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氨法烟气脱硫是目前应用较广泛的湿法脱硫技术之一,被应用于煤化工、钢铁、火电和有色金属、造纸等行业[1-2]。尽管氨法烟气脱硫法所需吸收剂氨水的成本高[3-9],但因其副产物硫酸铵((NH4)2SO4) 价值较高,仍被广泛应用于农业和工业领域[10-12]。在该工艺中,因存在结晶率低、晶核形成差[3]现象,会导致氨法脱硫系统出现分离难、运行不稳定等问题,严重制约了技术应用。实现有效的(NH4)2SO4结晶调控过程以获得晶粒大、数量多、近似棱柱体的(NH4)2SO4晶体,对氨法烟气脱硫技术的应用具有现实意义。
影响氨法烟气脱硫中(NH4)2SO4结晶的因素包括操作条件和杂质引入等[13-18]。其中,烟气杂质,包括有机杂质(如油类、酚类)和无机杂质(飞灰、Al3+、Fe3+、Cl−)[19-26],是影响(NH4)2SO4结晶的重要因素。飞灰是燃烧后烟气的重要组成部分,对(NH4)2SO4结晶的影响至关重要。一些学者关注到飞灰固体质量浓度对氨法烟气脱硫中(NH4)2SO4结晶的影响。徐亚琳等[19]和LIU等[27]发现飞灰固体质量浓度存在一个最佳值,当飞灰固体质量浓度过小时,(NH4)2SO4晶体呈多边形块状,而当飞灰固体质量浓度过大时,(NH4)2SO4晶体呈球状。溶液中存在适量飞灰,可防止大量(NH4)2SO4晶核产生。在实际运行过程中,飞灰的性质(尺寸、组成等)受原料、燃烧工况的影响较大[20]。因此,研究飞灰固体质量浓度及性质对(NH4)2SO4结晶的影响机制具有重要意义。
本研究分别从微观和宏观尺度系统研究了飞灰固体质量浓度、飞灰粒径及飞灰含碳量对(NH4)2SO4结晶晶形及粒径分布的影响,通过平均粒径结合均匀性对(NH4)2SO4结晶进行定量比较,并分析飞灰对(NH4)2SO4结晶的影响机制,以期为氨法烟气脱硫中(NH4)2SO4结晶的有效调控提供参考。
飞灰对氨法烟气脱硫中硫酸铵结晶的影响机制
Effect mechanism of fly ash on crystallization of (NH4)2SO4 in flue gas desulfurization by ammonia process
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摘要: 燃烧后烟气中飞灰的存在,对氨法烟气脱硫中硫酸铵((NH4)2SO4)结晶的影响至关重要。系统研究了飞灰固体质量浓度、粒径及含碳量对(NH4)2SO4结晶晶形、粒径大小和均匀性的影响,并分析了其影响机制。结果表明,当(NH4)2SO4溶液中飞灰固体质量浓度为1 200 mg·L−1时,(NH4)2SO4晶体的晶形最规则,晶体的平均粒径最大(320 µm),均匀性最高(0.40);飞灰粒径的增大对 (NH4)2SO4晶体的晶形规则性、平均粒径和均匀性的提高均有一定作用,飞灰中不含碳或含有高于4 %的碳,均有利于(NH4)2SO4晶体的晶形规则性、平均粒径的提高,但均匀性会略有下降。飞灰对(NH4)2SO4结晶的影响机制为:飞灰晶核影响(NH4)2SO4晶核的形成和生长,进而影响(NH4)2SO4晶面生长,从而影响(NH4)2SO4晶体的尺寸和均匀性。本研究可为氨法烟气脱硫中(NH4)2SO4结晶的有效调控提供参考。Abstract: The fly ash in the flue gas is very important to the crystallization of (NH4)2SO4 in ammonia flue gas desulfurization. In this paper, the effects of content, particle size and carbon content of fly ash on the crystal shape and particle size distribution of (NH4)2SO4 were studied systematically, and the effect mechanism was analyzed. The results showed that when the content of fly ash in (NH4)2SO4 solution was 1 200 mg·L−1, the crystal shape of (NH4)2SO4 crystals was the most regular, the average particle size of (NH4)2SO4 crystals was the largest (320 µm), and the uniformity was the highest (0.40). The increase of particle size could improve crystal shape, particle size and uniformity of (NH4)2SO4 crystals. When the fly ash contained no carbon or more than 4% carbon content it was helpful for improving crystal shape and particle size of (NH4)2SO4 crystals and was disadvantageous for the uniformity of (NH4)2SO4 crystals. The influence mechanism was that the formation of fly ash nucleus affected the formation and growth of (NH4)2SO4 crystal nucleus, and then affected the growth of (NH4)2SO4 crystal plane, and thus affected the size and uniformity of (NH4)2SO4 crystal.
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Key words:
- ammonia flue gas desulfurization /
- (NH4)2SO4 /
- fly ash /
- effect mechanism
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表 1 煤样的工业分析和元素分析
Table 1. Industrial and elemental analysis of coal sample
样品 工业分析 元素分析 Mar Aar Var FCar Cd Hd O d * Nd Sd 煤样 0.65% 8.97% 12.39% 77.99% 53.7% 2.82% 29.86% 1.07% 2.93% 注:*表示O通过差减法计算得出;ar—收到基;d—干燥基;M—水分;A—灰分;V—挥发分;FC—固定碳。 -
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