| Chemical looping combustion（Chemical Looping Combustion,CLC）sludge treatment technology can inhibit the production of pollutants such as dioxins and nitrogen oxides during the sludge incineration process.The full mixing of iron-based oxygen carrier and dried sewage sludge binary particles in the fluidized bed is a prerequisite for the implementation of this technology.However,there are big differences in density and particle size between the two,which are prone to particle separation.In this paper,the mixed fluidization characteristics of binary particles are studied.By means of signal noise reduction and feature extraction,a new method based on HHT method is proposed to determine the transition characteristics of the mixed state of oxygen carrier and sludge binary particles.The fluidization experiments of binary mixtures of dried sewage sludge and iron-based oxygen carrier were carried out in a plexiglass cold fluidized bed with 100 mm inner diameter in this study.The effects of particle size,mass ratio of dried sewage sludge and oxygen carrier and operating velocity on the fluidization characteristics were investigated.The results showed that the sludge can be mixed well with the oxygen carrier with mean particle size of 0.66 mm,and the minimum fluidization velocity(Umf)was equal to the minimum mixing operation velocity（Um）.When the mean particle size of oxygen carrier was 1.46 mm,it gradually transited from the separated fluidization state to the mixed fluidization state as the operating velocity increased,and the Um was greater than Umf in this condition.When the mean particle size of oxygen carrier was2.43 mm,the separated fluidization state was always maintained.Based on the characteristic value of the fluctuation of the pressure difference in the fluidized bed,it has positive application value to propose the judgment basis of the mixing/separation state of the binary particles.By means of pressure difference signal noise reduction and feature extraction,the Hilbert-Huang transform method is used to analyze the pressure difference signal to study the transition characteristics of the mixed state of the oxygen carrier and the sludge binary particles in the fluidized bed,and obtain the corresponding complete mixing critical velocity.And experimental results showed that the pressure drop of binary particles includes complete separation stage,transitional mixing stage,and complete mixing stage.In the complete separation stage,the spectral energy of high-frequency band is the largest,accounting for about 70%.In the transitional mixing stage,the spectral energy of middle-frequency band gradually increases to 70%with increase of wind velocity,while the spectral energy of high-frequency band rapidly decreases to about 20%.The spectral energies of high,medium and low frequency change little at higher wind velocities.With increase of sludge feeding amount,the transition velocity of complete mixing state increases from0.57 m/s to 0.65 m/s.Compared with the conventional pressure drop analysis method,HHT method is easy to determine the transition velocity of complete mixing state.It also has the virtues of small data bulk and fast analysis processing. |
