Numerical simulation on co-combustion and alkali metal distribution in an opposed firing boiler mixed with sludge

doi:10.3969/j.issn.2097-0706.2024.08.007

Abstract

Abstract:

Taking a 660 MW opposed firing boiler as the study object，the combustion features and distribution of alkali metals in the furnace during co-combustion with dehydrated sludge are studied by numerical simulation，and the influence factors including the blending layer， excess air coefficient and different Cl content in sludge are analyzed. The co-combustion with dehydrated sludge will increase the alkali metal mass concentration on the furnace side wall. The study indicates that blending sludge on the middle and upper layer of the burner can reduce the emission rate of alkali metals and lower the wall temperature near OFA nozzles. Increasing excess air coefficient can improve the burnout rate of pulverized coal and reduce the alkali metal mass concentration on the side wall. And decline of the Cl content in sludge can effectively reduce the concentration of alkali metals in flue gas and conversion rate of alkali metal compounds to NaCl. Blending sludges on the middle and upper layers of a co-combustion burner can reduce the excess air coefficient and alleviate the fouling， slagging and alkali metal high temperature corrosion in the furnace.

Key words: power station boiler, opposed firing boiler, co-combustion with sludge, in-furnace combustion, alkali metal, numerical simulation

CLC Number:

TK227.1

TONG Jialin, ZHANG Yan, LIU Wensheng, MAO Jianbo, YE Xuemin. Numerical simulation on co-combustion and alkali metal distribution in an opposed firing boiler mixed with sludge[J]. Integrated Intelligent Energy, 2024, 46(8): 50-58.

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项目	烟煤	干化污泥
w（C_ar)/%	58.60	19.63
w（H_ar)/%	3.33	3.32
w（O_ar)/%	7.28	11.19
w（N_ar)/%	0.79	3.21
w（S_ar)/%	0.63	0.70
w（A_ar)/%	19.77	41.95
w（M_t)/%	9.61	20.00
w（V_daf)/%	22.82	87.05
Q_ar.net/(MJ·kg^-1)	22.44	7.28
Q_d.net/(MJ·kg^-1)	24.50	9.73
w（Na_daf)/%	—	0.55
w（Cl_daf)/%	—	高Cl，0.45/低Cl，0.15

组分	烟煤	干化污泥
x(H₂)	57.084	88.150
x(CO)	26.778	11.850
x(CH₄)	26.138	0

反应方程	A	b	E(Cal·mol^-1)
Na⁺ + HCl → NaCl + H⁺	1.30×10¹⁵	0	9 990.0
NaCl + H⁺ → Na⁺ + HCl	1.10×10¹⁶	-0.5	4 557.1
NaOH + HCl → NaCl + H₂O	1.70×10¹⁴	0	0
NaCl + H₂O → NaOH + HCl	4.14×10¹²	0.6	32 161.8
NaO^- + HCl → NaCl + OH^-	1.30×10¹⁴	0	0
NaO^- + H₂O → NaOH + OH^-	1.30×10¹⁴	0	0
NaOH + OH^- → NaO^- + H₂O	2.23×10¹⁵	-0.4	-544.4
NaOH + H⁺ → Na⁺ + H₂O	5.00×10¹³	0	0
Na⁺ + H₂O → NaOH + H⁺	1.45×10¹¹	1.1	37 594.8

网格数/万	炉膛出口氧量/%	炉膛出口烟温/K	出口NO_x质量浓度/(mg·m^-3)
220	4.70	1 387	177
302	4.61	1 353	169
395	4.58	1 357	165

工况	掺烧位置	过量空气系数	污泥种类
1	C层燃烧器	1.2	高Cl污泥
2	D层燃烧器	1.2	高Cl污泥
3	E层燃烧器	1.2	高Cl污泥
4	D层燃烧器	1.1	高Cl污泥
5	D层燃烧器	1.3	高Cl污泥
6	D层燃烧器	1.2	低Cl污泥