Sulfur Recovery

Sulfur Recovery Chapter 16 Based on presentation by Prof. Art Kidnay Plant Block Schematic Adapted from Figure 7.1, Fundamentals of Natural Gas Processing, 2nd ed. Kidnay, Parrish, & McCartney Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 2Topics Introduction Properties of sulfur Sulfur recovery processes ▪ Claus Process ▪ Claus Tail Gas Cleanup Sulfur storage Safety and environmental considerations Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 3Introduction & Properties of Sulfur Updated: January 4, 2019 Copyright © 2017 John Jechura ([email protected]) Sulfur Crystals <a href="/goto?url=http://www.irocks.com/minerals/specimen/34046" target="_blank">http://www.irocks.com/minerals/specimen/34046 </a><a href="/goto?url=http://www.mccullagh.org/image/10d-5/sulfur.html" target="_blank">http://www.mccullagh.org/image/10d-5/sulfur.html </a>Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 5Molten Sulfur <a href="/goto?url=http://www.kamgroupltd.com/En/Post/7/Basic-info-on-elemental-Sulfur(HSE)" target="_blank">http://www.kamgroupltd.com/En/Post/7/Basic-info-on-elemental-Sulfur(HSE) </a>Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 6World Consumption of Sulfur Primary usage of sulfur to make sulfuric acid (90 – 95%) ▪ Other major uses are rubber processing, cosmetics, & pharmaceutical applications China primary market Ref: <a href="/goto?url=https://ihsmarkit.com/products/sulfur-chemical-economics-handbook.html" target="_blank">https://ihsmarkit.com/products/sulfur-chemical-economics-handbook.html </a>Report published December 2017 Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 7Sulfur Usage & Prices Natural gas & petroleum 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 Ref: <a href="/goto?url=http://ictulsa.com/energy/" target="_blank">http://ictulsa.com/energy/ </a>Updated December 24, 2018 “Cleaning up their act”, Gordon Cope, Hydrocarbon Engineering, pp 24-27, March 2011 Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 8U.S. sulfur production Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 9Sulfur 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 Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 10 Sulfur Vapor Species 1.0 S8 0.8 S2 0.6 0.4 S6 0.2 0.0 <ul style="display: flex;"><li style="flex:1">200 </li><li style="flex:1">400 </li><li style="flex:1">600 </li><li style="flex:1">800 </li><li style="flex:1">1000 </li><li style="flex:1">1200 </li><li style="flex:1">1400 </li></ul>Temperature, °F Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 11 Viscosity of Molten Sulfur 105 Pure Sulfur 104 103 102 101 100 <ul style="display: flex;"><li style="flex:1">400 </li><li style="flex:1">600 </li></ul>Temperature, °C 300 <ul style="display: flex;"><li style="flex:1">500 </li><li style="flex:1">700 </li><li style="flex:1">800 </li></ul>Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 12 Viscosity of Molten Sulfur 105 Pure Sulfur H2S Partial Pressure, 104 psia 0.0015 0.015 103 0.15 1.5 102 14.7 101 100 <ul style="display: flex;"><li style="flex:1">400 </li><li style="flex:1">600 </li></ul>Temperature, °C <ul style="display: flex;"><li style="flex:1">300 </li><li style="flex:1">500 </li><li style="flex:1">700 </li><li style="flex:1">800 </li></ul>Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 13 Viscosity of liquid sulfur Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 14 Sulfur recovery processes Updated: January 4, 2019 Copyright © 2017 John Jechura ([email protected]) Sulfur Recovery Typically a modified Claus process ▪ H2S rich stream burned with 1/3 stoichiometric air. Hot gases are then passed over alumina catalyst to produce free sulfur <ul style="display: flex;"><li style="flex:1">Combustion: </li><li style="flex:1">H2S + 1.5·O2 H2O + SO2 </li></ul>Claus Reaction: 2·H2S + SO2 D 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 Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 16 Modified Claus Process Petroleum Refining Technology & Economics – 5th Ed. by James Gary, Glenn Handwerk, & Mark Kaiser, CRC Press, 2007 Converters 400 – 700oF Burner & Reactor above 1800oF 2300-2700oF for NH3 destruction GPSA Engineering Data Book, 13th ed., Fig. 22-2, 2012 Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 17 Temperature Regimes for the Claus Process Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 18 Straight-through Claus Process gas reheat gas reheat 450°F gas reheat waste heat boiler <ul style="display: flex;"><li style="flex:1">420°F </li><li style="flex:1">400°F </li></ul>Claus #3 HP steam Claus #1 590°F Claus #2 acid gas LP <ul style="display: flex;"><li style="flex:1">453°F </li><li style="flex:1">300°F 407°F </li></ul>LP steam LP 600°F 270°F steam 375°F steam 350°F 110°F 8 psig condens condenser er <ul style="display: flex;"><li style="flex:1">condenser </li><li style="flex:1">condenser </li></ul>condenser boiler feed air water (BFW) BFW BFW sulfur BFW reaction furnace <ul style="display: flex;"><li style="flex:1">sulfur </li><li style="flex:1">sulfur </li><li style="flex:1">sulfur </li></ul>1700 - 2400°F tail gas Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 19 Equilibrium Conversion of H2S to S Temperature, o C <ul style="display: flex;"><li style="flex:1">204 </li><li style="flex:1">427 </li><li style="flex:1">871 </li><li style="flex:1">1316 </li><li style="flex:1">1538 </li></ul><ul style="display: flex;"><li style="flex:1">649 </li><li style="flex:1">1093 </li></ul>100 80 60 40 melting point boiling point <ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">400 </li><li style="flex:1">800 </li><li style="flex:1">1200 </li><li style="flex:1">1600 </li><li style="flex:1">2000 </li><li style="flex:1">2400 </li><li style="flex:1">2800 </li></ul>Temperature, °F Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 20 Equilibrium Conversion of H2S to S 100 Claus #3 Furnace & waste heat boiler Claus #2 <ul style="display: flex;"><li style="flex:1">1700 - 2400F </li><li style="flex:1">Claus #1 </li></ul>80 60 40 melting point boiling point <ul style="display: flex;"><li style="flex:1">0</li><li style="flex:1">400 </li><li style="flex:1">800 </li><li style="flex:1">1200 </li><li style="flex:1">1600 </li><li style="flex:1">2000 </li><li style="flex:1">2400 </li><li style="flex:1">2800 </li></ul>Temperature, °F Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 21 Hydrocarbons in the Claus Process Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 22 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 Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 23 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 Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 24 Split-flow Claus Process gas reheat gas reheat gas reheat HP steam <ul style="display: flex;"><li style="flex:1">Claus #3 </li><li style="flex:1">Claus #2 </li></ul><ul style="display: flex;"><li style="flex:1">Claus #2 </li><li style="flex:1">Claus #1 </li><li style="flex:1">2/3 flow </li></ul>1/3 flow <ul style="display: flex;"><li style="flex:1">LP </li><li style="flex:1">LP </li></ul>steam LP steam steam acid gas condenser BFW ccoonnddeennsseerr <ul style="display: flex;"><li style="flex:1">condenser </li><li style="flex:1">condenser </li><li style="flex:1">condenser </li><li style="flex:1">condenser </li></ul>air boiler feed water (BFW) BFW <ul style="display: flex;"><li style="flex:1">sulfur </li><li style="flex:1">sulfur </li><li style="flex:1">sulfur </li></ul>reaction furnace sulfur tail gas Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 25 Typical Claus Configurations Approximate concentration of Process variation H2S in feed (mol%) 55 - 100 30 - 55 15 - 30 10 - 15 5 - 10 Straight-through Straight-through + acid gas and/or air preheat Split-flow or acid gas and/or air preheat Split-flow with acid gas and/or air preheat Split-flow with fuel added, O2 enrichment, or with acid gas and air preheat Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 26 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) Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 27 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 Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 28 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 H2S Recycle Reducing Gas Catalytic Reactor Air Furnace Fuel <ul style="display: flex;"><li style="flex:1">Low Pressure </li><li style="flex:1">Low Pressure </li></ul>Steam H2O Steam Reboiler Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 29 SCOT Process To Stack Claus Tail Gas Reducing Gas H2S Recycle Catalytic Reactor Air Furnace Fuel Low Pressure Steam Low Pressure Steam Reboiler H2O Mix Claus tail gas with H2 and sulfur compounds to H2S CO and heat in Reactions: Catalytically convert all Cool reactor gas Strip H2S from gas & recycle to (exiting at ~570oF Claus in waste heat Typically use MDEA – can get to SO2 + 3H2 → H2S + 2H2O S2 + 2H2 → 2H2S COS + H2O → CO2+ H2S CS2 + 2H2O → CO2 + H2S inline burner exchanger and water wash to complete cooling. low H2S levels in Stack Gas & slip CO2 so it doesn’t build up in the recycle gas Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 30

Sulfur Recovery

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