The Pelletizability of Tea Waste and the Effect of Moisture Content and Pellet Diameter on Pellet Properties

Year 2025, Volume: 9 Issue: 2, 142 - 155, 30.12.2025

Mehmet Akif Tanriverdi , Bahadır Demirel , Osman Mert Yaz

Abstract

In this study, the pelletability of tea waste, a by product of tea factories, was investigated, along with the effects of different moisture contents and pellet diameters on the physical and mechanical properties of the resulting pellets. The experiments were conducted using two different moisture levels (8–9% and 11–12%) and three different pellet diameters (6, 8, and 10 mm). The findings revealed that moisture content is one of the most important parameters determining pellet quality. Pellets produced at higher moisture content (11–12%) exhibited significantly better performance in terms of mechanical strength, impact resistance, and fracture resistance under pressure compared to pellets with lower moisture content. Under low moisture conditions, pellets became more brittle, and strength losses were particularly pronounced in larger pellets. When evaluating the effects of pellet diameter, it was determined that as the diameter decreased, the mechanical integrity and strength properties of the pellets increased. Pellets with a diameter of 6 mm yielded the highest quality values, while pellets with a diameter of 10 mm exhibited weaker properties, especially under low humidity conditions. It has been confirmed that moisture content and pellet diameter have significant effects on all parameters defining pellet quality. Correlation and PCA results showed that properties such as mechanical strength, impact resistance, compressive strength, and density changed together and that high moisture–small diameter combinations were associated with higher quality pellets. It can be stated that tea waste can be converted into a high-quality pellet fuel without the use of any binder under suitable conditions, and that a moisture content of 10–12% and a diameter range of 6–8 mm are particularly favorable for tea waste pellet production. These findings point to significant potential for the energy-based utilization of tea waste in regions with intensive tea production.

Keywords

Biomass energy , Moisture content , Pellet diameter , Pelletization , Tea waste

References

• Bajwa, D. S., Peterson, T., Sharma, N., Shojaeiarani, J., & Bajwa, S. G. (2018). A review of densified solid biomass for energy production. Renewable and Sustainable Energy Reviews, 96, 296-305. https://doi.org/10.1016/j.rser.2018.07.040
• Bilgin, S., Koçer, A., Yılmaz, H., Acar, M., & Dok, M. (2016). Çay fabrikası atıklarınının peletlenmesi ve pelet fiziksel özelliklerinin belirlenmesi. Journal of Agricultural Faculty of Gaziosmanpaşa University (JAFAG), 33 (Ek sayı), 70-80.
• Cutz, L., Tiringer, U., Gilvari, H., Schott, D., Mol, A., & de Jong, W. (2021). Microstructural degradation during the storage of biomass pellets. Communications Materials, 2 (1), 2. https://doi.org/10.1038/s43246-020-00113-y
• Demirel, B. (2023). Determination of solid biofuel properties of hazelnut husk briquettes obtained at different compaction pressures. Biomass Conversion and Biorefinery, 13 (14), 13267-13278. https://doi.org/10.1007/s13399-023-04431-2
• Demirel, B., & Gürdil, G. (2022). Physical-Mechanical Parameters of Hazelnut Husk Bio-Briquettes Produced by a Horizontal Pressing Briquetting Machine. Black Sea Journal of Agriculture, 5 (4), 476-480. https://doi.org/10.47115/bsagriculture.1169764
• Demirel, C., Gürdil, G. A. K., Kabutey, A., & Herak, D. (2020). Effects of forces, particle sizes, and moisture contents on mechanical behaviour of densified briquettes from ground sunflower stalks and hazelnut husks. Energies, 13 (10), 2542. https://doi.org/10.3390/en13102542
• Dok M (2014). Karadeniz Bölgesinin tarımsal atıkpotansiyeli ve bunlardan pelet yakıt olarak yararlanılması. 4th National Workshop on Energy Agriculture and Biofuels, May 28–29, 2014, s. 211-222, Samsun.
• EN 14961-2:2011, Solid biofuels — Fuel specifications and classes — Part 2: Wood pellets.
• Filbakk, T., Skjevrak, G., Høibø, O., Dibdiakova, J., & Jirjis, R. (2011). The influence of storage and drying methods for Scots pine raw material on mechanical pellet properties and production parameters. Fuel Processing Technology, 92 (5), 871-878. https://doi.org/10.1016/j.fuproc.2010.12.001
• Gürdil, G. (2020). Environmental impact of bio-briquettes produced from agricultural residues concerning to CO2 emissions. Mustafa Kemal Üniversitesi Tarım Bilimleri Dergisi, 25 (2), 217-224. https://doi.org/10.37908/mkutbd.735750
• He, H., Wang, Y., Sun, Y., Sun, W., & Wu, K. (2024). From raw material powder to solid fuel pellet: A state-of-the-art review of biomass densification. Biomass and Bioenergy, 186, 107271. https://doi.org/10.1016/j.biombioe.2024.107271
• Kaliyan, N., & Morey, R. V. (2009). Factors affecting strength and durability of densified biomass products. Biomass and bioenergy, 33 (3), 337-359. https://doi.org/10.1016/j.biombioe.2008.08.005
• Kuranc, A., Stoma, M., Rydzak, L., & Pilipiuk, M. (2020). Durability Assessment of wooden pellets in relation with vibrations occurring in a logistic process of the final product. Energies, 13 (22), 5890. https://doi.org/10.3390/en13225890
• Li, W., Wang, M., Meng, F., Zhang, Y., & Zhang, B. (2022). A review on the effects of pretreatment and process parameters on properties of pellets. Energies, 15 (19), 7303. https://doi.org/10.3390/en15197303
• Lunguleasa, A., Olarescu, A., & Spirchez, C. (2024). Pellets obtained from the husks of sunflower seeds and beech sawdust for comparison. Forests, 15(6), 902. https://doi.org/10.3390/f15060902
• Mignogna, D., Szabó, M., Ceci, P., & Avino, P. (2024). Biomass Energy and Biofuels: Perspective, Potentials, and Challenges in the Energy Transition. Sustainability, 16 (16), 7036. https://doi.org/10.3390/su16167036
• Miranda, T., Montero, I., Sepúlveda, F. J., Arranz, J. I., Rojas, C. V., & Nogales, S. (2015). A review of pellets from different sources. Materials, 8 (4), 1413-1427. https://doi.org/10.3390/ma8041413
• Mortadha, H., Kerrouchi, H. B., Al-Othman, A., & Tawalbeh, M. (2025). A comprehensive review of biomass pellets and their role in sustainable energy: production, properties, environment, economics, and logistics. Waste and Biomass Valorization, 16 (9), 4507-4539. https://doi.org/10.1007/s12649-024-02873-x
• Mostafa, M. E., Hu, S., Wang, Y., Su, S., Hu, X., Elsayed, S. A., & Xiang, J. (2019). The significance of pelletization operating conditions: An analysis of physical and mechanical characteristics as well as energy consumption of biomass pellets. Renewable and Sustainable Energy Reviews, 105, 332-348. https://doi.org/10.1016/j.rser.2019.01.053
• Picchio, R., Latterini, F., Venanzi, R., Stefanoni, W., Suardi, A., Tocci, D., & Pari, L. (2020). Pellet production from woody and non-woody feedstocks: A review on biomass quality evaluation. Energies, 13 (11), 2937. https://doi.org/10.3390/en13112937
• Ribeiro, G. F., & Junior, A. B. (2023). The global energy matrix and use of agricultural residues for bioenergy production: A review with inspiring insights that aim to contribute to deliver solutions for society and industrial sectors through suggestions for future research. Waste Management & Research, 41 (8), 1283-1304. https://doi.org/10.1177/0734242X231154149
• Rupasinghe, R. L., Perera, P., Bandara, R., Amarasekera, H., & Vlosky, R. (2023). Insights into properties of biomass energy pellets made from mixtures of woody and non-woody biomass: a meta-analysis. Energies, 17 (1), 54. https://doi.org/10.3390/en17010054
• Sarker, T. R., Nanda, S., Meda, V., & Dalai, A. K. (2023). Densification of waste biomass for manufacturing solid biofuel pellets: a review. Environmental Chemistry Letters, 21 (1), 231-264. https://doi.org/10.1007/s10311-022-01510-0
• Serrano, C., Monedero, E., Lapuerta, M., & Portero, H. (2011). Effect of moisture content, particle size and pine addition on quality parameters of barley straw pellets. Fuel Processing Technology, 92(3), 699-706. https://doi.org/10.1016/j.fuproc.2010.11.031
• Stelte, W., Sanadi, A. R., Shang, L., Holm, J. K., Ahrenfeldt, J., & Henriksen, U. B. (2012). Recent developments in biomass pelletization-a review. BioResources, 7 (3), 4451-4490. https://doi.org/10.15376/biores.7.3.stelte
• Svensson, A., Almarstrand, M., Axelsson, J., Nilsson, M., Timmermann, E., & Govindarajan, V. (2024). Valorising Agricultural Residues into Pellets in a Sustainable Circular Bioeconomy. Problemy Ekorozwoju, 19 (2). https://doi.org/10.35784/preko.5808
• Temmerman, M., Rabier, F., Jensen, P. D., Hartmann, H., & Böhm, T. (2006). Comparative study of durability test methods for pellets and briquettes. Biomass and Bioenergy, 30 (11), 964-972. https://doi.org/10.1016/j.biombioe.2006.06.008
• Thanphrom, S., Hunt, A. J., Macquarrie, D. J., & Ngernyen, Y. (2022). Valorization of green tea waste from ready-to-drink industry through pelletization and use as solid fuel. Asia-Pacific Journal of Science and Technology. https://doi.org/10.14456/apst.2022.18
• Tumuluru, J. S. (2018). Effect of pellet die diameter on density and durability of pellets made from high moisture woody and herbaceous biomass. Carbon Resources Conversion, 1 (1), 44-54. https://doi.org/10.1016/j.crcon.2018.06.002
• Ungureanu, N., Vladut, V., Voicu, G., Dinca, M. N., & Zabava, B. S. (2018). Influence of biomass moisture content on pellet properties–review. Engineering for Rural Development, 17, 1876-1883. https://doi.org/10.22616/ERDev2018.17.N449
• Yaz, M. (2023). Adhesive wear behavior of FeB–FeMn–C coatings produced by GTAW. Materials Testing, 65 (8), 1190-1201. https://doi.org/10.1515/mt-2023-0164
• Yaz, M. (2024). Adhesive wear behavior and microstructure of FeCr–FeMn–FeB–C coatings. Materials Testing, 66 (1), 75-87. https://doi.org/10.1515/mt-2023-0347
• Yıldız, Z., & Topkoç, E. (2023). Tarımsal atıklardan elde edilen biyopeletlerin bazı yakıt özelliklerinin uluslararası pelet standartları ile karşılaştırılması. Artvin Çoruh Üniversitesi Orman Fakültesi Dergisi, 24 (2), 1-9. https://doi.org/10.17474/artvinofd.1231448
• Yılmaz, H. (2018). Mısır saplarının peletlenmesi ve pelet özelliklerinin belirlenmesi. Mediterranean Agricultural Sciences, 31 (3), 269-274. https://doi.org/10.29136/mediterranean.427730