Download - Ashwani K. Gupta
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1Simulation of Clause Furnace under HiTAC Conditions for Enhanced Sulfur Recovery
M. Sassi** S. Ben Rejab** and Ashwani K. Gupta* The Combustion Laboratory
University of Maryland, College Park*Email: [email protected]
Grad Student: Hatem Selim
** The Petroleum InstituteAbu Dhabi, UAE
International Workshop on Advances in Combustion ScienceIIT Kanpur
December 31, 2007 - Jan 2, 2008
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2Feature Presentation
outline UMD Information Air Pollution Control (APC) Review of the modified Claus process Process capacity and cost analysis Chemical equilibrium simulation CFD simulation Conclusions and perspectives
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Combustion Laboratory
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Combustion Laboratory
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Combustion Laboratory
The Combustion Laboratory at UMDTheme: Clean and efficient combustion of fossil, and new future fuels
State of the art Lab. with comprehensive Diagnostic & Experimental facilitiesPresent research supported by: NASA, ONR, AF, MDA, DoE, PI, and Industries
Sample Projects
Biomass gasification and Waste to clean fuel conversion (fuel reforming)
Mixing and ignition in rocket injectors
High speed combustion/Propulsion
Colorless Distributed Combustion in gas turbines using HiTAC technology
Underwater propulsion and two phase mixing
Micro-combustor with regeneration using gas and liquid fuels
Sensors and Diagnostics for flames and combustors
Sulfur removal from sour and acid gasFor details: Contact Professor A. K. Gupta, E-mail: [email protected]://www.enme.umd.edu/combustion/
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Combustion Laboratory
Evolution of APC
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Combustion Laboratory
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8OVERVIEW OF GAS PROCESSING
1
Sour Natural GasCH4, H2S, CO2
ALKANOLAMINESWEETENING
Sales GasCH4, liquid products
Acid Gas H2S, CO2
AirO2/N2
ACID/BASE
OXIDATION
TAIL GASCLEAN-UPINCINERATION
H2SRecycle
SO2
1. REDOX2. OXIDATION
SO2, H2O, CO2, N2
SULFUR DEGASSING
S S
SULFURRECOVERY
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4
(Refinery HT)
SOLIDSTORAGESOLIDIFICATION
Storage
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9MODIFIED CLAUS PROCESS FOR SULFUR RECOVERYMODIFIED CLAUS PROCESS FOR SULFUR RECOVERY
2H2S + SO2 3/2S2 + 2H2O HR= + 47 kJ, endothermichigh T
1. Combustion (Reaction Furnace)
H2S + 3/2O2 SO2 + H2O + heat (518 kJ)high T
3H2S + 3/2O2 3/8S8 + 3H2O + heat (626 kJ)OVERALL
2. Redox (Catalytic Converter)
2H2S + SO2 3/8S8 + 2H2O + heat (108 kJ)CAT.
low T
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10
REACTIONFURNACE
CONDENSER CONDENSER
WASTEHEAT
BOILER
CONDENSER
Liq. S8
Liq. S8
AIR
THERMAL STAGE
Liq. S8Liq. S8
Al2O3
CATALYTIC STAGES
SIMPLIFIED PROCESS SCHEME FOR THE CLAUS SULFUR RECOVERY PROCESS
RE-HEATER
Al2O3
RE-HEATER
2H2S: SO2N2, H2O
2H2S: SO2N2, H2O Tail gas
ACIDGAS
HIGH TEMP.
a b c
LOW TEMP.
CLAUS PLANT STRAIGHT-THROUGH CONFIGURATION30% & H2S
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11
PROJECTED WORLD SURPLUS
Source: Bill Kennedy, SHELL CANADA LIMITED, Sulphur 2004, Barcelona, Spain, Oct.24-27, 2004
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12
ADNOC HABSHAN PLANT ADNOC HABSHAN PLANT PROBLEM STATEMENTPROBLEM STATEMENT
Design a Sulfur Recovery Plant with a: Capacity 800 tonnes/day Sulfur Recovery of 99% Using Modified Claus Process +
Tail Gas Unit Composition of Feed Stream
10 %N2 Mole Percent
30 %CO2 Mole Percent
60 %H2S Mole Percent
30o CTemperature
1.4 barsPressure
Feed Stock Conditions
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13References: Clark Peter, SOGAT Proceedings-Workshop, Abu Dhabi, UAE, November 29 2005
CONV 3205oC
CONV 2225oC
CONV 1305oC
WHB F
THERMAL STAGE
CATALYTICSTAGE
TGCU
PRACTICALLIMIT
T
H
E
O
R
E
T
I
C
A
L
R
E
C
O
V
E
R
Y
O
F
S
U
L
F
U
R
(
%
)
(S8)
MODIFIED CLAUS PROCESSMODIFIED CLAUS PROCESS
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EQUILIBRIUM SULFUR CONVERSION
HR 108 kJ HR +47 kJresponsible for 60-70%
conversion in the furnace
%
T
H
E
O
R
E
T
I
C
A
L
C
O
N
V
E
R
S
I
O
N
T
O
S
U
L
F
U
R
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EQUILIBRIUM COMPOSITION OF SULFUR VAPOUR
S=S
> 95%
S S S
S SS
SS
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16
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Summary For Cost Analysis of a Sulfur Recovery Plant Designed on the Process
Simulator HYSYS
18.75 M$2.4 M$14.49 M$
Total Capital Total Capital InvestmentInvestment
@ 2006@ 2006
Working Working CapitalCapital@ 2002@ 2002
Fixed Capital Fixed Capital InvestmentInvestment
@ 2002@ 2002
3.46 M$0.77 M$1.02 M$
Total Total Production Production
CostCost
TotalTotalUtility CostUtility Cost
Total Total CatalystCatalyst
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18
CLAUS FURNACE
AIRCombustion chamber
2500oC 1300oC 600oC
flame zoneAnoxic zone
ProductsH2S + 3/2 O2 SO2 + H2O
H2S/O2 Ratio0.66
Conversion: 100%Conversion: 100%
Goal 2:1 HGoal 2:1 H22S to SOS to SO22 ratioratio
Air FeedAir Feed 2502 Kmole/h
SOUR GAS
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CLAUS FURNACE - ANOXIC, HIGH T PROCESSES (SULFUR SPECIES)
acid gas
O2 (N2)
Combustion chamber2500oC 1300oC
WHB600oC
flame
zone
Anoxic zone
Products3/2 S2 + 2 H2O 2 H2S + SO2
S2 + 2 H2O H2S + H2 + SO2 (favoured)
2 H2S 2 H2 + S2
2 H2 + SO2 2 H2O + 1/2 S2
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CHEMICAL MODEL OF THE REACTION FURNACE
large number ofpossible reactions
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CLAUS FURNACE THERMOCHEMICAL EQUILIBRIUM
we have used the STANJAN Code to explore the influence of varying the following parameters on the sulfur recovery in the Claus furnace :
- inlet hydrogen sulfide content in the H2S / CO2 mixture
- combustion temperature
- inlet temperature
-O2 content in the air
STANJAN interface
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H2 CH4 O2 H2O CO CO2 C H CH
CH3 O OH HO2 N2 AR N NH NO
NO2 S SH H2S SO SO2 SO3 HSO2 HOSO
HOSO2 SN S2 HOSHO COS HSNO HSO HOS HSOH
H2SO HS2 H2S2 H2SO4 CS
Species Included in the equilibrium kinetics mechanism
Numerical Effort
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Case 1: Varying H2S Content
50
55
60
65
70
75
80
25% 30% 35% 40% 45% 50% 55% 60% 65% 70% 75% 80% 85% 90% 95% 100%
H2S CONTENT
H
2
S
C
O
N
V
E
R
S
I
O
N
,
%
900
1000
1100
1200
1300
1400
1500
1600
T
E
M
P
E
R
A
T
U
R
E
,
K
we increase the H2S content from 25% to 100% in the inlet sour gas and see the evolution of the chemical equilibrium state.
We notice an increase in sulfur conversion with CO2 decrease.
Sulfur recovery as a function of H2S inlet content
H
2
S
c
o
n
v
e
r
s
i
o
n
,
%
T
e
m
p
e
r
a
t
u
r
e
,
K
H2S content
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Case 2: Varying Temperature
We consider a mixture of 50% H2S and 50% CO2 reacting with air: 21% O2 and 79% N2 in the furnace at varying combustion temperatures.
0
10
20
30
40
50
60
70
80
900 1200 1500 1800 2100 2400 2700 3000
TEMPERATURE, K
H
2
S
C
O
N
V
E
R
S
I
O
N
,
%
It is shown that an optimum sulfur recovery is obtained for a furnace temperature around 1500K
H
2
S
c
o
n
v
e
r
s
i
o
n
,
%
Temperature, K
Sulfur recovery as a function of temperature
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Case 3: Varying Inlet Temperature
In this case, we are just varying the inlet temperature of the reactants. 50% H2S / 50% CO2 and air: 21% O2 / 79% N2 are reacting in the furnace.
0
10
20
30
40
50
60
70
80
300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000 2100 2200 2300 2400 2500 2600
INLET TEMPERATURE, K
H
2
S
C
O
N
V
E
R
S
I
O
N
,
%
0
500
1000
1500
2000
2500
3000
E
Q
T
E
M
P
E
R
A
T
U
R
E
,
K
Despite the increase of the inlet temperature, we remark that the sulfur recovery is decreasing.
H
2
S
c
o
n
v
e
r
s
i
o
n
,
%
T
e
m
p
e
r
a
t
u
r
e
,
K
Sulfur recovery as a function of inlet temperature
Inlet temperature, K
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Case 4: Varying Oxygen Content in the Air
we vary the oxygen content in the air, starting from 21% until 100%, which reacts with a 50% H2S and 50% CO2 mixture at an inlet temperature equal to 300K.
H
2
S
c
o
n
v
e
r
s
i
o
n
,
%
60
62
64
66
68
70
72
74
21 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
O2 CONTENT, %
900
1100
1300
1500
1700
1900
2100
E
Q
T
E
M
P
E
R
A
T
U
R
E
,
K
T
e
m
p
e
r
a
t
u
r
e
,
K
Even though the oxygen enrichment is supposed to increase recovery, we notice that the H2S conversion decreases.
Sulfur recovery as a function of O2 content
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Reactor temperature versus equilibrium mole fraction of S2
Conversion efficiency = (Mass of S2)/(Mass of sulfur in H2S) Temperature around 1600K provides high sulfur removal efficiency
Equilibrium calculations [3H2S + 1.5O2 + 5.64N2 3H20 +1.5 S2 + 5.64 N2 ] 41 speciesMass fraction of molecular sulfur for the mole fraction case of:( H2S= 29.58%, O2= 14.79%, and N2= 55.62%)
1000 1200 1400 1600 1800 2000 2200 2400
Temperature (K)
0.16
0.17
0.18
0.19
0.20
0.21
0.22
0.23
0.24
S
2
M
a
s
s
f
r
a
c
t
i
o
n
0.500.520.540.560.580.600.620.640.660.680.700.720.740.76
Conversion efficiency
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Mass fraction of molecular sulfur for the mole fraction case of:(H2S= 26.9%, CO2= 8.97%, O2= 13.46%, N2= 50.62%).
Equilibrium calculations [3H2S + 1.5O2 + 5.64N2+ CO23H20 +1.5 S2 + 5.64 N2 + CO2] 41 species
Hydrogen sulfide conversion to S2 maximum at temperature ~1500K CO2 affects the process by reducing the optimum temperature
Reactor temperature versus equilibrium mole fraction of S2
1000 1100 1200 1300 1400 1500 1600 1700 1800 1900 2000
Temperature (K)
0.165
0.170
0.175
0.180
0.185
0.190
0.195
0.200
S
2
M
a
s
s
f
r
a
c
t
i
o
n
0.610.620.630.640.650.660.670.680.690.700.710.720.73
Conversion efficiency
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Sample Kinetics Calculation at 1600K
Major Species behavior with distance (time)
H2S as well as O2 mole fraction decreases with time (both curves are related) SO2 mole fraction increases due to the reaction between O2 and H2S S2 mole fraction increases due to the reaction between SO2 and H2S
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Sample Kinetics Calculation at 1600K
Minor Species behavior with distance (time)
General trend for minor species with distance (time) Species show peak behavior at the beginning, then get consumed during the terminating reactions
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Detailed Kinetics Calculation
Effect of Reactor Pressure
Effect of the reactor pressure on S2 mole fraction
Atmospheric pressure is favorable High pressure reduces S2 formation
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32Reaction pathways for H2S-O2 reaction(Click in the box and observe changes in color & width of arrows)
Detailed reaction pathways
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CFD SIMULATION OF THE CLAUS FURNACE
FLUENT is a CFD code dedicated to the simulation of fluid flow, heat and mass transfer, and a host of related phenomena involving turbulence, reactions, and multiphase flow. We have used it to simulate the combustion process in the Claus furnace.
Turbulence Model: Standard k - model
Turbulence- Chemistry Interaction Model: EDC
Boundary conditions:
Velocity inlet
Wall
Pressure outlet
Velocity inlet
Meshed geometry
Boundary Conditions
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CFD Results
Four cases are treated:
Air inlet
H2S inlet
O2 inlet
H2S inlet
O2 inlet
H2S inlet
Air inlet
H2S inlet
Case 1 Case 2
Case 3 Case 4
Temperature: 300 K
Velocity: 85 m/s
Temperature: 300 K
Velocity: 0.1 m/s
Temperature: 300 K
Velocity: 100 m/s
Temperature: 300 K
Velocity: 0.1 m/s
Temperature: 300 K
Velocity: 100 m/s
Temperature: 300 K
Velocity: 0.2 m/s
Temperature: 300 K
Velocity: 100 m/s
Temperature: 1000 K
Velocity: 0.66 m/s
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Case 1:
H2S + 1.5 [O2 + 3.76 N2] SO2 + H2O + 5.64N2
2 H2S + SO2 1.5 S2 + 2 H2S
Air inlet
Pure H2S inlet Q=0
Temperature: 300 K
Velocity: 0.1 m/s
Temperature: 300 K
Velocity: 85 m/s
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Case 1
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Case 1
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Case 2:
H2S + 1.5 O2 SO2 + H2O
2 H2S + SO2 1.5 S2 + 2 H2O
Q=0
Temperature: 300 K
Velocity: 0.1 m/s
Pure H2S inlet
Temperature: 300 K
Velocity: 100 m/s
Pure O2 inlet
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Case 2
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Case 2
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[H2S + CO2] + 1.5O2 SO2 + H2O + CO2
2 H2S + SO2 1.5 S2 + 2 H2O
Case 3:
H2S/CO2 inlet
Temperature: 300 K
Velocity: 0.2 m/s
Pure O2 inlet
Temperature: 300 K
Velocity: 100 m/s
Q=0
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Case 3
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Case 3
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Case 4:
[H2S + CO2] + 1.5 [O2 + 3.76 N2] SO2 + H2O + 5.64N2 + CO2
2 H2S + SO2 1.5 S2 + 2 H2O
Q=0
Temperature: 1000 K
Velocity: 0.66 m/s
H2S/CO2 inlet
Temperature: 300 K
Velocity: 100 m/s
Air inlet
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Case 4
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Case 4
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Temperature Distribution under Normal HiTAC and Condition
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SummaryThe Claus process for sulfur recovery has been known and used in theindustry for over 100 years. It involves thermal oxidation of hydrogen sulfideand its reaction with sulfur dioxide to form sulfur and water vapor. This processis equilibrium-limited and usually achieves efficiencies in the range of 94-97%,which have been regarded as acceptable in the past years. Nowadays strict airpollution regulations regarding hydrogen sulfide and sulfur dioxide emissionscall for nearly 100% efficiency, which can only be achieved with processmodifications. A detailed literature survey revealed that most of the earlystudies have focussed on the Claus catalytic stages and/or the tail gastreatment unit. While very little work has been devoted to explore the possibleimprovements to the combustion process in the Claus furnace. In this study wepresented numerical simulation results of the combustion and thermal stage ofThe Claus furnace burner. We specifically explored the improvements thatCould be made on the process by oxygen enrichment, reactants pre-heating,and injection port exchange between fuel and oxidant in the burner.
HiTAC is attractive for this process
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The End