Mass balance reforming

Based on this configuration, the reformer and combustor are modeled with partial differential equations. Since the thickness of the plates is relatively small, only the flow direction is considered. Using the equation of continuity, the component mass balances are constructed and the energy balance considering with heat loss and momentum balance are established as follows. 

Start-of-cycle kinetic lumps in KINPTR are summarized in Table V. A C5-light gas lump is required for mass balance. Thirteen hydrocarbon lumps are defined. The reforming kinetic behavior can be modeled without splitting the lumps into their individual isomers (e.g., isohexane and n-hexane). Also, the component distribution within the C5- lump can be described by simple correlations, as discussed later. The start-of-cycle reaction network that defines the interconversions between the 13 kinetic lumps is shown in Fig. 9. This reaction network results from kinetic studies on pure components and narrow boiling fractions of naphthas. It includes the basic reforming reactions... 

The conversion and yield of carbon dioxide and methane are defined in the opposite sense of the yield and conversion used in steam reformers in equations (7.125) and (7.126) and the same differential mass balance equations (7.127) and (7.128) are used. The mole fractions of all components are computed from similar relations as given before. 

In the following section, the component mass balances in the anode channel, some mixing rules, the equations for the cathode gas composition, the kinetics of the reforming and the electrochemical reactions and finally the equations for the fuel cell power are provided. 

The governing equations - that is, mainly the component and the total mass balances in the anode channels - are provided here in dimensionless form. The five ordinary differential equations (ODE) with respect to the spatial coordinate describe the development of the five unknowns in one single anode channel, namely the mole fractions, with i = CH4, H2O, H2, CO2, as well as the molar flow density inside the anode channel, y. Here, the Damkohler numbers, Da/, are the dimensionless reaction rate constant of the reforming and the oxidation reaction, respectively, the rj are the corresponding dimensionless reaction rates, and the v, j are the stoichiometric coefficients ... 

Conceptual Design of Internal Reforming in High-Temperature Fuel Cells The total mass balance of the combustion yields the cathode outlet flow rate ... 

Since the n-heptane reforming rate is much faster than catalyst deactivation rate, the reaction system considered, with appropriate assumptions, is represented by the following quasi-steady state mass balance equations ... 

Chapter 10 contains a literature survey of the basic fluidized bed reactor designs, principles of operation and modeling. The classical two- and three phase fluidized bed models for bubbling beds are defined based on heat and species mass balances. The fluid dynamic models are based on kinetic theory of granular flow. A reactive flow simulation of a particular sorption enhanced steam reforming process is assessed. 

Modelling of the steam reformer tubes The tubes are loaded with industrial catalyst pellets usually a supported nickel catalyst. In the mass balance equations methane and carbon dioxide are chosen to be the key components and their conversion and yield are defined as follows ... 

Toluene is a major aromatic constituent in catalytic reformate and one of the most important chemical intermediates obtained from this reaction. The kinetics of n-heptane reforming have been studied (39, 40), and the interest in toluene from this source antedates the use of platinum catalysts (76, 119, 145). While heptane is converted with considerably greater ease than hexane, this reaction is, on mass balance calculations, not sufficient to account for the toluene found in reformates. 

Equation (28.3)) is obtained from the total mass balance in combination with the ideal gas law and the isobaric assumption. The result shown here is obtained after several manipulation steps that also require the enthalpy balance. This equation is an ordinary differential equation with respect to the spatial coordinate. It describes the change of the gas velocity due to a local change in temperature (second term on the right-hand side) and due to changes in the total mole number due to mass exchange with the electrode (third term) or the reforming process (last term). 

Figure 6.2.32 shows results of simulations of the steam reforming process carried out by Froment and coworkers based on kinetic data and the respective heat and mass balances. 

The heterogeneous catalytic reforming reactions are supposed to take place on the gas-solid interface. In heterogeneous catalysis no species enter into the solid phase, hence for this process the species mass balance are solved only in the gas phase. For the adsorption process the reaction actually takes place within the solid adsorbent material. However, in the modeling approach employed by Wang et al. [161] a pseudo-homogeneous reaction model was adopted so that the CO2 capture reaction was approximated by a particle surface reaction thus the overall diffusion... 

A limited number of companies possess the basic knowledge and the experience which makes them able to prepare the basic engineering information-process flow diagrams with heat and mass balances, equipment specifications, specification of instrumentation and process control including safety precautions, operating manuals etc. -which is required for the design of an ammonia plant. These companies have also developed their own proprietary design of critical equipment, most often the ammonia synthesis converter and the primary reformer. 

An essential requirement of reformer operation is the addition of chlorine compounds to the feed to maintain the necessary chlorine content and hence the acidity of the alumina support. This requires a careful monitoring of the mass balance of chloride entering and leaving the catalyst beds, to maintain the chloride content of the catalyst at about 1.0 wt%. A strict control of water in the feed is also required to minimize chloride loss. 

An important task during data collection and model calibration is the overall mass and hydrogen balance across the reformer unit. The overall mass balance is simply a difference between the sum of all the feeds entering the unit and sum of all products leaving the unit While this concept is fundamentally simple, it can be difficult to realize in a real production plant... 

Reaction rates for the start-of-cycle reforming system are described by pseudo-monomolecular rates of change of the 13 kinetic lumps. That is, the rates of change of the lumps are represented by first-order mass action kinetics with the same adsorption isotherm applicable to each reaction step. Following the same format as Eq. (4), steady-state material balances for the hydrocarbon lumps are derived for a plug-flow, fixed bed catalytic reformer. A nondissociation, Langmuir-Hinshelwood adsorption model is employed. Steady-state material balances written over a differential fractional catalyst volume dv are the following ... 

The interaction of these two processes can be described by a simple isothermal model, which is based on balances of mass and charge. The model describes the extent of the reforming and oxidation reactions along the anode channel. The essential simulation results can easily be displayed in a conversion diagram which is a phase diagram of the two dynamic state variables, namely the extents of two reactions. 

If the water quantity added as feed increases up to a value corresponding to neutral energetic balance between exothermic and endothermic reaction steps, the overall process is denominated autothermal reformer (ATR). This approach combines both SR and POX catalytic processes and it has been recently proposed to optimize the performance in terms of compactness and efficiency of small-medium production plants. This technology could permit a compromise between the good efficiency of SR and the fast start up of POX. However, it needs a careful control of in going mass stream [6, 7]. 

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