Gaseous pollutants emissions from rotary kiln combustion of municipal sewage sludge

doi:10.11949/0438-1157.20230096

Abstract

Abstract:

The combustion experiments of municipal sludge were carried out on the rotary kiln test bench to study the effect of combustion temperature, particle size of sludge, and residence time in furnace and molar ratio of calcium to sulfur on the emission characteristics of gaseous pollutants during combustion. The results show that with the increase of incineration temperature, the emission concentration of SO₂ increases obviously, but the rising trend slows down with the increase of temperature. The emission concentration of NO also increased with the increase of temperature, but the effect was relatively small. With the increase of sludge particle size, the emission concentration of SO₂ decreased significantly, while the emission concentration of NO changed little. By reducing the furnace dip angle to prolong the residence time of sludge in the furnace, the emission of NO and SO₂ showed an increasing trend, while the concentration of CO emission decreased. However, when the furnace dip angle changed in the range of 1.5°—2.5°, the emission of gaseous pollutants did not change significantly. When the sludge was mixed with lime, the emission concentration of SO₂ decreased obviously, and gradually decreased with the increase of Ca/S molar ratio. When Ca/S exceeded 4, the effect of Ca/S molar ratio on emission reduction of SO₂ became smaller. The addition of quick lime also reduced the emission concentration of NO, but with the increase of Ca/S molar ratio, the emission concentration of NO rebounded.

Key words: sludge, rotary kiln, nitric oxide, sulfur dioxide, desulfuration

摘要：

在回转窑炉实验台上进行了市政污泥焚烧的系列实验，研究了焚烧温度、污泥粒径、炉内停留时间及钙硫摩尔比等因素对污泥焚烧过程中气态污染物排放特性的影响规律。结果表明：随着焚烧温度的升高，SO₂的排放浓度明显上升，但上升趋势随温度升高变缓；NO的排放浓度也随焚烧温度的升高而增加，但影响相对较小；随着污泥粒径的增加，SO₂的排放浓度有明显下降，而NO的排放浓度变化较小；通过减小炉体倾角延长污泥在炉内的停留时间后，NO及SO₂的排放总体均呈上升趋势，CO排放浓度则下降，但炉体倾角在1.5°~2.5°范围内变化时，各气态污染物的排放均无明显变化；污泥中掺混生石灰后，SO₂的排放浓度明显下降，且随Ca/S(摩尔比)的增大逐渐降低，Ca/S超过4之后对SO₂的减排影响变小；生石灰的加入也使NO的排放浓度降低，但随着Ca/S的提高，NO的排放浓度有所回升。

关键词: 污泥, 回转窑, 一氧化氮, 二氧化硫, 脱硫

CLC Number:

X 705

Yuhao CHEN, Xiaoping CHEN, Jiliang MA, Cai LIANG. Gaseous pollutants emissions from rotary kiln combustion of municipal sewage sludge[J]. CIESC Journal, 2023, 74(5): 2170-2178.

陈宇豪, 陈晓平, 马吉亮, 梁财. 市政污泥回转窑焚烧气态污染物排放特性研究[J]. 化工学报, 2023, 74(5): 2170-2178.

Figures/Tables 10

Fig.1 System diagram of rotary kiln test platform1—air compressor; 2—flowmeter; 3—valve; 4—stock bin; 5—worm feeder; 6—air inlet; 7—electrical heating; 8—slag discharge; 9—slag collection;10—insulation pipe; 11—filter cotton (dust removal); 12—anhydrous calcium chloride (desiccation); 13—flue gas analyzer; 14—bag-type dust remover;15—lye tank; 16—induced draft fan; 17—activated carbon; 18—digital display controller

Table 1 Results of industrial and elemental analysis of municipal sludge

试样	工业分析（空气干燥基）/%					元素分析（干燥基）/%
试样	M_t	A_d	V_d	FC_d		C	H	O	N	S
污泥	10.05	51.53	41.32	7.15		19.78	3.63	21.61	2.98	0.83

Table 2 Ash component of municipal sludge

成分	含量/%
SiO₂	41.78
Al₂O₃	23.56
Fe₂O₃	9.58
CaO	4.14
MgO	2.51
SO₃	1.65
TiO₂	0.75
K₂O	1.77
Na₂O	1.13
MnO₂	0.34
P₂O₅	9.12
总量	96.33

Table 3 Mass flow rate inside the material furnace under cold condition

炉体倾角/(°)	物料停留时间/min	质量流率/(g/s)
3.0	8.0	1.00
2.5	9.0	0.90
2.0	10.5	0.85
1.5	11.5	0.78
1.0	12.5	0.64

Fig.2 Effect of incineration temperature on emission concentration of NO and SO2

Fig.3 Effect of incineration temperature on emission concentration of CO

Fig.4 Effect of average particle size of sludge on NO and SO2 emission concentrations

Fig.5 Effect of residence time in furnace on NO and SO2 emission concentration

Fig.6 Effect of residence time in furnace on CO emission concentration

Fig.7 Effect of calcium-sulfur molar ratio on NO and SO2 emission concentration

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