Study On The Characteristics Of Two-stage Constant Temperature Pyrolysis Of Oily Sludge

Oily sludge is the main waste produced during the exploitation,transportation and refining of crude oil.If it is not properly treated,it will do harm to the environment.There are abundant petroleum hydrocarbons in oily sludge,which has high recycling value.Pyrolysis method has become the focus of research on the recovery and utilization of oily sludge in recent years because of its advantages of less pollutants and full recovery of resources.In this paper,the thermal weight loss of oily sludge,the influence of different pyrolysis methods and pyrolysis conditions on the pyrolysis products were analyzed through experiments,and the best experimental conditions were obtained,which improved the recovery rate of oily sludge.The main research content of this paper is divided into the following parts:First,thermogravimetric experiments were carried out on oily sludge samples to explore the basic pyrolysis characteristics at different heating rates,and the Doyle pyrolysis kinetics model was established and solved.The results showed that the weight loss of the sample was divided into four processes.The pyrolysis parameters were changed with the increase of heating rate.The activation energy of the reaction at 20℃/min decreased by 27% compared with that at 5℃/min.With the addition of HZSM-5 molecular sieve,the activation energy of the oil sludge reaction was reduced by 30% and the pyrolysis of the oil sludge was more sufficient.Then,temperature-programmed pyrolysis experiments were carried out on oily sludge samples.The results show that the lower final temperature leads to insufficient pyrolysis,while the higher final temperature leads to the fracture of C-H and C-C bonds in the pyrolysis products and increases the gas production.The suitable final temperature is conducive to the generation of pyrolytic oil and the development of the pore structure of pyrolysis slag.When the final pyrolysis temperature was 600℃,the oil recovery reached 74.8%,the calorific value was35.6MJ/kg,and the specific surface area of the pyrolysis slag reaches the maximum.However,hydrogen production reached the maximum at the final temperature of 700℃,which was 110%higher than that at 400℃.Increasing the heating rate will make the pyrolysis process more complete,but at the same time,the non-uniform decomposition of organic matter in the inner and outer layers inhibits the development of pore structure of pyrolysis slag.When the heating rate was 20℃/min,the oil recovery and hydrogen production were the best.When the heating rate was 10℃/min,the pore structure of pyrolysis slag was the best.Finally,the two-stage pyrolysis experiment of oil-bearing sludge was carried out.The results showed that the pyrolysis process was more sufficient in the two-stage pyrolysis,and the yield of pyrolysis products was further improved.The yield of pyrolysis oil is mainly affected by the first-order pyrolysis temperature,the structural characteristics of pyrolysis slag are mainly affected by the second-order pyrolysis temperature,while the yield of pyrolysis gas is jointly affected by the first and second order pyrolysis temperatures.Under the two-stage pyrolysis temperature combination of 500×800℃,the average oil recovery reached 76.2%,the hydrogen yield reached 2013 m L/g.In order to further improve the quality of pyrolysis oil,HZSM-5 molecular sieve was used to catalyze the two-stage pyrolysis of oily sludge.The results show that the molecular sieve has a strong aromatization selectivity.When the mass ratio of oily sludge to catalyst was 5:3,the best aromatization reaction could be achieved.The calorific value of the pyrolysis oil was increased to 37.7 MJ/kg,in which the content of aromatic hydrocarbons reached 37.6%.