Reactor temperature reforming

The reactor temperature can reach over 900°C in the secondary reformer due to the exothermic reaction heat. Typical analysis of the exit gas from the primary and the secondary reformers is shown in Table 5-1. 

Employing process conditions similar to those used for steam reforming of natural gas (e.g. fixed-bed reactors, temperatures in the 800-900 °C range) has been demonstrated to be inadequate for processing thermally unstable biomass liquids [29]. The most important problem is represented by coke formation, especially in the upper layer of the catalyst bed and in the reactor freeboard, that limits the operation time (e.g. 3—4 h on commercial Ni-based catalysts) and requires a long regeneration process for the catalyst (e.g. 6-8 h on commercial Ni-based catalysts). 

Heinzel et al. [77] compared the performance of a natural gas autothermal reformer with that of a steam reformer. The ATR reactor was loaded with a Pt catalyst on a metallic substrate followed by a fixed bed of Pt catalyst. In the start-up phase, the metallic substrate was electrically heated until the catalytic combustion of a stoichiometric methane-air mixture occurred. The reactor temperature was increased by the heat of the combustion reaction and later water was added to limit the temperature rise in the catalyst, while the air flow was reduced to sub-stoichiometric settings. With respect to the steam reformer, the behavior of the ATR reactor was more flexible regarding the start-up time and the load change, thus being more suitable for small-scale stationary applications. 

The catalytic bed (70 cm ), supported by a metallic gauze, is located in the reforming section. Water is fed to the reactor at the bottom of the metallic gauze. The temperature inside the reactor is monitored by four thermocouples one (Tcomb) is located on the SiC foam and the other three (T ref L, T ref M, T ref H) are located at 25, 50 and 75%, respectively, of the catalytic bed height to provide the reactor temperature axial profile. Moreover, additional thermocouples monitor... 

Even the process of experimental setup and measurement can be an issue. In a fixed bed laboratory reactor at reforming temperatures (near 800°C), the following sequence of reactions is thought to take place. Very near the... 

Figure 6 Reactor temperatures required to prevent thermodynamically the formation of elemental carbon in reforming of i-Cs,from thermodynamic calculations (Reprinted from Ahmed et al.f copyright (2001), with permission from Elsevier)...

A similar study reports the results of adding 100 ppm thiophene to As in the Palm et al. study,the catalyst is not described rather, it is identified only as a commercial naphtha reforming catalyst, presumably Pt-based. In their reactor, the reformate from the ATR step passes through separate high and low temperature shift reactors before being analyzed. Thus, it was not possible to determine the effect of sulfur on the reforming step alone, nor was any post-reaction characterization of the catalyst reported, for example to determine coke or sulfur content. Figure 16 shows the observed deactivation, as measured by a decrease in H2 and CO concentrations. 

Figure 35 H2 yields (moles of H2lmole of i-Cg) at different reactor temperatures for various experimental configurations used in non-thermal plasma reforming of i-Cg. Maximum H2 yield from i-Cg is nine as shown by dashed line (Reprintedfrom Sobacchi et alfi copyright (2002), with permission from Elsevier)...

The reactor temperature required to prevent coke formation varies considerably for the different processes. Table 2.1 summarizes the values calculated assuming thermodynamic equilibrium for 2,2,4-trimethylpentane reforming. Generally, the coking tendency increases in the following order at constant O/C ratio SR > ATR > POx. These calculations demonstrate that at steam to carbon ratios (S/C) > 2 and reaction temperatures > 600 °C, which is very common for hydrocarbon fuel processors, coke seems to be an unstable species especially under the conditions of steam reforming. 

Of the indirect liquefaction procedures, methanol synthesis is the most straightforward and well developed [Eq. (6)]. Most methanol plants use natural gas (methane) as the feedstock and obtain the synthesis gas by the steam reforming of methane in a reaction that is the reverse of the methanation reaction in Eq. (5). However, the synthesis gas can also be obtained by coal gasification, and this has been and is practiced. In one modern low-pressure procedure developed by Imperial Chemical Industries (ICI), the synthesis gas is compressed to a pressure of from 5 to 10 MPa and, after heating, fed to the top of a fixed bed reactor containing a copper/zinc catalyst. The reactor temperature is maintained at 250 to 270°C by injecting... 

Hydrogen is manufactured from methane by either steam reforming (reaction with steam) or partial oxidation (reaction with oxygen). Both processes are endothermic. What reactor temperature and pressure would you expect to be optimal for these processes What constraints might apply ... 

Typical reforming catalyst are bifunctional, with a metal function (Pt, Pt-Re, Pt-Ir, etc] and an acid function (chlorided alumina). During operation, along with the desired reactions, the deposition of carbonaceous material occurs over the metal and the acid sites (1). This coke is the most important factor affecting the lifetime of the catalyst. As a consequence of this deposition, the reactor temperature must be raised to maintain the same octane number In the reformate. The partially deactivated catalyst has different selectivity than the fresh one. This suggests that the coke is deposited to a different extent on the metallic and on the acid function, and that the more demanding reactions are preferentially deactivated (2). 

Shi, L., Bayless, D.J., and Prudich, M. A model of steam reforming of iso-octane The effect of thermal boundary conditions on hydrogen production and reactor temperature. International Journal of Hydrogen Energy, 2008, 33 (17), 4577. 

There are however concerns with durability or lifetime of the catalyst. There can be contaminants within the reformate, in particular sulfur compounds, that can render the catalyst completely inactive. In addition, if the reactor temperature operates too high or an unexpected over-temperature event occurs, the performance or durability of the catalyst can be seriously compromised. Additionally, the support of the catalyst can sinter over time on stream due to the presence of significant amounts of water. Fouling can be another issue, which impacts durability if very pure water or clean air is not used. While all these factors are present, catalyst formulations have been shown to operate for hundreds of hours with minimal to no degradation. 

Synthesis of ammonia in a packed bed, catalytic reactor Steam reforming of methane Composition Temperature 100-fold increase in nitrogen conversion >95% H2 and less than 30 ppm CO with a dolomite CO2 acceptor... 

Further increases in methane conversion were attained by using an additional bed downstream from the membrane bed. In addition, the reactor temperature was increased so that the second bed operates at temperatures higher than the autothermal operation. This allows for the dry reforming reaction to occur in the second bed thus increasing the conversion of the methane not consumed in the first bed. In this case the highest methane conversion was about 90% with CO and H2 selectivities of about 90% when the external temperature is 700°C. Similar results can be attained without heating if a third feed of O2 is added between the membrane bed and just before the second fixed bed. In this case, the temperature increase is realized by the partial oxidation reaction with no major loss of selectivity. 

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