Study On The Characteristics Of Char Production And Heavy Metals Solidification During Co-pyrolysis Of Industrial Sludge And Biomass

Industrial sludge can be quickly converted into products such as pyrolysis gas,oil,and sludge carbon through pyrolysis technology,so as to achieve resource utilization.However,industrial sludge has high sludge moisture content,low calorific value,and high heavy metal content.These characteristics can lead to high energy consumption,poor reaction characteristics,and low product quality during the pyrolysis process.Adding biomass to the co-pyrolysis system can provide energy,solidify heavy metals and improve product quality.Therefore,the co-pyrolysis technology of sludge and biomass is very promising.This article focused on the co-pyrolysis of industrial sludge and biomass to produce char and its solidification characteristics for heavy metals.The co-pyrolysis reaction synergy mechanism and char formation characteristics were firstly explored.The mechanism of migration and conversion of heavy metals in the process of co-pyrolysis was also studied.Finally,the process conditions of co-pyrolysis were optimized.The reaction energy consumption and the risk of heavy metals were evaluated under the optimal condition.The co-pyrolysis of industrial sludge with biomass and its main components to produce carbon was studied.Thermogravimetric experiments were conducted to study the co-pyrolysis synergy coupling characteristics and reaction kinetics.The fixed bed was used to investigate the co-pyrolysis rules under different conditions,and the char formation characteristics were studied from the aspects of functional groups and pore structure evolution.It was found that cellulose components can improve the char-forming polymerization degree and framework strength,and increase the type and content of surface functional groups.The activation energy of co-pyrolysis of sludge and lignin was 27.34 k J/mol,which was smaller than 16.79 k J/mol during sludge pyrolysis.The synergistic effect of co-pyrolysis of sludge and rice straw was obvious.Compared with the calculated value,the second decomposition stage of co-pyrolysis was extended from 405°C-470°C to 400°C-550°C,and the maximum weight loss rate is increased by about 29.51%.The functional groups in the char produced by sludge and rice straw at 500°C increased a lot,and new functional groups appeared.The specific surface area increased from 54.30m~2/g to 110.10m~2/g.In addition,the number of micro-pores and macro-pores increased,and the average pore size decreased.The solidification characteristics and mechanism of heavy metals were studied.The curing effects of heavy metals in co-pyrolysis char prepared under different temperatures,blending ratios,mixing schemes,etc.were compared.Through the BCR sequential extraction experiment and leaching experiment.The solidification mechanism of heavy metals was studied from the perspective of total amount,morphological transformation and leaching characteristics.It was found that with the increase of the biomass blending ratio and the degree of mixing,the F1 acid exchangeable state is converted into F3 oxidizable state and F4 residue state,and the curing effect of heavy metals is gradually improved.When the mass ratio of biomass and sludge is 2:1,the curing effect of co-pyrolysis char on Cu is 36%higher than that of pure sludge carbon.With the increasing of temperature,the leaching of heavy metals first decreased and then increased,.At500°C,the leaching rate of heavy metals in co-pyrolysis char reached the lowest value,and the leaching rates of Cd and Cr are 38.22%and 39.54%,respectively.The process optimization of co-pyrolysis of industrial sludge and biomass was studied.The influence mechanism of the three conditions of temperature,biomass blending ratio and heating rate on the heavy metal comprehensive index was investigated.A model was established by response surface methodology to optimize the optimal working conditions of co-pyrolysis.Under the optimized conditions,the energy consumption and heavy metal risk assessment of co-pyrolysis were carried out.It was found that the temperature of 549.61°C,the mass ratio of biomass and sludge of 1.8:1,and the heating rate of 15°C/min are the best conditions for the co-pyrolysis of industrial sludge and biomass to produce low heavy metal risk char.Under the optimal working conditions,the CRI index of carbon is only 33.35,and the ecological risk is low.The total calorific value of the product is greater than the total energy consumption of the drying and co-pyrolysis process under optimal working conditions.The total energy difference of the system is 3651k J/kg,which indicates that the can achieve self-heating operation,and obtain char with low heavy metal content.has significant economic benefits.The co-pyrolysis of sludge and biomass has significant economic benefits.