1. Introduction
Fossil fuels are used to satisfy a very significant fraction of the world energy demands. The use of fossil fuels comes with some adverse effects, prominent among which is the emission of CO2. Carbon dioxide significantly contributes to global warming and, consequently, causes climate change. This has called for international policies like the Kyoto protocol and Copenhagen summit that set limit on greenhouse gases (GHG) emission [1]. Renewable energy sources are carbon neutral and can present a favourable condition by reducing CO2 emissions to the atmosphere. Unfortunately, they are not yet in abundant supply to meet man’s demand. Much research and work are still needed to make them available in ample quantity to cater for our …show more content…
Syngas, though has lower energy contents when compared with methane, which has been previously utilized [17-24] as reactive gas in OTR. Notwithstanding, syngas is considered in the present work due to its great stability and predictability, high thermal and electrical efficiencies, can be produced from renewable sources and has reduced carbon emissions. Mesh of 36000 grid points was generated using GAMBIT 2.4 software and the computations were carried out using the CFD commercial code FLUENT 14.0. The membrane type LSCF-6428 was utilized for oxygen separation in the modelling as they are reported to have high oxygen partial pressure and are chemically stable at elevated temperature. The transfer of oxygen through the membrane was modelled with the aid of user defined functions (UDF). Synthetic gas in addition to CO2, which serves as diluent, is used as sweep gas in the oxygen transport reactor. CO2 is used as the diluent as it is proved to be very effective in syngas combustion [26]. The simulations were performed under laminar, steady state conditions considering Newtonian working fluids. Mass flow inlet conditions have been specified at feed and permeate sides while pressure outlet boundary conditions are specified at the exit sections of the feed and sweep sides. Due to the symmetry of the reactor around its axis, the geometry was …show more content…
The source term allows the permeation of only oxygen through the membrane and the flow rate of the specie is accounted for by the source/sink term. Species leave the membrane at one side and appear at the other side through the sink and source terms respectively. The oxygen permeation flux, J_(O_2 ), is positive at the sweep side (source term) and negative at the feed side (sink term). The term, Si, has the unit of kg/m3-s and the oxygen flux is calculated based on the permeation equation in mole/s. Based on that, the term Si can be obtained using the following equation after multiplication of oxygen flux by cell area and molecular weight of oxygen and dividing by the cell volume as
Fossil fuels are used to satisfy a very significant fraction of the world energy demands. The use of fossil fuels comes with some adverse effects, prominent among which is the emission of CO2. Carbon dioxide significantly contributes to global warming and, consequently, causes climate change. This has called for international policies like the Kyoto protocol and Copenhagen summit that set limit on greenhouse gases (GHG) emission [1]. Renewable energy sources are carbon neutral and can present a favourable condition by reducing CO2 emissions to the atmosphere. Unfortunately, they are not yet in abundant supply to meet man’s demand. Much research and work are still needed to make them available in ample quantity to cater for our …show more content…
Syngas, though has lower energy contents when compared with methane, which has been previously utilized [17-24] as reactive gas in OTR. Notwithstanding, syngas is considered in the present work due to its great stability and predictability, high thermal and electrical efficiencies, can be produced from renewable sources and has reduced carbon emissions. Mesh of 36000 grid points was generated using GAMBIT 2.4 software and the computations were carried out using the CFD commercial code FLUENT 14.0. The membrane type LSCF-6428 was utilized for oxygen separation in the modelling as they are reported to have high oxygen partial pressure and are chemically stable at elevated temperature. The transfer of oxygen through the membrane was modelled with the aid of user defined functions (UDF). Synthetic gas in addition to CO2, which serves as diluent, is used as sweep gas in the oxygen transport reactor. CO2 is used as the diluent as it is proved to be very effective in syngas combustion [26]. The simulations were performed under laminar, steady state conditions considering Newtonian working fluids. Mass flow inlet conditions have been specified at feed and permeate sides while pressure outlet boundary conditions are specified at the exit sections of the feed and sweep sides. Due to the symmetry of the reactor around its axis, the geometry was …show more content…
The source term allows the permeation of only oxygen through the membrane and the flow rate of the specie is accounted for by the source/sink term. Species leave the membrane at one side and appear at the other side through the sink and source terms respectively. The oxygen permeation flux, J_(O_2 ), is positive at the sweep side (source term) and negative at the feed side (sink term). The term, Si, has the unit of kg/m3-s and the oxygen flux is calculated based on the permeation equation in mole/s. Based on that, the term Si can be obtained using the following equation after multiplication of oxygen flux by cell area and molecular weight of oxygen and dividing by the cell volume as