Primary reformer catalysts

The catalyst that is used in the secondary reformer does not need to be as active as that in the primary reformer. Hence, the usual nickel concentration is about 15%, compared with 25% in the primary-reformer catalyst. 

The catalyst used was Katalco 23-1 Primary Reforming Catalyst, a commercial nickel reforming catalyst supported on alumina. Its chemical composition was reported as 10-14% NIO, 0.2% SIO2 balance AI2O3. It was supplied as hollow cylinders of size 5%-in O.D., 5/16-in 1.0. and 3/8-1n long, and had an apparent bulk density of 66 5 lb/ft. The rings were crushed and sieved to obtain the 24/32 mesh cut used In all of the experiments. 

The active component of the primary reformer catalyst is nickel, which is finely dispersed over the support material as crystallites produced by reduction of nickel oxide. The nickel oxide content of unreduced catalyst is between 15 and 25 %. 

A good primary reforming catalyst should meet the following requirements ... 

Figure 34. "Wagon Wheel primary reforming catalyst (UC1)...

Catalyst makers also succeeded in minimizing the activity reducing effect of the potassium in the alkalized catalysts [430], Pre-reduced primary reforming catalysts are now also marketed (ICI Katalco, Topsoe) [430], and splitloading of reformer tubes with more than one type of catalyst has now become very common. The benefitial effects concern pressure drop at increased plant load, carbon formation potential, catalyst activity, catalyst cost, and desired catalyst life. For example, a reformer tube may be loaded with 15 % alkali-free catalyst in pre-reduced form (top-section), 25 % unreduced alkali-promoted (middle section) and 60% alkali-free unreduced catalyst (bottom section). 

Rice, D. K., Loading of primary reformer catalyst tubes, Ammonia Plant Safety, 33 216-222 (1993). 

Metals. Metals or organometallic compounds such as arsenic, copper, lead, and vanadium also are poisons to the primary reforming catalysts. Metals are present in trace quantities and are usually removed during normal desul-... 

Pressure drop calculations are included, which use the Ergun relationship. This relationship predicts the pressure drop through packed beds, such as the primary reformer catalyst tubes and the secondary reformer (auto-thermal) bed. Measurements provide feedback that is used to update appropriate parameters in this relationship. 

From 1950, the demand for nitrogen fertilizers in North America led to the construction of many more ammonia plants all based on the steam reforming process. Modifications to the primary reforming catalysts by the incorporation of potash to reduce the level of caibon deposition have enabled operators in those parts of the World with no readily available supply of natural gas to use naphtha or refinery off-gases as feed for the primary reformer, and this has increased the versatility of the process even further. ... 

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... 

Naphtha desulfurization is conducted in the vapor phase as described for natural gas. Raw naphtha is preheated and vaporized in a separate furnace. If the sulfur content of the naphtha is very high, after Co—Mo hydrotreating, the naphtha is condensed, H2S is stripped out, and the residual H2S is adsorbed on ZnO. The primary reformer operates at conditions similar to those used with natural gas feed. The nickel catalyst, however, requires a promoter such as potassium in order to avoid carbon deposition at the practical levels of steam-to-carbon ratios of 3.5—5.0. Deposition of carbon from hydrocarbons cracking on the particles of the catalyst reduces the activity of the catalyst for the reforming and results in local uneven heating of the reformer tubes because the firing heat is not removed by the reforming reaction. 

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. 

The primary reformer is essentially a process furnace in which fuel is burned with air to indirectiy provide the heat of reaction to the catalyst contained within tubes. This area of the furnace is usually referred to as the radiant section, so named because this is the primary mechanism for heat transfer at the high (750—850°C) temperatures required by the process. Reforming pressures in the range 3 —4 MPa (30,000—40,000 atm) represent a reasonable compromise between cost and downstream compression requirements. 

Natural gas is reacted with steam on an Ni-based catalyst in a primary reformer to produce syngas at a residence time of several seconds, with an H2 CO ratio of 3 according to reaction (9.1). Reformed gas is obtained at about 930 °C and pressures of 15-30 bar. The CH4 conversion is typically 90-92% and the composition of the primary reformer outlet stream approaches that predicted by thermodynamic equilibrium for a CH4 H20 = 1 3 feed. A secondary autothermal reformer is placed just at the exit of the primary reformer in which the unconverted CH4 is reacted with O2 at the top of a refractory lined tube. The mixture is then equilibrated on an Ni catalyst located below the oxidation zone [21]. The main limit of the SR reaction is thermodynamics, which determines very high conversions only at temperatures above 900 °C. The catalyst activity is important but not decisive, with the heat transfer coefficient of the internal tube wall being the rate-limiting parameter [19, 20]. 

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. 

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 requirements in an ammonia unit can be reduced by lowering the steam-to-carbon ratio to the primary reformer. However a number of drawbacks can exist downstream in the I I I S and LTS reactors. The drawbacks include By-product formation in the HTS, Pressure drop buildup in the HTS, Reversible poisoning of the LTS catalyst, and Higher CO equilibrium concentrations exiting the HTS and LTS reactors. 

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