Abstract
N2O emissions from coal fired fluidized-bed combustion are approximately 30–360 mg/Nm3, much higher than that from pulverized coal combustion (less than 30 mg/Nm3). One approach to reduce the N2O is to reburn the biomass gasification gas in the coal-fired fluidized bed. In this paper, the effects of gasified biomass reburning on the integrated boiler system were investigated by both simulation and experimental methods. The simulation as well as experimental results revealed that the increase of the reburning ratio would decrease the theoretical air volume and boiler efficiency, while it would increase the fuel gas volume, combustion and exhuast gas temperature. The experimental results also indicated that the N2O removal could reach as high as 99% when the heat ratio of biomass gas to coal is 10.5%.
Highlights
Biomass reburning technology falls into two types: direct reburning and indirect reburning
As an indirect reburning technology, controlling NOX emissions using biomass gasification gas can avoid the fuel bunker blocking problem caused by the difficulty in breaking up biomass due to their unsuitable shapes, it can solve the slag and corrosion problems caused by the alkali metal and chlorine content, which are usually higher in biomass than in coal [8,9,10]
It is shown that biomass gasification gas could improve the NOx emissions reduction rate with the initial O2 concentration changed at the range of 0 to 5% and the reaction temperature changed from 1000 °C to 1400 °C
Summary
Biomass reburning technology falls into two types: direct reburning and indirect reburning. The influencing factors of biomass gas reburning includes gas components, excess air coefficient, reaction temperature of reburning zone, reburning ratio and residence time [1]. Combustible gas produced in the middle and high temperature zones was replaced with mixtures of CO/CO2/H2/CH4/C2Hx with compositions of 26.5/5.35/7.75/53.1/7.3 and 41.5/0/37.5/10.8/10.2, respectively They demonstrated that the difference of NOX emissions reduction with simulated gas and natural gas was less than 10%. It is shown that biomass gasification gas could improve the NOx emissions reduction rate with the initial O2 concentration changed at the range of 0 to 5% and the reaction temperature changed from 1000 °C to 1400 °C. When the excess air coefficient in the reburning zone is 0.9, NOx emissions reduction is improved with the increase of CH4 concentration. It is shown that the following reactions were playing a greater role in N2O emission reduction by biomass gasification gas: N2O( + M) N2 + O( + M)
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