洁净煤技术

2019, v.25;No.124(06) 43-50

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CFB锅炉低氮燃烧对炉内固硫影响研究进展
Research progress on the effect of low-NO_x combustion on furnace sulfur fixation in the CFB boiler

郝艳红;孟江涛;王菁;杨凤玲;程芳琴;
HAO Yanhong;MENG Jiangtao;WANG Jing;YANG Fengling;CHENG Fangqin;Shanxi Collaborative Innovation Center of High Value-added Utilization of Coal-related Wastes,State Environmental Protection Key Laboratory of Efficient Utilization Technology of Coal Waste Resources,Shanxi University;

摘要(Abstract):

随着火电厂烟气污染物排放标准的日益严格,循环流化床(CFB)锅炉多采用低氮燃烧技术在燃烧阶段降低NO_x的生成,但低氮燃烧应用会使炉内局部气氛,尤其是密相区的氧含量降低1%~4%,CO等还原性气氛增加1%~2%。固硫反应在不同氧浓度及还原性气氛条件下会表现出不同的反应路径,从而影响整个固硫反应速率和不同固硫产物的生成,导致最终固硫率的不同。因此CFB锅炉中引入低氮燃烧条件后会对炉内钙基固硫过程产生一定的影响。为了明晰低氮燃烧条件对CFB炉内钙基固硫反应的影响,保证燃烧中同时降低SO_2和NO_x的排放浓度,实现CFB锅炉中低氮燃烧技术与钙基固硫技术的耦合,综述了低氮燃烧反应条件对CFB锅炉炉内钙基固硫过程影响的研究现状,分别阐述了整个固硫过程中低氮还原性气氛及氧化-还原交变气氛条件对固硫剂煅烧、固硫剂固硫及固硫产物的分解转化3个不同反应阶段的影响。结果表明:CO_2浓度变化对CaCO_3煅烧影响较大且研究较多,气氛中CO_2的分压会直接减弱煅烧反应进行的程度;O_2和CO浓度变化对CaCO_3煅烧的影响未见报告,但从理论上推断影响较小,仍需进一步试验证明。在低氮燃烧形成的氧化-还原交变气氛下,炉内固硫反应过程变得复杂。氧气消失后,固硫率会降低20%左右,随着还原性气氛中CO含量的增加,固硫率还会进一步降低;随着CO等还原性气氛的增强,固硫产物CaSO_4稳定性降低,分解温度降低,CaS稳定性增强。但氧化、还原交变气氛下固硫产物的转化机制研究表明,当形成以CaS为内核,CaSO_4为外壳的固硫产物时,钙利用率和固硫效率会有所提高。可见,低氮燃烧气氛对硫化反应的影响具有不确定性。由于硫化反应的复杂性和固硫产物的不稳定性,目前尚无明确的针对不同固硫剂与反应温度和反应气氛的最佳匹配结果。因此,提出需进一步探究石灰石、电石渣等钙基固硫剂在不同氧浓度气氛及不同程度还原性气氛条件下的固硫反应机制,明确低氮燃烧条件对钙基固硫过程的影响,最终获得CFB锅炉低氮燃烧与炉内钙基固硫两者有机结合的优化反应条件,为实际生产提供可靠的理论依据。
With the constantimproving requisition of flue gas pollutants emission in thermal power plants, the low-nitrogen( low-NO_x) combustion technology is used in circulating fluidized bed(CFB) boilers to reduce the generation of NOx during the combustion phase. However,withthe use of the low-NOx combustion technology,the oxygen content in the local atmosphere especially in the dense phase zone decreases by 1% to 4%,and the reducing atmosphere such as CO increases by 1% to 2%. Desulfurizationreaction can show different reaction paths under different oxygen concentrations and reducing atmosphere conditions,which will affect the rate of overall sulfurfixing rate and the generation of different sulfur-fixing products,leading to the difference of the final sulfur fixation rate. Therefore,the low nitrogen combustion condition in the furnace definitively willimpact the process of calcium basedsulfur fixation.In order to clarify the influence of the low-NOxcondition on the calcium-based sulfur fixation in furnace and decrease the SO_2 and NOx emission at the same time,thus realize the coupling of low-NOxcombustion technology and calcium-based sulfur-fixing technology in CFB boiler,The influence of low nitrogen combustion reaction conditions on the calcium based sulfur fixation process in CFB boiler was reviewed in this paper.. The effects of reducing atmosphere and oxidation-reduction alternating atmosphere conditions on the calcination of sulfur-fixing agent,desulfurization and the decomposition and transformation of sulfur-fixing products were described respectively. The results show that thechange of CO_2 concentration has anadverse effect on the calcination of CaCO_3. The partial pressure of CO_2 in the atmosphere will directly weaken the degree of calcination reaction. However,there are no reports about the influence of the O_2 and CO concentration change on the CaCO_3 calcination.Theoretically,it could be inferred that it scarcely has effect on the calcination,but it needs further experimental proof. The current researchresults show that the process of sulfur fixation in the furnace is complicated under the oxidation-reduction alternating atmosphere.As the oxygen disappearing,the sulfur fixation rate decreases by about 20%. With the increase of CO concentration in the reducing atmosphere,the sulfur fixation rate further decreases.With the enhancement of reducing atmospheres such as CO content,the stability and decomposition temperature of the sulfur-fixing product CaSO_4 decreases,while the stability of CaS increases. When the atmosphere and temperature conditions are reasonably controlled to form sulfur-fixing products with CaS as the core and CaSO_4 as the shell,the calcium utilization rate and sulfur-fixing efficiency can be improved. In conclusion,the influence of the low-NOx condition on the desulfurization process is not deterministic. Meanwhile,due to the complexity of sulfurization reaction and the instability of sulfur fixing products,so far,there is no optimum operation condition suggestion about the best matching of different sulfur fixation agents with reaction temperature and reaction atmosphere. Therefore,it is necessary to further explore the sulfur fixation reaction mechanism of calcium based sulfur fixation agents such as limestone and carbide slag in different oxygen concentration atmosphere and reducing atmosphere to clarify the influence of low nitrogen combustion conditions on calcium based sulfur fixation process,and finally the ideal operating suggestion for the combination of low-NOx combustion and calcium-based sulfur fixation in furnace is obtained,which would provide a reliable theoretical basis for actual production.

关键词(KeyWords): CFB锅炉;低氮燃烧;还原性气氛;炉内钙基固硫;固硫产物转化
CFB boiler;low-NOx combustion;reducingatmosphere;calcium-based sulfur fixation in furnace;sulfur-fixing products transformation

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基金项目(Foundation): NSFC-山西省联合基金重点资助项目(U1610254);; 山西省重点研发计划重点资助项目(201703D111018);; 襄垣县固废综合利用科技攻关资助项目(2018XYSDCY-02)

作者(Author): 郝艳红;孟江涛;王菁;杨凤玲;程芳琴;
HAO Yanhong;MENG Jiangtao;WANG Jing;YANG Fengling;CHENG Fangqin;Shanxi Collaborative Innovation Center of High Value-added Utilization of Coal-related Wastes,State Environmental Protection Key Laboratory of Efficient Utilization Technology of Coal Waste Resources,Shanxi University;

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