Experimental Study On Co-carbonization Of Petrochemical Sludge With Coal Or Biomass

Petrochemical sludge produced by the treatment of petrochemical processing wastewater,and it mianly comes from the grease trap the flotation cell and the biochemical pool,including the grease trap bottom sludge,the flotation cell scum and the remaining activated sludge.Usually,petrochemical sludge contains a large amount of organic matter,hydrocarbons,oils and metal elements such as K,Na,Mg,Al,Ca,Fe,etc.,and has a high-water moisture,which generally accounts for 70-85%of the total solid waste of petrochemical enterprises,and is difficult to disposal.According to the National Hazardous Waste List,petrochemical sludge is classified as hazardous waste.The sludge drying-carbonization treatment technology is considered as a kind of clean processing method.For it has the characteristics of small secondary pollution,simple treatment of flue gas;moreover,its emission of greenhouse gas is far lower than the incineration method.Besides the organic matter of the raw sludge can be converted into usable energy and its carbonized products are harmless.Therefore,it has the important engineering application value to analyze the carbonized products of the petrochemical sludge and the experimental study of the energy utilization,especially the energy balance of the drying-carbonization system.Based on the study of sludge dewatering performance,the thermogravimetry was used to study the carbonization characteristics of the mixture of petrochemical sludge in different water moisture with coal and rice straw in different mass ratios.And their carbonization heat absorption,weight loss rate,the devolatilization characteristics and the solid yield were studied.Meanwhlie,the carbonization pilot test was carried out on the tube furnace,and the carbonized residue and carbonized oil of the mixsure of petrochemical sludge in different water content with coal and rice straw in different mass ratios were collected and analyzed,and the carbonized gas was analysized on-linely.Therefor the calorific value and yield of carbonized residue,oil and gas were obtained.Established the relationship between the heat demand for carbonization of petrochemical sludge and the carbonization gas production and oil calorific value.And the energy difference of the petrochemical sludge drying carbonization system was also established.The co-carbonization of petrochemical sludge with coal and rice straw can be divided into three stages:water precipitation stage,volatilization precipitation stage and carbonization stage.Activation energy of sludge,coal and rice straw carbonization volatile decomposition section are 25.11KJ/mol,31.08KJ/mol and 72.39KJ/mol respectively.The carbonization is beneficial to the stabilization of heavy metals in sludge.And the petrochemical sludge is carbonized on the new tube-fin carbonizer,where the carbonized volatiles are immediately burned.The SO₂and NO_x in combustion exhaust gas meet the GB13271-2014 boiler air pollutant discharge standard.Through the TG/DTG experiment,the relationship between the kinetic equation of volatile analysis in the co-carbonization and the sludge moisture content and sludge mixing ratio was fitted.The relational equation of the activation energy with sludge moisture content and sludge mixing ratio of the co-carbonization were established.Through the tubular experiment,the relational equation of the ratio of calorific value absolute and dry sludge of co-carbonized gas-oil with sludge moisture content and sludge mixing ratio was established.The data of the DSC test and the tube furnace experiment were used to establish the relational equation between the carbonization reaction heat E_d and the sludge moisture content and sludge mixing ratio.The influence of water on the energy of carbonized products shows that the energy of co-carbonized gas-oil of sludge and coal co-carbonization is negatively correlated with the moisture content of sludge,and the thermal energy of solid products positively correlated with the moisture content of sludge.The energy of co-carbonized gas of sludge and rice straw co-carbonized is positively correlated with the moisture content of sludge,while the energy of solid liquid products is negatively correlated with the moisture content of sludge.The energy difference of the petrochemical sludge drying carbonization system is-9.9^-10.76MJ/?kg dry sludge?,all of which are less than zero,meaning that Petrochemical sludge carbonization alone cannot meet the requirements of dry-carbonization energy balance,and the external heat source is needed to provide energy or increases its own calorific value by adding coal and rice straw.The pilot test of the petrochemical sludge drying carbonization system requires heat of 10.4087MJ/?kg dry sludge?,which is consistent with the calculated value of the dry-carbonization energy difference system formula of 10.76MJ/?kg dry sludge?.Compared with sludge-coal co-carbonization,under the same conditions,the yield of co-carbonized volatiles of petrochemical sludge and rice straw co-carbonization is high,and the mass ratio of co-carbonized solid product to dry sludge is low.In order to reduce the amount of carbonized solids and increase the heat of carbonized volatiles,chosing the co-carbonization of sludge and rice straw is the preferred scheme.On the other hand,when the energy balance condition of the dry-carbonization system is satisfied,the mixing ratio of sludge in co-carbonization of sludge and rice straw is higher,per unit mass of rice straw can treat with more petrochemical sludge,so the co-carbonization of petrochemical sludge and rice straw is better.Through the relational equation of the established system energy difference?Q and the the sludge carbonization moisture content w and the coal and sludge specific gravity p,the conditional formula for satisfying the system energy balance is obtained.The optimal working condition of the actual drying carbonization operation is:sludge and rice straw mixing,the moisture content and specific gravity of the sludge are 39.21%and 0.26,respectively.