Research On Co-pyrolysis Behavior Of Sewage Sludge And Lignocellulose Biomass And The Structure Evolution Of Pyrolysis Char

Pyrolysis technology can convert sewage sludge into high-value products(syngas,oil and char).However,the characteristics of sewage sludge(high moisture and ash content)lead to many problems such as low conversion efficiency,poor product quality and unstable reactor operation.Lignocellulose biomass has the characteristics of low moisture content,low ash content and high volatile content.Co-pyrolysis of sewage sludge and lignocellulose biomass can effectively solve the existing problems during individual pyrolysis process of sewage sludge.It is essential to reveal the thermal behavior and product evolution law during co-pyrolysis of sewage sludge and lignocellulose biomass,which can provide basic data and theoretical guidance for large-scale utilization of sludge pyrolysis.There are many kinds of lignocellulose biomass,and they have different influence on the co-pyrolysis behavior and the physico-chemical structure of pyrolysis char due to the differences in composition and chemical structure.Based on the main organic components of biomass(cellulose,hemicellulose and lignin),this thesis deeply studied the copyrolysis behavior of sewage sludge and lignocellulose biomass,as well as the physico-chemical structure evol ution of pyrolysis char.The main research contents and conclusions were as follows:(1)The influence of synergistic effects on the yield of pyrolysis char and volatile products was studied during co-pyrolysis of sludge and lignocellulose biomass.There existed synergistic effects during co-pyrolysis of sludge and cellulose,which can inhibit the volatiles releasing and promote the char formation.The most obvious synergistic effects happened when the cellulose blending ratio was 75%.For the co-pyrolysis of sludge and hemicellulose,the synergistic effects promoting the formation of volatile products took place in the temperature range of 220～300℃,while the synergistic effects promoting the formation of char occurred when the temperature increased to the range of 300～430℃.Overall,co-pyrolysis of sludge and hemicellulose had a weak promotion effect on the char formation.For the co-pyrolysis of sludge and lignin,there happened synergistic effects promoting the char formation at 50%lignin blending ratio,and no obvious effects on product yield were found under other blending ratios.There existed complex synergistic effects during co-pyrolysis of sludge and typical biomass(pine sawdust and wheat straw).The synergistic effects,which can promote the char formation,occurred with 50%pine sawdust blending ratio in the temperature range of 300～420℃ during co-pyrolysis of sludge and pine sawdust.There were synergistic effects affecting the product releasing rate with 25%and 50%wheat straw blending ratio in the temperature range of 270～375℃ during co-pyrolysis of sludge and wheat straw.The synergistic effects during co-pyrolysis process were the result of combined impact of cellulose,hemicellulose and lignin.(2)The influence of synergistic effects on the activation energy of co-pyrolysis of sludge and lignocellulose biomass was investigated.There existed synergistic effects on kinetic parameters of co-pyrolysis process,and the influence was related to the kinds and blending ratios of biomass.When the blending ratios of hemicellulose and lignin were respectively 75%and 50%,the experimental value of average activation energy for co-pyrolysis process was higher than the theoretical value.However,the experimental values of average activation energy for copyrolysis process with cellulose,hemicellulose and lignin were lower than the theoretical values under other blending ratios.When the blending ratio of wheat straw was 25%,the experimental value of average activation energy for co-pyrolysis process was higher than the theoretical value,while the experimental values of average activation energy for co-pyrolysis process with pine sawdust and wheat straw were lower than the theoretical values under other blending ratios..(3)The surface morphology and pore structure of co-pyrolysis char from sludge and lignocellulose biomass were investigated,and the effect of biomass on pore structure of copyrolysis char was obtained based on fractal theory.The addition of biomass improved the complexity of the surface morphology of co-pyrolysis char.Co-pyrolysis char had a continuous and complete pore distribution system,and the specific surface area of co-pyrolysis char was improved by mixing cellulose,hemicellulose and lignin.Under the comprehensive influence of cellulose,hemicellulose and lignin,the pore structure of co-pyrolysis char with pine sawdust and wheat straw became more developed,and the pore size distribution showed complicated variation law with the blending ratio.There was a good exponential relationship between the specific surface area and the pore fractal dimension for co-pyrolysis char.(4)The carbon microcrystal structure and the surface functional groups of co-pyrolysis char from sludge and lignocellulose biomass were explored.With the addition of cellulose and hemicellulose,the ordering degree of carbon microcrystal structure for co-pyrolysis char was increased.The ordering degree of carbon microcrystal structure for co-pyrolysis char was improved with 25%and 75%lignin blending ratio,while it was decreased with 50%lignin blending ratio.Cellulose,hemicellulose and lignin promoted the decomposition of C-O bond,OH bond,C=O bond and aromatic hydrocarbon structure in co-pyrolysis char.With the addition of pine sawdust and wheat straw,the ordering degree of carbon microcrystal structure for copyrolysis char was improved,and the decomposition of functional groups in co-pyrolysis char was promoted.