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Standpipe vibration of circulating fluidized bed (CFB) boiler will threaten its safe and stable operation. In order to solve the standpipe vibration, the mechanism of standpipe vibration was discovered based on the type B choking theory in the CFB system and the Ledinegg instability criteria for the gas-liquid flow. And the influence of several factors on the gas-solid flow, especially the reverse flow in the standpipe, was qualitatively analyzed according to the pressure and mass balance in the whole loop. The standpipe vibration is caused by the mismatch between the driving pressure and the resistance pressure drop in the whole loop. To suppress the standpipe vibration, it is necessary to optimize the flow and pressure parameters under stable working conditions, which can be achieved by four main methods of reducing the resistance of the returning valve and cyclone, increasing the circulating rate and the solid height in the standpipe. In engineering application, these four methods can be realized by appropriately increasing the aerated air velocity and the sectional area ratio between the riser and the standpipe, reducing the length of the passage and the height of the weir, increasing the effective material fraction and the inlet area of the cyclone. This paper theoretically analyzes the mechanism of standpipe vibration and proposes corresponding engineering solutions to guide the operation and design of CFB boilers. |
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