Chemical Looping Combustion Of Fuels Research Articles

Oxygen uncoupling behaviour for ilmenite ore oxygen carrier generated from a calcination treatment mixed with natural manganese ore

AbstractChemical looping with O2 uncoupling aims at using an oxygen carrier (OC) with O2 uncoupling behaviour to promote fuel conversion. Natural ilmenite ores have been considered highly promising OCs for chemical looping technology; however, they do not possess any O2 uncoupling behaviour. Mn‐modified ilmenite ores as OCs are capable of O2 uncoupling, while most of them are synthesized via complicated procedures by using costly chemicals. In this study, a strategy of calcination treatment on ilmenite ores mixed with manganese ores has been established to introduce Mn into the ilmenite OCs, endowing them with O2 uncoupling behaviour in a simple and low‐cost manner. The O2 uncoupling behaviour from Mn‐modified ilmenite ores is mainly due to the newly formed (Fe1−xMnx)2O3/(Fe1−xMnx)3O4 crystal phases generated during the calcination treatment, which also alleviate the thermodynamic limit of the Mn2O3‐Mn3O4 redox pair. As a result, the Mn‐modified ilmenite ore OCs can release O2 at high temperatures when decreasing the oxygen partial pressure. But more importantly, the reduced OCs can be restored in the air isothermally. This established simple calcination treatment method can be used as a low‐cost strategy for producing ilmenite‐based OCs with O2 uncoupling behaviour. The O2 uncoupling behaviour is expected to be beneficial to chemical looping combustion of fuels, promote fuel conversion, minimize OC loading, and reduce energy consumption.

Integrated diesel fueled chemical looping combustion for power generation and CO2 capture – Performance evaluation based on exergy analysis

An integrated process for gasification of diesel and chemical looping combustion of the gasified syngas for inherent power generation and CO2 capture is developed using Aspen Plus. This system consists of four main units, including (1) gasification of diesel into syngas to ensure complete fuel conversion, (2) chemical looping combustion using an alumina supported nickel-based oxygen carrier, (3) gas turbine-based power generation and (4) steam turbine-based power generation. The model shows a high accuracy (relative error: 2.98%) which is indicated by good agreement of operating temperature, product composition and net power generation between the simulation results and data from the literature. The performance of the integrated system is evaluated based on both energy and exergy analysis approaches. In order to improve the system performance, various split ratio of (diesel) syngas to the CLC unit and to the combustion are investigated. The analysis shows that both the flow rate of oxidation air and the split ratio of syngas to the combustion unit have considerable influences on system performance while the minor effect is found in the pressure ratio. For the overall efficiency, the highest electrical efficiency is 42% and the highest exergy efficiency is 65%.

Experimental and kinetic studies on in-situ CO2 gasification based chemical looping combustion of low ash coal using Fe2O3 as the oxygen carrier

Chemical looping combustion (CLC) technology has grabbed the attention for rectifying the carbon capture issues with minimal energy penalty. The direct utilization of solid fuels such as coal and biomass in CLC by in-situ gasification technology would reduce the complexity of the overall process. In the present study, in-situ CO2 gasification of direct-coal fueled CLC experiments are conducted using a fixed bed reactor under atmospheric pressure in a batch-wise mode of operation. The low cost metal oxide, Fe2O3, is used as the oxygen carrier particles for the CLC of a low ash based North East Indian coal. Pyrolysis and CO2 gasification experiments are performed with and without the presence of metal oxides for estimating the CO2 yield. The results show that the CO2 yield is increased from 17.5% (without metal oxides) to 88.7% (with metal oxides) under the N2 atmosphere. A highest CO2 yield of 96% is observed under in-situ CO2 gasification incorporated CLC conditions. Further, thermo gravimetric analysis (TGA) is conducted to study the conversion and instantaneous reactivity between the coal and metal oxides. It is estimated that 83% conversion of the coal-Fe2O3 mixture is attained under the CO2 atmosphere, while it is 57% in the N2 atmosphere. The kinetic parameters are estimated using the TGA data for the reaction between coal and metal oxide under N2 and CO2 atmosphere using reaction order models. It is found that the first and third order models show the best fit for the non-CLC and CLC process, respectively.

Experimental and kinetic analysis for particle scale modeling of a CuO-Fe2O3-Al2O3 oxygen carrier during reduction with H2 in chemical looping combustion applications

A kinetic analysis of the H2 reduction of a CuO-Fe2O3-Al2O3 oxygen carrier in gas phase fueled Chemical Looping Combustion of synthesis gas was utilized to derive particle scale representation. An experimentally driven study was carried out to provide an array of operational data sets for kinetic modelling approaches. The impact of key operational variables on the kinetics of the novel oxygen carrier were examined, with emphasis on the application of reliable phenomena driven particle scale models to describe the reduction behavior. Due to the novel nature of the material, a series of experimental studies were carried out to provide a fundamental understanding of how the material changed as oxygen was depleted from the structure due to reduction with H2. This include quantification of the complex mixed metal oxide phase and changes due to lattice oxygen depletion. It was found that H2 reduction occurs in a multistep process where CuFeAlO4 → Cu0+ + FeAl2O4 → Cu0+ + Fe0+ + Al2O3 as oxygen is depleted from the structure. This multistep process was successfully emulated through the use of a two interface Grainy pellet model in which reaction (kinetic) control was the main rate limiting step. This is validated through the examination of other potential rate limiting resistances. The model emulates changes in key operation variables with good accuracy.

Study of Conditions of Binary Particle Mixture Motion Applied to Chemical Looping Combustion of Fuel with Carbon Dioxide Capture

Chemical looping combustion and gasification of fuels with using metal oxides as oxygen carriers is a rapidly developing technology for capturing carbon dioxide. This technology is based on the use of interconnected reactors with a fluidized bed and circulating fluidized bed. Crucial in the technology is the reliable security of a high solid circulation rate between the reactors to maintain the desired temperature. When burning solid fuels, ash particles inevitably enter the metal oxide stream. This can lead to a change in the hydrodynamic parameters of an interconnected reactor system. In this paper, we present the results of an experimental study of fluidization conditions and hydrodynamics of a reactor with a circulating fluidized bed under motion conditions of binary mixtures of particles with different density. We also justified the conditions for simulating the particle sizes of heavy and light fractions as well as their mass in the reactor and a portion of a light fraction. We showed that, at a small addition of a light fraction, the minimum fluidization rate decreases markedly. Particle segregation was observed for large metal oxide particles, while light particles were found to be near the layer surface. The addition of a light fraction with a mass fraction of 3–12% does not significantly affect the mass flow profile of particles in a circulating fluidized bed reactor. The fractional composition of the particles in both the upward flow in the center and the downward stream near the walls of reactor is approximately the same. In the central part of the riser, the concentration of the light fraction was found to be slightly higher than its average value. The obtained results support the possibility of using the previously developed dependences for the calculation of hydrodynamics under motion conditions of binary mixtures of particles of different densities in the presence of a light fraction of 3–12%.

Characteristics of a 10 kW honeycomb reactor for natural gas fueled chemical-looping combustion

Chemical-looping combustion (CLC) is already treated as a promising way to capture CO2 in the utilization of fossil fuels. The most used reactors for the CLC are fluidized-beds, in which the fuel conversion and the conversion of fuel to CO2 is determined by the bed height. Here in this study, the CLC in an advanced 10 kW honeycomb reactor is studied by using natural gas as the fuel and Fe2O3 as the oxygen carrier. In the honeycomb reactor, a honeycomb chamber consisted by the oxygen carrier is employed to enhance the contact area and the disturbance between the fuel gas and the oxygen carrier. Both of these two enhancement are benefit for achieving a high CH4 conversion and a high conversion of CH4 to CO2. The experiment results show that three stages of Fe2O3 to Fe3O4, Fe3O4 to FeO and FeO to Fe are occurred in sequence during the reduction reaction of Fe2O3 and CH4 in the honeycomb reactor. The behaviors and the relationships for these complicated reactions, the oxygen transfer rate, the CH4 conversion and the conversion of CH4 to CO2 at different stages are further experimentally studied. Additionally, to increasing the conversion of CH4 to CO2 in the continuous operation, the characteristics for the honeycomb reactor in redox cycles are also experimentally investigated. Our study here would be expected to provide a new method for developing the energy and environment compatible systems.

Efficiency Improvement of an Iron-based Syngas Fueled Chemical Looping Combustion Plant with Carbon Capture

In this study the performances of two syngas fueled iron-based CLC plants, one using a conventional cold syngas cleaning system and the other one with hot syngas cleaning, were evaluated and compared. In the second configuration, before feeding the chemical looping fuel reactor, the syngas was cleaned at high temperatures using mainly a zinc-based desulfurization unit. The simulation results showed that the plant configured with a hot syngas cleaning system has a net electrical efficiency of 42.6%, which was 1.75% points higher than that of the plant with cold gas cleaning. It was also shown that both CLC plants can achieve more than 99% carbon capture rates.

ChemInform Abstract: Some Remarks on Direct Solid Fuel Combustion Using Chemical Looping Processes

AbstractReview: 48 refs.

Three-dimensional simulation of a coal gas fueled chemical looping combustion process

A three-dimensional numerical model has been developed to simulate the chemical looping combustion process in the fuel reactor. A bubbling fluidized bed with a length of 0.24 m, width 0.24 m and height 1 m was adopted as the fuel reactor. The oxygen carrier investigated here was initially prepared with 14 wt% of metal oxide CuO on 86 wt% of inert material Al 2O 3. The coal gas from coal gasification was used as the fuel and its composition was assumed as 55 vol.% CO, 30 vol.% H 2 and 15 vol.% CO 2. The flow patterns, distributions of gas components, profiles of bubbles and conversions of gas reactants were obtained. In addition, the effects of particle diameter and superficial gas velocity on the fuel conversion were studied, respectively. The fuel conversion would increase if the gas residence time and the surface to volume ratio of particles are increased.

An Advanced Power-Generation System With CO2 Recovery Integrating DME Fueled Chemical-Looping Combustion

Dimethyl ether (DME) is a promising alternative fuel, but direct combustion of DME will result in extra energy penalty for CO2 separation. In this paper, an advanced power-generation system with CO2 recovery integrating DME fueled chemical-looping combustion is proposed. In the reduction reactor, DME is oxidized by Fe2O3 into CO2 and H2O, and Fe2O3 is reduced into FeO simultaneously. Since the endothermic reduction in Fe2O3 with DME requires relatively low-grade thermal energy around 180°C, waste heat is used to provide the reaction heat. FeO is oxidized into Fe2O3 by air in the oxidation reactor, producing high-temperature flue gas to generate electricity through a thermal cycle. The gas production from the fuel reactor only consists of CO2 and H2O, so CO2 can be easily separated through condensing with no extra energy penalty. As a result, the thermal efficiency could be expected to be 58.6% at a turbine inlet temperature of 1288°C. This proposed system may provide a new approach for high efficient use of DME in the industrial fields, and offer a possibility of chemical-looping combustion with inherent CO2 capture for the alternative fuel.

Syngas combustion characteristics of four oxygen carrier particles for chemical-looping combustion in a batch fluidized bed reactor

Syngas combustion characteristics of oxygen carrier particles have been investigated. Experiments were performed on four oxygen carrier particles in a fluidized bed reactor. All four oxygen carrier particles showed high gas conversion, high CO2 selectivity, and low CO concentration in the reducer and very low NOx (NO, NO2, N2O) emissions in the oxidizer. Moreover, all particles showed good regeneration ability during successive reduction-oxidation cyclic tests up to the 10th cycle. The results indicate that inherent CO2 separation, NOx-free combustion, and long-term operation without reactivity decay of oxygen carrier particles are possible in a syngas fueled chemical-looping combustion system with NiO/bentonite, NiO/NiAl2O4, CoxOy/CoAl2O4, and OCN-650 particles. However, CoxOy/CoAl2O4 represented slight decay of oxidation reactivity with the number of cycles increased and the oxidation rate slower than other particles.

On the development of novel reactor concepts for chemical looping combustion

Abstract The paper describes the development of a novel reactor concept for natural gas fueled chemical looping combustion (CLC). The reactor is best described as a rotating bed reactor in which a doughnut shaped fixed bed containing an oxygen carrier material is rotated between different sectors where air and methane are fed. The gases are fed radially outwards through the fixed bed. Between the air and methane sectors are sectors where an inert gas is fed to avoid uncontrolled mixing of air and methane. The rationale for the choice of reactor is discussed and a CuO/Al 2 O 3 based oxygen carrier has been selected for the initial reactor evaluation. A major challenge with the proposed reactor setup is to avoid mixing between the air and methane side caused by the unavoidable insufficient sealing between the moving parts. Initial testing show that mixing is only partly avoided, and a degree of separation corresponding to around 80% is observed at ambient temperature for the first reactor prototype. Further work will be to improve the design in order to reduce gas mixing further and to demonstrate real CLC operation utilizing the reactor.

Natural Gas Combustion Characteristics in a Chemical-Looping Combustor with Three Different Oxygen Carrier Particles

Natural gas combustion characteristics of oxygen carrier particles were investigated in a batch type bubbling fluidized bed reactor (0.05 m ID, 0.6 m high). Three particles, NiO/bentonite, NiO/NiAl2O4, and CoxOy/CoAl2O4, were used as oxygen carrier particles. Natural gas and air were used as reactants for reduction and oxidation, respectively. All three oxygen carrier particles showed high gas conversion, high CO2 selectivity, and low CO concentration during reduction and no NOx (NO, NO2, N2O) emissions during oxidation. Moreover, all three particles showed good regeneration ability during successive reduction–oxidation cyclic tests up to the 10th cycle. The gas conversion, CO2 selectivity and CO concentration were maintained to 97% of initial values for all three particles. These results indicate that inherent CO2 separation, NOx-free combustion, and long-term operation without reactivity decay of oxygen carrier particles are possible in the natural gas fueled chemical-looping combustion system with NiO/beotonite, NiO/NiAl2O4 and CoxOy/CoAl2O4 particles.

05/00992 A new type of coal gas fueled chemical-looping combustion

05/00992 A new type of coal gas fueled chemical-looping combustion

A new type of coal gas fueled chemical-looping combustion

A new type of coal gas fueled chemical-looping combustion is experimentally investigated by means of a fixed-bed reactor operated at elevated pressure. Chemical-looping combustion may be carried out in two successive reactions between two reactors, a reduction reactor (coal gas with metal oxides) and an oxidation reactor (reduced metal with oxygen in the air), which may lead to a breakthrough in clean coal technology by simultaneously allowing efficient use of energy and greenhouse gas control. We have experimentally examined the kinetic behavior between solid looping materials and coal gas in a high-pressure fixed bed reactor. On the basis of the development of suitable material and the good reactivity with the fixed bed reactor, we have identified that the coal gas fueled chemical-looping combustor has much better reactivity than natural gas combustors, and this phenomenon is completely different from direct combustion with natural gas. The promising results obtained here will be valuable for the design of a practical reactor.

Investigation of a novel gas turbine cycle with coal gas fueled chemical-looping combustion

Investigation of a novel gas turbine cycle with coal gas fueled chemical-looping combustion

Reactivity study on a novel hydrogen fueled chemical-looping combustion

In this paper the reactivity study on hydrogen fueled chemical-looping combustion, which is capable of making breakthrough in simultaneous contribution to the efficient use of energy and being environmentally benign, has been carried out by a thermogravimetric analyzer (TGA) and a fixed bed reactor. The hydrogen fueled chemical-looping combustion in the new gas turbine cycle consists of two successive reactions: hydrogen fuel is reacted with metal oxide (reduction of metal oxide), instead of air or pure oxygen, and then the reduced metal is successively oxidized by air. Here, we have developed looping materials based on the integration of NiO, as solid reactants, with a composite metal oxide of NiAl 2O 4, as a binder, leading to a significant role in improving reaction rate, conversion, and regenerability in cyclic reaction in this combustor, compared with the other materials. These promising results indicated that this novel hydrogen fueled chemical-looping combustion is expected to be an effective use of hydrogen energy in power generation.

A novel gas turbine cycle with hydrogen-fueled chemical-looping combustion

In this paper we have proposed a novel gas turbine cycle with hydrogen-fueled chemical-looping combustion, and the system study on two hydrogen-fueled power plants, the new gas turbine cycle and an advanced gas turbine cycle with H 2/O 2 combustion, has been investigated with the aid of exergy principle (EUD methodology). The hydrogen fueled chemical-looping combustion in the new gas turbine cycle consists of two successive reactions: hydrogen fuel is reacted with metal oxide (reduction of metal oxide), and then instead of air or pure oxygen, the reduced metal is successively oxidized by the saturated air. As a result, the new hydrogen-fueled gas turbine cycle has a breakthrough performance, with at least about 12 percentage-point higher efficiency compared to the gas turbine cycle with H 2/O 2 combustion, and will be environmentally superior due to complete elimination of NO x formation. The promising results obtained here indicated that this novel gas turbine cycle with hydrogen-fueled chemical looping combustion could make a breakthrough in efficient use of hydrogen energy in power plants.