Gas Processes Handbook - 63

2019 GAS PROCESSES HANDBOOK
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GTL

Gas-to-Liquids (GTL)
Applications: To produce zero-sulfur synthetic fuels from natural gas. The process
can operate on a range of natural gas feedstocks, including fields containing high
carbon dioxide levels. The synthesis gas (syngas)-generation technology can be
tailored to conventional onshore locations or to remote or offshore locations where
space and weight are of particular concern.
Description: Natural gas is pretreated to remove sulfur, using a conventional
desulfurization technology (1). Steam and recycle gases are added, and the feed
is further heated before being passed to the syngas generation unit (2).
For conventional onshore locations, syngas production from natural gas occurs
via the Johnson Matthey (JM)/Davy Process Technology (Davy) combined reforming
process, a combination of primary steam reforming and oxygen-assisted autothermal
reforming. Part of the natural gas feedstock passes directly to the autothermal
reformer (ATR), and the remainder is mixed with steam and recycle gases before
passing to the CRG prereformer for the conversion of heavier hydrocarbons to
methane and the partial reforming of the feedstock. Addition of steam and further
heating are completed before the mixed gas passes to the primary steam methane
reformer (SMR), a conventional, down-fired, tubular reformer. The partially reformed
gas leaving the SMR is mixed with natural gas before passing to the ATR, where they
are partially combusted with oxygen and then reformed over a fixed catalyst bed to
provide low-methane syngas.
For remote and offshore locations, a compact reformer is employed downstream
of the CRG prereformer to produce the synthesis gas. The Davy/BP compact reformer
is a multi-tubular, counter-current reactor containing nickel catalyst in the tubes. Heat
for this endothermic reaction is provided by external firing of excess hydrogen (H2 )
produced by the process, with supplementary natural gas as required. Gas leaving
the syngas generation unit is cooled (3), and it generates sufficient steam to satisfy
process heating requirements. Excess condensate is removed.
Dry syngas is compressed in a single-stage centrifugal compressor (in the
compact reformer flowsheet) (4) and passed to a membrane-separation package
(5), where the surplus H2 is recovered and reused as fuel. The non-permeate product
from the membrane separation is fed to the conversion section (6), where the syngas
is converted into a mixed paraffin and wax product using a cobalt catalyst. The
reaction system employs two or more stages of the Davy/BP fixed-bed FT technology.
Unconverted syngas is recycled to the syngas generation unit.

Tail gas recycle
Natural
gas feed

4

1

LPG
Natural gas fuel

2

5
3
H2 makeup

6

7

Synthetic
crude

Naphtha
8

Kerosine
Diesel

Condensate
Hydrogen fuel

The wax products from the conversion section can be hydrocracked to produce
a pumpable synthetic crude, using conventional hydrocracking technology (7).
The synthetic crude can be further distilled into discrete liquid fuels, such as LPG,
naphtha, kerosine and diesel (8).

Operating conditions: A wide range of reformer operating conditions are possible
to optimize the process efficiency.
Installations: The compact reformer and fixed-bed FT processes have been
successfully demonstrated at BP's test facility in Nikiski, Alaska. This facility
operated between 2003 and 2009. The Johnson Matthey/Davy combined reforming
technology has been successfully employed at the 3,600-metric-tpd EMethanex
methanol plant in Egypt.
Licensor: Johnson Matthey

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