Scale-up and Demonstration of Fischer-Tropsch Technology

Proceedings of the 1 st Annual Gas Processing Symposium
H. Alfadala, G.V. Rex Reklaitis and M.M. El-Halwagi (Editors)
© 2009 Elsevier B.V. All rights reserved. 1
Scale-up and Demonstration of Fischer-Tropsch
Technology
Dag Schanke, a,d Matthias Wagner, b,d and Patrick Taylor c,d
a
StatoilHydro Research Centre, Trondheim, Norway
b
Lurgi GmbH, Frankfurt am Main, Germany
c
PetroSA, Mossel Bay, South Africa
d
GTL.F1 AG, Zurich, Switzerland
Abstract
PetroSA, Lurgi and StatoilHydro formed a joint venture in 2004 for the demonstration
and commercialisation of an advanced Fischer-Tropsch cobalt catalyst / slurry reactor
technology and have subsequently established the GTL technology licensing company,
GTL.F1. The construction of a 1000 bpd, 40 mill Euro demonstration plant was
sanctioned in 2002 which has been in operation since 2004.
The joint venture has proven the viability of an advanced Fischer-Tropsch cobalt
catalyst and reactor technology at a scale that minimises the scale-up risk of commercial
plants.
Keywords: Natural gas, GTL, Fischer-Tropsch
1. Introduction
With crude oil and energy prices rising to ever higher levels, conversion of natural gas
to hydrocarbon liquids (Gas-to-Liquids, GTL) represents an attractive route for
monetizing gas resources. For the gas resource owner, GTL is mainly an alternative to
LNG in cases where pipeline transport of gas to consumer markets is not possible. In the
liquid product market, GTL products are of very high quality and fit well into a middle
distillate market with tightening specifications.
StatoilHydro started development of GTL technology in the mid 1980’s, focussing
mainly on Fischer-Tropsch catalyst and reactor development. PetroSA has operated the
largest GTL plant in the world in Mossel Bay (South Africa) since 1992. PetroSA and
StatoilHydro formed a joint venture for demonstration and commercialisation of an
advanced FT cobalt catalyst / slurry reactor technology in 2002. Lurgi GmbH, a leading
licensor of gas conversion technologies (synthesis gas, methanol, ammonia and others)
joined the GTL joint venture in 2004. Shortly there after the three partners formed the
technology licensing company GTL.F1.
The construction of a 1000 bpd, 40 mill Euro demonstration plant was sanctioned in
2002, with site work commencing in early 2003. The plant was commissioned in May
2004 and has been in operation since.

2 D. Schanke et al.
2. FT Technology selection and scale-up issues
2.1. Reactor technology
With cobalt based low temperature FT technology widely recognized as the preferred
technology for maximising middle distillate yields, the choice is between a conventional
tubular fixed-bed reactor configuration and the new slurry bubble column type of
technology (see figure 1). In the fixed-bed reactor, the catalyst pellets (> 1mm size) are
located at the tube side, while the coolant (boiling water) is on the shell side. The slurry
bubble column reactor on the other hand has the catalyst (as a finely divided powder) on
the shell side of the heat exchanger and boiling water inside the tubes. A significant
advantage of the latter type of reactor is the efficient heat transfer, due to the turbulence
and mixing of the slurry. This enables the highly exothermic (heat releasing) reaction to
be controlled and the reactor can be operated essentially isothermally, which improves
the utilisation of catalyst due to the well known fact that the C5+ selectivity of a Fischer-
Tropsch catalyst will decrease with increasing temperature. A further consequence of
the improved heat transfer is the reduced heat transfer area required, leading to a
maximum capacity of a single slurry bubble column reactor currently around 20.000
bpd, compared to approximately 5.000 bpd for a fixed-bed reactor. An additional
benefit of the slurry reactor concept is the use of small catalyst particles, less than 1/10 th
of the size used in a fixed-bed reactor (where the particle size is dictated by the pressure
drop). This avoids intra-particle diffusion limitations which have been shown to give
reduced C5+ selectivity for particles >ca. 0.3 mm.
Steam
Water
TUBULAR FIXED BED REACTOR
SYNGAS
WAX
CATALYST-FILLED TUBES
GAS OUT
SLURRY BUBBLE COLUMN REACTOR
CATALYST-WAX
SLURRY
Steam
Water
SYNGAS
Fig. 1. Simplified sketch of tubular fixed-bed reactor and slurry bubble column reactor
GAS
OUT
WAX

Scale-up and demonstration of Fischer-Tropsch technology 3
2.2. Technology and scale-up issues
The advantages described in Ch. 2.1. were all identified and formed the basis for
StatoilHydro to select the slurry bubble column reactor concept as the preferred FT
technology at an early stage. A small Fischer-Tropsch (FT) pilot plant was built and
successfully operated from 1987-1994 to demonstrate the basic viability of the slurry
reactor / cobalt catalyst concept.
However, the slurry bubble column concept presents some specific challenges in terms
of satisfying key reactor functions as well as scaling up to commercial size reactors:
• Separation of wax product from the slurry. A significant fraction of the product will
not vaporise from the reactor and therefore has to be removed from the reactor as
liquid wax from a slurry with relatively high solids concentration. No technology is
available in the open market for such applications.
• Hydrodynamics and scale-up. A commercial scale slurry reactor will typically have
a diameter of 5-10 m. While there is a vast body of data available for smaller
columns and simple air-water systems, little or no information is available in the
public domain regarding the hydrodynamics of very large diameter vessels
operating in the appropriate flow regime and at conditions relevant for FT
synthesis.
• Catalyst robustness. The mixing and turbulence of the 3 phase gas-liquid-solid
makes it necessary to use a catalyst which is resistant to attrition and break-up.
Formation of catalyst fines will not have any negative impact on the catalytic
reaction as such, but will cause problems for wax-slurry separation techniques such
as filtration, sedimentation or hydro-cyclones. Contamination of the wax product
with catalyst fines will also lead to increased catalyst consumption as well as
undesired downstream effects in the product upgrading section of a GTL plant.
The concept of operating a slurry reactor with cobalt catalyst and with continuous wax
separation was proven in small scale pilot plants as well as larger non-reacting mock-up
units at an early stage. Recognising the potential scale-up challenges of the technology,
the philosophy of the partners has therefore been to go beyond the normal scale-up
through an intermediate size pilot plant and rather build a demonstration plant of semicommercial
size in order to minimize further scale-up risks for a commercial plant.
3. Demonstration plant
Some key data for the semi-commercial demonstration plant are shown in Table 1. and
its integration within the main GTL complex in Mossel Bay is shown in Fig. 2.
The demonstration plant is using Syngas from the existing PetroSA GTL plant.
However, the Syngas produced for the high temperature Fe-based FT process in the
PetroSA plant has a higher H2/CO ratio than the optimum ratio employed by the low
temperature cobalt catalyzed process. The composition is therefore adjusted in a

4 D. Schanke et al.
membrane process where some hydrogen is removed and returned to the main GTL
plant.
The preheated and purified Syngas enters the FT reactor and into a slurry of finely
divided, supported cobalt catalyst particles and molten wax. Light hydrocarbons,
unconverted Syngas, inert gases and water vapor then leave the reactor via an overhead
stream to the product recovery section, where they are separated into oil (C5+
hydrocarbons), aqueous phase and tail gas. The wax is separated from the slurry using a
proprietary continuous internal filtration process. The Fischer-Tropsch reaction also
produces a considerable amount of heat that is removed by the generation of steam in
heat-exchanger tubes inside the reactor.
The FT catalyst is loaded to the reactor via a separate system and catalyst can also be
loaded or removed online during operation.
The demonstration plant is fully integrated with the PetroSA main GTL complex
regarding utilities (nitrogen, plant air, steam, cooling water and electricity) and product
handling. The oil products are sent to the PetroSA product upgrading plant while the
wax product is routed to separate storage. Sharing of these functions has significantly
decreased the capital cost of the plant compared to a dedicated stand alone unit.
Table 1. Key data for semi-commercial plant
Production capacity Up to 1000 bpd
Reactor diameter 2.7 m
Syngas flow Up to 45.000 Nm 3 /h
Total structure height 40 m
Plot area 25 m x 30 m
Total cost Ca. 40 mill Euro
NATURAL
GAS
SYNGAS
PRODUCTION
Gas adjustment
H 2
HIGH TEMP.
F-T
Semi-
Commercial
Demo Plant
Liquids
Wax
PRODUCT
REFINING
Fig. 2. Integration of F-T demonstration plant with PetroSA GTL complex at Mossel
Bay, South Africa.

Scale-up and demonstration of Fischer-Tropsch technology 5
Fig. 3. Semi-commercial FT demo plant (Mossel Bay, South Africa)
4. Catalyst production
Scaling up production of the supported cobalt FT catalyst, while at the same time
satisfying the strict requirements for use in a slurry reactor, is not a trivial task. Starting
from laboratory recipes for preparation of catalyst at typically

6 D. Schanke et al.
To date, more than 100 tonnes of catalyst have been produced for use in the semicommercial
demo plant. The scale of production (up to 1 ton/d) ensures minimal scaleup
risk for the catalyst manufacturing plant for a commercial project.
5. Performance of the demonstration plant
5.1. Catalytic performance
During the catalyst manufacturing campaigns, an extensive program of quality control
was carried out, using a pilot plant and other catalyst test reactors. After developing and
optimising the catalyst manufacturing procedures, the activity and selectivity of catalyst
produced at large scale does not differ from catalyst produced in the laboratory.
Furthermore, it was found that the catalyst activity and selectivity in the semicommercial
demo plant was similar to what is usually observed in the pilot plant.
Table 2. Example demo plant performance
Feed gas composition
H2
CO
CO2+CH4+N2
58 mol %
27 mol %
Balance
Reactor pressure 1600 kPa
Reactor temperature 232 o C
Gas hourly space velocity 3950 Nm 3 /toncatalyst/h
Conversion per pass
H2
CO
66 %
67 %
5.2. Wax separation
Predictably, the separation of wax from the slurry has been the most challenging aspect
of the technology development. After very good results in smaller scale pilot reactors,
the first trials in the semi-commercial demo plant gave low wax separation performance
after some time of operation and higher than expected levels of catalyst fines in the wax
product.
After several modifications to the wax separation system as well as the introduction of a
2 nd generation FT catalyst, the plant was able to be operated at sustainable, high wax
separation rates with minimal catalyst fines in the wax product (see fig. 4). The
performance of the wax separation system is known to be strongly dependent on the
particle size distribution of the catalyst in the reactor slurry. It became apparent that the
attrition characteristics of the catalyst are a function of the scale of operation, the
operating conditions as well as the properties of the catalyst (Wagner, 2008). This is

Scale-up and demonstration of Fischer-Tropsch technology 7
illustrated in Table 3. Similar observations have been made by Zennaro (2006). Using
the 2 nd generation catalyst gives very low attrition rates in all reactors tested.
Table 3. Attrition rates measured for different catalysts measured in slurry bubble
columns of varying scale and type.
Relative attrition rate (1 st gen. cat. In pilot plant = 1.0)
Pilot plant Cold-flow column Semi-commercial
plant
1 st gen. catalyst 1.0 0.3 5
2 nd gen. catalyst 0.03 0.01 0.03
SUSTAINABLE WAX SEPARATION RATE (relative)
4,0
3,0
2,0
1,0
0,0
1st gen. cat.
2nd gen. cat.
Pilot plant Cold-flow Semi-commercial
Fig. 4. Relative wax separation rates (wax output/filter surface area, time) for different
catalysts in slurry bubble columns of varying scale and type.
5.3. Hydrodynamics
The hydrodynamics of the semi-commercial reactor was studied using different
methods:
- Overall and local gas hold-up was estimated using differential pressure
measurements
- Catalyst concentration profiles were calculated from slurry sampling at several
axial locations
- Temperature profiles were compared with simulation models

8 D. Schanke et al.
- Injection of radioactive tracers (gas, liquid and solid) to measure local or global
residence time distributions for the different phases.
The collected data provide unique insight into the hydrodynamics of a large scale slurry
bubble column reactor and will, together with suitable simulation models (e.g. CFD),
enable a safe scale-up to commercial size reactors in terms of predicting the
hydrodynamic behaviour. It is also obvious from the measurements that the
extrapolation of mixing parameters from models developed in smaller scale columns
would have given incorrect results, thus confirming the need for large scale verification
of this type of technology.
6. Conclusions
The experience from the technology demonstration project has clearly shown the need
for proving critical technology elements at a sufficient scale. Many of the challenges
encountered and solved in the project would not have been evident in a smaller scale
test unit. The project has now proven the viability of an advanced FT cobalt catalyst and
reactor technology at a scale that minimises the risk of further scale-up to commercial
plants.
References
M. Wagner, “Successful large scale Fischer-Tropsch technology demonstration”, 7 th GTLtec,
Doha 18-19 Feb. 2008
R. Zennaro, “The ENI-IFP/Axens GTL technology for the conversion of natural gas”, 6 th World
GTL Summit, London 17-19 May 2006