11 An Overview of Claus Offerings from Axens. 2 Sulfur Guard Nickel. CuO Arsine Guard PbO, CuO Hg Guard Chloride Guard Promoted aluminas, Organic.

11

An Overview of Claus Offerings from Axens

2

Sulfur Guard• Nickel. CuO

Arsine Guard• PbO, CuO

Hg Guard

Chloride Guard• Promoted aluminas, Organic Cl removal

Promoted Aluminas

Adsorbent Aluminas

Mole sieves

Catalyst Offerings

3

CR 3-7/CR-3S – promoted claus alumina

CRS-31/TL – Ti containing catalyst

AM/AMS – oxygen scavenger

CSM-31 – BTX removal catalyst

DR – active bed support

Summary of Products

4

There are typically two sections to be considered in the Sulfur Recovery Process• The thermal section

› > 1800 oF

• The catalytic section› Much lower temperatures,400 -650 oF

Overview of Sulfur Recovery

5

General SRU configuration

2/3 H2S + 1/3 SO2

COS + H2O

CS2 + 2 H2O

S + 2/3 H2O

CO2 + H2S (partially)

CO2 + 2 H2S (difficult)

2/3 H2S + 1/3 SO2 S + 2/3 H2O1/3 SO2 + 1/3 H2O

2/3 H2S + 1/3 SO2 S + 2/3 H2O

CO2, hydrocarbons + S COS, CS2

2/3 H2S

Breakthrough of oxygen (110 ppm)

1/3 H2S + 1/2 O2

50% of sulfur yield losses can be due to a low CS2 hydrolysis level!

Acid gas (H2S)

Air

FurnaceWHB

Reheater

Condenser Condenser Condenser

Reheater

Fuel gas

AirAir

Fuel gas To third converter,

TGTU or/and incinerator

Sulfur pit

Firstconverte

r

Secondconverter

6

Why two stages ?

Thermodynamic Limitations

2 H2S + SO2 3/x SX + 2 H2O

50

60

70

80

90

100

0 390 750 1110 1470 1830 2190 2550

Temperature (°F)

Con

vers

ion

H

2 S to

S (

%)

.

Cat

alyt

ic s

tage

.

Th

erm

al s

tage

.

The colder the better!(but dew point limitations + COS /CS2!)

The warmer the better!(hydrocarbons, ammonia)

7

From the inlet through the 1st condenser• Acid gas is burned with sufficient O2 to convert 1/3 of the H2S to SO2

› H2S + 3/2O2 SO2 + H2O

• Destroy all HC that enter with the Acid Gas› Carsul formation

• Destroy all NH3 that enters with SWS gas› Plugging in downstream condensers

Thermal Section

8

Refineries typically run rich acid gas streams• 70 – 90 % H2S

Gas plants typically run lean acid gas streams• < 50 % H2S

• Requires different configuration and will not be coveredO

ptions to increase Reactor Furnace temperature• O2 enrichment, increase through put and destroy incoming contaminants

Thermal Section

9

Flame Temperature Summary

2,735°F: Maximum for refractory protection

2,285°F: Minimum for NH3 destruction

1,925°F: Minimum for BTEX destruction

1,700°F: Minimum for flame stability

Source: John Sames, Sulphur Experts Inc.

10

Hydrocarbons• If not destroyed in the reaction furnace can lead to the formation of Carsuls, results in Delta P issues and rapid deactivation of Claus

• HC + S CS2

• CS2 must be destroyed in the first converter

Thermal Section

11

Excess CO2• CO2 + S COS• COS must be destroyed in the first converter

Thermal Section

12

SWS Gas• NH3 needs to be converted in the reaction furnace (> 2300 oF)

• Leads to NH3 salts which will deposit in condensers, resulting in Delta P issues

Thermal Section

13

Oxidation Reaction› H2S + 3/2O2 SO2 + H2O

•This sets up the standard Claus Reaction of a 2 to 1 ratio› With TGU ratio could be increased to 3 -1, or even 4-1 to reduce load on TGU

•Endothermic› 2H2S + SO2 3/2S2 + 2H2O

•60 - 70% of the sulfur is removed in the first condenser after the Reaction Furnace

•Generates medium pressure steam (450–600 #)

Thermal Section

14

Typical operating schemes• Re-heat, catalytic bed, condenser for sulfur recovery• 2nd Converter

› Inlet Temperature 410-420 oF, outlet 460 oF

• 3rd Converter› Inlet Temperature 395-400 oF, outlet 400-430 oF

• Inlet temperatures are typically 15-20 oF above dew point of Sulfur

• Too high outlet temperature from condensers will result in Sulfur carry over

Catalytic Section

15

2 Converter system will result in Sulfur recovery of 96 %

3 Converter system can be 97-98 % Sulfur recovery

Catalytic Section

16

Remove the unrecovered sulfur from the first condenser• Claus reaction aided by Claus catalyst

› Alumina, Titania, specialty catalysts

• Consists of three steps› Re-heating, conversion, cooling/condensing

• Typically first converter is run hot (450-480 oF inlet) to remove COS and CS2

Highly exothermic

Catalytic Section

17

Two plus converters

› 2H2S + SO2 3/6S6 + 2H2O

› 2H2S + SO2 3/8S8 + H2O

• 1st converter will remove 20-25 % of sulfur plus hydrolyze COS/CS2

• 2nd converter will remove 10 % of sulfur,› Temperature too low to convert COS/CS2

• 3rd plus conveters will remove 2-3 % of remaining sulfur

Catalytic Section

18

Because of large S6-8 molecules, maximum macro-porosity is required to reduce diffusion limitations

Catalytic Section

19

Alumina Selection Physical Characteristics

Large S8 molecules have to be evacuated from the catalyst

Diffusion constraints have to be minimized!

20

CR 3-7• This alumina catalyst is for standard Claus feeds where the

basic priorities are simple conversion of H2S and when low pressure drop requirements are imposed. This low-cost catalyst is attractive when there are no particular processing constraints.

• Equivalent to all competitive standard Claus catalyst on the market

• Available in ¼” and 3/16” sizes

• Surface Area = 285-350 m2/g

• Excellent abrasion resistance

• Low Density (39 lbs/cu ft)

• Macroporosity (>750 Å) = .224 ml/g, the highest in the industry

Claus Alumina for Better Performance

21

CR-3S Physico-chemical Optimization

37

42

47

52

57

62

67

72

0 800 1600 2400 3200 4000

Na2O (ppm)

Con

vers

ion

(%)

.

Claus, R2

CS2, R1

Diffusional constraints Activity-deactivation10 ppm O2, = 2s, Na2O = 2000 ppm 10(500) ppm O2 in R1(R2), = 2s, V0.1 = 16

The truth between constraints minimisation and compromises.

CR-3S combines both physical and chemical optimizations.

CS2 Conversion, %

0.3 0.4 0.5 0.6 0.7 0.8 0.9

52

48

44

40

36

Ratio of Ultra Macroporosity to Macroporosity, V1 / V0.1

Range forBestCompetitiveAluminas

V1 = Volume of pores greater than 1 µmV0.1 = Volume of pores greater than 0.1 µm

Constant macroporosity

V0.1= 20 ml/100 g

Constant macroporosity

V0.1= 16 ml/100 g

Range for CR 3SP

atented

22

Operate with an inlet temperature of 450 – 480 oF• Hydrolysis of COS/CS2 which requires a higher temperature

• Important from a Sulfur Recovery perspective• Reduce load on TGU• Outlet temperature of 580-630 oF

1st Converter

23

If you can provide us with Reaction Furnace inlet or outlet concentrations from 1st condenser, we can design a catalyst system that will give you optimum performance.

COS/CS2

24

COS/CS2 hydrolysis

• 50-70% conversion of CS2 with standard aluminas or hybrid Ti catalysts

• 95-100% hydrolysis of CS2 with CRS-31, a high Ti containing catalyst› Outlet temperature can be reduced to 570-590 oF

Reduced operating costs

• CS2 is the most difficult of these two species to hydrolyze in the first converter

• COS 80-90 % with standard aluminas or hybrid TI• COS 100 % hydrolyzed with CRS-31• Reduce demand on TGU plus reduce SO2 emissions

1st Converter

25

CRS 31Catalyst

A

Catalys

t B

Catalys

t C

CRS 31

TL

Shape Extrudate Pellet Extrudate Sphere Extrudate

TiO2, % 90 89 89 31.8 90

Al2O3, % - <1 - 61 -

SiO2, % - 7.1 7.3 6.4 -

Ca, % 3.2 <0.2 - - 3.2

Carbon, % - 2.8 <0.1 - -

Surface, m2/g 116 240 117 278 130

Bulk density, kg/m3 870 760 814 874 710

Crush strength, daN 2.6 / mm 1.4 1.2 / mm 16.2 15

TPV, ml/100g 29.8 62.0 45.1 41.5 35

Physical and Chemical Characteristics

26

Testing done at ASRL by a Middle East Gas company

Extreme conditions used• High levels of Xylene and Toluene

CRS-31 was tested as the best for CS2 conversion under these conditions

Titania and Alumina-Titania Hybrid Catalysts

27

0102030405060708090

100

0 10 20 30 40 50 60 70 80

% C

S2

Con

vers

ion

Time on Stream (h)

D

CRS-31

CompetitiveHybrid Ti

}B&C

Performance of Titania and Alumina-Titania Hybrid Catalysts

A

DF

E

Performance of Titania and Alumina-Titania Hybrid Catalysts

Source: Pierre Crevier

28

CS2 Hydrolysis in 1st ConverterAt Equilibrium.

Conditions: 6% H2S, 4% SO2, 1% CS2, 200 ppm O2, 30% H2O, N2 (balance)

CRS 31 flagship: in all cased the best catalyst. Catalyst C: comparable activity vs. CRS 21, somewhat > than

CR-3S, very sensitive to a temperature reductions.

0

10

20

30

40

50

60

70

80

90

1200 h-1 2400 h-1

CS

2 con

vers

ion

(%)

.

CRS 31

Catalyst C

CRS 21

CR-3S

535°F

20

30

40

50

60

70

80

90

100

1200 h-1 2400 h-1

CS2

conv

ersi

on (

%)

.

CRS 31

Catalyst C

CRS 21

CR-3S

610°F

29

6% H2S, 4% SO2, 1% CS2, 200 ppm O2, 30% H2O at 320°C

CS2 Hydrolysis Effciciency After 30 h

50

60

70

80

90

100

0.75 1.5 3 4.5 6

. S-7001 CRS 31

50

60

70

80

90

100

0.75 1.5 3 4.5 6

Contact time (s)

CS

2 Con

vers

ion

(%)

.

Comp A CRS 31

+ 24 %

+ 11 %

+ 6 %

30

CS2 Hydrolysis (R1)

40

50

60

70

80

90

100

0 15 30 45 60 75

Time (h)

CS

2 hy

drol

ysis

(%)

.

CRS 31

CR-3S

CA1

CA2

40

50

60

70

80

90

100

CS

2 hy

drol

ysis

(%)

.

CRS 31 CR-3S CA1 CA2

200 ppm O2

1500 ppm O2

200 ppm O2, = 3 s = 3 s, at the equilibrium

 Superiority of TiO2 over Al2O3: CRS 31 is the most efficient.

 Interest of an optimized speciality alumina (Na2O 2000 ppm, V0,1µm > 12 ml/100g with V1µm/V0,1µm > 0.7). CA: competitive alumina.

31

CRS 31 vs Alumina

CRS 31 TLCRS 31CR-3SAl2O3

Contact time

CS

2 c

on

vers

ion

CRS 31: Ultimate Claus performances

32

Best Strategies for TiO2 – Option 1

Al2O3

CRS 31Al2O3

R1 R2CRS 31 layer in R1

•Full COS-CS2 hydrolysis

•Higher overall recovery

•Similar life time than alumina loading

Contact time

CRS 31 TLCRS 31CR-3SAl2O3

CS

2 c

on

vers

ion

33

Best Strategies for TiO2 – Option 2

Full CRS 31 loading

•Outstanding sulphur recovery (thermodynamic limitation)

•Expended life time (> 10 years)

•Possible througput increase

CRS 31 CRS 31

R1 R2

Contact time

CRS 31 TLCRS 31CR-3SAl2O3

CS

2 c

on

vers

ion

34

2 converters 3 converters

SOR 4 years SOR 4 years

Alumina 95.1 92.9 98.1 96.7

CRS 31 in Cv 1 95.8 94.5 98.4 97.3

CRS 31 in Cv1&3

- 98.5 98.0

Case Study : 80% H2S

All simulations performed using Sulfur Experts’ Sulsim software

P. Crevier, E. Roisin, Sulphur 2008, Rome

-18%

-40%

-16%

-21%

35

US Refinery with two parallel SRUs• SRU 1 loaded with Hybrid Ti catalyst, plus alumina

› COS conversion = 98%

› CS2 conversion = 44%

• SRU 2 loaded with CRS-31, plus alumina› COS conversion = 99 %

› CS2 conversion = 100 %

COS/CS2 Conversion

36

US Gas Plant• CRS-31 bottom half of single converter, CBA

› COS conversion = 97%

› CS2 conversion = 100 %

US Gas Plant• Hybrid Ti catalyst in the bottom half of the first converter› COS conversion = 85 %

› CS2 conversion = 66%

COS/CS2 Conversion

37

Advantages of CRS 31 TL

1 m3 CRS 31

(0.92 tons)

1 m3 CRS 31 TL

(0.72 tons)=

CRS 31TL: same activity per volume than CRS 31, lower density (20%)

CRS 31 TL, higher cost / efficiency ratio

38

CRS-31 vs. CRS-31 TL

CRS-31 TL = Trilobe, CRS-31 = cylindrical

extrudate

CRS-31 TL density of 44.3 versus CRS-31 density

of 57 lb/cu ft

No difference in performance

70 references on CRS-31 TL showing equivalent

performance

39

Potential Problems• Sulfation of catalyst due to excess O2

› Excess O2 in reaction furnace

› In-line burners, direct re-heat between converters

› This can be eliminated by installing an O2 scavenger in the top of the bed

› Partial correction of problem by increasing H2S in feed and temperature to converters by 35-90 oF for approximately 12 hours

Catalytic Section

40

In-line burners in between converters can result in excess O2 entering the following converter resulting in Sulfation

Excess O2 to reaction furnace

Sulfation

41

Caused by sooting • Due to poor operation of the reaction furnace

Reduced throughput due to High Delta P

This problem can be reversed• Use a Sulfur wash

› Go sub Dew point for a period of time

› Sulfur lays down on the catalyst

› Increase temperature to heat soak levels

› Washes the soot off the catalyst. Reducing the Delta P

› May need to be performed several times in the event of extreme sooting

High Delta P in the 1st Converter

42

Lower the level in the sulfur pit

Shut off the reheater ahead of the converter with abnormally high ΔP

Operate the converter in sub-dew point mode for 12 to 16 hours•Time equivalent to production of sulfur = to ~ ⅓ the fresh catalyst weight

Return reheater to service and perform a heat soak

Expect to see black sulfur and soot to flow through the seal pot

Sulfur Wash Procedure

43

Repeat as necessary until pressure drop has been restored

A badly sooted bed may need two or three washes to remove the majority of carbon fines

This procedure has been practiced successfully by many operators

Sulfur Wash

44

References•Haji, M.N and Adab A.M. “Catalyst sulfur wash: a successful technique to remove soot from Claus catalyst beds online” LRGCC 2001

•Reprinted in Oil & Gas Journal – 11 June, 2001, vol 99.24 p 54-59

•R. Toor and J. Balken “Suncor Energy Inc Sulfur wash” LRGCC 2008

Sulfur Wash

45

Oxygen Scavenging

With direct reheaters, alumina catalysts in second and third converters have to be

protected by a layer of oxygen scavenger.

Oxygen scavengers are promoted aluminas.

Condenser

ReheaterAir

Fuel gas

2nd/3rd

converter

Combustion reaction:

Oxygen defficient = soot formation

Oxygen excess = sulfate formation!

46

O2 Scavenger

R2 conditions with competitve catalysts 2000ppm O2

l CaO = only a trap:

CaO + SO2 CaSO3

CaSO3 + 1/2 O2 CaSO4

l Fe / alumina = a real catalyst:

H2S

FeSO4 ‘FeS2’

O2

Oxygen Consumption, %

.

0

20

40

60

80

100

0 15 30 45 60 75Time on Stream , Hours

Alumina

Ca / alumina

Fe /Alumina AM

FeSO4 + 2 H2S = FeS2 + SO2 + 2 H20FeS2 + 3 O2 = FeSO4 + SO2

Fe / alumina = a real catalyst

H2S

FeSO4 FeS2

O2

47

A small layer on top of the second and third converter will protect the claus catalyst from sulfation

AM is in continuous regeneration in an H2S atmosphere.

CaO is only a trap and will be spent after a period of time

Claus catalyst has a very short life span in the face of O2

Summary of AM Catalyst

48

BTX Issues

Aromatic hydrocarbons: Benzene,Toluene and Xylene = a major problem in SRU

Performance of Claus catalysts in the presence of Toluene under first converter conditions

How to manage carsul formation

Performance of CRS 31 in the presence of BTX when used in commercial bed configuration:

CSM 31 / CRS 31

49

ASRL studies have shown that:

The presence of sulfates accelerates the reaction.

Higher SO2/H2S ratio quick deactivation

Especially, H2S/SO2 should be kept higher than 2

Carsul formation rate increases in the order:

Benzene: 1

Toluene: ~3

Xylenes: ~10

How to Accelerate Carsul Formation

P.D. Clark et al., « How do Claus Catalysts really work ? »Laurance Reid Gas Conditioning Conference, Norman, OK, February 2002

P. Crevier et al., « Quantifying the effect of individual aromatic contaminants on Claus catalyst » , LRGCC, Norman, OK, February 2001

50

Effect of Individual Contaminants

Axens Confidential

51

Axens’s Approach to Manage Carsul Poisoning

1 / Prevent the formation of sulfates and lower the SO2/H2S

2 / Convert nasty Toluene and Xylene to “catalytically friendly” Benzene (hydrodealkylation)

3 / Use Water gas shift conversion which produces H2 continuously:

CO + H2O H2 + CO2

SO2 + 3 H2 H2S + 2 H2O

52

Experimental Work 2 with ASRL

With Toluene : quick deactivation / severe fouling

Comparison of catalysts : 610 °F with vvh = 1200 h-1, 5000 ppmvToluene6% H2S, 4% SO2, 1% CS2, 30% H2O, 200 ppmv O2, N2 bal 100%

40

50

60

70

80

90

100

0 12 24 36 48 60 72

Time on stream (h)

CS

2 co

nve

rsio

n (

%)

CRS31 TiO2 catalyst

Promoted-TiO2 catalyst

CR3S alumina

CR-SU alumina

CR 4/8 alumina

Best competitive Alumina

53

CRS 31:• the most efficient catalyst anyway• deactivation occurs suddenly after 48 hours

ALUMINAS:• deactivation begins at S.O.R.

• CS2 conversion is too low (< 70%)

• more efficiency = more sensitive to deactivation

PROMOTED TITANIUM DIOXIDE:• acts more like alumina

CS2 Conversion with Toluene

CRS 31 is the best catalyst, but has to be protected by a top layer!

54

BTX Management with CSM31 + CRS 31

CSM 31 / CRS 31: 1/1

Dual bed CR 3S / CRS 31= 1 / 9 vs. CSM 31 / CRS 31= 1 / 1 - VVH = 1300 h-1H2S/SO2 = 1.5 - CS2 = 12% and COS = 8% of sulfur species

CO = 2.26% - H2 = 1.26% - BTX (7.5/5/1) = 2000 ppmv industrial gases

40

50

60

70

80

90

100

0 12 24 36 48 60 72

Time on stream (h)

CS2 conversion,%

500 °F

520 °F

610 °F

CR 3S +CRS31

CR 3S+CRS31

55

When BTX cause you troubles:

1/ Operate R1 at the lowest possible T°F

Carsul formation doubles with every 20 oF increase in temperature

2/ CRS 31 is the most efficient catalyst versus Claus reaction and COS/CS2 hydrolysis.

3/ Use a protective layer with 2 functions : lowering the SO2/H2S ratio and hydro-dealkylating aromatics

CSM 31 / CRS 31 dual bed is the solution!

Conclusions

56

Active Bed support for Claus unit• Replace inert supports with DR to improve activity of the Claus Unit

• Material is available in ½” and 3/8” spheres• Excellent crush strength• Lower cost of fill than standard inerts

DR

5757

Start-up/Shutdown

58

Once an SRU is started up it can often run for years continuously without the need to shut down

Catalyst replacement and boiler code requirements usually dictate the need to take the SRU offline

Start-up and shutdown are the times when the SRU is most at risk – most “incidents” occur here

Introduction

59

There are three Start-up cases to contend with•Cold Start-up with fresh catalyst•Cold Start-up with in-situ (used) catalyst•Hot Start-up

Start-up

60

General start-up sequence…

Start-up

61

Most critical points to monitor:•Fuel admission to the train•Check LEL with portable analyzer•Check Oxygen with portable analyzer

Start-up

62

Start-up

Rx.Furn.

Acid Gas

WHB Cond

Air

Conv

RH

Cond

Conv

RH

Cond

ConvRH

Air

FGCond

Check LEL before lighting anywherethere is fired equipment

63

Start-up

Rx.Furn.

Acid Gas

WHB Cond

Air

Conv

RH

Cond

Conv

RH

Cond

ConvRH

Air

FGCond

For all plant configurations check stoichiometric firing with O2 meter

64

For this unique, special condition, stoichiometric firing is not critical

XS air can be used - but only for this case

The focus needs to be on RF refractory curing

Follow manufacturers recommendation for temperature ramping of fresh or in situ refractory

Cold Start-up & Fresh Catalyst

65

Even in this case it is advisable to use quenching steam (more about this in a moment)

When the beds are up to temperature introduce acid gas

Cold Start-up & Fresh Catalyst

66

Now there are two points to be aware of:•RF refractory curing – as always

•Need to keep converters in an O2 free environment as they are heated up

Now the flexibility to use excess air is not possible, quenching steam is mandatory

Reaction Furnace must be started up on stoichiometric firing or a converter fire is possible if not probable

Cold Start-up with Used Catalyst

67

Many refineries have a significant amount of H2 in the fuel gas

It is noteworthy that although the heat of combustion of H2 is less than a third that of C1, the adiabatic flame temperature of H2 is higher than that of C1

Cold Start-up with Used Catalyst

68

Fuel gas firing needs to be tempered with quench steam to moderate the flame temperature

Use at 4 – 5 kg steam / kg of fuel

Hydrogen content of the fuel gas does not significantly affect this rule of thumb

Cold Start-up with Used Catalyst

69

Sequence summary:•Light off Thermal Oxidizer•Light off Reaction Furnace – Maintain Stoichiometry

•R.F. refractory curing•Light off / commission reheaters• Introduce acid gas

Cold Start-up with Used Catalyst

70

One of the more hazardous SRU scenarios

Ex. the plant tripped and is to be brought back online A.S.A.P.

Refractory curing is not a concern

The hot catalyst beds and R.F are the issues

Critical not to admit free oxygen to the beds

Danger of introducing fuel to hot RF

Hot Start-up

71

Start Thermal Oxidizer

Purge R.F. with 5 volume units of N2

Light off R.F. with fuel – switch immediately to acid gas

Light off / commission reheaters

The key is to limit successive attempts at lighting the R.F.

After two failed light off attempts re-purge the R.F. with 5 volume units of Nitrogen

Hot Start-up

72

Heat soak

Fuel gas firing

Air ramping

Air cooling

When things go wrong

Shutdown

73

In stock inventories for immediate delivery• CR-3S, CR, DR, AMS and CRS-31

We can provide Technical Assistance• Projections• Troubleshooting• On site loading and start-up support

We will guarantee the performance of our products

What We Can Provide

74

Ensure the tail gas analyzer is on line

The unit must be dried out under fuel gas firing

Pyrophoric material inevitably builds up in the SRU during operation

Burning this off in a controlled manner is the key to a safe shutdown

Close watch on catalyst bed temperature profiles

Record keeping & patience

Key Points for a Successful Shutdown

75

Many things can go wrong during a shutdown

There is always pressure from Maintenance to speed things up

Best Practice is to have the Lead Operator sign off a Shutdown Log with all the required steps pre-printed

Industry Best Practice

76

Increase all converter inlet temperatures to 260 °C or as high as possible if reheaters are steam heated

Reduce acid gas to increase temperature

For small trains < 100 TPD minimum 12 hrs

For larger trains minimum 24 hrs

Reason

•Remove SL from within catalyst pores

•Reduce the chance of fires in the beds

Heat Soak

77

Reduce acid gas to 25% – 30% of design rate

Introduce fuel gas

Drop out acid gas and set stoichiometric firing

Here it is VERY CRITICAL to maintain stoichiometry firing

Add quench steam: 4 – 5 kg per kg fuel

Check excess O2 at first condenser

Fuel Gas Firing

78

Use the maximum fuel rate subject to quench steam availability to maintain ~ 1300 °C in R.F.

Note that even for refineries mass flow rate on fuel gas firing is still less than process flow at the same burner heat release rate

More fuel flow means a faster shutdown

Continue until all sulfur rundowns have stopped flowing – this can take several days large plants > 400 MTD

Fuel Gas Firing

79

Shutdown the catalytic stage reheaters

Keep firing stoichiometrically until ALL beds are below 200 °C

Be patient

This is the step you don’t want to rush

Really have patience – tell maintenance to relax!

Fuel Gas Firing

80

This is one to take your time on

Verify that the tail gas analyser is in service

Even after the heat soak and fuel gas firing there are still combustible materials in the SRU•Residual sulfur deep in the catalyst pores•Pyrophoric iron

This has to be “burned off” in a controlled way

The main air valve is to big for fine control

Air Ramping

81

Use the trim air valve

Open the trim air valve in steps of 5% of valve opening

At each step, allow a minimum of 20 minutes before making another change to the trim valve position

Keep a close watch on tail gas analyzer for any sudden increases in SO2

Air Ramping

82

Ramp up air while reducing steam in small steps while maintaining ~ 1300 °C in the R.F.

When steam is blocked in excess oxygen should be about 14%

Fire this way with no steam for 8 hours

Increase air until flame becomes unstable

Shut off and isolate fuel gas when the R.F. temperature is about 450 °C

Air Ramping

83

Run air blowers at 50% of normal process flow with all valves open

(minimum discharge pressure – minimum temperature)

Continue cooling until the train reaches air blower temperature

Now maintenance can do their work safely

Air Ramping

84

The SO2 reading from the analyzer gives advance warning of a temperature excursion in a converter

Abnormal Situations

85Axens Confidential

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Time, Minutes

Conv

erte

r Tem

pera

ture

, °F

0

0.5

1

1.5

2

2.5

SO2

in T

ail G

as, %

Temperature Controlled SO2

0

200

400

600

800

1000

1200

1400

1600

1800

2000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Time, Minutes

Conv

erte

r Tem

pera

ture

, °F

0

0.5

1

1.5

2

2.5

SO2

in T

ail G

as, %

Temperature Controlled SO2

Something happened in the converter here

But the bed thermocouple

didn’t react until here

86

Rapid increase in tail gas SO2 during stoichiometric fuel firing•Go to sub-stoichiometric firing (~ 90 - 95%)

•Wait for SO2 to start coming down

•Return to stoichiometric firingR

apid increase in tail gas SO2 during air ramping

•Return to stoichiometric firing

•Wait for SO2 to start coming down

•Return to air ramping

Abnormal Situations

87

Reduce to R.F. air rate so as to achieve an H2S/SO2 ratio of between 6-10 in the tail gas

Raise the temperature of the second and third converters up to 235 °C if possible

At lower H2S/SO2 ratio and temperature it will take longer to react the sulphate

Operate in rejuvenation mode for 12 to 36 hours depending on ratio, temperature and plant size

Rejuvenation Procedure

88

It is sometimes used in gas plants that have aromatic contaminant issues

Refineries should never need to do regenerations

We do not recommend this procedure because of the risks involved

It is mentioned here only for completeness of a discussion of SRU operations

Regeneration

89

It is always desirable to keep an SRU running when that option is available

The unit is always stressed when either started up or shutdown

Typically this is when damage to refractory and other components occurs

Safe start-up and shut downs are achieved with careful planning, team work and patience

Concluding Remarks