Autothermal Chemical Looping Reforming Research Articles

Catalyst-enhanced autothermal chemical looping reforming: Intrinsic SMR kinetics and numerical simulation

In this work, we propose a catalyst-enhanced autothermal chemical looping reforming (CE-aCLR) to address the environmental concerns associated with toxic Ni-based oxygen carrier (OC) and the low fuel conversion related to the low reactivity of Fe-based OC. In this process, a non-toxic noble-metal-based steam methane reforming (SMR) catalyst is employed for methane conversion, while a Fe-based OC is employed for oxygen transfer between two reactors. Firstly, a commercial Rh-based SMR catalyst is studied in a micro-fixed bed reactor and its intrinsic reaction kinetics are determined. Then, a 1-D CE-aCLR model is developed based on a verified multi-scale aCLR model to facilitate analyzing commercial-scale feasibility. This model accounts for the essentials of the reactor hydrodynamics, mass and heat transfer, detailed reaction kinetics, and the influence of the solids residence time distribution in the fuel reactor. The main dimensions of a commercial CE-aCLR unit are determined and this unit is simulated using the developed model. The results demonstrate the feasibility of the novel, environmentally friendly process that enables high methane conversion using Fe-based OC within realistically sized reactors and an acceptable solid circulation rate. Moreover, sensitivity study shows that the CE-aCLR allows using OCs with low activity (potentially low cost) while maintaining high CH4 conversion.

Livestock Agriculture Greenhouse Gases for Electricity Production: Recent Developments and Future Perspectives

The focus of this review paper was to investigate innovations currently employed to capture and use greenhouse gases produced within livestock farms for energy production and expected future directions. The methods considered for data collection regarded a systematic review of the literature, where 50 journal articles were critically reviewed. The main findings identified that the conventional method used in transforming livestock agriculture greenhouse gases into energy regards the combustion of biogas. However, emerging methods encompass microbial fuel cells, dry biogas reforming, steam biogas reforming, auto thermal Chemical Looping Reforming (CLRa), and gas-to-liquid methods that convert methane to liquid hydrocarbons. The conclusions from the review are that there is a potential to integrate these methods in livestock agriculture in order to generate energy from greenhouse emissions and reduce the reliance on fossil fuels.

Research progress on chemical looping reforming of macromolecular components of volatiles from biomass pyrolysis based on decoupling strategy

This paper focuses on the development of chemical-looping reforming of macromolecular organic compounds from biomass pyrolysis based on decoupling strategy, including glycerol, benzene, and toluene. Firstly, the influence characteristics of pyrolysis conditions on the distribution of volatile are analyzed. Pyrolysis temperature and heating rate are the two most important factors. Three technical routes to prepare hydrogen-rich syngas by chemical-looping reforming of typical macromolecular components in the volatile components of biomass pyrolysis were emphatically discussed, which include auto-thermal chemical-looping reforming (CLRa), chemical-looping steam reforming (CLSR), and chemical-looping dry reforming (CLDR). The types of oxygen carriers, reforming characteristics, and reaction mechanisms related to the above three routes were compared. In the future, chemical-looping reforming based on the decoupling strategy focuses on developing oxygen carriers with high lattice oxygen reserves, fast transmission rate and good anti-coke formation performance, and more efficient fluidized bed reactors. At the same time, density functional theory calculations and reaction experiments combined to reveal the reaction mechanism, integrate and optimize the system's energy flow and material flow.

Production of hydrogen by chemical looping reforming of methane and biogas using a reactive and durable Cu-based oxygen carrier

The objective of this work was to assess the suitability of a synthetic Cu-based oxygen carrier in a continuous pilot plant for the production of blue and green hydrogen through the autothermal Chemical Looping Reforming (CLRa). In CLRa, methane is converted to a H2 + CO mixture through partial oxidation and reforming reactions in the fuel reactor. The degree of the partial oxidation of methane was defined by controlling the oxygen flow in the air reactor. Steam was used as reforming gas in natural gas to produce blue H2, but the existing CO2 in biogas was the reforming gas to produce green H2. Operating at 950 °C in the fuel and air reactors, CH4 conversion and H2 yield parameters were 96 % and 2.60 mol of H2 per mole of CH4, respectively. These experimental results were close to the theoretical values that could be achieved in the CLRa process. Furthermore, the physicochemical characterization of the samples extracted from the pilot plant throughout the experimental campaign revealed that the Cu-based oxygen carrier maintained its mechanical integrity and chemical stability under harsh operating conditions. Therefore, it can be concluded that Cu-based oxygen carriers can be considered a promising alternative to Ni-based materials for the production of blue and green hydrogen through the CLRa process.

Numerical simulation of commercial scale autothermal chemical looping reforming and bi-reforming for syngas production

Autothermal Chemical Looping Reforming (a-CLR) is an emerging technology that facilitates CO2 capture and minimizes energy losses in syngas production. The dual-fluidized bed process uses a bubbling fuel reactor (FR) and a riser air reactor (AR). A 1-D multiscale model was developed that couples fluidized bed hydrodynamics with intrinsic reaction kinetics, including catalyst deactivation by oxidation and coke formation. An a-CLR unit with a capacity equivalent to 50 conventional reformer tubes was considered to demonstrate feasibility. The effects of the catalyst activity, main operation conditions and CO2 co-feeding on the performance were then analyzed. The results confirm a-CLR is feasible with realistic reactors dimensions and solids circulation rate. To avoid the risk of sintering and catalyst deactivation, the oxygen carrier should only be slightly oxidized in the AR. Autothermal operation then requires an oxygen-to-CH4 feed ratio of around 1.2. The high catalyst-to-gas feed ratio in the FR and bubble-emulsion phase mass transfer limitations result in a low sensitivity of the methane conversion to the catalyst activity. A low H2O-to-CH4 feed ratio introduces a risk for coke formation in the bottom of the FR, but part of the feed methane is fully oxidized, producing H2O and CO2 in the emulsion phase and mitigating this risk. Co-feeding CO2 with CH4 and H2O is seen to allow adjusting the H2/CO-ratio of the syngas, but increases the risk of coke formation. Finally, heat recovery from the flue gas and syngas from both reactors by preheating the feed gases further increases the energy efficiency.

Autothermal chemical looping reforming process of different fossil liquid fuels

The autothermal Chemical-Looping Reforming (a-CLR) is a process where syngas is produced with two main advantages; there are captured CO2 emissions and the heat required for the syngas production is generated by the process itself. A Ni-based material is used as oxygen carrier circulating between two fluidized bed reactors: the fuel and air reactors. In this work, the auto-thermal conditions in a global H2 production process, integrated by the a-CLR process and a Water Gas Shift reactor, using different liquid fossil fuels were theoretically determined. The hydrogen production per mol of carbon in the fuel was similar for all fossil fuels, taking a value of 2.2 at the optimal operating temperature (700 °C). In addition, the possibility of working at low temperature for a maximum H2 production was experimentally demonstrated in a continuous 1 kWth a-CLR unit.

Modelling study of two chemical looping reforming reactor configurations: looping vs. switching

Autothermal Chemical Looping Reforming (CLR) is a promising technology for hydrogen production with integrated CO2 separation. However, the interconnected CLR reactor configuration is expected to present significant scale up challenges, especially under the pressurized conditions required for high process efficiency. These challenges can be circumvented by carrying out the reduction/oxidation reactions in a single bubbling/turbulent fluidized bed alternatively fed with fuel and air, henceforth called gas switching reforming (GSR). The primary drawbacks of the GSR concept are the undesired mixing between fuel and nitrogen after the gas feed switch and the need for high temperature valves at the reactor outlet. The performance of the CLR and GSR concepts are compared using a generic phenomenological model, applicable over different fluidization regimes. Results showed that the GSR process is best operated by separating the reduction and reforming reactions, whereas these reactions occur simultaneously in the CLR fuel reactor. This fundamental difference led to lower fuel conversion, but a higher heating value syngas in the GSR process. Separation of reduction and reforming steps in the GSR concept also allows for the efficient utilization of the off-gas fuel from a PSA unit for high purity pressurized hydrogen production. This makes the GSR process more applicable to hydrogen production with integrated CO2 capture, whereas the CLR concept is better suited to power production with pre-combustion CO2 capture.

Optimization of hydrogen production with CO2 capture by autothermal chemical-looping reforming using different bioethanol purities

Autothermal Chemical-Looping Reforming (a-CLR) is a process which allows hydrogen production avoiding the environmental penalty of CO2 emission typically produced in other processes. The major advantage of this technology is that the heat needed for syngas production is generated by the process itself. The heat necessary for the endothermic reactions is supplied by a Ni-based oxygen-carrier (OC) circulating between two reactors: the air reactor (AR), where the OC is oxidized by air, and the fuel reactor (FR), where the fuel is converted to syngas. Other important advantage is that this process also allows the production of pure N2 in the AR outlet stream. A renewable fuel such as bioethanol was chosen in this work due to their increasing worldwide production and the current excess of this fuel presented by different countries.In this work, mass and heat balances were done to determine the auto-thermal conditions that maximize H2 production, assuming that the product gas was in thermodynamic equilibrium. Three different types of bioethanol has been considered according to their ethanol purity; Dehydrated ethanol (≈100vol.%), hydrated ethanol (≈96vol.%), and diluted ethanol (≈52vol.%). It has been observed that the higher H2 production (4.62mol of H2 per mol of EtOH) has been obtained with the use of diluted ethanol and the surplus energy needed could be compensated by the energy save achieved during the purification of ethanol in the production process.

Simulation of hydrogen production through chemical looping reforming process in a packed-bed reactor

In the present work the numerical analysis of an autothermal chemical looping reforming (CLR) packed-bed reactor for hydrogen production is presented. The reactor works with Ni-based oxygen carriers, methane is used as fuel and continuous cyclic operations are simulated. The proposed process poses a number of challenges, namely the choice of the time-length of oxidation and reduction phases, the start-up temperature and the cycle design. This paper theoretically quantifies these challenges through numerical simulations. A 1D numerical reactor model, validated by comparison with experimental data available in literature, was developed. Results for the cyclic process are presented, and the effects on the feasibility of the process of a variation in operating conditions are discussed. It is concluded that an appropriate choice of both the initial temperature and the length of oxidation and reduction phases is essential prerequisite for the process feasibility and performances.

Hydrogen production by auto-thermal chemical-looping reforming in a pressurized fluidized bed reactor using Ni-based oxygen carriers

This work presents the experimental results obtained during auto-thermal chemical-looping reforming (CLRa) in a semicontinuous pressurized fluidized bed reactor working with two Ni-based oxygen carriers and using methane as fuel. During operation the effect of the total pressure, reduction reaction temperature, and oxygen carrier-to-fuel molar ratio on CH 4 conversion, gas outlet concentrations, and carbon formation was analyzed. In the range of pressures analyzed (up to 10 bars), it was found that an increase in the total operating pressure did not produce a negative effect on the gas product distribution obtained in the process. At all operating pressures the CH 4 conversion was very high (>98%) and no carbon formation was detected. The most important variable affecting the gas product distribution was the solid circulation rate, that is, the oxygen carrier-to-fuel molar ratio (NiO/CH 4). The oxygen carriers were physically and chemically characterized by several techniques before and after using in the pressurized fluidized bed reactor. Important changes in the surface texture and the solid structure of the oxygen carrier particles were not detected. These results suggest that these oxygen carriers could have a high durability, being suitable for use in a pressurized CLRa system.

Synthesis gas generation by chemical-looping reforming using a Nibased oxygen carrier

This work presents the experimental results obtained during auto-thermal chemical looping reforming (CLR) in a 900 Wth circulating fluidized bed reactor using methane as fuel. An oxygen carrier based on NiO and supported on J-Al2O3 was used during more than 50 hours of operation and the effect of different operating variables, like fuel reactor temperature, H2O/CH4 molar ratio and solid circulation rate, on CH4 conversion and gas product distribution was analyzed. It was found that in all operating conditions CH4 conversion was very high (>98%) and the most important variable affecting to the gas product distribution was the solid circulation rate, that is, NiO/CH4 molar ratio. During operation the oxygen carrier particles maintained their physical and chemical properties. These results suggest that this oxygen carrier could have a high durability, being a suitable oxygen carrier for a CLR system.

Hydrogen production by chemical-looping reforming in a circulating fluidized bed reactor using Ni-based oxygen carriers

This work presents the experimental results obtained during auto-thermal chemical-looping reforming (CLR) in a 900 W th circulating fluidized bed reactor under continuous operation using methane as fuel. Two oxygen carriers based on NiO and supported on γ-Al 2O 3 and α-Al 2O 3 were used during more than 50 h of operation with each oxygen carrier. During operation the effect of different operating variables, like fuel reactor temperature, H 2O/CH 4 molar ratio and solid circulation rate, on CH 4 conversion and gas product distribution was analyzed. It was found that in all operating conditions CH 4 conversion was very high (>98%) and the most important variable affecting to the gas product distribution was the solid circulation rate, that is, NiO/CH 4 molar ratio. Similar gas product distribution was obtained working with both oxygen carriers although at different NiO/CH 4 molar ratios. The oxygen carrier of NiO on α-Al 2O 3 needed lower NiO/CH 4 molar ratio to reach the same gas product composition than the oxygen carrier of NiO on γ-Al 2O 3. Working at optimal operating conditions, 2.5 moles of H 2 per mol of CH 4 could be obtained in this process. During operation the oxygen carrier particles maintained their physical and chemical properties. These results suggest that these oxygen carriers could have a high durability, being suitable oxygen carriers for a CLR system.

Using continuous and pulse experiments to compare two promising nickel-based oxygen carriers for use in chemical-looping technologies

Chemical-looping technologies have obtained widespread recognition as power or hydrogen production units with inherent carbon capture in a future scenario where CO 2 capture and storage (CCS) is reality. In this paper three different techniques are described; chemical-looping combustion and two categories of chemical-looping reforming. The three techniques are all based on oxygen carriers that are circulating between an air- and a fuel reactor, providing the fuel with undiluted oxygen. Two different oxygen carriers; NiO/NiAl 2O 4 (40/60 wt/wt) and NiO/MgAl 2O 4 (60/40 wt/wt) are compared. Both continuous and pulse experiments were performed in a batch laboratory fluidized bed working at 950 °C using methane as fuel. It was found that pulse experiments offer advantages in comparison to continuous experiments, particularly when evaluating suitable particles for autothermal chemical-looping reforming. Firstly, smaller conversion ranges can be investigated in more detail, and secondly, the onset and extent of carbon formation can be determined more accurately. Of the two oxygen carriers, NiO/MgAl 2O 4 offers several advantages at elevated temperatures, i.e. higher methane conversion, higher selectivity to reforming and lesser tendency for carbon formation.