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Emissions/Environmental Pollutants
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Design of an 80 LTD Sulphur Recovery Plant: Using Modified Claus Process
Supervisor – Dr. Ali Pilehvari (P.E, PhD)
Tosin OrimoyegunDepartment of Chemical & Natural Gas
Engineering
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Outline
• Overview of Gas processing
• Modified Claus Process
• Design basis
• Hysys, Promax and Hand Calculation
• Result summary
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Overview of Gas Processing Industry
Sulphur recovery unit is designed using Modified Claus Process
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Sulfur Removal Processes
Small scale/batch processes
• < 20lbs of sulfur recovery
• scavenger processes e.g.
Iron Sponge
Zinc Oxide
Chemsweet
Sulfa-check
Medium scale recovery
• 0.2 – 25 LTD of elemental sulfur
• Includes Lo-Cat 11 & CrystaSulf
Large scale recovery
• > 25 LTD sulfur recovery
• Claus Process & its variations
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Modified Claus Process for Sulphur Recovery
• Feed stream acid gas (Straight through: >55% - 100% H2S)
• Main unit operations: Oxidation (furnace) & Catalytic reaction (3 stage process)
• Tail gas is incinerated / TCGU
• Condensed Sulphur recovered
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• Contains N2, CO2, H2O, CO, H2, unreacted H2S and SO2, COS, CS2, sulfur
vapor, etc.
• Limits overall sulfur recovery efficiency to 96-97%
• Tail gas is incinerated (5000 ppmv H2S, < 2500 ppmv SO2) or treated in
TGCU depending on local EPA regulation
TGCU Processes (Tail Gas Clean Up)
• higher H2S conversion efficiencies (>99.9 %)
• further reduction in SO2 amount vented out
Tail Gas Handling
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1. Combustion (Reaction Furnace)
∆H @ 77oF = -223 100 Btu {1}
∆H @ 77oF = 20 400 Btu { 2}
2. Claus Reaction
∆H @ 77oF = -41 300 Btu {3}
Overall reaction:
∆H @ 77oF = -254 400 Btu {4}
Modified Claus Chemistry
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Process Control:
• Optimum conversion of H2S to sulfur is governed by:
• constant 2:1 stoichiometric ratio of H2S to SO2
• achieved by varying furnace air flow rate
• deviation from ratio results in decreased SRE
Modified Claus Process for Sulfur Recovery
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End product - SulfurSolid sulfur at ambient temperature
Gaseous sulfur allotropesS2
S6
S8
S3, S4, S5, S7 - detected but not fully characterized
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Uses:
• as one of the nutrients for crops
• intermediate feedstock in chemical and manufacturing industries
• production of sulfur bitumen
• other industries: pharmaceuticals, agricultural, cosmetics, water
treatment, steel picking, synthetic rubber vulcanization, etc.
End product – Elemental Sulphur
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Design a Sulfur Recovery Plant with:
– Capacity ≈ 80 LTD
– Sulfur Recovery of > 97%
– Three bed straight through configuration
Design basis
Feed ConditionsCom
p mol frac mols/hr
Temp = 120oF H2S 0.9 198.45
Flow Rate = 220.5 mols/hr CO2 0.04 8.82
Pressure = 8 psig = 22.7 psia H2O 0.05 11.03Air blower discharge Temp = 180oF C2 0.01 2.21
1 220.50
Source - Patent
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Hysys Model
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Promax Model
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Result - Hysys
Optimum air flow rate:
Sulfur Recovery Efficiency:
Sulfur in entering H2S = 0.9*220.5*32 = 6350.4lb/hr
Sulfur Recovered = 6304lb/hr
% SRE = 0.9926999.269%
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Result - Promax
Sulfur Recovery Furnace Temperature
% oF
450 95.76178703 2280.772453
455 96.60018709 2291.263676
460 97.17586448 2301.65494
464 97.32328731 2309.89643
465 97.32088486 2311.946916
470 97.15766914 2322.140318
475 96.84752858 2332.2359
480 96.46512268 2342.234455
485 96.04302214 2352.136788
490 95.59630649 2361.943749
495 95.13319688 2371.656223
500 94.65849743 2381.2751
505 94.17521901 2390.801295
510 93.68535555 2400.235741
Air Flow Rate
(mols/hr)
Air Flow Rate Vs SRE & Furnace Temperature
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Hand Calculation Procedure - Furnace
Procedure:
To determine flame temperature, %
conversion & duty
Steps:
1. Calculate total mols/hr air required for
combustion
2. Assume mols/hr H2S is converted to
sulfur
3. Material balance around furnace
4. Calculate Kp using reaction products
5. Determine equilibrium temperature from
Kp chart
6. Determine furnace duty at different values
of
7. Determine flame temperatures
8. Plot vs flame and equilibrium temperature
9. Determine actual mols/hr H2S converted
from plot
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Hand Calculation Procedure - Furnace
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Hand Calculation Procedure - Furnace
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Furnace Calculation – Result
x (mols/hr)Equilibrium Temp (Fig
Flame Temperatute (F)
89.52 1875 2,479.68
93.54 2150 2,474.4596.231 2400 2,395.94
From Plot:
x = 96.2 mols/hr
This is amt of H2S that actually reacted
(96.2/132.3)*100%
% Conversion in furnace = 72.71 %
Furnace Temp = 2390 F
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1st Catalytic Converter - Hand Calculation Procedure
3. Calculate Kp and determine equilibrium
temperature from Kp chart
4. Determine stream enthalpy and converter
heat balance from assumed values of
5. Determine flame temperatures
6. Plot stream enthalpies and converter heat
vs
7. Determine converter duty & actual mols/hr
H2S converted
Procedure:
To determine % conversion & converter duty
Steps:
1. Material balance around converter
2. Assume mols/hr H2S is converted to
sulfur (S8)
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Hand Calculation – 1st Catalytic Converter
Result
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Hand Calculation - Result
2nd Catalytic Converter 3rd Catalytic Converter
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Heat DutyHand Calculation
Promax Hysys
Duty Btu/hr
FurnaceWaste Heat
BoilerSulfur
Condenser Reheater Catalytic
ConverterSulfur
Condenser Stage 1 14,660,438.61 13,983,571.92 2,627,601.19 626,856.55 2,840,839.57 1,291,525.71 36,030,833.55
Stage 2 _ _ _ 340,712.94 2,061,235.20 645,827.98 3,047,776.12
Stage 3 _ _ _ 220,953.57 1,775,630.90 494,858.12 2,491,442.59
41,570,052.25
Blocks Duty (Btu/hr)Blower 194,943Waste Heat Boiler 12,988,780Condenser 2,820,970Reheater 1,030,360Condenser 2 1,865,160Reheater 2 367,693Condenser 3 845,212Reheater 3 337,984Condenser 4 423,763
20,874,865
Unit Operartions Duty (Btu/hr)Burner 7,012,000Cooler 12,160,000Splitter 1 40,340Claus 1 691,700Splitter 2 1,309,000Heater 347,300Claus 2 1,686,000Splitter 559,200Heater 373,100Claus 3 122,200Splitter 4 673,900
24,974,740
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Result Summary
HYSYSPROMA
X HAND CALCSRE, % 99.27 97.52 97.41 Air Flow Rate, mols/hr 472.50 464.00 509.33
Furnace/Burner (MMBtu/hr) 7.01 _ 14.66 Waste Heat Boiler (MMBtu/hr) _ 12.99 13.98
Total Heat Duty (MMBtu/hr) 24.97 20.87 41.57 Typical Tail Gas Composition (ppm) H2S (5000 ppmv) 2100 3382.1 1386.7941SO2 (2500 ppmv) 1000 1564 701.1880
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Recovery of sulfur from a hydrogen sulfide containing gas
WO 2005068357 A2 (US Patent)
Engineering data book-GPSA-12th
Handbook of Natural Gas and Processing
Linde Sulfur Process Technology
Gas Purification Kohl & Nielsen 5th Edition
Technical Article: Reduce Sulfur Emissions From Claus Sulfur & Recovery Unit
Tail Gas Treaters, Dow Chemicals
Sour Gas Processing 2015, Bryan Research & Engineering Inc.
References
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THANKYOu
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Backup Slides
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Basic Claus vs Modified Claus Process
Basic Claus reaction
• highly exothermic
• difficult to control
• Low sulfur recovery efficiency
• overheating of the reactor
• Modified Claus
• improvement on the basic Claus
process
• free flame oxidation ahead of
catalyst bed
• catalytic steps revision
• high SRE ranging from 90-99.9%
• basis of most sulfur recovery units
in use today
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Modified Claus Process for Sulfur Recovery
Other Side Reactions:
Reaction Furnace:
S
Reheater (hydrolysis)
H2S + CO2
2H2S + CO2
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Claus Process Technology
There are two basic process approaches depending on H2S concentration
in feed stream:
Straight through * Split flow
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Claus Process Technology
Straight through Claus process
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Claus Process Technology
Split-Flow Claus Process
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Other Variations
Oxygen Enrichment
• use of pure oxygen instead of air
• higher and stable flame temperatures
• low H2S concentration feed and smaller equipment use
• used in combination with other variations
Acid Gas Enrichment
• applied ahead of SRU to achieve richer acid gas stream
• a solvent that selectively absorbs all the H2S from the feed gas
stream is used
• The straight through process can then be used for sulfur recovery
Claus Process Technology
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TGCU (Tail Gas Clean Up) Processes
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Sulfur Recovery Process Applicability Chart
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Sulfur Vapor Specie Distribution
Bryan Research & Engineering – Sour Gas Processing, 2015
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Hand Calculation – Chart & Tables
Engineering Data book – 12th Edition
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Hand Calculation – Claus Equilibrium Constant Chart
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1st Cat Converter Procedure
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1st Cat Converter Procedure
