4.14. A comparative analysis of the dual fired downdraft gasifier
with rotary kiln pyrolysis gasification
At 450 C, 67% of biomass is converted into a combustible gas,
using an externally heated rotary kiln [34]. In addition to pyrolysis
gas, this type of reactors produce char and tar. The fuel obtained
from rotary kiln reactors can be used for direct combustion in
furnaces. The pyrolyser gas, produced at lower temperature will
have higher impurities. An additional gas treatment system is
needed to convert the pyrolysis gas suitable to operate internal
combustion engines (ICE) or gas turbines (GT).
Higher heating value of 10.1 MJNm3 was obtained by a rotary
kiln pyrolysis gasifier, due high hydrogen content (34.8%) and
methane (8.5%) [35]. Decomposition of methane is quoted as above
750 C of the reactor temperature. The dual fired gasifier operates
at 1100 C and has methane content as 1%. In rotary kiln pyrolysis
gasifiers 32e67% of the biomass is converted into pyrolysis gas,
whereas in the dual fired gasifier more than 98% of the biomass is
converted into producer gas.
With an integrated pyrolysis regenerated plant, fuel wood is
converted into 32% of syngas, 30% of char, 38% of tar and water [36].
This paper emphasizes on the required gas quality to operate gas
turbine or IC engines, as the tar content should be less than
100 mg Nm3 and the dust content less than 50 mgNm3. This
paper reports, the best range of biomass to power generation efficiency
is 15e20% [36]. In the dual fired gasifier system, 98.5% of
biomass is converted into producer gas. Producer gas to the power
generation efficiency of the improved system is 28%. The clean gas
obtained from the dual fired system is having the tar content less
than 50 mgNm3 and zero dust, which satisfies the required gas
quality to run GT and ICE, as reported in Ref. [36].
4.15. Ease of operation and maintenance
Reduction of the impurities in rawgas increases the reliability of
the system, by reducing the maintenance cycle. Reduction of the
maintenance cycle will result in a reduction in the operating cost.
When the maintenance of the system is improved it also improves
the reliability of the system. A comparison of the maintenance
schedule of the gas cleaning equipment is presented in Table 11.
From the Table 11 it may be noted that the maintenance cycle of
reactor III is reduced by a factor of 5e8 in comparison to reactor I.
Wet scrubbers used for gas cleaning are completely eliminated by
using reactor III.
4.14. A comparative analysis of the dual fired downdraft gasifier
with rotary kiln pyrolysis gasification
At 450 C, 67% of biomass is converted into a combustible gas,
using an externally heated rotary kiln [34]. In addition to pyrolysis
gas, this type of reactors produce char and tar. The fuel obtained
from rotary kiln reactors can be used for direct combustion in
furnaces. The pyrolyser gas, produced at lower temperature will
have higher impurities. An additional gas treatment system is
needed to convert the pyrolysis gas suitable to operate internal
combustion engines (ICE) or gas turbines (GT).
Higher heating value of 10.1 MJNm3 was obtained by a rotary
kiln pyrolysis gasifier, due high hydrogen content (34.8%) and
methane (8.5%) [35]. Decomposition of methane is quoted as above
750 C of the reactor temperature. The dual fired gasifier operates
at 1100 C and has methane content as 1%. In rotary kiln pyrolysis
gasifiers 32e67% of the biomass is converted into pyrolysis gas,
whereas in the dual fired gasifier more than 98% of the biomass is
converted into producer gas.
With an integrated pyrolysis regenerated plant, fuel wood is
converted into 32% of syngas, 30% of char, 38% of tar and water [36].
This paper emphasizes on the required gas quality to operate gas
turbine or IC engines, as the tar content should be less than
100 mg Nm3 and the dust content less than 50 mgNm3. This
paper reports, the best range of biomass to power generation efficiency
is 15e20% [36]. In the dual fired gasifier system, 98.5% of
biomass is converted into producer gas. Producer gas to the power
generation efficiency of the improved system is 28%. The clean gas
obtained from the dual fired system is having the tar content less
than 50 mgNm3 and zero dust, which satisfies the required gas
quality to run GT and ICE, as reported in Ref. [36].
4.15. Ease of operation and maintenance
Reduction of the impurities in rawgas increases the reliability of
the system, by reducing the maintenance cycle. Reduction of the
maintenance cycle will result in a reduction in the operating cost.
When the maintenance of the system is improved it also improves
the reliability of the system. A comparison of the maintenance
schedule of the gas cleaning equipment is presented in Table 11.
From the Table 11 it may be noted that the maintenance cycle of
reactor III is reduced by a factor of 5e8 in comparison to reactor I.
Wet scrubbers used for gas cleaning are completely eliminated by
using reactor III.
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