Investigation Of Pyrolysis Characteristics Of Oil-contaminated Drill Cuttings

The oil-based drilling fluid is widely used in the exploration of shale gas,since it has the advantages of cooling and lubricating effects.The exploration industry would inevitably produce a large amount of waste oil-contaminated drill cuttings(OCDCs).If untreated OCDCs are stacked and discarded at random,it would damage environment,endanger human health and limit the sustainable development.Therefore more attention should be paid to utilize the OCDCs as resource.Pyrolysis technology has high efficiency and low secondary pollution in the process of waste treating.It is an effective process to realize both environmental protection and sustainable development of resources.In order to improve the pyrolysis process of OCDCs,this paper mainly investigated and discussed the pyrolysis characteristics of OCDCs.1.This paper firstly studied the thermochemical kinetics characteristics of OCDCs at different heating rates.The kinetic parameters of OCDCs pyrolysis were calculated by model fitting method and distributed activation energy.It was compared together that the characteristics of OCDCs in combustion and pyrolysis process at different heating rates and the differences of kinetic parameters.2.It was investigated in the fixed-bed tube furnace that the effects of OCDCs pyrolysis at different conditions on the yields of products including non-condensed gases,pyrolysis oils and processed solids.The properties and compositions of pyrolysis products were analyzed after experiments.Finally,this paper put forward a system for OCDCs pyrolysis treatment.The main conclusions are as follows:(1)Heating rate is an important parameter affecting the process of OCDC pyrolysis.The TG-FTIR experiments showed that the total weight loss rate of OCDC pyrolysis was 30.64%when the temperature increased from 20℃ to 900℃.According to the thermogravimetric curves and pyrolysis products,the pyrolysis process of OCDCs could be divided into four stages:drying degassing,light oil pyrolysis,heavy oil decomposition and mineral cracking.(2)The pyrolysis kinetics parameters of organic matters in OCDCs at different heating rates were calculated by the model fitting method.It was found that the activation energy was from 94.08 kJ/mol to 98.49 kJ/mol.The results of distributed activation energy method showed that the activation energy range was from 79.21 kJ/mol～106.59 kJ/mol,and it decreased with the weight loss rate.(3)The processes for OCDCs combustion and pyrolysis were comparaed.The results showed that the combustion activation energy of organic matters in OCDCs ranged from 79.83 kJ/mol to 112.55 kJ/mol,which was larger than the values in the pyrolysis process.The activation energy for combustion process increased gradually with the weight loss rate.(4)The results in the fixed-bed experiments showed that the pyrolysis temperature and time were the main factors affecting the pyrolysis products distributions.When pyrolysis temperature was at 550℃,the optimum pyrolysis time was 80 min and the recovery rate of pyrolysis oil was up to about 65%.The experiments results also indicated that increasing the carrier gas flow could shorten the residence time in the furnace and reduce the possibilities of gases secondary cracking,resulting in the decrease in the NCG yield.The use of additives had catalytic effects to promot pyrolysis gas cracking and improve the yield of NCG.The yield of the pyrolysis residue remained stable under different pyrolysis conditions.(5)The compositions of NCG mainly included CO,CO2,H2,CH4 and CxHy(C2H4,C2H6,C3H6,C3H8).The heat value of NCG at 550℃ was 0.46 MJ/m3.The GC-MS results indicated that the compostions of pyrolysis oil at 350 ℃～550℃ were similar to those in extracted oil.Therefore,these pyrolysis oil could be recycled for drilling process.The oil content in the pyrolysis residue at 550℃ was 0.28%.It was found that the processed has met the emission requirements based on the analysis of heavy metal content.(6)Based on the pyrolysis process of OCDCs in TG analysis and the results in the fixed-bed experiments,the industrial system of treating OCDCs was put forward in the end of this paper.The pyrolysis gas was applied into this system as carrier gas for circulation.The NCG was conveyed for combustion to provide heat for pyrolysis.The whole process can reach the energy balance and help gain recovery oil.It is useful to realize the resource recycling and harmless treatment of OCDCs.