Hydrogen is reviewed as a possible new marine fuel, with emphasis on the challenges concerning sustainable production, on board use and safety and specifically the challenges concerning hydrogen storage.
The
process intensification possibilities of a gas–solid vortex
reactor have been studied for biomass fast pyrolysis using a combination
of experiments (particle image velocimetry) and non-reactive and reactive
three-dimensional computational fluid dynamics simulations. High centrifugal
forces (greater than 30g) are obtainable, which allows
for much higher slip velocities (>5 m s–1) and
more intense heat and mass transfer between phases, which could result
in higher selectivities of, for example, bio-oil production. Additionally,
the dense yet fluid nature of the bed allows for a relatively small
pressure drop across the bed (∼104 Pa). For the
reactive simulations, bio-oil yields of up to 70 wt % are achieved,
which is higher than reported in conventional fluidized beds across
the literature. Convective heat transfer coefficients between gas
and solid in the range of 600–700 W m–2 K–1 are observed, significantly higher than those obtained
in competitive reactor technologies. This is partly explained by reducing
undesirable gas–char contact times as a result of preferred
segregation of unwanted char particles toward the exhaust. Experimentally,
systematic char entrainment under simultaneous biomass–char
operation suggested possible process intensification and a so-called
“self-cleaning” tendency of vortex reactors.
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