Download Stage 1 Stage 2 Gas separator Gas separator H2 + CO2 H2 + CO2

FEASIBILITY OF BIOLOGICAL HYDROGEN PRODUCTION FROM BIOMASS
FOR UTILIZATION IN FUEL CELLS
P.A.M. Claassen 1), J.W. van Groenestijn 2), A.J.H. Janssen 3), E.W.J. van Niel 4), R.H. Wijffels 5)
1)
ATO-DLO; P.O. Box 17, 6700 AA Wageningen, The Netherlands
2)
TNO-MEP; P.O. Box 342, 7300 AH Apeldoorn, The Netherlands
3)
Paques Bio Systems bv.; P.O. Box 52, 8560 AB Balk, The Netherlands
4)
WAU, Lab Microbiology; Hesselink van Suchtelenweg 4, 6703 CT Wageningen, The Netherlands
5)
WAU, Food and Bioprocess Engineering Group; P.O. Box 8129, 6700 EV Wageningen, The Netherlands
Ph: 31.317.475325, Fax 31.317.475347, e-mail: [email protected]
ABSTRACT: The utilization of hydrogen in fuel cells is gaining worldwide interest. To meet the requirements for CO2
reduction, this hydrogen needs to be produced in a sustainable way. The biological production of hydrogen (BHP) from
biomass offers an opportunity to produce, decentrally, hydrogen from renewable resources.
In natural environments, hydrogen is produced concomittantly with the anaerobic conversion of organic matter to volatile
acids. However, as this hydrogen is consumed by methane producing bacteria, it remains unnoticed and unavailable. The
objective of microbial hydrogen production from biomass is, firstly, to uncouple hydrogen production from methanogenesis
by using (hyper)thermophilic bacteria. Secondly, the hydrogen stored in the produced volatile acids, e.g. acetic acid, is
recovered by using photofermentative bacteria in the presence of light. These fermentations will be coupled to make a
bioprocess (Fig. 1) in which the complete conversion of glucose to 12 mole hydrogen and 6 mole CO2 is established.
Aim and approach:
The aim of this project was to (i) establish the ability to
efficiently produce hydrogen from organic matter using
both
(hyper)thermophilic
and
photoheterotrophic
microorganisms and (ii) to provide an estimate concerning
the economical, ecological and technological feasibility of
this process.
Firstly, several strains of microorganisms were tested with
respect to hydrogen production from sugars, hydrolysate
from domestic organic waste and, when supplemented with
light, from organic acids. Secondly, a desk study was
performed to estimate the energy consumption and final
cost of hydrogen from this process in case of production on
a small-scale of approximately 500 m3 H2/h (equivalent to
39 kg/h), or 312 tonne H2 /year.
Experimental results:
The highest productivity of the tested (hyper)thermophilic
microorganisms, Thermotoga elfii, Caldicellulosiruptor
saccharolyticus and own isolates from hot springs, when
grown on sugars, was 0.01 g H2/L.h achieving a 100 %
conversion efficiency of sugars to hydrogen, CO2 and
acetate. The highest productivity of the photoheterotrophic
microorganisms, all Rhodopseudomonas spp., was 0.006 g
H2/L.h achieving a 70 % conversion efficiency of organic
acids to hydrogen. Both rates were the highest ever
recorded in each of their categories.
(Hyper)thermophilic microorganisms were shown to
convert sugars in hydrolysate from domestic organic waste
to hydrogen. The inhibiting effect of hydrogen on
production by (hyper)thermophilic microorganisms,
expressed as the partial hydrogen pressure, was extended
Gas separator
H2 + CO2
N2
BIOMASS
Gas separator
H2 + CO2
H2 + CO2
carbohydrates
organic acids
organic acids
Stage 1
Fig. 1
H2
LIGHT
Stage 2
Production of hydrogen from biomass in a 2 stage fermentation.
Stage 1 is for (hyper)thermophilic fermentation and stage 2 for the photoheterotrophic fermentation.
CO 2
from 1000 Pa (1,2,3) to over 10 000 Pa.
Desk study results:
The conversion of biomass to fermentable feedstock was
done using extrusion. The yield of feedstock was set at 400
g/kg dry biomass. Thus, for a production of 500 m3 H2/h,
the extrusion of 1013 kg biomass/h is required. The
bioprocess for the production of 500 m3 H2/h, consisting of
a (hyper)thermophilic fermentation followed by a
photoheterotrophic fermentation utilizing sunlight required
bioreactors of 95 and 300 m3, respectively. For hydrogen
recovery from the thermo-bioreactor, a recovery system
employing stripping was proposed, to prevent inhibition of
the (hyper)thermophilic microorganisms by the hydrogen.
Table 1
Investment costs for installations required for a
BHP process aimed at the production of 500 m3
H2/h or 312 tonne H2/year, from biomass.
The cost estimations were done using the calculation
programme Aspen Plus with the electrolyte-NRTLthermodynamic model. The contribution of the investment
costs and energy demand of the separate steps on the
production costs of hydrogen from biomass at zero value is
shown in Tables 1 and 2.
The data shown in Tables 1 and 2 result in an estimated
cost of EURO 2.74 /kg H2 , equivalent to 21 EURO ct/m3
H2 or, when this hydrogen is used in a fuel cell to generate
electricity (at 50 % conversion efficiency), 16 EURO
ct/kWh. The final cost estimation is based on free
availability of biomass, no hydrolysis costs and excludes
personnel costs, which are all potential cost factors. On the
other hand, process units have been considered separately,
thus precluding the opportunity to couple technical devices
and energy requiring and energy yielding units. For
comparative purposes, current cost prices for hydrogen
from small-scale production plants are presented in Table
3.
Table 3
Item
Investment
costs
Extruder
Bioreactors,
pumps etc.
Sun collector
Equipment
H2 recovery
thermobioreactor
Equipment
H2 recovery
photobioreactor
Total:
Table 2
Cost/kg
H2
(EURO)
1 045 455
Annual
capital
costs
(15%)
(EURO)
156 818
1 295 455
811 064
194 318
121 660
0.62
0.39
403 182
60 509
Technology
(EURO)
0.50
0.20
196 803
29 520
0.10
3 751 959
562 825
1.81
Energy consumption in installations required for
a BHP process aimed at the production of 500
m3 H2/h or 312 tonne H2 /year, from biomass.
Energy costs were based on 6.8 EURO ct/kWh.
Item
Extruder
Bioreactors
Recovery H2
thermobioreactor
Recovery H2
photobioreactor
Purification H2
Total:
Cost prices for hydrogen produced in smallscale installations at 100 – 1000 m3 H2/h
Energy
(GJ/h)
Cost/year
(EURO)
0.547
0.842
82 879
127 576
Cost/kg
H2
(EURO)
0.26
0.41
0.225
34 030
0.11
0.281
42 545
0.14
0.010
1.90
1 515
288 545
0.01
0.93
Steam-reforming of natural
gas
Electrolysis with conventional
electricity
Electrolysis with CO2-lean
electricity
BHP process from biomass
(estimate)
Steam-reforming of
biomethane
Electrolysis with wind energy
Electrolysis with photovoltaic
cells
Costs
(EURO
ct /m3
H2)
32
CO 2emission
(kg /m3
H2)
0.8
23
1.8
27-36
0
21
0
32
0
25
295
0
0
Besides the final cost of the produced hydrogen, the energy
balance of the BHP process has been considered. The
production of 500 m3 H2/h is equivalent to an energy
production of 4.72 GJ/h. The energy required for this
production is estimated at 1.90 GJ/h. Hence, a net energy
production in the form of hydrogen of 2.82 GJ/h is
obtained from 1013 kg biomass.
When the gross energy production is considered, together
with the presently available amount of compostable organic
waste in The Netherlands (2.7 million tonne/year; VAM,
1998) the BHP process is estimated to produce 12.6
PJ/year. The utilisation of hydrogen for the replacement of
coal in energy production will enable avoiding the annual
production of 1.1 Mtonne CO2, amounting to more than 4
% of the objective of the Dutch government for the year
2010.
Future research:
The mobilisation of fermentable feedstock from biomass is
an important bottleneck for every biofuel process,
including the BHP process (3). This is a technological
problem which can be solved by further development of
extrusion techniques to realise an efficiency of at least 60
% instead of 40 %. Besides increasing mobilisation, new
extrusion techniques may be developed to recover nonfermentable side-streams, such as lignin, with a value of
their own. The improved mobilisation will increase the
yield of hydrogen from biomass and hence the net energy
gain in the BHP process.
To meet the production of 500 m3 H2/h the volumetric
productivity of the (hyper)thermophilic fermentation has to
be increased by a factor of 10. This can be done by
conventional methods such as optimisation of culture
conditions and biomass retention. The sensitivity for
hydrogen is shown to have a major impact on the cost of
hydrogen recovery. The selection of new strains with
increased hydrogen tolerance will severely decrease the
costs involved in hydrogen recovery.
The productivity of the photoheterotrophic fermentation
has to be increased by a factor of 15. In this case the main
improvement has to come from technological
developments in improved illumination systems for more
efficient light transfer.
The energy requirement and investment costs of the
complete BHP process are substantial. This is partly due to
the fact that the biomass pretreatment, the fermentations
and the H2 recovery have been considered separately. The
integration of the separate units will enable savings on
energy consumption and the manifold application of
equipment in coupled process units.
Finally, other products in this bioprocess such as new
thermostable proteins from the first fermentation, new
secondary
metabolites
(vitamins)
from
the
photoheterotrophic fermentation, and even clean carbon
dioxide, produced on site, may find their own application
and thus contribute to making the BHP process
economically, ecologically and technologically viable.
Conclusion:
(Hyper)thermophilic and photoheterotrophic bacteria
produce hydrogen from biomass derived feedstock at
nearly theoretically possible efficiencies. The calculation of
costs encountered when running a small-scale hydrogen
producing plant shows a final cost price for hydrogen
which remains within the range of other sustainable
hydrogen producing processes. Hydrogen production by
bacteria from biomass in decentralized small-scale
production facilities seems a realistic approach to provide
fuel which is suited for utilisation in fuel cells.
Acknowledgements:
This project has been sponsored by the Dutch Ministries of
Economical Affairs, Physical Planning, Housing and
Environment, and Education, Culture and Science within
the programme EET. Additional funding has been provided
by the EU in the programme Quality of Life and
Management of Living Resources (Project: Biohydrogen
QLK5-1999-01267)
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1.
Kelly R.M. (1988) Growth and gas production by the
hyperthermophilic
archaebacterium,
Pyrococcus
furiosus. Biotech. Bioeng. 32:438-444
2.
Schäfer T., Schönheit P. (1991) Pyruvate metabolism
of the hyperthermophilic archaebacterium Pyrococcus
furiosus. Acetate formation from acetyl-CoA and ATP
synthesis are catalysed by an acetyl-CoA synthetase
(ADP-forming). Arch. Microbiol. 155:366-377
3.
Schröder C., Selig M., Schönheit P. (1994) Glucose
fermentation to acetate, CO2 and H2 in the anaerobic
hyperthermophilic eubacterium Thermotoga maritima:
involvement of the Embden-Meyerhof Pathway. Arch.
Microbiol. 161:460-470
4.
Claassen P.A.M., J.B. van Lier, A.M. Lopez
Contreras, E.W.J. van Niel, L. Sijtsma, A.J.M. Stams,
S.S. de Vries and R.A. Weusthuis (1999). Utilisation
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