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Osaka Gas’ residential polymer electrolyte fuel cell (PEFC) cogeneration system
About the fuel processing system

CO remover

Return to the process flow of the fuel processing system

Osaka Gas has developed its unique high-performance PROX (preferential oxidization) catalyst for ENE・FARM.

Principles
  • CO is reduced through preferential oxidization process: in this process, air is added to the CO shift converter outlet gas, and carbon monoxide (CO) reacts with oxygen (O2) on a catalyst, which is made of a noble metal, such as Pt (platinum) or Ru (ruthenium), and eventually is converted into carbon dioxide.
 

CO preferential oxidation reaction

 

* The molar ratio of O2 in the air added for preferential oxidation to CO in the CO shift converter outlet gas is referred to as the [O2]/[CO] ratio.

Influence of the reaction temperature
  • In the low temperature region, insufficient activity prevents the CO from being removed completely. In the high temperature region, the effect of a decrease in selectivity and side reactions such as reverse shift reactions causes the CO concentration to increase. (See the illustration.)
  • Osaka Gas’ new catalyst (Ru-based) is capable of removing CO to less than 1 ppm level. In addition, it has a very wide temperature range, allowing it to be used between 85 and 170˚C (optimum temperatures: 100 to 130˚C). For this reason, the new catalyst is highly robust and easy-to-use for the reactor design.
Comparison of CO preferential oxidization activity between a conventional catalyst and Osaka Gas’ catalyst (with the [O2]/[CO] ratio equal to 1.5)
Influence of the [O2]/[CO] ratio
  • A conventional catalyst cannot remove CO down to a level of less than 10 ppm without increasing the [O2]/[CO] ratio to 3. For this reason, in general practice a CO preferential oxidizer is designed in two stages, the first of which roughly removes CO with the [O2]/[CO] ratio set at about 1 and the second of which removes the CO down to a level of less than 10 ppm with the ratio set at about 3.
  • Osaka Gas’ catalyst is capable of removing CO to a level of less than 10 ppm even when the [O2]/[CO] ratio is equal to 1. Since CO is removed to a level of less than 1 ppm with the [O2]/[CO] ratio equal to 1.5, CO is removed using a one-stage reactor. With the fluctuation in control and the catalyst performance after deterioration taken into consideration, an [O2]/[CO] ratio equal to 1.5 is used normally. This enables the efficiency of the fuel processing system to be kept high.
 CO preferential oxidization activity of the conventional catalyst ([O2]/[CO] dependence)   CO preferential oxidization activity of Osaka Gas’ catalyst ([O2]/[CO] dependence)
Click here to look at Osaka Gas’ fuel processing system for ENE・FARM Osaka Gas’ unique technology that integrates all reactors into one package, enables the CO concentration to be reduced below 1 ppm.。

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