Yasuhiro Rai

Reaction Characteristics of Methanol Noncatalytic Partial Oxidation Stabilized by Ceramic Honeycomb

A ceramic honeycomb was employed in a 1-kW class compact tubular fuel reformer based on noncatalytic partial oxidation (POX) of methanol. POX was stabilized on the outlet surface of the ceramic honeycomb under various experimental conditions with different equivalence ratios (φ) and thermal loads (qload); the latter represents the thermal input to the reformer calculated from the lower heating value (LHV) of methanol. The best performance of the reformer was achieved at φ = 3.5, and the adiabatic flame temperature was achieved. The location where the reaction occurred was determined, and the reaction was found to stabilize at an almost identical location under a wide range of thermal load conditions. This robust feature of the reaction is a significant characteristic of the ceramic honeycomb. By inserting a secondary honeycomb downstream of the reaction region, it was possible to move the reaction region upstream. This shifting of the reaction region was a result of the energy regeneration attributed to the adiabatic features of the honeycomb, and resulted in an improvement in reformer performance.

Experimental Study on a Compact Methanol-Fueled Reformer With Heat Regeneration Using Ceramic Honeycomb

On the way to a new era of our society which will be based on hydrogen energy, it is needed to develop on-site hydrogen production systems to cover current insufficient infrastructures of hydrogen supply network systems. For this, a highly efficient compact reformer can be one of the most suitable solutions for on-site production of hydrogen which is supplied to distributed electric power-generation systems. But, the local and overall energy balance in the reformer should be precisely controlled since the reforming reaction processes of hydrocarbon fuels are very sensitive to reaction temperature in the reformer. For smaller reformers, in particular, the amount of heat loss through the outer surfaces is large enough to dominate the reactions. An appropriate way for thermal energy management, therefore, is necessary to accomplish highly efficient reformers. For these backgrounds, a compact tubular-typed fuel reformer was fabricated in this study, and was applied to produce hydrogen from methanol, focusing on the partial oxidation reaction (POR). The reformer was composed of a stainless steel pipe as the reactor exterior and ceramic honeycomb blocks inserted in two locations of the reactor. The honeycomb blocks are expected to assist the reforming reactions and transfer the thermal energy of the exhaust gas to the reaction region, acting as a heat regenerator. The upstream-side honeycomb block was aimed to perform an effective heat exchange from the reactor wall to the reactant gas. By inserting the block, the reforming reaction became stable at right after the block. The maximum hydrogen production was achieved in the condition of equivalence ratio, around 3.5. The other honeycomb block was inserted in the downstream of the reaction zone to convert the thermal energy of exhaust gas to radiation energy which can be transferred to the upstream reaction region. Comparing to the case without the downstream-side block, the temperature of the reaction region became higher. Gas temperatures in the downstream region, on the other hand, became lower. Methanol conversion ratio and hydrogen production ratio enhanced due to the higher temperature at the reaction region. These results indicate that the thermal energy possessed by the exhaust gas was regenerated in the reaction region by the downstream-side honeycomb block and contributes to enhance the efficiency of the fuel reformer.© 2010 ASME

Experimental study on a compact methanol-fueled reformer with heat regeneration using ceramic honeycomb (third report: observation of reaction structure and its effect on reforming characteristics)

A ceramic honeycomb is applied to a 1-kW class compact tubular-type fuel reformer based on non-catalytic partial oxidation (POX) of methanol. Liquid methanol was used due to its easy handling characteristics. It is confirmed that POX in a super-rich condition can be sustained within the reactor. In most conditions, the reaction was stabilized near the outlet surface of the ceramic honeycomb where the maximum temperature is observed. The maximum temperature reaches approximately the adiabatic flame temperature, therefore, the ceramic honeycomb works as an adiabatic layer and a reaction stabilizer which can sustain the reaction at a certain location. The location of the reaction varies with regard to the thermal load conditions. Stable and high conversion rate was obtained when the reaction is stabilized on the outlet surface of the ceramic honeycomb. This robust feature of reaction stabilization is a significant characteristic of the ceramic honeycomb. The reaction characteristic and its effect on the reforming performance are investigated in this study using detailed measurements of temperature distributions and gas components.

Experimental Study on a Compact Methanol-Fueled Reformer With Heat Regeneration Using Ceramic Honeycomb (2

A compact tubular-type fuel reformer was fabricated and operated under fuel-rich combustion conditions of methanol, focusing on the partial oxidation reaction (POR). Ceramic honeycomb strainer blocks were inserted in the reactor. In the authors’ previous study, Case-1 of only one honeycomb block insertion showed that the reaction region formed in the downstream of the block. This block worked as a reaction stabilizer. The other condition, Case-2, was operated with the secondary honeycomb block inserted in the downstream of the reaction region in addition to the first block. This geometrical structure sandwiched the reaction region between the two blocks, and the thermal energy possessed by the exhaust gas could be regenerated to the reaction region by radiation exchange between these two blocks, which resulted in enhancing the preheating of the premixed gas. By this effect, the methanol-conversion and hydrogen-production in Case-2 were enhanced by about 10% compared to Case-1. In the present study, the reaction characteristics of the fuel reformer were investigated in detail, by detecting the location of the reaction region. Detailed temperature profiles in the streamwise direction were measured with traversable thermocouples, and positive ion current distributions corresponding to the reaction region were measured with a Langmuir probe. It was confirmed by the both measurements that there exists a reaction region right after the first honeycomb block which accompanies with sharp temperature gradients. The estimated thickness of the reaction region, however, was as wide as several millimeters to a centimeter, which is believed to be a ‘mild reaction’ stabilized by the first honeycomb block. In Case-2, the high-temperature region became broader compared to Case-1, which indicates that the enhancement of preheating of premixed gas was achieved by the heat regenerated from the secondary honeycomb block.Copyright