University of Twente Student Theses
Techno-economic evaluation of a novel biomass pyrogasification process with an integrated sorption-shift system : a process for the conversion of waste to high-quality biochar and hydrogen with carbon capture and hydrogen upgrading
Buiteveld, J. (2021) Techno-economic evaluation of a novel biomass pyrogasification process with an integrated sorption-shift system : a process for the conversion of waste to high-quality biochar and hydrogen with carbon capture and hydrogen upgrading.
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| Abstract: | This thesis describes the development of a novel system that produces high-quality biochar and high-purity hydrogen out of biomass. The proposed system uses a combination of pyrolysis in an auger reactor, steam reforming, and a novel Sorption EnhancedWater Gas Shift (SEWGS) system based on Calcium Looping (CaL). This system uses calcium oxide (CaO) for CO2 capture and to shift theWater-Gas-Shift (WGS) reaction into the direction of hydrogen. A system parameter analysis identified key process parameters for optimal hydrogen/biochar production. Reactor temperature has been identified as the main key process parameter for the pyrolysis (¼600 °C) and steam-reforming system (¼750 °C), while system configuration is identified as the main key parameter for the sorption-shift system: a decoupled sorption-shift system can produce high purity hydrogen with H2 Vol % > 99.6%. The figure below displays the system configuration which is analysed in this research. An Aspen Plus model is constructed to simulate reactor stoichiometry, develop efficient heat integration, and for system analysis and evaluation. Results from the developed model are used for process optimization. The designed system operates at a reformer temperature of 750 °C, a final sorption shift temperature of 550 °C, and a Steam to Carbon (SC) ratio of 4.6 in the pre-reformer. Process simulations show an overall maximum energy efficiency of 74.9% based on chemical energy. High-quality biochar is produced: HHV=34.2 MJ/kg as well as high-quality hydrogen: 99.7% purity. Per ton of dry and ash-free biomass input (HHV = 18.0MJ/kg), the system produces 59 kg of hydrogen and 186 kg of biochar. A sensitivity analysis identified (pre-) reformer heating as the main bottleneck in the system. A financial model is constructed for the designed system based on cash-flow simulations. Biomass input cost and investment cost are identified as the main driver of hydrogen/biochar levelized cost of production. Heat exchanger size optimization is performed with respect to cost efficiency, resulting in a system with a levelized cost of hydrogen of e4.01 per kg combined with a levelized cost of biochar of e668 per ton. The optimized system with respect to cost efficiency has a thermal efficiency of 71.4 %. Subsidies are required for a profitable system. Compared to other sustainable high purity hydrogen production techniques, the designed system is compatible and produces high purity hydrogen at a significantly lower cost than hydrogen production by electrolysis. A societal analysis is performed which identified the analyzed technology as fittingwith future biomass-based policies of western European countries which focus on high quality bio-based raw materials. This analysis shows that there is sustainable biomass potential in Europe and the Netherlands for the developed technology. Biochar has many high-end applications, varying from pollutant removal from gases (activated carbon) to carbon sequestration (soil amendment). A model is designed for CO2 footprint calculations of the installation under operation, which shows a negativeCO2 footprint -1041 kgCO2 per ton of biomass input: the process has the potential to reverse globalwarming. Further process optimizations and development is recommended for a better understanding of CaL based SEWGS, especially for understanding Cal-based SEWGS kinetics. We wrote a research proposal for a (European) research project to further analyze SEWGS reactor mechanics. Upscaling of auger reactors for slow pyrolysis and implementing oxyfuel combustion for CaO regeneration are subjects that require further research. The oxy-fuel system is (shortly) analyzed, and shows a large future potential, especially in a combined process configuration with water electrolysis for hydrogen production. This research shows that a pyrogasification sorption enhanced water gas shift system can be a technical, economic, and societal feasible technology that delivers high-quality, sustainable products that fit the needs of the future sustainable economy. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Subject: | 43 environmental science, 52 mechanical engineering, 58 process technology |
| Programme: | Mechanical Engineering MSc (60439) |
| Link to this item: | https://purl.utwente.nl/essays/85770 |
| Export this item as: | BibTeX EndNote HTML Citation Reference Manager |
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