Experimental Study On The Dehydration And Desalination Of Refinery Oily Sludge By Ultrasonic Demulsification

As a by-product of the petroleum industry,the water content and oil content of oily sludge are both high.The recovery and utilization of oil through demulsification represent the development direction in the future.However,the oily sludge produced by refineries,with high degree of emulsification,complex composition and high salt content,is more difficult to be demulsified and recovered.An effective way of dehydration and desalination is needed to achieve the reduction and resource utilization of the oily sludge.Ultrasonic demulsification is an efficient,economical and environmentally friendly demulsification method.In this paper,ultrasonic demulsification is taken as the key technology to conduct dehydration and desalination treatment of refinery oily sludge.The influencing factors,demulsification mechanism and cooperative desalination characteristics in the demulsification process are studied.Firstly,the basic properties of oily sludge and the centrifugal conditions for oily sludge after ultrasonic demulsification are determined.The sludge used in this paper is a water-in-oil refinery sludge with a high water content,which has a relatively high salt content and strong stability.The oily sludge can be dehydrated by natural sedimentation after 5min of ultrasonic treatment with an amplitude of 100%;the addition of demulsifiers and pyrolysis residues of oily sludge can improve the dehydration rate,but the dehydration rate is still low,only 5.09%.It is found that the dehydration rate of sludge increases with the increase of centrifugal speed,temperature and centrifugal time.The improvement of dehydration rate is not obvious with the extension of centrifugation time.It is found that the best centrifugal conditions for the oily sludge after ultrasonic treatment are:centrifugal speed 8000r/min,centrifugal time 15min.Secondly,the influence of the main factors(sludge temperature,ultrasonic amplitude,ultrasonic time)of ultrasonic demulsification on the dehydration rate of sludge is studied.The increase of sludge temperature increases the dehydration rate as a whole.When the ultrasonic amplitude is 100%and the ultrasonic time is 5min,the dehydration rate increases from 50.9%to 52.7%after the sludge temperature rises from 20? to 40?.The dehydration rate of sludge first decreases and then increases with the increase of the ultrasonic amplitude,and first increases and then decreases with the extension of the ultrasonic time.The absolute value of the Zeta potential of the sludge and the DSC heat flow curve prove that ultrasonic can reduce the surface charge of the dispersed droplets and promote the aggregation of the droplets.The order of influence degree of the three factors is as follows:ultrasonic time>ultrasonic amplitude>sludge temperature.Considering the effectiveness and economy of dehydration,the optimal conditions of ultrasonic demulsification are as follows:sludge temperature 20?,ultrasonic amplitude 100%,ultrasonic time 5min.On this basis,the effects of different additives on ultrasonic demulsification of oily sludge are investigated,and the effects of different demulsification methods on oily sludge dehydration are compared.Four different types of chemical demulsifiers and oily sludge pyrolysis residues are used as additives to demulsify the oily sludge.The most effective additive is AR demulsifier with a dehydration rate of 74.04%.The oily sludge pyrolysis residue can increase the dehydration rate of oil sludge from 50.92%to 60.49%.Comparing several different demulsification methods,it is found that ultrasonic method can achieve better demulsification without heating.Finally,the ultrasonic desalination characteristics of oily sludge are investigated.As desalination and dehydration occur simultaneously,the trend of desalination rate with various influencing factors is basically the same as the trend of dehydration rate,but the desalination rate is relatively low,and the desalination rate of ultrasonic demulsification alone is only 36.14%.Different demulsification methods have different removal efficiency for different cations.The removal effect of heavy metal ions such as Cr and Ni is relatively good.To solve the problem of low desalination rate by ultrasonic alone,a secondary desalination method is proposed for the remaining sludge.When th e ratio of injection water to oily sludge is 2,the maximum desalination rate reaches 64.29%.