Achieving Ultra-Low Sulfur Levels in Refinery Fuel Gas

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Process schemes 1 & 2 are simply caustic washes without and with caustic regeneration (i.e. UOP Merox or Merichem Thiolex processes). The regenerative process licensing fees and extra equipment can usually be economically justified by reductions in caustic usage. Schemes 3 & 4 require catalyst beds operated at elevated temperatures. Scheme Sa represents a changeout of the existing amine with the Sulfinol solution. The Sulfinol process usually requires a reasonably high pressure (100 psig or more) and relatively higher circulation rates. Scheme Sb adds more circulation capacity. Retrofitting Ucarsol HS-10S solvent (Scheme Sc) will enhance the removal of HzS and COS. DGA may offer the potential (Scheme Sd) for improving the absorption of all three of the major compounds. The Sulfinol solvent process appears to be the only one whose claims can be substantiated by actual refinery data. Compression alone will enhance the absorptive efficiency of existing systems. Most of this improvement will come below about 120 psig. The Lo-Cat and Suiferox processes are aqueous chela ted iron-type processes which react with HzS to give elemental sulfur. 2.0 Combinations of Processes Using these individual process enhancement efficiencies as building blocks, potential combinations of processes were then devised and evaluated to achieve the desired total sulfur concentration of 40 ppmv. The sulfur specie and total sulfur removal efficiencies for the assumed process combinations are shown in TABLE 3 below and in the attached FIGURE 1. TABLE #3 - Fuel Gas Desulfurization· Removal Efficiencies - Combined Units • Potential ProceH Scheme 8.) Comp/Reg.NaOH 8.) HydroliReg.NaOH 10.) Hydrog/Hydrol I. One Rx b. Two Rx 11.) H/H • Enh.nced 12.) H/H • Compre •• ~ Removal Qf Sulfur So.ele. H.S RSH COS 96 88 95 86 86 82 88 88 98 S8 87 81 87 87 87 • Baaed on Estimatea - No Plant Data I Incremental TOtal Sulfur Removal (~ - ApproxJ 89 '- 89 .. 44 '- 60 .. 80 .. 92 '- It appears that in order to achieve a 40 ppmv sulfur level in the typical RFG stream, a combination of treating -11-