High-temperature steam reforming burners

The subsequent steam reforming section is operated at very high temperatures 850-900 °C. The SMR catalysts themselves are already active below 400 °C, but high temperatures are necessary to drive the strongly endothermic reaction forward [8]. In industry, nickel catalysts are used in high-alloy reaction tubes, which are heated by external burners. This design is expensive and leads to heat losses, although much of the heat is recuperated. Noble metal catalysts such as sup-... 

Natural gas systems with endothermic steam reformers often make use of the residual fuel from the anode in a reformer burner. Alternatively, the residual fuel could be combusted prior to a gas expander to boost performance. In an MCFC system, the residual fuel often is combusted to maximize the supply of CO2 to the cathode while at the same time providing air preheating. In an SOFC system, the residual fuel often is combusted to provide high-temperature air preheating. 

Their thermal efficiency is not very different and in a top-fired furnace can be as high as 95 %. The enthalpy difference between inlet and exit, often referred to as reformer duty, is made up of the heat required to raise the temperature to the level at the tube exit and the enthalpy of the reforming reaction. In a typical tubular steam reforming furnace, about 50% of the heat generated by combustion of fuel in the burners is transferred through the reformer tube walls and absorbed by the process gas (in a conventional ammonia plant primary reformer 60 % for reaction, 40% for temperature increase). 

Lee et al. [58] from Samsung reported development of a fixed-bed natural gas reformer coupled to a WGS reactor with an electrical power equivalent of 1 kW. The steam reformer was placed in the center of the subsystem, while the annular WGS fixed bed surrounded the reformer separated by an insulation layer. Commercial ruthenium catalyst served for steam reforming, while a copper-based catalyst was used for WGS. A natural gas burner supplied the energy needed by steam reformer. The reformer was operated between 850 and 930 C, while the shift reactor worked between 480 and 530 C. The carbon monoxide content of the reformate was reduced to 0.7 vol.% downstream the shift reactor despite its high operating temperature, because the reformer was operated at high S/C ratio between 3 and 5 the water surplus affected the equilibrium of the WGS reaction positively. At full load, the efficiency of this subsystem was 78% which decreased to 72% at 25% load. 

Transferred Duty. In order to supply the heat for the overall endothermic steam reforming reaction, the catalyst is loaded into a number of high alloy tubes placed inside a furnace equipped with burners. Typical inlet temperatures are 450-650 C, and the product gas leaves the reformer at 700-950°C depending on the applications. 

Steam export, which is often undesirable in hydrogen plants, can be minimized by adiabatic pre-reforming which allows high preheat temperatures of the reformer feed, and by preheating of the combustion air to the reformer burners. 

Aicher et al. [72] developed an autothermal reformer for diesel fuel dedicated to supplying a molten carbonate fuel cell system from Ansaldo Fuel Cells S.p.A., Italy. The diesel fuel (which contained less than 10 ppm sulfur for the pilot plant application) was injected into the steam and air flows, which were pre-heated by a diesel burner to 3 50 °C. The reactor itself was operated at 4 bar, a S/C ratio of 1.5 and high O/C ratio of 0.98, which makes the reactor into a steam supported partial oxidation device. Consequently, the dry hydrogen content of the reformate was rather low with less than 35 vol.%. The operating temperature of the honeycomb had to be kept well above 800 °C to prevent coke formation and the presence of light hydrocarbons such as ethylene and propylene in the reformate. The reactor was operated for 300 h, which led to a slight deterioration in the catalyst performance. 

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