Abstract
The unknown NOx distributions inside large-scale CFB (circulating fluidized bed) boilers have always hindered the economy of the SNCR (selective non-catalytic reduction) process. In this study, field tests were carried out on a typical 300 MW CFB boiler, where multi-level 316 L-made probe and Ecom-J2KN/Testo 350 analyzers were used to perform detailed two-dimensional distributions of flue gas composition at SNCR inlets for the first time. The penetration depth inside the horizontal flue pass was up to 7 m. The NOx distributions were analyzed in detail combining with the auxiliary test in the dilute phase zone. Key results show that the average O2 concentrations in #A and #C regions were 6.52% and 0.95%, respectively. The vertical NOx distributions of #A and #C SNCR inlets were similar, showing a trend of first increasing and then decreasing with peak value all appeared at 5 m depth, while the NOx distribution of #B SNCR inlet was basically increasing. Some local areas with extremely high NOx concentration (over 2000 mg/m3) were observed near the inclined edge of SNCR inlets, which has never been reported before. Based on this, the optimization of urea injections was conducted, which could save 15.7% of the urea solution consumption while ensuring ultra-low emission of NOx.
Highlights
In recent years, the circulating fluidized bed (CFB) technology has developed rapidly because of its advantages in fuel flexibility and load regulation [1,2,3,4]
The results provide the lasting source for the improvement of CFB combustor model, and a direct reference for the prediction of NOx distribution at selective non-catalytic reduction (SNCR) entrance to enhance de-NOx efficiency in large-scale CFB boilers
The vertical distributions of flue gas composition at #B SNCR inlet is exhibited in the corresponding dilute phase zone was not measured, it could be judged from the above analysis that the combustion share of the coal should be higher near the rear wall
Summary
The circulating fluidized bed (CFB) technology has developed rapidly because of its advantages in fuel flexibility and load regulation [1,2,3,4]. Various de-NOx combustion technologies emerged as the times required, including air-staging [11], improvement of cyclone efficiency [12], fluidization state specification [13], flue gas recirculation [14] and optimization of urea injection [15]. In the selective catalytic reduction (SCR) system commonly adopted in pulverized coal boiler, the non-uniform NOx distribution and flow field can be directly calculated [25] or even measured [26] due to low solid concentration and gas temperature. The results provide the lasting source for the improvement of CFB combustor model, and a direct reference for the prediction of NOx distribution at SNCR entrance to enhance de-NOx efficiency in large-scale CFB boilers
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