Chemical Looping Combustion Reactor Research Articles

Energy, Exergy, Economic and Exergoeconomic Analyses of Chemical Looping Combustion Plant Using Waste Bark for District Heat and Power Generation with Negative Emissions

The greenhouse gas emissions from the boiler of pulp and paper industries can be minimized by adapting chemical looping combustion (CLC) technology. This work aims to analyze the energy, exergy, economic, and exergoeconomic performance of an industrial scale CLC plant for district heat and electricity generation using waste bark from the paper and pulp industry. The CLC plant with one natural ore and one industrial waste oxygen carrier (OC) is modeled using Aspen Plus. The performance of the CLC plant has been compared to Örtofta combined heat and power plant without CO2 capture and with post‐combustion CO2 capture as the reference cases. Results showed that the CLC‐based power plant is energetically, exegetically, and economically efficient compared to the reference cases. The circulating fluidized bed boiler unit contributes the highest exergy destruction (about 50–80%). Among the CO2 capture plants, the CLC plant with ilmenite has the lowest levelized cost of district heat (4.58 € GJ−1), and a payback period (9.69 years) followed by the CLC plant with LD slag (5.91 € GJ−1 and 11.84 years), and the plant with PCC (6.94 € GJ−1 and 13.58 years). The exergoeconomic analysis reveals that the CLC reactors have the highest cost reduction potential, followed by the steam turbine.

First principle based rate equation (1pRE) for random pore model in Fe2O3 reduction reaction with CO

AbstractThe redox kinetics of the oxygen carriers are crucial in Chemical‐Looping Combustion (CLC) systems. The random pore model (RPM) was widely used to investigate the macroscale redox kinetics of oxygen carriers in previous studies, in which the reaction rate constants were obtained just by fitting the experimental data. This study presents a first principle based rate equation (1pRE) applied to the RPM to calculate the reaction rate constants directly using density functional theory (DFT). The 1pRE is integrated with the RPM that accounts for the effect of pore size distribution derived from the surface area evolution of reaction interface and product layer diffusion, thus bridging the gap between the microscale elementary surface reactions and macroscale overall conversion. The developed 1pRE predicts the reduction kinetics of Fe2O3 oxygen carriers accurately, thereby facilitating the optimization of design processes for oxygen carrier materials and the scale up of CLC reactors.

Design and first application of a novel laboratory reactor for alkali studies in chemical looping applications

Alkali compounds are readily released during biomass conversion and their complex interactions with reactor walls and sampling equipment makes detailed investigations challenging. This study evaluates a novel laboratory-scale fluidized bed reactor for chemical looping combustion (CLC) studies. The reactor design is based on detailed consideration of the behavior of alkali-containing molecules and aerosol particles and is guided by computational fluid dynamic simulations. The design allows for interactions between gaseous alkali and a fluidized bed, while minimizing alkali interactions with walls before and after the fluidized bed. The function of the laboratory reactor is demonstrated in experiments using online gas and alkali analysis. Alkali is continuously fed to the reactor as KOH or KCl aerosol with and without a fluidized bed of the oxygen carrier CaMn0.775Ti0.125Mg0.1O3-δ present in inert, reducing and oxidizing conditions at temperatures up to 900 °C. Alkali uptake by the OC is characterized in all conditions, and observed to sensitively depend on gas composition, reactor temperature and type of alkali compound. The experimental setup is concluded to have a significantly improved functionality compared to a previously used reactor, which opens up for detailed studies of interactions between alkali compounds and oxygen carriers used in CLC.

Is monolithic configuration superior to random packing in a fixed bed reactor for CLC like processes?

In light of the geometric deficiencies and diffusion constraints of conventional packed-bed reactors, the potential application of monolithic configurations in fixed-bed reactors was explored using the structure-resolved CFD approach. This work delves into how geometric features of fixed beds influence flow patterns and related transport phenomena. To assess the performance of mass transfer and heterogeneous reactions in different configurations, we conducted simulations of fixed-bed chemical looping combustion (CLC) processes, in which a simplified model of non-catalytic gas-solid reactions is implemented to reduce the computational costs. Our findings highlight the importance of face contact between reaction tube and the monolithic structure, which effectively eliminates the inherent wall effects of random packing and enhances the radial heat conduction. More uniform geometry in the monolithic configuration naturally suppresses violent interstitial channeling flow in the random packing. Notably, the honeycomb configuration demonstrates an exceptionally low pressure drop, about two orders of magnitude smaller than that of the Raschig ring packing, and the designable monolithic configurations offers the potential to further reduce the pressure drop with enlarged voidage. Open-cell foams exhibit excellent convective and radial heat transport properties, promote homogeneous flow fields, and demonstrate superior performance in conjugate transport and heterogeneous reactions.

Simulation of a Fuel Reactor for Chemical Looping Combustion with Oxygen Uncoupling

Simulation of a Fuel Reactor for Chemical Looping Combustion with Oxygen Uncoupling

Integration of a novel Chemical Looping Combustion reactor into a thermochemical energy storage system

This study analyses the performance of a back-up power process that uses a novel chemical looping packed bed air reactor to oxidize a batch of reduced solids while heating high pressure flowing air. In this arrangement, the solids are slowly oxidized by a diffusionally-controlled flow of oxygen perpendicular to the main air flow, thus imposing very long oxidation times for all reacting particles. A decay in the thermal power output of the reactor can be expected with time due to the increasing resistance to O2 diffusion towards the unreacted oxygen carrier particles as the reaction progresses. In this work, integration of the dynamic system formed by the reactor and the power plant used to produce power from the exploitation of the variable thermal output of the reactor is investigated. Different case studies are assessed for decarbonization of energy production and storage of renewable energy. The reactor is rated at a maximum 50 MWth power output in all cases, employing iron- or nickel-based particles as oxygen carrier. A simplified model for mass and heat transfer in the proximity of the wall orifices allows the definition of operating windows and reactor dimensions. In the chosen case examples, each single reactor operates in discharge mode for around 4–5 h (depending on plant configuration) as a back-up power generator, heating up a compressed air stream up to ∼ 1000 °C and achieving an energy density between 816 and 2214 kWhth/m3. Gas turbines in recuperative, steam injected and combined cycle power plant architectures integrated in the novel chemical looping combustion (CLC) reactor are investigated. Cycle efficiencies up to 49% are calculated for systems that make use of a single reactor configuration and exploit the residual heat for power production through a organic Rankine cycle (ORC) bottomed system. A more flexible multi-reactor configuration is also investigated to address the unavoidable decay in power output during discharge and provide power output controllability. The levelized cost of electricity (LCOE) is estimated be comparable to system elements from the literature when H2 is used as reducing gas. The use of biogas to reduce the solids during the energy charge stage is found to be particularly advantageous, leading to LCOE values between ∼ 120 and 175 €/MWh for the reference reactor system using iron-based solids. This also allows achieving negative CO2 emissions if the captured CO2 generated during the reduction stage is stored.

Dimensioning Air Reactor and Fuel Reactor of a Pressurized CLC Plant to Be Coupled to a Gas Turbine: Part 2, the Fuel Reactor

Bioenergy with Carbon Capture and Storage (BECCS) technologies are fundamental to reach negative CO2 emissions by removing it from the atmosphere and storing it underground. A promising solution to implement BECCS is pressurized Chemical Looping Combustion (CLC), which involves coupling a pressurized CLC reactor system to a turboexpander. The typical configuration chosen is to have an air reactor and a fuel reactor based on coupled circulating fluidized beds. The fluidization regime in both reactors is preferred to be fast fluidization to enhance gas particle contact and solids circulation among reactors. To design the two reactors, Aspen Plus software was used, given that the new version has a module for fluidized bed modeling. At first, the oxygen carrier was designed ex novo, but given that it is a composite compound mainly made by nickel oxide freeze-granulated on alumina (Ni40Al-FG), the molecular structure has been inserted in Aspen Plus. Then, based on the power of the gas turbine, the power output per kg of evolving fluid (in this case, depleted air) is calculated using Aspen Plus. Once the nitrogen content in the depleted air is known, the total air at the inlet of the air reactor is calculated. The fuel reactor is modeled by inserting the reduction reactions for nickel-based oxygen carriers. The paper presents a useful methodology for developing pressurized Chemical Looping Combustors to be coupled to gas turbines for power generation. The provided data will be cross-validated with 0D-models and experimental results.

Thermal integration of styrene production process with chemical looping combustion to reduce the CO2 emission by omitting the conventional methane combustion furnaces

Upstream petrochemical units like olefins and aromatics are among the biggest emitters of greenhouse gasses Innovative technologies for carbon capture and storage have received increasing attention for adjusting the conventional methods of processes. The chemical-looping combustion (CLC) technology is an alternative method to supply the required heat for endothermic processes. In this work, we suggested the thermal coupling of the CLC process and the ethylbenzene dehydrogenation (EBDH) process, in a single-stage reactor. The two processes are integrated, and the porous medium of the fixed bed is used to simulate the reaction leading to styrene monomer. Then some critical parameters of the EBDH reactor and the CLC reactors are discussed and compared with valid results from previous simulations. Using a new structure and implementing several optimizations improved the yield of useful styrene monomer and key factors of the EBDH process.

Study of Flow Patterns in a Moving Bed Reactor for Chemical Looping Combustion Based on Machine Learning Methods

Abstract A tower-type moving bed can be used as the air reactor in a chemical looping combustion system because of its low-pressure drop and smooth operation. In our previous simulation, a quasi-two-dimensional numerical model was established using discrete element method (DEM) approach to investigate the velocity and solid residence time distributions in the moving bed. In this work, the flow patterns under different operating and structural parameters are studied and optimized via machine learning methods. The random Forest regression model is applied to evaluate the importance of each variable to the solid flow pattern, while the feed forward neural network is applied to buildup a high-accuracy model to predict the solid axial velocity in the moving bed without the requirement to understand the physical mechanisms. Results show that the solid mass flux has the least impact on the mass flow index, while the axial position has the dominant influence and what comes next is the wedge angle, reactor angle, and ratio of down-comer diameter to reactor diameter. Further, based on the established feed forward neural network model, relation between the effective transition position and structural parameters of the moving bed is built, which provides valuable guidance for optimization of the reactor configuration.

Comparative exergoeconomic analysis of atmosphere and pressurized CLC power plants coupled with supercritical CO2 cycle

Recently, the incorporation of chemical looping combustion (CLC) and sCO2 Brayton cycle has been regarded as a promising technology for clean and efficient power generation. The intrinsic characteristics of the CLC reactors (interconnected circulating fluidized bed or fixed bed) allow them to operate at different pressures, leading to different technological directions. Therefore, a pair of “CLC coupled sCO2 cycle” systems was proposed, namely the atmosphere CLC (A-CLC-sCO2) and pressurized CLC (P-CLC-sCO2). The purpose of this paper is to determine which configuration holds more benefits from a combined exergetic and economic perspective. The operational boundary conditions for thermodynamic advantage of P-CLC-sCO2 over the optimized A-CLC-sCO2 was firstly investigated. Under respective optimal conditions, the exergy efficiency of P-CLC-sCO2 (51.09%) was found to be 1.16% higher than that of A-CLC-sCO2 (49.91%). Besides, the P-CLC-sCO2 exhibited a lower levelized cost of electricity (79.59 $/MWh) than A-CLC-sCO2 (81.31 $/MWh) when using a nickel-based oxygen carrier (OC), but the A-CLC-sCO2 could further reduce LCOE to 78.93 $/MWh by adopting ilmenite-based OC. In addition, the exergy and exergoeconomic analysis of the main components was carried out to find the system improvement strategies.

An implicit function formulation for optimization of discretized index-1 differential algebraic systems

A formulation for the optimization of index-1 differential algebraic equation systems (DAEs) is described that uses implicit functions to remove algebraic variables and equations from the optimization problem. The formulation uses the implicit function theorem to calculate derivatives of functions that remain in the optimization problem in terms of a reduced space of variables, allowing it to be solved with second-order nonlinear optimization algorithms. The formulation is shown to lead to more reliable solver convergence when compared with a full-space simultaneous formulation in challenging case studies involving a chemical looping combustion reactor. In a steady state simulation problem, the implicit function formulation solves 82 out of 100 instances, while the full space formulation solves only 42 out of 100 instances. In a dynamic optimization problem, the implicit function formulation solves 189 out of 200 instances, while the full space formulation solves only 152 out of 200 instances.

Simulation and Optimization of a Multistage Interconnected Fluidized Bed Reactor for Coal Chemical Looping Combustion.

This work established a three-dimensional model of a chemical looping system with multistage reactors coupled with hydrodynamics and chemical reactions. The thermal characteristics in the chemical looping combustion (CLC) system were simulated using coal as fuel and hematite as an oxygen carrier (OC). Some significant aspects, including gas composition, particle residence time, backmixing rate, wall erosion, carbon capture rate, etc., were investigated in the simulation. Owing to the optimization by adding baffles in the fuel reactor (FR), the gas conversion capacity of the multistage FR was high, where the outlet CO2 concentration was as high as 93.8% and the oxygen demand was as low as 3.8%. Through tracing and analyzing the path of char particles, we found that the residence time of most char particles was too short to be fully gasified. The residual char will be entrained into the air reactor (AR), reducing the CO2 capture rate, which is only 80.3%. In the simulation, the wall erosion on the cyclone could be relieved by increasing the height of the horizontal pipe. In addition, improving the structure of the AR loop seal could control the residual char entrained by OC particles to the AR, and the CO2 capture rate was increased up to 90% in the multistage CLC reactor.

Fate of NO and Ammonia in Chemical Looping Combustion─Investigation in a 300 W Chemical Looping Combustion Reactor System

Chemical looping combustion (CLC) is a novel combustion concept that transfers oxygen from air to fuel using an oxygen carrier that circulates between an air reactor and a fuel reactor. Thus, the combustion products, H2O and CO2, are obtained in a separate flow, and ideally, a pure CO2 gas stream is obtained after condensation of H2O. Consequently, CLC has a unique potential for avoiding the high costs and energy penalties of CO2 capture. Further, NO emissions can potentially be avoided. CLC is flameless, and the temperature is too low for the formation of thermal NOx. Moreover, fuel NOx and prompt NOx do not form in the air reactor in the absence of fuel. In the fuel reactor, the absence of oxygen prevents normal NOx formation. However, when using fuels containing nitrogen, NO may form in the fuel reactor because the oxygen carrier can oxidize fuel nitrogen compounds. To achieve a CO2 stream suited for storage, NO must be removed. Dependent upon how NO is removed, the process could be free from any NO emissions. NO formation and NO reduction were investigated in a 300 W CLC reactor by adding either NH3 or NO. The work involved two different oxygen carriers, Linz–Donawitz (LD) slag and ilmenite, two temperatures, 850 and 900°C, two circulation rates, and different flows of syngas fuel. Further, operation without fuel with a fully and partially oxidized oxygen carrier was studied. For LD slag, lower fuel flow promoted the formation of NO and decreased the reduction of NO. Likewise, higher temperatures raised NO formation and lowered NO reduction. Ilmenite, however, was by far more superior with respect to NO. Thus, NO formation only occurred in the absence of fuel and with a fully oxidized oxygen carrier. Likewise, NO was fully reduced to N2 for all conditions, except in the absence of fuel and with fully oxidized ilmenite.

Perovskite oxygen carrier with chemical memory under reversible chemical looping conditions with and without SO2 during reduction

Oxygen carrier materials (OCM) are usually exposed to sulfur-contained gases in the fuel reactor for chemical looping combustion. This work provides both experimental and model work to understand the SO2 effect on the heterogeneous redox kinetics of a CaMn0.375Ti0.5Fe0.125O3-δ-based perovskite oxygen carrier. The cycle reactivity and redox kinetics under reducing conditions were conducted with and without SO2 in a micro-fluidized bed thermogravimetric analysis technology (MFB-TGA). The redox kinetic behaviors were simulated by a bubbling fluidized bed reactor model coupled with a two-stage kinetic model. The SO2 can react with the perovskite to increase the oxygen transfer capacity from 4 wt% to 5 wt%. When the temperature is higher than 1173 K, SO2 has almost no effect on the H2 reduction reactivity, while the oxidation reactivity decreases by 50%, but the oxidation is still fast enough to achieve 4 wt% capacity within 8 s. When the temperature is lower than 1173 K, there is a significant sulfur-poisoning effect during oxidation and reduction. The analyses of XRD, SEM-EDS, and in-situ DRIFTS indicated that most of the absorbed sulfur mainly existed in the sulfate/sulfide shell on the particle surface. The chemical kinetics and physical structure of CaMn0.375Ti0.5Fe0.125O3-δ perovskite can be completely recovered in the absence of SO2, and this perovskite oxygen carrier is chemically memorable and reversible in its solid structure. The fundamental understanding of the sulfur effect on the redox kinetics and solid structure of the perovskite oxygen carrier provides a new insight to the material development and corresponding reaction mechanisms.

MP-PIC simulation of the gas-solid full-loop flow characteristics in a dual fluidized bed and validation with experimental data

• Full-loop flow characteristics are investigated by MP-PIC simulation. • Four flow zones are identified in the BFB. • The BFB and the lower U valve are working together as a particle buffer region. • The start-up characteristics among different parts are investigated based on simulation. It is necessary to investigate and understand the gas-solid flow characteristics for the design and optimized operation for chemical looping combustion reactors and other chemical process which involves dual fluidized bed (DFB) system. In this research, computational fluid dynamics simulation was performed in a lab-scale cold three-dimensional full-loop dual fluidized bed model based on the Particel-In-Cell (MP-PIC) method to understand its gas-solid flow characteristics. The simulated results were analyzed and validated with the pressure and electrical capacitance tomography (ECT) measurements. It has been shown that Wen-Yu/Ergun drag model is feasible for the prediction of the gas-solid flow dynamics of this DFB system. The simulated particle volume fraction and ECT results have a good agreement. In the bubbling fluidized bed (BFB), four flow zones are identified based on the bubble and particle behaviors. In each zone, bubbles are mainly concentrated in the middle region. Moreover, the fluidizing air in the chute functions as a secondary air of the BFB to facilitate the particle movement. The BFB and the lower U valve are working as one component and function as a particle buffer region. Therefore, the balance of the whole system is determined by the time when the riser reaches steady state. The higher the air inlet velocity of the riser, the sooner the system reaches steady operation. In addition, the start-up characteristics among the riser, the BFB and U-valve are investigated based on the simulation results. The results indicated that there is a start-up time lag between the riser and bubbling fluidized bed when they each reach steady state.

A framework for evaluating the effect of oxygen carrier characteristics on the performance of industrial-scale CLC using solid fuels

In this work we present a framework to find the potential heat recovery from Chemical Looping Combustion (CLC) using different combinations of oxygen carriers and solid fuels, based on thermodynamic equilibrium calculations. This framework requires thermodynamic information of the reacting species, which is readily available, and no kinetic information for each oxygen carrier, which is scarcer, is required. As the results of this framework are independent of the configuration of the CLC reactor, this tool can aid in the preliminary evaluation of oxygen carriers with potential for CLC applications and relevant operating conditions.

Numerical Analyses of Heterogeneous CLC Reaction and Transport Processes in Large Oxygen Carrier Particles

Heterogeneous chemical looping combustion (CLC) reactions and conjugate transports in large oxygen carrier particles were numerically investigated with computational fluid dynamics (CFD) approaches, in which a simplified noncatalytic reaction model was implemented for reducing intraparticle modelling computation. Volumic gas-solid reactions were treated as surface reactions based on the equivalent internal surface in the particle model. In large porous particles such as fixed bed CLC reactors, the heterogeneous reactions are often limited by intraparticle diffusion. Comprehensive analyses were conducted on transports across the particle surface and their influences on reactions inside the single particles. A threshold Reynolds number of external convections was found for the enhancement of intraparticle reactions. The heterogeneous reactions, intraparticle diffusions and interstitial transports in a fixed bed CLC reactor randomly packed with 597 spheres were thoroughly analysed with the same numerical approaches. Comprehensive insights of the temporal evolution and spatial distribution of scalars in the packed bed reactor were presented.

Kinetics of solid reactions with gas intermediates in chemical looping combustion

• Reaction route of the CLC reactions with gas intermediates were identified. • The effect of solid particle size ranges was analyzed. • The sensitivity of reaction temperature was determined. • The kinetics models could be used in the solid reactions with gas intermediates. Chemical looping combustion (CLC) is an advanced technology for converting solid fuel with in-situ CO 2 capture in a low-cost and sustainable way. However, unlike gaseous fuel, the CLC process of solid fuel is lack of the reaction understanding between fuel particles and OC particles (solid-to-solid), and this result directly influences the design of the reactor. In this context, the study focused on the solid reactions with gas intermediates taking place in the CLC reactor. Well-mixed solid particles of the coal char and the hematite were investigated on the thermogravimetric and mass spectrometry (TG-MS) system. The effects of different particle size ranges and different reaction temperatures were determined. The kinetics on this kind of solid reactions was calculated and discussed. The result showed that the carbon gasification was identified as the control step in reactions. The diffusional resistance of 45–75 µm char particles could be ignored. Two models of kinetic reactions were developed based on the contracting sphere rate law and the first order rate law. The Activation Energy E a of the surface reaction model and the first order reaction model was 208.75 kJ/mol and 224.75 kJ/mol, respectively. Overall, the experiments and the kinetic models carried out in the present work improved the reaction understanding on the field of the solid reactions with gas intermediates in CLC.

Hydrodynamics of dual circulating fluidized bed reactor for chemical looping combustion

Carbon dioxide (CO2) has been increasingly released to the environment with the increased electricity demand via fossil fuel combustion. The alternative solution is the combustion unit that prevents CO2 from releasing. Chemical looping combustion is the combustion unit that can achieve this objective and provides high purity of a CO2 product for meaningful uses. The high efficiency of the process is achieved by designing good reactor hydrodynamics. A dual circulating fluidized bed reactor was then investigated in this study. The two parameters were studied; the temperature of the reactor (A) and the ratio of coal velocity to the weight of oxygen carrier (B). The two responses were analyzed; 1) combustible gas percentage from a fuel reactor, and 2) CO2 percentage from an air reactor. The 3k factorial experimental was used for systematic experimental design which included the curvature behavior of the result. The results indicated that parameters A and B affected the combustible gas percentage from the fuel reactor. However, only B affected the CO2 percentage from the air reactor. The high A and B gave a high combustible gas percentage from the fuel reactor and high CO2 percentage from the air reactor. The high combustible gas percentage from the fuel reactor indicated the incomplete combustion and the high CO2 percentage from the air reactor indicated the high CO2 releasing to the environment. The low values of A and B then supported the proper hydrodynamics in these reactors which will provide the efficiency of fuel usage, the reduction of CO2 emission to the environment, and the mitigation of the environmental crisis.

Fast redox kinetics of a perovskite oxygen carrier measured using micro-fluidized bed thermogravimetric analysis

Redox kinetics of oxygen carrier in chemical looping combustion (CLC) is important for reactor design and its oxidation enthalpy is important in order to establish auto thermal demonstration. Most published redox kinetics of oxygen carrier has been measured by thermogravimetric analysis (TGA) which can include additional diffusion limitations and thus underestimate the overall kinetics. In this study, the redox kinetics of a new perovskite oxygen carrier (CaMn0.375Ti0.5Fe0.125O3-δ) was measured by a novel micro-fluidized bed thermogravimetric analysis (MFB-TGA) method which can achieve real-time weight measurement of oxygen carrier in a fluidizing state with similar mass and heat transfer characteristics as in a CLC reactor. The experimental data from MFB-TGA were analyzed with a reactor model. The redox kinetics was described by a two-stage model of gas-solid reaction. The effect of temperature, O2 concentrations and reducing gas type (H2 and CH4) on the redox kinetics in MFB-TGA was investigated and compared with other oxygen carriers such as natural manganese ore and ilmenite. It is observed that the oxidation of both manganese ore and ilmenite can be divided into two stages, a fast initial stage followed by a second slower stage, resulting in slower total oxidation rates. A very interesting finding is that there is only the fast initial stage for the oxygen carrier of CaMn0.375Ti0.5Fe0.125O3-δ, and the full oxidation of CaMn0.375Ti0.5Fe0.125O3-δ can be finished within ∼4 s which is ∼7.5 and ∼30 times faster than that of manganese ore and ilmenite. The reduction kinetics of CaMn0.375Ti0.5Fe0.125O3-δ by H2 is also ∼5 and ∼2.2 times faster than that of manganese ore and ilmenite, respectively. The kinetic parameters of three oxygen carriers were compared and the redox mechanism of CaMn0.375Ti0.5Fe0.125O3-δ was discussed.