Membrane Reactors for Energy Applications and Basic Chemical Production, 2015
This chapter discusses the application of membrane reactors for hydrogen production through autot... more This chapter discusses the application of membrane reactors for hydrogen production through autothermal reforming (ATR) reactions, with particular attention to the ATR of methane as fossil fuel and methanol and ethanol as biofuels. First the concept of ATR is explained, the catalysts used for such reactions are reported, and the traditional reactors are discussed. Afterwards, the membrane reactor concepts are discussed, and two possible configurations, namely the fluidized bed and the packed bed configuration, are discussed and compared. Modeling aspects of both reactors are introduced. Finally, the recent advances in membrane reactors for these reactions and future trends are discussed in the chapter.
ABSTRACT A novel experimental technique using a high speed Infrared (IR) camera combined with an ... more ABSTRACT A novel experimental technique using a high speed Infrared (IR) camera combined with an improved Digital Image Analysis (DIA) method for non-invasive concentration measurement with high spatial and temporal resolution has recently been developed by Dang et al. (2013). This paper reports the extension of the IR technique to freely bubbling and turbulent fluidization regimes to investigate and quantify lateral gas mixing characteristics in gas-solid fluidized beds. The mechanism of lateral gas mixing in the bubbling regime studied with the novel technique is in good agreement with values reported in the literature. The experimental results, interpreted with a plug flow model with superimposed dispersion for a homogeneous flow, show that the lateral gas mixing coefficient first increases with the increase of superficial gas velocities from the bubbling to the turbulent flow regime and then decreases for even higher velocities, which is consistent with earlier literature studies. The dependency of the lateral gas mixing coefficient on the Reynolds number using Amos' correlation (Amos and Mineo, 1993) has shown large discrepancies at low gas velocities (where the equation was extrapolated), while a good match was obtained at higher gas velocities. The experimental findings reported in this paper indicate that the novel IR/DIA technique can successfully be applied for mass transfer and gas mixing studies in gas-solids multiphase flows.
The gas-to-liquid process, consisting of the partial oxidation of methane (POM) followed by the F... more The gas-to-liquid process, consisting of the partial oxidation of methane (POM) followed by the Fischer-Tropsch reaction, is a promising alternative to conventional oil processing for the production of liquid fuels. The cost of a conventional POM process is mainly determined by cryogenic air separation and could be greatly reduced by using oxygen permselective perovskite membranes instead. These membranes operate at temperatures similar to POM processes and can thus be integrated into a catalytic membrane reactor. To investigate the implications of this integration an adiabatic thermodynamic analysis has been carried out for both oxygen- and air-based POM processes, focusing on the influence of the feed temperature and composition on the syngas yield and quality. This analysis revealed that much higher feed temperatures are required for air-based POM processes to reach similarly high syngas yields. Because the Fischer?Tropsch reaction is carried out at much lower temperatures, recuperative heat exchange becomes essential for air-based POM processes. This is preferably carried out inside the reactor using the reverse flow concept, since external heat transfer at elevated temperatures is expensive. To combine the POM reaction, air separation and recuperative heat exchange into a single apparatus a reverse-flow catalytic membrane reactor (RFCMR) is proposed.
Palladium Membrane Technology for Hydrogen Production, Carbon Capture and Other Applications, 2015
Introduction It is widely accepted that the problem of global warming will require a combination ... more Introduction It is widely accepted that the problem of global warming will require a combination of solutions ranging from carbon capture and sequestration (CCS) through to improved carbon effi ciency of fossil fuels and (in the long term) widespread use of renewable energy sources. In particular, as energy costs increase, the advantage of high energy-conversion effi ciency becomes very important. In this respect, fuel cell (FC) systems (with signifi cantly higher conversion efficiency than other energy conversion devices, particularly at small sizes) will become more important and their market share will increase accordingly (further enhanced by reductions in manufacturing costs). However, for FCs overall to achieve higher effi ciency, the energy carrier for those FCs (mostly H 2 ) should also be produced at higher effi ciency. This can be achieved by using membrane reactors, devices that integrate separation and reaction in a single unit, thus reducing the amount of equipment required and circumventing certain thermodynamic limitations that affect conventional systems. In this chapter, the application of membrane reactors as innovative reformers for combined heat and power (CHP) systems will be discussed. An overview of actual CHP systems will be outlined fi rst, then the advantages and disadvantages of applying novel reformers will be highlighted, and fi nally an energy analysis of a micro-CHP system with conventional and membrane reformers will be presented.
Complex hydrodynamic behavior of circulating fluidized beds makes their scale-up very complicated... more Complex hydrodynamic behavior of circulating fluidized beds makes their scale-up very complicated. In particular, large-scale lateral solids segregation causes a complex two-phase flow pattern which influences significantly their performance. Lateral solids segregation has been attributed to direct collisional interactions between particles as well as to interaction between gas-phase eddies and dispersed particles. However, these phenomena have not been investigated thoroughly. This article discusses an advanced 2-D hydrodynamic model developed for circulating fluidized beds based on the two-fluid concept. Because theory to model the interaction between gas-phase eddies and dispersed particles is not available, turbulence was modeled on a macroscopic scale using a modified Prandtl mixing length model. To model the influence of direct particle-particle collisions the kinetic theory for granular flow was applied based on the Chapman-Enskog theory of dense gases. For model validation purposes, a cold flow circulating fluidized bed was employed in which sand was transported with air as fluidizing agent. The column is equipped with pressure transducers to measure the axial pressure profile and with a reflective optical fiber probe to measure the local solids concentration and axial solids velocity. Theoretically calculated solids concentration and axial solids velocity agree satisfactorily with experiment, especially when one realizes that the model contains no adjustable parameters. In general, however, the model slightly underpredicted the experimentally observed lateral solids segregation and yielded a more peaked velocity profile compared to its experimental counterpart
Membrane Reactors for Energy Applications and Basic Chemical Production, 2015
This chapter discusses the application of membrane reactors for hydrogen production through autot... more This chapter discusses the application of membrane reactors for hydrogen production through autothermal reforming (ATR) reactions, with particular attention to the ATR of methane as fossil fuel and methanol and ethanol as biofuels. First the concept of ATR is explained, the catalysts used for such reactions are reported, and the traditional reactors are discussed. Afterwards, the membrane reactor concepts are discussed, and two possible configurations, namely the fluidized bed and the packed bed configuration, are discussed and compared. Modeling aspects of both reactors are introduced. Finally, the recent advances in membrane reactors for these reactions and future trends are discussed in the chapter.
ABSTRACT A novel experimental technique using a high speed Infrared (IR) camera combined with an ... more ABSTRACT A novel experimental technique using a high speed Infrared (IR) camera combined with an improved Digital Image Analysis (DIA) method for non-invasive concentration measurement with high spatial and temporal resolution has recently been developed by Dang et al. (2013). This paper reports the extension of the IR technique to freely bubbling and turbulent fluidization regimes to investigate and quantify lateral gas mixing characteristics in gas-solid fluidized beds. The mechanism of lateral gas mixing in the bubbling regime studied with the novel technique is in good agreement with values reported in the literature. The experimental results, interpreted with a plug flow model with superimposed dispersion for a homogeneous flow, show that the lateral gas mixing coefficient first increases with the increase of superficial gas velocities from the bubbling to the turbulent flow regime and then decreases for even higher velocities, which is consistent with earlier literature studies. The dependency of the lateral gas mixing coefficient on the Reynolds number using Amos' correlation (Amos and Mineo, 1993) has shown large discrepancies at low gas velocities (where the equation was extrapolated), while a good match was obtained at higher gas velocities. The experimental findings reported in this paper indicate that the novel IR/DIA technique can successfully be applied for mass transfer and gas mixing studies in gas-solids multiphase flows.
The gas-to-liquid process, consisting of the partial oxidation of methane (POM) followed by the F... more The gas-to-liquid process, consisting of the partial oxidation of methane (POM) followed by the Fischer-Tropsch reaction, is a promising alternative to conventional oil processing for the production of liquid fuels. The cost of a conventional POM process is mainly determined by cryogenic air separation and could be greatly reduced by using oxygen permselective perovskite membranes instead. These membranes operate at temperatures similar to POM processes and can thus be integrated into a catalytic membrane reactor. To investigate the implications of this integration an adiabatic thermodynamic analysis has been carried out for both oxygen- and air-based POM processes, focusing on the influence of the feed temperature and composition on the syngas yield and quality. This analysis revealed that much higher feed temperatures are required for air-based POM processes to reach similarly high syngas yields. Because the Fischer?Tropsch reaction is carried out at much lower temperatures, recuperative heat exchange becomes essential for air-based POM processes. This is preferably carried out inside the reactor using the reverse flow concept, since external heat transfer at elevated temperatures is expensive. To combine the POM reaction, air separation and recuperative heat exchange into a single apparatus a reverse-flow catalytic membrane reactor (RFCMR) is proposed.
Palladium Membrane Technology for Hydrogen Production, Carbon Capture and Other Applications, 2015
Introduction It is widely accepted that the problem of global warming will require a combination ... more Introduction It is widely accepted that the problem of global warming will require a combination of solutions ranging from carbon capture and sequestration (CCS) through to improved carbon effi ciency of fossil fuels and (in the long term) widespread use of renewable energy sources. In particular, as energy costs increase, the advantage of high energy-conversion effi ciency becomes very important. In this respect, fuel cell (FC) systems (with signifi cantly higher conversion efficiency than other energy conversion devices, particularly at small sizes) will become more important and their market share will increase accordingly (further enhanced by reductions in manufacturing costs). However, for FCs overall to achieve higher effi ciency, the energy carrier for those FCs (mostly H 2 ) should also be produced at higher effi ciency. This can be achieved by using membrane reactors, devices that integrate separation and reaction in a single unit, thus reducing the amount of equipment required and circumventing certain thermodynamic limitations that affect conventional systems. In this chapter, the application of membrane reactors as innovative reformers for combined heat and power (CHP) systems will be discussed. An overview of actual CHP systems will be outlined fi rst, then the advantages and disadvantages of applying novel reformers will be highlighted, and fi nally an energy analysis of a micro-CHP system with conventional and membrane reformers will be presented.
Complex hydrodynamic behavior of circulating fluidized beds makes their scale-up very complicated... more Complex hydrodynamic behavior of circulating fluidized beds makes their scale-up very complicated. In particular, large-scale lateral solids segregation causes a complex two-phase flow pattern which influences significantly their performance. Lateral solids segregation has been attributed to direct collisional interactions between particles as well as to interaction between gas-phase eddies and dispersed particles. However, these phenomena have not been investigated thoroughly. This article discusses an advanced 2-D hydrodynamic model developed for circulating fluidized beds based on the two-fluid concept. Because theory to model the interaction between gas-phase eddies and dispersed particles is not available, turbulence was modeled on a macroscopic scale using a modified Prandtl mixing length model. To model the influence of direct particle-particle collisions the kinetic theory for granular flow was applied based on the Chapman-Enskog theory of dense gases. For model validation purposes, a cold flow circulating fluidized bed was employed in which sand was transported with air as fluidizing agent. The column is equipped with pressure transducers to measure the axial pressure profile and with a reflective optical fiber probe to measure the local solids concentration and axial solids velocity. Theoretically calculated solids concentration and axial solids velocity agree satisfactorily with experiment, especially when one realizes that the model contains no adjustable parameters. In general, however, the model slightly underpredicted the experimentally observed lateral solids segregation and yielded a more peaked velocity profile compared to its experimental counterpart
Uploads