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Monday, May 3, 2010
Long Beach Convention Center
Fuel cell based cogeneration systems are attractive for household use because of both the heat and the electric power output achievable from these environmentally clean and efficient devices. The ability to operate fuel cell systems with an infrastructure fuel, such as natural gas, provides a tremendous advantage for distributed power generation.
Fuel efficiency is a key driver for the implementation of fuel cell systems and the efficiency is appropriately viewed over the life cycle of the system. A system with a large thermal mass will impose penalties in start-up time and fuel consumption. The autothermal reformer (ATR), which is based on co-feeding the fuel, oxygen, and steam, offers the advantages of faster startup and good load-following characteristics. It is estimated that, compared to steam reformer-based systems, the autothermal reformer based fuel processor would be lighter and will require less fuel energy during startup, will reach its nominal operating conditions quickly, and will be more responsive to changes in power demand. With less fuel energy consumed at startup, these systems are expected to be more energy efficient over their lifecycles changes.
The autothermal reactors typically use a noble metal catalyst, such as Rh, that support both the oxidation and reforming reactions, with the oxidation zone followed by the reforming zone where the oxygen concentration is extremely low (mole fraction of oxygen is less than 0.001). The temperature profiles consist of a sharp peak that can reach or exceed 1000°C, at which temperature the catalyst activity diminishes over time.
To maintain the catalyst durability and yet achieve the high activities achievable with noble metal based catalysts, we propose the use of two different catalyst sections in the ATR. In the first section of the ATR reactor, where temperatures are too high for the use of a noble metal catalyst, a hexa-aluminate type of catalyst will be used. This will be followed by the Rh-catalyst in the downstream section where temperatures below 850°C are expected. Hexa-aluminate related catalysts have been proposed as material of high heat resistance especially in the research of high-temperature catalytic combustion. While their activities are not as high as for the noble metal catalyst at low temperature, at temperatures above 900°C, conversion of methane approaches equilibrium values. A disadvantage of the hexa-aluminate catalyst is that during start-up, the catalyst needs to be heated to a higher temperature to initiate the oxidations reactions.
This work will present the results from experiments and simulations of a 1-kWe ATR reactor and investigates the effect of various parameters, such as flow and oxygen-to-carbon ratio on the minimum inlet temperature to sustain oxidation reactions within the hexa-aluminate catalyst. The temperature zones within the ATR segmented catalyst is also modeled and compared with experimental data.
Fuel efficiency is a key driver for the implementation of fuel cell systems and the efficiency is appropriately viewed over the life cycle of the system. A system with a large thermal mass will impose penalties in start-up time and fuel consumption. The autothermal reformer (ATR), which is based on co-feeding the fuel, oxygen, and steam, offers the advantages of faster startup and good load-following characteristics. It is estimated that, compared to steam reformer-based systems, the autothermal reformer based fuel processor would be lighter and will require less fuel energy during startup, will reach its nominal operating conditions quickly, and will be more responsive to changes in power demand. With less fuel energy consumed at startup, these systems are expected to be more energy efficient over their lifecycles changes.
The autothermal reactors typically use a noble metal catalyst, such as Rh, that support both the oxidation and reforming reactions, with the oxidation zone followed by the reforming zone where the oxygen concentration is extremely low (mole fraction of oxygen is less than 0.001). The temperature profiles consist of a sharp peak that can reach or exceed 1000°C, at which temperature the catalyst activity diminishes over time.
To maintain the catalyst durability and yet achieve the high activities achievable with noble metal based catalysts, we propose the use of two different catalyst sections in the ATR. In the first section of the ATR reactor, where temperatures are too high for the use of a noble metal catalyst, a hexa-aluminate type of catalyst will be used. This will be followed by the Rh-catalyst in the downstream section where temperatures below 850°C are expected. Hexa-aluminate related catalysts have been proposed as material of high heat resistance especially in the research of high-temperature catalytic combustion. While their activities are not as high as for the noble metal catalyst at low temperature, at temperatures above 900°C, conversion of methane approaches equilibrium values. A disadvantage of the hexa-aluminate catalyst is that during start-up, the catalyst needs to be heated to a higher temperature to initiate the oxidations reactions.
This work will present the results from experiments and simulations of a 1-kWe ATR reactor and investigates the effect of various parameters, such as flow and oxygen-to-carbon ratio on the minimum inlet temperature to sustain oxidation reactions within the hexa-aluminate catalyst. The temperature zones within the ATR segmented catalyst is also modeled and compared with experimental data.