Types steam reforming

Fig. 13. Radiant section of a Kellogg box-type steam reforming furnace.

As discussed, XRD has for many years been the standard, everyday characterization method for solid catalysts, and in almost every laboratory in this field there is access to an X-ray diffractometer. This instrument allows a wide variety of different characterizations, but there are also limitations of such equipment. For example, the limited resolution of an in-house diffractometer may often be insufficient for a detailed analysis. This point is illustrated in Fig. 5a, which shows the diffractogram of an industrial type steam-reforming catalyst consisting of nickel crystallites on a spinel support (35). The Ni(lll) and the spinel(400) lines overlap so that a detailed analysis is impossible. This problem can be overcome if the XRD... 

Miyasugi, T, et al. 1984. A Heat Exchanger Type Steam Reformer for Ammonia Production, Chem i-cal Engineering Progress, 80 64. 

Fig. 8.9 shows a chemically recuperated cycle [Bl] of the first type, i.e. chemical recuperation with steam reforming (steam/TCR). 

The TEM images of deposits observed on Catalyst I used for the steam reforming of naphthalene are shown in Fig. 5. Two types of deposits were observed and they were proved to be composed of mainly carbon by EDS elemental analysis. One of them is film-like deposit over catalysts as shown in Fig. 5(a). This type of coke seems to consist of a polymer of C H, radicals. The other is pyrolytic carbon, which gives image of graphite-like layer as shown in Fig. 5(b). Pyrolytic carbon seems to be produced in dehydrogenation of naphthalene. TPO profile is shown in Fig. 6. The peaks around 600 K and 1000 K are attributable to the oxidation of film-like carbon and pyrolytic carbon, respectively [11-13]. These results coincide with TEM observations. 

TEM-EDS and XPS analyses were conducted on Co/MgO catalysts. The results of surface analyses showed that Co metal is not supported on the MgO as particles, but covers MgO surface in the case of 12 wt.% Co/MgO calcined at 873 K followed by reduction. After the reduction of catalyst at 1173 K, both cobalt oxide and CoO-MgO solid solution are observed on the surface of catalyst. In the steam reforming of naphthalene, two types of coke deposited on the surface of catalyst are observed. These are assigned to film-like and graphite type carbon by TPO analysis. 

The catalytic combustor provides heat for the endothermic reforming reaction and the vaporization of liquid fuel. The endothermic reforming reaction is carried out in a parallel flow-type micro-channel of the reformer unit. It is well known that the methanol steam reforming reaction for hydrogen production over the Cu/ZnO/AbOs catalyst involves the following reactions [10]. Eq. (1) is the algebraic summation of Eqs. (2) and (3). 

Most industrial hydrogen is manufactured by the following hydrocarbon-based oxidative processes steam reforming of light hydrocarbons (e.g., NG and naphtha), POx of heavy oil fractions, and ATR. Each of these technological approaches has numerous modifications depending on the type of feedstock, reactor design, heat input options, by-product treatment,... 

Steam reforming is a heterogeneously catalyzed process, with nickel catalyst deposited throughout a preformed porous support. It is empirically observed in the industry, that conversion is proportional to the geometric surface area of the catalyst particles, rather than the internal pore area. This suggests that the particle behaves as an egg-shell type, as if all the catalytic activity were confined to a thin layer at the external surface. It has been demonstrated by conventional reaction-diffusion particle modelling that this behaviour is due to... 

Catalysts were prepared by incipient wetness impregnation of commercial supports using cobalt nitrate as a precursor. Metallic cobalt species were active centers in the ethanol steam reforming. Over 90% EtOH conversion achieved. Nature of support influences the type of byproduct formation. Ethylene, methane and CO are formed over Co supported on A1203, Si02 and MgO, respectively... 

Additionally, nickel is a well established steam-reforming catalyst. An ideal SOFC system operated on natural gas applies internal steam reforming, i.e., the reforming of the methane takes place in the anode compartment of the stack. This type of system is favored for system simplicity and costs (no external reformer), and for system efficiency because the heat generated by the cell reaction is directly used by the reform reaction, and hence the cooling requirements of the stack (by air at the cathode side) are significantly reduced. 

Figure 1-14 shows a simplified layout for an SOFC-based APU. The air for reformer operation and cathode requirements is compressed in a single compressor and then split between the unit operations. The external water supply shown in figure 1-14 will most likely not be needed the anode recycle stream provides water. Unreacted anode tail gas is recuperated in a tail gas burner. Additional energy is available in a SOFC system from enthalpy recovery from tail gas effluent streams that are typically 400-600°C. Current thinking is that reformers for transportation fuel based SOFC APUs will be of the exothermic type (i.e. partial oxidation or autothermal reforming), as no viable steam reformers are available for such fuels. 

The CH4 in the natural gas is usually converted to H2 and CO in a SR reactor. Steam reforming reactors yield the highest percentage of hydrogen of any reformer type. The basic SR reactions for methane and a generic hydrocarbon are ... 

It is possible to increase the efficiency to over 85% with an economic profit at higher thermal integration. There are two types of steam reformers for small-scale hydrogen production conventional reduced-scale reformers and specially designed reformers for fuel cells. 

Carbonaceous compounds can also form in the absence of a catalyst by free-radical, gas-phase condensation reactions. The formation of this pyrolytic carbon is known in steam-reforming reactors where it can be controlled to some extent by minimizing the free volume within the reactor chamber. This type of carbon does not form readily with methane but can be severe with larger hydrocarbons. The compounds formed by free-radical reactions tend to be quite different from the graphitic carbon formed by metal catalysts. For example, Lee et al. showed that the compounds formed by passing pure, undi-... 

Other important parameters in the steam reforming process are temperature, which depends on the type of oxygenate, the steam-to-carbon ratio and the catalyst-to-feed ratio. For instance, methanol and acetic acid, which are simple oxygenated organic compounds, can be reformed at temperatures lower than 800 °C. On the other hand, more complex biomass-derived liquids may need higher temperatures and a large amount of steam to gasify efficiently the carbonaceous deposits formed by thermal decomposition. 

A second type of substitution occurs in the form of substitutions of subprocesses within a particular process. For example, one step in the steam reforming process for ammonia production is the removal of carbon monoxide and carbon dioxide from the synthesis gas. A number of processes, which differ somewhat in energy and capital requirements, have been developed for this purpose. 

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