Carbon-capture and storage benefits: NOx reduction in O2/CO2 pulverized fuel combustion

Fuel combustion in a mixture of O
₂
/CO
₂
-recycled is an emerging technology for cost-effective power generation with carbon capture and sequestration that has extra benefits of NO
_x
emission reductions and lower flue gas cleanup cost. This paper presents experimental results of pulverized coal combustion in a 20 kW furnace on combustion in air and O
₂
/CO
₂
mixtures. The effectiveness of oxidant staging on reducing NO
_x
emissions was investigated for combustion in O
₂
/CO
₂
mixtures in comparison to that in air combustion. The fate of recycled NO
_x
in combustion with various oxidants and combustion conditions was also investigated. The results show that simply replacing the N
₂
in the combustion air with CO
₂
will result in a significant decrease of combustion gas temperatures. However, with a same firing rate and combustion stoichiometry, coal combustion in 30:70-O
₂
/CO
₂
produced a similar flame temperature profiles to those in air combustion, while producing a significantly lower furnace NO
_x
emission and a higher char burnout. The staged combustion tests show that oxidant-staging is a very effective method in reducing NO
_x
emissions for coal combustion in 30:70-O
₂
/CO
₂
, and can be more effective than in staged-air combustion. The recycled NO
_x
tests results show that the reduction efficiency of the recycled NO depends on the combustion media, combustion conditions and NO
_x
recycling injection locations, and is influenced by the coal properties but not by the recycled NO
_x
concentrations. Compared to those in air combustion, NO
_x
reduction efficiency in 30:70-O
₂
:CO
₂
is more sensitive to coal properties, particularly the coal fuel ratio.