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  2. 2. 1.0 Introduction Recovery of elemental sulphur from acid gas was first performed via the Claus processover 100 years ago. Many researches are done by do some Claus modifications which canalleviate operational difficulties and improve overall sulphur recovery. The Claus process hasbeen the standard of the sulphur recovery industry, but limitations and problems relating tocomposition may restrict its effectiveness. Numerous modifications hand improvement has beenapplied to the basic process in an effort to develop the optimum system for a certain set ofconditions.2.0 Definition of Process Improvement in Chemical Industries Process design trends or process improvement in chemical industry are related to thedevelopment of more efficient technologies. Two type’s most important approaches are processintegration and process intensification. Process integration looks for the integration of all operations involved in the productionof one specific product. This can be achieved through the development of integrated processesthat combine different steps into one single unit. When several operations can be carried out ina same single unit, the possibilities for improving the performance of the global process arehigher, especially if energy costs are considered. Process intensification we can define as an engineering expression that refers to makingchanges that render a manufacturing or processing design substantially improved in terms ofenergy efficiency, cost-effectiveness or enhancement of other qualities.3.0 Process improvement in Claus process3.1.1 Process Integration Sub dew point Claus process The conventional Claus process described above is limited in its conversion dueto the reaction equilibrium being reached. Like all exothermic reactions, greaterconversion can be achieved at lower temperatures, however as mentioned the Clausreactor must be operated above the sulfur dew point (120–150°C) to avoid liquid sulfurphysically deactivating the catalyst. To overcome this problem, the sub dew point Claus
  3. 3. process operates with reactors in parallel. When one reactor has become saturated withadsorbed sulfur, the process flow is diverted to the standby reactor. The reactor is thenregenerated by sending process gas that has been heated to 300–350°C to vaporizethe sulfur. This stream is sent to a condenser to recover the sulfur.3.1.2 Process Intensification In this process, the use of hydrogen is important to achieved higher flexibility. Not onlythat, the refiners will be minimizing for new development to change economy environment andto maximize output from existing equipment. In process improvement through processintensification, hydrogen used is quite limit but now, this change over time because : a) To reduce the excess capacities for better economy. This new environmental law utilizes the heavy feed oils. For Claus process, it receives sulphur more than ammonia from hydrotreaters which currently defined in process intensification. b) The higher volatility of crude oils and product prices is the reason for greater flexibility on refiners. c) The oxygen gas residue allows full conversion of crude oil to produce valuable products. This can make it more flexible and efficient.A tail gas clean-up process In the conventional Claus process is about 94% to 98% efficient in removing H2S. Manyimprovements have been developed to allow the process to obtain 99+% conversions, asemission limitshave tightened. A tail gas clean-up process is often used. An example is theamine-based tailgascean-up process, which reduces all of the sulfur compounds in the tailgasleaving the front-end Claus sulfur plant back to H2S, then uses selective amine absorption toremove the H2S while allowing most of the carbon dioxide to slip by. The H2S and carbondioxide removed by the amine are stripped from the amine and recycled back to the Claus plant,allowing an overall sulfur recovery in excess of 99.5%.Superclaus catalyst The Superclaus catalyst is designed to give complete and highly selective conversionof H2S to elemental sulfur, low formation of SO2, and low sensitivity to water concentrations inthe process gas so it has no Claus reaction reactivity. The catalyst consists of active metaloxides on a carrier. Its properties include the following: H2S conversion to sulfur higher than
  4. 4. 85%, not sensitive to excess air, not sensitive to high water concentrations, no Claus reaction,no CO/H2 oxidation, no formation of COS/CS2, and chemically and thermally stable with goodmechanical strength and long effective life. Two options for the Superclaus process are theSuperclaus 99 and the Superclaus 99.5 processes. Superclaus 99 consists of a thermal stagefollowed by three or four catalytic reactor stages, much like the Claus process. The first two orthree catalytic stages are loaded with the standard Claus catalyst while the final stage is loadedwith the new selective oxidation catalyst. In the Superclaus 99.5 process, a hydrogenation stage(using a cobalt/molybdenum catalyst) between the last Claus reactor and the selective oxidationreactor is added. Sulfur recovery in the Superclaus 99 process with 2 Claus stages is in therange of 98.9% - 99.4% and in the range of 99.3% - 99.6% with 3 Claus stages. Sulfur recoveryin the Superclaus 99.5 process is in the range of 99.2% - 99.6% with 2 Claus stages and 99.4%- 99.7% with 3 Claus stages.Oxygen Enrichment Of Sulfur Recovery Units (Sru) The underpinning theoretical concept that makes oxygen enrichment such an effectivemeans of briefly explained when in the Claus process, about one-third of the hydrogen sulfide inthe acid gas stream is combusted to sulfur dioxide which further reacts with the remaininghydrogen sulfide to form elemental sulfur and water in the vapor phase. The combustionreaction and approximately 60-70% of the conversion of hydrogen sulfide to sulfur, take place inthe thermal reactor at temperatures between 1100°C and 1400°C for typical refinery acid gasstreams. The remaining equilibrium conversion of hydrogen sulfide to sulfur takes place in aseries of catalytic reactors at much lower temperatures. Representative reactions aresummarized below H2S + 3/2 O2 SO2 + H2O (Combustion reaction) 2H2S + SO2 3S + 2H2O (Claus reaction) __________________________________________ 3H2S + 3/2 O2 3S + 3H2O (Overall reaction) Let’s, stoichiometrically, 100 kmol/h of hydrogen sulfide requires 50 kmol/h of oxygen. Ifall of the oxygen is provided by the air, 189 kmol/h of nitrogen comes along with the 50 kmol/hof oxygen. This nitrogen (over 50% by volume in the feed) contributes to a large amount of thepressure drop through the SRU due when an SRU is bottlenecked by hydraulic or residence
  5. 5. time limitations, oxygen enrichment of the combustion air reduces the nitrogen flow through theSRU, thereby allowing an increase in the acid gas and sour water stripper gas stream.. It alsoincreases the temperature in the first Claus step, a furnace. This allows for a more effectivedestruction of NH3 within this thermal section, thus contributing to the long-term stabilization ofthe Claus operation.Partial oxidation Partial oxidation with function is to convert liquid or solid hydrocarbons to hydrogen,carbon monoxide, carbon dioxide and water by gasification. After that, the gas will be used assynthesis gas or fuel gas and also as crude gas for hydrogen recovery. In this process development, partial oxidation can have some possibilities for refineryoperators. Below are some possibilities that have been found in the sulphur industry. There are : a) Heavy heating oil’s and residues in particular can be used as feedstock to partial oxidation plants in refineries which can be operated practically with no limit to the pollutant content. This possibilities can help feedstock can be used economically. b) The other possibility is the gas form partial oxidation can be used for fuel in an integrated gasification combined cycle power plant. This type of power plant particularly high efficiency and its emissions are low from pollutant. c) Gasification gas from partial oxidation can also be used as a synthesis gas because after appropriate pre-treatment, usually synthesis of gas to liquid, production of synthetic diesel or gasoline, for methanol or for ammonia production. The partial oxidation used to produce chemicals also broadens the economic base of the refinery. d) Besides that, partial oxidation can handle differing feedstock compositions, within wide limits. It was possible to use crude oil of different qualities in the refinery and to feed residues that cannot be utilized economically in the usual refining procedure.Advantage use of oxygen in partial oxidation Thus, the refinery operator can bring several advantages in sulphur industries. Theadvantage of this are state below : a) Cleaner and more advantageous reuse of residues.
  6. 6. b) Broadening of the economic base of the refinery. c) Wider range of products and thus greater economic flexibility of the refinery. d) A wider range of crude oil compositions to be processed.4.0 The Cost and Benefit of Improvement ProcessA tail gas clean-up process This technologies improvement has been developed to increase total sulphur removalabove 96% for basis Claus Unit. The larger number available choice require refiners to evaluateincreased sulfur discovery based on their specific needs versus the increase in capital andoperating cost of increased recovery.Superclaus catalyst This catalyst if function to give complete and highly selective conversion of H2S toelemental sulfur, low formation of SO2 and low sensitivity to water concentrations in the processgas. Other than that, higher activities have been achieved with catalysts that provide highersurface areas and macro porosityOxygen Enrichment of Sulfur Recovery Units (Sru) The most common driver for implementing SRU oxygen enrichment is to increaseprocessing capacity. The reduction of diluent nitrogen results in higher partial pressure ofhydrogen sulfide (H2S) in the process stream, which leads to higher conversions in the SRUcatalytic reactors. Also, the relative SRU tail gas flow rate is progressively reduced as oxygenenrichment is increased. The reduction in nitrogen entering the Tail Gas Cleanup Unit (TGCU)results in higher hydrogen sulfide partial pressures in the amine absorber. This results in betterabsorption and lower sulfur emissions than the air-based SRU operation. For the capital costsaving, depending on the enrichment technology, the cost of implementing SRU oxygenenrichment is only 5-20% of the cost for building a new SRU. Oxygen enrichment can also beeconomical for grassroots plants due to smaller equipment for the same capacity. Then for time saving, SRU oxygen enrichment can be implemented quickly. No “downtime” is required for low-level enrichment (up to 28% oxygen in air) as an oxygen diffuser can behot tapped into the air main. For higher levels of oxygen enrichment tie-ins and modifications
  7. 7. can be achieved within the timing of a normal turnaround. Oxygen-enriched operation hasproven to be both reliable and safe regardless of the chosen technologyPartial oxidation A long time ago, the principle users of the heavy oils and residues were power plantsand ships but it vanishing because the users must also convert to lower sulphur fuels. This costof burning is high due to sulphur fuels in power plants are steadily increasing becauserequirements of purity waste gases are increasing instead of the cost purification. Due toincreasing of higher costs of low sulphur fuels, the power plant operators often find that canreduced cost of waste-gas clean up makes them more economical than cheaper but highersulphur fuel. Both developments means that the refinery operator either cannot sell high-sulphurheating oil’s or residues at all or it can sell them only at low price is depends on both improvethe refinery hydrogen balance and economically get rid of high-sulphur oil’s and residues. Basically, a refinery with a crude oil capacity of 10 million can supply an IGCC powerplant with a power of about 350Mw. This can give the refinery another leg to stand and broadenthe economic base. The refinery can also react more flexibly to market requirements. Not all the refinery has its partial oxidation unit because in spite of these advantages, thehigh capital investment for such a unit and that it must result in greater economic utility beforeinvolve with existing structure of a refinery. This occur especially for GTL, the fast rising crudeoil price made production of these synthetic fuels increasingly more attractive and of course, thisadditional ultraclean fuel fits perfectly into the palette of product refinery.Conclusion As a conclusion, the sulphur industry refinery consist three bed basic Claus process thatcan be used for rich acid gas feeds but currently emission regulations required 99% and abovesulphur recovery to modification in the traditional Claus process or the addition of a secondarytail gas cleanup process. Lean acid gas feeds require a modification to the operation of theburner to produce temperature high enough to promote stable combustion. Other methods such as a catalytic "burner" may be used in place of the traditional burnerin some instances. To achieve the optimum Claus process design for any feed composition, allsuitable processes should be fully explored with a process simulator before making designdecisions.
  8. 8. References1. Reinardt, H. J., and Heisel, M. (1999). "Increasing the capacity of Claus plants with oxygen," Linde Reports on Science and Technology, No. 61, p. 2 ff.2. Paskall, H.G., and Sames, J.A. (2009). "Sulfur recovery by the modified Claus process," The Sulphur Experts, 12th Edition, Calgary.3. Perez, Haro., Juan et al.(1992). "O2 enrichment increases FCC operating flexibility," OGJ, p. 404. Sadeghbeigi, R.(1995) "Fluid Catalytic Cracking Handbook," Houston: Gulf Publishing.