Sulfur Recovery Chapter 16 Based on presentation by Prof. Art Kidnay
advertisement
Sulfur Recovery Chapter 16 Based on presentation by Prof. Art Kidnay John Jechura – jjechura@mines.edu Updated: April 21, 2016 Plant Block Schematic John Jechura – jjechura@mines.edu Updated: April 21, 2016 2 Topics • Introduction • Properties of sulfur • Sulfur recovery processes Claus Process Claus Tail Gas Cleanup • Sulfur storage • Safety and environmental considerations John Jechura – jjechura@mines.edu Updated: April 21, 2016 3 Topics • Introduction • Properties of sulfur • Sulfur recovery processes Claus Process Claus Tail Gas Cleanup • Sulfur storage • Safety and environmental considerations John Jechura – jjechura@mines.edu Updated: April 21, 2016 4 Sulfur Crystals Ref: Smithsonian Museum of Natural History John Jechura – jjechura@mines.edu Updated: April 21, 2016 5 Sulfur Crystalites Wai-o-tapu Hot Springs,North Island, NZ Ref: Wikipedia Commons John Jechura – jjechura@mines.edu Updated: April 21, 2016 6 Sulfur Usage & Prices • Fossil fuel production accounts for the majority of sulfur production • Primary consumption is agriculture & industry 65% for farm fertilizer: sulfur sulfuric acid phosphoric acid fertilizer • $50 per ton essentially disposal cost Chinese demand caused runup in 2007-2008 “Cleaning up their act”, Gordon Cope, Hydrocarbon Engineering, pp 24-27, March 2011 John Jechura – jjechura@mines.edu Updated: April 21, 2016 http://www.ictulsa.com/sulphur_history.pdf 7 U.S. sulfur production John Jechura – jjechura@mines.edu Updated: April 21, 2016 8 Topics • Introduction • Properties of sulfur • Sulfur recovery processes Claus Process Claus Tail Gas Cleanup • Sulfur storage • Safety and environmental considerations John Jechura – jjechura@mines.edu Updated: April 21, 2016 9 Sulfur Chemical Structure Pure sulfur exists as SX where X = 1 to 8 • The dominant species are S2, S6, & S8 • May be in ring structure or open chain • Species determined by temperature This composition greatly affects its properties! Octasulfur, S8 John Jechura – jjechura@mines.edu Updated: April 21, 2016 10 Sulfur Vapor Species Mol Fraction of Species 1.0 0.8 S8 S2 0.6 0.4 S6 0.2 0.0 200 400 600 800 1000 1200 1400 Temperature, °F John Jechura – jjechura@mines.edu Updated: April 21, 2016 11 Viscosity of Molten Sulfur 105 Pure Sulfur Viscosity, cp 104 103 102 101 100 300 400 500 600 700 800 Temperature, °C John Jechura – jjechura@mines.edu Updated: April 21, 2016 12 Viscosity of Molten Sulfur 105 Pure Sulfur H2S Partial Pressure, psia 0.0015 Viscosity, cp 104 0.015 103 0.15 10 1.5 2 14.7 101 100 300 400 500 600 700 800 Temperature, °C John Jechura – jjechura@mines.edu Updated: April 21, 2016 13 Viscosity of liquid sulfur John Jechura – jjechura@mines.edu Updated: April 21, 2016 14 Topics • Introduction • Properties of sulfur • Sulfur recovery processes Claus Process Claus Tail Gas Cleanup • Sulfur storage • Safety and environmental considerations John Jechura – jjechura@mines.edu Updated: April 21, 2016 15 Claus Process • Convert H2S to elemental sulfur H2S rich stream burned with 1/3 stoichiometric air. Hot gases are then passed over alumina catalyst to produce free sulfur Combustion: H2S + 1.5·O2 → H2O + SO2 Claus Reaction: 2·H2S + SO2 2·H2O + 3·S Sulfur formation reaction mildly exothermic Sulfur conversion reactors kept above 400oF (sulfur dew point) • The Claus reaction is reversible – therefore, 100% conversion can never be achieved Practically, Claus units are limited to about 96% recovery Tail gas units are used to provide improved conversion John Jechura – jjechura@mines.edu Updated: April 21, 2016 16 Straight-through Claus Process gas reheat HP steam waste heat boiler Claus #1 acid gas 110°F 8 psig 400°F Claus #2 Claus #3 453°F LP 300°F 407°F 590°F LP 600°F LP 270°F steam steam 375°F steam 350°F condenser air gas reheat 420°F gas reheat 450°F boiler feed water (BFW) reaction furnace 1700 - 2400°F BFW sulfur conde condenser nser BFW sulfur condenser BFW sulfur condenser sulfur tail gas John Jechura – jjechura@mines.edu Updated: April 21, 2016 17 Temperature Regimes for the Claus Process John Jechura – jjechura@mines.edu Updated: April 21, 2016 18 Equilibrium Conversion of H2S to S Percent Conversion of H2S to Sulfur Temperature, o C 204 427 649 871 1093 1316 1538 1600 2000 2400 2800 100 80 60 melting point boiling point 40 0 400 800 1200 Temperature, °F John Jechura – jjechura@mines.edu Updated: April 21, 2016 19 Percent Conversion of H2S to Sulfur Equilibrium Conversion of H2S to S 100 Claus #3 Claus #2 Claus #1 80 Furnace & waste heat boiler 1700 - 2400F 60 melting point boiling point 40 0 400 800 1200 1600 2000 2400 2800 Temperature, °F John Jechura – jjechura@mines.edu Updated: April 21, 2016 20 Hydrocarbons in the Claus Process John Jechura – jjechura@mines.edu Updated: April 21, 2016 21 Claus Process • Use multiple stages to obtain highest conversion Typically three • Various flow patterns Straight-through – best, used whenever possible Split flow – best at low H2S feed concentrations (5 to 30 mol% H2S) Sulfur recycle < 5% H2S Direct oxidation < 5% H2S John Jechura – jjechura@mines.edu Updated: April 21, 2016 22 Claus Process Claus unit feed usually contains H2S and CO2 • High concentrations of noncombustible components (CO2, N2) Lower flame temperature Difficult to maintain stable combustion furnace flame temperatures below 1700oF • Solutions include Preheating air Preheating acid gas feed Enriching oxygen in air Using split-flow process John Jechura – jjechura@mines.edu Updated: April 21, 2016 23 Split-flow Claus Process gas reheat gas reheat gas reheat HP steam 1/3 flow acid gas air Claus #3 Claus #2 #2 Claus Claus #1 2/3 flow LP steam LP steam condenser condenser condenser BFW BFW LP steam condenser condenser condenser condenser boiler feed water (BFW) reaction furnace sulfur sulfur sulfur sulfur tail gas John Jechura – jjechura@mines.edu Updated: April 21, 2016 24 Typical Claus Configurations Approximate concentration of H2S in feed (mol%) Process variation 55 - 100 Straight-through 30 - 55 Straight-through + acid gas and/or air preheat 15 - 30 Split-flow or acid gas and/or air preheat 10 - 15 Split-flow with acid gas and/or air preheat 5 - 10 Split-flow with fuel added, O2 enrichment, or with acid gas and air preheat John Jechura – jjechura@mines.edu Updated: April 21, 2016 25 Tail gas Clean Up Three process categories: • Direct oxidation of H2S to sulfur (Superclaus) 2 H2S + O2 → 2 S + 2 H2O • Sub-dew point Claus processes (Cold Bed Adsorption) • SO2 reduction and recovery of H2S (SCOT) John Jechura – jjechura@mines.edu Updated: April 21, 2016 26 Claus Tail Gas Cleanup • Conventional 3-stage Claus units recover 96 to 97.5% of sulfur Remainder was burned to SO2 and vented Adding fourth stage results in 97 to 98.5% recovery • Regulations now require 99.8 to 99.9% recovery • Meeting regulations requires modified technology John Jechura – jjechura@mines.edu Updated: April 21, 2016 27 Shell Claus Offgas Treating (SCOT) Four step process: • Mix feed with reducing gas (H2 and CO) • Convert all sulfur compounds to H2S • Cool the reactor gas • Strip H2S using amine To Stack Claus Tail Gas Fuel Catalytic Reactor Furnace Low Pressure Steam H 2O John Jechura – jjechura@mines.edu Updated: April 21, 2016 Regenerator Air Absorber Reducing Gas Quench tower H2S Recycle Low Pressure Steam Reboiler 28 SCOT Process To Stack Claus Tail Gas Fuel Catalytic Reactor Furnace Low Pressure Steam H 2O Regenerator Air Absorber Reducing Gas Quench tower H2S Recycle Low Pressure Steam Reboiler Mix Claus tail gas with H2 and CO and heat in inline burner John Jechura – jjechura@mines.edu Updated: April 21, 2016 29 SCOT Process To Stack Claus Tail Gas Fuel Catalytic Reactor Furnace Regenerator Air Absorber Reducing Gas Quench tower H2S Recycle Low Pressure Steam Low Pressure Steam Reboiler H 2O Catalytically convert all sulfur compounds to H2S Some typical reactions: SO2 + 3H2 = H2S + 2H2O S2 + 2H2 = 2H2S COS + H2O= CO2+ H2S CS2 + 2H2O = CO2 + H2S John Jechura – jjechura@mines.edu Updated: April 21, 2016 30 SCOT Process To Stack Claus Tail Gas Fuel Catalytic Reactor Furnace Regenerator Air Absorber Reducing Gas Quench tower H2S Recycle Low Pressure Steam H 2O Low Pressure Steam Reboiler Cool reactor gas (exiting at ~570oF [~300oC]) in waste heat exchanger and water wash to complete cooling. John Jechura – jjechura@mines.edu Updated: April 21, 2016 31 SCOT Process To Stack Claus Tail Gas Fuel Catalytic Reactor Furnace Low Pressure Steam H 2O Regenerator Air Absorber Reducing Gas Quench tower H2S Recycle Low Pressure Steam Reboiler Strip H2S from gas & recycle to Claus Typically use MDEA – can get to low H2S levels in Stack Gas & slip CO2 so it doesn’t build up in the recycle gas John Jechura – jjechura@mines.edu Updated: April 21, 2016 32 Alternate Conversion & Sulfur Removal Processes • SelectoxTM Proprietary catalyst removes need for furnace • CrystaSulf Uses modified liquid-phase Claus reaction Elemental sulfur removed by filtration Mid-range process to handle sulfur amounts between 0.1 and 20 tons per day John Jechura – jjechura@mines.edu Updated: April 21, 2016 33 Topics • Introduction • Properties of sulfur • Sulfur recovery processes Claus Process Claus Tail Gas Cleanup • Sulfur storage • Safety and environmental considerations John Jechura – jjechura@mines.edu Updated: April 21, 2016 34 Sulfur Piles Sulfur pile at North Vancouver, B.C., Canada, brought by rail from the province of Alberta Ref: Wikimedia Commons John Jechura – jjechura@mines.edu Updated: April 21, 2016 35 Sulfur “Blocking” Fort McMurray oil sands operations, Alberta, Canada John Jechura – jjechura@mines.edu Updated: April 21, 2016 36 Topics • Introduction • Properties of sulfur • Sulfur recovery processes Claus Process Claus Tail Gas Cleanup • Sulfur storage • Safety and environmental considerations John Jechura – jjechura@mines.edu Updated: April 21, 2016 37
