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

http://www.irocks.com/minerals/specimen/34046

http://www.mccullagh.org/image/10d-5/sulfur.html

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

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

1.0

s S8

e 0.8 i

c S2 e p S

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

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

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

▪ 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

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

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

r 204 427 649 871 1093 1316 1538 u f l 100 u S

o t

S 2

80 H

f o

n o i s r

e 60 v melting point n o C

n boiling point e c r

e 40 P 0 400 800 1200 1600 2000 2400 2800 Temperature, °F

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]) 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

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

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

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

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)

▪ 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

▪ 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 r

Reducing Gas r w o t e o t a

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

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

Mix Claus tail Catalytically convert all Cool reactor gas Strip H2S from gas & recycle to o gas with H2 and sulfur compounds to H2S (exiting at ~570 F Claus CO and heat in Reactions: in waste heat Typically use MDEA – can get to inline burner SO2 + 3H2 → H2S + 2H2O exchanger and low H2S levels in Stack Gas & S + 2H → 2H S 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

Ref: Wikimedia Commons

Fort McMurray oil sands operations, Alberta, Canada

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. ▪ $50 per ton essentially disposal cost Sulfur properties depends upon which sulfur species are present

▪ Dominant species are S2, S6, & S8 Dominant sulfur recovery process is modified Claus ▪ Extent controlled by chemical equilibrium, so can only get 96% conversion ▪ Tail Gas Cleanup process required for very low sulfur emissions Sulfur storage ▪ Temporary storage as hot liquid ▪ Shipping in pellets & long-term bulk storage as blocks