Primary steam reforming catalyst

The eight kinds of catalysts may be roughly classified as protective catalysts and economic catalysts . Co-Mo hydrogenation catalyst and zinc oxide desulfurizer are the protective catalysts for the primary steam reforming catalysts. The high-temperature shift catalyst protects the low-temperature shift catalyst, and the methanation catalyst are the protective catalyst for ammonia synthesis catalyst. The catalysts for primary- and secondary-steam reforming, low-temperature shift and ammonia synthesis are responsible for the conversions of raw materials and the yield of products, and have direct effect on economic benefits of the whole plant, and are thus called as economic catalysts. The amount of catalysts used depends on the process and raw material. Table 1.2 represents the amount of the eight kinds of catalysts used in the different processes. The total volume of the catalysts is about 330 m in every plant, while there are only two kinds of catalysts with the volume of about 100-140 m when heavy oil or coal is used as raw material. Both shift... 

The operation of a large synthetic ammonia plant based on natural gas involves a delicately balanced sequence of reactions. The gas is first desulfurized to remove compounds which will poison the metal catalysts, then compressed to 30 atm and reacted with steam over a nickel catalyst at 750°C in the primary steam reformer to produce H2 and oxides of carbon ... 

Remaining trace quantities of CO (which would poison the iron catalyst during ammonia synthesis) are converted back to CH4 by passing the damp gas from the scmbbers over a Ni methanation catalyst at 325° CO -t- 3H2, CRt -t- H2O. This reaction is the reverse of that occurring in the primary steam reformer. The synthesis gas now emerging has the approximate composition H2 74.3%, N2 24.7%, CH4 0.8%, Ar 0.3%, CO 1 -2ppm. It is compressed in three stages from 25 atm to 200 atm and then passed over a promoted iron catalyst at 380-450°C ... 

After the removal of sulfur, the primary steam reformer converts about 70% of the hydrocarbon feed into synthesis gas. Methane is mixed with steam and passed over a nickel catalyst. The main reforming reactions are ... 

In some cases a plant may have a pre-reformer. A pre-former is an adiabatic, fixed-bed reactor upstream of the primary reformer. It provides an operation with increased flexibility in the choice of feed stock it increases the life of the steam reforming catalyst and tubes it provides the option to increase the overall plant capacity and it allows the reformer to operate at lower steam-to-carbon ratios166. The hot flue gas from the reformer convection section provides the heat required for this endothermic reaction. 

Reaction (1) is the primary reforming reaction and is endothermic. Reaction (2) is the water-gas shift reaction and is exothermic. Both these reactions are limited by thermodynamic equilibrium. The overall reaction is endothermic and hence requires that additional fuel be combusted to supply heat. The conventional steam reformer is a fired furnace containing catalyst-filled tubes. The hydrocarbon and steam mixture is processed in the catalyst-filled tubes while external burners heat the tubes. Nickel supported on a ceramic matrix is the most common steam reforming catalyst. 

Thorium and uranium are used in cotmnercial catalytic systems. Industrially, thorium is used in the catalytic production of hydrocarbons for motor fuel. The direct conversion of synthetic gas to liquid fuel is accomplished by a Ni-Th02/Al203 catalyst that oxidatively cracks hydrocarbons with steam. The primary benefit to the incorporation of thorium is the increased resistance to coke deactivation. Industrially, UsOs also has been shown to be active in the decomposition of organics, including benzene and butanes and as supports for methane steam reforming catalysts. Uranium nitrides have also been used as a catalyst for the cracking of NH3 at 550 °C, which results in high yields of H2. 

The use of small catalyst particles in regions where heat transfer matters and larger particles in other zones to limit the pressure drop, as in primary steam reformers. 

During ammonia synthesis, the major reactions of production and purification of synthesis gas and the synthesis of ammonia, all are carried out over different catalysts. At least eight kinds of catalysts are used in the whole process, where natural gas or naphtha is used as feedstock and steam reforming is used to produce synthesis gas. These catalysts are Co-Mo hydrogenation catalyst, zinc oxide desulfurizer, primary- and secondary-steam reforming catalysts, high- and low-temperature shift catalysts, methanation catalyst and ammonia synthesis catalyst etc (Table 1.1). 

Hydrocarbon steam reforming catalysts are classified into natural gas steam reforming catalysts and light-oil steam reforming catalysts according to the feedstock, and primary- and secondary- steam reforming catalysts according to the processes. 

Hydrocarbons that can be fed to ammonia plants include natural gas, associated gas, liquid petroleum gas, and naphthas boiling up to 220 = C. Higher hydrocarbons are not used in primary steam reforming because it would lead to coke formation on the catalysts. Hydrocarbons are usually contaminated with variable quantities of different sulfur compotmds and often contain chlorides. These catalyst poisons must be removed before the other catalysts in the plant can operate in a satisfactory manner. 

Methane. The largest use of methane is for synthesis gas, a mixture of hydrogen and carbon monoxide. Synthesis gas, in turn, is the primary feed for the production of ammonia (qv) and methanol (qv). Synthesis gas is produced by steam reforming of methane over a nickel catalyst. 

Steam Reforming. In steam reforming, light hydrocarbon feeds ranging from natural gas to straight mn naphthas are converted to synthesis gas (H2, CO, CO2) by reaction with steam (qv) over a catalyst in a primary reformer furnace. This process is usually operated at 800—870°C and 2.17—2.86... 

In the catalytic steam reforming of natural gas (see Fig. 2), the hydrocarbon stream, principally methane, is desulfurized and, through the use of superheated steam (qv), contacts a nickel catalyst in the primary reformer at ca 3.04 MPa (30 atm) pressure and 800°C to convert methane to H2. 

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). 

Steam reforming needs a secondary fuel to provide the energy supply necessary for the reaction that occurs and a catalysts to improve the kinetic of this process. In Equation (3), the primary fuel is partially oxidised by a limited amount of oxygen. Partial oxidation produces less H2 per fuel unit than stream reforming, but the kinetic reaction is faster, it requires smaller reactors and neither catalyst nor energy supply from a secondary fuel. 

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. 

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. 

Steam reforming of hydrocarbons has become the most widely used process for producing hydrogen. One of the chief problems In the process Is the deposition of coke on the catalyst. To control coke deposition, high steam to hydrocarbon ratios, n, are used. However, excess steam must be recycled and It Is desirable to minimize the magnitude of the recycle stream for economy. Most of the research on this reaction has focused mainly on kinetic and mechanistic considerations of the steam-methane reaction at high values of n to avoid carbon deposition ( L 4). Therefore, the primary objective of this studyis to determine experimentally the minimum value of n for the coke-free operation at various temperatures for a commercial catalyst. 

Description The feedstock (natural gas as an example) is desulfurized, mixed with steam and converted into synthesis gas over nickel catalyst at approximately 40 bar and 800°C to 850°C in the primary reformer. The Uhde steam reformer is a top-fired reformer with tubes made of centrifugal high alloy steel and a proprietary "cold outlet manifold" system, which enhances reliability. 

Description Syngas preparation section. The feedstock is first preheated and sulfur compounds are removed in a desulfurizer (1). Steam is added, and the feedstock-steam mixture is preheated again. A part of the feed is reformed adiabatically in pre-reformer (2). The half of feedstock-steam mixture is distributed into catalyst tubes of the steam reformer (3) and the rest is sent to TEC s proprietary heat exchanger reformer, "TAF-X" (4), installed in parallel with (3) as the primary reforming. The heat required for TAF-X is supplied by the effluent stream of secondary reformer (5). Depending on plant capacity, the TAF-X (4) and/or the secondary reformer (5) can be eliminated. 

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