洁净煤技术

2020, v.26;No.126(02) 78-85

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NGD反应器气相流场及能耗特性研究
Study on the characteristics of gas flow field and energy consumption of NGD reactor

段璐;王实朴;
DUAN Lu;WANG Shipu;China Coal Research Institute Company of Energy Conservation;China Coal Research Institute;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;

摘要(Abstract):

高倍率灰钙循环脱硫(NGD)技术具有投资和运行成本低、占地面积小、节水和可避免有色烟羽等优点,在燃煤工业锅炉领域具有较好的发展前景,而已有研究主要关注脱硫反应过程及其影响因素,尚缺乏对NGD反应器内流场和能耗的认识。笔者基于熵产分析方法建立了NGD反应器能耗的定量分析模型,NGD反应器能耗包含因烟气散热引起的能耗和黏性流体流动引起的能耗,其中,黏性流体流动引起的能耗包含湍流耗散和壁面摩擦,此外,由于NGD反应器高度达20 m以上,其进、出口压降还应考虑位置势能变化,因此,NGD进、出口压降包含位置势能变化、湍流耗散和壁面摩擦引起的压降。以某30 t/h煤粉工业锅炉配套的NGD反应器为研究对象,采用CFD方法模拟脱硫反应器内的流场分布,并在此基础上通过能耗分析模型研究脱硫反应器内的能耗组成和分布。结果表明,CFD方法和能耗分析模型计算的NGD进、出口压降与测量值的偏差分别为0.4%和9.6%,因此,CFD方法和能耗分析模型能较为准确地预测脱硫反应器内黏性流体流动引起的能耗,NGD反应器内黏性流体流动和烟气散热引起的能耗分别占NGD总能耗的96.2%和3.8%,可见黏性流体流动对NGD能耗起主导作用,位置势能变化、湍流耗散和壁面摩擦引起的压降分别为237.6、347.4和57.5 Pa,可见湍流耗散对NGD反应器能耗起主导作用。将NGD反应器划分为上部主体反应区、中部加速区和下部烟气入口区,由于黏性流体流动过程中的能量耗散来自不同流层速度差引起的摩擦耗散,因此能耗大小主要取决于不同流层间的速度梯度,而中部加速区平均速度较大且流场分布极不均匀,导致单位体积湍流熵产远高于其他区域,因此其体积虽仅占3.6%,但其熵产占NGD反应器总熵产的53.8%;上部主体反应区速度分布较为均匀且平均速度较小,但其体积占NGD反应器体积的83.3%,因此中部的熵产仍然较大,占总熵产的40.1%;下部烟气入口区流场分布极为不均匀但平均流速较小,单位体积熵产率从下往上逐渐增大,其体积比为13.1%,熵产占总熵产的比值为6.1%。可见,上部和中部是能耗的主要区域,尤其是中部加速区是降低NGD反应器能耗的主要目标区域。
No gap desulfurization( NGD) has great prospects for the pulverized coal industrial boilers due to low investment and operating costs,saving space,saving water and refraining from the colored plume.However,the investigations reported mainly pay attention to the reaction process of desulfurization and its influence factors.It's still unclear about the flow field and the energy consumption inside the NGD reactor.Based on the entropy generation theory,a model for quantitatively predicting the energy consumption inside a NGD reactor was established.The energy consumption results from the heat loss of flue gas and the flow of viscous fluid.The energy consumption of flow is mainly attributed to the turbulent dissipation and fluid friction near the wall.In addition,the potential energy should not be neglected at the pressure drop of inlet and outlet as the NGD reactor is usually higher than 20 m.Thus,the pressure drop of NGD reactor can be attributed to the potential energy,turbulent dissipation and fluid friction near the wall.The numerical investigation was carried out for a NGD reactor from a 30 t/h pulverized coal industrial boiler by using CFD method.And the energy consumption and distribution inside the NGD reactor was analyzed by using the energy consumption model based on the CFD data.The results show that the CFD method and the energy consumption model can precisely predict the inlet and outlet pressure drop of NGD reactor with the deviations of 0.4% and 9.6% compared with the measured data,respectively.Therefore,CFD method and energy consumption analysis model can accurately predict the energy consumption caused by viscous fluid flow in the desulfurization reactor.The flow of viscous fluid is the main factor of energy consumption because the ratios of energy consumption due to the flow of viscous fluid and heat loss are 96.2% and 3.8%.It can be seen that viscous fluid flow plays a leading role in the energy consumption of NGD,and the pressure drops due to the change of potential energy,the turbulent dissipation and the fluid friction near the wall are 237.6,347.4 and 57.5 Pa respectively,indicating that the turbulent dissipation is the main factor for the energy consumption.The NGD reactor is divided into the middle part of speed-up zone and the underpart of flue gas inlet zone.Because the energy dissipation in the viscous fluid flow comes from the friction dissipation caused by the velocity difference of different flow layers,the energy consumption depends on the velocity gradient of fluid flow.The high velocity and the high non-uniform flow field inside the middle part of speed-up zone results in the highest entropy generation due to turbulent dissipation per volume. Therefore,although its volume accounts for only 3.6%,the ratios of entropy generation inside the middle part of speed-up zone is 53.8% with a small part of volume.The ratios of entropy generation and volume inside the upper part of main reaction zone are 40.1% and 88.3% with a low velocity and relatively homogenous flow field.The entropy generation increases with position with a low average velocity and a high non-uniform flow field inside the underpart of flue gas inlet zone.The ratio of entropy generation is 6.1% and the ratio of volume is 13.1%.It can be seen that the energy is mainly consumed in the upper part and the middle part.And,it will be most useful to decrease the energy consumption by modifying the middle part.

关键词(KeyWords): 高倍率灰钙循环脱硫;能耗;流场;反应器;熵产;计算流体力学
NGD;energy consumption;flow field;reactor;entropy generation;CFD

Abstract:

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基金项目(Foundation): 国家自然科学基金青年基金资助项目(51906095);; 中国煤炭科工集团有限公司国际合作项目(2019-TD-2-CXY003)

作者(Author): 段璐;王实朴;
DUAN Lu;WANG Shipu;China Coal Research Institute Company of Energy Conservation;China Coal Research Institute;National Energy Technology & Equipment Laboratory of Coal Utilization and Emission Control;

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