Experimental Study On Pyrolysis Characteristics And Nitrogen Conversion Pathway Of Ink Sludge

As a hazardous waste,the treatment and disposal of ink sludge has become an urgent environmental problem in ink printing industry.Although sludge incineration has a high capacity reduction rate,the byproduct pollutants produced by sludge incineration are difficult to deal with.Sludge pyrolysis technology has attracted more and more attention from scholars at home and abroad because of its high capacity reduction rate,high utilization rate of resources and less pollution by-products.Although the tar and gas produced by sludge pyrolysis can provide energy for sludge drying and pyrolysis,the sludge pyrolysis process is prone to produce nitrogen-containing pollutants,which may lead to a decrease in the quality of flammable gases.Therefore,through the pyrolysis experiment of ink sludge,the optimum temperature for the pyrolysis of ink sludge was determined,and the way of nitrogen conversion in the pyrolysis process of ink sludge was preliminarily explored.In this study,the weight loss law of the ink sludge pyrolysis process was investigated by thermogravimetric experiments.The ink sludge was pyrolyzed at different temperatures?500,600,700,800 and 900°C?,and the characteristics of the three-phase products of ink sludge pyrolysis gas,tar and residue were studied,and the pyrolysis product energy and sludge drying were utilized.The energy consumption and pyrolysis energy consumption were compared and analyzed.The results show that when the pyrolysis temperature is raised from 500°C to 900°C,the yield of pyrolysis gas increases significantly from 21.7%to 44.3%,in which the yield of CO and H₂ increases significantly,and the yield of CH₄increases first and then decreases.The CO₂ content gradually decreased.the sludge pyrolysis tar yield increased first and then decreased with the increase of temperature,reaching up to 30.5%at 600°C.It was found that the ink sludge pyrolysis tar was mainly composed of aromatic and heterocyclic aromatic compounds.The residue yield decreases with increasing temperature.The heavy metal in the residue with temperature above 700°C is not leached and the volatile organic content is low.By analyzing the energy required for sludge drying and pyrolysis with different initial moisture content and the release energy of pyrolysis products,it was found that the energy of pyrolysis gas and tar at medium and high temperature could not only meet the demand of sludge drying and pyrolysis energy consumption reduced from 80%to 5%,but also have more residual energy.Studies have shown that the optimum temperature for ink sludge pyrolysis is 808.06°C.The XPS analysis of the presence of nitrogen-containing functional groups in the ink sludge indicated that the sludge nitrogen mainly existed in the form of inorganic ammonium nitrogen,protein nitrogen and pyridinium nitrogen.The distribution characteristics of sludge nitrogen in the pyrolysis product three phases were studied by means of FT-IR,GC-MS and XPS.According to its distribution characteristics,the conversion pathway of nitrogen-containing functional groups in the ink sludge pyrolysis process was investigated.The results show that at 500-900°C,the gaseous nitrogen yield gradually increases,and the solid nitrogen yield is opposite.The tar nitrogen yield first increases and then decreases,and the yield at 600°C is the largest,accounting for 57.25%of the total nitrogen content.When the temperature is lower than 500°C,mainly inorganic ammonium nitrogen decomposition and a small amount of organic amine nitrogen cracking produce NH₃,which accounts for only 4.99%of the total nitrogen content.Nitrate nitrogen and nitrite nitrogen decomposition directly or indirectly produce NO_x.When the temperature exceeds 500°C,the aromatic amine nitrogen in the tar is cleaved to form aromatic heterocyclic nitrogen and aromatic nitrile nitrogen compounds with the production of HCN and NH₃.The polycondensation reaction of tar aromatic heterocyclic nitrogen and solid heterocyclic nitrogen at high temperature Formation of polycyclic nitrogen-containing aromatic hydrocarbons simultaneously produces HCN and NH₃.When a mineral element such as Fe or Ca is present at a high temperature,NH₃ is promoted to form N₂.