1. Introduction - Firenze University Press

3.2.4 Effect of the ATR operational temperature (TATR)
The ATR operating temperature is of high importance as it plays significant role on the syngas
quality: according to the chemical equilibrium, the higher the temperature, the higher the methane
conversion rate. On the other hand, in order to secure the autothermal conditions in the reactor,
more oxidant agent is required in the case that the temperature is high.
Furthermore, materials stability limits the maximum operating temperature to around 1100°C.
Figure 9a. Impact of TATR on PCU Figure 9b. Effect of TATR on the power plant
performance for the two purification methods for the two purification methods (CCR=90%).
(CCE=90%).
The ATR operating temperature is of high importance as it plays significant role on the syngas
quality: according to the chemical equilibrium, the higher the temperature, the higher the methane
conversion rate. On the other hand, in order to secure the autothermal conditions in the reactor,
more oxidant agent is required in the case that the temperature is high.
Furthermore, materials stability limits the maximum operating temperature to around 1100°C.
As is shown in Figure 9a, at low ATR temperatures, cryogenic systems consume more energy for
CO2 purification due to the increased presence of methane in the retentate stream.
Recovery and exergy efficiencies for separation with a distillation column are greater than those of
the corresponding flash separation method. This feature has a positive effect on the total system
when the combustion of the recovered fuel satisfies the required CO2 capture rate. In this case, for
TATR = 950°C, part of the methane is selected not to be recovered in order to meet the goal of
CCR=90%. Consequently, the net efficiency drops considerably, (Figure 9b). At high temperatures,
the oxy combustion option is more efficient than the cryogenic options by ca. 1%.
4. Conclusions
This study investigates the cryogenic method as an alternative choice for the rich-CO2 stream
purification after membrane separation, instead of simply combusting the retained combustibles.
Two proposed cryogenic systems are investigated: flash separation with internal cooling and
separation with distillation column. In the first case, electrical power is produced while the
separation efficiency is quite high, as 62.6% of the combustibles heat input is recovered. On the
other hand, separation by a distillation column may result in the complete separation of
combustibles, providing high purity in the final CO2 stream (>99%).
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