内构件对变径提升管内气固流动特性的影响

以催化裂化平衡剂和常温空气为介质,在变径提升管冷态模拟装置上,主要考察了不同操作条件下钝体及环管内构件对变径提升管扩径段内压降、轴径向颗粒浓度分布及径向不均匀指数的影响,并描述了扩径段内的气固流动结构。结果表明:在相同操作条件下,钝体结构产生的压降较环管大,可降低系统的有效压头;颗粒浓度分布受内构件影响明显,环管进气的射流效应使颗粒浓度降低,径向分布均匀性减小,而钝体的存在可明显改善环管结构的弊端,削弱射流作用,提高颗粒浓度,增大局部固气比,促使气固再分布,形成两相错流流动,强化气固接触,且在中心区域形成涡流,增强扩径段内的湍动程度;与环管结构相比,钝体内构件使扩径段内的颗粒径向不均匀指数减小,使颗粒分布更加均匀,且其受操作条件的影响比较小,操作稳定性更高。

EFFECT OF INTERNALS ON CHARACTERISTICS OF GAS-SOLIDS FLOW IN A VARIABLE DIAMETER RISER REACTOR

Effect of internals on the pressure drop, axial and radial solids concentration distribution and radial non-uniformity index inside a novel riser reactor with a diameter-enlarged bottom was emphatically studied in a cold model apparatus, and the flow structures inside the diameter-enlarged sections with different internals were proposed. The results show that the pressure drop of the diameter-enlarged section with a bluff-body is larger than that of the one with an annular pipe under the same operating condition, which diminishes the impetus of circulation. The solids concentration is affected by the internals apparently. The jet effect caused by annular pipe feeding lowers the solids concentration as well as worsens the radial uniformity while the bluff-body could overcome the drawbacks of annular pipe, weakening the jet action and increasing the solids holdup. Besides, gas and solids are redistributed by the bluff-body, forming a cross-flow which intensifies the gas-solids contacting, and a vortex, which promotes the turbulence inside the diameter-enlarged section. The radial non-uniformity index of solids concentration in the diameter-enlarged section with the bluff-body is much smaller, resulting in a more uniform solids distribution, and a small variation of the index as the operating conditions change, which exhibits higher operation stability.