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Modeling ash deposition and shedding during oxy-combustion of coal/rice husk blends at 70%inlet O_(2)

International Journal of Coal Science & Technology 2023年第2期10卷 196-209页

作者： Gautham Krishnamoorthy Department of Chemical Engineering UPSON Ⅱ Room 365241 Centennial DriveUniversity of North DakotaGrand ForksND 58202-7101USA

Co-firing rice husk(RH)and coal with carbon capture using oxy-combustion presents a net carbon negative energy produc-tion opportunity.In addition,the high fusion temperature of the non-sticky,silica rich,RH can mitigate ash deposition as well as promote shedding of deposits.To identify the optimum operating conditions,fuel particle sizes,and blend ratios that minimize ash deposition,a Computational Fluid Dynamic methodology with add-on ash deposition and shedding models were employed to predict outer ash deposition and shedding rates during co-combustion of coal/RH in AIR and O2/CO_(2)(70/30 vol%,OXY70)oxidizer compositions.After ensuring that the fly-ash particle size distributions and particle Stokes numbers near the deposition surface were accurately represented(to model impaction),appropriate models for coal ash and RH ash viscosities that were accurate in the temperature region(1200-1300 K)of interest in this study were identified.A particle viscosity and kinetic energy(PKE)based capture criterion was enforced to model the ash capture.An erosion/shed-ding criterion that takes the deposit melt fraction and the energy consumed during particle impact into account was also implemented.deposition rate predictions as well as the deposition rate enhancement(OXY70/AIR)were in good agreement with measured values.While the OXY70 scenario was associated with a significant reduction(60%-70%)in flue gas velocities,it also resulted in larger fly-ash particles.As a result,the PKE distributions of the erosive RH ash were similar in both scenarios and resulted in similar shedding rates.

关键词： CFD Oxy-Combustion ash deposition Shedding Co-firing

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Compositional and structural study of ash deposits spatially distributed in superheaters of a large biomass-fired CFB boiler

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Frontiers in Energy 2021年第2期15卷 449-459页

作者： Yishu XU Xiaowei LIU Jiuxin QI Tianpeng ZHANG Minghou XU Fangfang FEI Dingqing LI State Key Laboratory of Coal Combustion Huazhong University of Science and TechnologyWuhan 430074China School of Energy and Power Engineering Huazhong University of Science and TechnologyWuhan 430074China Guangdong Yudean Zhanjiang Biomass Power Plant Zhanjiang 524300China

Recognizing the nature and formation progress of the ash deposits is essential to resolve the deposition problem hindering the wide application of large-scale biomass-fired boilers.Therefore,the ash deposits in the superheaters of a 220 t/h biomass-fired CFB boiler were studied,including the platen(PS),the high-temperature(HTS),the upper and the lower low-temperature superheaters(LTS).The results showed that the deposits in the PSs and HTSs were thin(several millimeters)and compact,consisting of a yellow outer layer and snow-white inner layer near the tube surface.The deposits in the upper LTS appeared to be toughly sintered ceramic,while those in the lower LTS were composed of dispersive coarse ash particles with an unsintered surface.Detailed characterization of the cross-section and the initial layers in the deposits revealed that the dominating compositions in both the PSs and the HTSs were Cl and K(approximately 70%)in the form of KCl.Interestingly,the cross-section of the deposition in the upper LTS exhibited a unique lamellar structure with a major composition of Ca and S.The contents of Ca and Si increased from approximately 10%to approximately 60%in the deposits from the high temperature surfaces to the low temperature ones.It was concluded that the vaporized mineral matter such as KCl played the most important role in the deposition progress in the PS and the HTS.In addition,although the condensation of KCl in the LTSs also happened,the deposition of ash particles played a more important role.

关键词： ash deposition biomass combustion circulating fluidized bed initial layer structure analysis

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Effect of oil shale semi-coke on deposit mineralogy and morphology in the flue path of a CFB burning Zhundong lignite

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Frontiers in Energy 2021年第1期15卷 26-37页

作者： Zhuo LIU Jianbo LI Mingming ZHU Xiaofeng LU Zhezi ZHANG Dongke ZHANG Key Laboratory of Low-grade Energy Utilization Technologies and Systems of the Ministry of Education Chongqing UniversityChongqing 400044China Centre for Energy(M473) The University of Western Australia35 Stirling HighwayCrawley WA 6009Australia

The effect of oil shale semi-coke(SC)on the mineralogy and morphology of the ash deposited on probes situated in the flue path of a circulating fluidized bed(CFB)which burns Zhundong lignite(ZD)was investigated.10 wt%or 20 wt%SC was added to ZD,which were then combusted in the CFB furnace at 950℃.Two probes with vertical and horizontal orientations were installed in the flue duct to simulate ash deposition.Both windward and leeward ash deposits on probes(P_(1)W,P_(1)L,P_(2)W and P_(2)L)were analyzed by using a scanning electron microscopy with energy dispersive X-ray(SEM-EDX),X-ray diffraction(XRD),an inductively coupled plasma optical emission spectrometry ICP-OES,and a particle size analyzer.When ZD was burned alone,the P1W deposit was comprised of agglomerates(ash particles where Na_(2)SiO_(3)and Na_(2)SO_(4)were absent.As SC was added,the agglomerates in both P1W and P1L decreased.Moreover,SiO_(2)and Ca/Na aluminosilicates dominated the mineral phases whereas Na_(2)SiO_(3)and Na_(2)SO_(4)disappeared,showing a decrease in deposit stickiness.Likewise,the P2W deposit was found less spread on the probe,decreasing its deposition propensity.Na-bearing minerals turned into(Na,K)(Si_(3)Al)O_(8)and(Ca,Na)(Si,Al)4O8 in the P_(2)W deposit.Moreover,Na in the deposits decreased from 32 mg/g to less than 15 mg/g as SC presented.The addition of SC would therefore help alleviate the propensity of ash deposition in the flue path in the CFB combustion of ZD.

关键词： ash deposition circulating fluidized bed(CFB) mineral transformation oil shale semi-coke(SC) Zhundong lignite(ZD)

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In-situ sampling investigation of deposition and corrosion of convective heating surfaces in a grate type municipal solid waste incineration plant:a case study

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Waste Disposal and Sustainable Energy 2021年第4期3卷 299-308页

作者： Xiaobo Liu Qian Chen Ling Long Xiangfei Meng Guojun Lv Qunxing Huang Xuguang Jiang State Key Laboratory of Clean Energy Utilization Institute for Thermal Power EngineeringZhejiang UniversityHangzhouZhejiang 310027China Zhejiang University Qingshanhu Energy Research Center LinanHangzhouZhejiangChina

Metal corrosion and ash deposition are two common issues in municipal solid waste incineration(MSWI)plants.An in-situ sampling investigation was conducted in an MSWI plant in Jiangsu,China.The deposit samples were collected from 6 convective heating surfaces including the reheaters,superheaters,and economizer.The corrosion samples were obtained from a ruptured tube cut from the tertiary superheater.The element composition,crystal phases,and morphology of deposit and corrosion samples were characterized and analyzed.The results show that S contents of these deposits are 32-45 wt%,considerable Cl(10.63 wt%)was only detected in the deposits of the tertiary superheater.The composition of the deposits varies with the location because the flue gas temperature determines the thermodynamic trend of the sulfation reactions of different chlorides and the SO_(2)equilibrium partial pressure required in these reactions.Ca sulfates mainly exist in deposits at high temperatures(above approximately 500℃).Whereas alkali metal sulfates are the main component of deposits at low temperatures(below approximately 500℃).A multi-layer structure is exhibited on the cross-section of the corrosion samples.The discovery of Cl in the interface between the matrix and the oxide layer confirms that Cl can penetrate the outer oxide film.Besides,polysulfate components were observed inside the metal oxide layers,which indicates that a melt has occurred there.This study has provided a better understanding of ash deposition and corrosion phenomena in MSWI systems and more emphasis should be placed on the research of ash deposition and corrosion mechanisms.

关键词： Municipal solid waste ash deposition High temperature corrosion Sulfate Chloride

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Scavenging Effects of Kaolin on Fine ash Formation during Zhundong Coal Combustion

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Energy Engineering 2021年第3期118卷 459-471页

作者： Fangqi Liu Xianpeng Zeng Yimin Xia Zihao Wang Dunxi Yu State Key Laboratory of Coal Combustion School of Energy and Power EngineeringHuazhong University of Science and TechnologyWuhan430074China WISDRI Engineering&Research Incorporation Limited Wuhan430223China

The previous work found that the additive kaolin could scavenge not only sodium(Na)but also calcium(Ca)and magnesium(Mg),which is the important ash fluxing agents in low rank coal combustion.Such scavenging effects of kaolin on fine ash formation were studied in the present work.A typical Zhundong coal and its blends with kaolin at dosages of 1,2 and 4 wt%were combusted in an electrically heated drop tube furnace(DTF)at 1300℃.The fine ashes generated were collected and size segregated by a low pressure impactor(LPI).The morphology and chemical composition of fine ash were analyzed by scanning electron microscopy equipped with an energydispersive spectrometer(SEM-EDS).In addition,char/ash particles were sampled at various positions of DTF to elucidate how kaolin additive affected the fine ash formation process.The results further showed that apart from the scavenging of volatile Na,kaolin additive could also strongly scavenge the refractory Ca,Mg and Fe in the fine ash during Zhundong coal combustion,which transformed the sintered particles with irregular shape into melted spherical particles,and finally resulted in the considerable decrease of these elements in both PM_(0.4)and PM_(0.4-10)by melting and agglomeration.The close contacts between kaolin particles and coal resulted from physically mixing were a key factor responsible for the reaction of kaolin with the refractory Ca,Mg and Fe.

关键词： Zhundong coal kaolin fine ash basic elements sodium ash deposition

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