雖然脫硫后煙氣中的二氧化硫含量大大降低，但濕法脫硫工藝對三氧化硫的除去效果并不高(僅有30%左右),特別是設(shè)置脫硝裝置后進(jìn)入煙囪的SO3含量還有增加。經(jīng)濕法脫硫后的煙氣濕度增加，溫度降低(通常為45~55℃),因而煙氣更容易在煙囪內(nèi)壁結(jié)露，造成煙氣中的三氧化硫溶解形成腐蝕性很強(qiáng)的稀硫酸(PH值為2~3左右).同時(shí)由于溫度的降低，煙氣自拔力減小，造成煙囪處于正壓運(yùn)行，從而增加了腐蝕性酸液對筒壁的滲透侵蝕。此外，煙氣中攜帶的HCl、HF、NO2等也會溶于冷凝液中，形成腐蝕介質(zhì)。國際工業(yè)煙囪協(xié)會(CICIND)在其發(fā)布的《鋼煙囪標(biāo)準(zhǔn)規(guī)程》(1999年)中對脫硫后的煙氣腐蝕性能作了如下的說明：1-煙氣冷凝物中氯化物或氟化物的存在將加劇腐蝕程度;2-煙氣中的氯離子遇水蒸氣形成氯酸，它的化合溫度約為60℃，低于氯酸露點(diǎn)溫度時(shí)，就會產(chǎn)生嚴(yán)重的腐蝕，即使是化合中很少量的氯化物也會造成嚴(yán)重腐蝕。脫硫后凈煙氣是滲透性強(qiáng)、低溫、高濕、混合稀酸型的強(qiáng)腐蝕性氣體。

VF復(fù)合材料(“Poly-Fluorine-Vinyl ester” Composite)是公司與華中科技大學(xué)國家重點(diǎn)燃燒實(shí)驗(yàn)室進(jìn)行合作，借鑒美國工程院院士、麻省理工學(xué)院納米專家的寶貴經(jīng)驗(yàn)與建議，與武漢理工大學(xué)復(fù)合材料實(shí)驗(yàn)室聯(lián)合研發(fā)的適應(yīng)國內(nèi)煙囪防腐的新型防腐材料，該材料克服了以前煙囪防腐工程中出現(xiàn)的問題，使得施工周期大大縮短，煙囪使用壽命保持與機(jī)組同步。VF復(fù)合材料防腐系統(tǒng)的原理是：采用高壓噴射工藝將基于含氟改性乙烯基酯樹脂的V F復(fù)合材料在煙囪內(nèi)壁上原位聚合制備，在基體形成底涂層+ VF復(fù)合結(jié)構(gòu)層+VF防腐耐磨面層的多層復(fù)合材料結(jié)構(gòu)，使煙囪內(nèi)壁完全處于防腐層的保護(hù)之下。

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Although the SO2 content of the flue gas is lowered a lot after desulfurization, the wet desulfurization process is not so effective in removing SO3(only 30 percent or so), especially after the installation of denitration device, the level of SO3 is even higher. The humidity is increasing and the temperature is dropping (usually 45 to 55 Celsius degrees) after wet desulfurization, which leads to easier condense of flue gas and dissolution of the SO3 in flue gas to form a kind of dilute sulphuric acid with strong corrosivity whose PH value is between 2 and 3. Meanwhile with the dropping of temperature, the ability of the flue gas to extricate itself will be worse, and the chimney works in a positive pressure environment, which contributes to stronger corrosion of the corrosive acid to inner side of the chimney. In addition, the HCI, HF, NO2 carried in the flue gas will also dissolve in the condensate, which will produce corrosive media. The Standard Code for Steel Chimney (1999 edition) issued by CICIND has explanations on the corrosivity of flue gas: 1st, the existence of chloride and fluoride in the condensate will exacerbate the corrosion. 2nd, meeting water vapor the chloridion will become chloric acid, whose temperature to combine is about 60 Celsius degrees, and if the temperature is below the dew-point temperature of chloric acid, strong corrosion will be produced, even if there is little chloride in the combination. The clean flue gas after desulfurization is a kind of gas with strong penetration and corrosivity, low temperature, high humidity and mixed dilute acids.

In reference of the cherished suggestions and experience of the NAE member and Nano expert of MIT(Abbreviation of “Massachusetts Institute of Technology”), through a combined research with the Laboratory for Composite of “Wuhan University of Technology”, we successfully developed the VF composite which is a kind of new anticorrosive material and meets the requirements of domestic chimney anticorrosion. The VF composite overcomes the defects of previous anticorrosion engineering, thus shortens construction period and lengthens chimneys' service time. The anticorrosive mechanism of VF composite system is in situ polymerizing the VF composite of fluorinated modified vinyl ester resin via high pressure jet, which produces a multilayer composite structure of primer coating, VF Composite layer and VF anticorrosive and grind-resisting layer. In that way the in-wall of the chimney will be totally under the protection of the anticorrosive layers.

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