entry. In this case, flame temperature and gas temperature are lower. This way, low
O 2 concentrations may result in lower stability and flame propagation velocity and,
consequently, fuel may not burn completely. In parallel, there is a delay in the flame
ignition in oxycombustion and this may vary according to the particle size of fuel
and its properties, temperature, gas properties, heating rate, and aerodynamic
impacts (Wall et al. 2009; Toftegaard et al. 2010).
Finally, the formation and emission of pollutants in oxycombustion should be
considered. Due to the atmosphere rich in CO 2 and H 2 O, extremely acidic gases
such as SO x and NO x are formed, causing fouling and corrosion in the exhaust gas
output device, which may affect combustion efficiency and damage the equipment.
However, the emission is less intense due to pollutant reduction during flue gas
recycling, lower formation of thermal NO by N 2 removal, and higher CO concentrations (Stanger and Wall 2011; Normann et al. 2009).
3 Operational Implications for Oxycombustion-Enhanced
Performance
3.1 Oxygen Supply
Oxycombustion technology requires highly pure oxygen to function effectively. For
this purpose, there are some technologies that separate oxygen from air, such as
cryogenic air distillation, adsorption, absorption, and polymeric membranes.
However, only the first option, which requires an air separation unit (ASU), presents maturity for large-scale application. The other options are in the early stages
of research and development (R&D) and cannot be applied to the full-scale operations (Olajire 2010; Leung et al. 2014).
Conventionally, an ASU for oxycombustion should produce an oxygen stream
with purity ranging from 95 to 99%. Energy consumption of separation increases as
a function of oxygen purity. The purer the oxygen, the greater the amount of energy
consumption involved in the separation process, directly influencing the composition of the gases formed, oxycombustion performance, as well as overall cost of
the plant (Banaszkiewicz et al. 2014).
In terms of capacity, ASUs have been designed with design features to meet total
oxygen production from 1000 tons (30,000 Nm
3 /h) to 5500 tons (165,000 Nm
3 /h).
Today, the world’s largest plant with an ASU for oxygen supply operates at a
capacity of 4000 ton/d O 2 (Linde Group 2017). Therefore, assuming that, on a
500 MW oxycombustion power plant operating on an industrial scale, the oxygen
supply should be around 10,000 ton/d (Higginbotham et al. 2011), 3 more ASU
plants would necessarily have to operate simultaneously, or an ASU with greater
capacity than the existing ones should be developed. At the same time, the expected
energy consumption to separate 1 ton of oxygen from the air would be
150–200 kWh/t O 2 produced (540 kJ/kg), and the electrical energy necessary for
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O 2 concentrations may result in lower stability and flame propagation velocity and,
consequently, fuel may not burn completely. In parallel, there is a delay in the flame
ignition in oxycombustion and this may vary according to the particle size of fuel
and its properties, temperature, gas properties, heating rate, and aerodynamic
impacts (Wall et al. 2009; Toftegaard et al. 2010).
Finally, the formation and emission of pollutants in oxycombustion should be
considered. Due to the atmosphere rich in CO 2 and H 2 O, extremely acidic gases
such as SO x and NO x are formed, causing fouling and corrosion in the exhaust gas
output device, which may affect combustion efficiency and damage the equipment.
However, the emission is less intense due to pollutant reduction during flue gas
recycling, lower formation of thermal NO by N 2 removal, and higher CO concentrations (Stanger and Wall 2011; Normann et al. 2009).
3 Operational Implications for Oxycombustion-Enhanced
Performance
3.1 Oxygen Supply
Oxycombustion technology requires highly pure oxygen to function effectively. For
this purpose, there are some technologies that separate oxygen from air, such as
cryogenic air distillation, adsorption, absorption, and polymeric membranes.
However, only the first option, which requires an air separation unit (ASU), presents maturity for large-scale application. The other options are in the early stages
of research and development (R&D) and cannot be applied to the full-scale operations (Olajire 2010; Leung et al. 2014).
Conventionally, an ASU for oxycombustion should produce an oxygen stream
with purity ranging from 95 to 99%. Energy consumption of separation increases as
a function of oxygen purity. The purer the oxygen, the greater the amount of energy
consumption involved in the separation process, directly influencing the composition of the gases formed, oxycombustion performance, as well as overall cost of
the plant (Banaszkiewicz et al. 2014).
In terms of capacity, ASUs have been designed with design features to meet total
oxygen production from 1000 tons (30,000 Nm
3 /h) to 5500 tons (165,000 Nm
3 /h).
Today, the world’s largest plant with an ASU for oxygen supply operates at a
capacity of 4000 ton/d O 2 (Linde Group 2017). Therefore, assuming that, on a
500 MW oxycombustion power plant operating on an industrial scale, the oxygen
supply should be around 10,000 ton/d (Higginbotham et al. 2011), 3 more ASU
plants would necessarily have to operate simultaneously, or an ASU with greater
capacity than the existing ones should be developed. At the same time, the expected
energy consumption to separate 1 ton of oxygen from the air would be
150–200 kWh/t O 2 produced (540 kJ/kg), and the electrical energy necessary for
13 Biofuels from Microalgae …
275