Migration And Transformation Patterns Ofpahs In Flue Gas When Oil-Based Drilling Cuttings Are Used For Firing Ceramic Pellets

Oil-based drilling cuttings are abundant in petroleum hydrocarbon organics,which are classed as hazardous waste in China.Improper disposal of the wastes will cause severe harm to the human body and the environment.Using ceramic pellet kilns for co-treatment of oil-based drilling cuttings can successfully remove the organic contaminants in oil-based drilling cuttings,a topic that has garnered considerable attention in recent years.However,present research has primarily concentrated on optimizing the pottery-making process,with little consideration paid to the technique’s possible environmental concerns.Uncertainty regarding the formation and metabolism of polycyclic aromatic hydrocarbons（PAHs）in the flue gas during the burning of ceramic pellets hinders the control of flue gas pollution.In this study,the presence and phase partitioning of PAHs in the gas and particle phases of the flue gas during the firing of oil-based drilling cuttings to pottery pellets were investigated in the laboratory using oil-based drilling cuttings and calcium-based bentonite as the main raw materials,and the effects of various process parameters on the PAHs fugacity were investigated.The primary findings are as follows:The physicochemical characterization of the raw materials revealed that the oil-based drilling rock chips had a high volatile fraction（11.7%）and calorific value（1018 kcal/kg）,and that the mineral phases were dominated by quartz,barite,calcite,and dolomite,with Si O₂,Ba SO₄,and Al₂O₃contents of 35.4%,11.9%,and 8.4%,respectively.Calcium bentonite has a high ash content（90%）,the mineral phase is dominated by quartz,microplagioclase,montmorillonite,and illite,Si O₂and Al₂O₃up to 71.4%and 14.4%,respectively,based on Riley’s ternary phase diagram,and the two mixed pottery doping ratio is no more than 1:1.Moreover,thermogravimetric-differential thermal study reveals that the two largest mass loss peaks occur at approximately 100°C,whereas the melting point occurs at 1150°C.Therefore,the drying temperature must exceed 100°C,and the firing temperature must reach 1150°C.The study on the contamination characteristics of oil-based drilling cuttings revealed that it contains a high concentration of PAHs and their synthetic precursors,and the FTIR analysis detected the stretching vibrations of-OH,C-H,-C=O,-C=C-,and-C-O at peak heights of 3423,2956,1747,1619,and 1019 cm-1 respectively.In addition,a total of 9.26×10⁴mg/kg of petroleum hydrocarbons,5 benzene series（69.5mg/kg toluene,53.7 mg/kg ethylbenzene,196 mg/kg m-（p）xylene,96.2 mg/kg o-xylene）and 10 PAHs（up to 1307μg/kg,with the highest content of naphthalene and phenanthrene at 39.9%and 27.2%）,indicating that the oil-based drilling rock chip co-disposal process has the potential risk of PAHs emission.At varying temperatures,PAHs in both gas and particle phases exhibited an initial increase followed by a decline,and high temperatures promoted the formation of PAHs,which peaked at 900℃（1575μg/kg in the gas phase and 114μg/kg in the particle phase）.The low ring（2～3 ring）PAHs such as naphthalene,phenanthrene and fluorene accounted for 88～98%of the total PAHs in the gas phase,while the medium and high ring（4～6 ring）PAHs such as fluoranthene,pyrene,benzo[a]anthracene,quaternary,benzo[b]fluoranthene and benzo[k]fluoranthene were usually in the dominant position（22～88%）in the particle phase.Below 900℃,the increase in temperature promotes the formation of high-ring（5-to 6-ring）PAHs.High-ring（5-6ring）PAHs are the primary contributors to∑TEQ,with their contributions to∑TEQ in the gas and particle phases reaching up to 88%and 92%,respectively.High-ring PAHs are more likely to be enriched in the particulate phase,and the∑TEQ of PAHs in the particulate phase under high temperature conditions（12.2-17.9μg/kg）is greater than that in the gas phase.The analysis of the sources of PAHs reveals that the primary source of PAHs in the gas phase at 100°C is petroleum,and not less than200°C is the combustion source.Only the source of PAHs in the particulate phase at100°C is derived from petroleum;all other temperatures are derived from combustion.Gas-particle partitioning of PAHs is dominated by absorpti-on.The feedstock ratio had a significant positive correlation（p<0.05）with∑PAHs and∑TEQ in the gas and particulate phases,and the lower oil-based drilling rock chip addition（20%）reduced the free radical concentration and incomplete combustion reaction in the furnace tube,inhibited the formation of high cyclic PAHs and particulate matter,and the increment of∑TEQ in the gas and particulate phases was small（2.94μg/kg and 1.05μg/kg,respectively）.The aeration rate had a significant negative correlation（p<0.05）with∑PAHs and∑TEQ in the gas and particle phases,increasing the aeration rate reduced the residence time of organic matter,the synthesis reaction of PAHs could not be fully carried out,and PAHs in the gas and particle phases decreased.The results of principal component analysis showed that the dominant PAHs emission process parameters were ranked in order of importance as temperature>feedstock ratio>aeration.