SYNTHESIS GAS UTILIZATION FOR TRANSPORTATION FUEL PRODUCTION - Biomass as a Sustainable Energy Source for the Future - page 536

SNG is closely related to FTS. There is already quite some experience from the
production of SNG from coal. This makes it possible to quickly implement this tech-
nology to convert biomass into biofuel. Moreover, it has the advantage that the gas
produced this way can be easily incorporated in the existing fuel distribution infra-
structure: it can be mixed into the existing natural gas networks for applications such
as household heating or to fuel cars as is done with compressed natural gas.
SNG synthesis could be seen as FTS with a very low -value; whereas in FTS an

important aim is to minimize the methane production, in SNG synthesis, one wants to
maximize it. Thus, the main reaction, referred to as methanation, is

α

mol −1

3H 2 +CO CH 4 +H 2 O Δ r H = − 206 kJ ð RX : 17 : 3 Þ

⇄

Just like FTS, this reaction is strongly exothermal, making good heat removal a
key issue in reactor design. Two main reactor concepts have been proven suitable
for the production of SNG, namely, a series of adiabatic fixed bed reactors with
intermediate cooling and/or gas recycle and fluidized bed reactors (Kopyscinski
et al., 2010).
While in FTS for the production of liquid fuels the temperature must not be too
high because of the desire to minimize the production of methane, in methanation,
higher reaction temperatures can be used, typically 520 − 770 K. Pressures can vary

widely, but are typically in the range of 20 70 bar. However, operation close to atmos-

pheric pressure is also possible. Methanation reactors are normally not fed with syn-
gas, but with producer gas: a mixture containing mainly H 2 , CO, CO 2 ,H 2 O, and CH 4 .
Nickel is the most widely used catalyst for this reaction, due to its selectivity, activity,
and price. However, nickel-based catalysts are very vulnerable to catalyst poisons
such as sulfur species (e.g., H 2 S, COS, organic sulfur) and chlorine (Kopyscinski
et al., 2010). The equilibrium reaction given in (RX. 17.3) is strongly on the right
and nearly full conversion can be reached.
The first commercial plant for the production of SNG from coal, the Great Plains
Synfuels Plant, is located in North Dakota (United States). It was commissioned in
1984 and converts 18,000 t

-

day −1 of lignite coal into 4.8 million m 3 SNG. The metha-
nation takes place in two adiabatic fixed bed reactors in series with internal recycle,
the so-called Lurgi process (Kopyscinski et al., 2010). Today, more coal to SNG
plants are planned, especially in China.
From a sustainability point of view, it would be attractive to use biomass for the
production of SNG. The challenges of using biomass instead of coal arise from the
different chemical composition and different kind of impurities in the producer gas
such as organic sulfur and from the smaller unit size (Kopyscinski et al., 2010).
SNG production from syngas is not yet commercially applied. Worldwide, three
research centers are the main players in SNG R&D: the Energy Research Centre of
the Netherlands (ECN), the Centre for Solar Energy and Hydrogen Research
(ZSW, Germany), and the Paul Scherrer Institute (PSI, Switzerland). Currently, the
first plant to produce SNG is being built in Gothenburg, Sweden (tinyurl.com/
pfc2ggu). An experimental 20 MW plant was started up in 2013 and a commercial
80 − 100 MW plant should be ready in 2016.