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

Fuel combustion in a mixture of O2/CO2-recycled is an emerging technology for cost-effective power generation with carbon capture and sequestration that has extra benefits of NOx 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 O2/CO2 mixtures. The effectiveness of oxidant staging on reducing NOx emissions was investigated for combustion in O2/CO2 mixtures in comparison to that in air combustion. The fate of recycled NOx in combustion with various oxidants and combustion conditions was also investigated. The results show that simply replacing the N2 in the combustion air with CO2 will result in a significant decrease of combustion gas temperatures. However, with a same firing rate and combustion stoichiometry, coal combustion in 30∶70-O2/CO2 produced a similar flame temperature profiles to those in air combustion, while producing a significantly lower furnace NOx emission and a higher char burnout. The staged combustion tests show that oxidant-staging is a very effective method in reducing NOx emissions for coal combustion in 30∶70-O2/CO2, and can be more effective than in staged-air combustion. The recycled NOx tests results show that the reduction efficiency of the recycled NO depends on the combustion media, combustion conditions and NOx recycling injection locations, and is influenced by the coal properties but not by the recycled NOx concentrations. Compared to those in air combustion, NOx reduction efficiency in 30∶70-O2:CO2 is more sensitive to coal properties, particularly the coal fuel ratio