Study On Target-oriented Pyrolysis For Biogas Residue Biochar Preparation And Inorganic Nutrients Slow-release Properties

The resource utilization of biogas residue is an important process in the sustainable development of biogas engineering.The abundant biogas residue resource is difficult to disposal,which is riched in organic and inorganic nutrients.Pyrolysis technology enables the biogas residue utilization towards nutrients-riched biochar production.However,the characteristics of biogas residue biochar are sensitively affected by the pyrolysis process,leading an ambiguous regulation mechanism of nutrient content and morphology of biogas residue biochar effected by pyrolysis parameters.Therefore,this study investigated the inorganic nutrient morphology and release characteristics of biochar by regulating pyrolysis temperature,carrier gas type,and blending extrinsic additive agents for oriented preparation of potassium-riched biogas residue biochar,followed by a machine learning investigation for the prediction of key characteristics of biochar.The main research contents are as follows:（1）Based on thermogravimetry mass spectrometry（TG-MS）,the influence of the addition of incineration bottom ash on the pyrolysis of biogas residue was analyzed by kinetic study.The maximum weight loss peak of biogas residue appeared at 336.06°C during pyrolysis.The apparent activation energy of the Starink method was 188.32k J/mol.The addition of incineration bottom ash increased the pyrolysis activation energy of biogas residue to 209.06 k J/mol.The Coats-Redfern method and the release law of non-condensable gas further show that the incineration bottom ash plays different roles in the low-temperature zone and the high-emperature zone.The incineration bottom ash has an inhibitory effect on the pyrolysis of biogas residue,but it is conducive to the yield of solid-phase product biochar.（2）The effects of pyrolysis temperature and atmosphere（N₂,CO₂,air limited）on the physical and chemical properties of biogas residue biochar and other biochar were systematically studied.The polarity and aromaticity of biochar can be regulated by raw materials and temperature,the surface functional groups are only effectively regulated by temperature,and the pore structure is jointly regulated by raw materials,temperature,and atmosphere.High temperature（800°C）under CO₂ atmosphere contributes to microporous structure generation.The released total nitrogen（RTN）content of biogas residue biochar is 0.72-1.34 mg/g.High temperature suppresses the enrichment of RTN,but favors enrichment of total phosphorus where the proportion of available phosphorus decreases with the increase of preparation temperature.If the biogas residue of the national biogas project is completely manufactured to biochar,its long-term carbon sequestration potential is estimated as high as 7.42 MT CO₂ equivalent.（3）Potassium（K）-riched slow-release biochar was prepared by oriented pyrolysis blending biomass incineration bottom ash.The K species distribution and K⁺release characteristics of composite biochar were studied,and the slow-release potassium content in the composite biogas residue biochar increases from 0.86 mg/g to 6.88 mg/g.Composite biogas residue biochar shows K slow-release performance,of which the cumulative release amount is less than 80%of the total effective potassium content within 28 days.The K⁺release kinetics fits well with the power function equation.The slow-release performance is contributed by the formation of exchangeable potassium minerals.The regulation effect of incineration bottom ash has also been verified in maize silage composite biochar.（4）A database was established which includes raw material characteristics（Ash,C,H,O,N content）,pyrolysis parameters（pyrolysis temperature,heating rate,residence time）,and biochar characteristics.The BP neural network and support vector machine model were trained for accurate prediction of biochar yield,C content,ash content,p H,and specific surface area.The accuracy of the support vector machine model reaches 91.28%-93.55%,which accurately predicts the relevant characteristics.The correlation between the prediction results and the experimental data is 0.92-0.99.The liner kernel function in support vector machine is applicable for the prediction of different characteristics of biochar in this study.This study provides theoretical support for the pyrolyzed preparation of biogas residue biochar aimed at agricultural fertilizer,and provides technical reference for the resource utilization of biogas residue.