At the inlet of the HT-WGS reactor, water has been added
in different concentrations, as functions of temperature and
steam to biomass gasification ratio. In this way, the hydrogen
conversion efficiency was further improved by increasing the
HER from 87%, at the catalytic filter candle outlet, to 99%, at
the WGS reactors outlet, as obtained by simulations at 850 C
and S/B ¼ 2. The dry product gas from the WGS reactors (at
800 C and S/B ¼ 0.5) is characterized by a calculated composition
of 62% H2, 6%CH4, 0.4% CO and 31% CO2 (by volume), in
line with results reported in the literature [51] with a corresponding
gas yield of 1.8 Nm3/kg daf biomass.
The aim of this work is to check the possibility to reach a
hydrogen conversion chemical efficiency of about 66%
without input of auxiliary fuel, by exploiting off gas and waste
heat recovery loops. The hydrogen chemical efficiency,
calculated by (12), of the whole plant is shown below (Fig. 5) as
a function of the steam to biomass ratio and varying the
operating temperature [51]. The PSA unit is assumed to
operate at a pressure of 7 bar.
The hydrogen chemical efficiency always increases with
the gasification temperature: at 850 C the gasification reaction
rates are greater than at lower temperature. Moreover,