Chemical Looping Combustion of Biomass: Thermodynamic

Abstract

The most bothersome challenge for sustaining life on Earth is global warming caused by greenhouse gas emissions. Most countries currently rely on coal as their principal fossil fuel source for electricity generation. Coal-fired power stations release significant amounts of greenhouse gases, making the power industry a key contributor to anthropogenic CO2 emissions. To successfully restrict global warming, a significant transition to renewable energy sources is required. Agricultural biomass might be a viable alternative to fossil fuels for low-capacity energy generation. This strategy not only minimizes reliance on fossil fuels, but it also acts as a dependable supplement to solar and wind energy during the off-season, solving both energy needs and waste management concerns at the same time. As a result, there is an urgent need to improve power generation capabilities utilizing biomass, which is a carbon-negative and renewable fuel. Furthermore, incorporating a CO2 capture unit into this technology has the potential to change it from carbon-neutral to carbon-negative, giving a sustainable solution to decreasing CO2 emissions. Chemical Looping Combustion (CLC) is a contemporary method in which fuels generate both heat and power without any carbon emissions. The CLC method is fundamentally based on merging oxy-combustion and pre-combustion capture techniques. This eliminates direct air participation in the combustion process. Metal oxide is used in fuel reactors to provide oxygen for combustion of the fuel while the air reactor oxidizes the reduced form of metal oxide. Hydrogen is widely employed in the petrochemical sector for the upgrading of fossil fuels and the production of ammonia and methanol. It is also an ecologically friendly energy source for transportation and electricity generation. The three reactor Biomass Direct Chemical Looping (BDCL) system is a particularly efficient alternative when seeking to co-produce power and hydrogen utilizing CLC technology. This study uses aspenONE v10.0 to synthesis and simulate CLC-based power plants and BDCL plants. A rigorous parametric study is undertaken to discover opportunities for improving overall plant performance. The range of plant variations studied within this project falls into the subsequent four categories: 1) Conventional BFPP without CO2 capture, 2) CLC based BFPP with power generation alone, 3) CLC based BFPP with hydrogen and power co generation, 4) CLC based BFPP with hydrogen and power co-generation coupled with CO2 utilization plant. The overall performances of these configurations are examined based on the v energy, exergy, and environmental analyses. The first objective of the thesis is addressed by conducting the performance evaluation and comparison of conventional and CLC based BFPP combined with an Organic Rankine Cycle (ORC) system. The proposed CLC based BFPP is extended for co-generation of hydrogen and power in the second objective of thesis. Furthermore, the utilization of the produced hydrogen and carbon dioxide for the synthesis of methane and ammonia is also explored. The third objective of the thesis is addressed by conducting the performance evaluation and comparison of CLC based biomass fired power plants with different oxygen carriers. The fourth objective of the thesis is focused on the experimental studies to synthesize and performance assessment of novel nanofibrous oxygen carriers. Based on the research findings, it can be concluded that CLC based BFPP configuration is energetically, exergetically and environmentally efficient compared to the conventional BFPP. Furthermore, the net energy and exergy efficiencies of the three-reactor CLC plant with hydrogen co-generation are found to be 33.72% and 28.99%, respectively. These efficiencies are greater by 12.13% and 10.43% compared to CLC based BFPP. Also, the CLC based plants integrated with methane and ammonia synthesis may not be a better choice for power production due to significant loss in energy. It is also revealed that the bimetallic oxygen carrier (10% CuO + 90% Fe2O3) is a better option for achieving high process efficiency without considerably inflating overall operational costs as iron ore is largely available in India at lower cost as compared to copper ore. During CLC experimental tests with gaseous fuel, it is evident that the Fe2O3/Al2O3 composite nanofibres are more resistant to thermal sintering than the nanoparticles. Hence, these nanostructured oxygen carriers could be a promising option for lengthy CLC operations. This study demonstrates the superiority of chemical looping combustion-based biomass fired power plant for CO2 capture coupled with the carbon dioxide utilization plant over the conventional plant. The outcome of this study can provide the basis for potential improvement of CLC based BFPP. Additionally, the findings show great promise and open the way for a new direction in the creation of nanostructured OCs capable of exhibiting extraordinary redox cyclic stability.