The performance of a 30-kW gasifier–SOFC–GT system was evaluated using thermodynamic calculations. Nickel/Gadolinia Doped Ceria (Ni/GDC) anodes were utilized for Solid Oxide Fuel Cells (SOFCs). These systems can achieve high electrical efficiencies of above 50%. The goal of the study is to evaluate trends in system efficiency when carbon dioxide as a gasifier agent is increased in enhanced carbon dioxide system. Carbon dioxide content was increased in both systems, leading to variants of both systems as compositions changed until they could no longer function efficiently. The trends in system variants were monitored. Although the gross efficiency increased, the net efficiency of the enhanced carbon dioxide system dropped. Absorbed heat and delivered gross which deals with flow of energy in sources / sinks was lower in enhanced scheme. Auxiliary power consumed was higher in enhanced carbon dioxide system variants, indicating that the compressors consume more power. Delivered net power was dropping for the enhanced case variants. Enhanced carbon dioxide system variants seem to have a slightly higher total electrical efficiency by a close range of less than 1%.

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In our previous work (Part I), we evaluated the thermodynamic models of the biomass-fed integrated gasification solid oxide fuel cell system with a carbon capture and storage (BIGFC/CCS) unit. In this work (Part II), the techno-economic analysis of the proposed negative emission power plants is carried out. Levelized cost of electricity, net present value (NPV), payback period, internal rate of return (IRR), and levelized cost of negative carbon (LCNC) are the key economic parameters evaluated. The results of a series of sensitivity analysis show the impact of gasification agents and stepwise increase in biochar co-production on the performance of the system. The total overnight cost is estimated to be 6197 $/kW and 5567 $/kW for the air and steam-oxygen gasification BIGFC/CCS systems, respectively. Steam-oxygen gasification is found to be more economically beneficial than air gasification one for all of the cases studied. Economically viable biochar co-production cases are identified to ascertain the influence of capital cost, operating cost, biomass cost, plant capacity factor, and tax. Moreover, the effect of the carbon credit scenario on the economic indicators is also reported. The results show that the most effective economic performance from the steam-oxygen gasification case reported an NPV of $3542/M, an IRR of 24.2%, and a payback period of 3.3 years, with an LCNC of -322.5$/t of CO₂. Compiling the results from Part I and Part II shows that it is easier to achieve negative emission using the steam-oxygen gasification of a BIGFC/CCS system. These results are expected to be helpful for stakeholders in identifying appealing negative emissions power plant projects for near and long-term future investments.@en

This article is the first of a two-part series presenting the thermodynamic evaluation and techno-economics of developing negative-emission power plants. The aim of this research is to evaluate the potential of biochar co-production in negative-emission power plants based on biomass-fed integrated gasification solid oxide fuel cell systems with carbon capture and storage (BIGFC/CCS) units. The influence of two gasification agents, namely, air and steam-oxygen, on the proposed system is investigated. In Part I, we present the thermodynamic models. A sensitivity analysis is carried out to investigate the system response to stepwise increase in biochar co-production (up to 10% by weight). Providing a secondary oxy-combustor in the steam-oxygen gasification case has been shown to be a solution to meet the heat requirements of the allothermal gasification process. A comprehensive exergy analysis indicated significant efficiency improvement for the steam-oxygen gasification case. The results show that the biomass steam-oxygen gasification yields the higher electrical exergy efficiency (48.3%) and combined heat and power (CHP) exergy efficiency (54.6%) for the similar rates of biochar co-production. The specific power output per unit of CO₂ stored is 2.65 MW/(kg/s) and 3.58 MW/(kg/s) for the air and steam-oxygen gasification cases, respectively, when the biochar is co-produced at 10% by weight for the given biomass flow of 20 kg/s. Moreover, the total CO₂ stored due to the proposed system is calculated as 133.9 t/h, and it is estimated to remove 1.17 Mt of CO₂ from the atmosphere annually (when the biochar-based carbon storage is also considered). The models are used for the techno-economic analysis presented in Part II of the series.

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