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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2.
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3.
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4.
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