| Oily sludge is solid waste produced in the process of oil extraction,transportation,refining,and oily sewage treatment.According to relevant statistics,China’s oil industry produces millions of tons of oily sludge every year,and the total storage has exceeded 500 million tons.Oily sludge carries a variety of highly toxic pollutants such as polycyclic aromatic hydrocarbons,dioxins,heavy metal elements,etc.which has been listed in the national hazardous wastes catalogue（No.HW08）.The harmless disposal of oily sludge is the core problem to be solved urgently in the petroleum industry and environmental protection.At present,co-processing of oily sludge in cement kiln is one of the most promising and advanced safety technology.Moreover,the regulation of pollutant transformation and clinker mineral formation presents as key and difficulty of the high effective and clean energy conversion in cement kiln co-processing of oily sludge.In this study,based on the assumption of modification,process regulation,target induction and synergistic coupling,the high value modifying of oily sludge,synergistic coupling enhanced co-combustion of oil sludge and coal,the regulation of clinker mineral phase formation,and the non-toxic target induction and blocking mechanism of pollutants migration in the whole process of cement kiln co-processing of oily sludge were investigated.The main research results and innovations are as follows:（1）The physicochemical properties of oily sludge sample were clarified and mastered.Oily sludge was mainly composed of crude oil,water and solids,with contents of 9.76%,36.38%and 53.86%respectively.The contents of chemical composition of Si O2,Al2O3,Fe2O3 and Ca O in the drying basis of oily sludge were44.07%,16.58%,5.78%and 1.11%respectively.It also contained many heavy metal elements such as As,Cd,Cr,Ni and Mn.Besides,the ash content of oily sludge exceeded 80%,and the low calorific value was only 5.32MJ/kg,indicating that the fuel quality was poor.Moreover,the combustion process of oily sludge can be divided into water evaporation,light hydrocarbon volatilization,heavy hydrocarbon cracking and combustion,in which the weight loss rate of light hydrocarbon volatilization was the fastest.The results provided basic data for the cement kiln co-processing of oily sludge.（2）The high value modifying method as well as combustion enhancing method of oily sludge were defined,and the combustion characteristics of modified oily sludge were comprehensively evaluated.The modified oily sludge OS5-R5、OS7-T3、OS7-（R5-T5）3 prepared by blending oily sludge with 50%rice straw or 30%waste tire or 30%the compound that rice straw to waste tire at the ratio of 5:5 were of adequate quality.The low calorific value of OS5-R5、OS7-T3、OS7-（R5-T5）3 were more than11MJ/kg,and the comprehensive combustion index increased by 13.39,3.27 and 4.99times respectively compared with the original oily sludge.With the increase of heating rate and oxygen concentration,the combustion intensity of modified oily sludge increased.With the increase of heating rate from 5℃/min to 20℃/min,the comprehensive combustion indexes of OS5-R5、OS7-T3、OS7-（R5-T5）3 increased by12.52,12.08 and 13.28 times respectively.With the increase of oxygen concentration from10%to 100%,the comprehensive combustion indexes of OS5-R5、OS7-T3、OS7-（R5-T5）3 increased by 1.54,1.45 and 1.25 times respectively.（3）The characteristics of co-combustion of modified oily sludge and coal and their synergistic enhanced combustion effect were explored.As modified oily sludge OS5-R5、OS7-T3、OS7-（R5-T5）3 partially replace coal,the quality of mixed fuel became worse gradually.The suitable mixing ratio of OS5-R5,OS7-T3 and OS7-（R5-T5）3was 30%,so the low calorific value of mixed fuel C7-（OS5-R5）3,C7-（OS7-T3）3,C7-（OS7-（R5-T5）3）3 was about 20MJ/kg,which is about 16%lower than that of coal,but the comprehensive combustion index had no significant decrease.In the co-combustion process of modified oily sludge and coal,there was an obvious synergistic enhanced co-combustion effect at 420℃-750℃.In addition,with the increase of heating rate from 5℃/min to 20℃/min,the comprehensive combustion indexes of C7-（OS5-R5）3、C7-（OS7-T3）3、C7-（OS7-（R5-T5）3）3 increased by 5.07,4.19 and 4.77 times respectively.With the increase of oxygen concentration from 10%to 100%,the comprehensive combustion indexes of C7-（OS5-R5）3、C7-（OS7-T3）3、C7-（OS7-（R5-T5）3）3 increased by 3.09,2.97 and2.68 times respectively.（4）The characteristics of pollutant gases emission during the separate and mixed combustion of modified oily sludge and coal were revealed,and the control effect of combustion atmosphere and additives on pollutant gases emission was clarified.The pollutant gases in the separate and mixed combustion of modified oily sludge and coal mainly included NO,NO2,H2S and SO2.The emission concentration of NO was much higher than that of NO2,which was the main emission form of nitrogen pollutant gases.The emission concentration of H2S was lower than that of SO2,and H2S was easy to be further burned and converted into SO2.With the increase of oxygen concentration in the combustion atmosphere,the emission concentration of pollutant gases gradually increased.The reducing atmosphere was conducive to the reduction of NOx,so as to reduce NO and NO2 emission.Additives could control the emission of pollutant gases.The adsorption of polar molecules by montmorillonite was conducive to reducing the emission of pollutant gases.Ba O and Ca O could react with H2S and SO2 to form sulfate,so as to reduce the emission of them.（5）The influence of addition of modified oily sludge and coal on the sintering of cement clinker is explained,and the solidification regularity of heavy metals in clinker is revealed.The addition of mixed fuels C7-（OS5-R5）3、C7-（OS7-T3）3、C7-（OS7-（R5-T5）3）3could not only promote the decomposition of calcium carbonate and the formation of C3S in high temperature liquid phase during clinker sintering,but also improve the burnability of clinker.The mineral composition of all prepared clinker were C3S,C2S,C3A and C4AF,and no new mineral phase was formed.The strength of the clinker was high,and the compressive strength of the clinker was about 30MPa at 3d and 55MPa at 28d,respectively.The solidify rates of different heavy metals in clinker varied greatly.The solidify rates of Pb and Cd were only 20%to 30%.The solidify rates of As,Cu and Zn were about 50%to 60%.The solidify rates of Cr,Ni and Mn reached 80%to90%.Pb and As tended to be solidified in silicate phase,Cd,Cr,Cu,Ni and Mn tended to be solidified in mesophase,and Zn has no obvious solidification tendency.The research results will not only solve the key scientific problems involved in the oily sludge co-processing in cement kilns,supplying theoretical information for realizing harmless disposal and high effective utilization of oily sludge,but also provide a significant opportunity for the strategic transformation and upgrading of China’s cement industry. |
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