Experimental study on structural optimization of a supercritical circulating fluidized bed boiler with an annular furnace and six cyclones

Annular furnace CFBs with six cyclones represent new designs for large capacity CFB boilers over 660 MW. To investigate the gas-solid flow non-uniformity and its main influencing factors, an experimental study was carried out in the cold-test rig of an annular furnace CFB with six cyclones. The influence of furnace structure and cyclone arrangement on the non-uniformity of gas-solid flow was obtained. On the basis of these findings, the structure of the annular furnace CFB with six cyclones was optimized, and an optimal structure was obtained. The results show that for newly designed annular furnace CFBs, the non-uniformity of gas-solid flow among loops is no greater than that of traditional CFBs. In terms of uniformity, side cyclones rotating inward are superior to those rotating outward. The position of the side cyclones determines the basic solid circulating rate distribution trend and can dramatically improve flow non-uniformity. The middle cyclone positions and the symmetric modes of the cyclones do not determine the solid circulating rate distribution trend and have less effect on DEVGs. Forty-five degree chamfers of outer ring walls can reduce wall erosion and the non-uniformity of gas-solid flow in the circulating fluidized bed. Regarding the operating and structural conditions in this work, the optimal structure of annular furnace CFBs is Type 6: side cyclones rotating inward and b = a/2, d = 0.1c; the center of the middle cyclone inlet located at the centerline of the furnace cross-section; cyclones on the two sides of the furnace in an axisymmetric arrangement; and a furnace corner shape of 45° chamfers. Under the given operating conditions, the DEV_(Gs) for the optimal structure are approximately 4.0%~10.3%.     

循环流化床中心二次风的设计及实验研究

介绍了在炉膛中央设置水平布置杆式二次风和竖直布置柱式二次风两种结构。在冷态循环流化床上,研究了中心二次风的布置形式和布置高度,以及二次风率对床内沿高度方向的颗粒浓度分布的影响,并与同样高度的常规壁面二次风进行了对比。实验发现,空气分级后二次风下方的颗粒浓度随二次风率的提高而增大。二次风高度的增加伴随着底部密相区向上延伸。几种二次风布置形式中,水平杆式二次风结构布置时底部浓度最大。通过对射流的示踪发现,在高二次风速时中心二次风扩散到壁面区域,而在中心区域则缺少二次风气体,这不利于对中心区域的氧气补充。而水平杆式中心二次风射流在横向动量的作用下,射流进入床内时发生偏转,能够在床内形成较大的扩散面。另外,还讨论了中心二次风进一步在实际循环流化床锅炉中的应用所需要注意和解决的问题。     

Numerical analysis of flow instability in the water wall of a supercritical CFB boiler with annular furnace

In order to expand the study on flow instability of supercritical circulating fluidized bed (CFB) boiler, a new numerical computational model considering the heat storage of the tube wall metal was presented in this paper. The lumped parameter method was proposed for wall temperature calculation and the single channel model was adopted for the analysis of flow instability. Based on the time-domain method, a new numerical computational program suitable for the analysis of flow instability in the water wall of supercritical CFB boiler with annular furnace was established. To verify the code, calculation results were respectively compared with data of commercial software. According to the comparisons, the new code was proved to be reasonable and accurate for practical engineering application in analysis of flow instability. Based on the new program, the flow instability of supercritical CFB boiler with annular furnace was simulated by time-domain method. When 1.2 times heat load disturbance was applied on the loop, results showed that the inlet flow rate, outlet flow rate and wall temperature fluctuated with time eventually remained at constant values, suggesting that the hydrodynamic flow was stable. The results also showed that in the case of considering the heat storage, the flow in the water wall is easier to return to stable state than without considering heat storage.     

双支腿循环流化床炉膛翻床条件与防止控制试验研究

在双支腿循环流化床冷态试验台上进行了床料平衡试验,得到不同流化参数下风量和床压的动态曲线,基于并行流道阻力特性分析,提出双支腿炉膛翻床条件的预测方法,并模拟了控制逻辑对翻床的控制效果.结果表明:当流化风量大于临界翻床风量时,双支腿炉膛处于自平衡区,两侧炉膛的流化风量和床压的瞬时偏差能够相互纠正,两侧床料处于动态平衡;当流化风量小于临界翻床风量时,将发生翻床现象;临界翻床风量随着静止床料高度的增加而减小;采用调整风门开度的方法解决翻床问题存在局限性,床料平衡的首要策略是使双支腿系统处于自平衡状态运行.     

Gas-solid flow characteristics in high-density CFB

The gas-solid flow characteristics in the riser of a high density CFB of square (0.27 m×0.27 m×10.4 m) or circu-lar (? 0.187m×10.4 m) cross section, using Geldart B particles (quartz sand), was investigated experimentally. The influence of riser structure on the hydrodynamic behaviors of a high-density circulating fluidized bed was investigated. The solid circulation rate was up to 321 kg/(m2s) with the circular cross-section under the operating conditions of the main bed air velocity 12.1 m/s and loosen wind and back-feed wind flow 25.1 m3/h. Different operating conditions on realizing high density circulation was analyzed, while both solids circulation rate and particle holdup depended highly on operating conditions. The circulating gas-solid flow was accompanied by an evidently-dense character in the riser’s bottom zone and became fully developed in the middle and upper zones.     

下行床内颗粒浓度的电容层析成像测量的研究

利用电容层析成像(electrical capacitance tomography,ECT),以非侵入的方式,对下行床内气固流动情况进行测量研究。针对下行床内固体颗粒浓度低的特点,采用了SIRT图像重建算法,得到了高质量的ECT图像。在颗粒流量和流化风量变化的情况下测量了不同截面固体颗粒体积份额平均值的变化,得到了下行床内气固流动规律。实现了快速的下行床内粉粒体的ECT在线可视化测量,具有较大的工程和学术价值。     

燃烧器布置方式对循环流化床炉内气固流动特性的影响

以采用混合燃烧的循环流化床(CFB)锅炉为研究对象,利用Simple算法对其炉内气固流动进行了三维数值模拟,得到了不同工况下炉内颗粒的速度和体积浓度分布.结果表明:双侧布置二次进料口的方式优于单侧布置方式;对冲布置方式下,燃烧器布置位置h/Z为0.145、二次风速为35 m/s时,炉内的气固混合比较强烈,流动状态较稳定,能够形成密相区之外的二次高浓度颗粒流,是较为合理的布置方式.     

大型循环流化床锅炉固体颗粒流动及分布的数值模拟

对引进的４１０ｔ／ｈＰｙｒｏｆｌｏｗ商用循环流化床锅炉燃烧系统固体的流动过程及其分布特性进行了数字模拟,建立的流动模型采用小室模型模拟气固两相沿轴向的流动,采用“核心－环”流动结构模拟气固两相在径向的不均匀性,模拟时考虑了给料,固体颗粒磨损以及床料的宽筛分等特性,为引进大型商用循环流化床锅炉技术的消化吸收进行了初步的基础研究,并为进一步分析研究该循环流化床锅炉的整体特性奠定了基础。     

平行流蒸发器内气液两相流分配均匀性实验研究

平行流蒸发器内气液两相(特别是液相)在各扁管间的分配对其传热性能影响较大,如果各扁管间的气液分配不均匀其传热性能将显著地下降.在不同气-液流量下实验研究了6种不同形式的平行流蒸发器的分支管液体流量分配情况,实验中观察到流型以环状流为主.研究发现,对于竖直向下流动和竖直向上流动,用通过增加管径的方法不能改善液体流量在各分支管的分配,而主管中气液入口的位置对于流量分配均匀性影响较大.     

循环流化床冷态流动特性的试验研究

研究了循环流化床气固两相流动在轴向的宏观流体动力特性,采用计算机数据采集系统测量不同工况下沿主床高度上的压力分布,进而计算出空隙率沿循环流化床主床高度方向上的分布情况,研究不同操作条件(流化风速、存料量)对空隙率分布、物料循环量和压力平衡的影响。     

Axial solids mixing in a circulating fluidized bed

A phenomenological model of axial solids mixing in a circulating fluidized bed is formulated. The model allows for main specific features of the process: ascending motion of particles in the core zone and their descending motion in the annular zone (inner circulation of solids); substantial changes of particle concentration, sizes of core and annular zones over the bed height; net circulation of solids and the effect of the bottom bed on the process. The validity of initial postulates is confirmed by comparison of calculated and experimental curves of mixing.     

A cold model experimental study on the flow characteristics of bed material in a fluidized bed bottom ash cooler in a CFB boiler

IntroductionA fluidized bed bottom ash cooler is often used totreat high temperature bottom ash to reclaim heat andfine particles from the ash, and to have the ash easilytransported. Among the large CFB boilers in operation inthe world, there are many ash coolers that often workabnormally['-','].There are six fluidized bed bottom ash coolers in theimported 410im CFB boiler that was built and operatedin Gaoba power plant, Sichuan province, China in 1996N].High temperature slag-bond and jam …     

动网格技术在罩式炉流场模拟中的应用

利用动网格技术和流体力学的基本原理,通过计算机模拟罩式炉内保护气体的流场分布,在炉内流场达到稳定状态下,比较循环风机不同转速时气体流量的变化。计算结果表明气体的流量与风机转速呈线性关系,风机进出口的气体的压力与风机转速呈二次方关系,与理论公式一致,说明该方法是可行的。进一步运用该方法对罩式炉流场进行数值模拟,得出在风机转速为1700r/min下罩式炉内不同区域流场分布,结果显示沿罩式炉高度方向无论在钢卷的芯部还是外侧,循环气体的流速沿高度方向衰减,外侧最大气流速度从7.12m/s衰减为2.32m/s,芯部最大气流速度从17.29m/s衰减为3.34m/s。     

300 MW循环流化床锅炉气固流动特性的CPFD模拟

采用计算颗粒流体力学（CPFD）的方法对300 MW循环流化床锅炉内的气固两相流体动力学参数进行全床数值模拟研究,重点分析了循环流化床锅炉炉膛以及回料阀的气固流动特性,获得固相颗粒浓度和速度场在炉膛内的分布以及固体循环流量、系统压力平衡、回料阀的运行情况等锅炉关键参数。结果表明：颗粒浓度的轴向分布呈现明显的密相区和稀相区两部分,模拟得到的轴向压力分布与实际工况吻合较好,验证了CPFD方法模拟循环流化床锅炉的准确性;锅炉回料阀内压降最大,这与床料分布相符;回料阀返料室流化程度较高,而输运室流化程度较小,呈现鼓泡床状态,气泡大都贴壁逃逸。     

循环流化床锅炉设计中若干问题探讨

循环流化床燃烧技术是一种新型、高效、清洁的燃烧技术,有许多其它燃烧装置无法比拟的优势。但在循环流化床锅炉设计方面还有一些问题亟待解决,文章就循环流化床锅炉设计方面的一些问题,如气固两相流体动力特性对其设计的影响;一、二次风比例,燃烧份额对其设计的影响;炉内传热系数对其设计的影响等方面作了一些阐述。     

有关循环流化床锅炉的几个问题探讨

本文就循环倍率、炉膛温度、炉膛高度等循环流化床 (CFB)锅炉中常遇见的问题进行了分析和探讨。目前CFB锅炉存在的主要问题之一是如何降低飞灰可燃物含量和提高锅炉燃烧效率 ,相应的研究飞灰可燃物的形成、燃烧特性等对CFB锅炉的设计有着现实的意义。     

循环流化床锅炉设计中若干问题探讨

循环流化床燃烧技术是一种新型、高效、清洁的燃烧技术,有许多其它热工设备无法比拟的优势。 但在循环流化床锅炉设计方面还有一些方面亟待解决,文中就循环流化床锅炉设计方面的一些问题,如 气固两相流体动力特性对其设计的影响;一、二次风比例,燃烧份额对其设计的影响;炉内传热系数对其 设计的影响等方面作了一些阐述。     

循环流化床锅炉物料浓度分布的影响因素分析

循环流化床(CFB)锅炉炉膛物料浓度分布直接影响炉膛内的传热特性和锅炉负荷。基于CFB锅炉炉膛内气固两相流动特性,建立了密相区以上区域的物料浓度数学计算模型。以1台1 060 t/h CFB锅炉为研究对象,数值计算分析不同煤种、给煤粒度分布、流化风速、分离器效率及床压降对炉膛物料浓度分布的影响,计算分析结果表明,CFB锅炉运行中,针对不同煤质,可以通过优化给煤粒度分布和床压降来调节炉膛上部的物料浓度分布,低挥发分煤种的给煤粒度分布中细颗粒的比例要大一些。分离器性能越好,床质量越好,在相同的流化风速和床压降下,炉膛出口处物料浓度随d50、d99的减小而增大。     

压力分布对选择性流化床冷渣器物料流动及物料量的影响

以410 t/hCFB锅炉为研究对象,在分析"选择性流化床冷渣器-炉膛"系统压力分布特性的基础上,研究了压力分布特性对该种冷渣器物料流动及物料量的影响规律.结果发现:"冷渣器-炉膛"系统的压力分布特性对冷渣器物料平衡有重要影响.在稳定运行时,选择室的床层压降都小于另外3室,即选择室的床料量(或炉渣量)会小于其它3室;由于排渣的作用,冷渣器排渣室的床料量略少于中间2个冷却室;随着炉膛或冷渣器流化风速的增大,冷渣器内的床料量都将降低;炉膛和选择性流化床冷渣器之间是一种复杂的串并联关系,这使炉膛与冷渣器各室之间的气固流动参数相互制约,底渣流动的可控性较差.     

循环流化床锅炉物料平衡分析

循环流化床物料平衡是循环流化床燃烧的核心和基础,它影响到循环流化床燃烧效率和脱硫效率,并决定燃烧室内的热负荷分布。循环流化床“一进二出”的物料平衡系统是循环流化床的核心概念,也是理解循环流化床物料平衡的关键。本文介绍并分析了循环床物料平衡的某些问题,如循环流化床定态设计、床料质量和物料平衡模型等。循环流化床运行需要高的“床料质量”和较大物料循环量,要求流化床锅炉分离器分离效率曲线存在一个清晰的100％分离粒径截止点。循环流化床内物料平衡除了受分离器效率影响外,还受到给煤成灰及磨耗特性、床内颗粒分层、排渣方式及效率等因素的影响。