Effect of the distributor plugging ways on fluidization quality and particle stratification in air dense medium fluidized bed

Gas-solid fluidized bed separation is a highly efficient and clean technique for coal separation,and can effectively remove ash and sulfur contained gangue minerals from coal.However,the fine coal plugging distributor often leads to uneven fluidization and affects the separation effect.In this paper,different plugging ways were designed to study their effects on the fluidization characteristics and particle mixing.It was found that when the plugging phenomenon occurs,the minimum fluidization velocity of the fluidized bed gradually decreases as the plugging area enlarges.The difference between the top and the bottom of the bed minimum fluidization velocity increases accordingly,and a“stagnation phenomenon”occurs in the bed.The standard deviation of pressure fluctuations at the top of the bed is smaller than that at the bottom of the bed,which is the opposite of normal conditions.As the area of the plugging increases,the dead zone on the side wall of the fluidized bed significantly increases.The size of the dead zone is rapid reducing at the initial stage.It was noticed that the stratification of the low-density products is particularly affected by plugging,whereas the stratification of high-density products is not obviously influenced by certain conditions.

Fluidization stability and periodic fluctuations in gas–solid separation fluidized bed using Geldart A dense medium

Gas–solid separation fluidized bed is a typical method for coal separation without water utilization.Geldart A particles is also considered as the ideal dense medium to strengthen separation efficiency.Fluidization stability reflects the bed pressure fluctuations and the distribution of bubble and emulsion phases,affecting the separation performance.And the main frequency of pressure fluctuations can directly reflect the degree of pressure fluctuations.Therefore,the detailed fluidization stability is analyzed combined the method of standard deviation of pressure fluctuations,power spectral density,etc.,for Geldart A particles.The results showed that maintaining an appropriate gas velocity resulted in an average bed pressure of around 2000 Pa.The main frequency is mainly concentrated around 1–1.5 Hz.Finally,a prediction model of the main frequency of pressure fluctuations is established,and the error can be controlled within±0.15.The investigation further proved the stable fluidization of Geldart A particles and provides a method for predicting the main frequency of pressure fluctuations in the gas–solid separation fluidized bed.

Influence of bubbles on the segregated stability of fine coal in a vibrated dense medium gas-solid fluidized bed

In this paper,the variation of bubble size and number in the separation process of vibrated fluidized bed as well as the influence of bubble movement on the axial distribution of fine coal in different positions of the bed were studied.The result revealed that the size and number of bubbles is correlated with the fine coal separation effect in the separation process.When the bed is in a uniform and stable fluidized state,the size of bubbles in the separation process was in the range of 1-2.5 cm and the number of bubbles was reduced by nearly 50%,which is helpful to promote the stratification and segregation of fine coal.Thereby,after separation,the ash content of refined coal products of anthracite and 1/3 coking coal was reduced to 12.1% and 23.7% respectively,and the content of refined coal was up to 42.5% and 68.5% respectively,which show that the vibrated fluidized bed has a good separation performance,and can separate efficiently the coal of size−6+1 mm.