(468b) Optimized Gas Loop Design for Fischer-Tropsch Process

Optimized gas loop design for
Fischer-Tropsch process

The Fischer-Tropsch (FT) process is used
to convert a feedstock such as coal or biomass to syngas (CO + H₂),
and then to syncrude, which consists of a vast array of hydrocarbons ranging
from methane to C35-C40 hydrocarbons. The syncrude is further refined to yield
gasoline, diesel or kerosene fractions. The process has been in use since the
early 1930s, when the Germans used a cobalt catalyst-based fixed bed FT
synthesis reactor to obtain transportation fuels from coal. The process has
undergone considerable developments since then, and is operated under a variety
of conditions.

Potential feeds to the FT process
include natural gas, which would be reformed, or coal or biomass, which would
be gasified, to yield syngas in both cases. The syngas produced is then
processed in a Fischer-Tropsch reactor which yields the syncrude. The gas loop
thus consists of the feed, the syngas generation technology and the FT reactor
(Figure 1).

In general, it is desirable to generate
a syncrude with a majority of its components in the diesel or gasoline
fractions, while at the same time minimizing the production of methane. The
composition of the syncrude produced, however, depends on the gas loop, its
components and its design. The composition of the syngas is determined by the
type of feed and the type of syngas production technology used, and different
FT reactors favour specific syngas compositions to give the desirable output.
In this work, we model the different technologies available in the gas loop and
carry out studies to select optimized gas loops for each of the following
metrics: (1) minimizing methane generation, (2) increasing diesel cut
selectivity in the syncrude, and (3) increasing conversion efficiency with
respect to the feed. The optimization is conducted at two levels, the selection
of the appropriate combination of technologies for the units in the gas loop,
and in the optimization of operating conditions for each process unit. The
process technologies considered are steam reforming, partial oxidation and
autothermal reforming for the reformer; fixed bed, fluidized bed and entrained
flow reactors for the gasifier; and slurry phase, fluidized bed, turbulent
fluidized bed and fixed bed reactors for the Fischer-Tropsch synthesis reactor.
Reaction kinetics for the FT reactor are obtained from Wang et al. [2] for iron
catalyst based processes, and from Yates and Satterfield [3] for cobalt
catalyst based processes.

References

[1] A. de Klerk, ?Fischer-Tropsch fuels
refinery design' Energy Environ. Sci., 4 (2011) 1177-1205.

[2] Y-N. Wang, W-P. Ma, Y-J. Lu, J.
Yang, Y-Y. Xu, H-W. Xiang, Y-W. Li, Y-L. Zhao and B-J. Zhang, ?Kinetics
modelling of Fischer?Tropsch synthesis over an industrial Fe?Cu?K catalyst', Fuel,
82 (2003) 195?213.

[2] I.C. Yates and C.N. Satterfield, ?Intrinsic
kinetics of the Fischer-Tropsch synthesis on a cobalt catalyst', Energy and
Fuels, 5 (1991) 168-173.

 Figure 1.Gas loop for syncrude production [1]