Abstract
Energy storage from renewable sources is
maybe the main issues for the energy sector. Hydrogen seems to be the more
compact, flexible and clean solution. However a complete replacement of fossil
fuels with hydrogen will probably require some decades. Therefore a bridge
solution which concentrates investments on renewable hydrogen production is
desirable.
A first solution could be the direct
injection of hydrogen into the existing natural gas pipeline. A further way to
increase the need for renewable hydrogen bypassing the problem of its
distribution is the production of a substitute of natural gas.
If the power excess is due to lack of
demand, biomass could be gasified with electrolytic hydrogen to generate
directly a gas rich in methane. After water condensation such a gas could be
fed to a methanation process to convert almost completely carbon in methane.
Hydrogasification and methanation are exothermic processes: the heat
recoverable could be used for thermal application or to supply extra power to
the electrolyser.
If the power excess is due to problems
of grid stability, biomass could be gasified with electrolytic oxygen and the
syngas could be fed, together with other electrolytic oxygen, to a power unit.
The power units considered are steam and gas turbines, internal combustion
engines and high temperature fuel cells. The exhaust gas is composed almost
exclusively by CO2 and H2O. After water condensation, CO2
could be fed together electrolytic hydrogen to a methanation process to obtain
the substitute of natural gas. Heat from exhaust gas cooling and from methanation
process could be recovered to generate power suitable for imput into the grid.
In all cases the input is low value
energy (biomass and electric power which cannot be absorbed by the grid) and
the output is high value energy (substitute of natural gas and eventually
stable electric power).