Research I Technology I Catalysts

Prereforming

Leif Storgaard

� Prereforming was developed back in the 60’es

especially for town’s gas plants

� The technology disappeared in the 70’es when town gas

was replaced with natural gas

� Topsøe re-invented the technology in the 90’es

� Today more than 100 plants operate with prereformer

� Topsøe prereforming catalyst is installed in about 70 %

of all prereformers

History

Feed from HDS

Process steam

Prereformer

Waste heat channel

Tubularreformer

H2O (optional)

Typical installation of a prereformer

� Increase plant capacity

� Lower energy consumption

� No risk for carbon formation in tubular reformer

� Longer life time of tubes and catalyst in reformer

� Operate at lower steam to carbon ratio

� Operate on multiple feedstocks

� Longer life time of LTS catalyst

Why install a prereformer ?

∆H

CnHm + nH2O ⇔ nCO + H2 (694 kJ/mol

for C4H10)

CO + H2O ⇔ CO2 + H2 (-41 kJ/mol)

CO + 3H2 ⇔ H2O + CH4 (-206 kJ/mol)

°298

)2

m(n +

Prereforming reactions

400

450

500

550

0 20 40 60 80 100

Distance in bed, %

Be

d t

em

pe

ratu

re,

°C

Naturel gas LPG Naphtha

Temperature profiles in prereformer with

different feedstocks

0 20 40 60 80 100

Dis tance in Bed, %

430

440

450

460

470

480

490

Be

d t

em

pe

ratu

re,

°C

3 We e ks

1 2 M o n th s

2 2 M o n th s

4 5 M o n th s

5 9 M o n th s

Temperature profiles in natural gas prereformer using

Topsøe prereforming catalyst

� The prereforming catalyst deactivates mainly due to

sulphur poisoning

� Topsøe have developed a method to evaluate the

deactivation rate of the prereformer

(Z90 method)

� Based on Z90 method the remaining catalyst life time can

be estimated

� Based on Z90 method one get a quick warning if sulphur

leakage from HDS should increase

Evaluation of prereformer performance

450

470

490

510

0 20 40 60 80 100

Bed volume [%]

Temperature [°C

]

Measured temperatures

T90

Z90

90% of ∆Tmax

∆Tmax

maxin90 T9.0TT ∆∆∆∆××××−−−−====

Graphical deactivation plot – the Z90 method

0

10

20

30

40

50

60

70

80

90

0 10000 20000 30000 40000 50000

Operating Time, Hours

Graphical deactivation plot – the Z90 method

470

475

480

485

490

495

0 10 20 30 40 50 60 70 80 90 100

Bed height, %

TExit

TMin

Z90

T90

Temperature profile for the prereformer

at a naphtha-based plant

Graphical Deactivation Plot - Z90 Method

0

20

40

60

80

100

Time

Z90, %

Excessive sulphur poisoning Z90 plot

Operation

� The prereforming catalyst should be kept reduced

during shut down /start up

1. If the catalyst is oxidized some of the sulphur picked up

on the catalyst in the top will be released

2. This sulphur will be picked up by the catalyst further

down in the bed

3. The overall catalyst activity will decrease when the

sulphur is distributed to a larger part of the bed

Key parameters for prereforming catalysts

� Activity

� Sintering (ageing)

� Carbon resistance

� Sulphur tolerance

� Resistance to gum formation

� Mechanical stability

� Pressure drop

� During development of the new AR-401 catalyst the key

parameters have been optimized

� We have used new techniques to optimize the catalyst

� Compared to AR-30, the surface area of AR-401 has

been increased while maintaining the mechanical

strength

New prereforming catalyst AR-401

Total surface area of Singapore

10 m3 AR-401 =

Surface area

� The sintering rate (ageing) has been investigated in the

electronic microscope to find the optimum composition of

the catalyst that minimize sintering

Sintering

Sehested et al. J. Catalysis vol. 223 (2004)

Particle migration

From Science to Proven Technology From Science to Proven Technology –– by Brian Munchby Brian Munch

Sintering

AR-401 other features

� AR-401is delivered pre-reduced →

no reduction during start up

� As delivered AR-401 is stable in air →

loading do not require inert atmosphere

� AR-401 can tolerate exposure to condensing steam

Thank you for your attention