Dry
coal beneficiation has played a vital role during the initial
stage of coal cleaning in recent years. Successful utilization of
a gas–solid fluidized bed for >6 mm coal cleaning motivates
scholars to explore the possibility of fine coal cleaning using dry
beneficiation methods. In this study, pulsed flow was introduced into
a fluidized bed to optimize bubble behavior, thus improving the density
stability. The equation of minimum fluidization velocity (
U
mfp
) in a gas-vibro fluidized bed for coal preparation
was investigated theoretically. An equation has been proposed for
predicting
U
mfp
while considering changes
in the friction coefficient (
C
f
) in the
gas-vibro fluidized bed. Based on two-phase theory, the correlation
of bed density was determined by analyzing the bubble behavior in
the gas-vibro fluidized bed. The theoretical bed density was then
compared with experimental data of the bed density and separation
density. The predicted bed density in monodisperse and binary dense
medium systems was found to be consistent with the experimental results.
Overall, the equation of bed density is suitable for estimating the
separation density in the gas-vibro fluidized bed.
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.
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