Increasing the efficiency of chemical looping combustion of biomass by a dual-stage fuel reactor design to reduce carbon capture costs

Improving the oxygen demand in biomass CLC using manganese ores

Chemical Looping for Energy Technology: A Special Issue

Life cycle assessment of power-to-methane systems with CO2 supplied by the chemical looping combustion of biomass

Chemical looping combustion (CLC) of biomass has the potential to improve the electrical efficiency in power plants that utilize carbon capture and storage (CCS). This is attributed to the mild corrosive environment anticipated in the air reactor (AR). However, previous studies have measured alkali emissions in the AR, likely in the form of KOH(g), suggesting that alkali may transfer from the fuel reactor (FR) to the AR. To investigate the corrosive effect of KOH(g) release in the AR, a novel experimental set-up was developed to simulate two scenarios for the AR 1) Clean scenario: no release of KOH(g) in the AR (5 % O2 + 3 % H2O + N2 bal.) and 2) Alkali slip scenario: continuous release of KOH(g) in the AR (5 % O2 + 3 % H2O + N2 bal. + 16 ppm KOH(g)). The exposure was carried out at 700 °C and six alloys, relevant as superheater material, ranging from stainless steels to nickel-base (Ni-base) alloys as well as a FeCrAl alloy were investigated. The samples were exposed for a total of 168 h and the morphology of the corrosion products was investigated using SEM-EDX and XRD. The presented results suggest that KOH(g) significantly accelerates the corrosion of the stainless steels and Ni-base alloys investigated, by rapidly destroying the protective Cr-rich oxide scale, resulting in the formation of a multilayer oxide scale with inferior protective properties. On the contrary, the FeCrAl alloy retained a protective Al-rich oxide scale irrespective of the presence of KOH(g). The findings in this study highlight that the release of KOH(g) in the AR during combustion of biomass in CLC could introduce corrosion challenges for installed superheaters that can be significantly mitigated by utilizing FeCrAl alloys.

10 - Fundamentals of chemical looping combustion and introduction to CLC reactor design

This Thesis is concerned with chemical looping technologies for carbon capture and energy conversion of fossil fuels. In chemical looping, solid oxygen carriers are cyclically reduced and oxidised to aid reactions such as combustion, air separation, thermochemical splitting etc. Chemical looping combustion has been proven to be a cost-competitive solution for producing low carbon electricity. The caveat to advance this technology lies in the further improvements in efficiency and development of carriers with efficient oxygen release capacity. The research in this Thesis has three major directions aimed at developing chemical looping technologies: (a) to develop realistic models of CLC powerplants with advanced steam cycles, (b) to model novel chemical looping coupled supercritical CO2 cycles for ultrahigh efficiency power generation, and (c) to synthesise and test novel synthetic ternary oxides phase of ferrites in chemical looping CO2 capture and oxygen release. The coupling of chemical looping combustion of solid fuels with advanced steam-based power cycles, viz. supercritical, ultra-supercritical and advanced ultra-supercritical Rankine cycles was investigated in Chapter 4. The energy and exergy efficiencies of the various chemical looping combustion power plant configurations are compared against the reference plants without carbon capture. This work incorporates practical considerations for reactor design. With an upper operating temperature limit of 950 °C, the maximum efficiencies achievable by integrated gasification combined cycle chemical looping combustion (IGCC–CLC) and in situ gasification chemical looping combustion power plants (iG-CLC) are 41.3% and 41.5%, respectively. Overall, iG-CLC emerges as the most efficient CLC configuration. Comparing to an integrated gasification combined cycle without carbon capture, the energy efficiency penalties for capturing CO2 from iG-CLC coupled with subcritical, supercritical, ultra-supercritical or advanced ultra-supercritical steam cycles are 5.1%, 5.0%, 5.2% or 13.0%, respectively. The biomass-fired chemical looping combustion power plants also show low energy efficiency penalties (<2.5%) compared to the reference biomass power plants without CO2 capture. The modelling results suggest that chemical looping combustion will remain an attractive carbon capture technology for solid fuel power plants, in a future when supercritical steam turbines become the norm. Chapter 5 proposes a novel power cycle coupling the Allam cycle, which is a class of oxy-fuel combustion power cycles using supercritical CO2 (s-CO2) as the thermal fluid, with chemical looping air separation (CLAS) to achieve power generation with inherent capture of CO2. Compared to other conventional CO2 capture techniques, the Allam cycle stands out owing to its high fuel-to-electricity conversion efficiency (~55-59%), the elimination of the Rankine cycle and reduced physical footprint. A key source of energy penalty of Allam cycle comes from the air separation unit (ASU), which supplies pure oxygen via an energy intensive cryogenic process. The integration of CLAS system with the Allam cycle show that the Allam-chemical looping air separation (Allam-CLAS) process can achieve 56.04% net electrical efficiency with a 100% CO2 capture rate, when a Co3O4-based oxygen carrier is used. This is about 6% efficiency points higher than the Allam cycle coupled to a cryogenic ASU. The exergetic efficiency of the Allam-CLAS system driven by the Co3O4-CoO redox cycle is 57.13%, also more favourable than a conventional Allam-ASU system (with reported exergetic efficiency of 53.4%). The newly proposed Allam-CLAS power cycle in this thesis presents a highly efficient, and cost-competitive solution to generate zero-carbon electricity from natural gas. The performance of the oxygen carriers is vital to the overall CLC plant. It is also of utmost importance to develop oxygen carriers with multifunctional characteristics and high oxygen release capacities. In Chapter 6, the performance of two ternary oxides – Ba3Fe2O6 and Ba5Fe2O8 were investigated for chemical looping oxygen release and carbon dioxide capture. The structures of both barium ferrites were characterised because the relevant structural information is lacking in the literature. Temperature swing experiments in a TGA showed that Ba3Fe2O6 exhibits excellent recyclability and satisfactory chemical looping oxygen uncoupling (CLOU) activity. Reversible oxygen release and uptake was observed over temperature swing cycles between 550 and 950 °C. In comparison, Ba5Fe2O8 was less active for CLOU. On the other hand, Ba5Fe2O8 showed excellent performance in reversibly taking up CO2, with a CO2 capture capacity of ~7 wt% consistently over multiple CO2 capture cycles at 1000 °C. The evolution of the phase compositions of the two barium ferrites during CLOU and CO2 capture cycles was studied by in situ XRD at high temperatures in reactive gas environments. In summary, the work presented in this thesis has offered advancements to chemical looping technologies in the context of designing, optimising and understanding novel chemical looping processes and exploration of novel materials for chemical looping applications.

Comparative study of fuel-N and tar evolution in chemical looping combustion of biomass under both iG-CLC and CLOU modes

World depends on fossil fuel combustion for thermal energy generation. Fossil fuel combustion leads to the generation of CO2 and extinction of non-renewable resources. To meet the future energy demands replacement of existing technologies should take place in the view of large quantities of GHG’s emissions from fossil fuels and their extinction. Chemical looping combustion (CLC) is primarily a combustion technique with an inherent separation of CO2 from the flue gases. Due to its advantage of negativeCO2 emissions, chemical looping combustion got attention of many researchers since last one and half decade. Recent research advancements in the CLC provided a platform for further research and developments in chemical looping combustion of biomass. This paper reviewsthe CLC of biomass to present the overview of chemical looping combustion technology and its status of biomass utilization as a fuel in CLC reactors.

The unmixed combustion of biomass by chemical looping (Bio-CLC) has outstanding properties to produce energy by thermochemical conversion with CO2 capture at low economic and energetic costs as well as minimizing NOx emissions to the atmosphere. A detailed analysis of the experimental results during the biomass combustion in chemical looping combustion (CLC) units is useful to evaluate the Bio-CLC potential for future industrial up-scaling. This work compiles the results obtained during more than 500 h of combustion in the previous years at the Instituto de Carboquímica (ICB-CSIC). Different biomasses were burnt with several oxygen carriers in two singular CLC units. Critical key performance indicators, such as the CO2 capture rate and combustion efficiency, have been evaluated considering the combustion mode and the fluidization regime in the fuel reactor. Regarding the combustion mode, results by in situ gasification (iG-CLC) vs chemical looping with oxygen uncoupling (CLOU) are compared. As for the fluidization regime, it was bubbling in a 0.5 kWth CLC unit and circulating in a 50 kWth CLC unit. A methodical comparison of the results allows us to understand the fundamentals of the processes and to evaluate the different behaviors observed in each case. The operating conditions having major effects on the Bio-CLC performance were identified, as well as the operating conditions necessary to optimize the CO2 capture and the combustion efficiency. In addition, other issues are evaluated, such as the fate of fuel-N in a CLC process, the presence of tar compounds in the CO2 stream, or the interaction of ash compounds with the oxygen carrier particles. Finally, possible future actions are discussed to improve the performance of the Bio-CLC process as well as the possible development paths of new oxygen carriers.

This study discusses the potential corrosion of boiler materials in chemical-looping combustion (CLC) of biomass. The CLC of biomass has the potential to negative CO2 emission in heat and power production. Biomass fuels, however, typically contain compounds of alkali metals, especially potassium and chloride, which may lead to the corrosion of heat-transfer surfaces in the reactors. The influence of potassium-contaminated ilmenite bed material deposits on the corrosion of seven heat transfer materials used in the air and fuel reactors in CLC was studied using one-week lab-scale experiments. Samples with KCl and without any deposit were used as references. After the exposure, the cross-sectional surfaces of the metals were analyzed with SEM/EDX. The results suggested that potassium-contaminated ilmenite might lead to minor corrosion of all studied materials under the oxidizing conditions simulating the air reactor, i.e., 700 °C and dry air. Under reducing fuel reactor conditions, i.e., 450 °C and 550 °C and 50/50 CO2/H2O, corrosion was observed on ferritic steels, especially in the presence of HCl and with KCl deposit. In contrast, samples with uncontaminated and potassium-contaminated ilmenite deposits did not significantly differ from the samples without any deposit. Minor corrosion of ferritic steels was observed at 450 °C, while at 550 °C, the corrosion was more significant. The results suggested that ferritic steels are not suitable for the fuel reactor. Austenitic and nickel-based alloys did not corrode under the test conditions used in this work.

Chemical looping combustion of Victorian brown coal using Fe-based oxygen carriers

Chemical looping combustion (CLC) enables efficient combustion of hydrocarbon fuels while also producing a gas stream with high CO2 concentrations, suitable for carbon capture and storage (CCS). CLC of biomass in combination with CCS results in efficient removal of carbon dioxide from the atmosphere, i.e., negative emissions. However, biomass and waste-derived fuels can contain significant fractions of aggressive ash precursors, which can affect the operability and functionality of oxygen carriers. In this paper, the fate of common ash elements will be investigated thermodynamically in a system utilizing iron-based oxygen carriers: ilmenite and iron oxide. Multiphase, multicomponent equilibrium calculations were performed using databases from FACT and a user-defined database, with a specific focus on alkali (K and Na) and heavy metals (Cu, Zn, and Pb). A detailed and comprehensive comparison with available literature data from experimental investigations was performed, and compounds not available in the databases were identified. Due to a lack of thermodynamic data in the literature, thermodynamic properties for four compounds, K0.85Fe0.85Ti0.15O2, K0.4Fe0.4Ti0.6O2, KTi8O16, and KTi8O16.5, were obtained from first-principles calculations. The fate of ash elements is studied for CLC of three biomass and waste-derived solid fuels under relevant CLC conditions: 950 °C in the fuel reactor and 1050 °C in the air reactor. Results show that the choice of the oxygen carriers largely influences the behavior of the ash elements. Compared to CLC with iron oxide, ilmenite is more beneficial with respect to high-temperature corrosion since less potassium is released into the gas phase since the titanium content in ilmenite immobilizes both potassium and calcium. For both oxygen carriers, the most corrosive compounds are expected to leave with the gas in the fuel reactor, keeping the air reactor free from chlorides. It was found that the compound KTi8O16 is stable in reducing conditions and low potassium concentrations. This is in conformity with previous experimental data, where this phase has been identified in the interior of ilmenite particles used in oxygen carrier aided combustion of wood chips.

Limits to Paris compatibility of CO2 capture and utilization

A global scientific interest is observed for alternative utilization of biomass wastes in the context of circular economy. Transforming waste into biofuels is a sustainable solution for dealing with global environmental issues. This article reviews recent trends and the development of biomass waste combustion technologies for energy recovery. Not only the latest scientific progress on combustion processes but also several innovative advanced technologies, such as carbon capture and storage (BECCS) technologies, oxy-fuel combustion, and chemical looping combustion (CLC) are analyzed. More specifically, combustion technologies such as fixed bed combustion, bubbling fluidized bed combustion (BFBC), circulating fluidized bed combustion (CFBC), pulverized fuel combustion (PC), oxy-biomass combustion in pulverization systems (Oxy-PC), oxy-biomass combustion in Bubbling fluidized bed combustors (Oxy-BFB), oxy-biomass combustion in circulating fluidized bed systems (Oxy-CFB), and biomass chemical looping combustion (CLC) are analyzed. Advantages and limitations of each advanced combustion method are also discussed. In addition, recent applications of artificial intelligence (AI) and machine learning (ML) for optimizing bioenergy processes and mitigating greenhouse gas (GHGs) emissions are presented. The combination of these advanced combustion technologies (CCS/CLC) with intelligence tools (AI/ML) can lead to enhanced combustion efficiency, reduced secondary wastes, better waste management, and reduced emissions. This comprehensive analysis could assist scientists and decision-makers in choosing the appropriate sustainable advanced waste-to-energy (WtE) technology. More studies should be performed in advanced AI-based smart bioenergy production to optimize the best solution in alternative feedstocks, operating parameters, green nanomaterials, and zero emissions for enhanced plant performance and reduced environmental issues.

CO2 capture and utilization from supercritical coal direct chemical looping combustion power plant – Comprehensive analysis of different case studies