Prereforming

C8H18 + 8H20 - 17H2 + 8CO r kl Pc8h18Ph2o -Pl2Pco/Ki Ni/Mg-Al203 500-750 

C8H18 + 8C02 - 9H2 + 16CO h — 3 C8H18- C02 1 PcoP2H2 N Ni/Al203 800-900 

C8H18 + 16H20 - 25H2 + 8C02 k4 Pc8h18Ph2o - Ph2 Pco2 /K4 Ni/Mg-Al203 500-750 

The major advantages of incorporating an adiabatic prereforming step in reforming of high hydrocarbons include the following  

A wide variety of fuels such as diesel, jet fuel, and NATO F-76 have been reformed using adiabatic prereformers.103 Since the prereforming process is generally carried out at low temperatures, the catalyst must be highly active. Industries 

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Like M( F(7s, S()F(7s can integrate fuel reforming within the fuel cell stack, A prereformer converts a substantial amount of the natural gas using waste heat from the fuel cell, (iornpoiinds containing sulfur (e,g, thiophene, which is cornrnonlv added to natural gas as an odorant) must be removed before the reformer. Typically, a hvdrodesiilfii-rizer combined with a zinc oxide absorber is used. 

The desulfurized natural gas is mixed with the recycled depleted fuel stream containing steam formed in the fuel cell. About 75 percent of the methane is converted to hvdrogen and carbon monoxide in the prereformer. The hvdrogen-rich fuel is then passed over the fuel cell anode, where 85 percent is converted to electricity. The balance is burned with depleted air in the combustion zone. 

The hot combustion gas preheats the fresh air and the prereformer, and can be used further to generate steam. The system is cooled with 200 to 300 percent excess air, A 25-kW S()F(i generator system is shown in Fig, 27-69,... 

The 25 kW TSOFC power unit (see Siemens Westinghouse, above) was fitted with a prereformer similar to the FCE and operated with JP-8 (766 hours) and DF-2 (1555 hours) while the unit was installed at FCE s Highgrove Station. 

Composition of Some Industrial Steam Reforming Catalysts (NG = natural gas, HC = hydrocarbon, PR = prereforming, LPG = liquefied petroleum gas, SEC = secondary reforming)... 

Typically, the prereforming process is performed in an adiabatic fixed-bed reactor upstream of the main reformer. In the pre-reformer, higher... 

Irreversible and endothermic SR (reaction (29)) is followed by two equilibrium driven exothermic reactions, methanation (reaction (30)) and WGS (reaction (31)). The prereforming is carried out at a relatively low temperature range, 400 to 550°C, with the overall reaction being close to autothermal. Prereforming provides the following advantages ... 

Traces of sulfur can be eliminated prior to entering the main reformer, due to the lower operating temperatures of the prereformer, which favors the deposition of sulfur on the Ni-based pre-reforming catalyst. 

The prereformer allows for greater feed temperatures to the main reformer, thereby reducing the size of the latter. 

Typically, a Ni-based SR catalyst is used in the prereforming process. The catalyst must be highly active, since the reaction occurs at low temperatures. Alkali promoters, such as those used in a SR catalyst, are also used to reduce carbon formation. 

Pfefferle carried out prereforming of JP-4 fuel, feeding a mixture of fuel, H2, and steam with Pt and Rh supported on alumina containing 6% silica at a temperature below 700°C. The presence of H2 in the feed allows prereforming to occur at low temperatures and, subsequently, a S/C ratio as low as 1 can be used without substantial catalyst deactivation. More than 90% hydrocarbon conversion to methane, H2, CO, and CO2 was observed in prereformer without any catalyst deactivation. 

Fig. 10.28 Calculated temperature and stress distributions at the electrolyte for a 16-channel model under three different conditions (a) for standard condition ( 1), (b) for co-flow case ( 4), (c) prereforming case ( 2) in Table 10.2.

NiCoMo, NiW for shale oil NiCoMo, NiW for shale oil Prereforming regeneration NiMo NiMo + FeCl3 NiW/Al203 NiW/Al203... 

T.S. Christensen, Adiabatic Prereforming of Hydrocarbons - an Important Step in Syngas Production , Appl. Catal. A, 138 285-309 (1996). 

A prereformer partially completes the steam reforming reactions upstream of the main steam reformer at a much lower temperature by using a more active catalyst. One advantage... 

Another advantage is that a prereformer may be preferred in flowsheets for processing heavier feedstocks. The prereformer converts heavier hydrocarbons to methane before they are fed to the steam reformer. This allows the steam reformer to be designed for methane service. The prereforming catalysts are very sensitive to poisons. Therefore a good feed purification section is essential.70... 

Description Natural gas or another hydrocarbon feedstock is compressed (if required), desulfurized, mixed with steam and then converted into synthesis gas. The reforming section comprises a prereformer (optional, but gives particular benefits when the feedstock is higher hydrocarbons or naphtha), a fired tubular reformer and a secondary reformer, where process air is added. The amount of air is adjusted to obtain an H2/N2 ratio of 3.0 as required by the ammonia synthesis reaction. The tubular steam reformer is Topsoe s proprietary side-wall-fired design. After the reforming section, the synthesis gas undergoes high- and low-temperature shift conversion, carbon dioxide removal and methanation. 

Features, such as the inclusion of a prereformer, installation of a ring-type burner with nozzles for the secondary reformer and upgrading to an S-300 ammonia converter, are all features that can be applied for existing ammonia plants. These features will ease maintenance and improve plant efficiency. 

Description The generic flowsheet consists of feed pre-treatment, prereforming (optional), steam-HC reforming, shift conversion and hydrogen purification by pressure swing adsorption (PSA). However, it is often tailored to satisfy specific requirements. 

Description The gas feedstock is compressed (if required), desulfurized (1) and process steam is added. Process steam used is a combination of steam from the process condensate stripper and superheated medium pressure steam from the header. The mixture of natural gas and steam is preheated, prereformed (2) and sent to the tubular reformer (3). The prereformer uses waste heat from the flue-gas section of the tubular reformer for the reforming reaction, thus reducing the total load on the tubular reformer. Due to high outlet temperature, exit gas from the tubular reformer has a low concentration of methane, which is an inert in the synthesis. The synthesis gas obtainable with this technology typically contains surplus hydrogen, which will be used as fuel in the reformer furnace. If C02 is available, the synthesis gas composition can be adjusted, hereby minimizing the hydrogen surplus. Carbon dioxide can preferably be added downstream of the prereformer. 

The flue gas generated in the tubular reformer is used for preheat of reformer and prereformer feed, natural gas preheat, steam superheat and preheat of combustion air. The synthesis gas generated in the tubular reformer is cooled by high-pressure steam generation (4), preheat of boiler feed water and reboiling in the distillation section (5). 

Installing a prereformer or rich-gas step is another possibility to reduce primary reformer duty and stack temperature of the flue gas [462]-[470], especially in LPG-and naphtha-based plants... 

Catalyst Deactivation in Adiabatic Prereforming Experimental Methods and Models for Prediction of Performance... 

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