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 2 Copyright © 2019 John Jechura ([email protected]) Topics Introduction Properties of sulfur Sulfur recovery processes ▪ Claus Process ▪ Claus Tail Gas Cleanup Sulfur storage Safety and environmental considerations Updated: January 4, 2019 3 Copyright © 2019 John Jechura ([email protected]) Introduction & Properties of Sulfur Updated: January 4, 2019 Copyright © 2017 John Jechura ([email protected]) Sulfur Crystals http://www.irocks.com/minerals/specimen/34046 http://www.mccullagh.org/image/10d-5/sulfur.html Updated: January 4, 2019 5 Copyright © 2019 John Jechura ([email protected]) Molten Sulfur http://www.kamgroupltd.com/En/Post/7/Basic-info-on-elemental-Sulfur(HSE) Updated: January 4, 2019 6 Copyright © 2019 John Jechura ([email protected]) World 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: https://ihsmarkit.com/products/sulfur-chemical-economics-handbook.html Report published December 2017 Updated: January 4, 2019 7 Copyright © 2019 John Jechura ([email protected]) Sulfur 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 run- up in 2007-2008 Ref: http://ictulsa.com/energy/ “Cleaning up their act”, Gordon Cope, Updated December 24, 2018 Hydrocarbon Engineering, pp 24-27, March 2011 Updated: January 4, 2019 8 Copyright © 2019 John Jechura ([email protected]) U.S. sulfur production Updated: January 4, 2019 9 Copyright © 2019 John Jechura ([email protected]) 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 Updated: January 4, 2019 10 Copyright © 2019 John Jechura ([email protected]) Sulfur Vapor Species 1.0 s S8 e 0.8 i c S2 e p S f o 0.6 n o i t c a r F 0.4 l o M S6 0.2 0.0 200 400 600 800 1000 1200 1400 Temperature, °F Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 11 Viscosity of Molten Sulfur 105 Pure Sulfur 104 p c 3 , 10 y t i s o c 2 s 10 i V 101 100 300 400 500 600 700 800 Temperature, °C Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 12 Viscosity of Molten Sulfur 105 Pure Sulfur H2S Partial 104 Pressure, psia 0.0015 p c 3 0.015 , 10 y t 0.15 i s o 1.5 c 2 s 10 i 14.7 V 101 100 300 400 500 600 700 800 Temperature, °C 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 Combustion: H2S + 1.5·O2 H2O + SO2 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 16 Copyright © 2019 John Jechura ([email protected]) 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 o 2300-2700 F for NH3 destruction GPSA Engineering Data Book, 13th ed., Fig. 22-2, 2012 Updated: January 4, 2019 17 Copyright © 2019 John Jechura ([email protected]) 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 waste heat gas reheat boiler HP 450°F 420°F 400°F steam Claus #1 Claus #2 Claus #3 acid gas 600°F LP 590°F LP 453°F LP 300°F 407°F 270°F 110°F steam 375°F steam 350°F steam 8 psig condens condenser condenser condenser condenser er air boiler feed water (BFW) BFW reaction BFW BFW sulfur sulfur sulfur sulfur furnace 1700 - 2400°F tail gas Updated: January 4, 2019 19 Copyright © 2019 John Jechura ([email protected]) Equilibrium Conversion of H2S to S Temperature, o C r u f l 204 427 649 871 1093 1316 1538 u 100 S o t S 2 H f o 80 n o i s r e v n 60 o melting point C t n e boiling point c r e 40 P 0 400 800 1200 1600 2000 2400 2800 Temperature, °F Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 20 Equilibrium Conversion of H2S to S r u f l u 100 S o t Claus #3 S 2 Furnace & waste heat boiler Claus #2 H Claus #1 1700 - 2400F f o 80 n o i s r e v n 60 o C melting point t n e boiling point c r e 40 P 0 400 800 1200 1600 2000 2400 2800 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 2/3 flow Claus #1 CCllaauuss ##22 Claus #3 1/3 flow LP LP LP acid gas steam steam steam condenser ccoonnddeennsseerr ccoonnddeennsseerr ccoonnddeennsseerr air boiler feed water (BFW) BFW BFW reaction sulfur sulfur sulfur sulfur furnace 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 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 Updated: January 4, 2019 26 Copyright © 2019 John Jechura ([email protected]) 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 r e Reducing Gas r r w o t e o a t Catalytic Reactor b r r e Air h o c n s n e b e g A u e R Furnace Q Fuel Low Pressure Low Pressure Steam Steam Reboiler H2O Updated: January 4, 2019 29 Copyright © 2019 John Jechura ([email protected]) SCOT Process To Stack Claus Tail Gas H2S Recycle r e Reducing Gas r r w o t e o a t Catalytic Reactor b r r e Air h o c n s n e b e g A u Mix Claus tail Catalytically convert all Cool reactor gas e Strip H2S from gas & recycle to R Furnace Q o gas with H2 andFue l sulfur compounds to H2S (exiting at ~570 F Claus CO and heat in Reactions:Low Pressure in waste heat Typically useL MDEAow Pr e–sscanure get to Steam Steam Reboiler inline burner SO2 + 3H2 → H2S + 2H2O exchanger and low H2S levels in Stack Gas & S + 2H → 2H S H2O 2 2 2 water wash to slip CO2 so it doesn’t build up in COS + H O CO + H S 2 → 2 2 complete cooling. the recycle gas CS2 + 2H2O → CO2 + H2S Updated: January 4, 2019 Copyright © 2019 John Jechura ([email protected]) 30 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 Updated: January 4, 2019 31 Copyright © 2019 John Jechura ([email protected]) Sulfur storage Updated: January 4, 2019 Copyright © 2017 John Jechura ([email protected]) Sulfur Piles Sulfur pile at North Vancouver, B.C., Canada, brought by rail from the province of Alberta Ref: Wikimedia Commons Updated: January 4, 2019 33 Copyright © 2019 John Jechura ([email protected]) Sulfur “Blocking” Fort McMurray oil sands operations, Alberta, Canada Updated: January 4, 2019 34 Copyright © 2019 John Jechura ([email protected]) Summary Updated: January 4, 2019 Copyright © 2017 John Jechura ([email protected]) Summary Natural gas & petroleum production accounts for the majority of sulfur production ▪ Primary consumption is agriculture & industry, 65% for farm fertilizer.