• Energy Research

Abstract The present study experimentally quantified the pyrolysis behaviors of waste tea (WT) as a function of four heating rates using thermogravimetric-Fourier transform infrared spectrometry and pyrolysis-gas chromatography-mass spectrometry analyses. The maximum weight loss of WT (66.79%) occurred at the main stage of devolatilization between 187.0 and 536.5 °C. The average activation energy estimates of three sub-stages of devolatilization were slightly higher (161.81, 193.19 and 224.99 kJ/mol, respectively) by the Flynn-Wall-Ozawa than Kissinger-Akahira-Sunose method. Kinetic reaction mechanisms predicted using the master-plots were f (α) = (3/2)(1 − α)2/3[1 − (1 − α)1/3]−1, f (α) = (1 − α)2, and f (α) = (1 − α)2.5 for the three sub-stages, respectively. The prominent volatiles of the WT pyrolysis were CO2 > C O > phenol > CH4 > C O > NH3 > H2O > CO. A total of 33 organic compounds were identified including alkene, acid, benzene, furan, ketone, phenol, nitride, alcohol, aldehyde, alkyl, and ester. This study provides a theoretical and practical guideline to meeting the engineering challenges of introducing WT residues in the bioenergy sector.

Abstract The present study experimentally quantified the pyrolysis behaviors of waste tea (WT) as a function of four heating rates using thermogravimetric-Fourier transform infrared spectrometry and pyrolysis-gas chromatography-mass spectrometry analyses. The maximum weight loss of WT (66.79%) occurred at the main stage of devolatilization between 187.0 and 536.5 °C. The average activation energy estimates of three sub-stages of devolatilization were slightly higher (161.81, 193.19 and 224.99 kJ/mol, respectively) by the Flynn-Wall-Ozawa than Kissinger-Akahira-Sunose method. Kinetic reaction mechanisms predicted using the master-plots were f (α) = (3/2)(1 − α)2/3[1 − (1 − α)1/3]−1, f (α) = (1 − α)2, and f (α) = (1 − α)2.5 for the three sub-stages, respectively. The prominent volatiles of the WT pyrolysis were CO2 > C O > phenol > CH4 > C O > NH3 > H2O > CO. A total of 33 organic compounds were identified including alkene, acid, benzene, furan, ketone, phenol, nitride, alcohol, aldehyde, alkyl, and ester. This study provides a theoretical and practical guideline to meeting the engineering challenges of introducing WT residues in the bioenergy sector.

In a transition to a circular economy, second‐generation biomass energy has come to the forefront. The present study is aimed at characterizing biochar and byproducts of the pyrolysis of star anise residue (ANI) in the N2 and CO2 atmospheres as well as the kinetics and optimal reaction mechanisms based on the Flynn–Wall–Ozawa and Coats‐Redfern methods. The ANI pyrolysis involved three stages, with the first one (161.5–559.1°C) as the main phase. The activation energy was lower in the N2 atmosphere than in the CO2 atmosphere (179.44–190.17 kJ/mol). The primary volatile products generated during the ANI pyrolysis were small molecule products (H2O, CO2, CO, and CH4), organic acids, alcohols, and ketones. The atmosphere type exerted a minimal impact on the types of gases released, with the CO2 atmosphere increasing CO and CH4 emissions. The pyrolytic oil of ANI contained a variety of organic compounds, including alcohols, phenols, ketones, acids, sugars, and other nitrogen‐ and oxygen‐containing cyclic compounds, with its predominant compounds being acids, esters, ketones, and sugars. The elevated temperature range of 300–700°C enhanced the charring degree of the ANI biochar. The biochar showed stronger aromaticity in the CO2 atmosphere but better granularity in the N2 atmosphere. This study introduced an innovative perspective by showcasing the potential of ANI as a promising biomass source for energy generation and underscored its abundance, sustainability, and applicability as a raw material in fragrance production. It also emphasized the significance of CO2‐reuse technology as a means to mitigate CO2 emissions. The findings of this work offer a theoretical and practical basis for the comprehensive utilization and efficient disposal of star anise residues.

In a transition to a circular economy, second‐generation biomass energy has come to the forefront. The present study is aimed at characterizing biochar and byproducts of the pyrolysis of star anise residue (ANI) in the N2 and CO2 atmospheres as well as the kinetics and optimal reaction mechanisms based on the Flynn–Wall–Ozawa and Coats‐Redfern methods. The ANI pyrolysis involved three stages, with the first one (161.5–559.1°C) as the main phase. The activation energy was lower in the N2 atmosphere than in the CO2 atmosphere (179.44–190.17 kJ/mol). The primary volatile products generated during the ANI pyrolysis were small molecule products (H2O, CO2, CO, and CH4), organic acids, alcohols, and ketones. The atmosphere type exerted a minimal impact on the types of gases released, with the CO2 atmosphere increasing CO and CH4 emissions. The pyrolytic oil of ANI contained a variety of organic compounds, including alcohols, phenols, ketones, acids, sugars, and other nitrogen‐ and oxygen‐containing cyclic compounds, with its predominant compounds being acids, esters, ketones, and sugars. The elevated temperature range of 300–700°C enhanced the charring degree of the ANI biochar. The biochar showed stronger aromaticity in the CO2 atmosphere but better granularity in the N2 atmosphere. This study introduced an innovative perspective by showcasing the potential of ANI as a promising biomass source for energy generation and underscored its abundance, sustainability, and applicability as a raw material in fragrance production. It also emphasized the significance of CO2‐reuse technology as a means to mitigate CO2 emissions. The findings of this work offer a theoretical and practical basis for the comprehensive utilization and efficient disposal of star anise residues.

S and Cl distribution patterns and their evolution pathways were quantified during the co-combustions of textile dyeing sludge (TDS) and waste biochar (BC). S in the flue gas rose from 10.60% at 700 °C to 45.09% at 1000 °C for the mono-combustion of TDS in the air atmosphere. At 1000 °C, S in the bottom slag and flue gas grew by 2.65% and fell by 2.11%, respectively, for the TDS mono-combustion in the 30%O2/70%CO2 atmosphere. The 40% BC addition increased the S retention in the bottom slag by 30.39% and decreased its release to the flue gas by 34.50% by changing the evolution of CaSO4 and enabling more K to fix S as K2SO4. The decomposition of inorganic Cl was the main source of the Cl-containing gases. The 20%O2/80%CO2 atmosphere (36.29%) and 40% BC addition (27.26%) had higher Cl in the bottom slag than did TDS mono-combusted at 1000 °C (25.60%) by inhibiting the decomposition of organic Cl. Our study provides insights into the co-combustion of TDS and BC and controls on S and Cl for a cleaner production. Future research remains to conducted to verify scale-up experiments.

S and Cl distribution patterns and their evolution pathways were quantified during the co-combustions of textile dyeing sludge (TDS) and waste biochar (BC). S in the flue gas rose from 10.60% at 700 °C to 45.09% at 1000 °C for the mono-combustion of TDS in the air atmosphere. At 1000 °C, S in the bottom slag and flue gas grew by 2.65% and fell by 2.11%, respectively, for the TDS mono-combustion in the 30%O2/70%CO2 atmosphere. The 40% BC addition increased the S retention in the bottom slag by 30.39% and decreased its release to the flue gas by 34.50% by changing the evolution of CaSO4 and enabling more K to fix S as K2SO4. The decomposition of inorganic Cl was the main source of the Cl-containing gases. The 20%O2/80%CO2 atmosphere (36.29%) and 40% BC addition (27.26%) had higher Cl in the bottom slag than did TDS mono-combusted at 1000 °C (25.60%) by inhibiting the decomposition of organic Cl. Our study provides insights into the co-combustion of TDS and BC and controls on S and Cl for a cleaner production. Future research remains to conducted to verify scale-up experiments.

Abstract Flue gas-to-ash controls on sulfur (S) species of the combustion of textile dyeing sludge (TDS) are pivotal in the achievement of circular and cleaner economies. This experimental study aimed to characterize S transformations in TDS as a function of temperature (600–1000 °C) and blend ratios of spent mushroom substrate (SMS) and calcium oxide (CaO) through thermodynamic equilibrium simulations. The conversion ratio of S to flue gas from the mono-combustion of TDS rose by 29.7% between 600 and 1000 °C and was 92.9% at 1000 °C. The increasing sulfur dioxide (SO2) emission with the high temperature occurred from the decomposition of sulfates. The conversion of S to SO2 decreased significantly with an increase in SMS from 10 to 50% and enhanced the S distribution in fly ash. Potassium and phosphorous in SMS appeared to play a significant role in the conversion of S. The addition of CaO exhibited a good desulfurization performance, with the S content of ash peaking at 5.2% at 800 °C with 7% CaO. The desulfurization efficiency of CaO highly depended on the temperature and blend ratios. The addition of SMS facilitated the agglomeration to form large particles at 1000 °C and formed more micro pores on their surfaces. Our equilibrium simulations pointed to the important role of CaO-assisted co-combustion versus mono-combustion of TDS in the S retention as well as to the enhanced decomposition of calcium sulfate (CaSO4) by SMS. Chlorine had a better affinity toward potassium to promote the release of gaseous potassium chloride (KCl) which in turn appeared to react with SO2 in flue gas and formed sulfates through sulfation reaction.

Abstract Flue gas-to-ash controls on sulfur (S) species of the combustion of textile dyeing sludge (TDS) are pivotal in the achievement of circular and cleaner economies. This experimental study aimed to characterize S transformations in TDS as a function of temperature (600–1000 °C) and blend ratios of spent mushroom substrate (SMS) and calcium oxide (CaO) through thermodynamic equilibrium simulations. The conversion ratio of S to flue gas from the mono-combustion of TDS rose by 29.7% between 600 and 1000 °C and was 92.9% at 1000 °C. The increasing sulfur dioxide (SO2) emission with the high temperature occurred from the decomposition of sulfates. The conversion of S to SO2 decreased significantly with an increase in SMS from 10 to 50% and enhanced the S distribution in fly ash. Potassium and phosphorous in SMS appeared to play a significant role in the conversion of S. The addition of CaO exhibited a good desulfurization performance, with the S content of ash peaking at 5.2% at 800 °C with 7% CaO. The desulfurization efficiency of CaO highly depended on the temperature and blend ratios. The addition of SMS facilitated the agglomeration to form large particles at 1000 °C and formed more micro pores on their surfaces. Our equilibrium simulations pointed to the important role of CaO-assisted co-combustion versus mono-combustion of TDS in the S retention as well as to the enhanced decomposition of calcium sulfate (CaSO4) by SMS. Chlorine had a better affinity toward potassium to promote the release of gaseous potassium chloride (KCl) which in turn appeared to react with SO2 in flue gas and formed sulfates through sulfation reaction.

Given their non-biodegradable, space-consuming, and environmentally more benign nature, waste bicycle tires may be pyrolyzed for cleaner energies relative to the waste truck, car, and motorcycle tires. This study combined thermogravimetry (TG), TG-Fourier transform infrared spectroscopy (TG-FTIR), and pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) analyses to dynamically characterize the pyrolysis behavior, gaseous products, and reaction mechanisms of both waste rubber (RT) and polyurethane tires (PUT) of bicycles. The main devolatilization process included the decompositions of the natural, styrene-butadiene, and butadiene rubbers for RT and of urethane groups in the hard segments, polyols in the soft segments, and regenerated isocyanates for PUT. The main TG-FTIR-detected functional groups included C-H, C=C, C=O, and C-O for both waste tires, and also, N-H and C-O-C for the PUT pyrolysis. The main Py-GC/MS-detected pyrolysis products in the decreasing order were isoprene and D-limonene for RT and 4, 4'-diaminodiphenylmethane and 2-hexene for PUT. The kinetic, thermodynamic, and comprehensive pyrolysis index data verified the easier decomposition of PUT than RT. The pyrolysis mechanism models for three sub-stages of the main devolatilization process were best described by two-dimensional diffusion and two second-order models for RT, and the three consecutive reaction-order (three-halves order, first-order, and second-order) models for PUT.