Reactor tubular steam reforming

The approach being used to achieve this result was described recently by KTI reporting on work carried out for the Electric Power Research Institute (13). The basic scheme, in block diagram form, is shown in Figure 12. It consists of a hybrid reactor combining an advanced tubular steam reformer with an autothermal catalytic reformer. This combination overcomes the limitations of lower catalytic activity in HTSR systems toward the heavier hydrocarbons while retaining a significant part of the desired process characteristics. 

Simulation of tubular steam reformers and a comparison with industrial data are shown in many references, such as [250], In most cases the simulations are based on measured outer tube-wall temperatures. In [181] a basic furnace model is used, whereas in [525] a radiation model similar to the one in Section 3.3.6 is used. In both cases catalyst effectiveness factor profiles are shown. Similar simulations using the combined two-dimensional fixed-bed reactor, and the furnace and catalyst particle models described in the previous chapters are shown below using the operating conditions and geometry for the simple steam reforming furnace in the hydrogen plant. Examples 1.3, 2.1 and 3.2. Similar to [181] and [525], the intrinsic kinetic expressions used are the Xu and Froment expressions [525] from Section 3.5.2, but with the parameters from [541]. 

Tubular Fixed-Bed Reactors. Bundles of downflow reactor tubes filled with catalyst and surrounded by heat-transfer media are tubular fixed-bed reactors. Such reactors are used most notably in steam reforming and phthaUc anhydride manufacture. Steam reforming is the reaction of light hydrocarbons, preferably natural gas or naphthas, with steam over a nickel-supported catalyst to form synthesis gas, which is primarily and CO with some CO2 and CH. Additional conversion to the primary products can be obtained by iron oxide-catalyzed water gas shift reactions, but these are carried out ia large-diameter, fixed-bed reactors rather than ia small-diameter tubes (65). The physical arrangement of a multitubular steam reformer ia a box-shaped furnace has been described (1). 

Traditionally, the steam reforming reactor has a tubular design in which vertical tubes, loaded with catalyst, are surrounded by furnaces to supply the heat required for the strongly endothermic process, see Fig. 8.2. Combustion of natural gas supplies the heat to the tubes. 

Steam reforming refers to the endothermic, catalytic conversion of light hydrocarbons (methane to gasoline) in the presence of steam [see Eq. (5.1)]. The reforming reaction takes place across a nickel catalyst that is packed in tubes in an externally-fired, tubular furnace (the Primary Reformer). The lined chamber reactor is called the secondary reformer , and this is where hot process air is added to introduce nitrogen into the process. Typical reaction conditions in the Primary Reformer are 700°C to 830°C and 15 to 40 bar46. 

Fig. 1.20. Autothermal syngas generation by combining simultaneous autothermal reforming in an air/oxygen-fired fixed-bed reactor (ATR) and steam reforming in a gas-heated tubular fixed-bed reactor (GHR) [32, 33].

The intrinsic kinetics of the catalytic steam reforming of natural gas were determined from experiments in a tubular reactor in the temperature range of 823-953°K and in the pressure range of 5-15 bar. 

The steam reforming of methane cycle suffers from the problem of coke deposition on the catalyst bed. The primary objective of this project was to study the stability of a commercial nickel oxide catalyst for the steam reforming of methane. The theoretical minimum ratios of steam to methane that are required to avoid deposition of coke on the catalyst at various temperatures were calculated, based on equilibrium considerations. Coking experiments were conducted in a tubular reactor at atmospheric pressure in the range of 740-915°C. 

Gallucci F., Paturzo L., Basile A. A simulation study of the steam reforming of methane in a dense tubular membrane reactor. Int.J. Hydrogen Energy 2004 29 611-617. 

For some widely practiced processes, especially in the petroleum industry, reliable and convenient computerized models are available from a number of vendors or, by license, from proprietary sources. Included are reactor-regenerator of fluid catalytic cracking, hydro-treating, hydrocracking, alkylation with HF or H2SO4, reforming with Pt or Pt-Re catalysts, tubular steam cracking of hydrocarbon fractions, noncatalytic pyrolysis to ethylene, ammonia synthesis, and other processes by suppliers of catalysts. Vendors of some process simulations are listed in the CEP Software Directory (AIChE, 1994). 

Steam reforming is usually carried out in fired tubular reactors, with catalyst packed inside the tubes and fuel fired on the outside of the tubes to provide the heat of reaction. The product gas mixture contains carbon dioxide and water vapor as well as carbon monoxide and hydrogen and is conventionally known as synthesis gas or syngas. 

An alternative to filling or coating with a catalyst layer the microcharmels, with the related problems of avoiding maldistribution, which leads to a broad residence time distribution (RTD), is to create the microchannels between the void space left from a close packing of parallel filaments or wires. This novel MSR concept has been applied for the oxidative steam reforming of methanol [173]. Thin linear metallic wires, with diameters in the millimeter range, were close packed and introduced into a macro tubular reactor. The catalyst layer was grown on the external surface of these wires by thermal treatment. 

The third step is the heart of the process (steam reformer). Ni-based (Ni-Al2O3) catalysts, loaded in tubular reactors, favour the advancement of the following reactions ... 

Figure 2.18. Schematic representation of the pilot-plant for methane steam reforming. The R-1 is the reforming reactor, which contains a bundle of tweve palladium tubular membranes and a fluid-ized-bed of catalysts. From Adris et ij/.[2.381], with permission from Elsevier Science.

Catalytic testing was performed for steam reforming of methane in a tubular fixed-bed quartz reactor, at atmospheric pressure, in the temperature range Tr=600-800°C, using 0.2g of catalyst and molar ratios of CH4/H20=1 1 and 1 3 at a total flow rate of 50ml/mn. The catalyst was reduced in situ at 800°C in a flow of 5ml/mn of pure Ha- The products and reactants were analyzed by GC. The conversion and yields are calculated as described in a previous study [10]. 

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