Efficiency autothermal reformer

Today, different processes (steam reforming, autothermal reforming, partial oxidation, gasification) are available and commercially mature for hydrogen production from natural gas or coal. These processes would have to be combined with technologies for C02 capture and storage (CCS), to keep the emissions profile low. A power plant that combines electricity and hydrogen production can be more efficient than retrofitted C02 separation systems for conventional power plants. 

Autothermal reforming provides a fuel processor compromise that operates at a lower 0/C and lower temperature than the POX is smaller, quicker starting, and quicker responding than the SR and results in good H2 concentration and high efficiency. A catalytic POX must be used to reduce the reaction temperature to a value compatible with the SR temperature. Once started, surplus heat from other parts of the unit can be sent to the ATR to increase its efficiency. 

Equation 9-4 and related heats of reaction can be manipulated to show that the maximum efficiency is a state point function, regardless of path (steam reforming, partial oxidation, or autothermal reforming), and is achieved at the thermoneutral point. In practice, x is set slightly higher than the thermoneutral point so that additional heat is generated to offset heat losses from the reformer. Table 9-1 presents efficiencies at the thermoneutral point for various hydrocarbon fuels. 

Unlike the methane steam reformer, the autothermal reformer requires no external heat source and no indirect heat exchangers. This makes autothermal reformers simpler and more compact than steam reformers, resulting in lower capital cost. In an autothermal reformer, the heat generated by the POX reaction is fully utilized to drive the SR reaction. Thus, autothermal reformers typically offer higher system efficiency than POX systems, where excess heat is not easily recovered. 

Experimental results concerning the development of a small-scale 1 kW autothermal reformer of propane were reported by Rampe et al. [76]. In the proposed reactor, two reactions occur on a metal honeycomb structure coated with platinum. Air and water are mixed before they are fed to the reactor in counterflow to the product gas outside the reactor wall, where the water is vaporized and the steam and air are heated up. Then, they are mixed with propane at the bottom of the reactor. It was verified that the preheating operation mode led to about a 4% higher efficiency, since the higher inlet air temperature causes a higher temperature level in the reaction zone, resulting in improved kinetics of the reforming reaction. 

A compact design for a gasoline fuel processor for auxiliary power unit (APU) applications, including an autothermal reformer followed by WGS and selective oxidation stages, was reported by Severin et al. [83]. The overall fuel processor efficiency was about 77% with a start-up time of 30 min. 

Table 6) indicate that the fuel-processing efficiencies decrease in the order of steam reforming > autothermal reforming > partial oxidation for both gasoline and diesel fuels. 

The promising and efficient reforming options are the steam reforming and autothermal reforming processes, as can be seen in Table 6. We can compare these two efficient systems in order to observe the equilibrium behavior in the reforming section of the whole micro CHP system. Here, the results of the most efficient options, namely natural gas with steam reforming and autothermal reforming. 

Autothermal reforming reactor (ATR) is maintained under adiabatic conditions. There is no heat transfer from or to the reactor section during the reaction. The effect of S/C and O/C ratios on the net electric efficiency of the system with fuel cell has been calculated. The results are illustrated for different inlet temperatures (700° and 400°C) in Figures 7 and 8. A decrease of the S/C ratio decreases the efficiency. On the other hand, an... 

Autothermal reforming is a teim adopted for the process in which a mixture of air and steam serves as the oxidant in the conversion of hydrocarbon fuels to a hydrogen-rich product. This process has also been reported to become more efficient as a result of the use of monolithic catalyst beds [11]. An example of this has been the demonstration of a modified version of the fuel-rich partial oxidation process in which noble metal catalysts were used in place of nickel on ceramic monoliths [2j. In earlier reports where packed catalyst beds were used, the concept to control carbon formation, which was predicted by thermodynamic equilibrium at low air-to-fuel ratios, was demonstrated by introducing steam, in addition to air, as an oxidant. 

These partial oxidation reactions are exothermic and, thus, reformers are expected to be energy efficient and compact compared to the steam reforming. The partial oxidation of methane can be carried out by Ni, Co, Rh, and Pt group metals for the temperature range of 700-1000°C, while that of methanol has been studied over Cu-based catalysts in the temperature range of 200-300° C. Autothermal reforming of... 

If the water quantity added as feed increases up to a value corresponding to neutral energetic balance between exothermic and endothermic reaction steps, the overall process is denominated autothermal reformer (ATR). This approach combines both SR and POX catalytic processes and it has been recently proposed to optimize the performance in terms of compactness and efficiency of small-medium production plants. This technology could permit a compromise between the good efficiency of SR and the fast start up of POX. However, it needs a careful control of in going mass stream [6, 7]. 

In the ATR, feed is partially combusted with excess air to supply the heat needed to reform the remaining hydrocarbon feed. The hot autothermal reformer effluent is fed to the shell side of the KRES reforming exchanger, where it combines with the reformed gas exiting the catalyst-packed tubes. The combined stream flows across the shell side of the reforming exchanger where it efficiently supplies heat to the reforming reaction inside the tubes. 

Whereas Sect 2.4 describes how the purge gas from a plant producing methanol alone is treated by autothermal reforming, an investigation was made alternatively also into co-production of methanol and SNG (Substitute Natural Gas). Provided that either suitable consumers or a natural gas pipeline exist, this co-production appears reasonable because it leads to a considerable increase in the overall efficiency of the plant, i.e. the ratio of heat output to heat input. In the present case, this efficiency rises from 52.7 % for methanol production to 59.8 % if methanol and SNG are co-produced. 

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