Circulating fluidized bed pulverized coal gasification and combustion process is a complex multi-scale gas-solid flow process. In order to ensure safe, stable and efficient operation of the system, in-depth mechanism research on the gas-solid two-phase multi-scale flow characteristics inside the reactor is required. The reasonable particle concentration distribution of the organization provides a good contact area and reaction time between the coal powder particles and air or oxygen in order to improve the system operating efficiency and control the process.
In view of the complex gas-solid flow inside the circulating fluidized bed, the Circulating Fluidized Bed Laboratory of the Institute of Engineering Thermophysics, Chinese Academy of Sciences has carried out a complex flow process study based on the combination of fluid calculation and process tomography, and has studied the coal powder gasification process Gas-solid two-phase multi-scale flow characteristics in the reactor and gas-solid separation system. The numerical calculation uses the MP-PIC method, based on the CPFD calculation platform, embedded in the EMMS drag model. Through three-dimensional full-cycle numerical calculation and analysis, the gas-solid multi-scale motion characteristics inside the reactor were obtained, and the distribution of complex gas-solid flow field characteristics and particle circulation flow rate change characteristics were revealed. The experimental study uses capacitance tomography (ECT), microwave Doppler (Microwave Doppler), pressure and optical fiber signals, combined with signal cross-correlation theory, to monitor the particle distribution in the feeder in real time online, and to measure and Correlation analysis to obtain the average particle flow rate and circulating flow rate; through multi-mode fusion measurement and data fusion analysis, to provide solid particle concentration, velocity, pressure distribution information in different areas of the reactor; analysis obtained multi-scale circulating fluidized bed gas-solid Flow characteristics. Based on the fusion of calculation and measurement, the mass distribution law of solid particles between the reactors under the complicated furnace flow structure is obtained, which provides online monitoring tools and experimental databases for the design and large-scale pulverized coal gasification process.
The results show that: the numerical calculation results can better reflect the characteristics of the pressurized gas-solid flow field in the fluidized bed; the particle volume fraction and velocity distribution can reflect the circulation state of the particles passing through the four areas; the pressure drop in the bed is mainly concentrated in the bottom In the phase area, to analyze the pressure signal in the frequency domain, the internal and external pressure signals of the core tube must be analyzed separately; the EMMS drag model can accurately predict the radial distribution of pressure and solid concentration, but the solid flux prediction is lower than the experimental value. In the future, more in-depth research will be carried out on the model. Through this study, the detailed dynamic characteristic parameter distribution of the pressurized gas-solid full circulation loop was obtained, including the changes of key parameters such as the pressure balance of the circulation loop and the particle distribution characteristics of the dense phase zone, and the non-pressure flow rate of the pressurized gas-solid return flow was achieved Intrusive online measurement provides important parameter data for industrial design of pressurized gasification of circulating fluidized bed.
The above research has taken the lead in carrying out tomographic imaging and CPFD numerical calculation research of pressurized gas-solid flow process internationally. It combines electrical capacitance tomography, microwave Doppler and numerical calculation to realize online measurement of complex gas-solid flow process under pressure. The research results were invited to make two invited reports at the International Conference on FLUIDIZATION XVI, Guilin, China – Keynote speaker and Energy Engineering and Powder Technology International Conference, Krakow, Poland – Plenary Speaker . He was invited by the international journal Applied Thermal Engineering to write an overview article on gas-solid flow process tomography measurement. The article title is Application of electrical capacitance tomography in circulating fluidised beds – A review (10.1016 / j.applthermaleng.2020.115311). The research results were published in Powder Technology (10.1016 / j.powtec.2020.02.047), Particuology (10.1016 / j.partic.2019.05.002, 10.1016 / j.partic.2019.11.003), Measurement Science and Technology (10.1088 / 1361 -6501 / aafd7e), Transaction of Institute on Measurement and Control (10.1177 / 0142331219851913, 10.1177 / 0142331218808857) and other journals.
The above research was supported by the National Natural Science Foundation of China (61771455 and 61811530333), the Ministry of Science and Technology's major scientific research instrument project (2018YFF01013801), the Chinese Academy of Sciences' key foreign cooperation project, and the Royal Society Newton Advanced Fellowship-NA170124.
Fig.1 Experimental measurement of pressurized gas-solid full circulation circuit
Figure 2 CPFD calculation of pressurized gas-solid full circulation loop
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