(96c) Conceptual Design and Cost Estimation of an Offshore Autonomous Once-through Gas-to-Liquid Process Combined with Ammonia Synthesis

Conceptual design and cost estimation
of an offshore autonomous once-through gas-to-liquid process combined with
ammonia synthesis

A novel process concept is proposed for converting natural gas to
liquid Fischer-Tropsch products and ammonia (Figure1). An autothermal reformer
with enriched air as oxidant is applied for synthesis gas (syngas) production,
and because of the inert nitrogen a once-through Fischer-Tropsch synthesis is
the preferred option. In order to maximize the syngas conversion and the production
of heavy hydrocarbons, a staged reactor path with distributed hydrogen feed and
product withdraw is proposed. The hydrogen is produced by steam methane
reforming in a heat exchange reformer (gas heated reformer), heat integrated
with the hot effluent stream from the autothermal reformer. The nitrogen needed
for ammonia synthesis is produced from air membrane. Tail gas from the last
Fischer-Tropsch stage is sent to a gas turbine for power production. The hot
exhaust gas from the gas turbine is used for natural gas preheating. The
process is autonomous in the sense that it is self-sufficient with power and
water, and therefore well suited for production in remote locations such as a
floating production unit. The process concept is simple and inexpensive since
cryogenic air separation and fired heaters are not required. For the
Fisher-Tropsch synthesis microchannel reactors are considered.  Cost evaluation
is carried out to find out the economic feasibility of the process.

Figure 1: Block flow
diagram of the proposed process concept; water and steam are not shown