Xiahui Gui

Coal Preparation Technology: Status and Development in China

The rapid growth of coal production is supporting Chinas economic development. This paper discusses significant developments of coal preparation industry in China. The development direction of low-quality coal resources is also described, including the comprehensive utilization of resources and green coal preparation. Coal preparation may shift from the simple separation and production of highquality products to a comprehensive utilization of associated resources and lowquality coal. Green coal preparation is a new concept and involves a highly efficient coal preparation method based on the water cycle and comprehensive utilization of resources. This paper also describes a technology that transforms coal (mineral) resources (including natural, secondary, and artificial resources) into useful products (including raw materials and fuel) by separation, extraction, and processing for an eco-friendly approach to using secondary resources.

Study on Kinetic Modelling for Fine Coal Flotation

Flotation models are useful for practical quantitative work, many are widely used to assist in the design of new equipment and processes. The analyses of petrographical composition, size fraction, and density distributions of the coal sample were used to detect its floatability and quality characteristics. The flotation rate constant k values of the five traditional kinetic models parameters were calculated by software MATLAB7.0. In addition, we discussed a new kinetic model-fitting approach for coal flotation. Results show that the main gangue mineral in the fine coal is kaolinite. The middle density fraction of 1.40–1.60 g/cm3 has a high yield, which indicates that the coal sample is not easy to separate. The k value can reflect the floatability. During the flotation process, the k value decreases, and the floatability worsens. The experimental data of various size fractions show that the new modified model has more advantages compared with the five traditional models. The correlation coefficient (R 2) value of the new modified model is 1.00, and the SSE value is close to 0.

Study on Size and Density Distribution in Fine Coal Flotation

Mineral composition, size fraction, and density distributions of a fine coal sample were used to determine its floatability and quality characteristics. Flotation rate tests were conducted using different agitation speeds of flotation machines. The results showed that the ash of clean coal product increased gradually with increasing agitation speed and the floatability of coal became poor. The higher the agitation speed, the faster the flotation rate was. For coarse size coal with higher density, the recovery was low. For the same size particle and density, the higher the agitation speed, the higher the recovery. The relationship between energy (E) and recovery (ϵ) were estimated through the cubic expression. The model parameters were calculated using software MATLAB7.0. The experimental data of various size fractions showed that the fitting of the model was very good.

Effects of Energy Input on the Laboratory Column Flotation of Fine Coal

This study explored the effects of energy input and different energy increase patterns on the separation performance of a laboratory cyclonic–static microbubble flotation column in fine coal flotation. The energy input was changed by adjusting the circulating pump power and pulp residence time. Continuous flotation tests were designed by using five feed rates (i.e., different pulp residence time), which were 53.33, 80.00, 106.40, 133.60, and 160.00 g/min, and various useful power of the circulating pump (22.44, 30.14, 38.50, 46.86, 56.10, and 64.46 W). Results show that concentrate combustible recovery initially increased before reaching saturation distribution with increasing energy input absolute value. An ash content of 10.90% and combustible matter recovery of 92.84% were obtained at the energy input of 10098.00 J which is called the flotation saturation energy Es. Es is the essential condition and guarantee for a complete flotation process. A low ash content of clean coal was obtained with low energy input. With the increase of energy consumption, the additional coals recovered were coarse particles with low ash content and fine particles with high ash content. However, the ash content did not exhibit a significant change with the increase of energy input in this investigation. During the flotation process, a minimum critical flotation time T and critical circulation pump useful power P are required. If the P and T of a variable are less than the critical value, high combustible matter recovery could not be obtained by adding another variable to increase energy input. A reasonable mode of energy input was proposed that the absolute value of the energy input reaches Es; meanwhile, it ensures that each value of the P and T is greater than the critical values.

The Effect of Power Input on the Fine Coal Flotation Rate Constant

To explore the effect of the power input on the fine coal flotation rate constant, an energy consumption test system was established for the fine coal. In this investigation, the fine coal investigated was anthracite obtained from the flotation feed of the Xuehu Coal Preparation Plant of the Shenhuo mine in the Henan Province of China. A total of 65 sets of flotation rate tests were carried out with different power inputs at different flotation times. The relationship between the flotation rate constant and the power input at different flotation times was obtained. The result showed that the flotation rate displayed a constant increase, whereas the power input increased at any time during the flotation process. With the continuous increase of the power input, the increasing trend exhibited by the flotation rate constant decreases after reaching a maximum value. The calculation conjecture of the flotation rate constants and the power input were obtained by imitating the calculation method of the flotation kinetics model. Determining the value of the flotation power input and the flotation time during the flotation process of the different fine coal characteristics would therefore be helpful.

Flotation kinetics of easy-to-float fine coal

ABSTRACT Six flotation kinetics models were applied to fit the flotation kinetics results of easy-to-float fine coal. It was found that, except for the second-order kinetic model, the rest models are well suited for fitting the experimental data. The rate constant decreased as flotation time increased, indicating that the particle floatability in the pulp decreased. However, only a slight decrease in the rate constant was observed within 100 s, indicating that the coal samples have good floatability in general. X-ray photoelectron spectroscopy results show that the small proportion of hydrophilic oxygen-containing groups is responsible for the good floatability and fast flotation kinetics.

Effect of pH on the flocculation behaviors of kaolin using a pH-sensitive copolymer

pH-sensitive copolymers have been widely introduced to achieve rapid dewatering and consolidation of solids in mining and oil sands processing wastes. But no more attention has been given to the flocculation efficiency of solid suspensions as a function of pH using pH-sensitive copolymer. In this study, a pH-sensitive copolymer was synthesized and employed to investigate the flocculation behaviors of kaolin by focused beam reflectance measurement (FBRM). A titration test was introduced to characterize the copolymer conformation transition. The results demonstrated that at pH ranging from 3 to 6, with the pH increase, the zeta potential magnitude of kaolin particles increased, resulting in the repulsive forces between particles increasing. However, the hydrophobicity of kaolin increased as the pH increased. Thus, the hydrophobic forces could neutralize a part of the repulsive forces between particles and result in good and similar flocculation performances. At the pH greater than 6, the zeta potential magnitude of kaolin particles and copolymer molecules increased significantly, and the repulsive force between kaolin particles increased after copolymer addition due to the kaolin particles being more negatively charged, which resulted in poor flocculation efficiency and cloudy supernatant. It was concluded that the pH-sensitive copolymer could achieve both perfect flocculation efficiency and low moisture of filter cake at the isoelectric point of copolymer.

The Characterization of Flotation Selectivity of Different Size Coal Fractions

ABSTRACT To investigate the selectivity of different size fractions in the flotation process, the Fuerstenau upgrading equation was used to fit the results of flotation kinetics of various size fractions and to evaluate the flotation selectivity. The hydrophobic and hydrophilic functional groups on the surface of coal of different size fractions were analyzed quantitatively by Fourier Transform Infrared (FTIR) Spectroscopy, and a hydrophilicity index (HI) was defined. The difference in the values of HI was also applied to assess the flotation selectivity. The results show that the fitting constant k from the Fuerstenau upgrading equation is positively correlated to the flotation selectivity. The constant k values of the three size fractions are as follows: 3.16 for 0.25–0.125 mm, 2.86 for 0.125–0.074 mm, and 2.03 for –0.074 mm. It reflected that the selectivity of the coarse size fraction was the best, followed by the medium size fraction, and the selectivity of fine size fraction was the worst. The required clean ash content of 12% was achieved at a separation density of about 1.6 g/cm3. The difference in the HI values between 1.4–1.6 g/cm3 and > 1.6 g/cm3 determine the selectivity. The greater the difference in the HI values is, the better the selectivity is. The difference in the HI values were 1.2195 for 0.25–0.125 mm, 0.8327 for 0.125–0.074 mm, and 0.5873 for –0.074 mm, which is consistent with the results obtained using the Fuerstenau upgrading equation to characterize the selectivity of coal slime.

A new process based on a combination of gravity and flotation for the recovery of clean coal from flotation tailings

ABSTRACT Beneficiation of clean coal from flotation tailings with a high intergrown ash content is gaining popularity in China. It not only improves the utilization rate of coal resources but also reduces environmental pollution. In this paper, a novel gravity–flotation process is proposed to concentrate low-ash fine coal and includes the disposal of tailings via gravity, grinding liberation, and froth flotation. The experimental results show that the clean coal had an ash content of 12.33% and the yield from the flotation tailings was 32.24% with an ash content of 46.39%, which has economic value in the current market.

Optimization of a Teetered-Bed Separator Using Pulsed Water

ABSTRACT The teetered-bed separator (TBS) is widely used for coal particles with a size range of 2.0 mm to 0.25 mm separation based on hindered settling principles. However, a problem with teetered-bed units is the limited range of particle size in which an acceptable separation performance is achieved. To explore the probability of an extend size range of TBS, a pulsed-water supply with different frequencies and amplitudes was introduced to the traditional TBS in this study. The separation performance of 2 mm to 1 mm coarse fraction and 1 mm to 0.25 mm fine fraction were systematically compared with and without pulsed water, respectively. The results show that, for the 2 mm to 1 mm coarse fraction, little additional benefit was gained when pulsed water was used to supply the fluidization water to a traditional TBS. However, for a fine fraction of 1 mm to 0.25 mm, an optimal separation index—89.18% combustible recovery with 11.58% ash content and 468.41 efficiency index—was obtained when the frequency and amplitude were 1 Hz and 40 dm3/h, respectively. The efficiency index under the pulsed-water condition increased by 80.45, compared with that of constant upward water. It indicates that the bed was completely loosened through the forced oscillation and constant friction collision among the particles in the bed under the interaction of pulsed and continuous flow. The fine mud mechanical entrainment phenomenon in traditional TBS was avoided. Therefore, pulsed water can reduce the lower particle-size limit, which means that the upper limit size of the flotation feeding decreases. The amount of materials entered into flotation process also decreases, reducing the cost of actual industrial production.