Chemical Looping Combustion Unit Research Articles

Life Cycle Assessment of Wheat Straw Pyrolysis with Volatile Fractions Chemical Looping Combustion

Among the approaches to facilitating negative CO2 emissions is biochar production. Biochar is generated in the pyrolysis of certain biomasses. In the pyrolysis process, carbon in the biomass is turned into a solid, porous, carbon-rich, and stable material that can be captured from the soil after a period of from a few decades to several centuries. In addition to this long-term carbon sequestration role, biochar is also beneficial for soil performance as it helps to restore soil fertility and improves the retention and diffusion of water and nutrients. This work presents a Life Cycle Assessment of different pyrolysis approaches for biochar production. Biomass pyrolysis is performed in a fixed-bed reactor, which operates at a mild temperature (550 °C). Biochar is obtained as solid product of the pyrolysis, but there are also liquid (bio-oil) and gaseous products (syngas). The pyrolysis gas is partly used to fulfil the energy demand of the pyrolysis process, which is highly endothermic. In the conventional approach, CO2 is produced during the combustion of syngas and emitted to the atmosphere. Another approach to facilitate CO2 capture and thus obtain more negative CO2 emissions in the pyrolysis process is burning syngas and bio-oil in a Chemical Looping Combustion unit. Life Cycle Assessment was performed of these approaches toward biomass pyrolysis to evaluate their environmental impact. The Chemical Looping Combustion approach significantly reduced the values of 7 of the 16 environmental impact indicators studied, along with the Global Warming Potential among them, it slightly increased the value of one indicator related to the use of fossil resources, and it maintained the values of the remaining 8 indicators. Environmental impact reduction occurs due to the avoidance of CO2 and NOx emissions with Chemical Looping Combustion. The CO2 balances of the different pyrolysis approaches with Chemical Looping Combustion configurations were compared with a base case, which constituted the direct combustion of wheat straw to obtain thermal energy. Direct biomass combustion for the production of 17.1 MJ of thermal energy had CO2 positive emissions of 0.165 kg. If the gaseous fraction was burned by Chemical Looping Combustion, CO2 was captured and the emissions became increasingly negative, until a value of −3.30 kg/17.1 MJ was generated. If bio-oil was also burned by this technology, the negative trend of CO2 emissions continued, until they reached a value of −3.66 kg.

Techno-economic analysis of chemical looping processes with biomass resources for energy production and CO2 utilization. Comparison of CLC and CLOU technologies

Bioenergy coupled with carbon capture utilization and storage (BECCUS) is an attractive greenhouse gas mitigation technology that can produce negative CO2 emissions by combining bioenergy resources with the utilization or geological storage of the captured CO2.The main objective of this work was to evaluate the technical and economic feasibility of two BECCUS technologies based on chemical looping concept with two biomass waste as fuels, i.e., swine manure and pine sawdust, for the production of thermal energy and a pure CO2 stream that is subsequently used as raw material in agricultural greenhouses. Direct use of solid biomass resources was considered for the Chemical Looping with Oxygen Uncoupling option, whereas biogas production was the starting point for Chemical Looping Combustion.The profitability of the chemical looping scenarios was assessed through the Levelized Cost of CO2. This parameter was estimated at 218.31 €/t CO2 for the Chemical Looping Combustion scenario, a value much higher than those for the Chemical Looping with Oxygen Uncoupling scenarios (73.04–87.32 €/t CO2) due to the limited conversion degree of the carbon present in the fuel waste to biogas and the need for an additional experimental plant to the Chemical Looping Combustion unit, i.e., the biogas production plant. Comparing the Chemical Looping with Oxygen Uncoupling scenarios, the economic analysis revealed that the profitability of the biomass-fueled chemical looping facility was markedly sensitive to the selling price of the biomass resource. Furthermore, the values of the Levelized Cost of CO2 parameter for the Chemical Looping with Oxygen Uncoupling scenarios were lower than those estimated in other research studies that implemented BECCUS technologies and utilized the captured CO2 for identical purposes. In the particular case of swine manure, this result becomes even more noteworthy since it demonstrates that the energy use of this biomass resource through Chemical Looping with Oxygen Uncoupling technology is an economically profitable and environmentally sustainable solution to the difficult challenge of managing this livestock waste. Therefore, it can be concluded that Chemical Looping with Oxygen Uncoupling processes fed with biomass are a very attractive BECCUS technology for heat generation where, in addition, the pure CO2 stream obtained at the outlet of the fuel reactor can be considered a marketable, high value-added product.

Insights into the gas-solid hydrodynamics and thermochemical characteristics in a pilot-scale chemical looping combustion unit using MP-PIC

Chemical looping combustion (CLC) emerges as an efficient pathway for CO2 capture and storage, yet complex in-furnace phenomena are still far from being understood. Accordingly, the multiphase reactive flow during the CLC process in a pilot-scale dual circulation fluidized bed (DCFB) is numerically investigated by the multi-phase particle-in-cell method considering thermochemical sub-models. After model validations, the thermochemical behaviors and the impact of operating parameters on CLC performance are explored, followed by unveiling the underlying mechanisms of heat and mass transfer characteristics. The pressure gradient is explicitly correlated with the solid holdup in two reactors. Gas-solid flow in the fuel reactor (FR) is more heterogeneous than that in the air reactor (AR) due to complex reactions and large amounts of gas/particle exchanges with other parts of the DCFB, and the whole CLC unit shows good circulating and heat transfer performance. Higher temperatures improve fuel conversion and increase CO2 yield. Elevating the air/fuel ratio (ψ) significantly enhances CLC performance at ψ ≤ 1.0 but it insignificantly affects the CLC performance at ψ > 1.0. A higher total inlet flow rate leads to suppressed fuel conversion and a subsequent decline in CO2 yield. The particle heat transfer coefficient (HTC) in the AR is approximately 450 W/(m2·K), significantly higher than that in the FR of about 300 W/(m2·K).

Evaluation of CLC as a BECCS technology from tests on woody biomass in an auto-thermal 150-kW pilot unit

In this work, woody biomass is converted by chemical looping combustion (CLC) in the auto-thermally operated 150-kW pilot unit at SINTEF Energy Research in Norway, using ilmenite as an oxygen carrier. The pilot unit consists of two inter-connected circulating fluidized bed reactors, being the air and fuel reactor, respectively. The unit is simplified compared to many other lab and pilot units by not having a carbon stripper. The aim of the present study is to evaluate the main performance parameters when operating a relatively large CLC unit in auto-thermal mode, using a cheap natural mineral, ilmenite, as oxygen carrier. Another aspect with the tests is to verify if the omission of a carbon stripper can provide high enough capture efficiencies for solid fuels as biomass, with a large share of volatiles and a char remnant with high reactivity. As a comparison, tests with petcoke were performed, to assess the effect when using a fuel with a low share of volatiles and slow char conversion. The results imply that CO2 capture efficiencies can be well above 95 % in a larger industrial unit operating on biomass, even without a carbon stripper, but that a carbon stripper is definitely needed for fuels with less volatiles and low char reactivity.

Sulfur Interaction and Regeneration of CaMn0.775Ti0.125Mg0.1O2.9-δ Perovskite as Oxygen Carrier during Combustion of Sour Gas in a 500 Wth Chemical Looping Combustion Unit.

In the present study, the performance of a CaMn0.775Ti0.125Mg0.1O2.9-δ perovskite used as an oxygen carrier to burn sour gas with different H2S concentrations (up to 3000 vppm) in a continuous 500 Wth chemical looping combustion (CLC) prototype was investigated. After 29 h of sour gas combustion, the combustion efficiency had dropped by 18% in comparison with the reference test without sulfur addition. The characterization of the used particles of the perovskite confirmed that the presence of sulfur in the fuel gas had a poisonous effect through the formation of undesired compounds, such as CaSO4. The reactivity with CH4 and oxygen uncoupling capacity decreased, which could explain the decrease in the combustion efficiency. Two regeneration processes, one at high temperature (1273 K) and another one at low temperature (773-873 K), were carried out in a batch fluidized bed reactor to remove the amount of sulfur accumulated in the oxygen carrier particles. The detection of appreciable amounts of gaseous sulfur-based compounds (SO2 and H2S) during the experimentation and the postcharacterization results obtained through different techniques such as X-ray diffraction, ultimate analysis, and thermogravimetric analysis confirmed the effectiveness of both processes. Finally, the feasibility of implementation of the regeneration processes in a commercial CLC unit was thoroughly analyzed.

Techno-economic assessment of biomass and coal co-fueled chemical looping combustion unit integrated with supercritical CO2 cycle and Organic Rankine cycle

This study evaluates the effect of co-combustion of woody biomass and coal on the techno-economic performance of a 300 MWth in-situ gasification chemical looping combustion power plant. The circulating fluidized bed reactor system was designed and a modified macroscopic model was applied to predict the fuel conversion and the CO2 capture efficiency. The supercritical CO2 cycle and the Organic Rankine cycle were integrated with the heat sources for power generation. The results showed that increasing biomass share in the input thermal power, in addition to enhancing the CO2 capture efficiency, improves the coal conversion. Moreover, negative CO2 emissions are achieved as the biomass share exceeds 50 MWth. The net electrical efficiency of the plant is about 43.89% and grows slightly for higher biomass shares. For biomass share of 150 MWth, the CO2 capture efficiency increases from 79.27% to 90.87%. Also, the levelized cost of electricity (LCOE) rises by 15.9%–108.262 $/MWh due to higher biomass price. Despite this increased fuel cost, the LCOE is still lower than that value for the coal-fired power plant with conventional CO2 capture technology. Biomass utilization becomes more cost-effective than coal if the carbon tax is above 30 $/tCO2.

Numerical investigation of a 1MW full-loop chemical looping combustion unit with dual CFB reactors

Chemical looping combustion (CLC) is a novel carbon capture technology with inherent advantage of CO2 separation and less energy penalty. The oxygen carrier circulates between the reactors realizing the transportation of oxygen and heat and preventing the mixing of air with flue gas. Currently, it lacks researches on the industrial scale system which operates autothermal. In this work, three-dimensional simulations of 1MW chemical looping combustion unit with gaseous fuel are presented in the frame of Eulerian approach. The configuration with dual circulating fluidized bed reactors is built according to the experimental construction, including air reactor, fuel reactor, loop seals, cyclones and L-valve. The time-averaged and local pressure, temperature and gaseous products are predicted numerically and compared with experimental measurements. Simulation results show that the reduction level changes by 0.08 between reactors corresponding to the oxygen transfer. Due to the exothermic process in air reactor, the difference of outlet temperature between air reactor and fuel reactor is 63 °C. Moreover, the higher operating temperature and solid inventory are beneficial for raising the performance of system. Results turn out that the numerical models developed in this work can be used for investigating detailed characteristic or scale-up of CLC system with high accuracy, high efficiency and low cost.

Findings on the use of a Ca-based sorbent as an oxygen carrier precursor in a Chemical Looping Combustion unit

Limestone Chemical Looping Combustion (L-CLCTM) is a novel process to burn sulfurous fuels with intrinsic desulfurization and CO2 capture. L-CLCTM is based on using calcium-based sorbents as precursors for CaSO4 formation, which is used as an oxygen carrier. Its principle lies in the in-situ sulfur retention process performed in fluidized bed combustors burning solid fuels with high sulfur content. The target redox pair for the oxygen transference to the fuel is CaSO4/CaS. In this research work, experimental tests burning CH4, syngas and H2 with a moderate H2S concentration were conducted in a continuous CLC unit. This experimental campaign is first in a kind as there is hardly information about the CaSO4/CaS pair for the L-CLCTM process. High combustion efficiencies were achieved at moderate temperatures (800–850 °C) when burning H2 and syngas (∼96–99 %). Likewise, low CH4 combustion efficiency (∼59 %) was found even operating at a temperature as high as 945 °C. Additionally, experimental tests at different Ca/S molar ratios were performed. They revealed that it was possible to reach suitable sulfur retention values (∼82 %) by using a Ca/S molar ratio of 2.25. This value resulted in a very feasible ratio since it is commonly used in fluidized bed combustors.

Outstanding performance of a Cu-based oxygen carrier impregnated on alumina in chemical looping combustion

Chemical looping combustion (CLC) allows the combustion of a fuel with inherent CO2 capture by using an oxygen carrier to transfer the oxygen from the air to the fuel. Previously to the CLC scale-up, tests should be done in lab-scale CLC units to determine the combustion performance of promising oxygen carriers and, at the same time, to evaluate the durability of these materials. For that, the effect of operating conditions on the oxygen carrier ageing should be considered, which is often disregarded. In this work, tests were done burning a simulated biogas stream in a continuous 500 Wth CLC unit with a promising Cu-based oxygen carrier (Cu14Al_ICB). Operating conditions were carefully selected to maximize the durability of this oxygen carrier while complete CH4 combustion was achieved. These operating conditions were based on limiting both the variation of solids conversion by choosing suitable solids circulation rates and the oxidation degree of the particles in the air reactor by minimizing the air excess. Thus, the Cu14Al_ICB material exhibited an excellent mechanical resistance, estimating a particle lifetime of 20,000 h at 900 °C. In addition, copper migration to the surface of the particles and loss of copper were not relevant. This is the first time that under certain operating conditions, a Cu-based oxygen carrier can exhibit outstanding mechanical properties during continuous CLC operation at 900 °C.

Relevance of oxygen carrier properties on the design of a chemical looping combustion unit with gaseous fuels

AbstractChemical looping combustion (CLC) is a novel technology for the combustion of fuels with inherent CO2 capture. CLC is based on the transference of oxygen from air to fuel by means of an oxygen carrier which is based on a metal oxide. CuO/Al2O3 (14 wt.% CuO) and Fe2O3/Al2O3 (20 wt.% Fe2O3) particles have been used in several CLC units with different results when methane combustion was evaluated. In order to shed light on the main processes affecting methane conversion in CLC, a mathematical model for a dual circulating fluidized bed (DCFB) system was developed to simulate the behavior of CuO/Al2O3 and Fe2O3/Al2O3 in a CLC unit. The model consists of the coupling of individual fuel and air reactor models to simulate steady state of the CLC unit. Individual models consider both the fluid dynamics of the fluidized beds at the high velocity regime and the corresponding kinetics of oxygen carrier reactions, that is, reduction in the fuel reactor and oxidation in the air reactor. The model was validated using results obtained in a 120 kWth CLC unit with CuO/Al2O3 and Fe2O3/Al2O3 particles. The validated model was used to simulate the performance of these materials in the 10 MWth CLC unit. Desing parameters of the fuel and air reactors as well as the suitable particle size of the oxygen carriers were determined in order to achieve the complete combustion of natural gas in the CLC unit as a function of the oxygen carrier properties. © 2022 The Authors. Greenhouse Gases: Science and Technology published by Society of Chemical Industry and John Wiley & Sons Ltd.

Techno-economic analysis of a chemical looping combustion process for biogas generated from livestock farming and agro-industrial waste

Biogas is a renewable fuel that is generated from the decomposition of organic matter through the process of anaerobic digestion. The compound that provides biogas with its energy value is CH4, which accounts for between 40% and 75% of the gas, with CO2 being the other main component of this fuel. Although the biogas valorization process is carbon neutral, the overall process can become carbon negative with the application of CO2 capture technologies, such as chemical looping combustion (CLC). This work presents a techno-economic analysis of a 5 MWth plant for the generation of biogas from livestock farming and agro-industrial waste to produce electricity + heat or heat only (base cases), or for further treatment in a CLC unit (CLC cases), where the captured CO2 is converted into a raw material, e.g. for the production of greenhouse crops. Results from the comparative study of five different oxygen carriers used in CLC are also presented.The profitability of the base cases was evaluated by means of the Levelized Cost of Electricity (LCOE) and Levelized Cost of Thermal Energy (LCOTE) metrics, whereas the economic performance of the CLC cases was measured by the Levelized Cost of CO2 (LCOCO2). LCOE gave a value of €139.90/MWh for the base case, and LCOTE was €56.50/MWh for the modified base case, where biogas was combusted in a boiler to produce only heat. With regard to the CLC cases, LCOCO2 values ranged between €148.60 per tonne for a highly reactive, synthetic Cu-based oxygen carrier and €177.10 per tonne for ilmenite.Finally, by comparing the economic results obtained in this work with those found in the literature for conventional biogas production plants and greenhouse crop production processes, it can be concluded that the implementation of CLC technology in biogas plants has the potential to become a profitable and environmentally sustainable option for the valorization of organic waste because the CO2 generated in the fuel reactor of the CLC unit can be considered a marketable, high value-added product for the niche market of the greenhouse farming of horticultural crops.

Mechanistic study of chemical looping reactions between solid carbon fuels and CuO

Copper (Cu) based chemical-looping combustion (CLC) is a promising process that utilizes solid carbon fuel such as coal and biomass. Understanding the reaction kinetics in this process can facilitate the industrial design of CLC units. In this work, molecular dynamics (MD) simulations were performed to investigate the reaction kinetics of n-butane and two simplified solid carbon fuels (lignite and anthracite) with/without copper oxide (CuO) nanoparticle. In addition, experiments were conducted on the thermal characteristics, flammability, and flame speeds of CuO and solid carbon mixtures.For n-butane, oxidation on the CuO surface is the primary reaction since the activation energy of the surface reaction is much lower than that of oxygen (O2) combustion (9.2 vs. 53.3 kcal/mol). On the other hand, for lignite, there is a smaller difference in the activation energy of O2 combustion and surface reaction (23.04 vs. 6.34 kcal/mol). We hypothesize that some solid carbon fuels can have different reaction kinetics dependent upon temperature. This is proven by the case of a simplified anthracite coal: an Arrhenius plot shows that this solid carbon fuel has two different reaction kinetic regimes and the critical temperature for the change in kinetics is related to the oxygen uncoupling of the CuO nanoparticle. Like the modeling simulations, a change in activation energy is observed in the experimental results, where desorption of molecular oxygen from CuO becomes important.

Qualification of operating conditions to extend oxygen carrier utilization in the scaling up of chemical looping processes

Chemical looping combustion (CLC) is a technology allowing CO2 capture at low cost. The development of durable oxygen carrier materials is a key factor for the scale-up of CLC. Once a promising oxygen carrier has been identified dedicated studies into the effects of reaction conditions on the durability of these kinds of materials are required in order to improve their reliability before use at industrial scale. This method requires several long-term tests in CLC units each one of them to fixed conditions, which is time consuming and expensive. In this work, a low-effort method using thermogravimetric analysis was developed and validated against a high-effort method requiring the use of an oxygen carrier material for hundreds of hours in a CLC unit. The reaction pathways and variation in physico-chemical properties of a material with 14 wt% CuO impregnated on γ-Al2O3 during the course of 300 redox cycles were evaluated as a function of reaction temperature, variation in oxygen carrier conversion (ΔXs) and degree of oxidation/reduction in every redox cycle. As a result, preferred conditions to be used in a CLC unit were identified. In general, reactivity and mechanical integrity were not affected when the reaction temperature was 800 °C. However, a temperature of 900 °C was found to be potentially suitable when the material was highly reduced in each redox cycle and ΔXs was low. The use of this method for promising oxygen carriers can boost the identification of long lasting materials for the scale-up of chemical looping processes.

Feasibility of an integrated biomass-based CLC combustion and a renewable-energy-based methanol production systems

An integrated process layout for methanol production comprising different systems is proposed and numerically investigated. The core of the layout consists of a multiple interconnected fluidized bed system for the chemical looping combustion (CLC) of solid fuels. A coupled hydrodynamic and reactive model of the CLC system was applied to evaluate solid circulation rate, solid bed levels in different parts of the system, flue gas composition and flow rate, and thermal power production. System performances were evaluated by considering chemical and physical properties of six types of Mediterranean area biomass as fuels and of CuO supported on zirconia as oxygen carrier, respectively. The methanol production unit was modelled as a network of four adiabatic fixed beds in series with interstage cooling and its performances were evaluated by considering that the CO/CO2 stream coming from the CLC unit reacts over Cu/ZnO supported on alumina catalyst with a pure H2 stream coming from an array of electrolytic cells. The number of cells was evaluated by considering that a constant hydrogen production for converting the whole carbon content of the gaseous stream produced by the CLC process must be attained. By considering that only energy coming from renewable sources was fed to the cells array, the capability of the proposed process to be used as an energy storage system for excess energy production from renewable sources was assessed.

Redox performance of manganese ore in a fluidized bed thermogravimetric analyzer for chemical looping combustion

A key issue for commercial application of chemical looping combustion (CLC) technology is the selection of oxygen carriers (OCs) with good fluidization and high reactivity during the long-term redox operation. Conventional fluidized bed reactors and thermogravimetric analyzer (TGA) are fail to simultaneously satisfy the fluidization and real-time mass measurement of bed materials. A fluidized bed thermogravimetric analyzer (FB-TGA) combining the advantages of fluidized bed and TGA is believed to be a novel powerful tool for screening OCs for industrial CLC units. In this work, an innovative FB-TGA with a high weight measurement accuracy is designed to reflect the lifetime, redox reactivity, particle sintering and agglomeration characteristics of OCs during the CLC. Manganese ore was selected as a representative OC and redox cyclic tests with hydrogen as the reduction gas were conducted. Results indicate that the Mn3O4-MnO system acts as the main redox pair. The redox chemical reactions may intensify the attrition of manganese ore particles. This may be due to the pore-opening effect of H2 during the reduction of manganese ore, reducing mechanical strength and accelerating attrition of particles. In the reducing atmosphere, it is speculated that the generation of manganese silicates with a low melting point results in particle sintering and agglomeration at the bottom of the bed. The particle agglomeration gradually spreads inward and upward, and eventually leads to total collapse of the fluidized bed. Therefore, a high-grade manganese ore with less silicon element is more suitable for industrial CLC pilots.

Insitu gasification – chemical looping combustion of large coal and biomass particles: Char conversion and comminution

Utilization of large solid fuel particles in fluidized bed – Chemical Looping Combustion (CLC) has the benefits of reduced energy penalty related to carbon capture. When large fuel particles (mm-sized) are used, comminution plays a vital role in the fuel conversion rate, characteristics of ash, inventory loading and thus in the effective design of CLC systems. The present work deals with the conversion of char of large fuel particles and char fragmentation phenomenon in the insitu-gasification CLC environment. Three different coals and a woody biomass in the size range of + 8–25 mm are tested at three different bed temperatures (800 to 950 °C) in a hematite-based batch CLC unit, using steam as the fluidizing/gasification agent. The char conversion time is found to increase by 60 to 170% when particle size changes from 8 to 25 mm and reduced by 42 to 86% with the increase in bed temperature. Regardless of fuel type and feed size, the inception of char fragmentation is noticed in the very first quarter of conversion indicating its significant influence on the char burnout time. A minimum critical char size exists below which char weakening does not yield breakage, whose values vary between 4.4 and 14.2 mm depending on fuel type and feed size. Fuel type is found to be the prime influencer of char conversion time and fragmentation phenomena. This study recommends the use of large particles of all fuels up to 25 mm in CLC systems without any prior size reduction, except the high-ash coals.

On the optimization of physical and chemical stability of a Cu/Al2O3 impregnated oxygen carrier for chemical looping combustion

The objective of this study was to evaluate the effect of the chemical and thermal stress on the physical and chemical stability of a CuO/Al2O3 impregnated oxygen carrier during methane chemical looping combustion at high oxygen carrier to fuel ratios to ensure low solid conversion variations. The Cu-based particles were subjected to 130 h of operation in a 0.5 kWth chemical looping combustion unit burning CH4 at steady state and unchanged conditions. Two batches of particles were used to operate the fuel and air reactor either at 800 °C or 900 °C. A full solid characterization regarding crystalline compounds, oxidation state, ASTM attrition index, crushing strength and morphology analysis was carried out in order to investigate the physical and chemical stability of the oxygen carrier. Main conclusion derived from this research work is that the low oxygen carrier conversion variation allowed reducing the chemical stress and as consequence the copper loss from particles. However, the oxygen carrier was difficult to reoxidize at 900 °C due to the formation of CuAlO2. Operating at temperatures about 800 °C and at low solid conversion variation is proposed since copper loss was limited maintaining an adequate physical stability.

Conversion characteristics of lignite and petroleum coke in chemical looping combustion coupled with an annular carbon stripper

Chemical looping combustion (CLC) of solid fuels was studied in a 30 kW dual fluidized-bed system coupled with an annular carbon stripper for char separation by using a kaolin-promoted manganese ore oxygen carrier. Two solid fuels, a lignite and a petroleum coke, were tested in the CLC unit. The CLC unit was operated continuously for more than 160 h. The effects of the fuel size and residence time in the fuel reactor on the carbon capture efficiency and oxygen demand were investigated. The char separation efficiency of the annular carbon stripper reached 90%, and a maximum carbon capture efficiency of 97% was achieved for the 106–212 μm lignite. The carbon capture efficiency was affected by the fuel particle size and residence time. When >212 μm lignite particles were used, there was a ~ 12% oxygen demand. The carbon capture efficiency in the experiment with petroleum coke was only 45% due to the slow gasification rate. A model was applied to analyze the influence of key factors on the carbon capture efficiency. The redox kinetics of the tested oxygen carrier were studied by a micro-fluidized bed thermogravimetric analysis method.

Three-dimensional modelling of the multiphase hydrodynamics in a separated-gasification chemical looping combustion unit during full-loop operation

Separated-gasification chemical looping combustion (SG-CLC) is a clean utilization technology for fossil fuels, which can separate CO2 during high-performance combustion process with low degradation of oxygen carrier and zero-energy penalty. As an important part of the optimization, modelling and prediction of the multiphase hydrodynamics in the SG-CLC unit were conducted in this work. This unit consists of a gasifier (GR), a reduction reactor (RR) and an air reactor (AR). For thorough understanding of the flow behaviors of three phases (gas, oxygen carrier and sand phases), a three-dimensional computational fluid dynamics (CFD) model for SG-CLC system was first implemented. The main purpose is to predict multiphase hydrodynamics at the fuel side of this SG-CLC system due to its significant effects on combustion efficiency. The axial pressure profile predicted by the CFD model was validated by experimental data to demonstrate its feasibility. Then, based on this model, the hydrodynamics of different phases at fuel side (GR and RR) were investigated under fundamental condition, which indicated the gas-solid flow mechanism in circulation establishment process. Furthermore, effects of the operation condition on the hydrodynamics properties were investigated. The local gas-solid slip velocity in RR was fitted as the function of superficial fluidizing number Nr and axial position, which showed high accuracy for the prediction in this system.

Evaluation of different strategies to improve the efficiency of coal conversion in a 50 kWth Chemical Looping combustion unit

Minerals or industrial waste materials are considered promising oxygen carriers for coal combustion through in-situ Gasification Chemical Looping Combustion (iG-CLC) process in order to maintain CO2 capture at low cost. Nevertheless, complete coal combustion to CO2 and H2O is usually not achieved and different solutions have been outlined to improve it. The aim of this work is to analyze the potential of two of these strategies: (1) using a more reactive oxygen carrier; and (2) to have two fuel reactors by feeding the coal into the carbon stripper. Coal combustion in a 50 kWth CLC unit was carried out using two oxygen carrier materials, namely Norwegian ilmenite and Tierga iron-ore. Also, an additional test was carried out feeding the coal directly into the carbon stripper of the CLC unit, in contrast with the conventional coal feeding to the fuel reactor. CO2 capture efficiency was barely affected by the type of oxygen carrier material, but slightly lower values were obtained when coal was fed to the carbon stripper. In contrast, coal combustion efficiency was enhanced by using the iron-ore material, with a potential decrease of the total oxygen demand of 40%, achieving a minimum value of total oxygen demand of 4.1%. Also, the total oxygen demand was decreased by 24% when coal was fed to the carbon stripper due to the improvement in the combustion of the volatiles in the fuel reactor. The combination of both strategies has high potential to maximize the coal combustion via iG-CLC process.