Gasification gas was also sampled to determine tar content
using CEN/TS 15439:2006 Standard. The solvent isopropanol (2-
propanol) was used for tar collection. The homogeneous liquid
sampled was evaporated under well-defined conditions and the
evaporation residue was weighed to calculate the amount of tar
in g/Nm3 (CEN/TS 15439:2006). Gasification gas was also sampled
to determine H2S and NH3 contents. Besides H2S, some other sulphur
compounds may be found in syngas, however, as around
95% of the gaseous sulphur appeared as H2S, only this compound
was analysed in gasification gas. Several nitrogen gaseous compounds
may be formed during gasification. The formation of HCN
may occur, but in much lower contents than NH3. NOx is not usually
released, due to the reduction conditions used during gasification.
Therefore, only the content of NH3 was measured in
gasification gas.
H2S was analysed by method 11 of EPA (Environmental Protection
Agency). Sulphide was retained in an absorbing solution of
CdSO4 and then analysed by iodometry. Sulphur held in the condensation
system was also analysed, as SO4 2, using Capillary Ion
Electrophoresis. NH3 was analysed according to the method
CTM-027 of EPA. Ammonia was retained in an acidic absorbing
solution of H2SO4 0.1 N and then analysed potentiometrically with
a specific ion electrode.
After each experiment, solid bed residue, containing silica sand,
ashes and unconverted carbon, was collected and analysed. Silica
sand was separated from the remaining solids and char content
was determined.