ashwani k. gupta

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

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

Combustion Laboratory

Current Rankings:Current Rankings:

Computer Science 11Computer Science 11thth

Physics 14Physics 14thth

Engineering Engineering 1616thth

Mathematics 21stMathematics 21st


University of Maryland & ME Dept. 33,000 students 24,000 undergraduate + 9000 graduate students Engineering rated as #16 in the country ~1,000 in Mechanical Engineering (600+UG, 300+G) Mechanical Eng. Dept. -- 44 faculty ME Dept. 06-07 annual research budget ~$20 million Dept. rated 24th overall, 12th in research Combustion Research (~9 faculty in 3 Depts.) State-of-the-art combustion laboratory Combustion Laboratory includes 6-10 graduate

students, + several UG students. All students are fully supported.


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/


Evolution of APC

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

23

4

(Refinery HT)

SOLIDSTORAGESOLIDIFICATION

Storage

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

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

11

PROJECTED WORLD SURPLUS

Source: Bill Kennedy, SHELL CANADA LIMITED, Sulphur 2004, Barcelona, Spain, Oct.24-27, 2004

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

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

14

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

15

EQUILIBRIUM COMPOSITION OF SULFUR VAPOUR

S=S

> 95%

S S S

S SS

SS

17

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

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

19

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

20

CHEMICAL MODEL OF THE REACTION FURNACE

large number ofpossible reactions

21

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

22

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

23

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

24

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

25

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

26

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

27

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

28

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

29

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

30

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

31

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

32Reaction pathways for H2S-O2 reaction(Click in the box and observe changes in color & width of arrows)

Detailed reaction pathways

33

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

34

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

35

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

36

Case 1

37

Case 1

38

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

39

Case 2

40

Case 2

41

[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

42

Case 3

43

Case 3

44

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

45

Case 4

46

Case 4

47

Temperature Distribution under Normal HiTAC and Condition

48

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

49

The End

ashwani k. gupta

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