Reformer adiabatic temperature

Figure 3.9 Thermodynamic equilibrium gas composition and reformer adiabatic temperature versus air ratio (X) for gasoline reforming [7] feed temperatures were 400°C for air, 200°C for steam and 20°C for the fuel left, S/C = 0 right, S/C = 0.7.

It is critical to determine and control the steam-to-carbon (S/C) and/or oxygen-tointernal reforming) to avoid carbon deposition. Thermodynamic analysis is commonly used to estimate the minimum ratios. For example. Figure 33.18 shows the equilibrium number of moles of carbon per mole of methane introduced into an ATR as a function of S/C and O/C at two reformer inlet temperatures of 150 and 400 °C [8]. It can be seen that for aU values of O/C between 0 and 1.5, carbon deposition should not be a concern if an S/C > 1.2 is maintained in the fuel gas mixture entering the ATR (fiiUy mixed inlet stream). It should be noted that many thermodynamic calculations (as in this example) assume adiabatic equilibrium reactions and do not take into account reaction kinetic effects. The inclusion of reaction kinetics in the analysis may lead to different results. 

Figure 3.28 shows the adiabatic temperature rise, which is the increase in gas temperature in a perfectly insulated reactor, for a typical reformate for increasing conversion of carbon monoxide by a water-gas shift [57]. Owing to thermodynamic limitations and its exothermicity, the reaction is divided into two consecutive steps, known as high temperature and low temperature water-gas shifts on the industrial scale. However, two water-gas shift stages are only mandatory for fixed bed or monolithic reactors, which will be discussed in Section 5.2.1. High temperature... 

Figure 3.28 Adiabatic temperature rise (termed exotherm here) of reformate containing 53.1 vol.% hydrogen, 7.7 voL% carbon monoxide, 7.5 vol.% carbon dioxide, 31.4 vol.% steam and 0.3 vol.% methane versus carbon monoxide conversion by water-gas shift [57. ...

The start-up procedure relied on steam generation by water injection into the startup burners. The steam generators of the fuel processor were positioned in the area of the carbon monoxide dean-up equipment and could not provide steam during startup. However, steam addition was regarded as mandatory even during start-up, because the adiabatic temperature rise of the reformer under steam-free conditions of partial... 

Autothermal reforming reactor (ATR) is maintained under adiabatic conditions. There is no heat transfer from or to the reactor section during the reaction. The effect of S/C and O/C ratios on the net electric efficiency of the system with fuel cell has been calculated. The results are illustrated for different inlet temperatures (700° and 400°C) in Figures 7 and 8. A decrease of the S/C ratio decreases the efficiency. On the other hand, an... 

Adiabatic with Intermediate Heat Transfer. Many tubular reactor systems use a series of adiabatic reactors with heating or cooling between the reactor vessels. For example, naphtha reforming has endothermic reactions of removing hydrogen from saturated cyclical naphthene hydrocarbons to form aromatics. The process has multiple adiabatic reactors with fired furnaces between the reactors to heat the material back up to the required reactor inlet temperature. 

FIG. 19-3 Fixed-bed reactors with heat exchange, (a) Adiabatic downflow, (b) Adiabatic radial flow, low AP. (c) Built-in interbed exchanger, (d) Shell and tube, (e) Interbed cold-shot injection, (f) External interbed exchanger, (g) Autothermal shell, outside influent/effluent heat exchanger. (h) Multibed adiabatic reactors with interstage heaters, (t) Platinum catalyst, fixed-bed reformer for 5000 BPSD charge rates reactors 1 and 2 are 5.5 by 9.5 ft and reactor 3 is 6.5 by 12.0 ft temperatures 502 433, 502 => 471,502 => 496°C. To convert feet to meters, multiply by 0.3048 BPSD to m3/h, multiply by 0.00662. 

In the adiabatic oxyreactor, part of the hydrogen from the intermediate product leaving the reformer is selectively converted with added oxygen or air, thereby forming steam. This is followed by further dehydrogenation over the same noble-metal catalyst. Exothermic selective H2 conversion in the oxyreactor increases olefin product space-time yield and supplies heat for further endothermic dehydrogenation. The reaction takes place at temperatures between 500°C-600°C and at 4 bar-6 bar. 

Also important is the effect of the size and shape of the catalysts [428] on heat transfer and consequently performance. Unlike the most processes carried out under substantially adiabatic conditions, the endothermic steam reforming reaction in the tubes of the primary reformer has to be supplied continuously with heat as the gas passes through the catalyst. The strong dependency of the reaction rate on the surface temperature of the catalyst clearly underlines the need for efficient heat transfer over the whole length and crosssection of the catalyst. However, the catalyst material itself is a very poor conductor and does not transfer heat to any significant extent. Therefore, the main mechanism of heat transfer from the inner tube wall to the gas is convection, and its efficiency will depend on how well the gas flow is distributed in the catalyst bed. It is thus evident that the geometry of the catalyst particles is important. 

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