Evaluation of the potential for energy recovery from olive oil industry waste: Thermochemical conversion technologies as fuel improvement methods

The search for new sources of energy is one of the demands of current times. Traditional lignocellulosic biomass sources, used by Man since immemorial times, begin to suffer the effects of overuse, which is why to find new sources is so urgent, especially if those are associated with industrial or agroforestry waste sources. In this context, several options arise, some of which are object of concern, given the large volumes produced, and the environmental impacts associated with them. Olive pomace is one of these cases. Portugal assumes a prominent role in the production of olive oil and is, therefore, also a major producer of waste related with olive oil industry. Energy recovery of olive pomace is something that has been referenced in the bibliography since long ago. However, traditional forms of recovery, such as direct combustion, did not shown to be the best option, given the high content of volatiles of the product, and the problems associated with its storage and transportation. Thermochemical conversion technologies, such as torrefaction or pyrolysis, can play a decisive role here, since in addition to the increment in energy density, allow a very significative volume reduction, facilitating storage and transportation. In the present study, torrefaction and pyrolysis tests were carried out on olive pomace samples at different temperatures, respectively, 300, 400 and 500 °C, followed by the characterization of the obtained materials. There was a significative improvement in the energy content of the materials. The characterization of the Hardgrove Grindability Index (HGI) was also carried out, allowing comparison with coal grindability, and leaving an open door for the possibility of these residues being used as coal substitutes in coal-fueled power plants.