentina                                99.0 to 99.9


                                                                           1-2
Section 1    Introduction

                     Country             Overall Sulfur Recovery, %

            Jose Industrial, Venezuela              99.0
            Mexico                              98.5 to 99.9
            Venezuela                           98.5 to 99.5




                                                                      1-3
Section 2              Global Petroleum Market

2.1   Overview

                 The crude capacity limit was adopted to ensure that only truly small companies
                 who need additional time to comply can qualify for small refiner status. Refiners
                 who have relatively large crude capacity will probably be in a better position to
                 finance and install desulfurization equipment to meet national standards in 2004.
                 The U.S. Environmental Protection Agency (EPA) interprets its regulations to
                 require refiners applying for small refiner status to include only the crude capacity
                 in 1998 at refineries it owned, including refineries owned by subsidiaries, parent
                 companies and subsidiaries of the parent company, and partners in joint ventures.
                 The sulfur rule states that a small refiner must produce gasoline by processing
                 crude oil through a refinery-processing unit. American Society for Testing and
                 Materials (ASTM) D-2622-98, the design method for testing for sulfur content of
                 gasoline, will be used for this testing purpose by the year 2004.

                 In many respects, the new European specifications are similar to the Clean Air Act
                 (CAA) requirements imposed by the United States but, although the objectives are
                 compatible, the approach taken was different. In the United States, the general
                 approach was to create predictive models to calculate emission values for volatile
                 organic content (VOC), nitrogen oxides (NOX), and toxic compounds based on the
                 physical properties of the product fuel. Although this methodology is more complex
                 to understand and administer, it offers refiners greater flexibility in adjusting the
                 formulations to meet the environmental goals. However, the one notable exception
                 is that U.S. refiners are forced to use a minimum oxygen content for both
                 reformulated and oxygenated fuel programs. The following factors affect the
                 European refining industry:

                 (1)      Crude oil and refined product supply
                 (2)      Demand
                 (3)      Global competition
                 (4)      Environmental year 2000 and 2005 legislation
                 (5)      Imports
                 (6)      Costs
                 With the sulfur removal rates in European refineries averaging 70%, there is plenty
                 of scope for brimstone production for the future. In just 1 year, the targets set for
                 refiners to cut sulfur levels in transportation fuels have reduced into the distance.
                 In Germany, the new environmental laws require “sulfur-free fuels,” which means a
                 10-ppm sulfur level in gasoline. It may not be economical for some smaller refiners
                 to remain in business, and others will need to make significant investments.
                 Refiners must invest in new process units to process new clean fuels; these laws
                 will also reposition refineries to supply a product mix that more closely matches the
                 market’s demands. Table 2-1 represents the crude quality profile for Western
                 European refineries.


                                                                                                   2-1
Section 2     Global Petroleum Market

                  Table 2-1—Crude Quality Profile for Western European Refineries


                          Year                     1995          2000         2005         2010

              Average gravity, °API                  35.1           35.1         33.9         33.4

              Average sulfur, wt%                     1.1             1.1         1.2          1.3


            The European industries will have the new requirements spread uniformly across
            the entire continents. This contrasts to the United States, where a complicated
            patchwork was implemented with four gasoline types [reformulated gasoline
            (RFG), oxygenated, conventional, and California reformulated] and two diesel
            types (on- and off-road). RFG was required year-round in nine ozone
            nonattainment areas, with other areas having the option to use RFG as part of
            their plans to remain in compliance. Oxygenated fuels were required in the winter
            for nearly 40 metropolitan areas throughout the United States, some of which
            overlap with RFG areas. To further compliance of the U.S. program, baseline data
            from 1990 was used and antidumping provisions were enacted to prevent the
            quality of conventional gasoline from being degraded with undesirable components
            that the regulation had already removed from clean fuels. In addition, each
            company was given the option of meeting individual batch requirements or slightly
            more stringent average requirements.

            The European refiners have rigid specifications for each physical property that
            must be satisfied for a common fuel. Although U.S. refiners have more flexibility in
            adjusting each physical property to meet the calculated emission values, they have
            the added complexities of balancing the production and distribution of multiple
            fuels, as well as the additional administrative efforts. Although the approaches are
            different, the results are similar enough for some generalized comparisons to be
            made. Some lessons learned from the U.S. experience will be applicable in
            Europe.

            Sulfur has been identified as the critical component in gasoline that needs to be
            restricted by the federal Reformulated Gasoline specifications. Sulfur in gasoline
            does not affect engine emissions of HC, CO, and NOx, but it increases exhaust
            emissions of these pollutants by inhibiting catalyst performance. Sulfur inhibition is
            very sensitive to air/fuel ratio. The sensitivity of sulfur content on exhaust
            emissions is higher in newer advanced catalyst technology. The sulfur content in
            gasoline specifications under European law is 150 and 50 ppmw for the year 2000
            and 2005 limits, respectively. The sulfur content in diesel specifications under
            European law is 350 and 50 ppmw for the year 2000 and 2005 limits, respectively.
            To comply with the CAA, the U.S. refiners invested in reformulating gasoline and
            diesel for low-sulfur content, in the oxygenates [methyl tert-butyl ether (MTBE)


                                                                                               2-2
Section 2      Global Petroleum Market

            and, to a lesser extent, tertiary amyl ether (TAME)], isomerization,
            naphtha/reformate/cracked gasoline fractionation, aromatics extraction/separation,
            and gasoline blending automation. Production costs have averaged around
            $0.03/gal to make the new reformulated gasoline and $0.01/gal for low-sulfur
            diesel.

            The sulfur limits have the clearest definition with solid specifications for both years
            2000 and 2005. Led by automakers, sulfur is being attacked worldwide because it
            interferes with catalytic converter performance. To put these new limits into
            perspective, typical gasoline sulfur content in Europe is currently at ~ 200 ppm,
            and average diesel sulfur levels are at ~ 500 ppm.

            In the short term, increased North Sea production will flow primarily to Europe,
            displacing the Middle East and Former Soviet Union (FSU) volumes. Europe is
            also projected to absorb gradually more significant amounts of heavy Venezuelan
            production in order to supply feedstock-to-refinery conversion operations, as well
            as bunker demand. All of North Africa’s increased production is absorbed in the
            Mediterranean, and it is supplemented by the North Sea’s volumes and West
            African production. Iraqi production will also flow to Northern Europe. In the longer
            term, the crude market will become more constrained with respect to light, sweet
            crudes as North Sea production begins to decline. Supplies from Latin America
            and the FSU will increase, and the Middle East will become a much bigger shipper
            into the European continent. Essentially, all remaining refineries in Europe will
            need to add diesel desulfurization capability by year 2005. In addition, many will
            need to add expensive but versatile hydrocracking units to meet the low-sulfur,
            high-octane requirements of the new diesel fuel. It is expected that overall gasoline
            yields will drop as refiners respond to the tighter aromatic limits and adjust their
            heavy naphtha cutpoints upward.

            The overall net impact will be an environment of modestly better, although still not
            stellar, refining margins for the Western European industry. Unlike the experience
            of the U.S. refiners during the 1990s, these margins should be adequate to cover
            the significant investments that must be made. Because domestic production will
            not be capable of satisfying the local demand growth, Western Europe will be
            increasingly reliant on imported products, resulting in greater price volatility in the
            future. Price volatility will occur with increasing frequency because any surge in
            demand or disruption in domestic supply will need to be replenished by offshore
            sources, which may have significant time lags in their delivery ability.

            Figure 2-1 represents the crude capacity conversion units in Western Europe as
            21% and in the United States as 52% when compared to the other countries in
            1998.




                                                                                                2-3
Section 2                  Global Petroleum Market




                           Figure 2-1—Crude Capacity Conversion Units




2.2   Impacts from New Environmental Regulations in United States

                     Maintaining diesel fuel supplies in the face of increasing product demand and tight
                     refinery capacity will present refiners with a serious challenge by itself. The
                     reduced production capability, which results from a 15-ppm highway diesel fuel
                     sulfur limit, poses a considerable risk that diesel supplies will be inadequate to
                     meet demand. The U.S. environmental regulations have the following impacts:

                     (1)      Create inadequate diesel supplies
                     (2)      Increase fuel prices
                     (3)      Increase revamp activities for most refineries
                     (4)      Reduce net imported supplies
                     (5)      Produce a near-perfect operation
                     (6)      Lose product due to high severity desulfurization
                     (7)      Lose effective product due to reduction in product energy content
                     (8)      Maintain ability for 15-ppm cap diesel throughout the refinery’s distribution
                              system
                     (9)      Increase capital and operating costs
                     The new EPA Tier 2 emission regulations will require the following modifications:

                     (1)      Additional Fluid Catalyst Cracker (FCC) fed pretreat


                                                                                                       2-4
Section 2         Global Petroleum Market

            (2)      FC gasoline post-treat
            (3)      Additional H2 production
            (4)      Additional sulfur recovery
            (5)      Possible additional alkylation capacity
            (6)      Debottlenecking and utility upgrades
            The refining industry is committed to providing cleaner, more environmentally
            acceptable products to consumers. However, our national environmental goals
            must be consistent with our national energy needs. Close attention must be paid to
            the impact of future regulatory requirements on product supplies and energy
            security because the U.S. product refining and distribution system is already
            stretched to its limit. It is preferable that the EPA establish a cost-effective
            standard for engines and fuels that substantially reduces emissions and, yet, is
            close to the European regulations.




                                                                                          2-5
Section 3                  Evaluation of Key Elements for High Sulfur Recovery

                     The major impacts on the sulfur recovery units worldwide are not more than 15%
                     to 30% capacity increases. To achieve the higher sulfur recovery in existing plants
                     (with the possibility of additional changes), the actual performance test of the unit
                     should be evaluated to determine how much improvement is required. The
                     following key elements for higher sulfur recovery should be evaluated in a step-by-
                     step process to maintain the capital and operating costs within an acceptable
                     range.

3.1   Process Knowledge

                     The education of operators has taken a major step forward with the introduction in
                     annual training and seminars on the subject of optimizing sulfur plants. These
                     meetings not only deal intensively with the theoretical and practical aspects of
                     sulfur plant operations but also provide opportunities for operators from diverse
                     backgrounds to discuss and sometimes solve common problems.

                     The process knowledge could be gained from the experience of analyzing data
                     obtained during detailed engineering evaluations of an operating plant. Most such
                     tests are conducted on plants that are experiencing operational problems or have
                     problems with low sulfur recoveries. Engineers and operators who have a hands-
                     on understanding of the process are invaluable in conducting such trouble-
                     shooting activities. Based on the analysis of numerous detailed sulfur plant tests, it
                     has been reported that the potential causes of recovery efficiency losses can be
                     divided into the following categories:

                     (1)      Poor reaction stoichiometry
                     (2)      Catalyst deactivation
                     (3)      Operating the first converter when it is too cold
                     (4)      Operating the second and third converters when they are too hot
                     (5)      Bypassing gases around the conversion stages
                     (6)      High final condenser temperature
                     (7)      Liquid sulfur entrainment


3.2   Existing Process Evaluation

                     The thermodynamic limitations of the Claus equilibrium reaction do not allow the
                     attainment of sulfur recovery efficiencies greater than 90% to 96% for a two-stage
                     reactor plant and 95% to 98% for a three-stage reactor plant. In most existing
                     plants, the actual sulfur recovery efficiency is unknown because the feed
                     compositions to the sulfur recovery unit could vary as the result of the upset
                     upstream units or the variation of the summer and winter feed compositions.
                     However, if the existing equipment, piping, catalysts, and chemicals are not well
                     maintained, the actual sulfur recovery efficiency will not be the same as had been


                                                                                                       3-1
Section 3                  Evaluation of Key Elements for High Sulfur Recovery

                     originally designed. The test itself consists of collecting all operational data and
                     stream compositions between all vessels in the process where a change in
                     chemical composition has occurred. For the average sulfur plant, this process
                     requires taking samples from eight process streams. An analysis of process
                     streams of upstream and downstream units (such as amine, sour water, and tail-
                     gas cleanup units) often helps to identify process problems in the sulfur plant.
                     Operational changes are accepted because they are usually simple and easy to
                     implement without affecting operating costs. Indeed, the implementation of such
                     changes has resulted in significant improvements in the sulfur recovery efficiencies
                     of many plants. However, because modifications to process equipment could be
                     expensive, the benefits from these modifications should be considered carefully.
                     After the improved actual sulfur recovery efficiency takes place, a further
                     evaluation could proceed.

3.3   Process Modifications/Optimizations

                     The acid gas composition leaving the acid gas removal system has an impact on
                     sulfur recovery efficiency. To achieve the higher recovery expected of a modern
                     sulfur recovery unit, advances are being implemented in the modified Claus sulfur
                     recovery process itself. These advances are taking place in the process
                     technology as the result of evaluating the following key parameters:

                     (1)      Corrections (i.e., those listed previously as deficiencies in the process
                              design basis)
                     (2)      Optimization of the feed to the Claus unit by improving the upstream units
                              (such as gas treating to reduce impurities)
                     (3)      Providing an additional process downstream of the Claus unit (such as tail-
                              gas unit)
                     (4)      Switching from air to oxygen in order to destroy more impurities and
                              increase the capacity/recovery
                     (5)      Providing an acid gas and air preheater upstream of the reaction furnace
                     (6)      Changing the Claus catalyst or combining it with a high-performance
                              catalyst such as hydrolysis catalyst (with a ratio of 30% to 100%) and an
                              oxidation and reduction catalyst in order to increase the sulfur recovery
                     (7)      Converting the modified Claus process to WorleyParsons Beaven’s Sulfur
                              Removal BSR Hi-Activity process
                     (8)      Converting any SuperClaus, cold bed adsorption (CBA), Sub-dewpoint
                              process by Delta Engineering (MCRC), or Sulfreen process to the latest
                              technology WorleyParsons PROClaus process
                     (9)      Adding a new reactor with an additional heater and condenser


                                                                                                     3-2
Section 3              Evaluation of Key Elements for High Sulfur Recovery

                     (10)      Optimizing the sulfur recovery        unit   sulfur   recovery   unit   (SRU)
                               converter/condenser temperatures
                     (11)      Converting the amine solvent in the gas treating unit and any tail-gas unit
                               from a generic solvent to proprietary solvent to increase the volumetric
                               rate and improve the emissions

                     (12)      Optimizing the BSR reactor’s temperature and hydrogen consumption
                     (13)      Optimizing the amine flow rate and temperature for amine absorbers
                     (14)      Minimizing the steam consumption and stabilization of the acid gas’s
                               quality for amine regenerators
                     (15)      Minimizing the steam consumption stabilization of the acid gas’s quality for
                               sour water strippers

3.4   Selection of New Technology to Increase Sulfur Recovery

                     Typical sulfur recovery efficiencies for Claus plants are 90% to 96% for a two-
                     stage plant and 95% to 98% for a three-stage plant. Most countries require sulfur
                     recovery efficiencies in the range of 98.5% to > 99.9%. Tail-gas processes include
                     H2S absorption, recycling technologies, catalytic oxidation of H2S into elemental
                     sulfur, and a tail-gas incinerator process. Therefore, the sulfur constituents in the
                     Claus tail-gas must be reduced further.

                     The increasing standards of efficiency required by the pressure from
                     environmental protection has led to the development of a large number of Claus
                     tail-gas treatment units, based on different concepts, in order to remove the last
                     remaining sulfur species. The choice of the tail-gas treatment processes depends
                     on several criteria, including the sulfur recovery efficiency required, acid gas
                     composition, configuration, and capacity of the existing Claus unit. Table 3-1
                     presents the typical amounts of sulfur-containing compounds to be treated in the
                     Claus tail gas.

                     Table 3-1—Typical Sulfur Species in Claus Tail-gas Unit


                            Sulfur Species                Value

                      H2S (vol %)                       0.3 to 1.5
                      SO2 (vol %)                     0.15 to 0.75
                      COS (ppmv)                       200 to 5000
                      CS2 (ppmv)                       200 to 5000
                      Svap                           Saturated at T&P




                                                                                                         3-3
Section 3         Evaluation of Key Elements for High Sulfur Recovery

            When building a new plant, the feasibility study should be based on all the
            selection criteria, including the required sulfur recovery efficiency, minimum capital
            cost, and minimum unit modification. Table 3-2 presents the various tail-gas
            processes.

                                  Table 3-2—Different Tail-gas Processes


                     Tail-gas Treating (H2S recycle and selective cat oxidation process
                   Typical Solvent (MDEA, HS-101/103, Gas/Spec *SS, Sulfinol, Flexsorb)

             BSR/Amine Process          Shell SCOT/ARCO                    WorleyParsons BOC
                                                                           Recycle
             Resulf                     Dual-Solve                         BSR/Wet Oxidation
             BSR/Selectox               BSR/Hi-Activity/PROClaus           Super Claus
             DOXOSulfreen
                                             Incinerator Tail Gas
             Wellman-Lord               Clintox                           Elsorb
             Claus Master               Cansolv                           Bio-Claus
             Clausorb


            WorleyParsons proprietary PROClaus process combines the conventional Claus
            processing step with two selective reaction steps in a three or four-stage
            configuration that enhances the overall sulfur recovery up to 99.5%. The
            PROClaus process uses two highly selective catalysts for direct reduction of SO2
            and direct oxidation of H2S to elemental sulfur. This innovative processing scheme
            overcomes the sulfur yield limitations dictated by the Claus equilibrium. In
            addition, it offers distinct advantages over other competing technologies:

            (1)       No need to operate the Claus stages off-ratio as in the Super Claus
                      process, which reduces the recovery efficiency of the Claus stages, as
                      well as increases the inlet H2S concentration to the last, direct oxidation
                      stage.
            (2)       No need to operate at sub-dewpoint as in the CBA and MCRC processes,
                      which require routine valves switching and bed regeneration.
            (3)       No need to require a hydrogenation step because SO2 is converted
                      directly to elemental sulfur in the presence of the highly selective
                      Lawrence Berkeley National Laboratory (LBNL)catalyst.
            A demonstration unit for the PROClaus process is started in early 2001 at Puerto
            La Cruz, Venezuela. The PROClaus process’s technological, operational, and
            economic advantages over other commercial tail gas cleaning unit (TGCU)


                                                                                               3-4
Section 3     Evaluation of Key Elements for High Sulfur Recovery

            processes will certainly revolutionize how an efficient and cost-effective
            SRU/TGCU should be designed and operated in the future.

            Tables 3-3 and 3-4 present the comparisons of tail-gas cleanup processes with the
            sulfur recovery efficiency.

                        Table 3-3—Comparison of Tail-gas Cleanup Processes


                    Process              Converters       Sulfur Recovery, Relative Cost
                                                                  %

            Modified Claus                       3               97.0               1.00
            PROClaus                            3 –4            99-99.5             1.15
            Sub-dewpoint                         3               99.0               1.20
            Sub-dewpoint                         4               99.5               1.40
            Direct oxidation                     3               98.8               1.15
            Direct oxidation                     4               99.3               1.30
            BSR/Selectox                         4           98.5 to 99.0           1.45
            BSR/Hi-activity                      4               99.2               1.35
            BSR/amine or SCOT              3 + amine             99.9               1.70


                                  Table 3-4—Tail-gas Cleanup Process


                  Process            Capital Cost         Operating Cost          Efficiency, %

            BSR/Flexsorb                    5                    5                   99.99
            BSR/MDEA                        6                    5                   99.99
            HCR                             6                    5                   99.99
            Thiopaq                         4                    4                   99.99
            Clauspol                        3                    4                 99.5 to 99.9
            PROClaus                        2                    2                 99.2 to 99.5
            BSR/Hi-Activity                 3                    3                   99.2
            BSR/Selectox                    4                    3                   99.0
            ER Claus                        1                    1                   99.0




                                                                                              3-5
Section 3                  Evaluation of Key Elements for High Sulfur Recovery

3.5   Evaluation of Existing Process Control/Possibilities of Additional New
      Controls

                     To improve the higher sulfur recovery efficiency, the existing process control
                     should be evaluated first; additional new controls, along with the new equipment,
                     might then be required. Because of the shortcomings of feed forward control, it is
                     widely accepted that a tail-gas analyzer in closed loop control contributes from 3%
                     to 5% to the overall recovery efficiency on the conventional Claus SRU. By
                     comparison, a third conversion stage only contributes an additional 2% recovery at
                     a capital cost of 15%, and an enhanced Claus process contributes an additional
                     2% to 2.5% at a capital cost of 15% to 25%. Thus, the tail-gas analyzer is certainly
                     worthy of attention and merit in the overall scheme to attain high recovery
                     efficiencies. The achievement and maintenance of high sulfur recovery
                     efficiencies in the existing plants is a long-term commitment from all who are
                     involved in operating the plant. The key parameters for the process control in the
                     existing plants follow:

                     (1)      Provide good process design
                     (2)      Provide well-maintained equipment
                     (3)      Provide well-trained operators

                     (4)      Maintain the correct operating temperatures throughout the unit
                     (5)      Maintain the correct feed ratio (acid gas, air, oxygen) to the reaction
                              furnace/reactors for the main and side streams

                     (6)      Provide appropriate instrumentation, especially analyzers
                     (7)      Use active catalyst
                     (8)      Compare actual sulfur recovery versus calculated sulfur recovery
                     (9)      Correct any of above deficiencies to improve the sulfur recovery efficiency
                     The additional new control systems should be implemented in conjunction with the
                     existing control systems to prevent any deficiencies.

3.6   Process Monitoring

                     Process monitoring is the final phase of the optimization process. Advances in
                     process monitoring have given the operators and the regulatory authorities a better
                     daily account of plant performance. Monitoring is essential for implementing good
                     operating practices that emphasize preventive measures rather than corrective
                     actions to keep the plant running at optimal efficiency.




                                                                                                      3-6
Section 3               Evaluation of Key Elements for High Sulfur Recovery

                     The expected long-term efficiency is the goal for each plant. The thermodynamic
                     capability of the process determines the allowances for feed composition, process
                     configuration, types of reheaters used, operation above the sulfur dewpoint, sulfur
                     fog/mist losses, fluctuations in the air-to-acid gas ratio, and degradation of catalyst
                     activity and plant equipment, plus an allowance for the effects of transitory upsets
                     in upstream processes and equipment failures that occur from time to time. It is
                     further assumed that the plant is optimized and a good operational practice has
                     been established to maintain the optimal performance. Because the expected
                     efficiency is not a thermodynamic limit, the efficiency can be exceeded at any time
                     when circumstances result in the actual efficiency losses due to the factor being
                     less than assessed in determining the expected efficiency.

3.7   Capital and Operating Costs

                     One of the main selection criteria for the chosen technology is to achieve minimum
                     capital and operating costs. The easiest option is to select the technology with the
                     minimum modifications and minimum changes to the operation procedures and, at
                     the same time, to achieve the required sulfur recovery efficiency. Sometimes,
                     revamping the SRU units can take place during general turnarounds to eliminate
                     an additional plant shutdown. The existing plot plan should be evaluated to
                     eliminate the need for designing long piping that contains the hot fluids and the
                     need for new structures, and it should still be able to use the existing equipment as
                     much as possible.

3.8   Oxygen Enrichment Configurations

                     In recent years, the drive towards clean air and clean fuels created great demand
                     for additional hydrodesulfurization and sulfur recovery capacities in refineries and
                     gas plants worldwide. For many operators, the most economical route to acquire
                     incremental SRU capacities is to apply oxygen enrichment in their existing SRUs in
                     lieu of building new SRUs. This technology application enables operators to realize
                     significant cost savings in both capital investment and operating costs depending
                     on the desired capacity expansion.

                     3.8.1       Low-level Oxygen Enrichment (< 28% O2)

                     For a desired capacity increase of up to 20% to 25% of the original design sulfur
                     processing capacity, low-level oxygen enrichment technology is adequate. Low-
                     level oxygen enrichment is accomplished by injecting pure oxygen or oxygen-rich
                     air into the combustion air; i.e., oxygen is premixed with combustion air upstream
                     of the burner. No equipment modification is required in the existing SRU, other
                     than providing the tie-in point for oxygen injection in the combustion air line. An
                     SRU capacity increase of approximately 20% to 25% is achievable with low-level
                     oxygen enrichment. The capital cost investment is mainly in the installation of an


                                                                                                         3-7
Section 3     Evaluation of Key Elements for High Sulfur Recovery

            oxygen supply system, which is usually an oxygen supply line added to the
            reaction furnace burner.

            3.8.2      Medium-level Oxygen Enrichment (28% to 45% O2)

            For a desired capacity increase of up to 75% of the original design sulfur
            processing capacity, medium-level oxygen enrichment technology is required. The
            combustion air piping in a conventional SRU is not suitable for handling oxygen-
            rich air above 28% oxygen. The burner designed for air-only operation might not
            withstand the higher combustion temperature. In any case, direct injection of
            oxygen through separate nozzles from combustion air is recommended; hence,
            special burners designed for direct oxygen injection should be installed.

            The SURE burner is designed for efficient combustion in SRUs with oxygen
            enrichment. It can be used in either end-firing or tangential-firing designs The
            excellent mixing characteristics of the SURE burner, coupled with the higher
            combustion temperature attained in oxygen enrichment operation, allow the
            existing reaction furnace to be used with only minor modifications to accommodate
            the new burner.

            Oxygen enrichment considerably raises the reaction furnace temperature, which
            ensures complete destruction of undesired heavy hydrocarbons and ammonia,
            reduces formation of COS and CS2, and shortens gas residence time requirements
            for contaminant destruction.

            The capital cost investment is mainly in the installation of an oxygen supply system
            and a new oxygen-compatible burner.

            3.8.3      High-level Oxygen Enrichment (> 45% O2)

            For a capacity increase of up to 150% of the original design capacity, high-level
            oxygen enrichment is applicable. The thermal section of the existing SRU must be
            modified and/or have new equipment added, depending on which oxygen
            enrichment technology is chosen.

            3.8.3.1      Implementation of Oxygen Burning Processes
            Oxygen enrichment has been applied to Claus unit revamps because the
            economics are clearly favorable if an increase in sulfur production is required. New
            plants have been designed to use oxygen enrichment when a refiner sees a need
            for a “peak shaving” operation or the need to increase the capacity of a unit on a
            short-term basis to allow for the maintenance of a second unit. New Claus plants
            using oxygen without air are normally associated with gasification projects or gas
            plants, both of which can have a lean relatively constant composition feed.

            The minimum modifications required for a typical revamp are listed below:


                                                                                            3-8
Section 3         Evaluation of Key Elements for High Sulfur Recovery

            (1)      New burner
            (2)      Revised control system
            (3)      Revised shutdown systems
            (4)      Oxygen storage (if not available)
            (5)      Oxygen transfer line
            Normally the existing reaction furnace and waste heat boiler (WHB) could be used
            for the oxygen-enriched operation if the design temperature of their refractory is
            suitable for the oxygen enrichment. For some of the revamps discussed here, a
            new combustion chamber was installed for each plant. There were various reasons
            for this, namely corrosion of the old combustion chamber, replacement of the
            WHB, and a requirement for ammonia burning, but the main determining factor is
            the time allowed for the work on site. The short time allowed for the mechanical
            implementation of a revamp (typically 3 weeks) means that operations such as re-
            bricking a combustion chamber on site are too time-consuming; therefore,
            provision of a new combustion chamber with its refractory is favored. In the case of
            employing WorleyParsons/BOC Gases Company (BOC) SURE Double
            Combustion technology, a new reaction furnace/WHB is installed upstream and in
            series of the existing reaction furnace/WHB. In this case, the preinstalled new
            reaction furnace/WHB could easily be tied in with its existing counter part within
            the plant shutdown schedule. Table 3-5 presents the plant comparison before and
            after revamp.

            The SURE Double Combustion employs two combustion furnaces and WHBs
            arranged in series. All acid gas and combustion air are sent to the first furnace
            where the SURE burner is located. Part of the oxygen is injected directly into the
            first furnace through dedicated oxygen injection nozzles in the SURE burner. The
            combustion products from the first furnace are cooled in the first WHB and then
            flow into the second furnace. The remaining oxygen is injected into the second
            furnace by oxygen lances. The combustion products from the second furnace are
            cooled in the second WHB and then sent to the catalytic stages. The first WHB is
            designed to cool the combustion products to a temperature above 1,000 F
            (540 C), which is higher than the auto-ignition temperature of H2S and sulfur
            (about 500 F or 260 C), so that no igniter is required in the second furnace and
            there is no danger from buildup of an explosive mixture of acid gas and oxygen.




                                                                                            3-9
    Section 3                          Evaluation of Key Elements for High Sulfur Recovery

                                        Table 3-5—Revamp Plants Comparison
                              Before Plant Revamp,
                            metric tons per day (MTPD)                         After Plant Revamp, MTPD
      Refinery Item
                            S              NH3           O2            S            NH3          O2          O2 %
Refinery A                  60             —            —               90          —           —              —
Refinery B                  70              1.9         44.1            97           5.72       53.1          32.1
Refinery C                  15              0            8.6            24           1.53       13.9          33.2
Refinery D                  32              0.3         17.6            47           0.53       26.4          39.1
Refinery E                  42              0.3         24.7            80           4.84       44.8          41.7
             1
Refinery F                  48.9            1.9         27.3            45           6.34       32.3          29.8
Refinery G                New              —            —            75 x 2          1.20       63.1          95.0
Refinery H                  51              3.5         30.3            68           4.6        40.9          31.0
Refinery I                150              10.6         87.8          241           28.8       172.5          35.0
Refinery J                  19              0           11.0            43           0          25.0         100.0
Refinery K               240 x 2           —            —            426 x 2        —           —            100.0
             1
Refinery M                250              —            —             500           —           —            100.0
             1
Refinery N                  20             —            —               50          —           —            100.0
Refinery O                330              —            —             450           —           —            100.0
Refinery P                140              —            —             250           —           —             60.0
Refinery R               95/180            —            —            165/295        —           —             60.0
1
The sulfur production requirement decreased and sour water stripper (SWS) processing requirement significantly
increased.


                                 The investment cost associated with an oxygen enrichment revamp is only 15% to
                                 25% of a new air-based SRU. Oxygen enrichment also provides substantial cost
                                 savings for new SRUs by reducing the sizes of the equipment. Applying oxygen
                                 enrichment to a new SRU can cut the flow rate through the SRU by half at the
                                 same sulfur recovery capacity as compared to an air-only unit; this results in
                                 approximately 35% savings in investment cost, which excludes the cost of an
                                 onsite oxygen generation unit.

                                 Using oxygen enrichment will improve the following factors in sulfur recovery units:

                                 (1)       Increase unit capacity.
                                 (2)       Eliminate the limitation of air blower discharge pressure and plant
                                           hydraulics.



                                                                                                                3-10
Section 3         Evaluation of Key Elements for High Sulfur Recovery

            (3)       Increase processing SWS offgas.
            (4)       Increase combustion chamber temperature, and increase the stability of
                      the flame temperature for lean acid gases.
            (5)       Increase the tail gas unit capacity (cooling capacity of direct contact
                      condenser should be evaluated, and the amine circulation rate should be
                      examined to ensure adequate amine circulation for H2S absorption).
            (6)       Evaluate the existing degassing system and the sulfur rundown (required
                      for large percentage of sulfur capacity).
            (7)       Evaluate the existing incinerator (required for large percentage of sulfur
                      capacity).
            (8)       Facilitate the complete destruction of ammonia, heavy hydrocarbons [such
                      as benzene, toluene, and xylene (BTX)], and other contaminants.
            (9)       Increase accuracy by computational fluid dynamic (CFD) program (means
                      of predicting flame patterns for specified operating conditions).
            Various configuration options for high-level oxygen enrichment with
            WorleyParsons/BOC’s SURE Double Combustion process are available to suit the
            requirements of the individual facility.

            3.8.3.2        Conventional Configuration for High Capacity Expansion
            The conventional configuration involves the addition of a new reaction furnace
            burner, reaction furnace, and WHB boiler upstream of the existing reaction furnace
            (Figure 3-1). Gas effluent from the new waste boiler is routed to the existing
            reaction furnace, which serves as the second thermal stage. With this
            configuration the SURE Double Combustion technology allows SRU capacity to be
            expanded at considerably lower costs compared to building new air-based SRUs.
            The operator could save substantial initial investment cost even for new SRUs if
            oxygen is available or can be imported across the fence. Moreover, oxygen
            enrichment reduces the plot area required and, in fact, for operating facilities
            limited by plot space, oxygen enrichment might be the most viable option for SRU
            capacity expansion.

            Occasionally, existing reaction furnaces and WHBs cannot be reused because of
            original design limitations. In these cases, a two-pass WHB with an extended
            head can be designed in which the extended head serves as the second-stage
            reaction furnace and the second pass serves as the second WHB (Figure 3-2).
            This two-pass WHB configuration effectively reduces capital cost and conserves
            plot space requirement. In addition, the following benefits could be realized by
            operators:

            (1)       The new reaction furnace/WHB can be installed while the existing SRU is
                      still in operation. The new equipment can be tied in with the existing

                                                                                           3-11
Section 3                    Evaluation of Key Elements for High Sulfur Recovery

                                   reaction furnace/WHB during a short period shutdown or during the SRU
                                   turnaround time, thus minimizing the loss of plant throughput while the
                                   technology is implemented.
                       (2)         The simple piping for the SURE design reduces the possibility of
                                   accidental H2S emission and equipment failure compared to other
                                   commercially available processes.
                       (3)         The SURE Double Combustion design does not require shutting down and
                                   isolating a recycle loop when oxygen enrichment is not being used; this
                                   further improves the safety of the SURE process.
                       (4)         Changing the mode of operation between air-only and oxygen enrichment
                                   is simple and smooth for the SURE process, which involves only the
                                   oxygen supply system. The SRU itself is always ready to receive oxygen.



                        New                    Existing
            NH 3

            H 2S                     W              W
                              RF     H         RF   H
                   Burner
                                     B              B
            Air
                                                                          Reheater
            O2


                                                                            Converter


                                                                                        Condenser



                                                                     Sulfur Pit



                       Figure 3-1—Conventional SURE Double Combustion Configuration
                       Reusing Existing Reaction Furnace and WHB




                                                                                                     3-12
Section 3                   Evaluation of Key Elements for High Sulfur Recovery

                                            Reaction Furnace #2
              Reaction Furnace #1
            Burner                                         Oxygen
                                                                             Reheater




                                                                               Converter


                                                                                           Condenser



                                                                        Sulfur Pit




                         Figure 3-2—Conventional SURE Double Combustion Configuration
                         with New Two-pass WHBs




                         3.8.3.3      Innovative Configuration for High-capacity Expansion
                         When multiple SRU trains are involved, one set of common new equipment
                         (burner, reaction furnace, and WHB) can be shared by the various trains. The
                         existing reaction furnaces and WHBs of the individual trains can be used as the
                         second thermal stage. The effluent of the new WHB is split and routed to each of
                         the existing reaction furnaces (Figure 3-3). The new equipment could be installed
                         onsite while the SRU is in operation. Only a short downtime is needed to tie in the
                         new equipment for high-level oxygen enrichment. Typically, the revamp tie-in work
                         has been accomplished within 1 to 2 weeks, which is normally within the schedule
                         of a routine plant maintenance shutdown.

                         Having the hot effluent (>1,000 F) from the first thermal stage travel a very long
                         distance is undesirable. Therefore, if the individual trains are far away from each
                         other, it might be necessary to install a new common second thermal stage.
                         Depending on the required capacity, the second stage will either be a two pass
                         WHB sharing a common shell with the first stage or an individual boiler. The
                         relatively cool gas from the new second stage WHB is then split and tied into each
                         of the existing number one sulfur condensers (Figure 3-4). Oxygen consumption
                         can be reduced by treating part of the acid gas in the existing reaction furnaces
                         and WHBs of the individual units using air. The effluent gas is also routed to the
                         number one condenser and joins with the effluent of the new WHB for the
                         remaining Claus process. This configuration can also be applied when the sizes of
                         the existing reaction furnaces and WHBs are not adequate to handle the required


                                                                                                        3-13
Section 3        Evaluation of Key Elements for High Sulfur Recovery

            capacity increase alone. It can effectively reduce the pressure drop across the
            SRUs and hence provides greater flexibility in the event that additional Claus stage
            or tail gas treatment needs to be added to increase the sulfur recovery to meet
            more stringent emissions requirements. These common equipment configurations
            could be cost effective for the following revamp situations.

            A.    Spare Train Capacity Requirement
            Refer to the process configuration described in Figure 3-3; when no additional
            capacity is required during normal operation, existing reaction furnaces of both
            trains can be operated with air while the new reaction furnace/WHB can also be
            operated with air at reduced capacity. This operation mode will save oxygen cost.

            When one of the two trains is down, the reaction furnace of the operating train can
            be operated with air at reduced rate while the new reaction furnace/WHB is
            operated with oxygen to provide the spare train capacity with one single train
            operation. This operation mode will ensure that refinery or gas plant throughput is
            maintained and thus will avoid any loss of income.

            B.    Normal Capacity Expansion with Added Spare Train Capacity
            If additional sulfur processing capacity is required during normal operation, existing
            reaction furnaces of both trains can be operated with air at reduced capacity while
            the new reaction furnace/WHB operates with oxygen to provide the required
            additional capacity to both trains.

            When one of the two trains is down, the reaction furnace of the operating train can
            be operated with air at reduced rate while the new reaction furnace/WHB is
            operated with oxygen to provide the spare (double) train capacity with one single
            train operation. This operation mode will ensure that refinery or gas plant
            throughput is maintained and thus avoids any loss of income.




                                                                                             3-14
Section 3       Evaluation of Key Elements for High Sulfur Recovery

                                                                                                       ~
                                                                                               ConverterConverter
                                                     RF               WHB                         1        2
                                                                                                       ~
                          New
                                                     oxygen                                Condenser Condenser
                                                                           Condenser          2         3
                                                                              1




                            RF              WHB                                                     Existing
            Amine AG
            SWS AG              Burner
                       oxygen

                                                                                                           ~
                                                                                                   ConverterConverter
                                                         RF               WHB                         1        2
                                                                                                           ~

                                                         oxygen                              Condenser Condenser
                                                                             Condenser          2         3
                                                                                1




            Figure 3-3—Parallel SURE Double Combustion Configuration Using Existing
            Reaction Furnace and WHB as Second Thermal Stage Providing 150%
            Capacity Increase


                                                                                               ~
                                                                  ~                       ConverterConverter
                                                    RF        WHB                            1        2
                                    Acid Gas                                                   ~
                                       Air
                                                                  ~
                                                                                       Condenser Condenser
                                                                      Condenser           2         3
                                                                         1




                           RF                                     oxygen

            Amine AG
             SWS AG         Burner
                       oxygen


                                                                      ~                            ~
                                                                                            ConverterConverter
                                                     RF           WHB                          1        2
                                         Acid Gas                                                  ~
                                            Air
                                                                      ~
                                                                                         Condenser Condenser
                                                                                            2         3


            Figure 3-4 – Parallel SURE Double Combustion Configuration with New
            Reaction Furnace and Waste Heat Boilers Providing 150% Capacity Increase




                                                                                                                        3-15
Section 3         Evaluation of Key Elements for High Sulfur Recovery

            C.     Provide 300% Additional Capacity for Two Existing Parallel Trains
            The new reaction furnace/WHB can be designed to provide up to 150% additional
            sulfur processing capacity for each of the two existing parallel SRUs resulting in a
            total additional capacity of 300%. This operation mode would require the reaction
            furnace/WHB to be operated with oxygen during normal operation. Figure 3-5
            depicts the minimum cost configuration to double the sulfur processing capacity of
            both existing trains. Although this minimum cost configuration does not offer some
            desired operation flexibilities, it could be configured as described in Figure 3-6. If
            the new equipment is shut down, the existing reaction furnaces can be operated
            with up to 28% oxygen-enriched air and can still provide 125% of the original
            design capacity. This configuration and operation mode minimize the loss of sulfur
            processing capacity and still maintain more than half of the total required capacity
            if any one of the two trains is down or if the new equipment system is down.

            D.     Stage Wise Investment Option
            Considering the fact that configurations described in Figures 3-3 and 3-5 offer
            limited plant operation flexibility as when the new reaction furnace/WHB is down,
            the sulfur processing complex may suffer reduced or total loss of capacity.
            However, this configuration does provide a viable option for stage wise investment.
            If the process configurations described in Figures 3-2 and 3-4 are the most desired
            configurations that fit well into the existing designed equipment, plot space
            availability, and/or budget target, such a configuration can be implemented as a
            first-stage investment to accommodate the immediate needs. A second reaction
            furnace/WHB can be considered to install for the second train at a later time when
            budget is available to provide the desired operating flexibility while achieving the
            required sulfur processing capacity.

            3.8.3.4        WorleyParsons Latest Development – “PROClaus Process”
            WorleyParsons proprietary PROClaus (WorleyParsons RedOx Claus) process
            combines three distinct processing steps into one processing scheme:

            (1)       Conventional Claus reaction
            (2)       Selective reduction of SO2
            (3)       Selective oxidation of H2S
            This evolutionary process does not rely on tail gas hydrogenation, H2S-shifted
            Claus operation, or cyclic sub-dewpoint operation. Instead, the PROClaus process
            is a continuous dry catalytic process that operates the reaction furnace and the
            first Claus stage (or the second Claus stage) just like a conventional modified
            Claus unit, and the stage Claus is followed by a selective reduction stage and a
            selective oxidation stage. In a 3-stage or 4-stage configuration, PROClaus can
            achieve up to 99.5% overall sulfur recovery pending the acid gas compositions.
            Figure 3-7 presents the PROClaus configuration.


                                                                                             3-16
Section 3       Evaluation of Key Elements for High Sulfur Recovery



                                                                           ~
                                                                      ConverterConverter
                                       RF           WHB                  1        2
                                                                           ~
                          New
                                       oxygen                      Condenser Condenser
                                                     Condenser        2         3
                                                        1




                           RF        WHB                                 Existing
            Amine AG
            SWS AG          Burner
                       oxygen

                                                                               ~
                                                                        ConverterConverter
                                           RF       WHB                    1        2
                                                                               ~

                                           oxygen                   Condenser Condenser
                                                       Condenser       2         3
                                                          1


            Figure 3-5—Parallel SURE Double Combustion Configuration Using Existing
            Reaction Furnace and WHB as Second Thermal Stage Providing 300%
            Capacity Increase




                                                                                             3-17
Section 3                       Evaluation of Key Elements for High Sulfur Recovery

                                                                                        ~
                                                            ~                      ConverterConverter
                                                 RF         WHB                       1        2
                                 Acid Gas                   ~                            ~
                         New
                                                                                Condenser Condenser
                                                                Condenser          2         3
                                                Air
                                                                   1




                           RF                               oxygen
                                                                                      Existing
            Amine AG
             SWS AG
                            Burner
                       oxygen


                                                                ~                            ~
                                                                                     ConverterConverter
                                                       RF    WHB                        1        2
                                     Acid Gas                                                ~
                                                                ~
                                                                                 Condenser Condenser
                                                                    Condenser       2
                                                      Air                                     3
                                                                       1



              Figure 3-6—Parallel SURE Double Combustion Configuration with New
              Reaction Furnace and WHBs Providing 300% Capacity Increase




                                                                                                          3-18
Section 3                                  Evaluation of Key Elements for High Sulfur Recovery


                                                                                                 Air




                                                                   Claus                  Selective
                             HP Steam                                                                               Selective
                                                                  Converter               Reduction
                                                                                          Converter                 Oxidation
                                                                                                                    Converter
                                  Waste
                  Reaction                                                                                                                        O2
                                  Heat
                  Furnace                              Reheater               Reheater                      Reheater
                                  Boiler                                                                                                    AC
                                                       No. 1                  No. 2                         No. 3
                                            LP Steam               LP Steam
                                                                                      H2S/SO2                                 LP Steam
                                                                                                 LP Steam
Acid Gas                                                                                 AC
              K.O             BFW
                                                                                                                                                 Tail
              Drum                                                                              Condenser                     Condenser
                                            Condenser               Condenser
                                                                                                                                              Gas
                                              No. 1                   No. 2                       No. 3                         No. 4

    Water
            Air                                                                                       BFW                       BFW
                                              BFW                  BFW


                                                                                                                          M

                                                                                                                                         Liquid
                     Air Blower
                                                                                      Sulfur Pit                                         Sulfur

                                                                                                                       Sulfur Pump




                                  Figure 3-7—Three-stage PROClaus Process Flow Diagram




                                                                                                                                           3-19
Section 4     Conclusions

            Using conventional HDS units to deliver very low levels of sulfur depends on
            design parameters such as operating partial pressure of hydrogen, which dictates
            level of sulfur removal as well as catalyst life. In general, every refinery would need
            to invest in additional HDS capacity plant to address the lower limits for diesel.

            The key features in the regulatory effects of the sulfur removal facilities should
            include the new environmental regulations in the United States and in Europe,
            which will have many impacts on fuel productions, global petroleum markets,
            global petroleum demand, global trade flows, the refining industry, market outlook,
            crude oil supply, and the business environment. The key features affecting the
            selection of the tail-gas treating processes should involve the application of the
            most common well-known technologies. To select the proper tail-gas cleanup, all
            of the key step-by-step parameters should be considered.

            The new regulation will require increasing the sulfur capacity by 15% to 25%,
            which could be implemented by using oxygen enrichment in addition to other
            modifications to improve the sulfur recovery in order to meet the new EPA
            regulations.

            The PROClaus process presents the latest WorleyParsons technology of a 3 or 4-
            stage air-based PROClaus to achieve up to 99.5 percent overall sulfur recovery
            improve the sulfur recovery in order to meet the new EPA regulations. The
            PROClaus process is the most cost effective sulfur recovery process since there is
            no need for additional equipment for the tail gas unit. The capital and the
            operating costs are significantly lower than for a SRU/TGTU unit.




                                                                                               4-1
Section 5        Bibliography

            1.      EU Environmental Laws Impact Fuels Requirements, S.F. Venner,
                    published in HC Processing Magazine, May 2000.
            2.      Improving Sulfur Plant Performance, Sulfur 266.
            3.      Optimizing European Sulfur Recovery Plants, a Perspective, J.A. Sames,
                    and H.G. Paskall, Western Research, 1991.
            4.      PROClaus, New Performance in Sulfur Recovery, M. Rameshni,
                    Brimstone, Canmore, Canada, 2001
            5.      Silicon Carbide Supports New Improvements in Sulfur Recovery, Sulfur
                    269.
            6.      State-Of-the-Art in Gas Treating, M. Rameshni, British Sulphur
                    Conference, San Francisco, CA, 2000




                                                                                      5-1
                     Appendix

Acronyms and Abbreviations


                   *SS          symbology for Dow Solvent
                   API          American Petroleum Institute
                   ARCO         Atlantic Richfield Co. tail gas technology
                   ASTM         American Society for Testing and Materials
                   BOC          BOC Gases Company
                   BSR          Beavon sulfur removal
                   BTX          benzene, toluene, and xylene
                   CAA          Clean Air Act
                   CBA          cold bed adsorption
                   CFD          computational fluid dynamic
                   DOXO         DOXO Sulfreen Process
                   EPA          U.S. Environmental Protection Agency
                   EU           European Union
                   FCC          Fluid Catalyst Cracker
                   FSU          Former Soviet Union
                   GPA          Gas Processing Associations
                   HCR          HCR tail gas unit process
                   LBNL         Lawrence Berkeley National Laboratory
                   MCRC         Sub-dewpoint process by Delta Engineering
                   MDEA         methyldiethanolamine
                   MTBE         methyl tert-butyl ether
                   MTPD         metric tons per day
                   NOX          nitrogen oxides
                   NPRA         National Petrochemical and Refiners Association
                   PROClaus     WorleyParsons RedOx Claus
                   RFG          reformulated gasoline
                   SCOT         Shell SCOT tail gas unit
                   SRU          sulfur recovery unit
                   SWS          sour water stripper
                   T&P          temperature and pressure
                   TAME         tertiary amyl ether
                   TGCU         tail gas cleaning unit
                   UAE          United Arab Emirates
                   UK           United Kingdom
                   VOC          volatile organic content
                   WHB          waste heat boiler




                                                                                  A-1

				
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