This study investigates the technical feasibility of onboard
carbon capture in vehicles. In fact there are two different main
concepts of hybrid electric vehicles with batteries and range
extenders proposed. The first concept uses an Internal Combustion
Engine as range extender. Carbon dioxide is separated from the flue
gas of this Internal Combustion Engine by chemical or physical
absorption. In the second concept a solid oxide fuel cell (SOFC) is
used as a range extender. The CO remaining in the anode exhaust gas
is not combusted as usual by mixing anode and cathode exhaust gases
but shifted with water vapor, sufficient available in the anode
exhaust gas flow, to H₂ and CO₂. The H₂ is separated by a membrane
permeable only for H₂ and recycled by the methane flow to the SOFC
stack. Carbon dioxide can then be separated by simply condensing
the water vapor of the anode exhaust gas of the SOFC.
Carbon dioxide can either remain onboard chemically bonded,
e.g., as carbonate with the absorption media or stored in a
pressure vessel after desorption or condensation of the water
vapor. As one mole methane produces one mole CO₂, the CO₂ can be
stored in one chamber of a double chamber tank. The tank is, e.g.,
divided into two chambers with variable volume by a non-permeable
but flexible membrane; on the other side of this membrane methane
is stored. At the gasoline station the empty methane chamber is
filled with new methane and the CO₂ is discharged simultaneously
providing also simple fueling and CO₂ removal methods. Carbonate
can also be disposed at the gasoline station and calcinated in
centralized plants, i.e., CO₂ can be separated and CaO reused.
Furthermore all concepts are compared in fuel efficiency and
general feasibility. The SOFC concept seems to be the most
attractive one, because it shows the highest efficiency, uses the
simplest CO₂ capture concept and releases the captured CO₂ in
gaseous state, providing the simplest CO₂ discharging method.
