Study On Co-pyrolysis Characteristics Of Sludge And Straw And Combustion Characteristics Of Solid Products

Sludge is a solid waste with high water content and low calorific value in production and domestic wastewater.The co-pyrolysis of sludge and biomass is an important means to convert organic solid waste into energy.Sludge and biomass co-pyrolysis is an important method to treat sludge efficiently and utilize biomass resources.It can also effectively solve the problems caused by energy shortage and environmental pollution.Therefore,the co-pyrolysis characteristics of sludge and straw and the combustion characteristics of biochar as a solid product of co-pyrolysis were studied in detail in this paper.The fixed-bed experiment system was used to carry out co-pyrolysis experiments of biomass and sludge,and the three-phase products were tested under different thermostatic pyrolysis temperatures（500℃、600℃、700℃and 800℃）and mixing ratios（0%、25%、50%、75%and 100%）.The effects of pyrolysis temperature and mixing ratio on the release of pyrolysis gas products,bio-oil and physicochemical properties of biochar were investigated.As for the gas phase products,it was found that the higher content of volatile and organic matter made the CO₂,CO,CH₄and H₂produced by straw pyrolysis higher than that of sludge pyrolysis,and the release of these four gases showed a trend of first increasing and then decreasing with the increase of pyrolysis temperature,and the maximum amount was released at 700℃,indicating strong synergistic effect existed in the temperature mixed pyrolysis.The synergistic effect has a certain effect on the solid yield,and the biochar yield of the mixture mixed with 75%straw has the greatest effect.The experimental value of biochar yield is 2.73%-3.19%higher than the calculated value.With the increase of pyrolysis temperature,the specific surface area decreases first and then increases.At 600℃,due to the sufficient volatilization of organic matter in the pyrolysis process,some pores collapse and the surface collapses and melts.At the same time,the bio-oil produced in the pyrolysis process sticks to the surface of biochar and blocks the pores.Later,the specific surface area of biochar reached a maximum of 42.5 m²/g at 800℃.The addition of straw promotes the reaction between free radicals and accelerates the breaking of covalent bonds.Co-pyrolysis can promote dehydrogenation and CH₄reforming.Co-pyrolysis can accelerate decomposition,catalysis,cracking and aromatization,which promotes the release of gas in the process of co-pyrolysis.The mass release of gas increases the specific surface area and increases the porosity performance.The optimal temperature for sludge and straw pyrolysis was 700℃based on factors such as gas product release characteristics,yield,surface area and pore structure.Biochar with different straw mixing ratios（0%、25%、50%、75%and 100%）was prepared at 700℃.TG and DTG were used to explore four heating rates（10℃/min、20℃/min、30℃/min and 40℃/min）to analyze the combustion characteristics of biochar.By comparing the theoretical and experimental values of biochar TG,it is found that there is an obvious synergistic effect when 75%straw is added.The weight loss of the experimental value is much larger than the theoretical value,because the straw contains a large amount of organic matter and a certain amount of alkaline earth metal to promote the reaction.FWO and KAS were used to analyze the combustion kinetics of biochar.It was found that the trend of activation energy regions calculated by the two methods was the same,and the R²values were both above 0.9,indicating that FWO and KAS methods were suitable for the calculation of the combustion kinetics of biochar.In the process of biochar combustion,the hydroxyl group and carbonyl group on the surface of biochar are oxidized first.In addition,with the increase of combustion temperature,the carboxylic acid structure on the surface of biochar gradually increased.In this paper,the co-pyrolysis characteristics of sludge and straw and the combustion characteristics of solid products were studied,which provided an important reference value for the co-pyrolysis technology of agricultural waste and the efficient utilization of co-pyrolysis products.In this paper,the co-pyrolysis characteristics of sludge and straw and the combustion characteristics of solid products were studied,which provided an important reference value for the co-pyrolysis technology of agricultural waste and the efficient utilization of co-pyrolysis products.