新型超音速电弧喷涂锅炉水冷壁防护涂层

为获得火电厂锅炉运行工况下具有较高寿命的的水冷壁防护涂层,在已有涂层成分的基础上自行设计制作了一种新型防护涂层。采用超音速电弧喷涂的方式,在Q235钢基体上制备了自研FeCrNiBSi涂层和FeCrNi两种涂层。对两种涂层进行耐高温腐蚀性能试验,并通过光学显微镜、扫描电镜、X射线衍射仪等手段对涂层在熔盐环境下腐蚀前、后的表面形貌和腐蚀机理进行研究。结果表明,FeCrNiBSi涂层较之FeCrNi涂层具有更好的抗高温腐蚀性能和更高的表面硬度,硬度高使得涂层耐粉尘冲蚀性好,从而更适合于做火电厂锅炉水冷壁防护涂层。     

燃煤锅炉热力管道缺陷检测技术

作为燃煤电厂三大主机之一的锅炉,其稳定运行直接影响了整个燃煤电厂的安全性,而其中最易发生事故的锅炉热力管道的安全则是重中之重。介绍了水冷壁高温硫腐蚀、过热器再热器高温腐蚀、省煤器氧腐蚀这三种在锅炉热力管道中较为常见的缺陷的形成原理及危害,并重点介绍了可以用于检测这些缺陷的远场涡流检测技术、漏磁检测技术和电磁超声检测技术的原理、研究成果以及各自的优缺点。     

垃圾焚烧电厂过热器腐蚀影响因素及防护涂层研究进展

垃圾焚烧电厂过热器管道的高温腐蚀一直是制约电厂焚烧温度的关键问题,因此研究开发耐高温、耐腐蚀、长寿命的关键服役材料是保证垃圾焚烧炉正常有序运转及安全生产的关键。对近年来垃圾焚烧电厂腐蚀问题的研究现状进行了梳理,对近期垃圾焚烧电厂过热器腐蚀与防护的研究成果进行了综述。首先,从过热器腐蚀影响因素的角度,归纳了焚烧环境中存在氯、硫、温度、水蒸气等诸多因素影响下的腐蚀特点,对各个影响因素下的腐蚀机理进行了概述,氯作为影响腐蚀的关键因素,重点对氯导致腐蚀的活性氧化机理和电化学机理进行了阐述。其次,讨论了应用在过热器表面的涂层制备技术的发展,包括热喷涂、热扩散、堆焊、激光熔覆等,探讨了制备方法,以及应用技术的优缺点。分析了材料成分(Ni、Mo、Cr、Al、Si、Pt等元素)的添加与涂层耐腐蚀性能之间的关系。再次,从焚烧垃圾预处理的角度,进一步讨论前期可通过对垃圾脱水、添加共燃剂等方法,达到脱硫、脱氯的目的,以此降低烟气中硫、氯的含量,减小其对腐蚀的影响。最后,对垃圾焚烧电厂过热器管道材料和涂层的选择进行了总结和展望。     

燃煤火电厂锅炉“四管”的高温腐蚀

燃煤火电厂锅炉的高温腐蚀主要发生在受热面的“四 管”,即水冷壁管、过热器管、再热器管和省煤器管.腐蚀的主要类型是硫腐蚀、氯腐蚀、 水蒸汽腐蚀和钒腐蚀.本文综述了燃煤火电厂锅炉存在的典型高温腐蚀现象和机理,并简要 的介绍了一般防腐蚀措施.     

某电厂余热锅炉烟气侧低温段受热面的腐蚀积垢原因

某余热锅炉烟气侧低温段的腐蚀积垢现象严重影响了该锅炉的安全运行和传热效率。采用溶液分析、扫描电子显微镜、能谱分析、X-射线衍射等技术,研究分析了该余热锅炉模块6～8烟气侧受热面的固体附着物形貌和组成,分析了受热面腐蚀机理。结果显示:附着物均呈强酸性,主要含Fe、S、O三种元素,主要成分为铁的硫酸盐化合物以及铁的氧化物;根据烟气中SO_3含量和水蒸气分压,估算余热锅炉烟气的酸露点温度为150～176℃;模块6和模块8的背风侧表面存在硫酸盐类物质的堆积,显示出硫酸腐蚀特征,其他区域呈酸性湿烟气腐蚀特征,表面出现黄色片状的腐蚀产物。根据该余热锅炉运行现状提出了腐蚀控制建议。     

锅炉水冷壁高温腐蚀研究现状

本文针对锅炉运行过程中水冷壁的安全隐患之一的高温腐蚀问题进行了分析和探讨,认为靠近锅炉水冷壁的还原性气氛是造成高温腐蚀的重要原因之一。总结整理了改善锅炉水冷壁高温腐蚀的一般方法。     

硫铁矿制酸系统余热锅炉二级过热器管失效原因分析

分析了余热锅炉中二级过热器管(材质为12CrMoV)的失效原因,结果表明管子的腐蚀和超温可能与失效过程有关,但管子表面腐蚀是二级过热器管失效的主要原因。 利用X-射线衍射、金相、电子探针、红外、差热分析和化学分析等方法,研究了取自现场的腐蚀产物形貌、化学组份和结构。腐蚀产物主要是Fe_2O_3、Fe_2(SO_4)_3和铁的硫化物。因此腐蚀机制可能是Fe_2(SO_4)_3在高温下分解产生高分压的SO_3所引起的硫化和氧化。在分析结果的基础上,提出了解决这种问题的可能途径。     

火电厂的腐蚀故障

火电厂的腐蚀故障有：运行和停用中的氧腐蚀引起的省煤器管穿孔泄漏；由于酸、碱和氧作用造成水冷壁管腐蚀穿孔或脆爆；由于高温氧化引起的过热器管内外壁腐蚀和蠕胀破裂；水冷壁管结垢引发的腐蚀与超温变形；凝汽器管内外壁的各种类型腐蚀；汽轮机叶片的断裂及蒸汽初凝区的腐蚀；水冷机组空心导线腐蚀污塞及超温；发电机绕组结露引发的绝缘损坏和护环开裂。     

发电锅炉材料与防护涂层的磨蚀机制与研究展望

作为目前主要的电力供应设备和CO₂排放场所,随着“碳达峰-碳中和”目标的提出,燃煤发电锅炉逐渐向零碳/低碳排放的生物质发电锅炉和生物质-燃煤混烧发电锅炉方向发展。燃煤及生物质中含硫、含氯组分的腐蚀及磨损行为对锅炉安全长效运行构成严重威胁,因此,沉积防护涂层成为提高锅炉耐蚀耐磨性能的便捷高效手段。本文综述了目前燃煤锅炉、生物质锅炉及生物质-燃煤混烧锅炉基体材料和防护涂层在高温腐蚀及冲蚀磨损方面的研究成果,针对燃煤及生物质燃烧环境,总结了高温硫酸盐腐蚀及碱金属氯化物腐蚀机理,阐述了生物质-燃煤混烧环境中灰沉积-冲击机制,介绍了目前锅炉基体材料的应用现状,归纳了在腐蚀和磨损不同环境下合金涂层、陶瓷涂层、金属陶瓷涂层的设计原则、制备方法及应用现状。指出了当前锅炉防护研究亟待解决的问题,包括：热腐蚀机理研究不深入,缺乏准确的腐蚀-磨损预测模型,防护涂层种类较少。最后,提出采用材料基因组工程及机器学习方法来加速材料研发,开展腐蚀-磨损机理及多因素耦合模型的研究,同时强调粉末合成设计-涂层结构设计-服役性能评价一体化研究对新型防护涂层研发的重要性。     

锅炉热管常见早期失效形式分析

分析了水冷壁管、过热器管、再热器管、省煤器管、空气预热器管等锅炉热管的工作条件和主要失效形式。介绍了高温蠕变、短时过热、高温烟气腐蚀、飞灰磨损、低温腐蚀等热管失效形式的宏观形貌特征及失效机理。     

A thermodynamic approach on vapor-condensation of corrosive salts from flue gas on boiler tubes in waste incinerators

Thermodynamic equilibrium calculation was conducted to understand the effects of tube wall temperature, flue gas temperature, and waste chemistry on the type and amount of vapor-condensed “corrosive” salts from flue gas on superheater and waterwall tubes in waste incinerators. The amount of vapor-condensed compounds from flue gases at 650-950 °C on tube walls at 350-850 °C was calculated, upon combustion of 100 g waste with 1.6 stoichiometry (in terms of the air-fuel ratio). Flue gas temperature, rather than tube wall temperature, influenced the deposit chemistry of boiler tubes significantly. Chlorine, sulfur, sodium, potassium, and calcium contents in waste affected it as well.     

Corrosion experience with carbon steel in spray absorption FGD plant

Carbon steel is the traditional material for boiler flue gas ducts and stacks. The introduction of flue gas desulphurisation systems in existing power plant units requires major changes in the flue gas system from boilers to the flue stack. In the semidry spray absorption plant at Studstrupværk power plant carbon steel has been used. This concept was chosen to utilize part of the existing carbon steel ducting and avoid the use of expensive high alloyed materials and coating systems. During the first year of operation emission of fine flakes of rust from the ducting and the stack become a major problem. To overcome this, corrosion testings were performed in laboratory and in the plant. The corrosion problems were found to be related to an atmospheric corrosion with hygroscopic chloride containing deposits. The aim of the tests was to establish the critical humidity for corrosion of carbon steel in FGD plant products and deposits. The examinations cover products and deposits from different operational conditions and parts of the Studstrupværk power plant. The laboratory tests were followed by corrosion probe tests in the plant and full scale operation tests with the plant. The results of this programme showed that carbon steel can be used and corrosion can be kept at a very low level by controlling the humidity of the flue gas below 40% RH with fresh water as process water and down to 30% RH with salt water as process water. In practice this has to be controlled by the temperature difference between the flue gas and the adiabatic saturation temperature of the flue gas. Effective insulation of the ducting has been found to be of outmost importance as the humidity should be measured relative to the surface temperature. Experience from the plant shows that the most severe corrosion is found in cold spots.     

表面渗层和CrNiMo涂层材料的露点腐蚀*

基于我国电站锅炉排烟温度普遍偏高、烟气深度冷却利用过程中存在露点腐蚀的现状,文中以耐露点腐蚀材料316L钢作为对比材料,选取普通碳钢进行表面热喷涂和表面渗镍处理后在1000MW机组的锅炉上进行实炉露点腐蚀试验。结果表明:材料的腐蚀层厚度随壁面温度升高而减小;在40～60℃的金属壁面温度范围内,碳钢表面CrNiMo涂层和渗镍层因表面缺陷导致涂层严重腐蚀;在70～90℃的金属壁面温度范围内,腐蚀层厚度随温度变化趋于平稳,表面渗层材料具有和316L钢相当的耐露点腐蚀能力,碳钢表面喷涂CrNiMo耐腐蚀性能更为优越,3种材料均能满足火电厂烟气深度冷却利用的露点腐蚀性环境。     

Korrosion von ölgefeuerten Zentralheizungskesseln

Corrosion of oil-fired domestic boilers Depending on the surface temperature of the flue gas side the corrosion of oil fired domestic boilers proceeds either mainly by acid corrosion or by oxygen corrosion:

• – At surface temperatures of 60°C and higher the corrosion mechanism of acid corrosion prevails and the corrosion rates amount to 0.1–0.3 mm/year (values referred to continuous burner operation). The corrosion products consist of soluble iron(II)- and iron(III)sulfates. Higher corrosion rates can be attributed to an appreciable catalytic formation of sulfur trioxide on the corrosion products formed on the convective heating surfaces.
• – At surface temperatures of 40°C the mechanism of oxygen corrosion already dominates and the corrosion rates are about ten times higher (1.5–3 mm/year, referred to continous burner operation). The high portion of ioron oxide hydrates, especially goethit (α-FeOOH), makes the corrosion products difficult to remove.
• – Distinctly reduced service lives are also expected for the so called reduced temperature boilers (“Niedertemperaturkessel”) and low temperature boiers (“Tieftemperaturkessel”): According to the manufacturers these boilers may be operated at boiler water temperatures well below 60°C, as they are equipped with constructive measures to enhance the surface temperature on the flue gas side. However, these measures are only fully effective under stationary conditions.

Some of the results were obtained from weight loss measurements on test specimen made from St 35.8 and gray cast iron, that were exposed to the flue gases of an oil fired experimental boiler. Other important results come from field measurements of the sulfuric acid content of about 30 boilers that are in practical use.     

Der wartungsfreie Heißwasser-Boiler. Korreferat zu: Korrosionsschutz an Warmwasserboilern mit duroplastischen Kunststoffen

The maintenance-free hot water boiler. Corrosion protection of hot water boilers with duroplastics The corrosion damage caused by water is different from that caused by air. As there are always, in a hot water boiles boundary areas exposed to these media, the only materials suitable for boiler protection are those meeting the following requirements:

• The protection effect must be independent of the composition of the water.
• The composition of the water must not change in the boiler.
• The boilers concerned must not require maintenance.

But corrosion damage on hot water tanks is not conditioned by the composition of the water alone. There is also a possibility of contact corrosion if, e.g., copper pipes or copper beating elements are connected to galvanized boilers. A hot water boiler made of copper will therefore also suffer corrosion damage if material entrained from steel water piping becomes active. Even galvanization can only be applied at temperatures up to 60°C. Above this temperature iron becomes anodic and will corrode. Experience with boilers protected with the organic material known as Si 14 EG can be summed up as follows:

• 1 The duroplastic material known as Si 14 EG is proof against all types of drinking water approved by the public health authorities.
• 1 Some 15,000 boilers with such protection have now been in operation for five years without requiring maintenance, and without loss of protection effect.
• 1 As the hot water boilers thus protected also remain free from incrustations, the heat transfer, and thus the hot water output, remain constant.
• 1 The price of a hot water boiler made of carbon steel and protected with Si 14 EG is lower than that of a copper boiler of equal capacity.

The report concludes by listing the technical requirements for duroplastic coating: The areas to be protected must be accessible for working and inspection; edges must be chamfered; welds must be coherent and free from shrinking cavities and should be smoothed; pipe connections should welded flush with the boiler surface. The text is accompanied by photographs of duroplastically protected boilers.     

Which are the right test conditions for the simulation of high temperature alkali corrosion in biomass combustion?

The use of renewable energy sources for the generation of electricity has gained much interest in recent years. Biomass has the potential of being a CO₂ neutral energy source that could provide a significant proportion of the ever‐increasing energy demand. The easiest and most straightforward utilization of the energy content of biomass is direct combustion. The thermal energy of the biomass released in the combustion process is utilized by heating water or steam to produce electricity or heat or both (CHP). Whereas the heat production requires only modest temperatures in the water or steam circuit, producing electricity with high efficiency is not possible without high steam parameters (temperature and pressure). The heat market being quite saturated, the economic potential is in the electricity market. High heat transfer surface temperatures coupled with biomass fired steam generators have resulted, however, in serious corrosion of the heat transfer surfaces, especially in the hottest section of the convection superheaters. The type of corrosion found in biomass boilers is not encountered in fossil fuel fired boilers and the mechanism causing it is not fully understood. The development of new alloys that could withstand these harsh environments would benefit tremendously if the test conditions in the laboratory tests could be chosen so that they adequately resemble the corrosion environment in real boilers. Currently the high corrosion rate is believed to be caused by gaseous KCl that condense on the heat transfer surfaces. While KCl is certainly found in the corroded superheater tubes and probably has an important role in the corrosion reactions with the alloy, the formation of KCl on the cooled surface can also be heterogeneous. In this paper a discussion on the effect of alkali hydroxides, especially KOH, is presented. Biomass fuels have normally a high content of alkali metals and a low content of sulfur and chloride. The excess alkali will produce alkali hydroxides in the combustion environment. Alkali hydroxides then react with CO₂ in the flue gases to form carbonates as the flue gases are cooled. The reaction with CO₂, is however, very temperature dependent. The equilibrium being completely on the K₂CO₃ side with a gas temperature below 700 °C and completely on KOH side with a gas temperature above 900 °C. The hottest superheaters are normally located in the area where the flue gas temperature is 850°C–1000 °C. This makes KOH condensation on the tubes possible and subsequent heterogeneous reactions with HCl, SO₂ and CO₂ in molten phase forming KCl, K₂SO₂ or K₂CO₃. Although KOH is not thermodynamically stable at typical tube surface temperatures, a continuous flux condensing from the flue gases results in a corrosion environment on the tube where its activity has to be taken into account. Therefore it is suggested that KOH, either in gaseous or molten phase should be included in the laboratory test environments used for the testing of alloys for biomass combustion applications.     

某锅炉用水冷壁管腐蚀分析

燃煤锅炉水冷壁管发生腐蚀会影响锅炉的使用寿命,缩短其使用周期从而影响经济效益,甚至影响锅炉的安全使用。为分析其发生腐蚀的原因,利用能谱和X射线衍射等技术对20#钢锅炉水冷壁管的腐蚀特征进行分析,研究腐蚀机理及类型,并提出相关防护与控制措施。研究结果表明:燃料煤中的硫元素、氯元素以及硫酸盐是管道外壁腐蚀的主要因素,此外,管道外壁的高温氧化也会促进其发生腐蚀。1号试样的腐蚀速率为0.1925mm/a,2号试样的腐蚀速率为0.3150mm/a。     

Comparison of Different boiler tube materials and the corrosion resistance in burning of municipal waste

The aim of this paper is to investigate the corrosion risks in burning of pretreated municipal waste as additional fuel together with bark in a fluidized-bed boiler. It was deduced that the burning of bark alone did not cause corrosion in the materials tested. When the waste was burnt the corrosion of steels was insignificant when providing that the surface temperature of material was below 300°C. When the surface temperature was over this temperature, the burning of municipal waste caused corrosion in the conventional boiler steel. The stainless steels were not corroded even in these conditions. The impact of waste combustion on flue gas releases was also studied.