Abstract
To explore methods of reducing NOx emission from pulverized coal boilers, the effects of injecting ammonia solution and pyrolysis gas into the furnace on NOx emission were experimentally investigated on a 75 t/h pulverized coal boiler. Results show that the deep air staging with 30% separated over fire air (SOFA) creates a high temperature and strong reducing atmosphere in the reducing zone, providing the prerequisites for NOx reduction by ammonia solution and pyrolysis gas. Compared with deep air staging itself, NOx emission can be reduced by 16.7% when ammonia solution is injected from the reducing zone with a normalized stoichiometric ratio of 2.0. However, NOx reduction efficiency is largely affected by its injection position. Similarly, NOx emission is decreased by 28.2% through injecting pyrolysis gas with its calorific value of 10% into the furnace, while a further increase of pyrolysis gas input will not increase NOx reduction efficiency. When ammonia solution and pyrolysis gas are simultaneously injected into the furnace under deep air staging conditions, the overall NOx reduction efficiency reaches 92.0% and NOx emission is decreased to 39.1 mg/m3. Considering the increasingly strict NOx emission standard, these findings can provide theoretical and practical guides to the future NOx reduction in pulverized coal boilers.
Highlights
The extensive use of fossil fuels has been the powerful engine to promote the rapid development of the global economy, but their combustion process produces a large amount of air pollutants, and NOx is one major concern of them [1,2]
The injection position and amount of reducing agents should be carefully controlled to prevent them from being oxidized into NO. These findings reveal the effective denitrification effects of injecting reducing agents into proper and the maximum combined NOx reduction efficiency can be as high as 92.0% under optimal combustion scenario
The effects of injecting ammonia solution and pyrolysis gas into the furnace on NOx emission were experimentally investigated on a 75 t/h pulverized coal boiler
Summary
The extensive use of fossil fuels has been the powerful engine to promote the rapid development of the global economy, but their combustion process produces a large amount of air pollutants, and NOx is one major concern of them [1,2]. To reduce the harmful effects caused by NOx emission from fossil fuel combustion, many countries increase the proportion of renewable and clean energy sources. China and India where fossil fuel, especially coal is still the dominant energy source [3,4], NOx emission is inevitable and is still the major concern. The use of low-NOx combustion technologies such as horizontal bias combustion, air/fuel staged combustion and flue gas recirculation can no longer meet this requirement. These low-NOx combustion technologies are always used in combination with flue gas denitrification methods, including selective non-catalytic reduction (SNCR) [6,7] and selective catalytic reduction (SCR)
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