this process would be approximately 80 MW, causing a significant reduction of
about 7–11% in the efficiency of net electricity generation (Chorowski and Gizicki
2015).
3.2 Oxygen-Enrichment Methods in Combustion Systems
In addition to purity issues, another important point is the site for oxygen injection
production. Oxygen enrichment in combustion processes provides many benefits as
mentioned above; however, if the feeding system is not properly designed, problems such as furnace wall damage, non-uniform heating, and increased pollutant
emissions can be potentiated (Baukal 2013). According to Daood et al. (2012),
techniques for oxygen enrichment in oxycombustion are significantly different from
one another, due to the different equipment design requirements, but are similar in
regard to the reduced gas flows through the burner, increased residence time in
combustion zones, and improvement in fuel burnout.
Thus, there are four main oxygen-enrichment methods in oxycombustion systems, as shown in Fig. 1. One is by adding O 2 in the incoming combustion air
stream, also referred to as premix enrichment. Some systems use almost 100%
oxygen at the main combustion inlet. However, performance is lower due to the
large difference in the oxidizer speed of pure O 2 when compared to air (IHEA
2007). According to Lacava et al. (2006), most burners show enhanced performance and boost productivity with low-level enrichment (about 26% O 2 ), and only
some operate at higher enrichment levels (about 35% O 2 ). Generally, when O 2 is
added to the premix, the flame intensifies, the mixture between fuel/oxidizer is
adequate, and the gas stream is dried. However, there is a greater risk of burner
damage and explosion, due to the higher temperature, besides higher NO x emission
(Toftegaard et al. 2010).
The second method is the strategic injection of oxygen beside, beneath, or
through the air/fuel flame, also referred to as O 2 lancing. This method is generally
used for low O 2 levels. Its main advantage is that the flame can be better controlled,
and released heat is evenly distributed. Nevertheless, furnace design has to be
reconsidered (Baukal 2013).
The third method is to separate the injection of combustion air and O 2 into the
burner, referred to as air/oxygen/fuel combustion. O 2 concentration in the burner
will possibly be the same, as is the case for operation with air. In addition, it has the
flexibility to operate with dual fuels (liquid and gaseous) and the enrichment of
higher O 2 levels; however, significant risks are associated with the injection of
nearly pure oxygen into a high-temperature stream of fuel and flue gas (Baukal
2013).
The last method consists in the complete replacement of air by high-purity O 2 ,
referred to as oxyfuel combustion, where O 2 and fuel remain, and separation
and mixing only occur when they are inserted into the furnace. For safety reasons,
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I. Aguiar Severo et al.
about 7–11% in the efficiency of net electricity generation (Chorowski and Gizicki
2015).
3.2 Oxygen-Enrichment Methods in Combustion Systems
In addition to purity issues, another important point is the site for oxygen injection
production. Oxygen enrichment in combustion processes provides many benefits as
mentioned above; however, if the feeding system is not properly designed, problems such as furnace wall damage, non-uniform heating, and increased pollutant
emissions can be potentiated (Baukal 2013). According to Daood et al. (2012),
techniques for oxygen enrichment in oxycombustion are significantly different from
one another, due to the different equipment design requirements, but are similar in
regard to the reduced gas flows through the burner, increased residence time in
combustion zones, and improvement in fuel burnout.
Thus, there are four main oxygen-enrichment methods in oxycombustion systems, as shown in Fig. 1. One is by adding O 2 in the incoming combustion air
stream, also referred to as premix enrichment. Some systems use almost 100%
oxygen at the main combustion inlet. However, performance is lower due to the
large difference in the oxidizer speed of pure O 2 when compared to air (IHEA
2007). According to Lacava et al. (2006), most burners show enhanced performance and boost productivity with low-level enrichment (about 26% O 2 ), and only
some operate at higher enrichment levels (about 35% O 2 ). Generally, when O 2 is
added to the premix, the flame intensifies, the mixture between fuel/oxidizer is
adequate, and the gas stream is dried. However, there is a greater risk of burner
damage and explosion, due to the higher temperature, besides higher NO x emission
(Toftegaard et al. 2010).
The second method is the strategic injection of oxygen beside, beneath, or
through the air/fuel flame, also referred to as O 2 lancing. This method is generally
used for low O 2 levels. Its main advantage is that the flame can be better controlled,
and released heat is evenly distributed. Nevertheless, furnace design has to be
reconsidered (Baukal 2013).
The third method is to separate the injection of combustion air and O 2 into the
burner, referred to as air/oxygen/fuel combustion. O 2 concentration in the burner
will possibly be the same, as is the case for operation with air. In addition, it has the
flexibility to operate with dual fuels (liquid and gaseous) and the enrichment of
higher O 2 levels; however, significant risks are associated with the injection of
nearly pure oxygen into a high-temperature stream of fuel and flue gas (Baukal
2013).
The last method consists in the complete replacement of air by high-purity O 2 ,
referred to as oxyfuel combustion, where O 2 and fuel remain, and separation
and mixing only occur when they are inserted into the furnace. For safety reasons,
276
I. Aguiar Severo et al.