摘要
污泥在燃烧过程中Pb污染排放问题一直受到人们广泛关注。通过试验研究和模拟计算相结合的方法,借助电感耦合等离子质谱仪(ICP-MS)、比表面及孔隙度分析仪(BET)和X射线衍射(XRD)等试验测试方法分析了污泥燃烧过程中Pb的迁移转化特性,探讨了添加CaO、水分和酸性气体等因素对Pb挥发和固相富集的影响,结合密度泛函理论揭示了PbCl_(2)分子在不同表面吸附的活性强弱。试验结果表明,污泥在900℃燃烧后,Pb残留率增加到61.37%,主要是受熔融作用的影响。在燃烧温度为700~900℃时,添加4%CaO后不利于Pb在固相产物中的富集,而在1000℃高温下,添加4%CaO后Pb在固相产物中的残留率提高了7.82%。当污泥含水率为20%时,Pb残留率与燃烧干污泥相比减少了28.43%;酸性气体的存在有利于Pb的固定,但其促进作用随体积分数的变化不一致。CO_(2)对Pb的固定有明显的促进作用,体积分数越大越有利于Pb的富集,当模拟烟气中通入30%CO_(2)后,Pb的残留率提高了23.37%;而SO_(2)对Pb的固定有微弱的促进作用,且随着SO_(2)体积分数的增大,Pb的残留率先增大后减小,在通有0.15%SO_(2)的燃烧工况中,Pb残留率增大程度最佳,仅为4.82%。负载4%CaO的污泥分别在20%H_(2)O/20O_(2)/80N_(2)、20CO_(2)/20O_(2)/60N_(2)和0.15CO_(2)/20O_(2)/79.85N_(2)的工况下燃烧后Pb的残留率分别增大了−3.61%、8.77%和7.65%。模拟计算表明,PbCl_(2)分子在洁净CaO(001)表面吸附后,Pb原子和O_(surf)原子发生轨道杂化作用,而在预吸附有CO_(2)、SO_(2)和H_(2)O的CaO(001)表面上,PbCl_(2)分子的Pb原子会和O_(H)、O_(C)和O_(S)原子发生轨道杂化,这使得在预吸附有CO_(2)、SO_(2)和H_(2)O的CaO(001)表面上PbCl_(2)分子的吸附能较洁净表面相比分别增大了90.069、−13.458和−55.836 kJ/mol。综上所述,控制燃烧温度和添加适量的CaO可以有效提高Pb的残留率,水分存在会抑制Pb的固定,而CO_(2)和SO_(2)气氛有利于Pb在固相产物中的富集。
The problem of Pb pollution emission from sludge during its combustion has received a widespread attention.The migration and transformation characteristics of Pb during sludge combustion were analyzed by a combination of experimental studies and simulations with the help of inductively coupled plasma mass spectrometry(ICP-MS),specific surface and porosity analyzer(BET),and X-ray diffraction(XRD),etc.The influences of factors such as the addition of CaO,moisture,and acidic gases on the volatilization of Pb and the solid-phase enrichment were investigated,and the activity strength of the adsorption of PbCl_(2)molecules on different surfaces were revealed with the combination of the densityfunctional theory.The experimental results showed that the increase of Pb residue to 61.37%after sludge combustion at 900℃was mainly influenced by the melting effect.The addition of 4%CaO was unfavorable to the enrichment of Pb in the solid-phase product at combustion temperatures of 700−900℃,while the residual rate of Pb in the solid-phase product increased by 7.82%at 1000℃with the addition of 4%CaO.The Pb residual rate was reduced by 28.43%at 20%sludge moisture content compared to burnt dry sludge.The presence of acidic gases favored Pb immobilization,but the promotion varied inconsistently with concentration.CO_(2)had an obvious promotion effect on the fixation of Pb,and the larger the concentration,the more favorable to the enrichment of Pb,when the simulated flue gas was fed with 30%CO_(2),the residual rate of Pb increased by 23.37%.While SO_(2)had a weak promoting effect on Pb immobilization,and with the increase of SO_(2)concentration,the residual rate of Pb was firstly increased and then decreased,and in the combustion condition with 0.15%SO_(2),the residual rate of Pb was increased to the best extent,which was only 4.82%.The residual rate of Pb after the combustion of sludge loaded with 4%CaO at 20%H_(2)O/20O_(2)/80N_(2),20CO_(2)/20O_(2)/60N_(2)and 0.15CO_(2)/20O_(2)/79.85N_(2)increased by−3.61%,8.77%and 7.65%,respectively.Simulations showed that after the adsorption of PbCl_(2)molecules on the clean CaO(001)surface,the Pb atoms of Pb molecules underwent orbital hybridization with O_(surf)atoms,whereas on the surface of CaO(001)with pre-adsorbed CO_(2),SO_(2)and H_(2)O,the Pb atoms of PbCl_(2)molecules would undergo orbital hybridization with OH,OC,and OS atoms,which led to an increase of adsorption energies of PbCl_(2)molecules after adsorption on the surface of CaO(001)with pre-adsorbed CO_(2),SO_(2),and H_(2)O on the surface of CaO(001)with preadsorbed CO_(2),SO_(2)and OS atoms,which resulted in the increase of adsorption energy after adsorption by 90.069,−13.458 and−55.836 kJ/mol,respectively,compared with that on the clean surface.In summary,controlling the combustion temperature and adding an appropriate amount of CaO can effectively improve the residual rate of Pb,the presence of moisture inhibits the immobilization of Pb,and the CO_(2)and SO_(2)atmospheres are favorable for the enrichment of Pb in the solid-phase products.
作者
史一林
王彦霖
乔晓磊
贾里
李艳红
张欢
金燕
SHI Yilin;WANG Yanlin;QIAO Xiaolei;JIA Li;LI Yanhong;ZHANG Huan;JIN Yan(College of Electrical and Power Engineering,Taiyuan University of Technology,Taiyuan 030024,China;School of Electric Power,Civil Engineering and Architecture,Taiyuan 030013,China)
出处
《煤炭学报》
EI
CAS
CSCD
北大核心
2024年第9期3993-4005,共13页
Journal of China Coal Society
基金
国家自然科学基金资助项目(U1910214)。
