182
The European Physical Journal D
Table 1. Comparison of the energy efficiency of hydrogen pro- 4 Conclusions
duction for different methods in which electric energy is di-
rectly used for methane conversion into hydrogen.
The results of this investigations show that the energetic
parameters of the hydrogen production, i.e. the hydrogen
production rate (866 g (H2) h−1) and the energy efficiency
(577 g (H2) kWh−1), via methane pyrolysis in the atmo-
spheric pressure microwave plasma are attractive.
Taking into account the energy losses in the microwave
power supply (∼33%), the energy efficiency of hydrogen
production reaches about 381 g (H2) kWh−1 of the total
electric energy used.
The proposed atmospheric pressure microwave plasma
system for hydrogen production via methane pyrolysis is
expected to be of low cost and effective, and thus promis-
ing for applications in the distributed hydrogen produc-
tion.
Hydrogen
Initial
Energetic
mass yield
(g (H2) kWh−1
production method composition
)
Conventional methods
Water electrolysis
H2O
21
Plasma methods
Waveguide-based
cylinder-type MPS
(this paper)
CH4
381∗
Waveguide-based
cylinder-type MPS
CH4 + N2
85
This research was supported by the Ministry of Science
and Higher Education (MNiSW) under the programme
3020/T02/2006/31.
Electron beam [9] CH4 + H2O
3.6
6.7
40
Dielectric barrier
CH4 + air
References
CH4 + H2O
+ air
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CH4 + H2O
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∗
total electric energy used.
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Comparing results presented in this paper with those
obtained by us when using nitrogen swirl with methane
introduced to plasma by the central duct (Tab. 1, [19])
one can see that we improved much the energy efficiency
of hydrogen production. The total methane decomposi-
tion degree, reaching 99.88%, was also much higher than
13.2% presented in [19]. We suppose that residence time
of methane in high temperature region is the reason of
such different results. When nitrogen swirl was used then
it cooled space in the plasma vicinity causing that high
temperature region was limited to plasma only. However,
when only methane was introduced into the reactor there
was no cooling gas and high temperature region expands
beyond plasma. As a result methane residence time in high
temperature region was much longer comparing to that in
the experiment with nitrogen swirl.
Considering both the cost of methane and the to-
tal energy consumption (including losses in power sup-
plies), nowadays, among the hydrogen production meth-
ods, it seems that the conventional steam reforming of
methane [28] ensures the lowest cost of hydrogen pro-
duction. However, the conventional steam reforming of
methane is a large volume hydrogen production method.
When the distributed hydrogen production method are
considered, the microwave plasma method presented in
this paper seems to be attractive.