水力空化效应对水物化性质影响的实验研究

水力空化过程伴随着气泡的初生、生长、溃灭以及气泡溃灭产生的瞬间高温高压,这种空化效应对于空化介质本身产生怎样的影响一直缺乏研究。以单孔、五孔孔板型空化器为实验装置,研究水力空化效应对水物化性质的影响。首先,在相同空化时间和测量温度下,调节空化器不同入口压力(0.3 MPa、0.5 MPa、0.7 MPa、1 MPa),对孔板空化器内的空化水样进行电导率、溶解氧、pH的测试,分别得到水样三种性质随入口压力和时间变化曲线。实验结果表明,随着入口压力的增大,电导率先逐渐升高后逐渐降低:溶解氧先逐渐降低后逐渐回升;pH受水力空化效应影响较小,整体上没有明显的变化规律。

Effects of sintered metal distributor on fluidization quality of the air dense medium fluidized bed

Dry coal beneficiation using an air dense medium fluidized bed (ADMFB) requires the formation of a sta- ble and uniform bed from the dense medium. Others have shown that the structure and geometric parameters of the air distributor have a significant influence on the experimentally observed fluidization quality. In this study we used a sintered metal distributor (SMD) in the ADMFB separator and study its effect on the fluidization quality. The results show that for the same open area ratio (OAR), a smaller aper- ture in the SMD will provide improved fluidization quality. If aperture size is held constant bigger open area ratios result in improved fluidization quality. And, the fluidization quality also improves when the pressure drop across the SMD increases. A model relating distributor pressure drop and the geometric parameters of the SMD is also proposed.

Prediction of the position of coal particles in an air dense medium fluidized bed system

An air dense medium fluidized bed separator(ADMFBS) is used for dry beneficiation of coal using ultrafine magnetite particles as a pseudo-fluid medium. In this process, the coal particle gains additional weight due to coating on its surface and deposition at dead zone area by fine magnetite particles.Hence, the effective density of coal particle increases and the position of coal particle changes accordingly. In this work, an attempt was made to predict the position of coal particle in non-bubbling condition dense medium fluidized bed system. Coal particles of different shape such as cubical, rectangular prism,spherical and triangular prism with different projected area and density were used. The results show that the position of coal particle in air dense medium fluidized bed follows descending order with respect to the increase of density, projected area of coal particle and different shapes(i.e., triangular prism, cubical,rectangular prism and spherical). Empirical mathematical correlations were developed to predict the position of coal particle.

Effect of agitation on the characteristics of air dense medium fluidization

In order to study the effect of agitation on the characteristics of air dense medium fluidization, we designed and constructed an agitation device. Analyses were then conducted on the fluidization characteristics curves, the bed density stability and the average bubble rise velocity Uaunder different agitation conditions. The results indicated that a lower bed pressure drop(without considering lower gas velocity in a fixed bed stage) and higher minimum fluidized velocity are achieved with increasing agitation speed.The height d(distance between the lower blades and air distribution plate) at which the agitation paddle was located had a considerable effect on the stability of the bed density at 9.36 cm/s < U < 10.70 cm/s. The higher the value of d, the better the stability, and the standard deviation of the bed density fluctuation r dropped to 0.0364 g/cm^3 at the ideal condition of d = 40 mm. The agitation speed also had a significant influence on the fluidization performance, and r was only 0.0286 g/cm^3 at an agitation speed of N = 75 r/min. The average bubble rise velocity decreased significantly with increasing agitation speed under the operating condition of 1.50 cm/s < U–U_(mf)< 3.50 cm/s. This shows that appropriate agitation contributes to a significant improvement in the fluidization quality in a fluidized bed, and enhances the separation performance of a fluidized bed.