Study On The Effect Of CaO On The Migration And Transformation Characteristics Of N And S In The Thermal Treatment Process Of Oil Sludge

Oil sludge（OS）is one of the typical hazardous wastes produced in the petroleum industry.Among the many oily sludge treatment technologies,OS thermal treatment technology（pyrolysis and combustion）has significant advantages such as fast treatment speed,significant volume reduction and volume reduction effects,and recyclable resources and energy.However,global crude oil shows a trend of high sulfur content,and the production of high（medium）sulfur oil sludge is also increasing.Pyrolysis treatment will cause the nitrogen and sulfur in OS to migrate to the pyrolysis products,which increases the cost of reusing the pyrolysis products,and hinder the resource utilization of OS;Combustion treatment will make the nitrogen and sulfur in OS migrate into the flue gas in the form of pollutants,which increases the cost of flue gas desulfurization and denitrification,and reduce the economics of OS combustion treatment.Research and engineering practice have proved that calcium-based additives have good effects in the catalytic pyrolysis of organic matter and coal-burning pollutants.Therefore,this paper hopes to mix calcium-based additives into the oily sludge to inhibit the migration of sulfur into the pyrolysis oil and pyrolysis gas,promote the fixation of nitrogen and sulfur in the pyrolysis coke in a stable form,and reduce the emission concentration of nitrogen oxides and sulfur oxides in the combustion flue gas.This paper firstly uses thermogravimetric analyzer and tube furnace experimental system to study the transfer and transformation characteristics of nitrogen and sulfur during the pyrolysis and combustion process of OS with CaO.The results showed that the pyrolysis process of OS was divided into five stages:free water and light hydrocarbon removal（<160°C）,light component analysis（160～380°C）,heavy component cracking（380～560°C）,heavy component deep cracking and coke polycondensation（560～660°C）,inorganic mineral reaction（600～1200°C）.And the addition of CaO promoted the early cracking of heavy components.In the process of OS pyrolysis with CaO,aromatic sulfur,pyrrole nitrogen and oxide nitrogen were completely converted into other forms of nitrogen and sulfur,while a large amount of sulfide sulfur was generated and retained in the pyrolysis coke.The addition of CaO promoted the generation of pyrolysis oil,and slightly suppressed the nitrogen and sulfur content in the pyrolysis oil.At the same time,part of the sulfur was fixed in the pyrolysis coke in the form of stable Ca SO₄,which is beneficial to the resource utilization of pyrolysis products.The combustion process of OS was divided into four stages:free water volatilization（<170°C）,flammable light component combustion（170～380°C）,non-flammable heavy component and fixed carbon combustion（380～600°C）,inorganic mineral reaction（600～1200°C）,and the addition of CaO greatly reduced the comprehensive combustion performance of OS.During the combustion process of OS with CaO,the sulfur in OS was mainly fixed in the bottom ash,and nitrogen was mainly converted into nitrogen-containing gas to be released,when the Ca/S ratio reached 2 and at 900°C,the emission reduction rates of SO₂ and NO_x could reach 94.85%and83.73%,respectively.Therefore,OS fluidized combustion with CaO can significantly reduce SO₂ and NO_x emissions.In this paper,the thermogravimetry-mass spectrometry-infrared spectrometer was used to study the release characteristics of nitrogen and sulfur gas phase products during the pyrolysis and combustion of OS with CaO.The results showed that during the pyrolysis process,CaO promoted the emission reduction of H₂S,inhibited the generation of SO₂ below 1000°C,and promoted the generation of NH₃.During the combustion process,CaO significantly promotes the emission reduction of H₂S、SO₂、COS和CS₂ and the conversion of HCN to NH₃ and NO.In addition,CaO will react with CO₂ and minerals in OS,and the sulfur-fixed products will decompose and release SO₂ at about 1000°C.Therefore,when applying the heat treatment technology of OS with CaO,the proportion of CaO should be appropriately increased and the temperature should be controlled within 1000°C.