Study on deposition and decomposition characteristics of ammonium bisulfate/ammonium sulfate as by-product of denitration in coal-fired flue gas

doi:10.11949/0438-1157.20200972

Abstract

Abstract:

A special multi-stage temperature control experimental bench for simulated air preheater was built, and the generation, deposition and decomposition of ammonium bisulfate (ABS) and ammonium sulfate (AS) under different SO₃ concentrations, SO₃/NH₃ ratio, and different temperature conditions were studied. At the initial deposition site under high temperature conditions, the deposits are all liquid ABS, and its weight loss characteristics are basically the same as pure ABS. However, under lower temperature ranges, the characteristics of the sediments will change with SO₃/NH₃. When SO₃/NH₃ is 2∶1, the sediments are the mixture of H₂O, H₂SO₄ and a small amount of ABS, which exists in the form of dense droplets, and it has multi-stage decomposition characteristics. When SO₃/NH₃ is 1∶1 and 1∶2, the sediments are the dry AS power with strong dispersion, and its decomposition characteristics are basically the same as pure AS. The results can provide guidance for ABS prevention and control.

Key words: denitration, SO₃, ammonium bisulfate, ammonium sulfate, air preheater

摘要：

搭建模拟空预器多段控温实验台，研究不同SO₃浓度、SO₃/NH₃比、不同温度下硫酸氢铵（ABS）与硫酸铵（AS）的生成、沉积与分解特性。在高温条件下发生的初始沉积部位，沉积物均为液态ABS，其失重特性与纯ABS基本一致。而在低温条件下，则根据SO₃/NH₃比的不同沉积物特性有所变化。SO₃/NH₃比为2∶1时，沉积物为H₂O、H₂SO₄与少量ABS的混合物，以密集液滴形态存在，呈多段分解特性；SO₃/NH₃比为1∶1与1∶2时，沉积物为分散性较强的干AS粉末，分解特性与纯AS基本一致。研究结果可为ABS防控提供指导。

关键词: 烟气脱硝, SO₃, 硫酸氢铵, 硫酸铵, 空气预热器

CLC Number:

X 511

QING Mengxia, ZHANG Xin, LIU Liang, ZHANG Wei, WANG Lele, SU Sheng, KONG Fanhai, XIANG Jun. Study on deposition and decomposition characteristics of ammonium bisulfate/ammonium sulfate as by-product of denitration in coal-fired flue gas[J]. CIESC Journal, 2021, 72(2): 1132-1141.

卿梦霞, 张鑫, 刘亮, 张巍, 王乐乐, 苏胜, 孔凡海, 向军. 燃煤烟气脱硝副产物硫酸氢铵/硫酸铵沉积与分解特性研究[J]. 化工学报, 2021, 72(2): 1132-1141.

Figures/Tables 12

Fig.1 ABS/AS generation and deposition experiment system

Fig.2 Temperature change of reaction system

Table 1 ABS generation experimental conditions

SO₃浓度/(μl/L)	NH₃浓度/(μl/L)	SO₃/NH₃摩尔比	温度设置/℃	时间/h	流量/(ml/min)
50, 100, 250, 500,1000, 2000, 4000	50, 100, 250, 500, 1000, 2000, 4000	2∶1, 1∶1, 1∶2	410-270-130	12	500

Fig.3 The influence of SO3 concentration on the generation rate of ABS/AS

Fig.4 The influence of SO3/NH3 concentration on the initial deposition temperature of ABS/AS (a); relationship between initial deposition temperature and ABS acid dew point (b)

Fig.5 The apparent physical properties of ABS/AS after deposition under high temperature conditions

Fig.6 The surface morphology of sediments at room temperature (a)； FT-IR spectra of sediments in different temperature range (b)

Fig.7 The decomposition characteristics of sediments at different temperature ranges when SO3 concentration is 4000 and 500 μl/L under SO3/NH3 ratio is 2∶1 condition

Fig.8 The decomposition characteristics of sediments at different temperature ranges and SO3 concentrations under the conditions of SO3/NH3 ratio at 2∶1

Fig.9 The decomposition characteristics of sediments at different temperature ranges when SO3 concentration is 4000 and 500 μl/L under SO3/NH3 ratio is 1∶1 condition

Fig.10 The decomposition characteristics of sediments at different temperature ranges and SO3 concentrations under the conditions of SO3/NH3 ratio at 1∶1

Table 2 The formation and deposition characteristics of ABS/AS under different SO3 concentrations in a variable temperature range

SO₃/NH₃		390~300℃	300~296℃	296~223℃	223~185℃	185~131℃
1∶1;1∶2	>100 μl/L	大片液体; ABS	大液珠/小液滴; ABS	小液滴/白雾；ABS	白雾；AS	白雾；AS
1∶1;1∶2	< 100 μl/L	—	—	小液滴/白雾；ABS	小液滴→白雾；ABS→AS	白雾；AS
2∶1	>100 μl/L	大片液体; ABS	大液珠/小液滴; ABS	小液滴/白雾；ABS	小液滴; H₂O/H₂SO₄/ABS混合物	小液滴; H₂O/H₂SO₄/ABS混合物
2∶1	< 100 μl/L	—	—	小液滴/白雾；ABS	白雾→小液滴，ABS→H₂O/H₂SO₄/ABS混合物	小液滴; H₂O/H₂SO₄/ABS混合物

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