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Toscano, G.; Maceratesi, V. Valorising Agricultural Residues through Pelletisation. Encyclopedia. Available online: https://encyclopedia.pub/entry/19390 (accessed on 18 May 2024).
Toscano G, Maceratesi V. Valorising Agricultural Residues through Pelletisation. Encyclopedia. Available at: https://encyclopedia.pub/entry/19390. Accessed May 18, 2024.
Toscano, Giuseppe, Vittorio Maceratesi. "Valorising Agricultural Residues through Pelletisation" Encyclopedia, https://encyclopedia.pub/entry/19390 (accessed May 18, 2024).
Toscano, G., & Maceratesi, V. (2022, February 12). Valorising Agricultural Residues through Pelletisation. In Encyclopedia. https://encyclopedia.pub/entry/19390
Toscano, Giuseppe and Vittorio Maceratesi. "Valorising Agricultural Residues through Pelletisation." Encyclopedia. Web. 12 February, 2022.
Valorising Agricultural Residues through Pelletisation
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This entry is adapted from the peer-reviewed paper 10.3390/pr10020232

The agricultural sector and its related production chains are good sources of residual biomass. The pelletisation represents an effective alternative in order to valorise these agricultural wastes. Statistics show that over 60% of the available tree pruning comes from vine and olive cultivations, justifying several authors’ interest in the energetic valorisation of this biomass material. Pelletisation increases bulk, energy density and energy content, making this fuel close to traditional fuels such as coal.

pelletisation solid biofuel agripellet agricultural residues durability ash

1. Introduction

The agricultural sector and its related production chains are sources of a high amount of residual biomass, representing a significant feedstock for the bioenergy sector and potentially for the bio-based industry. The Italian agency ENEA estimated a yearly availability (excluding the zootechnical sector) of around 25 Mt dry matter (d.m.) of residual biomass from agriculture and forestry, corresponding to about 10 million tons of equivalent (Mtoe) thermal energy [1]. More than 5 Mt are constituted of tree prunings. Statistics show that over 60% of the available tree pruning comes from vine and olive cultivations, justifying several authors’ interest in the energetic valorisation of this biomass material [2][3][4][5][6][7].
Vineyard pruning residues are spread over 3.2 million hectares in Europe and 725,000 hectares in Italy [8], producing about 2.67 Mt/year, while olive prunings are about 2.3 Mt/year [9]. Vineyard pruning residues could partly replace traditional wood assortments for energy and industrial use [10]. 
Pelletisation is the most efficient process for increasing bulk and energy densities of residual biomass. To produce pellets, the biomass is pressed mechanically to compress the wood’s cell structure and make it denser. Thus, the energy density increases considerably, the moisture content decreases, and transport and storage costs are reduced [11][12][13]. Pellets are more homogeneous in size and structure than the raw biomass, an advantage that facilitates automated feeding in continuous boiler systems [14]. The low moisture content of about 8 to 11%, and the energy content of approximately up to 20 MJ/kg, allows them to burn with very high efficiency and makes this fuel close to traditional fuels such as coal [15].

Pelletisation can solve the problem of vineyard operators, who need to discard their residual material and often decide to burn it on fields causing environmental pollution. Finding some use for vineyard pruning residues would allow converting a disposal problem into a collateral production, with a potential for revenues or reduced management cost. Pruning residue harvesters have been developed to effectively recover vineyard pruning residues and make them available to the markets [16].

Pelletisation also improves other characteristics apart from bulk density. Pellets have high homogeneity, low moisture content, high energy density, and easy to handle, qualities essential for logistics and efficient use [17][18]. However, there are limited studies on the physical properties of pellet production from different orchard residues [19]. A. García-Maraver et al. tried to improve the quality of pellets from woody agricultural residues and their application in the domestic and industrial sectors, especially one of the most common woody residues in southern Spain (i.e., olive tree residues) [20]. Michela Zanetti et al. investigated the possibility of using vineyard pruning residues to produce type B pellets for non-industrial use as defined by the in-force international ISO standard. Some comparisons have been made with the requirements of the standard EN ISO 17225- 6:2014 for non-woody pellets (ISO, 2014c) [21].

This entry evaluated the pelletisation process of olive and vineyard prunings, pure or blended with variable quantities of spruce wood and the suitability of these biomass materials in agglomeration by extrusion. The pelletisation system chosen is in line with production at the farm scale. This activity is a further step to the practical application of this production chain, giving valuable indications to the involved stakeholders.

2. Current Insights

Considering the results thus generated, the choice to use olive and vineyard pruning residues to produce agripellets in small production systems represents a possible solution both for qualitative and technical aspects.
Agripellets produced from correctly harvested, and managed pruning residues can fulfill the limits of the UNI/TS 11773. The agripellets from olive pruning, in particular, are comparable to the standard quality reference in ISO 17225-2. Only the sample S0O100 slightly exceeded in the ash content (A), at 3.1% against 3.0% of the standard. This is probably linked to the low share of bark in olive pruning residues due to larger diameters if compared with vineyard prunings.
Although the pelletisation tests can return specific (e.g., pellet machine, die, roll speed) and not absolute results, they can also give a general indication of the suitability of pruning residues to be successfully pelletised. The blends richer in pruning residues showed higher D, up to 96.9 in the case of S20V80, probably due to a favorable physical–chemical composition. This value increases up to 98.3 for 100% vineyard pellets. According to the scientific literature, bulk density, holocellulose, lignin contents, and extractives are only some factors that can play a role in pellet formation and affect D [22]. The higher cohesion of agripellets produced with pruning residues was also demonstrated by the higher L of pellets exiting the die. In brief, some factors related to pruning residues facilitate the particles’ cohesion (positive correlation D vs. L), limiting the physical disaggregation (negative correlation D vs. F). A highly cohesive pellet is more resistant to mechanical stress and generates less fines [23]. The possibility of producing more integrated and homogeneous (same L) pellets during pelletisation can improve logistical aspects. 
If available at a low cost, the addition of spruce sawdust or another suitable forestry wood species can represent a solution to enhance pellet quality, improving some parameters.
The production of agripellets with added quantities of wood sawdust can potentially enhance this raw material when it comes from small companies that process wood and who do not have sufficient quantities to justify the autonomous production of pellets.

The results thus generated reveal that a higher percentage of spruce sawdust could require a greater compression at die level to reach high D. This would be linked to higher energy consumption with related economic and environmental costs. However, this is only an indication because the behavior of the tested typologies of pruning residue results are slightly different in terms of specific energy consumption.

3. Conclusions

When correctly harvested and managed, olive and vineyard pruning residues are suitable for pelletisation in small systems in line with production at the farm level. The results show that it is possible to reach the quality required by UNI/TS 11773 class I4 or ISO 17225-2 class I3. The physical–chemical differences among agricultural residue biomasses can be managed by appropriate blending to produce standard agripellets.

References

  1. Montola, V.; Colonna, N.; Alfano, V.; Gaeta, M.; Sasso, S.; De Luca, V.; De Angelis, C.; Soda, A.; Braccio, G. Censimento potenziale energetico biomasse, metodo indagine, atlante Biomasse su WEB-GIS. Ric. Sist. Elettr. 2009, 167, 141.
  2. Pizzi, A.; Foppa Pedretti, E.; Duca, D.; Rossini, G.; Mengarelli, C.; Ilari, A.; Mancini, M.; Toscano, G. Emissions of heating appliances fuelled with agropellet produced from vine pruning residues and environmental aspects. Renew. Energy 2018, 121, 513–520.
  3. Picchi, G.; Lombardini, C.; Pari, L.; Spinelli, R. Physical and chemical characteristics of renewable fuel obtained from pruning residues. J. Clean. Prod. 2018, 171, 457–463.
  4. Pari, L.; Suardi, A.; Santangelo, E.; García-Galindo, D.; Scarfone, A.; Alfano, V. Current and innovative technologies for pruning harvesting: A review. Biomass Bioenergy 2017, 107, 398–410.
  5. Sagani, A.; Hagidimitriou, M.; Dedoussis, V. Perennial tree pruning biomass waste exploitation for electricity generation: The perspective of Greece. Sustain. Energy Technol. Assess. 2019, 31, 77–85.
  6. Dyjakon, A.; García-Galindo, D. Implementing Agricultural Pruning to Energy in Europe: Technical, Economic and Implementation Potentials. Energies 2019, 12, 1513.
  7. Lenz, V.; Zeng, T. Summary of the MixBioPells Project Results; DBFZ: Leipzig, Germany, 2012.
  8. Toscano, G.; Alfano, V.; Scarfone, A.; Pari, L. Pelleting Vineyard Pruning at Low Cost with a Mobile Technology. Energies 2018, 11, 2477.
  9. Riva, G. Volume 1—I Sottoprodotti di Interesse del DM 6.7.2012—Inquadramento, Potenzialità e Valutazioni; CTI: Milano, Italy, 2013; p. 155. ISBN 978889061864 2.
  10. Ntalos, G.; Grigoriou, A. Characterisation and utilisation of vine prunings as a wood substitute for particleboard production. Ind. Crop. Prod. 2002, 16, 59–68.
  11. Li, H.; Liu, X.; Legros, R.; Bi, X.T.; Jim Lim, C.; Sokhansanj, S. Pelletization of torrefied sawdust and properties of torrefied pellets. Appl. Energy 2012, 93, 680–685.
  12. Stelte, W.; Holm, J.; Sanadi, A.; Barsberg, S.; Ahrenfeldt, J.; Henriksen, U. Fuel pellets from biomass: The importance of the pelletizing pressure and its dependency on the processing conditions. Fuel 2011, 90, 3285–3290.
  13. Tumuluru, J.S.; Wright, C.T.; Hess, J.R.; Kenney, K.L. A review of biomass densification systems to develop uniform feedstock commodities for bioenergy application. Biofuels Bioprod. Biorefining 2011, 5, 683–707.
  14. Stelte, W.; Holm, J.K.; Sanadi, A.R.; Barsberg, S.; Ahrenfeldt, J.; Henriksen, U.B. A study of bonding and failure mechanisms in fuel pellets from different biomass resources. Biomass Bioenergy 2011, 35, 910–918.
  15. Michal Holubcik, M.; Nosek, R.; Jandacka, J. Optimization of the Production Process of Wood Pellets by Adding Additives. Int. J. Energy Optim. Eng. 2012, 1, 20–40.
  16. Spinelli, R.; Magagnotti, N.; Nati, C. Harvesting vineyard pruning residues for energy use. Biosyst. Eng. 2010, 105, 316–322.
  17. Sirous, R.; da Silva, F.J.N.; da Cruz Tarelho, L.A.; Martins, N.A.D. Mixed biomass pelleting potential for Portugal, step forward to circular use of biomass residues. Energy Rep. 2020, 6, 940–945.
  18. Mostafa, M.E.; Hu, S.; Wang, Y.; Su, S.; Hu, X.; Elsayed, S.A.; Xiang, J. The significance of pelletization operating conditions: An analysis of physical and mechanical characteristics as well as energy consumption of biomass pellets. Renew. Sustain. Energy Rev. 2019, 105, 332–348.
  19. Zanetti, M.; Benoît, B.; Marini, D.; Sgarbossa, A.; Giorio, C.; Badocco, D.; Tapparo, A.; Grigolato, S.; Rogaume, C.; Rogaume, Y.; et al. Vineyard pruning residues pellets for use in domestic appliances: A quality assessment according to the EN ISO 17225. J. Agric. Eng. 2017, XLVIII, 612.
  20. García-Maraver, A.; Ramos-Ridao, A.F.; Ruiz, D.P.; Zamorano, M. Zamorano Quality of pellets from olive grove residual biomass. In Proceedings of the International Conference on Renewable Energies and Power Quality (ICREPQ’10), Granada, Spain, 23–25 March 2010.
  21. Kocer, A.; Kurklu, A. Production of pellets from pruning residues and determination of pelleting physical properties. Energy Sources Part A Recovery Util. Environ. Eff. 2020, 1–13.
  22. Castellano, J.M.; Gómez, M.; Fernández, M.; Esteban, L.S.; Carrasco, J.E. Study on the effects of raw materials composition and pelletization conditions on the quality and properties of pellets obtained from different woody and non woody biomasses. Fuel 2015, 139, 629–636.
  23. Whittaker, C.; Shield, I. Factors affecting wood, energy grass and straw pellet durability—A review. Renew. Sustain. Energy Rev. 2017, 71, 1–11.
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Subjects: Materials Science, Biomaterials
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Giuseppe Toscano
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Vittorio Maceratesi
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Update Date: 16 Feb 2022
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