Materials and Design 32(2011)671-681 Contents lists available at ScienceDirect Materials and design ELSEVIER journalhomepagewww.elsevier.com/locate/matdes Corrosion evaluation of one dry desulfurization equipment-Circulating fluidized bed boiler Yi Gong, Zhen-Guo Yang Department of Materials Science, Fudan University, Shanghai 200433, PR China ARTICLE INFO A BSTRACT As a clean fuel combustion technology, circulating fluidized bed(CFB) possesses various advantage Received 12 May 2010 mong them, flexibility in fuels and superiority in desulfurization are the two prominent ones and can Available online 7 August 2010 hereby facilitate sufficient utilization of high-sulfur fuels. But unfortunately, these low-grade fuel always introduce harsh service environment within the Cfb boilers and consequently result in severe degradation extent on relevant equipments, especially the high-temperature sulfur corrosion. In this eywords Failure analysis ent, by nearly ten characterization methods, comprehensive investigation was carried out on a whole CFB boiler during downtime, and special emphasis was particularly laid on the failure components ncluding one perforated nozzle along with its fractured inlet tube for primary air, and one perforated manhole door of refeed valve. Finally, countermeasure and suggestion was put forward, which can pro- vide instructive significance in corrosion prevention for the CFB boilers, even other desulfurization equip- ments, running under similar aggressive conditions in engineering practice. e 2010 Elsevier Ltd. All rights reserved 1 Introduction especially popularized in China in order to sat er natural con- dition of high reserves of low-grade coals [4 Statistically, in the With the increasing demand for energy conservation and envi- year 2008 over three quarters of total installed capacity of China ronmental protection, higher utilization of fossil fuels and lower was fossil power, and among which 66%(379 million kw) was mission of air pollution are presently the two prior concerns to from those plants installed with desulfurization equipments [5- fossil power plants. As for the former one, popularization of new- Hence, normal and safe operation of these FBC and FGD equip- generation ultra-supercritical (USC) boilers is the most effective ments is of critical importance for China [6 and attractive approach, and our previous work carried out an Only in terms of the FBC, three variants have been evolved since integrity evaluation of the dissimilar steels welded joints that are its introduction in 1970s, including bubbling fluidized bed(BFB). often encountered in these USC boilers [1]. with respect to the lat- circulating fluidized bed( CFB)and a hybrid type between BFB and ter one(air pollution). the sulfur pollution, which commonly refers CFB[ 7. Among them, CFB is presently the most universal FBC tech- to the sulfur dioxide, is actually the most hazardous factor result ogy thanks to its relatively higher combustion efficiency than ing in acid rain. So as to relieve the extent of this kind of pollution, BFB. Also for China, she now owns the largest amount and thermal there currently exist two common ways of desulfurization, one is capacity of CFB boilers in the world as well [8. The unique feature of the fluidized bed combustion(FBC) technology and the other is a Cfb boiler compared with the conventional boilers is the added the flue gas desulfurization(FGD) process. FBC is virtually a type equipment called cyclone, which is used to refeed the incompletely f dry desulfurization and desulfurizes simultaneously with ombusted fuel particles and ashes back into the furnace for re-fir bustion under dry condition in furnace, while FGD is a sort of ing, i.e. the circulating function. As a result, fuels can be fully utilized wet desulfurization and needs specific exteriorized FGD equip- and the sulfur in them can be sufficiently eliminated before being ments for desulfurizing amid wet condition. In fact, compared with exhausted. In addition, configurations of CFB boilers usually vary the conventional fossil power plants, the most distinct advantage according to different companies'designs, and the two leading ones of FBC and FGD is their supreme flexibility in fuels, such as coal, are from Foster Wheeler (FW, USA Finland) and gEc-alstom oil, biomass, peat, petrol coke and so on, particularly for those (France)[4. However in fact, high desulfurization efficiency com- w-grade fuels with high sulfur content [2,3]. Consequently, these monly brings about harsh service environment for the CFB boilers two kinds of world-widely used desulfurization technologies are at the same time, especially for those fire high-sulfur fuels like the petrol coke, and will consequently result in degradations on rele- Corresponding author. Tel: +86 21 65642523: fax: +86 21 65103056. ant equipments [9-15. But actually, large amount of the past re- searches mainly focused on the heat transfer efficiency [16-19 0261-3069/s- see front matter o 2010 Elsevier Ltd. All rights reserved. doi:10.1016 mates.2010.08.003Corrosion evaluation of one dry desulfurization equipment – Circulating fluidized bed boiler Yi Gong, Zhen-Guo Yang * Department of Materials Science, Fudan University, Shanghai 200433, PR China article info Article history: Received 12 May 2010 Accepted 3 August 2010 Available online 7 August 2010 Keywords: Failure analysis Corrosion Fracture abstract As a clean fuel combustion technology, circulating fluidized bed (CFB) possesses various advantages. Among them, flexibility in fuels and superiority in desulfurization are the two prominent ones and can hereby facilitate sufficient utilization of high-sulfur fuels. But unfortunately, these low-grade fuels always introduce harsh service environment within the CFB boilers and consequently result in severe degradation extent on relevant equipments, especially the high-temperature sulfur corrosion. In this event, by nearly ten characterization methods, comprehensive investigation was carried out on a whole CFB boiler during downtime, and special emphasis was particularly laid on the failure components including one perforated nozzle along with its fractured inlet tube for primary air, and one perforated manhole door of refeed valve. Finally, countermeasure and suggestion was put forward, which can pro￾vide instructive significance in corrosion prevention for the CFB boilers, even other desulfurization equip￾ments, running under similar aggressive conditions in engineering practice. 2010 Elsevier Ltd. All rights reserved. 1. Introduction With the increasing demand for energy conservation and envi￾ronmental protection, higher utilization of fossil fuels and lower emission of air pollution are presently the two prior concerns to fossil power plants. As for the former one, popularization of new￾generation ultra-supercritical (USC) boilers is the most effective and attractive approach, and our previous work carried out an integrity evaluation of the dissimilar steels welded joints that are often encountered in these USC boilers [1]. With respect to the lat￾ter one (air pollution), the sulfur pollution, which commonly refers to the sulfur dioxide, is actually the most hazardous factor result￾ing in acid rain. So as to relieve the extent of this kind of pollution, there currently exist two common ways of desulfurization, one is the fluidized bed combustion (FBC) technology and the other is the flue gas desulfurization (FGD) process. FBC is virtually a type of dry desulfurization and desulfurizes simultaneously with com￾bustion under dry condition in furnace, while FGD is a sort of wet desulfurization and needs specific exteriorized FGD equip￾ments for desulfurizing amid wet condition. In fact, compared with the conventional fossil power plants, the most distinct advantage of FBC and FGD is their supreme flexibility in fuels, such as coal, oil, biomass, peat, petrol coke and so on, particularly for those low-grade fuels with high sulfur content [2,3]. Consequently, these two kinds of world-widely used desulfurization technologies are especially popularized in China in order to satisfy her natural con￾dition of high reserves of low-grade coals [4]. Statistically, in the year 2008 over three quarters of total installed capacity of China was fossil power, and among which 66% (379 million kW) was from those plants installed with desulfurization equipments [5]. Hence, normal and safe operation of these FBC and FGD equip￾ments is of critical importance for China [6]. Only in terms of the FBC, three variants have been evolved since its introduction in 1970s, including bubbling fluidized bed (BFB), circulating fluidized bed (CFB) and a hybrid type between BFB and CFB [7]. Among them, CFB is presently the most universal FBC tech￾nology thanks to its relatively higher combustion efficiency than BFB. Also for China, she now owns the largest amount and thermal capacity of CFB boilers in the world as well [8]. The unique feature of a CFB boiler compared with the conventional boilers is the added equipment called cyclone, which is used to refeed the incompletely combusted fuel particles and ashes back into the furnace for re-fir￾ing, i.e. the circulating function. As a result, fuels can be fully utilized and the sulfur in them can be sufficiently eliminated before being exhausted. In addition, configurations of CFB boilers usually vary according to different companies’ designs, and the two leading ones are from Foster Wheeler (FW, USA/Finland) and GEC-Alstom (France) [4]. However in fact, high desulfurization efficiency com￾monly brings about harsh service environment for the CFB boilers at the same time, especially for those fire high-sulfur fuels like the petrol coke, and will consequently result in degradations on rele￾vant equipments [9–15]. But actually, large amount of the past re￾searches mainly focused on the heat transfer efficiency [16–19], 0261-3069/$ - see front matter 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2010.08.003 * Corresponding author. Tel.: +86 21 65642523; fax: +86 21 65103056. E-mail address: zgyang@fudan.edu.cn (Z.-G. Yang). Materials and Design 32 (2011) 671–681 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes