Chemical Looping Combustion Of Biomass Research Articles

Corrosivity of KOH(g) towards superheater materials in a simulated air reactor environment for 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.

Investigation on the oxygen-carrying performance and reaction kinetics of CaMnxFe1−xO3−δ perovskites prepared from red mud

In this study, two Ca/Mn/Fe perovskite oxygen carriers (i.e., CaMn0.5Fe0.5O3−δ and CaMn0.75Fe0.25O3−δ, respectively) were prepared using red mud and two pure reagents to recycle the red mud for the chemical looping combustion of biomass. The oxygen uncoupling (OU) capacity and redox cycle characteristics of perovskites were examined by thermogravimetric analysis (TGA) under a gaseous (H2, O2, N2) environment. With the same Mn/Fe mole ratio, reagent-based perovskites exhibited a higher total oxygen transport capacity, while perovskites derived from red mud exhibited a better cycling stability. The addition of red mud did not affect the reactivity of perovskites. The curves of conversion level vs time revealed that two control mechanisms are involved in the reaction between oxygen carriers and gaseous compounds. That is, the oxidation kinetics of perovskite oxygen carriers were mainly controlled by a chemical reaction, while the reduction kinetics were controlled by a chemical reaction at a low conversion level, and with the increase in the reduction degree, gas diffusion through the solid product layer was enhanced. In addition, kinetic parameters of OU and redox were obtained, and the grain model was considered to be suitable to describe reduction and oxidation reactions.

Impact of Particle Size Polydispersity on Chemical Looping Combustion of Biomass under a Continuous Injection Mode

Particle size polydispersity considerably influences the chemical looping combustion (CLC) of solid fuels. In the present work, a three-dimensional multiphase particle-in-cell (MP-PIC) method was established and applied to study the full-loop CLC of biomass under a continuous injection mode. After model validation, the gas–solid flow characteristics, solid circulation rate (SCR), particle mixing in a fuel reactor (FR), and biomass leakage at different oxygen carrier (OC) particle size distribution (PSD) widths and biomass densities were systematically explored. The results showed that OC particles significantly stratified within the FR and both loop seals. Moreover, the fluctuation amplitude of the SCR decreased as the OC PSD width increased. Small biomass particles were more likely to leak. The number fraction of total leaked biomass particles first decreased and then increased as the OC PSD width increased. In the FR, small OC particles were primarily distributed in the upper part of the bed, and large particles were mainly distributed in the lower part. In addition, within the test range, the magnitude of the density difference between biomass and OC particles positively correlated with the likelihood of biomass leaking. These observations are all beneficial for the design and optimization of the CLC process of biomass.

Performance of a volatiles distributor equipped with internal baffles under different fluidization regimes

Chemical looping combustion of biomass is a promising carbon capture technology due to its inherent CO 2 separation advantage. However, complete fuel conversion, particularly volatiles conversion for biomass, is usually not achieved in the fuel reactor. A novel concept named volatiles distributor (VD) has been proposed and tested in a cold-flow fluidized-bed, which shows good potential to achieve a more uniform horizontal distribution of the volatiles and improve the gas-solid contact. In this work, the VD has been further developed by introducing an array of internal baffles inside the VD. The objective is to improve the horizontal gas distribution and reduce the volatiles slip from the bottom of the VD. The results show that the uniformity of the horizontal distribution is improved significantly by the VD equipped with the internal baffles, especially in the single and multiple bubble regimes. The volatiles slip from the bottom of the VD is reduced by the installation of internal baffles according to the visual observation, even though there is a higher CO 2 concentration detected above the bottom edge of the VD near the wall. A pronounced back-mixing of gas near the wall in the main riser may be the principal reason for the higher measured CO 2 concentration. • The volatiles distributor (VD) was further developed by equipping internal baffles. • The horizontal distribution of volatiles is improved significantly by the VD. • The slip of volatiles from the bottom can be reduced by the internal baffles.

Thermodynamic Analysis on the Fate of Ash Elements in Chemical Looping Combustion of Solid Fuels─Iron-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.

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

Power-to-methane (PtM) systems may allow fluctuations in the renewable energy supply to be smoothed out by storing surplus energy in the form of methane. These systems work by combining the hydrogen produced by electrolysis with carbon dioxide from different sources to produce methane via the Sabatier reaction.The present work studies PtM systems based on the CO2 supplied by the chemical looping combustion (CLC) of biomass (PtM-bioCLC). Life- cycle- assessment (LCA) was performed on PtM-bioCLC systems to evaluate their environmental impact with respect to a specific reference case. The proposed configurations have the potential to reduce the value of the global warming potential (GWP) climate change indicator to the lowest values reported in the literature to date. Moreover, the possibility of effectively removing CO2 from the atmosphere through the concept of CO2 negative emissions was also assessed. In addition to GWP, as many as 16 LCA indicators were also evaluated and their values for the studied PtM-bioCLC systems were found to be similar to those of the reference case considered or even significantly lower in such categories as resource use-depletion, ozone depletion, human health, acidification potential and eutrophication. The results obtained highlight the potential of these newly proposed PtM schemes.

Corrosion of Heat Transfer Materials by Potassium-Contaminated Ilmenite Bed Particles in Chemical-Looping Combustion of Biomass

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.

Comparative Study: Impacts of Ca and Mg Salts on Iron Oxygen Carriers in Chemical Looping Combustion of Biomass.

Chemical looping combustion (CLC) is one of the most promising methods for carbon capture and storage (CCS). An oxygen carrier, i.e., a mineral that can be oxidized and reduced, is used to convert the fuel in the process. The produced CO2 is inherently separated from the air components that enables easier CCS. The use of biomass-based fuels is desirable since it can lead to negative CO2 emissions. On the other hand, alkali compounds from the biomass may interact with the oxygen carrier causing problems, such as deactivation of the oxygen carrier. The most common oxygen carriers contain iron, since iron-based ores and industrial waste materials are readily available and cost-efficient. Therefore, the interaction between the iron oxygen carriers and the biomass ash-forming compounds needs to be investigated. Since Ca/Mg are abundant in biomass, it is important to clarify how their compounds interact with the oxygen carrier. In this study, the effect of Ca/Mg carbonates, chlorides, nitrates, sulfates, and phosphates along with synthetic biomass-derived ash on iron oxides was investigated. Redox reactions were investigated at 950 °C during 5 h under both oxidizing and reducing atmospheres. The results showed that the effect of Ca/Mg salts on the oxygen carrier varied depending on the anion of the salt. Generally, the nitrate- and phosphate-based salts of both Ca and Mg showed the harshest effect regarding agglomeration of the oxygen carriers. It was shown that the Ca/Mg-based compounds interacted differently with iron oxides, which was an unexpected result.

Behavior of a manganese-iron mixed oxide doped with titanium in reducing the oxygen demand for CLC of biomass

Chemical Looping Combustion (CLC) is a promising carbon capture technology to contribute to the development of BioEnergy with Carbon Capture and Storage (BECCS) technologies. In CLC, the oxygen needed for combustion is supplied by a solid oxygen carrier. During the last years, intensive research has been conducted to identify potential oxygen carriers. Iron and manganese-based minerals allowed obtaining high CO2 capture efficiencies, but lower values for the combustion efficiency, that is, high oxygen demand values, due to the high content of volatiles in biomass. Manganese-iron mixed oxides doped with titanium possess the capability of releasing molecular oxygen under specific conditions which would enhance volatile conversion. The objective of the present work was to evaluate the potential of one of these materials ((Mn66Fe)-Ti7) to improve the combustion efficiency of CLC with biomass in a 0.5 kWth continuous CLC unit.Almost 100% of CO2 capture efficiency was obtained in all the experiments. Once the operational conditions for the synthetic material (Mn66Fe)-Ti7 were optimized, it was possible to reach oxygen demand values about 10% with the advantage that the (Mn66Fe)-Ti7 oxygen carrier presented magnetic properties that would facilitate its separation from biomass ashes in the fuel reactor.

Interaction of Iron Oxygen Carriers and Alkaline Salts Present in Biomass-Derived Ash

Chemical-looping combustion (CLC) is a unique method that is developed for carbon capture and storage (CCS) to mitigate the climate change. In CLC, an oxygen carrier is used to convert the fuel and the produced CO2 is inherently separated from air components, which makes it suitable for CCS. The CLC of biomass is a way to generate negative CO2 emissions. However, interactions between ash and oxygen carriers are a tough challenge as biomass-derived ashes consist of large amounts of reactive ash-forming matter such as alkaline and alkali earth metals. As iron-based oxygen carriers are one of the most commonly used ones, the interaction of the pure iron oxide and biomass-derived ash-forming matter needs to be further understood to overcome the deactivating effects of ash components on the oxygen carriers. Even though ash components may exist in different forms, the effects of K- and Na-based carbonates, chlorides, nitrates, phosphates, and sulfates on the pure iron oxide were mainly investigated in this study. The effect of synthetic biomass-derived ash on the iron oxygen carriers was also investigated to reveal the phases causing agglomeration or deactivation of the oxygen carriers. Experiments were performed at 950 °C for 5 h under both oxidizing and reducing atmospheres. After experiments, the obtained phases were analyzed by X-ray diffraction, and elemental mapping was performed by using scanning electron microscopy–energy-dispersive X-ray spectroscopy. Results showed that the Fe oxygen carrier was worst affected by KCl, KH2PO4, and NaNO3 in terms of agglomeration among the used salts. The presence of K and Si together in the ash caused a “bridge” formation between the oxygen carrier and the ash constituent, which increased the agglomeration. A strong Ca deposit on the outer layer of the Fe oxygen carrier was also observed when a mixture of salt was used to mimic ash. Even though some discrepancies were observed, generally thermodynamic calculations were successful in estimating the experimentally observed phases.

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

This paper analyzes the capabilities of a pilot-scale chemical looping combustion plant firing wood biomass in two stages to efficiently achieve negative carbon dioxide emissions. The utilized in situ gasification-chemical looping combustion (iG-CLC) process isolates the oxygen supply via air from the fuel conversion itself with the help of two separate fluidized bed reactors and an oxygen carrier to supply the necessary oxygen for the combustion. As a result, a relatively pure stream of carbon dioxide and steam is generated. Thus, the process makes capturing carbon emissions more feasible since it eliminates the need for the cost- and energy-intensive separation of the produced gases. A major issue when using biomass in a chemical looping plant is the high amount of the volatiles exiting unconverted. This problem was mitigated by using a two-stage fuel reactor system. Two bubbling fluidized beds were arranged one upon the other. The lower stage, where the fuel is introduced, is used to release the volatiles and partly convert them. The remaining volatiles rise up into the second stage and are further converted to a high degree. A series of experiments were carried out with a 25-kWth pilot plant located at the Hamburg University of Technology. Gas concentrations were continuously measured after both stages of the fuel reactor to see the gradual conversion of the fuel gases. Additionally, carbon slip at the exhaust was measured to show the effectiveness. The experiments with the reactor concept showed promising results since already at a reactor temperature of 850 °C, the total oxygen demand needed to oxidize the combustible component in the exhaust gas was well below 2%. The carbon dioxide (CO2) capture efficiency when using German hardwood slightly decreased to 93–96% compared to 97% for German lignite. In the future, the reactor design must prove that it scales and that the efficiency can be further increased. Nevertheless, firing biomass with a two-stage iG-CLC process might allow a cost-efficient negative carbon dioxide emission while generating heat with relatively high efficiency. Therefore, it might be a sustainable alternative to generate heat in the future.

Modelling of a combined biomass CLC combustion and renewable-energy-based methane production system for CO2 utilization

In this paper, an innovative process layout to promote the integration among the chemical looping combustion of biomass, solar hydrogen, and carbon methanation is proposed and numerically investigated. The core of the layout consists of a multiple interconnected fluidized bed (MFB) system for the chemical looping combustion of solid fuels. A coupled hydrodynamic and reactive model of the system was developed and applied to evaluate solid circulation rate, solid bed levels in different parts of the system, flue gas composition and flow rate, and power production. The performance of the system was evaluated by considering chemical and physical properties of olive wood, a biomass typical of Mediterranean area, as fuel and of CuO supported on zirconia as oxygen carrier, respectively. A complex reaction scheme comprising both gas–solid heterogeneous and gas-phase homogeneous reactions was considered. Results corresponding to steady state operation of MFB are presented in conjunction with an analysis of the operability of the system under the considered ranges of operating conditions.By considering that only energy coming from renewable sources (such as photovoltaic panels or wind turbines) was fed to the electrolysis cell (EC) array, the potential of the proposed process to be used as an energy storage system was assessed.

Numerical simulation of a chemical looping combustion of biomass: Hydrodynamic investigation

In the present work, the multi-phase particle-in-cell (MP-PIC) method, implemented in OpenFOAM, is used to simulate a biomass-fueled chemical looping combustion (CLC) process in a circulation mode. Hydrodynamics of the gas-particle flow are analyzed, mainly, through pressure drop along the reactor, solid volume fraction distribution, the solid circulation between the two connected reactors, and gas and solid fuel leakages. Preliminary simulations agree well with the experimental data reported in the literature. Additional simulations using various fluidization rates into both the fuel and air reactors and different solid inventories are then performed. Results show the relevance of the pressure balance between the reactors to decreasing the gas leakage. Increasing the solid mass in the system has a favorable impact on preventing gas mixing but it allows solid fuel particles to leak to the air reactor. This is due to the increase of the solid circulation between the reactors, thus causing biomass particles' entrainment by the oxygen carrier particles. Simulation results also reveal the higher impact of the air reactor fluidization rate on the solid circulation, with respect to that of the fuel reactor fluidization rate.

Improving the oxygen demand in biomass CLC using manganese ores

Negative Emission Technologies (NETs) should be implemented to reach the objectives set by the Paris Agreement to limit the average temperature increment to 2 °C. One of the options is the development of bioenergy with Carbon Capture and Storage (BECCS) technologies. In this sense, Chemical Looping Combustion (CLC) is one of the most efficient CO2 Capture technologies both from economical and energy points of view. In CLC, a solid oxygen carrier is used to transfer the oxygen from air to the fuel.In this work two manganese-based ores were used as oxygen carriers to burn three different types of biomass (pine sawdust and two Spanish agricultural residues) in a 0.5 kWth CLC continuous unit. Operational conditions were varied to evaluate their effect on the CO2 capture efficiency and the total oxygen demand of the process. Almost 100% of CO2 capture efficiency was reached working with pine sawdust as well as with almond shells. However, high values of total oxygen demand (10–20%) were found, which led to consider further technological solutions to increase the combustion efficiency. In this respect, fuel reactor outlet recycling was evaluated as an operational solution to reduce the oxygen demand with good results (about 30% reduction in the total oxygen demand value). NOx and tar formation from the CLC system were also evaluated. There were no NOx emissions during the experimental campaign and low tar content in the fuel reactor outlet gas was reached (0.3–3.2 g/Nm3), being naphthalene the major tar compound.

Chemical looping combustion integrated Organic Rankine Cycled biomass-fired power plant – Energy and exergy analyses

Global warming due to greenhouse emission is the most annoying problem for sustaining life on earth. Many researchers are contributing towards the development of sustainable energy technologies. Chemical Looping Combustion (CLC) is a modernistic technology in which fuels produce heat and power without carbon emission. Agricultural biomass can be a potential substitute to fossil fuels for low capacity energy generation. Further, CLC of biomass is a carbon negative technology which can address the present greenhouse gas emission problem. In this study, a novel configuration of CLC based biomass power plant integrated with Organic Rankine Cycle is proposed. The effects of key design parameters like oxygen carrier-to-biomass ratio, operating pressure of air/fuel reactors and air reactor operating temperature are studied to improve the process energy and exergy efficiencies. Integration of waste heat recovery recuperators with ORC cycle resulted in further increase of power output by 49.93 kW. The performance of the proposed configuration is compared with conventional power plant to highlight its advantages. The net power output of the final CLC integrated configuration and conventional power plants are 492.19 kW and 273.12 kW respectively. Finally, the individual unit wise exergy analysis is presented to identify the possible performance improvement options.

Potassium Ash Interactions with Oxygen Carriers Steel Converter Slag and Iron Mill Scale in Chemical-Looping Combustion of Biomass—Experimental Evaluation Using Model Compounds

Chemical-looping combustion (CLC) is a combustion technology in which a solid oxygen carrier is used to convert fuel. The oxygen carrier is oxidized in air and subsequently transferred to a separate reactor in which it reacts with the fuel. The produced CO2 is inherently separated from the air components, making CLC a promising technology for carbon capture and storage (CCS). CLC of biomass combined with CCS (bioenergy CCS; BECCS) is a way to generate negative CO2 emissions and thus interesting for climate change mitigation. Undesirable chemical reactions between ash and oxygen carriers are a challenge in BECCS because of the reactive nature of biomass ash. This article examines two low-cost steel industry byproducts that have shown desirable fuel conversion properties in CLC: iron mill scale (Glodskal B) and steel converter slag (LD-slag). Their interactions with potassium ash model compounds (KCl, K2CO3,K2SO4, and KH2PO4) in a reducing atmosphere have been investigated. Mixtures of oxygen carriers and potassium salt have been reduced for 6 h in CO and steam in a laboratory-scale fixed-bed reactor at 850 °C. The reduced samples have been analyzed with SEM/EDS and XRD. The reactivity of the mixtures during reduction and oxidation has also been examined by thermogravimetric analysis (TGA). K2CO3 increased the reaction rate for the reduction of Glodskal and inhibited the reactivity of LD-slag. KH2PO4 formed a K−P−Fe component with apparent low melting temperature with Glodskal, causing agglomeration, and decreased the reduction/oxidation rate in TGA. KH2PO4 formed a K−P−Ca component with apparent high melting temperature with LD-slag causing agglomeration but the reduction rate was not affected. The study suggests that the iron mill scale and LD-slag should not be rejected as oxygen carriers for CLC based on potassium ash interaction.

Numerical investigation of in situ gasification chemical looping combustion of biomass in a fluidized bed reactor

In-situ gasification chemical looping combustion (iG-CLC) depends on the solid fuel gasification rate and the contact between gasification products and oxygen carriers. In this work, a three-dimensional simulation is carried out to investigate the iG-CLC performance of biomass in a fluidized bed reactor by means of the multi-fluid model with the bubble-based bi-disperse drag model to consider the bubble effect on the interphase drag force. The model can give a reasonable prediction on the experimental results. The result reveals that an increase of operating pressure of 0.2 MPa can promote the CO2 yield by 5%, whereas the change of the feed port height from the reactor bottom also greatly influences the outlet gas compositions.

Robust decision making analysis of BECCS (bio-CLC) in a district heating and cooling grid

Additional investments to negative emission technologies, such as reforestation or bioenergy with carbon capture and storage (BECCS), are required to achieve Paris Agreement targets. Chemical-looping combustion of biomass (Bio-CLC) is an under-the-development combustion technology that could provide relatively low cost negative CO2 emissions. We modelled Bio-CLC units as a part of a city-level district heating and cooling (DHC) grid based on literature and our experimental work with Bio-CLC pilot plants. We applied robust decision-making (RDM) to identify preconditions that favour Bio-CLC over certain competing investment options.In the selected case study, a Bio-CLC unit had a 50% chance to be profitable (10% Internal rate of return or better) around the level of 10 €/tCO2 net income from captured bio-CO2. If the net income from captured bio-CO2 was below 10 €/tCO2, as currently, large heat pumps with COP of 3.5 were the most robust of the studied investment options. Traditional bio-CHP performed better than large heat pumps only when electricity market price was above 50 €/MWh and biomass price below 20 €/MWh. Performed RDM analysis provides a systemic background for both technology developers and DHC operators when considering the competitiveness of the technology in an uncertain future.

Reactivity improvement of ilmenite by calcium nitrate melt infiltration for Chemical Looping Combustion of biomass

Chemical Looping Combustion is a novel process that generates sequestration-ready CO2 from the combustion of woody biomass without requiring a gas separation step and without diluting the CO2 with N2 from air. This is achieved by oxidizing the fuel with lattice oxygen of a metal oxide oxygen carrier. When using cheap and abundant ilmenite ore (FeTiO3) as the oxygen carrier, the rather low reactivity towards volatiles released from the biomass upon devolatilization, as well as detrimental structural changes due to a segregation of Fe and Ti in the material, are of concern. These issues can be addressed by modifying ilmenite with Ca via melt infiltration. In this work, we demonstrate that this modification results in a good distribution of Ca throughout the ilmenite particles that a) prevents detrimental Fe/Ti segregation, b) improves the mechanical stability of the particle compared to materials prepared by solution impregnation and c) improves the reactivity of this material towards hydrogen and wet methane. Moreover, fixed bed experiments showed that the Ca modification not only resulted in increased methane conversion, but also in an increased degree of oxidation of gaseous intermediates CO and H2. We thus conclude that the performance of ilmenite in Chemical Looping processes can be significantly enhanced by Ca modification of ilmenite either prior to use or in-situ during operation of this bed material with Ca-rich fuels such as woody biomass.

Techno-Economic Evaluation of Bio-CLC: Assessing the Nordic Policy Situation

Negative emissions have been considered necessary in order to limit the temperature increase to 1.5°C as set in the Paris Agreement. Bioenergy combined with carbon capture and storage (BECCS) offers an attractive way to generate these negative emissions while simultaneously providing energy. One of such technologies is chemical-looping combustion of biomass (bio-CLC), which has been considered to economically outperform its alternatives such as oxy-fuel combustion. The Nordic district heating networks provide a suitable investment environment for CLC: the combined heat and power (CHP) plants already utilize large shares of biomass, which is only to be increased due to expected changes in legislation such as phasing out coal. The paper has two key objectives: to discuss and evaluate policies to further boost the development of BECCS, and to evaluate the feasibility of CLC installation in two alternate CHP plants under both the existing and introduced policies. The techno-economic evaluation is carried out in a generic Nordic district heating system in varied market scenarios using a cost-optimization model based on mixed-integer linear programming (MILP). As the main results, the existing policy framework (EU ETS) and an additional carbon tax were found insufficient to achieve positive net profit for the CLC investment. Adding an incentive for the negative emissions while generating heat or power was discussed be complex, with the latter also appearing ineffective due to relatively low district heat demand in the studied system. The investment was found to be feasible in a scenario in which the negative emissions were subsidized at 50 €/ton, while compensating CO2 transport and storage costs for the plant owner nearly led to positive net profit. The former option can be considered to be simpler to implement to the existing legislation, while the latter would potentially have a smaller risk to lead to excess utilization of biomass resources.