Oxidative torrefaction and torrefaction-based biorefining of biomass: a critical review

Document Type : Review Paper

Authors

1 Department of Chemical and Process Engineering, University of Moratuwa, Moratuwa, 10400, Sri Lanka.

2 Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan 701, Taiwan.

3 Research Center for Smart Sustainable Circular Economy, Tunghai University, Taichung 407, Taiwan.

4 Department of Mechanical Engineering, National Chin-Yi University of Technology, Taichung 411, Taiwan.

Abstract

Torrefaction is a vital pretreatment technology for thermochemical biorefinery applications like pyrolysis, gasification, and liquefaction. Oxidative torrefaction, an economical version of torrefaction, has recently gained much attention in the renewable energy field. Recent literature on inert and oxidative torrefaction was critically reviewed in this work to provide necessary guidance for future research and commercial implementations. The critical performance parameters of torrefaction for thermochemical biorefinery applications, such as solid yield, energy yield, carbon enhancement, higher heating value (HHV) enhancement, and energy-mass co-benefit index (EMCI), were also analyzed. Agricultural waste, woody biomass, and microalgae were considered. The analysis reveals that woody biomass could equally benefit from oxidative or inert torrefaction. In contrast, inert torrefaction was found more suitable for agricultural wastes and microalgae. Using flue gas as the oxidative torrefaction medium and waste biomass as the feedstock could achieve a circular economy, improving the sustainability of oxidative torrefaction for thermochemical biorefineries. The significant challenges in oxidative torrefaction include high ash content in torrefied agricultural waste, the oxidative thermal runaway of fibrous biomass during torrefaction, temperature control, and scale-up in reactors. Some proposed solutions to address these challenges are combined washing and torrefaction pretreatment, balancing oxygen content, temperature, and residence time, depending on the biomass type, and recirculating torrefaction gases.

Graphical Abstract

Oxidative torrefaction and torrefaction-based biorefining of biomass: a critical review

Highlights

  • Torrefaction is a vital pretreatment technology for thermochemical biorefinery applications.
  • Oxidative torrefaction is an economical version of torrefaction.
  • Woody biomass equally benefits from oxidative or inert torrefaction.
  • Inert torrefaction is more suitable for agricultural wastes and microalgae.
  • Significant challenges in oxidative torrefaction are identified, and solutions are presented.

Keywords


  1. Abdulyekeen, K.A., Umar, A.A., Patah, M.F.A., Daud, W.M.A.W., 2021. Torrefaction of biomass: production of enhanced solid biofuel from municipal solid waste and other types of biomass. Renew. Sust. Energy Rev. 150, 111436.
  2. Abelha, P., Mourão Vilela, C., Nanou, P., Carbo, M., Janssen, A., Leiser, S., 2019. Combustion improvements of upgraded biomass by washing and torrefaction. Fuel. 253, 1018-1033.
  3. Acharya, B., Pradhan, R.R., Dutta, A. 2015. Qualitative and kinetic analysis of torrefaction of lignocellulosic biomass using DSC-TGA-FTIR. AIMS Energy. 3(4), 760-773.
  4. Adnan, M.A., Fuad, M.A.H.M., Hasan, M.F., 2017. Oxidative torrefaction for pulverized palm biomass using air. J. Teknol. 79(7-4).
  5. Álvarez, A., Migoya, S., Menéndez, R., Gutiérrez, G., Pizarro, C., and Bueno, J.L., 2021. Torrefaction of short rotation coppice willow. characterization, hydrophobicity assessment and kinetics of the process. Fuel. 295, 120601.
  6. Atienza-Martínez, M., Fonts, I., ábrego, J., Ceamanos, J., Gea, G., 2013. Sewage sludge torrefaction in a fluidized bed reactor. Chem. Eng. J. 222, 534-545.
  7. Bach, Q.V., Chen, W.H., Lin, S.C., Sheen, H.K., Chang, J.S., 2016. Wet torrefaction of microalga Chlorella vulgaris ESP-31 with microwave- assisted heating. Energy Convers. Manage. 141, 163-170.
  8. Balagurumurthy, B., Singh, R., Ohri, P., Prakash, A., Bhaskar, T., 2015. Chapter 6-Thermochemical biorefinery. Recent Adv. Thermochem. Convers. Biomass. 157-174.
  9. Balat, M., 2008. Mechanisms of thermochemical biomass conversion processes. Part 1: reactions of pyrolysis. Energy Sources A: Recovery Util. Environ. Eff. 620-635.
  10. Barskov, S., Zappi, M., Buchireddy, P., Dufreche, S., Guillory, J., Gang, D., Hernandez, R., Bajpai, R., Baudier, J., Cooper, R., Sharp, R., 2019. Torrefaction of biomass: a review of production methods for biocoal from cultured and waste lignocellulosic feedstocks. Renewable Energy. 142, 624-642.
  11. Boateng, A.A., Mullen, C.A., 2013. Fast pyrolysis of biomass thermally pretreated by torrefaction. J. Anal. Appl. Pyrolysis. 100, 95-102.
  12. Brachi, P., Chirone, R., Miccio, M., Ruoppolo, G., 2019. Fluidized bed torrefaction of biomass pellets: a comparison between oxidative and inert atmosphere. Powder Technol. 357, 97-107.
  13. Cahyanti, M.N., Doddapaneni, T.R.K.C., Kikas, T., 2020. Biomass torrefaction: an overview on process parameters, economic and environmental aspects and recent advancements. Technol. 301, 122737.
  14. Cen, K., Chen, D., Wang, J., Cai, Y., Wang, L., 2016. Effects of water washing and torrefaction pretreatments on corn stalk pyrolysis: combined study using TG-FTIR and a fixed bed reactor. Energy Fuels. 30(12), 10627-10634.
  15. Cheah, W.Y., Sankaran, R., Show, P.L., Ibrahim, T.N.B.T., Chew, K.W., Culaba, A., Jo-Shu, C., 2020. Pretreatment methods for lignocellulosic biofuels production: Current advances, challenges and future prospects. Biofuel Res. J. 7(1), 1115-1127.
  16. Chen, W.H., Lu, K.M., Liu, S.H., Tsai, C.M., Lee, W.J., Lin, T.C., 2013. Biomass torrefaction characteristics in inert and oxidative atmospheres at various superficial velocities. Bioresour. Technol. 146, 152-160.
  17. Chen, W.H., Lu, K.M., Lee, W.J., Liu, S.H., Lin, T.C., 2014a. Non-oxidative and oxidative torrefaction characterization and SEM observations of fibrous and ligneous biomass. Appl. Energy. 114, 104-113.
  18. Chen, Y., Liu, B., Yang, H., Yang, Q., Chen, H., 2014b. Evolution of functional groups and pore structure during cotton and corn stalks torrefaction and its correlation with hydrophobicity. Fuel. 137, 41-49.
  19. Chen, W.H., Peng, J., Bi, X.T., 2015. A state-of-the-art review of biomass torrefaction, densi fi cation and applications. Renew. Sust. Energy Rev. 44, 847-866.
  20. Chen, W.H., Zhuang, Y.Q., Liu, S.H., Juang, T.T., Tsai, C.M., 2016a. Product characteristics from the torrefaction of oil palm fiber pellets in inert and oxidative atmospheres. Bioresour. Technol. 199, 367-374.
  21. Chen, Y., Cao, W., Atreya, A., 2016b. An experimental study to investigate the effect of torrefaction temperature and time on pyrolysis of centimeter-scale pine wood particles. Fuel Technol. 153, 74-80.
  22. Chen, D., Cen, K., Jing, X., Gao, J., Li, C., Ma, Z., 2017. An approach for upgrading biomass and pyrolysis product quality using a combination of aqueous phase bio-oil washing and torrefaction pretreatment. Bioresour. Technol. 233, 150-158.
  23. Chen, Z., Wang, M., Jiang, E., Wang, D., Zhang, K., Ren, Y., Jiang, Y., 2018. Pyrolysis of Torrefied Biomass. Trends Biotechnol. 36(12), 1287-1298.
  24. Chen, D., Chen, F., Cen, K., Cao, X., Zhang, J., Zhou, J., 2020. Upgrading rice husk via oxidative torrefaction: characterization of solid, liquid, gaseous products and a comparison with non-oxidative torrefaction. Fuel. 275, 117936.
  25. Chen, W.H., Lin, B.J., Lin, Y.Y., Chu, Y.S., Ubando, A.T., Show, P.L., Ong, H.C., Chang, J.S., Ho, S.H., Culaba, A.B., Pétrissans, A., Pétrissans, M., 2021. Progress in biomass torrefaction: principles , applications and challenges. Prog. Energy Combust. Sci. 82, 100887.
  26. Cheng, W., Zhu, Y., Zhang, W., Jiang, H., Hu, J., Zhang, X., Yang, H., Chen, H., 2022. Effect of oxidative torrefaction on particulate matter emission from agricultural biomass pellet combustion in comparison with non-oxidative torrefaction. Renewable Energy. 189, 39-51.
  27. Clausen, L.R., 2014. Integrated torrefaction vs. external torrefaction-a thermodynamic analysis for the case of a thermochemical biorefinery. Energy. 77, 597-607.
  28. Conag, A.T., Villahermosa, J.E.R., Cabatingan, L.K., Go, A.W., 2017. Energy densification of sugarcane bagasse through torrefaction under minimized oxidative atmosphere. J. Environ. Chem. Eng. 5(6), 5411-5419.
  29. Conag, A.T., Villahermosa, J.E.R., Cabatingan, L.K., Go, A.W., 2018. Energy densification of sugarcane leaves through torrefaction under minimized oxidative atmosphere. Energy Sust. Dev. 42, 160-169.
  30. Cremers, M., Koppejan, J., Sokhansanj, S., Melin, S., Madrali, S., 2015. Status overview of torrefaction technologies. IEA Bioenergy. 32, 1-54.
  31. Dai, L., Wang, Y., Liu, Y., Ruan, R., He, C., Yu, Z., Jiang, L., Zeng, Z., Tian, X., 2019. Integrated process of lignocellulosic biomass torrefaction and pyrolysis for upgrading bio-oil production: a state-of-the-art review. Renew. Sust. Energy Rev. 107, 20-36.
  32. Deng, L., Zhang, T., Che, D., 2013. Effect of water washing on fuel properties , pyrolysis and combustion characteristics , and ash fusibility of biomass. Fuel Process. Technol. 106, 712-720.
  33. Dhungana, A., Basu, P., Dutta, A., 2012. Effects of reactor design on the torrefaction of biomass. J. Energy Resour. Technol. 134(4), 1-11.
  34. Dong, Q., Zhang, S., Ding, K., Zhu, S., Zhang, H., Liu, X., 2018. Pyrolysis behavior of raw/torrefied rice straw after different demineralization processes. Biomass Bioenergy. 119, 229-236.
  35. Eseyin, A.E., Steele, P.H., Pittman, C.U., Ekpenyong, K.I., Soni, B., 2016. TGA Torrefaction Kinetics of Cedar Wood. J. Biofuels. 7(1), 20-27.
  36. Foust, T.D., Aden, A., Dutta, A., Phillips, S., 2009. An economic and environmental comparison of a biochemical and a thermochemical lignocellulosic ethanol conversion processes. Cellulose. 16(4), 547-565.
  37. Gronnow, M.J., Budarin, V.L., Mašek, O., Crombie, K.N., Brownsort, P.A., Shuttleworth, P.S., Hurst, P.R., Clark, J.H., 2013. Torrefaction/biochar production by microwave and conventional slow pyrolysis-comparison of energy properties. Gcb Bioenergy. 5(2), 144-152.
  38. Hisham, S.M., Uemura, Y., Tazli, A.M., 2016. Effects of temperature and concentration of Oxygen on torrefaction of empty fruit bunches. J. Jpn. Inst. Energy. 95(12), 1110-1114.
  39. Hu, J., Song, Y., Liu, J., Evrendilek, F., Buyukada, M., Yan, Y., Li, L., 2020. Combustions of torrefaction-pretreated bamboo forest residues: physicochemical properties, evolved gases, and kinetic mechanisms. Bioresour. Technol. 304, 122960.
  40. Joshi, Y., Di Marcello, M., Krishnamurthy, E., De Jong, W., 2015. Packed-bed torrefaction of bagasse under inert and oxygenated atmospheres. Energy Fuels. 29(8), 5078-5087.
  41. Kung, K.S., Thengane, S.K., Shanbhogue, S., Ghoniem, A.F., 2019. Parametric analysis of torrefaction reactor operating under oxygen-lean conditions. Energy. 181, 603-614.
  42. Lasek, J.A., Kopczyński, M., Janusz, M., Iluk, A., Zuwała, J., 2017. Combustion properties of torrefied biomass obtained from flue gas-enhanced reactor. Energy. 119, 362-368.
  43. Li, M.F., Shen, Y., Sun, J.K., Bian, J., Chen, C.Z., Sun, R.C., 2015. Wet torrefaction of bamboo in hydrochloric acid solution by microwave heating.  ACS Sust. Chem. Eng. 3(9), 2022-2029.
  44. Li, S.X., Chen, C.Z., Li, M.F., Xiao, X., 2018. Torrefaction of corncob to produce charcoal under nitrogen and carbon dioxide atmospheres. Bioresour. Technol. 249, 348-353.
  45. Li, X., Lu, Z., Chen, J., Chen, X., Jiang, Y., Jian, J., Yao, S., 2021. Effect of oxidative torrefaction on high temperature combustion process of wood sphere. Fuel. 286, 119379.
  46. Liu, Y., Rokni, E., Yang, R., Ren, X., Sun, R., Levendis, Y.A., 2021. Torrefaction of corn straw in oxygen and carbon dioxide containing gases: mass/energy yields and evolution of gaseous species. Fuel. 285, 119044.
  47. Lu, H., Gong, Y., Areeprasert, C., Ding, L., Guo, Q., Chen, W.H., Yu, G., 2021. Integration of biomass torrefaction and gasification based on biomass classification: a review. Energy Technol. 9(5), 2001108.
  48. Lu, K.M., Lee, W.J., Chen, W.H., Liu, S.H., Lin, T.C., 2012. Torrefaction and low temperature carbonization of oil palm fiber and eucalyptus in nitrogen and air atmospheres. Bioresour. Technol. 123, 98-105.
  49. Mamvura, T.A., Danha, G., 2020. Biomass torrefaction as an emerging technology to aid in energy production. Heliyon. 6(3), e03531.
  50. Mei, Y., Liu, R., Yang, Q., Yang, H., Shao, J., Draper, C., Zhang, S., Chen, H., 2015. Torrefaction of cedarwood in a pilot scale rotary kiln and the influence of industrial flue gas. Bioresour. Technol. 177, 355-360.
  51. Nachenius, R.W., Ronsse, F., Venderbosch, R.H., Prins, W., 2013. Biomass pyrolysis. Adv. Chem. Eng. Academic Press. 42, 75-139.
  52. Nhuchhen, D.R., Basu, P., Acharya, B., 2014. A comprehensive review on biomass torrefaction. Int. J. Renewable Energy Biofuels. 2014, 1-56.
  53. Nhuchhen, D.R., Basu, P., 2014. Experimental investigation of mildly pressurized torrefaction in air and nitrogen. Energy Fuels. 28(5), 3110-3121.
  54. Niu, Y., Lv, Y., Lei, Y., Liu, S., Liang, Y., Wang, D., Hui, S., 2019. Biomass torrefaction: properties, applications, challenges, and economy. Renew. Sust. Energy Rev. 115, 109395.
  55. Ong, H.C., Yu, K.L., Chen, W.H., Pillejera, M.K., Bi,X., Tran, K.Q., Pétrissans, A., Pétrissans, M., 2021. Variation of lignocellulosic biomass structure from torrefaction: a critical review. Renew. Sust. Energy Rev. 152, 111698.
  56. Onsree, T., Tippayawong, N., Williams, T., McCullough, K., Barrow, E., Pogaku, R., Lauterbach, J., 2019. Torrefaction of pelletized corn residues with wet flue gas. Bioresour. Technol. 285, 121330.
  57. Pang, S., 2019. Advances in thermochemical conversion of woody biomass to energy, fuels and chemicals. Biotechnol. Adv. 37(4), 589-597.
  58. Perera, S.M., Wickramasinghe, C., Samarasiri, B.K.T., Narayana, M., 2021. Modeling of thermochemical conversion of waste biomass-a comprehensive review. Biofuel Res. J. 8(4), 1481-1528.
  59. Pillejera, M.K.V., Chen, W.H., De Luna, M.D.G., 2017. Bamboo torrefaction in a high gravity (Higee) environment using a rotating packed bed. ACS Sust. Chem. Eng. 5(8), 7052-7062.
  60. Ramos-Carmona, S., Martínez, J.D., Pérez, J.F., 2018. Torrefaction of patula pine under air conditions: a chemical and structural characterization. Ind. Crops Prod. 118, 302-310.
  61. Ribeiro, J.M.C., Godina, R., Matias, J.C.D.O., Nunes, L.J.R., 2018. Future perspectives of biomass torrefaction: review of the current state-of-the-art and research development. Sustainability. 10(7), 2323.
  62. Rodionova, M.V., Bozieva, A.M., Zharmukhamedov, S.K., Leong, Y.K., Chi-Wei Lan, J., Veziroglu, A., Veziroglu, T.N., Tomo, T., Chang, J.S., Allakhverdiev, S.I., 2021. A comprehensive review on lignocellulosic biomass biorefinery for sustainable biofuel production. Int. J. Hydrogen Energy. 47(3), 1481-1498.
  63. Rousset, P., Macedo, L., Commandré, J.M., Moreira, A., 2012. Biomass torrefaction under different oxygen concentrations and its effect on the composition of the solid by-product. J. Anal. Appl. Pyrolysis. 96, 86-91.
  64. Sarvaramini, A., Larachi, F., 2014. Integrated biomass torrefaction-Chemical looping combustion as a method to recover torrefaction volatiles energy. Fuel. 116, 158-167.
  65. Sellappah, V., Uemura, Y., Hassan, S., Sulaiman, MH., Lam, M.K., 2016. Torrefaction of empty fruit bunch in the presence of combustion gas. Procedia Eng. 148, 750-757.
  66. Seo, M.W., Lee, S.H., Nam, H., Lee, D., Tokmurzin, D., Wang, S., Park, Y.K., 2022. Recent advances of thermochemical conversieon processes for biorefinery. Bioresour. Technol. 343, 126109.
  67. Shoulaifar, T.K., 2016. Chemical changes in biomass during Torrefaction. PhD Dissertation, Åbo Akademi University.
  68. So, C.L., Eberhardt, T.L., 2018. FTIR-based models for assessment of mass yield and biofuel properties of torrefied wood. Wood Sci. Technol. 52(1), 209-227.
  69. Su, Y., Zhang, S., Liu, L., Xu, D., Xiong, Y., 2018. Investigation of representative components of flue gas used as torrefaction pretreatment atmosphere and its effects on fast pyrolysis behaviors. Bioresour. Technol. 267, 584-590.
  70. Sui, P., Sokhansanj, S., Bi, X.T., Lim, C.J., Larsson, S.H., 2012. Drying characteristics and equilibrium moisture content of steam-treated Douglas fir (Pseudotsuga menziesii). Bioresour. Technol. 116, 396-402.
  71. Sulaiman, M.H., Uemura, Y., Azizan, M.T., Iskandar, B.S., 2015. Effect of torrefaction condition the mass yield, elementary composition and calorific value of empty fruit bunches (EFB). Aust. J. Basic Appl. Sci. 9(37), 300-303.
  72. Tan, M., Li, H., Huang, Z., Wang, Z., Xiong, R., Jiang, S., Zhang, J., Wu, Z., Li, C., Luo, L., 2021. Comparison of atmospheric and gas-pressurized oxidative torrefaction of heavy-metal-polluted rice straw. J. Clean Prod. 283, 124636.
  73. Tanyaket, T., Onsree, T., Tippayawong, N., Baratieri, M., 2020. Effect of oxidative torrefaction on characteristics of treated corncob pellets. J. Mech. Eng.. 41(1), 65-73.
  74. Thanapal, S.S., Chen, W., Annamalai, K., Carlin, N., Ansley, R.J., Ranjan, D., 2014. Carbon dioxide torrefaction of woody biomass. Energy Fuels. 28(2), 1147-1157.
  75. Tran, K.Q., Klemsdal, A.J., Zhang, W., Sandquist, J., Wang, L., Skreiberg, Ø., 2017. Fast hydrothermal liquefaction of native and torrefied wood. Energy Procedia. 105, 218-223.
  76. Tran, K.Q., Trinh, T.N., Bach, Q.V., 2016. Development of a biomass torrefaction process integrated with oxy-fuel combustion. Bioresour. Technol. 199, 408-413.
  77. Tumuluru, J.S., Sokhansanj, S., Hess, J.R., Wright, C.T., Boardman, R.D., 2011. A review on biomass torrefaction process and product properties for energy applications. Ind. Biotechnol. 7(5) 384-401.
  78. Tumuluru, J.S., Ghiasi, B., Soelberg, N.R., Sokhansanj, S., 2021. Biomass torrefaction process, product properties, reactor types, and moving bed reactor design concepts. Front Energy Res. 462.
  79. Tursi, A., 2019. A review on biomass: importance, chemistry, classification, and conversion. Biofuel Res. J. 6(2), 962-979.
  80. Uemura, Y., Omar, W., Othman, N.A., Yusup, S., Tsutsui, T., 2013. Torrefaction of oil palm EFB in the presence of oxygen. Fuel. 103, 156-160.
  81. Uemura, Y., Saadon, S., Osman, N., Mansor, N., Tanoue, K.I., 2015. Torrefaction of oil palm kernel shell in the presence of oxygen and carbon dioxide. Fuel. 144, 171-179.
  82. Uemura, Y., Sellappah, V., Trinh, T.H., Komiyama, M., Hassan, S., Tanoue, K., 2018. Improvement of energy density and energy yield of oil palm biomass by torrefaction in combustion gas. IOP Conf. Ser.: Mater. Sci. Eng. 458(1), 012061.
  83. van der Stelt, M.J.C., 2011. Chemistry and reaction kinetics of biowaste torrefaction. Technische Universiteit Eindhoven, Eindhoven.
  84. Wang, C., Peng, J., Li, H., Bi, X.T., Legros, R., Lim, C. J., Sokhansanj, S., 2013. Oxidative torrefaction of biomass residues and densification of torrefied sawdust to pellets. Bioresour. Technol. 127, 318-325.
  85. Wang, Z., Li, H., Lim, C.J., Grace, J.R., 2018. Oxidative torrefaction of spruce-pine-fir sawdust in a slot-rectangular spouted bed reactor. Energy Convers. Manage. 174, 276-287.
  86. Wang, Z., Lim, C.J., Grace, J. R., 2019. A comprehensive study of sawdust torrefaction in a dual-compartment slot-rectangular spouted bed reactor. Energy. 189, 116306.
  87. Yang, H., Yan, R., Chen, H., Lee, D.H., Zheng, C., 2007. Characteristics of hemicellulose, cellulose and lignin pyrolysis. Fuel. 86(12-13), 1781-1788.
  88. Zhang, S., Dong, Q., Chen, T., Xiong, Y., 2016. Combination of light bio-oil washing and torrefaction pretreatment of rice husk: its effects on physicochemical characteristics and fast pyrolysis behavior. Energy 30(4), 3030-3037.
  89. Zhang, S., Su, Y., Xu, D., Zhu, S., Zhang, H., Liu, X., 2018a. Effects of torrefaction and organic-acid leaching pretreatment on the pyrolysis behavior of rice husk. Energy. 149, 804-813.
  90. Zhang, C., Ho, S.H., Chen, W.H., Xie, Y., Liu, Z., Chang, J.S., 2018b. Torrefaction performance and energy usage of biomass wastes and their correlations with torrefaction severity index. Appl. Energy. 220, 598-604.
  91. Zhang, C., Wang, C., Cao, G., Chen, W.H., Ho, S.H., 2019a. Comparison and characterization of property variation of microalgal biomass with non-oxidative and oxidative torrefaction. Fuel. 246, 375-385.
  92. Zhang, C., Ho, S.H., Chen, W.H., Fu, Y., Chang, J.S., Bi, X., 2019b. Oxidative torrefaction of biomass nutshells: evaluations of energy efficiency as well as biochar transportation and storage. Appl. Energy. 235, 428-441.
  93. Zhang, S., Zhu, S., Zhang, H., Liu, X., Zhang, H., 2019c. Evaluation of pyrolysis behavior and products properties of rice husk after combined pretreatment of washing and torrefaction. Biomass Bioenergy. 127, 105293.
  94. Zhang, C., Ho, S.H., Chen, W.H., Wang, R., 2021a. Comparative indexes, fuel characterization and thermogravimetric-Fourier transform infrared spectrometer-mass spectrogram (TG-FTIR-MS) analysis of microalga Nannochloropsis Oceanica under oxidative and inert torrefaction. Energy. 230, 120824.
  95. Zhang, C., Ho, S.H., Chen, W.H., Wang, R., Show, P.L., Ong, H.C., 2021b. Oxidative torrefaction performance of microalga Nannochloropsis Oceanica towards an upgraded microalgal solid biofuel. J. Biotechnol. 338, 81-90.
  96. Zhang, L., Wang, Z., Ma, J., Kong, W., Yuan, P., Sun, R., Shen, B., 2021c. Analysis of functionality distribution and microstructural characteristics of upgraded rice husk after undergoing non-oxidative and oxidative torrefaction. Fuel. 310, 122477.
  97. Zhang, C., Li, F., Ho, S., Chen, W., Sandamali, D., Loke, P., 2022. Oxidative torrefaction of microalga Nannochloropsis Oceanica activated by potassium carbonate for solid biofuel production. Environ. Res. 212, 113389.
  98. Zhu, X., Zhou, S., Zhang, Z., Zhang, Y., Li, J., Ahmed, S., Yan, B., Chen, G., Li, N. 2021. Flue gas torrefaction of distilled spirit lees and the effects on the combustion and nitrogen oxide emission. Bioresour. Technol. 342, 125975.