Effects of steam pretreatment and co-production with ethanol on the energy efficiency and process economics of combined biogas, heat and electricity production from industrial hemp

Biotechnology for Biofuels

Zsolt Barta³  Emma Kreuger¹  Lovisa Björnsson² 

[1] Biotechnology, Lund University, P.O. Box 124, Lund, SE-221 00, Sweden

[2] Environmental and Energy Systems Studies, Lund University, P.O. Box 118, Lund, SE-221 00, Sweden

[3] Department of Applied Biotechnology and Food Science, Budapest University of Technology and Economics, Szt. Gellérttér 4, Budapest, H-1111, Hungary

关键词: Modelling;    Simulation;    Process design;    Methane;    Economy;    Bioenergy;    Biofuel;    Energy crop;    Cannabis sativa L.;   

Others  :  798093
DOI  :  10.1186/1754-6834-6-56

 received in 2012-10-04, accepted in 2013-04-08,  发布年份 2013

【 摘 要 】

Background

The study presented here has used the commercial flow sheeting program Aspen Plus™ to evaluate techno-economic aspects of large-scale hemp-based processes for producing transportation fuels. The co-production of biogas, district heat and power from chopped and steam-pretreated hemp, and the co-production of ethanol, biogas, heat and power from steam-pretreated hemp were analysed. The analyses include assessments of heat demand, energy efficiency and process economics in terms of annual cash flows and minimum biogas and ethanol selling prices (MBSP and MESP).

Results

Producing biogas, heat and power from chopped hemp has the highest overall energy efficiency, 84% of the theoretical maximum (based on lower heating values), providing that the maximum capacity of district heat is delivered. The combined production of ethanol, biogas, heat and power has the highest energy efficiency (49%) if district heat is not produced. Neither the inclusion of steam pretreatment nor co-production with ethanol has a large impact on the MBSP. Ethanol is more expensive to produce than biogas is, but this is compensated for by its higher market price. None of the scenarios examined are economically viable, since the MBSP (EUR 103–128 per MWh) is higher than the market price of biogas (EUR 67 per MWh). The largest contribution to the cost is the cost of feedstock. Decreasing the retention time in the biogas process for low solids streams by partly replacing continuous stirred tank reactors by high-rate bioreactors decreases the MBSP. Also, recycling part of the liquid from the effluent from anaerobic digestion decreases the MBSP. The production and prices of methane and ethanol influence the process economics more than the production and prices of electricity and district heat.

Conclusions

To reduce the production cost of ethanol and biogas from biomass, the use of feedstocks that are cheaper than hemp, give higher output of ethanol and biogas, or combined production with higher value products are primarily suggested. Further, practical investigations on increased substrate concentration in biogas and ethanol production, recycling of the liquid in anaerobic digestion and separation of low solids flows into solid and a liquid fraction for improved reactor applications deserves further attention.

【 授权许可】

   
2013 Barta et al.; licensee BioMed Central Ltd.

【 图 表 】

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