Photo by Emelie Jikander GREEN GAS RESEARCH OUTLOOK

Transcription

1 Effects of steam pretreatment and co-production with ethanol on the energy efficiency and process economics of combined biogas, heat and electricity production from hemp GREEN GAS RESEARCH OUTLOOK ZSOLT BARTA 1, EMMA KREUGER 2, LOVISA BJÖRNSSON 3, PUBLISHED IN BIOTECHNOLOGY FOR BIOFUELS 2013, 6:56 1 BME, HUNGARY, 2 BIOTECHNOLOGY, LUND UNIVERSITY 3 LUND UNIVERSITY Photo by Emelie Jikander.

2 What can we expect from a technoeconomic study Solved mass and energy balances: can be done precisely Economic performance production cost Much more uncertain than the techno part What do we need for a successful techno-economic analysis? As much reliable data as possible Rules of thumb Reasonable assumptions Conservative design

3 Why did we choose hemp (Cannabis sativa L.) as feedstock? High biomass yield Outcompetes weeds Photo by Emma Kreuger. Photo by Emelie Jikander. Slide made by Emma Kreuger.

4 Based on previous experimental studies t DM/year AD SP AD Et AD Et AD+ Cultivation: Civ. eng. Sven-Erik Svensson Dr. Thomas Prade Pretreatment and ethanol production: Dr. Zsolt Barta, Dr. Bálint Sipos, Prof. Guido Zacchi. AD-R SP AD-R Biogas: Dr. Emma Kreuger Prof. Lovisa Björnsson Sipos B. et al. 2010, Kreuger E. et al. 2011, Prade T. et al Slide made by Emma Kreuger.

5 Reactor technology in anaerobic digestion after the ethanol process Biogas Effluent Biogas Feed Effluent Feed Continuous stirred tank reactor (CSTR) 30 d hydraulic retention time Microbial biomass in the effluent 5 kg DM/(m3 x d), low degradability Sludge granules Upflow anaerobic sludge blanket (UASB) 1.5 d hydraulic retention time Microbial biomass retained 24 kg DM/(m3 x d)

6 Methodology summary Experimental data Aspen Plus Mass & energy balances Thermodynamic calculations Aspen Energy Analyzer (Pinch technology) Heat exchanger network optimization Vendor quotations Aspen Process Economic Evaluator Sizing & cost estimation of process equipment Excel model Production cost

7 What questions did we pose? Experimental energy yields: biogas < biogas after steam pretreatment < ethanol + biogas Questions: What are the overall process energy efficiencies, including electricity and district heat? What are the capital-intensive areas of the process? What are the main cost contributors? Does the steam pretreatment prior to anaerobic digestion pay off? Can we say that combined ethanol and biogas production is better/worse than standalone biogas production?

8 LHV energy efficiency (%) Energy efficiencies based on lower heating values (LHV) Ethanol Biomethane Electricity District heat AD AD-R SP-AD SP-AD-R Et-AD Et-UASB

9 Total direct cost D ir e c t c o s t ( m i ll i o n S w e d i s h K r o n o r ) 1000 Heat exchanger network Storage Combined heat and power Separation Anaerobic digestion Distillation Sim. sacch. and fermentation Pretreatment Feedstock handling AD AD-R SP-AD SP-AD-R Et-AD Et-UASB Direct costs are the costs of major and auxiliary equipments 1 US$ = 6.8 Swedish Kronor (SEK), 1 = 8.9 SEK

10 Capital investment Capital cost (million SwedishKronor) Fixed capital - Direct Fixed capital - Indirect Working capital AD AD-R SP-AD SP-AD-R Et-AD Et-UASB

11 Annual cash flow 800 MSEK/year Cost Income Deficit AD Slide made by Emma Kreuger. SP-AD Et-AD+

12 MSEK/year Annual cash flow Slide made by Emma Kreuger. Cost Income Deficit

13 Annual cash flows higher resolution 800 Annual costs (+) and incomes (-) in million Swedish Kronor Others 600 Utilities Enzymes 400 Chemicals 200 Capital Feedstock 0 District heat -200 Electricity Biomethane -400 Ethanol -600 AD AD-R SP-AD SP-AD-R Et-AD Et-UASB 13

14 Biomethane production cost (Swedish Kronor/MWh) Sensitivity analysis % AD -20% AD-R 1000 SP-AD SP-AD-R 500 Et-AD Et-UASB (wood) Feedstock price (Swedish Kronor/dry tonne)

15 Results and conclusions High energy outputs 60-84% of input were achieved Biofuel production from hemp is currently too expensive in Sweden Feed stock cost need to be reduced with 1/2 or all costs with 1/3 to reach viability Combined ethanol and biogas production had larger investments and operating costs than biogas production alone but the higher price was compensated by a higher income and the annual cash balance was equal The application of steam pretreatment prior AD changed the deficit with less than 10% Fractionation of the stillage (low TS) for digestion of the liquid in UASB instead of CSTR decreased the cost for AD drastically Fractionation of the residue and recycling of process water does improve the result if it results in a higher methane yield

16 Hemp can also be used for other things Hemp is too expensive for biofuel production in Sweden However, it has many other applications: -ropes, textiles -composites -cosmetics, soap -food applications After producing these value-added products, the residue (e.g. hemp hurds) can be used for biofuel production (Barta Z. et al. 2010).

17 Acknowledgements The Swedish Knowledge Centre for Renewable Transportation Fuels The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning This work is connected to the scientific program of the Development of quality-oriented and harmonized R+D+I strategy and functional model at BME" project. This project is supported by the New Hungary Development Plan (Project ID: TÁMOP4.2.1/B-09/1/KMR ) The Hungarian National Research Fund (OTKA-K72710) Thanks to Prof Guido Zacchi, Dr. Robbert Kleerebezem and Dr Mikael Lantz for advices and to Läckeby water group for information on prices and energy demands.

18 Budapest University of Technology and Economics. Lund University (Wikimedia, by Francois Polito) Thank you for your attention! Please cite this work as: Barta Z., Kreuger E., Björnsson L. Biotechnology for biofuels 2013, 6:56