燃煤机组SCR催化剂表面积灰板结层多重分形分析
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摘要
燃煤电站烟气中的飞灰在SCR催化剂表面沉积板结形成强垢是导致催化剂失活的重要原因,为及时清理催化剂表面强垢层,通常采用超声共振结合蒸汽吹扫将强垢去除,然而由于燃煤飞灰在催化剂表面的沉积板结使得强垢层形成较为稳定,导致现场高能耗操作下清灰效果不明显。为更好地研究飞灰在催化剂表面沉积板结对强垢形成的影响,借助现场小修期和SCR改造项目热态性能试验将不锈钢采样盘布置在3层催化剂层的迎风面进行采样,将3层SCR催化剂垢层样品采用原子力显微镜(AFM)进行表征测试,通过设置合适的阈值采用Matlab图形处理得到黑白二值图,并通过信息熵法获得盒子尺寸来分析多重分形标度区间的影响。结果表明,随着烟气的流程方向板结层的高程分区逐渐趋于碎片化,沉积飞灰粒度逐渐趋于均匀化,并随烟气流程的增加多重分形参数具有标度不变性;同时关联分形维数D_2随着烟气流程的增加逐渐与Hausdorff分形维数D_0接近;根据加权矩随变特性还发现板结层微观颗粒会随烟气流程的增加逐渐由疏松不均性演变为致密均匀性;由3层板结层多重分形谱对称性发现,随着烟气流程的延长,催化剂表面垢层多重分形谱宽度Δα明显增加,相应垢层表面粗糙度逐渐增加,且垢层表面奇异峰分布更加明显,催化剂表面飞灰板结形成垢层的主导因素主要源于小颗粒、小高程的概率分布点。研究表明,随着烟气流程的增加,催化剂表面垢层的多重分形特征明显,沉积飞灰颗粒粒度变小,板结层的均匀性增加,微观拓扑表面的高程聚类特征消失,为超声波共振与蒸汽吹扫等现场清灰操作提供理论依据。
The fly ash in the flue gas of coal-fired power station deposits a strong scale on the surface of the SCR catalyst,which is an important reason of catalyst deactivation. The ultrasonic resonance combined with steam purging method is usually used to clean the strong scale layer on the catalyst surface in time,However,due to the deposition of coal-fired fly ash on the surface of the catalyst,the formation of the strong scale layer is relatively stable,which results in the effect of ash removal under high-energy operation in the field not obvious.To better study the influence of fly ash deposition and agglomeration on the surface of the catalyst on the formation of strong scale,the stainless steel sampling tray was placed on the windward side of the three-layer catalyst layer for sampling by means of the field minor repair period and the thermal performance test of the SCR retrofit project.The samples of the three-layer SCR catalyst scale were characterized by atomic force microscopy( AFM).The black and white binary images were obtained by Matlab pattern processing by setting appropriate threshold values,and the box size was obtained by information entropy method to analyze the influence of multi-fractal scale interval.The results show that as the elevation zone of the stratification layer of the flue gas gradually becomes fragmented,the granularity of the deposited fly ash gradually becomes uniform,and the multi-fractal parameters have scale invariance with the increase of the flue gas flow.Meanwhile,the associated fractal dimension D_2 gradually closes to the Hausdorff fractal dimension D_0 with the increase of the flue gas flow.According to the variation property of weighted moment,it is found that the microscopic particles of the slab layer gradually change from loose non-uniformity to density uniformity with the increase of the flue gas flow.According to the multi-fractal spectrum symmetry of the three-layer slab layer,it is found that with the extension of the flue gas flow,the multi-fractal spectrum width Δα of the catalyst scale layer increases obviously,the surface roughness of the corresponding scale layer increases gradually,and the distribution of singular peaks on the surface of the scale layer is more obvious.The dominant factors of scale layer formation by fly ash deposition on the surface of the catalyst is mainly due to the probability distribution point of small particles and small elevation.The research shows that with the increase of flue gas flow,the multi-fractal characteristics of the scale layer on the catalyst surface become obvious,the particle size of the deposited fly ash becomes smaller,and the uniformity of the harden layer increases,and the elevation clustering feature of the micro-topological surface disappears,which provide a theoretical basis for on-site ash removal operations such as ultrasonic resonance and steam purge.
The fly ash in the flue gas of coal-fired power station deposits a strong scale on the surface of the SCR catalyst,which is an important reason of catalyst deactivation. The ultrasonic resonance combined with steam purging method is usually used to clean the strong scale layer on the catalyst surface in time,However,due to the deposition of coal-fired fly ash on the surface of the catalyst,the formation of the strong scale layer is relatively stable,which results in the effect of ash removal under high-energy operation in the field not obvious.To better study the influence of fly ash deposition and agglomeration on the surface of the catalyst on the formation of strong scale,the stainless steel sampling tray was placed on the windward side of the three-layer catalyst layer for sampling by means of the field minor repair period and the thermal performance test of the SCR retrofit project.The samples of the three-layer SCR catalyst scale were characterized by atomic force microscopy( AFM).The black and white binary images were obtained by Matlab pattern processing by setting appropriate threshold values,and the box size was obtained by information entropy method to analyze the influence of multi-fractal scale interval.The results show that as the elevation zone of the stratification layer of the flue gas gradually becomes fragmented,the granularity of the deposited fly ash gradually becomes uniform,and the multi-fractal parameters have scale invariance with the increase of the flue gas flow.Meanwhile,the associated fractal dimension D_2 gradually closes to the Hausdorff fractal dimension D_0 with the increase of the flue gas flow.According to the variation property of weighted moment,it is found that the microscopic particles of the slab layer gradually change from loose non-uniformity to density uniformity with the increase of the flue gas flow.According to the multi-fractal spectrum symmetry of the three-layer slab layer,it is found that with the extension of the flue gas flow,the multi-fractal spectrum width Δα of the catalyst scale layer increases obviously,the surface roughness of the corresponding scale layer increases gradually,and the distribution of singular peaks on the surface of the scale layer is more obvious.The dominant factors of scale layer formation by fly ash deposition on the surface of the catalyst is mainly due to the probability distribution point of small particles and small elevation.The research shows that with the increase of flue gas flow,the multi-fractal characteristics of the scale layer on the catalyst surface become obvious,the particle size of the deposited fly ash becomes smaller,and the uniformity of the harden layer increases,and the elevation clustering feature of the micro-topological surface disappears,which provide a theoretical basis for on-site ash removal operations such as ultrasonic resonance and steam purge.
引文
[1]国家发展改革委,国家能源局.能源发展“十三五”规划[EB/OL].(2016-12-26)[2019-01-05].https://baike.baidu.com/item/“十三五”能源规划/14664288Δfr=aladdin.
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[3]ZHANG W,LU C,DONG P,et al.Influence of deposited carbonblack particles on pressure drop with ceramic ultra-filtration for treatment of coal-fired flue gas[J].Journal of Chemical Engineering of Japan,2018,51(7):566-575.
[4]ZHANG W,LU C,DONG P,et al.Fractal reconstruction of microscopic rough surface for soot layer during ceramic filtration based on weierstrass-mandelbrot function[J].Industrial&Engineering Chemistry Research,2018,57(11):4033-4044.
[5]ZHANG W,LI C T,WEI X X,et al.Effects of cake collapse caused by deposition of fractal aggregates on pressure drop during ceramic filtration[J].Environmental Science&Technology,2011,45(10):4415-4421.
[6]苗强.脱硝技术的现状及展望[J].洁净煤技术,2017,23(2):12-19.MIAO Qiang.Progress and prospects of denitration technology[J].Clean Coal Technology,2017,23(2):12-19.
[7]高得力,杨学昌,王鹏.TiO2薄膜表面形貌的多重分形分析[J].清华大学学报(自然科学版),2012,52(1):128-132.GAO Deli,YANG Xuechang,WANG Peng.Multifractal analysis of Ti O2thin film eurface topographies[J].Journal of Tsinghua University(Science and Technology),2012,52(1):128-132.
[8]KUMAR J,ANANTHAKRISHNA G.Modeling the complexity of acoustic emission during intermittent plastic deformation:Power laws and multifractal spectra[J].Physical Review E,2018,97(1):1-3.
[9]XU Shanhua,REN Songbo,WANG Youde.Three-dimensional surface parameters and multi-fractal spectrum of corroded steel[J].Plos One,2015,10(6):1-15.
[10]孙霞,傅竹西,吴自勤.薄膜生长的多重分形谱的计算[J].计算物理,2001,18(3):247-252.SUN Xia,FU Zhuxi,WU Ziqin.Multifractal calculation of thin film growth[J].Chinese Journal of Computational Physics,2001,18(3):247-252.
[11]孙霞,吴自勤,黄畇.分形原理及应用[M].合肥:中国科学技术大学出版社,2006.
[12]HALSEY T C,JENSEN M H,KADANOFF L P,et al.Fractal measures and their singularities:The characterization of strange sets[J].Physical Review A,1986,33(2):1141-1151.
[13]SATO S,SANO M,SAWADA Y.Practical methods of measuring the generalized dimension and the largest lyapunov exponent in high dimensional chaotic systems[J].Progress of Theoretical Physics,1987,77(1):1-5.
[14]赵玉新,常帅,张振兴.地磁异常场的多重分形谱分析及构图法[J].测绘学报,2014,43(5):529-536.ZHAO Yuxin,CHANG Shuai,ZHANG Zhenxing.Multifractal spectrum analysis and mapping method of geomagnetic anomaly field[J].Acta Geodaetica et Cartographica Sinica,2014,43(5):529-536.
[15]MEISEL L V,JOHNSON M,COTE P J.Box-counting multifractal analysis[J].Physical Review A,1992,45(10):6989-6996.
[16]COWIE P A,SORNETTE D,VANNESTE C.Multifractal scaling properties of a growing fault population[J].Geophysical Journal International,1995,122(2):457-469.
[17]张济忠.分形[M].2版.北京:清华大学出版社,2011.