Topsoe Claus Tail Aug09 Low Res.ashx

7/28/2019 Topsoe Claus Tail Aug09 Low Res.ashx

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Claus unitTail gas treatment catalysts


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The TK catalyst amily


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Tail gas treatment catalysts

In the rening industry today, sulphur recovery is an extremelyimportant issue that oten does not get the attention it deserves.Sulphur is one o the dominant contaminants in petroleumractions, and legislation limits not only the sulphur content onished products, but also renery emissions to the atmosphere.Thereore, sulphur removal and recovery is a vital processor reneries and gas plant operations. In most locations, thesulphur is hydrotreated and thus converted to hydrogen sulphide(H

2S) which is easily scrubbed rom the various liquid and gas

streams. The H2S collected rom the hydrotreaters and/or gas

plants is then treated by the Claus or a similar process (Figure 1).

The Claus process

The Claus process utilises a combination o thermal andcatalytic process steps. Initially, the acid gas is enriched withsucient oxygen to convert some o the H

2S in the gas to SO

2

according to the ollowing reaction:2H

2S + 3O

2 2SO

2+ 2H

2O + Heat

The mixture o H2S and SO2 reacts according to the Clausreaction given below. At this stage, approximately 70% o liquidsulphur is recovered. The remaining gases are then ed to thecatalytic reaction section, where the ollowing reaction occurs:2H

2S + SO

2 3S + 2H

2O (Claus reaction)

The remaining efuent called Claus tail gas, apart romcombustible gases, also consists o H

2S, H

2, CO, CS

2, SO

2, and

COS. In order to meet the sulphur emission target Claus unitsoten have a tail gas treater or nal sulphur removal o the gases.

Tail gas treating

The tail gas hydrotreating unit works through a relatively simpleprocess. Because the sulphur compounds that need to beconverted are relatively easy to treat, catalyst activity is not aprimary requirement.

Due to the nature o the process, we can summarise andprioritise the desired catalyst properties as ollows:

low pressure drop-physical strength-thermal stability-longevity-HDS activity-

For tail gas hydrotreating operations, catalysts are typically o theCoMo type.

Figure 1: Sulphur recovery fow scheme


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Catalysts

Haldor Topse has developed three catalysts or tail gas treatingapplications covering a wide range o operating conditions andplant congurations.

These are:

Reactions

Sulphur compounds present in Claus tail gas are hydrotreatedwith a CoMo catalyst to H

2S at a temperature level o 250-275C

(480-525F) in the tail gas unit according to:

All o these reactions will reach equilibrium in the tail gas unitwhen applying any o Topses three CoMo type catalysts.

TopseTK-220

TopseTK-222

TopseTK-224

Shape Quadralobe Ring SphereNominal size, mm (in) 2.5 (1/10) 3.2 (1/8) 4.0 (1/6)

CoMo oxide, % wt ~14 ~18 ~12

Attrition index >98 >97 >98

Sock loading density,kg/m3 (lb/t3)

400 (25) 500 (31) 700 (44)

S2

+ 2H2 2H2S

SO2

+ 3H2 H2S + 2H2O

COS + H2O CO2 + H2S

CS2+ 2H

2O CO2 + 2H2S

CO + H2O CO2 + H2

Table 1: Typical catalyst properties

TK-220, 1/10 AQL

TK-222, 1/8 Ring

TK-224, 1/6 Sphere


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Catalyst activity

Topses tail gas treating catalysts are oered in dierent shapesand sizes due to pressure drop considerations. Furthermore, theyare designed with dierent porosities, average pore sizes, and

consequently dierent bulk densities to optimise the HDS activityor tail gas operation.

Pilot plant testing conrms that all three o Topses tail gastreating catalysts will provide the rener with the maximum sulphurconversion at the prevailing process conditions. This is shown inFigure 2.

All three catalysts will ensure the rener a long and stableperormance in the tail gas unit. In act, end-o-run or any oour tail gas catalysts is typically caused by an operational upsetsuch as burner operation issues causing soot ormation or atemperature runaway, rather than the gradual loss o catalyticactivity.

Pressure drop

The requirements or catalysts in tail gas treaters are quite dierentrom conventional hydrotreating applications. A very importantconsideration is the pressure drop across the catalyst bed, as theunit operates at almost ambient pressure, and the blower is theonly orce pushing the eed through the reactor. This is the reasonthat tail gas unit reactors are designed with a very large cross-sectional area and shallow bed depth. A typical reactor loading isshown in Figure 3.

Figure 2: Perormance o Topses tail gas catalyst at an inlet

temperature o 250C (480F)

Figure 3: Reactor loading diagramme


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Catalyst Sock loadedvoid raction, %

Relative pressure drop

TK-220, 1/10Quadralobe

48 1.00

TK-222, 1/8

Ring

53 0.15

TK-224, 1/6Sphere

35 0.95

Tail gas eed, Vol%H

2S 0.8

SO2

0.4

S8

0.1

CS2

0.1

COS 0.1

CO 0.3

CO2

3.0

CH4

0.1

H2

2.0

H2O 32.0

N2

61.1

Process conditions

Typical inlettemperature

250-275C480-525F

Air/Fuel Ratio 70-90% o stoichiometric

H2S/SO

2Ratio 2

Since the reactor pressure drop is ultimately determined by theshape and size o the catalyst particle, we have the opportunityto infuence the very important start-o-run (clean bed) pressuredrop across the reactor.

The start-o-run reactor bed pressure drop is determined by thebed void and the particle size, and Topses three dierent tailgas catalysts have the ollowing pressure drop characteristics:

As can be seen rom the above, Topse oers a number ocatalyst lling options in order to meet all needs o the rener.

For reners who really need a lower bed pressure drop, ourTK-222 1/8 ring meets this requirement. TK-222 has only 15%o the pressure drop o any o the other shapes utilised today,namely quadralobes and larger sized spheres. In act, TK-222

has the lowest pressure drop o any commercially availablecatalyst applicable or tail gas service. As such, it oers renersconsiderable advantages and opportunities or debottleneckingthe sulphur constraints o any renery by allowing a substantialincrease in throughput.

TK-15 and TK-10 are used as topping layers to improvedistribution as well as to provide the catalyst hold-downunction. TK-15 has 65% void and TK-10 has 55% void, which,coupled with the act that these layers are shallow, meansthat they contribute positively to the SOR pressure drop o thecatalyst ll.

Typical tail gas eed composition as well as operating conditionsor tail gas catalysts are shown in Table 3.

For more inormation about our tail gas catalysts or any o ourproducts and technologies, please contact your Haldor Topserepresentative.

Table 3: Tail gas eed and operating conditions

Table 2: Pressure drop characteristics


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A long lasting partnershipcombining knowledge with business

Your technology partner

Since 1940, Topse has specialised in heterogeneous catalysis,process development and engineering. A continuous ocuson research and development has ensured that Topsestechnologies and catalysts remain top o class. The many

dierent types o process plants supplied by Topse promotesynergy and give our clients the benet rom the experiencegained rom these plants.

Topses product portolio ranges rom catalyst productionand sales, licensing and engineering o proprietary catalyticprocessing units to in-house process development, projectmanagement and technical service. Proprietary knowledge o allthese elds ensures clients a competent business partner.

The Topse business portfolio

The rm commitment to catalysis and process technology hasstrengthened Topses position in a wide range o additionalbusiness areas: Development and supply o catalysts andtechnologies or the production o ammonia, methanol and other

petrochemicals, or gas conversion, oil rening and or emissioncontrol or the power and automotive industry.

Working with Topse, clients will benet not only rom our long-term knowledge o sulphur related processes, but also rom abroad portolio o other technologies and catalysts:

hydroprocessing and hydrogen production in the rening-and petrochemical industryammonia, methanol, DME, substitute natural gas (SNG)-and coal to liquid (CTL) in coal based industries


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The inormation and recommendations have been prepared by Topse specialists having a

thorough knowledge o the catalysts. However, any operation instructions should be considered to

be o a general nature and we cannot assume any liability or upsets or damage o the customers

plants or personnel. Nothing herein is to be construed as recommending any practice or any

product in violation o any patent, law or regulation.

CorporatePR

01.2

009.1

Haldor Topse A/S - Nymllevej 55 - 2800 Kgs. Lyngby - Denmark

Tel. +45 4527 2000 - Fax. +45 4527 2999 - www.topsoe.com

Topsoe Claus Tail Aug09 Low Res.ashx

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